How does the Poynting vector know who is the primary and who is the secondary of a transformer?

Question: I've read in several places that the Poynting vector is directed from the primary to the secondary of a transformer (we assume here that the primary is the winding that provide the AC energy, while the secondary is just connected to some resistive load); the simulation below shows the electric, magnetic, and Poynting vector fields around a transformer.
Assuming an ideal 1:1 transformer with identical windings, both the Electric and Magnetic fields are symmetric, so there is no way to know who is the primary and the secondary from these fields. But the Poynting vector is directed from the primary to the secondary, and I found that puzzling, because I can't figure out how the Poynting vector "knows that": indeed, assuming a power factor of 1 (ideal transformer), I can make the secondary primary, passing the same current as when it was a secondary, and then the secondary (that was the primary) will have the same current as when it was the primary. So, the currents being the same, how does the  Poynting vector can decide who is the primary and the secondary?
Comment: I'm always surprised that there are questions that receive no upvote, but at the same time answers to that question that receive 4 upvotes or more: if an answer is so good that it deserve 4 upvotes, then the corresponding question that HAS LEAD to that answer should receive at least 1 upvote. That's my humble opinion.
Answer: The electric and magnetic fields are symmetric, yes, but across different axes. The combined electromagnetic field has neither symmetry. Consider that $/$ and $|$ have symmetries similar to your pictures of the fields, but when you put them together the result ($\hspace{.05em}/\hspace{-0.25em}|$) has lost those symmetries. In particular, flipping the electric field along the magnetic field's vertical line of symmetry swaps the primary and secondary (and flips the Poynting vector accordingly).
In terms of currents and voltages, the primary is the one where the current drops from higher to lower voltage and the secondary is the one where the current rises from lower to higher voltage. I.e. the coils are identified simply by using the sign of $P=IV.$ (See also: Poynting's theorem.)
Answer: Building on the excellent answer of HTNW (and also thanks to the comments of Ján Lalinský), I wish to elaborate a bit about inverting the primary and the secondary.
It is true that the primary and the secondary can be inverted while keeping the same currents, so that the same magnetic field is generated in both case. But regarding the electric field, it is also dependent upon the charge distribution on the surface of the wires, according to Jefimenko's equations (see note below); this charge distribution increases (more or less linearly in most cases) in the direction of the increasing potentials for the secondary of a transformer, and decreases in the direction of the increasing potentials for the primary. So, by inverting the primary and the secondary, keeping all currents the same, the charge distribution will invert its direction in both the primary and the secondary. By symmetry, the electric field will be inverted, and
as a result, the Poynting vector will still be directed from the (new) primary to the (new) secondary. That explains the apparent paradox.
Note:
Jefimenko's equations connects the EM field with the sources:
$$\mathbf{E}(\mathbf{r}, t) = \frac{1}{4 \pi \varepsilon_0} \int \left[\frac{\mathbf{r}-\mathbf{r}'}{|\mathbf{r}-\mathbf{r}'|^3}\rho(\mathbf{r}', t_r) + \frac{\mathbf{r}-\mathbf{r}'}{|\mathbf{r}-\mathbf{r}'|^2}\frac{1}{c}\frac{\partial \rho(\mathbf{r}', t_r)}{\partial t} - \frac{1}{|\mathbf{r}-\mathbf{r}'|}\frac{1}{c^2}\frac{\partial \mathbf{J}(\mathbf{r}', t_r)}{\partial t} \right] dV',$$
$$\mathbf{B}(\mathbf{r}, t) = -\frac{\mu_0}{4 \pi} \int \left[\frac{\mathbf{r}-\mathbf{r}'}{|\mathbf{r}-\mathbf{r}'|^3} \times \mathbf{J}(\mathbf{r}', t_r) + \frac{\mathbf{r}-\mathbf{r}'}{|\mathbf{r}-\mathbf{r}'|^2} \times \frac{1}{c} \frac{\partial \mathbf{J}(\mathbf{r}', t_r)}{\partial t} \right] dV',$$
where $\mathbf r$′ is a point in the charge distribution, $\mathbf r$ is a point in space, and
$$t_r = t - \frac{|\mathbf{r}-\mathbf{r}'|}{c}$$
is the retarded time.
From these equations, it is not obvious that the E-field should be inverted if the charge distribution is inverted in the coils, but it should be possible to show the expected symmetry by a technical derivation.
Comment: Total electric field is not generated only by surface charges, because there is also induced electric field due to changing current. "Electromotive force", in context of a transformer or any inductive device, is a term usually used to mean the induced electromotive force, not the force of conservative electric field characterized by difference of potential on terminals.
Comment: @Ján Lalinský. I tried to answer to your objection in an edit of my answer.
Comment: > *"For electrical wires, the term $\frac{1}{c^2}\frac{\partial \mathbf{J}(\mathbf{r}', t_r)}{\partial t}$ is negligible"* -- what is the reason for this statement? If this term is neglected, induced electric field is neglected. Induced electric field cannot be neglected when explaining how transformer works.
Comment: @Ján Lalinský. Indeed, you are completely right. I have rewritten my answer. Thank you again for helping me and pointing out my mistakes.
Answer:
So, the currents being the same, how does the Poynting vector can decide who is the primary and the secondary?

The Poynting vector does not decide anything; it is just a quantity characterizing given EM field.
Energy in EM field near a transformer may flow in any direction, or not flow at all, depending on what is connected to which winding.
Usually we connect voltage source (hard-to-influence "voltage imposer") to one winding (called then the primary winding), and load (consumer) or nothing to the other winding (called then the secondary winding). EM energy then may or may not flow from the voltage source to the load depending on impedance of the device connected to the secondary, and in some cases it can even flow the opposite way. All depends on phases of current and voltage on the terminals, which in turn depends on behaviour of the devices connected there.
If the load is not a source of energy itself (the most common case), then the flow of energy is directed from the voltage source to the load.
If the load impedance is very high, there is almost no sustained power transfer, there is only oscillation of EM energy in the primary winding, charging up and discharging the ferromagnetic core.
If the load impedance is finite, there is some power transfer from the primary to the secondary and to the load. The most efficient transfer happens when impedance of the secondary is the same as that of the primary.
If the device on the secondary isn't a load, but a source of emf itself, then it is possible that power flows from the secondary to the primary and to the voltage source. This can happen when the device connected to the secondary can provide lots of its own energy (not the usual mode of operation).
Comment: You are right that the terms "primary" and "secondary" may lead to ambiguous readings of my question, as there are various sort of loads. Being not specified, I thought it was clear that my "primary" was the one that provides energy, while the secondary is simply connected to some purely resistive load. I will edit my question though.
Answer: Assuming we don't know which coil is primary and which is secondary. So we call the two coils coil 1 and coil 2
The voltage on coil 1 is $U_1$, and the voltage on coil 2 is $U_2$. Assuming that there is a current flowing into coil 1 from the high end of the voltage. The product of the complex conjugate of voltage and current is power. If the real part of the power in coil 1 is positive, it indicates that energy is flowing in from coil 1. Coil 1 is now a primary coil. Otherwise, coil 1 is a secondary coil. This method is equally effective for coil 2.
Don't ask Poynting vector. The energy flow from the primary coil to the secondary coil is not actually a Poynting vector. But the so-called mixed Poynting vector. This Poynting vector is the mutual energy flow part of the Poynting energy flow, not the self energy flow part. Because mutual energy flow is responsible for transferring energy flow from the primary coil to the secondary coil. On the contrary, self energy flow is reactive power and is not responsible for energy transfer from the primary coil to the secondary coil. for details please see:
http://www.sciepub.com/IJP/abstract/15049
Comment: "If the real part of the power in coil 1 is positive, it indicates that energy is flowing in from coil 1. Coil 1 is now a primary coil. Otherwise, coil 1 is a secondary coil." +1 for this part. Regarding your article, it's hard for me to believe Maxwell's equations are inexact. But I'm not really a physicist, so good luck.
Comment: @MikeTeX That's because my paper supports the existence of advanced waves. Due to the presence of advanced waves, the Maxwell equation is still correct, but the phase of the electromagnetic wave's magnetic field needs to be corrected. Additionally, for transformers, only the magnetic quasi state Maxwell equation is required. For the magnetic quasi state Maxwell equation, the magnetic field does not even need to be corrected for phase. Although most people do not recognize advanced waves. But there are famous scientists supporting its existence, including Einstein, Wheeler Feynman, Cramer
Comment: Do you have reference for Einstein etc. supporting advanced waves? well regarded books? Also, have you succeeded in convincing a professor of physics about your article? I'm curious, but there are so many theories by persons that think they have discovered something, that turn out to be just big errors of understanding right the physics....
Comment: Einstein support idea that time is equal in two direction.  Ritz   against this idea. They had a  debate in 1909: Walter Ritz and Albert Einstein. Zum gegenwärtigen Stand des Strahlungsproblems. Physikalische Zeitschrift. 1909, 10: 323–324.
Answer: The energy is transmitted by the Poynting vector, although it is correct, it is not very accurate. It should be said that for independent systems, such as simple circuits, which only include one power source and one resistor, transmission lines, waveguides, etc., the energy flow can be described by Poynting vectors. For discrete systems, the energy flow is transmitted by a part of the Poynting vector, the mutual energy flow. Discrete systems include the primary and secondary components of transformers, transmitting and receiving antennas, photon sources and sinks.
For discrete systems, the Poynting vector can be further subdivided into self energy flow and mutual energy flow. The energy flow between two parts in the system is mutual energy flow. For discrete systems, such as transformers. The Poynting vector of the primary coil belongs to the self energy flow. The Poynting vector of the secondary coil is also self energy flow. But there is an energy flow between the primary coil and the secondary coil. Self energy flow is reactive power. Mutual energy flow is the active power.
Our textbook today has not yet distinguished the mutual energy flow and self energy flow in the Poynting energy flow, so we cannot explain the energy flow from the primary to secondary of transformers. The following is a paper on the energy flow from the primary coil to the secondary coil of a transformer for reference.
http://www.sciepub.com/IJP/abstract/15049


Disable saving vector layer in QGIS, especially in DXF and KML file?

Question: Can you help me on how to disable the exportation of vector layers especially in AutoCAD DXF, DBF File and ESRI Shapefile?
Comment: The big problem is that it is *very* hard to stop people who have read access to data (for a valid reason) saving that data. The games companies spend millions on anti-duplication tech but that gets cracked. Do you care that much?
Comment: You're trying to get QGIs to be a viewer only ?
Comment: QGIS doesn't force you to export in any particular format. Are you trying to create a version of QGIS with those export options missing? To make it simpler for users?
Comment: my gis vectors are connected to mysql i would like to know if there is a way to secure the vectors loaded on qgis, i want that other users cant get or export the vectors.
Comment: So do you want: all your data in a mysql database; some people to have read and write access to the mysql DB (eg you); some people to have read access only to the DB; some people who do have read access to not be able to save the data outside the DB?
Answer: The only way would be to use WMS to view data so that no data is directly loaded to QGIS, and use wfs with featureid if required to edit.
Answer: You can actually disable the Save As vector functionality altogether in QGIS but this will only work provided that QGIS is running on Windows. It will be useful in an enterprise environment where the user doesn't have access to the Registry.

In QGIS go to Configuration > Customization > Tick the checkbox Enable customization.
Edit the system registry to set the following key to false:
hkey_current_user/Software/QGIS/CUSTOMIZATION/QgsVectorLayerSaveAsDialogBase/buttonBox

You can still right-click and select Save As but the dialogue box doesn't have the OK button.
Source: Prevent export to shapefile from postgis table in QGIS. I tested it on QGIS 2.x
Comment: @CarloGaffud you're most welcome. If the solution worked out for you, you can accept the answer to let other people know that it works.


Redeploy a smart contract on bsc testnet

Question: Is it possible to overwrite a smart contract used to deploy a bep20 token on testnet? I have made changes to a smart contract already deployed and wish to rewrite the smart contract already present, or will it create a new address once I do this
Answer: No. It is not possible to override or upgrade a deployed smart contract, unless you planned and prepared carefully for this scenario.
Comment: In that case is it possible to remove a token that I deployed off the network and repeat the same process
Answer: Yes, If you wrote the contract to be upgradable. This would entail creating a proxy contract that forwards all calls to the implementation contract. This sounds harder than it is, you can use Openzeppelin's plugins to handle all the backend work and all you have to do is write your contract a specific way.

(explained in their guide: https://docs.openzeppelin.com/upgrades-plugins/1.x/writing-upgradeable)

To answer the comment you asked in the other answer, yes and no. You can create a contract that has a self destruct function, and then call that function once it is deployed to delete the contract and send any remaining tokens to a specified wallet address. The blockchain is inherently immuatable, so without purposely coding your contract to conteract this immutability, the contract you deployed will always be on the blockchain.

(https://solidity-by-example.org/hacks/self-destruct/).


Emails on iOS and public Wifi

Question: On iOS, you enter your password, once, and you can then check your emails via the email app.
Does the app send the password everytime it updates your email?
Is it secure to check your emails this way while connected to a public wifi?
Comment: yes it re-authenticates, but yes, the connection is encrypted
Answer: Yes, the app stores your password an uses it to authenticate every time it queries your mail account. This is no different from a stationary mail client like Outlook or Thunderbird.
The password is not transmitted in clear over the network. It is either sent through a TLS encrypted connection or used in a challenge/response authentication scheme. So it is reasonably secure against interception.
In a public WLAN, there's an increased possibility of man-in-the-middle attacks, so you should make sure that your device is reasonably secure against that, for example by properly checking TLS certificates. If in doubt, use a VPN tunnel. This holds for all network services, not just E-mail.
Answer: Yes, the Device will store your password, this password will be protected within the device. Previously, i had intercepted the password being transmitted in clear text using ARP-Poisoning my network (on iPhone 5) but after the OS getting upgraded, this didnt work.
But now this is being replaced by "app-specific" passwords, where we need to generate a different password for our device eg. iPhone on the web portal eg. gmail. This portal generated password will be the new identifier for authentication to gmail.
The security of passwords stored locally depends on how the OS of the device protects the data and transmits it to pull emails from servers. Normally, device fetches emails via encrypted channels from email providers like gmail, outlook, etc. you can see that in your email settings.
Trying to access emails and/or any other information from open/public wifi should be avoided. if the email authentication over the network is happening in clear text, then there is a risk of the credentials being sniffed/disclosed. In short, it is not advisable. Better use Cellular data or tunnel the traffic using a VPN
In short, avoid public access points because, our device leaks out lots of information when connected to any hotspot, such information can tell much about the device.

Emails on iOS and public Wifi


Reference help: asymptotic reducibility of systems

Question: I was reading a paper about the reducibility of linear functional differential equations with quasi periodic coefficients. The paper talks about the asymptotic reducibility of systems. I don't the definition of  asymptotic reducibility of system. Could someone tell me the definition of that and give me a good reference to get more  about it ?
Thank you.
Answer: Well it depends on the paper, usually in that kind of problems reducibility means that you may find a change of coordinate that put your system in an other one whose coefficients are time independent. Asymptotic I can image that they are not able to find a change of coordinates that tranform your system in an other one whose coefficients are time independent, but maybe they are able to find $n$ transformation such that the first $n$ term of  are time independent. But you always have a time dependent remainder. Maybe if you link the paper I try to understand.


Prefixing database table names

Question: I have noticed a lot of companies use a prefix for their database tables. E.g. tables would be named MS_Order, MS_User, etc. Is there a good reason for doing this?
The only reason I can think of is to avoid name collision. But does it really happen? Do people run multiple apps in one database? Is there any other reason?
Comment: When you're lumbered with Oracle's idiotic 30 character name limit, prefixing your tables is a luxury you can't afford.
Answer: Personally, I don't see any value in it.  In fact, it's a bummer for intellisense-like features because everything begins with MS_. :)  The Master agrees with me too.
Answer: Huge schemas often have many tables with similar, but distinct, purposes.  Thus, various "segmented" naming conventions.
Darn, didn't get first post  :-)
Answer: Even when the database only contains one application, the prefixes can be useful in grouping like parts of the application together. So tables that containtain cutomer information might be prefixed with cust_, those that contain warehouse information might be prefixed with inv_ (for inventory), those that contain finacial information might be prefixed with fin_, etc.
Answer: In SQL Server 2005 and above the schema feature eliminates the need for any kind of prefix. A good example of their usage can be found by reading about the Schemas in AdventureWorks.
In some older versions of SQL server, having a prefix to create a pseudo namespace might of been useful with DBs with lots of tables.
Other than that I can't really see the point.
Comment: Thanks for the link, that's interesting.   Too bad "we" only have 2 schemas:  "dbo" and "tempdb" (Sybase uses the same or similar namespace convention, unsurprisingly)
Answer: I've worked on systems where there is an existing database for an application which was created and maintained by a different company and we've needed to add another app that uses large amounts of the same data with just a few extra tables of our own, so in that case having an app specific prefix can help with the separation.
Slightly tangentially to the original question, I've seen databases use prefixes to indicate the type of data that a table is holding. There'd be a prefix for lookup tables which are obviously pretty static in both size and content and a different prefix for the tables that contain variable data. This in turn may be broken into having one prefix for tables that are added to but not really changed like logging, processed orders, customer transactions etc, and and another for more variable data like customer balance or whatever. Link tables could also have their own prefix to separate them out too.
Answer: I have never seen a naming collision, as it usually doesn't make sense to put tables from different applications into the same database namespace. If you had some sort of reusable library that could be integrated into different applications, perhaps that might be a reason, but I haven't seen anything like that.
Though, now that I think about it, there are some cheap web hosting providers that only allow users to create a very small number of databases, so it would be possible to run a number of different applications using a single database, so long as the names didn't collide (and such a prefixing convention would certainly help).
Answer: Multiple applications using a particular table, correct.  Prefixes prevent name collision.  Also, it makes it rather simple to backup tables and keep them in the same database, just change the prefix and your backup will be fully functional, etc.  Aside from that, it's just good practice.
Answer: Prefixes are a good way to sort out which sql objects are associated with which app when multiple apps dip into the same database.
I have also prefixed sql objects differently within the same app to facilitate easier management of security.  i.e. all the objects with admin_ need this security applied and the rest need something else.
Prefixes can be handy for humans, search tools and scripts. If the situation is a simple one, however, there is probably no use for them at all.
Answer: It's most often use if several applications are sharing one database.  For example, if you install Wordpress, it prefixes all tables with "wp_".  This is good if you want your applications to share data very easily(sessions across all applications in your company, for example.)
There are better ways to accomplish this however, and I never prefix my table names, as each application has it's own self-contained database.

Prefixing database table names


Can I update an existing Apple ID with a newly created MobileMe email address?

Question: I've had an Apple ID for a while now and have many iTunes purchases associated with the account. Yesterday, I created a MobileMe account. I tried updating the existing Apple ID account e-mail with my new MobileMe address, but get an error about the MobileMe address already being associated with an iTunes account (I'm guessing it's automatically created when you create a MobileMe account). Is there a way to update my existing Apple ID to use my new MobileMe address so that I don't have to repurchase all of the apps and things I've downloaded on my original account?
Answer: As I have attempted to do this myself, Im pretty sure you cant combine the two. You can try contacting Apple Support but they will probably tell you the same thing.
Apple doesn't allow you merge AppleIDs or in other words use a mobileme AppleID for an iTunes account AppleID ( AppleIDs are just the username/email address I think). This sounds reasonable though because mobileme is a  yearly paid service and in the instance you canceled the mobileme account, it might lead to account problems (ie if you needed to reset your password for your iTunes account but it still had the mobileme email address as the AppleID/email)
You should still be able to make iTunes purchases, app purchases, etc with the original iTunes account you had set up.
Comment: Yeah, I just don't like using more than 1 e-mail address. I figured Apple would have had a solution or procedure in place so that if I get one of their premium service e-mail addresses (with MobileMe), that I'd be able to either transfer all my purchases over to that new Apple ID or something.
Comment: I agree it would be a lot easier to manage with just one, at least from a users perspective
Answer: You can call AppleCare as suggested and merge all your purchases from the old Apple Id to the new Apple Id.
I have multiple Apple IDs. Is there a way for me to consolidate them into a single Apple ID?
Sorry, but this is not possible at this time via our online tools. You can speak with an AppleCare representative, who can help you consolidate your registered Apple products. They can also help register your iPods, iPhones, or Mac computers under a single Apple ID.
Other links that could offer some insight:

https://appleid.apple.com/html/en_US/faq.html
http://www.apple.com/support/appleid/
http://support.apple.com/kb/HE40
Answer: Log onto your newer MobileMe account and change the email address to something else, say one of your temporary email addresses.  Wait a bit.  Then change your old account to use the MobileMe email address.
Comment: It looks like the e-mail address is un-editable, unless I'm looking in the wrong place. Screenshot: http://cl.ly/3n28061S1C3W0F2Q1h27
Comment: To add to that, when logging into my non MobileMe associated iTunes account, the e-mail address field is editable on that same page.
Answer: I doubt that it is possible to merge a mobile me account with your apple id, but try contacting the support - I think they are the ones to know for sure. See http://www.apple.com/support/itunes/ -> Authorization -> Troubleshooting -> "Email Us".


Interpretation of the electromagnetic field strength tensor as a spin-1 field

Question: If I understand correctly the electromagnetic field strength tensor $ F_{\mu\nu}$ could be considered as a spin-1 field. In that case, what can one say about the total spin and the $z$-component of the spin for this field? Also, how is $F_{\mu\nu}$'s spin related to that of the photon field ($A_{\mu}$)?
Answer: I think the existing answer is a pedagogical nightmare, which obfuscates the underlying truth: The spin of the Electromagnetic Field Strength tensor $F_{\mu\nu}$ is determined by its representation under the Lorentz group.
General Math:
$2$-Tensors live in the the tensor product space of a space and itself (that is what it means to be a tensor of rank $2$). If vectors live in the fundamental representation $V$, then $2$-tensors live in $V\otimes V$. It is a relatively simple mathematical fact that this 'square' tensor product can always be decomposed into Symmetric and Anti-Symmetric parts: $$V\otimes V \cong [V \odot V] \oplus [V \wedge V]$$
It is important to note that if $\operatorname{dim}(V) = n$:
$$\operatorname{dim}(V\otimes V) = n^2$$ and $$\operatorname{dim}(\operatorname{Sym}^2(V))= \frac{n(n+1)}{2},\quad \operatorname{dim}(\operatorname{Alt}^2(V)) = \frac{n(n-1)}{2}$$
That is to say, the space of $2$-tensors decomposes into symmetric tensors and anti-symmetric tensors. It is also well known that all representations of semi-simple lie groups appear as components of the direct sum within representations of tensor products of the fundamental representation. That is to say, because the tensor product space decomposes this way, each of those pieces of the direct sum must be a representation of the relevant group.
All of this is to say that Symmetric $2$-tensors and Anti-symmetric $2$-tensors, must represent fundamentally different kinds of physical quantities, because they are not the same dimension, and so cannot live in the same representation of the symmetry group our physics respects.
Specific to the physics: Representations of the Lorentz group can be indexed by pairs of half integers. $(j_1,j_2)$. The fundamental/vector representation can be identified with the $(\frac{1}{2},\frac{1}{2})$ rep. This is a spin-1 rep, because the spin of a rep is $j_1+j_2$, and the dimension is $(2j_1+1)(2j_2+1)$. The tensor product space in this case decomposes into the following direct sum:
$$
(\frac{1}{2},\frac{1}{2})\otimes(\frac{1}{2},\frac{1}{2}) = [(1,1)\oplus(0,0)]\oplus[(1,0)\oplus(0,1)] = [\operatorname{Sym}^2(V)]\oplus[\operatorname{Alt}^2(V)]
$$
Where I have intentionally grouped the representations into the symmetric and alternating parts. The way one should read the latter equation is: "The $16$ dimensional space of $2$-tensors on Minkowski space can be split into a $9$ dimensional Spin-$2$ traceless symmetric piece, the $1$-dimensional trace (transforms as a scalar because trace is invariant), and a $6$ dimensional Spin-$1$ anti-symmetric piece".
The Faraday tensor $F_{\mu\nu}$ is an anti-symmetric $2$-tensor. This means it must be a spin-$1$ object, because that is what anti-symmetric $2$-tensors are in special relativity. This is why the E and B fields behave like Euclidean vectors under rotations, but mix seemingly strangely under boosts.
All of this analysis can be done in the arena of spinors as well, as done by Stephen Blake, because the Tensor Product space of the bi-spinor representation of the Lorentz group also contains a copy of the representation of anti-symmetric tensors which we previously called $[(1,0)\oplus(0,1)]$. But I do not believe this is particularly enlightening when compared with starting in the more comfortable vector representation.
As for how the spins are 'related' it is merely that the Faraday tensor is constructed to be anti-symmetric tensor, from the potential vector $A^\mu$. Perhaps there is more to be said here about the exterior algebra and the action of the exterior derivative, but that is out of my wheelhouse. Lastly, the '$z$' component of the Faraday tensor does not particularly make sense, one needs two indices to specify a component of a $2$-tensor.
Answer: The spin of the electromagnetic field tensor $F_{\mu\nu}$ is best understood by writing it as a spinor. A spin 1 field is a represented by a symmetric spinor $\xi^{AB}$ or by a dotted symmetric spinor $\eta_{\dot{A}\dot{B}}$. In order to get the field transforming correctly under parity, the electromagnetic field has to be a direct sum using the symmetric spinor and it's complex conjugate dotted spinor.
\begin{equation}
F_{\mu\nu} \sim \xi^{AB}\oplus [\xi^{*}]_{\dot{A}\dot{B}}
\end{equation}
The symmetric spinor $\xi^{AB}$ has three independent complex components $\xi^{11},\xi^{12}=\xi^{21},\xi^{22}$. Linear combinations of these components correspond to the three complex components of the electromagnetic field $B^{r}+iE^{r}$. The source free Maxwell equations are obtained by acting on the symmetric spinor with the Hermitian momentum operator $\hat{p}^{\dot{A}}_{\ B}$
\begin{equation}
\hat{p}^{\dot{A}}_{\ B}\xi^{BC}=0
\end{equation}
This equation is similar to the Dirac equation for a massive spin 1/2 field. The photon is massless, so it has helicity = $\pm 1$ instead of spin (essentially spin 1 along or against the direction of flight). The photon has two helicity degrees of freedom, but the spin 1 field $F_{\mu\nu} \sim \xi^{AB}\oplus [\xi^{*}]_{\dot{A}\dot{B}}$ has six real components. The Maxwell equations $\hat{p}^{\dot{A}}_{\ B}\xi^{BC}=0$ project the spinor onto a two-dimensional subspace.
This is as far as I know how to answer the question at present. The gauge field $A^{\mu}$ is a four vector so it ought to be a Hermitian spinor field of type $X^{\dot{A}}_{\ B}$ which is the tensor product of two spin 1/2 fields. It has four components, so the gauge fixing must come in to reduce four to the two helicity degrees of freedom.


How to remove Sublime installed using the website instructions?

Question: I installed Sublime following steps from this Site. But I read on here that it is wrong way to install. Now my question is how do i remove it.
Comment: What does: sudo sed -i 's/sublime\.desktop/gedit.desktop/g' /usr/share/applications/defaults.list
do?
Answer: sudo rm -r /opt/Sublime\ Text\ 2
sudo rm /usr/bin/sublime
sudo rm /usr/share/applications/sublime.desktop
sudo sed -i 's/sublime\.desktop/gedit.desktop/g' /usr/share/applications/defaults.list

Comment: First of all try: `sudo dpkg -r sublime-text`
Comment: `sudo sed -i 's/sublime\.desktop/gedit.desktop/g' /usr/share/applications/defaults.list` should do that.
Answer: Those steps are not wrong, but it would be easier (and sometimes saver as pointed out by your link) to do it using a ppa. So if you still want to remove it then you will have to 'reverse' step 2, 3, 4 and 5 using the following commands.
Step 2 reverse sudo rm -R /opt/Sublime\ Text\ 2
Step 3 reverse sudo rm /usr/bin/sublime
Step 4 reverse sudo rm /usr/share/applications/sublime.desktop
Step 5 reverse sudo gedit /usr/share/applications/defaults.list and replace all occurrences of sublime.desktop with gedit.desktop


Questions about site concept in eclipses (and iviewsite in particular)

Question: 1) Can somebody please explain what a site is? I can't seem to find a proper definition of this term anywhere.
2) What is the purpose of the IViewSite interface?. It does not have any children (class or interface, as specified in the docs. This interface is not supposed to be extended. why define those two methods if there isn't a single class that implements them?
What is the purpose of an IViewSite variable since that variable will not have any properties and it has only pure virtual methods? There's no point in adapting to it either.
I already looked through the docs but I can 't seem to find a concrete explanation.
Ok upon further documenting I think I may have found out what a site is:

an object that gets associated with a workbench part (view or editor)
  by means of the init() method

But what exactly happens to that reference of the site? I dont know since Viewpart for example does not have a property that stores the reference to the site object. If anyone has a link to a diagram or something it would be much appreciated.
LE: Is the reference to the site object stored in some kind of register along with the reference to the object that
LE2 www@eclipsezone@com/eclipse/forums/t92910.html
" The IViewPart.init method is called to initialize the context for the view. An IViewSite object is passed, and contains methods to get the containing page, window, and other services is passed. " What is the use since there is no implementing class?..
Comment: Come on people, a little help here?
Answer: There is an implementing class, it's just not within scope of your Java Search (nor found during the JavaDoc generation, but nevertheless it exists).  You could also ask in the forums at eclipse.org itself.


What size start capacitor should I buy for my refrigerator compressor?

Question: What size (in horsepower) 3-in-1 start capacitor should i buy for my fridge compressor?  I have an LG LRSC26922TT from 2003. The compressor isnt staying on due to (i think the PTC hooked to the compressor). So i am eliminating the capacitors on top and the ptc on the compressor and putting a Supco 3-in-1 start capacitor in. I tried to upload pics but my phone is giving me crap. The nameplate inside says 3.5 amps in general. I'm trying to find out how much horsepower the compressor is by taking volts x amps = watts. And Watts ÷ 745.7 = horsepower ...anyone know the amp rating of the compressor at surge or continuous? OR the horsepower of the compressor? I can choose between 1/4 - 1/3 hp OR just 1/2 hp.
Comment: There should be a tag on the fridge or compressor that states the RLA , the reason for shutdown could be many other reasons, overheating the thermal overload on the motor, high head pressure, low pressure. Modern systems have more problems that are Freon based causing high temps and low head pressures. The cost of caps might be what an inexpensive volt meter that has a capacitance tester, most caps are in the 15-30 up to 150UF (micro fared) range. A ohm meter can be used to check charge discharge rates for a cap rather than throwing parts at it. It could be something as simple as a thermostat.
Comment: Did you ever get this resolved? If so, please give a check-mark to the answer that helped you the most, or write up your own answer explaining what you did to get it fixed and give yourself a check mark. That will help others with this kind of problem know that this has a resolution and is a good place to look for their answer
Answer: What is the PTC?    For the horsepower, you need to add in the power factor which is somewhere around 75% and use the input watts of +/- 1000 not the 745.7 figure you used. Is the compressor a psc which uses a capacitor all the time. What is a Supco 3 in 1 start capacitor? You have a lot of variables you need to consider. If you are not exactly sure what you are doing call a service tech or continue to play " Russian roulette"
Answer: If my guess is correct I think it will be around 15uf, however that said I see one capacitor is 100mfd, and the other 14mfd. (looking at parts online) . The entire overload and capacitor Run/Start setup is in the SUPCO package.
Looking online at the Supco 0410 type - it works with most refrigerators.  I can not say specific to your model I think you will be fine at 1/4 hp but check out Supco URCO410 - this is light commercial but tells the compressor types in app details.


How to transfer domain when reseller is down?

Question: I have a personal domain name registered as example.com it is down for whole one day. The reseller website is also down and their customer care is also not responding. Thus I can't access my domain panel. Now I want to transfer that domain under another reseller. How can I do it? Or where to reach to recover it?
Answer:
The reseller website is also down and their customer care is also not responding.

It does not matter, normally.
As long as you are speaking about a gTLD, your important contact is the registrar. It is the one under contracts to perform its duties regarding your domain. He may have resellers, but at the end of the day, it is the registrar that is responsible towards the registry and ICANN.
And among its duties is the fact that it has to honour any requested change in 24 hours at most.
You can have a look at ICANN page at https://www.icann.org/resources/pages/reseller-2013-05-03-en it even provides a way to handle cases of problems like yours.
The ICANN registrar agreement at https://www.icann.org/resources/pages/approved-with-specs-2013-09-17-en says this:

3.12 Obligations Related to Provision of Registrar Services by Third Parties. Registrar is responsible for the provision of Registrar Services for all Registered Names that Registrar sponsors being performed in compliance with this Agreement, regardless of whether the Registrar Services are provided by Registrar or a third party, including a Reseller. Registrar must enter into written agreements with all of its Resellers that enable Registrar to comply with and perform all of its obligations under this Agreement.
Answer: I assume the reseller is just a reseller from another registrar, because I have never seen an official domain registrar that ran out of business, but I have seen so many resellers that take down their own business.
So, first you should find your official registrar, then contact them.
The official registrar of the reseller can be found on the domain whois.
For example, I bought the domain example.com on my local hosting dewawebdotcom. When I checked the domain whois, the whois server says the registrar is Enom like the below image:

So, in that case, just contact enom.com to allow you to manage your domain.
Some years ago, I also had a similar problem. I handled a client's domain and he didn't know where it was from (maybe just bought from a freelancer or random people). So I contacted the registrar with my own email and, after giving proof of domain ownership, I was able to manage that domain (transferred to my account).
Comment: "because I have never seen an official domain registrar that ran out of business" Yet that exists. The most "famous" one: https://en.wikipedia.org/wiki/RegisterFly
Comment: **How** do you give proof of domain ownership when the domain is down and the reseller doesn't respond?
Comment: @KonradRudolph Who shows to be the registrant either in registrar whois server if displayed or more importantly even in the registrar DB? The registrar should be able to help you and you should be able to prove ownership in various ways, including invoices from reseller, proof of identity, etc. You need to go to registrar and expose the problem with reseller.
Comment: @Patrick My invoice lists the item as e.g. "yearly fee for 1 .me domain" (no specific domain names given), and the whois record only lists my reseller. And while not ideal this is, I believe, reasonably common. And, to clarify, my reseller is entirely above-board (and reliable).
Comment: "whois record only lists my reseller." If you mean as registrant, then it is wrong. If you have bad/unclear invoices, that is another topic you might want to fix with the provider of said invoice. Again, as said also in my reply, you need to go to your **registrar** and resolve the issue there.


Reusing marinade

Question: I've always been told you can't reuse marinade, so I always throw it out. But this evening, I marinated chicken, and then I took the chicken out (this was around ten minutes ago). Can I put a piece of fish in? It hasn't been sitting around, it hasn't been out of the fridge, and I haven't let it sit at all. Or am I still in danger?
Comment: Fish is usually cooked pretty lightly, often not all the way through. It's possible you would cook your fish for too short a time (let's say 2 minutes each side) to have killed off all the surface bacteria you put on it, i.e. by dipping it in marinade that had previously been the home of raw chicken. Salmonella in chicken. Since chicken gets cooked much more thoroughly, I would imagine doing it the other way around would be okay (marinate fish first, then chicken)--but I still wouldn't risk it myself.
Comment: Not recommended for personal use.  This is a form of cross-contamination, and I want to say this is not permitted from a commercial stand point.  If a patron gets sick let's say.  If you buy chicken from one purveyor and fish from another, who's the culprit?... the person marinading fish in chicken juice?
Answer: The reason to not reuse marinade is not because "it has been sitting around", it's because it would be cross-contamination, as Chef_Code said. It doesn't matter how long you have used it. The moment the chicken touched it, the bacteria on the chicken surface - and there are lots of them - were also in the marinade. If you now dump fish pieces in it, you'll add chicken bacteria to the fish bacteria. This is a big no-no in food safety.
The "direction" of reuse does not matter either. Your food is only proclaimed safe when you have been doing everything possible to minimize the risk. Introducing new bacteria (even though you assume they will be cooked dead afterwards) is unsafe behavior. So both chicken -> fish and fish -> chicken reuses, as well as any other possible kind of meat, is not safe.
In short, "don't reuse marinade" means exactly what it says on the label, just with all other food safety rules.
Comment: Out of curiosity: is it safe the other way around (e.g., first fish, then chicken in the same marinade) since chicken is cooked longer than fish?
Comment: It doesn't matter if the bacteria die or not, food safety isn't about that. Food safety is about 1) being easy to follow without reasoning and 2) avoiding all possible risks, and reducing the unavoidable ones. It is not safe to introduce new contamination to your chicken, even if you are going to kill it off later.
Comment: I asked because of comment on the question that was in part, "I would imagine doing it the other way around would be okay" -- which didn't really sound like a good idea, and therefore explicit clarification is always useful :)
Comment: @erica Good point, thanks. I added a paragraph about it in the answer.

Reusing marinade


How far away from the sun would I have to be for radiation not to kill me?

Question: If I were freely floating in space within our solar system, and nothing could kill me but radiation from the Sun, what would be the safe distance? I know that Earth´s distance from the Sun would be lethal and I read somewhere that Mars isn´t very homey when it comes to radiation. I need to know what distance a body would have to be from the Sun as to harbor human life with no radiation problems. Thanks in advance.
Comment: Can you exaplain what you mean by "I need to know...".    Since you'd be dead from lack of oxygen in a few minutes.  I'm not sure what you could need to know this for.  Understanding that might help. Also radiation from the sun isn't constant.  A solar storm would carry much more harmful particles.  And, well, cosmic radiation is there too.  So the simple answer is that if you don't have an atmosphere you need to worry about shielding.
Comment: "Kill me" over what time scale?  There are plenty of other sources of radiation in space: cosmic rays (astronauts saw flashes of light as cosmic rays hit the back of their eyes)
Comment: Nah, I´m immune to the other sources too, in this one question hehe :) Only the Sun would be a danger, and as to the time, well, no time frames other life being as normal as if on Earth, concerning radiation.
Answer: tl;dr, It depends. On a lot of things. Mostly on how long you wanna be alive. But this is an area of modern research, and one we are looking for an answer to currently.
Like mentioned in one of the comments, GCR (galactic cosmic rays) are a high threat, but as you responded, you don't want to incorporate these into this thought experiment. While I should mention not considering these is a significant loss of information if you want to really know what would physically happen, let's consider some variables.
First, solar cycles.
Solar cycles play an interesting role in radiation in the interplanetary medium. On one hand solar wind carries charged particles that could potentially be life threatening. On the other hand, at solar maximum these charged 'winds' actually deflect (to a certain extent) galactic cosmic rays, making it (if considering GCR) cumulatively safer during solar maximum. But in this thought experiment, we are not considering these GCR, so you're best bet would be timing your venture solar minimum (here is one instance where this thought experiment diverges from reality). A solar cycle lasts 11 years, so you would have to time things accordingly.
Next to consider is the fact that GCR come from distant, distant objects and carry the potential to kill you, so it would be reasonable to suggest that for an alien around another sun, our sun would contribute to the GCR and thus in theory, you would never be totally safe no matter how far away from the sun. There would always be a chance of receiving a certain amount of radiation, and with longer exposure in time, eventually it would be statistically improbable that you would survive indefinitely. If not if radiation poisoning, then at least of cancer.
Now, this is all assuming that it's just you, with no other forms of protection. Some of the deadliest radiation form the sun is charged particles, and so magnetic fields do wonders for preventing some of the most high energy (and thus most deadly) particles from reaching you. So if you have a strong magnetic field in your local vicinity (say the Earth, or a gas giant with a dynamo effect producing some magnetic fields) it will do a lot to keep you alive. The magnetic influences of some of the bodies are very, very large in comparison to the size of these objects so you could potentially benefit from them from quite a distance away. Similarly, if you're unlucky, they can be potentially harmful to you, as certain kinds of radiation get trapped in the magnetosphere of these objects (which again can be quite large).
So let's assume you're far away from these where their effects are negligible (again, may not be the best approximation). One thing that is unrelated to charged radiation from the sun is just the high-frequency light it emits. The sun is a G star so it peaks in the visible light, but a significant amount of light in its black body curve is produced in the UV and higher, which the Earths atmosphere blocks largely via water vapor. With no protection like this, the UV light and higher frequencies would eventually give you cancer or kill you from radiation poisoning.
So what then is the answer? It's hard to say; the interplanetary medium is a harsh place. It's these questions that modern space explorers are grappling with, and have yet to find satisfying answers to. Because of solar winds and electromagnetic radiation, you're question really boils down to time scale. How long do you want to be free of radiation sickness and cancer. And even then it's not a sure thing, it's a matter of chance, and the probabilities of that are entirely situationally dependent, with the difficulty to give any kind of answer increasing exponentially with the time scales you'd like to be alive.
Moral of the story? Find a strong magnetic field to help you out and you'll be off to a much better start.


What are they mining for in The Moon is a Harsh Mistress?

Question: I read Heinlein's The Moon is a Harsh Mistress some time ago and recall the mining operation but cannot for the life of me remember what they were digging up. Can anyone help me?
Comment: Wasn't it for water?
Comment: Welcome to the site, Greg (aka @user2840467). I came across this via the [review](http://scifi.stackexchange.com/review) queue; it's not an altogether terrible question, though I suspect some basic Googling could find the answer. However, I have edited out the pleasantries - they're not required here. Stack Exchange is a venue for questions and answers, not conversations. Give the [tour](http://scifi.stackexchange.com/tour) a read to see what I mean.
Answer: At that time, they were (as I recall) mining for two primary things; water (in the form of ice) & space ("cubic" as Mannie calls it; 'digging tunnels', such as for the barracks for the new Peace Dragoons, 1/2 way thru the story.  Mannie also talks about expanding farming areas & living space via mining.)
"Project Centerbore was years later" (as nearly as I can remember the phrase; I don't have a copy handy) is mentioned at one point, referencing the fact that mining for Uranium was later a significant thing, but not during this book.
Comment: @rosesunhill -- Exactly; early on, one of Mike's predictions includes an assumption of a massive increase in drilling for water (when he is predicting the time until economic collapse for Luna.)  At the time, space and water were all they really sought, via mining; living in a 3D environment (under ground) made mining for space comparable to homesteading on the surface of a planet; it's how you get more room to live, work, and grow plants/livestock/etc.  Finding ice was a boon to private citizens, leaving them less dependent on the Authority to sell them water.
Comment: Also, it was one use for the 'Slave Labor' of convicts coming to Luna; the Authority needed someone to dig & prospect for ice to keep their cisterns full to then sell to the discharged / free citizens of Luna.
Comment: Also much of the mining during the book was a smokescreen for building underground launch catapults.
Comment: Kind of; it was a way to employ some miners, but it wasn't so much a smokescreen -- the building of the new catapult was public knowledge (the warden even visited the construction, at one point), but they hid the location of WHERE they were building the new catapult.  They also re-purposed miners & mining equipment to form a kind of 'space defense' against incoming ships.  (Mining equipment being, primarily, powerful lasers.)
Comment: Absolutely on point. Luna was shipping grain back to Earth to support its hungry population and needed the water for crops. That was an unsustainable, open-ended cycle and Mike's predictions of impending food riots, starvation and the total collapse of Lunarian society formed the initial reasons for the rebellion.
Answer: They weren't necessarily mining, they were digging tunnels and caves to live and to farm in. They were shipping back grain to earth, far more than what was sustainable. This was a major factor in the revolution.
Comment: You're on point that shipping the grain back wasn't sustainable. But it was the water component of the grain that was running out. Plenty of rock to convert to food, not so much ice.


hp monitor has no signal when i boot to ubuntu cd

Question: When i boot to the cd on my emachines i have no problems and the disk has been tested in other pcs and laptops.  My son needs to work on our HP, but the monitor shows no signal when I boot to the cd.  The lights are flashing on the cd rom drive.  Does any body have a fix.  Last resort I can switch monitors.
Answer: What version of Ubuntu disc are you using?
You may need to change the kernel mode settings and add "nomodeset" or "i915.modeset=1" at the end of the boot parameters. The parameters you need to add will depend on what hardware your HP computer has (namely what type of graphics card it uses).
See this thread for more info.


How do I build a better blog website?

Question: I've spent the last few days building a website that I want to use a showcase for my written work, and as a personal blog. What fundamental changes should I make to improve a viewer's experience?
The site is AcfWorks.com
Comment: This is pretty broad as written, and sounds like you're asking for a critique of your blog.  Could you please [edit] to describe what you've done and what you think could be improved about it?  Try to be more specific -- are your questions about styling, tagging, length of posts, how you manage comments, promotion, or what?  I'm putting this on hold for now; after you edit it will go into a review queue for reopening.
Answer:
Choose a definite goal for your site. What do you want users to do? Look around, subscribe to an email list, join you on Facebook?
Cut down on extras that take away from your main goal. For example, the large image at the top of each page. Looks nice, doesn't tell the story.
Be more clear about what everything is. Did you write the content for these projects?
For example: Commercial Writing Examples
Comment: Totally agree. Icouldn't discern what the page is about. The images have no message.
Comment: Thank you! I away the "written works" section for now, made the header images a lot smaller, and tried to make the homepage a bit clearer. What do you think?

How do I build a better blog website?


Writing to an event log in ASP.NET on Windows Server 2008 IIS7

Question: I'm trying to use log4net to write to a customer event log under IIS7 on Windows Server 2008 SP1. However, account doesn't seem to have access to write to the event log. Does anyone have any suggestions?
Comment: Possible duplicate of [System.Security.SecurityException when writing to Event Log](https://stackoverflow.com/questions/1274018/system-security-securityexception-when-writing-to-event-log)
Answer: The problem is probably your event source.  You have to create an event source before you can write to the event log (if you don't, the Event log object tries to create one for you "automagically" the first time you write to the log).
You have to have hightened permissions to create an event log source.  In some of my web apps, I have put the code to create the event source into my setup (setup runs as admin, so I'm always guaranteed to be able to create the source).
You just have to create the source once.  After that, your ASP.Net app should have sufficient permissions to write entries specifying the source (or sources) that you created.
You can use an EventLogInstaller in your setup to create the source, or you could just write a little utility to call EventLog.CreateEventSource() as an admin.
I'll show you both ways:

// You would do this one from within an Installer class in a setup:
        private void InstallEventLog()
        {
            EventLogInstaller logInstaller;

            //Create an instance of an EventLogInstaller.
            logInstaller = new EventLogInstaller();

            //Set the source name of the event log.
            logInstaller.Source = "TheEventSourceName";
            Installers.Add(logInstaller);
        }

Method 2: just call CreateEventSource once as an admin (you could put the following code into a console app, for example, and run the console app as admin

EventLog.CreateEventSource("TheSourceName", "Application");

Bonus:
If you have Powershell installed on your server, you can do it from the Powershell command prompt:
(Make sure you are running Powershell as an admin)

[system.Diagnostics.EventLog]::CreateEventSource("SourceName", "Application")

Hop that helps
Comment: Clarifying point:  The string "SourceName" is whatever source name you want to use -- you can make it anything.  The string "Application" is a literal -- like you literally use the word "Application" (that specifies the Windows Application log vs. the System log etc).  The only exception would be if you are creating a whole custom event log and not just wanting to write to teh general Application event log.
Answer: Give the ASPNET permission to the event log.
Run -> regedit - > Browse to
HKEY_LOCAL_MACHINE
   \SYSTEM
      \CurrentControlSet
         \Services
            \Eventlog

Right click select permissions and give the ASPNET account full control
Comment: Not sure why this is being down voted so much.  It may not scale or even be acceptable for production, but it is a good answer that says specifically what the permission is, and how to give it.
Comment: That's probably a bad idea if you are distributing your app, there are IT admins who will not allow changes to the default security options.  You should be able to play within the sandbox.
Comment: The changes take only effect after you restart your aplication on IIS
Comment: Honestly I would still use my original answer (the one marked as an answer).  All of thse other methods require adding heightened permissions to the IIS account the original answer does not -- you just need to either run the setup as an admin, or run the single line of code once as an admin (while you are installing the web app)
Answer: IIS 8 permission solving answer
I am lazy and didn't create a special log in my code, instead I used:

System.Diagnostics.EventLog.WriteEntry("MyAppName", "Bla Bla SQL
  ERROR: "+sx.Message);

Just to complete Michael's answer
In IIS8 the user used by IIS when running server side code is : IIS_IUSRS
(actually its more complicated because there are virtual accounts within IIS_IUSRS but they get permissions from that account, see IIS_IUSRS and IUSR permissions in IIS8 form more details)
That user only requires READ permission on this registry node:

HKLM\System\CurrentControlSet\Services\Eventlog\Security

The reason for this is that when a new log source is written to, before creating it, the system wants to check that it doesn't exist so it needs to READ the source names.
Also, if you are using the iis express of visual studio, it will run under your personal credentials, so if you don't have read access permission to the registry node above you will need to add it too when debugging under visual studio.
(If administrators has permission to the node and your are in that group, it is not enough, you need to run visual studio 'as administrator' - which will work only from visual studio shortcut and not the sln shortcut)
Another note: If the computer is in a domain and you can't find the IIS_IUSRS account when editing registry permissions, it is likely you are looking in the wrong 'location', searching for the account on the domain active directory instead of the local computer)
Comment: Note, if the IIS_IUSRS user is missing in the list, you are probably viewing domain users - change the locations to the local computer. the user IUSRS in the domain is not the one you need
Comment: Also dont forget to restart the service (IIS)
Comment: If it still doesn't work, go to your app pool properties choose advanced settings then mark the 'enable 32 bit applications to true. Mine was false, but this helped a friend so try it.
Comment: The original answer would still work -- just run the code to create the event source as an admin 1 time.  Do it at the same time you are deploying the web app.  After than, your IIS app running at lower privilege will be able to write log entries using the new source.
Answer: I think a more secure option to @Michael Kniskern's good example is:
regedit...
HKEY_LOCAL_MACHINE
   \SYSTEM
      \CurrentControlSet
         \Services
            \Eventlog
                 \your_new_application_log
Give full control to just the specific application log created for the purposes of your application (in this example right-click your_new_application_log and set permissions there).  Once the new log name is created it will appear in the registry nested under eventlog node as above.
Answer: I'm using IIS 10, and set the pool identity to Local System
see reference : https://stackoverflow.com/a/9067391/9975799
Comment: Please provide essestial details from link because link may get expired in future.
Comment: I did the Item number 3 ( 3rd bullet ), set the Application Pool ( the one you are using on your site ) then set the identity to Local System


what is the word origin of myelo- as in myelofibrosis or myeloma?

Question: what is the word origin of myelo- as in myelofibrosis or myeloma? I know that these are plasma cancers originating in the bone marrow.
Comment: I'm voting to close this question as off-topic because it is about the etymology of words and not biology.
Comment: It's greek, and brings with it the meaning: "marrow", "spinal cord", or "brain". [source](http://www.etymonline.com/index.php?term=myelo-&allowed_in_frame=)
Answer: myelo- is from Greek related to the word for 'marrow'.
See also: http://www.dictionary.com/browse/myelo-
Most cancers are named in a similar matter, with the tissue of origin followed by the suffix "-oma": glioma from glial cells, sarcoma from the connective tissues/"flesh",
Answer: medical terms are mainly based on Greek and Latin words, myel(myelo) is a root which means bone marrow and it also can mean spinal cord , it depends on the word. in myeloma , myelo means bone marrow and oma is a suffix which means tumor just like lymphom( cancer of lymphatic system ).
ex: meylitis: inflammation of spinal cord , but , myeloma : cancer of the bone marrow
Comment: Read the comments of a respected user — comments that have been upvoted — and follow the injunction in the Help section on answering questions: [Answer well-asked questions](https://biology.stackexchange.com/help/how-to-answer).


Flow of freezing liquid or a melting solid

Question: If a liquid is freezing, is equation of continuity violated? As the liquid flows, some portion of it is getting frozen. The mass of the fluid thus keeps dropping. Similarly, when a molten fluid flows over a solid, its mass may increase because the solid over which it flows also melts. In either of these flows, can we assume that div u = 0, where u is the velocity vector.
Answer: The continuity equation is not violated in either of the situations you describe above. The generic continuity equation for some scalar quantity (such as density) can be written as
$\frac{\partial \psi}{\partial t} + \nabla . \psi\mathbf{u} = \sigma$,            (1)
where here $\psi$ is the some conseverd scalar quantity, $\mathbf{u}$ is the velocity field and $\sigma$ is the is the generation of $\psi$ per unit volume per unit time (or source term). This source term is introduced when you are adding or taking away from the substance under consideration (or indeed changing its state).
For a ordinary incompressible flow (with the fluid not changing state), the continuity equation can be written as
$\frac{\partial \rho}{\partial t} + \nabla . \rho\mathbf{u} = 0$.           (2)
Taking the density of the fluid to be constant we find (as you point out)
$\nabla . \mathbf{u} = 0$.            (3)
However, for the situation describe above, it is not this simplified version that will model the flow correctly as the density is not constant. As long as you model the substance with correct continuity equation, nothing will be violated. In fact, for the cases you speak of, you can still treat the molten metal, or melting ice and as the same continuous substance, but instead of the simplified version of the continuity equation (the divergence free condition you have stated (3)), would need to use equation (2). To model the flow only, where you would treat the solidification as a change in volume/mass you would also need to include the source term (equation (1)).
I hope this helps.
Comment: Thanks, your explanation was indeed helpful. I was actually looking at a flow of a liquid under gravity, for which $\vec{u}=w\vec{e}_z$. If eqn(3) was valid then w would be independent of z and Navier-Stokes equation will be $0=-\nabla{p}+\eta\Delta\vec{u}+\rho\vec{g}$. However, in case of a melting flow, I would have to use the general form of continuity equation (1) and I will no longer conclude that $w$ is a function of $x$ and $y$ alone. Am I thinking correctly?
Comment: $w$ here is a scalar. This is giving magnitude to the unit vector $\mathbf{e}_{z}$. The equation $\mathrm{div}\;\mathbf{u} = 0$ is just saying that the net flux though the surface of the relevent volume is zero. As you have written the defintition of $\mathbf{u}$ above, it has no dependency on x or y coords. If $w = w(x, y)$ so $\mathbf{u} = w(x, y)\mathbf{e}_{z}$ changing the type of flow considered will not nessecaraly change your definition of $w$. Also note, that the Navier-Stokes eqn. is a conservation of momentum eqn., the continuity eqn. for density above are conservation of mass...


How can I get a real map and write on it?

Question: I am in bad need to have a real map and add a route on it with some writing on it. Like the image attached. Any suggestions please
Comment: go on google maps, download the needed part, add writing in photoshop, done
Comment: Welcome to **GDSE** - gald to have you here. Please take a look around [tour] to get a sense of who we are as a community and what we're about. Please also look at [ask] and [answer] a question so that you can understand best practice in formatting your issue, and what to expect in replies. I'd also recommend a brief glance over [help/behavior] to learn what our community's behavioural expectations are. As initially written, your question is *very* unclear - one can see neither what you've tried nor where you're stuck - please refine to make clear your specific issue.
Answer: Google maps are copyright - and so technically not legal to use.
However you could use OpenStreetMap instead. Their maps are free to use for any purpose, under an Open licence.  To keep it simple, just take a screenshot, paste into the software of your choice and add annotations.
If you want to take it a little further, depending on your level of expertise, it's also possible to download the map as an SVG. Then you could open it in a vector image editor such as Inkscape (which is free), or in Adobe Illustrator, if you have access to that software.


How much carbon dioxide do we actually ingest from a can of coke?

Question: On this most trustworthy page it states that a 355 mL can of coke contains on average about 2.2 grams of carbon dioxide. As far as I know, this carbon dioxide can exist in solution as carbonic acid, and is what gives coke it's nice taste. However, when we open a can of coke, there is a hissing noise as carbon dioxide is released (presumably because the carbon dioxide was under a lot of pressure), and hence we never actually ingest 2.2 grams worth of carbon dioxide in the form of carbonic acid. Over time, the carbon dioxide continues to bubble out of solution. How would I get a rough estimate of the actual amount of carbon dioxide that I ingest in a 355 mL can of coke? (Just an order of magnitude, for instance ingesting 1% of the 2.2grams as opposed to 10% is a big difference). Also, how much would the temperature of the environment affect the amount of carbon dioxide lost?
Answer: Whatever $CO_2$ you ingest will ultimately be released from your drink in your stomach and will come out as burps. The solubility of $CO_2$ is $90cm^3$ per 100g of water at 1 bar pressure and room temperature. As temperature increases, this value decreases, which means that less amount of $CO_2$ stays in the water. For a 355ml can of cool drink (at room temperature), which we can assume as water, the amount of $CO_2$ present at normal atmospheric pressure comes out to be roughly 0.6g. This is the amount you ingest.(Roughly 25%). The rest is lost in two ways

When you open the can.
When you have burps.

For the burp part, you could perform a little experiment to get a rough estimate by trying to control your burps and blowing all that gas into a small balloon. But it would not really work because the gas is at atmospheric pressure and so would not enter the balloon.
You can look up the molar solubility values of $CO_2$ online.


unlndir script to undo the results of lndir

Question: The lndir command performs a shadow copy of a directory tree, but using symlinks. Files are symlinked rather than copied, while subdirectories are copied. It works fine, but I also need some kind of unlndir script that performs the opposite.
In other words, the behavior of unlndir would be:

If there's a symbolic link on the target tree pointing to a file in the source tree, remove the symbolic link.
Perform previous task recursively for all subdirectories that exist in both the source and the target tree.
If some subdirectory in the target tree becomes empty, remove it.

I realize this is similar to what GNU Stow does, but I am looking for a simpler shell-script based approach.
Do you know of any shell script that can do this?
Answer: Assuming GNU find(1):
find -P /some/dir -type l -xtype f -delete && find -P /some/dir -type d -empty -delete


Are there any "reserved" aura attributes for Aura?

Question: I had this on my previous question where id I defined the attribute "required" as a boolean validation would fail is there a list of these "reserved" attributes and their names for LWC Aura
Comment: Again, it's either Aura **or** LWC. They are two different technologies and follow different rules. Presumably, you're asking about Aura, so LWC should not be in the question title.
Answer: In Aura, you must begin attributes with a letter or underscore, and must contain only letters, numbers, and underscores. Documentation.
In LWC, you must not start any attribute name with on, aria, or data. You may not use the specific attribute names slot, part, or is. It is recommended that you do not start with an uppercase character, because it requires special syntax to address such properties. It is recommended you do not use HTML global attributes, but you can use them if you decorate them with @api. You must begin attributes with a letter or underscore, and must only contain letters, numbers, and underscores, as in Aura. Documentation.
required is not specifically reserved, and aside from a small handful of restrictions, you can use any names you want. In Aura, you can specifically use any name that meets the rules without reservation. As far as I know, there's no restriction on even using HTML global attributes if you really want to, although I wouldn't recommend it.


the regulatory size of a garment in way to be subject to tsitsit

Question: Is there a minimal size of a garment with four corners that makes it duty to tsitsit? Is there a one size fits all?
Answer: The size of clothes that need Tsitsit is treated in Gemara Menachot 40b-41a:

מאי טלית פטורה? אילימא דלית בה שיעורא, והתניא: טלית שהקטן מתכסה בו ראשו ורובו והגדול יוצא בה דרך עראי - חייבת בציצית, אין הקטן מתכסה בו ראשו ורובו אע"פ שהגדול יוצא בה עראי - פטורה,
What is meant by 'a garment exempt from zizith'? Does it mean a garment smaller than the prescribed measure? But it has been taught: A garment with which a child can cover his head and most of his body, and in which a grown-up person would walk out for a moment, is subject to zizith; but if a child cannot cover with it his head and most of his body, even though a grown-up person might walk out in it for a moment, it is exempt.

"A child" is not an accurate measure! To determine with which a grown-up preson would walk out for a moment is not easy. How this Gemara leads to precise sizes ?
The first step toward practical indications is to learn Rambam, Ahava, Tsitsit, 3, 1:

א  כְּסוּת שֶׁחַיָּב אָדָם לַעֲשׂוֹת בָּהּ צִיצִית מִן הַתּוֹרָה--הִיא כְּסוּת שֶׁיֵּשׁ לָהּ אַרְבַּע כְּנָפַיִם, אוֹ יָתֵר עַל אַרְבַּע; וְתִהְיֶה מִדָּתָהּ, כְּדֵי שֶׁיִּתְכַּסֶּה בָּהּ רֹאשׁוֹ וְרֻבּוֹ שֶׁלַּקָּטָן הַמְּהַלֵּךְ לְבַדּוֹ בַּשּׁוּק, וְאֵינוּ צָרִיךְ אַחֵר לְשָׁמְרוֹ וְלֵילֵךְ עִמּוֹ;
A garment to which the Torah obligates a person to attach tzitzit [must meet the following requirements]:
a) it must have four - or more than four - corners;
b) it must be large enough to cover both the head and the majority of the body of a child who is able to walk on his own in the marketplace without having someone else accompany him and watch him;

The question is how Rambam assumed that the age, the development step of this child is determined by his hability to walk on his own in the marketplace without having someone else accompany him and watch him? The Raavad answer that this is a deduction, such a garment must be possible to help a grown-up person to walk for a moment (a passage of the Gemara not pasted on Rambam), so this kid must be close to the size of an adult person (an adult is at least 13 years old according to Halacha). The Kessef Mishne infered from the fact that the passage concerning adult person is skipped by Rambam, that this is an other Halacha: An adult, if large sized, cannot simply keep a Talit which can cover head and most body of a child. It must suit him a minimum, per example he will not to be ashamed with this garment and be able to walk. So i Reuven is XXL and Shim'on Small size, the Talit of Shim'on is perhaps unable for Reuven's Mitsvat Tsitsit.
The Tur define the child as 9 years old. Kesef Mishne explains that this age is linked to the ability to be careful not to loose the Talit, not only the ability to walking alone on the streets. Magen Avraham understand that 9 years is choose because this is the age of Chinuch.
Shulchan Aruch Orach Chayim 16
He specifies that the size regards length and width (head and majority of the body in length and width), that the child must to fulfill the condition mentioned above for understanding the Tur. So we may deduct 9 years.
So, it is very relevant to verify if it is not too small for walking a few moment with it on ths street.


Do I keep the money at the end of GTA V?

Question: I now have the choice to kill Trevor or Michael or do Deathwish. But the thing I wanna know is, do I still get the money from 'The Big Score' heist if I choose Deathwish?
Answer: I'd recommend you saving the game before the mission and replay it with the different endings. That being said yes you'll get at least 20 million dollars either way:

 In any case you get a lot of money.
 If you choose to kill either Michel or Trevor, you'll spend the end mission killing them, after that Lester will give you a call (I only killed Trevor but am assuming its the same for Michel too, but I guess his family gets the money not Frank) telling you he can't reach one or the other (depending on who you killed) and he'll transfer you (Franklin) the killed character's cut too, so you'll get 40 million dollars. If you choose Death-wish, everyone lives, everyone gets 20 Million and you kill some other dudes instead.

One thing to note though:

 If you choose to kill one or the other, they are obviously dead after the mission, and are unplayable, you simply can't switch to them.

So yeah, that's that.
Comment: Question asks specifically about endings, no need for spoiler tags.
Answer: When you kill Trevor he gives Franklin and Michael more money, but if you kill Michael, Lester gives it to his family, so the best options are to, "kill Trevor" or "Deathwish" for keeping the most money money.


How much mass is in gravitational waves?

Question: Like photons, I understand gravitational waves to have no rest mass but mass due to their energy. Are gravitational waves a significant part of total mass and what are the main components (black hole collisions, big bang etc)?
Comment: The only useful concept of mass is rest mass. What you are calling mass is energy divided by $c^2$. As to your question, reformulated as how much energy is gloating around as gravitational waves, that is still to be found out.
Comment: please note that a bunch of collinear photons have zero mass. It is the "length" of the sum of all the fourvectors of the individual photons: the invariant mass, that characterizes a beam of photons building up a classical em waver , or a   beam of gravitons( presuming wuantizatiin of gravity) building up a classical gravitional wave.
Answer: Turning to the very useful cosmic energy inventory by Peebles and Fukugita, they estimate that gravitational radiation from massive black holes make up $10^{-7.5\pm 0.5}$ of the total energy of the universe, stellar binaries contribute the smaller $10^{-9\pm 1}$ and primeval gravitational waves are less than $10^{-10}$.
In short, they make up a rather small component. As comparison, they estimate stars to make up 0.0015 and planets $10^{-6}$ of the energy.
Comment: An excellent answer. Thanks for linking a paper anyone can view.


Why does physically touching a specific pin eliminate circuit issues?

Question: This is a strange question and I don't know if I will be able to describe it correctly. There have been several instances working with a system that basically consists of a board camera, an FPGA, and TFT display where I can eliminate image noise by physically touching a specific wire or pin. For example, the current system I'm working on has pretty strong red noise in the live camera image. If I specifically touch the CAM_DATA[7] pin (the MSB for red), the noise disappears. It also disappears when the oscilloscope probe is connected to that pin, but not when the ground clip is attached. What effect does a person touching a specific wire/pin have on a circuit and how can I reproduce this "solution" with a basic components? ( I have verified that the issue is not just a loose wire or loose connection that is coincidentally going away because I'm pushing on it.)
Comment: Every time in over forty years of working with electronics when we noticed a phenomenon like you describe there would be a standing joke: "I guess we will have to ship an engineer with every system" or "Make sure that the scope is on the BOM".
Comment: Capacitance to ground?
Comment: Tell us the type of signal being applied to the FPGA pin in question. E.g. Is it a logic level signal created by another IC on the same PCB? Or is it a signal directly from the camera? How long is the route of this signal? Is it confined to the PCB? Or, is it delivered over a wire or cable? If so, how long is that connection?
Comment: See [this answer](http://electronics.stackexchange.com/questions/195400/using-a-human-finger-to-test-a-circuit/195407#195407)
Comment: you should try to identify the cause, are you missing termination and thus seeing extra crosstalk?
Comment: It is probably capacitance. But it could also be a bad connection. In other words, that one IC pin might not be soldered correctly and is making intermittent contact. When you touch it, it makes good contact and the system works correctly. If that is the case, simply re flowing that one pin with solder may fix it. If it is a capacitance issue, adding a small capacitor  to that net should fix it.
Answer: Touching a pin does not eliminate the circuit issue, it just hides it. Your circuit still have an issue, and a big one - this particular CAM_DATA[7] bus signal has insufficient timing relative to bus clock, likely an insufficient hold time. A finger, or tweezers, or scope probe all do have some capacitance, 3pF, 5pF, or 10pF. Attaching a probe (or touching a pin) increases signal propagation delay (or elongates signal edge) on that particular signal, so it gets properly latched, and the overall data don't have intermittent corruption anymore.
Actually, the fact that you have discovered this kind of sensitivity is a good sign, since it likely means that the entire bus has a serious problem that must be fixed. Under some voltage or temperature or component variation the this effect can show up on some other data line. You need to check the entire bus for violation of hold time and make sure the data-clock relationship meets specifications with some margins. If the timing is tight, it could be that the bus does not have trace length matching, or something else.
Since it looks like the bus is an input to FPGA, advancing internal clock will fix the problem - it is likely that the clock insertion delay was uncounted for relative to the data I/O cell delay.
ADDITION: After the bus timing is fixed, I would recommend a quick and dirty test: when your system is running a relevant test, firmly press a wet finger over the bus traces, and see what happens. A good high-speed bus, with typical 50-Ohm traces and solid timing will continue to function, while a marginal bus will break down and show some garbage artifacts. Just applying a finger over solder mask increases the signal propagation delay along the bus transmission line (by 50-100ps), which might cause data integrity problem on a poorly implemented bus. Of course, the "wet finger test" does not replace a thorough validation of bus margins by clock timing margining and data skew checking.
There is an excellent elaboration on the "wet finger test".
Answer: The effect is to add some resistance and capacitance to ground (or to +V if you happen to touch that as well).  Mostly you are shifting (delaying) the edge of a signal.  Sometimes it is due to lengthening the rise time of the signal. Sometimes it due to attenuating the signal, so that it takes longer to "get up the rising slope" to the level where the edge is sensed.  If you touch +V instead of ground, you can sometimes decrease the rise time and shift the edge the other way.  In any case, for signals that are switching very close in time to their reference clock, this sort of disturbance shows up in the result.
If you could put the clock and the signal in question on a scope and watch what happens when you touch the pin, you would readily see what I've described.
Comment: And yes, as @Michael Karas put in his comment, I've also announced at times, "Well, we'll have to ship it with the scope probe attached".
Comment: Just update the user manual with a picture of where the user needs to press.
Answer: I don't have an answer for what's wrong but I have a quick and dirty work around if it has to go out the door. Take 2 pieces of small gauge solid insulated hook up wire (14-20 ga.) and tightly twist it together. Solder 1 end to the pin and the other to ground. Take your wire cutters and start trimming off the twisted wire until the image is stable. If the image never stabilizes start with a longer piece of twisted wire. That's always worked for me.
What you did is called a gimmick capacitor with about 1 picofarad per inch depending on wire size. They were SOP for tuning the finals amplifier on RF rigs to get the feed back from the plate to the grid just right. It is still useful anywhere you need a very small capacitance, particularly a variable one.
If it still won't stabilize I would try solding one wire to the pin and the other to V+ and start trimming again. If that does't fix it you do have a really weird problem.
When you touch a pin you also inject 300 to 600 microvolts of ~60 cycle AC on the pin as well.


How to store video path in database and play video in browser using asp.net?

Question: I would like to upload video path in database and it play video in my browser using asp.net and sql server.
Answer: It's very easy. At first you must create table in DB ( it can very simple table, just ID and video path ). Than, you must insert record into DB using OLE DB. TO show you video you must pull back video path and add it to you player on page. You must use google to search, there a plenty solutions on the internet.


Can I repartition my primary hard drive without removing the Lion recovery partition?

Question: Scenario:
I boot into Recovery mode and open Disk Utility. Then I select the primary hard drive and choose 1 partition. Will that destroy the recovery partition as well?
Answer: No destruction will happen - This repartitioning you propose is possible to safely do.
The recovery partition won't modify itself (since it's in use) and will survive attempts to erase itself when it's in charge.
You also can resize things in general when booted from the main OS as long as files that are stored in the area being trimmed are mobile and not in-use or locked.
You have to enable a debug mode for Disk Utility to see and work on the Recovery HD so it's planned to be something you have to know a trick and go out of your way to tamper with. (Note: Debug mode is removed in 10.11 with the redesigned Disk Utility app)
Comment: Awesome. I did a clean install of my wife's MacBook last night and I got to that part and didn't know what to expect so I just erased the disk. Thanks for the assurance. I like to repartition. Not sure if it is better or the same as erasing the drive - for a clean install purpose.
Comment: Partition forces a write to the partition map. In practice, it's rarely of use - but it feels nice and is that one step cleaner :-) I like to partition to three equal and then back to one to see the map change and back as well as exercise the formatting a bit. One time I caught a bad drive that way, so now I'm _that_ baseball player that has a superstitions routine for others to smile at :-)


consider you are stranded in deep space, and an alien agreed to drop you back home, how would you explain the location of earth in the galaxy?

Question: remember they have no concept of what humans have named stars and clusters
Comment: This is really more of a worldbuilding.stackexchange.com question, and even there, would require more constraints. At the very least things like: How much information does the lost individual have on in their mind or on their person? How much information on the individual star systems in the galaxy does the alien benefactor have?
Comment: Highly relevant, if not duplicates, https://astronomy.stackexchange.com/questions/19893/is-it-possible-to-figure-out-your-location-in-the-milky-way-if-you-are-suddenly
Comment: Welcome to astronomy SE! The question has the potential to be interesting, but please stick a bit to [ask], e.g. make a concise title. You should also mention what you consider "deep space". Is your hypothetical traveller somewhere in our galaxy? Or in our local cluster?
Comment: I disagree that it's off-topic or better suited in another SE. IMHO it's basically asking about what the voyager probes try to achieve: pin-pointing to Earth in a universal way
Answer: You need to find markers that are easily explained and easily visible. This is likely to require a lot of knowledge of astronomy.
You first find the Crab pulsar (the brightest(?) gamma/X-ray source in the Galaxy) and tell them head to there. That gets you relativity close, galactically speaking. Now your within ~2000pc from Earth. You have a problem of course if you are so far away that the location hasn't seen the Crab explode yet (assuming some sort of FTL technology).
Once your within a few thousand light years of Earth you just need to pull out your copy of the Gaia database and start matching stars based on stellar properties (their total luminosity and spectral colors) with the stars you can see. As your only a few thousand light years from Earth, the stars properties wont have changed much compared to what Earth observed.
If you didn't pack a copy of Gaia, then finding other "interesting stars" will help. Betelgeuse is few hundred parsecs away (a very bright very massive star), Sirius (a  star with a companion star that is the size of a planet (a white dwarf) in a 50 yr period) which is only a few light years way from Earth. Once you found Sirius then its a case of saying looking for the star with multiple planets, where several very large planets are in a very wide orbit, and several smaller inner rocky planets. Earth is the one with water.
Comment: Pulsars are not visible from anything but a small range of solid angle.
Answer: There are a number of questions about interstellar navigation in general and findng Earth in particular, in the Worldbuilding Stack Exchange. I have answered some of them.
https://worldbuilding.stackexchange.com/questions/120255/how-can-i-know-where-to-point-my-spaceship[1]
https://worldbuilding.stackexchange.com/questions/193694/how-far-would-we-have-to-travel-to-make-all-of-our-familiar-constellations-unrec/193721#193721[2]
I suggest a four step method to find the way back to Earth from any place within a hundred million light years in my answer at:
https://worldbuilding.stackexchange.com/questions/123371/how-can-i-locate-myself-in-a-random-point-of-space/123429#123429%5B1%5D[3]
And see my answer at: https://worldbuilding.stackexchange.com/questions/122461/can-my-spaceship-figure-out-its-position-using-cepheid-variables[4]
If you have traveled into deep space, interstellar space, in an Earth ship, you should have at least some basic knowledge of what Isaac Asimov called "galactogrphy", the "geography" of the galaxy.
So you should know the coordinates of various interstellar objects in one or more coordinate systems, and/or have books or computer files with a lot more coordinates.
Earthbound astronomers use several celestial coordinate systems  such as the equitorial, elliptic, and galactic coordinates, to express the directions to various objects as seen from the Solar System.
It is possible to map the positions of various objects in a 3 dimensional array, if the distances to those objects are also known.
The space traveller can tell the alien that there are 360 degrees in a full cirle, 60 arc minutes in a degree (21,600 minutes in a circle), and 60 arc seconds in an arc minute (1,296,000 arc seconds in a circle).  So that should help the alien convert your angular measurements into his angular measurements.
The Earth astronomical coordinate systems all have a latitude of zero at their equators and ranging from plus 90 degrees to minus 90 degrees at their poles.  And they have longitudes ranging from zero to 360 degrees - except for the equatorial system which is divided into 24 hours of 15 degrees, so that each minute is 15 arc minutes and each second is 15 arc seconds.
And if the space traveler is stranded soewhere in our galaxy, it should be a lot easier to find their way home if they remember the coordinates of various highly luminous astronomical bodies.
For example, the coordinates, and thus directions from Earth, to the center of our Milky Way Galaxy, the center of the Small Magellanic Cloud, the center of the Large Magellanic Cloud, the Center of the Andromeda Galaxy M31, the center of the Triangulum Galaxy M33, and the center of the great galaxy M87 in Virgo, should be more than enough data points to locate a relatively small region of our galaxy wher Earth should be.
And if he remembers the distances from Earth to those astronomical bodies the alien can make a 3-D computer image with spheres around the centers of those objects at the distances mentioned by the human. The spot where the spheres intersect should be the region of the galaxy where Earth is located.
How will the alien know how much distance is in an Earth light year?  Maybe the many advanced instruments a human space traveller has will include a timepiece.  Or maybe the alien will time the human's heartbeats and compare the rate in his time measurements with what the human thinks is the rate in human times mesurements.  Maybe the human will count out approximate seconds and the alien will time them to get the approximate ratio between time measurements.
And then it will be easy to calculate how far light will travel in an Earth light year.  A light year is the distance light travels in a Julian calendar year 365.25 days long.  And calculating the number of seconds in a year is so easy that I once calculated it in my head while walking to elementary schhool.  Anyway, you can use a calculator to find that there are 31,557,600 seconds in a Julian calendar year.
And of course the alien should have a good idea of how long an Earth year is if the alien is also a carbon based, liquid water using, oxygen breathing, lifeform.  In that case his planet would have to orbit its star at a distance where the planet would have a temperature where water is liquid in many regions.
Stars vary greatly in luminosity, and so their habitable zones where water would be liquid on a planet vary in size by thousands of times.  But there is a much smaller range of stellar luminosity and thus size of habitable zones in stars which are otherwise compatible with habitable planets.  The year lengths of habitable planets should vary by only a few times.
See pages 67 to 72 at Habitable Planets for Man, Stephen H. Dole, 1964:
https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf[4]
And if the human tells the alien that the angular diameter of the Sun is about half a degree as seen from Earth, that should help the alien calculate the approximate length of an Earth year.   Habital planets of more luminous stars would have lower angular diameters of the stars and longer years, while habitable planets of less luminous stars would have higher angular diameters of the stars and shorter years.
And if the human has measuring devices the alien can convert human length measurments into alien length measurements.  And if the human knows the length in human units of a parsec or a light year, the alien can calculate that distance in his measurements.
The borders and thus dimensions of our Milky Way Galaxy are rather fuzzy and vague, but if the human and alien societies use the same definitions, the ratio between human parsecs or light years and alien distances can be calculated.
If the human knows the absolute distances between Earth and the centers of the MIlky Way, Andromeda, Small Magellanc and Large Magellanic Galaxies, the relative distances between them and Earth can be found.  And so the region of the Galaxy where Earth is can be located.
There are a few open star clusters within a few hundred light years of Earth.
Two of them, the Hyades and the Pleiades, and the red giant star Aldebaran, are almost lined up when seen from Earth.  A line going toward the galactic center from the Pleiades past the Hyades and past Aldebaran will point close to the Solar System.
So once the relatively small region containing Earth is located, a search should be made for two open star clusters almost pointing toward the galactic center and almost in line with a red giant star.  And travelling along that line toward the galactic center should make the constellation of Orion behind the ship appear more and more like it is seen from Earth.
So those are my ideas how a human space traveler with sufficient astronomical information could find their way back to Earth.
Answer:
...how would you explain the location of earth in the galaxy?

I would first describe the two Voyager spacecraft to the aliens and tell them to go find at least one of them and bring it to me.
I would then ask them to study and decipher the drawings on the outside cover of the record, specifically the large "star-like" radial lines with binary numbers that represent various pulsar directions and frequencies in the neighborhood of Sol.
Of course I could also then ask them to back-calculate the trajectory from whence it came; which would be easier depends on how far we are currently in time versus how far we are in space from Voyager's origin. I haven't a clue how I ended up there so I'll give them both options and let them figure out which is best.

Source

An alternative to gold plated record?
For how long will the Voyager records remain playable?
Why did we send those golden records on Voyager crafts?
Did Huygens probe carry any hint to help find its home planet?
What technical challenges would be playing this LP in (actual) space?

The Voyagers and the solar system up to about 2018 from this answer to Where is Voyager 1 now (2021)?:
Comment: I think if they can find either of the Voyager spacecraft from a description like "They look like this, and are somewhere in that Galaxy", they either have such incredible detection capabilities that any general description of the Solar system would probably suffice, or they already know where Earth is.
Comment: I suspect the number would be cut down fairly significantly with  "Stars of around G2 spectral type, whose planets start out: Rockball, retrograde-rotating Greenhouse World, Lifebearing watery world with single moon 1/81 its mass, Desert World, Gas Giant (4 large moons), Gas Giant with significant rings (1 large moon),  Gas Giant knocked on its side, Gas giant with 1 large retrograde moon. Planetoid belt between #4 and #5."
Comment: @notovny with ~10^8 solar systems in the galaxy I wonder how may there are that would fit a "general description" of ours.
Answer: A third way.  There are more roads leading to Rome. They probably have a teletransporter. How to feed it the right coordinates, whitout consulting the hitchhikers guide to the galaxy?
I would ask them (if I talk alien...) to beam one of them to my galaxy. With my knowledge of the universe this is possible. The universe would look very different for them but I could give the specifics of a Milky Way specific varying over time so they should be able to look for this.
The next thing I should ask is to teletransport one of them into the Milky Way. Once in the alien could orient himself by looking for the horse nebula or some other one the closest to Earth.
Once there he could find the coordinates of the Earth. To know the first object is the most important.
He could also surfe the Milky Way and look for the first radio signals that were sent from Earth.
When he beams himself back it is no problem to beam me back but I doubt if I would ask it! I would ask them to let me stay and beam my loved ones to me. But the again...