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Michelson–Morley analogue for electrons using trapped ions to test Lorentz symmetry

Nature - Wed, 01/28/2015 - 01:00

Michelson–Morley analogue for electrons using trapped ions to test Lorentz symmetry

Nature 517, 7536 (2015). doi:10.1038/nature14091

Authors: T. Pruttivarasin, M. Ramm, S. G. Porsev, I. I. Tupitsyn, M. S. Safronova, M. A. Hohensee & H. Häffner

All evidence so far suggests that the absolute spatial orientation of an experiment never affects its outcome. This is reflected in the standard model of particle physics by requiring all particles and fields to be invariant under Lorentz transformations. The best-known tests of this important cornerstone of physics are Michelson–Morley-type experiments verifying the isotropy of the speed of light. For matter, Hughes–Drever-type experiments test whether the kinetic energy of particles is independent of the direction of their velocity, that is, whether their dispersion relations are isotropic. To provide more guidance for physics beyond the standard model, refined experimental verifications of Lorentz symmetry are desirable. Here we search for violation of Lorentz symmetry for electrons by performing an electronic analogue of a Michelson–Morley experiment. We split an electron wave packet bound inside a calcium ion into two parts with different orientations and recombine them after a time evolution of 95 milliseconds. As the Earth rotates, the absolute spatial orientation of the two parts of the wave packet changes, and anisotropies in the electron dispersion will modify the phase of the interference signal. To remove noise, we prepare a pair of calcium ions in a superposition of two decoherence-free states, thereby rejecting magnetic field fluctuations common to both ions. After a 23-hour measurement, we find a limit of h × 11 millihertz (h is Planck’s constant) on the energy variations, verifying the isotropy of the electron’s dispersion relation at the level of one part in 1018, a 100-fold improvement on previous work. Alternatively, we can interpret our result as testing the rotational invariance of the Coulomb potential. Assuming that Lorentz symmetry holds for electrons and that the photon dispersion relation governs the Coulomb force, we obtain a fivefold-improved limit on anisotropies in the speed of light. Our result probes Lorentz symmetry violation at levels comparable to the ratio between the electroweak and Planck energy scales. Our experiment demonstrates the potential of quantum information techniques in the search for physics beyond the standard model.

Categories: Literature

Anomalous dispersions of ‘hedgehog’ particles

Nature - Wed, 01/28/2015 - 01:00

Anomalous dispersions of ‘hedgehog’ particles

Nature 517, 7536 (2015). doi:10.1038/nature14092

Authors: Joong Hwan Bahng, Bongjun Yeom, Yichun Wang, Siu On Tung, J. Damon Hoff & Nicholas Kotov

Hydrophobic particles in water and hydrophilic particles in oil aggregate, but can form colloidal dispersions if their surfaces are chemically camouflaged with surfactants, organic tethers, adsorbed polymers or other particles that impart affinity for the solvent and increase interparticle repulsion. A different strategy for modulating the interaction between a solid and a liquid uses surface corrugation, which gives rise to unique wetting behaviour. Here we show that this topographical effect can also be used to disperse particles in a wide range of solvents without recourse to chemicals to camouflage the particles’ surfaces: we produce micrometre-sized particles that are coated with stiff, nanoscale spikes and exhibit long-term colloidal stability in both hydrophilic and hydrophobic media. We find that these ‘hedgehog’ particles do not interpenetrate each other with their spikes, which markedly decreases the contact area between the particles and, therefore, the attractive forces between them. The trapping of air in aqueous dispersions, solvent autoionization at highly developed interfaces, and long-range electrostatic repulsion in organic media also contribute to the colloidal stability of our particles. The unusual dispersion behaviour of our hedgehog particles, overturning the notion that like dissolves like, might help to mitigate adverse environmental effects of the use of surfactants and volatile organic solvents, and deepens our understanding of interparticle interactions and nanoscale colloidal chemistry.

Categories: Literature

Metal-catalysed azidation of tertiary C–H bonds suitable for late-stage functionalization

Nature - Wed, 01/28/2015 - 01:00

Metal-catalysed azidation of tertiary C–H bonds suitable for late-stage functionalization

Nature 517, 7536 (2015). doi:10.1038/nature14127

Authors: Ankit Sharma & John F. Hartwig

Many enzymes oxidize unactivated aliphatic C–H bonds selectively to form alcohols; however, biological systems do not possess enzymes that catalyse the analogous aminations of C–H bonds. The absence of such enzymes limits the discovery of potential medicinal candidates because nitrogen-containing groups are crucial to the biological activity of therapeutic agents and clinically useful natural products. In one prominent example illustrating the importance of incorporating nitrogen-based functionality, the conversion of the ketone of erythromycin to the –N(Me)CH2– group in azithromycin leads to a compound that can be dosed once daily with a shorter treatment time. For such reasons, synthetic chemists have sought catalysts that directly convert C–H bonds to C–N bonds. Most currently used catalysts for C–H bond amination are ill suited to the intermolecular functionalization of complex molecules because they require excess substrate or directing groups, harsh reaction conditions, weak or acidic C–H bonds, or reagents containing specialized groups on the nitrogen atom. Among C–H bond amination reactions, those forming a C–N bond at a tertiary alkyl group would be particularly valuable, because this linkage is difficult to form from ketones or alcohols that might be created in a biosynthetic pathway by oxidation. Here we report a mild, selective, iron-catalysed azidation of tertiary C–H bonds that occurs without excess of the valuable substrate. The reaction tolerates aqueous environments and is suitable for the functionalization of complex structures in the late stages of a multistep synthesis. Moreover, this azidation makes it possible to install a range of nitrogen-based functional groups, including those from Huisgen ‘click’ cycloadditions and the Staudinger ligation. We anticipate that these reactions will create opportunities to modify natural products, their precursors and their derivatives to produce analogues that contain different polarity and charge as a result of nitrogen-containing groups. It could also be used to help identify targets of biologically active molecules by creating a point of attachment—for example, to fluorescent tags or ‘handles’ for affinity chromatography—directly on complex molecular structures.

Categories: Literature

Effects of electron correlations on transport properties of iron at Earth’s core conditions

Nature - Wed, 01/28/2015 - 01:00

Effects of electron correlations on transport properties of iron at Earth’s core conditions

Nature 517, 7536 (2015). doi:10.1038/nature14090

Authors: Peng Zhang, R. E. Cohen & K. Haule

Earth’s magnetic field has been thought to arise from thermal convection of molten iron alloy in the outer core, but recent density functional theory calculations have suggested that the conductivity of iron is too high to support thermal convection, resulting in the investigation of chemically driven convection. These calculations for resistivity were based on electron–phonon scattering. Here we apply self-consistent density functional theory plus dynamical mean-field theory (DFT + DMFT) to iron and find that at high temperatures electron–electron scattering is comparable to the electron–phonon scattering, bringing theory into agreement with experiments and solving the transport problem in Earth’s core. The conventional thermal dynamo picture is safe. We find that electron–electron scattering of d electrons is important at high temperatures in transition metals, in contrast to textbook analyses since Mott, and that 4s electron contributions to transport are negligible, in contrast to numerous models used for over fifty years. The DFT+DMFT method should be applicable to other high-temperature systems where electron correlations are important.

Categories: Literature

Pollinator Loss May Put Poor Nations at Risk for Malnutrition, Study Says

Yale Environment 360 - Tue, 01/27/2015 - 11:14

Declining pollinator populations could leave as many as half of the people in developing countries facing nutritional deficiencies, according to researchers from the University of Vermont and the Harvard School of Public Health. In the study — the first to link pollinator declines directly to human nutrition — researchers collected detailed data about people's daily diets in parts of Zambia, Mozambique, Uganda, and Bangladesh. They found that in Mozambique, for example, many children and mothers are barely able to meet their needs for micronutrients, especially vitamin A, which is important for preventing blindness and infectious diseases. Fruits and vegetables were an important source of that nutrient for many people in the study, and those crops are highly dependent on pollinators, researchers say — for example, yields of mangoes, which are high in vitamin A, would likely be cut by 65 percent without them. Pollinator losses might also lead to folate deficiency, they say, which is associated with neural tube defects.

Categories: Environmental News

Senate vs science

Nature - Tue, 01/27/2015 - 01:00

Senate vs science

Nature 517, 7536 (2015). doi:10.1038/517527b

A few Republicans agreeing with basic climate research is not an environmental victory.

Categories: Literature

Obama acts alone on climate

Nature - Tue, 01/27/2015 - 01:00

Obama acts alone on climate

Nature 517, 7536 (2015). http://www.nature.com/doifinder/10.1038/517535a

Author: Jeff Tollefson

US president defies hostile Congress and takes action on global warming.

Categories: Literature

Unconscious thought not so smart after all

Nature - Tue, 01/27/2015 - 01:00

Unconscious thought not so smart after all

Nature 517, 7536 (2015). http://www.nature.com/doifinder/10.1038/517537a

Author: Alison Abbott

Study on decision-making stokes controversy over power of distracted mind.

Categories: Literature

Oil Spills Can Lead to Toxic Arsenic Water Contamination, Study Says

Yale Environment 360 - Mon, 01/26/2015 - 11:35

When petroleum breaks down in underground aquifers, toxic arsenic — up to 23 times the current drinking water

Water sampling at the Minnesota oil-spill test site. standard — can be released into groundwater, according to a study by U.S. Geological Survey and Virginia Tech researchers, who analyzed samples collected over 32 years from a petroleum-spill research site in Minnesota. Arsenic, a toxin and carcinogen linked to numerous forms of cancer, is naturally present in most soils and sediments, but is not typically a health concern because its chemical properties keep it bound within soil and minerals. However, certain chemical reactions associated with petroleum contamination and microbial activity in low-oxygen environments, such as in aquifers, change the chemical state of the arsenic so that it can enter the groundwater, researchers say.

Categories: Environmental News

How Technology Is Protecting World’s Richest Marine Reserve

Yale Environment 360 - Mon, 01/26/2015 - 07:32

After years of fitful starts, the Pacific island nation of Kiribati this month banned all commercial fishing inside its huge marine reserve. New satellite transponder technology is now helping ensure that the ban succeeds in keeping out the big fishing fleets. BY CHRISTOPHER PALA

Categories: Environmental News

South Africa Relocates Rhinos After Record Number Were Poached in 2014

Yale Environment 360 - Fri, 01/23/2015 - 10:39

Unable to curb poaching of rhinos within its borders, the South African government has relocated 100 rhinos to

A white rhino in Kruger National Park. neighboring countries in an effort to stem the illegal slaughter of the animals, Reuters reports. For security reasons, officials did not reveal to which countries the rhinos had been relocated. An additional 56 rhinos were moved from poaching hotspots within South Africa's Kruger National Park — where two-thirds of the killings happen — to an "intensive protection zone" within Kruger, officials said. Poachers killed a record number of the animals in South Africa last year — 1,215 rhinos, up 20 percent from the 2013 total — and 49 have been killed so far this year. The animals are hunted intensely because their horns, which some Asian cultures incorrectly believe contain medicinal properties, are worth an estimated $65,000 per kilogram on the black market.

Categories: Environmental News

Hunt for Philae hangs in the balance

Nature - Fri, 01/23/2015 - 01:00

Hunt for Philae hangs in the balance

Nature 517, 7536 (2015). http://www.nature.com/doifinder/10.1038/nature.2015.16775

Author: Elizabeth Gibney

Rosetta mission would have to sacrifice other science to search for comet lander.

Categories: Literature

US ocean sciences told to steer a new course

Nature - Fri, 01/23/2015 - 01:00

US ocean sciences told to steer a new course

Nature 517, 7536 (2015). http://www.nature.com/doifinder/10.1038/nature.2015.16780

Author: Alexandra Witze

Major report calls for cuts to infrastructure, including fledgling Ocean Observatories Initiative, to increase spending on science. 

Categories: Literature

Rapid Draining of Greenland Lakes Signals Massive Melting, Researchers Say

Yale Environment 360 - Thu, 01/22/2015 - 11:18

Researchers have discovered craters left behind when two lakes under the Greenland ice sheet rapidly drained recently — an indication

Crater left after a Greenland lake drained. that a massive amount of meltwater has started overflowing the ice sheet's natural plumbing and is causing "blowouts" that drain lakes away, they say. One of the two lakes once held billions of gallons of water and emptied to form a mile-wide crater in just a few weeks, researchers report in the journal The Cryosphere. The other lake, described this week in the journal Nature, was two miles wide and has filled and emptied twice in the last two years. The researchers suspect that as more meltwater reaches the base of the ice sheet, natural drainage tunnels along the Greenland coast are cutting further inland. The tunnels carry heat and water to areas that were once frozen to the bedrock, potentially causing the ice to melt even faster.

Categories: Environmental News

Wood Pellets: Green Energy or New Source of CO2 Emissions?

Yale Environment 360 - Thu, 01/22/2015 - 07:31

Burning wood pellets to produce electricity is on the rise in Europe, where the pellets are classified as a form of renewable energy. But in the U.S., where pellet facilities are rapidly being built, concerns are growing about logging and the carbon released by the combustion of wood biomass. BY ROGER REAL DROUIN

Categories: Environmental News

A call for beautiful prose in papers

Nature - Thu, 01/22/2015 - 01:00

A call for beautiful prose in papers

Nature 517, 7536 (2015). doi:10.1038/517531f

Author: Chris Woolston

A blog post urging scientists to write elegantly triggers online discussion.

Categories: Literature

US precision-medicine proposal sparks questions

Nature - Thu, 01/22/2015 - 01:00

US precision-medicine proposal sparks questions

Nature 517, 7536 (2015). http://www.nature.com/doifinder/10.1038/nature.2015.16774

Author: Sara Reardon

Announcement by President Obama comes amidst growing interest in targeted therapies.

Categories: Literature

Filtering Polluted Stormwater Through Soil Can Protect Salmon, Study Shows

Yale Environment 360 - Wed, 01/21/2015 - 11:21

Filtering polluted runoff from urban areas through a simple soil mixture dramatically reduced the water's toxic metal and

A pair of coho salmon. hydrocarbon content and made it safe for coho salmon and the insects they eat, according to new research. Scientists collected polluted runoff from a four-lane highway in Seattle, then filtered part of the water through a mixture of sand, compost, and shredded bark. Coho salmon and aquatic insects thrived in the filtered stormwater, but they quickly died in the unfiltered water, researchers reported in the journal Chemosphere. Chemical analyses showed that filtering the water through the soil mixture reduced toxic metals by 30 to 99 percent, polyaromatic hydrocarbons to levels at or below detection, and organic matter by more than 40 percent. The research supports the use of rain gardens and other natural stormwater filtration systems, the authors say.

Categories: Environmental News

Al Gore’s dream spacecraft is ready to fly

Nature - Wed, 01/21/2015 - 02:00

Al Gore’s dream spacecraft is ready to fly

Nature 517, 7534 (2015). http://www.nature.com/doifinder/10.1038/517256a

Author: Mark Zastrow

After almost 14 years in mothballs, DSCOVR probe will monitor conditions on Earth and in space.

Categories: Literature

Microbiology: Here's looking at you, squid

Nature - Wed, 01/21/2015 - 02:00

Microbiology: Here's looking at you, squid

Nature 517, 7534 (2015). http://www.nature.com/doifinder/10.1038/517262a

Author: Ed Yong

Margaret McFall-Ngai has dissected the relationship between a beautiful squid and its live-in bacteria — and found lessons for microbiome research on the way.

Categories: Literature

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