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Most Mac Owners Also Own a Windows PC, But Not Vice Versa

spock_iii Bad Math (814 comments)

When the size of Set 1 dwarfs the size of Set 2, the intersection of Sets 1 & 2 must always demonstrate the properties discussed in the article. Sorry to be a troll, but this just isn't quality science like dolphins with freakin' lasers on their heads.

more than 5 years ago
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Heart Monitors In Middle School Gym Class?

spock_iii Teaching the use of an HRM is valuable. (950 comments)

While your privacy concerns may be worth exploring, I have the feeling that this situation is quite innocent. The HRM is an extremely valuable tool when exercising, and it is worth knowing how to use it properly. In short, if you are not hitting a target heart rate, you may not be exercising effectively. If you exceed a certain limit, you may be doing yourself actual harm. At some point, a school may even be able to make the argument that this reduces their liability.

more than 5 years ago
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Staying In Shape vs. a Busy IT Job Schedule?

spock_iii You can work it in... (865 comments)

I've been in your shoes...even made it to 300lbs before I made some changes. [1] Eat small to medium size meals 6 times a day. It's not about quantity of a single feeding, but quality of what you eat and how often you eat. Split food into groups - protein, carbs, fats, vegetables. One serving of each at every meal, 6 times a day. (About every 3 hours.) Just get in the habbit of slaming it down at your desk during those 10 minute slash dot breaks. [2] Buy an adjustable bench. Not a bench/rack/whatever combo, just a padded bench. You should be able to adjust the bench to lay flat, and to 45 degrees up. If it can do 90 degrees up, better, but not necessary. This should cost about $100. [3] Get you a decent set of adjustable dumbells that allow you to dial up a weight with slip on, slip off plates. A good set will run about $400 - $500 dollars but is well worth it. It should allow weights between 10 and 60 lbs or so. [4] Buy a $30 book on weight training to learn good technique. The Schwartzeneger encylopedia is a good one. [5] At this point, you've spent about $600, less than a yearly gym membership and have something that fits in your place, even if it's a 1 room flat. You can work out on your terms. [6] Work out 3 to 4 times a week for 45 minutes. No more, no less. You should do 15 - 20 sets of a variety of exercises with 30 seconds to 2 minutes rest between sets. [7] You can do flys, pullovers, presses, and abs from the bench. You can have dumbells in hand and step from the floor to the bench to work legs, or dumbel between feet and extend. If you do this - only asking for a 2.5 hour comittment per week here - you will be exercising effectively and go through some amazing changes. Me? I lost 100lbs and now do inclined benches at over 315 lbs. The personal trainers ask me for help.

more than 5 years ago
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How Does Flash Media Fail?

spock_iii Have done some extensive testing... (357 comments)

For a prior employer, I had set up a process to qualify flash media for use in embedded products. There's a couple of different failure modes you are likely to see.

First off, when the actual flash media itself wears out, it takes longer and longer to erase individual sectors.

A flash device such as a USB stick or a CF card is slight more complicated because it has something known as an FTL (Flash Translation Layer). The FTL has the job of implementing the virtual media to flash sector translations, implementing wear leveling, and handling the awkward page erases. (Multiple sectors in a page, but you can only erase full pages.)

The FTL obviously must store some mapping information in the media in addition to your data.

If you start writing flash media, and time those writes, you see an initial rapid growth in the write timing that evetually levels off as the FTL tables swell to their constant operational size.

The over all flash write speed will level off to some average value that follows slow growth over a very very long tail as the media wears.

Early flash chips supported about 10,000 erases per page, and modern chips shipped by Samsung and others support a couple million erases per page. When you consider this is spread over say 4GB of media, you can understand that tail is very very long and flash media are probably comperable to hard drives in their MTBF these days.

Secondly, when flash actually does begin to fail, the media itself tends to exhibit a small number of different symptoms.

The flash may stat to show occasional data corruption when read. You might also have instances where data persists in the media only so long as power is applied. And then of course you have the fact that erases take longer and longer to achieve. Eventually erases or programming start timing out occasionaly.

With the FTL between you and the flash, you don't directly observe these effects. Presumably the FTL is smart enough to try and re-map your data elsewhere. In most cases there's ECC to attempt correction of moderately corrupted data. The real killers are when the data fails to persist after power cycling, when ECC fails to recover critical FTL data tables, or when there are no more spare sectors to re-map data too.

Those first two critical errors are likely to produce the lightbulb effect where your flash card or USB stick one day simply fails to come up when probed after device insertion. In more rare cases, the lack of spares may show up as some sort of reported write failure in your kernel logs assuming the flash device reports proper IDE/ATAPI/??? error data.

One final note -- please don't leave your USB stick inserted in the PC as you power it off! USB ports supply power and use a FET device to control that power. When you turn off the PC, the gates float and significant leakage current goes to the USB device. Some of the cheaper USB drives lack a key resistor that bleads this current away and protects the flash memory chips. This leads to data corruption. I have seen the FTL break in such sticks simply by doing POR on the PC.

Oh...almost forgot. When you put you flash stick through the washer and dryer, always use fabric softner or Bounce strips to reduce the static. :-)

more than 5 years ago
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Numerically Approximating the Wave Equation?

spock_iii Spectral Methods & Perturbations (260 comments)

You might take a look at what some of the astrophysics people are doing. At Northwestern they were using spectral methods to study the environment near event horizons.

In my own research modeling systems of laser cavities, non-linear absorbers/emitters and so forth, it was sometimes useful to start with the system and add the obstacle through a perturbation.

more than 7 years ago

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