February 2015 - mathfun@mailman.xmission.com

Re: [math-fun] Defective Sandisk uSD cards
by Henry Baker 15 Feb '15

15 Feb '15

FWIW, I purchased 2 more cards from Costco, so now only 1/6 cards were defective. Still worth benchmarking each before use, however. At 10:14 AM 2/15/2015, James Propp wrote: >Henry, > >If you'd bought just one card, and it was defective, would you be "amazed >to find that perhaps 100% of these devices did not meet their speed >requirement"? > >:-) > >(Kidding aside, I do get where Henry's coming from. And, in the absence of >priors, maybe 25% is the best estimate.) > >Jim Propp > >On Sun, Feb 15, 2015 at 10:19 AM, Henry Baker <hbaker1(a)pipeline.com> wrote: > >> I purchased 4 32GB uSD cards from Costco yesterday, and found to my amazement >> that one of the devices was faulty: while the maximum write rate was >20 MB/s, >> its minimum write rate was 1.2 MB/s, with an average write rate of 5.1 MB/s. >> >> While I suspect that this defective device will function correctly as a memory, >> I was amazed to find that perhaps 25% of these devices did not meet their speed >> requirement. >> >> BTW, if you run Linux, there is a "benchmarking" function for the disk formatting >> program which is quite useful. >> >> Now I'm going to have to test all of my SD cards in advance prior to using them.

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[math-fun] Defective Sandisk uSD cards
by Henry Baker 15 Feb '15

15 Feb '15

I purchased 4 32GB uSD cards from Costco yesterday, and found to my amazement that one of the devices was faulty: while the maximum write rate was >20 MB/s, its minimum write rate was 1.2 MB/s, with an average write rate of 5.1 MB/s. While I suspect that this defective device will function correctly as a memory, I was amazed to find that perhaps 25% of these devices did not meet their speed requirement. BTW, if you run Linux, there is a "benchmarking" function for the disk formatting program which is quite useful. Now I'm going to have to test all of my SD cards in advance prior to using them.

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[math-fun] More spinning black holes
by Henry Baker 15 Feb '15

15 Feb '15

Another "Interstellar" article, including hi-res stills: http://iopscience.iop.org/0264-9381/32/6/065001/article 8 movies from the paper: http://iopscience.iop.org/0264-9381/32/6/065001/media

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Re: [math-fun] effects of various (e.g. dietary) behaviors on your all-cause mortality (oversimplified picture) RCS
by Warren D Smith 14 Feb '15

14 Feb '15

RCS: I'm willing to believe that smoking is bad for your health, but beyond that, it's something of a puzzle. If the death rate from smoking is 2.7x nonsmoking, does it follow that, since American life expectancy is 80 years, that smokers only live to be 30? WDS: If your death rate changes to 1/K>0 times its old value, you do not live K times the expected lifespan. That would be true if death rate independent of age, but it is not. In fact, between ages 30 and 95, death rate is very well fit by an exponentially increasing function of age, "Gompertz's law" and death rate at age 95 in USA is about 200X death rate at age 30. As a result, if your death rate at each age changes to 1/K times its old value, you will live, in expectation, 12.3*ln(K) extra years. My chart gives reason to believe it is feasible to decrease your death rate to about 26% of the average person's, thus living about 16 years extra.

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[math-fun] effects of various (e.g. dietary) behaviors on your all-cause mortality (oversimplified picture)
by Warren D Smith 14 Feb '15

14 Feb '15

https://dl.dropboxusercontent.com/u/3507527/RelativeDeathRates.png

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[math-fun] another blot on Stanford
by Bill Gosper 14 Feb '15

14 Feb '15

Cris Moore> Maybe a good question is: can a student fill in the mu[lt]iplication table if they don't already know it (or extend it beyond the traditional 10x10)? If so, then I don't mind them memorizing it. Cris On Feb 13, 2015, at 1:37 AM, Bill Gosper <billgosper(a)gmail.com> wrote: http://dailycaller.com/2015/02/11/stanford-professor-says-memorizing-multip… --rwg Do you mean not memorizing it? I think filling in http://gosper.org/kellytbl.pdf makes a highly instructive drill. Unfortunately, the only kids who enjoy it are the ones who don't need it, --rwg

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Re: [math-fun] cause and effect: eating more eggs ==> die from heart problems?
by Henry Baker 14 Feb '15

14 Feb '15

The whole discussion about cholesterol, heart disease, eggs, etc., has been so contaminated with bias due to conflicts of interest that is is almost hopeless to try to set things straight. I've been following this discussion for about 50 years, and here's my best guess about what's really going on. 1. Cholesterol isn't bad for you; in fact, it's necessary for your brain to function & sex hormones to function. Apparently, the only "bad" cholesterol consists of little hard particles, but these do not come from _consuming_ cholesterol, but are manufactured within the body itself (perhaps after too high triglyceride levels). As best I can tell, there is no downside to consuming cholesterol, whatsoever. In particular, eggs are very good for you. 2. There is a microscopic fraction of humans that have a distinct genetic problem that causes incredibly high cholesterol levels. One of my graduate students at the University of Rochester in the early 1980's was such a person, and he died in his 30's of heart disease. There is nothing to be learned from these people that in any way applies to the rest of the population as a whole. 3. Blood cholesterol levels are typically divided into "low density lipoproteins" LDL and "high density lipoproteins" HDL; there is a slight positive correlation of LDL with heart disease and a negative correlation of HDL with heart disease. In general, high levels of HDL are correlated with long life. My wife is a genetic freak whose HDL levels exceed 90; HDL levels exceeding 60 are quite healthy. 4. People used to think that _consuming_ fat led to fat people; we now know it is the opposite: consuming carbs lead to fat people. Consuming fat encourages the body to burn fat, whereas consuming carbs encourages the body to store fat. In fact, consuming carbs upregulates insulin, which inhibits the burning of fat. 5. The healthiest people seem to ride on the edge of "ketosis", which means that they are typically burning fat, not carbs. Their body temperature may also be slightly lower than "normal". 6. Nearly all dietary studies done to date have not properly controlled for the types of bacteria in the gut. Since we now know (through "fecal transplants") that the types of gut bacteria can have major effects on the processing of foods during digestion, so virtually every dietary study will now have to be re-done. Gary Taubes's book "Good Calories, Bad Calories" is a very good introduction to the science & politics behind cholesterol. I've been corresponding with him for almost 10 years on these subjects. At 02:09 PM 2/13/2015, Warren D Smith wrote: >Consider egg consumption. Perhaps people with heart and >circulatory problems get worried about cholesterol and hence reduce >their egg consumption, because they are >worried about the cause==>effect relation "more eggs==>heart disease." > >As a result of that behavior -- which is "heart disease risk==>eat fewer eggs," >an opposite direction cause==>effect relation... >the people with lower egg consumption, would die *more* often from >heart disease... >leading to exactly the wrong conclusion from any study assessing >people's diets and >counting up their deaths! > >(Or, perhaps it was the right conclusion. >My point is: how can we tell?)

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[math-fun] Podcasts
by Jon Ziegler 14 Feb '15

14 Feb '15

This collection of math related podcasts may be of interest: http://mathbabe.org/2015/02/12/guest-post-a-survey-of-mathematical-podcasts Anybody here have any particular favorites? Regards, Jon

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Re: [math-fun] cause and effect: eating more eggs ==> die from heart problems?
by Henry Baker 14 Feb '15

14 Feb '15

There were periods in my life where I had 2 eggs for breakfast every morning for years at a time with no ill effects. I'm not doing it now, but only because I'm not that hungry. If you eat a "hearty" breakfast of bacon, eggs & hash browns, the hash browns are easily the most evil of the trio, as they cause an insulin spike when ingested. The most evil part of a McDonald's cheeseburger is the sugar-laden catsup, followed by the bun. The meat & cheese aren't the big offenders. At 03:44 PM 2/13/2015, Warren D Smith wrote: > >In particular, eggs are very good for you. > >--I have two mortality studies which both find, significantly, that >high egg consumption >(7 or more eggs/week) causes increased mortality. > >This suggests optimum egg consumption is 0-6 eggs/week, but within that >rather wide range, the studies I saw were unable to locate an optimum, >or find clear evidence anyplace within the range was worse than any >other. However, as I said, >reverse-causality effects could be happening to make that more difficult. >-- >Warren D. Smith >http://RangeVoting.org <-- add your endorsement (by clicking >"endorse" as 1st step)

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[math-fun] cause and effect: eating more eggs ==> die from heart problems?
by Warren D Smith 13 Feb '15

13 Feb '15

Consider egg consumption. Perhaps people with heart and circulatory problems get worried about cholesterol and hence reduce their egg consumption, because they are worried about the cause==>effect relation "more eggs==>heart disease." As a result of that behavior -- which is "heart disease risk==>eat fewer eggs," an opposite direction cause==>effect relation... the people with lower egg consumption, would die *more* often from heart disease... leading to exactly the wrong conclusion from any study assessing people's diets and counting up their deaths! (Or, perhaps it was the right conclusion. My point is: how can we tell?)

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