Search results for "Computational physics"

A Monte Carlo-based dosimetric characterization of Esteya® , an electronic surface brachytherapy unit

2018

PURPOSE The purpose of this work is threefold: First, to obtain the phase space of an electronic brachytherapy (eBT) system designed for surface skin treatments. Second, to explore the use of some efficiency enhancing (EFEN) strategies in the determination of the phase space. Third, to use the phase space previously obtained to perform a dosimetric characterization of the Esteya eBT system. METHODS The Monte Carlo study of the 69.5 kVp x-ray beam of the Esteya® unit (Elekta Brachytherapy, Veenendaal, The Netherlands) was performed with PENELOPE2014. The EFEN strategies included the use of variance reduction techniques and mixed Class II simulations, where transport parameters were fine-tune…

Monte Carlo Simulation of Harmonic Generation in GaAs structures operating under large-signal Conditions

2007

By using a multiparticles Monte Carlo technique, with a self-consistently coupled one-dimensional Poisson solver, we investigate the dependence of the nonlinear carrier dynamics in GaAs n+nn+ micro e submicro-structures operating under very intense sub-terahertz signals by: (i) the frequency and the intensity of the excitation signal and (ii) the length of the n region.

Fine Thermal Structure of a Coronal Active Region

2007

著者人数：12名

Exploring the Physical Limits of Saturation Contrast in Magnetic Resonance Imaging

2012

International audience; Magnetic Resonance Imaging has become nowadays an indispensable tool with applications ranging from medicine to material science. However, so far the physical limits of the maximum achievable experimental contrast were unknown. We introduce an approach based on principles of optimal control theory to explore these physical limits, providing a benchmark for numerically optimized robust pulse sequences which can take into account experimental imperfections. This approach is demonstrated experimentally using a model system of two spatially separated liquids corresponding to blood in its oxygenated and deoxygenated forms.

Challenges with balancing excitations in intermediate-band solar cells

2015

New insight into the potential of practical solar cells can be given through alternative modeling approaches like Monte Carlo simulations. In the present work, the performance of intermediate band solar cells was examined by this method. It is demonstrated that the balance of excitations from the valence band to the intermediate band and from the intermediate band to the conduction band is of great importance for the performance of such cells. Several cases with different distributions of photons given by ASTM standards have been employed in order to detect spectrum sensitivity. Incident photons are accounted for as they interact with the electrons in the valence band or in the intermediate…

Track reconstruction for theMu3eexperiment based on a novel Multiple Scattering fit

2017

The Mu3e experiment is designed to search for the lepton flavor violating decay μ + → e + e + e − . The aim of the experiment is to reach a branching ratio sensitivity of 10−16 . In a first phase the experiment will be performed at an existing beam line at the Paul-Scherrer Institute (Switzerland) providing 108 muons per second, which will allow to reach a sensitivity of 2 · 10−15 . The muons with a momentum of about 28 MeV/c are stopped and decay at rest on a target. The decay products (positrons and electrons) with energies below 53MeV are measured by a tracking detector consisting of two double layers of 50 μm thin silicon pixel sensors. The high granularity of the pixel detector with a …

A common optical algorithm for the evaluation of specular spin polarized neutron and Mössbauer reflectivities

2001

Using the general approach of Lax for multiple scattering of waves a 2x2 covariant expression for the reflectivity of polarized slow neutrons of a magnetic layer structure of arbitrary complexity is given including polarization effects of the external magnetic field. The present formalism is identical to the earlier published one for the (nuclear) resonant X-ray (Mossbauer) reflectivity and properly takes the effect of the external magnetic field of arbitrary direction on the neutron beam into account. The form of the reflectivity matrix allows for an efficient numerical calculation.

Computation of MHD buoyant flows at low Pr in a cubic enclosure with a full resolution of the Hartmann layers

2002

External noise effects on the electron velocity fluctuations in semiconductors

2008

We investigate the modification of the intrinsic carrier noise spectral density induced in low-doped semiconductor materials by an external correlated noise source added to the driving high-frequency periodic electric field. A Monte Carlo approach is adopted to numerically solve the transport equation by considering all the possible scattering phenomena of the hot electrons in the medium. We show that the noise spectra are strongly affected by the intensity and the correlation time of the external random electric field. Moreover this random field can cause a suppression of the total noise power.

Nonlinear inverse bremsstrahlung and highly anisotropic electron distributions

1996

A procedure is proposed to deal with the approximate solution of the kinetic equation for the velocity distribution function of electrons in a fully ionized plasma in the presence of strong, high frequency radiation. The Legendre polynomial expansion is applied after the kinetic equation has been written in an oscillating frame, where some directions are appropriately scaled, with the aim of making approximately isotropic, on the average, distributions that are otherwise anisotropic. The equations are derived for the isotropic part of the electron distribution in the scaled frame and for the scaling factor. The procedure is meant to display its potential in cases where the electron distribu…