Regarding SEO, is there difference between em and i, strong and b tags

Question: HTML tags, strong and b tags result visually same to bold, em and i tags for italic.
Does the search engines or browsers treat them differently or give priority one on another?

What to alternate tag should be used?
Comment: You should style you text for users, not for search engines.
Answer: Short answer, probably not
Matt Cutts of Google has said that strong and b originally had no affect on your SEO and that his opinion is that of 2013, they still didn't. Matt Cutts and  vs
When to use  vs
According to SEO Ability you should always use strong for text you want to emphasize content, but use for visual enhancements.

The difference between the two HTML tags is that bold makes text only
visually look bold, while strong also semantically emphasizes the
respective text as important and indicates that it is a meaningful
word or text section.

They continue and say:

If you want to highlight a text section as important in terms of
content, you should always use strong. You should only use bold if you
intend a purely optical highlighting, e.g. you want to visually
highlight a link or navigation bar from the rest of your page to make
the page look clearer
Comment: @Rob, you are correct, about bold.  My freudian slip.  In any case, the SO was asking about the SEO impact, not necessarily if one should separate application from presentation.
Comment: There is no such thing as ``. In any case, HTML should never be used for visual presentation. Use CSS instead and, rather than following some SEO site, [use the standard](https://html.spec.whatwg.org/dev/text-level-semantics.html#the-b-element) instead for guidance on usage.
Answer: HTML elements strong and em are the semantic elements of the current HTML5 standard. Check the description that this standard gives for the strong element:

The strong element represents strong importance, seriousness, or
urgency for its contents.

and for the em element:

The em element represents stress emphasis of its contents.

In turn, HTML elements b and i have no semantic meaning, which is clearly indicated by the current HTML5 standard (to b):

The b element represents a span of text to which attention is being
drawn for utilitarian purposes without conveying any extra importance
and with no implication of an alternate voice or mood...

and to i:

The i element represents a span of text in an alternate voice or mood,
or otherwise offset from the normal prose in a manner indicating a
different quality of text...

Mozilla also quite clearly defines the difference between these elements::

Do not confuse the  element with the , , or
elements. The  element represents text of certain importance,
 puts some emphasis on the text and the  element represents
text of certain relevance. The  element doesn't convey such special
semantic information; use it only when no others fit.

My answer to your question: Semantic elements (as opposed to non-semantic ones) can help in the accessibility of content in accordance with WAI-ARIA technology. Also, semantic elements can help search bots to understand the content of web pages in more detail, and these elements can be useful for voice search and for the Text To Speech technique. The use of semantic elements can help search engine optimization, but their importance to SEO depends on the search algorithm of each search engine.


Keep GUI from running at boot in Raspbian?

Question: I started running my Raspberry Pi with a monitor and keyboard, but I ended up decapitating it and don't need the GUI running anymore. How do I make it not start at boot?
Comment: What OS are you running? Assuming you are running a recent version of Raspbian you can run sudo raspi-config and select boot options from the menu and then console.
Comment: @SteveRobillard Thanks. Will the GUI still run in the background though?
Comment: No, you have to manually start it with startx, you can verify that by running the followinf ps aux it will show all the running processes no matter who owns the process
Answer: As suggested by steve use raspi-config for setting up the GUI.
Steps
1. on the prompt type
<code>sudo raspi-config
</code>

Step 2 Select the option highlighted "Boot Option"

Step 3 Based on your need select "Option B1/ Option B2".

Step 4 - Click on finish and the prompt will ask for system Reboot. The system will boot to console from now on.


Is it possible to back up network devices configs on a RADIUS server (automatically or manual)

Question: My question is about back up on RADIUS server. Is it possible to back up network devices configs on a RADIUS server (automatically or manual)
Comment: Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
Answer: Radius is a networking protocol, aimed at  Authentication, Authorization, and Accounting.
It is not designed to backup configurations.
Now a device that can act as a Radius server may be able to perform other roles, like a FTP server on which a network device can backup is config, especially if you radius server is Linux or Windows machine. But this has nothing to do with Radius itself. It would be two different services that happen to be hosted on the same device.
Comment: It's worth noting that it is common to use the same server for the two purposes (RADIUS, backups), if only because that server already has confidential data on it, and the backups of that server need to be kept confidential.


I'm getting 500 errors when working with Blocks

Question: I've got a site that uses Blocks pretty extensively throughout. Up until a few weeks ago, everything was functioning nominally. But recently, trying to save entries that contain more than just a few block types always produces a 500 server error. Needless to say, this makes it nearly impossible to update key sections of the site.
At first, I thought it might be an issue with some of the more complicated blocks that contain lots of fields (e.g., relationship fields), but further tests revealed that it doesn't seem to matter how complicated the blocks are. Adding even 3-4 blocks that just contain basic text fields can result in 500 errors more often than not.
We've reached out to the hosting provider but they haven't been much help. We could always beef up our hosting service (i.e., shell out more money for a more powerful server), but my fear is that would just be a band-aid, and this problem will raise its head again down the line.
Any ideas? Has anyone else run into similar issues with Blocks?
FWIW, the site in question is running on EE 2.11.7 and Blocks 1.4.3 (the most recent versions).
Answer: It looks like this was caused by our site running on an older version of PHP. Upgrading to a more recent version seems to have done the trick.


Can you wear padded armor under chainmail with plate armor over it?

Question: I mean realistically, historically, and definitely reasonably speaking, mail has been worn over a gambeson with plate armor over them for extra protection and doesn't hinder movement. So i mean how would that work if i wanted to do that? Any rules against it in d&d 5th edition?
Comment: Isn't this the same as [**Combining various AC-providing clothing and armor**](https://rpg.stackexchange.com/q/57309/33742)? Possibly combined with a quick read of PHB 145.
Answer: A suit of armor in the game comes with all the necessary plates, layers, and accessories. If you wear chain mail or plate armor, that explicitly includes the gambeson underlayer:

"...chain mail includes a layer of quilted fabric worn underneath the mail to prevent chafing and to cushion the impact of blows."
"A suit of plate includes ... thick layers of padding underneath the armor."

-PHB, p145
You don't have to buy padding separately, and you can't add an additional padded armor layer for additional defense.
Answer: What makes you think the mail does not have padding beneath it?
Mail without padding leaves you removing metal rings out of your flesh, and chaffs worse then sandpaper.
Full plate, and half plate both always have padding underneath them.
Scale Mail as well.
As the proud owner of a hand made chain mail coif, you always wear padding under your mail. Always.
Finally,  there was a period where plate over mail and padding existed, a brief period of time,  then they got smart and relized that any blow that could kill someone wearing plate killed then regardless of the chain mail. (Not counting the protecting the chainmail provided to the joints)
Because weapons kill people in plate harness via concusive force,  not by piercing thru the plate ( unless you have a 800+ pounds horse giving power to your lance).
They then just made small pieces of Chainmail sewn to the padding at critical points.
And the padding worn under plate harness is not as thick as a gamberson, as that would have drastically restricted mobility, increased weight, and made those wearing it die from heat exaustion during winter (minor exageration).
And from a mechanical standpoint of 5e.
5e relies on bounded accuracy. Anything that gives an extra point of ac here or there is potentially balance breaking, a magic +1 chain mail coats 1000s of gp.
Anything that gives bonuses should be looked at with extreme caution.
So not only should your chainmail already have padding, though not as thick as a gambisen, it would make the game less challenging,  ergo less fun.
You are adding a bonus by spending a couple of gp, a bonus that should cost 100 times that, and might not ever happen (DM fiat).
Comment: Thanks for clarifying, i was confused on whether or not it accounted for that


Drobo doesn't power up after Windows7 hibernation

Question: I am using a Drobo on a 64bit Windows7 Professional system. Often, when waking from hibernate mode, the Drobo doesn't power up. I have the latest (1.3.7) firmware in the Drobo.
Anyone know of a fix?
Comment: How is the Drobo connected to the PC? USB? Edit your original question to include this new information, the model number of the Drobo also.
Answer: (from drobo's website)
If your Drobo device is a Drobo FS, Drobo S, DroboPro or DroboElite, you can change the spin down time. In Drobo Dashboard, click Advanced Controls -> Tools -> Settings. Under the General tab, you will see the Disk Drive Spin Down slider. You can set this to best suit your needs. On DroboElite, the default is Never. On the other Drobo products that include this feature, the default is 15 minutes.
Note: Drobo employs this life-prolonging feature whether or not it is directly connected to a host computer or uses DroboShare.
Mac users have reported this same thing happening -  like Moab suggested - let us know the model number and connection type for better trouble shooting


What is a reasonable isolation voltage for an optocoupler/digital isolator?

Question: I need to isolate an input from my processor. What is a reasonable isolation voltage to look for optocoupler/digital isolator? I've pretty much decided to go with an RF isolator at this point because they use much less power and are easier to implement that traditional optocouplers. Also - from what I've read, I need a DC/DC converter with isolation to make sure there is an isolated power/ground for the isolated side of the isolator. Does this sound right?
Comment: It does sound right.  However, why do you want to have galvanic isolation in the first place?  There is no *universally reasonable* voltage rating for galvanic isolation.  The rating is determined by the application.  Either some standard dictates the isolation rating (e.g. 4 kV rms for patient isolation in medical devices).  Or, the high voltage threat dictates the isolation rating.
Comment: Basically there are two cases I'm worried about - 1) user putting in wrong voltage by accident (my thought is this is the main concern) and 2) power spikes caused by lighting hitting connected equipment.
Comment: I know most human ESD models are 10kV to 15kV for ESD resistance testing - I'm not really worried about this. I just want isolation from noise and over-voltage, possibly surges on external equipment.
Comment: As  Nick says - in some cases a standard sets the required minimum. Abset that, 1000V is "low" but will work in practice in most cases. 2000V+ is usually adequate. Note that in extreme cases it is not JUST isolation per se that counts. eg coupled dV/dT can cause triggering of devices if rise times are fast enough. This is not usually an issue.
Comment: On the same note - for isolating the power supply with a DC/DC converter - is it sufficient for the converter to match or exceed the isolator value or is there some math to do?
Comment: Isolated dc to dc converters may not do what you actually want because there is a possibility that the so-called isolated output will have small EMC capacitors on its output to input. I've seen this on one or two and this may still pose a problem for you.
Answer: If you want isolation from the mains you'll need 1000 to 2000 V isolation voltage. Most optocouplers will provide this. Just keep an eye on the pinning: a standard DIL package with standard pads won't give you the required 6mm clearance. You'll find packages with the rows of pins further apart:
Answer: It does sound right.
There is no universally reasonable voltage rating for galvanic isolation. The rating is determined by the application. Either some standard dictates the isolation rating (e.g. 4 kV rms for patient isolation in medical devices). Or, the high voltage threat dictates the isolation rating.
Threat 1.  User applying wrong voltage.  Take the highest wrong voltage that the user may possibly apply (e.g. 380 V rms) and add 1 kV rms.
Threat 2.  Lightning strike.  The trick is to use gas discharge tubes (GDT), which would shunt the lightning strike into the earth ground.  GDT take care of the bulk of the energy, of the lightning strike.  Add some TVS Zeners in parallel with the GDT.
Comment: So basically if it seems like it'd be uncommon for a lightning strike to affect this device then the lightning solutions comes at unjustifiable expense.
Comment: @Pugz  It's your decision to make.  Hazard-vulnerability-impact assessment is yours to make too.  You could check what the UL standards say about lightning protection for your type of device.


Relation between projective hierarchy and universally measurable sets

Question: Let $X$ be Polish. It is known that every analytic and coanalytic subset of $X$ is universally measurable. The Wikipedia article about universally measurable sets notes that (assuming projective determinance) every set in the projective hierarchy is universally measurable. Are there also universally measurable sets that are not related to the projective hierarchy, i.e. can not be constructed in this way?
Answer: Under the continuum hypothesis, or even just when
$2^{\aleph_0}<2^{\aleph_1}$, there must be universally measurable
sets that are not projective. The reason is that Hausdorff proved
that there are always universally null sets of size $\aleph_1$,
and since any subset of such a set is also universally null and
hence universally measureable, it follows that in ZFC there are at
least $2^{\aleph_1}$ many universally measurable sets of reals.
But there are only continuum many (boldface) projective sets. So
under CH and more generally if the continuum is less than $2^{\aleph_1}$, there must be universally
measurable sets that are not projective.
The following article seems to have a lot of information:
Paul Larson, Itay Neeman, and Saharon Shelah, Universally measurable sets in generic extensions, Fund. Math. 208 (2010), no. 2, 173--192.
Another way to argue is this: if there is a universally null set of size continuum (and this follows from CH by Hausdorff's argument), then all subsets of it will also be universally null and hence universally measurable, which give $2^{\frak c}$ many universally null sets. But there are only continuum many (boldface) projective sets. So in this case, there must be universally null sets that are not projective.
Comment: I think of the projective sets in terms of an $\omega$ hierarchy, taking projections and complements, rather than an $\omega_1$-hierarchy. Alternatively, one may think of the defining formulas, of which there are only countably many. If one allows real parameters, this gives continuum many boldface projective sets.
Comment: Thank you. I haven't thought about the fact that the projective hierarchy defines at most countably many new sets in each stage of the construction (similarly to the Borel hierarchy). Since the induction runs up to $\omega_1$ stages, there are only countably many projective sets.
Comment: Oh yes, of course: replace "countably many" by "continuum many" (which doesn't change your computations). It is really interesting to see the huge gap between the definable sets (projective hierarchy, defined from "inner" by unions) and the universally measurable sets (defined from "outer" by cutting, i.e. intersections of $\sigma$-algebras).
Answer: Thanks, Joel, for mentioning our paper.
By Martin-Steel, if there exist infinitely many Woodin cardinals, then every uncountable projective set contains a perfect set, so, by the result of Hausdorff mentioned by Joel there are universally null sets which are not projective.
On the other hand, it is apparently an open question whether it is consistent for all universally measurable sets to be $\Delta^{1}_{2}$ (see problem CG on Fremlin's list : https://www.essex.ac.uk/maths/people/fremlin/problems.pdf).
Finally, I should mention two improvements of Hausdorff's theorem :
(Reclaw) Any set of reals which is wellordered by a universally measurable relation is universally null (https://projecteuclid.org/download/pdf_1/euclid.rae/1212763971)
(Grzegorek) There is a universally null set whose cardinality is the smallest cardinality of a non-Lebesgue-null set. A proof of this can be found in Bukovsky's book (http://www.springer.com/gp/book/9783034800051)


Docker PULL stellar/quickstart error

Question: When I try pulling the Stellar image from the UNIX server with the command: '$docker pull stellar/quickstart' I get the error message : Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?. What should I do to get the docker daemon running - or, can I 'pull' it from somewhere else? ...many thanks!
Answer: type this command to check if your docker is running

sudo systemctl status docker

output should look like this if it is running

● docker.service - Docker Application Container Engine
Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor p
Active: active (running) since Tue 2019-07-02 11:28:40 UTC; 15min ago
<code>Docs: https://docs.docker.com
</code>
Main PID: 11911 (dockerd)
Tasks: 10
     CGroup: /system.slice/docker.service

Docker PULL stellar/quickstart error


Did the cross permanently affect the intra-trinitarian relationship?

Question: I have heard a religious definition of death as separation from God. This makes the death of Christ--God himself--a matter of incomprehensible existential crisis. Adding to this the imputation of sin on the Son, and the wrath of the Father poured out on him, it makes me wonder if this event does not affect the relationship of the members of the trinity in some permanent way. Is there any evidence of this in scripture?
Comment: Upvoted. I'm tempted to create multiple accounts just so I can upvote this more. I never even thought about this question. I hope someone answers it (and other readers upvote so the question bubbles to the top).
Comment: Interesting question. I would have to agree about the [death being separation](http://christianity.stackexchange.com/a/1707/30) thing, and that Christs death did indeed separate him in some sense from the Father, hence his call about "Why have you forsaken me?". in fact I think he experienced spiritual death (separation from God) prior to his physical death (separation from his mortal body). However with the reasoning you pose, wouldn't there be a conflict with God's immutability? Of course there must be an effect, but we cannot understand it as a permanent change to his internal character.
Comment: That's a good counter-argument. It seems like sound reasoning that it would contradict immutability (which is not without scriptural support itself), but I could potentially be convinced either way. It might be useful if you could expand on that to counter Affable Geek's position.
Comment: This is one of those questions that makes me doubt the trinity. If all three are equal why was the Son offered not the Father? If both are equally important why does the separation make the son cry "why have you forsaken me". The father would've been just as much forsaken. Anyway great question. It definitely gets me to think a lot of things.
Answer: Phillippians 2 says that because of Jesus' death, God the Father exalted Jesus. As 2:9 specifically says (and note the therefore):

Therefore God exalted him to the highest place
      and gave him the name that is above every name,
   that at the name of Jesus every knee should bow,
      in heaven and on earth and under the earth,

This theme is picked up by Athanasius, in De Incarnacione. His soteriology says our redemption was a gift that the Father gave the Son for his willingness to go through this separation. It's probably my favorite theory of how salvation works. The idea is that being God, both God the Father and God the Son already had everything. But out of an abundance of love, God the Father gave God the Son the opportunity to redeem that which was lost.
Answer: I have never thought about it that way.  Here is my view:
The idea of separation is the loss of fellowship and peace due to sin. Christ, as a man lost this peace and fellowship from God when becoming sin for us, but as God he lost nothing and can never loose anything. As God, Christ could endure the whole weight of sin, which as a man he never could have. As God he could bring the human soul and body back up from the separation.  I see no temporary or permanent change in the Son with the Father. This was human nature taking the punishment of human sin, but as God this could not destroy the God-Man. The result of this work was the exaltation of the human nature of Christ into his glorious kingdom. The Eternal Son was not exalted, per se, as God can't be made higher than He eternally is.
I think the immutability of God is the controlling idea here.


peltier cooler heatsink

Question: I am modifying a small cooler (mini fridge) that uses a Peltier cell. The cold side of the Peltier cell is in contact with the inside surface of the mini fridge. My question is: will gluing (with thermal paste) a heatsink on the mini fridge internal surface increase the cooling power of the mini fridge? Thanks
Comment: *If* the hot side of the Peltier device doesn't have a fan blowing air (preferably up) over its heatsink, adding one could make a significant improvement. It only needs a gentle forced airflow, so a fan run at low RPMs to keep it quiet would suffice.
Comment: Have been discussed earlier in a little bit different setting.  https://electronics.stackexchange.com/questions/112712/why-peltier-elements-have-smaller-heatsink-on-cold-side
Answer: Power is a difficult word here. A heatsink will not directly change the amount of thermal energy the peltier device can transport (from hot to cold side). It will, however, enhance the distribution of the thermal energy (i.e. cooling) in the fridge. Therefore, a controller (if the fridge has one) will be able to more often use the most efficient operating point of the peltier device and thus reduce the time to (re)reach the desired temperature. But wether you actually notice an effect depends a) on the isolation of the fridge and b) on wether temperature distribution inside the fridge matters to you.
My recommendation: Try it. Nothing bad can happen and you might see an effect.
Comment: Something "bad" could happen, actually. A turned off Peltier Element is just a very thermally conductive piece of metal. So if it makes the cooler overshoot, it may then also warm up quicker while the element is turned off, increasing the thermal ripple inside, which may be harmful to some food stuffs. Depends on the controller. Though a try will surely proof the effects given some measurement tools.
Comment: @Asmyldof So, thermal paste rather than thermal adhesive (in case the latter is what the OP was intending) would be better for the testing phase.
Comment: @AndrewMorton I would say that would be the advise even without my note. Especially when one does not (yet) know the control behaviour.
Answer: Most peltier-elements that I have seen, have a rated max difference between the hot and the cold side. I've seen alot in the ~70-100W range rated around ~70 degrees Celcius.
That means the cold side will be ~60-70 degrees colder than the warm side - so the cooler you can keep the warm side, the colder you'll get :)
Simplified example:
Hot side is kept at approximately 60 degrees => cold side can get down to 0 to -10 degrees C (depending on the rated temperature-delta).
If adding a heat sink or a fan increases total heat dissipation, it should help cool down the fridge :)
EDIT:
Just saw that you wanted to put the heatsink INSIDE the cooler - that most likely won't do anything. You need to lower the temperature of the hot side of the peltier in order to lower the cool side as well.
Answer: If it were that easy, the fridge mfr would have already done it. As mentioned, the heat sink size is selected based on a delicate balance of cooling effectiveness when on vs heat transfer when off. Increasing in on the cold side would just mean that when off, the sink will conduct heat back into the fridge faster. So ultimately it results in your Peltier element running more often to get the same net effect and may actually WASTE energy.
Comment: Two other reasons the fridge OEM might not add an internal heatsink: it would detract from the otherwise smooth interior, and it would add to the cost.

peltier cooler heatsink


Hard to shift into first and reverse, and weird noises

Question: I have a 2000 Honda Civic, and I've been having some issues with it.
It is very tough to shift into first, and sometimes when I shift into reverse I can hear the gears grinding and the car lurches a little, even when the car is not moving forward even a little. Another problem is that when the clutch is not pushed in, and I'm just stopped, I can hear a noise that just sounds like a crappy old fan or something, kinda just a buzzing. But when I push in the clutch it goes away. I think it might be the transmission or clutch fluid, or a bad part in the transmission but honestly I don't know much about cars. What is wrong with it?
Comment: Sounds like a throw-out bearing.
Comment: Are you sure you put in the clutch all the way?
Answer: It sounds like possibly a worn out clutch.
On vehicles with with self-adjusting hydraulic mechanisms (which I think the 2000 Civic has) as the clutch wears out the mechanism will 'tighten up' so that there is less travel as you press the pedal, up to a point where the clutch does not fully disengage and would exhibit the symptoms that you have mentioned.
This is the opposite to vehicles with traditional cable mechanisms which would experience slipping of a worn clutch unless a manual adjustment is made. The hydraulic mechanisms avoid this slipping.
Answer: Clutches disengage when you press the foot pedal; the energy of your foot moving is transmitted to the clutch either through a mechanical mechanism, or a hydraulic connection. Difficulty in engaging gears can result from the clutch's failure to disengage. This can be caused by misadjustment of the mechanical mechanism, or a leaky or otherwise faulty hydraulic connection.


How to improvise a pair of tweezers in the wild?

Question: From slivers caused by chopping wood, thorns from plants, or bee stings there have been times when out in the woods when a pair of tweezers would come in handy and none where on hand.  Are there are materials found in the outdoors that could be used to remove such foreign objects embedded in ones skin when fingernails and teeth will not do the trick?
Comment: I'm not sure you would get the accuracy with most natural items - but there are plenty of craft ways to make tweezers (lollipops for use like chopsticks) though that could apply to an outdoors technique. Handy on a pen knife though if you've got one.
Comment: I would just use my knife.  If you don't have a knife highly unlikely you could craft some tweezers.
Comment: @paparazzo the same skills for [making a stone axe](https://outdoors.stackexchange.com/questions/14963/how-do-you-make-a-stone-axe) will let youi make a knife.  Make the tools to make the tools....
Comment: @JamesJenkins I will hold with highly unlikely.  And I would never be in the wilderness without a knife.
Comment: For slivers + thorns I often prefer a needle over tweezers => another thorn may help?
Comment: If you get a sliver, perhaps you could attach together some very small cut pieces of wood, then you can use the wood tweezers to try to remove the sliver. Then, when you end up another sliver, you could attach some very small cut pieces of wood and use the wood tweezers to...
Comment: Not trying to be snarky, but the best advice I can offer is to always, always carry a multi-tool knife.  Of course, you could lose it half-way through the trip....
Answer: I've used bamboo tweezers before.  They're normally made by gluing two flat pieces of bamboo togther with a wedge in between, but with skill and suitable thread you could lash the blades together with a wooden wedge.  They can take a surprisingly sharp point or edge, but it wears fast.
However you'd need a knife to make them. The chances are if I had a knife I'd have tweezers, given that all my penknives, even my keyring one have tweezers. I always have at least that keyring knife on me, but rarely have another sort of knife -- and if I do, I've probably got a first aid kit with tweezers!
You also need a source of bamboo, which isn't exactly common in the wild in many countries.  It might be possible to use wood but you'd need one that's both reasonably hard (to get an edge) and fairly flexible.  Ash might work, perhaps starting from a fork in a branch.
Edit: I've had a little play with my last suggestion of (green) ash. Starting with a fork of twigs about 8mm in diameter a few minutes of whittling gave me tweezers that were capable of picking up a single hair. They were a little stiff and in trying to make them more flexible I broke the joint, but not right through. This was actually an improvement. Not having a splinter or sting for testing, I managed to pluck a couple of hairs. The tips could do with being harder - a little heat would help and even a few hours drying made a big difference. While I used secateurs for the initial cuts (I was in my own garden) the shaping was all done using a small sheath knife.

tools/materials

the first version, a little stiff to hold steady (with my left hand that's recovering from an injury)

The final version; after breaking the outside of one half and reshaping the tips these tweezers pluck hairs successfully.  They'd certainly do thorns and would be as good as many first aid kit tweezers for splinters (which is to say not great, and not as good as Victorinox)
Answer: Thread is often used for plucking eyebrow hair - perhaps this would work on slivers too. Assuming you were clothed, you could probably get hold of some thread.
You can view a great guide with text and video at https://www.wikihow.com/Thread-Your-Eyebrows
Comment: Seems like this is really a thing, can you include some detail on how to do it?  Assume I have downloaded the website TGO to my phone, and your answer is all I have to go on.  I don't have internet, just a copy of the web site.


An easy method to align a two layer PCB

Question: When I prepare a double layer DIY PCB using Press-n-Peel I have a problem aligning the bottom and top layer so that the holes and vias match on the copper between layers. Can you suggest any easy method that would minimize the wrong alignment?
Answer: Not easy, but I use an involved method that uses "alignment pins" to get perfect alignment every time.  This works very well with the toner transfer and photo paper method and might work for press and peel as well.

Dot the edges of your layout with evenly spaced pads used for alignment holes. 3 - 4 per side is sufficient.  You may need to distribute more into the center as well if the board is largish.  Use really small drill holes in the pads, so that you can accurately find the center.
Print the two sides to your transfer paper and make an additional copy with just the alignment holes.
Transfer the alignment holes to your board and use this as a guide to drill holes.  As an alternative, you could tape a normal paper copy of the holes to the board and use that as the guide.  But, I think it's more accurate to actually transfer it.  The size of holes should just small enough to pass pins or component leads through.  I like to use 18mil bits and use clipped off resistor leads as the alignment pins that I collect from previous projects.
After drilling, remove the toner by sanding or acetone.  You should be left with the bare copper again and drilled holes.
Drill out the two transfer paper layout sides with the same bit.  Note, I hand drill both the board and transfer paper holes, so that they are perfectly centered.  This can be tedious especially if you use thick boards.
Trim down the two transfer paper layouts sides, so that they are slightly smaller than the board.  This is important because you need to tape them down after the alignment procedure.
Align the two transfers over each side of the board, so that you can pass the alignment pins straight through the set of holes.  Then adjust each pin, so that they are all more or less perpendicular.  This should make everything aligned.  Carefully, tape down both transfer sides to the board securely and finally remove the pins.
Comment: This is great, but note that it may not work to pre-drill *all* of the holes when using photolithography. Drilled holes tend to have a small bump, and this bump lifts the photomask enough to allow UV light under feature edges. Keep the alignment holes well away from all features, and drill the pad holes after both sides have their etch masks (after exposing).
Answer: I have done something similar, it can be done two ways.

Use two points on the pcb as reference points, drill, and align each separately.
Hold both pieces up to the light, get both aligned, and staple or tape end of sheets together so it folds like a notebook.  This requires an extra two inches or so on the end to allow flexing around the end of the board.  Sometimes I also tape it to the board to keep it aligned.
Answer: I use the "envelope method" in conjunction with the toner transfer (ironing version). It is similar to the 2nd method that Erik described in his answer. I like it because it does not require you to drill any holes in the board to make the alignment. It consists of the following steps:

Add registration marks to both sides of your board (top and bottom). I usually place four 150 mil crosses (with 16mil traces) on the corners of the board.
Print both layers of your board on the transfer paper. I print the layers in glossy ink jet paper on a laser printer.
Place the pieces of paper with both layers together, against each other and align the registration marks against a bright light. You'll know the papers are aligned when the bar from the crosses merge with each other. Then you should see that the drill holes in both layers align as well.
Now the tricky part. WITHOUT MOVING the pieces of paper, tape 2 or 3 ends of the paper sheets together, making an envelope. You'll use the end(s) that are not taped to insert the blank board in the next step. If the sheets move, remove the tapes and go back to step 3.
Insert the clean blank board onto the envelope and iron both sides of the board as usual. Take care when started ironing the first side of the board and are about to turn the it around the first time to iron the other side, so that the tapes don't fall apart. The tapes may be molten because of the heat. That happened to me once. The 2nd layer fell off the board while the first had already been transfered. If that happens, scrub the board and start over again.

To help with the process, I also do the following:

I only solder the top layer on vias, never on pads. If I have to move the signal from one layer to the other, I never do it on pads. Instead, I bring the signal from the pad to a via, a few mm away from the pad and move the signal to the other layer there. This way, only the vias have to be carefully aligned between layers.
I design my boards so that its VIAS are as large as possible (usually 70 mil wide, with 20 mil drill holes);

Here's a link to a description of the alignment process that I find helpful. Scroll down to the section Aligning Masks for Double Sided Boards.
Good luck.
Comment: A small addition to this method: when using the toner transfer method, if you print the two sides onto the same sheet with proper clearance (one of them mirrored), then one side of the envelope does not need taping, you simply fold the paper into half. I usually align the PCB into this folding (pushing it as far as possible), then tape both sides of the PCB at one edge to the paper (one of the perpendicular edges next to the folded edge).
Comment: I use Gerber output files, and then `gerbv` to merge, mirror, rotate, etc. the layers and to print the output.
Comment: @Ricardo I export PS (post-script) files from Eagle, import into Photoshop, then arrange them on a 1200-dpi Letter size page.
Comment: @Laszlo That's a good suggestion. I would do that if I could get Eagle to print both layers into the same sheet, one far apart from the other, as you suggested. I've also tried to print twice on the same sheet but the heat from the toner messes up with the second print.
Answer: Include a couple registration marks, or use some vias or through-holes for alignment. Attach one side, drill the holes, then use those holes to align the other side.
In my experience, a typical printer introduces enough distortion that even with the most care, the alignment between the layers can't be really great. For layouts I'll be making in the basement, I make all the pads, traces, and vias as fat as I possibly can to accommodate distortions from the printer, my inaccurate manual drilling, etc.
Answer: My company used to make our own PC boards in-house.  This was back in the early '80s and there weren't any quick-turn PCB fab houses around.  We used DuPont Riston film with a proper laminator and had one of the local graphics houses make our negatives from the 2:1 mylar master artwork.  The sensitised PCB material was held in a glass vacuum frame with the negative sandwiched between the PCB and the glass.
Making double-sided boards was always a trial until we discovered a technique that worked extremely well.  What we did was to make a "L" shape out of un-etched PCB material, tape one negative to both arms of the "L" shape, then flip the whole thing over onto our light table and carefully line up the other negative.  This 2nd negative was then taped only to the long arm.  Because we were using our light table for alignment, we were able to achieve alignment accuracy down to a few (very few) mils.
In using this, we just flip the 2nd negative open, tuck the exposed PCB into the corner of the "L", flip the 2nd negative back down on top of the PCB, then put the whole thing into the glass vacuum frame and expose.  When the exposure was finished, flip the vacuum frame over and expose the other side.
This technique should be directly applicable to toner transfer.
Comment: How did you line up the other negative with the first on the light table? Do you have a photo of the "L" on a board? It's not quite clear to me.
Answer: My first method was to stick each side down onto an L shaped piece of scrap PCB.
That way you remove parallax errors between the layers and can get much better registration.
I now do it as follows:

Heat melt the first side onto the board and remove the backing.
Drill the holes based on registration marks on the PCB.
Register the second side using pins.

This works better since registration of the holes from the first side is absolute. Drill registration errors can be removed when I perforate the second side.
Downside is you have to be careful not to overheat the second side, or you lift / destroy the first side. It won't work through a laminator unless you pre-etch the first side and protect it. I'm still working on making this a reliable and repeatable process.
Comment: Method described by Dan D. can be improved by protecting the first side with Silicon-coated "cooking sheet" when heating the second-side for toner transfer. I don't know how it's called in other countries, but it's a paper you use to bake sticky stuff like chocolate cookies in your oven.
Comment: "Baking parchment" is another name for the material described by @TaisukeYamada
Answer: I know I'm kinda late for this, but check this video, it shows how to make it easy and very accurate. Basically almost the same as Ricardo explained, but it's better to see it in action.
Video is in Russian, but you don't need to know it to understand what happens.
https://www.youtube.com/watch?v=sjEUIdxX1LM
P.S. Method marked as answer here is pain in the ass, tried it many times and it is much more harder than that on the video. I tried to make it this way many times and had many troubles, that would probably lead to wasted time or even boards(if you etch not-aligned layout).
Comment: Thanks for the tip.
I've actually gone to a laser plotter.

An easy method to align a two layer PCB


An older fantasy book about a primitive girl who lived with dragons

Question: In the 90s I read a 3 book series about a girl who lived with or was close with dragons. They lived in a desert like environment with the dragons having a clan like social structure. The girl had befriended one of the young dragons who was looked poorly upon for having her as a friend or pet. If I remember correctly the girl had wild red hair and the people were described in a primitive way with like leather clothes and spears. The story was a typical coming of age and underdog story. I wish I could remember more details. The cover at the time for the first book may have had a dragon or two fighting with the girl on a rock with a spear? Hope this rings a bell for someone.
Answer: Are you perhaps thinking of the Half-blood Chronicles by Andre Norton and Mercedes Lackey, starting with The Elvenbane, published in 1991?

This is the story of Shana, a halfbreed born of the forbidden union of an Elvenlord father and a human mother. Her exiled mother dead, she was rescued and raised by dragons, a proud, ancient race who existed unbeknownst to elven or humankind. From birth, Shana was the embodiment of the Prophecy that the all-powerful Elvenlords feared. Her destiny is the enthralling adventure of a lifetime.

Shana is feral, so that would fit the "primitive" aspect of things. The dragon who takes her up is indeed teased about his "pet". I haven't found a cover with a spear, but she is a redhead.
Comment: @Emily: If this is your book, you can accept it by clicking on the checkmark by the voting buttons.
Comment: And if so, it will be a dupe of https://scifi.stackexchange.com/questions/27663/book-about-human-girl-who-lives-with-dragons (or I might make that one a dupe of this one due to greater detail).


Is there any evidence that this character survived the explosion in X-Men: Apocalypse?

Question: In X-Men Apocalypse, is there any evidence that:

 Havok/Alex Summers

survived the explosion of

 the X-Mansion

?
Answer: As of right now, no. However, it should be noted that this is an X-Men storyline, and the characters have a bad habit, in both the comics and films, to not stay dead. Ray Park's character, Toad, even comments on this, after seeing Jean Grey surviving his earlier slime attack and Storm still being okay after being dropped down an elevator shaft in the first film.
Comment: If there is any way for me to improve this answer, please let me know, and I will do my best.
Answer: He ded.
According to interviews Lucas Till (Alex Summers/Havok) did with CinemaBlend and EmpireOnline, he was explicitly told that his character had died in the explosion.

I thought it was really cool. I feel like people are always like 'Oh,
it's X-Men. It's X-Men you can always come back.' But I was like 'No,
I think it's cool that I died.' I think people were kind of nervous to
tell me that I died but I thought it was really neat.
How One Key X-Men Actor Feels About Being Killed Off In The Series

and

I figured it was just a matter of time. The producer and writers were
kind of feeling me out with, "Are you okay with the fact that you
die?" and I was, like, "Yes." That's something that people would talk
about, so I thought it was cool that I died. Havok was in three movies
and then I get to be remembered. It ended a chapter of my life and I
get to start a new one with MacGyver.
From X-Men to MacGyver: 8 questions with Lucas Till

That being said, he does recognise that his character could somehow return, if the writing requires it.

But also it is X-Men and you don't really see me die and if I can withstand cosmic energy coming from my chest I might be able to
withstand some extreme levels of heat. Maybe that level fell just
right so that maybe I survived, I don't know. I thought it was cool
though.
How One Key X-Men Actor Feels About Being Killed Off In The Series


Attend a lecture in computer science while travelling in the UK

Question: I'm planning a trip to the UK in May. I will stay in London, Edinburgh and Dundee. It would be very interesting for me to attend a lecture in computer science there. Am I allowed to do this as I am not a student in the UK? Where can I find information where and when the lectures take places?
Comment: What kind of lecture?  A lecture that is part of a course for enrolled students?  A research seminar?  A general-interest talk intended for the public?
Comment: the first one - a course for enrolled students
Answer: TLDR They won't post public timetables, so find someone at the university to suggest one and turn up, because people are in academica because they love their subject, love talking about their subject even more, and are highly likely to help you out even if its unofficially. /TLDR
No University I know of has a 'public listing' for 'normal' lectures but you still have a good few options:

UCL (University College London) has Lunch Hour Lectures which are open to anyone on a first come, first served basis. Accordingly though they may share more in common with the Royal Society Christmas Lectures, rather than your regular undergrad computer science lecture in terms of how they are aimed & delivered (maybe slightly more serious...).
Open Days as mentioned above are an option but you won't be able to sample a normal lecture at one.
It is not uncommon for postgraduate students to 'audit' modules (they sit in on lectures and do the coursework, but it isn't marked, and they don't sit exams). The purpose is to refresh or study a subject close to their research. Other times, they may just be interested in the subject and want to go along for fun!
This is permitted as a student/staff member and 'setting it up' is usually just a courtesy email requesting permission from the lecturer.
(With regards to your comment about not being a UK student, it wouldn't make any difference if you were a UK student as this courtesy is only extended to members from the same university.)
I mention this as having another 'odd' person in the class is not unheard of and most lecturers would be very unlikely so say no, especially if it was just one lecture, and even if they did feel the need to (perhaps they are new and concerned about regulations) they would be very nice about it. Your options are to use a contact at the university to ask, or go to the web page of the computer science department of that university and just ask someone who teaches undergraduate modules.*
Alternatively, if you know someone at a university, ask them to recommend a class and go along with them. Depending on the University & course some lectures will have a hundred or more students, and at the beginning of term especially its common for students to change their modules, so you won't be noticed. Undegraduates will know which classes would be best, while post-grads will know the lecturer! Remember that, for undergrads especially, its common to have interdisciplinary friendships through halls of residence or societies/clubs, so even if you don't know anyone in Computer Science or Engineering, ask for friends-of-friends.
If you don't know anyone yet, many universities run events open to the public. A common example is an open-day showing off final-year undergrad projects. I know Universities that do this for Engineering, Art and Architecture (at least!). There will be many members of academic staff present who you can approach.

*Bear in mind that most lecturers are very busy, and only ever get busier, so if you do want to contact one, best do it well in advance and don't be disheartened if you don't receive any response.
In theory lectures are controlled and not open to the public because priority must be given to the fee paying students, but your request is so far removed in spirit from that rule** no-one will give it a second thought. I know a lecturer who brings her daughter along as the subject is of particular interest to her, for example.
**With regards to comments above, I may of course be proven wrong, but I highly doubt its illegal in any sense, just against regulations of a particular institution. If you really care that much about doing it by the book, there will be some mechanism for prospective students to sit in mid-term for various reasons, find some way to use that (contact the admissions department or the student services).
I think this is a great idea, Good luck!
(EDIT: Universities like anything that boosts their profile so another way if you want to do it officially is say you are documenting your trip in some way (blog, for a school, etc) and contact their press office.)
(EDIT2: I removed a suggestion about getting a tip for a busy lecture and turning up alone, as Josh B is correct for a number of institutions, and I suppose its still a little rude even in the others! However I'd still recommend approaching a student to bring you along unofficially - they'll know appropriate lectures for which your presence will be unnoticed/harmless, and they can sign you in as a visitor and look after you for the day.)
Comment: My (UK) University very actively checked University ID cards of all people entering the Uni buildings. Anyone without a valid ID card would be asked to leave asap by the security staff. However, not all Uni's do this but it's something people should be aware of. (Though at worst you will just not get to the lecture you want to attend...)
Answer: Universities generally have Open Days for prospective students, where they can meet faculty member, attend sample lectures, learn about research activities going on in the department, talk to the current students. These activities may be limited across universities, as they might have different set of offerings and rules as part of these events.
You should check the University Department, which are closed to the place you will be staying at OR intend to travel.
For starters, this page will give you details about Open Days event at University of Oxford.
University of Dundee has its open days for Computing on 26th August and 28th September 2013, so you'll miss that.
University of London has its open days in September 2013.
City University of London will have its open days in June 2013.
University of Edinburgh will have its open days in June.
Comment: I'm looking for a "normal lecture", not for "open days"
Comment: @Dirty-flow I expect the official answer to attend lectures without paying a tuition fee is that it not is allowed. Attendance however is usually not checked. Then again after reading this question universities might change their mind  ;)
Comment: I don't think any university "officially" allows for non-students to attend lectures. Though, unless and until, they have access control doors to the lecture halls, they might not figure out if a person, who is not a student is attending a lecture. Then again, this would not be legal.
Answer: Some ideas:

MeetUp.com - here, you will, at least, find many events to register for attending, particularly in modern applications of Computer Science: various programming languages, concepts and hardware. Some hot topics you will find there are: Big Data, various web "camps" and coding sprints, hacker (the nice type - the ones that make things as in "I hacked this together") / hackerspace events. See also eventbrite. I can speak from personal experience that meetup.com is useful for computing related events though it also seems to be a place where general very broad and also niche interest place to find all kinds events (creative, languages, arts, outdoors etc. etc.) and the organisers - which, to my mind, is a very good thing indeed!
raspberrypi.org - this is a 25$ cheap kit computer that is taking the teaching of Computer Science to school kids by storm as well as a cult following among enthusiasts and hobbyists as in more serious experimental computing applications. The RaspberryPi is a British Designed and (largely) British assembled (in Wales) product. Look out for events on their blog.
Cafe-based talks/Cafe Scientific: Search for Cafe Scientifique or see http://www.cafescientifique.org/ - this is a worldwide movement that is just about self-explanatory - talks on Science in Cafes. The events are autonomously run, rather than under the umbrella of any organisation and some events have been held in UK - specific ones I can think of in the past include lectures on Brunel Bicentenary at Cafe Le Cafe Parisien in Portsmouth (don't work for them nor have a financial interest in them) and talks at The Art House Southampton thearthousesouthampton.co.uk (again no financial interest, they are a non-profit organisation)
Contact the British Computer Society - http://www.bcs.org/
Browse questions and profiles on StackExchange (hoster of this site) Computer Science Q&A https://cs.stackexchange.com/ for ideas
Twitter - again for ideas and to follow organisations for updates on events
Comment: Fair enough, that's a good defence.
Comment: Downvoted because this doesn't really answer the question, these are just related activities in the same field.
Comment: @AnkurBanerjee I disagree - in all 6 of my suggestions it would be possible to learn about computing talks going on. We don't know why the original poster would find it interesting to be in a talk with enrolled students, i.e. what do they ultimately want to gain from this. So perhaps my suggestions may address what this end goal might be - different story same ending. It's possible that in all 6 of my suggestions, the original poster would find contacts in the academic world who could signpost them to events.
Comment: Moreover it may be that what the original poster is not able to find what they were asking for - due to timing or not being able to attend a lecture theatre with students who have enrolled. So rather than say this can't be done my hope is that the alternatives I suggest achieve the same end goal for them.


Drywall fix doesn't match ceiling

Question: Repairing a textured ceiling. However the new drywall mud stayed gray rather than turning white.  I've never had this happen before, why is it gray? it isn't old or moldy.  it was mixed just for this job. It basically looks like it didn't dry at all though it is. What do I do to make it match the rest of the ceiling?
Comment: If it's dry and hard, just prime and paint. Not every mud changes color.
Answer: Mudding is only one step in the repair process.
Patch repair, tape, Mud, Texture, Primer, Paint.
Buy a can Homax spray texture and practice on piece of cardboard before doing the patched area. It is an acquired skill, make adjustments to the nozzle to get the matching texture size you need.
I usually start with a fine/small first, let that dry and then a medium on top of that.

Drywall fix doesn't match ceiling


Any reason to add screws if I only want to use glue?

Question: Building some bunk beds that will be pretty permanent and my plan was just to glue everything to make it nice and sturdy. If I'm gluing is there any reason to use screws at all, trying to make it look nice?
Comment: A lifetime master of Japanese joinery could probably make a strong bed without even the glue, based on years of training and experience in how wood joints behave under stress and how to work with the natural materials' strengths. If you use good joints and braces where needed, glue alone might well suffice. But for the rest of us mere mortals who are not PhD structural engineers, screws are cheap insurance. If it were my kids, I'd have dovetails, glue, screws, corner braces, and steel reinforcements.
Comment: One point about screws worth noting is that they act like internal clamping, so screws can be used to pull certain joints tight which is important for strong glue joints to form. And if left in place they act as security should the glue joint ever fail for any reason, e.g. shocks, regular movement stresses and expansion/contraction due to moisture changes year by year. Using screws does not at all have to mean you compromise on looks, the screws can be sited on surfaces that don't show or if used on show surfaces hidden by wood plugs (search for "counterboring" for more) making them invisible.
Comment: ...and a crash cage for the kid on the bottom bunk!
Comment: @LeeDanielCrocker you should post that as an answer, I'd upvote!
Answer: Lee's comment is right on Ryan. But in any case, we couldn't answer your question without more detail about the construction. Depending on what you're planning, even screws+glue might not be strong enough.
In particular, glue is only strong in shear, and not tension. It's also not effective on end-grain. With either screws or glue (or both), you'll still want the mechanical strength of the wood to be working for you, and that will mean non-trivial joints like mortise and tenon. Just butting pieces up against each other and joining them with glue and screws risks ending in tears.
A bed especially is subject to jumping and climbing stresses and has unconscious occupants much of the time.
If you can provide drawings we could give you something more specific. If it were me, I'd be thinking hard about a quick trip to IKEA :)
Comment: Extrapolating from the advice generated by past experience does tell us that even using a very strong adhesive as they were back in the day, and cutting joints generally to a very high standard, that it was recognised how much weaker a halving joint (lap joint) was in the real world. This wouldn't have been any real issue for something that just sat there, but the flexing that goes on when furniture was moved stresses all joints in a structure and these were known to fail. The higher seasonal movement in the wood due to the finishes used historically would have contributed to the problem.
Comment: That point about glue is a bit of a red herring as there wouldn't normally be situations where there you'd create a joint that's only in tension. And anyway in woodworking it's not about the glue itself usually, it's about the glue joint, which isn't exactly the same thing (thick glue line being weak, thin being strong, signifying that it's not about the adhesive per se).
Comment: @Graphus I guess I was thinking of maybe gluing a plywood "bottom" (that a mattress would lay on) to a simple perimeter frame. But it's an interesting point. And I think you're right that bets are somewhat off when talking about wood (rather than say metal) where all the adhesive has to do is bond more strongly than the lignin holding the fibers together :)
Comment: What exactly is your source on glue joints not being strong in tension?  Modern wood glues used properly are stronger than the surrounding wood in every test I've ever seen.
Comment: Dan Gelbart: https://youtu.be/EeEhS3zmnDg?t=832. But in fairness, his discussion is in the context of engineering materials, not wood. Also, he makes a distinction between _peel_ mode failure (like lifting Formica from corner of countertop)  and "pure tension" where the entire joint is stressed equally. As I mentioned in my reply to Graphus, these characteristics are perhaps less relevant to wood given its lower material strength, but it _would_ apply to joints themselves, like lap joint can peel where mortise/tenon can only shear. Joint fails whether it was the glue or lignin that gave way.


Doubling a soup recipe with a smaller than necessary pot

Question: In doubling a squash soup recipe, I've got all the ingredients in the pot except for the doubled amount of liquids (broth and water). I wonder whether I can wait to add the remaining 5 cups of liquid until I reheat before serving, or should I add it during the overnight storage of the soup? Or should I divide what I've got so far and add the remaining liquid and heat it up before storing? My concern is for the flavor melding aspect.
Answer: You should be fine adding the water whenever it's convenient, as long as there's enough water in it already that you were able to cook it properly (and purée if necessary and so on). You're basically just making concentrated soup just like what gets put into lots of cans; water will mix in just fine.


How do I corrupt an .exe for testing

Question: I need to run a test which requires that I corrupt a specific .exe file.  For security reasons I cannot upload this file to http://corrupt-a-file.net/.  Is there a known tool for Windows that I can use, or a recommended technique?
Comment: Bit off-topic as your question is about corrupting files, not really about testing.
Comment: Might be off topic, but... are you sure this external service is not injecting a virus?
Comment: @NielsvanReijmersdal, not that off-topic, it looks like setting up test data. Still I'm curious what kind of test is that.
Comment: @Niels thanks for your answer, the hex editor was the key.
Comment: @dzieciou - as for the test type, our software has some neat fail overs. I needed a quick way to corrupt an aspect of the software to trigger an event which in turn would replace the bad file(s).  Greatly appreciate the help!
Answer: If we define corrupt as not being able to start the executable, just open it with a text editor (like notepad++) and change some text around and save. Some executables might be to large to open, but I think a good text-editor should be able to handle most. Open the executable, if it still works, change more text around :)
The smallest changes will often result in a broken application.
Maybe have a look at the file with a hexeditor and change some of the important bits.
Comment: For big files this can be done simply in command line through file concatenation: http://stackoverflow.com/questions/2477271/concatenate-text-files-with-windows-command-line-dropping-leading-lines

How do I corrupt an .exe for testing


Why is my kitchen island sink gurgling when my dishwasher is draining?

Question: I noticed a few days ago that, whenever my dishwasher is draining, the sink in my kitchen island gurgles (glug, glug, glug). I THINK that the sink connects to the main kitchen sink drain underneath the floor. Any idea what could be causing this? Also, I'm not sure if it's related but I just noticed that my upstairs bathtub is draining really slowly now. But I'm pretty sure it's a separate line until it gets to the Septic connection like everything else.
Comment: Sounds like a blocked vent somewhere. Is the island sink noise a new development?
Comment: I'm curious as to why your dishwasher isn't draining thru the garbage disposal depicted in your diagram... Not allot of details to go on here but an educated guess would be a partial blockage in the drain system itself and/or improper or partially blocked venting.
Comment: @isherwood the sink gurgling is a new development.
Comment: @BillWeckel This is how it was set up when we bought the house.
Answer: There's a blockage in the venting where the island ties-in. The 2 locations are commonly vented together, due to that loop under the island sink. A T-fitting instead of a Wye may have been used to tie-in the island and this is why only a Wye or directional fitting should only ever be used.
Answer: I think it's because your sink drain and your dishwasher drain are somewhere connected. It's the same in mine.


How to practice Mindfulness Meditation?

Question: I have been researching this lately and thought it was amazing. I just don't know where to begin or know any techniques. Can someone list some?
Answer: The word 'mindfulness' means 'to remember' or 'keep in mind'. In the context of Buddhism, it means 'to remember' to practise the factors of the eightfold path.
For example, if you are speaking/talking, you remember to speak in a manner that is honest, pleasant/gentle, cordial & beneficial. This is practising mindfulness meditation when meditating upon speech.
If practising formal sitting meditation, mindfulness is to remember to keep the mind in state that does not have desire for or get distressed about anything in the world.
Therefore, in formal sitting meditation, how to practise mindfulness meditation is to sit without desire or worry & just sit with natural quiet. When this is done properly, awareness of breathing will arise naturally as a sign of right mindfulness & later pleasant feelings will arise as a sign of right mindfulness.
Answer: You won't learn this one from books, only by trying out and practicing it. The practice is to go beyond concepts like Now I'm meditating, this is good, bad, me, mine... and focus on the raw experience which is present. If you sit down to start meditating with the intention to be mindfull you might have the feeling Now I'm meditating, but in reality all you do is change postures.
You should have some basic instructions, but don't get into theory too much. It won't help you, it will only reinforce your opinions and ideas. I'd suggest to get to know the framework of Right Mindfulness, which are body, feelings, mindstates, mindobjects (dhamma).
The original teaching from the Buddha himself: Satipatthana Sutta: The Foundations of Mindfulness
A more practical guide from Ven. Yuttadhammo (the noting technique): How to Meditate
Answer: Recently I m reading a dharma book (The Chinese Version), which 25 great beings demonstrated how they practiced mindfulness meditation.
The winner is: Guan Shi Yin Bodhisattva practices on hearing:
http://www.cttbusa.org/shurangama5/shurangama5_12.asp
You might be interested to have a read of above link as well as 24 other practices.
May you be happy and at ease
Answer: Try starting with accesstoinsight.org, Jon Kabat Zinn, Joseph Goldstein, Google Search Inside Yourself.
Answer: How about The Bhante Yuttadhammo channel on YouTube? He has a lot of useful videos but check out "How to Meditate" for beginners. His online  videos are beginner to intermediate on much more than only mindfulness and he gives meditation courses from beginner to advanced.
The teachers below teach about the same way as Bhante Yuttadhammo and are very beginner friendly:
Joseph Goldstein, Bhante Bodhidhamma,  Gil Fronsdal
Just Google one of the above names in quotes and add "Dhamma talks"
There's a Youtuber called "Stephen Proctor" who gives outstanding beginning teachings on mindfulness meditation in my opinion. Has anyone else heard of him? Is it just me or can this guy really teach or what?
These teachers practice  the same way I try to practice but there are a lot of good teachers who might have a different approach.
Comment: Just checked him out. Thanks for the tip (not Robinhood). Plus seems like he sticks to the program - no woken stuff.I've looked for decades for someone with pure practice without any philosophy. It's kind of interesting that you say "beginning." I usually find that appellation a bit demeaning. I know of many "advanced" practitioners who  yet watch the breath, recite Namo Amitaba, you get my point. For me personally in stuff like math, genetics, etc. when I hear that, I'm already looking for "advanced."
Answer: The detail of the practice is outlined in Satipatthana Sutta and Anapanasati Sutta, but these instruction maybe difficult to follow for a beginner. Best is to take a course in it. 2 organisations with a reasonably wide outreach are:

http://www.internationalmeditationcentre.org/ and
http://www.dhamma.org

or alternatively look for a teacher in World Buddhist Directory.

How to practice Mindfulness Meditation?


Clifford gates are transversal What exactly does this transversal mean? What is the difference between non-Clifford gates and Clifford gates?

Question: Clifford gates are transversal What exactly does this transversal mean? What is the difference between non-Clifford gates and Clifford gates? Why is it simple for Clifford gates to implement transversal for quantum fault tolerance? Please explain the definitions, differences, and functions of the two in detail. I don't understand them very well, thank you.
Comment: Welcome to QC stackexchange! Your question is not very narrow and would require several pages of answer. I would suggest that you read up on fault-tolerance & transversality in the book by Nielsen & Chuang. The role that Clifford gates play in fault-tolerant quantum computing is more subtle and can be treated in an answer here.
Comment: please have a look at https://quantumcomputing.stackexchange.com/help/how-to-ask. Questions should be laser-focused on individual issues. You can ask separate questions in separate posts. Feel free to edit your post to make it more focused
Answer: Transversal and Clifford are not as closely linked as your question would seem to imply.
Transversal gates are those for which an error-correcting code can achieve the transformation on a logical qubit by applying that gate on each of the physical qubits. For example, in a 7-qubit code, if you can achieve logical Hadamard by applying Hadamard on each of the 7 physical qubits, that gate is transversal. These gates are the simplest to implement because they are automatically fault-tolerant: if an error occurs on one physical qubit, there is no action that can propagate it onto a different physical qubit in the same code because no two qubits in the block every interact. They are also particularly short gate sequences (just one time step), which has the knock-on effect of making the corresponding fault-tolerant threshold particularly high.
Now it happens that for some of the most common quantum error correcting codes, the gates that you can apply transversally coincide with the Clifford gates. Indeed, iirc, this is true for all self-dual CSS codes. But this is just a particular choice of error correcting code. There are other choices where it is not the Clifford gates that can be implemented transversally. In that sense, there's nothing particularly special about Clifford.
Comment: @IanGershonTeixeira Yes. And in contrast, you know that a universal set does not form a finite group.
Comment: It seems to me that the original paper shows that the set of transversal gates always forms a finite group (a discrete subset of the group of unitary gates closed under products and inverses). Is that correct?
Comment: In some other places (for example here https://quantumcomputing.stackexchange.com/questions/24399/why-does-fault-tolerant-transversal-phase-gate-p-only-work-with-doubly-even-co?noredirect=1&lq=1 and https://quantumcomputing.stackexchange.com/questions/15301/transversal-logical-gate-for-stabilizer-or-at-least-steane-code?noredirect=1&lq=1 ) it says that for phase gate $ P $ to be transversal you need the code to be double even. In your answer you say that Clifford is transversal for all self dual CSS codes. Is that because every self dual CSS code is doubly even?
Comment: Also, it might be added that although the set of transversal gates for a code may not necessarily coincide with the Clifford gates, it will never be a _universal_ gate set.
Comment: This is known as the Eastin-Knill Theorem. Wikipedia has a good explanation (https://en.wikipedia.org/wiki/Eastin%E2%80%93Knill_theorem). The original paper is worth reading for as well (https://arxiv.org/abs/0811.4262)


How can I adjust brightness when shooting high FPS video?

Question: I've FujiFilm Finepix S8500. It is capable of shooting high FPS videos. It works fine in broad daylight but when indoors, the video is always dark. What settings I can adjust to make the video brighter? I tried to adjust ISO and aperture but that does nothing. I also notice that the videos are darker if FPS is higher. I understand why this happens but is there anything to get a brighter video?
Comment: Is there some restriction on using studio lighting?
Comment: I don't have that gear.
Comment: Its a great bridge camera, however it has a small sensor. Small sensor means it can capture less information on its sensor, even when setting a high ISO setting. Its strength is the great zoom, but the image quality is so so.
Answer: Two ways
1) Larger aperture (the lower the number the larger the aperture) letting in more light, but also narrowing your depth of field).
2)
I would suggest a higher ISO, don't understand why that does not work for you. The current crop of camera's now are absolutely amazing at capturing low light environments that you cannot see with the naked eye.
One of the best cameras for this is the Sony a7s, just released (s for sensitivity).
It needs to be seen to be believed.

Sony a7s high ISO video link
Comment: ISO 400,000...!!  Sure it started getting unusably noisy (even seen through the rather lossy h.264 encoding) around 1 million, but that's still absolutely insane.  Wish they had a link to a higher quality version that would actually let you see the noise levels clearly though.
Comment: Hmm, found a video that is a bit better, it looks like it is about 2 stops better low light than the 5D Mark iii and $1000 cheaper.  Not bad, particularly when you throw in slog2 4k HDMI output.  Sadly probably not going to have a RAW video hack any time soon though. :(
Comment: Yes, an amazing camera, a full frame sensor, amazing ISO. Here is one between Canon 5D and Sony a7s with HD 1080. It gets really grainy at 400k, I would probably stop around 100k ISO. For video cameras, I think this is now king of the hill. https://www.youtube.com/watch?v=wGr_hXgJVGs
Comment: Yeah, I shot my own video on my 5D at 25,600 to compare to the footage shot on the a7s that was online.  That's how I got the two stop level.  25,600 (max on the 5D3) is about the same noise level as 100,000 on the a7s.
Answer: The best way is to add more light, I see you mentioned not having the equipment to do so. There are a couple of home hacks to get around that.
1) Remove lamp shades and use the highest wattage bulb you can. I also prefer the clear glass bulbs sometimes with a diffuser over them. I find that tends to be brighter than the hazed bulbs but I have official evidence to prove this just experience.
2) This is my favorite home light hack... Go to home depot and buy your self the the double halogen work light with stand. These work great for video as they are bright, easy to move around, come with a rotating head and are on a stand already, not to mention the best part, they are cheap!
3) Use halogen track lights in the room. This is also a way to get a nice light array for not a ton of money. Again they are super bright, easy to move around, just mount the track to a piece of 2x4 and you have a mini light array right there.
Reasons not to use a higher ISO:
In all cases I avoid increasing the ISO unless absolutely necessary. A higher ISO will increase noise and there are no 2 ways about it. I always exhaust my other options first, aperture, exposure time and simply turning on a light if I can.
Comment: Be carefull with halogen lighting, you may get some frames brighter and some frames darker because of the light's frequency, you may be able to adjust that in your camera though. Mine allows to switch between 60Hz and 50Hz if my memory serves well.
Answer: Only with a larger aperture to let in more light if a higher ISO isn't helping. Though the camera probably already uses a very large aperture for this high frame rate mode.
The more FPS the less light per frame obviously.
Your only other option would be to adjust the brightness in post which is a very limited option as it increases noise and can introduce artifacts but it might improve the footage a little bit. This usually works better if you can shoot in MJPEG instead of h.264/AVC. Try to shoot with the highest bitrate possible to have the biggest flexibility in post.
Usually you want to shoot with plenty of light when filming with a high frame rate, especially in-doors.
Comment: Increasing ISO, if possible would be preferable to boosting brightness in post as it would minimize certain types of noise in the recorded signal.
Comment: Of course, any camera adjustment should be preferred over "fix it in post".
Comment: ISO was my first attempt to counter the problem but, like I said, it does nothing. Videos at ISO 100 and 12800 are equally dark. I think this camera ignores the ISO settings for video.
The problem is camera specific. It's not a DSLR.


Is there a tool similar to powertop for macOS

Question: I am looking for a tool similer to powertop for macOS. I'd like to see which processes have the largest power use (activity monitor shows apps but not servers like nginx and node and I'd like to see the power use of those server processes too). Any suggestions?
Comment: Activity Monitor does show all processes. Check what is ticked in the View menu
Answer: In addition to the Energy tab in Activity Monitor, there is the command-line powermetrics that gives you more detailed information, such as CPU wattage and C-States. Try the --show-process-energy option for the same Energy Impact metric as Activity Monitor.
Answer: In Activity Monitor.app

Select View > 'All Processes'
Select the 'Energy' tab
Click on the column 'Energy Impact'
Answer: Not exactly like powertops, but you can use powermetrics:
sudo powermetrics --show-process-energy

More details from the manual:

powermetrics gathers and display CPU usage statistics (divided into
  time spent in user mode and supervisor
       mode), timer and interrupt wakeup frequency (total and, for near-idle workloads, those that resulted in pack-
       age idle exits), and on supported platforms, interrupt frequencies (categorized by CPU number), package C-
       state statistics (an indication of the time the core complex + integrated graphics, if any, were in low-power
       idle states), as well as the average execution frequency for each CPU when not idle.

Also, you might want to use the top command:
top -stats pid,command,power -o power -l 0

Answer: There's a tool called asitop, which looks like this:


What determines the frequency the Wayback Machine crawls one's website?

Question: I understand archive.org takes its website list to crawl from Alexa, but I don't understand how it decides the snapshot frequencies for each website. We can see some websites are crawled multiple times per day while others are crawled less than once a month. How is the frequency a website will be archive determined by the Wayback Machine?
Answer: The Wayback Machine archive is a combination of data from a large number of different crawls:

Alexa crawls, which appear after a 6 month delay
Our own crawls, which are seeded from the Alexa top million list and others
ArchiveTeam crawls, done by volunteers
ArchiveIt crawls, done by our 400+ partners, mostly libraries, many of which allow their data to be included in the general Wayback Machine

We have an experimental Wayback Machine search and explore interface at https://web-beta.archive.org/ which makes visible why each capture was made.
Answer: There's some information about this on Wikipedia,

Snapshots usually become available more than 6 months after they are archived or in some cases even later, 24 months or longer. The frequency of snapshots is variable, so not all tracked web site updates are recorded. There are sometimes intervals of several weeks or years between snapshots.
  https://en.wikipedia.org/wiki/Wayback_Machine
Comment: Although this answer is informative, it does not give hint about criteria determining the intervals between snapshot.


Spam Questions Increases

Question: Patents is getting a bunch of Spam lately. Is there anyway we can get the moderator to delete them more rapidly? I and others are flagging as spam and downvoting.
Answer: Ask Patents currently has no moderators. The Stack Exchange company was supposed to be moderating the site, but the staff member responsible for AP moderation, Robert Catarino, was unexpectedly fired in January.
Other sites in the Stack Exchange network are moderated by volunteers and host occasional moderator elections. That might be an option here if your community has members who would be willing to commit to a moderation role.
In order to get more moderators, you'll have to contact Stack Exchange staff and ask them either to appoint a new employee moderator or to start a moderator election. The best way to get in touch with them is probably to post a question on Meta Stack Exchange and flag it for [status-review].

In the meantime, there is a user group called Charcoal which is focused on identifying and deleting spam content across the network. If you come across a spam post that hasn't been deleted, feel free to post a link in our chat room. We'll gladly flag the post in order to help it reach the 6-flag threshold for deletion, and we can blacklist keywords/URLs/user accounts so that our automated spam-detection systems can identify it quicker next time.
Comment: I might be willing to provide moderation of Ask Patents since it is a pretty low volume SE site and most everybody is well behaved. Do you know how I would make SE aware of this?
Comment: I think the best thing to do is probably to start a discussion on [Meta Stack Exchange](https://meta.stackexchange.com) explaining the siutation. It might also be worth hopping in the [Tavern on the Meta](https://chat.meta.stackexchange.com/rooms/89/tavern-on-the-meta) chat room first to get a second opinion, since there are people there who would know better than me about what to do.

Spam Questions Increases


Changing Text cell color

Question: What can I set so that whenever I create a text cell, everything I enter into the text cell, whether plain text or some mathematical notation (Ctrl+9 on the Macintosh) is in a particular color I would like to choose?
Comment: The color of all text can be set by using Option Inspector to specify FontColor.
Comment: @bbgodfrey Thanks for this answer, but this sets all the colors ( I selected Blue ) to Blue. Even the input cell color is now blue, which I wanted to remain the usual black color.
Comment: Indeed, so.  That is what I meant by "color of all text "  Perhaps, progress can be made by means of a style sheet.
Answer: You can define a new style "BlueText" derived from the "Text" style.

Update
This a partial answer to an issue raised by the OP in a comment to this answer.
I will work up a step by step explanation as soon as I can find the time. Might be a day or two. Meanwhile, you might look at this answer and this one. Also, you might search this site for "stylesheet". BTW the code I show in the private stylesheet needs to be entered with the cell opened to raw form; i.e., select the cell and press Ctrl+Shift+E to get that view. Press the same key combo again to go back to normal display.
Comment: This looks like a possible excellent introduction to forming my own stylesheet. Are you using Mathematica 11.1.1? I opened a new notebook, saved it as BlueNotebook.nb. I selected the Format->Edit Stylesheet menu and entered BlueText in the "Enter a style menu" block. Then I entered the code you suggested. But then I don't know where those menus came from or what I am to do next. Can you add further explanation. I appreciate this answer.
Comment: @David. I have written the step-by-step tutorial on creating a stylesheet. You can find it [here](https://mathematica.stackexchange.com/q/153102/3066)
Comment: Outstanding! :-)  Your help over the years has been at a really exceptional level and have helped me to learn so much about Mathematica. Thanks again.

Changing Text cell color


Preview Pane for PDF Documents in File Manager

Question: Is there a program (e.g., file manager or PDF viewer) that provides a split view having a folder view and preview pane for PDF documents (ideally with the ability to scroll through the document like the preview pane in Windows 7)?
I have 100's of PDF documents that I need to preview rapidly. The file names are not helpful because they are auto-generated. I have used various file managers that generate thumbnails of the first page, but the thumbnails are too small to distinguish between documents. Additionally, it is often desirable to display subsequent pages in the same document.
I have tried batch opening the files in Foxit, but the number and size of files typically causes the program to crash.
I have tried Krusader, which spawns an external preview Krviewer window. This is not sufficient because it requires opening and closing the Krviewer for every file (similar to simply doing "open with..." an external program), which is slow.
Another StackExhange answer appears to show the desired behavior, but it does not appear to function in the installed version for Ubuntu 18.10 (Konqueror Version 5.0.97). See Konqueror and https://www.donationcoder.com/forum/index.php?topic=44064.0
Answer: Dolphin (KDE) has a split view ("Preview pane").
Downsides: Only first page is shown and not as clear as for example PDF XChange on Windows.


Is it possible to use Google Docs as a wiki?

Question: Is it possible somehow to easily use Google Docs as a wiki? I mean, I create a first document, then add a link to another one and so on, so the procedure is easy and fast and the different docs files are easily organized.
Answer: Google Docs does not make a good wiki.

Optimized for printed page, not viewing online (page margins, document margins) (Update in 2022: You can create pageless docs now, but they're not responsive still)
Always in edit mode (Update in 2022: View only mode exists now)
No mechanism to dynamically embed content or especially lists of documents in another document
No friendly URLs for documents
Does not link documents nearly as easy as in a wiki (requires interaction with menus/mouse and copying full URLs to documents)
Does not support text zooming fully (appears to work, but try it, hit CTRL-+ and some document components often don't display properly.  Basic documents work fine.)
No cross-document consistent styling

Update 2022: Except for the two issues commented on above, the rest are still accurate. IMO this makes Google Docs unsuitable for use as a wiki still.
Comment: Now, you can make full size documents without printing style https://support.google.com/docs/answer/11528737
Comment: @DanielBlazquez Thanks for the update. I've been using this and it is a great addition but has tons of its own problems too (docs are not responsive like they would be in a wiki). There's also a view-only mode now, I'm not sure if that was always there or if it was added.  Other issues afaik are all still there, so Google Docs as a wiki is still a no-go in my opinion.
Answer: Yes.
But you have to manually keep track of the URLs to the documents. And you have to setup manually the edit permissions per document as well.
Consider using sites.google.com.
Answer: I know this is way old, but I've wanted this functionality for a really long time, so I finally built a little wiki viewer for Google Docs. Check out an example at https://gwiki.kaelshipman.me, and the source code on GitHub: https://github.com/kael-shipman/libgwiki.
All it does is use Google's Drive API to fetch a document hierarchy from a "home" folder that you feed it. Then it builds a little UI around that hierarchy that provides a "main menu" at the top (for all direct children of the home folder) and a nested sub-menu on the side as you descend into the hierarchy.
(Note that the example asks for permission to view your google drive docs (for obvious reasons). If you're not comfortable with that, you can always just download the repo and set it up yourself, though you'll have to create a Google API key and client credentials.)
Comment: Looks interesting but I get this error: "This app is blocked
This app tried to access sensitive info in your Google Account. To keep your account safe, Google blocked this access."
Comment: Yes, google has gotten very aggressive with security measures these days. A good thing, yes, but it certainly makes it hard to demo a proof of concept...
Comment: @Kael Does that mean we don't get this error if we install the app on our own servers?
Comment: Mm, google does provide a way to turn their security features off, but only for gsuite users who are all on the same domain (there's a "this is an internal app" checkbox). I think you can also use it on your own server if you create your own google api creds and use your own user. But I don't think you can share it with others. Really annoying, but again, I guess I can appreciate what they're trying to do.
Answer: https://youneedawiki.com/ looks awesome, however to me what makes a wiki useful is the search functionality which is lacking from the free version, and only 1 user. That's as their model pushed users towards the paid version.
https://www.zoho.com/wiki/?src=zoho-home seems to do the trick for me (search + 3 users) in the free version.
Both allow you to import your existing G-Drive docs.
Answer: I noticed one feature in Google Drive that is relevant here:
Link lookup by text: you type in a text for the link, then you select it and press Ctrl+K. A dialog appears with two fields, and the field for the URL has drop-down list with suggestions that match the text. So this allows emulate easily some wiki-like functionality.
Comment: Why don't you add a screenshot?
Answer: There are many solutions and it all depends how you manage your information. The concept of wiki itself means quick. Quick answers, ease of access to information:

Use Google Docs with headings and document maps.  Add combination of bit.ly or url shorteners maybe keeping an organized table in Google Sheets of the hyperlinks. use Ctrl + K to insert links in a human readable form.
Use Google sites and build stuff by using HTML
Use third party apps such as Gwki(Gwiki had disabled the Google login), Zoho Wiki
Use a Google product to have a map (key | value) table like structure. You can have things such as categories > table with information > sub tables > sub categories > tables > sub-tables.
Answer: Disclaimer I have not yet used this tool
This tool looks promising: https://youneedawiki.com/
It allows you to create a wiki that is backed by Google Docs.
Comment: Please don't just post a library as an answer. At least demonstrate how it solves the problem.
Answer: I'm building https://kbee.app to solve this problem. We are heavy Google Drive users and really wanted to use it to power our internal wiki as well as our customer help center and didn't find anything that worked the way we wanted.
The interesting thing Kbee does that other tools in this space don't is that it builds static snapshots of your Google docs so navigation is lightning fast and the full-text search is powered by Algolia DocSearch so you get relevant results when you search.
We are looking at doing things like building a slackbot so you can access your wiki inside slack, a chrome extension so you can search in the omnibox for content, etc.
Answer: To second Sam's point: Google Docs also doesn't appear to have the option for the page width to automatically fit the browser width. So you either have significant unused space on both sides or have to constantly scroll sideways to read the text.
See also How to use full screen width in Google Docs


What is the formula used to calculate the loss in the FaceNet model?

Question: The FaceNet model returns the loss of the predictions and ground-truth classes. How is this loss calculated?
Answer: The loss function used is the triplet loss function.

Let me explain it part by part.
Notation
The $f^a_i$ means the anchor input image. The $f^p_i$ means the postive input image, which corresponds to the same people as the anchor image. The $f^n_i$ corresponds to the negative sample, which is a different person(input image) then the anchor image.
The formula explained step by step
The first part, $||f^a_i - f^p_i||^2_2$ basically calculates the distance between the anchor image output features and the postive image output features, which you want the distance to be as small as possible as the input is the same person. For the second part, $||f^a_i - f^n_i||^2_2$ , it calculates the distance of the output features of the anchor image and the negative image. You wnat the distance to be as large as possible as they are not the same person. Finally, the $\alpha$ term is a constant(hyperparameter) that adds to the loss to prevent negative loss.
How it works
The loss function optimizes for the largest distance between the anchor and negative sample and the smallest distance of the positive and anchor sample. It cleverly combines both metrics into one loss function. It can optimize for both case simultaneously in one loss function. If there is no negative sample, the model will not be able to differciate different person and vice versa.
Hope I can help you and have a nice day!
Comment: The question which i am linked ,what i want to ask is :Suppose i trained the images of two people say Bob , Thomas  .When i run the algorithm to detect the face of a totally different person from these two say John , then John is recognized as Bob or Thomas.How to avoid this ?
Comment: If you know how percentage is calculated , then can you explain it using an example (using image matrix) .You can explain this in this answer or in https://ai.stackexchange.com/questions/16175/three-step-threshold-in-facenet-model-of-face-recogniton or i can ask new question if you want


Travelling with Prescription Medications Through both France AND Spain over a Year's time

Question: I am going to be abroad studying in France and Spain over the course of a year, and am on long term medications that are extremely important for me to keep taking regularly at exact doses. I'm not sure how easy it will be to get prescriptions for the medications at the necessary regular intervals in both France and Spain over the year that I am abroad, so it would be more convenient and probably safer for my health for me to carry the amount that I need for the full time I'm abroad with me, unless foreign prescriptions are accepted at pharmacies. My medications are anti-psychotics, seizure, and blood pressure medications, so they're not anything that is taken for recreational use or should be prohibited in general. Will France allow me to take a year's supply of medication into the country if I have the proper letters and notes of prescription from my doctors, or would I have to find a doctor in France that will continue to prescribe me my medications while I am abroad, and the same while I am in Spain? Alternatively, does Spain take prescriptions written by foreign doctors, so that I can take only 4 or 5 months of medication to France and then fill prescriptions while in Spain, assuming my medication is available there? I have found it very difficult to find information on the exact amounts they will allow according to length of stay, and whether continuing on to another country is taken into account.
Comment: You first hurdle is actually getting a years supply.  That is quite difficult in the US.  You might want to work with a doctor or pharmacy that will ship the meds at regular intervals.
Comment: @Johns-305 In particular, even if a doctor wrote such a prescription, the insurance company won't pay over 30 days' (in some cases 90 days') supply.
Comment: @AndrewLazarus yes, that's why I'm pointing this out.  weather the formulary allows 90 days is drug specific.  The border is probably OP's lesser concern. :(
Comment: @Johns-305 I suppose if you were very wealthy and didn't care about the insurance, there's not much problem here. The sort of meds the OP is talking about aren't likely to be closely controlled, except for reimbursement.
Comment: @AndrewLazarus Again, it depends on the meds.  Some can't be dispensed for long periods at all because results have to be monitored.  That's something only OP's doctors can decide.  Shipping meds isn't that big a deal even using insurance, one just has to do the legwork to set it up.
Comment: http://www.douane.gouv.fr/articles/a13412-private-individuals-carrying-medicinal-products-in-france
Comment: The link provided by @audionuma suggests that the OP cannot ship at least some of the medication (psychotropics) and will have to import it personally.
Comment: I'm Canadian. Getting a large prescription and getting it covered is actually no issue. Probably should have mentioned that... forgot USA is different. Sorry guys.
Comment: The problem is entirely the crossing borders issue.
Answer:
I am going to be abroad studying in France and Spain over the course
  of a year, and am on long term medications that are extremely
  important for me to keep taking regularly at exact doses.

You should talk to your doctor about it. I'm not familiar with other two, but blood pressure medication requires periodic checkups as your body adjusts to it. It might be against the rules for your Dr to simply write you a 1 year prescription knowing you'd be away and without medical supervision.
Both France and Spain have English-speaking doctors. If the place you are attending to study attracts international students, they will surely be able to recommend some English speaking doctors. The prices are generally cheaper, and you might end up paying less for the medicine in those countries than your co-pay is here in USA.

unless foreign prescriptions are accepted at pharmacies

Prescriptions written by American doctors are not accepted in France, Spain or Germany. I tried.

Will France allow me to take a year's supply of medication into the
  country if I have the proper letters and notes of prescription from my
  doctors

Yes, it should:

Medicinal  drugs  for  personal  use  may  be  imported  in
  quantities   sufficient   for   a   3-month   treatment   without
  prescription (or for longer than 3 months, with a prescription),
  provided they are carried in your baggage