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Topics in dual models and extended solutions. [Bethe-Salpeter equation]

Description: Two main topics are explored. The first deals with the infinities arising from the one loop planar string diagram of the standard dual model. It is shown that for the number of dimensions d = 25 or 26, these infinities lead to a renormalization of the slope of the Regge trajectories, in addition to a renormalization of the coupling constant. The second topic deals with the propagator for a confined particle (monopole) in a field theory. When summed to all orders, this propagator is altogether free of singularities in the finite momentum plane, and an attempt is made to illustrate this. One examines the Bethe-Salpeter equation and shows that ladder diagrams are not sufficient to obtain this result. However, in a nonrelativistic approximation confinement is obtained and all poles disappear.
Date: June 1, 1977
Creator: Roth, R. S.
Partner: UNT Libraries Government Documents Department

Ab Initio Study of 40Ca with an Importance Truncated No-Core Shell Model

Description: We propose an importance truncation scheme for the no-core shell model, which enables converged calculations for nuclei well beyond the p-shell. It is based on an a priori measure for the importance of individual basis states constructed by means of many-body perturbation theory. Only the physically relevant states of the no-core model space are considered, which leads to a dramatic reduction of the basis dimension. We analyze the validity and efficiency of this truncation scheme using different realistic nucleon-nucleon interactions and compare to conventional no-core shell model calculations for {sup 4}He and {sup 16}O. Then, we present the first converged calculations for the ground state of {sup 40}Ca within no-core model spaces including up to 16{h_bar}{Omega}-excitations using realistic low-momentum interactions. The scheme is universal and can be easily applied to other quantum many-body problems.
Date: May 22, 2007
Creator: Roth, R & Navratil, P
Partner: UNT Libraries Government Documents Department

Reply to Comment on "Ab Initio Study of 40Ca with an Importance Truncated No-Core Shell Model"

Description: In their comment on our recent Letter [1] Dean et al. [2] criticize the calculations for the ground-state energy of {sup 40}Ca within the importance truncated no-core shell model (NCSM). In particular they address the role of configurations beyond the 3p3h level, which have not been included in the {sup 40}Ca calculations for large N{sub max} {h_bar}{Omega} model spaces. Before responding to this point, the following general statements are in order. For the atomic nucleus as a self-bound system, translational invariance is an important symmetry. The only possibility to preserve translational invariance when working with a Slater determinant basis is to use the harmonic oscillator (HO) basis in conjunction with a basis truncation according to the total HO excitation energy, i.e. N{sub max} {h_bar}{Omega}, as done in the ab initio NCSM. This is important not only for obtaining proper binding or excitation energies, but also for a correct extraction of physical wavefunctions. The spurious center-of-mass components can be exactly removed only if the HO basis and the N{sub max} {h_bar}{Omega} truncation are employed. The minimal violation of the translational invariance was one of the main motivations for developing the importance-truncation scheme introduced in the Letter. In this scheme, we start with the complete N{sub max} {h_bar}{Omega} HO basis space and select important configurations via perturbation theory. All symmetries are under control and our importance-truncated NCSM calculations are completely variational and provide an upper bound of the ground-state energy of the system. The restriction to the 3p3h level, made for computational reasons in the N{sub max} > 8 calculations for {sup 40}Ca, is not inherent to the importance truncation scheme. The explicit inclusion of 4p4h configurations--though computationally more demanding--is straight-forward, even for the largest N{sub max} {h_bar}{Omega} model spaces discussed. To demonstrate this fact we have performed full 4p4h calculations for ...
Date: January 4, 2008
Creator: Roth, R & Navratil, P
Partner: UNT Libraries Government Documents Department

From Nucleons To Nuclei To Fusion Reactions

Description: Nuclei are prototypes of many-body open quantum systems. Complex aggregates of protons and neutrons that interact through forces arising from quantum chromo-dynamics, nuclei exhibit both bound and unbound states, which can be strongly coupled. In this respect, one of the major challenges for computational nuclear physics, is to provide a unified description of structural and reaction properties of nuclei that is based on the fundamental underlying physics: the constituent nucleons and the realistic interactions among them. This requires a combination of innovative theoretical approaches and high-performance computing. In this contribution, we present one of such promising techniques, the ab initio no-core shell model/resonating-group method, and discuss applications to light nuclei scattering and fusion reactions that power stars and Earth-base fusion facilities.
Date: February 15, 2012
Creator: Quaglioni, S; Navratil, P; Roth, R & Horiuchi, W
Partner: UNT Libraries Government Documents Department

Ab Initio Calculations Of Light-Ion Reactions

Description: The exact treatment of nuclei starting from the constituent nucleons and the fundamental interactions among them has been a long-standing goal in nuclear physics. In addition to the complex nature of nuclear forces, one faces the quantum-mechanical many-nucleon problem governed by an interplay between bound and continuum states. In recent years, significant progress has been made in ab initio nuclear structure and reaction calculations based on input from QCD employing Hamiltonians constructed within chiral effective field theory. In this contribution, we present one of such promising techniques capable of describing simultaneously both bound and scattering states in light nuclei. By combining the resonating-group method (RGM) with the ab initio no-core shell model (NCSM), we complement a microscopic cluster approach with the use of realistic interactions and a microscopic and consistent description of the clusters. We discuss applications to light nuclei scattering, radiative capture and fusion reactions.
Date: March 12, 2012
Creator: Navratil, P; Quaglioni, S; Roth, R & Horiuchi, W
Partner: UNT Libraries Government Documents Department

Protection against UVA-induced photooxidative damage in mammalian cell lines expressing increased levels of metallothionein

Description: Metallothionein (MT) is an endogenous low molecular weight protein that is inducible in a variety of eukaryotic cells and has the ability to selectivity bind heavy metal ions such as zinc and the cadmium. Although the exact physiological role of MT is still not understood, there is strong evidence that MT is involved in providing cellular resistance against the damaging effects of heavy metals and in the regulation of intracellular zinc and copper. Recently, it has been demonstrated that MT can scavenge radiation-induced reactive oxygen intermediates in vitro, specifically hydroxyl and superoxide radicals, and because of these observations it has been suggested that MT may provide protection against radiation-induced oxidative stress in vivo. Cell lines expressing increased levels of MT have demonstrated resistance to ionizing radiation, to ultraviolet radiation, and also to various DNA damaging agents including melphalan and cis-diaminedichloroplatinum. It is therefore important to gain some insight into the relationship between cellular MT content and cellular resistance to radiation and other DNA damaging agents. In this study we investigated the role of MT in providing protection against monochromatic 365-nm UVA radiation, which is known to generate intracellular reactive oxygen species that are involved in both DNA damage and cell killing. For this purpose, we used zinc acetate, a potent inducer of MT, to elevate MT levels in V79 Chinese hamster fibroblasts prior to UVA exposure and determined cell survival for uninduced and induced cultures. In order to eliminate any zinc effects other than MT induction, we also isolated and characterized cadmium chloride-resistant clones of V79 cells that have increased steady-state levels of both MT mRNA and protein, and we examined their survival characteristics against 365-nm radiation in the absence of zinc acetate. 14 refs., 3 figs.
Date: January 1, 1990
Creator: Dudek, E.J. (Argonne National Lab., IL (USA) Illinois Inst. of Tech., Chicago, IL (USA). Dept. of Biology); Peak, J.G.; Peak, M.J. (Argonne National Lab., IL (USA)) & Roth, R.M. (Illinois Inst. of Tech., Chicago, IL (USA). Dept. of Biology)
Partner: UNT Libraries Government Documents Department

Industrial Development of Cornell Superconducting Cavities for CEBAF

Description: Properties of the Cornell five-cell superconducting accelerating cavity and the suitability of this cavity for the CEBAF linac are discussed.The advanced technology required to produce these cavities was already known to some companies and is being transferred to others.The status of development of these cavities by industry, including test results on three of these cavities is discussed.
Date: January 1, 1986
Creator: Palussek, A.; Heidt, Albert; Chargin, Anthony; Matheissen, Axel; Moss, Barry; Reece, Charles et al.
Partner: UNT Libraries Government Documents Department