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When relativistic heavy nuclei collide, they fleetingly interact to produce hot, dense matter—often interpreted as the quark–gluon plasma—containing roughly equal numbers of quarks and antiquarks. As the matter cools, it changes phase to a hadronic gas that includes nucleons and their antiparticles. And those antinucleons, when close enough in position and momentum, can form a stable bound state. The STAR collaboration, a team of hundreds of scientists from 54 institutions worldwide, has now found evidence for antihelium-4 in the debris created in high-energy collisions at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider. Consisting of two antiprotons and two antineutrons, ⁴He is the heaviest antinucleus yet detected. The experiment’s central detector, situated in a solenoidal magnetic field, is used to image the ionization trail left by charged particles and antiparticles as they traverse a gas-filled chamber. From measurements of the energy loss and the time of flight for the antiparticles to reach a secondary detector composed of 23 000 sensors, the collaboration unambiguously identified 18 ⁴He nuclei in a sample of 10¹² tracks from a billion gold-on-gold collisions; the figure shows such tracks, including one (red) from a ⁴He nucleus, for a typical event. The yield is consistent with expectations from thermodynamic and nucleosynthesis models and provides a benchmark for any future observations of ⁴He, or even heavier antimatter nuclei, from cosmic radiation. (H. Agakishiev et al., STAR collaboration, Nature, in press, doi:10.1038/nature10079.)—R. Mark Wilson

Despite global warming, the rate of water evaporation over land surfaces has steadily declined in the past few decades. That unexpected trend, observed by farmers and climate-change scientists alike, has been linked to a decline in surface wind speeds over the same period. The challenge of quantifying the stilling-winds phenomenon on a global scale was recently taken up by Robert Vautard and his colleagues at the Climate Science and Environment Laboratory in France and the European Centre for Medium-Range Weather Forecasts in the UK. By analyzing data from more than 800 weather stations, the researchers found that 73% reported that wind speeds measured 10 meters above the ground had declined by up to 15% from 1979 to 2008. As the image shows, some regions in Europe experienced declines of as much as 5 m/s per decade. After studying climate-model simulations, the researchers attribute much of the slowdown to an increase in topographical surface roughness from a surge in vegetation growth induced by excess atmospheric carbon and also anthropogenic activities such as urbanization. Less of a slowdown, or even an increase, was seen in regions that did not experience significant vegetation growth. The analysis assigned a lesser role to reduced atmospheric circulation caused by global warming. Wind energy enthusiasts should not necessarily be worried, say the researchers, since most wind turbines operate at 50–100 m, where the analysis did not detect any noticeable trend. (R. Vautard et al., Nat. Geo., in press, doi:10.1038/ngeo979.)—Jermey N. A. Matthews

Biological and medical researchers have long sought to study or control cellular function by inserting biomolecular probes inside the cell. But those probes, which include peptides and nucleic acids, must first cross the cell’s highly selective membrane. Traditional approaches to breaching that barrier are to chemically modify the probe or membrane and to pack the probe into a virus, which fuses to a cell’s membrane before depositing its load; both methods induce unwanted side effects and are limited to delivering specific molecular cargo. Now a team of US and South Korean scientists, led by Harvard University’s Hongkun Park, has developed a minimally invasive delivery method that exploits the ability of silicon nanowires to physically penetrate the cell’s membrane. The researchers prepared vertically aligned nanowire arrays with a density of roughly 25 million nanowires/cm² and altered their surface chemistries to enable noncovalent binding of a broad spectrum of molecules. With the nanowire platform, they were able to simultaneously assay the intracellular effects of distinct molecular probes. In one experiment, the researchers layered human fibroblasts, shown green in the scanning electron microscope image, across the nanowires, shown in blue. Nearly all of the cells were impaled within one hour and received the bound probes within 24 hours. Impaled cells continued to grow for several weeks, albeit at a slightly slower rate. (A. K. Shalek et al., Proc. Natl. Acad. Sci. USA, in press, doi:10.1073/pnas.0909350107.) — Jermey N. A. Matthews

With political sentiment growing in favor of greenhouse gas (GHG) restrictions, biofuels from plant cellulose are being considered among the alternatives to fossil fuels: Plants are renewable and biodegradable, and they sequester carbon. Yet a new report validates concerns that a global biofuels program could put intense pressure on land supply and distribution. To predict the impact of a biofuels-based economy on climate change, an international team of researchers from the US, Brazil, and China linked an economic model of land use with a terrestrial biogeochemical model of global GHG levels. The team considered two cases for cellulosic biofuel crop growth: The primary focus of case1 is on converting unfarmed areas such as forests, as shown in the image; of case 2, on exploiting existing farmland to the extent possible. In both cases, biofuel feedstock becomes a dominant global crop by year 2100, but in the process, total forest area is cut—by 56% in case 1 and by 24% in case 2. The loss of carbon-sequestering trees in case 1 results in a net release of carbon. In case 2, the gains from biofuel production ultimately lead to increased carbon sequestration in the farmed soil from the addition of nitrogen fertilizer, which paradoxically releases N₂O, another potent GHG. The research suggests that stabilizing GHG levels will require a limited and more efficient use of forests and fertilizers for biofuel crop production. (J. M. Melillo et al., Science Express, 22 October 2009, doi:10.1126/science.1180251. Image courtesy of Chris Neill, Marine Biological Laboratory, Woods Hole, MA.)—Jermey N. A. Matthews