Room temperature coherent control of defect spin qubits in silicon carbide

Electronic spins in semiconductors have been used extensively to explore the limits of external control over quantum mechanical phenomena. A long-standing goal of this research has been to identify or develop robust quantum systems that can be easily manipulated, for future use in advanced information and communication technologies. Recently, a point defect in diamond known as the nitrogen-vacancy centre has attracted a great deal of interest because it possesses an atomic-scale electronic spin state that can be used as an individually addressable, solid-state quantum bit (qubit), even at room temperature. These exceptional quantum properties have motivated efforts to identify similar defects in other semiconductors, as they may offer an expanded range of functionality not available to the diamond nitrogen-vacancy centre. Notably, several defects in silicon carbide (SiC) have been suggested as good candidates for exploration, owing to a combination of computational predictions and magnetic resonance data. Here we demonstrate that several defect spin states in the 4H polytype of SiC (4H-SiC) can be optically addressed and coherently controlled in the time domain at temperatures ranging from 20 to 300 kelvin. Using optical and microwave techniques similar to those used with diamond nitrogen-vacancy qubits, we study the spin-1 ground state of each of four inequivalent forms of the neutral carbon-silicon divacancy, as well as a pair of defect spin states of unidentified origin. These defects are optically active near telecommunication wavelengths, and are found in a host material for which there already exist industrial-scale crystal growth and advanced microfabrication techniques. In addition, they possess desirable spin coherence properties that are comparable to those of the diamond nitrogen-vacancy centre. This makes them promising candidates for various photonic, spintronic and quantum information applications that merge quantum degrees of freedom with classical electronic and optical technologies.     

The first hominin of Europe

The earliest hominin occupation of Europe is one of the most debated topics in palaeoanthropology. However, the purportedly oldest of the Early Pleistocene sites in Eurasia lack precise age control and contain stone tools rather than human fossil remains. Here we report the discovery of a human mandible associated with an assemblage of Mode 1 lithic tools and faunal remains bearing traces of hominin processing, in stratigraphic level TE9 at the site of the Sima del Elefante, Atapuerca, Spain. Level TE9 has been dated to the Early Pleistocene (approximately 1.2-1.1 Myr), based on a combination of palaeomagnetism, cosmogenic nuclides and biostratigraphy. The Sima del Elefante site thus emerges as the oldest, most accurately dated record of human occupation in Europe, to our knowledge. The study of the human mandible suggests that the first settlement of Western Europe could be related to an early demographic expansion out of Africa. The new evidence, with previous findings in other Atapuerca sites (level TD6 from Gran Dolina), also suggests that a speciation event occurred in this extreme area of the Eurasian continent during the Early Pleistocene, initiating the hominin lineage represented by the TE9 and TD6 hominins.     

Mechanism of shape determination in motile cells

The shape of motile cells is determined by many dynamic processes spanning several orders of magnitude in space and time, from local polymerization of actin monomers at subsecond timescales to global, cell-scale geometry that may persist for hours. Understanding the mechanism of shape determination in cells has proved to be extremely challenging due to the numerous components involved and the complexity of their interactions. Here we harness the natural phenotypic variability in a large population of motile epithelial keratocytes from fish (Hypsophrys nicaraguensis) to reveal mechanisms of shape determination. We find that the cells inhabit a low-dimensional, highly correlated spectrum of possible functional states. We further show that a model of actin network treadmilling in an inextensible membrane bag can quantitatively recapitulate this spectrum and predict both cell shape and speed. Our model provides a simple biochemical and biophysical basis for the observed morphology and behaviour of motile cells.     

Approximating Nonlinear Relations Between Susceptibility and Magnetic Contents in Rocks Using Neural Networks

Correlations between magnetic susceptibility and contents of magnetic minerals in rocks are important in interpreting magnetic anomalies in geophysical exploration and understanding magnetic behaviors of rocks in rock magnetism studies. Previous studies were focused on describing such correlations using a sole expression or a set of expressions through statistical analysis. In this paper, we use neural network techniques to approximate the nonlinear relations between susceptibility and magnetite and/or hematite contents in rocks. This is the first time that neural networks are used for such study in rock magnetism and magnetic petrophysics. Three multilayer perceptrons are trained for producing the best possible estimation on susceptibility based on magnetic contents. These trained models are capable of producing accurate mappings between susceptibility and magnetite and/or hematite contents in rocks. This approach opens a new way of quantitative simulation using neural networks in rock magnetism and petrophysical research and applications.     

Occurrence of Ord's kangaroo rat ( Dipodomys ordii ) along its eastern distributional limit in Nebraska

Changes in land use continue to alter habitats throughout Nebraska, and few studies have examined how such changes affect distributional limits of mammals. The distribution of Ord’s kangaroo rat ( Dipodomys ordii ) was last examined in eastern Nebraska about 4 decades ago. We examined the current eastern distributional limits of D. ordii to see whether its range had expanded, contracted, or remained constant in the state since the 1960s. Based on our study, kangaroo rats have experienced little change in distribution during recent decades. Herein, we report on data for 8 counties without prior records and a marginal range extension, as well as comment on habitat, reproduction, and taxonomic status of kangaroo rats in eastern Nebraska. Los cambios en el uso del suelo siguen modificando los hábitats a lo largo del estado de Nebraska, y pocos estudios han examinado cómo estos cambios afectan los límites de distribución de los mamíferos. La última evaluación de la distribución de la rata canguro de Ord ( Dipodomys ordii ) en el este de Nebraska se llevó a cabo hace 4 décadas. Examinamos los límites orientales actuales de la distribución de D. ordii para ver si su área de distribución se ha expandido, contraído o permanecido igual en el estado desde los años 1960. Con base en nuestra investigación, es posible decir que la distribución de las ratas canguro ha cambiado poco en décadas recientes. Aquí reportamos datos para 8 condados para los cuales no existían registros anteriores e informamos sobre una pequeña expansión de su área de distribución. También comentamos sobre el hábitat, la reproducción y la situación taxonómica de las ratas canguro en el este de Nebraska.     

The prolyl isomerase Pin1 regulates amyloid precursor protein processing and amyloid-beta production

Neuropathological hallmarks of Alzheimer's disease are neurofibrillary tangles composed of tau and neuritic plaques comprising amyloid-beta peptides (Abeta) derived from amyloid precursor protein (APP), but their exact relationship remains elusive. Phosphorylation of tau and APP on certain serine or threonine residues preceding proline affects tangle formation and Abeta production in vitro. Phosphorylated Ser/Thr-Pro motifs in peptides can exist in cis or trans conformations, the conversion of which is catalysed by the Pin1 prolyl isomerase. Pin1 has been proposed to regulate protein function by accelerating conformational changes, but such activity has never been visualized and the biological and pathological significance of Pin1 substrate conformations is unknown. Notably, Pin1 is downregulated and/or inhibited by oxidation in Alzheimer's disease neurons, Pin1 knockout causes tauopathy and neurodegeneration, and Pin1 promoter polymorphisms appear to associate with reduced Pin1 levels and increased risk for late-onset Alzheimer's disease. However, the role of Pin1 in APP processing and Abeta production is unknown. Here we show that Pin1 has profound effects on APP processing and Abeta production. We find that Pin1 binds to the phosphorylated Thr 668-Pro motif in APP and accelerates its isomerization by over 1,000-fold, regulating the APP intracellular domain between two conformations, as visualized by NMR. Whereas Pin1 overexpression reduces Abeta secretion from cell cultures, knockout of Pin1 increases its secretion. Pin1 knockout alone or in combination with overexpression of mutant APP in mice increases amyloidogenic APP processing and selectively elevates insoluble Abeta42 (a major toxic species) in brains in an age-dependent manner, with Abeta42 being prominently localized to multivesicular bodies of neurons, as shown in Alzheimer's disease before plaque pathology. Thus, Pin1-catalysed prolyl isomerization is a novel mechanism to regulate APP processing and Abeta production, and its deregulation may link both tangle and plaque pathologies. These findings provide new insight into the pathogenesis and treatment of Alzheimer's disease.     

Evolutionary genetics: CCR5 mutation and plague protection

A recent and prevalent mutation in the chemokine receptor CCR5 in humans of northern European ancestry has been proposed to provide protection against bubonic plague. Here we infect both normal and CCR5-deficient mice with the bacterium Yersinia pestis, the cause of the plague epidemics that wiped out one-third of Europeans in the Middle Ages, and find no difference in either bacterial growth or survival time between the two groups. Unless the pathogenesis of Yersinia infection differs markedly between mice and humans, our results indicate that CCR5 deficiency in people is unlikely to protect against plague.     

Weighing of biomolecules, single cells and single nanoparticles in fluid

Nanomechanical resonators enable the measurement of mass with extraordinary sensitivity. Previously, samples as light as 7 zeptograms (1 zg = 10(-21) g) have been weighed in vacuum, and proton-level resolution seems to be within reach. Resolving small mass changes requires the resonator to be light and to ring at a very pure tone-that is, with a high quality factor. In solution, viscosity severely degrades both of these characteristics, thus preventing many applications in nanotechnology and the life sciences where fluid is required. Although the resonant structure can be designed to minimize viscous loss, resolution is still substantially degraded when compared to measurements made in air or vacuum. An entirely different approach eliminates viscous damping by placing the solution inside a hollow resonator that is surrounded by vacuum. Here we demonstrate that suspended microchannel resonators can weigh single nanoparticles, single bacterial cells and sub-monolayers of adsorbed proteins in water with sub-femtogram resolution (1 Hz bandwidth). Central to these results is our observation that viscous loss due to the fluid is negligible compared to the intrinsic damping of our silicon crystal resonator. The combination of the low resonator mass (100 ng) and high quality factor (15,000) enables an improvement in mass resolution of six orders of magnitude over a high-end commercial quartz crystal microbalance. This gives access to intriguing applications, such as mass-based flow cytometry, the direct detection of pathogens, or the non-optical sizing and mass density measurement of colloidal particles.     

Histone demethylase JHDM2A is critical for Tnp1 and Prm1 transcription and spermatogenesis

Recent studies indicate that, similar to other covalent modifications, histone lysine methylation is subject to enzyme-catalysed reversion. So far, LSD1 (also known as AOF2) and the jumonji C (JmjC)-domain-containing proteins have been shown to possess histone demethylase activity. LSD1 catalyses removal of H3K4me2/H3K4me1 through a flavin-adenine-dinucleotide-dependent oxidation reaction. In contrast, JmjC-domain-containing proteins remove methyl groups from histones through a hydroxylation reaction that requires alpha-ketoglutarate and Fe(II) as cofactors. Although an increasing number of histone demethylases have been identified and biochemically characterized, their biological functions, particularly in the context of an animal model, are poorly characterized. Here we use a loss-of-function approach to demonstrate that the mouse H3K9me2/1-specific demethylase JHDM2A (JmjC-domain-containing histone demethylase 2A, also known as JMJD1A) is essential for spermatogenesis. We show that Jhdm2a-deficient mice exhibit post-meiotic chromatin condensation defects, and that JHDM2A directly binds to and controls the expression of transition nuclear protein 1 (Tnp1) and protamine 1 (Prm1) genes, the products of which are required for packaging and condensation of sperm chromatin. Thus, our work uncovers a role for JHDM2A in spermatogenesis and reveals transition nuclear protein and protamine genes as direct targets of JHDM2A.