Monte Carlo

Quantitative Comparison of the Spatial Distribution of Radar and Gauge Rainfall Data

by Anh Phuong Tran

Co-authored with Seong-Sim Yoon and Deg-Hyo Bae,
Published in Journal of Hydrometeorology

The common statement that rain gauge network usually provides better observation at specific points while weather... more The common statement that rain gauge network usually provides better observation at specific points while weather radar provides more accurate observation of the spatial distribution of rain field over a large area has never been subjected to quantitative evaluation. The aim of this paper is to evaluate the statement by using some statistical criteria. The Monte Carlo simulation experiment, Inverse Distance Weighting (IDW) interpolation method and cross validation technique are used to investigate the relation between the accuracy of the interpolated rainfall and the rain gauge density. The radar reflectivity - rainfall intensity (Z-R) relationship is constructed by the least square fitting method from observation data of radar and rain gauges. The variation in this relationship and the accuracy of the radar rainfall with rain gauge density are evaluated by using the Monte Carlo simulation experiment. Three storm events are selected as the case studies. The obtained results show that the accuracy of interpolated and radar rainfall increases nonlinearly with increasing gauge density. The higher correlation coefficient (γ) value of radar rainfall estimation, compared to gauge interpolation, especially in the convective storm, proves that radar observation provides a more accurate spatial structure of the rain field than gauge observation does.

Hot carriers relaxation in highly excited polar semiconductors: Hot phonons versus phonon–plasmon coupling

by tea eric

We present a study of the photo-excited charge carriers relaxation dynamics in polar semiconductors comparing... more We present a study of the photo-excited charge carriers relaxation dynamics in polar semiconductors comparing calculations to pump probe experiments. Hot carrier densities in the 10^18cm-3 range can easily be photo-generated using moderately intense optical excitations. This can lead to known phenomena, namely, hot phonon populations and the coupling of polar optical phonons with plasmon modes. However, these two phenomena can affect the hot carriers relaxation and have never been examined together. This is a problem for the theoretical study of future Hot Carrier Solar Cells, where the conditions allow both of these phenomena to occur. The charge carriers dynamics and the coupling of polar optical phonons with plasmon modes are treated by a Full Band Ensemble Monte Carlo simulation code featuring a self-consistent dielectric function. To take into consideration hot phonon populations and the subsequent phonon bottleneck for the carriers relaxation, the charge carriers simulation code is coupled to a phonon dedicated Ensemble Monte Carlo code. This enables for the first time an accurate study of both the charge carriers and phonon systems dynamics, the latter being most of the time overly simplified in previous studies. The present work explores to which extent the two aforementioned phenomena affect the photo-generated charge carriers relaxation in GaAs and can be easily adapted to other polar semiconductors.

Random imperfection fields to model the size effect in laboratory wood specimens

by Sara Casciati

Casciati S. and Domaneschi M. (2007). “Random imperfection fields to model the size effect in laboratory wood specimens”. Structural Safety, 29(4), 308-321. ISSN: 0167-4730.

DATA E LUOGO DI PUBBLICAZIONE: October 2007; Elsevier Science Bv, 1000 AE Amsterdam, Netherlands.

ABSTRACT. The composite nature of a wood continuum prevents one from extrapolating the results of laboratory tests on... more ABSTRACT. The composite nature of a wood continuum prevents one from extrapolating the results of laboratory tests on standard wood specimens to structural elements of significant size. Therefore, these elements are usually tested under standardized loading conditions in order to detect a sort of average material behaviour.
In this paper, the initial step consists, instead, of testing the material specimens. The extension of the results to structural elements is then pursued by introducing a random field, or, in a discretized model, a random array of imperfections.
The calibration of the suitable spatial distribution of the imperfections is then investigated by a mixed experimental–numerical approach, for a reference beam. The analyses on the relative finite elements model are iterated to match the response of the full scale laboratory tests.

KEYWORDS: Biaxial tests; Finite element model; Imperfections; Laboratory tests; Random field; Wood specimens

Cohesive Crack Propagation in a Random Elastic Medium

by Sara Casciati

Bruggi M., Casciati S., and Faravelli L. (2008). “Cohesive crack propagation in a random elastic medium”. Probabilistic Engineering Mechanics, 23(1), 23-35. ISSN: 0266-8920.

DATA E LUOGO DI PUBBLICAZIONE: January 2008; Elsevier Sci Ltd, Kidlington, Oxford OX5 1GB, Oxon, England.

ABSTRACT. The issue of generating non-Gaussian, multivariate and correlated random fields, while preserving the... more ABSTRACT. The issue of generating non-Gaussian, multivariate and correlated random fields, while preserving the internal auto-correlation structure of each single-parameter field, is discussed with reference to the problem of cohesive crack propagation. Three different fields are introduced to model the spatial variability of the Young modulus, the tensile strength of the material, and the fracture energy, respectively. Within a finite-element context, the crack-propagation phenomenon is analyzed by coupling a Monte Carlo simulation scheme with an iterative solution algorithm based on a truly-mixed variational formulation which is derived from the Hellinger–Reissner principle. The selected approach presents the advantage of exploiting the finite-element technology without the need to introduce additional modes to model the displacement discontinuity along the crack boundaries. Furthermore, the accuracy of the stress estimate pursued by the truly-mixed approach is highly desirable, the direction of crack propagation being determined on the basis of the principal stress criterion. The numerical example of a plain concrete beam with initial crack under a three-point bending test is considered. The statistics of the response is analyzed in terms of peak load and load–mid deflection curves, in order to investigate the effects of the uncertainties on both the carrying capacity and the post-peak behaviour. A sensitivity analysis is preliminarily performed and its results emphasize the negative effects of not accounting for the auto-correlation structure of each random field. A probabilistic method is then applied to enforce the auto-correlation without significantly altering the target marginal distributions. The novelty of the proposed approach with respect to other methods found in the literature consists of not requiring the a priori knowledge of the global correlation structure of the multivariate random field.

KEYWORDS: Multivariate non-Gaussian random fields; Auto-correlation; Cohesive crack propagation; Truly-mixed finite element method; Monte Carlo simulations

DAGS: distribution agnostic sequential Monte Carlo scheme for task execution time estimation

by Muhammad Adnan Siddique

Comparison of three regularized solution techniques in a three-dimensional inverse radiation problem

by hakan erturk

Inverse solution of radiative heat transfer in two-dimensional irregularly shaped enclosures

by hakan erturk

Accuracy of Monte Carlo Method Re-Examined on a Box-Shaped Furnace Problem

by hakan erturk

Daylight simulation with photon maps

by Roland Schregle

PhD Thesis. Universität des Saarlandes, Saarbrücken, October 2004

The aim of this thesis is to investigate the applicability of a novel image synthesis technique based on Monte Carlo... more The aim of this thesis is to investigate the applicability of a novel image synthesis technique based on Monte Carlo particle transport to daylight simulation. Many materials used in daylight simulation are specifically designed to redirect light, and as such give rise to complex effects such as caustics. The photon map technique was chosen for its efficent handling of these effects. To assess its ability to produce physically correct results which can be applied to lighting simulation, a validation was carried out based on analytical case studies and on simple experimental setups. As prerequisite to validation, the photon map´s inherent bias/noise tradeoff is investigated. This tradeoff depends on the density estimate bandwidth used in the reconstruction of the illumination. The error analysis leads to the development of a bias compensating operator which adapts the bandwidth according to the estimated bias in the reconstructed illumination.

Rendering with photon maps

by Roland Schregle

Diploma Thesis. University of Bonn, Department of Computer Science, 1998

The presentation of a recent addition to the suite of popular global illumination rendering methods is the focus of... more The presentation of a recent addition to the suite of popular global illumination rendering methods is the focus of this thesis. The photon map comprises a particle transport simulation with a density estimate characterized by independency of the scene geometry and the ability to efficiently model diffuse global illumination and caustics. Its embedding in existing ray tracing environments is straightforward; an implementation of the photon map and its integration in the Minimal Rendering Toolkit (MRT) is described in detail.

Bias compensation for photon maps

by Roland Schregle

Roland, S. (2003), Bias Compensation for Photon Maps. Computer Graphics Forum, 22: 729–742.

Density estimation techniques such as the photon map method rely on a particle transport simulation to reconstruct... more Density estimation techniques such as the photon map method rely on a particle transport simulation to reconstruct indirect illumination, which is proportional to the particle density. In the photon map framework, particles are usually located using nearest-neighbour methods due to their generality. However, these methods have an inherent tradeoff between local bias and noise in the reconstructed illumination, which depends on the density estimate bandwidth. This paper presents a bias compensating operator for nearest-neighbour density estimation which adapts the bandwidth according to the estimated bias in the reconstructed illumination.

Minority electron mobilities in GaAs, In0.53Ga0.47As, and GaAs0.50Sb0.50 calculated within an ensemble Monte Carlo model

by tea eric

The minority electron transport is crucial for the performances of heterojunction bipolar transistors (HBTs). Among... more The minority electron transport is crucial for the performances of heterojunction bipolar transistors (HBTs). Among the III-V semiconductors family, GaAsSb exhibits several advantages making it a serious candidate for the new generation of high speed HBTs. However, this alloy suffers from a lack of experimental studies. Properties such as electronic structure and charge carrier mobilities are of prime importance in theoretical device operation calculations. In this article, we investigate the minority electron mobilities by means of an ensemble Monte Carlo modeling including polar optical phonon–plasmon coupling through a self-consistent dielectric function. Realistic electronic structures are provided by a nonlocal empirical pseudopotential method. It is found that GaAs0.50Sb0.50 does not show a mobility enhancement for very high acceptor doping levels unlike GaAs and Ga0.47In0.53As.

On a modified Monte-Carlo method and variable soft sphere model for rarefied binary gas mixture flow simulation

by Pouyan Jahangiri

The effect of new terms in the improved algorithm, the modified direct simulation Monte-Carlo (MDSMC) method, is... more The effect of new terms in the improved algorithm, the modified direct simulation Monte-Carlo (MDSMC) method, is investigated by simulating a rarefied binary gas mixture flow inside a rotating cylinder. Dalton law for the partial pressures contributed by each species of the binary gas mixture is incorporated into our simulation using the MDSMC method and the direct simulation Monte-Carlo (DSMC) method. Moreover, the effect of the exponent of the cosine of deflection angle (a) in the inter molecular collision models, the variable soft sphere (VSS) and the variable hard sphere (VHS), is investigated in our simulation. The improvement of the results of simulation is pronounced using the MDSMC method when compared with the results of the DSMC method. The results of simulation using the VSS model show some improvements on the result of simulation for the mixture temperature at radial distances close to the cylinder wall where the temperature reaches the maximum value when compared with the results using the VHS model.

EM Shielding, Dosimetry Control and Xe(135)-Sm(149) Poisoning Effect for Nuclear Waste Treatment

by Syed Bahauddin Alam

Alam, Syed Bahauddin; Kabir, Hussain Mohammed Dipu; Sakib, Md. Nazmus; Shahnaz, Celia; Fattah, Shaikh Anowarul;
Power and Energy (PECon), 2010 IEEE International Conference on
Digital Object Identifier: 10.1109/PECON.2010.5697565
Publication Year: 2010 , Page(s): 101 - 106

A crucial yard mensuration of the shape up of a state is the level to which clean, low-priced and sustainable energy... more A crucial yard mensuration of the shape up of a state is the level to which clean, low-priced and sustainable energy resources are made available for the bulk assemblage. At present eons, equating cost factors, environmental issues, power generation with other substitute energy informants, atomic or nuclear power is turning into a popular alternative as an energy option. Though it is clean and safe alternative, nuclear waste is still a matter of great concern. In this paper, nuclear waste treatment for nuclear plant by radioactive and electromagnetic shielding via dose conversion factors, photons and neutrons response functions has been explained. Moreover, analyzing of Quality-Factor and Poisoning decay of Xenon and Samarium has been discussed. In this paper modernized radioactive waste treatment processes as well as secured data transmission from nuclear power plant to National Load Dispatch Center (NLDC) using digital watermarking is proposed as this type of vulnerable data transmission is a matter of great concern

Single-particle method for stochastic simulation of coagulation processes

by Alexander Vikhansky

Conservative method for the reduction of the number of particles in the Monte Carlo simulation method for kinetic equations

by Alexander Vikhansky

Iterative Monte Carlo Protein Design

by Camilo Rostoker

Co-authored with Reza Lotun