Search results for "Principle"
showing 10 items of 1023 documents
Bidirectional Nonorthogonal Schardin-Lau Interferometer
1990
We discuss the formation of self-images of a 2-D grating composed by two rulings of equal period, but in-plane rotated. We describe the in-register condition for setting the lensless Lau effect, with this type of gratings; and we propose to use the above configuration for interferometrically visualizing, in noncoherent light, phase structures, in two nonorthogonal directions.
Analytical Expressions for Radiative Losses in Solar Cells
2019
Analytical expressions for the fundamental losses in single junction solar cells are revised and improved. The losses are, as far as possible, described using parameters with clear physical interpretations. One important improvement compared to earlier work is the use of Lambert’s W function, which allows for analytical expressions for the voltage and current at the maximum power point. Other improvements include the use of Stefan Boltzmann’s law to describe the incoming energy flux as well as taking into account the fermionic nature of the electrons when calculating the thermalization loss. A new expression, which combines emission, Boltzmann and Carnot losses, is presented. Finally, an ex…
Superresolved imaging in digital holography by superposition of tilted wavefronts
2006
A technique based on superresolution by digital holographic microscopic imaging is presented. We used a two dimensional (2-D) vertical-cavity self-emitting laser (VCSEL) array as spherical-wave illumination sources. The method is defined in terms of an incoherent superposition of tilted wavefronts. The tilted spherical wave originating from the 2-D VCSEL elements illuminates the target in transmission mode to obtain a hologram in a Mach-Zehnder interferometer configuration. Superresolved images of the input object above the common lens diffraction limit are generated by sequential recording of the individual holograms and numerical reconstruction of the image with the extended spatial frequ…
White-light array generation with a diffractive lenslet array
1999
Abstract In this paper we present two different optical configurations providing a white-light array generator based on a diffractive lenslet array (DLA). In both cases, starting from a white-light point source we achieve a regularly spaced set of sharp light spots by use of a single DLA and a small number of extra lenses (only one or two). The first optical system permits us to change the separation between the intensity peaks in a tunable way. The second is very compact and consists only of diffractive lens elements. The key question in both set-ups is the use of achromatic Fourier-transform methods. In this way, we achieve, in a first-order approximation, the superposition of the chromat…
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…
Lau rings: In-register incoherent superposition of radial self-images
1989
Abstract We describe an optical method for obtaining in-register, incoherent superposition of self-images, with radial symmetry. That is, the Lau effect is implemented, either at infinity or at finite distances, in the form of bright and dark rings of high visibility. This is applied for visualizing radially phase structures, with good-signal-to-noise ratio.
Variation of extent of reaction in closed chemical equilibrium when changing the temperature at constant volume
2011
In this paper it is presented a thermodynamic analysis that aims to find the mathematical expression of the variation of extent of reaction with the infinitesimal variation in the temperature at constant volume of a chemical equilibrium mixture. The goal of this paper is to establish an alternative approach to avoid both the Le Chatelier's principle and the problems that emerge when trying to apply its qualitative statements. This attempt is based on the laws of thermodynamics.
Dosimetric study of the 15mm ROPES eye plaque
2004
The main aim of this paper is to make a study of dose-rate distributions obtained around the 15 mm, radiation oncology physics and engineering services, Australia (ROPES) eye plaque loaded with {sup 125}I model 6711 radioactive seeds. In this study, we have carried out a comparison of the dose-rate distributions obtained by the algorithm used by the Plaque Simulator (PS) (BEBIG GmbH, Berlin, Germany) treatment planning system with those obtained by means of the Monte Carlo method for the ROPES eye plaque. A simple method to obtain the dose-rate distributions in a treatment planning system via the superposition of the dose-rate distributions of a seed placed in the eye plaque has been develo…
Use of site symmetry in supercell models of defective crystals: Polarons in CeO2
2017
The authors thank R. Merkle and G. W. Watson for stimulating discussions. E. K. also acknowledges partial financial support from the Russian Science Foundation for the study of charged defects under the project 14-43-00052. A. C. also acknowledges financial support from the University of Latvia Foundation (Arnis Riekstins's "MikroTik" donation). E. K. and D. G. express their gratitude to the High Performance Computer Centre in Stuttgart (HLRS, project DEFTD 12939) for the provided computer facilities whereas R. A. E. thanks the St. Petersburg State University Computer Center for assistance in high-performance calculations.
Maxwell Theory as a Classical FieldTheory
2012
Hamilton’s variational principle and the Lagrangian mechanics that rests on it are exceedingly successful in their application to mechanical systems with a finite number of degrees of freedom. Hamilton’s principle characterizes the physically realizable orbits, among the set of all possible orbits, as being the critical elements of the action integral. The Lagrangian function, although not an observable on its own, is not only useful in deriving the equations of motion but is also an important tool for identifying symmetries of the theory and constructing the corresponding conserved quantities, via Noether’s theorem.