Follow Slashdot blog updates by subscribing to our blog RSS feed

 



Forgot your password?
typodupeerror

Comment: Re:not sure (Score 1) 248

by DirtySouthAfrican (#39634191) Attached to: Dental X-Rays Linked To Common Brain Tumor
It is my understanding that our DNA has repair mechanisms that will fix some of these radiation-induced errors, but that these repair mechanisms are quite slow, so total dose is not as important as how quickly it is received. The parent here is correct, except that density over time is also important. I suggest brushing up on radiation safety before you work with any more of that ionizing radiation ;)

Comment: Re:Slowing down. (Score 2) 155

Except the shock cone of say, an SR-71 Blackbird, originate at the nose and inlet cones of the aircraft, and these are specifically designed to keep the shockwaves ahead of the engines, and thus keep the airflow in the engines subsonic. What you are saying is mostly correct, except that this wall of sound is what happens when "sound" starts to behave non-linearly. When you try to push air faster than a certain speed, molecules begin to pile up, density increases, heat increases, and it stops behaving like air in the way we are used to. You don't need a sound source for this. The energy you are pumping into that shockwave will be plenty loud. I think some artillery create shock waves that can be felt before the cannon can be heard.

Comment: Re:Location (Score 1) 560

by DirtySouthAfrican (#33365194) Attached to: UVB-76 Broadcasts New Voice Message
Well, it does, actually. If you intercept a signal, you absorb part of it, so you are changing the electromagnetic field. If you are changing the electromagnetic field, you can be tracked (in principle). Of course you're not going to track a portable radio for reasons of practicality, but that's an issue of scale, and not something fundamentally inherent to the theory. In some circles it goes by the name of radar :)
Science

Invisibility Cloak Created In 3-D 113

Posted by kdawson
from the can-you-see-me-now dept.
An anonymous reader writes "Scientists have created the first device to render an object invisible in three dimensions. The 'cloak,' described in the journal Science (abstract; full text requires login), hid an object from detection using light of wavelengths close to those that are visible to humans. Previous devices have been able to hide objects from light travelling in only one direction; viewed from any other angle, the object would remain visible. This is a very early but significant step towards a true invisibility cloak." The "object" hidden in this work was a bump one micrometer high. The light used was just longer than the wavelengths our eyes detect. To get a visible-light cloak, the features of the cloaking metamaterial would need to be reduced in size from 300 nm to 10 nm.

Comment: Re:Not same as elevator (Score 2, Interesting) 296

by DirtySouthAfrican (#28257647) Attached to: Inflatable Tower Could Climb To the Edge of Space
Actually, "out of Earth's gravity well" would truly be the "edge of space", i.e., infinitely far away. As I understand, the biggest problem in getting to space is to spend as little time as possible in the deepest part of the well, because, going straight up, maintaining that altitude costs a lot of power. But if the structure is self-supporting, then you can hoist up your fuel and payload using more efficient means, since you don't have to actively maintain your altitude. It's called "gravity drag". I'm not really up on the numbers, but the first 10% costs you a helluva lot more fuel than the "last" 10%, for most values of $destination.

Comment: Re:string analogues (Score 3, Interesting) 236

by DirtySouthAfrican (#27579629) Attached to: Strings Link the Ultra-Cold With the Super-Hot
Well this is closer to "universality", which is a concept in field theory and condensed matter physics, in which the "atomic" characteristics of a system are largely irrelevant to its macroscopic properties, save for specifying a few parameters like viscosity or resistivity. Unlike your differential equation example, the equations for both are very different and non-trivial. When you start enumerating differential equations starting from the simplest you can write down, the harmonic oscillator, heat equation, diffusion equation and so forth pop out right away. You'll be writing for a long time before 11D supergravity equations of motion pop out.

Comment: What women want (Score 1) 349

by DirtySouthAfrican (#26985063) Attached to: How To Be A Geek Goddess

Many women are interested in using technology, they just don't want to dive in to quite the same depth. Or they may not be interested in the way most men approach it.

Or... and I'm going out on a limb here... many women don't want men telling them what they want. "Just don't want to dive into quite the same depth"? Dear lord.

Line Printer paper is strongest at the perforations.

Working...