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Extended hard-X-ray emission in the inner few parsecs of the Galaxy
Nature 520, 7549 (2015). doi:10.1038/nature14353
Authors: Kerstin Perez, Charles J. Hailey, Franz E. Bauer, Roman A. Krivonos, Kaya Mori, Frederick K. Baganoff, Nicolas M. Barrière, Steven E. Boggs, Finn E. Christensen, William W. Craig, Brian W. Grefenstette, Jonathan E. Grindlay, Fiona A. Harrison, Jaesub Hong, Kristin K. Madsen, Melania Nynka, Daniel Stern, John A. Tomsick, Daniel R. Wik, Shuo Zhang, William W. Zhang & Andreas Zoglauer
The Galactic Centre hosts a puzzling stellar population in its inner few parsecs, with a high abundance of surprisingly young, relatively massive stars bound within the deep potential well of the central supermassive black hole, Sagittarius A* (ref. 1). Previous studies suggest that the population of objects emitting soft X-rays (less than 10 kiloelectronvolts) within the surrounding hundreds of parsecs, as well as the population responsible for unresolved X-ray emission extending along the Galactic plane, is dominated by accreting white dwarf systems. Observations of diffuse hard-X-ray (more than 10 kiloelectronvolts) emission in the inner 10 parsecs, however, have been hampered by the limited spatial resolution of previous instruments. Here we report the presence of a distinct hard-X-ray component within the central 4 × 8 parsecs, as revealed by subarcminute-resolution images in the 20–40 kiloelectronvolt range. This emission is more sharply peaked towards the Galactic Centre than is the surface brightness of the soft-X-ray population. This could indicate a significantly more massive population of accreting white dwarfs, large populations of low-mass X-ray binaries or millisecond pulsars, or particle outflows interacting with the surrounding radiation field, dense molecular material or magnetic fields. However, all these interpretations pose significant challenges to our understanding of stellar evolution, binary formation, and cosmic-ray production in the Galactic Centre.
High-mobility three-atom-thick semiconducting films with wafer-scale homogeneity
Nature 520, 7549 (2015). doi:10.1038/nature14417
Authors: Kibum Kang, Saien Xie, Lujie Huang, Yimo Han, Pinshane Y. Huang, Kin Fai Mak, Cheol-Joo Kim, David Muller & Jiwoong Park
The large-scale growth of semiconducting thin films forms the basis of modern electronics and optoelectronics. A decrease in film thickness to the ultimate limit of the atomic, sub-nanometre length scale, a difficult limit for traditional semiconductors (such as Si and GaAs), would bring wide benefits for applications in ultrathin and flexible electronics, photovoltaics and display technology. For this, transition-metal dichalcogenides (TMDs), which can form stable three-atom-thick monolayers, provide ideal semiconducting materials with high electrical carrier mobility, and their large-scale growth on insulating substrates would enable the batch fabrication of atomically thin high-performance transistors and photodetectors on a technologically relevant scale without film transfer. In addition, their unique electronic band structures provide novel ways of enhancing the functionalities of such devices, including the large excitonic effect, bandgap modulation, indirect-to-direct bandgap transition, piezoelectricity and valleytronics. However, the large-scale growth of monolayer TMD films with spatial homogeneity and high electrical performance remains an unsolved challenge. Here we report the preparation of high-mobility 4-inch wafer-scale films of monolayer molybdenum disulphide (MoS2) and tungsten disulphide, grown directly on insulating SiO2 substrates, with excellent spatial homogeneity over the entire films. They are grown with a newly developed, metal–organic chemical vapour deposition technique, and show high electrical performance, including an electron mobility of 30 cm2 V−1 s−1 at room temperature and 114 cm2 V−1 s−1 at 90 K for MoS2, with little dependence on position or channel length. With the use of these films we successfully demonstrate the wafer-scale batch fabrication of high-performance monolayer MoS2 field-effect transistors with a 99% device yield and the multi-level fabrication of vertically stacked transistor devices for three-dimensional circuitry. Our work is a step towards the realization of atomically thin integrated circuitry.
A circuit mechanism for differentiating positive and negative associations
Nature 520, 7549 (2015). doi:10.1038/nature14366
Authors: Praneeth Namburi, Anna Beyeler, Suzuko Yorozu, Gwendolyn G. Calhoon, Sarah A. Halbert, Romy Wichmann, Stephanie S. Holden, Kim L. Mertens, Melodi Anahtar, Ada C. Felix-Ortiz, Ian R. Wickersham, Jesse M. Gray & Kay M. Tye
The ability to differentiate stimuli predicting positive or negative outcomes is critical for survival, and perturbations of emotional processing underlie many psychiatric disease states. Synaptic plasticity in the basolateral amygdala complex (BLA) mediates the acquisition of associative memories, both positive and negative. Different populations of BLA neurons may encode fearful or rewarding associations, but the identifying features of these populations and the synaptic mechanisms of differentiating positive and negative emotional valence have remained unknown. Here we show that BLA neurons projecting to the nucleus accumbens (NAc projectors) or the centromedial amygdala (CeM projectors) undergo opposing synaptic changes following fear or reward conditioning. We find that photostimulation of NAc projectors supports positive reinforcement while photostimulation of CeM projectors mediates negative reinforcement. Photoinhibition of CeM projectors impairs fear conditioning and enhances reward conditioning. We characterize these functionally distinct neuronal populations by comparing their electrophysiological, morphological and genetic features. Overall, we provide a mechanistic explanation for the representation of positive and negative associations within the amygdala.
Biomechanics: How grebes walk on water
Nature 520, 7549 (2015). doi:10.1038/520588a
The heaviest animals known to run on water pull off the feat by using quick strides and large feet that slap the surface.Western and Clark's grebes (Aechmophorus occidentalis and Aechmophorus clarkii; pictured) run as far as 20 metres on water and
Astronomy: Light direct from an alien world
Nature 520, 7549 (2015). doi:10.1038/520588b
Astronomers have spotted light reflected off a planet orbiting a distant sun, by teasing it out from the background starlight. The discovery allows direct calculations of the mass and other properties of the exoplanet, rather than inferring them using other methods.Jorge Martins of the
Biophysics: Bacteria swim to form crystals
Nature 520, 7549 (2015). doi:10.1038/520588c
Fast-swimming bacteria that live at the bottom of salt marshes spontaneously come together to form organized crystalline structures that move through water.The bacterium Thiovulum majus is a large, round cell with hundreds of small flagella, or tail-like structures, that spin to propel the
Hydrology: Groundwater under Antarctica
Nature 520, 7549 (2015). doi:10.1038/520588d
A groundwater network found beneath an Antarctic valley could support microbial life.Jill Mikucki of the University of Tennessee in Knoxville, Slawek Tulaczyk at the University of California, Santa Cruz, and their colleagues studied Taylor Valley using an airborne instrument to measure underground electrical resistivity,
Neuroscience: Brain waves go far in tinnitus
Nature 520, 7549 (2015). doi:10.1038/520588e
Many people hear ringing in the ears, known as tinnitus, and researchers now think it could involve abnormally linked brain waves that extend across a large part of the brain.William Sedley at Newcastle University, UK, Phillip Gander at the University of Iowa in Iowa
Metrology: Atomic clock smashes records
Nature 520, 7549 (2015). doi:10.1038/520589a
The world's best atomic clock has become even more accurate, neither gaining nor losing a second over 15 billion years — longer than the age of the Universe.The clock keeps time using 2,000 ultracold strontium atoms trapped in a laser lattice. Its pendulum is
Climate change: Weather extremes linked to warming
Nature 520, 7549 (2015). doi:10.1038/520589b
Global warming is responsible for three out of four hot temperature extremes around the world, and almost one-fifth of heavy precipitation events over land.Erich Fischer and Reto Knutti at the Swiss Federal Institute of Technology in Zurich used climate simulations to compare the frequencies
Physiology: Colour tunes the body clock
Nature 520, 7549 (2015). doi:10.1038/520589c
The changing brightness of sunlight during dawn and dusk is known to adjust circadian rhythms, but researchers now show that the shifting colour of the light does the same thing in mice.Timothy Brown, Robert Lucas and their co-workers at the University of Manchester, UK,
Palaeogenetics: Genomes reveal mammoth history
Nature 520, 7549 (2015). doi:10.1038/520589d
Genome sequences from two woolly mammoths provide a rare look at the genetic events leading up to extinction.Eleftheria Palkopoulou and Love Dalén at the Swedish Museum of Natural History in Stockholm sequenced the genomes of a woolly mammoth (Mammuthus primigenius; artist's impression
Seven days: 24–30 April 2015
Nature 520, 7549 (2015). http://www.nature.com/doifinder/10.1038/520590a
The week in science: Nepal quake’s devastating toll; malaria vaccine hopeful offers infants only small protection; why the US National Football League must pay out nearly US$1billion.
Embryo editing sparks epic debate
Nature 520, 7549 (2015). http://www.nature.com/doifinder/10.1038/520593a
Authors: David Cyranoski & Sara Reardon
In wake of paper describing genetic modification of human embryos, scientists disagree about ethics.
Bone DNA reveals humanity’s trek into South America
Nature 520, 7549 (2015). http://www.nature.com/doifinder/10.1038/520598a
Author: Ewen Callaway
Skeletons from Peru caves plot course for a single migration to the continent.
Collateral damage: How one misconduct case brought a biology institute to its knees
Nature 520, 7549 (2015). http://www.nature.com/doifinder/10.1038/520600a
Author: David Cyranoski
The fall out from the STAP case is still being felt across Japan.
Science in turmoil: After the Arab Spring
Nature 520, 7549 (2015). http://www.nature.com/doifinder/10.1038/520604a
Authors: Mohammed Yahia & Declan Butler
Four years after revolutions shook governments in North Africa and the Middle East, scientists face an uncertain future.
Personalized medicine: Time for one-person trials
Nature 520, 7549 (2015). doi:10.1038/520609a
Author: Nicholas J. Schork
Precision medicine requires a different type of clinical trial that focuses on individual, not average, responses to therapy, says Nicholas J. Schork.