114 research outputs found
ABC-SysBio-approximate Bayesian computation in Python with GPU support.
Motivation: The growing field of systems biology has driven demand for flexible tools to model and simulate biological systems. Two established problems in the modeling of biological processes are model selection and the estimation of associated parameters. A number of statistical approaches, both frequentist and Bayesian, have been proposed to answer these questions. Results: Here we present a Python package, ABC-SysBio, that implements parameter inference and model selection for dynamical systems in an approximate Bayesian computation (ABC) framework. ABC-SysBio combines three algorithms: ABC rejection sampler, ABC SMC for parameter inference and ABC SMC for model selection. It is designed to work with models written in Systems Biology Markup Language (SBML). Deterministic and stochastic models can be analyzed in ABC-SysBio
Estimating the Effect of Liver and Pancreas Volume and Fat Content on Risk of Diabetes: A Mendelian Randomization Study
Fat content and volume of liver and pancreas are associated with risk of diabetes in observational studies; whether these associations are causal is unknown. We conducted a Mendelian randomization (MR) study to examine causality of such associations. We used genetic variants associated (P < 5 × 10-8) with the exposures (liver and pancreas volume and fat content) using MRI scans of UK Biobank participants (n = 32,859). We obtained summary-level data for risk of type 1 (9,358 cases) and type 2 (55,005 cases) diabetes from the largest available genome-wide association studies. We performed inverse-variance weighted MR as main analysis and several sensitivity analyses to assess pleiotropy and to exclude variants with potential pleiotropic effects. Observationally, liver fat and volume were associated with type 2 diabetes (odds ratio per 1 SD higher exposure 2.16 [2.02, 2.31] and 2.11 [1.96, 2.27], respectively). Pancreatic fat was associated with type 2 diabetes (1.42 [1.34, 1.51]) but not type 1 diabetes, and pancreas volume was negatively associated with type 1 diabetes (0.42 [0.36, 0.48]) and type 2 diabetes (0.73 [0.68, 0.78]). MR analysis provided evidence only for a causal role of liver fat and pancreas volume in risk of type 2 diabetes (1.27 [1.08, 1.49] or 27% increased risk and 0.76 [0.62, 0.94] or 24% decreased risk per 1SD, respectively) and no causal associations with type 1 diabetes. Our findings assist in understanding the causal role of ectopic fat in the liver and pancreas and of organ volume in the pathophysiology of type 1 and 2 diabetes. [Abstract copyright: © 2022 by the American Diabetes Association.
Crystal surfaces with correlated disorder: Phase transitions between roughening and superroughening
A theory for surface transitions in the presence of a disordered pinning
potential is presented. Arbitrary disorder correlations are treated in the
framework of a dynamical functional renormalization group. The roughening
transition, where surface roughness and mobility behave discontinuously, is
shown to turn smoothly into the continuous superroughening transition, when the
range of disorder correlations is decreased. Implications for random-field
-models and vortex glasses are discussed.Comment: 13 pages with 2 figures, latex+revte
ABC-SysBio—approximate Bayesian computation in Python with GPU support
Motivation: The growing field of systems biology has driven demand for flexible tools to model and simulate biological systems. Two established problems in the modeling of biological processes are model selection and the estimation of associated parameters. A number of statistical approaches, both frequentist and Bayesian, have been proposed to answer these questions
Phase Diagram for Splay Glass Superconductivity
Localization of flux lines to splayed columnar pins is studied. A sine-Gordon
type renormalization group study reveals the existence of a Splay glass phase
and yields an analytic form for the transition temperature into the glass
phase. As an independent test, the characteristics are determined via a
Molecular Dynamics code. The glass transition temperature supports the RG
results convincingly. The full phase diagram of the model is constructed.Comment: 14 pages, uuencoded compressed tar file with 3 postscript figure
Interacting Arrays of Steps and Lines in Random Media
The phase diagram of two interacting planar arrays of directed lines in
random media is obtained by a renormalization group analysis. The results are
discussed in the contexts of the roughening of reconstructed crystal surfaces,
and the pinning of flux line arrays in layered superconductors. Among the
findings are a glassy flat phase with disordered domain structures, a novel
second-order phase transition with continuously varying critical exponents, and
the generic disappearance of the glassy ``super-rough'' phases found previously
for a single array.Comment: 4 pages, REVTEX 3.0, uses epsf,multicol, 3 .eps-figures, submitted to
PR
Glassy Roughness of a Crystalline Surface Upon a Disordered Substrate
The discrete Gaussian model for the surface of a crystal deposited on a
disordered substrate is studied by Monte Carlo simulations. A continuous
transition is found from a phase with a thermally-induced roughness to a glassy
one in which the roughness is driven by the disorder. The behavior of the
height-height correlations is consistent with the one-step replica symmetry
broken solution of the variational approximation. The results differ from the
renormalization group predictions and from recent simulations of a 2D
vortex-glass model which belongs to the same universality class.Comment: 12 pages (RevTeX) & 3 figures (PS) uuencode
Models of stress fluctuations in granular media
We investigate in detail two models describing how stresses propagate and
fluctuate in granular media. The first one is a scalar model where only the
vertical component of the stress tensor is considered. In the continuum limit,
this model is equivalent to a diffusion equation (where the r\^ole of time is
played by the vertical coordinate) plus a randomly varying convection term. We
calculate the response and correlation function of this model, and discuss
several properties, in particular related to the stress distribution function.
We then turn to the tensorial model, where the basic starting point is a wave
equation which, in the absence of disorder, leads to a ray-like propagation of
stress. In the presence of disorder, the rays acquire a diffusive width and the
angle of propagation is shifted. A striking feature is that the response
function becomes negative, which suggests that the contact network is
mechanically unstable to very weak perturbations. The stress correlation
function reveals characteristic features related to the ray-like propagation,
which are absent in the scalar description. Our analytical calculations are
confirmed and extended by a numerical analysis of the stochastic wave equation.Comment: 32 pages, latex, 18 figures and 6 diagram
Large time off-equilibrium dynamics of a manifold in a random potential
We study the out of equilibrium dynamics of an elastic manifold in a random
potential using mean-field theory. We find two asymptotic time regimes: (i)
stationary dynamics, (ii) slow aging dynamics with violation of equilibrium
theorems. We obtain an analytical solution valid for all large times with
universal scalings of two-time quantities with space. A non-analytic scaling
function crosses over to ultrametricity when the correlations become
long-range. We propose procedures to test numerically or experimentally the
extent to which this scenario holds for a given system.Comment: 12 page
Glassy transition in a disordered model for the RNA secondary structure
We numerically study a disordered model for the RNA secondary structure and
we find that it undergoes a phase transition, with a breaking of the replica
symmetry in the low temperature region (like in spin glasses). Our results are
based on the exact evaluation of the partition function.Comment: 4 pages, 3 figure
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