Shell model Monte Carlo methods
International Nuclear Information System (INIS)
We review quantum Monte Carlo methods for dealing with large shell model problems. These methods reduce the imaginary-time many-body evolution operator to a coherent superposition of one-body evolutions in fluctuating one-body fields; resultant path integral is evaluated stochastically. We first discuss the motivation, formalism, and implementation of such Shell Model Monte Carlo methods. There then follows a sampler of results and insights obtained from a number of applications. These include the ground state and thermal properties of pf-shell nuclei, thermal behavior of γ-soft nuclei, and calculation of double beta-decay matrix elements. Finally, prospects for further progress in such calculations are discussed. 87 refs
Monte Carlo Shell Model Mass Predictions
International Nuclear Information System (INIS)
The nuclear mass calculation is discussed in terms of large-scale shell model calculations. First, the development and limitations of the conventional shell model calculations are mentioned. In order to overcome the limitations, the Quantum Monte Carlo Diagonalization (QMCD) method has been proposed. The basic formulation and features of the QMCD method are presented as well as its application to the nuclear shell model, referred to as Monte Carlo Shell Model (MCSM). The MCSM provides us with a breakthrough in shell model calculations: the structure of low-lying states can be studied with realistic interactions for a nearly unlimited variety of nuclei. Thus, the MCSM can contribute significantly to the study of nuclear masses. An application to N∼20 unstable nuclei far from the β-stability line is mentioned
Monte Carlo methods and applications for the nuclear shell model
Dean, D. J.; White, J A
1998-01-01
The shell-model Monte Carlo (SMMC) technique transforms the traditional nuclear shell-model problem into a path-integral over auxiliary fields. We describe below the method and its applications to four physics issues: calculations of sdpf- shell nuclei, a discussion of electron-capture rates in pf-shell nuclei, exploration of pairing correlations in unstable nuclei, and level densities in rare earth systems.
Monte Carlo Methods and Applications for the Nuclear Shell Model
International Nuclear Information System (INIS)
The shell-model Monte Carlo (SMMC) technique transforms the traditional nuclear shell-model problem into a path-integral over auxiliary fields. We describe below the method and its applications to four physics issues: calculations of sd-pf-shell nuclei, a discussion of electron-capture rates in pf-shell nuclei, exploration of pairing correlations in unstable nuclei, and level densities in rare earth systems
Monte Carlo shell model for ab initio nuclear structure
International Nuclear Information System (INIS)
The Monte Carlo Shell Model (MCSM) has been developed mainly for conventional shell-model calculations with an assumed inert core. Recently the algorithm and code itself have been heavily revised and rewritten so as to accommodate massively parallel computing environments. Now we can apply the MCSM not only to conventional shell-model calculations but also to no-core calculations. The MCSM approach proceeds through a sequence of diagonalization steps within the Hilbert subspace spanned by the deformed Slater determinants in the HO single-particle basis. Importance truncated bases are stochastically sampled so as to minimize the energy variationally. By increasing the number of importance-truncated basis, the computed energy converges from above to the exact value and gives the variational upper bound. In benchmark calculations, there is a good agreement in p-shell nuclei between the results of the MCSM and of the FCI (Full Configuration Interaction) method. The N(shell)=5 results reveal the onset of systematic convergence pattern. Further work is needed to investigate the extrapolation to the infinite basis space in the N(shell) truncation
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.)
Collective excitations of nuclei in the Monte-Carlo shell model
International Nuclear Information System (INIS)
The formulation and recent applications of the Quantum Monte Carlo diagonalization (QMCD) method are reported. The QMCD has been proposed for solving the quantum many-body interacting systems, providing us with energy eigenvalues, transition matrix elements and wave functions. Its application to the nuclear shell model is referred to as the Monte Carlo Shell Model. By the Monte Carlo Shell Model calculations, the level structure of low-lying states can be studied with realistic interactions, providing a useful tool for nuclear spectroscopy. The Monte Carlo Shell Model has been applied to the study of a variety of nuclei, and can be characterized as the importance truncation scheme to the full diagonalization which is infeasible in many cases due to extremely large dimensions. Applications to the study of quadrupole collective states are discussed. (author)
History and future perspectives of the Monte Carlo shell model -from Alphleet to K computer-
International Nuclear Information System (INIS)
We report a history of the developments of the Monte Carlo shell model (MCSM). The MCSM was proposed in order to perform large-scale shell-model calculations which direct diagonalization method cannot reach. Since 1999 PC clusters were introduced for parallel computation of the MCSM. Since 2011 we participated the High Performance Computing Infrastructure Strategic Program and developed a new MCSM code for current massively parallel computers such as K computer. We discuss future perspectives concerning a new framework and parallel computation of the MCSM by incorporating conjugate gradient method and energy-variance extrapolation
The shell model Monte Carlo approach to level densities: recent developments and perspectives
Alhassid, Y
2016-01-01
We review recent advances in the shell model Monte Carlo approach for the microscopic calculation of statistical and collective properties of nuclei. We discuss applications to the calculation of (i) level densities in nickel isotopes, implementing a recent method to circumvent the odd-particle sign problem; (ii) state densities in heavy nuclei; (iii) spin distributions of nuclear levels; and (iv) finite-temperature quadrupole distributions.
The shell model Monte Carlo approach to level densities: Recent developments and perspectives
Energy Technology Data Exchange (ETDEWEB)
Alhassid, Y. [Yale University, Center for Theoretical Physics, Sloane Physics Laboratory, New Haven, Connecticut (United States)
2015-12-15
We review recent advances in the shell model Monte Carlo approach for the microscopic calculation of statistical and collective properties of nuclei. We discuss applications to the calculation of i) level densities in nickel isotopes, implementing a recent method to circumvent the odd-particle sign problem; ii) state densities in heavy nuclei; iii) spin distributions of nuclear levels; and iv) finite-temperature quadrupole distributions. (orig.)
The shell model Monte Carlo approach to level densities: Recent developments and perspectives
Alhassid, Y.
2015-12-01
We review recent advances in the shell model Monte Carlo approach for the microscopic calculation of statistical and collective properties of nuclei. We discuss applications to the calculation of i) level densities in nickel isotopes, implementing a recent method to circumvent the odd-particle sign problem; ii) state densities in heavy nuclei; iii) spin distributions of nuclear levels; and iv) finite-temperature quadrupole distributions.
International Nuclear Information System (INIS)
Strategic program field 5 was started in 2011 for the effective use of K-computer. In the field of the nuclear research, a large scale nuclear structure studies by Monte Carlo shell model calculation are being carried out at HPCI (High Performance Computing Infrastructure) Consortium. Since the introduction of the shell model by Mayer and Jensen in 1949, it succeeded in the explanation of magic numbers and has been very powerful theory. Recently, however, the great progress of nuclear physics at RIBF (RIKEN Beam Factory) and so on made it clear that the magic numbers disappear in the unstable nuclei, while different ones appear and evolutions of shell structure are considered. In this report the framework and recent results are described. In the second section of 'Shell Model Computation and Monte Carlo Shell Model', '2.1 Model space and effective interactions', '2.2 Strict diagonalization by Lanczos algorithm and its limitations' and '2.3 Framework of Monte Carlo shell model' are picked up with a figure of calculation example. In the third section 'Structure Exploration of Neutron Excess Nickel Isotopes by the Monte Carlo Shell Model' is explained showing the energy surfaces of 68Ni for 01+ and 02+. In the fourth section 'Monte Carlo Model Calculation without Assuming Closed Shell and its Visualization', density distributions in 8Be are shown after and before the angular momenta projection. In the fifth section of 'Development of Monte Carlo Shell Model Program at K-Computer', speeding up of Monte Carlo Shell Model by the parallel computation is shown. Finally it is pointed out that the HPCI program is planned to end 2015. Farther magic numbers are expected to be calculated before HPCI terminates. (S. Funahashi)
Level densities of heavy nuclei in the shell model Monte Carlo approach
Alhassid, Y.; Bertsch, G. F.; Gilbreth, C. N.; Nakada, H.; Özen, C.
2016-06-01
Nuclear level densities are necessary input to the Hauser-Feshbach theory of compound nuclear reactions. However, the microscopic calculation of level densities in the presence of correlations is a challenging many-body problem. The configurationinteraction shell model provides a suitable framework for the inclusion of correlations and shell effects, but the large dimensionality of the many-particle model space has limited its application in heavy nuclei. The shell model Monte Carlo method enables calculations in spaces that are many orders of magnitude larger than spaces that can be treated by conventional diagonalization methods and has proven to be a powerful tool in the microscopic calculation of level densities. We discuss recent applications of the method in heavy nuclei.
Collectivity in heavy nuclei in the shell model Monte Carlo approach
International Nuclear Information System (INIS)
The microscopic description of collectivity in heavy nuclei in the framework of the configuration-interaction shell model has been a major challenge. The size of the model space required for the description of heavy nuclei prohibits the use of conventional diagonalization methods. We have overcome this difficulty by using the shell model Monte Carlo (SMMC) method, which can treat model spaces that are many orders of magnitude larger than those that can be treated by conventional methods. We identify a thermal observable that can distinguish between vibrational and rotational collectivity and use it to describe the crossover from vibrational to rotational collectivity in families of even-even rare-earth isotopes. We calculate the state densities in these nuclei and find them to be in close agreement with experimental data. We also calculate the collective enhancement factors of the corresponding level densities and find that their decay with excitation energy is correlated with the pairing and shape phase transitions. (author)
Collectivity in Heavy Nuclei in the Shell Model Monte Carlo Approach
Özen, C; Nakada, H
2013-01-01
The microscopic description of collectivity in heavy nuclei in the framework of the configuration-interaction shell model has been a major challenge. The size of the model space required for the description of heavy nuclei prohibits the use of conventional diagonalization methods. We have overcome this difficulty by using the shell model Monte Carlo (SMMC) method, which can treat model spaces that are many orders of magnitude larger than those that can be treated by conventional methods. We identify a thermal observable that can distinguish between vibrational and rotational collectivity and use it to describe the crossover from vibrational to rotational collectivity in families of even-even rare-earth isotopes. We calculate the state densities in these nuclei and find them to be in close agreement with experimental data. We also calculate the collective enhancement factors of the corresponding level densities and find that their decay with excitation energy is correlated with the pairing and shape phase tran...
International Nuclear Information System (INIS)
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 (1) 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 (2) 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. (author)
Alhassid, Y; Liu, S; Mukherjee, A; Nakada, H
2014-01-01
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 $^{59-64}$Ni and of a heavy deformed rare-earth nucleus $^{162}$Dy and found them to be in close agreement with various experimental data sets.
A constrained-path quantum Monte-Carlo approach for the nuclear shell model
International Nuclear Information System (INIS)
The shell model is a powerful theoretical framework for studying the nuclear structure. Unfortunately, the exponential scaling of the many-body space with the number of nucleons or the number of valence levels strongly restricts its applicability. The Quantum Monte-Carlo (QMC) methods may then be considered as a possible alternative to the direct diagonalization of the Hamiltonian. They are based on a stochastic reformulation of the Schroedinger equation to reduce the many-body problem to a set of one-body problems, numerically tractable, describing independent particles that evolve in fluctuating external fields. The originality of the QMC scheme proposed in the present thesis is the use of a variational approach, with symmetry restoration before variation, to guide the Brownian motion and to constrain it in order to control the sign/phase problem that generally occurs in the QMC samplings for fermions. The 'yrast' spectroscopy we obtain for sd- and fp-shell nuclei with realistic residual interactions agree remarkably well with the results from an exact diagonalization of the Hamiltonian. Moreover, an openness towards strongly correlated electronic systems is presented through new QMC schemes recently developed for the two-dimensional Hubbard model. In contrast with the traditional samplings, they guarantee positive-weighted trajectories regardless the on-site interaction strength or the doping of the lattice. We demonstrate that these schemes are in fact related to the stochastic approach applied to the nuclear shell model. The origin of the systematic errors that emerge in these methods, although free from sign/phase problem with the Hubbard Hamiltonian, is also discussed. (author)
Shell Model Monte Carlo method in the $pn$-formalism and applications to the Zr and Mo isotopes
Ozen, C
2006-01-01
We report on the development of a new shell-model Monte Carlo algorithm which uses the proton-neutron formalism. Shell model Monte Carlo methods, within the isospin formulation, have been successfully used in large-scale shell-model calculations. Motivation for this work is to extend the feasibility of these methods to shell-model studies involving non-identical proton and neutron valence spaces. We show the viability of the new approach with some test results. Finally, we use a realistic nucleon-nucleon interaction in the model space described by (1p_1/2,0g_9/2) proton and (1d_5/2,2s_1/2,1d_3/2,0g_7/2,0h_11/2) neutron orbitals above the Sr-88 core to calculate ground-state energies, binding energies, B(E2) strengths, and to study pairing properties of the even-even 90-104 Zr and 92-106 Mo isotope chains.
Microscopic calculation of level densities: the shell model Monte Carlo approach
International Nuclear Information System (INIS)
The shell model Monte Carlo (SMMC) approach provides a powerful technique for the microscopic calculation of level densities in model spaces that are many orders of magnitude larger than those that can be treated by conventional methods. We discuss a number of developments: (i) Spin distribution. We used a spin projection method to calculate the exact spin distribution of energy levels as a function of excitation energy. In even-even nuclei we find an odd-even staggering effect (in spin). Our results were confirmed in recent analysis of experimental data. (ii) Heavy nuclei. The SMMC approach was extended to heavy nuclei. We have studied the crossover between vibrational and rotational collectivity in families of samarium and neodymium isotopes in model spaces of dimension approx. 1029. We find good agreement with experimental results for both state densities and 2> (where J is the total spin). (iii) Collective enhancement factors. We have calculated microscopically the vibrational and rotational enhancement factors of level densities versus excitation energy. We find that the decay of these enhancement factors in heavy nuclei is correlated with the pairing and shape phase transitions. (iv) Odd-even and odd-odd nuclei. The projection on an odd number of particles leads to a sign problem in SMMC. We discuss a novel method to calculate state densities in odd-even and odd-odd nuclei despite the sign problem. (v) State densities versus level densities. The SMMC approach has been used extensively to calculate state densities. However, experiments often measure level densities (where levels are counted without including their spin degeneracies.) A spin projection method enables us to also calculate level densities in SMMC. We have calculated the SMMC level density of 162Dy and found it to agree well with experiments
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.
Directory of Open Access Journals (Sweden)
F. Spada
2006-01-01
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.
Shell-model Monte Carlo simulations of the BCS-BEC crossover in few-fermion systems
DEFF Research Database (Denmark)
Zinner, Nikolaj Thomas; Mølmer, Klaus; Özen, C.;
2009-01-01
strength, particle number, and temperature. The subtle question of renormalization in a finite model space is addressed and the convergence of our method and its applicability across the BCS-BEC crossover is discussed. Our findings indicate that very good quantitative results can be obtained on the BCS...
Gao, Sijie
2014-01-01
We reconsider some fundamental problems of the thin shell model. First, we point out that the "cut and paste" construction does not guarantee a well-defined manifold because there is no overlap of coordinates across the shell. When one requires that the spacetime metric across the thin shell is continuous, it also provides a way to specify the tangent space and the manifold. Other authors have shown that this specification leads to the conservation laws when shells collide. On the other hand, the well-known areal radius $r$ seems to be a perfect coordinate covering all regions of a spherically symmetric spacetime. However, we show by simple but rigorous arguments that $r$ fails to be a coordinate covering a neighborhood of the thin shell if the metric across the shell is continuous. When two spherical shells collide and merge into one, we show that it is possible that $r$ remains to be a good coordinate and the conservation laws hold. To make this happen, different spacetime regions divided by the shells must...
Frontiers and challenges of nuclear shell model
International Nuclear Information System (INIS)
Two recent developments of the nuclear shell model are presented. One is a breakthrough in computational feasibility owing to the Monte Carlo Shell Model (MCSM). By the MCSM, the structure of low-lying states can be studied with realistic interactions for a wide, nearly unlimited basically, variety of nuclei. The magic numbers are the key concept of the shell model, and are shown to be different in exotic nuclei from those of stable nuclei. Its novel origin and robustness will be discussed. (orig.)
Volya, Alexander; Zelevinsky, Vladimir
2005-01-01
The Continuum Shell Model is an old but recently revived method that traverses the boundary between nuclear many-body structure and nuclear reactions. The method is based on the non-Hermitian energy-dependent effective Hamiltonian. The formalism, interpretation of solutions and practical implementation of calculations are discussed in detail. The results of the traditional shell model are fully reproduced for bound states; resonance parameters and cross section calculations are presented for ...
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
International Nuclear Information System (INIS)
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)
International Nuclear Information System (INIS)
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
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.
Frontiers and challenges of the nuclear shell model
International Nuclear Information System (INIS)
Two recent developments of the nuclear shell model are presented. One is a breakthrough in computational feasibility owing to the Monte Carlo Shell Model (MCSM). By the MCSM, the structure of low-lying states can be studied with realistic interactions for a wide, nearly unlimited basically, variety of nuclei. The magic numbers are the key concept of the shell model, and are shown to be different in exotic nuclei from those of stable nuclei. Its novel origin and robustness will be discussed. (orig.)
Pseudospin Conserving Shell Model Interactions
Ginocchio, Joseph N.
2010-01-01
Pseudospin symmetry is approximately conserved in nuclei. Normally shell model interactions are written in terms of spin an orbital angular momentum operators, not in terms of pseudospin and pseudo-orbital angular momentum operators. We determine the shell model interactions which conserve pseudospin symmetry and pseudo-orbital angular momentum symmetry and write them in terms of spin and orbital angular momentum operators including the tensor interaction. We show that, although the tensor in...
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.
Multi-major-shell shell model for heavy nuclei–an extended projected shell model
International Nuclear Information System (INIS)
The projected shell model (PSM) in its original version is an efficient shell model truncation scheme for well deformed nuclei. However, the model is applicable only to rotational motion, but not collective vibrations. In this paper, we discuss a scheme that extends the PSM applicability to low-lying rotational and vibrational states possibly in all kinds of heavy nuclei (from deformed via transitional to spherical), thus rendering it to be a more general multi-major-shell shell model for heavy nuclei. Three known types of vibration (β, γ, and scissors-mode) are discussed. (author)
Multi-Shell Shell Model for Heavy Nuclei
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 t...
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.
Applications of Continuum Shell Model
Volya, Alexander
2006-01-01
The nuclear many-body problem at the limits of stability is considered in the framework of the Continuum Shell Model that allows a unified description of intrinsic structure and reactions. Technical details behind the method are highlighted and practical applications combining the reaction and structure pictures are presented.
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.
Balmer, Jennifer A; Mykhaylyk, Oleksandr O; Schmid, Andreas; Armes, Steven P; Fairclough, J Patrick A; Ryan, Anthony J
2011-07-01
A two-population model based on standard small-angle X-ray scattering (SAXS) equations is verified for the analysis of core-shell structures comprising spherical colloidal particles with particulate shells. First, Monte Carlo simulations of core-shell structures are performed to demonstrate the applicability of the model. Three possible shell packings are considered: ordered silica shells due to either charge-dependent repulsive or size-dependent Lennard-Jones interactions or randomly arranged silica particles. In most cases, the two-population model produces an excellent fit to calculated SAXS patterns for the simulated core-shell structures, together with a good correlation between the fitting parameters and structural parameters used for the simulation. The limits of application are discussed, and then, this two-population model is applied to the analysis of well-defined core-shell vinyl polymer/silica nanocomposite particles, where the shell comprises a monolayer of spherical silica nanoparticles. Comprehensive SAXS analysis of a series of poly(styrene-co-n-butyl acrylate)/silica colloidal nanocomposite particles (prepared by the in situ emulsion copolymerization of styrene and n-butyl acrylate in the presence of a glycerol-functionalized silica sol) allows the overall core-shell particle diameter, the copolymer latex core diameter and polydispersity, the mean silica shell thickness, the mean silica diameter and polydispersity, the volume fractions of the two components, the silica packing density, and the silica shell structure to be obtained. These experimental SAXS results are consistent with electron microscopy, dynamic light scattering, thermogravimetry, helium pycnometry, and BET surface area studies. The high electron density contrast between the (co)polymer and the silica components, together with the relatively low polydispersity of these core-shell nanocomposite particles, makes SAXS ideally suited for the characterization of this system. Moreover
Recent shell-model results for exotic nuclei
Directory of Open Access Journals (Sweden)
Utsuno Yusuke
2014-03-01
Full Text Available We report on our recent advancement in the shell model and its applications to exotic nuclei, focusing on the shell evolution and large-scale calculations with the Monte Carlo shell model (MCSM. First, we test the validity of the monopole-based universal interaction (VMU as a shell-model interaction by performing large-scale shell-model calculations in two different mass regions using effective interactions which partly comprise VMU. Those calculations are successful and provide a deeper insight into the shell evolution beyond the single-particle model, in particular showing that the evolution of the spin-orbit splitting due to the tensor force plays a decisive role in the structure of the neutron-rich N ∼ 28 region and antimony isotopes. Next, we give a brief overview of recent developments in MCSM, and show that it is applicable to exotic nuclei that involve many valence orbits. As an example of its applications to exotic nuclei, shape coexistence in 32Mg is examined.
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.
Simple ablative implosion model: shell dynamics
International Nuclear Information System (INIS)
A simple model, derived from Newton's Second Law, for the ablative implosion of a thin spherical shell is presented. The scaling dependence of the implosion time, shell velocity, and mass loss on shell dimensions and the critical physical parameter, the ablation pressure, is derived. Finally, the model is used to examine implosion energy efficiency and to describe an interesting application, wall-recoil heating of a contained fuel gas
Clustering aspects and the shell model
Arima, A
2004-01-01
In this talk I shall discuss the clustering aspect and the shell model. I shall first discuss the $\\alpha$-cluster aspects based on the shell model calculations. Then I shall discuss the spin zero ground state dominance in the presence of random interactions and a new type of cluster structure for fermions in a single-$j$ shell in the presence of only pairing interaction with the largest multiplicity.
A model for planktic foraminiferal shell growth
Signes, M.; Bijma, Jelle; Hemleben, C.; Ott, R.
1993-01-01
In this paper we analyze the laws of growth that control planktic foraminiferal shell morpholoy. We assume that isometry is the key towards the understanding of their ontogeny. Hence, our "null hypothesis" is that these organisms construct isometric shells. To test this hypothesis, geometric models of their shells have been generated with a personal computer. It is demonstrated that early chambers in log-spirally coiled structures can not follow a strict isometric arrangement. In the real wor...
Monte Carlo modeling of Tajoura reactor
International Nuclear Information System (INIS)
From neutronics point of view, reactor modeling is concerned with the determination of the reactor neutronic parameters which can be obtained through the solution of the neutron transport equation. The attractiveness of the Monte Carlo method is in its capability of handling geometrically complicated problems and due to the nature of the method a large number of particles can be tracked from birth to death before any statistically significant results can be obtained. In this paper the MCNP, a Monte Carlo code, is implemented in the modeling of the Tajoura reactor. (author)
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.
IBM symmetries in realistic shell model states
International Nuclear Information System (INIS)
An approximate dynamical symmetry referring to IBM-type bosons is shown to be latent in the shell model eigenfunctions for 54Cr and 56Fe. No symmetry is assumed in the approach, which invokes only a realistic shell model interaction and an interpretation of the bosons as nucleon pairs. Particular emphasis is placed on the levels involved in M1 excitation. 25 refs., 4 tabs., 1 fig
Monte Carlo models: Quo vadimus?
Energy Technology Data Exchange (ETDEWEB)
Wang, Xin-Nian
2001-01-01
Coherence, multiple scattering and the interplay between soft and hard processes are discussed. These physics phenomena are essential for understanding the nuclear dependences of rapidity density and p{sub T} spectra in high-energy heavy-ion collisions. The RHIC data have shown the onset of hard processes and indications of high p{sub T} spectra suppression due to parton energy loss. Within the pQCD parton model, the combination of azimuthal anisotropy ({nu}{sub 2}) and hadron spectra suppression at large p{sub T} can help one to determine the initial gluon density in heavy-ion collisions at RHIC.
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...
SDS-2 modelling with DRAG-SHELL
International Nuclear Information System (INIS)
For SDS2 physics modelling, Ontario Hydro, 'now Ontario Power Generation' introduced an automated methodology driven by a shell script named SDS2-SHELL, which uses the supercell code MULTICELL and the lattice code POWDERPUFS-V, in order to provide appropriate incremental cross sections corresponding to various stages of poison injection in the moderator. With the current move to newer physics tools, RFSP-IST is now required to have the capability to perform SDS-2 analysis in the full-two- energy-group methodology. In order to achieve this functionality, a new shell script, DRAG-SHELL, which uses the supercell code DRAGON and the lattice code WIMS-IST, was developed. The new DRAG-SHELL methodology has been automated using a UNIX Korn shell script. The execution of the suite of codes and the manipulation of the huge input and output data required for SDS-2 simulation is achieved by using intuitive, English language keywords. Some of the features of DRAG-SHELL include maintaining consistency of code-to-code data transfer and the standardization of input formats. (author)
Monte Carlo modeling of liquid scinttilation spectra
Czech Academy of Sciences Publication Activity Database
Šimek, Ondřej; Šídlová, V.; Světlík, Ivo; Tomášková, Lenka
Praha : ČVUT v Praze, 2007, s. 90-93. ISBN 978-80-01-03901-4. [Dny radiační ochrany /29./. Kouty nad Desnou, Hrubý Jeseník (CZ), 05.11.2007-09.11.2007] Institutional research plan: CEZ:AV0Z10480505 Keywords : Monte Carlo modelling * liquid scintillation spectra * energy deposition Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders
BioShell-Threading: versatile Monte Carlo package for protein 3D threading
Gniewek, Pawel; Kolinski, Andrzej; Kloczkowski, Andrzej; Gront, Dominik
2014-01-01
Background The comparative modeling approach to protein structure prediction inherently relies on a template structure. Before building a model such a template protein has to be found and aligned with the query sequence. Any error made on this stage may dramatically affects the quality of result. There is a need, therefore, to develop accurate and sensitive alignment protocols. Results BioShell threading software is a versatile tool for aligning protein structures, protein sequences or sequen...
Modeling of microencapsulated polymer shell solidification
International Nuclear Information System (INIS)
A finite element transport model has been developed and implemented to complement experimental efforts to improve the quality of ICF target shells produced via controlled-mass microencapsulation. The model provides an efficient means to explore the effect of processing variables on the dynamics of shell dimensions, concentricity, and phase behavior. Comparisons with experiments showed that the model successfully predicts the evolution of wall thinning and core/wall density differences. The model was used to efficiently explore and identify initial wall compositions and processing temperatures which resulted in concentricity improvements from 65 to 99%. The evolution of trace amounts of water entering into the shell wall was also tracked in the simulations. Comparisons with phase envelope estimations from modified UNIFAP calculations suggest that the water content trajectory approaches the two-phase region where vacuole formation via microphase separation may occur
The flexible model and its shell
International Nuclear Information System (INIS)
The flexible model is a new type of model that can be used for describing complex systems including both numerical computation and symbolical operation. The idea of flexible modeling was presented according to the concept, principle, and method of Intelligent Engineering. This paper will first introduce the flexible model and the method of flexible modeling. Then, a kind of flexible model shell will be presented
The spherical collapse model with shell crossing
Sanchez-Conde, M A; Prada, F
2006-01-01
In this work, we study the formation and evolution of dark matter halos by means of the spherical infall model with shell-crossing. We present a framework to tackle this effect properly, that does not involve the adiabatic approximation, and is based on the numerical follow-up, with time, of that individual shell of matter that contains always the same fraction of mass with respect to the total mass. In this first step, we do not include angular momentum, velocity dispersion or triaxiality. Within this framework - named as the Spherical Shell Tracker (SST) - we investigate the dependence of the evolution of the halo with virial mass, with the adopted mass fraction of the shell, and for different cosmologies. We find that our results are very sensitive to a variation of the halo virial mass or the mass fraction of the shell that we consider. However, we obtain a negligible dependence on cosmology. Furthermore, we show that the effect of shell-crossing plays a crucial role in the way that the halo reaches the s...
Shell Model for Buoyancy-driven Turbulence
Kumar, Abhishek
2014-01-01
In this paper we construct shell models for convective turbulence, e.g., Rayleigh B\\'{e}nard convection, and stably-stratified turbulence. We simulate these models in the turbulent regime and show that the convective turbulence exhibits Kolmogorov spectrum for the kinetic energy, while the stably-stratified turbulence show Bolgiano-Obukhbov scaling.
SD-pair shell model for even-even systems
International Nuclear Information System (INIS)
A nucleon-pair shell model was proposed in 1993 by J. Q. Chen. Due to the success of the interacting boson model, the full shell model space in the nucleon-pair shell model was truncated to SD-pair subspace, called SD-pair shell model. Within this model, the experimental spectra in medium-weight and heavy nuclei, limiting cases in the interacting boson model, phase transitions, etc. can be reproduced approximately. (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.
Translational invariant shell model for Λ hypernuclei
Directory of Open Access Journals (Sweden)
Jolos R.V.
2016-01-01
Full Text Available We extend shell model for Λ hypernuclei suggested by Gal and Millener by including 2ћω excitations in the translation invariant version to estimate yields of different hyperfragments from primary p-shell hypernuclei. We are inspired by the first successful experiment done at MAMI which opens way to study baryon decay of hypernuclei. We use quantum numbers of group SU(4, [f], and SU(3, (λμ, to classify basis wave functions and calculate coefficients of fractional parentage.
Monte Carlo modelling for individual monitoring
International Nuclear Information System (INIS)
procedures) Monte Carlo modelling plays a fundamental role in characterizing the photon irradiation fields (direct and backscattered components analysis). Photon spectrum modification due to the presence of the calibration phantom as a function of both the incident angle and of the measurement position on the phantom face can be studied in detail by numerical simulations. These results give the possibility to optimize the dosemeter design and to test air kerma homogeneity regions on the calibration phantom surface (according to the ISO regulation). All the logical flow diagram of the type test procedure will be explained pointing out the role of each Monte Carlo computed parameter. Finally Monte Carlo studies for the characterization of neutron irradiation halls are concisely outlined, demonstrating the importance of a reliable description of the irradiation experiences for the calibration of personal dosemeters. Numerical simulations coupled with experiment allow separating the direct and scattered contributions to the detector and to determine their energy spectra. Furthermore the simulations can provide suitable information on the true thermal neutron fluence outside a thermal neutron facility in presence of a calibration phantom (calibrations in terms of Hp(10) for thermal neutrons). (author)
Monte Carlo modeling and meteor showers
International Nuclear Information System (INIS)
Prediction of short lived increases in the cosmic dust influx, the concentration in lower thermosphere of atoms and ions of meteor origin and the determination of the frequency of micrometeor impacts on spacecraft are all of scientific and practical interest and all require adequate models of meteor showers at an early stage of their existence. A Monte Carlo model of meteor matter ejection from a parent body at any point of space was worked out by other researchers. This scheme is described. According to the scheme, the formation of ten well known meteor streams was simulated and the possibility of genetic affinity of each of them with the most probable parent comet was analyzed. Some of the results are presented
Monte Carlo modeling and meteor showers
Kulikova, N. V.
1987-08-01
Prediction of short lived increases in the cosmic dust influx, the concentration in lower thermosphere of atoms and ions of meteor origin and the determination of the frequency of micrometeor impacts on spacecraft are all of scientific and practical interest and all require adequate models of meteor showers at an early stage of their existence. A Monte Carlo model of meteor matter ejection from a parent body at any point of space was worked out by other researchers. This scheme is described. According to the scheme, the formation of ten well known meteor streams was simulated and the possibility of genetic affinity of each of them with the most probable parent comet was analyzed. Some of the results are presented.
Mapping the Two-Component Atomic Fermi Gas to the Nuclear Shell-Model
DEFF Research Database (Denmark)
Özen, C.; Zinner, Nikolaj Thomas
2014-01-01
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...
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).
Monte Carlo modelling of TRIGA research reactor
Energy Technology Data Exchange (ETDEWEB)
El Bakkari, B., E-mail: bakkari@gmail.co [Reactor Operating Unit (UCR), National Centre of Sciences, Energy and Nuclear Techniques (CNESTEN/CENM), POB 1382, Rabat (Morocco); ERSN-LMR, Department of Physics, Faculty of Sciences, POB 2121, Tetuan (Morocco); Nacir, B. [Reactor Operating Unit (UCR), National Centre of Sciences, Energy and Nuclear Techniques (CNESTEN/CENM), POB 1382, Rabat (Morocco); El Bardouni, T. [ERSN-LMR, Department of Physics, Faculty of Sciences, POB 2121, Tetuan (Morocco); El Younoussi, C. [Reactor Operating Unit (UCR), National Centre of Sciences, Energy and Nuclear Techniques (CNESTEN/CENM), POB 1382, Rabat (Morocco); ERSN-LMR, Department of Physics, Faculty of Sciences, POB 2121, Tetuan (Morocco); Merroun, O. [ERSN-LMR, Department of Physics, Faculty of Sciences, POB 2121, Tetuan (Morocco); Htet, A. [Reactor Technology Unit (UTR), National Centre of Sciences, Energy and Nuclear Techniques (CNESTEN/CENM), POB 1382, Rabat (Morocco); Boulaich, Y. [Reactor Operating Unit (UCR), National Centre of Sciences, Energy and Nuclear Techniques (CNESTEN/CENM), POB 1382, Rabat (Morocco); ERSN-LMR, Department of Physics, Faculty of Sciences, POB 2121, Tetuan (Morocco); Zoubair, M.; Boukhal, H. [ERSN-LMR, Department of Physics, Faculty of Sciences, POB 2121, Tetuan (Morocco); Chakir, M. [EPTN-LPMR, Faculty of Sciences, Kenitra (Morocco)
2010-10-15
The Moroccan 2 MW TRIGA MARK II research reactor at Centre des Etudes Nucleaires de la Maamora (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({alpha}, {beta}) 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 modelling of TRIGA research reactor
International Nuclear Information System (INIS)
The Moroccan 2 MW TRIGA MARK II research reactor at Centre des Etudes Nucleaires de la Maamora (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 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.
Validation of Compton Scattering Monte Carlo Simulation Models
Weidenspointner, Georg; Hauf, Steffen; Hoff, Gabriela; Kuster, Markus; Pia, Maria Grazia; Saracco, Paolo
2014-01-01
Several models for the Monte Carlo simulation of Compton scattering on electrons are quantitatively evaluated with respect to a large collection of experimental data retrieved from the literature. Some of these models are currently implemented in general purpose Monte Carlo systems; some have been implemented and evaluated for possible use in Monte Carlo particle transport for the first time in this study. Here we present first and preliminary results concerning total and differential Compton scattering cross sections.
HSIAO, Chao-Tsung; Chahine, Georges L.
2013-01-01
A simplified three-dimensional (3-D) zero-thickness shell model was developed to recover the non-spherical response of thick-shelled encapsulated microbubbles subjected to ultrasound excitation. The model was validated by comparison with previously developed models and was then used to study the mechanism of bubble break-up during non-spherical deformations resulting from the presence of a nearby rigid boundary. The effects of the shell thickness and the bubble standoff distanc...
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.
Theoretical foundations of the nuclear shell model
International Nuclear Information System (INIS)
In this paper microscopic derivations of the empirical shell-model effective interactions are reviewed. First the authors discuss a time-dependent formalism of the folded-diagram theory. Starting from a realistic nuclear Hamiltonian H = T + VNN, this theory enables the authors to obtain formally a reduced model-space effective Hamiltonian Heff = H0 + Veff. Heff reproduces some, but not all, eigenvalues of H. Veff can be written as a folder diagram series and can be calculated in terms of G-matrices and the irreducible diagrams of the vertex function. A method for accurately treating the Pauli exclusion operator for the G-matrix is described. The s-d shell matrix elements of Veff calculated with the Bonn and the Paris VNN are compared with the Kuo-Brown matrix elements and the empirical matrix elements of Wildenthal
Biofilm growth: a lattice Monte Carlo model
Tao, Yuguo; Slater, Gary
2011-03-01
Biofilms are complex colonies of bacteria that grow in contact with a wall, often in the presence of a flow. In the current work, biofilm growth is investigated using a new two-dimensional lattice Monte Carlo algorithm based on the Bond-Fluctuation Algorithm (BFA). One of the distinguishing characteristics of biofilms, the synthesis and physical properties of the extracellular polymeric substance (EPS) in which the cells are embedded, is explicitly taken into account. Cells are modelled as autonomous closed loops with well-defined mechanical and thermodynamic properties, while the EPS is modelled as flexible polymeric chains. This BFA model allows us to add biologically relevant features such as: the uptake of nutrients; cell growth, division and death; the production of EPS; cell maintenance and hibernation; the generation of waste and the impact of toxic molecules; cell mutation and evolution; cell motility. By tuning the structural, interactional and morphologic parameters of the model, the cell shapes as well as the growth and maturation of various types of biofilm colonies can be controlled.
The Shell-Model Code NuShellX@MSU
Energy Technology Data Exchange (ETDEWEB)
Brown, B.A., E-mail: brown@nscl.msu.edu [Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824-1321 (United States); Rae, W.D.M. [Garsington, Oxfordshire, OX44 (United Kingdom)
2014-06-15
Use of the code NuShellX@MSU is outlined. It connects to the ENSDF data files for automatic comparisons to energy level data. Operator overlaps provide predictions for spectroscopic factors, two-nucleon transfer amplitudes, nuclear moments, gamma decay and beta decay.
Symmetries and deformations in the spherical shell model
Van Isacker, Piet
2016-01-01
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 (large N) the algebraic octupole interaction tends to that of the geometric collective model.
Neutrino nucleosynthesis in supernovae: Shell model predictions
International Nuclear Information System (INIS)
Almost all of the 3 · 1053 ergs liberated in a core collapse supernova is radiated as neutrinos by the cooling neutron star. I will argue that these neutrinos interact with nuclei in the ejected shells of the supernovae to produce new elements. It appears that this nucleosynthesis mechanism is responsible for the galactic abundances of 7Li, 11B, 19F, 138La, and 180Ta, and contributes significantly to the abundances of about 15 other light nuclei. I discuss shell model predictions for the charged and neutral current allowed and first-forbidden responses of the parent nuclei, as well as the spallation processes that produce the new elements. 18 refs., 1 fig., 1 tab
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
International Nuclear Information System (INIS)
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)
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)
Exchange bias and asymmetric hysteresis loops from a microscopic model of core/shell nanoparticles
International Nuclear Information System (INIS)
We present Monte Carlo simulations of hysteresis loops of a model of a magnetic nanoparticle with a ferromagnetic core and an antiferromagnetic shell with varying values of the core/shell interface exchange coupling which aim to clarify the microscopic origin of exchange bias observed experimentally. We have found loop shifts in the field direction as well as displacements along the magnetization axis that increase in magnitude when increasing the interfacial exchange coupling. Overlap functions computed from the spin configurations along the loops have been obtained to explain the origin and magnitude of these features microscopically
On the shell-model-connection of the cluster model
International Nuclear Information System (INIS)
Complete text of publication follows. The interrelation of basic nuclear structure models is a longstanding problem. The connection between the spherical shell model and the quadrupole collective model has been studied extensively, and symmetry considerations proved to be especially useful in this respect. A collective band was interpreted in the shell model language long ago [1] as a set of states (of the valence nucleons) with a specific SU(3) symmetry. Furthermore, the energies of these rotational states are obtained to a good approximation as eigenvalues of an SU(3) dynamically symmetric shell model Hamiltonian. On the other hand the relation of the shell model and cluster model is less well explored. The connection of the harmonic oscillator (i.e. SU(3)) bases of the two approaches is known [2] but it was established only for the unrealistic harmonic oscillator interactions. Here we investigate the question: Can an SU(3) dynamically symmetric interaction provide a similar connection between the spherical shell model and the cluster model, like the one between the shell and collective models? In other words: whether or not the energy of the states of the cluster bands, defined by a specific SU(3) symmetries, can be obtained from a shell model Hamiltonian (with SU(3) dynamical symmetry). We carried out calculations within the framework of the semimicroscopic algebraic cluster model [3,4] in order to find an answer to this question, which seems to be affirmative. In particular, the energies obtained from such a Hamiltonian for several bands of the (12C, 14C, 16O, 20Ne, 40Ca) + α systems turn out to be in good agreement with the experimental values. The present results show that the simple and transparent SU(3) connection between the spherical shell model and the cluster model is valid not only for the harmonic oscillator interactions, but for much more general (SU(3) dynamically symmetric) Hamiltonians as well, which result in realistic energy spectra. Via the
Pairing and realistic shell-model interactions
Covello, A; Gargano, A.; Kuo, T. T. S.
2012-01-01
This paper starts with a brief historical overview of pairing in nuclei, which fulfills the purpose of properly framing the main subject. This concerns the pairing properties of a realistic shell-model effective interaction which has proved very successful in describing nuclei around doubly magic 132Sn. We focus attention on the two nuclei 134Te and 134Sn with two valence protons and neutrons, respectively. Our study brings out the key role of one particle-one hole excitations in producing a ...
Shell model studies for nuclear astrophysics
International Nuclear Information System (INIS)
Shell model studies have contributed in recent years significantly to improve nuclear input required in simulations of the dynamics of astrophysical objects and their associated nucleosynthesis. This manuscript highlights a few examples like electron capture rates of importance for the evolution of core-collapse supernovae and the nucleosynthesis in thermonuclear supernovae, neutrino-nucleus cross sections with relevance to the supernova neutrino spectra and finally half lives of neutron-rich nuclei with magic neutron numbers which serve as waiting points in the mass flow of the astrophysical r-process
Systematic study of shell-model effective interaction in sd shell
International Nuclear Information System (INIS)
The spin-tensor decomposition method has been used to analyze the shell model effective interactions in sd shell systematically. Almost all the interactions have been studied, including the microscopic interactions and phenomenological ones. It can be noticed that the discrepancies between the central forces of microscopic interactions with the ones of empirical interactions are remarkable. (authors)
A shell model for turbulent dynamos
Nigro, G.; Perrone, D.; Veltri, P.
2011-06-01
A self-consistent nonlinear dynamo model is presented. The nonlinear behavior of the plasma at small scale is described by using a MHD shell model for fields fluctuations; this allow us to study the dynamo problem in a large parameter regime which characterizes the dynamo phenomenon in many natural systems and which is beyond the power of supercomputers at today. The model is able to reproduce dynamical situations in which the system can undergo transactions to different dynamo regimes. In one of these the large-scale magnetic field jumps between two states reproducing the magnetic polarity reversals. From the analysis of long time series of reversals we infer results about the statistics of persistence times, revealing the presence of hidden long-time correlations in the chaotic dynamo process.
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.
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 ...
On the shell-model connection of the cluster model
International Nuclear Information System (INIS)
It is shown that the cluster model can be derived from the spherical shell model not only for harmonic oscillator interactions, but for much more realistic Hamiltonians as well, which have dynamically broken U(3) symmetry. This connection justifies an U(3) selection rule for cluster states, and its usefulness is illustrated in studies of heavy ion resonances. (author)
Oscillating shells: A model for a variable cosmic object
Nunez, Dario
1997-01-01
A model for a possible variable cosmic object is presented. The model consists of a massive shell surrounding a compact object. The gravitational and self-gravitational forces tend to collapse the shell, but the internal tangential stresses oppose the collapse. The combined action of the two types of forces is studied and several cases are presented. In particular, we investigate the spherically symmetric case in which the shell oscillates radially around a central compact object.
Oscillating shells A model for a variable cosmic object
Núñez, D
1997-01-01
A model for a possible variable cosmic object is presented. The model consists of a massive shell surrounding a compact object. The gravitational and self-gravitational forces tend to collapse the shell, but the internal tangential stresses oppose the collapse. The combined action of the two types of forces is studied and several cases are presented. In particular, we investigate the spherically symmetric case in which the shell oscillates radially around a central compact object.
Nucleon pair approximation of the shell model: a brief review
International Nuclear Information System (INIS)
We present a brief introduction of the nucleon pair approximation (NPA) of the shell model in this paper. We review our recent calculated results which include level spectra and electromagnetic properties of low-lying states, by applying the NPA to even-even nuclei and to odd-A nuclei. We also apply this method to a few schematic systems such as single-j shell, to investigate the validity of SD-pair truncation of the shell model. (author)
Low Dimensional Models of Shell Vibrations. Parametrically Excited Vibrations of Cylinder Shells
Popov, A. A.; Thompson, J. M. T.; McRobie, F. A.
1998-01-01
Vibrations of cylindrical shells parametrically excited by axial forcing are considered. The governing system of two coupled non-linear partial differential equations is discretized by using Lagrange equations. The computation is simplified significantly by the application of computer algebra and as a result low dimensional models of shell vibrations are readily obtained. After applying numerical continuation techniques and ideas from dynamical systems theory, complete bifurcation diagrams are constructed. The principal aim is to investigate the interaction between different modes of shell vibration. Results for system models with two of the lowest modes are discussed.
The diabatic two-center shell model
International Nuclear Information System (INIS)
Diabatic single-particle representation for the microscopic description of central nucleus-nucleus collisions within the framework of dissipative diabatic dynamics (DDD) are investigated. Based on the scaling condition for diabatic states, two construction methods referred to as the methods of maximum overlap and maximum symmetry, respectively, are studied within a two-center shell model. The conservative diabatic potential and the associated mass tensor for the pure diabatic single-particle motion, are calculated as functions of three collective variables for 92Mo+92Mo and 86Kr+166Er. The calculated diabatic potentials are strongly repulsive and essentially depend only on the distance between the centers of mass in the region of strongly overlapping nuclei. The diabatic mass tensors are smooth functions of the collective variables and are close to the values for irrotational incompressible flow. (orig.)
Modelling apical constriction in epithelia using elastic shell theory.
Jones, Gareth Wyn; Chapman, S Jonathan
2010-06-01
Apical constriction is one of the fundamental mechanisms by which embryonic tissue is deformed, giving rise to the shape and form of the fully-developed organism. The mechanism involves a contraction of fibres embedded in the apical side of epithelial tissues, leading to an invagination or folding of the cell sheet. In this article the phenomenon is modelled mechanically by describing the epithelial sheet as an elastic shell, which contains a surface representing the continuous mesh formed from the embedded fibres. Allowing this mesh to contract, an enhanced shell theory is developed in which the stiffness and bending tensors of the shell are modified to include the fibres' stiffness, and in which the active effects of the contraction appear as body forces in the shell equilibrium equations. Numerical examples are presented at the end, including the bending of a plate and a cylindrical shell (modelling neurulation) and the invagination of a spherical shell (modelling simple gastrulation). PMID:19859751
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.
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 modelling for neutron guide losses
International Nuclear Information System (INIS)
In modern research reactors, neutron guides are commonly used for beam conducting. The neutron guide is a well polished or equivalently smooth glass tube covered inside by sputtered or evaporated film of natural Ni or 58Ni isotope where the neutrons are totally reflected. A Monte Carlo calculation was carried out to establish the real efficiency and the spectral as well as spatial distribution of the neutron beam at the end of a glass mirror guide. The losses caused by mechanical inaccuracy and mirror quality were considered and the effects due to the geometrical arrangement were analyzed. (author) 2 refs.; 2 figs
Single particle models in the shell correction approach
International Nuclear Information System (INIS)
We investigate the dependence of the shell correction energy on the parameters as they occur in the Nilsson model and the single particle model with a Woods-Saxon potential. We give criteria, how these parameters should be chosen in order that the shell correction energies become fairly model-independent. The different models yield now a value of about -20 MeV for 208Pb, substantially larger than in previous work. Its relation to the remainder of the mass formula fit is discussed. We find that shell energies have an extremum. The minimum occurs close to the conventional parameter values (except the potential diffuseness of the protons) and close to the minimum of the total binding energy. The minimum in shell energy corresponds to a maximum bunching of single particle states. The gross properties of these extremal shells agree considerably better with the experimental spectra (for both the neutrons and the protons) than those of conventional model parameters. (orig.)
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)
Structure models: from shell model to ab initio methods
Bacca, Sonia
2016-01-01
A brief review of models to describe nuclear structure and reactions properties is presented, starting from the historical shell model picture and encompassing modern ab initio approaches. A selection of recent theoretical results on observables for exotic light and medium-mass nuclei is shown. Emphasis is given to the comparison with experiment and to what can be learned about three-body forces and continuum properties.
Ly$\\alpha$ Spectra from Multiphase Outflows, and their Connection to Shell Models
Gronke, Max
2016-01-01
We perform Lyman-$\\alpha$ (Ly$\\alpha$) Monte-Carlo radiative transfer calculations on a suite of $2500$ models of multiphase, outflowing media, which are characterized by $14$ parameters. We focus on the Ly$\\alpha$ spectra emerging from these media, and investigate which properties are dominant in shaping the emerging Ly$\\alpha$ profile. Multiphase models give rise to a wide variety of emerging spectra, including single, double and triple peaked spectra. We find that the dominant parameters in shaping the spectra include (i) the cloud covering factor, $f_c$, in agreement with earlier studies, and (ii) the temperature and number density of residual HI in the hot ionized medium. We attempt to reproduce spectra emerging from multiphase models with `shell models' which are commonly used to fit observed Ly$\\alpha$ spectra, and investigate the connection between shell-model parameters and the physical parameters of the clumpy media. In shell models, the neutral hydrogen content of the shell is one of the key parame...
International Nuclear Information System (INIS)
Full text; Relative abundance of charged ions and mean charged ions are calculated following 1s and 2p vacancy production in potassium and calcium atoms. The calculations are performed with Monte Carlo simulation method. The simulation based on the tracing of all possible radiation, non-radiation transitions and electron shake off probabilities after inner shell vacancy creation. The radiative transition rates and electron shakes off processes are obtained with Multiconfiguration-Dirac-Fock (MCDF) wave functions model. The non-radiation transition rates are carried out using Dirac-Fock-Slater (DFS) wave functions. At 1s hole states in Potassium atom, the yield of K5+ ions are the prominent produces. The doubly charged K2+ ions predominate over K3+ ions after 2p shell ionization in potassium. On the other hand, the Ca3+ ions dominate over Ca2+ ions in Calcium. The considerations of closing some Coster-Kronig channels and electron shake off processes through the simulation improve the results of charged ions with the experimental data. The results of electron shake off probabilities are compared with other theoretical calculation. The results of relative abundance of charged ions agree well with the experimental data. (author)
de Oliveira, C. X.; Ferreira, N. S.; Mota, G. V. S.
2016-01-01
In this paper, we report a theoretical study of the inclusion complexes of Praziquantel (PZQ) and β-cyclodextrin (β-CD) in liquid water. The starting geometry has been carried out by molecular mechanics simulations, and afterwards optimized in B3LYP level with a 6-311G(d) basis set. Monte Carlo simulations have been used to calculate the solvation shell of the PZQ/β-CD inclusion complexes. Moreover, the vibrational frequencies and the infrared intensities for the PZQ/β-CD complex were computed using the B3LYP method. It is demonstrated that this combined model can yield well-converged thermodynamic data even for a modest number of sample configurations, which makes the methodology particularly adequate for understanding the solute-solvent interaction used for generating the liquid structures of one solute surrounded by solvent molecules. The complex solvation shell showed an increase of the water molecule level in relation to the isolated PZQ molecule because of the hydrophilic effect of the CD molecule. The infrared spectra showed that the contribution that originated in the PZQ molecule was not predominant in the upper-wave number region in the drug/β-CD. The movement that purely originated in the PZQ molecule was localized in the absorption band, ranging from 1328 to 1688 cm- 1.
Energy Technology Data Exchange (ETDEWEB)
Barrett, B R; Navratil, P; Vary, J P
2011-04-11
A long-standing goal of nuclear theory is to determine the properties of atomic nuclei based on the fundamental interactions among the protons and neutrons (i.e., nucleons). By adopting nucleon-nucleon (NN), three-nucleon (NNN) and higher-nucleon interactions determined from either meson-exchange theory or QCD, with couplings fixed by few-body systems, we preserve the predictive power of nuclear theory. This foundation enables tests of nature's fundamental symmetries and offers new vistas for the full range of complex nuclear phenomena. Basic questions that drive our quest for a microscopic predictive theory of nuclear phenomena include: (1) What controls nuclear saturation; (2) How the nuclear shell model emerges from the underlying theory; (3) What are the properties of nuclei with extreme neutron/proton ratios; (4) Can we predict useful cross sections that cannot be measured; (5) Can nuclei provide precision tests of the fundamental laws of nature; and (6) Under what conditions do we need QCD to describe nuclear structure, among others. Along with other ab initio nuclear theory groups, we have pursued these questions with meson-theoretical NN interactions, such as CD-Bonn and Argonne V18, that were tuned to provide high-quality descriptions of the NN scattering phase shifts and deuteron properties. We then add meson-theoretic NNN interactions such as the Tucson-Melbourne or Urbana IX interactions. More recently, we have adopted realistic NN and NNN interactions with ties to QCD. Chiral perturbation theory within effective field theory ({chi}EFT) provides us with a promising bridge between QCD and hadronic systems. In this approach one works consistently with systems of increasing nucleon number and makes use of the explicit and spontaneous breaking of chiral symmetry to expand the strong interaction in terms of a dimensionless constant, the ratio of a generic small momentum divided by the chiral symmetry breaking scale taken to be about 1 GeV/c. The
International Nuclear Information System (INIS)
A long-standing goal of nuclear theory is to determine the properties of atomic nuclei based on the fundamental interactions among the protons and neutrons (i.e., nucleons). By adopting nucleon-nucleon (NN), three-nucleon (NNN) and higher-nucleon interactions determined from either meson-exchange theory or QCD, with couplings fixed by few-body systems, we preserve the predictive power of nuclear theory. This foundation enables tests of nature's fundamental symmetries and offers new vistas for the full range of complex nuclear phenomena. Basic questions that drive our quest for a microscopic predictive theory of nuclear phenomena include: (1) What controls nuclear saturation; (2) How the nuclear shell model emerges from the underlying theory; (3) What are the properties of nuclei with extreme neutron/proton ratios; (4) Can we predict useful cross sections that cannot be measured; (5) Can nuclei provide precision tests of the fundamental laws of nature; and (6) Under what conditions do we need QCD to describe nuclear structure, among others. Along with other ab initio nuclear theory groups, we have pursued these questions with meson-theoretical NN interactions, such as CD-Bonn and Argonne V18, that were tuned to provide high-quality descriptions of the NN scattering phase shifts and deuteron properties. We then add meson-theoretic NNN interactions such as the Tucson-Melbourne or Urbana IX interactions. More recently, we have adopted realistic NN and NNN interactions with ties to QCD. Chiral perturbation theory within effective field theory (χEFT) provides us with a promising bridge between QCD and hadronic systems. In this approach one works consistently with systems of increasing nucleon number and makes use of the explicit and spontaneous breaking of chiral symmetry to expand the strong interaction in terms of a dimensionless constant, the ratio of a generic small momentum divided by the chiral symmetry breaking scale taken to be about 1 GeV/c. The resulting NN
Effective Interactions from No Core Shell Model
International Nuclear Information System (INIS)
We construct the many-body effective Hamiltonian for pf-shell by carrying out 2ℎ(Omega) NCSM calculations at the 2-body cluster level. We demonstrate how the effective Hamiltonian derived from realistic nucleon-nucleon (NN) potentials for the 2ℎ(Omega) NCSM space should be modified to properly account for the many-body correlations produced by truncating to the major pf-shell. We obtain two-body effective interactions for the pf-shell by using direct projection and use them to reproduce the results of large scale NCSM for other light Ca isotopes
Compressive behavior of a turtle's shell: experiment, modeling, and simulation.
Damiens, R; Rhee, H; Hwang, Y; Park, S J; Hammi, Y; Lim, H; Horstemeyer, M F
2012-02-01
The turtle's shell acts as a protective armor for the animal. By analyzing a turtle shell via finite element analysis, one can obtain the strength and stiffness attributes to help design man-made armor. As such, finite element analysis was performed on a Terrapene carolina box turtle shell. Experimental data from compression tests were generated to provide insight into the scute through-thickness behavior of the turtle shell. Three regimes can be classified in terms of constitutive modeling: linear elastic, perfectly inelastic, and densification regions, where hardening occurs. For each regime, we developed a model that comprises elasticity and densification theory for porous materials and obtained all the material parameters by correlating the model with experimental data. The different constitutive responses arise as the deformation proceeded through three distinctive layers of the turtle shell carapace. Overall, the phenomenological stress-strain behavior is similar to that of metallic foams. PMID:22301179
Study of nuclei around Z=28 by large-scale shell model calculations
International Nuclear Information System (INIS)
We study Cr and Ni isotopes by using Monte Carlo shell model (MCSM) calculations in a pfg9d5 model space which consists of the 0f1p shell, 0g9/2 and 1d5/2 orbits, in order to treat magic numbers 28, 50 and a sub-magic number 40. In MCSM, a wave function is represented as a linear combination of angular-momentum- and parity-projected deformed Slater determinants (MCSM bases) and we can obtain eigenstates in a large model space such as pfg9d5 space. We showed the change of N=40 magic behaviour in Cr and Ni isotopes and three 0+ states of 68Ni with different shapes and close energies. The calculated excitation energies of 68Ni reproduce experimental values including non-yrast and negative-parity states
Shell model description of band structure in 48Cr
International Nuclear Information System (INIS)
The band structure for normal and abnormal parity bands in 48Cr are described using the m-scheme shell model. In addition to full fp-shell, two particles in the 1d3/2 orbital are allowed in order to describe intruder states. The interaction includes fp-, sd- and mixed matrix elements
Statistical properties of the nuclear shell-model Hamiltonian
International Nuclear Information System (INIS)
The statistical properties of realistic nuclear shell-model Hamiltonian are investigated in sd-shell nuclei. The probability distribution of the basic-vector amplitude is calculated and compared with the Porter-Thomas distribution. Relevance of the results to the calculation of the giant resonance mixing parameter is pointed out. (Author)
Modelling hadronic interactions in cosmic ray Monte Carlo generators
Directory of Open Access Journals (Sweden)
Pierog Tanguy
2015-01-01
Full Text Available Currently the uncertainty in the prediction of shower observables for different primary particles and energies is dominated by differences between hadronic interaction models. The LHC data on minimum bias measurements can be used to test Monte Carlo generators and these new constraints will help to reduce the uncertainties in air shower predictions. In this article, after a short introduction on air showers and Monte Carlo generators, we will show the results of the comparison between the updated version of high energy hadronic interaction models EPOS LHC and QGSJETII-04 with LHC data. Results for air shower simulations and their consequences on comparisons with air shower data will be discussed.
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
Modelling cerebral blood oxygenation using Monte Carlo XYZ-PA
Zam, Azhar; Jacques, Steven L.; Alexandrov, Sergey; Li, Youzhi; Leahy, Martin J.
2013-02-01
Continuous monitoring of cerebral blood oxygenation is critically important for the management of many lifethreatening conditions. Non-invasive monitoring of cerebral blood oxygenation with a photoacoustic technique offers advantages over current invasive and non-invasive methods. We introduce a Monte Carlo XYZ-PA to model the energy deposition in 3D and the time-resolved pressures and velocity potential based on the energy absorbed by the biological tissue. This paper outlines the benefits of using Monte Carlo XYZ-PA for optimization of photoacoustic measurement and imaging. To the best of our knowledge this is the first fully integrated tool for photoacoustic modelling.
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. PMID:19658594
Generator coordinate method. Application to single-j shell model
International Nuclear Information System (INIS)
To prove availability of the generator coordinate method under consideration of many generator coordinates, both calculation results of this method and the shell model using exact diagonalization were compared. The calculation object is limited to the single-j shell model and simplified to quadruple deformation limit in disregard of paring correlation. The inner state of model nuclei was estimated by Nilsson model and used as the trial functions of the generator coordinate method. Three components of Euler angles and the surface vibration parameter γ were used as the generator coordinates. The results of four vacancies system agreed closely with the shell model. The system, of which half of shell was packed, showed behavior such as rigid rotor with triaxial asymmetrical deformation. This result was opposite to that of the meanfield approximation. (S.Y.)
Deriving the nuclear shell model from first principles
International Nuclear Information System (INIS)
A procedure for calculating microscopically the input for standard shell-model calculations, i.e., the core and single-particle energies plus the two-body effective model-space interactions, is presented and applied to nuclei at the start of the sd-shell. Calculations with the JISP16 and Idaho χEFT N3LO nucleon-nucleon interactions are performed and yield consistent results, which also are similar to phenomenological results in the sd-shell as well as with other theoretical calculations, utilizing other techniques. All results show only a weak A-dependence
Atomic-level models of the bacterial carboxysome shell
International Nuclear Information System (INIS)
The carboxysome is a bacterial microcompartment that functions as a simple organelle by sequestering enzymes involved in carbon fixation. The carboxysome shell is roughly 800 to 1400 angstroms in diameter and is assembled from several thousand protein subunits. Previous studies have revealed the three-dimensional structures of hexameric carboxysome shell proteins, which self-assemble into molecular layers that most likely constitute the facets of the polyhedral shell. Here, we report the three-dimensional structures of two proteins of previously unknown function, CcmL and OrfA (or CsoS4A), from the two known classes of carboxysomes, at resolutions of 2.4 and 2.15 angstroms. Both proteins assemble to form pentameric structures whose size and shape are compatible with formation of vertices in an icosahedral shell. Combining these pentamers with the hexamers previously elucidated gives two plausible, preliminary atomic models for the carboxysome shell.
Large space shell model calculations with small space results
Zamick, Larry; Yu, Xiafei
2015-01-01
We note that in large space shell model calculaiotns and experiment one sometimes get results, the form of which also appear in smaller space calculations. On the other hand there are some results which demand the large space approach.
A Justification of Two-Dimensional Nonlinear Viscoelastic Shells Model
Fushan Li
2012-01-01
By applying formal asymptotic analysis and Laplace transformation, we obtain two-dimensional nonlinear viscoelastic shells model satisfied by the leading term of asymptotic expansion of the solution to the three-dimensional equations.
Yet another Monte Carlo study of the Schwinger model
International Nuclear Information System (INIS)
Some methodological improvements are introduced in the quantum Monte Carlo simulation of the 1 + 1 dimensional quantum electrodynamics (the Schwinger model). Properties at finite temperatures are investigated, concentrating on the existence of the chirality transition and of the deconfinement transition. (author)
Recent improvements on Monte Carlo modelling at ATLAS
Soualah, Rachik; The ATLAS collaboration
2015-01-01
The most recent findings on the Monte Carlo simulation of proton-proton collisions at ATLAS are presented. In this, the most recent combined MPI and shower tunes performed using 7 TeV ATLAS data are reported, as well as improved modeling of electroweak processes, and processes containing top using recent MC generators and PDF sets.
MOSFET GATE CURRENT MODELLING USING MONTE-CARLO METHOD
Voves, J.; Vesely, J.
1988-01-01
The new technique for determining the probability of hot-electron travel through the gate oxide is presented. The technique is based on the Monte Carlo method and is used in MOSFET gate current modelling. The calculated values of gate current are compared with experimental results from direct measurements on MOSFET test chips.
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...
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.
Jacobi no-core shell model for p-shell nuclei
Liebig, S; Nogga, A
2015-01-01
We introduce an algorithm to obtain coefficients of fractional parentage for light $p$-shell nuclei. The coefficients enable to use Jacobi coordinates in no-core shell model calculations separating off the center-of-mass motion. Fully antisymmetrized basis states are given together with recoupling coefficients that allow one to apply two- and three-nucleon operators. As an example, we study the dependence on the harmonic oscillator frequency of $^3$H, $^4$He, $^6$He, $^6$Li and $^7$Li and extract their binding and excitation energies. The coefficients will be made openly accessible as HDF5 data files.
Realistic Shell-Model Calculations for Nuclei in the Region of Shell Closures off Stability
Covello, A; Coraggio, L.; Gargano, A.
1998-01-01
We have performed realistic shell-model calculations for nuclei around doubly magic 100Sn and 132Sn using an effective interaction derived from the Bonn A nucleon-nucleon potential. The results are in remarkably good agreement with the experimental data showing the ability of our effective interaction to provide an accurate description of nuclear structure properties.
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., 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 fractionation
International Nuclear Information System (INIS)
Standard modeling approaches can produce the most likely values of the formation constants of metal-ligand complexes if a particular set of species containing the metal ion is known or assumed to exist in solution equilibrium with complexing ligands. Identifying the most likely set of species when more than one set is plausible is a more difficult problem to address quantitatively. A Monte Carlo method of data analysis is described that measures the relative abilities of different speciation models to fit optical spectra of open-shell actinide ions. The best model(s) can be identified from among a larger group of models initially judged to be plausible. The method is demonstrated by analyzing the absorption spectra of aqueous Pu(IV) titrated with nitrate ion at constant 2 molal ionic strength in aqueous perchloric acid. The best speciation model supported by the data is shown to include three Pu(IV) species with nitrate coordination numbers 0, 1, and 2. Formation constants are β1=3.2±0.5 and β2=11.2±1.2, where the uncertainties are 95% confidence limits estimated by propagating raw data uncertainties using Monte Carlo methods. Principal component analysis independently indicates three Pu(IV) complexes in equilibrium. (c) 2000 Society for Applied Spectroscopy
Inference Networks for Sequential Monte Carlo in Graphical Models
Paige, Brooks; Wood, Frank
2016-01-01
We introduce a new approach for amortizing inference in directed graphical models by learning heuristic approximations to stochastic inverses, designed specifically for use as proposal distributions in sequential Monte Carlo methods. We describe a procedure for constructing and learning a structured neural network which represents an inverse factorization of the graphical model, resulting in a conditional density estimator that takes as input particular values of the observed random variables...
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 predictive model of shell morphology in CdSe/CdS core/shell quantum dots
International Nuclear Information System (INIS)
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/nm2. 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
Translational invariant shell model for Lambda hypernuclei
Czech Academy of Sciences Publication Activity Database
Jolos, R. V.; Majling, Lubomír; Majlingová, O.
Vol. 107. Les Ulis: E D P Sciences, 2016, s. 10004. ISSN 2100-014X. [7th International Conference on Nuclear Structure and Related Topics (NSRT). Dubna (RU), 14.07.2015-18.07.2015] R&D Projects: GA MŠk LG14004; GA ČR(CZ) GA15-04301S Institutional support: RVO:61389005 Keywords : hypernuclei * p-shell Subject RIV: BE - Theoretical Physics
Monte Carlo Euler approximations of HJM term structure financial models
Björk, Thomas; Tempone, Raul; Zouraris, Georgios E
2012-01-01
We present Monte Carlo-Euler methods for a weak approximation problem related to the Heath-Jarrow-Morton (HJM) term structure model, based on \\Ito 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.
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.
Coupled MHD-Monte Carlo transport model for dense plasmas
International Nuclear Information System (INIS)
A two-dimensional, two fluid model of the MHD equations has been coupled to a Monte Carlo transport model of high energy, non-Maxwellian ions. The MHD part of the model assumes complete ionization and includes a perfect gas law for a scalar pressure, a tensor artificial viscosity, electron and ion thermal conduction, electron-ion coupling, and a radiation loss term. A simple Ohm's Law is used with a B/sub theta/ magnetic field. The MHD equations were solved in Lagrangian coordinates. The conservation equations were differenced explicitly and the diffusion-type equations implicitly using the splitting technique. The Monte Carlo model solves the equation of motion for high energy ions, moving through and suffering small and large angle collisions with the fluid Maxwellian plasma. The source of high energy ions is the thermonuclear reactions of the hydrogen isotopes, or it may be an externally injected beam of neutralized ions. In addition to using the usual Maxwell averaged thermonuclear cross sections for calculating the number of reactions taking place within the Maxwellian plasma, the high energy ions may suffer collisions resulting in a reaction. In the Monte Carlo model all neutrons are assumed to escape, and all energetic ions of Z less than or equal to 2 are followed
Models for Self-Gravitating Photon Shells and Geons
Andréasson, Håkan; Thaller, Maximilian
2015-01-01
We prove existence of spherically symmetric, static, self-gravitating photon shells as solutions to the massless Einstein-Vlasov system. The solutions are highly relativistic in the sense that the ratio $2m(r)/r$ is close to $8/9$, where $m(r)$ is the Hawking mass and $r$ is the area radius. In 1955 Wheeler constructed, by numerical means, so called idealized spherically symmetric geons, i.e. solutions of the Einstein-Maxwell equations for which the energy momentum tensor is spherically symmetric on a time average. The structure of these solutions is such that the electromagnetic field is confined to a thin shell for which the ratio $2m/r$ is close to $8/9$, i.e., the solutions are highly relativistic photon shells. The solutions presented in this work provide an alternative model for photon shells or idealized spherically symmetric geons.
Relevance of accurate Monte Carlo modeling in nuclear medical imaging
Zaidi, H
1999-01-01
Monte Carlo techniques have become popular in different areas of medical physics with advantage of powerful computing systems. In particular, they have been extensively applied to simulate processes involving random behavior and to quantify physical parameters that are difficult or even impossible to calculate by experimental measurements. Recent nuclear medical imaging innovations such as single-photon emission computed tomography (SPECT), positron emission tomography (PET), and multiple emission tomography (MET) are ideal for Monte Carlo modeling techniques because of the stochastic nature of radiation emission, transport and detection processes. Factors which have contributed to the wider use include improved models of radiation transport processes, the practicality of application with the development of acceleration schemes and the improved speed of computers. This paper presents derivation and methodological basis for this approach and critically reviews their areas of application in nuclear imaging. An ...
Many-body forces in nuclear shell-model
International Nuclear Information System (INIS)
In the microscopic derivation of the effective Hamiltonian for the nuclear shell model many-body forces between the valence nucleons occur. These many-body forces can be discriminated in ''real'' many-body forces, which can be related to mesonic and internal degrees of freedom of the nucleons, and ''effective'' many-body forces, which arise by the confinement of the nucleonic Hilbert space to the finite-dimension shell-model space. In the present thesis the influences of such three-body forces on the spectra of sd-shell nuclei are studied. For this the two common techniques for shell-model calculations (Oak Ridge-Rochester and Glasgow representation) are extended in such way that a general three-body term in the Hamiltonian can be regarded. The studies show that the repulsive contributions of the considered three-nucleon forces become more important with increasing number of valence nucleons. By this the particle-number dependence of empirical two-nucleon forces can be qualitatively explained. A special kind of effective many-body force occurs in the folded diagram expansion of the energy-dependent effective Hamiltonian for the shell model. Thereby it is shown that the contributions of the folded diagrams with three nucleons are just as important as those with two nucleons. Thus it is to be suspected that the folded diagram expansion contains many-particle terms with arbitrary particle number. The present studies however show that four nucleon effects are neglegible so that the folded diagram expansion can be confined to two- and three-particle terms. In shell-model calculations which extend over several main shells the influences of the spurious center-of-mass motion must be regarded. A procedure is discussed by which these spurious degrees of freedom can be exactly separated. (orig.)
GPU based Monte Carlo for PET image reconstruction: detector modeling
International Nuclear Information System (INIS)
Monte Carlo (MC) calculations and Graphical Processing Units (GPUs) are almost like the dedicated hardware designed for the specific task given the similarities between visible light transport and neutral particle trajectories. A GPU based MC gamma transport code has been developed for Positron Emission Tomography iterative image reconstruction calculating the projection from unknowns to data at each iteration step taking into account the full physics of the system. This paper describes the simplified scintillation detector modeling and its effect on convergence. (author)
Few-body systems in a shell-model approach
International Nuclear Information System (INIS)
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.
Monte Carlo modelling of positron transport in real world applications
International Nuclear Information System (INIS)
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.
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.
Nuclear shell-model code for massive parallel computation, "KSHELL"
Shimizu, Noritaka
2013-01-01
A new code for nuclear shell-model calculations, "KSHELL", is developed. It aims at carrying out both massively parallel computation and single-node computation in the same manner. We solve the Schr\\"{o}dinger's equation in the $M$-scheme shell-model model space, utilizing Thick-Restart Lanczos method. During the Lanczos iteration, the whole Hamiltonian matrix elements are generated "on-the-fly" in every matrix-vector multiplication. The vectors of the Lanczos method are distributed and store...
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
Shell-model Hamiltonians from Density Functional Theory
Alhassid, Y; Fang, L; Sabbey, B
2005-01-01
The density functional theory of nuclear structure provides a many-particle wave function that is useful for static properties, but an extension of the theory is necessary to describe correlation effects or other dynamic properties. Here we propose a procedure to extend the theory by mapping the properties of the self-consistent mean-field Hamiltonian onto an effective shell-model Hamiltonian with two-body interactions. In this initial study, we consider the sd-shell nuclei Ne-20, Mg-24, Si-28, and Ar-36. Our first application is in the framework of the USD shell-model Hamiltonian, using its mean-field approximation to construct an effective Hamiltonian and partially recover correlation effects. We find that more than half of the correlation energy is due to the quadrupole interaction. We then follow a similar procedure but using the SLy4 Skyrme energy functional as our starting point and truncating the space to the spherical $sd$ shell. The constructed shell-model Hamiltonian is found to satisfy minimal cons...
Uncertainties in ozone concentrations predicted with a Lagrangian photochemical air quality model have been estimated using Bayesian Monte Carlo (BMC) analysis. Bayesian Monte Carlo analysis provides a means of combining subjective "prior" uncertainty estimates developed ...
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....
SD nucleon pair approximation of the shell model
International Nuclear Information System (INIS)
It is found that the SD-pair truncation is a good approximation of the shell model in the single-j case when the Hamiltonian consists of (monopole and quadrupole) pairing plus quadrupole type interaction. The SD-pair truncation deteriorates if the QQ-type interaction is artificially large compared with the monopole pairing interaction. In the degenerate sd, pf, and sdg shells in which Hamiltonian consists of pure QQ-type interaction, the basic properties of band structure remain intact in general although there is a large difference between the calculated energy levels and binding energies in the SD-pair truncated subspace and those calculated in the full shell model space. The difference in moment of inertia can be easily absorbed by adjusting interaction strengths. (author)
Photoionization modelling of metal-enriched nova shells
International Nuclear Information System (INIS)
A photoionization model has been developed to investigate the physical conditions in old nova shells with large metal abundances. Atomic rates at low temperatures are included in the model so that the evolution of shells can be traced from their hot, early stages to their later cool phases. X-ray processes are also included. A situation in which a region of lowest temperature but highest ionization can exist at the inner edge of a nebula is demonstrated. A non-uniform density distribution is compared with a uniform density and the observational consequences discussed. The shell of the old nova, CVP Pup, is analysed in detail and its evolution during its constant-luminosity phase traced. (author)
Realistic shell-model calculations for neutron deficient Sn isotopes
Energy Technology Data Exchange (ETDEWEB)
Andreozzi, F.; Coraggio, L.; Covello, A.; Gargano, A.; Kuo, T.T.; Li, Z.B.; Porrino, A. [Dipartimento di Scienze Fisiche, Universita di Napoli Federico II]|[Istituto Nazionale di Fisica Nucleare, Mostra d`Oltremare, Pad. 20, 80125 Napoli (Italy)]|[Department of Physics, SUNY, Stony Brook, New York 11794 (United States)
1996-10-01
We have performed shell-model calculations for {sup 102,103,104,105}Sn using two realistic effective interactions derived from the Bonn A and Paris nucleon-nucleon potentials, respectively. From the comparison of the calculated spectra of {sup 104}Sn and {sup 105}Sn with the experimental ones it turns out that the best agreement is obtained with the weaker tensor force potential (Bonn A). This agreement appears to be significantly better than for other nuclear regions, such as the {ital sd} shell, and thus encourages use of modern realistic potentials in shell-model calculations for medium- and heavy-mass nuclei. In addition, it supports confidence in our predictions of the spectra of the hitherto unknown isotopes {sup 102}Sn and {sup 103}Sn. {copyright} {ital 1996 The American Physical Society.}
Realistic shell-model calculations for neutron deficient Sn isotopes
International Nuclear Information System (INIS)
We have performed shell-model calculations for 102,103,104,105Sn using two realistic effective interactions derived from the Bonn A and Paris nucleon-nucleon potentials, respectively. From the comparison of the calculated spectra of 104Sn and 105Sn with the experimental ones it turns out that the best agreement is obtained with the weaker tensor force potential (Bonn A). This agreement appears to be significantly better than for other nuclear regions, such as the sd shell, and thus encourages use of modern realistic potentials in shell-model calculations for medium- and heavy-mass nuclei. In addition, it supports confidence in our predictions of the spectra of the hitherto unknown isotopes 102Sn and 103Sn. copyright 1996 The American Physical Society
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...
Final Report Fermionic Symmetries and Self consistent Shell Model
International Nuclear Information System (INIS)
In this final report in the field of theoretical nuclear physics we note important accomplishments.We were confronted with 'anomoulous' magnetic moments by the experimetalists and were able to expain them. We found unexpected partial dynamical symmetries--completely unknown before, and were able to a large extent to expain them. The importance of a self consistent shell model was emphasized.
Equations-of-motion approach to shell-model calculations
International Nuclear Information System (INIS)
The authors present an approach to shell-model calculations which works with the equations of motion for pair operators. A central feature of this approach is that it provides the natural framework for a wide variety of approximations. This should allow one to address specific features of the physics of a many-body problem in a particularly economical and practical way
Final Report Fermionic Symmetries and Self consistent Shell Model
Energy Technology Data Exchange (ETDEWEB)
Larry Zamick
2008-11-07
In this final report in the field of theoretical nuclear physics we note important accomplishments.We were confronted with "anomoulous" magnetic moments by the experimetalists and were able to expain them. We found unexpected partial dynamical symmetries--completely unknown before, and were able to a large extent to expain them.The importance of a self consistent shell model was emphasized.
Shell Model and Mean-Field Description of Band Termination
Zalewski, M; Nazarewicz, W; Stoitcheva, G; Zdunczuk, H
2007-01-01
We study nuclear high-spin states undergoing the transition to the fully stretched configuration with maximum angular momentum I_max within the space of valence nucleons. To this end, we perform a systematic theoretical analysis of non-fully-stretched I_max-2 and I_max-1 f_{7/2}^n seniority isomers and d_{3/2}^{-1} f_{7/2}^{n+1} intruder states in the A~44 nuclei from the lower-fp shell. We employ two theoretical approaches: (i) the density functional theory based on the cranked self-consistent Skyrme-Hartree-Fock method, and (ii) the nuclear shell model in the full sdfp configuration space allowing for 1p-1h cross-shell excitations. We emphasize the importance of restoration of broken angular momentum symmetry inherently obscuring the mean-field treatment of high-spin states. Overall good agreement with experimental data is obtained.
The shell model approach to the rotating turbulence
Reshetnyak, M
2003-01-01
Applications of the shell model of turbulence to the case of rapidly rotating bodies are considered. Starting from the classical GOY model we introduce the Coriolis force and obtain a $\\sim k^{-2}$ spectrum for 3D hydrodynamical turbulence for the free decay regime as well for the regime with external forcing. Additional modifications of the GOY model providing a realistic form of the helicity are proposed.
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.
Quantum Monte Carlo study of bilayer ionic Hubbard model
Jiang, M.; Schulthess, T. C.
2016-04-01
The interaction-driven insulator-to-metal transition has been reported in the ionic Hubbard model (IHM) for moderate interaction U , while its metallic phase only occupies a narrow region in the phase diagram. To explore the enlargement of the metallic regime, we extend the ionic Hubbard model to two coupled layers and study the interplay of interlayer hybridization V and two types of intralayer staggered potentials Δ : one with the same (in-phase) and the other with a π -phase shift (antiphase) potential between layers. Our determinant quantum Monte Carlo (DQMC) simulations at lowest accessible temperatures demonstrate that the interaction-driven metallic phase between Mott and band insulators expands in the Δ -V phase diagram of bilayer IHM only for in-phase ionic potentials; while antiphase potential always induces an insulator with charge density order. This implies possible further extension of the ionic Hubbard model from the bilayer case here to a realistic three-dimensional model.
Numerical treatment of a geometrically nonlinear planar Cosserat shell model
Sander, Oliver; Neff, Patrizio; Bîrsan, Mircea
2016-05-01
We present a new way to discretize a geometrically nonlinear elastic planar Cosserat shell. The kinematical model is similar to the general six-parameter resultant shell model with drilling rotations. The discretization uses geodesic finite elements (GFEs), which leads to an objective discrete model which naturally allows arbitrarily large rotations. GFEs of any approximation order can be constructed. The resulting algebraic problem is a minimization problem posed on a nonlinear finite-dimensional Riemannian manifold. We solve this problem using a Riemannian trust-region method, which is a generalization of Newton's method that converges globally without intermediate loading steps. We present the continuous model and the discretization, discuss the properties of the discrete model, and show several numerical examples, including wrinkling of thin elastic sheets in shear.
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...
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.
Statistical mechanics of shell models for 2D-Turbulence
Aurell, E; Crisanti, A; Frick, P; Paladin, G; Vulpiani, A
1994-01-01
We study shell models that conserve the analogues of energy and enstrophy, hence designed to mimic fluid turbulence in 2D. The main result is that the observed state is well described as a formal statistical equilibrium, closely analogous to the approach to two-dimensional ideal hydrodynamics of Onsager, Hopf and Lee. In the presence of forcing and dissipation we observe a forward flux of enstrophy and a backward flux of energy. These fluxes can be understood as mean diffusive drifts from a source to two sinks in a system which is close to local equilibrium with Lagrange multipliers (``shell temperatures'') changing slowly with scale. The dimensional predictions on the power spectra from a supposed forward cascade of enstrophy, and from one branch of the formal statistical equilibrium, coincide in these shell models at difference to the corresponding predictions for the Navier-Stokes and Euler equations in 2D. This coincidence have previously led to the mistaken conclusion that shell models exhibit a forward ...
Monte Carlo modeling of spallation targets containing uranium and americium
International Nuclear Information System (INIS)
Neutron production and transport in spallation targets made of uranium and americium are studied with a Geant4-based code MCADS (Monte Carlo model for Accelerator Driven Systems). A good agreement of MCADS results with experimental data on neutron- and proton-induced reactions on 241Am and 243Am nuclei allows to use this model for simulations with extended Am targets. It was demonstrated that MCADS model can be used for calculating the values of critical mass for 233,235U, 237Np, 239Pu and 241Am. Several geometry options and material compositions (U, U + Am, Am, Am2O3) are considered for spallation targets to be used in Accelerator Driven Systems. All considered options operate as deep subcritical targets having neutron multiplication factor of k∼0.5. It is found that more than 4 kg of Am can be burned in one spallation target during the first year of operation
Monte Carlo modelling of VR-1 reactor core
International Nuclear Information System (INIS)
The possibilities of reactor core analysis by precise Monte Carlo codes are gradually increasing along with the accessibility of computing power. In the case of zero power research reactors, where temperature and burn-up effects remain negligible, model can approximate the reality to a very high degree. In such a case, most of calculation uncertainty can be caused by uncertainties in technical specifications of fuel and reactor internals. Thus performance of the modelling and its predictive power can be significantly improved via comparison with a large set of experimental data that can be acquired during reactor operation and via subtle tuning and improving the calculation model. The paper describes the case for neutronics calculations of VR-1 zero power reactor core. (author)
Modeling and Computer Simulation: Molecular Dynamics and Kinetic Monte Carlo
Energy Technology Data Exchange (ETDEWEB)
Wirth, B.D.; Caturla, M.J.; Diaz de la Rubia, T.
2000-10-10
Recent years have witnessed tremendous advances in the realistic multiscale simulation of complex physical phenomena, such as irradiation and aging effects of materials, made possible by the enormous progress achieved in computational physics for calculating reliable, yet tractable interatomic potentials and the vast improvements in computational power and parallel computing. As a result, computational materials science is emerging as an important complement to theory and experiment to provide fundamental materials science insight. This article describes the atomistic modeling techniques of molecular dynamics (MD) and kinetic Monte Carlo (KMC), and an example of their application to radiation damage production and accumulation in metals. It is important to note at the outset that the primary objective of atomistic computer simulation should be obtaining physical insight into atomic-level processes. Classical molecular dynamics is a powerful method for obtaining insight about the dynamics of physical processes that occur on relatively short time scales. Current computational capability allows treatment of atomic systems containing as many as 10{sup 9} atoms for times on the order of 100 ns (10{sup -7}s). The main limitation of classical MD simulation is the relatively short times accessible. Kinetic Monte Carlo provides the ability to reach macroscopic times by modeling diffusional processes and time-scales rather than individual atomic vibrations. Coupling MD and KMC has developed into a powerful, multiscale tool for the simulation of radiation damage in metals.
Large-scale shell model calculations for structure of Ni and Cu isotopes
Tsunoda, Yusuke; Otsuka, Takaharu; Shimizu, Noritaka; Honma, Michio; Utsuno, Yutaka
2014-09-01
We study nuclear structure of Ni and Cu isotopes, especially neutron-rich ones in the N ~ 40 region by Monte Carlo shell model (MCSM) calculations in pfg9d5 model space (0f7 / 2 , 1p3 / 2 , 0f5 / 2 , 1p1 / 2 , 0g9 / 2 , 1d5 / 2). Effects of excitation across N = 40 and other gaps are important to describe properties such as deformation, and we include this effects by using the pfg9d5 model space. We can calculate in this large model space without any truncation, as an advantage of MCSM. In the MCSM, a wave function is represented as a linear combination of angular-momentum- and parity-projected deformed Slater determinants. We can study intrinsic shapes of nuclei by using quadrupole deformations of MCSM basis states before projection. In doubly-magic 68Ni, there are oblate and prolate deformed bands as well as the spherical ground state from the calculation. Such shape coexistence can be explained by introducing the mechanism called Type II shell evolution, driven by changes of configurations within the same nucleus mainly due to the tensor force.
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
Long-time behavior of MHD shell models
Frick, P.; Boffetta, G.; Giuliani, P.; Lozhkin, S.; Sokoloff, D.
2000-01-01
The long time behavior of velocity-magnetic field alignment is numerically investigated in the framework of MHD shell model. In the stationary forced case, the correlation parameter C displays a nontrivial behavior with long periods of high variability which alternates with periods of almost constant C. The temporal statistics of correlation is shown to be non Poissonian, and the pdf of constant sign periods displays clear power law tails. The possible relevance of the model for geomagnetic d...
International Nuclear Information System (INIS)
Gaussian measures of Gibbsian type are associated with some shell model of turbulence; they are constructed by means of the energy, a conserved quantity for the 3D inviscid and unforced shell model. We prove the existence of a unique global flow for a stochastic viscous shell model with the property that these Gibbs measures are invariant for this flow. Moreover, we prove that the deterministic inviscid shell model has a stationary solution with respect to these measures
A REMARK ON FORMAL MODELS FOR NONLINEARLY ELASTIC MEMBRANE SHELLS
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
This paper gives all the two-dimensional membrane models obtained from formal asymptotic analysis of the three-dimensional geometrically exact nonlinear model of a thin elastic shell made with a Saint Venant-Kirchhoff material. Therefore, the other models can be quoted as flexural nonlinear ones. The author also gives the formal equations solved by the associated stress tensor and points out that only one of those models leads, by linearization, to the “classical” linear limiting membrane model, whose juetification has already been established by a convergence theorem.
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.
A simple Monte Carlo model for crowd dynamics
Piazza, Francesco
2010-01-01
In this paper we introduce a simple Monte Carlo method for simulating the dynamics of a crowd. Within our model a collection of hard-disk agents is subjected to a series of two-stage steps, implying (i) the displacement of one specific agent followed by (ii) a rearrangement of the rest of the group through a Monte Carlo dynamics. The rules for the combined steps are determined by the specific setting of the granular flow, so that our scheme should be easily adapted to describe crowd dynamics issues of many sorts, from stampedes in panic scenarios to organized flow around obstacles or through bottlenecks. We validate our scheme by computing the serving times statistics of a group of agents crowding to be served around a desk. In the case of a size homogeneous crowd, we recover intuitive results prompted by physical sense. However, as a further illustration of our theoretical framework, we show that heterogeneous systems display a less obvious behavior, as smaller agents feature shorter serving times. Finally, ...
Symmetry-guided large-scale shell-model theory
Launey, Kristina D.; Dytrych, Tomas; Draayer, Jerry P.
2016-07-01
In this review, we present a symmetry-guided strategy that utilizes exact as well as partial symmetries for enabling a deeper understanding of and advancing ab initio studies for determining the microscopic structure of atomic nuclei. These symmetries expose physically relevant degrees of freedom that, for large-scale calculations with QCD-inspired interactions, allow the model space size to be reduced through a very structured selection of the basis states to physically relevant subspaces. This can guide explorations of simple patterns in nuclei and how they emerge from first principles, as well as extensions of the theory beyond current limitations toward heavier nuclei and larger model spaces. This is illustrated for the ab initio symmetry-adapted no-core shell model (SA-NCSM) and two significant underlying symmetries, the symplectic Sp(3 , R) group and its deformation-related SU(3) subgroup. We review the broad scope of nuclei, where these symmetries have been found to play a key role-from the light p-shell systems, such as 6Li, 8B, 8Be, 12C, and 16O, and sd-shell nuclei exemplified by 20Ne, based on first-principle explorations; through the Hoyle state in 12C and enhanced collectivity in intermediate-mass nuclei, within a no-core shell-model perspective; up to strongly deformed species of the rare-earth and actinide regions, as investigated in earlier studies. A complementary picture, driven by symmetries dual to Sp(3 , R) , is also discussed. We briefly review symmetry-guided techniques that prove useful in various nuclear-theory models, such as Elliott model, ab initio SA-NCSM, symplectic model, pseudo- SU(3) and pseudo-symplectic models, ab initio hyperspherical harmonics method, ab initio lattice effective field theory, exact pairing-plus-shell model approaches, and cluster models, including the resonating-group method. Important implications of these approaches that have deepened our understanding of emergent phenomena in nuclei, such as enhanced
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.
A shell model for tyre belt vibrations
Lecomte, C.; Graham, W. R.; Dale, M.
2010-05-01
We present a new formulation for the prediction of tyre belt vibrations in the frequency range 0-500 Hz. Our representation includes the effects of belt width, curvature and anisotropy, and also explicitly models the tyre sidewalls. Many of the associated numerical parameters are fixed by physical considerations; the remainder require empirical input. A systematic and general approach to this problem is developed, and illustrated for the specific example of a Goodyear Wrangler tyre. The resulting predictions for the radial response to radial forcing show good correspondence with experiment up to 300 Hz, and satisfactory agreement up to 1 kHz.
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...
Super-hypernuclei in the quark-shell model
International Nuclear Information System (INIS)
A super-hypernucleus is a nucleus which consists of many strange quarks as well as up and down quarks. An important part of the results of our recent investigation on the mass spectrum and other properties of super-hypernuclei in the quark-shell model is reported. It is expected that not only certain exotic nuclei such as the 'dideltas' (Dδ++++ and Dδ----). but also certain super-hypernuclei such as the 'hexalambda' (Hλ) and the 'vigintiquattuoralambda' (Vqλ) may appear as quasi-stable nuclei. However, in the quark-shell model, there is no qualitative reason why the 'dihyperon' or 'H dibaryon' (H) should be quasi-stable or even stable. Many other predictions including a sudden increase of the K/π ratio due to the production of super-hypernuclei in heavy-ion collisions at high energies are also made. (author)
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...
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.
Optimal thermalization in a shell model of homogeneous turbulence
Thalabard, Simon
2015-01-01
We investigate the turbulence-induced dissipation of the large scales in a statistically homogeneous flow using an "optimal closure," which one of us (BT) has recently exposed in the context of Hamiltonian dynamics. This statistical closure employs a Gaussian model for the turbulent scales, with corresponding vanishing third cumulant, and yet it captures an intrinsic damping. The key to this apparent paradox lies in a clear distinction between true ensemble averages and their proxies, most easily grasped when one works directly with the Liouville equation rather than the cumulant hierarchy. We focus on a simple problem for which the optimal closure can be fully and exactly worked out: the relaxation arbitrarily far-from-equilibrium of a single energy shell towards Gibbs equilibrium in an inviscid shell model of 3D turbulence. The predictions of the optimal closure are validated against DNS and contrasted with those derived from EDQNM closure.
Optimal thermalization in a shell model of homogeneous turbulence
Thalabard, Simon; Turkington, Bruce
2016-04-01
We investigate the turbulence-induced dissipation of the large scales in a statistically homogeneous flow using an ‘optimal closure,’ which one of us (BT) has recently exposed in the context of Hamiltonian dynamics. This statistical closure employs a Gaussian model for the turbulent scales, with corresponding vanishing third cumulant, and yet it captures an intrinsic damping. The key to this apparent paradox lies in a clear distinction between true ensemble averages and their proxies, most easily grasped when one works directly with the Liouville equation rather than the cumulant hierarchy. We focus on a simple problem for which the optimal closure can be fully and exactly worked out: the relaxation arbitrarily far-from-equilibrium of a single energy shell towards Gibbs equilibrium in an inviscid shell model of 3D turbulence. The predictions of the optimal closure are validated against DNS and contrasted with those derived from EDQNM closure.
Bursts and shocks in a continuum shell model
DEFF Research Database (Denmark)
Andersen, K.H.; Bohr, Tomas; Jensen, M.H.; Olesen, P.
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 right...... and left moving parts can be solved exactly. When this is supplemented by the approximate shock condition it is possible to find the symptotic form of the burst....
Holographic Shell Model: Stack Data Structure inside Black Holes
Davidson, Aharon
2011-01-01
We suggest that bits of information inhabit, universally and holographically, the entire black hole interior, a bit per a light sheet unit interval of order Planck area difference. The number of distinguishable (tagged by a binary code) configurations, counted within the context of a discrete holographic shell model, is given by the Catalan series. The area entropy formula is recovered, including the universal logarithmic correction, and the equipartition of mass per degree of freedom is prov...
Lowest eigenvalue of the nuclear shell model Hamiltonian
Shen, J J; Arima, A
2010-01-01
In this paper we investigate regular patterns of matrix elements of the nuclear shell model Hamiltonian $H$, by sorting the diagonal matrix elements from the smaller to larger values. By using simple plots of non-zero matrix elements and lowest eigenvalues of artificially constructed "sub-matrices" $h$ of $H$, we propose a new and simple formula which predicts the lowest eigenvalue with remarkable precisions.
Modeling glass dissolution with a Monte Carlo technique
International Nuclear Information System (INIS)
The authors present a Monte Carlo simulation method for modeling glass dissolution in aqueous solutions. This simulation method is consistent with transition state theory, and therefore also with the glass dissolution rate law, used for instance in the Grambow model. The simulation method allows one to add dynamics (kinetics) to the existing thermodynamic models for glass dissolution. Using this method, it is possible to model non stoichiometric dissolution of the glass. Besides, the authors introduce a simple, first version of a model in which they use the simulation method. In this model, they approximate the glass by a lattice. They assume that the glass contains two components: a network former and a network modifier. Bonds between two network formers are assumed to be much stronger than any other bond in the system. The authors observe that above a threshold value for the concentration of network modifiers, the glass dissolves fast. No surface layer develops and the dissolution rate is constant (linear stoichiometric dissolution). Below this threshold, the glass is more durable and surface layers are formed. As time goes on, the thickness of the surface layers grows. The dissolution of the glass is not stoichiometric. This behavior agrees with experimental results
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...
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...
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)
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.
Core-Shell Model of Folding-Unfolding Transitions (UFT) in Proteins
Aroutiounian, Svetlana
2008-03-01
There are ˜10^N conformations for a protein of length N to sort out randomly in search of lowest free energy state. Can protein folding be simple and fast? Core-shell model introduces principles, proposes mechanisms and scores residues of fast, reversible UFT in protein. According to it, during UFT the realm of intra-residual interactions leads the residue motion. The scaffold of hydrophilic residues forms external shell of unstructured, tube-like protein in unfolded state, just as the hydrophobic residues form internal scaffold -- core, of the protein in folded state. As UFT proceeds, residue slides into lowest-score position permitted by its structure. Model accounts for experimentally observed features of UFT. It is based on three principles: 1) During UFT protein is virtual - its features or structure are inferred only statistically and with limited precision; 2) Mechanism of UFT memory is not longitudinal, but transverse; 3) Native design overrides specific features of residues - the alphabet of amino acids assumes an intrinsic score-function. Per-residue mechanism of UFT is proposed and score-function is described. Difference graphs of transitional score-function and average genome-wide abundance index show that our score-function is the order parameter of UFT in protein and by virtue of being it, reveals transitional key residues. It echoes the multiple-tier and funnel concepts of FEL perspective. Monte Carlo simulations of UFT in myoglobin illustrate the idea.
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.
Monte Carlo likelihood inference for missing data models
Sung, Yun Ju; Geyer, Charles J.
2007-01-01
We describe a Monte Carlo method to approximate the maximum likelihood estimate (MLE), when there are missing data and the observed data likelihood is not available in closed form. This method uses simulated missing data that are independent and identically distributed and independent of the observed data. Our Monte Carlo approximation to the MLE is a consistent and asymptotically normal estimate of the minimizer θ* of the Kullback–Leibler information, as both Monte Carlo and observed data sa...
Monte Carlo validation of supercell model for BWR fuel assembly calculations
International Nuclear Information System (INIS)
The Monte Carlo method is used to validate a calculational model named as supercell model developed for the evaluation of LWR fuel box parameters. The TAPS reload-2 fuel box is chosen as a benchmark problem for the validation. The box parameters obtained using the supercell model and Monte Carlo method are compared. (auth.)
Ensemble bayesian model averaging using markov chain Monte Carlo sampling
Energy Technology Data Exchange (ETDEWEB)
Vrugt, Jasper A [Los Alamos National Laboratory; Diks, Cees G H [NON LANL; Clark, Martyn P [NON LANL
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 their seminal paper (Raftery etal. Mon Weather Rev 133: 1155-1174, 2(05)) has recommended the Expectation-Maximization (EM) algorithm for BMA model training, even though global convergence of this algorithm cannot be guaranteed. In this paper, we compare the performance of the EM algorithm and the recently developed Differential Evolution Adaptive Metropolis (DREAM) Markov Chain Monte Carlo (MCMC) algorithm for estimating the BMA weights and variances. Simulation experiments using 48-hour ensemble data of surface temperature and multi-model stream-flow forecasts show that both methods produce similar results, and that their performance is unaffected by the length of the training data set. However, MCMC simulation with DREAM is capable of efficiently handling a wide variety of BMA predictive distributions, and provides useful information about the uncertainty associated with the estimated BMA weights and variances.
International Nuclear Information System (INIS)
We discuss progress in quasi Monte Carlo methods for numerical calculation integrals or expected values and justify why these methods are more efficient than the classic Monte Carlo methods. Quasi Monte Carlo methods are found to be particularly efficient if the integrands have a low effective dimension. That's why We also discuss the concept of effective dimension and prove on the example of a stochastic Optimization model of the energy industry that such models can posses a low effective dimension. Modern quasi Monte Carlo methods are therefore for such models very promising.
Shell model - IBM correspondence and IBM interpretation of 52 Ti
International Nuclear Information System (INIS)
A shell model description of 52Ti, using a space of protons in the 1f7/2 orbit and neutrons in the 2p3/2, 1f5/2, and 2p1/2 orbits, is used to determine microscopically an IBM description of this nucleus, via an interpretation of the bosons as nucleon pairs. In the shell model calculation, a simple surface delta interaction is found to give significantly better reproduction of the data on this nucleus than a previously determined interaction optimised for nuclei throughout the shell. The implied IBM structure has the mixed-symmetry 2+ state concentrated in a level at 2.26 MeV, while the two-phonon 2+ state is fragmented over levels at 2.43 MeV and 4-5 MeV. These states do not mix significantly in the lowest eigenstates, in common with a recent phenomenological analysis, although the two-phonon 2+ state mixes strongly with a non-IBM state involving an excited neutron D pair. 18 refs., 3 tabs., 2 figs
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.
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 role in radiobiological modelling of radiotherapy outcomes
El Naqa, Issam; Pater, Piotr; Seuntjens, Jan
2012-06-01
Radiobiological models are essential components of modern radiotherapy. They are increasingly applied to optimize and evaluate the quality of different treatment planning modalities. They are frequently used in designing new radiotherapy clinical trials by estimating the expected therapeutic ratio of new protocols. In radiobiology, the therapeutic ratio is estimated from the expected gain in tumour control probability (TCP) to the risk of normal tissue complication probability (NTCP). However, estimates of TCP/NTCP are currently based on the deterministic and simplistic linear-quadratic formalism with limited prediction power when applied prospectively. Given the complex and stochastic nature of the physical, chemical and biological interactions associated with spatial and temporal radiation induced effects in living tissues, it is conjectured that methods based on Monte Carlo (MC) analysis may provide better estimates of TCP/NTCP for radiotherapy treatment planning and trial design. Indeed, over the past few decades, methods based on MC have demonstrated superior performance for accurate simulation of radiation transport, tumour growth and particle track structures; however, successful application of modelling radiobiological response and outcomes in radiotherapy is still hampered with several challenges. In this review, we provide an overview of some of the main techniques used in radiobiological modelling for radiotherapy, with focus on the MC role as a promising computational vehicle. We highlight the current challenges, issues and future potentials of the MC approach towards a comprehensive systems-based framework in radiobiological modelling for radiotherapy.
Monte Carlo simulations of lattice models for single polymer systems
Energy Technology Data Exchange (ETDEWEB)
Hsu, Hsiao-Ping, E-mail: hsu@mpip-mainz.mpg.de [Max-Planck-Institut für Polymerforschung, Ackermannweg 10, D-55128 Mainz (Germany)
2014-10-28
Single linear polymer chains in dilute solutions under good solvent conditions are studied by Monte Carlo simulations with the pruned-enriched Rosenbluth method up to the chain length N∼O(10{sup 4}). Based on the standard simple cubic lattice model (SCLM) with fixed bond length and the bond fluctuation model (BFM) with bond lengths in a range between 2 and √(10), we investigate the conformations of polymer chains described by self-avoiding walks on the simple cubic lattice, and by random walks and non-reversible random walks in the absence of excluded volume interactions. In addition to flexible chains, we also extend our study to semiflexible chains for different stiffness controlled by a bending potential. The persistence lengths of chains extracted from the orientational correlations are estimated for all cases. We show that chains based on the BFM are more flexible than those based on the SCLM for a fixed bending energy. The microscopic differences between these two lattice models are discussed and the theoretical predictions of scaling laws given in the literature are checked and verified. Our simulations clarify that a different mapping ratio between the coarse-grained models and the atomistically realistic description of polymers is required in a coarse-graining approach due to the different crossovers to the asymptotic behavior.
International Nuclear Information System (INIS)
Atomic reorganization starts by filling the initially inner-shell vacancy by a radiative transition (x-ray) or by a non-radiative transition (Auger and Coster-Kronig processes). New vacancies created during this atomic reorganization may in turn be filled by further radiative and non-radiative transitions until all vacancies reach the outermost occupied shells. The production of inner-shell vacancy in an atom and the de-excitation decays through radiative and non-radiative transitions may result in a change of the atomic potential; this change leads to the emission of an additional electron in the continuum (electron shake-off processes). In the present work, the ion charge state distributions (CSD) and mean atomic charge ions produced from inner shell vacancy de-excitation decay are calculated for neutral Ne , Ar and Kr atoms. The calculations are carried out using Monte Carlo (MC) technique to simulate the cascade development after primary vacancy production. The radiative and non-radiative transitions for each vacancy are calculated in the simulation. In addition, the change of transition energies and transition rates due to multi vacancies produced in the atomic configurations through the cascade development are considered in the present work. It is found that considering the electron shake off process and closing of non-allowed non-radiative channels improves the results of both charge state distributions (CSD) and average charge state. To check the validity of the present calculations, the results obtained are compared with available theoretical and experimental data. The present results are found to agree well with the available theoretical and experimental values. (author)
International Nuclear Information System (INIS)
Atomic reorganization starts by filling the initially inner-shell vacancy by a radiative transition (x-ray) or by a non-radiative transition (Auger and Coster-Kronig processes). New vacancies created during this atomic reorganization may in turn be filled by further radiative and non-radiative transitions until all vacancies reach the outermost occupied shells. The production of inner-shell vacancy in an atom and the de-excitation decays through radiative and non-radiative transitions may result in a change of the atomic potential; this change leads to the emission of an additional electron in the continuum (electron shake-off processes). In the present work, the ion charge state distributions (CSD) and mean atomic charge ions produced from inner-shell vacancy de-excitation decay are calculated for neutral Ne, Ar and Kr atoms. The calculations are carried out using Monte Carlo (MC) technique to simulate the cascade development after primary vacancy production. The radiative and non-radiative transitions for each vacancy are calculated in the simulation. In addition, the change of transition energies and transition rates due to multi vacancies produced in the atomic configurations through the cascade development are considered in the present work. It is found that considering the electron shake--off process and closing of non-allowed non-radiative channels improves the results of both charge state distributions (CSD) and average charge state. To check the validity of the present calculations, the results obtained are compared with available theoretical and experimental data. The present results are found to agree well with the available theoretical and experimental values.
Shell Model Study on High Spin States of 92Nb
Institute of Scientific and Technical Information of China (English)
WU; Yi-heng; WU; Xiao-guang; LI; Guang-sheng; LUO; Peng-wei; LIU; Jia-jian; HE; Chuang-ye; ZHENG; Yun; LI; Cong-bo; HU; Shi-peng; LI; Hong-wei; WANG; Jin-long
2013-01-01
High spin states of odd-odd nucleus 92Nb were investigated using the reaction 82Se(14N,4n)92Nb at a beam energy of 54 MeV.Spherical shell model calculations are performed in the model spaceπ(0f5/2,1p3/2,1p1/2,0g9/2)ν(1p1/2,0g9/2,1d5/2,0g7/2).It is suggested that the excitation of protons across the Z=38 core
Effective Field Theory and the No-Core Shell Model
Directory of Open Access Journals (Sweden)
Stetcua I.
2010-04-01
Full Text Available In ﬁnite model space suitable for many-body calculations via the no-core shell model (NCSM, I illustrate the direct application of the eﬀective ﬁeld theory (EFT principles to solving the many-body Schrödinger equation. Two diﬀerent avenues for ﬁxing the low-energy constants naturally arising in an EFT approach are discussed. I review results for both nuclear and trapped atomic systems, using eﬀective theories formally similar, albeit describing diﬀerent underlying physics.
Monte Carlo renormalization: Test on the triangular Ising model
International Nuclear Information System (INIS)
We test the performance of the Monte Carlo renormalization method using the Ising model on the triangular lattice. We apply block-spin transformations which allow for adjustable parameters so that the transformation can be optimized. This optimization takes into account the relation between corrections to scaling and the location of the fixed point. To this purpose we determine corrections to scaling of the triangular Ising model with nearest- and next-nearest-neighbor interactions, by means of transfer matrix calculations and finite-size scaling. We find that the leading correction to scaling just vanishes for the nearest-neighbor model. However, the fixed point of the commonly used majority-rule block-spin transformation lies far away from the nearest-neighbour critical point. This raises the question whether the majority rule is suitable as a renormalization transformation, because corrections to scaling are supposed to be absent at the fixed point. We define a modified block-spin transformation which shifts the fixed point back to the vicinity of the nearest-neighbour critical Hamiltonian. This modified transformation leads to results for the Ising critical exponents that converge faster, and are more accurate than those obtained with the majority rule. (author)
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%...
Truncation of Large Shell-Model Eigenproblems by Model Space Partitioning
Andreozzi, F; Porrino, A.
1999-01-01
A method for solving the shell-model eigenproblem in a severely truncated space, spanned by properly selected correlated states obtained by partitioning the full configuration space, is proposed. The method describes in a practically exact way the low energy spectroscopic properties of nuclei, as exemplified in schematic models. The applicability of the method to heavy nuclei as well in contexts different from the nuclear shell model is stressed
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.
All-glass shell scale models made with an adjustable mould
Belis, JLIF Jan; Pronk, ADC Arno; Schuurmans, WB; Blancke, T
2011-01-01
Ever since Lucio Blandini developed a doubly curved synclastic shell with adhesively bonded glass components, the concept of building a self-supporting glass-only shell has almost become within reach. In the current contribution a small-scaled experimental concept is presented of a self-supporting anticlastic all-glass shell scale model, created by means of an adaptable mould. First, different manufacturing parameters of relatively small shells are investigated, such as mould type, glass s...
A Monte Carlo model of the Varian IGRT couch top for RapidArc QA
International Nuclear Information System (INIS)
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. (note)
A Monte Carlo model of auroral hydrogen emission line profiles
Directory of Open Access Journals (Sweden)
J.-C. Gérard
2005-06-01
Full Text Available Hydrogen line profiles measured from space-borne or ground-based instruments provide useful information to study the physical processes occurring in the proton aurora and to estimate the proton flux characteristics. The line shape of the hydrogen lines is determined by the velocity distribution of H atoms along the line-of-sight of the instrument. Calculations of line profiles of auroral hydrogen emissions were obtained using a Monte Carlo kinetic model of proton precipitation into the auroral atmosphere. In this model both processes of energy degradation and scattering angle redistribution in momentum and charge transfer collisions of the high-energy proton/hydrogen flux with the ambient atmospheric gas are considered at the microphysical level. The model is based on measured cross sections and scattering angle distributions and on a stochastic interpretation of such collisions. Calculations show that collisional angular redistribution of the precipitating proton/hydrogen beam is the dominant process leading to the formation of extended wings and peak shifts in the hydrogen line profiles. All simulations produce a peak shift from the rest line wavelength decreasing with increasing proton energy. These model predictions are confirmed by analysis of ground-based H-β line observations from Poker Flat, showing an anti-correlation between the magnitude of the peak shift and the extent of the blue wing of the line. Our results also strongly suggest that the relative extension of the blue and red wings provides a much better indicator of the auroral proton characteristic energy than the position of the peak wavelength.
Holographic shell model: Stack data structure inside black holes?
Davidson, Aharon
2014-03-01
Rather than tiling the black hole horizon by Planck area patches, we suggest that bits of information inhabit, universally and holographically, the entire black core interior, a bit per a light sheet unit interval of order Planck area difference. The number of distinguishable (tagged by a binary code) configurations, counted within the context of a discrete holographic shell model, is given by the Catalan series. The area entropy formula is recovered, including Cardy's universal logarithmic correction, and the equipartition of mass per degree of freedom is proven. The black hole information storage resembles, in the count procedure, the so-called stack data structure.
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 structure of exotic nuclei beyond 132Sn
Covello, A; Coraggio, L.; Gargano, A.; Itaco, N.
2007-01-01
We report on a study of exotic nuclei around doubly magic 132Sn in terms of the shell model employing a realistic effective interaction derived from the CD-Bonn nucleon-nucleon potential. The short-range repulsion of the bare potential is renormalized by constructing a smooth low-momentum potential, V-low-k, that is used directly as input for the calculation of the effective interaction. In this paper we focus attention on the nuclei 134Sn and 135Sb which, with an N/Z ratio of 1.68 and 1.65, ...
Shell model analysis of N = 82 isotones above 132Sn
International Nuclear Information System (INIS)
Nuclei with up to 6 protons added to 132Sn are described within a truncated shell model basis formed by the proton orbits 0g7/2, 1d5/2, 1d3/2, 2s1/2 and 0h11/2. Single-particle energies and two-body interaction matrix elements are determined from experimental excitation energies in 133Sb and 134Te. These parameters are then used for calculating levels in 135I, 136Xe, 137Cs and 138Ba. The calculated energies agree well with experimental values in these 4 nuclei. (author)
Realistic shell-model calculations for Sn isotopes
Energy Technology Data Exchange (ETDEWEB)
Covello, A. [Napoli Federico-2 Univ. (Italy). Dipt. di Scienze Fisiche]|[Istituto Nazionale di Fisica Nucleare, Padua (Italy); Andreozzi, F. [Napoli Federico-2 Univ. (Italy). Dipt. di Scienze Fisiche]|[Istituto Nazionale di Fisica Nucleare, Padua (Italy); Coraggio, L. [Napoli Federico-2 Univ. (Italy). Dipt. di Scienze Fisiche]|[Istituto Nazionale di Fisica Nucleare, Padua (Italy); Gargano, A. [Napoli Federico-2 Univ. (Italy). Dipt. di Scienze Fisiche]|[Istituto Nazionale di Fisica Nucleare, Padua (Italy); Porrino, A. [Napoli Federico-2 Univ. (Italy). Dipt. di Scienze Fisiche]|[Istituto Nazionale di Fisica Nucleare, Padua (Italy)
1997-05-01
We report on a shell-model study of the Sn isotopes in which a realistic effective interaction derived from the Paris free nucleon-nucleon potential is employed. The calculations are performed within the framework of the seniority scheme by making use of the chain-calculation method. This provides practically exact solutions while cutting down the amount of computational work required by a standard seniority-truncated calculation. The behavior of the energy of several low-lying states in the isotopes with A ranging from 122 to 130 is presented and compared with the experimental one. (orig.)
Shell-model calculations in the A = 90 region
International Nuclear Information System (INIS)
This paper is a review of shell-model calculations for nuclei in the A = 90 region. The calculations fall into two categories depending on he way in which they estimate the effective interaction, i.e. Talmi-type or realistic approaches. In the former, up to two-body terms are considered, while many-body theory is used for the latter. Results from both approaches are given for N = 50 nuclei. Finally, results for nuclei beyond N = 50 are presented. (author)
The Nuclear Shell Model Toward the Drip Lines
Poves, A; Nowacki, F; Sieja, K
2011-01-01
We describe the "islands of inversion" that occur when approaching the neutron drip line around the magic numbers N=20, N=28 and N=40 in the framework of the Interacting Shell Model in very large valence spaces. We explain these configuration inversions (and the associated shape transitions) as the result of the competition between the spherical mean field (monopole) which favors magicity and the correlations (multipole) which favor deformed intruder states. We also show that the N=20 and N=28 islands are in reallity a single one, which for the Magnesium isotopes is limited by N=18 and N=32.
Holographic Shell Model: Stack Data Structure inside Black Holes
Davidson, Aharon
2011-01-01
We suggest that bits of information inhabit, universally and holographically, the entire black hole interior, a bit per a light sheet unit interval of order Planck area difference. The number of distinguishable (tagged by a binary code) configurations, counted within the context of a discrete holographic shell model, is given by the Catalan series. The area entropy formula is recovered, including the universal logarithmic correction, and the equipartition of mass per degree of freedom is proven. The black hole information storage resembles a stack data structure.
Combinatorial nuclear level density by a Monte Carlo method
Cerf, N.
1993-01-01
We present a new combinatorial method for the calculation of the nuclear level density. It is based on a Monte Carlo technique, in order to avoid a direct counting procedure which is generally impracticable for high-A nuclei. The Monte Carlo simulation, making use of the Metropolis sampling scheme, allows a computationally fast estimate of the level density for many fermion systems in large shell model spaces. We emphasize the advantages of this Monte Carlo approach, particularly concerning t...
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. PMID:20866731
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.
Modelling laser light propagation in thermoplastics using Monte Carlo simulations
Parkinson, Alexander
Laser welding has great potential as a fast, non-contact joining method for thermoplastic parts. In the laser transmission welding of thermoplastics, light passes through a semi-transparent part to reach the weld interface. There, it is absorbed as heat, which causes melting and subsequent welding. The distribution and quantity of light reaching the interface are important for predicting the quality of a weld, but are experimentally difficult to estimate. A model for simulating the path of this laser light through these light-scattering plastic parts has been developed. The technique uses a Monte-Carlo approach to generate photon paths through the material, accounting for absorption, scattering and reflection between boundaries in the transparent polymer. It was assumed that any light escaping the bottom surface contributed to welding. The photon paths are then scaled according to the input beam profile in order to simulate non-Gaussian beam profiles. A method for determining the 3 independent optical parameters to accurately predict transmission and beam power distribution at the interface was established using experimental data for polycarbonate at 4 different glass fibre concentrations and polyamide-6 reinforced with 20% long glass fibres. Exit beam profiles and transmissions predicted by the simulation were found to be in generally good agreement (R2>0.90) with experimental measurements. The simulations allowed the prediction of transmission and power distributions at other thicknesses as well as information on reflection, energy absorption and power distributions at other thicknesses for these materials.
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...
Modeling radiation from the atmosphere of Io with Monte Carlo methods
Gratiy, Sergey
Conflicting observations regarding the dominance of either sublimation or volcanism as the source of the atmosphere on Io and disparate reports on the extent of its spatial distribution and the absolute column abundance invite the development of detailed computational models capable of improving our understanding of Io's unique atmospheric structure and origin. To validate a global numerical model of Io's atmosphere against astronomical observations requires a 3-D spherical-shell radiative transfer (RT) code to simulate disk-resolved images and disk-integrated spectra from the ultraviolet to the infrared spectral region. In addition, comparison of simulated and astronomical observations provides important information to improve existing atmospheric models. In order to achieve this goal, a new 3-D spherical-shell forward/backward photon Monte Carlo code capable of simulating radiation from absorbing/emitting and scattering atmospheres with an underlying emitting and reflecting surface was developed. A new implementation of calculating atmospheric brightness in scattered sunlight is presented utilizing the notion of an "effective emission source" function. This allows for the accumulation of the scattered contribution along the entire path of a ray and the calculation of the atmospheric radiation when both scattered sunlight and thermal emission contribute to the observed radiation---which was not possible in previous models. A "polychromatic" algorithm was developed for application with the backward Monte Carlo method and was implemented in the code. It allows one to calculate radiative intensity at several wavelengths simultaneously, even when the scattering properties of the atmosphere are a function of wavelength. The application of the "polychromatic" method improves the computational efficiency because it reduces the number of photon bundles traced during the simulation. A 3-D gas dynamics model of Io's atmosphere, including both sublimation and volcanic
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 ...
Shell model description of low-lying states in Po and Rn isotopes
International Nuclear Information System (INIS)
The nuclear structure of polonium and radon 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 (PTSM). The analysis reveals the alignment of two protons in the 0h9/2 orbital at spin 8. (authors)
A Semi-Analytical Model for Buckling of Stiffened Cylindrical Shells
2013-01-01
Cylindrical shells are common configurations within the technology. The transition from the side to the bottom on a ship has the shape of a fourth of a cylindrical shell. Both ring and stringer stiffeners can be added to the shell for support. Buckling of this type of structure is an important area of interest. The main purpose of this thesis has been to make a semi-analytical model that can describe how a ring stiffened shell and stringer stiffened shell respond during buckling. A va...
Probability Distribution Function of Passive Scalars in Shell Models
Zhang, Xiao-Qiang; Wang, Guang-Rui; Chen, Shi-Gang
2008-04-01
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 δ correlated in time. Deterministic differential equations are regarded as nonlinear Langevin equation. Then, the Fokker Planck equations of PDF for passive scalars are obtained and solved numerically. In energy input range (n PDF) of passive scalars is near the Gaussian distribution. In inertial range (5 = 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.
Development of the Delta Shell as an integrated modeling environment
Donchyts, Gennadii; Baart, Fedor; Jagers, Bert
2010-05-01
Many engineering problem require the use of multiple numerical models from multiple disciplines. For example the use of river model for flow calculation coupled with groundwater model and rainfall-runoff model. These models need to be setup, coupled, run, results need to be visualized, input and output data need to be stored. For some of these steps a software or standards already exist, but there is a need for an environment allowing to perform all these steps.The goal of the present work is to create a modeling environment where models from different domains can perform all the sixe steps: setup, couple, run, visualize, store. This presentation deals with the different problems which arise when setting up a modelling framework, such as terminology, numerical aspects as well as the software development issues which arise. In order to solve these issues we use Domain Driven Design methods, available open standards and open source components. While creating an integrated modeling environment we have identified that a separation of the following domains is essential: a framework allowing to link and exchange data between models; a framework allowing to integrate different components of the environment; graphical user interface; GIS; hybrid relational and multi-dimensional data store; discipline-specific libraries: river hydrology, morphology, water quality, statistics; model-specific components Delta Shell environment which is the basis for several products such as HABITAT, SOBEK and the future Delft3D interface. It implements and integrates components covering the above mentioned domains by making use of open standards and open source components. Different components have been developed to fill in gaps. For exchaning data with the GUI an object oriented scientific framework in .NET was developed within Delta Shell somewhat similar to the JSR-275. For the GIS domain several OGC standards were used such as SFS, WCS and WFS. For storage the CF standard together with
Simplified vibration analysis method of shells of revolution using beam model
International Nuclear Information System (INIS)
A simplified vibration analysis method for the shells of revolution using the beam model is now under consideration. In the beam model, the relations between the shear forces and horizontal deformations are used for the calculations of the shear area and the relations between the overturning moments and rotation angles are for those of the inertia moment. The calculations of the vibration characteristics of the cylindrical shell, spherical shell and the cylindrical shell with the spherical cap were conducted to verify the accuracy of the beam model. The natural frequencies and the vibration modes of the proposed method are in good agreement with that of the FEM analysis using the axisymmetrical shell model. The proposed method is easily applicable to the vibration analysis of actual shell structures. (author)
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 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
Spin-tensor analysis of realistic shell model interactions
International Nuclear Information System (INIS)
In this paper various realistic shell model effective interactions are analyzed in terms of their central, vector, and tensor components. The effective forces were obtained from phenomenological (Hamada-Johnston) as well as from modern meson-exchange (Bonn-Juelich and Paris) nucleon-nucleon potentials and were calculated to various approximations within the framework of perturbation theory. For all forces examined, the dominant contribution comes from the central part. The vector component is small for the bare G-matrix interaction, especially for T=0, but is considerably modified by renormalization. The tensor component is somewhat larger than the vector component and is relatively larger for the Hamada-Johnston potential than for the Bonn-Juelich and Paris potentials. Centroids in j-j and SU(3) coupling were obtained with and without noncentral contributions; considerable sensitivity was observed in the SU(3) basis
Development of Monte Carlo automatic modeling functions of MCAM for TRIPOLI-ITER application
Lu, L.; Lee, Y. K.; Zhang, J. J.; Li, Y.; Zeng, Q.; Wu, Y. C.
2009-07-01
TRIPOLI is a Monte Carlo particle transport code simulating the three-dimensional transport of neutrons and photons with the Monte Carlo method, and it can be used for many applications to nuclear devices with complex geometries; however, modeling of a complex geometry is a time-consuming and error-prone task. The recently developed functions of Monte Carlo Automatic Modeling (MCAM) system, which is an interface code that can facilitate Monte Carlo modeling by employing the CAD technology, have implemented the bidirectional conversion between the CAD model and the TRIPOLI computation model. In this study, different geometric representations of CAD system and TRIPOLI code and the methodology of bidirectional conversion between them were introduced. A TRIPOLI input file of International Thermonuclear Experimental Reactor (ITER) benchmark model, which was distributed to validate the Monte Carlo modeling tools, was created and applied to simulate D-T fusion neutron source sampling and calculate first wall loading. Then the results were compared with that of Monte Carlo N-Particle (MCNP) and the good agreements present the feasibility and validity.
International Nuclear Information System (INIS)
Prediction of radionuclides release is a central issue in the performance assessment of nuclear waste repositories. To this aim a model of radionuclides migration through the repository barriers must be set up, accounting for the uncertainties affecting the process. In this context, the present paper presents the application of Monte Carlo simulation to a Markovian modeling framework proposed in the literature; two cases are presented to highlight the value added by the flexibility of the Monte Carlo simulation approach. (authors)
International Nuclear Information System (INIS)
Summary report of ANSYS finite element models developed for dome load analysis of Hanford 100-series single-shell tanks and double-shell tanks. Document provides user interface for selecting proper tank model and changing of analysis parameters for tank specific analysis. Current dome load restrictions for the Hanford Site underground waste storage tanks are based on existing analyses of record (AOR) that evaluated the tanks for a specific set of design load conditions. However, greater flexibility is required in controlling dome loadings applied to the tanks due to day-to-day operations and waste retrieval activities. This requires the development of an analytical model with sufficient detail to evaluate various dome loading conditions not specifically addressed in the AOR
International Nuclear Information System (INIS)
Comparison of photographs of explosive experiments to the Casseopeia A supernova remnant reveals a striking similarity. The similarity could indicate the presence of a relatively cool, underlying shell in the Casseopeia A remnant. As this shell expands and fragments, the observable features are produced by hot gases squirting through the cracks - as in explosive experiments. The existence of such underlying shells in supernova remnants supports the author's model of solar system formation
Giancarlo Mauri; Citrolo, Andrea G.
2013-01-01
The hydrophobic-polar (HP) model has been widely studied in the field of protein structure prediction (PSP) both for theoretical purposes and as a benchmark for new optimization strategies. In this work we introduce a new heuristics based on Ant Colony Optimization (ACO) and Markov Chain Monte Carlo (MCMC) that we called Hybrid Monte Carlo Ant Colony Optimization (HMCACO). We describe this method and compare results obtained on well known HP instances in the 3 dimensional cubic lattice to tho...
The shell model. Towards a unified description of nuclear structure
International Nuclear Information System (INIS)
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 (σ·τ)(σ·τ). 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 β stability, addressing the vanishing of some magic closures that can be explained in terms of intruder states. (author)
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.
International Nuclear Information System (INIS)
This paper discusses the derivation of an effective shell-model hamiltonian starting from a realistic nucleon–nucleon potential by way of perturbation theory. More precisely, we present the state of the art of this approach when the starting point is the perturbative expansion of the Q-hat-box vertex function. Questions arising from diagrammatics, intermediate-states and order-by-order convergences, and their dependence on the chosen nucleon–nucleon potential, are discussed in detail, and the results of numerical applications for the p-shell model space starting from chiral next-to-next-to-next-to-leading order potentials are shown. Moreover, an alternative graphical method to derive the effective hamiltonian, based on the Z-hat-box vertex function recently introduced by Suzuki et al., is applied to the case of a non-degenerate (0+2)ħω model space. Finally, our shell-model results are compared with the exact ones obtained from no-core shell-model calculations. - Highlights: ► The derivation of nuclear realistic shell-model effective hamiltonians is studied. ► Perturbation theory. ► Diagrammatics, intermediate-states and order-by-order convergences are investigated. ► Shell-model calculations in degenerate and non-degenerate model spaces are presented. ► Shell-model results are compared with the exact ones.
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......-similar PDFs for longitudinal velocity differences are also presented for the rotating 3D turbulence case....
Kim, Su-Young
2012-01-01
Just as growth mixture models are useful with single-phase longitudinal data, multiphase growth mixture models can be used with multiple-phase longitudinal data. One of the practically important issues in single- and multiphase growth mixture models is the sample size requirements for accurate estimation. In a Monte Carlo simulation study, the…
Preparation of hollow shell ICF targets using a depolymerizing model
International Nuclear Information System (INIS)
A new technique for producing hollow shell laser fusion capsules was developed that starts with a depolymerizable mandrel. In this technique we use poly(alpha-methylstyrene) (PAMS) beads or shells as mandrels which are overcoated with plasma polymer. The PAMS mandrel is thermally depolymerized to gas phase monomer, which diffuses through the permeable and thermally more stable plasma polymer coating, leaving a hollow shell. We have developed methods for controlling the size of the PAMS mandrel by either grinding to make smaller sizes or melt sintering to form larger mandrels. Sphericity and surface finish are improved by heating the PAMS mandrels in hot water using a surfactant to prevent aggregation. Using this technique we have made shells from 200 μm to 5 mm diameter with 15 to 100 μm wall thickness having sphericity better than 2 μm and surface finish better than 10 nm RMS
Latimer, Heejeong K; Jaykus, Lee-Ann; Morales, Roberta A; Cowen, Peter; Crawford-Brown, Douglas
2002-05-01
Salmonella enteritidis (SE) is a common foodbome pathogen, the transmission of which is primarily associated with the consumption of contaminated Grade A shell eggs. In order to estimate the level of SE present in raw shell eggs, it is necessary to consider the protective effects of the egg albumin, which effectively inhibits SE growth in a time- and temperature-dependent manner. In this study, a SE growth model was produced by combining two mathematical equations that described both the extended lag phase of SE growth (food component) and a SE growth model (pathogen component). This biphasic growth model was then applied to various egg handling scenarios based on the farm-to-table continuum, including in-line and off-line processing facilities with consideration of key events in production, processing, transportation, and storage. Seasonal effects were also studied. Monte Carlo simulation was used to characterize variability in temperature and time parameter values influencing the level of SE to which individuals are exposed. The total level of SE consumed was estimated under best, most likely, and time-temperature abusive handling scenarios. The model estimated that, in most cases, there was no SE growth in contaminated eggs handled under most likely practices, because 10-70% of the yolk membrane remained intact. Under abusive handling scenarios, complete loss of yolk membrane integrity frequently occurred by the time eggs reach the distribution phase, followed by subsequent SE growth, which was often quite rapid. In general, the effect of season and processing method (in-line vs. off-line) was minimal. Further sensitivity analysis demonstrated that the initial SE contamination level significantly influenced the final exposure levels only under no-abuse or mildly abusive conditions. The results of our study suggest that, for maximum reduction of SE exposure level, cooling strategies should not only focus on the on-farm or processing phases, but should emphasize
Nucleon-pair approximation to the nuclear shell model
Energy Technology Data Exchange (ETDEWEB)
Zhao, Y.M., E-mail: ymzhao@sjtu.edu.cn [Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Arima, A. [Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Musashi Gakuen, 1-26-1 Toyotamakami Nerima-ku, Tokyo 176-8533 (Japan)
2014-12-01
Atomic nuclei are complex systems of nucleons–protons and neutrons. Nucleons interact with each other via an attractive and short-range force. This feature of the interaction leads to a pattern of dominantly monopole and quadrupole correlations between like particles (i.e., proton–proton and neutron–neutron correlations) in low-lying states of atomic nuclei. As a consequence, among dozens or even hundreds of possible types of nucleon pairs, very few nucleon pairs such as proton and neutron pairs with spin zero, two (in some cases spin four), and occasionally isoscalar spin-aligned proton–neutron pairs, play important roles in low-energy nuclear structure. The nucleon-pair approximation therefore provides us with an efficient truncation scheme of the full shell model configurations which are otherwise too large to handle for medium and heavy nuclei in foreseeable future. Furthermore, the nucleon-pair approximation leads to simple pictures in physics, as the dimension of nucleon-pair subspace is always small. The present paper aims at a sound review of its history, formulation, validity, applications, as well as its link to previous approaches, with the focus on the new developments in the last two decades. The applicability of the nucleon-pair approximation and numerical calculations of low-lying states for realistic atomic nuclei are demonstrated with examples. Applications of pair approximations to other problems are also discussed.
Analytical positron range modelling in heterogeneous media for PET Monte Carlo simulation
Energy Technology Data Exchange (ETDEWEB)
Lehnert, Wencke; Meikle, Steven R [Discipline of Medical Radiation Sciences, Faculty of Health Sciences, University of Sydney, PO Box 170, Lidcombe NSW 1825 (Australia); Gregoire, Marie-Claude; Reilhac, Anthonin, E-mail: wlehnert@uni.sydney.edu.au [Australian Nuclear Science and Technology Organisation, Lucas Heights NSW 2234 (Australia)
2011-06-07
Monte Carlo simulation codes that model positron interactions along their tortuous path are expected to be accurate but are usually slow. A simpler and potentially faster approach is to model positron range from analytical annihilation density distributions. The aims of this paper were to efficiently implement and validate such a method, with the addition of medium heterogeneity representing a further challenge. The analytical positron range model was evaluated by comparing annihilation density distributions with those produced by the Monte Carlo simulator GATE and by quantitatively analysing the final reconstructed images of Monte Carlo simulated data. In addition, the influence of positronium formation on positron range and hence on the performance of Monte Carlo simulation was investigated. The results demonstrate that 1D annihilation density distributions for different isotope-media combinations can be fitted with Gaussian functions and hence be described by simple look-up-tables of fitting coefficients. Together with the method developed for simulating positron range in heterogeneous media, this allows for efficient modelling of positron range in Monte Carlo simulation. The level of agreement of the analytical model with GATE depends somewhat on the simulated scanner and the particular research task, but appears to be suitable for lower energy positron emitters, such as {sup 18}F or {sup 11}C. No reliable conclusion about the influence of positronium formation on positron range and simulation accuracy could be drawn.
Kinetic Monte Carlo modelling of neutron irradiation damage in iron
Energy Technology Data Exchange (ETDEWEB)
Gamez, L. [Instituto de Fusion Nuclear, UPM, Madrid (Spain); Departamento de Fisica Aplicada, ETSII, UPM, Madrid (Spain)], E-mail: linarejos.gamez@upm.es; Martinez, E. [Instituto de Fusion Nuclear, UPM, Madrid (Spain); Lawrence Livermore National Laboratory, LLNL, CA 94550 (United States); Perlado, J.M.; Cepas, P. [Instituto de Fusion Nuclear, UPM, Madrid (Spain); Caturla, M.J. [Departamento de Fisica Aplicada, Universidad de Alicante, Alicante (Spain); Victoria, M. [Instituto de Fusion Nuclear, UPM, Madrid (Spain); Marian, J. [Lawrence Livermore National Laboratory, LLNL, CA 94550 (United States); Arevalo, C. [Instituto de Fusion Nuclear, UPM, Madrid (Spain); Hernandez, M.; Gomez, D. [CIEMAT, Madrid (Spain)
2007-10-15
Ferritic steels (FeCr based alloys) are key materials needed to fulfill the requirements expected in future nuclear fusion facilities, both for magnetic and inertial confinement, and advanced fission reactors (GIV) and transmutation systems. Research in such field is actually a critical aspect in the European research program and abroad. Experimental and multiscale simulation methodologies are going hand by hand in increasing the knowledge of materials performance. At DENIM, it is progressing in some specific part of the well-linked simulation methodology both for defects energetics and diffusion, and for dislocation dynamics. In this study, results obtained from kinetic Monte Carlo simulations of neutron irradiated Fe under different conditions are presented, using modified ad hoc parameters. A significant agreement with experimental measurements has been found for some of the parameterization and mechanisms considered. The results of these simulations are discussed and compared with previous calculations.
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.
R and D on automatic modeling methods for Monte Carlo codes FLUKA
International Nuclear Information System (INIS)
FLUKA is a fully integrated particle physics Monte Carlo simulation package. It is necessary to create the geometry models before calculation. However, it is time- consuming and error-prone to describe the geometry models manually. This study developed an automatic modeling method which could automatically convert computer-aided design (CAD) geometry models into FLUKA models. The conversion program was integrated into CAD/image-based automatic modeling program for nuclear and radiation transport simulation (MCAM). Its correctness has been demonstrated. (authors)
International Nuclear Information System (INIS)
Full text: Aim Motion of lung tumours due to respiratory motion is a significant problem in radiotherapy. The aim of this work was to develop a Monte Carlo model of a commercially available motion phantom. Method The Geant4 C++ based Monte Carlo package was used to replicate the QUASAR motion phantom from Modus Medical. The physical QUASAR phantom contains moving inserts which represent the target and is capable of numerous dosimetric and imaging quality assurance functions. The Monte Carlo phantom model in this work allows the user to import patient respiratory data recorded with the Varian Real-time Position Management system. The spatial and temporal motion of the virtual phantom is determined by the patient data, therefore, making it ideal for patient specific QA. A user interface was created that allows patient data and scoring options to be assigned as well as media and density selections for all inserts. Results The virtual QUASAR Monte Carlo phantom is able to replicate patient motion and determine the effects of motion on dose distributions. The Monte Carlo model replicates patient superior inferior respiratory motion accurately and creates a platform for patient specific QA and TPS verification. Furthermore, dose calculation within the phantom can be performed with the increased accuracy of Monte Carlo and compared with measurements. Conclusion The added accuracy of dose-calculation afforded by Monte Carlo methods along with the ability to QA motion management protocols makes the virtual QUASAR phantom a useful tool in motion management for radiotherapy.
Quantum Monte Carlo calculations of light nuclei
International Nuclear Information System (INIS)
Quantum Monte Carlo calculations using realistic two- and three-nucleon interactions are presented for nuclei with up to eight nucleons. We have computed the ground and a few excited states of all such nuclei with Greens function Monte Carlo (GFMC) and all of the experimentally known excited states using variational Monte Carlo (VMC). The GFMC calculations show that for a given Hamiltonian, the VMC calculations of excitation spectra are reliable, but the VMC ground-state energies are significantly above the exact values. We find that the Hamiltonian we are using (which was developed based on 3H, 4He, and nuclear matter calculations) underpredicts the binding energy of p-shell nuclei. However our results for excitation spectra are very good and one can see both shell-model and collective spectra resulting from fundamental many-nucleon calculations. Possible improvements in the three-nucleon potential are also be discussed
Cluster properties of nuclear states in the modern shell model approach
International Nuclear Information System (INIS)
In this presentation we summarize our progress in the study of α-clustering in the shell model configuration interaction approach. We put forward Cluster-Nucleon Configuration Interaction Model where the study of clustering is facilitated by the SU(3) symmetry of the cluster channels and by Orthogonality Condition Model. Pioneering methods and results concerning α spectroscopic factors in sd-shell nuclei and in 16 O treated in p-sd shell are presented. Comparison with experimental data is in favor of the approach
Shell-Model Effective Operators for Muon Capture in $^{20}Ne$
Siiskonen, T; Hjorth-Jensen, M
1999-01-01
It has been proposed that the discrepancy between the partially-conserved axial-current prediction and the nuclear shell-model calculations of the ratio $C_P/C_A$ in the muon-capture reactions can be solved in the case of ^{28}Si by introducing effective transition operators. Recently there has been experimental interest in measuring the needed angular correlations also in ^{20}Ne. Inspired by this, we have performed a shell-model analysis employing effective transition operators in the shell-model formalism for the transition $^{20}Ne(0^+_{g.s.})+\\mu^- \\to ^{20}F(1^+; 1.057 MeV) + \
Symmetry-dictated trucation: Solutions of the spherical shell model for heavy nuclei
International Nuclear Information System (INIS)
Principles of dynamical symmetry are used to simplify the spherical shell model. The resulting symmetry-dictated truncation leads to dynamical symmetry solutions that are often in quantitative agreement with a variety of observables. Numerical calculations, including terms that break the dynamical symmetries, are shown that correspond to shell model calculations for heavy deformed nuclei. The effective residual interaction is simple, well-behaved, and can be determined from basic observables. With this approach, we intend to apply the shell model in systematic fashion to all nuclei. The implications for nuclear structure far from stability and for nuclear masses and other quantities of interest in astrophysics are discussed
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.
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.
Monte Carlo simulation of diblock copolymer microphases by means of a 'fast' off-lattice model
DEFF Research Database (Denmark)
Besold, Gerhard; Hassager, O.; Mouritsen, Ole G.
We present a mesoscopic off-lattice model for the simulation of diblock copolymer melts by Monte Carlo techniques. A single copolymer molecule is modeled as a discrete Edwards chain consisting of two blocks with vertices of type A and B, respectively. The volume interaction is formulated in terms...
Modelling photon transport in non-uniform media for SPECT with a vectorized Monte Carlo code.
Smith, M F
1993-10-01
A vectorized Monte Carlo code has been developed for modelling photon transport in non-uniform media for single-photon-emission computed tomography (SPECT). The code is designed to compute photon detection kernels, which are used to build system matrices for simulating SPECT projection data acquisition and for use in matrix-based image reconstruction. Non-uniform attenuating and scattering regions are constructed from simple three-dimensional geometric shapes, in which the density and mass attenuation coefficients are individually specified. On a Stellar GS1000 computer, Monte Carlo simulations are performed between 1.6 and 2.0 times faster when the vector processor is utilized than when computations are performed in scalar mode. Projection data acquired with a clinical SPECT gamma camera for a line source in a non-uniform thorax phantom are well modelled by Monte Carlo simulations. The vectorized Monte Carlo code was used to stimulate a 99Tcm SPECT myocardial perfusion study, and compensations for non-uniform attenuation and the detection of scattered photons improve activity estimation. The speed increase due to vectorization makes Monte Carlo simulation more attractive as a tool for modelling photon transport in non-uniform media for SPECT. PMID:8248288
Gamow shell model description of proton scattering on Ne18
Jaganathen, Y.; Michel, N.; Płoszajczak, M.
2014-03-01
Background: The structure of weakly bound/unbound nuclei close to particle drip lines is different from that around the valley of beta stability. A comprehensive description of these systems goes beyond the standard shell model (SM) and demands an open quantum system description of the nuclear many-body system. Purpose: For that purpose, we are using the Gamow shell model (GSM), which provides a fully microscopic description of bound and unbound nuclear states, nuclear decays, and reactions. We formulate the GSM in coupled-channel (GSM-CC) representation to describe low-energy elastic and inelastic scattering of protons on Ne18. Method: The GSM-CC formalism is applied to a translationally invariant Hamiltonian with an effective finite-range two-body interaction. We discuss in detail the GSM-CC formalism in coordinate space and give the description of the novel equivalent potential method for solving the GSM-CC system of integrodifferential equations. This method is then applied for the description of (p,p') reaction cross-sections. The reactions channels are built by GSM wave functions for the ground state 0+ and the first excited 2+ of Ne18 and a proton wave function expanded in different partial waves. The completeness of this basis is verified by comparing GSM and GSM-CC energies of low-energy resonant states in Na19. The differences between the two calculations provide a measure of the missing configurations in the GSM-CC calculation of low-energy states of Na19 due to the restriction on the number of excited states of Ne18. Results: We present the first application of the GSM-CC formalism for the calculation of excited states of Ne18 and Na19, the excitation function, and the elastic/inelastic differential cross-sections in the Ne18(p,p') reaction at different energies. This is the first unified description of the spectra and reaction cross-sections in the GSM formalism. The method is shown to be both feasible and accurate. The approximate equivalence of GSM
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
already exist for the study of low energy supersymmetry and the MSSM in particular, this workshop will instead focus on tools for alternative TeV-scale physics models. The main goals of the workshop are: To survey what is available. To provide feedback on user experiences with Monte Carlo tools for BSM......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...
Ab initio no-core shell model with continuum
Navratil, Petr
2008-04-01
The ab initio no-core shell model (NCSM) is a many-body approach to nuclear structure of light nuclei. The NCSM adopts an effective interaction theory to transform fundamental inter-nucleon interactions into effective interactions for a specified nucleus in a selected harmonic oscillator basis space [1]. The method is capable of predicting nuclear structure from inter-nucleon forces derived from quantum chromodynamics by means of chiral effective field theory [2]. NCSM extensions to the microscopic description of nuclear reactions are now under development. In my talk, I will first discuss our recent calculations of the ^4He total photo-absorption cross section using two- and three-nucleon interactions from chiral effective field theory [3]. I will then outline our effort to augment the NCSM by the resonating group method (RGM) technique to develop a new method capable of describing simultaneously both bound states and nuclear reactions on light nuclei [4]. This approach, which preserves translational symmetry and the Pauli principle, will allow us to calculate cross sections of reactions important for astrophysics and describe weakly-bound systems from first principles. I will present our first phase shift results for neutron scattering off ^3H, ^4He and ^7Li and proton scattering off ^3He, ^4He and ^7Be using realistic nucleon-nucleon potentials. 3mm [1] P. Navr'atil, J. P. Vary and B. R. Barrett, Phys. Rev. C 62, 054311 (2000). [2] P. Navr'atil and V. G. Gueorguiev and J. P. Vary, W. E. Ormand and A. Nogga, Phys. Rev. Lett. 99, 042501 (2007). [3] S. Quaglioni and P. Navr'atil, Phys. Lett. B 652, 370 (2007). [4] S. Quaglioni and P. Navr'atil, arXiv:0712.0855.
Monte Carlo simulations of models for accelerator transmutation of waste
International Nuclear Information System (INIS)
The Los Alamos Accelerator Transmutation of Waste (ATW) program is directed toward the dual goals of alleviating the problems associated with existing high-level radioactive defense wastes, and of developing systems for the generation of fission energy with minimal production of high-level, long-lived nuclear wastes. In the Los Alamos ATW concept, a high-current, high-energy proton accelerator creates and intense flux of neutrons through spallation in heavy metal targets. The high neutron flux levels available in such systems allow the rapid burning even of nuclides with small cross sections, the design of systems with dilute inventories, and the operation of systems far from criticality. A crucial tool for ATW simulations is the LAHET Code System (LCS), which consists of the Los Alamos version of the HETC Monte Carlo code, a special version of the MCNP code, and several tallying and postprocessing utilities. Here we present results for a baseline system designed to transmute technetium. 16 refs
Shell Correction and Pairing Energies in the Dinuclear System Model
Institute of Scientific and Technical Information of China (English)
WANG Nan; LI Jun-Qing; ZHAO En-Guang
2008-01-01
We investigate the dependences of the potential energy surfaces(PES)and the fusion probabilities for some cold fusion reactions leading to super-heavy elements on the nuclear shell effect and pairing energy.It is found that the shell effect plays an important role in the fusion of the super-heavy element while pairing energy's contribution is insignificant.The fusion probabilities and evaporation residue cross sections as functions of the Ge-isotope projectile bombarding 208 Pb are also investigated.It is found that evaporation residue cross sections do not always increase with the increasing neutron number of Ge-isotope.
From Kuo–Brown to today's realistic shell-model calculations
International Nuclear Information System (INIS)
This paper is an homage to the seminal work of Gerry Brown and Tom Kuo, where shell model calculations were performed for 18O and 18F using an effective interaction derived from the Hamada–Johnston nucleon–nucleon potential. That work has been the first successful attempt to provide a description of nuclear structure properties starting from the free nucleon–nucleon potential. We shall compare the approach employed in the 1966 paper with the derivation of a modern realistic shell-model interaction for sd-shell nuclei, evidencing the progress that has been achieved during the last decades
Particle-Number Projected Hartree-Fock-Bogoliubov Study with Effective Shell Model Interactions
Maqbool, I; Ganai, P A; Ring, P
2010-01-01
We perform particle-number projected mean-field study using the recently developed symmetry-projected Hartree-Fock-Bogoliubov (HFB) equations. Realistic calculations have been performed in sd- and fp-shell nuclei using the shell model empirical intearctions, USD and GXPFIA. It is demonstrated that the mean-field results for energy surfaces, obtained with these shell model interactions, are quite similar to those obtained using the density functional approaches. Further, it is shown that particle-number projected results, for neutron rich isotopes, can lead to different ground-state shapes in comparison to the bare HFB calculations.
Adaptation of the B1 leakage model to Monte Carlo criticality calculations
International Nuclear Information System (INIS)
This paper presents an attempt to consistently adapt the B1 homogeneous leakage model within Monte Carlo criticality calculations based on the power iteration method. Unlike deterministic lattice codes, most of Monte Carlo-based reactor physics codes perform lattice calculations without introducing leakage models. The critical flux is however required to accurately compute homogenized cross sections and diffusion coefficients in the context of lattice physics computation. In our proposed approach, a fundamental mode approximation is introduced in the Monte Carlo K-effective power iteration method. Similarly to the deterministic implementation of the lattice code DRAGON (typically the collision probability method), B1 equations are solved at each cycle, leading to Monte Carlo estimates for the critical buckling B2 and for the group-dependent leakage rates. These leakage reactions are then introduced in the neutron random walk. This approach is discussed on legacy PWR pin cell cases, by direct comparison with results obtained by the collision probability method. This approach leads to consistent results between the Monte Carlo and the deterministic computational ways of the DRAGON code. (author)
Accurately modeling Gaussian beam propagation in the context of Monte Carlo techniques
Hokr, Brett H.; Winblad, Aidan; Bixler, Joel N.; Elpers, Gabriel; Zollars, Byron; Scully, Marlan O.; Yakovlev, Vladislav V.; Thomas, Robert J.
2016-03-01
Monte Carlo simulations are widely considered to be the gold standard for studying the propagation of light in turbid media. However, traditional Monte Carlo methods fail to account for diffraction because they treat light as a particle. This results in converging beams focusing to a point instead of a diffraction limited spot, greatly effecting the accuracy of Monte Carlo simulations near the focal plane. Here, we present a technique capable of simulating a focusing beam in accordance to the rules of Gaussian optics, resulting in a diffraction limited focal spot. This technique can be easily implemented into any traditional Monte Carlo simulation allowing existing models to be converted to include accurate focusing geometries with minimal effort. We will present results for a focusing beam in a layered tissue model, demonstrating that for different scenarios the region of highest intensity, thus the greatest heating, can change from the surface to the focus. The ability to simulate accurate focusing geometries will greatly enhance the usefulness of Monte Carlo for countless applications, including studying laser tissue interactions in medical applications and light propagation through turbid media.
Bruscaglioni, Piero; Poggi, P.; Macelloni, Giovanni; Paloscia, Simonetta
2003-04-01
This paper describes an application of the Monte Carlo method to the evaluation of backscattering response to microwave sounding of vegetation. After a brief introductory discussion on the different approaches commonly employed to the numerical simulation of scattering from vegetation, we describe our model based on representing the vegetation medium as a collection of elementary scatterers of simple shapes, and dealing directly with electromagnetic field interaction with these elements. Plant structures are built assembling the single elements by the Lindenmayer systems fractal technique. We presents some examples of computations on models of different kinds of vegetation showing the potential of modeling in understanding scattering behavior. A brief discussion on the issue of second order scattering effects is also included.
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.
Sigma models with off-shell N=(4,4) supersymmetry and noncommuting complex structures
Goteman, M; Rocek, M; Ryb, Itai
2009-01-01
We describe the conditions for extra supersymmetry in N=(2,2) supersymmetric nonlinear sigma models written in terms of semichiral superfields. We find that these models allow additional off-shell supersymmetry. The (4,4) supersymmetry introduces geometrical structures on the target-space which are conveniently described in terms of Yano f-structures and Magri-Morosi concomitants. On-shell, we relate the new structures to the known bi-hypercomplex structures.
Monte Carlo Renormalization Group Analysis of Lattice $\\phi^4$ Model in $D=3,4$
Itakura, M
1999-01-01
We present a simple, sophisticated method to capture renormalization group flow in Monte Carlo simulation, which provides important information of critical phenomena. We applied the method to $D=3,4$ lattice $\\phi^4$ model and obtained renormalization flow diagram which well reproduces theoretically predicted behavior of continuum $\\phi^4$ model. We also show that the method can be easily applied to much more complicated models, such as frustrated spin models.
Genius, Margarita; Strazzera, Elisabetta
2005-01-01
A Monte Carlo analysis is conducted to assess the validity of the bivariate modeling approach for detection and correction of different forms of elicitation effects in Double Bound Contingent Valuation data. Alternative univariate and bivariate models are applied to several simulated data sets, each one characterized by a specific elicitation effect, and their performance is assessed using standard selection criteria. The bivariate models include the standard Bivariate Probit model, and an al...
Csányi, Éva; Boda, Dezső; Gillespie, Dirk; Kristóf, Tamás
2011-01-01
A reduced model of a sodium channel is analyzed using Dynamic Monte Carlo simulations. These include the first simulations of ionic current under approximately physiological ionic conditions through a model sodium channel and an analysis of how mutations of the sodium channel’s DEKA selectivity filter motif transform the channel from being Na+ selective to being Ca2+ selective. Even though the model of the pore, amino acids, and permeant ions is simplified, the model reproduces the fundamenta...
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.
Implementation of a Monte Carlo based inverse planning model for clinical IMRT with MCNP code
He, Tongming Tony
In IMRT inverse planning, inaccurate dose calculations and limitations in optimization algorithms introduce both systematic and convergence errors to treatment plans. The goal of this work is to practically implement a Monte Carlo based inverse planning model for clinical IMRT. The intention is to minimize both types of error in inverse planning and obtain treatment plans with better clinical accuracy than non-Monte Carlo based systems. The strategy is to calculate the dose matrices of small beamlets by using a Monte Carlo based method. Optimization of beamlet intensities is followed based on the calculated dose data using an optimization algorithm that is capable of escape from local minima and prevents possible pre-mature convergence. The MCNP 4B Monte Carlo code is improved to perform fast particle transport and dose tallying in lattice cells by adopting a selective transport and tallying algorithm. Efficient dose matrix calculation for small beamlets is made possible by adopting a scheme that allows concurrent calculation of multiple beamlets of single port. A finite-sized point source (FSPS) beam model is introduced for easy and accurate beam modeling. A DVH based objective function and a parallel platform based algorithm are developed for the optimization of intensities. The calculation accuracy of improved MCNP code and FSPS beam model is validated by dose measurements in phantoms. Agreements better than 1.5% or 0.2 cm have been achieved. Applications of the implemented model to clinical cases of brain, head/neck, lung, spine, pancreas and prostate have demonstrated the feasibility and capability of Monte Carlo based inverse planning for clinical IMRT. Dose distributions of selected treatment plans from a commercial non-Monte Carlo based system are evaluated in comparison with Monte Carlo based calculations. Systematic errors of up to 12% in tumor doses and up to 17% in critical structure doses have been observed. The clinical importance of Monte Carlo based
Itagaki, N.; Matsuno, H.; Suhara, T.
2015-01-01
The antisymmetrized quasi-cluster model (AQCM) is a method to describe a transition from the alpha-cluster wave function to the jj-coupling shell model wave function. In this model, the cluster-shell transition is characterized by only two parameters; R representing the distance between alpha clusters and Lambda describing the breaking of alpha clusters, and the contribution of the spin-orbit interaction, very important in the jj-coupling shell model, can be taken into account starting with t...
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.
A Shell/3D Modeling Technique for the Analysis of Delaminated Composite Laminates
Krueger, Ronald; OBrien, T. Kevin
2000-01-01
A shell/3D modeling technique was developed for which a local solid finite element model is used only in the immediate vicinity of the delamination front. The goal was to combine the accuracy of the full three-dimensional solution with the computational efficiency of a shell finite element model. Multi-point constraints provided a kinematically compatible interface between the local 3D model and the global structural model which has been meshed with shell finite elements. Double Cantilever Beam, End Notched Flexure, and Single Leg Bending specimens were analyzed first using full 3D finite element models to obtain reference solutions. Mixed mode strain energy release rate distributions were computed using the virtual crack closure technique. The analyses were repeated using the shell/3D technique to study the feasibility for pure mode I, mode II and mixed mode I/II cases. Specimens with a unidirectional layup and with a multidirectional layup were simulated. For a local 3D model, extending to a minimum of about three specimen thicknesses on either side of the delamination front, the results were in good agreement with mixed mode strain energy release rates obtained from computations where the entire specimen had been modeled with solid elements. For large built-up composite structures the shell/3D modeling technique offers a great potential for reducing the model size, since only a relatively small section in the vicinity of the delamination front needs to be modeled with solid elements.
Reservoir Modeling Combining Geostatistics with Markov Chain Monte Carlo Inversion
DEFF Research Database (Denmark)
Zunino, Andrea; Lange, Katrine; Melnikova, Yulia;
2014-01-01
geostatistics. The geostatistical algorithm learns the multiple-point statistics from prototype models, then generates proposal models which are tested by a Metropolis sampler. The solution of the inverse problem is finally represented by a collection of reservoir models in terms of facies and porosity, which...
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…
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…
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 and...
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
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…
International Nuclear Information System (INIS)
Lattice versions with restricted suppersymmetry of simple (1+1)-dimensional supersymmetric models are numerically studied using a local hamiltonian Monte Carlo method. The pattern of supersymmetry breaking closely follows the expectations of Bartels and Bronzan obtain in an alternative lattice formulation. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Seubert, A.; Langenbuch, S.; Velkov, K.; Zwermann, W. [Gesellschaft fuer Anlagen- und Reaktorsicherheit mbH (GRS), Garching (Germany). Forschungsinstitute
2007-07-01
An overview is given of the recent progress at GRS concerning deterministic transport and Monte Carlo methods with thermal-hydraulic feedback. The development of the time-dependent 3D discrete ordinates transport code TORT-TD is described which has also been coupled with ATHLET. TORT-TD/ATHLET allows 3D pin-by-pin coupled analyses of transients using few energy groups and anisotropic scattering. As a step towards Monte Carlo steady-state calculations with nuclear point data and thermal-hydraulic feedback, MCNP has been prepared to incorporate thermal-hydraulic parameters. Results obtained for selected test cases demonstrate the applicability of deterministic and Monte Carlo neutron transport models coupled with thermo-fluiddynamics. (orig.)
Elementary isovector spin and orbital magnetic dipole modes revisited in the shell model
International Nuclear Information System (INIS)
A review is given on the status of mainly spin magnetic dipole modes in some sd- and fp-shell nuclei studied with inelastic electron and proton scattering, and by β+-decay. Particular emphasis is also placed on a fairly new, mainly orbital magnetic dipole mode investigated by high-resolution (e,e') and (p,p') scattering experiments on a series of fp-shell nuclei. Both modes are discussed in terms of the shell model with various effective interactions. (orig.)
Riccardo LUCCHETTI; Pigini, Claudia
2011-01-01
In this paper, we run a Monte Carlo analysis of the finite-sample performance of an Information Matrix Test put forward by Smith (1985) for bivariate censored models. We use the bivariate probit model and Heckman selection model as examples.;Approximating the finite-sample distribution of this test statistic by its asymptotic distribution can lead to very misleading results: its size is severely distorted even in samples that common practice would judge to be perfectly adequate for asymptotic...
Monte Carlo model of CO adsorption on supported Pt nanoparticle
International Nuclear Information System (INIS)
For molecular simulations with thousands of atoms it is desirable to use a lattice gas model because it is fast and easy-to-use for computations. Unfortunately, simulation of adsorption on heterogeneous surfaces within this model is rather complicated due to a large variety of available adsorption site types. We propose the combined model with lattice representation of adsorbent atoms and arbitrary location of adsorbate atoms. Using this model simulation of CO adsorption on supported Pt nanoparticles has been performed. With the proposed approach the above-mentioned difficulties were successfully overcome.
Monte Carlo model of CO adsorption on supported Pt nanoparticle
Energy Technology Data Exchange (ETDEWEB)
Myshlyavtsev, A.V. [Omsk State Technical University, Omsk (Russian Federation); Institute of Hydrocarbons Processing SB RAS, Omsk (Russian Federation); Stishenko, P.V., E-mail: PVStishenko@omgtu.ru [Omsk State Technical University, Omsk (Russian Federation)
2010-06-15
For molecular simulations with thousands of atoms it is desirable to use a lattice gas model because it is fast and easy-to-use for computations. Unfortunately, simulation of adsorption on heterogeneous surfaces within this model is rather complicated due to a large variety of available adsorption site types. We propose the combined model with lattice representation of adsorbent atoms and arbitrary location of adsorbate atoms. Using this model simulation of CO adsorption on supported Pt nanoparticles has been performed. With the proposed approach the above-mentioned difficulties were successfully overcome.
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...... tendency to foetal loss is heritable. The data possess a complicated dependence structure due to replicate pregnancies for the same woman, and a given family pattern. We conclude that a tendency to foetal loss is heritable. The model is of great interest in genetic epidemiology, because it considers both...
Assessment of large basis shell model wave functions for the Li isotopes
International Nuclear Information System (INIS)
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 6,7Li ground states were analysed using the same shell model wave functions. It was found that the results obtained by using 0ℎω 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
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.
Stability of core–shell nanowires in selected model solutions
International Nuclear Information System (INIS)
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
On the Modeling of Shells in Multibody Dynamics
Bauchau, Olivier A.; Choi, Jou-Young; Bottasso, Carlo L.
2000-01-01
Energy preserving/decaying schemes are presented for the simulation of the nonlinear multibody systems involving shell components. The proposed schemes are designed to meet four specific requirements: unconditional nonlinear stability of the scheme, a rigorous treatment of both geometric and material nonlinearities, exact satisfaction of the constraints, and the presence of high frequency numerical dissipation. The kinematic nonlinearities associated with arbitrarily large displacements and rotations of shells are treated in a rigorous manner, and the material nonlinearities can be handled when the, constitutive laws stem from the existence of a strain energy density function. The efficiency and robustness of the proposed approach is illustrated with specific numerical examples that also demonstrate the need for integration schemes possessing high frequency numerical dissipation.
A shell-model investigation of the binding energies of some exotic isotopes of sodium and magnesium
International Nuclear Information System (INIS)
Standard shell-model calculations of the binding energies of the neutron-rich isotopes of sodium and magnesium are in strong disagreement with the experimental values near N=20. It is shown that the discrepancy can be explained by allowing neutron excitations from the dsub(3/2) shell into the fsub(7/2) shell. (author)
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.
Dorval, Eric
2016-01-01
Neutron transport calculations by Monte Carlo methods are finding increased application in nuclear reactor simulations. In particular, a versatile approach entails the use of a 2-step pro-cedure, with Monte Carlo as a few-group cross section data generator at lattice level, followed by deterministic multi-group diffusion calculations at core level. In this thesis, the Serpent 2 Monte Carlo reactor physics burnup calculation code is used in order to test a set of diffusion coefficient model...
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
Modelling and Dynamic Response of Steel Reticulated Shell under Blast Loading
Ximei Zhai; Yonghui Wang
2013-01-01
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 w...
Perturbation analysis for Monte Carlo continuous cross section models
International Nuclear Information System (INIS)
Sensitivity analysis, including both its forward and adjoint applications, collectively referred to hereinafter as Perturbation Analysis (PA), is an essential tool to complete Uncertainty Quantification (UQ) and Data Assimilation (DA). PA-assisted UQ and DA have traditionally been carried out for reactor analysis problems using deterministic as opposed to stochastic models for radiation transport. This is because PA requires many model executions to quantify how variations in input data, primarily cross sections, affect variations in model's responses, e.g. detectors readings, flux distribution, multiplication factor, etc. Although stochastic models are often sought for their higher accuracy, their repeated execution is at best computationally expensive and in reality intractable for typical reactor analysis problems involving many input data and output responses. Deterministic methods however achieve computational efficiency needed to carry out the PA analysis by reducing problem dimensionality via various spatial and energy homogenization assumptions. This however introduces modeling error components into the PA results which propagate to the following UQ and DA analyses. The introduced errors are problem specific and therefore are expected to limit the applicability of UQ and DA analyses to reactor systems that satisfy the introduced assumptions. This manuscript introduces a new method to complete PA employing a continuous cross section stochastic model and performed in a computationally efficient manner. If successful, the modeling error components introduced by deterministic methods could be eliminated, thereby allowing for wider applicability of DA and UQ results. Two MCNP models demonstrate the application of the new method - a Critical Pu Sphere (Jezebel), a Pu Fast Metal Array (Russian BR-1). The PA is completed for reaction rate densities, reaction rate ratios, and the multiplication factor. (author)
Tian, Zhen; Folkerts, Michael; Shi, Feng; Jiang, Steve B; Jia, Xun
2015-01-01
Monte Carlo (MC) simulation is considered as the most accurate method for radiation dose calculations. Accuracy of a source model for a linear accelerator is critical for the overall dose calculation accuracy. In this paper, we presented an analytical source model that we recently developed for GPU-based MC dose calculations. A key concept called phase-space-ring (PSR) was proposed. It contained a group of particles that are of the same type and close in energy and radial distance to the center of the phase-space plane. The model parameterized probability densities of particle location, direction and energy for each primary photon PSR, scattered photon PSR and electron PSR. For a primary photon PSRs, the particle direction is assumed to be from the beam spot. A finite spot size is modeled with a 2D Gaussian distribution. For a scattered photon PSR, multiple Gaussian components were used to model the particle direction. The direction distribution of an electron PSRs was also modeled as a 2D Gaussian distributi...
International Nuclear Information System (INIS)
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
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...
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.
Mean field theory of nuclei and shell model. Present status and future outlook
International Nuclear Information System (INIS)
Many of the recent topics of the nuclear structure are concerned on the problems of unstable nuclei. It has been revealed experimentally that the nuclear halos and the neutron skins as well as the cluster structures or the molecule-like structures can be present in the unstable nuclei, and the magic numbers well established in the stable nuclei disappear occasionally while new ones appear. The shell model based on the mean field approximation has been successfully applied to stable nuclei to explain the nuclear structure as the finite many body system quantitatively and it is considered as the standard model at present. If the unstable nuclei will be understood on the same model basis or not is a matter related to fundamental principle of nuclear structure theories. In this lecture, the fundamental concept and the framework of the theory of nuclear structure based on the mean field theory and the shell model are presented to make clear the problems and to suggest directions for future researches. At first fundamental properties of nuclei are described under the subtitles: saturation and magic numbers, nuclear force and effective interactions, nuclear matter, and LS splitting. Then the mean field theory is presented under subtitles: the potential model, the mean field theory, Hartree-Fock approximation for nuclear matter, density dependent force, semiclassical mean field theory, mean field theory and symmetry, Skyrme interaction and density functional, density matrix expansion, finite range interactions, effective masses, and motion of center of mass. The subsequent section is devoted to the shell model with the subtitles: beyond the mean field approximation, core polarization, effective interaction of shell model, one-particle wave function, nuclear deformation and shell model, and shell model of cross shell. Finally structure of unstable nuclei is discussed with the subtitles: general remark on the study of unstable nuclear structure, asymptotic behavior of wave
Comparison of neutron diffusion and Monte Carlo models for a fission wave
Energy Technology Data Exchange (ETDEWEB)
Osborne, A. G.; Deinert, M. R. [Department of Mechanical Engineering, University of Texas at Austin, Austin, TX (United States)
2013-07-01
Many groups have used neutron diffusion simulations to study fission wave phenomena in natural or depleted uranium. However, few studies of fission wave phenomena have been published that use Monte Carlo simulations to confirm the results of diffusion models for this type of system. In the present work we show the results of a criticality and burnup simulation of a traveling wave reactor using MCNPX 2.7.0. The characteristics of the fission wave in this simulation are compared with those from a simple one-dimensional, one-group neutron diffusion model. The diffusion simulations produce a wave speed of 5.9 cm/yr versus 5.3 cm/yr for the Monte Carlo simulations. The axial flux profile in the Monte Carlo simulation is similar in shape to the diffusion results, but with different peak values, and the two profiles have an R2 value of 0.93. The {sup 238}U, {sup 239}Np and {sup 239}Pu burnup profiles from the diffusion simulation show good agreement with the Monte Carlo simulations, R values of 0.98, 0.93 and 0.97 respectively are observed. (authors)
Experimental study and Monte Carlo modeling of the Cherenkov effect
Energy Technology Data Exchange (ETDEWEB)
Mishev, A.; Angelov, I.; Duverger, E.; Gschwind, R.; Makovicka, L. E-mail: libor.makovicka@pu-pm.univ-fcomte.fr; Stamenov, J
2001-12-01
Studies realised at the Institute for Nuclear Research and Nuclear Energy (INRNE) particularly in cosmic ray detection and construction of Muonic Cherenkov Telescope at the South West University 'Neofit Rilski' Blagoevgrad show the need to develop a theoretical model based on observed phenomena and to refinement of this for detection system optimisation. The Cherenkov effect was introduced in EGS4 code system. The first simulations realised in collaboration between the french and the bulgarian team were consecrated to different geometries of water tank in total reflection. An additional modeling of photons mean trajectory and the mean number of reflections in the tank were made. This simple model was compared with experimental data realised with {sup 60}Co gamma source, the telescope and the most efficient water tank. A trajectory simulation of Cherenkov photons in water tank was made. An efficiency estimation of the detector registration was calculated. The atmospheric model was introduced in EGS4 code and a comparison between CORSIKA5.62 and EGS4 codes was made.
W. Colgan; W. T. Pfeffer; H. Rajaram; W. Abdalati; J. Balog
2012-01-01
Due to the abundance of observational datasets collected since the onset of its retreat (c. 1983), Columbia Glacier, Alaska, provides an exciting modeling target. We perform Monte Carlo simulations of the form and flow of Columbia Glacier, using a 1-D (depth-integrated) flowline model, over a wide range of parameter values and forcings. An ensemble filter is imposed following spin-up to ensure that only simulations that accurately reproduce observed pre-retreat glacier geome...
Study of the tritium production in a 1-D blanket model with Monte Carlo methods
Cubí Ricart, Álvaro
2015-01-01
In this work a method to collapse a 3D geometry into a mono dimensional model of a fusion reactor blanket is developed and tested. Using this model, neutron and photon uxes and its energy deposition will be obtained with a Monte Carlo code. This results will allow to calculate the TBR and the thermal power of the blanket and will be able to be integrated in the AINA code.
Monte Carlo fixed-lag smoothing in state-space models
Cuzol, A.; Mémin, E.
2013-01-01
International audience This paper presents an algorithm for Monte Carlo fixed-lag smoothing in state-space models de-fined by a diffusion process observed through noisy discrete-time measurements. Based on a par-ticles approximation of the filtering and smoothing distributions, the method relies on a simulation technique of conditioned diffusions. The proposed sequential smoother can be applied to general 5 non linear and multidimensional models, like the ones used in environmental applica...
Monte Carlo fixed-lag smoothing in state-space models
Cuzol, A.; Mémin, E.
2014-01-01
This paper presents an algorithm for Monte Carlo fixed-lag smoothing in state-space models defined by a diffusion process observed through noisy discrete-time measurements. Based on a particle approximation of the filtering and smoothing distributions, the method relies on a simulation technique of conditioned diffusions. The proposed sequential smoother can be applied to general nonlinear and multidimensional models, like the ones used in environmental applications. The smo...
Monte Carlo fixed-lag smoothing in state-space models
Cuzol, Anne; Mémin, Etienne
2014-01-01
International audience This paper presents an algorithm for Monte Carlo fixed-lag smoothing in state-space models de-fined by a diffusion process observed through noisy discrete-time measurements. Based on a par-ticles approximation of the filtering and smoothing distributions, the method relies on a simulation technique of conditioned diffusions. The proposed sequential smoother can be applied to general 5 non linear and multidimensional models, like the ones used in environmental applica...
Monte Carlo calculations of the finite density Thirring model
Alexandru, Andrei; Bedaque, Paulo F; Ridgway, Gregory W; Warrington, Neill C
2016-01-01
We present results of the numerical simulation of the two-dimensional Thirring model at finite density and temperature. The severe sign problem is dealt with by deforming the domain of integration into complex field space. This is the first example where a fermionic sign problem is solved in a quantum field theory by using the holomorphic gradient flow approach, a generalization of the Lefschetz thimble method.
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.
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.
Randomly dispersed particle fuel model in the PSG Monte Carlo neutron transport code
International Nuclear Information System (INIS)
High-temperature gas-cooled reactor fuels are composed of thousands of microscopic fuel particles, randomly dispersed in a graphite matrix. The modelling of such geometry is complicated, especially using continuous-energy Monte Carlo codes, which are unable to apply any deterministic corrections in the calculation. This paper presents the geometry routine developed for modelling randomly dispersed particle fuels using the PSG Monte Carlo reactor physics code. The model is based on the delta-tracking method, and it takes into account the spatial self-shielding effects and the random dispersion of the fuel particles. The calculation routine is validated by comparing the results to reference MCNP4C calculations using uranium and plutonium based fuels. (authors)
A Monte Carlo model for seeded atomic flows in the transition regime
International Nuclear Information System (INIS)
A simple model for the numerical determination of separation effects in seeded atomic gas flows is presented. The model is based on the known possibility to provide a statistically convergent estimate of the exact solution for a linear transport equation using the test particle Monte Carlo method. Accordingly, the flow field of the main gas is preliminary calculated and as a second step the linear transport equations obtained by fixing the target distribution in the collision term of the Boltzmann equation for both main and minority components are solved. Both solutions are based on appropriately devised test particle Monte Carlo methods. The second step, the critical one in evaluating the separation effects, is exact and thereby completely free of numerical diffusion. The model is described in details and illustrated by 2D test cases of atomic separation in shock fronts.
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.
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.
International Nuclear Information System (INIS)
We propose an analytical model for backscattered luminance in fog and derive an expression for the visibility signal-to-noise ratio as a function of meteorological visibility distance. The model uses single scattering processes. It is based on the Mie theory and the geometry of the optical device (emitter and receiver). In particular, we present an overlap function and take the phase function of fog into account. The results of the backscattered luminance obtained with our analytical model are compared to simulations made using the Monte Carlo method based on multiple scattering processes. An excellent agreement is found in that the discrepancy between the results is smaller than the Monte Carlo standard uncertainties. If we take no account of the geometry of the optical device, the results of the model-estimated backscattered luminance differ from the simulations by a factor 20. We also conclude that the signal-to-noise ratio computed with the Monte Carlo method and our analytical model is in good agreement with experimental results since the mean difference between the calculations and experimental measurements is smaller than the experimental uncertainty
A vectorized Monte Carlo code for modeling photon transport in SPECT
International Nuclear Information System (INIS)
A vectorized Monte Carlo computer code has been developed for modeling photon transport in single photon emission computed tomography (SPECT). The code models photon transport in a uniform attenuating region and photon detection by a gamma camera. It is adapted from a history-based Monte Carlo code in which photon history data are stored in scalar variables and photon histories are computed sequentially. The vectorized code is written in FORTRAN77 and uses an event-based algorithm in which photon history data are stored in arrays and photon history computations are performed within DO loops. The indices of the DO loops range over the number of photon histories, and these loops may take advantage of the vector processing unit of our Stellar GS1000 computer for pipelined computations. Without the use of the vector processor the event-based code is faster than the history-based code because of numerical optimization performed during conversion to the event-based algorithm. When only the detection of unscattered photons is modeled, the event-based code executes 5.1 times faster with the use of the vector processor than without; when the detection of scattered and unscattered photons is modeled the speed increase is a factor of 2.9. Vectorization is a valuable way to increase the performance of Monte Carlo code for modeling photon transport in SPECT
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.
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.
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.
Shell-model study of partial muon-capture rates in light nuclei
International Nuclear Information System (INIS)
The nuclear shell model is used to study ordinary muon capture of light nuclei in the p, sd and p-sd shell-model spaces. Several well-established two-body interactions are applied to calculate the involved nuclear matrix elements and the emerging results are compared with each other. The resulting theoretical partial muon-capture rates are compared with experimental data and their stability against different model spaces and interactions studied. The effects of the induced-pseudoscalar strength, CP, on the capture rates is discussed. The relation between the allowed partial muon capture rates and the Gamow-Teller strength function is stressed. (orig.)
Systematic spectroscopic study of neutron rich nuclei within a new shell model context
International Nuclear Information System (INIS)
An iterative approach for diagonalizing nuclear Shell Model (SM) Hamiltonian matrices, developed few years ago, has been used for performing large scale shell model calculations around the doubly-magic 132 Sn. Calculated spectra and transition strengths correctly reproduces the available experimental data, and have been used for probing the prediction of collective algebraic models in this region, in particular for isotopes on which few measures are available. The calculation predicts an increasing neutron weight in the isotopes departing from the doubly-magic 132Sn and moving toward the neutron drip line.
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.
A CAD based automatic modeling method for primitive solid based Monte Carlo calculation geometry
International Nuclear Information System (INIS)
The Multi-Physics Coupling Analysis Modeling Program (MCAM), developed by FDS Team, China, is an advanced modeling tool aiming to solve the modeling challenges for multi-physics coupling simulation. The automatic modeling method for SuperMC, the Super Monte Carlo Calculation Program for Nuclear and Radiation Process, was recently developed and integrated in MCAM5.2. This method could bi-convert between CAD model and SuperMC input file. While converting from CAD model to SuperMC model, the CAD model was decomposed into several convex solids set, and then corresponding SuperMC convex basic solids were generated and output. While inverting from SuperMC model to CAD model, the basic primitive solids was created and related operation was done to according the SuperMC model. This method was benchmarked with ITER Benchmark model. The results showed that the method was correct and effective. (author)
Rodriguez-Guzman, R; Bertsch, George F
2007-01-01
We describe a procedure for mapping a self-consistent mean-field theory (also known as density functional theory) into a shell model Hamiltonian that includes quadrupole-quadrupole and monopole pairing interactions in a truncated space. We test our method in the deformed N=Z sd-shell nuclei Ne-20, Mg-24 and Ar-36, starting from the Hartree-Fock plus BCS approximation of the USD shell model interaction. A similar procedure is then followed using the SLy4 Skyrme energy density functional in the particle-hole channel plus a zero-range density-dependent force in the pairing channel. Using the ground-state solution of this density functional theory at the Hartree-Fock plus BCS level, an effective shell model Hamiltonian is constructed. We use this mapped Hamiltonian to extract quadrupolar and pairing correlation energies beyond the mean field approximation. The rescaling of the mass quadrupole operator in the truncated shell model space is found to be almost independent of the coupling strength used in the pairing...
A sequential Monte Carlo model of the combined GB gas and electricity network
International Nuclear Information System (INIS)
A Monte Carlo model of the combined GB gas and electricity network was developed to determine the reliability of the energy infrastructure. The model integrates the gas and electricity network into a single sequential Monte Carlo simulation. The model minimises the combined costs of the gas and electricity network, these include gas supplies, gas storage operation and electricity generation. The Monte Carlo model calculates reliability indices such as loss of load probability and expected energy unserved for the combined gas and electricity network. The intention of this tool is to facilitate reliability analysis of integrated energy systems. Applications of this tool are demonstrated through a case study that quantifies the impact on the reliability of the GB gas and electricity network given uncertainties such as wind variability, gas supply availability and outages to energy infrastructure assets. Analysis is performed over a typical midwinter week on a hypothesised GB gas and electricity network in 2020 that meets European renewable energy targets. The efficacy of doubling GB gas storage capacity on the reliability of the energy system is assessed. The results highlight the value of greater gas storage facilities in enhancing the reliability of the GB energy system given various energy uncertainties. -- Highlights: •A Monte Carlo model of the combined GB gas and electricity network was developed. •Reliability indices are calculated for the combined GB gas and electricity system. •The efficacy of doubling GB gas storage capacity on reliability of the energy system is assessed. •Integrated reliability indices could be used to assess the impact of investment in energy assets
Energy Technology Data Exchange (ETDEWEB)
Peterson, S W; Polf, J; Archambault, L; Beddar, S [Department of Radiation Physics, Unit 94, University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030 (United States); Bues, M; Ciangaru, G; Smith, A [Proton Therapy Center, Unit 130, University of Texas M D Anderson Cancer Center, 1840 Old Spanish Trail, Houston, TX 77030 (United States)], E-mail: swpeters@mdanderson.org
2009-05-21
The purpose of this study is to validate the accuracy of a Monte Carlo calculation model of a proton magnetic beam scanning delivery nozzle developed using the Geant4 toolkit. The Monte Carlo model was used to produce depth dose and lateral profiles, which were compared to data measured in the clinical scanning treatment nozzle at several energies. Comparisons were also made between measured and simulated off-axis profiles to test the accuracy of the model's magnetic steering. Comparison of the 80% distal dose fall-off values for the measured and simulated depth dose profiles agreed to within 1 mm for the beam energies evaluated. Agreement of the full width at half maximum values for the measured and simulated lateral fluence profiles was within 1.3 mm for all energies. The position of measured and simulated spot positions for the magnetically steered beams agreed to within 0.7 mm of each other. Based on these results, we found that the Geant4 Monte Carlo model of the beam scanning nozzle has the ability to accurately predict depth dose profiles, lateral profiles perpendicular to the beam axis and magnetic steering of a proton beam during beam scanning proton therapy.
Monte Carlo modeling of neutron imaging at the SINQ spallation source
International Nuclear Information System (INIS)
Modeling of the Swiss Spallation Neutron Source (SINQ) has been used to demonstrate the neutron radiography capability of the newly released MPI-version of the MCNPX Monte Carlo code. A detailed MCNPX model was developed of SINQ and its associated neutron transmission radiography (NEUTRA) facility. Preliminary validation of the model was performed by comparing the calculated and measured neutron fluxes in the NEUTRA beam line, and a simulated radiography image was generated for a sample consisting of steel tubes containing different materials. This paper describes the SINQ facility, provides details of the MCNPX model, and presents preliminary results of the neutron imaging. (authors)
Implementation of a Monte Carlo method to model photon conversion for solar cells
International Nuclear Information System (INIS)
A physical model describing different photon conversion mechanisms is presented in the context of photovoltaic applications. To solve the resulting system of equations, a Monte Carlo ray-tracing model is implemented, which takes into account the coupling of the photon transport phenomena to the non-linear rate equations describing luminescence. It also separates the generation of rays from the two very different sources of photons involved (the sun and the luminescence centers). The Monte Carlo simulator presented in this paper is proposed as a tool to help in the evaluation of candidate materials for up- and down-conversion. Some application examples are presented, exploring the range of values that the most relevant parameters describing the converter should have in order to give significant gain in photocurrent
Multi-level Monte Carlo for stochastically modeled chemical kinetic systems
Anderson, David F
2011-01-01
A chemical reaction network involves multiple reactions and species. The simplest stochastic models of such networks treat the system as a continuous time Markov chain with the state being the number of molecules of each species and with reactions modeled as possible transitions of the chain. While there are methods that generate exact sample paths of the Markov chain, their computational cost scales linearly with the number of reaction events. Therefore, such methods become computationally intense for even moderately sized systems. This drawback is greatly exacerbated when such simulations are performed in conjunction with Monte Carlo techniques, as is the norm, which require the generation of many paths. We show how to extend a recently proposed multi-level Monte Carlo approach to this stochastic chemical kinetic setting, lowering the computational complexity needed to compute expected values of functions of the state of the system to a specified accuracy. The extension is non-trivial and a novel coupling o...
Extended shell-model calculation for even N=82 isotones with realistic effective interactions
Holt, A; Osnes, E; Hjorth-Jensen, M; Suhonen, J
1997-01-01
The shell model within the $2s1d0g_{7/2}0h_{11/2}$ shell is applied to calculate nuclear structure properties of the even Z=52 - 62, N=82 isotones. The results are compared with experimental data and with the results of a quasiparticle random-phase approximation (QRPA) calculation. The interaction used in these calculations is a realistic two-body G-matrix interaction derived from modern meson-exchange potential models for the nucleon-nucleon interaction. For the shell model all the two-body matrix elements are renormalized by the $\\hat{Q}$-box method whereas for the QRPA the effective interaction is defined by the G-matrix.
Quantum collapse of a self-gravitating thin shell and statistical model of quantum black hole
International Nuclear Information System (INIS)
The quantum collapse of a self-gravitating thin shell in the minisuperspace models is revisited on the assumption that the shell is composed of N distinguishable identical particles. The ground state of the shell is found and defined as a quantum black hole (QBH). We show that the energy of single particle in the QBH is dependent on N, and N has an up-limit for a stable QBH. The effective exciting energy of single particle is determined, which is universally 1/2 of the Planck energy for the full-filled QBHs. We also propose a simple statistical model of QBH and show that a QBH is full-filled at low temperatures and half-filled at high temperatures. The specific heat of QBH is found to be positive at low temperatures and the relation of the QBH mass with its temperature is obtained in the high-temperature limit of our model
Stability of core-shell nanowires in selected model solutions
Kalska-Szostko, B.; Wykowska, U.; Basa, A.; Zambrzycka, E.
2015-03-01
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 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...
Fazzolari, Fiorenzo A.; Carrera, Erasmo
2014-02-01
In this paper, the Ritz minimum energy method, based on the use of the Principle of Virtual Displacements (PVD), is combined with refined Equivalent Single Layer (ESL) and Zig Zag (ZZ) shell models hierarchically generated by exploiting the use of Carrera's Unified Formulation (CUF), in order to engender the Hierarchical Trigonometric Ritz Formulation (HTRF). The HTRF is then employed to carry out the free vibration analysis of doubly curved shallow and deep functionally graded material (FGM) shells. The PVD is further used in conjunction with the Gauss theorem to derive the governing differential equations and related natural boundary conditions. Donnell-Mushtari's shallow shell-type equations are given as a particular case. Doubly curved FGM shells and doubly curved sandwich shells made up of isotropic face sheets and FGM core are investigated. The proposed shell models are widely assessed by comparison with the literature results. Two benchmarks are provided and the effects of significant parameters such as stacking sequence, boundary conditions, length-to-thickness ratio, radius-to-length ratio and volume fraction index on the circular frequency parameters and modal displacements are discussed.
A Robust Monte Carlo Model for the Extraction of Biological Absorption and Scattering In Vivo
Bender, Janelle E.; Vishwanath, Karthik; Moore, Laura K.; Brown, J. Quincy; Chang, Vivide; Palmer, Gregory M.; Ramanujam, Nirmala
2009-01-01
We have a toolbox to quantify tissue optical properties that is composed of specialized fiberoptic probes for UV-visible diffuse reflectance spectroscopy and a fast, scalable inverse Monte Carlo (MC) model. In this paper, we assess the robustness of the toolbox for quantifying physiologically relevant parameters from turbid tissue-like media. In particular, we consider the effects of using different instruments, fiberoptic probes, and instrument-specific settings for a wide range of optical p...
The massive Schwinger model on the lattice studied via a local Hamiltonian Monte-Carlo method
International Nuclear Information System (INIS)
A local Hamiltonian Monte-Carlo method is used to study the massive Schwinger model. A non-vanishing quark condensate is found and the dependence of the condensate and the string tension on the background field is calculated. These results reproduce well the expected continuum results. We study also the first-order phase transition which separates the weak and strong coupling regimes and find evidence for the behaviour conjectured by Coleman. (author)
Nagata, H; Žukovič, M.; Idogaki, T.
2013-01-01
The three-dimensional XY model with bilinear-biquadratic exchange interactions $J$ and $J'$, respectively, has been studied by Monte Carlo simulations. From the detailed analysis of the thermal variation of various physical quantities, as well as the order parameter and energy histogram analysis, the phase diagram including two different ordered phases has been determined. There is a single phase boundary from a paramagnetic to a dipole-quadrupole ordered phase, which is of second order in a ...
International Nuclear Information System (INIS)
We briefly present our atomistic kinetic Monte Carlo approach to model the diffusion of point-defects in Fe-based alloys, and therefore to simulate diffusion induced mass transport and subsequent nano-structural and microchemical changes. This methodology has been hitherto successfully applied to the simulation of thermal annealing experiments. We here present our achievements in the generalization of this method to the simulation of neutron irradiation damage. (authors)
Bayesian inference of BWR model parameters by Markov chain Monte Carlo
International Nuclear Information System (INIS)
In this paper, the Markov chain Monte Carlo approach to Bayesian inference is applied for estimating the parameters of a reduced-order model of the dynamics of a boiling water reactor system. A Bayesian updating strategy is devised to progressively refine the estimates, as newly measured data become available. Finally, the technique is used for detecting parameter changes during the system lifetime, e.g. due to component degradation
PARTICLE SWARM OPTIMIZATION OF SOLAR CENTRAL RECEIVER SYSTEMS FROM A MONTE CARLO DIRECT MODEL
Farges, Olivier; Bézian, Jean-Jacques; El Hafi, Mouna; Fudym, Olivier; Bru, Hélène
2013-01-01
Considering the investment needed to build a solar concentrating facility, the performance of such an installation has to be maximized. This is the reason why the preliminary design step is one of the most important stage of the project process. This paper presents an optimization approach coupling a Particle Swarm Optimization algorithm with a Monte Carlo algorithm applied to the design of Central Receiver Solar systems. After the validation of the direct model from experimental data, severa...
Photopolymerizable hydrogels for implants: Monte-Carlo modeling and experimental in vitro validation
Schmocker, Andreas; Khoushabi, Azadeh; Schizas, Constantin; Bourban, Pierre-Etienne; Pioletti, Dominique; Moser, Christophe
2014-01-01
Photopolymerization is commonly used in a broad range of bioapplications, such as drug delivery, tissue engineering, and surgical implants, where liquid materials are injected and then hardened by means of llumination to create a solid polymer network. However, photopolymerization using a probe, e.g., needle guiding both the liquid and the curing illumination, has not been thoroughly investigated. We present a Monte Carlo model that takes into account the dynamic absorption and scattering par...
Monte Carlo tests of the Rasch model based on scalability coefficients
DEFF Research Database (Denmark)
Christensen, Karl Bang; Kreiner, Svend
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....
SCOUT: A Fast Monte-Carlo Modeling Tool of Scintillation Camera Output
Hunter, William C. J.; Barrett, Harrison H.; Lewellen, Thomas K.; Miyaoka, Robert S.; Muzi, John P.; Li, Xiaoli; McDougald, Wendy; MacDonald, Lawrence R.
2010-01-01
We have developed a Monte-Carlo photon-tracking and readout simulator called SCOUT to study the stochastic behavior of signals output from a simplified rectangular scintillation-camera design. SCOUT models the salient processes affecting signal generation, transport, and readout. Presently, we compare output signal statistics from SCOUT to experimental results for both a discrete and a monolithic camera. We also benchmark the speed of this simulation tool and compare it to existing simulation...
SCOUT: a fast Monte-Carlo modeling tool of scintillation camera output†
Hunter, William C. J.; Barrett, Harrison H.; Muzi, John P.; McDougald, Wendy; MacDonald, Lawrence R.; Miyaoka, Robert S.; Lewellen, Thomas K.
2013-01-01
We have developed a Monte-Carlo photon-tracking and readout simulator called SCOUT to study the stochastic behavior of signals output from a simplified rectangular scintillation-camera design. SCOUT models the salient processes affecting signal generation, transport, and readout of a scintillation camera. Presently, we compare output signal statistics from SCOUT to experimental results for both a discrete and a monolithic camera. We also benchmark the speed of this simulation tool and compare...
Topological excitations and Monte-Carlo simulation of the Abelian-Higgs model
International Nuclear Information System (INIS)
The phase structure and topological excitations, in particular the magnetic monopole current density, are investigated in a Monte-Carlo simulation of the lattice version of the four-dimensional Abelian-Higgs model. The monopole current density is found to be large in the confinement phase and rapidly decreasing in the Coulomb and Higgs phases. This result supports the view that confinement is neglected with the condensation of monopole-antimonopole pairs
An analytical solution to a simplified EDXRF model for Monte Carlo code verification
International Nuclear Information System (INIS)
The objective of this study is to obtain an analytical solution to the scalar photon transport equation that can be used to obtain benchmark results for the verification of energy dispersive X-Ray fluorescence (EDXRF) Monte Carlo simulation codes. The multi-collided flux method (multiple scattering method) is implemented to obtain analytical expressions for the space-, energy-, and angle-dependent scalar photon flux for a one dimensional EDXRF model problem. In order to obtain benchmark results, higher-order multiple scattering terms are included in the multi-collided flux method. The details of the analytical solution and of the proposed EDXRF model problem are presented. Analytical expressions obtained are then used to calculate the energy-dependent current. The analytically-calculated energy-dependent current is compared with Monte Carlo code results. The findings of this study show that analytical solutions to the scalar photon transport equation with the proposed model problem can be used as a verification tool in EDXRF Monte Carlo code development.
On Spectral Laws of 2D--Turbulence in Shell Models
Frick, Peter; Aurell, Erik
1993-01-01
We consider a class of shell models of 2D-turbulence. They conserve inertially the analogues of energy and enstrophy, two quadratic forms in the shell amplitudes. Inertially conserving two quadratic integrals leads to two spectral ranges. We study in detail the one characterized by a forward cascade of enstrophy and spectrum close to Kraichnan's $k^{-3}$--law. In an inertial range over more than 15 octaves, the spectrum falls off as $k^{-3.05\\pm 0.01}$, with the same slope in all models. We i...
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.
Shell-model study of spin modes in nuclei and nuclear forces
International Nuclear Information System (INIS)
Spin-dependent modes in nuclei are studied by shell-model method with the use of new shell-model Hamiltonians which properly take into account important roles of tensor interactions. New Hamiltonians can describe spin degrees of freedom in nuclei remarkably well. Nuclear weak processes at stellar environments are investigated based on these successes. New neutrino-nucleus reaction cross sections on 12C are applied to light-element synthesis in supernova explosions. The production rate for 11B/7Li is pointed out to be useful to determine v-oscillation parameters, in particular, v-mass hierarchy. New e-capture rates in Ni isotopes are obtained and implications for element synthesis are discussed. The monopole-based universal interaction is applied to study structure of p-sd shell nuclei and 40Ar as well as v-induced reactions on 40Ar. Repulsive corrections in the isospin T=1 monopoles are shown to be important for proper shell evolutions in neutron-rich carbon isotopes. The repulsive correction is pointed out to be due to three-body forces, in particular, the Fujita-Miyazawa force. Roles of the three-body forces on the shell evolution of neutron-rich calcium isotopes, the closed- shell nature of 48 Ca and M1 transition in 48 Ca are studied on top of the two-body G-matrix obtained by including core-polarization effects in larger spaces (≤24ℏω). Effects of the inclusion of g9/2-shell are also discussed
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
International Nuclear Information System (INIS)
We present a hierarchical Bayesian method for estimating the density and size distribution of subclad-flaws in French Pressurized Water Reactor (PWR) vessels. This model takes into account in-service inspection (ISI) data, a flaw size-dependent probability of detection (different functions are considered) with a threshold of detection, and a flaw sizing error distribution (different distributions are considered). The resulting model is identified through a Markov Chain Monte Carlo (MCMC) algorithm. The article includes discussion for choosing the prior distribution parameters and an illustrative application is presented highlighting the model's ability to provide good parameter estimates even when a small number of flaws are observed
Development of Monte Carlo model of high-energy nuclear interactions
International Nuclear Information System (INIS)
Monte Carlo code CASCADE for calculation of inelastic hadron- and nucleus-nucleus interactions at energies from several tens of MeV up to several tens of GeV and for modelling of nuclear-physical processes accompanying transport of particles and nuclei in matter is improved due to a more detailed model of decay of highly excited residual (after-intranuclear-cascade) nuclei. Results of calculations are in good agreement with experiment. However, there are some deviations for light isotope production, which prompt the necessity of developing more correct models of evaporation and strong asymmetric high-energy fission
Systematic study of proton-neutron pairing correlations in the nuclear shell model
International Nuclear Information System (INIS)
A shell-model study of proton-neutron pairing in 2p1f shell nuclei using a parametrized Hamiltonian that includes deformation and spin-orbit effects as well as isoscalar and isovector pairing is reported. By working in a shell-model framework we are able to assess the role of the various modes of proton-neutron pairing in the presence of nuclear deformation without violating symmetries. Results are presented for 44Ti, 45Ti, 46Ti, 46V, and 48Cr to assess how proton-neutron pair correlations emerge under different scenarios. We also study how the presence of a one-body spin-obit interaction affects the contribution of the various pairing modes.
Shell-model description of weakly bound and unbound nuclear states
International Nuclear Information System (INIS)
A consistent description of weakly bound and unbound nuclei requires an accurate description of the particle continuum properties when carrying out multiconfiguration mixing. This is the domain of the Gamow Shell Model (GSM) which is the multiconfigurational shell model in the complex k-plane formulated using a complete Berggren ensemble representing bound single-particle (s.p.) states, s.p. resonances, and non-resonant complex energy continuum states. We discuss the salient features of effective interactions in weakly bound systems and show selected applications of the GSM formalism to p-shell nuclei. Finally, a development of the new non-perturbative scheme based on Density Matrix Renormalization Group methods to select the most significant continuum configurations in GSM calculations is discussed shortly. (orig.)
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....
International Nuclear Information System (INIS)
Highlights: •We measured characteristic X-ray yields of thick W, Mo, Zr by 5–29 keV electrons. •Our measured data are in general in good agreement with the MC results with ∼10%. •Error of 10% of characteristic X-ray yields will produce errors of 2–7% for BIXS. -- Abstract: Inner-shell characteristic X-ray yields are one of the important ingredients in the β-ray induced X-ray spectrometry (BIXS) technique which can be used to perform tritium content and depth distribution analyses in plasma facing materials (PLMs) and other tritium-containing materials, such as W, Mo, Zr. In this paper, the measurements of K, L, M-shell X-ray yields Y(E) of pure thick W (Z = 74), Mo (Z = 42) and Zr (Z = 40) element targets produced by electron impact in the energy range of 5–29 keV are presented. The experimental data for Y(E) are compared with the corresponding predictions from Monte Carlo (MC) calculations using the general purpose MC code PENELOPE. In general, a good agreement is obtained between the experiment and the MC calculations for the variation of Y(E) with the impact energy both in shape and in magnitude with ∼10%. The effect of uncertainty of inner-shell characteristic X-ray yields on the BIXS technique is also discussed
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...
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.
Espel, Federico Puente
The main objective of this PhD research is to develop a high accuracy modeling tool using a Monte Carlo based coupled system. The presented research comprises the development of models to include the thermal-hydraulic feedback to the Monte Carlo method and speed-up mechanisms to accelerate the Monte Carlo criticality calculation. Presently, deterministic codes based on the diffusion approximation of the Boltzmann transport equation, coupled with channel-based (or sub-channel based) thermal-hydraulic codes, carry out the three-dimensional (3-D) reactor core calculations of the Light Water Reactors (LWRs). These deterministic codes utilize nuclear homogenized data (normally over large spatial zones, consisting of fuel assembly or parts of fuel assembly, and in the best case, over small spatial zones, consisting of pin cell), which is functionalized in terms of thermal-hydraulic feedback parameters (in the form of off-line pre-generated cross-section libraries). High accuracy modeling is required for advanced nuclear reactor core designs that present increased geometry complexity and material heterogeneity. Such high-fidelity methods take advantage of the recent progress in computation technology and coupled neutron transport solutions with thermal-hydraulic feedback models on pin or even on sub-pin level (in terms of spatial scale). The continuous energy Monte Carlo method is well suited for solving such core environments with the detailed representation of the complicated 3-D problem. The major advantages of the Monte Carlo method over the deterministic methods are the continuous energy treatment and the exact 3-D geometry modeling. However, the Monte Carlo method involves vast computational time. The interest in Monte Carlo methods has increased thanks to the improvements of the capabilities of high performance computers. Coupled Monte-Carlo calculations can serve as reference solutions for verifying high-fidelity coupled deterministic neutron transport methods
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...
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.
Noor, Ahmed K. (Editor); Belytschko, Ted (Editor); Simo, Juan C. (Editor)
1989-01-01
Topics presented include asymptotic analysis and computation for shells, the edge effects in the Reissner-Mindlin plate theory, nonlinear problems of geometrically exact shell theories, and developments in variational methods for high performance plate and shell elements. Also presented are an assumed strain solid element model for geometrically nonlinear shell analysis, shell finite elements with six degrees of freedom per node, hierarchic plate and shell models based on p-extension, and a simple shell element formulation for large-scale elastoplastic analysis. Also discussed are the assessment of computational models for multilayered composite cylinders, shell models for impact analysis, analysis of shell structures subjected to contact-impacts, and the application of shell theory to cardiac mechanics.
International Nuclear Information System (INIS)
Increasing use is being made of computer codes to predict the dynamic response of the containment of fast reactors following a hypothetical energy excursion. This paper reports on UK work to validate those aspects of the containment codes concerned with the prediction of the deformation of the primary vessel and other thin shell structures. The two containment codes ASTARTE and SEURBNUK are being developed in the UK and their general features and ability to reproduce experimental results have been reviewed elsewhere. Both codes have the basic capability for solving the time dependent flow of compressible fluids in two-dimensional axisymmetric geometry. ASTARTE uses a Langrangian finite difference formulation whereas SEURBNUK, under joint development by the UKAEA and JRC Ispra, uses an Eulerian approach. A structural analysis capability is also required and for thin tanks, eg the primary vessel, the deformation has a significant effect on the pressure field and must be computed simultaneously with the fluid motion. A thin shell model has therefore been incorporated into the codes to calculate the deformation of vessels either within the coolant or bounding it. The model assumes that the thickness of the shell is small compared with its characteristic length and that the normal stress through the shell can be neglected. Bending theory is incorporated by allowing the stresses to vary through the thickness. Material behaviour can be elasto-plastic; the von Mises yield criterion and Prandtl-Reuss flow rule are used in conjunction with the mechanical sub-layer model. Coupling of shell and fluid is achieved by different techniques in the two codes but in both it is implicit that there is free slip of fluid along the shell. (orig.)
Shell model tests of the interacting boson model description of nuclear collective motion
International Nuclear Information System (INIS)
The results of a large shell-model calculation of a pseudo-nucleus which displays striking behavior suggestive of rotational phenomena are presented. In these calculations, a specific and physically reasonable single-particle structure is given to the wave functions, and an explicit two-body residual interaction is used. The calculations show the coupling of key low-lying neutron and proton states of valence particles can lead to collective rotational features which appear to be more distinct and which extend to higher angular momenta as the number of particles increases and that those states which are rotational are dominated by states formed by coupling J = 0 and J = 2 two-particle states. Considerable supporting evidence is offered for the validity of the assumptions of the interacting boson model. 2 references
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 ...
A Monte Carlo Renormalization Group Approach to the Bak-Sneppen model
Mikeska, Bernhard
1996-01-01
A recent renormalization group approach to a modified Bak-Sneppen model is discussed. We propose a self-consistency condition for the blocking scheme to be essential for a successful RG-method applied to self-organized criticality. A new method realizing the RG-approach to the Bak-Sneppen model is presented. It is based on the Monte-Carlo importance sampling idea. The new technique performs much faster than the original proposal. Using this technique we cross-check and improve previous results.
Relaxational dynamics and precursor domains in the non-linear shell model
International Nuclear Information System (INIS)
The dynamics of a two dimensional shell model with double-well core-shell interaction is simulated by means of a molecular dynamics technique. Snapshots of the lattice displacement pattern reveal the presence of precursor order domains near the ferroelectric transition while the dynamical structure factor exhibits a quasielastic component in addition to the ferroelectric soft mode peak. On the other hand, the local dynamics of particles is characterized by two different time scales corresponding to the coexistence of inter and intra-well motion. All these features are in qualitative agreement with experimental observations in several ferroelectric materials. (author). 29 refs, 4 figs
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.
Light Nuclei in the Framework of the Symplectic No-core Shell Model
Draayer, Jerry P.; Dytrych, Tomas; Sviratcheva, Kristina D.; Bahri, Chairul; Vary, James P.
2007-01-01
A symplectic no-core shell model (Sp-NCSM) is constructed with the goal of extending the {\\it 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 {\\it ab-initio} NCSM with that of the $\\mathrm{Sp}(3,\\mathbb{R})\\supset\\mathrm{SU}(3)$ group-t...
Semiempirical Shell Model Tabulated Masses for Translead Elements with Magic Proton Number Z = 126
Liran, S.; Marinov, A.(Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria); Zeldes, N.
2001-01-01
We present two tables of calculated masses of translead nuclei, for 351 nuclei with N from 94 to 126 and Z from 82 to 100, and for 1969 nuclei with N from 126 to 184 and Z from 82 to 126. The tables are calculated from a semiempirical shell-model mass equation based on Z = 126 as a proton magic number which seems to be highly extrapolatable inside shell regions. Useful separation and decay energies are given as well. Some properties of the calculated masses and applications to superheavy elem...
The one-boson exchange potential and the shell-model of mass 18 nuclei
International Nuclear Information System (INIS)
A shell model calculation of spectra of mass 18 nuclei is performed using as nucleon-nucleon interaction the momentum space one-boson exchange potentials. The calculations were done using the Brueckuer reaction G-matrix bare matrix elements only and bare plus core polarization
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...
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
A diagonalization algorithm revisited and applied to the nuclear shell model
Bianco, D; Andreozzi, F; Lo Iudice, N.; Porrino, A.; Knapp, F
2011-01-01
Abstract An importance sampling iterative algorithm for diagonalizing large matrices is upgraded and adopted for large scale nuclear shell model calculations using a spin uncoupled basis. Its numerical implementation shows that the iterative procedure converges rapidly to the exact eigensolutions achieving an effective drastic cut of the sizes of the Hamiltonian matrix.
An Importance Sampling Algorithm for Diagonalizing the Nuclear Shell-Model Hamiltonian
International Nuclear Information System (INIS)
We have developed an iterative algorithm for generating exact eigensolutions of large matrices and endowed it with an importance sampling which allows for a reduction of the sizes of the matrices while keeping full control of the accuracy of the eigensolutions. We illustrate the potential of the method through its application to the nuclear shell-model eigenproblem
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.
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.
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.
Development of a Monte Carlo model for the Brainlab microMLC.
Belec, Jason; Patrocinio, Horacio; Verhaegen, Frank
2005-03-01
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. PMID:15798255
Development of a Monte Carlo model for the Brainlab microMLC
International Nuclear Information System (INIS)
Stereotactic radiosurgery with several static conformal beams shaped by a micro multileaf collimator (μMLC) 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 μMLC 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
Development of a Monte Carlo model for the Brainlab microMLC
Belec, Jason; Patrocinio, Horacio; Verhaegen, Frank
2005-03-01
Stereotactic radiosurgery with several static conformal beams shaped by a micro multileaf collimator (μMLC) 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 μMLC 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.
Development of a Monte Carlo model for the Brainlab microMLC
Energy Technology Data Exchange (ETDEWEB)
Belec, Jason; Patrocinio, Horacio; Verhaegen, Frank [Medical Physics Department, McGill University Health Centre, McGill University, Montreal General Hospital, 1650 Cedar Avenue, Montreal, Quebec, H3G1A4 (Canada)
2005-03-07
Stereotactic radiosurgery with several static conformal beams shaped by a micro multileaf collimator ({mu}MLC) 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 {mu}MLC 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.
Design and evaluation of a Monte Carlo based model of an orthovoltage treatment system
International Nuclear Information System (INIS)
The aim of this study was to develop a flexible framework of an orthovoltage treatment system capable of calculating and visualizing dose distributions in different phantoms and CT datasets. The framework provides a complete set of various filters, applicators and X-ray energies and therefore can be adapted to varying studies or be used for educational purposes. A dedicated user friendly graphical interface was developed allowing for easy setup of the simulation parameters and visualization of the results. For the Monte Carlo simulations the EGSnrc Monte Carlo code package was used. Building the geometry was accomplished with the help of the EGSnrc C++ class library. The deposited dose was calculated according to the KERMA approximation using the track-length estimator. The validation against measurements showed a good agreement within 4-5% deviation, down to depths of 20% of the depth dose maximum. Furthermore, to show its capabilities, the validated model was used to calculate the dose distribution on two CT datasets. Typical Monte Carlo calculation time for these simulations was about 10 minutes achieving an average statistical uncertainty of 2% on a standard PC. However, this calculation time depends strongly on the used CT dataset, tube potential, filter material/thickness and applicator size.
Design and evaluation of a Monte Carlo based model of an orthovoltage treatment system
Energy Technology Data Exchange (ETDEWEB)
Penchev, Petar; Maeder, Ulf; Fiebich, Martin [IMPS University of Applied Sciences, Giessen (Germany). Inst. of Medical Physics and Radiation Protection; Zink, Klemens [IMPS University of Applied Sciences, Giessen (Germany). Inst. of Medical Physics and Radiation Protection; University Hospital Marburg (Germany). Dept. of Radiotherapy and Oncology
2015-07-01
The aim of this study was to develop a flexible framework of an orthovoltage treatment system capable of calculating and visualizing dose distributions in different phantoms and CT datasets. The framework provides a complete set of various filters, applicators and X-ray energies and therefore can be adapted to varying studies or be used for educational purposes. A dedicated user friendly graphical interface was developed allowing for easy setup of the simulation parameters and visualization of the results. For the Monte Carlo simulations the EGSnrc Monte Carlo code package was used. Building the geometry was accomplished with the help of the EGSnrc C++ class library. The deposited dose was calculated according to the KERMA approximation using the track-length estimator. The validation against measurements showed a good agreement within 4-5% deviation, down to depths of 20% of the depth dose maximum. Furthermore, to show its capabilities, the validated model was used to calculate the dose distribution on two CT datasets. Typical Monte Carlo calculation time for these simulations was about 10 minutes achieving an average statistical uncertainty of 2% on a standard PC. However, this calculation time depends strongly on the used CT dataset, tube potential, filter material/thickness and applicator size.
Theoretical and experimental stress analyses of ORNL thin-shell cylinder-to-cylinder model 4
International Nuclear Information System (INIS)
The last in a series of four thin-shell cylinder-to-cylinder models was tested, and the experimentally determined elastic stress distributions were compared with theoretical predictions obtained from a thin-shell finite-element analysis. The models in the series are idealized thin-shell structures consisting of two circular cylindrical shells that intersect at right angles. There are no transitions, reinforcements, or fillets in the junction region. This series of model tests serves two basic purposes: (1) the experimental data provide design information directly applicable to nozzles in cylindrical vessels, and (2) the idealized models provide test results for use in developing and evaluating theoretical analyses applicable to nozzles in cylindrical vessels and to thin piping tees. The cylinder of model 4 had an outside diameter of 10 in., and the nozzle had an outside diameter of 1.29 in., giving a d0/D0 ratio of 0.129. The OD/thickness ratios were 50 and 20.2 for the cylinder and nozzle respectively. Thirteen separate loading cases were analyzed. For each loading condition one end of the cylinder was rigidly held. In addition to an internal pressure loading, three mutually perpendicular force components and three mutually perpendicular moment components were individually applied at the free end of the cylinder and at the end of the nozzle. The experimental stress distributions for each of the 13 loadings were obtained using 157 three-gage strain rosettes located on the inner and outer surfaces. Each of the 13 loading cases was also analyzed theoretically using a finite-element shell analysis developed at the University of California, Berkeley. The analysis used flat-plate elements and considered five degrees of freedom per node in the final assembled equations. The comparisons between theory and experiment show reasonably good agreement for this model. (U.S.)
Theoretical and experimental stress analyses of ORNL thin-shell cylinder-to-cylinder model 3
International Nuclear Information System (INIS)
The third in a series of four thin-shell cylinder-to-cylinder models was tested, and the experimentally determined elastic stress distributions were compared with theoretical predictions obtained from a thin-shell finite-element analysis. The models are idealized thin-shell structures consisting of two circular cylindrical shells that intersect at right angles. There are no transitions, reinforcements, or fillets in the junction region. This series of model tests serves two basic purposes: the experimental data provide design information directly applicable to nozzles in cylindrical vessels; and the idealized models provide test results for use in developing and evaluating theoretical analyses applicable to nozzles in cylindrical vessels and to thin piping tees. The cylinder of model 3 had a 10 in. OD and the nozzle had a 1.29 in. OD, giving a d0/D0 ratio of 0.129. The OD/thickness ratios for the cylinder and the nozzle were 50 and 7.68 respectively. Thirteen separate loading cases were analyzed. In each, one end of the cylinder was rigidly held. In addition to an internal pressure loading, three mutually perpendicular force components and three mutually perpendicular moment components were individually applied at the free end of the cylinder and at the end of the nozzle. The experimental stress distributions for all the loadings were obtained using 158 three-gage strain rosettes located on the inner and outer surfaces. The loading cases were also analyzed theoretically using a finite-element shell analysis developed at the University of California, Berkeley. The analysis used flat-plate elements and considered five degrees of freedom per node in the final assembled equations. The comparisons between theory and experiment show reasonably good agreement for this model. (U.S.)
Tuckwell, W.; Bezak, E.; Yeoh, E.; Marcu, L.
2008-09-01
A Monte Carlo tumour model has been developed to simulate tumour cell propagation for head and neck squamous cell carcinoma. The model aims to eventually provide a radiobiological tool for radiation oncology clinicians to plan patient treatment schedules based on properties of the individual tumour. The inclusion of an oxygen distribution amongst the tumour cells enables the model to incorporate hypoxia and other associated parameters, which affect tumour growth. The object oriented program FORTRAN 95 has been used to create the model algorithm, with Monte Carlo methods being employed to randomly assign many of the cell parameters from probability distributions. Hypoxia has been implemented through random assignment of partial oxygen pressure values to individual cells during tumour growth, based on in vivo Eppendorf probe experimental data. The accumulation of up to 10 million virtual tumour cells in 15 min of computer running time has been achieved. The stem cell percentage and the degree of hypoxia are the parameters which most influence the final tumour growth rate. For a tumour with a doubling time of 40 days, the final stem cell percentage is approximately 1% of the total cell population. The effect of hypoxia on the tumour growth rate is significant. Using a hypoxia induced cell quiescence limit which affects 50% of cells with and oxygen levels less than 1 mm Hg, the tumour doubling time increases to over 200 days and the time of tumour growth for a clinically detectable tumour (109 cells) increases from 3 to 8 years. A biologically plausible Monte Carlo model of hypoxic head and neck squamous cell carcinoma tumour growth has been developed for real time assessment of the effects of multiple biological parameters which impact upon the response of the individual patient to fractionated radiotherapy.
International Nuclear Information System (INIS)
A Monte Carlo tumour model has been developed to simulate tumour cell propagation for head and neck squamous cell carcinoma. The model aims to eventually provide a radiobiological tool for radiation oncology clinicians to plan patient treatment schedules based on properties of the individual tumour. The inclusion of an oxygen distribution amongst the tumour cells enables the model to incorporate hypoxia and other associated parameters, which affect tumour growth. The object oriented program FORTRAN 95 has been used to create the model algorithm, with Monte Carlo methods being employed to randomly assign many of the cell parameters from probability distributions. Hypoxia has been implemented through random assignment of partial oxygen pressure values to individual cells during tumour growth, based on in vivo Eppendorf probe experimental data. The accumulation of up to 10 million virtual tumour cells in 15 min of computer running time has been achieved. The stem cell percentage and the degree of hypoxia are the parameters which most influence the final tumour growth rate. For a tumour with a doubling time of 40 days, the final stem cell percentage is approximately 1% of the total cell population. The effect of hypoxia on the tumour growth rate is significant. Using a hypoxia induced cell quiescence limit which affects 50% of cells with and oxygen levels less than 1 mm Hg, the tumour doubling time increases to over 200 days and the time of tumour growth for a clinically detectable tumour (109 cells) increases from 3 to 8 years. A biologically plausible Monte Carlo model of hypoxic head and neck squamous cell carcinoma tumour growth has been developed for real time assessment of the effects of multiple biological parameters which impact upon the response of the individual patient to fractionated radiotherapy
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...
Anomalous Scaling from Controlled Closure in a Shell Model of Turbulence
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 she...
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.
Revisiting the monopole components of effective interactions for the shell model
Wang, X. B.; Dong, G. X.
2015-12-01
In this paper, we revisit the monopole components of effective interactions for the shell model. Without going through specific nuclei or shell gaps, universal roles of central, tensor, and spin-orbit forces can be proved, reflecting the intrinsic features of shell model effective interactions. For monopole matrix elements, even and odd channels of central force often have a canceling effect. However, for the contributions to the shell evolution, its even and odd channels could have both positive or negative contributions, enhancing the role of central force on the shell structure. Tensor force is generally weaker than central force. However, for the effect on shell evolutions, tensor force can dominate or play a competitive role. A different systematics has been discovered between T = 1 and 0 channels. For example, tensor force, well established in the T = 0 channel, becomes uncertain in the T = 1 channel. We calculate the properties of neutron-rich oxygen and calcium isotopes in order to study T = 1 channel interactions further. It is learned that the main improvements of empirical interactions are traced to the central force. For non-central forces, antisymmetric spin-orbit (ALS) force, originated from many-body perturbations or three-body force, could also play an explicit role. T = 1 tensor forces are less constrained so their effect can differ in different empirical interactions. The influence of tensor force may sometimes be canceled by many-body effects. For T = 0 channels of effective interactions, which is the main source of neutron-proton correlations, central and tensor forces are the leading components. For T = 1 channels, which can act between like-particles, the request for many-body correlations could be more demanding, so that the monopole anomaly of the T = 1 channel might be more serious.
Quantum spin models with long-range interactions and tunnelings: a quantum Monte Carlo study
Maik, Michał; Hauke, Philipp; Dutta, Omjyoti; Zakrzewski, Jakub; Lewenstein, Maciej
2012-11-01
We use a quantum Monte Carlo method to investigate various classes of two-dimensional spin models with long-range interactions at low temperatures. In particular, we study a dipolar XXZ model with U(1) symmetry that appears as a hard-core boson limit of an extended Hubbard model describing polarized dipolar atoms or molecules in an optical lattice. Tunneling, in such a model, is short-range, whereas density-density couplings decay with distance following a cubic power law. We also investigate an XXZ model with long-range couplings of all three spin components—such a model describes a system of ultracold ions in a lattice of microtraps. We describe an approximate phase diagram for such systems at zero and at finite temperature, and compare their properties. In particular, we compare the extent of crystalline, superfluid and supersolid phases. Our predictions apply directly to current experiments with mesoscopic numbers of polar molecules and trapped ions.
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.
Hobler, Gerhard; Bradley, R. Mark; Urbassek, Herbert M.
2016-05-01
Sigmund's model of spatially resolved sputtering is the underpinning of many models of nanoscale pattern formation induced by ion bombardment. It is based on three assumptions: (i) the number of sputtered atoms is proportional to the nuclear energy deposition (NED) near the surface, (ii) the NED distribution is independent of the orientation and shape of the solid surface and is identical to the one in an infinite medium, and (iii) the NED distribution in an infinite medium can be approximated by a Gaussian. We test the validity of these assumptions using Monte Carlo simulations of He, Ar, and Xe impacts on Si at energies of 2, 20, and 200 keV with incidence angles from perpendicular to grazing. We find that for the more commonly-employed beam parameters (Ar and Xe ions at 2 and 20 keV and nongrazing incidence), the Sigmund model's predictions are within a factor of 2 of the Monte Carlo results for the total sputter yield and the first two moments of the spatially resolved sputter yield. This is partly due to a compensation of errors introduced by assumptions (i) and (ii). The Sigmund model, however, does not describe the skewness of the spatially resolved sputter yield, which is almost always significant. The approximation is much poorer for He ions and/or high energies (200 keV). All three of Sigmund's assumptions break down at grazing incidence angles. In all cases, we discuss the origin of the deviations from Sigmund's model.
Monte Carlo Modelling of Single-Crystal Diffuse Scattering from Intermetallics
Directory of Open Access Journals (Sweden)
Darren J. Goossens
2016-02-01
Full Text Available Single-crystal diffuse scattering (SCDS reveals detailed structural insights into materials. In particular, it is sensitive to two-body correlations, whereas traditional Bragg peak-based methods are sensitive to single-body correlations. This means that diffuse scattering is sensitive to ordering that persists for just a few unit cells: nanoscale order, sometimes referred to as “local structure”, which is often crucial for understanding a material and its function. Metals and alloys were early candidates for SCDS studies because of the availability of large single crystals. While great progress has been made in areas like ab initio modelling and molecular dynamics, a place remains for Monte Carlo modelling of model crystals because of its ability to model very large systems; important when correlations are relatively long (though still finite in range. This paper briefly outlines, and gives examples of, some Monte Carlo methods appropriate for the modelling of SCDS from metallic compounds, and considers data collection as well as analysis. Even if the interest in the material is driven primarily by magnetism or transport behaviour, an understanding of the local structure can underpin such studies and give an indication of nanoscale inhomogeneity.
Monte Carlo simulation of an arc therapy treatment by means of a PC distribution model
International Nuclear Information System (INIS)
It would be always desirable to have an independent assessment of a planning system. Monte Carlo (MC) offers an accurate way of checking dose distribution in non homogeneous volumes. Nevertheless, its main drawback is the long processing times needed. A distribution model to simulate arc-therapy treatments with Monte Carlo techniques has been developed. This model divides the individual tasks with a physical sense. In this way, not only the CPU time is substantially reduced but a detailed analysis can be achieved. A distribution program modifies the input parameters in the code to send a different task to each processor. This model has been installed on a PC network without any resident software. This model works independently of the operating system pre-installed. The PC acting as a server exports the required operating system (Linux), the MC code and the input data, as well as it stores all the results. Some very complex radiosurgery treatments simulated using this model leads a CPU time about one hour. (orig.)
The Physical Models and Statistical Procedures Used in the RACER Monte Carlo Code
International Nuclear Information System (INIS)
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
International Nuclear Information System (INIS)
Experiments were made on a setup consisting of a large-scale twin-assembly model of the primary circuit of an integral reactor and of a model of a containment shell which is a means for confining the outflow of coolant from the reactor. The large-scale model of an AST-500 reactor has vertical dimensions close to the actual dimensions and similar coefficients of hydraulic resistance and volume ratios of the principal elements the circuit with natural circulation. The model of the containment shell is a vertical cylindrical vessel with a size of 426 x 12 mm, a height of 9.78 m, and a volume of 1.24 m3. The volume scale of the reactor model and of the model of the containment shell is 1:170. The elements of the latter model are made from steel 20. The models of the reactor and of the containment shell are joined through two pipelines with a size of 57 x 3.5 mm and shut-off valves with a diameter of 50 mm mounted thereon. A total of 70 experiments were made to simulate leakage of the primary circuit of the integrated reactor and the outflow of coolant into the containment shell. The authors have provided detailed information on the large-scale model, have described the experimental conditions, and have reported on the main results of their study of the development of an accident involving the loss of coolant in the reactor-containment shell system. The present article reports on a study of the thermohydraulic processes and the gas distribution in the containment shell. Since the designs of the model and of the actual containment shell of the AST-500 reactor are not identical, the authors assume that the results reported can be used in appropriate computer programs describing the processes which occur in containment vessels of atomic power stations (containment shells, protective shells, sealed assemblies)
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.
International Nuclear Information System (INIS)
A hybrid model is developed for describing the effects of oxygen addition to argon glow discharges. The species taken into account in the model include Ar atoms in the ground state and the metastable level, O2 gas molecules in the ground state and two metastable levels, O atoms in the ground state and one metastable level, O3 molecules, Ar+, O+, O2+ and O- ions, as well as the electrons. The hybrid model consists of a Monte Carlo model for electrons and fluid models for the other plasma species. In total, 87 different reactions between the various plasma species are taken into account. Calculation results include the species densities and the importance of their production and loss processes, as well as the dissociation degree of oxygen. The effect of different O2 additions on these calculation results, as well as on the sputtering rates, is discussed.
International Nuclear Information System (INIS)
After an accidental release of radionuclides to the inhabited environment the external gamma irradiation from deposited radioactivity contributes significantly to the radiation exposure of the population for extended periods. For evaluating this exposure pathway, three main model requirements are needed: (i) to calculate the air kerma value per photon emitted per unit source area, based on Monte Carlo (MC) simulations; (ii) to describe the distribution and dynamics of radionuclides on the diverse urban surfaces; and (iii) to combine all these elements in a relevant urban model to calculate the resulting doses according to the actual scenario. This paper provides an overview about the different approaches to calculate photon transport in urban areas and about several dose calculation codes published. Two types of Monte Carlo simulations are presented using the global and the local approaches of photon transport. Moreover, two different philosophies of the dose calculation, the 'location factor method' and a combination of relative contamination of surfaces with air kerma values are described. The main features of six codes (ECOSYS, EDEM2M, EXPURT, PARATI, TEMAS, URGENT) are highlighted together with a short model-model features intercomparison
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.
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
Fission yield calculation using toy model based on Monte Carlo simulation
International Nuclear Information System (INIS)
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 (Rc), mean of left curve (μL) and mean of right curve (μR), deviation of left curve (σL) and deviation of right curve (σR). 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
Experiments with encapsulation of Monte Carlo simulation results in machine learning models
Lal Shrestha, Durga; Kayastha, Nagendra; Solomatine, Dimitri
2010-05-01
Uncertainty analysis techniques based on Monte Carlo (MC) simulation have been applied in hydrological sciences successfully in the last decades. They allow for quantification of the model output uncertainty resulting from uncertain model parameters, input data or model structure. They are very flexible, conceptually simple and straightforward, but become impractical in real time applications for complex models when there is little time to perform the uncertainty analysis because of the large number of model runs required. A number of new methods were developed to improve the efficiency of Monte Carlo methods and still these methods require considerable number of model runs in both offline and operational mode to produce reliable and meaningful uncertainty estimation. This paper presents experiments with machine learning techniques used to encapsulate the results of MC runs. A version of MC simulation method, the generalised likelihood uncertain estimation (GLUE) method, is first used to assess the parameter uncertainty of the conceptual rainfall-runoff model HBV. Then the three machines learning methods, namely artificial neural networks, M5 model trees and locally weighted regression methods are trained to encapsulate the uncertainty estimated by the GLUE method using the historical input data. The trained machine learning models are then employed to predict the uncertainty of the model output for the new input data. This method has been applied to two contrasting catchments: the Brue catchment (United Kingdom) and the Bagamati catchment (Nepal). The experimental results demonstrate that the machine learning methods are reasonably accurate in approximating the uncertainty estimated by GLUE. The great advantage of the proposed method is its efficiency to reproduce the MC based simulation results; it can thus be an effective tool to assess the uncertainty of flood forecasting in real time.
Monte Carlo Modeling of Cascade Gamma Rays in 86Y PET imaging: Preliminary results
Zhu, Xuping; El Fakhri, Georges
2009-01-01
86Y is a PET agent that could be used as an ideal surrogate to allow personalized dosimetry in 90Y radionuclide therapy. However, 86Y also emits cascade gamma rays. We have developed a Monte Carlo program based on SimSET to model cascade gamma rays in PET imaging. The new simulation was validated with the GATE simulation package. Agreements within 15% were found in spatial resolution, apparent scatter fraction (ratio of coincidences outside peak regions in line source sinograms), singles and ...
Hybrid parallel programming models for AMR neutron Monte-Carlo transport
International Nuclear Information System (INIS)
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 peta-flop supercomputer Tera100. (authors)
Exact modeling of the torus geometry with Monte Carlo transport code
International Nuclear Information System (INIS)
It is valuable to model torus geometry exactry for the neutronics design of fusion reactor in order to assess neutronics characteristics such as tritium breeding ratio, heat generation rate, etc, near the plasma. Monte Carlo code MORSE-GG which plays important role in the radiation streaming calculation of fusion reactors had been able to deal with the geometry composed of second order surfaces. The MORSE-GG program is modified to be able to deal with torus geometry which has fourth order surface by solving biquadratic equations, hoping that MORSE-GG code becomes more effective for the neutronics calculation of the Tokamak fusion reactor. (author)
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.
Time-implicit Monte-Carlo collision algorithm for particle-in-cell electron transport models
International Nuclear Information System (INIS)
A time-implicit Monte-Carlo collision algorithm has been developed to allow particle-in-cell electron transport models to be applied to arbitrarily collisional systems. The algorithm is formulated for electrons moving in response to electric and magnetic accelerations and subject to collisional drag and scattering due to a background plasma. The correct fluid or streaming transport results are obtained in the respective limits of strongly- or weakly-collisional systems, and reasonable behavior is produced even for time steps greatly exceeding the magnetic-gyration and collisional-scattering times
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.
Four shells atomic model to computer the counting efficiency of electron-capture nuclides
International Nuclear Information System (INIS)
The present paper develops a four-shells atomic model in order to obtain the efficiency of detection in liquid scintillation courting, Mathematical expressions are given to calculate the probabilities of the 229 different atomic rearrangements so as the corresponding effective energies. This new model will permit the study of the influence of the different parameters upon the counting efficiency for nuclides of high atomic number. (Author) 7 refs
An extended empirical model for L- and M-shell ionizations of atoms
Talukder, M R
2011-01-01
An extension of the analytical model of Talukder et al (Int. J. Mass Spectrom. 269 (2008) 118) is proposed to estimate electron impact single L- and M-shell ionization cross sections of atoms with incident energy from threshold to ultra-relativistic range. Comparisons are made with other theoretical calculations. It is found that this model agrees well with the experimental data and quantum calculations.
Multistep shell model description of spin-aligned neutron–proton pair coupling
International Nuclear Information System (INIS)
The recently proposed spin-aligned neutron–proton pair coupling scheme is studied within a non-orthogonal basis in term of the multistep shell model. This allows us to identify simultaneously the roles played by other configurations such as the normal pairing term. The model is applied to four-, six- and eight-hole N=Z nuclei below the core 100Sn.
Guérin, Bastein; Fakhri, Georges El
2008-01-01
We have developed and validated a realistic simulation of random coincidences, pixelated block detectors, light sharing among crystal elements and dead-time in 2D and 3D positron emission tomography (PET) imaging based on the SimSET Monte Carlo simulation software. Our simulation was validated by comparison to a Monte Carlo transport code widely used for PET modeling, GATE, and to measurements made on a PET scanner.
Unfiltered Monte Carlo-based tungsten anode spectral model from 20 to 640 kV
Hernandez, A. M.; Boone, John M.
2014-03-01
A Monte Carlo-based tungsten anode spectral model, conceptually similar to the previously-developed TASMIP model, was developed. This new model provides essentially unfiltered x-ray spectra with better energy resolution and significantly extends the range of tube potentials for available spectra. MCNPX was used to simulate x-ray spectra as a function of tube potential for a conventional x-ray tube configuration with several anode compositions. Thirty five x-ray spectra were simulated and used as the basis of interpolating a complete set of tungsten x-ray spectra (at 1 kV intervals) from 20 to 640 kV. Additionally, Rh and Mo anode x-ray spectra were simulated from 20 to 60 kV. Cubic splines were used to construct piecewise polynomials that interpolate the photon fluence per energy bin as a function of tube potential for each anode material. The tungsten anode spectral model using interpolating cubic splines (TASMICS) generates minimally-filtered (0.8 mm Be) x-ray spectra from 20 to 640 kV with 1 keV energy bins. The rhodium and molybdenum anode spectral models (RASMICS and MASMICS, respectively) generate minimally-filtered x-ray spectra from 20 to 60 kV with 1 keV energy bins. TASMICS spectra showed no statistically significant differences when compared with the empirical TASMIP model, the semi-empirical Birch and Marshall model, and a Monte Carlo spectrum reported in AAPM TG 195. The RASMICS and MASMICS spectra showed no statistically significant differences when compared with their counterpart RASMIP and MASMIP models. Spectra from the TASMICS, MASMICS, and RASMICS models are available in spreadsheet format for interested users.
Application of a Monte Carlo method for modeling debris flow run-out
Luna, B. Quan; Cepeda, J.; Stumpf, A.; van Westen, C. J.; Malet, J. P.; van Asch, T. W. J.
2012-04-01
A probabilistic framework based on a Monte Carlo method for the modeling of debris flow hazards is presented. The framework is based on a dynamic model, which is combined with an explicit representation of the different parameter uncertainties. The probability distribution of these parameters is determined from an extensive collected database with information of back calibrated past events from different authors. The uncertainty in these inputs can be simulated and used to increase confidence in certain extreme run-out distances. In the Monte Carlo procedure; the input parameters of the numerical models simulating propagation and stoppage of debris flows are randomly selected. Model runs are performed using the randomly generated input values. This allows estimating the probability density function of the output variables characterizing the destructive power of debris flow (for instance depth, velocities and impact pressures) at any point along the path. To demonstrate the implementation of this method, a continuum two-dimensional dynamic simulation model that solves the conservation equations of mass and momentum was applied (MassMov2D). This general methodology facilitates the consistent combination of physical models with the available observations. The probabilistic model presented can be considered as a framework to accommodate any existing one or two dimensional dynamic model. The resulting probabilistic spatial model can serve as a basis for hazard mapping and spatial risk assessment. The outlined procedure provides a useful way for experts to produce hazard or risk maps for the typical case where historical records are either poorly documented or even completely lacking, as well as to derive confidence limits on the proposed zoning.
SCOUT: a fast Monte-Carlo modeling tool of scintillation camera output
Hunter, William C. J.; Barrett, Harrison H.; Muzi, John P.; McDougald, Wendy; MacDonald, Lawrence R.; Miyaoka, Robert S.; Lewellen, Thomas K.
2013-06-01
We have developed a Monte-Carlo photon-tracking and readout simulator called SCOUT to study the stochastic behavior of signals output from a simplified rectangular scintillation-camera design. SCOUT models the salient processes affecting signal generation, transport, and readout of a scintillation camera. In this work, we compare output signal statistics from SCOUT to experimental results for both a discrete and a monolithic camera. We also benchmark the speed of this simulation tool and compare it to existing simulation tools. We find this modeling tool to be relatively fast and predictive of experimental results. Depending on the modeled camera geometry, we found SCOUT to be 4 to 140 times faster than other modeling tools.
Electric conduction in semiconductors: a pedagogical model based on the Monte Carlo method
International Nuclear Information System (INIS)
We present a pedagogic approach aimed at modelling electric conduction in semiconductors in order to describe and explain some macroscopic properties, such as the characteristic behaviour of resistance as a function of temperature. A simple model of the band structure is adopted for the generation of electron-hole pairs as well as for the carrier transport in moderate electric fields. The semiconductor behaviour is described by substituting the traditional statistical approach (requiring a deep mathematical background) with microscopic models, based on the Monte Carlo method, in which simple rules applied to microscopic particles and quasi-particles determine the macroscopic properties. We compare measurements of electric properties of matter with 'virtual experiments' built by using some models where the physical concepts can be presented at different formalization levels
Coagulation of nanoparticles in reverse micellar systems: a Monte Carlo model.
Jain, Ravi; Shukla, Diwakar; Mehra, Anurag
2005-11-22
The process of formation of nanoparticles obtained by mixing two micellized, aqueous solutions has been simulated using the Monte Carlo technique. The model includes the phenomena of finite nucleation, growth via intermicellar exchange, and coagulation of nanoparticles after their formation. Using the model, an exploratory study has been conducted to analyze whether the coagulation of nanoparticles is the reason for the formation of nanoparticles whose sizes are comparable to the size of the reverse micelles. The model explains the possible mechanism of coagulation of semiconductor nanoparticles formed within reverse micelles and its effect on the evolution of their size with time. The model is predictive in nature, and the simulation results compare well with those observed experimentally. PMID:16285836
International Nuclear Information System (INIS)
The thesis proceeded in the context of dating by thermoluminescence. This method requires laboratory measurements of the natural radioactivity. For that purpose, we have been using a germanium spectrometer. To refine the calibration of this one, we modelled it by using a Monte-Carlo computer code: Geant4. We developed a geometrical model which takes into account the presence of inactive zones and zones of poor charge-collection within the germanium crystal. The parameters of the model were adjusted by comparison with experimental results obtained with a source of 137Cs. It appeared that the form of the inactive zones is less simple than is presented in the specialized literature. This model was widened to the case of a more complex source, with cascade effect and angular correlations between photons: the 60Co. Lastly, applied to extended sources, it gave correct results and allowed us to validate the simulation of matrix effect. (author)
SCOUT: a fast Monte-Carlo modeling tool of scintillation camera output
International Nuclear Information System (INIS)
We have developed a Monte-Carlo photon-tracking and readout simulator called SCOUT to study the stochastic behavior of signals output from a simplified rectangular scintillation-camera design. SCOUT models the salient processes affecting signal generation, transport, and readout of a scintillation camera. In this work, we compare output signal statistics from SCOUT to experimental results for both a discrete and a monolithic camera. We also benchmark the speed of this simulation tool and compare it to existing simulation tools. We find this modeling tool to be relatively fast and predictive of experimental results. Depending on the modeled camera geometry, we found SCOUT to be 4 to 140 times faster than other modeling tools. (paper)
Iterative optimisation of Monte Carlo detector models using measurements and simulations
Marzocchi, O.; Leone, D.
2015-04-01
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.
US Fish and Wildlife Service, Department of the Interior — This SeaLevel Affecting Marshes Model SLAMM report presents a model for projecting the effects of sealevel rise on coastal marshes and related habitats on Shell...
Almonacid, S; Simpson, R; Teixeira, A
2007-11-01
Egg and egg preparations are important vehicles for Salmonella enteritidis infections. The influence of time-temperature becomes important when the presence of this organism is found in commercial shell eggs. A computer-aided mathematical model was validated to estimate surface and interior temperature of shell eggs under variable ambient and refrigerated storage temperature. A risk assessment of S. enteritidis based on the use of this model, coupled with S. enteritidis kinetics, has already been reported in a companion paper published earlier in JFS. The model considered the actual geometry and composition of shell eggs and was solved by numerical techniques (finite differences and finite elements). Parameters of interest such as local (h) and global (U) heat transfer coefficient, thermal conductivity, and apparent volumetric specific heat were estimated by an inverse procedure from experimental temperature measurement. In order to assess the error in predicting microbial population growth, theoretical and experimental temperatures were applied to a S. enteritidis growth model taken from the literature. Errors between values of microbial population growth calculated from model predicted compared with experimentally measured temperatures were satisfactorily low: 1.1% and 0.8% for the finite difference and finite element model, respectively. PMID:18034720
Research on Reliability Modelling Method of Machining Center Based on Monte Carlo Simulation
Directory of Open Access Journals (Sweden)
Chuanhai Chen
2013-03-01
Full Text Available The aim of this study is to get the reliability of series system and analyze the reliability of machining center. So a modified method of reliability modelling based on Monte Carlo simulation for series system is proposed. The reliability function, which is built by the classical statistics method based on the assumption that machine tools were repaired as good as new, may be biased in the real case. The reliability functions of subsystems are established respectively and then the reliability model is built according to the reliability block diagram. Then the fitting reliability function of machine tools is established using the failure data of sample generated by Monte Carlo simulation, whose inverse reliability function is solved by the linearization technique based on radial basis function. Finally, an example of the machining center is presented using the proposed method to show its potential application. The analysis results show that the proposed method can provide an accurate reliability model compared with the conventional method.
Modelling the magnetic properties of thin metallic films using Monte-Carlo simulation
International Nuclear Information System (INIS)
In this thesis, Monte Carlo studies of the static critical behaviour of metallic magnetic thin-films are presented. The studies make use of a finite size scaling method designed for anisotropic shaped structures. This finite size scaling method is based on an assumption that a single correlation length is required to describe a thin-film close to its critical temperature and has led to the derivation of formulae from which thin-film critical temperatures and exponents can be extracted. Monte Carlo simulations for Ising thin-films are carried out in order to verify the validity of the assumption and hence the formulae. Various algorithms and seed numbers for a random number generator are tested to minimise statistical errors. These studies also show the evolution from 2D to 3D-like behaviours as the films' thicknesses are increased. Critical temperatures and exponents are investigated for simple cubic (SC), body centred cubic (BCC) and face centred cubic (FCC) thin-films. Our Ising 2D and 3D results are also shown to give good agreement with previous Monte Carlo work. We then move on to study in a more realistic model of a magnetic thin-film in which the 'exchange parameters' and anisotropic constants are extracted from 'first principles' electronic structure calculations, and used in Monte Carlo simulations of classical Heisenberg model. We model thin-films of Fe grown on a W(001) substrate which have been subjected to extensive experimental investigation. In line with the Mermin-Wagner theorem, we find a slow convergence for the magnetisation with the system size L in 2D which is consistent with expected absence of finite magnetisation in the finite temperatures in the thermodynamic limit. From the thin-film results in finite size systems, the magnetisation in the surface layers is weaker than those in the inner layers and a similar trend is found for the susceptibility. Slow magnetisation convergence with size is also observed for all thin-films (thickness
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
Fitting complex population models by combining particle filters with Markov chain Monte Carlo.
Knape, Jonas; de Valpine, Perry
2012-02-01
We show how a recent framework combining Markov chain Monte Carlo (MCMC) with particle filters (PFMCMC) may be used to estimate population state-space models. With the purpose of utilizing the strengths of each method, PFMCMC explores hidden states by particle filters, while process and observation parameters are estimated using an MCMC algorithm. PFMCMC is exemplified by analyzing time series data on a red kangaroo (Macropus rufus) population in New South Wales, Australia, using MCMC over model parameters based on an adaptive Metropolis-Hastings algorithm. We fit three population models to these data; a density-dependent logistic diffusion model with environmental variance, an unregulated stochastic exponential growth model, and a random-walk model. Bayes factors and posterior model probabilities show that there is little support for density dependence and that the random-walk model is the most parsimonious model. The particle filter Metropolis-Hastings algorithm is a brute-force method that may be used to fit a range of complex population models. Implementation is straightforward and less involved than standard MCMC for many models, and marginal densities for model selection can be obtained with little additional effort. The cost is mainly computational, resulting in long running times that may be improved by parallelizing the algorithm. PMID:22624307
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...
The derivation of Particle Monte Carlo methods for plasma modeling from transport equations
Longo, Savino
2008-01-01
We analyze here in some detail, the derivation of the Particle and Monte Carlo methods of plasma simulation, such as Particle in Cell (PIC), Monte Carlo (MC) and Particle in Cell / Monte Carlo (PIC/MC) from formal manipulation of transport equations.
Effects of human model configuration in Monte Carlo calculations on organ doses from CT examinations
International Nuclear Information System (INIS)
A new dosimetry system, WAZA-ARI, is being developed to estimate radiation dose from Computed Tomography (CT) examination in Japan. The dose estimation in WAZA-ARI utilizes organ dose data, which have been derived by Monte Carlo calculations using Particle and Heavy Ion Transport code System, PHITS. A Japanese adult male phantom, JM phantom, is adapted as a reference human model in the calculations, because the physique and inner organ masses agree well with the average values for Japanese adult males. On the other hand, each patient has arbitrary physical characteristics. Thus, the effects of human body configuration on organ doses are studied by applying another Japanese male model and the reference phantom by the International Commission on Radiological Protection (ICRP) to PHITS. In addition, this paper describes computation conditions for the three human models, which are constructed in the format of voxel phantom with different resolutions. (author)
A Monte-Carlo model of ionic transport across a solid interface
International Nuclear Information System (INIS)
An improved Monte-Carlo model of ionic transport across a solid interface in two-dimensional triangular lattice is presented. The new features of the model are: (i) more-realistic form of the microscopic potential of the ion-ion interaction, and (ii) accounting of the mutual ion interactions up to second nearest neighbors. This way it is possible to simulate more flexible the ionic transport across the real interface between a fast-ion conducting glass and the intercalate in the cathode of a Lithium thin-film battery. Numerical results computed with this model are presented by emphasizing on the influence of the internal interface on the ion distribution, the site energies and the open circuit voltage. (author). 15 refs, 5 figs
Anagnostopoulos, Konstantinos N; Nishimura, Jun
2015-01-01
The IIB matrix model has been proposed as a non-perturbative definition of superstring theory. In this work, we study the Euclidean version of this model in which extra dimensions can be dynamically compactified if a scenario of spontaneously breaking the SO(10) rotational symmetry is realized. Monte Carlo calculations of the Euclidean IIB matrix model suffer from a very strong complex action problem due to the large fluctuations of the complex phase of the Pfaffian which appears after integrating out the fermions. We employ the factorization method in order to achieve effective sampling. We report on preliminary results that can be compared with previous studies of the rotational symmetry breakdown using the Gaussian expansion method.
Anagnostopoulos, K.; Azuma, T.; Nishimura, J.
The IKKT or IIB matrix model has been postulated to be a non perturbative definition of superstring theory. It has the attractive feature that spacetime is dynamically generated, which makes possible the scenario of dynamical compactification of extra dimensions, which in the Euclidean model manifests by spontaneously breaking the SO(10) rotational invariance (SSB). In this work we study using Monte Carlo simulations the 6 dimensional version of the Euclidean IIB matrix model. Simulations are found to be plagued by a strong complex action problem and the factorization method is used for effective sampling and computing expectation values of the extent of spacetime in various dimensions. Our results are consistent with calculations using the Gaussian Expansion method which predict SSB to SO(3) symmetric vacua, a finite universal extent of the compactified dimensions and finite spacetime volume.
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...... from the sample will have a finite spatial coherence that cannot be accounted for by MC simulation. To estimate this intensity distribution adequately we have developed a novel method for modeling a focused Gaussian beam in MC simulation. This approach is valid for a softly as well as for a strongly...... 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...
Application of Monte Carlo method in modelling physical and physico-chemical processes
International Nuclear Information System (INIS)
The seminar was held on September 9 and 10, 1982 at the Faculty of Nuclear Science and Technical Engineering of the Czech Technical University in Prague. The participants heard 11 papers of which 7 were inputed in INIS. The papers dealt with the use of the Monte Carlo method for modelling the transport and scattering of gamma radiation in layers of materials, the application of low-energy gamma radiation for the determination of secondary X radiation flux, the determination of self-absorption corrections for a 4π chamber, modelling the response function of a scintillation detector and the optimization of geometrical configuration in measuring material density using backscattered gamma radiation. The possibility was studied of optimizing modelling with regard to computer time, and the participants were informed of comouterized nuclear data libraries. (M.D.)
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.
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.
Monte-Carlo modeling of exchange bias properties in amorphous magnets
International Nuclear Information System (INIS)
We explore the effect of interfacial disorder on exchange bias properties of a soft ferromagnet with a negligible intrinsic anisotropy exchange coupled to a hard amorphous magnet with a random magnetic anisotropy, based on an extensive Monte Carlo simulation. The interfacial disorder is introduced by using a '±J’' model. As compared to the conventionally crystalline ferromagnet/antiferromagnet bilayers, pronounced values and sign inversion in the exchange field are obtained at low temperature after cooling even under a weak field. However, the coercivity in the amorphous system not only shows smaller values, but also exhibits an opposite trend. Different from the ordered crystalline systems, the intrinsic properties of the Harris–Plischke–Zuckermann Hamiltonian rather than the domain structure determine the coercive fields and the shapes of hysteresis loops with different temperatures and cooling fields in the random magnetic anisotropy model, and hence the exchange bias. This theoretical work opens a new avenue for magnetism of the exchange bias and for its applications. - Highlights: • Hard amorphous magnets with random magnetic anisotropy are studied. • Exchange bias may be pronounced and positive after cooling under weak fields. • A reduced coercivity exhibiting a peak behavior is observed in amorphous magnets. • An extensive Monte Carlo simulation with a constrained acceptance rate is used
Monte-Carlo modeling of exchange bias properties in amorphous magnets
Energy Technology Data Exchange (ETDEWEB)
Hu, Yong; Du, An, E-mail: duanneu@126.com
2015-11-01
We explore the effect of interfacial disorder on exchange bias properties of a soft ferromagnet with a negligible intrinsic anisotropy exchange coupled to a hard amorphous magnet with a random magnetic anisotropy, based on an extensive Monte Carlo simulation. The interfacial disorder is introduced by using a '±J’' model. As compared to the conventionally crystalline ferromagnet/antiferromagnet bilayers, pronounced values and sign inversion in the exchange field are obtained at low temperature after cooling even under a weak field. However, the coercivity in the amorphous system not only shows smaller values, but also exhibits an opposite trend. Different from the ordered crystalline systems, the intrinsic properties of the Harris–Plischke–Zuckermann Hamiltonian rather than the domain structure determine the coercive fields and the shapes of hysteresis loops with different temperatures and cooling fields in the random magnetic anisotropy model, and hence the exchange bias. This theoretical work opens a new avenue for magnetism of the exchange bias and for its applications. - Highlights: • Hard amorphous magnets with random magnetic anisotropy are studied. • Exchange bias may be pronounced and positive after cooling under weak fields. • A reduced coercivity exhibiting a peak behavior is observed in amorphous magnets. • An extensive Monte Carlo simulation with a constrained acceptance rate is used.
Jedrychowski, M.; Bacroix, B.; Salman, O. U.; Tarasiuk, J.; Wronski, S.
2015-08-01
The work focuses on the influence of moderate plastic deformation on subsequent partial recrystallization of hexagonal zirconium (Zr702). In the considered case, strain induced boundary migration (SIBM) is assumed to be the dominating recrystallization mechanism. This hypothesis is analyzed and tested in detail using experimental EBSD-OIM data and Monte Carlo computer simulations. An EBSD investigation is performed on zirconium samples, which were channel-die compressed in two perpendicular directions: normal direction (ND) and transverse direction (TD) of the initial material sheet. The maximal applied strain was below 17%. Then, samples were briefly annealed in order to achieve a partly recrystallized state. Obtained EBSD data were analyzed in terms of texture evolution associated with a microstructural characterization, including: kernel average misorientation (KAM), grain orientation spread (GOS), twinning, grain size distributions, description of grain boundary regions. In parallel, Monte Carlo Potts model combined with experimental microstructures was employed in order to verify two main recrystallization scenarios: SIBM driven growth from deformed sub-grains and classical growth of recrystallization nuclei. It is concluded that simulation results provided by the SIBM model are in a good agreement with experimental data in terms of texture as well as microstructural evolution.
Multi-shell model of ion-induced nucleic acid condensation
Energy Technology Data Exchange (ETDEWEB)
Tolokh, Igor S.; Drozdetski, Aleksander; Pollack, Lois; Baker, Nathan A.; Onufriev, Alexey
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”.
A geometrical model for the Monte Carlo simulation of the TrueBeam linac
International Nuclear Information System (INIS)
Monte Carlo simulation of linear accelerators (linacs) depends on the accurate geometrical description of the linac head. The geometry of the Varian TrueBeam linac is not available to researchers. Instead, the company distributes phase-space files of the flattening-filter-free (FFF) beams tallied at a plane located just upstream of the jaws. Yet, Monte Carlo simulations based on third-party tallied phase spaces are subject to limitations. In this work, an experimentally based geometry developed for the simulation of the FFF beams of the Varian TrueBeam linac is presented. The Monte Carlo geometrical model of the TrueBeam linac uses information provided by Varian that reveals large similarities between the TrueBeam machine and the Clinac 2100 downstream of the jaws. Thus, the upper part of the TrueBeam linac was modeled by introducing modifications to the Varian Clinac 2100 linac geometry. The most important of these modifications is the replacement of the standard flattening filters by ad hoc thin filters. These filters 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 performed with a diode detector for radiation fields ranging from 3 × 3 to 40 × 40 cm2 at depths of maximum dose of 5 and 10 cm. Indicators of agreement between the experimental data and the simulation results obtained with the proposed geometrical model were the dose differences, the root-mean-square error and the gamma index. The same comparisons were performed for dose profiles obtained from Monte Carlo simulations using the phase-space files distributed by Varian for the TrueBeam linac as the sources of particles. Results of comparisons show a good agreement of the dose for the ansatz geometry similar to that obtained for the simulations with the TrueBeam phase-space files for all fields and depths considered, except for the
Using a Monte Carlo model to predict dosimetric properties of small radiotherapy photon fields
International Nuclear Information System (INIS)
Accurate characterization of small-field dosimetry requires measurements to be made with precisely aligned specialized detectors and is thus time consuming and error prone. This work explores measurement differences between detectors by using a Monte Carlo model matched to large-field data to predict properties of smaller fields. Measurements made with a variety of detectors have been compared with calculated results to assess their validity and explore reasons for differences. Unshielded diodes are expected to produce some of the most useful data, as their small sensitive cross sections give good resolution whilst their energy dependence is shown to vary little with depth in a 15 MV linac beam. Their response is shown to be constant with field size over the range 1-10 cm, with a correction of 3% needed for a field size of 0.5 cm. BEAMnrc has been used to create a 15 MV beam model, matched to dosimetric data for square fields larger than 3 cm, and producing small-field profiles and percentage depth doses (PDDs) that agree well with unshielded diode data for field sizes down to 0.5 cm. For fields sizes of 1.5 cm and above, little detector-to-detector variation exists in measured output factors, however for a 0.5 cm field a relative spread of 18% is seen between output factors measured with different detectors--values measured with the diamond and pinpoint detectors lying below that of the unshielded diode, with the shielded diode value being higher. Relative to the corrected unshielded diode measurement, the Monte Carlo modeled output factor is 4.5% low, a discrepancy that is probably due to the focal spot fluence profile and source occlusion modeling. The large-field Monte Carlo model can, therefore, currently be used to predict small-field profiles and PDDs measured with an unshielded diode. However, determination of output factors for the smallest fields requires a more detailed model of focal spot fluence and source occlusion.
Full modelling of the MOSAIC animal PET system based on the GATE Monte Carlo simulation code
International Nuclear Information System (INIS)
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(TM) 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(TM) 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
Experimental Study and Monte Carlo Modeling of Calcium Borosilicate Glasses Leaching
International Nuclear Information System (INIS)
During aqueous alteration of glass an alteration layer appears on the glass surface. The properties of this alteration layer are of great importance for understanding and predicting the long-term behavior of high-level radioactive waste glasses. Numerical modeling can be very useful for understanding the impact of the glass composition on its aqueous reactivity and long-term properties but it is quite difficult to model these complex glasses. In order to identify the effect of the calcium content on glass alteration, seven oxide glass compositions (57SiO2 17B2O3 (22-x)Na2OxCaO 4ZrO2; 0 < x < 11) were investigated and a Monte Carlo model was developed to describe their leaching behavior. The specimens were altered at constant temperature (T = 90 deg. C) at a glass-surface-area-to-solution-volume (SA/V) ratio of 15 cm-1 in a buffered solution (pH 9.2). Under these conditions all the variations observed in the leaching behavior are attributable to composition effects. Increasing the calcium content in the glass appears to be responsible for a sharp drop in the final leached boron fraction. In parallel with this experimental work, a Monte Carlo model was developed to investigate the effect of calcium content on the leaching behavior especially on the initial stage of alteration. Monte Carlo simulations performed with this model are in good agreement with the experimental results. The dependence of the alteration rate on the calcium content can be described by a quadratic function: fitting the simulated points gives a minimum alteration rate at about 7.7 mol% calcium. This value is consistent with the figure of 8.2 mol% obtained from the experimental work. The model was also used to investigate the role of calcium in the glass structure and it pointed out that calcium act preferentially as a network modifier rather than a charge compensator in this kind of glasses. (authors)
Convex-based void filling method for CAD-based Monte Carlo geometry modeling
International Nuclear Information System (INIS)
Highlights: • We present a new void filling method named CVF for CAD based MC geometry modeling. • We describe convex based void description based and quality-based space subdivision. • The results showed improvements provided by CVF for both modeling and MC calculation efficiency. - Abstract: CAD based automatic geometry modeling tools have been widely applied to generate Monte Carlo (MC) calculation geometry for complex systems according to CAD models. Automatic void filling is one of the main functions in the CAD based MC geometry modeling tools, because the void space between parts in CAD models is traditionally not modeled while MC codes such as MCNP need all the problem space to be described. A dedicated void filling method, named Convex-based Void Filling (CVF), is proposed in this study for efficient void filling and concise void descriptions. The method subdivides all the problem space into disjointed regions using Quality based Subdivision (QS) and describes the void space in each region with complementary descriptions of the convex volumes intersecting with that region. It has been implemented in SuperMC/MCAM, the Multiple-Physics Coupling Analysis Modeling Program, and tested on International Thermonuclear Experimental Reactor (ITER) Alite model. The results showed that the new method reduced both automatic modeling time and MC calculation time
Nuclear binding energies: Global collective structure and local shell-model correlations
International Nuclear Information System (INIS)
Nuclear binding energies and two-neutron separation energies are analysed starting from the liquid-drop model and the nuclear shell model in order to describe the global trends of the above observables. We subsequently concentrate on the Interacting Boson Model (IBM) and discuss a new method in order to provide a consistent description of both, ground-state and excited-state properties. We address the artefacts that appear when crossing mid-shell using the IBM formulation and perform detailed numerical calculations for nuclei situated in the 50-82 shell. We also concentrate on local deviations from the above global trends in binding energy and two-neutron separation energies that appear in the neutron-deficient Pb region. We address possible effects on the binding energy, caused by mixing of low-lying 0+ intruder states into the ground state, using configuration mixing in the IBM framework. We also study ground-state properties using a macroscopic-microscopic model. Detailed comparisons with recent experimental data in the Pb region are amply discussed
Accuracy of dynamic calculations using shell models under local impulse loading
International Nuclear Information System (INIS)
Depending on soil conditions and load cases in dynamic calculations of nuclear power plants today more exact mathematical models may be used. For axisymmetric structures like reactor buildings, steel containments, circular tanks or coolant towers mathematical idealisations are used which especially deal with axisymmetric shell models. The calculations for these structures mentioned above, in the last 10 years, were generally carried out by applying specialised and qualified FE-programs. In order to qualify the results obtained using axisymmetric shell models as well the approved computer program MESY (Schrader 1976, 1978) several comparisons between computation and measurements were performed. As an example for these comparisons, impulse loadings, such as aircraft impact, applied by means of a pendulum on the HDR reactor will be shown. The analytical results were obtained prior to the general tests based on a loading function measured in a preliminary test step. In these calculations 11 harmonics were considered in the frequency range up to 80 Hz. Typical results will be shown and discussed, particularly the distribution of the maximum acceleration in the meridional and circumferential direction of the building. The analytical results for the structural response obtained using axisymmetric shell models conform satisfactorily to test results, especially in the area of load introduction in both (meridian and circumferential) directions. (orig.)
Shell Models of RMHD Turbulence and the Heating of Solar Coronal Loops
Buchlin, E.; Velli, Marco C.
2007-01-01
A simplified nonlinear numerical model for the development of incompressible magnetohydrodynamics in the presence of a strong magnetic field B|| and stratification, nicknamed 'Shell-Atm,' is presented. In planes orthogonal to the mean field, the nonlinear incompressible dynamics is replaced by two-dimensional shell models for the complex variables u and b, allowing one to reach large Reynolds numbers while at the same time carrying out sufficiently long integrations to obtain good statistics at moderate computational cost. The shell models of different planes are coupled by Alfve'n waves propagating along B||. The model may be applied to open or closed magnetic field configurations where the axial field dominates and the plasma pressure is low; here we apply it to the specific case of a magnetic loop of the solar corona heated by means of turbulence driven by photospheric motions, and we use statistics for its analysis. The Alfven waves interact nonlinearly and form turbulent spectra in the directions perpendicular and, through propagation, also parallel to the mean field. A heating function is obtained and shown to be intermittent; the average heating is consistent with values required for sustaining a hot corona and is proportional to the aspect ratio of the loop to the -1.5 power, and haracteristic properties of heating events are distributed as power laws. Crosscorrelations show a delay of dissipation compared with energy content.
Generalization of α-Decay Cluster-Model to Nuclei Near Spherical and Deformed Shell Closures
Institute of Scientific and Technical Information of China (English)
XUChang; RENZhong-Zhou
2004-01-01
The cluster model of a-decay is extended to the regions around doubly magic spherical nucleus 208Pb and around deformed shell closure 270Hs, respectively. The effects of spherical shell closures (N=126 and Z=82) on α-decay are investigated by introducing an N-dependent α-preformation factor and a Z-dependent one inspired by a microscopic model. Good agreement between the theoretical a-decay half-lives and the measured ones is obtained for the spherical nuclei near the doubly magic nucleus 208Pb, where the nuclear shell effect is included in the expression of α-preformation factor. The cluster model is also generalized for the decay of deformed nuclei. The branching ratios of α-decays from the ground state of a parent nucleus to the ground state (0+) of its deformed daughter nucleus and to the first excited state (2+) are calculated in the framework of the cluster model. The results indicate that a measurement of α spectroscopy is a feasible method to extract the information of nuclear deformation of superheavy nuclei around the deformed nucleus 270Hs.
Generalization of α-Decay Cluster-Model to Nuclei Near Spherical and Deformed Shell Closures
Institute of Scientific and Technical Information of China (English)
XU Chang; REN Zhong-Zhou
2004-01-01
The cluster model of α-decay is extended to the regions around doubly magic spherical nucleus 208pb and around deformed shell closure 270Hs, respectively. The effects of spherical shell closures (N = 126 and Z = 82) on α-decay are investigated by introducing an N-dependent α-preformation factor and a Z-dependent one inspired by a microscopic model. Good agreement between the theoretical α-decay half-lives and the measured ones is obtained for the spherical nuclei near the doubly magic nucleus 208 Pb, where the nuclear shell effect is included in the expression of α-preformation factor. The cluster model is also generalized for the decay of deformed nuclei. The branching ratios of a-decays from the ground state of a parent nucleus to the ground state (0+) of its deformed daughter nucleus and to the first excited state (2+) are .calculated in the framework of the cluster model. The results indicate that a measurement of c spectroscopy is a feasible method to extract the information of nuclear deformation of superheavy nuclei around the deformed nucleus 270 Hs.
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.
Applicability of the extended P+QQ model in the upper part of the f7/2 shell
International Nuclear Information System (INIS)
The P0+P2+QQ force has been completely revised, and in its new form, it is capable of describing nuclear structure of N approx. = Z nuclei well. This paper investigates the applicability of the extended P+QQ model in the upper part of the f7/2 shell using shell model calculations. It is shown that the extended P+QQ model can account for the collective bands of most 52 ≤ A ≤ 56 nuclei as well as the lower part of the f7/2 shell. However, considerable discrepancy with experiment exists for 52Fe, which suggests the limit of the applicability of this force. (author)
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.
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.
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 ...
Structure of liposome encapsulating proteins characterized by X-ray scattering and shell-modeling
Energy Technology Data Exchange (ETDEWEB)
Hirai, Mitsuhiro, E-mail: mhirai@gunma-u.ac.jp; Kimura, Ryota; Takeuchi, Kazuki; Hagiwara, Yoshihiko [Gunma University, 4-2 Aramaki, Maebashi, Gunma 371-8510 (Japan); Kawai-Hirai, Rika [Gunma University, 3-39-15 Shouwa, Maebashi 371-8512 (Japan); Ohta, Noboru [JASRI, 1-1-1 Kuoto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan); Igarashi, Noriyuki; Shimuzu, Nobutaka [KEK-PF, 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)
2013-11-01
Wide-angle X-ray scattering data using a third-generation synchrotron radiation source are presented. Lipid liposomes are promising drug delivery systems because they have superior curative effects owing to their high adaptability to a living body. Lipid liposomes encapsulating proteins were constructed and the structures examined using synchrotron radiation small- and wide-angle X-ray scattering (SR-SWAXS). The liposomes were prepared by a sequential combination of natural swelling, ultrasonic dispersion, freeze-throw, extrusion and spin-filtration. The liposomes were composed of acidic glycosphingolipid (ganglioside), cholesterol and phospholipids. By using shell-modeling methods, the asymmetric bilayer structure of the liposome and the encapsulation efficiency of proteins were determined. As well as other analytical techniques, SR-SWAXS and shell-modeling methods are shown to be a powerful tool for characterizing in situ structures of lipid liposomes as an important candidate of drug delivery systems.
Study of nickel nuclei by (p,d) and (p,t) reactions. Shell model interpretation
International Nuclear Information System (INIS)
The experimental techniques employed at the Nuclear Science Institute (Grenoble) and at Michigan State University are described. The development of the transition amplitude calculation of the one-or two-nucleon transfer reactions is described first, after which the principle of shell model calculations is outlined. The choices of configuration space and two-body interactions are discussed. The DWBA method of analysis is studied in more detail. The effects of different approximations and the influence of the parameters are examined. Special attention is paid to the j-dependence of the form of the angular distributions, on effect not explained in the standard DWBA framework. The results are analysed and a large section is devoted to a comparative study of the experimental results obtained and those from other nuclear reactions. The spectroscopic data obtained are compared with the results of shell model calculations
Matrix diagonalization algorithm and its applicability to the nuclear shell model
International Nuclear Information System (INIS)
An importance-sampling iterative algorithm for diagonalizing shell model Hamiltonian matrices is reviewed and implemented in a spin uncoupled basis. Shell model spaces of dimensions up to N 9 are considered. The analysis shows that about 10% of the basis states are enough to bring the eigenvalues to convergence. This fraction of states, however, is insufficient to lead to convergence of the transition strengths, thereby limiting the applicability of the method to not too large spaces. In its domain of validity, the method yields a large number of eigensolutions and can be usefully adopted for rather complete studies of low-energy spectroscopy. This is done here for 132,134Xe isotopes. The calculation yields spectra and electromagnetic responses in fairly good agreement with the available experimental data and unveils the properties of the low-energy states of these isotopes, including their proton-neutron symmetry.
On Spectral Laws of 2D-Turbulence in Shell Models
Frick, P; Frick, Peter; Aurell, Erik
1993-01-01
We consider a class of shell models of 2D-turbulence. They conserve inertially the analogues of energy and enstrophy, two quadratic forms in the shell amplitudes. Inertially conserving two quadratic integrals leads to two spectral ranges. We study in detail the one characterized by a forward cascade of enstrophy and spectrum close to Kraichnan's $k^{-3}$--law. In an inertial range over more than 15 octaves, the spectrum falls off as $k^{-3.05\\pm 0.01}$, with the same slope in all models. We identify a ``spurious'' intermittency effect, in that the energy spectrum over a rather wide interval adjoing the viscous cut-off, is well approximated by a power-law with fall-off significantly steeper than $k^{-3}$.
Effective Field Theory and the Gamow Shell Model: The 6He Halo Nucleus
Rotureau, J
2012-01-01
We combine Halo/Cluster Effective Field Theory (H/CEFT) and the Gamow Shell Model (GSM) to describe the $0^+$ ground state of $\\rm{^6He}$ as a three-body halo system. We use two-body interactions for the neutron-alpha particle and two-neutron pairs obtained from H/CEFT at leading order, with parameters determined from scattering in the p$_{3/2}$ and s$_0$ channels, respectively. The three-body dynamics of the system is solved using the GSM formalism, where the continuum states are incorporated in the shell model valence space. We find that in the absence of three-body forces the system collapses, since the binding energy of the ground state diverges as cutoffs are increased. We show that addition at leading order of a three-body force with a single parameter is sufficient for proper renormalization and to fix the binding energy to its experimental value.
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. PMID:20365864
Modeling of thin structures in eddy current testing with shell elements
Ospina, A.; Santandrea, L.; Le Bihan, Y.; Marchand, C.
2010-11-01
The modeling and design of eddy currents sensors for non-destructive testing applications, generally, requires numerical methods. Among these methods, the finite element method is one of the most used. Indeed, it presents a great capability to treat a large variety of configurations. However, in the study of eddy current testing problems, the existence of structures that have a geometrical dimension smaller than the others (thin air gaps, coatings...) will lead to difficulties related to the meshing process. The introduction of particular elements such as shell elements allows to simplify the modeling of these problems. In this paper, the shell elements are used in two different 2D axisymmetric formulations, the electric formulation a* and the magnetic formulation t-ϕ in order to simulate the behaviour of the electromagnetic fields. The results obtained with the two formulations are compared with analytical solutions.
Structure of liposome encapsulating proteins characterized by X-ray scattering and shell-modeling
International Nuclear Information System (INIS)
Wide-angle X-ray scattering data using a third-generation synchrotron radiation source are presented. Lipid liposomes are promising drug delivery systems because they have superior curative effects owing to their high adaptability to a living body. Lipid liposomes encapsulating proteins were constructed and the structures examined using synchrotron radiation small- and wide-angle X-ray scattering (SR-SWAXS). The liposomes were prepared by a sequential combination of natural swelling, ultrasonic dispersion, freeze-throw, extrusion and spin-filtration. The liposomes were composed of acidic glycosphingolipid (ganglioside), cholesterol and phospholipids. By using shell-modeling methods, the asymmetric bilayer structure of the liposome and the encapsulation efficiency of proteins were determined. As well as other analytical techniques, SR-SWAXS and shell-modeling methods are shown to be a powerful tool for characterizing in situ structures of lipid liposomes as an important candidate of drug delivery systems
Stochastic shell models driven by a multiplicative fractional Brownian-motion
Bessaih, Hakima; Garrido-Atienza, María J.; Schmalfuss, Björn
2016-04-01
We prove existence and uniqueness of the solution of a stochastic shell-model. The equation is driven by an infinite dimensional fractional Brownian-motion with Hurst-parameter H ∈(1 / 2 , 1) , and contains a non-trivial coefficient in front of the noise which satisfies special regularity conditions. The appearing stochastic integrals are defined in a fractional sense. First, we prove the existence and uniqueness of variational solutions to approximating equations driven by piecewise linear continuous noise, for which we are able to derive important uniform estimates in some functional spaces. Then, thanks to a compactness argument and these estimates, we prove that these variational solutions converge to a limit solution, which turns out to be the unique pathwise mild solution associated to the shell-model with fractional noise as driving process.
Microscopic shell-model description of an exotic nucleus ^{16}C
Fujii, S; Mizusaki, T; Otsuka, T; Sebe, T
2007-01-01
The structure of neutron-rich carbon isotopes ^{14, 16, 18}C is described by introducing a new microscopic method of the no-core shell-model type. The model space is composed of the 0s, 0p, 1s0d, and 1p0f shells. The effective interaction is microscopically derived from the CD-Bonn potential and the Coulomb force through a unitary transformation. Calculated low-lying energy levels of ^{16}C agree well with the experiment. The B(E2;2_{1}^{+} \\to 0_{1}^{+}) value is calculated with the bare charges. The anomalously hindered B(E2) value for ^{16}C, measured recently, is reproduced.
Calibration and validation of a Monte Carlo model for PGNAA of chlorine in soil
International Nuclear Information System (INIS)
A prompt gamma-ray neutron activation analysis (PGNAA) system was used to calibrate and validate a Monte Carlo model as a proof of principle for the quantification of chlorine in soil. First, the response of an n-type HPGe detector to point sources of 60Co and 152Eu was determined experimentally and used to calibrate an MCNP4a model of the detector. The refined MCNP4a detector model can predict the absolute peak detection efficiency within 12% in the energy range of 120-1400 keV. Second, a PGNAA system consisting of a light-water moderated 252Cf (1.06 μg) neutron source, and the shielded and collimated HPGe detector was used to collect prompt gamma-ray spectra from Savannah River Site (SRS) soil spiked with chlorine. The spectra were used to calculate the minimum detectable concentration (MDC) of chlorine and the prompt gamma-ray detection probability. Using the 252Cf based PGNAA system, the MDC for Cl in the SRS soil is 4400 μg/g for an 1800-second irradiation based on the analysis of the 6110 keV prompt gamma-ray. MCNP4a was used to predict the PGNAA detection probability, which was accomplished by modeling the neutron and gamma-ray transport components separately. In the energy range of 788 to 6110 keV, the MCNP4a predictions of the prompt gamma-ray detection probability were generally within 60% of the experimental value, thus validating the Monte Carlo model. (author)
Energy Technology Data Exchange (ETDEWEB)
Thomas, M.S. (Royal Military Coll. of Canada, Kingston, Ontario); Gruber, B. (Technische Univ. Clausthal, Clausthal-Zellerfeld (Germany, F.R.). Inst. fuer Theoretische Physik)
1982-01-01
In this article symmetry chains for the atomic shell model are investigated which lead from the group SO(8l+-5) to the subgroup SOsub(L)(3). The tail group SOsub(L)(3) corresponds to total orbital angular momentum. Along these chains total orbital angular momentum L is a good quantum number, but not total spin S. Total orbital angular momentum can be considered as being made up of four quasi angular momenta.
Rayleigh-Taylor finger instability mixing in hydrodynamic shell convection models
Mocak, Miroslav; Mueller, Ewald
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 mea...
Spectral statistics of rare-earth nuclei: Investigation of shell model configuration effect
Sabri, H
2015-01-01
The spectral statistics of even-even rare-earth nuclei are investigated by using all the available empirical data for Ba, Ce, Nd, Sm, Gd, Dy, Er, Yb and Hf isotopes. The Berry- Robnik distribution and Maximum Likelihood estimation technique are used for analyses. An obvious deviation from GOE is observed for considered nuclei and there are some suggestions about the effect due to mass, deformation parameter and shell model configurations.
An upgraded version of an importance sampling algorithm for large scale shell model calculations
Energy Technology Data Exchange (ETDEWEB)
Bianco, D; Andreozzi, F; Lo Iudice, N; Porrino, A [Universita di Napoli Federico II, Dipartimento Scienze Fisiche, Monte S. Angelo, via Cintia, 80126 Napoli (Italy); S, Dimitrova, E-mail: loiudice@na.infn.i [Institute of Nuclear Research and Nuclear Energy, Sofia (Bulgaria)
2010-01-01
An importance sampling iterative algorithm, developed few years ago, for generating exact eigensolutions of large matrices is upgraded so as to allow large scale shell model calculations in the uncoupled m-scheme. By exploiting the sparsity properties of the Hamiltonian matrix and projecting out effectively the good angular momentum, the new importance sampling allows to reduce drastically the sizes of the matrices while keeping full control of the accuracy of the eigensolutions. Illustrative numerical examples are presented.
Plattenburg, Joseph; Dreyer, Jason T.; Singh, Rajendra
2016-06-01
This paper proposes a new analytical model for a thin cylindrical shell that utilizes a homogeneous cardboard liner to increase modal damping. Such cardboard liners are frequently used as noise and vibration control devices for cylindrical shell-like structures in automotive drive shafts. However, most prior studies on such lined structures have only investigated the associated damping mechanisms in an empirical manner. Only finite element models and experimental methods have been previously used for characterization, whereas no analytical studies have addressed sliding friction interaction at the shell-liner interface. The proposed theory, as an extension of a prior experimental study, uses the Rayleigh-Ritz method and incorporates material structural damping along with frequency-dependent viscous and Coulomb interfacial damping formulations for the shell-liner interaction. Experimental validation of the proposed model, using a thin cylindrical shell with three different cardboard liner thicknesses, is provided to validate the new model, and to characterize the damping parameters. Finally, the model is used to investigate the effect of the liner and the damping parameters on the modal attenuation of the shell vibration, in particular for the higher-order coupled shell modes.
Monte Carlo study of Lefschetz thimble structure in one-dimensional Thirring model at finite density
Fujii, Hirotsugu; Kikukawa, Yoshio
2015-01-01
We consider the one-dimensional massive Thirring model formulated on the lattice with staggered fermions and an auxiliary compact vector (link) field, which is exactly solvable and shows a phase transition with increasing the chemical potential of fermion number: the crossover at a finite temperature and the first order transition at zero temperature. We complexify its path-integration on Lefschetz thimbles and examine its phase transition by hybrid Monte Carlo simulations on the single dominant thimble. We observe a discrepancy between the numerical and exact results in the crossover region for small inverse coupling $\\beta$ and/or large lattice size $L$, while they are in good agreement at the lower and higher density regions. We also observe that the discrepancy persists in the continuum limit keeping the temperature finite and it becomes more significant toward the low-temperature limit. This numerical result is consistent with our analytical study of the model's thimble structure. And these results imply...
Banks, Bruce A.; Stueber, Thomas J.; Norris, Mary Jo
1998-01-01
A Monte Carlo computational model has been developed which simulates atomic oxygen attack of protected polymers at defect sites in the protective coatings. The parameters defining how atomic oxygen interacts with polymers and protective coatings as well as the scattering processes which occur have been optimized to replicate experimental results observed from protected polyimide Kapton on the Long Duration Exposure Facility (LDEF) mission. Computational prediction of atomic oxygen undercutting at defect sites in protective coatings for various arrival energies was investigated. The atomic oxygen undercutting energy dependence predictions enable one to predict mass loss that would occur in low Earth orbit, based on lower energy ground laboratory atomic oxygen beam systems. Results of computational model prediction of undercut cavity size as a function of energy and defect size will be presented to provide insight into expected in-space mass loss of protected polymers with protective coating defects based on lower energy ground laboratory testing.
Atucha-2 PHWR Monte Carlo MCNP5 and KENO-VI models development and application
International Nuclear Information System (INIS)
The geometrical complexity and the peculiarities of Atucha-2 PHWR require the adoption of advanced Monte Carlo codes for performing realistic neutronic simulations. Core models of Atucha-2 PHWR were developed using both MCNP5 and KENOVI codes. The developed models were applied for calculating reactor criticality states at beginning of life, reactor cell constants and control rods volumes. The last two applications were relevant for performing successive three dimensional neutron kinetic analyses since it was necessary to correctly evaluate the effect of each oblique control rod in each cell discretizing the reactor. These corrective factors were then applied to the cell cross sections calculated by the two dimensional deterministic lattice physics code HELIOS. (authors)
Monte Carlo simulation of local correlation and cluster formation in model fcc binary alloys
International Nuclear Information System (INIS)
Through the simulation with the Monte Carlo method is carried out the atomistic description of structure in a model fcc binary alloys A - B, which present at low-temperature trends to ordering. We use the ABV model of the alloy within the pair interaction approach with nearest neighbors and constant ordering energy. The dynamic was introduced through a vacancy which exchanges places with the atoms of nearest neighbors. The simulation was made on a fcc lattice with 256, 2048, 16,384 and 62,500 sites, using periodic boundary conditions to avoid edge effects. It was determined the probability of formation of different atomic clusters A13 - mBm (m = 0, 1, 2, ...13) consisting of 13 atoms as a function of the concentration and temperature, as well as the first short-range order parameters of Warren-Cowley. We found that in some regions of temperature and concentration is observed compositional and thermal polymorphism of clusters. (author)
Monte Carlo simulation of atomic aggregates formation in model bcc binary alloys. Preliminary report
International Nuclear Information System (INIS)
By means of the Monte Carlo simulation an atomistic description of the structure of model bcc binary alloys was made. We used ABV model of the alloy where the approach of pair interaction to first neighbours with constant ordering energy is assumed. The dynamics was introduced by means of a vacancy that interchanges of place with nearest neighbouring atoms. The simulations were made in a bcc lattice with 128, 1024, 8192 and 16000 sites, applying periodic boundary conditions to avoid edge effects. We calculate the formation probabilities of different atomic aggregate A9-m Bm (m = 0, 1, 2,... 9) as function of concentration of the components and the temperature. In some regions of temperature and concentration, compositional and thermal polymorphism of aggregates is observed. (author)
Šolc, J.; Kovář, P.; Dryák, P.
2016-03-01
A Monte Carlo (MC) model of a mechanically-cooled High Purity Germanium detection system IDM-200-V™ manufactured by ORTEC® was created, optimized and validated within the scope of the Joint Research Project ENV57 ``Metrology for radiological early warning networks in Europe''. The validation was performed for a planar source homogeneously distributed on a filter placed on top of the detector end cap and for point sources positioned farther from the detector by comparing simulated full-energy peak (FEP) detection efficiencies with the ones measured with two or three different pieces of the IDM detector. True coincidence summing correction factors were applied to the measured FEP efficiencies. Relative differences of FEP efficiencies laid within 8% that is fully satisfactory for the intended use of the detectors as instruments for airborne radioactivity measurement in field-stations. The validated MC model of the IDM-200-V™ detector is now available for further MC calculations planned in the ENV57 project.
Measurement and Monte Carlo modeling of the spatial response of scintillation screens
International Nuclear Information System (INIS)
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 simulation based inverse propagation method for stochastic model updating
Bao, Nuo; Wang, Chunjie
2015-08-01
This paper presents an efficient stochastic model updating method based on statistical theory. Significant parameters have been selected implementing the F-test evaluation and design of experiments, and then the incomplete fourth-order polynomial response surface model (RSM) has been developed. Exploiting of the RSM combined with Monte Carlo simulation (MCS), reduces the calculation amount and the rapid random sampling becomes possible. The inverse uncertainty propagation is given by the equally weighted sum of mean and covariance matrix objective functions. The mean and covariance of parameters are estimated synchronously by minimizing the weighted objective function through hybrid of particle-swarm and Nelder-Mead simplex optimization method, thus the better correlation between simulation and test is achieved. Numerical examples of a three degree-of-freedom mass-spring system under different conditions and GARTEUR assembly structure validated the feasibility and effectiveness of the proposed method.
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.
Samejima, Masaki; Akiyoshi, Masanori; Mitsukuni, Koshichiro; Komoda, Norihisa
We propose a business scenario evaluation method using qualitative and quantitative hybrid model. In order to evaluate business factors with qualitative causal relations, we introduce statistical values based on propagation and combination of effects of business factors by Monte Carlo simulation. In propagating an effect, we divide a range of each factor by landmarks and decide an effect to a destination node based on the divided ranges. In combining effects, we decide an effect of each arc using contribution degree and sum all effects. Through applied results to practical models, it is confirmed that there are no differences between results obtained by quantitative relations and results obtained by the proposed method at the risk rate of 5%.
Zhao, L; Cluggish, B; Kim, J S; Pardo, R; Vondrasek, R
2010-02-01
A Monte Carlo charge breeding code (MCBC) is being developed by FAR-TECH, Inc. to model the capture and charge breeding of 1+ ion beam in an electron cyclotron resonance ion source (ECRIS) device. The ECRIS plasma is simulated using the generalized ECRIS model which has two choices of boundary settings, free boundary condition and Bohm condition. The charge state distribution of the extracted beam ions is calculated by solving the steady state ion continuity equations where the profiles of the captured ions are used as source terms. MCBC simulations of the charge breeding of Rb+ showed good agreement with recent charge breeding experiments at Argonne National Laboratory (ANL). MCBC correctly predicted the peak of highly charged ion state outputs under free boundary condition and similar charge state distribution width but a lower peak charge state under the Bohm condition. The comparisons between the simulation results and ANL experimental measurements are presented and discussed. PMID:20192325
A Monte Carlo model for determination of binary diffusion coefficients in gases
Panarese, A.; Bruno, D.; Colonna, G.; Diomede, P.; Laricchiuta, A.; Longo, S.; Capitelli, M.
2011-06-01
A Monte Carlo method has been developed for the calculation of binary diffusion coefficients in gas mixtures. The method is based on the stochastic solution of the linear Boltzmann equation obtained for the transport of one component in a thermal bath of the second one. Anisotropic scattering is included by calculating the classical deflection angle in binary collisions under isotropic potential. Model results are compared to accurate solutions of the Chapman-Enskog equation in the first and higher orders. We have selected two different cases, H 2 in H 2 and O in O 2, assuming rigid spheres or using a model phenomenological potential. Diffusion coefficients, calculated in the proposed approach, are found in close agreement with Chapman-Enskog results in all the cases considered, the deviations being reduced using higher order approximations.