Ultrathin organic material enhances e-skin display

University of Tokyo researchers have developed an ultrathin, ultraflexible, protective layer and demonstrated its use by creating an air-stable, organic light-emitting diode (OLED) display. This technology will enable creation of electronic skin (e-skin) displays of blood oxygen level, e-skin heart rate sensors for athletes and many other applications.

Integrating electronic devices with the human body to enhance or restore body function for biomedical applications is the goal of researchers around the world. In particular, wearable electronics need to be thin and flexible to minimize impact where they attach to the body. However, most devices developed so far have required millimeter-scale thickness glass or plastic substrates with limited flexibility, while micrometer-scale thin flexible organic devices have not been stable enough to survive in air.

The research group of Professor Takao Someya and Dr. Tomoyuki Yokota at the University of Tokyo's Graduate School of Engineering has developed a high-quality protective film less than two micrometers thick that enables the production of ultrathin, ultraflexible, high performance wearable electronic displays and other devices. The group developed the protective film by alternating layers of inorganic (Silicon Oxynitrite) and organic (Parylene) material. The protective film prevented passage of oxygen and water vapor in the air, extending device lifetimes from the few hours seen in prior research to several days. In addition, the research group were able to attach transparent indium tin oxide (ITO) electrodes to an ultrathin substrate without damaging it, making the e-skin display possible.

Using the new protective layer and ITO electrodes, the research group created polymer light-emitting diodes (PLEDs) and organic photodetectors (OPDs). These were thin enough to be attached to the skin and flexible enough to distort and crumple in response to body movement. The PLEDs were just three micrometers thick and over six times more efficient than previously reported ultrathin PLEDs. This reduced heat generation and power consumption, making them particularly suitable for direct attachment to the body for medical applications such as displays for blood oxygen concentration or pulse rate. The research group also combined red and green PLEDs with a photodetector to demonstrate a blood oxygen sensor.

"The advent of mobile phones has changed the way we communicate. While these communication tools are getting smaller and smaller, they are still discrete devices that we have to carry with us," says Someya. He continues, "What would the world be like if we had displays that could adhere to our bodies and even show our emotions or level of stress or unease? In addition to not having to carry a device with us at all times, they might enhance the way we interact with those around us or add a whole new dimension to how we communicate."

Saturn spacecraft samples interstellar dust

NASA's Cassini spacecraft has detected the faint but distinct signature of dust coming from beyond our solar system. The research, led by a team of Cassini scientists primarily from Europe, is published this week in the journal Science.

But among the myriad microscopic grains collected by Cassini, a special few—just 36 grains—stand out from the crowd. Scientists conclude these specks of material came from interstellar space—the space between the stars.Cassini has been in orbit around Saturn since 2004, studying the giant planet, its rings and its moons. The spacecraft has also sampled millions of ice-rich dust grainswith its cosmic dust analyzer instrument. The vast majority of the sampled grains originate from active jets that spray from the surface of Saturn's geologically active moon Enceladus.

Alien dust in the solar system is not unanticipated. In the 1990s, the ESA/NASA Ulysses mission made the first in-situ observations of this material, which were later confirmed by NASA's Galileo spacecraft. The dust was traced back to the local interstellar cloud: a nearly empty bubble of gas and dust that our solar system is traveling through with a distinct direction and speed.

"From that discovery, we always hoped we would be able to detect these interstellar interlopers at Saturn with Cassini. We knew that if we looked in the right direction, we should find them," said Nicolas Altobelli, Cassini project scientist at ESA (European Space Agency) and lead author of the study. "Indeed, on average, we have captured a few of these dust grains per year, travelling at high speed and on a specific path quite different from that of the usual icy grains we collect around Saturn."

The tiny dust grains were speeding through the Saturn system at over 45,000 mph (72,000 kilometers per hour), fast enough to avoid being trapped inside the solar system by the gravity of the sun and its planets.

"We're thrilled Cassini could make this detection, given that our instrument was designed primarily to measure dust from within the Saturn system, as well as all the other demands on the spacecraft," said Marcia Burton, a Cassini fields and particles scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, and a co-author of the paper.

Importantly, unlike Ulysses and Galileo, Cassini was able to analyze the composition of the dust for the first time, showing it to be made of a very specific mixture of minerals, not ice. The grains all had a surprisingly similar chemical make-up, containing major rock-forming elements like magnesium, silicon, iron and calcium in average cosmic proportions. Conversely, more reactive elements like sulfur and carbon were found to be less abundant compared to their average cosmic abundance.

"Cosmic dust is produced when stars die, but with the vast range of types of stars in the universe, we naturally expected to encounter a huge range of dust types over the long period of our study," said Frank Postberg of the University of Heidelberg, a co-author of the paper and co-investigator of Cassini's dust analyzer.

Stardust grains are found in some types of meteorites, which have preserved them since the birth of our solar system. They are generally old, pristine and diverse in their composition. But surprisingly, the grains detected by Cassini aren't like that. They have apparently been made rather uniform through some repetitive processing in the interstellar medium, the researchers said.

The authors speculate on how this processing of dust might take place: Dust in a star-forming region could be destroyed and recondense multiple times as shock waves from dying stars passed through, resulting in grains like the ones Cassini observed streaming into our solar system.

"The long duration of the Cassini mission has enabled us to use it like a micrometeorite observatory, providing us privileged access to the contribution of dust from outside our solar system that could not have been obtained in any other way," said Altobelli.

No trace of Neanderthal DNA on Y chromosome of modern men

Modern men have no traces of Neanderthal DNA on their Y chromosome, the first-ever analysis of the male Neanderthal sex chromosome has revealed.

The disappearance of the Neanderthal Y chromosome may be due to genetic incompatibilities between the two species that led to miscarriages, suggests a study published today in the American Journal of Human Genetics.

The Y chromosome is passed exclusively from father to son.

Until now, all sequencing of the Neanderthal genome had been done on females because those happened to be the specimens that provided enough good-quality DNA, the study's lead author, Dr Fernando Mendez of Stanford University, said.

"Characterising the Neanderthal Y chromosome helps us to better understand the population divergence that led to Neanderthals and modern humans," he said.

"It also enables us to explore possible genetic interactions between archaic and modern [gene] variants within hybrid offspring."

It is widely known that modern non-Africans have around 2.5 to 4 per cent Neanderthal DNA in their genes, but the Y chromosome is special, Dr Mendez said.

"Either you get the whole Y chromosome, or you get nothing," he said.

Analysis compared ancient and modern Y chromosomes

Dr Mendez and his colleagues compared the Y chromosome of a 49,000 year-old Neanderthal male found in El Sidron in Spain, with the Y chromosome from two modern humans.

Their analysis supports earlier data that estimated Neanderthals and modern humans diverged from their common ancestor around 588,000 years ago.

They also found the Neanderthal Y chromosome was distinct from any Y chromosome observed in modern humans, suggesting the lineage is extinct.

The researchers then searched for evidence that would explain why the Neanderthal Y chromosome disappeared.

"The Y chromosome has a number of genes that are specific for male functions, like making sperm, so we said maybe we'd find something in one of those, but we didn't," Dr Mendez said.

These genes did contain mutations that distinguished Neanderthals from modern humans, but none would have adversely affected their function.

Chemical composition of dust from beyond the solar system analyzed

A Heidelberg-designed dust detector on the Cassini space probe -- known as the cosmic dust analyser (CDA) -- has identified several extremely rare and minuscule particles of interstellar dust from outside our solar system, and examined their chemical composition. Surprisingly it turns out that the different dust particles are very similar in composition and have collected the whole element mix of the cosmos. The experts therefore suspect that dust is continually destroyed, reformed and thereby homogenised in the "witch's cauldron" of outer space. The results of an international research team, including scientists from the Institute of Earth Sciences and the Klaus Tschira Laboratory for Cosmochemistry of Heidelberg University, are published in "Science."

"Interstellar dust is one of the last bastions of the unknown in space, its individual particles being only about 200 nanometres in size and very hard to find," explains Prof. Dr. Mario Trieloff, earth scientist from Heidelberg University. The dust is part of the interstellar material consisting of gas and helium, as well as heavy metals, and which can arise from the condensation processes of stars and planets. These particles are the raw material that were the main building blocks for Earth and other terrestrial planets.

When it comes to studying interstellar dust, science has so far depended on particles reaching our solar system. The Stardust space probe was already able to capture particles of the very weak flux crossing our solar system. "But these particles were unusually large, so the research findings are possibly not representative," Prof. Trieloff says. By contrast, the Cassini probe could identify 36 particles of interstellar dust among millions of planetary dust particles. Furthermore the CDA is in a position to analyse them on the spot with the assistance of mass spectrometry. This has enabled much more precise results than before.

Dr. Frank Postberg, on a Heisenberg grant at the Institute for Earth Science, notes that mass spectrometric measurements can now be made for the first time on "a statistically significant quantity of such dust particles." This process had only become possible through a complex series of tests conducted in Heidelberg to calibrate laboratory models of the CDA. To achieve this aim, silicate dust had to be accelerated in the laboratory to upwards of 40 km a second, which is roughly the speed of interstellar dust.

"The result of the measurements was truly amazing," Dr. Postberg reports. "The 36 particles of interstellar origin, that are very similar in their composition, contain a mix of the most important rock-forming elements -- magnesium, iron, silicon and calcium -- in average cosmic abundance. Although a dust particle has a mass of less than a trillionth of a gram, the whole element mix of the cosmos is collected there, with the exception of very volatile gases. Such particles cannot be found in our solar system." Most scientists had expected dust populations with different compositions, corresponding to the different processes of origin in atmospheres of dying stars. These differences are also found in the stellar dust of meteorites, which is highly individual in its isotope composition. "Our data tells a completely different story," he underlines.

According to the scientists, the dust has lost its individuality because it was homogenised in the cosmic "witch's cauldron" of the interstellar medium. It contains gigantic, million-degree hot bubbles of supernova explosions, whose edges arise from shock fronts expanding at hundreds of kilometres per second, explains Dr. Nicolas Altobelli, who is the first author and a scientist at the European Space Agency (ESA). There had already been a theory, he says, that interstellar dust can survive this energy-rich environment for only a few hundred million years and that very few "lucky survivors" succeed in reaching newly forming planetary systems as intact stellar dust. The latest research results now confirm that most particles are destroyed and reformed in molecular clouds, i.e. cool, dense regions of outer space. Interstellar winds bring these particles as homogenised dust into our solar system.

New species of tumbleweed is just as bad as its parents

The humble tumbleweed — that icon of the American West, blowing across the dusty, dry landscape of every old Western movie — is an immigrant.

And it isn’t a single species, but several. The first known tumbleweed species to arrive in the United States, Salsola tragus, or Russian thistle, is thought to have hitched a ride in a package of flax seed that some Russian immigrants brought with them to South Dakota in 1873. Over the years, other tumbleweed species arrived, including S. australis, which is thought to be a native of Australia or South Africa, though their paths into the country are less well known.

The species all look pretty similar, though despite the name, they don’t all tumble. They are all weeds, and ones that can pose a fire hazard during drought — a flaming ball of dry plant material that can be blown from place to place. It’s such a serious problem that scientists have even suggested importing fungi from Russia to control the plants.

So scientists have incentive to keep track of the tumbleweed invasion. In 2002, researchers reported that there was a new tumbleweed on the scene in California, S. ryanii. The new species was truly new; it combined the 36 chromosomes of S. tragus with the 18 chromosomes of S. australis to form a hybrid species with 54 chromosomes. S. ryanii was an intermediate of its two parents, with traits like fruit size and tumbling behavior falling square in the middle of the two others. And in 2008, scientists predicted that this made it likely that S. ryanii wouldn’t be as much of a problem as its parent species because it wouldn’t be as well adapted to the landscape.

It appears that isn’t the case. Shana Welles, now at the University of Arizona, and Norman Ellstrand of the University of California, Riverside surveyed tumbleweeds at 53 sites across California. In 2002, S. ryaniihad been found in just two places in the San Joaquin Valley, but in 2012, the researchers found the plant in nine. In addition, the species also showed up at six other sites, including in coastal areas near San Francisco and Ventura. Clearly, the weed is spreading, Welles and Ellstrand report March 29 in theAmerican Journal of Botany.

“It seems likely that the range of S. ryanii will continue to expand and [the species] is likely to become an important invasive species,” the team writes. It’s now another lookalike invader that can cause problems in the drought-prone West.

It’s even possible that S. ryanii could become an invasive species in other countries, the scientists say, should its seeds find a way to hitchhike across international borders, just like its great-great-great-great-great-grandparents did.