talmud gemara - Doesn't prat u'klal mean that there are unnecessary words in torah?

This answer about R.Yishmael's 13 talmudic principles quotes the Artscroll siddur thus:

Prat U'Klal - When specific cases are followed by a generalization, the rule applies by any case in the generalization, and is not limited to the cases. An example would be that with regarding lost objects the verse says: "So too you should do to his garment, so too you should do to his donkey, so too you should do to any lost object of your brother". Therefore, one has to return all lost objects, and not just donkeys and garments.

This seems to suggest that the specifics are not actually necessary; the torah could have just given us the general law ("you should do to any lost object of your brother", in this case). But I was taught that there are no unnecessary words in torah. So what purpose do the specific cases serve?

Answer

Because the specific cases do teach us something about the scope of the general statement.

In this example, the Mishnah (Bava Metzia 27a) points out that a garment has unique identifying marks (simanim) and an owner who is looking for it (tov'im), and that this therefore delimits "any lost object of your brother": it has to be returned only if it has these two features. Which means, for example, that a mass-produced item that has no identifying marks, like a coin, need not be returned even if someone is claiming it; conversely, an item with such a mark, if you know that the owner has given up hope of finding it, needn't be returned either.

(Incidentally, this is an example of binyan av, the third of the 13 principles: a specific example serves as a paradigm for other, similar, cases. As Shmuel Brill pointed out in his comment to that question, the Gemara often uses this device without mentioning it by name.)

The Gemara (ibid.) goes on to point out that the Torah's mention of a donkey teaches us that, since a donkey and its saddle always go together (saddles are made to measure for each individual animal), then if you find a saddled donkey, and the owner is unable to provide a siman for the donkey but is able to identify the saddle, then you have to return both.

---

This is aside from the non-literal levels of meaning in the Torah. Again using this example, the Lubavitcher Rebbe zt"l, in one of his talks (Likkutei Sichos, vol. 1, p. 157) explains that each of the four specific lost objects that the Torah mentions (there are also an ox and a sheep mentioned two verses earlier) represent four types of people who have "lost their way" in serving G-d, each failing in a different aspect, but all of whom can be "returned" to Him through teshuvah.

taamei mitzvot reasons - What is the significance of the Mishcan in Judaism?

A good part of Sefer Shemos discusses the tedious details of the construction of the mishcan (tabernacle). To the layman, these commandments seem very illogical.

Aside from the fact that God commanded us to build a mishcan, is there any meaning behind the mishcan?

Answer

God's overarching command to build the Mishkan is Shemot 25:8:

וְעָשׂוּ לִי מִקְדָּשׁ וְשָׁכַנְתִּי בְּתוֹכָם

And they shall make Me a sanctuary and I will dwell in their midst.

R' Samson Raphael Hirsch, in his commentary¹ on this verse, explains that its two clauses present two intertwined purposes for this construct, each alluded two by one of our names for it:

• 
  

  "And they shall make me a sanctuary" - a "Mikdash" - requires us to set aside space and materials in a prescribed manner for God's service, symbolizing "giving up the whole of our private and public life to the fulfillment of the Torah."

  
  



• 
  

  "And I will dwell in their midst" refers to God's responding to our sanctifiation by dwelling - "Mishkan" - amongst us, putting "the protecting and blessing-giving presence of God in our midst, manifesting itself in the happiness of our private and national lives."

  
  

So that the sphere within which we have to try and find the meaning of the Tabernacle as a whole, and its component parts in detail, is simply mutual covenant-relationship between God and Israel, brought about by the giving and acceptace of the Torah.

R' Hirsch's commentary goes on to explore the symbolism of every material and technique used in constructing the Mishkan, every component and vessel contained in it, and, elsewhere in the Torah, every service performed in it - all fleshing out details of and variations on this basic dual theme of our dedication to God and His kindness to us. If you want to learn more about elegant, edifying significance to be found in every detail of the Mishkan and the service therein, I highly recommend study of R' Hirsch's commentary on the rest of Shemot 25 - 30 and then on the passages in Vayikra and elsewhere that describe the various services.

^{1. Quotations below are taken from an earlier English translation, the one I have on hand.}

golus exile - how does one get 10 "Lost Tribes"?

There were 12 shevatim that got land in Eretz Yisroel , which split into 2 territories - Yehuda and Yisroel. In the land of Yehuda we had Shimon, Yehuda and Binyomin.

12-3 = 9 , yet the reference is always to 10 - even the tearing of the garment towards the beginning of Melachym. I would even argue the number should be 8 as the vast majority of Levi was in Yehuda.

So , whence 10?

halacha - Why do we say the normal Mishnayos after Birkas HaTorah on Tisha BeAv?

After Birkas HaTorah in the morning, we say a Pasuk (VaYedaber ... YeVarechecha ... VaAni Avarachem), a Mishna (Eilu Dvarim SheEin LaHem Shiyur ... VeTalmud Torah) and some Gemara (Eilu Devarim SheAdam Ochel ... VeTalmud Torah Keneged Kulam).

We say those verses to fulfill our obligation to learn Torah after Birkas HaTorah.

On the morning of Tisha BeAv we only learn the "sad" parts of Torah. Why don't we replace these phrases with more "appropriate" verses (kind of like how we replace Mishnayos before Kaddish)?

Answer

Rav Moshe Einstadter of Cleveland, Ohio told me that for several years he actually switched to saying pesukim from Eicha, and Mishnayos and Gemara related to mourning. He switched back after some time.

Rav Ezra Neuberger (Rosh Kollel of Kollel Avoads Levi of Ner Israel) explained that these segments are not arbitrary, or just happen to be conveniently related to Torah. He explained that they really complete the Birkas HaTorah, in that each one highlights an element of what Torah study is, and therefore they are very much connected to the beracha. The verses communicate that Torah is a beracha, the Mishna communicates that Torah is boundless, and the Gemara communicates that Torah surpasses this world. Therefore, they are singularly appropriate to accompany the beracha, and they really are, in a sense, part of the beracha. We don't replace them because they are more intrinsic to that part of the service.

(@DoubleAA's point not withstanding)

halacha theory - What happened in R' Chananya's penthouse (18 Dvarim)?

Speaking of Beyt Shamai, Yerushalmi Shabbat 9a also here:

Background:

"ואלו הן ההלכות שאמרו בעליית חנניה בן חזקיה בן גרון
שעלו לבקרו ונמנו ורבו ב"ש על ב"ה
ושמנה עשר דברים גזרו בו ביום:"

These are the halachos that were taught in the attic of Chaninah ben Chizkiya ben Garon: When they went up to visit him and voted, Beis Shamay held the majority over Beis Hillel. Eighteen decrees were enacted on that very day.

Action:

"אותו היום היה קשה לישראל כיום שנעשה בו העגל.
רבי אליעזר אומר בו ביום גדשו את הסאה.

רבי יהושע אומר בו ביום מחקו אותה.
...
תנא ר' יהושע אונייא תלמידי ב"ש עמדו להן מלמטה והיו הורגין בתלמידי ב"ה.
תני ששה מהן עלו והשאר עמדו עליהן בחרבות וברמחים.
תני שמונה עשרה דבר גזרו ובשמונה עשרה רבו."

That day was as difficult for Israel as the day the Golden Calf was made. Rebi Eliezer says, on that day they overfilled the measure. Rebi Yehoshua says, on that day they emptied it.

It was taught: R. Yehoshua taught, "The students of Beis Shamai stood bellow and were killing the students of Beis Hillel." It was taught: Six of them went up and the rest stood over them with swords and spears. It was taught: Eighteen decrees were enacted on that day....

Please explain what was going on in that penthouse and how those 18 regulations were ruled. Is that the accepted way of resolving Halochos, forcing the other side into the minority?

tanach - Why does the Mishna misquote the Tanakh?

In a number of instances, the Mishna provides quotes from Tanakh that differ from the versions of Tanakh that we have today. So, for example, Sotah 6:4 (31b). There, the mishna quotes Deuteronomy 19:15 as saying "על פי שנים עדים", but the Masoretic Text reads "שני" instead of "שנים". Similarly, Sotah 7:5 (32a) quotes Joshua 8:23 as saying "וכל ישראל וזקיניו ושטריו", while the Masoretic Text renders the fourth word as ושוטרים (without the suffix). I have seen other examples of this phenomenon elsewhere and, while they're not significant differences, I wonder why the text of the Mishna was never updated to reflect the precise phraseology of scripture?

-

[With many thanks to @DoubleAA, if you consult Shabbat 55b you can see where Tosafot also comment upon this phenomenon (s.v. מעבירים כתיב) and, in Gilyon haShas, R' Akiva Eger brings an impressively exhaustive list of other instances in which this phenomenon also occurs: passages in the Bavli, the Yerushalmi, midrashim and mefarshim on Chumash. He also refers to another Tosafot (Niddah 33a, s.v. והנושא) that makes reference to this issue, though without offering an explanation for it.]

equilibrium - Effect of Temperature on pH of Water

The $K_\mathrm w$ is a function of temperature. It is $10^{-14}$ at $25\ \mathrm{^\circ C}$. When the temperature is $50\ \mathrm{^\circ C}$, the $K_\mathrm w$ can be calculated to be somewhere around $10^{-12}$ using Vant Hoff's equation, but this is so weird.

MY ATTEMPT

If we will solve for $K_\mathrm w=10^{-12}$, we get $\rm pH=6$. Will the water become acidic due to increase in temperature?

Why does gamma correction of image use two different definitions of gamma?

I've noticed that the gamma value used in level adjustment of Photoshop and Canvas is 'opposite' of gamma values defined in Wikipedia or MATLAB imadjust documentation.

In Wikipedia or MATLAB, high gamma (>1) will make an image darker, whereas in Photoshop high gamma (>1) will make an image brighter.

I've also noticed that, even among image processing software, Zeiss' Zen software uses high gamma (>1) to make an image darker.

There seem to be two definitions of gamma value. This is just confusing... I assume that this is related to 'gamma encoding' and 'gamma correction'. But can anyone explain the rationale of these two defintions and when to use which one?

Vout = Vin ^gamma % Wikipedia or MATLAB


Vout = Vin ^1/gamma % Photoshop or Canvas

transform - Power Spectral Density computation and units

I want to make some calculs of power spectral densité of signal. For example a real voltage signal (physical unit : $V$) in time $g(t)$, its fourier transform $G(f)$ and $S_g(f)$. As far as I know, the power spectral density units for g(t) is $V^2/Hz$. However, I find in various sources the following equation to calculate the power spectral density : $S_g(f)=|G(f)|^2=G(f)G(-f)$

I do not understand this "definition" (of course the most fundamental definition of PSD is given by the Wienner-Kintchine theorem) , as it leads to a spectral density in $V^2/Hz^2$.

Regards, Mike

halacha theory - What's so slave-ish in the Hebrew Slave?

I'm trying to compare the status and duties of a Hebrew slave that sells himself to slavery versus a man that agrees to work for 7 years (שכיר שבוע), as in B"M 9,11: "שְׂכִיר שַׁבָּת, שְׂכִיר חֹדֶשׁ, שְׂכִיר שָׁנָה, שְׂכִיר שָׁבוּעַ, יָצָא בַיּוֹם, גּוֹבֶה כָל הַיּוֹם".

Here are some points of similarity:

1. They both don't work on Shabbos and Yom Tov


2. They both own their property, and their body is not their master's property


3. While at work (practically for all the time) their profits (incl. lost and found) belong to the master


4. They stay married with kids


5. They stay obligated in all Mitzvos


6. All negative commandments toward one's fellow Jew hold for both (Ona'a, beating etc)


7. The master pays money to both

Here are some points of differences:

1. Master pays in advance vs after the work


2. Master can't force him to do a disregarding job, one that will "reveal his slavery"


3. Master has to equal his conditions to his own


4. Master is obligated to pay him some extra on freeing, and some more.

The last list in comparison to the first does not justify, in my opinion, the "essence of slavery" - to call this Jew a slave, especially in comparison to a real slave - Eved Knaani, whose body is his master's property!

As usual, unfortunately, I couldn't find an official definition of a "slave" - what qualities make one a Hebrew slave. Hence the question: why a Hebrew slave is called really a "slave" and not, for example, a persistent/diligent/enduring employee?

grammar - What is Vて+た construction?

I came across Vて+た construction in a song I've been listening to:

あなたのその瞳をただ見つめてた

Can someone explain what it means? I've tried looking for it in some grammar books but unfortunately I couldn't find it.

grammar - What's wrong with using 内に in this sentence?

My textbook claims that this is an incorrect usage of uchi ni:

彼が会社に行っている内に、贈り物が届きました
While he is commuting to the office, a present arrived.

Why is this wrong? It looks fine to me.

coordination compounds - Why is tetracyanonickelate square planar?

Why is tetracyanonickelate, $\ce{[Ni(CN)4]^{2-}}$ square planar?

• $\ce{CN}$, for being a strong field, would not follow Hund's rule.



• the central atom $\ce{Ni}$ would have a +2 charge so its configuration would change from $\ce{3d^8 4s^2}$ to $\ce{3d^8 4s^0}$


• Using the statements above and using crystal field theory I get its hybridization as $\ce{dsp^3}$, which suggests that its shape must be trigonal bipyramidal while it is not.

minhag - Matzah meal before פסח

On the subject of not eating Matzah before פסח, may one eat products containing Matzah meal in that time?

Answer

It is prohibited to eat Matzah on Erev Pesach, however cooked or boiled matzah-meal products are permitted according to all the Poskim. Fried Matzah-meal products, however, should be avoided (see Sha'ar ha-Tziyun 444:1). Baked Matzah-meal products, such as cakes or cookies, are prohibited; Harav S.Z. Auerbach (Erev Pesach Shechal b'Shabbos, pg. 207); Shevet ha-Levi 8:117.

meaning - What is the difference between 調子【ちょうし】 (choushi) and 具合【ぐあい】 (guai)?

Both words mean condition. In what context do we use them? Is one for expressing the condition of living things and the other one for the non-living things?

halacha - Why do people feel that there is a NEED to wear tzitzit?

There is a law in the torah (and the meforshiim afterwards) to attach tzitzit to all four cornered garments that you will wear.

Ok. I understand that.

But where did it come to pass that some people say one is required to wear tzitzit?

If I am not wearing a four corned garment, why should I go out of my way to acquire one?

Is it a halachic obligation to? or is this just custom?

food - "Chometz" Cookies on Pesaḥ

According to the Sephardic tradition that egg matzah can be permissible on Passover (see e.g. http://etzion.org.il/vbm/english/archive/moadim70/02-70moed.htm), is there any reason why they would not eat most regular cookie recipes which usually can easily be finished within 18 minutes and don't generally require water (assuming it could be manufactured in a special Pesach/matzah bakery with kosher-for-Pesach flour)?

music - Which parts of the Chazon Haftorah get sad tune (Eicha trop)?

The Shabbos before Tisha B'Av gets a very sad Haftorah, known as Chazon. It's Isaiah 1:1--27. (I recommend you open the text in a new window, or else the answers to this question will make no sense.)

Tradition has it that most of it is chanted with the extra-sad tune used for Lamentations (Eicha), instead of the usual Haftorah tune. But which parts? Is there an official source on this? Is it still a matter of local custom? Or even individual preference?

halacha - Contradictions between Federal and State Laws as they relate to Dina De'Malchusa

I am wondering about the laws of Dina d'malchuta dina in the United States when there is a contradiction between state and federal laws.

Case in point: In 2012 both Colorado and Washington passed state legislation that legalized the use of recreational marijuana. However, marijuana is still illegal under the federal Controlled Substance Act. Until recently¹, the US Justice Department was still considering what policy to approach in such a discrepancy, which revolves around the ambiguously implied exo-constitutional powers stipulated in the 10th amendment².

All of this makes me wonder about what the halacha would say. Disregarding the halachic issue of drug use, is it permissible to do something that's legalized in your state but illegal federally? What does the halacha say about state/federal conflicts of laws?

I'm not so familiar with current American state laws, otherwise I would have picked an example that is only halachically problematic because of its dina d'malcuta dina issue (and as has been answered previously, the issues of marijuana are broader than that).

---

_{1. As of August 29, 2013, Attorney General Eric Holder has authorized Washington and Colorado "to create a regime that would regulate and implement the ballot initiatives that legalized the use of marijuana for adults."}

_{2. The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.}

coordination compounds - Why isn't the orbital angular momentum also considered while calculating the magnetic moments 3d transition elements?

My textbook (Chapter: The d- and f- Block Elements) makes an interesting assertion, however, without any reason to back it up.

Paramagnetism arises from the presence of unpaired electons, each such electron having a magnetic moment associated with its spin angular momentum and orbital angular momentum. For the compounds of the first series of transition metals, the contribution of the orbital angular momentum is effectively quenched and hence is of no significance. For these, the magnetic moment is determined by the number of unpaired electrons and is calculated by using the ‘spin-only’ formula, i.e.,

$$\mu = \sqrt{n (n + 2)}$$

where $n$ is the number of unpaired electrons and $\mu$ is the magnetic moment in units of Bohr magneton (BM). A single unpaired electron has a magnetic moment of $1.73$ Bohr magnetons (BM).

Now from what I've learnt from my physics classes last week, the magnetic moment of an electron is calculated using the formula:

$$\frac{m}{L} = \frac{e}{2 m_e}$$

Magnetic moment of revolving electron,

$$m = \frac{e}{2 m_e}L$$

In vector form,

$$\vec{m} = - \frac{e}{2m_e}\vec{L}$$

Where $m$ is the mass of the electron, $e$ is the magnitude of charge associated with the electron and $L$ is the angular momentum of the electron.

Now as I understand it, the angular momentum of an electron in an atom is the resultant of the electron's spin angular momentum and its orbital angular momentum.

But (as you can clearly see) my textbook exhibits an unexplained enthusiasm for only the spin angular momentum. It dismisses the contribution of the orbital angular momentum, as inconsequential, when determining the magnetic moments of electrons in the 3d elements.

As for the 'reason' provided by my textbook:

For the compounds of the first series of transition metals, the contribution of the orbital angular momentum is effectively quenched and is hence of no significance.

Well, I fail to see how that even counts as a 'reason'. I did ask my teacher about this, but she expressed her reluctance to go into the details; she's of the opinion that my particular query is “not worth clarifying” since it has no significance from the examination point of view (“Just give them what's in the textbook Aaron, nothing more and certainly not anything less”).

Subsequent internet searches have not yield any satisfying explanation (Perhaps I didn't use the right keywords while searching?).

So I'll just break up my question, point-wise, and list them below:

1. 
   

   Is the orbital angular really of no significance when calculating the magnetic dipole moment for 3d elements? If it is significant, is there any 'educational' purpose behind that omission in my textbook, or is it just a mistake?

   
   


2. 
   

   (As stated in the book) What causes the 'quenching'? How is this 'quenching' effect caused?

   
   


3. 
   
   

   Do the transition elements of the other periods also have "insignificant" orbital angular momentum contributions? Is it for the same reason as the 3d transition elements.

   
   

fast days - Why do we not say selichot on Tisha B'Av?

Every fast day on the Jewish calendar has its set of selichot that are said. The one exception to this is Tisha B'Av. This seems counter-intuitive to me because Tisha B'Av is the day when we mourn the destruction of the first and second Temples, which were destroyed because of our sins. It seems like Tisha B'Av should have selichot even more so than other fast days. So why do we not say them?

sexuality - Why can't one have marital relations with the light on?

The Gemara forbids relations during the day or by the light of a lamp (Niddah 17a). According to tradition, relations should take place at night and in the dark.

Why is one not allowed to have the light on when he's engaged in marital relations?

tanach - ALL Names of God

Where can I find an exhaustive list of all of the names of Hashem (preferably שמות and כינוים) in Tanach and elsewhere?

Is this too ill-defined a topic to have an exhaustive answer?

Do the 70 in the midrash on Shir Hashirim count?

Answer

Sepher Shorshei HaShemot by Rabbi Moshe Zecuto is an exhaustive listing of divine names. It is an alphabetical index. Each entry lists the source of the name as well as its usage.

grammar - Meaning of 'だろうと'

What is the meaning of 「だろうと」 in the following sentence, and how can we translate last part of sentence(bold one).

今や人型の死とした存在は、無感動な声で終わりの拳を握り締めた。彼の攻撃を防げる者など存在せず、しかも何発だろうと発射可能。

Thank you very much for help!

Answer

(Making an answer out of Chocolate's comment)

(何~~)だろうと means the same as (何~~)でも.

I don't know the context, but the last bit of the sentence means something like:

[...] it is possible to fire as many shots as wished

chutz laaretz - What tribe are the Bene Israel in India descended from?

What tribe(s) are the Bene Israel of India descended from?

kanji - Why is 着 used for both "to wear" [着]{き}る and "to arrive" [着]{つ}く?

The usual situation with multiple kun readings for a kanji is that they are closely related in meaning (like [上]{あ}がる, [上]{のぼ}る). But with [着]{き}る and [着]{つ}く I fail to see any semantic connection. Why is the same character used? Did one of the meanings formerly use another character that became the same by simplification?

Answer

Etymology aside, I see a semantic connection between the two verbs, in that 着る and 着く both have a meaning of 'attachment', with 着く having at least some overlap with 付く. 着物 is something attached to your body. It is a bit unintuitive but you can make the leap of arriving at a place as entering into it and becoming spatially attached to it as in　駅に着く.

I didn't find an 'official' source, but I found one QA site answer that supposes a similar thing:

１）身につける＝着る

２）行きつく＝到着

Also see the link for lots of different opinions.

electronegativity - How fast do electrons move around the nucleus?

Electrons, as we all know, are incredibly small. Smaller things do tend to move faster, right? So exactly how fast considering how small they are? Also, does the electonegativity between two atoms alter the speed of the electron?

sexuality - How can I curb my sexual desire?

I am looking for the best and most practical suggestion as to what a man can do to curb his yetzer hara (evil inclination) for sexual desire. Please provide sources for why your answer should be effective, and be specific as to why you think your answer is most practical.

word choice - Difference between 冗談 and ジョーク?

I have encountered two words for "joke": 冗談{じょうだん} and ジョーク.

What is the difference in meaning or usage between the two? I have tried Googling but found nothing particularly helpful.

halacha - Are there any leniencies for shortening the torah reading so the cycle takes more than a year?

In a small community without a learned ba'al koreh, it can be difficult to assemble enough readers to read the entire weekly parsha to a suitable degree of proficiency. Is there any provision in halacha for reading less, provided the entire torah is read over the course of the cycle (which will take more than a year in this case)?

I understand that some have a triennial cycle instead of the annual one (I've heard this said of Israeli communities in particular). I have the impression, perhaps mistaken, that those communities have a received tradition of the triennial cycle; they didn't just do it for expedience. Here I'm asking about a community that would otherwise read the entire parsha and complete the cycle in a year, except that they don't have enough good-enough readers. Short of fixing their ba'al koreh deficiency, what can such a community do?

Answer

I heard from R. Nota Greenblatt, the posek of the South that if the baal korei has trouble reading the whole thing you can further subdivide the parsha, as the original enactment of krias hatorah wasnt to finish it each year.

Related answer.

prayer book - Why do we use yud, yud?

Possible Duplicate:
Double Yud as G-ds Name

In the siddur we often do not write out the four letter name of God (yud,kay, vav, kay) but instead write yud, yud. Why do we do this? Is this a different name of God (for example, can it be erased)? Why do we choose this letter combination as a stand in for the 4-letter name?

inorganic chemistry - Questions on Neutral oxides

Neutral oxides, are non metal oxides which are neither acidic nor basic. I have noticed a pattern for neutral oxides which I am unsure actually holds true.

$\ce{CO}$, $\ce{H2O}$, $\ce{NO}$ and $\ce{N2O}$ are examples of neutral oxides. It seems that neutral oxides will always have 1 oxygen atom. While non metal oxides with more than 1 oxygen atom seems to always be acidic oxide. ($\ce{CO2}$, $\ce{SO3}$, $\ce{SO2}$ and $\ce{P4O10}$).

Is this a coincidence? Are there any neutral oxides with more than one oxygen atom?

Answer

Cl2O has one oxygen atom and is an acidic oxide. Thus, not all non metal oxides with one oxygen atom are neutral oxide. Also, not all neutral oxides have only one oxygen atom. N2O2, a neutral oxide but has more than one oxygen atom.

hefsek interruption - Answering amen to netilat yadayim after your own brocha

You've washed your hands and made a brocha 'al netilat yadayim' and are now waiting for the baal habayit to say hamotzi. If you then hear someone else washing their hands and making the bracha (a common occurrence) should you answer amen to that bracha, or is it considered an interruption?

Related question.

Answer

In the Shulchan Aruch Harav it says two or three words (that have nothing to do with the meal) are not considered a Hefsek:

ומכל מקום אין צריך ליזהר אלא מלדבר באיזה עסק וענין אחר אבל שיחה בעלמא ב' או ג' תיבות אינן חשובין הפסק לדברי הכל אפילו במים אחרונים (כיון שאין בהם ענין שלם) וכל שכן שמותר להשיב הן או לאו כששואלין אותו דבר.‏

tefilla - What is the point of praying if your fate is already decided on Rosh Hashana?

It says in Rosh Hashana

" On the New Year, [first of Tishrei] all who have entered the earth pass before Him, one by one, like young sheep, as it says: “He that fashioned the heart of them all, Who understands all their deeds”

" All are judged on New Year and their doom is sealed on the Day or Atonement."

So if your fate is sealed on Yom Kippur then why do we pray or give tzedakah or even do teshuvah and try to change are fate if it is already sealed.

For example in Shemona Esray we pray that the crop of this year should be good and another bracha is healing the sick.

So why do we pray for all those things if it is already decided on Rosh Hashana and Yom Kippur

experimental chemistry - Separating iron from blood

How can I separate iron from blood, without doing any damage to the blood/haemoglobin?

I have thought about using a magnet, but apparently iron in blood is not magnetic, and I have also looked at filtration techniques but not sure if that will affect the haemoglobin.

Updated Dec 2017: Let me add some context, I was/am looking for an alternative for chelation therapy such as Desferaloxamine infusions to remove iron in patients with iron overload as a result of repeated transfusions due to anemia

word choice - When to use 出て来る over 出る

Here is a sentence from the children's story ももたろう, describing when the child appears from within the giant peach.

桃の中から赤ちゃんが出てきました。

My dictionary lists 出て来る as meaning "to come out" with a note that it is a "special class, kuru verb." It also separately lists 出る as capable of meaning "to come forth."

What does using 出て来る accomplish over just using 出る?

I originally read 出て来る as two separate words: the て form of 出る + 来る, translating it as "exited and came." Is that essentially the etymology of 出て来る? Is 出て来る merely an idiom that my dictionary happens to list as a separate word?

Answer

The difference between 出る and 出てくる is that the later is specifically oriented towards the speaker (and if included, which is not always the case, also the hearer).
Compare the next two examples:

 a. 家から出てきた。
    [Someone] came out of the house.
 b. 家を出ていった。
    [Someone] left the house. OR [Someone] left for good.

In (a), we are located outside of the house, and the person inside the house comes out. As a result he is outside with us. Since where we are is "here", the person in the house moves to "here", i.e. comes. That is the meaning of the verb くる. In (b), we are inside the house (=here), and the person leaves, i.e. moves from "here" to some other place that is not "here". And that's the meaning of the verb いく.
But if you just use 出る then the locative specification (the information from where the person comes, and where the person moves to) is simply missing.
However, there is also a temporal use of ～てきた・いった. That is not surprising because linguists know that many languages treat temporal expressions like locative expressions. Most of the examples by Wang Muye have a temporal meaning.

c. 雨が降ってきた。
   It had come to rain.
d. 物価は上がっていくだろう。
   Prices will go up from now on.

Hope that helps.

chemistry in fiction - Could we possibly discover new extraterrestrial elements and minerals?

So, after dissolving a good portion of my brain by watching a ton of sci-fi, I started thinking about all of the strange new materials that we will supposedly have in the future. For example, the ever-present "di-lithium" in Star Trek. But, as I started thinking about it, I thought it was a little ridiculous (I know science-FICTION) that all these exotic elements could exist. No matter where a species comes from in the galaxy or universe, they would be working with the exact same Table of Elements as us. Furthermore, so long as they are similar to human-life, i.e. they breathe oxygen, need water, etc., and therefore live on similar planets, wouldn't the compounds be the same as well?

Let's say we are 250 million years into the future and have discovered superluminal space-flight at 100,000,000c. Say we cruise around to inhabitable planets throughout the galaxy and universe. Upon landing on these new worlds, the elements and compounds we find would be the same that occur on Earth, right? Would we still find diamonds, rubies, uranium, iron, etc.? Or is it possible that there are combinations of the elements yet unknown? Is it for certain that we have catalogued every element and isotope that occurs naturally? I understand that new compounds could be formed, but as far as the base elements and the naturally occurring minerals, have we found them all?

Answer

One thing which can be said with absolute certainty is that no species in the Universe (or even all their combined efforts) will even come close to exhausting the daunting enormity of chemical space. When you drag combinatorics into a problem, you can easily stumble on massive numbers, and this is the case here; it has been roughly calculated that there are on the order of $10^{60}$ "chemically reasonable" distinct molecules below a molar mass of $\mathrm{500\ g\ mol^{-1}}$! This means that almost all chemical substances which can exist, never will exist, be it from natural or artificial production.

No matter how far chemistry develops, we will always be interested in investigating the chemical composition of new samples, and will always find many new compounds doing so. Most of the time we'll find the same of what we do on Earth; there's no escaping the fact that $\ce{N_2}$ and $\ce{Al2O3}$ are very stable substances, for example, and can exist in a wide range of conditions. But there will always be something new for us waiting out there. Organic substances are tremendously varied thanks to the concatenability of carbon atoms. One might think inorganic substances are far less variable, but just the class of silicate minerals is enormous, and many polymorphs of the same substances can exist.

Having said that, at least one area of chemistry seems far closer to being exhausted; the elements themselves. There is no possibility of us having "missed" any element among the first 112, and we're still filling in the gaps at higher atomic numbers, but each heavier element discovered involves ever more complicated procedures and lower yields. Much of the experimentally determined properties of elements above $\mathrm{Z=104}$ come from the analysis of a tiny amount of atoms, as little as tens of them. Each new element is significantly more difficult to synthesize, and is less stable, which is hampering progress. We don't yet know very well how to get past $\mathrm{Z=122}$ or so even in principle, and are unsure how accessible the ultraheavy elements will prove to be. There is still great academic interest in several aspects of the elements and their isotopes, but current research deals with the production of very shortlived species, which have limited applicability.

In all, we will always find something new to explore, but whether we will always find something strange depends on what you mean by the word. There are still many, many substances to find which will display impressive biochemical properties, for example, and many lethal or crippling diseases today might still become curable in the future. But there is zero chance of finding a substance which makes magic real, which unlocks faster-than-light travel, which has endochronic properties or which can be used to make overunity engines and perpetual motion devices. Ultimately, Chemistry is a form of applied quantum electrodynamics, a subsection of Physics, and quantum electrodynamics is a very developed theory with incredible precision. Thus, there is little room for surprises, and they likely will not come from a chemical system unless it is very specially tailored, rather than randomly found in nature.

halacha - At what age does negiah start applying for non-immediate family?

Wikipedia's article "Negiah" begins:

The term negiah (Hebrew: נגיעה‎), literally "touch," is the concept in Halakha that forbids or restricts physical contact with a member of the opposite sex (except for one's spouse, children, siblings, grandchildren, parents, and grandparents). A person who abides by this halakha is colloquially described as a shomer negiah ("one observant of negiah").

If I have a young female cousin, at what age does she become forbidden to touch? I'm a guy in my mid-twenties.

According to R' Yosef Karo and others, "negiah" means "any touching at all". According to the Rambam and others, "negiah" means "affectionate touching". Whichever opinion is correct, the prohibition will start once she reaches a certain age, or a certain developmental stage. When will it start?

Please cite sources.

For help choosing among the conflicting views, CYLOR.

halacha - Touched acovered place while learning-may i continue learning?

Many times, in the middle of learning i will absentmindedly touch my scalp under my yarmulke, or my shoulder under my sleeve. Do i have to stop learning to wash my hands? may i continue without washing?

Answer

I personally asked Rav Herschel Schachter if one is scratching their scalp in the middle of learning if they need to interrupt their learning and go wash their hands.

He answered me that some poskim (he did not tell me which ones, though I link some opinions he may have been referring to below) rule that since nowadays we take showers on a much more regular basis one doesn't need to stop and wash their hands. As the halacha of washing hands after touching a "makom mechuse" was said in a time period where people took showers very infrequently.

The Shulchan Aruch 92:7 writes, “A dirty area is [defined as] the [normally] covered parts of a person’s body, because they contain beads of sweat. For instance, scratching one’s head [is considered touching a dirty place].” This refers to rubbing the roots of one’s hair, but if someone only touches the top of his head, he does not need to wash his hands (Shulchan Aruch HaRav; Mishnah Berurah 162:58, 164:10).

Kaf HaChaim 4, small paragraphs 75 and 98, is lenient even if one scratches the roots of his hairs which are not covered with a hat, because there is no sweat there.

Tzitz Eliezer, part 7, 2:14 concludes that if he washed his head and his hair is clean, even a person who scratches the roots of his hairs does not need to wash his hands.

See here.

For an interesting explanation why people in Mediaeval ages didnt bath see here:

This latter “disease” point was very common; it was believed in many parts of Europe that water could carry disease into the body through the pores in the skin. According to one medical treaty of the 16th century, “Water baths warm the body, but weaken the organism and widen pores. That’s why they can be dangerous and cause different diseases, even death.” It wasn’t just diseases from the water itself they were worried about. They also felt that with the pores widened after a bath, this resulted in infections of the air having easier access to the body. Hence, bathing became connected with spread of diseases, not just immorality.

For most lower class citizens, particularly men, this resulted in them completely forgoing bathing. During this time, people tended to restrict their hygienic arrangements to just washing hands, parts of the face, and rinsing their mouths. Washing one’s entire face was thought to be dangerous as it was believed to cause catarrh and weaken the eyesight, so even this was infrequent.

halacha - Do other Chasidic communities follow Shulchan Aruch HaRav?

The Maggid of Mezeritch told the Baal HaTanya to put together a Shulchan Aruch for Chasidim. The result is the Shulchan Aruch HaRav, which is used as a final authority for halacha in Chabad communities in most cases. Wikipedia asserts that it is used as such by "most Hasidim", but in my experience I have not seen it on the shelves of Chasidic shuls or batei midrash.

Do any other communities rely on it as a final authority rather than the Mechaber, the Rema, the Mishna Berura, the Kitzur, etc.?

Which communities rely on which other texts is also interesting.

halacha - Is a Child Born to Jewish Mother and Father Outside of Marriage a Mamzer?

I was reading that a child born to a married Jewish mother to a father who is not her husband is a Mamzer (bastard). But what if the parents are both Jewish, neither of them are married but they have a child together?

What is the child considered in that case? Still a mamzer?

Molecule with 13 total electrons

Is there a stable molecule with total number of electrons equal to 13? Molecule can be either organic or inorganic

tamei tahor ritual purity - Does clay used as a foundation count as clay or as the ground?

The mishnah in Keilim 6:1 describes a stove made in two ways: a pot resting on three metal^* pegs that are either (1) attached at the ground via clay, or (2) stuck into the ground. In the first case, the clay gives the stove the status of a "clay stove", which is susceptible to tumah, whereas in the second case, there is no susceptibility to tumah.

‮העושה שלושה פטפוטין בארץ, וחיברן בטיט להיות שופת עליהן את הקדירה: טמאה. קבע שלושה מסמרין בארץ להיות שופת עליהן את הקדירה: אף על פי שעשה בראשן מקום שתהא הקדירה יושבת, טהורה.

If he put three props into the ground and joined them [to the ground] with clay so that a pot could be set on them, [the structure] is susceptible to impurity. If he set three nails in the ground so that a pot could be set on them, even though a place was made on the top for the pot to rest, [the structure] is not susceptible to impurity. (translation from Sefaria)

Imagine a case where you create a clay foundation, strengthening the ground with clay (and leaving the clay flush with the ground). What would be the rule when pegs are stuck into such a clay foundation? Would it be considered as attached to the ground (and hence not susceptible to tumah) or as attached via clay to the ground (and hence susceptible)?

---

See also this question.

^* I know that some commentaries read the initial sentence as referring to clay props, but I'm asking according to those who don't (or according to everyone, if the material doesn't matter). See also the tosefta Keilim BK 5:1 which seems to support a read of metal props.

conjugations - Causative せる/させる vs. す/さす

How wide is the usage of causative (使役) す/さす comparatively to せる/させる?

Answer

Historically, 「す/さす」 is older than 「せる/させる」.

Just like many other pairs of older and newer words/phrases with the same meanings, the older forms are used more often and actively in Western Japan than in Eastern Japan. (That is if you know anything about Japanese history.)

To say "What are you making me say?", for instance,

Tokyoites would tend to say:

「何{なに}を言{い}わせるんだよ！」

while Osakans would be likely to say:

「何を言わすねん！」

In schools, however, regardless of what part of the country we are from, we all basically learn to use 「せる/させる」 in "Standard" Japanese. You would rarely, if not never, see or hear 「す/さす」 used in the media these days.

Thus, both forms may be used equally often "at homes" across the country, but in school, business, media, etc., 「せる/させる」 would be the dominant form.

halacha - When do you place the Mezuzah?

Possible Duplicate:

Mezzuzahs- putting them up, and saying brachot…

When do you place the Mezuzah? 30 days after beginning rental or moving in?

Answer

See the section from Oholei Yeshurun that I quoted in this answer. The language used there for when to start the clock is "upon entering." I expect that that refers to moving in, not to any off-site formal transaction.

Reading of 入る - 「はいる」 vs 「いる」

Sometimes I'm having trouble choosing the reading for 入る. There was a related question about the reading of 入れる, however my JMdict-based dictionary marks both 入る{はいる} and 入る{いる} as intransitive verbs (自動詞) - is it correct? If so, then how to choose among them? My particular sentence in question this time is

ためしに、ドアと窓をはずしてみたら、風がどどっと入{?}ってきて、一瞬で空気が入{い}れかわった

The second reading is certain (from 入{い}れ替{か}わる), but I'm not sure about the first one: the dictionary has "to enter/to go into/to break into" among the meanings for 入る{はいる}, and "to come in/to flow into" for 入る{いる}, and both seem to fit here.

And BTW, is どどっと an onomatopoeic word? Failed to find anything close in the dictionary.

Answer

Basically, in contemporary Japanese, intransitive 入る = /hairu/. The /iru/ readings are essentially all survivals from an earlier stage in which 入る was just /iru/. (In fact, /hairu/ is basically /hau/ "crawl" + /iru/, which is why sometimes in older texts you see it written 這入る).

So your best bet is to assume that 入る is /hairu/ on its own and /ir-/ in compound words (入り口 = /iriguchi/, 入れ替わる = /irekawaru/), and learn the exceptions one by one. There are quite a few such exceptions in the dictionary, but you won't actually encounter one very often. Most of them have a fairly old-fashioned or literary feel and are pretty rare nowadays. The big exception to this is 気に入る /ki ni iru/ but it seems you have that one down already.

(If it makes you feel any better, misreading the 入る in expressions like 神に入る as /hairu/ is relatively common even among native Japanese speakers, precisely because /iru/ is an exceptional reading these days.)

So: どどっと入る is almost certainly /dodotto hairu/, because it's not a set phrase, and so there's no reason for 入る to have anything other than its standard reading. And どどっと is probably mimetic, yeah, don't know about onomatopoeic. Try looking up どっと -- it's basically a reduplicated form of that.

sources mekorot - Why a human Messiah?

I understand that Mashiach is going to be a human. What is the source for this, and are there any explanations why it must be so? Can't G-d Himself redeem us?

halacha - Male tzniut: Swimwear

Seeing as summer is coming, I thought I'd clear up a few questions about male tzniut with regards to swimwear. Namely, my real question is: what is required? I live in southern California, so outside of the Jewish community, there is for all intents and purposes no modesty standard whatsoever.

Here are my questions:

1. Would I be fine wearing a rash-guard (ie a t-shirt designed for swimming/bodyboarding) and shorts that come below the knees (preferably these will have ties so I can tighten them around the area below my knees so they won't come up)?


2. What are the rules of men and women swimming together? If I'm at a non-Jewish relative's house and they're having a pool party and certain aunts and uncles of mine are swimming in the pool, am I allowed to swim as well, provided that we're all related?

_{Note: I'm not yet Jewish, but am in the process of converting, meaning that my family isn't Jewish. This may or may not affect how tzniut applies in my case, but I think that it's at least worth mentioning, just in case. It's understood that I'm not Jewish yet so I'm not technically obligated to keep tzniut, but I do, and since I plan by living by halacha for the rest of my life, I figure it's best to know and do now, rather than later.}

Answer

For Question 2: Igros Moshe forbids swimming in mixed beaches. There is no practical halachic difference between cousins/aunts/uncles and non-relatives for Yichud, negiya, etc. (especially that a convert is considered a new-born child).

Even by women, Igros Moshe says to be stringent and not swim with a male lifeguard (she is technically not doing anything wrong, and he is "busy with his work").

halacha - Wanted: stories about shaatnez

My daughter has a school project about shaatnez. One of the requirements is to tell a few stories demonstrating how people were particularly careful about the laws of shaatnez, preferably with sources. They can be classic or contemporary. Any contributions will be most appreciated!

names - Formal Hebrew honorific for one's mother

Many men, when going up for an aliya, tell the gabbai their name as, e.g. "Reuven ben Rav Yaakov", even if "Yaakov," the father, isn't actually a Rabbi." I believe the reason for this practice is to honor the father by not saying his name without an honorific.

Is there an honorific that's used commonly when referring to one's mother? For example, if Reuven was to ask the gabbai to mention his brother in a "Mi Shebeirach", in which one traditionally identifies the patient with his/her mother, how should he say the name? "Shim'on ben Giveret Leah"? "... Imi (my mother) Leah"?

Happy Mothers' Day!

Answer

"Ha-isha" (האשה) is a title of respect that has the advantage of sounding perfectly natural.

sukkah - Putting poison inside bamboo rods (s'chach)

It says in Shulchan Aruch (OC Siman 629 Sif 3) that one may cover a Sukkah with "chitzim" (arrows) that don't have a "beis kibbul." However, if they do have a "beis kibbul," then it's not valid for schach. "Beis kibbul" basically means some opening or cup that can be a receptacle, and can therefore be made tamei (impure). The Magen Avraham writes (ad loc., Sif-Katan 2) that "kanim" (rods) that have a "beis kibbul" are valid, since they weren't made to be "m'kabel". Seemingly this is similar to our bamboo sticks or the like that people use for schach. However, what about if one would put some sort of "chomer" (a poison or the like) used to kill bugs inside of the sticks? I'm not talking about a spray or something of the like – rather something that has to it mamoshos (substance) that sits in the sticks and helps to kill the bugs. Even though these kanim, like the M"A says, weren't made to be a beis kibbul, since l'maseh (practically) they are being used in such a way, does this invalidate it for being schach?

fourier transform - Create an aliased image in FD

Is there an accurate way to create an aliased image from the Fourier transform of the original image?

in other words, i have the Fourier coefficients of an image and i want to make down-sample in frequency domain.

Answer

I am trying to construct an aliasing image.

I=rgb2gray(imread('Liver.png')); % a 512*512 image 
subplot(1,2,1),imshow(I),title('Original image')  % shown on the left side of figure below

when you implement F=fftshift(fft2(I));, the corresponding axis represent the frequency range of [-255:256]/512; and the cut-off frequency U = V = 256/512 = 0.5;

based on Nyquist Sampling Theorem, the sampling periods in spatial domain should satisfy

delta_x<=1/(2*U)=1;
delta_y<=1/(2*V)=1;

to avoid the aliasing.

So if your bandwidth of recorder is 64 * 64, the corresponding point interval in spatial domain is 1 / (64/256) = 4. Thus,

Ia=imresize(I(1:4:end,1:4:end),[512 512]);
subplot(1,2,2),imshow(Ia),title('Aliased image') % shown on the right side of the figure below

You can observe the aliasing effect at the edge.

greetings - Arimasu as a parting phrase

Hope this is an appropriate question!

I visited Tokyo back in September and got by on some very basic Japanese (though more often with the help of their good grasp on English).

Anyway, there was a couple of times I heard as a parting phrase... once from a barman and I believe another in a restaurant. I thought it was just "arimasu" or "arimasen" by itself though I may have missed a particle or other word. I tried to look it up when I was there and have searched many times over the last few months to decipher it but with no luck.

The curiosity is still getting to me, could anyone here shed some light on how that might be used as a parting phrase?

Answer

I guess you've misheard heavily slurred ありがとうございます.

When spoken very quickly, ありがとうございます can be pronounced like ありゃーっす！ or ありわーっす！ or あざーっす！ And ありがとうございました can be more like ありゃーしたぁ！ or あーした！

Similarly, slurred いらっしゃいませ can sound like しあわせ, ラッシュアワースリー, or even エアロスミス.

grammar - The meanings of ものだ

Could someone please explain to me the different meanings that ものだ can have at the end of a sentence ? Here are some examples I understand the general meaning of, but I don't understand the logic/grammar behind ものだ

• 留学したいものだ


• 約束は守るものだ


• 父は以前はバスで仕事に行ったものだ



• 生徒はもっと勉強するものだ

Answer

There are four basic usages/meanings of the sentence-ending ものだ/ものです/ものである, etc. In colloquial speech, 「もの」 often changes to 「もん」.

1) Exclamation, deep emotion, surprise, praise, etc.

2) General tendencies and cold facts.

3) Advice based on common sense, customs, etc.

4) Recollection and reminiscence.

The context in which 「～～ものだ」 appears should tell you which usage/meaning it is being used for. My advice would be to not over-analyze the short phrase 「ものだ」, which consists only of two words. Instead, try to get used to the usages by reading a lot and forming many example sentences yourself.

Now, let us take a look at the sentences you have listed.

「留学{りゅうがく}したいものだ。」 "I really would like to study abroad."

would clearly be type #1 above. The speaker's wish to go study abroad is rather strong here.

「約束{やくそく}は守{まも}るものだ。」 "People should keep their promises."

would be type #3 because that is common sense.

「父{ちち}は以前{いぜん}はバスで仕事{しごと}に行{い}ったものだ。」 "Daddy used to commute to work by bus."

Type #4, no sweat. It is about how something used to be done. The key phrase is 「以前は」 with the contrastive 「は」. The father commuted by bus before, but not anymore.

「生徒{せいと}はもっと勉強{べんきょう}するものだ。」 "Students should study harder."

This would be a split between types #2 and #3. A larger context would probably tell us which one.

history - Sources for Hassidic views on marital celibacy/asceticism?

My understanding is the traditional view of Ger Hassidism was that marital celibacy was a good idea, once all procreative needs had been met.

My impression is that Chabad-Lubavitch never advocated an attitude towards asceticism in marriage. (Is this correct?) I'm sure other Hassidic groups have their own traditional views.

Can these views be traced to a source? Be it sociological, historical, religious, "the writings and teachings of Rebbe [Grand Rabbi] so-and-so"?

technology - Can DNA be used as evidence to prove that someone is Jewish?

Apparently, there were a number of child Holocaust survivors who were separated from their parents and never found them. They were adopted and raised by Non-Jewish families.

As they became adults, traces of their history emerge as people tell them that they are actually Jewish. But, as they had been raised as non-Jews and not being circumcised, they have no definitive proof that they are. There are no relatives and no historical records identifying them or their families.

Halachically, can someone use the results of a DNA test to prove Jewish identity? If this has been done, how reliable are such results?

Thermodynamics entropy and temperature

In thermodynamics, whenever heat is released from the system to the surroundings, temperature of surroundings remains unchanged but entropy increases. But entropy is a function of temperature. How is it possible?

grammar - Can particle と be used with 分かる?

Back to basics. Sometimes I see something that undoes everything I think I know.

私はあなたがいつも忙しいことを分かっています。
私はあなたがいつも忙しいと分かっています。
I know that you are always busy.

Which of the above is correct? I have seen several instances of 分かる used with と, but I'm confused because nothing is being quoted, either directly or indirectly when using this verb.

When/is it ever correct to use と分かっています if there isn't an implied verb like 思う/言う etc. in between.

Answer

私はあなたがいつも忙しいことを分かっています。
私はあなたがいつも忙しいと分かっています。

Grammatically speaking, both are perfectly correct. The quotative particle と can be used with many verbs like 知る, 分かる, 見なす, 認識する and 捉える. Another simpler example:

高いことを知っていて買った。

高いと知っていて買った。
I bought it knowing it's expensive.

In ordinary conversations, perhaps people prefer ～と simply because it's shorter. ～ことを is preferred in formal or complicated sentences. And you can omit 私は and topicalize the nominalized こと-part instead:

あなたがいつも忙しいことは分かっています。

drush - Why is there a guilt offering and not a sin offering for slander?

I read this on Chabad.org in its discussion of Parshat Vayikra:

• The different types of “sin offering” (chatat) brought to atone for transgressions committed erroneously by the high priest, the entire community, the king or the ordinary Jew;

• The “guilt offering” (asham) brought by one who has misappropriated property of the Sanctuary, who is in doubt as to whether he transgressed a divine prohibition, or who has committed a “betrayal against G‑d” by swearing falsely to defraud a fellow man.

It seems that the asham, or guilt offering, applies to a lesser category of sins than the sin offering, chatat. For example, asham is used when there is merely a suspicion that a sin has been committed. However, it is odd to me to find the sin of slander, which is generally considered a fundamental Jewish transgression--and, along with stealing, a breach of the Ten Commandments--listed among these "second-class" sins.

What are some interpretations for why this is so?

Answer

This question contains two incorrect assumptions.

One incorrect assumption is that a guilt offering (korban asham) is less serious than a sin offering (korban chatas). The Ramban 5:15 indicates that the opposite is true, and the Rama (O.C. 603:1) actually quotes as accepted halakha: one must expend greater effort in repenting from a sin that he might have committed than for one that he know for certain that he has committed.

Second is the issue of "slander". From google: "slander (n.): the action or crime of making a false spoken statement damaging to a person's reputation". This is not mentioned in the verse whatsoever; the case of "defrauding" that is referred to by the Torah here is where someone swears that he is not holding onto the property of his fellow man, when he actually is.

Either way, the main point of the sacrifice is to help the repentant person atone for defrauding his fellow, not for the misuse of God's name. (I say that because intentionally swearing falsely, in general, is subject to the punishment of lashes; see Temurah 3b - even though one has to bring an extra sacrifice for each denial only if it includes a swearing). Thus, the sacrifice isn't such a big deal, because the main idea for repentance here is that the person return the property that he denied. However, because it's still inappropriate for someone to think that they can just deny having someone's property and give it back later, the Torah requires a sacrifice to be brought as well. (Sefer Hachinuch 129)

halacha - Play a woodwind instrument on Shabbat?

Is it forbidden to play a woodwind instrument, such as a recorder, on Shabbat?

I want to say it's forbidden, because (I think) musical instruments were played in the beit haMikdash. However, even though they were played, were they made? In other words, would it be considered a "work" in that it's "work" that is forbidden on Shabbat?

Answer

It's forbidden (Shulchan Aruch, OC 338:1). He gives no reason (as usual), but, if I recall correctly, the reason the rabbis instituted this prohibition was as a safeguard lest one come to fix the instrument as needed while playing. (I know little about woodwinds, but I guess that might include putting in a new reed.)

image processing - count blood cells

How to count blood cells in opencv? The problem is that they stick together.

The example picture :

Maybe pairwise geometric histogram (Geometric Histograms) suitable for matching partial circle shape?

quantum chemistry - Generating molecular graph Laplacian based on Hückel theory

While studying graphs and graph Laplacians from "Laplacian eigenvectors of graphs: Perron-Frobenius and Faber-Krahn type theorems.", I encountered a type of graph Laplacians that rise from quantum chemistry. This matrix is consists of off-diagonal elements called resonance integrals and diagonal terms called Coulomb integrals. This is a sparse matrix, meaning that the matrix elements corresponding to non-connected atoms are zero. It is further mentioned that

... the entries of this matrix, H, are tabulated for different atoms and bonds.

I was looking online to find some table that gives this information and write a package to compute this matrix given a SMILES entry. As an alternative, I also looked for an already existing package that provides this matrix. The only thing I found was the implementation of the extended Hückel method in RDKit, which requires molecule conformation as input (apparently, eHM needs atom coordinates).

I was wondering if anyone can point me to such a table or python package or let me know if I'm missing something.

Answer

You're describing simple Hückel theory. This is usually applied to $\pi$-conjugated systems to understand the stabilization in conjugated and aromatic molecules.

There are a variety of Python packages, for example:

I believe the version from Plasser will read in files using Open Babel's python interface, so certainly you could handle SMILES.

People would perturb the $\alpha$ (atom site energies) and $\beta$ (bond interaction) parameters in various ways. It's hard to find good tabulations of these, but the best appears to be: "A brief review and table of semiempirical parameters used in the Hueckel molecular orbital method" J. Chem. Eng. Data 1967 122 pp. 235-246

You mention the somewhat related Extended Hückel theory (EHT). This considers both $\sigma$ and $\pi$ bonds and is thus a lot more useful, although as you mention you need coordinates to calculate overlap values, etc.

history - How was Tevilas Ezra effective in limiting conjugal relations?

Many go to mikve (perform ritual immersion) every morning. One reason for this is voluntary continuation of a cancelled decree, Tevilas Ezra, meant to limit conjugal relations by requiring immersion between relations and prayer.

Besides another reason for it, common daily immersion preserves modesty by preventing that day's mikve-goers from knowing who else had relations the previous night.*

If everyone was anyway immersing every day, how was the decree effective in limiting conjugal relations?

Are there any sources that explain the decree's effectiveness based on immersion having been a major ordeal in those times?

---

^{* However, women (who can be presumed to have relations on the night they immerse) do little to prevent meeting each other at the mikve, and I don't know of a custom for women to immerse every night.}

How can I measure the harmonicity of an audio spectrum?

I would like to estimate the "harmonicity" (harmonics-to-noise ratio ?) of an audio signal from its spectrum. What kind of algorithm can I use?

halacha - Should Ashkenazim say 'מוריד הטל' in Israel?

The Rema (114:3) brings the Tur who says that Ashkenazim do not say 'מוריד הטל' in the amidah:

"Us, the Ashkenazim, do not commemorate the 'טל' [i.e. say 'מוריד הטל'], not in the summer days nor in the rainy season..."

Is it considered 'minhag eretz Yisrael' to say מוריד הטל and should Ashkenazim forgo the psak of the Rema and say מוריד הטל in Israel?

(This question is inspired by a conversation I had with a fellow Jew who said that for Ashkenazim who don't say 'מוריד הטל' in Israel it is as if they have not said Amidah - I believe he was bringing the opinion of Rav Shlomo Zalman Auerbach)

hashkafah philosophy - Why is resurection of the dead a fundamental of faith according to the Rambam?

The Rambam defines the resurrection of the dead as a fundamental of Judaism. However, unlike the Ramban, the Rambam holds that first there is Moshiach, then resurrection, and then the final result of souls' return to Olam Habah.

According to the Ramban, I can understand resurrection being a fundamental of faith - it is the end game of the whole creation and its purpose, according to the Ramban.

However, the Rambam doesn't count a belief in Olam Habah as fundamental, rather the intermediary stage of the resurrection.

If it is just a reward and punishment thing (that this is the way the ultimate reward and punishment will be melted out, and don't think punishment will only be spiritual or exists in this world, or something like that), it would seem to be subsumed into the fundamental of believing in reward and punishment. Why does it get its own fundamental, and not even as a continuation of the one of reward and punishment?

Answer

After some consideration, I think the straight forward answer for the Rambam is as follows.

The Rambam holds that the purpose of the times of Moshiach is to do Mitzvos to merit Olam Haba. That works nicely for those who will live then, but what about those who lived before? With what will they merit Olam Haba?

For that, the answer is Techiyas HaMeisim. They will come back (if they were worthy - he says that Olam HaTechiya is only for Tzaddikim) and have their chance to live in Messianic times before going on to merit Olam Haba.

This is a fundamental just like reward and punishment are fundamental - the belief that the reward is achievable in actuality for the individual is just as important as believing in the abstract in reward and punishment. Otherwise you might think you can avoid the punishment, but be in Golus and not have a chance at the reward.

In other words, if a person perceives that their Torah and Mitzvos now are worth so little, as measured by the reward they will get for it vs. the reward for those who live in the Messianic era, it would be similar to someone believing there is no reward or punishment at all. They will believe that their Avodas HaShem is (close to) worthless, and that ultimately what they do is of little consequence.

Nevertheless its position in the Ikkarim is understood to be after Moshiach, because it is precisely the opportunity represented by Yemos HaMoshiach that demands the same opportunity for those who died before.

כנלע"ד

halacha - Davening whilst on a road-trip, what must I do?

If I'm driving long distance on a road-trip, (approx. 400 miles, leaving house at 3am, arriving at approximately 9am) am I required to stop the car, get out, and daven Shacharit at or before sunrise? Is there a way I can daven while still driving? If I were to get an audio recording of a chazzan leading the service, say amen at the right points etc., would this count?

Those that I'm going with are not Jewish, so it'd be kind of awkward to tell them to wait in the car for an hour.

Answer

As jake pointed out in his comment, if you'll be arriving by 9 AM, then just daven when you reach your destination.

If you're going to be on the road during the entire timeframe for Shacharis, though, then you can stop for just Shema and Shemoneh Esrei (those shouldn't take more than 10-15 minutes or so), and say the rest of Shacharis while driving. (It is true that there are parts that it's customary to stand for, but that's just that - a custom, not an absolute halachic requirement.)

A recording wouldn't help for any of this. It's questionable whether you can fulfill your obligation by hearing a berachah (or whatever) live over the telephone or radio or whatever; but as far as I know it's undisputed that a pre-recorded voice doesn't count for anything.

shabbat - Candle Lighting Time: Why Then?

Why 18 minutes (or other minhagim). Where did these numbers come from?

Answer

There's an article on the subject at Hirhurim, by Rabbi Ari Enkin. He cites two reasons that are given for the 18-minute figure:

1. 
   

   It's based on a Gemara in Shabbos (35b), where it says that six shofar blasts were blown to announce that Shabbos will be starting soon; the third one is the signal for lighting candles, then "he waits as much time as it takes to roast a small fish," blows the last three blasts, and Shabbos begins. This amount of time is elsewhere stated to be 18 minutes.

   
   



2. 
   

   It's in deference to the opinion of Sefer Yereim (by R' Eliezer of Metz, one of the Tosafists), who says that the halachic day ends (and thus Shabbos begins) a 1-mil walk before sunset. There are various opinions as to how long a 1-mil walk is, ranging from 18-24 minutes, but 18 minutes is the most widespread (in connection with other laws such as the amount of time that it takes for dough to become chametz), and therefore it was adopted here too.

   
   

calendar - How accurate is the Molad?

To the best of my knowledge the Molad is every 29.5 days + 793 Chalakim. Is there any information showing if the current Molad calculation is accurate scientifically? If it is off by how much is it off? How far off culmitavely are we now from the actual timing of the new moon?

stoichiometry - Simplest way to balance any chemical equation

In your opinion, what would be the simplest way to balance any size of the chemical equation?

For example here is an equation: $$\ce{C12H26 + O2 -> CO2 + H2O}$$

I saw some ways by putting letters in front of each molecule, but I just don't get too much how to do this with this method! My teacher is always speaking about another method, but it simply doesn't feel logic/mathematics is enough for me.

Answer

You can do this in the 'guided trial-and-error' method that LordStryker showed which is probably quickest for simple reactions, or approach it in a purely mathematical fashion which is the method I will explain. This method works well for arbitrarily difficult reactions.

Your chemical equation contains 3 atomic species: $\ce{C}$, $\ce{H}$ and $\ce{O}$. This means that you need 3 equations to balance. First I write the chemical reaction as follows: $$\ce{a C12H26 + b O2 -> c CO2 + d H2O}$$ Now I will write the 3 equalities for the 3 atomic species that we have: \begin{align} 12a &= c \tag{for C}\\ 26a &= 2d \tag{for H}\\ 2b &= 2c + d \tag{for O} \end{align} The numerical constants in front of $a$, $b$, $c$ and $d$ come from the number of atoms that are in the molecule for which they are included.

As you may have noticed, this system of equations is ill-defined, because we have 4 unknowns ($a$ to $d$) and only 3 equations. The reason is that we can pick any multiple of the equation without it becoming incorrect,¹ just against convention. This means that we can simply set one of the unknowns to any value. Let's say $a = 1$ for now and revisit this choice after solving the equations.

With $a = 1$ it immediately follows that $c = 12$ and $d = 13$. From those two it then follows that $b = 18.5$. Our balanced reaction becomes:² $$\ce{C12H26 + 18.5 O2 -> 12 CO2 + 13 H2O}$$

In principle this is already correct, but convention is to have only integer numbers in the equation (i.e. no decimal points) therefore we need to revisit our choice of $a = 1$ and pick it such that all numbers will become integers. In this case you can easily see that this will happen for $a = 2$ which then results in $$\ce{2C12H26 + 37 O2 -> 24 CO2 + 26 H2O}$$

If for some reason it is not easy to see which value for $a$ you would need then you can multiply by a large power of 10 to make all the decimals disappear and then check the greatest common divisor of the 4 numbers and divide by that to obtain the same equation.

---

Notes

1. 
   
   

   Compare $10=10$ to the multiplied version $30=30$, both are correct, but they are just different by a factor $3$.

   
   


2. 
   

   I'm not sure whether you are familiar with linear algebra, but if you are you will probably have noticed that the set of equations is a linear set so you could solve it through matrix manipulations which makes this method applicable to arbitrarily complex chemical reactions.

   
   

halacha - Why do mourning practices surrounding suicide differ from Shulchan Aruch?

It used to be that a person who committed suicide was buried in a separate part of the cemetery and the relatives did not sit shiva (see Shulchan Aruch YD 345). We no longer do these things and we treat a suicide as a regular death. On what basis is this done?

organic chemistry - Clarification in the mechanism for Molisch's test for glucose

Wikipedia says

Molisch's test is a sensitive chemical test, named after Austrian botanist Hans Molisch, for the presence of carbohydrates, based on the dehydration of the carbohydrate by sulfuric acid or hydrochloric acid to produce an aldehyde, which condenses with two molecules of a phenol (usually α-naphthol, though other phenols such as resorcinol and thymol) also give colored products), resulting in a red- or purple-coloured compound.

Can somebody provide an arrow pushing diagram to illustrate the intermediate steps of these reactions? (especially for the dehydration of glucose) Also, for the reaction with of 5-(hydroxymethyl)furfural with 2 moles of phenol, it seems that the acyl group is acting like an electrophile and naphthol is engaged in an electrophilic aromatic substitution, but then again, I am not sure how 2 moles of naphthol combined there. Any help would be appreciated.

Answer

YUSUF HASAN: 5-Hydroxymethyl furfural (5-HMF) 1 when protonated on the carbonyl oxygen becomes a reactive electrophile. Addition of phenol 2 at the reactive para-position affords 3 which deprotonates at the para-position, rearomatizing the ring to a phenol and liberating a proton. Secondary alcohol 4 is protonated on oxygen with loss of water to form stabilized cation 5. A second equivalent of phenol adds to the cation as previously described leading to the triarylmethane 6. The methane hydrogen is susceptible to oxidation by atomspheric oxygen, which is in a triplet state (unpaired electrons behaving as a free radical). Resonance stabilized radical 8 is formed along with the hydroperoxy radical 7, which can abstract the hydrogen from triarylmethane 6 forming more of radical 8 and hydrogen peroxide. Oxidation of radical 8 with oxygen gives the resonance stabilized carbocation 9 and superoxide anion, aka, superoxide radical anion 10. This species can be protonated by the the strong acid conditions of the Molisch test to form more of the hydroperoxy radical 7.

safety - In practice, how dangerous is liquid oxygen as an oxidizing agent?

The Wikipedia page on liquid oxygen tells us

Liquid oxygen is also a very powerful oxidizing agent [...], if soaked in liquid oxygen, some materials such as coal briquettes, carbon black, etc., can detonate unpredictably from sources of ignition such as flames, sparks or impact from light blows.

I have heard similar warnings about LOX in texts about amateur and semi-professional rocketry, but I know nobody who has ever handled stuff like this.

In practice, say I spill some LOX and soak paper lying around (that maybe has been warmed by a desk lamp), will that burst into a fireball?

Maybe more to the point, how do I assess such risks short of conducting foolhardy experiments? Is there a way to estimate the maximum effect a given amount of spillage on a given material may have?

halacha - Setting up non-Jews for marriage

Is one halachicly allowed to set up two non-Jews for marriage? I don't see why it should be an issue,but not sure. I wondered if anyone discusses this.

words - What is the correct response to "Chazaq u'Baruch!"?

When a person gets an aliyah or other synagogue privilege the congregants of an Ashkenazic synagogue generally thanks him by saying "Shokyach!" or "Yasherkoach!" to which he responds "Baruch Tehiye!".

What is the correct response to the Sephardi version of this phrase, "Chazaq u'Baruch"?

Answer

According to Wikipedia "Baruch Tehiye" is an acceptable response, but "Chazak Ve'Ematz" is the common one. Among Morrocans it would be "Kulchem Beruchim".

organic chemistry - Reason for the stronger acidic property of phenol than alcohol

In phenol, pulling the $\mathrm{p}_z$ electrons from the oxygen atom into the ring causes the hydrogen atom to be more partially positive than it is in aliphatic alcohols. This means it is much more easily lost from phenol than it is from aliphatic alcohols, so phenol has a stronger acidic property than ethanol.

Could someone please explain the link between the $\mathrm{p}_z$ electrons of oxygen overlapping with the cloud of delocalised electrons of the phenol ring and the increase in positivity of the bonded hydrogen … which in turns allows phenol to lose a proton more easily?

halacha theory - When why and how was the Talmud sealed

Throughout my life I've heard that the Talmud is sealed and rabbinic enactment can't be repealed. But from where do we know this? Why was it done? HOW was it done? A gzeirah? A minhag?

minhag - Why has it not become customary for people to wish each other "Good Yontiff" on Purim?

I can't recall people wishing each other "Gut Yuntiff" (or similar, like "Good Yom Tov") or any reference to Yom Tov on Purim. (Maybe someone does, but I'm unaware of this.)

Why don't people do this considering that Esther 9:19 and 9:22 both refer to the 14th day of Adar (Purim) as יום טוב?

How to compute the impulse response from a transfer function

Say I have a transfer function, for example:

$$H(z)=\frac{1}{1+0.1z^{-30}}$$

How can I compute the impulse response?

(This is just an example, the important thing is that it is in closed symbolic form!)

If I understand correctly, if I could just rewrite $H(z)$ as some polynomial in $z^-1$ (by using a Taylor expansion), I could just read off the coefficients.

But is there another way?

organic chemistry - Nomenclature of a cyclohexyl ether and locant position enumeration

As far as I know, 'ethoxy' should be given the locant '1' as it is a functional group. The compound should thus be named 1-ethoxy-2,2-dimethylcyclohexane.

However, I was told that the correct name is 2-ethoxy-1,1-dimethylcyclohexane. Can anyone please explain why this is so? My teacher explained this to me in terms of the lowest locant sum rule, which I just discovered doesn't even exist.

Answer

The smallest sum of locants rule does not exist in the IUPAC recommendations. The application of this ‘rule’ can lead to wrong results in many instances.

The corresponding section in the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book) actually reads as follows:

P-14.3.5 Lowest set of locants

The lowest set of locants is defined as the set that, when compared term by term with other locant sets, each cited in order of increasing value, has the lowest term at the first point of difference; for example, the locant set ‘2,3,5,8’ is lower than ‘3,4,6,8’ and ‘2,4,5,7’.
(…)

With regard to numbering of locants, simple prefixes (simple substituent groups consisting of just one part that describes an atom, or group of atoms as a unit, for example methyl and ethoxy) are considered together with equal seniority:

P-14.4 NUMBERING

When several structural features appear in cyclic and acyclic compounds, low locants are assigned to them in the following decreasing order of seniority:

(…)

(f) detachable alphabetized prefixes, all considered together in a series of increasing numerical order;

(…)

Therefore, the example is named as 2-ethoxy-1,1-dimethylcyclohexane rather than 1-ethoxy-2,2-dimethylcyclohexane since the locant set ‘1,1,2’ is lower than ‘1,2,2’.

grammar - How does 別に function as an adverb?

I know that 別に means "not particularly" sometimes, but what is its role in this sentence?

別に山田の私服を見るのは、はじめてってわけじゃないんだけどな。

I assume it means something like "it's not exactly the first time I've seen Yamada in plain clothes", but I don't know what exactly 別に is doing or what verb it's modifying.

halacha - Should someone who isn't 100% certain of God's existence be considered a kofer?

I was told by two respected Roshai Yeshiva that one who isn't certain of God's existence (an agnostic) is not deemed to be a kofer (denier of His existence) as long as he thinks that His existence is probable. So one who is 51% sure of God's existence is not a kofer, but one who is 49% sure of it is. They both admitted that they had no source for this, but thought it was logical.

Can anyone provide a source for this? Are there other views? Does one have to be 100% certain of God's existence to not be considered a kofer? Is someone who isn't convinced that God exists, but is a fully practicing Jew because of Pascal's wager considered a kofer?