119,517 research outputs found
Screening in coupled low-dimensional systems: an effective polarizability picture
The screening of an individual low-dimensional object can be strongly
influenced by the objects nearby. We propose that such environment's influence
can be absorbed into an effective polarizability, instead of its intrinsic
polarizability. Using a toy system consists of two spatially separated 2DEG
layers gas an example, this picture is analytically deduced via a
multi-component RPA theoretical method. We show that the resultant effective
polarizability of backside layer is just the dielectric function describing the
system's collective plasmon excitations. Furthermore, several interesting
topics are discussed, e.g. the mutual modulation of Friedel oscillation, the
ultimate screening limit imposed by metal layer, smoothing potential
inhomogeneity in back screening configuration.Comment: 6 pages, 4 figure
Non-neutral charged two-dimension system and its quasihole structure
Most of our current knowledge on condensed matters contains a default
assumption: the matters are neutral charged. On the other hand, the
two-dimension(2D) vortex-Coulomb gas charge analogy is a very successful
theoretical tool in explaining superfluid, type-II superconductor and
fractional quantum Hall effect(FQHE), because the interaction among vortices
show similarity with 2D Coulomb potential. Here, by breaking the 'neutral
charged' assumption, we suggest the positively charged 2D semiconductor system
can possess non-trivial particle-like charge centers(called 'quasihole'), which
is the charge version of 'vortex'. Using the hypernetted-chain (HNC)
approximation, the structure of quasihole is elucidated. Numerical calculations
show that the quasihole can be projected onto another 2D layer, producing an
electric field configuration characterized by 3/2 topological charge.Comment: 6 pages, 3 figure
An artificial charge-density-wave conductor realized by double quantum wells
Charge-density-wave (CDW) is a modulation of the conduction electron density
in a conductor. Under low temperature, it can spontaneously happen in some
compounds that consist of anisotropic one-dimensional crystal structures, via a
strong electron-lattice interaction mechanism. Many celebrated phenomena, e.g.
non-linear transport, narrow-band noise, mode-locking5 and chaos under AC
voltage, etc., have been reported in CDW. However, evaluating the application
potential of CDW conductors has been hampered by the inconvenient shapes and
sizes of CDW single crystals. Although modern fabrication technology can partly
resolve those troubles, (for example, cleaved film and nanowire NbSe3 device),
the imperfections induced by fabrication that corrupt measured properties are
not easy to control and estimate. Here we demonstrate a convenient CDW
conductor fabricated by semiconductor double quantum wells (DQW) in a
field-effect transistor (FET) configuration: a modulated electron density in
one QW resulted from the charged QW nearby. The electric field dependent
depinning transport characteristic of CDW is clearly present. This "artificial"
CDW, capable of integrating with semiconductor industry, may give fresh impetus
to revive the interests in CDW
Empirical Study of the GARCH model with Rational Errors
We use the GARCH model with a fat-tailed error distribution described by a
rational function and apply it for the stock price data on the Tokyo Stock
Exchange. To determine the model parameters we perform the Bayesian inference
to the model. The Bayesian inference is implemented by the Metropolis-Hastings
algorithm with an adaptive multi-dimensional Student's t-proposal density. In
order to compare the model with the GARCH model with the standard normal errors
we calculate information criterions: AIC and DIC, and find that both criterions
favor the GARCH model with a rational error distribution. We also calculate the
accuracy of the volatility by using the realized volatility and find that a
good accuracy is obtained for the GARCH model with a rational error
distribution. Thus we conclude that the GARCH model with a rational error
distribution is superior to the GARCH model with the normal errors and it can
be used as an alternative GARCH model to those with other fat-tailed
distributions.Comment: 10 page
Box-Cox transformation of firm size data in statistical analysis
Firm size data usually do not show the normality that is often assumed in
statistical analysis such as regression analysis. In this study we focus on two
firm size data: the number of employees and sale. Those data deviate
considerably from a normal distribution. To improve the normality of those data
we transform them by the Box-Cox transformation with appropriate parameters.
The Box-Cox transformation parameters are determined so that the transformed
data best show the kurtosis of a normal distribution. It is found that the two
firm size data transformed by the Box-Cox transformation show strong linearity.
This indicates that the number of employees and sale have the similar property
as a firm size indicator. The Box-Cox parameters obtained for the firm size
data are found to be very close to zero. In this case the Box-Cox
transformations are approximately a log-transformation. This suggests that the
firm size data we used are approximately log-normal distributions.Comment: 4 pages, 9 figure
Inexact Shift-and-Invert Arnoldi for Toeplitz Matrix Exponential
We revisit the shift-and-invert Arnoldi method proposed in [S. Lee, H. Pang,
and H. Sun. {\it Shift-invert Arnoldi approximation to the Toeplitz matrix
exponential}, SIAM J. Sci. Comput., 32: 774--792, 2010] for numerical
approximation to the product of Toeplitz matrix exponential with a vector. In
this approach, one has to solve two large scale Toeplitz linear systems in
advance. However, if the desired accuracy is high, the cost will be
prohibitive. Therefore, it is interesting to investigate how to solve the
Toeplitz systems inexactly in this method. The contribution of this paper is in
three regards. First, we give a new stability analysis on the Gohberg-Semencul
formula (GSF) and define the GSF condition number of a Toeplitz matrix. It is
shown that, when the size of the Toeplitz matrix is large, our result is
sharper than the one given in [M. Gutknecht and M. Hochbruck. {\it The
stability of inversion formulas for Toeplitz matrices}, Linear Algebra Appl.,
223/224: 307--324, 1995]. Second, we establish a relation between the error of
Toeplitz systems and the residual of Toeplitz matrix exponential. We show that
if the GSF condition number of the Toeplitz matrix is medium sized, then the
Toeplitz systems can be solved in a low accuracy. Third, based on this
relationship, we present a practical stopping criterion for relaxing the
accuracy of the Toeplitz systems, and propose an inexact shift-and-invert
Arnoldi algorithm for the Toeplitz matrix exponential problem. Numerical
experiments illustrate the numerical behavior of the new algorithm, and show
the effectiveness of our theoretical results.Comment: 17 page
Study for (anti)hypertriton and light (anti)nuclei production in high energy collisions at = 200 GeV
We used the parton and hadron cascade (PACIAE) model and the dynamically
constrained phase-space coalescence (DCPC) model to investigate the production
of (anti)hypertriton and light (anti)nuclei generated by 0-10% centrality
12C+12C, 24Mg+24Mg, 40Ca+40Ca and 64Cu+64Cu collisions at
= 200 GeV with |y| < 1.5 and pT < 5. We studied the yield ratios of
antiparticle to particle and the rapidity distributions of the different
(anti)nuclei, and found that the amount of antimatter produced is significantly
lower than that of the corresponding particles, the results of theoretical
model are well consistent with PHOBOS data. The yield ratios of the particle to
antiparticle in different transverse momentum region is also given, and we
found the ratios is increased with the increase of the transverse momentum.Comment: 7pages, 3figures. arXiv admin note: text overlap with arXiv:1209.418
Green's function relativistic mean field theory for hypernuclei
The relativistic mean-field theory with Green's function method is extended
to study hypernuclei. Taking hypernucleus Ca as an
example, the single-particle resonant states for hyperons are
investigated by analyzing density of states and the corresponding energies and
widths are given. Different behaviors are observed for the resonant states,
i.e., the distributions of the very narrow and states are
very similar as bound states while that of the wide and
states are like scattering states. Besides, the impurity effect of
hyperons on the single-neutron resonant states are investigated. For most of
the resonant states, both the energies and widths decrease with adding more
hyperons due to the attractive interaction. Finally, the
energy level structure of hyperons in the Ca hypernucleus isotopes
with mass number are studied, obvious shell structure and small
spin-orbit splitting are found for the single- spectrum.Comment: 10pages, 6 figures,2 table
Combinatorics of the Springer correspondence for classical Lie algebras and their duals in characteristic 2
We give a combinatorial description of the Springer correspondence for
classical Lie algebras of type or and their duals
in characteristic 2. The combinatorics used here is of the
same kind as those appearing in the description of (generalized) Springer
correspondence for unipotent case of classical groups by Lusztig in odd
characteristic and by Lusztig and Spaltentstein in characteristic 2. It is very
nice that this combinatorics gives a unified description for (generalized)
Springer correspondences of classical groups in all cases, namely, in ,
and in all characteristics. Moreover, it gives
rise to close formulas for computing the correspondences.Comment: 30 page
A Probit Network Model with Arbitrary Dependence
In this paper, we adopt a latent variable method to formulate a network model
with arbitrarily dependent structure. We assume that the latent variables
follow a multivariate normal distribution and a link between two nodes forms if
the sum of the corresponding node parameters exceeds the latent variable. The
dependent structure among edges is induced by the covariance matrix of the
latent variables. The marginal distribution of an edge is a probit function. We
refer this model to as the \emph{Probit Network Model}. We show that the moment
estimator of the node parameter is consistent. To the best of our knowledge,
this is the first time to derive consistency result in a single observed
network with globally dependent structures. We extend the model to allow node
covariate information.Comment: 16 page
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