292 research outputs found
Resonant Charge Relaxation as a Likely Source of the Enhanced Thermopower in FeSi
The enhanced thermopower of the correlated semiconductor FeSi is found to be
robust against the sign of the relevant charge carriers. At \,\,70
K, the position of both the high-temperature shoulder of the thermopower peak
and the nonmagnetic-enhanced paramagnetic crossover, the Nernst coefficient
assumes a large maximum and the Hall mobility diminishes to
below 1 cm/Vs. These cause the dimension-less ratio / a
measure of the energy dispersion of the charge scattering time
to exceed that of classical metals and semiconductors by two orders of
magnitude. Concomitantly, the resistivity exhibits a hump and the
magnetoresistance changes its sign. Our observations hint at a resonant
scattering of the charge carriers at the magnetic crossover, imposing strong
constraints on the microscopic interpretation of the robust thermopower
enhancement in FeSi.Comment: 5 pages, 3 figure
The Phosphidosilicates AE2Li4SiP4 (AE=Ca, Sr, Eu) Ba4Li16Si3P12
The quaternary phosphidosilicates AE2Li4SiP4 (AE=Ca, Sr, Eu) and Ba4Li16Si3P12 were synthesized by heating the elements and Li3P under argon atmosphere. Their crystal structures were determined by single crystal X-ray diffraction. AE2Li4SiP4 crystallize in a new layered structure type (P21/m, Z=2) with CdI2-analoguos layers. Edge sharing CaP6 octahedra are separated by layers of vertex-sharing SiP4 and LiP4 tetrahedra, which contain additional chains of LiP6 octahedra. Ba4Li16Si3P12 forms likewise a new structure type (P21/c, Z=16) with a three-dimensional network of SiP4, Si2P6 and LiP4 entities as well as one phosphorus site not bonded to silicon. Barium is located in capped trigonal prisms of phosphorus which form strongly corrugated layers. 31P and 29Si solid-state NMR spectra confirm the crystal structures of the compounds AE2Li4SiP4. 7Li spectra show only one signal in spite of quite different crystallographic positions, which indicate possible Li+ mobility. However, this signal is much broader compared to the known Li+ conducting phosphidosilicates. Accordingly, electrochemical impedance measurements show low Li+ conductivities
Co-development of Firm Foundings and Regional Clusters
ABSTRACT: Although firm foundings and the formation of regional clusters are two processes that have separately attracted a lot of scientific attention during recent years, not much research has been conducted to analyse the interrelation between these two processes. This paper gives some new insights into this relation and a framework is presented into which empirical observations and theoretical considerations can be placed. The core elements are the effects the two processes have on each other in the different stages of cluster formation and development
Application of the Coupled Eulerian Lagrangian method to the prediction of single-grain cutting forces in grinding
Continuous technological advancements in the field of grinding technology and improved grinding tools have contributed to the development of high performance grinding processes. One example of such a process is internal traverse grinding (ITG) with electroplated cBN grinding wheels, where the tool consists of a conical roughing zone and a cylindrical finishing zone. Since the tool is fed in axial direction into a revolving workpiece, spindle deflections induced by varying process forces can lead to contour errors along the bore. Numerical simulations are a valuable tool to overcome the challenges associated with such high performance processes. Whenever spindle deflections need to be considered, accurate prediction of the process forces is paramount. Finite Element (FE) simulations have been widely used for the prediction of forces in cutting processes such as turning and milling, where only a small number of active cutting edges is considered, and where the geometry of these cutting edges is clearly defined. Grinding tools, on the other hand, contain a large number of grains with varying geometric characteristics. We recently proposed a multi-scale simulation system for the simulation of ITG processes, where a geometric kinematic grinding simulation, based on a database of digitalised grains of a real grinding wheel, was used to determine the grain engagements [1]. The process forces were obtained from summation of the contributions of all active grains at any given time, based on a force model on the individual grain level. The force model takes the material removal rate and an approximation of the rake angle into account, and was calibrated via finite element simulations.
In recent years, the Coupled Eulerian Lagrangian method (CEL), which is part of the commercial finite element software Abaqus, has been applied to simulate various cutting processes. No remeshing is necessary in this framework, and separation of chips from the workpiece can be modelled without element deletion. The application of CEL to the simulation of single grain cutting is therefore a promising approach to further improve the force model included in the process simulation of ITG. In this work, the kinematics of ITG are incorporated into a single grain cutting simulation, and the suitability of the CEL method for the problem is evaluated with a focus on the chip formation, separation and self-contact between the chip and the workpiece
Crossover from coherent to incoherent scattering in spin-orbit dominated Sr2IrO4
Strong spin-orbit interaction in the two dimensional compound Sr2IrO4 leads
to the formation of Jeff=1/2 isospins with unprecedented dynamics. In Raman
scattering a continuum attributed to double spin scattering is observed. With
higher excitation energy of the incident Laser this signal crosses over to an
incoherent background. The characteristic energy scale of this cross over is
identical to that of intensity resonance effects in phonon scattering. It is
related to exciton-like orbital excitations that are also evident in resonant
X-Ray scattering. The crossover and evolution of incoherent excitations are
proposed to be due to their coupling to spin excitations. This signals a
spin-orbit induced entanglement of spin, lattice and charge degrees of freedoms
in Sr2IrO4.Comment: 20 pages, 7 figure
Improved Arithmetic Performance by Combining Stateful and NonâStateful Logic in Resistive Random Access Memory 1Tâ1R Crossbars
Computing-in-memory (CIM) is a promising approach for overcoming the memory-wall problem in conventional von-Neumann architectures. This is done by performing certain computation tasks directly in the storage subsystem without transferring data between storage and processing units. Stateful and non-stateful CIM concepts are recently attracting lots of interest, which are demonstrated as logical complete, energy efficient, and compatible with dense crossbar structures. However, sneak-path currents in passive resistive random access memory (RRAM) crossbars degrade the operation reliability and require the usage of active 1 Transistorâ1 Resistance (1T-1R) bitcell designs. In this article, the arithmetic performance and reliability are investigated based on experimental measurements and variability-aware circuit simulations. Herein, it is aimed for the evaluation of logic operations specifically with fully integrated 1Tâ1R crossbar devices. Based on these operations, an N-bit full adder with optimized energy consumption and latency is demonstrated by combining stateful and non-stateful CIM logic styles with regard to the specific conditions in active 1Tâ1R RRAM crossbars
Spin-wave stiffness of the Dzyaloshinskii-Moriya helimagnet compounds Fe1âxCoxSi studied by small-angle neutron scattering
The spin wave stiffness was measured by small-angle neutron scattering method in the Dzyaloshinskii-Moriya helimagnet compounds Fe1âxCoxSi with x=0.25,0.30,0.50. It has been shown that the spin wave dispersion in the fully polarized state is anisotropic due to Dzyaloshinskii-Moriya interaction. It is reflected in the neutron scattering pattern as two circles for neutrons obtaining and losing the magnon energy, respectively. The centers of the circles are shifted by the momentum transfer oriented along the applied magnetic field H and equal to the wave vector of the spiral ±ks. The radius of the circles is directly related to the stiffness of spin waves and depends on the magnetic field. We have found that the spin-wave stiffness A change weakly with temperature for each individual compound. On the other hand, the spin-wave stiffness A increases linearly with x in contrast to the x dependences of the critical temperature Tc and the low-temperature ordered moment. Experimentally obtained values of the stiffness A approve quantitative applicability of the Bak-Jensen model for the compounds under study
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