Search results for "Statistical physics"
showing 10 items of 1402 documents
Computing Strong Shocks in Ultrarelativistic Flows: A Robust Alternative
1999
In recent years, shock capturing methods have started to be used in numerical simulations in Relativistic Fluid Dynamics (RFD). These techniques lead to explicit numerical codes that are able to successfully simulate the extreme conditions of the ultrarelativistic regime. After [2], an explicit, ready-to-use description of the full spectral decomposition of the Jacobian matrices of the RFD system is available, and this allows us to implement Marquina’s scheme [3] in RFD. The scheme is seen to maintain the good behavior shown in [3] with respect to certain numerical pathologies.
A neural network clustering algorithm for the ATLAS silicon pixel detector
2014
A novel technique to identify and split clusters created by multiple charged particles in the ATLAS pixel detector using a set of artificial neural networks is presented. Such merged clusters are a common feature of tracks originating from highly energetic objects, such as jets. Neural networks are trained using Monte Carlo samples produced with a detailed detector simulation. This technique replaces the former clustering approach based on a connected component analysis and charge interpolation. The performance of the neural network splitting technique is quantified using data from proton-proton collisions at the LHC collected by the ATLAS detector in 2011 and from Monte Carlo simulations. …
Stock markets and quantum dynamics: A second quantized description
2009
In this paper we continue our description of stock markets in terms of some non-abelian operators which are used to describe the portfolio of the various traders and other observable quantities. After a first prototype model with only two traders, we discuss a more realistic model of market involving an arbitrary number of traders. For both models we find approximated solutions for the time evolution of the portfolio of each trader. In particular, for the more realistic model, we use the stochastic limit approach and a fixed point like approximation. © 2007 Elsevier B.V. All rights reserved
The evolution of the meaning of blood hyperviscosity in cardiovascular physiopathology: Should we reinterpret Poiseuille?
2009
In the 1960s and 1970s, a number of researchers (including ourselves) involved in the study of cardiovascular pathophysiology and particularly in the development of techniques to quantify blood flow, came across the observation that, along with vessel diameter, also blood viscosity plays an important role not only in theory but also in practice. Until then, viscosity was thought to play only a marginal role in determining blood flow, a concept which was based on the 1828 theories of Jean Louis Marie Poiseuille (Fig. 1, and [1]).1 In his well-known formula, named after its fathers Hagen2 and Poiseuille,
Local properties of quantum chemical systems: the LoProp approach.
2004
A new method is presented, which makes it possible to partition molecular properties like multipole moments and polarizabilities, into atomic and interatomic contributions. The method requires a subdivision of the atomic basis set into occupied and virtual basis functions for each atom in the molecular system. The localization procedure is organized into a series of orthogonalizations of the original basis set, which will have as a final result a localized orthonormal basis set. The new localization procedure is demonstrated to be stable with various basis sets, and to provide physically meaningful localized properties. Transferability of the methyl properties for the alkane series and of t…
Excess free energy of nanoparticles in a polymer brush
2008
Abstract We present an efficient method for direct determination of the excess free energy Δ F of a nanoparticle inserted into a polymer brush. In contrast to Widom's insertion method, the present approach can be efficiently implemented by Monte Carlo or Molecular Dynamics methods also in a dense environment. In the present investigation the method is used to determine the free energy penalty Δ F ( R , D ) for placing a spherical particle with an arbitrary radius R at different positions D between the grafting plane and the brush surface. Deep inside the brush, or for dense brushes, one finds Δ F ∝ R 3 whereas for shallow nanoclusions Δ F ∝ R 2 , regardless of the particle interaction (…
Single-chain conformations in symmetric binary polymer blends: Quantitative comparison between self-consistent field calculations and Monte Carlo sim…
1998
Single-chain properties in a symmetric binary polymer blend are studied by self-consistent field calculations and Monte Carlo simulations. Within the self-consistent field scheme, the statistical mechanics of a cluster of neighboring polymers is solved. Interactions among the polymers of a cluster and composition fluctuations within a cluster are incorporated exactly, a mean field approximation is invoked for intercluster interactions and long-range fluctuations. The results are compared to large scale Monte Carlo simulations for a broad range of chain lengths. While we find nearly quantitative agreement for single chain propertiese.g., the reduction of the chain dimensions of the minority …
New quantum Monte Carlo formulation for modeling trans-polyacetylene properties: specific heat calculation
2004
Abstract In this paper we propose a new hybridization scheme for numerical simulation based on the determinantal quantum Monte Carlo and analytical model to treat the vibration mode of one-dimensional trans -polyacetylene chain. We use both of the extended Hubbard model (EHM) and Peierls–Hubbard model to compute the specific heat for different assumptions. For both the two models, our results indicate that the behavior of the specific heat is characterized by a maximum. We also introduce the effect of dimerization through Peierls–Hubbard model. In this case it is found that the specific heat magnitude is slightly more important when compared to specific heat value found with the EHM case. M…
Dynamic Density Functional Theories for Inhomogeneous Polymer Systems Compared to Brownian Dynamics Simulations
2017
Dynamic density functionals (DDFs) are popular tools for studying the dynamical evolution of inhomogeneous polymer systems. Here, we present a systematic evaluation of a set of diffusive DDF theories by comparing their predictions with data from particle-based Brownian dynamics (BD) simulations for two selected problems: Interface broadening in compressible A/B homopolymer blends after a sudden change of the incompatibility parameter, and microphase separation in compressible A:B diblock copolymer melts. Specifically, we examine (i) a local dynamics model, where monomers are taken to move independently from each other, (ii) a nonlocal "chain dynamics" model, where monomers move jointly with…
Conformations, Transverse Fluctuations and Crossover Dynamics of a Semi-Flexible Chain in Two Dimensions
2014
We present a unified scaling description for the dynamics of monomers of a semiflexible chain under good solvent condition in the free draining limit. We consider both the cases where the contour length $L$ is comparable to the persistence length $\ell_p$ and the case $L\gg \ell_p$. Our theory captures the early time monomer dynamics of a stiff chain characterized by $t^{3/4}$ dependence for the mean square displacement(MSD) of the monomers, but predicts a first crossover to the Rouse regime of $t^{2\nu/{1+2\nu}}$ for $\tau_1 \sim \ell_p^3$, and a second crossover to the purely diffusive dynamics for the entire chain at $\tau_2 \sim L^{5/2}$. We confirm the predictions of this scaling descr…