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Toward the Jamming Threshold of Sphere Packings: Tunneled Crystals  [PDF]
S. Torquato,F. H. Stillinger
Physics , 2007, DOI: 10.1063/1.2802184
Abstract: We have discovered a new family of three-dimensional crystal sphere packings that are strictly jammed (i.e., mechanically stable) and yet possess an anomalously low density. This family constitutes an uncountably infinite number of crystal packings that are subpackings of the densest crystal packings and are characterized by a high concentration of self-avoiding "tunnels" (chains of vacancies) that permeate the structures. The fundamental geometric characteristics of these tunneled crystals command interest in their own right and are described here in some detail. These include the lattice vectors (that specify the packing configurations), coordination structure, Voronoi cells, and density fluctuations. The tunneled crystals are not only candidate structures for achieving the jamming threshold (lowest-density rigid packing), but may have substantially broader significance for condensed matter physics and materials science.
Toward a microscopic description of reactions involving exotic nuclei  [PDF]
P. Descouvemont,M. S. Hussein
Physics , 2013, DOI: 10.1103/PhysRevLett.111.082701
Abstract: We propose an extension of the Continuum Discretized Coupled Channels (CDCC) method, where the projectile is described by a microscopic cluster model. This microscopic generalization (MCDCC) only relies on nucleon-target interactions, and therefore presents an important predictive power. Core excitations can be included without any further parameter. As an example we investigate the $\lipb$ elastic scattering at $E_{lab}=27$ and 35 MeV. The $^7$Li nucleus is known to present an $\alpha+t$ cluster structure, and is well described by the Resonating Group Method. An excellent agreement is obtained for the $\lipb$ elastic cross sections, provided that breakup channels are properly included. We also present an application to inelastic scattering, and discuss future applications of the MCDCC.
Microscopic description of $η$-photoproduction on light nuclei  [PDF]
V. B. Belyaev,N. V. Shevchenko,S. A. Rakityansky,W. Sandhas,S. Sofianos
Physics , 2001, DOI: 10.1063/1.1436669
Abstract: A microscopic four-body description of near-threshold coherent photoproduction of the $\eta$ meson on the (3N)-nuclei is given. The photoproduction cross-section is calculated using the Finite Rank Approximation (FRA) of the nuclear Hamiltonian. The results indicate that the final state interaction of the $\eta$ meson with the residual nucleus plays an important role in the photoproduction process. Sensitivity of the results to the choice of the $\eta N$ T-matrix is investigated. The importance of obeying the condition of $\eta N$ unitarity is demonstrated.
Microscopic theory of the jamming transition of harmonic spheres  [PDF]
Ludovic Berthier,Hugo Jacquin,Francesco Zamponi
Physics , 2011, DOI: 10.1103/PhysRevE.84.051103
Abstract: We develop a microscopic theory to analyze the phase behaviour and compute correlation functions of dense assemblies of soft repulsive particles both at finite temperature, as in colloidal materials, and at vanishing temperature, a situation relevant for granular materials and emulsions. We use a mean-field statistical mechanical approach which combines elements of liquid state theory to replica calculations to obtain quantitative predictions for the location of phase boundaries, macroscopic thermodynamic properties and microstructure of the system. We focus in particular on the derivation of scaling properties emerging in the vicinity of the jamming transition occurring at large density and zero temperature. The new predictions we obtain for pair correlation functions near contact are tested using computer simulations. Our work also clarifies the conceptual nature of the jamming transition, and its relation to the phenomenon of the glass transition observed in atomic liquids.
A microscopic mean-field theory of the jamming transition  [PDF]
Hugo Jacquin,Ludovic Berthier,Francesco Zamponi
Physics , 2010, DOI: 10.1103/PhysRevLett.106.135702
Abstract: Dense particle packings acquire rigidity through a nonequilibrium jamming transition commonly observed in materials from emulsions to sandpiles. We describe athermal packings and their observed geometric phase transitions using fully equilibrium statistical mechanics and develop a microscopic many-body mean-field theory of the jamming transition for soft repulsive spherical particles. We derive analytically some of the scaling laws and exponents characterizing the transition and obtain predictions for microscopic correlation functions of jammed states that are amenable to experimental verifications, and whose accuracy we confirm using computer simulations.
Microscopic Description of Induced Fission  [PDF]
N. Schunck
Physics , 2013, DOI: 10.1088/1742-6596/436/1/012058
Abstract: Selected aspects of the description of neutron-induced fission in 240Pu in the framework of the nuclear energy density functional theory at finite temperature are presented. In particular, we discuss aspects pertaining to the choice of thermodynamic state variables, the evolution of fission barriers as function of the incident neutron energy, and the temperatures of the fission fragments.
Macroscopic and Microscopic Description of Black Diholes  [PDF]
Roberto Emparan,Edward Teo
Physics , 2001, DOI: 10.1016/S0550-3213(01)00319-4
Abstract: We study configurations consisting of a pair of non-extremal black holes in four dimensions, both with the same mass, and with charges of the same magnitude but opposite sign---diholes, for short. We present such exact solutions for Einstein-Maxwell theory with arbitrary dilaton coupling, and also solutions to the U(1)^4 theories that arise from compactified string/M-theory. Despite the fact that the solutions are very complicated, physical properties of these black holes, such as their area, charge, and interaction energy, admit simple expressions. We also succeed in providing a microscopic description of the entropy of these black holes using the `effective string' model, and taking into account the interaction between the effective string and anti-string.
Microscopic description of the beta delayed deuteron emission from \bbox{^6}He  [PDF]
Attila Csoto,Daniel Baye
Physics , 1993, DOI: 10.1103/PhysRevC.49.818
Abstract: The beta delayed deuteron emission from $^6$He is studied in a dynamical microscopic cluster model. This model gives a reasonably good description for all the subsystems of $^6$He and $^6$Li in a coherent way, without any free parameter. The beta decay transition probability to the $^6$Li ground state is underestimated by a few percents. The theoretical beta delayed deuteron spectrum is close to experiment but it is also underestimated by about a factor 1.7. We argue that, in spite of their different magnitudes, both underestimations might have a common origin. The model confirms that the neutron halo part of the $^6$He wave function plays a crucial role in quenching the beta decay toward the $\alpha$ + d channel.
Can the jamming transition be described using equilibrium statistical mechanics?  [PDF]
Ludovic Berthier,Hugo Jacquin,Francesco Zamponi
Statistics , 2010, DOI: 10.1088/1742-5468/2011/01/P01004
Abstract: When materials such as foams or emulsions are compressed, they display solid behaviour above the so-called `jamming' transition. Because compression is done out-of-equilibrium in the absence of thermal fluctuations, jamming appears as a new kind of a nonequilibrium phase transition. In this proceeding paper, we suggest that tools from equilibrium statistical mechanics can in fact be used to describe many specific features of the jamming transition. Our strategy is to introduce thermal fluctuations and use statistical mechanics to describe the complex phase behaviour of systems of soft repulsive particles, before sending temperature to zero at the end of the calculation. We show that currently available implementations of standard tools such as integral equations, mode-coupling theory, or replica calculations all break down at low temperature and large density, but we suggest that new analytical schemes can be developed to provide a fully microscopic, quantitative description of the jamming transition.
Toward understanding the microscopic origin of nuclear clustering  [PDF]
J. Oko?owicz,W. Nazarewicz,M. P?oszajczak
Physics , 2012, DOI: 10.1002/prop.201200127
Abstract: Open Quantum System (OQS) description of a many-body system involves interaction of Shell Model (SM) states through the particle continuum. In realistic nuclear applications, this interaction may lead to collective phenomena in the ensemble of SM states. We claim that the nuclear clustering is an emergent, near-threshold phenomenon, which cannot be elucidated within the Closed Quantum System (CQS) framework. We approach this problem by investigating the near-threshold behavior of Exceptional Points (EPs) in the realistic Continuum Shell Model (CSM). The consequences for the alpha-clustering phenomenon are discussed.
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