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$_1$ and F$_2$) 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$_1$ and F$_2$. The formula is applied to study both zero bias conductance and finite bias current. The current conducted by crossed AR involving F$_1$, F$_2$ and S is particularly unusual, in which an electron with spin $\sigma$ incident from one of the ferromagnets picks up another electron with spin $\bar{\sigma}$ 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