191 research outputs found
Scaling Analysis of the Site-Diluted Ising Model in Two Dimensions
A combination of recent numerical and theoretical advances are applied to
analyze the scaling behaviour of the site-diluted Ising model in two
dimensions, paying special attention to the implications for multiplicative
logarithmic corrections. The analysis focuses primarily on the odd sector of
the model (i.e., that associated with magnetic exponents), and in particular on
its Lee-Yang zeros, which are determined to high accuracy. Scaling relations
are used to connect to the even (thermal) sector, and a first analysis of the
density of zeros yields information on the specific heat and its corrections.
The analysis is fully supportive of the strong scaling hypothesis and of the
scaling relations for logarithmic corrections.Comment: 15 pages, 3 figures. Published versio
The Effects of Next-Nearest-Neighbor Interactions on the Orientation Dependence of Step Stiffness: Reconciling Theory with Experiment for Cu(001)
Within the solid-on-solid (SOS) approximation, we carry out a calculation of
the orientational dependence of the step stiffness on a square lattice with
nearest and next-nearest neighbor interactions. At low temperature our result
reduces to a simple, transparent expression. The effect of the strongest trio
(three-site, non pairwise) interaction can easily be incorporated by modifying
the interpretation of the two pairwise energies. The work is motivated by a
calculation based on nearest neighbors that underestimates the stiffness by a
factor of 4 in directions away from close-packed directions, and a subsequent
estimate of the stiffness in the two high-symmetry directions alone that
suggested that inclusion of next-nearest-neighbor attractions could fully
explain the discrepancy. As in these earlier papers, the discussion focuses on
Cu(001).Comment: 8 pages, 3 figures, submitted to Phys. Rev.
Naturalistic Driving: User and Task Analysis
Cognitive Task Analysis and methods for analyzing Naturalistic Decision Making are powerful tools that can be applied to transportation research. In conjunction with simulators, these methods allow increased understanding of real user interactions with their in-vehicle systems, and the decision processes involved in the operational aspects of driving, navigating, and using infotainment support systems. Adopting this approach facilitates investigation of driver performance under a range of workload and stress conditions, which supports future development of a prototypical model that will encapsulate the cognitive and perceptual-motor demands of driving in the presence of situational stressors under both high- and low-workload conditions
Surface critical behavior of two-dimensional dilute Ising models
Ising models with nearest-neighbor ferromagnetic random couplings on a square
lattice with a (1,1) surface are studied, using Monte Carlo techniques and
star-tiangle transformation method. In particular, the critical exponent of the
surface magnetization is found to be close to that of the perfect model,
beta_s=1/2. The crossover from surface to bulk critical properties is
discussed.Comment: 6 pages in RevTex, 3 ps figures, to appear in Journal of Stat. Phy
Correlations in nano-scale step fluctuations: comparison of simulation and experiments
We analyze correlations in step-edge fluctuations using the
Bortz-Kalos-Lebowitz kinetic Monte Carlo algorithm, with a 2-parameter
expression for energy barriers, and compare with our VT-STM line-scan
experiments on spiral steps on Pb(111). The scaling of the correlation times
gives a dynamic exponent confirming the expected step-edge-diffusion
rate-limiting kinetics both in the MC and in the experiments. We both calculate
and measure the temperature dependence of (mass) transport properties via the
characteristic hopping times and deduce therefrom the notoriously-elusive
effective energy barrier for the edge fluctuations. With a careful analysis we
point out the necessity of a more complex model to mimic the kinetics of a
Pb(111) surface for certain parameter ranges.Comment: 10 pages, 9 figures, submitted to Physical Review
Effective knowledge management in translational medicine
<p>Abstract</p> <p>Background</p> <p>The growing consensus that most valuable data source for biomedical discoveries is derived from human samples is clearly reflected in the growing number of translational medicine and translational sciences departments across pharma as well as academic and government supported initiatives such as Clinical and Translational Science Awards (CTSA) in the US and the Seventh Framework Programme (FP7) of EU with emphasis on translating research for human health.</p> <p>Methods</p> <p>The pharmaceutical companies of Johnson and Johnson have established translational and biomarker departments and implemented an effective knowledge management framework including building a data warehouse and the associated data mining applications. The implemented resource is built from open source systems such as i2b2 and GenePattern.</p> <p>Results</p> <p>The system has been deployed across multiple therapeutic areas within the pharmaceutical companies of Johnson and Johnsons and being used actively to integrate and mine internal and public data to support drug discovery and development decisions such as indication selection and trial design in a translational medicine setting. Our results show that the established system allows scientist to quickly re-validate hypotheses or generate new ones with the use of an intuitive graphical interface.</p> <p>Conclusions</p> <p>The implemented resource can serve as the basis of precompetitive sharing and mining of studies involving samples from human subjects thus enhancing our understanding of human biology and pathophysiology and ultimately leading to more effective treatment of diseases which represent unmet medical needs.</p
Fluctuations, line tensions, and correlation times of nanoscale islands on surfaces
We analyze in detail the fluctuations and correlations of the (spatial)
Fourier modes of nano-scale single-layer islands on (111) fcc crystal surfaces.
We analytically show that the Fourier modes of the fluctuations couple due to
the anisotropy of the crystal, changing the power spectrum of the fluctuations,
and that the actual eigenmodes of the fluctuations are the appropriate linear
combinations of the Fourier modes. Using kinetic Monte Carlo simulations with
bond-counting parameters that best match realistic energy barriers for hopping
rates, we deduce absolute line tensions as a function of azimuthal orientation
from the analyses of the fluctuation of each individual mode. The
autocorrelation functions of these modes give the scaling of the correlation
times with wavelength, providing us with the rate-limiting kinetics driving the
fluctuations, here step-edge diffusion. The results for the energetic
parameters are in reasonable agreement with available experimental data for
Pb(111) surfaces, and we compare the correlation times of island-edge
fluctuations to relaxation times of quenched Pb crystallites.Comment: 11 pages, 8 figures; to appear in PRB 70, xxx (15 Dec 2004), changes
in MC and its implication
Interface Fluctuations on a Hierarchical Lattice
We consider interface fluctuations on a two-dimensional layered lattice where
the couplings follow a hierarchical sequence. This problem is equivalent to the
diffusion process of a quantum particle in the presence of a one-dimensional
hierarchical potential. According to a modified Harris criterion this type of
perturbation is relevant and one expects anomalous fluctuating behavior. By
transfer-matrix techniques and by an exact renormalization group transformation
we have obtained analytical results for the interface fluctuation exponents,
which are discontinuous at the homogeneous lattice limit.Comment: 14 pages plain Tex, one Figure upon request, Phys Rev E (in print
Correlation between radiographic signs of third molar proximity with inferior alveolar nerve and postoperative occurrence of neurosensory disorders: A prospective, double-blind study
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