542 research outputs found
The Pfaffian solution of a dimer-monomer problem: Single monomer on the boundary
We consider the dimer-monomer problem for the rectangular lattice. By mapping
the problem into one of close-packed dimers on an extended lattice, we rederive
the Tzeng-Wu solution for a single monomer on the boundary by evaluating a
Pfaffian. We also clarify the mathematical content of the Tzeng-Wu solution by
identifying it as the product of the nonzero eigenvalues of the Kasteleyn
matrix.Comment: 4 Pages to appear in the Physical Review E (2006
Factor PD-Clustering
Factorial clustering methods have been developed in recent years thanks to
the improving of computational power. These methods perform a linear
transformation of data and a clustering on transformed data optimizing a common
criterion. Factorial PD-clustering is based on Probabilistic Distance
clustering (PD-clustering). PD-clustering is an iterative, distribution free,
probabilistic, clustering method. Factor PD-clustering make a linear
transformation of original variables into a reduced number of orthogonal ones
using a common criterion with PD-Clustering. It is demonstrated that Tucker 3
decomposition allows to obtain this transformation. Factor PD-clustering makes
alternatively a Tucker 3 decomposition and a PD-clustering on transformed data
until convergence. This method could significantly improve the algorithm
performance and allows to work with large dataset, to improve the stability and
the robustness of the method
Optimal synchronization of directed complex networks
We study optimal synchronization of networks of coupled phase oscillators. We
extend previous theory for optimizing the synchronization properties of
undirected networks to the important case of directed networks. We derive a
generalized synchrony alignment function that encodes the interplay between
network structure and the oscillators' natural frequencies and serves as an
objective measure for the network's degree of synchronization. Using the
generalized synchrony alignment function, we show that a network's
synchronization properties can be systematically optimized. This framework also
allows us to study the properties of synchrony-optimized networks, and in
particular, investigate the role of directed network properties such as nodal
in- and out-degrees. For instance, we find that in optimally rewired networks
the heterogeneity of the in-degree distribution roughly matches the
heterogeneity of the natural frequency distribution, but no such relationship
emerges for out-degrees. We also observe that a network's synchronization
properties are promoted by a strong correlation between the nodal in-degrees
and the natural frequencies of oscillators, whereas the relationship between
the nodal out-degrees and the natural frequencies has comparatively little
effect. This result is supported by our theory, which indicates that
synchronization is promoted by a strong alignment of the natural frequencies
with the left singular vectors corresponding to the largest singular values of
the Laplacian matrix
Anomalous suppression of the shot noise in a nanoelectromechanical system
In this paper we report a relaxation-induced suppression of the noise for a
single level quantum dot coupled to an oscillator with incoherent dynamics in
the sequential tunneling regime. It is shown that relaxation induces
qualitative changes in the transport properties of the dot, depending on the
strength of the electron-phonon coupling and on the applied voltage. In
particular, critical thresholds in voltage and relaxation are found such that a
suppression below 1/2 of the Fano factor is possible. Additionally, the current
is either enhanced or suppressed by increasing relaxation, depending on bias
being greater or smaller than the above threshold. These results exist for any
strength of the electron-phonon coupling and are confirmed by a four states toy
model.Comment: 7 pages, 7 eps figures, submitted to PRB; minor changes in the
introductio
On the handling performance of a vehicle with different front-to-rear wheel torque distributions
The handling characteristic is a classical topic of vehicle dynamics. Usually, vehicle handling
is studied through the analysis of the understeer coe�cient in quasi-steady-state maneuvers. In
this paper, experimental tests are performed on an electric vehicle with four independent mo-
tors, which is able to reproduce front-wheel-drive, rear-wheel-drive and all-wheel-drive (FWD,
RWD and AWD, respectively) architectures. The handling characteristics of each architecture
are inferred through classical and new concepts. More speci�cally, the study presents a pro-
cedure to compute the longitudinal and lateral tire forces, which is based on a �rst estimate
and a subsequent correction of the tire forces that guarantee the equilibrium. A yaw moment
analysis is then performed to identify the contributions of the longitudinal and lateral forces.
The results show a good agreement between the classical and new formulations of the un-
dersteer coe�cient, and allow to infer a relationship between the understeer coe�cient and
the yaw moment analysis. The handling characteristics for the considered maneuvers vary
with the vehicle speed and front-to-rear wheel torque distribution. In particular, an apparently
surprising result arises at low speed, where the RWD architecture is the most understeering
con�guration. This outcome is discussed through the yaw moment analysis, highlighting the
yaw moment caused by the longitudinal forces of the front tires, which is signi�cant for high
values of lateral acceleration and steering angle
Theory of impedance networks: The two-point impedance and LC resonances
We present a formulation of the determination of the impedance between any
two nodes in an impedance network. An impedance network is described by its
Laplacian matrix L which has generally complex matrix elements. We show that by
solving the equation L u_a = lambda_a u_a^* with orthonormal vectors u_a, the
effective impedance between nodes p and q of the network is Z = Sum_a [u_{a,p}
- u_{a,q}]^2/lambda_a where the summation is over all lambda_a not identically
equal to zero and u_{a,p} is the p-th component of u_a. For networks consisting
of inductances (L) and capacitances (C), the formulation leads to the
occurrence of resonances at frequencies associated with the vanishing of
lambda_a. This curious result suggests the possibility of practical
applications to resonant circuits. Our formulation is illustrated by explicit
examples.Comment: 21 pages, 3 figures; v4: typesetting corrected; v5: Eq. (63)
correcte
FoldIndex©: a simple tool to predict whether a given protein sequence is intrinsically unfolded
Summary: An easy-to-use, versatile and freely available graphic web server, FoldIndex© is described: it predicts if a given protein sequence is intrinsically unfolded implementing the algorithm of Uversky and co-workers, which is based on the average residue hydrophobicity and net charge of the sequence. FoldIndex© has an error rate comparable to that of more sophisticated fold prediction methods. Sliding windows permit identification of large regions within a protein that possess folding propensities different from those of the whole protein. Availability: FoldIndex© can be accessed at http://bioportal.weizmann.ac.il/fldbin/findex Contact: [email protected] Supplementary information: http://www.weizmann.ac.il/sb/faculty_pages/Sussman/papers/suppl/Prilusky_200
Sampling Theorem and Discrete Fourier Transform on the Riemann Sphere
Using coherent-state techniques, we prove a sampling theorem for Majorana's
(holomorphic) functions on the Riemann sphere and we provide an exact
reconstruction formula as a convolution product of samples and a given
reconstruction kernel (a sinc-type function). We also discuss the effect of
over- and under-sampling. Sample points are roots of unity, a fact which allows
explicit inversion formulas for resolution and overlapping kernel operators
through the theory of Circulant Matrices and Rectangular Fourier Matrices. The
case of band-limited functions on the Riemann sphere, with spins up to , is
also considered. The connection with the standard Euler angle picture, in terms
of spherical harmonics, is established through a discrete Bargmann transform.Comment: 26 latex pages. Final version published in J. Fourier Anal. App
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