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Notes on DBranes
"... This is an introduction to the properties of Dbranes, topological defects in string theory on which string endpoints can live. Dbranes provide a simple description of various nonperturbative objects required by string duality, and give new insight into the quantum mechanics of black holes and the ..."
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This is an introduction to the properties of Dbranes, topological defects in string theory on which string endpoints can live. Dbranes provide a simple description of various nonperturbative objects required by string duality, and give new insight into the quantum mechanics of black holes and the nature of spacetime at the shortest distances. The first two thirds of these lectures closely follow the earlier ITP lectures hepth/9602052, written with S. Chaudhuri and C. Johnson. The final third includes more extensive applications to string duality. Dbranes are extended objects, topological defects in a sense, defined by the property that strings can end on them. They were discovered by studying the R → 0 limit of open string theory, where the different behaviors of open and closed strings led to a seeming paradox. 1 From the study of this limit one can argue that the usual Type I, Type IIA and Type IIB string theories are different states in a single theory, which also contains states with arbitrary configurations of Dbranes. Moreover this argument is purely perturbative, in that it does not require any strongcoupling continuation or use of the BPS
Algorithmic Aspects of Symbolic Switch Network Analysis
 IEEE Trans. CAD/IC
, 1987
"... A network of switches controlled by Boolean variables can be represented as a system of Boolean equations. The solution of this system gives a symbolic description of the conducting paths in the network. Gaussian elimination provides an efficient technique for solving sparse systems of Boolean eq ..."
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A network of switches controlled by Boolean variables can be represented as a system of Boolean equations. The solution of this system gives a symbolic description of the conducting paths in the network. Gaussian elimination provides an efficient technique for solving sparse systems of Boolean equations. For the class of networks that arise when analyzing digital metaloxide semiconductor (MOS) circuits, a simple pivot selection rule guarantees that most s switch networks encountered in practice can be solved with O(s) operations. When represented by a directed acyclic graph, the set of Boolean formulas generated by the analysis has total size bounded by the number of operations required by the Gaussian elimination. This paper presents the mathematical basis for systems of Boolean equations, their solution by Gaussian elimination, and data structures and algorithms for representing and manipulating Boolean formulas.
Exact Solutions of FourDimensional Black Holes in String Theory
"... We construct an exact conformal field theory as an SL(2, R) × SU(2)/U(1) 2 gauged WZW model, which describes a black hole in four dimensions. Another exact solution, describing a black membrane in four dimensions (in the sense that the event horizon is an infinite plane) is found as an SL(2, R)×U(1 ..."
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We construct an exact conformal field theory as an SL(2, R) × SU(2)/U(1) 2 gauged WZW model, which describes a black hole in four dimensions. Another exact solution, describing a black membrane in four dimensions (in the sense that the event horizon is an infinite plane) is found as an SL(2, R)×U(1) 2 /U(1) gauged WZW model. Both the black hole and the black membrane carry axionic charge. Finally, we construct an exact solution of a 4D black hole with electromagnetic field, as an SL(2, R) × SU(2) × U(1)/U(1) 2 gauged WZW model. This black hole carries both electric and axionic charges. String theory is the first consistent quantum theory that accomodates gravity. However, it is not clear wheather it could be established as the quantum theory of gravity. As a theory of gravity we would expect that string theory would exhibit features
TIDAL FORCES IN COLD BLACK HOLE SPACETIMES
"... We investigate here the behavior of a few spherically symmetric static acclaimed black hole solutions in respect of tidal forces in the geodesic frame. It turns out that the forces diverge on the horizon of cold black holes (CBH) while for ordinary ones, they do not. It is pointed out that Kruskall ..."
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We investigate here the behavior of a few spherically symmetric static acclaimed black hole solutions in respect of tidal forces in the geodesic frame. It turns out that the forces diverge on the horizon of cold black holes (CBH) while for ordinary ones, they do not. It is pointed out that Kruskallike extensions do not render the CBH metrics nonsingular. We present a CBH that is available in the BransDicke theory for which the tidal forces do not diverge on the horizon and in that sense it is a better one. 1.
Proposal to Jefferson Lab PAC 29 A CLEAN MEASUREMENT OF THE NEUTRON SKIN OF 208 Pb THROUGH PARITY VIOLATING ELECTRON SCATTERING Spokesmen:
"... The difference between the neutron radius Rn of a heavy nucleus and the proton radius Rp is believed to be several percent. This neutron skin has proven to be elusive to pin down experimentally in a rigorous fashion. The proposed Lead Radius Experiment PREX will measure the parityviolating electrow ..."
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The difference between the neutron radius Rn of a heavy nucleus and the proton radius Rp is believed to be several percent. This neutron skin has proven to be elusive to pin down experimentally in a rigorous fashion. The proposed Lead Radius Experiment PREX will measure the parityviolating electroweak asymmetry in the elastic scattering of polarized electrons from 208 Pb at an energy of 850 MeV and a scattering angle of 6. Since the Z0 boson couples mainly to neutrons, this asymmetry provides a clean measurement of Rn with a projected experimental precision of ±1 %. In addition to being a fundamental test of nuclear theory, a precise measurement of Rn pins down the density dependence of the symmetry energy of neutron rich nuclear matter which has impacts on neutron star structure, heavy ion collisions, and atomic parity violation experiments. 3 Proposal Update: 208
Axial quasinormal modes of neutron stars: Accounting for the superfluid in the crust
, 2009
"... We present the results of the first study of global oscillations of relativistic stars with both elastic crusts and interpenetrating superfluid components. For simplicity, we focus on the axial quasinormal modes. Our results demonstrate that the torsional crust modes are essentially unaffected by t ..."
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We present the results of the first study of global oscillations of relativistic stars with both elastic crusts and interpenetrating superfluid components. For simplicity, we focus on the axial quasinormal modes. Our results demonstrate that the torsional crust modes are essentially unaffected by the coupling to the gravitational field. This is as expected since these oscillations are known to be weak gravitationalwave sources. In contrast, the presence of a loosely coupled superfluid neutron component in the crust can have a significant effect on the oscillation spectrum. We show that the entrainment between the superfluid and the crust nuclei is a key parameter in the problem. Our analysis highlights the need for a more detailed understanding of the coupled crustsuperfluid at the microphysical level. Our numerical results have, even though we have not considered magnetised stars, some relevance for efforts to carry out seismology based on quasiperiodic oscillations observed in the tails of magnetar flares. In particular, we argue that the sensitive dependence on the entrainment may have to be accounted for in attempts to match theoretical models to observational data.
PREX Recent Results and Future Prospects
"... electroweak asymmetry in the elastic scattering of polarized electrons from ..."
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electroweak asymmetry in the elastic scattering of polarized electrons from
WAVES OF MIGRATION
"... The Cuban exodus is now over 41 years old and has brought close to a million Cuban immigrants to American soil — about 12 percent of the Cuban population. That exodus harbors distinct waves of immigrants, alike only in their final rejection of Cuba. The focus of this paper is on the exodus of Cubans ..."
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The Cuban exodus is now over 41 years old and has brought close to a million Cuban immigrants to American soil — about 12 percent of the Cuban population. That exodus harbors distinct waves of immigrants, alike only in their final rejection of Cuba. The focus of this paper is on the exodus of Cubans in the nineties during what Castro himself called “el período especial ” — the special period that resulted when the collapse of communism in the Soviet Union and Eastern Europe meant the end of the Soviet subsidy that Cuba had received for nearly 30 years. This research is part of a larger research project on the Cuban exodus and the Cuban revolution that began on the heels of the revolutionary transformation of Cuban society in 1959 and that, while intermittent, has never ceased and is ongoing still in the present. The goal of my research is to capture the processes of political disaffection of participants in this major historical drama, emphasizing the contrasts along the four major waves of the exodus not only in their social characteristics but also in their attitudes as members of different political generations. To establish the characteristics of this last wave, however, I often need to contrast it to earlier waves. Hence, I will first briefly depict the differences between the 4 major waves of the exodus. Each of the 4 major waves of the Cuban exodus has been characterized by a very different social composition with respect to their social class, race, education, gender and family composition, and values — differences that resulted from the changing phases of the Cuban revolution. They render the Cuban community in the U.S. today an extremely heterogeneous one, not only in terms of the dramatic contrasts in their social characteristics but also in terms of their processes of political disaffection as what E. F. Kunz (1973) called “vintages ” — “refugee groups that are distinct in character, background, and avowed political faith ” (p. 137).