Search results for "Computational physics"
showing 10 items of 725 documents
Structure solution of zeolites by automated electron diffraction tomography - Impact and treatment of preferential orientation
2014
Abstract In this paper the reliability of structure solution of nano-crystalline porous compounds with preferred orientation based on automated electron diffraction tomography (ADT) is discussed. It will be shown that the limitations of the data acquisition geometry can be overcome by completing the missing diffraction data with additional diffraction information. Apart from different ways of sample preparation, data merging with either additional ADT data sets or intensities derived from X-ray powder diffraction comprise an effective way to improve the accuracy of the structure solution.
Critical analysis of the spin-rotation constants of CF2 and CCl2: A theoretical investigation
2005
Quantum chemical ab initio calculations for the spin-rotation constants of difluorocarbene (CF2) and dichlorocarbene (CCl2) were carried out using coupled-cluster techniques with sequences of correlation-consistent basis sets. Theoretical best estimates were obtained using extrapolation to the complete basis-set limit and taking into account corrections for core correlation, additional diffuse functions and zero-point vibrational effects. It is demonstrated that such accurate theoretical estimates can be used either to support or to challenge the analysis of the experimental spectra and the reliability of the resulting data. 2005 Elsevier B.V. All rights reserved.
Algorithmic Information Theory and Computational Complexity
2013
We present examples where theorems on complexity of computation are proved using methods in algorithmic information theory. The first example is a non-effective construction of a language for which the size of any deterministic finite automaton exceeds the size of a probabilistic finite automaton with a bounded error exponentially. The second example refers to frequency computation. Frequency computation was introduced by Rose and McNaughton in early sixties and developed by Trakhtenbrot, Kinber, Degtev, Wechsung, Hinrichs and others. A transducer is a finite-state automaton with an input and an output. We consider the possibilities of probabilistic and frequency transducers and prove sever…
Real-space grids and the Octopus code as tools for the development of new simulation approaches for electronic systems.
2015
This Open Access Article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
A coupled Finite Volume–Smoothed Particle Hydrodynamics method for incompressible flows
2016
Abstract An hybrid approach is proposed which allows to combine Finite Volume Method (FVM) and Smoothed Particle Hydrodynamics (SPH). The method is based on the partitioning of the computational domain into a portion discretized with a structured grid of hexahedral elements (the FVM-domain ) and a portion filled with Lagrangian particles (the SPH-domain ), separated by an interface made of triangular elements. A smooth transition between the solutions in the FVM and SPH regions is guaranteed by the introduction of a layer of grid cells in the SPH-domain and of a band of virtual particles in the FVM one (both neighboring the interface), on which the hydrodynamic variables are obtained throug…
Erratum: “TG-43 U1 based dosimetric characterization of model 67-6520 Cs-137 brachytherapy source”
2012
Purpose: Brachytherapy treatment has been a cornerstone for management of various cancer sites, particularly for the treatment of gynecological malignancies. In low dose rate brachytherapy treatments,C137s sources have been used for several decades. A new C137s source design has been introduced (model 67-6520, source B3-561) by Isotope Products Laboratories (IPL) for clinical application. The goal of the present work is to implement the TG-43 U1 protocol in the characterization of the aforementioned C137s source. Methods: The dosimetriccharacteristics of the IPLC137s source are measured using LiF thermoluminescent dosimeters in a Solid Water™ phantom material and calculated using Monte Carl…
A quasi chemistry-transport model mode for EMAC
2010
Abstract. A quasi chemistry-transport model mode (QCTM) is presented for the numerical chemistry-climate simulation system ECHAM/MESSy Atmospheric Chemistry (EMAC). It allows for a quantification of chemical signals through suppression of any feedback between chemistry and dynamics. Noise would otherwise interfere too strongly. The signal is calculated from the difference of two QCTM simulations, a reference simulation and a sensitivity simulation. In order to avoid the feedbacks, the simulations adopt the following offline chemical fields: (a) offline mixing ratios of radiatively active substances enter the radiation scheme, (b) offline mixing ratios of nitric acid enter the scheme for re-…
Nonlinear PCA for Spatio-Temporal Analysis of Earth Observation Data
2020
Remote sensing observations, products, and simulations are fundamental sources of information to monitor our planet and its climate variability. Uncovering the main modes of spatial and temporal variability in Earth data is essential to analyze and understand the underlying physical dynamics and processes driving the Earth System. Dimensionality reduction methods can work with spatio-temporal data sets and decompose the information efficiently. Principal component analysis (PCA), also known as empirical orthogonal functions (EOFs) in geophysics, has been traditionally used to analyze climatic data. However, when nonlinear feature relations are present, PCA/EOF fails. In this article, we pro…
An Appearance-Like Reactor Experiment To Measure Ue3
2004
Conventional reactor neutrino experiments are dissapearance experiments, and thus have less sensitivity to small mixing angles than appearance experiments do. It has been recently shown that future reactor neutrino experiments consisiting of a near and far detector are competitive with first-generation superbeams in order to determine sin^2{2 theta_{13}} down to 10^{-2}. We show that by using the antineutrino-electron elastic scattering at the near detector around the configuration where dsigma^{bar{\nu}_e}/dT presents a dynamical zero, an appearance-like experiment can be simulated, with a sensitivity comparable to the one achieved with the inverse beta-decay reaction in the far detector. …
A low energy bound atomic electron Compton scattering model for Geant4
2014
Abstract A two-body fully relativistic three-dimensional scattering framework has been utilised to develop an alternative Compton scattering computational model to those adapted from Ribberfors’ work for Monte Carlo modelling of Compton scattering. Using a theoretical foundation that ensures the conservation of energy and momentum in the relativistic impulse approximation, this new model, the Monash University Compton scattering model, develops energy and directional algorithms for both the scattered photon and ejected Compton electron from first principles. The Monash University Compton scattering model was developed to address the limitation of the Compton electron directionality algorith…