1,281 research outputs found
Nonequilibrium transport through a quantum dot weakly coupled to Luttinger liquids
We study the nonequlibrium transport through a quantum dot weakly coupled to
Luttinger liquids (LL). A general current expression is derived by using
nonequilibrium Green function method. Then a special case of the dot with only
a single energy level is discussed. As a function of the dot's energy level, we
find that the current as well as differential conductance is strongly
renormalized by the interaction in the LL leads. In comparison with the system
with Fermi liquid (FL) leads, the current is suppressed, consistent with the
suppression of the electron tunneling density of states of the LL; and the
outset of the resonant tunneling is shifted to higher bias voltages. Besides,
the linear conductance obtained by Furusaki using master equation can be
reproduced from our result.Comment: 8 pages, 3 figures, Late
Analytical result on the supercurrent through a superconductor/quantum-dot/superconductor junction
We present an analytical result for the supercurrent across a
superconductor/quantum-dot/superconductor junction. By converting the current
integration into a special contour integral, we can express the current as a
sum of the residues of poles. These poles are real and give a natural
definition of the Andreev bound states. We also use the exact result to explain
some features of the supercurrent transport behavior.Comment: 8 pages, 2 figure
Study and analysis of value stream for Yesco production
This research addresses the application of lean manufacturing concepts to the make-to-order production process sector with a focus on the entertainment sign industry. The goal of this research is to investigate the production: process of Young Electric Sign Company (YESCO) and develop a current state value stream map for different work orders from the time the work order is distributed by the department of layout to the time the finished product is ready to crate. Also, we will analyze production sequences, cycle time, labor time, lead-time and down time for each step of the production process. After the analysis, a more efficient and future state value stream map will be developed by eliminating the non value-added activities and suggestions and recommendations for better manufacturing strategy will be proposed
Andreev reflection through a quantum dot coupled with two ferromagnets and a superconductor
We study the Andreev reflection (AR) in a three terminal mesoscopic hybrid
system, in which two ferromagnets (F and F) are coupled to a
superconductor (S) through a quantum dot (QD). By using non-equilibrium Green
function, we derive a general current formula which allows arbitrary spin
polarizations, magnetization orientations and bias voltages in F and F.
The formula is applied to study both zero bias conductance and finite bias
current. The current conducted by crossed AR involving F, F and S is
particularly unusual, in which an electron with spin incident from
one of the ferromagnets picks up another electron with spin from
the other one, both enter S and form a Cooper pair. Several special cases are
investigated to reveal the properties of AR in this system.Comment: 15 pages, 7 figures, LaTe
Probing Spin States of Coupled Quantum Dots by dc Josephson Current
We propose an idea for probing spin states of two coupled quantum dots (CQD),
by the dc Josephson current flowing through them. This theory requires weak
coupling between CQD and electrodes, but allows arbitrary inter-dot tunnel
coupling, intra- and inter- dot Coulomb interactions. We find that the Coulomb
blockade peaks exhibit a non-monotonous dependence on the Zeeman splitting of
CQD, which can be understood in terms of the Andreev bound states. More
importantly, the supercurrent in the Coulomb blockade valleys may provide the
information of the spin states of CQD: for CQD with total electron number N=1,3
(odd), the supercurrent will reverse its sign if CQD becomes a magnetic
molecule; for CQD with N=2 (even), the supercurrent will decrease sharply
around the transition between the spin singlet and triplet ground states of
CQD.Comment: 10 pages, 3 figure
Theory of Nonequilibrium Coherent Transport through an Interacting Mesoscopic Region Weakly Coupled to Electrodes
We develop a theory for the nonequilibrium coherent transport through a
mesoscopic region, based on the nonequilibrium Green function technique. The
theory requires the weak coupling between the central mesoscopic region and the
multiple electrodes connected to it, but allows arbitrary hopping and
interaction in the central region. An equation determining the nonequilibrium
distribution in the central interacting region is derived and plays an
important role in the theory. The theory is applied to two special cases for
demonstrations, revealing the novel effects associated with the combination of
phase coherence, Coulomb interaction, and nonequilibrium distribution.Comment: 10 Pages, 5 figure
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