Chronos

According to Wikipedia, the threshold for fibrillation is 60 mA for AC, 300-500 mA for DC. On reflection, it seems I'd previously cached the AC value as the value for all currents, so that was skewing my argument.

Given these figures, a 1k Ohm total resistance (internal plus skin plus body) would lead to a 12 mA current (painful but not fibrillation-inducing), whereas 200 Ohms / 40 Ohms total resistance would be required for 12 VAC / VDC to be potentially lethal. So, yeah, now that I think about it, a car battery probably couldn't be lethal unless conduct... (read more)

It's worth noting that the reason we use clamps on the ends of the jumper cables is because pressure increases surface area in contact, which decreases resistance for the simple reason of Ohm's law applied to parallel resistors. (Three 1k Ohm resistors have a parallel resistance of only 333 Ohms. It's meaningless to give a single figure for copper -> wet skin resistance without also giving the surface area for which the figure is valid.)

This means that incidental touching of metal is extremely unlikely to kill anyone, but accidentally clamping your finger, gripping metal tightly, or anything else that applies pressure to your skin will dramatically raise the risk.

It does if the skin is wet. Once you're through the skin, the human body's resistance is quite low, in the single-digit kiloohm range at most, because the human body is mostly salt water (a fantastically good conductor by non-metallic standards). The biggest barrier to current is the upper layer of dead, dry cells on the epidermis. And lead-acid batteries have a fairly low internal resistance, which allows them to produce high currents if the load is also low resistance (a required feature when cranking the engine).

It's worth noting that, while 12 volts won't normally penetrate dry skin under most humidity conditions, you really do need to be careful. Pressure increases surface-to-surface contact, which decreases resistance, which lowers the voltage threshold. So can moisture, like even small amounts of sweat. And a car battery does have sufficient current to injure or kill a human being quite easily. (Voltage penetrates insulators, current actually does damage. The zap you get from static electricity is in the range of thousands of volts, but the current is negligible.)

I was taught a slightly different procedure, which is the same as the one listed as the first result on Google for "jumper cables":

1. Line up the cars, pop the hood on both cars, get out the jumper cables, make sure both cars have their engines turned off, check that the dead battery looks safe (no cracks, leaks, or swelling), and try to scrape off any corrosion on the terminals.
2. Connect one red clip to the positive (+) terminal of the dead battery.
3. Connect the other red clip to the positive (+) terminal of the good battery.
4. Connect one black clip

Washing bacteria down the drain is certainly the primary purpose for using soap, by far, but surfactants like soap also kill a few bacteria by lysis (disruption of the cell membrane, causing the cells to rapidly swell with water and burst). In practice, this is so minor it's not worth paying attention to: bacteria have a surrounding cell wall made of a sugar-protein polymer that resists surfactants (among other things), dramatically slowing down the process to the point that it's not practical to make use of it.

(Some bacteria are more vulnerable to surfac... (read more)

I'm a bit irked by the continued persistence of "LHC might destroy the world" noise. Given no evidence, the prior probability that microscopic black holes can form at all, across all possible systems of physics, is extremely small. The same theory (String Theory[1]) that has led us to suggest that microscopic black holes might form at all is also quite adamant that all black holes evaporate, and equally adamant that microscopic ones evaporate faster than larger ones by a precise factor of the mass ratio cubed. If we think the theory is talking... (read more)

I'm a bit irked by the continued persistence of "LHC might destroy the world" noise. Given no evidence, the prior probability that microscopic black holes can form at all, across all possible systems of physics, is extremely small. The same theory (String Theory[1]) that has led us to suggest that microscopic black holes might form is also quite adamant that all black holes evaporate, and just as adamant that microscopic ones evaporate faster than larger ones, by a precise factor of the mass ratio cubed. If we think the theory is talking compl... (read more)

I'm afraid I can't say much beyond what I've already said, except that Google places a fairly high value on detecting fraudulent activity.

I'd be surprised if I discovered that no bad guys have ever tried to simulate the search behavior of unique users. But (a) assuming those bad guys are a problem, I strongly suspect that the folks worried about search result quality are already on to them; and (b) I suspect bad guys who try such techniques give up in favor of the low hanging fruit of more traditional bad-guy SEO techniques.

I think it's interesting to note that this is the precise reason why Google is so insistent on defending its retention of user activity logs. The logs contain proxies under control of the end user, rather than the content producer, and thus allow a clean estimate of (the end user's opinion of) search result quality. This lets Google spot manipulation after-the-fact, and thus experiment with new algorithm tweaks that would have counterfactually improved the quality of results.

(Disclaimer: I currently work at Google, but not on search or anything like it, and this is a pretty straightforward interpretation starting from Google's public statements about logging and data retention.)

And while some of their costs are borne by others, a lot of their taxes going to roads are also wasted.

This doesn't make sense, because dollars are fungible. If WM reaps a greater monetary value from the highway system than it spends on the highway system via taxes, WM comes out ahead.

So I don't see how this is an indictment of WM -- the harm lies in the shift of the structure of production to a less efficient one, not in a transfer of wealth to the Waltons.

Then we're in violent agreement. I didn't intend the highway bit to be an indictment of WM,... (read more)

FWIW, I agree with wnoise, public funding of a library is a subsidy for the users of the library. If publicly funded libraries didn't exist, privately funded ones would, and those privately funded libraries would charge people money just as surely as a privately funded museum charges admissions. (And they'd probably have a "Second Tuesday of the month is free" special, much like a museum.)

Note: when I say something is a "subsidy" I am attempting to state a fact, not attempting to make a moral judgment. In the specific case of a publi... (read more)

I've never understood the "IHS subsidizes Wal-Mart" argument. It would only be a subsidy if WM got access to it on preferential terms to the rest of us. But they don't. Whatever use of the IHS they make, everyone else had the same opportunity. It's not like WM stupidly built up their whole infrastructure and then one day said, "Oh crap! This will be an utter failure unless there's a free interstate highway system! Quick! Government! Build it with other people's money!"

Of course. The subsidy is implicit in the system, rather than exp... (read more)

I suppose I should qualify that, as it's a bit unfair to Buffett.

Yes, Buffett is a professional investor and more expert than me at it, which counts for quite a bit. But he's also human, and humans don't do a very good job of anticipating economic activity beyond a horizon of a few years. Importantly, most humans have a laughably brief idea of what constitutes a "long term".

I'd estimate that Buffett's bet constitutes quite a few bits of evidence toward the profitability of Wal-mart over, say, a 2 year time horizon. But I was already leaning in... (read more)

Ah, I managed to come up with a more concrete example of where Wal-mart is leaving local information on the table.

Wal-mart has large displays of featured items, internally known as COMAC. (No, I don't know what it stands for, either.) These items come in as a bulk shipment, go on the shelf for two weeks, then come down: anything left over goes on the shelf or into the backstock bins. (A little birdie told me that they've eliminated the backstock bins for almost all departments now, so I'm not sure what they do with the leftovers now.) They form the big... (read more)

And on the timescale of 5 or even 10 years, he may even be right. Yay for him.

Re: "telling stories"... When it comes to refusal to calculate, the Austrians seem closely akin to the people who claim that morality is "mysterious". They're looking at the mistakes of others (principally Keynes) and trying to reverse stupidity.

Which is a shame, because they do have a few insights here and there that strike me as being so correct they're painfully obvious in hindsight.

As a separate sidebar regarding logistics, it's interesting to note that Wal-mart's shipping component is effectively being subsidized by the federal government, by way of the U.S. Interstate system.

While I'm not so much of a libertarian that I think the Interstate system was a bad idea, it is important to note that the Interstate system created an entire category of business (shipping via truck) that directly harmed two existing industries (shipping via boat, shipping via train) and stunted the growth of a third (shipping via plane). This would be all fi... (read more)

I'm not full up on Hayek specifically, but the Austrian point in general is that regulations create barriers that shift the average size of a corporation, and the shift is almost exclusively upward because it takes a larger company to hire lawyers to figure out what the regulations mean. This creates a selective pressure for larger corporations, due to an artificially imposed economy of scale.

Specifically, what is it about Wal-mart that is so economically scalable? Wal-mart is not like Intel: they don't make a ten billion dollar investment, then earn pro... (read more)

Actually, I'm not by any stretch of the imagination convinced that Wal-mart is a highly profitable corporation by any long-term measure: that is, I'm quite convinced (probability greater than 0.99) that Wal-mart is sacrificing long-term growth and sustainability in favor of superficial short-term gains. Upper management is desperate to do anything to make the stock price budge, long term be damned. Eventually, this superficiality will expose itself as the house of cards it truly is.

The recent news regarding firing over 10,000 employees at Sam's Club is s... (read more)