The basic operating principle of a solar cell is that an electron in the valence band of a semiconductor material absorbs a photon and jumps across an energy "band gap" into the conduction band. The result is an electron and a positively charged hole, which do not move separately through the semiconductor but instead form a bound state called an exciton. To extract electrical energy, the electron is collected at one electrode and the hole at another.

Light from the Sun comes in a range of wavelengths and therefore an ideal solar cell should be very efficient at converting this broad spectrum into electricity. Unfortunately, semiconductors with a fixed band gap are not very good at doing this. In particular, longer-wavelength photons do not have enough energy to make an electron to jump the band gap and will not be converted into electrical energy. Photons with energies greater than the band gap will be converted, but regardless of their energy they will only create just one electron–hole pair. Any excess energy will be dissipated in the semiconductor as heat.

"We are starting to look back to the epoch that is probably when the first stars were turning on," says Robert Simcoe, an astronomer at the Massachusetts Institute of Technology who built the instrument that acquired the spectrum of the far-off gas. "This is the very first [chemical] measurement that anybody has made in any environment at these early times."

The Big Bang, which occurred 13.7 billion years ago, showered the cosmos with hydrogen and helium. Aside from a trace of primordial lithium, heavier elements – which astronomers call metals – arose later, after stars formed and exploded, casting oxygen, iron and other metals into space. Furthermore, the first stars radiated extreme ultraviolet light that ionized gas, tearing electrons from the hydrogen nuclei. The universe is still ionized today.

Carl Sagan

Physics arXiv

To the Google-it-downloading public, this can be confusing and frustrating. However, this is science: examination leads to different theories; theories are vigorously debated, verified or refuted. Then, everyone in the science community decides to go in the direction of the new paradigm. Probably why a lot of scientist (at least in the US) don't go into politics.

The ice sheets in Greenland and Antarctica are melting at an ever-quickening pace. Since 1992, they have contributed 11 millimetres — or one-fifth — of the total global sea-level rise, say researchers. The two polar regions are now losing mass three times faster than they were 20 years ago, with Greenland alone now shedding ice at about five times the rate observed in the early 1990s.

The ice — whose long-suspected presence has now been confirmed by NASA's orbiting MESSENGER probe — seems to be much purer than ice inside similar craters on Earth's Moon, suggesting that the closest planet to the Sun could be a better trap for icy materials delivered by comets and asteroids. Three papers detailing the findings are published today in Science.

A new observation has revealed a galaxy that isn't just bending the rule, but completely breaking it. In most systems, the black hole's mass is about 0.1 percent of the mass of the galaxy's central bulge. Remco van den Bosch and colleagues identified a black hole with a mass that's about 59 percent of the mass of the central bulge. In fact, this black hole is one of the most massive ever observed, a striking discovery in a galaxy much smaller than our own. The galaxy itself is a bit on the small side, and the researchers suggest that we might want to look at the black holes in more galaxies this size.

NGC 1277 lies 220 million light-years away in the constellation Perseus. The galaxy is only ten percent the size and mass of our own Milky Way. Despite NGC 1277's diminutive size, the black hole at its heart is more than 11 times as wide as Neptune's orbit around the Sun.

Without an agreement, sequestration would be imposed automatically beginning in the first week of January. It could slash the U.S. R&D investment by 8.4%--some $58 billion--over five years. That would mean laboratory closures and layoffs, the experts said, and it would jeopardize current research in areas ranging from genetic medicine and advanced manufacturing to batteries that could allow a 10-fold increase in the range of electric cars. It might also discourage a new generation from careers in science and engineering. 

If we don't, other countries will make a first and successful run at our closest neighbor, and we will be scrambling like a nostalgic recast of Sputnik in 1957:

Indian Space Research Organisation - Wikipedia

It could serve as a launching pad for further deep space exploration, such as asteroids; such as Mars. Richard Branson could get his space hotels, and another generation of astronauts would see an Earthrise, and be forever affected, no longer feeling part of a particular "tribe," but human: an earthling.

The presence of nanogaps within the grating structures led to substantial field localization and amplification – propagating surface plasmon polaritons (SPPs) travel as surface waves with high field intensity towards the metallic nanogap where the sudden field discontinuity causes “extreme crowding” of the surface charges, leading to very high field intensities.

BaBar (Physics World) - Wikipedia explains how it was named

The BaBar detector at the PEP-II facility at SLAC in California was designed to study the collisions of electrons and positrons and to determine the differences between matter and antimatter. In particular, physicists working on the experiment are interested in the violation of the charge–parity symmetry (or CP violation). Although the detector was decommissioned in the spring of 2008, data collected during the period of operation continue to be analysed.

They have some exciting new results from one of the rover's instruments. On the one hand, they'd like to tell everybody what they found, but on the other, they have to wait because they want to make sure their results are not just some fluke or error in their instrument.

It's a bind scientists frequently find themselves in, because by their nature, scientists like to share their results. At the same time, they're cautious because no one likes to make a big announcement and then have to say "never mind."

The exciting results are coming from an instrument in the rover called SAM. "We're getting data from SAM as we sit here and speak, and the data looks really interesting," John Grotzinger, the principal investigator for the rover mission, says during my visit last week to his office at NASA's Jet Propulsion Laboratory in Pasadena, Calif. That's where data from SAM first arrive on Earth. "The science team is busily chewing away on it as it comes down," says Grotzinger.

Physics arXiv

The equations of general relativity are smooth, even at the tiniest scales. But in the early 1960s, the American physicist John Wheeler pointed out that in quantum mechanics, ordinary properties of spacetime, such as position, momentum and so on, have an uncertainty associated with them. That implies that spacetme must be uncertain as well. Wheeler famously described it as "quantum foam".

Physicists would dearly love to study this foam but there's a problem. Spacetime only becomes foam-like on the tiniest scale, at so-called Planck lengths of 10^-35metres or so.

Probing that distance is obviously difficult. One way to do it is by accelerating particles to huge energies, which allows physicists to determine their position accurately, thereby probing very small volumes of space.

But the energies required are around 10¹⁹GeV, many orders of magnitude higher than today's particle accelerators. There's no likelihood of reaching this energy on Earth in the foreseeable future so physicists are more or less resigned to the idea that they’ll never get their hands on quantum foam.

They may change today thanks to a fascinating idea from Jacob Bekenstein, a physicist at the Hebrew University of Jerusalem in Israel. Bekenstein says he has worked out a way to measure the structure of spacetime on the Planck scale using a simple experiment involving little more than a block of glass and a laser.

In essence, the experiment is straightforward. Bekenstein's goal is to move the block by a distance that is about equal to the Planck length. His method is simple: zap the block with a single photon.

The photon carries a small amount of moment and consequently pushes the block as it enters the glass, giving it some momentum. As the photon leaves the block, the block comes to rest.

So the result of the photon's passage is that it moves the block a small distance.

Bekenstein's idea is that if this distance is smaller than the Planck length, then the block cannot move and the photon cannot pass through it.

So the experiment involves measuring the number of photons that pass through the block. If the number is fewer than predicted by classical optics, then that proves the existence of quantum foam.