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971.
C. Benjamin T. Jonckheere A. Zazunov T. Martin 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(3):279-289
We consider a model for a single molecule with a large frozen spin
sandwiched in between two BCS superconductors at equilibrium, and
show that this system has a π junction behavior at low
temperature. The π shift can be reversed by varying the other
parameters of the system, e.g., temperature or the position of the
quantum dot level, implying a controllable π junction with
novel application as a Josephson current switch. We show that the mechanism
leading to the π shift can be explained simply in terms of the contributions
of the Andreev bound states and of the continuum of states above the superconducting gap.
The free energy for certain configuration of parameters shows a
bistable nature, which is a necessary pre-condition for
achievement of a qubit. 相似文献
972.
H.-K. Zhao Q. Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(4):419-427
We have investigated the spectral density of shot noise for the
system of a quantum dot (QD) coupled to two single-wall carbon
nanotube terminals irradiated with a microwave field on the QD. The
terminal features are involved in the shot noise through modifying
the self-energy of QD. The contributions of carbon nanotube
terminals to the shot noise exhibit obvious behaviors. The novel
side peaks are associated with the photon absorption and emission
procedure accompanying the suppression of shot noise. The shot noise
in balanced absorption belongs to sub-Poissonian, and it is
symmetric with respect to the gate voltage. The differential shot
noise displays intimate relation with the nature of carbon nanotubes
and the applied microwave field. It exhibits asymmetric behavior
for the unbalanced absorption case versus gate voltage. The Fano
factor of the system exhibits the deviation of shot noise from the
Schottky formula, and the structures of terminals obviously
contribute to it. The super-Poissonian and sub-Poissonian shot noise
can be achieved in the unbalanced absorption in different regime of
source-drain bias. 相似文献
973.
S. Duhot R. Mélin 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):289-296
A Cooper pair from a s-wave superconductor (S) entering a conventional charge density wave (CDW) below the Peierls gap dephases
on the Fermi wavelength while one particle states are localized on the CDW coherence length ξCDW. It is thus practically impossible to observe a Josephson current through a CDW. The paths following different sequences
of impurities interfere destructively, due to the different electron and hole densities in the CDW. The same conclusion holds
for averaging over the conduction channels in the ballistic system. We apply two microscopic approaches to this phenomenon:
(i) a Blonder, Tinkham, Klapwijk (BTK) approach for a single highly transparent S-CDW interface; and (ii) the Hamiltonian
approach for the Josephson effect in a clean CDW and a CDW with non magnetic disorder. The Josephson effect through a spin
density wave (SDW) is limited by the coherence length ξSDW, not by the Fermi wave-length. A Josephson current through a SDW might be observed in a structure with contacts on a SDW
separated by a distance ξSDW. 相似文献
974.
Sub Hur Hodeok Jang Yonghoon Kim Hanlim Lee Seongtaek Hwang Yunje Oh Y. J. Sung Y. S. Kim Jichai Jeong 《Optical and Quantum Electronics》2007,39(7):561-569
We investigate the performance limits of a pico-cell system using the radio- over-fiber technique with an electroabsorption
modulator (EAM) in a 2.4 GHz wireless local area network (WLAN) environment. To understand the performance limits of the system
using an EAM as the optical transceiver, we vary the optical modulation index (OMI) of the transmitter for different bias
voltages to the EAM. Power margins in the links are found to estimate a possible service range, and packet loss rates (PLRs)
in the pico-cell system are measured to evaluate the transmission performance. The total service range can be extended up
to 3 m by adjusting the OMI of the transmitter for different applied bias voltages to the EAM. 相似文献
975.
M. Ludwig P. Abell 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(1):97-105
Social networks in communities, markets, and societies self-organise through the interactions of many individuals. In this
paper we use a well-known
mechanism of social interactions — the balance of sentiment in triadic
relations — to describe the development of social networks. Our model
contrasts with many existing network models, in that people not only
establish but also break up relations whilst the network evolves. The
procedure generates several interesting network features such as a variety
of degree distributions and degree correlations. The resulting network
converges under certain conditions to a steady critical state where temporal
disruptions in triangles follow a power-law distribution. 相似文献
976.
The paper discusses the basic design of the critical facility, whose main purpose is the physics validation of AHWR. Apart
from moderator level control, the facility will have shutdown systems based on shutoff rods and multiple ranges of neutron
detection systems. In addition, it will have a flux mapping system based on 25 fission chambers, distributed in the core.
We are planning to use this reactor for experiments with a suitable source to simulate an ADS system. Any desired sub-criticality
can be achieved by adjusting the moderator level. Apart from perfecting our experimental techniques, in simple configurations,
we intend to study the one-way coupled core in this facility. Preliminary calculations, employing a Monte Carlo code TRIPOLI,
are presented.
相似文献
977.
A. B. Shapoval M. G. Shnirman 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(3):399-403
This paper considers a one-parameter family of sand-piles.
The family exhibits the crossover
between the models with deterministic and stochastic relaxation.
The mean pile height is used to describe the crossover.
The height densities corresponding to the models with relaxation
of both types approach one another as the parameter increases.
Relaxation is supposed to deal
with the local losses of grains by a fixed amount.
In that case the densities show a step-like behaviour
in contrast to the peaked shape
found in the models with the local loss of grains down
to a fixed level
[S. Lübeck, Phys. Rev. E 62, 6149 (2000)].
A spectral approach based on the long-run properties of the pile height
considers the models with deterministic and random relaxation
more accurately and
distinguishes between the two cases for admissible parameter values. 相似文献
978.
979.
提出了一种基于聚类的选择性支持向量机集成预测模型.为提高支持向量机集成的泛化能力,采用自组织映射和K均值聚类算法结合的聚类组合算法,从每簇中选择出精度最高的子支持向量机进行集成,可以保证子支持向量机有较高精度并提高了子支持向量机之间的差异度.该方法能以较小的代价显著提高支持向量机集成的泛化能力.采用该方法对Mackey-Glass混沌时间序列和Lorenz系统生成的混沌时间序列进行预测实验,结果表明可以对混沌时间序列进行准确预测,验证了该方法的有效性.
关键词:
支持向量机
集成
混沌时间序列
聚类 相似文献
980.
文章全面、系统地介绍了近藤效应、近藤问题、近藤共振现象的起源和研究历史的发展过程,提供了一个清晰而准确的近藤物理问题的图像.同时,文章还讨论了近年来近藤共振现象在各种低维电子关联系统中的实现. 相似文献