Can insulators send charges to other objects?

Question: Basically, a plastic rod (an insulator) won't be able to receive charges from a charged conductor, but if I charge this rod by friction and then make it touch my hand, will my hand get charged? If so it does, does this mean that insulators can't receive a charge, but can send a charge out of it?
Answer: An insulator cannot propagate a charge  through its lattice . Look at

The surface of an insulator, depending on the material, can give up an electron, thus becoming positively charge, or accept an electron at an empty energy level and thus become negatively charged.
Answer: An insulator can receive and release a flow of electricity. A classic experiment is to charge a rod by rubbing with fur. One charged the insulator can emit an electrostatic discharge (ESD). There typically isn't a lot of current, but the voltage can be thousands of volts. When vacuum tubes were being used they used so much current that such a tiny current pulse was insignificant. But with modern transistors an ESD has more than enough power to destroy the transistors. So transistor devices have to be designed to avoid ESD damage.


Where can I find a driver for a specific HP printer?

Question: I would like to install a driver for HP LaserJet 4250n on a Windows 7 machine. The HP site gives me a universal driver which is not what I need. After installing that driver, I have a new icon in Devices and Printers, "HP Universal Printing PCL6". When I choose this "printer" after clicking Ctrl+P, a window opens in which I can input the address of the actual printer I want to use. It does work in that the printer prints the things I need, but it's twice as much clicking as I'd like. Can't I just install a driver for the actual printer I'm using? Where can I find it?
Comment: How are you adding the printer exactly to Windows?  The printer is a network printer, which means, you should be adding the printer my the ip address.  **The type of driver you think you want does not exist for the pritner you have.**
Comment: Maybe you can set some preferences in the properties page of that "virtual" printer?
Answer: It depends on how you install the driver itself, in your case "traditional mode" is the way to go.
I got this from the "HP Universal Print Driver" manual:

Because the HP Universal Print Driver is flexible, you can install it in Traditional or Dynamic mode—and you can
  have both running on your PC at once.
  Traditional mode functions exactly like the product-specific drivers you are accustomed to using.
  When installed
  in Traditional mode, the HP Universal Print Driver is associated with a specific print device, which you can then
  select from an application's Print menu. Once selected, the
  driver functions as a traditional, product-specific driver.
Answer: This one should work. I remember having to use vista drivers for win 7 in the past with no issues http://h20000.www2.hp.com/bizsupport/TechSupport/SoftwareDescription.jsp?lang=en&cc=us&prodTypeId=18972&prodSeriesId=412144&prodNameId=412158&swEnvOID=2093&swLang=8&mode=2&taskId=135&swItem=lj-24656-6
The driver for that printer for win7 is actually included with windows as standard, so you should really use that.


Terms and greement page

Question: Hello i want to do like the page also add buttons like
Is there a learning tutorial link or video or someone help
 Thank you
Comment: What are the buttons supposed to do apart from adding an item to a list?
Answer: You have the terms and condition list - now read this list as the way we read any custom list either using SharePoint workflow, Nintex workflow or Microsoft Flow. And while sending an email notification to users about this "terms and condition" read the "Terms" description field, Is Term Accepted? checkbox field - then add these fields reference into the send email notification action body and in the send email send the item URL link - this way when the user gets the email will get the direct link to the list item and user action whether accepted or not accepted the terms, can be recorded in the same list.

Terms and greement page


Why the exchangeability of random variables is essential in hierarchical bayesian models?

Question: Why the exchangeability of random variables is essential for the hierarchical Bayesian modeling?
Answer: Exchangeability is not an essential feature of a hierarchical model (at least not at the observational level).  It is basically a Bayesian analogue of "independent and identically distributed" from the standard literature.  It is simply a way of describing what you know about the situation at hand.  This is namely that "shuffling" does not alter your problem.  One way I like to think of this is to consider the case where you were given $x_{j}=5$ but you were not told the value of $j$.  If learning that $x_{j}=5$ would lead you to suspect particular values of $j$ more than others, then the sequence is not exchangeable.  If it tells you nothing about $j$, then the sequence is exchangeable.  Note that exhcangeability is "in the information" rather than "in reality" - it depends on what you know.
While exchangeability is not essential in terms of the observed variables, it would probably be quite difficult to fit any model without some notion of exchangeability, because without exchangeability you basically have no justification for pooling observations together.  So my guess is that your inferences will be much weaker if you don't have exchangeability somewhere in the model.  For example, consider $x_{i}\sim N(\mu_{i},\sigma_{i})$ for $i=1,\dots,N$.  If $x_{i}$ are completely exchangeable then this means $\mu_{i}=\mu$ and $\sigma_{i}=\sigma$.  If $x_{i}$ are conditionally exchangeable given $\mu_{i}$ then this means $\sigma_{i}=\sigma$.  If $x_{i}$ are conditionally exchangeable given $\sigma_{i}$ then this means $\mu_{i}=\mu$.  But note that in either of these two "conditionally exchangeable" cases, the quality of inference is reduced compared to the first, because there are an extra $N$ parameters that get introduced into the problem. If we have no exchangeability, then we basically have $N$ unrelated problems.
Basically exchangeability means we can make the inference $x_{i}\to \text{parameters}\to x_{j}$ for any $i$ and $j$ which are partly exchangeable
Answer: "Essential" is too vague. But surpressing the technicalities, if the sequence $X=\{X_i\}$ is exchangeable then the $X_i$ are conditionally independent given some unobserved parameter(s) $\Theta$ with a probability distribution $\pi$. That is, $p(X) = \int p(X_i|\Theta)d\pi(\Theta)$. $\Theta$ needn't be univariate or even finite dimensional and may be further represented as a mixture, etc.
Exchangability is essential in the sense that these conditional independence relationships allow us to fit models we almost certainly couldn't otherwise.
Answer: It isn't! I'm no expert here, but i'll give my two cents.
In general when you have a hierarchical model, say
$y|\Theta_{1} \sim \text{N}(X\Theta_{1},\sigma^2)$
$\Theta_{1}|\Theta_{2} \sim\text{N}(W\Theta_{2},\sigma^2)$
We make conditional independence assumptions, i.e., conditional on $\Theta_{2}$, the $\Theta_{1}$ are exchangeable. If the second level is not exchangeable, than you can incluce another level that makes it exchangeable. But even in the case that you can't make an assumption of exchaganbelity, the model may still be a good fit to your data at the first level.
Last, but not least, exchangeability is important only if you wanna think in terms of De Finetti's representation theorem. You might just think that priors are regularization tools that help you to fit your model. In this case, the exchangeability assumption is as good as it is your model fit to the data. In other words, if you think of Bayesian hierarchical model as way to get  abetter fit to your data, then exchangeability is not essential in any sense.
Comment: @Mancel Don't indent your formulaes; otherwise, they will be rendered as verbatim (`...` in HTML). See [here](http://stats.stackexchange.com/editing-help) for further information on Markdown formatting.


Is there any difference between a stream's Longitudinal Profile and its Elevation Profile?

Question: I have derived elevation profile of a river channel using USGS SRTM 1 ArcSec. I am interested to know whether Elevation Profile and Longitudinal Profile are synonymous?
Comment: Same thing in my opinion
Comment: I have skimmed through Google but didn't find any reference, could you please provide any reference for more clarification?
Answer: An elevation profile or a topographic profile is a two-dimensional cross sectional view of the landscape. It provides a side view of the relief of the terrain along a line drawn between two locations on a topographic map.
Whereas, the longitudinal profile is a two-dimensional view along the river, and it characterizes average stream slopes and depths of riffles, pools, runs, glides, rapids and step/pools. Longitudinal profiles are measured in the downstream direction.
In your case you said you have derived elevation profile of a river channel, which I think it is longitudinal profile.
Comment: So I would have to indicate riffles, runs, glides etc on the Elevation Profile plotted from Digital Elevation Model to call is as 'Longitudinal Profile'?
Comment: I just had a walk 5 km long, started at point a, took a road B and use road c to return to point a. If I want to represent elevation change along the route I think both items will do
Answer: Both are same. Longitudinal elevation is Elevation along the line or stream line.
But Cross section elevation is elevations across the line.


Abusive, but not rude

Question: I came across a post, which was basically gibberish like "hsuheuduehuhfuheufhufe".  Originally I marked it as spam, but it was not accepted.  Why?  It should have been marked at rude and abusive.  Perhaps a new feature could be to separate the 2, so that such a post, which is definitely abusive, but not rude?  Thanks.
Comment: It says rude OR abusive, not and, so you can use that flag for either reason.
Comment: I think moderators tend to forget this guidance, that's why I prefer to add a comment under flagged post: [Why don't we treat rubbish the same as spam?](https://meta.stackexchange.com/a/234035/165773)
Comment: However, I would also like to know why that cannot be spam
Comment: You should ask the people on the site that rejected the flag, sites have their own definitions of spam.
Comment: _"why that cannot be spam"_ Because "spam" is unsolicited commercial advertising, not banging mindlessly on the keyboard.
Comment: okay... but many of the time people talk about like "dont spam me" on social media so gibberish is sort-of spam
Answer: Rude and abusive are (to some extent) the same thing. You've already known that you should flag gibberish as rude or abusive. That's a good start. You should also know that gibberish adds no value to the sites. It actively harms the overall quality of user-generated content on Stack Exchange, thus abusive.
Flags are meant to report specifically bad posts or behavior on Stack Exchange, so use them accordingly. Flag real spam as spam, and flag offensive (with bad words) or garbage posts as rude or abusive.
On Stack Exchange, the term "spam" specifically means "unsolicited commercial advertising". Don't confuse it with that "spam" you see in social media.
Comment: Perhaps we could separate them so it wouldnt be so misleading
Comment: @XcoderX Answer updated.

Abusive, but not rude


Permanent video connection between two office locations

Question: I'm looking to hang a screen (with PC attached to it) in two geographically separate office locations, near the coffee machines. I want there to be a permanent video connection where two people in both locations could casually talk to one another. A webcam + Skype does not seem all that practical, given the (occasional) poor stability of Skype and the fact that one would have to setup a connection manually every morning. All should preferably be automatically started and should the connection fail, it should auto-recover. Does anyone have any suggestions what the best solution for this would be?
Answer: If you want a reliable solution, you might want to try Cisco's video conferencing solutions.
Alternatively, you can try SIP soft-phones with video capability. There're are many free and paid solutions.
An older standard for this is H.323 and there are loads of software/hardware solutions based on this as well. Windows used to ship with NetMeeting which is a very nice H.323 client.
If you really want uninterruptable video streaming, you can try Windows Media Encoder, which is a free download form Microsoft. You'll have to set it up to stream the webcam on both ends. Because you're doing live video streaming, you don't have to worry about connections being dropped as the video players will automatically retry.
To make many of these work, you may also need a VPN connection between the two locations.


Relationship between current and voltage (I know little physics)

Question: I'm a little confused about the relationship between voltage, current and resistance. I do know V=IR; but as to the relationship between voltage and current- (holding resistance to be constant) does a change in voltage cause a change in current or is it a change in current causing a change in voltage? I might not even be understanding current and voltage properly I don't even know
Comment: I'm voting to close this question as off-topic because of lack of elementary research.
Answer: Which is the cause and which is the effect is irrelevant. There is a linear relationship between them (at least when only resistors are involved), and that is what is important in analyzing circuits.
However, from the standpoint of fundamental physics, a difference in electrical potential (voltage) causes charge to flow (current) if it can flow. Flowing charges do not necessarily cause a difference in electrical potential. So you should think of voltage as the cause and current as the effect.
Answer: No. A current through a resistor can & does produce a voltage drop. As charges move through a resistor, they collide with lattice ions. When an electron collides with an ion, it can drop from conductance band down to valence. This is a drop in energy state since the valence band is a lower energy state than conduction band, ie more negative. As a result, the lattice ion gains an electron, becomes more negatively charged, & a photon is emitted to conserve energy. The resistor feels warm as it radiates heat due to conduction.
Clearly the voltage drop across the resistor is a result of charge flow through it, ie current.
But if a resistor is connected directly across a CVS, constant voltage source,  then the current is determined by V/R.
Either one, I or V, can be the independent quantity, the other being dependent.
V=IR, is a functional relation, not causal, since either one can cause the other.
Claude Abraham


Sitecore 10.0 IdentityServer4 How do I update Microsoft.Identitymodel.Tokens.Saml from 5.2.0 to 5.2.4?

Question: We are using Sitecore 10.0 with IdentityServer4 trying to get SustainSys Saml2 to work.  SustainSys Saml2 uses Microsoft.Identitymodel.Tokens.Saml 5.2.4 but Sitecore 10 IdentityServer4 uses an outdated Microsoft.Identitymodel.Tokens.Saml 5.2.0 because of a reference to WSFederation 5.2.0.  How can I update Sitecore IdentityServer4 to use the 5.2.4 version?
Answer: In your scenario, yes you will need to update your Microsoft.IdentityModel.Tokens.Saml and Microsoft.IdentityModel.Xml assemblies to match your version 5.2.4
This of course means you need to ensure Sitecore.IdentityServer.Host.deps.json is synced to reflect your updated assembly versions.
Please test and verify this works. If not, there is probably more dependent assemblies such as Newtonsoft.Json, Microsoft.Extensions.DependencyModel which you should match the correct versions too.
Please note you need to keep track of which changes you make to default Sitecore Identity Server configuration, should you upgrade in future so that you don't break it again.
Hope this helps.


Disabling a ListView in C#, but still showing the current selection

Question: I have a ListView control, and I'm trying to figure out the easiest/best way to disallow changing the selected row(s), without hiding the selected row(s).
I know there's a HideSelection property, but that only works when the ListView is still enabled (but not focused). I need the selection to be viewable even when the ListView is disabled.
How can I implement this?
Answer: You could also make the ListView ownerdraw. You then have complete control over how the items look whether they are selected or not or whether the ListView itself is enabled or not. The DrawListViewItemEventArgs provides a way to ask the ListView to draw individual parts of the item so you only have to draw the bits you're interested in. For example, you can draw the background of the item but leave it up to the ListView to draw the text.
Answer: There are two options, change the selected rows disabled colors.  Or change all the other rows to simulate they are disabled except for the selected one.  The first option is obviously the easiest, and the second option obviously is going to need some extra protections.
I have actually done the first option before and it works quite well.  You just have to remember to change the colors back to the defaults in case another row is selected later on in the process.
Answer: Implement SelectedIndexChanged and do this
    private void listViewABC_SelectedIndexChanged(object sender, EventArgs e)
    {
        listViewABC.SelectedItems.Clear();
    }


What happens if I change the polarity of the battery?

Question: Suppose if i charge a capacitor. Now if I reverse the polarity of the battery, how much is the heat produce during that process? My book says as change in energy = 0 (in capacitor) therefore heat produce 2cv^2. Can somebody actually explain me what will happen when the polarity is changed and provide me with some other way of explaining this answer?
Comment: This sounds to me as *theoretical* nonsense, just like: https://electronics.stackexchange.com/questions/439582/heat-lost-in-ideal-capacitor-charging
Comment: " Now i reverse the polarity of the battery .How much is the heat produce during that process . " How heavy is the battery, how much distance do you move it? :-) Serious: An ideal capacitor can not consume energy. What happens is that the energy is consumed in the battery, first when charging, then again when charging with the opposite voltage. I have to go now but I am sure somebody will give a long answer about this.
Comment: If there are no resistances involved there will be no heat generated. Show the circuit.
Comment: @Huisman Yes, but ... . The ideal resistanceless examples fail to deal with the infinitely large current flows. Add those in and multiply and divide by a few infinities and it all works out :-). ie the ideal cases are unworkable because of infinities. The real world resistances make it calculable. [So. Yes. That's what you effectively were saying :-)].
Comment: @Huisman Indeed, if you can ever get that zero Ohm circuit. What I'm saying (and I'd doubt that we disagree greatly) is that in practice you have resistance presence and the laws of Physics apply. If we have typical wire, typical capacitors, typical batteries, or even the very best, we understand "well enough" what will happen. As we approach "ideality" we probably need plasma physics, arc-flash shields and luck if we are to understand what happens (and not to die). Which is not what we get to in most cases.
Comment: @Chu just the battery and capacitor
Comment: Two impulses of current, then, but no heat energy. There will be RF energy due to the impulses.
Comment: @Chu There will ALWAYS be heat produced. In the ideal case with no resistance there will be infinite current. Infinity^2 x 0 will automagically come out to 0.5 x C x V^2 :-). In any real world the current and resistance and capacitance and energy will sort it out amongst themselves.
Comment: @RussellMcMahon I disagree with *Infinity^2 x 0 will automagically come out to 0.5 x C x V^2*. Because \$ \infty^2 \cdot 0\$ is **not defined** and will **not** come to any (predictable) value
Answer: Ideal dielectrics = insulators such as capacitors and batteries have no effective series resistance (ESR).
Ideal dielectrics do not exist.
All dielectrics have ESR which follow the losses defined by Ohm's Law and thermal resistance that determines the temperature rise in the dielectric.
When reversing the charge on a polarized dielectric Capacitor ( Cap.), the insulation may break down and destroy the part, especially if the circuit impedance is as low as the ESR  of the cap.  If the reverse voltage is > 5% of the forward rating the risk of damage increases exponentially, although in current limited circuits some polarized caps can withstand -10% of Vmax for peak AC audio signals with some forward DC bias voltage.
When reversing a non-polarized capacitor the energy previously stored and not decayed by self-leakage resistance \$E=0.5CV^2\$ which is the same quantity of energy stored after apply the same voltage reverse.
However to invert these charges, the cap. will conduct \$I_{peak}=\dfrac{2|V|}{ESR}\$ in peak current with an exponential decay  of \$\tau= ESR*C\$ [s] for current as the exponential reversal of voltage.  The energy dissipated during thi discharge/charge process is from the ESR current*voltage power  losses as explained in your textbook.
We say power dissipation=+ve is a positive value and generated power=-ve has a negative polarity, yet the energy product of the power P(t) and time integral is just  an  energy transfer ( as it is neither created or destroyed).  So as the energy stored is the same quantity as before but just as if the leads were reversed yet power had to be generated  by some supply and lost in the cap. during the process.
NPO/COG ceramix are low density ceramics are known to have low ESR as well as plastic film caps in the milliohm range thus will conduct very high current.
Batteries are like massive capacitors due to the high relative dielectric constant, , Dk ( or \$\epsilon _r\$), so a similar heat loss power process occurs going from one polarized  voltage level to a higher state of charge (SOC) voltage to store more energy.
Answer: When the capacitor is first charged, it has received \$\frac{1}{2}C(+V)^2\$ joules of energy from the battery.
By reversing the battery, you create a potential difference which causes current to flow in the opposite direction, which will at first discharge the capacitor, until the voltage across it returns to zero. At that point the capacitor stores no energy at all.
But current continues to flow, since the battery and capacitor still have unequal potential differences, and this will begin charging the capacitor again, to the opposite polarity, until the voltage across the capacitor equals the battery voltage, this time −V.
At that point the capacitor has \$\frac{1}{2}C(-V)^2\$ joules of energy. Due to the squaring of potential difference V, energy stored is always positive, independent of the sign of the potential difference, and now it has the same amount of stored energy that it started with, when it was initially charged to +V potential difference. The only change is the sign of the potential difference.
So, during this process, the capacitor potential difference goes from maximum voltage +V, to zero, and finally to a potential difference of −V. It starts and ends with the same energy stored, a net change of zero joules.
As for how much heat energy is created, this relates to the fact that it is impossible to connect an ideal capacitor across an ideal battery, when the resistance around the loop is zero, because this would result in infinite current flow, absurd.
In reality the resistance around the loop cannot be zero, and the algebra shows that the energy transfer from battery to capacitor, and capacitor to battery is 50% efficient, due to energy lost in that resistance. That is, if a capacitor is charged to potential difference V, via a resistive path, so that it now has \$\frac{1}{2}CV^2\$ joules of energy, that same amount, \$\frac{1}{2}CV^2\$ joules of heat, must have been created in the loop's resistance.
Since these are the potential phases in your scenario:

Initial charging from 0V to +V potential difference, creating \$\frac{1}{2}CV^2\$ of heat,

Discharge of the capacitor, to 0V, creating \$\frac{1}{2}CV^2\$ of heat,

Charging from 0V to −V potential difference, creating \$\frac{1}{2}CV^2\$ of heat,

Perhaps another discharge from -V to 0V, again producing \$\frac{1}{2}CV^2\$ of heat.

All of those add up a total of \$2CV^2\$ of heat energy, but I think your question doesn't account for the last phase. Does the original question?


Can you craft maps of the Nether?

Question: So we know that a maps location is based on the first time you look at it, but can you craft a map of the Nether?
Answer: Yes, but they don't do you much good.  From the wiki:

While maps in the Nether work, it has
a ceiling, and all that will be shown
is red and gray. The only useful
function is finding where you are in
relation to where you made the map.
Additionally, the direction indicator
rapidly spins and is not a good
indicator of direction. Remembering
that maps are East at the top and that
the L corner of nether blocks points
north is more reliable. And as long as
the map was created near a portal,
that map's center will always be that
portal.
Comment: That would be pretty good, to be fair. You can see where you are in relation to your portal.
Comment: @The Yes, I guess that could be useful. I'll have to map the nether to see if it is worth it.
Answer: You can break the ceiling of the Nether (although getting there is only safe in Creative), so if you break the ceiling the map might map out the actual landscape. I haven't tried this, but I think it would work well.
Comment: If you have your own question, you should ask in a different question, not put it in an answer here. And your answer doesn't seem to add anything that is not stated or inferred from the accepted answer.

Can you craft maps of the Nether?


Could you give annotated examples regarding the grammar of a sentence in classical Chinese where 爾 is used as an adverbial suffix?

Question: 爾 here used as an adverbial suffix of classical Chinese.
Answer: 爾/尔 in Classical Chinese can be used similarly to 然, roughly meaning "thus/so/in such a manner", changing the word to which it's suffixed into an adverb. Here's an example from Mencius 孟子 we can analyze:

一簞食,一豆羹:得之則生,弗得則死。嘑爾而與之,行道之人弗受;蹴爾而與之,乞人不屑也。

My attempt at a faithful English translation:

A basket of rice, a platter of soup: with them one survives; without them one dies. When offered insultingly, a vagabond would not accept them; when offered trampled, even a beggar would reject them.

Here we see 爾 modify the verbs 嘑 (to insult) and 蹴 (to trample) to convert them into adverbs that indicate how the food is offered.
Answer: Examples for 尔 used as a adverbial suffix:
莞尔,an adverb for "smile".
卓尔,an adverb for… er… "act extraordinarily".
率尔,an adverb for "act rashly, etc.".
Links above are references for the character and phrases, maybe a little elusive for non-native speakers, but you can have a glance.


keyboard navigation

Question: On ubuntu 16.04 (100% satisfaction) I used to select and open folders/files on desktop using keyboard, up/down, left/right arrow keys; not the mouse. I cannot do this anymore on ubuntu 20.04
Any work around ?
Comment: Are you still using Unity (default on 16.04) as your desktop on 20.04, or have you switched to GNOME shell (now the default).
Comment: Switched to Gnome-shel... tried Unity and Nemo on Vbox, lots of lags and other non convenient behaviors, got back (Vbox) to gnome.
Answer: Desktop icons are now provided by a Gnome Shell extension, which is still very new and underdevelopped.
A workaround is to navigate your icons in the file manager: they live in the "Desktop" folder.
If an active desktop is critical in your workflow, you better move to a desktop environment that fully supports them: Xubuntu, Kubuntu, ... Ubuntu uses Gnome Shell. Gnome Shell does not support an active desktop at all. Ubuntu wants to support it, but has to resort to a half ready Gnome Shell extension to do so, because the file manager Files (nautilus) does not anymore support this.
A rather technical option would be to move to the nemo or caja file managers, so these can manage the desktop.
Comment: Thank's for the reply. The topic is not that important -just a question of fingers confort using laptop pad : I do prefer using keyboard.

keyboard navigation


Water has quit running thru my humidifier.

Question: Furnace humidifier dry as a bone.  have changed the filter, duh, that is the only thing I know how to do! Bottom line, there is no water running through it.
Answer: Novice
Check the humidity
The humidifier should only turn on if the humidity is below a set level.  Make sure the humidity is actually below this level.
Clean the inlet
Check the inlet (where the water comes in), and make sure it's not all gunked up.
Check the valve
If the humidifier supply line connects to the water supply via a saddle valve, close and reopen the valve (and consider replacing the valve, which will require shutting off the water since the valve pokes a hole in the pipe).
Set the humidistat
If a humidistat is used, make sure it's set properly.
Intermediate
Check for water at the solenoid
Close the valve supplying the humidifier, and remove the supply tube from the supply side of the solenoid. Open the valve just a bit, and make sure water is coming from the tube.
TIP: Wrap a rag/towel around the open end of the hose, and hold it tight when opening the valve.  The rag/towel will prevent the water from spraying out the end of the tube. Also, don't forget to hold the rag/towel wrapped tube over a bucket.
Check for power at the humidistat
Open up the humidistat, and use a multimeter/voltmeter to make sure the humidistat has power (most likely 24 volts).
NOTE: Depending on the installation, the humidistat may only have power when the furnace is running.
Check for power at the solenoid
With the humidistat open, and the furnace running. Set the humidistat to the highest setting, and check to see if you have voltage going to the solenoid.
Answer: I would like to expand on the point above about closing and reopening the saddle valve. (see "Check the valve")
Your saddle valve may be clogged with fine particles that have settled in the pipe, especially so if the valve has been installed on the bottom of the pipe.
You can try to clear the clog by FULLY closing the valve and reopening it. You might encounter some resistance as the pin is driven through the clog and back into the pipe, be sure to close the valve FULLY.
Good Luck.


Is it necessary to rebuild your modules when you rebuild the kernel?

Question: ... if you are using a subset of the original list of modules? I tried this recently and the kernel couldn't boot, and then when I did a full rebuild it apparently worked. But since I only tried this once I can't be absolutely sure that there wasn't some other thing I changed between the first and second rebuilds. I could try it again, I suppose, but it'll take time :P
Answer: Yes, you need to rebuild all of your modules.
Answer: There was some work to make modules (somewhat) version independent, in that each function essentially recorded its prototype and the module refused to load if there was any mismatch. I haven't followed this too closely, so I don't know if that was ripped out.
Short answer: Your safest bet is to recompile, the kernel hackers are adamant at not having a stable API (let alone ABI) inside the kernel. Even a configuration change could change data structure layout changes.


Canadian Permanent Resident entering Canada with expired US passport

Question: I'm a US citizen and a Canadian Permanent Resident. During my visit to my terminally ill mother in the US last year my passport expired. I just noticed it and am returning to my home in Canada at the end of February. With the Covid epidemic going on it will take too long to renew my passport. I do have my valid Canadian permanent resident card and since my passport is expired and can't fly I'm planning on crossing by Land. Will I have any problems entering Canada with my Canadian permanent resident card and expired US passport. I do have my birth certificate and my valid US drivers license to show that I am who I say am.
Comment: Is your US drivers license "enhanced"?
Comment: Why do you have a US driver's license if you don't reside in the US?  In normal times an expedited US passport application takes far less than a month, though I don't know how things are these days (in fact my experience with non-expedited applications is roughly two weeks, but that's not recent).
Answer: A late answer, but anyway, a permanent resident has a statutory, absolute right to enter Canada, once their status is established by a valid permanent resident card.
From recent experiences, you might still be reminded of the "need" of a passport; but it is not a big deal unless your identity is questioned. It might be that in the past passport stamps are often used as evidence when the officer examines the compliance with residency obligations, but nowadays (almost) everything is electronically recorded.
In fact I could not find any legal requirement for a permanent resident to have a passport when physically entering Canada, despite certain IRCC/CBSA websites implying or having implied so. Although for international flights, the Secure Air Travel Regulations does obligate the airlines to check a passport or NEXUS card before boarding a passenger. A PR card alone will not accepted by the airlines as a travel document.
However, at airports, a permanent resident card alone is accepted by the automatic kiosks. But a non-US/Canadian-citizen NEXUS members without a passport may not be able to use the NEXUS lane or kiosks.
Comment: The right of permanent residents to enter Canada is also enshrined in the *Charter*, although *Charter* rights are not absolute.


How many times can you try to create a candidate block/sec in Casper?

Question: According to this post, you can create only one candidate block/sec for next block in general POS formula. Same in Casper? If it's different, how many candidate blocks can you create in a second in Casper?
Answer: The latest form of Casper, as I understand it, uses a different algorithm. At any given height, validators are selected in a random order to produce a block at that height. If an individual validator fails to do this in time, the network will allow the next validator in line to try.
There's not a concept of a "candidate" block. A validator may theoretically make any number of blocks when given the chance. However, if a validator makes a block that does not end up in the chain (a "dunkle"), that validator is penalized equal to the block reward. There's little reason to make more than one block.
For more information, you can read the Mauve Paper
Comment: Can only selected validators create a next block? You don't need to try to create many candidate blocks to satisfy the criterion such as 0000... in Bitcoin's PoW block hash?
Comment: That's correct. There's no PoW involved.


In Signal Messenger what is the purpose of verifying a safety number?

Question: I've read the official page on safety numbers but they are still unclear to me. Without verification, there still is end to end encryption, so what difference does it make? Is it that a phone number is easy to spoof so an adversary could pretend to be someone else but with a safety number verified you would know if it's not really them?
Answer: The safety number is actually the fingerprint of your public key.
By verifying this, you verify that the public key you are encrypting the messages to, is in fact the same as the keys used by the other party in the conversation.
If not verified, you could be encrypting your keys with a Man in The Middle's keys, which then proceeds to decrypt the messages, read them, and reencrypt them with the recipients key. You would be none the wiser.
By verifying that the public keys is identical for both participants, you remove the possibility of a MiTM attack.
It's explained in detail in this blog post from Signal.
Comment: Why isn't this normally necessary with things like secure websites, how do they protect against MiTM attacks? Is it that usually users don't have the opportunity to exchange something physical but with smartphones there's the option so it's just an additional layer that can be added in this situation?
Comment: @northerner TLS as used on the web is based on trusted third parties, the Certificate Authorities. Users may compare fingerprints to verify that they get the same cert. [More info here](https://security.stackexchange.com/questions/20803/how-does-ssl-tls-work).


Can I use 1000v rectifier diodes instead of 600v rectifier diodes?

Question: I plan on doing some wiring but the directions are asking for 1A 600v rectifier diodes. I could only get my hand on 1000v rectifier diodes and before I continue I want to make sure this is safe as if I wont cause a fire or a short or make something blow up.
Comment: generally, the higher the voltage limit, the higher the drop-out voltage. That voltage might not be missed by your circuit, but remember that a higher drop-out will cause more heat for the same load. it won't instantly blow-up, but do keep an eye on the case temp at first.
Answer: In general, it is safe to be overly conservative with a component specification. If your design calls for 600V rated diodes, then using diodes rated for 1000V shouldn't hurt anything, all else begin equal.
However, you have only provided information for the voltage rating. If the 1000V diodes can't handle 1A of current, or are insufficient in some other area, you could still have issues.
Answer: The only situation in which you would not be able to increase the voltage rating (all other performance metrics being equal) would be if the circuit depends on the reverse breakdown behaviour of the diode. No* properly designed circuit, however, will rely on the reverse breakdown behaviour of a conventional diode.
*Note: there may be exceptions, but they will be exceedingly rare, and I can't think of any case where a Zener or avalanche diode wouldn't be a superior choice.
Comment: If the circuit is a 240V mains AC voltage power rectifier, (or even a 3 phase 480V) could it be argued that 1000V may provide better protection from stray transient high voltages (power spikes) than the reference 600V diode of exact same spec and impedance etc? Since a diode is a semiconductor it's impedance might move somewhat.
Comment: @Tomachi It would just rectify the spike as well. You shouldn't rely on your rectifier to also protect from surge voltages.
Answer: There is unlikely to be any negative consequences to doing this, just make sure they are big enough to handle the current.  That rating is just the maximum reverse voltage they can take.  More is better.
If they are recommending a specific part, you may want to look at some of the specs like reverse recovery time or forward voltage drop, but it almost certainly doesn't matter.


Why is downloading repository updates so slow?

Question: Okay, I have Ubuntu version 11.10 and I wish to upgrade to 12.04. Whenever I open the Update Manager and click "Check," it has taken literally over an hour to download the cache. I cannot update without checking the cache; attempts in the console (as suggested  here) have failed.
What do I do in order to update without waiting over three hours to download the entire cache? Or how do I get it to download quicker?
EDIT: Saw this page, it provided no help. Just false hope. Oh, and no, my internet works just fine; normally I have a 600kb/s download rate. No dial-up here.
Comment: Try changing your server. to do that go-to ubuntu software center and edit-software sources, then in the ubuntu software tab, select "download from" to another server or "Other", then it will automatically select the best server for your location
Comment: I tried that, and it gave me hope! But then it shot me down. D: Thank you though.
Comment: What just happened? still slow? may be you have thousands (or millions) of repositories installed, isn't it?
Comment: I literally just installed this Ubuntu today, about 7 hours ago. :P I have absolutely nothing on here but the operating system and stock software. I unchecked everything except "Canonocial Supported" in Software Sources, which I assume would be the OS update. And yes, still slow.
Comment: Please see http://askubuntu.com/questions/135818/the-size-of-apt-get-update-lists-is-too-big/ to see if this is the problem you are experiencing.
Comment: No. No such console output.
Comment: Try this upgrade procedure from [Official Page](https://help.ubuntu.com/community/PreciseUpgrades/).
Answer: I tried again later and it worked. So it solved itself. I think it was probably just my internet having a hiccup, but only to this computer. Which is weird.


Where to use "the"

Question: Which sentence is correct?
are we meeting before the class or
are we meeting before class
Comment: Neither is incorrect, though it might be more natural to leave out 'the'.
Comment: ... Perversely, "Are we meeting before the lesson?" needs the definite article.
Comment: One lesson is apparently specific. But those educated with private tutors do things _before lessons_. (I googled _princess "before lessons"_).
Answer: When a noun is used without an article, linguists often call it a zero article or zero determiner.
This occurs, among other reasons, for many events or places that are part of a regular routine, thus requiring no specificity.

She wanted to run some errands before dinner.

But

She wanted to run some errands before the dinner.

In the first sentence, dinner is a routine event occurring so regularly — and for most English speakers roughly at the same time, except for those who call it tea or supper— that it's often used as a time reference. In the second, a specific event is implied, such as a formal dinner at a hotel or a dinner party at her own home, i.e., a specific, not routine, event.
Your question most likely falls into this category. If a native speaker asks another

Do you want to meet before class?

the time reference is common to both speakers' routines and need not be further specified.
If instead, a native speaker asks:

Do you want to meet before the class?

the other may ask, "Which class?" unless the other already knows what specific class, say, a master class conducted by a famous musician, is meant.
Comment: I disagree. I'd class this as a [null article](https://english.stackexchange.com/questions/239585/why-do-people-omit-the-definite-article/427204#427204), not zero article, usage. A corresponding example is 'He tends bar.'
Comment: So you're one of those linguists who don't _often_ call it _zero article_, but I linked to a reputable source that does. Argue with them, not me. Whether zero or null, the main point is that the article _isn't there_.
Comment: No. OP asks 'Where to use "the" ', not just 'Should I use "the" here?' and is asking for general guidance, which requires analysis where possible. The linked thread provides this.
Comment: Asking which of two choices requires only enough general guidance to determine in which situations the OP would say _before class_ vs. _before the class_.

Where to use "the"


Unreachable rubik cube positions.

Question: Are there positions of the Rubik's Cube which cannot be reached by applying the standard moves starting from the solved cube? If so, how many such positions are there?
Comment: For one, notice the middle blocks are fixed relative to one another. permute them and youll get unreachable positions
Comment: Lots has been written about this question, try [here](http://en.wikipedia.org/wiki/Rubik%27s_family_cubes_of_all_sizes#Unreachable_states_for_cubes_of_all_sizes) for a start.
Comment: Rotate a corner clockwise (or anticlockwise) and you won't be able to reach that position.
Comment: The same for flipping an edge piece.
Answer: 11 out of 12 random positions are unreachable.
This first part just looks at the positions of cublets, without regard to their orientation.
It is possible to place the corners in all $8!$ position permutations.  Separately, it is possible to place all edge pieces in all $12!$ position permutations.  But it is not possible to apply a permutation that swaps only two corners or two edges.
This is easily seen.  All possible permutations arise from the application of 6 basic permutations corresponding to quarter-turns on each face.  Each of these quarter-turns cycles 4 corners (an odd permutation, equivalent to 3 swaps, an odd number) and 4 edges (also an odd permutation).  The combination of these two cycles is an even permutation (3+3=6 swaps, an even number), so any series of basic moves also results in an even permutation.  This sets an upper bound of $\dfrac{8!12!}{2}$ position permutations.
It is possible to construct permutations that solely cycle the positions of 3 corners or 3 edges, so using these 3-cycles you can independendly reach all $\dfrac{8!}2$ even corner permutations and $\dfrac{12!}2$ even edge permutations, resulting in $\dfrac{8!12!}{4}$ total even position permutations.  Turning one face throws both the corners and edges into odd permutations, and from here using the 3-cycle moves you can reach all $\dfrac{8!12!}{4}$ odd position permutations.  Add these together and you get a lower bound of $\dfrac{8!12!}{2}$ reachable position permutations, which meets the upper bound.
In the second part here I'm talking about changing the orientations of the cubes, without changing their positions.
Corner rotations:
Moves exist that jointly counter-rotate any two corner pieces without affecting any other changes.  This sets a lower bound of $3^7$ possible rotations of the corner pieces.
Consider a rotation labeling system for the corner cubes.  Mark one facelet of each corner as special.  Each corner cubelet position has a face whose normal points upward or downward, and call this position 0, the one clockwise from it 1, and the next clockwise 2.  You will find that each basic move preserves the sum of these orientation numbers modulo 3, which sets an upper bound of $3^7$ possible corner orientations.
Edge rotations:
Move sequences exist that jointly flip any two edge pieces without affecting any other changes.  This sets a lower bound of $2^{11}$ possible rotations of the edge pieces.
If you put together an arbitrary orientation numbering system like the corner orientation numbering system above, you'll find that all basic moves preserve the sum of orientations modulo 2.  This sets an upper bound of $2^{11}$ possible rotations of the edge pieces.
So the cube in total has $\dfrac{8!12!2^{11}3^{7}}{2}$ permutations reachable through basic moves.
If you disassemble a cube you can place the corners in any of $8!$ position permutations and $3^8$ orientations, and the edges in any of $12!$ position permutations and $2^{12}$ orientations.  This totals to $8!12!2^{12}3^{8}$ possible configurations, which means 11 out of 12 potential configurations are not reachable through basic moves.
Answer: There are obviously some positions that are unreachable, and one way to get there is to twist a corner once. To elaborate on @NovaDenizen's answer, I tried many ways to make a cube unsolvable. First, there are two ways to get an unreachable position just by twisting a corner, and that is to twist it once clockwise or counterclockwise. This accounts for two 'sets' of unreachable positions. Each set is made up of all of the positions reachable with normal moves from a particular starting position. Another way to make a cube unsolvable, is to flip one edge. This accounts for another set of unreachable positions. Combining a twisted corner and a flipped edge yields two more sets of unreachable positions. The final way is to switch two corners, but this is identical to switching two edges. Doing an algorithm, such as the V-perm, can make two switched corners change to two switched edges. Combine this with the other five unreachable sets, and you will have a total of 11 unreachable sets. Given that the number of possible positions of a 3x3x3 Rubik's Cube is 43,252,003,274,489,856,000, and that there are 11 other sets of unreachable positions, you will have a total of 519,024,039,293,878,272,000 positions. This means that if you take apart the whole cube(except for the centers), you have a 1 in 12 chance that you will be able to solve it using normal turns, and not by taking apart the cube. Hope this helped.
Comment: Funny names: a twisted corner is a *quark* / *antiquark*, two twisted corners with opposed orientation are a *meson*, three twisted corners with the same orientation are a  *baryon* / *antibaryon*. More in http://www.math.niu.edu/~rusin/known-math/95/rubik.physics.
Comment: Just like the particles in atomic science.
Answer: Yes, there are.  These arise from to quick observations: pieces move as part of a $3\times 3$ cube, not as individual faces, and center cubes must stay in the center, which is also true with corner pieces and side faces.  Without loss of generality you can fix the center pieces, and then there are $8$ corner pieces $12$ side pieces.  This gives us a maximum of $$8!12!=19313344512000$$  However I'm sure there are many fewer reachable positions than this, as pointed out in the comments.  But this number already shows how many fewer positions this is the the overall number of permutations of 26 cubes: $$\frac{8!12!}{26!}=\frac{1}{20881492632000}$$ which is obviously a pretty small number.  Obviously this isn't nearly exhaustive, but I hope this helps (also, I completely ignored changing orientation, which can definitely happen).
Comment: The first maximum should be multiplied by $3^82^{12}$ for orientations of the cubies. Wikipedia has a good discussion. It is in fact a factor $12$ down from this
Answer: I think a better way to ask your question would be to ask if there are configurations of the colored stickers, if you peel them off and move them, that don't correspond to cube positions reachable from the solved position by standard moves (or conversely are not solvable starting positions), and the answer is an emphatic "yes" -- for example, if you take the two stickers on one of the edge pieces and reverse them, the resulting cube is unsolvable.  I don't have any numbers, but I suspect that the number of unsolvable configurations of the stickers is several orders of magnitude higher than the number of solvable configurations.
Comment: The OP explicitly stated "by applying standard moves", so moving stickers doesn't count.  This answer does not address the intent of the OP.
Comment: That depends on how you interpret "positions" -- positions of the stickers (which is the interesting question, the one I answered, and how I interpreted the OP) or positions of the cube when scrambled using standard moves (in which case the answer is tautologically and vacuously "no," you can just undo the scrambling moves) -- I apologize for assuming that the OP wanted to ask something interesting instead of something silly.  Oh, and both NovaDenizen and dirty derwin took interpretations equivalent to moving the stickers.  I can't be wrong if they are right.
Comment: @user128390 I took dirty derwin's answer to be weaker than moving stickers - he seems to be saying that you could make an edge piece a corner piece, and vice-versa. Which is silly!
Comment: @user1729 -- to be fair, there is a difference between moving the stickers and disassembling/reassembling the cube (by moving stickers, for example, you could wind up with a yellow-yellow edge piece, which can't happen if you disassemble without peeling), and NovaDenizen's answer at least could be interpreted as disassembling the cube instead of moving stickers (dirty derwin specifically talks about "moving individual faces," i.e. peeling and moving stickers), but neither of these fit Tpofofn's overly restrictive requirement that the only thing allowed is standard moves.
Comment: @user128390 Actually, I think I mis-interpreted the other answer. But I am not sure any more...

Unreachable rubik cube positions.


Heating pad for fermentation

Question: Is there any concern with warming up a fermentation by placing the bucket/carboy on an electric heating pad? Will it kill the yeast that settles on the bottom?
Comment: I don't have the rep yet for a comment, but this is just to echo what Scott says in his answer. I use a Fermwrap in tandem with a chest freezer, and a Ranco dual-stage temperature control unit. I also tape the temperature probe to the side of my carboy or bucket, with some bubble wrap to act as insulation, and can maintain temperatures within a very narrow range with this configuration. This also makes it very easy to ramp up temperatures or cold crash, as needed. I would think a heating pad would serve just as well as the Fermwrap. Note that if you're taping the probe (or the Fermwrap), you s
Answer: It depends upon how hot the heat pad gets - you want to use a pad that doesn't go above 30°C/85°F.  I use a waterproof pad that was originally intended as a pet warmer. It has an adjustable thermostat to set the highest temperature it will reach. I have mine set to 25°C/75°F. So, even though it is connected to a temperature controller, the heat pad thermostat ensures that the underside of the carboy doesn't go above a safe temperature.
Answer: You'll want to ensure consistent temperatures.  If your heating pad goes above seventy degrees Fahrenheit, you'll need a temperature controller to prevent it from going above.  The ideal way to do this would be to have a heating pad that turns on the moment it is supplied power.  I know a few you have to plug them in, turn them on, and then they'll run.  You'll need a way to automatically have it start heating once it receives power.
Get a temperature controller.  I use a Johnson Controls Digital Thermostat Control Unit.  You'll need to affix the temperature probe to the side of your carboy/bucket.  The ideal way to do this is to tape it to the side of the vessel, and place several layers worth of bubble wrap over it to act as insulation.  If possible, try to avoid wrapping the pad over the bubble wrap, as that could heat the insulation and skew your reading.  This way, the probe is getting only the temperature of the wort, and it'll turn on and off as the temperature hits the set thresholds.
Alternatively, I've heard good things about Fermwrap, but have never used one.
Comment: I use a heating pad marketed for homebrew like the one Northern Brewer sells (identical w/ different branding).
Comment: I use a heat pad made for homebrew, similar to Northern Brewer's:
http://www.northernbrewer.com/shop/brewing/brewing-equipment/fermenting-equipment/home-brew-heat-mat.html

It's hooked up to a Ranco temp controller, with the probe taped to fermenter like how Scott recommends, except I use a piece of foam from the craft store, not bubble wrap. Works great. I've got a pumpkin porter sitting on it right now.

One caution, based on experience: don't use a heat pad meant for heating your bed. It's designed to cycle on/off automatically, won't allow consistent temperature control.
Answer: Another way to approach it is to put the fermenter in a large plastic tub and fill the tub with water.  Put an aquarium heater in the water.  You may want to put the heater on a timer.  The water provides a thermal buffer to reduce temp swings.
Comment: When doing this, you'll want to ensure you have an adequate heater.  I've heard stories of people having to ratchet up the temperatures to the mid-70's just to maintain a high 60's temp since the heater wasn't sized properly for the swamp cooler.

Heating pad for fermentation


What is the way to calculate "Risky PV (Present Value)" (discounting including the probability of default) from bond yield curve?

Question: Instead of using CDS spread to do risky discounting, I would like to use the bond yield curve. Can I directly use the discounting factors from the bond yield curve or do I need to figure out the probabilities of default like in a CDS curve and use them for the risky discounting?
Answer: Yes, you can consider a bond yield curve to be like any funding curve, and in particular get risky discount factors from it, and use them, for example, to discount cash flows.
Test that if you pv the bonds used to build the yield curve, you get back the input dirty price. Be careful how you interpolate. Don't mix different kinds of instruments (e.g. zero-recovery and highly collateralized, even if they have the same probability of default).
Comment: Thank you so much for the prompt response. Makes sense. I will check for the consistency of the seniority of the bonds. Much appreciated.


How to use fiber-optic LC connector with my MacBook Pro for access to LTO-5 tape drive?

Question: I'd like to use an LTO-5 tape drive to provide long term backup storage for files on my MacBook Pro that I wish to archive.  It appears the drive uses a fiber-optic LC connector.  Is there a way to connect such a drive to my MacBook Pro so I can back up files using it from my laptop?  If not, is there a LTO tape solution that works with MacBooks?
Answer: The only way that I know of connecting a MacBook (any modern laptop) to a fiber channel drive/drive subsystem is with a a device like the ATTO Thunderlink FC3162, however, they are prohibitively expensive.
What might be a much cheaper and more effective alternative is to build another machine (a cheap PC will work well) and install a Fibre Channel HBA to connect to your LTO tape system.  I've done something very similar with FreeBSD and a Fibre Channel array that served as storage and Time Capsule backup using drives; I'm sure a tape solution would work just as easily.
Comment: Do any of the LTO tape drives not use fibre optic?
Comment: I'm not sure what you mean by the question.
Comment: Are there LTO drives that more readily can be used with a MacBook, e.g., don't have LC optical out.
Comment: Doing an Internet search, I found the [MagStore LT08](https://amzn.to/2PYa8Jd) which is Thunderbolt 3 to Tape - no Fibre channel conversion necessary.  It too is very expensive, however and I've never actually used this.


A word for mourning future endings/loss

Question: I have often felt melancholy at the beginning of good things, trips, events, etc. in anticipation of their ending or loss. I would sometimes even sob when dating my husband (before we married) somehow mourning the future loss of this stage of our relationship. Is there a word for this particular feeling?
Comment: I think 'chronophobia' doesn't cover the 'fear of future loss of a happy season' aspect so much as the 'irretrievability of any time that is now in the past' aspect.
Answer: My first thought was 'anxiety'; however I understand the sentiment underlying your question/feeling; so the answer goes beyond being anxious. Other words which also come to mind are as follows:                                                                                Fatalism: Definition of fatalism
: a doctrine that events are fixed in advance so that human beings are powerless to change them; also : a belief in or attitude determined by this doctrine ·fatalism that regards social problems as simply inevitable
fatalist
  \ˈfā-tə-list\ noun
—
fatalistic
  \ˌfā-tə-ˈli-stik\ adjective
—
fatalistically
  \ˌfā-tə-ˈli-sti-k(ə-)lē\ adverb (https://www.merriam-webster.com/dictionary/fatalist)                                                                                or Definition of catastrophize
catastrophized;  catastrophizing;  catastrophizes
: to imagine the worst possible outcome of an action or event : to think about a situation or event as being a catastrophe or having a potentially catastrophic outcome ·It's easy to have one bad night of sleep and catastrophize that you'll never sleep well again.
 —Katherine Sharkey,  quoted in Allure,  June 2012
·Our minds are constantly in the past or the future—we'll ruminate on what's too late to change or catastrophize about what hasn't happened yet.
 —Diana Winston,  quoted in O, The Oprah Magazine,  1 Feb. 2013
·This meal needed to be special. Special and kosher. With this in mind, I began to catastrophize: What if I screwed the whole thing up? What if I unknowingly broke a rule of kashrut, effectively tainting the whole meal and ruining the start to the holiday season?
 —Gabi Moskowitz,  City Paper,  3 Oct. 2012
·Learning not to catastrophize and to think more helpful and truthful thoughts can bring down stress …
 —Mary Jean Porter,  Pueblo (Colorado) Chieftain,  13 Nov. 2012 (https://www.merriam-webster.com/dictionary/catastrophize)                                                                                or even Definition of denouement (within the vein of your personal experiences in regard to dating...certainly NOT involving fatalities)
1 : the final outcome of the main dramatic complication in a literary work ·In the denouement, the two lovers commit suicide.
2 : the outcome of a complex sequence of events (https://www.merriam-webster.com/dictionary/denouement)                                                                                And yet, the notion is more anchored in a certainty how 'fleeting' all things involving 'time' itself tend to be...nothing on earth lasts forever; so, at the end of this matter, a 'moral-of-the-story' would be to embrace the temporary for all it's worth for "Whereas ye know not what shall be on the morrow. For what is your life? It is even a vapour, that appeareth for a little time, and then vanisheth away." James 4:14
Answer: Anticipatory grief Wikipedia refers to a grief reaction that occurs before an impending loss or event. Typically, the impending loss is death but can be from non-death-related losses such as you describe.
Better may be Saudade a mass noun. Oxford English Your mention of sadness during a happy time (dating your to be husband) led me to this word.

It's the feeling of longing, of joy, of nostalgia, of yearning, of
  belonging, of dreaming, of desire.

And it can occur before during or after life's event(s):
From this blog: a blog

This [saudade] is what I feel in this moment, in anticipation of my first
  river trip of the season.
This [saudade] is what sinks me deep into myself every single fall, when I put
  my paddle away for the [end] season.
It's [saudade] the feeling that brings me to tears as I sit on this airplane
  next to my amazing husband.
Saudade isn't a sad feeling, exactly, although it brings me to tears as  often as it brings me to joy.

A word for mourning future endings/loss


Where on a Linux file system should someone put media intended to be accessible by all user accounts?

Question: If I have photos, mp3s, books and other miscellaneous stuff that I want all users to able to access from a common directory, where on a Linux file system should I put that directory? In /usr/share, or just in /usr, or create a new top-level directory instead?
Answer: I usually put this in /home/media, I create a media unix group that owns it with a setgid bit.
As root, or using sudo:
groupadd media
mkdir -p /home/media
chown -R root.media /home/media
chmod g+s /home/media

Then I put each user that needs to access these data in the media group.
You could also use ACLs to manage each user's right for the directory.
You could also use /srv/media if you prefer, but I like home for shared documents. Anything in /usr is to be avoided for this unless you're talking about static files.
Comment: /srv is the place recommended by the FHS: "site-specific data which is served by this system."
Comment: or `/opt` or `/some-madeup-term` (my personal fave: `/middleearth`).  `/usr/local` (or even `/usr/local/shared`) would be OK, but not ideal.  i dislike `/home` for this purpose because `/home` is for user directories, and i consider data files outside the scope.  on a true multiuser installation, tho, it's probably more appropriate.
Comment: I agree with most of your comments. However, I don't agree with `/usr/local`, which is a subsection of `/usr`, which imo is dedicated to static, read-only data. `/usr/local` is more likely to contain locally compiled programs or administration scripts.

As for `/srv`, I listed it because it seems like the best place according to the FHS, but then it's for data "served by this system". To me, photos, mp3, etc on a desktop are more of user data, which belong to `/home`. They're not really "served" by the machine so to say.
Comment: `/usr/local/shared` is not listed in the FHS, but there is `/usr/local/share` which is the local equivalent of `/usr/share`, which contains static files used by programs that do not belong in `/usr/lib`, so it's definitely not a good place for varying data such as user documents imo.
Comment: `share` is what i meant, oops.  it depends on the data and the usage -- on my home server, i handle most of the content generation, my user owns the files, but i want them accessible via network shares.  putting everything under `/middleearth` (or `/srv`) allows me to create the Samba shares without letting Samba anywhere near my user's home directory.  it's useful for my use case.  in a multiuser system, you centralize the data for the same reason -- so you can give users 1, 2, & 3 access to the data without letting them into eachother's home directories.
Comment: Why not add write permissions to the directory? At least on my machine (Ubuntu 15.10), the folder is given write permissions to the user that created it (which has to be root), but no one else. Speaking of that, you may want to specify you need `su` or `sudo` to execute all these commands.
Answer: I use /av - it's nice and short so it's easy to type.
FHS compliance is not an issue. FHS is a standard for your distribution and applications to follow. A distribution or application should never create a top-level directory, but as a user and system administrator, the filesystem namespace is yours to use as you wish.
Putting it in /home is a bad idea, as that directory is for home directories. Your shared media directory is not a home directory. Consider that if you use /home/media and later need to create a user called 'media'.
Similarly, avoid directories that are managed by your distribution. /usr/share/media is a bad idea, since a package in your distribution might well use that path.
/usr/local, /opt and /srv are defined places where you have control of the namespace underneath, but /opt is usually for application directories and /srv for data that the host is serving up. /usr/local/share may be appropriate, but that's just too long a path for my liking.
Above all, remember it's your filesystem so there's nothing wrong with creating a new top-level directory.
Comment: amen brothah man.  as i mentioned earlier, i use `/middleearth`, as it's memorable, but i do symlink to `/me` for a handy shortcut.
Answer: <mode=pedant>
According to the Filesystem Hierarchy Standard, /usr is for "shareable, read-only data"; /usr/share is for "read-only architecture independent data files. ... for example, a site with i386, Alpha, and PPC platforms might maintain a single /usr/share directory that is centrally-mounted"
So yes, a subdirectory of /usr/share seems like an appropriate choice.
</mode>
<mode=pragmatist>
Less pedantically, /home (as suggested by raphink) seems like a good choice. You probably have /home on its own partition, both so that you can easily blow away the rest of the OS without touching user data (eg, when doing an upgrade or reinstall) and for ease of backup (as everything you care to back up is stored under /home), and for space management reasons (on most home boxes, the partition with /home ends up being the one that runs out of space first).
</mode>
Comment: I wouldn't consider photos and mp3s to be read-only files. I tend to edit my photos quite often ;-)
Comment: And videos might have a habit of disappearing after they've been watched once or twice... and most media library programs (I'm thinking of iTunes, but f-spot does something similar, and I bet rhthymbox and songbird do as well) will have some kind of database with play count information and so on - and that definitely doesn't belong under /usr. /home seems like a sensible choice, even if it's not strictly FHS-compliant.


IRC Bots Behind HTTP Proxies

Question: I'm trying to run an IRC bot in a Debian based server. Its behind a HTTP proxy, so, I need to 'export http_proxy' for normal usage. The problem I'm facing with the bot is that, as far as I know it doesn't support proxies. Anyway to make the HTTP proxy transparent to the program, something like tsocks?
Answer: Try proxychains. It behaves much like tsocks, but works better (on my laptop Opera worked with proxychains, but not with tsocks) and supports HTTP proxies. And, of course, your proxy should support and allow HTTP CONNECT method.

IRC Bots Behind HTTP Proxies


Photodiode in photovoltaic mode, overcoming saturation

Question: can anyone explain to me why moving to configuration (b) overcame the problems I was having with the photodiode saturating?
Many thanks,
John
Answer: In photovoltaic mode, you are measuring the short circuit current produced by the diode.  Ideally, that means you present it with 0 impedance (the short circuit).  B works better than A since 1 Ω is closer to 0 than 50 Ω is.
The usual way to do this is with a active circuit that keeps the voltage across the diode at 0 while creating a voltage signal proportional to the diode current.  Put another way, this is done with a transimpedance amplifier with 0 input voltage:

When the photodiode is illumnated, it will produce reverse current.  The direction of that current is down in the schematic above.  The opamp will drive the right side of R1 to whatever it takes to null out the voltage on its negative input, since the positive input is connected to 0 V.  The result is that the opamp output voltage is proportional to the current thru the diode, with R1 being the proportionality constant.  For example, if R1 were 100 kΩ, then the gain of this circuit is 100 kΩ, which could be expressed as 100 mV per microamp.
Answer: Current flows across the photodiode from cathode to anode: potential is built up against the forward conduction direction of the diode, this is what actually gives you saturation. The answer from @krufra is wrong.
In this 'photovoltaic' mode charge builds up across the diode like a capacitor and is dissipated across your 50 Ω resistor (case A). The responsively drops as more light is incident. You can think of it as the electrons having to do more and more work charge is built up, the diode responds less as the voltage builds.
In case B you have simply lowered the resistor value making it easier for charge to flow away from the anode.  With less of a potential build up across the diode then you would expect to see less of a non-linear drop off of the diodes responsively to light. I'd imaging that your second circuit might product a lot less signal.
The best way of getting linear (voltage proportional to amount of light) that doesn't saturate is by using a transimpedance amplifier. This can be relatively cheap with modern op amps. Olin's answer is mostly right but photovoltaic mode is when the diode is hooked up so that it develops a voltage across some resistive element where as photoconductive mode is when it is configured (with a transimpedance amplifier) to see 0 Ω resistance across its output.
Answer: Because Si junction has 0.6 V knee and is in parallel to the current source represented by photons reaching the PN junction. So if the voltage drop on the 50 ohm resistor caused by current generated by photons is greater than 0.6 V the parallel diode begins to conduct and seems that saturation is reached. When you place a 1 ohm resistor the maximum illumination can be 50 times greater before 0.6 V is reached.


How do I use my flak guns?

Question: I purchased some flak guns for my ship and they are supposedly good against fighters and missiles.  However when I shoot them they seem to just head straight out the sides of my ship not really aimed at anything.  How do I actually hit an incoming missile with them?
Answer: It is possible to orient the ship so that the the flak explosions destroy the incoming rockets, but in the heat of the battle its much more realistic to just keep spamming the secondary and hope it hits something. The ammo of for the Flak secondary is unlimited and the fire rate is rather high, so you can just keep the secondary fire button pressed during a whole battle, also because the flak projectiles explode, you don't need pinpoint accuracy.
There is not much you can do against incoming missiles, your best option is a good deflector. There is also an Ordnance Targeting subsystem, that lets you manually target incoming torpedoes and mines (with turrets), but trying to hunt down missiles one-by-one in a battle is just suicide, it's only useful in less hectic situations, like clearing minefields.
Answer: I found the flak cannons to be completely ineffective against torpedos and mines, however the energy absorbing deflectors work well enough as a countermeasure to these.
When dealing with ordinary missiles, flak seems to be most effective whilst your ship is at full speed and most importantly steering away from a broadside encounter.
Try to position your ship so that the missiles are not directly behind you but just offset to the rear, as when you are in motion this puts more flak fire directly in the path of missiles.
The exact angle differs per ship but as you look behind you, you'll be able to see where the flak is exploding and adjust the the angle to keep missile trajectory running through the same area.

How do I use my flak guns?


Set a trap up / set up a trap

Question: are both phrases correct? E.g.
She set a trap up for her brothet-in-law.
He set up a trap in secret.
Comment: Or you could just say "set a trap". The "up" is not required.
Answer: I believe, it's a separable phrasal verb, so you could say both without changing the meaning, so I would say both are correct. A lot of phrasal verbs with two parts are separable and without changing the meaning. E.g. I picked my wife up from the airport. I picked up my wife from the airport. Or: I took my wife out to dinner. I took out my wife to dinner.
If the object is a pronoun though, then it must go between the parts of the phrasal verb. E.g. She set it (the trap) up. NOT: She set up it (the trap.)
This whole spiel only applies to two part phrasal verbs with objects though.
ALSO, set a trap means you prepare it to be sprung, whereas set up a trap is to set up the trap "mechanism" from scratch. The meaning often overlaps though.
Comment: Right. The technical term for this spiel is ["Particle Shift"](https://english.stackexchange.com/a/168764/15299). It allows shifting of the particle to go after a noun object, but not after a pronoun object.

Set a trap up / set up a trap