Detecting shock waves in cosmological smoothed particle hydrodynamics simulations
Pfrommer, C; Ensslin, T A; Jubelgas, M; Pfrommer, Christoph; Springel, Volker; Ensslin, Torsten A.; Jubelgas, Martin
2006-01-01
We develop a formalism for the identification and accurate estimation of the strength of structure formation shocks during cosmological smoothed particle hydrodynamics simulations. Shocks not only play a decisive role for the thermalization of gas in virialising structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. Our formalism is applicable both to ordinary non-relativistic thermal gas, and to plasmas composed of CRs and thermal gas. To this end, we derive an analytical solution to the one-dimensional Riemann shock tube problem for a composite plasma of CRs and thermal gas. We apply our methods to study the properties of structure formation shocks in high-resolution hydrodynamic simulations of the LCDM model. We find that most of the energy is dissipated in weak internal shocks with Mach numbers M~2 which are predominantly central flow shocks or merger shock waves traversing halo centres. Collapsed cosmological structures are surrounded by external ...
Testing Subhalo Abundance Matching in Cosmological Smoothed Particle Hydrodynamics Simulations
Simha, Vimal; Dave, Romeel; Fardal, Mark; Katz, Neal; Oppenheimer, Benjamin D
2010-01-01
Subhalo abundance matching (SHAM) is a technique for populating simulated dark matter distributions with galaxies, assuming a monotonic relation between a galaxy's stellar mass or luminosity and the mass of its parent dark matter halo or subhalo. We examine the accuracy of SHAM in two cosmological SPH simulations, one of which includes momentum-driven winds. The SPH simulations indeed show a nearly monotonic relation between stellar mass and halo mass provided that, for satellite galaxies, we use the mass of the subhalo at the epoch when it became a satellite. In each simulation, the median relation for central and satellite galaxies is nearly identical, though a somewhat larger fraction of satellites are outliers. SHAM-assigned masses (at z=0-2), luminosities (R-band at z=0), or star formation rates (at z=2) have a 68% scatter of 0.09-0.15 dex relative to the true simulation values. When we apply SHAM to the subhalo population of collisionless N-body simulation with the same initial conditions as the SPH run...
Cosmology and particle physics
Turner, Michael S.
1988-01-01
The interplay between cosmology and elementary particle physics is discussed. The standard cosmology is reviewed, concentrating on primordial nucleosynthesis and discussing how the standard cosmology has been used to place constraints on the properties of various particles. Baryogenesis is discussed, showing how a scenario in which the B-, C-, and CP-violating interactions in GUTs provide a dynamical explanation for the predominance of matter over antimatter and for the present baryon-to-photon ratio. It is shown how the very early dynamical evolution of a very weakly coupled scalar field which is initially displaced from the minimum of its potential may explain a handful of very fundamental cosmological facts which are not explained by the standard cosmology.
Cosmological Reflection of Particle Symmetry
Maxim Khlopov
2016-01-01
The standard model involves particle symmetry and the mechanism of its breaking. Modern cosmology is based on inflationary models with baryosynthesis and dark matter/energy, which involves physics beyond the standard model. Studies of the physical basis of modern cosmology combine direct searches for new physics at accelerators with its indirect non-accelerator probes, in which cosmological consequences of particle models play an important role. The cosmological reflection of particle symmetr...
Cosmological parameter estimation using Particle Swarm Optimization
Prasad, J.; Souradeep, T.
2014-03-01
Constraining parameters of a theoretical model from observational data is an important exercise in cosmology. There are many theoretically motivated models, which demand greater number of cosmological parameters than the standard model of cosmology uses, and make the problem of parameter estimation challenging. It is a common practice to employ Bayesian formalism for parameter estimation for which, in general, likelihood surface is probed. For the standard cosmological model with six parameters, likelihood surface is quite smooth and does not have local maxima, and sampling based methods like Markov Chain Monte Carlo (MCMC) method are quite successful. However, when there are a large number of parameters or the likelihood surface is not smooth, other methods may be more effective. In this paper, we have demonstrated application of another method inspired from artificial intelligence, called Particle Swarm Optimization (PSO) for estimating cosmological parameters from Cosmic Microwave Background (CMB) data taken from the WMAP satellite.
Particle physics and cosmology
Energy Technology Data Exchange (ETDEWEB)
Kolb, E.W.
1986-10-01
This series of lectures is about the role of particle physics in physical processes that occurred in the very early stages of the bug gang. Of particular interest is the role of particle physics in determining the evolution of the early Universe, and the effect of particle physics on the present structure of the Universe. The use of the big bang as a laboratory for placing limits on new particle physics theories will also be discussed. Section 1 reviews the standard cosmology, including primordial nucleosynthesis. Section 2 reviews the decoupling of weakly interacting particles in the early Universe, and discusses neutrino cosmology and the resulting limits that may be placed on the mass and lifetime of massive neutrinos. Section 3 discusses the evolution of the vacuum through phase transitions in the early Universe and the formation of topological defects in the transitions. Section 4 covers recent work on the generation of the baryon asymmetry by baryon-number violating reactions in Grand Unified Theories, and mentions some recent work on baryon number violation effects at the electroweak transition. Section 5 is devoted to theories of cosmic inflation. Finally, Section 6 is a discussion of the role of extra spatial dimensions in the evolution of the early Universe. 78 refs., 32 figs., 6 tabs.
Smoothed Particle Hydrodynamic Simulator
Energy Technology Data Exchange (ETDEWEB)
2016-10-05
This code is a highly modular framework for developing smoothed particle hydrodynamic (SPH) simulations running on parallel platforms. The compartmentalization of the code allows for rapid development of new SPH applications and modifications of existing algorithms. The compartmentalization also allows changes in one part of the code used by many applications to instantly be made available to all applications.
Cosmological Reflection of Particle Symmetry
Directory of Open Access Journals (Sweden)
Maxim Khlopov
2016-08-01
Full Text Available The standard model involves particle symmetry and the mechanism of its breaking. Modern cosmology is based on inflationary models with baryosynthesis and dark matter/energy, which involves physics beyond the standard model. Studies of the physical basis of modern cosmology combine direct searches for new physics at accelerators with its indirect non-accelerator probes, in which cosmological consequences of particle models play an important role. The cosmological reflection of particle symmetry and the mechanisms of its breaking are the subject of the present review.
Energy Technology Data Exchange (ETDEWEB)
Shafi, Qaisar [Univ. of Delaware, Newark, DE (United States); Barr, Steven [Univ. of Delaware, Newark, DE (United States); Gaisser, Thomas [Univ. of Delaware, Newark, DE (United States); Stanev, Todor [Univ. of Delaware, Newark, DE (United States)
2015-03-31
1. Executive Summary (April 1, 2012 - March 31, 2015) Title: Particle Theory, Particle Astrophysics and Cosmology Qaisar Shafi University of Delaware (Principal Investigator) Stephen M. Barr, University of Delaware (Co-Principal Investigator) Thomas K. Gaisser, University of Delaware (Co-Principal Investigator) Todor Stanev, University of Delaware (Co-Principal Investigator) The proposed research was carried out at the Bartol Research included Professors Qaisar Shafi Stephen Barr, Thomas K. Gaisser, and Todor Stanev, two postdoctoral fellows (Ilia Gogoladze and Liucheng Wang), and several graduate students. Five students of Qaisar Shafi completed their PhD during the period August 2011 - August 2014. Measures of the group’s high caliber performance during the 2012-2015 funding cycle included pub- lications in excellent refereed journals, contributions to working groups as well as white papers, and conference activities, which together provide an exceptional record of both individual performance as well as overall strength. Another important indicator of success is the outstanding quality of the past and current cohort of graduate students. The PhD students under our supervision regularly win the top departmental and university awards, and their publications records show excellence both in terms of quality and quantity. The topics covered under this grant cover the frontline research areas in today’s High Energy Theory & Phenomenology. For Professors Shafi and Barr they include LHC related topics including supersymmetry, collider physics, fl vor physics, dark matter physics, Higgs boson and seesaw physics, grand unifi and neutrino physics. The LHC two years ago discovered the Standard Model Higgs boson, thereby at least partially unlocking the secrets behind electroweak symmetry breaking. We remain optimistic that new and exciting physics will be found at LHC 14, which explain our focus on physics beyond the Standard Model. Professors Shafi continued his
The Cosmology - Particle Physics Connection
Trodden, Mark(Center for Particle Cosmology, Department of Physics & Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104, United States)
2006-01-01
Modern cosmology poses deep and unavoidable questions for fundamental physics. In this plenary talk, delivered in slightly different forms at the {\\it Particles and Nuclei International Conference} (PANIC05) in Santa Fe, in October 2005, and at the {\\it CMB and Physics of the Early Universe International Conference}, on the island of Ischia, Italy, in April 2006, I discuss the broad connections between cosmology and particle physics, focusing on physics at the TeV scale, accessible at the nex...
The Cosmology - Particle Physics Connection
Trodden, M
2006-01-01
Modern cosmology poses deep and unavoidable questions for fundamental physics. In this plenary talk, delivered in slightly different forms at the {\\it Particles and Nuclei International Conference} (PANIC05) in Santa Fe, in October 2005, and at the {\\it CMB and Physics of the Early Universe International Conference}, on the island of Ischia, Italy, in April 2006, I discuss the broad connections between cosmology and particle physics, focusing on physics at the TeV scale, accessible at the next and future generations of colliders
Particle cosmology comes of age
Energy Technology Data Exchange (ETDEWEB)
Turner, M.S.
1987-12-01
The application of modern ideas in particle physics to astrophysical and cosmological settings is a continuation of a fruitful tradition in astrophysics which began with the application of atomic physics, and then nuclear physics. In the past decade particle cosmology and particle astrophysics have been recognized as 'legitimate activities' by both particle physicists and astrophysicists and astronomers. During this time there has been a high level of theoretical activity producing much speculation about the earliest history of the Universe, as well as important and interesting astrophysical and cosmological constraints to particle physics theories. This period of intense theoretical activity has produced a number of ideas most worthy of careful consideration and scrutiny, and even more importantly, amenable to experimental/observational test. Among the ideas which are likely to be tested in the next decade are: the cosmological bound to the number of neutrino flavors, inflation, relic WIMPs as the dark matter, and MSW neutrino oscillations as a solution to the solar neutrino problems. 94 refs.
Particle Creation in Bouncing Cosmologies
Celani, Diogo C F; Vitenti, Sandro D P
2016-01-01
We investigate scalar particle creation in a set of bouncing models where the bounce occurs due to quantum cosmological effects described by the Wheeler-DeWitt equation. The scalar field can be either conformally or minimally coupled to gravity, and it can be massive or massless, without self interaction. The analysis is made for models containing a single radiation fluid, and for the more realistic case of models containing the usual observed radiation and dust fluids, which can fit most of the observed features of our Universe, including an almost scale invariant power spectrum of scalar cosmological perturbations. In the conformal coupling case, the particle production is negligible. In the minimal coupling case, for massive particles, the results point to the same physical conclusion within observational constraints: particle production is most important at the bounce energy scale, and it is not sensitive neither to its mass nor whether there is dust in the background model. The only caveat is the case wh...
SPHGR: Smoothed-Particle Hydrodynamics Galaxy Reduction
Thompson, Robert
2015-02-01
SPHGR (Smoothed-Particle Hydrodynamics Galaxy Reduction) is a python based open-source framework for analyzing smoothed-particle hydrodynamic simulations. Its basic form can run a baryonic group finder to identify galaxies and a halo finder to identify dark matter halos; it can also assign said galaxies to their respective halos, calculate halo & galaxy global properties, and iterate through previous time steps to identify the most-massive progenitors of each halo and galaxy. Data about each individual halo and galaxy is collated and easy to access. SPHGR supports a wide range of simulations types including N-body, full cosmological volumes, and zoom-in runs. Support for multiple SPH code outputs is provided by pyGadgetReader (ascl:1411.001), mainly Gadget (ascl:0003.001) and TIPSY (ascl:1111.015).
Particle propagation in cosmological backgrounds
Arteaga, Daniel
2007-01-01
We study the quantum propagation of particles in cosmological backgrounds, by considering a doublet of massive scalar fields propagating in an expanding universe, possibly filled with radiation. We focus on the dissipative effects related to the expansion rate. At first order, we recover the expected result that the decay rate is determined by the local temperature. Beyond linear order, the decay rate has an additional contribution governed by the expansion parameter. This latter contribution is present even for stable particles in the vacuum. Finally, we analyze the long time behaviour of the propagator and briefly discuss applications to the trans-Planckian question.
Particle creation in bouncing cosmologies
Celani, Diogo C. F.; Pinto-Neto, Nelson; Vitenti, Sandro D. P.
2017-01-01
We investigate scalar particle creation in a set of bouncing models where the bounce occurs due to quantum cosmological effects described by the Wheeler-DeWitt equation. The scalar field can be either conformally or minimally coupled to gravity, and it can be massive or massless, without self-interaction. The analysis is made for models containing a single radiation fluid and for the more realistic case of models containing the usual observed radiation and dust fluids, which can fit most of the observed features of our universe, including an almost scale invariant power spectrum of scalar cosmological perturbations. In the conformal coupling case, the particle production is negligible. In the minimal coupling case, for massive particles, the results point to the same physical conclusion within observational constraints: particle production is most important at the bounce energy scale, and it is not sensitive either to its mass or to whether there is dust in the background model. The only caveat is the case where the particle mass is larger than the bounce energy scale. On the other hand, the energy density of produced massive particles depend on their masses and the energy scale of the bounce. For very large masses and deep bounces, this energy density may overcome that of the background. In the case of massless particles, the energy density of produced particles can become comparable to the background energy density only for bounces occurring at energy scales comparable to the Planck scale or above, which lies beyond the scope of this paper: we expect that the simple Wheeler-DeWitt approach we are using should be valid only at scales a few orders of magnitude below the Planck energy. Nevertheless, in the case in which dust is present, there is an infrared divergence, which becomes important only for scales much larger than today's Hubble radius.
The dialogue between particle physics and cosmology
Energy Technology Data Exchange (ETDEWEB)
Sadoulet, B.
1988-04-01
In the last decade, a very close relationship has developed between particle physics and cosmology. The purpose of these lectures is to introduce particle physicists to the many scientific connections between the two fields. Before entering into the discussion of specific topics, it will first be shown that particle physics and cosmology are completely interdependent. 173 refs., 35 figs., 5 tabs.
Neutrinos in particle physics, astronomy, and cosmology
Xing, Zhi-Zhong
2011-01-01
""Neutrinos in Particle Physics, Astronomy and Cosmology"" provides a comprehensive and up-to-date introduction to neutrino physics, neutrino astronomy and neutrino cosmology. The intrinsic properties and fundamental interactions of neutrinos are described, as is the phenomenology of lepton flavor mixing, seesaw mechanisms and neutrino oscillations. The cosmic neutrino background, stellar neutrinos, supernova neutrinos and ultrahigh-energy cosmic neutrinos, together with the cosmological matter-antimatter asymmetry and other roles of massive neutrinos in cosmology, are discussed in detail. Thi
Cosmological anomalies and exotic smoothness structures
Asselmeyer-Maluga, Torsten; Brans, Carl H.
2001-01-01
It seems to be generally accepted that apparently anomalous cosmological observations, such as accelerating expansion, etc., necessarily are inconsistent with standard general relativity and standard matter sources. Following the suggestions of S{\\l}adkowski, we point out that in addition to exotic theories and exotic matter there is another possibility. We refer to exotic differential structures on ${\\mathbb R}^4$ which could be the source of the observed anomalies without changing the Einst...
Particle physics in astrophysics and cosmology
Rees, Martin J.
1990-08-01
This paper briefly outlines some topics of current interest on the interface between astrophysics/cosmology and particle physics. These include: the implications of the cosmic light element abundances; evidence for non-baryonic dark matter, and the prospects for experimental searches; cosmic strings; and `inflationary' cosmology.
Smoothed particle hydrodynamics and magnetohydrodynamics
Price, Daniel J.
2012-02-01
This paper presents an overview and introduction to smoothed particle hydrodynamics and magnetohydrodynamics in theory and in practice. Firstly, we give a basic grounding in the fundamentals of SPH, showing how the equations of motion and energy can be self-consistently derived from the density estimate. We then show how to interpret these equations using the basic SPH interpolation formulae and highlight the subtle difference in approach between SPH and other particle methods. In doing so, we also critique several 'urban myths' regarding SPH, in particular the idea that one can simply increase the 'neighbour number' more slowly than the total number of particles in order to obtain convergence. We also discuss the origin of numerical instabilities such as the pairing and tensile instabilities. Finally, we give practical advice on how to resolve three of the main issues with SPMHD: removing the tensile instability, formulating dissipative terms for MHD shocks and enforcing the divergence constraint on the particles, and we give the current status of developments in this area. Accompanying the paper is the first public release of the NDSPMHD SPH code, a 1, 2 and 3 dimensional code designed as a testbed for SPH/SPMHD algorithms that can be used to test many of the ideas and used to run all of the numerical examples contained in the paper.
NDSPMHD Smoothed Particle Magnetohydrodynamics Code
Price, Daniel J.
2011-01-01
This paper presents an overview and introduction to Smoothed Particle Hydrodynamics and Magnetohydrodynamics in theory and in practice. Firstly, we give a basic grounding in the fundamentals of SPH, showing how the equations of motion and energy can be self-consistently derived from the density estimate. We then show how to interpret these equations using the basic SPH interpolation formulae and highlight the subtle difference in approach between SPH and other particle methods. In doing so, we also critique several 'urban myths' regarding SPH, in particular the idea that one can simply increase the 'neighbour number' more slowly than the total number of particles in order to obtain convergence. We also discuss the origin of numerical instabilities such as the pairing and tensile instabilities. Finally, we give practical advice on how to resolve three of the main issues with SPMHD: removing the tensile instability, formulating dissipative terms for MHD shocks and enforcing the divergence constraint on the particles, and we give the current status of developments in this area. Accompanying the paper is the first public release of the NDSPMHD SPH code, a 1, 2 and 3 dimensional code designed as a testbed for SPH/SPMHD algorithms that can be used to test many of the ideas and used to run all of the numerical examples contained in the paper.
Particle Aspects of Cosmology and Baryogenesis
Riazuddin, M
2003-01-01
An introduction to particle aspects of cosmology with particular refrence to primordial nucleosynthesis, dark matter and baryogenesis is provided. In particular, various scenarios-GUT baryogenesis, electroweak baryogenesis and baryogenesis through leptogenesis are reviewed.
Dark Energy, Particle Physics and Cosmology
Turner, Michael S.
2012-05-01
Dark energy and cosmic acceleration is one of the three pillars of the current cosmological paradigm. Moreover, both raise fundamental issues in cosmology and particle physics. In particle physics, the dark energy problem is intimately related to the perplexing issue of why the quantum energy of the vacuum is so small. In cosmology, the nature of the dark energy is crucial to understanding the destiny of the Universe. I will discuss the status of current models for dark energy -- including vacuum energy and rolling scalar fields -- their implications for cosmology and for particle physics and how they can be tested by WFIRST. I will also address the status of the possibility that cosmic acceleration is explained by modifying or replacing general relativity.
Cosmological particle creation in the lab?
Schützhold, Ralf
2012-01-01
One of the most striking examples for the production of particles out of the quantum vacuum due to external conditions is cosmological particle creation, which is caused by the expansion or contraction of the Universe. Already in 1939, Schr\\"odinger understood that the cosmic evolution could lead to a mixing of positive and negative frequencies and that this "would mean production or annihilation of matter, merely by the expansion". Later this phenomenon was derived via more modern techniques of quantum field theory in curved space-times by Parker (who apparently was not aware of Schr\\"odinger's work) and subsequently has been studied in numerous publications. Even though cosmological particle creation typically occurs on extremely large length scales, it is one of the very few examples for such fundamental effects where we actually may have observational evidence: According to the inflationary model of cosmology, the seeds for the anisotropies in the cosmic microwave background (CMB) and basically all large ...
Institute of Scientific and Technical Information of China (English)
姜春艳
2012-01-01
The smoothed particle hydrodynamics (SPH) simulation is a powerful tool in studying galaxy formation and evolution. In this review, standard formulation of SPH is summarized. And then the implementation of baryonic physics in cosmological SPH simulations are illustrated, including star formation, galactic wind feedback, AGN feedback, and thermal conduction. uring the past years, much progress has been made on improving the physical modeling in hydro dynamical simulations, by nvoking more sophisticated treatments of star formation, supernovae feedback, AGN feedback and so on. The implementation of these baryonic physics in SPH simulations has helped us a lot in understanding how galaxies form and evolve in the universe. However, due to our limited knowledge of these baryonic physics, these models, are still far from being perfect. Many further studies are therefore needed in future to improve these physical modeling in simulations.%平滑流体动力学(SPH)数值模拟是我们研究星系形成与演化的一个重要工具.先介绍了SPH的基本原理和基本方程,然后以恒星形成、星系风反馈、AGN反馈和热传导为例,介绍了平滑流体动力学数值模拟中的重子物理及实施方法.这些模型在一定程度上都取得了成功,对更好地理解星系的形成和演化起到了促进作用.
An Owner's Guide to Smoothed Particle Hydrodynamics
Martin, T.J.; Pearce, F. R.; Thomas, P. A.
1993-01-01
We present a practical guide to Smoothed Particle Hydrodynamics (\\SPH) and its application to astrophysical problems. Although remarkably robust, \\SPH\\ must be used with care if the results are to be meaningful since the accuracy of \\SPH\\ is sensitive to the arrangement of the particles and the form of the smoothing kernel. In particular, the initial conditions for any \\SPH\\ simulation must consist of particles in dynamic equilibrium. We describe some of the numerical difficulties that may be...
Nonequilibrium Flows with Smooth Particle Applied Mechanics.
Kum, Oyeon
Smooth particle methods are relatively new methods for simulating solid and fluid flows though they have a 20-year history of solving complex hydrodynamic problems in astrophysics, such as colliding planets and stars, for which correct answers are unknown. The results presented in this thesis evaluate the adaptability or fitness of the method for typical hydrocode production problems. For finite hydrodynamic systems, boundary conditions are important. A reflective boundary condition with image particles is a good way to prevent a density anomaly at the boundary and to keep the fluxes continuous there. Boundary values of temperature and velocity can be separately controlled. The gradient algorithm, based on differentiating the smooth particle expressions for (urho) and (Trho), does not show numerical instabilities for the stress tensor and heat flux vector quantities which require second derivatives in space when Fourier's heat -flow law and Newton's viscous force law are used. Smooth particle methods show an interesting parallel linking them to molecular dynamics. For the inviscid Euler equation, with an isentropic ideal gas equation of state, the smooth particle algorithm generates trajectories isomorphic to those generated by molecular dynamics. The shear moduli were evaluated based on molecular dynamics calculations for the three weighting functions, B spline, Lucy, and Cusp functions. The accuracy and applicability of the methods were estimated by comparing a set of smooth particle Rayleigh -Benard problems, all in the laminar regime, to corresponding highly-accurate grid-based numerical solutions of continuum equations. Both transient and stationary smooth particle solutions reproduce the grid-based data with velocity errors on the order of 5%. The smooth particle method still provides robust solutions at high Rayleigh number where grid-based methods fails. Considerably fewer smooth particles are required than atoms in a corresponding molecular dynamics
School on Particle Physics, Gravity and Cosmology
Brandenberger, Robert
These lectures present a brief review of inflationary cosmology, provide an overview of the theory of cosmological perturbations, and then focus on the conceptual problems of the current paradigm of early universe cosmology, thus motivating an exploration of the potential of string theory to provide a new paradigm. Specifically, the string gas cosmology model is introduced, and a resulting mechanism for structure formation which does not require a period of cosmological inflation is discussed. The School consisted of level-up courses intended for PhD students, as well as updating courses for postdocs and researchers. In addition, a few propaedeutical crash courses were organized to bridge the gaps in the attendance and to facilitate an active participation. The courses were held mostly on the blackboard. The audience was assumed to have at least a PhD student level either in phenomenological particle theory, in astroparticle physics or in field and string theory. One of the aims of the School was to bring together researchers of these different areas and to update them on one another's discipline. The School was divided in two workshops: Interface between Cosmology and Particle Physics Courses: W. GRIMUS and S. PETCOV: Neutrino Phenomenology A. MASIERO and F. FERUGLIO: Beyond the Standard Model P. ULLIO: Introduction to Dark Matter N. BILIC: Black holes phenomenology 2) Particle Physics, Gravity and String Theory Courses: R. BRANDENBERGER: Topics in Cosmology J. ZANELLI: Black holes physics C. NUNEZ: StringsGauge Correspondence A. JEVICKI: AdS/CFT G. DALL'AGATA: String vacua and moduli stabilization C. BURGESS: Cosmology and Strings G. CARDOSO: Black Holes and String Theory Seminars were held during the School: Seminars: D. DENEGRI: New physics at LHC D. WARK: Neutrino Experiments C. BACCIGALUPI: Review on Cosmological Experiments A. MUELLER: Experimental evidence of Black Holes S. LIBERATI: Astrophysical constraints on Lorentz violation In addition the following
Particle physics constraints from future cosmological surveys
CERN. Geneva
2016-01-01
The next generation of cosmological surveys (of large scale structures, CMB polarisation, 21cm line), approved (Euclid, SKA, ...) or submitted (COrE+, LiteBird), have the potential to return a lot of relevant information for particle physics. I will present and comment some of the most recent sensitivity forecasts related to neutrino physics, light relics and Dark Matter properties.
Tensor classification of structure in smoothed particle hydrodynamics density fields
Forgan, Duncan; Lucas, William; Rice, Ken
2016-01-01
As hydrodynamic simulations increase in scale and resolution, identifying structures with non-trivial geometries or regions of general interest becomes increasingly challenging. There is a growing need for algorithms that identify a variety of different features in a simulation without requiring a "by-eye" search. We present tensor classification as such a technique for smoothed particle hydrodynamics (SPH). These methods have already been used to great effect in N-Body cosmological simulations, which require smoothing defined as an input free parameter. We show that tensor classification successfully identifies a wide range of structures in SPH density fields using its native smoothing, removing a free parameter from the analysis and preventing the need for tesselation of the density field, as required by some classification algorithms. As examples, we show that tensor classification using the tidal tensor and the velocity shear tensor successfully identifies filaments, shells and sheet structures in giant m...
Cosmological Particle Production Without Bogolubov Coefficients
Hamilton, A J; Parikh, M K; Hamilton, Alex J.; Kabat, Daniel; Parikh, Maulik K.
2003-01-01
We present an efficient new technique for calculating the amount of particle production in a cosmological background. The expectation value of the number operator for a given momentum mode can be extracted from the Feynman propagator. We demonstrate the computational economy of the technique by applying it to various cosmologies. We also show that the appropriate Feynman propagator, with boundary conditions that encode the initial state, can be constructed by the method of images. Our technique uses a first-quantized approach so, unlike conventional Bogolubov transformations, it may be amenable to a string-theoretic generalization.
Cosmological particle production and generalized thermodynamic equilibrium
Zimdahl, W
1998-01-01
With the help of a conformal, timelike Killing-vector we define generalized equilibrium states for cosmological fluids with particle production. For massless particles the generalized equilibrium conditions require the production rate to vanish and the well known ``global'' equilibrium of standard relativistic thermodynamics is recovered as a limiting case. The equivalence between the creation rate for particles with nonzero mass and an effective viscous fluid pressure follows as a consequence of the generalized equilibrium properties. The implications of this equivalence for the cosmological dynamics are discussed, including the possibility of a power-law inflationary behaviour. For a simple gas a microscopic derivation for such kind of equilibrium is given on the basis of relativistic kinetic theory.
Dual-support Smoothed Particle Hydrodynamics
Ren, Huilong; Zhuang, Xiaoying; Rabczuk, Timon
2016-01-01
In this paper we develop a dual-support smoothed particle hydrodynamics (DS-SPH) that naturally satisfies the conservation of momentum, angular momentum and energy when the varying smoothing length is utilized. The DS-SPH is based on the concept of dual-support, which is introduced to consider the unbalanced interactions between the particles with different smoothing lengths. Our DS-SPH formulation can be implemented in traditional SPH with little changes and improve the computational efficiency. Several numerical examples are presented to demonstrate the capability of the method.
Nonequilibrium flows with smooth particle applied mechanics
Energy Technology Data Exchange (ETDEWEB)
Kum, Oyeon [Univ. of California, Davis, CA (United States)
1995-07-01
Smooth particle methods are relatively new methods for simulating solid and fluid flows through they have a 20-year history of solving complex hydrodynamic problems in astrophysics, such as colliding planets and stars, for which correct answers are unknown. The results presented in this thesis evaluate the adaptability or fitness of the method for typical hydrocode production problems. For finite hydrodynamic systems, boundary conditions are important. A reflective boundary condition with image particles is a good way to prevent a density anomaly at the boundary and to keep the fluxes continuous there. Boundary values of temperature and velocity can be separately controlled. The gradient algorithm, based on differentiating the smooth particle expression for (uρ) and (Tρ), does not show numerical instabilities for the stress tensor and heat flux vector quantities which require second derivatives in space when Fourier`s heat-flow law and Newton`s viscous force law are used. Smooth particle methods show an interesting parallel linking to them to molecular dynamics. For the inviscid Euler equation, with an isentropic ideal gas equation of state, the smooth particle algorithm generates trajectories isomorphic to those generated by molecular dynamics. The shear moduli were evaluated based on molecular dynamics calculations for the three weighting functions, B spline, Lucy, and Cusp functions. The accuracy and applicability of the methods were estimated by comparing a set of smooth particle Rayleigh-Benard problems, all in the laminar regime, to corresponding highly-accurate grid-based numerical solutions of continuum equations. Both transient and stationary smooth particle solutions reproduce the grid-based data with velocity errors on the order of 5%. The smooth particle method still provides robust solutions at high Rayleigh number where grid-based methods fails.
Fundamentals of Cosmological Particle Physics
Khlopov, Maxim Yu
2012-01-01
This current updated and expanded (this is an up-dated English translation of Prof. Khlopov's book "Osnovy kosmomikrofiziki", URSS, 2004) text reflects the large number of scientific advances, both theoretical and experimental, within the discipline of cosmic particle physics in the last 10 years. Some of the topics that have been added or updated include but are not limited to: HND or CMD+HND scenarios being implemented into sterile neutrino scenarios, the ramifications of extending the forms of dark matter with respect to our view of neutrinos, the origin of baryon matter and the need for nonbaryonic matter in current theories, problems the existence of dark matter raises with respect to cosmic particle physics and the relationship with (meta) stable (super) weakly interacting particles predicted by the extension of the standard model, restrictions on baryon and lepton photons, as well as problems associated with expansion, just to name a few. These and many other topics are readdressed in light of recent b...
Academic Training: Cosmology for particle physicists
Françoise Benz
2005-01-01
2004-2005 ACADEMIC TRAINING PROGRAMME LECTURE SERIES 9, 10, 11, 12 & 13 May from 11.00 to 12.00 hrs - Main Auditorium, bldg. 500 on 9, 10, 12 and 13 May, Council Chamber, bldg. 503, on 11 May Cosmology for particle physicists S. CARROLL / Enrico Fermi Institute, Univ. of Chicago, USA The past few years have seen dramatic breakthroughs and spectacular and puzzling discoveries in astrophysics and cosmology. We know much about the universe, but understand very little. Open questions include the nature of the dark matter and dark energy, the origin of the matter/antimatter asymmetry, the possibility of inflation, and the role of string theory and extra dimensions in the early universe. All of these issues impact strongly on, and will be heavily influenced by, upcoming experiments in particle physics. I will give an overview of current questions at the overlap of cosmology and particle physics, and discuss some theoretical and experimental questions likely to be important in the near future. ENSEIGNEME...
Academic Training: Cosmology for particle physicists
Françoise Benz
2005-01-01
2004-2005 ACADEMIC TRAINING PROGRAMME LECTURE SERIES 9, 10, 11, 12 & 13 May from 11.00 to 12.00 hrs - Main Auditorium, bldg. 500 on 9, 10, 12 and 13 May, Council Chamber, bldg. 503, on 11 May Cosmology for particle physicists S. CARROLL / Enrico Fermi Institute, Univ. of Chicago, USA The past few years have seen dramatic breakthroughs and spectacular and puzzling discoveries in astrophysics and cosmology. We know much about the universe, but understand very little. Open questions include the nature of the dark matter and dark energy, the origin of the matter/antimatter asymmetry, the possibility of inflation, and the role of string theory and extra dimensions in the early universe. All of these issues impact strongly on, and will be heavily influenced by, upcoming experiments in particle physics. I will give an overview of current questions at the overlap of cosmology and particle physics, and discuss some theoretical and experimental questions likely to be important in the near future. ENSEIG...
Academic Training: Cosmology for particle physicists
Françoise Benz
2005-01-01
2004-2005 ACADEMIC TRAINING PROGRAMMELECTURE SERIES9, 10, 11, 12 & 13 Mayfrom 11.00 to 12.00 hrs - Main Auditorium, bldg. 500 on 9, 10, 12 and 13 May, Council Chamber, bldg. 503, on 11 MayCosmology for particle physicistsS. CARROLL / Enrico Fermi Institute, Univ. of Chicago, USAThe past few years have seen dramatic breakthroughs and spectacular and puzzling discoveries in astrophysics and cosmology. We know much about the universe, but understand very little. Open questions include the nature of the dark matter and dark energy, the origin of the matter/antimatter asymmetry, the possibility of inflation, and the role of string theory and extra dimensions in the early universe. All of these issues impact strongly on, and will be heavily influenced by, upcoming experiments in particle physics. I will give an overview of current questions at the overlap of cosmology and particle physics, and discuss some theoretical and experimental questions likely to be important in the near future.ENSEIGNEMENT ACADEMIQUEAC...
Particle Creation in Kaluza-Klein Cosmology
Huang, W H
1989-01-01
We exactly calculate the particle number $N$ of scalar fields which are created from an initial vacuum in certain higher-dimensional cosmological models. The spacetimes in these models are the four-dimensional Chitre-Hartle or radiation-dominated universe with extra spaces which are static or power-law contracting. Except for some models in which no particles could be produced, the distribution of created particles shows a thermal behavior, at least in the limit of high three-dimensional "momentum" $k$. In some models, $N$ does not depend on the magnitude of the extra-dimensional "momentum" $k_c$ if $k_c$ is nonvanishing. A cutoff momentum $k_c$ may emerge in some models, and particles with $k\\le k_c$ could not be produced. We also discuss these results.
Cosmology, physics of particles and nuclei
Energy Technology Data Exchange (ETDEWEB)
NONE
2003-07-01
A recent trend, already noted in the previous activity report, is the cross-fertilization between cosmology and high-energy physics, with some twenty research articles at this interface in the last 2 years. Results are presented along 3 main directions. 1) Cosmology and astro-particle physics. One may quote among others: the idea that dark matter may not be as weakly interacting as previously thought; a general study of the growth of small perturbations in the context of higher-dimensional theories; a possible explanation of the smallness of the cosmological constant through violation of Lorentz invariance in the gravity sector. In the field of observational cosmology, a 3-point correlation has been detected for the first time using gravitational lensing experiments. 2) Particle physics beyond the standard model. New developments in this field are triggered by progress on both experimental and theoretical sides. The first unambiguous observation of neutrino oscillations implies that neutrinos have non-zero masses. The constraints imposed by existing data on models based on the seesaw mechanism have been studied. The 'de-construction' of supersymmetric theories, inspired by recent advances in higher-dimensional theories, leads to a parameter-free prediction for the mass of the Higgs boson. 3) Strong interactions. Experiments at Hera have triggered new studies of hadronic interactions in the regime of high parton densities, which is also the high-energy limit for QCD: the phenomenon of 'parton saturation' is expected to occur. QCD calculations have been applied to various observables: jet physics, diffractive processes at Hera and in collider experiments, and multiplicity correlations in phase space. (A.C.)
Topics in particle filtering and smoothing
Saha, Saikat
2009-01-01
Particle filtering/smoothing is a relatively new promising class of algorithms to deal with the estimation problems in nonlinear and/or non- Gaussian systems. Currently, this is a very active area of research and there are many issues that are not either properly addressed or are still open. One of
A numerical study of the Regge Calculus and Smooth Lattice methods on a Kasner cosmology
Brewin, Leo
2015-01-01
Two lattice based methods for numerical relativity, the Regge Calculus and the Smooth Lattice Relativity, will be compared with respect to accuracy and computational speed in a full 3+1 evolution of initial data representing a standard Kasner cosmology. It will be shown that both methods provide convergent approximations to the exact Kasner cosmology. It will also be shown that the Regge Calculus is of the order of 110 times slower than the Smooth Lattice method.
Particle Pair Production in Cosmological General Relativity
Oliveira, Firmin J
2012-01-01
The Cosmological General Relativity of Carmeli, a 5-dimensional theory of time, space and velocity, predicts the existence of an acceleration $a_0 = c / \\tau$ due to the expansion of the universe, where $c$ is the speed of light in vacuum, $\\tau = 1/h$ is the Hubble-Carmeli time constant, where $h$ is the Hubble constant at zero distance and no gravity. The Carmeli force on a particle of mass $m$ is $F_c = m a_0$, a fifth force in nature. The fields resulting from the solution of the Einstein field equations in 5-D CGR and the Carmeli force are used to hypothesize the production of a particle and its antiparticle. The mass of each particle is found to be $m=\\tau c^3 / 4 G$, where $G$ is Newton's constant. The vacuum mass density derived from the physics is $\\rho_{vac} = -3/8 \\pi G \\tau^2$. The cosmological constant is then given by $\\Lambda = 3 / \\tau^2$. We derive an expression for $\\tau$ given by $\\tau = \\sqrt{(45 \\zeta (1 - g) c^3 \\hbar^3) / (4\\pi^3 G \\mu \\alpha^2 k^3 \\beta^3 T^3)}$, where $\\zeta$ is the b...
Cosmology of Universe Particles and Beyond
Xu, Wei
2016-06-01
For the first time in history, all properties of cosmology particles are uncovered and described concisely and systematically, known as the elementary particles in contemporary physics.Aligning with the synthesis of the virtual and physical worlds in a hierarchical taxonomy of the universe, this theory refines the topology framework of cosmology, and presents a new perspective of the Yin Yang natural laws that, through the processes of creation and reproduction, the fundamental elements generate an infinite series of circular objects and a Yin Yang duality of dynamic fields that are sequenced and transformed states of matter between the virtual and physical worlds.Once virtual objects are transformed, they embody various enclaves of energy states, known as dark energy, quarks, leptons, bosons, protons, and neutrons, characterized by their incentive oscillations of timestate variables in a duality of virtual realities: energy and time, spin and charge, mass and space, symmetry and antisymmetry.As a consequence, it derives the fully-scaled quantum properties of physical particles in accordance with numerous historical experiments, and has overcome the limitations of uncertainty principle and the Standard Model, towards concisely exploring physical nature and beyond...
Protostellar outflows with Smoothed Particle Magnetohydrodynamics (SPMHD)
Bürzle, Florian; Stasyszyn, Federico; Dolag, Klaus; Klessen, Ralf S
2011-01-01
The protostellar collapse of a molecular cloud core is usually accompanied by outflow phenomena. The latter are thought to be driven by magnetorotational processes from the central parts of the protostellar disc. While several 3D AMR/nested grid studies of outflow phenomena in collapsing magnetically supercritical dense cores have been reported in the literature, so far no such simulation has been performed using the Smoothed Particle Hydrodynamics (SPH) method. This is mainly due to intrinsic numerical difficulties in handling magnetohydrodynamics within SPH, which only recently were partly resolved. In this work, we use an approach where we evolve the magnetic field via the induction equation, augmented with stability correction and divergence cleaning schemes. We consider the collapse of a rotating core of one solar mass, threaded by a weak magnetic field initially parallel to the rotation axis so that the core is magnetically supercritical. We show, that Smoothed Particle Magnetohydrodynamics (SPMHD) is a...
Modeling Water Waves with Smoothed Particle Hydrodynamics
2013-09-30
flows, such as undertow, longshore currents, and rip currents. APPROACH The approach is based on improving various aspects of the SPH code ...Smoothed Particle Hydrodynamics ( SPH ) is a meshless numerical method that is being developed for the study of nearshore waves and other Navy needs. The...Lagrangian nature of SPH allows the modeling of wave breaking, surf zones, ship waves, and wave-structure interaction, where the free surface becomes
Particle Physics And Cosmology In Supersymmetric Models
Morrissey, D E
2005-01-01
The Standard Model (SM) of particle physics provides an excellent description of the elementary particle interactions observed in particle collider experiments, but the model does less well when it is applied to cosmology. Recent measurements of the Universe over very large distances indicate the existence of non-luminous dark matter and an excess of baryons over anti-baryons. The SM is unable to account for either of these results, implying that an extension of the SM description is needed. One such extension is supersymmetry. Within the minimal supersymmetric version of the SM, the MSSM, the lightest superpartner particle can make up the dark matter, and the baryon asymmetry can be generated by the mechanism of electroweak baryogenesis (EWBG). In this work, we examine these issues together in order to find out whether the MSSM can account for both of them simultaneously. We find that the MSSM can explain both the baryon asymmetry and the dark matter, but only over a very constrained region of the model para...
Tensor classification of structure in smoothed particle hydrodynamics density fields
Forgan, Duncan; Bonnell, Ian; Lucas, William; Rice, Ken
2016-04-01
As hydrodynamic simulations increase in scale and resolution, identifying structures with non-trivial geometries or regions of general interest becomes increasingly challenging. There is a growing need for algorithms that identify a variety of different features in a simulation without requiring a `by eye' search. We present tensor classification as such a technique for smoothed particle hydrodynamics (SPH). These methods have already been used to great effect in N-Body cosmological simulations, which require smoothing defined as an input free parameter. We show that tensor classification successfully identifies a wide range of structures in SPH density fields using its native smoothing, removing a free parameter from the analysis and preventing the need for tessellation of the density field, as required by some classification algorithms. As examples, we show that tensor classification using the tidal tensor and the velocity shear tensor successfully identifies filaments, shells and sheet structures in giant molecular cloud simulations, as well as spiral arms in discs. The relationship between structures identified using different tensors illustrates how different forces compete and co-operate to produce the observed density field. We therefore advocate the use of multiple tensors to classify structure in SPH simulations, to shed light on the interplay of multiple physical processes.
Cosmological Particle Production at Strong Coupling
Rangamani, Mukund; Van Raamsdonk, Mark
2015-01-01
We study the dynamics of a strongly-coupled quantum field theory in a cosmological spacetime using the holographic AdS/CFT correspondence. Specifically we consider a confining gauge theory in an expanding FRW universe and track the evolution of the stress-energy tensor during a period of expansion, varying the initial temperature as well as the rate and amplitude of the expansion. At strong coupling, particle production is inseparable from entropy production. As a result, we find significant qualitative differences from the weak coupling results: at strong coupling the system rapidly loses memory of its initial state as the amplitude is increased. Furthermore, in the regime where the Hubble parameter is parametrically smaller than the initial temperature, the dynamics is well modelled as a plasma evolving hydrodynamically towards equilibrium.
Resolving mixing in Smoothed Particle Hydrodynamics
Read, J I; Agertz, O
2009-01-01
Standard formulations of smoothed particle hydrodynamics (SPH) are unable to resolve mixing at fluid boundaries. We use an error and stability analysis of the generalised SPH equations of motion to prove that this is due to two distinct problems. The first is a leading order error in the momentum equation. This should decrease with increasing neighbour number, but does not because numerical instabilities cause the kernel to be irregularly sampled. We identify two important instabilities: the clumping instability and the banding instability, and we show that both are cured by a suitable choice of kernel. The second problem is the local mixing instability (LMI). This occurs as particles attempt to mix on the kernel scale, but are unable to due to entropy conservation. The result is a pressure discontinuity at boundaries that pushes fluids of different entropy apart. We cure the LMI by using a temperature weighted density estimate that both reduces errors in the continuity equation and allows individual particle...
PREFACE Particles, Strings and Cosmology (PASCOS)
Cabrera, Susana; Hirsch, Martin; Mitsou, Vasiliki; Muñoz, Carlos; Pastor, Sergio; Amparo Tórtola, María; Valle, José W. F.; Vives, Óscar
2010-11-01
The XVI Symposium in the Particles, Strings and Cosmology (PASCOS) series took place on 19-23 July 2010, in the historic city of Valencia, and was hosted by the Instituto de Física Corpuscular (IFIC), the largest particle physics laboratory of the Spanish National Research Council (CSIC), jointly operated with the University of Valencia. The PASCOS series of annual symposia is dedicated to the latest advances on the study of the forces that govern the elementary constituents of matter - the microcosm - and their effects on the understanding of the Universe at large - the macrocosm. Indeed the basic principles of uncertainty and mass-energy equivalence imply that when one probes deep inside the subatomic scale, one inevitably excites states of very high energy and mass which were copiously produced at the Big Bang. Recreating these particles in the laboratory is tantamount to tracing back the very early history of the universe. The interface of particle physics, string theory and cosmology has indeed become a highly active field of research at the frontier of human knowledge and the PASCOS meetings aim to bring together researchers from the three areas so as to facilitate the exchange of ideas and to identify possible synergies. The series started in the mid-nineties in the United States, where the first events took place. However it has by now become truly global, having circulated through India, South Korea, the United Kingdom, Canada and Germany. The aim of the conference was to review the recent progress in particle physics, string theory and cosmology, promoting the exchange of ideas and discussing future prospects. With the startup of LHC and the launch of the Planck satellite as well as many other experiments under way or planned, PASCOS2010 looked at an exciting future, giving theorists an opportunity to prepare for this wealth of new data and the stringent tests to which they will subject the existing theories. While the conferences in this series have
Workshop on advances in smooth particle hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Wingate, C.A.; Miller, W.A.
1993-12-31
This proceedings contains viewgraphs presented at the 1993 workshop held at Los Alamos National Laboratory. Discussed topics include: negative stress, reactive flow calculations, interface problems, boundaries and interfaces, energy conservation in viscous flows, linked penetration calculations, stability and consistency of the SPH method, instabilities, wall heating and conservative smoothing, tensors, tidal disruption of stars, breaking the 10,000,000 particle limit, modelling relativistic collapse, SPH without H, relativistic KSPH avoidance of velocity based kernels, tidal compression and disruption of stars near a supermassive rotation black hole, and finally relativistic SPH viscosity and energy.
Impact modeling with Smooth Particle Hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Stellingwerf, R.F.; Wingate, C.A.
1993-07-01
Smooth Particle Hydrodynamics (SPH) can be used to model hypervelocity impact phenomena via the addition of a strength of materials treatment. SPH is the only technique that can model such problems efficiently due to the combination of 3-dimensional geometry, large translations of material, large deformations, and large void fractions for most problems of interest. This makes SPH an ideal candidate for modeling of asteroid impact, spacecraft shield modeling, and planetary accretion. In this paper we describe the derivation of the strength equations in SPH, show several basic code tests, and present several impact test cases with experimental comparisons.
Particle physics and cosmology in supersymmetric models
Morrissey, David Edgar
The Standard Model (SM) of particle physics provides an excellent description of the elementary particle interactions observed in particle collider experiments, but the model does less well when it is applied to cosmology. Recent measurements of the Universe over very large distances indicate the existence of non-luminous dark matter and an excess of baryons over anti-baryons. The SM is unable to account for either of these results, implying that an extension of the SM description is needed. One such extension is supersymmetry. Within the minimal supersymmetric version of the SM, the MSSM, the lightest superpartner particle can make up the dark matter, and the baryon asymmetry can be generated by the mechanism of electroweak baryogenesis (EWBG). In this work, we examine these issues together in order to find out whether the MSSM can account for both of them simultaneously. We find that the MSSM can explain both the baryon asymmetry and the dark matter, but only over a very constrained region of the model parameter space. The strongest constraints on this scenario come from the lower bound on the Higgs boson mass, and the upper bound on the electric dipole moment of the electron. Moreover, upcoming experiments will probe the remaining allowed parameter space in the near future. Some of these constraints may be relaxed by going beyond the MSSM. With this in mind, we also investigate the nMSSM, a minimal singlet extension of the MSSM. We find that this model can also explain both the dark matter and the baryon asymmetry.
Multiscale modeling with smoothed dissipative particle dynamics.
Kulkarni, Pandurang M; Fu, Chia-Chun; Shell, M Scott; Leal, L Gary
2013-06-21
In this work, we consider two issues related to the use of Smoothed Dissipative Particle Dynamics (SDPD) as an intermediate mesoscale model in a multiscale scheme for solution of flow problems when there are local parts of a macroscopic domain that require molecular resolution. The first is to demonstrate that SDPD with different levels of resolution can accurately represent the fluid properties from the continuum scale all the way to the molecular scale. Specifically, while the thermodynamic quantities such as temperature, pressure, and average density remain scale-invariant, we demonstrate that the dynamic properties are quantitatively consistent with an all-atom Lennard-Jones reference system when the SDPD resolution approaches the atomistic scale. This supports the idea that SDPD can serve as a natural bridge between molecular and continuum descriptions. In the second part, a simple multiscale methodology is proposed within the SDPD framework that allows several levels of resolution within a single domain. Each particle is characterized by a unique physical length scale called the smoothing length, which is inversely related to the local number density and can change on-the-fly. This multiscale methodology is shown to accurately reproduce fluid properties for the simple problem of steady and transient shear flow.
Fundamental Particle Structure in the Cosmological Dark Matter
Khlopov, Maxim Yu
2013-01-01
The nonbaryonic dark matter of the Universe is assumed to consist of new stable forms of matter. Their stability reflects symmetry of micro world and mechanisms of its symmetry breaking. Particle candidates for cosmological dark matter are lightest particles that bear new conserved quantum numbers. Dark matter particles may represent ideal gas of non-interacting particles. Self-interacting dark matter weakly or superweakly coupled to ordinary matter is also possible, reflecting nontrivial pattern of particle symmetry in the hidden sector of particle theory. In the early Universe the structure of particle symmetry breaking gives rise to cosmological phase transitions, from which macroscopic cosmological defects or primordial nonlinear structures can be originated. Primordial black holes (PBHs) can be not only a candidate for dark matter, but also represent a universal probe for super-high energy physics in the early Universe. Evaporating PBHs turn to be a source of even superweakly interacting particles, while...
Introduction to particle cosmology the standard model of cosmology and its open problems
Bambi, Cosimo
2016-01-01
This book introduces the basic concepts of particle cosmology and covers all the main aspects of the Big Bang Model (expansion of the Universe, Big Bang Nucleosynthesis, Cosmic Microwave Background, large scale structures) and the search for new physics (inflation, baryogenesis, dark matter, dark energy). It also includes the majority of recent discoveries, such as the precise determination of cosmological parameters using experiments like WMAP and Planck, the discovery of the Higgs boson at LHC, the non-discovery to date of supersymmetric particles, and the search for the imprint of gravitational waves on the CMB polarization by Planck and BICEP. This textbook is based on the authors’ courses on Cosmology, and aims at introducing Particle Cosmology to senior undergraduate and graduate students. It has been especially written to be accessible even for those students who do not have a strong background in General Relativity and quantum field theory. The content of this book is organized in an easy-to-use ...
Simulating frictional contact in smoothed particle hydrodynamics
Institute of Scientific and Technical Information of China (English)
WANG; Jian; WU; Hao; GU; ChongShi; HUA; Hui
2013-01-01
Smoothed Particle Hydrodynamics (SPH) is a powerful tool for large deformation computation of soil flow. However, the method to simulate frictional contact in the framework of SPH is still absent and needs to be developed. This paper presents an algorithm to simulate frictional contact between soil and rigid or deformable structure in the framework of SPH. In this algo-rithm, the computational domain is divided into several sub-domains according to the existing contact boundaries, and contact forces are used as bridges of these sub-domains to fulfill problem solving. In the process of the SPH discretization for govern-ing equation of each sub-domain, the inherent problem of boundary deficiency of SPH is handled properly. Therefore, the par-ticles located at contact boundary can have precise acceleration, which is critical for contact detection. Then, based on the as-sumption that the SPH particle of soil can slightly penetrate into the structure, the contact forces along normal and tangential directions of the contact surface are computed by momentum principle, and the frictional force is modified if sliding occurs.Compared with previous methods, in which only particle-to-particle contact is considered or frictional sliding is just ignored,the method proposed in this study is more efficient and accurate, and is suitable for simulating interaction between soft materi-als and rigid or deformable structures, which are very common in geotechnical engineering. A number of numerical tests have been carried out to verify the accuracy and stability of the proposed algorithm, and the results have been compared with ana-lytical solutions or FEM results. The consistency obtained from these comparisons indicates that the algorithm is robust and can enhance the computing capability of SPH.
A Smoothed Particle Hydrodynamics approach for poroelasticity
Osorno, Maria; Steeb, Holger
2016-04-01
Within the framework of the SHynergie project we look to investigate hydraulic fracturing and crack evolving in poroelastic media. We model biphasic media assuming incompressible solid grain and incompressible pore liquid. Modeling evolving fractures and fracture networks in elastic and poroelastic media by mesh-based numerical approaches, like X-FEM, is especially in 3-dim a challenging task. Therefore, we propose a meshless particle method for fractured media based on the Smoothed Particle Hydrodynamics (SPH) approach. SPH is a meshless Lagrangian method highly suitable for the simulation of large deformations including free surfaces and/or interfaces. Within the SPH method, the computational domain is discretized with particles, avoiding the computational expenses of meshing. Our SPH solution is implemented in a parallel computational framework, which allows to simulate large domains more representative of the scale of our study cases. Our implementation is carefully validated against classical mesh-based approaches and compared with classical solutions for consolidation problems. Furthermore, we discuss fracture initiation and propagation in poroelastic rocks at the reservoir scale.
An analysis of smoothed particle hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Swegle, J.W.; Attaway, S.W.; Heinstein, M.W.; Mello, F.J. [Sandia National Labs., Albuquerque, NM (United States); Hicks, D.L. [Michigan Technological Univ., Houghton, MI (United States)
1994-03-01
SPH (Smoothed Particle Hydrodynamics) is a gridless Lagrangian technique which is appealing as a possible alternative to numerical techniques currently used to analyze high deformation impulsive loading events. In the present study, the SPH algorithm has been subjected to detailed testing and analysis to determine its applicability in the field of solid dynamics. An important result of the work is a rigorous von Neumann stability analysis which provides a simple criterion for the stability or instability of the method in terms of the stress state and the second derivative of the kernel function. Instability, which typically occurs only for solids in tension, results not from the numerical time integration algorithm, but because the SPH algorithm creates an effective stress with a negative modulus. The analysis provides insight into possible methods for removing the instability. Also, SPH has been coupled into the transient dynamics finite element code PRONTO, and a weighted residual derivation of the SPH equations has been obtained.
An implicit Smooth Particle Hydrodynamic code
Energy Technology Data Exchange (ETDEWEB)
Knapp, Charles E. [Univ. of New Mexico, Albuquerque, NM (United States)
2000-05-01
An implicit version of the Smooth Particle Hydrodynamic (SPH) code SPHINX has been written and is working. In conjunction with the SPHINX code the new implicit code models fluids and solids under a wide range of conditions. SPH codes are Lagrangian, meshless and use particles to model the fluids and solids. The implicit code makes use of the Krylov iterative techniques for solving large linear-systems and a Newton-Raphson method for non-linear corrections. It uses numerical derivatives to construct the Jacobian matrix. It uses sparse techniques to save on memory storage and to reduce the amount of computation. It is believed that this is the first implicit SPH code to use Newton-Krylov techniques, and is also the first implicit SPH code to model solids. A description of SPH and the techniques used in the implicit code are presented. Then, the results of a number of tests cases are discussed, which include a shock tube problem, a Rayleigh-Taylor problem, a breaking dam problem, and a single jet of gas problem. The results are shown to be in very good agreement with analytic solutions, experimental results, and the explicit SPHINX code. In the case of the single jet of gas case it has been demonstrated that the implicit code can do a problem in much shorter time than the explicit code. The problem was, however, very unphysical, but it does demonstrate the potential of the implicit code. It is a first step toward a useful implicit SPH code.
On the kernel and particle consistency in smoothed particle hydrodynamics
Sigalotti, Leonardo Di G; Rendón, Otto; Vargas, Carlos A; Peña-Polo, Franklin
2016-01-01
The problem of consistency of smoothed particle hydrodynamics (SPH) has demanded considerable attention in the past few years due to the ever increasing number of applications of the method in many areas of science and engineering. A loss of consistency leads to an inevitable loss of approximation accuracy. In this paper, we revisit the issue of SPH kernel and particle consistency and demonstrate that SPH has a limiting second-order convergence rate. Numerical experiments with suitably chosen test functions validate this conclusion. In particular, we find that when using the root mean square error as a model evaluation statistics, well-known corrective SPH schemes, which were thought to converge to second, or even higher order, are actually first-order accurate, or at best close to second order. We also find that observing the joint limit when $N\\to\\infty$, $h\\to 0$, and $n\\to\\infty$, as was recently proposed by Zhu et al., where $N$ is the total number of particles, $h$ is the smoothing length, and $n$ is th...
Ambipolar diffusion in smoothed particle magnetohydrodynamics
Wurster, James; Ayliffe, Ben A
2014-01-01
In partially ionised plasmas, the magnetic field can become decoupled from the neutral gas and diffuse through it in a process known as ambipolar diffusion. Although ambipolar diffusion has been implemented in several grid codes, we here provide an implementation in smoothed particle magnetohydrodynamics (SPMHD). We use the strong coupling approximation in which the ion density is negligible, allowing a single fluid approach. The equations are derived to conserve energy, and to provide a positive definite contribution to the entropy. We test the implementation in both a simple 1D SPMHD code and the fully 3D code PHANTOM. The wave damping test yields agreement within 0.03-2 per cent of the analytical result, depending on the value of the collisional coupling constant. The oblique C-shocks test yields results that typically agree within 4 per cent of the semi-analytical result. Our algorithm is therefore suitable for exploring the effect ambipolar diffusion has on physical processes, such as the formation of st...
Creation of unstable particles and decoherence in semiclassical cosmology
Castagnino, M A; Lombardo, F C; Castagnino, Mario; Landau, Susana; Lombardo, Fernando C.
1999-01-01
We consider a simple cosmological model in order to show the importance of unstable particle creation for the validity of the semiclassical approximation. Using the mathematical structure of rigged Hilbert spaces we show that particle creation is the seed of decoherence which enables the quantum to classical transition.
An investigation of particles suspension using smoothed particle hydrodynamics
Pazouki, Arman; Negrut, Dan
2013-11-01
This contribution outlines a method for the direct numerical simulation of rigid body suspensions in a Lagrangian-Lagrangian framework using extended Smoothed Particle Hydrodynamics (XSPH) method. The dynamics of the arbitrarily shaped rigid bodies is fully resolved via Boundary Condition Enforcing (BCE) markers and updated according to the general Newton-Euler equations of motion. The simulation tool, refered to herien as Chrono::Fluid, relies on a parallel implementation that runs on Graphics Processing Unit (GPU) cards. The simulation results obtained for transient Poiseuille flow, migration of cylinder and sphere in Poiseuille flow, and distribution of particles at different cross sections of the laminar flow of dilute suspension were respectively within 0.1%, 1%, and 5% confidence interval of analytical and experimental results reported in the literature. It was shown that at low Reynolds number, Re = O(1), the radial migration (a) behaves non-monotonically as the particles relative distance (distance over diameter) increases from zero to two; and (b) decreases as the particle skewness and size increases. The scaling of Chrono::Fluid was demonstrated in conjunction with a suspension dynamics analysis in which the number of ellipsoids went up to 3e4. Financial support was provided in part by National Science Foundation grant NSF CMMI-084044.
A field theory characterization of interacting adiabatic particles in cosmology
Arteaga, Daniel
2008-01-01
We explore the adiabatic particle excitations of an interacting field in a cosmological background. By following the time-evolution of the quantum state corresponding to the particle excitation, we show how the basic properties characterizing the particle propagation can be recovered from the two-point propagators. As an application, we study the background-induced dissipative effects on the propagation of a two-level atom in an expanding universe.
A field theory characterization of interacting adiabatic particles in cosmology
Energy Technology Data Exchange (ETDEWEB)
Arteaga, Daniel [Departament de Fisica Fonamental and Institut de Ciencies del Cosmos, Facultat de Fisica, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona (Spain)], E-mail: darteaga@ub.edu
2008-08-07
We explore the adiabatic particle excitations of an interacting field in a cosmological background. By following the time evolution of the quantum state corresponding to the particle excitation, we show how the basic properties characterizing the particle propagation can be recovered from the two-point propagators. As an application, we study the background-induced dissipative effects on the propagation of a two-level atom in an expanding universe.
Fundamental Particle Structure in the Cosmological Dark Matter
Khlopov, Maxim
2013-11-01
The nonbaryonic dark matter of the universe is assumed to consist of new stable forms of matter. Their stability reflects symmetry of micro-world and mechanisms of its symmetry breaking. Particle candidates for cosmological dark matter are lightest particles that bear new conserved quantum numbers. Dark matter particles may represent ideal gas of noninteracting particles. Self-interacting dark matter weakly or superweakly coupled to ordinary matter is also possible, reflecting nontrivial pattern of particle symmetry in the hidden sector of particle theory. In the early universe the structure of particle symmetry breaking gives rise to cosmological phase transitions, from which macroscopic cosmological defects or primordial nonlinear structures can be originated. Primordial black holes (PBHs) can be not only a candidate for dark matter, but also represent a universal probe for superhigh energy physics in the early universe. Evaporating PBHs turn to be a source of even superweakly interacting particles, while clouds of massive PBHs can serve as nonlinear seeds for galaxy formation. The observed broken symmetry of the three known families may provide a simultaneous solution for the problems of the mass of neutrino and strong CP-violation in the unique framework of models of horizontal unification. Dark matter candidates can also appear in the new families of quarks and leptons and the existence of new stable charged leptons and quarks is possible, hidden in elusive "dark atoms." Such possibility, strongly restricted by the constraints on anomalous isotopes of light elements, is not excluded in scenarios that predict stable double charged particles. The excessive -2 charged particles are bound in these scenarios with primordial helium in O-helium "atoms," maintaining specific nuclear-interacting form of the dark matter, which may provide an interesting solution for the puzzles of the direct dark matter searches. In the context of cosmoparticle physics, studying
Moving least-squares corrections for smoothed particle hydrodynamics
Directory of Open Access Journals (Sweden)
Ciro Del Negro
2011-12-01
Full Text Available First-order moving least-squares are typically used in conjunction with smoothed particle hydrodynamics in the form of post-processing filters for density fields, to smooth out noise that develops in most applications of smoothed particle hydrodynamics. We show how an approach based on higher-order moving least-squares can be used to correct some of the main limitations in gradient and second-order derivative computation in classic smoothed particle hydrodynamics formulations. With a small increase in computational cost, we manage to achieve smooth density distributions without the need for post-processing and with higher accuracy in the computation of the viscous term of the Navier–Stokes equations, thereby reducing the formation of spurious shockwaves or other streaming effects in the evolution of fluid flow. Numerical tests on a classic two-dimensional dam-break problem confirm the improvement of the new approach.
Classical N-particle cosmology in 2+1 dimensions
Hooft, G. 't
1993-01-01
In 2+1 dimensional cosmology particles are topological defects in a universe that is nearly everywhere flat. The author uses a time dependent triangulation procedure of space to formulate the laws of evolution and to construct the phase space of this system. A theorem is derived from which it follow
Classical N-particle cosmology in 2+1 dimensions
Hooft, G. 't
1993-01-01
In 2+1 dimensional cosmology particles are topological defects in a universe that is nearly everywhere flat. The author uses a time dependent triangulation procedure of space to formulate the laws of evolution and to construct the phase space of this system. A theorem is derived from which it
Particle Physics Meets Cosmology -- The Search for Decaying Neutrinos.
Henry, Richard C.
1982-01-01
Detection of neutrino decay may have profound consequences for both particle physics and cosmology, providing a deep connection between physics of the very large and physics of the very small. Describes this link and discusses the nature and status of the search for decaying neutrinos. (Author/JN)
Cosmological particle creation in conformal gravity
Directory of Open Access Journals (Sweden)
Berezin Victor
2016-01-01
Full Text Available We constructed the conformally invariant model for scalar particle creation induced by strong gravitational fields. Starting from the “usual” hydrodynamical description of the particle motion written in the Eulerian coordinates we substituted the particle number conservation law (which enters the formalism by “the particle creation law”, proportional to the square of the Weyl tensor (following the famous result by Ya. B. Zel‘dovich and A. A. Starobinsky. Then, demanding the conformal invariance of the whole dynamical system, we have got both the (Weyl-conformal gravity and the Einstein–Hilbert–dilaton gravity action integral. Thus, we obtained something like the induced gravity suggested first by A. D. Sakharov. It is shown that the resulting system is self-consistent. Some future developments of the theory are discussed in the concluding Chapter.
Precision measurement for particle physics and cosmology
Graham, Peter
2017-01-01
Axions and other light particles are strongly motivated. For example, the axion is the crucial element in the recently proposed solution to the hierarchy problem using dynamical relaxation in the early universe. However, such particles are challenging to search for experimentally. Precision measurement technologies such as atom interferometry, nuclear magnetic resonance, high precision magnetometry, and torsion balances allow novel, highly sensitive experiments for direct detection of such light dark matter and of gravitational waves. Thus precision measurement technologies open new avenues for probing the origin and composition of the universe.
Particle motions in oscillatory flow over a smooth bed
DEFF Research Database (Denmark)
Jensen, Karsten Lindegård; Sumer, B. Mutlu; Fredsøe, Jørgen;
2014-01-01
such as the probability distribution of particle position in the vertical, and the horizontal and vertical particle velocities, among others, are determined. The particle is observed to reach heights of 2.5-3d, similar to that characterizing a typical bedload particle in sediment transport.......This study investigates particle motions near the bed in an oscillating tunnel with a smooth bed. Trajectories of a heavy particle were recorded in two dimensions (horizontal and vertical) and in time. The wave boundary layer Reynolds number is Re = 520000. Kinematical quantities...
Visualization of Cosmological Particle-Based Datasets
Navrátil, Paul Arthur; Bromm, Volker
2007-01-01
We describe our visualization process for a particle-based simulation of the formation of the first stars and their impact on cosmic history. The dataset consists of several hundred time-steps of point simulation data, with each time-step containing approximately two million point particles. For each time-step, we interpolate the point data onto a regular grid using a method taken from the radiance estimate of photon mapping. We import the resulting regular grid representation into ParaView, with which we extract isosurfaces across multiple variables. Our images provide insights into the evolution of the early universe, tracing the cosmic transition from an initially homogeneous state to one of increasing complexity. Specifically, our visualizations capture the build-up of regions of ionized gas around the first stars, their evolution, and their complex interactions with the surrounding matter. These observations will guide the upcoming James Webb Space Telescope, the key astronomy mission of the next decade.
Nuclear and particle physics, astrophysics and cosmology (NPAC) capability review
Energy Technology Data Exchange (ETDEWEB)
Redondo, Antonio [Los Alamos National Laboratory
2010-01-01
The present document represents a summary self-assessment of the status of the Nuclear and Particle Physics, Astrophysics and Cosmology (NPAC) capability across Los Alamos National Laboratory (LANL). For the purpose of this review, we have divided the capability into four theme areas: Nuclear Physics, Particle Physics, Astrophysics and Cosmology, and Applied Physics. For each theme area we have given a general but brief description of the activities under the area, a list of the Laboratory divisions involved in the work, connections to the goals and mission of the Laboratory, a brief description of progress over the last three years, our opinion of the overall status of the theme area, and challenges and issues.
A new insight into the consistency of smoothed particle hydrodynamics
Sigalotti, Leonardo Di G; Klapp, Jaime; Vargas, Carlos A; Campos, Kilver
2016-01-01
In this paper the problem of consistency of smoothed particle hydrodynamics (SPH) is solved. A novel error analysis is developed in $n$-dimensional space using the Poisson summation formula, which enables the treatment of the kernel and particle approximation errors in combined fashion. New consistency integral relations are derived for the particle approximation which correspond to the cosine Fourier transform of the classically known consistency conditions for the kernel approximation. The functional dependence of the error bounds on the SPH interpolation parameters, namely the smoothing length $h$ and the number of particles within the kernel support ${\\cal{N}}$ is demonstrated explicitly from which consistency conditions are seen to follow naturally. As ${\\cal{N}}\\to\\infty$, the particle approximation converges to the kernel approximation independently of $h$ provided that the particle mass scales with $h$ as $m\\propto h^{\\beta}$, with $\\beta >n$. This implies that as $h\\to 0$, the joint limit $m\\to 0$, $...
Smoothed Particle Hydrodynamics: Applications Within DSTO
2006-10-01
dimensional SPH code. They used SPH to model wave overtopping on the decks of offshore platforms and ships and used moving boundary particles to create...loading on offshore structures is a subject area which is now becoming amenable to detailed study using sophisticated computational fluid dynamics codes...incorporation of bending, torsional stiffness, and hydrodynamic loads, thus making it ideal for the simulation of umbilical cables on ROVs and AUVs
Exotic smoothness, noncommutative geometry and particle physics
Sladkowski, J
1994-01-01
We investigate how exotic differential structures may reveal themselves in particle physics. The analysis is based on the A. Connes' construction of the standard model. It is shown that, if one of the copies of the spacetime manifold is equipped with an exotic differential structure, compact object of geometric origin may exist even if the spacetime is topologically trivial. Possible implications are discussed. An SU(3)\\otimes SU(2)\\otimes U(1) gauge model is constructed. This model may not be realistic but it shows what kind of physical phenomena might be expected due to the existence of exotic differential structures on the spacetime manifold.
Tests of the particle physics-physical cosmology interface
Energy Technology Data Exchange (ETDEWEB)
Schramm, D.N. [Chicago Univ., IL (United States)]|[Fermi National Accelerator Lab., Batavia, IL (United States)
1993-01-01
Three interrelated interfaces of particle physics and physical cosmology are discussed: (1) inflation and other phase transitions; (2) Big Bang Nucleosynthesis (and also the quark-hadron transition); and (3) structure formation (including dark matter). Recent observations that affect each of these topics are discussed. Topic number 1 is shown to be consistent with the COBE observations but not proven and it may be having problems with some age-expansion data. Topic number 2 has now been well-tested and is an established ``pillar`` of the Big Bang. Topic number 3 is the prime arena of current physical cosmological activity. Experiments to resolve the current exciting, but still ambiguous, situation following the COBE results are discussed.
Tests of the particle physics-physical cosmology interface
Energy Technology Data Exchange (ETDEWEB)
Schramm, D.N. (Chicago Univ., IL (United States) Fermi National Accelerator Lab., Batavia, IL (United States))
1993-01-01
Three interrelated interfaces of particle physics and physical cosmology are discussed: (1) inflation and other phase transitions; (2) Big Bang Nucleosynthesis (and also the quark-hadron transition); and (3) structure formation (including dark matter). Recent observations that affect each of these topics are discussed. Topic number 1 is shown to be consistent with the COBE observations but not proven and it may be having problems with some age-expansion data. Topic number 2 has now been well-tested and is an established pillar'' of the Big Bang. Topic number 3 is the prime arena of current physical cosmological activity. Experiments to resolve the current exciting, but still ambiguous, situation following the COBE results are discussed.
Cosmological parameter estimation using Particle Swarm Optimization (PSO)
Prasad, Jayanti
2011-01-01
Obtaining the set of cosmological parameters consistent with observational data is an important exercise in current cosmological research. It involves finding the global maximum of the likelihood function in the multi-dimensional parameter space. Currently sampling based methods, which are in general stochastic in nature, like Markov-Chain Monte Carlo(MCMC), are being commonly used for parameter estimation. The beauty of stochastic methods is that the computational cost grows, at the most, linearly in place of exponentially (as in grid based approaches) with the dimensionality of the search space. MCMC methods sample the full joint probability distribution (posterior) from which one and two dimensional probability distributions, best fit (average) values of parameters and then error bars can be computed. In the present work we demonstrate the application of another stochastic method, named Particle Swarm Optimization (PSO), that is widely used in the field of engineering and artificial intelligence, for cosmo...
One-particle-irreducible consistency relations for cosmological perturbations
Goldberger, Walter D; Nicolis, Alberto
2013-01-01
We derive consistency relations for correlators of scalar cosmological perturbations which hold in the "squeezed limit" in which one or more of the external momenta become soft. Our results are formulated as relations between suitably defined one-particle irreducible N-point and (N-1)-point functions that follow from residual spatial conformal diffeomorphisms of the unitary gauge Lagrangian. As such, some of these relations are exact to all orders in perturbation theory, and do not rely on approximate deSitter invariance or other dynamical assumptions (e.g., properties of the operator product expansion or the behavior of modes at horizon crossing). The consistency relations apply model-independently to cosmological scenarios where the time evolution is driven by a single scalar field. Besides reproducing the known results for single-field inflation in the slow roll limit, we verify that our consistency relations hold more generally, for instance in ghost condensate models in flat space. We comment on possible...
Smooth Particle Hydrodynamics-based Wind Representation
Energy Technology Data Exchange (ETDEWEB)
Prescott, Steven [Idaho National Lab. (INL), Idaho Falls, ID (United States); Smith, Curtis [Idaho National Lab. (INL), Idaho Falls, ID (United States); Hess, Stephen [Idaho National Lab. (INL), Idaho Falls, ID (United States); Lin, Linyu [Idaho National Lab. (INL), Idaho Falls, ID (United States); Sampath, Ram [Idaho National Lab. (INL), Idaho Falls, ID (United States)
2016-12-01
and computation time. An advanced method of combing results from grid-based methods with SPH through a data-driven model is proposed. This method could allow for more accurate simulation of particle movement near rigid bodies even with larger SPH particle sizes. If successful, the data-driven model would eliminate the need for a SPH turbulence model and increase the simulation domain size. Continued research beyond the scope of this project will be needed in order to determine the viability of a data-driven model.
Smoothed Particle Hydrodynamics Method for Two-dimensional Stefan Problem
Tarwidi, Dede
2016-01-01
Smoothed particle hydrodynamics (SPH) is developed for modelling of melting and solidification. Enthalpy method is used to solve heat conduction equations which involved moving interface between phases. At first, we study the melting of floating ice in the water for two-dimensional system. The ice objects are assumed as solid particles floating in fluid particles. The fluid and solid motion are governed by Navier-Stokes equation and basic rigid dynamics equation, respectively. We also propose a strategy to separate solid particles due to melting and solidification. Numerical results are obtained and plotted for several initial conditions.
Stable smoothed particle magnetohydrodynamics in very steep density gradients
Lewis, Benjamin T; Monaghan, Joseph J; Price, Daniel J
2015-01-01
The equations of smoothed particle magnetohydrodynamics (SPMHD), even with the various corrections to instabilities so far proposed, have been observed to be unstable when a very steep density gradient is necessarily combined with a variable smoothing length formalism. Here we consider in more detail the modifications made to the SPMHD equations in LBP2015 that resolve this instability by replacing the smoothing length in the induction and anisotropic force equations with an average smoothing length term. We then explore the choice of average used and compare the effects on a test `cylinder-in-a-box' problem and the collapse of a magnetised molecular cloud core. We find that, aside from some benign numerical effects at low resolutions for the quadratic mean, the formalism is robust as to the choice of average but that in complicated models it is essential to apply the average to both equations; in particular, all four averages considered exhibit similar conservation properties. This improved formalism allows ...
Smoothed Particle Hydrodynamics Model for Reactive Transport and Mineral Precipitation
Energy Technology Data Exchange (ETDEWEB)
Tartakovsky, Alexandre M.; Scheibe, Timothy D.; Redden, George; Meakin, Paul; Fang, Yilin
2006-06-30
A new Lagrangian particle model based on smoothed particle hydrodynamics was used to simulate pore scale precipitation reactions. The side-by-side injection of reacting solutions into two halves of a two-dimensional granular porous medium was simulated. Precipitation on grain surfaces occurred along a narrow zone in the middle of the domain, where the reacting solutes mixed to generate a supersaturated reaction product. The numerical simulations qualitatively reproduced the behavior observed in related laboratory experiments.
Launch Environment Water Flow Simulations Using Smoothed Particle Hydrodynamics
Vu, Bruce T.; Berg, Jared J.; Harris, Michael F.; Crespo, Alejandro C.
2015-01-01
This paper describes the use of Smoothed Particle Hydrodynamics (SPH) to simulate the water flow from the rainbird nozzle system used in the sound suppression system during pad abort and nominal launch. The simulations help determine if water from rainbird nozzles will impinge on the rocket nozzles and other sensitive ground support elements.
Gravitational particle production in oscillating backgrounds and its cosmological implications
Ema, Yohei; Jinno, Ryusuke; Mukaida, Kyohei; Nakayama, Kazunori
2016-09-01
We study the production of light particles due to the oscillation of the Hubble parameter or the scale factor. Any coherently oscillating scalar field, irrespective of its energy fraction in the Universe, imprints such an oscillating feature on them. Not only Einstein gravity but the extended gravity models, such as models with nonminimal (derivative) coupling to gravity and f (R ) gravity, lead to oscillation of the scale factor. We present a convenient way to estimate the gravitational particle production rate in these circumstances. Cosmological implications of gravitational particle production, such as dark matter/radiation and moduli problem, are discussed. For example, if the theory is described solely by the standard model plus the Peccei-Quinn sector, the Starobinsky R2 inflation may lead to an observable amount of axion dark radiation.
Gravitational Particle Production in Oscillating Background and Its Cosmological Implications
Ema, Yohei; Mukaida, Kyohei; Nakayama, Kazunori
2016-01-01
We study production of light particles due to oscillation of the Hubble parameter or the scale factor. Any coherently oscillating scalar field, irrespective of its energy fraction in the universe, imprints such an oscillating feature on them. Not only the Einstein gravity but extended gravity models, such as models with non-minimal (derivative) coupling to gravity and $f(R)$ gravity, lead to oscillation of the scale factor. We present a convenient way to estimate the gravitational particle production rate in these circumstances. Cosmological implications of gravitational particle production, such as dark matter/radiation and moduli problem, are discussed. For example, if the theory is described solely by the standard model plus the Peccei-Quinn sector, the Starobinsky $R^2$ inflation may lead to observable amount of axion dark radiation.
Particle physics and cosmology, Task C. Progress report, January 1992--April 1993
Energy Technology Data Exchange (ETDEWEB)
Turner, M.S.
1993-05-01
The research has spanned many topics at the boundary of particle physics and cosmology. The major focus has been in the general areas of inflationary cosmology, cosmological phase transitions, astrophysical constraints to particle physics theories, and dark matter/structure formation as it relates to particle physics. Some attention is given to axion physics. Narrative summaries of the research of the individual group members are given, followed by a list of publications.
Particle physics meets cosmology - The search for decaying neutrinos
Henry, R. C.
1982-01-01
The fundamental physical implications of the possible detection of massive neutrinos are discussed, with an emphasis on the Grand Unified Theories (GUTs) of matter. The Newtonian and general-relativistic pictures of the fundamental forces are compared, and the reduction of electromagnetic and weak forces to one force in the GUTs is explained. The cosmological consequences of the curved-spacetime gravitation concept are considered. Quarks, leptons, and neutrinos are characterized in a general treatment of elementary quantum mechanics. The universe is described in terms of quantized fields, the noninteractive 'particle' fields and the force fields, and cosmology becomes the study of the interaction of gravitation with the other fields, of the 'freezing out' of successive fields with the expansion and cooling of the universe. While the visible universe is the result of the clustering of the quark and electron fields, the distribution of the large number of quanta in neutrino field, like the mass of the neutrino, are unknown. Cosmological models which attribute anomalies in the observed motions of galaxies and stars to clusters or shells of massive neutrinos are shown to be consistent with a small but nonzero neutrino mass and a universe near the open/closed transition point, but direct detection of the presence of massive neutrinos by the UV emission of their decay is required to verify these hypotheses.
Calibrating an updated smoothed particle hydrodynamics scheme within gcd+
Kawata, D.; Okamoto, T.; Gibson, B. K.; Barnes, D. J.; Cen, R.
2013-01-01
We adapt a modern scheme of smoothed particle hydrodynamics (SPH) to our tree N-body/SPH galactic chemodynamics code gcd+. The applied scheme includes implementations of the artificial viscosity switch and artificial thermal conductivity proposed by Morris & Monaghan, Rosswog & Price and Price to model discontinuities and Kelvin-Helmholtz instabilities more accurately. We first present hydrodynamics test simulations and contrast the results to runs undertaken without artificial viscosity switch or thermal conduction. In addition, we also explore the different levels of smoothing by adopting larger or smaller smoothing lengths, i.e. a larger or smaller number of neighbour particles, Nnb. We demonstrate that the new version of gcd+ is capable of modelling Kelvin-Helmholtz instabilities to a similar level as the mesh code, athena. From the Gresho vortex, point-like explosion and self-similar collapse tests, we conclude that setting the smoothing length to keep Nnb as high as ˜58 is preferable to adopting smaller smoothing lengths. We present our optimized parameter sets from the hydrodynamics tests.
3D description of particle detachment from a smooth surface
Liberzon, Alex; Traugott, Hadar; International CollaborationTurbulence Research Collaboration
2011-11-01
This study explores the necessary turbulent flow conditions for initial entrainment of particles from smooth beds into zero-mean-shear flow in an oscillating grid chamber as compared to the bounded shear flow created in a lid-driven cavity. The experiments are not designed to fully mimic the real problem of sediment transport but rather identify key mechanisms, utilizing direct observation and quantification of particle motion at the beginning, during and after lift-off. In both turbulent flows, particle image velocimetry (PIV) and three-dimensional particle tracking velocimetry (3D-PTV) are used to determine the properties of turbulent flows and to track the movement of individual particles through the various phases of the resuspension. The combination of the experimental methods allow to correlate in a quantitative manner the flow conditions responsible for rolling, pick-up, detachment and re-entrainment of particles. The study is supported by the Israel Science Foundation under grant 782/08.
A generalized transport-velocity formulation for smoothed particle hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Zhang, Chi; Hu, Xiangyu Y., E-mail: xiangyu.hu@tum.de; Adams, Nikolaus A.
2017-05-15
The standard smoothed particle hydrodynamics (SPH) method suffers from tensile instability. In fluid-dynamics simulations this instability leads to particle clumping and void regions when negative pressure occurs. In solid-dynamics simulations, it results in unphysical structure fragmentation. In this work the transport-velocity formulation of Adami et al. (2013) is generalized for providing a solution of this long-standing problem. Other than imposing a global background pressure, a variable background pressure is used to modify the particle transport velocity and eliminate the tensile instability completely. Furthermore, such a modification is localized by defining a shortened smoothing length. The generalized formulation is suitable for fluid and solid materials with and without free surfaces. The results of extensive numerical tests on both fluid and solid dynamics problems indicate that the new method provides a unified approach for multi-physics SPH simulations.
A method of smoothed particle hydrodynamics using spheroidal kernels
Fulbright, Michael S.; Benz, Willy; Davies, Melvyn B.
1995-01-01
We present a new method of three-dimensional smoothed particle hydrodynamics (SPH) designed to model systems dominated by deformation along a preferential axis. These systems cause severe problems for SPH codes using spherical kernels, which are best suited for modeling systems which retain rough spherical symmetry. Our method allows the smoothing length in the direction of the deformation to evolve independently of the smoothing length in the perpendicular plane, resulting in a kernel with a spheroidal shape. As a result the spatial resolution in the direction of deformation is significantly improved. As a test case we present the one-dimensional homologous collapse of a zero-temperature, uniform-density cloud, which serves to demonstrate the advantages of spheroidal kernels. We also present new results on the problem of the tidal disruption of a star by a massive black hole.
Propagation of light pseudoscalar particles in a cosmological background.
Tinebra, F.
1995-12-01
The interaction between light pseudoscalar particles, having properties much like those of the invisible axion, and the cosmic-microwave-background electromagnetic field is considered in a simple cosmic evolutionary scenario. The quantum theory of this interaction is hence canonically developed and applied to study seed, possibly of cosmological origin, extragalactic radiation fields. After looking at the issue of anisotropies in the microwave cosmic-background radiation spectrum, the main arguments setting limits on the couplings of the right, popular, invisible axion are briefly reviewed. By allowing for a minimal extension of the Big Bang Standard Cosmology, namely by a primordial magnetic field, the author argues that a hypothetical, very light pseudoscalar particle, not too different from the recently proposed alternate version of the invisible axion, could give rise to very peculiar observational effects in the microwave cosmic background radiation sector. In a quite simplified version of such a model, the most important effect which emerges is the issue of a highly polarized, wavelength-dependent quadrupolar-like anisotropy. This prediction could be feeling with the claimed, at present well-established observation of a quadrupolar component in the cosmic microwave background radiation by COBE satellite.
Effects of cosmological constant on motion of UHECR particles
Institute of Scientific and Technical Information of China (English)
CHEN; Shaoxia; CHANG; Zhe
2005-01-01
Recent astronomical observations manifest that about two-thirds of the whole energy in the Universe is contributed by a small positive cosmological constant ∧ (＞ 0).Then, an asymptotically de Sitter spacetime is premised naturally. However, physics in the de Sitter spacetime is very different from that in the Minkowski spacetime. As the first step, a covariant formalism of the kinematics in the de Sitter spacetime is presented here.By solving exactly the equations of motion for a field, we obtain the dispersion relation of a free particle. It is noticed that the dispersion relation is dependent on the degree of freedom of angular momentum of the particle. We show the threshold anomaly of the ultra high energy cosmic ray disappears naturally in the framework of the de Sitter kinematics.
On the coupling between spinning particles and cosmological gravitational waves
Milillo, Irene; Montani, Giovanni
2008-01-01
The influence of spin in a system of classical particles on the propagation of gravitational waves is analyzed in the cosmological context of primordial thermal equilibrium. On a flat Friedmann-Robertson-Walker metric, when the precession is neglected, there is no contribution due to the spin to the distribution function of the particles. Adding a small tensor perturbation to the background metric, we study if a coupling between gravitational waves and spin exists that can modify the evolution of the distribution function, leading to new terms in the anisotropic stress, and then to a new source for gravitational waves. In the chosen gauge, the final result is that, in the absence of other kind of perturbations, there is no coupling between spin and gravitational waves.
General Relativistic Smoothed Particle Hydrodynamics code developments: A progress report
Faber, Joshua; Silberman, Zachary; Rizzo, Monica
2017-01-01
We report on our progress in developing a new general relativistic Smoothed Particle Hydrodynamics (SPH) code, which will be appropriate for studying the properties of accretion disks around black holes as well as compact object binary mergers and their ejecta. We will discuss in turn the relativistic formalisms being used to handle the evolution, our techniques for dealing with conservative and primitive variables, as well as those used to ensure proper conservation of various physical quantities. Code tests and performance metrics will be discussed, as will the prospects for including smoothed particle hydrodynamics codes within other numerical relativity codebases, particularly the publicly available Einstein Toolkit. We acknowledge support from NSF award ACI-1550436 and an internal RIT D-RIG grant.
Smoothed particle hydrodynamics method from a large eddy simulation perspective
Di Mascio, A.; Antuono, M.; Colagrossi, A.; Marrone, S.
2017-03-01
The Smoothed Particle Hydrodynamics (SPH) method, often used for the modelling of the Navier-Stokes equations by a meshless Lagrangian approach, is revisited from the point of view of Large Eddy Simulation (LES). To this aim, the LES filtering procedure is recast in a Lagrangian framework by defining a filter that moves with the positions of the fluid particles at the filtered velocity. It is shown that the SPH smoothing procedure can be reinterpreted as a sort of LES Lagrangian filtering, and that, besides the terms coming from the LES convolution, additional contributions (never accounted for in the SPH literature) appear in the equations when formulated in a filtered fashion. Appropriate closure formulas are derived for the additional terms and a preliminary numerical test is provided to show the main features of the proposed LES-SPH model.
Smoothed Particle Hydrodynamic of Hydraulic Jumps in Spillways
Jonsson, Patrick
2015-01-01
This thesis focus on the complex natural phenomena of hydraulic jumps using the numerical method Smoothed Particle Hydrodynamics (SPH). A hydraulic jump is highly turbulent and associated with turbulent energy dissipation, air entrainment, surface waves and spray and strong dissipative processes. It can be found not only in natural streams and in engineered open channels, but also in your kitchen sink at home. The dissipative features are utilized in hydropower spillways and stilling basins t...
Mirror-type Boundary Condition in Smoothed Particle Hydrodynamics
Marjani, A.; Edge, B. L.
2013-12-01
The main purpose of this study is to enhance the Smoothed Particle Hydrodynamics (SPH) method that can accurately simulate the hydrodynamic forces on a structure and can be used for determining efficient designs for wave energy devices. Smoothed particle hydrodynamics is a method used in various fields of study. Unlike the finite difference method (FDM), SPH is a Lagrangian mesh-free method in which each particle moves according to the property of the surrounding flow and governing conservation equations, and carries the properties of water such as density, pressure and mass. Smoothed Particle Hydrodynamics is recently applied to a wide range of fluid mechanics problems. Although it is known as a highly accurate model, slow performance in 3D interface is one of its drawbacks. Not only the computational time becomes very long but also the number of processors and required memory are not easily available. Practical applications deal with high Reynolds numbers that requires high resolution to achieve adequate accuracy. A large number of coastal engineering problems are geometrically symmetric; hence, as a solution, mirror boundary condition is introduced and applied to two different tests in this paper, one is the impact of solitary wave on a large circular cylinder and the other is the interaction of dam break wave and structure. Mirror boundary condition can either produce a remarkable speedup with the same number of processors or the same running time with less number of processors. Regarding the fact that SPH algorithm yields Np log(Np) particle interactions at each time step, reducing the number of particles by a factor of 2 decreases the total number of interactions by a factor greater than 2. In other words, the relation between computational time and the number of particles does not behave like a linear function. Results show that smaller number of particles results in fewer particle interactions and less communications between processors. We believe that this
Effects of the quantum vacuum in particle physics and cosmology
Energy Technology Data Exchange (ETDEWEB)
Smirnov, Juri
2014-11-26
In this work we investigate numerous effects of virtual particles on processes relevant for particle physics and cosmology. A central question is, whether radiative spontaneous electroweak symmetry breaking can be combined with neutrino mass generation, we find that the answer is affirmative. We discuss the implication of the RSSB on the neutrino mass phenomenology and low-energy observables. Furthermore, by comparing the models to experimental data we find that several anomalies in the present observations favour particular scenarios over the pure Standard Model hypothesis. We are able to show, that the presence of sterile neutrinos with active-sterile mixing of order 10{sup -3} and masses in the TeV range leads to a reduced invisible decay width of the Z-boson and can bring the NuTeV observations in agreement with theoretical expectations. The models we discuss naturally incorporate long lived particles which can serve as dark matter candidates and we investigate this phenomenologically. We find that the combination of the requirements leads to interesting constraints on the model and parameter space. We find that loop induced electromagnetic moments for the neutral dark matter candidates, lead to interactions with charged particles. We use this and derive new constraints from existing XENON100 and LUX data. In addition we study how vacuum effects can backreact on a given geometry in electromagnetism and semiclassical gravity. We find that in the case of gravity the conformal set up plays a special role and indicate several ideas for further investigation of this topic.
One-particle-irreducible consistency relations for cosmological perturbations
Goldberger, Walter D.; Hui, Lam; Nicolis, Alberto
2013-05-01
We derive consistency relations for correlators of scalar cosmological perturbations that hold in the “squeezed limit” in which one or more of the external momenta become soft. Our results are formulated as relations between suitably defined one-particle-irreducible N-point and (N-1)-point functions that follow from residual spatial conformal diffeomorphisms of the unitary gauge Lagrangian. As such, some of these relations are exact to all orders in perturbation theory and do not rely on approximate de Sitter invariance or other dynamical assumptions (e.g., properties of the operator product expansion or the behavior of modes at the horizon crossing). The consistency relations apply model-independently to cosmological scenarios in which the time evolution is driven by a single scalar field. Besides reproducing the known results for single-field inflation in the slow-roll limit, we verify that our consistency relations hold more generally, for instance, in ghost condensate models in flat space. We comment on possible extensions of our results to multifield models.
Galaxy mergers on a moving mesh: a comparison with smoothed-particle hydrodynamics
Hayward, Christopher C; Springel, Volker; Hernquist, Lars; Vogelsberger, Mark
2013-01-01
Galaxy mergers have been investigated for decades using smoothed particle hydrodynamics (SPH), but recent work highlighting inaccuracies inherent in the traditional SPH technique calls into question the reliability of previous studies. We explore this issue by comparing a suite of Gadget-3 SPH simulations of idealised (i.e., non-cosmological) isolated discs and galaxy mergers with otherwise identical calculations performed using the moving-mesh code Arepo. When black hole (BH) accretion and active galactic nucleus (AGN) feedback are not included, the star formation histories (SFHs) obtained from the two codes agree well. When BHs are included, the code- and resolution-dependent variations in the SFHs are more significant, but the agreement is still good, and the stellar mass formed over the course of a simulation is robust to variations in the numerical method. During a merger, the gas morphology and phase structure are initially similar prior to the starburst phase. However, once a hot gaseous halo has forme...
Scaling laws for implicit viscosities in smoothed particle hydrodynamics
Bierwisch, Claas; Polfer, Pit
2017-06-01
Smoothed particle hydrodynamics (SPH) is a particle-based method which solves continuum equations such as the Navier-Stokes equations. A periodic fluidic system under homogeneous shear is studied using SPH in the present work. The total pressure of the system and the shear stress contributions from the SPH interaction terms for pressure and viscosity as well as the contribution caused by velocity fluctuations are analyzed. It is found that the pressure and the shear stress contributions obey certain scaling laws depending on physical properties of the system such as compressibility, viscosity and shear rate as well as the spatial resolution. Some of the identified relations resemble scaling laws for the rheology of dense granular flows. These findings render an assessment of the convergence with respect to the spatial resolution of SPH simulations possible. Furthermore, the similarities between numerical SPH particles and physical grains in dense flow provide a deeper understanding of the nature of the SPH method.
SPHRAY: A Smoothed Particle Hydrodynamics Ray Tracer for Radiative Transfer
Altay, Gabriel; Pelupessy, Inti
2008-01-01
We introduce SPHRAY, a Smoothed Particle Hydrodynamics (SPH) ray tracer designed to solve the 3D, time dependent, radiative transfer (RT) equations for arbitrary density fields. The SPH nature of SPHRAY makes the incorporation of separate hydrodynamics and gravity solvers very natural. SPHRAY relies on a Monte Carlo (MC) ray tracing scheme that does not interpolate the SPH particles onto a grid but instead integrates directly through the SPH kernels. Given initial conditions and a description of the sources of ionizing radiation, the code will calculate the non-equilibrium ionization state (HI, HII, HeI, HeII, HeIII, e) and temperature (internal energy/entropy) of each SPH particle. The sources of radiation can include point like objects, diffuse recombination radiation, and a background field from outside the computational volume. The MC ray tracing implementation allows for the quick introduction of new physics and is parallelization friendly. A quick Axis Aligned Bounding Box (AABB) test taken from compute...
Multiscale simulation of ideal mixtures using smoothed dissipative particle dynamics
Petsev, Nikolai D.; Leal, L. Gary; Shell, M. Scott
2016-02-01
Smoothed dissipative particle dynamics (SDPD) [P. Español and M. Revenga, Phys. Rev. E 67, 026705 (2003)] is a thermodynamically consistent particle-based continuum hydrodynamics solver that features scale-dependent thermal fluctuations. We obtain a new formulation of this stochastic method for ideal two-component mixtures through a discretization of the advection-diffusion equation with thermal noise in the concentration field. The resulting multicomponent approach is consistent with the interpretation of the SDPD particles as moving volumes of fluid and reproduces the correct fluctuations and diffusion dynamics. Subsequently, we provide a general multiscale multicomponent SDPD framework for simulations of molecularly miscible systems spanning length scales from nanometers to the non-fluctuating continuum limit. This approach reproduces appropriate equilibrium properties and is validated with simulation of simple one-dimensional diffusion across multiple length scales.
A Vector Potential implementation for Smoothed Particle Magnetohydrodynamics
Stasyszyn, Federico
2014-01-01
The development of smooth particle magnetohydrodynamic (SPMHD) has significantly improved the simulation of complex astrophysical processes. However, the preservation the solenoidality of the magnetic field is still a severe problem for the MHD. A formulation of the induction equation with a vector potential would solve the problem. Unfortunately all previous attempts suffered from instabilities. In the present work, we evolve the vector potential in the Coulomb gauge and smooth the derived magnetic field for usage in the momentum equation. With this implementation we could reproduce classical test cases in a stable way. A simple test case demonstrates the possible failure of widely used direct integration of the magnetic field, even with the usage of a divergence cleaning method.
Modelling free surface flows with smoothed particle hydrodynamics
Directory of Open Access Journals (Sweden)
L.Di G.Sigalotti
2006-01-01
Full Text Available In this paper the method of Smoothed Particle Hydrodynamics (SPH is extended to include an adaptive density kernel estimation (ADKE procedure. It is shown that for a van der Waals (vdW fluid, this method can be used to deal with free-surface phenomena without difficulties. In particular, arbitrary moving boundaries can be easily handled because surface tension is effectively simulated by the cohesive pressure forces. Moreover, the ADKE method is seen to increase both the accuracy and stability of SPH since it allows the width of the kernel interpolant to vary locally in a way that only the minimum necessary smoothing is applied at and near free surfaces and sharp fluid-fluid interfaces. The method is robust and easy to implement. Examples of its resolving power are given for both the formation of a circular liquid drop under surface tension and the nonlinear oscillation of excited drops.
Chi-squared smoothed adaptive particle-filtering based prognosis
Ley, Christopher P.; Orchard, Marcos E.
2017-01-01
This paper presents a novel form of selecting the likelihood function of the standard sequential importance sampling/re-sampling particle filter (SIR-PF) with a combination of sliding window smoothing and chi-square statistic weighting, so as to: (a) increase the rate of convergence of a flexible state model with artificial evolution for online parameter learning (b) improve the performance of a particle-filter based prognosis algorithm. This is applied and tested with real data from oil total base number (TBN) measurements from three haul trucks. The oil data has high measurement uncertainty and an unknown phenomenological state model. Performance of the proposed algorithm is benchmarked against the standard form of SIR-PF estimation which utilises the Normal (Gaussian) likelihood function. Both implementations utilise the same particle filter based prognosis algorithm so as to provide a common comparison. A sensitivity analysis is also performed to further explore the effects of the combination of sliding window smoothing and chi-square statistic weighting to the SIR-PF.
Smoothed dissipative particle dynamics with angular momentum conservation
Energy Technology Data Exchange (ETDEWEB)
Müller, Kathrin, E-mail: k.mueller@fz-juelich.de; Fedosov, Dmitry A., E-mail: d.fedosov@fz-juelich.de; Gompper, Gerhard, E-mail: g.gompper@fz-juelich.de
2015-01-15
Smoothed dissipative particle dynamics (SDPD) combines two popular mesoscopic techniques, the smoothed particle hydrodynamics and dissipative particle dynamics (DPD) methods, and can be considered as an improved dissipative particle dynamics approach. Despite several advantages of the SDPD method over the conventional DPD model, the original formulation of SDPD by Español and Revenga (2003) [9], lacks angular momentum conservation, leading to unphysical results for problems where the conservation of angular momentum is essential. To overcome this limitation, we extend the SDPD method by introducing a particle spin variable such that local and global angular momentum conservation is restored. The new SDPD formulation (SDPD+a) is directly derived from the Navier–Stokes equation for fluids with spin, while thermal fluctuations are incorporated similarly to the DPD method. We test the new SDPD method and demonstrate that it properly reproduces fluid transport coefficients. Also, SDPD with angular momentum conservation is validated using two problems: (i) the Taylor–Couette flow with two immiscible fluids and (ii) a tank-treading vesicle in shear flow with a viscosity contrast between inner and outer fluids. For both problems, the new SDPD method leads to simulation predictions in agreement with the corresponding analytical theories, while the original SDPD method fails to capture properly physical characteristics of the systems due to violation of angular momentum conservation. In conclusion, the extended SDPD method with angular momentum conservation provides a new approach to tackle fluid problems such as multiphase flows and vesicle/cell suspensions, where the conservation of angular momentum is essential.
Modeling electrokinetic flows by consistent implicit incompressible smoothed particle hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Pan, Wenxiao; Kim, Kyungjoo; Perego, Mauro; Tartakovsky, Alexandre M.; Parks, Michael L.
2017-04-01
We present an efficient implicit incompressible smoothed particle hydrodynamics (I2SPH) discretization of Navier-Stokes, Poisson-Boltzmann, and advection-diffusion equations subject to Dirichlet or Robin boundary conditions. It is applied to model various two and three dimensional electrokinetic flows in simple or complex geometries. The I2SPH's accuracy and convergence are examined via comparison with analytical solutions, grid-based numerical solutions, or empirical models. The new method provides a framework to explore broader applications of SPH in microfluidics and complex fluids with charged objects, such as colloids and biomolecules, in arbitrary complex geometries.
Generating optimal initial conditions for smooth particle hydrodynamics (SPH) simulations
Energy Technology Data Exchange (ETDEWEB)
Diehl, Steven [Los Alamos National Laboratory; Rockefeller, Gabriel M [Los Alamos National Laboratory; Fryer, Christopher L [Los Alamos National Laboratory
2008-01-01
We present a new optimal method to set up initial conditions for Smooth Particle Hydrodynamics Simulations, which may also be of interest for N-body simulations. This new method is based on weighted Voronoi tesselations (WVTs) and can meet arbitrarily complex spatial resolution requirements. We conduct a comprehensive review of existing SPH setup methods, and outline their advantages, limitations and drawbacks. A serial version of our WVT setup method is publicly available and we give detailed instruction on how to easily implement the new method on top of an existing parallel SPH code.
(Participation in high energy physics): Task C, Particle physics and cosmology
Energy Technology Data Exchange (ETDEWEB)
Turner, M.S.
1992-05-01
Over the past year or so the research of our group has spanned many topics at the boundary of particle physics and cosmology. The major focus has been in the general areas of inflation, cosmological phase transitions, astrophysical constraints to particle physics theories, and dark matter/structure formation as it relates to particle physics. Narrative summaries of the research of the individual group members are given in this paper.
Rubakov, V A
2014-01-01
In these lectures we first concentrate on the cosmological problems which, hopefully, have to do with the new physics to be probed at the LHC: the nature and origin of dark matter and generation of matter-antimatter asymmetry. We give several examples showing the LHC cosmological potential. These are WIMPs as cold dark matter, gravitinos as warm dark matter, and electroweak baryogenesis as a mechanism for generating matter-antimatter asymmetry. In the remaining part of the lectures we discuss the cosmological perturbations as a tool for studying the epoch preceeding the conventional hot stage of the cosmological evolution.
Smoothed Particle Hydrodynamics modeling of granular column collapse
Szewc, Kamil
2016-01-01
The Smoothed Particle Hydrodynamics (SPH) is a particle-based, Lagrangian method for fluid-flow simulations. In this work, fundamental concepts of this method are first briefly recalled. Then, the ability to accurately model granular materials using an introduced visco-plastic constitutive rheological model is studied. For this purpose sets of numerical calculations (2D and 3D) of the fundamental problem of the collapse of initially vertical cylinders of granular materials are performed. The results of modeling of columns with different aspect ratios and different angles of internal friction are presented. The numerical outcomes are assessed not only with respect to the reference experimental data but also with respect to other numerical methods, namely the Distinct Element Method and the Finite Element Method. In order to improve the numerical efficiency of the method, the Graphics Processing Units implementation is presented and some related issues are discussed. It is believed that this study corresponds t...
Smoothed Particle Magnetohydrodynamics: A State of the Union
Lewis, Benjamin T; Tricco, Terrence S
2016-01-01
Obtaining a stable magnetohydrodynamical (MHD) formalism in SPH - i.e. smoothed particle magnetohydrodynamics (SPMHD) - has proven remarkably difficult. To implement MHD requires two steps: a modification to the momentum equation and an induction equation, and both present challenges. We first provide an overview of how SPMHD is implemented, and then discuss how this implementation fails and the limitation of various corrective methods - with particular reference to the effects of particle disorder. Although there are many problems for which, with careful choice of corrective measures, good results can be obtained, we then show that, at the very limits of the state of the art, the ability to perform stable MHD calculations in SPH is curtailed by numerical issues.
SPAMCART: a code for smoothed particle Monte Carlo radiative transfer
Lomax, O.; Whitworth, A. P.
2016-10-01
We present a code for generating synthetic spectral energy distributions and intensity maps from smoothed particle hydrodynamics simulation snapshots. The code is based on the Lucy Monte Carlo radiative transfer method, i.e. it follows discrete luminosity packets as they propagate through a density field, and then uses their trajectories to compute the radiative equilibrium temperature of the ambient dust. The sources can be extended and/or embedded, and discrete and/or diffuse. The density is not mapped on to a grid, and therefore the calculation is performed at exactly the same resolution as the hydrodynamics. We present two example calculations using this method. First, we demonstrate that the code strictly adheres to Kirchhoff's law of radiation. Secondly, we present synthetic intensity maps and spectra of an embedded protostellar multiple system. The algorithm uses data structures that are already constructed for other purposes in modern particle codes. It is therefore relatively simple to implement.
CRKSPH - A Conservative Reproducing Kernel Smoothed Particle Hydrodynamics Scheme
Frontiere, Nicholas; Owen, J Michael
2016-01-01
We present a formulation of smoothed particle hydrodynamics (SPH) that employs a first-order consistent reproducing kernel function, exactly interpolating linear fields with particle tracers. Previous formulations using reproducing kernel (RK) interpolation have had difficulties maintaining conservation of momentum due to the fact the RK kernels are not, in general, spatially symmetric. Here, we utilize a reformulation of the fluid equations such that mass, momentum, and energy are all manifestly conserved without any assumption about kernel symmetries. Additionally, by exploiting the increased accuracy of the RK method's gradient, we formulate a simple limiter for the artificial viscosity that reduces the excess diffusion normally incurred by the ordinary SPH artificial viscosity. Collectively, we call our suite of modifications to the traditional SPH scheme Conservative Reproducing Kernel SPH, or CRKSPH. CRKSPH retains the benefits of traditional SPH methods (such as preserving Galilean invariance and manif...
SPAMCART: a code for smoothed particle Monte Carlo radiative transfer
Lomax, O
2016-01-01
We present a code for generating synthetic SEDs and intensity maps from Smoothed Particle Hydrodynamics simulation snapshots. The code is based on the Lucy (1999) Monte Carlo Radiative Transfer method, i.e. it follows discrete luminosity packets, emitted from external and/or embedded sources, as they propagate through a density field, and then uses their trajectories to compute the radiative equilibrium temperature of the ambient dust. The density is not mapped onto a grid, and therefore the calculation is performed at exactly the same resolution as the hydrodynamics. We present two example calculations using this method. First, we demonstrate that the code strictly adheres to Kirchhoff's law of radiation. Second, we present synthetic intensity maps and spectra of an embedded protostellar multiple system. The algorithm uses data structures that are already constructed for other purposes in modern particle codes. It is therefore relatively simple to implement.
CRKSPH - A Conservative Reproducing Kernel Smoothed Particle Hydrodynamics Scheme
Frontiere, Nicholas; Raskin, Cody D.; Owen, J. Michael
2017-03-01
We present a formulation of smoothed particle hydrodynamics (SPH) that utilizes a first-order consistent reproducing kernel, a smoothing function that exactly interpolates linear fields with particle tracers. Previous formulations using reproducing kernel (RK) interpolation have had difficulties maintaining conservation of momentum due to the fact the RK kernels are not, in general, spatially symmetric. Here, we utilize a reformulation of the fluid equations such that mass, linear momentum, and energy are all rigorously conserved without any assumption about kernel symmetries, while additionally maintaining approximate angular momentum conservation. Our approach starts from a rigorously consistent interpolation theory, where we derive the evolution equations to enforce the appropriate conservation properties, at the sacrifice of full consistency in the momentum equation. Additionally, by exploiting the increased accuracy of the RK method's gradient, we formulate a simple limiter for the artificial viscosity that reduces the excess diffusion normally incurred by the ordinary SPH artificial viscosity. Collectively, we call our suite of modifications to the traditional SPH scheme Conservative Reproducing Kernel SPH, or CRKSPH. CRKSPH retains many benefits of traditional SPH methods (such as preserving Galilean invariance and manifest conservation of mass, momentum, and energy) while improving on many of the shortcomings of SPH, particularly the overly aggressive artificial viscosity and zeroth-order inaccuracy. We compare CRKSPH to two different modern SPH formulations (pressure based SPH and compatibly differenced SPH), demonstrating the advantages of our new formulation when modeling fluid mixing, strong shock, and adiabatic phenomena.
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Trimble, Virginia [Department of Physics and Astronomy, University of California-Irvine, CA 92697-4575 (United States); Las Cumbres Global Telescope Network, Goleta, CA 93117 (United States)
2007-05-07
Here are two textbooks, both published by Springer and each roughly half devoted to cosmology-the large scale structure and evolution of the Universe. I can imagine a context (not the same context) in which each would be useful. And there the similarities largely end. Bergstrom and Goobar's (hereafter B and G) other topic is particle astrophysics, and they are addressing students who already have some knowledge of advanced quantum mechanics and classical field theory (or who can master some relativistic dynamics and the Dirac equation on the basis of a couple of very information-dense appendices). The book is meant for use at the graduate level, probably the second year by US standards (the authors are from Stockholm). Schneider (hereafter PS), on the other hand, begins with galaxies, and then alternates between cosmological topics of gradually increasing sophistication (expanding universe to CMB fluctuations) and additional galactic topics-clusters, quasars and all. The book is meant as the second half of an introductory astronomy/astrophysics course for physics majors, and in the US would fit into an upper division 'capstone' course. Each is meant for a single semester class at the target level, and might be squeezed into a 10-week term with elimination of some topics. B and G is a paperback of a second edition, with colour confined to a central block of plates, relatively few graphs and drawings, but lots of complex equations. PS is a hard cover translation from a German original, with colour used freely in astronomical images and graphs throughout, with fewer and less complex equations. Though the nominal difference in copyright date is only two years (2006 for PS, 2004 for B and G), the former is considerably more up to date, mentioning, for instance, that the third year WMAP results are not different enough from the first year to justify redoing drawings and such (I agree). What can you expect to get if you buy one or both of these? B and G
Kelvin-Helmholtz instabilities in Smoothed Particle Hydrodynamics
Valcke, Sander; Roediger, Elke; Dejonghe, Herwig
2010-01-01
In this paper we investigate whether Smoothed Particle Hydrodynamics (SPH), equipped with artificial conductivity, is able to capture the physics of density/energy discontinuities in the case of the so-called shearing layers test, a test for examining Kelvin-Helmholtz (KH) instabilities. We can trace back each failure of SPH to show KH rolls to two causes: i) shock waves travelling in the simulation box and ii) particle clumping, or more generally, particle noise. The probable cause of shock waves is the Local Mixing Instability (LMI), previously identified in the literature. Particle noise on the other hand is a problem because it introduces a large error in the SPH momentum equation. We also investigate the role of artificial conductivity (AC). Including AC is necessary for the long-term behavior of the simulation (e.g. to get $\\lambda=1/2, 1$ KH rolls). In sensitive hydrodynamical simulations great care is however needed in selecting the AC signal velocity, with the default formulation leading to too much ...
Link, R; Link, Robert; Pierce, Michael J.
1998-01-01
We describe a new approach for the determination of cosmological parameters using gravitational lensing systems with multiple arcs, exploiting the fact that a given cluster can produce multiple arcs from sources over a broad range in redshift. The coupling between the critical radius of a single arc and the projected mass density of the lensing cluster can be avoided by considering the relative positions of two or more arcs. Cosmological sensitivity appears through the angular size-redshift relation. We consider simulated data constructed using a more general form for the potential, realistic sources, and an assumed cosmology and present a method for simultaneously inverting the lens and extracting the cosmological parameters. The input data required are the image and measured redshifts for the arcs. The technique relies upon the conservation of surface brightness in gravitationally lensed systems. We find that for a simple lens model our approach can recover the cosmological parameters assumed in the constru...
SPHRAY: A Smoothed Particle Hydrodynamics Ray Tracer for Radiative Transfer
Altay, Gabriel; Croft, Rupert A. C.; Pelupessy, Inti
2011-03-01
SPHRAY, a Smoothed Particle Hydrodynamics (SPH) ray tracer, is designed to solve the 3D, time dependent, radiative transfer (RT) equations for arbitrary density fields. The SPH nature of SPHRAY makes the incorporation of separate hydrodynamics and gravity solvers very natural. SPHRAY relies on a Monte Carlo (MC) ray tracing scheme that does not interpolate the SPH particles onto a grid but instead integrates directly through the SPH kernels. Given initial conditions and a description of the sources of ionizing radiation, the code will calculate the non-equilibrium ionization state (HI, HII, HeI, HeII, HeIII, e) and temperature (internal energy/entropy) of each SPH particle. The sources of radiation can include point like objects, diffuse recombination radiation, and a background field from outside the computational volume. The MC ray tracing implementation allows for the quick introduction of new physics and is parallelization friendly. A quick Axis Aligned Bounding Box (AABB) test taken from computer graphics applications allows for the acceleration of the raytracing component. We present the algorithms used in SPHRAY and verify the code by performing all the test problems detailed in the recent Radiative Transfer Comparison Project of Iliev et. al. The Fortran 90 source code for SPHRAY and example SPH density fields are made available online.
Metal diffusion in smoothed particle hydrodynamics simulations of dwarf galaxies
Williamson, David John; Kawata, Daisuke
2016-01-01
We perform a series of smoothed particle hydrodynamics simulations of isolated dwarf galaxies to compare different metal mixing models. In particular, we examine the role of diffusion in the production of enriched outflows, and in determining the metallicity distributions of gas and stars. We investigate different diffusion strengths, by changing the pre-factor of the diffusion coefficient, by varying how the diffusion coefficient is calculated from the local velocity distribution, and by varying whether the speed of sound is included as a velocity term. Stronger diffusion produces a tighter [O/Fe]-[Fe/H] distribution in the gas, and cuts off the gas metallicity distribution function at lower metallicities. Diffusion suppresses the formation of low-metallicity stars, even with weak diffusion, and also strips metals from enriched outflows. This produces a remarkably tight correlation between "metal mass-loading" (mean metal outflow rate divided by mean metal production rate) and the strength of diffusion, even...
SPHGal: Smoothed Particle Hydrodynamics with improved accuracy for Galaxy simulations
Hu, Chia-Yu; Walch, Stefanie; Moster, Benjamin P; Oser, Ludwig
2014-01-01
We present the smoothed-particle hydrodynamics implementation SPHGal which incorporates several recent developments into the GADGET code. This includes a pressure-entropy formulation of SPH with a Wendland kernel, a higher order estimate of velocity gradients, a modified artificial viscosity switch with a strong limiter, and artificial conduction of thermal energy. We conduct a series of idealized hydrodynamic tests and show that while the pressure-entropy formulation is ideal for resolving fluid mixing at contact discontinuities, it performs conspicuously worse when strong shocks are involved due to the large entropy discontinuities. Including artificial conduction at shocks greatly improves the results. The Kelvin-Helmholtz instability can be resolved properly and dense clouds in the blob test dissolve qualitatively in agreement with other improved SPH implementations. We further perform simulations of an isolated Milky Way like disk galaxy and find a feedback-induced instability developing if too much arti...
Simulations of dolphin kick swimming using smoothed particle hydrodynamics.
Cohen, Raymond C Z; Cleary, Paul W; Mason, Bruce R
2012-06-01
In competitive human swimming the submerged dolphin kick stroke (underwater undulatory swimming) is utilized after dives and turns. The optimal dolphin kick has a balance between minimizing drag and maximizing thrust while also minimizing the physical exertion required of the swimmer. In this study laser scans of athletes are used to provide realistic swimmer geometries in a single anatomical pose. These are rigged and animated to closely match side-on video footage. Smoothed Particle Hydrodynamics (SPH) fluid simulations are performed to evaluate variants of this swimming stroke technique. This computational approach provides full temporal and spatial information about the flow moving around the deforming swimmer model. The effects of changes in ankle flexibility and stroke frequency are investigated through a parametric study. The results suggest that the net streamwise force on the swimmer is relatively insensitive to ankle flexibility but is strongly dependent on kick frequency.
Smoothed Particle Magnetohydrodynamics IV - Using the Vector Potential
Price, Daniel J
2009-01-01
In this paper we investigate the use of the vector potential as a means of maintaining the divergence constraint in the numerical solution of the equations of Magnetohydrodynamics (MHD) using the Smoothed Particle Hydrodynamics (SPH) method. We derive a self-consistent formulation of the equations of motion using a variational principle that is constrained by the numerical formulation of both the induction equation and the curl operator used to obtain the magnetic field, which guarantees exact and simultaneous conservation of momentum, energy and entropy in the numerical scheme. This leads to a novel formulation of the MHD force term, unique to the vector potential, which differs from previous formulations. We also demonstrate how dissipative terms can be correctly formulated for the vector potential such that the contribution to the entropy is positive definite and the total energy is conserved. On a standard suite of numerical tests in one, two and three dimensions we find firstly that the consistent formul...
Axisymmetric smoothed particle hydrodynamics with self-gravity
García-Senz, D; Cabezon, R M; Bravo, E
2008-01-01
The axisymmetric form of the hydrodynamic equations within the smoothed particle hydrodynamics (SPH) formalism is presented and checked using idealized scenarios taken from astrophysics (free fall collapse, implosion and further pulsation of a sun-like star), gas dynamics (wall heating problem, collision of two streams of gas) and inertial confinement fusion (ICF, -ablative implosion of a small capsule-). New material concerning the standard SPH formalism is given. That includes the numerical handling of those mass points which move close to the singularity axis, more accurate expressions for the artificial viscosity and the heat conduction term and an easy way to incorporate self-gravity in the simulations. The algorithm developed to compute gravity does not rely in any sort of grid, leading to a numerical scheme totally compatible with the lagrangian nature of the SPH equations.
The small-scale turbulent dynamo in smoothed particle magnetohydrodynamics
Tricco, Terrence S; Federrath, Christoph
2016-01-01
Supersonic turbulence is believed to be at the heart of star formation. We have performed smoothed particle magnetohydrodynamics (SPMHD) simulations of the small-scale dynamo amplification of magnetic fields in supersonic turbulence. The calculations use isothermal gas driven at rms velocity of Mach 10 so that conditions are representative of star-forming molecular clouds in the Milky Way. The growth of magnetic energy is followed for 10 orders in magnitude until it reaches saturation, a few percent of the kinetic energy. The results of our dynamo calculations are compared with results from grid-based methods, finding excellent agreement on their statistics and their qualitative behaviour. The simulations utilise the latest algorithmic developments we have developed, in particular, a new divergence cleaning approach to maintain the solenoidal constraint on the magnetic field and a method to reduce the numerical dissipation of the magnetic shock capturing scheme. We demonstrate that our divergence cleaning met...
Smoothed Particle Magnetohydrodynamics Simulations of Protostellar Jets and Turbulent Dynamos
Tricco, Terrence S; Federrath, Christoph; Bate, Matthew R
2013-01-01
We presents results from Smoothed Particle Magnetohydrodynamics simulations of collapsing molecular cloud cores, and dynamo amplification of the magnetic field in the presence of Mach 10 magnetised turbulence. Our star formation simulations have produced, for the first time ever, highly collimated magnetised protostellar jets from the first hydrostatic core phase. Up to 40% of the initial core mass may be ejected through this outflow. The primary difficulty in performing these simulations is maintaining the divergence free constraint of the magnetic field, and to address this issue, we have developed a new divergence cleaning method which has allowed us to stably follow the evolution of these protostellar jets for long periods. The simulations performed of supersonic MHD turbulence are able to exponentially amplify magnetic energy by up to 10 orders of magnitude via turbulent dynamo. To reduce numerical dissipation, a new shock detection algorithm is utilised which is able to track magnetic shocks throughout ...
Protostellar jets and magnetised turbulence with smoothed particle magnetohydrodynamics
Tricco, Terrence
2016-01-01
Magnetic fields are an integral component of the formation of stars. During my thesis work, I built new methods to model magnetic fields in smoothed particle magnetohydrodynamics which enforce the divergence-free constraint on the magnetic field and reduce numerical dissipation of the magnetic field. Using these methods, we have performed simulations of isolated protostar formation, studying the production of jets and outflows of material and their effect on transporting angular momentum away from the protostar and reducing the efficiency of star formation. A major code comparison project on the small-scale turbulent dynamo amplification of magnetic fields was performed, using conditions representative of molecular clouds, the formation site of stars. The results were compared against results from grid-based methods, finding excellent agreement on their statistics and qualitative behaviour. I will outline the numerical methods developed, and present the results from our protostar and molecular cloud simulations.
An Hourglass Control Algorithm for Lagrangian Smooth Particle Hydrodynamics
Ganzenmüller, Georg C
2014-01-01
This paper presents a stabilization scheme which addresses the rank-deficiency problem in meshless collocation methods for solid mechanics. Specifically, Smooth-Particle Hydrodynamics (SPH) in the Total Lagrangian formalism is considered. This method is rank-deficient in the sense that the SPH approximation of the deformation gradient is not unique with respect to the positions of the integration points. The non-uniqueness can result in the formation of zero-energy modes. If undetected, these modes can grow and completely dominate the solution. Here, an algorithm is introduced, which effectively suppresses these modes in a fashion similar to hour-glass control mechanisms in Finite-Element methods. Simulations utilizing this control algorithm result exhibit much improved stability, accuracy, and error convergence properties. In contrast to an alternative method which eliminates zero-energy modes, namely the use of additional integration points, the here presented algorithm is easy to implement and computationa...
Cosmology as Relativistic Particle Mechanics: From Big Crunch to Big Bang
Russo, J G
2004-01-01
Cosmology can be viewed as geodesic motion in an appropriate metric on an `augmented' target space; here we obtain these geodesics from an effective relativistic particle action. As an application, we find some exact (flat and curved) cosmologies for models with N scalar fields taking values in a hyperbolic target space for which the augmented target space is a Milne universe. The singularities of these cosmologies correspond to points at which the particle trajectory crosses the Milne horizon, suggesting a novel resolution of them, which we explore via the Wheeler-deWitt equation.
Simulating deposition of high density tailings using smoothed particle hydrodynamics
Babaoglu, Yagmur; Simms, Paul H.
2017-08-01
Tailings are a slurry of silt-sized residual material derived from the milling of rock. High density (HD) tailings are tailings that have been sufficiently dewatered to a point where they exhibit a yield stress upon deposition. They form gently sloped stacks on the surface when deposited; this eliminates or minimizes the need for dams or embankments for containment. Understanding the flow behaviour of high density tailings is essential for estimating the final stack geometry and overall slope angle. This paper focuses on modelling the flow behaviour of HD tailings using smoothed particle hydrodynamics (SPH) method incorporating a `bi-viscosity' model to simulate the non-Newtonian behaviour. The model is validated by comparing the numerical results with bench scale experiments simulating single or multi-layer deposits in two-dimensions. The results indicate that the model agreed fairly well with the experimental work, excepting some repulsion of particles away from the bottom boundary closer to the toe of the deposits. Novel aspects of the work, compared to other simulation of Bingham fluids by SPH, are the simulation of multilayer deposits and the use of a stopping criteria to characterize the rest state.
Smoothed Particle Hydrodynamics for the Simulation of Laser Produced Plasmas
Griffith, Alec; Holladay, Tyler; Murillo, Michael S.
2016-10-01
To address the design and interpretation of experiments at next generation light sources such as at the SLAC LCLS and the LANL proposed MaRIE a simulation of the laser produced plasma targets has been developed. Smoothed particle hydrodynamics is used to capture the full experimental time and length scales, large degrees of deformation, and the experimental environment's open boundary conditions. Additionally the model incorporates plasma transport with thermal conduction, the electric potential, and a two species model of the electrons and ions. The electron and ion particle representations in SPH allow for time dependent ionization and recombination while addressing the disparate masses of the two species. To gain computational speedup our simulation takes advantage of parallelism, and to reduce computational cost we have explored using data structures such as the linked cell list and octree as well as algorithmic techniques such as the fast mutipole method. We will discuss the results of simulating several possible experimental configurations using our model. This work was supported by the Los Alamos National Laboratory computational physics workshop.
Hybrid molecular-continuum simulations using smoothed dissipative particle dynamics.
Petsev, Nikolai D; Leal, L Gary; Shell, M Scott
2015-01-28
We present a new multiscale simulation methodology for coupling a region with atomistic detail simulated via molecular dynamics (MD) to a numerical solution of the fluctuating Navier-Stokes equations obtained from smoothed dissipative particle dynamics (SDPD). In this approach, chemical potential gradients emerge due to differences in resolution within the total system and are reduced by introducing a pairwise thermodynamic force inside the buffer region between the two domains where particles change from MD to SDPD types. When combined with a multi-resolution SDPD approach, such as the one proposed by Kulkarni et al. [J. Chem. Phys. 138, 234105 (2013)], this method makes it possible to systematically couple atomistic models to arbitrarily coarse continuum domains modeled as SDPD fluids with varying resolution. We test this technique by showing that it correctly reproduces thermodynamic properties across the entire simulation domain for a simple Lennard-Jones fluid. Furthermore, we demonstrate that this approach is also suitable for non-equilibrium problems by applying it to simulations of the start up of shear flow. The robustness of the method is illustrated with two different flow scenarios in which shear forces act in directions parallel and perpendicular to the interface separating the continuum and atomistic domains. In both cases, we obtain the correct transient velocity profile. We also perform a triple-scale shear flow simulation where we include two SDPD regions with different resolutions in addition to a MD domain, illustrating the feasibility of a three-scale coupling.
Hybrid molecular-continuum simulations using smoothed dissipative particle dynamics
Energy Technology Data Exchange (ETDEWEB)
Petsev, Nikolai D.; Leal, L. Gary; Shell, M. Scott [Department of Chemical Engineering, University of California at Santa Barbara, Santa Barbara, California 93106-5080 (United States)
2015-01-28
We present a new multiscale simulation methodology for coupling a region with atomistic detail simulated via molecular dynamics (MD) to a numerical solution of the fluctuating Navier-Stokes equations obtained from smoothed dissipative particle dynamics (SDPD). In this approach, chemical potential gradients emerge due to differences in resolution within the total system and are reduced by introducing a pairwise thermodynamic force inside the buffer region between the two domains where particles change from MD to SDPD types. When combined with a multi-resolution SDPD approach, such as the one proposed by Kulkarni et al. [J. Chem. Phys. 138, 234105 (2013)], this method makes it possible to systematically couple atomistic models to arbitrarily coarse continuum domains modeled as SDPD fluids with varying resolution. We test this technique by showing that it correctly reproduces thermodynamic properties across the entire simulation domain for a simple Lennard-Jones fluid. Furthermore, we demonstrate that this approach is also suitable for non-equilibrium problems by applying it to simulations of the start up of shear flow. The robustness of the method is illustrated with two different flow scenarios in which shear forces act in directions parallel and perpendicular to the interface separating the continuum and atomistic domains. In both cases, we obtain the correct transient velocity profile. We also perform a triple-scale shear flow simulation where we include two SDPD regions with different resolutions in addition to a MD domain, illustrating the feasibility of a three-scale coupling.
Beyond Standard Model Physics: At the Frontiers of Cosmology and Particle Physics
Lopez-Suarez, Alejandro O.
I begin to write this thesis at a time of great excitement in the field of cosmology and particle physics. The aim of this thesis is to study and search for beyond the standard model (BSM) physics in the cosmological and high energy particle fields. There are two main questions, which this thesis aims to address: 1) what can we learn about the inflationary epoch utilizing the pioneer gravitational wave detector Adv. LIGO?, and 2) what are the dark matter particle properties and interactions with the standard model particles?. This thesis will focus on advances in answering both questions.
Vittorio, Nicola
2017-01-01
Modern cosmology has changed significantly over the years, from the discovery to the precision measurement era. The data now available provide a wealth of information, mostly consistent with a model where dark matter and dark energy are in a rough proportion of 3:7. The time is right for a fresh new textbook which captures the state-of-the art in cosmology. Written by one of the world's leading cosmologists, this brand new, thoroughly class-tested textbook provides graduate and undergraduate students with coverage of the very latest developments and experimental results in the field. Prof. Nicola Vittorio shows what is meant by precision cosmology, from both theoretical and observational perspectives.
Simulating Magnetized Laboratory Plasmas with Smoothed Particle Hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Johnson, Jeffrey N. [Univ. of California, Davis, CA (United States)
2009-01-01
The creation of plasmas in the laboratory continues to generate excitement in the physics community. Despite the best efforts of the intrepid plasma diagnostics community, the dynamics of these plasmas remains a difficult challenge to both the theorist and the experimentalist. This dissertation describes the simulation of strongly magnetized laboratory plasmas with Smoothed Particle Hydrodynamics (SPH), a method born of astrophysics but gaining broad support in the engineering community. We describe the mathematical formulation that best characterizes a strongly magnetized plasma under our circumstances of interest, and we review the SPH method and its application to astrophysical plasmas based on research by Phillips [1], Buerve [2], and Price and Monaghan [3]. Some modifications and extensions to this method are necessary to simulate terrestrial plasmas, such as a treatment of magnetic diffusion based on work by Brookshaw [4] and by Atluri [5]; we describe these changes as we turn our attention toward laboratory experiments. Test problems that verify the method are provided throughout the discussion. Finally, we apply our method to the compression of a magnetized plasma performed by the Compact Toroid Injection eXperiment (CTIX) [6] and show that the experimental results support our computed predictions.
Metal Diffusion in Smoothed Particle Hydrodynamics Simulations of Dwarf Galaxies
Williamson, David; Martel, Hugo; Kawata, Daisuke
2016-05-01
We perform a series of smoothed particle hydrodynamics simulations of isolated dwarf galaxies to compare different metal mixing models. In particular, we examine the role of diffusion in the production of enriched outflows and in determining the metallicity distributions of gas and stars. We investigate different diffusion strengths by changing the pre-factor of the diffusion coefficient, by varying how the diffusion coefficient is calculated from the local velocity distribution, and by varying whether the speed of sound is included as a velocity term. Stronger diffusion produces a tighter [O/Fe]-[Fe/H] distribution in the gas and cuts off the gas metallicity distribution function at lower metallicities. Diffusion suppresses the formation of low-metallicity stars, even with weak diffusion, and also strips metals from enriched outflows. This produces a remarkably tight correlation between “metal mass-loading” (mean metal outflow rate divided by mean metal production rate) and the strength of diffusion, even when the diffusion coefficient is calculated in different ways. The effectiveness of outflows at removing metals from dwarf galaxies and the metal distribution of the gas is thus dependent on the strength of diffusion. By contrast, we show that the metallicities of stars are not strongly dependent on the strength of diffusion, provided that some diffusion is present.
Dusty gas with one fluid in smoothed particle hydrodynamics
Laibe, Guillaume
2014-01-01
In a companion paper we have shown how the equations describing gas and dust as two fluids coupled by a drag term can be reformulated to describe the system as a single fluid mixture. Here we present a numerical implementation of the one-fluid dusty gas algorithm using Smoothed Particle Hydrodynamics (SPH). The algorithm preserves the conservation properties of the SPH formalism. In particular, the total gas and dust mass, momentum, angular momentum and energy are all exactly conserved. Shock viscosity and conductivity terms are generalised to handle the two-phase mixture accordingly. The algorithm is benchmarked against a comprehensive suit of problems: dustybox, dustywave, dustyshock and dustyoscill, each of them addressing different properties of the method. We compare the performance of the one-fluid algorithm to the standard two-fluid approach. The one-fluid algorithm is found to solve both of the fundamental limitations of the two- fluid algorithm: it is no longer possible to concentrate dust below the ...
A switch to reduce resistivity in smoothed particle magnetohydrodynamics
Tricco, Terrence S
2013-01-01
Artificial resistivity is included in Smoothed Particle Magnetohydrodynamics simulations to capture shocks and discontinuities in the magnetic field. Here we present a new method for adapting the strength of the applied resistivity so that shocks are captured but the dissipation of the magnetic field away from shocks is minimised. Our scheme utilises the gradient of the magnetic field as a shock indicator, setting {\\alpha}_B = h|gradB|/|B|, such that resistivity is switched on only where strong discontinuities are present. The advantage to this approach is that the resistivity parameter does not depend on the absolute field strength. The new switch is benchmarked on a series of shock tube tests demonstrating its ability to capture shocks correctly. It is compared against a previous switch proposed by Price & Monaghan (2005), showing that it leads to lower dissipation of the field, and in particular, that it succeeds at capturing shocks in the regime where the Alfv\\'en speed is much less than the sound spe...
Investigating the Global Collapse of Filaments Using Smoothed Particle Hydrodynamics
Clarke, Seamus D
2015-01-01
We use Smoothed Particle Hydrodynamic simulations of cold, uniform density, self-gravitating filaments, to investigate their longitudinal collapse timescales; these timescales are important because they determine the time available for a filament to fragment into cores. A filament is initially characterised by its line-mass, $\\mu$, its radius, $R$ (or equivalently its density $\\rho\\!=\\!\\mu/\\pi R^2$), and its aspect ratio, $A\\;\\,(\\equiv Z/R$, where $Z$ is its half-length). The gas is only allowed to contract longitudinally, i.e. parallel to the symmetry axis of the filament (the $z$-axis). Pon et al. (2012) have considered the global dynamics of such filaments analytically. They conclude that short filaments ($A\\! \\!5$) undergo end-dominated collapse, i.e. two dense clumps form at the ends of the filament and converge on the centre sweeping up mass as they go, on a time-scale $t_{_{\\rm END}} \\sim 0.98\\,A^{1/2}\\,(G\\rho)^{-1/2}$. Our simulations do not corroborate these predictions. First, for all $A\\! > \\!2$, ...
The Giant Impact Simulations with Density Independent Smoothed Particle Hydrodynamics
Hosono, Natsuki; Makino, Junichiro; Genda, Hidenori; Ida, Shigeru
2016-01-01
At present, the giant impact (GI) is the most widely accepted model for the origin of the Moon. Most of the numerical simulations of GI have been carried out with the smoothed particle hydrodynamics (SPH) method. Recently, however, it has been pointed out that standard formulation of SPH (SSPH) has difficulties in the treatment of a contact discontinuity such as a core-mantle boundary and a free surface such as a planetary surface. This difficulty comes from the assumption of differentiability of density in SSPH. We have developed an alternative formulation of SPH, density independent SPH (DISPH), which is based on differentiability of pressure instead of density to solve the problem of a contact discontinuity. In this paper, we report the results of the GI simulations with DISPH and compare them with those obtained with SSPH. We found that the disk properties, such as mass and angular momentum produced by DISPH is different from that of SSPH. In general, the disks formed by DISPH are more compact: while form...
Yokoyama, Jun'ichi; Suto, Yasushi
1991-01-01
A phenomenological model to produce isocurvature baryon-number fluctuations is proposed in the framework of inflationary cosmology. The resulting spectrum of density fluctuation is very different from the conventional Harrison-Zel'dovich shape. The model, with the parameters satisfying several requirements from particle physics and cosmology, provides an appropriate initial condition for the minimal baryon isocurvature scenario of galaxy formation discussed by Peebles.
Exotic Smoothness and Quantum Gravity II: exotic R^4, singularities and cosmology
Asselmeyer-Maluga, T
2011-01-01
Since the first work on exotic smoothness in physics, it was folklore to assume a direct influence of exotic smoothness to quantum gravity. In the second paper, we calculate the "smoothness structure" part of the path integral in quantum gravity for the exotic R^4 as non-compact manifold. We discuss the influence of the "sum over geometries" to the "sum over smoothness structure". There are two types of exotic R^4: large (no smooth embedded 3-sphere) and small (smooth embedded 3-sphere). A large exotic R^4 can be produced by using topologically slice but smoothly non-slice knots whereas a small exotic R^4 is constructed by a 5-dimensional h-cobordism between compact 4-manifolds. The results are applied to the calculation of expectation values, i.e. we discuss the two observables, volume and Wilson loop. Then the appearance of naked singularities is analyzed. By using Mostow rigidity, we obtain a justification of area and volume quantization again. Finally exotic smoothness of the R^4 produces in all cases (sm...
Fluctuations of the cosmic background temperature in unstable-particle cosmologies
Energy Technology Data Exchange (ETDEWEB)
Doroshkevich, A.G.; Khlopov, M.Y.
1985-07-01
Introduction of unstable elementary particles of finite mass into the standard cosmological model will weaken the predicted temperature fluctuations of the microwave background on all angular scales, except perhaps for the quadrupole mode. The small-scale anisotropy is estimated. Analysis of large-scale temperature anisotropies might test the unstable-particle model.
Vanaverbeke, S.; Keppens, R.; Poedts, S.; Boffin, H.
2009-01-01
We describe the algorithms implemented in the first version of GRADSPH, a parallel, tree-based, smoothed particle hydrodynamics code for simulating self-gravitating astrophysical systems written in FORTRAN 90. The paper presents details on the implementation of the Smoothed Particle Hydro (SPH) desc
Explicit 3D continuum fracture modeling with smooth particle hydrodynamics
Benz, W.; Asphaug, E.
1993-01-01
Impact phenomena shaped our solar system. As usual for most solar system processes, the scales are far different than we can address directly in the laboratory. Impact velocities are often much higher than we can achieve, sizes are often vastly larger, and most impacts take place in an environment where the only gravitational force is the mutual pull of the impactors. The Smooth Particle Hydrodynamics (SPH) technique has been applied in the past to the simulations of giant impacts. In these simulations, the colliding objects were so massive (at least a sizeable fraction of the Earth's mass) that material strength was negligible compared to gravity. This assumption can no longer be made when the bodies are much smaller. To this end, we have developed a 3D SPH code that includes a strength model to which we have added a von Mises yielding relation for stresses beyond the Hugoniot Elastic Limit. At the lower stresses associated with brittle failure, we use a rate-dependent strength based on the nucleation of incipient flaws whose number density is given by a Weibull distribution. Following Grady and Kipp and Melosh et al., we introduce a state variable D ('damage'), 0 less than D less than 1, which expresses the local reduction in strength due to crack growth under tensile loading. Unfortunately for the hydrodynamics, Grady and Kipp's model predicts which fragments are the most probable ones and not the ones that are really formed. This means, for example, that if a given laboratory experiment is modeled, the fragment distribution obtained from the Grady-Kipp theory would be equivalent to a ensemble average over many realizations of the experiment. On the other hand, the hydrodynamics itself is explicit and evolves not an ensemble average but very specific fragments. Hence, there is a clear incompatibility with the deterministic nature of the hydrodynamics equations and the statistical approach of the Grady-Kipp dynamical fracture model. We remedy these shortcomings
Cosmology and Particle Physics beyond Standard Models Ten Years of the SEENET-MTP Network
Álvarez-Gaumé, Luis; Stojkovic, Dejan
2014-01-01
This publication - "Cosmology and Particle Physics beyond Standard Models" - is dedicated to the celebration of the tenth anniversary of the Southeastern European Network in Mathematical and Theoretical Physics (SEENET-MTP). As a Theme Collection, rather than a Monograph or Proceedings, this volume presents a number of reports and overviews, a few research papers and a short note. However, some of them are excellent examples of a nowadays increasingly deep interplay between particle physics and cosmology. Contributions span a wide range of topics in cosmology, particle physics, but also gravity, including the interface of these fields. The presented work is of both theoretical and experimental/ observational nature. The contributions represent recent progress in their respective fields: inflation, dark matter, neutrino physics, supersymmetry, collider physics, string theory, quantum gravity, black hole physics and massive gravity.
The giant impact simulations with density independent smoothed particle hydrodynamics
Hosono, Natsuki; Saitoh, Takayuki R.; Makino, Junichiro; Genda, Hidenori; Ida, Shigeru
2016-06-01
At present, the giant impact (GI) is the most widely accepted model for the origin of the Moon. Most of the numerical simulations of GI have been carried out with the smoothed particle hydrodynamics (SPH) method. Recently, however, it has been pointed out that standard formulation of SPH (SSPH) has difficulties in the treatment of a contact discontinuity such as a core-mantle boundary and a free surface such as a planetary surface. This difficulty comes from the assumption of differentiability of density in SSPH. We have developed an alternative formulation of SPH, density independent SPH (DISPH), which is based on differentiability of pressure instead of density to solve the problem of a contact discontinuity. In this paper, we report the results of the GI simulations with DISPH and compare them with those obtained with SSPH. We found that the disk properties, such as mass and angular momentum produced by DISPH is different from that of SSPH. In general, the disks formed by DISPH are more compact: while formation of a smaller mass moon for low-oblique impacts is expected with DISPH, inhibition of ejection would promote formation of a larger mass moon for high-oblique impacts. Since only the improvement of core-mantle boundary significantly affects the properties of circumplanetary disks generated by GI and DISPH has not been significantly improved from SSPH for a free surface, we should be very careful when some conclusions are drawn from the numerical simulations for GI. And it is necessary to develop the numerical hydrodynamical scheme for GI that can properly treat the free surface as well as the contact discontinuity.
Modeling rainfall-runoff processes using smoothed particle hydrodynamics with mass-varied particles
Chang, Tsang-Jung; Chang, Yu-Sheng; Chang, Kao-Hua
2016-12-01
In this study, a novel treatment of adopting mass-varied particles in smoothed particle hydrodynamics (SPH) is proposed to solve the shallow water equations (SWEs) and model the rainfall-runoff process. Since SWEs have depth-averaged or cross-section-averaged features, there is no sufficient dimension to add rainfall particles. Thus, SPH-SWE methods have focused on modeling discharge flows in open channels or floodplains without rainfall. With the proposed treatment, the application of SPH-SWEs can be extended to rainfall-runoff processes in watersheds. First, the numerical procedures associated with using mass-varied particles in SPH-SWEs are introduced and derived. Then, numerical validations are conducted for three benchmark problems, including uniform rainfall over a 1D flat sloping channel, nonuniform rain falling over a 1D three-slope channel with different rainfall durations, and uniform rainfall over a 2D plot with complex topography. The simulated results indicate that the proposed treatment can avoid the necessity of a source term function of mass variation, and no additional particles are needed for the increase of mass. Rainfall-runoff processes can be well captured in the presence of hydraulic jumps, dry/wet bed flows, and supercritical/subcritical/transcritical flows. The proposed treatment using mass-varied particles was proven robust and reliable for modeling rainfall-runoff processes. It can provide a new alternative for investigating practical hydrological problems.
Smoothed Particle Inference: A Kilo-Parametric Method for X-ray Galaxy Cluster Modeling
Peterson, J. R.; Marshall, P. J.; Andersson, K.
2005-01-01
We propose an ambitious new method that models the intracluster medium in clusters of galaxies as a set of X-ray emitting smoothed particles of plasma. Each smoothed particle is described by a handful of parameters including temperature, location, size, and elemental abundances. Hundreds to thousands of these particles are used to construct a model cluster of galaxies, with the appropriate complexity estimated from the data quality. This model is then compared iteratively with X-ray data in t...
Equations of motion in Double Field Theory: from classical particles to quantum cosmology
Kan, Nahomi; Shiraishi, Kiyoshi
2012-01-01
The equation of motion for a point particle in the background field of double field theory is considered. We find that the motion is described by a geodesic flow in the doubled geometry. Inspired by analysis on the particle motion, we propose a modified model of quantum string cosmology, which includes two scale factors. The report is based on Phys. Rev. D84 (2011) 124049 [arXiv:1108.5795].
Cosmological evolution of thermal relic particles in $f(R)$ gravity
Capozziello, S; Lambiase, G; Pizza, L
2015-01-01
By considering $f(R)$ gravity models, the cosmic evolution is modified with respect to the standard $\\Lambda$CDM scenario. In particular, the thermal history of particles results modified. In this paper, we derive the evolution of relics particles (WIMPs) assuming a reliable $f(R)$ cosmological solution and taking into account observational constraints. The connection to the PAMELA experiment is also discussed. Results are consistent with constraints coming from BICEP2 and PLANCK experiments.
Particle creation and non-adiabatic transitions in quantum cosmology
Massar, S
1998-01-01
The aim of this paper is to compute transitions amplitudes in quantum cosmology, and in particular pair creation amplitudes and radiative transitions. To this end, we apply a double adiabatic development to the solutions of the Wheeler-DeWitt equation restricted to mini-superspace wherein gravity is described by the scale factor $a$. The first development consists in working with instantaneous eigenstates, in $a$, of the matter Hamiltonian. The second development is applied to the gravitational part of the wave function and generalizes the usual WKB approximation. We then obtain an exact equation which replaces the Wheeler-DeWitt equation and determines the evolution, i.e. the dependence in $a$, of the coefficients of this double expansion. When working in the gravitational adiabatic approximation, the simplified equation delivers the unitary evolution of transition amplitudes occurring among instantaneous eigenstates. Upon abandoning this approximation, one finds that there is an additional coupling among ma...
22nd SLAC Summer Institute on Particle Physics: Particle physics, astrophysics and cosmology
Chan, J.; Deporcel, L.
The seven-day school portion of the Institute revolved around the question of dark matter: where is it and what is it? Reviews were given of microlensing searches for baryonic dark matter, of dark matter candidates in the form of neutrinos and exotic particles, and of low-noise detection techniques used to search for the latter. The history of the universe, from the Big Bang to the role of dark matter in the formation of large-scale structure, was also covered. Other lecture series described the astrophysics that might be done with x-ray timing experiments and through the detection of gravitational radiation. As in past years, the lectures each morning were followed by stimulating afternoon discussion sessions, in which students could pursue with the lecturers the topics that most interested them. The Institute concluded with a three-day topical conference covering recent developments in theory and experiment. Highlights from the astrophysical and cosmological arenas included observations of anisotropy in the cosmic microwave background, and of the mysterious gamma-ray bursters. From terrestrial accelerators came tantalizing hints of the top quark and marked improvements in precision electroweak measurements, among many other results. Selected papers are indexed separately for inclusion in the Energy Science and Technology Database.
PKDGRAV3: Beyond Trillion Particle Cosmological Simulations for the Next Era of Galaxy Surveys
Potter, Douglas; Teyssier, Romain
2016-01-01
We report on the successful completion of a 2 trillion particle cosmological simulation to z=0 run on the Piz Daint supercomputer (CSCS, Switzerland), using 4000+ GPU nodes for a little less than 80h of wall-clock time or 350,000 node hours. Using multiple benchmarks and performance measurements on the US Oak Ridge National Laboratory Titan supercomputer, we demonstrate that our code PKDGRAV3, delivers, to our knowledge, the fastest time-to-solution for large-scale cosmological N-body simulations. This was made possible by using the Fast Multipole Method in conjunction with individual and adaptive particle time steps, both deployed efficiently (and for the first time) on supercomputers with GPU-accelerated nodes. The very low memory footprint of PKDGRAV3 allowed us to run the first ever benchmark with 8 trillion particles on Titan, and to achieve perfect scaling up to 18000 nodes and a peak performance of 10 Pflops.
Energy Technology Data Exchange (ETDEWEB)
Turner, M.S.
1992-05-01
Over the past year or so the research of our group has spanned many topics at the boundary of particle physics and cosmology. The major focus has been in the general areas of inflation, cosmological phase transitions, astrophysical constraints to particle physics theories, and dark matter/structure formation as it relates to particle physics. Narrative summaries of the research of the individual group members are given in this paper.
Particle creation in a f(R) theory with cosmological constraints
Pereira, S H
2014-01-01
In this paper we study the creation of super-massive real scalar particles in the framework of a $f(R)=R-\\beta/R^n$ modified gravity theory, with parameters constrained by observational data. The analysis is restrict to a homogeneous and isotropic flat and radiation dominated universe. We compare the results to the standard Einstein gravity with cosmological constant ($\\Lambda CDM$ model), and we show that the total number density of created particles in the $f(R)$ model is very close to the standard case. Another interesting result is that the spectrum of created particles is $\\beta$ independent at early times.
From stringy particle physics to moduli stabilisation and cosmology
Energy Technology Data Exchange (ETDEWEB)
Honecker, Gabriele [Institute for Physics (WA THEP) and Cluster of Excellence PRISMA, Johannes Gutenberg University, Mainz (Germany)
2016-04-15
Intersecting D6-branes provide a geometrically intuitive road to stringy particle physics models, where D6-branes stuck at orbifold singularities can lead to the stabilisation of deformation moduli, and the QCD axion can arise from the open string sector in a very constrained way compared to pure field theory. We demonstrate this interplay of different physical features here through an explicit model. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Three-Dimensional Smoothed Particle Hydrodynamics Simulation for Liquid Droplet with Surface Tension
Terissa, Hanifa; Barecasco, Agra; Naa, Christian Fredy
2013-01-01
We provide a basic method of Smoothed Particle Hydrodynamics (SPH) to simulate liquid droplet with surface tension in three dimensions. Liquid droplet is a simple case for surface tension modeling. Surface tension works only on fluid surface. In SPH method, we simply apply the surface tension on the boundary particles of liquid. The particle on the 3D boundary was detected dynamically using Free-Surface Detection algorithm. The normal vector and curvature of the boundary surface were calculat...
Indian Academy of Sciences (India)
Chandel S; Ram Shri
2016-03-01
The paper deals with the study of particle creation and bulk viscosity in the evolution of spatially homogeneous and anisotropic Bianchi type-V cosmological models in the framework of Saez–Ballester theory of gravitation. Particle creation and bulk viscosity are considered as separate irreversible processes. The energy–momentum tensor is modified to accommodate the viscous pressure and creation pressure which is associated with the creation of matter out of gravitational field. A special law of variation of Hubble parameter is applied to obtain exact solutions of field equations in two types of cosmologies, one with power-law expansion and the other with exponential expansion. Cosmological model with power-law expansion has a Big-Bang singularity at time $t = 0$, whereas the model with exponential expansion has no finite singularity. We study bulk viscosity and particle creation in each model in four different cases. The bulk viscosity coefficient is obtained for full causal, Eckart’s and truncated theories. All physical parameters are calculated and thoroughly discussed in both models.
Kapilevich, L V; Zaĭtseva, T N; Nosarev, A V; D'iakova, E Iu; Petlina, Z R; Ogorodova, L M; Ageev, B G; Magaeva, A A; Itin, V I; Terekhova, O G; Medvedev, M A
2012-02-01
Contractile responses of airways segments of porpoises inhaling nanopowder CoFe2O4 were stidued by means of a mechanographic method. Inhalation of the nanosize particles of CoFe2O4 in vivo and in vitro testing the nanomaterial on isolated smooth muscles led to potentiation histaminergic, cholinergic contractile activity in airways of porpoises and to strengthening of adrenergic relaxing answers. Nanosize particles vary amplitude of hyperpotassium reductions in smooth muscle segments of airways similarly to the effect of depolymerizing drug colchicine.
Implication of Sterile Fermions in Particle Physics and Cosmology
Lucente, Michele
2016-01-01
The neutrino mass generation mechanism, the nature of dark matter and the origin of the baryon asymmetry of the Universe are three compelling questions that cannot be accounted for in the Standard Model of particle physics. In this thesis we focus on all these issues by providing a possible solution in terms of a minimal extension of the Standard Model, consisting in the addition of a set of sterile fermions to the field content of the theory. Sterile fermions are gauge singlet fields, that can interact via mixing with the active neutrinos. We focus on the Inverse Seesaw mechanism, which is characterised by a low (TeV or lower) new physics scale and that can be tested in current and future experimental facilities. We present the model building analysis that points towards the minimal realisations of the mechanism, and the phenomenological study in order to accommodate light neutrino masses and to impose all the relevant experimental constraints in the model, as well as the expected experimental signatures. We...
Saro, A.; De Lucia, G.; Borgani, S.; Dolag, K.
2010-08-01
We present a detailed comparison between the galaxy populations within a massive cluster, as predicted by hydrodynamical smoothed particle hydrodynamics (SPH) simulations and by a semi-analytic model (SAM) of galaxy formation. Both models include gas cooling and a simple prescription of star formation, which consists in transforming instantaneously any cold gas available into stars, while neglecting any source of energy feedback. This simplified comparison is thus not meant to be compared with observational data, but is aimed at understanding the level of agreement, at the stripped-down level considered, between two techniques that are widely used to model galaxy formation in a cosmological framework and which present complementary advantages and disadvantages. We find that, in general, galaxy populations from SAMs and SPH have similar statistical properties, in agreement with previous studies. However, when comparing galaxies on an object-by-object basis, we find a number of interesting differences: (i) the star formation histories of the brightest cluster galaxies (BCGs) from SAM and SPH models differ significantly, with the SPH BCG exhibiting a lower level of star formation activity at low redshift, and a more intense and shorter initial burst of star formation with respect to its SAM counterpart; (ii) while all stars associated with the BCG were formed in its progenitors in the SAM used here, this holds true only for half of the final BCG stellar mass in the SPH simulation, the remaining half being contributed by tidal stripping of stars from the diffuse stellar component associated with galaxies accreted on the cluster halo; (iii) SPH satellites can lose up to 90 per cent of their stellar mass at the time of accretion, due to tidal stripping, a process not included in the SAM used in this paper; (iv) in the SPH simulation, significant cooling occurs on the most massive satellite galaxies and this lasts for up to 1 Gyr after accretion. This physical process is
Bode, P; Bode, Paul; Ostriker, Jeremiah P.
2003-01-01
An improved implementation of an N-body code for simulating collisionless cosmological dynamics is presented. TPM (Tree-Particle-Mesh) combines the PM method on large scales with a tree code to handle particle-particle interactions at small separations. After the global PM forces are calculated, spatially distinct regions above a given density contrast are located; the tree code calculates the gravitational interactions inside these denser objects at higher spatial and temporal resolution. The new implementation includes individual particle time steps within trees, an improved treatment of tidal forces on trees, new criteria for higher force resolution and choice of time step, and parallel treatment of large trees. TPM is compared to P^3M and a tree code (GADGET) and is found to give equivalent results in significantly less time. The implementation is highly portable (requiring a Fortran compiler and MPI) and efficient on parallel machines. The source code can be found at http://astro.princeton.edu/~bode/TPM/
Particle Creation in Pre-Big-Bang Cosmology theory and observational consequences
Durrer, R; Sakellariadou, M
2000-01-01
We present some phenomenological aspects of the pre-big-bang cosmological model inspired by the duality properties of string theory. In particular, assuming the spatial sections of the homogeneous background geometry to be isotropic, we discuss the quantum production of perturbations of the background fields (gravitons, dilatons, moduli fields), as well as the production of particles which do not contribute to the background, which we call ``seeds''. As such we consider the cases of electromagnetic and axionic seeds. We also discuss their possible observational consequences, for example, we study whether they can provide the origin of primordial galactic magnetic fields, and whether they can generate the initial fluctuations leading to the formation of large-scale structure and the measured cosmic microwave background anisotropies. We finally analyze axion and photon production in four dimensional anisotropic pre-big-bang cosmological models.
Cosmological particle-in-cell simulations with ultra-light axion dark matter
Veltmaat, Jan
2016-01-01
We study cosmological structure formation with ultra-light axion dark matter (or "fuzzy dark matter", FDM) using a particle-mesh scheme to account for the quantum pressure arising in the Madelung formulation of the Schr\\"odinger-Poisson equations. Sub-percent level energy conservation and correct linear behavior are demonstrated. Whereas the code gives rise to the same core-halo profiles as direct simulations of the Schr\\"odinger equation, it does not reproduce the detailed interference patterns at the resolution used here. In cosmological simulations with FDM inital conditions, we find a maximum relative difference of O($10\\%$) in the power spectrum near the quantum Jeans length compared to using a standard N-body code with identical initial conditions. This shows that the effect of quantum pressure during nonlinear structure formation cannot be neglected for precision constraints on a dark matter component consisting of ultra-light axions.
Cosmological particle-in-cell simulations with ultralight axion dark matter
Veltmaat, Jan; Niemeyer, Jens C.
2016-12-01
We study cosmological structure formation with ultralight axion dark matter, or "fuzzy dark matter" (FDM), using a particle-mesh scheme to account for the quantum pressure arising in the Madelung formulation of the Schrödinger-Poisson equations. Subpercent-level energy conservation and correct linear behavior are demonstrated. Whereas the code gives rise to the same core-halo profiles as direct simulations of the Schrödinger equation, it does not reproduce the detailed interference patterns. In cosmological simulations with FDM initial conditions, we find a maximum relative difference of O(10%) in the power spectrum near the quantum Jeans length compared to using a standard N -body code with identical initial conditions. This shows that the effect of quantum pressure during nonlinear structure formation cannot be neglected for precision constraints on a dark matter component consisting of ultralight axions.
Comparison of Particle Flow Code and Smoothed Particle Hydrodynamics Modelling of Landslide Run outs
Preh, A.; Poisel, R.; Hungr, O.
2009-04-01
In most continuum mechanics methods modelling the run out of landslides the moving mass is divided into a number of elements, the velocities of which can be established by numerical integration of Newtońs second law (Lagrangian solution). The methods are based on fluid mechanics modelling the movements of an equivalent fluid. In 2004, McDougall and Hungr presented a three-dimensional numerical model for rapid landslides, e.g. debris flows and rock avalanches, called DAN3D.The method is based on the previous work of Hungr (1995) and is using an integrated two-dimensional Lagrangian solution and meshless Smooth Particle Hydrodynamics (SPH) principle to maintain continuity. DAN3D has an open rheological kernel, allowing the use of frictional (with constant porepressure ratio) and Voellmy rheologies and gives the possibility to change material rheology along the path. Discontinuum (granular) mechanics methods model the run out mass as an assembly of particles moving down a surface. Each particle is followed exactly as it moves and interacts with the surface and with its neighbours. Every particle is checked on contacts with every other particle in every time step using a special cell-logic for contact detection in order to reduce the computational effort. The Discrete Element code PFC3D was adapted in order to make possible discontinuum mechanics models of run outs. Punta Thurwieser Rock Avalanche and Frank Slide were modelled by DAN as well as by PFC3D. The simulations showed correspondingly that the parameters necessary to get results coinciding with observations in nature are completely different. The maximum velocity distributions due to DAN3D reveal that areas of different maximum flow velocity are next to each other in Punta Thurwieser run out whereas the distribution of maximum flow velocity shows almost constant maximum flow velocity over the width of the run out regarding Frank Slide. Some 30 percent of total kinetic energy is rotational kinetic energy in
Non-isothermal diffusion in a binary mixture with smoothed particle hydrodynamics
Thieulot, C; Espanol, P
2005-01-01
We explore the possibility of controlling the pattern formation in a purely diffusive binary mixture described by a van der Waals equation of state in non-isothermal situations. Simulations are conducted with a previously formulated thermodynamically consistent smoothed particle hydrodynamics model
A Method to Improve First Order Approximation of Smoothed Particle Hydrodynamics
Institute of Scientific and Technical Information of China (English)
CHEN Si; ZHOU Dai; BAO Yan; DONG Shi-lin
2008-01-01
Smoothed particle hydrodynamics (SPH) is a useful meshless method. The first and second ordersare the most popular derivatives of the field function in the mechanical governing equations. New methodswere proposed to improve accuracy of SPH approximation by the lemma proved. The lemma describes therelationship of functions and their SPH approximation. Finally, the error comparison of SPH method with orwithout our improvement was carried out.
Non-isothermal diffusion in a binary mixture with smoothed particle hydrodynamics
Thieulot, C; Espanol, P
2005-01-01
We explore the possibility of controlling the pattern formation in a purely diffusive binary mixture described by a van der Waals equation of state in non-isothermal situations. Simulations are conducted with a previously formulated thermodynamically consistent smoothed particle hydrodynamics model
Institute of Scientific and Technical Information of China (English)
胡甫强; 毕学工
2009-01-01
提出基于物理的、实时的技术模拟水体,根据Smoothed Particle Hydrodynamics方法求解流体动力学的Navier-Stokes方程,并运用Marching Cubes体绘制算法重建流体表面.实验表明基于粒子的方法能模拟流体所特有的飞溅、漩涡等现象,Marching Cubes在表面重建的高效性使模拟达到实时、交互的应用.
Cosmological solutions with gravitational particle production and non-zero curvature
Paliathanasis, Andronikos; Pan, Supriya
2016-01-01
In a homogeneous and isotropic universe with non-zero spatial curvature we consider the effects of gravitational particle production in the dynamics of the universe. We show that the dynamics of the universe in such a background are characterized by a single nonlinear differential equation which is significantly dependent on the rate of particle creation and whose solutions can be dominated by curvature effects at early times. For different particle creation rates we apply the singularity test in order to find the analytic solutions of the background dynamics. We describe the behavior of the cosmological solutions for both open and closed universes. We also show how the effects of curvature can be produced by the presence of a second perfect fluid with an appropriate equation of state.
The generation model of particle physics and the cosmological matter-antimatter asymmetry problem
Robson, B A
2016-01-01
The matter-antimatter asymmetry problem, corresponding to the virtual nonexistence of antimatter in the universe, is one of the greatest mysteries of cosmology. Within the framework of the Generation Model (GM) of particle physics, it is demonstrated that the matter-antimatter asymmetry problem may be understood in terms of the composite leptons and quarks of the GM. It is concluded that there is essentially no matter-antimatter asymmetry in the present universe and that the observed hydrogen-antihydrogen asymmetry may be understood in terms of statistical fluctuations associated with the complex many-body processes involved in the formation of either a hydrogen atom or an antihydrogen atom.
Late time cosmological phase transitions 1: Particle physics models and cosmic evolution
Frieman, Joshua A.; Hill, Christopher T.; Watkins, Richard
1991-01-01
We described a natural particle physics basis for late-time phase transitions in the universe. Such a transition can seed the formation of large-scale structure while leaving a minimal imprint upon the microwave background anisotropy. The key ingredient is an ultra-light pseudo-Nambu-Goldstone boson with an astronomically large (O(kpc-Mpc)) Compton wavelength. We analyze the cosmological signatures of and constraints upon a wide class of scenarios which do not involve domain walls. In addition to seeding structure, coherent ultra-light bosons may also provide unclustered dark matter in a spatially flat universe, omega sub phi approx. = 1.
Cosmological histories from the Friedmann equation: The universe as a particle
Mortsell, Edvard
2016-01-01
In this note, we discuss how possible expansion histories of the universe can be inferred in a simple way, for arbitrary energy contents. No new physical results are obtained, but the goal is rather to discuss an alternative way of writing the Friedmann equation in order to facilitate an intuitive understanding of the possible solutions; for students and researchers alike. As has been noted in passing by others, this specific form of the Friedmann equation allows us to view the universal expansion as a particle rolling along a frictionless track. Specific examples depicted include the current concordance cosmological model as well as a stable static universal model.
An immersed boundary method for smoothed particle hydrodynamics of self-propelled swimmers
Hieber, S. E.; Koumoutsakos, P.
2008-10-01
We present a novel particle method, combining remeshed Smoothed Particle Hydrodynamics with Immersed Boundary and Level Set techniques for the simulation of flows past complex deforming geometries. The present method retains the Lagrangian adaptivity of particle methods and relies on the remeshing of particle locations in order to ensure the accuracy of the method. In fact this remeshing step enables the introduction of Immersed Boundary Techniques used in grid based methods. The method is applied to simulations of flows of isothermal and compressible fluids past steady and unsteady solid boundaries that are described using a particle Level Set formulation. The method is validated with two and three-dimensional benchmark problems of flows past cylinders and spheres and it is shown to be well suited to simulations of large scale simulations using tens of millions of particles, on flow-structure interaction problems as they pertain to self-propelled anguilliform swimmers.
Remeshed smoothed particle hydrodynamics simulation of the mechanical behavior of human organs.
Hieber, Simone E; Walther, Jens H; Koumoutsakos, Petros
2004-01-01
In computer aided surgery the accurate simulation of the mechanical behavior of human organs is essential for the development of surgical simulators. In this paper we introduce particle based simulations of two different human organ materials modeled as linear viscoelastic solids. The constitutive equations for the material behavior are discretized using a particle approach based on the Smoothed Particle Hydrodynamics (SPH) method while the body surface is tracked using level sets. A key aspect of this approach is its flexibility which allows the simulation of complex time varying topologies with large deformations. The accuracy of the original formulation is significantly enhanced by using a particle reinitialization technique resulting in remeshed Smoothed Particle Hydrodynamics (rSPH). The mechanical parameters of the systems used in the simulations are derived from experimental measurements on human cadaver organs. We compare the mechanical behavior of liver- and kidney-like materials based on the dynamic simulations of a tensile test case. Moreover, we present a particle based reconstruction of the liver topology and its strain distribution under a small local load. Finally, we demonstrate a unified formulation of fluid structure interaction based on particle methods.
Ellwanger, Ulrich
2012-01-01
In this book, the author leads the reader, step by step and without any advanced mathematics, to a clear understanding of the foundations of modern elementary particle physics and cosmology. He also addresses current and controversial questions on topics such as string theory. The book contains gentle introductions to the theories of special and general relativity, and also classical and quantum field theory. The essential aspects of these concepts are understood with the help of simple calculations; for example, the force of gravity as a consequence of the curvature of the space-time. Also treated are the Big Bang, dark matter and dark energy, as well as the presently known interactions of elementary particles: electrodynamics, the strong and the weak interactions including the Higgs boson. Finally, the book sketches as yet speculative theories: Grand Unification theories, supersymmetry, string theory and the idea of additional dimensions of space-time. Since no higher mathematical or physics expertise is r...
Directory of Open Access Journals (Sweden)
Danilewicz Andrzej
2015-02-01
Full Text Available A theoretical base of SPH method, including the governing equations, discussion of importance of the smoothing function length, contact formulation, boundary treatment and finally utilization in hydrocode simulations are presented. An application of SPH to a real case of large penetrations (crater creating into the soil caused by falling mass in Dynamic Replacement Method is discussed. An influence of particles spacing on method accuracy is presented. An example calculated by LS-DYNA software is discussed. Chronological development of Smooth Particle Hydrodynamics is presented. Theoretical basics of SPH method stability and consistency in SPH formulation, artificial viscosity and boundary treatment are discussed. Time integration techniques with stability conditions, SPH+FEM coupling, constitutive equation and equation of state (EOS are presented as well.
Energy Technology Data Exchange (ETDEWEB)
Tartakovsky, Alexandre M.; Panchenko, Alexander
2016-01-01
We present a novel formulation of the Pairwise Force Smoothed Particle Hydrodynamics Model (PF-SPH) and use it to simulate two- and three-phase flows in bounded domains. In the PF-SPH model, the Navier-Stokes equations are discretized with the Smoothed Particle Hydrodynamics (SPH) method and the Young-Laplace boundary condition at the fluid-fluid interface and the Young boundary condition at the fluid-fluid-solid interface are replaced with pairwise forces added into the Navier-Stokes equations. We derive a relationship between the parameters in the pairwise forces and the surface tension and static contact angle. Next, we demonstrate the accuracy of the model under static and dynamic conditions. Finally, to demonstrate the capabilities and robustness of the model we use it to simulate flow of three fluids in a porous material.
Tartakovsky, Alexandre M.; Panchenko, Alexander
2016-01-01
We present a novel formulation of the Pairwise Force Smoothed Particle Hydrodynamics (PF-SPH) model and use it to simulate two- and three-phase flows in bounded domains. In the PF-SPH model, the Navier-Stokes equations are discretized with the Smoothed Particle Hydrodynamics (SPH) method, and the Young-Laplace boundary condition at the fluid-fluid interface and the Young boundary condition at the fluid-fluid-solid interface are replaced with pairwise forces added into the Navier-Stokes equations. We derive a relationship between the parameters in the pairwise forces and the surface tension and static contact angle. Next, we demonstrate the model's accuracy under static and dynamic conditions. Finally, we use the Pf-SPH model to simulate three phase flow in a porous medium.
Sandalski, Stou
Smooth particle hydrodynamics is an efficient method for modeling the dynamics of fluids. It is commonly used to simulate astrophysical processes such as binary mergers. We present a newly developed GPU accelerated smooth particle hydrodynamics code for astrophysical simulations. The code is named neptune after the Roman god of water. It is written in OpenMP parallelized C++ and OpenCL and includes octree based hydrodynamic and gravitational acceleration. The design relies on object-oriented methodologies in order to provide a flexible and modular framework that can be easily extended and modified by the user. Several pre-built scenarios for simulating collisions of polytropes and black-hole accretion are provided. The code is released under the MIT Open Source license and publicly available at http://code.google.com/p/neptune-sph/.
Mesh-free modelling of liquid crystals using modified smoothed particle hydrodynamics
Yakutovich, Mikhail; Care, Chris; Newton, CJP; Cleaver, Doug
2010-01-01
We present a generalisation of the Modified Smooth Particle Hydrodynamics simulation technique capable of simulating static and dynamic liquid crystalline behaviour. This generalisation is then implemented in the context of the Qian-Sheng description of nematodynamics. To test the method, we first use it to simulate switching in both a Freedericksz setup and a chiral hybrid aligned nematic\\ud cell. In both cases, the results obtained give excellent agreement with previously published results....
Applying Contact Angle to a 2D Multiphase Smoothed Particle Hydrodynamics Model
Farrokhpanah, Amirsaman; Samareh, Babak; Mostaghimi, Javad
2016-01-01
Equilibrium contact angle of liquid drops over horizontal surfaces has been modeled using Smoothed Particle Hydrodynamics (SPH). The model is capable of accurate implementation of contact angles to stationary and moving contact lines. In this scheme, the desired value for stationary or dynamic contact angle is used to correct the profile near the triple point. This is achieved by correcting the surface normals near the contact line and also interpolating the drop profile into the boundaries. ...
Cleary, Paul W; Prakash, Mahesh
2004-09-15
Particle-based simulation methods, such as the discrete-element method and smoothed particle hydrodynamics, have specific advantages in modelling complex three-dimensional (3D) environmental fluid and particulate flows. The theory of both these methods and their relative advantages compared with traditional methods will be discussed. Examples of 3D flows on realistic topography illustrate the environmental application of these methods. These include the flooding of a river valley as a result of a dam collapse, coastal inundation by a tsunami, volcanic lava flow and landslides. Issues related to validation and quality data availability are also discussed.
Moreno Chaparro, Nicolas
2013-06-01
A variational multi scale approach to model blood flow through arteries is proposed. A finite element discretization to represent the coarse scales (macro size), is coupled to smoothed dissipative particle dynamics that captures the fine scale features (micro scale). Blood is assumed to be incompressible, and flow is described through the Navier Stokes equation. The proposed cou- pling is tested with two benchmark problems, in fully coupled systems. Further refinements of the model can be incorporated in order to explicitly include blood constituents and non-Newtonian behavior. The suggested algorithm can be used with any particle-based method able to solve the Navier-Stokes equation.
Numerical modelling of coastal defences using the smoothed particle hydrodynamic method
Crespo, Alejandro; Altomare, Corrado; Rogers, Benedict D.; Dominguez, Jose; Gironella Cobos, Xavier
2013-01-01
The present paper reports the results of the application of the Smoothed Particle Hydrodynamics (SPH) method to model the wave run-up over an armour breakwater. The units that form the outer layer of the structure have been modelled in 3D to validate the response under wave attacks. The open-source GPU DualSPHysics code has been used because of its capability to simulate millions of particles required for an accurate modelling. The run-up heights have been computed and compared with empirical...
Artificial viscosity in simulation of shock waves by smoothed particle hydrodynamics
Nejad-Asghar, M; Soltani, J
2007-01-01
The artificial viscosity is reconsidered in smoothed particle hydrodynamics to prevent inter-particle penetration, unwanted heating, and unphysical solutions. The coefficients in the Monaghan's standard artificial viscosity are considered as time variable, and a restriction on them is proposed such that avoiding the undesired effects in the subsonic regions. The shock formation in adiabatic and isothermal cases are used to study the ability of this modified artificial viscosity recipe. The computer experiments show that the proposal appears to work and the accuracy of this restriction is acceptable.
Raymond, Samuel J.; Jones, Bruce; Williams, John R.
2016-12-01
A strategy is introduced to allow coupling of the material point method (MPM) and smoothed particle hydrodynamics (SPH) for numerical simulations. This new strategy partitions the domain into SPH and MPM regions, particles carry all state variables and as such no special treatment is required for the transition between regions. The aim of this work is to derive and validate the coupling methodology between MPM and SPH. Such coupling allows for general boundary conditions to be used in an SPH simulation without further augmentation. Additionally, as SPH is a purely particle method, and MPM is a combination of particles and a mesh. This coupling also permits a smooth transition from particle methods to mesh methods, where further coupling to mesh methods could in future provide an effective farfield boundary treatment for the SPH method. The coupling technique is introduced and described alongside a number of simulations in 1D and 2D to validate and contextualize the potential of using these two methods in a single simulation. The strategy shown here is capable of fully coupling the two methods without any complicated algorithms to transform information from one method to another.
Gusti, T. P.; Hertanti, D. R.; Bahsan, E.; Soeryantono, H.
2013-12-01
Particle-based numerical methods, such as Smoothed Particle Hydrodynamics (SPH), may be able to simulate some hydrodynamic and morphodynamic behaviors better than grid-based numerical methods. This study simulates hydrodynamics in meanders and advection and turbulent diffusion in straight river channels using Microsoft Excel and Visual Basic. The simulators generate three-dimensional data for hydrodynamics and one-dimensional data for advection-turbulent diffusion. Fluid at rest, sloshing, and helical flow are simulated in the river meanders. Spill loading and step loading are done to simulate concentration patterns associated with advection-turbulent diffusion. Results indicate that helical flow is formed due to disturbance in morphology and particle velocity in the stream and the number of particles does not have a significant effect on the pattern of advection-turbulent diffusion concentration.
Three-Dimensional Smoothed Particle Hydrodynamics Simulation for Liquid Droplet with Surface Tension
Terissa, Hanifa; Naa, Christian Fredy
2013-01-01
We provide a basic method of Smoothed Particle Hydrodynamics (SPH) to simulate liquid droplet with surface tension in three dimensions. Liquid droplet is a simple case for surface tension modeling. Surface tension works only on fluid surface. In SPH method, we simply apply the surface tension on the boundary particles of liquid. The particle on the 3D boundary was detected dynamically using Free-Surface Detection algorithm. The normal vector and curvature of the boundary surface were calculated simultaneously with 3D boundary surface reconstruction using Moving Least-Squares (MLS) method. Before the reconstruction, the coordinate system was transformed into a local coordinate system. Afterwards, the surface tension force which depends on curvature of the surface, was calculated and applied on the boundary particles of the droplet. We present the simulation result of droplet motion with gravity force. By using the basic method of SPH for fluid modeling, and a combination of 3D Free-Surface Detection algorithm ...
Energy Technology Data Exchange (ETDEWEB)
Kulkarni, Suchita C.
2011-08-08
We look at various methods of exploring the connection between particle physics and cosmology. We focus on various aspects of dark matter analysis. We begin with the smallest scales and look at collider phenomenology first. We discuss how the analysis of CP-properties of particles within Supersymmetry, one of the most accepted theories giving us a dark matter candidate. For this matter we take a specific case of the CP-violation in the super-partner of the tau lepton, the stau. Going slightly more towards astroparticle physics, we next study can the dark matter in the Universe be semi-relativistic. Thus, we use our prior knowledge of the cosmic scale properties of dark matter to draw implications for particle physics. In the next step, we look at large scales and examine the evolution of relationship between dark matter haloes and the background dark matter density fields. We use methods similar to field theory techniques of particle physics to understand this evolution of mapping. (orig.)
Cosmological Implications of High-Energy Neutrino Emission from the Decay of Long-Lived Particle
Ema, Yohei; Moroi, Takeo
2014-01-01
We study cosmological scenario in which high-energy neutrinos are emitted from the decay of long-lived massive particles at the cosmic time later than the redshift of 10^6. The high-energy neutrino events recently observed by the IceCube experiment suggest a new source of high-energy cosmic-ray neutrinos; decay of a heavy particle can be one of the possibilities. We calculate the spectrum of the high-energy neutrinos emitted from the decay of long-lived particles, taking account of the neutrino scattering processes with background neutrinos. Then, we derive bounds on the scenario using the observation of high-energy cosmic-ray neutrino flux. We also study constraints from the spectral distortions of the cosmic microwave background, taking into account both the current (COBE/FIRAS) and future (PIXIE) bounds. In addition, we show that the PeV neutrinos observed by the IceCube experiment can originate from the decay of a massive particle with its mass as large as O(10^10 GeV).
Predictor-corrector schemes for visualization of smoothed particle hydrodynamics data.
Schindler, Benjamin; Fuchs, Raphael; Biddiscombe, John; Peikert, Ronald
2009-01-01
In this paper we present a method for vortex core line extraction which operates directly on the smoothed particle hydrodynamics (SPH) representation and, by this, generates smoother and more (spatially and temporally) coherent results in an efficient way. The underlying predictor-corrector scheme is general enough to be applied to other line-type features and it is extendable to the extraction of surfaces such as isosurfaces or Lagrangian coherent structures. The proposed method exploits temporal coherence to speed up computation for subsequent time steps. We show how the predictor-corrector formulation can be specialized for several variants of vortex core line definitions including two recent unsteady extensions, and we contribute a theoretical and practical comparison of these. In particular, we reveal a close relation between unsteady extensions of Fuchs et al. and Weinkauf et al. and we give a proof of the Galilean invariance of the latter. When visualizing SPH data, there is the possibility to use the same interpolation method for visualization as has been used for the simulation. This is different from the case of finite volume simulation results, where it is not possible to recover from the results the spatial interpolation that was used during the simulation. Such data are typically interpolated using the basic trilinear interpolant, and if smoothness is required, some artificial processing is added. In SPH data, however, the smoothing kernels are specified from the simulation, and they provide an exact and smooth interpolation of data or gradients at arbitrary points in the domain.
Directory of Open Access Journals (Sweden)
Zhu Xiao
2016-05-01
Full Text Available In this paper, a novel nonlinear framework of smoothing method, non-Gaussian delayed particle smoother (nGDPS, is proposed, which enables vehicle state estimation (VSE with high accuracy taking into account the non-Gaussianity of the measurement and process noises. Within the proposed method, the multivariate Student’s t-distribution is adopted in order to compute the probability distribution function (PDF related to the process and measurement noises, which are assumed to be non-Gaussian distributed. A computation approach based on Ensemble Kalman Filter (EnKF is designed to cope with the mean and the covariance matrix of the proposal non-Gaussian distribution. A delayed Gibbs sampling algorithm, which incorporates smoothing of the sampled trajectories over a fixed-delay, is proposed to deal with the sample degeneracy of particles. The performance is investigated based on the real-world data, which is collected by low-cost on-board vehicle sensors. The comparison study based on the real-world experiments and the statistical analysis demonstrates that the proposed nGDPS has significant improvement on the vehicle state accuracy and outperforms the existing filtering and smoothing methods.
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
@@ The sixth Conference on Advanced Topics in the Interdisciplinary Fields of Particle Paysics.Nuclear Paysic8and Cosmology was held on July 22-27,2007 in Lijiang,Yunan Province.Over 70 scientists who were activelv working in the fields attended the conference and 42 physicists gave talks.9 papers have been selected to be published in the proceedings.
Improvement of the Second Order Approximation of the Smoothed Particle Hydrodynamics
Institute of Scientific and Technical Information of China (English)
CHEN Si; ZHOU Dai; DONG Shi-lin; LI Hua-feng; YANG Guang
2008-01-01
The smoothed particle hydrodynamics (SPH), as a fully Lagrangian particle method, has been successfully applied to astrophysical problems and extended to elastic dynamics and computational fluid dynamics.High order derivatives have to be approximated when elastic dynamics problems are modeled. However, the approximation errors in SPH could lead to computational failure in the case that the order of derivative is high.A novel method was proposed in order to improve the accuracy of SPH method, which shows the relationship between the selected functions and their SPH approximations. The entire involved system was represented by a finite number of particles that carry individual mass and occupy individual space, and the integral interpolation was approximated by a summation interpolation. In addition, error comparison was made between SPH method with and without the present improvement.
Turbulence modulation by micro-particles in smooth and rough channels
De Marchis, M.; Milici, B.
2016-11-01
Inertial micro-particles, dispersed in turbulent flows, are affected by the local dynamics of the carrier flow field. The presence of a relative dilute loading of particles entails some relevant changes in the mean velocity field. Moreover, the roughness of the solid boundary affects both the carrier and the carried phase dynamics and their mutual interaction. The underlying physics has been exhaustively tackled in the so-called one-way coupling regime, i.e., negligible action of particles onto the fluid, whereas many aspects of the particle back-reaction have been much less investigated and are still poorly understood. Thus the research in this area remains very active. In order to understand the mutual interaction between carrier and carried phases, direct numerical simulations are particularly suitable, even at low Reynolds number. Here, particle laden flow over a complex domain is investigated at friction Reynolds number Reτ = 180. The numerical analysis is based on the Euler-Lagrange approach, taking into account the fluid-particle interaction (two-way coupling). Point forces are used to represent the back-effect of particles on the turbulence and the effect of the wall's roughness is taken into account modeling the elastic rebound of particles onto it, instead of using a virtual rebound model. The interest is focused on the effect of micro-particles of different inertia on fluid and particle statistics in the near-wall region. In particular, turbulent and solid phase statistics are compared with those obtained for a one-way coupled flow, for the same Reynolds number in smooth and rough channel flow configurations.
Energy Technology Data Exchange (ETDEWEB)
Gelmini, Graciela B [Department of Physics and Astronomy, UCLA, 475 Portola Plaza, Los Angeles, CA 90095 (United States); Gondolo, Paolo, E-mail: gelmini@physics.ucla.edu, E-mail: paolo@physics.utah.edu [Department of Physics, University of Utah, 115 S 1400 E 201, Salt Lake City, UT 84112 (United States)
2008-10-15
Weakly interacting massive particles (WIMPs) constitute one of very few probes of cosmology before big bang nucleosynthesis (BBN). We point out that in scenarios in which the Universe evolves in a non-standard manner during and after WIMP kinetic decoupling, the horizon mass scale at decoupling can be smaller and the dark matter WIMPs can be colder than in standard cosmology. This would lead to much smaller first objects in hierarchical structure formation. In low reheating temperature scenarios the effect may be large enough to noticeably enhance indirect detection signals in GLAST and other detectors, by up to two orders of magnitude.
Coupled discrete element and smoothed particle hydrodynamics simulations of the die filling process
Breinlinger, Thomas; Kraft, Torsten
2016-11-01
Die filling is an important part of the powder compaction process chain, where defects in the final part can be introduced—or prevented. Simulation of this process is therefore a goal for many part producers and has been studied by some researchers already. In this work, we focus on the influence of the surrounding air on the powder flow. We demonstrate the implementing and coupling of the discrete element method for the granular powder and the smoothed particle hydrodynamics method for the gas flow. Application of the method to the die filling process is demonstrated.
DualSPHysics: Open-source parallel CFD solver based on Smoothed Particle Hydrodynamics (SPH)
Crespo, A. J. C.; Domínguez, J. M.; Rogers, B. D.; Gómez-Gesteira, M.; Longshaw, S.; Canelas, R.; Vacondio, R.; Barreiro, A.; García-Feal, O.
2015-02-01
DualSPHysics is a hardware accelerated Smoothed Particle Hydrodynamics code developed to solve free-surface flow problems. DualSPHysics is an open-source code developed and released under the terms of GNU General Public License (GPLv3). Along with the source code, a complete documentation that makes easy the compilation and execution of the source files is also distributed. The code has been shown to be efficient and reliable. The parallel power computing of Graphics Computing Units (GPUs) is used to accelerate DualSPHysics by up to two orders of magnitude compared to the performance of the serial version.
Gonnet, Pedro
2014-01-01
This paper describes a new fast and implicitly parallel approach to neighbour-finding in multi-resolution Smoothed Particle Hydrodynamics (SPH) simulations. This new approach is based on hierarchical cell decompositions and sorted interactions, within a task-based formulation. It is shown to be faster than traditional tree-based codes, and to scale better than domain decomposition-based approaches on hybrid shared/distributed-memory parallel architectures, e.g. clusters of multi-cores, achieving a $40\\times$ speedup over the Gadget-2 simulation code.
Smoothed particle hydrodynamics modelling in continuum mechanics: fluid-structure interaction
Directory of Open Access Journals (Sweden)
Groenenboom P. H. L.
2009-06-01
Full Text Available Within this study, the implementation of the smoothed particle hydrodynamics (SPH method solving the complex problem of interaction between a quasi-incompressible fluid involving a free surface and an elastic structure is outlined. A brief description of the SPH model for both the quasi-incompressible fluid and the isotropic elastic solid is presented. The interaction between the fluid and the elastic structure is realised through the contact algorithm. The results of numerical computations are confronted with the experimental as well as computational data published in the literature.
Mesh-free modeling of liquid crystals using modified smoothed particle hydrodynamics.
Yakutovich, M V; Care, C M; Newton, C J P; Cleaver, D J
2010-10-01
We present a generalization of the modified smooth particle hydrodynamics simulation technique capable of simulating static and dynamic liquid crystalline behavior. This generalization is then implemented in the context of the Qian-Sheng description of nematodynamics. To test the method, we first use it to simulate switching in both a Fréedericksz setup and a chiral hybrid aligned nematic cell. In both cases, the results obtained give excellent agreement with previously published results. We then apply the technique in a three-dimensional simulation of the switching dynamics of the post aligned bistable nematic device.
An explicit scheme for ohmic dissipation with smoothed particle magneto-hydrodynamics
Tsukamoto, Yusuke; Inutsuka, Shu-ichiro
2013-01-01
In this paper, we present an explicit scheme for Ohmic dissipation with smoothed particle magneto-hydrodynamics (SPMHD). We propose a SPH discretization of Ohmic dissipation and solve Ohmic dissipation part of induction equation with the supertime-stepping method (STS) which allows us to take a longer time-step than Courant-Friedrich-Levy stability condition. Our scheme is second-order accurate in space and first-order accurate in time. Our numerical experiments show that optimal choice of the parameters of STS for Ohmic dissipation of SPMHD is {\
Energy Technology Data Exchange (ETDEWEB)
Somasundaram, Deepak S [UNLV; Trabia, Mohamed [UNLV; O' Toole, Brendan [UNLV; Hixson, Robert S [NSTec
2014-01-23
This paper describes our work to characterize the variables affecting the smoothed particle hydrodynamics (SPH) method in the LS-DYNA package for simulating high-velocity flyer plate impact experiments. LS-DYNA simulations are compared with one-dimensional experimental data of an oxygen-free high-conductivity (OFHC) copper flyer plate impacting another plate of the same material. The comparison is made by measuring the velocity of a point on the back surface of the impact plate using the velocity interferometer system for any reflector (VISAR) technique.
Nassiri, Ali; Vivek, Anupam; Abke, Tim; Liu, Bert; Lee, Taeseon; Daehn, Glenn
2017-06-01
Numerical simulations of high-velocity impact welding are extremely challenging due to the coupled physics and highly dynamic nature of the process. Thus, conventional mesh-based numerical methodologies are not able to accurately model the process owing to the excessive mesh distortion close to the interface of two welded materials. A simulation platform was developed using smoothed particle hydrodynamics, implemented in a parallel architecture on a supercomputer. Then, the numerical simulations were compared to experimental tests conducted by vaporizing foil actuator welding. The close correspondence of the experiment and modeling in terms of interface characteristics allows the prediction of local temperature and strain distributions, which are not easily measured.
Numerical simulation of hydro-elastic problems with smoothed particle hydro-dynamics method
Institute of Scientific and Technical Information of China (English)
刘谋斌; 邵家儒; 李慧琦
2013-01-01
Violent free surface flows with strong fluid-solid interactions can produce a tremendous pressure load on structures, resu-lting in elastic and even plastic deformations. Modeling hydro-elastic problems with structure deformations and a free surface break-up is difficult by using routine numerical methods. This paper presents an improved Smoothed Particle Hydrodynamics (SPH) method for modeling hydro-elastic problems. The fluid particles are used to model the free surface flows governed by Navier-Stokes equations, and the solid particles are used to model the dynamic movement and deformation of the elastic solid objects. The impro-ved SPH method employs a Kernel Gradient Correction (KGC) technique to improve the computational accuracy and a Fluid-Solid Interface Treatment (FSIT) algorithm with the interface fluid and solid particles being treated as the virtual particles against their counterparts and a soft repulsive force to prevent the penetration and a corrective density approximation scheme to remove the nume-rical oscillations. Three typical numerical examples are simulated, including a head-on collision of two rubber rings, the dam break with an elastic gate and the water impact onto a forefront elastic plate. The obtained SPH results agree well with experimental obse-rvations and numerical results from other sources.
Lei, Huan; Baker, Nathan A.; Wu, Lei; Schenter, Gregory K.; Mundy, Christopher J.; Tartakovsky, Alexandre M.
2016-08-01
Thermal fluctuations cause perturbations of fluid-fluid interfaces and highly nonlinear hydrodynamics in multiphase flows. In this work, we develop a multiphase smoothed dissipative particle dynamics (SDPD) model. This model accounts for both bulk hydrodynamics and interfacial fluctuations. Interfacial surface tension is modeled by imposing a pairwise force between SDPD particles. We show that the relationship between the model parameters and surface tension, previously derived under the assumption of zero thermal fluctuation, is accurate for fluid systems at low temperature but overestimates the surface tension for intermediate and large thermal fluctuations. To analyze the effect of thermal fluctuations on surface tension, we construct a coarse-grained Euler lattice model based on the mean field theory and derive a semianalytical formula to directly relate the surface tension to model parameters for a wide range of temperatures and model resolutions. We demonstrate that the present method correctly models dynamic processes, such as bubble coalescence and capillary spectra across the interface.
Energy Technology Data Exchange (ETDEWEB)
Lei, Huan; Baker, Nathan A.; Wu, Lei; Schenter, Gregory K.; Mundy, Christopher J.; Tartakovsky, Alexandre M.
2016-08-05
Thermal fluctuations cause perturbations of fluid-fluid interfaces and highly nonlinear hydrodynamics in multiphase flows. In this work, we develop a novel multiphase smoothed dissipative particle dynamics model. This model accounts for both bulk hydrodynamics and interfacial fluctuations. Interfacial surface tension is modeled by imposing a pairwise force between SDPD particles. We show that the relationship between the model parameters and surface tension, previously derived under the assumption of zero thermal fluctuation, is accurate for fluid systems at low temperature but overestimates the surface tension for intermediate and large thermal fluctuations. To analyze the effect of thermal fluctuations on surface tension, we construct a coarse-grained Euler lattice model based on the mean field theory and derive a semi-analytical formula to directly relate the surface tension to model parameters for a wide range of temperatures and model resolutions. We demonstrate that the present method correctly models the dynamic processes, such as bubble coalescence and capillary spectra across the interface.
Dynamic analysis of a floating body in the fluid by using the smoothed particle hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Jun, Chul Woong; Sohn, Jeong Hyun; Lee, Kyung Chang [Pukyong National University, Busan (Korea, Republic of)
2015-07-15
This paper describes a method for the prediction of behavior of a floating-type structure using an experiment and numerical analysis according to the various marine conditions. The sloshing simulation is considered to verify the behavior of fluid. The fluid is expressed by a set of particles, the motion of fluid is calculated by using SPH (Smoothed particle hydrodynamics). Numerical results are compared with experiments. A wave tank and linear shaker are used in order to express the sloshing environment. Monaghan boundary force is employed to calculate the interacting force between fluid and boundary. Four wave periods are used to consider the various marine conditions in the fluid-structure interacting simulation. The longitudinal motion of a floating body is compared to each other. As a result, the solution of numerical analysis shows the similar tendency compared to the experiment results.
Tricco, Terrence S.; Price, Daniel J.; Bate, Matthew R.
2016-10-01
We present an updated constrained hyperbolic/parabolic divergence cleaning algorithm for smoothed particle magnetohydrodynamics (SPMHD) that remains conservative with wave cleaning speeds which vary in space and time. This is accomplished by evolving the quantity ψ /ch instead of ψ. Doing so allows each particle to carry an individual wave cleaning speed, ch, that can evolve in time without needing an explicit prescription for how it should evolve, preventing circumstances which we demonstrate could lead to runaway energy growth related to variable wave cleaning speeds. This modification requires only a minor adjustment to the cleaning equations and is trivial to adopt in existing codes. Finally, we demonstrate that our constrained hyperbolic/parabolic divergence cleaning algorithm, run for a large number of iterations, can reduce the divergence of the magnetic field to an arbitrarily small value, achieving ∇ ṡ B = 0 to machine precision.
High-resolution Smoothed Particle Hydrodynamics simulations of the merger of binary white dwarfs
Lorén-Aguilar, P; García-Berro, E
2009-01-01
We present the results of a set of high-resolution simulations of the merging process of two white dwarfs. In order to do so, we use an up-to-date Smoothed Particle Hydrodynamics code which incorporates very detailed input physics and an improved treatment of the artificial viscosity. Our simulations have been done using a large number of particles (4x10^5) and cover the full range of masses and chemical compositions of the coalescing white dwarfs. We also compare the time evolution of the system during the first phases of the coalescence with that obtained using a simplified treatment of mass transfer, we discuss in detail the characteristics of the final configuration, we assess the possible observational signatures of the merger, like the associated gravitational waveforms and the fallback X-ray flares, and we study the long-term evolution of the coalescence.
Tricco, Terrence S; Bate, Matthew R
2016-01-01
We present an updated constrained hyperbolic/parabolic divergence cleaning algorithm for smoothed particle magnetohydrodynamics (SPMHD) that remains conservative with wave cleaning speeds which vary in space and time. This is accomplished by evolving the quantity $\\psi / c_h$ instead of $\\psi$. Doing so allows each particle to carry an individual wave cleaning speed, $c_h$, that can evolve in time without needing an explicit prescription for how it should evolve, preventing circumstances which we demonstrate could lead to runaway energy growth related to variable wave cleaning speeds. This modification requires only a minor adjustment to the cleaning equations and is trivial to adopt in existing codes. Finally, we demonstrate that our constrained hyperbolic/parabolic divergence cleaning algorithm, run for a large number of iterations, can reduce the divergence of the field to an arbitrarily small value, achieving $\
Smooth- and rough-wall boundary layer structure from high spatial range particle image velocimetry
Squire, D. T.; Morrill-Winter, C.; Hutchins, N.; Marusic, I.; Schultz, M. P.; Klewicki, J. C.
2016-10-01
Two particle image velocimetry arrangements are used to make true spatial comparisons between smooth- and rough-wall boundary layers at high Reynolds numbers across a very wide range of streamwise scales. Together, the arrangements resolve scales ranging from motions on the order of the Kolmogorov microscale to those longer than twice the boundary layer thickness. The rough-wall experiments were obtained above a continuous sandpaper sheet, identical to that used by Squire et al. [J. Fluid Mech. 795, 210 (2016), 10.1017/jfm.2016.196], and cover a range of friction and equivalent sand-grain roughness Reynolds numbers (12 000 ≲δ+≲ 18000, 62 ≲ks+≲104 ). The smooth-wall experiments comprise new and previously published data spanning 6500 ≲δ+≲17 000 . Flow statistics from all experiments show similar Reynolds number trends and behaviors to recent, well-resolved hot-wire anemometry measurements above the same rough surface. Comparisons, at matched δ+, between smooth- and rough-wall two-point correlation maps and two-point magnitude-squared coherence maps demonstrate that spatially the outer region of the boundary layer is the same between the two flows. This is apparently true even at wall-normal locations where the total (inner-normalized) energy differs between the smooth and rough wall. Generally, the present results provide strong support for Townsend's [The Structure of Turbulent Shear Flow (Cambridge University Press, Cambridge, 1956), Vol. 1] wall-similarity hypothesis in high Reynolds number fully rough boundary layer flows.
Directory of Open Access Journals (Sweden)
Xu Li
2015-06-01
Full Text Available Smoothed particle hydrodynamics (SPH, as a Lagrangian, meshfree method, is supposed to be useful in solving acoustic problems, such as combustion noise, bubble acoustics, etc., and has been gradually used in sound wave computation. However, unphysical oscillations in the sound wave simulation cannot be ignored. In this paper, an artificial viscosity term is added into the standard SPH algorithm used for solving linearized acoustic wave equations. SPH algorithms with or without artificial viscosity are both built to compute sound propagation and interference in the time domain. Then, the effects of the smoothing kernel function, particle spacing and Courant number on the SPH algorithms of sound waves are discussed. After comparing SPH simulation results with theoretical solutions, it is shown that the result of the SPH algorithm with the artificial viscosity term added attains good agreement with the theoretical solution by effectively reducing unphysical oscillations. In addition, suitable computational parameters of SPH algorithms are proposed through analyzing the sound pressure errors for simulating sound waves.
Saintillan, David; Darve, Eric; Shaqfeh, Eric S. G.
2005-03-01
Large-scale simulations of non-Brownian rigid fibers sedimenting under gravity at zero Reynolds number have been performed using a fast algorithm. The mathematical formulation follows the previous simulations by Butler and Shaqfeh ["Dynamic simulations of the inhomogeneous sedimentation of rigid fibres," J. Fluid Mech. 468, 205 (2002)]. The motion of the fibers is described using slender-body theory, and the line distribution of point forces along their lengths is approximated by a Legendre polynomial in which only the total force, torque, and particle stresslet are retained. Periodic boundary conditions are used to simulate an infinite suspension, and both far-field hydrodynamic interactions and short-range lubrication forces are considered in all simulations. The calculation of the hydrodynamic interactions, which is typically the bottleneck for large systems with periodic boundary conditions, is accelerated using a smooth particle-mesh Ewald (SPME) algorithm previously used in molecular dynamics simulations. In SPME the slowly decaying Green's function is split into two fast-converging sums: the first involves the distribution of point forces and accounts for the singular short-range part of the interactions, while the second is expressed in terms of the Fourier transform of the force distribution and accounts for the smooth and long-range part. Because of its smoothness, the second sum can be computed efficiently on an underlying grid using the fast Fourier transform algorithm, resulting in a significant speed-up of the calculations. Systems of up to 512 fibers were simulated on a single-processor workstation, providing a different insight into the formation, structure, and dynamics of the inhomogeneities that occur in sedimenting fiber suspensions.
Valdez-Balderas, Daniel; Rogers, Benedict D; Crespo, Alejandro J C
2012-01-01
Starting from the single graphics processing unit (GPU) version of the Smoothed Particle Hydrodynamics (SPH) code DualSPHysics, a multi-GPU SPH program is developed for free-surface flows. The approach is based on a spatial decomposition technique, whereby different portions (sub-domains) of the physical system under study are assigned to different GPUs. Communication between devices is achieved with the use of Message Passing Interface (MPI) application programming interface (API) routines. The use of the sorting algorithm radix sort for inter-GPU particle migration and sub-domain halo building (which enables interaction between SPH particles of different subdomains) is described in detail. With the resulting scheme it is possible, on the one hand, to carry out simulations that could also be performed on a single GPU, but they can now be performed even faster than on one of these devices alone. On the other hand, accelerated simulations can be performed with up to 32 million particles on the current architec...
Lesgourgues, Julien; Miele, Gennaro; Pastor, Sergio
2013-01-01
The role that neutrinos have played in the evolution of the Universe is the focus of one of the most fascinating research areas that has stemmed from the interplay between cosmology, astrophysics and particle physics. In this self-contained book, the authors bring together all aspects of the role of neutrinos in cosmology, spanning from leptogenesis to primordial nucleosynthesis, their role in CMB and structure formation, to the problem of their direct detection. The book starts by guiding the reader through aspects of fundamental neutrino physics, such as the standard cosmological model and the statistical mechanics in the expanding Universe, before discussing the history of neutrinos in chronological order from the very early stages until today. This timely book will interest graduate students and researchers in astrophysics, cosmology and particle physics, who work with either a theoretical or experimental focus.
The Problem of Time and Quantum Cosmology in the Relational Particle Mechanics Arena
Anderson, Edward
2011-01-01
Most readers' main interest in this article will be its reviews of the problem of time (POT) in quantum gravity (QG) in Secs 11, 16. Namely, that `time' in GR and in ordinary QM are mutually incompatible notions, which is problematic in trying to put these 2 theories together to form a theory of QG. I also establish relational particle models (RPM's) as useful for the study of the POT and of quantum cosmology (QC). I also unlock RPMs' configuration spaces, classical dynamics and QM in simple concrete examples. I use these to further our understanding of the histories, records, semiclassical, naive Schrodinger interpretation and hidden time strategies toward resolving the POT, alongside considering Halliwell's combination of the first 3. My relational whole-universe models are comparable to minisuperspace in amount of resemblance to full GR, but with a number of different resemblances including various midisuperspace-like ones which render RPM's appropriate as POT models. One point of view is that the best one...
Kunze, Kerstin E
2016-01-01
Cosmology is becoming an important tool to test particle physics models. We provide an overview of the standard model of cosmology with an emphasis on the observations relevant for testing fundamental physics.
Carroll, Sean; Hauser, Marc D
2007-01-01
"On the theoretical side, particle phenomenologists will continue to develop physics beyond the Standard Model; string theorists are connecting ore strongly to cosmology and astrophysics/With the recent advent of whole-genome sequencing and increasingly complete surveys of genetic variation, we are now routinely studying 500 thousand variations at a time, enabling complete genome wide surveys in many human populations and in specific disease populations./The most exciting developments today sit at the intersection between science and philosophy.
Molteni, Diego; Battaglia, Onofrio Rosario
2016-01-01
We study the phenomenon of the "walking droplet", by means of numerical fluid dynamics simulations using a standard version of the Smoothed Particle Hydrodynamics method. The phenomenon occurs when a millimetric drop is released on the surface of an oil of the same composition contained in a container subjected to vertical oscillations of frequency and amplitude close to the Faraday instability threshold. At appropriate values of the parameters of the system under study, the liquid drop jumps permanently on the surface of the vibrating fluid forming a localized wave-particle system, reminding the behavior of a wave particle quantum system as suggested by de Broglie. In the simulations, the drop and the wave travel at nearly constant speed, as observed in experiments. In our study we made relevant simplifying assumptions, however we observe that the wave-drop coupling is easily obtained. This fact suggests that the phenomenon may occur in many contexts and opens the possibility to study the phenomenon in an ex...
Ganzenmüller, Georg C; Hiermaier, Stefan; Steinhauser, Martin O
2012-01-01
We propose a thermodynamically consistent and energy-conserving temperature coupling scheme between the atomistic and the continuum domain. The coupling scheme links the two domains using the DPDE (Dissipative Particle Dynamics at constant Energy) thermostat and is designed to handle strong temperature gradients across the atomistic/continuum domain interface. The fundamentally different definitions of temperature in the continuum and atomistic domain - internal energy and heat capacity versus particle velocity - are accounted for in a straightforward and conceptually intuitive way by the DPDE thermostat. We verify the here-proposed scheme using a fluid, which is simultaneously represented as a continuum using Smooth Particle Hydrodynamics, and as an atomistically resolved liquid using Molecular Dynamics. In the case of equilibrium contact between both domains, we show that the correct microscopic equilibrium properties of the atomistic fluid are obtained. As an example of a strong non-equilibrium situation, we consider the propagation of a steady shock-wave from the continuum domain into the atomistic domain, and show that the coupling scheme conserves both energy and shock-wave dynamics. To demonstrate the applicability of our scheme to real systems, we consider shock loading of a phospholipid bilayer immersed in water in a multi-scale simulation, an interesting topic of biological relevance.
Crespo, Alejandro C; Dominguez, Jose M; Barreiro, Anxo; Gómez-Gesteira, Moncho; Rogers, Benedict D
2011-01-01
Smoothed Particle Hydrodynamics (SPH) is a numerical method commonly used in Computational Fluid Dynamics (CFD) to simulate complex free-surface flows. Simulations with this mesh-free particle method far exceed the capacity of a single processor. In this paper, as part of a dual-functioning code for either central processing units (CPUs) or Graphics Processor Units (GPUs), a parallelisation using GPUs is presented. The GPU parallelisation technique uses the Compute Unified Device Architecture (CUDA) of nVidia devices. Simulations with more than one million particles on a single GPU card exhibit speedups of up to two orders of magnitude over using a single-core CPU. It is demonstrated that the code achieves different speedups with different CUDA-enabled GPUs. The numerical behaviour of the SPH code is validated with a standard benchmark test case of dam break flow impacting on an obstacle where good agreement with the experimental results is observed. Both the achieved speed-ups and the quantitative agreement with experiments suggest that CUDA-based GPU programming can be used in SPH methods with efficiency and reliability.
Identifying and analysing protostellar disc fragments in smoothed particle hydrodynamics simulations
Hall, Cassandra; Forgan, Duncan; Rice, Ken
2017-09-01
We present a new method of identifying protostellar disc fragments in a simulation based on density derivatives, and analyse our data using this and the existing CLUMPFIND method, which is based on an ordered search over all particles in gravitational potential energy. Using smoothed particle hydrodynamics, we carry out nine simulations of a 0.25 M⊙ disc around a 1 M⊙ star, all of which fragment to form at least two bound objects. We find that when using all particles ordered in gravitational potential space, only fragments that survive the duration of the simulation are detected. When we use the density derivative method, all fragments are detected, so the two methods are complementary, as using the two methods together allows us to identify all fragments, and to then determine those that are likely to be destroyed. We find a tentative empirical relationship between the dominant azimuthal wavenumber in the disc m and the maximum semimajor axis a fragment may achieve in a simulation, such that amax∝1/m. We find the fragment destruction rate to be around half that predicted from population synthesis models. This is due to fragment-fragment interactions in the early gas phase of the disc, which can cause scattering and eccentricity pumping on short time-scales, and affects the fragment's internal structure. We therefore caution that measurements of eccentricity as a function of semimajor axis may not necessarily constrain the formation mechanism of giant planets and brown dwarfs.
Directory of Open Access Journals (Sweden)
Alejandro C Crespo
Full Text Available Smoothed Particle Hydrodynamics (SPH is a numerical method commonly used in Computational Fluid Dynamics (CFD to simulate complex free-surface flows. Simulations with this mesh-free particle method far exceed the capacity of a single processor. In this paper, as part of a dual-functioning code for either central processing units (CPUs or Graphics Processor Units (GPUs, a parallelisation using GPUs is presented. The GPU parallelisation technique uses the Compute Unified Device Architecture (CUDA of nVidia devices. Simulations with more than one million particles on a single GPU card exhibit speedups of up to two orders of magnitude over using a single-core CPU. It is demonstrated that the code achieves different speedups with different CUDA-enabled GPUs. The numerical behaviour of the SPH code is validated with a standard benchmark test case of dam break flow impacting on an obstacle where good agreement with the experimental results is observed. Both the achieved speed-ups and the quantitative agreement with experiments suggest that CUDA-based GPU programming can be used in SPH methods with efficiency and reliability.
Directory of Open Access Journals (Sweden)
Georg C Ganzenmüller
Full Text Available We propose a thermodynamically consistent and energy-conserving temperature coupling scheme between the atomistic and the continuum domain. The coupling scheme links the two domains using the DPDE (Dissipative Particle Dynamics at constant Energy thermostat and is designed to handle strong temperature gradients across the atomistic/continuum domain interface. The fundamentally different definitions of temperature in the continuum and atomistic domain - internal energy and heat capacity versus particle velocity - are accounted for in a straightforward and conceptually intuitive way by the DPDE thermostat. We verify the here-proposed scheme using a fluid, which is simultaneously represented as a continuum using Smooth Particle Hydrodynamics, and as an atomistically resolved liquid using Molecular Dynamics. In the case of equilibrium contact between both domains, we show that the correct microscopic equilibrium properties of the atomistic fluid are obtained. As an example of a strong non-equilibrium situation, we consider the propagation of a steady shock-wave from the continuum domain into the atomistic domain, and show that the coupling scheme conserves both energy and shock-wave dynamics. To demonstrate the applicability of our scheme to real systems, we consider shock loading of a phospholipid bilayer immersed in water in a multi-scale simulation, an interesting topic of biological relevance.
Hydrodynamics coalescence collision of three liquid drops in 3D with smoothed particle hydrodynamics
Directory of Open Access Journals (Sweden)
Alejandro Acevedo-Malavé
2012-12-01
Full Text Available The Smoothed Particle Hydrodynamics method (SPH has been useful to model continuous fluid. This method is employed to obtain approximate numerical solutions of the equations in fluid dynamics by replacing the fluid with a set of particles. These particles may be interpreted as corresponding to interpolation points from which properties of the fluid can be determined. The SPH method is particularly useful when the fluid motion produces a big deformation and a large velocity of the whole fluid. In this study, the SPH method is applied to simulate for the first time the hydrodynamic collision of three equal-size liquid drops in the three-dimensional space. Ranges of value for the droplets collision velocity are chosen giving rise to the following different results for the collision: permanent coalescence, fragmentation, and flocculation of the drops. The velocity vector fields formed inside the drops during the collision process are presented. Three possible scenarios for fragmentation of liquid drops are shown. Multiple satellite drops arise from the ligaments on the surface of the formed bigger drop.
3D Simulation of Dam-break effect on a Solid Wall using Smoothed Particle Hydrodynamics
Suprijadi,; Naa, Christian; Putra, Anggy Trisnawan
2013-01-01
Dam is built for water supply, water flow or flooding control and electricity energy storage, but in other hand, dam is one of the most dangerous natural disaster in many countries including in Indonesia. The impact of dam break in neighbour area and is huge and many flooding in remote area, as happen in Dam Situ Gintung in Tangerang (close to Jakarta) in 2009. Smoothed Particle Hydrodynamics (SPH), is one of numerical method based on Lagrangian grid which is ap- plied in astrophysical simulation may be used to solve the simulation on dam break effect. The development of SPH methods become alternative methods to solving Navier Stokes equation, which is main key in fluid dynamic simulation. In this paper, SPH is developed for supporting solid par- ticles in use for 3D dam break effect (3D-DBE) simulation. Solid particle have been treated same as fluid particles with additional calculation for converting gained position became translation and rotation of solid object in a whole body. With this capability, the r...
Smooth Particle Hydrodynamics Simulation of Micro-Cup-Extrusion Using a Graphit-ic Coating
Directory of Open Access Journals (Sweden)
Li Shi-Cheng
2014-01-01
Full Text Available Microextrusion is becoming increasingly important for the manufacturing of microcomponents. However, this reduction in scale to a microlevel means that the influence of friction and the need for suitable lubrication are greatly increased. This study therefore looks at the use of a low-friction and highly wear resistant Graphit-ic coating on the mold-forming section of a microextrusion mold, this coating being applied by a closed-field unbalanced magnetron sputter ion plating technique. A microcup of CuZn33 brass alloy was then extruded, with a wall thickness of 0.45 mm, outside diameter of 2.9 mm, and an internal diameter of 2 mm. The experimental results in which extrusion uses the mold coating with Graphit-ic film are compared against the experimental results in which extrusion uses the mold uncoating with Graphit-ic film. This showed that the load was decreased a lot and the self-lubricating solid coating facilitates a smooth extrusion process. As the extrusion rate was quite high, smoothed particle hydrodynamics method simulations of the extrusion process were conducted, these being then compared with the experimental results. These result showed that the SPH simulation can be applied to show the deformation of materials and predict the load trend.
Directory of Open Access Journals (Sweden)
Abdelraheem M. Aly
2015-02-01
Full Text Available A stabilized incompressible smoothed particle hydrodynamics (ISPH method with the addition of a density invariant relaxation condition in the pressure calculations is applied to simulations of highly nonlinear liquid sloshing problems. By applying the Neumann boundary condition when solving pressure, the performance of the present ISPH method is enhanced significantly. Two large-amplitude free sloshing problems under a resonance sway excitation were carried out in a square and a rectangular tank with filling-depths ratios of 20% and 50% of tank height, respectively, and compared with the available published experimental results. To extend the validation of the method, numerical simulations for sloshing problems with the varying density of a floating body as well as a middle baffle, which also generates strongly nonlinear free surface flow, were conducted. The results showed that the present ISPH method produces smooth pressure distribution and significantly reduces spurious oscillation. The proposed ISPH method was shown to be robust and accurate in long time simulation of highly nonlinear sloshing problems.
Sigalotti, Leonardo Di G; Troconis, Jorge; Sira, Eloy; Peña-Polo, Franklin; Klapp, Jaime
2014-07-01
We study numerically liquid-vapor phase separation in two-dimensional, nonisothermal, van der Waals (vdW) liquid drops using the method of smoothed particle hydrodynamics (SPH). In contrast to previous SPH simulations of drop formation, our approach is fully adaptive and follows the diffuse-interface model for a single-component fluid, where a reversible, capillary (Korteweg) force is added to the equations of motion to model the rapid but smooth transition of physical quantities through the interface separating the bulk phases. Surface tension arises naturally from the cohesive part of the vdW equation of state and the capillary forces. The drop models all start from a square-shaped liquid and spinodal decomposition is investigated for a range of initial densities and temperatures. The simulations predict the formation of stable, subcritical liquid drops with a vapor atmosphere, with the densities and temperatures of coexisting liquid and vapor in the vdW phase diagram closely matching the binodal curve. We find that the values of surface tension, as determined from the Young-Laplace equation, are in good agreement with the results of independent numerical simulations and experimental data. The models also predict the increase of the vapor pressure with temperature and the fitting to the numerical data reproduces very well the Clausius-Clapeyron relation, thus allowing for the calculation of the vaporization pressure for this vdW fluid.
Cosmological Simulations using GCMHD+
Barnes, David J; Wu, Kinwah
2011-01-01
Radio observations of galaxy clusters show that the intra cluster medium is permeated by \\mu G magnetic fields. The origin and evolution of these cosmological magnetic fields is currently not well understood and so their impact on the dynamics of structure formation is not known. Numerical simulations are required to gain a greater understanding and produce predictions for the next generation of radio telescopes. We present the galactic chemodynamics smoothed particle magnetohydrodynamic (SPMHD) code (GCMHD+), which is an MHD implementation for the cosmological smoothed particle hydrodynamic code GCD+. The results of 1, 2 and 3 dimensional tests are presented and the performance of the code is shown relative to the ATHENA grid code. GCMHD+ shows good agreement with the reference solutions produced by ATHENA. The code is then used to simulate the formation of a galaxy cluster with a simple primordial magnetic field embedded in the gas. A homogeneous seed field of 10^-11 G is amplified by a factor of 10^3 durin...
Cosmological simulations using GCMHD+
Barnes, David J.; Kawata, Daisuke; Wu, Kinwah
2012-03-01
Radio observations of galaxy clusters show that the intracluster medium is permeated by ? magnetic fields. The origin and evolution of these cosmological magnetic fields is currently not well understood, and so their impact on the dynamics of structure formation is not known. Numerical simulations are required to gain a greater understanding and produce predictions for the next generation of radio telescopes. We present the galactic chemodynamics smoothed particle magnetohydrodynamics (SPMHD) code (GCMHD+), which is an MHD implementation for the cosmological smoothed particle hydrodynamics code GCD+. The results of 1D, 2D and 3D tests are presented and the performance of the code is shown relative to the ATHENA grid code. GCMHD+ shows good agreement with the reference solutions produced by ATHENA. The code is then used to simulate the formation of a galaxy cluster with a simple primordial magnetic field embedded in the gas. A homogeneous seed field of 3.5 × 10-11 G is amplified by a factor of 103 during the formation of the cluster. The results show good agreement with the profiles found in other magnetic cluster simulations of similar resolution.
Coupling of Smoothed Particle Hydrodynamics with Finite Volume method for free-surface flows
Marrone, S.; Di Mascio, A.; Le Touzé, D.
2016-04-01
A new algorithm for the solution of free surface flows with large front deformation and fragmentation is presented. The algorithm is obtained by coupling a classical Finite Volume (FV) approach, that discretizes the Navier-Stokes equations on a block structured Eulerian grid, with an approach based on the Smoothed Particle Hydrodynamics (SPH) method, implemented in a Lagrangian framework. The coupling procedure is formulated in such a way that each solver is applied in the region where its intrinsic characteristics can be exploited in the most efficient and accurate way: the FV solver is used to resolve the bulk flow and the wall regions, whereas the SPH solver is implemented in the free surface region to capture details of the front evolution. The reported results clearly prove that the combined use of the two solvers is convenient from the point of view of both accuracy and computing time.
Multiple Staggered Mesh Ewald: Boosting the Accuracy of the Smooth Particle Mesh Ewald Method
Wang, Han; Fang, Jun
2016-01-01
The smooth particle mesh Ewald (SPME) method is the standard method for computing the electrostatic interactions in the molecular simulations. In this work, the multiple staggered mesh Ewald (MSME) method is proposed to boost the accuracy of the SPME method. Unlike the SPME that achieves higher accuracy by refining the mesh, the MSME improves the accuracy by averaging the standard SPME forces computed on, e.g. $M$, staggered meshes. We prove, from theoretical perspective, that the MSME is as accurate as the SPME, but uses $M^2$ times less mesh points in a certain parameter range. In the complementary parameter range, the MSME is as accurate as the SPME with twice of the interpolation order. The theoretical conclusions are numerically validated both by a uniform and uncorrelated charge system, and by a three-point-charge water system that is widely used as solvent for the bio-macromolecules.
Numerical simulation of liquid jet breakup using smoothed particle hydrodynamics (SPH)
Pourabdian, Majid; Morad, Mohammad Reza
2016-01-01
In this paper, breakup of liquid jet is simulated using smoothed particle hydrodynamics (SPH) which is a meshless Lagrangian numerical method. For this aim, flow governing equations are discretized based on SPH method. In this paper, SPHysics open source code has been utilized for numerical solutions. Therefore, the mentioned code has been developed by adding the surface tension effects. The proposed method is then validated using dam break with obstacle problem. Finally, simulation of twodimensional liquid jet flow is carried out and its breakup behavior considering one-phase flow is investigated. Length of liquid breakup in Rayleigh regime is calculated for various flow conditions such as different Reynolds and Weber numbers and the results are validated by an experimental correlation. The whole numerical solutions are accomplished for both Wendland and cubic spline kernel functions and Wendland kernel function gave more accurate results. The results are compared to MPS method for inviscid liquid as well. T...
Variational Time Integration Approach for Smoothed Particle Hydrodynamics Simulation of Fluids
da Silva, Leandro Tavares
2015-01-01
Variational time integrators are derived in the context of discrete mechanical systems. In this area, the governing equations for the motion of the mechanical system are built following two steps: (a) Postulating a discrete action; (b) Computing the stationary value for the discrete action. The former is formulated by considering Lagrangian (or Hamiltonian) systems with the discrete action being constructed through numerical approximations of the action integral. The latter derives the discrete Euler-Lagrange equations whose solutions give the variational time integrator. In this paper, we build variational time integrators in the context of smoothed particle hydrodynamics (SPH). So, we start with a variational formulation of SPH for fluids. Then, we apply the generalized midpoint rule, which depends on a parameter $\\alpha$, in order to generate the discrete action. Then, the step (b) yields a variational time integration scheme that reduces to a known explicit one if $\\alpha\\in\\{0,1\\}$ but it is implicit oth...
Recent advances in the smoothed-particle hydrodynamics technique: Building the code SPHYNX
Cabezon, Ruben M; Figueira, Joana
2016-01-01
A novel computational hydrocode oriented to Astrophysical applications is described, discussed and validated in the following pages. The code, called SPHYNX, is of Newtonian type and grounded on the Euler-Lagrange formulation of the smoothed-particle hydrodynamics technique. The distinctive features of the code are: the use of an integral approach to estimating the gradients; the use of a flexible family of interpolators called sinc kernels, which suppress pairing instability; and the incorporation of a new type of volume elements which provides a better partition of the unity. The ensuing hydrodynamic code conserves mass, linear and angular momentum, energy, entropy and preserves kernel normalization even in strong shocks. By a careful choice of the index of the sinc kernel and the number of neighbors in the SPH summations, there is a substantial improvement in the estimation of gradients. Additionally, the new volume elements reduce the so-called tensile instability. Both features help to suppress much of t...
Nejad-Asghar, Mohsen
2008-01-01
The heating of the ion-neutral (or ambipolar) diffusion may affect the thermal phases of the molecular clouds. We present an investigation on the effect of this heating mechanism in the thermal instability of the molecular clouds. A weakly ionized one dimensional slab geometry, which is allowed for self-gravity and ambipolar diffusion, is chosen to study its thermal phases. We use the thermodynamic evolution of the slab to obtain the regions where slab cloud becomes thermally unstable. We investigate this evolution using the model of ambipolar diffusion with two-fluid smoothed particle hydrodynamics, as outlined by Hosking & Whitworth. Firstly, some parts of the technique are improved to test the pioneer works on behavior of the ambipolar diffusion in an isothermal self-gravitating slab. Afterwards, the improved two-fluid technique is used for thermal evolution of the slab. The results show that the thermal instability may persist inhomogeneities with a large density contrast at the intermediate parts of ...
Pahar, Gourabananda; Dhar, Anirban
2017-04-01
A coupled solenoidal Incompressible Smoothed Particle Hydrodynamics (ISPH) model is presented for simulation of sediment displacement in erodible bed. The coupled framework consists of two separate incompressible modules: (a) granular module, (b) fluid module. The granular module considers a friction based rheology model to calculate deviatoric stress components from pressure. The module is validated for Bagnold flow profile and two standardized test cases of sediment avalanching. The fluid module resolves fluid flow inside and outside porous domain. An interaction force pair containing fluid pressure, viscous term and drag force acts as a bridge between two different flow modules. The coupled model is validated against three dambreak flow cases with different initial conditions of movable bed. The simulated results are in good agreement with experimental data. A demonstrative case considering effect of granular column failure under full/partial submergence highlights the capability of the coupled model for application in generalized scenario.
Applying Contact Angle to a 2D Multiphase Smoothed Particle Hydrodynamics Model
Farrokhpanah, Amirsaman; Mostaghimi, Javad
2016-01-01
Equilibrium contact angle of liquid drops over horizontal surfaces has been modeled using Smoothed Particle Hydrodynamics (SPH). The model is capable of accurate implementation of contact angles to stationary and moving contact lines. In this scheme, the desired value for stationary or dynamic contact angle is used to correct the profile near the triple point. This is achieved by correcting the surface normals near the contact line and also interpolating the drop profile into the boundaries. Simulations show that a close match to the chosen contact angle values can be achieved for both stationary and moving contact lines. This technique has proven to reduce the amount of nonphysical shear stresses near the triple point and to enhance the convergence characteristics of the solver.
Institute of Scientific and Technical Information of China (English)
WANG Zhongtao; LI Xinzhong; LIU Peng; TAO Yanqi
2016-01-01
Submarine landslides can cause severe damage to marine engineering structures. Their sliding velocity and runout distance are two major parameters for quantifying and analyzing the risk of submarine landslides. Currently, commercial calculation programs such as BING have limitations in simulating underwater soil movements. All of these processes can be consistently simulated through a smoothed particle hydrodynamics (SPH) depth integrated model. The basis of the model is a control equation that was developed to take into account the effects of soil consolidation and erosion. In this work, the frictional rheological mode has been used to perform a simulation study of submarine landslides. Time-history curves of the sliding body’s velocity, height, and length under various conditions of water depth, slope gradient, contact friction coefficient, and erosion rate are compared; the maximum sliding distance and velocity are calculated; and patterns of variation are discussed. The findings of this study can provide a reference for disaster warnings and pipeline route selection.
How smooth are particle trajectories in a $\\Lambda$CDM Universe?
Rampf, Cornelius; Frisch, Uriel
2015-01-01
Very. Indeed, it is shown here that in a flat, cold dark matter (CDM) dominated Universe with positive cosmological constant ($\\Lambda$), modelled in terms of a Newtonian and collisionless fluid, particle trajectories are analytical in time (representable by a convergent Taylor series) until at least a finite time after decoupling. The time variable used for this statement is the cosmic scale factor, i.e., the "$a$-time", and not the cosmic time. For this, a Lagrangian-coordinates formulation of the Euler-Poisson equations is employed, originally used by Cauchy for 3-D incompressible flow. Temporal analyticity for $\\Lambda$CDM is found to be a consequence of novel explicit all-order recursion relations for the $a$-time Taylor coefficients of the Lagrangian displacement field, from which we derive the convergence of the $a$-time Taylor series. A lower bound for the $a$-time where analyticity is guaranteed and shell-crossing is ruled out is obtained, whose value depends only on $\\Lambda$ and on the initial spat...
A smooth dissipative particle dynamics method for domains with arbitrary-geometry solid boundaries
Gatsonis, Nikolaos A.; Potami, Raffaele; Yang, Jun
2014-01-01
A smooth dissipative particle dynamics method with dynamic virtual particle allocation (SDPD-DV) for modeling and simulation of mesoscopic fluids in wall-bounded domains is presented. The physical domain in SDPD-DV may contain external and internal solid boundaries of arbitrary geometries, periodic inlets and outlets, and the fluid region. The SDPD-DV method is realized with fluid particles, boundary particles, and dynamically allocated virtual particles. The internal or external solid boundaries of the domain can be of arbitrary geometry and are discretized with a surface grid. These boundaries are represented by boundary particles with assigned properties. The fluid domain is discretized with fluid particles of constant mass and variable volume. Conservative and dissipative force models due to virtual particles exerted on a fluid particle in the proximity of a solid boundary supplement the original SDPD formulation. The dynamic virtual particle allocation approach provides the density and the forces due to virtual particles. The integration of the SDPD equations is accomplished with a velocity-Verlet algorithm for the momentum and a Runge-Kutta for the entropy equation. The velocity integrator is supplemented by a bounce-forward algorithm in cases where the virtual particle force model is not able to prevent particle penetration. For the incompressible isothermal systems considered in this work, the pressure of a fluid particle is obtained by an artificial compressibility formulation for liquids and the ideal gas law for gases. The self-diffusion coefficient is obtained by an implementation of the generalized Einstein and the Green-Kubo relations. Field properties are obtained by sampling SDPD-DV outputs on a post-processing grid that allows harnessing the particle information on desired spatiotemporal scales. The SDPD-DV method is verified and validated with simulations in bounded and periodic domains that cover the hydrodynamic and mesoscopic regimes for
Pakmor, R; Roepke, F K; Hillebrandt, W
2012-01-01
Mergers of two carbon-oxygen white dwarfs have long been suspected to be progenitors of Type Ia Supernovae. Here we present our modifications to the cosmological smoothed particle hydrodynamics code Gadget to apply it to stellar physics including but not limited to mergers of white dwarfs. We demonstrate a new method to map a one-dimensional profile of an object in hydrostatic equilibrium to a stable particle distribution. We use the code to study the effect of initial conditions and resolution on the properties of the merger of two white dwarfs. We compare mergers with approximate and exact binary initial conditions and find that exact binary initial conditions lead to a much more stable binary system but there is no difference in the properties of the actual merger. In contrast, we find that resolution is a critical issue for simulations of white dwarf mergers. Carbon burning hotspots which may lead to a detonation in the so-called violent merger scenario emerge only in simulations with sufficient resolutio...
PASCOS 2012 - 18th International Symposium on Particles Strings and Cosmology
2014-03-01
The XVII International Conference on Strings, Particles and Cosmology, PASCOS 2012, was held in the City of Mérida, Mexico, from June 3-8, 2012. The conference series is aimed at exploring the interface and interplay between particle physics, string theory and cosmology. With the advent of new data, the emphasis of the XVIII edition of PASCOS was on phenomenology and the interpretation of recent observational and experimental results. The conference followed the format of previous conferences in this series, with plenary reviews and contributed presentations in parallel sessions. The lectures covered a wide range of subjects which included: Dark matter and dark energy, flavor physics and CP violation, neutrino physics, supersymmetry, Higgs physics, baryogenesis and EDMs, supergravity, high energy cosmic rays, string and F-theory GUTs, and string phenomenology. This is the first time that PASCOS was held in Latin America. The aim to do it in Mexico was to engage the Latin American community and thus to bring the conference to a wider and different audience, a goal which was thoroughly achieved. The venue was held at the Hotel Fiesta Americana in the beautiful city of Mérida. The social events included a reception with typical local food at the Katun restaurant, conference dinner at the historical Quinta Montes Molina, and an excursion to the archeological site of Dzibilchaltún including a swim at the famous cenote. PASCOS 2012 was possible thanks to the generous support of the following sponsors: CONACyT (Consejo Nacional de Ciencia y Tecnología), UNAM (Universidad Nacional Autónoma de México: Consejo Técnico de la Investigación Científica, Instituto de Ciencias Nucleares, Instituto de Física), Cinvestav, (Centro de Estudios Avanzados del IPN: U. Zacatanco, U. Mérida and Secretaría General), ICyTDF (Instituto Científico y Tecnológico del D.F.), PIFI (Programa Integral de Fortalecimiento Institucional, Universidad de Guanajuato, Campus León), SMF
Ji, Zhe; Xu, Fei; Takahashi, Akiyuki; Sun, Yu
2016-12-01
In this paper, a Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH) framework is presented utilizing the parallel architecture of single- and multi-GPU (Graphic Processing Unit) platforms. The program is developed for water entry simulations where an efficient potential based contact force is introduced to tackle the interaction between fluid and solid particles. The single-GPU SPH scheme is implemented with a series of optimization to achieve high performance. To go beyond the memory limitation of single GPU, the scheme is further extended to multi-GPU platform basing on an improved 3D domain decomposition and inter-node data communication strategy. A typical benchmark test of wedge entry is investigated in varied dimensions and scales to validate the accuracy and efficiency of the program. The results of 2D and 3D benchmark tests manifest great consistency with the experiment and better accuracy than other numerical models. The performance of the single-GPU code is assessed by comparing with serial and parallel CPU codes. The improvement of the domain decomposition strategy is verified, and a study on the scalability and efficiency of the multi-GPU code is carried out as well by simulating tests with varied scales in different amount of GPUs. Lastly, the single- and multi-GPU codes are further compared with existing state-of-the-art SPH parallel frameworks for a comprehensive assessment.
Holladay, Robert; Griffith, Alec; Murillo, Michael S.
2016-10-01
A computational model has been developed to study the evolution of a plasma generated by next-generation advanced light sources such as SLAC's LCLS and LANL's proposed MaRIE. Smoothed Particle Hydrodynamics (SPH) is used to model the plasma evolution because of the ease with which it handles the open boundary conditions and large deformations associated with these experiments. Our work extends the basic SPH method by utilizing a two-fluid model of an electron-ion plasma that also incorporates time dependent ionization and recombination by allowing the SPH fluid particles to have an evolving mass based on the mean ionization state of the plasma. Additionally, inter-species heating, thermal conduction, and electric fields are also accounted for. The effects of various initial conditions and model parameters will be presented, with the goal of using this framework to develop a model that can be used in the design and interpretation of future experiments. This work was supported by the Los Alamos National Laboratory Computational Physics Workshop.
Smoothed Particle Hydrodynamics simulations of white dwarf collisions and close encounters
Lorén-Aguilar, P; García-Berro, E
2010-01-01
The collision of two white dwarfs is a quite frequent event in dense stellar systems, like globular clusters and galactic nuclei. In this paper we present the results of a set of simulations of the close encounters and collisions of two white dwarfs. We use an up- to-date smoothed particle hydrodynamics code that incorporates very detailed input physics and an improved treatment of the artificial viscosity. Our simulations have been done using a large number of particles (~ 4 \\times 10^5) and covering a wide range of velocities and initial distances of the colliding white dwarfs. We discuss in detail when the initial eccentric binary white dwarf survives the closest approach, when a lateral collision in which several mass transfer episodes occur is the outcome of the newly formed binary system, and which range of input parameters leads to a direct collision, in which only one mass transfer episode occurs. We also discuss the characteristics of the final configuration and we assess the possible observational s...
A smoothed particle hydrodynamics (SPH) study of sediment dispersion on the seafloor
Tran-Duc, Thien; Phan-Thien, Nhan; Khoo, Boo Cheong
2017-08-01
Ocean-scale sediment dispersion and sedimentation problems are studied using the Smoothed Particle Hydrodynamics (SPH). A SPH formulation based on a mixture model for two-phase flows is developed to investigate the problem. The sediment mass transport via the settling advection and the turbulent diffusion of the suspended sediment are fully accounted for in the current SPH model. The simulations are carried out in an opened boundary domain with a unidirectional underlined current, with relevant deposition/re-suspension boundary conditions on the seafloor. The factors influencing the sedimentation process, such as the hindering and the bottom shear stress effects, are also considered. The simulation results reveal that the sediment convection near the sediment source location is caused by both the ocean current and secondary density driven flows that are created by the concurrent settling motion of suspended sediment particles, while the downstream sediment transport in the far field is only driven by the ocean current. The peak sediment concentration in the ambient ocean water is found to correlate with the sediment release rate, and the settlement rate is inversely proportional to the initial height of the disturbed sediment.
Mayoral-Villa, Estela; Alvarado-Rodríguez, Carlos E; Klapp, Jaime; Gómez-Gesteira, Moncho; Sigalotti, Leonardo Di G
2016-04-01
A smoothed particle hydrodynamics (SPH) model is presented for simulating the decay chain transport of radionuclides in confined aqueous solutions. The SPH formulation is based on the open-source parallel code DualSPHysics extended to solve the advective-diffusion equation for the evolution of the concentration field coupled to the fluid-dynamic equations, including the effects of radioactive decay of the tracer contaminants. The performance of the method is demonstrated for environmental engineering problems dealing with the transport of contaminants in still and flowing water. The results from a series of benchmark test calculations are described in two- and three-space dimensions, where the advection, diffusion, and radioactive decay modes are tested separately and in combined form. The accuracy of the present SPH transport model is shown by direct comparison with the analytical solutions and results from other SPH approaches. For a given problem, convergence of the SPH solution is seen to increase with decreasing particle size and spacing.
Mayoral-Villa, Estela; Alvarado-Rodríguez, Carlos E.; Klapp, Jaime; Gómez-Gesteira, Moncho; Di G. Sigalotti, Leonardo
2016-04-01
A smoothed particle hydrodynamics (SPH) model is presented for simulating the decay chain transport of radionuclides in confined aqueous solutions. The SPH formulation is based on the open-source parallel code DualSPHysics extended to solve the advective-diffusion equation for the evolution of the concentration field coupled to the fluid-dynamic equations, including the effects of radioactive decay of the tracer contaminants. The performance of the method is demonstrated for environmental engineering problems dealing with the transport of contaminants in still and flowing water. The results from a series of benchmark test calculations are described in two- and three-space dimensions, where the advection, diffusion, and radioactive decay modes are tested separately and in combined form. The accuracy of the present SPH transport model is shown by direct comparison with the analytical solutions and results from other SPH approaches. For a given problem, convergence of the SPH solution is seen to increase with decreasing particle size and spacing.
Numerical Simulation of Interacting Stellar Winds Model Using Smoothed Particle Hydrodynamics (SPH)
Thronson, H. A., Jr.; Li, P. S.; Kwok, S.
1997-12-01
In the past decade, the Interacting Stellar Winds (ISW) model has been shown to be successful in explaining the formation of planetary nebulae, Wolf-Rayet nebulae, slow novae, and supernovae. Since analytical methods applied to the ISW model have been limited to the spherical symmetric (1D) geometry, numerical methods are necessary for axisymmetric (2D) or arbitrary (3D) geometries, such as the study of formation and evolution of planetary nebulae, and for symbiotic nova outbursts. The Smoothed Particle Hydrodynamics (SPH) algorithm has been developed to study hydrodynamics using the particle method. This algorithm has been applied in many different fields successfully. In this paper, we apply the SPH algorithm using the TREE code to the problem of interacting winds dynamics. We present three simulations: (1) the interaction of two winds in spherical symmetry to demonstrate the validity of the algorithm in dealing with ISW modeling, (2) the formation and evolution of an axisymmetric nebula in the first 500 years, and (3) the interacting-colliding winds caused by a slow nova outburst in a symbiotic system. It is the first time that the SPH algorithm has been applied to an ISW simulation. The SPH algorithm is proved to be an accurate and powerful tool in studying ISW model. This work is supported by NASA's US ISO program and the University of Calgary.
An alternative smooth particle hydrodynamics formulation to simulate chemotaxis in porous media.
Avesani, Diego; Dumbser, Michael; Chiogna, Gabriele; Bellin, Alberto
2016-08-27
Chemotaxis, the microorganisms autonomous motility along or against the concentration gradients of a chemical species, is an important, yet often neglected factor controlling the transport of bacteria through saturated porous media. For example, chemotactic bacteria could enhance bioremediation by directing their own motion to residual contaminants trapped in low hydraulic conductive zones of contaminated aquifers. The aim of the present work is to develop an accurate numerical scheme to model chemotaxis in saturated porous media and other advective dominating flow systems. We propose to model chemotaxis by using a new class of meshless Lagrangian particle methods we recently developed for applications in fluid mechanics. The method is based on the Smooth Particle Hydrodynamics (SPH) formulation of (Ben Moussa et al., Int Ser Numer Math, 13(1):29-62, 2006), combined with a new Weighted Essentially Non-Oscillatory (WENO) reconstruction technique on moving point clouds in multiple space dimensions. The purpose of this new numerical scheme is to fully exploit the advantages of SPH among traditional mesh-based and mesh-free schemes and to overcome drawbacks related to the use of standard SPH for modeling chemotaxis in porous media. First, we test the new scheme against analytical reference solutions. Then, under the assumption of complete mixing at the Darcy scale, we perform two-dimensional conservative solute transport simulations under steady-state flow conditions, to show the capability of the proposed new scheme to model chemotaxis.
Kordilla, Jannes; Pan, Wenxiao; Tartakovsky, Alexandre
2014-12-14
We propose a novel smoothed particle hydrodynamics (SPH) discretization of the fully coupled Landau-Lifshitz-Navier-Stokes (LLNS) and stochastic advection-diffusion equations. The accuracy of the SPH solution of the LLNS equations is demonstrated by comparing the scaling of velocity variance and the self-diffusion coefficient with kinetic temperature and particle mass obtained from the SPH simulations and analytical solutions. The spatial covariance of pressure and velocity fluctuations is found to be in a good agreement with theoretical models. To validate the accuracy of the SPH method for coupled LLNS and advection-diffusion equations, we simulate the interface between two miscible fluids. We study formation of the so-called "giant fluctuations" of the front between light and heavy fluids with and without gravity, where the light fluid lies on the top of the heavy fluid. We find that the power spectra of the simulated concentration field are in good agreement with the experiments and analytical solutions. In the absence of gravity, the power spectra decay as the power -4 of the wavenumber-except for small wavenumbers that diverge from this power law behavior due to the effect of finite domain size. Gravity suppresses the fluctuations, resulting in much weaker dependence of the power spectra on the wavenumber. Finally, the model is used to study the effect of thermal fluctuation on the Rayleigh-Taylor instability, an unstable dynamics of the front between a heavy fluid overlaying a light fluid. The front dynamics is shown to agree well with the analytical solutions.
Institute of Scientific and Technical Information of China (English)
CAI Wei; XU Yi; CHEN Jun-zhu; HUANG Shu-ru; LU Zhen-ya; WANG Zhan-kun
2005-01-01
Objective: To observe the effect of Yangxueqingnao particles on rat vascular smooth muscle cell (VSMC) proliferation induced by lysophosphatidic acid (LPA). Methods: The amount of3H-TdR (3H-thymidine) admixed in cultured rat VSMC was measured and mitogen-activated protein kinase (MAPK) activity and lipid peroxidation end product malondialdehyde (MDA)content of the VSMC were assayed. Results: 1×10-9, 1×10-8, 1×10-7 mol/L LPA in a concentration dependent manner, induced the amount of 3H-TdR admixed, MAP kinase activity, and MDA content of the cultured rat VSMC to increase. However, 5%, 10%,and 15% Yangxueqingnao serum preincubation resulted in a decrease of 23.0%, 42.0%, and 52.0% (P＜0.01) respectively in the amount of 3H-TdR admixed, a decline in VSMC MAP kinase activity of 13.9% (P＜0.05), 29.6% (P＜0.01), and 48.9% (P＜0.01)respectively, and also, a decrease in MDA content of VSMC of 19.4%, 24.7%, and 43.2% (P＜0.01) respectively, in the 1×10-7mol/L LPA-treated VSMC. Conclusions: LPA activates the proliferation and lipid peroxidation of VSMC in a concentration dependent manner. The LPA-induced VSMC proliferation is related to the activity of MAP kinases, enzymes involved in an intracellular signalling pathway. The results of the present study showed that Yangxueqingnao particles can effectively inhibit LPA-induced VSMC proliferation, MAP kinase activation, and reduce lipid peroxidative lesion.
Energy Technology Data Exchange (ETDEWEB)
Jo, Young Beom; Kim, Eung Soo [Seoul National Univ., Seoul (Korea, Republic of)
2014-10-15
It becomes more complicated when considering the shape and phase of the ground below the seawater. Therefore, some different attempts are required to precisely analyze the behavior of tsunami. This paper introduces an on-going activities on code development in SNU based on an unconventional mesh-free fluid analysis method called Smoothed Particle Hydrodynamics (SPH) and its verification work with some practice simulations. This paper summarizes the on-going development and verification activities on Lagrangian mesh-free SPH code in SNU. The newly developed code can cover equation of motions and heat conduction equation so far, and verification of each models is completed. In addition, parallel computation using GPU is now possible, and GUI is also prepared. If users change input geometry or input values, they can simulate for various conditions geometries. A SPH method has large advantages and potential in modeling of free surface, highly deformable geometry and multi-phase problems that traditional grid-based code has difficulties in analysis. Therefore, by incorporating more complex physical models such as turbulent flow, phase change, two-phase flow, and even solid mechanics, application of the current SPH code is expected to be much more extended including molten fuel behaviors in the sever accident.
Smoothed particle hydrodynamics model of non-aqueous phase liquid flow and dissolution
Energy Technology Data Exchange (ETDEWEB)
Tartakovsky, Alexandre M.; Meakin, Paul; Ward, Anderson L.
2009-01-01
A smoothed particle hydrodynamics model was developed to simulate the flow of mixtures of aqueous and non-aqueous phase liquids in porous media and the dissolution of the non-aqueous phase in the aqueous phase. The model was used to study the effects of pore-scale heterogeneity and anisotropy on the steady state dense non-aqueous phase liquid (DNAPL) saturation when gravity driven DNAPL displaces water from initially water saturated porous media. Pore-scale anisotropy was created by using co-oriented non overlapping elliptically shaped grains to represent the porous media. After a steady state DNAPL saturation was reached, water was injected until a new steady state DNAPL saturation was reached. The amount of trapped DNAPL was found to be greater when DNAPL is displaced in the direction of the major axes of the soil grains than when it is displaced in the direction of the minor axes of the soil grains. The amount of trapped DNAPL was also found to increase with decreasing initial saturation of the continuous DNAPL phase. For the conditions used in our simulations, the saturation of the trapped NAPL with a smaller initial DNAPL saturation was more than 3 times larger than the amount of trapped DNAPL with a larger initial saturation. These simulations were carried out assuming that the DNAPL did not dissolve in water. Simulations including the effect of dissolution of DNAPL in the aqueous phase were also performed, and effective (macroscopic) mass transfer coefficients were determined.
Thomas, David M
2016-01-01
Negative superhumps are believed to arise in cataclysmic variable systems when the accretion disk is tilted with respect to the orbital plane. Slow retrograde precession of the line-of-nodes results in a signal---the negative superhump---with a period slightly less than the orbital period. Previous studies have shown that tilted disks exhibit negative superhumps, but a consensus on how a disk initially tilts has not been reached. Analytical work by Lai suggests that a magnetic field on the primary can lead to a tilt instability in a disk when the dipole moment is offset in angle from the spin axis of the primary and when the primary's spin axis is, itself, not aligned with the angular momentum axis of the binary orbit. However, Lai did not apply his work to the formation of negative superhumps. In this paper, we add Lai's model to an existing smoothed particle hydrodynamics code. Using this code, we demonstrate the emergence of negative superhumps in the "light curve" for a range of magnetic dipole moments. W...
Deformation of Soft Tissue and Force Feedback Using the Smoothed Particle Hydrodynamics
Liu, Xuemei; Wang, Ruiyi; Li, Yunhua; Song, Dongdong
2015-01-01
We study the deformation and haptic feedback of soft tissue in virtual surgery based on a liver model by using a force feedback device named PHANTOM OMNI developed by SensAble Company in USA. Although a significant amount of research efforts have been dedicated to simulating the behaviors of soft tissue and implementing force feedback, it is still a challenging problem. This paper introduces a kind of meshfree method for deformation simulation of soft tissue and force computation based on viscoelastic mechanical model and smoothed particle hydrodynamics (SPH). Firstly, viscoelastic model can present the mechanical characteristics of soft tissue which greatly promotes the realism. Secondly, SPH has features of meshless technique and self-adaption, which supply higher precision than methods based on meshes for force feedback computation. Finally, a SPH method based on dynamic interaction area is proposed to improve the real time performance of simulation. The results reveal that SPH methodology is suitable for simulating soft tissue deformation and force feedback calculation, and SPH based on dynamic local interaction area has a higher computational efficiency significantly compared with usual SPH. Our algorithm has a bright prospect in the area of virtual surgery. PMID:26417380
A novel method for modeling Neumann and Robin boundary conditions in smoothed particle hydrodynamics
Ryan, Emily M.; Tartakovsky, Alexandre M.; Amon, Cristina
2010-12-01
We present a novel smoothed particle hydrodynamics (SPH) method for diffusion equations subject to Neumann and Robin boundary conditions. The Neumann and Robin boundary conditions are common to many physical problems (such as heat/mass transfer), and can prove challenging to implement in numerical methods when the boundary geometry is complex. The new method presented here is based on the approximation of the sharp boundary with a diffuse interface and allows an efficient implementation of the Neumann and Robin boundary conditions in the SPH method. The paper discusses the details of the method and the criteria for the width of the diffuse interface. The method is used to simulate diffusion and reactions in a domain bounded by two concentric circles and reactive flow between two parallel plates and its accuracy is demonstrated through comparison with analytical and finite difference solutions. To further illustrate the capabilities of the model, a reactive flow in a porous medium was simulated and good convergence properties of the model are demonstrated.
Khorasanizade, Sh.; Sousa, J. M. M.
2016-03-01
A Segmented Boundary Algorithm (SBA) is proposed to deal with complex boundaries and moving bodies in Smoothed Particle Hydrodynamics (SPH). Boundaries are formed in this algorithm with chains of lines obtained from the decomposition of two-dimensional objects, based on simple line geometry. Various two-dimensional, viscous fluid flow cases have been studied here using a truly incompressible SPH method with the aim of assessing the capabilities of the SBA. Firstly, the flow over a stationary circular cylinder in a plane channel was analyzed at steady and unsteady regimes, for a single value of blockage ratio. Subsequently, the flow produced by a moving circular cylinder with a prescribed acceleration inside a plane channel was investigated as well. Next, the simulation of the flow generated by the impulsive start of a flat plate, again inside a plane channel, has been carried out. This was followed by the study of confined sedimentation of an elliptic body subjected to gravity, for various density ratios. The set of test cases was completed with the simulation of periodic flow around a sunflower-shaped object. Extensive comparisons of the results obtained here with published data have demonstrated the accuracy and effectiveness of the proposed algorithms, namely in cases involving complex geometries and moving bodies.
Geometrical on-the-fly shock detection in smoothed particle hydrodynamics
Beck, A. M.; Dolag, K.; Donnert, J. M. F.
2016-05-01
We present an on-the-fly geometrical approach for shock detection and Mach number calculation in simulations employing smoothed particle hydrodynamics (SPH). We utilize pressure gradients to select shock candidates and define up- and downstream positions. We obtain hydrodynamical states in the up- and downstream regimes with a series of normal and inverted kernel weightings parallel and perpendicular to the shock normals. Our on-the-fly geometrical Mach detector incorporates well within the SPH formalism and has low computational cost. We implement our Mach detector into the simulation code GADGET and alongside many SPH improvements. We test our shock finder in a sequence of shock tube tests with successively increasing Mach numbers exceeding by far the typical values inside galaxy clusters. For all shocks, we resolve the shocks well and the correct Mach numbers are assigned. An application to a strong magnetized shock tube gives stable results in full magnetohydrodynamic setups. We simulate a merger of two idealized galaxy clusters and study the shock front. Shock structures within the merging clusters as well as the cluster shock are well captured by our algorithm and assigned correct Mach numbers.
Nishiura, Daisuke; Furuichi, Mikito; Sakaguchi, Hide
2015-09-01
The computational performance of a smoothed particle hydrodynamics (SPH) simulation is investigated for three types of current shared-memory parallel computer devices: many integrated core (MIC) processors, graphics processing units (GPUs), and multi-core CPUs. We are especially interested in efficient shared-memory allocation methods for each chipset, because the efficient data access patterns differ between compute unified device architecture (CUDA) programming for GPUs and OpenMP programming for MIC processors and multi-core CPUs. We first introduce several parallel implementation techniques for the SPH code, and then examine these on our target computer architectures to determine the most effective algorithms for each processor unit. In addition, we evaluate the effective computing performance and power efficiency of the SPH simulation on each architecture, as these are critical metrics for overall performance in a multi-device environment. In our benchmark test, the GPU is found to produce the best arithmetic performance as a standalone device unit, and gives the most efficient power consumption. The multi-core CPU obtains the most effective computing performance. The computational speed of the MIC processor on Xeon Phi approached that of two Xeon CPUs. This indicates that using MICs is an attractive choice for existing SPH codes on multi-core CPUs parallelized by OpenMP, as it gains computational acceleration without the need for significant changes to the source code.
Braun, Anika; Cuomo, Sabatino; Wang, Xueliang; Zhang, Luqing
2016-04-01
Debris flows and landslide dams are a major natural hazard causing high socioeconomic risk in inhabited mountainous areas. This is also true for vast parts of southwestern China, which are highly prone to slope failures due to several factors, such as a humid climate with high precipitation in the summer months, geological predisposing factors with highly weathered sedimentary rocks and a high seismicity. Not only do the landslides and flooding related to landslide dams threaten residents, buildings and transportation structures, but also do flooding conditions endanger power supply, which relies in this region partly on hydropower. In order to assess the potential of landslides to block rivers, it is crucial to understand which factors influence possible run-out distances and how they can be quantified. In the study we are presenting a numerical modeling analysis for a particular case of a complex landslide in Ningnan county, southwestern China, which transformed into a debris flow and blocked the river and the major road leading through the valley after heavy rainfall. For this purpose a quasi-3D Smooth Particle Hydrodynamics (SPH) model was implemented that can account for geotechnical slope parameters, run-out distance, velocities and deposition heights. A digital terrain model and the geometry information of the landslide were used as input data in order to estimate the relevant geotechnical parameters by back-analysis. The results of the analysis can be used for the prediction of run-out distances for future events at this site and other similar sites.
A smooth particle hydrodynamics code to model collisions between solid, self-gravitating objects
Schäfer, C.; Riecker, S.; Maindl, T. I.; Speith, R.; Scherrer, S.; Kley, W.
2016-05-01
Context. Modern graphics processing units (GPUs) lead to a major increase in the performance of the computation of astrophysical simulations. Owing to the different nature of GPU architecture compared to traditional central processing units (CPUs) such as x86 architecture, existing numerical codes cannot be easily migrated to run on GPU. Here, we present a new implementation of the numerical method smooth particle hydrodynamics (SPH) using CUDA and the first astrophysical application of the new code: the collision between Ceres-sized objects. Aims: The new code allows for a tremendous increase in speed of astrophysical simulations with SPH and self-gravity at low costs for new hardware. Methods: We have implemented the SPH equations to model gas, liquids and elastic, and plastic solid bodies and added a fragmentation model for brittle materials. Self-gravity may be optionally included in the simulations and is treated by the use of a Barnes-Hut tree. Results: We find an impressive performance gain using NVIDIA consumer devices compared to our existing OpenMP code. The new code is freely available to the community upon request. If you are interested in our CUDA SPH code miluphCUDA, please write an email to Christoph Schäfer. miluphCUDA is the CUDA port of miluph. miluph is pronounced [maßl2v]. We do not support the use of the code for military purposes.
Albano, Raffaele; Sole, Aurelia; Mirauda, Domenica; Adamowski, Jan
2016-10-01
Large debris, including vehicles parked along floodplains, can cause severe damage and significant loss of life during urban area flash-floods. In this study, the authors validated and applied the Smoothed Particle Hydrodynamics (SPH) model, developed in Amicarelli et al. (2015), which reproduces in 3D the dynamics of rigid bodies driven by free surface flows, to the design of flood mitigation measures. To validate the model, the authors compared the model's predictions to the results of an experimental setup, involving a dam breach that strikes two fixed obstacles and three transportable floating bodies. Given the accuracy of the results, in terms of water depth over time and the time history of the bodies' movements, the SPH model explored in this study was used to analyse the mitigation efficiency of a proposed structural intervention - the use of small barriers (groynes) to prevent the transport of floating bodies. Different groynes configurations were examined to identify the most appropriate design and layout for urban area flash-flood damage mitigation. The authors found that groynes positioned upstream and downstream of each floating body can be effective as a risk mitigation measure for damage resulting from their movement.
García-Senz, Domingo; Escartín, José A; Ebinger, Kevin
2014-01-01
The smoothed particle hydrodynamics (SPH) technique is a numerical method for solving gas-dynamical problems that has been applied to simulate the evolution of a wide variety of astrophysical systems. The method has a second-order accuracy, with a resolution that is usually much larger in the compressed regions than in the diluted zones of the fluid. In this work, we propose and check a scheme to balance and equalize the resolution of SPH between high and low density regions. This method relies in the versatility of a family of interpolators called Sinc kernels, which allows to increase the quality of interpolations just varying a single parameter (the exponent of the Sinc function). The scheme is checked and validated through a number of numerical tests, going from standard one-dimensional Riemann problems in shock tubes, to multidimensional simulations of explosions, hydrodynamic instabilities and the collapse of a sun-like polytrope. The analysis of the hydrodynamical simulations suggests that the scheme d...
Hosono, Natsuki; Makino, Junichiro
2016-01-01
Hydrodynamical simulations of rotating disk play important roles in the field of astrophysical and planetary science. Smoothed Particle Hydrodynamics (SPH) has been widely used for such simulations. It, however, has been known that with SPH, a cold and thin Kepler disk breaks up due to the unwanted angular momentum transfer. Two possible reasons have been suggested for this breaking up of the disk; the artificial viscosity (AV) and the numerical error in the evaluation of pressure gradient in SPH. Which one is dominant has been still unclear. In this paper, we investigate the reason for this rapid breaking up of the disk. We implemented most of popular formulations of AV and switches and measured the angular momentum transfer due to both AV and the error of SPH estimate of pressure gradient. We found that the angular momentum transfer due to AV at the inner edge triggers the breaking up of the disk. We also found that the classical von-Neumann-Richtmyer-Landshoff type AV with a high order estimate for $\
Hu, Haoyue; Eberhard, Peter
2016-10-01
Process simulations of conduction mode laser welding are performed using the meshless Lagrangian smoothed particle hydrodynamics (SPH) method. The solid phase is modeled based on the governing equations in thermoelasticity. For the liquid phase, surface tension effects are taken into account to simulate the melt flow in the weld pool, including the Marangoni force caused by a temperature-dependent surface tension gradient. A non-isothermal solid-liquid phase transition with the release or absorption of additional energy known as the latent heat of fusion is considered. The major heat transfer through conduction is modeled, whereas heat convection and radiation are neglected. The energy input from the laser beam is modeled as a Gaussian heat source acting on the initial material surface. The developed model is implemented in Pasimodo. Numerical results obtained with the model are presented for laser spot welding and seam welding of aluminum and iron. The change of process parameters like welding speed and laser power, and their effects on weld dimensions are investigated. Furthermore, simulations may be useful to obtain the threshold for deep penetration welding and to assess the overall welding quality. A scalability and performance analysis of the implemented SPH algorithm in Pasimodo is run in a shared memory environment. The analysis reveals the potential of large welding simulations on multi-core machines.
A smooth particle hydrodynamics code to model collisions between solid, self-gravitating objects
Schäfer, Christoph M; Maindl, Thomas I; Speith, Roland; Scherrer, Samuel; Kley, Wilhelm
2016-01-01
Modern graphics processing units (GPUs) lead to a major increase in the performance of the computation of astrophysical simulations. Owing to the different nature of GPU architecture compared to traditional central processing units (CPUs) such as x86 architecture, existing numerical codes cannot be easily migrated to run on GPU. Here, we present a new implementation of the numerical method smooth particle hydrodynamics (SPH) using CUDA and the first astrophysical application of the new code: the collision between Ceres-sized objects. The new code allows for a tremendous increase in speed of astrophysical simulations with SPH and self-gravity at low costs for new hardware. We have implemented the SPH equations to model gas, liquids and elastic, and plastic solid bodies and added a fragmentation model for brittle materials. Self-gravity may be optionally included in the simulations and is treated by the use of a Barnes-Hut tree. We find an impressive performance gain using NVIDIA consumer devices compared to ou...
Smoothed Particle Magnetohydrodynamics III. Multidimensional tests and the div B = 0 constraint
Price, D J
2005-01-01
In two previous papers (Price & Monaghan 2004a,b) (papers I,II) we have described an algorithm for solving the equations of Magnetohydrodynamics (MHD) using the Smoothed Particle Hydrodynamics (SPH) method. The algorithm uses dissipative terms in order to capture shocks and has been tested on a wide range of one dimensional problems in both adiabatic and isothermal MHD. In this paper we investigate multidimensional aspects of the algorithm, refining many of the aspects considered in papers I and II and paying particular attention to the code's ability to maintain the div B = 0 constraint associated with the magnetic field. In particular we implement a hyperbolic divergence cleaning method recently proposed by Dedner et al. (2002) in combination with the consistent formulation of the MHD equations in the presence of non-zero magnetic divergence derived in papers I and II. Various projection methods for maintaining the divergence-free condition are also examined. Finally the algorithm is tested against a wi...
Brehm, Bernhard
2016-01-01
Bianchi models are posited by the BKL picture to be essential building blocks towards an understanding of generic cosmological singularities. We study the behaviour of spatially homogeneous anisotropic vacuum spacetimes of Bianchi type VIII and IX, as they approach the big bang singularity. It is known since 2001 that generic Bianchi IX spacetimes converge towards the so-called Mixmaster attractor as time goes towards the singularity. We extend this result to the case of Bianchi VIII vacuum. The BKL picture suggests that particle horizons should form, i.e. spatially separate regions should causally decouple. We prove that this decoupling indeed occurs, for Lebesgue almost every Bianchi VIII and IX vacuum spacetime.
Chemo-Dynamical Evolution of Disk Galaxies, Smoothed Particles Hydrodynamics Approach
Berczik, P.
In this paper I present, the new Chemo-Dynamical code, incorporated to the standard Smoothed Particle Hydrodynamics (CD-SPH). This code used to modelling the complex evolution of disk galaxy systems. The more detailed description of SPH code and the Star Formation (SF) and Super Novae (SN) algorithms you can find in our earlier work Berczik P. & Kravchuk S.G., 1996, ApSpSci, 245, 27. The galaxy presented via tree component system. The Dark Matter Halo described as an external gravitational potential with distribution of Dark Matter density (Burkert A. 1995, ApJ, 447, L25): ρDM (r) = frac ρ0 (1 + r / r0) cdot (1 + r / r0)2. The total mass of Dark Matter Halo is 1012 Modot. The second component is a hot coronal gas, with Thot ~106 K. This component presented as a uniformly distributed SPH gas with initial solid body rotation and with additisional random velocity component Δ V ~100 km/sec. The total mass of this component is 5 cdot 1010 Modot. The last component is a cold gas (Tcold ~104 K). This component presented also as a uniformly distributed SPH gas with initial solid body rotation and with additional random velocity component Δ V ~10 km/sec. The total mass of this component also is 5 cdot 1010 Modot. In the paper presented a more complex and may be more realistic incorporation of SF & SN in the SPH code. The presented calculation is clearly show, what the some interestiong and important properties of isolated disk galaxies we can explain using this simple, tree component "collapsing" model. In the frame of this approach we are able to reproduce the presently observed kinematics of star and gaseous components as well as their distributions and heavy element abundances. The developed model provide the realystic description of dynamics and chemical evolution of typical disk galaxies over the Hubble timescale.
Sigalotti, Leonardo Di G.; Troconis, Jorge; Sira, Eloy; Peña-Polo, Franklin; Klapp, Jaime
2015-07-01
The rapid evaporation and explosive boiling of a van der Waals (vdW) liquid drop in microgravity is simulated numerically in two-space dimensions using the method of smoothed particle hydrodynamics. The numerical approach is fully adaptive and incorporates the effects of surface tension, latent heat, mass transfer across the interface, and liquid-vapor interface dynamics. Thermocapillary forces are modeled by coupling the hydrodynamics to a diffuse-interface description of the liquid-vapor interface. The models start from a nonequilibrium square-shaped liquid of varying density and temperature. For a fixed density, the drop temperature is increased gradually to predict the point separating normal boiling at subcritical heating from explosive boiling at the superheat limit for this vdW fluid. At subcritical heating, spontaneous evaporation produces stable drops floating in a vapor atmosphere, while at near-critical heating, a bubble is nucleated inside the drop, which then collapses upon itself, leaving a smaller equilibrated drop embedded in its own vapor. At the superheat limit, unstable bubble growth leads to either fragmentation or violent disruption of the liquid layer into small secondary drops, depending on the liquid density. At higher superheats, explosive boiling occurs for all densities. The experimentally observed wrinkling of the bubble surface driven by rapid evaporation followed by a Rayleigh-Taylor instability of the thin liquid layer and the linear growth of the bubble radius with time are reproduced by the simulations. The predicted superheat limit (Ts≈0.96 ) is close to the theoretically derived value of Ts=1 at zero ambient pressure for this vdW fluid.
Sigalotti, Leonardo Di G; Troconis, Jorge; Sira, Eloy; Peña-Polo, Franklin; Klapp, Jaime
2015-07-01
The rapid evaporation and explosive boiling of a van der Waals (vdW) liquid drop in microgravity is simulated numerically in two-space dimensions using the method of smoothed particle hydrodynamics. The numerical approach is fully adaptive and incorporates the effects of surface tension, latent heat, mass transfer across the interface, and liquid-vapor interface dynamics. Thermocapillary forces are modeled by coupling the hydrodynamics to a diffuse-interface description of the liquid-vapor interface. The models start from a nonequilibrium square-shaped liquid of varying density and temperature. For a fixed density, the drop temperature is increased gradually to predict the point separating normal boiling at subcritical heating from explosive boiling at the superheat limit for this vdW fluid. At subcritical heating, spontaneous evaporation produces stable drops floating in a vapor atmosphere, while at near-critical heating, a bubble is nucleated inside the drop, which then collapses upon itself, leaving a smaller equilibrated drop embedded in its own vapor. At the superheat limit, unstable bubble growth leads to either fragmentation or violent disruption of the liquid layer into small secondary drops, depending on the liquid density. At higher superheats, explosive boiling occurs for all densities. The experimentally observed wrinkling of the bubble surface driven by rapid evaporation followed by a Rayleigh-Taylor instability of the thin liquid layer and the linear growth of the bubble radius with time are reproduced by the simulations. The predicted superheat limit (T(s)≈0.96) is close to the theoretically derived value of T(s)=1 at zero ambient pressure for this vdW fluid.
Pütz, Martin; Nielaba, Peter
2016-08-01
We report the influence of the strength of heat bath coupling on the demixing behavior in spinodal decomposing one component liquid-vapor systems. The smoothed particle hydrodynamics (SPH) method with a van der Waals equation of state is used for the simulation. A thermostat for SPH is introduced that is based on the Berendsen thermostat. It controls the strength of heat bath coupling and allows for quenches with exponential temperature decay at a certain thermalization time scale. The present method allows us to bridge several orders of magnitude in the thermalization time scale. The early stage is highly affected by the choice of time scale. A transition from exponential growth to a 1 /2 ordinary power law scaling in the characteristic lengths is observed. At high initial temperatures the growth is logarithmic. The comparison with pure thermal simulations reveals latent heat to raise the mean system temperature. Large thermalization time scales and thermal conductivity are figured out to affect a stagnation of heating, which is explained with convective processes. Furthermore, large thermalization time scales are responsible for a stagnation of growth of domains, which is temporally embedded between early and late stage of phase separation. Therefore, it is considered as an intermediate stage. We present an aspect concerning this stage, namely that choosing larger thermalization time scales increases the duration. Moreover, it is observed that diffuse interfaces are formed during this stage, provided that the stage is apparent. We show that the differences in the evolution between pure thermal simulations and simulations with an instantaneously scaled mean temperature can be explained by the thermalization process, since a variation of the time scale allows for the bridging between these cases of limit.
Mao, Wenbin; Li, Kewei; Sun, Wei
2016-12-01
Computational modeling of heart valve dynamics incorporating both fluid dynamics and valve structural responses has been challenging. In this study, we developed a novel fully-coupled fluid-structure interaction (FSI) model using smoothed particle hydrodynamics (SPH). A previously developed nonlinear finite element (FE) model of transcatheter aortic valves (TAV) was utilized to couple with SPH to simulate valve leaflet dynamics throughout the entire cardiac cycle. Comparative simulations were performed to investigate the impact of using FE-only models vs. FSI models, as well as an isotropic vs. an anisotropic leaflet material model in TAV simulations. From the results, substantial differences in leaflet kinematics between FE-only and FSI models were observed, and the FSI model could capture the realistic leaflet dynamic deformation due to its more accurate spatial and temporal loading conditions imposed on the leaflets. The stress and the strain distributions were similar between the FE and FSI simulations. However, the peak stresses were different due to the water hammer effect induced by the fluid inertia in the FSI model during the closing phase, which led to 13-28% lower peak stresses in the FE-only model compared to that of the FSI model. The simulation results also indicated that tissue anisotropy had a minor impact on hemodynamics of the valve. However, a lower tissue stiffness in the radial direction of the leaflets could reduce the leaflet peak stress caused by the water hammer effect. It is hoped that the developed FSI models can serve as an effective tool to better assess valve dynamics and optimize next generation TAV designs.
Simulation of central sloshing experiments with smoothed particle hydrodynamics (SPH) method
Energy Technology Data Exchange (ETDEWEB)
Vorobyev, Alexander, E-mail: alexander.vorobyev@kit.edu [Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen 76344 (Germany); Kriventsev, Vladimir, E-mail: vladimir.kriventsev@kit.edu [Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen 76344 (Germany); Maschek, Werner, E-mail: werner.maschek@kit.edu [Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen 76344 (Germany)
2011-08-15
Highlights: > Central sloshing experiments are simulated with meshless SPH-based method. > Presence of obstacles and asymmetries on the central peak formation are studied. > The high central peak is observed only in strongly symmetrical geometry. > Results are compared with sloshing simulations by 3D reactor code SIMMER-IV. - Abstract: Liquid sloshing phenomena can be observed whenever a liquid in a container has an unrestrained surface and can be excited. A particular type of sloshing motion can occur during the core meltdown of a liquid metal cooled reactor (LMR) and can lead to a compaction of the fuel in the center of the core possibly resulting in energetic nuclear power excursions. This phenomenon was studied in series of 'centralized sloshing' experiments with a central water column collapsing inside the surrounding cylindrical tank. These experiments provide data for a benchmark exercise for accident analysis codes. To simulate 'centralized sloshing' phenomena, a numerical method should be capable to predict the motion of the free surface of a liquid, wave propagation and reflection from the walls. In this study, a meshless method based on smoothed particle hydrodynamics (SPH) for the simulation of a 3D free surface liquid motion has been developed. The proposed method is applied to the simulation of 'centralized sloshing' experiments. Simulation results are compared with the experimental results as well as with results of computations performed with the 3D code SIMMER-IV which is an advanced reactor safety analysis code that implements the traditional mesh-based numerical method. In a series of numerical calculations it is shown that overall motion of the liquid is in a good agreement with experimental observations. Dependence on the initial and geometrical symmetry is studied and compared with experimental data.
Ballesteros, Guillermo; Ringwald, Andreas; Tamarit, Carlos
2016-01-01
We present a minimal extension of the Standard Model (SM) providing a consistent picture of particle physics from the electroweak scale to the Planck scale and of cosmology from inflation until today. Three right-handed neutrinos $N_i$, a new color triplet $Q$ and a complex SM-singlet scalar $\\sigma$, whose vacuum expectation value $v_\\sigma \\sim 10^{11}$ GeV breaks lepton number and a Peccei-Quinn symmetry simultaneously, are added to the SM. At low energies, the model reduces to the SM, augmented by seesaw generated neutrino masses and mixing, plus the axion. The latter solves the strong CP problem and accounts for the cold dark matter in the Universe. The inflaton is comprised by a mixture of $\\sigma$ and the SM Higgs and reheating of the Universe after inflation proceeds via the Higgs portal. Baryogenesis occurs via thermal leptogenesis. Thus, five fundamental problems of particle physics and cosmology are solved at one stroke in this unified Standard Model - Axion - Seesaw - Higgs portal inflation (SMASH...
Ballesteros, Guillermo; Redondo, Javier; Ringwald, Andreas; Tamarit, Carlos
2017-08-01
We present a minimal extension of the Standard Model (SM) providing a consistent picture of particle physics from the electroweak scale to the Planck scale and of cosmology from inflation until today. Three right-handed neutrinos Ni, a new color triplet Q and a complex SM-singlet scalar σ, whose vacuum expectation value vσ ~ 1011 GeV breaks lepton number and a Peccei-Quinn symmetry simultaneously, are added to the SM. At low energies, the model reduces to the SM, augmented by seesaw generated neutrino masses and mixing, plus the axion. The latter solves the strong CP problem and accounts for the cold dark matter in the Universe. The inflaton is comprised by a mixture of σ and the SM Higgs, and reheating of the Universe after inflation proceeds via the Higgs portal. Baryogenesis occurs via thermal leptogenesis. Thus, five fundamental problems of particle physics and cosmology are solved at one stroke in this unified Standard Model—axion—seesaw—Higgs portal inflation (SMASH) model. It can be probed decisively by upcoming cosmic microwave background and axion dark matter experiments.
Kiselev, V V
2012-01-01
A huge value of cosmological constant characteristic for the particle physics and the inflation of early Universe are inherently related to each other: one can construct a fine-tuned superpotential, which produces a flat potential of inflaton with a constant density of energy V=\\Lambda^4 after taking into account for leading effects due to the supergravity, so that an introduction of small quantum loop-corrections to parameters of this superpotential naturally results in the dynamical instability relaxing the primary cosmological constant by means of inflationary regime. The model phenomenologically agrees with observational data on the large scale structure of Universe at \\Lambda~10^{16} GeV.
Marsh, David J E
2015-01-01
Axions comprise a broad class of particles that can play a major role in explaining the unknown aspects of cosmology. They are also extraordinarily well-motivated within high energy physics, and so axion cosmology offers us a unique view onto these theories. I present a comprehensive and pedagogical view on the cosmology and astrophysics of axion-like particles, starting from inflation and progressing via the CMB and structure formation up to the present-day Universe. I briefly review the motivation and models for axions in particle physics and string theory. The primary focus is on the population of ultralight axions created via vacuum realignment, and its role as a dark matter (DM) candidate with distinctive phenomenology. Cosmological observations place robust constraints on the axion mass and relic density in this scenario, and I review where such constraints come from. I next cover aspects of galaxy formation with axion DM, and ways this can be used to further search for evidence of axions. An absolute l...
Holenberg, Yulia; Lavrenteva, Olga M; Shavit, Uri; Nir, Avinoam
2012-12-01
We report experimental evidence of an effect opposite to the "solidification" of small bubbles in liquid where the surface can become immobile. Namely, it is demonstrated that smooth solid spheres falling in a yield-stress fluid under the action of gravity can behave similar to drops. Particle tracking velocimetry was used to determine the shape of the yielded region around solid spherical particles undergoing slow stationary motion in 0.07% w/w Carbopol gel due to gravity under creeping flow conditions. The flow field inside the yielded region was determined by particle image velocimetry. It was found that the shape of the yielded region and the flow field around slow-moving rough particles is similar to the published results of numerical simulations, whereas those around smooth spheres resemble the experimental results obtained for viscous drops. The effect was explained by a slip of the gel on the smooth surface. Most likely, the slip originated from seepage of clean water from the gel, forming a thin lubricating layer near the solid surface.
Physics on all scales. Scalar-tensor theories of quantum gravity in particle physics and cosmology
Energy Technology Data Exchange (ETDEWEB)
Henz, Tobias
2016-05-10
In this thesis, we investigate dilaton quantum gravity using a functional renormalization group approach. We derive and discuss flow equations both in the background field approximation and using a vertex expansion as well as solve the fixed point equations globally to show how realistic gravity, connecting ultraviolet and infrared physics, can be realized on a pure fixed point trajectory by virtue of spontaneous breaking of scale invariance. The emerging physical system features a dynamically generated moving Planck scale resembling the Newton coupling as well as slow roll inflation with an exponentially decreasing effective cosmological constant that vanishes completely in the infrared. The moving Planck scale might make quantum gravity experimentally accessible at a different energy scale than previously believed. We therefore not only provide further evidence for the existence of a consistent quantum theory of gravity based on general relativity, but also offer potential solutions towards the hierarchy and cosmological constant problems, thereby opening up exciting opportunities for further research.
On the Dynamics of the Massless Spin-1 Particles in the Rotating Cosmological Models
Salti, M; Havare, A; Korunur, M; Salti, Mustafa; Aydogdu, Oktay; Havare, Ali; Korunur, Murat
2005-01-01
In the present article, we have considered massless Duffin-Kemmer-Petiau equation for the general rotating space-times, and obtain its second order form in this cosmological model. Considering this second order differential equation for some well-known cosmological model which are included by the our general line-element, we obtain exact solution of the massless Duffin-Kemmer-Petiau equation. On the other hand, by using spinor form of the Maxwell equations the propagation problem is reduced to the solution of the second order differential equation of complex combination of the electric and magnetic fields. For these two different approach we obtain the spinors in terms of field strength tensor.
Directory of Open Access Journals (Sweden)
X. W. Tang
2013-01-01
actual test of marble material. Typical results of the axial stress-strain response from infinitesimal to finite deformation as well as the progressive failure process for the marble tests are given and the influences of various factors are discussed. It is found that only provided proper choices of particle momentum equation and the smoothing length parameter, the SPH method is capable for favorably reproducing the deformation and progressive failure evolution in rock-like materials under quasistatic compression loads.
Shnapp, Ron
2014-01-01
Resuspension of solid particles by a tornado-like vortex from surfaces of different roughness is studied using a three-dimensional particle tracking velocimetry (3D-PTV) method. By utilizing the three-dimensional information on particle positions, velocities and accelerations before, during and after the resuspension (lift-off) event, we demonstrate that the resuspension efficiency is significantly higher from the rough surface, and propose a mechanistic model of this peculiar effect. The results indicate that for all Reynolds numbers tested, the resuspension rate, as well as particle velocities and accelerations, are higher over the rough surface, as compared to the smooth counterpart. The results and the model can help to improve modeling and analysis of resuspension rates in engineering and environmental applications.
Zentner, A R
2003-01-01
Improvements in observational techniques have transformed cosmology into a field inundated with ever-expanding, high-quality data sets and driven cosmology toward a standard model where the classic cosmological parameters are accurately measured. I briefly discuss some of the methods used to determine cosmological parameters, particularly primordial nucleosynthesis, the magnitude- redshift relation of supernovae, and cosmic microwave background anisotropy. I demonstrate how cosmological data can be used to complement particle physics and constrain extensions to the Standard Model. Specifically, I present bounds on light particle species and the properties of unstable, weakly-interacting, massive particles. Despite the myriad successes of the emerging standard cosmological model, unanswered questions linger. Numerical simulations of structure formation predict galactic central densities that are considerably higher than observed. They also reveal hundreds of satellites orbiting Milky Way-like galaxies while th...
Ye, Ting; Phan-Thien, Nhan; Lim, Chwee Teck; Peng, Lina; Shi, Huixin
2017-06-01
In biofluid flow systems, often the flow problems of fluids of complex structures, such as the flow of red blood cells (RBCs) through complex capillary vessels, need to be considered. The smoothed dissipative particle dynamics (SDPD), a particle-based method, is one of the easy and flexible methods to model such complex structure fluids. It couples the best features of the smoothed particle hydrodynamics (SPH) and dissipative particle dynamics (DPD), with parameters having specific physical meaning (coming from SPH discretization of the Navier-Stokes equations), combined with thermal fluctuations in a mesoscale simulation, in a similar manner to the DPD. On the other hand, the immersed boundary method (IBM), a preferred method for handling fluid-structure interaction problems, has also been widely used to handle the fluid-RBC interaction in RBC simulations. In this paper, we aim to couple SDPD and IBM together to carry out the simulations of RBCs in complex flow problems. First, we develop the SDPD-IBM model in details, including the SDPD model for the evolving fluid flow, the RBC model for calculating RBC deformation force, the IBM for treating fluid-RBC interaction, and the solid boundary treatment model as well. We then conduct the verification and validation of the combined SDPD-IBM method. Finally, we demonstrate the capability of the SDPD-IBM method by simulating the flows of RBCs in rectangular, cylinder, curved, bifurcated, and constricted tubes, respectively.
Buchmüller, O L; de Roeck, A; Ellis, Jonathan Richard; Flächer, H; Heinemeyer, S; Isidori, G; Olive, K A; Paradisi, P; Ronga, F J; Weiglein, G
2008-01-01
In view of the imminent start of the LHC experimental programme, we use the available indirect experimental and cosmological information to estimate the likely range of parameters of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), using a Markov-chain Monte Carlo (MCMC) technique to sample the parameter space. The 95% confidence-level area in the (m_0, m_1/2) plane of the CMSSM lies largely within the region that could be explored with 1/fb of integrated luminosity at 14 TeV, and much of the 68% confidence-level area lies within the region that could be explored with 50/pb of integrated luminosity at 10 TeV. A same-sign dilepton signal could well be visible in most of the 68% confidence-level area with 1/fb of integrated luminosity at 14 TeV. We discuss the sensitivities of the preferred ranges to variations in the most relevant indirect experimental and cosmological constraints and also to deviations from the universality of the supersymmetry-breaking contributions to the mass...
Directory of Open Access Journals (Sweden)
Alejandro Acevedo-Malavé
2012-06-01
Full Text Available In this study, the SPH method is applied to simulate for the first time the multiple hydrodynamics collisions and the formation of clusters of equally sized liquid drops in three-dimensional space. Smoothed Particle Hydrodynamics is a Lagrangian mesh-free formalism and has been useful to model continuous fluid. This formalism is employed to solve the Navier-Stokes equations by replacing the fluid with a set of particles. These particles are interpolation points from which properties of the fluid can be determined. We observe that when the velocity of collision varies between 0.2 mm/ms and 30.0 mm/ms different results may arise, such as: coalescence, fragmentation and formation of clusters of liquid drops. The velocity vector fields formed inside the drops during the collision process are shown.
Directory of Open Access Journals (Sweden)
Alejandro Acevedo-Malavé
2012-06-01
Full Text Available Smoothed Particle Hydrodynamics (SPH is a Lagrangian mesh-free formalism and has been useful to model continuous fluid. This formalism is employed to solve the Navier-Stokes equations by replacing the fluid with a set of particles. These particles are interpolation points from which properties of the fluid can be determined. In this study, the SPH method is applied to simulate the hydrodynamics interaction of many drops, showing some settings for the coalescence, fragmentation and flocculation problem of equally sized liquid drops in three-dimensional spaces. For small velocities the drops interact only through their deformed surfaces and the flocculation of the droplets arises. This result is very different if the collision velocity is large enough for the fragmentation of droplets takes place. We observe that for velocities around 15 mm/ms the coalescence of droplets occurs. The velocity vector fields formed inside the drops during the collision process are shown.
Ma, Anxin; Hartmaier, Alexander
2016-12-01
A crystal plasticity (CP) modelling approach based on smooth-particle hydrodynamics (SPH) has been developed to study severe plastic deformation of crystalline materials. The method has been implemented and validated by comparing the stress distribution and stress evolution of several SPH and FEM simulations for an anisotropic elastic material. The findings show that the SPH method produces an efficient and numerically robust solution for solid-mechanics boundary value problems. Furthermore, the approach has been extended to incorporate a CP model and employed to simulate FCC polycrystals under the equal-channel angular pressing (ECAP) condition. It was found that the polycrystal contains four distinct regions with different deformation mechanisms. For the case that friction between deformable particles and boundary particles was neglected, more than one half of the grains suffered severe plastic deformation. The CP-SPH developed here thus is demonstrated to be a powerful tool to study grain refinement under severe plastic deformation.
Marsh, David J. E.
2016-07-01
Axions comprise a broad class of particles that can play a major role in explaining the unknown aspects of cosmology. They are also well-motivated within high energy physics, appearing in theories related to CP-violation in the standard model, supersymmetric theories, and theories with extra-dimensions, including string theory, and so axion cosmology offers us a unique view onto these theories. I review the motivation and models for axions in particle physics and string theory. I then present a comprehensive and pedagogical view on the cosmology and astrophysics of axion-like particles, starting from inflation and progressing via BBN, the CMB, reionization and structure formation, up to the present-day Universe. Topics covered include: axion dark matter (DM); direct and indirect detection of axions, reviewing existing and future experiments; axions as dark radiation; axions and the cosmological constant problem; decays of heavy axions; axions and stellar astrophysics; black hole superradiance; axions and astrophysical magnetic fields; axion inflation, and axion DM as an indirect probe of inflation. A major focus is on the population of ultralight axions created via vacuum realignment, and its role as a DM candidate with distinctive phenomenology. Cosmological observations place robust constraints on the axion mass and relic density in this scenario, and I review where such constraints come from. I next cover aspects of galaxy formation with axion DM, and ways this can be used to further search for evidence of axions. An absolute lower bound on DM particle mass is established. It is ma > 10-24eV from linear observables, extending to ma ≳ 10-22eV from non-linear observables, and has the potential to reach ma ≳ 10-18eV in the future. These bounds are weaker if the axion is not all of the DM, giving rise to limits on the relic density at low mass. This leads to the exciting possibility that the effects of axion DM on structure formation could one day be detected
Moving mesh cosmology: tracing cosmological gas accretion
Nelson, Dylan; Genel, Shy; Sijacki, Debora; Keres, Dusan; Springel, Volker; Hernquist, Lars; 10.1093/mnras/sts595
2013-01-01
We investigate the nature of gas accretion onto haloes and galaxies at z=2 using cosmological hydrodynamic simulations run with the moving mesh code AREPO. Implementing a Monte Carlo tracer particle scheme to determine the origin and thermodynamic history of accreting gas, we make quantitative comparisons to an otherwise identical simulation run with the smoothed particle hydrodynamics (SPH) code GADGET-3. Contrasting these two numerical approaches, we find significant physical differences in the thermodynamic history of accreted gas in haloes above 10^10.5 solar masses. In agreement with previous work, GADGET simulations show a cold fraction near unity for galaxies forming in massive haloes, implying that only a small percentage of accreted gas heats to an appreciable fraction of the virial temperature during accretion. The same galaxies in AREPO show a much lower cold fraction, <20% in haloes above 10^11 solar masses. This results from a hot gas accretion rate which, at this same halo mass, is an order o...
MultiNest: an efficient and robust Bayesian inference tool for cosmology and particle physics
Feroz, F; Bridges, M
2008-01-01
We present further development and the first public release of our multimodal nested sampling algorithm, called MultiNest. This Bayesian inference tool calculates the evidence, with an associated error estimate, and produces posterior samples from distributions that may contain multiple modes and pronounced (curving) degeneracies in high dimensions. The developments presented here lead to further substantial improvements in sampling efficiency and robustness, as compared to the original algorithm presented in Feroz & Hobson (2008), which itself significantly outperformed existing MCMC techniques in a wide range of astrophysical inference problems. The accuracy and economy of the MultiNest algorithm is demonstrated by application to two toy problems and to a cosmological inference problem focussing on the extension of the vanilla $\\Lambda$CDM model to include spatial curvature and a varying equation of state for dark energy. The MultiNest software, which is fully parallelized using MPI and includes an inte...
Energy Technology Data Exchange (ETDEWEB)
Szczerbinska, Barbara [Dakota State Univ., Madison, SD (United States)
2016-02-22
For last five years Center for Theoretical Underground Physics and Related Areas (CETUP*) serves as a collaboration point for scientists from around the world interested in theoretical and experimental aspects of underground science. The mission of CETUP* is to promote an organized research in physics, astrophysics, geoscience, geomicrobiology and other fields related to the underground science and provide a stimulating environment for creative thinking and open communication between researches of varying ages and nationalities in dynamic atmosphere of intense scientific interactions. Scientists invited to participate in the program will not only provide theoretical support to the underground science, but they will also examine core questions of the 21st century including: What is dark matter? How well do we know the neutrino parameters?, How have neutrinos shaped the evolution of the universe?, How were the heavy elements made?, What are the fundamental underlying symmetries of the Universe? Is there a Grand Unified Theory of the Universe? How do supernovae explode? Studies of Neutrino Physics and Dark Matter are of high interest to particle and nuclear physicists, astrophysicists and cosmologists. Ongoing and proposed Neutrino and Dark Matter experiments are expected to unveil the answers to fundamental questions about the Universe. This year summer program was focused exactly on these subjects bringing together experts in dark matter, neutrino physics, particle physics, nuclear physics and astrophysics and cosmology. CETUP*2015 consisted of 5 week long program (June 14 – July 18, 2015) covering various theoretical and experimental aspects in these research areas. The two week long session on Dark Matter physics (June 14 – June 26) was followed by two week long program on Neutrino physics (July 6 – July 18). The international conference entitled IXth International Conference on Interconnection Between Particle Physics and Cosmology (PPC) was hosted at CETUP
Cosmological simulations with TreeSPH
Katz, N; Hernquist, L E; Katz, Neal; Weinberg, David H; Hernquist, Lars
1995-01-01
We describe numerical methods for incorporating gas dynamics into cosmological simulations and present illustrative applications to the cold dark matter (CDM) scenario. Our evolution code, a version of TreeSPH (Hernquist \\& Katz 1989) generalized to handle comoving coordinates and periodic boundary conditions, combines smoothed--particle hydrodynamics (SPH) with the hierarchical tree method for computing gravitational forces. The Lagrangian hydrodynamics approach and individual time steps for gas particles give the algorithm a large dynamic range, which is essential for studies of galaxy formation in a cosmological context. The code incorporates radiative cooling for an optically thin, primordial composition gas in ionization equilibrium with a user-specified ultraviolet background. We adopt a phenomenological prescription for star formation that gradually turns cold, dense, Jeans-unstable gas into collisionless stars, returning supernova feedback energy to the surrounding medium. In CDM simulations, some...
Directory of Open Access Journals (Sweden)
Jie Yang
2014-01-01
Full Text Available We study the effect of ultrahigh energy collisions of two particles with different energies near the horizon of a 2+1 dimensional BTZ black hole (BSW effect. We find that the particle with the critical angular momentum could exist inside the outer horizon of the BTZ black hole regardless of the particle energy. Therefore, for the nonextremal BTZ black hole, the BSW process is possible on the inner horizon with the fine tuning of parameters which are characterized by the motion of particle, while, for the extremal BTZ black hole, the particle with the critical angular momentum could only exist on the degenerated horizon, and the BSW process could also happen there.
Price, Daniel J
2015-01-01
We describe a simple method for simulating the dynamics of small grains in a dusty gas, relevant to micron-sized grains in the interstellar medium and grains of centimetre size and smaller in protoplanetary discs. The method involves solving one extra diffusion equation for the dust fraction in addition to the usual equations of hydrodynamics. This "diffusion approximation for dust" is valid when the dust stopping time is smaller than the computational timestep. We present a numerical implementation using Smoothed Particle Hydrodynamics (SPH) that is conservative, accurate and fast. It does not require any implicit timestepping and can be straightforwardly ported into existing 3D codes.
Chamcham, Khalil; Silk, Joseph; Barrow, John D.; Saunders, Simon
2017-04-01
Part I. Issues in the Philosophy of Cosmology: 1. Cosmology, cosmologia and the testing of cosmological theories George F. R. Ellis; 2. Black holes, cosmology and the passage of time: three problems at the limits of science Bernard Carr; 3. Moving boundaries? – comments on the relationship between philosophy and cosmology Claus Beisbart; 4. On the question why there exists something rather than nothing Roderich Tumulka; Part II. Structures in the Universe and the Structure of Modern Cosmology: 5. Some generalities about generality John D. Barrow; 6. Emergent structures of effective field theories Jean-Philippe Uzan; 7. Cosmological structure formation Joel R. Primack; 8. Formation of galaxies Joseph Silk; Part III. Foundations of Cosmology: Gravity and the Quantum: 9. The observer strikes back James Hartle and Thomas Hertog; 10. Testing inflation Chris Smeenk; 11. Why Boltzmann brains do not fluctuate into existence from the de Sitter vacuum Kimberly K. Boddy, Sean M. Carroll and Jason Pollack; 12. Holographic inflation revised Tom Banks; 13. Progress and gravity: overcoming divisions between general relativity and particle physics and between physics and HPS J. Brian Pitts; Part IV. Quantum Foundations and Quantum Gravity: 14. Is time's arrow perspectival? Carlo Rovelli; 15. Relational quantum cosmology Francesca Vidotto; 16. Cosmological ontology and epistemology Don N. Page; 17. Quantum origin of cosmological structure and dynamical reduction theories Daniel Sudarsky; 18. Towards a novel approach to semi-classical gravity Ward Struyve; Part V. Methodological and Philosophical Issues: 19. Limits of time in cosmology Svend E. Rugh and Henrik Zinkernagel; 20. Self-locating priors and cosmological measures Cian Dorr and Frank Arntzenius; 21. On probability and cosmology: inference beyond data? Martin Sahlén; 22. Testing the multiverse: Bayes, fine-tuning and typicality Luke A. Barnes; 23. A new perspective on Einstein's philosophy of cosmology Cormac O
Asselmeyer-Maluga, Torsten; Król, Jerzy
2011-01-01
In this paper we present a model where the modified Landau-like levels of charged particles in a magnetic field are determined due to the modified smoothness of $\\mathbb{R}^{4}$ as underlying structure of the Minkowski spacetime. Then the standard smoothness of $\\mathbb{R}^{4}$ is shifted to the exotic $\\mathbb{R}_{k}^{4}$, $k=2p$, $p=1,2...$. This is achieved by superstring theory using gravitational backreaction induced from a strong, almost constant magnetic field on standard $\\mathbb{R}^{4}$. The exact string background containing flat $\\mathbb{R}^{4}$ is replaced consistently by the curved geometry of $SU(2)_{k}\\times\\mathbb{R}$ as part of the modified exact backgrounds. This corresponds to the change of smoothness on $\\mathbb{R}^{4}$ from the standard $\\mathbb{R}^{4}$ to some exotic $\\mathbb{R}_{k}^{4}$. The calculations of the spectra are using the CFT marginal deformations and Wess-Zumino-Witten (WZW) models. The marginal deformations capture the effects of the magnetic field as well as its gravitatio...
Bartelmann, Matthias; Berg, Daniel; Kozlikin, Elena; Lilow, Robert; Viermann, Celia
2014-01-01
We use the non-equlibrium statistical field theory for classical particles, recently developed by Mazenko and Das and Mazenko, together with the free generating functional we have previously derived for point sets initially correlated in phase space, to calculate the time evolution of power spectra in the free theory, i.e. neglecting particle interactions. We provide expressions taking linear and quadratic momentum correlations into account. Up to this point, the expressions are general with respect to the free propagator of the microscopic degrees of freedom. We then specialise the propagator to that expected for particles in cosmology treated within the Zel'dovich approximation and show that, to linear order in the momentum correlations, the linear growth of the cosmological power spectrum is reproduced. Quadratic momentum correlations return a first contribution to the non-linear evolution of the power spectrum, for which we derive a simple closed expression valid for arbitrary wave numbers. This expressio...
Corrosion Resistance of a Sand Particle-Modified Enamel Coating Applied to Smooth Steel Bars
Directory of Open Access Journals (Sweden)
Fujian Tang
2014-09-01
Full Text Available The protective performance of a sand particle-modified enamel coating on reinforcing steel bars was evaluated in 3.5 wt% NaCl solution by electrochemical impedance spectroscopy (EIS. Seven percentages of sand particles by weight were investigated: 0%, 5%, 10%, 20%, 30%, 50% and 70%. The phase composition of the enamel coating and sand particles were determined with the X-ray diffraction (XRD technique. The surface and cross-sectional morphologies of the sand particle-modified enamel coating were characterized using scanning electron microscopy (SEM. XRD tests revealed three phases of sand particles: SiO2, CaCO3 and MgCO3. SEM images demonstrated that the enamel coating wetted well with the sand particles. However, a weak enamel coating zone was formed around the sand particles due to concentrated air bubbles, leading to micro-cracks as hydrogen gas pressure builds up and exceeds the tensile strength of the weak zone. As a result, the addition of sand particles into the enamel coating reduced both the coating and corrosion resistances.
A few remarks on the relationship between elementary particle physics, gravitation and cosmology
Mostepanenko, V M
2016-01-01
We discuss some current problems in the relationship between elementary particle physics and gravitation, i.e., in the subject investigated by Prof.~K.~P.~Staniukovich half a century ago. Specifically, the inflationary stage of the Universe evolution, originating from the vacuum polarization and particle creation, corrections to Newton's gravitational law due to exchange of light elementary particles or spontaneous compactification of extra dimensions, and constraints on the parameters of axions as probable constituents of dark matter in our Universe are considered. It is pointed out that presently the relationship between elementary particles and gravitation has become an experimental science, and many experiments, directed towards resolution of all related problems, are performed in many countries.
Neutrino properties from cosmology
DEFF Research Database (Denmark)
Hannestad, S.
2013-01-01
In recent years precision cosmology has become an increasingly powerful probe of particle physics. Perhaps the prime example of this is the very stringent cosmological upper bound on the neutrino mass. However, other aspects of neutrino physics, such as their decoupling history and possible non-s...
9th International Conference on Interconnections between Particle Physics and Cosmology
2015-01-01
Recent advances in observational astronomy and the discovery of 125-GeV Higgs boson have brought paradigm shifts on the potential connections between new fundamental particles and our understanding of their impact on the early universe and its evolution. With the content of the universe well known from astrophysical observations, a key aspect is that 27% of the universe appears to consist of dark matter. If current theories are correct, the particle physics candidate for this matter may well be observed in ongoing direct and/or indirect dark matter detection experiments or at the LHC. In addition, about 69% of the universe, the dark energy, still remains a significant mystery that major theoretical attempts are trying to understand. The objectives of PPC 2015 are to analyze the connection between dark matter and particle physics models, discuss the connections among dark matter, grand unification models and recent neutrino results, explore predictions for ongoing and forthcoming experiments, develop a theore...
THE CONVERGENCE OF PARTICLE-IN-CELL SCHEMES FOR COSMOLOGICAL DARK MATTER SIMULATIONS
Energy Technology Data Exchange (ETDEWEB)
Myers, Andrew; Colella, Phillip; Van Straalen, Brian, E-mail: ATMyers@lbl.gov [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States)
2016-01-10
Particle methods are a ubiquitous tool for solving the Vlasov–Poisson equation in comoving coordinates, which is used to model the gravitational evolution of dark matter (DM) in an expanding universe. However, these methods are known to produce poor results on idealized test problems, particularly at late times, after the particle trajectories have crossed. To investigate this, we have performed a series of one- and two-dimensional “Zel’dovich pancake” calculations using the popular particle-in-cell (PIC) method. We find that PIC can indeed converge on these problems provided that the following modifications are made. The first modification is to regularize the singular initial distribution function by introducing a small but finite artificial velocity dispersion. This process is analogous to artificial viscosity in compressible gas dynamics, and, as with artificial viscosity, the amount of regularization can be tailored so that its effect outside of a well-defined region—in this case, the high-density caustics—is small. The second modification is the introduction of a particle remapping procedure that periodically reexpresses the DM distribution function using a new set of particles. We describe a remapping algorithm that is third-order accurate and adaptive in phase space. This procedure prevents the accumulation of numerical errors in integrating the particle trajectories from growing large enough to significantly degrade the solution. Once both of these changes are made, PIC converges at second order on the Zel’dovich pancake problem, even at late times, after many caustics have formed. Furthermore, the resulting scheme does not suffer from the unphysical, small-scale “clumping” phenomenon known to occur on the pancake problem when the perturbation wavevector is not aligned with one of the Cartesian coordinate axes.
Trajectories of point particles in cosmology and the Zel'dovich approximation
Bartelmann, Matthias
2014-01-01
Using a Green's function approach, we compare the trajectories of classical Hamiltonian point particles in an expanding space-time to the effectively inertial trajectories in the Zel'dovich approximation. It is shown that the effective gravitational potential accelerating the particles relative to the Zel'dovich trajectories vanishes exactly initially as a consequence of the continuity equation, and acts only during a short, early period. The Green's function approach suggests an iterative scheme for improving the Zel'dovich trajectories, which can be analytically solved. We construct these trajectories explicitly and show how they interpolate between the Zel'dovich and the exact trajectories. The effective gravitational potential acting on the improved trajectories is substantially smaller at late times than the potential acting on the exact trajectories. The results may be useful for Lagrangian perturbation theory and for numerical simulations.
Akerib, Daniel S.; Carroll, Sean M.; Kaminokowski, Marc; Ritz, Steven; White, Nicholas E. (Technical Monitor)
2002-01-01
The past few years have seen dramatic breakthroughs and spectacular and puzzling discoveries in astrophysics and cosmology. In many cases, the new observations can only be explained with the introduction of new fundamental physics. Here we summarize some of these recent advances. We then describe several problems in astrophysics and cosmology, ripe for major advances, the resolution of which will likely require new physics.
Producing a scale-invariant spectrum of perturbations in a Hagedorn phase of string cosmology.
Nayeri, Ali; Brandenberger, Robert H; Vafa, Cumrun
2006-07-14
We study the generation of cosmological perturbations during the Hagedorn phase of string gas cosmology. Using tools of string thermodynamics we provide indications that it may be possible to obtain a nearly scale-invariant spectrum of cosmological fluctuations on scales which are of cosmological interest today. In our cosmological scenario, the early Hagedorn phase of string gas cosmology goes over smoothly into the radiation-dominated phase of standard cosmology, without having a period of cosmological inflation.
Energy Technology Data Exchange (ETDEWEB)
Pan, Wenxiao; Daily, Michael D.; Baker, Nathan A.
2015-12-01
We demonstrate the accuracy and effectiveness of a Lagrangian particle-based method, smoothed particle hydrodynamics (SPH), to study diffusion in biomolecular systems by numerically solving the time-dependent Smoluchowski equation for continuum diffusion. The numerical method is first verified in simple systems and then applied to the calculation of ligand binding to an acetylcholinesterase monomer. Unlike previous studies, a reactive Robin boundary condition (BC), rather than the absolute absorbing (Dirichlet) boundary condition, is considered on the reactive boundaries. This new boundary condition treatment allows for the analysis of enzymes with "imperfect" reaction rates. Rates for inhibitor binding to mAChE are calculated at various ionic strengths and compared with experiment and other numerical methods. We find that imposition of the Robin BC improves agreement between calculated and experimental reaction rates. Although this initial application focuses on a single monomer system, our new method provides a framework to explore broader applications of SPH in larger-scale biomolecular complexes by taking advantage of its Lagrangian particle-based nature.
Shahriari, S; Maleki, H; Hassan, I; Kadem, L
2012-10-11
Evaluating shear induced hemodynamic complications is one of the major concerns in design of the mechanical heart valves (MHVs). The monitoring of these events relies on both numerical simulations and experimental measurements. Currently, numerical approaches are mainly based on a combined Eulerian-Lagrangian approach. A more straightforward evaluation can be based on the Lagrangian analysis of the whole blood. As a consequence, Lagrangian meshfree methods are more adapted to such evaluation. In this study, smoothed particle hydrodynamics (SPH), a fully meshfree particle method originated to simulate compressible astrophysical flows, is applied to study the flow through a normal and a dysfunctional bileaflet mechanical heart valves (BMHVs). The SPH results are compared with the reference data. The accumulation of shear stress patterns on blood components illustrates the important role played by non-physiological flow patterns and mainly vortical structures in this issue. The statistical distribution of particles with respect to shear stress loading history provides important information regarding the relative number of blood components that can be damaged. This can be used as a measure of the response of blood components to the presence of the valve implant or any implantable medical device. This work presents the first attempt to simulate pulsatile flow through BMHVs using SPH method.
Bothun, Greg
2011-10-01
Ever since Aristotle placed us, with certainty, in the Center of the Cosmos, Cosmological models have more or less operated from a position of known truths for some time. As early as 1963, for instance, it was ``known'' that the Universe had to be 15-17 billion years old due to the suspected ages of globular clusters. For many years, attempts to determine the expansion age of the Universe (the inverse of the Hubble constant) were done against this preconceived and biased notion. Not surprisingly when more precise observations indicated a Hubble expansion age of 11-13 billion years, stellar models suddenly changed to produce a new age for globular cluster stars, consistent with 11-13 billion years. Then in 1980, to solve a variety of standard big bang problems, inflation was introduced in a fairly ad hoc manner. Inflation makes the simple prediction that the net curvature of spacetime is zero (i.e. spacetime is flat). The consequence of introducing inflation is now the necessary existence of a dark matter dominated Universe since the known baryonic material could comprise no more than 1% of the necessary energy density to make spacetime flat. As a result of this new cosmological ``truth'' a significant world wide effort was launched to detect the dark matter (which obviously also has particle physics implications). To date, no such cosmological component has been detected. Moreover, all available dynamical inferences of the mass density of the Universe showed in to be about 20% of that required for closure. This again was inconsistent with the truth that the real density of the Universe was the closure density (e.g. Omega = 1), that the observations were biased, and that 99% of the mass density had to be in the form of dark matter. That is, we know the universe is two component -- baryons and dark matter. Another prevailing cosmological truth during this time was that all the baryonic matter was known to be in galaxies that populated our galaxy catalogs. Subsequent
Cosmology Theory and Observations
Dolgov, A D
1998-01-01
The comparison of the Standard Cosmological Model (SCM) with astronomical observations, i.e. theory versus experiment, and with the Minimal Standard Model (MSM) in particle physics, i.e. theory versus theory, is discussed. The main issue of this talk is whether cosmology indicates new physics beyond the standard $SU(3)\\times SU(2)\\times U(1)$ model with minimal particle content. The answer to this question is strongly and definitely "YES". New, yet unknown, physics exists and cosmology presents very weighty arguments in its favor.
Pavlov, Yu V
2013-01-01
The problem is solved of describing scale factors of a homogeneous isotropic spaces-time such that the exact solution for the scalar field with a nonconformal coupling to curvature can be obtained from solutions for the conformally coupled field by redefining the mass and momentum. Explicit expressions for dependence of time from the large-scale factor are presented in the form of Abelian integrals in these cases. The exact solution for a scalar field with Gauss-Bonnet type coupling with curvature is received and it is shown that the corresponding nonconformal additions can dominate at the particles creation by gravitational field.
Ganzenmüller, G. C.; Sauer, M.; May, M.; Hiermaier, S.
2016-05-01
We present a stabilization scheme for elastoplastic Smooth-Particle Hydrodynamics (SPH) which overcomes two major challenges: (i) the tensile instability inherent to the updated Lagrangian approach is suppressed and (ii) the rank-deficiency instability inherent to the nodal integration approach is cured. To achieve these goals, lessons learned from the Finite-Element Method are transferred to SPH. In particular, an analogue of hourglass control is derived for SPH, which locally linearizes the deformation field to obtain stable and accurate solutions, without the need to resort to stabilization via excessive artificial viscosity. The resulting SPH scheme combines the ability of updated Lagrangian SPH to model truly large deformations with the accuracy and stability needed to faithfully perform simulations. This claim is supported by the analysis of problematic cases and the simulation of an impact scenario.
Shi, Chuanqi; An, Yi; Wu, Qiang; Liu, Qingquan; Cao, Zhixian
2016-06-01
We simulate the generation of a landslide-induced impulse wave with a newly-developed soil-water coupling model in the smoothed particle hydrodynamics (SPH) framework. The model includes an elasto-plastic constitutive model for soil, a Navier-Stokes equation based model for water, and a bilateral coupling model at the interface. The model is tested with simulated waves induced by a slow and a fast landslide. Good agreement is obtained between simulation results and experimental data. The generated wave and the deformation of the landslide body can both be resolved satisfactorily. All parameters in our model have their physical meaning in soil mechanics and can be obtained from conventional soil mechanics experiments directly. The influence of the dilatancy angle of soil shows that the non-associated flow rule must be selected, and the value of the dilatancy angle should not be chosen arbitrarily, if it is not determined with relative experiments.
Energy Technology Data Exchange (ETDEWEB)
McLellan, J.; Kaya, T.; Goldak, J., E-mail: joshuamclellan@cmail.carleton.ca, E-mail: Tarik.Kaya@carleton.ca, E-mail: jgoldak@mrco2.carleton.ca [Carleton Univ., Ottawa, Ontario (Canada)
2014-07-01
A microchannel heat exchanger (MCHX) is a technology that provides increased thermal efficiency in a small volume relative to other types of heat exchangers via an extremely high surface area-to-volume ratio. This characteristic is specifically valued when considering use in small modular reactors. With relatively little design information for commercial MCHXs available in open literature, development of a robust model and optimization thereof for use in nuclear reactors takes on significant importance. Some applications of this technology involve phase change, which is a challenging modelling problem given large volumetric changes of the liquid and gas phases, as well as moving boundaries at the phase interface. This problem is mitigated by use of a Lagrangian formulation such as smoothed particle hydrodynamics (SPH), whose use in the development of the MCHX model is discussed. Additionally, the Kriging optimization algorithm is introduced, including its use to generate a suitable MCHX design. (author)
Energy Technology Data Exchange (ETDEWEB)
Schuchardt, Karen L.; Chase, Jared M.; Daily, Jeffrey A.; Elsethagen, Todd O.; Palmer, Bruce J.; Scheibe, Timothy D.
2009-06-15
The Support Architecture for Large-Scale Subsurface Analysis (SALSSA) provides an extensible framework, sophisticated graphical user interface (GUI), and underlying data management system that simplifies the process of running subsurface models, tracking provenance information, and analyzing the model results. The SALSSA software framework is currently being applied to validating the Smoothed Particle Hydrodynamics (SPH) model. SPH is a three-dimensional model of flow and transport in porous media at the pore scale. Fluid flow in porous media at velocities common in natural porous media occur at low Reynolds numbers and therefore it is important to verify that the SPH model is producing accurate flow solutions in this regime. Validating SPH requires performing a series of simulations and comparing these simulation flow solutions to analytical results or numerical results using other methods. This validation study is being facilitated by the SALLSA framework, which provides capabilities to setup, execute, analyze, and administer these SPH simulations.
Moving Mesh Cosmology: Properties of Gas Disks
Torrey, Paul; Sijacki, Debora; Springel, Volker; Hernquist, Lars
2011-01-01
We compare the structural properties of galaxies formed in cosmological simulations using the smoothed particle hydrodynamics (SPH) code GADGET with those using the moving-mesh code AREPO. Both codes employ identical gravity solvers and the same sub-resolution physics but use very different methods to track the hydrodynamic evolution of gas. This permits us to isolate the effects of the hydro solver on the formation and evolution of galactic disks. In a matching sample of GADGET and AREPO haloes we fit simulated gas disks with exponential profiles. We find that the cold gas disks formed using AREPO have systematically larger disk scale lengths and higher specific angular momenta than their GADGET counterparts. The reason for these differences is rooted in the inaccuracies of the SPH solver and calls for a reassessment of commonly adopted feedback prescriptions in cosmological simulations.
Axion-Like Particle Imprint in Cosmological Very-High-Energy Sources
Energy Technology Data Exchange (ETDEWEB)
Dominguez, A.; /Seville U. /IAA, Granada /Madrid, Autonoma U.; Sanchez-Conde, M.A.; /IAC, La Laguna /IAC, La Laguna /KIPAC, Menlo Park /SLAC; Prada, F.; /IAA, Granada
2012-06-13
Discoveries of very high energy (VHE) photons from distant blazars suggest that, after correction by extragalactic background light (EBL) absorption, there is a flatness or even a turn-up in their spectra at the highest energies that cannot be easily explained by the standard framework. Here, it is shown that a possible solution to this problem is achieved by assuming the existence of axion-like particles (ALPs) with masses {approx} 1 neV. The ALP scenario is tested making use of observations of the highest redshift blazars known in the VHE energy regime, namely 3C 279, 3C 66A, PKS 1222+216 and PG 1553+113. In all cases, better fits to the observed spectra are found when including ALPs rather than considering EBL only. Interestingly, quite similar critical energies for photon/ALP conversions are also derived, independently of the source considered.
Bringing Bell's theorem back to the domain of Particle Physics & Cosmology
Hiesmayr, Beatrix C
2015-01-01
John St. Bell was a physicist working most of his time at CERN and contributing intensively and sustainably to the development of Particle Physics and Collider Physics. As a hobby he worked on so-called "foundations of quantum theory", that was that time very unpopular, even considered to be scientifically taboo. His 1964-theorem, showing that predictions of local realistic theories are different to those of quantum theory, initiated a new field in quantum physics: quantum information theory. The violation of Bell's theorem, for instance, is a necessary and sufficient criterion for generating a secure key for cryptography at two distant locations. This contribution shows how Bell's theorem can be brought to the realm of high energy physics and presents the first conclusive experimental feasible test for weakly decaying neutral mesons on the market. Strong experimental and theoretical limitations make a Bell test in weakly decaying systems such as mesons and hyperons very challenging, however, these systems sh...
Lundberg, Wayne R.
2012-03-01
The no-boundary wave function includes a prescription for restoring causality to particle theory via instantons. To leading order in h, the instanton wave function terms IR and S correspond to area and curvature of a finite representation. For QG theories in which the gravitational quantum has an area, such as Ambjorn dynamical triangulation, the imaginary S term represents particle energy. This establishes the form of the action as required to pass the Seiberg, Susskind & Toumbas (IASSNS 2000) Causality criterion. By following Harari's approach to preon algebra and the eight-fold way, a non-commutative algebra is setup with 1-1 correspondence to band theory. A band is defined as a closed string with intrinsic curvature/tension/energy. Thus a finitary, causal CFT is established which has an AdS-2 dual space in the deep-deep throat of an information-preserving black hole. The geometry of the `extra' scalar field of such an I-PBH is shown to be astrophysically vast and smooth - and thus is a candidate explanation for the observational signature of dark matter.
Shahriari, S; Kadem, L; Rogers, B D; Hassan, I
2012-11-01
This paper aims to extend the application of smoothed particle hydrodynamics (SPH), a meshfree particle method, to simulate flow inside a model of the heart's left ventricle (LV). This work is considered the first attempt to simulate flow inside a heart cavity using a meshfree particle method. Simulating this kind of flow, characterized by high pulsatility and moderate Reynolds number using SPH is challenging. As a consequence, validation of the computational code using benchmark cases is required prior to simulating the flow inside a model of the LV. In this work, this is accomplished by simulating an unsteady oscillating flow (pressure amplitude: A = 2500 N ∕ m(3) and Womersley number: W(o) = 16) and the steady lid-driven cavity flow (Re = 3200, 5000). The results are compared against analytical solutions and reference data to assess convergence. Then, both benchmark cases are combined and a pulsatile jet in a cavity is simulated and the results are compared with the finite volume method. Here, an approach to deal with inflow and outflow boundary conditions is introduced. Finally, pulsatile inlet flow in a rigid model of the LV is simulated. The results demonstrate the ability of SPH to model complex cardiovascular flows and to track the history of fluid properties. Some interesting features of SPH are also demonstrated in this study, including the relation between particle resolution and sound speed to control compressibility effects and also order of convergence in SPH simulations, which is consistently demonstrated to be between first-order and second-order at the moderate Reynolds numbers investigated.
Gibbons, Gary W
2013-01-01
In this paper we lay down the foundations for a purely Newtonian theory of cosmology, valid at scales small compared with the Hubble radius, using only Newtonian point particles acted on by gravity and a possible cosmological term. We describe the cosmological background which is given by an exact solution of the equations of motion in which the particles expand homothetically with their comoving positions constituting a central configuration. We point out, using previous work, that an important class of central configurations are homogeneous and isotropic, thus justifying the usual assumptions of elementary treatments. The scale factor is shown to satisfy the standard Raychaudhuri and Friedmann equations without making any fluid dynamic or continuum approximations. Since we make no commitment as to the identity of the point particles, our results are valid for cold dark matter, galaxies, or clusters of galaxies. In future publications we plan to discuss perturbations of our cosmological background from the p...
DEFF Research Database (Denmark)
Xu, C.B.; Zheng, J.P.; Zhang, W.
2008-01-01
Cigarette smoke is a strong risk factor for cardiovascular disease. However, the underlying molecular mechanisms that lead to cigarette smoke-associated cardiovascular disease remain elusive. With functional and molecular methods, we demonstrate for the first time that lipid-soluble cigarette smoke...... particles (dimethylsulfoxide-soluble cigarette smoke particles; DSP) increased the expression of endothelin type B (ET(B)) receptors in arterial smooth muscle cells. The increased ET(B) receptors in arterial smooth muscle cells was documented as enhanced contractility (sensitive myograph technique...
Quirós, I
2004-01-01
I discuss possible implications a symmetry relating gravity with antigravity might have for smoothing out of the cosmological constant puzzle. For this purpose, a very simple model with spontaneous symmetry breaking is explored, that is based on Einstein-Hilbert gravity with two self-interacting scalar fields. The second (exotic) scalar particle with negative energy density, could be interpreted, alternatively, as an antigravitating particle with positive energy.
Measuring Ejecta from Inspiralling Binary Neutron Stars using Smoothed-particle Hydrodynamics
Rizzo, Monica; O'Shaughnessy, Richard; Faber, Joshua
2017-01-01
Gravitational waves, detectable perturbations in spacetime, can arise from astrophysical systems such as inspiralling binary neutron stars, the remnants of the core collapse of massive stars. In the inspiral process, neutron stars, composed of highly dense nuclear matter, are torn apart by each others gravity and eject matter. Using both gravitational waves and direct observations of ejected matter, we may gain valuable new information about the composition of neutron stars. Using several previously studied test cases, we seek to determine how the amount of ejected matter depends on the physical parameters of these systems. To do this, we use a particle-based hydrodynamics code which can accurately simulate binary neutron star systems with variable equation of state, spin, mass ratio, and eccentricity, and includes the lowest-order effects from gravitational wave emission. I would like to thank RIT's College of Science as well as the Center for Computational Relativity and Gravitation for support and funding.
Directory of Open Access Journals (Sweden)
Alejandro Acevedo-Malavé
2012-06-01
Full Text Available Here the SPH method is applied to simulate in the three-dimensional space the multiple hydrodynamics collisions and formation of clusters of equal-size liquid drops in a vacuum environment. For a range of velocity values from 0.2 mm/ms to 30.0 mm/ms we observe three possible scenarios, such as: coalescence and cluster formation of drops. When the collision velocity is too low the droplets interact only through their deformed surfaces. If this velocity is around 15.0 mm/ms the coalescence of the drops is observed, and after some time starting on t=0 a flat circular section is observed between the colliding drops. This interface disappears when the dynamics runs and the drops finally coalesce. The velocity vector fields were computed for the different scenarios showing some zones inside the drops where the fluid velocity is diminished and other zones where the SPH particles are accelerated.
Cosmological structure formation shocks and cosmic rays in hydrodynamical simulations
Pfrommer, C; Ensslin, T A; Jubelgas, M; Pfrommer, Christoph; Springel, Volker; Ensslin, Torsten A.; Jubelgas, Martin
2006-01-01
Cosmological shock waves during structure formation not only play a decisive role for the thermalization of gas in virializing structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. We discuss a novel numerical treatment of the physics of cosmic rays in combination with a formalism for identifying and measuring the shock strength on-the-fly during a smoothed particle hydrodynamics simulation. In our methodology, the non-thermal CR population is treated self-consistently in order to assess its dynamical impact on the thermal gas as well as other implications on cosmological observables. Using this formalism, we study the history of the thermalization process in high-resolution hydrodynamic simulations of the Lambda cold dark matter model. Collapsed cosmological structures are surrounded by shocks with high Mach numbers up to 1000, but they play only a minor role in the energy balance of thermalization. However, this finding has important consequences fo...
Classical and quantum cosmology
Calcagni, Gianluca
2017-01-01
This comprehensive textbook is devoted to classical and quantum cosmology, with particular emphasis on modern approaches to quantum gravity and string theory and on their observational imprint. It covers major challenges in theoretical physics such as the big bang and the cosmological constant problem. An extensive review of standard cosmology, the cosmic microwave background, inflation and dark energy sets the scene for the phenomenological application of all the main quantum-gravity and string-theory models of cosmology. Born of the author's teaching experience and commitment to bridging the gap between cosmologists and theoreticians working beyond the established laws of particle physics and general relativity, this is a unique text where quantum-gravity approaches and string theory are treated on an equal footing. As well as introducing cosmology to undergraduate and graduate students with its pedagogical presentation and the help of 45 solved exercises, this book, which includes an ambitious bibliography...
Fernandez, J W; Das, R; Cleary, P W; Hunter, P J; Thomas, C D L; Clement, J G
2013-01-01
In the neck of the femur, about 70% of the strength is contributed by the cortical bone, which is the most highly stressed part of the structure and is the site where failure is almost certainly initiated. A better understanding of cortical bone remodelling mechanisms can help discern changes at this anatomical site, which are essential if an understanding of the mechanisms by which hips weaken and become vulnerable to fracture is to be gained. The aims of this study were to (i) examine a hypothesis that low strain fields arise because of subject-specific Haversian canal distributions causing bone resorption and reduced bone integrity and (ii) introduce the use of a meshless particle-based computational modelling approach SPH to capture bone remodelling features at the level of the Haversian canals. We show that bone remodelling initiated by strain at the Haversian level is highly influenced by the subject-specific pore distribution, bone density, loading and osteocyte density. SPH is shown to be effective at capturing the intricate bone pore shapes that evolved over time.
Energy Technology Data Exchange (ETDEWEB)
Margraf, J
2012-06-12
material flows through a still mesh. This is not typically done in an ALE3D analysis, especially if Lagrange elements exist. Deforming Lagrange elements would certainly tangle with a Eulerian mesh eventually. The best method in this case is to have an advecting mesh positioned as some relaxed version of the pre and post Lagrange step; this gives the best opportunity of modeling a high energy event with a combination of Lagrange and ALE elements. Dyne3D is another explicit dynamic analysis code, ParaDyn being the parallel version. ParaDyn is used for predicting the transient response of three dimensional structures using Lagrangian solid mechanics. Large deformation and mesh tangling is often resolved through the use of an element deletion scheme. This is useful to accommodate component failure, but if it is done purely as a means to preserve a useful mesh it can lead to problems because it does not maintain continuity of the material bulk response. Whatever medium exists between structural components is typically not modeled in ParaDyn. Instead, a structure either has a known loading profile applied or given initial conditions. The many included contact algorithms can calculate the loading response of materials if and when they collide. A recent implementation of an SPH module in which failed or deleted material nodes are converted to independent particles is currently being utilized for a variety of spall related problems and high velocity impact scenarios. Figure 4 shows an example of a projectile, given an initial velocity, and how it fails the first plate which generates SPH particles which then interact with and damage the second plate.
Directory of Open Access Journals (Sweden)
Daywitt W. C.
2009-04-01
Full Text Available Both the big-bang and the quasi-steady-state cosmologies originate in some type of Planck state. This paper presents a new cosmological theory based on the Planck- vacuum negative-energy state, a state consisting of a degenerate collection of negative- energy Planck particles. A heuristic look at the Einstein field equation provides a con- vincing argument that such a vacuum state could provide a theoretical explanation for the visible universe.
Directory of Open Access Journals (Sweden)
Martina Blazkova
2009-10-01
Full Text Available High-density polyethylene (PE foils were modified by an Ar+ plasma discharge and subsequent grafting with biomolecules, namely glycine (Gly, polyethylene glycol (PEG, bovine serum albumin (BSA, colloidal carbon particles (C or BSA and C (BSA + C. As revealed by atomic force microscopy (AFM, goniometry and Rutherford Backscattering Spectroscopy (RBS, the surface chemical structure and surface morphology of PE changed dramatically after plasma treatment. The contact angle decreased for the samples treated by plasma, mainly in relation to the formation of oxygen structures during plasma irradiation. A further decrease in the contact angle was obvious after glycine and PEG grafting. The increase in oxygen concentration after glycine and PEG grafting proved that the two molecules were chemically linked to the plasma-activated surface. Plasma treatment led to ablation of the PE surface layer, thus the surface morphology was changed and the surface roughness was increased. The materials were then seeded with vascular smooth muscle cells (VSMC derived from rat aorta and incubated in a DMEM medium with fetal bovine serum. Generally, the cells adhered and grew better on modified rather than on unmodified PE samples. Immunofluorescence showed that focal adhesion plaques containing talin, vinculin and paxillin were most apparent in cells on PE grafted with PEG or BSA + C, and the fibres containing α-actin, β-actin or SM1 and SM2 myosins were thicker, more numerous and more brightly stained in the cells on all modified PE samples than on pristine PE. An enzyme-linked immunosorbent assay (ELISA revealed increased concentrations of focal adhesion proteins talin and vinculin and also a cytoskeletal protein β-actin in cells on PE modified with BSA + C. A contractile protein α-actin was increased in cells on PE grafted with PEG or Gly. These results showed that PE activated with plasma and subsequently grafted with bioactive molecules and colloidal C
Parizek, Martin; Kasalkova, Nikola; Bacakova, Lucie; Slepicka, Petr; Lisa, Vera; Blazkova, Martina; Svorcik, Vaclav
2009-11-20
High-density polyethylene (PE) foils were modified by an Ar(+) plasma discharge and subsequent grafting with biomolecules, namely glycine (Gly), polyethylene glycol (PEG), bovine serum albumin (BSA), colloidal carbon particles (C) or BSA and C (BSA + C). As revealed by atomic force microscopy (AFM), goniometry and Rutherford Backscattering Spectroscopy (RBS), the surface chemical structure and surface morphology of PE changed dramatically after plasma treatment. The contact angle decreased for the samples treated by plasma, mainly in relation to the formation of oxygen structures during plasma irradiation. A further decrease in the contact angle was obvious after glycine and PEG grafting. The increase in oxygen concentration after glycine and PEG grafting proved that the two molecules were chemically linked to the plasma-activated surface. Plasma treatment led to ablation of the PE surface layer, thus the surface morphology was changed and the surface roughness was increased. The materials were then seeded with vascular smooth muscle cells (VSMC) derived from rat aorta and incubated in a DMEM medium with fetal bovine serum. Generally, the cells adhered and grew better on modified rather than on unmodified PE samples. Immunofluorescence showed that focal adhesion plaques containing talin, vinculin and paxillin were most apparent in cells on PE grafted with PEG or BSA + C, and the fibres containing alpha-actin, beta-actin or SM1 and SM2 myosins were thicker, more numerous and more brightly stained in the cells on all modified PE samples than on pristine PE. An enzyme-linked immunosorbent assay (ELISA) revealed increased concentrations of focal adhesion proteins talin and vinculin and also a cytoskeletal protein beta-actin in cells on PE modified with BSA + C. A contractile protein alpha-actin was increased in cells on PE grafted with PEG or Gly. These results showed that PE activated with plasma and subsequently grafted with bioactive molecules and colloidal C
Pan, Wenxiao; Bao, Jie; Tartakovsky, Alexandre M.
2014-02-01
A Robin boundary condition for the Navier-Stokes equations is used to model slip conditions at the fluid-solid boundaries. A novel continuous boundary force (CBF) method is proposed for solving the Navier-Stokes equations subject to the Robin boundary condition. In the CBF method, the Robin boundary condition is replaced by the homogeneous Neumann boundary condition and a volumetric force term added to the momentum conservation equation. Smoothed particle hydrodynamics (SPH) method is used to solve the resulting Navier-Stokes equations. We present solutions for two- and three-dimensional flows subject to various forms of the Robin boundary condition in domains bounded by flat and curved boundaries. The numerical accuracy and convergence are examined through comparison of the SPH-CBF results with the solutions of finite difference or finite-element method. Considering the no-slip boundary condition as a special case of the slip boundary condition, we demonstrate that the SPH-CBF method accurately describes both the no-slip and slip conditions.
Nordendale, Nikolas A.; Heard, William F.; Sherburn, Jesse A.; Basu, Prodyot K.
2016-03-01
The response of structural components of high-strength cementitious (HSC) materials to projectile impact is characterized by high-rate fragmentation resulting from strong compressive shock waves coupled with reflected tensile waves. Accurate modeling of armor panels of such brittle materials under high-velocity projectile impact is a complex problem requiring meticulous experimental characterization of material properties. In a recent paper by the authors, an approach to handle such problems based on a modified Advanced Fundamental Concrete (AFC) constitutive model was developed. In the HSC panels considered in this study, an analogous approach is applied, and the predictions are verified with ballistic impact test data. Traditional Lagrangian finite element analysis (FEA) of these problems tends to introduce errors and suffers from convergence issues resulting from large deformations at free surfaces. Also, FEA cannot properly account for the issues of secondary impact of spalled fragments when multiple armor panels are used. Smoothed particle hydrodynamics (SPH) is considered to be an attractive alternative to resolve these and other issues. However, SPH-based quantitative results have been found to be less accurate than the FEA-based ones when the deformations are not sufficiently large. This paper primarily focuses on a comparison of FEA and SPH models to predict high-velocity projectile impact on single and stacked HSC panels. Results are compared to recent ballistic experiments performed as a part of this research, and conclusions are drawn based on the findings.
Hints of the Existence of Axion-Like-Particles From the Gamma-Ray Spectra of Cosmological Sources
Energy Technology Data Exchange (ETDEWEB)
Sanchez-Conde, M.A.; /IAA, Granada /SLAC; Paneque, D.; Bloom, E.; /KIPAC, Menlo Park; Prada, F.; /IAA, Granada /UC, Santa Cruz; Dominguez, A.; /IAA, Granada /Seville U.
2009-06-23
Axion Like Particles (ALPs) are predicted to couple with photons in the presence of magnetic fields. This effect may lead to a significant change in the observed spectra of gamma-ray sources such as AGNs. Here we carry out a detailed study that for the first time simultaneously considers in the same framework both the photon/axion mixing that takes place in the gamma-ray source and that one expected to occur in the intergalactic magnetic fields. An efficient photon/axion mixing in the source always means an attenuation in the photon flux, whereas the mixing in the intergalactic medium may result in a decrement and/or enhancement of the photon flux, depending on the distance of the source and the energy considered. Interestingly, we find that decreasing the value of the intergalactic magnetic field strength, which decreases the probability for photon/axion mixing, could result in an increase of the expected photon flux at Earth if the source is far enough. We also find a 30% attenuation in the intensity spectrum of distant sources, which occurs at an energy that only depends on the properties of the ALPs and the intensity of the intergalactic magnetic field, and thus independent of the AGN source being observed. Moreover, we show that this mechanism can easily explain recent puzzles in the spectra of distant gamma-ray sources, like the possible detection of TeV photons from 3C 66A (a source located at z=0.444) by MAGIC and VERITAS, which should not happen according to conventional models of photon propagation over cosmological distances. Another puzzle is the recent published lower limit to the EBL intensity at 3.6 {micro}m (which is almost twice larger as the previous one), which implies very hard spectra for some detected TeV gamma-ray sources located at z=0.1-0.2. The consequences that come from this work are testable with the current generation of gamma-ray instruments, namely Fermi (formerly known as GLAST) and imaging atmospheric Cherenkov telescopes like
Nonstandard cosmologies from physics beyond the Standard model
Khlopov, M. Yu.
2016-01-01
The modern cosmology is based on inflationary models with baryosynthesis and dark matter/energy.It implies extension of particle symmetry beyond the Standard model. Studies of physical basis of the modern cosmology combine direct searches for new physics at accelerators with its indirect non-accelerator probes, in which cosmological consequences of particle models play important role. The cosmological consequences of particle models inevitably go beyond the 'standard' cosmological $\\Lambda$CD...
Energy Technology Data Exchange (ETDEWEB)
Ellwanger, Ulrich [Paris-Sud Univ. (France). Lab. de Physique Theorique et Hautes Energies
2015-07-01
The aim of this text is to present the present status of our knowledges of the natural laws from cosmology to the elementary particles. The text begins with a survey starting from the universe via atoms, their nuclei until to the elementary particles. Thereafter the corresponding concepts and physical phenomena are detailedly discussed. Finally the at time still speculative theories are briefly scatched. (HSI)
Development and Application of Smoothed Particle Hydrodynamics%光滑粒子流体动力学的研究进展及应用
Institute of Scientific and Technical Information of China (English)
董添文; 柳和生; 黄益宾; 余忠
2014-01-01
本文从光滑粒子流体动力学（Smoothed particle hydrodynamics ，SPH）方法的基本理论出发，论述了经典SPH方法存在的问题：插值不连续，边界处理，张力不稳定性；对五种改进的SPH算法（NSPH ，RKPM ，CSPM ，MLSPH ，ISPH ）的原理及特点进行了总结。并总结了SPH方法在可压缩流，不可压缩流，材料的变形与冲击断裂中的应用情况。最后，结合SPH在工程领域中的应用提出几点展望。%This paper proceeds from the basic theory of the smoothed particle hydrodynamics .Several problems such as discontinuity of interpolating ,boundary treatment ,tensile instability are discussed .Five types of modified SPH methods such as NSPH (normal-ized SPH) ,RKPM (Reproducing kernel method) ,CSPM(Corrective smoothed particle method) ,MLSPH(Moving least squares par-ticle hydrodynamics) ,ISPH(Incompressible SPH) ,are summarized .The applications of SPH in the compressible flow ,incompress-ible flow ,the deformation or fracture of material are reviewed .Finally ,the application prospect of SPH in industry is discussed .
Haddad, Bouchra; Palacios, David; Pastor, Manuel; Zamorano, José Juan
2016-09-01
Lahars are among the most catastrophic volcanic processes, and the ability to model them is central to mitigating their effects. Several lahars recently generated by the Popocatépetl volcano (Mexico) moved downstream through the Huiloac Gorge towards the village of Santiago Xalitzintla. The most dangerous was the 2001 lahar, in which the destructive power of the debris flow was maintained throughout the extent of the flow. Identifying the zone of hazard can be based either on numerical or empirical models, but a calibration and validation process is required to ensure hazard map quality. The Geoflow-SPH depth integrated numerical model used in this study to reproduce the 2001 lahar was derived from the velocity-pressure version of the Biot-Zienkiewicz model, and was discretized using the smoothed particle hydrodynamics (SPH) method. The results of the calibrated SPH model were validated by comparing the simulated deposit depth with the field depth measured at 16 cross sections distributed strategically along the gorge channel. Moreover, the dependency of the results on topographic mesh resolution, initial lahar mass shape and dimensions is also investigated. The results indicate that to accurately reproduce the 2001 lahar flow dynamics the channel topography needed to be discretized using a mesh having a minimum 5 m resolution, and an initial lahar mass shape that adopted the source area morphology. Field validation of the calibrated model showed that there was a satisfactory relationship between the simulated and field depths, the error being less than 20% for 11 of the 16 cross sections. This study demonstrates that the Geoflow-SPH model was able to accurately reproduce the lahar path and the extent of the flow, but also reproduced other parameters including flow velocity and deposit depth.
Energy Technology Data Exchange (ETDEWEB)
Virey, J.M
2007-12-15
The author reviews his contributions in particle physics and cosmology. The first part is dedicated to the study of non standard signals collected in particle collisions. It is shown that a pure hadronic interaction, weak compared with QCD, can stay un-observed and be detected only by studying spin asymmetries. He has also studied important and unique information carried by these spin asymmetries on the chiral structure and scalar structure of new interactions. The models describing this new physics appear as low energy applications of more general models concerning sub-structures or great unification, or more specific models in supersymmetry or string theory. As an illustration he presents a study of the features of supersymmetry in cases where the R-parity is broken. The second part is dedicated to the study of cosmological parameters and particularly of the properties of black energy. It is shown that assumptions on the characteristics of the black energy have a great impact on the determination of other parameters when interpreting experimental data. Another point is the determination of constraints on the black energy from the analysis of observation data.
Cosmological Probes for Supersymmetry
Directory of Open Access Journals (Sweden)
Maxim Khlopov
2015-05-01
Full Text Available The multi-parameter character of supersymmetric dark-matter models implies the combination of their experimental studies with astrophysical and cosmological probes. The physics of the early Universe provides nontrivial effects of non-equilibrium particles and primordial cosmological structures. Primordial black holes (PBHs are a profound signature of such structures that may arise as a cosmological consequence of supersymmetric (SUSY models. SUSY-based mechanisms of baryosynthesis can lead to the possibility of antimatter domains in a baryon asymmetric Universe. In the context of cosmoparticle physics, which studies the fundamental relationship of the micro- and macro-worlds, the development of SUSY illustrates the main principles of this approach, as the physical basis of the modern cosmology provides cross-disciplinary tests in physical and astronomical studies.
Cosmological Probes for Supersymmetry
Khlopov, Maxim
2015-01-01
The multi-parameter character of supersymmetric dark-matter models implies the combination of their experimental studies with astrophysical and cosmological probes. The physics of the early Universe provides nontrivial effects of non-equilibrium particles and primordial cosmological structures. Primordial black holes (PBHs) are a profound signature of such structures that may arise as a cosmological consequence of supersymmetric (SUSY) models. SUSY-based mechanisms of baryosynthesis can lead to the possibility of antimatter domains in a baryon asymmetric Universe. In the context of cosmoparticle physics, which studies the fundamental relationship of the micro- and macro-worlds, the development of SUSY illustrates the main principles of this approach, as the physical basis of the modern cosmology provides cross-disciplinary tests in physical and astronomical studies.
Quantum Cosmology: Effective Theory
Bojowald, Martin
2012-01-01
Quantum cosmology has traditionally been studied at the level of symmetry-reduced minisuperspace models, analyzing the behavior of wave functions. However, in the absence of a complete full setting of quantum gravity and detailed knowledge of specific properties of quantum states, it remained difficult to make testable predictions. For quantum cosmology to be part of empirical science, it must allow for a systematic framework in which corrections to well-tested classical equations can be derived, with any ambiguities and ignorance sufficiently parameterized. As in particle and condensed-matter physics, a successful viewpoint is one of effective theories, adapted to specific issues one encounters in quantum cosmology. This review presents such an effective framework of quantum cosmology, taking into account, among other things, space-time structures, covariance, the problem of time and the anomaly issue.
STUDY ON THE SMOOTHED PARTICLE HYDRODYNAMICS METHOD%光滑粒子流体动力学方法研究
Institute of Scientific and Technical Information of China (English)
陈建设; 徐绯; 黄其青
2008-01-01
光滑粒子流体动力学(smoothed particle hydrodynamics, SPH)方法在模拟大变形问题时具有明显的优势,但是由于粒子的不连续性,致使其计算精度较低.文中对光滑粒子流体动力学方法中函数及其一阶导数的核估计进行详细研究.讨论传统的SPH方法和改进的CSPH (corrective smoothed particle hydrodynamics)方法的离散思想,在Taylor展开的基础上引入修正的MSPH(modified smoothed particle hydrodynamics)方法,并推导一维和二维情况下函数的核估计和函数的一阶导数核估计的离散形式.最后通过数值算例,对三种不同的SPH方法的计算精度进行详细比较,结果表明,CSPH和MSPH方法可以极大提高边界粒子的计算精度,在二维情况下,MSPH方法的计算精度要优于CSPH方法.
Cosmological D-instantons and cyclic universes
Bergshoeff, EA; Collinucci, A; Roest, D; Russo, JG; Townsend, PK
2005-01-01
For models of gravity coupled to hyperbolic sigma models, such as the metric-scalar sector of IIB supergravity, we show how smooth trajectories in the 'augmented target space' connect FLRW cosmologies to non-extremal D-instantons through a cosmological singularity. In particular, we find closed cycl
Jones, Bernard J. T.
2017-04-01
Preface; Notation and conventions; Part I. 100 Years of Cosmology: 1. Emerging cosmology; 2. The cosmic expansion; 3. The cosmic microwave background; 4. Recent cosmology; Part II. Newtonian Cosmology: 5. Newtonian cosmology; 6. Dark energy cosmological models; 7. The early universe; 8. The inhomogeneous universe; 9. The inflationary universe; Part III. Relativistic Cosmology: 10. Minkowski space; 11. The energy momentum tensor; 12. General relativity; 13. Space-time geometry and calculus; 14. The Einstein field equations; 15. Solutions of the Einstein equations; 16. The Robertson–Walker solution; 17. Congruences, curvature and Raychaudhuri; 18. Observing and measuring the universe; Part IV. The Physics of Matter and Radiation: 19. Physics of the CMB radiation; 20. Recombination of the primeval plasma; 21. CMB polarisation; 22. CMB anisotropy; Part V. Precision Tools for Precision Cosmology: 23. Likelihood; 24. Frequentist hypothesis testing; 25. Statistical inference: Bayesian; 26. CMB data processing; 27. Parametrising the universe; 28. Precision cosmology; 29. Epilogue; Appendix A. SI, CGS and Planck units; Appendix B. Magnitudes and distances; Appendix C. Representing vectors and tensors; Appendix D. The electromagnetic field; Appendix E. Statistical distributions; Appendix F. Functions on a sphere; Appendix G. Acknowledgements; References; Index.
Quantum cosmological metroland model
Anderson, E.; Franzen, A.T.
2010-01-01
Relational particle mechanics is useful for modelling whole-universe issues such as quantum cosmology or the problem of time in quantum gravity, including some aspects outside the reach of comparably complex mini-superspace models. In this paper, we consider the mechanics of pure shape and not scale
Terapixel imaging of cosmological simulations
Feng, Yu; Di Matteo, Tiziana; Khandai, Nishikanta; Sargent, Randy; Nourbakhsh, Illah; Dille, Paul; Bartley, Chris; Springel, Volker; Jana, Anirban; Gardner, Jeffrey
2011-01-01
The increasing size of cosmological simulations has led to the need for new visualization techniques. We focus on Smoothed Particle Hydrodynamical (SPH) simulations run with the GADGET code and describe methods for visually accessing the entire simulation at full resolution. The simulation snapshots are rastered and processed on supercomputers into images that are ready to be accessed through a web interface (GigaPan). This allows any scientist with a web-browser to interactively explore simulation datasets in both in spatial and temporal dimensions, datasets which in their native format can be hundreds of terabytes in size or more. We present two examples, the first a static terapixel image of the MassiveBlack simulation, a P-GADGET SPH simulation with 65 billion particles, and the second an interactively zoomable animation of a different simulation with more than one thousand frames, each a gigapixel in size. Both are available for public access through the GigaPan web interface. We also make our imaging so...
Smooth sandwich gravitational waves
Podolsky, J
1999-01-01
Gravitational waves which are smooth and contain two asymptotically flat regions are constructed from the homogeneous pp-waves vacuum solution. Motion of free test particles is calculated explicitly and the limit to an impulsive wave is also considered.
The Cosmological Memory Effect
Tolish, Alexander; Wald, Robert M.
2016-01-01
The "memory effect" is the permanent change in the relative separation of test particles resulting from the passage of gravitational radiation. We investigate the memory effect for a general, spatially flat FLRW cosmology by considering the radiation associated with emission events involving particle-like sources. We find that if the resulting perturbation is decomposed into scalar, vector, and tensor parts, only the tensor part contributes to memory. Furthermore, the tensor contribution to m...
Silk, Joseph
2008-11-01
The field of cosmology has been transformed since the glorious decades of the 1920's and 1930's when theory and observation converged to develop the current model of the expanding universe. It was a triumph of the theory of general relativity and astronomy. The first revolution came when the nuclear physicists entered the fray. This marked the debut of the hot big bang, in which the light elements were synthesized in the first three minutes. It was soon realised that elements like carbon and iron were synthesized in exploding stars. However helium, as well as deuterium and lithium, remain as George Gamow envisaged, the detritus of the big bang. The climax arrived with one of the most remarkable discoveries of the twentieth century, the cosmic microwave background radiation, in 1964. The fossil glow turned out to have the spectrum of an ideal black body. One could not imagine a stronger confirmation of the hot and dense origin of the universe. This discovery set the scene for the next major advance. It was now the turn of the particle physicists, who realized that the energies attained near the beginning of the universe, and unachievable in any conceivable terrestrial accelerator, provided a unique testing ground for theories of grand unification of the fundamental forces. This led Alan Guth and Andrei Linde in 1980 to propose the theory of inflation, which solved outstanding puzzles of the big bang. One could now understand why the universe is so large and homogeneous, and the origin of the seed fluctuations that gave rise to large-scale structure. A key prediction was that the universe should have Euclidean geometry, now verified to a precision of a few percent. Modern cosmology is firmly embedded in particle physics. It merits a text written by a particle physicist who can however appreciate the contributions of astronomy that provide the foundation and infrastructure for the theory of the expanding universe. There are now several such texts available. The most
Sanders, RH; Papantonopoulos, E
2005-01-01
I discuss the classical cosmological tests, i.e., angular size-redshift, flux-redshift, and galaxy number counts, in the light of the cosmology prescribed by the interpretation of the CMB anisotropies. The discussion is somewhat of a primer for physicists, with emphasis upon the possible systematic
Brandenberger, R H; Brandenberger, Robert H.; Magueijo, Joao
1999-01-01
We review a few off-the-beaten-track ideas in cosmology. They solve a variety of fundamental problems; also they are fun. We start with a description of non-singular dilaton cosmology. In these scenarios gravity is modified so that the Universe does not have a singular birth. We then present a variety of ideas mixing string theory and cosmology. These solve the cosmological problems usually solved by inflation, and furthermore shed light upon the issue of the number of dimensions of our Universe. We finally review several aspects of the varying speed of light theory. We show how the horizon, flatness, and cosmological constant problems may be solved in this scenario. We finally present a possible experimental test for a realization of this theory: a test in which the Supernovae results are to be combined with recent evidence for redshift dependence in the fine structure constant.
Nonstandard cosmologies from physics beyond the Standard model
Khlopov, M Yu
2016-01-01
The modern cosmology is based on inflationary models with baryosynthesis and dark matter/energy.It implies extension of particle symmetry beyond the Standard model. Studies of physical basis of the modern cosmology combine direct searches for new physics at accelerators with its indirect non-accelerator probes, in which cosmological consequences of particle models play important role. The cosmological consequences of particle models inevitably go beyond the 'standard' cosmological $\\Lambda$CDM model and some possible feature of such 'nonstandard'cosmological scenarios is the subject of the present brief review.
Institute of Scientific and Technical Information of China (English)
强洪夫; 陈福振; 高巍然
2011-01-01
Modified equations for surface tension are derived by modifying normal and curvature with corrected smoothed particle method (CSPM). It is based on smoothed particle hydrodynamics (SPH) method with surface tension proposed by Morris. Both Morris and our method are tested via a semicircular problem. Factors that affect accuracy are investigated including surface definition, normal and curvature calculation. Smoothed length in curvature calculation is also confirmed reasonable. Furthermore, formation of a liquid drop with initial square shape under surface tension is simulated. Compared with Morris method and grid-based volume of fluid method,it is proved that the accuracy of our method is higher and particle distribution is more homogeneous. Finally, coalescence process of two oil drops in water under surface tension is simulated.%在Morris提出的表面张力SPH方法基础上,通过引入CSPM方法对边界法向的计算和曲率的计算进行修正,得到表面张力修正方程组;通过半圆形算例测试方法和Morris方法在边界定位、法向计算和曲率计算等影响表面张力关键因素的求解精度,研究曲率计算中应采用的光滑长度值.模拟初始方形液滴在表面张力作用下的自然变化过程,并与Morris方法及VOF有限体积法进行对比,表明方法精度较高,稳定性较好.最后,模拟水溶液中两个油滴的互溶过程.
Bonometto, S A; Musco, I; Mainini, R; Maccio', A V
2014-01-01
Models including an energy transfer from CDM to DE are widely considered in the literature, namely to allow DE a significant high-z density. Strongly Coupled cosmologies assume a much larger coupling between DE and CDM, together with the presence of an uncoupled warm DM component, as the role of CDM is mostly restricted to radiative eras. This allows us to preserve small scale fluctuations even if the warm particle, possibly a sterile neutrino, is quite light, O(100 eV). Linear theory and numerical simulations show that these cosmologies agree with LCDM on supergalactic scales; e.g., CMB spectra are substantially identical. Simultaneously, simulations show that they significantly ease problems related to the properties of MW satellites and cores in dwarfs. SC cosmologies also open new perspectives on early black hole formation, and possibly lead towards unificating DE and inflationary scalar fields.
Cosmological Perturbations in Antigravity
Oltean, Marius
2014-01-01
We compute the evolution of cosmological perturbations in a recently proposed Weyl-symmetric theory of two scalar fields with oppositely-signed conformal couplings to Einstein gravity. It is motivated from the minimal conformal extension of the Standard Model, such that one of these scalar fields is the Higgs while the other is a new particle, the dilaton, introduced to make the Higgs mass conformally symmetric. At the background level, the theory admits novel geodesically-complete cyclic cosmological solutions characterized by a brief period of repulsive gravity, or "antigravity", during each successive transition from a Big Crunch to a Big Bang. We show that despite the necessarily wrong-signed kinetic term of the dilaton in the full action, its cosmological solutions are stable at the perturbative level.
Relativistic Fractal Cosmologies
Ribeiro, Marcelo B
2009-01-01
This article reviews an approach for constructing a simple relativistic fractal cosmology whose main aim is to model the observed inhomogeneities of the distribution of galaxies by means of the Lemaitre-Tolman solution of Einstein's field equations for spherically symmetric dust in comoving coordinates. This model is based on earlier works developed by L. Pietronero and J.R. Wertz on Newtonian cosmology, whose main points are discussed. Observational relations in this spacetime are presented, together with a strategy for finding numerical solutions which approximate an averaged and smoothed out single fractal structure in the past light cone. Such fractal solutions are shown, with one of them being in agreement with some basic observational constraints, including the decay of the average density with the distance as a power law (the de Vaucouleurs' density power law) and the fractal dimension in the range 1 <= D <= 2. The spatially homogeneous Friedmann model is discussed as a special case of the Lemait...
Cool Core Clusters from Cosmological Simulations
Rasia, E; Murante, G; Planelles, S; Beck, A M; Biffi, V; Ragone-Figueroa, C; Granato, G L; Steinborn, L K; Dolag, K
2015-01-01
We present results obtained from a set of cosmological hydrodynamic simulations of galaxy clusters, aimed at comparing predictions with observational data on the diversity between cool-core and non-cool-core clusters. Our simulations include the effects of stellar and AGN feedback and are based on an improved version of the Smoothed-Particle-Hydrodynamics code GADGET-3, which ameliorates gas mixing and better captures gas-dynamical instabilities by including a suitable artificial thermal diffusion. In this Letter, we focus our analysis on the entropy profiles, our primary diagnostic to classify the degree of cool-coreness of clusters, and on the iron profiles. In keeping with observations, our simulated clusters display a variety of behaviors in entropy profiles: they range from steadily decreasing profiles at small radii, characteristic of cool-core systems, to nearly flat core isentropic profiles, characteristic of non cool-core systems. Using observational criteria to distinguish between the two classes of...
Thermal Tachyacoustic Cosmology
Agarwal, Abhineet
2014-01-01
An intriguing possibility that can address pathologies in both early universe cosmology (i.e. the horizon problem) and quantum gravity (i.e. non-renormalizability), is that particles at very high energies and/or temperatures could propagate arbitrarily fast. A concrete realization of this possibility for the early universe is the Tachyacoustic (or Speedy Sound) cosmology, which could also produce a scale-invariant spectrum for scalar cosmological perturbations. Here, we study Thermal Tachyacoustic Cosmology (TTC), i.e. this scenario with thermal initial conditions. We find that a phase transition in the early universe, around the scale of Grand Unified Theories (GUT scale; $T\\sim 10^{15}$ GeV), during which the speed of sound drops by $25$ orders of magnitude within a Hubble time, can fit current CMB observations. We further discuss how production of primordial black holes constrains the cosmological acoustic history, while coupling TTC to Horava-Lifshitz gravity leads to a lower limit on the amplitude of ten...
Thermal tachyacoustic cosmology
Agarwal, Abhineet; Afshordi, Niayesh
2014-08-01
An intriguing possibility that can address pathologies in both early Universe cosmology (i.e. the horizon problem) and quantum gravity (i.e. nonrenormalizability), is that particles at very high energies and/or temperatures could propagate arbitrarily fast. A concrete realization of this possibility for the early Universe is the tachyacoustic (or speedy sound) cosmology, which could also produce a scale-invariant spectrum for scalar cosmological perturbations. Here, we study thermal tachyacoustic cosmology (TTC), i.e. this scenario with thermal initial conditions. We find that a phase transition in the early Universe, around the scale of the grand unified theory (GUT scale; T ˜1015 GeV), during which the speed of sound drops by 25 orders of magnitude within a Hubble time, can fit current CMB observations. We further discuss how production of primordial black holes constrains the cosmological acoustic history, while coupling TTC to Horava-Lifshitz gravity leads to a lower limit on the amplitude of tensor modes (r≳10-3), that are detectable by CMBpol (and might have already been seen by the BICEP-Keck Collaboration).
Ryan, M.
1972-01-01
The study of cosmological models by means of equations of motion in Hamiltonian form is considered. Hamiltonian methods applied to gravity seem to go back to Rosenfeld (1930), who constructed a quantum-mechanical Hamiltonian for linearized general relativity theory. The first to notice that cosmologies provided a simple model in which to demonstrate features of Hamiltonian formulation was DeWitt (1967). Applications of the ADM formalism to homogeneous cosmologies are discussed together with applications of the Hamiltonian formulation, giving attention also to Bianchi-type universes. Problems involving the concept of superspace and techniques of quantization are investigated.
Steyerl, A; Müller, G; Golub, R
2015-01-01
The important role of geometric phases in searches for a permanent electric dipole moment of the neutron, using Ramsey separated oscillatory field nuclear magnetic resonance, was first investigated by Pendlebury $\\textit{et al.}$ [Phys. Rev. A $\\mathbf{70}$, 032102 (2004)]. Their analysis was based on the Bloch equations. In subsequent work using the spin density matrix Lamoreaux and Golub [Phys. Rev. A $\\mathbf{71}$, 032104 (2005)] showed the usual relation between the frequency shifts and the correlation functions of the fields seen by trapped particles in general fields (Redfield theory). More recently we presented a solution of the Schr\\"odinger equation for spin-$1/2$ particles in circular cylindrical traps with smooth walls and exposed to arbitrary fields [Steyerl $\\textit{et al.}$, Phys.Rev. A $\\mathbf{89}$, 052129 (2014)]. Here we extend this work to show how the Redfield theory follows directly from the Schr\\"odinger equation solution and include wall roughness, cylindrical trap geometry with arbitra...
Belinski, V
2009-01-01
The talk at international conference in honor of Ya. B. Zeldovich 95th Anniversary, Minsk, Belarus, April 2009. The talk represents a review of the old results and contemporary development on the problem of cosmological singularity.
Cosmology from start to finish.
Bennett, Charles L
2006-04-27
Cosmology is undergoing a revolution. With recent precise measurements of the cosmic microwave background radiation, large galaxy redshift surveys, better measurements of the expansion rate of the Universe and a host of other astrophysical observations, there is now a standard, highly constrained cosmological model. It is not a cosmology that was predicted. Unidentified dark particles dominate the matter content of our Universe, and mysteries surround the processes responsible for the accelerated expansion at its earliest moments (inflation?) and for its recent acceleration (dark energy?). New measurements must address the fundamental questions: what happened at the birth of the Universe, and what is its ultimate fate?
Tolish, Alexander; Wald, Robert M.
2016-08-01
The "memory effect" is the permanent change in the relative separation of test particles resulting from the passage of gravitational radiation. We investigate the memory effect for a general, spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology by considering the radiation associated with emission events involving particle-like sources. We find that if the resulting perturbation is decomposed into scalar, vector, and tensor parts, only the tensor part contributes to memory. Furthermore, the tensor contribution to memory depends only on the cosmological scale factor at the source and observation events, not on the detailed expansion history of the universe. In particular, for sources at the same luminosity distance, the memory effect in a spatially flat FLRW spacetime is enhanced over the Minkowski case by a factor of (1 +z ).
The Cosmological Memory Effect
Tolish, Alexander
2016-01-01
The "memory effect" is the permanent change in the relative separation of test particles resulting from the passage of gravitational radiation. We investigate the memory effect for a general, spatially flat FLRW cosmology by considering the radiation associated with emission events involving particle-like sources. We find that if the resulting perturbation is decomposed into scalar, vector, and tensor parts, only the tensor part contributes to memory. Furthermore, the tensor contribution to memory depends only on the cosmological scale factor at the source and observation events, not on the detailed expansion history of the universe. In particular, for sources at the same luminosity distance, the memory effect in a spatially flat FLRW spacetime is enhanced over the Minkowski case by a factor of $(1 + z)$.
Cosmology and astrophysics 1992
Krauss, L M
1992-01-01
I review recent developments in cosmology and astrophysics relevant to particle physics, focussing on the following questions: What's new in 1992? What have we learned since the last ICHEP meeting in 1990? and What are the prospects for the future? AMong the topics explicitly discussed are: COBE, Large Scale Structure, and Dark Matter; Bib Bang Nucleosynthesis; the Solar Neutrino Problem; and High Energy Gamma Ray PHysics.
Energy Technology Data Exchange (ETDEWEB)
Wesson, P.S.
1979-10-01
The Cosmological Principle states: the universe looks the same to all observers regardless of where they are located. To most astronomers today the Cosmological Principle means the universe looks the same to all observers because density of the galaxies is the same in all places. A new Cosmological Principle is proposed. It is called the Dimensional Cosmological Principle. It uses the properties of matter in the universe: density (rho), pressure (p), and mass (m) within some region of space of length (l). The laws of physics require incorporation of constants for gravity (G) and the speed of light (C). After combining the six parameters into dimensionless numbers, the best choices are: 8..pi..Gl/sup 2/ rho/c/sup 2/, 8..pi..Gl/sup 2/ rho/c/sup 4/, and 2 Gm/c/sup 2/l (the Schwarzchild factor). The Dimensional Cosmological Principal came about because old ideas conflicted with the rapidly-growing body of observational evidence indicating that galaxies in the universe have a clumpy rather than uniform distribution. (SC)
光滑粒子动力学方法的发展与应用%DEVELOPMENTS AND APPLICATIONS OF SMOOTHED PARTICLE HYDRODYNAMICS
Institute of Scientific and Technical Information of China (English)
刘谋斌; 宗智; 常建忠
2011-01-01
Smoothed particle hydrodynamics (SPH) is a Lagrangian meshfree particle method, and has been widely applied to different areas in engineering and science.SPH method uses a set of particles to discretize the computational domain and to represent the state of the system being modeled, and approximates the governing equations based on the set of particles.This paper provides an overview on the development, numerical aspects, and applications of the SPH method.The basic concepts, consistency, boundary treatment, stability and computational efficiency of the SPH method have been discussed.Applications of the SPH method to compressible and incompressible fluid flows as well as to rapid deformation and failure of elastic-plastic materials have been addressed.Finally the paper concludes with remarks of the merits and defects of the SPH methods,and with some predictions of numerical method development and application areas.%光滑粒子动力学(smoothed particle hydrodynamics,SPH)是一种拉格朗日型无网格粒子方法,已经成功地应用到了工程和科学的众多领域.SPH使用粒子离散及代表所模拟的介质,并且基于粒子体系估算和近似介质运动的控制方程.本文分析和综述了SPH模拟方法的发展历程、数值方法与应用进展.介绍了SPH方法的基本思想;从连续性、边界处理、稳定性和计算效率4个方面阐述了SPH方法的研究现状;介绍了SPH方法近年来在可压缩流动、不可压缩流动以及弹塑性材料高速变形与失效方面的一些典型应用;并对SPH方法的发展与应用进行了预测与展望.
A LAGUERRE VORONOI BASED SCHEME FOR MESHING PARTICLE SYSTEMS.
Bajaj, Chandrajit
2005-06-01
We present Laguerre Voronoi based subdivision algorithms for the quadrilateral and hexahedral meshing of particle systems within a bounded region in two and three dimensions, respectively. Particles are smooth functions over circular or spherical domains. The algorithm first breaks the bounded region containing the particles into Voronoi cells that are then subsequently decomposed into an initial quadrilateral or an initial hexahedral scaffold conforming to individual particles. The scaffolds are subsequently refined via applications of recursive subdivision (splitting and averaging rules). Our choice of averaging rules yield a particle conforming quadrilateral/hexahedral mesh, of good quality, along with being smooth and differentiable in the limit. Extensions of the basic scheme to dynamic re-meshing in the case of addition, deletion, and moving particles are also discussed. Motivating applications of the use of these static and dynamic meshes for particle systems include the mechanics of epoxy/glass composite materials, bio-molecular force field calculations, and gas hydrodynamics simulations in cosmology.
Kursunoglu, N.
2003-06-01
This paper was originally published without the accompanying figures. The complete paper is published in the Appendix of AIP Conference Proceedings 672, Short Distance Behavior of Fundamental Interactions, edited by B. N. Kursunoglu et al., pp. 210-219, 2003. The correct citation to be used for this paper is AIP Conference Proceedings 624, Cosmology and Elementary Particle Physics, edited by B. N. Kursunoglu et al., pp. 201-210, 2002. The online version of this paper has been corrected.
Sanders, Robert H
2016-01-01
The advent of sensitive high-resolution observations of the cosmic microwave background radiation and their successful interpretation in terms of the standard cosmological model has led to great confidence in this model's reality. The prevailing attitude is that we now understand the Universe and need only work out the details. In this book, Sanders traces the development and successes of Lambda-CDM, and argues that this triumphalism may be premature. The model's two major components, dark energy and dark matter, have the character of the pre-twentieth-century luminiferous aether. While there is astronomical evidence for these hypothetical fluids, their enigmatic properties call into question our assumptions of the universality of locally determined physical law. Sanders explains how modified Newtonian dynamics (MOND) is a significant challenge for cold dark matter. Overall, the message is hopeful: the field of cosmology has not become frozen, and there is much fundamental work ahead for tomorrow's cosmologis...
Narimani, Ali; Scott, Douglas
2011-01-01
Although it is possible that some fundamental physical constants could vary in time, it is important to only consider dimensionless combinations, such as the fine structure constant or the equivalent coupling constant for gravity. Once all such dimensionless numbers have been given, then we can be sure that our cosmological picture is governed by the same physical laws as that of another civilization with an entirely different set of units. An additional feature of the standard model of cosmology raises an extra complication, namely that the epoch at which we live is a crucial part of the model. This can be defined by giving the value of any one of the evolving cosmological parameters. It takes some care to avoid inconsistent results for constraints on variable constants, which could be caused by effectively fixing more than one parameter today. We show examples of this effect by considering in some detail the physics of Big Bang nucleosynthesis, recombination and microwave background anisotropies, being care...
光滑粒子动力学方法及其应用%On Smoothed Particle Hydrodynamics Method and its Application
Institute of Scientific and Technical Information of China (English)
刘鹏; 刘更; 刘天祥; 姚艳
2005-01-01
光滑粒子动力学(Smoothed Particle Hydrodynamics,SPH)方法是近年来得到广泛发展和应用的无网格方法的一个重要分支,它是一种纯Lagrangian方法.本文对现有的光滑粒子动力学方法进行了综述,介绍了该方法的理论基础、连续介质守恒方程、方法稳定性的改善等,重点阐述了边界条件的处理,并给出了SPH方法的算例.最后,介绍了SPH方法的最新进展状况.
Kordilla, J.; Shigorina, E.; Tartakovsky, A. M.; Pan, W.; Geyer, T.
2015-12-01
Under idealized conditions (smooth surfaces, linear relationship between Bond number and Capillary number of droplets) steady-state flow modes on fracture surfaces have been shown to develop from sliding droplets to rivulets and finally (wavy) film flow, depending on the specified flux. In a recent study we demonstrated the effect of surface roughness on droplet flow in unsaturated wide aperture fractures, however, its effect on other prevailing flow modes is still an open question. The objective of this work is to investigate the formation of complex flow modes on fracture surfaces employing an efficient three-dimensional parallelized SPH model. The model is able to simulate highly intermittent, gravity-driven free-surface flows under dynamic wetting conditions. The effect of surface tension is included via efficient pairwise interaction forces. We validate the model using various analytical and semi-analytical relationships for droplet and complex flow dynamics. To investigate the effect of surface roughness on flow dynamics we construct surfaces with a self-affine fractal geometry and roughness characterized by the Hurst exponent. We demonstrate the effect of surface roughness (on macroscopic scales this can be understood as a tortuosity) on the steady-state distribution of flow modes. Furthermore we show the influence of a wide range of natural wetting conditions (defined by static contact angles) on the final distribution of surface coverage, which is of high importance for matrix-fracture interaction processes.
Energy Technology Data Exchange (ETDEWEB)
Greenwood, Eric, E-mail: esg3@buffalo.ed [CERCA, Department of Physics, Case Western Reserve University, Cleveland, OH 44106-7079 (United States); Dai, De Chang; Stojkovic, Dejan [HEPCOS, Department of Physics, SUNY at Buffalo, Buffalo, NY 14260-1500 (United States)
2010-09-06
We study the evolution of time-dependent fluctuations and particle production in an expanding dS and contracting AdS universe. Using the functional Schroedinger formalism we are able to probe the time-dependent regime which is out of the reach of the standard approximations like the Bogolyubov method. In both cases, the evolution of fluctuations is governed by the harmonic oscillator equation with time-dependent frequency. In the case of an expanding dS universe we explicitly show that the frequency of fluctuations produced at a certain moment diminish in time, while the distribution of the created particles quickly approaches the thermal radiation of the dS space. In the case of a contracting AdS universe we show that the frequency of fluctuations produced at a certain moment grow in time. Nominally, the temperature of radiation diverges as the Big Crunch is approaching, however, increasing oscillations of the spectrum make the temperature poorly defined, which is in agreement with the fact that AdS space does not have an event horizon which would cause thermal radiation. Unlimited growth of fluctuations indicates that an eventual tunneling into AdS vacuum would have catastrophic consequences for our universe.
Classically Stable Nonsingular Cosmological Bounces
Ijjas, Anna; Steinhardt, Paul J.
2016-09-01
One of the fundamental questions of theoretical cosmology is whether the Universe can undergo a nonsingular bounce, i.e., smoothly transit from a period of contraction to a period of expansion through violation of the null energy condition (NEC) at energies well below the Planck scale and at finite values of the scale factor such that the entire evolution remains classical. A common claim has been that a nonsingular bounce either leads to ghost or gradient instabilities or a cosmological singularity. In this Letter, we consider a well-motivated class of theories based on the cubic Galileon action and present a procedure for explicitly constructing examples of a nonsingular cosmological bounce without encountering any pathologies and maintaining a subluminal sound speed for comoving curvature modes throughout the NEC violating phase. We also discuss the relation between our procedure and earlier work.
Double field theory inspired cosmology
Wu, Houwen; Yang, Haitang
2014-07-01
Double field theory proposes a generalized spacetime action possessing manifest T-duality on the level of component fields. We calculate the cosmological solutions of double field theory with vanishing Kalb-Ramond field. It turns out that double field theory provides a more consistent way to construct cosmological solutions than the standard string cosmology. We construct solutions for vanishing and non-vanishing symmetry preserving dilaton potentials. The solutions assemble the pre- and post-big bang evolutions in one single line element. Our results show a smooth evolution from an anisotropic early stage to an isotropic phase without any special initial conditions in contrast to previous models. In addition, we demonstrate that the contraction of the dual space automatically leads to both an inflation phase and a decelerated expansion of the ordinary space during different evolution stages.
Matrix Model Approach to Cosmology
Chaney, A; Stern, A
2015-01-01
We perform a systematic search for rotationally invariant cosmological solutions to matrix models, or more specifically the bosonic sector of Lorentzian IKKT-type matrix models, in dimensions $d$ less than ten, specifically $d=3$ and $d=5$. After taking a continuum (or commutative) limit they yield $d-1$ dimensional space-time surfaces, with an attached Poisson structure, which can be associated with closed, open or static cosmologies. For $d=3$, we obtain recursion relations from which it is possible to generate rotationally invariant matrix solutions which yield open universes in the continuum limit. Specific examples of matrix solutions have also been found which are associated with closed and static two-dimensional space-times in the continuum limit. The solutions provide for a matrix resolution of cosmological singularities. The commutative limit reveals other desirable features, such as a solution describing a smooth transition from an initial inflation to a noninflationary era. Many of the $d=3$ soluti...
The Smoothed Particle Hydrodynamics Method for Solving Some Dam Break Problems%几种溃坝问题的SPH方法数值模拟
Institute of Scientific and Technical Information of China (English)
汪继文; 林昊
2011-01-01
Smoothed Particle Hydrodynamics method is a meshfree, Lagrangian, particle method which develops in the past twenty years. It is to actually evaluate spatial gradients without the use of any grid and has the adaptive nature, thus it doesn' t suffer from the problems associated with mesh tangling and distortion. Therefore it has been extensively applied to various areas. Applies the SPH method to the shallow-water equation ,and then simulates obstacles,floating objects in dam-break problem through using the method of combining virtual particles. And through the numerical experiment proves the feasibility of this method in simulation of complex fluid motion. It laid the foundation for the further development and wider application of SPH method.%光滑粒子流体动力学(Smoothed Particle Hydrodynamics,SPH)法是近二十年来发展起来的一种纯的拉格朗日无网格粒子方法.由于它计算空间导数时不需要使用网格并且具有自适应性质,从而避免了高维拉氏网格法中的网格缠结和扭曲的麻烦,被广泛地应用到了各种领域.通过介绍SPH方法并结合浅水波方程,引入处理边界问题常用的虚粒子方法.利用SPH方法结合虚粒子的方式讨论了对于溃坝问题中常见的漂浮物和障碍物的模拟,并通过数值实验的方式证明了此方法在模拟复杂流体运动上的可行性,为SPH方法的进一步发展和广泛应用奠定了基础.
Plionis, M.
2004-07-01
The recent scientific efforts in Astrophysics & Cosmology have brought a revolution to our understanding of the Cosmos. Amazing results is the outcome of amazing experiments! The huge scientific, technological & financial effort that has gone into building the 10-m class telescopes as well as many space and balloon observatories, essential to observe the multitude of cosmic phenomena in their manifestations at different wavelengths, from gamma-rays to the millimetre and the radio, has given and is still giving its fruits of knowledge. These recent scientific achievements in Observational and Theoretical Cosmology were presented in the "Multiwavelength Cosmology" conference that took place on beautiful Mykonos island in the Aegean between 17 and 20 June 2003. More than 180 Cosmologists from all over the world gathered for a four-day intense meeting in which recent results from large ground based surveys (AAT/2-df, SLOAN) and space missions (WMAP, Chandra, XMM, ISO, HST) were presented and debated, providing a huge impetus to our knowledge of the Cosmos. The future of the subject (experiments, and directions of research) was also discussed. The conference was devoted mostly on the constraints on Cosmological models and galaxy formation theories that arise from the study of the high redshift Universe, from clusters of galaxies, and their evolution, from the cosmic microwave background, the large-scale structure and star-formation history. Link: http://www.wkap.nl/prod/b/1-4020-1971-8
Complex Lagrangians and phantom cosmology
Andrianov, A A; Kamenshchik, A Yu
2006-01-01
Motivated by the generalization of quantum theory for the case of non-Hermitian Hamiltonians with PT symmetry, we show how a classical cosmological model describes a smooth transition from ordinary dark energy to the phantom one. The model is based on a classical complex Lagrangian of a scalar field. Specific symmetry properties analogous to PT in non-Hermitian quantum mechanics lead to purely real equation of motion.
Gelmini, Graciela B
1996-01-01
Talks given at the V Taller de Particulas y Campos (V-TPyC) and V Taller Latinoam. de Fenomenologia de las Interac. Fundam. (V-TLFIF), Puebla, Mexico, 10/30 - 11/3 1995. These lectures are devoted to elementary particle physicists and assume the reader has very little or no knowledge of cosmology and astrophysics. After a brief historical introduction to the development of modern cosmology and astro-particles in which the Hot Big Bang model is defined, the Robertson-Walker metric and the dynamics of the Friedmann-Robertson-Walker cosmology are discussed in section 2. In section 3 the main observational features of the Universe are reviewed, including a description of our neighbourhood, homogeneity and isotropy, the cosmic background radiation, the expansion, the age and the matter content of the Universe. A brief account of the thermal history of the Universe follows in section 4, and relic abundances are discussed in section 5. Section 6 is devoted to primordial nucleosynthesis, section 7 to structure format...
The cosmological simulation code GADGET-2
Springel, V
2005-01-01
We discuss the cosmological simulation code GADGET-2, a new massively parallel TreeSPH code, capable of following a collisionless fluid with the N-body method, and an ideal gas by means of smoothed particle hydrodynamics (SPH). Our implementation of SPH manifestly conserves energy and entropy in regions free of dissipation, while allowing for fully adaptive smoothing lengths. Gravitational forces are computed with a hierarchical multipole expansion, which can optionally be applied in the form of a TreePM algorithm, where only short-range forces are computed with the `tree'-method while long-range forces are determined with Fourier techniques. Time integration is based on a quasi-symplectic scheme where long-range and short-range forces can be integrated with different timesteps. Individual and adaptive short-range timesteps may also be employed. The domain decomposition used in the parallelisation algorithm is based on a space-filling curve, resulting in high flexibility and tree force errors that do not depe...
Energy Technology Data Exchange (ETDEWEB)
Pan, Wenxiao; Li, Dongsheng; Tartakovsky, Alexandre M.; Ahzi, Said; Khraisheh, Marwan; Khaleel, Moe
2013-09-01
We present a new smoothed particle hydrodynamics (SPH) model for friction stir welding (FSW). FSW has broad commercial application in the marine, aerospace, rail, and automotive industries. However, development of the FSW process for each new application has remained largely empirical. Few established numerical modeling techniques have been developed that can explain and predict important features of the process physics involved in FSW. This is particularly true in the areas of material flow and mixing mechanisms. In this paper, we present a novel modeling approach to simulate FSW that may have significant advantages over current finite element or finite difference based methods. Unlike traditional grid-based methods, Lagrangian particle methods such as SPH can simulate the dynamics of interfaces, large material deformations, and the material’s strain and temperature history without employing complex tracking schemes. Three-dimensional simulations of FSW on AZ31 Mg alloy are performed. The temperature history and distribution, grain size, microhardness as well as the texture evolution are presented. Numerical results are found to be in good agreement with experimental observations.
Steinhardt, Paul Joseph
1995-01-01
Observational tests during the next decade may determine if the evolution of the Universe can be understood from fundamental physical principles, or if special initial conditions, coincidences, and new, untestable physical laws must be invoked. The inflationary model of the Universe is an important example of a predictive cosmological theory based on physical principles. In this talk, we discuss the distinctive fingerprint that inflation leaves on the cosmic microwave background anisotropy. We then suggest a series of five milestone experimental tests of the microwave background which could determine the validity of the inflationary hypothesis within the next decade. The paper is a Review based on a Plenary talk given at the Snowmass Workshop on Particle Astrophysics and Cosmology, 1995 It will appear in the Proceedings edited by E. Kolb and R.Peccei. Software package for computing filter functions and band power estimates available thru world-wide-web at http://dept.physics.upenn.edu/~www/as tro-cosmo/ .
Quantum Gravity and Cosmology: an intimate interplay
Sakellariadou, Mairi
2017-08-01
I will briefly discuss three cosmological models built upon three distinct quantum gravity proposals. I will first highlight the cosmological rôle of a vector field in the framework of a string/brane cosmological model. I will then present the resolution of the big bang singularity and the occurrence of an early era of accelerated expansion of a geometric origin, in the framework of group field theory condensate cosmology. I will then summarise results from an extended gravitational model based on non-commutative spectral geometry, a model that offers a purely geometric explanation for the standard model of particle physics.
Fourtakas, G.; Rogers, B. D.
2016-06-01
A two-phase numerical model using Smoothed Particle Hydrodynamics (SPH) is applied to two-phase liquid-sediments flows. The absence of a mesh in SPH is ideal for interfacial and highly non-linear flows with changing fragmentation of the interface, mixing and resuspension. The rheology of sediment induced under rapid flows undergoes several states which are only partially described by previous research in SPH. This paper attempts to bridge the gap between the geotechnics, non-Newtonian and Newtonian flows by proposing a model that combines the yielding, shear and suspension layer which are needed to predict accurately the global erosion phenomena, from a hydrodynamics prospective. The numerical SPH scheme is based on the explicit treatment of both phases using Newtonian and the non-Newtonian Bingham-type Herschel-Bulkley-Papanastasiou constitutive model. This is supplemented by the Drucker-Prager yield criterion to predict the onset of yielding of the sediment surface and a concentration suspension model. The multi-phase model has been compared with experimental and 2-D reference numerical models for scour following a dry-bed dam break yielding satisfactory results and improvements over well-known SPH multi-phase models. With 3-D simulations requiring a large number of particles, the code is accelerated with a graphics processing unit (GPU) in the open-source DualSPHysics code. The implementation and optimisation of the code achieved a speed up of x58 over an optimised single thread serial code. A 3-D dam break over a non-cohesive erodible bed simulation with over 4 million particles yields close agreement with experimental scour and water surface profiles.
An improved SPH scheme for cosmological simulations
Beck, A. M.; Murante, G.; Arth, A.; Remus, R.-S.; Teklu, A. F.; Donnert, J. M. F.; Planelles, S.; Beck, M. C.; Förster, P.; Imgrund, M.; Dolag, K.; Borgani, S.
2016-01-01
We present an implementation of smoothed particle hydrodynamics (SPH) with improved accuracy for simulations of galaxies and the large-scale structure. In particular, we implement and test a vast majority of SPH improvement in the developer version of GADGET-3. We use the Wendland kernel functions, a particle wake-up time-step limiting mechanism and a time-dependent scheme for artificial viscosity including high-order gradient computation and shear flow limiter. Additionally, we include a novel prescription for time-dependent artificial conduction, which corrects for gravitationally induced pressure gradients and improves the SPH performance in capturing the development of gas-dynamical instabilities. We extensively test our new implementation in a wide range of hydrodynamical standard tests including weak and strong shocks as well as shear flows, turbulent spectra, gas mixing, hydrostatic equilibria and self-gravitating gas clouds. We jointly employ all modifications; however, when necessary we study the performance of individual code modules. We approximate hydrodynamical states more accurately and with significantly less noise than standard GADGET-SPH. Furthermore, the new implementation promotes the mixing of entropy between different fluid phases, also within cosmological simulations. Finally, we study the performance of the hydrodynamical solver in the context of radiative galaxy formation and non-radiative galaxy cluster formation. We find galactic discs to be colder and more extended and galaxy clusters showing entropy cores instead of steadily declining entropy profiles. In summary, we demonstrate that our improved SPH implementation overcomes most of the undesirable limitations of standard GADGET-SPH, thus becoming the core of an efficient code for large cosmological simulations.
Neves, J C S
2015-01-01
In the Nietzschean philosophy, the concept of force from physics is important to build one of its main concepts: the will to power. The concept of force, which Nietzsche found out in the Classical Mechanics, almost disappears in the physics of the XX century with the Quantum Field Theory and General Relativity. Is the Nietzschean world as contending forces, a Dionysian cosmology, possible in the current science?
Alvarez, Enrique
1985-01-01
Some cosmological consequences of the assumption that superstrings are more fundamental objects than ordinary local quantum fields are examined. We study, in particular, the dependence of both the string tension and the temperature of the primordial string soup on cosmic time. A particular scenario is proposed in which the universe undergoes a contracting ``string phase'' before the ordinary ``big bang,'' which according to this picture is nothing but the outcome of the transition from nonlocal to local fundamental physics.
Grant, E.; Murdin, P.
2000-11-01
During the early Middle Ages (ca 500 to ca 1130) scholars with an interest in cosmology had little useful and dependable literature. They relied heavily on a partial Latin translation of PLATO's Timaeus by Chalcidius (4th century AD), and on a series of encyclopedic treatises associated with the names of Pliny the Elder (ca AD 23-79), Seneca (4 BC-AD 65), Macrobius (fl 5th century AD), Martianus ...
Brax, Philippe
2016-01-01
We investigate scalar-tensor theories where matter couples to the scalar field via a kinetically dependent conformal coupling. These models can be seen as the low-energy description of invariant field theories under a global Abelian symmetry. The scalar field is then identified with the Goldstone mode of the broken symmetry. It turns out that the properties of these models are very similar to the ones of ultralocal theories where the scalar-field value is directly determined by the local matter density. This leads to a complete screening of the fifth force in the Solar System and between compact objects, through the ultralocal screening mechanism. On the other hand, the fifth force can have large effects in extended structures with large-scale density gradients, such as galactic halos. Interestingly, it can either amplify or damp Newtonian gravity, depending on the model parameters. We also study the background cosmology and the linear cosmological perturbations. The background cosmology is hardly different f...
Bojowald, Martin
The universe, ultimately, is to be described by quantum theory. Quantum aspects of all there is, including space and time, may not be significant for many purposes, but are crucial for some. And so a quantum description of cosmology is required for a complete and consistent worldview. At any rate, even if we were not directly interested in regimes where quantum cosmology plays a role, a complete physical description could not stop at a stage before the whole universe is reached. Quantum theory is essential in the microphysics of particles, atoms, molecules, solids, white dwarfs and neutron stars. Why should one expect this ladder of scales to end at a certain size? If regimes are sufficiently violent and energetic, quantum effects are non-negligible even on scales of the whole cosmos; this is realized at least once in the history of the universe: at the big bang where the classical theory of general relativity would make energy densities diverge. 1.Lachieze-Rey, M., Luminet, J.P.: Phys. Rept. 254,135 (1995), gr-qc/9605010 2.BSDeWitt1967Phys. Rev.160511131967PhRv..160.1113D0158.4650410.1103/PhysRev.160.1113DeWitt, B.S.: Phys. Rev. 160(5), 1113 (1967) 3.Wiltshire, D.L.: In: Robson B., Visvanathan N., Woolcock W.S. (eds.) Cosmology: The Physics of the Universe, pp. 473-531. World Scientific, Singapore (1996). gr-qc/0101003 4.Isham C.J.: In: DeWitt, B.S., Stora, R. (eds.) Relativity, Groups and Topology II. Lectures Given at the 1983 Les Houches Summer School on Relativity, Groups and Topology, Elsevier Science Publishing Company (1986) 5.Klauder, J.: Int. J. Mod. Phys. D 12, 1769 (2003), gr-qc/0305067 6.Klauder, J.: Int. J. Geom. Meth. Mod. Phys. 3, 81 (2006), gr-qc/0507113 7.DGiulini1995Phys. Rev. D5110563013381161995PhRvD..51.5630G10.1103/PhysRevD.51.5630Giulini, D.: Phys. Rev. D 51(10), 5630 (1995) 8.Kiefer, C., Zeh, H.D.: Phys. Rev. D 51, 4145 (1995), gr-qc/9402036 9.WFBlythCJIsham1975Phys. Rev. D117684086991975PhRvD..11..768B10.1103/PhysRevD.11.768Blyth, W
Indian Academy of Sciences (India)
Sabine Kraml
2006-10-01
There is a strong and growing interplay between particle physics and cosmology. In this talk, I discuss some aspects of this interplay concerning dark matter candidates put forth by theories beyond the standard model. In explaining the requirements for collider tests of such dark matter candidates, I focus in particular on the case of the lightest neutralino in the MSSM.
Baryogenesis and the new cosmology
Indian Academy of Sciences (India)
Mark Trodden
2004-02-01
I begin this talk with a brief review of the status of approaches to understanding the origin of the baryon asymmetry of the Universe (BAU). I then describe a recent model unifying three seemingly distinct problems facing particle cosmology: the origin of inflation, the generation of the BAU and the nature of dark energy.
Sterile neutrino constraints from cosmology
DEFF Research Database (Denmark)
Hamann, Jan; Hannestad, Steen; Raffelt, Georg G.
2012-01-01
The presence of light particles beyond the standard model's three neutrino species can profoundly impact the physics of decoupling and primordial nucleosynthesis. I review the observational signatures of extra light species, present constraints from recent data, and discuss the implications...... of possible sterile neutrinos with O(eV)-masses for cosmology....
Standard Model Background of the Cosmological Collider
Chen, Xingang; Xianyu, Zhong-Zhi
2016-01-01
The inflationary universe can be viewed as a "Cosmological Collider" with energy of Hubble scale, producing very massive particles and recording their characteristic signals in primordial non-Gaussianities. To utilize this collider to explore any new physics at very high scales, it is a prerequisite to understand the background signals from the particle physics Standard Model. In this paper we describe the Standard Model background of the Cosmological Collider.
Arkani-Hamed, Nima
2015-01-01
We study the imprint of new particles on the primordial cosmological fluctuations. New particles with masses comparable to the Hubble scale produce a distinctive signature on the non-gaussianities. This feature arises in the squeezed limit of the correlation functions of primordial fluctuations. It consists of particular power law, or oscillatory, behavior that contains information about the masses of new particles. There is an angular dependence that gives information about the spin. We also have a relative phase that crucially depends on the quantum mechanical nature of the fluctuations and can be viewed as arising from the interference between two processes. While some of these features were noted before in the context of specific inflationary scenarios, here we give a general description emphasizing the role of symmetries in determining the final result.
Cosmological Structure Formation
Primack, Joel R
2015-01-01
LCDM is remarkably successful in predicting the cosmic microwave background and large-scale structure, and LCDM parameters have been determined with only mild tensions between different types of observations. Hydrodynamical simulations starting from cosmological initial conditions are increasingly able to capture the complex interactions between dark matter and baryonic matter in galaxy formation. Simulations with relatively low resolution now succeed in describing the overall galaxy population. For example, the EAGLE simulation in volumes up to 100 cubic Mpc reproduces the observed local galaxy mass function nearly as well as semi-analytic models. It once seemed that galaxies are pretty smooth, that they generally grow in size as they evolve, and that they are a combination of disks and spheroids. But recent HST observations combined with high-resolution hydrodynamic simulations are showing that most star-forming galaxies are very clumpy; that galaxies often undergo compaction which reduces their radius and ...
Revisiting Cosmological parameter estimation
Prasad, Jayanti
2014-01-01
Constraining theoretical models with measuring the parameters of those from cosmic microwave background (CMB) anisotropy data is one of the most active areas in cosmology. WMAP, Planck and other recent experiments have shown that the six parameters standard $\\Lambda$CDM cosmological model still best fits the data. Bayesian methods based on Markov-Chain Monte Carlo (MCMC) sampling have been playing leading role in parameter estimation from CMB data. In one of the recent studies \\cite{2012PhRvD..85l3008P} we have shown that particle swarm optimization (PSO) which is a population based search procedure can also be effectively used to find the cosmological parameters which are best fit to the WMAP seven year data. In the present work we show that PSO not only can find the best-fit point, it can also sample the parameter space quite effectively, to the extent that we can use the same analysis pipeline to process PSO sampled points which is used to process the points sampled by Markov Chains, and get consistent res...
Cosmological perturbations in antigravity
Oltean, Marius; Brandenberger, Robert
2014-10-01
We compute the evolution of cosmological perturbations in a recently proposed Weyl-symmetric theory of two scalar fields with oppositely signed conformal couplings to Einstein gravity. It is motivated from the minimal conformal extension of the standard model, such that one of these scalar fields is the Higgs while the other is a new particle, the dilaton, introduced to make the Higgs mass conformally symmetric. At the background level, the theory admits novel geodesically complete cyclic cosmological solutions characterized by a brief period of repulsive gravity, or "antigravity," during each successive transition from a big crunch to a big bang. For simplicity, we consider scalar perturbations in the absence of anisotropies, with potential set to zero and without any radiation. We show that despite the necessarily wrong-signed kinetic term of the dilaton in the full action, these perturbations are neither ghostlike nor tachyonic in the limit of strongly repulsive gravity. On this basis, we argue—pending a future analysis of vector and tensor perturbations—that, with respect to perturbative stability, the cosmological solutions of this theory are viable.
Gill, S P D; Gibson, B K; Flynn, C; Ibata, R A; Lewis, G F; Gill, Stuart P.D.; Knebe, Alexander; Gibson, Brad K.; Flynn, Chris; Ibata, Rodrigo A.; Lewis, Geraint F.
2002-01-01
An adaptive multi grid approach to simulating the formation of structure from collisionless dark matter is described. MLAPM (Multi-Level Adaptive Particle Mesh) is one of the most efficient serial codes available on the cosmological 'market' today. As part of Swinburne University's role in the development of the Square Kilometer Array, we are implementing hydrodynamics, feedback, and radiative transfer within the MLAPM adaptive mesh, in order to simulate baryonic processes relevant to the interstellar and intergalactic media at high redshift. We will outline our progress to date in applying the existing MLAPM to a study of the decay of satellite galaxies within massive host potentials.
Xenakis, A M; Lind, S J; Stansby, P K; Rogers, B D
2017-03-01
Tsunamis caused by landslides may result in significant destruction of the surroundings with both societal and industrial impact. The 1958 Lituya Bay landslide and tsunami is a recent and well-documented terrestrial landslide generating a tsunami with a run-up of 524 m. Although recent computational techniques have shown good performance in the estimation of the run-up height, they fail to capture all the physical processes, in particular, the landslide-entry profile and interaction with the water. Smoothed particle hydrodynamics (SPH) is a versatile numerical technique for describing free-surface and multi-phase flows, particularly those that exhibit highly nonlinear deformation in landslide-generated tsunamis. In the current work, the novel multi-phase incompressible SPH method with shifting is applied to the Lituya Bay tsunami and landslide and is the first methodology able to reproduce realistically both the run-up and landslide-entry as documented in a benchmark experiment. The method is the first paper to develop a realistic implementation of the physics that in addition to the non-Newtonian rheology of the landslide includes turbulence in the water phase and soil saturation. Sensitivity to the experimental initial conditions is also considered. This work demonstrates the ability of the proposed method in modelling challenging environmental multi-phase, non-Newtonian and turbulent flows.
Institute of Scientific and Technical Information of China (English)
王裴; 秦承森; 张树道; 刘超
2004-01-01
光滑粒子流体动力学(Smoothed Particle Hydrodynamics)方法是一种无网格的拉氏计算方法,具有计算格式简单、易于计算大变形问题等优势.用二维SPH程序模拟了冲击加载下金属铝表面的沟槽状缺陷产生微射流的过程,得到了喷射物的总质量、最大速度和质量-速度曲线.还计算了相同深度、不同夹角的沟槽微射流,并与实验结果进行了比较.结果表明:计算得到的喷射物总质量和最大速度与实验结果符合较好,SPH方法对于估算金属表面的微射流提供了一种有效的数值模拟手段.
物体入水的光滑粒子法模拟%Simulation of Water Entry with Smoothed Particle Hydrodynamics Method
Institute of Scientific and Technical Information of China (English)
杨秀峰; 彭世镠; 刘谋斌
2011-01-01
利用LANS-α (Lagrangian-averaged Navier-Stokes-alpha)模型对传统的光滑粒子法进行改进.通过模拟半浮力和零浮力水平圆柱的入水过程,验证改进的光滑粒子法.模拟结果与实验以及其它数值模拟结果符合的很好,表明改进的光滑粒子法适用于研究物体入水问题.%A modified Smoothed Particle Hydrodynamics (SPH) in Lagrangian-averaged Navier-Stokes-alpha (LANS-α) model was developed to simulate water entry flow. Water entry of a half buoyant cylinder and a neutrally buoyant cylinder were simulated. SPH results are in good agreement with reported experiments and numerical results of others. It shows that the modified SPH method is practicable in simulation of water entry flow.
Institute of Scientific and Technical Information of China (English)
龙丽平; 张建宇; 丁桦; 费斌军
2007-01-01
从基本的无网格光滑粒子法SPH(Smoothed Particle Hydrodynamics)近似出发,修正了模拟固体力学中大变形弹塑性碰撞的SPH方法.在边界处采用修正的边界条件,弹塑性分析过程中采用增量理论计算应力,迭代过程中用守恒光滑法进行滤波修正消除拉力不稳定.对SPH方法进行了程序实现,给出了杆弹塑性碰撞的算例.计算分析表明,SPH方法节点的影响域较大、精度较相同节点间距有限元法的结果有一定差距,但是通过增加粒子数量可以提高SPH的精度,保持了其简单性和计算大变形的特性.
Xenakis, A. M.; Lind, S. J.; Stansby, P. K.; Rogers, B. D.
2017-03-01
Tsunamis caused by landslides may result in significant destruction of the surroundings with both societal and industrial impact. The 1958 Lituya Bay landslide and tsunami is a recent and well-documented terrestrial landslide generating a tsunami with a run-up of 524 m. Although recent computational techniques have shown good performance in the estimation of the run-up height, they fail to capture all the physical processes, in particular, the landslide-entry profile and interaction with the water. Smoothed particle hydrodynamics (SPH) is a versatile numerical technique for describing free-surface and multi-phase flows, particularly those that exhibit highly nonlinear deformation in landslide-generated tsunamis. In the current work, the novel multi-phase incompressible SPH method with shifting is applied to the Lituya Bay tsunami and landslide and is the first methodology able to reproduce realistically both the run-up and landslide-entry as documented in a benchmark experiment. The method is the first paper to develop a realistic implementation of the physics that in addition to the non-Newtonian rheology of the landslide includes turbulence in the water phase and soil saturation. Sensitivity to the experimental initial conditions is also considered. This work demonstrates the ability of the proposed method in modelling challenging environmental multi-phase, non-Newtonian and turbulent flows.
Madura, Thomas; Gull, Theodore R.; Clementel, Nicola; Paardekooper, Jan-Pieter; Kruip, Chael; Corcoran, Michael F.; Hamaguchi, Kenji; Teodoro, Mairan
2015-01-01
We present the first 3D prints of output from a supercomputer simulation of a complex astrophysical system, the colliding stellar winds in the massive (>120 MSun), highly eccentric (e ~ 0.9) binary Eta Carinae. Using a consumer-grade 3D printer (Makerbot Replicator 2X), we successfully printed 3D smoothed particle hydrodynamics simulations of Eta Carinae's inner (r ~110 AU) wind-wind collision interface at multiple orbital phases. These 3D prints reveal important, previously unknown 'finger-like' structures at orbital phases shortly after periastron (φ ~1.045) that protrude radially outward from the spiral wind-wind collision region. We speculate that these fingers are related to instabilities (e.g. Rayleigh-Taylor) that arise at the interface between the radiatively-cooled layer of dense post-shock primary-star wind and the hot, adiabatic post-shock companion-star wind. The success of our work and easy identification of previously unknown physical features highlight the important role 3D printing can play in the visualization and understanding of complex 3D time-dependent numerical simulations of astrophysical phenomena.
Religion, theology and cosmology
Directory of Open Access Journals (Sweden)
John T. Fitzgerald
2013-10-01
Full Text Available Cosmology is one of the predominant research areas of the contemporary world. Advances in modern cosmology have prompted renewed interest in the intersections between religion, theology and cosmology. This article, which is intended as a brief introduction to the series of studies on theological cosmology in this journal, identifies three general areas of theological interest stemming from the modern scientific study of cosmology: contemporary theology and ethics; cosmology and world religions; and ancient cosmologies. These intersections raise important questions about the relationship of religion and cosmology, which has recently been addressed by William Scott Green and is the focus of the final portion of the article.
Boeyens, Jan CA
2010-01-01
The composition of the most remote objects brought into view by the Hubble telescope can no longer be reconciled with the nucleogenesis of standard cosmology and the alternative explanation, in terms of the LAMBDA-Cold-Dark-Matter model, has no recognizable chemical basis. A more rational scheme, based on the chemistry and periodicity of atomic matter, opens up an exciting new interpretation of the cosmos in terms of projective geometry and general relativity. The response of atomic structure to environmental pressure predicts non-Doppler cosmical redshifts and equilibrium nucleogenesis by alp
Bojowald, Martin
1999-01-01
A complete model of the universe needs at least three parts: (1) a complete set of physical variables and dynamical laws for them, (2) the correct solution of the dynamical laws, and (3) the connection with conscious experience. In quantum cosmology, item (2) is the quantum state of the cosmos. Hartle and Hawking have made the `no-boundary' proposal, that the wavefunction of the universe is given by a path integral over all compact Euclidean 4-dimensional geometries and matter fields that hav...
Fabris, J C; Rodrigues, D C; Batista, C E M; Daouda, M H
2012-01-01
We review the difficulties of the generalized Chaplygin gas model to fit observational data, due to the tension between background and perturbative tests. We argue that such issues may be circumvented by means of a self-interacting scalar field representation of the model. However, this proposal seems to be successful only if the self-interacting scalar field has a non-canonical form. The latter can be implemented in Rastall's theory of gravity, which is based on a modification of the usual matter conservation law. We show that, besides its application to the generalized Chaplygin gas model, other cosmological models based on Rastall's theory have many interesting and unexpected new features.
Testing the running of the cosmological constant with Type Ia Supernovae at high z
Espana-Bonet, C; Shapiro, I L; Solà, J; Espana-Bonet, Cristina; Ruiz-Lapuente, Pilar; Shapiro, Ilya L.; Sola, Joan
2004-01-01
Within the Quantum Field Theory context the idea of a "cosmological constant" (CC) evolving with time looks quite natural as it just reflects the change of the vacuum energy with the typical energy of the universe. In the particular frame of Ref.[30], a "running CC" at low energies may arise from generic quantum effects near the Planck scale, M_P, provided there is a smooth decoupling of all massive particles below M_P. In this work we further develop the cosmological consequences of a "running CC" by addressing the accelerated evolution of the universe within that model. The rate of change of the CC stays slow, without fine-tuning, and is comparable to H^2 M_P^2. It can be described by a single parameter, \
Coasting cosmologies with time dependent cosmological constant
Pimentel, L O; Pimentel, Luis O.
1999-01-01
The effect of a time dependent cosmological constant is considered in a family of scalar tensor theories. Friedmann-Robertson-Walker cosmological models for vacumm and perfect fluid matter are found. They have a linear expansion factor, the so called coasting cosmology, the gravitational "constant" decreace inversely with time; this model satisfy the Dirac hipotesis. The cosmological "constant" decreace inversely with the square of time, therefore we can have a very small value for it at present time.
Quantum Cosmology for Tunneling Universes
Kim, Sang Pyo
2004-01-01
In a quantum cosmological model consisting of a Euclidean region and a Lorentzian region, Hartle-Hawking's no-bounary wave function, and Linde's wave function and Vilenkin's tunneling wave function are briefly described and compared with each other. We put a particular emphasis on semiclassical gravity from quantum cosmology and compare it with the conventional quantum field theory in curved spacetimes. Finally, we discuss the recent debate on catastrophic particle production in the tunneling universe between Rubakov and Vilenkin within the semiclassical gravity.
Hinterbichler, Kurt; Levy, Aaron; Matas, Andrew
2011-01-01
The symmetron is a scalar field associated with the dark sector whose coupling to matter depends on the ambient matter density. The symmetron is decoupled and screened in regions of high density, thereby satisfying local constraints from tests of gravity, but couples with gravitational strength in regions of low density, such as the cosmos. In this paper we derive the cosmological expansion history in the presence of a symmetron field, tracking the evolution through the inflationary, radiation- and matter-dominated epochs, using a combination of analytical approximations and numerical integration. For a broad range of initial conditions at the onset of inflation, the scalar field reaches its symmetry-breaking vacuum by the present epoch, as assumed in the local analysis of spherically-symmetric solutions and tests of gravity. For the simplest form of the potential, the energy scale is too small for the symmetron to act as dark energy, hence we must add a cosmological constant to drive late-time cosmic acceler...
Agarwal, Nishant; Khoury, Justin; Trodden, Mark
2009-01-01
We develop a fully covariant, well-posed 5D effective action for the 6D cascading gravity brane-world model, and use this to study cosmological solutions. We obtain this effective action through the 6D decoupling limit, in which an additional scalar degree mode, \\pi, called the brane-bending mode, determines the bulk-brane gravitational interaction. The 5D action obtained this way inherits from the sixth dimension an extra \\pi self-interaction kinetic term. We compute appropriate boundary terms, to supplement the 5D action, and hence derive fully covariant junction conditions and the 5D Einstein field equations. Using these, we derive the cosmological evolution induced on a 3-brane moving in a static bulk. We study the strong- and weak-coupling regimes analytically in this static ansatz, and perform a complete numerical analysis of our solution. Although the cascading model can generate an accelerating solution in which the \\pi field comes to dominate at late times, the presence of a critical singularity prev...
Energy Technology Data Exchange (ETDEWEB)
Chimento, L P; Forte, M [Physics Department, UBA, 1428 Buenos Aires (Argentina); Devecchi, F P; Kremer, G M; Ribas, M O; Samojeden, L L, E-mail: kremer@fisica.ufpr.br, E-mail: devecchi@fisica.ufpr.br, E-mail: chimento@df.uba.ar [Physics Department, UFPR, 81531-990 Curitiba (Brazil)
2011-07-08
In this work we review if fermionic sources could be responsible for accelerated periods during the evolution of a FRW universe. In a first attempt, besides the fermionic source, a matter constituent would answer for the decelerated periods. The coupled differential equations that emerge from the field equations are integrated numerically. The self-interaction potential of the fermionic field is considered as a function of the scalar and pseudo-scalar invariants. It is shown that the fermionic field could behave like an inflaton field in the early universe, giving place to a transition to a matter dominated (decelerated) period. In a second formulation we turn our attention to analytical results, specifically using the idea of form-invariance transformations. These transformations can be used for obtaining accelerated cosmologies starting with conventional cosmological models. Here we reconsider the scalar field case and extend the discussion to fermionic fields. Finally we investigate the role of a Dirac field in a Brans-Dicke (BD) context. The results show that this source, in combination with the BD scalar, promote a final eternal accelerated era, after a matter dominated period.
Newtonian cosmology - Problems of cosmological didactics
Energy Technology Data Exchange (ETDEWEB)
Skarzynski, E.
1983-03-01
The article presents different methods of model construction in Newtonian cosmology. Newtonian cosmology is very convenient for discussion of local problems, so the problems presented are of great didactic importance. The constant k receives a new interpretation in relativistic cosmology as the curvature of the space in consequence of the greater informational capacity of Riemann space in comparison to Euclidean space. 11 references.
Bouncing Brane Cosmologies from Warped String Compactifications
Kachru, S
2003-01-01
We study the cosmology induced on a brane probing a warped throat region in a Calabi-Yau compactification of type IIB string theory. For the case of a BPS D3-brane probing the Klebanov-Strassler warped deformed conifold, the cosmology described by a suitable brane observer is a bouncing, spatially flat Friedmann-Robertson-Walker universe with time-varying Newton's constant, which passes smoothly from a contracting to an expanding phase. In the Klebanov-Tseytlin approximation to the Klebanov-Strassler solution the cosmology would end with a big crunch singularity. In this sense, the warped deformed conifold provides a string theory resolution of a spacelike singularity in the brane cosmology. The four-dimensional effective action appropriate for a brane observer is a simple scalar-tensor theory of gravity. In this description of the physics, a bounce is possible because the relevant energy-momentum tensor can classically violate the null energy condition.
Campanelli, L
2016-01-01
In the Ratra scenario of inflationary magnetogenesis, the kinematic coupling between the photon and the inflaton undergoes a nonanalytical jump at the end of inflation. Using smooth interpolating analytical forms of the coupling function, we show that such unphysical jump does not invalidate the main prediction of the model, which still represents a viable mechanism for explaining cosmic magnetization. Nevertheless, there is a spurious result associated with the nonanaliticity of the coupling, to wit, the prediction that the spectrum of created photons has a power-law decay in the ultraviolet regime. This issue is discussed using both semiclassical approximation and smooth coupling functions.
Exotic smoothness and particle physics
Sladkowski, J
1996-01-01
Short introduction to exotic differential structures on manifolds is given. The possible physical context of this mathematical curiosity is discussed. The topic is very interesting although speculative.
Cosmological Aspects of Spontaneous Baryogenesis
De Simone, Andrea
2016-01-01
We investigate cosmological aspects of spontaneous baryogenesis driven by a scalar field, and present general constraints that are independent of the particle physics model. The relevant constraints are obtained by studying the backreaction of the produced baryons on the scalar field, the cosmological expansion history after baryogenesis, and the baryon isocurvature perturbations. We show that cosmological considerations alone provide powerful constraints, especially for the minimal scenario with a quadratic scalar potential. Intriguingly, we find that for a given inflation scale, the other parameters including the reheat temperature, decoupling temperature of the baryon violating interactions, and the mass and decay constant of the scalar are restricted to lie within ranges of at most a few orders of magnitude. We also discuss possible extensions to the minimal setup, and propose two ideas for evading constraints on isocurvature perturbations: one is to suppress the baryon isocurvature with nonquadratic scal...
Concordance cosmology without dark energy
Rácz, Gábor; Beck, Róbert; Szapudi, István; Csabai, István
2016-01-01
According to the general relativistic Birkhoff's theorem, spherically symmetric regions in an isotropic universe behave like mini-universes with their own cosmological parameters. We estimate local expansion rates for a large number of such regions, and use the volume-averaged increment of the scale parameter at each time step in an otherwise standard cosmological $N$-body simulation. The particle mass, corresponding to a coarse graining scale, is an adjustable parameter. This mean field approximation neglects tidal forces and boundary effects, but it is the first step towards a non-perturbative statistical backreaction calculation. We show that a volume-averaged simulation with the $\\Omega_m=1$ Einstein--de~Sitter setting in each region closely tracks the expansion and structure growth history of a $\\Lambda$CDM cosmology, and confirm the numerical results with analytic calculations as well. The very similar expansion history guarantees consistency with the concordance model and, due to the small but characte...
Timelike information broadcasting in cosmology
Blasco, Ana; Martin-Benito, Mercedes; Martin-Martinez, Eduardo
2015-01-01
We study the transmission of information and correlations through quantum fields in cosmological backgrounds. With this aim, we make use of quantum information tools to quantify the classical and quantum correlations induced by a quantum massless scalar field in two particle detectors, one located in the early universe (Alice's) and the other located at a later time (Bob's). In particular, we focus on two phenomena: a) the consequences on the transmission of information of the violations of the strong Huygens principle for quantum fields, and b) the analysis of the field vacuum correlations via correlation harvesting from Alice to Bob. We will study a standard cosmological model first and then assess whether these results also hold if we use other than the general relativistic dynamics. As a particular example, we will study the transmission of information through the Big Bounce, that replaces the Big Bang, in the effective dynamics of Loop Quantum Cosmology.
Holographic curvature perturbations in a cosmology with a space-like singularity
Energy Technology Data Exchange (ETDEWEB)
Ferreira, Elisa G.M. [Department of Physics, McGill University,3600 University St., Montréal, QC, H3A 2T8 (Canada); Brandenberger, Robert [Department of Physics, McGill University,3600 University St., Montréal, QC, H3A 2T8 (Canada); Institute for Theoretical Studies, ETH Zürich,Clausiusstr. 47, Zürich, CH-8092 (Switzerland)
2016-07-19
We study the evolution of cosmological perturbations in an anti-de-Sitter (AdS) bulk through a cosmological singularity by mapping the dynamics onto the boundary conformal fields theory by means of the AdS/CFT correspondence. We consider a deformed AdS space-time obtained by considering a time-dependent dilaton which induces a curvature singularity in the bulk at a time which we call t=0, and which asymptotically approaches AdS both for large positive and negative times. The boundary field theory becomes free when the bulk curvature goes to infinity. Hence, the evolution of the fluctuations is under better controle on the boundary than in the bulk. To avoid unbounded particle production across the bounce it is necessary to smooth out the curvature singularity at very high curvatures. We show how the bulk cosmological perturbations can be mapped onto boundary gauge field fluctuations. We evolve the latter and compare the spectrum of fluctuations on the infrared scales relevant for cosmological observations before and after the bounce point. We find that the index of the power spectrum of fluctuations is the same before and after the bounce.
Dye, H A
2011-01-01
We construct two knot invariants. The first knot invariant is a sum constructed using linking numbers. The second is an invariant of flat knots and is a formal sum of flat knots obtained by smoothing pairs of crossings. This invariant can be used in conjunction with other flat invariants, forming a family of invariants. Both invariants are constructed using the parity of a crossing.
A divergence-cleaning scheme for cosmological SPMHD simulations
Stasyszyn, F A; Beck, A M
2012-01-01
In magnetohydrodynamics (MHD), the magnetic field is evolved by the induction equation and coupled to the gas dynamics by the Lorentz force. We perform numerical smoothed particle magnetohydrodynamics (Spmhd) simulations and study the influence of a numerical magnetic divergence. For instabilities arising from divergence B related errors, we find the hyperbolic/parabolic cleaning scheme suggested by Dedner et al. 2002 to give good results and prevent numerical artifacts from growing. Additionally, we demonstrate that certain current Spmhd implementations of magnetic field regularizations give rise to unphysical instabilities in long-time simulations. We also find this effect when employing Euler potentials (divergenceless by definition), which are not able to follow the winding-up process of magnetic field lines properly. Furthermore, we present cosmological simulations of galaxy cluster formation at extremely high resolution including the evolution of magnetic fields. We show synthetic Faraday rotation maps ...
Moving mesh cosmology: properties of neutral hydrogen in absorption
Bird, Simeon; Sijacki, Debora; Zaldarriaga, Matias; Springel, Volker; Hernquist, Lars
2012-01-01
We examine the distribution of neutral hydrogen in cosmological simulations carried out with the new moving-mesh code AREPO and compare it with the corresponding GADGET simulations based on the smoothed particle hydrodynamics (SPH) technique. The two codes use identical gravity solvers and baryonic physics implementations, but very different methods for solving the Euler equations, allowing us to assess how numerical effects associated with the hydro-solver impact the results of simulations. Here we focus on an analysis of the neutral gas, as detected in quasar absorption lines. We find that the high column density regime probed by Damped Lyman-alpha (DLA) and Lyman Limit Systems (LLS) exhibits significant differences between the codes. GADGET produces spurious artefacts in large halos in the form of gaseous clumps, boosting the LLS cross-section. Furthermore, it forms halos with denser central baryonic cores than AREPO, which leads to a substantially greater DLA cross-section from smaller halos. AREPO thus p...
Narlikar, Jayant Vishnu
2002-01-01
The third edition of this successful textbook is fully updated and includes important recent developments in cosmology. It begins with an introduction to cosmology and general relativity, and goes on to cover the mathematical models of standard cosmology. The physical aspects of cosmology, including primordial nucleosynthesis, the astroparticle physics of inflation, and the current ideas on structure formation are discussed. Alternative models of cosmology are reviewed, including the model of Quasi-Steady State Cosmology, which has recently been proposed as an alternative to Big Bang Cosmology.
Negative Energy Cosmology and the Cosmological Constant
Prokopec, Tomislav
2011-01-01
It is well known that string theories naturally compactify on anti-de Sitter spaces, and yet cosmological observations show no evidence of a negative cosmological constant in the early Universe's evolution. In this letter we present two simple nonlocal modifications of the standard Friedmann cosmology that can lead to observationally viable cosmologies with an initial (negative) cosmological constant. The nonlocal operators we include are toy models for the quantum cosmological backreaction. In Model I an initial quasiperiodic oscillatory epoch is followed by inflation and a late time matter era, representing a dark matter candidate. The backreaction in Model II quickly compensates the negative cosmological term such that the Ricci curvature scalar rapidly approaches zero, and the Universe ends up in a late time radiation era.
Boguna, Marian; Krioukov, Dmitri
2013-01-01
Networks often represent systems that do not have a long history of studies in traditional fields of physics, albeit there are some notable exceptions such as energy landscapes and quantum gravity. Here we consider networks that naturally arise in cosmology. Nodes in these networks are stationary observers uniformly distributed in an expanding open FLRW universe with any scale factor, and two observers are connected if one can causally influence the other. We show that these networks are growing Lorentz-invariant graphs with power-law distributions of node degrees. New links in these networks not only connect new nodes to existing ones, but also appear at a certain rate between existing nodes, as they do in many complex networks.
Institute of Scientific and Technical Information of China (English)
张新民
2011-01-01
宇宙暗物质和暗能量是21世纪粒子物理和宇宙学研究中的两个重大的科学问题,文章首先简述了宇宙学研究的历史和现状以及对粒子物理学提出的新的挑战,接着较详细地介绍了暗物质、暗能量和反物质相关的科学问题以及在国际上这个研究领域近年来所取得的进展,最后展望了中国在暗物质和暗能量实验探测研究方面的前景.%Unveiling the nature of dark matter and dark energy is one of the main tasks of particle physics and cosmology in the 21st century. We first present an overview of the history and current status of research in cosmology, at the same time emphasizing the new challenges in particle physics. Then we focus on the scientific issues of dark energy,dark matter and anti-matter,and review the recent progress made in these fields. Finally, we discuss the prospects for future research on the experimental probing of dark matter and dark energy in China.
Vankov, A
1998-01-01
The suggested alternative cosmology is based on the idea of barion symmetric universe, in which our home universe is a representative of multitude of typical matter and antimatter universes. This alternative concept gives a physically reasonable explanation of all major problems of the Standard Cosmological Model. Classification Code MSC: Cosmology 524.8 Key words: standard cosmological model, alternative cosmology, barionic symmetry, typical universe, quasars, cosmic rays.
Black holes and the positive cosmological constant
Bhattacharya, Sourav
2013-01-01
We address some aspects of black hole spacetimes endowed with a positive cosmological constant, i.e. black holes located inside a cosmological event horizon. First we establish a general criterion for existence of cosmological event horizons. Using the geometrical set up built for this, we study classical black hole no hair theorems for both static and stationary axisymmetric spacetimes. We discuss cosmic Nielsen-Olesen strings as hair in Schwarzschild-de Sitter spacetime. We also give a general calculation for particle creation by a Killing horizon using complex path analysis and using this we study particle creation in Schwarzschild-de Sitter spacetime by both black hole and the cosmological event horizons.
Isotropic cosmological singularities other matter models
Tod, K P
2003-01-01
Isotropic cosmological singularities are singularities which can be removed by rescaling the metric. In some cases already studied (gr-qc/9903008, gr-qc/9903009, gr-qc/9903018) existence and uniqueness of cosmological models with data at the singularity has been established. These were cosmologies with, as source, either perfect fluids with linear equations of state or massless, collisionless particles. In this article we consider how to extend these results to a variety of other matter models. These are scalar fields, massive collisionless matter, the Yang-Mills plasma of Choquet-Bruhat, or matter satisfying the Einstein-Boltzmann equation.
Energy Technology Data Exchange (ETDEWEB)
Weinstein, M
2003-11-19
This paper discusses the problem of inflation in the context of Friedmann-Robertson-Walker Cosmology. We show how, after a simple change of variables, one can quantize the problem in a way which parallels the classical discussion. The result is that two of the Einstein equations arise as exact equations of motion; one of the usual Einstein equations (suitably quantized) survives as a constraint equation to be imposed on the space of physical states. However, the Friedmann equation, which is also a constraint equation and which is the basis of the Wheeler-DeWitt equation, acquires a welcome quantum correction that becomes significant for small scale factors. We then discuss the extension of this result to a full quantum mechanical derivation of the anisotropy ({delta}{rho}/{rho}) in the cosmic microwave background radiation and the possibility that the extra term in the Friedmann equation could have observable consequences. Finally, we suggest interesting ways in which these techniques can be generalized to cast light on the question of chaotic or eternal inflation. In particular, we suggest that one can put an experimental bound on how far away a universe with a scale factor very different from our own must be, by looking at its effects on our CMB radiation.
Aref'eva, I. Ya.; Volovich, I. V.
2011-08-01
Classical versions of the Big Bang cosmological models of the universe contain a singularity at the start of time, hence the time variable in the field equations should run over a half-line. Nonlocal string field theory equations with infinite number of derivatives are considered and an important difference between nonlocal operators on the whole real line and on a half-line is pointed out. We use the heat equation method and show that on the half-line in addition to the usual initial data a new arbitrary function (external source) occurs that we call the daemon function. The daemon function governs the evolution of the universe similar to Maxwell's demon in thermodynamics. The universe and multiverse are open systems interacting with the daemon environment. In the simplest case the nonlocal scalar field reduces to the usual local scalar field coupled with an external source which is discussed in the stochastic approach to inflation. The daemon source can help to get the chaotic inflation scenario with a small scalar field.
Tipler, Frank J.
1996-09-01
I show that if Newtonian gravity is formulated in geometrical language, then Newtonian cosmology is as rigorous as relativistic cosmology. In homogeneous and isotropic universes, the geodesic deviation equation in Newtonian cosmology is proven to be exactly the same as the geodesic deviation equation in relativistic Friedmann cosmologies. This equation can be integrated to yield a constraint equation formally identical to the Friedmann equation. However, Newtonian cosmology is more general than Friedmann cosmology: by generalizing the flat-space Newtonian gravity force law to Riemannian metrics, I show that ever-expanding and recollapsing universes are allowed in any homogeneous and isotropic spatial geometry.
Cosmology with matter diffusion
Calogero, Simone
2013-01-01
We construct a viable cosmological model based on velocity diffusion of matter particles. In order to ensure the conservation of the total energy-momentum tensor in the presence of diffusion, we include a cosmological scalar field $\\phi$ which we identify with the dark energy component of the Universe. The model is characterized by only one new degree of freedom, the diffusion parameter $\\sigma$. The standard $\\Lambda$CDM model can be recovered by setting $\\sigma=0$. If diffusion takes place ($\\sigma >0$) the dynamics of the matter and of the dark energy fields are coupled. We argue that the existence of a diffusion mechanism in the Universe can serve as a theoretical motivation for interacting models. We constrain the background dynamics of the diffusion model with Supernovae, H(z) and BAO data. We also perform a perturbative analysis of this model in order to understand structure formation in the Universe. We calculate the impact of diffusion both on the CMB spectrum, with particular attention to the integr...
Institute of Scientific and Technical Information of China (English)
周小平; 赵毅; 钱七虎
2015-01-01
The problem of rock failure is discontinuous one. The numerical results depend on meshes and computational efficiency is low when finite element method is applied to simulate the failure of rock. Standard smoothed particle hydrodynamics(SPH) method is mesh-free numerical one,which is mainly applied to model the problem of fluid. In this paper,a corrected smoothed particle hydrodynamics,in which constitutive relation of fluid is replaced by constitutive relation of elasto-brittle solid and Weibull statistical approach is used to describe the heterogeneity of the rock-like materials,is developed to simulate the failure of heterogeneous elasto-brittle rock. The corrected smoothed particle hydrodynamics overcomes the shortcomings of finite element method. The numerical results is independence of meshes and computational efficiency is high when the corrected smoothed particle hydrodynamics is applied to simulate growth and coalescence of cracks. The corrected smoothed particle hydrodynamics is helpful to understanding and predicting complex fracture processes of rock-like materials.%岩石破坏问题是非连续问题。采用传统的有限元方法模拟岩石破坏时，计算结果依赖于网格，计算效率低。光滑粒子流体动力学(SPH)法主是一种模拟流体的无网格方法。对SPH法进行改进，将SPH法中流体的本构关系修正为弹脆性固体的本构关系，采用Weibull统计方法描述岩石材料的非均匀性，使SPH法能有效地模拟各向异性弹脆性岩石的破坏。改进的SPH法克服了有限元的缺点，在模拟裂纹启裂、扩展和连接时，计算结果不依赖网格，计算效率高。通过对单轴压缩条件下岩石破坏的数值计算结果表明：改进的SPH法能有效地理解和预测岩石材料的复杂破裂过程。
Conservative smoothing versus artificial viscosity
Energy Technology Data Exchange (ETDEWEB)
Guenther, C.; Hicks, D.L. [Michigan Technological Univ., Houghton, MI (United States); Swegle, J.W. [Sandia National Labs., Albuquerque, NM (United States). Solid and Structural Mechanics Dept.
1994-08-01
This report was stimulated by some recent investigations of S.P.H. (Smoothed Particle Hydrodynamics method). Solid dynamics computations with S.P.H. show symptoms of instabilities which are not eliminated by artificial viscosities. Both analysis and experiment indicate that conservative smoothing eliminates the instabilities in S.P.H. computations which artificial viscosities cannot. Questions were raised as to whether conservative smoothing might smear solutions more than artificial viscosity. Conservative smoothing, properly used, can produce more accurate solutions than the von Neumann-Richtmyer-Landshoff artificial viscosity which has been the standard for many years. The authors illustrate this using the vNR scheme on a test problem with known exact solution involving a shock collision in an ideal gas. They show that the norms of the errors with conservative smoothing are significantly smaller than the norms of the errors with artificial viscosity.
Testing cosmology with galaxy clusters
DEFF Research Database (Denmark)
Rapetti Serra, David Angelo
2011-01-01
PASCOS 2011 will be held in Cambridge UK. The conference will be hosted by the Centre for Theoretical Cosmology (DAMTP) at the Mathematical Sciences site in the University of Cambridge. The aim of the conference is to explore and develop synergies between particle physics, string theory and cosmo......) Andrei Linde (Stanford University) Avi Loeb (Harvard University) Dieter Luest (LMU/MPI, Munich) Juan Maldacena (IAS, Princeton) Liam McAllister (Cornell University) John McGreevy (Physics, MIT)...
Molecular hydrogen regulated star formation in cosmological SPH simulations
Thompson, Robert; Jaacks, Jason; Choi, Jun-Hwan
2013-01-01
It has been shown observationally that star formation (SF) correlates tightly with the presence of molecular hydrogen (H2). Therefore it would be important to investigate its implication on galaxy formation in a cosmological context. In the present work, we track the H2 mass fraction within our cosmological smoothed particle hydrodynamics (SPH) code GADGET-3 using an equilibrium analytic model by Krumholz et al. This model allows us to regulate the star formation in our simulation by the local abundance of H2 rather than the total cold gas density, and naturally introduce the dependence of star formation on metallicity. We investigate implications of the equilibrium H2-based SF model on galaxy population properties, such as the stellar-to-halo mass ratio (SHMR), baryon fraction, cosmic star formation rate density (SFRD), galaxy specific SFR, galaxy stellar mass functions (GSMF), and Kennicutt-Schmidt (KS) relationship. The advantage of our work over the previous ones is having a large sample of simulated gala...
Developments in inflationary cosmology
Indian Academy of Sciences (India)
Arjun Berera
2009-01-01
This talk presents some recent work that has been done in inflationary cosmology. First a brief review is given of the inflation scenario and its basic models. After that, one of the main problems in developing inflationary models has been the requirement of a very flat inflation potential. In solving this problem, supersymmetry has played a major role, and the reasons will be discussed and a specific example of the SUSY hybrid model will be examined. Some problems introduced by SUSY such as the and gravitino problems will then be discussed. Then in a different direction, the quintessential inflation model will be examined as a proposal where a single scalar field plays the role of both the inflaton at early time and the dark energy field later. The final topic covered is developments in understanding dissipation and particle production processes during the inflationary phase.
Lyth, David
2016-01-01
Written by an award-winning cosmologist, this brand new textbook provides advanced undergraduate and graduate students with coverage of the very latest developments in the observational science of cosmology. The book is separated into three parts; part I covers particle physics and general relativity, part II explores an account of the known history of the universe, and part III studies inflation. Full treatment of the origin of structure, scalar fields, the cosmic microwave background and the early universe are provided. Problems are included in the book with solutions provided in a separate solutions manual. More advanced extension material is offered in the Appendix, ensuring the book is fully accessible to students with a wide variety of background experience.
The Standard Cosmological Model
Scott, D
2005-01-01
The Standard Model of Particle Physics (SMPP) is an enormously successful description of high energy physics, driving ever more precise measurements to find "physics beyond the standard model", as well as providing motivation for developing more fundamental ideas that might explain the values of its parameters. Simultaneously, a description of the entire 3-dimensional structure of the present-day Universe is being built up painstakingly. Most of the structure is stochastic in nature, being merely the result of the particular realisation of the "initial conditions" within our observable Universe patch. However, governing this structure is the Standard Model of Cosmology (SMC), which appears to require only about a dozen parameters. Cosmologists are now determining the values of these quantities with increasing precision in order to search for "physics beyond the standard model", as well as trying to develop an understanding of the more fundamental ideas which might explain the values of its parameters. Althoug...
Cosmology With Extra Dimensions
Martín, J
2005-01-01
We review several properties of models that include extra dimensions, focusing on aspects related to cosmology and particle physics phenomenology. The properties of effective four dimensional inflationary geometry are studied in two distinct frameworks: (i) in Kaluza- Klein (KK) compactifications and (ii) in braneworld scenarios. From numerical simulations we find that inflationary braneworlds are unstable if the scale of inflation is too large in comparison with the stabilization scale of the interbrane distance. The analysis of perturbations confirms the existence of a tachyon associated with the volume modulus of the extra dimensions both in braneworlds and KK compactifications. With the numerical program BRANECODE non- perturbative properties of braneworlds are studied. We fully understand the non-perturbative consequences of this instability. Generic attractors are (i) an increase of the interbrane distance and the formation of a naked singularity, (ii) the brane colli...
Splotch: Visualizing Cosmological Simulations
Dolag, K; Gheller, C; Imboden, S
2008-01-01
We present a light and fast, public available, ray-tracer {\\tt Splotch} software tool which supports the effective visualization of cosmological simulations data. We describe the algorithm it relies on, which is designed in order to deal with point-like data, optimizing the ray-tracing calculation by ordering the particles as a function of their ``depth'' defined as a function of one of the coordinates or other associated parameter. Realistic three-dimensional impressions are reached through a composition of the final color in each pixel properly calculating emission and absorption of individual volume elements. We describe several scientific as well as public applications realized with {\\tt Splotch}. We emphasize how different datasets and configurations lead to remarkable different results in terms of the images and animations. A few of these results are available online.
Nojiri, S; Oikonomou, V K
2016-01-01
We combine the unimodular gravity and mimetic gravity theories into a unified theoretical framework, which is proposed to solve the cosmological constant problem and the dark matter issue. After providing the formulation of the unimodular mimetic gravity and investigating all the new features that the vacuum unimodular gravity implies, by using the underlying reconstruction method, we realize some well known cosmological evolutions, with some of these being exotic for the ordinary Einstein-Hilbert gravity. Specifically we provide the vacuum unimodular mimetic gravity description of the de Sitter cosmology, of the perfect fluid with constant equation of state cosmology, of the Type IV singular cosmology and of the $R^2$ inflation cosmology. Moreover, we investigate how cosmologically viable cosmologies, which are compatible with the recent observational data, can be realized by the vacuum unimodular mimetic gravity. Since in some cases, the graceful exit from inflation problem might exist, we provide a qualita...
Merlin, Emiliano; Grassi, Tommaso; Piovan, Lorenzo; Chiosi, Cesare
2009-01-01
We present EvoL, the new release of the Padova N-body code for cosmological simulations of galaxy formation and evolution. In this paper, the basic Tree + SPH code is presented and analysed, together with an overview on the software architectures. EvoL is a flexible parallel Fortran95 code, specifically designed for simulations of cosmological structure formation on cluster, galactic and sub-galactic scales. EvoL is a fully Lagrangian self-adaptive code, based on the classical Oct-tree and on the Smoothed Particle Hydrodynamics algorithm. It includes special features such as adaptive softening lengths with correcting extra-terms, and modern formulations of SPH and artificial viscosity. It is designed to be run in parallel on multiple CPUs to optimize the performance and save computational time. We describe the code in detail, and present the results of a number of standard hydrodynamical tests.
Roos, Matts
2015-01-01
The Fourth Edition of Introduction to Cosmology provides a concise, authoritative study of cosmology at an introductory level. Starting from elementary principles and the early history of cosmology, the text carefully guides the student on to curved spacetimes, special and general relativity, gravitational lensing, the thermal history of the Universe, and cosmological models, including extended gravity models, black holes and Hawking's recent conjectures on the not-so-black holes.
Gasperini, Maurizio
2011-03-01
Preface; Acknowledgements; Notation, units and conventions; 1. A short review of standard and inflationary cosmology; 2. The basic string cosmology equations; 3. Conformal invariance and string effective action; 4. Duality symmetries and cosmological solutions; 5. Inflationary kinematics; 6. The string phase; 7. The cosmic background of relic gravitational waves; 8. Scalar perturbations and the anisotropy of the CMB radiation; 9. Dilaton phenomenology; 10. Elements of brane cosmology; Index.
Cosmological Structure Formation Shocks and Cosmic Rays in Hydrodynamical Simulations
Pfrommer, C.; Springel, V.; Enβlin, T. A.; Jubelgas, M.
Cosmological shock waves during structure formation not only play a decisive role for the thermalization of gas in virializing structures but also for the acceleration of relativistic cosmic rays (CRs) through diffusive shock acceleration. We discuss a novel numerical treatment of the physics of cosmic rays in combination with a formalism for identifying and measuring the shock strength on-the-fly during a smoothed particle hydrodynamics simulation. In our methodology, the non-thermal CR population is treated self-consistently in order to assess its dynamical impact on the thermal gas as well as other implications on cosmological observables. Using this formalism, we study the history of the thermalization process in high-resolution hydrodynamic simulations of the Lambda cold dark matter model. Collapsed cosmological structures are surrounded by shocks with high Mach numbers up to 1000, but they play only a minor role in the energy balance of thermalization. However, this finding has important consequences for our understanding of the spatial distribution of CRs in the large-scale structure. In high resolution simulations of galaxy clusters, we find a low contribution of the averaged CR pressure, due to the small acceleration efficiency of lower Mach numbers of flow shocks inside halos and the softer adiabatic index of CRs. These effects disfavour CRs when a composite of thermal gas and CRs is adiabatically compressed. However, within cool core regions, the CR pressure reaches equipartition with the thermal pressure leading, to a lower effective adiabatic index and thus to an enhanced compressibility of the central intracluster medium. This effect increases the central density and pressure of the cluster, and thus the resulting X-ray emission and the central Sunyaev-Zel'dovich flux decrement. The integrated Sunyaev-Zel'dovich effect, however, is only slightly changed.
The First Generation of Stars in Lambda-CDM Cosmology
Energy Technology Data Exchange (ETDEWEB)
Gao, Liang; /Durham U. /Garching, Max Planck Inst.; Abel, T.; /KIPAC, Menlo Park; Frenk, C.S.; Jenkins, A.; /Durham U.; Springel, V.; /Garching, Max Planck Inst.; Yoshida,; /Nagoya U.
2006-10-10
We have performed a large set of high-resolution cosmological simulations using smoothed particle hydrodynamics (SPH) to study the formation of the first luminous objects in the {Lambda}CDM cosmology. We follow the collapse of primordial gas clouds in eight early structures and document the scatter in the properties of the first star-forming clouds. Our first objects span formation redshifts from z {approx} 10 to z {approx} 50 and cover an order of magnitude in halo mass. We find that the physical properties of the central star-forming clouds are very similar in all of the simulated objects despite significant differences in formation redshift and environment. This suggests that the formation path of the first stars is largely independent of the collapse redshift; the physical properties of the clouds have little correlation with spin, mass, or assembly history of the host halo. The collapse of proto-stellar objects at higher redshifts progresses much more rapidly due to the higher densities, which accelerates the formation of molecular hydrogen, enhances initial cooling and shortens the dynamical timescales. The mass of the star-forming clouds cover a broad range, from a few hundred to a few thousand solar masses, and exhibit various morphologies: some have disk-like structures which are nearly rotational supported; others form flattened spheroids; still others form bars. All of them develop a single protostellar ''seed'' which does not fragment into multiple objects up to the moment that the central gas becomes optically thick to H{sub 2} cooling lines. At this time, the instantaneous mass accretion rate onto the centre varies significantly from object to object, with disk-like structures having the smallest mass accretion rates. The formation epoch and properties of the star-forming clouds are sensitive to the values of cosmological parameters.
Concordance cosmology without dark energy
Rácz, Gábor; Dobos, László; Beck, Róbert; Szapudi, István; Csabai, István
2017-07-01
According to the separate universe conjecture, spherically symmetric sub-regions in an isotropic universe behave like mini-universes with their own cosmological parameters. This is an excellent approximation in both Newtonian and general relativistic theories. We estimate local expansion rates for a large number of such regions, and use a scale parameter calculated from the volume-averaged increments of local scale parameters at each time step in an otherwise standard cosmological N-body simulation. The particle mass, corresponding to a coarse graining scale, is an adjustable parameter. This mean field approximation neglects tidal forces and boundary effects, but it is the first step towards a non-perturbative statistical estimation of the effect of non-linear evolution of structure on the expansion rate. Using our algorithm, a simulation with an initial Ωm = 1 Einstein-de Sitter setting closely tracks the expansion and structure growth history of the Λ cold dark matter (ΛCDM) cosmology. Due to small but characteristic differences, our model can be distinguished from the ΛCDM model by future precision observations. Moreover, our model can resolve the emerging tension between local Hubble constant measurements and the Planck best-fitting cosmology. Further improvements to the simulation are necessary to investigate light propagation and confirm full consistency with cosmic microwave background observations.
Energy Technology Data Exchange (ETDEWEB)
Koivisto, Tomi [Institute for Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo (Norway); Wills, Danielle [Centre for Particle Theory, Department of Mathematical Sciences, Durham University, South Road, Durham, DH1 3LE (United Kingdom); Zavala, Ivonne, E-mail: t.s.koivisto@astro.uio.no, E-mail: d.e.wills@durham.ac.uk, E-mail: e.i.zavala@rug.nl [Centre for Theoretical Physics, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands)
2014-06-01
Disformally coupled cosmologies arise from Dirac-Born-Infeld actions in Type II string theories, when matter resides on a moving hidden sector D-brane. Since such matter interacts only very weakly with the standard model particles, this scenario can provide a natural origin for the dark sector of the universe with a clear geometrical interpretation: dark energy is identified with the scalar field associated to the D-brane's position as it moves in the internal space, acting as quintessence, while dark matter is identified with the matter living on the D-brane, which can be modelled by a perfect fluid. The coupling functions are determined by the (warped) extra-dimensional geometry, and are thus constrained by the theory. The resulting cosmologies are studied using both dynamical system analysis and numerics. From the dynamical system point of view, one free parameter controls the cosmological dynamics, given by the ratio of the warp factor and the potential energy scales. The disformal coupling allows for new scaling solutions that can describe accelerating cosmologies alleviating the coincidence problem of dark energy. In addition, this scenario may ameliorate the fine-tuning problem of dark energy, whose small value may be attained dynamically, without requiring the mass of the dark energy field to be unnaturally low.
Evolution of inhomogeneities in unstable-neutrino cosmologies
Energy Technology Data Exchange (ETDEWEB)
Doroshkevich, A.G.; Klypin, A.A.; Kotok, E.V.
1986-06-01
An attempt is made to show that many of the problems associated with the standard stable-particle pancake cosmology can be resolved by modifying the cosmological model and the spectrum of primordial irregularities. Equations describing the growth of primordial perturbations in a cosmological model initially dominated by heavy unstable neutrinos are derived. The one-dimensional approximation is used to study evolution during the nonlinear growth phase. 25 references.
Indian Academy of Sciences (India)
Tarun Sandeep
2004-10-01
Cosmology is passing through a golden phase of rapid advance. The cosmology workshop at ICGC-2004 attracted a large number of research contributions to diverse topics of cosmology. I attempt to classify and summarize the research work and results of the oral and poster presentations made at the meeting.
Disney, M J
2000-01-01
It is argued that some of the recent claims for cosmology are grossly overblown. Cosmology rests on a very small database: it suffers from many fundamental difficulties as a science (if it is a science at all) whilst observations of distant phenomena are difficult to make and harder to interpret. It is suggested that cosmological inferences should be tentatively made and sceptically received.
Quantum cosmological metroland model
Energy Technology Data Exchange (ETDEWEB)
Anderson, Edward [DAMTP, Cambridge (United Kingdom); Franzen, Anne, E-mail: ea212@cam.ac.u, E-mail: a.t.franzen@uu.n [Spinoza Institute, Utrecht (Netherlands)
2010-02-21
Relational particle mechanics is useful for modelling whole-universe issues such as quantum cosmology or the problem of time in quantum gravity, including some aspects outside the reach of comparably complex mini-superspace models. In this paper, we consider the mechanics of pure shape and not scale of four particles on a line, so that the only physically significant quantities are ratios of relative separations between the constituents' physical objects. Many of our ideas and workings extend to the N-particle case. As such models' configurations resemble depictions of metro lines in public transport maps, we term them 'N-stop metrolands'. This 4-stop model's configuration space is a 2-sphere, from which our metroland mechanics interpretation is via the 'cubic' tessellation. This model yields conserved quantities which are mathematically SO(3) objects like angular momenta but are physically relative dilational momenta (i.e. coordinates dotted with momenta). We provide and interpret various exact and approximate classical and quantum solutions for 4-stop metroland; from these results one can construct expectations and spreads of shape operators that admit interpretations as relative sizes and the 'homogeneity of the model universe's contents', and also objects of significance for the problem of time in quantum gravity (e.g. in the naive Schroedinger and records theory timeless approaches).
CERN. Geneva
2015-01-01
Lecture review, question collection: accelerators, detectors, particle and heavy ion physics, cosmology / Az előadások megbeszélése, kérdések összegyűjtése: gyorsítók, detektorok, részecske- és nehézion-fizika, kozmológia
Spin precession in anisotropic cosmologies
Energy Technology Data Exchange (ETDEWEB)
Kamenshchik, A.Yu. [Universita di Bologna, Dipartimento di Fisica e Astronomia, Bologna (Italy); L. D. Landau Institute for Theoretical Physics, Moscow (Russian Federation); INFN, Bologna (Italy); Teryaev, O.V. [Joint Institute for Nuclear Research, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation); Lomonosov Moscow State University, Moscow (Russian Federation)
2016-05-15
We consider the precession of a Dirac particle spin in some anisotropic Bianchi universes. This effect is present already in the Bianchi-I universe. We discuss in some detail the geodesics and the spin precession for both the Kasner and the Heckmann-Schucking solutions. In the Bianchi-IX universe the spin precession acquires the chaotic character due to the stochasticity of the oscillatory approach to the cosmological singularity. The related helicity flip of fermions in the very early universe may produce the sterile particles contributing to dark matter. (orig.)
Classically stable non-singular cosmological bounces
Ijjas, Anna
2016-01-01
One of the fundamental questions of theoretical cosmology is whether the universe can undergo a non-singular bounce, i.e., smoothly transit from a period of contraction to a period of expansion through violation of the null energy condition (NEC) at energies well below the Planck scale and at finite values of the scale factor such that the entire evolution remains classical. A common claim has been that a non-singular bounce either leads to ghost or gradient instabilities or a cosmological singularity. In this letter, we examine cubic Galileon theories and present a procedure for explicitly constructing examples of a non-singular cosmological bounce without encountering any pathologies and maintaining a sub-luminal sound speed for co-moving curvature modes throughout the NEC violating phase. We also discuss the relation between our procedure and earlier work.
Tseytlin, Arkady A
1992-01-01
Aspects of string cosmology for critical and non-critical strings are discussed emphasizing the necessity to account for the dilaton dynamics for a proper incorporation of ``large - small" duality. This drastically modifies the intuition one has with Einstein's gravity. For example winding modes, even though contribute to energy density, oppose expansion and if not annihilated will stop the expansion. Moreover we find that the radiation dominated era of the standard cosmology emerges quite naturally in string cosmology. Our analysis of non-critical string cosmology provides a reinterpretation of the (universal cover of the) recently studied two dimensional black hole solution as a conformal realization of cosmological solutions found previously by Mueller.
Dimensionless constants, cosmology and other dark matters
Tegmark, M; Rees, M; Wilczek, F; Tegmark, Max; Aguirre, Anthony; Rees, Martin; Wilczek, Frank
2006-01-01
We identify 31 dimensionless physical constants required by particle physics and cosmology, and emphasize that both microphysical constraints and selection effects might help elucidate their origin. Axion cosmology provides an instructive example, in which these two kinds of arguments must both be taken into account, and work well together. If a Peccei-Quinn phase transition occurred before or during inflation, then the axion dark matter density will vary from place to place with a probability distribution. By calculating the net dark matter halo formation rate as a function of all four relevant cosmological parameters and assessing other constraints, we find that this probability distribution, computed at stable solar systems, is arguably peaked near the observed dark matter density. If cosmologically relevant WIMP dark matter is discovered, then one naturally expects comparable densities of WIMPs and axions, making it important to follow up with precision measurements to determine whether WIMPs account for ...
Julien Lesgourgues presents his book "Neutrino Cosmology"
2013-01-01
The role that neutrinos have played in the evolution of the Universe is the focus of one of the most fascinating research areas that has stemmed from the interplay between cosmology, astrophysics and particle physics. In this self-contained book, the authors bring together all aspects of the role of neutrinos in cosmology, spanning from leptogenesis to primordial nucleosynthesis and from their role in CMB and structure formation, to the problem of their direct detection. The book starts by guiding the reader through aspects of fundamental neutrino physics, such as the standard cosmological model and statistical mechanics in the expanding Universe, before discussing the history of neutrinos chronologically from the very early stages until today. "Neutrino Cosmology" by Julien Lesgourgues, Gianpiero Mangano, Gennaro Miele, Sergio Pastor, Cambridge University Press, 2013, ISBN 9781107013957. Monday 22 April 2013 at 4 p.m. in the Library, 52-1-052. Tea and coffee will be served...
Exact Scalar-Tensor Cosmological Solutions via Noether Symmetry
Belinchón, J A; Mak, M K
2016-01-01
In this paper, we investigate the Noether symmetries of a generalized scalar-tensor, Brans-Dicke type cosmological model, in which we consider explicit scalar field dependent couplings to the Ricci scalar, and to the scalar field kinetic energy, respectively. We also include the scalar field self-interaction potential into the gravitational action. From the condition of the vanishing of the Lie derivative of the gravitational cosmological Lagrangian with respect to a given vector field we obtain three cosmological solutions describing the time evolution of a spatially flat Friedman-Robertson-Walker Universe filled with a scalar field. The cosmological properties of the solutions are investigated in detail, and it is shown that they can describe a large variety of cosmological evolutions, including models that experience a smooth transition from a decelerating to an accelerating phase.
Tipler, Frank J.
1996-10-01
It is generally believed that it is not possible to rigorously analyze a homogeneous and isotropic cosmological model in Newtonian mechanics. I show on the contrary that if Newtonian gravity theory is rewritten in geometrical language in the manner outlined in 1923-1924 by Élie Cartan [Ann. Ecole Norm. Sup. 40, 325-412 (1923); 41, 1-25 (1924)], then Newtonian cosmology is as rigorous as Friedmann cosmology. In particular, I show that the equation of geodesic deviation in Newtonian cosmology is exactly the same as equation of geodesic deviation in the Friedmann universe, and that this equation can be integrated to yield a constraint equation formally identical to the Friedmann equation. However, Newtonian cosmology is more general than Friedmann cosmology: Ever-expanding and recollapsing universes are allowed in any noncompact homogeneous and isotropic spatial topology. I shall give a brief history of attempts to do cosmology in the framework of Newtonian mechanics.
Evolving extrinsic curvature and the cosmological constant problem
Capistrano, Abraão J. S.; Cabral, Luis A.
2016-10-01
The concept of smooth deformation of Riemannian manifolds associated with the extrinsic curvature is explained and applied to the Friedmann-Lemaître-Robertson-Walker cosmology. We show that such deformation can be derived from the Einstein-Hilbert-like dynamical principle may produce an observable effect in the sense of Noether. As a result, we show how the extrinsic curvature compensates both quantitative and qualitative differences between the cosmological constant Λ and the vacuum energy {ρ }{vac} obtaining the observed upper bound for the cosmological constant problem at electroweak scale. The topological characteristics of the extrinsic curvature are discussed showing that the produced extrinsic scalar curvature is an evolving dynamical quantity.
Statistical methods for cosmological parameter selection and estimation
Liddle, Andrew R
2009-01-01
The estimation of cosmological parameters from precision observables is an important industry with crucial ramifications for particle physics. This article discusses the statistical methods presently used in cosmological data analysis, highlighting the main assumptions and uncertainties. The topics covered are parameter estimation, model selection, multi-model inference, and experimental design, all primarily from a Bayesian perspective.
Testing CCDM Cosmology with the Radiation Temperature-Redshift Relation
Baranov, I; Lima, J A S
2016-01-01
The standard $\\Lambda$CDM model can be mimicked at the background and perturbative levels (linear and non-linear) by a class of gravitationally induced particle production cosmology dubbed CCDM cosmology. However, the radiation component in the CCDM model follows a slightly different temperature-redshift $T(z)$-law which depends on an extra parameter, $\
The Cosmological Constant Problem, an Inspiration for New Physics
Nobbenhuis, Stefanus Johannes Bernardus
2006-01-01
We have critically compared different approaches to the cosmological constant problem, which is at the edge of elementary particle physics and cosmology. This problem is deeply connected with the difficulties formulating a theory of quantum gravity. After the 1998 discovery that our universe's
Gauge Invariant Cosmological Perturbation Theory
Durrer, R
1993-01-01
After an introduction to the problem of cosmological structure formation, we develop gauge invariant cosmological perturbation theory. We derive the first order perturbation equations of Einstein's equations and energy momentum ``conservation''. Furthermore, the perturbations of Liouville's equation for collisionless particles and Boltzmann's equation for Compton scattering are worked out. We fully discuss the propagation of photons in a perturbed Friedmann universe, calculating the Sachs--Wolfe effect and light deflection. The perturbation equations are extended to accommodate also perturbations induced by seeds. With these general results we discuss some of the main aspects of the texture model for the formation of large scale structure in the Universe (galaxies, clusters, sheets, voids). In this model, perturbations in the dark matter are induced by texture seeds. The gravitational effects of a spherically symmetric collapsing texture on dark matter, baryonic matter and photons are calculated in first orde...
Stabilizing Moduli with String Cosmology
Watson, S
2005-01-01
In this talk I will discuss the role of finite temperature quantum corrections in string cosmology and show that they can lead to a stabilization mechanism for the volume moduli. I will show that from the higher dimensional perspective this results from the effect of states of enhanced symmetry on the one-loop free energy. These states lead not only to stabilization, but also suggest an alternative model for cold dark matter. At late times, when the low energy effective field theory gives the appropriate description of the dynamics, the moduli will begin to slow-roll and stabilization will generically fail. However, stabilization can be recovered by considering cosmological particle production near the points of enhanced symmetry leading to the process known as moduli trapping.
Noncommutative Fluid and Cosmological Perturbations
Das, Praloy
2016-01-01
In the present paper we have developed a Non-Commutative (NC) generalization of perfect fluid model from first principles, in a Hamiltonian framework. The noncommutativity is introduced at the Lagrangian (particle) coordinate space brackets and the induced NC fluid bracket algebra for the Eulerian (fluid) field variables is derived. Together with a Hamiltonian this NC algebra generates the generalized fluid dynamics that satisfies exact local conservation laws for mass and energy thereby maintaining mass and energy conservation. However, nontrivial NC correction terms appear in charge and energy fluxes. Other non-relativistic spacetime symmetries of the NC fluid are also discussed in detail. This constitutes the NC fluid dynamics and kinematics. In the second part we construct an extension of Friedmann-Robertson-Walker (FRW) cosmological model based on the NC fluid dynamics presented here. We outline the way in which NC effects generate cosmological perturbations bringing in anisotropy and inhomogeneity in th...
Holographic signatures of cosmological singularities.
Engelhardt, Netta; Hertog, Thomas; Horowitz, Gary T
2014-09-19
To gain insight into the quantum nature of cosmological singularities, we study anisotropic Kasner solutions in gauge-gravity duality. The dual description of the bulk evolution towards the singularity involves N=4 super Yang-Mills theory on the expanding branch of deformed de Sitter space and is well defined. We compute two-point correlators of Yang-Mills operators of large dimensions using spacelike geodesics anchored on the boundary. The correlators show a strong signature of the singularity around horizon scales and decay at large boundary separation at different rates in different directions. More generally, the boundary evolution exhibits a process of particle creation similar to that in inflation. This leads us to conjecture that information on the quantum nature of cosmological singularities is encoded in long-wavelength features of the boundary wave function.
Cosmological and supernova neutrinos
Energy Technology Data Exchange (ETDEWEB)
Kajino, T. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan Department of Astronomy, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033 (Japan); Aoki, W. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Balantekin, A. B. [Department of Physics, University of Wisconsin - Madison, Wisconsin 53706 (United States); Cheoun, M.-K. [Department of Physics, Soongsil University, Seoul 156-743 (Korea, Republic of); Hayakawa, T. [Japan Atomic Energy Agency, Shirakara-Shirane 2-4, Tokai-mura, Ibaraki 319-1195 (Japan); Hidaka, J. [National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Hirai, Y.; Shibagaki, S. [National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan and Department of Astronomy, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-0033 (Japan); Kusakabe, M. [School of Liberal Arts and Science, Korea Aerospace University, Goyang 412-791 (Korea, Republic of); Mathews, G. J. [Department of Physics, University of Notre Dame, IN 46556 (United States); Nakamura, K. [Waseda University, Ohkubo 3-4-1, Shinjuku, Tokyo 169-8555 (Japan); Pehlivan, Y. [Mimar Sinan GSÜ, Department of Physics, Şişli, İstanbul 34380 (Turkey); Suzuki, T. [Nihon University, Sakurajosui 3-25-40, Setagaya-ku, Tokyo 156-8550 (Japan)
2014-06-24
The Big Bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) anisotropies are the pillars of modern cosmology. It has recently been suggested that axion which is a dark matter candidate in the framework of the standard model could condensate in the early universe and induce photon cooling before the epoch of the photon last scattering. Although this may render a solution to the overproduction problem of primordial {sup 7}Li abundance, there arises another serious difficulty of overproducing D abundance. We propose a hybrid dark matter model with both axions and relic supersymmetric (SUSY) particles to solve both overproduction problems of the primordial D and {sup 7}Li abundances simultaneously. The BBN also serves to constrain the nature of neutrinos. Considering non-thermal photons produced in the decay of the heavy sterile neutrinos due to the magnetic moment, we explore the cosmological constraint on the strength of neutrino magnetic moment consistent with the observed light element abundances. Core-collapse supernovae eject huge flux of energetic neutrinos which affect explosive nucleosynthesis of rare isotopes like {sup 7}Li, {sup 11}B, {sup 92}Nb, {sup 138}La and {sup 180}Ta and r-process elements. Several isotopes depend strongly on the neutrino flavor oscillation due to the Mikheyev-Smirnov-Wolfenstein (MSW) effect. Combining the recent experimental constraints on θ{sub 13} with predicted and observed supernova-produced abundance ratio {sup 11}B/{sup 7}Li encapsulated in the presolar grains from the Murchison meteorite, we show a marginal preference for an inverted neutrino mass hierarchy. We also discuss supernova relic neutrinos (SRN) that may indicate the softness of the equation of state (EoS) of nuclear matter and adiabatic conditions of the neutrino oscillation.
Cosmological consequences of an adiabatic matter creation process
Nunes, Rafael C
2016-01-01
In this paper we investigate the cosmological consequences of a continuous matter creation associated with the production of particles by the gravitational field acting on the quantum vacuum. To illustrate this, three phenomenological models are considered. An equivalent scalar field description is presented for each models. The effects on the cosmic microwave background power spectrum are analyzed for the first time in the context of adiabatic matter creation cosmology. Further, we introduce a model independent treatment, $Om$, which depends only on the Hubble expansion rate and the cosmological redshift to distinguish any cosmological model from $\\Lambda$CDM by providing a null test for the cosmological constant, meaning that, for any two redshifts $z_1$, $z_2$, $Om (z)$ is same, i.e. $Om (z_1)- Om (z_2)= 0$. Also, this diagnostic can differentiate between several cosmological models by indicating their quintessential/ phantom behavior without knowing the accurate value of the matter density, and the presen...