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High-pressure, high-temperature phase stability of iron-poor dolomite and the structures of dolomite-IIIc and dolomite-V
No full textSelf-Learning Method for Construction of Analytical Interatomic Potentials to Describe Laser-Excited Materials
No full textLarge-scale simulations using interatomic potentials provide deep insight into the processes occurring in solids subject to external perturbations. The atomistic description of laser-induced ultrafast nonthermal phenomena, however, constitutes a particularly difficult case and has so far not been possible on experimentally accessible length scales and timescales because of two main reasons: (i) ab initio simulations are restricted to a very small number of atoms and ultrashort times and (ii) simulations relying on electronic temperature- () dependent interatomic potentials do not reach the necessary ab initio accuracy. Here we develop a self-learning method for constructing -dependent interatomic potentials which permit ultralarge-scale atomistic simulations of systems suddenly brought to extreme nonthermal states with density-functional theory (DFT) accuracy. The method always finds the global minimum in the parameter space. We derive a highly accurate analytical -dependent interatomic potential () for silicon that yields a remarkably good description of laser-excited and -unexcited Si bulk and Si films. Using () we simulate the laser excitation of Si nanoparticles and find strong damping of their breathing modes due to nonthermal melting
Multiple phase transitions in Sc doped amorphous nanocomposites under high pressure
No full textSubnanosecond switching speed from an amorphous state with stable crystal precursors to the crystalline state was recently achieved in amorphous Sc-doped Sb2Te3 (a-SST) phase change materials (PCMs), which is about two orders of magnitude faster than that in the well-studied Ge2Sb2Te5 and Ge1Sb2Te4 PCMs. However, the phase change mechanism and phase stability of a-SST remain unknown. Here, we prepared amorphous Sc0.3Sb2Te3 nanocomposites within a minute amount of face-centered-cubic (FCC) type nanograins embedded in the amorphous matrix. Using in situ high-pressure synchrotron X-ray diffraction, we found that nanograins were frustrated under high pressure and gradually dissolved into the matrix around 11.0 GPa. Beyond 11.0 GPa, the a-SST matrix transformed into a uniform high density metallic like amorphous state with a five orders of magnitude drop in electric resistivity compared to the pristine materials. When further compressed to 23.97 GPa, the high density amorphous (HDA) phase switched into a body-centered-cubic (BCC) high-pressure structure, a different phase from the ambient pressure crystalline structure. Upon decompression back to ambient pressure, a pure amorphous phase was sustained. The present study provides additional insight into the phase change mechanism of amorphous nanocomposites.Part of this research was carried out at the Extreme Conditions Beamline (P02.2) at DESY, a member of Helmholtz Association (HGF). We are very thankful to Konstantin Glazyrin for the technical support. This work was supported by the National Natural Science Foundation of China under Grants Nos. 11804010, U1530402, and 51527801 and China Postdoctoral Science Foundation (Grant No. 2016M600909). The beamline 13-ID-D (GeoSoiEnviroCARS) was supported by the National Science Foundation (NSF)—Earth Sciences (No. EAR-1128799)—and Department of Energy (DOE)—GeoSciences (No. DE-FG02-94ER14466). APS was supported by DOE-BES, under Contract No. DE-AC02-06CH11357
Measurement of the cross section for electroweak production of a Z boson, a photon and two jets in proton-proton collisions at 13 TeV and constraints on anomalous quartic couplings
No full textA measurement is presented of the cross section for electroweak production of a Z boson and a photon in association with two jets (Zjj) in proton-proton collisions. The Z boson candidates are selected through their decay into a pair of electrons or muons. The process of interest, electroweak Zjj production, is isolated by selecting events with a large dijet mass and a large pseudorapidity gap between the two jets. The measurement is based on data collected at the CMS experiment at 13 TeV, corresponding to an integrated luminosity of 35.9 fb. The observed significance of the signal is 3.9 standard deviations, where a significance of 5.2 standard deviations is expected in the standard model. These results are combined with published results by CMS at 8 TeV, which leads to observed and expected respective significances of 4.7 and 5.5 standard deviations. From the 13 TeV data, a value is obtained for the signal strength of electroweak Zjj production and bounds are given on quartic vector boson interactions in the framework of dimension-eight effective field theory operators
Measurement of the associated production of a Z boson with charm or bottom quark jets in proton-proton collisions at 13 TeV
No full textRatios of cross sections, σ(Z+c jets)/σ(Z+jets),σ(Z+b jets)/σ(Z+jets), and σ(Z+c jets)/σ(Z+b jets) in the associated production of a Z boson with at least one charmor bottom quark jet are measured in proton-proton collisions at √s=13 TeV. The data sample, collected by the CMS experiment at the CERN LHC, corresponds to an integrated luminosity of 35.9 fb−1, with a fiducial volume of pT>30 GeV and |η|25 GeV and |η|<2.4, and the dilepton mass satisfies 71<mZ<111 GeV. The measured values are σ(Z+c jets)/σ(Z+jets) =0.102±0.002±0.009,σ(Z+b jets)/σ(Z+jets) =0.0633±0.0004±0.0015, and σ(Z+c jets)/σ(Z+b jets) =1.62±0.03±0.15. Results on the inclusive and differential cross section ratios as functions of jet and Z boson transverse momentum are compared with predictions from leading and next-to-leading order perturbative quantum chromodynamics calculations. These are the first measurements of the cross section ratios at 13 TeV, and the measurement precision is better than that of the current theoretical prediction
Combined X-ray and neutron single-crystal diffraction in diamond anvil cells
No full textIt is shown that it is possible to perform combined X-ray and neutron singlecrystal studies in the same diamond anvil cell (DAC). A modified Merrill– Bassett DAC equipped with an inflatable membrane filled with He gas has been developed. It can be used on laboratory X-ray and synchrotron diffractometers as well as on neutron instruments. The data processing procedures and a joint structural refinement of the high-pressure synchrotron and neutron singlecrystal data are presented and discussed for the first time
Soft corrections to inclusive deep-inelastic scattering at four loops and beyond
No full textWe study the threshold corrections for inclusive deep-inelastic scattering (DIS) and their all-order resummation. Using recent results for the QCD form factor, related anomalous dimensions and Mellin moments of DIS structure functions at four loops we derive the complete soft and collinear contributions to the DIS Wilson coefficients at four loops. For a general SU(n) gauge group the results are exact in the large-n approximation and for QCD with n = 3 we present precise approximations. We extend the threshold resummation exponent G in Mellin-N space to the fifth logarithmic (NLL) order collecting the terms (α ln N) to all orders in the strong coupling constant α. We study the numerical effect of the NLL corrections using both the fully exponentiated form and the expansion of the coefficient function in towers of logarithms. As a byproduct, we derive a numerical result for the complete pole structure of the QCD form factor in the parameter of dimensional regularization ε at four loops
speckle-tracking: a Software Suite for Ptychographic X-ray Speckle Tracking
No full textIn recent years, x-ray speckle tracking techniques have emerged as viable tools for wavefront metrology and sample imaging applications. These methods are based on the measurement of near-field images. Thanks to the simple experimental set-up, high angular sensitivity and compatibility with low coherence sources these methods have been actively developed for use with synchrotron and laboratory light sources. Not only do speckle-tracking techniques give the potential for high resolution imaging, but they also provide rapid and robust characterisation of aberrations of x-ray optical elements, focal spot profiles and the sample position and transmission properties. In order to realise these capabilities, we require software implementations that are equally rapid and robust. To address this need, a software suite has been developed for the 'ptychographic x-ray speckle tracking technique' -- an x-ray speckle based method suitable for highly divergent wavefields. The software suite is written in Python 3, with an OpenCL back end for GPU and multi-CPU core processing. It is accessible as a Python module, through the command line or through a graphical user interface and is available as source code under version 3 or later of the GNU General Public License
