Follow Slashdot blog updates by subscribing to our blog RSS feed

 



Forgot your password?
typodupeerror

Comment: Re:There are quite a few haters on this thread but (Score 1) 214

Further, if this was in existence a few decades ago, perhaps we would have nipped Scientology in the bud before it landed in the UK.

If it were in existence ~1400 years ago, perhaps we would have nipped Islam in the bud.

If it were in existence ~2000 years ago, perhaps we would have nipped Christianity in the bud.

And I wonder how many readers agreed with my first line, then threw a shit-fit when they got to my second line.

-

Comment: Re:Aren't they called Currents? (Score 1) 61

by rgbatduke (#49750055) Attached to: Subsurface Ocean Waves Can Be More Than 500 Meters High

To be fussy (and as a physicist I am nothing if not fussy), one can either describe everything in fluid motion as waves simply because the medium is (somewhat) elastic and one can construct a wave equation to describe the propagation of pressure differences, or one can use the Navier-Stokes equations straight up and solve for bulk transport properties. We don't usually refer to the bulk transport as waves. When I stir my wort making beer and get it going in a nice cylindrical eddy in the cylindrical pot, decomposing this bulk transport in a wave description makes little sense, even though the motion is undoubtedly periodic, and it is difficult to see it as the outcome of a suitable transformation of the N-S equations into a real-valued second order PDE in space and effectively second order in time, which is what one usually "expects" for "waves". Second order in time leads to solutions that are either exponential (not waves) or harmonic (waves), with life getting more complicated to the extent that things are generally nonlinear in the N-S equations.

Similarly, I personally wouldn't describe the thermohaline circulation of the ocean as "a wave", or stable currents as "waves", or the flow of water downhill in a stream as "waves", or laminar flow in general as "waves" and am not sure that I'd even describe eddies and the onset of turbulence as waves, although there finally, in the vicinity of the conditions where laminar instabilities can grow and initiate turbulence, a wave description might start to be sensible as periodic propagating wave-like structures appear (even though they probably don't satisfy any sort of sensible wave equation)

Note that your example of shock waves is a good one, as they result when the overpressure in air waves exceeds one atmosphere, at which point (if not long before) the wave equation that was very nearly linear becomes very definitely nonlinear, as the wave underpressure is clipped at 0 atm (a vacuum) but the overpressure is unconstrained. The resulting nonlinear equations can support e.g. solitonic solutions, propagating hyperbolic secants plus a reverberations as the air subsides into normal waves again from nonlinearities in the dispersion. I'd still categorize these as "waves" as they represent a specific limiting behavior of the wave equation with nonlinearities.

So the real question is, are the waves discovered by the MIT volken describable by suitably approximated/linearized second order time equations with complex time solutions (granting that one will still have second order space equations describing the fluctuations away from equilibrium in the bulk medium) ? Or are they first order in time, describing bulk transport but without any elastic "wave" to the wave? Are they just currents in the ocean, or are they currents in the ocean with periods, with wavelengths, or even with solitonic properties e.g. shock fronts?

After all, we know already that the ocean supports waves with wavelengths constrained only by its physical and thermoisobaric geometry and boundaries. There is no "low frequency cutoff" per se in the wave equation that describes sound waves in the water that I know of. In much of the deep ocean, the speed of sound is around 1.5 km/sec, so a 10 Hz wave has a wavelength of 150 meters. A wave with wavelength 500 m has a frequency of 3 Hz. Of course waves with this sort of wavelength propagate in the free ocean in all 3 dimensions, so variations 500 meters "high" can and almost certainly do exist.

It is this last terminology that is very odd. In a transverse wave propagating on e.g. a one dimensional string, the wave amplitude can be described as being thus and such "high", where high is understood to be perpendicular to the direction of propagation. In surface waves in the water (a mix of longitudinal and transverse waves) the wave one can discuss the longitudinal and transverse wavelengths together or separately, but again given horizontal propagation on the gravity constrained surface, transverse is understood as "high", a wave is so and so many meters high.

Underwater waves are a different matter altogether. For one thing, there is no sharp interface like the water's top surface, constraining them. Sound waves are longitudinal, and one would not usually describe the amplitude as a "height" even if they were propagating or were standing waves constrained by the top and bottom boundary conditions in the vertical dimension or were a superposition of a horizontal travelling wave and a vertical stationary wave -- a sound wave propagating from right to left between two hard sheets might have modes that could be so described, but the vertical wavelengths are not really transverse wave amplitudes.

What one would like to do is interpret these words as "there exist transverse waves in the deep ocean with actual bulk transport of water up and down by distances of up to 250 meters (each way) around some undisplaced mean, with the displacement occurring in space and time. This is hard to imagine in a highly compressed dense fluid effectively constrained between two surfaces, because it has to satisfy a continuity equation -- one cannot move water up without more water flowing in to replace it on the bottom from somewhere, and without it flowing out of the way on top to somewhere.

Structures like this are not impossible to the N-S equation -- little is, really. One can imagine, for example, a set of convective rolls that propagate around in some closed path. In order for this to be "a wave", IMO the rolls cannot be stationary in their local medium, but actually have to propagate on top of any bulk transport of the medium in e.g. a current. Convective rolls in the Gulf Stream that are just going around in the moving frame but are moving relative to the stationary ground wouldn't count, as the bulk transport is driven by something (thermohaline density changes, atmospheric flow, coriolis forces, non-Markovian history, and boundary conditions) completely independent of the process that creates and amplifies the convective rolls.

rgb

Comment: "instead of air"??? (Score 1) 116

by radtea (#49744845) Attached to: Hydrogen-Powered Drone Can Fly For 4 Hours at a Time

The Hycopter uses its frame to store energy in the form of hydrogen instead of air

This makes it sound like there are all kinds of quadcopters out there that are using air to store energy. This is news to me, although given the low density of compressed-air storage I'd be pretty surprised if it's true.

Anyone have any idea why anyone would say this, as opposed to "instead of batteries"?

Comment: Automate Science (Score 1) 612

by tjstork (#49714503) Attached to: A Plan On How To Stop Sexism In Science

The simple answer is, who cares? Why should we be trusting science to a bunch of arrogant people that cost too much, live to short, and have such an inefficient method of programming anyway? Science itself is something that should be automated, to create a world where everyone gets to know exactly how to do whatever they want to do, without all the whiny political bs about it? Wah, women can whine about being unemployed just as much as automated men increasingly are.

Comment: Re:Good thing climate change isn't real! (Score 1) 293

by Alsee (#49707527) Attached to: Larson B Ice Shelf In Antarctica To Disintegrate Within 5 Years

My first hit for "Global warming"+"times faster" yields this link: As the Earth moved out of ice ages over the past million years, the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years. In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly ten times faster than the average rate of ice-age-recovery warming.

All the opinions you mentioned are, at best, poorly informed.

-

Comment: Re:Pretty sure the heat death of the universe will (Score 2) 386

by radtea (#49678689) Attached to: Criticizing the Rust Language, and Why C/C++ Will Never Die

Are you sure? FooBar() and foobar() are different functions in C but the same function in Fortran, so calling foobar() from C in a fortran-compiled libfb.so is probably not going to have the effect you intended if both FooBar() and foobar() are present in libfb.so, if it is even possible at all (name-mangling might be happening).

I was writing Fortran/C multi-language applications twenty years ago, so yeah, despite a few issues this is easily possible. There was some weirdness, as I recall, because Fortran implicitly pushed the size of arrays onto the stack, so you had to do some fiddling to accommodate them. There were a few other minor issues, but what the GP said is essentially correct: Fortran is link-compatible with C. C++ mangles names, so unless functions are declared with C linkage (extern "C") all bets are off.

Pretty much any language can be interfaced with any other using tools like swig (dunno if anyone still uses that--it's been almost 10 years since I wrote any multi-language code, thankfully).

Comment: Re:Why non-conclusive? (Score 1) 65

Personally, when I gamble and end up about 3/4 of a million dollars in the hole, I assume that I lost.

That sounds more like a conclusion than an assumption.

But the question isn't "Who won?" It is: "On the basis of this result what can we say about who will win next time?"

I don't know what kind of measures they used, and there are a couple of links in this discussion to papers pointing out how problematic p-values are, but it is perfectly possible for the weaker competitor to win any given competition. All it requires is that the width of the performance distributions be large enough to give significant overlap between the players.

People who don't understand statistics are baffled by this. They see individual instances, but statistics is about distributions. We can, by measuring instances, make judgements about the distributions they are drawn from, and knowing about the distributions we can make predictions about future instances.

In the present case, it appears that the observed distribution of performance was such that it wasn't possible to distinguish clearly between the case where the computer is slightly better than the humans but the humans got lucky, and the case where the humans are definitely better than the computer.

Comment: Re:Around the block (Score 5, Insightful) 429

by radtea (#49639581) Attached to: Why Companies Should Hire Older Developers

I may not know "what works", but I sure do know what won't.

Age is not a great arbiter of such things, but it's still true that without age there are some experiences that are hard to get.

I remember when "structured programming" was the silver bullet du jour. Then it was OO. Then it was Java (this is hard to believe, but really, Java was touted as the solution to all our ills, and people believed it for a while, rushing out to re-write perfectly good code in Java and frequently ruining it in the process) Today it's FP.

All of these, except maybe Java, brought some real good to the table. There were a variety of side-trends that never really got off the ground, at least as silver bullets, like 5GLS, whatever they are.

An older developer has had the opportunity to watch these decade-long trends and make better judgements about the curve of adoption. Will Haskell ever become a mainstream language? Nope, although it'll be used in some niche areas, the way SmallTalk still is. Will FP techniques and ideas filter in to all kinds of other languages? Well, duh. Already happening. Is it worth learning a little Haskell and maybe come category theory? Sure. You can do that even while thinking the claim "apart from the runtime, Haskell is functionally pure" is precisely as impressive as the claim "apart from all the sex I've had, I'm a virgin."

Not all older developers will get any utility out of their experience. Some become cynical and dismissive. A very, very few retain their naive enthusiasm for the Next Great Thing. But many of them have a nuanced and informed attitude toward new technology that makes them extremely valuable as the technical navigator for teams they're on.

Basic is a high level languish. APL is a high level anguish.

Working...