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Search Results: 1 - 10 of 248602 matches for " Q. P. Xu "
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A Bjorken sum rule for semileptonic $Ω_b$ decays to ground and excited charmed baryon states
Q. P. Xu
Physics , 1993, DOI: 10.1103/PhysRevD.48.5429
Abstract: We derive a Bjorken sum rule for semileptonic $\Omega_b$ decays to ground and low-lying negative-parity excited charmed baryon states, in the heavy quark limit. We discuss the restriction from this sum rule on form factors and compare it with some models.
Spin Hall effect and zitterbewegung in an electron waveguide
P. Brusheim,H. Q. Xu
Physics , 2005, DOI: 10.1103/PhysRevB.74.205307
Abstract: We study spin-resolved probability distributions for electrons in a multichannel waveguide in the presence of a spin-orbit interaction. For a spin-polarized electron injection, a zitterbewegung pattern is predicted in the probability distribution of electrons in the waveguide. For a spin-unpolarized injection, the spin-resolved electron probability in the waveguide shows spin accumulations. In addition to the spin Hall phenomenon, namely accumulations of opposite spins at the lateral edges of the waveguide, we predict the existence of a regular stripe pattern of spin accumulations in the internal region of the waveguide. We show that the predicted zitterbewegung and spin Hall effect stem from the same mechanism and are formed from coherent states of electrons in the waveguide.
Catching the zitterbewegung
P. Brusheim,H. Q. Xu
Physics , 2008,
Abstract: We demonstrate how the zitterbewegung charge oscillations can be detected through a charge conductance measurement in a three-terminal junction. By tuning the spin-orbit interaction strength or an external magnetic field the zitterbewegung period can be modulated, translating into complementary conductance oscillations in the two outgoing leads of the junction. The proposed experimental setup is within the reach of demonstrated technology and material parameters, and enables the observation of the so far elusive zitterbewegung phenomenon.
Strong and Radiative $D^\ast$ Decays
Patrick J. O'Donnell,Q. P. Xu
Physics , 1994, DOI: 10.1016/0370-2693(94)00975-9
Abstract: We use the relativistic light--front quark model to show that both strong and radiative $D^\ast$ decays are in good agreement with the 1992 CLEO II results. In particular the coupling for $D^{\ast}\ra D \pi$ is consistent with the experimental upper limit. The key point is the relativistic treatment of the quark spin.
Chiral symmetry and many-body nonleptonic decays of heavy hadrons
Q. P. Xu,A. N. Kamal
Physics , 1993,
Abstract: We suggest that, similar to the many applications of chiral effective Lagrangian made recently to semileptonic decays of heavy hadrons involving Goldstone bosons, chiral symmetry can also be applied to many-body nonleptonic decays of heavy hadrons. As examples we establish the chiral effective Hamiltonian for some typical many-body nonleptonic decays of bottom hadrons. We discuss the lowest-order contributions coming from such a Hamiltonian. We emphasize that wide applications of this method are possible.
Semileptonic and Exclusive Rare B Decays
Patrick J. O'Donnell,Q. P. Xu
Physics , 1994, DOI: 10.1016/0370-2693(94)90095-7
Abstract: The exclusive rare decay $B \ra K^\ast \gamma$ takes place in a region of maximum recoil, $q^{2}=0$, posing a problem for nonrelativistic quark models which are usually thought to be most reliable at zero recoil. The Bauer--Stech--Wirbel (BSW) model, formulated in the infinite--momentum--frame (IMF) formalism, is designed to work at $q^2=0$. We show in this model that the ratio relating the decay $B \ra K^\ast \gamma$ and the $q^2$--spectrum of the semileptonic decay $B\ra \rho e {\bar \nu}$, becomes independent of the wave function in the SU(3) flavor symmetry limit. We show that this feature is also true in relativistic quark models formulated in the IMF or light--cone formalism, if the $b$ quark is infinitely heavy. In fact, these relativistic models, which have a different spin structure from the BSW case, reduce to the BSW model in the heavy $b$--quark limit. A direct measurement of the $q^2$--spectrum of the semileptonic decay can therefore provide accurate information for the exclusive rare decay.
Chiral symmetry and many-body nonleptonic decays of bottom hadrons
Q. P. Xu,A. N. Kamal
Physics , 1993,
Abstract: Chiral symmetry can be applied to many-body nonleptonic decays of heavy hadrons. We establish the chiral effective Hamiltonian for some typical many-body nonleptonic decays of bottom hadrons. We discuss the lowest-order contributions coming from such a Hamiltonian and present, as an example, a calculation of decay distributions of $B^-\to D^+ D^-_s \pi^-$ and $B^-\to D^{\ast +} D^-_s \pi^-$. We emphasize that wide applications of this method are possible.
Supercurrent and multiple Andreev reflections in an InSb nanowire Josephson junction
H. A. Nilsson,P. Samuelsson,P. Caroff,H. Q. Xu
Physics , 2012, DOI: 10.1021/nl203380w
Abstract: Epitaxially grown, high quality semiconductor InSb nanowires are emerging material systems for the development of high performance nanoelectronics and quantum information processing and communication devices, and for the studies of new physical phenomena in solid state systems. Here, we report on measurements of a superconductor-normal conductor-superconductor junction device fabricated from an InSb nanowire with aluminum based superconducting contacts. The measurements show a proximity induced supercurrent flowing through the InSb nanowire segment, with a critical current tunable by a gate, in the current bias configuration and multiple Andreev reflection characteristics in the voltage bias configuration. The temperature dependence and the magnetic field dependence of the critical current and the multiple Andreev reflection characteristics of the junction are also studied. Furthermore, we extract the excess current from the measurements and study its temperature and magnetic field dependences. The successful observation of the superconductivity in the InSb nanowire based Josephson junction device indicates that InSb nanowires provide an excellent material system for creating and observing novel physical phenomena such as Majorana fermions in solid state systems.
The Control of a Beamline Over Intranet
X. J. Yu,Q. P. Wang,P. S. Xu
Computer Science , 2001,
Abstract: The machines and beamlines controlled by VME industrial networks are very popular in accelerator faculties. Recently new software technology, among of which are Internet/Intranet application, Java language, and distributed calculating environment, changes the control manner rapidly. A program based on DCOM is composed to control of a variable included angle spherical grating monochromator beamline at National Synchrotron Radiation Laboratory (NSRL) in China. The control computer with a residential DCOM program is connected to Intranet by LAN, over which the user-end-operating program located in another computer sends driving beamline units' commands to the control computer. And also a web page coded in Java, published by the WWW service running in the control computer, is simply illustrated how to use web browser to query the states of or to control the beamline units.
Lande-like formula for the g factors of hole-nanowire subband edges
D. Csontos,U. Zülicke,P. Brusheim,H. Q. Xu
Physics , 2008, DOI: 10.1103/PhysRevB.78.033307
Abstract: We have analyzed theoretically the Zeeman splitting of hole-quantum-wire subband edges. As is typical for any bound state, their g factor depends on both an intrinsic g factor of the material and an additional contribution arising from a finite bound-state orbital angular momentum. We discuss the quantum-confinement-induced interplay between bulk-material and orbital effects, which is nontrivial due to the presence of strong spin-orbit coupling. A compact analytical formula is provided that elucidates this interplay and can be useful for predicting Zeeman splitting in generic hole-wire geometries.
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