Search results for "Computational physics"

Modulation instability scenario in negative index materials

2010

We present an investigation of the critical frequency windows permitting modulation instability in negative index materials. The principal motivation for our analysis stems from the impact of the inevitable presence of the effective dispersive magnetic permeability in addition to the effective dielectric permittivity determining the propagation model for ultrashort pulses in negative index materials. We emphasize the influence of nonlinear dispersion terms, arising out of the combinatorial effect of the dispersive permeability with the nonlinear polarization, over the MI phenomena, the outcome of its development achieved by using linear stability analysis. Gain spectrum investigation has be…

Nonlinear Current Generation in Degenerate Semiconductors Embedded in Constant and Low-Frequency Electric Fields

2006

The explicit analytical forms of nonlinear currents in degenerate semiconductors serving as sources of coherent radiation in the wavelength millimetric and submillimetric ranges are established.

Monte Carlo dosimetric characterization of the Cs-137 selectron/LDR source: evaluation of applicator attenuation and superposition approximation effe…

2004

The purpose of this study is to calculate the dose rate distribution for the Amersham Cs-137 pellet source used in brachytherapy with the Selectron low-dose-rate remote afterloading system in gynaecological applications using the Monte Carlo code GEANT4. The absolute dose rate distribution for the pellet source was obtained and presented as a one-dimensional absolute dose rate table as well as in the Task Group 43 dose-calculation formalism. In this study, excellent agreement was found between the point source theoretical model using fitted polynomial values and Monte Carlo calculations of the dose rate distribution for the pellet source. A comparison study was also made between the dose ra…

Time-domain-induced polarization: Full-decay forward modeling and 1D laterally constrained inversion of Cole-Cole parameters

2012

Time-domain-induced polarization has significantly broadenedits field of reference during the last decade, from mineralexploration to environmental geophysics, e.g., for clay and peatidentification and landfill characterization. Though, insufficientmodeling tools have hitherto limited the use of time-domaininducedpolarization for wider purposes. For these reasons, anew forward code and inversion algorithm have been developedusing the full-time decay of the induced polarization response,together with an accurate description of the transmitter waveformand of the receiver transfer function, to reconstruct thedistribution of the Cole-Cole parameters of the earth. The accuratemodeling of the tra…

SU-GG-T-70: A Dosimetric Study of the MicroSelectron HDR Ir-192 Brachytherapy Source

2010

Purpose: Recently the manufacturer of the mHDR‐v2 HDR Ir‐192 brachytherapy source clarified design changes that may alter the existing dosimetric data for this source. The object of this study was to obtain new dose rate tables following the TG‐43 formalism and to provide these data in close proximity to the source with high spatial resolution including the electron dosimetric contributions from Ir‐192 disintegration. Methods and Material: To study the source we used three different Monte Carlo codes: MCNP5, GEANT4, and Penelope. The source was located inside a 40 cm radius water phantom. Dose and kerma were obtained using 0.1 mm thick voxels to provide high‐resolution dosimetry near the so…

SU-E-T-508: Monte Carlo Dosimetric Study of the CSM40 Low Dose Rate Source

2013

Purpose: There is a LDR 137Cs brachytherapy source, CSM40, developed by Eckert & Ziegler BEBIG. Fundamental dosimetric datasets to be used on treatment planning systems do not exist for this source. This study aims to obtain quality dosimetric data for this source for its use in clinical practice as required by AAPM and ESTRO. Methods: Penelope2008 and GEANT4 Monte Carlo codes were used to characterize this source dosimetry. Water composition and mass density was that recommended by AAPM. Due to the typical energies of the 137 Cs, dose for small distances can be approximated by collisional kerma. Therefore, we have considered collisional kerma for r<20 cm. To provide adequate spatial resolu…

Dosimetry revisited for the HDR I192r brachytherapy source model mHDR-v2

2010

Purpose: Recently, the manufacturer of the HDR I 192 r mHDR-v2 brachytherapysource reported small design changes (referred to herein as mHDR-v2r) that are within the manufacturing tolerances but may alter the existing dosimetric data for this source. This study aimed to (1) check whether these changes affect the existing dosimetric data published for this source; (2) obtain new dosimetric data in close proximity to the source, including the contributions from I 192 r electrons and considering the absence of electronic equilibrium; and (3) obtain scatterdose components for collapsed cone treatment planning system implementation. Methods: Three different Monte Carlo(MC) radiation transport co…

Response to “Comment on ‘Comparison and uncertainty evaluation of different calibration protocols and ionization chambers for low-energy surface brac…

2016

Analysis of equations arising in gyrotron theory

2012

The gyrotron is a microwave source whose operation is based on the stimulated cyclotron radiation of electrons oscillating in a static magnetic field. Powerful gyrotrons can be used to heat nuclear fusion plasma. In addition, they have found a wide utility in plasma diagnostics, plasma chemistry, radars, extra-high-resolution spectroscopy, high-temperature processing of materials, medicine, etc. However, the main application of gyrotrons is in electron cyclotron resonance heating in tokamaks and stellarators. Equations describing gyrotron operation are ordinary differential equations and Schrödinger type partial differential equations. The present paper provides a survey of the analytical a…

A multi-reading method for dosimetric TL measurements with CaSO4:Dy phosphors

1979

Abstract A technique of dosimetric TL measurement for CaSO 4 :Dy phosphors is proposed. It is based on the results obtained in previous works, in which an approximately multi-Gaussian energetic distribution of the traps associated with the dosimetric peak and a different supralinear behaviour of the Gaussians were found. A single dosimeter is read a number of times by successive heating cycles which, starting always from room temperature, reach higher and higher final temperatures; in this manner it is possible to obtain consistent information on the dose several times. The drawback of the usual TL measurements, that is the total emptying of the dosimeter during one measurement, is then avo…