Why don't Presbyterians have altars?

Question: Why don't Presbyterians have altars in their churches or in their homes? Who administers the sacraments, especially communion, then without an altar? Do children help out at all? In other churches, children can be selected as 'altar-servers'.
Comment: In particular, the question would benefit from a definition of what you mean by an "altar."
Comment: Every Presbyterian church I've gone to has had an altar, but it's used differently than you suggest.
Comment: This asks too many questions for one question, besides apparently being based on partial or incorrect information about Presbyterian churches.
Answer: (Although I can't speak for all Presbyterians, as we are diverse bunch, I think that what I say here is representative of the mainstream. I welcome correction if I am wrong about this.)
When Communion is served, we do use a table of some kind. The table recalls the Last Supper, at which the practice of Communion was instituted; Matthew 26:20, Mark 14:18, Luke 22:14 and John 13:23 all say that Jesus and the disciples were gathered at table. In any case, it is practical to have a flat surface for everything else to rest on.
It is typical for the table to be an actual table (wooden, four legs at the corners, etc.) rather than an altar (big block of stone). This is because the Reformed tradition does not view Communion as a sacrificial event, and does not have the Catholic concept of a sacrificing priesthood. An altar is a place for offering sacrifices but a table is a place for having dinner. Also, there is a general aesthetic sense that churches ought not to be too ornamented, so some may prefer a simpler piece of wooden furniture to an elaborately carved stone altar. I have personally seen quite a bit of variation in the level of decoration for the table.
Moreover, the Presbyterian tradition has tended to offer Communion less frequently than some other denominations. So the table may not even be a permanent fixture, but is brought out whenever it is needed. In contrast, the preaching of the Word is ubiquitous, so in some church buildings you will see a central pulpit where you might expect a table or altar. In my present church, we do have a permanent table, where the Communion vessels are always shown - this is meant to be a reminder that we should be ready for Jesus to arrive at any moment. In other churches you might see candlesticks, a cross, a Bible, and so on.
You also ask who administers the sacrament, and whether children may be involved as helpers. We do have a person who does this, a "minister", who has been ordained and who (as a result of training followed by church approval) is considered capable of the job. Church law may allow other people to act in place of the regular minister, under certain circumstances. The minister may be helped by other people during the course of the service - holding plates of bread and so forth. Compared to high-liturgical denominations, the Presbyterians have rather less apparatus to deal with (incense, bells, different kinds of cloth, etc.) and so there is correspondingly less of a role for the helpers. They also don't have special clothes to wear.
Regarding children, I would think that anyone assisting ought at least to be baptized - even if they do not receive the sacrament themselves, helpers are still participating in the event. They should also be physically able to do what is asked. So I think anyone who could receive communion could also assist, including children in principle, whereas unbaptized people of any age would not do so. Actually choosing the helpers would be the responsibility of the session (the governing committee of the local church) together with the minister, ultimately subject to the judgement of the presbytery and higher bodies. Again, given the nature of the role, there's not much need for more than about half a minute of training, so we wouldn't tend to have a fixed body of designated helpers - at my present church, the session chooses people from the congregation in general.
Comment: Ok well having been raised a Presbyterian in the mainline denomination I am not sure I agree with all that is here. There is quite a variation in high and low churches. Presbyterians as a whole and their history would lean them as a Mainline low and high liturgical church. Perhaps it would be safe to say in between an Anglican and a Methodist. So our church was very High Church resembling an Anglican or High Methodist. Although we did not have an altar our Communion Table was in front of the Cloister and was ornate and appeared as an Altar.
Answer: The Presbyterian model of the Lord's Supper is explicitly laid out in the Westminster Confession, which until about a hundred and thirty years ago was followed by most Presbyterian Churches to the letter. Today, really only the Free Kirk (or the "wee frees" as they are known) still maintain this strict tradition.
There are no altars as Christ's sacrifice on the altar of Calvary was sufficient. As his sacrifice is sufficient for grace, there is no need to recreate or re-enact this event at all (as does the Roman Catholic Church with their Mass). There are no private altars, as the Lord's Supper is a communal event, hence the name communion. We do not need altars, as Revelation 21:23 states:

An I saw no temple therein: for the Lord God Almighty and the Lamb are the temple of it.

And, in Hebrews 13:10:

We have an altar, whereof they have no right to eat which serve the tabernacle.

That altar is Christ, not any other temple. The church building itself is most definitely not a temple containing an altar.
Thus, the communion table is not an altar, instead it is a plain wooden table with chairs. Its purpose is to follow the model of Christ's Last Supper as accurately as possible within the constraints of practicality and sobriety (i.e. only bread and wine is consumed, not an entire meal, only the elders are seated, it is not every Lord's Day).
The sacrament of the Lord's Supper (one of the two sacraments Christ gave us, the other being Baptism) is to be administered by the ministers of the church (the teaching elder and ruling elders). Children are not supposed to receive communion until they have been confirmed. No adults, except elders or deacons should administer the sacraments.
This all said, few Presbyterian churches still maintain this strict adherence to the Westminster Confession. I have attended many Presbyterian churches in New Zealand and Canada where the communion table was as ornate as an altar, children are served communion, etc.
For further reading and context, I recommend the following passages from the Westminster Confession:

The Confession of Faith, Chapter XXIX: The Lord's Supper
The Directory of the Publick Worship of God: Of the celebration of the communion, or sacrament of the Lord's Supper
Comment: Welcome to the site, Peter. Excellent answer. +1. To keep you on the right track I recommend seeing [Template Questions](http://meta.christianity.stackexchange.com/q/3409/) and [What Christianity.StackExchange is and what it is not](http://meta.christianity.stackexchange.com/q/1379/) to get a good feel for what this site tries to be about. I hope to see you post again soon.
Comment: Sorry, but in the US both the PCA and the OPC hold to the WCF.
Answer: I haven't been a Presbyterian for very long, but as part of my initiation as a member, I was told that part of the reason not to have an altar which is a closed box such as more liturgical churches have was to allow people to see that there was nothing magic hidden inside the box that would suggest that communion involves transubstantiation.
Comment: Welcome to the site. Thank you for sharing. Were you just told this, or can it be found in one of the books or something that you were given to prepare?
Answer: I am not quite sure what Presbyterian type of church you attend. In the mainline Presbyterian churches the Cloister serves what some would view as an altar. Our communion table is made of stone, so I have no clue what you are talking about? Also the elements are always laid there as well as a bible. On top of this, this may raise your blood pressure, we have quite ornate symbols and carvings of the last supper, christ and the saints. I do not think all Presbyterian churches are the same. I attended an Orthodox Presbyterian church as a visitor recently and it was nothing like the Presbyterian church I was raised in, not even remotely. It was different in some beliefs and liturgy and practice. I did not feel comfortable in it at all.
Comment: Welcome to Christianity.SE. For a quick overview, please take the [Site Tour](http://christianity.stackexchange.com/tour). And for some tips on writing good answers here, please see: [What makes a good supported answer?](http://meta.christianity.stackexchange.com/questions/692/what-makes-a-good-supported-answer). The question itself is a bit scattered, and may well be closed before long.

Why don't Presbyterians have altars?


Signal problem with Samsung Galaxy Y GT-S5630 mobile

Question: I am using Samsung Galaxy Y GT-S5630 phone with IDEA network provider. I am having signal loss problems many times a times. When I try to make a call, it says "Network unavailable". I though this might be the problem IDEA network, but it was not. I tried checking the same sim card in another mobile and it's working fine, this issue is  being observed mostly for every 4-5 minutes. How can I resolve this?
Answer: Different network providers may use different masts.
The company of the second sim will have a stronger presence in your area than the company from the first sim.
Therefore, the ideal move would be to get yourself a sim from the same provider of the second sim.
I hope this helps,
Nicholas
Answer: Your phone probably is fixed in 3G mode or is in auto 3G/GSM mode. I suggest you to switch to GSM only mode. That way you won't face a network problem.

Go to Settings > Wireless and Networks > Mobile networks > Network
  Mode

Select GSM only from that menu.
Also try going to Network Operators from the mobile network menu and try selecting a network manually.


How to avoid an implicit "return" in coffeescript in conditional expressions?

Question: I am implementing a function that has deferred value to return and within the function I have many nested conditional expressions:
e.g.:
deferred = Q.defer()
FS.readFile("foo.txt", "utf-8", (error, text) ->
    if error
      deferred.reject(new Error(error))
    else
      deferred.resolve(text)
)
return deferred.promise

which than will be compiled into:
var deferred;

deferred = Q.defer();

FS.readFile("foo.txt", "utf-8", function(error, text) {
  if (error) {
    --> return <-- deferred.reject(new Error(error));
  } else {
    --> return <-- deferred.resolve(text);
  }
});

return deferred.promise;

I need only the last return, but not the if/else returns (i.e. --> return <-- in the compiled code)
How can I avoid such a behavior (implicit returns where they are do not needed) of the coffeescript compiler?
Comment: This isn't the problem you think it is. The returns in question are returning from the inner callback function. This is desirable behaviour, and it's not interfering with your outer function's `return` in any way.
Answer: Coffeescript automatically returns the result of the last expressions, so if you don't want it to return the results of the if then you need to add another expressions. In this case, just add return.
FS.readFile "foo.txt", "utf-8", (error, text) ->
  if error
    deferred.reject new Error(error)
  else
    deferred.resolve text
  return

Also, error is already an Error object, so you can just reject it directly.
deferred.reject(error)

Comment: Thank you! It works, but it looks for me like it will be compiled in "if/else expression following by return();" and than all the other code
Comment: @static Yep, and that's totally fine.
Comment: I mean it looks for me like will be compiled into:

`var deferred;

deferred = Q.defer();

FS.readFile("foo.txt", "utf-8", function(error, text) {
  if (error) {
    deferred.reject(new Error(error));
  } else {
    deferred.resolve(text);
  }
});

return;

return deferred.promise;`

So like two returns after a function
Comment: @static Are you sure your indentation is correct? It definitely shouldn't come out like that.
Comment: ok, because of the indentation it will be one return in the function and one return out there. but still, I find it little bit weired...
But really, thank you!
Answer: You can't, exactly. You can either ignore them when not needed (which is the most common thing to do) or provide an explicit alternative by adding an additional statement at the end of the function. I think trying to do this all the time in your code base is fighting a war against the language you cannot win, so my personal recommendation is just accept Mr. Ashkenas's implicit return and go on your merry way.
fs.readFile "foo.txt", "utf-8", (error, text) ->

  # postfix style if statement here avoids the else
  # of course, the value returned you may not like, so
  # you probably won't use this style, but my boilerplate for
  # error handling is
  # return callback(error) if error

  return deferred.reject(new Error(error)) if error
  deferred.resolve(text)

  # Here you can add an explicit return like
  return

  # or some other expression
  null

  # or 'this' in cases where chainability might be nice
  this

  # or so you don't accidentally delete this statement later thinking it is
  # useless
  return null

any of those forms will work, but in practice I don't see these commonly
Comment: But the inner return really does matter. See http://programmaticallyspeaking.com/why-i-hate-implicit-return-in-coffeescript.html and http://awardwinningfjords.com/2012/05/08/beware-coffeescript-comprehensions.html for why.
Comment: Thank you! it is really a little bit weired to run into such a situation with a return statement
Comment: It's unfamiliar, but over time it will become familiar and probably won't bother you. I've never heard experienced coffeescripters mention this as troublesome.
Comment: Because it's not troublesome. The inner returns have no baring on the outer function. Ignore them.
Comment: Because that's the way Coffeescript works, I have formed a habit of typing a 'return' immediately each time after typing '->' and a carrige return.
Answer: i always do it like this:
f = ->
  deferred = Q.defer()
  FS.readFile ..., ( error, text ) ->
    return deferred.reject error if error?
    deferred.resolve text
  return deferred.promise

the first return is there to stop execution, not to return a value.
you still get an additional (and meaningless) return in your JS from the last line of the callback; to avoid that one, insert an additional return null (or simply return if you prefer that).
i'm not sure i like CoffeeScript's implicit return insertion; it might be claimed that 'explicit is better than implicit'. also, it could be argued that the first return shouldn't be a return but another keyword, like, say, stop or finish or somesuch.
as an unrelated sidenote, i haven't observed any noticeable advantage when using promises. to the contrary, i found them quite intrusive in my code, what with those deferreds and other concepts that are put on top of asynchronous programming.


What funds do I need for a Schengen visa?

Question: My husband is a student in Munich. I wish to travel to germany and be with him for 3 months. What is the funds requirement for a Schengen visa.
Answer: The funds requirement for your subsistence in Germany will be around €4000, but you will also have to convince the visa official that you are going to leave the Schengen area afterwards.

The best way to do that is a stable, well-paid job. The pattern of income and expenditure matters, not just the amount of money when you make the application.
Another way are solid ties to the local economy and society at your place of residence. That can mean relatives who do not travel with you, or owning property.
Depending on his financial situation and residency status, your husband may be able to file a written bond with the municipal authorities where he promises to pay for any cost of overstay (unintentional or intentional). Such a Verpflichungserklärung is no guarantee of a visa, but it can help.
Instead of a tourist visa for 90 days, ask on Expatriates Stack Exchange about family reunification visa.


Workflow for animating part of the bigger graphic. GIF or sprite maybe?

Question: Could someone provide a fine crafted footage of how to animate only part of the image? Let's say we have a image 1366x500 showing some device mockup and we only want to animate the screen of that device which would be smth around 80x30px. The image will go then for a website background. Would be even better to add a hyperlink with that animated screen. Any thoughts?
Answer: If i get you right and the big picture wont animate and get "replaced" on the little screen: it is possible with responsive webdesign.
choosing-a-responsive-image-solution
and just replace the big image with ur animated gif via media queries on the small screen
Answer: Well, the idea of an Animated GIF is that the entire image is replaced with another, like a flipbook. So this isn't possible with that format.
Sounds like  what you are trying to achieve is to animate a UI screen on a device, in which you would need to use a program like After Effects to animate your screen, then place it over a photo of your device. After that you export to GIF or Flash or whatever.
Check out the UI presentation templates from a company like Creative Dash. They offer templates for popular devices, and most are compatible with After Effects.
Answer: you have a variety of options: already mentioned, and probably your best bet is to use media queries for showing certain screens certain things.
css3 offers up multiple background images, which you could tailor with media queries.
if you are using an actual img / element in your markup, don't forget that you can apply background images to it via css. i've seen a cool demo before where a background .jpg was used on an animated .gif....although i don't think this works exactly for your solution. but awesome to know nonetheless. it was something like this:

.pix-bg{
padding:100px 200px 7px 30px; /** these are random. use padding **/
background:url("animated-pix-ng.jpg") 0 0 no-repeat;


Forms bound to updateable ADO recordsets are not updateable when the source includes a JOIN

Question: I'm developing an application in Access 2007.  It uses an .accdb front end connecting to an SQL Server 2005 backend. I use forms that are bound to ADO recordsets at runtime.  For the sake of efficiency, the recordsets usually contain only one record, and are queried out on the server:
Public Sub SetUpFormRecordset(cn As ADODB.Connection, rstIn As ADODB.Recordset,      rstSource As String)
Dim cmd As ADODB.Command
Dim I As Long

Set cmd = New ADODB.Command

cn.Errors.Clear

'   Recordsets based on command object Execute method are Read Only!

With cmd
    Set .ActiveConnection = cn
    .CommandType = adCmdText
    .CommandText = rstSource
End With

With rstIn
    .CursorType = adOpenKeyset
    .LockType = adLockPessimistic                           'Check the locktype after   opening; optimistic locking is worthless on a bound
End With                                                    ' form, and ADO might open optimistically without firing an error!

rstIn.Open cmd, , adOpenKeyset, adLockPessimistic           'This should run the query on the server and return an updatable recordset

With cn
    If .Errors.Count <> 0 Then
        For Each errADO In .Errors
            Call HandleADOErrors(.Errors(I))
            I = I + 1
        Next errADO
    End If
End With
End Sub

rstSource (the string containg the TSQL on which the recordset is based) is assembled by the calling routine, in this case from the Open event of the form being bound:
Private Sub Form_Open(Cancel As Integer)
Dim rst As ADODB.Recordset
Dim strSource As String, DefaultSource as String
Dim lngID As Long

lngID = Forms!MyParent.CurrentID

strSource = "SELECT TOP (100) PERCENT dbo.Customers.CustomerID,   dbo.Customers.LegacyID,  dbo.Customers.Active, dbo.Customers.TypeID, dbo.Customers.Category, " & _
"dbo.Customers.Source, dbo.Customers.CustomerName, dbo.Customers.CustAddrID, dbo.Customers.Email, dbo.Customers.TaxExempt, dbo.Customers.SalesTaxCode, " & _
"dbo.Customers.SalesTax2Code, dbo.Customers.CreditLimit, dbo.Customers.CreationDate, dbo.Customers.FirstOrder, dbo.Customers.LastOrder, " & _
"dbo.Customers.nOrders, dbo.Customers.Concurrency, dbo.Customers.LegacyLN, dbo.Addresses.AddrType, dbo.Addresses.AddrLine1, dbo.Addresses.AddrLine2, " & _
"dbo.Addresses.City, dbo.Addresses.State, dbo.Addresses.Country, dbo.Addresses.PostalCode, dbo.Addresses.PhoneLandline, dbo.Addresses.Concurrency " & _
"FROM dbo.Customers INNER JOIN " & _
"dbo.Addresses ON dbo.Customers.CustAddrID = dbo.Addresses.AddrID "
strSource = strSource & "WHERE dbo.Customers.CustomerID= " & lngID

With Me                             'Default is Set up for editing one record
    If Not Nz(.RecordSource, vbNullString) = vbNullString Then
        If .Dirty Then .Dirty = False   'Save any changes on the form
        .RecordSource = vbNullString
    End If

    If rst Is Nothing Then          'Might not be first time through
        DefaultSource = .RecordSource
    Else
        rst.Close
        Set rst = Nothing
    End If
End With

Set rst = New ADODB.Recordset
Call setupformrecordset(dbconn, rst, strSource)    'dbconn is a global variable

With Me
    Set .Recordset = rst
End With

End Sub

The recordset that is returned from setupformrecordset is fully updateable, and its .Supports property shows this.  It can be edited and updated in code.
The entire form, however, is read only, even though it's .AllowEdits and .AllowAdditions properties are both true. Even the fields from the right hand side (the 'many' side) cannot be edited.
Removing the INNER JOIN clause from the TSQL (restricting strSource to one table) makes the form fully editable.
I've verified that the TSQL includes priimary key fields from both tables, and each table includes a timestamp field for concurrency.
I tried changing the .CursorType and .CursorLocation properties of the recordset to no avail.
What am I doing wrong?
Comment: This kind of code: "If Not Nz(.RecordSource, vbNullString) = vbNullString Then" makes my head hurt. Why not "If Not IsNull(.RecordSource)"? If .RecordSource can't be Null and is a ZLS when empty, then "Len(.RecordSource)=0" would be the correct test.
Comment: "Although the Supports method may return True for a given functionality, it does not guarantee that the provider can make the feature available under all circumstances. The Supports method simply returns whether the provider can support the specified functionality, assuming certain conditions are met. For example, the Supports method may indicate that a Recordset object supports updates, even though the cursor is based on a multiple table join — some columns of which are not updateable." - http://msdn.microsoft.com/en-us/library/ms676500%28VS.85%29.aspx
Answer: I think you want to set the Unique Table dynamic property on the recordset.
Comment: Thanks for the suggestion - I tried it, but it made no difference.
Answer: A work-around that I've found is to use an 'IN' clause.  For example:
SELECT  c.*
FROM    CATEGORY        c
WHERE   c.category_id IN (
            SELECT  p.category_id
            FROM    PRODUCT     p
            JOIN    CUST_ORDER  o   ON o.product_id = p.product_id
            WHERE   p.product_type  = 'Widget'
            AND     o.units         > 50
        )

Obviously, the hard-coded values can be passed into the subroutine (and bind variables utilized).  The important thing to note is that the IN clause can have any number of joins and the Resultset will still be updatable.
If you need fields from more than one table, you could try creating a database view and/or using DLookup().


Are solder fumes bad for me?

Question: I do a fair bit of soldering (lead-free). Is breathing in solder/flux/paste fumes actually going to harm me?
Are cheap fume extractors worth buying?
Comment: Solder fumes are pretty much entirely vaporized flux.  Different people react differently to the fumes.  This ranges from absolutely no discernible effect at all over decades of daily exposure to triggering an asthma attack the first time someone is exposed to the fumes.  Oldsters: keep doing what you've been doing for decades.  Newbies: buy an inexpensive fan-type extractor with attached filter - and USE it.
Comment: Note that traditional rosin flux is also called "colophony incense," also "kolophonium."  It's meant to be inhaled ...but read up on incense allergies, also on "sensitizing" during repeated exposure.  ("Rosin" is just pine-sap with the volatiles or "turpentine" boiled out.)
Answer: Solder fumes aren't very good for you. Some people can become sensitized to flux fumes, especially from the older rosin flux used in cored solder, and get breathing problems:
Controlling health risks from rosin (colophony) based solder fluxes
The no-clean flux isn't as bad.
I once felt quite ill after assembling about 30 boards that I had to do myself as my distributor wanted them very quickly.
Breathing out whilst you are soldering each joint helps a lot, if you don't have fume extraction.
Comment: 'The no-clean flux isn't as bad.' - really? The products containing no-clean flux are usually sold with a 'Harmful if inhaled', 'May cause allergy or asthma symptoms or breathing difficulties if inhaled', 'May cause respiratory irritation' warnings (besides others) ... ([example](https://www.chipquik.com/msds/TS391SNL.pdf))
Answer: My first reaction to your question was, yes the fumes are going to harm you.  My second was to conduct some quick research.
Amazingly, as I quote next, Lead-Free Solder inhalation can lead to pneumonia and a 24-48h flu.

INHALATION: Inhalation of dusts and fumes may cause irritation of the upper respiratory tract. Inhalation of freshly formed metal oxides may cause metal fume fever, a brief (24-48 H) flu-like illness. Inhalation of tin oxide may cause pneumonia.

According to the MSDS from Weller on some of their non-lead solder.
You can guarantee this must be a frequent event or the company would not be disclosing this in such a cavalier manner.
Comment: @Boris_yo [Lead is toxic](https://en.wikipedia.org/wiki/Lead#Toxicity), pure or otherwise.  Kamil is complaining about the inconsistency of the laws, not saying that one situation is healthier than the other.
Comment: @Boris_yo I think yes, this is same thing. This is metal alloy not containing lead (Pb). All this mess with lead or non-lead solders comes from EU, where we can't use lead because its toxic, but we can put pure lead into river or lake while fishing :D
Comment: Non-lead and lead-free solder is same thing?
Comment: One problem is that the soldering is heated up, the fishing gear isn't.
Comment: So lead is toxic but pure lead is not? What toxin does non-pure lead contain that makes it toxic?
Answer: Breathing the fumes is not good for you. With the additional flux required to get
good SMD solder joints there are more fumes.
I just bought a Weller WSA350 smoke absorber. It was $50 new. A three pack
of filters is pn WSA350F. This works OK. A unit with a stronger fan would
be better. After a few hours of soldering there is a fair amount of white
powder on the carbon filter. The fan looks like a standard 5" boxed fan so
I may try getting a more powerful one.
When the weather is good I have cross ventilation so I put an exhaust
fan in the window near my bench.
Answer: Fume extractors are worth every penny in my opinion. Smoke goes in - no smoke comes out - and the best bit is that the air smells clean.
If you're in the UK, get the cheap Maplins one for £15.
Comment: The cheap ones seem not to work that well, though: https://www.ncbi.nlm.nih.gov/pubmed/9838864
Answer: All solder fumes can cause occupational asthma and other health problems (leaded and lead-free) if used for long periods at a time.
The best solder wire contains something called Rosin that helps the solder flow when hot. This causes asthma if you are over exposed and is irreversible. Other solder wires that are Rosin free cause other health problems and are rubbish to solder with.
Invest in a good extractor, not a cheap one. Trust me, it's not worth the risk and I'm talking from experience. I have occupational asthma from solder fumes containing Rosin (colophony) after my job as an RF Development technician. I was employed in that position for 18 months only and am now registered disabled with lung damage after being challenge tested at the Royal Brompton Hospital in London.
This thread is old but I thought i'd post it in case anybody new reads it.
Download the safety data sheet from the internet for the solder wire you are using and read the hazards before using it.
I had no previous lung problems before that job, I was physically fit, 6' 5" tall, 17 stones and I was 38 years old at that time. I had no idea how damaging those fumes could be. Like cigarettes, the fumes can also be invisible to the naked eye, but are more damaging. If you are doing a lot of soldering make sure you take a lot of breaks and get some fresh air inside you as well as having a decent extractor that sucks well. Position the extractor hose directly above the area you are soldering and make sure it is working properly before going anywhere near the area being soldered. You should be okay if you do that. If you don't have an extractor then stick to about 10 minutes of soldering a day and then get plenty of fresh air inside you afterwards and you should be okay. Hope this helps.
Comment: good feedback. i run a repair shop and i'd say i do soldering at most 10 minutes max in a day. its in a small room with low ceilings. im curious to what happens to the fumes over time? as my place isn't very well ventilated. wouldn't want to have a toxic contaminated room.
Answer: You could always try building one. I've been meaning to one of these days, but I haven't done a whole lot of soldering recently. Googling turns up a bunch of people that have done this before in different ways.

https://web.archive.org/web/20120404100956/http://outroot.com/blog/2009/12/01/high-performance-diy-fume-extractor/
https://web.archive.org/web/20080411152255/http://www.waldemeyer.com/soldrx.htm
https://web.archive.org/web/20100404191446/http://www.raphnet.net/divers/fume_extractor/index_en.php
https://www.instructables.com/id/DIY-Fume-Extractor/
https://www.hackster.io/GeekRex/5-powerful-diy-fume-extractor-7dbee2
https://medium.com/@rxseger/diy-fume-extractor-for-soldering-safely-41ef29f46ab5
Comment: Sadly only one of those links still works.  Seems like link rot on the web is getting faster as time goes by.
Comment: Updated dead links with some new google results. Let's see how long these ones last!
Answer: Yes, but it all about exposure time.
If you solder 8h per day and 5 days per week your exposure is quite high and the odds of side effect if you don't ventilate it away is quite high.
On the other hand, if you solder a couple of prototype boards now and then, and you don't directly inhale the fumes the amount of chemicals is probably not that high.
Answer: I've been soldering daily for 35-odd years and the only time I do anything about fumes is if I'm doing a production batch, when I stick a 4" fan at the side of the bench to blow air across, which is as effective as extraction, and doesn't get in the way. Unless you are allergic or find it annoying I wouldn't worry too much unless you're doing it continuously all day.
I do find the flux in LF solder significantly more irritating, which is another reason I rarely use it.
Comment: And besides... hardly anyone notices that extra finger growing out of your forehead.. (LOL Sorry I could not resist.) (Also 35+ years and counting--->)
Comment: "Unless you are allergic or find it annoying I wouldn't worry too much" Never to late to get a new allergy! Use fume extractors. Almost everyone I know who have worked with professional PCB assembly most of their life have gathered their fair share of allergies or lung problems. You don't get those from "bad luck", you get them from toxic chemicals.
Answer: I work very closely with my pieces.  I worked on electronic boards years ago and did not find I had a problem but I also worked in a professional environment that filtered the room.  When I first started working with solder at home I thought that I was just going to be working a few times here and there (Stained Glass Hobby).  I quickly found after 3 hours of soldering that I had a head ache and the next morning my sinuses were bothering me. I also found that my eyes were gunked up.  Thinking this is just pollen I returned the following day to my beloved project and soldered for 4 hours.  I did this for 3 consecutive days until I realized that it was more damaging than I thought.
Now I have to wait for my sinus membrane to recover before I can get back to my project (which takes more solder than the average computer board).  I have also found that my joints hurt. I don't know if this is part of the exposure or just age.  I have now ordered one fume extractor for up close and will be looking into another.
If you are working with solder, and it is sporadic, I suggest you have a small one.  If you work with solder regularly, I suggest a strong one.  I am now researching different ones to see which would be appropriate for my usage.
Answer: Solder fumes can have halides in them. The flux containes halides which means bromine and chlorine for most fluxes. These ions are not good to breathe in. With most fluxes you can check the content of the flux in it's corresponding datasheet if it's available.

Are solder fumes bad for me?


AppExchange Security Review of Client

Question: We are planning to release an offering to AppExchange. Our offering includes clients which interacts sfdc endpoints. However, the client does not interact with gzip encoding. Will it be an issue for the security review?
Answer: The client will also be tested. In this case, the best thing to do is set everything up on one of your machines and give them RDP (or equivalent) access, with an admin account. This allows them to log in, install the instrumentation code they need, and conduct the review with the least hassle.
The security review team can't install third party code like this on corporate equipment, and installation of client code is often time consuming, which directly adds to your wait time.
The main thing that they will look for is how/where you store credentials (see the secure coding guidelines for more info), but also what is logged and what data is sent out.

AppExchange Security Review of Client


How to search only unanswered questions with an open bounty ?

Question: Is there a way to search only unanswered questions with an open bounty on StackOverflow ?
Comment: possible duplicate of [How can I search for bounty questions?](http://meta.stackexchange.com/questions/54476/how-can-i-search-for-bounty-questions)
Answer: As of the date of this post, there isn't a way to filter on whether or not a question has a bounty on it.
The closest you can get is hasnotice:1 answers:0 closed:0, which will include some extra posts with a notice.
See the clickable Advanced Search Tips on the search page for more options.

I should add that maybe you don't want to be doing this. Just because a bountied question has an answer it doesn't mean that it is answered. I've received a bounty before when 3 answers were posted before mine.
Comment: I think something's changed behind the scenes: `hasnotice` gets me nothing in the way of questions with bounties
Comment: thanks! thanks helps. I'm not familiar enough with the system to know what "hasnotice" conflates with hasbounty. Cheers!
Comment: Looks like this still works after the search update earlier this month. Nice!


Is the distinction between parametric and non-parametric statistics always clear-cut?

Question: Is the distinction between parametric and non-parametric statistics always clear-cut or do examples of a statistic exists which cannot clearly assigned to one of these categories?
Answer: There are semiparametric methods which fall somewhere in between. A famous example is the Cox proportional hazards model, which has a nonparametric and a parametric model component.


What happens to a body if it rotates extremely fast?

Question: I am thinking on a object, e.g. ball or planet that starts rotating with increasing speed. Let's assume that his speed get's closer to the speed of light, what happens to this object? There are several forces acting. But I always get caught thinking that it will get heavier and heavier because of the additional energy which is needed to accelerate it. Is that all? Or anything else interesting happens?
Comment: As a rotating body approaches the speed of light, the molecular attractions tend to break under the stress from the centrifugal force.You might want to look up for a video by veritasium on youtube, where they have addressed this very problem.
Comment: I assume by "his speed" you mean the velocity on the most outer part? using rotation is oftenly tried approach "to overcome" the speed barrier so you will find lots of explanation on that. One fundamental problem with this is you would need a physically impossible object.
Comment: @Bort I see, so it is really more complicated that I thought.
Comment: its not impossible to do, far from that, but there is always this danger that you try do "break" relativity theory by breaking physics somewhere else. One further example that I think is in many textbooks is a ski driver that drives over a gap. At first it will seem that the result (does he make it over the gap?) depends on the frame of reference (due to length contraction), but the resolution in the end is that you cannot assume the ski to be a rigid body, because a rigid body has sound velocity of infinity which is larger than $c$
Comment: @Abhinav Yes, this conflict situation is interesting for me. Thanks for the keywords for youtube. :-)
Answer: Note that "c" means linear velocity, not angular. Then, you would refer to tangential velocity.
If an object rotated at relativistic (tangential) velocity, then each "shell" will have a different space and time compression. By contraction of the tangent lengthes, the perceived length of large circles would be smaller than $2\pi r$, leaning to 0 lenght at equator as the tangential speed approach c.
Appart from that, yes you would need more and more energy to accelerate it, and also the material coherency of the object is unlikely to resist to centrifugal force !
Comment: So an object rotating at the speed of light would be a point particle or infinitely small line?
Comment: c - 7.83088611035e-62 (to reach the planck length) would be very fast though.
Answer: A phenomenon which has been observed in stars and planets is that when the body rotates faster and faster, the object becomes more and more elongated, thus some points in the object are farther away from the rotation axis, increasing the relative moment of inertia and requiring more torque to accelerate the body by the same amount.
This effect has also been observed in everyday objects and in everyday devices. For example, the governors on steam engines exhibit this effect. When it spins slowly, the weights are almost all the way in. When it rotates faster, the weights swing outward and are further away from the shaft, requiring more torque to maintain constant angular acceleration.
Comment: Highly interesting!


Regex for valid mysql table field

Question: I'm developing a php application that requires the creation of database fields, based on a source data. This data contains spaces, accents, characteres like slashes etc.
Right now I'm parsing this data, validating spaces, accents, but I would like to do it by a regular expresion that simply returns a valid database field name.
Is this possible ?
Thanks.
Comment: Possibly. What have you tried so far?
Answer: If I was told to do this, I would start reading the rules for defining a column name in MySQL.
You can read these rules here : http://dev.mysql.com/doc/refman/5.7/en/identifiers.html.
I have selected MySQL 5.7 but read the documentation for your targetd version.

Regex for valid mysql table field


Entity Framework 7 - Cannot open database requested by the login. The login failed

Question: I've decided to use EF7 form my "home made" web application. I created my DbContext which contains this:
protected override void OnConfiguring(DbContextOptionsBuilder options)
{
    options.UseSqlServer(@"Data Source=NameOfSQLServer;Database=MyDb;Integrated Security=True");
}

However when I run app, I've got this error:

Cannot open database  requested by the login. The login failed.

That's quite shocking for me, because I used that connection string in EF6 and it worked like a charm.
Any idea what's wrong?
Answer: Entity Framework does not change your connection string. It just passes this through to SqlClient. You can eliminate EF from the equation and test your connection string actually works with this code:
using (var connection = new System.Data.SqlClient.SqlConnection(connectionString))
{
    connection.Open(); // <-- this should fail if the login doesn't work
}

Chances are something is wrong in the connection string, the database setup, or both.


FlywayException: Unable to scan for SQL migrations in location: classpath:db/migration

Question: I'm trying to start using flyway with maven integration but can't make it work.
I'm following the documentation seems to be very simple so no strange things seem to be done.
My pom.xml is the following:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.test</groupId>
  <artifactId>test</artifactId>
  <version>0.0.1-SNAPSHOT</version>

  <build>
        <plugins>

            <plugin>
                <groupId>org.flywaydb</groupId>
                <artifactId>flyway-maven-plugin</artifactId>
                <version>3.0</version>
                <configuration>
                    <url>jdbc:mysql://localhost:3306/test</url>
                    <user>test_fede</user>
                    <password>test_fede</password>
                </configuration>
                <dependencies>
                    <dependency>
                        <groupId>mysql</groupId>
                        <artifactId>mysql-connector-java</artifactId>
                        <version>5.1.21</version>
                    </dependency>
                </dependencies>
            </plugin>
        </plugins>
    </build>

  <dependencies>
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>13.0.1</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.21</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.8.1</version>
            <scope>compile</scope>
        </dependency>
  </dependencies>
</project>

I have the directory resources/db/migration/ without any migration yet.
When I issuing flyway:info on cygwin or cmd I got an flyway error:
$ mvn compile flyway:info
[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Building Unnamed - com.test:test:jar:0.0.1-SNAPSHOT
[INFO]    task-segment: [compile, flyway:info]
[INFO] ------------------------------------------------------------------------
[INFO] [resources:resources {execution: default-resources}]
[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 0 resource
[INFO] [compiler:compile {execution: default-compile}]
[INFO] Nothing to compile - all classes are up to date
[INFO] [flyway:info {execution: default-cli}]
[INFO] Database: jdbc:mysql://localhost:3306/test (MySQL 5.5)
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] org.flywaydb.core.api.FlywayException: Unable to scan for SQL migrations in location: classpath:db/migration

Embedded error: Unable to determine URL for classpath location: db/migration (ClassLoader: org.codehaus.classworlds.RealmClassLoader@5bcdbf6)
[INFO] ------------------------------------------------------------------------
[INFO] For more information, run Maven with the -e switch
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1 second
[INFO] Finished at: Tue May 06 11:06:15 CST 2014
[INFO] Final Memory: 17M/223M
[INFO] ------------------------------------------------------------------------

Can give me a hand on this?
Thans a lot.
Comment: Check my this answer hopefully it becomes helpful, https://stackoverflow.com/a/59478383/9437031
Comment: Check this is may help: https://stackoverflow.com/a/65561481/6150881
Answer: This also happens if the compile goal is not executed before calling flyway:migrate. Actually this IS included in the quick start manual. It says:

mvn compile flyway:migrate

However if you miss that detail and start to just call mvn flyway:migrate, the SQL file will not get copied into the target directory (actually the target directory will not even exist) and you get this cryptic error.
Answer: Well, just for you to know.
I found the problem, it happens when we setup flyway in our environment but we don't have any migration to be executed.
It shouldn't display a classpath error but fortunately it's working.
By the way, another problem I found is that after executing init if we check with info nothing is displayed. And if we add a new migration with V1 then info won't show it unless we change it to V1_1
Hope to help
Comment: This was probably due to maven not creating the output directory if the input directory is empty. P.S.: You probably don't need init. That's for existing databases only. For new ones migrate is enough.
Answer: I had a similar problem and it was because when I created the migration directory I gave it the name db.migration directly.
By creating the directory db and then inside it the migration directory it worked.
Answer: I ran into the same problem. In my case, I had my migration script in the wrong directory that had caused the issue. I moved the script V1__Create_person_table.sql to the right directory at resources/db/migration/ and it worked!!
Answer: I faced the same issue. But when i obeserved the logs keenly i found flywaydb is looking in db/migration folder for the script but my script is in db/migrate. so, after correcting the path from db/migrate to db/migration it works!!.
Answer: I had a similar problem too. in my case i thought i had named the directories correctly after triple checking everything. Turned out that i typed migrations instead of migration. As soon as i fixed this everything was fine.
Just before this i had another issue with the underscore after the version marker (V1) in the migration filename. It needs to be a dunder (double underscore) so its always V1__description.sql .
Seems like none of the flyway issues i encounter are big mess-up's. it's always something small that can be easily fixed. It's just about finding out what the problem is. That's the hard part.
Comment: Wow 3 hours later, thats it.
Answer: Here's a dumb mistake I've made where I got this pesky error:
Make sure you set your packaging as jar not pom in your pom.xml. Then mvn install and make sure you have a jar for that project in your M2 folder otherwise you will get this error since the migration file wasn't copied over and found.


Starting Daemon from Cocoa application

Question: Anyone can please provide sample code to launch a daemon from cocoa application using AuthorizationRef.
Answer: A daemon is generally defined as a long-running system service that has no user interaction. If that is what you mean by daemon then this is the wrong way to solve your problem most likely. Daemons should be started through launchctl and should have a preferences plist in /Library/LaunchDaemons or ~/Library/LaunchDaemons depending on whether they are system-wide or user-specific. Communication between your user application and the daemon can be done any way you please but I've found NotificationCenter (CFNotificationCenterRef) to be useful for such things.
However, if what you really need is to launch a tool to perform a specific task and that tool needs special privileges then check out the sample code here :
http://developer.apple.com/library/mac/#documentation/Security/Conceptual/authorization_concepts/03authtasks/authtasks.html%23//apple_ref/doc/uid/TP30000995-CH206-TPXREF33

Starting Daemon from Cocoa application


Propagation delay vs. transmission delay

Question: What's the difference between propagation delay and transmission delay?
Answer: Propagation delay focuses on speed of signal travel through a medium:  fiber, copper, air, etc.  Transmission delay is overall delay, including delays through equipment as well as media.
Answer: Propagation delay is tightly related to the physical medium that the signal is sent from. It might be an optic fiber, coaxial cable or a twisted pair copper wire.
Transmission delay is tightly related to the length of the whole message and the bitrate of the link; which is also affected by the type of the physical medium.
Though it might be completely two different things at the first glance, they might affect each other. Because the actual bitrate of the medium is also dedicated to the type of the physical medium.


How To load data that are accessed from database to html form

Question: I am trying to access data from table with GetString() method  and that data is stored in some variable  then it  must be loaded to html form when i am click the  submit button. How to it? Please help me......
Answer: This question is too general.
In order to access the database you need a web server running server-side code in a language such as ASP.NET, Java, PHP, etc. The server code would be responsible for using a "GetString()" method to read the table and populate data in the form (or even better, return it to an MVC View or to JavaScript via AJAX to load it onto the HTML form).


If A is a field and is contained in an affine K-domain, then A is algebraic

Question: I am trying to understand the intuition as well as the proof of the following theorem:
Let $A$ be be an algebra over a field $K$. If $A$ is a field and is contained in an affine $K$-domain, then $A$ is algebraic.
The proof that I am looking at is on pages 8 and 9 of this book.
Some of my questions are:

Why do we need to consider the maximal K-algebraically independent subset?
"For b ∈ $Quot(B)$, multiplication by b gives an $L$-linear endomorphism of $Quot(B)$"- Why is it $L$-linear?
"Choosing an $L$-basis of $Quot(B)$, we obtain a map φ: $Quot(B)$ → $L^{m×m}$ assigning to each b ∈ $Quot(B)$ the representation matrix of this endomorphism." - How do we find this matrix? Do we just multiply the $L$-basis elements in $Quot(B)$ by $b$ and write what we get as columns? Where are the $m$'s coming from?

The rest of the proof also is unclear to me but thought I'd ask these questions first. If there is another proof of this that you could direct me to, that would also be great.
Answer: (1) Actually, it's A maximal $K$-algebraically independent subset - there can certainly be more than one. "Maximal" is used with respect to the partial ordering by inclusion. The set is chosen to be maximal so that $a_{r + 1}$, $\ldots$, $a_n$ will be algebraic over $L = K(a_1, \ldots a_r)$. This is what guarantees that $\textrm{Quot}(B) = L(a_{r + 1}, \ldots, a_n)$ is finite-dimensional over $L$.
(2) Automatically, if $R \subseteq S$ are commutative rings, and $s_0 \in S$, the mapping $u \colon S \to S$ defined by $u(s) = s_0 s$ is $R$-linear.
(3) $m$ is the dimension of $\textrm{Quot(B)}$ over $L$. Your description is correct. If a basis of $\textrm{Quot(B)}$ over $L$ is $\{b_1, \ldots, b_m \}$, then the first column will be the coordinates of $bb_1$ in thhat basis.
Prop. 7.9 in Atiyah-Macdonald is close, but not identical.


Difference between adiabatic and nonadiabatic tunneling for molecule

Question: What is the difference between adiabatic and nonadiabatic tunneling for a molecule in a laser-field?
Does nonadiabatic tunneling necessarily relate to the Conical intersection or curve-crossing?
Comment: there is a short answer here https://chemistry.stackexchange.com/questions/100458/what-is-the-difference-between-non-adiabatic-coupling-and-diabatic-coupling
Comment: Can you provide a reference for these terminologies? I have never heard of non-adiabatic or adiabatic tunneling. I have seen things similar to what I would guess this is using both diabatic and adiabatic representations. Generally though, nonadiabatic almost always has to do with conical interesections.
Comment: Hi here is one of the references..https://aip.scitation.org/doi/10.1063/1.463981
Comment: Look at D. Yarkony, Chem. Rev., 2012, 112 (1), pp 481–498 for a thorough review of the subject.
Answer: This is very far from a complete answer, especially w.r.t the part of your question regarding "laser fields". After doing some reading, nonadiabatic tunneling is conceptually the same as adiabatic tunneling except that one allows for coupling to another adiabatic state.
Adiabatic tunneling is the phenomenon where a particle described by a wavefunction is propagating on a potential and begins with less energy than the height of the barrier it approaches. One finds, however, that there is amplitude of the wavefunction on the other side of the barrier despite the particle having insufficient energy to cross the barrier.
Now, in physics and chemistry, nonadiabatic processes typically describe those processes where it is a bad approximation to consider only a single potential energy surface. That is, both surfaces may be adiabatic states, but these states are coupled in some manner. In general, there will always be some small coupling between states that are not too far apart in energy.
Nonadiabatic tunneling just describes the situation that one does not neglect this coupling between states. To a first approximation, nothing will change and one will find the same amplitudes as a function of position and time. If you consider the presence of the higher-energy adiabatic state as a perturbation of the Hamiltonian of the original particle, then the zeroth order picture will just be adiabatic tunneling. The next term will be something like the case where the particle is either reflected or transmitted over the barrier, but it does so by first "visiting" the higher-energy adiabatic state.
Now, with that description in mind, I think it is reasonable to say that nonadiabatic tunneling does not necessarily have to be involved with with conical intersections or curve crossing. Nonadiabatic tunneling is just regular tunneling which allows other states to couple with the original state. Now, of course, conical intersections and curve crossing could very well come into play in nonadiabatic tunneling because this would just be another form of coupling one could introduce.

As an aside, the description I give where the higher-energy state is a perturbation on the original system is probably not a good one in general as one could imagine very strong coupling between the potentials (as would be the case with a conical intersection).


Upper density, and nested sets

Question: For a given $A \in \mathbb{N}$, we define the upper desnity $\bar d(A)$ by
\begin{equation*}
\bar d(A) = \limsup_{N \to \infty} \frac{A \cap [N]}{N}
\end{equation*}
where $[N]$ denotes the set $\{1,2,\dots, N\}$. My question is, if we have a sequence of sets
\begin{equation*}
A_1 \supseteq A_2 \supseteq \dots \supseteq A_n \supseteq \dots
\end{equation*}
such that
\begin{equation*}
\bigcap_{n \geq 1} A_n = \varnothing
\end{equation*}
then do we we have
\begin{equation*}
\liminf_{n \to \infty} \bar d(A_n) = 0
\end{equation*}
I'm not sure if this is obvious or not. I was thinking that a way to prove this statement is to first define $\frac{1}{2} A_1 \subseteq \mathbb{N}$ to be such that it includes every other element of $A_1$. Then we would have $\bar d(\frac{1}{2} A_1) = \frac{1}{2} \bar d(A_1)$, and there is an $m \in \mathbb{N}$ such that $A_m \subseteq \frac{1}{2} A_1$, so $\bar d(A_m) \leq \frac{1}{2} \bar d(A_1) \leq \frac{1}{2}$. Carrying on like this we get a subsequence which decays as $\frac{1}{2^k}$ which implies the claim. This argument does feel a bit fishy to me though.
Comment: By $A\in\mathbb N$ I think you mean $A\subseteq\mathbb N$.
Answer: As a counterexample, how about $A_n=\Bbb N \setminus[n]$?
Answer: No.  $A_n=\mathbb{N}-[n]$ is a counterexample.  There is no reason why $A_m$ must be a subset of your $\frac12A_1$.

Upper density, and nested sets


how to create quick access menu using css

Question: My apologies if I am asking for the code but pls let me know how to create quick access menu just like salesforce using only css.
I know how to create a dropwdown using css and display it inside an visual force page but I am unable to toggle it(hide/show).
Answer: I don't think this is very related to Visualforce or Salesforce. But here is a codepen example for you to take a look at: https://codepen.io/surjithctly/pen/pLDwe You should be able to figure out by following this.
Answer: If you are interested - you can look at the Lightning Design System for the new Global Navigation CSS:
SLDS Global Navigation


dnsmasq: Block manipulated dns responses pointing at captive portal site

Question: After setting up a raspberry pi based router (behind two other routers) using debian stretch, iptables, dnsmasq and hostapd, I have come to learn a seemingly endless amount of interesting options that are by far not available in the proprietary world.
With regard to one very nasty problem however, I did not find a solution yet: Certain very poorly designed internet routers manipulate dns responses pointing any dns request at their own configuration site as long as they are not on the line.
In my case this leads to - oh wonder! - dozens of warnings related to bad certificates on https connections. When it comes to http connections, fun is to be expected.
Given that dnsmasq is already configured properly to use specified dns servers for external traffic and to use locally configured addresses as well as assigned dhcp leases for internal traffic:
Is it possible to configure dnsmasq in such a manner that manipulated responses, which point at a local address range, even though they belong to a non-local domain, are being filtered as invalid?
Example: DNS request for anysite.com to 126.96.36.199 is being intercepted by 192.168.2.1 pointing at 192.168.2.1; as the latter however is not being addressed by any top level domain, such responses shall be discarded until the actual 220.127.116.11 can be reached.
Even though it might seem obvious - would this type of problem be solved for all kinds of clients by enabling and configuring the dnssec features of dnsmasq?
Thanks in advance!
Answer: The <code>--stop-dns-rebind</code> option will cause dnsmasq to ignore any address responses which are in private IP address space.


How do I run Homebrew vi on macOS instead of the older version Apple provided?

Question: I have recently upgraded to Vim 8 using Homebrew, but my vi commands still load the OS-provided version 7.4 of Vim. I could add an alias to vi, but is there another way?
Comment: if you just want to go with vim 8, then you can simply remove vim 7.4 from your system. It will automatically solve your problem.
Answer: This is happening because the OS's vi is ahead of Homebrew vi in the PATH.
While you could fix it by putting /usr/local/bin ahead of /usr/bin in the PATH, that would be a security hole since Homebrew gives ownership of that directory to your user. That permission change from the macOS default means that even an extremely unsophisticated malware could use this hole to get root privileges. All they'd have to do is add some other common command here like ls, then pass the commands through to /bin/ls until they see you've run it through sudo, then they take over.
This is a general principle, not specific to Vi, Macs, or Homebrew at all: never place user-writeable PATH elements ahead of those that can only be modified by root.
There are several ways to solve this problem:

Replace the OS's vi and vim binaries with symlinks to the Homebrew versions:
$ cd /bin
$ sudo mv vi vi-7.4
$ sudo ln -s /usr/local/bin/vi .
$ cd /usr/bin
$ sudo mv vim vim-7.4
$ sudo ln -s /usr/local/bin/vim .

I do not recommend this solution, but it is what the original version of the question asked for, so there it is.
Notice that this doesn't delete the OS-provided versions, just renames them so you still have access to them by appending -7.4 if you need to later.
Since all three of the directories in the prior solution are in the default user PATH on macOS, you don't actually need the symlinks unless you have local software that has hardcoded /bin or /usr/bin paths to vi or vim. Just move the system versions shadowing Homebrew's versions out of the way:
$ sudo mv /bin/vi /bin/vi-7.4
$ sudo mv /usr/bin/vim /usr/bin/vim-7.4

That causes vi and vim commands to fall through to the Homebrew versions in /usr/local/bin.
Both solutions above will break the next time you upgrade macOS because the OS installer will put the Apple-provided versions back in /bin and /usr/bin, so the solution I actually recommend is to add aliases to your ~/.bashrc file:
alias vi=/usr/local/bin/vim
alias vim=/usr/local/bin/vim

This lets you switch back to the OS-provided version of Vim easily by quoting the alias:
$ 'vi' somefile.txt         # forces use of /bin/vi

You might also want to add this to ~/.bash_profile:
export EDITOR=/usr/local/bin/vim

Several commands use $EDITOR instead of hard-coding a call to vi.
Another option you have is to remove the Homebrew build of Vim and install MacVim instead. It also installs to /usr/local/bin, but unlike Homebrew Vim, it installs a command that isn't shadowed by the OS version, mvim. By default, that command launches the GUI MacVim editor, but with this alias, you can have your vi and your Terminal editor, too:
alias vi='mvim -v'

The -v flag tells it not to launch the GUI, but to edit in the Terminal instead.
If you choose this option, make a similar change to the EDITOR definition.
Among the many nice features you get with MacVim is integration with the OS clipboard: pasting from the OS clipboard into Terminal.app running stock or Homebrew Vim you already have, but I find it nice to go the other direction as well: "yank" commands in mvim -v under Terminal.app also sends the yanked text to the OS clipboard so I can paste it into some other program.
Comment: In response to the security concern, the responder here considers the security concern to be "bikeshedding": https://discourse.brew.sh/t/is-it-dangerous-to-have-usr-local-bin-ahead-of-usr-bin-in-your-path/6097
Comment: Note that methods 1 and 2 are difficult on recent macOS versions:  `mv: rename vi to vi-7: Operation not permitted`.  The alias in method 3 is still a good solution.
Answer: Homebrew has an option --with-override-system-vi that can be used with brew install vim to do this.
Comment: `Error: invalid option: --with-override-system-vi`
Answer: Since I don't have enough points to make a comment and i have seen --with-override-system-vi a ton of times I hope this helps someone else. Options were removed from brew - [github]: https://github.com/Homebrew/homebrew-core/issues/41128
I ended up switching to neovim https://neovim.io/
Steps if you want to do the same.

brew install neovim
In my .zshrc file I added alias vim="nvim"
Comment: Welcome to [vi.se]! This actually has quite some potential for an answer, especially if you mention the alternative ("If you want to override internal tools you'll have to put them in your path before the internal tools.") and particularly if you add details on how/what to add to `$PATH` to make this work! I'd definitely upvote such an updated answer.


Why do I get "loading failed" when trying to add Membership Organization to a new membership type?

Question: I am setting up a new install of CiviCRM on the latest Wordpress (self hosted). I am trying to set up membership types, but when I go to enter the Membership Organization, I get a "Loading failed" message (see screenshot). I have already created two contact records of type Organization, including the default org which this setup is for. I am logged in as the super admin, so it should not be a permissions error. Also, there are no existing membership types. Any ideas appreciated.
Thanks.
Comment: check civicrm error log - That should give you an idea
Comment: Enable wp_debug and see if you are getting any PHP error
Comment: If I can't get past this step, I can't use CiviCRM at all for this site. Anyone have any ideas please?
Comment: Thanks for the suggestion Ramesh. Unfortunately, there is nothing in ConfigAndLog. I tried it with debugging and backtrace turned on as well. Is there another place I should be looking?
Comment: Thanks for the suggestion Ramesh. I tried that, but no errors appeared when I tried to add a new membership type and got "loading failed" again. It's a strange mystery!
Comment: In that case try to install fresh copy of CiviCRM again and try the same - else share me your credential let me try to find the issue - send me your details to firstname.lastname@example.com
Answer: Well, I finally tracked this down. But before I go into that, I should say that I initially worked around the issue by creating the Membership Types right in the Civi table using phpMyAdmin.
Later, though, I noticed I was getting the same "Loading failed" when trying to add a tag to a contact using the tag tree popup. I also could not create a new mail message. It always got stuck on "initializing." So I went searching for more help and found an old post on the CiviCRM community forum by @Coleman that seemed to be related to the issues I was experiencing.
Based on that post, I started to disable WordPress plugins. I narrowed it down to the All In One WP Security plugin. Then I narrowed it down to the plugin's firewall measures. Finally, I found the culprit, the "Enable legacy 5G Firewall Protection" setting. By unchecking that, I was able to restore proper functionality in CiviCRM.
I hope this helps someone else out there who might be getting "loading failed" issues. It will most likely be related to the firewall and what is in the .htaccess file.
Thanks again to those of you who offered help.


splitting and merging the json files from batch jobs in aws

Question: I am working on a project where I am splitting a single file with a bunch of sentences into chunks for further sending to a third-party API for sentiment analysis.
The third-party API has a limitation of up to 5000 characters of limitation and which is why I am splitting the file into chunks of 40 sentences each. Each chunk will be sent to a batch job via AWS SQS and processed for sentiment analysis from a third-party API. I wanted to merge all of the processed files into one file. I couldn't find the logic to merge the files.

For example,
the input file,
<code>chunk1: sentence1....sentence1... sentence1....

chunk2: sentence2....sentence2... sentence2....
</code>
The input file is separated into chunks. Each of these chunks is sent separately to a batch job via SQS. The batch job will call the external API for sentiment analysis. Each file will be uploaded to the S3 bucket as separate files.
Output file:
<code>{"Chunk1": "sentence1....sentence1...sentence1....",
"Sentiment": "positive."}
</code>
All I wanted is to have the output in a single file but couldn't find the logic to merge the output files.
Logic I tried:
For each input file, I send a UUID to every chunk as ametadata and merge them with another lambda function. But the problem here is I am not sure when all of the chunks are processed and when to invoke the lambda function to merge the files.
If you have any better logic to merge the files, please share it here.
Answer: This sounds like a perfect use case for the AWS Step Function service.  Step Functions allow you to have ordered tasks (which can be implemented by Lambdas). One of the state types, called Map,  allows you to kick off many tasks in parallel and wait for all of those to finish before proceeding to the next step.
So a quick high level state flow would be something like:

First state takes a file as input and breaks up the file into multiple chunks
The second state would be a map state with a task that takes a file as input and sends to the sentiment analysis and saves output.  The map state will kick off a task for each small file and retrieve the sentiment analysis.
The third and final task state will take all of the files and combine them in whatever way you deem appropriate.

It may take a bit of googling and reading the user guides but your workflow is exactly the use case this service was designed for and it sounds like you already have some of these steps implemented as their own Lambda functions, you'll just need to tweak those to be compatible with how Step Functions receive and push data out instead of using SQS.
That being said, I'm not sure how you want to merge the files as each section was analyzed separately and may have it's own sentiment and I'm not sure how to summarize the sentiment as a whole.
Resources:

https://aws.amazon.com/blogs/aws/new-step-functions-support-for-dynamic-parallelism/
Comment: Thanks, JD. I am checking on this solution. Apologies for the delayed response.


For any integers $a$ and $b$, $ab = 0$ implies $a = 0$ or $b = 0$. Prove that this remains true mod prime numbers but not true mod a composite number.

Question: I roughly understand modular arithmetic but I am having trouble starting the problem. I can prove it for just integers but I can't seem to relate it to mod primes and composites?
Comment: By definition, a composite number $q$ is the product of two smaller integers. What is that product modulo $q$?
Answer: Here are two strategies that will work:

Start with a single example. Is the statement true in the integers modulo $6$? Why not, exactly? How does your argument generalize to other composite numbers?
Start by writing out definitions. What does it mean for a modulus $n$ to be a composite number? What does it mean for an integer to be congruent to $0$ modulo $n$? Can you find a way to plug these definitions into the problem you're trying to solve?
Answer: Well, in the residue class ring ${\Bbb Z}_m$, $m\geq 2$, each element $a\ne 0$ is either a unit or a zero divisor. An element $a\ne 0$ is a unit if $\gcd(a,m)=1$, otherwise a zero divisor.
The implication $ab=0\rightarrow a=0\vee b=0$ holds iff $a$ or $b$ is not a zero divisor.


Positive geometry and log singularities

Question: In order to define a positive geometry it is a requirement that has to be a logarithmic singularities on the boundaries, for example for an interval (endpoints $a$ and $b$) the canonical form is
$$\frac{dx(b-a)}{(b-x)(x-a)}$$ My question is: Why do we need that logarithm singularities requirement in order to get that differential form?
Answer: I'm not sure I understood exactly what you want to know.
Anyhow, a positive geometry is an oriented geometry that has a canonical form. A canonical form is a differential form with dlog divergences, which is like d$x/x$ for a boundary $x=0$, on all the boundaries of the geometry. Moreover, the residue of the canonical form on a boundary must be equal to the canonical form of the boundary. Finally, the canonical form of a point is equal to 1 for a positively oriented point and to -1 for a negatively oriented point.
Your example is the canonical form of a segment $a<x<b$ with an orientation form equal to d$x$. Following the definition, to verify that the expression is indeed correct we need to verify that the residue in $x=a$ is equal to 1, since $x=a$ is a positively oriented point, and the residue in $x=b$ is equal to -1, since $x=b$ is a negatively oriented point.
Your expression for the canonical form can also be rewritten as
$$\Omega(x)= \text{dlog}(x-a)-\text{dlog}(x-b)=\frac{\text{d} x}{x-a}-\frac{\text{d} x}{x-b}$$
The residue $Res_{x=a}(\Omega(x))$ for example can be computed as
$$Res_{x=a}(\Omega(x))=\lim_{x\to a}(x-a)(\frac{1}{x-a}-\frac{1}{x-b})=1$$
The idea of the canonical form can be generalized to non-logarithmic singularities for polytopes, as proposed in https://arxiv.org/abs/2005.03612, but the topic remains still in development for more general geometries.
I hope this answer was helpful!

Positive geometry and log singularities


Blender USD export won't save Emissive texture as part of USD Preview Surface

Question: I'm trying to create assets using Blender, save them as USDs with their texture information, and bring them into UE5. I'm having two major issues that are holding me back. The first is that when I try to save USDs, the only textures that will be saved are Diffuse, Roughness, Metallic, and Normal maps. I have an asset that requires a custom Emissive map, but when I try to save it, that map is never included in the textures folder. The second issues is that when I bring my USD file into Unreal, it reads the Normal Map as an sRGB which totally breaks it.
I am working on version 3.1.2 currently. I've tried plugging my emissive map into the correct BSDF input. There are no other nodes involved, just Emissive Texture color output to Emissive BSDF input. It looks good in the viewport, but doesn't save when exported. I've tried doing a "workaround" that I've seen a lot online where an emissive map is plugged into an Emission Shader node, and added to the BSDF node before being plugged into the Material Output. Still nothing. I've tried making the emissive a flat value to see if that will be read by Unreal. No dice. I've even tried downloading the Nvidia Omniverse plugin for Blender to see if that helps and it made it even worse. Plugging all of my textures into the correct texture inputs in the OMNI PBR material graph meant that only the diffuse map would be saved into the textures folder, and in Unreal, would be plugged into the inputs for each texture map.
I know that emissive textures can be saved to USDs, because I can export assets from Unreal with their materials and emissive textures as USDs. When reimported, their emissive textures will be plugged into the correct input on the USD Preview Surface instance. For whatever reason, it just doesn't work coming out of Blender. I would just create my USDs this way but exporting a USD from Unreal means that it creates a gross file structure where all objects and materials are all USDs that are read by one hierarchical USD that describes the whole scene.
My other issue is that when I bring USDs from Blender into Unreal, it doesn't automatically set the correct compression settings on normal maps. This means that they're being read as sRGB rather than RGB by the engine, which totally breaks them. I've tried setting the normal texture input nodes in Blender to non-color and raw before exporting as USD, but it doesn't seem to make a difference. I've also tried editing the UE5 USD Plugin material to include a function to convert sRGB to RGB but it didn't work at all. I'm also going to post about this issue on the UE forum just to see what I can find.
Let me know if anyone has had this issue, or if there's a workaround. Thanks!
Comment: This is the [Blender manual entry](https://docs.blender.org/manual/en/latest/files/import_export/usd.html) on USD import/export. There seem to be quite a few limitations at the moment. Read the Materials section on [Exporter limitations](https://docs.blender.org/manual/en/latest/files/import_export/usd.html#exporter-limitations).
Comment: "a few limitations" sounds a bit of a euphemism to me: "Very simple versions of the materials are exported, using only the Viewport Display color, metallic, and roughness." Basically, there seem to be no actual material support, only preview options are. Which most people don't even set by default.
Answer: When using Mac:

Install 'Xcode' and 'USDZ Tools'
Install 'Python 3.7.9'
Install 'numpy' to Python
Export myfile.gltf (embed textures) file from Blender
Use command line tool:
usdzconvert myfile.gltf myfile.usdz


Difference vector target and genomic target

Question: In Pfu turbo DNA Polymerase AD information sheet (and possibly in many other) different amplification targets are divided in Genomic DNA targets, Vector DNA targets and cDNAs.
What is the difference between the first two?
Answer: Genomic DNA is a DNA that has whole set of genetic data of an organism. You usually extract it with a whole DNA extraction kit.
Vector DNA is a vector (usually a plasmid, it can also be artificial chromosome,...the type of vector depends on the species and strategy you are using) that has you desired string of DNA in it (for example a gene you want to insert in to a organism) and you are using it to get your recombinant DNA to the organism.
I hope it helps!
Comment: Genomic DNA is usually bigger and more complex than plasmid DNA which is a relatively simple DNA ring of limited size.


Recovering Files from SD Card

Question: I accidently moved my iMac with the SD card inserted and the card got bent, it cannot be read anymore. Not sure if it can be recovered. I was wondering if somehow the files are stored on the HD. I did not import the (RAW) files.
Answer: Depending on how the SD card was damaged someone with some electronic skills might be able to straighten things out enough to get the files off of it. Possibly a phone repair shop? They might need to extract the memory chip circuitry from the damaged card and put it in another card, or even just re-solder some leads. Impossible to tell without actually examining the card in person
If, however, the actual memory chip in the card was damaged, you are out of luck.
Answer: I you just put the SD are in the reader, the system will only mount the device.
If you did not import the files, they will not be present on your hard drive.

Recovering Files from SD Card


How to record video in iphone

Question: HI,
I need to record video using iPhone. To do that i used UIImagePickerController. I have an iPhone 3G, with me. when i run my code to check if source type available it says device not supported. My OS is 3.2.1, where i am wrong, can some one tell me what i need to change.
Also is there some other way to record video. What i need to do is to get the video stream as it is recorded.
<code>    UIImagePickerController *picker = [[UIImagePickerController alloc] init];
picker.delegate = self;

NSArray *sourceTypes =
[UIImagePickerController availableMediaTypesForSourceType:picker.sourceType];
if (![sourceTypes containsObject:(NSString *)kUTTypeVideo ]){
    NSLog(@"device not supported");
    return;
}

//picker.allowsEditing = YES;
picker.sourceType = UIImagePickerControllerSourceTypeCamera;
picker.mediaTypes =  [NSArray arrayWithObject:(NSString *)kUTTypeVideo];
picker.videoQuality = UIImagePickerControllerQualityTypeHigh;

[self presentModalViewController:picker animated:YES];
</code>
Thanks,
Answer: That is because the 3G isn't supported for video recording.
Comment: Please flag this as the correct answer: this place is give and take.
Comment: there are apps like iCamcorder which records video on iPhone 3G, and I know they did something, so this isnt correct answer.
Comment: hmmm - if indeed they are able to utilise the same frameworks for video recording - see the WWDC2010 vids free on iTunes to developers for video recording - an active working example is available.
Answer: Lance is correct. The native UIImagePickerController does not work on iPhone 3G. If an app does do video recording on a 3G they are doing a hack like taking multiple photos in succession and manually encoding a video file using the individual images.

How to record video in iphone


Can i use other regression types that arent based in decision trees to use it like a weak learners in gradient boosting?

Question: I was thinking if i can use polynomial regression like a weak learners in gradient boosting but i read that decision trees are used for that and i cannot find anything that show me the possibility of other weak learners could be used.
Answer: The issue of using any linear model (a polynomial regression is a particular case of a linear model, with polynomial features), is that an ensemble of linear models is still a linear model. So, the family of models to optimize from given by the boosted polynomial regression and the single polynomial regression are the same.
This doesn't happen with trees, as an ensemble of trees cannot be expressed as a tree anymore, so that's why trees are used more in the context of gbms.
Comment: I realized that couple months ago , it can be proved a final model is a linear model and either equivalent or worse than a model to any weak learner.
Answer: Any machine learning algorithm can be used as a weak learner for gradient boosting. Certain algorithms will work better and certain algorithms will work worse.
Linear regression tries to minimize the sum of square errors (SSE). The first linear regression model might not leave any errors for subsequent linear regressions models to fit, thus there would be no advantage to gradient boosting in that case.


Orbital definition

Question: In some sources, including my textbook it is cited that an atomic orbital is the 3 dimensional region where the probability of finding an electron is 90-95% . But, Other sources such as Wikipedia state otherwise. To quote Wikipedia,
"In quantum mechanics, an atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom"
With relevance to the fact that an orbital is always a wave function I agree that it can be regarded as a mathematical function, But what is this reference to "a pair of electrons"This has confused me.What is the the true definition of an orbital?
I am new to this forum and Chemistry, please excuse me if there's some misconception. Thanks
Comment: *Graphical representations* are usually drawn for the 95% probability integral, but the actual orbital is the function describing the distribution of said probabillity (not the integral!). Wikipedia is right, your textbook sloppily written.
Comment: As for the _pair_ thing, read about [spin](https://en.wikipedia.org/wiki/Spin_(physics)), or rather don't, just take it for granted that _two_ electrons may occupy the same orbital. Also, welcome to Chem.SE.
Answer: The mathematical definition is the most rigorous. The presence of the positively charged nucleus means that there is a pull on a negatively charged electron, which we describe with the potential energy. But electrons can only exist with certain discrete energy values. To do a full analysis you need to find the wavefunction that describes the electron. For a given electron, the wavefunction* at point (x, y, z) gives you the probability of finding the electron at the location; this is non-zero pretty much everywhere in space but is only significantly above zero in a very small region: this is what the first definition is getting at. Once you have the wavefunction you can calculate some properties, like the angular momentum. Since each electron has a discrete energy, each electron can be described by a set of four numbers, derived from the wavefunction: principle number (n), orbital angular momentum (l), magnetic angular momentum ($m_l$) and spin number ($m_s$). The spin number can be either +1/2 or -1/2 but we usually ignore it since normally that value doesn't affect the energy of the electron; this is the source of that "pair of electrons" business.
To summarize: An orbital is a specific state of an electron, characterized by its energy and various angular momenta and rigorously described by a mathematical function that satisfies Schroedinger's equation. This can be represented visually in many ways, such as showing the 95% probability solid, or as a line on a molecular-orbital diagram.
*Really this should be the wavefunction times its complex conjugate.

Orbital definition


How to remove a course reversal (hold) on a Garmin 530W?

Question: How can I remove a course reversal, (hold) from the FLP page on an RNAV approach ?  If I want to do a straight in (NoPT) it will not allow me to remove the hold without removing the whole waypoint.
Answer: When loading a straight in approach into a GNS430/530, once you select the airport, approach and IAF, then hit ENT to either load approach or load the approach and activate, it will bring up a dialogue which asks if you want to fly a course reversal at the IAF.  If you select no, then no hold will be placed in the flight plan.  If you have entered the course reversal at the IAF for a straight in approach, you can still remove it by opening the FPL page, highlight the hold and press CLR to remove it.  It will ask you if you want to remove the course reversal one final time.  Select yes and press ENT.


SimpleTest for Wordpress plugins

Question: Does anyone has any insight on unit-testing wordpress plugins with Simpletest, or other testing packages?
Answer: I've never worked with Wordpress or its plugin architecture.  However I would like to say SimpleTest is seriously outdated.  PHPUnit has way more features and is actively maintained.  A quick search yielded this: http://github.com/johnbintz/mockpress

SimpleTest for Wordpress plugins


Does uniform conditional distribution imply independence?

Question: Take two random variable $X,Y$ and suppose $X$ is distributed uniformly on $[0,1]$ conditional on $Y$. Does this imply that $X$ is independent of $Y$? Could you make an example?
Answer: Independence would mean that knowing the value of $Y$ gives no information on the value of $X$.
So here $X$ will be independent of $Y$ only if $X$ has a uniform marginal distribution on $[0,1]$, and the conditional distribution $X|Y$ is uniform on $[0,1]$ independent of the value of $Y$.
An example be a uniform (joint) distribution over the unit square.

Here are some examples using Tetris blocks:
For the "S" block

we have $p[X|Y=\text{middle}]=p[X]=\text{uniform}$, but $X$ is certainly not independent of $Y$.
While for the "O" block

we have $p[X|Y]=p[X]=\text{uniform}$, so $X$ is independent of $Y$.
Comment: So the point is that it is not the particular form of $p[X|Y]$ that matters, but the fact that it does not depend on the value of $Y$.
Comment: @user3285148: There's no such thing as "the standard normal exception". (Source: A Google search for this exact phrase gives only this question, and some unrelated Linkedin profiles). As GeoMatt22 explains, it's not the particular form of the conditional distribution that matters (be it Uniform, Normal, Gamma or whatever), only that it is the same distribution for every possible value of Y.
Comment: I might have misunderstood. If $X|Y$ is uniform on $[0,1]$ for all $Y$ values, then yes it is independent: The value of $Y$ does not enter into the formula for $p[X|Y]$. I thought you meant just you had one particular $Y$ value.
Comment: I added an example of $X$ uniform for only *some* $Y$, where the marginal is uniform but $X$ **does** depend on $Y$.
Comment: Thanks. However is it true that if $X$ conditional on $Y$ is distributed as a standard Normal then $X$ and $Y$ are independent?
Comment: So can I say that "the standard normal exception does not apply to the uniform"?
Answer: If the conditional pdf of $X$ given $Y$ is the same density function for all values of $Y$ (in the support of $f_Y(y)$), that is, $f_{X\mid Y}(x\mid y)$ equals $g(x)$ where the value of $g$ does not depend on $y$ at all, then
$$f_X(x) = \int f_{X,Y}(x,y) \mathrm dy  = \int f_{X\mid Y}(x\mid y)\cdot f_Y(y)\mathrm dy = g(x)\int f_Y(y)\mathrm dy = g(x),$$ that is, the unconditional pdf of $X$ is the same as the common conditional pdf
of $X$ given $Y$. In particular,
uniformity does not have anything to do with it at all: what we need is that it is always the same density function regardless of the value of $y$.
Suppose that $f_{X,Y}(x,y)$ has value $1$ on (the interior of) the unit square. Then $f_{X\mid Y}(x\mid y) \sim U(0,1)$ and $X$ and $Y$ are both
independent  $U(0,1)$ random variables.
Suppose that $f_{X,Y}(x,y)$ has value $2y$ on (the interior of) the unit square. Then $f_{X\mid Y}(x\mid y) \sim U(0,1)$, and $X \sim U(0,1)$ also. Note that $X$ and $Y$ are independent random variables but $Y$ is not a $U(0,1)$ random variable.
Suppose that $f_{X,Y}(x,y)$ has value $2x$ on (the interior of) the unit square. Then $f_{X\mid Y}(x\mid y) = 2x\mathbf 1_{\{x\colon x \in (0,1)\}}$ and the unconditional density of $X$ is the same density.  $X$ and $Y$  are independent random variables but $X$ is not a $U(0,1)$ random variable. Uniform distribution of $X$ is not needed: what is needed is that $f_{X\mid Y}(x\mid y)$ is the same for all choices of
$y$.


Can you throw a hand axe upwards over a wall and into a group of enemies?

Question: Can a player character throw a hand-axe upwards over a wall, into an enemy group that is on the opposite side of the wall? If so, what penalties would apply?
Answer: You can throw an axe over a wall, but it isn't an attack.
The wall provides total cover and "A target with total cover can't be targeted directly by an attack..." This means that tossing a weapon over the wall can't be resolved as the Attack action.
However, if you want to attempt something that isn't covered by the rules, you are explicitly allowed to Improvise an Action, per the combat chapter of the PH. How the success of this action is determined and the result of success are at the completion discretion of the DM. They could call for an ability check from you, make a saving throw for the target, or even just say that it bounces harmlessly off the helmet of the target. If the action is successful, the DM could determine that the target is dealt 1 damage, 1d12 damage, or even 1d6 for every 10 ft of height of the toss damage. It's completely up to them.
Answer: Rules as Written - No
As per the Cover rules, any attack at a creature that you aren't able to see, due to an obstacle completely obscuring the enemy, is treated as if they had Full Cover.

A target with total cover can't be targeted directly by an attack or a spell, although some spells can reach such a target by including it in an area of effect. A target has total cover if it is completely concealed by an obstacle.

In the case of your example, you won't be able to target or hit any enemy with the thrown axe.
Think of this as a real world example of throwing a ball over a fence at a friend who is trying not to be hit.  Any momentum in the throw will be lost on the way up, and you wouldn't know where behind the fence your friend was standing.
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](http://chat.stackexchange.com/rooms/68524/discussion-on-answer-by-nyoze-can-you-throw-a-hand-axe-upwards-over-a-wall-and-i).
Comment: You might want to clarify what you mean by "momentum in the throw will be lost on the way up".
Answer: Putting aside the rules... I don't see why not.
But, if you want to do it effectively, there's a few more issues.
Aiming
Firstly, assuming the wall is opaque, you're effectively throwing it blind. Determining the effectiveness of this would be pure chance, and I'd say it'd be entirely up to the DM on how that chance is handled. You may be able to roll for how effectively you threw the axe, but even a nat 20 roll wouldn't determine a hit.
The DM would likely factor in the direction you're throwing it, ask what you're using as a frame of reference (like sounds, or flickering shadows) and likely ask for a perception check to identify your target, then depending on what the target is doing (standing still? moving about?) determine the accuracy of your perceptive abilities.
Damage
While this might be a bit of overkill, but the skill used to determine damage is used to determine the damage of a direct hit. For example, you use Strength to bury an axe in your opponent's skull. In this instance, that would be completely irrelevant. It would be entirely up to the weight of the weapon to deal the damage.
So, in this instance, let's say the wall is 15ft high. To be safe, you throw it roughly 20ft, just to be sure. On the way back down, you'd rely on the weight and speed of the weapon to deal the damage. At ~20ft off the ground, it'd only reach ~60ft/s/s, which means that at ~2lb, the damage dealt would be a little more than a nasty knock, and that'd even be if it hit the right way around!
So all in all, this would likely be either completely useless, or used as a distraction more than anything. The effort involved in even getting this to work properly is over the top, and it would therefore make sense that anything in Full Cover (as Nyoze has explained) is impossible to hit. At this point, it'd be safe to say that physics and D&D do not mix well.

Thanks to Nyoze for helping me figure out the math on this one
Comment: "In this instance, that would be completely irrelevant." Does strength determine how high you can throw something?  "At ~2lb, it'd only reach ~60ft/s/s" How does weight factor into acceleration?  Clarifying those points may improve your answer.
Comment: @Yakk, sure the higher you throw it, the more damage it may cause. But then hitting the target would become even more difficult, because factoring in more strength can throw off your precision.
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](http://chat.stackexchange.com/rooms/68525/discussion-on-answer-by-ben-can-you-throw-a-hand-axe-upwards-over-a-wall-and-int).
Answer: Yes, one can toss an axe over a wall. But it is not an attack.
There is no accuracy, precision or strength in such an action. You won't be rolling any d20, but there is a chance the axe would hit someone on the other side. There are 3 sides of the action: making the axe go over the wall, finding where it will fall and evading/dealing damage.
This is how I'd adjucate the action:

Make a Strength(handaxe) check DC10 to make it go over the wall. This is not an attack roll, just a ability check. Maybe the character can't even lift.
Select a random space on the other side of the wall. The DM should see where it might land, choose some squares, assign numbers to them and roll a pure dice.
If the space is occupied, allow the creature on the other side to make a Dexterity (DC 11) save. Now the falling axe is a "setback trap". Let the damage be the normal handaxe damage for the characer. On a successful save the character evades the axe and it hits the ground.
Answer: I would allow it. However I would also apply modifiers such that the player throwing the axe would get a blindness modifier and any strength modifiers are removed.
When you throw an object it is possible to aim if you have a grasp of how and where it will impact a surface. Throwing with no vision impacts the aim. In dnde5 it could also mean that there is full cover, but that would not be the case if one used something like a siege weapon (think mortar), so I discount that as a valid conclusion.
When you throw an object over 45 degrees, the launching speed (aka. the strength modifier) is affected and gravity comes to account for most of the impact.
Thus if you are able to (by other means than vision) aim at a target, you would be able to hit it. It is important to note that a weapon such as a hand-axe is difficult to throw as it tumbles in the air and the location of impact is will have to be "blindly" aimed at around four foot from the ground at a certain location. There is the option to add the 50% chance to miss due to blind fire, which should apply in the case where the wall is not transparent.
Comment: Hi RLFP, thanks for elaborating. I've undeleted this answer and [removed a line indicating revision](https://rpg.meta.stackexchange.com/questions/3454/dont-signal-your-edits-in-text) due to our policy to avoid those.
Answer: Short answer: yes.
It breaks down into two parts, since it can't be treated as a normal attack.
On the player's side of the wall:
The player is trying to throw an object over a wall. It's not an attack on a specific enemy, so it is a feat. You can do the checks you think are most appropriate to test if they succeed. Keep in mind that just throwing it anywhere over the wall is easier than throwing it at a particular square on the other side of the wall. If they try to aim at a particular square, then the checks should be more difficult.
On the far side of the wall:
An axe falls from the sky. Does it hurt anyone? If the player picked a square and passed the check, then it lands there. If not, then you can use some die rolls to randomize where it lands. From there you might want to treat the falling axe as a dangerous trap with the character needing a passive perception check to see if they notice the axe before it hits them. Even if they notice they probably then need to make a dex check to evade harm. If it hits them then you as DM have free reign to calculate how much damage a falling axe does. The player's stats shouldn't be used here, because the player didn't make a standard attack. What happened on the other side of the wall is irrelevant now. All we care about now is that an axe weighing X pounds fell from Y height and landed on a guy.