readings - Appending 内 to a company name is read ない or うち?

For example, if I say マイクロソフト内のパートナーシップは強いです, is the 内 here read as うち or ない?

Answer

「内」 in the form:

「Proper Noun + 内」

is always read 「ない」. I just could not think of an exception to this "rule".

thermodynamics - Does all processes that consume energy from outside result in negative entropy change?

In any spontaneous process entropy increases.In biological systems disordered elements are converted into highly ordered tissues etc(-ve entropy change) which make up living organisms. But, it requires energy from the sun(ultimately). So,does that mean all processes that consume energy from outside result in negative entropy change? Endothermic reactions consume energy in the form of heat from outside so, is all endothermic reactions causing the entropy to decrease?

Answer

Entropy increases in a spontaneous evolution of an isolated system… other than that, there is no general law on the evolution of entropy.

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does that mean all processes that consume energy from outside result in negative entropy change?

No. When you heat a solid, it increases its entropy.

endothermic reactions causing the entropy to decrease?

Endothermic reactions which cause entropy to decrease have both ∆H positive and ∆S negative, so they will have a positive ∆G, i.e. their are not thermodynamically favorable.

grammar - Help with には and にとって

I need help understanding why にとって cannot be used in this circumstance:

その仕事は私｛には/*にとって｝出来ない。 ( * denotes unacceptable)

This is what I read:

にとって cannot be used when it marks an experiencer or agent

But I get confused when this sentence is acceptable:

これは我々にとって無視できない問題だ。

Isn't 我々 an agent? 我々 is the one who is doing the ignoring right? So what am I understanding wrongly?

Answer

にとって 'As from the point of view of ' is a sentence modifier. The sentence has to be meaningful without it, and it implies that its truth depends on whose point of view it is described from.

これは(無視できない)問題だ

'This is a(n) (unignorable) problem.'

我我にとって、これは(無視できない)問題だ
'For us, this is a(n) (unignorable) problem.'

これは、我我にとって、(無視できない)問題だ　　[これは can be moved to the front.]
'Regarding this, from the point of view of us, it is a(n) (unignorable) problem.'

に in question here is a dative case marker, which optionally marks the subject of the embedded clause of a potential verb.

我我がこれを無視する
'We ignore this.'

[我我{が/に}これを無視]できる　[する is deleted before できる due to the irregularity of potential form.]
'It is possible that we ignore this.'

これは、我我{が/に}無視できる　　[これは can be topicalized and moved to the front.]
'Regarding this, it is possible that we ignore it.'

As usual in Japanese, the subject can be omitted, and be understood implicitly:

これは、(我我{が/に})無視できる
'It is possible that we ignore this.'

Attaching にとって to this sentence does not work semantically because the possibility is independent of the point of view.

* 我我にとって、これは(我我{が/に})無視できる
　'For us, it is possible that we ignore this.'

gas laws - Why don't heavy and light gases separate in the atmosphere?

Everyone must have heard that balloons are filled with helium, and the fact associated with it that helium gas is light and light gases always go upward.

There comes a question to mind: if the molar mass of $\ce{CO2}$ is greater than that of $\ce{O2}$ and $\ce{N2}$, then why doesn't $\ce{CO2}$ occupy the lower layer of the atmosphere, since it is heavier than $\ce{O2}$ and $\ce{N2}$, as in the case of balloons, where helium being light rise upwards.

Answer

That's because of two reasons. One is entropy, the ultimate force of chaos and disorder. Sure, gases would like to be arranged according to their density, but even above that, they would like to be mixed, because mixing creates a great deal of entropy. If you prevent the mixing, then they would behave just as you expected. Indeed, a balloon filled with $\ce{CO2}$ would drop right to the floor and remain there.

On the other hand, if you allow mixing, light gases wouldn't necessarily go upward. Just pierce that balloon with helium, and... Well, you won't actually see much, but in fact, the helium will disperse in the atmosphere and remain there. True, its contents in the upper layers would be somewhat higher, but only somewhat. It is not like a layer of pure helium floating atop all those $\ce{O2}$ and $\ce{N2}$.

The importance of entropy is by no means limited to gases. Think of all that salt in the oceans. Salt is much more dense than water; wouldn't it just drop to the ocean floor? Well, no, it rather wouldn't.

The other reason is the constant action of winds and currents mentioned by Zhe. They stir the atmosphere (or sea water, for that matter) and make it even more uniform than it might have been otherwise.

nevua prophecy - Can Isaiah 11:2 be used a basis for the belief that the king messiah will be a prophet?

If a recent thread, I asked, "Will the king messiah be a prophet?"

@b a cited a source from Rambam's Hilkhot Teshuva, 9.2 which states, "מפני שאותו המלך שיעמוד מזרע דויד בעל חכמה יהיה יתר משלמה, ונביא גדול הוא קרוב ממשה רבנו." But, I did not see Rambam directly refer to an actual pasuk that explicitly states that the king messiah would be a prophet. (However, I do realize that a lot of ideas or notions are not explicitly stated in scripture, but otherwise inferred through various exegetical techniques.)

So, I did a little research using the technique of inference by analogy.

I suppose it is the ruach elohim that causes one to prophecy [truthfully].

For example, in Num. 11:25, it is written,

And Adonai descended in a cloud, and He spoke to him, and He took of the spirit that was upon him and put [it] upon the seventy elders. And, it came to pass, when the spirit rested upon them, they prophesied, but they did not [prophesy] again.

וירד יהוה בענן וידבר אליו ויאצל מן־הרוח אשר עליו ויתן על־שבעים איש הזקנים ויהי כנוח עליהם הרוח ויתנבאו ולא יספו

Now, in Isaiah 11:2, a pasuk that is often cited as referring to the future king messiah, it is written,

And the spirit of Adonai will rest upon him, the spirit of wisdom and understanding, the spirit of counsel and might, the spirit of knowledge and of the fear of Adonai

ונחה עליו רוח יהוה רוח חכמה ובינה רוח עצה וגבורה רוח דעת ויראת יהוה

Based on the similar phrases employed in each pasuk, is it an accurate inference from analogy (edit: binyan av) that the king messiah would indeed be able to prophesy (and thus, be a prophet) since the spirit of Adonai rests upon him, just as the seventy elders prophesied "when the spirit [of Adonai] rested upon them"?

acid base - Titration curve graph, finding exact point of the equivalence point

I plotted all my data points and made this graph in excel. Now I need to find the volume of titrant required to read the equivalence point, as well as the pH after 18.5 mL of titrant have been added. If there any... best/correct way to go about this or anything in excel I should use to point the exact points on the line I have? Or am I just taking my best guess looking at it here?

Answer

Assuming the titration involves a strong acid and a strong base, the equivalence point is where the pH equals 7. From inspection alone and the use of a ruler, you can approximate that to be at 25.88mL of NaOH.

To show the equivalence point on a the curve, just draw a line from where the pH is equal to 7 and line it up with the titration curve. I show this in the attached image.

To calculate the pH at 18.5mL, you need to know the molarity of the acid, for which you first need the identity of the acid (for stoichiometric purposes) and the acid's concentration which you can from your titration data. Then you calculate the number of excess moles of acid present after reacting with the 18.5mL of NaOH titrant. The pH is the negative logarithm of the concentration of the protons. Remember that the moles of protons is not necessarily equal to the moles of acid since acids can release more than one proton.

halacha - Are thoughts of sin punished halachically?

Inspired by this question, I got interested in the question of halakhic punishment for thoughts of sin?

In general, the Torah is not so concerned and doesn't judge how people feel or what their desires are. It is mainly concerned in how we act.

On one side

• the gmara in Kiddushin 40a explicitly says that Hashem doesn’t regard a bad thought that doesn’t lead to action as an action (artscroll comments “hence there is no punishment for the thought”)


• another gmara (end of Bava Batra 164b) says all men think of sin every single day (presumably meaning it is not punishable)

On the other side

• later in Kiddushin 40a the gmara says that thoughts of sins one has performed and now considers permitted are punished


• in Shabbat 64a we see the army returning from the war in Midian offered a korban to atone against their lustful thoughts


• R Chaim mi Volozhin writes (Nefesh HaChaim, gate 1, ch. 4) that the body is like a mishkan, the mind is the kodesh hakodashim and thinking unclean thoughts is a desecration even greater than defiling the Kodesh Hakodoshim since the Mishkan is physical and the mind is even more holy and spiritual

So how is the halakha judging thoughts of sin? Are specific halakhic works codifying this (as opposed to more philosophical discussions)?

solutions - What is the solvent and what is the solute?

This question is and I am learning about mixtures, solutions, solutes, solvents, and other terms related to these words.

I know that a solute is the substance being mixed with or dissolved into the solvent.

Substances and mixtures: are these solvents and solutes correct?

1. coffee with milk - solvent:coffee , solute:milk


2. salt water - solvent:water , solute:salt


3. air freshener - solvent:air , solute:scent


4. brass - solvent:zinc , solute:copper

Answer

In a binary homogeneous mixture, the component present in the larger amount is generally called the "solvent". The component present in the smaller amount is generally the "solute".

In your first example, however, it is more complicated as coffee is already a complex solution (but mainly water). Milk is not a homogeneous mixture. It is a fat/protein emulsion (also mainly water).

The other three are solutions: salt water is a solution of a solid dissolved in a liquid (which is the most familiar type), air freshener (one dispersed) is a solution of one gas in others (but air itself is a mixture), and brass is a solid solution.

word choice - 「覚える」と「思い出す」の違い - what's the difference of oboeru and omoidasu?

I hear both fairly often but i still can't tell the difference and when to use what.

I found this answer in yahoo answers but it seems like there is a difference in opinion (?) - not sure, didn't understand some of the answers.

I usually hear omoidashita (思い出した) when someone suddenly recalls something. And I am sure I heard oboetenaino? (覚えてないの) a few times and to me it seems like the person is saying: "you don't remember do you?".

So it seems to me that they both mean the same thing. Is this correct?

For example:

Person1: 覚えてないの?
Person2: 思い出せない

Is this valid?

So I guess my questions are:

• Do they mean the same thing?


• Are they interchangeable?

Answer

覚える remember or "keep remembering"; 思い出す recall. These two words are supposed to illustrate the difference in meaning, not politeness.

Interesting tidbit: 覚える comes from 思ふ via 思はゆ, with ゆ being an alternative to (ら)る, the　自発・受身・可能の助動詞. So 覚える would literally be "able to think" because you have remembered it. On the other hand, 思い出す would be "to come out with a thought."

Rather than one example where they are similar, let's consider two sentences that shows how they're different:

誕生日、覚えていてくれたんですか!? 嬉しい！
She is happy because he did not forget her birthday. ("kept remembering")

突如、彼は思い出した。今日は葵の誕生日だったということを。
He had forgotten it and remembered (recalled) it just now.

Now try to exchange the two expressions:

その瞬間、彼は覚えた。
Makes no sense.

What you could say is

その瞬間、体当たりを覚えた。
It learned tackle in that instant.

Here it means 身に付ける, 体得する. What comes before を覚えた is some skill or feeling (酒の味を覚える[=知る]). The point is that you learn it and then "keep remembering" it.

記憶喪失とかなんとか言われてあたしは……あたしは…　すごく心配……本当に、誕生日、思い出してくれたんですか？

Alright, this sounds a bit construed, but I hope it gets the point across. It came to back to his mind at that moment.

More examples:

あのときのことは今もよく覚えている

この本を彼に返すことを覚えておいてね

犬が芸を覚える

新しい仕事に生き甲斐を覚える

楽しかった昔のことを忽然と思い出す

約束を急に思い出す

祖父が死んだ日のことをぼんやりと思い出す

intermolecular forces - Why does bromine increase the viscosity of olive oil?

Does bromine bond to the carbon in unsaturated fatty acids and break the double bonds between oxygen and carbon? Does this increase the viscosity of olive oil? Could someone give an elaborated explanation?

This question arose from a lab experiment. Viscosity goes up because less double bondings makes the fatty acids more “packable”. But why would bromine want to break the bonds?

organic chemistry - Comparison of the rate of SN1 and SN2 reaction

It is known that $\mathrm{S_N1}$ (Substitution Nucleophilic Unimolecular) follows the order of rate of reaction:

Tertiary ($3^\circ$) > Secondary ($2^\circ$) > Primary ($1^\circ$)

For $\mathrm{S_N2}$ (Substitution Nucleophilic Bimolecular) the order of rate:

Tertiary ($3^\circ$) < Secondary ($2^\circ$) < Primary ($1^\circ$)

But what is the effective rate of reaction, if we consider that both $\mathrm{S_N1}$ and $\mathrm{S_N2}$ may occur?

Let us assume that we are using $\ce{NaOH(aq)}$ as the reagent, and using n-butyl chloride ($1^\circ$), isobutyl chloride ($2^\circ$), and tert-butyl chloride ($3^\circ$). As water is used, substitution will be favoured, and for this discussion, let us neglect any elimination reaction occurring. In this case, what would be the effective rates of reaction for these cases?

particle が - Neutral vs. Exhaustive が

The particle が has a property that implies that, of all items from some group, the sentences applies exclusively to the noun before it. For example, in a room of people from different countries, saying 「私がアメリカ人です」 would imply that you are the only American in the room.

However, it is also possible to use a more neutral が without this meaning. For example, 「雨が降る」 is neutral and isn't comparing the rain to anything.

So how do you know when the particle が carries this exclusive-definition and when it doesn't?

Answer

Warning... this answer presents things differently from the more complex and accurate model, which can be found here: http://www.lel.ed.ac.uk/~heycock/papers/topic-draft.pdf

I can't think of how to summarize the model in that paper to fit in an answer, so instead I'm going to present a different model (mostly from my intuition, so do take it with a grain of salt) which works for a more limited number of sentences, but I think lines up result-wise with the model in that paper.

---

Taking a basic XがY clause...

The determiners of the semantics of が are:

1. whether Y is temporary or permanent,*



2. whether X is new or old information,


3. whether the clause is embedded or not

---

When you have a temporary predicate, the neutral reading of が becomes possible.

雨が降っている。
"Rain is falling."

天気が寒い。

"The weather is cold."

牛が草を食べている。
"A cow is eating grass."

_{(Note: all of these can be made exhaustive by placing stress on the が-marked argument.)}

However, if the が-marked argument is already in discourse, then you would mark it by は.

「雨はどう？」「雨はまだ降っている。」 (You could, and normally would just drop 雨は entirely, but it's okay to have it, and necessary if you say some other stuff before answering the question. Using 雨が would sound weird, as if you aren't responding to the question but just making a statement.)

「今日の天気は寒いねー。」 (Using が would be exhaustive here)

「あの牛は草を食べている。」 (Using が would be exhaustive here)

There are some things which are in discourse by construction, such as 私, or things marked by その, あの, 今日の etc. -- so if they are accompanied by が the only way to read them is as exhaustive reading despite the possibility introduced by a temporary predicate.

---

When you have a permanent predicate, it is necessarily the exhaustive reading of 「が」:

太郎が背が高い。

アメリカに生まれた人がアメリカ人だ。

牛が草を食べる。

So you instead mark these things with は to get a neutral reading.

---

What I've said so far holds true at the top level of the sentence. However, in (most) subordinate clauses, the only reading available for は is the contrasitive reading, so instead things fall back to が (regardless of temporary/permanent or old/new distinctions):

太郎は私が好きな本を捨てた。

_{[*] These are called "stage-level predicate" and "individual-level predicate" in the literature.}

halacha - Borrowing vs renting money

Is it wrong to "rent" a Jewish person some money?
Since he needs to use it, and once he is done using it he will pay you back.

Answer

Rabbi Reisman in Hilchos Ribis deals with this. If you are going to spend the money, then that is defined as a loan and any fee for that 'rental' is 'ribis'. Renting property means that you return the same property that you rented, such as renting a tractor to plow your field. That is why there is a discussion as to borrowing flour to make a cake and when, if the price changes, returning the same amount of flour is or is not ribis. Trying to use English syntax and calling the use of the money 'rent' does not change the halacha.

@Fred points to Legendary Coins and Currency as a valid use of coins that can be rented rather than loaned. In this case, the coins themselves must be returned.

I apologize to @Fred for mistyping the citation. Thank you @DoubleAA for correcting it.

number - Shelosha Ve'esrim?

Who knows twenty-three?

Please cite/link your sources, if possible. After about one business day, I will:

• 
  

  Upvote all interesting answers.

  
  



• 
  

  Accept the best answer.

  
  


• 
  

  Go on to the next number.

  
  

Answer

23 cubits (and a fraction) is the difference in elevation between the Spring of Eitam and the courtyard of the Beis Hamikdash.

The importance of this is that this spring was the source for the Kohen Gadol's mikvah, which was situated atop one of the gates (twenty cubits above the courtyard) and which was three cubits tall. In this way the water could flow into the mikvah based on gravity alone, without requiring pumps or the like, which would disqualify it. (Yoma 31a)

How do I predict the solubility of a compound in a mixture of water and an organic co-solvent?

I'm trying to predict the solubility of long alcohols (e.g. 1-octanol, 1-decanol or 1-dodecanol) in a mixture of water and an organic co-solvent such as DMSO, acetonitrile or ethyl acetate.

For example, decanol in water with 25% DMSO or saturated with ethyl acetate (8.3%). I of course know the solubility of alcohols in water, but not in organic solvents or in mixtures.

I found a server to predict the solubility of any compound in any solvent, but I'm not sure how accurate it is and it only does predictions for pure solvents, not mixtures: http://showme.physics.drexel.edu/onsc/models/multisolvent.php

Any input on this would be greatly appreciated!

filters - Compute the time derivative of a noisy digital signal?

The issue is that my signal is very noisy. I need extract its time derivative as accurate as possible. P.S. I do not have any prior knowledge on the signal (black box).

On forums some suggested Savitzky-Golay filter.

Any idea please? If so, is there any c++ library for the purpose?

In fact, for my application I need to compute optical-flow like information for control purpose. I compute an estimate using image information. Then I need to compute the time derivative of this estimate.

4th order Savitzky Golay filter introduces delay, yet I need the output in real-time (real time control). For info:

• The signal is regularly sampled;


• The noise is not defined but bounded;


• The output needs to be real-time: delay-minimal;


• The signal is black box: I only get a measure each iteration.

tanach - If kings were supposed to be from Shevet Yehuda, why was Shaul from Binyamin anointed?

If kings were supposed to be from Shevet Yehuda, why was Shaul from Binyamin anointed?

tefilla - What siddur do Open Orthodox people use?

Do followers of Avraham Weiss’s Open Orthodoxy have their own siddur or use someone else’s? I’d be curious about any ways their liturgy might differ from the mainstream.

Answer

Many of the people who daven at the Hillel Minyan at Northwestern University (where I davened in college) associate with the Open Orthodox movement. Most of them daven with the Koren Sacks siddur. Some others use the Artscroll Siddur edition that includes the prayers for Israel, TzaHa"L, the United States, etc.

Since they use mainstream siddurim, their liturgy does not really differ from the mainstream. Most of the difference between them and more mainstream Orthodox Jews is difference in interpretation in hashkafa/halacha (depending on who you ask).

computer vision - Good features / algorithms for recognizing car-models in images

I have a question concerning object recognition, especially recognizing car-models! I am at the beginning of a work about identifying the same car-model in different images. At the moment I think one of the best algorithm for 3D object recognition is SIFT but after playing around a bit with a demo implementation I have the strange feeling this algorithm has some problems with shiny metal objects like cars, especially if they have different colors.

Does anyone know some work on this area in general some suitable algorithm for the task of finding the same car-model in different images?

Thanks in advance for your help!

Answer

I would have a look at the so called "bag of words" or "visual words" approach. It is increasingly used for image categorization and identification. This algorithm usually starts by detecting robust points, such as SIFT points, in an image. The region around these found points (the 128 bit SIFT descriptor in your case) is used.

In the most simple form, one can collect all data from all descriptors from all images and cluster them, for example using k-means. Every original image then has descriptors that contribute to a number of clusters. The centroids of these clusters, i.e. the visual words, can be used as a new descriptor for the image. Basically you hope that the clusters an image its descriptors contribute to, is indicative of the image category.

Again, in the most simple case, you have a list of clusters, and per image, you count which of these clusters contained descriptors from that image and how many. This is similar to the Term Frequency/ Inverse Document Frequency (TD/IFD) method used in text retrieval. See this quick and dirty Matlab script.

This approach is actively researched and there are many much more advanced algorithms around.

The VLfeat website contains a nice more advanced demo of this approach, classifying the caltech 101 dataset. Also noteworthy, are results and software from Caltech itself.

inorganic chemistry - Why do nitrogen molecules not act as ligands in haemoglobin?

Nitrogen molecules $(\ce{N2})$ have lone pairs, which, as far as I know, is the property of oxygen molecules $(\ce{O2})$ that allows them to act as ligands bonding to iron in haemoglobin in the blood. Why then is atmospheric nitrogen unable to act as a ligand and form dative bonds to iron in the blood as oxygen is able to?

expressions - Is there a Japanese equivalent of knock-knock jokes?

For those (non-natives, etc.) who maybe aren't familiar, knock-knock jokes are one of the lowest, most basic forms of American "comedy". They follow this format:

• A: Knock, knock


• B: Who's there?



• A: [Something]


• B: [Something] who?


• A: [Dumb punchline]

Here's an example:

• A: Knock, knock


• B: Who's there?



• A: "Boo"


• B: "Boo" who?


• A: It's just me, you don't have to cry.　→　さぁ〜〜〜むッ！

  注：「"Boo" who」とは「Boo hoo」の同音で、「Boo hoo」とは英語の泣き[喚]{わめ}きの擬声語。

You can make up just about anything and fit it into the format of a knock-knock joke.

So does Japanese have some similar ubiquitous format for making easy "jokes"?

Answer

I don't think there are any call-and-response jokes in Japanese, which is sort of an important feature of knock-knock jokes. As for jokes, which follow a particular pattern, there are simple plays on words, which everyone knows and which involve two words or phrases, which are (at least quasi-)homophones, usually at the beginning and at the end of a sentence, which when read without distinguishing the homophones are preferably some sort of tautology (e.g. いぬがいぬ) or simply unintelligible (e.g. でんわにだれもでんわ). Some all-time favourites

• [布団]{ふ・とん}が吹っ飛んだ。


• ゴキブリの動きぶり。


• 電話に誰もでんわ。


• この鶏肉取りにくい。


• [生姜]{しょう・が}ないからしょうがない。


• 犬がいぬ。


• イルカはいるか。

They are of a similar standard and similar to knock-knock jokes in that everyone gets the joke (or what's left of it) and everyone knows at least a couple of them. Also, everyone is free to make up their own.

grammar - How to say "ever" in this context

I want to say:

I don't think cats are ever friendly.

The only "ever" I know is using ことがある　but that doesn't seem appropriate. My attempt without the "ever" is:

猫が友好的じゃないものと思います。

Btw, have I used もの correctly to make this into a statement about cats in general?

Answer

I would personally suggest using 「決{けっ}して～～ない」 to say "not ~~ ever ~~" as in:

「ネコは決して人{ひと}なつっこい生{い}き物{もの}ではないと思{おも}います。」

「ネコは決して人なつっこくないと思います。」

「友好的{ゆうこうてき}」 sounds pretty stiff, so I changed it to 「人なつっこい」.

「じゃない」 is OK even though I used 「ではない」. 「じゃない」, however, can replace 「ではない」　only in my first sentence. In the second sentence, you cannot say 「ひとなつっこくじゃない」 or 「ひとなつっこいじゃない」.

(「じゃない」, for some reason, is very popular among J-learners, but using it is not as easy as many of them seem to think. For instance, if you said 「人なつっこいじゃない」, it has an affirmative meaning --"friendly, eh?". the negative form of the i-adjective 「人なつっこい」 is 「人なつっこくない」. One cannot say it using 「じゃない」. 「友好的じゃない」, however, is grammatical because 友好的 is a na-adjective.)

I would not feel too comfortable if you used 「もの」 instead of 「生き物」 to talk about animals.

halacha - How much of a gap in schach is acceptable?

How large of a gap is allowed in a sukkah's schach (roof) without invalidating it? (in tefachim and inches/feet, if possible)

Would it make a difference if the gap was in the middle of the roof, or on the side (=next to the wall) [דופן עקומה]?

Related question: How much invalid material invalidates schach?

Answer

Sukka 17a Mishnah:

הרחיק את הסיכוך מן הדפנות שלשה טפחים פסולה בית שנפחת וסיכך על גביו אם יש מן הכותל לסיכוך ארבע אמות פסולה

If the s'chach is distanced more than 3 handsbreadths from the walls then it is invalid. If the roof caved, and you put schach into the breach, if there are more than 4 cubits from the wall then it is invalid.

If there is airspace, you have 3 handsbreadths. If there is invalid schach material, then you have 4 cubits from the wall.

S.A. 632:2

אויר בין בגדולה בין בקטנה שוים דבין באמצע בין מן הצד בשלשה טפחים פסולה בפחות משלשה כשרה ומצטרף להשלים הסוכה ואין ישנים תחתיו

Airspace, whether in the middle or on the side, invalidates at 3 tefachim. At less than 3, it counts to complete the Sukkah but you shouldn't sleep under it.

Rama:

ודוקא שהולך על פני כל הסוכה

[It only cannot be slept under] if it spans the length of the Sukkah.

death - Are there burial requirements for pets?

Halacha requires certain burial practices for people, because people are special. Are there any requirements or, especially, prohibitions regarding pets who have died? Is it acceptable to cremate them, or must they be buried? If buried, are there requirements about how?

(The pets, of course, are not Jewish, but we have obligations to our animals while they live so I am wondering if there are any when they no longer do.)

Answer

The Torah itself says (Ex. 22:30) that the meat of an animal that is tereifah (fatally injured) should be "thrown to the dogs." Now, granted, the animal wasn't necessarily a pet when it was alive (whether anyone back then kept pets is pretty uncertain anyway), but you had the obligation to feed it before yourself (Berachos 40a based on Deut. 11:15), and you couldn't work it on Shabbos (Ex. 20:10), yet we see that once the animal is dead you can dispose of it any way you want.

---

A couple of other sources that may bear on this:

• 
  

  Jeremiah (22:19) says of King Yehoyakim, "He will be buried like a donkey, dragged and cast outside the gates of Jerusalem." Radak paraphrases: just as a donkey's "burial" consists of dragging the carcass out and throwing it in the trash, so will be the fate of Yehoyakim's body. So evidently there is no need to treat a dead donkey with any kind of respect (and that's not an animal that otherwise might have been used for food).

  
  


• 
  

  The Mishnah (Temurah 7:4,6) lists various cases where a dead animal has to be either buried or burned, because it is prohibited for use (whether because of its sanctity, such as a disqualified offering; or as a punishment to its owner, like an ox that gored someone to death). The implication is that these cases have special rules because of these reasons, but that an ordinary animal carcass can be disposed of however you like.

  
  

grammar - Why is the て-form being used before ん？

In the following sentence:

誰｛だれ｝探｛さが｝してんの

What is the grammatical reason for 探｛さが｝す to be used in て-form before ん?

Answer

誰探してんの is a contracted form of 誰探してるの, which in turn is a contracted form of 誰(を)探しているの ("Who are you looking for?", notice the progressive form). More generally:

• ている contracts to てる. (See this chart)



• /r/ + vowel before a /n/ consonant can turn into ん in casual speech. (Do not confuse this ん as explanatory-の.)

Examples:

• わからない。 → わかんない。
  wakaranai → wakan'nai


• 見てるの。　→　見てんの。
  miteruno → miten'no


• 寝るなよ。　→　寝んなよ。
  nerunayo → nen'nayo



• しゃべりなさい。 → しゃべんなさい。
  shaberinasai → shaben'nasai


• 食べられないよ。 → 食べらんないよ。
  taberarenaiyo → taberan'naiyo

Related:

fft - What does the exponential term in the Fourier transform mean?

We know that Fourier transform $F(\omega)$ of function $f(t)$ is summation from $-\infty$ to $+\infty$ product of $f(t)$ and $e^{-j \omega t}$:

$$ F(\omega) = \int\limits_{-\infty}^{+\infty} f(t) \ e^{-j \omega t} \ dt $$

Here, what does the exponential term mean?

Answer

It's a complex exponential that rotates forever on the complex plane unit circle:

$$e^{-j\omega t} = \cos(\omega t) + j \sin(\omega t).$$

You can think of Fourier transform as calculating correlation between $f(t)$ and a complex exponential of each frequency, comparing how similar they are. Complex exponentials like that have the nice quality that they can be time-shifted by multiplying them with a complex number of unit magnitude (a constant complex exponential). If the Fourier transform result at a particular frequency is a non-real complex number, then the complex exponential of that frequency can be multiplied by that complex number to get it shifted in time so that the correlation to $f(t)$ is maximized.

word choice - When to use: "say", "speak", "tell" or "express"

When browsing through journal entries by various people, I've recently been noticing the words 述{の}べる and 語{かた}る used fairly frequently but I'm not sure when they should be used over 話{はな}す and 言{い}う etc as I think there's a lot of overlap.

Would it be possible for me to ask when the following words should be used?

• 言{い}う: to say


• 述{の}べる: to express/state/say


• 表{あらわ}す: to express (as per @yadokari's comment, I'm not sure how 表す and 述べる differ.)


• 話{はな}す: to speak/talk


• 語{かた}る: to talk/tell


• 伝{つた}える: to convey/tell


• 告{つ}げる: to inform/tell


• 教{おし}える: to inform

Answer

Let me try:

言う： The only thing on your list that I'd actually translate as "to say" or "to tell". This is sort of "neutral" in that it really just means to say. For example:

「彼女がいない」と言ったでしょう？ = He doesn't have a girlfriend, I told you so already!

Note that as I am not giving any context you could equivalently translate the sentence as: He said he didn't have a girlfriend, or did he not!

述べる： Can mean "to express" or "to state":

英語で自分の考えを述べるのは難しい。= It is difficult to express one's thoughts in English.

(Example sentence taken from jisho.org)

話す："to talk", as you wrote above. For example:

今お母さんと話しています。= I'm talking to mum right now.

おしゃべりな人と話したくない。= I don't want to talk to talkative people.

伝える：　"to convey" as in "Say hello to X.":

田中さんにこの知らせを伝えて下さい。= Please pass these new onto Mr. Tanaka.

告げる： I've not heard this one before (which doesn't mean much) but it seems to mean "to tell" or "to convey" again. Examples (again taken from jisho.org):

もし私がそれを知っているなら、私はそれをあなたに告げるだろう。= If I knew it, I would tell you.

教える： Can mean "to teach" or "to tell". For example:

あなたの電話番号を教えて下さい。= Can you give me your phone number?

彼は日本語学校で日本語を教えています。= He's teaching Japanese at a Japanese language school.

This answer is incomplete but I hope this helps.

midrash - Acacia wood or Cedar

The verse mentions one of the materials in the Mishkan was עצי שטים. Artscroll and others translate it as acacia wood.

Rashi on the pasuk quotes Midrash Tanchumah (#9) that Yaakov planted ארזים in Egypt and commanded his children to bring them with them to the wilderness. Usually ארזים is translated as cedar wood.

Which is it? Acacia or cedar?

Answer

ארז, which you translated as cedar, is actually the name of a group of 10 (or 4) different types of trees (see the gemara in R"H on .כג, and the gemara in B"B), one of which is שיטא, which apparently Artscroll translates as accacia.

gentiles - Has Judaism succeeded or failed at being a light unto the nations?

In Isaiah 42:6 we read

I the LORD have called thee in righteousness, and have taken hold of thy hand, and kept thee, and set thee for a covenant of the people, for a light of the nations

I have seen it argued that it is a responsibility for Jews to act as example to the people of the world. Based on the fact that throughout global history Jews have had a very minor influence, and even today there are billions of people who have never heard of or are at best only remotely aware of the existence of Judaism at all, I would like to know if any Rabbinic authority has written on the subject of the seeming failure of the Jewish people to successfully be a light to the nations?

organic chemistry - Determining chirality after considering conformational interconversion in a cyclohexane

Basically I want to know what does the question mean when it says "taking into consideration conformational interconversions."

I assume it means, when I draw the mirror image of the given compound, the mirror image can be same as the compound itself (the case with option (a) and option (c) ) or it (the mirror image) can be same as confomer of the compound (the case for option (a) and option (b) ), for the compound to be achiral.

Note: option (a) shows both the features because option (a) is same as it's confomer and it is same as it's mirror image as well.

Is my assumption correct?

Answer

Your analysis is correct. The stipulation "taking into consideration conformational interconversions" means that conformational interconversion is fast. That's important because compounds that we consider achiral can have chiral conformations. I used the example of butane in a previous question.

In this problem, three compounds are given that have multiple stereocenters, compounds b, c, and d. A common way to decide whether a compound with multiple stereocenters is chiral is to look for planes or points of symmetry within the compound. Compound c has a plane of symmetry, so it is clearly achiral. Neither of compounds b or d has a plane of symmetry in the drawn conformations, which means that those conformations are chiral. However, as you suggest, chair flip of b gives the mirror image of the original drawing, which means the original and mirror image are equivalent, assuming that the two conformations can interconvert.

There are many cases where conformations cannot interconvert, and that leads to very interesting compounds that don't even require a stereocenter to be chiral (again see earlier question).

halacha theory - I thought Gezeirah Shavah requires Mesorah

In Masecheth Rosh Hashanah (9b), the Gemara uses a Gezeirah Shavah from Tishrei, with the word שנה, to support the Mishnah's ruling that 'Orlah is counted from Tishrei. In response, however, the Gemara challenges that Nisan has the same word and, therefore, the Gezeirah Shavah could be applied to Nisan, a point which is subsequently rejected based on a logical argument.

Wait a second! I thought that a Gezeirah Shavah can only be established by a tradition from one's teacher! While I understand the logical argument on both sides of this particular debate, of what relevance is either argument? Either there's a tradition, or there isn't. So what's going on here?!

halacha theory - Keeping up with "local" standards of modesty and dress - of religious Jews, or of society at large

In dealing with issues relating to Tzeni'uth (modesty) and clothing, a lot depends on "local" standards of dress. For example, the RaMBa"M (here) explains that in places where women do not normally go out with just their hair covered, but with veils as well, they should be sure to wear veils as a matter of Halachah. However, since any deviation in the local standard would be a violation of this principle, it would stand to reason that we ought never to have changed our standard of dress from the time of Sinai. Since that is observably not the case, does this mean that, both in practice and in Halachah, we recognize societal standards in determining how we ought to dress in terms of modesty?

women - woman posting a picture of herself on social media

From a halachic perspective, is it modest for a religious woman - especially someone who is single - to post her picture profile on social media?

rambam - No divine form for the Oral Law?

This seriously puzzles me. The Oral Law in the form of the Mishnah (and the following Gemmorah), which is the six Sdarim, is well known, and the Gemmorah itself testifies (Shabbos 31a) its division is of divine origin.
However, when Rambam wrote his Mishne Torah, he chose a completely different Seder of 14 tractates. Next came HaTurim and made it into four, with his own subdivisions.

So does it mean the Oral Law does not have a fixed divine structure as the written Torah?

Why are there different names for the same kanji radical?

I was wondering why some of the names for kanji radicals are different depending on the source.

For example, right now I'm learning radicals on kaniwani and they called 「丶」 drop, but on my kanji learning app they called it a dot. The terms they call it are similar but still different. I would like to know which source is more credible or reliable to study kanji radicals.

digital communications - How to estimate and compensate for doppler shift in wireless signals?

I was wondering what good method(s) exist for the estimation (and subsequent compensation) of doppler shift for transmitted signals, be they acoustic or RF, in the context of comms.

The question: Specifically, if the degree of doppler shift is varying over the duration of a packet, how best to estimate (track it?) and then compensate for it. Assume we have a trainer sequence. You may also assume the signal passband BW is on the order of its carrier. (e.g, if the passband signal exists from 2500-7500 Hz, its BW is 5000Hz, as is its carrier.)

Some additional background for context:

• One method I found during my research:
  
  
  
  • Since I have a trainer sequence and know its frequency, first I estimate its received frequency.
  
  
  • Next, I resample the entire packet by a ratio that is related to the speed of the wave in the medium, my known transmitted frequency, and my new estimated doppler shifted frequency.
  
  
  • This works well in simulations, but the weak points are that the frequency estimation must be very accurate, and it also assumes the doppler shift is not changing during the duration of the packet.
  
  
  
  

Are there any other methods that can be utilized to solve the problem when the doppler is changing during the duration of the packet? What is the opinion of the above aforementioned method?

Many thanks!

Answer

This is a very common communications problem. Look in a textbook for "frequency synchronization"; whole books have been written on these and related topics. The technique that you would choose is a function of the specifics of your system. There are two common sources of frequency offset:

• 
  

  Differences in frequency between the reference oscillator at the transmitter and receiver. This error is usually small, depending upon the precision of the timebases available, and can be mitigated at some cost. Cheap crystal oscillators typically achieve 50 parts per million of error or better (although this does drift as the crystal ages). If you have a larger budget, you can use something like a Rubidium standard, which provides ~1 part per trillion of frequency error. A cheaper and increasingly common approach is to use a GPS receiver that has precision frequency output (typically 10 MHz). The highly accurate timebase available from the GPS constellation can be used to train the reference precisely on-frequency.

  
  


• 
  
  

  Physical dynamics effects between the transmitter and receiver. One notable example in which this comes into play are for satellite communications applications (especially in lower orbits), where the satellite is moving (and accelerating) very rapidly relative to any observer on the Earth. The high radial velocity of the satellite toward the receiver will cause a Doppler shift, and any change in that velocity caused by its orbit will cause that shift to change over time. In applications where you have these sort of dynamics, you typically can't mitigate it much, so you're left with building a receiver that tolerates the effects.

  
  

So how does a receiver synchronize with the transmitter in these cases?

• 
  

  One common approach useful for phase- or frequency-modulated signals is to use a phase-locked loop. Design of PLLs is a complex topic in itself, but in essence, they are feedback systems can be used to acquire and track phase and frequency offset while your receiver is in operation. If you only need frequency synchronization, then you can use a frequency-locked loop instead; while they will not provide phase synchronization for you, they often have better acquisition properties.

  
  


• 
  

  As an alternative to a feedback loop, there are also feedforward approaches to estimating frequency or phase offset. One feedforward approach would take advantage of your training sequence to estimate the frequency error based on how the phase offset changes over the course of the sequence. If the frequency offset changes as time goes on, however, you would need to repeat the estimation procedure to allow your receiver to catch up.

  
  
  


• 
  

  Another technique is to design your system to be robust to (reasonably small) frequency offsets. Differentially-encoded phase modulation is an example of this (although frequency error will show up as a phase offset after differential decoding, which must be handled). Frequency-modulated waveforms such as FSK also have some level of resistance to frequency offset, as long as the offset is small relative to the amount of frequency deviation used by the transmitter.

  
  

This very short summary really just scratches the surface of some of the more well-known approaches. Synchronization can be a difficult problem to solve in practical ways, and there has been much research over the years on different ways to do it. It's going to depend upon exactly how your system is structured, and one very important variable: the target SNR. There isn't a single "correct" answer. I will make one textbook recommendation; while it is very expensive, "Synchronization Techniques for Digital Receivers" by Mengali is a comprehensive text on timing, phase, and frequency synchronization.

software implementation - Why can Quadrature Demodulation demod a Frequency Modulated Signal?

I use a Quadrature Demodulator in my SDR application, which is defined as:

$\angle (S_n, S_{n+1})=arctan(S_{n+1}*\overline{S_{n}})$

So practically its amplitude is the angle between two Samples $S_n$ and $S_{n+1}$ where $n$ refers to a position in a sequence of complex values of I and Q. $\overline{S}$ be the complex conjugate.

I understand that for Quadrature based modulation the phase-changes contain the information. But why can I demodulate frequency-modulated Signals with a Quadrature Demodulator. This modulator is often referred to as FM Demod. Can somebody explain me why that is?

Best, Marius

handwriting - Is it standard practice, or acceptable, to connect strokes in certain characters of hiragana?

I've been learning my hiragana from here:

http://yosida.com/en/hiragana.html

For the characters fu, mu, mo, na, ra, yu, and ya, I see a discrepancy between what's in the little box and what shows up when you click the character to see it being drawn. For these characters, the little boxes show several strokes seemingly connected in smooth lines, while the drawings will show strongly separated marks.

Which "style" -- if that's the appropriate word -- is preferable?

Answer

I'm not Japanese, but based on what I know it is up to you to choose which style you would like to write in. However, as I commented previously, I recommend that you stick with the "handwritten" style rather than the "printed" one if you are using a pen or pencil. However, if you are using a brush then perhaps the other is more appropriate.

There is a great article about the differences of Japanese scripts linked here. The article notes which styles of writing you might find more frequently in Japan and the context. At the bottom, there is a large entry about handwriting which compares many different "styles".

All are correct, but the criterion is whether Japanese can recognize that your "ふ" looks like a "ふ". I might note that stroke order and stroke count are really important. For example, if you choose to draw "ふ" in 2 strokes instead of "4", you might just want to make sure that Japanese people can recognize it.

Probably the two or three characters that end up being stylized are そ、ふ、and ゆ.

Here is another short article that talks about the differences in writing style.

parshanut torah comment - "The days of mourning for my father" - why wait?

The Posuk says(27,41):

יִקְרְבוּ יְמֵי אֵבֶל אָבִי וְאַהַרְגָה אֶת יַעֲקֹב אָחִי:

Translated as:"Let the days of mourning for my father draw near, I will then kill my brother Jacob. "

The question is why wait until then?

bond - Why does Nitrogen form N₂ (and not N₄) while but Phosphorus forms P₄ (and not P₂)?

$\ce{N2}$ is a gas
$\ce{P4}$ is a solid
$\ce{N}$ and $\ce{P}$ are in the same group in the periodic table

The bond enthalpies are:
$\ce{N#N}$ triple bond is $949~ \mathrm{kJ/mol}$

$\ce{P#P}$ triple bond is $490~ \mathrm{kJ/mol}$

$\ce{P-P}$ single bond is $200 ~ \mathrm{kJ/mol}$

$\ce{N-N}$ single bond is $159-296 ~ \mathrm{kJ/mol}$

So why does $\ce{P}$ go to $\ce{P4}$ not $\ce{P2}$ and why does $\ce{N}$ go to $\ce{N2}$ and not $\ce{N4}$?

frequency - Why is oversampling helpful to an anti-alias filter?

Why does oversampling make the job of an anti-alias filter easier? I don't understand the intuition on why it becomes helpful.

Isn't it economical to just keep the sampling rate at the minimal level, that is twice the highest frequency of the signal, in that way, we can save energy, and processing and computational power.

shabbat - Is it appropriate to sing Aishet Chayel for a childless woman?

I have seen a tradition that has husbands using Proverbs 31 ("Aishet Chayel") to bless their wives, with children rising up and going to the mother and kissing her. This text even has reference to "her children" rising up to bless her.

If a woman has no children is it appropriate for her husband to use this traditional Aishet Chayel blessing on Shabbat?

Answer

Just a copy/paste from a nice article on the subject found HERE

Avigdor Shinan introduces “Eishet Chayil” in the Siddur that he edited and annotated, as follows: This biblical passage has been included in the Siddur since the 17th century (when Kabbalists established other portions of the Friday night liturgy, such as poem Lecha Dodi—jb). Its recitation on Friday evening is interpreted alternately as referring to Shabbat, the Tora, or the Divine Presence, and it describes the Sephira of Malchut according to the Kabbalists. Nevertheless, many today understand it as a song of praise and thanks that the members of the family sing in honor of the matriarch of the home for all that she does during the week in general, and what she has done getting ready for Shabbat in particular.

Assuming that singing Ashet Chayil does not trigger any unpleasant feelings for his wife, then there is no problem singing it as the passage is a allegory (indeed the source for Ashet Chayil is in the book of Mishlei) as mentioned above and verses like "her children rise up" can be interpreted on a deeper level.

I encourage you to read the whole article to get a deeper understanding of Ashet Chayil

parashat noach - What effect did Migdal Bavel have on world languages?

In 1764 BCE (or about 1930 BCE adjusting for the missing years (Wikipedia link), everyone (perhaps under Nimrod's command?) had built the Migdal Bavel, and that Hashem caused a dispersion and confusion of their unified language due to this (Tower of Babel) (Genesis 11:1-9):

Now the entire earth was of one language and uniform words. And it came to pass when they traveled from the east, that they found a valley in the land of Shinar and settled there.... And they said, "Come, let us build ourselves a city and a tower with its top in the heavens, and let us make ourselves a name, lest we be scattered upon the face of the entire earth." ... And the Lord said, "Lo! [they are] one people, and they all have one language, and this is what they have commenced to do.... Come, let us descend and confuse their language, so that one will not understand the language of his companion." And the Lord scattered them from there upon the face of the entire earth, and they ceased building the city. Therefore, He named it Babel, for there the Lord confused the language of the entire earth, and from there the Lord scattered them upon the face of the entire earth.

On this, Rashi says that they all spoke Lashon Hakodesh (presumably Hebrew) and that it was a gathering of all the different peoples ("One nation to another nation, Mizraim to Cush; and Cush to Put; and Put to Canaan"). As it was less than 400 years after the Mabul (Noah's Flood), I doubt there was much time for language development anyway.

What exactly does this mean? Put more directly, what languages did people speak before and after the dispersion of Migdal Bavel?

Note that it seems from archaeology (Wikipedia link) that there were other written languages continually in use both before and after that time, perhaps most famous of which is Egyptian hieroglyphics (yet interestingly no record of Hebrew or Aramaic writing until several centuries later). For all I know the archaeology could be partially or entirely incorrect, but it is worth keeping in mind in context of this question. But beyond the simple reading of the verses, what do the actual Torah sources say about what languages were in use before and after Migdal Bavel and what effect the dispersion had on language?

Note also that this question has some relevancy to mine (though I couldn't find one specifically about the dispersion's effect on language).

sources mekorot - Names of mazalot in Judaism

Yesterday we discussed that during Zayin Adar we eat fish due to the constellation of Adar. Rambam lists these mazalot, and uses them extensively when discussing calendar calculations. They are also featured in later piyutim that we say during Pesach and Shemini Atzeret. However, I could only find a reference to the 12 constellations in Berakhot 32b without their names. Do you know any earlier Jewish sources that Rambam could use to create his list?

Answer

I summarise the really good comments that my question received:

Double AA suggested Pirkei deRabbi Eliezer, which is really hard to date, but according to researchers most parts are from late Antiquity, and by the 8th century had more or less its final form. In chapter 6 we read:

כל הכוכבים משרתים לשבעה כוכבים של שעות, ושמן כל"ש צמח"ן: כוכב, לבנה, שבתאי, צדק, מאדים, חמה, נוגה. והם משרתים לשבעה ימי השבוע: יום א' כוכב חמה, יום ב' צדק לבנה, יום ג' נוגה מאדים, יום ד' שבתאי כוכב, יום ה' חמה צדק, יום ו' לבנה נוגה, יום ז' מאדים שבתאי. וכולם משרתים לי"ב מזלות שהן כנגד י"ב חדשים, ואלו הן: טלה, שור, תאומים, סרטן, אריה, בתולה, מאזנים, עקרב, קשת, גדי, דלי, דגים. ואלו שנבראו במעשה בראשית לנהוג את העולם*

All the stars minister to the seven planets, and their names are KaLaSh TzaMChaN (כל"ש צמח"ן): Mercury (כ'), Moon (ל'), Saturn (ש'), Jupiter (צ'), Mars (מ'), Sun (ח'), Venus (נ'). And they minister to the seven days of the week: On the first day Mercury and Sun, on the second day Jupiter and Moon, on the third day Venus and Mars, on the fourth day Saturn and Mercury, on the fifth day Sun and Jupiter, on the sixth day Moon and Venus, on the seventh day Mars and Saturn. And all of them minister to the twelve constellations, which correspond to the twelve months, and they are: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius, and Pisces. And they were created during the Creation to drive the world.

Uber Chacham commented that we can read about the mazalot in Rashi's commentary (11th century) to Rosh Hashanah 11b (even though Rambam probably didn't have access to it):

ר"א אומר אותו היום י"ז במרחשון היה יום שמזל כימה עולה ביום גלגל חמה עגול הוא, חציו למעלה מן הקרקע וחציו למטה מן הקרקע, ושנים עשר מזלות קבועין בו וזה סדרן, טלה שור תאומים סרטן אריה בתולה מאזנים עקרב קשת גדי דלי דגים. וסימניך טש"ת סא"ב מע"ק גד"ד, ששה מהן שקועין למטה וששה מהם למעלה

R. Eliezer says: That day was the seventeenth of Marheshvan, a day on which the constellation of Pleiades rises at daybreak, the Sun is round, half of it above the ground and half of it below the ground, and contains twelve permanent constellations, and this is their order: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricornus, Aquarius, and Pisces. And its mnemonic is TaShaT SaEV MaAK GaDaD (טש"ת סא"ב מע"ק גד"ד), six of them immersed below, six of them above.

_{* Translation recycled from Sefaria}

Yaacov Deane listed many mystical works, like Sefer Yetzirah 5:5 (or 5:2 or 5:4 in other versions), which should have existed by the 3rd century. Sefer Raziel haMalakh contains many parts that were edited in the late antiquity, and at many places refers to the mazalot, here's one complete list.

halacha - Does a married woman have to cover her hair to make a bracha?

When making a bracha with shem u'malchut, one should not have erva (nakedness) exposed. For married women, their hair is considered to be erva. So does a woman who is married have to cover her hair when she makes a bracha?

biochemistry - Why DNA is negatively charged and what makes it so?

1. What part in the strand contributes to the overall non neutral charge?


2. DNA is not isolated in the body, so what keeps it stable while being charged?


3. Why is it important for DNA to be charged?

Answer

As cibrail said, DNA is a polymer of nucleotides. They join themselves through phosphodiester bonds (a specific kind of covalent bond) that can grow to as much as millions of nucleotides.

What part in the strand contributes to the overall non neutral charge?

The reason why DNA is negatively charged is the phosphate group that makes up every nucleotide (pentose + nitrogenous base + phosphate). When forming part of the phosphodiester bond, they retain 1 of 2 negative charges (the other being lost to form the other ester bond to a new pentose, that's why the bond is called "phospho-di-ester").

Lehninger 5th edition. Part of figure 25-5

DNA is not isolated in the body, so what keeps it stable while being charged?

The main molecules in charge of that are proteins called histones. They have alkali features and positive charge, and so, they neutralize these negative charges. On the other hand, that's not the main point of histones. Histones play a really important key role in the regulation and compaction of DNA within the nucleus of the cell, and are important targets of diverse molecules that want to alter DNA structure and function:

Lehninger 5th edition.Figure 24-26

Why is it important for DNA to be charged?

It has great importance because cell machinery is adapted to that property. If DNA wasn't negatively charged, the structural fundamentals of interactions between DNA and transcription factors would be completely different. Thanks to the fact that it is negatively charged, it becomes spontaneously pretty straight when denaturalised, because negative charges repel themselves. It forms very wide curves. And of course, histones wouldn't be able to join DNA and exert their key regulating functions.

stereochemistry - What's the difference between alpha-glucose and beta-glucose?

What's the difference between $\alpha$-D-glucose and $\beta$-D-glucose? Are they isomers? Or do they differ in their elemental composition?

Answer

$\alpha$-D-glucose and $\beta$-D-glucose are stereoisomers - they differ in the 3-dimensional configuration of atoms/groups at one or more positions.

$\alpha$-D-glucose

$\beta$-D-glucose

Note that the structures are almost identical, except that in the $\alpha$ form, the $\ce{OH}$ group on the far right is down, and, in the $\beta$ form, the $\ce{OH}$ group on the far right is up.

More specifically, they are a class of stereoisomer called an anomer. Anomers are capable of interconverting in solution. All cyclic structures of monosaccharides exhibit anomeric $\alpha$ (down) and $\beta$ (up) versions. These differences occur at the anomeric acetal carbon (the only carbon with two $\ce{C-O}$ bonds.

These two forms exist because all monosaccharides also have an open-chain form with one fewer stereocenter. When the chain closes to the cyclic structure, the aldehyde or ketone carbon becomes a stereocenter, and it can do so in either configuration. One configuration is preferred ($\beta$), but both exist.

Open chain form of glucose:

In the presence of acid or base (although water can fulfill this role if need be), the two anomers interconvert through the open form until dynamic equilibrium is established. The mechanism below starts with $\alpha$ in the upper left and finishes with $\beta$ in the lower right. The open-chain form is in the middle.

torah study - What level of understanding is required in "learning" for purposes of making a siyum?

When learning as part of a coordinated group siyum, what level of understanding of the material is expected/required? How do you know if you've done enough to fulfill the mitzvah? Is it about effort expended, or about reaching a certain level of accomplishment (e.g. that you could pass some sort of test on the content)? How does somebody who is not already extremely learned (like, say, a ba'al t'shuvah), but who wants to help, know if his efforts will be useful?

This answer addresses learning in English rather than Aramaic and says it's more than just reading the words, which makes sense to me, but that doesn't actually say what level of proficiency one should be able to demonstrate.

molecules - Atomic properties

This may be a very broad question. I always asked myself how scientists manage to find out the exact molecular structures of for instance water or carbohydrates. How do they know? How do they know the angle between the bonds in water? Is there a classical example demonstrating and substantiating current knowledge on molecular level of structure?

The if we go to atoms, how do people know what charge an ion has? How can be know we have atoms with 7 protons for instance?

Probably there are zillion ways required to find out, but could you give me some general examples?

halacha - You accidentally broke your fast. Now what?

What are you supposed to do if you inadvertently broke your fast*? Do you:

1. keep going;



2. extend it (if so, how long);


3. cancel it (if so, do you make it up a different day)?

_{*This question is for day-fasts only.}

Answer

The Mishna Brura OC 549 sk 3 says to continue fasting if you accidentally ate.

In OC 568 sk 3 he says you can still say Aneinu at Mincha if it is a public fast day (as opposed to a personal one).

In OC 568 sk 8 he says that you do not need to fast again on a different day for accidental eating on the public fasts as well as any personal fast that has a fixed date (eg Yahrtzeit).

This halacha is not limited to Yom Kippur and Tish'a b'Av, but applies to "minor" fasts, as well.

halacha - Mayim Achronim at The Pesach Seder

Why in the Order of the Seder (that is Kadesh urchatz…) do we not include Mayim Achronim while we do we include the regular washing and the washing before dipping the vegetable into saltwater when all three are Halachic requirements? Why does the Mayim Achronim get ignored in the List of Things to do?

spectroscopy - Is it true that heavy water is not blue?

I believe I saw this claim somewhere on the internet a long time ago. Specifically, it was claimed that the difference could be observed by filling one long, straight tube with light water and one with heavy water, and looking through both tubes lengthwise (so that light has to travel through the tubes' lengths before reaching the eye), whereupon the light water would appear blue as it does in the oceans, and the heavy water would not. The explanation given was that heavy water has a different vibrational spectrum because of the greater mass of the $^2$H atom, which seemed perfectly plausible.

However, I am no longer able to find a source for this claim, which is strange because if it were true, surely it would not be so difficult to find a source?

Answer

Based on your description, I may have found the article you originally saw, or at least one very similar.

Researchers from Dartmouth College published a paper$\mathrm{^1}$ in which they report, among other things, the results of viewing sunlit white paper through two 3 meter lengths of plexiglass; one filled with $\ce{H2O}$ and one with $\ce{D2O}$. Sure enough, because of the lower frequency of the maximum absorption of $\ce{D2O}$ in the red to near IR wavelengths, the blue color that is characteristic of $\ce{H2O}$ is far less pronounced in $\ce{D2O}$. This website is based on the published paper and additionally shows a photograph of the blue colored $\ce{H2O}$ on the left with the far less colored $\ce{D2O}$ on the right:

1) "Why is Water Blue", Charles L. Braun and Sergei N. Smirnov, J. Chem. Edu., 1993, 70(8), 612

product recommendation - Where can I find the current water level of the Kineret to see the effect of mentioning Morid Hageshem?

Throughout the winter we pray Mashiv HaRuach UMorid HaGeshem. My understanding is that it is said for Eretz Yisroel dwellers (unlike V'sain Tal Umatar LBracha which is said for your locale). As we pray for it I am interested in knowing if there is an online source to find out what is the current water level of the Kineret?

Answer

See:

marriage - Having children when both parents are Tay-Sachs carriers

This is an obvious CYLOR question, but I am interested in whatever halachic information is available out there.

Suppose a couple got married without ever getting genetically tested for Tay-Sachs. When they decide to have a child, they are both tested and both turn out to be carriers. Does the mitzvah of having children still apply to them?

Also, is it acceptable for two people who know that they are carriers to get married in the first place?

Answer

When I went for genetic testing, the secular geneticist told me that her rule of thumb was "oh they'll just test each pregnancy and terminate the Tay-Sachs ones." Suffice to say that Rabbi Moshe Feinstein vehemently opposed that logic. His student Rabbi Tendler is therefore opposed to amniocentesis as the couple will then be pressured to terminate -- when according to Rabbi Feinstein it's not permitted to do so. (Note that other rabbis are more lenient in some unfortunate cases.)

I think the majority of Orthodox poskim today will tell you that two carriers really should look for other people to marry. It's the least-bad option. Hence the importance of checking for compatibility well before a relationship gets underway. (Rabbi Feinstein himself recommended finding one's carrier status as soon as one decides that s/he is "seriously of dating age", while the tests could be done earlier he didn't want more anxiety weighing on people. Today Dor Yeshorim removes the stigma by no one knowing their actual status.)

Should a couple realize they're both carriers: Rabbi Feinstein had ruled "if a man has a condition such that, regardless of who he marries, there's a 50% chance that his child will have medical problems but a life expectancy of several decades with treatment ... he should have faith and get married", with others questioning this. That's a far, far cry from saying that a couple who know there's a 25% chance any child they have won't survive preschool age should have "faith."!

In short:

• A couple who know they're both carriers shouldn't get married.



• If they're already married and determine they're carriers, it's reasonable to question whether the mitzva to try to conceive conventionally would apply -- as the emotional cost here is so high. I'd assume many would advise against it.


• Adoption, or IVF with preimplantation testing, are both complex options that may be advisable, pending a couple's consultation with their rabbi.

gifts - What to present to the rabbi

My friend is going to meet rabbi, to talk about house management, and she wants to bring some present to him. What you would present to the rabbi, and what you should not to? Please explain why.

electrochemistry - Why is the water reduction of oxygen favored in acidic conditions?

The standard reduction potential of diatomic oxygen in acidic conditions is +1.23 volts. However, the standard reduction potential of diatomic oxygen in basic conditions is only +0.40 volts.

Why is the reduction of diatomic oxygen by acidic media more favored than the reduction of oxygen by water that is basic?

I can think of a few reasons:

1) We are likely going to be forming negative two oxidation state oxygen anions when we oxidize diatomic oxygen. Oxygen adopts an oxidation state of negative two except in peroxides, which aren't very stable, and I don't think the oxygen radical will be very stable in solution.

Can someone provide a less fluffy reason that we're going to be forming negative two oxidation state oxygen atoms? I'd imagine that the electronegativity and electron affinity of oxygen are two reasons it might favor the negative two oxidation state over the negative one oxidation state in solution. I.e. why doesn't this occur to a significant extent?

$\ce{O2 + 2e^- -> 2O^-}$

Or this?

$\ce{O2 + 2e^- -> HOOH}$

2) From the above we can deduce that water is the product; water is pretty stable in either acidic or basic medium - i.e. it won't react to a large extent with either hydronium or hydroxide ion. Plus the oxygen in water has a -2 oxidation state. So if we look at our skeleton half reaction:

$\ce{O2 + 4e^- -> 2H2O}$

We realize that we need a source of protons. And the proton source in acidic medium is likely hydronium ion.

However, in basic medium, the proton source is water. I'd imagine that water is a poorer proton source than hydronium ion.

So would this account for the difference in standard reduction potential of oxygen in media that vary in pH?

I understand that voltage is an extension of K through the Nernst equation; is what I'm seeing here basically that the protonation of a base ($\ce{O^2-}$) is more favored in acidic rather than basic media? Could there also be kinetic factors? In other words, why is this statement true?

Also:

1) What's the mechanism for the reduction of diatomic oxygen?

2) Why is the reduction of protons at high pH less favored than the reduction of protons at low pH? My first guess: you don't find as many protons in basic solutions. But then, protons don't exist by themselves anyway. So what can the proton source be? I'm guessing that in basic pH, there doesn't exist much hydronium ion. So the only two sources of protons are water and hydroxide anion. Heterolytically cleaving the hydroxide anion to form the highly basic oxide anion doesn't seem thermodynamically favorable. Cleaving water to form hydroxide anions ... are we running into a Le Chatlier's Principle effect?

ETA: Or should I be considering proton activities? Is the activity of the proton less in basic solution than in acidic solution?

Answer

If you look at the half equations, you will see when you add them together, you get 1.23 V, 1.22 V, and 1.23 V.

As the mixture becomes more basic, it is more difficult for the oxygen to grab $H^+$ ions and easier for $H_2$ to lose electrons to generate $H^+$ ions.

The mechanism probably involves these combinations: $O_2, H_2O_2, H^+, HO_2^-, H_3O_2^-, H_2O, and\ HO^-$.

kinetics - Rate-limiting in transition state theory

Suppose an initial state $A$ can transition to either state $C$ or state $D$. Suppose further that both of these two processes are rate-limited by a transition to the same intermediate state $B$, as follows:

Note that $\Delta G_{AB}> \Delta G_{BC}>\Delta G_{BD}$.

According to transition state theory, rates are determined by the rate-limiting step. So the rate of each process will be the same,

\begin{align} r_{A\to C}&=r_{A\to B} \\ r_{A\to D}&=r_{A\to B} \end{align}

from which it follows that the number of transitions made during some large $\Delta t$ will also be the same,

\begin{align} N_{A\to C}&=r_{A\to B}\Delta t \\ N_{A\to D}&=r_{A\to B}\Delta t \end{align}

However, if we were to consider the two pathways collectively then we would predict more transitions to be made to state $D$ than $B$ since $\Delta G_{BD}<\Delta G_{BC}$.

How do we resolve this apparent discrepancy?

Answer

In transition state theory (TST, goldbook) one of the necessary assumptions is that reactants and products are in equilibrium. In principle this gives us \begin{align}\ce{ A &<=> [AB]^{$\ddagger$} -> B\\ B &<=> [AB]^{$\ddagger$} -> A\\ A &<=> B, }\end{align} and in addition to this, also \begin{align}\ce{ B &<=> [BC]^{$\ddagger$} -> C & B &<=> [BD]^{$\ddagger$} -> D\\ C &<=> [BC]^{$\ddagger$} -> B & D &<=> [BD]^{$\ddagger$} -> B\\ B &<=> C & B &<=> D, }\end{align} as well as \begin{align}\ce{ C <=> [BC]^{$\ddagger$} -> & B <=> [BD]^{$\ddagger$} -> D\\ D <=> [BD]^{$\ddagger$} -> & B <=> [BC]^{$\ddagger$} -> C\\ C <=> & B <=> D, }\end{align} and $$\ce{ C <=> A <=> D\\ [AB]^{$\ddagger$} <=> [BC]^{$\ddagger$} <=> [BD]^{$\ddagger$} }.$$

You can use TST to estimate rate constants. $$k = \frac{\mathcal{k}_\mathrm{B} T}{\mathrm{h}} \exp\left\{ −\frac{\Delta^\ddagger{}G^\circ}{\mathcal{R} T}\right\}$$

Since all components have to be in equilibrium, you can predict a ratio between them via Boltzmann statistics, hence: $$\frac{N([BC]^{\ddagger})}{N([BD]^{\ddagger})} = \exp\left\{ −\frac{\Delta^\ddagger{}G^\circ([BC]^{\ddagger})-\Delta^\ddagger{}G^\circ([BD]^{\ddagger})}{\mathcal{R} T}\right\}=\frac{N(C)}{N(D)} $$

The preceding equilibrium does not need to be considered to determine the ratio of the products. However, it is important to note, that there are many assumptions necessary for TST to work. For example, at higher temperatures, anharmonic corrections have to be considered. More crucial is the assumption, that the transition can be described as a translatory movement, i.e. it is treated with classical mechanics.

For a system with a preceding equilibrium, it is well possible, that the TST approximation breaks down completely.

fft - Overlap-Add versus Overlap-Save

What differences or other criteria can be used to help decide between using overlap-add and overlap-save for filtering? Both overlap-add and overlap-save are described as algorithms for doing FFT based fast convolution of data streams with FIR filter kernels. What are the latency, computational efficiency or caching locality (etc.) differences, if any? Or are they the same?

Answer

Essentially, OS is slightly more efficient since it does not require the addition of the overlapping transients. However, you may want to use OA if you need to reuse the FFTs with zero-padding rather than repeated samples.

Here is a quick overview from an article I wrote a while ago

Fast convolution refers to the blockwise use of circular convolution to accomplish linear convolution. Fast convolution can be accomplished by OA or OS methods. OS is also known as “overlap- scrap” . In OA filtering, each signal data block contains only as many samples as allows circular convolution to be equivalent to linear convolution. The signal data block is zero-padded prior to the FFT to prevent the filter impulse response from “wrapping around” the end of the sequence. OA filtering adds the input-on transient from one block with the input-off transient from the previous block. In OS filtering, shown in Figure 1, no zero-padding is performed on the input data, thus the circular convolution is not equivalent to linear convolution. The portions that “wrap around” are useless and discarded. To compensate for this, the last part of the previous input block is used as the beginning of the next block. OS requires no addition of transients, making it faster than OA.

bond - Physical intuition behind negative values for wave function?

So a positive and a positive wave function create a bonding orbital where the probability of finding an electron is summed while a positive and a negative create an anti-bonding orbital with a lower electron probability in the region between them leading to a repulsion. My confusion stems from not having any idea as to what a negative wave function is representing - can anyone give me some physical intuition on how this negative wave function could be correlated to something in reality?

(I tried asking this question on physics.SE but it would seem that in physics you just don't talk about or use the wave function until after you square it)

homework - When Z>1 are repulsive forces dominant or are attractive forces dominant?

According to PVreal = ZRT

If z >1 repulsive forces are dominant or are attractive forces? Different teachers are telling contradictory answers and after referring a few books, I have become more confused.

Points for ATTRACTIVE FORCES are dominant:

• At high pressure the molecules do not strike the walls with full impact as they are dragged back by attractive forces.


• When molecules are farther away from each other(as Vreal > Videal) the attractive forces are dominant.


• Repulsive force are dominant when he molecules are almost in contact .

Points for REPULSIVE FORCES are dominant:

• At high pressure the molecules are close each other that attractive forces are negligible but molecular size is significant.Thus repulsive forces are significant


• As volume of real gas is more than volume of ideal gas , the real gas is more difficult to compress.Thus repulsive forces are dominating.

There was a question where P = 12atm T = 350K and Z = 1.2(after calculation). It was given that repulsive force are dominant.But my teacher said it was wrong and it should be attractive forces.

organic chemistry - Ring contraction in a carbocation due to ring strain and back bonding

Today our teacher told us that the following carbocation rearrangement occurs due to back bonding. I could not really follow what he meant. Can someone please explain what is actually happening during the following carbocation rearrangement, and why it happens?

Answer

The rearrangement has little to do with ring strain and a lot to do with resonance stabilization.

The ring strain in a cyclobutane ring is ~26.3 kcal/mol, while the ring strain in a cyclopropane ring is ~27.5 kcal.mol (reference). This isn't much of a difference, certainly not enough to drive a reaction one way or the other.

The reason that cyclobutyl carbocations generally rearrange to cyclopropylcarbinyl carbocations is due to resonance stabilization. Here are some drawings that may help, if you build a model and look at the model that will help even more. The $\ce{C-C}$ bonds in a cyclopropane ring are approximately $\ce{sp^{3.74}}$ hybridized (see here), said differently, they have a lot of p-character in the bond. In fact, the p-character is so high that a cyclopropane compound will absorb bromine much like an olefin. If that cyclopropane high p-character bond (orbital) can align itself with the p-orbital on the carbocation center, it will stabilize the carbocation, just like a p-orbital on an adjacent double bond (the allyl system) stabilizes a carbocation.

here's another representation

Typically we discuss two conformations of the cyclopropane ring with the carbocation p-orbital, a bisected and a perpendicular conformation. In the bisected conformation the cyclopropane $\ce{C-C}$ bond lies in the same plane as the carbocation p-orbital. The carbocation p-orbital and the $\ce{C-C}$ orbital which resembles a p-orbital (because it is high in p-character) overlap! In the perpendicular conformation, the cyclopropane $\ce{C-H}$ bond is in the same plane as the carbocation p-orbital, the $\ce{C-C}$ bond is not - there is no carbocation stabilization by the cyclopropane ring in this conformation. Molecules where the bisected conformation can be attained show stabilization due to the stabilizing overlap between the carbocation p-orbital and the p-like $\ce{C-C}$ cyclopropane ring bond. Sometimes we use resonance structures such as the following to denote this stabilization.