New Scientist: Using crime data from southern California, Jeffrey Brantingham of the University of California, Los Angeles, and his colleagues set out to calculate how the movements of criminals and victims create opportunities for crime, and how police can reduce it. They came up with a pair of equations that could explain how local crime hotspots form—which turned out to be similar to those that describe molecular reactions and diffusion.
Monthly Archives: February 2010
Is the debate over light momentum resolved?
Science: What is the formula for the momentum of light zipping through a transparent material? That may sound like a question on a high-school physics quiz, but physicists have been debating the matter ever since two different formulas were proposed more than 100 years ago. Now Stephen Barnett, a theorist at the University of Strathclyde in Glasgow, U.K., says he has resolved the famed “Abraham-Minkowski dilemma.” Both formulas are correct, he says, but they denote different things and apply in different contexts.
After glitches, Mars rover inches towards readiness
BBC News: It weighs almost a ton, has cost more than $2 billon and, in 2013, it will be lowered on to the surface of Mars with a landing system that has never been tried before.
The Mars Science Laboratory will “revolutionize investigations in science on other planets,” says Doug McCuistion, director of Nasa’s Mars exploration program.
It will, he says, lay the foundations for future missions that will eventually bring Martian rocks to Earth.
“The ability to put a metric ton on the surface… gives us the capability to undertake sample collection,” says McCuistion. “To collect and launch samples back into orbit will require that size of a vehicle.”
But it has been a rather bumpy road to revolution, including 1000 parts made from a “bad batch” of titanium
The project has been struggling with technical challenges for several years, but Jim Green, the director of Nasa’s planetary science division, recently announced to the planetary science subcommittee that the project had finally turned the corner.
Did design flaws doom the LHC?
Nature News: Running more than a year behind schedule and at half its intended energy, the world’s most powerful particle accelerator is slated to begin its first full scientific run this week. Along with relief, the occasion is bringing some soul-searching. One senior scientist who helped to build the Large Hadron Collider (LHC) at CERN, Europe’s particle-physics laboratory near Geneva, Switzerland, is claiming that the cause of the delay—a major accident in 2008—could have been avoided.
“Any technical fault is a human fault,” says Lucio Rossi, a physicist who oversaw the production of the accelerator’s superconducting magnets. In a paper published this week, he concludes that the catastrophic failure of a splice between two magnets was not a freak accident but the result of poor design and lack of quality assurance and diagnostics. The project, he says, will be coping with the consequences for many months to come.
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T2K neutrino observed at Super-Kamiokande
KEK: The Japanese-led multinational T2K collaboration announced today that they had made the first detection of a neutrino which had travelled 295 km from their neutrino beamline at the Japanese Proton Accelerator Research Complex (J-PARC) facility in Tokai village to the Super- Kamiokande underground neutrino detector near the west coast of Japan.
“Switching on one of the world’s first neutrino superbeams is a great achievement,” said CERN Director General Rolf Heuer. “Even in a time of financial difficulty around the globe, it’s important not to lose sight of the fact that basic science is and always will be a crucial element of progress. It is therefore heartening to see such an important new basic science initiative getting underway now.”
“It is a big step forward,” said T2K spokesperson Takashi Kobayashi. “We’ve been working hard for more than 10 years to make this happen.”
J-PARC now produces the world’s most powerful neutrino beams to study neutrino oscillations.
“Neutrinos are the elusive ghosts of particle physics,” Kobayashi explains. “They come in three types, called electron neutrinos, muon neutrinos, and tau neutrinos, which used to be thought to be immutable.”
Interacting only weakly with matter, neutrinos can traverse the entire earth with vastly less attenuation than light passing through a window. The very weakness of their interactions allows physicists to make what should be very accurate predictions of their behavior, and thus it came as a shock when measurements of the flux of neutrinos coming from the thermonuclear reactions which power our sun were far lower than predicted.
A second anomaly was then clearly demonstrated in 1998 by Super-Kamiokande, when it showed that the flux of different types of neutrino generated within our atmosphere by cosmic ray interactions was different depending on whether the neutrinos were coming from above or below (which should not have been possible given our understanding of particle physics). Other experiments, such as Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND), have conclusively demonstrated that these anomalies are caused by neutrino oscillations, whereby one type of neutrino turns into another.
The first T2K event seen in Super-Kamiokande is seen in the image above. Each dot is a photomulipler tube which has detected photons. The two circles of hits indicate that a neutrino has probably produced a particle called a π 0, perfectly in time with the arrival of a pulse of neutrinos from J-PARC. Another faint circle surrounds the viewpoint of this image, showing a third particle was created by the neutrino.
The T2K experiment has been built to make measurements of unprecedented precision of known neutrino oscillations, and to look for a so-far unobserved type of oscillation which would cause a small fraction of the muon neutrinos produced at J-PARC to become electron neutrinos by the time they reach Super-Kamiokande.
Observing the new type of oscillation would open the prospect of comparing the oscillations of neutrinos and anti-neutrinos, which many theorists believe may be related to one of the great mysteries in fundamental physics—why is there more matter than anti-matter in the universe? “The observation of this first neutrino means that the hunt has just begun,” said Koichiro Nishikawa, director of the Institute for Particle and Nuclear Studies at KEK and founder of T2K. “The first physics results are expected later this year.” Today’s news he says, “is the beginning.”
Interest in tabletop x-ray lasers broadens out
AAAS Meeting: Margaret Murnane and Henry Kapteyn group at JILA, a joint institute of the University of Colorado at Boulder and NIST, has made some breakthroughs on how to build a tabletop x-ray laser. The laser could be used for super high-resolution imaging, while also giving scientists a new way to at the nanoscale at objects such as a single cell.
Murnane and Kapteyn presented highlights of their research at the American Association for the Advancement of Science annual meeting in San Diego.
“Our goal is to create a laser beam that contains a broad range of x-ray wavelengths all at once that can be focused both in time and space,” Murnane said. “If we have this source of coherent light that spans a huge region of the electromagnetic spectrum, we would be able to make the highest resolution light-based tabletop microscope in existence that could capture images in 3-D and tell us exactly what we are looking at. We’re very close.”
Most of today’s x-ray lasers require so much power that they rely on fusion laser facilities the size of football stadiums or larger, making their use impractical. Murnane and Kapteyn generate coherent laser-like x-ray beams by using an intense femtosecond laser and combining hundreds or thousands of visible photons together with a desktop-size system.
They can already generate laser-like x-ray beams in the soft x-ray region and believe they have discovered how to extend the process all the way into the hard x-ray region of the electromagnetic spectrum.
“If we can do this, it could lead to all kinds of possibilities,” Kapteyn said. “It might make it possible to improve x-ray imaging resolution at your doctor’s office by a thousand times. The x-rays we get in the hospital now are limited. For example, they can’t detect really small cancers because the x-ray source in your doctor’s office is more like a light bulb, not a laser. If you had a bright, focused laser-like x-ray beam, you could image with far higher resolution.”
Their method can be thought of as a coherent version of the x-ray tube, according to Murnane. In an x-ray tube, an electron is boiled off a filament, then it is accelerated in an electric field before hitting a solid target, where the kinetic energy of the electron is converted into incoherent x-rays. These incoherent x-rays are like the incoherent light from a light bulb or flashlight—they aren’t very focused.
In the tabletop setup, instead of boiling an electron from a filament, they pluck part of the quantum wave function of an electron from an atom using a very intense laser pulse. The electron is then accelerated and slammed back into the ion, releasing its energy as an x-ray photon. Since the laser field controls the motion of the electron, the x-rays emitted can retain the coherence properties of a laser, Murnane said.
Being able to build a tabletop x-ray laser is just the beginning, said Kapteyn.
“An analogy that is pretty close to what is going on in this field is the MRI, which started as just a fundamental investigation,” said Kapteyn. “People then started using it for microscopy, and then it progressed into a medical diagnostic technique.”
Waves broke Wilkins ice shelf
The Economist: In 2008 part of the Wilkins ice shelf on the edge of the Antarctic peninsula suddenly disintegrated.
The Wilkins shelf may or may not have been the victim, ultimately, of climate change. Regardless of what weakened it, though, it was not rising temperatures that caused the sudden breakup. Peter Bromirski of the Scripps Institution of Oceanography in San Diego thinks he knows what did: a little-studied phenomenon called infragravity waves.
A simple concussion test
NPR: Doctors use expensive CT scanners and MRI machines thousands of times every day to look for brain damage. But sometimes cheap and simple is definitely better.
The earthquake risk to megacities
washingtonpost.com: Megacities are something new on the planet. Earthquakes are something very old. The two are a lethal combination, as seen in the recent tragedy in Port-au-Prince, where more than 200 000 people perished—a catastrophe that scientists say is certain to be repeated somewhere, and probably soon, with death tolls that once again stagger the mind.
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Raw climate data to be made available by weather agencies
Yahoo! News: The world weather agencies have agreed to collect more precise temperature data under a proposal from the UK’s Met Office.
The proposal asks climate scientists around the world to measure land surface temperatures as often as several times a day, and allow independent scrutiny of the data—a move that would go some way toward answering demands by skeptics for access to the raw figures used to predict climate change.
“This effort will ensure that the datasets are completely robust and that all methods are transparent,” said the Met Office. The agency added that “any such analysis does not undermine the existing independent datasets that all reflect a warming trend.”
The proposal was approved in principle by some 150 delegates meeting under the auspices of the World Meteorological Organization this week in Antalya, Turkey.