3,095 research outputs found
Polytypism and Unexpected Strong Interlayer Coupling of two-Dimensional Layered ReS2
The anisotropic two-dimensional (2D) van der Waals (vdW) layered materials,
with both scientific interest and potential application, have one more
dimension to tune the properties than the isotropic 2D materials. The
interlayer vdW coupling determines the properties of 2D multi-layer materials
by varying stacking orders. As an important representative anisotropic 2D
materials, multilayer rhenium disulfide (ReS2) was expected to be random
stacking and lack of interlayer coupling. Here, we demonstrate two stable
stacking orders (aa and a-b) of N layer (NL, N>1) ReS2 from ultralow-frequency
and high-frequency Raman spectroscopy, photoluminescence spectroscopy and
first-principles density functional theory calculation. Two interlayer shear
modes are observed in aa-stacked NL-ReS2 while only one interlayer shear mode
appears in a-b-stacked NL-ReS2, suggesting anisotropic-like and isotropic-like
stacking orders in aa- and a-b-stacked NL-ReS2, respectively. The frequency of
the interlayer shear and breathing modes reveals unexpected strong interlayer
coupling in aa- and a-b-NL-ReS2, the force constants of which are 55-90% to
those of multilayer MoS2. The observation of strong interlayer coupling and
polytypism in multi-layer ReS2 stimulate future studies on the structure,
electronic and optical properties of other 2D anisotropic materials
Zero differential resistance state of two dimensional electron systems in strong magnetic fields
Zero differential resistance state is found in response to direct current
applied to 2D electron systems at strong magnetic field and low temperatures.
Transition to the state is accompanied by sharp dip of negative differential
resistance, which occurs above threshold value of the direct current.
The state depends significantly on the temperature and is not observable above
several Kelvins. Additional analysis shows lack of the linear stability of the
2D electron systems at and inhomogeneous, non-stationary pattern of
the electric current in the zero differential resistance state. We suggest that
the dc bias induced redistribution of the 2D electrons in energy space is the
dominant mechanism leading to the new electron state.Comment: 5 pages, 3 figure
Modeling Multi-wavelength Pulse Profiles of Millisecond Pulsar PSR B1821-24
PSR B182124 is a solitary millisecond pulsar (MSP) which radiates
multi-wavelength pulsed photons. It has complex radio, X-ray and -ray
pulse profiles with distinct peak phase-separations that challenge the
traditional caustic emission models. Using the single-pole annular gap model
with suitable magnetic inclination angle () and viewing angle
(), we managed to reproduce its pulse profiles of three
wavebands. It is found that the middle radio peak is originated from the core
gap region at high altitudes, and the other two radio peaks are originated from
the annular gap region at relatively low altitudes. Two peaks of both X-ray and
-ray wavebands are fundamentally originated from annular gap region,
while the -ray emission generated from the core gap region contributes
somewhat to the first -ray peak. Precisely reproducing the
multi-wavelength pulse profiles of PSR B182124 enables us to understand
emission regions of distinct wavebands and justify pulsar emission models.Comment: Accepted for publication in Ap
Influence of nonideal voltage measurement on parameter estimation in permanent-magnet synchronous machines
This paper investigates the influence of nonideal voltage measurements on the parameter estimation of permanentmagnet synchronous machines (PMSMs). The influence of nonideal voltage measurements, such as the dc bus voltage drop, zero shift in the amplifier, and voltage source inverter nonlinearities, on the estimation of different machine parameters is investigated by theoretical and experimental analysis. For analysis, a model-reference-adaptive-system-based estimator is first described for the parameter estimation of the q-axis inductance, stator winding resistance, and rotor flux linkage. The estimator is then applied to a prototype surface-mounted PMSM to investigate the influence of nonideal voltage measurement on the estimation of various machine parameter values. It shows that, at low speed, the inverter nonlinearity compensation has significant influence on both the rotor flux linkage and winding resistance estimations while, at high speed, it has significant influence only on the winding resistance estimation and has negligible influence on the rotor flux linkage estimation. In addition, the inverter nonlinearity compensation will not influence the q-axis inductance estimation when it is under id = 0 control. However, the dc bus voltage drop due to the load variation and zero shift in the amplifier will significantly influence the q-axis inductance estimation. © 2011 IEEE
NMDA Receptors of Gastric-Projecting Neurons in the Dorsal Motor Nucleus of the Vagus Mediate the Regulation of Gastric Emptying by EA at Weishu (BL21)
A large number of studies have been conducted to explore the efficacy of electroacupuncture (EA) for the treatment of gastrointestinal motility. While several lines of evidence addressed the basic mechanism of EA on gastrointestinal motility regarding effects of limb and abdomen points, the mechanism for effects of the back points on gastric motility still remains unclear. Here we report that the NMDA receptor (NMDAR) antagonist kynurenic acid inhibited the gastric emptying increase induced by high-intensity EA at BL21 and agonist NMDA enhanced the effect of the same treatment. EA at BL21 enhanced NMDAR, but not AMPA receptor (AMPAR) component of miniature excitatory postsynaptic current (mEPSC) in gastric-projecting neurons of the dorsal motor nucleus of the vagus (DMV). In sum, our data demonstrate an important role of NMDAR-mediated synaptic transmission of gastric-projecting DMV neurons in mediating EA at BL21-induced enhancement of gastric emptying
A Visualization method for machine translation evaluation results
PACLIC 20 / Wuhan, China / 1-3 November, 200
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