MATERIALS ENGINEERING

Speaking at the 237th National Meeting of the American Chemical Society in Salt Lake City, Utah, Gerard Harbison, Ph.D., and colleagues described using computer simulations to analyze a variety of potential peroxide-based explosives in the same chemical class as triacetone triperoxide (TATP). That powerful, easy-to-make explosive was used by the "shoe bomber," Richard Reid, in his failed attempt to blow up a transatlantic airline flight in 2001. TATP has also been used by suicide bombers in the Palestinian Intifada.

Harbison's team became intrigued by "Internet lore," reports circulating on the Web claiming creation of another explosive — tetracetone tetraperoxide (TeATeP) — which is reputedly a more lethal relative to TATP. Initially working on detection methods of peroxide explosives for the Defense Advanced Research Projects Agency, the group instead began to investigate the structure of TeATeP to evaluate likelihood of its use as a terrorist's weapon.

"Our analysis indicates that potentially new and destructive terrorist materials, which would tax our detection capabilities, may be too unstable for a practical synthesis," said Harbison, a chemist at the University of Nebraska-Lincoln. "We consider it unlikely that any of the previous syntheses were actually successful, and the Internet myths about TeATeP are nothing more than that. So the good news is basically this is something we don't have to worry about."

The group investigated 20 molecular structures of various acetone peroxide compounds and found that all substances larger than TATP are likely too sensitive to be used as weapons. "The energies we're seeing in the analysis are extreme enough," Harbison said, adding that a review of previous TeATeP synthesis reports raised many questions. "If you look at the actual literature on people who claim to have made TeATeP, it's very ambiguous. We think probably what happened when people thought they were making TeATeP was that they were actually making TATP."

This synthesis error is common and often fatal, Harbison said. When trying to make TATP, a less stable relative, diacetone diperoxide, often is created. "The nice thing about doing this on the computer is first it's safe, and our results are so close to what's been experimentally measured that we have a great deal of confidence with what we're doing," Harbison said. "We're really at the stage where we can evaluate threats — potential molecules that might be dangerous — and we can really make some sort of judgment about whether those molecules are going to present a hazard in the future. We can test things with computers at a level of reliability that's comparable to personally doing the synthesis and evaluating material yourself."

There's a lot of research that deals with known threats, Harbison said. But his groups' research focuses on the idea that emerging threats will always exist. "Presumably you'd like to anticipate the threats before they come along. We're now pushing it a little further and discussing potential threats.

"Using computational chemistry, we can narrow down the domain of potential hazards, things that aren't going to be on the horizon. I think we now know so much more about not just what works for improvised-explosive-device detection but also what doesn't work, and we don't have to try it out (experimentally). We did five years ago."

Professor Drell, a professor emeritus at the SLAC National Accelerator Center, a senior fellow at Stanford University's Hoover Institution and an adviser on technical national security and arms-control for the US Government, has recently co-authored a report called Nuclear Weapons in 21st Century US National Security, in collaboration with the American Association for the Advancement of Science, the American Physical Society and the Center for Strategic and International Studies.

In his article for Physics World, he explains how and why there is need now, more than ever, to introduce globally ratified systems to control the spread of nuclear arms.

Professor Drell explains: "The world is teetering on the edge of a new and more perilous nuclear era, facing a growing danger that nuclear weapons – the most devastating instrument of annihilation ever invented – may fall into the hands of 'rogue states' or terrorist organizations that do not shrink from mass murder on an unprecedented scale.

His article makes two recommendations to Obama and his team. The first is to 'revisit Reykjavik' – Reykjavik hosted a summit in 1986 where former US President Ronald Reagan and then Soviet premier Mikhail Gorbachev agreed to begin reducing the size of their respected countries' nuclear arsenals. As the US and Russia still possess more than 90 per cent of the world's nuclear warheads, it is imperative that they take the lead, Drell says.

Drell's second recommendation is that the new Obama administration should adopt a process for bringing the Comprehensive Test Ban Treaty (CTBT) into effect. "The new administration should initiate a timely bipartisan, congressional review of the value of the CTBT for US security," he says.

Drell concludes: "With these two steps outlined above, President Obama has a historic opportunity to start down a practical path towards achieving his stated goal of 'eliminating all nuclear weapons.'"

Due to its large mirror and location in outer space, the James Webb Space Telescope (scheduled for launch in 2013) will offer astronomers the first real possibility of finding those answers. In a new study, Lisa Kaltenegger (Harvard-Smithsonian Center for Astrophysics) and Wesley Traub (Jet Propulsion Laboratory) examined the ability of JWST to characterize the atmospheres of hypothetical Earth-like planets during a transit, when part of the light of the star gets filtered through the planet's atmosphere. They found that JWST would be able to detect certain gases called biomarkers, such as ozone and methane, only for the closest Earth-size worlds.

"We'll have to be really lucky to decipher an Earth-like planet's atmosphere during a transit event so that we can tell it is Earth-like," said Kaltenegger. "We will need to add up many transits to do so - hundreds of them, even for stars as close as 20 light-years away."

"Even though it's hard, it will be an incredibly exciting endeavor to characterize a distant planet's atmosphere," she added.

In a transit event, a distant, extrasolar planet crosses in front of its star as seen from Earth. As the planet transits, gases in its atmosphere absorb a tiny fraction of the star's light, leaving fingerprints specific to each gas. By splitting the star's light into a rainbow of colors or spectrum, astronomers can look for those fingerprints. Kaltenegger and Traub studied whether those fingerprints would be detectable by JWST.

Their study has been accepted for publication in The Astrophysical Journal.

The transit technique is very challenging. If Earth were the size of a basketball, the atmosphere would be as thin as a sheet of paper, so the resulting signal is incredibly tiny. Moreover, this method only works when the planet is in front of its star, and each transit lasts for a few hours at most.

Kaltenegger and Traub first considered an Earth-like world orbiting a Sun-like star. To get a detectable signal from a single transit, the star and planet would have to be extremely close to Earth. The only Sun-like star close enough is Alpha Centauri A. No such world has been found yet, but technology is only now becoming capable of detecting Earth-sized worlds.

The study also considered planets orbiting red dwarf stars. Such stars, called type M, are the most abundant in the Milky Way - far more common than yellow, type G stars like the Sun. They are also cooler and dimmer than the Sun, as well as smaller, which makes finding an Earth-like planet transiting an M star easier.

An Earth-like world would have to orbit close to a red dwarf to be warm enough for liquid water. As a result, the planet would orbit more quickly and each transit would last a couple of hours to mere minutes. But it would undergo more transits in a given amount of time. Astronomers could improve their chances of detecting the atmosphere by adding the signal from several transits, making red dwarf stars appealing targets because of their more frequent transits.

An Earth-like world orbiting a star like the Sun would undergo a 10-hour transit once every year. Accumulating 100 hours of transit observations would take 10 years. In contrast, an Earth orbiting a mid-sized red dwarf star would undergo a one-hour transit once every 10 days. Accumulating 100 hours of transit observations would take less than three years.

"Nearby red dwarf stars offer the best possibility of detecting biomarkers in a transiting Earth's atmosphere," said Kaltenegger.

"Ultimately, direct imaging - studying photons of light from the planet itself - may prove a more powerful method of characterizing the atmosphere of Earth-like worlds than the transit technique," said Traub.

Both NASA's Spitzer and Hubble Space Telescopes have studied the atmospheric compositions of extremely hot, gas-giant extrasolar planets. The characterization of a "pale blue dot" is the next step from there, whether by adding up hundreds of transits of one planet or by blocking out the starlight and analyzing the planet's light directly.

In a best-case scenario, Alpha Centauri A may turn out to have a transiting Earth-like planet that no one has spotted yet. Then, astronomers would need only a handful of transits to decipher that planet's atmosphere and possibly confirm the existence of the first twin Earth.

This research was partially funded by NASA.

Journal reference:

1. L. Kaltenegger, W.A. Traub. Transits of Earth-Like Planets. The Astrophysical Journal, 2009; (in press) [link]

Joseph Irudayaraj, a Purdue University associate professor of agricultural and biological engineering, developed the nanoscale, multifunctional probes, which have antibodies on board, to search out and attach to cancer cells.

A paper detailing the technology was released last week in the online version of Angewandte Chemie, an international chemistry journal.

"If we have a tumor, these probes should have the ability to latch on to it," Irudayaraj said. "The probe could carry drugs to target, treat as well as reveal cancer cells."

Scientists have developed probes that use gold nanorods or magnetic particles, but Irudayaraj's nanoprobes use both, making them easier to track with different imaging devices as they move toward cancer cells.

The magnetic particles can be traced through the use of an MRI machine, while the gold nanorods are luminescent and can be traced through microscopy, a more sensitive and precise process. Irudayaraj said an MRI is less precise than optical luminescence in tracking the probes, but has the advantage of being able to track them deeper in tissue, expanding the probes' possible applications.

The probes, which are about 1,000 times smaller than the diameter of a human hair, contain the antibody Herceptin, used in treatment of metastatic breast cancer. The probes would be injected into the body through a saline buffering fluid, and the Herceptin would find and attach to protein markers on the surface of cancer cells.

"When the cancer cell expresses a protein marker that is complementary to Herceptin, then it binds to that marker," Irudayaraj said. "We are advancing the technology to add other drugs that can be delivered by the probes."

Irudayaraj said better tracking of the nanoprobes could allow doctors to pinpoint the location of known tumors and better treat the cancer.

The novel probes were tested in cultured cancer cells. Irudayaraj said the next step would be to run a series of tests in mice models to determine the dose and stability of the probes.

The research was funded through a National Institute of Health grant, as well as by the Purdue Research Foundation. Irudayaraj is head of a biological engineering team that includes postdoctoral researcher Chungang Wang and graduate student Jiji Chen.

The work could also allow for the quick recharging of batteries in electric cars, although that particular application would be limited by the amount of power available to a homeowner through the electric grid.

The work, led by Gerbrand Ceder, the Richard P. Simmons Professor of Materials Science and Engineering, is reported in the March 12 issue of Nature. Because the material involved is not new — the researchers have simply changed the way they make it — Ceder believes the work could make it into the marketplace within two to three years.

State-of-the-art lithium rechargeable batteries have very high energy densities — they are good at storing large amounts of charge. The tradeoff is that they have relatively slow power rates — they are sluggish at gaining and discharging that energy. Consider current batteries for electric cars. "They have a lot of energy, so you can drive at 55 mph for a long time, but the power is low. You can't accelerate quickly," Ceder said.

Why the slow power rates? Traditionally, scientists have thought that the lithium ions responsible, along with electrons, for carrying charge across the battery simply move too slowly through the material.

About five years ago, however, Ceder and colleagues made a surprising discovery. Computer calculations of a well-known battery material, lithium iron phosphate, predicted that the material's lithium ions should actually be moving extremely quickly.

"If transport of the lithium ions was so fast, something else had to be the problem," Ceder said.

Further calculations showed that lithium ions can indeed move very quickly into the material but only through tunnels accessed from the surface. If a lithium ion at the surface is directly in front of a tunnel entrance, there's no problem: it proceeds efficiently into the tunnel. But if the ion isn't directly in front, it is prevented from reaching the tunnel entrance because it cannot move to access that entrance.

Ceder and Byoungwoo Kang, a graduate student in materials science and engineering, devised a way around the problem by creating a new surface structure that does allow the lithium ions to move quickly around the outside of the material, much like a beltway around a city. When an ion traveling along this beltway reaches a tunnel, it is instantly diverted into it. Kang is a coauthor of the Nature paper.

Using their new processing technique, the two went on to make a small battery that could be fully charged or discharged in 10 to 20 seconds (it takes six minutes to fully charge or discharge a cell made from the unprocessed material).

Ceder notes that further tests showed that unlike other battery materials, the new material does not degrade as much when repeatedly charged and recharged. This could lead to smaller, lighter batteries, because less material is needed for the same result.

"The ability to charge and discharge batteries in a matter of seconds rather than hours may open up new technological applications and induce lifestyle changes," Ceder and Kang conclude in their Nature paper.

This work was supported by the National Science Foundation through the Materials Research Science and Engineering Centers program and the Batteries for Advanced Transportation Program of the U.S. Department of Energy. It has been licensed by two companies.

Journal reference:

1. Byoungwoo Kang & Gerbrand Ceder. Battery materials for ultrafast charging and discharging. Nature, 2009; 458 (7235): 190 DOI: 10.1038/nature07853

It is most important for the laser output power to be set correctly – if it is too low the strength of the welding connection is reduced because it does not extend over the full cross section of the metal sheets, if it is too high the laser cuts right through them.

Until now welders have gauged the right laser output by trial and error and then kept it constant. A complicating factor exists, however, in that the protective glass gets dirty after a while and lets less laser light through onto the metal. If this happens earlier than usual, hours can pass before it is noticed and the metal sheets may not be properly welded. Today, welding processes are only monitored without adjustment of the laser power because the achievalble frame rate of about thousand evaluated images per second is not sufficient. For a closed loop control, frame rates of more than 10 kilohertz – equivalent to 10,000 images per second – are needed for a robust surveillance of the rapidly moving full penetration hole.

Researchers at the Fraunhofer Institute for Physical Measurement Techniques IPM in Freiburg have now developed a control system for laser welding processes which adapts the output to the given situation.

"Our system analyzes 14,000 images per second and uses the acquired data to adjust the laser output," explains IPM project manager Andreas Blug.

So how does the system manage to analyze the images more than ten times faster than conventional software? "We use special cameras in which a tiny processor is integrated in each pixel. All these processors – 25,000 in total – work simultaneously. In conventional image processing systems the data are handled consecutively by just a small number of computer processors," says Blug.

The new systems are referred to as "Cellular Neural Networks" (CNN). Just a few microseconds after the image is taken the camera delivers an analyzed picture of the contours of the full penetration hole. For small holes the system increases the output, for large ones it reduces it. "In developing this adjustment system we have achieved the first industrial application of CNN technology," says Blug. A prototype already exists, and the researchers now intend to test the system in production.

In the new study, Jon Schwantes and colleagues note increased concern about the possibility of terrorists smuggling radioactive materials to make illegal nuclear weapons. As a result, scientists are stepping up efforts to identify and track the source of these radioactive materials using the advanced tools and techniques of a new field called "nuclear archaeology."

The scientists describe efforts to determine the origin of an unknown sample of plutonium (Pu) found in 2004 in a bottle at a waste burial trench at the Hanford nuclear site in Washington. Hanford is the earliest location for U.S. plutonium production for nuclear weapons and now the focus of a massive environmental cleanup effort due to high levels of radioactive waste that remain at the site.

Using multiple pairs of "parent" Pu and "daughter" uranium (U) isotopes, the researchers were able to correct for chemical fractionation that occurred as a result of repackaging in 2004 and determine the age of the sample. Using this technique, they estimated that the Pu in the sample had been separated from U and fission products in 1944, making it the oldest known sample of bomb-grade plutonium produced in a reactor. The only older known samples of Pu-239 were produced by the late Glenn Seaborg and his associates in the beginning of the 1940's when the existence of the element was first confirmed and characterized.

The study identified the Clinton reactor in Oak Ridge, Tenn., as reactor of origin for this material, by comparing reactor burnup modeling results with measurements of minor Pu isotopes. These results were also supported by a series of historical documents tracking the material's movement from Oak Ridge and the processing at Hanford. "Aside from the historical significance of this find, this work provides the public a rare glimpse at a real-world example of the science behind and power of modern-day nuclear forensics," the scientists note.

Journal reference:

1. Schwantes et al. Nuclear Archeology in a Bottle: Evidence of Pre-Trinity U.S. Weapons Activities from a Waste Burial Site. Analytical Chemistry, 2009; 81 (4): 1297 DOI: 10.1021/ac802286a