Search results for "Computational physics"

More on the determination of the coronal heating function from Yohkoh data

2002

Two recent works have analyzed a solar large and steady coronal loop observed with Yohkoh/SXT in two filter passbands to infer the distribution of the heating along it. Priest et al. (2000) modelled the distribution of the temperature obtained from filter ratio method with an analytical approach, and concluded that the heating was uniform along the loop. Aschwanden (2001) found that a uniform heating led to an unreasonably large plasma column depth along the line of sight, and, using a two component loop model, that a footpoint-heated model loop (with a minor cool component) yields more acceptable physical solutions. We revisit the analysis of the same loop system, considering conventional …

On the importance of background subtraction in the analysis of coronal loops observed with TRACE

2010

In the framework of TRACE coronal observations, we compare the analysis and diagnostics of a loop after subtracting the background with two different and independent methods. The dataset includes sequences of images in the 171 A, 195 A filter bands of TRACE. One background subtraction method consists in taking as background values those obtained from interpolation between concentric strips around the analyzed loop. The other method is a pixel-to-pixel subtraction of the final image when the loop had completely faded out, already used by Reale & Ciaravella 2006. We compare the emission distributions along the loop obtained with the two methods and find that they are considerably differen…

Parallel Calculation of CCSD and CCSD(T) Analytic First and Second Derivatives.

2007

In this paper we present a parallel adaptation of a highly efficient coupled-cluster algorithm for calculating coupled-cluster singles and doubles (CCSD) and coupled-cluster singles and doubles augmented by a perturbative treatment of triple excitations (CCSD(T)) energies, gradients, and, for the first time, analytic second derivatives. A minimal-effort strategy is outlined that leads to an amplitude-replicated, communication-minimized implementation by parallelizing the time-determining steps for CCSD and CCSD(T). The resulting algorithm is aimed at affordable cluster architectures consisting of compute nodes with sufficient memory and local disk space and that are connected by standard co…

Phonon-to-spin mapping in a system of a trapped ion via optimal control

2015

We propose a protocol for measurement of the phonon number distribution of a harmonic oscillator based on selective mapping to a discrete spin-1/2 degree of freedom. We consider a system of a harmonically trapped ion, where a transition between two long-lived states can be driven with resolved motional sidebands. The required unitary transforms are generated by amplitude-modulated polychromatic radiation fields, where the time-domain ramps are obtained from numerical optimization by application of the chopped random basis algorithm (CRAB). We provide a detailed analysis of the scaling behavior of the attainable fidelities and required times for the mapping transform with respect to the size…

Diffuse solar radiation statistics for Italy

1981

Abstract In this paper diffuse radiation is correlated with usually measured or more easy computable quantities in order to have a larger number of data available for the various applications of solar energy. Here are used two types of correlation: (a) diffuse radiation as a function of global and extraterrestrial radiation; (b) diffuse radiation as a function of ralative sunshine and extraterrestrial radiation. On the basis of the above correlations, empirical equations have been proposed and their coefficients have been calculated by fitting the experimental data of three Italian stations. The degree of accuracy of the fit has been estimated by a coefficient introduced and called by us “r…

A Brightening Coronal Loop Observed byTRACE. II. Loop Modeling and Constraints on Heating

2000

This is the second of two papers dedicated to the brightening of a coronal loop observed by the Transition Region and Coronal Explorer (TRACE) on 1998 June 26; it aims at hydrodynamic modeling of the brightening. Since the loop geometry is practically unchanged during the brightening, the evolution of the plasma confined in the loop is described with a one-dimensional hydrodynamic time-dependent numerical model, and from the results the emission along the loop in the TRACE 171 A band is synthesized. The information from Paper I is used to derive the geometry and the initial configuration of the loop as well as for comparison with the results of the model. The modeling is focused to determin…

Self-consistent field theory based molecular dynamics with linear system-size scaling

2012

We present an improved field-theoretic approach to the grand-canonical potential suitable for linear scaling molecular dynamics simulations using forces from self-consistent electronic structure calculations. It is based on an exact decomposition of the grand canonical potential for independent fermions and does neither rely on the ability to localize the orbitals nor that the Hamilton operator is well-conditioned. Hence, this scheme enables highly accurate all-electron linear scaling calculations even for metallic systems. The inherent energy drift of Born-Oppenheimer molecular dynamics simulations, arising from an incomplete convergence of the self-consistent field cycle, is circumvented …

W3 theory: robust computational thermochemistry in the kJ/mol accuracy range

2003

We are proposing a new computational thermochemistry protocol denoted W3 theory, as a successor to W1 and W2 theory proposed earlier [Martin and De Oliveira, J. Chem. Phys. 111, 1843 (1999)]. The new method is both more accurate overall (error statistics for total atomization energies approximately cut in half) and more robust (particularly towards systems exhibiting significant nondynamical correlation) than W2 theory. The cardinal improvement rests in an approximate account for post-CCSD(T) correlation effects. Iterative T_3 (connected triple excitations) effects exhibit a basis set convergence behavior similar to the T_3 contribution overall. They almost universally decrease molecular bi…

2021

Electronic circular dichroism (ECD) is a powerful spectroscopy method for investigating chiral properties at the molecular level. ECD calculations with the commonly used linear-response time-dependent density functional theory (LR-TDDFT) framework can be prohibitively costly for large systems. To alleviate this problem, we present here an ECD implementation within the projector augmented-wave method in a real-time-propagation TDDFT framework in the open-source GPAW code. Our implementation supports both local atomic basis sets and real-space finite-difference representations of wave functions. We benchmark our implementation against an existing LR-TDDFT implementation in GPAW for small chir…

A Numerical Study of Relativistic Jets

1996

Numerical simulations of supersonic jets are able to explain the structures observed in many VLA images of radio sources. The improvements achieved in classical simulations (see Hardee, these proceedings) are in contrast with the almost complete lack of relativistic simulations the reason being that numerical difficulties arise from the highly relativistic flows typical of extragalactic jets. For our study, we have developed a two-dimensional code which is based on (i) an explicit conservative differencing of the special relativistic hydrodynamics (SRH) equations and (ii) the use of an approximate Riemann solver (see Marti et al. 1995a,b and references therein).