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Newly Spotted Frozen World Orbits In a Binary Star System

yesterdaystomorrow Re:Colder than Earth? Not so fast. (34 comments)

No depth of troposphere can turn a Neptune or Pluto warmer than Earth.

Neptune's interior temperature is thought to be 7000K. Venus, a bit smaller than Earth, has a surface >500K hotter than its tropopause. I see no physical reason that this super-Earth couldn't have much more atmosphere than Venus. 220K from tropopause to surface would get you to liquid water.

about three weeks ago
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Newly Spotted Frozen World Orbits In a Binary Star System

yesterdaystomorrow Colder than Earth? Not so fast. (34 comments)

We know nothing about this planet's atmosphere. The low flux of energy from its star tells us that its stratosphere (if present) must be very cold, but says nothing about its surface temperature. It could have a much deeper troposphere, and thus a much stronger greenhouse effect than Earth has.

about three weeks ago
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Small Genetic Change Responsible For Blond Hair

yesterdaystomorrow Re:It's a gene (125 comments)

Someone in molecular and computational biology (like me) would also call the controlling element a gene. Science journalism is far too often full of such odd definitions and misunderstandings.

The "gene encodes a protein" idea still seems quite common in educational efforts that at least *ought* to have real scientists behind them. See, for example, page 4 of http://www.genome.gov/Pages/Ed.... One who monitors the science news also will frequently encounter press releases like "We sequenced organism X's genome and it contains (pick a number) genes, compared to the (human gene count du jour)." Presumably molecular biologists provided these numbers, but they appear to refer to protein coding sequences only. Oh, well, it's no sillier than counting galaxies (I'm an astrophysicist, and we pretend to do that frequently).

about 2 months ago
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Small Genetic Change Responsible For Blond Hair

yesterdaystomorrow Re:It's a gene (125 comments)

ORF (Open Reading Frame) is typically used for the case you described, and has been for some time now.

I don't think that's what I'm getting at. To switch to a different set of metaphors, "ORF" is a syntactic term while "gene" is a semantic term. Only a subset of ORFs are transcribed, as I understand it. A sequence of letters and spaces ending with a period is not necessarily a meaningful sentence.

In any case, the original article claimed that blondness was not controlled by a "gene". But by the old definition of "gene" that's nonsense. Someone working in, say, evolutionary dynamics would certainly call the controlling element here a "gene".

about 2 months ago
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Small Genetic Change Responsible For Blond Hair

yesterdaystomorrow It's a gene (125 comments)

Originally, "gene" meant "heritable element". Outside of molecular biology, it still does. That DNA can encode the construction of protein was the first connection molecular biologists discovered from genotype to phenotype. This caused them to mistakenly redefine "gene", because they supposed it was the only connection. Since they have now found other kinds of heritable elements in DNA, it is time for them to revert to the older definition, and come up with some other term for the subset of genes that encode protein.

about 2 months ago
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Ask Slashdot: Minimum Programming Competence In Order To Get a Job?

yesterdaystomorrow Re:Key is non-programming skills (466 comments)

Yes, yes, yes. To be a programmer is like being a writer. The most important thing for a writer isn't spelling and grammar, but knowledge of something worth writing about.

about 3 months ago
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NASA Forgets How To Talk To ICE/ISEE-3 Spacecraft

yesterdaystomorrow Re:Why so expensive? (166 comments)

Here's how it works.

In the NASA system, the first thing any project needs is a cost estimate from the bean counters. They employ a vast amount of historical data to estimate costs. To get project approval, you must promise to spend that much money: if you don't, NASA management will assume you don't understand the difficulty, and will fail. Then, of course, you must actually build a project organization with a staff capable of spending the money.

This can go wrong rather badly. If the project is actually a lot easier than the bean counters assumed, you have now set yourself up for a massive overrun. Squander is harder to manage than lean development. But when you overrun, the data is duly entered in the bean counters' database, and the next similar project has to come up with even more money.

Communications may be the area where costing is the farthest from the real state of the art.

about 5 months ago
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Mathematician: Is Our Universe a Simulation?

yesterdaystomorrow Re:Not very plausible (745 comments)

It's just a difference of degree.

The degrees matter. Above some (small) scale it makes no sense to simulate something when the thing itself scales well but the simulation scales poorly.

There are hard physical limits on information processing that cannot be exceeded: https://en.wikipedia.org/wiki/... NB that these limits directly imply that any finite region of space can be fully simulated by a sufficiently large, (non-deterministic) linear bounded automaton--an abstract computational machine less powerful than a Turing machine.

But the question isn't about a full simulation by an abstraction. That's indistinguishable from the real thing, so it's untestable. The question is whether physics exhibits some signature of an incomplete simulation by a concrete machine with characteristics familiar to us.

about 5 months ago
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Online Database Allows Scientists To Recreate Early Telescopes

yesterdaystomorrow Re:Buy a Galileo Scope (52 comments)

Elitest git.

Sorry, but don't talk rubbish. A £100 (so $200 at best) Celestron reflector will show your kids Jupiter, Saturn, individual craters on Mars, come with tripod, EQ mount and a range of eyepieces. An extra $50 or so and you can get a kit of cheap eyepieces and a barlow in a nice Celestron-branded kit.

Yep. The Edmund Astroscan is a popular telescope for professional astronomers to keep around for when they just want to enjoy a view of the sky, or share it with friends. Not very expensive, but a lot of fun.

about 5 months ago
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Mathematician: Is Our Universe a Simulation?

yesterdaystomorrow Not very plausible (745 comments)

Mathematics, especially simulation, is actually a very weak approach to physical phenomena in themselves. It's good for human insight *about* the phenomena, but in most cases the equations are intractable and a simulation is miserably inefficient at getting the specifics right. A small molecule can assemble itself in picoseconds without mathematics, but a simulation takes a huge supercomputer run. If you'd like to simulate something bigger, you'll find that simulation scales very badly.

about 5 months ago
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Solar Pressure May Help Kepler Return To Planet-Hunting Duties

yesterdaystomorrow Re:Light Sail (46 comments)

This is fascinating, but what I find even more interesting is why they couldn't use a similar technique to make the need for the attitude control wheels obsolete? It would require a spacecraft much different than Kepler, but would it not be possible to use sails to orient a similar craft no matter what area of the sky it wanted to point to?

The advantages are obvious, but there are disadvantages:

1. It doesn't work near the Earth, because atmospheric drag, magnetic torque, and gravity gradient torque are all considerably larger than radiation pressure.

2. The forces are tiny, so your spacecraft won't be very agile. If you need to reorient to change targets or point an antenna at Earth to send your downlink, it'll take awhile.

3. While as an exercise in applied physics radiation pressure may be the simplest attitude control method, it doesn't fit NASA's engineering approach, where teams of specialists make cautious, incremental changes to what their predecessors did. Here, there are few precedents, and the specialists usually don't understand them.

Note that we are not talking about the pressure of the solar wind. That's much smaller that the pressure of solar radiation.

about 8 months ago
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Particle Physicists Facing Insane Competition For Work

yesterdaystomorrow Re:Unreasonable expectations (226 comments)

It is precisely because of the arrogance your are displaying that nobody in their right mind (and left hemisphere) would hire a physicists. There are as smart engineering students as "smart physics students".

I never said that engineers weren't smart. The focus of engineering education has both advantages and disadvantages. Often. the best results come from teamwork between physicists and engineers. Physicists tend not to be so good at the messy practicalities.

about a year ago
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Particle Physicists Facing Insane Competition For Work

yesterdaystomorrow Unreasonable expectations (226 comments)

Young people should not go into physics expecting to become tenured professors. It might happen, but it's unlikely. And besides, why would you want to? Because your professor thinks you should aspire to it? It's actually not that great a job.

However. physics is still a great field of study because you can take it so many places. You can do engineering that engineers can't do because while they know the shortcuts while you know the fundamentals. I know a number of physicists who work in medical imaging, for example. The best RF engineer I know has a physics degree. A physicist needs great math skills, and unlike mathematicians, needs to be able to apply them in the real world. A smart physics student will take some classes outside of physics, and make mental connections between fields. If you're at a university, you should exploit the situation (and avoid being exploited).

about a year ago
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Galileo: Right On the Solar System, Wrong On Ice

yesterdaystomorrow Re:More false history (206 comments)

Well, let's not be so impolite. Nevertheless, I agree that Galileo was strongly driven by his desire to win whatever debate he was involved in. This was a serious character flaw, and a big problem in his dealings with the Inquisition. They allowed him the out of saying that the Earth's motion was merely a convenient hypothesis. That would have been consistent with his argument that the Earth's motion was not detectable by its inhabitants because motion is relative. But he wouldn't take the next obvious step: if motion is relative, which objects you consider your fixed reference is arbitrary. He was certainly smart enough to see this, but his desire to win overtook his reasoning facilities, I think.

about a year ago
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MIT Reports 400 GHz Graphene Transistor Possible With 'Negative Resistance'

yesterdaystomorrow Re:And again.. (123 comments)

So, if this new technology ever becomes practical, you'll see it in fast clocking cores where essentially every gate and flip flop is busy all of the time. The surrounding support circuits will still be silicon.

Heh, so the internal logic is running at 400GHZ, and the rest of the chip is running at 10GHZ? Is that even practical?

Yes. Clock speed mismatch in different parts of a system is common with current technology. Cores commonly clock faster than memories, and much faster than many peripherals.

about a year ago
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MIT Reports 400 GHz Graphene Transistor Possible With 'Negative Resistance'

yesterdaystomorrow Re:And again.. (123 comments)

You're cynicism is valid in this case. This is just rehashing research from 20 years ago on negative differential resistance (NDR) two-terminal devices.

Logic based on two terminal NDR devices has been around for more than 50 years (tunnel diodes, neon tubes, ...). Its big problem is input-output isolation: cascading elements is tricky. But these guys are using four terminal devices in a three terminal NDR mode, so they don't have that problem.

Graphene switches have an on-off current ratio of ~3 (tiny and useless),

Well, that depends. The ECL gates that Cray used for their early supercomputers had nearly constant current. Some specialized applications still use ECL. If you're changing state frequently, low static current may not actually save power. So, if this new technology ever becomes practical, you'll see it in fast clocking cores where essentially every gate and flip flop is busy all of the time. The surrounding support circuits will still be silicon.

about a year ago
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Around 2,000 Fukushima Workers At Risk of Thyroid Cancer

yesterdaystomorrow Re:Heightened Risk != Cancer Victim (124 comments)

Next time, don't build a nuclear power plant where it can be hit by a tsunami, though. That was just stupid.

Except that the enormous loss of life wasn't because they built a nuke on the coast. It was because (like everyone who has a coast), they built *everything* on the coast: homes, schools, factories, offices, railroads, etc. The reactor complex actually turned out to be one of the safest places to be during the tsunami.

1 year,9 days
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Around 2,000 Fukushima Workers At Risk of Thyroid Cancer

yesterdaystomorrow Re:Consider the alternative (124 comments)

Except that you don't mine pure uranium, you mine uranium ore (pitchblende), and you need a lot of it to extract a bit of natural uranium. Even worse, pitchblende itself is not as easily mined as coal, because if you have got a coalbed, it consists of mostly, well, coal. If you mine pitchblende, then you go through a lot of rock you need to discard first.

Coal exists in narrow seams, too. Massive, destructive strip mining or very dangerous underground mining are required to access it. Coal mining would need to be a million times less unhealthy and destructive than uranium mining to be competitive on safety and environmental impact. It isn't.

1 year,9 days
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Around 2,000 Fukushima Workers At Risk of Thyroid Cancer

yesterdaystomorrow Re:Consider the alternative (124 comments)

Well, well, uranium just appears out of the thin air and does not have to be mined and refined. It is also not like uranium mining was considered prison labour because it was so dangerous.

Coal and uranium mining are both very dangerous. But the big difference is that while you need tons of uranium to fuel a nuke, you need megatons of coal to fuel a coal plant. The difference in quantity of material and waste dominates the hazard calculation.

1 year,9 days
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Around 2,000 Fukushima Workers At Risk of Thyroid Cancer

yesterdaystomorrow Re:Consider the alternative (124 comments)

Would coal pollution necessitate an evacuation zone? It absolutely would if coal was held to the same standards as nuclear.

1 year,9 days

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