ALBERT

Description: 〈p〉The recent discovery of ferromagnetism in two-dimensional (2D) van der Waals (vdW) materials holds promises for spintronic devices with exceptional properties. However, to use 2D vdW magnets for building spintronic nanodevices such as magnetic memories, key challenges remain in terms of effectively switching the magnetization from one state to the other electrically. Here, we devise a bilayer structure of Fe〈sub〉3〈/sub〉GeTe〈sub〉2〈/sub〉/Pt, in which the magnetization of few-layered Fe〈sub〉3〈/sub〉GeTe〈sub〉2〈/sub〉 can be effectively switched by the spin-orbit torques (SOTs) originated from the current flowing in the Pt layer. The effective magnetic fields corresponding to the SOTs are further quantitatively characterized using harmonic measurements. Our demonstration of the SOT-driven magnetization switching in a 2D vdW magnet could pave the way for implementing low-dimensional materials in the next-generation spintronic applications.〈/p〉

Description: Flowering time is one of the key determinants of crop adaptation to local environments during domestication. However, the genetic basis underlying flowering time is yet to be elucidated in most cereals. Although staple cereals, such as rice, maize, wheat, barley, and sorghum, have spread and adapted to a wide range of ecological environments during domestication, it is yet to be determined whether they have a common genetic basis for flowering time. In this study, we show, through map-based cloning, that flowering time in sorghum is controlled by a major quantitative trait locus (QTL) Heading Date 1 ( HD1 ), located on chromosome 10. The causal gene encodes the CONSTANS gene family which contains a CCT domain. A 5-bp deletion of a minor allele present in the coding sequence leads to a gene frameshift that delays flowering in sorghum. In contrast, in foxtail millet, association mapping of HD1 showed a common causal site with a splicing variant from "GT" to "AT" that was highly correlated with flowering time. In addition, the rice HD1 gene is known to harbor several causal variants controlling flowering time. These data indicate that the major flowering time QTL HD1 was under parallel domestication in sorghum, foxtail millet, and rice. The pattern of common mixed minor, or even rare, causal alleles in HD1 across different species may be representative of the genetic basis of the domestication syndrome. Furthermore, large DNA sequence analysis of HD1 revealed multiple origins for domesticated sorghum and a single origin for domesticated foxtail millet.

Description: Phosphorylation of histone H4 serine 47 (H4S47ph) is catalyzed by Pak2, a member of the p21-activated serine/threonine protein kinase (Pak) family and regulates the deposition of histone variant H3.3. However, the phosphatase(s) involved in the regulation of H4S47ph levels was unknown. Here, we show that three phosphatases (PP1α, PP1β and Wip1) regulate H4S47ph levels and H3.3 deposition. Depletion of each of the three phosphatases results in increased H4S47ph levels. Moreover, PP1α, PP1β and Wip1 bind H3-H4 in vitro and in vivo , whereas only PP1α and PP1β, but not Wip1, interact with Pak2 in vivo . These results suggest that PP1α, PP1β and Wip1 regulate the levels of H4S47ph through directly acting on H4S47ph, with PP1α and PP1β also likely regulating the activity of Pak2. Finally, depletion of PP1α, PP1β and Wip1 leads to increased H3.3 occupancy at candidate genes tested, elevated H3.3 deposition and enhanced association of H3.3 with its chaperones HIRA and Daxx. These results reveal a novel role of three phosphatases in chromatin dynamics in mammalian cells.

Description: Paracrine regulation in mesenchymal stem cells: the role of Rap1 Cell Death and Disease 6, e1932 (October 2015). doi:10.1038/cddis.2015.285 Authors: Y Zhang, Z Zhang, F Gao, H-F Tse, V Tergaonkar & Q Lian

Description: Differences between 3-D numerical predictions of earthquake ground motion in the Mygdonian basin near Thessaloniki, Greece, led us to define four canonical stringent models derived from the complex realistic 3-D model of the Mygdonian basin. Sediments atop an elastic bedrock are modelled in the 1D-sharp and 1D-smooth models using three homogeneous layers and smooth velocity distribution, respectively. The 2D-sharp and 2D-smooth models are extensions of the 1-D models to an asymmetric sedimentary valley. In all cases, 3-D wavefields include strongly dispersive surface waves in the sediments. We compared simulations by the Fourier pseudo-spectral method (FPSM), the Legendre spectral-element method (SEM) and two formulations of the finite-difference method (FDM-S and FDM-C) up to 4 Hz. The accuracy of individual solutions and level of agreement between solutions vary with type of seismic waves and depend on the smoothness of the velocity model. The level of accuracy is high for the body waves in all solutions. However, it strongly depends on the discrete representation of the material interfaces (at which material parameters change discontinuously) for the surface waves in the sharp models. An improper discrete representation of the interfaces can cause inaccurate numerical modelling of surface waves. For all the numerical methods considered, except SEM with mesh of elements following the interfaces, a proper implementation of interfaces requires definition of an effective medium consistent with the interface boundary conditions. An orthorhombic effective medium is shown to significantly improve accuracy and preserve the computational efficiency of modelling. The conclusions drawn from the analysis of the results of the canonical cases greatly help to explain differences between numerical predictions of ground motion in realistic models of the Mygdonian basin. We recommend that any numerical method and code that is intended for numerical prediction of earthquake ground motion should be verified through stringent models that would make it possible to test the most important aspects of accuracy.

Description: Simulating seismic waves with uniform grid in heterogeneous high-velocity contrast media requires small-grid spacing determined by the global minimal velocity, which leads to huge number of grid points and small time step. To reduce the computational cost, discontinuous grids that use a finer grid at the shallow low-velocity region and a coarser grid at high-velocity regions are needed. In this paper, we present a discontinuous grid implementation for the collocated-grid finite-difference (FD) methods to increase the efficiency of seismic wave modelling. The grid spacing ratio n could be an arbitrary integer n  ≥ 2. To downsample the wavefield from the finer grid to the coarser grid, our implementation can simply take the values on the finer grid without employing a downsampling filter for grid spacing ratio n  = 2 to achieve stable results for long-time simulation. For grid spacing ratio n  ≥ 3, the Gaussian filter should be used as the downsampling filter to get a stable simulation. To interpolate the wavefield from the coarse grid to the finer grid, the trilinear interpolation is used. Combining the efficiency of discontinuous grid with the flexibility of collocated-grid FD method on curvilinear grids, our method can simulate large-scale high-frequency strong ground motion of real earthquake with consideration of surface topography.

Description: Author(s): X. Q. Liu, X. B. Li, L. Zhang, Y. Q. Cheng, Z. G. Yan, M. Xu, X. D. Han, S. B. Zhang, Z. Zhang, and E. Ma [Phys. Rev. Lett. 108, 239602] Published Tue Jun 05, 2012

Description: Author(s): X. Q. Liu, X. B. Li, L. Zhang, Y. Q. Cheng, Z. G. Yan, M. Xu, X. D. Han, S. B. Zhang, Z. Zhang, and E. Ma Using electron microscopy and diffraction techniques, as well as first-principles calculations, we demonstrate that as much as 35% of the total Ge atoms in the cubic phase of Ge_{2} Sb_{2} Te_{5} locate in tetrahedral environments. The Ge-vacancy interactions play a crucial stabilizing role, leading... [Phys. Rev. Lett. 106, 025501] Published Thu Jan 13, 2011

Description: Based on Rossi X-ray Timing Explorer ( RXTE ) observational data, we study the timing and spectral properties of some peculiar low-frequency (LF) quasi-periodic oscillations (QPOs), which have been found at the peak luminosity of the outburst of some transient black hole (BH) binaries: the 2005 outburst of GRO J1655–40, the 2003 outburst of H1743–322 and the 1998 outburst of XTE J1550–564. Appearing in the ultraluminous state, these QPOs from different sources show some common properties. The amplitude is very weak (less than 1 per cent) and the quality factor is larger than 6. Moreover, these QPOs (about several Hz) sometimes show up simultaneously with another QPO (about 10 Hz), but their frequencies are not harmonically related. We also find that the frequencies of these QPOs are inversely correlated with the mass of the BH, which implies that these QPOs might be correlated with the innermost stable circular orbit. The QPO frequency is also negative correlated with the inner disc radius among BHs. However, its frequency is too low to ascribe it to the Keperlian orbit frequency. Moreover, we discuss the physical origin of these QPOs and we suggest that they are not produced by the viscous variability of the inner disc either.

Description: Author(s): L. Z. Zhang, Z. F. Wang, S. X. Du, H.-J. Gao, and Feng Liu We predict the existence of a Dirac state in a monolayer TiB2 sheet (m-TiB2), a two-dimensional metal diboride, based on first-principles calculations. The band structure of m-TiB2 is found to be characterized with anisotropic Dirac cones with the largest Fermi velocity of 0.57×106 m/s, which is abo... [Phys. Rev. B 90, 161402] Published Fri Oct 03, 2014