13,293 research outputs found
Variational approach to dequantization
We present a dequantization procedure based on a variational approach whereby
quantum fluctuations latent in the quantum momentum are suppressed. This is
done by adding generic local deformations to the quantum momentum operator
which give rise to a deformed kinetic term quantifying the amount of
``fuzzyness'' caused by such fluctuations. Considered as a functional of such
deformations, the deformed kinetic term is shown to possess a unique minimum
which is seen to be the classical kinetic energy. Furthermore, we show that
extremization of the associated deformed action functional introduces an
essential nonlinearity to the resulting field equations which are seen to be
the classical Hamilton-Jacobi and continuity equations. Thus, a variational
procedure determines the particular deformation that has the effect of
suppressing the quantum fluctuations, resulting in dequantization of the
system.Comment: 6 pages, 1 figure. v2: changes in presentation and conten
Design used as a resource In the Increase in the value of goods and cultures: project design and competitive integration in the estrada real territory, Brazil (phase II)
The Clustering Characteristics of HI-Selected Galaxies from the 40% ALFALFA Survey
The 40% Arecibo Legacy Fast ALFA (ALFALFA) survey catalog (\alpha.40) of
approximately 10,150 HI-selected galaxies is used to analyze the clustering
properties of gas-rich galaxies. By employing the Landy-Szalay estimator and a
full covariance analysis for the two-point galaxy-galaxy correlation function,
we obtain the real-space correlation function and model it as a power law,
\xi(r) = (r/r_0)^(-\gamma), on scales less than 10 h^{-1} Mpc. As the largest
sample of blindly HI-selected galaxies to date, \alpha.40 provides detailed
understanding of the clustering of this population. We find \gamma = 1.51 +/-
0.09 and r_0 = 3.3 +0.3, -0.2 h^{-1} Mpc, reinforcing the understanding that
gas-rich galaxies represent the most weakly clustered galaxy population known;
we also observe a departure from a pure power law shape at intermediate scales,
as predicted in \Lambda CDM halo occupation distribution models. Furthermore,
we measure the bias parameter for the \alpha.40 galaxy sample and find that HI
galaxies are severely antibiased on small scales, but only weakly antibiased on
large scales. The robust measurement of the correlation function for gas-rich
galaxies obtained via the \alpha.40 sample constrains models of the
distribution of HI in simulated galaxies, and will be employed to better
understand the role of gas in environmentally-dependent galaxy evolution.Comment: 30 pages, 10 figures, accepted by Ap
Sensorless position control of permanent magnet motors with pulsating current injection and compensation of motor end-effects
End effects in linear tubular motors and compensated position sensorless control based on pulsating voltage injection
Path Integral Molecular Dynamics within the Grand Canonical-like Adaptive Resolution Technique: Simulation of Liquid Water
Quantum effects due to the spatial delocalization of light atoms are treated
in molecular simulation via the path integral technique. Among several methods,
Path Integral (PI) Molecular Dynamics (MD) is nowadays a powerful tool to
investigate properties induced by spatial delocalization of atoms; however
computationally this technique is very demanding. The abovementioned limitation
implies the restriction of PIMD applications to relatively small systems and
short time scales. One possible solution to overcome size and time limitation
is to introduce PIMD algorithms into the Adaptive Resolution Simulation Scheme
(AdResS). AdResS requires a relatively small region treated at path integral
level and embeds it into a large molecular reservoir consisting of generic
spherical coarse grained molecules. It was previously shown that the
realization of the idea above, at a simple level, produced reasonable results
for toy systems or simple/test systems like liquid parahydrogen. Encouraged by
previous results, in this paper we show the simulation of liquid water at room
conditions where AdResS, in its latest and more accurate Grand-Canonical-like
version (GC-AdResS), is merged with two of the most relevant PIMD techniques
available in literature. The comparison of our results with those reported in
literature and/or with those obtained from full PIMD simulations shows a highly
satisfactory agreement
Recurring patterns of atrial fibrillation in surface ECG predict restoration of sinus rhythm by catheter ablation
Background Non-invasive tools to help identify patients likely to benefit from catheter ablation (CA) of atrial fibrillation (AF) would facilitate personalised treatment planning. Aim To investigate atrial waveform organisation through recurrence plot indices (RPI) and their ability to predict CA outcome. Methods One minute 12-lead ECG was recorded before CA from 62 patients with AF (32 paroxysmal AF; 45 men; age 57±10 years). Organisation of atrial waveforms from i) TQ intervals in V1 and ii) QRST suppressed continuous AF waveforms (CAFW), were quantified using RPI: percentage recurrence (PR), percentage determinism (PD), entropy of recurrence (ER). Ability to predict acute (terminating vs. non-terminating AF), 3-month and 6-month postoperative outcome (AF vs. AF free) were assessed. Results RPI either by TQ or CAFW analysis did not change significantly with acute outcome. Patients arrhythmia-free at 6-month follow-up had higher organisation in TQ intervals by PD (
Is there a third order phase transition for supercritical fluids?
We prove that according to Molecular Dynamics (MD) simulations of liquid
mixtures of Lennard-Jones (L-J) particles, there is no third order phase
transition in the supercritical regime beyond Andrew's critical point. This
result is in open contrast with recent theoretical studies and experiments
which instead suggest not only its existence but also its universality
regarding the chemical nature of the fluid. We argue that our results are solid
enough to go beyond the limitations of MD and the generic character of L-J
models, thus suggesting a rather smooth liquid-vapor thermodynamic behavior of
fluids in supercritical regime.Comment: 13 pages, 6 figure
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