349 research outputs found
Spin glass models with Kac interactions
In this paper I will review my work on disordered systems -spin glass model
with two body and body interactions- with long but finite interaction
range . I will describe the relation of these model with Mean Field Theory
in the Kac limit and some attempts to go beyond mean field.Comment: Proceedings of the Stat-phys23 conferenc
Zero-Temperature Dynamics of Ising Spin Systems Following a Deep Quench: Results and Open Problems
We consider zero-temperature, stochastic Ising models with nearest-neighbor
interactions and an initial spin configuration chosen from a symmetric
Bernoulli distribution (corresponding physically to a deep quench). Whether a
final state exists, i.e., whether each spin flips only finitely many times as
time goes to infinity (for almost every initial spin configuration and
realization of the dynamics), or if not, whether every spin - or only a
fraction strictly less than one - flips infinitely often, depends on the nature
of the couplings, the dimension, and the lattice type. We review results,
examine open questions, and discuss related topics.Comment: 10 pages (LaTeX); to appear in Physica
Multiaxial fatigue of cast aluminium EN AC-42000 T6 (G-AlSi7Mg0.3 T6) for automotive safety components under constant and variable amplitude loading
Regarding the fatigue behaviour of EN AC-42000 T6 (A 356 T6), which is the most frequently used cast aluminium alloy for automotive safety components, especially under non-proportional constant and variable normal and shear stress amplitudes with changing principal stress directions, a poor level of knowledge was available. The reported investigations show that, under non-proportional normal and shear stresses, fatigue life is increased in contrast to ductile steels where life is reduced due to changing principal stress directions. This behaviour caused by the low ductility of this alloy (e < 10%) compared to quenched and tempered steels suggests the application of the Normal (Principal) Stress Hypothesis (NSH). For all of the investigated stress states under multiaxial constant and variable (Gaussian spectrum) amplitudes without and with mean stresses, the NSH was able to depict the life increase by the non-proportionality and delivered, for most cases, conservative but non-exaggerated results
Glassy dynamics near zero temperature
We numerically study finite-dimensional spin glasses at low and zero
temperature, finding evidences for (i) strong time/space heterogeneities, (ii)
spontaneous time scale separation and (iii) power law distributions of flipping
times. Using zero temperature dynamics we study blocking, clustering and
persistence phenomena
Angiotensinogen gene promoter haplotype and microangiopathy-related cerebral damage: results of the Austrian Stroke Prevention Study
BACKGROUND AND PURPOSE: Microangiopathy-related cerebral damage (MARCD) is a common finding in the elderly. It may lead to cognitive impairment and gait disturbances. Arterial hypertension and age are the most important risk factors. We assessed the association between MARCD and sequence alterations in the promoter region of the angiotensinogen (AGT) gene. METHODS: We studied 410 randomly selected community-dwelling individuals aged 50 to 75 years. MARCD was defined as early confluent or confluent white matter hyperintensities or lacunes on a 1.5-T MRI. The AGT promoter was analyzed by temporal temperature gradient gel electrophoresis and automated sequencing. RESULTS: We detected 4 polymorphic sites, at positions -6, -20, -153, and -218. They created 5 haplotypes, which we coded as A (-6:g, -20:a, -153:g, -218g), B (-6:a, -20:c, -153:g, -218:g), C (-6:a, -20:c, -153:a, -218:g), D (-6:a, -20:a, -153:g, -218:g), and E (-6:a, -20:a, -153:g, -218:a). MARCD was seen in 7 subjects (63.6%) carrying 2 copies of the B haplotype (B/B), in 12 subjects (38.7%) carrying 1 copy of the B haplotype in the absence of the A haplotype (B+/A-), but in only 70 subjects (19.0%) in the remaining cohort (P:<0.001). The odds ratios for the B/B and the B+/A- genotypes were 8.0 (95% CI, 2.1 to 31.1; P:=0.003) and 1.8 (95% CI, 0.8 to 4.2; P:=0.14) after adjustment for possible confounders. CONCLUSIONS: The B haplotype of the AGT promoter in the absence of the wild-type A haplotype might represent a genetic susceptibility factor for MARCD
Metastable States in Spin Glasses and Disordered Ferromagnets
We study analytically M-spin-flip stable states in disordered short-ranged
Ising models (spin glasses and ferromagnets) in all dimensions and for all M.
Our approach is primarily dynamical and is based on the convergence of a
zero-temperature dynamical process with flips of lattice animals up to size M
and starting from a deep quench, to a metastable limit. The results (rigorous
and nonrigorous, in infinite and finite volumes) concern many aspects of
metastable states: their numbers, basins of attraction, energy densities,
overlaps, remanent magnetizations and relations to thermodynamic states. For
example, we show that their overlap distribution is a delta-function at zero.
We also define a dynamics for M=infinity, which provides a potential tool for
investigating ground state structure.Comment: 34 pages (LaTeX); to appear in Physical Review
Transfer Learning for Domain Adaptation in MRI: Application in Brain Lesion Segmentation
Magnetic Resonance Imaging (MRI) is widely used in routine clinical diagnosis
and treatment. However, variations in MRI acquisition protocols result in
different appearances of normal and diseased tissue in the images.
Convolutional neural networks (CNNs), which have shown to be successful in many
medical image analysis tasks, are typically sensitive to the variations in
imaging protocols. Therefore, in many cases, networks trained on data acquired
with one MRI protocol, do not perform satisfactorily on data acquired with
different protocols. This limits the use of models trained with large annotated
legacy datasets on a new dataset with a different domain which is often a
recurring situation in clinical settings. In this study, we aim to answer the
following central questions regarding domain adaptation in medical image
analysis: Given a fitted legacy model, 1) How much data from the new domain is
required for a decent adaptation of the original network?; and, 2) What portion
of the pre-trained model parameters should be retrained given a certain number
of the new domain training samples? To address these questions, we conducted
extensive experiments in white matter hyperintensity segmentation task. We
trained a CNN on legacy MR images of brain and evaluated the performance of the
domain-adapted network on the same task with images from a different domain. We
then compared the performance of the model to the surrogate scenarios where
either the same trained network is used or a new network is trained from
scratch on the new dataset.The domain-adapted network tuned only by two
training examples achieved a Dice score of 0.63 substantially outperforming a
similar network trained on the same set of examples from scratch.Comment: 8 pages, 3 figure
- …