halacha - Being exposed to Christmas music

I understand that for many people, this is almost impossible to do - as long as you go shopping anywhere outside a Jewish neighborhood, or if you turn on the television, you will be exposed to Christmas music. Similarly, if you work in an office and someone puts on the easy listening station for people to listen to, you will be exposed to a LOT of Christmas music.

Assuming you're able to avoid actively seeking out such music (for example, not shopping at Macy's Department Store during this time of the year), are there any other halachic things a person should be aware of if there is the potential for being exposed to Christmas music? For example, are we enjoined not to watch a television show if there is the possibility of some Christmas music being featured?

halacha - Guitar during public weekday prayers

Is anyone aware of any halakhic opinion regarding the playing of musical instruments, guitar for example, in shul on a weekday, not shabbo. Does it have the same religious stigma and opposition as having an organ in shul did at the beginning of the reform movement? Is it still seen as a move towards the practices of other religions?

bayesian estimation - Kalman Filter Covariance

I've recently started playing with the Kalman filter for a simple 2D (x,y,dx,dy) tracking toy problem. But I seem to have some misunderstanding on what I can expect from the filter. I'm interested in plotting the uncertainty ellipse from the corrected covariance matrix but noticed a few observations:

• 
  

  The covariance decreases to a steady state regardless of how much error I introduce into the measurement.

  
  
  


• 
  

  The variance for x and y are exactly the same even though I introduce more measurement errors in y.

  
  

Staring at the maths for a bit it seems that this is how the vanilla Kalman Filter works. What I'm expecting is the opposite of the two points mentioned above. In the end I want to plot an uncertainty ellipse that reflects the error I'm observing. Is this possible at all? Do I have to do some post processing on the covariance matrix?

ANSWER:

It occurred to me what I needed was a Kalman Filter that has the ability to adapt its covariance. I found this paper that details a few different methods to do this.

http://www.gmat.unsw.edu.au/snap/publications/almagbile_etal2010a.pdf‎

acid base - Why does potassium react the most vigorously with water?

Link to exam

Which metal reacts most vigorously with water?

(A) Ca (B) K (C) Mg (D) Na

The given answer is B and the reasoning is that is is the most electropositive since it the furthest left and down according to periodic trends.

However, isn't $\ce{K}$ the conjugate acid from a strong base -- $\ce{KOH}$? So isn't the conjugate base of a strong acid quite weak? So why would $\ce{K}$ react strongly?

Answer

I might be wrong here, but I believe that the question asks about the metals in their atomic (non ionic) form.

In order for a $\ce{KOH}$ bond to form, the K must be ionized (since the $\ce{KOH}$ bond is ionic). This means that when $\ce{KOH}$ dissolves in water it'll form the $\ce{K}^+$ electrolyte, which is not the same thing as a pure $\ce{K}$ atom with its 19th electron.

A $\ce{K}$ atom, then, since it's the most electropositive of that list, is the one to react "more vigorously" (which I guess it refers to more speed/energy) with water (a polar molecule).

I hope this helped you. I'm sorry if I'm wrong!

physical chemistry - Is activation energy temperature-independent?

I know that activation energy for a reaction is the extra energy given to the reactants to reach the threshold energy so that they can collide and react. But then, why is it said that the activation energy does not depend on the temperature?

If the temperature is higher, the reactant molecules have a higher kinetic energy, and thus the energy difference between the threshold energy and the energy of the molecules will decrease, that is, the activation energy will decrease.

Answer

There is a simple (some might say simplistic) way to get an intuition about this and it involves thinking at the molecular or atomic level rather than about the bulk properties of the reaction (the thermodynamic view).

For a simple reaction where molecule A has to bang into molecule B to create molecule C, the reaction will only happen if the amount of energy involved in the collision is large enough. The amount of energy involved depends on the nature of the reaction which is determined by the electronic structures of A and B. Within limits, those electronic structures don't vary with temperature and a given reaction will only occur when there is enough energy in the collision for the reaction to happen.

What changes with temperature isn't the energy required for the reaction to occur, it is the number of molecules that have enough energy to overcome the barrier. At higher temperatures more molecules have that energy, but the amount of energy required doesn't change. The amount of energy require to initiate the reaction is roughly equivalent to the activation energy. It can be calculated by looking at the way the overall rate of the reaction changes with temperature. So the rate of reaction changes with temperature but not the barrier to the reaction happening.

This view is a little simplified but it gives the right intuition about the problem.

Which bodily fluids are kosher?

The only secretion from the human body that I know to be kosher is human milk. I am curious to know which other bodily fluids are kosher.

For example, is it kosher to drink sweat or tears? What about mucus?

Assume that a person has only eaten pareve kosher food, and later vomits it out. Is this vomit kosher?

There's at least a dozen other related questions that come to mind, but I'll stop here to avoid being gratuitously gross. In general, which bodily fluids are kosher and which ones are not?

slang - Is being called an オタク derogatory?

This question spawns from the comments here.

I've heard that オタク could or could not be derogatory. During the times I've been in Japan and heard it used, I didn't think that it had any connotation of being an insulting term, but is this true?

I'm not sure about other countries, but in America as a borrowed word, many people are proud to be called an "オタク" depending on the circumstance. Is it not the same in Japan?