Forgot your password?
typodupeerror

Comment: Re:IAMA PDL user (Score 1) 94

by Dr. Zowie (#38953723) Attached to: Perl Data Language 2.4.10 released

Yes, this is an ongoing problem, and it is what made Python the more popular solution. Perl is easy to write, but harder to write well -- the whole point of the language is that it is rich and expressive, without a lot of imposed structure. People who write Perl as they learn tend to write crappy, unmaintainable Perl. The result is that most students' first experience with Perl is of crappy, unmaintainable spaghetti-Perl. Those students often grow up to become Perl-haters.

Python is more novice-friendly but harder to to be expressive in for experts, so grizzled longhairs (like me) tend to scoff at it.

That sort of pattern happened before: there was a time when Pascal attracted a lot of mindshare and people scoffed at the woolier "C". Entire OSes were written in Pascal (gasp). But in the long run people migrated back to C and (when it was invented) C++, because, well, Pascal is easy to learn but it sucks for experts.

There are lots of solutions for getting one's work done. PDL is superior for some tasks, Python/NumPy is arguably superior for others (like learning). I wish people would get over it and code, instead of tribal hating. But that is what people, well, do.

+ - Oldest Known Tetrapod Found->

Submitted by qazsedcft
qazsedcft (911254) writes "The oldest footprints ever made by four-legged creatures have been discovered by scientists, forcing them to reconsider a critical period in evolution: the point at which fish crawled out of the water onto land to evolve into reptiles, mammals and eventually humans. The "hand" and "foot" prints are 18m years older than the earliest, previously confirmed fossil remains of "tetrapods" or four-legged vertebrates and were left by lizard-like creatures up to 2.5 metres long. The discovery, reported in tomorrow's issue of the journal Nature, was made in a former quarry in the Holy Cross Mountains in south-eastern Poland. The fossil footprints can be reliably dated to the early Middle Devonian period, around 395 million years ago."
Link to Original Source

Comment: Re:not a "real" monopole (Score 2, Informative) 256

by Dr. Zowie (#29313211) Attached to: "Overwhelming" Evidence For Magnetic Monopoles

It is not possible to create a true monopole from dipoles, because any "g'zinta" field lines to your favorite point in space have to matched by an equal number of "g'zouta" field lines from the same place.

These spin-glass phenomena are only quasi-monopoles: all the "g'zinta" field lines are squished into a small tube, leaving the "g'zoutas" free to splay out almost like a true monopole. But the divergence is still zero (there are no field line endpoints).

Compare to a spray nozzle that sprays water in all directions from a garden hose. If the spray is broad and strong enough, it might sort of hide the hose itself, so that you could convince your kid brother that the nozzle is a magical water-creator (i.e. that the flow through the nozzle has positive divergence). But in fact, there's a garden hose feeding the nozzle, and every bit of water that comes out through the nozzle is balanced by an equal bit coming into the nozzle from the hose.

In that analogy, your nozzle is interesting because the spray pattern is similar to the pattern from a mythical water-creator, but it still won't solve the problem of drought in California, which a true water-creator would.

Comment: Re:not a "real" monopole (Score 5, Informative) 256

by Dr. Zowie (#29312269) Attached to: "Overwhelming" Evidence For Magnetic Monopoles

Classic case of science journalists overblowing a mundane result. Yes, connected quasi-monopoles are interesting. they are visible in any conducting medium. But there's a HUGE difference between a quasi-monopole that is at the end of a finite-length, shielded dipole and a true monopole that actually violates the magnetic divergence-free condition.

In solar physics we call such things "unipoles" to distinguish them from the infinitely harder-to-find "monopoles". Unipoles are all over the surface of the Sun, because the conductive interior hides the field lines that connect opposing unipoles.

It is disingenuous at best and downright deceptive at worst to call the HZB result "evidence for magnetic monopoles", because it ain't.

The only plausible true magnetic monopole detection ever was still in Blas Cabrera's instrument at Stanford in the 1980s. It was never replicated, so it is unknown whether they exist but are extremely rare (and Cabrera was just lucky) or whether his detector glitched.

Comment: Actually, more interesting than that... (Score 4, Interesting) 354

Since he seems to have been convicted under the EAR, which is a set of regulations having to do with rendering technical aid to foreigners, and not the ITAR, which is a set of regulations about exporting actual objects (such as munitions or rocket-control thingies), there is very close parsing required of the law to figure out what is Right or not.

After all, the material he distributed wasn't classified, and in principle the 1st Amendment to the U.S. constitution allows you to say whatever you want to whomever you want (provided that you aren't directly inciting a crime, or lying, or distributing classified information). It's especially interesting because most violations of the EAR never get to trial -- they are generally settled by defense contractors who are eager to make good so that the flow of federal dollars doesn't dry up -- so this is likely to be a strong legal precedent. In this case, as in so many, my guess is that he had the standard language in his federal contract -- essentially "I agree to abide by ITAR and EAR" -- so that the regulations can be enforced via contract law even if the ITAR and EAR are eventually found to be unconstitutional if applied to general citizens.

The most scary situation involving EAR/ITRAR is that I know of no legal precedent at all for the EAR in the case of a gifted, privately funded enthusiast just screwing around -- but it applies to many things that even hobbyists do now. If you take an interest in (say) cheap image stabilization systems or inertial guidance of vehicles, and share your work with some of your friends down at the rocket club (who happen to be exchange students from the Pacific Rim), the regulations say that you are liable for millions of dollars in fines and many years of jail time -- even though those technologies are well within the range of gifted college students today (and affordable for an enthusiast to tinker with). I have no idea what the outcome of such a case would be -- only that the legal bills would be immense and the hypothetical hobbyist's life would be put on hold for years, if the Feds decided to take an interest.

Comment: Some ideas... (Score 5, Interesting) 249

by Dr. Zowie (#26882707) Attached to: Physics Experiments To Inspire Undergraduates?

Ultrasonic tape measure / speed of sound experiment. Ultrasonic transducers are easy to come by; students should send some pulses out one, and then sense the return pulse, giving either a numeric indicator or a voltage level that corresponds to the delay time. A little electronics heavy, but if they have had a background in electronics it should be pretty fun. Proof of concept: ultrasonic tape measures at Home Depot for $15. (Trick: you have to build some kind of ultrasonic horn to channel the pulse and collect the return pulse -- otherwise it diffuses too much)

Lunar range finder. Get a green laser pointer and modulate it with a digital stream. Mount a beamsplitter on a little telescope and point it at one of the Apollo landing sites. Send the laser pointer beam out the telescope, pick up the return signal with a photodiode at the eyepiece. With digital correlation, you can measure the distance to the Moon in only a few minutes of integration. This may be a little ambitious for a 36 hour project, but it makes a dandy six-week independent project. As a side bonus, have them calculate the strength of the return signal. It turns out that the experiment wouldn't work without the retroreflectors planted there by the astronauts.

Million-volt van de graaf generator. Given a length of acrylic tubing, a long rubber band, a couple of brushes, a motor, and a big metal ball you too can make sparks that leap halfway across the room. If you really do get a megavolt, you can put a Geiger counter nearby and look for gamma rays(!)

Barometer. Make a barometer that can measure the height of your building. Pretty simple to do - just requires mercury, a glass tube, and care, or (for a more sensitive one, but harder to calibrate) an columnn of vacuum oil with a sealed partial vacuum at the top - but very moving: you can demonstrate the mass of air with remarkably simple equipment.

Pipe organ. Have them cut the tubes to length to create a scale.

Spectroscope. Stanford used to give out posters that could be folded up to make a little spectroscope, with a $0.10 transmission grating slide as a dispersive element. I handed them out to my CU students and asked them to do "something interesting" with them. One of them taped over the slit. Another one used razor blades and sketched the Fraunhofer spectrum of the Sun. Yet another used it to debug a sputtering apparatus for his work/study job. You probably don't want to be that open-ended, but you can certainly ask them to make one and calibrate it using fluorescent lights. Everyone but tape-boy really felt inspired by actually *seeing* spectral absorption and emission lines.

Doppler radar. Not as hard as it once was, this may still be on the ambitious side. Edmund Scientific has microwave transmitters that will serve. Heterodyne the signal with the return pulses, the output frequency gives you the speed.

Measure the curvature of the Earth using a car's odometer and a sextant. Cheap but effective can be had for $25-$30 at sailing supply stores. Have the students travel about 60-100 miles north or south and measure the altitude of a celestial object at both places at the same time of day. Students can "shoot the Sun" at true noon on successive days (compensating for the analemma) or "shoot Polaris" on successive nights at the same time. (Even Polaris is about a degree off the pole, so you can't shoot Polaris at different times on the same night without compensating for that...)

Comment: Big deal...Mir had a ham usenet feed... (Score 1) 330

by Dr. Zowie (#26720173) Attached to: Students Call Space Station With Home-Built Radio

...from University of Hawaii, in the early 1990s. A colleague of mine was a postdoc there and introduced me to the guys that did it. They had set it up pretty much for kicks, after a long string of voice contacts ith the cosmonauts (who must have been pretty bored up on their end too...)

Comment: Perl Data Language (Score 2, Informative) 250

by Dr. Zowie (#26671477) Attached to: Open Source Software For Experimental Physics?

Perl Data Language is quite nice -- it has all the blended hackish glue-code goodness of Perl (which could be a plus or a minus depending on your personal style). CPAN (the big Perl repository) has a lot of free stuff for access to serial, parallel, and USB ports so you can control your equipment and acquire data. PerlXS (built into Perl) gives you nice access to C libraries, and PP (a meta-language that comes with PDL) helps you sidestep a lot of cruft if you have to use a C module to import large volumes of data.

PDL has built-in commands for plotting 2-D stuff via PGPLOT or PLPLOT, and 3-D stuff via GL. I use it for all my publications.

Some prefer NumPy or SciPy, the Python equivalents of PDL, but (IMAO) Python isn't as expressive as Perl, and the external libraries, while extensive, cannot compete with CPAN for completeness or hugeness.

Comment: PDL (from Perl), GDL (from IDL), NumPy/SciPy (Score 1) 250

by Dr. Zowie (#26671425) Attached to: Open Source Software For Experimental Physics?

Perl Data Language is my personal favorite for data acquisition and manipulation - it is an extension to Perl that gives you the usual data analysis and plotting goodies, plus a nice mix of access to C code (via XS), access to the huge CPAN trove of modules (via, er, CPAN), GUI-isms (via PerlTK), and serial port / USB port access for instrument control and data acquisition.

It's based on Perl, which can either be a huge plus or a huge minus depending on whether you like Perl.

If you want bondage-and-discipline, you can go with GDL, which is an open-source clone of IDL. GDL's main advantage is that it is a clone of IDL, which has become the dominant language in some sectors of physics. GDL's main disadvantage is that it is a clone of IDL, which is among the more evil, bletcherous, pitfall-laden, wretched buggy cesspits of quasi-language that exist.

Numeric Python is reputed to be good, but it's not nearly as expressive nor as flexible as Perl. Matter of taste, really.

Gnu Octave is a MatLab clone, but does not have access to the huge library of add-on modules that you can buy for MatLab. Still, many modules exist and if you like the syntax you can stick with it.

Another good place to start is the wikipedia comparison of numerical analysis packages.

In every non-trivial program there is at least one bug.

Working...