Forgot your password?

Comment: Re:What am I missing here? (Score 3, Insightful) 223

by DrLudicrous (#47037557) Attached to: Scientists Propose Collider That Could Turn Light Into Matter
Think of photons as the central point from which oscillating magnetic and electric fields originate. And that this point moves through space at ~3x10^8 m/s. It is kind of like throwing two stones into water and watching the resulting interference patterns, excepts that the centers of those patterns are moving instead of stationary. Hence, collision isn't really an apt description.

Comment: Spectroscopy with MRI (Score 3, Informative) 23

by DrLudicrous (#45501307) Attached to: Detecting Chemicals Through Bone
Disclaimer: I am a physicist who works in MRI. MRI can be used to measure concentrations of certain biochemicals. MRI is sensitive enough to different proton-containing species that the frequency difference between fat and water causes image artifacts that can pose great difficulty. Not all biomolecules are sufficiently concentrated in the brain, or have a spectrum that is unique enough to be measured in vivo. A good example of a brain chemical that can be measured is N-acetyl aspartate (NAA), which has a proton peak at around 2 ppm that doesn't overlap with much else. Magnetic resonance spectroscopy is very difficult, and is most easily accomplished on research scanners operating at 3 tesla or higher. The reason for this is that rather than letting all hydrogen nuclei contribute to one signal that is then spatially located, one must parse what kinds of nuclei (i.e. what their chemical shift is) within each voxel. This not only imposes technical difficulties, but reduces the signal to noise ratio, potentially requiring more signal averaging in order to see sufficient signal above the noise floor.

Students Banned From Bringing Pencils To School 426

Posted by samzenpus
from the watch-how-you-play dept.

US Embassy Categorizes Beijing Air Quality As 'Crazy Bad' 270

Posted by samzenpus
from the it-totally-sucks dept.
digitaldc writes "Pollution in Beijing was so bad Friday the US embassy, which has been independently monitoring air quality, ran out of conventional adjectives to describe it, at one point saying it was 'crazy bad.' The embassy later deleted the phrase, saying it was an 'incorrect' description and it would revise the language to use when the air quality index goes above 500, its highest point and a level considered hazardous for all people by US standards. The hazardous haze has forced schools to stop outdoor exercises, and health experts asked residents, especially those with respiratory problems, the elderly and children, to stay indoors."

Comment: Re:Ohio University Press Release is Misleading (Score 1) 97

by DrLudicrous (#33046784) Attached to: How a Key Enzyme Repairs Sun-Damaged DNA
Ohio STATE University. Not Ohio University. There is a huge world of difference. And PR is important, relying on the general media to disseminate information from original scientific journal articles doesn't work. Scientists should be the ones presenting their work, not journalists who are at best mildly fluent in the research areas they cover.

Happy Towel Day 122

Posted by samzenpus
from the wringing-out-the-wit dept.

Mars Images Reveal Evidence of Ancient Lakes 128

Posted by timothy
from the older-I-get-the-wetter-mars-was dept.

Scientists Say a Dirty Child Is a Healthy Child 331

Posted by samzenpus

Revisiting the Original Reviews of Windows Vista 414

Posted by CmdrTaco
from the take-with-a-grain-of-salt dept.
harrymcc writes 'We now know that a remarkable percentage of consumers and businesses decided to spurn Windows Vista and stay with XP. But did the reviews of Vista serve as an early warning that it had major problems? I looked back at the evaluations in nine major publications and found that they expressed some caution--but on the whole, they were far from scathing. Some were downright enthusiastic.'

Comment: Re:spoooooky (Score 3, Informative) 287

by DrLudicrous (#29489389) Attached to: Dead Salmon's "Brain Activity" Cautions fMRI Researchers
It detects the oxygenation of blood. The mechanism behind this is a different magnetic moment of oxygenated hemoglobin, oxygenated hemoglobin is diamagnetic vs paramagnetic while deoxygenated. This is called the BOLD effect (Blood Oxygen Level Dependent). The difference in the two conditions magnetic property affects the MRI signal lifetime in the near vicinity. This results in contrast developing between tissues with oxygenated blood vs tissue with deoxygenated blood. The idea behind fMRI is that when you use a certain part of the brain, it requires oxygenated blood, which will lead to contrast. Unfortunately, due to low overall signal strength/contrast-to-noise ratio, the image must be signal averaged. Hence if you were tapping your finger to see which part of your brain "lights up", you would have to repeat this action, and have your MRI scan be synced to your action so that the same part of the brian is being imaged over the same interval each time. It's tricky, but my understanding is that it's quite feasible. There are many other mechanisms for causing localized signal lifetime changes, without having RTFA, I can't be sure what they took under consideration.

Comment: Re:Different everywhere? (Score 1) 451

by DrLudicrous (#29432807) Attached to: Favorite seasonal transition?
I am a Colombian-American, CaleÃ±o to be exact. BogotÃ is very temperate, whereas Cali is very very tropical: hot and humid most of the year. But the escape to the mountains is still the same, just oh so much more dramatic. I prefer *up* the hill, I can't take 80s and 90s with humidity all the time. So sticky... but the nights are wonderful. Up the hill gets a bit chilly... some panela will take care of that, perhaps sancochito... or in your case, ajiaco.

Comment: How this works (Score 4, Informative) 237

by DrLudicrous (#29394785) Attached to: NASA Scientists Levitate Mice
Disclaimer: I'm an MR Physicist.

Regarding gradients: The gradients used in MRI vary in *position*. Yes in time, as well, but only because they are pulsed. We can ignore ramping issues to first order. Since the field varies as a function of position, when you move around, indeed the flux is changing which can induce currents in looped conductors so as to oppose the change. This is called induction. Many people, my self included, notice a strange sensation when first entering an MRI magnet. This is because the field is only homogeneous over a relatively small volume, outside of which there are once again field gradients (these are different than the intentional field gradients used to obtain an MRI image). It is probably not axons but something in the ear that is picking this up, I am not sure. Also, field strength has *nothing* to do with this effect. It's how fast the field changes as a function of position, i.e. the gradient, combined with the velocity of the pickup object.

Regarding repulsion: Water is diamagnetic. That means that the little spins (i.e. electrons) orbiting the atoms of a water molecule tend to align *against* the applied field direction. These spins will experience a repulsive force, hence the levitation.

Comment: Build a clock radio! (Score 1) 364

by DrLudicrous (#28716489) Attached to: Low-Budget Electronics Projects For High School?
Have them build a clock radio, with alarm. Lots of digital logic, cheap. A breadboard is useful so as to avoid soldering, and some kits to go with the breadboard (little wire segments). If you make them run it off of wall current, they'll have to learn how to go from AC to DC. Might take a few months of working in groups to do, but you can learn a lot that way.
