2.3.0 Watermarks not showing on product images

Question: Watermarks are not showing up on product images in v2.3.0.
Steps to reproduce

Create categories
Create products
Modify buggy image uploader to work around bug so you actually can upload an image.
Upload a watermark (use watermark in this issue  as a watermark example)
set image opacity to 10, image size to 40x50, image position to tile, and saved configuration.
tap the Cache Management link in the system message. Then, refresh the invalid cache.

2.3.0 Docs state:
Complete the Base, Thumbnail, Small, and Swatch Image image settings as follows. The fields in each section are the same.

Enter the Image Opacity as a percentage. For example: 40
Enter the Image Size, in pixels. For example: 200 x 200
Tap Upload, and choose the image file that you want to use.
Set Image Position to determine where the watermark appears.
When complete, tap Save Config .
When prompted to refresh the cache, tap the Cache Management link in the system message. Then, refresh the invalid cache. Even tried to clear all available clear catch options inside cache management.

....still no watermark on product images.
2.3.0 Installation
No third party modules
No errors in browser console, or magento logs.
Opened ticket
And posted in forum
Other users with similar problem but some on older than 2.3:
here, here, here, here
How do you resolve this?
Answer: Did you try with a gif? I think that worked for us before.


What would happen if the location of a filter on a lens were changed?

Question: Most lenses have filter threads in front of the front element.  However, some lenses have filter threads behind the rear element, such as some fisheye lenses b/c the front element protrudes too far forward to place a filter in front of it.  What optical consequences would changing the position of the filter have?  Would it matter (optically) if a filter is placed behind the rear element of a lens that wasn't originally designed for such placement?
Comment: [Sometimes it matters](https://www.lensrentals.com/blog/2017/09/rental-camera-gear-destroyed-by-the-solar-eclipse-of-2017/) (see ND System Damage).

)
Comment: @xenoid But that wasn't the fault of using a normally-mounted-on-the-front ND behind the lens; that was a problem with expecting the built-in ND to do a job it isn't capable of: preventing damage to the camera when pointing at direct sunlight. I.e.: the renter just failed to protect the equipment, by not understanding what ND filters are for, and why solar filters *in front of the lens* are absolutely necessary.
Answer: If you put a filter behind the lens, it will change the focus a bit as the converging light rays are refracted as they pass through the filter. (I think it shifts the focal position by about 1/3 the thickness of the filter glass) - This is why many lenses (especially Manual focus ones) that use rear filters usually have a clear filter installed for normal use, to keep the focus in sync with the marked focusing ranges.
This is also why DSLRs modified for astrophotography (by removing the standard infra-red blocking filter, which also blocks a lot of hydrogen-alpha light (the red colour in emission nebulae), usually replace it with a clear or different IR filter rather than just removing the original - if you just remove the original, then because the filter on the sensor is no longer there, the effective focal distance to the sensor changes and no longer matches the separate AF sensor(s) which are set up to match the main sensor + filter combination.
With an AF camera, adding a rear filter affects both the main and AF sensors - so as long as it can still reach focus, you're probably OK - the camera may think the subject distance is different, but that shouldn't normally be a problem.
I have a vague memory that some rear filter lenses didn't come with a clear filter for normal use, but were intended for use with thin gelatine(?) filters - presumably since they're a lot thinner than typical glass ones, the shift is a lot less.
Comment: Never thought about that refraction effect: adding a rear filter makes it difficult to reach infinity focus.
Comment: @Ralf - If i'm visualising things correctly, it should move the focal position further away from the lens - the converging rays from the lens hit the filter, and are refracted as they enter the filter so they're less converging, then are refracted again as the leave the filter restoring the original convergence. Net effect is that the focal point ends up a bit further away from the lens - and since you move the lens further away from the sensor to focus closer (or an equivalent effect with internal focus lenses), you should still be able to reach infinity focus (though apparently closer)..
Answer: There's no real optical difference if the filter is uniform, clean, and of decent quality.
If the filter is dirty or has large spots that are darker or different colors from other parts of the filter, the further back in the optical chain the filter is placed, the more defined those defects will be in the resulting images when the same aperture is used.
For graduated density filters, the further back in the optical chain, the more defined the transition will be in the resulting photos when the same aperture setting is used.
Answer: The reason to have filter inside the lens or behind last element instead of in front is mostly convenience and price. Such construction is used mostly for long telefoto lenses where the front element is very huge (90 or more millimeters) or on wide angle lens where (usually) front element is very curvy and to have filter in front is need to use some filter system with 150mm plates.
Also when you have CP filter or variable ND filter is much more easy to put it inside the lenses (for telefoto) instead of making person to try to reach the front of the lens to turn the dial.
Comment: An adapter that allows the use of a filter behind the lens is effectively the same as what I am asking about.  I am concerned about *optical* consequences, not practical issues, such as accessibility or broken mirrrors (which isn't an issue with mirrorless).
Comment: Thanks for the info.  I'm wondering about the optical consequences of changing the filter location in a lens that wasn't originally designed for the altered position.  For instance, putting the filter behind the rear element of a lens designed for filters in front of the front element or vice versa
Comment: @xiota, this is very rarely possible. To have filter after last element you should have appropriate construction. If not you can broke the mirror (for example)
Comment: i don't think its that rarely possible to use a lens which was designed to have the filter in front to get the filter in the back. just think about the adapters for the canon eos r or for the nikon z line. there the adapters are holding the filter and nothing will be damaged. in such situations it would be nice to know if there are consequences.
Comment: @LuZel, those are special adapters, not adapting the lens itself to add filter behind


Halal Restaurants in Seoul South Korea

Question: I am travelling to Seoul this winter. I want to know about some good restaurants having halal food and also having spicy food as well. If there are some Pakistani restaurants having biryani that will be more good to know.
Comment: Not answering your question, just FYI: I know the ship building town of Geoji in the far south of the country has a large Pakistani community with many restaurants.
Comment: You should enjoy the seafood :)
Answer: I hope these links from the official Korea Tourism Organisation website, visitkorea, will help you:

Muslim Food Guide
Religious concerns / Halal Restaurants in Korea
Comment: Could you include relevant information in your answer? These links might die.
Answer: Usmania International Restaurant

Usmania is a Pakistani restaurant expressing authentic Pakistani taste
  in both its interior and food. The menu features about a hundred
  dishes, ranging from whole wheat bread, lamb, beef or chicken, but
  does not offer any pork dishes or alcoholic beverages, which are
  prohibited by the Koran. Inside the restaurant, you will find a
  variety of Pakistani decorations such as traditional shishas (water
  pipes) and silk carpets. Beef kebabs and tandoori chicken are
  favorites among Korean diners.
  Here is the
  Official Website of Usmania Restaurant

Address: Seoul-si Yongsan-gu Itaewon-dong 119-7
Tel: 02-798-7155
How to get there: Subway Line 6, Itaewon Station Exit 1, 5 minutes' walk
Comment: As a general guideline, Itaewon is the place to go when looking for halal food. A lots of restaurants owned by people from countries with a mostly muslim population.

Halal Restaurants in Seoul South Korea


What's the difference in Biblical Hebrew between "zahav" and "paz"?

Question: What's the difference in Biblical Hebrew between "zahav" and "paz"? Artscroll calls one "gold", the other "fine gold."  Any other distinctions?
Answer: Well, Ibn Ezra (to Songs 5:10) says that paz actually means "precious stones." Rashi seems to agree, because he explains זהב מופז (I Kings 10:18) as meaning that "it gleams like a pearl", and in Daniel 10:5 he also says that כתם אופז means "an arrangement of pearls."
Radak on the verse in Kings brings three possible translations for מופז: refined (i.e. "made into paz"); a placename (i.e., "from Ufaz" - compare Jer. 10:9); or simply "good gold" (Targum Yonasan). (Lehavdil, Strong's concordance derives מופז and פז from an assumed root פזז, "to separate, to distinguish.")
So according to this view, paz indeed means refined gold, as opposed to zahav which is just the generic term for the metal.
Answer: Gold makes sense because its targum is sometimes דהבא and biblically it is paralleled by זהב, by כתם, and by חרוץ, along with other classical contexts where alternative translation is impossible, as the phrase פעמני פז. Evidence for "refined" comes from the parallel of 2 Chronicles 9:17 "ויצפהו זהב טהור" and 1 Kings 10:18 "ויצפהו זהב מופז" (targum דהבא טבא) as well as the Greek translation δόκιµος refined. However, ben Sira parallels it with the gemstones פנינים and ברקת and b. Yoma 44b has "זָהָב מוּפָז שֶׁדּוֹמֶה לְפָז" which suggests they are not to be conflated; Rashi there comments that a פז is a pearl, but, in addition to evidence from parallels, the Biblical+classical phrases כלי פז, עטרת פז, etc. demand a material of which tools or vessels can be formed. לבושי פז and ביגדי פז in  Sidrei Avodah l'Yom Kippur allow for gold but not pearls. y. Yoma 23a quotes two alternative translations of the obviously related מופז, an adjective used to describe gold in 1 Kings 10:18. "מופז רבי פטרוקי אחוה דרבי דרוסא בשם רבי בא בר בינה דומה לאש מצתת בגפרית אמר רבי אבין לשם מקומו הוא נקרא זהב מאופז." Rabbi Patricius the brother of Rabbi Drosa in the name of Rabbi Abba b. Binah says that it is "Like fire kindled with sulphur;" i.e. blue (green and red gold are also discussed in Judaic sources) or dancing. The Semitic root פזז meaning dance is found in Biblical Hebrew, Arabic, etc. Rabbi Abin says it is formed by lenition of an א, for "from Uphaz," to which a second witness is MT Jeremiah 10:9's "זָהָב֙ מֵֽאוּפָ֔ז". Daniel 10:5's "כֶ֥תֶם אוּפָֽז" is a confirmation of the original א and a a weak challenge to the proper-noun theory and the vocalization of MT Jeremiah 10:9, though the Bible several times mentions כֶ֣תֶם אוֹפִֽיר, gold of Ophir. An alternative א-spelling doesn't conflict with Rabbi Patricius' position, however, because Breishis Rabbah spells the verb "אופזים" they danced. Abin and the Jeremiah vocalizer appear to be conflating זהב מאופז and זהב מאופיר (1 Kings 10:11), Ophir being a Biblical source of gold. TJ Jeremiah 10:9 reads "דַהֲבָא מֵאוֹפִיר" and Peshitta Jeremiah 10:9 has "ܕܗܒܐ ܡܢ ܐܘܦܝܪ," idem, but the three separate mentions and lectio suggests this is an emendation. The Peshitta has the same in 1 Kings 10:18. In part because the location of Ophir is completely unknown, we cannot reconstruct Uphaz as an alternative spelling.
In my opinion, the likeliest explanation is that the word פז refers to refined gold of quality good enough to be reflective when polished, so that it dances like flame when handled in light, a common metaphor in English as well. The connection to פזז dance is probably a folk etymology, though evidence of early association with a verb stem is found in מופז/מאופז, but it preserves the real meaning. Because פזז can also be spelled with an א and there was contamination from אופיר, it is not possible to reliably reconstruct whether "reflective/refined gold" or "gold from Ophir" was intended by אופז, by מאופז and by מופז, though my instinct is that the MT preserves the older version. The meaning of the b. Yoma is obscure and, looking at the parallel in y. Yoma, possibly itself confused. Ben Sira and early Jewish liturgy -- think מרשות הא-ל הגדול והנורא/ומרשות מפז ומפנינים יקרה With the permission of the Great and Wonderful God/And with the permission of He more precious than rubies and פז in the Simchat Torah blessings -- along with b. Yoma, may indicate a gemstone also called פז; however, almost all Biblical uses clearly refer to gold. The only possible exceptions IMO are SoS 5:15 and Lam. 4:2, and neither demands it.


Why are Vortigaunts violent in Half Life 1, but peaceful in Half Life 2?

Question: Why are vortigaunts violent in Half Life 1, but peaceful in Half Life 2?
Comment: There is one area in HL1 where the vortigaunts are peaceful (i.e. they won't attack Gordon Freeman unless he attacks first).  Unfortunately, it's so late in the game that there's a strong tendency on the part of the player to "shoot first and ask questions later".
Comment: @ReginaldBlue If memory serves me well, the Vorts won't attack Freeman when he is in Xen, in general. This is true even at the beginning of the game, when the player is teletransported to Xen for a brief moment right after the resonance cascade.
Comment: I was afraid someone would ask that... according to the strategywiki for half-life... the 'segment' is called "Interloper" and the area is called "Factory".  Quoting from the wiki:  "They are passive until attacked".
Comment: @ReginaldBlue Which area is that?
Comment: @MarcRanolfi Correct, the scene in question plays out on the homeworld of the invading aliens.
Answer: Vortigaunts in Half-Life 1 are an enslaved (or merely subservient) species ruled by the Nihilanth after they were driven from their homeworld by the Combine. The green collars they wear in Half-Life 1 are evidence of this slavery.
Comment: As well as the bracelets they wear. Periodically in HL2, you'll hear them thank Freeman for releasing them from their bondage.
Comment: Is that ever mentioned in the games?


Binary Equivalent vs. Computer code(Ascii or UTF)

Question: Does computer convert every stuff using Ascii or UTF?
Meaning if there is a mathematical calculation including 65 (as a number) will it convert it into binary (00100001)?
And then how it differentiate it with 'A', whose code point is also 65 with code 00100001?
Comment: Computer does not convert anything, it does not know the meaning of variables, but gets firmatting for display to present for human.
Comment: This does not seem to be a computer *science* question. That said, your questions may have been answered [here](http://cs.stackexchange.com/questions/3390/how-does-a-computer-work).
Comment: Binary is electrical signals via switches in a circuit. Ascii tables are used above the most basic levels. 65 is 6 and 5. Six is also 2+2+2. 65 doesn't mean anything to a computer unless it is in a piece of software that tells the computer to read it in decimal form. Ask 65 to be translated by the ascii table and you get A, but the software has to tell the CPU what "it" is first. 'A' could be a letter or a reference or a variable, it depends on the context. The answer is software, firmware, integrated software... Software is everywhere, MS Word, Chrome Browser, Firefox...
Answer: I am not an expert in the field, but I can try to give an approximately correct answer.
Reading from memory itself, you can not diferentiate between lets say ints and characters.
The compiled program is compiled with locations of where to find the operator that is needed, in this case print for ints and for chars. You must specify how to represent that data in your print command.
Example in c:
<code>printf("ASCII value = %d, Character = %c\n", ch , ch );
</code>
This code will first represent data at location ch as a number and than as a char.
Let me give another example:
Let us say that your language can "add" strings, in form of concatenating one onto another. How can computer know which "add" to use, if you cannot learn of data type from memory? The compiler compiled the program with address to the appropriate "add" command, according to data type you specified your operands to be.
Moral of the story: you cannot learn of data type from memory.
Hopefully this clears it out.


How to connect NRF24 receiver and Micro SD Card Module to Arduino UNO

Question: I would like to know how to connect a NRF24 receiver and Micro SD card module to Arduino board. I have already connected the NRF24 module to the arduino board but now i can't connect the Micro SD card module since the ports like 13,12,11 are used by the NRF24 module. Is there a way to connect those two modules?. I'm trying to save the receiving data on the Micro SD card.
Answer: SPI is a multi-drop bus protocol. That means that multiple devices can share the same physical communication medium (wires).
The only thing that needs to be "unique" for a device is its chip select pin which the master device (Arduino) uses to choose which of the devices on the SPI bus it's talking to.
So you can share pins 11, 12 and 13, but choose a different chip select pin for each device.
However, SD cards are notorious for not working well with other devices (especially with some cheap breakout boards) and your mileage may vary.


Generating random points along network using ArcObjects

Question: How do I generate some random points along a network?
I am trying to do it with ArcObjects in the VBA environment.
Answer: If you have either an ArcInfo, 3D Analyst, or Spatial Analyst license you could use the Create Random Points (Data Management) tool to create random points along line features.
You can call geoprocessing tools from VBA, but you should know that VBA is being deprecated and is not available in 10.1 and later. This UC presentation suggests how you can migrate from VBA/VB6 to the .NET framework.


High Phred Quality score VCF file

Question: I am working on ION Torrent S5 XL and I am facing to an issue with VCF output generated by the variant caller of thermofisher. It stating on VCF 4.1 that Phred Quality Score is on a range of 0 to 255. In my VCF I have values over than 255. Do you know if there is a way to transform these values?
Comment: Let me rephrase to see if I understood: your output exceeds the max value explained by its manual? Could you post an example? My only guess is that either the structure is wrong or there is a bug, or the program is not well documented.
Comment: Hi Llopis, here's an example: chr17 7577104 . AGGA AAAA,AAGA,AGA,AGAA,AGGG,AGTA 35144.8 PASS. 35144.8 is QUAL Score into the VCF
Comment: Please can you [edit] the question to include it in the right formatting? Also could you post the command you used to get this VCF ?
Answer: See this post on the GATK forums.
It is normal to see values above 255.  The QUAL score is the posterior probability that all samples in your callset are homozygous reference. I quote Sheila's response from the thread posted above:

The QUAL score is the Phred-scaled posterior of AC = 0. We use the AC priors and the PLs to get the likelihood of the data given each AC, then use those to get the posterior probability for each AC. From there, the calculation is 1 - Pr{AC > 0}.

Please see the GATK post in Methods and Algorithms for the nitty gritty details. Beware, Bayesian statistics abound.
Answer: GATK's HaplotypeCaller and freebayes are two more variant caller that output QUAL values greater than 255. The reason for that is, that each read have its part on calculation that value. This results in the higher the read depth at this position the higher the QUAL value.
To get something useful out of this value, the usual thing that is done, is to calculate the quality per depth (QD) by just divide the QUAL value by the read depth.
Note whenever you try a different variant caller, you have to find out whether the QUAL value is read depth dependend or not.

High Phred Quality score VCF file


Which Solution Handles Publisher/Subscriber Scenario Better?

Question: The scenario is publisher/subscriber, and I am looking for a solution which can give the feasibility of sending one message generated by ONE producer across MULTIPLE consumers in real-time. the light weight this scenario can be handled by one solution, the better!
In case of AMQP servers I've only checked out Rabbitmq and using rabbitmq server for pub/sub pattern each consumer should declare an anonymous, private queue and bind it to an fanout exchange, so in case of thousand users consuming one message in real-time there will be thousands or so anonymous queue handling by rabbitmq.
But I really do not like the approach by the rabbitmq, It would be ideal if rabbitmq could handle this pub/sub scenario with one queue, one message , many consumers listening on one queue!
what I want to ask is which AMQP server or other type of solutions (anyone similar including XMPP servers or Apache Kafka or ...) handles the pub/sub pattern/scenario better and much more efficient than RabbitMQ with consuming  (of course) less server resource?
preferences in order of interest:

in case of AMQP enabled server handling the pub/sub scenario with only ONE or LESS number of queues (as explained)
handling thousands of consumers in a light-weight manner, consuming less server resource comparing to other solutions in pub/sub pattern
clustering, tolerating  failing of nodes
Many Language Bindings ( Python and Java at least)
easy to use and administer

I know my question may be VERY general but I like to hear the ideas and suggestions for the pub/sub case.
thanks.
Answer: In general, for RabbitMQ, if you put the user in the routing key, you should be able to use a single exchange and then a small number of queues (even a single one if you wanted, but you could divide them up by server or similar if that makes sense given your setup).
If you don't need guaranteed order (as one would for, say, guaranteeing that FK constraints wouldn't get hit for a sequence of changes to various SQL database tables), then there's no reason you can't have a bunch of consumers drawing from a single queue.
If you want a broadcast-message type of scenario, then that could perhaps be handled a bit differently. Instead of the single user in the routing key, which you could use for non-broadcast-type messages, have a special user type, say, __broadcast__, that no user could actually have, and have the users to broadcast to stored in the payload of the message along with the message itself.
Your message processing code could then take care of depositing that message in the database (or whatever the end destination is) across all of those users.
Edit in response to comment from OP:
So the routing key might look something like this message.[user] where [user] could be the actual user if it were a point-to-point message, and a special __broadcast__ user (or similar user name that an actual user would not be allowed to register) which would indicate a broadcast style message.
You could then place the users to which the message should be delivered in the payload of the message, and then that message content (which would also be in the payload) could be delivered to each user. The mechanism for doing that would depend on what your end destination is. i.e. do the messages end up getting stored in Postgres, or Mongo DB or similar?
Comment: can you be more exact? what do you mean by  `put the user in the routing key` ? I did not get it's relation with exchange and small number of queues. it would be really appreciated if you could explain more. and as mentioned the scenario is sending one message across single queue to all the consumers, making sure all consumers receive a copy of that message, and messages after that. if you can point to any kind of documentation that would be fine also.
by the way thanks for your answer :)
Comment: Clarified above; also question about what the end destination of the messages are.


Does modified Morlet wavelet function satisfy the admissibility condition?

Question: Does modified Morlet wavelet function satisfy the admissibility condition ?
Do you have any reference for the answer please.
Thanks.
Answer: No, it doesn't (at least not in theory). You know that the admissibility condition is
$$\int_{-\infty}^{\infty}\frac{|\Psi(\omega)|^2}{|\omega|}d\omega<\infty$$
where $\Psi(\omega)$ is the Fourier transform of the mother wavelet $\psi(t)$. If $\Psi(\omega)$ decays sufficiently fast (which is the case for the Morlet wavelet) then the admissibility condition reduces to $\Psi(0)=0$, i.e. $\psi(t)$ must satisfy a zero-mean condition. However, this condition is not satisfied for the Morlet wavelet. So the Morlet wavelet is not admissible, but in practice this is no problem because $\Psi(0)$ is very small.
[1] M. Vetterli, J. Kovačević: Wavelets and Subband Coding
Comment: I think there are 2 definitions for Morlet function. first one is $  \psi (t)= \frac{1}{ \sqrt{ \pi f_{b} } } \big( e^{j2\pi f_{c}t}- e^{-f_{b}(\pi f_{c})^{2}}  \big)  e^{ \frac{-t^{2}}{f_{b}} }$. The second definition is $  \psi (t)= \frac{1}{ \sqrt{ \pi f_{b} } } e^{j2\pi f_{c}t}  e^{ \frac{-t^{2}}{f_{b}} }$  So I guess it's not admissible for the 2nd definition. Do you agree? @matt-l
Comment: @Electricman: Yes, the first one has a correction term to make the original Morlet wavelet (your second formula) admissible.


Should I keep a credit card open if I don't need it any more?

Question: Should I keep a credit card open if I don't need it any more?
Comment: Are you planning to get any (other) credit in the near to intermediate future? Do you have any other credit cards or lines of credit available? Does it charge you a fee?
Answer: Generally, you should keep it open. There are, however, several situations where you wouldn't want to. Here are some things to consider:

Does the card have an annual fee? If so, and if you aren't getting at least the amount of the fee worth of benefits out of the card (airline miles, points, etc.) then you should probably cancel it.
Do you have enough self-control not to spend money you don't have? If not, then you should get rid of the card.
As previous answers have stated, canceling this card could impact your credit score negatively. An additional open credit card can effect your credit in two major ways:

change the average age of your accounts (older is better)
change your utilized credit percent (used credit / total available credit, less used is better)

Canceling a card could negatively impact either of these areas of your credit profile.
Comment: +1 for the fee part especially.  Don't keep a card with a fee if you don't need to.
Answer: If you've held the card for a while, and the card doesn't carry an annual balance, then hold on to it.  The age affects your credit score.
Answer: If canceling the card will affect your debt ratio, don't cancel it.  The debt you carry should be less than 30% of the total credit your have.


Google maps timeline queries

Question: I know I can use Google maps timeline to see where I have been at some point in time. Is it also possible to have more sophisticated queries, like when was the last time I visited some place?
Answer: This is not an easy solution but you can export the KML file and if you know the coordinates of the place (obtainable in maps/timeline) you can run a search on the KML file using a text editor that can handle a large file easily (notepad++) or a script (Python might be easy here).
The JSON file might be easier to handle but I don't know much about JSON.

Google maps timeline queries


How big would a rocket without stages have to be?

Question: Using currently available fuels and technology and an unlimited budget. How big would a rocket without stages have to be to make it to a stable orbit?
and how big would a rocket without staged have to be to escape Earth's gravity? "edited" - or for the easier question how big would the rocket have to be if it was massless and only the fuel had mass?
Comment: How massive your payload is? The fuel need depends heavily on the payload (the thing you want to put up there). You should look the [Tsiolkovsky rocket equation](http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation), and this [NASA](http://exploration.grc.nasa.gov/education/rocket/guided.htm) page can be useful also.
Comment: Sounds like a perfect question for what-if.xkcd.com :-) .  Further, aside from the question of being able to lift your own fuel load, how about a machine which initially is airplane-like and then switches to ballistic?  Is dropping wings allowed or would that count as a "stage" ?
Comment: The only payload is the rocket and the useful empty space it would contain. No dropping of wings is allowed. I'm just wondering if it is possible at present or do we need something like a 10km high rocket or bigger maybe?
Comment: There is also the alternative method proposed by Jules Verne, i.e. cannon launch.  No need to carry your propellant with you.
Answer: A rocket "without stages" is a one-stage rocket.  There have been proposals of this type before.  You can often find mentions of SSTO, which means "single stage to orbit".  The X-33 was a fairly recent R&D attempt at this.  That was a spaceplane and the rocket all in one.
The present question has a different attempt.  It is asking about SSTO minimum size with no requirements for reentry, and apparently no payload requirement either.  That's difficult to answer in a fully theoretical sense, without just saying "it's zero".  If you allow the engineering into the discussion, it seems like there should obviously be an answer.
Further complicating things is the fact that the size of the rocket doesn't necessarily affect the mass fraction of propellant of the tank itself.  It is important to look for this number for tanks specifically.  NASA gives these examples:
<code>Propellant  Rocket Percent Propellant for Earth Orbit
Solid Rocket     96%
Kerosene-Oxygen  94%
Hypergols        93%
Methane-Oxygen   90%
Hydrogen-Oxygen  83%
</code>
There's no obvious academic reason I can't assume an orbital Solid Rocket tank that weighs 1 kg, and is still 96% propellent.  As far as tanks go, they physically have a mass proportional to the volume of stuff held in it (to first order..).
Nonetheless, my 1 kg orbital rocket is sure to be highly ineffective.  In fact, the Delta v to LEO will increase because air drag and gravity drag will be higher for this rocket.  Air drag, mainly.  Out of the normal 10 km/s to orbit, around 1 km/s is typically air drag.
A completely accurate way to answer your question would then be to find out when drag gets so large that the tank mass itself satisfies the rocket equation as the payload.  To do that, I have to get a metric for air drag.  I'll assume it goes about the same speed as other rockets (because decreasing the speed increases gravity drag).  That means that this is purely a consequence of surface area to mass ratio.
$$ \Delta v_{drag} \propto \frac{A}{M} \propto \frac{R^2}{R^3} \propto \frac{1}{R} \propto M^{-1/3} \\
\Delta v_{drag} = \Delta v_{nominal} \left( \frac{ M }{ M_{nominal} } \right)^{-1/3} $$
I'm ball-parking things, so I'll assume that the nominal case is a shuttle that has delta v from drag of 1 km/s and weighs 1e6 kg.  Now, we formalize the total Delta v and plug it into the rocket equation.
$$ \Delta v = 9 km/s + \Delta v_{drag} \\
v_e = 4 km/s \\
\Delta v = v_\text{e} \ln \frac {m_0} {m_1} $$
Plug and chug...
$$ 9 km/s + 1 km/s \left( \frac{ M }{ 1,000,000 kg } \right)^{-1/3} = 4 km/s \times \ln \frac{1}{0.04} \\
M = 17,179 \text{ kg} $$
The more I look at this, the more I realize this really is your answer.  This is a rocket that weighs 17 tonnes.  Its delta v to orbit is 12.8 km/s, as opposed to the normal (more favorable) 10 km/s, and this is because of the higher air drag because of its size.  It will stand 47 feet tall, and it will deliver its own tank into orbit (which weighs 680 kg).  Nothing else.
This is your answer, because you can not go any larger without adding multiple stages.
Is this an efficient way to deliver tanks into orbit?  No.  However, as people have pointed out before, if we wanted tanks in orbit, we would have used the shuttle external tank, which was 300 m/s short of full orbit when it was dropped into the ocean.
It's still sort of somewhat the most efficient way to deliver a tank to orbit at that size.  If you want more tanks in orbit for cheaper, you'll need larger rockets, so that they'll be more efficient.  However, I think the problem would reduce to the same thing if you continued to scale it up, and left the rest as empty space.  This is a completely insane idea, but it would follow the same mathematics I used here.  In other words, you strap a large empty tank onto the solid booster rocket.
Obviously, a better approach would be to take up inflatable modules in a normal rocket.  If you absolutely needed rigid tanks, perhaps you could wrap them like Russian dolls around each other, forming a rocket larger than the 17 tonne baseline.  Then you would unpack them when you got to orbit.  Now you have lots of tanks, and can proceed with your evil plan.
I hereby call our plan "Single Tank To Orbit", abbreviated STTO.
Comment: Thanks for that 17 tonne answer, I guess the extension on this would be what is the magic number for one that could land safely under it's own power;-) I wonder if that's in wolfram?
Answer: Couple of additional points to AlanSE answer

You can experiment with rocket equation by yourself using WolframAlpha. Just plug in your own values for final mass (payload), exhaust velocity etc.
Lockheed Martin X-33 was supposed to be technology demonstrator for VentureStar single-stage-to-orbit spaceplane. So you can use its design specifications to compare with estimates from rocket equation. VentureStar was expected to deliver 20 tonnes of payload to low-earth orbit, and then safely return back to the surface. The mass at launch would have been 1000 tonnes.
One possibility to avoid the tyranny of the rocket equation is to use the atmospheric  oxygen as oxidizer, that is to use air-breathing jet engines to provide at least part of delta-v. The scramjet technology could provide the speeds in the atmosphere up to Mach 12-17, thus reducing the delta-v needed for the final acceleration into orbit.


Stock options and cash settlement

Question: Lets assume I buy one long call option on AAPL and as the expiry day gets closer the option is in the money. If I decide to exercise that option will there be a cash settlement or a delivery of the underlaying?
Answer: For stock options it is most common with delivery of the underlying stock while cash settlement is most common for options with an index as underlying.
Answer: You don't exercise it. Unless, of course, your goal was to buy 100 shares of Apple.
When a long call is in the money, there will be value in excess of the in-the-money-ness, even a small amount of time value up until expiration. Unless the stock is very thinly traded, and the market maker for the options really doesn't want to grab a few dollars, most expiring options are sold, not exercised.
Keep in mind, the markets are closed over the weekend, but world events go on. If you let the option exercise upon expiration, you have a weekend that can set you up for a market drop on Monday, pulling the stock down, possibly below the exercise price.
To answer your specific question - the exercise of a stock option results in a long stock position (or short in case you bought a put.
Answer: It makes sense to exercise an ITM long call if:
1) You want to own the stock.  If there is significant time premium remaining and it's greater than your commission costs for the transactions, you would sell the option and then buy the stock outright.  Otherwise, just sell the call to close.
2) You cannot sell the call for its intrinsic value (the bid price is less than the stock's price less the strike price).  For an example, read my reply here:
Why hold calls until expiration?
Answer: When you exercise the ITM option, the shares will delivered into your account. If you don't have enough money to buy the shares, your brokerage should front you the margin. You only get cash when you sell the option or sell the shares for a profit.
Comment: the strike price is below the stock price if the call option expires in the money.you are the call buyer who can exercise for shares of stock.if you want money you can sell the option back for profit.

Stock options and cash settlement


Can I use a 4x6x16 top beam for a cantilevered swing set?

Question: I have a 4x6x16 beam that I would like to use on a new swing set. If I span 12 feet between supports, can I leave one or both ends cantilevered to support an additional swing?
Answer: Yes - I have a swing set that we purchased that was exactly that construction with 4x6 legs and a 16' 4x6 main beam with one swing cantilevered on one end. Ours was made by Woodplay
Answer: 4x6x16 is a good sized beam.  Enough for a swing set anyway.  As for the cantilever, how large of a cantilever are you talking?  The general rule of thumb in architecture is no more than 30%.  So for example, a 30% of a 16' beam is 4.8', which would be just under 2 1/2 feet on each side.  Thats a little tight but in this case you could probably get away with 3 feet on each side as the moment is still very near or over the support.  You can do some quick beam calculations here.
https://skyciv.com/free-beam-calculator/
Comment: I think I'll span 12 feet and cantilever 3 or 4 on one end but I just found out the 4x6 is shorter than I thought. Will it work if I screw two 2x6's together?
Comment: That should be ok.  I'll assume it is attached to the ground in some way.  Bolting 2x6's together is fine. but use 3" structural screws or lag bolts.  I'm a big fan of GRK


Kernel updates without rebooting

Question: Similar to some of the topics touched on in this question, Is it important to reboot Linux after a kernel update?, I was curious if there was a way in which one could apply kernel updates to the system without rebooting. I know that there is a vendor called Ksplice that offer features like this.  However, I was curious if there was a way to perform this same task without a commercial offering or perhaps an alternative to Ksplice since it looks like some of the feature sets may have changed since they were purchased by Oracle.  Ideally, if there is a script or way that I can add some files to perform this on CentOS, Red Hat, and/or Ubuntu would be great.
Comment: You can evidently use Ksplice for free on Ubuntu and Ferdora as well as Oracle. From the webpage: "Ksplice Uptrack is available for Oracle
    Linux, free of charge, for Oracle Linux customers with a Premier
    support subscription. Additionally, anyone can use Ksplice Uptrack
    for free on Ubuntu Desktop and Fedora.  "
Comment: Is kexec even viable anymore?
Answer: KSplice was a novel piece of code and nothing similar has been written for Linux. While it possible (and probable) that somebody can fork the old open source code and continue development, there are presently no alternative pieces of software in distribution for hot patching a running Linux kernel.
Answer: kexec is a nice way of doing fast reboot. While this isn't 'live upgrading your kernel', it does some interesting things such as bypassing BIOS, POST and BootLoader...
Some additional informations can be found through Ubuntu 'RapidReboot' topic : https://wiki.ubuntu.com/RapidReboot
Answer: (Disclosure: I work for Canonical)
Since you asked, for Ubuntu specifically, Canonical now delivers this service on 16.04.

http://blog.dustinkirkland.com/2016/10/canonical-livepatch.html
https://www.ubuntu.com/server/livepatch

This uses the live patching technology in the upstream Linux kernel since 4.0 was released.

Kernel updates without rebooting


Using two references in the same ADMUX

Question: I'm making a project and I neee to use 2 different references on the same ADMUX. One reference is 0-5V and the other is 0-2.5V. I'm aware that I can use the reference of the Arduino to the 5V sensor. But how I put a 2.5V reference while using the 5V at the same time?
Comment: Do you really need 10-bit precision on both voltages?
Comment: You can try to read 2.5V sensor twice, sum it and divide by two. Or you can double the input voltage by using non-inverting OP AMP with amplification factor 2. Or if you don't mind half resolution, you can use 5V reference voltage and just read it.
Answer: First of all a reference is just a voltage, not a range.
If you use a reference of say 5V than your analogRead(...) calls will return a 10 bit number where 0 stands for 0V and 1023 stands for 5V.
Second, the AREF pin is there for that purpose: feed your 2.5V reference to that pin and use:
analogReference(EXTERNAL);
analogRead(...);

when you want to read using the 2.5V reference (0 stands for 0V and 1023 stands for 2.5V in this case), or
analogReference(DEFAULT);
analogRead(...);

when you want to read using the 5V reference (supposing your Arduino is powered by 5V).
UPDATE
Nothing can be done at the exact same time on an Arduino/ATmega328 because it has one single processing unit. In case of analog to digital conversion you can not even perform two conversions on two pins too fast because you have only one ADC which is multiplexed (shared) among all the analog pins.
You have no choice to perform one reading, wait, then perform the other reading. You can change the voltage reference between the two conversions though, but you need to ensure the internal ADC capacitor is properly discharged: if you read a 5V line and then read a 2.5V line without discharging the internal ADC you are more than probably going to always read the maximum value.
How long you will have to wait depends on the impedance of the line you are sampling: higher the impedance, longer the time you have to wait for the ADMUX capacitor to discharge/charge up (Arduino/ATmega328 ADC is a store and sample comparator).
Comment: But how? In the ADMUX, one pin needs to be configured to 5V and other is configured to 2.5, and I need to do the conversion at the same time. And also I need the code in AVR.
Comment: Are you using the ATmega328 internal ADMUX or an external component? In case it's an exaternal component, which is the EXACT part number?
Comment: If you have a 2.5 V reference connected to the AREF pin, then calling `analogReference(DEFAULT)` will short that to +5V, possibly destroying your voltage reference or the Arduino. C.f. the warning in the [documentation of analogReference()](https://www.arduino.cc/en/Reference/AnalogReference).

Using two references in the same ADMUX


Rules to determine "unforced errors" and "winners" in tennis?

Question: Is there any rule to understand when a shot is an "unforced error" or a "winner" in a objective meaning?
Answer: I'd say that, roughly : An unforced error is when a player shoots the ball and sends it out of the field or in the net, and if this error comes "only" from poor judgement or execution from the player . A winner is when a player shoots the ball so that he wins the point on this shoot (the opponent does not reach the ball).
I don't think there is a written rule for it, as this may be only used for statistical purposes.
EDIT : Maybe this question will be closed as this seems to be a duplicate of this one : When does a point count as a winner and when as unforced error?
Comment: In my opinion it is not so easy: when a player play a smash and the opponent touch the ball with the racket sending it in the tribune. Reading your reply it seems an "unforced", isn't it?
Comment: Nope. This error is a froced one, caused by the player's good play. The unforced error occurs when it comes from a poor judgement or execution. But judging whether an error is forced or unforced is quite subjective.
Answer: There is a clear cut definition for a Winner statistic. If Player A hits the ball & Player B is unable to touch it with his racquet before the ball bounces twice,
then it's a Winner for Player A. A Service Winner is another name for Ace. So this statistic is very objective.
However, when it comes to Unforced Error, the decision is purely subjective. It depends of the situation. If Player A
hits the ball in the middle of the court & Player B has ample time to play the shot but sends it out or into the net, then it's an Unforced Error. However, if Player B is on the run while playing the shot & sends it out or into the net then it would not count as an Unforced Error but rather Forced Error.
So this statistic is purely subjective.
Ofcourse, no official rules. They are mere statistics.
Comment: A service winner is not the same thing as an ace. Ace is an untouched serve by the returner's racquet. A service winner can be touched.


Changing the modified date of a message in Exchange 2010

Question: My organization is in the middle of a process to move their Exchange 2010 messaging system from one archiving platform to another. As part of this process, we need to restore all archived messages back into users' email accounts, and then let the new system import them again. The problem is that when the messages are dumped back, the modified date on the message is set to the date it was restored, which trips up message archiving and basically means nobody will have anything archived for six months.
So you don't have to ask: no, our archiving platform only uses the modified timestamp on the message and cannot be altered to temporarily use the sent or received timestamp instead to determine whether to archive it. We and others have asked for the feature, but it doesn't exist right now.
What we're looking for is a method to go through the user's mailbox and alter the modified timestamp of each message (or preferably received more than X months ago) to the received date of the message. We also don't want to spend more on this tool per user than we're spending on the archiving solution in the first place. We've run across a few tools that are something ridiculous like $25 per user. I don't think we're even paying close to that for Exchange and the archiving solution put together.
Whatever we settle on should function on a live mailbox with no downtime. Playing around with PST imports and hacky little things like that isn't going to work.
We're fine with programming/scripting, if anyone knows the best way through PowerShell, COM automation or some other way to best handle this.
Answer: If you set PR_LAST_MODIFICATION_TIME on the item to whatever timestamp you want, that should do the trick. The simplest way to do this is probably with EWS, but you could accomplish it with any other toolset that will give you access to MAPI extended properties. With that in mind, you might find Outlook Redemption useful as well.


How to bowl a "Doosra" in the game of cricket?

Question: I have seen finger spinners in the game of cricket spinning the ball both ways without changing their action. How is it done?
Answer: Its seems to be very easy/smooth/effortless but arduous to deliver like Saqlain Mushtaq . But not impossible required more effort and skill(practice).
Hold the ball like a fast bowler normally would, with the index and middle fingers on either side of the seam. For better ball control, the index finger should just about touch the seam. The thumb may rest on the ball but usually does not contribute to delivery. The remaining two fingers are used to hold the ball in place. The run-up involved in bowling the doosra is the same as in a normal off-break.
*It's possible to bowl doosra legally: *
Read more at:
http://timesofindia.indiatimes.com/articleshow/38660280.cms?utm_source=contentofinterest&utm_medium=text&utm_campaign=cppst
Reference:
https://www.thenational.ae/sport/doosra-can-easily-be-delivered-within-the-rules-contends-mushtaq-1.237419


Is there a nuance 今天早晨 conveys that 今天早上 does not?

Question: I have a feeling that one might mean slightly earlier. Is this right?
Comment: 今天早晨 is written, like from a book or for when you are speaking to someone of higher status. 今天早上 is more colloquial.
Answer: As pointed out by xiaohouzi79, 晨 actually carries the meaning of sunrise, hence implying early morning. However this indication is weak, especially when you contrast 早晨 and 早上。
However 早上 would cover the entire morning, say, from 6am to 11:59am. Therefore in a way, it is less specific.
If we want to refer to extremely early morning, before dawn, say 3am to 6am. We sometimes use the word 清晨 and if we are talking about "morning" as in "after midnight" (00:01 to 3am for example) we usually use the word 凌晨 .
So after sunrise, we usually just say 早上 , since that time period is not close to 晨 (sunrise) anymore.
Comment: Just a supplement.According to the old dictinoary 《说文》,晨 is created on the base of 辰(the lower part). 辰 was a time mark represents 7:00-9:00 am in ancient times.With the upper part 日(the sun), you may understand why it means the time related to sunrise. I also agree that 早晨 gives me a feeling of early morning.
Answer: Here are Baidu entries for 早晨 and 早上 should you be able to read them.
Generally speaking, people will treat 早晨 and 早上 exactly the same way unless explicitly directed other ways. It's OK to translate both of them to morning.
In case you want to express early morning or daybreak, you may consider using 清晨.
Answer: 晨 itself means early morning or daybreak so 早晨 is early morning.
早上 is for the morning period and can also be used throughout the entire morning period.
Comment: @xiaohuozi, your Chinese is so good! it sounds from one of your prev. posts that you are married. otherwise you can go on the famous Chinese show [非诚勿扰](http://baike.baidu.com/view/1664023.htm)。 :)
Comment: @Lagoona - One of my good friends here in Australia went on that show a couple of months ago in a special show which was for Australian contestants only. They brought both the men and the ladies from Australia. Although he didn't do well because his friends made him look bad during the friends interview part.
Comment: @xiaohuozi, WOW that's outstanding! I watched that episode too. This world is so small. Were you the friend who made him look bad?  ;)
Comment: @Lagoona - The link to the show is here http://www.jstv.com/c/ws/fcwr/201107/t20110724_538002.shtml I was in China at the time the filming was done but the friend part was filmed in Australia. He is the first guy in the linked episode.
Answer: I agree with Terry that 早上 and 早晨 are synonymous, with perhaps very slight differences in connotation. Pace Gapton, I wouldn't say that 早上 can always refer to any time from early morning to 11:59 am; for that time period, in some cases it is better to use the more general term 上午.
One place this distinction is important is in greetings. A person writing an email to a colleague at 10:30 am wouldn't start their email with 早上好 ("good morning") because it sounds like the writer just got up. In this case, the looser term 上午好 is more appropriate.


Apache2 how to access .html file outside website root

Question: I am trying to create a localhost website that has multiple links to redirect to other .html files on the raspberry pi. These other .html files and websites are located in a folder located at /home/pi/sites. The website root is located at /var/www/html . My current index.html file for the localhost website has a hyperlink which redirects to the .htm file of another website. When I try to open the hyperlink on the localhost website, I get an error 404. If I run the html file not as a local host, but through the web browser, the hyperlink works. Please help me setup the localhost.
Comment: you'd probably want to show the HTML you have, and ask this question on stackoverflow, as this is not at all raspberry pi specific - and there's a LOT more HTML experts on stackoverflow than here :p
Answer: Not a great idea as security settings can get in a right mix as the web pages (and services) run under the user www-data and not the user pi.
If you determined to do this (and it's really not a good idea for security of the website) then Apache lets you do it with the alias module (mod_alias).  Once enabled, you can set something like the following:
<code>Alias /data /home/pi/sites
<Directory /data>
     Order allow,deny
     Allow from all
</Directory>
</code>
Then http://192.168.1.12/data/sitepage.html points to the file /home/pi/sites/sitepage.html
Details of this module can be found on the Apache site But please note this can be messed up with redirects and care needs to be taken as to order (see lower part of the linked page).  Very sure this will trip WordPerfect or even WordPress (sorry about that) web sites up :-)
Comment: `` - Ordinarily, it would the _target_ path (that is outside the DocumentRoot) of the `Alias` (eg. `/home/pi/sites`) that you would need to enable access to. You would expect the source path to already be accessible.


Is a glacier advancing or retreating? How to tell?

Question:
What are the most common ways you would use to tell whether a given mountain glacier is advancing or retreating, judging only by its present state by looking at it? Please list anything you can think of.
Could a stream of water flowing out from under the glacier be a sign of it retreating?
Comment: I don't think you could tell just by looking at the glacier.  Possibly by looking at the ground in front of it - e.g. is the rock fresh or weathered? - but even that seems doubtful.  I think any meaningful measure of advance or retreat has to be done over several years at least.
Answer: The easiest way is to look a the glacier margins. If the ice is in contact with vegetation or rock covered in lichens or moss, it means it is most likely advancing. If you see a band of life-less rock in between the ice and the first plants/lichens/moss, it means it is retreating.
Some examples I've seen myself:
This glacier in Geenland is advancing, you can see the ice and vegetation in contact

Same glacier, you can see how it is even pushing vegetation, proving it is advancing

However, advancing glaciers are the exception. In most cases they are reatreating and what you see is a band of life-less rock surrounding the ice like this:
Retreating Amalia glacier in Patagonia

The advancing or retreating state of a glacier can have different time-scales. For example a glacier can be retreating on a decade scale, but it might advance every winter, but the recession on summer is large enough to produce a net retreat every year. Small glaciers can also react very quick to weather variations, therefore even if one is receding at a century scale, it can advance one year due to exceptional snow accumulation over few years. So you have to interpret this observations with care, and consider what's the timescale at which the plants/moss/lichens can colonize the rock in the area, which in temperate and low elevations will be between a few years and a decade.
Moraines, trim lines and other features can tell you about the advancing/receding history of a glacier at longer timescales.
Comment: I like the approach of this answer because it explains how you can make an immediate assessment. I wonder, though, if you can elaborate on circumstances where this best applies and might not apply; for example, it seems less likely there'd be a noticeable lifeless band at higher altitudes or rockier terrain.
Comment: It has to do with te time scale of the advance/recess. Moraines and pro-glacial lakes are more difficult to assess and reveal a longer timescale. Vegetation instead  grows quite fast, in just a few years you get moos, lichen and grass, so you can see if it advancing/retreating at that time scale. This method applies anywhere where there is vegetation, with lichens and mosses this works even in the arctic or antarctic, however in the very high arctic or inner antarctic it will be useless due to the lack of lichens and mosses.
Comment: @trondhansen That's right, I'm not saying in any way that moraines are not a good indicator, they are indeed one of the main tools to study the history of a glaciar (paleoglaciology). I'm just saying that the interpretation of moraines is a bit more difficult, but is definitely a great tool.
However, if you want to asses the current state of a glacier I think the above method is better, because moraines can take a while to form and some time they are not visible, as many glaciers fronts are in lakes or fjords, and the moraine method don't work well in lateral moraines.
Comment: this answer explains it fully,the pile of rocks and gravel in contact with the glacier will be there if it is expanding at all elevations even if the temparature is sub zero all year,if it is retracting the pile will be away from the glacier.
Comment: But using the piles of rock (i.e. moraines) is more uncertain. Because dead ice can have a pile of rock. And you will often find piles of rock associated  to old periods of advance. So a glacier can be advancing towards an old moraine and with your approach you would think it is receding.
Comment: @CamiloRada an old moraine will normally have some plants or other signs of the age like no sand on top of the rocks at the  surface.
Answer: The only signs I know of to identify glacial retreat on first meeting is the presence or absence of "dead ice", the presence of "push" on moraines, and the state of any terminal lake.

Dead-ice is a term used to refer to lumps of ice left behind by a retreating glacier, they're generally cloaked in thick layers of debris that insulate them from solar heating, they don't necessarily show a current state of retreat as they can persist for many years after the glacier abandons them.
Moraine Push is a sign of current advancement or surge of the glacier, basically the glacier bulldozers existing moraine deposits as it advances down valley, this creates several telltale formations, ice flowing over the top of lateral moraines, established moraines (trees and all) being churned and pushed over by advancing ice.
I have heard that terminal lakes are only ever found in glacial valleys with retreating ice, as they form between the face or toe of the glacier and the terminal moraine formed by a stable glacier this could well be accurate.

These are identifiers that can indicate advance or retreat, either current or historic, but at a glance there are no definitive signs of any long-term trend in the glaciers' behaviour. This is chiefly because glaciers advance and retreat on a seasonal basis so a particular feature may be the product of one winter of heavy snow (some years ago) or one very hot summer.
Answer: If, before winter snows start and temps consistently drop below sustained freezing there is less total ice mass than they prior year at the same point, it  is shrinking or in decline.  If there is more, it is growing that year. If a pattern of multiple years in the same direction, that is what the glacier is doing. Reduction of mass can be from melting or sublimation, it does not matter.  Increase can be snow, other freezing precipitation, or other water sources, again, does not mater where the ice came from, only that there is an increase.  These are simply the meaning of growing or receding.  They cannot be determined by looking, they require long term observation.
Receding and advancing are actually a different concept.  They are movement of the glacier.  A glacier may be declining in size while still advancing in its path, or it may be growing, but receding, often by getting thicker at its origin.  Again, recession and advancing cannot really be detected by simple observation, it requires comparison over time and often there may be a localize short term advance while the glacier has a general average recession action.
Think of Arctic glaciers as an example.  It is generally agreed that most are in decline and shrinking in total size.  And yet, many continue to advance as can be seen by there repeated calving into the sea.  Not all, but many keep the same front edge, roughly with the sea.  A chunk breaks off, and the mass behind moves forward to replace it.  The total size though, behind that front, to the sides and the depth, the part of the glacier that feeds the advance continues to shrink though.
Answer: Just my thought.  If the glacier is at least a few degrees below 32 °F (0 °C) steady state it's probably advancing.  If at 32 °F it probably melting.
Comment: @JeopardyTempest y: Err... If the H20 in a glacier was above 32F/0C, it wouldn't be ice any more, would it?  So the glacier wouldn't be there.
Comment: The dihydrogen monoxide or the air temperature?  Certainly the air temperature will vary regularly, but given the mass and energy transfer rates, wouldn't actually think going above 32 F would be a direct correlation with retreat (though it would cause some melting along the surface)
Comment: Sorry, I intended to specify the glacier proper temperature.
Comment: Touché, I should have said at 32 indeed :-/


Periods of non-circular Schwarzschild orbits

Question: I have been thinking about non-circular orbits in the Schwarzschild spacetime. How would you define a period of one orbit? I was thinking, in terms of proper time, for $r$, how long it takes to go from one apogee to another. For $\phi$, again in terms of $\tau$, how long it takes to cover $2\pi$. What about $t$, though? Is my reasoning wrong?
Answer: You actually described two inequivalent definitions of "period," both legitimate. The paper

Geisler and McVittie (1965), "Orbital periods in the Schwarzschild space-time" (http://adsabs.harvard.edu/full/1965AJ.....70...14G)

considers essentially the same two definitions of "period" that you described. One is the time from one perihelion to the next; they call this the anomalistic period. The other is the lapse between two successive passages across $\phi=0$; they call this the sidereal period. The two periods are not the same. Both periods may be expressed either in terms of the object's own proper time $\tau$, or in terms of the coordinate time $t$. These again are not the same.
The key is to specify the worldline by expressing all of the coordinates as functions of a shared parameter, which we can take to be the object's proper time. Then we have functions $r(\tau)$, $\phi(\tau)$, and $t(\tau)$. We need all of these functions anyway to solve the free-fall equations that define what "orbit" means. Given those functions, we can use $r(\tau)$ to compute what those authors called the anomalistic period, or we can use $\phi(\tau)$ to compute what those authors called the sidereal period, both in terms of the object's proper time. To relate those proper-time periods to coordinate-time periods, we can use the function $t(\tau)$.
Comment: I realise that each of these defines a period for the given coordinate and that these are not equivalent. I don't really like the formalism of this paper, I might try to re-derive the periods in terms of other quantities.
Comment: @Gordon  Okay, I guess I misunderstood the purpose of the question. Were you asking if there should be a third period, one corresponding to the function $t(\tau)$?
Comment: No worries, your answer helps a lot. I was asking 1. if this is a legitimate way of thinking about periods of Schwarzschild orbits, 2. how one would go about calculating them.
Comment: @Gordon  Yes, you are thinking about the orbits correctly. Thanks to the symmetry of the Schwarzschild metric, these definitions that at first seem to be coordinate-dependent can actually be turned into (less concise) coordinate-independent definitions. So they are legitimate. As far as how one would calculate them, the hard part is determining which worldlines correspond to orbits (free-fall). I don't have any good hints to offer. The farthest I've ever gone with non-circular orbits is to write down the free-fall eqn's for $r,\phi,t$ that need to be solved, but I haven't actually solved them.
Comment: Thank you. Just so we are on the same page, what do you mean by free-fall equations? I presume the equations of motion for the metric. As to which world-lines correspond to orbits, I am considering non-circular geodesics: these lie in a plane, and precess between two radii (the perigee and the apogee).
Comment: @Gordon  By free-fall equations, I mean the equations that a world-line must satisfy in order to be a geodesic (to represent an object in free-fall, such as an orbit). For the Schwarzschild metric, I wrote them out explicitly in $t,x,y,z$ coordinates at the end of this post: https://physics.stackexchange.com/a/436873/206691. I mention this because most people write them in spherical coordinates, which (despite the name) obscures their spherical symmetry. Writing them in $x,y,z$ coordinates makes the spherical symmetry obvious. But for non-circular orbits, I don't know if this helps much.
Answer: $\let\a=\alpha \let\b=\beta \let\phi=\varphi \let\De=\Delta \def\D#1#2{{d#1\over d#2}} \def\dr{\dot r}  \def\dt{\dot t}
\def\dx{\dot x} \def\dphi{\dot\phi} \def\half{{\textstyle {1 \over 2}}}$
If I could assume you can read Italian I would have an easy life - had
only to give a link. But since I find it unlikely, I'll write a
synthesis of essential points.
Consider a general metric
$$d\tau^2 = g_{\a\b}\,dx^\a dx^\b.\tag1$$
We are interested in timelike geodesics, which can be parametrized with
proper time $\tau$. Then coordinates are functions of $\tau$:
$$x^\a = x^\a(\tau) \qquad dx^\a = \D {x^\a}\tau\,d\tau$$
and from (1) we have
$$g_{\a\b}\,\dx^\a \dx^\b = 1.\tag2$$
It can be shown that geodesics obey a variational principle with
lagrangian
$$W = \half\,g_{\a\b}\,\dx^\a \dx^\b.$$
Eq. (2) shows that $W$ is a constant of the motion, with $2W=1$ on
a timelike geodesics.
Schwarzschild's metric, restricted to the plane $\theta=\pi/2$, is
$$d\tau^2 = \left(\!1 - {1\over r}\!\right) dt^2 -
              {dr^2\over 1 - 1/r} - r^2 d\phi^2$$
where units were so chosen $G=1$, $c=1$, $2M=1$ ($M$ Sun's mass). Then
$$2W = {r - 1 \over r}\,\dt^2 - {r \over r - 1}\,\dr^2 -
       r^2 \dphi^2 = 1$$
Since $W$ doesn't depend on $t$ and on $\phi$, we have the constants
of the motion
$${r - 1 \over r}\,\dt = E \qquad r^2 \dphi = J.\tag3$$
Substituting (3) into (2) we have
$$\dr^2 = E^2 - \left(\!1 - {1 \over r}\!\right)\!
              \left(\!1 + {J^2 \over r^2}\right)\!.\tag4$$
Integrating eq. (4) by separation of variables we get $\tau(r)$ and
the radial period. Unfortunately an elliptic integral is involved.
As to $\phi$, from the second of (3) and (4) we have
$${J^2 \over r^4} \left(\!\D r\phi\!\right)^{\!\!2} =
     E^2 - \left(\!1 - {1 \over r}\!\right)\!
       \left(\!1 + {J^2 \over r^2}\right)$$
which gives $\phi(r)$, again as an elliptic integral. An approximation
is possible to deduce perihelion precession (I'll not show how to do it).
Instead I find a problem if the azimuthal period is of interest. The
reason is the following. Let's start form perihelion: when $\phi$
increases by $2\pi$ we are not yet arrived at another perihelion,
because of precession. This shows qualitatively that azimuthal period
is less than radial one. But a further increment by $2\pi$ brings us
still farther from perihelion, and I expect that the latter $2\pi$
variation of $\phi$ takes a different time from the former (larger or
smaller?) So it seems that a well definite azimuthal period doesn't
exist.
Edit. But an average period can be defined. let $T_r$ be the radial period, $\De\phi$ the perihelion advance in time $T_r$. Then in the average $\phi$ advances by $2\pi$ in time
$$T_\phi = {2 \pi\,T_r \over 2\pi + \De\phi}.$$
Comment: Thank you. How do you derive the final formula?
Comment: @Gordon Do you mean the one for $T_\varphi$?
Comment: Yes. I can see how it works, apart for the extra $2\pi$ in the denominator. If over a $T_r$ period $\phi$ advances by $\Delta\phi$, then isn't $T_{\phi} = (2\pi/\Delta\phi) T_r$?
Comment: Any ideas @Elio Fabri?
Comment: @Gordon Sorry I'd missed your reply.
*If over a $T_r$ period $\varphi$ advances by $\Delta\varphi$, then
isn't $T_\varphi=(2\pi/\Delta\varphi)\,T_r$?* No, because
$\Delta\varphi$ is perihelion advance. $\varphi$ increases by
$2\pi+\Delta\varphi$.


Subspace clustering with random transformation

Question: One approach for clustering a high dimensional dataset is to use linear transformation, and the most common approaches are PCA and random projection (where random projection arises from the Johnson-Lindenstrauss Lemma). I was wondering why we can't use other random transformation  s like when our transformation matrix $R$ was drawn from a uniform distribution?
Comment: Johnson–Lindenstrauss random projections (there are by now several different algorithms) approximately preserve distances. Other random transformations might not.
Answer: It is possible that choosing $R$ according to a uniform distribution with zero mean constitutes a Johnson–Lindenstrauss random projection (i.e., it approximately preserves distances). See for example a paper by Achlioptas which suggests three distributions that definitely work: a zero-mean Gaussian, a random $\pm 1$, and a specific distribution on $\{0,\pm 1\}$. It is probable that using the methods in the paper, the case of the uniform distribution can also be analyzed.


which wires to connect when installing a dimmer switch?

Question: I have a new dimmer switch that to replace an old standard light switch. The old switch has 4 cables coming into it as in the picture.

and the new one purchased from amazon is Lutron GL-600H-DK. It has 2 black wires and 1 green as in the picture. I watched some videos on youtube but still have doubts on which wires go with which and where does the extra black wire in the in the old switch go?
And would this work with standard light bulbs?
Answer: Edit: From your picture and descriptions you appear to have a three way switch.
Your dimmer is a single pole dimmer.  Meaning it is designed to operate in one location.
A Lutron three way dimmer that is similar to what you have would have one red, one red/white striped, one solid black, and a green.
The two blacks off the switch wire to the black on the dimmer.  The one red goes to red, the one black goes to the red/white striped off the dimmer, and the green goes to the bare copper.
Be sure to turn off power first, and make sure the dimmer is rated for the correct load: Incandescent, LEDs, total wattage.
Comment: They're on the same screw.  That's really all that counts.  If you want to breakdown and analyze the circuit you'd be opening up a whole different can of worms.  And yes you bought the wrong dimmer.
Comment: I actually believe this isn't a four way -- note that two wires seem to be going to the same corner on the switch...
Comment: Yes, I believe your right.
Comment: Thanks for yiur answer. So the 2 black cables that are attached to the lower right corner are actually the same? And another question, the dimmer above is the wrong one and would not work with it?


Temperature of electroweak phase transition

Question: How does one estimate the temperature at which electroweak phase transition (EWPT) occurred? Somewhere I have read it is around 100GeV but the reason was not explained.
Comment: I assume [this](http://arxiv.org/pdf/1401.1827v2.pdf) is the paper you looked at? They seem to imply it is a numerical result, rather than an analytical one.
Comment: @SRS I provided a detailed answer with all the relevant numbers.
Comment: I believe the answers here calculate when one can see on mass shell the particles involved in the electroweak sector, and not the the temperature in the cosmological scale. see my answer here https://physics.stackexchange.com/questions/406285/does-the-lhc-see-electro-weak-symmetry-breaking/406299?noredirect=1#comment910396_406299
Comment: Looking further, I think the confusion comes because the low scale, 246 is talking of the potential where the higgs transits , whereas the cosmological phase transition, i.e. the transition to a different higgs potential comes at very high energies in cosmology, of order 10^12GeV. that is when the VEV becomes 246. two different energy scales for the same phenomenon.
Answer: We calculate the free energy (density) for the Higgs field $\phi$ at finite temperature. In the Standard Model, this looks like
$\mathcal{F}_{SM}(\phi,T) = -\frac{\pi^2}{90}g_* T^4+V_{SM}(\phi, T) \ ,$
where $g_*$ is the number of degrees of freedom in the SM ($g_*=106.75$).
The potential has the form
$V_{SM}(\phi,T) = D(T^2-T_0^2)\phi^2 - ET\phi^3+\frac{\lambda_T}{4}\phi^4\ ,$
with $D,E,T_0^2,\lambda_T$ some factors depending on particle masses, coupling constants, the Higgs v.e.v. and temperature.
At the phase transition (PT), there are two degenerate minima of the potential. One sits at $\phi=0$, where we are in the symmetric phase, the other is at $\phi=\phi_0$, where we are in the broken phase. If my quick calculation is correct, this leads to a critical temperature $T_c\approx 163 GeV$.
Note that in this case, the order parameter of the PT $\phi_c/T_c$ is very small. This means for one thing, that the PT is only very weakly first order and else, that perturbation theory is no longer reliable and we need to do non-perturbative calculations.
(Though the procedure is standard, I took this paper from Carena, Megevand, Quirós and Wagner as reference, just because it was the closest at hand, not because I particularly like it, which I don't btw.)
Comment: Thanks for the reference. For non-expert (which I am), the historical references given in the paper like M. E. Carrington, Phys. Rev. D45 (1992) 2933 seem easier to understand. But it's true that your reference gives all the explicit formula to be able to do the numerical application.
Answer: Let's define $T_{EW}$ the temperature where the coefficient $m^2_H(T)$ of the operator $H^2$ in the SM lagrangian vanishes:
$$
m_H^2(T=T_{EW})=0\,.
$$
For $T>T_{EW}$ the Higgs vev is vanishing, the EW symmetry in unbroken, and the elementary particles are massless. For $T<T_{EW}$ the the vev is non-vanishing, $v_T\propto -m_H^2/\lambda\neq 0$, the EW is broken spontaneously, and the various elementary particles acquire masses $m_i$.
Let's now determine $T_{EW}$ quantitatively. Since $m_i\simeq 0$ for $T\simeq T_{EW}$ is OK to make an expansion in small $m/T$. In this regime the 1-loop corrections to the Higgs potential from the thermal propagators are, expanded at leading order in $m/T$, given by
\begin{equation}
m^2(\tilde{T}_{EW})=m^2_{T=0}+\tilde{T}_{EW}^2\left[\frac{y_t^2}{4}+\frac{\lambda}{2}+\frac{g^{\prime\,2}}{16}+\frac{3g_2^2}{16}\right]
\end{equation}
where $m^2_{T=0}=m_H(T=0)=-\lambda v_{T=0}^2$, with $v_{T=0}=246$ GeV and $2\lambda v_{T=0}=m_h^2=(125\mathrm{GeV})^2$. The negative mass-squared receive positive thermal mass contributions form the loops of the particles the Higgs couples to.
The leading contribution to $m_H^2(T)$ is, non-sorprisingly, coming from the largest couploing, top quark yukawa $y_t=\sqrt{2}m_t/v_{T=0}$. Neglecting the gauge couplings and the higg-self coupling, and solving $m^2(\tilde{T}_{EW})=0$ for $T_{EW}$ we get
\begin{equation}
\tilde{T}^2_{EW}\simeq m_h^2 v^2/m_t^2\simeq (178\mathrm{GeV})^2\,.
\end{equation}
Answer: higgs field causing electroweak transition. before higgs field w,z boson photon all are massless. but higgs field gives masses to them and symmetry spontaneously break. because if particles having masses then su(2)u(1) symmetry break. all gauge symmetry break if we give mass to the particles.so transition must have to have below 125.6 gev that is the mass of higgs boson.
peoples are thinking about there may be another background field which causes strong and electroweak seperation.so that field can break the underlying symmetry.
In the standard model, the Higgs field is an SU(2) doublet, a complex scalar with four real components (or equivalently with two complex components). Its (weak hypercharge) U(1) charge is 1. That means that it transforms as a spinor under SU(2). Under U(1) rotations, it is multiplied by a phase, which thus mixes the real and imaginary parts of the complex spinor into each other—so this is not the same as two complex spinors mixing under U(1) (which would have eight real components between them), but instead is the spinor representation of the group U(2).
The Higgs field, through the interactions specified (summarized, represented, or even simulated) by its potential, induces spontaneous breaking of three out of the four generators ("directions") of the gauge group SU(2) × U(1): three out of its four components would ordinarily amount to Goldstone bosons, if they were not coupled to gauge fields.
However, after symmetry breaking, these three of the four degrees of freedom in the Higgs field mix with the three W and Z bosons (W+, W− and Z), and are only observable as spin components of these weak bosons, which are now massive; while the one remaining degree of freedom becomes the Higgs boson—a new scalar particle.
The photon as the part that remains massless
Comment: hi, i don't think this answers the question. the question was about calculating the temperature of the phase transition between two different phases, what you answered was the details of the two phases.
Answer: I don't think that an unambiguous justification can be given because the dynamic of the electroweak symmetry breaking (EWSB) is still unknown. We don't have a well established theory describing how the Higgs scalar potential evolves with the temperature. When people talk about the scale of the EWSB, they usually refer to two possible things:

before EWSB, the weak bosons are massless. After EWSB, they get a mass (91 GeV for $Z^0$ and 80 GeV for $W^\pm$). The scale is therefore of the order of the mass of the weak bosons, roughly 100 GeV.
before EWSB, the Higgs vacuum expectation value (v.e.v.) is 0, the field is symmetric. After EWSB, the v.e.v. is about 246 GeV. So again, the v.e.v. value is representative of the scale of the EWSB, still of the order of 100 GeV.


Set bash_profile to open with Sublime Text 2 by default

Question: I'd like Sublime Text 2, not TextEdit, to be the default program to open my bash_profile file when I call open ~/.bash_profile in Terminal. Normally I would just control-click on the file in Finder to set the default program, but given that bash_profile is hidden I'm not sure how to go about this.
Comment: Have you tried unhiding it? Also, though I'm not sure if this would work, you could create your own foobar.bash_profile file and set the default program like you stated above.
Answer: You can temporarily show hidden files. In terminal write:
defaults write com.apple.finder AppleShowAllFiles TRUE
and then killall Finder to restart Finder.
Change what you need and then hide hidden files again by changing TRUE to FALSE.
Edit: Making this more explicit. In Finder, locate .bash_profile, open up the properties by right click + "Get Info". Then change the "Open with" to Sublime Text 2. This works, I just tried it.
Comment: @Mark I think you misunderstood. I updated the instructions. This method sets the default so that it does not open in TextEdit.
Comment: this is the correct answer.
Answer: What about:
subl .bash_profile

instead of open. You can launch Sublime Text with subl, and append a filename to open it.
Comment: this doesn't answer the OP
Answer: You can do open -a "Sublime Text 2" ~/.profile Assuming that name is what's on the app's bundle.
Answer: I do this all the time, but i do it from the command line:
My bash profile has the st macro mapped to:
alias st='/Applications/Sublime\ Text.app/Contents/SharedSupport/bin/subl'
And in the terminal i just type:
st ~/.bash_profile
Answer: Sublime Text Shortcut Guide

Open Mac Terminal
Go to homebrew.sh; copy and enter the following:
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
Enter brew install wget
Enter the following into your Mac Terminal: open ~/.bash_profile but if for whatever reason you don't have one configured, enter
sudo nano .bash_profile.  Please be advised, this solution presumes you are the root user of your system/device.
Open another tab within the terminal-window and check Ruby version (e.g. ruby -v); if absent, become sufficiently by Rubified by entering: brew install ruby
Download Sublime Text 3, then go to root/usr (e.g. cd alexanderjsingleton/).
Next after you've installed Sublime 3, open /Applications/Sublime\ Text.app/Contents/SharedSupport/bin/subl
Create a symlink called sublime by entering ln -s "/Applications/Sublime Text.app/Contents/SharedSupport/bin/subl" /usr/local/bin/sublime
Enter the following into your Mac Terminal: open ~/.bash_profile but if for whatever reason you don't have one configured, enter
sudo nano .bash_profile.
Exit and open your bash profile; the following example should be contained in the profile export PATH=/usr/local/bin:$PATH.  This is the same file location for other user-profile settings for applications like iTerm.
Test by entering the directory of app-files (e.g. sublime .).
Boom!  A special thanks to the great Ashley Nolan's blog, though for
whatever reason my new MacBookPro couldn't access the bash-profile, so I had to create one, which is why I included that caveat in step 4.  I trust
this will assuage any systemAdmin anguish fellow developers may take for granted. :D


Netilat Yadaim Source

Question: Where in tanach is the mitzvah of Netilat Yadaim shown / present?
I am essentially asking for the source of the mitzvah.
Comment: https://judaism.stackexchange.com/questions/32186/who-commanded-us-and-for-what
Comment: It's a rabbinic mitzvah. You're not going to find an unequivocal source in Tanach
Comment: @JoelK what pasuk(im) did Chazal mention when formulating their mitzva?
Comment: @JoelK I agree with Rabbi Kaii that they are looking for a source of the mitzvah in the Torah, this does not mean that it cannot also be Rabbinic. They even asked for possible for an example of it being shown...
Comment: The Bracha says "Asher kidishanu bemitzvotav" shouldn't that indicate that it's directly from Hashem?
Comment: @Eak2449 see e.g. https://judaism.stackexchange.com/questions/96767/where-are-we-commanded-to-read-the-hallel
Comment: @Eak2449 the simplest explanation of the blessing is that there is a commandment to listen to the Rabbis. But the Ritva points out that in fact the Rabbis command us to do what Hashem wants us to do even though he didn't outright command it. So the two are very nuanced (but important) differences.
Answer: Hand washing is a rabbinic command, but the Sages did find a hint אסמכתא to it in Leviticus 15:11. See Chullin 106a:

רבא אמר מצוה לשמוע דברי ר"א בן ערך דכתיב וכל אשר יגע בו הזב וידיו לא שטף במים אמר ר"א בן ערך מכאן סמכו חכמים לנטילת ידים מן התורה
Rava says: It is a mitzva to listen to the statement of Rabbi Elazar ben Arakh, as it is written with regard to a man who experiences a gonorrhea-like discharge [zav]: "And whomever he that has the issue touches, without having rinsed his hands in water," he contracts ritual impurity (Leviticus 15:11), and Rabbi Elazar ben Arakh says: From here the Sages based washing of the hands upon a verse from the Torah.
Answer: See Berachos 53b

אָמַר רַב נַחְמָן בַּר יִצְחָק: אֲנָא לָא זִילַאי וְלָא זִיוַאי וְלָא
זוּהֲמַאי יָדַעְנָא אֶלָּא מַתְנִיתָא יָדַעְנָא. דְּאָמַר רַב יְהוּדָה
אָמַר רַב וְאָמְרִי לַהּ בְּמַתְנִיתָא תָּנָא: ״וְהִתְקַדִּשְׁתֶּם״
אֵלּוּ מַיִם רִאשׁוֹנִים, ״וִהְיִיתֶם קְדֹשִׁים״ אֵלּוּ מַיִם
אַחֲרוֹנִים, ״כִּי קָדוֹשׁ״ — זֶה שֶׁמֶן, ״אֲנִי ה׳ אֱלֹהֵיכֶם״ — זוֹ
בְּרָכָה.  Rav Naḥman bar Yitzḥak said of this: I do not know of Zilai
or Zivai or Zuhamai; rather, I know a baraita, as Rav Yehuda said that
Rav said, and some say that it was taught in a baraita: It is stated:
"And you shall sanctify yourselves, and you shall be holy, for holy am
I, the Lord your God" (Leviticus 20:26). With regard to this verse,
the Sages said: And you shall sanctify yourselves, these are the first
waters with which one washes his hands before the meal; and you shall
be holy, these are the final waters; for holy, this is oil which one
spreads on his hands; am I, the Lord your God, this is the Grace after
Meals blessing.

(Exodus 30:19): "And Aaron and his sons shall wash their hands and their feet . . . when they come near to the altar to minister."
This is the direct commandment in the Torah for handwashing, but do know that this applies specifically to Kohanim and to temple service.
However we want all of the Jewish people, specifically the Kohanim to be pure, and so all Jews wash their hands before bread.
Also you can see in Tehillim 26:6

ואֶרְחַ֣ץ בְּנִקָּי֣וֹן כַּפָּ֑י וַֽאֲסֹֽבְבָ֖ה אֶת־מִזְבַּֽחֲךָ֣
יְהֹוָֽה:  6 I washed my hands with cleanliness, and I encompassed
Your altar, O Lord.

There are tons of references and examples of hand washing in my humble opinion in Tanach. Interestingly Avraham washes the Angels feet who visit him due. Though this is different (the Kohanim though wash both hands and feet) you can see that there are many references depending how specific or vague you are interested in being.

Netilat Yadaim Source


installing Grid Engine "cannot reach qmaster"

Question: I want to install Grid Engine on my laptop.
I am using Ubuntu 11.10 under VirtualBox 4.1.6.
(The purpose of installing Grid Engine is not to compute anything, I just want a working Grid Engine environment to be able try out bash scripting for array jobs etc. The jobs which I would run would just do "sleep", so the cluster would consist of only one single node. My laptop has a dualcore CPU but I don't know if that's relevant here.)
I am following the instructions from http://astoryworthtelling.wordpress.com/2009/08/25/installing-sge-on-ubuntu-single-machine-local-install/ and have tried to install Grid Engine like this:
sudo apt-get install gridengine-master gridengine-exec gridengine-client gridengine-qmon gridengine-common

Then I start qmon with sudo. The GUI starts alright, I click on "Queue Control". What then happens is that a window pops up saying "cannot reach qmaster":

If I click "Retry" I get another popup which is slightly more informative, "Unable to contact qmaster using port 6444 on host "anton-VirtualBox":

My question is, how can I fix this? Help to get Grid Engine running and fixing this would be very much appreciated, thank you.
P.S.: One more thing, maybe it helps to help track down the error. When I try to use qstat from within bash, I get this message:
anton@anton-VirtualBox:~$ qstat
error: commlib error: access denied (client IP resolved to host name "localhost". This is not identical to clients host name "anton-VirtualBox")
error: unable to contact qmaster using port 6444 on host "anton-VirtualBox"

P.P.S.: I have some experience using Grid Engine, but absolutely zero installing or administering it.
Answer: Essentially it's complaining that a reverse lookup of your IP returns localhost instead of anton-Virtualbox and your queue is setup to use anton-Virtualbox as the qmaster.  So you need to update your hosts file.
Mine reads:
my.full.local.ip        my.fully.qualified.hostname    shorthostname
127.0.1.1               my.fully.qualified.hostname    shorthostname
127.0.0.1               localhost
...


2018 Tax Gift Question

Question: Can a married couple be given separate gift checks of $15000 from the same person and not have it count as income on their 2018 returns? Is there any penalty for the giver?
Comment: A country tag would be helpful, as different countries have different tax laws!
Comment: These are true gifts, not part of any other transaction given out of generosity?
Comment: Jenn please confirm country, as answers seem to assume US so far.
Answer: Assuming US since question uses the annual gift tax exclusion rate for US.
The annual gift tax exclusion is per person giving to another person. So a parent could give 2x to couple by giving to husband and wife, or a couple could give 4x to another couple. There is no filing requirement created if the gift amount is under the annual exclusion.
If gifts exceed the annual exclusion amount (or if gifts are given by each spouse), the giver has a filing requirement, not the recipient (it's not reported as income on the recipients return). The giver files Form 709 with their return, but they won't actually owe gift tax unless they have exhausted their lifetime exemption ($11.2 million, or double for couples if planned properly).
Comment: In the case of a "split gift", the giver must file form 709 even if each half is less than the exclusion amount. https://www.irs.gov/newsroom/tax-tips-to-help-you-determine-if-your-gift-is-taxable
Answer: In the U.S., with the facts stated, there is no need for the giver or recipients to file a gift tax return.
Comment: In the U.S., recipients do not need to file a gift tax return at all under any circumstances (though the IRS may come after them for the gift tax due if the gift is large and the donor has thumbed his/her nose at the IRS and not filed a gift tax return at all).

2018 Tax Gift Question


GFCI Won't rest. shows no LED Light but has power

Question: I have a GFCI outlet in the kitchen that shows no LED color status, cannot reset but still has power and downstream.  Also, I notice that when I plug my coffee maker on the upstream outlet between another working GFCI, when I press the reset button on the GFCI in question, I hear the coffee maker start to :jump start.  Is there a short or is it just a bad GFCI?
Comment: What outlets turn off when you hit TEST on the GFCI in question?
Comment: Are we talking about 2 gfc,on same breaker?  Shut of breaker to check.  I think the first gfci is shot .And they put 2 gfci on same circuit .Witch is fine, If so when you push reset that happens .  Have you done any electrical work before this happend?
Comment: There has been no electrical work since I purchased home brand new 10 years ago. Neither the REST nor the Test button work.  The breakers are not tripped  all outlets have power including the gfci in question. The first gfci shows green light and when I test the both gfci outlets I get a good wired condition from my gfci outlet tester. I also get a good wired condition from the regular outlet that is in between both gfci outlets and the coffee machine is plugged into.
Comment: So these two GFCI receptacles are on the same standard breaker, right? Do you know whether the circuit following the malfunctioning receptacle is connected via the load terminals of the malfunctioning receptacle or is pigtailed so the malfunctioning receptacle would not respond to a ground fault in the following circuit?
Comment: A GFCI receptacle in our kitchen is on a dedicated 20 A circuit. It has two LEDs, neither of which is lit when the receptacle is on. If I push the test button the receptacle is depowered and the lower LED is lit amber. If I switch off the breaker, the receptacle is of course depowered, and no LED comes on. If I switch the breaker back on, the receptacle is powered (no reset necessary) and no LED is lit.
Answer: GFCI receptacles very rarely go bad. So before your run out, buy and replace a GFCI. First let's try and determine if it is bad GFCI or something else is wrong. First unplug every appliance and turn off every light on the circuit and see if the GFCI will reset. If it does reset then try plugging in and run every appliance and turn on every light one at a time. If any appliance trips the GFCI then your appliance is bad and it needs to be replaced. If turning your light on and the GFCI trips then the fixture is probably malfunctioning and needs to be repaired.
If the GFCI trips when no load is on it, then after you turn your power off, pull you receptacle out and disconnect the load side conductors of on the GFCI. Carefully turn your power on and see if your GFCI resets. If it does not reset then it may be bad, but if it does reset then you have a problem with you downstream wiring. Now you have to go through the entire circuit and check to see what is in failure.
That means you reconnect the load side conductors and remove each device in sequence and test to see when you get a trip. Once you get a trip you have isolated the problem and repairs need to be made.
It's really a step by step procedure, but it is also why when you call an electrical contractor they can't give you a set price since they don't know how long it will take find and repair the problem.
Hopefully it will just be a bad appliance or GFCI. Good luck.
Comment: Doing the first step and I went ahead and cut off the circuit that powers the GFCI in question.  It only powers 4 outlets:  The GFCI, one for the disposal, one for the coffee maker, one for the frig and another spare.  When I turn off the breaker & unplug all outlets,  The GFCI reset button doesn't reset.
Comment: Sorry, it powers 5 total outlets.
Comment: @Abraham - If you don't turn the breaker back on after you remove all of the appliances, the GFCI won't reset. Sort of like you can't take the car out of park unless your foot is on the brake.
Answer: Dose the white wired side say line and charge if so move your coffee outlet white wires and put both whites to to corresponding holes that should fix the outlet the reason for this is a gfci is meant to be idiot proof charge is to connect the outlets connected to the gfci so if water gets in it the gfci will shut it down if there are 8 holes to put wires in put the two black wires in the holes corresponding with the first black you put it there will be 4 holes on blacks side 2 on top two on bottom use the bottom holes on both sets of holes
Comment: Hello, and welcome to Home Improvement. It's really hard to understand this; would you break it into sentences? And, you should probably [take our tour](//diy.stackexchange.com/tour) so you'll know how best to contribute here.


Is there a correlation between modern Middle East uprisings/wars and Ramadan?

Question: One cannot help but notice that the current shelling of Israel by Hamas has started in the month of Ramadan. So did the war of 1973 and a few other troubles. Is this just a coincidence, or is there indeed a correlation between the likelihood of trouble in the Middle East and Ramadan?
Comment: @MarkC.Wallace: there were a lot more than 3 wars or uprisings in Middle East. Should be enough data to figure out whether the probability of a trouble in Middle East is more than 1/12 to start in the month of Ramadan than other months.
Comment: but it also happened to be ramadan. (That's why it is sometimes called the Ramadan war, not to be confused with the Ramadan offensive in which Egypt invaded North Yemen in 1963)
Comment: The War of 1973 was started on an Israeli holiday (The Day of Atonement) to increase the chance of catching them off guard.
Comment: I'm confused by your use of the term "correlation"? Are you asking for a statistical analysis of the probability of three attacks occurring during the same holiday? Is the pattern statistically significant? or are you asking for historical analysis of something?
Comment: @Michael I'm unaware of statistical analysis that focused on the months of Ramadan but there are clear statistics showing that war/rebellion/trouble is much more likely during summer, and is at least partly blamed on heat making everyone a bit more tense (although the main reason is that war is difficult in winter, but this is assuming the war was planned and not spontaneous). I can easily imagine that hunger ( + heat ) can put everybody in a bad mood looking for trouble.
Answer: The "sacred" or "prohibited" months during which fighting is banned are Rajab, Muharram, Dhul-Qaʻdah, and Dhul- Hijjah. The fasting month (Ramadan) is not one of these. So, if the shariʻa is actually strictly implemented there will be (purely statistically) a one in eight chance that any war will take place in Ramadan.
Answer: there is no correlation from religious view , and there is  nothing in Islamic jurisprudence will courage people to do wars on Ramadan time  , but actually  most of  big Victories in Islamic history have take place in Ramadan like bader and ain jalout and malaz kurd battles , and for that reason Muslims will feel optimistic about wars in Ramadan
Comment: That's what I suspect: the increase of religious fever in Ramadan + empty stomach due to fasting + more than usual talk about victories over infidel - does it lead to more violence outbreaks? If we would list all the violent troubles started in the Middle East, would the ones that started on Ramadan be more than 1/12th of them?
Comment: in fact fighting is proscribed during Ramadan... But as always that's taken rather loosely to just mean fighting with other muslims, infidels are fair game...