Wednesday, July 31, 2019

discrete signals - Understanding the Windowing Method in PSD Calculation



I have some issues understanding the use of a window (it doesn't matter which one) to calculate the Power Spectral Density of a signal.


For example say I want to use the hann window, with $N = 1024$, knowing that my signal length is $X > N$, $X$ is arbitrary.


How should I calculate the PSD :


Take 1024 samples from the signal, multiply them in the time domain with window function. Then transform those 1024 time values. After that take the next 1024 samples of the signal and do the same thing, then add the result to the spectrum that I got the first time and so on?


That's the way I understood this, but to be honest I'm not sure that it is a right way?



Answer



I don't really understand what do you mean by multiply them in the time domain and multiply them with window function. I think that you are trying to implement the Welch's PSD calculation. If so, steps should be:



  • Split your data into possibly overlapping segments of length $N$

  • Preferably remove the mean of each segment.


  • Window each of the segments by multiplying with window function $w$ of your choice.

  • Compute the Fourier Spectrum of such segment (you just calculated the modified periodogram)

  • Continue until all segments are processed, then average all of them. This will produce your PSD.

  • The last step is to scale your average by a proper factor.


For more details I am suggesting you refer to this document (Chapter 12 should be interesting for you, as well as previous ones):



Heinzel G., et al. - Spectrum and spectral density estimation by the DFT, including a comprehensive list of window functions and some new flat-top windows



Possibly you can compare your results with pwelch function. For more theory, you can refer here (guys from Mathworks were most likely using this book). If you are using MATLAB, then this code should be helpful - very quick and dirty comparison I used years ago for pwelch. No overlapping, just two segments, but I am sure it could be a good starting point for you.



% Generate the random signal
N = 2048;
x = randn(2*N,1);
% Create the window and precompute scale
win = hann(N);
s_win = norm(win,2)^2;
% Calculate the Welch's PSD
Pxx_welch = pwelch(x,win,0,N);
% Initialize the variable to store all segments
Pxx = zeros(N,2);

for k = 0:1
x1 = x(1+k*N:(k+1)*N); % Take a segment
xw = x1.*win; % Multiply by window
% Square the magnitude and scale
Pxx(:,k+1) = abs(fft(xw)).^2./s_win;
end
% Average all segments
Pxx = mean(Pxx,2);
% Normalize accordingly to pwelch
Pxx = Pxx./(2*pi);

% Take only first half of frequencies
Pxx = Pxx(1:length(Pxx)/2+1);
% Preserve the energy (we just chopped-off half of spectrum), but do not
% modify first frequency bin as it is unique (mean value of a signal)
Pxx(2:end-1) = 2*Pxx(2:end-1);
% Plot the difference between two PSD's
plot(abs(Pxx_welch-Pxx))
title('Difference between pwelch and implementation')

Below is the plot of the difference between pwelch and the above implementation. One might notice that it is purely related to a round-off error.



enter image description here


halacha - Which actions are prohibited even to save a life?


I know that many commandments, e.g. keeping Shabbat, not lying, etc., must be violated if doing so is necessary to save a life.


For which commandments is this not true? Does it ever matter how many lives it saves (for example, could you kill one person to save the lives of five), or whether or not it is your own life?



Answer



See Rambam Hilchot Yesodei Hatorah Chapter 5


Basically:


The Torah says (Vayikra 18:5) "which a man will perform and live by them". Our Rabbis learn that this means a person doesn't have to kill himself to perform Mitzvot. The exception to this rule are "The Big Three": idol worship, forbidden sexual relations, and murder. If someone gives him a choice to transgress these or die, he must choose to die. There are however, caveats, this does not apply across the board.


With Regard to other Mitzvot (not the Big Three):





  • Important note: The Rambam is of the opinion that a person may not sacrifice his life for any Mitzvah that is not the Big Three. The Kesef Mishna (commentary on the Rambam) says that many Poskim say that one can choose to sacrifice himself, even if he doesn't have to Halachically.




  • In a regular time (i.e. when there is no decree against Jewish practice)




    • If the Jew is being told to transgress the commandments for the non-Jew's benefit (i.e. selfish reasons), he can transgress the commandment.




    • If the Jew is being told to transgress the commandment, because he wants the Jew to go against G-d's Torah (i.e. ideological reasons), it depends:





      • if it is in public (i.e. ten Jewish witnesses), he must give up his life




      • if it is in private, he should transgress







    • According to the Nimukei Yosef (brought in the aforementioned Kesef Mishna), even the Rambam would agree that a great and holy man may choose to give up his life for any Mitzvah, in order to make a point to the Jews of that generation about the holiness of all the precepts in the Torah.






  • In a time of decree against Jewish practice




    • One must give up his life for any commandment, whether it is public or private.





    • The Talmud (Sanhedrin 74A see English here) adds that even if the decree is against a Jewish practice that is not a Mitzvah (e.g. changing the color of your shoe strap to conform to non-Jewish styles), one must give up their life rather than comply.








With regards to giving up one person to save many, the Rambam (Halacha 5) generally prohibits it unless the Jews are asked to give up a specific person who was already sentenced to die by the hands of a Jewish court.


It does not matter how many lives you would be saving by giving up the one person, you are not allowed to do it.


And see Halachot 6-8 for which prohibitions are allowed to be transgressed in order to save someones life.



Modelling propagation of sound wave by particle simulation


How might one model the propagation of a sound wave through a 3D environment with obstacles in it?


My initial thought would be to use freely moving particles that repel one another; with sufficiently many particles I see no reason why the simulation wouldn't work.


However, if any particle could collide with any other then this introduces a huge complexity hit.


So I'm wondering whether the particles could be effectively anchored on a sphere packed lattice (dodecahedron?), so each particle has 18 neighbours. (you could think of placing one tennis ball on the table, then six fitting around it, now 6 can be fitted on top, and by symmetry 6 could be fitted underneath. so the original ball has 18 neighbours.


And then shockwaves could propagate through this mesh, and at each iteration each particle just needs to calculate the resultant force of its 18 neighbours acting on it.


I can't see whether this model would work or not. I suspect it is going to model sound propagating through a diamond rather than sound propagating through air, but isn't it going to be essentially the same?


Also, this isn't quite on topic for DSP, my apologies. Can anyone recommend a more suitable place to ask this question?




renyōkei - Verb Stem vs. の Nominalizations


I've been wondering about the difference between verb stem (e.g. 話) vs. の (e.g. 話すの) nominalizations.


From what i gather, both nominalizations refer to different things. It seems the verb stems refer to the objects involved in the doing (like those used in を). For example, life in relation to living (暮らし in relation to 暮らす) and speech in relation to speaking (話 vs. 話す).


While の refers to the act itself (described by the verb). So, for example, (as I have a sore throat), 話すのは難しい。(i.e. the act of speaking is difficult).


Am I right about this? Thanks!




electrochemistry - Redox Mg+Copper(II)


If I put solid magnesium in a solution of Copper(II) sulfate, what reaction occurs that causes the bubbles? Looking at the Potential tables the only reaction that theoretically occurs is the reduction of copper and oxidation of magnesium...so why there are bubbles? https://www.youtube.com/watch?v=LkUX5vhLjJ0



Answer



Copper (II) sulfate hydrolyzes in water and makes the solution slightly acidic. Then the magnesium is reacting with the weak acid, displacing hydrogen, as well as displacing the copper.


Magnesium displaces hydrogen only slowly with pure water, partly because the magnesium hydroxide product is only sparingly soluble. Just a little acid, even from an ammonium salt or (as here) hydrolysis of a transition metal salt, is enough to dissolve the hydroxide and launch the hydrogen displacement.


talmud gemara - What is the logical explanation for קם ליה בדרבה מיניה?


HodofHod:



In essence, the idea is this:
If a person does one act, and with that one act incurs two different kinds of penalties, we only apply the stricter one. So if a person (for example) borrows a cow and then slaughters it on Shabbos, he incurs two penalties: monetary restitution to the owner of the cow, and the death penalty for violating Shabbos. In this case, Beis Din only applies the stricter punishment, death, and the lesser one, the money, is waived.

Again, there are other details and complexities, but this is the general idea.



Can anybody give me a logical explanation for this concept? I don't think the transgressor could care less about the fine when he's dealing with the death penalty.




Simple, streaming, lossless image compression



Does anyone know of any image compression techniques with the following characteristics:



  • lossless

  • streaming - I want to compress on the fly, pixel-by-pixel.

  • low-memory overhead - I can afford to buffer a single line, but ideally not even that.

  • no dynamic dictionaries

  • "real-world" images only, so performance on "nasty cases" like chequerboards is not important

  • 2-3x compression (5x-10x would be even better, but that's asking a lot I know)

  • can operate on 10-16 bit pixels (depending on my camera)



My images will be ~1k pixels wide, with pixel rates of ~20Mpix/sec. The pixel depth will be something between 10 and 16 bits per pixel (depending on the choice of camera). Assume sub-16-bit pixel widths would be represented within a 16-bit word for now, rather than needing to be extracted from a continuous bit-stream.


Some form of delta+arithmetic coding perhaps?



Answer



You can consider using Huffyuv : http://neuron2.net/www.math.berkeley.edu/benrg/huffyuv.html


This is no great better than simple zip, but still slightly optimized for images.


Any Image related compression comes from the techniques like Vector quantization or Transform coding. In order to make use of transform such as DCT/Wavelet yet make it lossless you can think of JPEG-LS or JPEG2000 for compression. Only thing is, it is not streaming in your sense of definition.


culture - What are the stereotypical qualities of a gaijin trying to speak/write Japanese to a Japanese person?


There are plenty of stereotypical qualities of a Japanese speaking person trying to speak English, so, would I be correct in assuming the reverse is also the case, and if so, what would the most notable features be?


I ask this both out of curiosity and on the off chance I ever need to actually try communicating with people in a way that doesn't result in my casual humiliation.



Answer



I'm not sure if this is within the scope of your question, but the following is about highly stereotyped traits of "gaijin-speech" found in manga and net forums. They are explained in pages like this, this and this. Please note that they do not reflect how foreigners speak Japanese in reality. Unsurprisingly, some of them are rude or displeasing especially to the users of each language.


Western speakers trying to speak Japanese:




  • Wrong intonation, accent, vowel length, double consonant: ニホーンゴワーカリマセーン, オモシローイデース, ビクーリデス

  • Trilled/rolled ラリルレロ sounds

  • Overuse of personal pronouns: ワターシ, アナータハー

  • Unconditional sentence-end です: 見るデス, 行けデス

  • Overuse/misuse of sentence-end ナ, ヨ, etc: 本当ヨ!

  • Use of katakanized English when excited: オーノー! ワーオ! ホワット!?

  • Use of ミー and ユー as person pronouns: ユーは何しに日本へ?


Chinese speakers trying to speak Japanese:





  • アル, ネー or ヨー at the end of every sentence: 私は中国人アル
    (This is based on a pidgin Japanese language but later established as role language. アル was rather common 30 years ago or so, but today it's usually a rude way to simulate Chinese accent.)




  • Insertion of の between a verb and こと, とき, etc: 食べるのこと, 見るのとき




Korean speaker trying to speak Japanese:




  • ニダ (Korean copula similar to Japanese です) at the end of every sentence: 私は韓国人ニダ
    (This is almost always rude.)


equilibrium - Predicting pH of an acidic salt of an weak acid and weak base


Suppose we want to calculate pH of an $\ce{NH4HCO3}$ solution of known concentration. Now, $\ce{NH4+}$ will be hydrolised to give $\ce{H+}$ ions. Some $\ce{HCO3-}$ ions will be converted to (i) $\ce{H2CO3}$ and $\ce{OH-}$ and some will give (ii) $\ce{H+}$ and $\ce{CO3^2-}$


\begin{align} \ce{HCO3- + H2O &<=> H2CO3 + OH− }& 1/K_\mathrm{a1}\\ \ce{HCO3- + H2O &<=> CO3^2- + H3O+ }& K_\mathrm{a2}\\ \ce{NH4+ + H2O &<=> NH3 (aq) + H3O+ }& 1/K_\mathrm{b}\\ \end{align}





  1. I am not sure how to take account of both $\ce{H3O+}$ and $\ce{OH-}$ in the calculation of pH.




  2. Will the third equilibium costant be $1/K_\mathrm{b}$?





Answer



The main reactions which take place are


1)Ionization of $\ce{HA-}$: $\ce{HA- -> H+ +A^2-}$



2)Hydrolysis of $\ce{HA-}$: $\ce{HA- + H+ -> H2A}$


3)Hydrolysis of cation: $\ce{B+ + H2O -> BOH + H+}$


for reaction $1$, $$k_{a2}=\frac{[H^+][A^{2-}]}{[HA^-]}$$


for reaction $2$, $$k_{a1}=\frac{[HA^-][H^+]}{[H_2A]}$$


for reaction $3$, $$k_h=\frac{k_w}{k_b}=\frac{[BOH][H^+]}{[B^+]}$$


At any moment, $$\ce{[H^+]=[BOH] +[A^{2-}]-[H2A]}$$ $$[H^+]=\frac{[NH^{4+}].k_w}{[H^+]k_b}+\frac{k_{a2}.[HCO_3^-]}{[H^+]}-\frac{[HCO_3^-][H^+]}{k_{a1}}$$ Rearranging the terms to get $\ce{[H+]}$, $$[H^+]=\sqrt{\frac{\frac{[NH_4^+].k_w}{k_b}+k_{a2}[HCO_3^-]}{1+\frac{[HCO_3^-]}{k_{a1}}}}$$ $$[H^+]=\sqrt{\frac{k_{a1}\cdot \big(\frac{[NH_4^+].k_w}{k_b}+k_{a2}[HCO_3^-]\big)}{k_{a1}+[HCO_3^-]}}$$


Now we will have to make 2 assumptions. First lets assume that $k_{a1}<<[HCO_3^-]$ so that $k_{a1}+[HCO_3^-]=[HCO_3^-]$


$$[H^+]=\sqrt{\frac{k_{a1}\cdot \big(\frac{[NH_4^+].k_w}{k_b}+k_{a2}[HCO_3^-]\big)}{[HCO_3^-]}}$$


If you assume that neither hydrolysis nor the dissociation goes too far, you can assume the concentration of bicarbonate ion to be equal to the initial concentration (say C). Since Ammonium bicarbonate dissociates to give two products in 1:1 ratio, concentration of ammonium produced is equal to the concentration of bicarbonate ion produced.




I saw this formula for calculation pH of such salts in my textbook but no derivation was given: $$[H^+]=\sqrt{k_{a1}\cdot\big(\frac{k_w}{k_b}+k_{a2}\big)}$$ The above formula can be obtained if you consider the last assumption. (Clarification needed)



Tuesday, July 30, 2019

tznius modesty - Which communities do not allow women to drive cars?


Which communities do not allow women to drive cars?



I know the Belzer hassidim do not allow this, but I do not know about any other communities.




halacha theory - Why are some Mishnayot formulated positively and some negatively?


I'm a bit of a nagger, but I think the question is legit:


I start with an assumption that the formulation of the Mishnah was purposeful and not circumstantial, that Rebbe did put much thought in right wording.


We know that a Succah must be taller than a meter and up to 10 meters high (approx). This fact could be formulated in two ways, a positive - whats's required, or a negative - what's forbidden.


The starting Mishnah in Succah is a par-excellence example of a negative formulation:



"סֻכָּה שֶׁהִיא גְבוֹהָה לְמַעְלָה מֵעֶשְׂרִים אַמָּה, פְּסוּלָה.
רַבִּי יְהוּדָה מַכְשִׁיר. וְשֶׁאֵינָהּ גְּבוֹהָה עֲשָׂרָה טְפָחִים, וְשֶׁאֵין לָהּ שְׁלֹשָׁה דְּפָנוֹת, וְשֶׁחַמָּתָהּ מְרֻבָּה מִצִּלָּתָהּ, פְּסוּלָה."



A sukkah taller than twenty cubits is invalid. Rabbi Yehudah validates it. And one which is not ten hand-breadths tall, or does not contain three walls, or whose [area of] sun is greater than its shade is invalid.



Rebbe could easily formulate it in a positive way [my proposition]:



איזוהי סוכה כשרה? כל שהיא גבוהה עשרה טפחים ולא יותר על 20 אמה.
שיש לה ג' דפנות וצילתה מרובה בחמתה.


What Succah would be Kosher? One that's higher than a meter and up to 10 meters, has 3 walls and has more shadow than straight sunlight.



Please note, that my version is not lengthier and covers exactly the same amount of information.


This negative approach is very common with the Mishnah, for example, "לוּלָב הַגָּזוּל וְהַיָּבֵשׁ, פָּסוּל. שֶׁל אֲשֵׁרָה וְשֶׁל עִיר הַנִּדַּחַת, פָּסוּל. נִקְטַם רֹאשׁוֹ, נִפְרְצוּ עָלָיו, פָּסוּל.". Sometimes the Mishnah does speak in a positive way (RA"S 3,2): "כָּל הַשּׁוֹפָרוֹת כְּשֵׁרִין חוּץ מִשֶּׁל פָּרָה, מִפְּנֵי שֶׁהוּא קֶרֶן."



Personally, as a father and a Mechanech, I'm a big fan of the Positive Psychology approach to education, namely instead of repeatedly reciting the forbidden activities, I prefer to strengthen the desired behavior.


Did someone research on that specific point - how does the Mishnah benefit from such formulations?




kanji - Can I write Japanese name "Midori" this way - 緑?


There is female Japanese name "Midori," and I want to know the ways I can write it. I know it means "green," but maybe the name and "green" are different words sometimes.


I used google-translator to get variants. I want to know if all of those variants are used to write the name Midori. Otherwise I am interested in what they mean.



As far as I can understand, the first variants are kanji and next ones are hiragana:



  • ミドリ


  • みどり and みどりの


What is the difference between these? What does the "no" mean?



Answer



Searching on a name dictionary you'll get a long long list (93) of "midori" as a girl's given name. This excludes "midori" being used as a family name or a place name.


"Midori" is not limited to the kanji for green though. It can be made up of other kanji having 名乗り (nanori - name reading) of "mi", "do", "ri", "mido", "dori" compounded to form "midori".


And yes you can use or as a standalone kanji for the name Midori.


For brevity I will not list all 93:



Kana and Kanji mix:




みど梨


みど理


みど里


み外里


み登り



3 Kanji compounds:



三十里



三都里


光巴里


光都里


妙登利



2 Kanji compounds:



三彩


光鳥


実酉



常緑


碧里




There is also the possibility that a name is spelled purely in Hiragana:



みどり



In this case, writing that person's name using Kanji would be wrong.


For Midorino:




緑野 [みどりの] (Don't worry about the meaning of "no" it's just the way the name sounds) it can be both a girl's name and a family name.


緑埜 [みどりの] is a family name instead of a girl's name.



Alternatively it could be Midori + Genitive case marker の.



i.e. みどりの本 to mean "Midori's book"


or 緑の本 to mean "a green (coloured) book"



aqueous solution - Does the amount of solute affect rate of solvation?


I know that in order to increase the rate of solvation, you need to increase how often solute and solvent particles come into contact.


You can do it by:




  1. agitating the mixture

  2. increasing the surface area of the solute

  3. heating up the solvent


But my question is: Does adding more solute (like adding more salt to water) increase the rate of solvation since the contact surface area is larger?


Edit: The original question in the book describes dissolving a certain amount of $\ce{NaCl}$ into water and asks, “What can be done to increase the rate of dissolution without affecting solubility?” I assume the rate is measured by how fast the mass of $\ce{NaCl}$ is consumed, which is $-\frac{dW}{dt}$.



Answer



If the answers are to be exclusive, then obvious choice is agitating the mixture.


If the answers are not to be exclusive, then agitating the mixture + increased surface by adding more solute increases $\frac{\mathrm{d}c}{\mathrm{d}t}$


Adding more solute does not increase rate of solvation, but as the absolute surface increases, it increases $\frac{\mathrm{d}c}{\mathrm{d}t}$.



Note also without affecting solubility from your comment, so increasing temperature is out.


books generally - Reading foreign literature: perspectives and experiences


I'd like to hear how people make their decisions about reading, watching, and listening to materials that express non-Jewish ideas and imagery... both in your study and in your entertainment.


There are all sorts of issues involved in censorship, and I don't want to be extreme in unnecessary ways. On the other hand, Judaism holds an understanding that our Creator actually does care where our loyalties lie, and what we fill our heart and mind with. What we read, see, and listen to can affect our sensitivity to what is good, our imagination, and our loyalties. So Tanach suggests a concept of modesty in not looking at things that are foreign to Biblical Israelite worship. If you really believe that these things have a basis in reality, then your engagement with what is right and good will probably involve choices about what materials to let into your life.


This question affects me in two different ways. Firstly, I'm not Jewish, so on a halachic level that probably also makes a difference. But in terms of my loyalty to Hashem alone and desire to come close to Him through goodness, the decision is still important to me, whether or not it seems culturally normal in my society. The thing is, I don't have a Jewish identity, and so somehow I still have the identity of my own nation and family heritage... and I love literature, art, etc. But the near-complete pervasion of non-Jewish cultural expressions with Germanic-magical, Christian, or anti-religious themes can make this attempt seem futile and confining. Is there anything from my culture that I can bring to God in my understanding of how He's revealed Himself to Israel, and yet also wants a connection, a level of holiness, with every nation He has created? I think that every part of life, the religious parts and all the other parts, exist equally in the context of creation and therefore of relationship with the Maker of what is in the world.


The other way is that I'm enrolled to study an Honours research year at university in Medieval Studies, because I did my undergraduate degree in Medieval literature. During that period I was a committed Christian, because that's how I was brought up, but for the last year I have been learning a lot about Judaism and also haven't really been reading medieval European literature. It's saturated in both Catholic devotion and in magical imagery. Part of me feels I should be able to read it without being affected by it, since I don't believe it, and just comment from a distance or enjoy the parts that are positive and good. But in another sense, I don't want to look at this kind of material. The reason I want to do this Honours year now is because it will be a great opportunity to choose a topic related to Jewish literature in the Middle Ages, and learn more about the history of Jewish experience and faith. But doing so will no doubt include comparison with surrounding literatures, even if only to understand the mutual interactions between Jewish and foreign literature of the past. I have to make a decision about how open I'm willing to be about what I read and become desensitised towards, and know well whether that attitude comes from Biblical Judaism or from somewhere else. It could change my plans for this year; it will probably affect my direction in the years after that, or at least the attitude with which I approach the study.


I know that in both areas this isn't a straightforward question, but I'm sure there are both rabbinic and personal perspectives that could help. In that it is a personal question I'm also talking about it with a few rabbis I know and with other friends and family.




organic chemistry - Conformations of butane


Would these be valid conformations of butane? I tried matching these up with the group but my drawings all seem rotated versus the book.


I'm fairly sure my anti conformer is correct, along with my gauche conformer. I'm not too sure about the two eclipsed conformers; from what I understand, there are two eclipsed conformations - one with strong torsional strain resulting from the methyl group interacting with the other methyl group, and the other resulting from the methyl groups interacting with the hydrogens, right?


Also, can we consider the dihedral angle to be the angle between the methyl groups?


enter image description here


enter image description here


Another problem is that what I've drawn doesn't seem to match with the book's energy diagram too. I'd expect the anti-conformer to be the lowest in energy, but I'd also expect a difference in E for the two eclipsed conformations. One should have more torsional strain from placing the two methyl groups next to each other and the other, less, because the methyl groups are eclipsing the comparatively small hydrogen.



Answer




You have got them correct. Just your diagrams in eclipsed should have very close bonds. In your third diagram, one $\ce H$ is a bit far for another.


Wikipedia provides a nice description for this.


A diagram too :


enter image description here


You are correct.


grammar - What's the difference between ~てある and ~た (past form)?


As I understand it てある is rather different to ている in that it refers to a resultant state rather than an ongoing action.


However I wonder, what then is the practical difference between a resultant state and a past action?


For example,



昼ごはんを作ってある (昼ごはんは作ってある?)



昼ごはんを作った



both mean “I made dinner” right? Is there any major difference or is it some small nuance?


Would てある not apply if you were speaking of something you did last week and thus the dinner has since been eaten whilst it would work if you were speaking of the dinner you're about to eat?




parshanut torah comment - Why does Rashi say "I don't know"?


The Posuk says (Genesis 28:5):



וַיִּשְׁלַח יִצְחָק אֶת יַעֲקֹב וַיֵּלֶךְ פַּדֶּנָה אֲרָם אֶל לָבָן בֶּן בְּתוּאֵל הָאֲרַמִּי אֲחִי רִבְקָה אֵם יַעֲקֹב וְעֵשָׂו




To which Rashi comments on the fact that the Posuk says that Rivkah was both the Mother of Yackov and Eisav:



אם יעקב ועשו: איני יודע מה מלמדנו



Why does the Torah say it, and if he does not know the reason why does Rashi mention it at all?



Answer





  • The Maskil LeDavid on the verse brings a fascinating explanation.


    He says Rashi is explaining what Yitzchok was telling Yaakov. Yitzchok told Yaakov, I'm sending you to Lavan, but be careful, since I don't know what kind of man he is (i.e. Tzaddik or Rasha). Normally we can tell the nature of an uncle by looking at the majority of his nephews, but I have two sons, one righteous and one wicked, so there is no majority, and therefore it could go either way.



    This then, is how to read Rashi: Rivka is the Mother of Yaakov and Eisav, and therefore I don't know what Lavan's nature is. This is what the Passuk is coming to teach us.




  • The Siftei Chachamim writes that Rashi was aware of the many interpretations by various commentaries, but he wasn't sure which one was correct according to the simple meaning of the verse.




  • The Lubavitcher Rebbe, based on his thesis that Rashi is only coming to explain the simple meaning of the verse (and only quotes Midrashim that can be used to explain the simple meaning), says (Likutei Sichot volume 5, pg 1 footnote 2) that when Rashi says, "I don't know", it isn't because he is not aware of any of the answers given, but rather is not aware of any answer that explains the simple meaning of the verse.


    This also explains why there are some instances where Rashi gives an explanation in his commentary on the Talmud, but says I don't know in his commentary on the Torah.


    [See there for a list of locations where Rashi says "I don't know" or something similar, including places where Rashi says "I don't know" and then proceeds to give a reason.]





atoms - Z* effective charge and Ionization Energy


I'm trying to figure out the patterns for Ionization Energies. I am familiar with the periodic trend, however things become quite different when we hit the 1st I.E. For example, Na has an I.E(1) of 495.8 kJ while its second I.E. rockets up to 4562 kJ while the atoms towards the right are much lower than this. The trend says that the I.E. increase up and right of the periodic table, which is not the case here.


My point is, in order to get a better estimate, would it be safe to say that the Zeff charge and atom size relate to the I.E?


Example: Effective Charges


Mg = 2 Al = 1 S = 4 Si = 2 Na = 1



We see that the strongest pull towards the charged center would be Al and Na in this case. However, having Al being the smaller atom would require more energy to remove the electron from its valence shell.


Now in the case of first Ionization Energy we have:


Mg = 3 Al = 2 S = 5 Si = 3 Na = 2


In this case, Na now has reduced its size due to the fact it jumped from n=3 to n=2 level and Al also reduced in size but is still a bigger atom than Na due to our trend.


My question is, is this approach fairly accurate or should I be looking somewhere else?



Answer



Using the common idiom: "full subshells are stable"


It is a little more compact to use the incorrect explanation and correct it than to explain in terms of correct. Also, when you hear this incorrect explanation, you will understand what is meant.


Yes, size is a factor (thus the "up" part- IE is higher in lower periods), but the observed anomaly in second-ionization energies in $\ce{Na}$ and $\ce{Al}$ is better related to removal of an electron from a full subshell.


$\ce{Na}$ has an electron configuration of $\ce{[Ne] 3s^1}.$ The first ionization gives $\ce{Na}$ makes it $\ce{[Ne]}$, the same as a noble gas- full 2p subshell. Because full subshells are stable, it takes a lot of energy to remove the first electron from it. $\ce{Al}$ is analogous; the second ionization means removing an electron from a full subshell.



The same is observed in the first ionization energies (in $kJ/mol$): $$\ce{Na}:495$$$$\ce{Mg}:737$$$$\ce{Al}:577$$ Ionization of $\ce{Mg}$ removes an electron from a full $\ce{3s}$ subshell, so it is a little higher than the trend.


There are many factors that contribute to exact values, but these are difficult to predict, which is why they taught a simple version in your class.


Correcting the myth


While it is common to refer to full subshells as being more stable, it isn't really what is going on. In reality, the next electron added in destabilized. This occurs because of shielding. Outer electrons feel repulsion from inner electrons, thus outer electrons are easier to remove than inner ones. The saying that "half-filled subshells are stable" is also used. Again, it is that the next added electron is destabilized, but in this case it is because the energy needed to spin pair the two electrons.


Monday, July 29, 2019

environmental chemistry - How to determine source of air pollution


It should be determined by some metal markers (meaning originating from traffic etc.) but I cannot find any source which would describe it. Thanks.



Answer



The main idea is the following: you will need multiple sampling points and record enough data to obtain a representative dataset. Then when drawing wind roses with high percentiles (let say P95 or above) you will be able to easily point out an unique source of a relevant and exclusive pollutant.


But of course, reality is much complex... And there are some adverse effects that you must address before pointing out the source with a reasonable confidence.


First you better be not so close to the source, in order to measure immission instead of emission. Then environment and local conditions will average out. And wind speed, wind direction and concentrations become meaningful. In this case high percentiles likely originate from your source.


Second, your analyte must be relevant and if possible exclusive from your source. Measuring CO2 is not a good choice when monitoring traffic (it is stable, widespread thus global and not exclusively produced by traffic), NO is a better one because it is local, reactive and strongly related to high compression ratio thermal engine combustion source.


Third, if there are multiple isotropic sources, you will get nothing useful using wind roses. And your problem becomes really tricky.


history - Yerushalmi Versus Bavli


What are the differences between the two Talmuds? or are there differences? Why did the two Talmuds develop separately or did they? Why do we Poskin like the Bavli or do we? Is it true that the difference between Sefardim and Ashkenazim is on the Basis of this original argument and what is the source for saying so?


Basically, I am asking for the historical developments of the Talmuds and their current day implications?



Answer



There are lots of differences. Among the more obvious ones:




  • Dialect - the Bavli is written in Eastern Aramaic, the Yerushalmi in Western Aramaic. There are differences in vocabulary (such as B. חזי = Y. חמי, both meaning "see" - we in fact use both of these in the second Kol Chamira on Erev Pesach morning), in word forms (the Bavli tends to drop final ן in words like תנינא, the Yerushalmi usually preserves it), and in technical terminology (such as B. תא שמע = Y. נישמעיניה מן הדא).





  • Presentation: the Yerushalmi is a lot briefer, and doesn't have a lot of the extensive discussion and parry-and-thrust found in the Bavli.




  • Editorial: sometimes the Yerushalmi jumps from one topic to another without explanation (as in Sanhedrin 10:1, where after mentioning the comparison of Torah to nails it asks, without preamble, "How many nails can be in it?" referring to an issue about wearing hobnailed boots on Shabbos), while the Bavli will usually preface the new topic with an appropriate quotation from a Mishnah or the like. Similarly, the Bavli often spells out the corollaries that can be deduced from an Amora's statement, where the Yerushalmi won't do so.




  • Coverage: the Yerushalmi covers all of Seder Zera'im while the Bavli doesn't. Conversely, the Bavli covers most of Kodshim while the Yerushalmi doesn't. (In both cases, though, this may be due to missing parts.)





  • Commentaries: the Bavli has Rashi, the Yerushalmi has other commentaries (the standards in most masechtos are Pnei Moshe and Korban Ha'eidah, which certainly explain it adequately - but after all, there was only one Rashi).




The reason they developed separately is simply that in that era there were two major centers of Jewish life and of Torah study, in Eretz Yisrael and in Bavel. They exchanged information constantly (through the נחותי, "traveling scholars," mentioned often in the Gemara, like R' Dimi and Ravin), but still, each of them had its own distinct style of learning (see Bava Metzia 85a and Sanhedrin 24a). The Yerushalmi's development ended much earlier (and some historians say that in fact it was never really properly finished) because of Roman persecution that nearly emptied Eretz Yisrael of its Jews.


There are occasional differences in halachah between the two Talmuds, and when that's so, we generally decide according to the Bavli. The main reason for this is that, as above, the Bavli was finished later than the Yerushalmi, so הלכה כבתראי - we follow the later authorities (since they had access to the earlier material and consciously differed with it).


There are historians who argue that the differences between Sephardim and Ashkenazim reflect the earlier differences between the Jews of Bavel and Eretz Yisrael, respectively. Others argue that it goes back to the differences between the Jews of southern vs. northern Eretz Yisrael. Still others attribute most of them to the differences between the surrounding cultures in which they lived - Christian vs. Muslim. Historically, it is certainly true that the "Romaniote" communities of the Byzantine Empire were more influenced by Eretz Yisrael, and indeed some of them focused more on the Yerushalmi - I believe that the Yanina community (in Jerusalem and in New York) still does so. But then the question would really be whether the Romaniotes were the forerunners of the Ashkenazim.


free will bechira - What happens if the accused sotah doesn't consent to the ritual?


Chapter 5 of B'midbar describes the ritual for the woman accused by her husband of adultery. It includes this, after the kohein declares to her what will happen:



וְאָמְרָה הָאִשָּׁה, אָמֵן אָמֵן


and the woman shall say: 'Amen, Amen.' (end of 5:22)




And just in case there's any doubt, in 21 it says the kohein causes her to swear an oath.


What happens if the woman doesn't consent to saying "amen, amen" or swearing the oath? Does the ritual proceed anyway, even though the torah says she has to say these things? Is the ritual halted, and she and her angry husband go home to resolve their differences (or not)? Does everybody just wait, until someone gives up? Or what?



Answer



The Mishna in Sotah 1:4-5 and 3:3 explains that until the name of G-d is erased, the Beit Din tries to prevent the name from being erased, but convincing her to tell the truth.


The Talmud explains how they go about convincing her to confess (if she is guilty).


If she admits to wrongdoing, or refuses to go through with the process, she is divorced from the husband without the husband having to pay the Ketubah fees.


If they have already erased the name of G-d, she is forced to drink, unless she admits to her guilt (Mishnah 3:3 and Rambam Sotah 4:6).


sources mekorot - Tosefta vs. Toras Cohanim


This past Shabbos someone said over to me a particular sugia they were learning in Taharos and a maklokes Rishonim (an argument between Rishonim, medieval rabbis) in a particular analysis. One Rishon was basing himself partially on a Tosefta and his understanding of it. Among the the Rishonim on the other side of the maklokes were those who brought a proof from Toras Cohanim (Sifra). While we could obviously discuss and try and understand other points of this maklokes we began thinking if there is any "klal" (general statement) in regards to what's stronger (in terms of halacha -- not neccessarily practical halacha but more in the context of such a maklokes) a Tosefta or a "braisa" (I suppose that is the best thing to call it) from Toras Cohanim. Similar questions have been asked in the past in regards to what's stronger Bavli or Yerushalmi or a Tosefta or Yerushalmi.


Is there any klal in this?


(Note: It could be since Tosefta is also just a "collection" of braisos and Toras Cohanim is also braisos it may be no different. However the fact that some were include in Toras Cohanim and others included in Tosefta might show the difference.




talmud gemara - Sharp sword on the throat


The Gemara says Berachot 10a



אפי' חרב חדה מונחת על צוארו של אדם אל ימנע עצמו מן הרחמים




Even if a sharp sword is resting on one's thought he shouldn't hold back from (asking for) mercy."


Why does the Gemara have to say "sharp" rather than just a sword? A sword usually makes a connotation of sharpness.




homework - Hybridization of tetraamminecopper(II) sulfate


$\ce{Cu^2+} $ has 9 electrons and a d-orbital and is almost completely filled (except 1 electron vacant) and $\ce{NH3}$ donates an electron eventually forming $\mathrm{sp^3}$ hybrid orbitals.


But it has a square planar geometry hence completely contradicting the above reasoning. Please explain what the hybridization is?




organic chemistry - Doubts about IUPAC nomenclature of 4-ethyl-1-fluoro-2-nitrobenzene


Why is 4-ethyl-1-fluoro-2-nitrobenzene (structure is in the attached picture) called so ?


Shouldn't it be called as 1-ethyl-4-fluoro-3-nitrobenzene since the precedence of ethyl is greater than halogens?



4-ethyl-1-fluoro-2-nitrobenzene




Sunday, July 28, 2019

halacha - Do I sit Shiva after my parents if I am converted to Judaism?


If the parents of a ger pass away, must the convert sit shiva for them? If so, is it preferable to sit shiva in the mourner's hometown or the parent's hometown?




mussar ethics - Would halacha permit bombing Auschwitz?


I know there's a lot of talk about whether Allied forces during World War II could have / should have taken military action directly against the Holocaust. I'm not opening that can of worms here.


One of the options suggested was "they could have bombed the railroad tracks leading to Auschwitz"; another one is "they could have bombed the extermination camp itself."


For theory's sake: would halacha permit bombing the camp (and thus directly killing several thousand innocent people in it right now) so the Nazis couldn't use it to kill millions more?


One similar question is the halacha regarding shooting down a hijacked airplane. After some very complicated discussion, Rabbi J David Bleich concludes that halacha would prohibit it, but:




  • I'm not sure everyone agrees (see comments there; I recall hearing about a teleconference shiur for rabbis given by ... I think Rabbi Dr Moshe Tendler ... several days after 9/11, concluding otherwise on this issue).





  • I've heard that some halachic ethics apply differently in times of war, not sure how that influences this.




  • Is the hijacked-plane case completely analogous to the extermination-camp case?






rabbis - Rav Yaakov Moshe Hillel and wearing tzitzios out


Does someone know anything about Rav Yaakov Moshe Hillel shlita hamekubal stating that tzitzios should be worn outside the clothes? I read it once but without any sources on a web forum. It would be quite surprising as one of the argument to tuck them is based on kabbalah and the Arizal.



Answer



In his book Geburat HaAri (pg. 137) he brings the AriZal and explains that according to him they should be exposed because in Shaar HaKawanot (7c) the Ari says that there is a Miswa to behold the Sisiot (see Debarim 15:39).


He expounds on this immensely in his Sefer Wayashov HaYam (vol. 1 Siman 3).



grammar - How to express appositives in Japanese


I have been searching high and low for how to express appositives in Japanese, yet the most I have come across is how to express something like "my friend John". I would like to know how to express more complex appositives in Japanese, something like:




1.) Dogs, one of my favorite animals, are going to be featured in tonight's show.
2.) John, the person you were talking to yesterday, will be at the party tonight.
3.) Brian McKnight, a very popular R&B singer, has just written a book about the music industry.



More specifically, I was writing a post and trying to express the following idea:



I had learned that Japanese people consume the greatest amounts of iodine, up to 13 mg per day!



I have expressed the first part of the sentence below, but have no clue how I would express the appositive "up to 13mg per day" without outright creating a new sentence.




日本の人が最も大量のヨウ素を食べることを知った。



I appreciate any help you can provide.



Answer



I don't think categorically ruling that "complexity" is always bad would be wise. A lot of rather sophisticated constructions are perfectly natural to a native speaker, and thus may be preferable over simplified options.


Now, in the case of your sentence:



I had learned that Japanese people [...]



... I'd say that depending somewhat on the context, connecting the first statement with the second using けれども or some of its variants (けど, けれど) would result in a natural and not overly complex sentence, and there are many other simple options as well (が, possibly ~て-form and more, aside those presented by @krnk).



Depending on your feeling towards your finding (thinking of the exclamation mark), you may want to follow that up with something like なんと to express a sense of "surprise".


acid base - Hydrolysis of salt


The hydrolysis of salt tells you whether a salt is acidic or basic. But it does not tell you how acidic or basic a salt is. Is there a way to determine this?


My guess is that taking of the weak base part of a salt( presuppose that it is acidic) and see how many hydronium ion it could produce. So the more hydronium ions, the more acidic this salt is?




minhag - Line break before למען ירבו ימיכם


In most of my prayer books there is a line break before למען ירבו ימיכם in the second chapter of the Shema (see also this one from Vilna or Zhytomyr):



וְהָיָ֗ה אִם־שָׁמֹ֤עַ תִּשְׁמְעוּ֙ אֶל־מִצְוֺתַ֔י אֲשֶׁ֧ר אָֽנֹכִ֛י מְצַוֶּ֥ה אֶתְכֶ֖ם הַיּ֑וֹם לְאַֽהֲבָ֞ה אֶת־יְהוָ֤ה אֱלֹֽהֵיכֶם֙ וּלְעָבְד֔וֹ בְּכָל־לְבַבְכֶ֖ם וּבְכָל־נַפְשְׁכֶֽם׃ וְנָֽתַתִּ֧י מְטַֽר־אַרְצְכֶ֛ם בְּעִתּ֖וֹ יוֹרֶ֣ה וּמַלְק֑וֹשׁ וְאָֽסַפְתָּ֣ דְגָנֶ֔ךָ וְתִֽירֹשְׁךָ֖ וְיִצְהָרֶֽךָ׃ וְנָֽתַתִּ֛י עֵ֥שֶׂב בְּשָֽׂדְךָ֖ לִבְהֶמְתֶּ֑ךָ וְאָֽכַלְתָּ֖ וְשָׂבָֽעְתָּ׃ הִשָּֽׁמְר֣וּ לָכֶ֔ם פֶּ֥ן יִפְתֶּ֖ה לְבַבְכֶ֑ם וְסַרְתֶּ֗ם וַֽעֲבַדְתֶּם֙ אֱלֹהִ֣ים אֲחֵרִ֔ים וְהִשְׁתַּֽחֲוִיתֶ֖ם לָהֶֽם׃ וְחָרָ֨ה אַף־יְהוָ֜ה בָּכֶ֗ם וְעָצַ֤ר אֶת־הַשָּׁמַ֨יִם֙ וְלֹֽא־יִהְיֶ֣ה מָטָ֔ר וְהָ֣אֲדָמָ֔ה לֹ֥א תִתֵּ֖ן אֶת־יְבוּלָ֑הּ וַֽאֲבַדְתֶּ֣ם מְהֵרָ֗ה מֵעַל֙ הָאָ֣רֶץ הַטֹּבָ֔ה אֲשֶׁ֥ר יְהוָ֖ה נֹתֵ֥ן לָכֶֽם׃ וְשַׂמְתֶּם֙ אֶת־דְּבָרַ֣י אֵ֔לֶּה עַל־לְבַבְכֶ֖ם וְעַֽל־נַפְשְׁכֶ֑ם וּקְשַׁרְתֶּ֨ם אֹתָ֤ם לְאוֹת֙ עַל־יֶדְכֶ֔ם וְהָי֥וּ לְטֽוֹטָפֹ֖ת בֵּ֥ין עֵֽינֵיכֶֽם׃ וְלִמַּדְתֶּ֥ם אֹתָ֛ם אֶת־בְּנֵיכֶ֖ם לְדַבֵּ֣ר בָּ֑ם בְּשִׁבְתְּךָ֤ בְּבֵיתֶ֨ךָ֙ וּבְלֶכְתְּךָ֣ בַדֶּ֔רֶךְ וּֽבְשָׁכְבְּךָ֖ וּבְקוּמֶֽךָ׃ וּכְתַבְתָּ֛ם עַל־מְזוּז֥וֹת בֵּיתֶ֖ךָ וּבִשְׁעָרֶֽיךָ׃


לְמַ֨עַן יִרְבּ֤וּ יְמֵיכֶם֙ וִימֵ֣י בְנֵיכֶ֔ם עַ֚ל הָֽאֲדָמָ֔ה אֲשֶׁ֨ר נִשְׁבַּ֧ע יְהוָ֛ה לַאֲבֹֽתֵיכֶ֖ם לָתֵ֣ת לָהֶ֑ם כִּימֵ֥י הַשָּׁמַ֖יִם עַל־הָאָֽרֶץ׃




Although in Emden, Heidenheim and Artscroll there isn't, and it doesn't seem to be a general minhag for Böhmen-Mähren-Ungarn countries based on this machzor from Prague. In the Torah scroll there is no line break either. Where does this minhag come from and what is its meaning?



Answer



The issue is discussed in detail by R' Hamburger in Volume 4 of his priceless series, Shorshei Minhag Ashkenaz, and a bit shorther, but in English in the kitzur edition. His main point is that in Ashkenaz most Jews became unfamiliar with the proper melody of Torah reading over the centuries (see Orach Chayim 61:24), so they didn't read it anymore aloud and they also finished it earlier than the rabbi. As they were waiting for the rabbi, he started to read it aloud, and he had multiple reasons to do this. First of all, on Berakhot 12b, when the reading of the last paragraph in the evening is discussed, the mishnah uses the word remind (מזכירין) instead of remember (זוכרין). So by reading out aloud the last paragraph, he could remind the congregation of the Exodus, which is a positive commandment based on Devarim 16:3:



לֹֽא־תֹאכַ֤ל עָלָיו֙ חָמֵ֔ץ שִׁבְעַ֥ת יָמִ֛ים תֹּֽאכַל־עָלָ֥יו מַצּ֖וֹת לֶ֣חֶם עֹ֑נִי כִּ֣י בְחִפָּז֗וֹן יָצָ֨אתָ֙ מֵאֶ֣רֶץ מִצְרַ֔יִם לְמַ֣עַן תִּזְכֹּ֗ר אֶת־י֤וֹם צֵֽאתְךָ֙ מֵאֶ֣רֶץ מִצְרַ֔יִם כֹּ֖ל יְמֵ֥י חַיֶּֽיךָ׃


Thou shalt eat no leavened bread with it; seven days shalt thou eat unleavened bread therewith, even the bread of affliction; for in haste didst thou come forth out of the land of Egypt; that thou mayest remember the day when thou camest forth out of the land of Egypt all the days of thy life.



The exact meaning of all the days of your life is discussed in the well known mishnah and in the Haggadah. This explains well the recital of the last paragraph, but not the verse Devarim 11:21. However, this verse is of particular importance, because if someone errs during the recital of the Shema, but remembers that he has already said it, there is no need to return to the beginning of the paragraph (Berakhot 16a). Many rabbis considered this verse suitable to bless all the Jews that made the effort to come to the synagogue, and read it aloud. (While there were others that opposed this practice, saying he shouldn't have anything else in mind when fulfilling the commandment of reciting the Shema.) I would also add that the word למען in Devarim 16:3 can allude to Devarim 11:21.


The line break can hint that from this point on the rabbi reads the verses aloud, which is recorded in multiple places, such as in Divrei Kehilot by R' Geiger:




And the rabbi (and if he is not present in the synagogue it is upon the teachers from the leaders of the community to take his place) says aloud למען ירבו until אמת with the teamim.



On p. 5 of the Sefas Yisroel siddur it is also written:



.'הרב הקורא שמע בטעמים מרים קולו מ'למען ירבו' עד 'אמת


The rabbi, who reads Shema with the teamim raises his voice from למען ירבו until אמת.



It is also mentioned in the Hungarian Jewish Encyclopedia:




The rabbi recites this part of the [second] chapter aloud.



minhag - Meforshim Nick"names


It has become common practice to refer to most meforshim by acronyms of their name (eg Rashi, Rosh, etc.). When and why did this practice start, and is it proper?



Answer



In a sense it goes back at least to the Gemara. R' Sherira Gaon points out that the names of some Amoraim that begin with ר (for example: Rabbah, Rava, Rafram) are actually shortened forms of "Rav" plus their personal name: רב+אבא=רבה (or רבא); similarly רב+אפרים=רפרם; and so forth. Also "Reish" (Lakish) is a similar short form for רבי שמעון.



Saturday, July 27, 2019

kanji choice - Itadakimasu: connotations of 戴 vs 頂?


Today I learned that itadaku can be written as 戴く or 頂く. According to Tangorin, 頂 means "place on the head; receive; top of head; top; summit; peak" and 戴 has the overlapping meaning "be crowned with; live under (a ruler); receive."


When would you choose one over the other? Does it depend on the occasion?



Answer



None of the monolingual dictionaries I've looked up explains the difference. In everyday writings, you can just stick to 頂く when it's used as a normal verb, and (~て)いただく when it's used as a subsidiary verb (because subsidiary verbs are written in hiragana anyway).


戴く is not particularly difficult for native speakers, but this character was not even a 常用漢字 until 2010, and even after that いただく is not listed as a kun-reading of this kanji.



From 常用漢字表


So 戴く is one of those "alternative kanji" you may consider using instead of common ones if you need to do some creative writings. Other such kanji include 唄う, 護る, 哭く, 往く and 訊く. There are hundreds of kanji that only basically novelists and lyricists use on a regular basis. I think 戴く tends to look older and more dignified.


Finally, there seem to be quite a few clickbait online articles which are saying there is some deep and essential difference. Please ignore low-quality articles which cite no authoritative references. Perhaps this explanation by ALC is worth reading.


halacha - Is Juneau, Alaska -- surrounded by natural barriers -- a natural eruv



I recently visited Juneau, Alaska. It is a small city of 35,000. The city limits are quite large, however -- 3,225 square miles -- but much of this area is separated from downtown Juneau on Douglas Island. According to Wikipedia, Downtown Juneau sits at sea level, with tides averaging 16 feet (5 m), below steep mountains about 3,500 feet (1,100 m) to 4,000 feet (1,200 m) high. Atop these mountains is the Juneau Icefield, a large ice mass from which about 30 glaciers flow. Because the city is surrounded by ice or water, there are no roads in or out of town, and the only way to come or go is by air or sea. Given this, could the glacier ice and the ocean be considered like mechitzas (walls) and enclose the city like an eruv?




halacha - Is mundane speech allowed in shul?


Does anyone know the halacha regarding if one is allowed to talk in shul (divrei chulin)


I'm not referring to times of prayer, but general even after prayer.


Seems that mundane speech is forbidden according to halacha, but I see almost everyone doing it, even Rabbis answer their phones and shmooze in the synagogue.


Is there a clear cut halacha on this?



Answer



The Aruch Hashulchan paskens like common practice that it is permitted (see here and here), justifying it as follows:




The Arukh Ha-Shulchan (Orach Chaim 151:5) asked why people speak idle chatter in (even non-Chassidic) synagogues after prayer services and answered that we must follow the view of the Ramban and Ran that when synagogues are founded with the condition that certain non-holy things will take place in them (such as eating or speaking idle chatter), then in cases of need these activities are permitted. And, continues the Arukh Ha-Shulchan, we must find these friendly discussions to be needed. He rules this way even though the Shulchan Arukh rules against the Ramban and Ran.



Edit: I would add that it seems that the Bach permits sichas chullin bein gavra legavra (see here for more), which surely takes place in a shul. My strong suspicion is that "sichas chullin" and/or "sicha beteila" is a homonym, and means different things to different people.


meaning - Difference between 夫 and 主人?


The words [夫]{おっと}and [主人]{しゅ・じん} both mean "husband".


What's the difference between them?



Answer



The meaning is basically the same as you said: husband.


According to this website the main difference is in the situation in which you use these words.


Simply put:


「夫」: You can use it in most situations.


「主人」: Mostly used when talking with superiors or people you're not very familiar with.



BONUS:


「旦那{だんな}」: Is used when you are speaking with people you are familiar with.


To be even more precise it seems that 「夫」 is used as the opposite word of 「妻{つま}」 (wife). On the other hand 主人 bears a bit more the meaning of "house chief" or "master" (of the house).


I can expand more maybe later (I gotta go back to work now :p ).


history - Did Rashi wear a yarmulke?


Tractate Sofrim (14:14) records two opinions that concern the wearing of a head covering during the Shema: there are those who say that it is not necessary, and there are those who say that it is necessary, since one whose head is uncovered may not pronounce the name of God. According to the Bet Yosef (Tur, OC 91:3), the halakha is in accordance with the latter opinion (that a head covering must be worn), since that was the opinion codified by Rabbeinu Yerucham (Sefer Toldot 16:7, 148d).



Interestingly, the Darkhei Moshe (Tur, OC 282:1) records the fact that there was a French custom to follow the other opinion, and not to wear a head covering when reading Torah. His source for this is the Or Zarua, which notes ([II:43]) that this was not merely a local custom, but something that the Rabbonim in France were doing.


The gradual stabilisation of the custom of wearing a head covering all day long was at times a controversial subject (with yarmulkes occasionally being drawn onto the heads of rabbis in drawings), but the image of bareheaded men reading Torah or reciting Shema is striking.


To which rabbonim in France was the Or Zarua referring? Did Rashi wear a yarmulke? Did he ever discuss the obligation to do so in his responsa?




organic chemistry - Stereochemistry: synthesis of an epoxide


This is a procedure to synthesize a propylene oxide.


enter image description here


I wonder if the inversion occurs or not after the reaction. That is, I want to know which product is correct in the diagram above.


I thought that this reaction is an SN2 reaction, so inversion occurs. However, I'm a little confused because the whole reaction is intramolecular. Is it correct that this reaction is SN2, and the inversion occurs?



Answer



"Is it correct that this reaction is SN2, and the inversion occurs?" Yes, and yes, so the product is the one on the top.


mechanism



"Inversion" in this context doesn't mean that every substituent has to be flipped. Maybe it's clearer if you take away the intramolecular aspect of it. This is a typical SN2 reaction as introduced in many textbooks:


sn2


Would you agree, here, that the stereochemistry at carbon has undergone inversion? It is nothing to do with the methyl group or the hydrogen, but rather it is because of the fact that the chloride (that was originally pointing down) was replaced with an oxygen (that is now pointing up).


Now to make it an intramolecular reaction, just replace the R with a single bond to the OH.


bond - What allows sulfur and phosphorus to expand their octet?


There are many compounds in which the stability of a molecule is not governed by the presence of octet configuration in central atom. In most of the cases the central atom is generally sulfur or phosphorus. In these cases either the central atom has 6 electrons, or sometimes the electron count exceeds 8 and 10 or 12 electrons in its valence electron shell.


This makes the concept of octet somewhat incorrect. My question is how can they increase their octet to such an extent?


Could someone explain this in relation with sulfur trioxide?



Answer



Whether sulfur or phosphorous actually expand their octet is contested within the chemistry community. Another term for this octet expansion is "hypervalency." You can find many works of research regarding hypervalency. The consensus, according to Wikipedia, is that both can expand their octets, but not to a significant extent. In other words, d-orbital utilization is low at best.


Regarding sulfur trioxide, this article may be of interest.



We find no evidence to support notions of p π –d π back-donation from oxygen to sulfur.




Regarding the octet concept, it's only a guideline at best, and nothing more. I wouldn't put too much stock into the concept. If you insist on using it, then only apply it to the following elements: $\ce{C, N, O}$, and $\ce{F}$. And note that for carbon, there are well known exceptions in organic chemistry - carbocations (which have less than an octet of electrons). Carbocations however tend to exist mainly as reactive intermediates. Therefore, a more nuanced statement might be $\ce{C, N, O}$, and $\ce{F}$, when involved in neutral and thermodynamically stable compounds, generally have 8 valence electrons.



this makes the concept of octet somewhat incorrect.



infinite impulse response - How to design very narrow, sharp lowpass filters - Only DC needed?


I asked exact the same here one year ago: One year ago question I asked this question again here, because after one year, I have learned more about DSP and am thinking ways to improve it.


Filter description




  • Filter input data rate is 64kHz




  • Filter output data rate is 0.5Hz - 2Hz





  • The filter is preferably to have bandwidth of 1mHz with very sharp transition area, since only DC is needed and the noises at 0-5Hz is large.




The answer I got


The averaging data is the best DC I can get. I bought this answer. However, it now becomes plausible to me, since a filter always have a bandwidth and frequency responses. Averaging is essentially a FIR with no superior characteristics.


Questions




  1. Shall the filter be designed in this way: 9 stages of halfband filters(64kHz -> 125Hz). Followed by three stages of cascaded integrator–comb (CIC) filters with R=5. Then the output will be fed into a 1st order IIR filter?





  2. Maybe 16 stages of halfband filters? (64kHz -> 0.9765625Hz) And then be fed into an IIR filter.




  3. How shall the filter be designed?






Friday, July 26, 2019

experimental chemistry - What is the correct way to verify a structure's geometry, for example for benzene?


My goal is to compare a calculated bond length with experimental data. Benzene is obviously common enough to expect sufficient experimental data to be available for it on the internet.


I have found two sources for the C-C bond length in benzene, and the numbers differ very slightly. This source says 140 pm for benzene, while this source says 139 pm for benzene. Both claim their number comes from x-ray diffraction.


Is the discrepancy possibly attributable to a difference in solvent? Is a difference of 1 pm even significant? What is a good way to know for sure which quantity is correct?



Answer



A deviation within the low picometres is nothing to worry about, there are many reasons for this.


Primary literature, like peer-reviewed journals, will always publish an analysis of the obtained values along with any error bars, i.e. how accurate the measurement is. When you have disagreeing values it is worthwhile to have a look at these, too.

Secondary literature, like encyclopaedias, will usually only quote values and might not include all details due to their general reference nature.


Quite often if you have different values, the conditions of the measurement simply were not the same. Also keep in mind, that within the recent years a lot of progress has been made for spectroscopic measurements. Hence you can find values from older publications that are significantly different from more modern values.


For example Tamagawa et al. reported $r_g(\ce{C-C}) = 139.9 \pm 0.1~\mathrm{pm}$.[1] They used a method, which combines diffraction and spectroscopic data. This article was published in 1976 and it was introduced with the following paragraph. I think that pretty much summarises the predicament of modern structural analysis.



It is often found that the structural data of the most basic molecules are not very up-to-date because such molecules were studied in the early stages of the development of experimental methods for structure determination. Benzene is one such molecule.



And since then many more studies on benzene have probably been published. Chemspider.com lists (currently) seven data sets[2] and I am confident this is just the tip of the iceberg.


In a quite recent publication by Budzianowski and Katrusiak the crystal structure of benzene has been studied at various pressures. They pressure froze the molecule(s) in situ in phase I.[3]
We learn from this, that there is more than one phase in which benzene crystallises. And a little more digging leads us to a publication by Piermarini et al. dealing with the crystal structure of benzene II at 25 kbar.[4] But I will not go into that and rather focus on the former publication.
This paper illustrates nicely that there cannot be only one true value for the compound. I will reproduce a part of table 2 from the publication here. $$ \text{Bond lengths (}\mathring{\mathrm{A}}\text{) and angles (}^\circ\text{) for benzene in phase I.}\\ \begin{array}{llll} & 0.3~\mathrm{GPa} & 0.7~\mathrm{GPa} & 1.1~\mathrm{GPa} \\\hline \mathrm{C1—C2} & 1.40 (4) & 1.397 (8) & 1.420 (16) \\ \mathrm{C2—C3} & 1.38 (8) & 1.384 (10) & 1.41 (3) \\ \mathrm{C3—C1^i} & 1.38 (5) & 1.354 (10) & 1.32 (2) \\\hline \end{array}\\ \text{Symmetry code: (i)} 1-x; -y; -z. $$



As you can see even in a single crystal structures, the bond lengths are not equal. This is obviously due to packing effects and intermolecular interactions. When we talk about a single value for the carbon carbon bond length in benzene, then we assume an idealised, even rigid, molecule.


And there are more ways to obtain the geometry of a molecule: IR, microwave, Raman to name a few.[5] Nowadays we can employ computational chemistry and try to predict bond lengths, but there is a catch to that, too. These calculations take place at absolute zero and no pressure and we have a couple of other approximations in the mix. You can have a look at the Computational Chemistry Comparison and Benchmark DataBase, which lists values from 138.3 to 144.3 pm for the carbon carbon bond.[6] For example, my own calculation on the MP2/def2-SVP level of theory gives me a carbon carbon bond length of 140.0 pm. But that is a value that corresponds to a stationary point on the potential energy surface. We all know that this molecule has thirty vibrational modes, which are not yet accounted for. Below is just one, one that I find particularly funny.


geometry of benzene MP2/def2-SVP exemplary vibrational mode of benzene


TL;DR Don't worry about deviations of about 1 pm. When there are larger differences, look at the original publications about the conditions and trustworthiness of their measurements. Always consider the error margins on your own experiments when you compare values. It also depends on how accurate you need your value to be before you go and dig deep into publications from 50 years ago. (For what it is worth, you could round 139 pm to 140 pm.)


Notes and References



  1. Tamagawa, K.; Iijima, T.; Kimura, M. Molecular structure of benzene. J. Mol. Struct. 1976, 30 (2), 243–253. DOI: 10.1016/0022-2860(76)87003-2.

  2. CSID:236, http://www.chemspider.com/Chemical-Structure.236.html (accessed November 18, 2018)

  3. Budzianowski, A.; Katrusiak, A. Pressure-frozen benzene I revisited. Acta Crystallogr Sect B 2006, 62 (1), 94–101. DOI: 10.1107/S010876810503747X.

  4. Piermarini, G. J.; Mighell, A. D.; Weir, C. E.; Block, S. Crystal Structure of Benzene II at 25 Kilobars. Science 1969, 165 (3899), 1250–1255. DOI: 10.1126/science.165.3899.1250.


  5. Wikipedia has a longer list: Molecular Geometry.

  6. Unfortunately I am unable to generate a permalink from the database: http://cccbdb.nist.gov/ I welcome you to play around a little by yourself.
    However, I'll include the summary from the geometry comparison between the C1–C2 bond length:

    distance is atom 1 (C) to atom 2 (C)
    Experimental bond length is 1.397 Å Calculated bond lengths range from 1.383 to 1.443 Å
    The bar charts show differences (theory - experiment) and the range is −0.046 to 0.046 Å






halacha - Will editing genome of embryo having Jewish parents diminish Jewish status of later child?



There's a dreadful genetic illness known as Tay-Sachs requiring two carriers to activate the fatal effects in a child.



Probably, in reaction to the 20th century eugenics movement and its terrible results, I seems most poskim would be against any alteration of the human genome for any reason, and probably forbid it for their communities, in the name of the sanctity of human life.


There will come a time when humanity develops the technology to edit a child's genome, and to also completely identify the key genes responsible for full-blown Tay-Sachs.


Assuming two Jewish parents desired to conceive a child using IVF from which the Tay-Sachs had been edited out along the way, would this still be forbidden?


If so, would only the parents suffer the moral consequences? Or would any Jewish child whose genome had been edited in any manner even for therapeutic purposes, no longer be considered fully Jewish (i.e. mamzer or karet) as a deterrent against such an action?




tefilla - Davening for the demise of the wicked


Is it a mitzvah,permissible, forbidden to daven for a Jewish wicked person to die? If the wicked person is someone who is trying convert Jews to Christianity would that make a difference? I am looking for some sources from the Talmud, Rishonim and/or Achronim.




halacha - Should a chazan who missed a day count the omer with a b'racha?


In general, someone who misses a complete day's counting the omer continues to count without preceding his count with the b'racha (benediction) normally recited for the mitzva of counting. (In fact whether he should recite it is unclear, and we rule that, because of that inclarity, he should not.) I'm wondering about a shatz (leader of the prayer service). In many synagogues, he recites the b'racha aloud (also having in mind to exempt anyone listening). What if the shatz has missed a day? Presumably, like anyone who missed a day, he doesn't recite the b'racha aloud — but is there an exception made for a shatz, whether so as not to embarrass him or for some other reason?




electronic configuration - How many d-eletrons are in the outer shell of following compounds:


How many d-electrons are in the outer shell of the metals in following compounds:


$\ce{ZnS}$ and $\ce{NiS}$


So sulphur does not has any $\ce{d}$ electrons and $\ce{Zn}$ has $10\ce{d}$ electrons.


But I am pretty sure that this question is more complex to answer like that.


What is considered as the outer shell? as $\ce{Zn}$ has the electrons in the $3\ce{d}$ shell but there is still a filled $4\ce{p}$ shell?


Does it also matter that it is a compound ? ($\ce{ZnS}$ not only $\ce{Zn}$). As I see no reason why they included $\ce{S}$ but I guess it has an important reason.


I am new to transition metals, any help would be really appreciated.




organic chemistry - Identifying an unknown compound(w/ NMR/IR)?


I need some help identifying the following unknown compound. Any suggestions or hints regarding the possible compound would be highly appreciated.


So far I am thinking the broad peak on the IR is an alcohol that somehow mixed with possible sp3 CH bonds.And the peak around 1600 around is I think a sp Carbon-Carbon bond. The compound should have four distinct groups of protons. Beyond this basic analysis, I couldn't really come up with a compound. Please help.



NMR


enter image description here enter image description here


EDIT(07/09/14): I have updated the question with newer NMR(below the first NMR) and IR.


Some other additional info I worked out in the Lab:


look: white powder like solid.


mp: 116.3-119.0


Solubility Water - insoluble NaOH - insoluble Sulfuric Acid - soluble


Classification Tests: Water Insoluble Phenol Test - positive; a dark red precipitate formed. Chromic Acid Test - positive; green precipitate formed. Bromine Test for Unsaturation - positive; Bromine discoloration happened until about 2 ml of Bromine was added. White precipitate formed.


This is my first time doing these tests so please don't consider their results too strictly. My Instructor said IR is much safer way to determine functional groups.




kana usage - Why is Toyota typically written in Katakana? (トヨタ)


Presumably, as a Japanese name, it should be written in Chinese characters or in hiragana.



Answer



It's a matter of stylistic choice which is hard to explain logically. It's kind of like asking why many Western companies adopted lowercase logos these days, which apparently look "grammatically wrong" to English learners :-)


In general, katakana names often have a "international", "modern", or "technical" impression, which is definitely good for a high-tech company like Toyota. On the other hand, kanji names tend to look somewhat "old", "classic" or "traditional" to the eyes of Japanese people. If you have the textbook knowledge of when to use katakana in everyday writings, you can probably feel why it's so.


As a matter of fact, a majority of technology companies prefer katakana or alphabet branding over kanji branding even when their official names are in kanji. Toyota and Mazda switched their official names to katakana many years ago. Honda retains the official company name in kanji, but we rarely see the kanji name in news and ads. Some companies like Nissan still use kanji along with alphabet.


To take another example, beer/whiskey breweries in Japan tend to have katakana names/brand, (キリンビール, アサヒビール, サッポロビール, ...) while sake/shochu makers tend to have kanji names (白鶴酒造, 菊正宗酒造, ...). Oh, I didn't even know that キリンビール is still officially 麒麟麦酒株式会社.


Related:




hebrew - Extra yud in Yerushalaim


Why and by whom was there a yud added to make "ירושלים" instead of the original "ירושלם"?




organic chemistry - Can a meso compund be rotated in ANY sort of way in order to show its achirality?


Are there any limits to rotating a compound in order to prove that its chirality or achirality? (assuming that you're rotating about a single bond)




Thursday, July 25, 2019

pronunciation - words often mispronounced




What are some words commonly mispronounced? (Not by elision/reduction (like ה׳‎→אדְני‎) or assimilation (like תזכרו‎→תשׂכרו‎), but rather words that are pronounced wrong simply because that's how people think they should be pronounced.) I'm excluding from this request errors in stress (emphasis), as those are, alas, too numerous to list. I'm including, however, words mispronounced in a person's own dialect (הברה), though others would consider them correctly pronounced. And I mean any "Jewish" word: a word relevant to, and mispronounced in, Jewish life, be it Hebrew, Yiddish, Aramaic, or other.




avot patriarch fathers - Did Yitzchak not Fulfill the Mitzvah of "Be Fruitful and Multiply"?


According to the understanding of many commentators "pru u'revu" (be fruitful and multiply) is a positive commandment which is not fulfilled unless a man has both a son and daughter as offspring. Based on this understanding it would seem that Yitzchak did not fulfill this commandment. Is this correct? Are there any sources that indicate that either:



  • He had a daughter

  • He was exempt from this mitzvah




halacha - Can you derive benefit from another Jew's melacha if it happened a long time ago?


We aren't supposed to derive benefit from melachot performed by other Jews on Shabbos. But what if it didn't happen this Shabbos?


What if our guest brought a bottle of liquor as a gift last Shabbos, and we understand he carried it outside an eiruv. This Shabbos, can we drink it? If we did, is the transgression equivalent to having drunk it last Shabbos?


What if the melacha happened many weeks (/months/years) ago?


Note: I understand that the obvious assumption is that the answer is "No, we can't drink it," but I am curious to see if this is authoritatively treated in a source.



Answer



In terms of deriving benefit from the actions done by a Jew on Shabbat the Shulchan Aruch (OC 318:1 and Mishna Berurah and Biur Halacha there) distinguish between a number of cases:



  • If a biblical prohibition was violated purposefully (deoraita bemeizid) then no one can derive benefit from it for the rest of shabbat, and the violator himself cannot derive benefit forever.

  • If a biblical prohibition was violated accidentally (deoraita beshogeg) then no one including himself can derive benefit from it for the rest of shabbat and everyone is permitted to derive benefit after shabbat. (Some are lenient here in a case of need.)


  • If a rabbinic prohibition was violated purposefully (derabanan bemeizid) then no one including himself can derive benefit from it for the rest of shabbat and everyone is permitted to derive benefit after shabbat. (Some question this ruling and forbid him from deriving benefit from it forever.)

  • If a rabbinic prohibition was violated accidentally (derabanan beshogeg) then it is permitted to all to benefit immediately.


A caveat:



  • Some hold that the above is true if violating the prohibition changed the object physically, but if something was carried between domains illegally then it remains permitted. Others dispute this distinction.


computer vision - Camera Calibration using Single Input Image


Given a camera, permanently located at the same position, angle and distance from what is being captured, and a single calibration image ( a row of vertical lines [ | | | | ] ), how would one go about using the image to apply correction (barrel distortion) to all subsequent images?


Numerous examples exist online for the camera calibration problem, but most attempt to achieve the correction through guess-work, or highly involved processes to correct real-world images. However, I cannot find anything on calibrating a camera whose position and subject is always at the same position, and where the expected positions of vertical lines are known prior to correction.


The closest I've come to my approach is the plumb-line calibration method described by brown (1971).


Are there any algorithms or pseudo code out there which describes an approach to calibrate using a single input image of vertical lines (where distortion would be clealry visible by the gap between each line)?


Close-Range Camera Calibration - D.C, Brown




word order - When stating a non-Japanese name, should the surname come first?


When stating a full non-Japanese name, should one use the "Surname Firstname" rule used for Japanese names (i.e. "Smith John / スミス ジョン") or the name's native rule (in the case of an English name, "Firstname Surname" (i.e. "John Smith / ジョン スミス")).



Which format would native Japanese speakers use, when stating an obviously non-Japanese full name?



Answer



Typically, you state it in the order that is normal for your language. Koreans and Chinese say their family name first, Americans say it last. Japanese people are well aware of that language difference, so they expect us to keep our names in the original order. They also use the original order when saying foreign names themselves.


The only times I put my last name first is when I'm required to do so, as in opening a bank account.


grammar - Help me to understand やらなきゃいけない and やらなきゃならな い


Need more clarity on short forms.




  • やらなきゃいけない

  • やらなければいけません

  • やらなきゃならない


  • やらなければなりません



As per my understanding all phrase will give same meaning. "Must do". I know this is very basic question but need to get more clarity on short forms, because in most of the conversion they are using short forms and not able to understand some times.


やらなきゃいけない is short form of やらなければいけません
やらなきゃならない is short form of やらなければなりません



  1. Is my understaind correct?

  2. Please also explain related short forms.




Answer



やらなきゃ is a contracted/collapsed form of やらなければ.
いけません and なりません are the polite forms of いけない and ならない, respectively.


So やらなきゃいけない (or ~いけません in polite form) is a contracted form of やらなければいけない (or ~いけません in polite form). Same goes with the ~ならない/~なりません versions.


We also have:




  • やらなくてはいけない/ならない (or ~いけません/~なりません in polite form)

  • やらなくちゃいけない/ならない (contracted form of やらなくてはいけない/ならない)

  • やらないといけない (or ~いけません in polite form)


  • やらねばならない (or ~なりません in polite form) ← sounds a bit literary/stiff



People will sometimes use だめ (+ だ、です etc.) instead of いけない/ならない etc.


In colloquial speech you'd also hear shortened forms such as:




  • やらなきゃ。(shortened/contracted form of やらなければならない/いけない)

  • やらなくちゃ。(shortened/contracted form of やらなくてはならない/いけない)

  • やらなくては。


  • やらないと。(shortened form of やらないといけない)

  • やらねば。(shortened form of やらねばならない) ← less common in casual speech



Wednesday, July 24, 2019

shabbat - When do you take off a Tallis which was put on for the Torah reading?


I have seen in many Ashkenazi synagogues that the person called to the reading of the Torah at Shabbos mincha puts on a tallis.


Typically, he takes this tallis off after the kedusho of the repetition of the Amidah.


I thought he wears the Tallis so as not to embarrass someone who is not dressed well when he goes up to read.


Therefore it would seem he could take it off immediately after the reading. Why is it worn after the Torah reading?


If it is to be worn for the Amidah, why is it not worn until the end in order not to disturb concentration in the repetition of the Amidah?




grammar - History of だ、です、 and である


Historically where did all of these different forms arise, and when are they used? I noticed that だ and である both have their place in different 文法形, what is the difference in their meaning? I know that in things like 論文 as well as, apparently, on Wikipedia である is used, but I really don't know why.




electronic configuration - In which cases does the 3d subshell take precedence over the 4s subshell?



I've learnt in Chemistry that for example in Chromium, the 4s subshell only has one electron in favor of making the 3d subshell half-full. Also, for Copper the same happens.


What other circumstances does this happen under? Do ions obey the same pattern, e.g. Mn+?




halacha - Bas Cohen having relations with a non-Jew


It says in SA YD Siman 305 that a Bas Cohen that has a bechor (firstborn) with a non-Jew there is chiyuv of pidyon haben since the Bas Cohen through having relations with the non-Jew she looses her status of being a Bas Cohen. What about if a not-frum (irreligious) Bas Cohen before becoming a baalas teshuva (religious person) had relations with a non-Jew. Then after becoming frum (religious) later got married to a Yisrael and had a bechor. Is there a chiyuv of making a pidyon haben on that child? (My doubt is because through the relations with the non-Jew before becoming frum perhaps she lost her status of being a Bas Cohen.)




digital communications - Understanding the Matched Filter

I have a question about matched filtering. Does the matched filter maximise the SNR at the moment of decision only? As far as I understand, ...