How do I contact the Brotherhood of Steel?

Question: Am having a bit of difficulty trying to get in contact with the Brotherhood of Steel.  Have found Hidden Valley and looked in all the bunkers but still nothing.  Are they triggered by a particular quest or lvl up?  Or have I missed something simple yet vital?
Answer: You can only enter the Brotherhood of Steel bunker if you discovered a dead Brotherhood of Steel Paladin and recovered their password, if you have Veronica with you or if you are told to find them by either House or Yes Man. As a last resort you can also pick the very hard lock (100 skill required).
Entering the bunker for the first time always starts the Still in the Dark quest
See the Hidden Valley Bunker for more details.
Comment: Thanks that was just what i needed.  Now i just need to work out how to get my gear back!
Answer: There are 4 bunkers in Hidden Valley. Just as you go past the gate for Hidden Valley, it's just to your left. It has a tree stump on top of it, the fence will be next to it too.
Once inside the first part of bunker, the door will be locked, needing a skill at 100. Or, an easy way to get inside at level 2 is to just go to town 188, pick up the bodyguard in there, then come back to Hidden Valley. She will open it for you quick and easier.
Oh, once most missions are done, the elder will tell you to come back later. That means you need to go out of the bunker and come back in 2-3 days' time. Then, more quests will open with both the elder and that paladin.
Comment: I must have gone back to the area a dozen times trying to get into the one bunker that the quest marker takes me to.  I finally read the first sentence in this post and didn't need to read any more.  Thanks.
Answer: There is another way to get in through the Hidden Valley that I accidentally stumbled upon:
I forgot which bunker it was, but it had the door with computer next to it. You go into the room while crouching. Hide behind the crates or boxes in the room and wait like 20 seconds. Then walk out and you will see 3 of them standing at the door. Go talk to them and you will be given some quest you have to do.
Answer: Kill a paladin located at Caesar's meeting on the quest Out of the burning pan. Yes you will get all of security after you but it's worth it.


Oracle Creating ER Diagrams and Data Dictionaries

Question: I am new to Oracle Databases and would like to develop a data dictionary and ER Diagrams for our existing databases. Do you have any tips, scripts, tools for doing so?
Comment: You can check [dbForge Studio for Oracle](https://www.devart.com/dbforge/oracle/studio/) Enterprise edition and [dbForge Documenter for Oracle](https://www.devart.com/dbforge/oracle/documenter/). 30-day trial is available, try right now!
Answer: Oracle's Data Modeller can reverse-engineer from an existing database. They were charging for it at one time, but it is now free to use.
Comment: And it comes bundled with Oracle's SQL Developer 3
Answer: We're using Sybase's PowerDesigner though I admit, its quite overkill for what you want.  We're using to support our full software engineering effort, from diagraming use-cases for requirements gathering, capturing those requirements, conceptual and physical models (database, object oriented code, infrastructure, etc), requirements/functionality verification matrices...
Basically anything UML-oriented that helps us to discover, architect, track and implement business solutions from an IT perspective.
Don't be fooled by the "Sybase" name - it supports MANY major RDBMS's and UML diagram formats and has templates for them all.  Its a very cool tool.
Answer: The free oracle sql developer data modeller works well. note that this is a seperate download than the one bundled with sql developer. The data model tool in sql developer does not have as many features.
http://www.oracle.com/technetwork/developer-tools/datamodeler/overview/index.html
It has some video walkthroughs.
file-> import -> data dictionary. You add a connection to a database and decide what you want to reverse engineer.
Note that the model part will be a mess and will take you time to make it neat enough to read. When oracle reverse engineers, it gives you a physical model and not an ERD. You can change the Physical Model into an ERD. However, most people do  not know what an ERD is and think an ERD is a physical model. ERDs have minimal value at the stage where your data model exists. There is no good reason to keep a physical model (which is easier for developers to read) and an ERD.
As far as data dictionary... This usually means documentation about your data model. The best way to do that is to use the tool and to use the "comment" command. Oracle allows you to create comments for all tables, columns and objects and store them in the database. This way you can have documentation in the database that is queriable. Sql Developer data modeller can query this.
You can do this in the GUI, but I find it faster to use "comment" commands and put it in the database from sql scripts, then pull it, instead of clicking on each object. Google "oracle sql comment" for details on how this works.
Answer: I know that SQLServer works with Visio; I'm not sure if Oracle does or not, never tried it, but Visio has a LOT of tricks up its sleeves.
Also, if you're in a reasonably large business, Visio isn't that hard to scrape up a copy of, albeit the license can be a little rich. But professional teams in reasonably large businesses usually already have Visio so it's not that big of a deal.
If anyone can deny or confirm that Visio will do this for Oracle as it does for SqlServer that would be awesome.
Comment: Visio comes with an Oracle driver - you can reverse engineer Oracle databases with it.  Note that you need Visio Pro for the database reverse engineer feature.  Another nice feature of visio is that you can add back FK relationships that are missing from the database.  This makes the structure much clearer.  You can also make multiple diagrams from the same repository to illustrate different parts of the model.
Comment: Today I learned...
Answer: I answered same question in https://stackoverflow.com/questions/8140387/oracle-extract-graphical-database-representation/8149947#8149947
See below.
For a free tool I recommend schema spy, http://schemaspy.sourceforge.net/.
It needs Java Runtime.
Look to http://schemaspy.sourceforge.net/sample/relationships.html to see diagrams it generate.
simple usage with oracle hr template is given below.
<code>SET JDBC_ORACLE_JAR=C:\oracle\product\10.2.0\client_1\jdbc\lib\ojdbc14.jar
SET CONNECTION_USERNAME=hr
SET CONNECTION_PASSWORD=hr
SET TNS_DATABASE_NAME=orcl
SET SCHEMA_NAME=HR
SET TABLE_NAME='EMP'
SET OUTPUT_NAME=HR_EMP

java -jar schemaSpy_5.0.0.jar -dp %JDBC_ORACLE_JAR% -db %TNS_DATABASE_NAME% -o     schemaOutput%OUTPUT_NAME% -u %CONNECTION_USERNAME% -p %CONNECTION_PASSWORD% -i %TABLE_NAME%.* -schemas %SCHEMA_NAME% -hq -noviews -loglevel severe

java -jar schemaSpy_5.0.0.jar -dp %JDBC_ORACLE_JAR% -db %TNS_DATABASE_NAME% -o     schemaOutput%OUTPUT_NAME% -u %CONNECTION_USERNAME% -p %CONNECTION_PASSWORD%  -schemas %SCHEMA_NAME% -hq -noviews -loglevel severe
</code>
First one will give you diagram with tables starting with EMP .
Second one will give you diagram with all tables in hr schema .
Comment: I would like to ask a question. What is etiquette of dealing with duplicate questions and answers?
Answer: We use Dataedo for generating data dictionaries and ERDs for all our databases - Oralce & SQL Servers. You just connect to a database, schema is imported into repository and you can describe each element with UI. Tool enables splitting large databases into logical modules, defining missing FKs and UKs, use rich text and paste images. Using physical and logical FKs tool creates simple ERDs.
Each time database schema changes you can import those changes and they are automatically reflected in repository.
Data dictionary with ERDs are exported to PDF or interactive HTML.
I'm the product manager of Dataedo.


"This question already has a lousy answer here"

Question: There is an aspect of duplicate questions I have long wondered about: I often see questions that are similar or identical to an existing question, but the answers to the older question are poor or incomplete in various ways. What is the right thing to do in such cases? Closing the question as a duplicate, or not asking it at all (if I am about to ask but discover a duplicate without a good answer) only serves to perpetuate the lack of a good answer.
Answer: Ask your question again. Link to the existing one, explain that the solutions there didn't help you, or that there are no solutions at all. Make sure your question is a better one than the dupe (more detailed, clearer, better researched, whatever) and then we can close the old one as a dupe of yours.
Comment: ... if the new question gets a less lousy answer.
Comment: @muru, in fact what prompted me to finally ask this was one of my own recent questions; and indeed it has a better answer already. (To avoid misunderstandings: in that case, the answers to the earlier question were not "lousy", just less than perfect.)
Comment: @alexis also, if both questions have answers worth saving, you can flag one with a custom mod flag and suggest we merge them.
Comment: Thank you, that's good to know. It's not clear from the dialogs.
Answer: This situation is partially due to voting patterns. People don't like to downvote lousy answers, because doing so makes them look ungrateful (if only in their own eyes) and cost them rep. Add some sympathy upvotes and voila! - you have an upvoted answer which makes the question an eligible target for dupe closing.
So, if you're about to ask a question and have found a duplicate with a +1 answer which can't possibly help, just downvote that answer and ask. People won't be able to close your question if the dupe target doesn't have at least a half-decent answer:

Of course, this advice doesn't apply to cases where the answers in question are outdated or dealing with an issue which is not identical. In that case, @terdon's advice fully applies: you should be able to easily explain why your question is not a duplicate, so there's no problem to begin with.
Answer: Close as duplicate. If necessary, answer the existing question, edit it to improve the question (there's almost always room to do so!), or add a bounty to it.
If something got a lousy answer once, asking twice isn't going to magically make a better answer appear. Better to have everything consolidated so the voting system can work.
Comment: There's no magic to it: New questions get read more and answered more than old ones. There's little motivation to answer an old question, where the OP has long ago moved on and the trail of low-voted answers almost ensures a new, 0-vote answer will never be read.
Comment: Anyway I often try to apply your advice to edit the question, but it's not that simple: If an old question didn't get to the heart of the issue (making it a poor or misleading question), it usually cannot be fixed without invalidating the existing answers.
Answer: ** Not an answer but I cannot add a comment with reputation < 50 **
As a reader of forums like this I get very frustrated with sites that kill a question as a duplicate - when google brought me to the 'killed' question.
Worst of all is when it gets closed with "answered elsewhere", but no reference. While, perhaps, that might have some relevance to whoever asked the question (do your research better) - it does not help someone who comes here later and does not know how your search mechanism works - to find that other better or worse question.
So, "reputation permitting" I am going to up-vote the answer that suggests to "duplicate-tag" the earlier question, especially if "new questions" get more weight from search engines.
Request to moderators: please ALWAYS add a link to the 'other', i.e. "not a dup" question. Many thanks!
Comment: Actually, it is impossible to close as a duplicate without a link on SE. The only way to mark something as a dupe is to provide the target question it is a duplicate of. So don't worry, this is one problem that doesn't exist here.
Comment: Do you have an example on unix.SE that was closed with "answered elsewhere"? I thought we were pretty careful about closing only with a follow-on reference
Comment: not offhand. unix.SE is not *.SE and maybe *.SE in general is much better than others. But it is a very very big red flag for me. Takes a long time for me to forget and follow links from a search engine - OR - I am extremely desperate. In short, I read the question - and past frustrations came up - I am just the reader and this does not help! SOO!! very glad to hear that unix.SE has the reader in mind!
Comment: and I wish I could edit my comment - so many missing words... but I expect, or hope, that over time I will proof-read my comments better.
Comment: As roaima says, I believe that the [SE] system doesn't allow a question to be closed (indeed, doesn't allow a user to vote to close a question) *as a duplicate* without specifying a duplicate target.  Here are a couple of things that *can* happen, however: (1) Question `A` gets closed as a duplicate of question `B`, and then question `B` gets deleted.  This should be flagged for moderator attention. (2) Somebody writes a *comment* saying "this question has been answered elsewhere" (without a reference), and then the question gets closed for other reason(s).  Or maybe doesn't get closed at all.


SharePoint visual webparts for NewForm with client side coding

Question: I need to use visual web parts to create a new item form for a list.
I know I can do this by using SSOM..
But I want to reduce the load on the server
Can I use CSOM?.. Or is CSOM mainly for sandbox solution?
Right now I am trying to write JavaScript code on ascx page but I am having issues with client context
Please let me know if you have better ideas.
I am working with sp2010 visual web parts.
I do not want to use SharePoint designer and infopath
Thanks in advance...
Comment: What do you do in this form "newform"? validation some fields? create more field and manipulate?
Comment: In my visual web part I have a asp drop down control which is binded with SharePoint list items. On change in JavaScript I need to get the selected text and using caml search the selected text in a different SharePoint list in which the selected text is a lookup column and display all such items..
Answer: There is a workaround to get the (C#) CSOM to work in a farm solution (the name for solutions that encompass code that needs to be installed on the server), there is an SP StackExchange answer on that here: CSOM in FarmSolution
You could also use a Sandbox solution as you mentioned; C# code in sandbox solutions is deprecated but you could create a webpart that used just the JavaScript Object Model (JSOM) to accomplish what you need. It's worth noting that you can create visual web parts in Sandbox solutions now as well.
As a final alternative, unless you need to leverage the webpart framework (passing values between web parts, or configuration properties) you could just create an HTML/CSS/JavaScript solution and implement it via source code on the aspx pages or something like the Content Editor Web Part -- this is the route that I currently use for light customization on SP2010.
For some more references on using the JSOM and JavaScript REST API see the following MSDN article on Javascript development in 2013 -- the vast majority of JSOM functionality is available in both versions, and 2010 supports ListData operations with REST:

REST: http://msdn.microsoft.com/en-us/library/office/jj164022(v=office.15).aspx
JSOM: http://msdn.microsoft.com/en-us/library/office/jj163201(v=office.15).aspx
Comment: Hi john, Thanks. But I have a requirement of fetching data from different list and displaying it on the web part.. Basically I have a drop down and once I select an option it should fetch data from a different list where the selected item in drop down will be a lookup.. I need to perform such functionalities.. Any suggestions?
Comment: Well my suggestion would be to do it client side and use the JSOM since it can easily accomplish everything you're describing; but if you're not comfortable in Javascript and can turn on the user code service in your environment I would suggest implementing a Sandbox Solution -- otherwise just leave everything Server Side in a farm solution (although that is the least preferred method for many reasons!)
Comment: Yes, I am trying to use jsom but the code always gives me an error when I use get enumerator I get this error the collection has not been initialized it may not be requested or the request has not been executed. It may need to be explicit
Comment: Remember that Javascript code all executes asynchronously, you have to load the collection you want using `context.load(clientObjectOrCollection)` then use `executeQueryAsync` to retrieve the information and operate on it inside of a callback. I modified my answer a bit to provide a better JSOM reference, you can find list operation examples here: http://msdn.microsoft.com/en-us/library/office/jj163201(v=office.15).aspx#BasicOps_SPListItemTasks
Comment: Yeah I have already done that.. I am not sure what the issue is..
Comment: Guess what I changed the code a bit and it worked.. I was writing on query succeed inside document.ready.. Finally.. Wonder why this was happening though
Comment: Take a look at using `SP.SOD.executeFunc` and `SP.SOD.executeOrDelayUntilScriptLoaded` instead of `document.ready` http://www.ilovesharepoint.com/2010/08/sharepoint-scripts-on-demand-spsod.html
Comment: Hi I am working with cascading drop down in a visual web part. I am able to complete this functionality using c# but I want to implement this functionality using JavaScript jquery basically I want to reduce load on server. Can anyone please help. Thanks in advance


How to prevent melting too much paraffin in a hybrid LOX-paraffin rocket?

Question: In a hybrid LOX rocket, only the flow of LOX may be controlled. The amount of paraffin melted by heat is determined by the very complex heat transfer from gas to solid paraffin. If the mixture of propellants is too fuel rich or too oxygen rich, the efficiency will suffer. The temperature of the paraffin before launch may influence the efficiency. A start in a very hot climate may be impossible.
Answer: You just found the primary shortcoming of hybrid engines: fuel flow cannot be controlled on the fly. The engine can be shut down and restarted unlike common SRB, but throttlability is lousy and lossy. And lots and lots of promising fuels were abandoned due to bad melting or evaporation temperatures.
You can prepare the optimal fuel a'priori by choosing the parafin composition - longer hydrocarbons will have higher melting point. Other additives may reduce impact of parafin melting; composite the parafin with fibrous material (cellulose/paper, cotton, polyethylene fiber) and despite parafin melting, the shape will be retained until the fiber burns out. Or just tune your combustion parameters (oxidizer supply, chamber pressure) to such that parafin surface ablates before the heat from the surface gets to transfer deeper.
Comment: (you may also try cooling the parafin with the LOX. Say, the LOX must flow on the outside of the combustion/fuel chamber before being injected; parafin is cooled, LOX is heated/evaporated providing more energy. Of course as you'll have a lot of trouble controlling the temperature, this may introduce combustion stability problems as mix of gaseous and liquid oxygen is injected... well, no easy solution here, it's rocket science!)
Comment: But in solid parafin heat transport is very low, it is a bad thermal conductor.


Distribution of Number of Approvers

Question: Every transaction directly references two previous transactions. But I was wondering, does this also mean that every transaction will be referenced by exactly two transactions or will it be random? If it is random, what does the distribution look like?
Comment: They will have to be referenced by at least one transaction to give them a chance of being confirmed. Some transactions (e.g. milestones) will be approved by very many transactions), while others only have one. I don't have a full node handy so I'll wait for someone else who wants to write a script to evaluate this :-)
Answer: Let us assume every transaction directly references exactly k other transactions (k = 2 in the case of IOTA). Now under uniform random tip selection, every transaction will on average be referenced by k other transactions (due to the stationarity property).
The histograms below provide a visual proof of this. I assumed a network delay of h = 1 with 40k transactions per simulation. For comparison purposes, I am including two examples for the issue-rate λ (10 and 20).

Distribution of Number of Approvers


What effect does the thickness of metal plates have on capacitance?

Question: Clearly a decrease in thickness of the dielectric increases capacitance, but how about the metal plates on a parallel plate capacitor? If you increase or decrease the thickness too much will you see a increase/decrease in capacitance? Is there an optimal thickness of the metal plates?
Comment: The simplest idea about gradually increasing the thickness isn't hard to gather. It provides more volume for the charges to spread out within and a little bit more surface area for a few more excess charges to accumulate across. It's a sea of charges either way, though. This may support greater currents due to the cross-sectional area but there is little other change. But most of the effect of the dielectric on capacitance happens between the plates. And the round trip path integral of the electric field (the round trip potential difference) must still sum to zero. Not much change, 1st order.
Comment: This is experimentally supported by olden-day air gap variable capacitors used to tune AM radios, where the plate thickness wasn't a consideration (however the gaps were) in their construction. You could buiild them with thicker or thinner plates, based upon your desire for sturdiness to bumps and dings, but the main design issue was the spacing.
Answer: Think of metal film capacitors which literally have a metal film vapor deposited onto the dielectric. The less metal thickness the less the waste in mass and bulk and metal. It only needs to be thick enough to have full conductivity. Adding thickness just adds mass and bulk with no gain, so optimal thickness is to be as thin as possible.
Note that metal plates need to be thick enough to hold their own weight and shape, as in old style air-gap adjustable capacitors. The plates were about 5 mils thick.
Note that high-energy capacitors for arc simulation will use a thick dielectric with metal foil, soaked in a light oil as a coolant and to prevent internal arcing. These capacitors can be the size of a shoe-box to the size of a filing cabinet, so you just accept their size and weight, normally not portable at all.
What does affect capacitance is the thickness of the dielectric, so the thinner the better, but it must be thick enough to block/handle the rated voltage. More metal (and dielectric) in terms of windings also increases capacitance.
I am sure you have noticed that for a given voltage, more capacitance means a larger capacitor. If the voltage is fixed but you increase capacitance, you have a larger capacitor. For this reason capacitor manufactures offer electrolytics in both tall and skinny, as well as short and fat styles. Most designs make use of some compromise between too much height or too much width, then they chose parts that fit that style.
This is where the compactness of todays capacitors pay off with smaller foot-prints on the board.
Comment: @gstudent Very thin films (for example less than tens of nanometers for copper) often do not conduct well due to interface effects, so you typically need to be at least that thick.  Depending on the power handling characteristics, you might want thicker as well so that there is less resistive heating.
Comment: What constitutes "thick enough to have full conductivity" i.e. at what thickness do you lose full conductivity?
Comment: Depends on the metal deposited by vapor. Many atoms thick to be sure, but this is where lab equipment determines minimum thickness based on ohms ^2 cm. Also this vapor deposit has to be equal over all conductive surfaces to have consistent product accuracy.


KitKat issue: device turns on when plugged in

Question: Yesterday I updated my Samsung S4 to 4.4.2 (I9500UBUFNA2 - Kernel 3.4.5-742022 18-Feb-2014) via Kies 3. If device is turned off then I plug in, picture of measuring battery image appears for 2 seconds and then disappears as usual, then instead of battery level image, phone turns on. Same behaviour when I turn it off while charging: phone turns on again. I think battery level image cannot load due to a Kernel problem. Any idea ? Thank you.
Answer: Solved: installed I9500XXUFNB3 (via ODIN)


How to prevent iPad from using Personal Hotspot?

Question: My iPhone5 keeps advertising itself as a Personal Hotspot even though I set that to off. My WiFi only iPad keeps connecting to the iPhone HotSpot every time my WiFi router fails. This is driving up my data usage. How do I make the iPad forget the Personal Hotspot? I have already factory defaulted the Network Settings but it appears anyway. I have also changed the Personal Hotspot password on the iPhone and it connects anyway.
Answer: On the iPad, in Settings > Wifi, tap the 'i' in a circle icon next to the listing for the Personal Hotspot, then tap the Forget This Network tab.
You should make absolutely sure the Personal Hotspot is turned off. Looking at Settings > Personal Hotspot, it is pretty unambiguous.
You should also check to see if Instant Hotspot has been enabled:

Instant hotspot
You can use Personal Hotspot on your iPhone to provide Internet access to your other devices without additional setup. You'll need to sign in to iCloud using the same Apple ID as your iPhone. Also, your cellular provider needs to provision your Personal Hotspot.
To get Internet access from your iPhone:
On your iPad or iPod touch, go to Settings > Wi-Fi on your other iOS device and select your iPhone or iPad that has a cellular connection.
On your Mac, go to the Wi-Fi menu at the top of your screen and select your iPhone or iPad that has a cellular connection.

From this Apple Support Page
Comment: This is of course correct, but has the weakness of causing your computer to forget the network as well.

This is a really annoying flaw in apple's password sharing features... my ipad has LTE, but once my computer (a mac) connects to the hotspot on my iphone my ipad also connects. there doesn't seem to be any way other than turning off wifi to prevent that.


Is destroying money Bal Tashchit

Question: Aside from the national legality of destroying currency, does the Torah consider the intention of lowering inflation a valid reason for destroying money, or will it fall under Bal Tashchit?
Comment: Are you asking if the Department of the Treasury (or people working on its behalf) are halachically allowed to destroy bills?
Comment: I am asking if Jews working for the Dept of the Treasury, or on their on volition, are Halachically able to destroy currency.
Comment: There could possibly be a distinction between destroying gold coins (which have significant intrinsic value) and destroying paper bills (that only have value by the government's fiat). I can't imagine how destroying paper bills on behalf of the Treasury could possibly be forbidden.
Answer: Rambam Melachim 6.10 says wasting other items not just fruit trees:

וְלֹא הָאִילָנוֹת בִּלְבַד. אֶלָּא כָּל הַמְשַׁבֵּר כֵּלִים. וְקוֹרֵעַ בְּגָדִים. וְהוֹרֵס בִּנְיָן. וְסוֹתֵם מַעְיָן. וּמְאַבֵּד מַאֲכָלוֹת דֶּרֶךְ הַשְׁחָתָה. עוֹבֵר בְּלֹא תַשְׁחִית. וְאֵינוֹ לוֹקֶה אֶלָּא מַכַּת מַרְדּוּת מִדִּבְרֵיהֶם
Not only trees but breaking tools, ripping clothes, destroying buildings blocking springs destroying food one transgresses "Bal Tashchis" but one gets rabbinical lashes (only destroying fruit bearing trees gets lashes for Torah Transgression.

Kesf Mishna provides source for Rambam which is primarily talking about wasting money:

שבת פרק רבי אליעזר דאורג (דף ק''ה:) המקרע בגדיו בחמתו והמשבר כליו בחמתו והמפזר מעותיו בחמתו יהא בעיניך כעובד עבודה זרה שכך אומנותו של יצר הרע היום אומר לו עשה כך וכו' עד שאומר לו עבוד עבודה זרה ועובד
  ..... one who disperses his money to lose them is like someone who worships idols......

Banknotes are just a a Representation of currency and are only worth the assets which the country owns, so if the government destroy notes they are just making their currency stronger there is no destruction of actual assets. But anyone burning his own banknotes without government knowing is wasting his rights to the govenment assets for no reason when he could have spent it on something useful (the affromentioned items in the Rambam). So it's Grama of Bal Tashchis
Comment: I'm not sure this is correct. The Rambam wrote that it's only forbidden to destroy 'Derech Hashchosa'. Here, the guy has a 'constructive' purpose of fighting inflation. Maybe that is enough of a reason to validate the destruction and make the action no longer a forbidden one of 'Bal Tashchis'.
Comment: Also, do you know how much money one would need to destroy to have any effect on the economy of the United States?
Comment: @Salmononius2 without the Federal reserves instruction he has achieved nothing destroying the notes, despite his "lofty" intentions they just think the notes are still circulating and the value of currency will not rise. So he is achieving Bal Tashchis (but then again *shote patur min hamitzvos* so if that applies he might not be *chayav*))
Comment: @Salmononius2 also read David Kenner's point as to why your suggestion is farfetched
Comment: It might be far-fetched, but that's the question being asked. It's a Kasheh Fun A Maaseh. :) On a serious note, the OP did write in a comment that we might be talking about a Treasury employee, so that is one practical case. Besides, I'm not convinced that the effectiveness of an action matters here, only the person's intent. If one intends to do something productive, I wouldn't be shocked if you told me that was enough to stop it from being 'Derech Hashchosa', regardless of how outlandish the action might be (but as you mentioned above, at a certain point the person is probably a Shote...)

Is destroying money Bal Tashchit


How to adjust for making candy from corn syrup instead of sugar?

Question: I've recently started to experiment with making hard candy from straight corn syrup rather than conventional sugar, and so far it has worked remarkably well. Aside from increased sweetness and improved mouthfeel in the final product, the process is faster and more reliable — there is no need to wait for sugar granules to dissolve, and the corn syrup boils nearly uniformly from start to finish without any need to adjust the heat or any risk of going out of control. It's been consistent enough that I'm comfortable leaving the pot entirely unattended on a timer until nearly the final minute and doing other tasks while waiting for the syrup to come up to temperature.
However, hard candy recipes produced in this way seem to end up slightly softer than they do when making them with traditional sugar, and it's really not clear to me why this is — if this is due to the corn syrup requiring a higher temperature to reach the same moisture level; if fructose sugar glass just softer generally even at the same hydration, or something else.
For hard candy at least, I've considered trying to add back in some amount of regular sugar again to try to be able to make harder sugar glass, but I have especially for more specific candy types like nougat (that are sensitive to viscosity/hydration) it really isn't clear to me how to compensate for this difference.
Unfortunately despite searching I have yet to find even a shred of information on the subject of making candy using corn syrup in this way; all of the google search results are polluted with sources that do little else but spout the evils of corn syrup and decry the very concept of using anything but the One True Saccharide for candy-making, and with "fructose free" candy recipes that straight-up walk you through the process of hydrolyzing part of the sugar to make the fructose yourself, without bothering to mention that fact.
Does anyone have any sources or know where I can find actual information on how to use corn syrup for candy-making, and how to compensate when making a substitution for regular sugar?
In a perfect world I'd love if I could find a reference source with information on how to derive (or even just tables listing) the temperature/hydration and hardness curves for different sugar mixtures, but even just basic information and recipes would be great.
The particular syrup I'm using here is Golden Barrel High Fructose 55 (although my question isn't limited to just this syrup in particular). Here's the description from the datasheet:

High Fructose Corn Syrup 55 is a second generation high fructose syrup. The principle sugars, fructose and dextrose, give it a sweetness comparable in most foods and beverages to sucrose or invert sugar. The high sweetness level of high fructose corn syrup 55 provides desirable characteristics to carbonated drinks, still drinks, and processed foods.

Also, here's my best sugar glass recipe at this point, for reference:

Dispense 1 lb of HFCS55 into a pot. Place the pot on the stove on high and set a timer for 14 minutes. Return once the timer goes off and continue to heat for about another minute, until temperature reaches 310 F. Remove from heat and wait for it to cool below safe temperature for additives. Stir in color and flavor, and process into desired shape.
Answer: This document seemed like it might answer your question as it talks about the temperature it takes to crystallize supersaturated sucrose solutions in the presence of fructose glucose and corn syrup.
https://www.researchgate.net/publication/242257775_Crystallization_of_the_supersaturated_sucrose_solutions_in_the_presence_of_fructose_glucose_and_corn_syrup
From what I know about candy making it is because sugar starts out as a crystal it can recrystallize after heating easier. With hard candy (glass candy) you're manipulating the sugars to reform the crystals how you want them.


Characterization of Tychonoff spaces in terms of open sets

Question: Metrizability and complete regularity are topological properties that are, in a sense, different from the Hausdorff condition because they are not defined purely in the terms of the open sets, but rather using some external object, namely $\mathbb R$. Now a space is metrizable if it has the weak topology induced by a function $d : X \times X \rightarrow \mathbb R$ satisfying the properties of a metric, but metrization theorems tell us that an equivalent condition is that $X$ is regular and has a sigma-discrete basis (and this is purely topological). Is there a similiar characterization of Tychonoff spaces that makes no reference to $\mathbb R$ whatsoever?
Comment: http://en.wikipedia.org/wiki/Tychonoff_space#Embeddings
Comment: Here's one $\mathbb{R}$-free characterization: a space is Tychonoff iff it has a Hausdorff compactification. Is that the sort of thing you want?
Comment: I don't necessarily buy the distinction you're making between open sets and "external objects." After all, talking about open sets is the same thing as talking about functions to the Sierpinski space. Does the Sierpinski space count as an external object?
Comment: I don't think, because it still makes a reference to an external object.
Comment: There's a natural bijection between the set of continuous functions from a $T_0$ space to the Sierpinski space and the topology of the space, but there's no such bijection between the topology of a regular space and the the set of continuous functions to the unit interval. I don't know category theory so I don't know how to make this precise but I think you should get the intuitive feeling that the Sierpinski space is in some sense canonical and minimal. Anyway the answer given is what I've been looking for (I actually read the book but managed to miss that part)
Answer: A $T_1$ space $X$ is completely regular if and only if it has a basis $\mathcal{B}$ such that

For every $x \in X$ and every $U \in \mathcal{B}$ that contains $x$, there exists $V \in \mathcal{B}$ such that $x \notin V$ and $U \cup V = X$.
For any $U, V \in \mathcal{B}$ satisfying $U \cup V = X$, there exist $U', V' \in \mathcal{B}$ such that $X \setminus V \subset U'$, $X \setminus U \subset V'$ and $U' \cap V' = \varnothing$.

The proof can be found in
Frink, Orrin Compactifications and semi-normal spaces. Amer. J. Math. 86 1964 602–607.
The statement I've given above is actually dual to the statement of this paper. I took it directly from Engelking's General topology, which is the book I strongly recommend for finding references to this kind of questions.
Answer: Another answer was given by Aarts and De Groot in Complete regularity as a separation axiom Canadian Journal of Mathematics 21 1969 96–105. Frink's condition sets things up for a proof a la Urysohn's Lemma; Aarts and De Groot's condition is in terms of subbases and the proof proceeds by constructing a Hausdorff compactification.
Answer: Suppose that $(X,\mathcal{T})$ is a topological space. Then define a relation $\prec$ on $\mathcal{T}$ by letting $U\prec V$ if and only if $\overline{U}\subseteq V$. Define a relation $\ll$ on $\mathcal{T}$ by letting $U\ll V$ if and only if there is some $(U_{r})_{r\in[0,1]\cap\mathbb{Q}}$ such that $U_{0}=U,U_{1}=V$ and $\overline{U_{r}}\subseteq U_{s}$ whenever $r<s$. Then

the space $(X,\mathcal{T})$ is regular if and only if for each $U\in\mathcal{T}$, we have $U=\bigcup\{V\in\mathcal{T}|V\prec U\}$, and
the space $(X,\mathcal{T})$ is completely regular if and only if for each $U\in\mathcal{T}$, we have $U=\bigcup\{V\in\mathcal{T}|V\ll U\}$.

This characterization of regular and completely regular spaces is the way that one typically defines regularity and complete regularity in point-free topology. In fact, in point-free topology it is much more convenient to use this characterization of complete regularity than it is to use the characterization of complete regularity in terms of frame homomorphisms from the real numbers to your frame.
Perhaps the most illuminating characterizations of complete regularity are the following characterizations.
Let $X$ be a topological space. Then the following are equivalent:

$X$ is completely regular.
$X$ has a compatible proximity.
$X$ has a compatible uniformity.

Of course, proximities and uniformities impose additional external structure on topological spaces.


How does the report system in League of Legends work?

Question: I have been wondering this for a while now. I have played dozens of games where people want to report me because I was playing poorly, but how many reports does it take to get into the Tribunal?
Comment: Keep in mind that reports for being a bad player don't really count towards this system, those reports are used purely for the matchmaking system (as a way of avoiding being matched with people)
Comment: @ChrisRasys Yes, that's true but I was pretty scared when 4 premades decided to report me for intentionally feeding when I was 3-7 :P. (and definetely not intentionally feeding)
Comment: If the report reason is "Intentionally Feeding" it will actually count towards this system, since this reason has nothing to do with skill. What Chris Rasys is saying just applys to the "Unskilled Player" Reason.
Answer: There is no set number of reports that automatically determines whether or not you will come before the Tribunal.
In section 14 of the Tribunal FAQ, you'll find the information that addresses your question.

I just got reported. Does this mean I will be reviewed by the Tribunal?
It depends, but not necessarily. Players are only reviewed by the Tribunal if there is significant evidence to support a need for their behavior to be reviewed. Our system takes a variety of factors into account as player reports roll in, so simply getting reported once is unlikely to land you in front of the Tribunal. Here are a few of the factors considered before you find yourself on the docket:

Accounts that accrue a large volume of player reports are much more likely to be reviewed.
New accounts are judged more stringently than veterans.
The reputation of the player who is reporting you will also be taken into account. Reports made by level 30 summoners with clean record will be weighed more heavily than those submitted by newer accounts and/or those whose reputation has been tarnished by frequent harassment reports.

As you can see, there are a number of factors that go into Tribunal reports, and this is not the full list, as Riot does not disclose that. The linked FAQ should be able to answer any other questions that you have about the Tribunal process.
Answer: I can't tell you exact number but this is how it seems to work. Let's say you were mad and started feeding so 3 members of your team and 2 of the other reported you. That wouldn't do much, but get you headed on your way to the tribunal. Now if you did it again and people reported you again then you'd probably be sent to the tribunal where the user base decides on if you should be punished or not. Depending on the chat logs and what the users said that reported you. You could receive a temp ban, perma ban, or just a warning. If this keeps going it will lead to a perma ban.
One exception to the reporting system is the "Bad Player/Noob" Report option. Riot has said that they will not punish anyone for being bad. Reporting anyone with that option does nothing. So if they are reporting you for being bad, don't worry about account bans. But do try to get better as it's more fun if you are winning. Good luck on the rift!
Comment: As I already reacted to ChrisRasys It was once with 4 premade trolls (and ofcourse some games when I just lost my lane) Most of the time when you are losing your lane badly or just playing bad you'll have atleast one person who will start flaming and try to make everyone report you :p. Thanks for your answer!
Comment: If I remember correctly, a certain amount of "Bad Player" reports will lower your psuedo-ELO for non-ranked queues.
Answer: A detailed video can be found here:

Its presented by Riot on how the whole system works, and the reasons why they chose it, it's pretty lengthy and overkill for the information you need.
Comment: This answer would be more useful if you summarized the key and interesting points in the video.


How to test if user is filtering post list in dashboard

Question: I am using the following code to enable a hierarchical exclusion filtering system in the dashboard when users access post lists and media library.
Admin posts & media are hidden to all users, while "teachers" and "students" have restrictions. Teachers may view they're own stuff and students data. students are restricted to their role-group.
The problem is that if a restricted user attempts to filter in the dashboard the post list, the action will be ignored because my filtering system will override.
There should be a way to apply my filtering system only when the users are not selecting an allowed filter. I see that the url changes on user filtering, adding some parameters but this is an unreliable system IMO.
Any idea?
//********** post & media lists filtered by user role & category ****************
function posts_for_current_role($query) {
global $students_allowed_cat;
global $teachers_allowed_cat;
global $pagenow;
    if($query->is_admin && !current_user_can('administrator')) {
        //$filtered_cat = '3,22';
        $user = wp_get_current_user();

        if( 'edit.php' == $pagenow   ){
            if ( in_array( 'teacher', (array) $user->roles ) ) {
                //The user has the "teacher" role
                $filtered_cat = $teachers_allowed_cat;
            }
            if ( in_array( 'student', (array) $user->roles ) ) {
                //The user has the "student" role
                $filtered_cat = $students_allowed_cat;
            }
            $query->set('cat',  $filtered_cat);
        }
        if( in_array( $pagenow, array( 'upload.php', 'admin-ajax.php' )  ) ){
            // hide media from admin
            $query->set('author',  '-1');
        }

    }
    return $query;
}

if( !current_user_can('administrator') ){
add_filter('pre_get_posts', 'posts_for_current_role');

Answer: I have found a solution, using  $query->get('cat'): when restricted users select "all categories" $query->get('cat') will return '0', so in this case I will apply filtering, otherwise my code won't run, allowing user-selected filter (in a restricted range) to be applied
/********** post & media lists filtered by user role & category ****************
function posts_for_current_role($query) {
global $students_allowed_cat;
global $teachers_allowed_cat;
global $pagenow;
    if($query->is_admin && !current_user_can('administrator')) {
        $user = wp_get_current_user();

        if( 'edit.php' == $pagenow   ){
            if ($query->get('cat') == '0'){
                if ( in_array( 'teacher', (array) $user->roles ) ) {
                    //The user has the "teacher" role
                    $filtered_cat = $teachers_allowed_cat;
                }
                if ( in_array( 'student', (array) $user->roles ) ) {
                    //The user has the "student" role
                    $filtered_cat = $students_allowed_cat;
                }
                $query->set('cat',  $filtered_cat);
            }
        }
        if( in_array( $pagenow, array( 'upload.php', 'admin-ajax.php' )  ) ){
            // hide media from admin
            $query->set('author',  '-1');
        }

    }
    return $query;
}


When to perform Asr prayer

Question: In Bangladesh generally hanafi madhab is followed.So call for Asr prayer is given which it is twice length shadow plus shadow at its zawal time.I read in a residential institution.Suppose time for Asr starting time is 3.10pm according to Shafii and 3.55pm according to Hanafi madhhab.The time for sunset is 5.35pm.But I have no scope to perform salat from 3.25pm to 4.40 pm.So which thing is best for me?Is it to perform salat before the  call for Asr prayer at 4.00 pm as in Islam it is told not to delay in Islam or it is better to perform salat after 4.40pm as Adhan(call for prayer) is needed for prayer.Please give proof to your answer basing on hadith.
Comment: IMO this question should be closed it is not only a duplicate of an existing and answered question, it was also asked by the OP before as a partial question beside the fact that this is a specific matter with no general benfit for others!
Comment: You can perform any fard prayer between the adhan time of the actual prayer until the adhan time of the following, but it is recommended to perform it as early as possible. So if you stick on hanafi madhab do it at 4:40 else be aware that calculation methods are not that exact.
Comment: How can it be duplicate one?I have given a condition that call for adhan I given at 4.00.So if I perform my prayer before 3.25 I am missing Sunnat e Muakkadah according to most of the hanafi scholars and wajib according to some of the hanafi scholars(source:Fatwa e Alamgiri).Again if I perform my salat after adhan I have to become late in performing prayer.I am asking which is the better choice here.
Comment: The answer of the duplicate question answers your question. The details you are asking about are not of general benefit as even at 4:40 you still can pray the sunna al muakada as it is simply a sunnah qabliya (sunnah which needs to be performed before fard) as you have enough time until maghrib adhan.
Comment: You haven't understood my question.I am asking which is better.If I perform my Salat at 4.40 pm then it becomes too late .Again I perform my Salat at 3.20pm according to Shafi madhab it becomes early but then Salat is performed before adhan.
Comment: 4:40 isn't too late you still have about one hour till maghrib!
Answer: i think you have these options to select from:

pray after 4.40 because there is a hadith:
https://sunnah.com/bukhari/9/55

Narrated Abu Huraira: Allah's Messenger (ﷺ) said, "Whoever could get
  one rak'a (of the Fajr prayer) before sunrise, he has got the
  (morning) prayer and whoever could get one rak'a of the 'Asr prayer
  before sunset, he has got the ('Asr) prayer."

pray before 3.25 but after 3.10, because, as i know, 1 length shadow is also accepted in hanafi mazhab: proof:
http://islamqa.org/hanafi/qibla-hanafi/34498

However, the one shadow-length opinion, which is the position of Abu
  Hanifa's main students, Abu Yusuf and Muhammad ibn al-Hasan, was also
  chosen by major Hanafi imams, as mentioned by al-Haskafi in Durr
  al-Mukhtar and by al-Shurunbulali in Maraqi al-Falah.

moreover, i think, one length version, which is accepted by majority of hanafi scholars, seems is error, because i have not seen any hadith that says that. >after half an hour: i have found now though it does not clearly say that 2 shadows is asr time's start. < for example, see this site: http://www.islamweb.net/emainpage/index.php?page=showfatwa&Option=FatwaId&Id=92052 : and the hadith which they show as evidence for that position in fact says its time is from 1 length to 2 lengths!

pray before 3.10, from zuhr time, which is nearly in 12:10, because it is not said in the hadithes "plus shadow at its zawal time". i have asked about this here. one length means 45 degrees of sun above 0 degree horizon line, and as i see in stellarium, even at zenith sun is under or nearly at 45 degrees.

When to perform Asr prayer


Adding a new switch with an independent light in an existing circuit

Question: I have two switches at the bottom of my stairs in the basement. One switch is a three way to the switch at the top of my stairs. The other switch lights a series of lights all connected to the same circuit.
One of those lights is in the pantry and what I would like to do is isolate that light from the rest by adding a single pole switch to the room.
The switch at the bottom of the stairs would still light up the rest of the lights.
Comment: How hard would it be to feed a new cable from the bottom-of-the-basement-stairs switch box to the pantry?
Comment: Is there an always-hot available in the ceiling?  Can you post a photo of the inside of the box for the bottom-of-stairs switches for that matter?
Comment: It depends on how it is wired if that light has a run to the switch location you could be in luck and adding a 2 switch on 1 yoke could bee all that is needed but some photos of the wires in the switch box would be helpful in figuring this out.
Comment: I can add a new hot from the bottom of the stairs or I can make a junction in the ceiling and feed the new switch and existing light. Not sure if that works or not?
Comment: I could show photos but not sure how to do that as I am a bit of a newb in this forum
Answer: Based on the input by the contributors, I was able to make an informed decision. I passed a new cable down through the wall to the main switch box at the bottom of the stairs. I wired in the new wire and passed the wire across to the pantry room. I removed the wire from the fixture and tied those together in a junction box. I passed the new cable down to the new box and passed a new wire from the box to the existing electrical box. The fixture box is plastic and doesn't have a ground screw so I just capped it off with a wire nut. I wired the light and the switch without any issue.


What is the best way for an end user to get all the contact and activity data from the database?

Question: Our group is using CiviCRM to house membership data for a small food cooperative.  We've lost our web developer and we're trying to get all of our data out of CiviCRM with only the user interface tools.  I've tried the various search tools, but the results are perplexing.  When I go to Search >> Find  Activities and search without any filtering, I get 124 activities.  When I do Custom Searches >> Activity Search without any filtering, I get 898 activities.  The discrepancy between the two is confusing, but if I assume the custom searches gives me the complete list, then my problem is that custom search doesn't allow me to specify which fields to download.  The regular activity search provides over 80 data points whereas custom search only gives 13 data points.  Feel free to point me to documentation if it's covered out there.  Thank you.
Answer: The difference in counts might be explained by the fact that at one time Find Activities only returned results where the With Contact field wasn't empty, and a quick check on the public demo suggests that's still true.
That also seems true for Advanced Search.
You can also try Search Builder, but the list of fields is minimal.
If you're using Drupal, you could try creating a View on the Drupal side that lists the activities.
Answer: Custom searches often have built-in filters that may not be very obvious, where as built-in searches allow you to query data with limited restriction. My suggestion to you would be to create a smart group of "All Contacts" (if you don't already have one), then use Search > Advanced Search and change the Display Results As filter as needed - e.g. start with Display Results As = Activities, then work through the list of entities as desired:

Hope this helps!


How are you supposed to judge ISO's effect on the image if you are looking through the viewfinder?

Question: When you look through the viewfinder, how do you prevent potentially taking bad photos by misjudging the ISO? You can see what the focus will be like and depth of field and the shutter speed isn't too difficult to judge. But the picture could look super good in the view finder but look horrible after because the ISO was set wrong. How can I make the view finder incorporate ISO before I take the photo so I don't need to take time to take multiple photos, or use live view?
Answer: You basically can't, at least not any any current cameras that I know of. What you can do, though, is practice a lot - even if it's just throwaway shoots you do. But use your gear as much as possible under varying light conditions, so that after inspecting the results over time, you get a feel for how the ISO settings on your gear will affect the final product. And keep in mind that, if you replace your gear, the characteristics may be totally different, so you may need to repeat the exercise.
Answer: Many cameras allow you to turn on options to display information, such as Tv, Av, and ISO in the viewfinder. But you've still got to look at it and pay attention to the numbers within your view.
Keep in mind that "ISO" itself is not what makes many pictures noisy. It's the very minute amounts of light we are allowing  into the camera that require the high analog amplification of high ISO values that does that.
For an example of how shooting the same scene under the same light using the same exposure time and aperture results in very similar results regardless of whether the ISO was set at a high setting when shot, or whether the image was shot at ISO 100 and then pushed that many stops digitally after the fact, please see:
What is "ISO" on a digital camera?
and a follow up to it:
Should higher ISOs really be preferred (all other things being equal)?
as well as this related question:
Is it better to shoot with a higher ISO, or use lower ISO and raise the exposure in post-processing?
Answer: Experience and learning from mistakes.
Tools like light meters and phone apps can help.
Mirrorless cameras are another good way.
Also automatic modes like aperture priority, automatic, or program can help.
But in the end, nothing is as useful as being willing to make a bad picture. The good part is nobody else cares much if you do. So getting experience is easy if you are willing to practice.


Would working on a personal project in my off time that could be used at my workplace (small communication tool) be seen as good?

Question: I've thought of something useful I could potentially build for my team that I'd like to work on in my off time. It would be a simple tool that helps with communication. It would mostly be for my own practice and something I don't want any strict deadlines on as it's just something I thought would be handy. Would presenting this when it's finished be viewed as a good thing or would it be seen negatively? My reasoning is that it could be viewed that I should have just put that effort into assigned tasks A.K.A my work.
Comment: So you basically want to do work for the company when you aren't actually getting paid for it ( during non working hours )?
Comment: @sf02 honestly it's mainly for my own practice (my own benefit). That I'd make something that could be useful is secondary.
Comment: That is fine if you want to work on projects for practice for fun or learning, but if it is something directly related to work that will benefit the company you should be properly compensated.
Comment: @sf02 I completely agree
Comment: @sf02 > I personnally see no issue not being directly compensated as I consider learning something new as a valuable thing on long term, for your career in or out of this company.
Answer: I would suggest you tell your manager/boss that you have an idea that will make communication better. If he/she thinks it's a good idea you might actually get a go ahead to do it as part of your work. If he/she does not think it is a good enough idea to spend resources on (which is not the same as it not being a good idea) then ask if it would be ok if you worked on it on your own time. Worst case scenario you are once again told no, and you can just make it anyway to practice but never implement it at work. Asking after it is already finished might raise questions on when you created this tool.
Comment: I like this suggestion since it's seems to be best of both worlds.
Answer: As long as your "pet project" does not cause you deviate from your assigned tasks, you're welcome to have them.

My reasoning is that it could be viewed that I should have just put that effort into assigned tasks A.K.A my work.

Not if you complete your assigned activities in time, with quality.
However, there's a silver lining.

If you're doing it in "overtime" (outside company-paid time) and using your own resources, it's fine.
However, if you're using company resources (hardware/ software) and if you have no problem with your company claiming the ownership of the developed tool, you're good to go. Otherwise if you want the tool to be licensed for yourself, or, even open-source, you should check your contract once again, there might be clause mentioning any work you do using company provided resource belonging to the company.
If you have significant amount of "free" time (i.e., company-paid time for which you have no work allocation) that you're investing (or planning to invest) into it, you may need to inform your manager about your work assignment, and then run the idea past your manager, to get an approval.
Answer: It's a bit of a complicated area of law sometimes. But it is possible. Things to keep in mind:

Anything you work on in the office will probably belong to the company
Anything you work on using work materials, equipment, code, APIs, etc. will belong to the company
In some jurisdictions, if it is related to the company in some way, it will belong to the company
Some company policies (attempt) to make anything you work on while employed, their property
Even if you're happy with all of that, you still must work on your assigned tasks

If the above are true, working on it at home may breach company policy
Other than that, feel free to work on it. Tips:

Make the tool generic and not tethered strongly to work
Work on it solely at home. Upload it to github/etc.
Seek permission from your boss before you download from github
Don't be discouraged if they decide not to use it
Ensure you use your personal time
Answer: You can do whatever you want in your spare time. If it implies bringing added value to your employer while in the meantime learning something new, I really don't see how your employer would consider this a bad thing as from their perpspective it's basically free stuff.
However, I would suggest being careful as people tend to get entiled, even with free stuff. As soon as you will have disclosed this tool nobody ever wanted to pay for, people will start thinking about how it could be improved with new features. As soon as people will start to use it, they will probably discover bugs and expect you to solve it. As the initial work was done for free, some might expect you to do these changes and fixes for free too, maybe with some kind of emergency especially if this is really useful. So I would be very careful when delivering the product and mention the "support policy" right away. i.e: "I wanted to learn xxx and in the meantime we were in need of a tool for doing xxx, so I gave it a try. Please be aware that I can not offer any guarantee over the stability nor the future support of it"
As a side remark, while some people will probably consider (it's already the case in comments) that working for free is stupid, I personnally appreciate that kind of mindset: you're basically not "working for free", but learning stuff while practicing on real-life situations, and the ROI you'll probably get in the long term, not immediately. From my perpective, solving real problems is the best way to learn new technologies/languages. The downside is that people easily take this behaviour for granted and may have a negative feeling when/if you suddenly stop doing it for whatever reasons.


Any detriment to hanging a bike by its front wheel?

Question: I came across the below image today and thought it a great idea for storing bikes. However I wasn't sure if literally hanging a bike by its front wheel might cause undue stress to either the wheel itself or the front forks. Has anyone else done this to no ill effect? In the image below the back wheels don't even seem to be touching the floor, which I would have thought would take some of the weight.
Comment: @John: some people have more bikes than heads.
Comment: If the front wheel isn't strong enough for this, you certainly don't want to try riding that bike!
Comment: There aren't enough helmets.
Comment: @BrianDrummond The wheel necessarily must be able to take the strain of being hung like that (due to symmetry). However the fork, under normal usage, will only need to take compression forces as opposed to tension. It is possible to design a bike that is road worthy, but is not safe to hang like that, in theory. In practice, such a bike would be too unpractical.
Comment: @John Only for bikes are rideable. One has no front tire.
Comment: Its fine for the bike.  Notice they've used a cloth or webbing strap through the rim to spread load and prevent marring of the rim and braking surface?  Can't tell how well the horizontal hanger rail is fastened to the three angle-brackets for the shelf - hope its not just sitting there.  Speaking of sitting there, those helmets should be on hooks or clipped onto something.  Doesn't take much to knock them off onto the hard concrete floor.   Final observation - the bikes will swing and clang about if theres any wind or a bump, kinda like a wind chime.  Not ideal but not bad either.
Comment: @John: Not every place has mandatory helmet laws.
Answer: You'd have to calulate the actual forces to be 100% sure but it's not going to be a problem: forces on front wheel/fork/headset while e.g. just sitting on the bike, braking or landing jumps will be (much) higher than the force applied from hanging it.
That being said, I do note at least two problems with this setup: first, good luck getting one of the center bikes out without touching or getting stuck in another bike. Second: from the picture it seems like you'd have to hold the bike with one hand then use the other to attach it. Ok for a roadbike, but for anything heavier that is just hard. Usually these systems have an open 'C'-shaped fixed hook into which you simply hang the bike which is much more convenient.
Comment: I would assume you un-clip the entire hanger from the "shelf" by its Carabiner clip, attatch the hanger to the wheel then lift the whole assembly up so that it would only require the Carabiner clip being pushed onto its loop, which i imagine probably isnt as bad, but is still pretty awkward.
Comment: You pull the velcro and stand back.
Comment: Lifting the bike shouldn't be too difficult: the top of the wheel looks like it's at about shoulder height and you just need to take up enough of the weight to allow you to either undo the carabiner or detach what looks like velcro. You can probably do that by bending your arm double at the elbow so your hand's at your shoulder, and then lifting with your legs.
Answer: No, there are no problems with doing this.
Bike shops frequently hang bikes in a similar way.
And when I lived in small house in the inner city, I hung all of the family bikes in a similar way for years, without observing any problems.
It's remarkably easy to get the bike up onto the hook or peg, when you learn how. Those in the picture don't look as easy. The rack I built used big butcher's hooks.
Edit: Bike wheels are designed to carry the bike's weight plus up to 100 kg of rider. They work by the spokes being in tension, with the load distributed around the wheel. This Cyclingnews Maintenance & repair article shows the tension of the spokes for various rims. The minimum spoke tension from all the wheels in the list is 51 "kg force" (500 N). The maximum tension described is over 175 kg. Conclusion: hanging a 20 kg bike by the wheel is a non-issue, even if the load is carried by a single spoke.
Comment: Bike wheels are designed to withstand pressure, not extension from carrying bike's weight.
Comment: @MikhailBatcer When the bike is on the ground, the spokes above the hub are carrying some portion of the load in tension (i.e. the hub is hanging from the spokes that are above it)
Answer: I've done this before and it worked out nicely. I never had a problem with the forks (even with shocks, though if they are expensive shocks you'll want to lock them first), headjoints, anything. Turning them to face the wall (so its like they are riding up the wall) makes it easier to get them in and out. Even with a 40lbs. crappy, huge BSO-grade MTB it wasn't hard to stow or recover. Maybe my (tiny) wife would have found it more difficult, but anyway 40lbs. isn't very heavy* and its about as heavy as bikes get.
Not sure if I would do this with racing rims that have huge gaps between spoke sections, but then again a racing bike is ~1/3 the weight of a 40lbs. pile of poo -- so it probably wouldn't be an issue even then.
[*I mean 40lbs. isn't heavy to lift or carry... 40lbs. feels enormously heavy and sluggish to ride when you're used to slipping around on something 1/3 the weight!]
Answer: There shouldn't be a problem with this.  As was said, bike shops do it all the time.  Even a lightweight wheel needs to be strong enough to hold the bike and cyclist.


Locking for bcm2835 library?

Question: I'm using adafruit's DHT22 temperature and humidity sensor, with a modified version of their driver, which in turn uses this bcm2835 library.  My modification is that, instead of bailing on failure to read cleanly (which seemed to me to be all too frequent - frequently getting a checksum failure multiple times out of 10 or 20 runs), it tries again.
When I run this repeatedly (every 2 seconds, from another program that updates an LCD display with the results), I am in rare instances (though I can make them less rare, by tweaking how things get run) getting into a situation where there are two (or more) instances of the program running, and neither seems to be getting anywhere, thus effectively causing my display program to block, and not be updated.  If I kill both programs, then (up to) 2 seconds later, a new instance is run, and that works fine, so I'm pretty sure this is just a case of the two programs clobbering each other.
What I'd ideally like is for there to be some sort of mutex lock on the access, which I think and hope would simply prevent this scenario (the second instance might block, but the first instance would eventually get its data and succeed).
My question, then, is what would be some reasonable ways I could do this locking, either inside or outside of the bcm2835 library?
I found this related question, though it's doing things in assembler, and the bcm2835 library seems to be pure C code.
Thoughts I've considered are:

Adding a new call within the library that uses flock on the fd for /dev/mem.  This seems like it may be problematically low-granularity - taking a lock on the whole /dev/mem mapping.
The same, but using some other method (which I'm not sure I know if/how this can be done), which would acquire a mutex just for the specific mapped address space relevant to the pin being accessed within e.g. bcm2835_gpio_fsel.  This strikes me as my ideal, I'm just not sure how to accomplish it.
Something custom to my application, and not related to /dev/mem at all.  This strikes me as a bit of a hack, but might be the easiest to do.

So, any thoughts on best practices, and/or ways to accomplish option 2 above?  Thanks.
Answer: I presume all the programs use your driver to access the display. If so then the locking mechanism is all up to you. You can define your own locking file (e.g. /var/run/.bcm_lock) and use that to control access using the familiar flock.

Locking for bcm2835 library?


Lattice based cryptography vs BB84

Question: Am I correct in thinking that post-quantum cryptography such as lattice-based solutions run on classical computers are resistant to quantum attacks (as opposed to RMS), whereas quantum key distribution schemes such as the BB84 are designed to run on quantum computers to communicate between them?
Comment: "Am I correct"-type questions are not well suited for here. I mean, what would be an answer: "Yes"?
Comment: Short answer: 1. Yes, you are right. 2. You don't need a full QC to run BB84, just some quantum device (which, I guess, is what you mean).
Answer: Post-quantum crypto schemes run on classical computers and are hoped to be secure against quantum attacks. Quantum key distribution such as bb84 or e91 run on quantum hardware (although does not require the full power of a quantum computer) and is provably secure (subject to certain underlying assumptions about lab security etc) against quantum attack.
Comment: It is important to note that all QKD algorithms involve a significant classical components for authentication, information reconciliation, and privacy enhancement. While these may be provably resistant against quantum attack they are quite complex. Hence there may be vulnarabilities in specific implementations.

Lattice based cryptography vs BB84


Is it forbidden to build extravagant mosques?

Question: What does Islam say about:

Building huge mosques.
Building overly tall minarets.
Extravagantly adorning and decorating mosques.
Decorating mosques with valuable metals or jewels.

??
Answer: On building mosques
Building mosques is among the best deeds one may do:

He who built a mosque for Allah, Allah would build a house for him like it in Paradise. (See for example sahih al-Bukhari, sahih Muslim)

In one narration an-Nasa-I and ibn Majah added

"Whoever builds a Masjid in which Allah is remembered, ..."

In another ibn Majah added:

'Whoever builds a mosque for the sake of Allah (from his own wealth) ...

Another version of this hadith in sunan ibn Majah says:

"Whoever builds a mosque for the sake of Allah, like a sparrow's nest for Allah or even smaller, Allah will build for him a house in Paradise."

These ahadith show the importance of building a mosque and also what is necessary for the acceptance for that beside this one may read in the Qur'an another condition:

And [there are] those [hypocrites] who took for themselves a mosque for causing harm and disbelief and division among the believers and as a station for whoever had warred against Allah and His Messenger before. And they will surely swear, "We intended only the best." And Allah testifies that indeed they are liars. (107)
  Do not stand [for prayer] within it - ever. A mosque founded on righteousness from the first day is more worthy for you to stand in. Within it are men who love to purify themselves; and Allah loves those who purify themselves. (9:107-108)

How the first mosque look alike?

In the lifetime of Allah's Messenger (ﷺ) the mosque was built of adobes, its roof of the leaves of date-palms and its pillars of the stems of date-palms. Abu Bakr did not alter it. 'Umar expanded it on the same pattern as it was in the lifetime of Allah's Messenger (ﷺ) by using adobes, leaves of date-palms and changing the pillars into wooden ones. 'Uthman changed it by expanding it to a great extent and built its walls with engraved stones and lime and made its pillars of engraved stones and its roof of teak wood. (Sahih al-Bukhari and sunan abi Dawod)

It was anything but extravagant it hardly looked like any mosque now!
On extravagance
Allah the Almighty says:

O children of Adam, take your adornment at every masjid, and eat and drink, but be not excessive. Indeed, He likes not those who commit excess. (7:31)

Even if we are recommended to wear our best clothes when visiting a mosque we are asked not to be excessive as is the general ruling in Islam:

And [they are] those who, when they spend, do so not excessively or sparingly but are ever, between that, [justly] moderate (25:67)

Therefore the prophet () said:

The Last Hour will not come until people vie with one another about mosques. (Sunan abi Daowd, sunan ibn Majah and sunan an-Nasa-i)

In his introduction to the hadith describing the first mosque and the expandation during the lifetime of 'Omar ibn al-Khattab in his sahih imam al-Bukhari also quoted the following statements:

'Umar ordered that the mosque be rebuilt and he said: Protect the people from rain, but beware of using red or yellow (for adornment) and distracting the people.
  Anas said: They build mosques about boast about that, but they do not use them for worship except rarely.
  Ibn 'Abbaas said: You are going to adorn (mosques) as the Jews and Christians adorn (their places of worship). (Source of the translation: islamqa #[97497])11

(See also in sunan abi Dawod)
These statements should show that extravagance is not the goal of building a mosque a mosque in first place is a place of worship anything (any extravagance) that might disturb you during your prayer is frowned upon (or even haram) in a mosque (based on ahadith such as here in sahih al-Bukhari).


Model State Object and User State Object

Question: User State Object sets its value in session that's way we can get value from any where but model state object which is nothing more then a Jobject which doesn't use session to store value then how model state variable remain it's value when we come back later
Answer: The Model is not intended to save anything (I am not talking about model cache), because that is a job for session. That is why model very often uses User State to retrieve some data form the session, for example the states of different filters.
Comment: that means model state variables will be lost as soon as we navigate to different view ( that using other model) .? but if we want to save values for cross view we Have to use user State Variable.? **and yes Thanks**
Comment: Yes you need to use a User State to save the values across different views.


How Random are Equipment Rewards in Smash Bros 4?

Question: Consensus appears to be that in Smash 4 all equipment reward possibilities are completely random, but there are special rules:
The rolling reward ticker appears to reward players based on what stage they are fighting on.
You apparently are more likely to receive rewards for the character you are using. But there must be some caveats to this, as a player who almost exclusively uses DeDeDe I seem to have mostly sword/glove/badge items.
There is general consensus that the higher difficulty you play at, the better the rewards you get. So, instead of a 100lb Hammer you might get a 100ton hammer.
Has anyone delved deeper into the reward system to determine what the likelihood of receiving different types of equipment or custom moves actually is?
For example, how likely is it that I get a custom move that I already have, for the character I'm playing with vs one I don't have yet. What about the characters I'm playing against? Or the stage I'm on.
I've noticed a lot of strange things. For example: I thought it was impossible to get duplicates of custom moves, but I've received "Top Spin Gordo" at least 3 times, but I still lack the 3rd Gordo customization. I've also received every type of defense equipment for DeDeDe, but none of his attack equipment.
Do I have to play above a certain difficulty level to get certain kind of rewards? Is Beam Sword only obtainable at 7+ difficulty, or only in Tour, or only in Trophy Rush?
I'm not trying to ask multiple questions here, but is there any higher understanding of how the reward system works and how to obtain specific types of rewards?
EDIT:
I've made a few observations:

Target Bomb seems to be prone to granting custom moves with the character you are currently using.
Trophy Rush seems to be prone to granting duplicates of custom moves.
Classic is a toss-up. Difficulty level seems to only affect the number of rewards you get, not the quality. Custom moves seem to be rarer than equipment. Equipment seems to be more likely from the board you are playing on and the characters you are fighting. Speed/defense/attack equipment appears to be given out in a ratio 3/2/1 (I appear to get 3x as much speed equipment out of classic as attack equipment).
All Star gives you the same kinds of equipment regardless of difficulty level, hard gives you more equipment. This mode actually earns you more equipment than trophies, but the equipment seems to be based on the characters you battle. You're equally prone to collecting custom moves as you are equipment, and custom moves tend toward not being duplicates (till you get them all anyway, then it's of course all duplicates). Speed/defense/attack equipment appears to be equal.
Crazy Orders gives you a ton of equipment, but I don't have the custom characters to analyze the types of equipment you actually get beyond level 20.

In none of the cases am I seeing that better equipment is likely from any particular difficulty level. It only appears that you simply get more at higher difficulties, and thus have a better chance through repeating odds.
EDIT:
I've made the following further observations:

After receiving many duplicates of speed/agility related equipment I have finally received the first of said type with the "risky respawner" effect. This is the first negative effect I have found, and I appear to have earned it after earning 4 "safe respawner" items in a row (somehow 4 rounds of classic awarded 4 safe-respawner items).
After earning my first pair of "max power gloves" I went on to earn 2 more "max power gloves" with my next two rounds of classic. This is interesting because it not only is a 3rd level item, but it's an attack item (which I had not been earning). Since I am still using similar difficulty levels, this leads me to believe you simply earn better things after you have acquired more of a particular item.

So: Getting 5 safe-respawner items "unlocked" the risky-respawner items.
Getting enough speed/defense items finally "unlocked" the higher-grade attack items.
Answer: Through my experiences with the game so far, once you acquire so many of the same item the game will start to drop better versions of that item and continue to give improved versions until the stat cap for the item is reached. After that, the game will start to drop a different item and start that process over again.
Or at least this is how it worked for me, I got many of the same item in a row.


The confirmation speed of the transaction is related to the number of nodes

Question: The transaction confirmation speed is proportional to the number of nodes.?
Answer: If you mean MINING nodes, then not really.
A block has a difficulty and a gas size.
If it takes too much time to mine, the difficulty will decrease and make it easier for miners to mine.
If you have only one miner to mine the blocks (with veyr low computing power), the difficulty will decrease in order to make block mining time to arround 15 seconds.
If you have many miners with different computing power, the difficulty will also adjust.
So the number of mining nodes has an impact, but a small one and only during a reduced time period.
Comment: So what changes can affect the speed of recognition?


Did any of the social science experiments by the Nazis in WWII get published?

Question: I've read that the Nazi's did a lot of cruel experimentation on Jews during WWII. I was wondering if any of these studies were published, and if they still exist. Preferably available in English.
Comment: ask on history.se or historyofscience.se, much better answers to be expected there
Comment: I wouldn't call these experiments 'social science', 'medical' might be ok but 'biological experiments on humans' would fit even better. They did a lot of stuff to humans no ethics commity today would permit you to do to mice.
Comment: A place to look for citations might start here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1323276/
Comment: There was news coverage of a US company using the results of Dr Mengele's experiments a couple of years ago... don't have a link to hand, but should be easy to find...
Answer: Well, USA infected Guatemalans with STD's and has aided the cartels in México. The nazis werent the only ones and the controversy  about using such data is still around.
You can find some information here:
The Arolsen Archives ( Information on victims of the Holocaust and concentration camp prisoners, this can, sadly, give you some jkeywords to look for in repositories) https://collections.arolsen-archives.org/en/search/
Also the papers can still be found online. I'm not sure you will find them in english, but the library of the congress of USA and the holocaust memorial archives would be a good start if you want to search them out in english rather than german.
Comment: Sorry to be harsh, but this does not look like a good answer to me. The first sentence is more like a comment; it is a digression, and possibly one that might attract strong controversy. The rest is more or less a link-only answer, except that some of the links are too generic to be useful ("search in the library of congress").
Comment: Could you add a direct link to one of these papers then? Or a citation-like reference to it and a brief excerpt?
Comment: @Federico Poloni The topic is already controversial. OP asked if the papers were published and where could they be found in english and if they still exist. The link is to records that does exist and a general idea of where are files in english. The question isn't precise enough, but at least we can try to provide a general help.


DH parameters to solve forward kinematics problem

Question: When solving the kinematics problem for a robot using DH parameters, if there are some passive joints between the actuator and the end effector, do I have to define the axis and transformations of passive joints too just like for active joints?
Comment: Short answer: yes. For a longer answer: Do you have passive joints because you have a parallel structure (Stewart platform, hexapod, tripod) or do you have a serial structure with e.g. passive compliant joints? For parallel structures you might get away with not modelling the joints as DH. For serial structures you should probably model them as DH.
Answer: Yes.  Geometrically computing the static joint-space coordinates in terms of Cartesian coordinates (for example), it is irrelevant if a joint is active or passive.  For non-serial chains, some coordinates may be expressible in terms of others, so may be omitted from the IK calculation and computed by substitution afterward.


What is the highest recorded temperature in space

Question: What is the highest recorded temperature in space? I'm not asking about Planck temperature that is a fraction of a second before the Big Bang. I'm asking about the temperature that has been recorded by an instrument.
Comment: I can't swear to the accuracy of this, but you might enjoy this video.  https://www.youtube.com/watch?v=4fuHzC9aTik
Answer: Well this infograhic puts gas heated by a supernova at about 55 million Celsius.
And that's not even the highest temperature we can just "find" out there, even if we discard supernovae and stellar cores.  The gas in a cluster of galaxies (the ICM) can have temperatures on the orders of 10 million to 100 million Kelvin.  Such a high temperature gas emits high energy photons such as X-rays via bremsstrahlung radiation, and these are observable (and have been observed) by X-ray telescopes.
There's this review article from 2003 that covers the basic methodologies and measurements made on ICMs, including (but decidedly not limited to) temperature.


Can God replace his covenent with Abraham?

Question: In the book of Genesis, God makes the covenant of circumcision with Abraham for him and his descendants.  In verse 7 we are told this is an everlasting covenant.
How does this go in hand with the fact that a new covenant is established by at the Last Supper?
This question is addressed to any Churches that believe in the New Covenant theology (Catholic,Lutheran,Reformed,etc.)
Comment: I assume you're not referring to the specific theological framework called [New Covenant Theology](https://en.wikipedia.org/wiki/New_Covenant_theology)? If not, then this is really too broad, the various denominations have widely different views on the relationship between the New Covenant and the various covenants found in the Old Testament.
Answer: We know that Paul refers to this passage in a spiritual type as circumcising the heart.

Rom 2:29 But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
Col 2:11 In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ:

Paul has not created a new understanding of circumcision of the heart, but is following the same idea presented in centuries before from the Old Testament.

Deut 10:16 Circumcise therefore the foreskin of your heart, and be no more stiffnecked.
Deut 17:11 And the LORD thy God will circumcise thine heart, and the heart of thy seed, to love the LORD thy God with all thine heart, and with all thy soul, that thou mayest live.
Jer 4:4 Circumcise yourselves to the LORD, and take away the foreskins of your heart,

Thus "covenant of circumcision" is not understood as of the foreskin, but of the heart.  And at the same time, it remains an eternal covenant, as found in the seed Jesus Christ.

Gal 3:16 Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ.

Of course, not all understood the spiritual and the seed, rather than the physical.

Acts 10:45 And they of the circumcision which believed were astonished, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Ghost.

This misunderstanding eventually led to the Jerusalem Council (Acts 15).
So, the covenant of circumcision understood as referring to Jesus Christ and of the heart is an eternal covenant.
Comment: your answer is very satisfactory, thank you! There is one last bit I'd wish yo answer before I accept it. If that is the case, that the circumcision was always understood to be of the heart, then why does Luke 22:20 refer to it as the "new covenant "?
Answer: Does God 'replace' his covenant with Abraham ?
What relationship does the 'new' covenant bear to the 'everlasting' covenant ?

In Genesis 17: 3-14, God is quite clearly expressing two different covenants.
One is an everlasting covenant with Abraham and his 'seed' (which is clearly, from hindsight, a spiritual seed). This is made clear in the New Testament writings in Romans and Galatians particularly, but also many other places.

Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ. [Galatians 3:16, KJV]

The other covenant regards the natural nation of the Hebrews and the need for a country with borders to house them. Within that country, God will express, on earth, the prophecies regarding the Coming which will enable the everlasting covenant.
Within that nation, within its borders, God will display, by artefacts and by rituals, many representations of the everlasting covenant which will not fully come into force until the death of the Testator of the Testament.

For where a testament is, there must also of necessity be the death of the testator. [Hebrews 9:16, KJV]

For the everlasting covenant is also an everlasting Testament.
Once the everlasting testament is fully established it supersedes all the figures and temporary arrangements which pointed towards it and which foretold it. All of which required a covenant between God and the nation of Israel in order to facilitate the project of setting forth the everlasting covenant, as a testimony, among all nations, upon earth.
If I wish to build a substantial building, say a block of apartments, then I may commission an architect to provide a model of the building in order to demonstrate to those involved in its building - and also to its future occupants - what it will be.
But after the building is built, there is no need for the model. Nobody can live in the model. The model is superseded.
It becomes redundant.
It is 'old'.

In that he saith, A new covenant, he hath made the first old. Now that which decayeth and waxeth old is ready to vanish away. [Hebrews 8:13, KJV]
Comment: Hello Nigel, thanks for answering. I am bit confused because one one hand the covenant of the Old Testament is refereed to as everlasting in Isaiah 24:5. However on the other hand, also in the Old Testament it's refereed to as passing, Jeremiah 31:31-34
Comment: @Dan The first - in Isaiah - refers to the everlasting covenant/testament. The second refers to the first covenant which has now passed away and is redundant. The everlasting covenant is that which is determined by God before the foundation of the world. The 'first' covenant on earth which involves the Law is that which is superseded once the everlasting Testament is brought in through the death of the Testator.


How do I purchase Monero when I live in US?

Question: Why is it that many exchanges don't allow me to trade when they find out I live in USA? What good is Monero if I can't purchase or sell?
Comment: https://localmonero.co/ is one site. For Monero mining and trading, you will need a wallet. Here's a wallet: https://mymonero.com/.
Answer: There are plenty of exchanges that allow you to trade Monero, even if you live in the US.
Answer:
Why is it that many exchanges don't allow me to trade when they find out I live in USA?

There are regulations that companies must follow to have US customers, many companies feel that there is a lot of paperwork and delay.

What good is Monero if I can't purchase or sell?

Some companies have jumped through the hoops, those that haven't allow you to hold the money or withdraw it; "trading" isn't allowed.
Visit Wikipedia for information about alternative trading systems.
Coindesk offers these explanations:

"Stonewalled by FINRA, Up to 40 Crypto Securities Wait in Limbo for Launch" (Jun 17 2019):

"The Takeaway:

FINRA has sat for months on roughly 40 broker-dealer applications from companies dealing in crypto assets, denying them a broker-dealer license that would let these firms offer securities in the U.S.
Some think FINRA, a self-regulatory organization, is holding off on these approvals at the SEC's request, as the agency has yet to offer clear guidance.
Frustrated crypto startups may look to abandon the U.S. entirely, and focus on launching in other jurisdictions.

Some startups have been waiting at least a year, with a few standing by for as many as 14 months, without seeing any movement from FINRA, three of the sources said."
"Juan Hernandez, CEO and founder of securities trading platform OpenFinance, told CoinDesk that FINRA has been slow, but that this did not necessarily indicate that there was any sort of order preventing approvals.
OpenFinance, tZERO, SharesPost and Templum Markets are ATSs (alternative trading system) that received approval to list digital assets last year – meaning they would have received their approvals while other companies were still waiting. These firms have already conducted some initial security token transactions.
SeedInvest, an equity crowdfunding platform acquired by crypto startup Circle last year, is also an ATS, though the platform cannot list cryptocurrencies for trading at this time, including security tokens.
Hernandez told CoinDesk that FINRA has "been slow to push forward a couple filings but … they did allow [SeedInvest] to push forward with the caveat that they need to do additional filings to be able to transact with digital securities.".

"SEC, FINRA Issue Explanation of Crypto Custodian Approval Delay" (July 8 2019):

"The U.S. Securities and Exchange Commission (SEC) and the Financial Industry Regulatory Authority (FINRA) believe there are a number of questions they need to address before they can approve crypto companies' applications to become broker-dealers."
...
"Broker-dealers in the U.S. are legally registered and regulated entities which are able to purchase or sell securities, both on their own behalf, as well as for clients. Some companies want to use digital assets as securities, allowing them to market to institutional investors who cannot hold or directly purchase these assets.
While a broker can prove that it possesses the private keys to a crypto wallet, it would be difficult to prove that no other entity does, the statement says, explaining:

"It may not be able to demonstrate that no other party has a copy of the private key and could transfer the digital asset security without the broker-dealer's consent."

The joint statement comes in response to questions from market participants, the document says.
Companies applying for broker-dealer approvals have been sitting in limbo for months, with some firms waiting more than a year, as CoinDesk previously reported.
Many of these firms claimed that the SEC imposed a moratorium on broker-dealer approvals for firms which touch digital assets, while others said that cryptocurrency-based securities simply present novel issues that the regulatory agencies must first assess. Monday's joint statement would appear to be a confirmation of the latter theory.
Crypto exchange Gemini was the most recent firm to apply for a broker-dealer approval.".

Bittrex's answer is a bit cryptic, quoting the relevant bits and pieces:

"Does this mean that Bittrex is leaving the US?
Bittrex is proud to be a U.S. Digital Asset Trading Platform. U.S. customers will have access to a more limited number of markets as compared to what Non-U.S. Customers have on the Bittrex International platform. Like other industry participants, we will continue to advocate for laws and regulations that foster innovation."
"What if I'm a corporate customer?
Bittrex International isn't only for individual or personal accounts. All eligible international customers, including corporate customers, will be redirected to the Bittrex International website once it's launched. Corporate customers within the U.S. will continue using Bittrex.com.".
"Customers who have completed Enhanced Verification by providing a non-U.S. government ID and who reside outside of the U.S. will be eligible to access to Bittrex International.".
"What happens when the new international platform launches?
Once launched, non-U.S. customers will be redirected to the Bittrex International site (https://International.Bittrex.com), and U.S. customers will remain on Bittrex.com."
"All customers will continue to have access to all of the same tokens, trading pairs and wallets on Bittrex.com (even if you are redirected to https://international.bittrex.com), and non-U.S. customers who are eligible to access the international platform will be able to trade new tokens only available on Bittrex International. U.S.-based customers will continue to use the Bittrex.com site and will not have access to the new tokens available on Bittrex International."
"What's in it for me?
We've taken the best of Bittrex.com, such as industry-leading security practices, access to 24/7 customer support and a secure, reliable and advanced digital asset trading platform, to create Bittrex International. With the regulatory certainty and streamlined token listing process provided by the Malta Virtual Financial Assets Act, Bittrex International will be able to list blockchain projects within weeks. This means that our international customers will have access to the newest, most innovative blockchain projects without delay. In fact, if you're interested in an exciting, new and authentic blockchain project, there's a good chance we'll have it listed very soon!".