word choice - Asking a question with "da" and "datta"

We use "desu" and "deshita" to make the polite form and "ka" to make it a question, for example:

Tokyo ga suki desu ka? (Do you like Tokyo?)
Tokyo ga suki deshita ka? (Did you like Tokyo?)

How can I ask the same questions using the dictionary, casual forms of "desu" and "deshita" which are "da" and "datta"?

Should I add "ka" at the end of a sentence? Or just replace "desu" and "deshita" with "da" and "datta"?

P.S. I don't need a long explanation, but rather a simple answer. The information I've found so far is ambiguous.

P.S.2

How common and ok to use this in informal speech (without ka)?:

Tokyo ga suki da/datta?

Just yes or no.

Answer

All of desu, deshita, and datta appear normally before ka.

But da is an exception. In main clauses (like your examples), da is deleted before ka:

 desu    + ka   →　　 desu ka
 deshita + ka   →　deshita ka
 da      + ka   →　　      ka
 datta   + ka   →　　datta ka

In subordinate clauses (like [dare da ka] shiranai), da sometimes appears before ka.

---

Although you want a short answer, you should also consider alternate ways of forming questions, for example using rising intonation, omitting ka. In informal speech, people don't always use the textbook-style question with ka at the end.

organic chemistry - Measuring sweetness

According to my textbook, sucralose is about 500 times sweeter than sucrose. How is this measured? Does one have to use blind taste tests, or is there a quantitative chemical way of measuring sweetness?

Answer

According to Ullmann’s Encyclopedia of Industrial Chemistry, the determination of sweetness intensities requires sensory tests. Therefore, panellists are used, which have to be adapted to the test procedures according to their sensory abilities. The results have to be evaluated on a statistical basis because of individual variations in sweetness perception.

The sweetness intensity factor (or sweetness power) is the factor by which an sucrose solution with equal sweetness is more concentrated than a solution of the sweetener. However, such sweetness intensities depend on the sweetener concentration and the sucrose concentration used for comparison. Commonly used values are often based on comparison with sucrose solutions with a concentration of 0.1 mol/l or similar.

bandwidth - Is there a condition for bandpass sampling?

Consider a signal that has lowest frequency component $F_l$ and highest frequency component $F_h$. According to the theory of bandpass sampling, this signal can be sampled and succesfully recoverd if sampled at a frequency ($F_s$) twice the difference between highest and lowest frequency.

that is, $F_s=2 \cdot \left(F_h-F_l\right)$.

My doubt is , Is there a condition or restriction on $F_h$ and $F_l$ for bandpass sampling?

Answer

It's generally not true that a band pass signal can be sampled and recovered without error if $f_s>2B$ is satisfied, where $B=f_h-f_l$ is the signal's bandwidth. This condition is just necessary but not sufficient.

You have to make sure that the aliased spectra do not overlap. This results in the following condition on the sampling frequency:

$$\frac{2f_h}{n+1}

If Eq. $(1)$ can only be satisfied for $n=0$, you get the familiar Nyquist sampling theorem where $f_s$ must be greater than twice the highest frequency of the signal: $f_s>2f_h$. The lowest possible sampling frequency is obtained for the largest integer $n$ such that $(1)$ is still satisfied. This maximum value of $n$ is given by

$$n_{max}=\left\lfloor\frac{f_l}{B}\right\rfloor\tag{2}$$

where $B=f_h-f_l$ is the bandwidth. Eq. $(2)$ is obtained from $(1)$ by computing the largest value of $n$ such that the left-most term is still less than the right-most term.

As an example, take a band pass signal with $f_l=10\text{ kHz}$ and $f_h=30\text{ kHz}$. From $(2)$, Eq. $(1)$ can only be satisfied for $n=0$, so you have to choose $f_s>2f_h=60\text{ kHz}$, which is a stricter condition than just requiring $f_s>2B=40\text{ kHz}$. However, if $f_l=10\text{ kHz}$ and $f_h=14\text{ kHz}$, the maximum value of $n$ for which $(1)$ is satisfied is $n=2$, which gives you a range $2\cdot 14/3=9.332B=8\text{ kHz}$.

Are there sources that any minute not learned Torah is a sin?

I was recently referred to the Even HaEzel on the Rambam in the 3rd chapter of Hilchos Melachim. Reb Isser Zalman Meltzer (the author) writes there that there is no sin of Bittul Torah for a regular individual (i.e. not a king) if he is doing something to enjoy himself. This would imply that reading a novel, shmoozing, or anything one does for his enjoyment (as long as it's not a sin, obviously) is not considered Bittul Torah.

Are there any Rishonim or Achronim which disagree with this and hold that every minute you can learn and don't is considered Bittul Torah? I would also appreciate any other sources which hold like the Even HaEzel.

physical chemistry - Is there a reason for the mathematical form of the equilibrium constant?

Why are the two molarities multiplied and not added, and why is each raised to the power of the coefficient rather than multiplied by it? What is the reasoning behind this form? Was it simply determined that the probability of reaction was proportionate to both and thus they are multiplied together? I'd like to know whether its form is purely empirical or has a theoretical backing.

Answer

After much research and work, I wrote a little explanation (not that the other answers weren't good, they just weren't well written for someone who didn't know about thermodynamics and other concepts …):

The below results were determined experimentally but this explanation gives some insight into why they are the way they are. Whilst many factors affect the probability of a reaction occurring, and thus the rate, the affect of concentration can be quite easily determined. Consider the following reaction:

$$\ce{a X + b Y -> c Z}$$

The probability of it occurring can be broken down into the probability of the particles reacting in a space, and the probability of them being in a space, thus:

$$P(reaction)=P(\ce{a X} \in \Delta V)\times P(\ce{b Y} \in \Delta V) \times P(\ce{X\bond{->}Y} \in \Delta V)$$

Wherein the probability $P$ of an atom being in certain volume $\Delta V$ is multiplied with the final probability of a collision (here displayed as $\ce{X\bond{->}Y}$) happening in said volume. The probability of a molecule being in a set space can be determined from its concentration:

$$C=\frac nV$$

$$P(\ce{1X} \in \Delta V)= C \times 6.02 \times 10^{23} \times 10^3 \frac{L}{m^3} \times \Delta V$$

This equation assumes that $\Delta V$ is in cubic meters and concentration is in $\mathrm{mol/L}$, however this may not be the case. The main concept is that the probability of one particle being present in some area is proportional to the concentration and some scaling factor:

$$P(\ce{X} \in \Delta V)=K_S×C(\ce{X})$$

Based on basic probability, it is known that the probability of a particles being in the volume is equal to the probability of one particle being in there to the power of $a$. Thus from this, assuming the scaling constant is $K_S$, and that the probability of a reaction occurring at the given temperature in the given space if particles are present is equal to $K_R$, the probability of a reaction occurring based on concentration is as shown below:

$$P(reaction)=K_R K_S^{a+b} [\ce{X}]^a [\ce{Y}]^b$$

If a reversible reaction is considered, the overall direction can be determined by finding the ratio between the rates of the reactions in each direction. Thus the ratio of backward reaction to forward reaction for the below reaction can be identified. (Note the constants on the top and bottoms are different)

$$\ce{a W + b X <=> c Y + d Z}$$

$$K_\mathrm{tot}= \frac{K_{R\ce{A}} K_S^{a+b} [\ce{W}]^a [\ce{X}]^b}{K_{R\ce{B}} K_S^{c+d} [\ce{Y}]^c [\ce{Z}]^d }$$

Dynamic equilibrium is the state for a reversible reaction, in which the rate of both the forward and backward direction is equal and thus the overall change is zero. In this case, the ratio would equal one.

$$1 = \frac{K_{R\ce{A}} K_S^{a+b} [\ce{W}]^a [\ce{X}]^b}{K_{R\ce{B}} K_S^{c+d} [\ce{Y}]^c [\ce{Z}]^d }$$

It can be easier however, to simplify repetitive calculations to just the concentrations, and create a new constant from all the constants shown:

$$\frac{K_{R\ce{B}} K_S^{c+d}}{K_{R\ce{A}} K_S^{a+b} }=\frac{[\ce{W}]^a [\ce{X}]^b}{[\ce{Y}]^c [\ce{Z}]^d }$$

This is the equilibrium constant, although it does change with temperature as the average kinetic energy of particles changes. The calculations made on the concentrations come up with a value called the concentration quotient ($Q$) which is equal to the equilibrium constant when a dynamic equilibrium is reached.

grammar - How to denote the object and the subject of potential form verbs clearly?

The source in where I studied told me that you mark the object of potential form with が particle instead of を particle because potential form is just a state, no actual action is taken. It specifically told me that を can be used but が is better. I know how to make sentences where I'm the subject. 山が登れない : I can't climb the mountain. 彼が言っていることが聞こえない : I can't hear what he is saying. But what if I want to say "He can't eat apples" or "Alice can't go to school" or even "Bob can't kill Tanaka". With が、を、は I could be mistaken in saying "Tanaka can't kill Bob" instead of "Bob can't kill Tanaka". Can が also denote the subject or only the object?

Answer

The particle you are looking for is に.

He can't eat apples.

≒ 彼はりんごを食べられない。
≒ 彼にりんごは食べられない。

Bob can't kill Tanaka.
≒ ボブは田中を殺せない。
≒ ボブに田中は殺せない。

He can't climb this mountain.
≒ 彼はこの山を登れない。
≒ 彼にこの山は登れない。

the reason why he can't climb this mountain
≒ 彼がこの山を登れない理由

≒ 彼にこの山が登れない理由

He can't hear what I am saying.
≒ 彼に私が言っていることは聞こえない。
≒ 彼に私の言っていることは聞こえない。 (ga-no conversion)

Alice can't go to school.
アリスは学校に行けない。
(You cannot say アリスに学校に行けない. Probably because there is already に?)

(Different words are topicalized using は, but I don't know which is "better"...)

EDIT: changed the fifth example above for consistency.

kanji - Is 云 related to 𠫓 in any way?

Depending on the kanji face the left element 言 in multi-element kanjis like 語 is sometimes depicted with 丶 instead of top 一 . It makes me think that the same transformation occurs for 𠫓: 云 changes to 𠫓 in multi-element kanjis. Is this true or not?

Answer

As a fuller answer, no, 云 does not change to 𠫓 in multi-element kanji, and these are not related characters.

The character 云 is a regular kanji / hanzi, originally a pictogram for "cloud" that was later repurposed to spell the homophonic word meaning "to say". (Details on Wiktionary.)The 云 character is used as a component of the larger characters 雲 and 曇, and the 云 character gets somewhat compressed, but the strokes remain essentially the same in shape and number.

The character 𠫓 looks quite similar to 云, depending on the font, but this is a very different character. 𠫓 appears to be an alternative or ancestor form of the ㄊ character in the Zhuyin script, also known as bopomofo, used as an alphabet to phonetically spell out Mandarin. ㄊ is essentially the letter T in bopomofo, and it was derived from an old alternative form of the modern character 突, read as tū in Mandarin. (Details on Wiktionary for ㄊ and for 突.) The chart here shows how to spell various Mandarin sounds using various transcription systems. The sixth column, labeled "Zhuyin Fuhao", contains the bopomofo spellings. The table is in alphabetical order. Scroll down to the section starting with t and you will see the ㄊ character used to spell all of the initial t sounds.

adc - How do you simultaneously undersample and oversample?

"Undersampling" and "Oversampling" are common terms when referring to the choice of sampling frequency for analog to digital data conversion. Is it possible to Undersample and Oversample a waveform at the same time? Examples showing why or why not will be helpful.

The system in question has one real passband analog input and one real passband digital output. This is a practical example of a technique used in digital radio receivers.

Please preface your answer with spoiler notation by typing the following two characters first ">!"

Answer

Undersampling is also known as "bandpass sampling" and "IF sampling". Consider the sampling of an 11 Hz sine wave and a 1 Hz sine wave, both sampled by a 10 Hz sampling clock as in the figure below:

The samples that are produced (the red circles) for both waveforms are identical. Thus the 11 Hz "Intermediate Freuency" or IF has been downconverted in the sampling process to 1 Hz. We can use this technique to undersample a bandpass waveform, and thereby down-convert it at the same time (putting our waveform of interest in the first Nyquist zone: ±$F_s/2$ where $F_s$ is the sampling freqquency). A key requirement that satisfies Nyquist is that the sampling rate used must exceed twice the bandwidth of the signal (note I said bandwidth, not highest frequency!).

That is "Undersampling" as most often described. To oversample a waveform, we sample at a rate significantly higher than the Nyquist criteria, with one motivation to increase the SNR as limited by quantization noise (by sampling hgiher, the same quantization noise is spread over a wider digital frequency, which we can subsequently filter down to our bandwidth of interest and thereby eliminate a significant amount of the noise). Therefore to both undersample and oversample a waveform, we choose a sampling frequency that is significantly larger than the signal bandwidth (thus oversample), and then use a multiple of this sampling clock to down-convert the waveform of interest positioned at a higher IF frequency (undersample).

For example, consider a waveform that occupies 10 KHz of BW that resides at 20.25 MHz. If we sample this with a 10 MSps sampling clock, we would be both undersampling and oversampling at the same time. (The undersampling creates a digital waveform with 10 KHz of BW at 250 KHz, which is oversampled at 10 MSps).

halacha - If a person stops doing the bad action or begins to do the right action, why does he still need to do Teshuvah for a חטא (sin)?

If a person stops doing the bad action or begins to do the right action, why does he still need to do Teshuvah for a חטא (sin)? In other words, why do you need to do Teshuvah if you have stopped the behavior?

chanuka - What was the volume of oil for one day's lighting of the Menorah?

Large jars for storing oil or wine were common in Judah. For 100’s of years, oil and wine were the commodities that were used to pay tribute and taxes. Many storage jars were standardized and may have held 40-50 liters of product. I am curious if the single cruse of oil was of this character.

^{Storage Jars From Ramat Rachel}

In The Talmud Shabbos 21b it says: ולא מצאו אלא פך אחד של שמן שהיה מונח בחותמו של כהן גדול ולא היה בו אלא להדליק יום אחד

And only one cruse of oil was found which lay with the seal of the High Priest and there was only enough for one day’s lighting.

How much oil did the jug contain for one day's lighting?

^{The artifact, a clay seal the size of a button, is inscribed with the Aramaic words meaning “Pure for G-d.”
Photo Credit: Israel Antiquities Authority}

Answer

They used a half of a lug of oil in each candle every night, in order that it would last through the longest night of the year (Menachos 88b). A lug is 6 egg volumes. An egg volume is disputed, but it's accepted to be either around 57 (R' Chaim Naeh) or 100 (Chazon Ish) mL.

So the volume per candle was about 172 or 294 mL, or about 1200 or 2050 mL total.

Correlation between frequency and initial phase estimates using FFT

Why is there a high negative correlation between frequency estimation errors and initial phase estimation errors when measured using FFT? I have a simple code showing this negative correlation. is there a known explanation for that? here is the code

clear all;clc;close all;

%%
T = 0.2;
fs = 500;
f = 200;
ts = 1/fs;
snr = 5;
n = fs*T;
t = linspace(0,T-ts,n);
theta = 0.1;
y = exp(1i*2*pi*(f.*t + theta));

for count = 1:2000
    count;
    yy  =  awgn(y,snr,'measured');
    NFFT = 2^16;
    fVals = fs/NFFT.*[0:NFFT-1];
    X = fft(yy,NFFT)./n;
    plot(abs(X))
    [~,M] = findpeaks(abs(X),'MinPeakheight',0.8);
    measuredAngle = angle(X(M))/2/pi;
    errfreq(count) = fVals(M) - f;

    errph(count) = measuredAngle - theta;
end
cov(errfreq,errph)
corrcoef(errfreq,errph)


ans =
    1.0000   -0.8506
   -0.8506    1.0000

history - Why don't we see magic today?

Throughout Tanach and Talmud, there are numerous recorded uses and practitioners of magic¹.

From Pharaoh's magicians to Shaul's necromancer, and magic cucumbers to were-donkeys, the references are numerous. These are not only brought as stories, but oftentimes as factors in halacha.

My question is, why don't we see magic practiced today? Does it still exist? Is it still theoretically do-able or has "nature changed"? If it's no longer possible, when did this change occur?

---

• ^{1: (When I say "magic", I refer to supernatural powers that stem from the forces of impurity in the world. Commonly referred to as "sorcery" or "'black' magic", it was used to do things that are naturally impossible, such as necromancy, transforming objects into other objects, and "creating" things (as long as they're larger than a barley-corn). Frequently "sheidim" (demons) and their powers were employed in the use of magic. Not to be confused with illusions and illusionists.)}

thermodynamics - Does an irreversible reaction have an equilbrium between reactants and products?

Retrospective analysis 2/13/2017 -- The barium sulfate example is a poor choice. Equilibrium equations should really be defined using activities, and the activity of solid barium sulfate is by definition 1.

A previous question, Is every chemical reaction in equilibrium?, started much discussion. I objected to the answer that Curt F. gave and challenged him to derive the equilibrium reaction for a particular irreversible reaction. He countered with a reply indicating that I should make the specific case a separate question - so here it is. I'm going to change the reaction slightly. Given the following reaction between barium chloride and sodium sulfate, does "the" chemical equilibrium exist?

$$\ce{BaCl2(aq) + Na2SO4(aq) -> BaSO4 v + 2NaCl(aq)}$$

I contend that "the" equilibrum between reactants and products such as $$K_{\text{eq}} = \frac{\ce{[BaSO4][NaCl]^2}}{\ce{[BaCl2][Na2SO4]}}$$ doesn't exist since when the barium sulfate precipitates there could be a microgram or a kilogram as the product. Furthermore adding solid barium sulfate to the product will not shift the reaction to the left.

I'd agree that calling the reaction irreversible and saying that $K_{\text{eq}}$ doesn't exist is a tautology. So given reaction between $\ce{aA + bB}$ to form products $\ce{cC + dD}$ then the reaction is a reversible reaction if the equilibrium such as $$K_{\text{eq}} = \frac{\ce{[C]^{c}[D]^{d}}}{\ce{[A]^{a}[B]^{b}}}$$ exists and if such an equilibrium doesn't exist then it is an irreversible reaction.

There are obviously "some" equilibrium in the reaction, but not "the" equilibrium between products and reactants.

• Water has an autoionization equilibrium and $\ce{H2SO4}$ has two $\mathrm{p}K_\mathrm{a}$'s.


• Barium sulfate has a $K_{\text{sp}}$.


• Also the barium sulfate precipitate isn't static once formed. It is dissolving and reprecipitating at the same rate, but the rates depend on the surface area of the precipitate not the "concentration" (or mass) of the precipitate.

So, if I'm wrong, how do you calculate $K_{\text{eq}}$ for the overall reaction given? Assume you mix $500\mathrm{ml}$ of $0.1$ molar barium chloride with $500\mathrm{ml}$ of $0.1$ molar sodium sulfate. What is $K_{\text{eq}}$?!

Answer

The reaction you are interested in is the precipitation of barium sulfate, a relatively insoluble salt.

The reverse of this reaction is the dissolution of barium sulfate crystals. The dissolution kinetics of barium sulfate have been studied in a variety of systems over the decades. Here are a few links:

• 
  

  Kornicker et al. 1991 reported that barium sulfate dissolution into water reached equilibrium in less than 30 minutes at 25 °C and took about 5 minutes at 60 °C. They also presented a rate law for $\ce{BaSO4}$ dissolution of $r=k A (C_{eq} - C)^2$, where $A$ is the specific area of the barium sulfate crystals, $C_{eq}$ is the equilibrium concentration of barium sulfate, and $C$ the instantaneous concentration of dissolved barium sulfate. This rate law had been used historically (see refs.) but these authors advocate instead for a first-order rate law.

  
  


• 
  
  

  Dove and Czank 1995 also disagreed with second-order rate law of Kornicker et al. and proposed a first-order reaction for $\ce{BaSO4}$, i.e. $r = k A (C_{eq} - C)$.

  
  

I couldn't find any references for barite solubility in sodium chloride solution, but I think it is safe to say that the solubility is finite. Probably the kinetics of dissolution would not be more than an order of magnitude different than in pure water.

Since this dissolution is the reverse of the precipitation reaction you are interested in, and since the literature is clear that dissolution happens at non-zero rates, then both "reverse" reaction and forward reaction must be happening in your system. That sounds like the definition of a dynamic equilibrium to me.

Note the appearance of $A$ in the equations. The surface area of barium sulfate solid involved in the equilibrium determines the kinetics. Usually we assume that the affect of $A$ is the same for dissolution and precipitation kinetics, so that the effects cancel out. This is why we say that the activity of a solid phase is 1 and does not vary. However, the effects of $A$ do not always cancel out. The solubility of nanoparticles of $\ce{BaSO4}$ is probably higher than the solubility of bulk $\ce{SO4}$ for this reason.

Experimentally, one could probe the dynamics of the equilibrium by mixing $\ce{^131BaSO4(s)}$, i.e. radiolabeled barium sulfate, with a saturated solution of $\ce{^138BaSO4(aq)}$. This could be done even in a sodium chloride solution. At regular time intervals, samples of the solution would be taken, which could be filtered to remove any traces of solid particulates, and the levels of the radiotracer that had entered solution could be measured.

I don't know, quantitatively, what the outcome of the experiment would be, especially in sodium chloride solution. But I am 100% confident that at some time scale, probably within tens of minutes, radioactivity would appear in the liquid solution. That indicates that there is an equilibrium.

The relevant equilibrium constant in this case is the $K_{sp}$ for barium sulfate, as was alluded to in both your question and in the comments.

syntax - Is it possible to join directly い-adj + この + noun?

I came across this multiple choice sentence within my homework exercises:

I assume that the correct answer is 気に入った. However, the この demonstrative seems out of place to me. I would rather use just one modifier, either 自然が多い or この like this:

自然が多い町が気に入った。
この町が気に入った。

or, using both 自然か多い and この, I would say something like:

自然が多くて、この町が気に入った。

However, I can't understand why and how come both modifiers are put together directly in this fashion:

自然が多いこの町…

What am I missing here?

Thank you very much

Answer

I can't understand why and how come both modifiers are put together directly in this fashion: 自然が多いこの町...

In the phrase 「自然が多いこの町」, 自然が多い is a relative clause that modifies この町.

［自然が多い］この町
This town ［which has a lot of nature /which is rich in nature］
< Its non-relative version is:
この町は、自然が多い。 This town is rich in nature.

Is it possible to join directly い-adj + この + noun?

Yes. You can say 「自然が多いこの町」, 「美しいその町」, 「かわいいあの子」 etc. but NOT 「自然が多くてこの町」, 「美しくてその町」, 「かわいくてあの子」 etc.

When combining an adjective and a demonstrative determiner, you use the attributive form (連体形) of the adjective, like this...

かわいい子 + あの子 (i-adjective + demonstrative determiner)
→ ◎「かわいいあの子」 but not ☓「かわいくてあの子」

きれいな家 + この家 (na-adjective + demonstrative determiner)
→ ◎「きれいなこの家」 but not ☓「きれいでこの家」

Compare:

自然が多い町 + きれいな町 (i-adjective + na-adjective)
→ ◎「自然が多くてきれいな町」 〇「自然が多いきれいな町」

きれいな町 + 静かな町 (na-adjective + na-adjective)
→ ◎「きれいで静かな街」 〇～△「きれいな静かな街」

優しい人 + かわいい人 (i-adjective + i-adjective)
→ ◎「優しくてかわいい人」 〇～△「優しいかわいい人」　　

What are characteristics of different MR images?

MR tools are used in many sectors such as medicine and mining. MR stands for magnetic resonance and MRI for magnetic resonance imaging. What are characteristics of different MR images? What are typical noise to signal ratios and other important decision factors?

halacha - Can somone admit to being a invalid witness?

If somone admits that they are a invalid witness do we believe them? Does it matter whether they're saying they're invalid because of a Aveira or a bad midda?

biochemistry - How far has "self-organizing chemistry" gone?

This is my first question here so, please, bear with me if I go out of the style or the scope of the SE section. I think I am quite new here, so I am prone to make mistakes.

I am a molecular biologist (not a chemist, that's why I really don't know where to look for references) who wants to know more about the field of very complex chemistry-I mean the possible real experimental designs producing an increase in the number, size and network topology (as a measure of organization) of the chemical system in question. My primarily research interests have been (and still are) in the fields of theoretical, system and synthetic biology with implications for the origins of life so I could say I'm pretty aware of all the progress going on with our attempts of replicating the processes occurring in the living cells and to synthesize "artificial living organisms" related to biology. But what I'm not very aware of (because I'm not a chemist and don't know all the possible places I could look for) are other chemical reaction systems which could possibly lead to complex self-organizing behaviour. By these words I mean reactions able to produce molecules of increased dimensions (both in size and molecular weight), increased number of different reaction products (e.g. reactions generating diversity) and reaction networks able to produce increased organization between the reactions participating in them (e.g. reactions the products of which can interact with each other and form new reaction networks among themselves and even their reaction products can repeat the process generating an increase in the relationships among the reactions of the network).

I am aware of complex self-catalyzing reactions like the Belousov-Zhabotinski's reaction which are far from equilibrium but my point here isn't "only" to generate a system out of equilibrium but to understand what chemicals ("real-world" chemicals we know exist, not some hypothetical compounds we design for our needs in computer database) could potentially form a network of self-organizing reactions which can replicate and enlarge itself if given enough "raw materials". I'm not talking here about replicating biological molecules, In fact the point of my question is can such "self-organizing" networks be created with chemicals that have nothing to od with biomolecules? Can we (even in theory) use some other class (or classes) of organic molecules that could form complex interactions among themselves able to produce a network able to replicate (and even diversify) itself given enough "raw materials", e.g. substrates? Have any such experiments been done (or at least proposed) for any class of molecules different than the biomolecules we know today?

In short, can we use any class (or classes) of organic molecules to design "artificial biochemistry" and has anybody in the chemical literature explored (or even only proposed) such options? Is there any papers (in journals specialized in only in chemistry) exploring (or even only just mentioning) the idea for any particular chemicals (or interactions among classes of chemicals) you are aware of? Has such research ever been done and if so which chemicals it explored? To be as concise as possible has any chemist in any journal ever tried to propose the idea of building an "artificial biochemistry" of any kind?

Thank you very much.

halacha - Are Orthodox Jews opposed to women singing in public, particularly if the woman is singing to a fussy baby in an attempt to soothe it?

My sister lives in Williamsburg, Brooklyn, New York City, and the neighborhood has a large population of Orthodox Jews and, I think, Hassidim (I don't really understand the difference, but that is a subject for another question). She has two kids, both young, and when they were babies, she would sometimes sing to them as she pushed the stroller or rode the bus or subway.

She frequently noticed that when she sang, Orthodox Jewish men would give her nasty looks. She didn't care very much, because it was a public place and there aren't any laws against singing, but I am curious as to why she got the "stink eye".

I heard some vague rumors about Orthodox Judaism and women singing, but I haven't been able to find any conclusive evidence one way or the other. Poking around on this site, I came across this quote:

The Sedei Hemed was relying on the Divrei Heifetz (113b), who "stated that as long as a woman is not singing sensual love songs, and as long as a man does not intend to derive pleasure from her voice, there is no prohibition, such as if she is... singing a lullaby to a baby, or is wailing at a funeral." [4] Rabbi Weinberg also cited the Sefer ha-Eshkol (Hilkhot Tefillah sec. 4 or 7), that listening to a woman sing is prohibited only where there is sexual pleasure. Rabbi Weinberg reasoned that if the Sedei Hemed could permit funeral dirges due to their lacking sexual pleasure, then he could permit Shabbat zemirot on the same grounds. It is obvious that we today can likewise permit by the same logic any song which does not lead to sexual thoughts. Thus, this interpretation that kol ishah is like etzba ketana, i.e. permitted where sexual pleasure is absent, is not only apparent from the simple meaning of Rambam's words, but is also endorsed by Rabbi Yehiel Weinberg.
- Source, cited in this answer

My sister's singing obviously falls under the category of singing a lullaby to a baby, so it would seem that some people agree that there isn't a problem with it.

Is there a reason why Orthodox Jewish men seemed to take offense at my sister singing?

Answer

The Parameters of Kol Isha by Rabbi Howard Jachter addresses this. See the full article for the details, but here are some excerpts:

The Gemara (Berachot 24a) states, “The voice of a woman is Ervah, as the Pasuk [in Shir Hashirim 2:14] states ‘let me hear your voice because your voice is pleasant and appearance attractive.’” Rashi explains that the Pasuk in Shir Hashirim indicates that a woman’s voice is attractive to a man, and is thus prohibited to him. [...]

Both Rav Ovadia Yosef (ibid) and Rav Yehuda Henkin (Teshuvot Bnei Banim 3:127) reject the claim that this prohibition does not apply today since men nowadays are accustomed to hear a woman’s voice. These authorities explain that since the Gemara and Shulchan Aruch codify this prohibition, we do not enjoy the right to abolish it. The Gemara and its commentaries do not even hint at a possibility that this prohibition might not apply if men become habituated to hearing a woman’s voice. Thus, all recognized Poskim agree that the prohibition of Kol Isha applies today.

commentaries - Looking for Passages of harsh criticism in the Shakh

Notwithstanding the fact that the Shakh includes a passage in the introduction to his Nequdat Kesef, claiming that his objections to other scholars are meant only respectfully, I have heard it said that several of his remarks were rather caustic. Can anybody substantiate that claim? Preferably with references to passages within his various commentaries that can then be checked.

history - What has the Holocaust taught us as a people?

The Holocaust was one of the most horrific and important events in our history. What have rabbis said are lessons we should take from it?

I am looking for lessons that should apply to all Jews, particularly those that should apply to our lives and outlook. References to notable speeches or documents addressing this topic would be a welcome addition to any answers, as I'm looking more for consensus or "generally notable" answers (such as from rabbis of major influence), rather than individual opinions.

Answer

The Lubavitcher Rebbe said to many survivors that from the Holocaust we see that one cannot rely on human feelings of morality. Until the Holocaust, many thought that the more cultured one was, the more intellectual one was, the more moral one would be. With the Holocaust, the entire Modern Western culture was shown to false. Scientists and Musicians either watched or actively participated in mass murder.

http://www.chabad.org/library/article_cdo/aid/64888/jewish/The-Rebbe-on-the-Holocaust.htm

halacha - Do women need to count the Omer?

Is counting the Omer nowadays considered a time-bound Mitzva that women are exempt from?

digital communications - Fractional spaced equalizer + timing (clock) recovery

I am trying to figure out how timing recovery is used after equalization (or, being more correct, when the equalizer is in the timing recovery loop), having a T/2 fractional spaced equalizer and using the Gardner algorithm as timing error detector. The usual situation is to have the equalizer output at 1sample/symbol, by having downsampled, or combining the outputs of the even and odd filters. The latter is my case (case (a) in figure). But Gardner algorithm works at 2samples/symbol, so I wonder what I must do with the samples coming out from the even and odd filters. Must I multiplex the outputs of the two filters so I have a 2samples/symbol, as depicted in (b)?

Regards,

grammar - What is the difference between 頃 and とき?

For example in the sentence below:

と言うより、うんと若い頃は公共の場において、注意される側だったはずです。

Rather, when I was younger I'd expect to be the one getting cautioned in public.

How does using 頃 change the meaning from using とき in this sentence and more generally? Thanks.

Answer

By using either 時{とき} or 頃{ころ} you are describing a time relation between (at least) two events, states, or actions (let's say A and B).

With 時 the relation between A and B is closer like English "when", "while", "at the time". With 頃 the relation is more vague like English "around the time", "around".

Just like in English you can also use 頃 to express not only the sheer relation, but also your attitude (you don't remember exact order of actions or their relation, our you don't want to provide such information, so you say "around the time").

With naturally vague expressions ("in youth") 若い頃 or 若い時 it's just a difference in style.

It does not matter if either A or B is a point in time or a period of time. However 頃's vagueness creates a span of time in which the relation between A and B occurs.

organic chemistry - IUPAC naming - choosing the main branch

What are the rules for choosing main branch?

Wikipedia states:

Identification of the parent hydrocarbon chain. This chain must obey the following rules, in order of precedence:

1. It should have the maximum number of substituents of the suffix functional group. By suffix, it is meant that the parent functional group should have a suffix, unlike halogen substituents. If more than one functional group is present, the one with highest precedence should be used.


2. It should have the maximum number of multiple bonds


3. It should have the maximum number of single bonds.


4. It should have the maximum length.

I don't understand how 3 and 4 differ. Which single bonds are we counting? Only carbon-carbon single bonds in the main chain, right?

Also, I heard there is a rule that says if you've two equal length chains, then choose the more substituted one. Why is it not given here?

And now now imagine you've two choices for a chain, like this:

The chemdoodle program gives the name as 2-(1-Hydroxybutyl)-3-methylhexanoic acid .

I simply do not understand why the methyl substituted chain is chosen instead of hydroxy substituted one and how that fits with IUPAC rules given in Wikipedia.

product recommendation - Metzudat Tzion on the Torah

Was there a Metzudat Tzion written on the Torah? If so, does anyone know if it is available online or for sale?

I always loved this commentary as it explained the hard words on the Nach.

Answer

It was written on all of the Prophets and the Writings with the exception of Ruth, Lamentations and Esther. It was not written on Chumash.

Source

grammar - How is 懐く read in this case?

I came across this word in a manga page, on the top right speech bubble. I'm not sure whether this Kanji should be read as なつく or いだく. Moreover, neither of the readings make too much sense to me, should I interpret this phrase as "Aren't you getting too attached?" or something along these lines, since it's (apparently) in the passive form?

inorganic chemistry - What is the chemical structure / hybridization of sulfuric acid?

I was looking at the chemical structure of $\ce{H2SO4}$.

Intuitively, I would have expected this molecule to be square planar in accordance with $p^2d^2$ or $sp^2d$ hybridization, but instead it is shown to be in a tetrahedral geometry consistent with $sp^3$ hybridization. Why is this?

I guess that an alternative way of asking this question is: What is the hybridization of the sulfur atom in $\ce{H2SO4}$?

Answer

It is much easier to explain it on simpler example – $\ce{O3}$ molecule. It has structure of resonance hybrid of $\ce{O=O+-O-}$ and its mirror. And of course, central atom has hybridization state $sp^2$. One bond here is normal covalent bond and another bond is dative: an electron pair is donated onto vacant orbital of $\ce{O}$ atom with all electrons paired. in $\ce{H2SO4}$ molecule to bonds are simple covalent ($\ce{S-OH}$ ones) and two are dative ($\ce{S-O}$ ones). A common concept of electron unpairing to my knowledge is proved brocken by quantum chemistry calculations and spectral experiments for hypervalent compounds of $\ce{P}$ and $\ce{S}$.

A little more interesting example is $\ce{XeF2}$ molecule, where three-atom four-electron bond $\ce{F-Xe-F}$ are formed, that can be think of as reasonance hybrid of structure $\ce{F-Xe+\ F-}$ and its mirror $\ce{F- \ Xe+-F}$

Of course, this scheme is still far from perfect, as reality is much more complicated, but if you do not wish to take course of quantum chemistry, it should be enough. However, I'll recommend to search for "MO LCAO model": it is quite simple and very useful. It is also often used in advanced chemistry books and articles.

Shabbat with time dilation in space

I know there is some discussion in space/planets..

How would you keep shabbos in space?

The Rabbi I asked this shabbat pretty much said the same thing; and you go by Jerusalem time when in doubt.

However, afterwards I was thinking about the laws of relativity and space-time. So based on our current understanding of relativity.. time and space are not always "static".

Example being the faster you move in space the slower time goes.

http://en.wikipedia.org/wiki/Time_dilation

So if we start cruising off to other planets are very high speeds, time would "move slower".. and 25 earth-hours will not equal 25 hours in your spacecraft or whatever it may be.

So how long does shabbat last in space at "warp" speed?

Maybe I watch too much sci-fi.. thanks in advance.

eretz yisrael - How does one travelling from Israel abroad (or vice versa) perform Shnayim Mikra when the parshiyot are out of sync?

Shulchan Aruch 285 codifies the obligation for each individual to read that week's parshah, the text twice and the (Aramaic) translation once.

In some years (e.g. this year, 5779) the parshiyot read in Israel and the Diaspora are one week out of sync for a number of weeks.

What does someone do when travelling from Israel to the Diaspora during this time? Would he have to read the parashah in the Diaspora a second time? Or maybe his reading the week before counts?

What does someone do when travelling from the Diaspora to Israel? Does he need to (at some point) read the parashah that he will miss hearing?

Does it make a difference if one knows that he will be returning home after his trip? Can he stick to his original schedule, despite being out of sync with where he is spending that shabbat?

drugs - Is there any difference between Meprobamate and Equanil?

My textbook mentions Meprobamate and Equanil separately, under Anxiolytic drugs and even provides two (not-so) different structures to back their claim.

However, Wikipedia would beg to differ:

Meprobamate — marketed as Miltown by Wallace Laboratories and Equanil by Wyeth...

Which would naturally imply, that Meprobamate and Equanil are...the same thing. ಠ_ಠ

A quick search with Google Images got me this:

Now this particular textbook I use has, over the years, gained notoriety among several generations of us students as the Mater Omnium Errorum. So in all likelihood, my textbook's the one that's wrong here.

But since I'm not a Pharmacologist, I'd appreciate it if someone could verify if Meprobamate and Equanil are the exact, same, chemical.

I tried Google, but that endeavor wasn't particularly helpful.

Answer

Pharmaceuticals with meprobamate as the active compound are marketed by different companies under different names.

Meprobamate is the International Nonproprietary Name (INN) for the drug.

Whether two pharmeceuticals with the same active components acutally have the same kinetics does depend on additional factors, such as the type of the filler.

analytical chemistry - What is the proton NMR spectrum of p-methoxyphenol?

I think there will be two pairs of doublets, since the hydrogens adjacent to the $\ce{OCH3}$ and those adjacent to the $\ce{OH}$ group will be in different environments. The answer, however, is that there'll be a singlet for 4 Hydrogens.

To give some context, I am extremely unused to the proton NMR of benzene derivatives, and any (introductory) links telling me a bit about it would be appreciated. I'm aware of the theory behind NMR spectrosocopy, the 'n+1' rule, and the ways to tell if two Hydrogens are magnetically equivalent.

て form - What does しまおう mean?

～おう means "let's do something", while てしまう seems to mean completion of an action (A dictionary of basic japanese grammar). In Nihongo so-matome n3 there is this example: 今日は飲んじゃおう! which they translate to I'm going to have a drink!. What exactly does ～てしまおう mean?

I've seen some google results for this question, but they were on reddit and few other websites I can't access from this network.

Answer

The te-form is used for stringing verbs together to combine their meanings:

飲[む]{L} + しまう→飲[んで]{LL} + しまう→飲んでしまう

しまう usually means "to complete something", but what it actually means depends on context. In an answer to an earlier question, its combined meaning with 飲む is explained as "drinking without thinking about consequences". An example of 〜しまう meaning "to complete something" (from naruto's comment):

賞味期限が明日だから、今日飲んでしまおう
It'll expire soon, so better drink it all today

The volitional form is used to mean things like will, invitation, doubt or presumption. Here, しまう is conjugated to the volitional form and because the sentence starts 「今日は」, you can guess that it means the speaker's will to do something.

飲んでしま[う]{L}→飲んでしま[おう]{LL}

If you view 飲んでしまう as "drink unresponsibly", then 飲んでしまおう will become "I'll drink unresponsibly/anyway".

For comparison, volitional without 〜しまう:

飲[む]{L}→飲[もう]{LL} (I'll drink, let's drink)

In Japanese, te-form + aux is often contracted when it connects to frequently used auxiliary verbs like 〜しまう or 〜いる. 飲ん[でしま]{LLL}う becomes 飲ん[じゃ]{LL}う and 言って[い]{L}る becomes 言ってる. The contracted form conjugates to the volitional form just like the longer one.

飲ん[でしま]{LL}おう↔飲ん[じゃ]{LL}おう

minhag - Golden kaftan + high beaver hat?

Normally, those wearing a golden kaftan (with a shtreimel) for shabbes and simchos, will wear a flat beaver hat on weekdays. Are there any of those who wear a high beaver hat instead?

halacha - Can non-Jews utilize the princple of bittul berov?

The concept of bittul berov means that in certain cases, if some non-kosher food gets mixed up in as much kosher food of the same type such that nobody knows which piece is the non-kosher part, the non-kosher bit becomes nullified, making everything acceptable to be eaten. Does this rule apply to non-Jews as well? This could come up in a situation where some food is known to be ever min ha chai, but would be nullified in a greater amount of food that is known to be acceptable for b'nei Noach to eat.

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Inspired by this comment

synagogue - What's a good technique for a not-so-strong person to do [Ashkenazi] Hagbaha?

I've seen many people shy away when asked to do Hagbaha (‏הגבהה‏), thinking themselves too weak. I know for a fact that it doesn't take that much strength to do it correctly, so I'd love to see a writeup of proper technique.

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See also the Sefaradi version of this question.

Answer

My Hagbaha Guidelines

1. Make sure there is an empty chair behind you to sit down on at the end


2. Roll the torah to a seam in the klaf sections. This is not to aid the one performing it, but helps if one pulls the Torah outward with too much force in the process of lifting it up, that a tear will occur on a seam where it can be repaired instead in the middle of a section of klaf.


3. Make sure that it's rolled tight, without a lot of slack, so it doesn't start trying to rollout wider than your arms are wide when you lift it up. Being able to show 4 columns is nice but not required.


4. Make sure your hands are all the way at the top of the handles, in contact with the disks. That way, the torah will rest on your hands, rather than being supported by the friction of your hands on the handles, which is a lot harder on your hands.


5. Pull the Torah off the shulchan about 4-6 inches (of the actual torah body, not just the Atzei Chaim [handles]) to give you leverage to tilt the Torah up against the edge of the shulchan.


6. Bend your knees so you do some of the lifting with your knees while you apply downward pressure on the atzei chayim, lifting the torah off the shulchan into a nearly upright position, still leaning against the shulchan.


7. Now comes the tricky part: This is the moment where strength counts and not just technique. You lift up and away from the shulchan to raise the Torah. It's here where if you're going to stumble it's most likely to happen due to the transfer of weight from the shulchan to your arms/wrists and need to lift it at nearly the same time if you want to look like you know what you're doing. For this I have no magic method to insure success. The more you've bent your knees, the more work your knees can do instead of your arms.


8. Lift it up, - in terms of how high, I think it probably most comfortable to have your hands at about the same level as your shoulder. (I think it's nice to get it all the way over your head but it's not always easy) Once you have stopped lifting, then it should be fairly easy to steady it and wait for the congregation to say V'zot.... Optionally, you may want to turn from side to side once to make sure everyone can see the Torah too.


9. If you turn, make sure to start and stop turning slowly. Otherwise, you'll be fighting the angular momentum of the torah, and it will try to tip out of your hands.



10. Lower just your arms to bring the Torah down to a comfortable height so you can now sit down with it. Once seated, bring your wrists down to your knees to (a) further releive the weight on them, and (b) this usually helps with the gelilah also.


11. Help roll the Torah in a little as well so the klaf doesn't hang too much, and remember to ease up your grip on the Atzei chayim a little because the golel can't turn them if you're still rigidly gripping them. The disks should mostly still be resting on your hands.


12. Hold the Torah throughout the Haftorah if this is the minhag of the shul. Don't try to pass it off to a kid or the golel.

As I said in #6, I do feel there is a strength component too, but technique greatly helps. Therefore, as a rightie, I will not do Hagbaha on heavy sifrei torah until we get several parshiot into the book of B'reishit because a combination of the sheer weight on my left side along with the awkward imbalance of it, makes for a shaky hagbaha. This is one area I prefer not to test my limitations. I would advise anyone who has not had a lot of experience with Hagbaha to take the same into account.

halacha - Can someone [be] tovel accidentally? (Does tovelling need kavanah?)

Does tovelling, either for vessels or a person, require kavanah (intent) to achieve the purification?
Let's say someone went bathing in the river, or for whatever reason just fell in naked; for dishes, someone could have just dropped it.

The entire concept of tumah and taharah seems to be of a spiritual/mental nature, which is why it might seem that you need to intend to purify yourself/dishes. On the other hand, the end result either way is that it was dunked in the water.

history - Why was the Mishna written in Hebrew while the Gemara wasn't?

By the time of the Mishna, people speaking in Aramaic on a day-to-day basis. Nonetheless, R' Yehuda Hanasi wrote the Mishna in Hebrew. So were the Toseftas and the Braisos.

Why?

On the other hand, the Talmud Yerushalmi was written only a few generations later was written in Aramaic.

Why the change?

Answer

Aside from the excellent points that SethJ made in the comments here and to the other related question, we do find R. Yehudah Hanassi himself disparaging the use of Aramaic:

"Rebbi says: in the Land of Israel, why use Syriac [= Aramaic, see Rashi and Tosafos]? Either use the holy language, or Greek" (Sotah 49b and Bava Kamma 83a).

In the latter place, Rashi and Tosafos point out that the dialect of Aramaic spoken at the time in Eretz Yisrael was corrupt as compared to "purer" forms of it spoken elsewhere. So presumably R. Yehudah wouldn't have considered it a fit language for a major literary work.

grammar - trying to learn reading Japanese

I'm learning Japanese and currently I finished the hiragana and katakana charts.

A friend of mine suggested me to start reading something simple to build a vocabulary , so I found a children's story but I'm stuck on trying to read the first phrase:

むかしむかし、あるところに、おじいさんとおばあさんが住んでいました。

How can I learn new words if I can't even understand where a word begins and where it ends ?

I understand that I need to learn grammar because simply knowing hiragana-katakana I can't even separate the words in the phrase.

I tried looking online for Japanese courses but they try to teach basic 'survival phrases' to speak and listen to Japanese people but for now I want to learn hot to read and possibly write in Japanese so could you tell me where I can find good resources, preferably online, that teaches me how to read and write in Japanese and most important thing how to recognise the words in a phrase in a language without spaces.

Answer

If you're reading online then I suggest installing the Rikaichan plugin to your browser. Hovering over the words gives you the meaning and the conjugation of the verbs etc.

The real problem is that you need to learn kanji. Trying to read hiragana with no spaces is a nightmare. The kanji break up the stream into manageable chunks.

Also, become familiar with the particles. These are usually really helpful for delineating where words end.

むかしむかし、あるところに、おじいさんとおばあさんが住んでいました。

Once upon a time, in some place, there lived an old man and an old women

I've highlighted the particles in bold. In this particular sentence, that separates all the words for you.

Finally don't get too disheartened if you struggle with the story. I have a set of children's books which claim to be for beginners but which contain complex grammar and obscure words. You'll get there in the end.

Atomic radius definition disproved - Bohr's model to Schroedinger's wave equation

According to the Schrödinger wave equation, Bohr's model of atomic orbitals is disproved and a new formalism that describes atomic orbitals is introduced.

It follows that the definition of atomic radius - "the distance between the center of the nucleus to the outermost orbit" - doesn't make sense, given that the new theory does not describe atomic orbitals as discrete entities in space.

If an orbital has no exact boundary, then what exactly is the definition of atomic radius and how can I calculate it?

particle って - Meaning of 男性がときどき見せる[これって脈アリサイン]

In the below sentence I translated the first part as "Men sometimes display" but cannot figure out the meaning of [これって脈アリサイン].

男性{だんせい}がときどき見{み}せる[これって脈{みゃく}アリサイン]

Answer

これって”脈アリ”サイン　 ＝Might this be the "there-is-a-chance" sign?

When you want to find a hot spring or a valuable metals, you have to check 水脈 (the hot water pathway underground) or 鉱脈 (metalliferous vein) in advance.

脈がある means that there is such a 脈, which is something good, positive, and welcomed.

Now in the modern colloquial Japanese, "脈アリ" means that there is the possibility that the person likes you, has a positive feeling toward you, has a date with you, or becomes your lover.

男性がときどき見せる[これって脈アリサイン]

[The sign of positive feeling toward you, maybe,] that men show you sometimes

electrochemistry - Why use a salt bridge at all in an electrochemical cell?

I was reading about electrochemical cells and I really don't understand why a salt bridge is needed. Can't you just combine the solutions? I've found a lot of webpages explaining electrochemical cells but strangely enough none of them seem to find this important enough to explain. All thoughts appreciated :)

halacha - Is toothpaste an issue on Shabbat?

I heard that squeezing the toothpaste tube might be considered wringing. Does this have any basis?

Answer

Some say yes, some say no.

The issue is not only wringing, but also whether the paste turning into froth is considered nolad, something new that came to be on Shabbat. For a comprehensive overview of the issues involved and which poskim have ruled what, see Yabia Omer Vol. IV O"H #30, where Rav Ovadia rules that it is permissible to brush your teeth using regular toothpaste on Shabbat.

For a summary of that responsum, here is the Yalkut Yosef 326:14:

Some Poskim ruled that even someone who brushes teeth with toothpaste every day may not do so on Shabbat for various reasons. One reason given for this is that when one brushes, the toothpaste becomes frothy with suds, and therefore this is an act of molid. Another reason given is that vigorous brushing might cause the gums to bleed.

Other Poskim ruled that it is permitted as long as one places the toothpaste directly into one's teeth and not on the toothbrush. Yet other Poskim ruled that even more leniently, permitting one to brush one's teeth on Shabbat just as one does on the weekdays and with regular toothpaste. They explained that it is not necessary to use special, liquid toothpaste, since brushing teeth is not an act of the melakha of memare'ah, nor is it an act of molid. Furthermore, this is not forbidden as an example of using medical treatments on Shabbat.

In practice, anyone who would feel uncomfortable if he does not brush his teeth on Shabbat because of bad breath or some other reason may brush them. This applies, however, only to someone who regularly brushes his teeth so that he will not necessarily cause his gums to bleed on Shabbat.

transition metals - Why is enthalpy of atomization of Mn exceptionally low?

Transition elements usually have high values, especially so for greater number of unpaired electrons. Why the exception here?

learning - Does anyone have advice on how to get over/through/around the intermediate language plateau? (Self-learner)

How do you get through this? Especially in regards to reading. How do you practice reading at beyond the beginner level (No little black sambo's or whatever other children's books like I found in the local free bin when I was a teenager) when a light novel is still light years beyond me. And a newspaper is just as hard.

I know around 600-800 kanji, and I can pass the level 2 listening JLPT, though I'm not quite there for reading and grammar (I can barely pass level 3 on those), but I feel like I've been spinning my wheels and not getting anywhere for a long time now.

What are good techniques for learning to read in Japanese? Especially for self-taught students of Japanese.

What are techniques to push through the vast wasteland that is "intermediate"?

Answer

• Study comprehensive grammars with lots of examples. Not textbooks. These are the best (there are three).


• use a mnemonic kanji learning system. This one is awesome. Learning meaning and reading separate is fine because it is more efficient. Utilize similarities between kanji as much as possible, as relating knowledge to new ideas will make learning much faster.


• Go to Japan, and stay there for a long time. Talk to Japanese people as much as possible.


• Make a regular study period of at least an hour every day. Never skip. Read materials that you are interested in, and write down the words you don't know. You can look up grammar in those books (organized alphabetically) or ask here.


• Throughout the day, while walking or whatever, take out that list and study it. You can keep a list of Kanji to study, too.


• Another great use of walking time is repeating difficult phrases. Tongue twisters (早口言葉) found on the internet or any phrase that you have trouble saying is fine. Say it a thousand times on the way to work and make sure it's fluent.



• Never settle for "kinda" understanding something. Be thorough in studying out every new vocab, kanji or grammar that you find.

everyday chemistry - Why do some gases liquefy easily under pressure and normal room temperature?

Is this a combination of Boyle's and Charles' Laws or simply one of them?

I'm confused as to which applies. I don't feel I fully understand the implications of both laws individually and I'm wondering why it's easy to take a gas like butane and liquefy it under pressure at "normal" temperatures and why other gases need to be cooled to extremely low temperatures or very high pressures to liquefy.

I understand that temperature, pressure and volume are all related, I just don't know which rules apply and how and how they all interact. How do these laws apply to changes of state from gas to liquid?

I'm sure this is stuff I forgot from 10th grade but I'd love to hear an explanation again.

tanach - Evidences for Messiah to redeem people

I read that the awaited Messiah will cause to re-establish the Kingdom of God and redeem the Israelites so what are the evidences in Tanach and Talmud to support this claim ?

mourning aveilus - Would an avel who visits the Kotel need to do an extra tearing?

In the back of a siddur, I saw one of the halachot state that one who has not visited the Kotel ("Western Wall" in Jerusalem) within 30 days should tear his clothes when he comes to the Kotel.

Let's say an avel (mourner) can't get a minyan in his home. He goes to the Kotel to pray with a minyan, there. An avel would already be wearing torn clothes during his week of shiva. If he goes to the Kotel would he need to tear again (same shirt, or perhaps wear a different shirt), or is the torn shirt that he is already wearing for his own aveilut sufficient?

Answer

Wearing torn clothing isn't the command. A tear for one event doesn't help at all for another later event. Even if another relative passes away during Shiva he would need to tear again (YD 340:21-23; see there for details about when one can add on to an existing tear and when one tear can count for two simultaneous events).

organic chemistry - Clarification on the $mathrm{S_N2}$ mechanism

The question is about the specifics of the $\mathrm{S_N2}$ mechanism (nucleophilic bi-molecular substitution).

(Source: Wikipedia)

As we know that in this reaction the nucelophile ($\ce{Nu-}$) approaches the molecule. The main step (According to the molecular orbital theory) of the reaction is that the the nucleophile bonds with its lone pair in the anti-bonding molecular orbital (ABMO) of the central carbon atom. As this happens the leaving group ($\ce{Lg}$) is kicked off by gradual weakening of the $\ce{C-Lg}$ bond. Now the thing that bothers me here is:

Why does carbon prefer to add electrons in its ABMO? As the $\ce{Lg}$ has to bond with the carbon atom there has to be an increase in bond order whereas, while electrons are pushed into the ABMO it clearly decreases the bond order, which directly indicates the instability of bond formation.
The main question being, what makes the reaction favourable? What is the 'driving force'? Why does it take place when there is a decrease in bond order?

Answer

Why does carbon prefer to add electrons in its ABMO?

Well, preferring is a bit of a strong word. Orbital interactions that are productive towards forming and breaking bonds can only happen between a filled and an empty orbital. Therefore, you should always identify a HOMO (highest occupied molecular orbital) and a LUMO (lowest unoccupied molecular orbital), compare their energies and thereby decide whether they are able to react.

Here, the lowest unoccupied orbital of the carbon compound is typically the $\ce{C-Lg}$ antibonding $\unicode{x3c3}^*$ orbital — because that is the antibonding orbital belonging to the leaving group (I am aware that this is circular reasoning). Its energy is also somewhat favourable with respect to the energy of the filled lone pair orbital of the nucleophile meaning the two can react well.

As the $\ce{Lg}$ has to bond with the carbon atom there has to be an increase in bond order …

No. Why?

electrons are pushed into the ABMO it clearly decreases the bond order …

To specify: decreases the bond order *of the $\ce{C-Lg}$ bond.

which directly indicates the instability of bond formation.

No, it doesn’t. It only indicates that the $\ce{C-Lg}$ bond is being broken and the leaving group is getting ready to leave.

Why does it take place when there is a decrease in bond order?

You fail to see that while the bond order of the $\ce{C-Lg}$ bond is steadily decreasing the bond order of the $\ce{C-Nu}$ bond is steadily increasing. At any point in time on the reaction coordinate, the sum of both bond orders is $1$.

The main question being, what makes the reaction favourable? What is the 'driving force'?

Two things: the formation of a more stable $\ce{C-X}$ bond (meaning that $\ce{C-Nu}$ is a stronger bond than $\ce{C-Lg}$) and the liberation of a better stabilised anionic species $\ce{Lg-}$ as opposed to $\ce{Nu-}$.

Actually, in many $\mathrm{S_N2}$ reactions only one of those two factors is the driving force. And while we tend to write $\ce{Nu-}$ and $\ce{Lg-}$, we should always remember that these compounds need not be anions. For example, $\ce{H2O}$ is a very good leaving group (after alcohols have been protonated) but not an anion. The same is true for $\ce{N2}$ (from a diazonium salt). And equally, water or ammonia can be nucleophiles although they are neutral compounds.

So it can well be that the reaction is only driven by the liberation of a neutral compound and thereby the removal of charges (as would be the case in the $\mathrm{S_N2}$ reaction of iodide and a protonated alcohol when $\ce{HI}$ is used to generate iodoalkanes). It might also be that the reaction is driven only by the stronger $\ce{C-Nu}$ bond — or by the breaking of the weaker $\ce{C-Lg}$ bond as would be the case in nucleophilic substitutions with tosylate ($\ce{Me-C6H4-SO3-}$) or mesylate ($\ce{MeSO3-}$) as leaving groups.

There is not one same truth for all $\mathrm{S_N2}$ reactions.

statistical mechanics - Probability of finding a molecule in the ground vibrational level

I wanted to estimate the probability of finding a molecule in the ground vibrational level using the Boltzmann distribution:

$$ p_i = \frac{e^{-\epsilon_i/kT}}{\sum_{i=0}^{N}e^{-\epsilon_i/kT}} $$

Using the quantum harmonic oscillator as a model for the energy

$$ \epsilon_i = h\nu (i+1/2) =/i=0/=\frac{h\nu}{2} $$

In the Boltzmann distribution, we have the state of interest divided by the sum of all possible states. But how should I treat the denominator?

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Searching a bit I found that the analytical expression for this geometric series is ($i$ not imaginary number)

$$ \sum_{i=0}^{N}e^{-i h\nu/kT} = \frac{1}{1 - e^{h\nu/kT}} $$

However, is this using a shifted energy scale for the harmonic potential? In that the vibrational energies are $0$, $h\nu$, $2h\nu$, ..., and not $\frac{1}{2}h\nu$, $\frac{3}{2}h\nu$, $\frac{5}{2}h\nu$, ...? Should I make sure I use the same energy scale for the nominator and denominator in the Boltzmann distribution?

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Doing what porphyrin suggested, I get

$$ \sum_{i=0}^{\infty} e^{-h\nu(i+\frac{1}{2})/kT} = e^{-h\nu/kT} \sum_{i=0}^{\infty} e^{- ih\nu/kT} $$

Expanding the four first terms

$$ e^{-h\nu/kT} \sum_{i=0}^{\infty} e^{- ih\nu/kT} = (e^{-h\nu/kT} \cdot 1) + (e^{-h\nu/kT} \cdot e^{-h\nu/kT}) + (e^{-h\nu/kT} \cdot e^{-2h\nu/kT}) + (e^{-h\nu/kT} \cdot e^{-3h\nu/kT}) \\ = e^{-h\nu/kT} + e^{-2h\nu/kT} + e^{-3h\nu/kT} + e^{-4h\nu/kT} = \sum_{1}^{\infty}e^{-n\cdot h\nu/kT} $$

which has an analytical expression for the converged value, right?

Answer

You're on the right track.

Also, using $i$ as an index can be confusing some times because it can be confused with the imaginary number; however, here it should not present a problem. As a matter of habbit however, I like to use $j$ or $n$ or something else..there are only so many letters in the alphabet.

The sum in the denominator is called the partition function, and has the form

$$Z = \sum_{j}e^{-\frac{\epsilon_j}{kT}}$$

For the harmonic, oscillator $\epsilon_j = (\frac{1}{2}+j)\hbar \omega$ for $j \in \{ 0,1,2.. \}$

Note that $\epsilon_0 \neq 0$ there exists a zero point energy.

Let's write out a few terms $$Z = e^{-\frac{\hbar \omega/2}{kT}} + e^{-\frac{\hbar \omega3/2}{kT}} + e^{-\frac{\hbar \omega5/2}{kT}} +..... $$

factoring out $e^{-\frac{\hbar \omega/2}{kT}}$

$$Z = e^{-\frac{\hbar \omega/2}{kT}} \left( 1+ e^{-\frac{\hbar \omega}{kT}} + e^{-\frac{2\hbar \omega}{kT}} +.....\right) $$

The sum in the bracket takes the form of a geometric series whose sum converges as shown below $$1+x+x^2+... = \frac{1}{(1-x)} $$ herein, $ x \equiv e^{-\frac{\hbar\omega}{kT}} $

Putting all of this together

$$Z = \frac{e^{-\frac{\hbar \omega/2}{kT}}}{(1-e^{-\frac{\hbar\omega}{kT}})}$$

Now, $$p_0 = \frac{e^{-\epsilon_0/kT}}{Z} = \frac{e^{-\frac{\hbar \omega/2}{kT}}}{Z} = \frac{e^{-\frac{\hbar \omega/2}{kT}}}{\frac{e^{-\frac{\hbar \omega/2}{kT}}}{(1-e^{-\frac{\hbar\omega}{kT}})}} = (1-e^{-\frac{\hbar\omega}{kT}}) $$

translation - て form followed by て, 「見てて」

I have heard a couple of times now the て form of a verb followed by て (or perhaps it was って?) used as an imperative. Some examples are 見てて and 黙ってて, when asking someone to look and be quiet respectively.

I am also aware of this question, but in that circumstance, the listener is being asked to "stay waiting" as I understand. However, in the case of 見てて, this interpretation seems odd when all that's needed is a quick look. (A child was asking the father to look at a toy)

I assume the phrase is still a contraction of 見ていて, but how should I understand it, and what is the difference between this and 見て? What about other verbs?

Edit

Here is an example usage of 見てて in a similar situation.

Answer

I think you have almost grasped the "tournure" and I have few to contribute, but...

I assume the phrase is still a contraction of 見ていて

That's correct. As for the example, the girl in the film says おとう、見てて. That corresponds to "Look at me (doing this), Dad."

it would mean something like "check out this website (and continue doing so for a nontrivial period of time)"? Similarly, 黙ってて would mean "be quiet, and stay quiet"?

Yes, I guess so. Of course, you need context to be more precise, but I can hardly think of other possibilities.

halacha - Can one use a gas grill for both meat and dairy (with lots of other caveats)

The basic question is, can the same grill be used for meat and milk. But this question has a few sub-questions/caveats and cases that I'm curious about.

1- I'll assume that the same grill grates cannot be used for both meat and dairy. However, if one were to remove the grates (and any drip-pans etc), and clean the grill thoroughly, could one then use that grill for dairy (pizza for example)? Would one have to wait between the meat and dairy cooking?

2- I'll assume that cooking fish on the same grate as meat, even not at the same time, is not allowed. However, can one cook fish on a separate grate? Would you even need to clean the grill? Would you have to wait in between? Is there a difference if the grill is covered or uncovered?

3- I'll assume that vegetables cooked on the same grate as meat can never be eaten with dairy, even if they were not on the grill at the same moment. However, if one uses separate grates, can one eat the vegetables with dairy?

4- Is there a way of kashering a grill to the point where even the grates do not need to be replaced? For example, could one conceivably leave the grill on for a while, and then immediately use the grill for dairy/fish/food expected to be eaten with dairy?

5- Reverse the questions. Once someone used a grill for pizza, what must be done before using it for meat? Once someone used a grill for fish, what must be done before using it for dairy?

(If relevant, assume all questions are asked relative to generally accepted practice of Orthodox Judaism, please source all answers and note differences between Ashkenazi and Sephardic opinions)

halacha - May a man become a gynecologist?

Is there any discussion among the halachic authorities as to whether or not a man can choose to pursue a medical career in gynaecology? The issue that I would presume exists is that unlike other parts of medicine the focus here is solely on the female reproductive system there may be problems of tznius. I have also read anecdotal evidence that there is an increased likelihood of sexual misconduct among those doctors.

Is there any halachic discussion as to the appropriateness (or not) of a man becoming a gynecologist?

hashkafah philosophy - Moral Culpability in the Garden

Did Adam and Eve have moral culpability in the Garden before they ate from the tree of knowledge of Good and Evil? It would seem that they were like small children in that sense, they were amoral--not because they did not care for morality, but because they had no concept of it.

If Adam and Eve had no concept of morality, of right and wrong, how is it fair to punish them for their behavior? Prior to eating the apple, Adam could not have said: "Eve, do not ask me to do that, it would be wrong." He had no idea it would be wrong to eat the apple.

It seems pretty central to morality that the agent must be aware of what he/she is doing for moral blame to fall upon them. If they were morally blame-less for eating the apple, then why the painful punishments?

tefilla - Which part of שחרית would you identify as "prayer"?

What part of שחרית would you identify as "prayer"?

parshanut torah comment - The Meaning of Aishdas

I have read that Aishdas (Deut. 33:2) means "fiery law" or something of the sort. However, doesn't the word das with the meaning of law/religion come from Persian (i.e. did not have the meaning of law in Biblical times)? Can someone help me out here?

creation - Is a "Golem" the same thing as a person created through Sefer Yetzirah?

Is a "Golem" the same thing as a person created through Sefer Yetzirah? Please be clear with your answer.

halacha - Self-defense (in a case of one's capital, not a capital case)

There is a well known rule that if A is threatening B's life, B may kill A, if necessary, to prevent that.

Is there any such rule in non-capital cases? Specifically:

• If A is threatening B with physical injury, can B injure A to prevent it?


• If A is threatening B with monetary harm, can B financially injure A to prevent it?

If so, then:

1. Does B's injury of A have to be proportionate to what A would have otherwise done? For example, if A is seeking to inflict $100's worth of damage on B's possessions, can B, to prevent that, inflict $100's worth of damage on A's? $100.25's worth? $1,000,000's worth? Likewise, if A is seeking to damage B's person to a certain degree (monetary degree in terms of nezek, or to some degree as defined by some other standard), can B damage A to the same degree? to a higher degree?


2. Would B have any liability to A thereafter (in bes din)?

Of course, for practical guidance in any specific case, each person should consult his rabbi; this question is about general rules.

internet - Is this really in the Talmud?

I've seen this before on anti-semetic sites - is it really in the Talmud?

Extracts from the Jewish text the Talmud

"Just the Jews are humans, the non-Jews are no humans, but cattle" Kerithuth 6b, page 78, Jebhammoth 61

"The non-Jews have been created to serve the Jews as slaves" Midrasch Talpioth 225

"Sexual intercourse with non-Jews is like sexual intercourse with animals" Kethuboth 3b

"The non-Jews have to be avoided even more than sick pigs" Orach Chaiim 57, 6a

"The birth rate of non-Jews has to be suppressed massively" Zohar 11,4b

"As you replace lost cows and donkeys, so you shall replace non-Jews" Lore Dea 377, 1

Answer

rosends got it right.

But I'll go through the quotes anyhow.

A. Non-Jews aren't humans. Keritot 6b.

There are a handful of specific technical laws in the Bible that pertain to "an adam" which the Talmud interprets as "Jews only"; for a non-Jew we are more lenient. The idea simply is that most of the Torah's laws were intended for a Jewish audience, so sometimes "an adam" was taken for granted to mean "a Jew." NOWHERE do we ever find "you can kill/rob/rape/disgrace etc. a non-Jew because they're not human." Instead, some technical laws were intended on a focus within the Jewish population. For instance:

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  If you use the special formula for Temple oil and apply it to a commoner, not a high priest, you get in really big trouble with G-d. But you only get in really big trouble if you apply it to a Jewish commoner. If you apply the oil to a non-Jew, you don't get in big trouble. That's the instance in Keritot 6b. (As for why the distinction: the concern is that you'd try to make everyone "ritually special", which would make no one ritually special, and would ruin the centralization. This became a problem in Jewish history as seen in the books of Judges and Kings -- people would set up their own idolatrous pseudo-Temples wherever they wanted, and find whatever pseudo-priests they could.) The Torah really wasn't concerned about what non-Jews do with it.

  
  
  


• 
  

  Suppose a Jewish woman cheats on her husband and has a child from that union. If the "boyfriend" was Jewish, we call the child a mamzer and they're prohibited from marrying into the mainstream. If the boyfriend wasn't Jewish, the child is a regular Jew and can marry normally. Again, presumably the Torah was more concerned with what people were more likely to do, which is mess up within their community, and therefore bothered to add a penalty in that case.

  
  

B. Something from Medrish Talpiot

A non-authoritative work that was done long after the Talmud. I don't know what it says and frankly I don't care. You also have to realize that many medieval works were done around the time of the Crusades with massive Christian persecution, so the message many Jews needed to hear to stay alive was an "us good, them bad" one. Update: Fred checked the Midrash Talpiot and couldn't find this quotation anyhow. Thank you Fred!

C. Relations with non-Jews. Ketubot 3b.

Close, but no cigar. It's not in the Talmud there, but something similar to it appears in one of the commentaries (Tosafot, a family of rabbis in France in the 1100s) there. Again it's a technical discussion about which penalties apply if someone has relations with someone they shouldn't (see A above); the Torah was more concerned about applying penalties in the common case, which was people messing up with their neighbors, not a far-away foreigner.

D. Avoid non-Jews. Orach Chaim "57,6a"

Orach Chaim is a section of Shulchan Aruch, a work that was done a thousand years after the Talmud. Chapter 57 is a rather cut-and-dry piece about the morning prayers, and it has only two subsections; nothing at all to do with non-Jews here. So I have no idea what this one is about.

E. Birthrate -- Zohar.

I have no idea. The Zohar was "discovered" in the 1200s. It's not the Talmud. Fred checked the Zohar anyhow and couldn't find it. This one also is totally bizarre in light of Deut. 7:7: "It was not because you had greater numbers than all the other nations that God embraced you and chose you; you are among the smallest of all the nations."

F. Replacement -- "Lore Dea."

I think you mean "Yoreh Deah" (and if you're making mistakes like that, you really don't know what you're talking about, do you?) That's another section of Shulchan Aruch. It's actually talking about viewing slaves (not "all non-Jews") as property that should be replaced. It's a troubling statement, and it falls into the broader question about how Judaism allowed slavery a very long time ago.

electrochemistry - Deriving a reduction potential from two other reduction potentials

Given:

\begin{align} \ce{Co^{3+}(aq) + e- &-> Co^{2+}(aq)} & E° &= \pu{+1.82 V} \\ \ce{Co^{2+}(aq) + 2e- &-> Co(s)} & E° &= \pu{-0.28 V} \end{align}

what is the standard reduction potential for $\ce{Co^{3+}(aq) +3e- -> Co(s)}$?

If I add up these two half-equations to get the desired half-equation, I get $E^\circ = \pu{+1.54 V}$. But the correct answer is $\pu{+ 0.42 V}$!

Am I missing something?

blessing - Why is the wording of the beracha upon shaking the arba minim only on lulav?

The beracha upon shaking the arba minim is 'על נטילת לולב'? Why is the focus on the lulav specifically rather than a more general blessing like 'על נטילת ארבעה מינים'?

loanwords - Is one transcription of "Andrew" more standard than another?

I recently looked at the disambiguation page for Andrew on the Japanese Wikipedia, and found that there were several "アンドルー"s, and several "アンドリュー"s.

I couldn't discern any trend that one form tended to be from an earlier time period and the latter was from a later time period, or that one form was from certain languages and the other was from other languages.

Are both forms considered normal transcriptions of "Andrew", or is one form considered more normal than the other?

Answer

Check the top line on Wikipedia:

日本ではしばしば習慣的にアンドリューとも表記されるが、英語での発音は [ˈændruː] であり決して r の後に /j/ を付けて発音されることはない。

"It is frequently habitually written 'andoryuu' in Japan, but as a matter of fact the English has no 'y' sound after the R." So, "andoryuu" is the habit but "andoruu" is supposed to be more accurate. Does it sound right to you?

I notice as well that アンドルー・ロイド・ウェバー has had his name changed to アンドリュー on his Wiki page, so I'm thinking that "andoruu" is sometimes corrected to "andoryuu" by well meaning folks, but someone on Wikipedia is annoyed by this because it doesn't match up to their imaginary perfect representation of IPA in katakana.

medicine - Unconsciousness in Jewish Thought

Yes, that pun was intended.

We know that sleep is 1/60 of death, and dreaming is 1/60 of prophecy (Brachos 57b). This is because it's a partial death, in which a piece of the Neshamah leaves the body - just enough to be noticeable, but not too much. Likewise, the Neshamah gets a glimpse of the future during its out of body experience, which we see as dreams (Maharsha).

What happens when one goes into a coma? The mind is totally unconscious; there are no dreams in a coma. Furthermore, it's not at all what Hollywood would have you believe: one does not wake up from a coma feeling refreshed. Does this mean that the Neshamah is trapped inside the body like it is when a person is awake? Does a larger portion, or all of, the Neshamah leave the body, and it's too much to be refreshed or dream?

Answer

After doing a bit of looking into the topic, I think I may have found some sources to answer this question. I'll wait until others comment, to hear what they think, before I select this as the correct answer.

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As discussed in this Chabad article and this question, there are five levels of the soul: nefesh, ruach, neshamah, chaya, and yechidah. As mentioned in both of those sources, the neshamah refers to the thinking part of a person, the ruach is the emotional part of a person, and the nefesh is the life force and desires of a person.

When we drift off into the subconscious, we still are able to think on some level. It's for this reason that we're able to interpret the 1/60 of prophecy contained in dreams. This is because not all of the neshamah has left the body - 59/60 of it remains. But in the unconscious state, the brain focuses its energies on the basic needs in order to keep the body alive. There is no thinking done whatsoever. It's like the entire neshamah has left and no thinking is occurring, in order to leave the nefesh to keep the body alive.

Another proof can be brought from Bava Basra 10a:

Yosef the son of R' Yehoshua had been ill and fell into a trance. His father asked him: "What did you see?" He replied, "I saw a world upside down, the upper below and the lower above." He said to him, "You saw a well regulated world."

From the fact that he saw a higher level of Olam HaEmes than one sees in dreams, which reflect but 1/60 of what the neshamah normally sees, it's quite possible that more of his neshamah went up to Shamayim, and thus he was able to bring back a clearer picture.

TL;DR: If I am correct, the entire neshamah leaves the body, and one is all but dead in the unconscious state.