Shell model the Monte Carlo way
Energy Technology Data Exchange (ETDEWEB)
Ormand, W.E.
1995-03-01
The formalism for the auxiliary-field Monte Carlo approach to the nuclear shell model is presented. The method is based on a linearization of the two-body part of the Hamiltonian in an imaginary-time propagator using the Hubbard-Stratonovich transformation. The foundation of the method, as applied to the nuclear many-body problem, is discussed. Topics presented in detail include: (1) the density-density formulation of the method, (2) computation of the overlaps, (3) the sign of the Monte Carlo weight function, (4) techniques for performing Monte Carlo sampling, and (5) the reconstruction of response functions from an imaginary-time auto-correlation function using MaxEnt techniques. Results obtained using schematic interactions, which have no sign problem, are presented to demonstrate the feasibility of the method, while an extrapolation method for realistic Hamiltonians is presented. In addition, applications at finite temperature are outlined.
Novel Extrapolation Method in the Monte Carlo Shell Model
Shimizu, Noritaka; Mizusaki, Takahiro; Otsuka, Takaharu; Abe, Takashi; Honma, Michio
2010-01-01
We propose an extrapolation method utilizing energy variance in the Monte Carlo shell model in order to estimate the energy eigenvalue and observables accurately. We derive a formula for the energy variance with deformed Slater determinants, which enables us to calculate the energy variance efficiently. The feasibility of the method is demonstrated for the full $pf$-shell calculation of $^{56}$Ni, and the applicability of the method to a system beyond current limit of exact diagonalization is shown for the $pf$+$g_{9/2}$-shell calculation of $^{64}$Ge.
Monte Carlo Shell Model for ab initio nuclear structure
Directory of Open Access Journals (Sweden)
Abe T.
2014-03-01
Full Text Available We report on our recent application of the Monte Carlo Shell Model to no-core calculations. At the initial stage of the application, we have performed benchmark calculations in the p-shell region. Results are compared with those in the Full Configuration Interaction and No-Core Full Configuration methods. These are found to be consistent with each other within quoted uncertainties when they could be quantified. The preliminary results in Nshell = 5 reveal the onset of systematic convergence pattern.
Unified description of pf-shell nuclei by the Monte Carlo shell model calculations
Energy Technology Data Exchange (ETDEWEB)
Mizusaki, Takahiro; Otsuka, Takaharu [Tokyo Univ. (Japan). Dept. of Physics; Honma, Michio
1998-03-01
The attempts to solve shell model by new methods are briefed. The shell model calculation by quantum Monte Carlo diagonalization which was proposed by the authors is a more practical method, and it became to be known that it can solve the problem with sufficiently good accuracy. As to the treatment of angular momentum, in the method of the authors, deformed Slater determinant is used as the basis, therefore, for making angular momentum into the peculiar state, projected operator is used. The space determined dynamically is treated mainly stochastically, and the energy of the multibody by the basis formed as the result is evaluated and selectively adopted. The symmetry is discussed, and the method of decomposing shell model space into dynamically determined space and the product of spin and isospin spaces was devised. The calculation processes are shown with the example of {sup 50}Mn nuclei. The calculation of the level structure of {sup 48}Cr with known exact energy can be done with the accuracy of peculiar absolute energy value within 200 keV. {sup 56}Ni nuclei are the self-conjugate nuclei of Z=N=28. The results of the shell model calculation of {sup 56}Ni nucleus structure by using the interactions of nuclear models are reported. (K.I.)
Benchmark calculation of no-core Monte Carlo shell model in light nuclei
Abe, T; Otsuka, T; Shimizu, N; Utsuno, Y; Vary, J P; 10.1063/1.3584062
2011-01-01
The Monte Carlo shell model is firstly applied to the calculation of the no-core shell model in light nuclei. The results are compared with those of the full configuration interaction. The agreements between them are within a few % at most.
New Generation of the Monte Carlo Shell Model for the K Computer Era
Shimizu, Noritaka; Tsunoda, Yusuke; Utsuno, Yutaka; Yoshida, Tooru; Mizusaki, Takahiro; Honma, Michio; Otsuka, Takaharu
2012-01-01
We present a newly enhanced version of the Monte Carlo Shell Model method by incorporating the conjugate gradient method and energy-variance extrapolation. This new method enables us to perform large-scale shell-model calculations that the direct diagonalization method cannot reach. This new generation framework of the MCSM provides us with a powerful tool to perform most-advanced large-scale shell-model calculations on current massively parallel computers such as the K computer. We discuss the validity of this method in ab initio calculations of light nuclei, and propose a new method to describe the intrinsic wave function in terms of the shell-model picture. We also apply this new MCSM to the study of neutron-rich Cr and Ni isotopes using the conventional shell-model calculations with an inert 40Ca core and discuss how the magicity of N = 28, 40, 50 remains or is broken.
Nuclear Level Density of ${}^{161}$Dy in the Shell Model Monte Carlo Method
Özen, Cem; Nakada, Hitoshi
2012-01-01
We extend the shell-model Monte Carlo applications to the rare-earth region to include the odd-even nucleus ${}^{161}$Dy. The projection on an odd number of particles leads to a sign problem at low temperatures making it impractical to extract the ground-state energy in direct calculations. We use level counting data at low energies and neutron resonance data to extract the shell model ground-state energy to good precision. We then calculate the level density of ${}^{161}$Dy and find it in very good agreement with the level density extracted from experimental data.
Microsopic nuclear level densities by the shell model Monte Carlo method
Alhassid, Y; Gilbreth, C N; Nakada, H; Özen, C
2016-01-01
The configuration-interaction shell model approach provides an attractive framework for the calculation of nuclear level densities in the presence of correlations, but the large dimensionality of the model space has hindered its application in mid-mass and heavy nuclei. The shell model Monte Carlo (SMMC) method permits calculations in model spaces that are many orders of magnitude larger than spaces that can be treated by conventional diagonalization methods. We discuss recent progress in the SMMC approach to level densities, and in particular the calculation of level densities in heavy nuclei. We calculate the distribution of the axial quadrupole operator in the laboratory frame at finite temperature and demonstrate that it is a model-independent signature of deformation in the rotational invariant framework of the shell model. We propose a method to use these distributions for calculating level densities as a function of intrinsic deformation.
Directory of Open Access Journals (Sweden)
Alhassid Y.
2014-04-01
Full Text Available The shell model Monte Carlo (SMMC method enables calculations in model spaces that are many orders of magnitude larger than those that can be treated by conventional methods, and is particularly suitable for the calculation of level densities in the presence of correlations. We review recent advances and applications of SMMC for the microscopic calculation of level densities. Recent developments include (i a method to calculate accurately the ground-state energy of an odd-mass nucleus, circumventing a sign problem that originates in the projection on an odd number of particles, and (ii a method to calculate directly level densities, which, unlike state densities, do not include the spin degeneracy of the levels. We calculated the level densities of a family of nickel isotopes 59−64Ni and of a heavy deformed rare-earth nucleus 162Dy and found them to be in close agreement with various experimental data sets.
Constrained-path quantum Monte Carlo approach for non-yrast states within the shell model
Energy Technology Data Exchange (ETDEWEB)
Bonnard, J. [INFN, Sezione di Padova, Padova (Italy); LPC Caen, ENSICAEN, Universite de Caen, CNRS/IN2P3, Caen (France); Juillet, O. [LPC Caen, ENSICAEN, Universite de Caen, CNRS/IN2P3, Caen (France)
2016-04-15
The present paper intends to present an extension of the constrained-path quantum Monte Carlo approach allowing to reconstruct non-yrast states in order to reach the complete spectroscopy of nuclei within the interacting shell model. As in the yrast case studied in a previous work, the formalism involves a variational symmetry-restored wave function assuming two central roles. First, it guides the underlying Brownian motion to improve the efficiency of the sampling. Second, it constrains the stochastic paths according to the phaseless approximation to control sign or phase problems that usually plague fermionic QMC simulations. Proof-of-principle results in the sd valence space are reported. They prove the ability of the scheme to offer remarkably accurate binding energies for both even- and odd-mass nuclei irrespective of the considered interaction. (orig.)
Wako, H
1989-12-01
Monte Carlo simulations of a small protein, crambin, were carried out with and without hydration energy. The methodology presented here is characterized, as compared with the other similar simulations of proteins in solution, by two points: (1) protein conformations are treated in fixed geometry so that dihedral angles are independent variables rather than cartesian coordinates of atoms; and (2) instead of treating water molecules explicitly in the calculation, hydration energy is incorporated in the conformational energy function in the form of sigma giAi, where Ai is the accessible surface area of an atomic group i in a given conformation, and gi is the free energy of hydration per unit surface area of the atomic group (i.e., hydration-shell model). Reality of this model was tested by carrying out Monte Carlo simulations for the two kinds of starting conformations, native and unfolded ones, and in the two kinds of systems, in vacuo and solution. In the simulations starting from the native conformation, the differences between the mean properties in vacuo and solution simulations are not very large, but their fluctuations around the mean conformation during the simulation are relatively smaller in solution than in vacuo. On the other hand, in the simulations starting from the unfolded conformation, the molecule fluctuates much more largely in solution than in vacuo, and the effects of taking into account the hydration energy are pronounced very much. The results suggest that the method presented in this paper is useful for the simulations of proteins in solution.
Directory of Open Access Journals (Sweden)
F. Spada
2006-02-01
Full Text Available A new multiple-scattering Monte Carlo 3-D radiative transfer model named McSCIA (Monte Carlo for SCIAmachy is presented. The backward technique is used to efficiently simulate narrow field of view instruments. The McSCIA algorithm has been formulated as a function of the Earth's radius, and can thus perform simulations for both plane-parallel and spherical atmospheres. The latter geometry is essential for the interpretation of limb satellite measurements, as performed by SCIAMACHY on board of ESA's Envisat. The model can simulate UV-vis-NIR radiation.
First the ray-tracing algorithm is presented in detail, and then successfully validated against literature references, both in plane-parallel and in spherical geometry. A simple 1-D model is used to explain two different ways of treating absorption. One method uses the single scattering albedo while the other uses the equivalence theorem. The equivalence theorem is based on a separation of absorption and scattering. It is shown that both methods give, in a statistical way, identical results for a wide variety of scenarios. Both absorption methods are included in McSCIA, and it is shown that also for a 3-D case both formulations give identical results. McSCIA limb profiles for atmospheres with and without absorption compare well with the one of the state of the art Monte Carlo radiative transfer model MCC++.
A simplification of the photon statistics may lead to very fast calculations of absorption features in the atmosphere. However, these simplifications potentially introduce biases in the results. McSCIA does not use simplifications and is therefore a relatively slow implementation of the equivalence theorem. For the first time, however, the validity of the equivalence theorem is demonstrated in a spherical 3-D radiative transfer model.
Temporal structures in shell models
DEFF Research Database (Denmark)
Okkels, F.
2001-01-01
The intermittent dynamics of the turbulent Gledzer, Ohkitani, and Yamada shell-model is completely characterized by a single type of burstlike structure, which moves through the shells like a front. This temporal structure is described by the dynamics of the instantaneous configuration of the shell...
Shell model and spectroscopic factors
Energy Technology Data Exchange (ETDEWEB)
Poves, P. [Madrid Univ. Autonoma and IFT, UAM/CSIC, E-28049 (Spain)
2007-07-01
In these lectures, I introduce the notion of spectroscopic factor in the shell model context. A brief review is given of the present status of the large scale applications of the Interacting Shell Model. The spectroscopic factors and the spectroscopic strength are discussed for nuclei in the vicinity of magic closures and for deformed nuclei. (author)
Energy Technology Data Exchange (ETDEWEB)
Cansizoglu, H., E-mail: hxis@ualr.edu; Yurukcu, M.; Cansizoglu, M.F.; Karabacak, T.
2015-05-29
Vertically aligned core/shell nanowire (nanorod) arrays are favorable candidates in many nano-scale devices such as solar cells, detectors, and integrated circuits. The quality of the shell coating around nanowire arrays is as crucial as the quality of the nanowires in device applications. For this reason, we worked on different physical vapor deposition (PVD) techniques and conducted Monte Carlo simulations to estimate the best deposition technique for a conformal shell coating. Our results show that a small angle (≤ 45°) between incoming flux of particles and the substrate surface normal is necessary for PVD techniques with a directional incoming flux (e.g. thermal or e-beam evaporation) for a reasonable conformal coating. On the other hand, PVD techniques with an angular flux distribution (e.g. sputtering) can provide a fairly conformal shell coating around nanowire arrays without a need of small angle deposition. We also studied the shape effect of the arrays on the conformality of the coating and discovered that arrays of the tapered-top nanorods and the pyramids can be coated with a more conformal and thicker coating compared to the coating on the arrays of flat-top nanowires due to their larger openings in between structures. Our results indicate that conventional PVD techniques, which offer low cost and large scale thin film fabrication, can be utilized for highly conformal and uniform shell coating formation in core/shell nanowire device applications. - Highlights: • We examined the shell coating growth in core/shell nanostructures. • We investigated the effect of physical vapor deposition method on the conformality of the shell. • We used Monte Carlo simulations to simulate the shell growth on nanowire templates. • Angular atomic flux (i.e., sputtering at high pressure) leads to conformal and uniform coatings. • A small angle (< 45°) to the directional flux needs to be introduced for conformal coatings.
Recent Advances in Shell Evolution with Shell-Model Calculations
Utsuno, Yutaka; Tsunoda, Yusuke; Shimizu, Noritaka; Honma, Michio; Togashi, Tomoaki; Mizusaki, Takahiro
2014-01-01
Shell evolution in exotic nuclei is investigated with large-scale shell-model calculations. After presenting that the central and tensor forces produce distinctive ways of shell evolution, we show several recent results: (i) evolution of single-particle-like levels in antimony and cupper isotopes, (ii) shape coexistence in nickel isotopes understood in terms of configuration-dependent shell structure, and (iii) prediction of the evolution of the recently established $N=34$ magic number towards smaller proton numbers. In any case, large-scale shell-model calculations play indispensable roles in describing the interplay between single-particle character and correlation.
Shell Models of Magnetohydrodynamic Turbulence
Plunian, Franck; Frick, Peter
2012-01-01
Shell models of hydrodynamic turbulence originated in the seventies. Their main aim was to describe the statistics of homogeneous and isotropic turbulence in spectral space, using a simple set of ordinary differential equations. In the eighties, shell models of magnetohydrodynamic (MHD) turbulence emerged based on the same principles as their hydrodynamic counter-part but also incorporating interactions between magnetic and velocity fields. In recent years, significant improvements have been made such as the inclusion of non-local interactions and appropriate definitions for helicities. Though shell models cannot account for the spatial complexity of MHD turbulence, their dynamics are not over simplified and do reflect those of real MHD turbulence including intermittency or chaotic reversals of large-scale modes. Furthermore, these models use realistic values for dimensionless parameters (high kinetic and magnetic Reynolds numbers, low or high magnetic Prandtl number) allowing extended inertial range and accu...
Multi-Shell Shell Model for Heavy Nuclei
Sun, Y; Sun, Yang; Wu, Cheng-Li
2003-01-01
Performing a shell model calculation for heavy nuclei has been a long-standing problem in nuclear physics. Here we propose one possible solution. The central idea of this proposal is to take the advantages of two existing models, the Projected Shell Model (PSM) and the Fermion Dynamical Symmetry Model (FDSM), to construct a multi-shell shell model. The PSM is an efficient method of coupling quasi-particle excitations to the high-spin rotational motion, whereas the FDSM contains a successful truncation scheme for the low-spin collective modes from the spherical to the well-deformed region. The new shell model is expected to describe simultaneously the single-particle and the low-lying collective excitations of all known types, yet keeping the model space tractable even for the heaviest nuclear systems.
An investigation of ab initio shell-model interactions derived by no-core shell model
Wang, XiaoBao; Dong, GuoXiang; Li, QingFeng; Shen, CaiWan; Yu, ShaoYing
2016-09-01
The microscopic shell-model effective interactions are mainly based on the many-body perturbation theory (MBPT), the first work of which can be traced to Brown and Kuo's first attempt in 1966, derived from the Hamada-Johnston nucleon-nucleon potential. However, the convergence of the MBPT is still unclear. On the other hand, ab initio theories, such as Green's function Monte Carlo (GFMC), no-core shell model (NCSM), and coupled-cluster theory with single and double excitations (CCSD), have made many progress in recent years. However, due to the increasing demanding of computing resources, these ab initio applications are usually limited to nuclei with mass up to A = 16. Recently, people have realized the ab initio construction of valence-space effective interactions, which is obtained through a second-time renormalization, or to be more exactly, projecting the full-manybody Hamiltonian into core, one-body, and two-body cluster parts. In this paper, we present the investigation of such ab initio shell-model interactions, by the recent derived sd-shell effective interactions based on effective J-matrix Inverse Scattering Potential (JISP) and chiral effective-field theory (EFT) through NCSM. In this work, we have seen the similarity between the ab initio shellmodel interactions and the interactions obtained by MBPT or by empirical fitting. Without the inclusion of three-body (3-bd) force, the ab initio shell-model interactions still share similar defects with the microscopic interactions by MBPT, i.e., T = 1 channel is more attractive while T = 0 channel is more repulsive than empirical interactions. The progress to include more many-body correlations and 3-bd force is still badly needed, to see whether such efforts of ab initio shell-model interactions can reach similar precision as the interactions fitted to experimental data.
Cluster model of s- and p-shell hypernuclei
Indian Academy of Sciences (India)
Mohammad Shoeb; Alemiye Mamo; Amanuel Fessahatsion
2007-06-01
The binding energy ( ) of the s- and p-shell hypernuclei are calculated variationally in the cluster model and multidimensional integrations are performed using Monte Carlo. A variety of phenomenological -core potentials consistent with the -core energies and a wide range of simulated s-state potentials are taken as input. The of $_{ }^{6}$He is explained and $_{ }^{5}$He and $_{ }^{5}$H are predicted to be particle stable in the -core model. The results for s-shell hypernuclei are in excellent agreement with those of non-VMC calculations. The $_{}^{10}$Be in model is overbound for combinations of and potentials. A phenomenological dispersive three-body force, , consistent with the of $_{}^{9}$Be in the model underbinds $_{ }^{10}$Be. The incremental values for the s- and p-shell cannot be reconciled, consistent with the finding of earlier analyses.
Isogeometric shell formulation based on a classical shell model
Niemi, Antti
2012-09-04
This paper constitutes the first steps in our work concerning isogeometric shell analysis. An isogeometric shell model of the Reissner-Mindlin type is introduced and a study of its accuracy in the classical pinched cylinder benchmark problem presented. In contrast to earlier works [1,2,3,4], the formulation is based on a shell model where the displacement, strain and stress fields are defined in terms of a curvilinear coordinate system arising from the NURBS description of the shell middle surface. The isogeometric shell formulation is implemented using the PetIGA and igakit software packages developed by the authors. The igakit package is a Python package used to generate NURBS representations of geometries that can be utilised by the PetIGA finite element framework. The latter utilises data structures and routines of the portable, extensible toolkit for scientific computation (PETSc), [5,6]. The current shell implementation is valid for static, linear problems only, but the software package is well suited for future extensions to geometrically and materially nonlinear regime as well as to dynamic problems. The accuracy of the approach in the pinched cylinder benchmark problem and present comparisons against the h-version of the finite element method with bilinear elements. Quadratic, cubic and quartic NURBS discretizations are compared against the isoparametric bilinear discretization introduced in [7]. The results show that the quadratic and cubic NURBS approximations exhibit notably slower convergence under uniform mesh refinement as the thickness decreases but the quartic approximation converges relatively quickly within the standard variational framework. The authors future work is concerned with building an isogeometric finite element method for modelling nonlinear structural response of thin-walled shells undergoing large rigid-body motions. The aim is to use the model in a aeroelastic framework for the simulation of flapping wings.
Isothermal Circumstellar Dust Shell Model for Teaching
Robinson, G.; Towers, I. N.; Jovanoski, Z.
2009-01-01
We introduce a model of radiative transfer in circumstellar dust shells. By assuming that the shell is both isothermal and its thickness is small compared to its radius, the model is simple enough for students to grasp and yet still provides a quantitative description of the relevant physical features. The isothermal model can be used in a…
Shell Model Depiction of Isospin Mixing in sd Shell
Energy Technology Data Exchange (ETDEWEB)
Lam, Yi Hua; Smirnova, Nadya A. [CENBG (CNRS/IN2P3 - Universite Bordeaux 1) Chemin du Solarium, 33175 Gradignan (France); Caurier, Etienne [IPHC, IN2P3-CNRS et Universite Louis Pasteur, 67037 Strasbourg (France)
2011-11-30
We constructed a new empirical isospin-symmetry breaking (ISB) Hamiltonian in the sd(1s{sub 1/2}, 0d{sub 5/2} and 0d{sub 3/2}) shell-model space. In this contribution, we present its application to two important case studies: (i){beta}-delayed proton emission from {sup 22}Al and (ii) isospin-mixing correction to superallowed 0{sup +}{yields}0{sup +}{beta}-decay ft-values.
Derivation of a poroelastic flexural shell model
Mikelic, Andro
2015-01-01
In this paper we investigate the limit behavior of the solution to quasi-static Biot's equations in thin poroelastic flexural shells as the thickness of the shell tends to zero and extend the results obtained for the poroelastic plate by Marciniak-Czochra and Mikeli\\'c. We choose Terzaghi's time corresponding to the shell thickness and obtain the strong convergence of the three-dimensional solid displacement, fluid pressure and total poroelastic stress to the solution of the new class of shell equations. The derived bending equation is coupled with the pressure equation and it contains the bending moment due to the variation in pore pressure across the shell thickness. The effective pressure equation is parabolic only in the normal direction. As additional terms it contains the time derivative of the middle-surface flexural strain. Derivation of the model presents an extension of the results on the derivation of classical linear elastic shells by Ciarlet and collaborators to the poroelastic shells case. The n...
Monte Carlo exploration of warped Higgsless models
Energy Technology Data Exchange (ETDEWEB)
Hewett, JoAnne L.; Lillie, Benjamin; Rizzo, Thomas Gerard [Stanford Linear Accelerator Center, 2575 Sand Hill Rd., Menlo Park, CA, 94025 (United States)]. E-mail: rizzo@slac.stanford.edu
2004-10-01
We have performed a detailed Monte Carlo exploration of the parameter space for a warped Higgsless model of electroweak symmetry breaking in 5 dimensions. This model is based on the SU(2){sub L} x SU(2){sub R} x U(1){sub B-L} gauge group in an AdS{sub 5} bulk with arbitrary gauge kinetic terms on both the Planck and TeV branes. Constraints arising from precision electroweak measurements and collider data are found to be relatively easy to satisfy. We show, however, that the additional requirement of perturbative unitarity up to the cut-off, {approx_equal} 10 TeV, in W{sub L}{sup +}W{sub L}{sup -} elastic scattering in the absence of dangerous tachyons eliminates all models. If successful models of this class exist, they must be highly fine-tuned. (author)
Monte Carlo Exploration of Warped Higgsless Models
Hewett, J L; Rizzo, T G
2004-01-01
We have performed a detailed Monte Carlo exploration of the parameter space for a warped Higgsless model of electroweak symmetry breaking in 5 dimensions. This model is based on the $SU(2)_L\\times SU(2)_R\\times U(1)_{B-L}$ gauge group in an AdS$_5$ bulk with arbitrary gauge kinetic terms on both the Planck and TeV branes. Constraints arising from precision electroweak measurements and collider data are found to be relatively easy to satisfy. We show, however, that the additional requirement of perturbative unitarity up to the cut-off, $\\simeq 10$ TeV, in $W_L^+W_L^-$ elastic scattering in the absence of dangerous tachyons eliminates all models. If successful models of this class exist, they must be highly fine-tuned.
Monte Carlo Simulation of River Meander Modelling
Posner, A. J.; Duan, J. G.
2010-12-01
This study first compares the first order analytical solutions for flow field by Ikeda et. al. (1981) and Johanesson and Parker (1989b). Ikeda et. al.’s (1981) linear bank erosion model was implemented to predict the rate of bank erosion in which the bank erosion coefficient is treated as a stochastic variable that varies with physical properties of the bank (e.g. cohesiveness, stratigraphy, vegetation density). The developed model was used to predict the evolution of meandering planforms. Then, the modeling results were analyzed and compared to the observed data. Since the migration of meandering channel consists of downstream translation, lateral expansion, and downstream or upstream rotations. Several measures are formulated in order to determine which of the resulting planform is closest to the experimental measured one. Results from the deterministic model highly depend on the calibrated erosion coefficient. Since field measurements are always limited, the stochastic model yielded more realistic predictions of meandering planform evolutions. Due to the random nature of bank erosion coefficient, the meandering planform evolution is a stochastic process that can only be accurately predicted by a stochastic model. Quasi-2D Ikeda (1989) flow solution with Monte Carlo Simulation of Bank Erosion Coefficient.
Mapping the Two-Component Atomic Fermi Gas to the Nuclear Shell-Model
DEFF Research Database (Denmark)
Özen, C.; Zinner, Nikolaj Thomas
2014-01-01
of the external potential becomes important. A system of two-species fermionic cold atoms with an attractive zero-range interaction is analogous to a simple model of nucleus in which neutrons and protons interact only through a residual pairing interaction. In this article, we discuss how the problem of a two......-component atomic fermi gas in a tight external trap can be mapped to the nuclear shell model so that readily available many-body techniques in nuclear physics, such as the Shell Model Monte Carlo (SMMC) method, can be directly applied to the study of these systems. We demonstrate an application of the SMMC method...
Monte Carlo modelling of TRIGA research reactor
El Bakkari, B.; Nacir, B.; El Bardouni, T.; El Younoussi, C.; Merroun, O.; Htet, A.; Boulaich, Y.; Zoubair, M.; Boukhal, H.; Chakir, M.
2010-10-01
The Moroccan 2 MW TRIGA MARK II research reactor at Centre des Etudes Nucléaires de la Maâmora (CENM) achieved initial criticality on May 2, 2007. The reactor is designed to effectively implement the various fields of basic nuclear research, manpower training, and production of radioisotopes for their use in agriculture, industry, and medicine. This study deals with the neutronic analysis of the 2-MW TRIGA MARK II research reactor at CENM and validation of the results by comparisons with the experimental, operational, and available final safety analysis report (FSAR) values. The study was prepared in collaboration between the Laboratory of Radiation and Nuclear Systems (ERSN-LMR) from Faculty of Sciences of Tetuan (Morocco) and CENM. The 3-D continuous energy Monte Carlo code MCNP (version 5) was used to develop a versatile and accurate full model of the TRIGA core. The model represents in detailed all components of the core with literally no physical approximation. Continuous energy cross-section data from the more recent nuclear data evaluations (ENDF/B-VI.8, ENDF/B-VII.0, JEFF-3.1, and JENDL-3.3) as well as S( α, β) thermal neutron scattering functions distributed with the MCNP code were used. The cross-section libraries were generated by using the NJOY99 system updated to its more recent patch file "up259". The consistency and accuracy of both the Monte Carlo simulation and neutron transport physics were established by benchmarking the TRIGA experiments. Core excess reactivity, total and integral control rods worth as well as power peaking factors were used in the validation process. Results of calculations are analysed and discussed.
Monte Carlo models of dust coagulation
Zsom, Andras
2010-01-01
The thesis deals with the first stage of planet formation, namely dust coagulation from micron to millimeter sizes in circumstellar disks. For the first time, we collect and compile the recent laboratory experiments on dust aggregates into a collision model that can be implemented into dust coagulation models. We put this model into a Monte Carlo code that uses representative particles to simulate dust evolution. Simulations are performed using three different disk models in a local box (0D) located at 1 AU distance from the central star. We find that the dust evolution does not follow the previously assumed growth-fragmentation cycle, but growth is halted by bouncing before the fragmentation regime is reached. We call this the bouncing barrier which is an additional obstacle during the already complex formation process of planetesimals. The absence of the growth-fragmentation cycle and the halted growth has two important consequences for planet formation. 1) It is observed that disk atmospheres are dusty thr...
Reporting Monte Carlo Studies in Structural Equation Modeling
Boomsma, Anne
2013-01-01
In structural equation modeling, Monte Carlo simulations have been used increasingly over the last two decades, as an inventory from the journal Structural Equation Modeling illustrates. Reaching out to a broad audience, this article provides guidelines for reporting Monte Carlo studies in that fiel
Shape coexistence: the shell model view
Poves, A.
2016-02-01
We shall discuss the meaning of the ‘nuclear shape’ in the laboratory frame proper to the spherical shell model. A brief historical promenade will bring us from Elliott’s SU3 breakthrough to today’s large scale shell model calculations. A section is devoted to the algebraic model which extends drastically the field of applicability of Elliot’s SU3, providing a precious heuristic guidance for the exploration of collectivity in the nuclear chart. Shape coexistence and shape mixing will be shown to occur as the result of the competition between the main actors in the nuclear dynamics; the spherical mean field, and the pairing and quadrupole-quadrupole interactions. These ideas will be illustrated with examples in magic nuclei (40Ca and 68Ni); neutron rich semi-magic (32Mg, and 64Cr); and in proton rich N = Z (72Kr).
Nuclear level density: Shell-model approach
Sen'kov, Roman; Zelevinsky, Vladimir
2016-06-01
Knowledge of the nuclear level density is necessary for understanding various reactions, including those in the stellar environment. Usually the combinatorics of a Fermi gas plus pairing is used for finding the level density. Recently a practical algorithm avoiding diagonalization of huge matrices was developed for calculating the density of many-body nuclear energy levels with certain quantum numbers for a full shell-model Hamiltonian. The underlying physics is that of quantum chaos and intrinsic thermalization in a closed system of interacting particles. We briefly explain this algorithm and, when possible, demonstrate the agreement of the results with those derived from exact diagonalization. The resulting level density is much smoother than that coming from conventional mean-field combinatorics. We study the role of various components of residual interactions in the process of thermalization, stressing the influence of incoherent collision-like processes. The shell-model results for the traditionally used parameters are also compared with standard phenomenological approaches.
Delta Shell: Integrated Modeling by Example
Donchyts, G.; Jagers, B.; Baart, F.; Geer, P. V.
2011-12-01
We present the integrated modeling environment Delta Shell. It supports the full workflow of integrated environmental modeling: setup, configuration, simulation, analysis and reporting of results. Many components of the environment can be reused independently, allowing development of scientific, geospatial and other applications focused on data analysis, editing, visualization and storage. One of the unique features is that the Delta Shell environment integrates models from many different fields, such as hydrodynamics, hydrology, morphology, ecology, water quality, geospatial and decision support systems. This integration is possible due to flexible general data types, lightweight model coupling framework, the plugin system and the inclusion of a number of high quality open source components. Here we will use the open source morphological model XBeach as an example showing how to integrate models into the Delta Shell environment. Integration of XBeach adds a graphical interface which can be used to make testing coastal safety for complicated coastal areas easier. By using this example, we give an overview of the modeling framework and its possibilities. To increase the usability, the model is integrated with a coastal profile data set covering the whole coast of the Netherlands. This gives the end user a system to easily use the model for scanning the safety of the Dutch coast. The reuse of the components of the environment individually or combined is encouraged. They are available as separate components and have minimal or no dependencies on other components. This includes libraries to work with scientific multidimensional data, geospatial data (in particular geospatial coverages: values of some quantities defined on a spatial domain), editors, visualisation of time-dependent data and the modeling framework (projects, data linking, workflow management, model integration). Most components and the XBeach example are available as open source.
Symmetries and deformations in the spherical shell model
Van Isacker, P.; Pittel, S.
2016-02-01
We discuss symmetries of the spherical shell model that make contact with the geometric collective model of Bohr and Mottelson. The most celebrated symmetry of this kind is SU(3), which is the basis of Elliott’s model of rotation. It corresponds to a deformed mean field induced by a quadrupole interaction in a single major oscillator shell N and can be generalized to include several major shells. As such, Elliott’s SU(3) model establishes the link between the spherical shell model and the (quadrupole component of the) geometric collective model. We introduce the analogue symmetry induced by an octupole interaction in two major oscillator shells N-1 and N, leading to an octupole-deformed solution of the spherical shell model. We show that in the limit of large oscillator shells, N\\to ∞ , the algebraic octupole interaction tends to that of the geometric collective model.
MODELING LEACHING OF VIRUSES BY THE MONTE CARLO METHOD
A predictive screening model was developed for fate and transport of viruses in the unsaturated zone. A database of input parameters allowed Monte Carlo analysis with the model. The resulting kernel densities of predicted attenuation during percolation indicated very ...
Shell model for warm rotating nuclei
Energy Technology Data Exchange (ETDEWEB)
Matsuo, M.; Yoshida, K. [Kyoto Univ. (Japan); Dossing, T. [Univ. of Copenhagen (Denmark)] [and others
1996-12-31
Utilizing a shell model which combines the cranked Nilsson mean-field and the residual surface and volume delta two-body forces, the authors discuss the onset of rotational damping in normal- and super-deformed nuclei. Calculation for a typical normal deformed nucleus {sup 168}Yb indicates that the rotational damping sets in at around 0.8 MeV above the yrast line, and about 30 rotational bands of various length exists at a given rotational frequency, in overall agreement with experimental findings. It is predicted that the onset of rotational damping changes significantly in different superdeformed nuclei due to the variety of the shell gaps and single-particle orbits associated with the superdeformed mean-field.
Shell Model States in the Continuum
Shirokov, A M; Mazur, I A; Vary, J P
2016-01-01
We suggest a method for calculating scattering phase shifts and energies and widths of resonances which utilizes only eigenenergies obtained in variational calculations with oscillator basis and their dependence on oscillator basis spacing $\\hbar\\Omega$. We make use of simple expressions for the $S$-matrix at eigenstates of a finite (truncated) Hamiltonian matrix in the oscillator basis obtained in the HORSE ($J$-matrix) formalism of quantum scattering theory. The validity of the suggested approach is verified in calculations with model Woods--Saxon potentials and applied to calculations of $n\\alpha$ resonances and non-resonant scattering using the no-core shell model.
Dynamical symmetries of the shell model
Energy Technology Data Exchange (ETDEWEB)
Van Isacker, P
2000-07-01
The applications of spectrum generating algebras and of dynamical symmetries in the nuclear shell model are many and varied. They stretch back to Wigner's early work on the supermultiplet model and encompass important landmarks in our understanding of the structure of the atomic nucleus such as Racah's SU(2) pairing model and Elliot's SU(3) rotational model. One of the aims of this contribution has been to show the historical importance of the idea of dynamical symmetry in nuclear physics. Another has been to indicate that, in spite of being old, this idea continues to inspire developments that are at the forefront of today's research in nuclear physics. It has been argued in this contribution that the main driving features of nuclear structure can be represented algebraically but at the same time the limitations of the symmetry approach must be recognised. It should be clear that such approach can only account for gross properties and that any detailed description requires more involved numerical calculations of which we have seen many fine examples during this symposium. In this way symmetry techniques can be used as an appropriate starting point for detailed calculations. A noteworthy example of this approach is the pseudo-SU(3) model which starting from its initial symmetry Ansatz has grown into an adequate and powerful description of the nucleus in terms of a truncated shell model. (author)
Event-chain Monte Carlo for classical continuous spin models
Michel, Manon; Mayer, Johannes; Krauth, Werner
2015-10-01
We apply the event-chain Monte Carlo algorithm to classical continuum spin models on a lattice and clarify the condition for its validity. In the two-dimensional XY model, it outperforms the local Monte Carlo algorithm by two orders of magnitude, although it remains slower than the Wolff cluster algorithm. In the three-dimensional XY spin glass model at low temperature, the event-chain algorithm is far superior to the other algorithms.
A model of layered prismatic shells
Jaiani, George
2016-05-01
The present paper is devoted to a model for elastic layered prismatic shells which is constructed by means of a suggested in the paper approach which essentially differs from the known approaches for constructing models of laminated structures. Using Vekua's dimension reduction method after appropriate modifications, hierarchical models for elastic layered prismatic shells are constructed. We get coupled governing systems for the whole structure in the projection of the structure. The advantage of this model consists in the fact that we solve boundary value problems separately for each ply. In addition, beginning with the second ply, we use a solution of a boundary value problem of the preceding ply. We indicate ways of investigating boundary value problems for the governing systems. For the sake of simplicity, we consider the case of two plies, in the zeroth approximation. However, we also make remarks concerning the cases when either the number of plies is more than two or higher-order approximations (hierarchical models) should be applied. As an example, we consider a special case of deformation and solve the corresponding boundary value problem in the explicit form.
Quantum Monte Carlo methods algorithms for lattice models
Gubernatis, James; Werner, Philipp
2016-01-01
Featuring detailed explanations of the major algorithms used in quantum Monte Carlo simulations, this is the first textbook of its kind to provide a pedagogical overview of the field and its applications. The book provides a comprehensive introduction to the Monte Carlo method, its use, and its foundations, and examines algorithms for the simulation of quantum many-body lattice problems at finite and zero temperature. These algorithms include continuous-time loop and cluster algorithms for quantum spins, determinant methods for simulating fermions, power methods for computing ground and excited states, and the variational Monte Carlo method. Also discussed are continuous-time algorithms for quantum impurity models and their use within dynamical mean-field theory, along with algorithms for analytically continuing imaginary-time quantum Monte Carlo data. The parallelization of Monte Carlo simulations is also addressed. This is an essential resource for graduate students, teachers, and researchers interested in ...
Monte-Carlo simulation-based statistical modeling
Chen, John
2017-01-01
This book brings together expert researchers engaged in Monte-Carlo simulation-based statistical modeling, offering them a forum to present and discuss recent issues in methodological development as well as public health applications. It is divided into three parts, with the first providing an overview of Monte-Carlo techniques, the second focusing on missing data Monte-Carlo methods, and the third addressing Bayesian and general statistical modeling using Monte-Carlo simulations. The data and computer programs used here will also be made publicly available, allowing readers to replicate the model development and data analysis presented in each chapter, and to readily apply them in their own research. Featuring highly topical content, the book has the potential to impact model development and data analyses across a wide spectrum of fields, and to spark further research in this direction.
Monte Carlo studies of model Langmuir monolayers.
Opps, S B; Yang, B; Gray, C G; Sullivan, D E
2001-04-01
This paper examines some of the basic properties of a model Langmuir monolayer, consisting of surfactant molecules deposited onto a water subphase. The surfactants are modeled as rigid rods composed of a head and tail segment of diameters sigma(hh) and sigma(tt), respectively. The tails consist of n(t) approximately 4-7 effective monomers representing methylene groups. These rigid rods interact via site-site Lennard-Jones potentials with different interaction parameters for the tail-tail, head-tail, and head-head interactions. In a previous paper, we studied the ground-state properties of this system using a Landau approach. In the present paper, Monte Carlo simulations were performed in the canonical ensemble to elucidate the finite-temperature behavior of this system. Simulation techniques, incorporating a system of dynamic filters, allow us to decrease CPU time with negligible statistical error. This paper focuses on several of the key parameters, such as density, head-tail diameter mismatch, and chain length, responsible for driving transitions from uniformly tilted to untilted phases and between different tilt-ordered phases. Upon varying the density of the system, with sigma(hh)=sigma(tt), we observe a transition from a tilted (NNN)-condensed phase to an untilted-liquid phase and, upon comparison with recent experiments with fatty acid-alcohol and fatty acid-ester mixtures [M. C. Shih, M. K. Durbin, A. Malik, P. Zschack, and P. Dutta, J. Chem. Phys. 101, 9132 (1994); E. Teer, C. M. Knobler, C. Lautz, S. Wurlitzer, J. Kildae, and T. M. Fischer, J. Chem. Phys. 106, 1913 (1997)], we identify this as the L'(2)/Ov-L1 phase boundary. By varying the head-tail diameter ratio, we observe a decrease in T(c) with increasing mismatch. However, as the chain length was increased we observed that the transition temperatures increased and differences in T(c) due to head-tail diameter mismatch were diminished. In most of the present research, the water was treated as a hard
SD-Pair Shell Model for Identical Nuclear Systems
Institute of Scientific and Technical Information of China (English)
LUO Yan-An; PAN Feng; NING Ping-Zhi; Jerry P. Draayer
2005-01-01
@@ Typical spectra corresponding to vibrational, rotational and γ-soft cases were studied within the framework of nucleon-pair shell model truncated to SD-subspace. It is found that the three limiting cases all can be reproduced approximately. The analysis not only shows that the IBM indeed has a sound shell model foundation, but also confirms that the truncation scheme adopted in the SD-pair shell model seems to be reasonable.
Multiscaling in superfluid turbulence: A shell-model study
Shukla, Vishwanath; Pandit, Rahul
2016-10-01
We examine the multiscaling behavior of the normal- and superfluid-velocity structure functions in three-dimensional superfluid turbulence by using a shell model for the three-dimensional (3D) Hall-Vinen-Bekharevich-Khalatnikov (HVBK) equations. Our 3D-HVBK shell model is based on the Gledzer-Okhitani-Yamada shell model. We examine the dependence of the multiscaling exponents on the normal-fluid fraction and the mutual-friction coefficients. Our extensive study of the 3D-HVBK shell model shows that the multiscaling behavior of the velocity structure functions in superfluid turbulence is more complicated than it is in fluid turbulence.
Quantum Monte Carlo diagonalization method as a variational calculation
Energy Technology Data Exchange (ETDEWEB)
Mizusaki, Takahiro; Otsuka, Takaharu [Tokyo Univ. (Japan). Dept. of Physics; Honma, Michio
1997-05-01
A stochastic method for performing large-scale shell model calculations is presented, which utilizes the auxiliary field Monte Carlo technique and diagonalization method. This method overcomes the limitation of the conventional shell model diagonalization and can extremely widen the feasibility of shell model calculations with realistic interactions for spectroscopic study of nuclear structure. (author)
Shell Model Description of Neutron-Deficient Sn Isotopes
Institute of Scientific and Technical Information of China (English)
Erdal Dikmen
2009-01-01
The shell model calculations in the sdgh major shell for the neutron-deficient 106,107,108,109Sn isotopes have been carried out by using CD-Bonn and Nijmegenl two-body effective nucleon-nucleon interactions. The single-shell states and the corresponding matrix elements needed for describing Sn isotopes are reconstructed to calculate the coefficient of fractional parantage by reducing the calculation requirements. This reconstruction allows us to do the shell model calculations of the neutron deficient Sn isotopes in very reasonable time. The results are compared to the recent high-resolution experimental data and found to be in good agreement with experiments.
Gas discharges modeling by Monte Carlo technique
Directory of Open Access Journals (Sweden)
Savić Marija
2010-01-01
Full Text Available The basic assumption of the Townsend theory - that ions produce secondary electrons - is valid only in a very narrow range of the reduced electric field E/N. In accordance with the revised Townsend theory that was suggested by Phelps and Petrović, secondary electrons are produced in collisions of ions, fast neutrals, metastable atoms or photons with the cathode, or in gas phase ionizations by fast neutrals. In this paper we tried to build up a Monte Carlo code that can be used to calculate secondary electron yields for different types of particles. The obtained results are in good agreement with the analytical results of Phelps and. Petrović [Plasma Sourc. Sci. Technol. 8 (1999 R1].
Modeling neutron guides using Monte Carlo simulations
Wang, D Q; Crow, M L; Wang, X L; Lee, W T; Hubbard, C R
2002-01-01
Four neutron guide geometries, straight, converging, diverging and curved, were characterized using Monte Carlo ray-tracing simulations. The main areas of interest are the transmission of the guides at various neutron energies and the intrinsic time-of-flight (TOF) peak broadening. Use of a delta-function time pulse from a uniform Lambert neutron source allows one to quantitatively simulate the effect of guides' geometry on the TOF peak broadening. With a converging guide, the intensity and the beam divergence increases while the TOF peak width decreases compared with that of a straight guide. By contrast, use of a diverging guide decreases the intensity and the beam divergence, and broadens the width (in TOF) of the transmitted neutron pulse.
Off-shell BCJ Relation in Nonlinear Sigma Model
Chen, Gang; Liu, Hanqing
2016-01-01
We investigate relations among tree-level off-shell currents in nonlinear sigma model. Under Cayley parametrization, we propose and prove a general revised BCJ relation for even-point currents. Unlike the on-shell BCJ relation, the off-shell one behaves quite differently from Yang-Mills theory although the algebraic structure is the same. After performing the permutation summation in the revised BCJ relation, the sum is non-vanishing, instead, it equals to the sum of sub-current products with the BCJ coefficients under a specific ordering, which is presented by an explicit formula. Taking on-shell limit, this identity is reduced to the on-shell BCJ relation, and thus provides the full off-shell correspondence of tree-level BCJ relation in nonlinear sigma model.
Monte Carlo methods and models in finance and insurance
Korn, Ralf
2010-01-01
Offering a unique balance between applications and calculations, this book incorporates the application background of finance and insurance with the theory and applications of Monte Carlo methods. It presents recent methods and algorithms, including the multilevel Monte Carlo method, the statistical Romberg method, and the Heath-Platen estimator, as well as recent financial and actuarial models, such as the Cheyette and dynamic mortality models. The book enables readers to find the right algorithm for a desired application and illustrates complicated methods and algorithms with simple applicat
Quasi-Monte Carlo methods for the Heston model
Jan Baldeaux; Dale Roberts
2012-01-01
In this paper, we discuss the application of quasi-Monte Carlo methods to the Heston model. We base our algorithms on the Broadie-Kaya algorithm, an exact simulation scheme for the Heston model. As the joint transition densities are not available in closed-form, the Linear Transformation method due to Imai and Tan, a popular and widely applicable method to improve the effectiveness of quasi-Monte Carlo methods, cannot be employed in the context of path-dependent options when the underlying pr...
Simple model on collisionless thin-shell instability growth
Doria, Domenico; Dieckmann, Mark E
2016-01-01
The manuscript discusses a simple model on the Thin Shell Instability (TSI) growth phenomenon at early stage, by only imposing the fulfillment of conservation laws; and in particular just applying the laws of mass and linear momentum conservation, without taking into account the energy partitioning inside the thin shell.
Shell Model Estimate of Electric Dipole Moments for Xe Isotopes
Teruya, Eri; Yoshinaga, Naotaka; Higashiyama, Koji
The nuclear Schiff moments of Xe isotopes which induce electric dipole moments of neutral Xe atoms is theoretically estimated. Parity and time-reversal violating two-body nuclear interactions are assumed. The nuclear wave functions are calculated in terms of the nuclear shell model. Influences of core excitations on the Schiff moments in addition to the over-shell excitations are discussed.
Calibration and Monte Carlo modelling of neutron long counters
Tagziria, H
2000-01-01
The Monte Carlo technique has become a very powerful tool in radiation transport as full advantage is taken of enhanced cross-section data, more powerful computers and statistical techniques, together with better characterisation of neutron and photon source spectra. At the National Physical Laboratory, calculations using the Monte Carlo radiation transport code MCNP-4B have been combined with accurate measurements to characterise two long counters routinely used to standardise monoenergetic neutron fields. New and more accurate response function curves have been produced for both long counters. A novel approach using Monte Carlo methods has been developed, validated and used to model the response function of the counters and determine more accurately their effective centres, which have always been difficult to establish experimentally. Calculations and measurements agree well, especially for the De Pangher long counter for which details of the design and constructional material are well known. The sensitivit...
Shell Model for Warm Rotating Nuclei
Matsuo, M; Vigezzi, E; Broglia, R A; Yoshida, K
1997-01-01
In order to provide a microscopic description of levels and E2 transitions in rapidly rotating nuclei with internal excitation energy up to a few MeV, use is made of a shell model which combines the cranked Nilsson mean-field and the residual surface delta two-body force. The damping of collective rotational motion is investigated in the case of a typical rare-earth nucleus, namely \\Yb. It is found that rotational damping sets in at around 0.8 MeV above the yrast line, and the levels which form rotational band structures are thus limited. We predict at a given rotational frequency existence of about 30 rotational bands of various lengths, in overall agreement with the experimental findings. The onset of the rotational damping proceeds quite gradually as a function of the internal excitation energy. The transition region extends up to around 2 MeV above yrast and it is characterized by the presence of scars of discrete rotational bands which extend over few spin values and stand out among the damped transition...
Energy transfers in shell models for magnetohydrodynamics turbulence.
Lessinnes, Thomas; Carati, Daniele; Verma, Mahendra K
2009-06-01
A systematic procedure to derive shell models for magnetohydrodynamic turbulence is proposed. It takes into account the conservation of ideal quadratic invariants such as the total energy, the cross helicity, and the magnetic helicity, as well as the conservation of the magnetic energy by the advection term in the induction equation. This approach also leads to simple expressions for the energy exchanges as well as to unambiguous definitions for the energy fluxes. When applied to the existing shell models with nonlinear interactions limited to the nearest-neighbor shells, this procedure reproduces well-known models but suggests a reinterpretation of the energy fluxes.
Thin Shell Model for NIF capsule stagnation studies
Hammer, J. H.; Buchoff, M.; Brandon, S.; Field, J. E.; Gaffney, J.; Kritcher, A.; Nora, R. C.; Peterson, J. L.; Spears, B.; Springer, P. T.
2015-11-01
We adapt the thin shell model of Ott et al. to asymmetric ICF capsule implosions on NIF. Through much of an implosion, the shell aspect ratio is large so the thin shell approximation is well satisfied. Asymmetric pressure drive is applied using an analytic form for ablation pressure as a function of the x-ray flux, as well as time-dependent 3D drive asymmetry from hohlraum calculations. Since deviations from a sphere are small through peak velocity, we linearize the equations, decompose them by spherical harmonics and solve ODE's for the coefficients. The model gives the shell position, velocity and areal mass variations at the time of peak velocity, near 250 microns radius. The variables are used to initialize 3D rad-hydro calculations with the HYDRA and ARES codes. At link time the cold fuel shell and ablator are each characterized by a density, adiabat and mass. The thickness, position and velocity of each point are taken from the thin shell model. The interior of the shell is filled with a uniform gas density and temperature consistent with the 3/2PV energy found from 1D rad-hydro calculations. 3D linked simulations compare favorably with integrated simulations of the entire implosion. Through generating synthetic diagnostic data, the model offers a method for quickly testing hypothetical sources of asymmetry and comparing with experiment. Prepared by LLNL under Contract DE-AC52-07NA27344.
A generalized hard-sphere model for Monte Carlo simulation
Hassan, H. A.; Hash, David B.
1993-01-01
A new molecular model, called the generalized hard-sphere, or GHS model, is introduced. This model contains, as a special case, the variable hard-sphere model of Bird (1981) and is capable of reproducing all of the analytic viscosity coefficients available in the literature that are derived for a variety of interaction potentials incorporating attraction and repulsion. In addition, a new procedure for determining interaction potentials in a gas mixture is outlined. Expressions needed for implementing the new model in the direct simulation Monte Carlo methods are derived. This development makes it possible to employ interaction models that have the same level of complexity as used in Navier-Stokes calculations.
Yüksel, Yusuf; Akıncı, Ümit
2016-12-01
Using Monte Carlo simulations, we have investigated the dynamic phase transition properties of magnetic nanoparticles with ferromagnetic core coated by an antiferromagnetic shell structure. Effects of field amplitude and frequency on the thermal dependence of magnetizations, magnetization reversal mechanisms during hysteresis cycles, as well as on the exchange bias and coercive fields have been examined, and the feasibility of applying dynamic magnetic fields on the particle have been discussed for technological and biomedical purposes.
Elastic turbulence in a shell model of polymer solution
Ray, Samriddhi Sankar
2016-01-01
We show that, at low inertia and large elasticity, shell models of viscoelastic fluids develop a chaotic behaviour with properties similar to those of elastic turbulence. The low dimensionality of shell models allows us to explore a wide range both in polymer concentration and in Weissenberg number. Our results demonstrate that the physical mechanisms at the origin of elastic turbulence do not rely on the boundary conditions or on the geometry of the mean flow.
Monte Carlo Euler approximations of HJM term structure financial models
Björk, Tomas
2012-11-22
We present Monte Carlo-Euler methods for a weak approximation problem related to the Heath-Jarrow-Morton (HJM) term structure model, based on Itô stochastic differential equations in infinite dimensional spaces, and prove strong and weak error convergence estimates. The weak error estimates are based on stochastic flows and discrete dual backward problems, and they can be used to identify different error contributions arising from time and maturity discretization as well as the classical statistical error due to finite sampling. Explicit formulas for efficient computation of sharp error approximation are included. Due to the structure of the HJM models considered here, the computational effort devoted to the error estimates is low compared to the work to compute Monte Carlo solutions to the HJM model. Numerical examples with known exact solution are included in order to show the behavior of the estimates. © 2012 Springer Science+Business Media Dordrecht.
JEWEL - a Monte Carlo Model for Jet Quenching
Zapp, Korinna; Wiedemann, Urs Achim
2009-01-01
The Monte Carlo model JEWEL 1.0 (Jet Evolution With Energy Loss) simulates parton shower evolution in the presence of a dense QCD medium. In its current form medium interactions are modelled as elastic scattering based on perturbative matrix elements and a simple prescription for medium induced gluon radiation. The parton shower is interfaced with a hadronisation model. In the absence of medium effects JEWEL is shown to reproduce jet measurements at LEP. The collisional energy loss is consistent with analytic calculations, but with JEWEL we can go a step further and characterise also jet-induced modifications of the medium. Elastic and inelastic medium interactions are shown to lead to distinctive modifications of the jet fragmentation pattern, which should allow to experimentally distinguish between collisional and radiative energy loss mechanisms. In these proceedings the main JEWEL results are summarised and a Monte Carlo algorithm is outlined that allows to include the Landau-Pomerantschuk-Migdal effect i...
Modeling plate shell structures using pyFormex
DEFF Research Database (Denmark)
Bagger, Anne; Verhegghe, Benedict; Hertz, Kristian Dahl
2009-01-01
A shell structure made of glass combines a light-weight structural concept with glass’ high permeability to light. If the geometry of the structure is plane-based facetted (plate shell structure), the glass elements will be plane panes, and these glass panes will comprise the primary load-bearing...... element analysis software Abaqus as a Python script, which translates the information to an Abaqus CAE-model. In pyFormex the model has been prepared for applying the meshing in Abaqus, by allocation of edge seeds, and by defining geometry sets for easy handling....... at Ghent University, has been used to accommodate a parametric generation of plate shell structures. This generation includes the basic facetted shell geometry, joint areas that reproduce given connection characteristics, loads and boundary conditions. From pyFormex the model is exported to the finite...
Modeling the carbon isotope composition of bivalve shells (Invited)
Romanek, C.
2010-12-01
The stable carbon isotope composition of bivalve shells is a valuable archive of paleobiological and paleoenvironmental information. Previous work has shown that the carbon isotope composition of the shell is related to the carbon isotope composition of dissolved inorganic carbon (DIC) in the ambient water in which a bivalve lives, as well as metabolic carbon derived from bivalve respiration. The contribution of metabolic carbon varies among organisms, but it is generally thought to be relatively low (e.g., organism and high (>90%) in the shells from terrestrial organisms. Because metabolic carbon contains significantly more C-12 than DIC, negative excursions from the expected environmental (DIC) signal are interpreted to reflect an increased contribution of metabolic carbon in the shell. This observation contrasts sharply with modeled carbon isotope compositions for shell layers deposited from the inner extrapallial fluid (EPF). Previous studies have shown that growth lines within the inner shell layer of bivalves are produced during periods of anaerobiosis when acidic metabolic byproducts (e.g., succinic acid) are neutralized (or buffered) by shell dissolution. This requires the pH of EPF to decrease below ambient levels (~7.5) until a state of undersaturation is achieved that promotes shell dissolution. This condition may occur when aquatic bivalves are subjected to external stressors originating from ecological (predation) or environmental (exposure to atm; low dissolved oxygen; contaminant release) pressures; normal physiological processes will restore the pH of EPF when the pressure is removed. As a consequence of this process, a temporal window should also exist in EPF at relatively low pH where shell carbonate is deposited at a reduced saturation state and precipitation rate. For example, EPF chemistry should remain slightly supersaturated with respect to aragonite given a drop of one pH unit (6.5), but under closed conditions, equilibrium carbon isotope
Geometrically nonlinear creeping mathematic models of shells with variable thickness
Directory of Open Access Journals (Sweden)
V.M. Zhgoutov
2012-08-01
Full Text Available Calculations of strength, stability and vibration of shell structures play an important role in the design of modern devices machines and structures. However, the behavior of thin-walled structures of variable thickness during which geometric nonlinearity, lateral shifts, viscoelasticity (creep of the material, the variability of the profile take place and thermal deformation starts up is not studied enough.In this paper the mathematical deformation models of variable thickness shells (smoothly variable and ribbed shells, experiencing either mechanical load or permanent temperature field and taking into account the geometrical nonlinearity, creeping and transverse shear, were developed. The refined geometrical proportions for geometrically nonlinear and steadiness problems are given.
A predictive model of shell morphology in CdSe/CdS core/shell quantum dots
Energy Technology Data Exchange (ETDEWEB)
Gong, Ke; Kelley, David F., E-mail: dfkelley@ucmerced.edu [Chemistry and Chemical Biology, University of California, Merced, 5200 North Lake Road, Merced, California 95343 (United States)
2014-11-21
Lattice mismatch in core/shell nanoparticles occurs when the core and shell materials have different lattice parameters. When there is a significant lattice mismatch, a coherent core-shell interface results in substantial lattice strain energy, which can affect the shell morphology. The shell can be of uniform thickness or can be rough, having thin and thick regions. A smooth shell minimizes the surface energy at the expense of increased lattice strain energy and a rough shell does the opposite. A quantitative treatment of the lattice strain energy in determining the shell morphology of CdSe/CdS core/shell nanoparticles is presented here. We use the inhomogeneity in hole tunneling rates through the shell to adsorbed hole acceptors to quantify the extent of shell thickness inhomogeneity. The results can be understood in terms of a model based on elastic continuum calculations, which indicate that the lattice strain energy depends on both core size and shell thickness. The model assumes thermodynamic equilibrium, i.e., that the shell morphology corresponds to a minimum total (lattice strain plus surface) energy. Comparison with the experimental results indicates that CdSe/CdS nanoparticles undergo an abrupt transition from smooth to rough shells when the total lattice strain energy exceeds about 27 eV or the strain energy density exceeds 0.59 eV/nm{sup 2}. We also find that the predictions of this model are not followed for CdSe/CdS nanoparticles when the shell is deposited at very low temperature and therefore equilibrium is not established.
Shell-model studies of the N=14 and 16 shell closures in neutron-rich nuclei
Institute of Scientific and Technical Information of China (English)
YUAN Cen-Xi; QI Chong; XU Fu-Rong
2009-01-01
Shell-model studies on the N = 14 and 16 shell closures in neutron-rich Be, C, O and Ne isotopes are presented. We calculate, with the WBT interaction, the excited states in these nuclei. The calculations agree with recent experiment data. Excited energies and B(E2) values are displayed to discuss the shell closures.Our results support the N = 16 shell closure in these isotopes, while indicating a disappearance of N = 14 shell closure in Be and C isotopes.
Shell model states around $^{208}Pb$
Liendo, J A; Gómez, R; Caussyn, D D
2015-01-01
The experimental binding energies of single-particle and single-hole neutron states belonging to neutron shells that extend from N = 126 to 184 and 82 to 126 respectively, have been reproduced by solving Schr\\"{o}edinger's equation with a potential containing the traditional Woods-Saxon (WS) plus spin-orbit (SO) potential [1-6], and a superficial term proportional to the derivative of a Woods-Saxon like potential. The agreement between theory and experiment has been achieved by varying the strength of the superficial potential for each state studied, until the theoretical binding energy matches the corresponding measured value. Our results indicate the existence of a explicit relationship between the strength of the superficial potential and the orbital angular momentum quantum number $\\ell$ of the state. This dependence has been used to make reasonable predictions for the excitation energy centroids of states located inside and outside the neutron shells investigated. Comparisons are made with results report...
A semianalytic Monte Carlo code for modelling LIDAR measurements
Palazzi, Elisa; Kostadinov, Ivan; Petritoli, Andrea; Ravegnani, Fabrizio; Bortoli, Daniele; Masieri, Samuele; Premuda, Margherita; Giovanelli, Giorgio
2007-10-01
LIDAR (LIght Detection and Ranging) is an optical active remote sensing technology with many applications in atmospheric physics. Modelling of LIDAR measurements appears useful approach for evaluating the effects of various environmental variables and scenarios as well as of different measurement geometries and instrumental characteristics. In this regard a Monte Carlo simulation model can provide a reliable answer to these important requirements. A semianalytic Monte Carlo code for modelling LIDAR measurements has been developed at ISAC-CNR. The backscattered laser signal detected by the LIDAR system is calculated in the code taking into account the contributions due to the main atmospheric molecular constituents and aerosol particles through processes of single and multiple scattering. The contributions by molecular absorption, ground and clouds reflection are evaluated too. The code can perform simulations of both monostatic and bistatic LIDAR systems. To enhance the efficiency of the Monte Carlo simulation, analytical estimates and expected value calculations are performed. Artificial devices (such as forced collision, local forced collision, splitting and russian roulette) are moreover foreseen by the code, which can enable the user to drastically reduce the variance of the calculation.
Monte Carlo modelling of positron transport in real world applications
Marjanović, S.; Banković, A.; Šuvakov, M.; Petrović, Z. Lj
2014-05-01
Due to the unstable nature of positrons and their short lifetime, it is difficult to obtain high positron particle densities. This is why the Monte Carlo simulation technique, as a swarm method, is very suitable for modelling most of the current positron applications involving gaseous and liquid media. The ongoing work on the measurements of cross-sections for positron interactions with atoms and molecules and swarm calculations for positrons in gasses led to the establishment of good cross-section sets for positron interaction with gasses commonly used in real-world applications. Using the standard Monte Carlo technique and codes that can follow both low- (down to thermal energy) and high- (up to keV) energy particles, we are able to model different systems directly applicable to existing experimental setups and techniques. This paper reviews the results on modelling Surko-type positron buffer gas traps, application of the rotating wall technique and simulation of positron tracks in water vapor as a substitute for human tissue, and pinpoints the challenges in and advantages of applying Monte Carlo simulations to these systems.
Monte Carlo Numerical Models for Nuclear Logging Applications
Directory of Open Access Journals (Sweden)
Fusheng Li
2012-06-01
Full Text Available Nuclear logging is one of most important logging services provided by many oil service companies. The main parameters of interest are formation porosity, bulk density, and natural radiation. Other services are also provided from using complex nuclear logging tools, such as formation lithology/mineralogy, etc. Some parameters can be measured by using neutron logging tools and some can only be measured by using a gamma ray tool. To understand the response of nuclear logging tools, the neutron transport/diffusion theory and photon diffusion theory are needed. Unfortunately, for most cases there are no analytical answers if complex tool geometry is involved. For many years, Monte Carlo numerical models have been used by nuclear scientists in the well logging industry to address these challenges. The models have been widely employed in the optimization of nuclear logging tool design, and the development of interpretation methods for nuclear logs. They have also been used to predict the response of nuclear logging systems for forward simulation problems. In this case, the system parameters including geometry, materials and nuclear sources, etc., are pre-defined and the transportation and interactions of nuclear particles (such as neutrons, photons and/or electrons in the regions of interest are simulated according to detailed nuclear physics theory and their nuclear cross-section data (probability of interacting. Then the deposited energies of particles entering the detectors are recorded and tallied and the tool responses to such a scenario are generated. A general-purpose code named Monte Carlo N– Particle (MCNP has been the industry-standard for some time. In this paper, we briefly introduce the fundamental principles of Monte Carlo numerical modeling and review the physics of MCNP. Some of the latest developments of Monte Carlo Models are also reviewed. A variety of examples are presented to illustrate the uses of Monte Carlo numerical models
A Monte Carlo Model of Light Propagation in Nontransparent Tissue
Institute of Scientific and Technical Information of China (English)
姚建铨; 朱水泉; 胡海峰; 王瑞康
2004-01-01
To sharpen the imaging of structures, it is vital to develop a convenient and efficient quantitative algorithm of the optical coherence tomography (OCT) sampling. In this paper a new Monte Carlo model is set up and how light propagates in bio-tissue is analyzed in virtue of mathematics and physics equations. The relations,in which light intensity of Class 1 and Class 2 light with different wavelengths changes with their permeation depth,and in which Class 1 light intensity (signal light intensity) changes with the probing depth, and in which angularly resolved diffuse reflectance and diffuse transmittance change with the exiting angle, are studied. The results show that Monte Carlo simulation results are consistent with the theory data.
Few-body systems in a shell-model approach
Energy Technology Data Exchange (ETDEWEB)
Toelle, Simon
2014-02-10
In this thesis, I introduce and compare an implementation of two different shell models for physical systems consisting of multiple identical bosons. In the main part, the shell model is used to study the energy spectra of bosons with contact interactions in a harmonic confinement as well as those of unconfined He clusters. The convergence of the shell-model results is investigated in detail as the size of the model space is increased. Furthermore, possible improvements such as the smearing of contact interactions or a unitary transformation of the potentials are utilised and assessed. Systems with up to twelve bosons are considered. Moreover, I test a procedure to determine scattering observables from the energy spectra of fermions in a harmonic confinement. Finally, the position and width of resonances are extracted from the dependence of the energy spectra on the oscillator length.
Strain in the mesoscale kinetic Monte Carlo model for sintering
DEFF Research Database (Denmark)
Bjørk, Rasmus; Frandsen, Henrik Lund; Tikare, V.;
2014-01-01
Shrinkage strains measured from microstructural simulations using the mesoscale kinetic Monte Carlo (kMC) model for solid state sintering are discussed. This model represents the microstructure using digitized discrete sites that are either grain or pore sites. The algorithm used to simulate...... anisotropic strains for homogeneous powder compacts with aspect ratios different from unity. It is shown that the line direction biases shrinkage strains in proportion the compact dimension aspect ratios. A new algorithm that corrects this bias in strains is proposed; the direction for collapsing the column...
Dynamical Monte Carlo method for stochastic epidemic models
Aiello, O E
2002-01-01
A new approach to Dynamical Monte Carlo Methods is introduced to simulate markovian processes. We apply this approach to formulate and study an epidemic Generalized SIRS model. The results are in excellent agreement with the forth order Runge-Kutta method in a region of deterministic solution. Introducing local stochastic interactions, the Runge-Kutta method is not applicable, and we solve and check it self-consistently with a stochastic version of the Euler Method. The results are also analyzed under the herd-immunity concept.
3D Monte Carlo radiation transfer modelling of photodynamic therapy
Campbell, C. Louise; Christison, Craig; Brown, C. Tom A.; Wood, Kenneth; Valentine, Ronan M.; Moseley, Harry
2015-06-01
The effects of ageing and skin type on Photodynamic Therapy (PDT) for different treatment methods have been theoretically investigated. A multilayered Monte Carlo Radiation Transfer model is presented where both daylight activated PDT and conventional PDT are compared. It was found that light penetrates deeper through older skin with a lighter complexion, which translates into a deeper effective treatment depth. The effect of ageing was found to be larger for darker skin types. The investigation further strengthens the usage of daylight as a potential light source for PDT where effective treatment depths of about 2 mm can be achieved.
Monte Carlo Simulation of Kinesin Movement with a Lattice Model
Institute of Scientific and Technical Information of China (English)
WANG Hong; DOU Shuo-Xing; WANG Peng-Ye
2005-01-01
@@ Kinesin is a processive double-headed molecular motor that moves along a microtubule by taking about 8nm steps. It generally hydrolyzes one ATP molecule for taking each forward step. The processive movement of the kinesin molecular motors is numerically simulated with a lattice model. The motors are considered as Brownian particles and the ATPase processes of both heads are taken into account. The Monte Carlo simulation results agree well with recent experimental observations, especially on the relation of velocity versus ATP and ADP concentrations.
Gauge Potts model with generalized action: A Monte Carlo analysis
Energy Technology Data Exchange (ETDEWEB)
Fanchiotti, H.; Canal, C.A.G.; Sciutto, S.J.
1985-08-15
Results of a Monte Carlo calculation on the q-state gauge Potts model in d dimensions with a generalized action involving planar 1 x 1, plaquette, and 2 x 1, fenetre, loop interactions are reported. For d = 3 and q = 2, first- and second-order phase transitions are detected. The phase diagram for q = 3 presents only first-order phase transitions. For d = 2, a comparison with analytical results is made. Here also, the behavior of the numerical simulation in the vicinity of a second-order transition is analyzed.
Transition Strength Sums and Quantum Chaos in Shell Model States
Kota, V K B; Kar, K; Gómez, J M G; Retamosa, J
2000-01-01
For the embedded Gaussian orthogonal ensemble (EGOE) of random matrices, the strength sums generated by a transition operator acting on an eigenstate vary with the excitation energy as the ratio of two Gaussians. This general result is compared to exact shell model calculations, with realistic interactions, of spherical orbit occupancies and Gamow-Teller strength sums in some $(ds)$ and $(fp)$ shell examples. In order to confirm that EGOE operates in the chaotic domain of the shell model spectrum, calculations are carried out using two different interpolating hamiltonians generating order-chaos transitions. Good agreement is obtained in the chaotic domain of the spectrum, and strong deviations are observed as nuclear motion approaches a regular regime (transition strength sums appear to follow the Dyson's $\\Delta_3$ statistic). More importantly, they shed new light on the newly emerging understanding that in the chaotic domain of isolated finite interacting many particle systems smoothed densities (they inclu...
Markov chain Monte Carlo simulation for Bayesian Hidden Markov Models
Chan, Lay Guat; Ibrahim, Adriana Irawati Nur Binti
2016-10-01
A hidden Markov model (HMM) is a mixture model which has a Markov chain with finite states as its mixing distribution. HMMs have been applied to a variety of fields, such as speech and face recognitions. The main purpose of this study is to investigate the Bayesian approach to HMMs. Using this approach, we can simulate from the parameters' posterior distribution using some Markov chain Monte Carlo (MCMC) sampling methods. HMMs seem to be useful, but there are some limitations. Therefore, by using the Mixture of Dirichlet processes Hidden Markov Model (MDPHMM) based on Yau et. al (2011), we hope to overcome these limitations. We shall conduct a simulation study using MCMC methods to investigate the performance of this model.
Evolutionary Sequential Monte Carlo Samplers for Change-Point Models
Directory of Open Access Journals (Sweden)
Arnaud Dufays
2016-03-01
Full Text Available Sequential Monte Carlo (SMC methods are widely used for non-linear filtering purposes. However, the SMC scope encompasses wider applications such as estimating static model parameters so much that it is becoming a serious alternative to Markov-Chain Monte-Carlo (MCMC methods. Not only do SMC algorithms draw posterior distributions of static or dynamic parameters but additionally they provide an estimate of the marginal likelihood. The tempered and time (TNT algorithm, developed in this paper, combines (off-line tempered SMC inference with on-line SMC inference for drawing realizations from many sequential posterior distributions without experiencing a particle degeneracy problem. Furthermore, it introduces a new MCMC rejuvenation step that is generic, automated and well-suited for multi-modal distributions. As this update relies on the wide heuristic optimization literature, numerous extensions are readily available. The algorithm is notably appropriate for estimating change-point models. As an example, we compare several change-point GARCH models through their marginal log-likelihoods over time.
Monte Carlo model for electron degradation in methane
Bhardwaj, Anil
2015-01-01
We present a Monte Carlo model for degradation of 1-10,000 eV electrons in an atmosphere of methane. The electron impact cross sections for CH4 are compiled and analytical representations of these cross sections are used as input to the model.model.Yield spectra, which provides information about the number of inelastic events that have taken place in each energy bin, is used to calculate the yield (or population) of various inelastic processes. The numerical yield spectra, obtained from the Monte Carlo simulations, is represented analytically, thus generating the Analytical Yield Spectra (AYS). AYS is employed to obtain the mean energy per ion pair and efficiencies of various inelastic processes.Mean energy per ion pair for neutral CH4 is found to be 26 (27.8) eV at 10 (0.1) keV. Efficiency calculation showed that ionization is the dominant process at energies >50 eV, for which more than 50% of the incident electron energy is used. Above 25 eV, dissociation has an efficiency of 27%. Below 10 eV, vibrational e...
Chaotic and regular instantons in helical shell models of turbulence
De Pietro, Massimo; Biferale, Luca
2016-01-01
Shell models of turbulence have a finite-time blowup, i.e. the enstrophy diverges while the single shell velocities stay finite, in the inviscid limit. The signature of this blowup is represented by self-similar instantonic structures traveling coherently through the inertial range. These solutions might influence the energy transfer and the anomalous scaling properties empirically observed for the forced and viscous models. In this paper we present a study of the instantonic solutions for a class of shell-models of turbulence based on the exact decomposition of the Navier-Stokes equations in helical eigenstates. We found that depending on the helical structure of the shell interactions instantons are chaotic or regular. Some instantonic solutions tend to recover mirror symmetry for scales small enough. All models that have anomalous scaling develop regular non-chaotic instantons. Vice-versa, models that have mean field non-anomalous scaling in the stationary regime are those that have chaotic instantons. Fin...
Testing refined shell-model interactions in the sd shell: Coulomb excitation of Na26
Siebeck, B; Blazhev, A; Reiter, P; Altenkirch, R; Bauer, C; Butler, P A; De Witte, H; Elseviers, J; Gaffney, L P; Hess, H; Huyse, M; Kröll, T; Lutter, R; Pakarinen, J; Pietralla, N; Radeck, F; Scheck, M; Schneiders, D; Sotty, C; Van Duppen, P; Vermeulen, M; Voulot, D; Warr, N; Wenander, F
2015-01-01
Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal sd interaction (USD) describing nuclei within the sd shell yielded two new interactions—USDA and USDB—causing changes in the theoretical description of these nuclei. Purpose: Transition matrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus Na26 with 7 valence neutrons and 3 valence protons outside the doubly-magic 16O core is used as a test case. Method: A radioactive beam experiment with Na26 (T1/2=1,07s) was performed at the REX-ISOLDE facility (CERN) using Coulomb excitation at safe energies below the Coulomb barrier. Scattered particles were detected with an annular Si detector in coincidence with γ rays observed by the segmented MINIBALL array. Coulomb excitation cross sections...
Dynamic fracture modeling in shell structures based on XFEM
Larsson, R.; Mediavilla, J.; Fagerström, M.
2011-01-01
Through-the-thickness crack propagation in thin-walled structures is dealt with in this paper. The formulation is based on the cohesive zone concept applied to a kinematically consistent shell model enhanced with an XFEM-based discontinuous kinematical representation. The resulting formulation compr
Bursts and shocks in a continuum shell model
DEFF Research Database (Denmark)
Andersen, Ken Haste; Bohr, Tomas; Jensen, M.H.
1998-01-01
We study a burst event, i.e., the evolution of an initial condition having support only in a finite interval of k-space, in the continuum shell model due to Parisi. We show that the continuum equation without forcing or dissipation can be explicitly written in characteristic form and that the rig...
Longitudinal functional principal component modelling via Stochastic Approximation Monte Carlo
Martinez, Josue G.
2010-06-01
The authors consider the analysis of hierarchical longitudinal functional data based upon a functional principal components approach. In contrast to standard frequentist approaches to selecting the number of principal components, the authors do model averaging using a Bayesian formulation. A relatively straightforward reversible jump Markov Chain Monte Carlo formulation has poor mixing properties and in simulated data often becomes trapped at the wrong number of principal components. In order to overcome this, the authors show how to apply Stochastic Approximation Monte Carlo (SAMC) to this problem, a method that has the potential to explore the entire space and does not become trapped in local extrema. The combination of reversible jump methods and SAMC in hierarchical longitudinal functional data is simplified by a polar coordinate representation of the principal components. The approach is easy to implement and does well in simulated data in determining the distribution of the number of principal components, and in terms of its frequentist estimation properties. Empirical applications are also presented.
Shell Model Study on the Proton Pigmy Dipole Resonances in ~(17, 18)Ne
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
The proton pygmy dipole resonances (PDRs) in proton rich nuclei 17, 18Ne have been investigated in the framework of interacting shell model. The shell model with the self-consistent Skyrme-Hartree-Fock wave functions has well reproduced
Monte Carlo autofluorescence modeling of cervical intraepithelial neoplasm progression
Chu, S. C.; Chiang, H. K.; Wu, C. E.; He, S. Y.; Wang, D. Y.
2006-02-01
Monte Carlo fluorescence model has been developed to estimate the autofluorescent spectra associated with the progression of the Exo-Cervical Intraepithelial Neoplasm (CIN). We used double integrating spheres system and a tunable light source system, 380 to 600 nm, to measure the reflection and transmission spectra of a 50 μm thick tissue, and used Inverse Adding-Doubling (IAD) method to estimate the absorption (μa) and scattering (μs) coefficients. Human cervical tissue samples were sliced vertically (longitudinal) by the frozen section method. The results show that the absorption and scattering coefficients of cervical neoplasia are 2~3 times higher than normal tissues. We applied Monte Carlo method to estimate photon distribution and fluorescence emission in the tissue. By combining the intrinsic fluorescence information (collagen, NADH, and FAD), the anatomical information of the epithelium, CIN, stroma layers, and the fluorescence escape function, the autofluorescence spectra of CIN at different development stages were obtained.We have observed that the progression of the CIN results in gradually decreasing of the autofluorescence intensity of collagen peak intensity. In addition, the existence of the CIN layer formeda barrier that blocks the autofluorescence escaping from the stroma layer due to the strong extinction(scattering and absorption) of the CIN layer. To our knowledge, this is the first study measuring the CIN optical properties in the visible range; it also successfully demonstrates the fluorescence model forestimating autofluorescence spectra of cervical tissue associated with the progression of the CIN tissue;this model is very important in assisting the CIN diagnosis and treatment in clinical medicine.
A Monte Carlo Simulation Framework for Testing Cosmological Models
Directory of Open Access Journals (Sweden)
Heymann Y.
2014-10-01
Full Text Available We tested alternative cosmologies using Monte Carlo simulations based on the sam- pling method of the zCosmos galactic survey. The survey encompasses a collection of observable galaxies with respective redshifts that have been obtained for a given spec- troscopic area of the sky. Using a cosmological model, we can convert the redshifts into light-travel times and, by slicing the survey into small redshift buckets, compute a curve of galactic density over time. Because foreground galaxies obstruct the images of more distant galaxies, we simulated the theoretical galactic density curve using an average galactic radius. By comparing the galactic density curves of the simulations with that of the survey, we could assess the cosmologies. We applied the test to the expanding-universe cosmology of de Sitter and to a dichotomous cosmology.
Monte Carlo Modeling of Crystal Channeling at High Energies
Schoofs, Philippe; Cerutti, Francesco
Charged particles entering a crystal close to some preferred direction can be trapped in the electromagnetic potential well existing between consecutive planes or strings of atoms. This channeling effect can be used to extract beam particles if the crystal is bent beforehand. Crystal channeling is becoming a reliable and efficient technique for collimating beams and removing halo particles. At CERN, the installation of silicon crystals in the LHC is under scrutiny by the UA9 collaboration with the goal of investigating if they are a viable option for the collimation system upgrade. This thesis describes a new Monte Carlo model of planar channeling which has been developed from scratch in order to be implemented in the FLUKA code simulating particle transport and interactions. Crystal channels are described through the concept of continuous potential taking into account thermal motion of the lattice atoms and using Moliere screening function. The energy of the particle transverse motion determines whether or n...
Markov Chain Monte-Carlo Models of Starburst Clusters
Melnick, Jorge
2015-01-01
There are a number of stochastic effects that must be considered when comparing models to observations of starburst clusters: the IMF is never fully populated; the stars can never be strictly coeval; stars rotate and their photometric properties depend on orientation; a significant fraction of massive stars are in interacting binaries; and the extinction varies from star to star. The probability distributions of each of these effects are not a priori known, but must be extracted from the observations. Markov Chain Monte-Carlo methods appear to provide the best statistical approach. Here I present an example of stochastic age effects upon the upper mass limit of the IMF of the Arches cluster as derived from near-IR photometry.
Modelling a gamma irradiation process using the Monte Carlo method
Energy Technology Data Exchange (ETDEWEB)
Soares, Gabriela A.; Pereira, Marcio T., E-mail: gas@cdtn.br, E-mail: mtp@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)
2011-07-01
In gamma irradiation service it is of great importance the evaluation of absorbed dose in order to guarantee the service quality. When physical structure and human resources are not available for performing dosimetry in each product irradiated, the appliance of mathematic models may be a solution. Through this, the prediction of the delivered dose in a specific product, irradiated in a specific position and during a certain period of time becomes possible, if validated with dosimetry tests. At the gamma irradiation facility of CDTN, equipped with a Cobalt-60 source, the Monte Carlo method was applied to perform simulations of products irradiations and the results were compared with Fricke dosimeters irradiated under the same conditions of the simulations. The first obtained results showed applicability of this method, with a linear relation between simulation and experimental results. (author)
Testing the spin-cutoff parameterization with shell-model calculations
Spinella, William M
2013-01-01
The nuclear level density, an important input to Hauser-Feshbach calculations, depends not only on excitation energy but also on angular momentum J. The J-dependence of the level density at fixed excitation energy E_x is usually parameterized via the spin-cutoff factor sigma. We carefully test the statistical accuracy of this parameterization for a large number of spectra computed using semi-realistic interactions in the interacting shell model, with a nonlinear least-squares fit of sigma and finding the error bar in sigma. The spin-cutoff parameterization works well as long as there are enough states to be statistical. In turn, the spin-cutoff factor can be related to the average value of J^2 at a fixed excitation energy, and we briefly investigate extracting from a thermal calculation such as one might do via Monte Carlo.
Accelerating Monte Carlo Markov chains with proxy and error models
Josset, Laureline; Demyanov, Vasily; Elsheikh, Ahmed H.; Lunati, Ivan
2015-12-01
In groundwater modeling, Monte Carlo Markov Chain (MCMC) simulations are often used to calibrate aquifer parameters and propagate the uncertainty to the quantity of interest (e.g., pollutant concentration). However, this approach requires a large number of flow simulations and incurs high computational cost, which prevents a systematic evaluation of the uncertainty in the presence of complex physical processes. To avoid this computational bottleneck, we propose to use an approximate model (proxy) to predict the response of the exact model. Here, we use a proxy that entails a very simplified description of the physics with respect to the detailed physics described by the "exact" model. The error model accounts for the simplification of the physical process; and it is trained on a learning set of realizations, for which both the proxy and exact responses are computed. First, the key features of the set of curves are extracted using functional principal component analysis; then, a regression model is built to characterize the relationship between the curves. The performance of the proposed approach is evaluated on the Imperial College Fault model. We show that the joint use of the proxy and the error model to infer the model parameters in a two-stage MCMC set-up allows longer chains at a comparable computational cost. Unnecessary evaluations of the exact responses are avoided through a preliminary evaluation of the proposal made on the basis of the corrected proxy response. The error model trained on the learning set is crucial to provide a sufficiently accurate prediction of the exact response and guide the chains to the low misfit regions. The proposed methodology can be extended to multiple-chain algorithms or other Bayesian inference methods. Moreover, FPCA is not limited to the specific presented application and offers a general framework to build error models.
The complete ellipsoidal shell-model in EEG imaging
Directory of Open Access Journals (Sweden)
2006-01-01
Full Text Available This work provides the solution of the direct Electroencephalography (EEG problem for the complete ellipsoidal shell-model of the human head. The model involves four confocal ellipsoids that represent the successive interfaces between the brain tissue, the cerebrospinal fluid, the skull, and the skin characterized by different conductivities. The electric excitation of the brain is due to an equivalent electric dipole, which is located within the inner ellipsoid. The proposed model is considered to be physically complete, since the effect of the substance surrounding the brain is taken into account. The direct EEG problem consists in finding the electric potential inside each conductive space, as well as at the nonconductive exterior space. The solution of this multitransmission problem is given analytically in terms of elliptic integrals and ellipsoidal harmonics, in such way that makes clear the effect that each shell has on the next one and outside of the head. It is remarkable that the dependence on the observation point is not affected by the presence of the conductive shells. Reduction to simpler ellipsoidal models and to the corresponding spherical models is included.
A Monte Carlo-based model of gold nanoparticle radiosensitization
Lechtman, Eli Solomon
The goal of radiotherapy is to operate within the therapeutic window - delivering doses of ionizing radiation to achieve locoregional tumour control, while minimizing normal tissue toxicity. A greater therapeutic ratio can be achieved by utilizing radiosensitizing agents designed to enhance the effects of radiation at the tumour. Gold nanoparticles (AuNP) represent a novel radiosensitizer with unique and attractive properties. AuNPs enhance local photon interactions, thereby converting photons into localized damaging electrons. Experimental reports of AuNP radiosensitization reveal this enhancement effect to be highly sensitive to irradiation source energy, cell line, and AuNP size, concentration and intracellular localization. This thesis explored the physics and some of the underlying mechanisms behind AuNP radiosensitization. A Monte Carlo simulation approach was developed to investigate the enhanced photoelectric absorption within AuNPs, and to characterize the escaping energy and range of the photoelectric products. Simulations revealed a 10 3 fold increase in the rate of photoelectric absorption using low-energy brachytherapy sources compared to megavolt sources. For low-energy sources, AuNPs released electrons with ranges of only a few microns in the surrounding tissue. For higher energy sources, longer ranged photoelectric products travelled orders of magnitude farther. A novel radiobiological model called the AuNP radiosensitization predictive (ARP) model was developed based on the unique nanoscale energy deposition pattern around AuNPs. The ARP model incorporated detailed Monte Carlo simulations with experimentally determined parameters to predict AuNP radiosensitization. This model compared well to in vitro experiments involving two cancer cell lines (PC-3 and SK-BR-3), two AuNP sizes (5 and 30 nm) and two source energies (100 and 300 kVp). The ARP model was then used to explore the effects of AuNP intracellular localization using 1.9 and 100 nm Au
Shell Model Description of $^{102-108}$Sn Isotopes
Trivedi, T; Negi, D; Mehrotra, I
2012-01-01
We have performed shell model calculations for neutron deficient even $^{102-108}$Sn and odd $^{103-107}$Sn isotopes in $sdg_{7/2}h_{11/2}$ model space using two different interactions. The first set of interaction is due to Brown {\\it et al.} and second is due to Hoska {\\it et al}. The calculations have been performed using doubly magic $^{100}$Sn as core and valence neutrons are distributed over the single particle orbits 1$g_{7/2}$, 2$d_{5/2}$, 2$d_{3/2}$, 3$s_{1/2}$ and 1$h_{11/2}$. In more recent experimental work for $^{101}$Sn [Phys. Rev. Lett. {\\bf 105} (2010) 162502], the g.s. is predicted as 5/2$^+$ with excited 7/2$^+$ at 172 keV. We have also performed another two set of calculations by taking difference in single particle energies of 2$d_{5/2}$ and 1$g_{7/2}$ orbitals by 172 keV. The present state-of-the-art shell model calculations predicts fair agreements with the experimental data. These calculations serve as a test of nuclear shell model in the region far from stability for unstable Sn isotop...
Shell Model Description of 102-108Sn Isotopes
Trivedi, T.; Srivastava, P. C.; Negi, D.; Mehrotra, I.
2012-05-01
We have performed shell model calculations for neutron deficient even 102-108Sn and odd 103-107Sn isotopes in sdg7/2h11/2 model space using two different interactions. The first set of interaction is due to Brown et al. and second is due to Hoska et al. The calculations have been performed using doubly magic 100Sn as core and valence neutrons are distributed over the single particle orbits 1g7/2, 2d5/2, 2d3/2, 3s1/2 and 1h11/2. In more recent experimental work for 101Sn [I. G. Darby et al., Phys. Rev. Lett. 105 (2010) 162502], the g.s. is predicted as 5/2+ with excited 7/2+ at 172 keV. We have also performed another two set of calculations by taking difference in single particle energies of 2d5/2 and 1g7/2 orbitals by 172 keV. The present state-of-the-art shell model calculations predict fair agreement with the experimental data. These calculations serve as a test of nuclear shell model in the region far from stability for unstable Sn isotopes near the doubly magic 100Sn core.
Optimizing Muscle Parameters in Musculoskeletal Modeling Using Monte Carlo Simulations
Hanson, Andrea; Reed, Erik; Cavanagh, Peter
2011-01-01
Astronauts assigned to long-duration missions experience bone and muscle atrophy in the lower limbs. The use of musculoskeletal simulation software has become a useful tool for modeling joint and muscle forces during human activity in reduced gravity as access to direct experimentation is limited. Knowledge of muscle and joint loads can better inform the design of exercise protocols and exercise countermeasure equipment. In this study, the LifeModeler(TM) (San Clemente, CA) biomechanics simulation software was used to model a squat exercise. The initial model using default parameters yielded physiologically reasonable hip-joint forces. However, no activation was predicted in some large muscles such as rectus femoris, which have been shown to be active in 1-g performance of the activity. Parametric testing was conducted using Monte Carlo methods and combinatorial reduction to find a muscle parameter set that more closely matched physiologically observed activation patterns during the squat exercise. Peak hip joint force using the default parameters was 2.96 times body weight (BW) and increased to 3.21 BW in an optimized, feature-selected test case. The rectus femoris was predicted to peak at 60.1% activation following muscle recruitment optimization, compared to 19.2% activation with default parameters. These results indicate the critical role that muscle parameters play in joint force estimation and the need for exploration of the solution space to achieve physiologically realistic muscle activation.
Probability Distribution Function of Passive Scalars in Shell Models
Institute of Scientific and Technical Information of China (English)
LIU Chun-Ping; ZHANG Xiao-Qiang; LIU Yu-Rong; WANG Guang-Rui; HE Da-Ren; CHEN Shi-Gang; ZHU Lu-Jin
2008-01-01
A shell-model version of passive scalar problem is introduced, which is inspired by the model of K. Ohkitani and M. Yakhot [K. Ohkitani and M. Yakhot, Phys. Rev. Lett. 60 (1988) 983; K. Ohkitani and M. Yakhot, Prog. Theor. Phys. 81 (1988) 329]. As in the original problem, the prescribed random velocity field is Gaussian and 5 correlated in time. Deterministic differential equations are regarded as nonlinear Langevin equation. Then, the Fokker-Planck equations of PDF for passive scalars axe obtained and solved numerically. In energy input range (n < 5, n is the shell number.), the probability distribution function (PDF) of passive scalars is near the Gaussian distribution. In inertial range (5 < n < 16) and dissipation range (n ≥ 17), the probability distribution function (PDF) of passive scalars has obvious intermittence. And the scaling power of passive scalar is anomalous. The results of numerical simulations are compared with experimental measurements.
The continuum shell-model neutron states of 209Pb
Indian Academy of Sciences (India)
Ramendra Nath Majumdar
2003-12-01
The neutron strength distributions of the three high-spin 117/2, 2ℎ11/2 and 113/2 states of 209Pb have been obtained within the formalism of the core-polarisation effect where the effect of interaction of the neutron shell-model states of 209Pb with the collective vibrational states (originating also from the giant resonances) have been taken into consideration. The theoretical results have been discussed in the light of works on 117/2, 2ℎ11/2 and 113/2 neutron orbitals of 209Pb. The shell-model energies of the neutron states have been obtained by Skyrme–Hartree–Fock method.
Nuclear Level Density: Shell Model vs Mean Field
Sen'kov, Roman
2015-01-01
The knowledge of the nuclear level density is necessary for understanding various reactions including those in the stellar environment. Usually the combinatorics of Fermi-gas plus pairing is used for finding the level density. Recently a practical algorithm avoiding diagonalization of huge matrices was developed for calculating the density of many-body nuclear energy levels with certain quantum numbers for a full shell-model Hamiltonian. The underlying physics is that of quantum chaos and intrinsic thermalization in a closed system of interacting particles. We briefly explain this algorithm and, when possible, demonstrate the agreement of the results with those derived from exact diagonalization. The resulting level density is much smoother than that coming from the conventional mean-field combinatorics. We study the role of various components of residual interactions in the process of thermalization, stressing the influence of incoherent collision-like processes. The shell-model results for the traditionally...
Anomalous scaling in a non-Gaussian random shell model for passive scalars
Institute of Scientific and Technical Information of China (English)
2007-01-01
In this paper, we have introduced a shell-model of Kraichnan's passive scalar problem. Different from the original problem, the prescribed random velocity field is non-Gaussian and δ correlated in time, and its introduction is inspired by She and Lév(e)que (Phys. Rev. Lett. 72,336 (1994)). For comparison, we also give the passive scalar advected by the Gaussian random velocity field. The anomalous scaling exponents H(p) of passive scalar advected by these two kinds of random velocities above are determined for structure function with values of p up to 15 by Monte Carlo simulations of the random shell model, with Gear methods used to solve the stochastic differential equations. We find that the H(p) advected by the non-Gaussian random velocity is not more anomalous than that advected by the Gaussian random velocity. Whether the advecting velocity is non-Gaussian or Gaussian, similar scaling exponents of passive scalar are obtained with the same molecular diffusivity.
Nucleon-Pair Shell Model: Magnetic Excitations for Ba Isotopes
Institute of Scientific and Technical Information of China (English)
LUO YanAn; NING PingZhi
2002-01-01
Magnetic excitations for Ba isotopes are discussed within the nucleon-pair shell model trmicated iti the SDsubspace. With the SD pair determined by a surface-δ interaction, M1 transitions for 1344Ba are well fitted. The M1 andM3 transitions for 132Ba and 130Ba are also predicted. It is shown that the statement, the collective magnetic propertiesarc due to the orbital motion of nucleons, is approximately valid.
Projected shell model study of band structure of 90Nb
Kumar, Amit; Singh, Dhanvir; Gupta, Anuradha; Singh, Suram; Bharti, Arun
2016-05-01
A systematic study of two-quasiparticle bands of the odd-odd 90Nb nucleus is performed using the projected shell model approach. Yrast band with some other bands have been obtained and back-bending in moment of inertia has also been calculated and compared with the available experimental. On comparing the available experimental data, it is found that the treatment with PSM provides a satisfactory explanation of the available data.
Mixed-Symmetry Shell-Model Calculations in Nuclear Physics
Gueorguiev, V G
2010-01-01
We consider a novel approach to the nuclear shell model. The one-dimensional harmonic oscillator in a box is used to introduce the concept of an oblique-basis shell-model theory. By implementing the Lanczos method for diagonalization of large matrices, and the Cholesky algorithm for solving generalized eigenvalue problems, the method is applied to nuclei. The mixed-symmetry basis combines traditional spherical shell-model states with SU(3) collective configurations. We test the validity of this mixed-symmetry scheme on 24Mg and 44Ti. Results for 24Mg, obtained using the Wilthental USD intersection in a space that spans less than 10% of the full-space, reproduce the binding energy within 2% as well as an accurate reproduction of the low-energy spectrum and the structure of the states - 90% overlap with the exact eigenstates. In contrast, for an m-scheme calculation, one needs about 60% of the full space to obtain compatible results. Calculations for 44Ti support the mixed-mode scheme although the pure SU(3) ca...
Hopping electron model with geometrical frustration: kinetic Monte Carlo simulations
Terao, Takamichi
2016-09-01
The hopping electron model on the Kagome lattice was investigated by kinetic Monte Carlo simulations, and the non-equilibrium nature of the system was studied. We have numerically confirmed that aging phenomena are present in the autocorrelation function C ({t,tW )} of the electron system on the Kagome lattice, which is a geometrically frustrated lattice without any disorder. The waiting-time distributions p(τ ) of hopping electrons of the system on Kagome lattice has been also studied. It is confirmed that the profile of p (τ ) obtained at lower temperatures obeys the power-law behavior, which is a characteristic feature of continuous time random walk of electrons. These features were also compared with the characteristics of the Coulomb glass model, used as a model of disordered thin films and doped semiconductors. This work represents an advance in the understanding of the dynamics of geometrically frustrated systems and will serve as a basis for further studies of these physical systems.
Monte Carlo model for electron degradation in xenon gas
Mukundan, Vrinda
2016-01-01
We have developed a Monte Carlo model for studying the local degradation of electrons in the energy range 9-10000 eV in xenon gas. Analytically fitted form of electron impact cross sections for elastic and various inelastic processes are fed as input data to the model. Two dimensional numerical yield spectrum, which gives information on the number of energy loss events occurring in a particular energy interval, is obtained as output of the model. Numerical yield spectrum is fitted analytically, thus obtaining analytical yield spectrum. The analytical yield spectrum can be used to calculate electron fluxes, which can be further employed for the calculation of volume production rates. Using yield spectrum, mean energy per ion pair and efficiencies of inelastic processes are calculated. The value for mean energy per ion pair for Xe is 22 eV at 10 keV. Ionization dominates for incident energies greater than 50 eV and is found to have an efficiency of 65% at 10 keV. The efficiency for the excitation process is 30%...
Anlauf, H; Manakos, P; Mannel, T
1994-01-01
We present the Monte Carlo event generator {\\tt WOPPER} for pair production of $W$'s and their decays at high energy $e^+e^-$ colliders. {\\tt WOPPER} includes the effects from finite $W$ width and focusses on the calculation of higher order electromagnetic corrections in the leading log approximation including soft photon exponentiation and explicit generation of exclusive hard photons.
Microscopic Shell Model Calculations for the Fluorine Isotopes
Barrett, Bruce R.; Dikmen, Erdal; Maris, Pieter; Vary, James P.; Shirokov, Andrey M.
2015-10-01
Using a formalism based on the No Core Shell Model (NCSM), we have determined miscroscopically the core and single-particle energies and the effective two-body interactions that are the input to standard shell model (SSM) calculations. The basic idea is to perform a succession of a Okubo-Lee-Suzuki (OLS) transformation, a NCSM calculation, and a second OLS transformation to a further reduced space, such as the sd-shell, which allows the separation of the many-body matrix elements into an ``inert'' core part plus a few valence-nucleons calculation. In the present investigation we use this technique to calculate the properties of the nuclides in the Fluorine isotopic chain, using the JISP16 nucleon-nucleon interaction. The obtained SSM input, along with the results of the SSM calculations for the Fluorine isotopes, will be presented. This work supported in part by TUBITAK-BIDEB, the US DOE, the US NSF, NERSC, and the Russian Ministry of Education and Science.
The Shell Model as Unified View of Nuclear Structure
Caurier, E; Nowacki, F; Poves, A; Zuker, A P
2004-01-01
The last decade has witnessed both quantitative and qualitative progresses in Shell Model studies, which have resulted in remarkable gains in our understanding of the structure of the nucleus. Indeed, it is now possible to diagonalize matrices in determinantal spaces of dimensionality up to 10^9 using the Lanczos tridiagonal construction, whose formal and numerical aspects we will analyze. Besides, many new approximation methods have been developed in order to overcome the dimensionality limitations. Furthermore, new effective nucleon-nucleon interactions have been constructed that contain both two and three-body contributions. The former are derived from realistic potentials (i.e., consistent with two nucleon data). The latter incorporate the pure monopole terms necessary to correct the bad saturation and shell-formation properties of the realistic two-body forces. This combination appears to solve a number of hitherto puzzling problems. In the present review we will concentrate on those results which illust...
A wind-shell interaction model for multipolar planetary nebulae
Steffen, W; Esquivel, A; Garcia-Segura, G; Garcia-Diaz, Ma T; Lopez, J A; Magnor, M
2013-01-01
We explore the formation of multipolar structures in planetary and pre-planetary nebulae from the interaction of a fast post-AGB wind with a highly inhomogeneous and filamentary shell structure assumed to form during the final phase of the high density wind. The simulations were performed with a new hydrodynamics code integrated in the interactive framework of the astrophysical modeling package SHAPE. In contrast to conventional astrophysical hydrodynamics software, the new code does not require any programming intervention by the user for setting up or controlling the code. Visualization and analysis of the simulation data has been done in SHAPE without external software. The key conclusion from the simulations is that secondary lobes in planetary nebulae, such as Hubble 5 and K3-17, can be formed through the interaction of a fast low-density wind with a complex high density environment, such as a filamentary circumstellar shell. The more complicated alternative explanation of intermittent collimated outflow...
Phases and phase transitions in the algebraic microscopic shell model
Directory of Open Access Journals (Sweden)
Georgieva A. I.
2016-01-01
Full Text Available We explore the dynamical symmetries of the shell model number conserving algebra, which define three types of pairing and quadrupole phases, with the aim to obtain the prevailing phase or phase transition for the real nuclear systems in a single shell. This is achieved by establishing a correspondence between each of the pairing bases with the Elliott’s SU(3 basis that describes collective rotation of nuclear systems. This allows for a complete classification of the basis states of different number of particles in all the limiting cases. The probability distribution of the SU(3 basis states within theirs corresponding pairing states is also obtained. The relative strengths of dynamically symmetric quadrupole-quadrupole interaction in respect to the isoscalar, isovector and total pairing interactions define a control parameter, which estimates the importance of each term of the Hamiltonian in the correct reproduction of the experimental data for the considered nuclei.
Monte Carlo modeling and optimization of buffer gas positron traps
Marjanović, Srđan; Petrović, Zoran Lj
2017-02-01
Buffer gas positron traps have been used for over two decades as the prime source of slow positrons enabling a wide range of experiments. While their performance has been well understood through empirical studies, no theoretical attempt has been made to quantitatively describe their operation. In this paper we apply standard models as developed for physics of low temperature collision dominated plasmas, or physics of swarms to model basic performance and principles of operation of gas filled positron traps. The Monte Carlo model is equipped with the best available set of cross sections that were mostly derived experimentally by using the same type of traps that are being studied. Our model represents in realistic geometry and fields the development of the positron ensemble from the initial beam provided by the solid neon moderator through voltage drops between the stages of the trap and through different pressures of the buffer gas. The first two stages employ excitation of N2 with acceleration of the order of 10 eV so that the trap operates under conditions when excitation of the nitrogen reduces the energy of the initial beam to trap the positrons without giving them a chance to become annihilated following positronium formation. The energy distribution function develops from the assumed distribution leaving the moderator, it is accelerated by the voltage drops and forms beams at several distinct energies. In final stages the low energy loss collisions (vibrational excitation of CF4 and rotational excitation of N2) control the approach of the distribution function to a Maxwellian at room temperature but multiple non-Maxwellian groups persist throughout most of the thermalization. Optimization of the efficiency of the trap may be achieved by changing the pressure and voltage drops and also by selecting to operate in a two stage mode. The model allows quantitative comparisons and test of optimization as well as development of other properties.
Institute of Scientific and Technical Information of China (English)
ZHANG Xiao-Qiang; WANG Guang-Rui; CHEN Shi-Gang
2008-01-01
We propose a new approach to the old-standing problem of the anomaly of the scaling exponents of passive scalars of turbulence.Different to the original problem,the distribution function of the prescribed random velocity field is multi-dimensional normal and delta-correlated in time.Here,our random velocity field is spatially correlative.For comparison,we also give the result obtained by the Gaussian random velocity field without spatial correlation.The anomalous scaling exponents H (p) of passive scalar advected by two kinds of random velocity above are determined for structure function up to p= 15 by numerical simulations of the random shell model with Runge-Kutta methods to solve the stochastic differential equations.We observed that the H (p)'s obtained by the multi-dimensional normal distribution random velocity are more anomalous than those obtained by the independent Gaussian random velocity.
A Monte Carlo model of the Varian IGRT couch top for RapidArc QA.
Teke, T; Gill, B; Duzenli, C; Popescu, I A
2011-12-21
The objectives of this study are to evaluate the effect of couch attenuation on quality assurance (QA) results and to present a couch top model for Monte Carlo (MC) dose calculation for RapidArc treatments. The IGRT couch top is modelled in Eclipse as a thin skin of higher density material with a homogeneous fill of foam of lower density and attenuation. The IGRT couch structure consists of two longitudinal sections referred to as thick and thin. The Hounsfield Unit (HU) characterization of the couch structure was determined using a cylindrical phantom by comparing ion chamber measurements with the dose predicted by the treatment planning system (TPS). The optimal set of HU for the inside of the couch and the surface shell was found to be respectively -960 and -700 HU in agreement with Vanetti et al (2009 Phys. Med. Biol. 54 N157-66). For each plan, the final dose calculation was performed with the thin, thick and without the couch top. Dose differences up to 2.6% were observed with TPS calculated doses not including the couch and up to 3.4% with MC not including the couch and were found to be treatment specific. A MC couch top model was created based on the TPS geometrical model. The carbon fibre couch top skin was modelled using carbon graphite; the density was adjusted until good agreement with experimental data was observed, while the density of the foam inside was kept constant. The accuracy of the couch top model was evaluated by comparison with ion chamber measurements and TPS calculated dose combined with a 3D gamma analysis. Similar to the TPS case, a single graphite density can be used for both the thin and thick MC couch top models. Results showed good agreement with ion chamber measurements (within 1.2%) and with TPS (within 1%). For each plan, over 95% of the points passed the 3D gamma test.
Estimation of Schiff moments using the nuclear shell model
Teruya, Eri; Yoshinaga, Naotaka; Arai, Ryoichi; Higashiyama, Koji
2014-09-01
The existence of finite permanent electric dipole moment (EDM) of an elementary particle or an atom indicates violation of time-reversal symmetry. The time reversal invariance implies violation of charge and parity symmetry through the CPT theorem. The predicted fundamental particle's EDMs are too small to be observed in the Standard Model. However, some models beyond the Standard Model produce much larger EDMs which may be observed in future. Thus, if we observe finite EDMs, we can conclude that we need a new extended model for the Standard Model and the specific value of an EDM gives a constraint on constructing a new model. Experimental efforts searching for atomic EDMs are now in progress. The EDM of a neutral atom is mainly induced by the nuclear Schiff moment, since the electron EDM is very small and the nuclear EDM is shielded by outside electrons owing to the Schiff theorem. In this work we estimate the Schiff moments for the lowest 1/2+ states of Xe isotopes around the mass 130. The nuclear wave functions beyond mean-field theories are calculated in terms of the nuclear shell model. We discuss influences of core excitations and over shell excitations on the Schiff moments.
Shell model approach for nuclei with mass around 220
Kaiura, Yukiko; Yoshinaga, Naotaka; Higashiyama, Koji
2014-09-01
Ra and Th isotopes with mass around 220 belonging to a transitional region between spherical and deformed regions have fascinated our interest from the past. In particular, since a large number of negative parity states are observed in low-lying states, collective octupole correlations are supposed to be important. In this talk we report the nuclear structure of Po, Rn, Ra and Th isotopes in terms of the pair truncated shell model, the basic ingredients of which consist of nuclear collective models. The 208Pb is considered as the doubly-magic core. The conventional pairing plus quadrupole interaction is employed. Energy levels and electric transitions are compared between theory and experiment.
Study of nuclear clustering using the modern shell model approach
Volya, Alexander; Tchuvil'Sky, Yury
2014-03-01
Nuclear clustering, alpha decays, and multi-particle correlations are important components of nuclear dynamics. In this work we use the modern configuration-interaction approach with most advanced realistic shell-model Hamiltonians to study these questions. We utilize the algebraic many-nucleon structures and the corresponding fractional parentage coefficients to build the translationally invariant wave functions of the alpha-cluster channels. We explore the alpha spectroscopic factors, study the distribution of clustering strength, and discuss the structure of an effective 4-body operator describing the in-medium alpha dynamics in the multi-shell valence configuration space. Sensitivity of alpha clustering to the components of an effective Hamiltonian, which includes its collective and many-body components, as well as isospin symmetry breaking terms, are of interest. We offer effective techniques for evaluation of the cluster spectroscopic factors satisfying the orthogonality conditions of the respective cluster channels. We present a study of clustering phenomena, single-particle dynamics, and electromagnetic transitions for a number of nuclei in p-sd shells and compare our results with the experimentally available data. This work is supported by the U.S. Department of Energy under contract number DE-SC0009883.
Monte Carlo Glauber wounded nucleon model with meson cloud
Zakharov, B G
2016-01-01
We study the effect of the nucleon meson cloud on predictions of the Monte Carlo Glauber wounded nucleon model for $AA$, $pA$, and $pp$ collisions. From the analysis of the data on the charged multiplicity density in $AA$ collisions we find that the meson-baryon Fock component reduces the required fraction of binary collisions by a factor of $\\sim 2$ for Au+Au collisions at $\\sqrt{s}=0.2$ TeV and $\\sim 1.5$ for Pb+Pb collisions at $\\sqrt{s}=2.76$ TeV. For central $AA$ collisions the meson cloud can increase the multiplicity density by $\\sim 16-18$\\%. We give predictions for the midrapidity charged multiplicity density in Pb+Pb collisions at $\\sqrt{s}=5.02$ TeV for the future LHC run 2. We find that the meson cloud has a weak effect on the centrality dependence of the ellipticity $\\epsilon_2$ in $AA$ collisions. For collisions of the deformed uranium nuclei at $\\sqrt{s}=0.2$ TeV we find that the meson cloud may improve somewhat agreement with the data on the dependence of the elliptic flow on the charged multi...
Monte Carlo Modeling Electronuclear Processes in Cascade Subcritical Reactor
Bznuni, S A; Zhamkochyan, V M; Polyanskii, A A; Sosnin, A N; Khudaverdian, A G
2000-01-01
Accelerator driven subcritical cascade reactor composed of the main thermal neutron reactor constructed analogous to the core of the VVER-1000 reactor and a booster-reactor, which is constructed similar to the core of the BN-350 fast breeder reactor, is taken as a model example. It is shown by means of Monte Carlo calculations that such system is a safe energy source (k_{eff}=0.94-0.98) and it is capable of transmuting produced radioactive wastes (neutron flux density in the thermal zone is PHI^{max} (r,z)=10^{14} n/(cm^{-2} s^{-1}), neutron flux in the fast zone is respectively equal PHI^{max} (r,z)=2.25 cdot 10^{15} n/(cm^{-2} s^{-1}) if the beam current of the proton accelerator is k_{eff}=0.98 and I=5.3 mA). Suggested configuration of the "cascade" reactor system essentially reduces the requirements on the proton accelerator current.
SKIRT: the design of a suite of input models for Monte Carlo radiative transfer simulations
Baes, Maarten
2015-01-01
The Monte Carlo method is the most popular technique to perform radiative transfer simulations in a general 3D geometry. The algorithms behind and acceleration techniques for Monte Carlo radiative transfer are discussed extensively in the literature, and many different Monte Carlo codes are publicly available. On the contrary, the design of a suite of components that can be used for the distribution of sources and sinks in radiative transfer codes has received very little attention. The availability of such models, with different degrees of complexity, has many benefits. For example, they can serve as toy models to test new physical ingredients, or as parameterised models for inverse radiative transfer fitting. For 3D Monte Carlo codes, this requires algorithms to efficiently generate random positions from 3D density distributions. We describe the design of a flexible suite of components for the Monte Carlo radiative transfer code SKIRT. The design is based on a combination of basic building blocks (which can...
Arita, Ken-ichiro
2014-01-01
Shell structures in single-particle energy spectra are investigated against regular tetrahedral type deformation using radial power-law potential model. Employing a natural way of shape parametrization which interpolate sphere and regular tetrahedron, we find prominent shell effects at rather large tetrahedral deformations, which bring about shell energies much larger than the cases of spherical and quadrupole type shapes. We discuss the semiclassical origin of these anomalous shell structures using periodic orbit theory.
A Monte Carlo reflectance model for soil surfaces with three-dimensional structure
Cooper, K. D.; Smith, J. A.
1985-01-01
A Monte Carlo soil reflectance model has been developed to study the effect of macroscopic surface irregularities larger than the wavelength of incident flux. The model treats incoherent multiple scattering from Lambertian facets distributed on a periodic surface. Resulting bidirectional reflectance distribution functions are non-Lambertian and compare well with experimental trends reported in the literature. Examples showing the coupling of the Monte Carlo soil model to an adding bidirectional canopy of reflectance model are also given.
Monte Carlo simulations of the HP model (the "Ising model" of protein folding)
Li, Ying Wai; Wüst, Thomas; Landau, David P.
2011-09-01
Using Wang-Landau sampling with suitable Monte Carlo trial moves (pull moves and bond-rebridging moves combined) we have determined the density of states and thermodynamic properties for a short sequence of the HP protein model. For free chains these proteins are known to first undergo a collapse "transition" to a globule state followed by a second "transition" into a native state. When placed in the proximity of an attractive surface, there is a competition between surface adsorption and folding that leads to an intriguing sequence of "transitions". These transitions depend upon the relative interaction strengths and are largely inaccessible to "standard" Monte Carlo methods.
Projected shell model study of neutron-deficient 122Ce
Indian Academy of Sciences (India)
Rani Devi; B D Sehgal; S K Khosa
2006-09-01
The observed excited states of 122Ce nucleus have been studied in the frame-work of projected shell model (PSM). The yrast band has been studied up to spin 26 ħ. The first band crossing has been predicted above a rotational frequency of 0.4 MeV/ħ that corresponds to first backbending. The calculation reproduces the experimentally observed ground state band up to spin 14ħ. The electromagnetic quantities, transition quadrupole moments and -factors are predicted and there is a need to measure these quantities experimentally.
Shell-model calculations of nuclei around mass 130
Teruya, E.; Yoshinaga, N.; Higashiyama, K.; Odahara, A.
2015-09-01
Shell-model calculations are performed for even-even, odd-mass, and doubly-odd nuclei of Sn, Sb, Te, I, Xe, Cs, and Ba isotopes around mass 130 using the single-particle space made up of valence nucleons occupying the 0 g7 /2 ,1 d5 /2 ,2 s1 /2 ,0 h11 /2 , and 1 d3 /2 orbitals. The calculated energies and electromagnetic transitions are compared with the experimental data. In addition, several typical isomers in this region are investigated.
Magnetic reversals in a modified shell model for magnetohydrodynamics turbulence.
Nigro, Giuseppina; Carbone, Vincenzo
2010-07-01
The aim of the paper is the study of dynamo action using a simple nonlinear model in the framework of magnetohydrodynamic turbulence. The nonlinear behavior of the system is described by using a shell model for velocity field and magnetic field fluctuations, modified for the magnetic field at the largest scale by a term describing a supercritical pitchfork bifurcation. Turbulent fluctuations generate a dynamical situation where the large-scale magnetic field jumps between two states which represent the opposite polarities of the magnetic field. Despite its simplicity, the model has the capability to describe a long time series of reversals from which we infer results about the statistics of persistence times and scaling laws of cancellations between opposite polarities for different magnetic diffusivity coefficients. These properties of the model are compared with real paleomagnetic data, thus revealing the origin of long-range correlations in the process.
Shell model of optimal passive-scalar mixing
Miles, Christopher; Doering, Charles
2015-11-01
Optimal mixing is significant to process engineering within industries such as food, chemical, pharmaceutical, and petrochemical. An important question in this field is ``How should one stir to create a homogeneous mixture while being energetically efficient?'' To answer this question, we consider an initially unmixed scalar field representing some concentration within a fluid on a periodic domain. This passive-scalar field is advected by the velocity field, our control variable, constrained by a physical quantity such as energy or enstrophy. We consider two objectives: local-in-time (LIT) optimization (what will maximize the mixing rate now?) and global-in-time (GIT) optimization (what will maximize mixing at the end time?). Throughout this work we use the H-1 mix-norm to measure mixing. To gain a better understanding, we provide a simplified mixing model by using a shell model of passive-scalar advection. LIT optimization in this shell model gives perfect mixing in finite time for the energy-constrained case and exponential decay to the perfect-mixed state for the enstrophy-constrained case. Although we only enforce that the time-average energy (or enstrophy) equals a chosen value in GIT optimization, interestingly, the optimal control keeps this value constant over time.
A shell finite element model of the pelvic floor muscles.
d'Aulignac, D; Martins, J A C; Pires, E B; Mascarenhas, T; Jorge, R M Natal
2005-10-01
The pelvic floor gives support to the organs in the abdominal cavity. Using the dataset made public in (Janda et al. J. Biomech. (2003) 36(6), pp. 749-757), we have reconstructed the geometry of one of the most important parts of the pelvic floor, the levator ani, using NURB surfaces. Once the surface is triangulated, the corresponding mesh is used in a finite element analysis with shell elements. Based on the 3D behavior of the muscle we have constructed a shell that takes into account the direction of the muscle fibers and the incompressibility of the tissue. The constitutive model for the isotropic strain energy and the passive strain energy stored in the fibers is adapted from Humphrey's model for cardiac muscles. To this the active behavior of the skeletal muscle is added. We present preliminary results of a simulation of the levator ani muscle under pressure and with active contraction. This research aims at helping simulate the damages to the pelvic floor that can occur after childbirth.
Alpha Decay in the Complex Energy Shell Model
Betan, R Id
2012-01-01
Alpha emission from a nucleus is a fundamental decay process in which the alpha particle formed inside the nucleus tunnels out through the potential barrier. We describe alpha decay of $^{212}$Po and $^{104}$Te by means of the configuration interaction approach. To compute the preformation factor and penetrability, we use the complex-energy shell model with a separable T=1 interaction. The single-particle space is expanded in a Woods-Saxon basis that consists of bound and unbound resonant states. Special attention is paid to the treatment of the norm kernel appearing in the definition of the formation amplitude that guarantees the normalization of the channel function. Without explicitly considering the alpha-cluster component in the wave function of the parent nucleus, we reproduce the experimental alpha-decay width of $^{212}$Po and predict an upper limit of T_{1/2}=5.5x10^{-7} sec for the half-life of $^{104}$Te. The complex-energy shell model in a large valence configuration space is capable of providing ...
Effective quantum Monte Carlo algorithm for modeling strongly correlated systems
Kashurnikov, V. A.; Krasavin, A. V.
2007-01-01
A new effective Monte Carlo algorithm based on principles of continuous time is presented. It allows calculating, in an arbitrary discrete basis, thermodynamic quantities and linear response of mixed boson-fermion, spin-boson, and other strongly correlated systems which admit no analytic description
Improved Monte Carlo model for multiple scattering calculations
Institute of Scientific and Technical Information of China (English)
Weiwei Cai; Lin Ma
2012-01-01
The coupling between the Monte Carlo (MC) method and geometrical optics to improve accuracy is investigated.The results obtained show improved agreement with previous experimental data,demonstrating that the MC method,when coupled with simple geometrical optics,can simulate multiple scattering with enhanced fidelity.
Monte Carlo estimation of the conditional Rasch model
Akkermans, Wies M.W.
1994-01-01
In order to obtain conditional maximum likelihood estimates, the so-called conditioning estimates have to be calculated. In this paper a method is examined that does not calculate these constants exactly, but approximates them using Monte Carlo Markov Chains. As an example, the method is applied to
Monte Carlo estimation of the conditional Rasch model
Akkermans, W.
1998-01-01
In order to obtain conditional maximum likelihood estimates, the conditioning constants are needed. Geyer and Thompson (1992) proposed a Markov chain Monte Carlo method that can be used to approximate these constants when they are difficult to calculate exactly. In the present paper, their method is
Monte Carlo simulation of quantum statistical lattice models
Raedt, Hans De; Lagendijk, Ad
1985-01-01
In this article we review recent developments in computational methods for quantum statistical lattice problems. We begin by giving the necessary mathematical basis, the generalized Trotter formula, and discuss the computational tools, exact summations and Monte Carlo simulation, that will be used t
Shell model description of low-lying states in Po and Rn isotopes
Higashiyama, Koji; Yoshinaga, Naotaka
2014-03-01
Nuclear structure of the Po and Rn isotopes is theoretically studied in terms of the spherical shell model with the monopole- and quadrupole-pairing plus quadrupole-quadrupole effective interaction. The experimental energy levels of low-lying states are well reproduced. The shell model results are examined in detail in a pair-truncated shell model. The analysis reveals the alignment of two protons in the 0h9/2 orbital at spin 8.
Shell model description of low-lying states in Po and Rn isotopes
Directory of Open Access Journals (Sweden)
Higashiyama Koji
2014-03-01
Full Text Available Nuclear structure of the Po and Rn isotopes is theoretically studied in terms of the spherical shell model with the monopole- and quadrupole-pairing plus quadrupole-quadrupole effective interaction. The experimental energy levels of low-lying states are well reproduced. The shell model results are examined in detail in a pair-truncated shell model. The analysis reveals the alignment of two protons in the 0h9/2 orbital at spin 8.
Monte Carlo modeling of ultrasound probes for image guided radiotherapy
Energy Technology Data Exchange (ETDEWEB)
Bazalova-Carter, Magdalena, E-mail: bazalova@uvic.ca [Department of Radiation Oncology, Stanford University, Stanford, California 94305 and Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia V8W 2Y2 (Canada); Schlosser, Jeffrey [SoniTrack Systems, Inc., Palo Alto, California 94304 (United States); Chen, Josephine [Department of Radiation Oncology, UCSF, San Francisco, California 94143 (United States); Hristov, Dimitre [Department of Radiation Oncology, Stanford University, Stanford, California 94305 (United States)
2015-10-15
Purpose: To build Monte Carlo (MC) models of two ultrasound (US) probes and to quantify the effect of beam attenuation due to the US probes for radiation therapy delivered under real-time US image guidance. Methods: MC models of two Philips US probes, an X6-1 matrix-array transducer and a C5-2 curved-array transducer, were built based on their megavoltage (MV) CT images acquired in a Tomotherapy machine with a 3.5 MV beam in the EGSnrc, BEAMnrc, and DOSXYZnrc codes. Mass densities in the probes were assigned based on an electron density calibration phantom consisting of cylinders with mass densities between 0.2 and 8.0 g/cm{sup 3}. Beam attenuation due to the US probes in horizontal (for both probes) and vertical (for the X6-1 probe) orientation was measured in a solid water phantom for 6 and 15 MV (15 × 15) cm{sup 2} beams with a 2D ionization chamber array and radiographic films at 5 cm depth. The MC models of the US probes were validated by comparison of the measured dose distributions and dose distributions predicted by MC. Attenuation of depth dose in the (15 × 15) cm{sup 2} beams and small circular beams due to the presence of the probes was assessed by means of MC simulations. Results: The 3.5 MV CT number to mass density calibration curve was found to be linear with R{sup 2} > 0.99. The maximum mass densities in the X6-1 and C5-2 probes were found to be 4.8 and 5.2 g/cm{sup 3}, respectively. Dose profile differences between MC simulations and measurements of less than 3% for US probes in horizontal orientation were found, with the exception of the penumbra region. The largest 6% dose difference was observed in dose profiles of the X6-1 probe placed in vertical orientation, which was attributed to inadequate modeling of the probe cable. Gamma analysis of the simulated and measured doses showed that over 96% of measurement points passed the 3%/3 mm criteria for both probes placed in horizontal orientation and for the X6-1 probe in vertical orientation. The
Partial dynamical symmetry in the symplectic shell model
Energy Technology Data Exchange (ETDEWEB)
Escher, J. [TRIUMF, Vancouver, British Columbia (Canada); Leviatan, A. [Hebrew Univ., Racah Inst. of Physics, Jerusalem (Israel)
2000-08-01
We present an example of a partial dynamical symmetry (PDS) in an interacting fermion system and demonstrate the close relationship of the associated Hamiltonians with a realistic quadrupole-quadrupole interaction, thus shedding light on this important interaction. Specifically, in the framework of the symplectic shell model of nuclei, we prove the existence of a family of fermionic Hamiltonians with partial SU(3) symmetry. We outline the construction process for the PDS eigenstates with good symmetry and give analytic expressions for the energies of these states and E2 transition strengths between them. Characteristics of both pure and mixed-symmetry PDS eigenstates are discussed and the resulting spectra and transition strengths are compared to those of real nuclei. The PDS concept is shown to be relevant to the description of prolate, oblate, as well as triaxially deformed nuclei. Similarities and differences between the fermion case and the previously established partial SU(3) symmetry in the interacting boson model are considered. (author)
The shell model approach: Key to hadron structure
Energy Technology Data Exchange (ETDEWEB)
Lipkin, H.J. (Weizmann Inst. of Science, Rehovoth (Israel). Dept. of Nuclear Physics)
1989-08-14
A shell model approach leads to a simple constituent quark model for hadron structure in which mesons and baryons consist only of constituent quarks. Hadron masses are the sums of the constituent quark effective masses and a hyperfine interaction inversely proportional to the product of these same masses. Hadron masses and magnetic moments are related by the assumption that the same effective mass parameter appears in the additive mass term, the hyperfine interaction, and the quark magnetic moment, both in mesons and baryons. The analysis pinpoints the physical assumptions needed for each relation and gives two new mass relations. Application to weak decays and recent polarized EMC data confirms conclusions previously obtained that the current quark contribution to the spin structure of the proton vanishes, but without need for the questionable assumption of SU(3) symmetry relating hyperon decays and proton structure. SU(3) symmetry breaking is clarified. 24 refs.
U(5)-O(6) Phase Transition in the SD-Pair Shell Model
Institute of Scientific and Technical Information of China (English)
WANG Fu-Rong; LIU Lin; LUO Yan-An; PAN Feng; DRAAYER J. P.
2008-01-01
U(5)-O(6) transitional behaviour in the SD-pair shell model is studied. The results show that the U(5)-O(6) transitional patterns of the interacting boson model can be reproduced in the SD-pair shell model approximately.
Logarithmic discretization and systematic derivation of shell models in two-dimensional turbulence.
Gürcan, Ö D; Morel, P; Kobayashi, S; Singh, Rameswar; Xu, S; Diamond, P H
2016-09-01
A detailed systematic derivation of a logarithmically discretized model for two-dimensional turbulence is given, starting from the basic fluid equations and proceeding with a particular form of discretization of the wave-number space. We show that it is possible to keep all or a subset of the interactions, either local or disparate scale, and recover various limiting forms of shell models used in plasma and geophysical turbulence studies. The method makes no use of the conservation laws even though it respects the underlying conservation properties of the fluid equations. It gives a family of models ranging from shell models with nonlocal interactions to anisotropic shell models depending on the way the shells are constructed. Numerical integration of the model shows that energy and enstrophy equipartition seem to dominate over the dual cascade, which is a common problem of two-dimensional shell models.
Projected shell model study of quasiparticle structure of arsenic isotopes
Energy Technology Data Exchange (ETDEWEB)
Verma, Preeti; Sharma, Chetan; Singh, Suram [Department of Physics and Electronics, University of Jammu, Jammu, 180006 (India); Bharti, Arun, E-mail: arunbharti_2003@yahoo.co.in [Department of Physics and Electronics, University of Jammu, Jammu, 180006 (India); Khosa, S.K. [Department of Physics and Electronics, University of Jammu, Jammu, 180006 (India); Bhat, G.H. [Department of Physics, University of Kashmir, Srinagar, 190006 (India); Sheikh, J.A. [Department of Physics, University of Kashmir, Srinagar, 190006 (India); Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States)
2013-11-20
Odd-mass isotopic chain of {sup 67–79}As has been studied within the context of the projected shell model. Deformed single-particle states generated by the standard Nilsson potential are used to calculate various nuclear structure properties like yrast spectra, rotational frequencies and reduced transition probabilities. The study of band structures of these As nuclei based on the band diagrams indicates the presence of multi-quasiparticle structure in the high spin realm of these nuclei. Rotational alignment phenomenon has also been studied in terms of band crossing which is understood to occur due to the rotational alignment of g{sub 9/2} neutron pair. We also have compared the results of the present calculations with the available experimental as well as the other theoretical data and an overall good agreement has been achieved between the two.
Partial Dynamical Symmetry in the Symplectic Shell Model
Escher, J; Escher, Jutta; Leviatan, Amiram
2002-01-01
We present an example of a partial dynamical symmetry (PDS) in an interacting fermion system and demonstrate the close relationship of the associated Hamiltonians with a realistic quadrupole-quadrupole interaction, thus shedding new light on this important interaction. Specifically, in the framework of the symplectic shell model of nuclei, we prove the existence of a family of fermionic Hamiltonians with partial SU(3) symmetry. We outline the construction process for the PDS eigenstates with good symmetry and give analytic expressions for the energies of these states and E2 transition strengths between them. Characteristics of both pure and mixed-symmetry PDS eigenstates are discussed and the resulting spectra and transition strengths are compared to those of real nuclei. The PDS concept is shown to be relevant to the description of prolate, oblate, as well as triaxially deformed nuclei. Similarities and differences between the fermion case and the previously established partial SU(3) symmetry in the Interact...
Kalinko, Aleksandr; Bauer, Matthias; Timoshenko, Janis; Kuzmin, Alexei
2016-11-01
Classical molecular dynamics (MD) and reverse Monte Carlo methods coupled with ab initio multiple-scattering extended x-ray absorption fine structure (EXAFS) calculations were used for modeling of scheelite-type AWO4 (A = Ca, Sr, Ba) W L 3-edge EXAFS spectra. The two theoretical approaches are complementary and allowed us to perform analysis of full EXAFS spectra. Both methods reproduce well the structure and dynamics of tungstates in the outer coordination shells, however the classical MD simulations underestimate the W-O bond MSRD due to a neglect of quantum zero-point-motion. The thermal vibration amplitudes, correlation effects and anisotropy of the tungstate structure were also estimated.
Hinzke, Denise; Nowak, Ulrich
1999-01-01
Using Monte Carlo methods we investigate the thermally activated magnetization switching of small ferromagnetic particles driven by an external magnetic field. For low uniaxial anisotropy one expects that the spins rotate coherently while for sufficiently large anisotropy the reversal should be due to nucleation. The latter case has been investigated extensively by Monte Carlo simulation of corresponding Ising models. In order to study the crossover from coherent rotation to nucleation we use...
Optical Monte Carlo modeling of a true portwine stain anatomy
Barton, Jennifer K.; Pfefer, T. Joshua; Welch, Ashley J.; Smithies, Derek J.; Nelson, Jerry; van Gemert, Martin J.
1998-04-01
A unique Monte Carlo program capable of accommodating an arbitrarily complex geometry was used to determine the energy deposition in a true port wine stain anatomy. Serial histologic sections taken from a biopsy of a dark red, laser therapy resistant stain were digitized and used to create the program input for simulation at wavelengths of 532 and 585 nm. At both wavelengths, the greatest energy deposition occurred in the superficial blood vessels, and subsequently decreased with depth as the laser beam was attenuated. However, more energy was deposited in the epidermis and superficial blood vessels at 532 nm than at 585 nm.
A systematic study of Lyman-Alpha transfer through outflowing shells: Model parameter estimation
Gronke, Max; Dijkstra, Mark
2015-01-01
Outflows promote the escape of Lyman-$\\alpha$ (Ly$\\alpha$) photons from dusty interstellar media. The process of radiative transfer through interstellar outflows is often modelled by a spherically symmetric, geometrically thin shell of gas that scatters photons emitted by a central Ly$\\alpha$ source. Despite its simplified geometry, this `shell model' has been surprisingly successful at reproducing observed Ly$\\alpha$ line shapes. In this paper we perform automated line fitting on a set of noisy simulated shell model spectra, in order to determine whether degeneracies exist between the different shell model parameters. While there are some significant degeneracies, we find that most parameters are accurately recovered, especially the HI column density ($N_{\\rm HI}$) and outflow velocity ($v_{\\rm exp}$). This work represents an important first step in determining how the shell model parameters relate to the actual physical properties of Ly$\\alpha$ sources. To aid further exploration of the parameter space, we ...
A new Monte Carlo simulation model for laser transmission in smokescreen based on MATLAB
Lee, Heming; Wang, Qianqian; Shan, Bin; Li, Xiaoyang; Gong, Yong; Zhao, Jing; Peng, Zhong
2016-11-01
A new Monte Carlo simulation model of laser transmission in smokescreen is promoted in this paper. In the traditional Monte Carlo simulation model, the radius of particles is set at the same value and the initial cosine value of photons direction is fixed also, which can only get the approximate result. The new model is achieved based on MATLAB and can simulate laser transmittance in smokescreen with different sizes of particles, and the output result of the model is close to the real scenarios. In order to alleviate the influence of the laser divergence while traveling in the air, we changed the initial direction cosine of photons on the basis of the traditional Monte Carlo model. The mixed radius particle smoke simulation results agree with the measured transmittance under the same experimental conditions with 5.42% error rate.
MARMOSET: The Path from LHC Data to the New Standard Model via On-Shell Effective Theories
Arkani-Hamed, N; Mrenna, S; Schuster, P; Thaler, J; Toro, N; Wang, L T; Arkani-Hamed, Nima; Knuteson, Bruce; Mrenna, Stephen; Schuster, Philip; Thaler, Jesse; Toro, Natalia; Wang, Lian-Tao
2007-01-01
We describe a coherent strategy and set of tools for reconstructing the fundamental theory of the TeV scale from LHC data. We show that On-Shell Effective Theories (OSETs) effectively characterize hadron collider data in terms of masses, production cross sections, and decay modes of candidate new particles. An OSET description of the data strongly constrains the underlying new physics, and sharply motivates the construction of its Lagrangian. Simulating OSETs allows efficient analysis of new-physics signals, especially when they arise from complicated production and decay topologies. To this end, we present MARMOSET, a Monte Carlo tool for simulating the OSET version of essentially any new-physics model. MARMOSET enables rapid testing of theoretical hypotheses suggested by both data and model-building intuition, which together chart a path to the underlying theory. We illustrate this process by working through a number of data challenges, where the most important features of TeV-scale physics are reconstructe...
Exploring uncertainty in glacier mass balance modelling with Monte Carlo simulation
Machguth, H.; Purves, R.S.; Oerlemans, J.; Hoelzle, M.; Paul, F.
2008-01-01
By means of Monte Carlo simulations we calculated uncertainty in modelled cumulative mass balance over 400 days at one particular point on the tongue of Morteratsch Glacier, Switzerland, using a glacier energy balance model of intermediate complexity. Before uncertainty assessment, the model was tun
Stress Resultant Based Elasto-Viscoplastic Thick Shell Model
Directory of Open Access Journals (Sweden)
Pawel Woelke
2012-01-01
Full Text Available The current paper presents enhancement introduced to the elasto-viscoplastic shell formulation, which serves as a theoretical base for the finite element code EPSA (Elasto-Plastic Shell Analysis [1–3]. The shell equations used in EPSA are modified to account for transverse shear deformation, which is important in the analysis of thick plates and shells, as well as composite laminates. Transverse shear forces calculated from transverse shear strains are introduced into a rate-dependent yield function, which is similar to Iliushin's yield surface expressed in terms of stress resultants and stress couples [12]. The hardening rule defined by Bieniek and Funaro [4], which allows for representation of the Bauschinger effect on a moment-curvature plane, was previously adopted in EPSA and is used here in the same form. Viscoplastic strain rates are calculated, taking into account the transverse shears. Only non-layered shells are considered in this work.
Investigating Lithosphere Strength With Thin-Shell Tectonic Modeling
Moder, C.; Carena, S.
2007-12-01
The behavior of many major faults on Earth can only be explained if they are assumed to be much weaker than expected from Byerlee's Law alone. However, there is no agreement over what is a realistic range of friction parameters for faults, or its possible dependency on fault network geometry. Both can be studied with numerical forward modeling, but this requires knowledge of the detailed 3-D geometry of the faults. The latter is now available for most of California, thanks to the SCEC Community Fault Model (southern California) and to the USGS program "3-D Geologic Maps and Visualization" (San Francisco Bay and surrounding region). We model the behavior of the California fault network with the finite-element code SHELLS. We use as input a coarse global grid, with local high-resolution representation of actual faults based on the existing 3-D fault maps. By comparing the simulation results with data on fault-slip rates, we can determine how the faults in this network interact, the role of small faults, and we can quantify the typical fault strength in a continental transform plate boundary setting.
Microscopic imaging through turbid media Monte Carlo modeling and applications
Gu, Min; Deng, Xiaoyuan
2015-01-01
This book provides a systematic introduction to the principles of microscopic imaging through tissue-like turbid media in terms of Monte-Carlo simulation. It describes various gating mechanisms based on the physical differences between the unscattered and scattered photons and method for microscopic image reconstruction, using the concept of the effective point spread function. Imaging an object embedded in a turbid medium is a challenging problem in physics as well as in biophotonics. A turbid medium surrounding an object under inspection causes multiple scattering, which degrades the contrast, resolution and signal-to-noise ratio. Biological tissues are typically turbid media. Microscopic imaging through a tissue-like turbid medium can provide higher resolution than transillumination imaging in which no objective is used. This book serves as a valuable reference for engineers and scientists working on microscopy of tissue turbid media.
Simulating the co-encapsulation of drugs in a "smart" core-shell-shell polymer nanoparticle.
Buxton, Gavin A
2014-03-01
A coarse-grained lattice Monte Carlo method is used to simulate co-encapsulation and delivery of both a hydrophilic and hydrophobic drug from polymer nanoparticles. In particular, core-shell-shell polymer nanoparticles with acid-labile bonds are simulated, and the preferential release of the encapsulated drugs near more acidic tumors is captured. While these simple models lack the molecular details of a real system, they can reveal interesting insights concerning the effects of entropy and enthalpy in these systems.
Recent Developments in No-Core Shell-Model Calculations
Energy Technology Data Exchange (ETDEWEB)
Navratil, P; Quaglioni, S; Stetcu, I; Barrett, B R
2009-03-20
We present an overview of recent results and developments of the no-core shell model (NCSM), an ab initio approach to the nuclear many-body problem for light nuclei. In this aproach, we start from realistic two-nucleon or two- plus three-nucleon interactions. Many-body calculations are performed using a finite harmonic-oscillator (HO) basis. To facilitate convergence for realistic inter-nucleon interactions that generate strong short-range correlations, we derive effective interactions by unitary transformations that are tailored to the HO basis truncation. For soft realistic interactions this might not be necessary. If that is the case, the NCSM calculations are variational. In either case, the ab initio NCSM preserves translational invariance of the nuclear many-body problem. In this review, we, in particular, highlight results obtained with the chiral two- plus three-nucleon interactions. We discuss efforts to extend the applicability of the NCSM to heavier nuclei and larger model spaces using importance-truncation schemes and/or use of effective interactions with a core. We outline an extension of the ab initio NCSM to the description of nuclear reactions by the resonating group method technique. A future direction of the approach, the ab initio NCSM with continuum, which will provide a complete description of nuclei as open systems with coupling of bound and continuum states is given in the concluding part of the review.
The shell model. Towards a unified description of nuclear structure
Energy Technology Data Exchange (ETDEWEB)
Poves, Alfredo [Departamento de Fisica Teorica, Universidad Autonoma Cantoblanco, 28049 - Madrid (Spain); Collaboration: La Direction des Sciences de la Matiere du CEA (FR); Le Fonds National de la Recherche Scientifique de Belgique (BE)
1998-12-31
In this series of lectures we present the foundations of the spherical shell model that we treat as an approximation to the exact solution of the full secular problem. We introduce the notions of valence space, effective interaction and effective operator. We analyse the structure of the realistic effective interactions, identifying their monopole part with the spherical mean field. The multipole Hamiltonian is shown to have a universal (simple) form that includes pairing (isovector and isoscalar), quadrupole, octupole, deca-pole, and ({sigma}{center_dot}{tau})({sigma}{center_dot}{tau}). We describe the methods of resolution of the secular problem, in particular the Lanczos method. The model is applied to the description of nuclear deformation and its relationship with the deformed mean field theories is studied. We propose a new symmetry, `quasi`-SU3, to understand deformation in the spherical basis. Finally, we discuss the domain of nuclei very far from the valley of {beta} stability, addressing the vanishing of some magic closures that can be explained in terms of intruder states. (author) 53 refs., 20 figs., 3 tabs.
Core-shell particles as model compound for studying fouling
DEFF Research Database (Denmark)
Christensen, Morten Lykkegaard; Nielsen, Troels Bach; Andersen, Morten Boel Overgaard;
2008-01-01
Synthetic colloidal particles with hard cores and soft, water-swollen shells were used to study cake formation during ultrafiltration. The total cake resistance was lowest for particles with thick shells, which indicates that interparticular forces between particles (steric hindrance...... and electrostatic repulsion) influenced cake formation. At low pressure the specific cake resistance could be predicted from the Kozeny-Carman equation. At higher pressures, the resistance increased due to cake compression. Both cake formation and compression were reversible. For particles with thick shells...... the permeate flux could be enhanced by lowering the pressure. Hence, the amount of water-swollen material influences both cake thickness and resistance....
On two-dimensionalization of three-dimensional turbulence in shell models
DEFF Research Database (Denmark)
Chakraborty, Sagar; Jensen, Mogens Høgh; Sarkar, A.
2010-01-01
Applying a modified version of the Gledzer-Ohkitani-Yamada (GOY) shell model, the signatures of so-called two-dimensionalization effect of three-dimensional incompressible, homogeneous, isotropic fully developed unforced turbulence have been studied and reproduced. Within the framework of shell...
Universality of the Ising and the S=1 model on Archimedean lattices: A Monte Carlo determination
Malakis, A.; Gulpinar, G.; Karaaslan, Y.; Papakonstantinou, T.; Aslan, G.
2012-03-01
The Ising models S=1/2 and S=1 are studied by efficient Monte Carlo schemes on the (3,4,6,4) and the (3,3,3,3,6) Archimedean lattices. The algorithms used, a hybrid Metropolis-Wolff algorithm and a parallel tempering protocol, are briefly described and compared with the simple Metropolis algorithm. Accurate Monte Carlo data are produced at the exact critical temperatures of the Ising model for these lattices. Their finite-size analysis provide, with high accuracy, all critical exponents which, as expected, are the same with the well-known 2D Ising model exact values. A detailed finite-size scaling analysis of our Monte Carlo data for the S=1 model on the same lattices provides very clear evidence that this model obeys, also very well, the 2D Ising model critical exponents. As a result, we find that recent Monte Carlo simulations and attempts to define effective dimensionality for the S=1 model on these lattices are misleading. Accurate estimates are obtained for the critical amplitudes of the logarithmic expansions of the specific heat for both models on the two Archimedean lattices.
Fabricating Thin-Shell Heat-Transfer Models
Avery, D. E.; Ballard, G. K.; Wilson, M. L.; Allen, J. H., Sr.
1985-01-01
Freestanding shells produced for experimental aerodynamic-heating tests. Heat transfer shells require several steps and several precise molds. First, interlocking aluminum male and female molds fabricated. Holes for thermocouples drilled through male mold at desired locations. Wires having same diameter as thermocouple wire placed through holes in male mold flush to female mold. Epoxy exposed to vacuum to remove air bubbles poured between male and female molds to form thin female mold. Once mold cured, wires removed and aluminum molds separated.
FREYA-a new Monte Carlo code for improved modeling of fission chains
Energy Technology Data Exchange (ETDEWEB)
Hagmann, C A; Randrup, J; Vogt, R L
2012-06-12
A new simulation capability for modeling of individual fission events and chains and the transport of fission products in materials is presented. FREYA ( Fission Yield Event Yield Algorithm ) is a Monte Carlo code for generating fission events providing correlated kinematic information for prompt neutrons, gammas, and fragments. As a standalone code, FREYA calculates quantities such as multiplicity-energy, angular, and gamma-neutron energy sharing correlations. To study materials with multiplication, shielding effects, and detectors, we have integrated FREYA into the general purpose Monte Carlo code MCNP. This new tool will allow more accurate modeling of detector responses including correlations and the development of SNM detectors with increased sensitivity.
Dynamos at extreme magnetic Prandtl numbers: insights from shell models
Verma, Mahendra K.; Kumar, Rohit
2016-12-01
We present an MHD shell model suitable for computation of various energy fluxes of magnetohydrodynamic turbulence for very small and very large magnetic Prandtl numbers $\\mathrm{Pm}$; such computations are inaccessible to direct numerical simulations. For small $\\mathrm{Pm}$, we observe that both kinetic and magnetic energy spectra scale as $k^{-5/3}$ in the inertial range, but the dissipative magnetic energy scales as $k^{-11/3}\\exp(-k/k_\\eta)$. Here, the kinetic energy at large length scale feeds the large-scale magnetic field that cascades to small-scale magnetic field, which gets dissipated by Joule heating. The large-$\\mathrm{Pm}$ dynamo has a similar behaviour except that the dissipative kinetic energy scales as $k^{-13/3}$. For this case, the large-scale velocity field transfers energy to the large-scale magnetic field, which gets transferred to small-scale velocity and magnetic fields; the energy of the small-scale magnetic field also gets transferred to the small-scale velocity field, and the energy thus accumulated is dissipated by the viscous force.
Auxiliary-field quantum Monte Carlo methods in nuclei
Alhassid, Y
2016-01-01
Auxiliary-field quantum Monte Carlo methods enable the calculation of thermal and ground state properties of correlated quantum many-body systems in model spaces that are many orders of magnitude larger than those that can be treated by conventional diagonalization methods. We review recent developments and applications of these methods in nuclei using the framework of the configuration-interaction shell model.
Precise comparison of the Gaussian expansion method and the Gamow shell model
Masui, Hiroshi; Michel, Nicola; Płoszajczak, Marek
2014-01-01
We perform a detailed comparison of results of the Gamow Shell Model (GSM) and the Gaussian Expansion Method (GEM) supplemented by the complex scaling (CS) method for the same translationally-invariant cluster-orbital shell model (COSM) Hamiltonian. As a benchmark test, we calculate the ground state $0^{+}$ and the first excited state $2^{+}$ of mirror nuclei $^{6}$He and $^{6}$Be in the model space consisting of two valence nucleons in $p$-shell outside of a $^{4}$He core. We find a good overall agreement of results obtained in these two different approaches, also for many-body resonances.
The No-Core Gamow Shell Model: Including the continuum in the NCSM
Barrett, B R; Michel, N; Płoszajczak, M
2015-01-01
We are witnessing an era of intense experimental efforts that will provide information about the properties of nuclei far from the line of stability, regarding resonant and scattering states as well as (weakly) bound states. This talk describes our formalism for including these necessary ingredients into the No-Core Shell Model by using the Gamow Shell Model approach. Applications of this new approach, known as the No-Core Gamow Shell Model, both to benchmark cases as well as to unstable nuclei will be given.
Towards a unified realistic shell-model Hamiltonian with the monopole-based universal force
Kaneko, K; Sun, Y; Tazaki, S
2013-01-01
We propose a unified realistic shell-model Hamiltonian employing the pairing plus multipole Hamiltonian combined with the monopole interaction constructed starting from the monopole-based universal force by Otsuka it et al. (Phys. Rev. Lett. 104, 012501 (2010)). It is demonstrated that the proposed PMMU model can consistently describe a large amount of spectroscopic data as well as binding energies in the pf and pf5/2g9/2 shell spaces, and could serve as a practical shell model for even heavier mass regions.
Markov chain Monte Carlo methods in directed graphical models
DEFF Research Database (Denmark)
Højbjerre, Malene
Directed graphical models present data possessing a complex dependence structure, and MCMC methods are computer-intensive simulation techniques to approximate high-dimensional intractable integrals, which emerge in such models with incomplete data. MCMC computations in directed graphical models...
Neutrinoless double beta nuclear matrix elements around mass 80 in the nuclear shell-model
Yoshinaga, N.; Higashiyama, K.; Taguchi, D.; Teruya, E.
2015-05-01
The observation of the neutrinoless double-beta decay can determine whether the neutrino is a Majorana particle or not. For theoretical nuclear physics it is particularly important to estimate three types of matrix elements, namely Fermi (F), Gamow-Teller (GT), and tensor (T) matrix elements. In this paper, we carry out shell-model calculations and also pair-truncated shell-model calculations to check the model dependence in the case of mass A=82 nuclei.
Neutrinoless double beta nuclear matrix elements around mass 80 in the nuclear shell-model
Directory of Open Access Journals (Sweden)
Yoshinaga N.
2015-01-01
Full Text Available The observation of the neutrinoless double-beta decay can determine whether the neutrino is a Majorana particle or not. For theoretical nuclear physics it is particularly important to estimate three types of matrix elements, namely Fermi (F, Gamow-Teller (GT, and tensor (T matrix elements. In this paper, we carry out shell-model calculations and also pair-truncated shell-model calculations to check the model dependence in the case of mass A=82 nuclei.
Single-cluster-update Monte Carlo method for the random anisotropy model
Rößler, U. K.
1999-06-01
A Wolff-type cluster Monte Carlo algorithm for random magnetic models is presented. The algorithm is demonstrated to reduce significantly the critical slowing down for planar random anisotropy models with weak anisotropy strength. Dynamic exponents zcluster algorithms are estimated for models with ratio of anisotropy to exchange constant D/J=1.0 on cubic lattices in three dimensions. For these models, critical exponents are derived from a finite-size scaling analysis.
Energy Technology Data Exchange (ETDEWEB)
Davis JE, Eddy MJ, Sutton TM, Altomari TJ
2007-03-01
Solid modeling computer software systems provide for the design of three-dimensional solid models used in the design and analysis of physical components. The current state-of-the-art in solid modeling representation uses a boundary representation format in which geometry and topology are used to form three-dimensional boundaries of the solid. The geometry representation used in these systems is cubic B-spline curves and surfaces--a network of cubic B-spline functions in three-dimensional Cartesian coordinate space. Many Monte Carlo codes, however, use a geometry representation in which geometry units are specified by intersections and unions of half-spaces. This paper describes an algorithm for converting from a boundary representation to a half-space representation.
Eversion of bistable shells under magnetic actuation: a model of nonlinear shapes
Seffen, Keith A.; Vidoli, Stefano
2016-06-01
We model in closed form a proven bistable shell made from a magnetic rubber composite material. In particular, we incorporate a non-axisymmetrical displacement field, and we capture the nonlinear coupling between the actuated shape and the magnetic flux distribution around the shell. We are able to verify the bistable nature of the shell and we explore its eversion during magnetic actuation. We show that axisymmetrical eversion is natural for a perfect shell but that non-axisymmetrical eversion rapidly emerges under very small initial imperfections, as observed in experiments and in a computational analysis. We confirm the non-uniform shapes of shell and we study the stability of eversion by considering how the landscape of total potential and magnetic energies of the system changes during actuation.
Off-shell superconformal nonlinear sigma-models in three dimensions
Kuzenko, Sergei M; Tartaglino-Mazzucchelli, Gabriele; von Unge, Rikard
2010-01-01
We develop superspace techniques to construct general off-shell N=1,2,3,4 superconformal sigma-models in three space-time dimensions. The most general N=3 and N=4 superconformal sigma-models are constructed in terms of N=2 chiral superfields. Several superspace proofs of the folklore statement that N=3 supersymmetry implies N=4 are presented both in the on-shell and off-shell settings. We also elaborate on (super)twistor realisations for (super)manifolds on which the three-dimensional N-extended superconformal groups act transitively and which include Minkowski space as a subspace.
Generic form of Bayesian Monte Carlo for models with partial monotonicity
Rajabalinejad, M.; Spitas, C.
2012-01-01
This paper presents a generic method for the safety assessments of models with partial monotonicity. For this purpose, a Bayesian interpolation method is developed and implemented in the Monte Carlo process. integrated approach is the generalization of the recently developed techniques used in safet
LASER-DOPPLER VELOCIMETRY AND MONTE-CARLO SIMULATIONS ON MODELS FOR BLOOD PERFUSION IN TISSUE
DEMUL, FFM; KOELINK, MH; KOK, ML; HARMSMA, PJ; GREVE, J; GRAAFF, R; AARNOUDSE, JG
1995-01-01
Laser Doppler flow measurements and Monte Carlo simulations on small blood perfusion flow models at 780 nm are presented and compared. The dimensions of the optical sample volume are investigated as functions of the distance of the laser to the detector and as functions of the angle of penetration o
Kim, Jee-Seon; Bolt, Daniel M.
2007-01-01
The purpose of this ITEMS module is to provide an introduction to Markov chain Monte Carlo (MCMC) estimation for item response models. A brief description of Bayesian inference is followed by an overview of the various facets of MCMC algorithms, including discussion of prior specification, sampling procedures, and methods for evaluating chain…
A study of the XY model by the Monte Carlo method
Suranyi, Peter; Harten, Paul
1987-01-01
The massively parallel processor is used to perform Monte Carlo simulations for the two dimensional XY model on lattices of sizes up to 128 x 128. A parallel random number generator was constructed, finite size effects were studied, and run times were compared with those on a CRAY X-MP supercomputer.
Generic Form of Bayesian Monte Carlo For Models With Partial Monotonicity
Rajabalinejad, M.
2012-01-01
This paper presents a generic method for the safety assessments of models with partial monotonicity. For this purpose, a Bayesian interpolation method is developed and implemented in the Monte Carlo process. integrated approach is the generalization of the recently developed techniques used in safet
Preliminary Monte Carlo Results for the Three-Dimensional Holstein Model
Institute of Scientific and Technical Information of China (English)
吴焰立; 刘川; 罗强
2003-01-01
Monte Carlo simulations are used to study the three-dimensional Holstein model. The relationship between the band filling and the chemical potential is obtained for various phonon frequencies and temperatures. The energy of a single electron or a hole is also calculated as a function of the lattice momenta.
Vrugt, J.A.; Braak, ter C.J.F.; Clark, M.P.; Hyman, J.M.; Robinson, B.A.
2008-01-01
There is increasing consensus in the hydrologic literature that an appropriate framework for streamflow forecasting and simulation should include explicit recognition of forcing and parameter and model structural error. This paper presents a novel Markov chain Monte Carlo (MCMC) sampler, entitled di
Confronting uncertainty in model-based geostatistics using Markov Chain Monte Carlo simulation
Minasny, B.; Vrugt, J.A.; McBratney, A.B.
2011-01-01
This paper demonstrates for the first time the use of Markov Chain Monte Carlo (MCMC) simulation for parameter inference in model-based soil geostatistics. We implemented the recently developed DiffeRential Evolution Adaptive Metropolis (DREAM) algorithm to jointly summarize the posterior distributi
An Evaluation of a Markov Chain Monte Carlo Method for the Rasch Model.
Kim, Seock-Ho
2001-01-01
Examined the accuracy of the Gibbs sampling Markov chain Monte Carlo procedure for estimating item and person (theta) parameters in the one-parameter logistic model. Analyzed four empirical datasets using the Gibbs sampling, conditional maximum likelihood, marginal maximum likelihood, and joint maximum likelihood methods. Discusses the conditions…
Particle Markov Chain Monte Carlo Techniques of Unobserved Component Time Series Models Using Ox
DEFF Research Database (Denmark)
Nonejad, Nima
This paper details Particle Markov chain Monte Carlo techniques for analysis of unobserved component time series models using several economic data sets. PMCMC combines the particle filter with the Metropolis-Hastings algorithm. Overall PMCMC provides a very compelling, computationally fast...
Markov Chain Monte Carlo Estimation of Item Parameters for the Generalized Graded Unfolding Model
de la Torre, Jimmy; Stark, Stephen; Chernyshenko, Oleksandr S.
2006-01-01
The authors present a Markov Chain Monte Carlo (MCMC) parameter estimation procedure for the generalized graded unfolding model (GGUM) and compare it to the marginal maximum likelihood (MML) approach implemented in the GGUM2000 computer program, using simulated and real personality data. In the simulation study, test length, number of response…
Ensemble Bayesian model averaging using Markov Chain Monte Carlo sampling
Vrugt, J.A.; Diks, C.G.H.; Clark, M.
2008-01-01
Bayesian model averaging (BMA) has recently been proposed as a statistical method to calibrate forecast ensembles from numerical weather models. Successful implementation of BMA however, requires accurate estimates of the weights and variances of the individual competing models in the ensemble. In t
Shell model for heavy nuclei and its application in nuclear astrophysics
Sun, Y
2006-01-01
Performing shell model calculations for heavy nuclei is a long-standing problem in nuclear physics. The shell model truncation in the configuration space is an unavoidable step. The Projected Shell Model (PSM) truncates the space under the guidance of the deformed mean-field solutions. This implies that the PSM uses a novel and efficient way to bridge the two conventional methods: the deformed mean-field approximations, which are widely applied to heavy nuclei but able to describe the physics only in the intrinsic frame, and the spherical shell model diagonalization method, which is most fundamental but feasible only for small systems. We discuss the basic philosophy in construction of the PSM (or generally PSM-like) approach. Several examples from the PSM calculations are presented. Astrophysical applications are emphasized.
A measurement-based generalized source model for Monte Carlo dose simulations of CT scans
Ming, Xin; Feng, Yuanming; Liu, Ransheng; Yang, Chengwen; Zhou, Li; Zhai, Hezheng; Deng, Jun
2017-03-01
The goal of this study is to develop a generalized source model for accurate Monte Carlo dose simulations of CT scans based solely on the measurement data without a priori knowledge of scanner specifications. The proposed generalized source model consists of an extended circular source located at x-ray target level with its energy spectrum, source distribution and fluence distribution derived from a set of measurement data conveniently available in the clinic. Specifically, the central axis percent depth dose (PDD) curves measured in water and the cone output factors measured in air were used to derive the energy spectrum and the source distribution respectively with a Levenberg–Marquardt algorithm. The in-air film measurement of fan-beam dose profiles at fixed gantry was back-projected to generate the fluence distribution of the source model. A benchmarked Monte Carlo user code was used to simulate the dose distributions in water with the developed source model as beam input. The feasibility and accuracy of the proposed source model was tested on a GE LightSpeed and a Philips Brilliance Big Bore multi-detector CT (MDCT) scanners available in our clinic. In general, the Monte Carlo simulations of the PDDs in water and dose profiles along lateral and longitudinal directions agreed with the measurements within 4%/1 mm for both CT scanners. The absolute dose comparison using two CTDI phantoms (16 cm and 32 cm in diameters) indicated a better than 5% agreement between the Monte Carlo-simulated and the ion chamber-measured doses at a variety of locations for the two scanners. Overall, this study demonstrated that a generalized source model can be constructed based only on a set of measurement data and used for accurate Monte Carlo dose simulations of patients’ CT scans, which would facilitate patient-specific CT organ dose estimation and cancer risk management in the diagnostic and therapeutic radiology.
Directory of Open Access Journals (Sweden)
Shchekoturova S. D.
2015-04-01
Full Text Available The article presents an analysis of an innovative activity of four Russian metallurgical enterprises: "Ruspolimet", JSC "Ural Smithy", JSC "Stupino Metallurgical Company", JSC "VSMPO" via mathematical modeling using Monte Carlo method. The results of the assessment of innovative activity of Russian metallurgical companies were identified in five years dynamics. An assessment of the current innovative activity was made by the calculation of an integral index of the innovative activity. The calculation was based on such six indicators as the proportion of staff employed in R & D; the level of development of new technology; the degree of development of new products; share of material resources for R & D; degree of security of enterprise intellectual property; the share of investment in innovative projects and it was analyzed from 2007 to 2011. On the basis of this data the integral indicator of the innovative activity of metallurgical companies was calculated by well-known method of weighting coefficients. The comparative analysis of integral indicators of the innovative activity of considered companies made it possible to range their level of the innovative activity and to characterize the current state of their business. Based on Monte Carlo method a variation interval of the integral indicator was obtained and detailed instructions to choose the strategy of the innovative development of metallurgical enterprises were given as well
Monte-Carlo Inversion of Travel-Time Data for the Estimation of Weld Model Parameters
Hunter, A. J.; Drinkwater, B. W.; Wilcox, P. D.
2011-06-01
The quality of ultrasonic array imagery is adversely affected by uncompensated variations in the medium properties. A method for estimating the parameters of a general model of an inhomogeneous anisotropic medium is described. The model is comprised of a number of homogeneous sub-regions with unknown anisotropy. Bayesian estimation of the unknown model parameters is performed via a Monte-Carlo Markov chain using the Metropolis-Hastings algorithm. Results are demonstrated using simulated weld data.
Shell-model representations of the proton-neutron symplectic model
Energy Technology Data Exchange (ETDEWEB)
Ganev, H.G. [Joint Institute for Nuclear Research, Dubna (Russian Federation)
2015-07-15
The representation theory of the recently introduced proton-neutron symplectic model in the many-particle Hilbert space is considered. The relation of the Sp(12, R) irreducible representations (irreps) with the shell-model classification of the basis states is considered by extending of the state space to the direct product space of SU{sub p} (3) x SU{sub n} (3) irreps, generalizing in this way the Elliott's SU(3) model for the case of two-component system. The Sp(12, R) model appears then as a natural multi-major-shell extension of the generalized proton-neutron SU(3) scheme, which takes into account the core collective excitations of monopole and quadrupole, as well as dipole type associated with the giant resonance vibrational degrees of freedom. Each Sp(12, R) irreducible representation is determined by a symplectic bandhead or an intrinsic U(6) space which can be fixed by the underlying proton-neutron shell-model structure, so the theory becomes completely compatible with the Pauli principle. It is shown that this intrinsic U(6) structure is of vital importance for the appearance of the low-lying collective bands without involving a mixing of different symplectic irreps. The full range of low-lying collective states can then be described by the microscopically based intrinsic U(6) structure, renormalized by coupling to the giant resonance vibrations. (orig.)
How random are matrix elements of the nuclear shell model Hamiltonian?
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
In this paper we study the general behavior of matrix elements of the nuclear shell model Hamiltonian.We find that nonzero off-diagonal elements exhibit a regular pattern,if one sorts the diagonal matrix elements from smaller to larger values.The correlation between eigenvalues and diagonal matrix elements for the shell model Hamiltonian is more remarkable than that for random matrices with the same distribution unless the dimension is small.
How random are matrix elements of the nuclear shell model Hamiltonian?
Institute of Scientific and Technical Information of China (English)
SHEN JiaJie; ZHAO YuMing
2009-01-01
In this paper we study the general behavior of matrix elements of the nuclear shell model Hamiltonlan.We find that nonzero off-diagonal elements exhibit a regular pattern,if one sorts the diagonal matrix elements from smaller to larger values.The correlation between eigenvalues and diagonal matrix elements for the shell model Hamiltonian is more remarkable than that for random matrices with the same distribution unless the dimension is small.
Improvements of the Analytical Model of Monte Carlo
Institute of Scientific and Technical Information of China (English)
HE Qing-Fang; XU Zheng; TENG Feng; LIU De-Ang; XU Xu-Rong
2006-01-01
@@ By extending the conduction band structure, we set up a new analytical model in ZnS. Compared the results with both the old analytical model and the full band model, it is found that they are possibly in reasonable agreement with the full band method and we can improve the calculation precision. Another important work is to reduce the programme computation time using the method of data fitting scattering rate curves.
Comparison of three-shell and simplified volume conductor models in magnetoencephalography.
Stenroos, Matti; Hunold, Alexander; Haueisen, Jens
2014-07-01
Experimental MEG source imaging studies have typically been carried out with either a spherically symmetric head model or a single-shell boundary-element (BEM) model that is shaped according to the inner skull surface. The concepts and comparisons behind these simplified models have led to misunderstandings regarding the role of skull and scalp in MEG. In this work, we assess the forward-model errors due to different skull/scalp approximations and due to differences and errors in model geometries. We built five anatomical models of a volunteer using a set of T1-weighted MR scans and three common toolboxes. Three of the models represented typical models in experimental MEG, one was manually constructed, and one contained a major segmentation error at the skull base. For these anatomical models, we built forward models using four simplified approaches and a three-shell BEM approach that has been used as reference in previous studies. Our reference model contained in addition the skull fine-structure (spongy bone). We computed signal topographies for cortically constrained sources in the left hemisphere and compared the topographies using relative error and correlation metrics. The results show that the spongy bone has a minimal effect on MEG topographies, and thus the skull approximation of the three-shell model is justified. The three-shell model performed best, followed by the corrected-sphere and single-shell models, whereas the local-spheres and single-sphere models were clearly worse. The three-shell model was the most robust against the introduced segmentation error. In contrast to earlier claims, there was no noteworthy difference in the computation times between the realistically-shaped and sphere-based models, and the manual effort of building a three-shell model and a simplified model is comparable. We thus recommend the realistically-shaped three-shell model for experimental MEG work. In cases where this is not possible, we recommend a realistically
High-resolution and Monte Carlo additions to the SASKTRAN radiative transfer model
Directory of Open Access Journals (Sweden)
D. J. Zawada
2015-06-01
Full Text Available The Optical Spectrograph and InfraRed Imaging System (OSIRIS instrument on board the Odin spacecraft has been measuring limb-scattered radiance since 2001. The vertical radiance profiles measured as the instrument nods are inverted, with the aid of the SASKTRAN radiative transfer model, to obtain vertical profiles of trace atmospheric constituents. Here we describe two newly developed modes of the SASKTRAN radiative transfer model: a high-spatial-resolution mode and a Monte Carlo mode. The high-spatial-resolution mode is a successive-orders model capable of modelling the multiply scattered radiance when the atmosphere is not spherically symmetric; the Monte Carlo mode is intended for use as a highly accurate reference model. It is shown that the two models agree in a wide variety of solar conditions to within 0.2 %. As an example case for both models, Odin–OSIRIS scans were simulated with the Monte Carlo model and retrieved using the high-resolution model. A systematic bias of up to 4 % in retrieved ozone number density between scans where the instrument is scanning up or scanning down was identified. The bias is largest when the sun is near the horizon and the solar scattering angle is far from 90°. It was found that calculating the multiply scattered diffuse field at five discrete solar zenith angles is sufficient to eliminate the bias for typical Odin–OSIRIS geometries.
High resolution and Monte Carlo additions to the SASKTRAN radiative transfer model
Directory of Open Access Journals (Sweden)
D. J. Zawada
2015-03-01
Full Text Available The OSIRIS instrument on board the Odin spacecraft has been measuring limb scattered radiance since 2001. The vertical radiance profiles measured as the instrument nods are inverted, with the aid of the SASKTRAN radiative transfer model, to obtain vertical profiles of trace atmospheric constituents. Here we describe two newly developed modes of the SASKTRAN radiative transfer model: a high spatial resolution mode, and a Monte Carlo mode. The high spatial resolution mode is a successive orders model capable of modelling the multiply scattered radiance when the atmosphere is not spherically symmetric; the Monte Carlo mode is intended for use as a highly accurate reference model. It is shown that the two models agree in a wide variety of solar conditions to within 0.2%. As an example case for both models, Odin-OSIRIS scans were simulated with the Monte Carlo model and retrieved using the high resolution model. A systematic bias of up to 4% in retrieved ozone number density between scans where the instrument is scanning up or scanning down was identified. It was found that calculating the multiply scattered diffuse field at five discrete solar zenith angles is sufficient to eliminate the bias for typical Odin-OSIRIS geometries.
Monte Carlo modeling of a Novalis Tx Varian 6 MV with HD-120 multileaf collimator.
Vazquez-Quino, Luis Alberto; Massingill, Brian; Shi, Chengyu; Gutierrez, Alonso; Esquivel, Carlos; Eng, Tony; Papanikolaou, Nikos; Stathakis, Sotirios
2012-09-06
A Monte Carlo model of the Novalis Tx linear accelerator equipped with high-definition multileaf collimator (HD-120 HD-MLC) was commissioned using ionization chamber measurements in water. All measurements in water were performed using a liquid filled ionization chamber. Film measurements were made using EDR2 film in solid water. Open rectangular fields defined by the jaws or the HD-MLC were used for comparison against measurements. Furthermore, inter- and intraleaf leakage calculated by the Monte Carlo model was compared against film measurements. The statistical uncertainty of the Monte Carlo calculations was less than 1% for all simulations. Results for all regular field sizes show an excellent agreement with commissioning data (percent depth-dose curves and profiles), well within 1% of difference in the relative dose and 1 mm distance to agreement. The computed leakage through HD-MLCs shows good agreement with film measurements. The Monte Carlo model developed in this study accurately represents the new Novalis Tx Varian linac with HD-MLC and can be used for reliable patient dose calculations.
Monte Carlo study of single-barrier structure based on exclusion model full counting statistics
Institute of Scientific and Technical Information of China (English)
Chen Hua; Du Lei; Qu Cheng-Li; He Liang; Chen Wen-Hao; Sun Peng
2011-01-01
Different from the usual full counting statistics theoretical work that focuses on the higher order cumulants computation by using cumulant generating function in electrical structures, Monte Carlo simulation of single-barrier structure is performed to obtain time series for two types of widely applicable exclusion models, counter-flows model,and tunnel model. With high-order spectrum analysis of Matlab, the validation of Monte Carlo methods is shown through the extracted first four cumulants from the time series, which are in agreement with those from cumulant generating function. After the comparison between the counter-flows model and the tunnel model in a single barrier structure, it is found that the essential difference between them consists in the strictly holding of Pauli principle in the former and in the statistical consideration of Pauli principle in the latter.
Nguyen, Jennifer; Hayakawa, Carole K; Mourant, Judith R; Venugopalan, Vasan; Spanier, Jerome
2016-05-01
We present a polarization-sensitive, transport-rigorous perturbation Monte Carlo (pMC) method to model the impact of optical property changes on reflectance measurements within a discrete particle scattering model. The model consists of three log-normally distributed populations of Mie scatterers that approximate biologically relevant cervical tissue properties. Our method provides reflectance estimates for perturbations across wavelength and/or scattering model parameters. We test our pMC model performance by perturbing across number densities and mean particle radii, and compare pMC reflectance estimates with those obtained from conventional Monte Carlo simulations. These tests allow us to explore different factors that control pMC performance and to evaluate the gains in computational efficiency that our pMC method provides.
Reservoir Modeling Combining Geostatistics with Markov Chain Monte Carlo Inversion
DEFF Research Database (Denmark)
Zunino, Andrea; Lange, Katrine; Melnikova, Yulia;
2014-01-01
, multi-step forward model (rock physics and seismology) and to provide realistic estimates of uncertainties. To generate realistic models which represent samples of the prior distribution, and to overcome the high computational demand, we reduce the search space utilizing an algorithm drawn from...
USTIFICATION OF A TWO-DIMENSIONAL NONLINEAR SHELL MODEL OF KOITER'S TYPE
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A two-dimensional nonlinear shell model"of Koiter's type"has recently been proposed by the first author. It is shown here that, according to two mutually exclusive sets of assumptions bearing on the associated manifold of admissible inextensional displacements, the leading term of a formal asymptotic expansion of the solution of this two-dimensional model, with the thickness as the"small" parameter, satisfies either the two-dimensional equations of a nonlinearly elastic "membrane" shell or those of a nonlinearly elastic "flexural" shell. These conclusions being identical to those recently drawn by B. Miara, then by V. Lods and B. Miara, for the leading term of a formal asymptotic expansion of the solution of the equations of three-dimensional nonlinear elasticity, again with the thickness as the "small" parameter, the nonlinear shell model of Koiter's type considered here is thus justified, at least formally.
Spherical Shell Cosmological Model and Uniformity of Cosmic Microwave Background Radiation
Vlahovic, Branislav
2012-01-01
Considered is spherical shell as a model for visible universe and parameters that such model must have to comply with the observable data. The topology of the model requires that motion of all galaxies and light must be confined inside a spherical shell. Consequently the observable universe cannot be defined as a sphere centered on the observer, rather it is an arc length within the volume of the spherical shell. The radius of the shell is 4.46 $\\pm$ 0.06 Gpc, which is for factor $\\pi$ smaller than radius of a corresponding 3-sphere. However the event horizon, defined as the arc length inside the shell, has the size of 14.0 $\\pm$ 0.2 Gpc, which is in agreement with the observable data. The model predicts, without inflation theory, the isotropy and uniformity of the CMB. It predicts the correct value for the Hubble constant $H_0$ = 67.26 $\\pm$ 0.90 km/s/Mpc, the cosmic expansion rate $H(z)$, and the speed of the event horizon in agreement with observations. The theoretical suport for shell model comes from gen...
Monte Carlo modeling of atomic oxygen attack of polymers with protective coatings on LDEF
Banks, Bruce A.; Degroh, Kim K.; Auer, Bruce M.; Gebauer, Linda; Edwards, Jonathan L.
1993-01-01
Characterization of the behavior of atomic oxygen interaction with materials on the Long Duration Exposure Facility (LDEF) assists in understanding of the mechanisms involved. Thus the reliability of predicting in-space durability of materials based on ground laboratory testing should be improved. A computational model which simulates atomic oxygen interaction with protected polymers was developed using Monte Carlo techniques. Through the use of an assumed mechanistic behavior of atomic oxygen interaction based on in-space atomic oxygen erosion of unprotected polymers and ground laboratory atomic oxygen interaction with protected polymers, prediction of atomic oxygen interaction with protected polymers on LDEF was accomplished. However, the results of these predictions are not consistent with the observed LDEF results at defect sites in protected polymers. Improved agreement between observed LDEF results and predicted Monte Carlo modeling can be achieved by modifying of the atomic oxygen interactive assumptions used in the model. LDEF atomic oxygen undercutting results, modeling assumptions, and implications are presented.
Monte Carlo Simulation of the Potts Model on a Dodecagonal Quasiperiodic Structure
Institute of Scientific and Technical Information of China (English)
WEN Zhang-Bin; HOU Zhi-Lin; FU Xiu-Jun
2011-01-01
By means of a Monte Carlo simulation, we study the three-state Potts model on a two-dimensional quasiperiodic structure based on a dodecagonal cluster covering pattern. The critical temperature and exponents are obtained from finite-size scaling analysis. It is shown that the Potts model on the quasiperiodic lattice belongs to the same universal class as those on periodic ones.%@@ By means of a Monte Carlo simulation, we study the three-state Potts model on a two-dimensional quasiperiodic structure based on a dodecagonal cluster covering pattern.The critical temperature and exponents are obtained from finite-size scaling analysis.It is shown that the Potts model on the quasiperiodic lattice belongs to the same universal class as those on periodic ones.
Large-scale Monte Carlo simulations for the depinning transition in Ising-type lattice models
Si, Lisha; Liao, Xiaoyun; Zhou, Nengji
2016-12-01
With the developed "extended Monte Carlo" (EMC) algorithm, we have studied the depinning transition in Ising-type lattice models by extensive numerical simulations, taking the random-field Ising model with a driving field and the driven bond-diluted Ising model as examples. In comparison with the usual Monte Carlo method, the EMC algorithm exhibits greater efficiency of the simulations. Based on the short-time dynamic scaling form, both the transition field and critical exponents of the depinning transition are determined accurately via the large-scale simulations with the lattice size up to L = 8912, significantly refining the results in earlier literature. In the strong-disorder regime, a new universality class of the Ising-type lattice model is unveiled with the exponents β = 0.304(5) , ν = 1.32(3) , z = 1.12(1) , and ζ = 0.90(1) , quite different from that of the quenched Edwards-Wilkinson equation.
TRIPOLI-4{sup ®} Monte Carlo code ITER A-lite neutronic model validation
Energy Technology Data Exchange (ETDEWEB)
Jaboulay, Jean-Charles, E-mail: jean-charles.jaboulay@cea.fr [CEA, DEN, Saclay, DM2S, SERMA, F-91191 Gif-sur-Yvette (France); Cayla, Pierre-Yves; Fausser, Clement [MILLENNIUM, 16 Av du Québec Silic 628, F-91945 Villebon sur Yvette (France); Damian, Frederic; Lee, Yi-Kang; Puma, Antonella Li; Trama, Jean-Christophe [CEA, DEN, Saclay, DM2S, SERMA, F-91191 Gif-sur-Yvette (France)
2014-10-15
3D Monte Carlo transport codes are extensively used in neutronic analysis, especially in radiation protection and shielding analyses for fission and fusion reactors. TRIPOLI-4{sup ®} is a Monte Carlo code developed by CEA. The aim of this paper is to show its capability to model a large-scale fusion reactor with complex neutron source and geometry. A benchmark between MCNP5 and TRIPOLI-4{sup ®}, on the ITER A-lite model was carried out; neutron flux, nuclear heating in the blankets and tritium production rate in the European TBMs were evaluated and compared. The methodology to build the TRIPOLI-4{sup ®} A-lite model is based on MCAM and the MCNP A-lite model. Simplified TBMs, from KIT, were integrated in the equatorial-port. A good agreement between MCNP and TRIPOLI-4{sup ®} is shown; discrepancies are mainly included in the statistical error.
Simulation model based on Monte Carlo method for traffic assignment in local area road network
Institute of Scientific and Technical Information of China (English)
Yuchuan DU; Yuanjing GENG; Lijun SUN
2009-01-01
For a local area road network, the available traffic data of traveling are the flow volumes in the key intersections, not the complete OD matrix. Considering the circumstance characteristic and the data availability of a local area road network, a new model for traffic assignment based on Monte Carlo simulation of intersection turning movement is provided in this paper. For good stability in temporal sequence, turning ratio is adopted as the important parameter of this model. The formulation for local area road network assignment problems is proposed on the assumption of random turning behavior. The traffic assignment model based on the Monte Carlo method has been used in traffic analysis for an actual urban road network. The results comparing surveying traffic flow data and determining flow data by the previous model verify the applicability and validity of the proposed methodology.
Zhai, Xue; Fei, Cheng-Wei; Choy, Yat-Sze; Wang, Jian-Jun
2017-01-01
To improve the accuracy and efficiency of computation model for complex structures, the stochastic model updating (SMU) strategy was proposed by combining the improved response surface model (IRSM) and the advanced Monte Carlo (MC) method based on experimental static test, prior information and uncertainties. Firstly, the IRSM and its mathematical model were developed with the emphasis on moving least-square method, and the advanced MC simulation method is studied based on Latin hypercube sampling method as well. And then the SMU procedure was presented with experimental static test for complex structure. The SMUs of simply-supported beam and aeroengine stator system (casings) were implemented to validate the proposed IRSM and advanced MC simulation method. The results show that (1) the SMU strategy hold high computational precision and efficiency for the SMUs of complex structural system; (2) the IRSM is demonstrated to be an effective model due to its SMU time is far less than that of traditional response surface method, which is promising to improve the computational speed and accuracy of SMU; (3) the advanced MC method observably decrease the samples from finite element simulations and the elapsed time of SMU. The efforts of this paper provide a promising SMU strategy for complex structure and enrich the theory of model updating.
Energy Technology Data Exchange (ETDEWEB)
Swaminathan-Gopalan, Krishnan; Stephani, Kelly A., E-mail: ksteph@illinois.edu [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)
2016-02-15
A systematic approach for calibrating the direct simulation Monte Carlo (DSMC) collision model parameters to achieve consistency in the transport processes is presented. The DSMC collision cross section model parameters are calibrated for high temperature atmospheric conditions by matching the collision integrals from DSMC against ab initio based collision integrals that are currently employed in the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) and Data Parallel Line Relaxation (DPLR) high temperature computational fluid dynamics solvers. The DSMC parameter values are computed for the widely used Variable Hard Sphere (VHS) and the Variable Soft Sphere (VSS) models using the collision-specific pairing approach. The recommended best-fit VHS/VSS parameter values are provided over a temperature range of 1000-20 000 K for a thirteen-species ionized air mixture. Use of the VSS model is necessary to achieve consistency in transport processes of ionized gases. The agreement of the VSS model transport properties with the transport properties as determined by the ab initio collision integral fits was found to be within 6% in the entire temperature range, regardless of the composition of the mixture. The recommended model parameter values can be readily applied to any gas mixture involving binary collisional interactions between the chemical species presented for the specified temperature range.
Monte Carlo Based Toy Model for Fission Process
Kurniadi, R; Viridi, S
2014-01-01
Fission yield has been calculated notoriously by two calculations approach, macroscopic approach and microscopic approach. This work will proposes another calculation approach which the nucleus is treated as a toy model. The toy model of fission yield is a preliminary method that use random number as a backbone of the calculation. Because of nucleus as a toy model hence the fission process does not represent real fission process in nature completely. Fission event is modeled by one random number. The number is assumed as width of distribution probability of nucleon position in compound nuclei when fission process is started. The toy model is formed by Gaussian distribution of random number that randomizes distance like between particle and central point. The scission process is started by smashing compound nucleus central point into two parts that are left central and right central points. These three points have different Gaussian distribution parameters such as mean ({\\mu}CN, {\\mu}L, {\\mu}R), and standard d...
Direct Monte Carlo Measurement of the Surface Tension in Ising Models
Hasenbusch, M
1992-01-01
I present a cluster Monte Carlo algorithm that gives direct access to the interface free energy of Ising models. The basic idea is to simulate an ensemble that consists of both configurations with periodic and with antiperiodic boundary conditions. A cluster algorithm is provided that efficently updates this joint ensemble. The interface tension is obtained from the ratio of configurations with periodic and antiperiodic boundary conditions, respectively. The method is tested for the 3-dimensional Ising model.
Energy Technology Data Exchange (ETDEWEB)
Battaile, C.C.; Buchheit, T.E.; Holm, E.A.; Neilsen, M.K.; Wellman, G.W.
1999-01-12
The microstructural evolution of heavily deformed polycrystalline Cu is simulated by coupling a constitutive model for polycrystal plasticity with the Monte Carlo Potts model for grain growth. The effects of deformation on boundary topology and grain growth kinetics are presented. Heavy deformation leads to dramatic strain-induced boundary migration and subsequent grain fragmentation. Grain growth is accelerated in heavily deformed microstructures. The implications of these results for the thermomechanical fatigue failure of eutectic solder joints are discussed.
Cosmological constraints on generalized Chaplygin gas model: Markov Chain Monte Carlo approach
Xu, Lixin; Lu, Jianbo
2010-01-01
We use the Markov Chain Monte Carlo method to investigate a global constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy from the latest observational data: the Constitution dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. In a non-flat universe, the constraint results for GCG model are, $\\Ome...
Essays on Quantitative Marketing Models and Monte Carlo Integration Methods
R.D. van Oest (Rutger)
2005-01-01
textabstractThe last few decades have led to an enormous increase in the availability of large detailed data sets and in the computing power needed to analyze such data. Furthermore, new models and new computing techniques have been developed to exploit both sources. All of this has allowed for addr
An explicit model of expanding cylindrical shells subjected to high explosive detonations
Energy Technology Data Exchange (ETDEWEB)
Martineau, R.L.; Prime, M.B.; Anderson, C.A. [Los Alamos National Lab., NM (United States); Smith, F.W. [Colorado State Univ., Fort Collins, CO (United States)
1999-04-01
A viscoplastic constitutive model was formulated to model the high strain-rate expansion of thin cylindrical shells subjected to internal explosive detonations. This model provides insight into the development of plastic instabilities, which occur on the surface of the shells prior to failure. The effects of shock heating and damage in the form of microvoid nucleation, growth, and coalescence were incorporated using the Johnson-Cook strength model with the Mie-Grueneisen equation of state and a modified Gurson yield surface. This model was implemented into ABAQUS/Explicit as a user material subroutine. A cylindrical copper shell was modeled using both axisymmetric and plane strain elements. The high explosive material inside of the cylinder was simulated using the high explosive burn model in ABAQUS/Explicit. Two experiments were conducted involving explosive-filled, copper cylinders and good agreement was obtained between the numerical results and experimental data.
Assessment of large basis shell model wave functions for the Li isotopes
Energy Technology Data Exchange (ETDEWEB)
Karataglidis, S.; Brown, B.A. [Michigan State Univ., East Lansing, MI (United States); Dortmans, P.J.; Amos, K. [Melbourne Univ., Parkville, VIC (Australia). School of Physics
1997-06-01
The Li isotopes are good examples with which the shell model can be tested for cluster-like behaviour, as large space (no core) shell model wave functions may be constructed. The cross sections and analysing power for the inelastic scattering of electron and proton scattering data for {sup 6,7}Li ground states were analysed using the same shell model wave functions. It was found that the results obtained by using 0{Dirac_h}{omega} structure model wave functions is unable to reproduce the magnitude of the data. Meanwhile, those obtained by using the larger space models are able to reproduce the low-angle part of the cross section, but all model results severely underestimate the cross section above 20 deg. Meanwhile, in the case of analysing power, all model calculations give reasonable representation of the data. 13 refs., 3 figs.
A Monte Carlo Uncertainty Analysis of Ozone Trend Predictions in a Two Dimensional Model. Revision
Considine, D. B.; Stolarski, R. S.; Hollandsworth, S. M.; Jackman, C. H.; Fleming, E. L.
1998-01-01
We use Monte Carlo analysis to estimate the uncertainty in predictions of total O3 trends between 1979 and 1995 made by the Goddard Space Flight Center (GSFC) two-dimensional (2D) model of stratospheric photochemistry and dynamics. The uncertainty is caused by gas-phase chemical reaction rates, photolysis coefficients, and heterogeneous reaction parameters which are model inputs. The uncertainty represents a lower bound to the total model uncertainty assuming the input parameter uncertainties are characterized correctly. Each of the Monte Carlo runs was initialized in 1970 and integrated for 26 model years through the end of 1995. This was repeated 419 times using input parameter sets generated by Latin Hypercube Sampling. The standard deviation (a) of the Monte Carlo ensemble of total 03 trend predictions is used to quantify the model uncertainty. The 34% difference between the model trend in globally and annually averaged total O3 using nominal inputs and atmospheric trends calculated from Nimbus 7 and Meteor 3 total ozone mapping spectrometer (TOMS) version 7 data is less than the 46% calculated 1 (sigma), model uncertainty, so there is no significant difference between the modeled and observed trends. In the northern hemisphere midlatitude spring the modeled and observed total 03 trends differ by more than 1(sigma) but less than 2(sigma), which we refer to as marginal significance. We perform a multiple linear regression analysis of the runs which suggests that only a few of the model reactions contribute significantly to the variance in the model predictions. The lack of significance in these comparisons suggests that they are of questionable use as guides for continuing model development. Large model/measurement differences which are many multiples of the input parameter uncertainty are seen in the meridional gradients of the trend and the peak-to-peak variations in the trends over an annual cycle. These discrepancies unambiguously indicate model formulation
Forward and adjoint radiance Monte Carlo models for quantitative photoacoustic imaging
Hochuli, Roman; Powell, Samuel; Arridge, Simon; Cox, Ben
2015-03-01
In quantitative photoacoustic imaging, the aim is to recover physiologically relevant tissue parameters such as chromophore concentrations or oxygen saturation. Obtaining accurate estimates is challenging due to the non-linear relationship between the concentrations and the photoacoustic images. Nonlinear least squares inversions designed to tackle this problem require a model of light transport, the most accurate of which is the radiative transfer equation. This paper presents a highly scalable Monte Carlo model of light transport that computes the radiance in 2D using a Fourier basis to discretise in angle. The model was validated against a 2D finite element model of the radiative transfer equation, and was used to compute gradients of an error functional with respect to the absorption and scattering coefficient. It was found that adjoint-based gradient calculations were much more robust to inherent Monte Carlo noise than a finite difference approach. Furthermore, the Fourier angular discretisation allowed very efficient gradient calculations as sums of Fourier coefficients. These advantages, along with the high parallelisability of Monte Carlo models, makes this approach an attractive candidate as a light model for quantitative inversion in photoacoustic imaging.
Monte Carlo simulation based toy model for fission process
Kurniadi, Rizal; Waris, Abdul; Viridi, Sparisoma
2016-09-01
Nuclear fission has been modeled notoriously using two approaches method, macroscopic and microscopic. This work will propose another approach, where the nucleus is treated as a toy model. The aim is to see the usefulness of particle distribution in fission yield calculation. Inasmuch nucleus is a toy, then the Fission Toy Model (FTM) does not represent real process in nature completely. The fission event in FTM is represented by one random number. The number is assumed as width of distribution probability of nucleon position in compound nuclei when fission process is started. By adopting the nucleon density approximation, the Gaussian distribution is chosen as particle distribution. This distribution function generates random number that randomizes distance between particles and a central point. The scission process is started by smashing compound nucleus central point into two parts that are left central and right central points. The yield is determined from portion of nuclei distribution which is proportional with portion of mass numbers. By using modified FTM, characteristic of particle distribution in each fission event could be formed before fission process. These characteristics could be used to make prediction about real nucleons interaction in fission process. The results of FTM calculation give information that the γ value seems as energy.
Stability of core–shell nanowires in selected model solutions
Energy Technology Data Exchange (ETDEWEB)
Kalska-Szostko, B., E-mail: kalska@uwb.edu.pl; Wykowska, U.; Basa, A.; Zambrzycka, E.
2015-03-30
Highlights: • Stability of the core–shell nanowires in environmental solutions were tested. • The most and the least aggressive solutions were determined. • The influence of different solutions on magnetic nanowires core was found out. - Abstract: This paper presents the studies of stability of magnetic core–shell nanowires prepared by electrochemical deposition from an acidic solution containing iron in the core and modified surface layer. The obtained nanowires were tested according to their durability in distilled water, 0.01 M citric acid, 0.9% NaCl, and commercial white wine (12% alcohol). The proposed solutions were chosen in such a way as to mimic food related environment due to a possible application of nanowires as additives to, for example, packages. After 1, 2 and 3 weeks wetting in the solutions, nanoparticles were tested by Infrared Spectroscopy, Atomic Absorption Spectroscopy, Transmission Electron Microscopy and X-ray diffraction methods.
A viscoplastic model of expanding cylindrical shells subjected to internal explosive detonations
Energy Technology Data Exchange (ETDEWEB)
Martineau, Rick L. [Colorado State Univ., Fort Collins, CO (United States)
1998-04-01
Magnetic flux compression generators rely on the expansion of thin ductile shells to generate magnetic fields. These thin shells are filled with high explosives, which when detonated, cause the shell to expand to over 200% strain at strain-rates on the order of 10^{4} s^{-1}. Experimental data indicate the development and growth of multiple plastic instabilities which appear in a quasi-periodic pattern on the surfaces of the shells. These quasi-periodic instabilities are connected by localized zones of intense shear that are oriented approximately 45° from the outward radial direction. The quasi-periodic instabilities continue to develop and eventually become through-cracks, causing the shell to fragment. A viscoplastic constitutive model is formulated to model the high strain-rate expansion and provide insight into the development of plastic instabilities. The formulation of the viscoplastic constitutive model includes the effects of shock heating and damage in the form of microvoid nucleation, growth, and coalescence in the expanding shell. This model uses the Johnson-Cook strength model with the Mie-Grueneisen equation of state and a modified Gurson yield surface. The constitutive model includes the modifications proposed by Tvergaard and the plastic strain controlled nucleation introduced by Neeleman. The constitutive model is implemented as a user material subroutine into ABAQUS/Explicit, which is a commercially available nonlinear explicit dynamic finite element program. A cylindrical shell is modeled using both axisymmetric and plane strain elements. Two experiments were conducted involving plane wave detonated, explosively filled, copper cylinders. Instability, displacement, and velocity data were recorded using a fast framing camera and a Fabry-Perot interferometer. Good agreement is shown between the numerical results and experimental data. An additional explosively bulged cylinder experiment was also performed and a photomicrograph of an
A viscoplastic model of expanding cylindrical shells subjected to internal explosive detonations
Energy Technology Data Exchange (ETDEWEB)
Martineau, R.L.
1998-04-01
Magnetic flux compression generators rely on the expansion of thin ductile shells to generate magnetic fields. These thin shells are filled with high explosives, which when detonated, cause the shell to expand to over 200% strain at strain-rates on the order of 10{sup 4} s{sup {minus}1}. Experimental data indicate the development and growth of multiple plastic instabilities which appear in a quasi-periodic pattern on the surfaces of the shells. These quasi-periodic instabilities are connected by localized zones of intense shear that are oriented approximately 45{degree} from the outward radial direction. The quasi-periodic instabilities continue to develop and eventually become through-cracks, causing the shell to fragment. A viscoplastic constitutive model is formulated to model the high strain-rate expansion and provide insight into the development of plastic instabilities. The formulation of the viscoplastic constitutive model includes the effects of shock heating and damage in the form of microvoid nucleation, growth, and coalescence in the expanding shell. This model uses the Johnson-Cook strength model with the Mie-Grueneisen equation of state and a modified Gurson yield surface. The constitutive model includes the modifications proposed by Tvergaard and the plastic strain controlled nucleation introduced by Neeleman. The constitutive model is implemented as a user material subroutine into ABAQUS/Explicit, which is a commercially available nonlinear explicit dynamic finite element program. A cylindrical shell is modeled using both axisymmetric and plane strain elements. Two experiments were conducted involving plane wave detonated, explosively filled, copper cylinders. Instability, displacement, and velocity data were recorded using a fast framing camera and a Fabry-Perot interferometer. Good agreement is shown between the numerical results and experimental data. An additional explosively bulged cylinder experiment was also performed and a photomicrograph of
All $(4,1)$: Sigma Models with $(4,q)$ Off-Shell Supersymmetry
Hull, Chris
2016-01-01
Off-shell $(4,q)$ supermultiplets in 2-dimensions are constructed for $q=1,2,4$. These are used to construct sigma models whose target spaces are hyperk\\"ahler with torsion. The off-shell supersymmetry implies the three complex structures are simultaneously integrable and allows us to construct actions using extended superspace and projective superspace, giving an explicit construction of the target space geometries.
Numerical Study of Light Transport in Apple Models Based on Monte Carlo Simulations
Directory of Open Access Journals (Sweden)
Mohamed Lamine Askoura
2015-12-01
Full Text Available This paper reports on the quantification of light transport in apple models using Monte Carlo simulations. To this end, apple was modeled as a two-layer spherical model including skin and flesh bulk tissues. The optical properties of both tissue types used to generate Monte Carlo data were collected from the literature, and selected to cover a range of values related to three apple varieties. Two different imaging-tissue setups were simulated in order to show the role of the skin on steady-state backscattering images, spatially-resolved reflectance profiles, and assessment of flesh optical properties using an inverse nonlinear least squares fitting algorithm. Simulation results suggest that apple skin cannot be ignored when a Visible/Near-Infrared (Vis/NIR steady-state imaging setup is used for investigating quality attributes of apples. They also help to improve optical inspection techniques in the horticultural products.
Monte Carlo simulation for kinetic chemotaxis model: An application to the traveling population wave
Yasuda, Shugo
2017-02-01
A Monte Carlo simulation of chemotactic bacteria is developed on the basis of the kinetic model and is applied to a one-dimensional traveling population wave in a microchannel. In this simulation, the Monte Carlo method, which calculates the run-and-tumble motions of bacteria, is coupled with a finite volume method to calculate the macroscopic transport of the chemical cues in the environment. The simulation method can successfully reproduce the traveling population wave of bacteria that was observed experimentally and reveal the microscopic dynamics of bacterium coupled with the macroscopic transports of the chemical cues and bacteria population density. The results obtained by the Monte Carlo method are also compared with the asymptotic solution derived from the kinetic chemotaxis equation in the continuum limit, where the Knudsen number, which is defined by the ratio of the mean free path of bacterium to the characteristic length of the system, vanishes. The validity of the Monte Carlo method in the asymptotic behaviors for small Knudsen numbers is numerically verified.
Comparing analytical and Monte Carlo optical diffusion models in phosphor-based X-ray detectors
Kalyvas, N.; Liaparinos, P.
2014-03-01
Luminescent materials are employed as radiation to light converters in detectors of medical imaging systems, often referred to as phosphor screens. Several processes affect the light transfer properties of phosphors. Amongst the most important is the interaction of light. Light attenuation (absorption and scattering) can be described either through "diffusion" theory in theoretical models or "quantum" theory in Monte Carlo methods. Although analytical methods, based on photon diffusion equations, have been preferentially employed to investigate optical diffusion in the past, Monte Carlo simulation models can overcome several of the analytical modelling assumptions. The present study aimed to compare both methodologies and investigate the dependence of the analytical model optical parameters as a function of particle size. It was found that the optical photon attenuation coefficients calculated by analytical modeling are decreased with respect to the particle size (in the region 1- 12 μm). In addition, for particles sizes smaller than 6μm there is no simultaneous agreement between the theoretical modulation transfer function and light escape values with respect to the Monte Carlo data.
Modeling of hysteresis loops by Monte Carlo simulation
Directory of Open Access Journals (Sweden)
Z. Nehme
2015-12-01
Full Text Available Recent advances in MC simulations of magnetic properties are rather devoted to non-interacting systems or ultrafast phenomena, while the modeling of quasi-static hysteresis loops of an assembly of spins with strong internal exchange interactions remains limited to specific cases. In the case of any assembly of magnetic moments, we propose MC simulations on the basis of a three dimensional classical Heisenberg model applied to an isolated magnetic slab involving first nearest neighbors exchange interactions and uniaxial anisotropy. Three different algorithms were successively implemented in order to simulate hysteresis loops: the classical free algorithm, the cone algorithm and a mixed one consisting of adding some global rotations. We focus particularly our study on the impact of varying the anisotropic constant parameter on the coercive field for different temperatures and algorithms. A study of the angular acceptation move distribution allows the dynamics of our simulations to be characterized. The results reveal that the coercive field is linearly related to the anisotropy providing that the algorithm and the numeric conditions are carefully chosen. In a general tendency, it is found that the efficiency of the simulation can be greatly enhanced by using the mixed algorithm that mimic the physics of collective behavior. Consequently, this study lead as to better quantified coercive fields measurements resulting from physical phenomena of complex magnetic (nanoarchitectures with different anisotropy contributions.
Modeling of hysteresis loops by Monte Carlo simulation
Nehme, Z.; Labaye, Y.; Sayed Hassan, R.; Yaacoub, N.; Greneche, J. M.
2015-12-01
Recent advances in MC simulations of magnetic properties are rather devoted to non-interacting systems or ultrafast phenomena, while the modeling of quasi-static hysteresis loops of an assembly of spins with strong internal exchange interactions remains limited to specific cases. In the case of any assembly of magnetic moments, we propose MC simulations on the basis of a three dimensional classical Heisenberg model applied to an isolated magnetic slab involving first nearest neighbors exchange interactions and uniaxial anisotropy. Three different algorithms were successively implemented in order to simulate hysteresis loops: the classical free algorithm, the cone algorithm and a mixed one consisting of adding some global rotations. We focus particularly our study on the impact of varying the anisotropic constant parameter on the coercive field for different temperatures and algorithms. A study of the angular acceptation move distribution allows the dynamics of our simulations to be characterized. The results reveal that the coercive field is linearly related to the anisotropy providing that the algorithm and the numeric conditions are carefully chosen. In a general tendency, it is found that the efficiency of the simulation can be greatly enhanced by using the mixed algorithm that mimic the physics of collective behavior. Consequently, this study lead as to better quantified coercive fields measurements resulting from physical phenomena of complex magnetic (nano)architectures with different anisotropy contributions.
Kinetic Model for a Spherical Rolling Robot with Soft Shell in a Beeline Motion
Directory of Open Access Journals (Sweden)
Sheng Zhang
2014-02-01
Full Text Available A simplified kinetic model called Spring Pendulum is developed for a spherical rolling robot with soft shell in order to meet the needs of attitude stabilization and controlling for the robot. The elasticity and plasticity of soft shell is represented by some uniform springs connected to the bracket in this model. The expression of the kinetic model is deduced from Newtonian mechanics principles. Testing data of the driving angle acquired from a prototype built by authors indicate that testing data curve accords to the theoretic kinetic characteristic curve, so the kinetic model is validated
Critical behavior of the random-bond Ashkin-Teller model: A Monte Carlo study
Wiseman, Shai; Domany, Eytan
1995-04-01
The critical behavior of a bond-disordered Ashkin-Teller model on a square lattice is investigated by intensive Monte Carlo simulations. A duality transformation is used to locate a critical plane of the disordered model. This critical plane corresponds to the line of critical points of the pure model, along which critical exponents vary continuously. Along this line the scaling exponent corresponding to randomness φ=(α/ν) varies continuously and is positive so that the randomness is relevant, and different critical behavior is expected for the disordered model. We use a cluster algorithm for the Monte Carlo simulations based on the Wolff embedding idea, and perform a finite size scaling study of several critical models, extrapolating between the critical bond-disordered Ising and bond-disordered four-state Potts models. The critical behavior of the disordered model is compared with the critical behavior of an anisotropic Ashkin-Teller model, which is used as a reference pure model. We find no essential change in the order parameters' critical exponents with respect to those of the pure model. The divergence of the specific heat C is changed dramatically. Our results favor a logarithmic type divergence at Tc, C~lnL for the random-bond Ashkin-Teller and four-state Potts models and C~ln lnL for the random-bond Ising model.
Stolarski, R. S.; Butler, D. M.; Rundel, R. D.
1977-01-01
A concise stratospheric model was used in a Monte-Carlo analysis of the propagation of reaction rate uncertainties through the calculation of an ozone perturbation due to the addition of chlorine. Two thousand Monte-Carlo cases were run with 55 reaction rates being varied. Excellent convergence was obtained in the output distributions because the model is sensitive to the uncertainties in only about 10 reactions. For a 1 ppby chlorine perturbation added to a 1.5 ppby chlorine background, the resultant 1 sigma uncertainty on the ozone perturbation is a factor of 1.69 on the high side and 1.80 on the low side. The corresponding 2 sigma factors are 2.86 and 3.23. Results are also given for the uncertainties, due to reaction rates, in the ambient concentrations of stratospheric species.
Monte Carlo tests of the Rasch model based on scalability coefficients
DEFF Research Database (Denmark)
Christensen, Karl Bang; Kreiner, Svend
2010-01-01
that summarizes the number of Guttman errors in the data matrix. These coefficients are shown to yield efficient tests of the Rasch model using p-values computed using Markov chain Monte Carlo methods. The power of the tests of unequal item discrimination, and their ability to distinguish between local dependence...... and unequal item discrimination, are discussed. The methods are illustrated and motivated using a simulation study and a real data example....
Critical Exponents of the Classical 3D Heisenberg Model A Single-Cluster Monte Carlo Study
Holm, C; Holm, Christian; Janke, Wolfhard
1993-01-01
We have simulated the three-dimensional Heisenberg model on simple cubic lattices, using the single-cluster Monte Carlo update algorithm. The expected pronounced reduction of critical slowing down at the phase transition is verified. This allows simulations on significantly larger lattices than in previous studies and consequently a better control over systematic errors. In one set of simulations we employ the usual finite-size scaling methods to compute the critical exponents $\
Monte Carlo Study of the Xy-Model on SIERPIŃSKI Carpet
Mitrović, Božidar; Przedborski, Michelle A.
2014-09-01
We have performed a Monte Carlo (MC) study of the classical XY-model on a Sierpiński carpet, which is a planar fractal structure with infinite order of ramification and fractal dimension 1.8928. We employed the Wolff cluster algorithm in our simulations and our results, in particular those for the susceptibility and the helicity modulus, indicate the absence of finite-temperature Berezinskii-Kosterlitz-Thouless (BKT) transition in this system.
Monte Carlo Tests of Nucleation Concepts in the Lattice Gas Model
Schmitz, Fabian; Virnau, Peter; Binder, Kurt
2013-01-01
The conventional theory of homogeneous and heterogeneous nucleation in a supersaturated vapor is tested by Monte Carlo simulations of the lattice gas (Ising) model with nearest-neighbor attractive interactions on the simple cubic lattice. The theory considers the nucleation process as a slow (quasi-static) cluster (droplet) growth over a free energy barrier $\\Delta F^*$, constructed in terms of a balance of surface and bulk term of a "critical droplet" of radius $R^*$, implying that the rates...
Monte Carlo path sampling approach to modeling aeolian sediment transport
Hardin, E. J.; Mitasova, H.; Mitas, L.
2011-12-01
Coastal communities and vital infrastructure are subject to coastal hazards including storm surge and hurricanes. Coastal dunes offer protection by acting as natural barriers from waves and storm surge. During storms, these landforms and their protective function can erode; however, they can also erode even in the absence of storms due to daily wind and waves. Costly and often controversial beach nourishment and coastal construction projects are common erosion mitigation practices. With a more complete understanding of coastal morphology, the efficacy and consequences of anthropogenic activities could be better predicted. Currently, the research on coastal landscape evolution is focused on waves and storm surge, while only limited effort is devoted to understanding aeolian forces. Aeolian transport occurs when the wind supplies a shear stress that exceeds a critical value, consequently ejecting sand grains into the air. If the grains are too heavy to be suspended, they fall back to the grain bed where the collision ejects more grains. This is called saltation and is the salient process by which sand mass is transported. The shear stress required to dislodge grains is related to turbulent air speed. Subsequently, as sand mass is injected into the air, the wind loses speed along with its ability to eject more grains. In this way, the flux of saltating grains is itself influenced by the flux of saltating grains and aeolian transport becomes nonlinear. Aeolian sediment transport is difficult to study experimentally for reasons arising from the orders of magnitude difference between grain size and dune size. It is difficult to study theoretically because aeolian transport is highly nonlinear especially over complex landscapes. Current computational approaches have limitations as well; single grain models are mathematically simple but are computationally intractable even with modern computing power whereas cellular automota-based approaches are computationally efficient
MODELING OF NONLINEAR DEFORMATION AND BUCKLING OF ELASTIC INHOMOGENEOUS SHELLS
Directory of Open Access Journals (Sweden)
Bazhenov V.A.
2014-06-01
Full Text Available The paper outlines the fundamentals of the method of solving static problems of geometrically nonlinear deformation, buckling, and postbuckling behavior of thin thermoelastic inhomogeneous shells with complex-shaped mid-surface, geometrical features throughout the thickness, and multilayer structure under complex thermomechanical loading. The method is based on the geometrically nonlinear equations of three-dimensional thermoelasticity and the moment finiteelement scheme. The method is justified numerically. Comparing solutions with those obtained by other authors and by software LIRA and SCAD is conducted.
Mixed isoparametric finite element models of laminated composite shells
Noor, A. K.; Andersen, C. M.
1977-01-01
Mixed shear-flexible isoparametric elements are presented for the stress and free vibration analysis of laminated composite shallow shells. Both triangular and quadrilateral elements are considered. The 'generalized' element stiffness, consistent mass, and consistent load coefficients are obtained by using a modified form of the Hellinger-Reissner mixed variational principle. Group-theoretic techniques are used in conjunction with computerized symbolic integration to obtain analytic expressions for the stiffness, mass and load coefficients. A procedure is outlined for efficiently handling the resulting system of algebraic equations. The accuracy of the mixed isoparametric elements developed is demonstrated by means of numerical examples, and their advantages over commonly used displacement elements are discussed.
Nonclassical models of the theory of plates and shells
Annin, B. D.; Volchkov, Yu. M.
2016-09-01
Publications dealing with the study of methods of reducing a three-dimensional problem of the elasticity theory to a two-dimensional problem of the theory of plates and shells are reviewed. Two approaches are considered: the use of kinematic and force hypotheses and expansion of solutions of the three-dimensional elasticity theory in terms of the complete system of functions. Papers where a three-dimensional problem is reduced to a two-dimensional problem with the use of several approximations of each sought function (stresses and displacements) by segments of Legendre polynomials are also reviewed.
Partial Conservation Law in a Schematic Single j Shell Model
Pereira, Wesley; Zamick, Larry; Escuderos, Alberto; Neergård, Kai
2016-01-01
We report the discovery of a partial conservation law obeyed by a schematic Hamiltonian of two protons and two neutrons in a j shell. In our Hamiltonian the interaction matrix element of two nucleons with combined angular momentum J is linear in J for even J and constant for odd J. It turns out that in some stationary states the sum J_p + J_n of the angular momenta J_p and J_n of the proton and neutron pairs is conserved. The energies of these states are given by a linear function of J_p + J_n. The systematics of their occurrence is described and explained.
Monte Carlo method of radiative transfer applied to a turbulent flame modeling with LES
Zhang, Jin; Gicquel, Olivier; Veynante, Denis; Taine, Jean
2009-06-01
Radiative transfer plays an important role in the numerical simulation of turbulent combustion. However, for the reason that combustion and radiation are characterized by different time scales and different spatial and chemical treatments, the radiation effect is often neglected or roughly modelled. The coupling of a large eddy simulation combustion solver and a radiation solver through a dedicated language, CORBA, is investigated. Two formulations of Monte Carlo method (Forward Method and Emission Reciprocity Method) employed to resolve RTE have been compared in a one-dimensional flame test case using three-dimensional calculation grids with absorbing and emitting media in order to validate the Monte Carlo radiative solver and to choose the most efficient model for coupling. Then the results obtained using two different RTE solvers (Reciprocity Monte Carlo method and Discrete Ordinate Method) applied on a three-dimensional flame holder set-up with a correlated-k distribution model describing the real gas medium spectral radiative properties are compared not only in terms of the physical behavior of the flame, but also in computational performance (storage requirement, CPU time and parallelization efficiency). To cite this article: J. Zhang et al., C. R. Mecanique 337 (2009).
Energy Technology Data Exchange (ETDEWEB)
Murata, Isao [Osaka Univ., Suita (Japan); Mori, Takamasa; Nakagawa, Masayuki; Itakura, Hirofumi
1996-03-01
The method to calculate neutronics parameters of a core composed of randomly distributed spherical fuels has been developed based on a statistical geometry model with a continuous energy Monte Carlo method. This method was implemented in a general purpose Monte Carlo code MCNP, and a new code MCNP-CFP had been developed. This paper describes the model and method how to use it and the validation results. In the Monte Carlo calculation, the location of a spherical fuel is sampled probabilistically along the particle flight path from the spatial probability distribution of spherical fuels, called nearest neighbor distribution (NND). This sampling method was validated through the following two comparisons: (1) Calculations of inventory of coated fuel particles (CFPs) in a fuel compact by both track length estimator and direct evaluation method, and (2) Criticality calculations for ordered packed geometries. This method was also confined by applying to an analysis of the critical assembly experiment at VHTRC. The method established in the present study is quite unique so as to a probabilistic model of the geometry with a great number of spherical fuels distributed randomly. Realizing the speed-up by vector or parallel computations in future, it is expected to be widely used in calculation of a nuclear reactor core, especially HTGR cores. (author).
Finite Element Modeling of a Fluid Filled Cylindrical Shell with Active Constrained Layer Damping
Institute of Scientific and Technical Information of China (English)
ZHANG Yi; ZHANG Zhi-yi; TONG Zong-peng; HUA Hong-xing
2005-01-01
On the basis of the piezoelectric theory, Mindlin plate theory, viscoelastic theory and ideal fluid equa tion, the finite element modeling of a fluid-filled cylindrical shell with active constrained layer damping (ACLD) was discussed. Energy methods and Lagrange's equation were used to obtain dynamic equations of the cylindrical shell with ACLD treatments, which was modeled as well with the finite element method. The GHM (Golla-Hughes-McTavish) method was applied to model the frequency dependent damping of viscoelastic material. Ideal and incompressible fluid was considered to establish the dynamic equations of the fluid-filled cylindrical shell with ACLD treatments, Numerical results obtained from the finite element analysis were compared with those from an experiment. The comparison shows that the proposed modeling method is accurate and reliable.
Ansari, R.; Rouhi, S.; Aryayi, M.
2016-01-01
The vibrational behavior of double-walled carbon nanotubes is studied by the use of the molecular structural and cylindrical shell models. The spring elements are employed to model the van der Waals interaction. The effects of different parameters such as geometry, chirality, atomic structure and end constraint on the vibration of nanotubes are investigated. Besides, the results of two aforementioned approaches are compared. It is indicated that by increasing the nanotube side length and radius, the computationally efficient cylindrical shell model gives rational results.
Symplectic Symmetry and the Ab Initio No-Core Shell Model
Energy Technology Data Exchange (ETDEWEB)
Draayer, Jerry P.; Dytrych, Tomas; Sviratcheva, Kristina D.; Bahri, Chairul; /Louisiana State U.; Vary, James P.; /Iowa State U. /LLNL, Livermore /SLAC
2007-03-14
The symplectic symmetry of eigenstates for the 0{sub gs}{sup +} in {sup 16}O and the 0{sub gs}{sup +} and lowest 2{sup +} and 4{sup +} configurations of {sup 12}C that are well-converged within the framework of the no-core shell model with the JISP16 realistic interaction is examined. These states are found to project at the 85-90% level onto very few symplectic representations including the most deformed configuration, which confirms the importance of a symplectic no-core shell model and reaffirms the relevance of the Elliott SU(3) model upon which the symplectic scheme is built.
The fundamental solution for a consistent complex model of the shallow shell equations
Directory of Open Access Journals (Sweden)
Matthew P. Coleman
1999-09-01
Full Text Available The calculation of the Fourier transforms of the fundamental solution in shallow shell theory ostensibly was accomplished by J. L. Sanders [J. Appl. Mech. 37 (1970, 361-366]. However, as is shown in detail in this paper, the complex model used by Sanders is, in fact, inconsistent. This paper provides a consistent version of Sanders's complex model, along with the Fourier transforms of the fundamental solution for this corrected model. The inverse Fourier transforms are then calculated for the particular cases of the shallow spherical and circular cylindrical shells, and the results of the latter are seen to be in agreement with results appearing elsewhere in the literature.
Shear-flexible finite-element models of laminated composite plates and shells
Noor, A. K.; Mathers, M. D.
1975-01-01
Several finite-element models are applied to the linear static, stability, and vibration analysis of laminated composite plates and shells. The study is based on linear shallow-shell theory, with the effects of shear deformation, anisotropic material behavior, and bending-extensional coupling included. Both stiffness (displacement) and mixed finite-element models are considered. Discussion is focused on the effects of shear deformation and anisotropic material behavior on the accuracy and convergence of different finite-element models. Numerical studies are presented which show the effects of increasing the order of the approximating polynomials, adding internal degrees of freedom, and using derivatives of generalized displacements as nodal parameters.
Neutrinoless Double Beta Nuclear Matrix Elements Around Mass 80 in the Nuclear Shell Model
Yoshinaga, Naotaka; Higashiyama, Koji; Taguchi, Daisuke; Teruya, Eri
The observation of the neutrinoless double-beta decay can determine whether the neutrino is a Majorana particle or not. In its theoretical nuclear side it is particularly important to estimate three types of nuclear matrix elements, namely, Fermi (F), Gamow-Teller (GT), and tensor (T) types matrix elements. The shell model calculations and also the pair-truncated shell model calculations are carried out to check the model dependence on nuclear matrix elements. In this work the neutrinoless double-beta decay for mass A = 82 nuclei is studied. It is found that the matrix elements are quite sensitive to the ground state wavefunctions.
Models of spherical shells as sources of Majumdar-Papapetrou type spacetimes
García-Reyes, Gonzalo
2016-01-01
By starting with a seed Newtonian potential-density pair we construct relativistic thick spherical shell models for a Majumdar-Papapetrou type conformastatic spacetime. As simple example, we considerer a family of Plummer type relativistic spherical shells. These objects are then used to model a system composite by a dust disk and a halo of matter. We study the equatorial circular motion of test particles around the structures. Also the stability of the orbits is analyzed for radial perturbation using an extension of the Rayleigh criterion. The models considered satisfying all the energy conditions.
Monte Carlo tools for Beyond the Standard Model Physics , April 14-16
DEFF Research Database (Denmark)
Badger...[], Simon; Christensen, Christian Holm; Dalsgaard, Hans Hjersing;
2011-01-01
This workshop aims to gather together theorists and experimentalists interested in developing and using Monte Carlo tools for Beyond the Standard Model Physics in an attempt to be prepared for the analysis of data focusing on the Large Hadron Collider. Since a large number of excellent tools....... To identify promising models (or processes) for which the tools have not yet been constructed and start filling up these gaps. To propose ways to streamline the process of going from models to events, i.e. to make the process more user-friendly so that more people can get involved and perform serious collider...
Badal Soler, Andreu
2008-01-01
Els programes de simulació Monte Carlo de caràcter general s'utilitzen actualment en una gran varietat d'aplicacions.Tot i això, els models geomètrics implementats en la majoria de programes imposen certes limitacions a la forma dels objectes que es poden definir. Aquests models no són adequats per descriure les superfícies arbitràries que es troben en estructures anatòmiques o en certs aparells mèdics i, conseqüentment, algunes aplicacions que requereixen l'ús de models geomètrics molt detal...
Yasuda, Shugo
2015-01-01
A Monte Carlo simulation for the chemotactic bacteria is developed on the basis of the kinetic modeling, i.e., the Boltzmann transport equation, and applied to the one-dimensional traveling population wave in a micro channel.In this method, the Monte Carlo method, which calculates the run-and-tumble motions of bacteria, is coupled with a finite volume method to solve the macroscopic transport of the chemical cues in the field. The simulation method can successfully reproduce the traveling population wave of bacteria which was observed experimentally. The microscopic dynamics of bacteria, e.g., the velocity autocorrelation function and velocity distribution function of bacteria, are also investigated. It is found that the bacteria which form the traveling population wave create quasi-periodic motions as well as a migratory movement along with the traveling population wave. Simulations are also performed with changing the sensitivity and modulation parameters in the response function of bacteria. It is found th...
Adaptive Multi-GPU Exchange Monte Carlo for the 3D Random Field Ising Model
Navarro, C A; Deng, Youjin
2015-01-01
The study of disordered spin systems through Monte Carlo simulations has proven to be a hard task due to the adverse energy landscape present at the low temperature regime, making it difficult for the simulation to escape from a local minimum. Replica based algorithms such as the Exchange Monte Carlo (also known as parallel tempering) are effective at overcoming this problem, reaching equilibrium on disordered spin systems such as the Spin Glass or Random Field models, by exchanging information between replicas of neighbor temperatures. In this work we present a multi-GPU Exchange Monte Carlo method designed for the simulation of the 3D Random Field Model. The implementation is based on a two-level parallelization scheme that allows the method to scale its performance in the presence of faster and GPUs as well as multiple GPUs. In addition, we modified the original algorithm by adapting the set of temperatures according to the exchange rate observed from short trial runs, leading to an increased exchange rate...
Modeling weight variability in a pan coating process using Monte Carlo simulations.
Pandey, Preetanshu; Katakdaunde, Manoj; Turton, Richard
2006-10-06
The primary objective of the current study was to investigate process variables affecting weight gain mass coating variability (CV(m) ) in pan coating devices using novel video-imaging techniques and Monte Carlo simulations. Experimental information such as the tablet location, circulation time distribution, velocity distribution, projected surface area, and spray dynamics was the main input to the simulations. The data on the dynamics of tablet movement were obtained using novel video-imaging methods. The effects of pan speed, pan loading, tablet size, coating time, spray flux distribution, and spray area and shape were investigated. CV(m) was found to be inversely proportional to the square root of coating time. The spray shape was not found to affect the CV(m) of the process significantly, but an increase in the spray area led to lower CV(m) s. Coating experiments were conducted to verify the predictions from the Monte Carlo simulations, and the trends predicted from the model were in good agreement. It was observed that the Monte Carlo simulations underpredicted CV(m) s in comparison to the experiments. The model developed can provide a basis for adjustments in process parameters required during scale-up operations and can be useful in predicting the process changes that are needed to achieve the same CV(m) when a variable is altered.
Directory of Open Access Journals (Sweden)
M. S. Mayeed
2014-01-01
Full Text Available Applying the reptation algorithm to a simplified perfluoropolyether Z off-lattice polymer model an NVT Monte Carlo simulation has been performed. Bulk condition has been simulated first to compare the average radius of gyration with the bulk experimental results. Then the model is tested for its ability to describe dynamics. After this, it is applied to observe the replenishment of nanoscale ultrathin liquid films on solid flat carbon surfaces. The replenishment rate for trenches of different widths (8, 12, and 16 nms for several molecular weights between two films of perfluoropolyether Z from the Monte Carlo simulation is compared to that obtained solving the diffusion equation using the experimental diffusion coefficients of Ma et al. (1999, with room condition in both cases. Replenishment per Monte Carlo cycle seems to be a constant multiple of replenishment per second at least up to 2 nm replenished film thickness of the trenches over the carbon surface. Considerable good agreement has been achieved here between the experimental results and the dynamics of molecules using reptation moves in the ultrathin liquid films on solid surfaces.
A double-step truncation procedure for large-scale shell-model calculations
Coraggio, L; Itaco, N
2016-01-01
We present a procedure that is helpful to reduce the computational complexity of large-scale shell-model calculations, by preserving as much as possible the role of the rejected degrees of freedom in an effective approach. Our truncation is driven first by the analysis of the effective single-particle energies of the original large-scale shell-model hamiltonian, so to locate the relevant degrees of freedom to describe a class of isotopes or isotones, namely the single-particle orbitals that will constitute a new truncated model space. The second step is to perform an unitary transformation of the original hamiltonian from its model space into the truncated one. This transformation generates a new shell-model hamiltonian, defined in a smaller model space, that retains effectively the role of the excluded single-particle orbitals. As an application of this procedure, we have chosen a realistic shell-model hamiltonian defined in a large model space, set up by seven and five proton and neutron single-particle orb...
Modeling of the growth of GaAs–AlGaAs core–shell nanowires
Voorhees, Peter W; Davis, Stephen H
2017-01-01
Heterostructured GaAs–AlGaAs core–shell nanowires with have attracted much attention because of their significant advantages and great potential for creating high performance nanophotonics and nanoelectronics. The spontaneous formation of Al-rich stripes along certain crystallographic directions and quantum dots near the apexes of the shell are observed in AlGaAs shells. Controlling the formation of these core–shell heterostructures remains challenging. A two-dimensional model valid on the wire cross section, that accounts for capillarity in the faceted surface limit and deposition has been developed for the evolution of the shell morphology and concentration in AlxGa1− xAs alloys. The model includes a completely faceted shell–vapor interface. The objective is to understand the mechanisms of the formation of the radial heterostructures (Al-rich stripes and Al-poor quantum dots) in the nanowire shell. There are two issues that need to be understood. One is the mechanism responsible for the morphological evolution of the shells. Analysis and simulation results suggest that deposition introduces facets not present on the equilibrium Wulff shapes. A balance between diffusion and deposition yields the small facets with sizes varying slowly over time, which yield stripe structures, whereas deposition-dominated growth can lead to quantum-dot structures observed in experiments. There is no self-limiting facet size in this case. The other issue is the mechanism responsible for the segregation of Al atoms in the shells. It is found that the mobility difference of the atoms on the {112} and {110} facets together determine the non-uniform concentration of the atoms in the shell. In particular, even though the mobility of Al on {110} facets is smaller than that of Ga, Al-rich stripes are predicted to form along the {112} facets when the difference of the mobilities of Al and Ga atoms is sufficiently large on {112} facets. As the size of the shell increases, deposition
Monte Carlo Studies of Phase Separation in Compressible 2-dim Ising Models
Mitchell, S. J.; Landau, D. P.
2006-03-01
Using high resolution Monte Carlo simulations, we study time-dependent domain growth in compressible 2-dim ferromagnetic (s=1/2) Ising models with continuous spin positions and spin-exchange moves [1]. Spins interact with slightly modified Lennard-Jones potentials, and we consider a model with no lattice mismatch and one with 4% mismatch. For comparison, we repeat calculations for the rigid Ising model [2]. For all models, large systems (512^2) and long times (10^ 6 MCS) are examined over multiple runs, and the growth exponent is measured in the asymptotic scaling regime. For the rigid model and the compressible model with no lattice mismatch, the growth exponent is consistent with the theoretically expected value of 1/3 [1] for Model B type growth. However, we find that non-zero lattice mismatch has a significant and unexpected effect on the growth behavior.Supported by the NSF.[1] D.P. Landau and K. Binder, A Guide to Monte Carlo Simulations in Statistical Physics, second ed. (Cambridge University Press, New York, 2005).[2] J. Amar, F. Sullivan, and R.D. Mountain, Phys. Rev. B 37, 196 (1988).
Shell Tectonics: A Mechanical Model for Strike-slip Displacement on Europa
Rhoden, Alyssa Rose; Wurman, Gilead; Huff, Eric M.; Manga, Michael; Hurford, Terry A.
2012-01-01
We introduce a new mechanical model for producing tidally-driven strike-slip displacement along preexisting faults on Europa, which we call shell tectonics. This model differs from previous models of strike-slip on icy satellites by incorporating a Coulomb failure criterion, approximating a viscoelastic rheology, determining the slip direction based on the gradient of the tidal shear stress rather than its sign, and quantitatively determining the net offset over many orbits. This model allows us to predict the direction of net displacement along faults and determine relative accumulation rate of displacement. To test the shell tectonics model, we generate global predictions of slip direction and compare them with the observed global pattern of strike-slip displacement on Europa in which left-lateral faults dominate far north of the equator, right-lateral faults dominate in the far south, and near-equatorial regions display a mixture of both types of faults. The shell tectonics model reproduces this global pattern. Incorporating a small obliquity into calculations of tidal stresses, which are used as inputs to the shell tectonics model, can also explain regional differences in strike-slip fault populations. We also discuss implications for fault azimuths, fault depth, and Europa's tectonic history.
DEFF Research Database (Denmark)
Almegaard, Henrik
2004-01-01
A new statical and conceptual model for membrane shell structures - the stringer system - has been found. The principle was first published at the IASS conference in Copenhagen (OHL91), and later the theory has been further developed (ALMO3)(ALMO4). From the analysis of the stringer model it can...... be concluded that all membrane shells can be described by a limited number of basic configurations of which quite a few have free edges....
Core-scale solute transport model selection using Monte Carlo analysis
Malama, Bwalya; James, Scott C
2013-01-01
Model applicability to core-scale solute transport is evaluated using breakthrough data from column experiments conducted with conservative tracers tritium (H-3) and sodium-22, and the retarding solute uranium-232. The three models considered are single-porosity, double-porosity with single-rate mobile-immobile mass-exchange, and the multirate model, which is a deterministic model that admits the statistics of a random mobile-immobile mass-exchange rate coefficient. The experiments were conducted on intact Culebra Dolomite core samples. Previously, data were analyzed using single- and double-porosity models although the Culebra Dolomite is known to possess multiple types and scales of porosity, and to exhibit multirate mobile-immobile-domain mass transfer characteristics at field scale. The data are reanalyzed here and null-space Monte Carlo analysis is used to facilitate objective model selection. Prediction (or residual) bias is adopted as a measure of the model structural error. The analysis clearly shows ...
Multi-shell model of ion-induced nucleic acid condensation
Tolokh, Igor S.; Drozdetski, Aleksander V.; Pollack, Lois; Baker, Nathan A.; Onufriev, Alexey V.
2016-04-01
We present a semi-quantitative model of condensation of short nucleic acid (NA) duplexes induced by trivalent cobalt(iii) hexammine (CoHex) ions. The model is based on partitioning of bound counterion distribution around single NA duplex into "external" and "internal" ion binding shells distinguished by the proximity to duplex helical axis. In the aggregated phase the shells overlap, which leads to significantly increased attraction of CoHex ions in these overlaps with the neighboring duplexes. The duplex aggregation free energy is decomposed into attractive and repulsive components in such a way that they can be represented by simple analytical expressions with parameters derived from molecular dynamic simulations and numerical solutions of Poisson equation. The attractive term depends on the fractions of bound ions in the overlapping shells and affinity of CoHex to the "external" shell of nearly neutralized duplex. The repulsive components of the free energy are duplex configurational entropy loss upon the aggregation and the electrostatic repulsion of the duplexes that remains after neutralization by bound CoHex ions. The estimates of the aggregation free energy are consistent with the experimental range of NA duplex condensation propensities, including the unusually poor condensation of RNA structures and subtle sequence effects upon DNA condensation. The model predicts that, in contrast to DNA, RNA duplexes may condense into tighter packed aggregates with a higher degree of duplex neutralization. An appreciable CoHex mediated RNA-RNA attraction requires closer inter-duplex separation to engage CoHex ions (bound mostly in the "internal" shell of RNA) into short-range attractive interactions. The model also predicts that longer NA fragments will condense more readily than shorter ones. The ability of this model to explain experimentally observed trends in NA condensation lends support to proposed NA condensation picture based on the multivalent "ion binding
Flicstein, Jean; Pata, S.; Chun, L. S. H. K.; Palmier, Jean F.; Courant, J. L.
1998-05-01
A model for ultraviolet induced chemical vapor deposition (UV CVD) for a-SiN:H is described. In the simulation of UV CVD process, activate charged centers creation, species incorporation, surface diffusion, and desorption are considered as elementary steps for the photonucleation and photodeposition mechanisms. The process is characterized by two surface sticking coefficients. Surface diffusion of species is modeled with a gaussian distribution. A real time Monte Carlo method is used to determine photonucleation and photodeposition rates in nanostructures. Comparison of experimental versus simulation results for a-SiN:H is shown to predict the morphology temporal evolution under operating conditions down to atomistic resolution.
Molecular mobility with respect to accessible volume in Monte Carlo lattice model for polymers
Diani, J.; Gilormini, P.
2017-02-01
A three-dimensional cubic Monte Carlo lattice model is considered to test the impact of volume on the molecular mobility of amorphous polymers. Assuming classic polymer chain dynamics, the concept of locked volume limiting the accessible volume around the polymer chains is introduced. The polymer mobility is assessed by its ability to explore the entire lattice thanks to reptation motions. When recording the polymer mobility with respect to the lattice accessible volume, a sharp mobility transition is observed as witnessed during glass transition. The model ability to reproduce known actual trends in terms of glass transition with respect to material parameters, is also tested.
Monte Carlo renormalization-group investigation of the two-dimensional O(4) sigma model
Heller, Urs M.
1988-01-01
An improved Monte Carlo renormalization-group method is used to determine the beta function of the two-dimensional O(4) sigma model. While for (inverse) couplings beta = greater than about 2.2 agreement is obtained with asymptotic scaling according to asymptotic freedom, deviations from it are obtained at smaller couplings. They are, however, consistent with the behavior of the correlation length, indicating 'scaling' according to the full beta function. These results contradict recent claims that the model has a critical point at finite coupling.
Lu, Jianbo; Xu, Lixin; Wu, Yabo; Liu, Molin
2011-01-01
We use the Markov Chain Monte Carlo method to investigate a global constraints on the modified Chaplygin gas (MCG) model as the unification of dark matter and dark energy from the latest observational data: the Union2 dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. In a flat universe, the constraint results for MCG model are, $\\Omega_{b}h^{2}=0...
Development of a Monte Carlo model for the Brainlab microMLC.
Belec, Jason; Patrocinio, Horacio; Verhaegen, Frank
2005-03-07
Stereotactic radiosurgery with several static conformal beams shaped by a micro multileaf collimator (microMLC) is used to treat small irregularly shaped brain lesions. Our goal is to perform Monte Carlo calculations of dose distributions for certain treatment plans as a verification tool. A dedicated microMLC component module for the BEAMnrc code was developed as part of this project and was incorporated in a model of the Varian CL2300 linear accelerator 6 MV photon beam. As an initial validation of the code, the leaf geometry was visualized by tracing particles through the component module and recording their position each time a leaf boundary was crossed. The leaf dimensions were measured and the leaf material density and interleaf air gap were chosen to match the simulated leaf leakage profiles with film measurements in a solid water phantom. A comparison between Monte Carlo calculations and measurements (diode, radiographic film) was performed for square and irregularly shaped fields incident on flat and homogeneous water phantoms. Results show that Monte Carlo calculations agree with measured dose distributions to within 2% and/or 1 mm except for field size smaller than 1.2 cm diameter where agreement is within 5% due to uncertainties in measured output factors.
Directory of Open Access Journals (Sweden)
S. J. Noh
2011-04-01
Full Text Available Applications of data assimilation techniques have been widely used to improve hydrologic prediction. Among various data assimilation techniques, sequential Monte Carlo (SMC methods, known as "particle filters", provide the capability to handle non-linear and non-Gaussian state-space models. In this paper, we propose an improved particle filtering approach to consider different response time of internal state variables in a hydrologic model. The proposed method adopts a lagged filtering approach to aggregate model response until uncertainty of each hydrologic process is propagated. The regularization with an additional move step based on Markov chain Monte Carlo (MCMC is also implemented to preserve sample diversity under the lagged filtering approach. A distributed hydrologic model, WEP is implemented for the sequential data assimilation through the updating of state variables. Particle filtering is parallelized and implemented in the multi-core computing environment via open message passing interface (MPI. We compare performance results of particle filters in terms of model efficiency, predictive QQ plots and particle diversity. The improvement of model efficiency and the preservation of particle diversity are found in the lagged regularized particle filter.
MARMOSET: The Path from LHC Data to the New Standard Model via On-Shell Effective Theories
Energy Technology Data Exchange (ETDEWEB)
Arkani-Hamed, Nima; Schuster, Philip; Toro, Natalia; /Harvard U., Phys. Dept.; Thaler, Jesse; /UC, Berkeley /LBL, Berkeley; Wang, Lian-Tao; /Princeton U.; Knuteson, Bruce; /MIT, LNS; Mrenna, Stephen; /Fermilab
2007-03-01
We describe a coherent strategy and set of tools for reconstructing the fundamental theory of the TeV scale from LHC data. We show that On-Shell Effective Theories (OSETs) effectively characterize hadron collider data in terms of masses, production cross sections, and decay modes of candidate new particles. An OSET description of the data strongly constrains the underlying new physics, and sharply motivates the construction of its Lagrangian. Simulating OSETs allows efficient analysis of new-physics signals, especially when they arise from complicated production and decay topologies. To this end, we present MARMOSET, a Monte Carlo tool for simulating the OSET version of essentially any new-physics model. MARMOSET enables rapid testing of theoretical hypotheses suggested by both data and model-building intuition, which together chart a path to the underlying theory. We illustrate this process by working through a number of data challenges, where the most important features of TeV-scale physics are reconstructed with as little as 5 fb{sup -1} of simulated LHC signals.
Yuan, Jiankui; Zheng, Yiran; Wessels, Barry; Lo, Simon S; Ellis, Rodney; Machtay, Mitchell; Yao, Min
2016-12-01
A virtual source model for Monte Carlo simulations of helical TomoTherapy has been developed previously by the authors. The purpose of this work is to perform experiments in an anthropomorphic (RANDO) phantom with the same order of complexity as in clinical treatments to validate the virtual source model to be used for quality assurance secondary check on TomoTherapy patient planning dose. Helical TomoTherapy involves complex delivery pattern with irregular beam apertures and couch movement during irradiation. Monte Carlo simulation, as the most accurate dose algorithm, is desirable in radiation dosimetry. Current Monte Carlo simulations for helical TomoTherapy adopt the full Monte Carlo model, which includes detailed modeling of individual machine component, and thus, large phase space files are required at different scoring planes. As an alternative approach, we developed a virtual source model without using the large phase space files for the patient dose calculations previously. In this work, we apply the simulation system to recompute the patient doses, which were generated by the treatment planning system in an anthropomorphic phantom to mimic the real patient treatments. We performed thermoluminescence dosimeter point dose and film measurements to compare with Monte Carlo results. Thermoluminescence dosimeter measurements show that the relative difference in both Monte Carlo and treatment planning system is within 3%, with the largest difference less than 5% for both the test plans. The film measurements demonstrated 85.7% and 98.4% passing rate using the 3 mm/3% acceptance criterion for the head and neck and lung cases, respectively. Over 95% passing rate is achieved if 4 mm/4% criterion is applied. For the dose-volume histograms, very good agreement is obtained between the Monte Carlo and treatment planning system method for both cases. The experimental results demonstrate that the virtual source model Monte Carlo system can be a viable option for the
The Physical Models and Statistical Procedures Used in the RACER Monte Carlo Code
Energy Technology Data Exchange (ETDEWEB)
Sutton, T.M.; Brown, F.B.; Bischoff, F.G.; MacMillan, D.B.; Ellis, C.L.; Ward, J.T.; Ballinger, C.T.; Kelly, D.J.; Schindler, L.
1999-07-01
This report describes the MCV (Monte Carlo - Vectorized)Monte Carlo neutron transport code [Brown, 1982, 1983; Brown and Mendelson, 1984a]. MCV is a module in the RACER system of codes that is used for Monte Carlo reactor physics analysis. The MCV module contains all of the neutron transport and statistical analysis functions of the system, while other modules perform various input-related functions such as geometry description, material assignment, output edit specification, etc. MCV is very closely related to the 05R neutron Monte Carlo code [Irving et al., 1965] developed at Oak Ridge National Laboratory. 05R evolved into the 05RR module of the STEMB system, which was the forerunner of the RACER system. Much of the overall logic and physics treatment of 05RR has been retained and, indeed, the original verification of MCV was achieved through comparison with STEMB results. MCV has been designed to be very computationally efficient [Brown, 1981, Brown and Martin, 1984b; Brown, 1986]. It was originally programmed to make use of vector-computing architectures such as those of the CDC Cyber- 205 and Cray X-MP. MCV was the first full-scale production Monte Carlo code to effectively utilize vector-processing capabilities. Subsequently, MCV was modified to utilize both distributed-memory [Sutton and Brown, 1994] and shared memory parallelism. The code has been compiled and run on platforms ranging from 32-bit UNIX workstations to clusters of 64-bit vector-parallel supercomputers. The computational efficiency of the code allows the analyst to perform calculations using many more neutron histories than is practical with most other Monte Carlo codes, thereby yielding results with smaller statistical uncertainties. MCV also utilizes variance reduction techniques such as survival biasing, splitting, and rouletting to permit additional reduction in uncertainties. While a general-purpose neutron Monte Carlo code, MCV is optimized for reactor physics calculations. It has the
Model uncertainties of local-thermodynamic-equilibrium K-shell spectroscopy
Nagayama, T.; Bailey, J. E.; Mancini, R. C.; Iglesias, C. A.; Hansen, S. B.; Blancard, C.; Chung, H. K.; Colgan, J.; Cosse, Ph.; Faussurier, G.; Florido, R.; Fontes, C. J.; Gilleron, F.; Golovkin, I. E.; Kilcrease, D. P.; Loisel, G.; MacFarlane, J. J.; Pain, J.-C.; Rochau, G. A.; Sherrill, M. E.; Lee, R. W.
2016-09-01
Local-thermodynamic-equilibrium (LTE) K-shell spectroscopy is a common tool to diagnose electron density, ne, and electron temperature, Te, of high-energy-density (HED) plasmas. Knowing the accuracy of such diagnostics is important to provide quantitative conclusions of many HED-plasma research efforts. For example, Fe opacities were recently measured at multiple conditions at the Sandia National Laboratories Z machine (Bailey et al., 2015), showing significant disagreement with modeled opacities. Since the plasma conditions were measured using K-shell spectroscopy of tracer Mg (Nagayama et al., 2014), one concern is the accuracy of the inferred Fe conditions. In this article, we investigate the K-shell spectroscopy model uncertainties by analyzing the Mg spectra computed with 11 different models at the same conditions. We find that the inferred conditions differ by ±20-30% in ne and ±2-4% in Te depending on the choice of spectral model. Also, we find that half of the Te uncertainty comes from ne uncertainty. To refine the accuracy of the K-shell spectroscopy, it is important to scrutinize and experimentally validate line-shape theory. We investigate the impact of the inferred ne and Te model uncertainty on the Fe opacity measurements. Its impact is small and does not explain the reported discrepancies.
Directory of Open Access Journals (Sweden)
V. S. Zarubin
2015-01-01
Full Text Available Liquid hydrogen and oxygen are used as the oxidizer and fuel for liquid rocket engines. Liquefied natural gas, which is based on methane, is seen as a promising motor fuel for internal combustion engines. One of the technical problems arising from the use of said cryogenic liquid is to provide containers for storage, transport and use in the propulsion system. In the design and operation of such vessels it is necessary to have reliable information about their temperature condition, on which depend the loss of cryogenic fluids due to evaporation and the stress-strain state of the structural elements of the containers.Uneven temperature distribution along the generatrix of the cylindrical thin-walled shell of rocket cryogenic tanks, in a localized zone of cryogenic liquid level leads to a curvature of the shell and reduce the permissible axle load in a hazard shell buckling in the preparation for the start of the missile in flight with an increasing acceleration. Moving the level of the cryogenic liquid during filling or emptying the tank at a certain combination of parameters results in an increase of the local temperature distribution nonuniformity.Along with experimental study of the shell temperature state of the cryogenic container, methods of mathematical modeling allow to have information needed for designing and testing the construction of cryogenic tanks. In this study a mathematical model is built taking into account features of heat transfer in a cryogenic container, including the boiling cryogenic liquid in the inner surface of the container. This mathematical model describes the temperature state of the thin-walled shell of cylindrical cryogenic tank during filling and emptying. The work also presents a quantitative analysis of this model in case of fixed liquid level, its movement at a constant speed, and harmonic oscillations relative to a middle position. The quantitative analysis of this model has allowed to find the limit options
Monte Carlo based statistical power analysis for mediation models: methods and software.
Zhang, Zhiyong
2014-12-01
The existing literature on statistical power analysis for mediation models often assumes data normality and is based on a less powerful Sobel test instead of the more powerful bootstrap test. This study proposes to estimate statistical power to detect mediation effects on the basis of the bootstrap method through Monte Carlo simulation. Nonnormal data with excessive skewness and kurtosis are allowed in the proposed method. A free R package called bmem is developed to conduct the power analysis discussed in this study. Four examples, including a simple mediation model, a multiple-mediator model with a latent mediator, a multiple-group mediation model, and a longitudinal mediation model, are provided to illustrate the proposed method.
Quantitative photoacoustic tomography using forward and adjoint Monte Carlo models of radiance
Hochuli, Roman; Arridge, Simon; Cox, Ben
2016-01-01
Forward and adjoint Monte Carlo (MC) models of radiance are proposed for use in model-based quantitative photoacoustic tomography. A 2D radiance MC model using a harmonic angular basis is introduced and validated against analytic solutions for the radiance in heterogeneous media. A gradient-based optimisation scheme is then used to recover 2D absorption and scattering coefficients distributions from simulated photoacoustic measurements. It is shown that the functional gradients, which are a challenge to compute efficiently using MC models, can be calculated directly from the coefficients of the harmonic angular basis used in the forward and adjoint models. This work establishes a framework for transport-based quantitative photoacoustic tomography that can fully exploit emerging highly parallel computing architectures.
Institute of Scientific and Technical Information of China (English)
Xingzhe Wang; Xiaojing Zheng
2009-01-01
Based on the generalized variational principle of magneto-thermo-elasticity of a ferromagnetic thin shell established (see, Analyses on nonlinear coupling of magneto-thermo-elasticity of ferromagnetic thin shell-Ⅰ), the present paper developed a finite element modeling for the mechanical-magneto-thermal multi-field coupling of a ferromagnetic thin shell. The numerical modeling composes of finite element equations for three sub-systems of magnetic, thermal and deformation fields, as well as iterative methods for nonlinearities of the geometrical large-deflection and the multi-field coupling of the ferromagnetic shell. As examples, the numerical simulations on magneto-elastic behaviors of a ferromagnetic cylindrical shell in an applied magnetic field, and magneto-thermo-elastic behaviors of the shell in applied magnetic and thermal fields are carried out. The results are in good agreement with the experimental ones.
Fission yield calculation using toy model based on Monte Carlo simulation
Energy Technology Data Exchange (ETDEWEB)
Jubaidah, E-mail: jubaidah@student.itb.ac.id [Nuclear Physics and Biophysics Division, Department of Physics, Bandung Institute of Technology. Jl. Ganesa No. 10 Bandung – West Java, Indonesia 40132 (Indonesia); Physics Department, Faculty of Mathematics and Natural Science – State University of Medan. Jl. Willem Iskandar Pasar V Medan Estate – North Sumatera, Indonesia 20221 (Indonesia); Kurniadi, Rizal, E-mail: rijalk@fi.itb.ac.id [Nuclear Physics and Biophysics Division, Department of Physics, Bandung Institute of Technology. Jl. Ganesa No. 10 Bandung – West Java, Indonesia 40132 (Indonesia)
2015-09-30
Toy model is a new approximation in predicting fission yield distribution. Toy model assumes nucleus as an elastic toy consist of marbles. The number of marbles represents the number of nucleons, A. This toy nucleus is able to imitate the real nucleus properties. In this research, the toy nucleons are only influenced by central force. A heavy toy nucleus induced by a toy nucleon will be split into two fragments. These two fission fragments are called fission yield. In this research, energy entanglement is neglected. Fission process in toy model is illustrated by two Gaussian curves intersecting each other. There are five Gaussian parameters used in this research. They are scission point of the two curves (R{sub c}), mean of left curve (μ{sub L}) and mean of right curve (μ{sub R}), deviation of left curve (σ{sub L}) and deviation of right curve (σ{sub R}). The fission yields distribution is analyses based on Monte Carlo simulation. The result shows that variation in σ or µ can significanly move the average frequency of asymmetry fission yields. This also varies the range of fission yields distribution probability. In addition, variation in iteration coefficient only change the frequency of fission yields. Monte Carlo simulation for fission yield calculation using toy model successfully indicates the same tendency with experiment results, where average of light fission yield is in the range of 90
Bakhet, Nady; Hussein, Tarek
2015-01-01
Large Extra Dimensions Models have been proposed to remove the hierarchy problem and give an explanation why the gravity is so much weaker than the other three forces. In this work, we present an analysis of Monte Carlo data events for new physics signatures of spin-2 Graviton in context of ADD model with total dimensions $D=4+\\delta,$ $\\delta = 1,2,3,4,5,6 $ where $ \\delta $ is the extra special dimension, this model involves missing momentum $P_{T}^{miss}$ in association with jet in the final state via the process $pp(\\bar{p}) \\rightarrow G+jet$, Also, we present an analysis in context of the RS model with 5-dimensions via the process $pp(\\bar{p}) \\rightarrow G+jet$, $G \\rightarrow e^{+}e^{-}$ with final state $e^{+}e^{-}+jet$. We used Monte Carlo event generator Pythia8 to produce efficient signal selection rules at the Large Hadron Collider with $\\sqrt{s}$=14TeV and at the Tevatron $\\sqrt{s}$=1.96TeV .
Contribution of Monte-Carlo modeling for understanding long-term behavior of nuclear glasses
Energy Technology Data Exchange (ETDEWEB)
Minet, Y.; Ledieu, A.; Devreux, F.; Barboux, P.; Frugier, P.; Gin, S
2004-07-01
Monte-Carlo methods have been developed at CEA and Ecole Polytechnique to improve our understanding of the basic mechanisms that control glass dissolution kinetics. The models, based on dissolution and recondensation rates of the atoms, can reproduce the observed alteration rates and the evolutions of the alteration layers on simplified borosilicate glasses (based on SiO{sub 2}-B{sub 2}O{sub 3}-Na{sub 2}O) over a large range of compositions and alteration conditions. The basic models are presented, as well as their current evolutions to describe more complex glasses (introduction of Al, Zr, Ca oxides) and to take into account phenomena which may be predominant in the long run (such as diffusion in the alteration layer or secondary phase precipitation). The predictions are compared with the observations performed by techniques giving structural or textural information on the alteration layer (e.g. NMR, Small Angle X-ray Scattering). The paper concludes with proposals for further evolutions of Monte-Carlo models towards integration into a predictive modeling framework. (authors)
Directory of Open Access Journals (Sweden)
S. J. Noh
2011-10-01
Full Text Available Data assimilation techniques have received growing attention due to their capability to improve prediction. Among various data assimilation techniques, sequential Monte Carlo (SMC methods, known as "particle filters", are a Bayesian learning process that has the capability to handle non-linear and non-Gaussian state-space models. In this paper, we propose an improved particle filtering approach to consider different response times of internal state variables in a hydrologic model. The proposed method adopts a lagged filtering approach to aggregate model response until the uncertainty of each hydrologic process is propagated. The regularization with an additional move step based on the Markov chain Monte Carlo (MCMC methods is also implemented to preserve sample diversity under the lagged filtering approach. A distributed hydrologic model, water and energy transfer processes (WEP, is implemented for the sequential data assimilation through the updating of state variables. The lagged regularized particle filter (LRPF and the sequential importance resampling (SIR particle filter are implemented for hindcasting of streamflow at the Katsura catchment, Japan. Control state variables for filtering are soil moisture content and overland flow. Streamflow measurements are used for data assimilation. LRPF shows consistent forecasts regardless of the process noise assumption, while SIR has different values of optimal process noise and shows sensitive variation of confidential intervals, depending on the process noise. Improvement of LRPF forecasts compared to SIR is particularly found for rapidly varied high flows due to preservation of sample diversity from the kernel, even if particle impoverishment takes place.
Monte Carlo simulation as a tool to predict blasting fragmentation based on the Kuz Ram model
Morin, Mario A.; Ficarazzo, Francesco
2006-04-01
Rock fragmentation is considered the most important aspect of production blasting because of its direct effects on the costs of drilling and blasting and on the economics of the subsequent operations of loading, hauling and crushing. Over the past three decades, significant progress has been made in the development of new technologies for blasting applications. These technologies include increasingly sophisticated computer models for blast design and blast performance prediction. Rock fragmentation depends on many variables such as rock mass properties, site geology, in situ fracturing and blasting parameters and as such has no complete theoretical solution for its prediction. However, empirical models for the estimation of size distribution of rock fragments have been developed. In this study, a blast fragmentation Monte Carlo-based simulator, based on the Kuz-Ram fragmentation model, has been developed to predict the entire fragmentation size distribution, taking into account intact and joints rock properties, the type and properties of explosives and the drilling pattern. Results produced by this simulator were quite favorable when compared with real fragmentation data obtained from a blast quarry. It is anticipated that the use of Monte Carlo simulation will increase our understanding of the effects of rock mass and explosive properties on the rock fragmentation by blasting, as well as increase our confidence in these empirical models. This understanding will translate into improvements in blasting operations, its corresponding costs and the overall economics of open pit mines and rock quarries.
No-Core Shell Model Calculations in Light Nuclei with Three-Nucleon Forces
Energy Technology Data Exchange (ETDEWEB)
Barrett, B R; Vary, J P; Nogga, A; Navratil, P; Ormand, W E
2004-01-08
The ab initio No-Core Shell Model (NCSM) has recently been expanded to include nucleon-nucleon (NN) and three-nucleon (3N) interactions at the three-body cluster level. Here it is used to predict binding energies and spectra of p-shell nuclei based on realistic NN and 3N interactions. It is shown that 3N force (3NF) properties can be studied in these nuclear systems. First results show that interactions based on chiral perturbation theory lead to a realistic description of {sup 6}Li.
Energy Technology Data Exchange (ETDEWEB)
Shen Huishen, E-mail: hsshen@mail.sjtu.edu.c [Department of Engineering Mechanics, Shanghai Jiao Tong University, Shanghai 200030 (China); State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200030 (China)
2010-08-30
A nonlocal shear deformable shell model is developed for buckling of microtubules embedded in an elastic matrix of cytoplasm under bending in thermal environments. The results reveal that the lateral constraint has a significant effect on the buckling moments of a microtubule when the foundation stiffness is sufficiently large.
Shell model study of $^{40}$Ca muon capture and the $(0^+, 0)
Gorringe, T P
2006-01-01
We report results from shell model studies of muon capture on $^{40}$Ca to low-lying levels of $^{40}$K. We discuss the comparison between calculated capture rates, measured capture rates and analogous transitions in ($e$,$e^{\\prime}$) scattering in terms of the particle-hole structure of the $^{40}$Ca-$^{40}$K nuclei. We highlight the $^{40}$Ca$(0^+, 0)
Non-perturbative model for the half-off-shell $gamma N N$ vertex
Kondratyuk, S.; Scholten, O.
1999-01-01
Submitted to: Phys. Rev. C Abstract: Form factors in the nucleon-photon vertex with one off-shell nucleon are calculated by dressing the vertex with pion loops up to infinite order. Cutting rules and dispersion relations are implemented in the model. Using the prescription of minimal substitution we
How the viscous subrange determines inertial range properties in turbulence shell models
Schoerghofer, N.; Kadanoff, L.; Lohse, D.
1995-01-01
We calculate static solutions of the `GOY¿ shell model of turbulence and do a linear stability analysis. The asymptotic limit of large Reynolds numbers is analyzed. A phase diagram is presented which shows the range of stability of the static solution. We see an unexpected oscillatory dependence of
Shell model for time-correlated random advection of passive scalars
DEFF Research Database (Denmark)
Andersen, Ken Haste; Muratore-Ginanneschi, P.
1999-01-01
We study a minimal shell model for the advection of a passive scalar by a Gaussian time-correlated velocity field. The anomalous scaling properties of the white noise limit are studied analytically. The effect of the time correlations are investigated using perturbation theory around the white...
An application of the 3-dimensional q-deformed harmonic oscillator to the nuclear shell model
Raychev, P P; Lo-Iudice, N; Terziev, P A
1998-01-01
An analysis of the construction of a q-deformed version of the 3-dimensional harmonic oscillator, which is based on the application of q-deformed algebras, is presented. The results together with their applicability to the shell model are compared with the predictions of the modified harmonic oscillator.
Large-scale shell-model study of the Sn isotopes
Directory of Open Access Journals (Sweden)
Osnes Eivind
2015-01-01
Full Text Available We summarize the results of an extensive study of the structure of the Sn isotopes using a large shell-model space and effective interactions evaluated from realistic two-nucleon potentials. For a fuller account, see ref. [1].
Ab Initio No-Core Shell Model Calculations Using Realistic Two- and Three-Body Interactions
Energy Technology Data Exchange (ETDEWEB)
Navratil, P; Ormand, W E; Forssen, C; Caurier, E
2004-11-30
There has been significant progress in the ab initio approaches to the structure of light nuclei. One such method is the ab initio no-core shell model (NCSM). Starting from realistic two- and three-nucleon interactions this method can predict low-lying levels in p-shell nuclei. In this contribution, we present a brief overview of the NCSM with examples of recent applications. We highlight our study of the parity inversion in {sup 11}Be, for which calculations were performed in basis spaces up to 9{Dirac_h}{Omega} (dimensions reaching 7 x 10{sup 8}). We also present our latest results for the p-shell nuclei using the Tucson-Melbourne TM three-nucleon interaction with several proposed parameter sets.
A viscoplastic model of expanding cylindrical shells subject to internal explosive detonations
Energy Technology Data Exchange (ETDEWEB)
Martineau, R.L.; Anderson, C.A. [Los Alamos National Lab., NM (United States); Smith, F.W. [Colorado State Univ., Fort Collins, CO (United States)
1998-12-31
Thin cylindrical shells subjected to internal explosive detonations expand outwardly at strain-rates on the order 10{sup 4} s{sup {minus}1}. At approximately 150% strain, multiple plastic instabilities appear on the surface of these shells in a quasi-periodic pattern. These instabilities continue to develop into bands of localized shear and eventually form cracks that progress in a way that causes the shell to break into fragments. The entire process takes less than 100 microseconds from detonation to complete fragmentation. Modeling this high strain-rate expansion and generation of instabilities prior to fragmentation is the primary focus of this paper. Applications for this research include hypervelocity accelerators, flux compression generators, and explosive containment vessels for terrorist threats and power plants.
Modelling and Dynamic Response of Steel Reticulated Shell under Blast Loading
Directory of Open Access Journals (Sweden)
Ximei Zhai
2013-01-01
Full Text Available Explicit finite element programme LS-DYNA was used to simulate a long-span steel reticulated shell under blast loading to investigate the structural dynamic responses in this paper. The elaborate finite element model of the Kiewitt-8 single-layer reticulated shell with span of 40 m subjected to central blast loading was established and all the process from the detonation of the explosive charge to the demolition, including the propagation of the blast wave and its interaction with structure was reproduced. The peak overpressure from the numerical analysis was compared with empirical formulas to verify the credibility and applicability of numerical simulation for blast loading. The dynamic responses of the structure under blast loading with different TNT equivalent weights of explosive and rise-span ratios were obtained. In addition, the response types of Kiewitt-8 single-layer reticulated shell subjected to central explosive blast loading were defined.
Simulation of low Schottky barrier MOSFETs using an improved Multi-subband Monte Carlo model
Gudmundsson, Valur; Palestri, Pierpaolo; Hellström, Per-Erik; Selmi, Luca; Östling, Mikael
2013-01-01
We present a simple and efficient approach to implement Schottky barrier contacts in a Multi-subband Monte Carlo simulator by using the subband smoothening technique to mimic tunneling at the Schottky junction. In the absence of scattering, simulation results for Schottky barrier MOSFETs are in agreement with ballistic Non-Equilibrium Green's Functions calculations. We then include the most relevant scattering mechanisms, and apply the model to the study of double gate Schottky barrier MOSFETs representative of the ITRS 2015 high performance device. Results show that a Schottky barrier height of less than approximately 0.15 eV is required to outperform the doped source/drain structure.
Hybrid Parallel Programming Models for AMR Neutron Monte-Carlo Transport
Dureau, David; Poëtte, Gaël
2014-06-01
This paper deals with High Performance Computing (HPC) applied to neutron transport theory on complex geometries, thanks to both an Adaptive Mesh Refinement (AMR) algorithm and a Monte-Carlo (MC) solver. Several Parallelism models are presented and analyzed in this context, among them shared memory and distributed memory ones such as Domain Replication and Domain Decomposition, together with Hybrid strategies. The study is illustrated by weak and strong scalability tests on complex benchmarks on several thousands of cores thanks to the petaflopic supercomputer Tera100.
Studies on top-quark Monte Carlo modelling for Top2016
The ATLAS collaboration
2016-01-01
This note summarises recent studies on Monte Carlo simulation setups of top-quark pair production used by the ATLAS experiment and presents a new method to deal with interference effects for the $Wt$ single-top-quark production which is compared against previous techniques. The main focus for the top-quark pair production is on the improvement of the modelling of the Powheg generator interfaced to the Pythia8 and Herwig7 shower generators. The studies are done using unfolded data at centre-of-mass energies of 7, 8, and 13 TeV.
Monte Carlo simulation of Prussian blue analogs described by Heisenberg ternary alloy model
Yüksel, Yusuf
2015-11-01
Within the framework of Monte Carlo simulation technique, we simulate magnetic behavior of Prussian blue analogs based on Heisenberg ternary alloy model. We present phase diagrams in various parameter spaces, and we compare some of our results with those based on Ising counterparts. We clarify the variations of transition temperature and compensation phenomenon with mixing ratio of magnetic ions, exchange interactions, and exchange anisotropy in the present ferro-ferrimagnetic Heisenberg system. According to our results, thermal variation of the total magnetization curves may exhibit N, L, P, Q, R type behaviors based on the Néel classification scheme.
Rejection-free Monte Carlo algorithms for models with continuous degrees of freedom.
Muñoz, J D; Novotny, M A; Mitchell, S J
2003-02-01
We construct a rejection-free Monte Carlo algorithm for a system with continuous degrees of freedom. We illustrate the algorithm by applying it to the classical three-dimensional Heisenberg model with canonical Metropolis dynamics. We obtain the lifetime of the metastable state following a reversal of the external magnetic field. Our rejection-free algorithm obtains results in agreement with a direct implementation of the Metropolis dynamic and requires orders of magnitude less computational time at low temperatures. The treatment is general and can be extended to other dynamics and other systems with continuous degrees of freedom.
DEFF Research Database (Denmark)
Blasone, Roberta-Serena; Madsen, Henrik; Rosbjerg, Dan
2008-01-01
uncertainty estimation (GLUE) procedure based on Markov chain Monte Carlo sampling is applied in order to improve the performance of the methodology in estimating parameters and posterior output distributions. The description of the spatial variations of the hydrological processes is accounted for by defining...... the identifiability of the parameters and results in satisfactory multi-variable simulations and uncertainty estimates. However, the parameter uncertainty alone cannot explain the total uncertainty at all the sites, due to limitations in the distributed data included in the model calibration. The study also indicates...
Variational Monte Carlo study of magnetic states in the periodic Anderson model
Kubo, Katsunori
2015-03-01
We study the magnetic states of the periodic Anderson model with a finite Coulomb interaction between f electrons on a square lattice by applying variational Monte Carlo method. We consider Gutzwiller wavefunctions for the paramagnetic, antiferromagnetic, ferromagnetic, and charge density wave states. We find an antiferromagnetic phase around half-filling. There is a phase transition accompanying change in the Fermi-surface topology in this antiferromagnetic phase. We also study a case away from half-filling, and find a ferromagnetic state as the ground state there.
A study of potential energy curves from the model space quantum Monte Carlo method
Energy Technology Data Exchange (ETDEWEB)
Ohtsuka, Yuhki; Ten-no, Seiichiro, E-mail: tenno@cs.kobe-u.ac.jp [Department of Computational Sciences, Graduate School of System Informatics, Kobe University, Nada-ku, Kobe 657-8501 (Japan)
2015-12-07
We report on the first application of the model space quantum Monte Carlo (MSQMC) to potential energy curves (PECs) for the excited states of C{sub 2}, N{sub 2}, and O{sub 2} to validate the applicability of the method. A parallel MSQMC code is implemented with the initiator approximation to enable efficient sampling. The PECs of MSQMC for various excited and ionized states are compared with those from the Rydberg-Klein-Rees and full configuration interaction methods. The results indicate the usefulness of MSQMC for precise PECs in a wide range obviating problems concerning quasi-degeneracy.
Energy Technology Data Exchange (ETDEWEB)
Gu, M; Schmidt, M; Beiersdorfer, P; Chen, H; Thorn, D B; Tr?bert, E; Behar, E; Kahn, S M
2005-02-05
We present high resolution laboratory spectra of K-shell X-ray lines from inner-shell excited and ionized ions of oxygen, obtained with a reflection grating spectrometer on the electron beam ion trap (EBIT-I) at the Lawrence Livermore National Laboratory. Only with a multi-ion model including all major atomic collisional and radiative processes, are we able to identify the observed K-shell transitions of oxygen ions from O III to O VI. The wavelengths and associated errors for some of the strongest transitions are given, taking into account both the experimental and modeling uncertainties. The present data should be useful in identifying the absorption features present in astrophysical sources, such as active galactic nuclei and X-ray binaries. They are also useful in providing benchmarks for the testing of theoretical atomic structure calculations.
Caffarel, Michel; Giner, Emmanuel; Scemama, Anthony; Ramírez-Solís, Alejandro
2014-12-09
We present a comparative study of the spatial distribution of the spin density of the ground state of CuCl2 using Density Functional Theory (DFT), quantum Monte Carlo (QMC), and post-Hartree-Fock wave function theory (WFT). A number of studies have shown that an accurate description of the electronic structure of the lowest-lying states of this molecule is particularly challenging due to the interplay between the strong dynamical correlation effects in the 3d shell and the delocalization of the 3d hole over the chlorine atoms. More generally, this problem is representative of the difficulties encountered when studying open-shell metal-containing molecular systems. Here, it is shown that qualitatively different results for the spin density distribution are obtained from the various quantum-mechanical approaches. At the DFT level, the spin density distribution is found to be very dependent on the functional employed. At the QMC level, Fixed-Node Diffusion Monte Carlo (FN-DMC) results are strongly dependent on the nodal structure of the trial wave function. Regarding wave function methods, most approaches not including a very high amount of dynamic correlation effects lead to a much too high localization of the spin density on the copper atom, in sharp contrast with DFT. To shed some light on these conflicting results Full CI-type (FCI) calculations using the 6-31G basis set and based on a selection process of the most important determinants, the so-called CIPSI approach (Configuration Interaction with Perturbative Selection done Iteratively) are performed. Quite remarkably, it is found that for this 63-electron molecule and a full CI space including about 10(18) determinants, the FCI limit can almost be reached. Putting all results together, a natural and coherent picture for the spin distribution is proposed.
Proceedings of a symposium on the occasion of the 40th anniversary of the nuclear shell model
Energy Technology Data Exchange (ETDEWEB)
Lee, T.S.H.; Wiringa, R.B. (eds.)
1990-03-01
This report contains papers on the following topics: excitation of 1p-1h stretched states with the (p,n) reaction as a test of shell-model calculations; on Z=64 shell closure and some high spin states of {sup 149}Gd and {sup 159}Ho; saturating interactions in {sup 4}He with density dependence; are short-range correlations visible in very large-basis shell-model calculations ; recent and future applications of the shell model in the continuum; shell model truncation schemes for rotational nuclei; the particle-hole interaction and high-spin states near A-16; magnetic moment of doubly closed shell +1 nucleon nucleus {sup 41}Sc(I{sup {pi}}=7/2{sup {minus}}); the new magic nucleus {sup 96}Zr; comparing several boson mappings with the shell model; high spin band structures in {sup 165}Lu; optical potential with two-nucleon correlations; generalized valley approximation applied to a schematic model of the monopole excitation; pair approximation in the nuclear shell model; and many-particle, many-hole deformed states.
The fundamental solution for a consistent complex model of the shallow shell equations
Matthew P. Coleman
1999-01-01
The calculation of the Fourier transforms of the fundamental solution in shallow shell theory ostensibly was accomplished by J. L. Sanders [J. Appl. Mech. 37 (1970), 361-366]. However, as is shown in detail in this paper, the complex model used by Sanders is, in fact, inconsistent. This paper provides a consistent version of Sanders's complex model, along with the Fourier transforms of the fundamental solution for this corrected model. The inverse Fourier transforms are then calculated for th...
Modelling of scintillator based flat-panel detectors with Monte-Carlo simulations
Reims, N.; Sukowski, F.; Uhlmann, N.
2011-01-01
Scintillator based flat panel detectors are state of the art in the field of industrial X-ray imaging applications. Choosing the proper system and setup parameters for the vast range of different applications can be a time consuming task, especially when developing new detector systems. Since the system behaviour cannot always be foreseen easily, Monte-Carlo (MC) simulations are keys to gain further knowledge of system components and their behaviour for different imaging conditions. In this work we used two Monte-Carlo based models to examine an indirect converting flat panel detector, specifically the Hamamatsu C9312SK. We focused on the signal generation in the scintillation layer and its influence on the spatial resolution of the whole system. The models differ significantly in their level of complexity. The first model gives a global description of the detector based on different parameters characterizing the spatial resolution. With relatively small effort a simulation model can be developed which equates the real detector regarding signal transfer. The second model allows a more detailed insight of the system. It is based on the well established cascade theory, i.e. describing the detector as a cascade of elemental gain and scattering stages, which represent the built in components and their signal transfer behaviour. In comparison to the first model the influence of single components especially the important light spread behaviour in the scintillator can be analysed in a more differentiated way. Although the implementation of the second model is more time consuming both models have in common that a relatively small amount of system manufacturer parameters are needed. The results of both models were in good agreement with the measured parameters of the real system.
Iterative optimisation of Monte Carlo detector models using measurements and simulations
Energy Technology Data Exchange (ETDEWEB)
Marzocchi, O., E-mail: olaf@marzocchi.net [European Patent Office, Rijswijk (Netherlands); Leone, D., E-mail: debora.leone@kit.edu [Institute for Nuclear Waste Disposal, Karlsruhe Institute of Technology, Karlsruhe (Germany)
2015-04-11
This work proposes a new technique to optimise the Monte Carlo models of radiation detectors, offering the advantage of a significantly lower user effort and therefore an improved work efficiency compared to the prior techniques. The method consists of four steps, two of which are iterative and suitable for automation using scripting languages. The four steps consist in the acquisition in the laboratory of measurement data to be used as reference; the modification of a previously available detector model; the simulation of a tentative model of the detector to obtain the coefficients of a set of linear equations; the solution of the system of equations and the update of the detector model. Steps three and four can be repeated for more accurate results. This method avoids the “try and fail” approach typical of the prior techniques.
Hertog, Maarten L. A. T. M.; Scheerlinck, Nico; Nicolaï, Bart M.
2009-01-01
When modelling the behaviour of horticultural products, demonstrating large sources of biological variation, we often run into the issue of non-Gaussian distributed model parameters. This work presents an algorithm to reproduce such correlated non-Gaussian model parameters for use with Monte Carlo simulations. The algorithm works around the problem of non-Gaussian distributions by transforming the observed non-Gaussian probability distributions using a proposed SKN-distribution function before applying the covariance decomposition algorithm to generate Gaussian random co-varying parameter sets. The proposed SKN-distribution function is based on the standard Gaussian distribution function and can exhibit different degrees of both skewness and kurtosis. This technique is demonstrated using a case study on modelling the ripening of tomato fruit evaluating the propagation of biological variation with time.
Monte Carlo Simulation of a Novel Classical Spin Model with a Tricritical Point
Cary, Tyler; Scalettar, Richard; Singh, Rajiv
Recent experimental findings along with motivation from the well known Blume-Capel model has led to the development of a novel two-dimensional classical spin model defined on a square lattice. This model consists of two Ising spin species per site with each species interacting with its own kind as perpendicular one dimensional Ising chains along with complex and frustrating interactions between species. Probing this model with Mean Field Theory, Metropolis Monte Carlo, and Wang Landau sampling has revealed a rich phase diagram which includes a tricritical point separating a first order magnetic phase transition from a continuous one, along with three ordered phases. Away from the tricritical point, the expected 2D Ising critical exponents have been recovered. Ongoing work focuses on finding the tricritical exponents and their connection to a supersymmetric critical point.
DEFF Research Database (Denmark)
Tycho, Andreas; Jørgensen, Thomas Martini; Andersen, Peter E.
2002-01-01
A Monte Carlo (MC) method for modeling optical coherence tomography (OCT) measurements of a diffusely reflecting discontinuity emb edded in a scattering medium is presented. For the first time to the authors' knowledge it is shown analytically that the applicability of an MC approach to this opti......A Monte Carlo (MC) method for modeling optical coherence tomography (OCT) measurements of a diffusely reflecting discontinuity emb edded in a scattering medium is presented. For the first time to the authors' knowledge it is shown analytically that the applicability of an MC approach...... to this optical geometry is firmly justified, because, as we show, in the conjugate image plane the field reflected from the sample is delta-correlated from which it follows that the heterodyne signal is calculated from the intensity distribution only. This is not a trivial result because, in general, the light...... focused beam, and it is shown that in free space the full three-dimensional intensity distribution of a Gaussian beam is obtained. The OCT signal and the intensity distribution in a scattering medium have been obtained for several geometries with the suggested MC method; when this model and a recently...
Evaluation of angular scattering models for electron-neutral collisions in Monte Carlo simulations
Janssen, J. F. J.; Pitchford, L. C.; Hagelaar, G. J. M.; van Dijk, J.
2016-10-01
In Monte Carlo simulations of electron transport through a neutral background gas, simplifying assumptions related to the shape of the angular distribution of electron-neutral scattering cross sections are usually made. This is mainly because full sets of differential scattering cross sections are rarely available. In this work simple models for angular scattering are compared to results from the recent quantum calculations of Zatsarinny and Bartschat for differential scattering cross sections (DCS’s) from zero to 200 eV in argon. These simple models represent in various ways an approach to forward scattering with increasing electron energy. The simple models are then used in Monte Carlo simulations of range, straggling, and backscatter of electrons emitted from a surface into a volume filled with a neutral gas. It is shown that the assumptions of isotropic elastic scattering and of forward scattering for the inelastic collision process yield results within a few percent of those calculated using the DCS’s of Zatsarinny and Bartschat. The quantities which were held constant in these comparisons are the elastic momentum transfer and total inelastic cross sections.
FINITE ELEMENT FOR STRESS-STRAIN STATE MODELING OF TWO-LAYERED AXIALLY SYMMETRIC SHELLS
Directory of Open Access Journals (Sweden)
K. S. Kurochka
2015-07-01
Full Text Available Subject of Research. Computation of composite material designs requires application of numerical methods. The finiteelement method usage is connected with surface approximation problems. Application of volumetric and laminar elements leads to systems with large sizes and a great amount of computation. The objective of this paper is to present an equivalent two-layer mathematical model for evaluation of displacements and stresses of cross-ply laminated cone shells subjected to uniformly distributed load. An axially symmetric element for shell problems is described. Method. Axially symmetric finite element is proposed to be applied in calculations with use of correlation for the inner work of each layer separately. It gives the possibility to take into account geometric and physical nonlinearities and non-uniformity in the layers of the shell. Discrete mathematical model is created on the base of the finite-element method with the use of possible motions principle and Kirchhoff–Love assumptions. Hermite element is chosen as a finite one. Cone shell deflection is considered as the quantity sought for. Main Results. One-layered and two-layered cone shells have been considered for proposed mathematical model verification with known analytical and numerical analytical solutions, respectively. The axial displacements of the two-layered cone are measured with an error not exceeding 5.4 % for the number of finite elements equal to 30. The proposed mathematical model requires fewer nodes to define the finite element meshing of the system and much less computation time. Thereby time for finding solution decreases considerably. Practical Relevance. Proposed model is applicable for computation of multilayered designs under axially symmetric loads: composite high-pressure bottles, cylinder shaped fiberglass pipes, reservoirs for explosives and flammable materials, oil and gas storage tanks.
Korostil, Igor A; Peters, Gareth W; Cornebise, Julien; Regan, David G
2013-05-20
A Bayesian statistical model and estimation methodology based on forward projection adaptive Markov chain Monte Carlo is developed in order to perform the calibration of a high-dimensional nonlinear system of ordinary differential equations representing an epidemic model for human papillomavirus types 6 and 11 (HPV-6, HPV-11). The model is compartmental and involves stratification by age, gender and sexual-activity group. Developing this model and a means to calibrate it efficiently is relevant because HPV is a very multi-typed and common sexually transmitted infection with more than 100 types currently known. The two types studied in this paper, types 6 and 11, are causing about 90% of anogenital warts. We extend the development of a sexual mixing matrix on the basis of a formulation first suggested by Garnett and Anderson, frequently used to model sexually transmitted infections. In particular, we consider a stochastic mixing matrix framework that allows us to jointly estimate unknown attributes and parameters of the mixing matrix along with the parameters involved in the calibration of the HPV epidemic model. This matrix describes the sexual interactions between members of the population under study and relies on several quantities that are a priori unknown. The Bayesian model developed allows one to estimate jointly the HPV-6 and HPV-11 epidemic model parameters as well as unknown sexual mixing matrix parameters related to assortativity. Finally, we explore the ability of an extension to the class of adaptive Markov chain Monte Carlo algorithms to incorporate a forward projection strategy for the ordinary differential equation state trajectories. Efficient exploration of the Bayesian posterior distribution developed for the ordinary differential equation parameters provides a challenge for any Markov chain sampling methodology, hence the interest in adaptive Markov chain methods. We conclude with simulation studies on synthetic and recent actual data.
Clinical management and burden of prostate cancer: a Markov Monte Carlo model.
Directory of Open Access Journals (Sweden)
Chiranjeev Sanyal
Full Text Available BACKGROUND: Prostate cancer (PCa is the most common non-skin cancer among men in developed countries. Several novel treatments have been adopted by healthcare systems to manage PCa. Most of the observational studies and randomized trials on PCa have concurrently evaluated fewer treatments over short follow-up. Further, preceding decision analytic models on PCa management have not evaluated various contemporary management options. Therefore, a contemporary decision analytic model was necessary to address limitations to the literature by synthesizing the evidence on novel treatments thereby forecasting short and long-term clinical outcomes. OBJECTIVES: To develop and validate a Markov Monte Carlo model for the contemporary clinical management of PCa, and to assess the clinical burden of the disease from diagnosis to end-of-life. METHODS: A Markov Monte Carlo model was developed to simulate the management of PCa in men 65 years and older from diagnosis to end-of-life. Health states modeled were: risk at diagnosis, active surveillance, active treatment, PCa recurrence, PCa recurrence free, metastatic castrate resistant prostate cancer, overall and PCa death. Treatment trajectories were based on state transition probabilities derived from the literature. Validation and sensitivity analyses assessed the accuracy and robustness of model predicted outcomes. RESULTS: Validation indicated model predicted rates were comparable to observed rates in the published literature. The simulated distribution of clinical outcomes for the base case was consistent with sensitivity analyses. Predicted rate of clinical outcomes and mortality varied across risk groups. Life expectancy and health adjusted life expectancy predicted for the simulated cohort was 20.9 years (95%CI 20.5-21.3 and 18.2 years (95% CI 17.9-18.5, respectively. CONCLUSION: Study findings indicated contemporary management strategies improved survival and quality of life in patients with PCa. This
The First 24 Years of Reverse Monte Carlo Modelling, Budapest, Hungary, 20-22 September 2012
Keen, David A.; Pusztai, László
2013-11-01
This special issue contains a collection of papers reflecting the content of the fifth workshop on reverse Monte Carlo (RMC) methods, held in a hotel on the banks of the Danube in the Budapest suburbs in the autumn of 2012. Over fifty participants gathered to hear talks and discuss a broad range of science based on the RMC technique in very convivial surroundings. Reverse Monte Carlo modelling is a method for producing three-dimensional disordered structural models in quantitative agreement with experimental data. The method was developed in the late 1980s and has since achieved wide acceptance within the scientific community [1], producing an average of over 90 papers and 1200 citations per year over the last five years. It is particularly suitable for the study of the structures of liquid and amorphous materials, as well as the structural analysis of disordered crystalline systems. The principal experimental data that are modelled are obtained from total x-ray or neutron scattering experiments, using the reciprocal space structure factor and/or the real space pair distribution function (PDF). Additional data might be included from extended x-ray absorption fine structure spectroscopy (EXAFS), Bragg peak intensities or indeed any measured data that can be calculated from a three-dimensional atomistic model. It is this use of total scattering (diffuse and Bragg), rather than just the Bragg peak intensities more commonly used for crystalline structure analysis, which enables RMC modelling to probe the often important deviations from the average crystal structure, to probe the structures of poorly crystalline or nanocrystalline materials, and the local structures of non-crystalline materials where only diffuse scattering is observed. This flexibility across various condensed matter structure-types has made the RMC method very attractive in a wide range of disciplines, as borne out in the contents of this special issue. It is however important to point out that since
Caffarel, Michel; Scemama, Anthony; Ramírez-Solís, Alejandro
2014-01-01
We present a comparative study of the spatial distribution of the spin density (SD) of the ground state of CuCl2 using Density Functional Theory (DFT), quantum Monte Carlo (QMC), and post-Hartree-Fock wavefunction theory (WFT). A number of studies have shown that an accurate description of the electronic structure of the lowest-lying states of this molecule is particularly challenging due to the interplay between the strong dynamical correlation effects in the 3d shell of the copper atom and the delocalization of the 3d hole over the chlorine atoms. It is shown here that qualitatively different results for SD are obtained from these various quantum-chemical approaches. At the DFT level, the spin density distribution is directly related to the amount of Hartree-Fock exchange introduced in hybrid functionals. At the QMC level, Fixed-node Diffusion Monte Carlo (FN-DMC) results for SD are strongly dependent on the nodal structure of the trial wavefunction employed (here, Hartree-Fock or Kohn-Sham with a particula...
Maleki, Mahboubeh; Amani-Tehran, Mohammad; Latifi, Masoud; Mathur, Sanjay
2014-01-01
Release profile of drug constituent encapsulated in electrospun core-shell nanofibrous mats was modeled by Peppas equation and artificial neural network. Core-shell fibers were fabricated by co-axial electrospinning process using tetracycline hydrochloride (TCH) as the core and poly(l-lactide-co-glycolide) (PLGA) or polycaprolactone (PCL) as the shell materials. The density and hydrophilicity of the shell polymers, feed rates and concentrations of core and shell phases, the contribution of TCH in core material and electrical field were the parameters fed to the perceptron network to predict Peppas constants in order to derive release pattern. This study demonstrated the viability of the prediction tool in determining drug release profile of electrospun core-shell nanofibrous scaffolds.
Abrosimov, N. A.
1999-11-01
Nonlinear three-dimensional problems of dynamic deformation, buckling, and posteritical behavior of composite shell structures under pulsed loads are analyzed. The structure is assumed to be made of rigidly joined plates and shells of revolution along the lines coinciding with the coordinate directions of the joined elements. Individual structural elements can be made of both composite and conventional isotropic materials. The kinematic model of deformation of the structural elements is based on Timoshenko-type hypotheses. This approach is oriented to the calculation of nonstationary deformation processes in composite structures under small deformations but large displacements and rotation angles, and is implemented in the context of a simplified version of the geometrically nonlinear theory of shells. The physical relations in the composite structural elements are based on the theory of effective moduli for individual layers or for the package as a whole, whereas in the metallic elements this is done in the framework of the theory of plastic flow. The equations of motion of a composite shell structure are derived based on the principle of virtual displacements with some additional conditions allowing for the joint operation of structural elements. To solve the initial boundary-value problem formulated, an efficient numerical method is developed based on the finite-difference discretization of variational equations of motion in space variables and an explicit second-order time-integration scheme. The permissible time-integration step is determined using Neumann's spectral criterion. The above method is especially efficient in calculating thin-walled shells, as well as in the case of local loads acting on the structural element, when the discretization grid has to be condensed in the zones of rapidly changing solutions in space variables. The results of analyzing the nonstationary deformation processes and critical loads are presented for composite and isotropic
Wheeler, M
2013-01-01
We study the scalar product S_{l,m} between an on-shell and an off-shell Bethe state in models with SU(3)-invariance, where l and m denote the cardinalities of the two sets of Bethe roots. We construct recursion relations relating S_{l,m} to scalar products of smaller dimension, namely S_{l-1,m} and S_{l,m-1}. Solving these recursion relations we obtain new multiple integral expressions for S_{l,m}, whose integrands are (l+m) \\times (l+m) determinants, and closely related to the Slavnov determinant expression for the SU(2) scalar product.
Fraenkel, Dan
2015-01-13
A recent Monte Carlo (MC) simulation study of the primitive model (PM) of ionic solutions ( Abbas, Z. et al. J. Phys. Chem. B 2009 , 113 , 5905 ) has resulted in an extensive "mapping" of real aqueous solutions of 1-1, 2-1, and 3-1 binary electrolytes and a list of "recommended ionic radii" for many ions. For the smaller cations, the model-experiment fitting process gave much larger radii than the respective crystallographic radii, and those cations were therefore claimed to be hydrated. In Part 1 (DOI 10.1021/ct5006938 ) of the present work, the above study for the unrestricted PM - dubbed MC-UPM - has been confronted with the Smaller-ion Shell (SiS) treatment ( Fraenkel, D. Mol. Phys. 2010 , 108 , 1435 ), or "DH-SiS", by comparing the range and quality of model-experiment fits of the mean ionic activity coefficient as a function of ionic concentration. Here I compare the ion-size parameters (ISPs) of "best fit" of the two models and argue that since ISPs derived from DH-SiS are identical with (or close to) crystallographic or thermochemical ionic diameters for both cations and anions, and they do not depend on the counterion - they are more reliable, as physicochemical entities, than the PM-derived "recommended ionic radii".
Predictive uncertainty analysis of a saltwater intrusion model using null-space Monte Carlo
DEFF Research Database (Denmark)
Herckenrath, Daan; Langevin, Christian D.; Doherty, John
2011-01-01
Because of the extensive computational burden and perhaps a lack of awareness of existing methods, rigorous uncertainty analyses are rarely conducted for variable-density flow and transport models. For this reason, a recently developed null-space Monte Carlo (NSMC) method for quantifying predicti...... was compared with that computed through linear analysis. The results were in good agreement, with the NSMC method estimate showing a slightly smaller range of prediction uncertainty than was calculated by the linear method.......Because of the extensive computational burden and perhaps a lack of awareness of existing methods, rigorous uncertainty analyses are rarely conducted for variable-density flow and transport models. For this reason, a recently developed null-space Monte Carlo (NSMC) method for quantifying prediction....... Random noise was added to the observations to approximate realistic field conditions. The NSMC method was used to calculate 1000 calibration-constrained parameter fields. If the dimensionality of the solution space was set appropriately, the estimated uncertainty range from the NSMC analysis encompassed...
A Monte-Carlo based model of the AX-PET demonstrator and its experimental validation.
Solevi, P; Oliver, J F; Gillam, J E; Bolle, E; Casella, C; Chesi, E; De Leo, R; Dissertori, G; Fanti, V; Heller, M; Lai, M; Lustermann, W; Nappi, E; Pauss, F; Rudge, A; Ruotsalainen, U; Schinzel, D; Schneider, T; Séguinot, J; Stapnes, S; Weilhammer, P; Tuna, U; Joram, C; Rafecas, M
2013-08-21
AX-PET is a novel PET detector based on axially oriented crystals and orthogonal wavelength shifter (WLS) strips, both individually read out by silicon photo-multipliers. Its design decouples sensitivity and spatial resolution, by reducing the parallax error due to the layered arrangement of the crystals. Additionally the granularity of AX-PET enhances the capability to track photons within the detector yielding a large fraction of inter-crystal scatter events. These events, if properly processed, can be included in the reconstruction stage further increasing the sensitivity. Its unique features require dedicated Monte-Carlo simulations, enabling the development of the device, interpreting data and allowing the development of reconstruction codes. At the same time the non-conventional design of AX-PET poses several challenges to the simulation and modeling tasks, mostly related to the light transport and distribution within the crystals and WLS strips, as well as the electronics readout. In this work we present a hybrid simulation tool based on an analytical model and a Monte-Carlo based description of the AX-PET demonstrator. It was extensively validated against experimental data, providing excellent agreement.
Optical model for port-wine stain skin and its Monte Carlo simulation
Xu, Lanqing; Xiao, Zhengying; Chen, Rong; Wang, Ying
2008-12-01
Laser irradiation is the most acceptable therapy for PWS patient at present time. Its efficacy is highly dependent on the energy deposition rules in skin. To achieve optimal PWS treatment parameters a better understanding of light propagation in PWS skin is indispensable. Traditional Monte Carlo simulations using simple geometries such as planar layer tissue model can not provide energy deposition in the skin with enlarged blood vessels. In this paper the structure of normal skin and the pathological character of PWS skin was analyzed in detail and the true structure were simplified into a hybrid layered mathematical model to character two most important aspects of PWS skin: layered structure and overabundant dermal vessels. The basic laser-tissue interaction mechanisms in skin were investigated and the optical parameters of PWS skin tissue at the therapeutic wavelength. Monte Carlo (MC) based techniques were choused to calculate the energy deposition in the skin. Results can be used in choosing optical dosage. Further simulations can be used to predict optimal laser parameters to achieve high-efficacy laser treatment of PWS.
An Efficient Monte Carlo Method for Modeling Radiative Transfer in Protoplanetary Disks
Kim, Stacy
2011-01-01
Monte Carlo methods have been shown to be effective and versatile in modeling radiative transfer processes to calculate model temperature profiles for protoplanetary disks. Temperatures profiles are important for connecting physical structure to observation and for understanding the conditions for planet formation and migration. However, certain areas of the disk such as the optically thick disk interior are under-sampled, or are of particular interest such as the snow line (where water vapor condenses into ice) and the area surrounding a protoplanet. To improve the sampling, photon packets can be preferentially scattered and reemitted toward the preferred locations at the cost of weighting packet energies to conserve the average energy flux. Here I report on the weighting schemes developed, how they can be applied to various models, and how they affect simulation mechanics and results. We find that improvements in sampling do not always imply similar improvements in temperature accuracies and calculation speeds.
Dynamic Value at Risk: A Comparative Study Between Heteroscedastic Models and Monte Carlo Simulation
Directory of Open Access Journals (Sweden)
José Lamartine Távora Junior
2006-12-01
Full Text Available The objective of this paper was to analyze the risk management of a portfolio composed by Petrobras PN, Telemar PN and Vale do Rio Doce PNA stocks. It was verified if the modeling of Value-at-Risk (VaR through the place Monte Carlo simulation with volatility of GARCH family is supported by hypothesis of efficient market. The results have shown that the statistic evaluation in inferior to dynamics, evidencing that the dynamic analysis supplies support to the hypothesis of efficient market of the Brazilian share holding market, in opposition of some empirical evidences. Also, it was verified that the GARCH models of volatility is enough to accommodate the variations of the shareholding Brazilian market, since the model is capable to accommodate the great dynamic of the Brazilian market.
Core-scale solute transport model selection using Monte Carlo analysis
Malama, Bwalya; Kuhlman, Kristopher L.; James, Scott C.
2013-06-01
Model applicability to core-scale solute transport is evaluated using breakthrough data from column experiments conducted with conservative tracers tritium (3H) and sodium-22 (22Na ), and the retarding solute uranium-232 (232U). The three models considered are single-porosity, double-porosity with single-rate mobile-immobile mass-exchange, and the multirate model, which is a deterministic model that admits the statistics of a random mobile-immobile mass-exchange rate coefficient. The experiments were conducted on intact Culebra Dolomite core samples. Previously, data were analyzed using single-porosity and double-porosity models although the Culebra Dolomite is known to possess multiple types and scales of porosity, and to exhibit multirate mobile-immobile-domain mass transfer characteristics at field scale. The data are reanalyzed here and null-space Monte Carlo analysis is used to facilitate objective model selection. Prediction (or residual) bias is adopted as a measure of the model structural error. The analysis clearly shows single-porosity and double-porosity models are structurally deficient, yielding late-time residual bias that grows with time. On the other hand, the multirate model yields unbiased predictions consistent with the late-time -5/2 slope diagnostic of multirate mass transfer. The analysis indicates the multirate model is better suited to describing core-scale solute breakthrough in the Culebra Dolomite than the other two models.
Evidence for Symplectic Symmetry in Ab Initio No-Core Shell Model Results for Light Nuclei
Energy Technology Data Exchange (ETDEWEB)
Dytrych, Tomas; Sviratcheva, Kristina D.; Bahri, Chairul; Draayer, Jerry P.; /Louisiana State U.; Vary, James P.; /Iowa State U. /LLNL, Livermore /SLAC
2007-04-24
Clear evidence for symplectic symmetry in low-lying states of {sup 12}C and {sup 16}O is reported. Eigenstates of {sup 12}C and {sup 16}O, determined within the framework of the no-core shell model using the JISP16 NN realistic interaction, typically project at the 85-90% level onto a few of the most deformed symplectic basis states that span only a small fraction of the full model space. The results are nearly independent of whether the bare or renormalized effective interactions are used in the analysis. The outcome confirms Elliott's SU(3) model which underpins the symplectic scheme, and above all, points to the relevance of a symplectic no-core shell model that can reproduce experimental B(E2) values without effective charges as well as deformed spatial modes associated with clustering phenomena in nuclei.
The Density Matrix Renormalization Group Method and Large-Scale Nuclear Shell-Model Calculations
Dimitrova, S S; Pittel, S; Stoitsov, M V
2002-01-01
The particle-hole Density Matrix Renormalization Group (p-h DMRG) method is discussed as a possible new approach to large-scale nuclear shell-model calculations. Following a general description of the method, we apply it to a class of problems involving many identical nucleons constrained to move in a single large j-shell and to interact via a pairing plus quadrupole interaction. A single-particle term that splits the shell into degenerate doublets is included so as to accommodate the physics of a Fermi surface in the problem. We apply the p-h DMRG method to this test problem for two $j$ values, one for which the shell model can be solved exactly and one for which the size of the hamiltonian is much too large for exact treatment. In the former case, the method is able to reproduce the exact results for the ground state energy, the energies of low-lying excited states, and other observables with extreme precision. In the latter case, the results exhibit rapid exponential convergence, suggesting the great promi...
Full modelling of the MOSAIC animal PET system based on the GATE Monte Carlo simulation code
Merheb, C.; Petegnief, Y.; Talbot, J. N.
2007-02-01
Positron emission tomography (PET) systems dedicated to animal imaging are now widely used for biological studies. The scanner performance strongly depends on the design and the characteristics of the system. Many parameters must be optimized like the dimensions and type of crystals, geometry and field-of-view (FOV), sampling, electronics, lightguide, shielding, etc. Monte Carlo modelling is a powerful tool to study the effect of each of these parameters on the basis of realistic simulated data. Performance assessment in terms of spatial resolution, count rates, scatter fraction and sensitivity is an important prerequisite before the model can be used instead of real data for a reliable description of the system response function or for optimization of reconstruction algorithms. The aim of this study is to model the performance of the Philips Mosaic™ animal PET system using a comprehensive PET simulation code in order to understand and describe the origin of important factors that influence image quality. We use GATE, a Monte Carlo simulation toolkit for a realistic description of the ring PET model, the detectors, shielding, cap, electronic processing and dead times. We incorporate new features to adjust signal processing to the Anger logic underlying the Mosaic™ system. Special attention was paid to dead time and energy spectra descriptions. Sorting of simulated events in a list mode format similar to the system outputs was developed to compare experimental and simulated sensitivity and scatter fractions for different energy thresholds using various models of phantoms describing rat and mouse geometries. Count rates were compared for both cylindrical homogeneous phantoms. Simulated spatial resolution was fitted to experimental data for 18F point sources at different locations within the FOV with an analytical blurring function for electronic processing effects. Simulated and measured sensitivities differed by less than 3%, while scatter fractions agreed
Nuclear Chaotic Behavior in a Two-j Shell Coupled with a Rotor Model
Institute of Scientific and Technical Information of China (English)
GUO Lu; ZHOU XianRong; MENG Jie; ZHAO EnGuang
2002-01-01
The chaotic properties for six particles interacting by a monopolc pairing force in a two-.j stiell modelcoupled with a deformed core are studied in the frame of particle-rotor model. The nearest-neighbor distribution ofenergy levels and spectral rigidity in the two-j shell arc compared with those in the single-j case. The result, s show thatthe system is more regular in the two-j model than that in the single-j case.
Triaxial projected shell model study of chiral rotation in odd-odd nuclei
Energy Technology Data Exchange (ETDEWEB)
Bhat, G.H. [Department of Physics, University of Kashmir, Srinagar, 190 006 (India); Sheikh, J.A. [Department of Physics, University of Kashmir, Srinagar, 190 006 (India); Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 (United States); Palit, R., E-mail: palit@tifr.res.in [Department of Nuclear and Atomic Physics, Tata Institute of Fundamental Research, Colaba, Mumbai, 400 005 (India)
2012-01-20
Chiral rotation observed in {sup 128}Cs is studied using the newly developed microscopic triaxial projected shell model (TPSM) approach. The observed energy levels and the electromagnetic transition probabilities of the nearly degenerate chiral dipole bands in this isotope are well reproduced by the present model. This demonstrates the broad applicability of the TPSM approach, based on a schematic interaction and angular-momentum projection technique, to explain a variety of low- and high-spin phenomena in triaxial rotating nuclei.
Shell model estimate of electric dipole moments in medium and heavy nuclei
Teruya, E.; Yoshinaga, N.; Higashiyama, K.
2014-03-01
It is evidence for an extension of the Standard Model in particle physics, if static electric dipole moments (EDMs) are measured for any elementary particle. The nuclear EDM arises mainly from two sources: one comes from asymmetric charge distribution in a nucleus and the other is due to the nucleon intrinsic EDM. We estimate the nuclear EDMs from two sources for the 1/21+ states in Xe isotopes by a shell model approach using full orbitals between magic numbers 50 and 82.
Itagaki, N.; Matsuno, H.; Suhara, T.
2016-09-01
The antisymmetrized quasi-cluster model (AQCM) is a method to describe transitions from the α cluster wave functions to jj-coupling shell model wave functions. In this model, the cluster-shell transition is characterized by only two parameters: R representing the distance between α clusters and Λ describing the breaking of α clusters. The contribution of the spin-orbit interaction, very important in the jj-coupling shell model, can be taken into account starting with the α cluster model wave function. In this article we show the generality of AQCM by extending the application to heavier regions: various 4N nuclei from 4He to 100Sn. The characteristic magic numbers of the jj-coupling shell model, 28 and 50, are described starting with the α cluster model. The competition of two different configurations is discussed in 20Ne (16O + one quasi-cluster and 12C + two quasi-clusters) and 28Si (pentagon shape of five quasi-clusters and 12C + 16O). Also, we compare the energy curves for the α + 40Ca cluster configuration calculated with and without the α breaking effect in 44Ti.
US Fish and Wildlife Service, Department of the Interior — This Sea-Level Affecting Marshes Model (SLAMM) report presents a model for projecting the effects of sea-level rise on coastal marshes and related habitats on Shell...
DEFF Research Database (Denmark)
Nielsen, Bo Bjerregaard; Nielsen, Martin S.; Santos, Ilmar
2017-01-01
The work gives a theoretical and experimental contribution to the problem of smart materials connected to double curved flexible shells. In the theoretical part the finite element modeling of a double curved flexible shell with a piezoelectric fiber patch with interdigitated electrodes (IDEs...
Praus, Petr; Svoboda, Ladislav; Tokarský, Jonáš; Hospodková, Alice; Klemm, Volker
2014-02-01
Core/shell CdS/ZnS nanoparticles were modelled in the Material Studio environment and synthesized by one-pot procedure. The core CdS radius size and thickness of the ZnS shell composed of 1-3 ZnS monolayers were predicted from the molecular models. From UV-vis absorption spectra of the CdS/ZnS colloid dispersions transition energies of CdS and ZnS nanostructures were calculated. They indicated penetration of electrons and holes from the CdS core into the ZnS shell and relaxation strain in the ZnS shell structure. The transitions energies were used for calculation of the CdS core radius by the Schrödinger equation. Both the relaxation strain in ZnS shells and the size of the CdS core radius were predicted by the molecular modelling. The ZnS shell thickness and a degree of the CdS core coverage were characterized by the photocatalytic decomposition of Methylene Blue (MB) using CdS/ZnS nanoparticles as photocatalysts. The observed kinetic constants of the MB photodecomposition (kobs) were evaluated and a relationship between kobs and the ZnS shell thickness was derived. Regression results revealed that 86% of the CdS core surface was covered with ZnS and the average thickness of ZnS shell was about 12% higher than that predicted by molecular modelling.
Monte Carlo based verification of a beam model used in a treatment planning system
Wieslander, E.; Knöös, T.
2008-02-01
Modern treatment planning systems (TPSs) usually separate the dose modelling into a beam modelling phase, describing the beam exiting the accelerator, followed by a subsequent dose calculation in the patient. The aim of this work is to use the Monte Carlo code system EGSnrc to study the modelling of head scatter as well as the transmission through multi-leaf collimator (MLC) and diaphragms in the beam model used in a commercial TPS (MasterPlan, Nucletron B.V.). An Elekta Precise linear accelerator equipped with an MLC has been modelled in BEAMnrc, based on available information from the vendor regarding the material and geometry of the treatment head. The collimation in the MLC direction consists of leafs which are complemented with a backup diaphragm. The characteristics of the electron beam, i.e., energy and spot size, impinging on the target have been tuned to match measured data. Phase spaces from simulations of the treatment head are used to extract the scatter from, e.g., the flattening filter and the collimating structures. Similar data for the source models used in the TPS are extracted from the treatment planning system, thus a comprehensive analysis is possible. Simulations in a water phantom, with DOSXYZnrc, are also used to study the modelling of the MLC and the diaphragms by the TPS. The results from this study will be helpful to understand the limitations of the model in the TPS and provide knowledge for further improvements of the TPS source modelling.
Multiscaling in Hall-magnetohydrodynamic turbulence: insights from a shell model.
Banerjee, Debarghya; Ray, Samriddhi Sankar; Sahoo, Ganapati; Pandit, Rahul
2013-10-25
We show that a shell-model version of the three-dimensional Hall-magnetohydrodynamic (3D Hall-MHD) equations provides a natural theoretical model for investigating the multiscaling behaviors of velocity and magnetic structure functions. We carry out extensive numerical studies of this shell model, obtain the scaling exponents for its structure functions, in both the low-k and high-k power-law ranges of three-dimensional Hall-magnetohydrodynamic, and find that the extended-self-similarity procedure is helpful in extracting the multiscaling nature of structure functions in the high-k regime, which otherwise appears to display simple scaling. Our results shed light on intriguing solar-wind measurements.
Development of numerical models for Monte Carlo simulations of Th-Pb fuel assembly
Directory of Open Access Journals (Sweden)
Oettingen Mikołaj
2017-01-01
Full Text Available The thorium-uranium fuel cycle is a promising alternative against uranium-plutonium fuel cycle, but it demands many advanced research before starting its industrial application in commercial nuclear reactors. The paper presents the development of the thorium-lead (Th-Pb fuel assembly numerical models for the integral irradiation experiments. The Th-Pb assembly consists of a hexagonal array of ThO2 fuel rods and metallic Pb rods. The design of the assembly allows different combinations of rods for various types of irradiations and experimental measurements. The numerical model of the Th-Pb assembly was designed for the numerical simulations with the continuous energy Monte Carlo Burnup code (MCB implemented on the supercomputer Prometheus of the Academic Computer Centre Cyfronet AGH.
Measurement and Monte Carlo modeling of the spatial response of scintillation screens
Energy Technology Data Exchange (ETDEWEB)
Pistrui-Maximean, S.A. [CNDRI (NDT using Ionizing Radiation) Laboratory, INSA-Lyon, 69621 Villeurbanne (France)], E-mail: spistrui@gmail.com; Letang, J.M. [CNDRI (NDT using Ionizing Radiation) Laboratory, INSA-Lyon, 69621 Villeurbanne (France)], E-mail: jean-michel.letang@insa-lyon.fr; Freud, N. [CNDRI (NDT using Ionizing Radiation) Laboratory, INSA-Lyon, 69621 Villeurbanne (France); Koch, A. [Thales Electron Devices, 38430 Moirans (France); Walenta, A.H. [Detectors and Electronics Department, FB Physik, Siegen University, 57068 Siegen (Germany); Montarou, G. [Corpuscular Physics Laboratory, Blaise Pascal University, 63177 Aubiere (France); Babot, D. [CNDRI (NDT using Ionizing Radiation) Laboratory, INSA-Lyon, 69621 Villeurbanne (France)
2007-11-01
In this article, we propose a detailed protocol to carry out measurements of the spatial response of scintillation screens and to assess the agreement with simulated results. The experimental measurements have been carried out using a practical implementation of the slit method. A Monte Carlo simulation model of scintillator screens, implemented with the toolkit Geant4, has been used to study the influence of the acquisition setup parameters and to compare with the experimental results. An algorithm of global stochastic optimization based on a localized random search method has been implemented to adjust the optical parameters (optical scattering and absorption coefficients). The algorithm has been tested for different X-ray tube voltages (40, 70 and 100 kV). A satisfactory convergence between the results simulated with the optimized model and the experimental measurements is obtained.
A Monte Carlo method for critical systems in infinite volume: the planar Ising model
Herdeiro, Victor
2016-01-01
In this paper we propose a Monte Carlo method for generating finite-domain marginals of critical distributions of statistical models in infinite volume. The algorithm corrects the problem of the long-range effects of boundaries associated to generating critical distributions on finite lattices. It uses the advantage of scale invariance combined with ideas of the renormalization group in order to construct a type of "holographic" boundary condition that encodes the presence of an infinite volume beyond it. We check the quality of the distribution obtained in the case of the planar Ising model by comparing various observables with their infinite-plane prediction. We accurately reproduce planar two-, three- and four-point functions of spin and energy operators. We also define a lattice stress-energy tensor, and numerically obtain the associated conformal Ward identities and the Ising central charge.
Energy Technology Data Exchange (ETDEWEB)
Gelß, Patrick, E-mail: p.gelss@fu-berlin.de; Matera, Sebastian, E-mail: matera@math.fu-berlin.de; Schütte, Christof, E-mail: schuette@mi.fu-berlin.de
2016-06-01
In multiscale modeling of heterogeneous catalytic processes, one crucial point is the solution of a Markovian master equation describing the stochastic reaction kinetics. Usually, this is too high-dimensional to be solved with standard numerical techniques and one has to rely on sampling approaches based on the kinetic Monte Carlo method. In this study we break the curse of dimensionality for the direct solution of the Markovian master equation by exploiting the Tensor Train Format for this purpose. The performance of the approach is demonstrated on a first principles based, reduced model for the CO oxidation on the RuO{sub 2}(110) surface. We investigate the complexity for increasing system size and for various reaction conditions. The advantage over the stochastic simulation approach is illustrated by a problem with increased stiffness.
Monte Carlo method for critical systems in infinite volume: The planar Ising model.
Herdeiro, Victor; Doyon, Benjamin
2016-10-01
In this paper we propose a Monte Carlo method for generating finite-domain marginals of critical distributions of statistical models in infinite volume. The algorithm corrects the problem of the long-range effects of boundaries associated to generating critical distributions on finite lattices. It uses the advantage of scale invariance combined with ideas of the renormalization group in order to construct a type of "holographic" boundary condition that encodes the presence of an infinite volume beyond it. We check the quality of the distribution obtained in the case of the planar Ising model by comparing various observables with their infinite-plane prediction. We accurately reproduce planar two-, three-, and four-point of spin and energy operators. We also define a lattice stress-energy tensor, and numerically obtain the associated conformal Ward identities and the Ising central charge.
Huang, Guanghui; Wan, Jianping; Chen, Hui
2013-02-01
Nonlinear stochastic differential equation models with unobservable state variables are now widely used in analysis of PK/PD data. Unobservable state variables are usually estimated with extended Kalman filter (EKF), and the unknown pharmacokinetic parameters are usually estimated by maximum likelihood estimator. However, EKF is inadequate for nonlinear PK/PD models, and MLE is known to be biased downwards. A density-based Monte Carlo filter (DMF) is proposed to estimate the unobservable state variables, and a simulation-based M estimator is proposed to estimate the unknown parameters in this paper, where a genetic algorithm is designed to search the optimal values of pharmacokinetic parameters. The performances of EKF and DMF are compared through simulations for discrete time and continuous time systems respectively, and it is found that the results based on DMF are more accurate than those given by EKF with respect to mean absolute error.
Monte Carlo markovian modeling of modal competition in dual-wavelength semiconductor lasers
Chusseau, Laurent; Philippe, Fabrice; Jean-Marie, Alain
2014-03-01
Monte Carlo markovian models of a dual-mode semiconductor laser with quantum well (QW) or quantum dot (QD) active regions are proposed. Accounting for carriers and photons as particles that may exchange energy in the course of time allows an ab initio description of laser dynamics such as the mode competition and intrinsic laser noise. We used these models to evaluate the stability of the dual-mode regime when laser characteristics are varied: mode gains and losses, non-radiative recombination rates, intraband relaxation time, capture time in QD, transfer of excitation between QD via the wetting layer. . . As a major result, a possible steady-sate dualmode regime is predicted for specially designed QD semiconductor lasers thereby acting as a CW microwave or terahertz-beating source whereas it does not occur for QW lasers.
Study of dispersion forces with quantum Monte Carlo: toward a continuum model for solvation.
Amovilli, Claudio; Floris, Franca Maria
2015-05-28
We present a general method to compute dispersion interaction energy that, starting from London's interpretation, is based on the measure of the electronic electric field fluctuations, evaluated on electronic sampled configurations generated by quantum Monte Carlo. A damped electric field was considered in order to avoid divergence in the variance. Dispersion atom-atom C6 van der Waals coefficients were computed by coupling electric field fluctuations with static dipole polarizabilities. The dipole polarizability was evaluated at the diffusion Monte Carlo level by studying the response of the system to a constant external electric field. We extended the method to the calculation of the dispersion contribution to the free energy of solvation in the framework of the polarizable continuum model. We performed test calculations on pairs of some atomic systems. We considered He in ground and low lying excited states and Ne in the ground state and obtained a good agreement with literature data. We also made calculations on He, Ne, and F(-) in water as the solvent. Resulting dispersion contribution to the free energy of solvation shows the reliability of the method illustrated here.
Newton, Paul K; Mason, Jeremy; Bethel, Kelly; Bazhenova, Lyudmila; Nieva, Jorge; Norton, Larry; Kuhn, Peter
2013-05-01
The classic view of metastatic cancer progression is that it is a unidirectional process initiated at the primary tumor site, progressing to variably distant metastatic sites in a fairly predictable, although not perfectly understood, fashion. A Markov chain Monte Carlo mathematical approach can determine a pathway diagram that classifies metastatic tumors as "spreaders" or "sponges" and orders the timescales of progression from site to site. In light of recent experimental evidence highlighting the potential significance of self-seeding of primary tumors, we use a Markov chain Monte Carlo (MCMC) approach, based on large autopsy data sets, to quantify the stochastic, systemic, and often multidirectional aspects of cancer progression. We quantify three types of multidirectional mechanisms of progression: (i) self-seeding of the primary tumor, (ii) reseeding of the primary tumor from a metastatic site (primary reseeding), and (iii) reseeding of metastatic tumors (metastasis reseeding). The model shows that the combined characteristics of the primary and the first metastatic site to which it spreads largely determine the future pathways and timescales of systemic disease.
Equivalence between local Fermi gas and shell models in inclusive muon capture from nuclei
Energy Technology Data Exchange (ETDEWEB)
Amaro, J.E.; Nieves, J.; Valverde, M. [Universidad de Granada, Departamento de Fisica Moderna, Granada (Spain); Maieron, C. [INFN, Sezione di Catania, Catania (Italy)
2005-06-01
Motivated by recent studies of inclusive neutrino nucleus processes and muon capture within a correlated local Fermi gas model (LFG), we discuss the relevance of nuclear finite-size effects in these reactions at low energy, in particular for muon capture. To disentangle these effects from others coming from the reaction dynamics we employ here a simple uncorrelated shell model that embodies the typical finite-size content of the problem. The integrated decay widths of muon atoms calculated with this shell model are then compared for several nuclei with those obtained within the uncorrelated LFG, using in both models exactly the same theoretical ingredients and parameters. We find that the two predictions are in quite good agreement, within 1-7%, when the shell model density and the correct energy balance is used as input in the LFG calculation. The present study indicates that, despite the low excitation energies involved in the reaction, integrated inclusive observables, like the total muon capture width, are quite independent of the fine details of the nuclear wave functions. (orig.)
Chumachenko, E. N.
2008-08-01
The necessity to develop and optimize new technological processes of gas moulding of shells under the superplasticity conditions, which ensure large elongation and complexity of the shape of end items, makes the specialists in the field of mathematical simulation to pose and solve problems of constant improvement of the imitation models. Because of a large number of "embedded" nonlinearities (the physical properties of the material, friction, and unknown boundaries), the solution of such problems requires large computer resources, high qualification of designers, and large amount of labor. In the present paper, we consider the problems of express analysis of pattern change of spatial shells on the basis of estimation of the behavior of their critical cross-sections. We solve problems of moulding of titan shells (made of VT6 alloy) in a matrix of complicated shape. We theoretically and experimentally justify the methods for predicting and constructing the optimal technological processes of shell deformation under conditions close to superplasticity by using the 2.5D designing procedures.
Živković, Jelena V; Trutić, Nataša V; Veselinović, Jovana B; Nikolić, Goran M; Veselinović, Aleksandar M
2015-09-01
The Monte Carlo method was used for QSAR modeling of maleimide derivatives as glycogen synthase kinase-3β inhibitors. The first QSAR model was developed for a series of 74 3-anilino-4-arylmaleimide derivatives. The second QSAR model was developed for a series of 177 maleimide derivatives. QSAR models were calculated with the representation of the molecular structure by the simplified molecular input-line entry system. Two splits have been examined: one split into the training and test set for the first QSAR model, and one split into the training, test and validation set for the second. The statistical quality of the developed model is very good. The calculated model for 3-anilino-4-arylmaleimide derivatives had following statistical parameters: r(2)=0.8617 for the training set; r(2)=0.8659, and r(m)(2)=0.7361 for the test set. The calculated model for maleimide derivatives had following statistical parameters: r(2)=0.9435, for the training, r(2)=0.9262 and r(m)(2)=0.8199 for the test and r(2)=0.8418, r(av)(m)(2)=0.7469 and ∆r(m)(2)=0.1476 for the validation set. Structural indicators considered as molecular fragments responsible for the increase and decrease in the inhibition activity have been defined. The computer-aided design of new potential glycogen synthase kinase-3β inhibitors has been presented by using defined structural alerts.
Effect of nonlinearity in hybrid kinetic Monte Carlo-continuum models.
Balter, Ariel; Lin, Guang; Tartakovsky, Alexandre M
2012-01-01
Recently there has been interest in developing efficient ways to model heterogeneous surface reactions with hybrid computational models that couple a kinetic Monte Carlo (KMC) model for a surface to a finite-difference model for bulk diffusion in a continuous domain. We consider two representative problems that validate a hybrid method and show that this method captures the combined effects of nonlinearity and stochasticity. We first validate a simple deposition-dissolution model with a linear rate showing that the KMC-continuum hybrid agrees with both a fully deterministic model and its analytical solution. We then study a deposition-dissolution model including competitive adsorption, which leads to a nonlinear rate, and show that in this case the KMC-continuum hybrid and fully deterministic simulations do not agree. However, we are able to identify the difference as a natural result of the stochasticity coming from the KMC surface process. Because KMC captures inherent fluctuations, we consider it to be more realistic than a purely deterministic model. Therefore, we consider the KMC-continuum hybrid to be more representative of a real system.
Farah, J.; Martinetti, F.; Sayah, R.; Lacoste, V.; Donadille, L.; Trompier, F.; Nauraye, C.; De Marzi, L.; Vabre, I.; Delacroix, S.; Hérault, J.; Clairand, I.
2014-06-01
Monte Carlo calculations are increasingly used to assess stray radiation dose to healthy organs of proton therapy patients and estimate the risk of secondary cancer. Among the secondary particles, neutrons are of primary concern due to their high relative biological effectiveness. The validation of Monte Carlo simulations for out-of-field neutron doses remains however a major challenge to the community. Therefore this work focused on developing a global experimental approach to test the reliability of the MCNPX models of two proton therapy installations operating at 75 and 178 MeV for ocular and intracranial tumor treatments, respectively. The method consists of comparing Monte Carlo calculations against experimental measurements of: (a) neutron spectrometry inside the treatment room, (b) neutron ambient dose equivalent at several points within the treatment room, (c) secondary organ-specific neutron doses inside the Rando-Alderson anthropomorphic phantom. Results have proven that Monte Carlo models correctly reproduce secondary neutrons within the two proton therapy treatment rooms. Sensitive differences between experimental measurements and simulations were nonetheless observed especially with the highest beam energy. The study demonstrated the need for improved measurement tools, especially at the high neutron energy range, and more accurate physical models and cross sections within the Monte Carlo code to correctly assess secondary neutron doses in proton therapy applications.
Farah, J; Martinetti, F; Sayah, R; Lacoste, V; Donadille, L; Trompier, F; Nauraye, C; De Marzi, L; Vabre, I; Delacroix, S; Hérault, J; Clairand, I
2014-06-07
Monte Carlo calculations are increasingly used to assess stray radiation dose to healthy organs of proton therapy patients and estimate the risk of secondary cancer. Among the secondary particles, neutrons are of primary concern due to their high relative biological effectiveness. The validation of Monte Carlo simulations for out-of-field neutron doses remains however a major challenge to the community. Therefore this work focused on developing a global experimental approach to test the reliability of the MCNPX models of two proton therapy installations operating at 75 and 178 MeV for ocular and intracranial tumor treatments, respectively. The method consists of comparing Monte Carlo calculations against experimental measurements of: (a) neutron spectrometry inside the treatment room, (b) neutron ambient dose equivalent at several points within the treatment room, (c) secondary organ-specific neutron doses inside the Rando-Alderson anthropomorphic phantom. Results have proven that Monte Carlo models correctly reproduce secondary neutrons within the two proton therapy treatment rooms. Sensitive differences between experimental measurements and simulations were nonetheless observed especially with the highest beam energy. The study demonstrated the need for improved measurement tools, especially at the high neutron energy range, and more accurate physical models and cross sections within the Monte Carlo code to correctly assess secondary neutron doses in proton therapy applications.
Kieftenbeld, Vincent; Natesan, Prathiba
2012-01-01
Markov chain Monte Carlo (MCMC) methods enable a fully Bayesian approach to parameter estimation of item response models. In this simulation study, the authors compared the recovery of graded response model parameters using marginal maximum likelihood (MML) and Gibbs sampling (MCMC) under various latent trait distributions, test lengths, and…
Multi-shell model of ion-induced nucleic acid condensation
Energy Technology Data Exchange (ETDEWEB)
Tolokh, Igor S. [Department of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, USA; Drozdetski, Aleksander V. [Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA; Pollack, Lois [School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853-3501, USA; Baker, Nathan A. [Advanced Computing, Mathematics, and Data Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA; Division of Applied Mathematics, Brown University, Providence, Rhode Island 02912, USA; Onufriev, Alexey V. [Department of Computer Science, Virginia Tech, Blacksburg, Virginia 24061, USA; Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
2016-04-21
We present a semi-quantitative model of condensation of short nucleic acid (NA) duplexes in- duced by tri-valent cobalt hexammine (CoHex) ions. The model is based on partitioning of bound counterion distribution around single NA duplex into “external” and “internal” ion binding shells distinguished by the proximity to duplex helical axis. The duplex aggregation free energy is de- composed into attraction and repulsion components represented by simple analytic expressions. The source of the short-range attraction between NA duplexes in the aggregated phase is the in- teraction of CoHex ions in the overlapping regions of the “external” shells with the oppositely charged duplexes. The attraction depends on CoHex binding affinity to the “external” shell of nearly neutralized duplex and the number of ions in the shell overlapping volume. For a given NA duplex sequence and structure, these parameters are estimated from molecular dynamics simula- tion. The attraction is opposed by the residual repulsion of nearly neutralized duplexes as well as duplex configurational entropy loss upon aggregation. The estimates of the aggregation free energy are consistent with the experimental range of NA duplex condensation propensities, including the unusually poor condensation of RNA structures and subtle sequence effects upon DNA conden- sation. The model predicts that, in contrast to DNA, RNA duplexes may condense into tighter packed aggregates with a higher degree of duplex neutralization. The model also predicts that longer NA fragments will condense easier than shorter ones. The ability of this model to explain experimentally observed trends in NA condensation, lends support to proposed NA condensation picture based on the multivalent “ion binding shells”.
The structure of the spherical tensor forces in the USD and GXPF1A shell model Hamiltonians
Institute of Scientific and Technical Information of China (English)
WANG Han-Kui; GAO Zao-Chun; CHEN Yong-Shou; GUO Jian-You; CHEN Yong-Jing; TU Ya
2011-01-01
The realistic shell model Hamiltonians, USD and GXPF1A, have been transformed from the particle-particle (normal) representation to the particle-hole representation (multipole-multipole)by using the known formulation in Ref. [1].The obtained multipole-multipole terms were compared with the known spherical tensor forces, including the coupled ones. It is the first time the contributions of the coupled tensor forces to the shell model Hamiltonian have been investigated. It has been shown that some coupled-tensor forces, such as [r2Y2σ]1,also give important contributions to the shell model Hamiltonian.
Large-scale shell-model calculations on the spectroscopy of $N<126$ Pb isotopes
Qi, Chong; Fu, G J
2016-01-01
Large-scale shell-model calculations are carried out in the model space including neutron-hole orbitals $2p_{1/2}$, $1f_{5/2}$, $2p_{3/2}$, $0i_{13/2}$, $1f_{7/2}$ and $0h_{9/2}$ to study the structure and electromagnetic properties of neutron deficient Pb isotopes. An optimized effective interaction is used. Good agreement between full shell-model calculations and experimental data is obtained for the spherical states in isotopes $^{194-206}$Pb. The lighter isotopes are calculated with an importance-truncation approach constructed based on the monopole Hamiltonian. The full shell-model results also agree well with our generalized seniority and nucleon-pair-approximation truncation calculations. The deviations between theory and experiment concerning the excitation energies and electromagnetic properties of low-lying $0^+$ and $2^+$ excited states and isomeric states may provide a constraint on our understanding of nuclear deformation and intruder configuration in this region.
Deformed shell model study of heavy N=Z nuclei and dark matter detection
Sahu, R
2016-01-01
Deformed shell model (DSM) based on Hartree-Fock intrinsic states is applied to address two current problems of interest. Firstly, in the $f_{5/2}pg_{9/2}$ model space with jj44b effective interaction along with isospin projection, DSM is used to describe the structure of the recently observed low-lying $T=0$ and $T=1$ bands in the heavy odd-odd N=Z nucleus $^{66}$As. DSM results are close to the data and also to the shell model results. For the $T=1$ band, DSM predicts structural change at $8^+$ just as in the shell model. In addition, the lowest two $T=0$ bands are found to have quasi-deuteron structure above a $^{64}$Ge core and the $5^+$ and $9^+$ levels of the third $T=0$ band are found to be isomeric states. Secondly, in a first application of DSM to dark matter, detection rates for the lightest supersymmetric particle (a dark matter candidate) are calculated with $^{73}$Ge as the detector.
A Coarse-Grained DNA Model Parameterized from Atomistic Simulations by Inverse Monte Carlo
Directory of Open Access Journals (Sweden)
Nikolay Korolev
2014-05-01
Full Text Available Computer modeling of very large biomolecular systems, such as long DNA polyelectrolytes or protein-DNA complex-like chromatin cannot reach all-atom resolution in a foreseeable future and this necessitates the development of coarse-grained (CG approximations. DNA is both highly charged and mechanically rigid semi-flexible polymer and adequate DNA modeling requires a correct description of both its structural stiffness and salt-dependent electrostatic forces. Here, we present a novel CG model of DNA that approximates the DNA polymer as a chain of 5-bead units. Each unit represents two DNA base pairs with one central bead for bases and pentose moieties and four others for phosphate groups. Charges, intra- and inter-molecular force field potentials for the CG DNA model were calculated using the inverse Monte Carlo method from all atom molecular dynamic (MD simulations of 22 bp DNA oligonucleotides. The CG model was tested by performing dielectric continuum Langevin MD simulations of a 200 bp double helix DNA in solutions of monovalent salt with explicit ions. Excellent agreement with experimental data was obtained for the dependence of the DNA persistent length on salt concentration in the range 0.1–100 mM. The new CG DNA model is suitable for modeling various biomolecular systems with adequate description of electrostatic and mechanical properties.
A Monte Carlo model of hot electron trapping and detrapping in SiO2
Kamocsai, R. L.; Porod, W.
1991-02-01
High-field stressing and oxide degradation of SiO2 are studied using a microscopic model of electron heating and charge trapping and detrapping. Hot electrons lead to a charge buildup in the oxide according to the dynamic trapping-detrapping model by Nissan-Cohen and co-workers [Y. Nissan-Cohen, J. Shappir, D. Frohman-Bentchkowsky, J. Appl. Phys. 58, 2252 (1985)]. Detrapping events are modeled as trap-to-band impact ionization processes initiated by high energy conduction electrons. The detailed electronic distribution function obtained from Monte Carlo transport simulations is utilized for the determination of the detrapping rates. We apply our microscopic model to the calculation of the flat-band voltage shift in silicon dioxide as a function of the electric field, and we show that our model is able to reproduce the experimental results. We also compare these results to the predictions of the empirical trapping-detrapping model which assumes a heuristic detrapping cross section. Our microscopic theory accounts for the nonlocal nature of impact ionization which leads to a dark space close to the injecting cathode, which is unaccounted for in the empirical model.
Monte Carlo model of the Studsvik BNCT clinical beam: description and validation.
Giusti, Valerio; Munck af Rosenschöld, Per M; Sköld, Kurt; Montagnini, Bruno; Capala, Jacek
2003-12-01
The neutron beam at the Studsvik facility for boron neutron capture therapy (BNCT) and the validation of the related computational model developed for the MCNP-4B Monte Carlo code are presented. Several measurements performed at the epithermal neutron port used for clinical trials have been made in order to validate the Monte Carlo computational model. The good general agreement between the MCNP calculations and the experimental results has provided an adequate check of the calculation procedure. In particular, at the nominal reactor power of 1 MW, the calculated in-air epithermal neutron flux in the energy interval between 0.4 eV-10 keV is 3.24 x 10(9) n cm(-2) s(-1) (+/- 1.2% 1 std. dev.) while the measured value is 3.30 x 10(9) n cm(-20 s(-1) (+/- 5.0% 1 std. dev.). Furthermore, the calculated in-phantom thermal neutron flux, equal to 6.43 x 10(9) n cm(-2) s(-1) (+/- 1.0% 1 std. dev.), and the corresponding measured value of 6.33 X 10(9) n cm(-2) s(-1) (+/- 5.3% 1 std. dev.) agree within their respective uncertainties. The only statistically significant disagreement is a discrepancy of 39% between the MCNP calculations of the in-air photon kerma and the corresponding experimental value. Despite this, a quite acceptable overall in-phantom beam performance was obtained, with a maximum value of the therapeutic ratio (the ratio between the local tumor dose and the maximum healthy tissue dose) equal to 6.7. The described MCNP model of the Studsvik facility has been deemed adequate to evaluate further improvements in the beam design as well as to plan experimental work.
Analytical models of icosahedral shells for 3D optical imaging of viruses
Jafarpour, Aliakbar
2014-01-01
A modulated icosahedral shell with an inclusion is a concise description of many viruses, including recently-discovered large double-stranded DNA ones. Many X-ray scattering patterns of such viruses show major polygonal fringes, which can be reproduced in image reconstruction with a homogeneous icosahedral shell. A key question regarding a low-resolution reconstruction is how to introduce further changes to the 3D profile in an efficient way with only a few parameters. Here, we derive and compile different analytical models of such an object with consideration of practical optical setups and typical structures of such viruses. The benefits of such models include 1) inherent filtering and suppressing different numerical errors of a discrete grid, 2) providing a concise and meaningful set of descriptors for feature extraction in high-throughput classification/sorting and higher-resolution cumulative reconstructions, 3) disentangling (physical) resolution from (numerical) discretization step and having a vector ...
Dynamo onset as a first-order transition: lessons from a shell model for magnetohydrodynamics.
Sahoo, Ganapati; Mitra, Dhrubaditya; Pandit, Rahul
2010-03-01
We carry out systematic and high-resolution studies of dynamo action in a shell model for magnetohydrodynamic (MHD) turbulence over wide ranges of the magnetic Prandtl number PrM and the magnetic Reynolds number ReM. Our study suggests that it is natural to think of dynamo onset as a nonequilibrium first-order phase transition between two different turbulent, but statistically steady, states. The ratio of the magnetic and kinetic energies is a convenient order parameter for this transition. By using this order parameter, we obtain the stability diagram (or nonequilibrium phase diagram) for dynamo formation in our MHD shell model in the (PrM-1,ReM) plane. The dynamo boundary, which separates dynamo and no-dynamo regions, appears to have a fractal character. We obtain a hysteretic behavior of the order parameter across this boundary and suggestions of nucleation-type phenomena.
Modeling and optimal vibration control of conical shell with piezoelectric actuators
Institute of Scientific and Technical Information of China (English)
Wang Weiyuan; Wei Yingjie; Wang Cong; Zou Zhenzhu
2008-01-01
In this paper numerical simulations of active vibration control for conical shell structure with distributed piezoelectric actuators is presented. The dynamic equations of conical shell structure are derived using the finite element model (FEM) based on Mindlin's plate theory. The results of modal calculations with FEM model are accurate enough for engineering applications in comparison with experiment results. The Electromechanical influence of distributed piezoelectric actuators is treated as a boundary condition for estimating the control force. The independent modal space control (IMSC) method is adopted and the optimal linear quadratic state feedback control is implemented so that the best control performance with the least control cost can be achieved. Optimal control effects are compared with controlled responses with other non-optimal control parameters. Numerical simulation results are given to demonstrate the effectiveness of the control scheme.
Large-scale shell-model calculations of nuclei around mass 210
Teruya, E.; Higashiyama, K.; Yoshinaga, N.
2016-06-01
Large-scale shell-model calculations are performed for even-even, odd-mass, and doubly odd nuclei of Pb, Bi, Po, At, Rn, and Fr isotopes in the neutron deficit region (Z ≥82 ,N ≤126 ) assuming 208Pb as a doubly magic core. All the six single-particle orbitals between the magic numbers 82 and 126, namely, 0 h9 /2,1 f7 /2,0 i13 /2,2 p3 /2,1 f5 /2 , and 2 p1 /2 , are considered. For a phenomenological effective two-body interaction, one set of the monopole pairing and quadrupole-quadrupole interactions including the multipole-pairing interactions is adopted for all the nuclei considered. The calculated energies and electromagnetic properties are compared with the experimental data. Furthermore, many isomeric states are analyzed in terms of the shell-model configurations.
Lattice dynamics and spin-phonon interactions in multiferroic RMn2O5: Shell model calculations
Litvinchuk, A. P.
2009-08-01
The results of the shell model lattice dynamics calculations of multiferroic RMn2O5 materials (space group Pbam) are reported. Theoretical even-parity eigenmode frequencies are compared with those obtained experimentally in polarized Raman scattering experiments for R=Ho,Dy. Analysis of displacement patterns allows to identify vibrational modes which facilitate spin-phonon coupling by modulating the Mn-Mn exchange interaction and provides explanation of the observed anomalous temperature behavior of phonons.
An application of the three-dimensional q-deformed harmonic oscillator to the shell model
Energy Technology Data Exchange (ETDEWEB)
Raychev, P.P. [Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' , Monte S Angelo, via Cintia, I-80125 Napoli (Italy); Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigrad Road, BG-1784 Sofia (Bulgaria); Roussev, R.P.; Terziev, P.A. [Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 72 Tzarigrad Road, BG-1784 Sofia (Bulgaria); Lo Iudice, N. [Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' , Monte S Angelo, via Cintia, I-80125 Napoli (Italy)
1998-10-01
A procedure for the construction of a q-deformed version of the Hamiltonian of the three-dimensional harmonic oscillator (HO), based on the application of q-deformed algebras, is presented. The spectrum of this Hamiltonian is not degenerated in the quantum number of the q-deformed angular momentum. The results together with their applicability to the shell model are compared with the predictions of the modified HO. (author)
Exploring uncertainty in glacier mass balance modelling with Monte Carlo simulation
Directory of Open Access Journals (Sweden)
H. Machguth
2008-12-01
Full Text Available By means of Monte Carlo simulations we calculated uncertainty in modelled cumulative mass balance over 400 days at one particular point on the tongue of Morteratsch Glacier, Switzerland, using a glacier energy balance model of intermediate complexity. Before uncertainty assessment, the model was tuned to observed mass balance for the investigated time period and its robustness was tested by comparing observed and modelled mass balance over 11 years, yielding very small deviations. Both systematic and random uncertainties are assigned to twelve input parameters and their respective values estimated from the literature or from available meteorological data sets. The calculated overall uncertainty in the model output is dominated by systematic errors and amounts to 0.7 m w.e. or approximately 10% of total melt over the investigated time span. In order to provide a first order estimate on variability in uncertainty depending on the quality of input data, we conducted a further experiment, calculating overall uncertainty for different levels of uncertainty in measured global radiation and air temperature. Our results show that the output of a well calibrated model is subject to considerable uncertainties, in particular when applied for extrapolation in time and space where systematic errors are likely to be an important issue.
Exploring uncertainty in glacier mass balance modelling with Monte Carlo simulation
Directory of Open Access Journals (Sweden)
H. Machguth
2008-06-01
Full Text Available By means of Monte Carlo simulations we calculated uncertainty in modelled cumulative mass balance over 400 days at one particular point on the tongue of Morteratsch Glacier, Switzerland, using a glacier energy balance model of intermediate complexity. Before uncertainty assessment, the model was tuned to observed mass balance for the investigated time period and its robustness was tested by comparing observed and modelled mass balance over 11 years, yielding very small deviations. Both systematic and random uncertainties are assigned to twelve input parameters and their respective values estimated from the literature or from available meteorological data sets. The calculated overall uncertainty in the model output is dominated by systematic errors and amounts to 0.7 m w.e. or approximately 10% of total melt over the investigated time span. In order to provide a first order estimate on variability in uncertainty depending on the quality of input data, we conducted a further experiment, calculating overall uncertainty for different levels of uncertainty in measured global radiation and air temperature. Our results show that the output of a well calibrated model is subject to considerable uncertainties, in particular when applied for extrapolation in time and space where systematic errors are likely to be an important issue.
FPGA Hardware Acceleration of Monte Carlo Simulations for the Ising Model
Ortega-Zamorano, Francisco; Cannas, Sergio A; Jerez, José M; Franco, Leonardo
2016-01-01
A two-dimensional Ising model with nearest-neighbors ferromagnetic interactions is implemented in a Field Programmable Gate Array (FPGA) board.Extensive Monte Carlo simulations were carried out using an efficient hardware representation of individual spins and a combined global-local LFSR random number generator. Consistent results regarding the descriptive properties of magnetic systems, like energy, magnetization and susceptibility are obtained while a speed-up factor of approximately 6 times is achieved in comparison to previous FPGA-based published works and almost $10^4$ times in comparison to a standard CPU simulation. A detailed description of the logic design used is given together with a careful analysis of the quality of the random number generator used. The obtained results confirm the potential of FPGAs for analyzing the statistical mechanics of magnetic systems.
Macroion solutions in the cell model studied by field theory and Monte Carlo simulations.
Lue, Leo; Linse, Per
2011-12-14
Aqueous solutions of charged spherical macroions with variable dielectric permittivity and their associated counterions are examined within the cell model using a field theory and Monte Carlo simulations. The field theory is based on separation of fields into short- and long-wavelength terms, which are subjected to different statistical-mechanical treatments. The simulations were performed by using a new, accurate, and fast algorithm for numerical evaluation of the electrostatic polarization interaction. The field theory provides counterion distributions outside a macroion in good agreement with the simulation results over the full range from weak to strong electrostatic coupling. A low-dielectric macroion leads to a displacement of the counterions away from the macroion.
A Thermodynamic Model for Square-well Chain Fluid: Theory and Monte Carlo Simulation
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
A thermodynamic model for the freely jointed square-well chain fluids was developed based on the thermodynamic perturbation theory of Barker-Henderson, Zhang and Wertheim. In this derivation Zhang's expressions for square-well monomers improved from Barker-Henderson compressibility approximation were adopted as the reference fluid, and Wertheim＇s polymerization method was used to obtain the free energy term due to the bond connectivity. An analytic expression for the Helmholtz free energy of the square-well chain fluids was obtained. The expression without adjustable parameters leads to the thermodynamic consistent predictions of the compressibility factors, residual internal energy and constant-volume heat capacity for dimer,4-mer, 8-mer and 16-mer square-well fluids. The results are in good agreement with the Monte Carlo simulation. To obtain the MC data of residual internal energy and the constant-volume heat capacity needed, NVT MC simulations were performed for these square-well chain fluids.
Monte Carlo based geometrical model for efficiency calculation of an n-type HPGe detector.
Cabal, Fatima Padilla; Lopez-Pino, Neivy; Bernal-Castillo, Jose Luis; Martinez-Palenzuela, Yisel; Aguilar-Mena, Jimmy; D'Alessandro, Katia; Arbelo, Yuniesky; Corrales, Yasser; Diaz, Oscar
2010-12-01
A procedure to optimize the geometrical model of an n-type detector is described. Sixteen lines from seven point sources ((241)Am, (133)Ba, (22)Na, (60)Co, (57)Co, (137)Cs and (152)Eu) placed at three different source-to-detector distances (10, 20 and 30 cm) were used to calibrate a low-background gamma spectrometer between 26 and 1408 keV. Direct Monte Carlo techniques using the MCNPX 2.6 and GEANT 4 9.2 codes, and a semi-empirical procedure were performed to obtain theoretical efficiency curves. Since discrepancies were found between experimental and calculated data using the manufacturer parameters of the detector, a detail study of the crystal dimensions and the geometrical configuration is carried out. The relative deviation with experimental data decreases from a mean value of 18-4%, after the parameters were optimized.
Monte Carlo based geometrical model for efficiency calculation of an n-type HPGe detector
Energy Technology Data Exchange (ETDEWEB)
Padilla Cabal, Fatima, E-mail: fpadilla@instec.c [Instituto Superior de Tecnologias y Ciencias Aplicadas, ' Quinta de los Molinos' Ave. Salvador Allende, esq. Luaces, Plaza de la Revolucion, Ciudad de la Habana, CP 10400 (Cuba); Lopez-Pino, Neivy; Luis Bernal-Castillo, Jose; Martinez-Palenzuela, Yisel; Aguilar-Mena, Jimmy; D' Alessandro, Katia; Arbelo, Yuniesky; Corrales, Yasser; Diaz, Oscar [Instituto Superior de Tecnologias y Ciencias Aplicadas, ' Quinta de los Molinos' Ave. Salvador Allende, esq. Luaces, Plaza de la Revolucion, Ciudad de la Habana, CP 10400 (Cuba)
2010-12-15
A procedure to optimize the geometrical model of an n-type detector is described. Sixteen lines from seven point sources ({sup 241}Am, {sup 133}Ba, {sup 22}Na, {sup 60}Co, {sup 57}Co, {sup 137}Cs and {sup 152}Eu) placed at three different source-to-detector distances (10, 20 and 30 cm) were used to calibrate a low-background gamma spectrometer between 26 and 1408 keV. Direct Monte Carlo techniques using the MCNPX 2.6 and GEANT 4 9.2 codes, and a semi-empirical procedure were performed to obtain theoretical efficiency curves. Since discrepancies were found between experimental and calculated data using the manufacturer parameters of the detector, a detail study of the crystal dimensions and the geometrical configuration is carried out. The relative deviation with experimental data decreases from a mean value of 18-4%, after the parameters were optimized.
Monte Carlo modeling of cavity imaging in pure iron using back-scatter electron scanning microscopy
Yan, Qiang; Gigax, Jonathan; Chen, Di; Garner, F. A.; Shao, Lin
2016-11-01
Backscattered electrons (BSE) in a scanning electron microscope (SEM) can produce images of subsurface cavity distributions as a nondestructive characterization technique. Monte Carlo simulations were performed to understand the mechanism of void imaging and to identify key parameters in optimizing void resolution. The modeling explores an iron target of different thicknesses, electron beams of different energies, beam sizes, and scan pitch, evaluated for voids of different sizes and depths below the surface. The results show that the void image contrast is primarily caused by discontinuity of energy spectra of backscattered electrons, due to increased outward path lengths for those electrons which penetrate voids and are backscattered at deeper depths. Size resolution of voids at specific depths, and maximum detection depth of specific voids sizes are derived as a function of electron beam energy. The results are important for image optimization and data extraction.
Of bugs and birds: Markov Chain Monte Carlo for hierarchical modeling in wildlife research
Link, W.A.; Cam, E.; Nichols, J.D.; Cooch, E.G.
2002-01-01
Markov chain Monte Carlo (MCMC) is a statistical innovation that allows researchers to fit far more complex models to data than is feasible using conventional methods. Despite its widespread use in a variety of scientific fields, MCMC appears to be underutilized in wildlife applications. This may be due to a misconception that MCMC requires the adoption of a subjective Bayesian analysis, or perhaps simply to its lack of familiarity among wildlife researchers. We introduce the basic ideas of MCMC and software BUGS (Bayesian inference using Gibbs sampling), stressing that a simple and satisfactory intuition for MCMC does not require extraordinary mathematical sophistication. We illustrate the use of MCMC with an analysis of the association between latent factors governing individual heterogeneity in breeding and survival rates of kittiwakes (Rissa tridactyla). We conclude with a discussion of the importance of individual heterogeneity for understanding population dynamics and designing management plans.
Efficient Monte Carlo and greedy heuristic for the inference of stochastic block models
Peixoto, Tiago P
2014-01-01
We present an efficient algorithm for the inference of stochastic block models in large networks. The algorithm can be used as an optimized Markov chain Monte Carlo (MCMC) method, with a fast mixing time and a much reduced susceptibility to getting trapped in metastable states, or as a greedy agglomerative heuristic, with an almost linear $O(N\\ln^2N)$ complexity, where $N$ is the number of nodes in the network, independent on the number of blocks being inferred. We show that the heuristic is capable of delivering results which are indistinguishable from the more exact and numerically expensive MCMC method in many artificial and empirical networks, despite being much faster. The method is entirely unbiased towards any specific mixing pattern, and in particular it does not favor assortative community structures.
World-line quantum Monte Carlo algorithm for a one-dimensional Bose model
Energy Technology Data Exchange (ETDEWEB)
Batrouni, G.G. (Thinking Machines Corporation, 245 First Street, Cambridge, Massachusetts 02142 (United States)); Scalettar, R.T. (Physics Department, University of California, Davis, California 95616 (United States))
1992-10-01
In this paper we provide a detailed description of the ground-state phase diagram of interacting, disordered bosons on a lattice. We describe a quantum Monte Carlo algorithm that incorporates in an efficient manner the required bosonic wave-function symmetry. We consider the ordered case, where we evaluate the compressibility gap and show the lowest three Mott insulating lobes. We obtain the critical ratio of interaction strength to hopping at which the onset of superfluidity occurs for the first lobe, and the critical exponents {nu} and {ital z}. For the disordered model we show the effect of randomness on the phase diagram and the superfluid correlations. We also measure the response of the superfluid density, {rho}{sub {ital s}}, to external perturbations. This provides an unambiguous characterization of the recently observed Bose and Anderson glass phases.
Sadi, M; Dabir, B
2003-01-01
Monte Carlo Method is one of the most powerful techniques to model different processes, such as polymerization reactions. By this method, without any need to solve moment equations, a very detailed information on the structure and properties of polymers are obtained. The number of algorithm repetitions (selected volumes of reactor for modelling which represent the number of initial molecules) is very important in this method. In Monte Carlo method calculations are based on the random number of generations and reaction probability determinations. so the number of algorithm repetition is very important. In this paper, the initiation reaction was considered alone and the importance of number of initiator molecules on the result were studied. It can be concluded that Monte Carlo method will not give accurate results if the number of molecules is not satisfied to be big enough, because in that case , selected volume would not be representative of the whole system.
No-Core Shell Model for A = 47 and A = 49
Energy Technology Data Exchange (ETDEWEB)
Vary, J P; Negoita, A G; Stoica, S
2006-11-13
We apply the no-core shell model to the nuclear structure of odd-mass nuclei straddling {sup 48}Ca. Starting with the NN interaction, that fits two-body scattering and bound state data, we evaluate the nuclear properties of A = 47 and A = 49 nuclei while preserving all the underlying symmetries. Due to model space limitations and the absence of three-body interactions, we incorporate phenomenological interaction terms determined by fits to A = 48 nuclei in a previous effort. Our modified Hamiltonian produces reasonable spectra for these odd-mass nuclei. In addition to the differences in single-particle basis states, the absence of a single-particle Hamiltonian in our no-core approach complicates comparisons with valence effective NN interactions. We focus on purely off-diagonal two-body matrix elements since they are not affected by ambiguities in the different roles for one-body potentials and we compare selected sets of fp-shell matrix elements of our initial and modified Hamiltonians in the harmonic oscillator basis with those of a recent model fp-shell interaction, the GXPF1 interaction of Honma et al. While some significant differences emerge from these comparisons, there is an overall reasonably good correlation between our off-diagonal matrix elements and those of GXPF1.
Shen, Hui-Shen
2010-06-01
Buckling and postbuckling analysis is presented for axially compressed microtubules (MTs) embedded in an elastic matrix of cytoplasm. The microtubule is modeled as a nonlocal shear deformable cylindrical shell which contains small scale effects. The surrounding elastic medium is modeled as a Pasternak foundation. The governing equations are based on higher order shear deformation shell theory with a von Kármán-Donnell-type of kinematic nonlinearity and include the extension-twist and flexural-twist couplings. The thermal effects are also included and the material properties are assumed to be temperature-dependent. The small scale parameter e (0) a is estimated by matching the buckling load from their vibrational behavior of MTs with the numerical results obtained from the nonlocal shear deformable shell model. The numerical results show that buckling load and postbuckling behavior of MTs are very sensitive to the small scale parameter e (0) a. The results reveal that the MTs under axial compressive loading condition have an unstable postbuckling path, and the lateral constraint has a significant effect on the postbuckling response of a microtubule when the foundation stiffness is sufficiently large.
Rayleigh-Taylor finger instability mixing in hydrodynamic shell convection models
Mocak, Miroslav
2010-01-01
Mixing processes in stars driven by composition gradients as a result of the Rayleigh-Taylor instability are not anticipated. They are supported only by hydrodynamic studies of stellar convection. We find that such mixing occurs below the bottom edge of convection zones in our multidimensional hydrodynamic shell convection models. It operates at interfaces created by off-center nuclear burning, where less dense gas with higher mean molecular weight is located above denser gas with a lower mean molecular weight. We discuss the mixing under various conditions with hydrodynamic convection models based on stellar evolutionary calculations of the core helium flash in a 1.25 Msun star, the core carbon flash in a 9.3 Msun star, and of oxygen burning shell in a star with a mass of 23 Msun. We simulate the hydrodynamic behavior of shell convection during various phases of stellar evolution with the Eulerian hydrodynamics code HERAKLES in two and three spatial dimensions. Initial models for this purpose are obtained by...
3D MODELS COMPARISON OF COMPLEX SHELL IN UNDERWATER AND DRY ENVIRONMENTS
Directory of Open Access Journals (Sweden)
S. Troisi
2015-04-01
Full Text Available In marine biology the shape, morphology, texture and dimensions of the shells and organisms like sponges and gorgonians are very important parameters. For example, a particular type of gorgonian grows every year only few millimeters; this estimation was conducted without any measurement instrument but it has been provided after successive observational studies, because this organism is very fragile: the contact could compromise its structure and outliving. Non-contact measurement system has to be used to preserve such organisms: the photogrammetry is a method capable to assure high accuracy without contact. Nevertheless, the achievement of a 3D photogrammetric model of complex object (as gorgonians or particular shells is a challenge in normal environments, either with metric camera or with consumer camera. Indeed, the successful of automatic target-less image orientation and the image matching algorithms is strictly correlated to the object texture properties and of camera calibration quality as well. In the underwater scenario, the environment conditions strongly influence the results quality; in particular, water’s turbidity, the presence of suspension, flare and other optical aberrations decrease the image quality reducing the accuracy and increasing the noise on the 3D model. Furthermore, seawater density variability influences its refraction index and consequently the interior orientation camera parameters. For this reason, the camera calibration has to be performed in the same survey conditions. In this paper, a comparison between the 3D models of a Charonia Tritonis shell are carried out through surveys conducted both in dry and underwater environments.
Baring, M G; Reynolds, S P; Grenier, I; Goret, P; Baring, Matthew G.; Ellison, Donald C.; Reynolds, Stephen P; Grenier, Isabelle; Goret, Philippe
1999-01-01
Supernova remnants (SNRs) are widely believed to be the principal source of galactic cosmic rays. Such energetic particles can produce gamma-rays and lower energy photons via interactions with the ambient plasma. In this paper, we present results from a Monte Carlo simulation of non-linear shock structure and acceleration coupled with photon emission in shell-like SNRs. These non-linearities are a by-product of the dynamical influence of the accelerated cosmic rays on the shocked plasma and result in distributions of cosmic rays which deviate from pure power-laws. Such deviations are crucial to acceleration efficiency and spectral considerations, producing GeV/TeV intensity ratios that are quite different from test particle predictions. The Sedov scaling solution for SNR expansions is used to estimate important shock parameters for input into the Monte Carlo simulation. We calculate ion and electron distributions that spawn neutral pion decay, bremsstrahlung, inverse Compton, and synchrotron emission, yieldin...
Kadoura, Ahmad
2011-06-06
Lennard‐Jones (L‐J) and Buckingham exponential‐6 (exp‐6) potential models were used to produce isotherms for methane at temperatures below and above critical one. Molecular simulation approach, particularly Monte Carlo simulations, were employed to create these isotherms working with both canonical and Gibbs ensembles. Experiments in canonical ensemble with each model were conducted to estimate pressures at a range of temperatures above methane critical temperature. Results were collected and compared to experimental data existing in literature; both models showed an elegant agreement with the experimental data. In parallel, experiments below critical temperature were run in Gibbs ensemble using L‐J model only. Upon comparing results with experimental ones, a good fit was obtained with small deviations. The work was further developed by adding some statistical studies in order to achieve better understanding and interpretation to the estimated quantities by the simulation. Methane phase diagrams were successfully reproduced by an efficient molecular simulation technique with different potential models. This relatively simple demonstration shows how powerful molecular simulation methods could be, hence further applications on more complicated systems are considered. Prediction of phase behavior of elemental sulfur in sour natural gases has been an interesting and challenging field in oil and gas industry. Determination of elemental sulfur solubility conditions helps avoiding all kinds of problems caused by its dissolution in gas production and transportation processes. For this purpose, further enhancement to the methods used is to be considered in order to successfully simulate elemental sulfur phase behavior in sour natural gases mixtures.
Modeling of composite latex particle morphology by off-lattice Monte Carlo simulation.
Duda, Yurko; Vázquez, Flavio
2005-02-01
Composite latex particles have shown a great range of applications such as paint resins, varnishes, water borne adhesives, impact modifiers, etc. The high-performance properties of this kind of materials may be explained in terms of a synergistical combination of two different polymers (usually a rubber and a thermoplastic). A great variety of composite latex particles with very different morphologies may be obtained by two-step emulsion polymerization processes. The formation of specific particle morphology depends on the chemical and physical nature of the monomers used during the synthesis, the process temperature, the reaction initiator, the surfactants, etc. Only a few models have been proposed to explain the appearance of the composite particle morphologies. These models have been based on the change of the interfacial energies during the synthesis. In this work, we present a new three-component model: Polymer blend (flexible and rigid chain particles) is dispersed in water by forming spherical cavities. Monte Carlo simulations of the model in two dimensions are used to determine the density distribution of chains and water molecules inside the suspended particle. This approach allows us to study the dependence of the morphology of the composite latex particles on the relative hydrophilicity and flexibility of the chain molecules as well as on their density and composition. It has been shown that our simple model is capable of reproducing the main features of the various morphologies observed in synthesis experiments.
Voxel2MCNP: software for handling voxel models for Monte Carlo radiation transport calculations.
Hegenbart, Lars; Pölz, Stefan; Benzler, Andreas; Urban, Manfred
2012-02-01
Voxel2MCNP is a program that sets up radiation protection scenarios with voxel models and generates corresponding input files for the Monte Carlo code MCNPX. Its technology is based on object-oriented programming, and the development is platform-independent. It has a user-friendly graphical interface including a two- and three-dimensional viewer. A row of equipment models is implemented in the program. Various voxel model file formats are supported. Applications include calculation of counting efficiency of in vivo measurement scenarios and calculation of dose coefficients for internal and external radiation scenarios. Moreover, anthropometric parameters of voxel models, for instance chest wall thickness, can be determined. Voxel2MCNP offers several methods for voxel model manipulations including image registration techniques. The authors demonstrate the validity of the program results and provide references for previous successful implementations. The authors illustrate the reliability of calculated dose conversion factors and specific absorbed fractions. Voxel2MCNP is used on a regular basis to generate virtual radiation protection scenarios at Karlsruhe Institute of Technology while further improvements and developments are ongoing.
Worm Monte Carlo study of the honeycomb-lattice loop model
Energy Technology Data Exchange (ETDEWEB)
Liu Qingquan, E-mail: liuqq@mail.ustc.edu.c [Hefei National Laboratory for Physical Sciences at Microscale, Department of Modern Physics, University of Science and Technology of China, Hefei, 230027 (China); Deng Youjin, E-mail: yjdeng@ustc.edu.c [Hefei National Laboratory for Physical Sciences at Microscale, Department of Modern Physics, University of Science and Technology of China, Hefei, 230027 (China); Garoni, Timothy M., E-mail: t.garoni@ms.unimelb.edu.a [ARC Centre of Excellence for Mathematics and Statistics of Complex Systems, Department of Mathematics and Statistics, University of Melbourne, Victoria 3010 (Australia)
2011-05-11
We present a Markov-chain Monte Carlo algorithm of worm type that correctly simulates the O(n) loop model on any (finite and connected) bipartite cubic graph, for any real n>0, and any edge weight, including the fully-packed limit of infinite edge weight. Furthermore, we prove rigorously that the algorithm is ergodic and has the correct stationary distribution. We emphasize that by using known exact mappings when n=2, this algorithm can be used to simulate a number of zero-temperature Potts antiferromagnets for which the Wang-Swendsen-Kotecky cluster algorithm is non-ergodic, including the 3-state model on the kagome lattice and the 4-state model on the triangular lattice. We then use this worm algorithm to perform a systematic study of the honeycomb-lattice loop model as a function of n{<=}2, on the critical line and in the densely-packed and fully-packed phases. By comparing our numerical results with Coulomb gas theory, we identify a set of exact expressions for scaling exponents governing some fundamental geometric and dynamic observables. In particular, we show that for all n{<=}2, the scaling of a certain return time in the worm dynamics is governed by the magnetic dimension of the loop model, thus providing a concrete dynamical interpretation of this exponent. The case n>2 is also considered, and we confirm the existence of a phase transition in the 3-state Potts universality class that was recently observed via numerical transfer matrix calculations.
Large-scale shell-model analysis of the neutrinoless $\\beta\\beta$ decay of $^{48}$Ca
Iwata, Y; Otsuka, T; Utsuno, Y; Menendez, J; Honma, M; Abe, T
2016-01-01
We present the nuclear matrix element for the neutrinoless double-beta decay of $^{48}$Ca based on large-scale shell-model calculations including two harmonic oscillator shells ($sd$ and $pf$ shells). The excitation spectra of $^{48}$Ca and $^{48}$Ti, and the two-neutrino double-beta decay of $^{48}$Ca are reproduced in good agreement to experiment. We find that the neutrinoless double-beta decay nuclear matrix element is enhanced by about 30\\% compared to $pf$-shell calculations. This reduces the decay lifetime by almost a factor of two. The matrix-element increase is mostly due to pairing correlations associated with cross-shell $sd$-$pf$ excitations. We also investigate possible implications for heavier neutrinoless double-beta decay candidates.
Corner wetting in the two-dimensional Ising model: Monte Carlo results
Energy Technology Data Exchange (ETDEWEB)
Albano, E V [INIFTA, Universidad Nacional de La Plata, CC 16 Suc. 4, 1900 La Plata (Argentina); Virgiliis, A De [INIFTA, Universidad Nacional de La Plata, CC 16 Suc. 4, 1900 La Plata (Argentina); Mueller, M [Institut fuer Physik, Johannes Gutenberg Universitaet, Staudinger Weg 7, D-55099 Mainz (Germany); Binder, K [Institut fuer Physik, Johannes Gutenberg Universitaet, Staudinger Weg 7, D-55099 Mainz (Germany)
2003-01-29
Square LxL (L=24-128) Ising lattices with nearest neighbour ferromagnetic exchange are considered using free boundary conditions at which boundary magnetic fields are applied, i.e., at the two boundary rows ending at the lower left corner a field +h acts, while at the two boundary rows ending at the upper right corner a field -h acts. For temperatures T less than the critical temperature T{sub c} of the bulk, this boundary condition leads to the formation of two domains with opposite orientations of the magnetization direction, separated by an interface which for T larger than the filling transition temperature T{sub f} (h) runs from the upper left corner to the lower right corner, while for T
Institute of Scientific and Technical Information of China (English)
Xingzhe Wang; Xiaojing Zheng
2009-01-01
Based on the generalized variational principle of magneto-thermo-elasticity of the ferromagnetic elastic medium, a nonlinear coupling theoretical modeling for a ferromagnetic thin shell is developed. All governing equations and boundary conditions for the ferromagnetic shell are obtained from the variational manipulations on the magnetic scalar potential, temperature and the elastic displacement related to the total energy functional. The multi-field couplings and geometrical nonlinearity of the ferromagnetic thin shell are taken into account in the modeling. The general modeling can be further deduced to existing models of the magneto-elasticity and the thermo-elasticity of a ferromagnetic shell and magneto-thermo-elasticity of a ferromagnetic plate, which axe coincident with the ones in literature.
Buckling and postbuckling of radially loaded microtubules by nonlocal shear deformable shell model.
Shen, Hui-Shen
2010-05-21
This paper presents an investigation on the buckling and postbuckling of microtubules (MTs) subjected to a uniform external radial pressure in thermal environments. The microtubule is modeled as a nonlocal shear deformable cylindrical shell which contains small scale effects. The governing equations are based on higher order shear deformation shell theory with a von Kármán-Donnell-type of kinematic nonlinearity and include the extension-twist and flexural-twist couplings. The thermal effects are also included and the material properties are assumed to be temperature-dependent. A singular perturbation technique is employed to determine the buckling pressure and postbuckling equilibrium paths. The small scale parameter e(0)a is estimated by matching the buckling pressure of MTs measured from the experiments with the numerical results obtained from the nonlocal shear deformable shell model. The numerical results show that buckling pressure and postbuckling behavior of MTs are very sensitive to the small scale parameter e(0)a. The results reveal that the 13_3 microtubule has a stable postbuckling path, whereas the 13_2 microtubule has an unstable postbuckling behavior due to the presence of skew angles.
The circumstellar structure of the Be shell star φ Persei. II. Modeling
Hummel, W.; Štefl, S.
2001-03-01
We model Fe Ii 5317 emission lines and phase resolved He I 6678 and 5876 emission lines of the bright B2e&sdO shell binary phi Per to find the size and shape of the excitation region inside the circumprimary disk. We find the Fe Ii 5317 emission to originate within 9 stellar radii in an axisymmetric disk around the primary. Orbital phase variations of He I 6678 are fit in terms of a disk sector with disk radius of 10 stellar radii and opening angle of =~ 120degr facing the secondary. This region can be alternatively described by an intersection of a sphere around the secondary and the circumprimary disk with a penetration depth of about 7 R_*. Similar fit values are found for He I 5876. The enigmatic orbital phase precedence of shell occurrence in the He I emission features is discussed. We favor a model in which the inner He I shell is deformed because of differential rotation in combination with a finite recombination time. Based on observations collected at the Ondřejov Observatory (of the Academy of Sciences of the Czech Republic), the German-Spanish Astronomical Center (DSAZ) -- Calar Alto (operated by the Max-Plank-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy) and Observatoire de Haute-Provence (OHP; CNRS, France).
Large scale shell model calculations for even-even $^{62-66}$Fe isotopes
Srivastava, P C
2009-01-01
The recently measured experimental data of Legnaro National Laboratories on neutron rich even isotopes of $^{62-66}$Fe with A=62,64,66 have been interpreted in the framework of large scale shell model. Calculations have been performed with a newly derived effective interaction GXPF1A in full $\\it{fp}$ space without truncation. The experimental data is very well explained for $^{62}$Fe, satisfactorily reproduced for $^{64}$Fe and poorly fitted for $^{66}$Fe. The increasing collectivity reflected in experimental data when approaching N=40 is not reproduced in calculated values. This indicates that whereas the considered valence space is adequate for $^{62}$Fe, inclusion of higher orbits from $\\it{sdg}$ shell is required for describing $^{66}$Fe.
β-decay half-life of V50 calculated by the shell model
Haaranen, M.; Srivastava, P. C.; Suhonen, J.; Zuber, K.
2014-10-01
In this work we survey the detectability of the β- channel of 2350V leading to the first excited 2+ state in 2450Cr. The electron-capture (EC) half-life corresponding to the transition of 2350V to the first excited 2+ state in 2250Ti had been measured earlier. Both of the mentioned transitions are 4th-forbidden non-unique. We have performed calculations of all the involved wave functions by using the nuclear shell model with the GXPF1A interaction in the full f-p shell. The computed half-life of the EC branch is in good agreement with the measured one. The predicted half-life for the β- branch is in the range ≈2×1019 yr whereas the present experimental lower limit is 1.5×1018 yr. We discuss also the experimental lay-out needed to detect the β--branch decay.
Ab Initio No Core Shell Model - Recent Results and Further Prospects
Vary, James P; Potter, Hugh; Caprio, Mark A; Smith, Robin; Binder, Sven; Calci, Angelo; Fischer, Sebastian; Langhammer, Joachim; Roth, Robert; Aktulga, Hasan Metin; Ng, Esmond; Yang, Chao; Oryspayev, Dossay; Sosonkina, Masha; Saule, Erik; Çatalyürek, Ümit
2015-01-01
There has been significant recent progress in solving the long-standing problems of how nuclear shell structure and collective motion emerge from underlying microscopic inter-nucleon interactions. We review a selection of recent significant results within the ab initio No Core Shell Model (NCSM) closely tied to three major factors enabling this progress: (1) improved nuclear interactions that accurately describe the experimental two-nucleon and three-nucleon interaction data; (2) advances in algorithms to simulate the quantum many-body problem with strong interactions; and (3) continued rapid development of high-performance computers now capable of performing $20 \\times 10^{15}$ floating point operations per second. We also comment on prospects for further developments.
The Mass Shell of the Nelson Model without Cut-Offs
Bachmann, S; Pizzo, A
2011-01-01
The massless Nelson model describes non-relativistic, spinless quantum particles interacting with a relativistic, massless, scalar quantum field. The interaction is linear in the field. We analyze the one particle sector. First, we construct the renormalized mass shell of the non-relativistic particle for an arbitrarily small infrared cut-off that turns off the interaction with the low energy modes of the field. No ultraviolet cut-off is imposed. Second, we implement a suitable Bogolyubov transformation of the Hamiltonian in the infrared regime. This transformation depends on the total momentum of the system and is non-unitary as the infrared cut-off is removed. For the transformed Hamiltonian we construct the mass shell in the limit where both the ultraviolet and the infrared cut-off are removed. Our approach is constructive and leads to explicit expansion formulae which are amenable to rigorously control the S-matrix elements.
Diffenderfer, Eric S; Dolney, Derek; Schaettler, Maximilian; Sanzari, Jenine K; McDonough, James; Cengel, Keith A
2014-03-01
The space radiation environment imposes increased dangers of exposure to ionizing radiation, particularly during a solar particle event (SPE). These events consist primarily of low energy protons that produce a highly inhomogeneous dose distribution. Due to this inherent dose heterogeneity, experiments designed to investigate the radiobiological effects of SPE radiation present difficulties in evaluating and interpreting dose to sensitive organs. To address this challenge, we used the Geant4 Monte Carlo simulation framework to develop dosimetry software that uses computed tomography (CT) images and provides radiation transport simulations incorporating all relevant physical interaction processes. We found that this simulation accurately predicts measured data in phantoms and can be applied to model dose in radiobiological experiments with animal models exposed to charged particle (electron and proton) beams. This study clearly demonstrates the value of Monte Carlo radiation transport methods for two critically interrelated uses: (i) determining the overall dose distribution and dose levels to specific organ systems for animal experiments with SPE-like radiation, and (ii) interpreting the effect of random and systematic variations in experimental variables (e.g. animal movement during long exposures) on the dose distributions and consequent biological effects from SPE-like radiation exposure. The software developed and validated in this study represents a critically important new tool that allows integration of computational and biological modeling for evaluating the biological outcomes of exposures to inhomogeneous SPE-like radiation dose distributions, and has potential applications for other environmental and therapeutic exposure simulations.
Solution of deterministic-stochastic epidemic models by dynamical Monte Carlo method
Aièllo, O. E.; Haas, V. J.; daSilva, M. A. A.; Caliri, A.
2000-07-01
This work is concerned with dynamical Monte Carlo (MC) method and its application to models originally formulated in a continuous-deterministic approach. Specifically, a susceptible-infected-removed-susceptible (SIRS) model is used in order to analyze aspects of the dynamical MC algorithm and achieve its applications in epidemic contexts. We first examine two known approaches to the dynamical interpretation of the MC method and follow with the application of one of them in the SIRS model. The working method chosen is based on the Poisson process where hierarchy of events, properly calculated waiting time between events, and independence of the events simulated, are the basic requirements. To verify the consistence of the method, some preliminary MC results are compared against exact steady-state solutions and other general numerical results (provided by Runge-Kutta method): good agreement is found. Finally, a space-dependent extension of the SIRS model is introduced and treated by MC. The results are interpreted under and in accordance with aspects of the herd-immunity concept.
Energy Technology Data Exchange (ETDEWEB)
Parsons, Neal, E-mail: neal.parsons@cd-adapco.com; Levin, Deborah A., E-mail: deblevin@illinois.edu [Department of Aerospace Engineering, The Pennsylvania State University, 233 Hammond Building, University Park, Pennsylvania 16802 (United States); Duin, Adri C. T. van, E-mail: acv13@engr.psu.edu [Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, 136 Research East, University Park, Pennsylvania 16802 (United States); Zhu, Tong, E-mail: tvz5037@psu.edu [Department of Aerospace Engineering, The Pennsylvania State University, 136 Research East, University Park, Pennsylvania 16802 (United States)
2014-12-21
The Direct Simulation Monte Carlo (DSMC) method typically used for simulating hypersonic Earth re-entry flows requires accurate total collision cross sections and reaction probabilities. However, total cross sections are often determined from extrapolations of relatively low-temperature viscosity data, so their reliability is unknown for the high temperatures observed in hypersonic flows. Existing DSMC reaction models accurately reproduce experimental equilibrium reaction rates, but the applicability of these rates to the strong thermal nonequilibrium observed in hypersonic shocks is unknown. For hypersonic flows, these modeling issues are particularly relevant for nitrogen, the dominant species of air. To rectify this deficiency, the Molecular Dynamics/Quasi-Classical Trajectories (MD/QCT) method is used to accurately compute collision and reaction cross sections for the N{sub 2}({sup 1}Σ{sub g}{sup +})-N{sub 2}({sup 1}Σ{sub g}{sup +}) collision pair for conditions expected in hypersonic shocks using a new potential energy surface developed using a ReaxFF fit to recent advanced ab initio calculations. The MD/QCT-computed reaction probabilities were found to exhibit better physical behavior and predict less dissociation than the baseline total collision energy reaction model for strong nonequilibrium conditions expected in a shock. The MD/QCT reaction model compared well with computed equilibrium reaction rates and shock-tube data. In addition, the MD/QCT-computed total cross sections were found to agree well with established variable hard sphere total cross sections.
A background error covariance model of significant wave height employing Monte Carlo simulation
Institute of Scientific and Technical Information of China (English)
GUO Yanyou; HOU Yijun; ZHANG Chunmei; YANG Jie
2012-01-01
The quality of background error statistics is one of the key components for successful assimilation of observations in a numerical model.The background error covariance(BEC)of ocean waves is generally estimated under an assumption that it is stationary over a period of time and uniform over a domain.However,error statistics are in fact functions of the physical processes governing the meteorological situation and vary with the wave condition.In this paper,we simulated the BEC of the significant wave height(SWH)employing Monte Carlo methods.An interesting result is that the BEC varies consistently with the mean wave direction(MWD).In the model domain,the BEC of the SWH decreases significantly when the MWD changes abruptly.A new BEC model of the SWH based on the correlation between the BEC and MWD was then developed.A case study of regional data assimilation was performed,where the SWH observations of buoy 22001 were used to assess the SWH hindcast.The results show that the new BEC model benefits wave prediction and allows reasonable approximations of anisotropy and inhomogeneous errors.
Critical Casimir force and its fluctuations in lattice spin models: exact and Monte Carlo results.
Dantchev, Daniel; Krech, Michael
2004-04-01
We present general arguments and construct a stress tensor operator for finite lattice spin models. The average value of this operator gives the Casimir force of the system close to the bulk critical temperature T(c). We verify our arguments via exact results for the force in the two-dimensional Ising model, d -dimensional Gaussian, and mean spherical model with 2Monte Carlo simulations for three-dimensional Ising, XY, and Heisenberg models we demonstrate that the standard deviation of the Casimir force F(C) in a slab geometry confining a critical substance in-between is k(b) TD(T) (A/ a(d-1) )(1/2), where A is the surface area of the plates, a is the lattice spacing, and D(T) is a slowly varying nonuniversal function of the temperature T. The numerical calculations demonstrate that at the critical temperature T(c) the force possesses a Gaussian distribution centered at the mean value of the force = k(b) T(c) (d-1)Delta/ (L/a)(d), where L is the distance between the plates and Delta is the (universal) Casimir amplitude.
Monte Carlo Modeling of Computed Tomography Ceiling Scatter for Shielding Calculations.
Edwards, Stephen; Schick, Daniel
2016-04-01
Radiation protection for clinical staff and members of the public is of paramount importance, particularly in occupied areas adjacent to computed tomography scanner suites. Increased patient workloads and the adoption of multi-slice scanning systems may make unshielded secondary scatter from ceiling surfaces a significant contributor to dose. The present paper expands upon an existing analytical model for calculating ceiling scatter accounting for variable room geometries and provides calibration data for a range of clinical beam qualities. The practical effect of gantry, false ceiling, and wall attenuation in limiting ceiling scatter is also explored and incorporated into the model. Monte Carlo simulations were used to calibrate the model for scatter from both concrete and lead surfaces. Gantry attenuation experimental data showed an effective blocking of scatter directed toward the ceiling at angles up to 20-30° from the vertical for the scanners examined. The contribution of ceiling scatter from computed tomography operation to the effective dose of individuals in areas surrounding the scanner suite could be significant and therefore should be considered in shielding design according to the proposed analytical model.
Development of a randomized 3D cell model for Monte Carlo microdosimetry simulations
Energy Technology Data Exchange (ETDEWEB)
Douglass, Michael; Bezak, Eva; Penfold, Scott [School of Chemistry and Physics, University of Adelaide, North Terrace, Adelaide 5005, South Australia (Australia) and Department of Medical Physics, Royal Adelaide Hospital, North Terrace, Adelaide 5000, South Australia (Australia)
2012-06-15
Purpose: The objective of the current work was to develop an algorithm for growing a macroscopic tumor volume from individual randomized quasi-realistic cells. The major physical and chemical components of the cell need to be modeled. It is intended to import the tumor volume into GEANT4 (and potentially other Monte Carlo packages) to simulate ionization events within the cell regions. Methods: A MATLAB Copyright-Sign code was developed to produce a tumor coordinate system consisting of individual ellipsoidal cells randomized in their spatial coordinates, sizes, and rotations. An eigenvalue method using a mathematical equation to represent individual cells was used to detect overlapping cells. GEANT4 code was then developed to import the coordinate system into GEANT4 and populate it with individual cells of varying sizes and composed of the membrane, cytoplasm, reticulum, nucleus, and nucleolus. Each region is composed of chemically realistic materials. Results: The in-house developed MATLAB Copyright-Sign code was able to grow semi-realistic cell distributions ({approx}2 Multiplication-Sign 10{sup 8} cells in 1 cm{sup 3}) in under 36 h. The cell distribution can be used in any number of Monte Carlo particle tracking toolkits including GEANT4, which has been demonstrated in this work. Conclusions: Using the cell distribution and GEANT4, the authors were able to simulate ionization events in the individual cell components resulting from 80 keV gamma radiation (the code is applicable to other particles and a wide range of energies). This virtual microdosimetry tool will allow for a more complete picture of cell damage to be developed.
Wirth, Erin A.; Long, Maureen D.; Moriarty, John C.
2017-01-01
Teleseismic receiver functions contain information regarding Earth structure beneath a seismic station. P-to-SV converted phases are often used to characterize crustal and upper-mantle discontinuities and isotropic velocity structures. More recently, P-to-SH converted energy has been used to interrogate the orientation of anisotropy at depth, as well as the geometry of dipping interfaces. Many studies use a trial-and-error forward modeling approach for the interpretation of receiver functions, generating synthetic receiver functions from a user-defined input model of Earth structure and amending this model until it matches major features in the actual data. While often successful, such an approach makes it impossible to explore model space in a systematic and robust manner, which is especially important given that solutions are likely non-unique. Here, we present a Markov chain Monte Carlo algorithm with Gibbs sampling for the interpretation of anisotropic receiver functions. Synthetic examples are used to test the viability of the algorithm, suggesting that it works well for models with a reasonable number of free parameters (<˜20). Additionally, the synthetic tests illustrate that certain parameters are well constrained by receiver function data, while others are subject to severe trade-offs-an important implication for studies that attempt to interpret Earth structure based on receiver function data. Finally, we apply our algorithm to receiver function data from station WCI in the central United States. We find evidence for a change in anisotropic structure at mid-lithospheric depths, consistent with previous work that used a grid search approach to model receiver function data at this station. Forward modeling of receiver functions using model space search algorithms, such as the one presented here, provide a meaningful framework for interrogating Earth structure from receiver function data.
Nightingale, M.P.; Blöte , H.W.J.
1996-01-01
The principle and the efficiency of the Monte Carlo transfer-matrix algorithm are discussed. Enhancements of this algorithm are illustrated by applications to several phase transitions in lattice spin models. We demonstrate how the statistical noise can be reduced considerably by a similarity transf
Ivantsov, Ilya; Ferraz, Alvaro; Kochetov, Evgenii
2016-01-01
We perform quantum Monte Carlo simulations of the itinerant-localized periodic Kondo-Heisenberg model for the underdoped cuprates to calculate the associated spin correlation functions. The strong electron correlations are shown to play a key role in the abrupt destruction of the quasi long-range antiferromagnetic order in the lightly doped regime.
Ivantsov, Ilya; Ferraz, Alvaro; Kochetov, Evgenii
2016-12-01
We perform quantum Monte Carlo simulations of the itinerant-localized periodic Kondo-Heisenberg model for the underdoped cuprates to calculate the associated spin correlation functions. The strong electron correlations are shown to play a key role in the abrupt destruction of the quasi-long-range antiferromagnetic order in the lightly doped regime.
Quantum Monte Carlo study of the cooperative binding of NO2 to fragment models of carbon nanotubes
Lawson, John W.; Bauschlicher Jr., Charles W.; Toulouse, Julien; Filippi, Claudia; Umrigar, C.J.
2008-01-01
Previous calculations on model systems for the cooperative binding of two NO2 molecules to carbon nanotubes using density functional theory and second order Moller–Plesset perturbation theory gave results differing by 30 kcal/mol. Quantum Monte Carlo calculations are performed to study the role of e
Meta-Analysis of Single-Case Data: A Monte Carlo Investigation of a Three Level Model
Owens, Corina M.
2011-01-01
Numerous ways to meta-analyze single-case data have been proposed in the literature, however, consensus on the most appropriate method has not been reached. One method that has been proposed involves multilevel modeling. This study used Monte Carlo methods to examine the appropriateness of Van den Noortgate and Onghena's (2008) raw data multilevel…
A Monte-Carlo study for the critical exponents of the three-dimensional O(6) model
Loison, D.
1999-09-01
Using Wolff's single-cluster Monte-Carlo update algorithm, the three-dimensional O(6)-Heisenberg model on a simple cubic lattice is simulated. With the help of finite size scaling we compute the critical exponents ν, β, γ and η. Our results agree with the field-theory predictions but not so well with the prediction of the series expansions.
Discrete-Layer Piezoelectric Plate and Shell Models for Active Tip-Clearance Control
Heyliger, P. R.; Ramirez, G.; Pei, K. C.
1994-01-01
The objectives of this work were to develop computational tools for the analysis of active-sensory composite structures with added or embedded piezoelectric layers. The targeted application for this class of smart composite laminates and the analytical development is the accomplishment of active tip-clearance control in turbomachinery components. Two distinct theories and analytical models were developed and explored under this contract: (1) a discrete-layer plate theory and corresponding computational models, and (2) a three dimensional general discrete-layer element generated in curvilinear coordinates for modeling laminated composite piezoelectric shells. Both models were developed from the complete electromechanical constitutive relations of piezoelectric materials, and incorporate both displacements and potentials as state variables. This report describes the development and results of these models. The discrete-layer theories imply that the displacement field and electrostatic potential through-the-thickness of the laminate are described over an individual layer rather than as a smeared function over the thickness of the entire plate or shell thickness. This is especially crucial for composites with embedded piezoelectric layers, as the actuating and sensing elements within these layers are poorly represented by effective or smeared properties. Linear Lagrange interpolation polynomials were used to describe the through-thickness laminate behavior. Both analytic and finite element approximations were used in the plane or surface of the structure. In this context, theoretical developments are presented for the discrete-layer plate theory, the discrete-layer shell theory, and the formulation of an exact solution for simply-supported piezoelectric plates. Finally, evaluations and results from a number of separate examples are presented for the static and dynamic analysis of the plate geometry. Comparisons between the different approaches are provided when
A Monte Carlo Method for Summing Modeled and Background Pollutant Concentrations.
Dhammapala, Ranil; Bowman, Clint; Schulte, Jill
2017-02-23
Air quality analyses for permitting new pollution sources often involve modeling dispersion of pollutants using models like AERMOD. Representative background pollutant concentrations must be added to modeled concentrations to determine compliance with air quality standards. Summing 98(th) (or 99(th)) percentiles of two independent distributions that are unpaired in time, overestimates air quality impacts and could needlessly burden sources with restrictive permit conditions. This problem is exacerbated when emissions and background concentrations peak during different seasons. Existing methods addressing this matter either require much input data, disregard source and background seasonality, or disregard the variability of the background by utilizing a single concentration for each season, month, hour-of-day, day-of-week or wind direction. Availability of representative background concentrations are another limitation. Here we report on work to improve permitting analyses, with the development of (1) daily gridded, background concentrations interpolated from 12km-CMAQ forecasts and monitored data. A two- step interpolation reproduced measured background concentrations to within 6.2%; and (2) a Monte Carlo (MC) method to combine AERMOD output and background concentrations while respecting their seasonality. The MC method randomly combines, with replacement, data from the same months, and calculates 1000 estimates of the 98(th) or 99(th) percentiles. The design concentration of background + new source is the median of these 1000 estimates. We found that the AERMOD design value (DV) + background DV lay at the upper end of the distribution of these thousand 99(th) percentiles, while measured DVs were at the lower end. Our MC method sits between these two metrics and is sufficiently protective of public health in that it overestimates design concentrations somewhat. We also calculated probabilities of exceeding specified thresholds at each receptor, better informing
Calibration, characterisation and Monte Carlo modelling of a fast-UNCL
Energy Technology Data Exchange (ETDEWEB)
Tagziria, Hamid, E-mail: hamid.tagziria@jrc.ec.europa.eu [European Commission, Joint Research Center, ITU-Nuclear Security Unit, I-21027 Ispra (Italy); Bagi, Janos; Peerani, Paolo [European Commission, Joint Research Center, ITU-Nuclear Security Unit, I-21027 Ispra (Italy); Belian, Antony [Department of Safeguards, SGTS/TAU, IAEA Vienna Austria (Austria)
2012-09-21
This paper describes the calibration, characterisation and Monte Carlo modelling of a new IAEA Uranium Neutron Collar (UNCL) for LWR fuel, which can be operated in both passive and active modes. It can employ either 35 {sup 3}He tubes (in active configuration) or 44 tubes at 10 atm pressure (in its passive configuration) and thus can be operated in fast mode (with Cd liner) as its efficiency is higher than that of the standard UNCL. Furthermore, it has an adjustable internal cavity which allows the measurement of varying sizes of fuel assemblies such as WWER, PWR and BWR. It is intended to be used with Cd liners in active mode (with an AmLi interrogation source in place) by the inspectorate for the determination of the {sup 235}U content in fresh fuel assemblies, especially in cases where high concentrations of burnable poisons cause problems with accurate assays. A campaign of measurements has been carried out at the JRC Performance Laboratories (PERLA) in Ispra (Italy) using various radionuclide neutron sources ({sup 252}Cf, {sup 241}AmLi and PuGa) and our BWR and PWR reference assemblies, in order to calibrate and characterise the counter as well as assess its performance and determine its optimum operational parameters. Furthermore, the fast-UNCL has been extensively modelled at JRC using the Monte Carlo code, MCNP-PTA, which simulates both the neutron transport and the coincidence electronics. The model has been validated using our measurements which agreed well with calculations. The WWER1000 fuel assembly for which there are no representative reference materials for an adequate calibration of the counter, has also been modelled and the response of the counter to this fuel assembly has been simulated. Subsequently numerical calibrations curves have been obtained for the above fuel assemblies in various modes (fast and thermal). The sensitivity of the counter to fuel rods substitution as well as other important aspects and the parameters of the fast
2016-01-01
Background Self-contained tests estimate and test the association between a phenotype and mean expression level in a gene set defined a priori. Many self-contained gene set analysis methods have been developed but the performance of these methods for phenotypes that are continuous rather than discrete and with multiple nuisance covariates has not been well studied. Here, I use Monte Carlo simulation to evaluate the performance of both novel and previously published (and readily available via R) methods for inferring effects of a continuous predictor on mean expression in the presence of nuisance covariates. The motivating data are a high-profile dataset which was used to show opposing effects of hedonic and eudaimonic well-being (or happiness) on the mean expression level of a set of genes that has been correlated with social adversity (the CTRA gene set). The original analysis of these data used a linear model (GLS) of fixed effects with correlated error to infer effects of Hedonia and Eudaimonia on mean CTRA expression. Methods The standardized effects of Hedonia and Eudaimonia on CTRA gene set expression estimated by GLS were compared to estimates using multivariate (OLS) linear models and generalized estimating equation (GEE) models. The OLS estimates were tested using O’Brien’s OLS test, Anderson’s permutation \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} }{}${r}_{F}^{2}$\\end{document}rF2-test, two permutation F-tests (including GlobalAncova), and a rotation z-test (Roast). The GEE estimates were tested using a Wald test with robust standard errors. The performance (Type I, II, S, and M errors) of all tests was investigated using a Monte Carlo simulation of data explicitly modeled on the re-analyzed dataset. Results GLS estimates are inconsistent between data
Directory of Open Access Journals (Sweden)
Jeffrey A. Walker
2016-10-01
Full Text Available Background Self-contained tests estimate and test the association between a phenotype and mean expression level in a gene set defined a priori. Many self-contained gene set analysis methods have been developed but the performance of these methods for phenotypes that are continuous rather than discrete and with multiple nuisance covariates has not been well studied. Here, I use Monte Carlo simulation to evaluate the performance of both novel and previously published (and readily available via R methods for inferring effects of a continuous predictor on mean expression in the presence of nuisance covariates. The motivating data are a high-profile dataset which was used to show opposing effects of hedonic and eudaimonic well-being (or happiness on the mean expression level of a set of genes that has been correlated with social adversity (the CTRA gene set. The original analysis of these data used a linear model (GLS of fixed effects with correlated error to infer effects of Hedonia and Eudaimonia on mean CTRA expression. Methods The standardized effects of Hedonia and Eudaimonia on CTRA gene set expression estimated by GLS were compared to estimates using multivariate (OLS linear models and generalized estimating equation (GEE models. The OLS estimates were tested using O’Brien’s OLS test, Anderson’s permutation ${r}_{F}^{2}$ r F 2 -test, two permutation F-tests (including GlobalAncova, and a rotation z-test (Roast. The GEE estimates were tested using a Wald test with robust standard errors. The performance (Type I, II, S, and M errors of all tests was investigated using a Monte Carlo simulation of data explicitly modeled on the re-analyzed dataset. Results GLS estimates are inconsistent between data sets, and, in each dataset, at least one coefficient is large and highly statistically significant. By contrast, effects estimated by OLS or GEE are very small, especially relative to the standard errors. Bootstrap and permutation GLS
The two-phase issue in the O(n) non-linear $\\sigma$-model: A Monte Carlo study
Alles, B.; Buonanno, A.; Cella, G.
1996-01-01
We have performed a high statistics Monte Carlo simulation to investigate whether the two-dimensional O(n) non-linear sigma models are asymptotically free or they show a Kosterlitz- Thouless-like phase transition. We have calculated the mass gap and the magnetic susceptibility in the O(8) model with standard action and the O(3) model with Symanzik action. Our results for O(8) support the asymptotic freedom scenario.
Wilson, Robert H.; Dooley, Kathryn A.; Morris, Michael D.; Mycek, Mary-Ann
2009-02-01
Light-scattering spectroscopy has the potential to provide information about bone composition via a fiber-optic probe placed on the skin. In order to design efficient probes, one must understand the effect of all tissue layers on photon transport. To quantitatively understand the effect of overlying tissue layers on the detected bone Raman signal, a layered Monte Carlo model was modified for Raman scattering. The model incorporated the absorption and scattering properties of three overlying tissue layers (dermis, subdermis, muscle), as well as the underlying bone tissue. The attenuation of the collected bone Raman signal, predominantly due to elastic light scattering in the overlying tissue layers, affected the carbonate/phosphate (C/P) ratio by increasing the standard deviation of the computational result. Furthermore, the mean C/P ratio varied when the relative thicknesses of the layers were varied and the elastic scattering coefficient at the Raman scattering wavelength of carbonate was modeled to be different from that at the Raman scattering wavelength of phosphate. These results represent the first portion of a computational study designed to predict optimal probe geometry and help to analyze detected signal for Raman scattering experiments involving bone.
Mesh-based Monte Carlo code for fluorescence modeling in complex tissues with irregular boundaries
Wilson, Robert H.; Chen, Leng-Chun; Lloyd, William; Kuo, Shiuhyang; Marcelo, Cynthia; Feinberg, Stephen E.; Mycek, Mary-Ann
2011-07-01
There is a growing need for the development of computational models that can account for complex tissue morphology in simulations of photon propagation. We describe the development and validation of a user-friendly, MATLAB-based Monte Carlo code that uses analytically-defined surface meshes to model heterogeneous tissue geometry. The code can use information from non-linear optical microscopy images to discriminate the fluorescence photons (from endogenous or exogenous fluorophores) detected from different layers of complex turbid media. We present a specific application of modeling a layered human tissue-engineered construct (Ex Vivo Produced Oral Mucosa Equivalent, EVPOME) designed for use in repair of oral tissue following surgery. Second-harmonic generation microscopic imaging of an EVPOME construct (oral keratinocytes atop a scaffold coated with human type IV collagen) was employed to determine an approximate analytical expression for the complex shape of the interface between the two layers. This expression can then be inserted into the code to correct the simulated fluorescence for the effect of the irregular tissue geometry.
Matsumoto, T.
2007-09-01
Monte Carlo simulations are performed to evaluate depth-dose distributions for possible treatment of cancers by boron neutron capture therapy (BNCT). The ICRU computational model of ADAM & EVA was used as a phantom to simulate tumors at a depth of 5 cm in central regions of the lungs, liver and pancreas. Tumors of the prostate and osteosarcoma were also centered at the depth of 4.5 and 2.5 cm in the phantom models. The epithermal neutron beam from a research reactor was the primary neutron source for the MCNP calculation of the depth-dose distributions in those cancer models. For brain tumor irradiations, the whole-body dose was also evaluated. The MCNP simulations suggested that a lethal dose of 50 Gy to the tumors can be achieved without reaching the tolerance dose of 25 Gy to normal tissue. The whole-body phantom calculations also showed that the BNCT could be applied for brain tumors without significant damage to whole-body organs.
Monte Carlo Uncertainty Quantification Using Quasi-1D SRM Ballistic Model
Directory of Open Access Journals (Sweden)
Davide Viganò
2016-01-01
Full Text Available Compactness, reliability, readiness, and construction simplicity of solid rocket motors make them very appealing for commercial launcher missions and embarked systems. Solid propulsion grants high thrust-to-weight ratio, high volumetric specific impulse, and a Technology Readiness Level of 9. However, solid rocket systems are missing any throttling capability at run-time, since pressure-time evolution is defined at the design phase. This lack of mission flexibility makes their missions sensitive to deviations of performance from nominal behavior. For this reason, the reliability of predictions and reproducibility of performances represent a primary goal in this field. This paper presents an analysis of SRM performance uncertainties throughout the implementation of a quasi-1D numerical model of motor internal ballistics based on Shapiro’s equations. The code is coupled with a Monte Carlo algorithm to evaluate statistics and propagation of some peculiar uncertainties from design data to rocker performance parameters. The model has been set for the reproduction of a small-scale rocket motor, discussing a set of parametric investigations on uncertainty propagation across the ballistic model.
Kumar, A; Chauhan, S
2017-03-08
Obesity is one of the most provoking health burdens in the developed countries. One of the strategies to prevent obesity is the inhibition of pancreatic lipase enzyme. The aim of this study was to build QSAR models for natural lipase inhibitors by using the Monte Carlo method. The molecular structures were represented by the simplified molecular input line entry system (SMILES) notation and molecular graphs. Three sets - training, calibration and test set of three splits - were examined and validated. Statistical quality of all the described models was very good. The best QSAR model showed the following statistical parameters: r(2) = 0.864 and Q(2) = 0.836 for the test set and r(2) = 0.824 and Q(2) = 0.819 for the validation set. Structural attributes for increasing and decreasing the activity (expressed as pIC50) were also defined. Using defined structural attributes, the design of new potential lipase inhibitors is also presented. Additionally, a molecular docking study was performed for the determination of binding modes of designed molecules.
Monte carlo method-based QSAR modeling of penicillins binding to human serum proteins.
Veselinović, Jovana B; Toropov, Andrey A; Toropova, Alla P; Nikolić, Goran M; Veselinović, Aleksandar M
2015-01-01
The binding of penicillins to human serum proteins was modeled with optimal descriptors based on the Simplified Molecular Input-Line Entry System (SMILES). The concentrations of protein-bound drug for 87 penicillins expressed as percentage of the total plasma concentration were used as experimental data. The Monte Carlo method was used as a computational tool to build up the quantitative structure-activity relationship (QSAR) model for penicillins binding to plasma proteins. One random data split into training, test and validation set was examined. The calculated QSAR model had the following statistical parameters: r(2) = 0.8760, q(2) = 0.8665, s = 8.94 for the training set and r(2) = 0.9812, q(2) = 0.9753, s = 7.31 for the test set. For the validation set, the statistical parameters were r(2) = 0.727 and s = 12.52, but after removing the three worst outliers, the statistical parameters improved to r(2) = 0.921 and s = 7.18. SMILES-based molecular fragments (structural indicators) responsible for the increase and decrease of penicillins binding to plasma proteins were identified. The possibility of using these results for the computer-aided design of new penicillins with desired binding properties is presented.
Tests of the modified Sigmund model of ion sputtering using Monte Carlo simulations
Hofsäss, Hans; Bradley, R. Mark
2015-05-01
Monte Carlo simulations are used to evaluate the Modified Sigmund Model of Sputtering. Simulations were carried out for a range of ion incidence angles and surface curvatures for different ion species, ion energies, and target materials. Sputter yields, moments of erosive crater functions, and the fraction of backscattered energy were determined. In accordance with the Modified Sigmund Model of Sputtering, we find that for sufficiently large incidence angles θ the curvature dependence of the erosion crater function tends to destabilize the solid surface along the projected direction of the incident ions. For the perpendicular direction, however, the curvature dependence always leads to a stabilizing contribution. The simulation results also show that, for larger values of θ, a significant fraction of the ions is backscattered, carrying off a substantial amount of the incident ion energy. This provides support for the basic idea behind the Modified Sigmund Model of Sputtering: that the incidence angle θ should be replaced by a larger angle Ψ to account for the reduced energy that is deposited in the solid for larger values of θ.
Monte Carlo simulations for a Lotka-type model with reactant surface diffusion and interactions.
Zvejnieks, G; Kuzovkov, V N
2001-05-01
The standard Lotka-type model, which was introduced for the first time by Mai et al. [J. Phys. A 30, 4171 (1997)] for a simplified description of autocatalytic surface reactions, is generalized here for a case of mobile and energetically interacting reactants. The mathematical formalism is proposed for determining the dependence of transition rates on the interaction energy (and temperature) for the general mathematical model, and the Lotka-type model, in particular. By means of Monte Carlo computer simulations, we have studied the impact of diffusion (with and without energetic interactions between reactants) on oscillatory properties of the A+B-->2B reaction. The diffusion leads to a desynchronization of oscillations and a subsequent decrease of oscillation amplitude. The energetic interaction between reactants has a dual effect depending on the type of mobile reactants. In the limiting case of mobile reactants B the repulsion results in a decrease of amplitudes. However, these amplitudes increase if reactants A are mobile and repulse each other. A simplified interpretation of the obtained results is given.
Modeling Monte Carlo of multileaf collimators using the code GEANT4
Energy Technology Data Exchange (ETDEWEB)
Oliveira, Alex C.H.; Lima, Fernando R.A., E-mail: oliveira.ach@yahoo.com, E-mail: falima@cnen.gov.br [Centro Regional de Ciencias Nucleares do Nordeste (CRCN-NE/CNEN-PE), Recife, PE (Brazil); Lima, Luciano S.; Vieira, Jose W., E-mail: lusoulima@yahoo.com.br [Instituto Federal de Educacao, Ciencia e Tecnologia de Pernambuco (IFPE), Recife, PE (Brazil)
2014-07-01
Radiotherapy uses various techniques and equipment for local treatment of cancer. The equipment most often used in radiotherapy to the patient irradiation is linear accelerator (Linac). Among the many algorithms developed for evaluation of dose distributions in radiotherapy planning, the algorithms based on Monte Carlo (MC) methods have proven to be very promising in terms of accuracy by providing more realistic results. The MC simulations for applications in radiotherapy are divided into two parts. In the first, the simulation of the production of the radiation beam by the Linac is performed and then the phase space is generated. The phase space contains information such as energy, position, direction, etc. of millions of particles (photons, electrons, positrons). In the second part the simulation of the transport of particles (sampled phase space) in certain configurations of irradiation field is performed to assess the dose distribution in the patient (or phantom). Accurate modeling of the Linac head is of particular interest in the calculation of dose distributions for intensity modulated radiation therapy (IMRT), where complex intensity distributions are delivered using a multileaf collimator (MLC). The objective of this work is to describe a methodology for modeling MC of MLCs using code Geant4. To exemplify this methodology, the Varian Millennium 120-leaf MLC was modeled, whose physical description is available in BEAMnrc Users Manual (20 11). The dosimetric characteristics (i.e., penumbra, leakage, and tongue-and-groove effect) of this MLC were evaluated. The results agreed with data published in the literature concerning the same MLC. (author)
Comparison of truncated shell model calculations in the laboratory and intrinsic systems
Energy Technology Data Exchange (ETDEWEB)
Catara, F.; Insolia, A.; Sambataro, M.; Maglione, E.; Vitturi, A.
1985-08-01
We perform, in the case of particles moving in a single-j level, shell model calculations in which the angular momentum of the individual pairs is restricted to a maximum value. The comparison with the full calculation shows the need for including at least the G pairs in the model space in order to reproduce the correct moments of inertia and transition rates of the different rotational bands. We also show that a level scheme very close to that obtained in the laboratory system can be alternatively obtained by angular momentum projection starting from intrinsic states evaluated in the intrinsic frame.
Nanoflares and MHD turbulence in coronal loops: a hybrid shell model.
Nigro, Giuseppina; Malara, Francesco; Carbone, Vincenzo; Veltri, Pierluigi
2004-05-14
A model to describe injection, due to footpoint motions, storage, and dissipation of MHD turbulence in coronal loops, is presented. The model is based on the use of the shell technique in the wave vector space applied to the set of reduced MHD equations. Numerical simulation showed that the energy injected is efficiently stored in the loop where a significant level of magnetic and velocity fluctuations is obtained. Nonlinear interactions among these fluctuations give rise to an energy cascade towards smaller scales where energy is dissipated in an intermittent fashion. The statistical analysis performed on the intermittent dissipative events compares well with all observed properties of nanoflare emission statistics.
Shell model estimate of electric dipole moments in medium and heavy nuclei
Directory of Open Access Journals (Sweden)
Teruya E.
2014-03-01
Full Text Available It is evidence for an extension of the Standard Model in particle physics, if static electric dipole moments (EDMs are measured for any elementary particle. The nuclear EDM arises mainly from two sources: one comes from asymmetric charge distribution in a nucleus and the other is due to the nucleon intrinsic EDM. We estimate the nuclear EDMs from two sources for the 1/21+ states in Xe isotopes by a shell model approach using full orbitals between magic numbers 50 and 82.
Two center shell model with Woods-Saxon potentials: adiabatic and diabatic states in fusion
Díaz-Torres, A; Diaz-Torres, Alexis; Scheid, Werner
2005-01-01
A realistic two-center shell model for fusion is proposed, which is based on two spherical Woods-Saxon potentials and the potential separable expansion method. This model describes the single-particle motion in a fusing system. A technique for calculating stationary diabatic states is suggested which makes use of the formal definition of those states, i.e., they minimize the radial nonadiabatic coupling between the adiabatic states. As an example the system $^{16}$O + $^{40}$Ca $\\to$ $^{56}$Ni is discussed.
Atomically thin spherical shell-shaped superscatterers based on a Bohr model.
Li, Rujiang; Lin, Xiao; Lin, Shisheng; Liu, Xu; Chen, Hongsheng
2015-12-18
Graphene monolayers can be used for atomically thin three-dimensional shell-shaped superscatterer designs. Due to the excitation of the first-order resonance of transverse magnetic (TM) graphene plasmons, the scattering cross section of the bare subwavelength dielectric particle is enhanced significantly by five orders of magnitude. The superscattering phenomenon can be intuitively understood and interpreted with a Bohr model. In addition, based on the analysis of the Bohr model, it is shown that contrary to the TM case, superscattering is hard to achieve by exciting the resonance of transverse electric (TE) graphene plasmons due to their poor field confinements.
Reflection Asymmetric Shell Model for the Description of Octupole Rotational Bands
Institute of Scientific and Technical Information of China (English)
GAO Zao-Chun; CHEN Yong-Shou
2001-01-01
The reflection asymmetric shell model has been formulated to describe the high spin states of octupole-deformed nuclei. The long-range separable forces of quadrupole, octupole and hexadecapole, as well as monopole and quadrupole pairing, are included in the Hamiltonian. The bases, on which the Hamiltonian is diagonalized, are the eigenstates of angular momentum and parity obtained by projecting the octupole-deformed multi-quasiparticle states onto good angular momentum and good parity. The general features of rotational octupole bands in eveneven nuclei can be reproduced by the model and the calculated result is in good agreement with experiment.
Zhou, Chenggang; Landau, D. P.; Schulthess, Thomas C.
2006-01-01
By considering the appropriate finite-size effect, we explain the connection between Monte Carlo simulations of two-dimensional anisotropic Heisenberg antiferromagnet in a field and the early renormalization group calculation for the bicritical point in $2+\\epsilon$ dimensions. We found that the long length scale physics of the Monte Carlo simulations is indeed captured by the anisotropic nonlinear $\\sigma$ model. Our Monte Carlo data and analysis confirm that the bicritical point in two dime...
Emergence of cluster structures and collectivity within a no-core shell-model framework
Launey, K. D.; Dreyfuss, A. C.; Draayer, J. P.; Dytrych, T.; Baker, R.
2014-12-01
An innovative symmetry-guided concept, which capitalizes on partial as well as exact symmetries that underpin the structure of nuclei, is discussed. Within this framework, ab initio applications of the theory to light nuclei reveal the origin of collective modes and the emergence a simple orderly pattern from first principles. This provides a strategy for determining the nature of bound states of nuclei in terms of a relatively small fraction of the complete shell-model space, which, in turn, can be used to explore ultra-large model spaces for a description of alpha-cluster and highly deformed structures together with the associated rotations. We find that by using only a fraction of the model space extended far beyond current no-core shell-model limits and a long-range interaction that respects the symmetries in play, the outcome reproduces characteristic features of the low-lying 0+ states in 12 C (including the elusive Hoyle state and its 2+ excitation) and agrees with ab initio results in smaller spaces. This is achieved by selecting those particle configurations and components of the interaction found to be foremost responsible for the primary physics governing clustering phenomena and large spatial deformation in the ground-state and Hoyle-state rotational bands of 12 C. For these states, we offer a novel perspective emerging out of no-core shell-model considerations, including a discussion of associated nuclear deformation, matter radii, and density distribution. The framework we find is also extensible to negative-parity states (e.g., the 3-1 state in 12C) and beyond, namely, to the low-lying 0+ states of 8Be as well as the ground-state rotational band of Ne, Mg, and Si isotopes. The findings inform key features of the nuclear interaction and point to a new insight into the formation of highly-organized simple patterns in nuclear dynamics.
Mohammad, S. Noor
2010-09-01
Semiconductor nanotubes, including carbon nanotubes, have vast potential for new technology development. The fundamental physics and growth kinetics of these nanotubes are still obscured. Various models developed to elucidate the growth suffer from limited applicability. An in-depth investigation of the fundamentals of nanotube growth has, therefore, been carried out. For this investigation, various features of nanotube growth, and the role of the foreign element catalytic agent (FECA) in this growth, have been considered. Observed growth anomalies have been analyzed. Based on this analysis, a new shell model and a general hypothesis have been proposed for the growth. The essential element of the shell model is the seed generated from segregation during growth. The seed structure has been defined, and the formation of droplet from this seed has been described. A modified definition of the droplet exhibiting adhesive properties has also been presented. Various characteristics of the droplet, required for alignment and organization of atoms into tubular forms, have been discussed. Employing the shell model, plausible scenarios for the formation of carbon nanotubes, and the variation in the characteristics of these carbon nanotubes have been articulated. The experimental evidences, for example, for the formation of shell around a core, dipole characteristics of the seed, and the existence of nanopores in the seed, have been presented. They appear to justify the validity of the proposed model. The diversities of nanotube characteristics, fundamentals underlying the creation of bamboo-shaped carbon nanotubes, and the impurity generation on the surface of carbon nanotubes have been elucidated. The catalytic action of FECA on growth has been quantified. The applicability of the proposed model to the nanotube growth by a variety of mechanisms has been elaborated. These mechanisms include the vapor-liquid-solid mechanism, the oxide-assisted growth mechanism, the self
Models of the SL9 Impacts I. Ballistic Monte-Carlo Plume
Harrington, J; Harrington, Joseph; Deming, Drake
2001-01-01
We model the Comet Shoemaker-Levy 9 - Jupiter impact plumes to calculate synthetic plume views, atmospheric infall fluxes, and debris patterns. Our plume is a swarm of ballistic particles with one of several mass-velocity distributions (MVD). The swarm is ejected instantaneously and uniformly into a cone from its apex. Upon falling to the ejection altitude, particles slide with horizontal deceleration following one of several schemes. The model ignores hydrodynamic and Coriolis effects. We adjust plume tilt, opening angle, and minimum velocity, and choose MVD and sliding schemes, to create impact patterns that match observations. Our best match uses the power-law MVD from the numerical impact model of Zahnle and Mac Low, with velocity cutoffs at 4.5 and 11.8 km/sec, cone opening angle of 75 degrees, cone tilt of 30 degrees from vertical, and a sliding constant deceleration of 1.74 m/sec^2. A mathematically-derived feature of Zahnle and Mac Low's published cumulative MVD is a thin shell of mass at the maximum ...
Monte Carlo modeling of Lead-Cooled Fast Reactor in adiabatic equilibrium state
Energy Technology Data Exchange (ETDEWEB)
Stanisz, Przemysław, E-mail: pstanisz@agh.edu.pl; Oettingen, Mikołaj, E-mail: moettin@agh.edu.pl; Cetnar, Jerzy, E-mail: cetnar@mail.ftj.agh.edu.pl
2016-05-15
Graphical abstract: - Highlights: • We present the Monte Carlo modeling of the LFR in the adiabatic equilibrium state. • We assess the adiabatic equilibrium fuel composition using the MCB code. • We define the self-adjusting process of breeding gain by the control rod operation. • The designed LFR can work in the adiabatic cycle with zero fuel breeding. - Abstract: Nuclear power would appear to be the only energy source able to satisfy the global energy demand while also achieving a significant reduction of greenhouse gas emissions. Moreover, it can provide a stable and secure source of electricity, and plays an important role in many European countries. However, nuclear power generation from its birth has been doomed by the legacy of radioactive nuclear waste. In addition, the looming decrease in the available resources of fissile U235 may influence the future sustainability of nuclear energy. The integrated solution to both problems is not trivial, and postulates the introduction of a closed-fuel cycle strategy based on breeder reactors. The perfect choice of a novel reactor system fulfilling both requirements is the Lead-Cooled Fast Reactor operating in the adiabatic equilibrium state. In such a state, the reactor converts depleted or natural uranium into plutonium while consuming any self-generated minor actinides and transferring only fission products as waste. We present the preliminary design of a Lead-Cooled Fast Reactor operating in the adiabatic equilibrium state with the Monte Carlo Continuous Energy Burnup Code – MCB. As a reference reactor model we apply the core design developed initially under the framework of the European Lead-cooled SYstem (ELSY) project and refined in the follow-up Lead-cooled European Advanced DEmonstration Reactor (LEADER) project. The major objective of the study is to show to what extent the constraints of the adiabatic cycle are maintained and to indicate the phase space for further improvements. The analysis
Dynamic Critical Behavior of Multi-Grid Monte Carlo for Two-Dimensional Nonlinear $\\sigma$-Models
Mana, Gustavo; Mendes, Tereza; Pelissetto, Andrea; Sokal, Alan D.
1995-01-01
We introduce a new and very convenient approach to multi-grid Monte Carlo (MGMC) algorithms for general nonlinear $\\sigma$-models: it is based on embedding an $XY$ model into the given $\\sigma$-model, and then updating the induced $XY$ model using a standard $XY$-model MGMC code. We study the dynamic critical behavior of this algorithm for the two-dimensional $O(N)$ $\\sigma$-models with $N = 3,4,8$ and for the $SU(3)$ principal chiral model. We find that the dynamic critical exponent $z$ vari...
Mathematical modelling of scanner-specific bowtie filters for Monte Carlo CT dosimetry
Kramer, R.; Cassola, V. F.; Andrade, M. E. A.; de Araújo, M. W. C.; Brenner, D. J.; Khoury, H. J.
2017-02-01
The purpose of bowtie filters in CT scanners is to homogenize the x-ray intensity measured by the detectors in order to improve the image quality and at the same time to reduce the dose to the patient because of the preferential filtering near the periphery of the fan beam. For CT dosimetry, especially for Monte Carlo calculations of organ and tissue absorbed doses to patients, it is important to take the effect of bowtie filters into account. However, material composition and dimensions of these filters are proprietary. Consequently, a method for bowtie filter simulation independent of access to proprietary data and/or to a specific scanner would be of interest to many researchers involved in CT dosimetry. This study presents such a method based on the weighted computer tomography dose index, CTDIw, defined in two cylindrical PMMA phantoms of 16 cm and 32 cm diameter. With an EGSnrc-based Monte Carlo (MC) code, ratios CTDIw/CTDI100,a were calculated for a specific CT scanner using PMMA bowtie filter models based on sigmoid Boltzmann functions combined with a scanner filter factor (SFF) which is modified during calculations until the calculated MC CTDIw/CTDI100,a matches ratios CTDIw/CTDI100,a, determined by measurements or found in publications for that specific scanner. Once the scanner-specific value for an SFF has been found, the bowtie filter algorithm can be used in any MC code to perform CT dosimetry for that specific scanner. The bowtie filter model proposed here was validated for CTDIw/CTDI100,a considering 11 different CT scanners and for CTDI100,c, CTDI100,p and their ratio considering 4 different CT scanners. Additionally, comparisons were made for lateral dose profiles free in air and using computational anthropomorphic phantoms. CTDIw/CTDI100,a determined with this new method agreed on average within 0.89% (max. 3.4%) and 1.64% (max. 4.5%) with corresponding data published by CTDosimetry (www.impactscan.org) for the CTDI HEAD and BODY phantoms
Shell Effect of Superheavy Nuclei in Self-consistent Mean-Field Models
Institute of Scientific and Technical Information of China (English)
RENZhong-Zhou; TAIFei; XUChang; CHENDing-Han; ZHANGHu-Yong; CAIXiang-Zhou; SHENWen-Qing
2004-01-01
We analyze in detail the numerical results of superheavy nuclei in deformed relativistic mean-field model and deformed Skyrme-Hartree-Fock model. The common points and differences of both models are systematically compared and discussed. Their consequences on the stability of superheavy nuclei are explored and explained. The theoreticalresults are compared with new data of superheavy nuclei from GSI and from Dubna and reasonable agreement is reached.Nuclear shell effect in superheavy region is analyzed and discussed. The spherical shell effect disappears in some cases due to the appearance of deformation or superdeformation in the ground states of nuclei, where valence nucleons occupysignificantly the intruder levels of nuclei. It is shown for the first time that the significant occupation of vaJence nucleons on the intruder states plays an important role for the ground state properties of superheavy nuclei. Nuclei are stable in the deformed or superdeformed configurations. We further point out that one cannot obtain the octupole deformation of even-even nuclei in the present relativistic mean-field model with the σ，ω and ρ mesons because there is no parityviolating interaction and the conservation of parity of even-even nuclei is a basic assumption of the present relativistic mean-field model.
A hybrid Monte Carlo model for the energy response functions of X-ray photon counting detectors
Wu, Dufan; Xu, Xiaofei; Zhang, Li; Wang, Sen
2016-09-01
In photon counting computed tomography (CT), it is vital to know the energy response functions of the detector for noise estimation and system optimization. Empirical methods lack flexibility and Monte Carlo simulations require too much knowledge of the detector. In this paper, we proposed a hybrid Monte Carlo model for the energy response functions of photon counting detectors in X-ray medical applications. GEANT4 was used to model the energy deposition of X-rays in the detector. Then numerical models were used to describe the process of charge sharing, anti-charge sharing and spectral broadening, which were too complicated to be included in the Monte Carlo model. Several free parameters were introduced in the numerical models, and they could be calibrated from experimental measurements such as X-ray fluorescence from metal elements. The method was used to model the energy response function of an XCounter Flite X1 photon counting detector. The parameters of the model were calibrated with fluorescence measurements. The model was further tested against measured spectrums of a VJ X-ray source to validate its feasibility and accuracy.
A hybrid Monte Carlo model for the energy response functions of X-ray photon counting detectors
Energy Technology Data Exchange (ETDEWEB)
Wu, Dufan; Xu, Xiaofei [Key Laboratory of Particle & Radiation Imaging, Tsinghua University, Ministry of Education (China); Department of Engineering Physics, Tsinghua University, Beijing 100084 (China); Zhang, Li, E-mail: zli@mail.tsinghua.edu.cn [Key Laboratory of Particle & Radiation Imaging, Tsinghua University, Ministry of Education (China); Department of Engineering Physics, Tsinghua University, Beijing 100084 (China); Wang, Sen [Key Laboratory of Particle & Radiation Imaging, Tsinghua University, Ministry of Education (China); Department of Engineering Physics, Tsinghua University, Beijing 100084 (China)
2016-09-11
In photon counting computed tomography (CT), it is vital to know the energy response functions of the detector for noise estimation and system optimization. Empirical methods lack flexibility and Monte Carlo simulations require too much knowledge of the detector. In this paper, we proposed a hybrid Monte Carlo model for the energy response functions of photon counting detectors in X-ray medical applications. GEANT4 was used to model the energy deposition of X-rays in the detector. Then numerical models were used to describe the process of charge sharing, anti-charge sharing and spectral broadening, which were too complicated to be included in the Monte Carlo model. Several free parameters were introduced in the numerical models, and they could be calibrated from experimental measurements such as X-ray fluorescence from metal elements. The method was used to model the energy response function of an XCounter Flite X1 photon counting detector. The parameters of the model were calibrated with fluorescence measurements. The model was further tested against measured spectrums of a VJ X-ray source to validate its feasibility and accuracy.
Direct simulation Monte Carlo modeling of relaxation processes in polyatomic gases
Pfeiffer, M.; Nizenkov, P.; Mirza, A.; Fasoulas, S.
2016-02-01
Relaxation processes of polyatomic molecules are modeled and implemented in an in-house Direct Simulation Monte Carlo code in order to enable the simulation of atmospheric entry maneuvers at Mars and Saturn's Titan. The description of rotational and vibrational relaxation processes is derived from basic quantum-mechanics using a rigid rotator and a simple harmonic oscillator, respectively. Strategies regarding the vibrational relaxation process are investigated, where good agreement for the relaxation time according to the Landau-Teller expression is found for both methods, the established prohibiting double relaxation method and the new proposed multi-mode relaxation. Differences and applications areas of these two methods are discussed. Consequently, two numerical methods used for sampling of energy values from multi-dimensional distribution functions are compared. The proposed random-walk Metropolis algorithm enables the efficient treatment of multiple vibrational modes within a time step with reasonable computational effort. The implemented model is verified and validated by means of simple reservoir simulations and the comparison to experimental measurements of a hypersonic, carbon-dioxide flow around a flat-faced cylinder.
Dynamical Models for NGC 6503 using a Markov Chain Monte Carlo Technique
Puglielli, David; Courteau, Stéphane
2010-01-01
We use Bayesian statistics and Markov chain Monte Carlo (MCMC) techniques to construct dynamical models for the spiral galaxy NGC 6503. The constraints include surface brightness profiles which display a Freeman Type II structure; HI and ionized gas rotation curves; the stellar rotation, which is nearly coincident with the ionized gas curve; and the line of sight stellar dispersion, with a sigma-drop at the centre. The galaxy models consist of a Sersic bulge, an exponential disc with an optional inner truncation and a cosmologically motivated dark halo. The Bayesian/MCMC technique yields the joint posterior probability distribution function for the input parameters. We examine several interpretations of the data: the Type II surface brightness profile may be due to dust extinction, to an inner truncated disc or to a ring of bright stars; and we test separate fits to the gas and stellar rotation curves to determine if the gas traces the gravitational potential. We test each of these scenarios for bar stability...
Monte Carlo model of neutral-particle transport in diverted plasmas
Energy Technology Data Exchange (ETDEWEB)
Heifetz, D.; Post, D.; Petravic, M.; Weisheit, J.; Bateman, G.
1981-11-01
The transport of neutral atoms and molecules in the edge and divertor regions of fusion experiments has been calculated using Monte-Carlo techniques. The deuterium, tritium, and helium atoms are produced by recombination in the plasma and at the walls. The relevant collision processes of charge exchange, ionization, and dissociation between the neutrals and the flowing plasma electrons and ions are included, along with wall reflection models. General two-dimensional wall and plasma geometries are treated in a flexible manner so that varied configurations can be easily studied. The algorithm uses a pseudo-collision method. Splitting with Russian roulette, suppression of absorption, and efficient scoring techniques are used to reduce the variance. The resulting code is sufficiently fast and compact to be incorporated into iterative treatments of plasma dynamics requiring numerous neutral profiles. The calculation yields the neutral gas densities, pressures, fluxes, ionization rates, momentum transfer rates, energy transfer rates, and wall sputtering rates. Applications have included modeling of proposed INTOR/FED poloidal divertor designs and other experimental devices.
A geometrical model for the Monte Carlo simulation of the TrueBeam linac
Rodriguez, Miguel; Fogliata, Antonella; Cozzi, Luca; Sauerwein, Wolfgang; Brualla, Lorenzo
2015-01-01
Monte Carlo (MC) simulation of linacs depends on the accurate geometrical description of the head. The geometry of the Varian TrueBeam linac is not available to researchers. Instead, the company distributes phase-space files (PSFs) of the flattening-filter-free (FFF) beams tallied upstream the jaws. Yet, MC simulations based on third party tallied PSFs are subject to limitations. We present an experimentally-based geometry developed for the simulation of the FFF beams of the TrueBeam linac. The upper part of the TrueBeam linac was modeled modifying the Clinac 2100 geometry. The most important modification is the replacement of the standard flattening filters by {\\it ad hoc} thin filters which were modeled by comparing dose measurements and simulations. The experimental dose profiles for the 6~MV and 10~MV FFF beams were obtained from the Varian Golden Data Set and from in-house measurements for radiation fields ranging from $3\\times3$ to $40\\times40$ cm$^2$. The same comparisons were done for dose profiles ob...
Fredriksson, Ingemar; Burdakov, Oleg; Larsson, Marcus; Strömberg, Tomas
2013-12-01
The tissue fraction of red blood cells (RBCs) and their oxygenation and speed-resolved perfusion are estimated in absolute units by combining diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry (LDF). The DRS spectra (450 to 850 nm) are assessed at two source-detector separations (0.4 and 1.2 mm), allowing for a relative calibration routine, whereas LDF spectra are assessed at 1.2 mm in the same fiber-optic probe. Data are analyzed using nonlinear optimization in an inverse Monte Carlo technique by applying an adaptive multilayered tissue model based on geometrical, scattering, and absorbing properties, as well as RBC flow-speed information. Simulations of 250 tissue-like models including up to 2000 individual blood vessels were used to evaluate the method. The absolute root mean square (RMS) deviation between estimated and true oxygenation was 4.1 percentage units, whereas the relative RMS deviations for the RBC tissue fraction and perfusion were 19% and 23%, respectively. Examples of in vivo measurements on forearm and foot during common provocations are presented. The method offers several advantages such as simultaneous quantification of RBC tissue fraction and oxygenation and perfusion from the same, predictable, sampling volume. The perfusion estimate is speed resolved, absolute (% RBC×mm/s), and more accurate due to the combination with DRS.
Regan, Caitlin; Hayakawa, Carole K.; Choi, Bernard
2016-03-01
Laser speckle imaging (LSI) enables measurement of relative blood flow in microvasculature and perfusion in tissues. To determine the impact of tissue optical properties and perfusion dynamics on speckle contrast, we developed a computational simulation of laser speckle contrast imaging. We used a discrete absorption-weighted Monte Carlo simulation to model the transport of light in tissue. We simulated optical excitation of a uniform flat light source and tracked the momentum transfer of photons as they propagated through a simulated tissue geometry. With knowledge of the probability distribution of momentum transfer occurring in various layers of the tissue, we calculated the expected laser speckle contrast arising with coherent excitation using both reflectance and transmission geometries. We simulated light transport in a single homogeneous tissue while independently varying either absorption (.001-100mm^-1), reduced scattering (.1-10mm^-1), or anisotropy (0.05-0.99) over a range of values relevant to blood and commonly imaged tissues. We observed that contrast decreased by 49% with an increase in optical scattering, and observed a 130% increase with absorption (exposure time = 1ms). We also explored how speckle contrast was affected by the depth (0-1mm) and flow speed (0-10mm/s) of a dynamic vascular inclusion. This model of speckle contrast is important to increase our understanding of how parameters such as perfusion dynamics, vessel depth, and tissue optical properties affect laser speckle imaging.
Chiapetto, M.; Messina, L.; Becquart, C. S.; Olsson, P.; Malerba, L.
2017-02-01
This work presents a revised set of parameters to be used in an Object kinetic Monte Carlo model to simulate the microstructure evolution under neutron irradiation of reactor pressure vessel steels at the operational temperature of light water reactors (∼300 °C). Within a "grey-alloy" approach, a more physical description than in a previous work is used to translate the effect of Mn and Ni solute atoms on the defect cluster diffusivity reduction. The slowing down of self-interstitial clusters, due to the interaction between solutes and crowdions in Fe is now parameterized using binding energies from the latest DFT calculations and the solute concentration in the matrix from atom-probe experiments. The mobility of vacancy clusters in the presence of Mn and Ni solute atoms was also modified on the basis of recent DFT results, thereby removing some previous approximations. The same set of parameters was seen to predict the correct microstructure evolution for two different types of alloys, under very different irradiation conditions: an Fe-C-MnNi model alloy, neutron irradiated at a relatively high flux, and a high-Mn, high-Ni RPV steel from the Swedish Ringhals reactor surveillance program. In both cases, the predicted self-interstitial loop density matches the experimental solute cluster density, further corroborating the surmise that the MnNi-rich nanofeatures form by solute enrichment of immobilized small interstitial loops, which are invisible to the electron microscope.
Clustering and heterogeneous dynamics in a kinetic Monte Carlo model of self-propelled hard disks.
Levis, Demian; Berthier, Ludovic
2014-06-01
We introduce a kinetic Monte Carlo model for self-propelled hard disks to capture with minimal ingredients the interplay between thermal fluctuations, excluded volume, and self-propulsion in large assemblies of active particles. We analyze in detail the resulting (density, self-propulsion) nonequilibrium phase diagram over a broad range of parameters. We find that purely repulsive hard disks spontaneously aggregate into fractal clusters as self-propulsion is increased and rationalize the evolution of the average cluster size by developing a kinetic model of reversible aggregation. As density is increased, the nonequilibrium clusters percolate to form a ramified structure reminiscent of a physical gel. We show that the addition of a finite amount of noise is needed to trigger a nonequilibrium phase separation, showing that demixing in active Brownian particles results from a delicate balance between noise, interparticle interactions, and self-propulsion. We show that self-propulsion has a profound influence on the dynamics of the active fluid. We find that the diffusion constant has a nonmonotonic behavior as self-propulsion is increased at finite density and that activity produces strong deviations from Fickian diffusion that persist over large time scales and length scales, suggesting that systems of active particles generically behave as dynamically heterogeneous systems.
Properties of Carbon-Oxygen White Dwarfs From Monte Carlo Stellar Models
Fields, C E; Petermann, I; Iliadis, C; Timmes, F X
2016-01-01
We investigate properties of carbon-oxygen white dwarfs with respect to the composite uncertainties in the reaction rates using the stellar evolution toolkit, Modules for Experiments in Stellar Astrophysics (MESA) and the probability density functions in the reaction rate library STARLIB. These are the first Monte Carlo stellar evolution studies that use complete stellar models. Focusing on 3 M$_{\\odot}$ models evolved from the pre main-sequence to the first thermal pulse, we survey the remnant core mass, composition, and structure properties as a function of 26 STARLIB reaction rates covering hydrogen and helium burning using a Principal Component Analysis and Spearman Rank-Order Correlation. Relative to the arithmetic mean value, we find the width of the 95\\% confidence interval to be $\\Delta M_{{\\rm 1TP}}$ $\\approx$ 0.019 M$_{\\odot}$ for the core mass at the first thermal pulse, $\\Delta$$t_{\\rm{1TP}}$ $\\approx$ 12.50 Myr for the age, $\\Delta \\log(T_{{\\rm c}}/{\\rm K}) \\approx$ 0.013 for the central temperat...
Numazawa, Satoshi; Smith, Roger
2011-10-01
Classical harmonic transition state theory is considered and applied in discrete lattice cells with hierarchical transition levels. The scheme is then used to determine transitions that can be applied in a lattice-based kinetic Monte Carlo (KMC) atomistic simulation model. The model results in an effective reduction of KMC simulation steps by utilizing a classification scheme of transition levels for thermally activated atomistic diffusion processes. Thermally activated atomistic movements are considered as local transition events constrained in potential energy wells over certain local time periods. These processes are represented by Markov chains of multidimensional Boolean valued functions in three-dimensional lattice space. The events inhibited by the barriers under a certain level are regarded as thermal fluctuations of the canonical ensemble and accepted freely. Consequently, the fluctuating system evolution process is implemented as a Markov chain of equivalence class objects. It is shown that the process can be characterized by the acceptance of metastable local transitions. The method is applied to a problem of Au and Ag cluster growth on a rippled surface. The simulation predicts the existence of a morphology-dependent transition time limit from a local metastable to stable state for subsequent cluster growth by accretion. Excellent agreement with observed experimental results is obtained.
A stochastic Markov chain approach for tennis: Monte Carlo simulation and modeling
Aslam, Kamran
This dissertation describes the computational formulation of probability density functions (pdfs) that facilitate head-to-head match simulations in tennis along with ranking systems developed from their use. A background on the statistical method used to develop the pdfs , the Monte Carlo method, and the resulting rankings are included along with a discussion on ranking methods currently being used both in professional sports and in other applications. Using an analytical theory developed by Newton and Keller in [34] that defines a tennis player's probability of winning a game, set, match and single elimination tournament, a computational simulation has been developed in Matlab that allows further modeling not previously possible with the analytical theory alone. Such experimentation consists of the exploration of non-iid effects, considers the concept the varying importance of points in a match and allows an unlimited number of matches to be simulated between unlikely opponents. The results of these studies have provided pdfs that accurately model an individual tennis player's ability along with a realistic, fair and mathematically sound platform for ranking them.
Single-site Lennard-Jones models via polynomial chaos surrogates of Monte Carlo molecular simulation
Kadoura, Ahmad Salim
2016-06-01
In this work, two Polynomial Chaos (PC) surrogates were generated to reproduce Monte Carlo (MC) molecular simulation results of the canonical (single-phase) and the NVT-Gibbs (two-phase) ensembles for a system of normalized structureless Lennard-Jones (LJ) particles. The main advantage of such surrogates, once generated, is the capability of accurately computing the needed thermodynamic quantities in a few seconds, thus efficiently replacing the computationally expensive MC molecular simulations. Benefiting from the tremendous computational time reduction, the PC surrogates were used to conduct large-scale optimization in order to propose single-site LJ models for several simple molecules. Experimental data, a set of supercritical isotherms, and part of the two-phase envelope, of several pure components were used for tuning the LJ parameters (ε, σ). Based on the conducted optimization, excellent fit was obtained for different noble gases (Ar, Kr, and Xe) and other small molecules (CH4, N2, and CO). On the other hand, due to the simplicity of the LJ model used, dramatic deviations between simulation and experimental data were observed, especially in the two-phase region, for more complex molecules such as CO2 and C2 H6.
Non-Local effective SU(2) Polyakov-loop models from inverse Monte-Carlo methods
Bahrampour, Bardiya; von Smekal, Lorenz
2016-01-01
The strong-coupling expansion of the lattice gauge action leads to Polyakov-loop models that effectively describe gluodynamics at low temperatures, and together with the hopping expansion of the fermion determinant provides insight into the QCD phase diagram at finite density and low temperatures, although for rather heavy quarks. At higher temperatures the strong-coupling expansion breaks down and it is expected that the interactions between Polyakov loops become non-local. Here, we therefore test how well pure SU(2) gluodynamics can be mapped onto different non-local Polyakov models with inverse Monte-Carlo methods. We take into account Polyakov loops in higher representations and gradually add interaction terms at larger distances. We are particularly interested in extrapolating the range of non-local terms in sufficiently large volumes and higher representations. We study the characteristic fall-off in strength of the non-local couplings with the interaction distance, and its dependence on the gauge coupl...
Bui, Khoa; Papavassiliou, Dimitrios
2012-02-01
The effective thermal conductivity (Keff) of carbon nanotube (CNT) composites is affected by the thermal boundary resistance (TBR) and by the dispersion pattern and geometry of the CNTs. We have previously modeled CNTs as straight cylinders and found that the TBR between CNTs (TBRCNT-CNT) can suppress Keff at high volume fractions of CNTs [1]. Effective medium theory results assume that the CNTs are in a perfect dispersion state and exclude the TBRCNT-CNT [2]. In this work, we report on the development of an algorithm for generating CNTs with worm-like geometry in 3D, and with different persistence lengths. These worm-like CNTs are then randomly placed in a periodic box representing a realistic state, since the persistence length of a CNT can be obtained from microscopic images. The use of these CNT geometries in conjunction with off-lattice Monte Carlo simulations [1] in order to study the effective thermal properties of nanocomposites will be discussed, as well as the effects of the persistence length on Keff and comparisons to straight cylinder models. References [1] K. Bui, B.P. Grady, D.V. Papavassiliou, Chem. Phys. Let., 508(4-6), 248-251, 2011 [2] C.W. Nan, G. Liu, Y. Lin, M. Li, App. Phys. Let., 85(16), 3549-3551, 2006
Direct simulation Monte Carlo modeling of relaxation processes in polyatomic gases
Energy Technology Data Exchange (ETDEWEB)
Pfeiffer, M., E-mail: mpfeiffer@irs.uni-stuttgart.de; Nizenkov, P., E-mail: nizenkov@irs.uni-stuttgart.de; Mirza, A., E-mail: mirza@irs.uni-stuttgart.de; Fasoulas, S., E-mail: fasoulas@irs.uni-stuttgart.de [Institute of Space Systems, University of Stuttgart, Pfaffenwaldring 29, D-70569 Stuttgart (Germany)
2016-02-15
Relaxation processes of polyatomic molecules are modeled and implemented in an in-house Direct Simulation Monte Carlo code in order to enable the simulation of atmospheric entry maneuvers at Mars and Saturn’s Titan. The description of rotational and vibrational relaxation processes is derived from basic quantum-mechanics using a rigid rotator and a simple harmonic oscillator, respectively. Strategies regarding the vibrational relaxation process are investigated, where good agreement for the relaxation time according to the Landau-Teller expression is found for both methods, the established prohibiting double relaxation method and the new proposed multi-mode relaxation. Differences and applications areas of these two methods are discussed. Consequently, two numerical methods used for sampling of energy values from multi-dimensional distribution functions are compared. The proposed random-walk Metropolis algorithm enables the efficient treatment of multiple vibrational modes within a time step with reasonable computational effort. The implemented model is verified and validated by means of simple reservoir simulations and the comparison to experimental measurements of a hypersonic, carbon-dioxide flow around a flat-faced cylinder.
Kwak, Moon K.; Heo, Seok; Jeong, Moonsan
2009-04-01
This paper is concerned with the dynamic modelling, active vibration controller design and experiments for a cylindrical shell equipped with piezoelectric sensors and actuators. The dynamic model was derived by using Rayleigh-Ritz method based on the Donnel-Mushtari shell theory. The actuator equations which relate the applied voltages to the generalized force and sensor equations which relate the generalized displacements to the sensor output voltages for the piezoelectric wafer were derived based on the pin-force model. The equations of motion along with the piezoelectric sensor equations were then reduced to modal forms considering the modes of interest. An aluminium shell was fabricated to demonstrate the effectiveness of the modelling and control techniques. The boundary conditions at both ends of the shell were assumed to be a shear diaphragm in the numerical analysis. Theoretical natural frequencies of the aluminium shell were then calculated and compared to experimental result. They were in good agreement with experimental result for the first two free-vibration modes. The multi-input and multi-output positive position feedback controller, which can cope with the first two vibration modes, was designed based on the block-inverse theory and was implemented digitally using the DSP board. The experimental results showed that vibrations of the cylindrical shell can be successfully suppressed by the piezoelectric actuator and the proposed controller.
Energy Technology Data Exchange (ETDEWEB)
Weathers, J.B. [Shock, Noise, and Vibration Group, Northrop Grumman Shipbuilding, P.O. Box 149, Pascagoula, MS 39568 (United States)], E-mail: James.Weathers@ngc.com; Luck, R. [Department of Mechanical Engineering, Mississippi State University, 210 Carpenter Engineering Building, P.O. Box ME, Mississippi State, MS 39762-5925 (United States)], E-mail: Luck@me.msstate.edu; Weathers, J.W. [Structural Analysis Group, Northrop Grumman Shipbuilding, P.O. Box 149, Pascagoula, MS 39568 (United States)], E-mail: Jeffrey.Weathers@ngc.com
2009-11-15
The complexity of mathematical models used by practicing engineers is increasing due to the growing availability of sophisticated mathematical modeling tools and ever-improving computational power. For this reason, the need to define a well-structured process for validating these models against experimental results has become a pressing issue in the engineering community. This validation process is partially characterized by the uncertainties associated with the modeling effort as well as the experimental results. The net impact of the uncertainties on the validation effort is assessed through the 'noise level of the validation procedure', which can be defined as an estimate of the 95% confidence uncertainty bounds for the comparison error between actual experimental results and model-based predictions of the same quantities of interest. Although general descriptions associated with the construction of the noise level using multivariate statistics exists in the literature, a detailed procedure outlining how to account for the systematic and random uncertainties is not available. In this paper, the methodology used to derive the covariance matrix associated with the multivariate normal pdf based on random and systematic uncertainties is examined, and a procedure used to estimate this covariance matrix using Monte Carlo analysis is presented. The covariance matrices are then used to construct approximate 95% confidence constant probability contours associated with comparison error results for a practical example. In addition, the example is used to show the drawbacks of using a first-order sensitivity analysis when nonlinear local sensitivity coefficients exist. Finally, the example is used to show the connection between the noise level of the validation exercise calculated using multivariate and univariate statistics.
Guan, Xiaofei; Ma, Manman; Gan, Zecheng; Xu, Zhenli; Li, Bo
2016-11-01
The distribution of ions near a charged surface is an important quantity in many biological and material processes, and has been therefore investigated intensively. However, few theoretical and simulation approaches have included the influence of concentration-induced variations in the local dielectric permittivity of an underlying electrolyte solution. Such local variations have long been observed and known to affect the properties of ionic solution in the bulk and around the charged surface. We propose a hybrid computational model that combines Monte Carlo simulations with continuum electrostatic modeling to investigate such properties. A key component in our hybrid model is a semianalytical formula for the ion-ion interaction energy in a dielectrically inhomogeneous environment. This formula is obtained by solving for the Green's function Poisson's equation with ionic-concentration-dependent dielectric permittivity using a harmonic interpolation method and spherical harmonic series. We also construct a self-consistent continuum model of electrostatics to describe the effect of ionic-concentration-dependent dielectric permittivity and the resulting self-energy contribution. With extensive numerical simulations, we verify the convergence of our hybrid simulation scheme, show the qualitatively different structures of ionic distribution due to the concentration-induced dielectric variations, and compare our simulation results with the self-consistent continuum model. In particular, we study the differences between weakly and strongly charged surfaces and multivalencies of counterions. Our hybrid simulations conform particularly the depletion of ionic concentrations near a charged surface and also capture the charge inversion. We discuss several issues and possible further improvement of our approach for simulations of large charged systems.
Modelling heterotachy in phylogenetic inference by reversible-jump Markov chain Monte Carlo.
Pagel, Mark; Meade, Andrew
2008-12-27
The rate at which a given site in a gene sequence alignment evolves over time may vary. This phenomenon--known as heterotachy--can bias or distort phylogenetic trees inferred from models of sequence evolution that assume rates of evolution are constant. Here, we describe a phylogenetic mixture model designed to accommodate heterotachy. The method sums the likelihood of the data at each site over more than one set of branch lengths on the same tree topology. A branch-length set that is best for one site may differ from the branch-length set that is best for some other site, thereby allowing different sites to have different rates of change throughout the tree. Because rate variation may not be present in all branches, we use a reversible-jump Markov chain Monte Carlo algorithm to identify those branches in which reliable amounts of heterotachy occur. We implement the method in combination with our 'pattern-heterogeneity' mixture model, applying it to simulated data and five published datasets. We find that complex evolutionary signals of heterotachy are routinely present over and above variation in the rate or pattern of evolution across sites, that the reversible-jump method requires far fewer parameters than conventional mixture models to describe it, and serves to identify the regions of the tree in which heterotachy is most pronounced. The reversible-jump procedure also removes the need for a posteriori tests of 'significance' such as the Akaike or Bayesian information criterion tests, or Bayes factors. Heterotachy has important consequences for the correct reconstruction of phylogenies as well as for tests of hypotheses that rely on accurate branch-length information. These include molecular clocks, analyses of tempo and mode of evolution, comparative studies and ancestral state reconstruction. The model is available from the authors' website, and can be used for the analysis of both nucleotide and morphological data.
Institute of Scientific and Technical Information of China (English)
Richard M. Males; Jeffrey A. Melby
2011-01-01
The US Army Corps of Engineers has a mission to conduct a wide array of programs in the arenas of water resources,including coastal protection.Coastal projects must be evaluated according to sound economic principles,and considerations of risk assessment and sea level change must be included in the analysis.Breakwaters are typically nearshore structures designed to reduce wave action in the lee of the structure,resulting in calmer waters within the protected area,with attendant benefits in terms of usability by navigation interests,shoreline protection,reduction of wave runup and onshore flooding,and protection of navigation channels from sedimentation and wave action.A common method of breakwater construction is the rubble mound breakwater,constructed in a trapezoidal cross section with gradually increasing stone sizes from the core out.Rubble mound breakwaters are subject to degradation from storms,particularly for antiquated designs with under-sized stones insufficient to protect against intense wave energy.Storm waves dislodge the stones,resulting in lowering of crest height and associated protective capability for wave reduction.This behavior happens over a long period of time,so a lifecycle model (that can analyze the damage progression over a period of years) is appropriate.Because storms are highly variable,a model that can support risk analysis is also needed.Economic impacts are determined by the nature of the wave climate in the protected area,and by the nature of the protected assets.Monte Carlo simulation (MCS)modeling that incorporates engineering and economic impacts is a worthwhile method for handling the many complexities involved in real world problems.The Corps has developed and utilized a number of MCS models to compare project alternatives in terms of their costs and benefits.This paper describes one such model,Coastal Structure simulation (CSsim) that has been developed specifically for planning level analysis of breakwaters.
Alcaraz, Olga; Trullàs, Joaquim; Tahara, Shuta; Kawakita, Yukinobu; Takeda, Shin'ichi
2016-09-01
The results of the structural properties of molten copper chloride are reported from high-energy X-ray diffraction measurements, reverse Monte Carlo modeling method, and molecular dynamics simulations using a polarizable ion model. The simulated X-ray structure factor reproduces all trends observed experimentally, in particular the shoulder at around 1 Å-1 related to intermediate range ordering, as well as the partial copper-copper correlations from the reverse Monte Carlo modeling, which cannot be reproduced by using a simple rigid ion model. It is shown that the shoulder comes from intermediate range copper-copper correlations caused by the polarized chlorides.
Directory of Open Access Journals (Sweden)
Kępisty Grzegorz
2015-09-01
Full Text Available In this paper, we compare the methodology of different time-step models in the context of Monte Carlo burnup calculations for nuclear reactors. We discuss the differences between staircase step model, slope model, bridge scheme and stochastic implicit Euler method proposed in literature. We focus on the spatial stability of depletion procedure and put additional emphasis on the problem of normalization of neutron source strength. Considered methodology has been implemented in our continuous energy Monte Carlo burnup code (MCB5. The burnup simulations have been performed using the simplified high temperature gas-cooled reactor (HTGR system with and without modeling of control rod withdrawal. Useful conclusions have been formulated on the basis of results.
Energy Technology Data Exchange (ETDEWEB)
Procassini, R.J. [Lawrence Livermore National lab., CA (United States)
1997-12-31
The fine-scale, multi-space resolution that is envisioned for accurate simulations of complex weapons systems in three spatial dimensions implies flop-rate and memory-storage requirements that will only be obtained in the near future through the use of parallel computational techniques. Since the Monte Carlo transport models in these simulations usually stress both of these computational resources, they are prime candidates for parallelization. The MONACO Monte Carlo transport package, which is currently under development at LLNL, will utilize two types of parallelism within the context of a multi-physics design code: decomposition of the spatial domain across processors (spatial parallelism) and distribution of particles in a given spatial subdomain across additional processors (particle parallelism). This implementation of the package will utilize explicit data communication between domains (message passing). Such a parallel implementation of a Monte Carlo transport model will result in non-deterministic communication patterns. The communication of particles between subdomains during a Monte Carlo time step may require a significant level of effort to achieve a high parallel efficiency.
Energy Technology Data Exchange (ETDEWEB)
Praus, Petr, E-mail: petr.praus@vsb.cz [Department of Analytical Chemistry and Material Testing, VŠB-Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava-Poruba (Czech Republic); Regional Materials Science and Technology Centre, VŠB-Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava (Czech Republic); Svoboda, Ladislav [Department of Analytical Chemistry and Material Testing, VŠB-Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava-Poruba (Czech Republic); Tokarský, Jonáš [Nanotechnology Centre, VŠB-Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava-Poruba (Czech Republic); IT4Innovations Centre of Excellence, VŠB-Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava-Poruba (Czech Republic); Hospodková, Alice [Department of Semiconductors, Institute of Physics ASCR, v. v. i., The Academy of Science of the Czech Republic, Na Slovance 1999/2, 182 21 Prague 8 (Czech Republic); Klemm, Volker [Institute of Materials Science, TU Bergakademie Freiberg, Gustav-Zeuner-Street 5, D-09599 Freiberg (Germany)
2014-02-15
Core/shell CdS/ZnS nanoparticles were modelled in the Material Studio environment and synthesized by one-pot procedure. The core CdS radius size and thickness of the ZnS shell composed of 1–3 ZnS monolayers were predicted from the molecular models. From UV–vis absorption spectra of the CdS/ZnS colloid dispersions transition energies of CdS and ZnS nanostructures were calculated. They indicated penetration of electrons and holes from the CdS core into the ZnS shell and relaxation strain in the ZnS shell structure. The transitions energies were used for calculation of the CdS core radius by the Schrödinger equation. Both the relaxation strain in ZnS shells and the size of the CdS core radius were predicted by the molecular modelling. The ZnS shell thickness and a degree of the CdS core coverage were characterized by the photocatalytic decomposition of Methylene Blue (MB) using CdS/ZnS nanoparticles as photocatalysts. The observed kinetic constants of the MB photodecomposition (k{sub obs}) were evaluated and a relationship between k{sub obs} and the ZnS shell thickness was derived. Regression results revealed that 86% of the CdS core surface was covered with ZnS and the average thickness of ZnS shell was about 12% higher than that predicted by molecular modelling.
A nonlocal shell model for mode transformation in single-walled carbon nanotubes.
Shi, M X; Li, Q M; Huang, Y
2009-11-11
A second-order strain gradient nonlocal shell model is established to study the mode transformation in single-walled carbon nanotubes (SWCNTs). Nonlocal length is calibrated carefully for SWCNTs in reference to molecular dynamics (MD) simulations through analysis of nonlocal length effects on the frequencies of the radial breathing mode (RBM) and circumferential flexural modes (CFMs) and its effects on mode transformation. All analyses show that only a negative second-order nonlocal shell model is appropriate to SWCNTs. Nonlocal length is evidently related to vibration modes and the radius-to-thickness ratio. It is found that a nonlocal length is approximately 0.1 nm in an average sense when RBM frequency is concerned. A nonlocal length of 0.122-0.259 nm is indicated for the mode transformation in a selected group of armchair SWCNTs. 2:1 and 1:1 internal resonances are found for the same SWCNT based on different models, which implies that the internal resonance mechanism depends on the model employed. Furthermore, it is shown that an effective thickness of approximately 0.1 nm is more appropriate to SWCNTs than 0.066 nm.
Wang, Yinglong; Qin, Aili; Chu, Lizhi; Deng, Zechao; Ding, Xuecheng; Guan, Li
2017-02-01
We simulated the nucleation and growth of Si nanoparticles produced by pulse laser deposition using Monte Carlo method at the molecular (microscopic) level. In the model, the mechanism and thermodynamic conditions of nucleation and growth of Si nanoparticles were described. In a real physical scale of target-substrate configuration, the model was used to analyze the average size distribution of Si nanoparticles in argon ambient gas and the calculated results are in agreement with the experimental results.
Motome, Yukitoshi; Penc, Karlo; Shannon, Nic
2005-01-01
The antiferromagnetic Heisenberg model on a pyrochlore lattice under external magnetic field is studied by classical Monte Carlo simulation. The model includes bilinear and biquadratic interactions; the latter effectively describes the coupling to lattice distortions. The magnetization process shows a half-magnetization plateau at low temperatures, accompanied with strong suppression of the magnetic susceptibility. Temperature dependence of the plateau behavior is clarified. Finite-temperatur...
Monte Carlo calculation model for heat radiation of inclined cylindrical flames and its application
Chang, Zhangyu; Ji, Jingwei; Huang, Yuankai; Wang, Zhiyi; Li, Qingjie
2017-02-01
Based on Monte Carlo method, a calculation model and its C++ calculating program for radiant heat transfer from an inclined cylindrical flame are proposed. In this model, the total radiation energy of the inclined cylindrical flame is distributed equally among a certain number of energy beams, which are emitted randomly from the flame surface. The incident heat flux on a surface is calculated by counting the number of energy beams which could reach the surface. The paper mainly studies the geometrical evaluation criterion for validity of energy beams emitted by inclined cylindrical flames and received by other surfaces. Compared to Mudan's formula results for a straight cylinder or a cylinder with 30° tilt angle, the calculated view factors range from 0.0043 to 0.2742 and the predicted view factors agree well with Mudan's results. The changing trend and values of incident heat fluxes computed by the model is consistent with experimental data measured by Rangwala et al. As a case study, incident heat fluxes on a gasoline tank, both the side and the top surface are calculated by the model. The heat radiation is from an inclined cylindrical flame generated by another 1000 m3 gasoline tank 4.6 m away from it. The cone angle of the flame to the adjacent oil tank is 45° and the polar angle is 0°. The top surface and the side surface of the tank are divided into 960 and 5760 grids during the calculation, respectively. The maximum incident heat flux on the side surface is 39.64 and 51.31 kW/m2 on the top surface. Distributions of the incident heat flux on the surface of the oil tank and on the ground around the fire tank are obtained, too.
Directory of Open Access Journals (Sweden)
Martin J Bishop
2014-09-01
Full Text Available Light scattering during optical imaging of electrical activation within the heart is known to significantlydistort the optically-recorded action potential (AP upstroke, as well as affecting the magnitude of the measured response of ventricular tissue to strong electric shocks. Modelling approaches based on the photondiffusion equation have recently been instrumental in quantifying and helping to understand the origin of the resulting distortion. However, they are unable to faithfully represent regions of non-scattering media, such assmall cavities within the myocardium which are filled with perfusate during experiments. Stochastic Monte Carlo (MC approaches allow simulation and tracking of individual photon `packets' as they propagate through tissuewith differing scattering properties. Here, we present a novel application of the MC method of photon scattering simulation, applied for the first time to the simulation of cardiac optical mapping signals withinunstructured, tetrahedral, finite element computational ventricular models. The method faithfully allows simulation of optical signals over highly-detailed, anatomically-complex MR-based models, includingrepresentations of fine-scale anatomy and intramural cavities. We show that optical action potential upstroke is prolonged close to large subepicardial vessels than further away from vessels, at times having a distinct `humped' morphology.Furthermore, we uncover a novel mechanism by which photon scattering effects around vessels cavities interact with `virtual-electrode' regions of strong de-/hyper-polarised tissue surrounding cavitiesduring shocks, significantly reducing the apparent optically-measured epicardial polarisation. We therefore demonstrate the importance of this novel optical mapping simulation approach along with highly anatomically-detailed models to fully investigate electrophysiological phenomena driven by fine-scale structural heterogeneity.
Thin‐shell modeling of neotectonics in the Azores‐Gibraltar Region
Jiménez-Munt, Ivone; Bird, M.; Fernàndez, Manel
2001-01-01
We applied the thin‐shell neotectonic modeling method to study the neotectonics of the Africa/Eurasia plate boundary in the Azores‐Gibraltar region. The plate boundary consists of a simple fault system running from Azores to the Gorringe Bank where it branches along the Betics and Rift‐Tell thrust fronts. Major faults in west Iberia and NW Africa have also been incorporated. Results are compared with seismic strain rates, fault slip rates and stress orientations. The best estimate for the fau...
A lattice Boltzmann study of non-hydrodynamic effects in shell models of turbulence
Benzi, R.; Biferale, L.; Sbragaglia, M.; Succi, S.; Toschi, F.
2004-10-01
A lattice Boltzmann scheme simulating the dynamics of shell models of turbulence is developed. The influence of high-order kinetic modes (ghosts) on the dissipative properties of turbulence dynamics is studied. It is analytically found that when ghost fields relax on the same timescale as the hydrodynamic ones, their major effect is a net enhancement of the fluid viscosity. The bare fluid viscosity is recovered by letting ghost fields evolve on a much longer timescale. Analytical results are borne out by high-resolution numerical simulations. These simulations indicate that the hydrodynamic manifold is very robust towards large fluctuations of non-hydrodynamic fields.
Recent developments of the projected shell model based on many-body techniques
Directory of Open Access Journals (Sweden)
Sun Yang
2015-01-01
Full Text Available Recent developments of the projected shell model (PSM are summarized. Firstly, by using the Pfaffian algorithm, the multi-quasiparticle configuration space is expanded to include 6-quasiparticle states. The yrast band of 166Hf at very high spins is studied as an example, where the observed third back-bending in the moment of inertia is well reproduced and explained. Secondly, an angular-momentum projected generate coordinate method is developed based on PSM. The evolution of the low-lying states, including the second 0+ state, of the soft Gd, Dy, and Er isotopes to the well-deformed ones is calculated, and compared with experimental data.
Shell model estimate of electric dipole moments in medium and heavy nuclei
Teruya, Eri; Yoshinaga, Naotaka; Higashiyama, Koji
2015-05-01
Existence of the electric dipole moment (EDM) is deeply related with time-reversal invariance. The EDMof a diamagnetic atom is mainly induced by the nuclear Schiff moment. After carrying out the shell model calculations to obtain wavefunctions for Xe isotopes, we evaluate nuclear Schiff moments for Xe isotopes to estimate their atomic EDMs. We estimate the contribution from each single particle orbital for the Schiff moment. It is found that the contribution on the Schiff moment is very different from orbital to orbital.
Shell model estimate of electric dipole moments in medium and heavy nuclei
Directory of Open Access Journals (Sweden)
Teruya Eri
2015-01-01
Full Text Available Existence of the electric dipole moment (EDM is deeply related with time-reversal invariance. The EDMof a diamagnetic atom is mainly induced by the nuclear Schiff moment. After carrying out the shell model calculations to obtain wavefunctions for Xe isotopes, we evaluate nuclear Schiff moments for Xe isotopes to estimate their atomic EDMs. We estimate the contribution from each single particle orbital for the Schiff moment. It is found that the contribution on the Schiff moment is very different from orbital to orbital.
Elastic Constants of Superconducting MgB2 from Molecular Dynamics Simulations with Shell Model
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
The elastic constants of superconducting MgB2 are calculated using a molecular dynamics method (MD)with shell model. The lattice parameters, five independent elastic constants, equations of state (EOS), Debye temperature, and bulk modulus of MgB2 are obtained. Meanwhile, the dependence of the bulk modulus B, the lattice parameters a and c, and the unit cell volume V on the applied pressure are presented. It is demonstrated that the method introduced here can well reproduce the experimental results with a reasonable accuracy.
Shell-model-like Approach (SLAP) for the Nuclear Properties in Relativistic Mean field Theory
Institute of Scientific and Technical Information of China (English)
MENG Jie; GUO Jian-you; LIU Lang; ZHANG Shuang-quan
2006-01-01
A Shell-model-like approach suggested to treat the pairing correlations in relativistic mean field theory is introduced,in which the occupancies thus obtained have been iterated back into the densities.The formalism and numerical techniques are given in detail.As examples,the ground state properties and low-lying excited states for Ne isotopes are studied.The results thus obtained are compared with the data available.The binding energies,the odd-even staggering,as well as the tendency for the change of the shapes in Ne isotopes are correctly reproduced.
Kumada, H; Saito, K; Nakamura, T; Sakae, T; Sakurai, H; Matsumura, A; Ono, K
2011-12-01
Treatment planning for boron neutron capture therapy generally utilizes Monte-Carlo methods for calculation of the dose distribution. The new treatment planning system JCDS-FX employs the multi-purpose Monte-Carlo code PHITS to calculate the dose distribution. JCDS-FX allows to build a precise voxel model consisting of pixel based voxel cells in the scale of 0.4×0.4×2.0 mm(3) voxel in order to perform high-accuracy dose estimation, e.g. for the purpose of calculating the dose distribution in a human body. However, the miniaturization of the voxel size increases calculation time considerably. The aim of this study is to investigate sophisticated modeling methods which can perform Monte-Carlo calculations for human geometry efficiently. Thus, we devised a new voxel modeling method "Multistep Lattice-Voxel method," which can configure a voxel model that combines different voxel sizes by utilizing the lattice function over and over. To verify the performance of the calculation with the modeling method, several calculations for human geometry were carried out. The results demonstrated that the Multistep Lattice-Voxel method enabled the precise voxel model to reduce calculation time substantially while keeping the high-accuracy of dose estimation.
Monte-Carlo event generation for a two-Higgs-doublet model with maximal CP symmetry
Brehmer, Johann
2012-01-01
Recently a two-Higgs-doublet model with maximal symmetry under generalised CP transformations, the MCPM, has been proposed. The theory features a unique fermion mass spectrum which, although not describing nature precisely, provides a good approximation. It also predicts the existence of five Higgs bosons with a particular signature. In this thesis I implemented the MCPM into the Monte-Carlo event generation package MadGraph, allowing the simulation of any MCPM tree-level process. The generated events are in a standardised format and can be used for further analysis with tools such as PYTHIA or GEANT, eventually leading to the comparison with experimental data and the exclusion or discovery of the theory. The implementation was successfully validated in different ways. It was then used for a first comparison of the MCPM signal events with the SM background and previous searches for new physics, hinting that the data expected at the LHC in the next years might provide exclusion limits or show signatures of thi...
Modeling the Biophysical Effects in a Carbon Beam Delivery Line using Monte Carlo Simulation
Cho, Ilsung; Cho, Sungho; Kim, Eun Ho; Song, Yongkeun; Shin, Jae-ik; Jung, Won-Gyun
2016-01-01
Relative biological effectiveness (RBE) plays an important role in designing a uniform dose response for ion beam therapy. In this study the biological effectiveness of a carbon ion beam delivery system was investigated using Monte Carlo simulation. A carbon ion beam delivery line was designed for the Korea Heavy Ion Medical Accelerator (KHIMA) project. The GEANT4 simulation tool kit was used to simulate carbon beam transporting into media. An incident energy carbon ion beam in the range between 220 MeV/u and 290 MeV/u was chosen to generate secondary particles. The microdosimetric-kinetic (MK) model is applied to describe the RBE of 10% survival in human salivary gland (HSG) cells. The RBE weighted dose was estimated as a function of the penetrating depth of the water phantom along the incident beam direction. A biologically photon-equivalent Spread Out Bragg Peak (SOBP) was designed using the RBE weighted absorbed dose. Finally, the RBE of mixed beams was predicted as a function of the water phantom depth.
Arunraj, N S; Mandal, Saptarshi; Maiti, J
2013-06-01
Modeling uncertainty during risk assessment is a vital component for effective decision making. Unfortunately, most of the risk assessment studies suffer from uncertainty analysis. The development of tools and techniques for capturing uncertainty in risk assessment is ongoing and there has been a substantial growth in this respect in health risk assessment. In this study, the cross-disciplinary approaches for uncertainty analyses are identified and a modified approach suitable for industrial safety risk assessment is proposed using fuzzy set theory and Monte Carlo simulation. The proposed method is applied to a benzene extraction unit (BEU) of a chemical plant. The case study results show that the proposed method provides better measure of uncertainty than the existing methods as unlike traditional risk analysis method this approach takes into account both variability and uncertainty of information into risk calculation, and instead of a single risk value this approach provides interval value of risk values for a given percentile of risk. The implications of these results in terms of risk control and regulatory compliances are also discussed.
Monte Carlo study of the double and super-exchange model with lattice distortion
Energy Technology Data Exchange (ETDEWEB)
Suarez, J R; Vallejo, E; Navarro, O [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, 04510 Mexico D. F. (Mexico); Avignon, M, E-mail: jrsuarez@iim.unam.m [Institut Neel, Centre National de la Recherche Scientifique (CNRS) and Universite Joseph Fourier, BP 166, 38042 Grenoble Cedex 9 (France)
2009-05-01
In this work a magneto-elastic phase transition was obtained in a linear chain due to the interplay between magnetism and lattice distortion in a double and super-exchange model. It is considered a linear chain consisting of localized classical spins interacting with itinerant electrons. Due to the double exchange interaction, localized spins tend to align ferromagnetically. This ferromagnetic tendency is expected to be frustrated by anti-ferromagnetic super-exchange interactions between neighbor localized spins. Additionally, lattice parameter is allowed to have small changes, which contributes harmonically to the energy of the system. Phase diagram is obtained as a function of the electron density and the super-exchange interaction using a Monte Carlo minimization. At low super-exchange interaction energy phase transition between electron-full ferromagnetic distorted and electron-empty anti-ferromagnetic undistorted phases occurs. In this case all electrons and lattice distortions were found within the ferromagnetic domain. For high super-exchange interaction energy, phase transition between two site distorted periodic arrangement of independent magnetic polarons ordered anti-ferromagnetically and the electron-empty anti-ferromagnetic undistorted phase was found. For this high interaction energy, Wigner crystallization, lattice distortion and charge distribution inside two-site polarons were obtained.
Modeling the biophysical effects in a carbon beam delivery line by using Monte Carlo simulations
Cho, Ilsung; Yoo, SeungHoon; Cho, Sungho; Kim, Eun Ho; Song, Yongkeun; Shin, Jae-ik; Jung, Won-Gyun
2016-09-01
The Relative biological effectiveness (RBE) plays an important role in designing a uniform dose response for ion-beam therapy. In this study, the biological effectiveness of a carbon-ion beam delivery system was investigated using Monte Carlo simulations. A carbon-ion beam delivery line was designed for the Korea Heavy Ion Medical Accelerator (KHIMA) project. The GEANT4 simulation tool kit was used to simulate carbon-ion beam transport into media. An incident energy carbon-ion beam with energy in the range between 220 MeV/u and 290 MeV/u was chosen to generate secondary particles. The microdosimetric-kinetic (MK) model was applied to describe the RBE of 10% survival in human salivary-gland (HSG) cells. The RBE weighted dose was estimated as a function of the penetration depth in the water phantom along the incident beam's direction. A biologically photon-equivalent Spread Out Bragg Peak (SOBP) was designed using the RBE-weighted absorbed dose. Finally, the RBE of mixed beams was predicted as a function of the depth in the water phantom.
Monte Carlo Study of Topological Defects in the 3D Heisenberg Model
Holm, C; Holm, Christian; Janke, Wolfhard
1994-01-01
We use single-cluster Monte Carlo simulations to study the role of topological defects in the three-dimensional classical Heisenberg model on simple cubic lattices of size up to $80^3$. By applying reweighting techniques to time series generated in the vicinity of the approximate infinite volume transition point $K_c$, we obtain clear evidence that the temperature derivative of the average defect density $d\\langle n \\rangle/dT$ behaves qualitatively like the specific heat, i.e., both observables are finite in the infinite volume limit. This is in contrast to results by Lau and Dasgupta [{\\em Phys. Rev.\\/} {\\bf B39} (1989) 7212] who extrapolated a divergent behavior of $d\\langle n \\rangle/dT$ at $K_c$ from simulations on lattices of size up to $16^3$. We obtain weak evidence that $d\\langle n \\rangle/dT$ scales with the same critical exponent as the specific heat.As a byproduct of our simulations, we obtain a very accurate estimate for the ratio $\\alpha/\
Monte Carlo Modeling of Minor Actinide Burning in Fissile Spallation Targets
Malyshkin, Yury; Pshenichnov, Igor; Mishustin, Igor; Greiner, Walter
2014-06-01
Minor actinides (MA) present a harmful part of spent nuclear fuel due to their long half-lives and high radio-toxicity. Neutrons produced in spallation targets of Accelerator Driven Systems (ADS) can be used to transmute and burn MA. Non-fissile targets are commonly considered in ADS design. However, additional neutrons from fission reactions can be used in targets made of fissile materials. We developed a Geant4-based code MCADS (Monte Carlo model for Accelerator Driven Systems) for simulating neutron production and transport in different spallation targets. MCADS is suitable for calculating spatial distributions of neutron flux and energy deposition, neutron multiplication factors and other characteristics of produced neutrons and residual nuclei. Several modifications of the Geant4 source code described in this work were made in order to simulate targets containing MA. Results of MCADS simulations are reported for several cylindrical targets made of U+Am, Am or Am2O3 including more complicated design options with a neutron booster and a reflector. Estimations of Am burning rates are given for the considered cases.
Aoun, Bachir
2016-05-01
A new Reverse Monte Carlo (RMC) package "fullrmc" for atomic or rigid body and molecular, amorphous, or crystalline materials is presented. fullrmc main purpose is to provide a fully modular, fast and flexible software, thoroughly documented, complex molecules enabled, written in a modern programming language (python, cython, C and C++ when performance is needed) and complying to modern programming practices. fullrmc approach in solving an atomic or molecular structure is different from existing RMC algorithms and software. In a nutshell, traditional RMC methods and software randomly adjust atom positions until the whole system has the greatest consistency with a set of experimental data. In contrast, fullrmc applies smart moves endorsed with reinforcement machine learning to groups of atoms. While fullrmc allows running traditional RMC modeling, the uniqueness of this approach resides in its ability to customize grouping atoms in any convenient way with no additional programming efforts and to apply smart and more physically meaningful moves to the defined groups of atoms. In addition, fullrmc provides a unique way with almost no additional computational cost to recur a group's selection, allowing the system to go out of local minimas by refining a group's position or exploring through and beyond not allowed positions and energy barriers the unrestricted three dimensional space around a group.
Risk analysis of gravity dam instability using credibility theory Monte Carlo simulation model.
Xin, Cao; Chongshi, Gu
2016-01-01
Risk analysis of gravity dam stability involves complicated uncertainty in many design parameters and measured data. Stability failure risk ratio described jointly by probability and possibility has deficiency in characterization of influence of fuzzy factors and representation of the likelihood of risk occurrence in practical engineering. In this article, credibility theory is applied into stability failure risk analysis of gravity dam. Stability of gravity dam is viewed as a hybrid event considering both fuzziness and randomness of failure criterion, design parameters and measured data. Credibility distribution function is conducted as a novel way to represent uncertainty of influence factors of gravity dam stability. And combining with Monte Carlo simulation, corresponding calculation method and procedure are proposed. Based on a dam section, a detailed application of the modeling approach on risk calculation of both dam foundation and double sliding surfaces is provided. The results show that, the present method is feasible to be applied on analysis of stability failure risk for gravity dams. The risk assessment obtained can reflect influence of both sorts of uncertainty, and is suitable as an index value.
Monte Carlo Technique Used to Model the Degradation of Internal Spacecraft Surfaces by Atomic Oxygen
Banks, Bruce A.; Miller, Sharon K.
2004-01-01
Atomic oxygen is one of the predominant constituents of Earth's upper atmosphere. It is created by the photodissociation of molecular oxygen (O2) into single O atoms by ultraviolet radiation. It is chemically very reactive because a single O atom readily combines with another O atom or with other atoms or molecules that can form a stable oxide. The effects of atomic oxygen on the external surfaces of spacecraft in low Earth orbit can have dire consequences for spacecraft life, and this is a well-known and much studied problem. Much less information is known about the effects of atomic oxygen on the internal surfaces of spacecraft. This degradation can occur when openings in components of the spacecraft exterior exist that allow the entry of atomic oxygen into regions that may not have direct atomic oxygen attack but rather scattered attack. Openings can exist because of spacecraft venting, microwave cavities, and apertures for Earth viewing, Sun sensors, or star trackers. The effects of atomic oxygen erosion of polymers interior to an aperture on a spacecraft were simulated at the NASA Glenn Research Center by using Monte Carlo computational techniques. A two-dimensional model was used to provide quantitative indications of the attenuation of atomic oxygen flux as a function of the distance into a parallel-walled cavity. The model allows the atomic oxygen arrival direction, the Maxwell Boltzman temperature, and the ram energy to be varied along with the interaction parameters of the degree of recombination upon impact with polymer or nonreactive surfaces, the initial reaction probability, the reaction probability dependence upon energy and angle of attack, degree of specularity of scattering of reactive and nonreactive surfaces, and the degree of thermal accommodation upon impact with reactive and non-reactive surfaces to be varied to allow the model to produce atomic oxygen erosion geometries that replicate actual experimental results from space. The degree of
Reščič, J.; Kalyuzhnyi, Y. V.; Cummings, P. T.
2016-10-01
The approach developed earlier to describe the dimerizing shielded attractive shell (SAS) primitive model of chemical association due to Cummings and Stell is generalized and extended to include a description of a polymerizing SAS model. Our extension is based on the combination of the resummed thermodynamic perturbation theory for central force (RTPT-CF) associating potential and self consistent scheme, which takes into account the changes in the system free volume due to association. Theoretical results for thermodynamical properties of the model at different bonding length, density and temperature are compared against newly generated computer simulation results. The theory gives very accurate predictions for the model with bonding length L * from the range 0 < L * < 0.6 at all values of the density and temperature studied, including the limit of infinitely large temperature.
Soniat, Thomas M.; Klinck, John M.; Powell, Eric N.; Cooper, Nathan; Abdelguerfi, Mahdi; Hofmann, Eileen E.; Dahal, Janak; Tu, Shengru; Finigan, John; Eberline, Benjamin S.; La Peyre, Jerome F.; LaPeyre, Megan K.; Qaddoura, Fareed
2012-01-01
A numerical model is presented that defines a sustainability criterion as no net loss of shell, and calculates a sustainable harvest of seed (market oysters (≥75 mm). Stock assessments of the Primary State Seed Grounds conducted east of the Mississippi from 2009 to 2011 show a general trend toward decreasing abundance of sack and seed oysters. Retrospective simulations provide estimates of annual sustainable harvests. Comparisons of simulated sustainable harvests with actual harvests show a trend toward unsustainable harvests toward the end of the time series. Stock assessments combined with shell-neutral models can be used to estimate sustainable harvest and manage cultch through shell planting when actual harvest exceeds sustainable harvest. For exclusive restoration efforts (no fishing allowed), the model provides a metric for restoration success-namely, shell accretion. Oyster fisheries that remove shell versus reef restorations that promote shell accretion, although divergent in their goals, are convergent in their management; both require vigilant attention to shell budgets.
Development of CT scanner models for patient organ dose calculations using Monte Carlo methods
Gu, Jianwei
There is a serious and growing concern about the CT dose delivered by diagnostic CT examinations or image-guided radiation therapy imaging procedures. To better understand and to accurately quantify radiation dose due to CT imaging, Monte Carlo based CT scanner models are needed. This dissertation describes the development, validation, and application of detailed CT scanner models including a GE LightSpeed 16 MDCT scanner and two image guided radiation therapy (IGRT) cone beam CT (CBCT) scanners, kV CBCT and MV CBCT. The modeling process considered the energy spectrum, beam geometry and movement, and bowtie filter (BTF). The methodology of validating the scanner models using reported CTDI values was also developed and implemented. Finally, the organ doses to different patients undergoing CT scan were obtained by integrating the CT scanner models with anatomically-realistic patient phantoms. The tube current modulation (TCM) technique was also investigated for dose reduction. It was found that for RPI-AM, thyroid, kidneys and thymus received largest dose of 13.05, 11.41 and 11.56 mGy/100 mAs from chest scan, abdomen-pelvis scan and CAP scan, respectively using 120 kVp protocols. For RPI-AF, thymus, small intestine and kidneys received largest dose of 10.28, 12.08 and 11.35 mGy/100 mAs from chest scan, abdomen-pelvis scan and CAP scan, respectively using 120 kVp protocols. The dose to the fetus of the 3 month pregnant patient phantom was 0.13 mGy/100 mAs and 0.57 mGy/100 mAs from the chest and kidney scan, respectively. For the chest scan of the 6 month patient phantom and the 9 month patient phantom, the fetal doses were 0.21 mGy/100 mAs and 0.26 mGy/100 mAs, respectively. For MDCT with TCM schemas, the fetal dose can be reduced with 14%-25%. To demonstrate the applicability of the method proposed in this dissertation for modeling the CT scanner, additional MDCT scanner was modeled and validated by using the measured CTDI values. These results demonstrated that the
Anomalous Scaling from Controlled Closure in a Shell Model of Turbulence
Lvov, V S; Pomyalov, A; Procaccia, I; L'vov, Victor S.; Pierotti, Daniela; Pomyalov, Anna; Procaccia, Itamar
1998-01-01
We present a model of hydrodynamic turbulence for which the program of computing the scaling exponents from first principles can be developed in a controlled fashion. The model consists of $N$ suitably coupled copies of the "Sabra" shell model of turbulence. The couplings are chosen to include two components: random and deterministic, with a relative importance that is characterized by a parameter called $\\epsilon$. It is demonstrated, using numerical simulations of up to 25 copies and 28 shells that in the $N\\to functions whose scaling exponents are anomalous. The theoretical calculation of the scaling exponents follows verbatim the closure procedure suggested recently for the Navier-Stokes problem, with the additional advantage that in the $N\\to procedure. The main result of this paper is a finite and closed set of scale-invariant equations for the 2nd and 3rd order statistical objects of the theory. This set of equations takes into account terms up to order $\\epsilon^4$ and neglects terms of order $\\epsilo...
Light Nuclei in the Framework of the Symplectic No-Core Shell Model
Energy Technology Data Exchange (ETDEWEB)
Draayer, Jerry P.; Dytrych, Tomas; Sviratcheva, Kristina D.; Bahri, Chairul; /Louisiana State U.; Vary, James P.; /Iowa State U. /LLNL, Livermore /SLAC
2007-04-02
A symplectic no-core shell model (Sp-NCSM) is constructed with the goal of extending the ab-initio NCSM to include strongly deformed higher-oscillator-shell configurations and to reach heavier nuclei that cannot be studied currently because the spaces encountered are too large to handle, even with the best of modern-day computers. This goal is achieved by integrating two powerful concepts: the ab-initio NCSM with that of the Sp(3,R) {contains} SU(3) group-theoretical approach. The NCSM uses modern realistic nuclear interactions in model spaces that consists of many-body configurations up to a given number of {h_bar}{Upsilon} excitations together with modern high-performance parallel computing techniques. The symplectic theory extends this picture by recognizing that when deformed configurations dominate, which they often do, the model space can be better selected so less relevant low-lying {h_bar}{Upsilon} configurations yield to more relevant high-lying {h_bar}{Upsilon} configurations, ones that respect a near symplectic symmetry found in the Hamiltonian. Results from an application of the Sp-NCSM to light nuclei are compared with those for the NCSM and with experiment.
No-Core Shell Model for 48-Ca, 48-Sc and 48-Ti
Energy Technology Data Exchange (ETDEWEB)
Popescu, S; Stoica, S; Vary, J P; Navratil, P
2004-10-26
The authors report the first no-core shell model results for {sup 48}Ca, {sup 48}Sc and {sup 48}Ti with derived and modified two-body Hamiltonians. We use an oscillator basis with a limited {bar h}{Omega} range around 40/A{sup 1/3} = 11 MeV and a limited model space up to 1 {bar h}{Omega}. No single-particle energies are used. They find that the charge dependence of the bulk binding energy of eight A = 48 nuclei is reasonably described with an effective Hamiltonian derived from the CD-Bonn interaction while there is an overall underbinding by about 0.4 MeV/nucleon. However, resulting spectra exhibit deficiencies that are anticipated due to: (1) basis space limitations and/or the absence of effective many-body interactions; and, (2) the absence of genuine three-nucleon interactions. They introduce phenomenological modifications to obtain fits to total binding and low-lying spectra. The resulting no-core shell model opens a path for applications to experiments such as the double-beta ({beta}{beta}) decay process.
Monte-Carlo based Uncertainty Analysis For CO2 Laser Microchanneling Model
Prakash, Shashi; Kumar, Nitish; Kumar, Subrata
2016-09-01
CO2 laser microchanneling has emerged as a potential technique for the fabrication of microfluidic devices on PMMA (Poly-methyl-meth-acrylate). PMMA directly vaporizes when subjected to high intensity focused CO2 laser beam. This process results in clean cut and acceptable surface finish on microchannel walls. Overall, CO2 laser microchanneling process is cost effective and easy to implement. While fabricating microchannels on PMMA using a CO2 laser, the maximum depth of the fabricated microchannel is the key feature. There are few analytical models available to predict the maximum depth of the microchannels and cut channel profile on PMMA substrate using a CO2 laser. These models depend upon the values of thermophysical properties of PMMA and laser beam parameters. There are a number of variants of transparent PMMA available in the market with different values of thermophysical properties. Therefore, for applying such analytical models, the values of these thermophysical properties are required to be known exactly. Although, the values of laser beam parameters are readily available, extensive experiments are required to be conducted to determine the value of thermophysical properties of PMMA. The unavailability of exact values of these property parameters restrict the proper control over the microchannel dimension for given power and scanning speed of the laser beam. In order to have dimensional control over the maximum depth of fabricated microchannels, it is necessary to have an idea of uncertainty associated with the predicted microchannel depth. In this research work, the uncertainty associated with the maximum depth dimension has been determined using Monte Carlo method (MCM). The propagation of uncertainty with different power and scanning speed has been predicted. The relative impact of each thermophysical property has been determined using sensitivity analysis.