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Search Results: 1 - 10 of 106441 matches for " Xiang-Song Chen "
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Quantized electron transport by interference-induced quantum dots of two cross-travelling surface acoustic waves
Xiang-Song Chen
Physics , 2006,
Abstract: In traditional approaches of obtaining quantized acoustoelectric current, a narrow channel is fabricated to form quantum dots, which hold a fixed number of electrons at a certain depth. We propose a natural way of forming quantum dots without the narrow channel, by the interference of two surface acoustic waves (SAWs) propagating across each other. A wide transportation area is defined by the usual (but widely separated) split-gate structure with another independent gate in between. This design can increase the quantized current by one to two orders of magnitude. The three-gate structure also allows separate control of the barrier height and the side-gate pinch-off voltage, thus avoids current leakage through the area beneath the side gates.
Inertial mass = gravitational mass, what about momentum?
Xiang-Song Chen
Physics , 2012,
Abstract: It has been tested precisely that the inertial and gravitational masses are equal. Here we reveal that the inertial and gravitational momenta may differ. More generally, the inertial and gravitational energy-momentum tensors may not coincide: Einstein's general relativity requires the gravitational energy-momentum tensor to be symmetric, but we show that a symmetric inertial energy-momentum tensor would ruin the concordance between conservations of quantized energy and charge. The nonsymmetric feature of the inertial energy-momentum tensor can be verified unambiguously by measuring the transverse flux of a collimated spin-polarized electron beam, and leads to a serious implication that the equivalence principle and Einstein's gravitational theory cannot be both exact.
Reverse the force direction at long distance by a running coupling
Xiang-Song Chen
Physics , 2005,
Abstract: We reveal that a suitable running coupling $\alpha(q^2)$ can reverse the direction of the one-particle-exchange (OPE) force at long distance if (and under general assumptions, only if) the exchanged particle has a mass $m$, either intrinsic or effective. The essential requirement on $\alpha(q^2)$ is an extrapolating restriction $\alpha (-m^2)<0$. The running of $\alpha(q^2)$ can be from either renormalization-group evolution or certain derivatives in the Lagrangian. Reversal of the OPE force direction at long distance (namely, attraction transits to repulsion, or vice versa) may have important implications for gravity and cosmic acceleration, particle and nuclear physics, and also condensed matter properties such as superconductivity.
Gauge invariance and hadron structure
Xiang-Song Chen,Fan Wang
Physics , 1998,
Abstract: We prove that the {\em gauge dependent} gluon spin, gluon and quark orbital angular momenta operators have {\em gauge invariant} expectation values on hadron states with {\em definite} momentum and polarization, therefore the conventional decomposition of nucleon spin into contributions from the spin and orbital angular momentum of quark and gluon is {\em gauge independent}. Similar conclusions apply to the {\em gauge dependent} quark momentum and kinetic energy operators, and accordingly nucleon momentum and mass structures.
On the quantization accuracy of the acoustoelectric current
Xiang-Bai Chen,Xiang-Song Chen,Jie Gao
Physics , 2008, DOI: 10.1016/j.ssc.2009.09.045
Abstract: By deriving analytical formulae for the quantization accuracy of the acoustoelectric current, we reveal that: 1) the flatness of the current plateau for the typical present devices has reached the theoretical limit of about 100ppm over a 1/1000 change of the gate voltage; 2) increasing the transport channel length, and counterintuitively, increasing the acoustic wavelength as well, would improve the quantization accuracy, and very promisingly up to 0.01ppm as required for a quantum current standard.
Energy-momentum tensor is nonsymmetric for spin-polarized photons
Xiang-Bai Chen,Xiang-Song Chen
Physics , 2012,
Abstract: It has been assumed for a century that the energy-momentum tensor of the photon takes a symmetric form, with the renowned Poynting vector assigned as the same density for momentum and energy flow. Here we show that the symmetry of the photon energy-momentum tensor can actually be inferred from the known difference between the diffraction patterns of light with spin and orbital angular momentum, respectively. The conclusion is that the symmetric expression of energy-momentum tensor is denied, and the nonsymmetric canonical expression is favored.
Some Problems in Defining Functional Integration over the Gauge Group
Wei-Min Sun,Xiang-Song Chen,Fan Wang
Physics , 2000,
Abstract: We find that sometimes the usual definition of functional integration over the gauge group through limiting process may have internal difficulties.
A Note on Functional Integral over the Local Gauge Group
Wei-Min Sun,Xiang-Song Chen,Fan Wang
Physics , 2001,
Abstract: We evaluated some particular type of functional integral over the local gauge group C^{\infty}({\bf R}^n, U(1)) by going to a discretized lattice. The results explicitly violates the property of the Haar measure. We also analysed the Faddeev-Popov method through a toy example. The results also violates the property of the Haar measure.
A simple proof that $C^{\infty}({\bf R}^n,U(1))$ does not have a Haar measure
Wei-Min Sun,Xiang-Song Chen,Fan Wang
Physics , 2001,
Abstract: We give a simple proof that there does not exist a Haar measure on the group $C^{\infty}({\bf R}^n,U(1))$.
Spin content of the nucleon in a valence and sea quark mixing model
Di Qing,Xiang-Song Chen,Fan Wang
Physics , 1997, DOI: 10.1103/PhysRevC.57.31
Abstract: A dynamical valence and sea quark mixing model is shown to fit the baryon ground state properties as well as the spin content of the nucleon. The relativistic correction and the $q^3{\leftrightarrow} q^3q\bar{q}$ transition terms induced by the quark axial vector current $\bar{\psi}\vec{\gamma}\gamma^5\psi$ in this model space is responsible for the quark spin reduction.
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