432 research outputs found
Pairing, crystallization and string correlations of mass-imbalanced atomic mixtures in one-dimensional optical lattices
We numerically determine the very rich phase diagram of mass-imbalanced
binary mixtures of hardcore bosons (or equivalently -- fermions, or
hardcore-Bose/Fermi mixtures) loaded in one-dimensional optical lattices.
Focusing on commensurate fillings away from half filling, we find a strong
asymmetry between attractive and repulsive interactions. Attraction is found to
always lead to pairing, associated with a spin gap, and to pair crystallization
for very strong mass imbalance. In the repulsive case the two atomic components
remain instead fully gapless over a large parameter range; only a very strong
mass imbalance leads to the opening of a spin gap. The spin-gap phase is the
precursor of a crystalline phase occurring for an even stronger mass imbalance.
The fundamental asymmetry of the phase diagram is at odds with recent
theoretical predictions, and can be tested directly via time-of-flight
experiments on trapped cold atoms.Comment: 4 pages, 4 figures + Supplementary Materia
Achievement of therapeutic target in subjects on statin treatment in clinical practice. Results of the STAR (Statins Target Assessment in Real practice) study
The primary aim of the STAR Study (Statins Target Assessment in Real practice) was to determine the LDLcholesterol reduction and to analyse patient’s and therapeutic factors associated to LDL-cholesterol target attainment in newly treated subjects with statins in an unselected population in clinical practice setting. Administrative databases (including pharmaceutical prescriptions and hospital admissions) and laboratory test databases (including LDL-cholesterol values) of five Local Health Units, distributed in Emilia Romagna, Toscana and Umbria, were linked. A retrospective cohort study was conducted and all subjects aged ≥18 years with a first prescription for statins (newly treated subjects) between January 1st, 2007 and June 30th, 2008 were included. All statin prescriptions over a 12 months follow-up period were considered and used to calculate adherence to treatment. Baseline and follow-up LDL-cholesterol, respectively, were defined according to the nearest determination to the first prescription for statins and to the end of the follow-up period. A total of 3.232 subjects was included, 1.516 males (47%) and 1.716 females (53%), with an average age equal to 65,9 ± 11,3 years. Among included subjects, 22,6% had a gap to LDL-cholesterol target <10%, 30,0% between 10 and 29%, 20,7% between 30 and 49%, and 26,7% ≥50%. Among those with a gap to target ≥50%, 30-49%, and 10-29%, respectively, LDLcholesterol target was attained by 7,1%, 41,8%, and 62,3% of subjects. LDL-cholesterol target attainment was associated to gap to target, adherence with treatment, and type of statin
IgA-BEM for 3D Helmholtz problems using conforming and non-conforming multi-patch discretizations and B-spline tailored numerical integration
An Isogeometric Boundary Element Method (IgA-BEM) is considered for the numerical solution of Helmholtz problems on 3D bounded or unbounded domains, admitting a smooth multi-patch representation of their finite boundary surface. The discretization spaces are formed by C0 inter-patch continuous functional spaces whose restriction to a patch simplifies to the span of tensor product B-splines composed with the given patch NURBS parameterization. Both conforming and non-conforming spaces are allowed, so that local refinement is possible at the patch level. For regular and singular integration, the proposed model utilizes a numerical procedure defined on the support of each trial B-spline function, which makes possible a function-by-function implementation of the matrix assembly phase. Spline quasi-interpolation is the common ingredient of all the considered quadrature rules; in the singular case it is combined with a B-spline recursion over the spline degree and with a singularity extraction technique, extended to the multi-patch setting for the first time. A threshold selection strategy is proposed to automatically distinguish between nearly singular and regular integrals. The non-conforming C0 joints between spline spaces on different patches are implemented as linear constraints based on knot removal conditions, and do not require a hierarchical master-slave relation between neighbouring patches. Numerical examples on relevant benchmarks show that the expected convergence orders are achieved with uniform discretization and a small number of uniformly spaced quadrature nodes
QUANTIZATION OF A CLASS OF PIECEWISE AFFINE TRANSFORMATIONS ON THE TORUS
We present a unified framework for the quantization of a family of discrete
dynamical systems of varying degrees of "chaoticity". The systems to be
quantized are piecewise affine maps on the two-torus, viewed as phase space,
and include the automorphisms, translations and skew translations. We then
treat some discontinuous transformations such as the Baker map and the
sawtooth-like maps. Our approach extends some ideas from geometric quantization
and it is both conceptually and calculationally simple.Comment: no. 28 pages in AMSTE
Quantum-classical correspondence on compact phase space
We propose to study the -norm distance between classical and quantum
phase space distributions, where for the latter we choose the Wigner function,
as a global phase space indicator of quantum-classical correspondence. For
example, this quantity should provide a key to understand the correspondence
between quantum and classical Loschmidt echoes. We concentrate on fully chaotic
systems with compact (finite) classical phase space. By means of numerical
simulations and heuristic arguments we find that the quantum-classical fidelity
stays at one up to Ehrenfest-type time scale, which is proportional to the
logarithm of effective Planck constant, and decays exponentially with a maximal
classical Lyapunov exponent, after that time.Comment: 26 pages. 9 figures (31 .epz files), submitted to Nonlinearit
Parabolic maps with spin: Generic spectral statistics with non-mixing classical limit
We investigate quantised maps of the torus whose classical analogues are
ergodic but not mixing. Their quantum spectral statistics shows non-generic
behaviour, i.e.it does not follow random matrix theory (RMT). By coupling the
map to a spin 1/2, which corresponds to changing the quantisation without
altering the classical limit of the dynamics on the torus, we numerically
observe a transition to RMT statistics. The results are interpreted in terms of
semiclassical trace formulae for the maps with and without spin respectively.
We thus have constructed quantum systems with non-mixing classical limit which
show generic (i.e. RMT) spectral statistics. We also discuss the analogous
situation for an almost integrable map, where we compare to Semi-Poissonian
statistics.Comment: 29 pages, 20 figure
Efficiency of informational transfer in regular and complex networks
We analyze the process of informational exchange through complex networks by
measuring network efficiencies. Aiming to study non-clustered systems, we
propose a modification of this measure on the local level. We apply this method
to an extension of the class of small-worlds that includes {\it declustered}
networks, and show that they are locally quite efficient, although their
clustering coefficient is practically zero. Unweighted systems with small-world
and scale-free topologies are shown to be both globally and locally efficient.
Our method is also applied to characterize weighted networks. In particular we
examine the properties of underground transportation systems of Madrid and
Barcelona and reinterpret the results obtained for the Boston subway network.Comment: 10 pages and 9 figure
Crystal properties of eigenstates for quantum cat maps
Using the Bargmann-Husimi representation of quantum mechanics on a torus
phase space, we study analytically eigenstates of quantized cat maps. The
linearity of these maps implies a close relationship between classically
invariant sublattices on the one hand, and the patterns (or `constellations')
of Husimi zeros of certain quantum eigenstates on the other hand. For these
states, the zero patterns are crystals on the torus. As a consequence, we can
compute explicit families of eigenstates for which the zero patterns become
uniformly distributed on the torus phase space in the limit . This
result constitutes a first rigorous example of semi-classical equidistribution
for Husimi zeros of eigenstates in quantized one-dimensional chaotic systems.Comment: 43 pages, LaTeX, including 7 eps figures Some amendments were made in
order to clarify the text, mainly in the 4 first sections. Figures are
unchanged. To be published in: Nonlinearit
Quantum cat maps with spin 1/2
We derive a semiclassical trace formula for quantized chaotic transformations
of the torus coupled to a two-spinor precessing in a magnetic field. The trace
formula is applied to semiclassical correlation densities of the quantum map,
which, according to the conjecture of Bohigas, Giannoni and Schmit, are
expected to converge to those of the circular symplectic ensemble (CSE) of
random matrices. In particular, we show that the diagonal approximation of the
spectral form factor for small arguments agrees with the CSE prediction. The
results are confirmed by numerical investigations.Comment: 26 pages, 3 figure
Role of transport performance on neuron cell morphology
The compartmental model is a basic tool for studying signal propagation in
neurons, and, if the model parameters are adequately defined, it can also be of
help in the study of electrical or fluid transport. Here we show that the input
resistance, in different networks which simulate the passive properties of
neurons, is the result of an interplay between the relevant conductances,
morphology and size. These results suggest that neurons must grow in such a way
that facilitates the current flow. We propose that power consumption is an
important factor by which neurons attain their final morphological appearance.Comment: 9 pages with 3 figures, submitted to Neuroscience Letter
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