cmatteri

You can buy (or build from a kit if you can solder) a functional geiger counter that will detect gamma radiation (what cobalt-60 emits) for under 100 USD. They're a bit too big to put on a keychain, but you can easily keep one in a backpack.

I found the frequency of contamination of scrap metal with radioisotopes to be disturbingly high (this article lists several more cases in addition to those in the wikipedia article: https://slate.com/technology/2013/05/asos-investigation-into...), and we don't seem to be able to reliably detect contaminated goods at the border.

Reading these articles inspired me to build a geiger counter to confirm that none of the metal items I own are contaminated. I used a kit (from https://sites.google.com/site/diygeigercounter/ , but other sites sell them as well) to build a detector that can reliably measure gamma for about $60. Tubes that can detect alpha (e.g. from contamination with Americium-241) as well as test sources (with comparable activity to an ionization smoke detector, i.e. safe and legal for anyone in the US to own) for both alpha and gamma are slightly more expensive but readily available.

Shouldn't the mill be able to precisely drill very small holes for you? Perhaps you could you use the pick and place machine to put small pins in the holes which would be soldered in place on both sides. You could conceivably use one 2-layer board and two 1-layer boards, each with alignment holes drilled in them, pins inserted and solder paste applied to make a 4-layer board. There would be a thin gap between the boards, but since everything is soldered together, would it matter?

I believe it contains on the order of twice as much flux, but I can't find a source for that at the moment. So I don't think flux fumes are much more of a concern than with leaded solder (for which you should have good ventilation or a fan). I did have a ball of solder shoot towards me when I was first getting a feel for it, so you definitely need safety glasses, though I understand this can occur with leaded solder as well, and you want to wear glasses anyways to keep clipped leads out of your eyes.

The use of leaded paint indoors and of leaded gasoline were particularly dangerous, but there are still numerous potential sources of lead exposure, especially in certain industries, but also for the average person. Exposure has decreased, but the safe blood lead level has also been reduced as we become increasingly aware of the harms of sub-clinical lead poisoning.

Two interesting properties of lead's toxicity that weren't mentioned in the article are its potency and its ability to accumulate. A blood lead level of 10 ug/dL is often listed as a threshold for concern (though for children 5 ug/dL or less is more appropriate). A typical blood volume for an adult is around 50 dL (according to Wikipedia), so 10 ug/dL would mean that there are 500 ug of lead in your blood. Lead has a density of 11.3 g/cm^3, so 500 ug has a volume of 44.2 nL. If you have every used a 2 uL pipette, you would have an idea of how small of a volume 44.2 nL is (for those who haven't, it's somewhere in the range of a grain of sand http://en.wikipedia.org/wiki/Orders_of_magnitude_%28volume%2...). Although not all the lead we ingest is absorbed and lead is distributed throughout various organs, this should give a sense of how potent of a toxin lead is. Lead is also cleared from the body fairly slowly, so the amount of exposure per day needed to build up to a toxic level is even lower. These two properties, combined with the ubiquity of lead in our society, the long timescales over which it causes harm, and widespread ignorance of or apathy towards its harms are why I find it a particularly frightening toxin.

One source that could be relevant to some in the HN crowd is electronics solder. Although Europe banned the use of lead in electronic components and solder in most applications in 2006 with RoHS, leaded solder is still mostly legal and common in the US (it looks like CA has partially adopted RoHS http://en.wikipedia.org/wiki/Restriction_of_Hazardous_Substa...). It is fairly easy to use leaded hand solder safely, but it is also entirely plausible that a child with inadequate training or supervision could ingest a significant amount of lead while soldering, from the small flakes of solder that accumulate on your workbench, dust, or lead oxides on a sponge. I had no idea how toxic lead was when I taught myself to solder in high school, and I'm glad I didn't do it much then for that reason.

I have recently started using Sn96.5Ag3Cu0.5 (lead free) solder, and although it is somewhat more expensive that leaded solder, with proper tools, plated PCBs, and correct technique it is really quite easy to use. I have some aggressive rosin-activated flux on hand (that requires cleanup) but I haven't needed to use it so far. I would highly recommend trying out Sn96.5Ag3Cu0.5, especially if you're sharing a workspace with children, who are far more susceptible to lead for various reasons.

A fair number of materials that you might encounter can contain lead as an additive, including plastic, brass, bronze, steel (http://en.wikipedia.org/wiki/Free_machining_steel), and metal/hobby/industrial/artist paints. It's always worth looking up what hazardous compounds may be present in something before putting a grinder to it (again, something I hadn't mastered in high school).

More along the lines of the article, here is another particularly egregious historical use of lead as a color in candy. In this case the compound, lead (II) chromate, also contained hexavalent chromium, another particularly hazardous chemical (http://books.google.co.uk/books?id=aC9NAAAAMAAJ&pg=PA93&dq=%...).

Does anyone have any thoughts on the comfort (for extended use in an office) and effectiveness of the QC-20 vs the QC-15. It seems the QC-20 is better on both counts, despite its in ear design. One downside to the QC-20 is that he battery isn't replaceable, but I plan to use them plugged in, so they should still work even when the battery can't hold much charge.

The article doesn't say, so it's worth mentioning that you can type ctrl-R multiple times to search further back into command history.

Play this song for the full experience http://www.youtube.com/watch?v=zQuH4woPDn0

Or P2P services, which could potentially present a greater threat to Google. Only a small fraction of network users are willing and able to run a personal server, and even those that do aren't capable of competing with Google in terms of hardware.

Decentralized content sharing could remove those obstacles, and a high bandwidth network could facilitate the adoption of P2P services.

I was going to suggest mapping both jf and fj to escape so you could mash the two keys at the same time without worrying about order, but jk and kj would work as well

Their function 10^(5.5-pH) * (mg/cl sugar + 1) does seem to imply that sugar and acidity have a synergistic effect, where the +1 in the sugar term is a hack to keep the result from being 0 if the sugar is 0. This doesn't make sense, as a modest increase in sugar, say from 0 to 1 would double the result regardless of the pH.