mSUGRA boundary conditions and the MSSM

Question: I read that in the MSSM with mSUGRA boundary conditions, the mass spectrum of the model is determined by five parameters at the GUT scale: $m_0$ (universal scalar mass), $m_{1/2}$ (universal gaugino mass), $A_0$ (universal trilinear coupling), $\tan \beta$ (ratio of Higgs vevs), and sign[$\mu$] (Higgs/Higgsino mass parameter). I have two questions: First, why is it the sign of $\mu$ rather than $\mu$? Second, why $\mu$ can take the two opposite signs?
Answer: I guess I know the answer now.
In the MSSM, once we minimise the scalar potential of the Higgs, we obtain:
$$M_z^2 = 2[-|\mu|^2 + \frac{1} {\tan^2\beta - 1 } (m_{H_d}^2 - \tan^2\beta m_{H_u}^2)]$$
For simplicity, in the large $\tan\beta$ limit, this can be written as, $$M_z^2 = -2 (|\mu|^2 + m_{H_u}^2)$$
Where $M_z$ is known from experiments, and the soft-breaking parameter $m_{H_u}$ is determined by the GUT-scale input parameters (universal scalar $m_0$, universal gauigino $m_{1/2}$, and a universal trilinear $A_0$)
So there is a constraint on $\mu$ (i.e. for a choice of input parameters, we want $\mu$ to take the value that gives the correct $M_z$). Solving for $\mu$:
$$|\mu| = \pm \sqrt{-0.5 M_z^2 - m_{H_u}^2}$$
So, the sign of $\mu$ is free but not the value of $\mu$, and the solution could be positive or negative. The absolute value appearing here is because, in the universality condition where everything is real, $\mu$ must be real.
Comment: you don't honor your nick, you are the kind of member we want on this site, the kind that likes to get his hands dirty with the problems
Comment: @Anirbit I believe I was reading Martin's Susy primer: http://arxiv.org/abs/hep-ph/9709356.
Comment: @stupidity Can you paste the reference from where you were learning this?
Comment: The second equation doesn't make sense, you have a negative Z mass?
Comment: @user788171 $m_{H_u}^2$ is negative at the weak scale, allowing electroweak symmetry breaking radiatively. I suggest that you read Martin's reference that I mentioned earlier.
Answer: That's correct  -  EWSB imposes $\partial V / \partial H_u = 0$ and $\partial V / \partial H_d = 0$, leading to (see Martin p.91)
$m_{H_u}^2  + |\mu|^2 - b \cot \beta - m_Z^2/2 \cos 2\beta =0$
$m_{H_d}^2  + |\mu|^2 - b \tan \beta + m_Z^2/2 \cos 2\beta =0$
If we input the soft-breaking masses  $m_{H_u}$ and $m_{H_d}$, $\tan \beta$, and the $Z$-boson mass $m_Z$, we can solve for $b$, soft-breaking bi-linear, and $|\mu|$, but the sign of $\mu$ remains undetermined.
The CMSSM/mSUGRA uses this convenient parametrization which trades $b$ and $|\mu|$ as inputs for $m_Z$, sgn $\mu$ and $\tan \beta$ as inputs.

mSUGRA boundary conditions and the MSSM


How can I get genie lamp parts besides from the Squeal of Fortune?

Question: The Lamp of the Djinn update says that genie lamp parts can be earned from the Squeal of Fortune, and from skilling and combat drops. However, I have not gotten a single part from skilling or combat. Do I need to do certain skilling activities or kill certain monsters to get the lamp parts? Do some drop lamp parts more often than others?
Answer: I believe it is pure luck, and it is extremely rare. My stats aren't that great, but while I was slaying, I managed to get a drop. Taking into account that this was after like 10 hours of training in 2 days. It is pretty rare, and None of my mates have gotten anything yet, and they are more "intense" players than me.
Answer: When that update was released the most common way to get the lamp parts was slayer. Attacking demons, dragons, or aberrant specters gave the highest chance or these lamp drops.


How do I modify a Yaesu FT-726R from Japan with limited VHF 2 meter bands to use US VHF 2 meter bands?

Question: I purchased this online an love the radio but VHF is limited to 144.00 to 146.00. Our local repeater is at 146.760. Any help would be appreciated. Thanks.
Answer: There are also so-called mods for the ham radios, and some sites have a collection of them. Out of respect for their work, I won't just copy the instructions, but you can find this one with coverage extension under the name "Expansion mod for the Yaesu FT-726". Mods.dk is such a place, and so is this one: http://www.fracassi.net/iw2ntf/manuali/All%20Yaesu%20Mods.pdf


My Chrysler 300

Question: someone put sugar in my tank I had it dropped and clean but when they put it back together when you drive at 35-40 mph, it vibrates underneath the car what do you think it is?
Comment: I would check to see if the exhaust system was rehung improperly. It may have been moved out of the way during the tank work.
Answer: First thing I would check is the tank loose?
If so tighten the mounting bolts.
Depending on the design it should be pretty easy to jack up the car and check how loose the tank is.
Answer: Is that all they did? Sugar in your tank? Are you sure they did nothing else?
That's a rear-wheel drive car, right? I think you may have lost a driveshaft balance weight. Coincidental. Unless... the vandal also loosened your lug nuts or u-joint nuts, either of which could make a car vibrate unpredictably at speed.
Answer: Return your vehicle to the garage that carried out the work in case they need to do any rectification work, or, advise you of anything else that may be developing

My Chrysler 300


What are best-practices for running Windows Update on a Hyper-V server with running VM's?

Question: I have four VM's running on a Windows Server 2008 R2 box - not 'core.' What is the best way to install Windows Updates on that server? Do I need to shut the VM's down first in case it wants a reboot? Is there a way to configure Windows Updates to do the shutdown itself?
Answer: WIndows saves the VM's then restarts. If saving takes too long some vm's just fail and restart from cold boot.
Server 8 can - in a cluster - empty the machine by moving the VM's over first, but that is not in standard 2008 R2, sadly.
We do save / shutdown before upating the virtual servers. But we only have three.
Comment: I did an experiment this morning as I ran updates on the VM host server. I paused & took snapshots of all the VM's before rebooting. When the server came back up all the VM's woke up too with no ill effects.
Comment: Small? I have al arger server and we sometimes get a rese here and there - possibly a timeout saving all the vm's.
Answer: Assuming that you are working in a Hyper-V cluster you'll want to manually move all the guests from the host to another host then patch the host.
If you are in a standalone config you'll want to down the guests then patch the server.


How are the edges of an image obtained with anisotropic diffusion?

Question: I already know how to implement the method and obtain a correctly diffused image, but in the papers related to the topic there is usually an edge map that's calculated after the diffusion is performed as an "edge detector scheme" (like in the original Perona and Malik paper) and compared to gaussian smoothing  (canny detector) mentioning something related to scale-spaces. I'm making an implementation in MATLAB so I would like to know how is this edge map calculated as shown in the picture.
Answer: They compare the same idea of edge detection after some smoothing. They compare edge aware smoothing in the form of anisotropic diffusion vs. non edge aware method in the form of gaussian blur.


Is direct sunlight reflected from white animal fur affected by a polarizer?

Question: I have a friend with a bright white cat. Photographs of this cat outdoors in direct sunlight feature either a glowing white blob or very underexposed surroundings, depending on what the point-and-shoot camera decided to meter on. I'm currently living far from said friend and cat, was considering sending an extra polarizer that I have sitting around, but don't have a similar test subject handy. Can anyone enlighten me as to how much, if at all, a polarizer will affect light reflecting from white fur? I should also mention that this is sleek, surface-like fur, not the puffball kind, which is why I think there's any chance of it working at all...
Comment: Not what the OP asked, but HDR might work if the cat is slow.
Answer: There are two components to the light being reflected off the fur.  The predominant one is likely diffuse scattering.  A polarizer won't help with that.  There may be some more "reflection" looking sheen, especially if the light is coming from somewhat behind the cat.  That probably is polarized, so a polarizing filter should be able to accentuate or attenuate it, depending on how the filter is rotated.
However, the fundamental problem is a small bright thing in a large and much darker picture.  That's not going to get exposed properly by the automatic algorithms in most cameras.  One way or another, you have to expose so that the brightest part of the cat doesn't saturate the sensor.  Yes, the surrounding scene will then seem darker, but this is quite fixable with non-linear brightening in post-processing.  A logarithmic sloshing towards the bright end usually works well for scenes with high contrast, but only if the information was properly captured (the bright parts aren't blown).
There are several ways with most cameras to expose so that the bright parts aren't blown.  You can use center spot metering, push the button partway with the cat in center (this freezes the exposure), then frame as desired and snap by pushing the button all the way.  Some cameras have a mode that looks at many spots and exposes for the brightest.  Or you can use the brute force method and just set the automatic exposure compensation to -2 or something.  Just don't forget to set it back when you're done photographing the cat.
Comment: Yes, it's this near-specular sheen component that I'm specifically hoping to cut, since it confuses the camera much more than diffuse white, and doesn't make for great pictures regardless of exposure...
Answer: Using a polarization filter does actually have an effect on fur. You can see an example in this article: How to Photograph Your Dog: 9 – Polarizers for Perfect Pet Portraits
However, the effect doesn't help your case at all.
What you would need would be to reduce the reflected light from the white fur while affecting the rest of the scene less. The polarizing filter will instead leave some reflected light from the fur unaffected, while reducing most everything else by 50%. You get the exact opposite of what you need.
Comment: Good link, thanks! The post actually shows that the filter *does* cut glare from the sheen of the coat, although the photos have been adjusted so that the result is overall lighter. This tells me that it could be worth sending a filter to mess around with, anyway.


Continuous functions between topological spaces

Question: I am having some troubles in proving continuity of functions between topological spaces. I'm still working on some basic examples. I understand that sums, products and composition of continuous functions are also continuous. For example, consider the function $$f: \mathbb{R}\rightarrow S^1$$ given by $$f(t)=(\cos t,\sin t).$$ How do I prove continuity using the definition? I can pick one open set in $S^1$ with the usual topology but I don't know how to compute its pre-image. Another example is the quotient map $$q:X\rightarrow X/E$$ given by $$q(x)=[x]_E,$$ where $E$ is as equivalence relation. My problem is the same, I don't know how to compute the pre-image of an arbitrary open set. I'd really appreciate if someone could give me some help.
Comment: For arbitrary topologies, we tend to check the pre-image of elements of some topological basis rather than arbitrary open sets.  In maps between metric spaces, this gives us precisely the $\epsilon$-$\delta$ definition of continuity.
Answer: For your first example, let $V\subset \mathbb S^1$ be an open set. Then by the definition of subspace topology, there is an open set $U\subset \mathbb R^2$ so that $V = U\cap \mathbb S^1$. Now using the fact that $g(t) = (\cos t, \sin t)$ is a continuous function from $\mathbb R$ to $\mathbb R^2$, $g^{-1}(U)$ is open in $\mathbb R$. But
$$f^{-1}(V) = f^{-1}(U\cap \mathbb S^1) = g^{-1}(U) ,$$
thus $f^{-1}(V)$ is open and so $f$ is continuous.
Now for the quotient map $q : X\to X/E$, continuity of $q$ follows directly from the definition of the topology on $X/E$. We say that a set $U \subset X/E$ is open if and only if $q^{-1}(U)$ is open in $X$. Thus by definition $q$ is continuous....
Answer: You don't always use the open-set-pullback argument to check for continuity. You need to use the machinery that's already been developed.
For your first example, note that $S^1$ has the subspace topology from $\mathbb{R}^2$, which in turn has product topology. Now what is the characterizing property for a product space?
As for the quotient space, look at how the (quotient) topology on $X/E$ is defined in the first place.


Should I connect the ground in the outlet for the dryer and the panel?

Question: the ground wire for the dryer is not connected at the panel, or at the outlet.
Is this correct or do, or do I need to land the ground wire at the panel and land ground wire to the actual dryer plug wall plug?
Answer: Older electric dryer circuits allowed the use of 120/240V non-grounding 3-prong receptacles. These were NEMA 10-50 configuration. In these circuits the neutral served as both the neutral and the grounding conductor.
If the ground wire existed though it definitely should have been used, but it is not uncommon to find what you describe.
I would certainly terminate the ground at the panel at the very least. A best case scenario would be to replace the receptacle with a 4-prong dryer receptacle and change the cord on the dryer to match.


Which video editor for Linux has the video speed control effect?

Question: I have so far tried Pitivi and Shotcut, but neither of these seem to have this effect, by which one could speed up or slow down certain segments of a video. Also, Shotcut doesn't even work very well on my system and tends to crash at every opportunity. Unfortunately my bandwidth is limited, so I don't have much of a chance to try out many such video editors. If someone knows one such editor for Linux, I would find such answer very helpful.
Answer: You can change the speed of parts of a video with Kdenlive.
However you can only set a specific speed for a specific part so if you want to have it slowly increase or decrease the speed you need to cut the video multiple times (right click->cut) and change it to a different percentage for each fragment.
To change the speed right click the cut part of the video->Change speed. See here.
Answer: You can use Blender, it is packaged on the must known linux distributions.
features
desired feature:

The Video Editor includes:

Live preview, luma waveform, chroma vectorscope and histogram
displays.
Audio mixing, syncing, scrubbing and waveform visualization.
Up to 32 slots for adding video, images, audio, scenes, masks and
effects.
Speed control, adjustment layers, transitions, keyframes, filters and more!

see: https://blender.stackexchange.com/


Running with clothes

Question: I have created a character with multiple layers of clothing and am trying to make her run with the cloths responding realistically. My issue is that every time she runs, using cloth physics, her cloths all ride up to her midriff. I have weight painted the upper clothing to make them stay still, but can't make the lower work properly. I have maximized the steps and played with the settings to no avail...
I don't know how to put the character up for people to look at... any help would be very appreciated!!
Answer: Pinning may be your answer.  Go into EDIT MODE and select some vertecies where you want the cloth to remain, [CTL][G] to group them and under your Cloth Simulation settings in the Physics Tab, select Pinning and the group which you formed.  This will at least keep the spots pinned to the locations where you want them to remain while allowing the remainder of the simulation to flow as normal.  I've used this before and it may require a little playing to get the pinning correct to keep from some weird artifacts forming in the sim, but it should be helpful for you.  If you have to, you may need to add a HOOK to the vertecies you have pinned and parent the hook to your mesh (I don't recall if pinning stays in one selection of 3D space or moved with the animation, therefore the possible use of the hook)

Running with clothes


How to show my Connected App

Question: We have connected a third party application into Salesforce by making it a Connected App. In the manage app section we have also set it to show on multiple tabs but we are not able to see the app. Is there some other configuration that needs to be done in order to show a connected App in Salesforce Lightning?
We are seeing the app in Salesforce Class though.
Answer:
Goto Setup-->App Manager-->App Name
In 'Lightning Experience App Manager' Section there is a column
'Visible In Lightning Experience'.Check if it sets to true.
If it is Managed Package and it is unchecked then you need to
contact to your 3rd party application and make it visible in
lightning.
If it is unmanaged package,you can click on edit and Set 'Show in
Lightning Experience' to true.

One more thing you need to check is if the Application is accessible to your profile or not.You will find the same when you edit the App.
Let me know if it helps.

How to show my Connected App


Replace LED on PCB with multiple smaller LEDs

Question: I have a small amplifier with a bright blue LED (dome-shaped with a height of 6mm and a diameter of 3mm). I am building a new case and I want to replace the LED with (three) smaller ones, preferably white. How can I calculate what the required specifics of the new LEDs need to be to create an equivalent circuit to the one blue LED? Is this even possible?
Comment: Check what resistor is in series with the LED, then check from what supply voltage it is powered Then you'll know how much voltage you have available, and you can decide to wire your new LEDs in series or in parallel with resistors.
Comment: Thank you! There is a 10kOhm resistor in series with the LED. The voltage between the power supply and just before the resistor is 11.5V. The voltage drop over the resistor is 8.2V. This means there is 3.3V available for the LEDs? Can I replace the resistor with a smaller one to make more voltage available so I can connect three in series?
Comment: It all depends on how the led is driven… if it's a simple resistor it's easy (already answered) if it's something more complex you need to study the circuit
Answer:
There is a 10kOhm resistor in series with the LED. The voltage between the power supply and just before the resistor is 11.5V. The voltage drop over the resistor is 8.2V. This means there is 3.3V available for the LEDs?

So there is 3V3 across the LED, which is normal for a blue LED.
Power supply is 11.5V and there is 8.2V across the 1k resistor, so current through the LED is 8.2mA.
If you use 3 white LEDs, these will have Vf somewhere around 3V-3.4V, so 9-10V total. You can wire them all three in series with a 470 ohm resistor, so there will be 1.5-2.5V on the resistor you'll get about 5mA maximum. Three LEDs at 5mA should be a bit brighter than one LED at 8.2mA, but that depends on the LEDs, so adjust resistor value accordingly.
Comment: Allright, I think I get it now. I don't think it matters much but the resistor is in fact a 10kOhm, but this will result in all currents divided by 10 and therefore a dimmer light (than expected with 1k resistor)?
Comment: Yes, correct. You don't have to replace the LED/resistor, if that's easier leave them in, just disconnect a pin, and connect the new LEDs where it is most convenient. Also, super bright power buttons are annoying, especially on an amp if you use it while watching a movie at night, so maybe 10x lower current is a good idea.
Answer: Similar size and construction white and blue LEDs are typically interchangeable electrically (they both use a blue die).
Replacing one with three is more involved to do it "right" and you'd need to figure out the circuit and measure the current (since the specs for the original LED are unlikely to be available).
Just putting three white LEDs in parallel in place of the original blue one may work well enough and you might want to try that first. Worst case is the LEDs are too uneven brightness or they don't last long, it should not hurt the rest of the amplifier if you do it correctly.


How do pulsars and magnetars emit lots of radiation?

Question: Firstly I thought that Pulsars are rapidly rotating, highly magnetic compact stars. The rotating magnetic field of a pulsar acts as a generator, accelerating energetic charged particles that then stream along the field lines". At a glance the answer looks quite decent but second look does not convinces me. First important thing how are these magnetic fields are formed? For a electrically charged particles moving in a ring generates a magnetic field but the particles in neutron stars are neutrons which are electrically neutral.
Then a second one was the equations which are involved in it, when protons collide with electrons during the formation of neutron star they form neutrons and give out neutrino, to what I have learnt, the equation does not feels good as when a neutron gets converted into a proton by beta decay an electron and an anti-neutrino is emitted so if we reverse this in time a proton, electron and anti-neutrino forms a neutron which is different from the previous equation, why are there two sets of equations for this?
Answer: welcome in the stack-community. Here are my proposed answers:
$\mathrm{I}.$ A pulsar is a neutron star that is mostly made up of neutrons. On the surface, gravitational pressure does not hinder the $\beta^{-}$ decay of neutrons, and so charged particles such as electrons and protons can form a magnetic field due to the whirling rotation of these objects. The small size and the high angular momentum create enormous magnetic fields capable of "tapering" the atoms.
$\mathrm{II.}$ It is not correct to say that electrons collide on protons, during the gravitational collapse. More precisely, due to the gravitational pressure, a $\beta$-inverse decay is triggered, which can be written as:
$$ \bar{\nu}_{e} + p \rightarrow n + e^+$$
i.e. electronic anti-neutrino, $\bar{\nu}_e$, and a proton, p, exchange a $W^+$ virtual boson, and produce a neutron plus a positron. This positrons then collide with the free elctrons in the star during the collapsing and emits photons:
$$e^-+e^+\rightarrow 2\gamma$$
P.s. Thanks to @Triatticus for the corrections to the photons counting in the electron-positron annihilation.
Comment: Should be $e^+ + e^- \rightarrow \gamma + \gamma$
Comment: Yes @Triatticus, you are right. Just a bad typo, i'll edit.
Comment: Thank you so much sir.


Sorted Combobox

Question: I am using a databinding with a combobx to show my objects in a drop down list. The combo box needs to sort the data within it automatically in alphabetical order after databinding.  How can this be done?  I would like the logic to be generic and applied to the combo box directly, and not on the objects being bound to it.
Comment: My binding data source can be a List<> of anything, since this control will be called from various places with different data.  I tried implementing the OnDataSourceChanged() method and sort the datasource using reflection and the display field, but since I don't really know what the datasource is I didn't manage to find a generic way.
Answer: A databound combobox cannot be sorted directly.  You have to sort the underlying datasource.  This is from MSDN:
Attempting to set the Sorted property on a data-bound control raises an
ArgumentException. You must sort the data using the underlying data model.

So you might be able to use a SortedList as a binding source.
Answer: Try to use this, it is working fine with me. Only change the names of controls
private void sellingTableDataGridView_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
     if (sellingTableDataGridView.CurrentCell.ColumnIndex == 5) {
         mainItemsDataBindingSource.Sort = "ItemCodeID";
     }
}

Sorted Combobox


How do you know if you're supposed to get the Electorate badge?

Question: I just reached 600 votes, but I wasn't awarded the Electorate badge. How do I find out what my ratio of Qustion:Answer votes are?
Answer: see this

Voted on 600 questions and 25% or more of total votes are on questions.

So you currently voted on 380 question and 226 answer (606 total). You still have to vote on 220 question to get the badge.
see also : Electorate badge rules?
Answer: To see your question/answer ratio, you can look at your profile.  Under your list of answers, you will see a "votes cast" section.
This section breaks out your total up and down votes, and your votes by questions and answers:
Comment: no [Freehand Circle](http://meta.stackexchange.com/questions/19478/the-many-memes-of-meta/19775#19775)?
Comment: I debated it, but my freehand circles are abysmal :(


are 4AA batteries (6V) power my arduino

Question: I'm actually new to using arduino , and trying to make a simple car, using two dc motors, a l298n and an arduino, the problem is that a 9v battery doesn't seem enough to just power the l298n and one dc motor , but in the internet some people use an 4AA battery which is 6v and power the arduino 4 dc motors and the l298n so how ?
Comment: Have you seen any of these Q+As? https://arduino.stackexchange.com/search?q=l298n
Answer: I understand you situation completely as I had also previously experienced the same problem. 9 V batteries are not enough to get the job done.
Therefore, I suggest you to use two 3.7 V Batteries. These batteries are a great alternative and had solved my problem. I hope it will do the same to you.
Answer: The name Arduino refers to dozens if not hundreds of different board and processor designs. Since a specific board / processor was not asked about we can only talk in generic terms.
Almost all Arduinos run at either 5 Volts or 3.3 Volts and contain a regulator to convert a wide range of Voltages to this value. That said, these regulators need a minimal drop between the input voltage and the desired regulated voltage in order to operate.  Some require less and are referred to as LDO or Low Drop Out regulators.
As a worse case, consider if this Arduino does not use an LDO regulator and operates at 5 Volts. The difference between the 6 Volt input and Arduino operating Voltage is only 1 Volt. Further, consider if the batteries were not fresh and were only supplying, say, 5.5 Volts. Finally, consider if one or both motors started drawing heavy current from the batteries causing a further drop in Voltage. Any of these cases could cause the Arduino to reset / behave unexpectedly.
Consider trying to use the 9 Volt battery to power the Arduino and the 6 Volt battery to power the motors.
Answer: To properly answer your question instead of taking a SWAG as I did would Be for you to post links giving technical information on each of the hardware devices and which Arduino you are using.
Nine Volt (smoke alarm) batteries do not have enough power to properly power an Arduino. Use some larger cells. There are so many places that show this improper configuration, it just will not last if it even works for a short while. Great for the battery manufacturers.
You can also purchase a SEPIC converter for a few bucks, this is a combination Buck/Boost converter. You set the output voltage you want and it will maintain it as long as you're getting the minimum voltage from the battery, even if the battery is at 3.5V and the output is at 5V. The input will range from about 3V to 30V and it will maintain its setpoint. This range is dependent on the device you pick.
The L298N is about the worce choice you can make for the motor driver. It has darlington bipolar outputs, that drop about 1.4 volts per lead or 2.8 - 3.2 volts to the motor depending on the load. That voltage drop is burnt up as heat and is doing nothing useful. Purchase an H-Bridge that is large enough to drive the motor that has MOSFET outputs, you will be much happier with that.
For batteries use whatever is convenient, the SEPIC converter solves that problem. Best to pick them to power the motor and use the SEPIC to power the Arduino Vin pin at about 7.5V. Doing it via the Vin is not as efficient as doing a 5V direct but you get the additional filtering on that input circuit. A lot depends on which Arduino we are talking about. Since you did not mention one I am assuming either a UNO or Nano.

are 4AA batteries (6V) power my arduino


week-over-week impacts on IV of of options with close to before/after EOY expirations

Question: Tomorrow is the last trading day of 2023. Compared to last week, I noticed that $SPY ATM or close-to ATM options for the end of month/quarter (Dec-29) exp experienced a spike in IV since yesterday, however, the opposite effect (downward pressure) happened on the IV of same-strike options for the first week of Jan-2024.
I cannot explain this change in vol space. Could somebody help me in the right direction?
Answer: Implied total variance is the actual volatility quantity being bet on with options. IV is a convenient way to discuss total variance because the numbers are more intuitive. Let $\tau$ be the total variance, $\sigma$ be the implied volatility, and $T$ be time to expiration. Then
$$
\tau = T \sigma^2
$$
What you observed, in lay terms, was the expected realized volatility between the two expiration dates falling. As long as the difference in total variance between the long and short dated is greater than zero, there is no arbitrage.


Motion planning for non-serial chain robotic arms

Question: I am trying to do position motion planning with inverse kinematics for the MeArm model.
I followed MoveIt tutorials and was able to achieve what I wanted with their provided robot example. However, I found out that the solvers MoveIt uses only support serial chains (here).
Is there any alternative method for doing motion planning/IK that supports non-serial chain robotic arms ?
Answer: You can try and use this:
https://github.com/RobeeContech/hardware_interface_wrappers
This is a repo we created for managing a unique transmission of our SCARA robot.
This is not maintained but it works fine as far as our tests go and we made it public if someone wants to use it.
you can look at those for references:
https://github.com/RobeeContech/transmission_manager
https://github.com/RobeeContech/robee_transmissions
this opens an abstract class to wrap your hardware interface and thus you can work with a normal serial ik solver
This means that there is quite a lot to write on your own and calculate your transmissions accordingly.
Answer: Running a search in google, return this repo, which, apparently can tackle your issue.
https://github.com/davetcoleman/moveit_whole_body_ik
On the other hand, it seems that none of the "officially" supported kinematic plugins can handle non-serial chains so probably you'll need to build something customized
Answer: Moveit implements by default a kdl based inverse kinematics implemened with its kinematic plugins. This works "ok" for serial robots. For complex robots like yours the intended approach ia to develop your own kinematic plugin.


Are questions asking how well a piece of hardware does X accepted?

Question: Triggered by How many players would this VPS be able to take?: Are questions that essentially ask this accepted?

I am looking at x hardware ([specs]), and I'd like to know how well it does ([clearly defined task]) at [some load]. How many [tasks] could it handle at one time?

On one hand, it's not exactly asking for a recommendation. On the other, it does ask for information to help make a purchase decision.
Thoughts?
Comment: And, if they are on-topic, at what point do we draw the line?
Comment: In my opinion, these create way too big of a grey area for us, but at the same time I think they could fit.
Answer: Disclosure: I provided an example on the linked question
I think this straddles the line of "pre-purchase" information. This question has already purchased the hardware and is really asking a configuration question: How many players can the hardware support.
However, the question could easily be adjusted to something like: "I want to support X players, what hardware do I need?" This would lead to the same answer I provided and would very clearly be a pre-purchase question.

Regarding the comment by ArtOfCode on where the line should be drawn, I think that depends on the requirements of the question and if it is truly a request for information about a possible purchase. If the question is getting into configuration, such as

How do I configure the server to use all of my cores
How do I limit ram usage to only X

Then it is headed off topic. These are clearly not related to the hardware or performance of the system.
The line, to me, is at the point where the user is tweaking a setting to get better performance.
Comment: Just a thought: if you see a question (like mine) where hardware is already purchased, it could potentially be edited to make it into a *pre-purchase* question without having to do anything else (such as closing as off-topic) with it.


Baloon air lock not inflating after second day

Question: I'm making mead for the first time. I used bakers yeast and a baloon as an air lock . The tutorial said that the yeast will be off gasing for 3 weeks but my mead only off gased the first day. Now it's a bit inflated but nothing compared the first day
Is it okay or should I add more yeast. It's in a warm environment
Answer: You may not have a perfect seal, so the gas is dissipating into the atmosphere. This is not a problem. The airlock serves only as a safety mechanism - it prevents buildup of gas, while also preventing anything getting into the container. An airlock is one of many ways to achieve this. You can put a bit of aluminium foil over the lid, a teatowel, anything that won't let dust or bugs through, basically.
Don't worry about the balloon, and never ever use the airlock (whatever type you use) as an indication of fermentation. Gas coming out can be caused by more than just fermentation, and no gas coming out can be caused by more than an absence of fermentation. If you want data, you need to measure the liquid with a hydrometer.
Answer: In case your fermentation has indeed deaccelerated this soon (and I agree with Frazbro that your balloon airlock is no indicator of that), it might be, along other factors, because of too much honey (high initial gravity musts are harder to ferment) or too little nutrient (honey itself does not have the necessary nutrients to keep your yeast healthy).
Two simple techniques you can employ, even with the setup you are using, are:

Oxygenate the must. Remove the airlock and agitate your fermenter to dissipate the carbon dioxide and let more oxygen in. You can do this once or twice a day for the first few days of fermentation without fear of oxidizing your mead.
Add nutrients. Boil some water (50mL is enough) and bread yeast (10g) for a few minutes to kill the yeast and add it to the must. The yeast husk will feed your fermenting yeast.
Answer: Your bottle is a screw top. Air could very easily be escaping through the threads of the jar top.
Don't rely on visible action to prove fermentation is happening. You need take SG readings to see if there is any sugar, and you need to take a second one a few days later to see if the SG is still going down. If it's still going down, then you are fermenting. If it's not then your fermentation may be stuck.
By the look of what's inside your jar, you either have a lot of floating solids or you have a healthy Krausen on top which to some degree probably means you are still fermenting.
Also the moisture at the shoulders of that jar look pretty wet to me, which generally also means you are still offgassing CO2, which doesn't always mean you are still fermenting, but is another indicator that you may be.
Finally, I have seen ferments complete so fast I thought the yeast never activated. Only after checking the SG did I realize oh, it's already finished. I had one do that quite literally overnight. Poof, done.


What is a MIME type?

Question: I have been reading about how to build plug-ins and this "MIME type" keeps getting discussed in it. I have tried to look into it and know that it is Multipurpose Internet Mail Extensions (MIME) but no suitable explanation of how it relates to browser plug-ins, as in what I need to know about it for building plug-ins, is provided, please explain in clear and simple words. What is it? Why do plug-ins have a MIME type?
Answer: A MIME type is a label used to identify a type of data. It is used so software can know how to handle the data. It serves the same purpose on the Internet that file extensions do on Microsoft Windows.
So if a server says "This is text/html" the client can go "Ah, this is an HTML document, I can render that internally", while if the server says "This is application/pdf" the client can go "Ah, I need to launch the FoxIt PDF Reader plugin that the user has installed and that has registered itself as the application/pdf handler."
You'll most commonly find them in the headers of HTTP messages (to describe the content that an HTTP server is responding with or the formatting of the data that is being POSTed in a request) and in email headers (to describe the message format and attachments).
Comment: Could this serve as a metaphor for ports on IP level?
Answer: MIME stands for Multi-purpose Internet Mail Extensions. MIME types form a standard way of classifying file types on the Internet. Internet programs such as Web servers and browsers all have a list of MIME types, so that they can transfer files of the same type in the same way, no matter what operating system they are working in.
A MIME type has two parts: a type and a subtype. They are separated by a slash (/). For example, the MIME type for Microsoft Word files is application and the subtype is msword. Together, the complete MIME type is application/msword.
Although there is a complete list of MIME types, it does not list the extensions associated with the files, nor a description of the file type. This means that if you want to find the MIME type for a certain kind of file, it can be difficult. Sometimes you have to look through the list and make a guess as to the MIME type of the file you are concerned with.
Comment: Now there is [a list](https://developer.mozilla.org/docs/Web/HTTP/Basics_of_HTTP/MIME_types/Common_types) w/ MIME types & extensions from MDN. You can also [send a PR](https://github.com/mdn/content/blob/main/files/en-us/web/http/basics_of_http/mime_types/common_types/index.html) to improve it.
Answer: MIME stands for Multipurpose Internet Mail Extensions. It's a way of identifying files on the Internet according to their nature and format.
For example, using the Content-type header value defined in a HTTP response, the browser can open the file with the proper extension/plugin.
Internet Media Type (also Content-type) is the same as a MIME type. MIME types were originally created for emails sent using the SMTP protocol. Nowadays, this standard is used in a lot of other protocols, hence the new naming convention "Internet Media Type".
A MIME type is a string identifier composed of two parts: a type and a subtype.

The "type" refers to a logical grouping of many MIME types that are closely related to each other; it's no more than a high level category.
"subtypes" are specific to one file type within the "type".

The x- prefix of a MIME subtype simply means that it's non-standard.
The vnd prefix means that the MIME value is vendor specific.
Source
Comment: Interestingly I see on my Linux scripts are `application/x-shellscript` type files and I could not find same MIME w/out `x-` (`application/shellscript`) on the internet.
Answer: Simple Explanation by Analogy
Scenario 1:
Imagine someone sent you this letter:

ഹായ്, നിങ്ങൾക്ക് എങ്ങനെയുണ്ട്? ഏറ്റവും പുതിയ റിപ്പോർട്ട് എന്താണ്?

What does it mean?  ¯\(ツ)/¯ Consider the steps involved:

First, identify the language (is it Tamil?). Identifying the language takes a lot of computational energy: are you going to check all the languages in the world?
You can only decode, after you identify the language.

Scenario 2:

Language: Malayalam (see translation link) ഹായ്, നിങ്ങൾക്ക് എങ്ങനെയുണ്ട്? ഏറ്റവും പുതിയ റിപ്പോർട്ട് എന്താണ്??

Now, the language is identified up-front (Malayalam, not Tamil), and is written on the letter. Half the work is done, and you can proceed to decode it.
Tying the analogy back in with HTML
Because there are different data formats, specifying them up front allows the corresponding client to properly interpret and "render" the data, with little computational effort. Remember, computers communicate using 1s and 0s. This is effectively what happens when HTML is sent to you:
MIME TYPE: MP3 1001010101....
MIME TYPE: PDF 1001010101....
Once you know the MIME type, you can play the audio and view the PDF, with zero effort.
These analogies are not perfect but hopefully you can see the problem it was intended to solve, as well as the solution.
Answer: I couldn't possibly explain it better than Wikipedia does in Media type:

In addition to e-mail applications, Web browsers also support various MIME types. This enables the browser to display or output files that are not in HTML format.

In other words, it helps the browser (or content consumer, because it may not just be a browser) determine what content they are about to consume; this means a browser may be able to make a decision on the correct plugin to use to display content, or a media player may be able to load up the correct codec or plugin.
Answer: It is useful to think of MIME in the context of the client-server model. Clients and servers communicate over what is known as the HTTP protocol. In an HTTP request or response, we can have a body. The Content-Type or MIME type specifies what is the type of the body, like text/javascript or something else like audio, video, etc.
However, MIME types are not limited just to HTTP.
As the name suggests, MIME stands for Multipurpose Internet Mail Extensions. Originally, SMTP only supported ASCII-encodings. However, there as a need for more. We could use MIME to slap a label on the content being transmitted or received.

What is a MIME type?


Just Intonation confusion

Question: Could anybody explain to me what is affected by Just Intonation? The melodic and harmonic intervals or the scale degrees and distance from the tonic?
Answer: Just Intonation is a tuning system; that is, it defines the tuning of a scale. We commonly use equal temperament, which is a compromise  (or temperament) that allows us to play in all keys with a limited number of notes (without constant retuning).
Just Intonation defines the actual size of the intervals, or the tuning of the notes with respect to the tonic (as does any temperament). If you look at the Wikipedia article for Equal Temperament, there's a good comparison to Just Intonation.
I use this practically when I'm playing in a concert band. We can dynamically change the tuning of our instruments using our mouth positioning (embouchure), tuning slides, garden variety slides (i.e. trombones), and so on. When I know I've got a third in a chord, I'll play it slightly flat (in equal temperament). This results in just intonation. If you split all the parts up and used a equally tempered tuner, you'd think our thirds were flat, and our fifths were slightly sharp. That's the effect of using just intonation. It changes the tuning system.
It's worth noting that none of the note names or scales change. There isn't a notation that tells us to play with just intonation, but we tend to do so if it's possible, because it sounds better.
Comment: I wouldn't call just intonation a temperament. Tempering is the process of detuning certain notes _away_ from just intonation, with the intent of making a compromise that allows you to play reasonably well in multiple keys while using only a limited number of notes.
Comment: @leftaroundabout Good catch, I remembered the wrong definition. I think it is fixed now.
Comment: But because just intonation is not a temperament, it is not useful as a way of defining the tuning of a scale.  Or rather the other way around.  In any event, just intonation is most useful in the context of tuning chords, one at a time.  Your answer acknowledges this by noting that you'll play a note slightly flatter if it is the third of a (major) chord, but confuses the issue by using words such as "scale" and "temperament." If the pitch of A varies depending on whether it's part of an F chord or a D chord, that isn't establishing the pitches of a scale; it's creating inconsistency in them.
Answer: To add to endorph's answer:
If you're used to 12-equal temperament (the octave divided into 12 equal semitones), then playing in just intonation entails making distinctions you hadn't made before: there are situations where two notes would be played at the same pitch in 12-equal but at different pitches in just intonation.
In 12-equal, there is a 12-step circle of fifths. But in just intonation, a sequence of downward fifths or upward fourths never gets back to its starting point.
This might seem obvious -- after all, even if we play e.g. G# and A flat at the same pitch, the note names are different, which gives a clue that they are not inherently identical. But there's another issue which means that even notes with the same name can sometimes need to be played as different pitches.
Start, say, at C, and go up four just perfect fifths. This takes you to G, D, A and E. But a major third above C is a little lower than E -- it is lower by a syntonic comma. (Sorry about the additional jargon on that web page, but near the bottom of it is some notation on two staves which should, I hope, make things clearer.)
If you are playing in just intonation, you will need to work out how many syntonic commas to lower or raise notes so that your thirds are in tune: a major third needs to be narrowed by a comma (e.g. plain C to lowered E) and a minor third needs to be widened by a comma (e.g. lowered E to plain G).
A thing to be aware of is that some chord progressions that are very common in tonal harmony cause the pitch to drift downwards by a syntonic comma. For example, suppose that the key is C major, and there's the chord sequence C major, F major, d minor, G major, C major. The initial C is plain (not lowered); so's the F of the F major chord. So that F major chord's third, A, is lowered by one comma. So in the d minor chord, the A is lowered (and the F is plain), so the D is lowered, too. So the following G and C are lowered, too. The phenomenon's known as (syntonic) comma drift.
In Syntonic Tuning: A Sixteenth-Century Composer's Soundscape (Music Theory Online: the Online Journal for the Society for Music Theory, Volume 10, Number 1, February 2004), Roger Wibberley cites a passage from Josquin des Prez's Ave Maria Virgo Serena where, in the course of 8 bars (45-52) the pitch drops by five syntonic commas! (Wibberley's example 1 is b.44-53.)
Comment: Wibberley uses that example to argue that Josquin would've used Pythagorean tuning, where the ditone 81:64 is used instead of a major third, and 32:27 is used instead of a minor third. The online copy of his paper in my link contains links to examples with audio in Pythagorean and just tuning.
Comment: By my reckoning, that's virtually into the key a semitone lower. How does any muso recover from that?
Comment: @Tim I haven't read the paper yet, but I've sung the piece a few times, and I can assure you that Pythagorean or equal-tempered tuning is not necessary to avoid going flat. One approach is to pick one part and tune its melodic intervals to stay on pitch, then to tune the other parts harmonically to that one. This usually results in the other parts having to alter the pitch of a sustained or repeated note by a syntonic comma (in contrast to the assumption underlying any analysis that exposes any comma pump). Also 5 commas is about 107.5 cents, so more than an equal semitone.

Just Intonation confusion


What differences are there between built-in Administrator and other Administrators?

Question: Are there any significant differences in the rights, privileges, permissions, or other powers held by the built-in Administrator account, and those held by non-built-in Administrator accounts?
Answer: Some applications are incorectly coded to look for the SID of the well known Administrator account.  This was an issue in the early days of NT4 but don't think it's an issue now...
I don't think any applications match on the name "Administrator" since that is Engish specific and is a very poor programming practice.  "Administrateur" and other language matches would have to be accounted for.
Instead applications should match on the SID of the local group Administrators
Comment: Actually, I did have a rather large well known vendor in the IT operations space that checked permissions against the "Administrators" group - i.e. checked the name of the group. Strangely none of the QA processes found this, until I reviewed the authorization code and found it... and this was only a couple years ago.
Answer: The only difference is that the built-in administrator account SID is well known.  This makes for bad programming logic by 3rd parties, but otherwise that is the only difference.
Answer: One small difference, is when a folder is created by any administrator, the default owner for that folder is the Administrators group.
This is not so much a difference between administrators and Administrator, but a possible effect that might possibly have other consequences.
Also note that this default is configurable, and anyway it is no longer supported by Vista/7/2008.


All apps deleted

Question: Please help, I was trying to power on my Android phone, it took longer time than usual but when it eventually Powers on all my third party apps had been deleted but my files are still intact, what caused this and can I recover my phone back?
Comment: Backup. Backup everything. What if you lose your phone? That no one can recover. There are a lot of apps for that. Probably you can not recover your data, because rooting it deletes everything. There is a little chance that there is some loophole what you make an answer for you, but don't have too much hope.
Comment: But how can I back up some app data for example I have 7gb of courses i downloaded on pluralsight app for offline use and I can't see the files on my phone storage
Answer: Sounds like you may have booted up in SAFEmode on your Android device. When you boot into SAFEmode all 3rd party apps are organically disabled to allow for more accurate troubleshooting of the device. You will know that you are in SAFEmode by looking at the bottom left corner of the device, If it reads SAFEmode than that would be your issue. In the event that is not the issue please let me know
Comment: Safe mode is not the case because there's no safe mode displayed and I even tried later and was able to put the phone on safe mode and back to the normal State but the problem persists

All apps deleted


Windows 8 & Ubuntu 14.04 lts boot problem

Question: I have installed Ubuntu 14.04 LTS alongside the Windows 8.1 through the installation guide provided by Ubuntu but I cannot see the grub on the screen whenever the computer boots up to select between Windows or ubuntu. Therefore I cannot run the PC with Ubuntu which I have installed.
here is the Boot Repair report link
http://paste.ubuntu.com/10178568/
please help me with this issue
thanks
Comment: I've had this same issue that I could not figure out (until I bought a new laptop) so I no longer dual boot. For me, in my HP I had to press F9 (boot options), select Ubuntu and then grub would load. Select Ubuntu again, and it would boot up. I also found a shortcut by enabling network boot in bios (f12). I would press f12,it would quickly see there was no network boot and bring up grub so I could get into Ubuntu. By no means is this a solution or an answer to your question, just a way you might be able to get into Ubuntu until you get an actual answer. F keys may very by brand.
Answer: What brand/model computer?
Many brands now modify UEFI to only boot a "Windows" entry in UEFI, but will boot the hard drive entry, so we have to copy grub or shim into the efi folder so system thinks it is booting the hard drive.
But you have installed Ubuntu in BIOS boot on an UEFI system. To easily dual boot you need to have Ubuntu in UEFI boot mode. Boot-Repair can in its advanced mode uninstall grub-pc(BIOS) and install grub-efi-amd64(UEFI). But you must boot in UEFI mode to convert.
Shows install with screen shots for both BIOS(purple) & UEFI(grub menu), so you know which you are using.
https://help.ubuntu.com/community/UEFI
It also looks like you had an UEFI boot and had run the old version of Boot-Repair that renamed the Windows efi file. Boot-Repair does not do that any more as there now are better ways. But you need to undo the rename. Not sure if new copy of Boot-Repair will do that or not.
This was the original Windows UEFI boot file:
/EFI/Microsoft/Boot/bkpbootmgfw.efi
And a grub or shim file was copied into the Microsoft folder and renamed to this:
 /EFI/Microsoft/Boot/bootmgfw.efi
You want to fully backup the entire efi partition, just in case and rename bkpbootmgfw.efi back to bootmgfw.efi. then you should be able to directly boot Windows from UEFI menu.
If an HP or Sony you may then need to copy grub or shim into /EFI/Boot and rename it to bootx64.efi.
If you need more detail, already posted here:
Dual boot Win 8 / Ubuntu loads only Win
windows 8.1 changes boot order
How do I get my HP laptop to boot into grub from my new efi file?
Dual boot but only Windows boots


Vista won't boot. I don't have the installation disk with me, can I install Ubuntu to access my files even though vista won't boot?

Question: I have managed to access my files with the demo but I'd like the full version. If I install Ubuntu while my vista OS isn't working will I lose my files?
Comment: Please clarify: demo (=live DVD/CD?), full version (=installation on local hard disk?), working (=...?) Also, consider shortening the title.
Answer: I would boot to the live CD and back up the files from Vista onto a separate drive.  Then do a full Ubuntu install and try to forget Vista ever existed.
Answer: When dynamically resizing partitions (especially shrinking), as usually happens when you install Ubuntu alongside Windows, there is always a small but significant risk of data loss. So if there are no backups, this is not a good way to access the data.
The same CD/DVD/USB that you boot from to install Ubuntu can first be used to access and back up any documents and other important files. Just select Try Ubuntu instead of Install Ubuntu. You'll get a working Ubuntu desktop which you can use to access files in the broken Windows system.
To back up your data files, don't put them on the live environment's desktop -- files written to the Ubuntu live CD/DVD/USB environment exist in memory only and disappear when the system shuts down or reboots. Instead, put them on an external drive (not the one you booted from), burn them to a CD/DVD, email them to yourself, transfer them over the network to another machine (Ubuntu supports networked file sharing with Windows machines), or use a cloud storage service like DropBox or Ubuntu One ... just make sure your files are somewhere safe.
Now that you've done that, unless you intend to attempt recovery or reinstallation of the broken Windows system, you can simply install Ubuntu and tell the installer to use the entire disk, overwriting the old Windows system.
You Try Ubuntu, you don't have to reboot to start the installation -- when you're done backing up your files, just run the Ubuntu installer by double-clicking the Install Ubuntu icon on the desktop.
Answer: You will keep your files, as long as you don't format your hard disk. Choose the option to install Ubuntu alongside Windows.
Comment: Ok cool. Is there a minimum amount of free space I'll need for u Ubuntu (I'm going to use version 10.04.4)? And if I later find my vista installation disk will I be able to repair it without losing my files now that I have Ubuntu as well?
Comment: 1.- You will need about 4 GB, but it is a good idea to have 8 or 10 GB, depending on the size of your /home directory ("Documents", "Music", etc. in Windows). During installation, you will be asked whether you like to "import" your personal files. 2.- I would advise not to install 10.04, because it is no longer maintained. If you prefer a long-term edition, download 12.04. Otherwise, install 12.10. 3.- You don't lose your files if you don't format your disk with Ubuntu. A Vista disk should be able to repair your boot without formating.
Comment: Yeah. I'd use a newer version but someone else gave me the disk and I currently don't have the ability to download and burn one myself. I was thinking I could update it later but also I'm not sure if my computer can handle it. I have a bit over 6GB and I've started the installation


wavefunction collapse and uncertainty principle

Question:
We all know that wavefunction collapse when it is observed. Uncertainty principle states that $\sigma_x \sigma_p \geq \frac {\hbar}{2}$. When wavefunction collapse, doesn't $\sigma_x$ become $0$?, as we will know the location of the particle. Or does standard deviation just become smaller?
After collapse occurs, what happens to the particle? Does the particle resurrect into a wavefunction form?
What can be an observer that triggers wavefunction collapse? (electron wavefunction does not collapse when meeting with electrons; but some macroscopic objects seem to become observers....)
What happens to the energy of a particle/wave packet after the collapse?
Answer: The  terminology of collapse of the wavefunction is an unfortunate one .
Take an oscillating AC line and use a scope to measure it and display it. Is the AC 50 herz wavefunction collapsed because we observe it on the scope?
The AC wave function is just a mathematical description of the voltage and current on the line and allows us to calculate the amplitude and time dependance  of the energy it carries.
An equally unfortunate concept is the matter wave. The particle is not a continuous soup distributing its matter in space and time the way of an AC voltage  or other classical wave. You will never find 1/28th of a particle, it is either there in your measuring instruments or it is not, and it is governed by a probability wave mathematical description, not a "matter wave"
Even more so, the wavefunction manifestation of a particle does not collapse when we measure it the way a balloon collapses when pierced by a pin, because it is just a mathematical description of the probability to find a particle in a particular (x,y,z) with a particular (p_x,p_y,p_z) within the constraints of the Heisenber Uncertainty Principle.

When wavefunction collapse, doesn't σx become 0?, as we will know the location of the particle. Or does standard deviation just become smaller?

We know the location of the particle at that specific coordinate where we had our measuring instrument with the specifice momentum that our insturments measured, within the instrument errors. The probability of finding it there after the fact is 1. It is the nature of all probability distributions that after the detection they become one. example: the probability I will die in the next ten years is 50%. At the instant of my death the probability is one that I am dead.
σx is not a standard deviation in the error sense.
σxσp≥ℏ2  says that: if I want to know the location of my particle within a region about the x point with uncertainty/accuracy  σx , the  σp  I can measure simultaneously is constrained to be  within an uncertainty that follows the constraint σxσp≥ℏ2.

Does the particle resurrect into a wavefunction form?

The particle keeps it dual nature of particle or probability wave according to the momentum it still carries and will be appropriately detected as a particle or a probability wave by the next experimenter. It is not a balloon to have been destroyed by the measurement.

What can be an observer that triggers wavefunction collapse? (electron wavefunction does not collapse when meeting with electrons; but some macroscopic objects seem to become observers....)

In principle, any interaction of a particle that changes its momentum and position is an observer except that some interactions are quantum mechanical because of the HUP and the nature of the interaction and some are macroscopic manifestations in our instruments of the passage of a particle or probability wave of a particle. We usually call observers the classical macroscopic detectors, be they people or instruments. At the microcosm  quantum level we have interactions governed by the probability wave functions.

What happens to the energy of a particle/wave packet after the collapse?

Energy and momentum are conserved absolutely, so it will depend on what sort of detection of the particle took place. Some will be carried off by the particle if it has not been absorbed into the detector, as for example these particles in this bubble chamber photograph which continually interact with the transparent liquid of the bubble chamber. In this case a tiny bit of the energy is taken by kicked off electrons (first detector atom of liquid, final detector photographic plate) which show by the ionisation the passage of the particle, which is certainly not  idiotically "collapsing" .
Comment: What does this deviation in position show when the position of a particle is measured? I can't understand why this spread is observed. It is like the electron is measured many times but this can't be true. Thanks in advance.
Comment: When one measures something, there is always an experimental error. If one makes many measurements one can have a distribution of experimental errors. The uncertainty principle says that there are variables coupled quantum mechanically, in this case momentum and position, that introduce and inherent deviation in the "error" curve. from the simple statistical errors. No matter how accurate one makes the instrument there will be Δx associate with it, dependent on the accuracy Δp of the momentum measurement.


Google analytics - Find what time users entered the site from traffic source

Question: The title says it all, I'm trying to find what time each visit came from a particular traffic source. EG if I wanted to find all the times that users visited from Google (Organic) - Can I do this i GA?
Answer: Yes, you can do this.

Create a custom Advanced Segment that only shows traffic from Google
Go to Visitors > Visitor Trending > Visits
Click on the Clock icon in the 'Graph by' section to show Visits by Hour

An easy way to test this without creating a custom segment is to use the default segment 'Non-paid search traffic'.  This should show a similar pattern to Google organic search traffic.
Answer: Unfortunately, it doesn't look like Google Analytics will allow you to drill down beyond a particular day, though it will let you expand to weekly or monthly views. To get that kind of data, you'd need to use a different services, possibly a real-time analytics script.


Associated sigma matrices and physical meaning

Question: I am having issues in giving correct physical meaning to the associated sigma matrices:
\begin{equation} \sigma_+ = \begin{pmatrix} 0&1\\ 0&0\end{pmatrix} \text{ and } \sigma_-=\begin{pmatrix} 0&0\\ 1&0\end{pmatrix}\end{equation}
Is the $\sigma_+$ related to emission and $\sigma_-$ to absorption or is it the opposite? In Dirac notation I have always written $\sigma_+=|1\rangle\langle 0|$ thinking intuitively about absorption, but given the matrix form above (which I am pretty sure it's right) and defining $|0\rangle = \begin{pmatrix} 1\\ 0\end{pmatrix} $ and $|1\rangle = \begin{pmatrix} 0\\ 1\end{pmatrix} $ I don't get $\sigma_+ |0\rangle = |1\rangle$.
Answer: Your vector definitions of $|0\rangle$ and $|1\rangle$ should be switched based on the form you gave for the $\sigma_+$ and $\sigma_-$ matrices. $\sigma_+$ acts on the spin-down state $|0\rangle$ to turn it into the spin-up state $|1\rangle$. $\sigma_-$ does the opposite: it takes spin up to spin down. These operators do not represent observable quantities because they are not Hermitian (they're not even symmetric). There is also no clear association with a physical process. Emission and adsorption require some thing (like electromagnetic radiation) to carry the extra energy away, so you would need to add extra things into your theory before you could even talk about these processes.
If you remember the creation and annihilation operators for the quantum harmonic oscillator, or the raising and lowering operators for angular momentum, the $\sigma_\pm$ matrices are just the spin-1/2 versions of these operators.
Comment: It is conventional to use $(1, 0)$ for spin up and $(0,1)$ for spin down. This is arbitrary, but there needs to be consistency between how you define spin up/down and how you define the sigma matrices.
Comment: Thank you, so is it common use switching the definitions for the vectors I wrote? Or is it arbitrary? Of course I know you can make up your own conventions as long as they are coherent in your work, but I was wondering which one is the most common


Electrical Switches

Question: Sorry for the newbie question but am I correct to say both of these schematics are representative of (push button) switches? If not what is the difference between them? Do they work differently? Thanks in advance.
Comment: The bottom picture could be a relay contact (coil not shown).
Answer: The top one is a push button: Closed (making a connection) when you push it. As soon as you let go the contact opens again.
Example: the keys on your computer's keyboard
Bottom one is a toggle switch, you flip it, it stays closed even if you don't touch it anymore. It opens when you flip the switch again.
Example: the light switch in a room.
Answer: The top one is normally open, but closed by pusing on the button. When you release the button, the contact is opened.
The bottom one is a switch that has two stable positions, one open and one closed, like the ones we use to turn the light on or off.
Answer: The top one is a momentarily  switch, since its only connected momentarily.
The bottom one is a Maintained switch, the connection is basically maintain until it is modified.
You can also check the Momentary vs. Maintained section in this switch basics tutorial from sparkfun

Electrical Switches


Half-duplexing with mechanical SPDT switches

Question: I was able to implement a half-duplex system using an SPDT switch and a relay board and tested it in a lab environment. I'm about to test it against orbiting CubeSats. I understand that the return time for a packet to LEO could be less than 8 ms, depending on altitude and elevation angle. This might be too quick for the mechanical SPDT switch. Do all CubeSats add some delay to enable half-duplexing? If that's the case, what is the typical delay time added to enable half-duplexing?
Answer: I have no intimate knowledge of any amateur cubesats, but:
It's very unlikely; these satellites are about all primarily transverters. This a) means they can themselves operate in TX and RX simultaneously, by isolating RX from TX by means of frequency, and b) that they don't need any memory to operate, but just receive and transmit amplification, filtering and a mixer.
So, the bad news is, it's very unlikely you get more than a roundtrip at the speed of light to switch. The good news is that you don't need that much isolation, anyways, as you can use a frequency duplexer.
Of course, there's also digipeaters, which actually use the same downlink frequency as uplink frequency.
Let's assume the digipeater would artificially wait much more than necessary:
If you delay relaying, then you "risk" another transmission happening while you wait. Two options there:

You go to "deaf" mode while you wait: This reduces the time transmissions could be captured to a duty cycle of $\frac{T_{\text{packet}}}{T_{\text{wait}}}$; this could very well lead to repeat transmissions, and thus congestion of the medium.
You accumulate messages for a while, then relay them "en bloc" after some delay. This increases your duty cycle, but can lead to much bigger latency (which might not be desirable in a network!)

So, if I remember correctly (and that's a big if) at least PSAT2 had something like a 10s "hold time", so, mode 2, for APRS packets. However, that thing was never in APRS digipeater mode (again, IIRC), because that was just a fallback mode.
I have a faint memory that things like PSK31 are simply transverted.
So, in the end, this depends on the operating mode of your satellite; can't give a general statement.


Voltage supply plus ideal current source connected to capacitor in series

Question: This might be a wierd question but I was asked this in an interview. I know the basic behaviour of an RC network when it is connected to a battery (practical situation) and also the ideal situation when there is an ideal constant current source in series charging a capacitor (when the circuit is like a loop). However, what will happen if there is both an ideal current source along with a voltage supply in series with the capacitor. Edit: Added a picture, need to sketch the capacitor voltage at node A.
Comment: Please post a diagram
Comment: @Nitesh Suryavanshi, And how did you answer the question?
Comment: I kindoff fumbled the question. I wasn't sure so I just said the voltage across the capacitor increases linearly like a ramp but said wasn't sure what happens when it equals the supply voltage.
Comment: But I think I have an idea. The supply voltage acts as some type of initial condition voltage for the capacitor right?
Answer:
However, what will happen if there is both an ideal current source
along with a voltage supply \$\color{red}{\boxed{\text{in series}}}\$ with the capacitor.

A voltage source that is \$\color{red}{\boxed{\text{in series}}}\$ with a current source is relegated to obscurity. You might just as well remove the voltage source and replace it with a short-circuit. The current source wins every time and defines the current flow.
On the other hand, a voltage source in parallel with a current source is different - the voltage source wins and defines the voltage; the current source is of no-consequence and can be replaced by an open-circuit i.e. removed.
Answer: In addition to the Andy aka's answer, it would be interesting to consider the voltages in this arrangement in both cases - when the voltage source is connected in the same and opposite direction to the current source.
In the first case, the voltages of the capacitor and the voltage source are subtracted... and they determine the total voltage across the current source. It will continously increasing up to infinity.
In the second case, the voltages of the capacitor and the voltage source are summed. The total voltage across the current source will initially decreasing up to zero. Then, it will change (reverse) its polarity and will continously increasing up to infinity.
It is also useful to introduce a ground and to investigate the circuit when each of its nodes is connected to ground (a good question for another interview:)
I have explained a similar arrangement in another question -
Why is the voltage drop created by a current source added? ...

... that maybe will be useful for you.
Think of the resistor as of a capacitor; if you are uniformly increasing the resistance, the resemblance will be amazing...


up-to-date database of open access policies *and* publication fees?

Question: Sherpa Romeo does a good job aggregating open access policies for a large number of academic journals. This lets me see what OA options (self-archiving of various kinds, full 'diamond' OA with fee, etc.) are available for a given journal. However, it doesn't include information about overall article processing charges (APCs)/OA fees for different routes (e.g., what are the page charges or OA fees for a given journal?)
The Eigenfactor index of Open Access fees has some information, but seems to be out of date.  The web page says it's "Powered by Eigenfactor.org and journalprices.com" but going to journalprices.com and clicking "get started" takes you to an old, slightly broken web page; the original Excel sheet can be retrieved from the Wayback machine, but was last modified in 2013.
Academic accelerator has some information: information seems uneven (is it crowd-sourced?), and the site looks sketchy/ad-heavy/ugly.
Obviously keeping such a database up to date would represent a lot of effort, but I'm curious what the best current set of resources is (an ideal version would have open access to the database and would allow easy comparison of journals within a (sub)field ...)
Answer: The DOAJ (Directory of Open Access Journals) contains curated data about APCs, but only for open access journals.
Here is an example showing a journal without any charges ("Diamond OA") and one with APCs ("Gold OA"):


How to use Time Machine with File Vault

Question: I have a Mac with one user using File Vault.  I am enabling Time Machine. How do I make sure the File Vaulted directory gets backed up?
Comment: If my answer helped you, please accept it by clicking the tick mark next to it. Otherwise, please comment on what is missing. Thanks!
Comment: @daniel it did.  and i did (and upvoted). sorry for the delay...
Answer: Log out with the Time Machine disk attached. It will first recover disk space, then backup. This is the only method supported by Apple.
If you only want to encrypt some files, you can create encrypted disk images using Disk Utility and copy those files there, trashing and secure deleting the originals afterwards. The Sparse Bundle format is the technology underlying FileVault.
Comment: @hvgotcodes: Added info you asked in your duplicate question to my answer.
Comment: I've been suffering for years because of this. Once a week at least, I log off, so it backs up my ~.
Comment: How long do you have to log out for?  Do you know of any alternatives?
Comment: You only have to log out while it backs up, the time varies depending on the amount of changes.
Comment: @hvgotcodes: It's just another step during logout, like recovering FileVault disk space. It displays a progress bar during logout just like with recovering disk space. Once it's done, you see the login screen, and if the screen lighting is dimmed because of the long idle time, it goes back to full.
Answer: FileVault 1 in Snow Leopard
Logging out
The method supported by Apple is as described in the accepted answer.
In addition: if using a laptop you should use AC power, or prefer to backup while on battery power (the default to not backup while on battery power probably began in Mac OS X 10.5.3).
Without logging out
See answers to the Ask Different question:

How can I get Time Machine to back up the contents of a File Vault while logged in?

FileVault 1 in Lion
Logging out
No different from the routine for Snow Leopard.
Without logging out
Work in progress, broader than FileVault 1:

How can Time Machine in Lion backup the volume content (not the bands) of a sparse bundle disk image?

How to use Time Machine with File Vault


What is the difference between a math text book and a math reference book?

Question: I saw the list of books suggested by my college. There are two categories, one for text book and the other for reference book. For abstract algebra, they have Dummit and Foote, Abstract Algebra as textbook, and Herstein, Topics in Algebra as reference book. Both seem to be similar, but, don't know, the difference in how they were categorised.
Comment: Maybe the text book defines the curriculum and the reference book is the recommended book for those who want more material?
Answer: In general terms, a textbook is a book you can read from the beginning to learn a new subject - perhaps on your own, perhaps in a course. Not necessarily quite that linear, since you will need to double back to reread and refresh. When you're done with the book and the course (do the exercises!) you will more or less know the material.
If you need to check some particular definition or theorem a textbook might not be the best place to look, since the idea may be spread out over several pages or sections. A reference book is likely to be more compact. (Sometimes wikipedia is a good "reference book" for things you already know something about.)
That said, both the books you ask about are textbooks, designed for an abstract algebra class. Herstein is harder/deeper/faster than Dummit and Foote. Your college is suggesting that the course will rely on D&F but that you may be able to learn a little more from a different perspective from Herstein. They may also be suggesting that you should buy D&F but consult Herstein in the library.
Comment: "Herstein is harder/deeper/faster than Dummit and Foote." - Precise expression of experience. Will get into Herstein too. Thank you.
Comment: To know the difference clearly in the context, can you suggest a abstract algebra reference book?
Comment: As I say in my answer, wikipedia is a good reference book. For example, early in abstract algebra you will learn Lagrange's theorem. I don't know where it is in either of those books, but here is a quick overview: https://en.wikipedia.org/wiki/Lagrange%27s_theorem_(group_theory)


How can I get a UAE multi-entry visa?

Question: I have 3-month, single-entry visit visa for the UAE. However, I would like to have a multiple entry visa. Can I change the current visa and, if not, what can I do?
Answer: You cannot change the current visa, you can only extend it.
To get a multiple entry visa:

Someone has to apply from the UAE on your behalf. This is usually a tour operator, a hotel, a permanent resident (or citizen), or a legal entity such as a company or establishment.
If you have freehold property in the UAE, you can get a multiple stay visa.
If you are traveling via Emirates, certain nationalities can apply online for  a tourist multiple entry visa from emirates.com (the facility is actually provided by VFS global and also available at dubaivisa.net).

How can I get a UAE multi-entry visa?


Why does a sheet of paper stick to the end of a vacuum cleaner?

Question: What makes a piece of paper or other material hard to pull away from the end of a vacuum cleaner once it's covering the opening?  What force are you acting against when you try to pull it away?  Also, why does the end of the vacuum cleaner stick to a wall, floor or other hard surface?
Comment: Because it sucks!
Answer: Suppose the piece of paper sticks to the end of your vacuum cleaner, and for simplicity let's assume no air passes through the sheet or on the sides of it.
The vacuum cleaner proceeds to suck air from the tube as long as it can with its limited capability. What it is effectively doing is reducing amount of air, and therefore the pressure, in the pipe.
This leads to a pressure imbalance: on one side of the sheet, there is air at the usual atmospheric pressure. On the other side, air at a slightly lower pressure. It's this difference in pressure that causes this force, which, in an ideal situation, is equal to the pressure difference times the surface of the part of the sheet attached to the top of the pipe, $F = S\Delta p$.
Comment: what about the case where it's against the wall or the floor - in which case it seems like the pressure shouldn't make a difference, because the surface is too solid to be moved by the air pressure?
Comment: so is it effectively the weight of all the air in the atmosphere pushing against the paper, with nothing pushing from the other side to cancel it out?
Comment: Yes, I think you can say it's due to the weight of all the rest of the air. In the case of the wall, it's effectively the vacuum cleaner which is pushed against the wall by pressure, in a sense. The pressure of the region of air near the top of the tube, and near the wall, is lower then in the rest of the room.
Answer: Like the fish that discovers water last, we don't normally notice the 15 pounds per square inch (psi) of atmospheric pressure that we live in. A vacuum cleaner can help us notice the air pressure without us having to jump out of our fish tank (Earths' atmosphere).
This pressure of 15 psi surrounds us and everything we touch. The vacuum cleaner reduces the pressure a little by constantly removing air from the hose, and this normally causes a focused wind that is useful for cleaning.
When a piece of paper blocks this wind, the pressure in the hose decreases further, down to some maximum pressure difference that the motor is capable of reaching. If it can drop the pressure to 14 psi in the hose, and the hose's nozzle has an opening of one square inch, then there will be one pound of force holding the paper on the nozzle. (I choose 14 psi to keep the math simple.)
This pound of force comes from more air molecules hitting the outside of the paper than the side that is looking into the hose.
As for the wall or the corner, it does not matter that the house has thick walls and that you can not tell where the full 15 psi is being applied. Nature finds it automatically.
Here is another way to look at it:  Every part of the vacuum cleaner is exposed to 15 psi all around it except for the nozzle opening. The nozzle opening is only experiencing 14 psi. This is enough to cause the nozzle opening to press against whatever surface is blocking or slowing the airflow.
Another example: If you put a funnel on the opening you can increase the effective size of the nozzle opening. If the wide side of the funnel is round and six inches in diameter, then its area will be about 28 square inches. Unblocked, this will not do much. Now, use a bowling ball to cover this opening. A vacuum cleaner that can drop the pressure to 14 psi when no air is moving will now be able to generate 28 pounds of lifting force, letting you pick up the bowling ball via the suction alone. This fact was used by a vacuum cleaner company to show how strong their vacuum cleaners are, but I believe any other brand of vacuum cleaner could have done it too.
Comment: thanks, i think that was what was counter-intuitive to me - just how strong normal atmospheric pressure is.


six months or in June

Question: 去以六月息者也。
Hello it's Zhuangzi Enjoyment in Untroubled Ease, first chapter.
My question:
Does he rest for six months or in June. Is Chinese the same in both cases? Does 者 mean he who goes for rest for six months?
Comment: http://yingyu.100xuexi.com/view/specdata/20130117/fa2fa9e5-7695-46b1-bad6-ee3bee73655d.html
Answer: In Chinese, although both a phrase like "six months" and the word "June" contain the characters 六 and 月, there will often be a measure word if we are talking about a specific quantity of months (i.e. in the "six months" case), the same way there will be a measure word for something like "six cats" ("六只猫") or "six books" ("六本书").
Thus, it should be generally possible to distinguish between "June" ("六月") and "six months" ("六个月"). (月 uses the word 个.) However, in this case, given the 去以, "six months" reads better ("the past six months" instead of "the past June"), at least to me as someone who does not know the context.
So I can only give you the "general" case of whether one can distinguish between what is essentially "the Xth month" and "X months" in Chinese (i.e. yes). vermillon's answer resolves the question of why I'd still presume "six months" here -- it's simply a classical Chinese thing I wasn't aware of (and it does read better).
Your assessment of 者 (as something to the effect of "he who") appears to be correct. As seen in these dictionary examples (note: the dictionary definitions itself are sometimes very unhelpful or downright probably wrong, but the examples should be fine), 者 can be appended to some sort of descriptor (whether one that takes the purpose of an adjective or a verb) to mean "the individual(s) who" or the such. For instance, 受害者 means "the individual(s) who were harmed", and 第三者 is "[those of a] third party", and the webpage gives the example "他猛击进攻者。"
I am not sure about the exact translation given the 也 which I'm having difficulty accounting for, but things otherwise sound fine.
Answer: Others have already answered the question, but you should also note that at the time the Zhuangzi was composed, there was no such thing as "June". There was a 6th month, but it's the 6th month of the Chinese calendar, whose months shouldn't be translated as Jan/Feb/etc.
As for the comment about classifiers, the question is about Classical Chinese and 六月 was the way to say six months.
Comment: Ah, the classifier thing makes more sense now. I hadn't looked closely at the source so I was just giving a general explanation for how things work _now_, but it occurred to me that "six months" inexplicably read much better than "the sixth month" (and my lack of idea as to why, beyond that maybe this was a classical Chinese thing, was kind of getting on my nerves.)
Answer: a general explanation: the bird flies 6 months without stop until arrives nanhai.
Answer: It helps to look at some of the translations available, which are not authoritative, but are suggestive. Burton Watson, for example, translates: 'He beats the whirlwind and rises ninety thousand li, setting off on the sixth-month gale." Thus he takes 六月 as the sixth month, and 息 as the "breath" of the sixth month, which can be a very gusty time of year.  Watson's interpretations are not usually original, though it is often difficult to figure out who he is following. Using this interpretation, the 者 is probably NOT 'he-who' but makes explicit that the peng uses the winds of the sixth month as its means (instrument) for departing.

six months or in June


is there an OP_RETURN or MEMO field in Tezos transactions?

Question: I'm looking for a way to store information (few bytes) in a Tezos transaction, on BTC I'm using OP_RETURN field but is there a similar field in Tezos transactions ?
Answer: It depends on what you're trying to do. Are you sending these transactions to anyone? To a specific address?
In the most general case, you could take advantage of the fact that Tezos transactions are batches by default. Whenever you create a transaction, you would add another transaction to the operation that passes a bit of information to a smart-contract. The smart-contract itself need not do anything with that information, it can just drop it and return, for example:
<code>parameter bytes;
storage unit;
code {CDR; NIL operation; PAIR};
</code>
Support for batch operations is currently lacking in the command-line interface, but here's a blog post explaining how you can create them with RPC calls
https://medium.com/@bakenrolls/sending-multiple-transactions-in-one-batch-using-tezos-rpc-6cab3a21f254

This will do the job but it wouldn't be a bad idea to add native support for a memo field in transactions in future protocol versions.
Comment: I'm trying to send these transactions to a specific address in order to keep a trace of the memo content. Currently I'm evaluating two possibilities, either adding this memo in a transaction or record it into a dedicated smart contract
Comment: As a rule of thumb, it's a good idea not to record any data on the chain unless the validity of a future transaction will depend on that data. If all you need is to track that it happened, you may just as well pass that data as a parameter to your transactions but not store it.
Comment: indeed, this is the reason why I'm looking for the best way to pass data as parameter ;-)


For two LUKS volumes made with the same password, can stealing the encryption key from one volume allow access to the other?

Question: A running computer has two LUKS volumes that were made with the same password. One volume is open (key is in RAM), the other is closed.
If the running computer is stolen, is the closed volume safe?
If sha256 is broken, is the closed volume safe?
Answer: It should be safe. If the running computer is stolen and memory is read, it's the master key that will be revealed, allowing decryption of only that volume. The password itself is only used transiently when you open the volume to decrypt the master key. The other volume, despite using the same password to decrypt its constituent master key, will have a different master key.
When you use a system like LUKS, you are not encrypting data directly with your password. Rather, a completely random key is generated that is used to encrypt your data. This key is called the master key, sometimes called a data encryption key. This master key is itself encrypted with another key (derived from your password), called the slot key, or key encryption key. The encrypted master key is then stored directly in the encrypted volume. Because each volume will use a different master key, revealing one master key says nothing about the other, nor does it say anything about your password.
An attacker can attempt to brute force your password. This is done by guessing a password, processing it, and seeing if it can successfully decrypt the master key. They will only succeed if your password is very weak due to the processing algorithm LUKS uses, called PBKDF2. This algorithm runs your password through a hash function a huge number of times. It is intended to take approximately one second on a consumer computer. While waiting one second to see if your password is correct won't bother the end-user, it does mean that cracking the password becomes significantly harder.


Are Electron Collisions Possible in nuclear fusion?

Question: Can electrons ever collide with other electrons during nuclear fusion? Or do they repel each other because of Coulomb's law?
Comment: In nuclear fusion, you're almost always colliding bare nuclei.
Comment: As well, nuclei repel each other
Answer: Let us clear up the physics.
Nuclear fusion happens when two nuclei on the left side of the rising binding energy per nucleon curve  scatter off each other with enough energy to overcome the coulomb barrier, so that the stronger attractive nuclear forces can  act.
This means  that the nuclei are bare of electrons, and the way that this can happen is in a plasma , a gas of ions and electrons which happens at very high temperatures.
This means that there are energetic electrons in a fusion  plasma, but electron+electron can only give interesting results at very high energies, creating new particle-antiparticle pairs in the process. No fusion as lepton number is conserved. Electrons just scatter off each other according to the coulomb solution of the quantum mechanical scattering .
How to manipulate plasma to bring it to the energies needed for enough fusion of nuclei to get a positive result in energy spent versus energy output is a research project the world over.
Answer: Hmm good question. My intuition would be 'almost never'.
When all species in the plasma are in thermal equilibrium, they have the same energies, the same Coulomb wall to overcome as protons do, but they cannot tunnel into any potential minimum.
So as anything in the universe, they will have a nonzero probability to collide, but this will be quenched by the non-existent Gamow factor.


Can electromagnetic fields be used to deconstruct and reconstruct atoms?

Question: I was thinking one day and came up with a theory after reading about how scientists were studying anti-matter by using electro magnetic fields to separate matter from the anti-matter they made.  It got me thinking would it be possible to use very powerful electromagnetic fields to break down the atomic structure of objects or build things in this way?
Is this atomic reconstruction with electromagnetic fields theoretically possible?
That is, is it theoretically possible to use electromagnetic fields generated by a machine to separate the parts of an atom thereby deconstructing an object on the atomic/subatomic level?
I'm not asking about breaking molecular bonds but rather actual atoms apart.  If it's possible to break atoms apart with electromagnetic fields, is it also possible to use a similar process to assemble them?
Comment: Josh, have your studies come to the fact that  atoms are composed out of a nucleus which is composed by protons and neutrons bound together by the strong force and electrons on the outside ? You deconstruct atoms , making them ions every time you rub the cat. If you mean deconstructing nuclei, magnetic fields are not strong enough to break the binding of the strong force.
Comment: What do you mean by breaking atoms apart?  Do you only want to strip electrons or do you also want to tear the nucleus apart?
Comment: What you seem to be thinking is some kind of atom-level 3D printer
Answer: It is doable, easily, if you consider time-dependent EM fields - or, more specifically, pulses of light. This is because light can be focused into a tight focal spot of ~ wavelength size, thus squeezing a lot of energy (and thus EM field) into a tight spot. This is impossible using static fields, which can't reach maxima except at their sources. Just as importantly, one can prepare really short pulses of radiation that compress into a short (i.e. few femtoseconds) time the energy stored in a laser medium over a millisecond or so. This allows quite modest energies - of millijoule order - to create electric fields comparable with the atomic electric fields (as in John Rennie's answer) for long enough to ionize just about any atom.
Note that this does not need a macroscopic sample (although actually observing stuff usually does!). If you manage by some means to get a single atom to sit still at a known position (which is a doable but nontrivial exercise) then firing enough strong laser pulses will ionize it, releasing one electron. You can of course release more electrons but it will naturally get harder and harder (so that triple ionization is the most you can hope for). Photon energies (which are proportional to the frequency) are not really a concern in this high-intensity regime, where multiphoton ionization and tunnel ionization take over as the main mechanisms as one goes from optical to IR and lower frequencies.

Regarding the converse in your question, we have nothing like the technology to "atomically print" a table, atom by atom, and I would question the feasibility of such a scheme. Optical tweezers, for example, can be used to move molecules around and depositing them on a surface could potentially work, but their spatial resolution is limited (by the wavelength, which can't be too short or stuff starts to break). Even worse, you'd have to work at it for something like geological-scale times to get anything sizable.
On the other hand, metamaterials are a good example where we can build materials to atomic-scale detail so that they have the macroscopic properties we want, including such exotica as negative refraction indices or strongly chiral media. While it does not exactly fit the bill you ask for, I think it is fundamentally more cool with the added bonus of being feasible.
Answer: It's exceedingly difficult to tear apart an isolated atom with an electric field. It's a lot easier to ionise a gas of many atoms, but the mechanism is different. Let's stick to an isolated atom for now to see why it's hard.
Consider an isolated hydrogen atom. The binding energy of the proton and electron is 13.6eV and the average separation is about 0.05nm. So to tear the electron and proton apart you need a field gradient of about 13.6V per 0.05nm. Converting this to more sensible units gives about 2.7 $\times$ 10$^{11}$ volts/metre, and this is far above what we can create in the lab.
I did say it's easier to ionise a gas of many atoms. Suppose you apply a strong electric field to a hydrogen gas, and suppose there is a stray electron somewhere in the gas. Let's not worry where the electron came from; maybe a passing cosmic ray produced it. Anyhow, the free electron will start to accelerate along the electric field lines and at some point it will crash into an atom. If the collision energy is significantly greater than 13.6eV the electron will ionise the atom it hits, and now you have two free electrons. Those two electrons will in turn accelerate and collide with other atoms and you get an electron avalanche. The mean free path of an electron in air is about 0.5 microns, so the corresponding electric field is 27MV/m and this is easily achievable. There's more on this in the Wikipedia article on Paschen's law.
Comment: @annav: my interpretation of the question is whether it's possible to tear apart an isolated atom with just an electric field, and the answer is "in practice, no". Triboelectricity doesn't seem to me to have any connection with what the OP is asking.
Comment: @John Rennie Hi John, the scale of the electric field strength for ionizing one single hydrogen atom is not that impossible, according to my materials. If we take the electric-field of a laser into account, then the $2.7\times10^{11}$V/m(or $2.7\times10^{9}$V/cm) corresponds to an intensity of approximately $1.9\times10^{16}$W/cm^2. A paper from Optical Society of America named 'Relativistic Optics' said a record intensity of $10^{21}$ W/cm^2 has been demonstrated in University of Michigan, and that was in 2004.
Comment: "How does it work? :

An Ecoflow ionises the fuel by directing a specific and powerful static magnetic field right into the fuel supply line. Through a process known as magnetohydrodynamics the fuels ability to combine with oxygen improves and greater energy Is released from the fuel." http://www.aussiemagnotherapy.com.au/Enhancing_fuel_efficiency_with_magnetic_ionisation.php . One can ionize with magnetic fields. There is also the triboelectric effect.ionisation by rubbing which shows that the energies are easily available. http://en.wikipedia.org/wiki/Triboelectric_effect
Comment: @sphericalchicken - A laser produces an intense electric field over a very short distance. An optical laser will not ionise an isolated hydrogen atom because its photons contain too little energy. In a gas of hydrogen atoms it may cause ionisation due to heating, and the resulting atomic collisions, but this isn't what the question was asking.
Comment: Why do you need 2.7E11 V/m if you aren't a meter away?  In other words, can't you do it with a lower energy field if you are closer to the atom?
Answer: Electric strength =5.145175226 X 10^11N/C
Magnetic strength  = 235125.6635 T
so Velocity of the electron =
 E/B =2.188266.117 m.s^-1 = C/137