3,606 research outputs found
Persistent spin current in a spin-orbit coupling/normal hybrid ring
We investigate the equilibrium property of a mesoscopic ring with spin orbit
(SO) interaction. It is well known that for a normal mesoscopic ring threaded
by a magnetic flux, the electron acquires a Berry phase that induces the
persistent (charge) current. Similarly, the spin of electron acquires a spin
Berry phase traversing the ring with SO interaction. It is this spin Berry
phase that induces a persistent spin current. To demonstrate its existence, we
calculate the persistent spin current without accompanying charge current in
the normal region in a hybrid mesoscopic ring. We point out that this
persistent spin current describes the real spin motion and can be observed
experimentally.Comment: 4 pages, 3 figure
Split Bregman Method for Sparse Inverse Covariance Estimation with Matrix Iteration Acceleration
We consider the problem of estimating the inverse covariance matrix by
maximizing the likelihood function with a penalty added to encourage the
sparsity of the resulting matrix. We propose a new approach based on the split
Bregman method to solve the regularized maximum likelihood estimation problem.
We show that our method is significantly faster than the widely used graphical
lasso method, which is based on blockwise coordinate descent, on both
artificial and real-world data. More importantly, different from the graphical
lasso, the split Bregman based method is much more general, and can be applied
to a class of regularization terms other than the nor
Transcriptome and proteome profiling of adventitious root development in hybrid larch (Larix kaempferi × Larix olgensis)
Research on Injected Effect and Heat-transfer Characteristics of Narrow-Slit Injection Orifice Used for the Screw Compressor
A narrow-slit injection orifice which is used for the screw compressor injection is described in this paper. Different from the traditional injection orifice, the orifice is slit shaped but not circular. Liquid which is injected by the narrow-slit injection orifice appears as a curtain shape so that the heat transfer area is increased. The cooling effect is enhanced and then the efficiency of the compressor is improved. The injected velocity of the orifice is simulated through the CFD software, and then the experiments are carried out. The study verified the accuracy of the simulation results. It will provide a theoretical foundation for the design of the narrow-slit injection orifice used for the screw compressor
(meso-5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane)copper(II) bis(O,S-dibenzyl dithiophosphate)
In the crystal structure of the title compound, [Cu(C16H36N4)](C14H14O2PS2)2, the CuII atom is located on an inversion center and is chelated by four N atoms of the macrocyclic meso-5,5,7,12,12,14- hexamethyl-1,4,8,11-tetraazacyclotetradecane ligand in a square-planar geometry, with Cu—N distances of 2.013 (3) and 2.014 (3) Å. In the crystal structure, one O,S-dibenzyl dithiophosphate counter-anion links with the CuII complex cation through N—H⋯O and N—H⋯S hydrogen bonding. During the synthesis, the structure of the anion re-arranged from O,O′-dibenzyl dithiophosphate in the starting material to O,S-dibenzyl dithiophosphate in the title compound
Persistent spin current in nano-devices and definition of the spin current
We investigate two closely related subjects: (i) existence of a pure
persistent spin current in semiconducting mesoscopic device with a spin-orbit
interaction's (SOI), and (ii) the definition of the spin current in the
presence of SOI. Through physical argument from four physical pictures in
different aspects, we provide strong evidences that the persistent spin current
does exist in a device with SOI in the absence of any magnetic materials. This
persistent spin current is an analog of the persistent charge current in a
mesoscopic ring threaded by a magnetic flux, and it describes the real spin
motion and can be measured experimentally. We then investigate the definition
of the spin current. We point out that (i) the non-zero spin current in the
equilibrium SOI device is the persistent spin current, (ii) the spin current is
in general not conserved, and (iii) the Onsager relation is violated for the
spin transport no matter what definition of the spin current is used. These
issues, the non-zero spin current in the equilibrium case, the non-conserved
spin current, and the violation of the Onsager relation, are intrinsic
properties of spin transport. We note that the conventional definition of the
spin current has very clear physical intuition and describes the spin motion
very well. Therefore we feel that the conventional definition of the spin
current makes physical sense and there is no need to modify it. In addition,
the relationship between the persistent spin current and transport spin
current, the persistent linear and angular spin currents in the SOI region of
the hybrid ring, are discussed. Finally, we show that if the spin-spin
interaction is included into the Hamiltonian, the persistent spin current is
automatically conserved using the conventional definition.Comment: 20 pages, 18 figures, the long version of Phys. Rev. Lett. 98, 196801
(2007
- …