Diquark interaction and gaps for color superconductivity

Using flow equations, we derive an effective quark-quark interaction and obtain the coupled set of gap equations for the condensates of the CFL phase of massless $N_f=3$ dense QCD. The formalism developed here enables one to consider more general case of nonzero $s$-quark mass.Comment: 3 pages, Lattice2002(nonzerot), talk presented at 20th International Symposium on Lattice Field Theory (LATTICE2002), Boston, Massachusetts, 24-29 June 200

Answer Sets for Logic Programs with Arbitrary Abstract Constraint Atoms

In this paper, we present two alternative approaches to defining answer sets for logic programs with arbitrary types of abstract constraint atoms (c-atoms). These approaches generalize the fixpoint-based and the level mapping based answer set semantics of normal logic programs to the case of logic programs with arbitrary types of c-atoms. The results are four different answer set definitions which are equivalent when applied to normal logic programs. The standard fixpoint-based semantics of logic programs is generalized in two directions, called answer set by reduct and answer set by complement. These definitions, which differ from each other in the treatment of negation-as-failure (naf) atoms, make use of an immediate consequence operator to perform answer set checking, whose definition relies on the notion of conditional satisfaction of c-atoms w.r.t. a pair of interpretations. The other two definitions, called strongly and weakly well-supported models, are generalizations of the notion of well-supported models of normal logic programs to the case of programs with c-atoms. As for the case of fixpoint-based semantics, the difference between these two definitions is rooted in the treatment of naf atoms. We prove that answer sets by reduct (resp. by complement) are equivalent to weakly (resp. strongly) well-supported models of a program, thus generalizing the theorem on the correspondence between stable models and well-supported models of a normal logic program to the class of programs with c-atoms. We show that the newly defined semantics coincide with previously introduced semantics for logic programs with monotone c-atoms, and they extend the original answer set semantics of normal logic programs. We also study some properties of answer sets of programs with c-atoms, and relate our definitions to several semantics for logic programs with aggregates presented in the literature

The mean-square dichotomy spectrum and a bifurcation to a mean-square attractor

The dichotomy spectrum is introduced for linear mean-square random dynamical systems, and it is shown that for finite-dimensional mean-field stochastic differential equations, the dichotomy spectrum consists of finitely many compact intervals. It is then demonstrated that a change in the sign of the dichotomy spectrum is associated with a bifurcation from a trivial to a non-trivial mean-square random attractor

Drastic Reduction of Shot Noise in Semiconductor Superlattices

We have found experimentally that the shot noise of the tunneling current $I$ through an undoped semiconductor superlattice is reduced with respect to the Poissonian noise value $2eI$, and that the noise approaches 1/3 of that value in superlattices whose quantum wells are strongly coupled. On the other hand, when the coupling is weak or when a strong electric field is applied to the superlattice the noise becomes Poissonian. Although our results are qualitatively consistent with existing theories for one-dimensional mulitple barriers, the theories cannot account for the dependence of the noise on superlattice parameters that we have observed.Comment: 4 Pages, 3Figure

Kinetics of the photosubstitution of cis-bis(benzonitrile)dichloroplatinum(II) in chloroform

Under 254 nm irradiation cis-[Pt(C6H5CN)2Cl2] is converted to H2PtCl6. Absorption of light by both the metal complex and the solvent contribute to the first step of this process, suggested to form HPt(C6H5CN) Cl3. A linear dependence of the reaction rate on light intensity appears to rule out chlorination by trichloromethyl radicals. However, at higher light intensities a higher order dependence on intensity develops, and under 313 nm irradiation is dominant, and a reaction between trichloromethyl radical and the excited state complex is proposed to account for this

On finite-density QCD at large Nc

Deryagin, Grigoriev, and Rubakov (DGR) have shown that in finite-density QCD at infinite Nc the Fermi surface is unstable with respect to the formation of chiral waves with wavenumber twice the Fermi momentum, while the BCS instability is suppressed. We show here that at large, but finite Nc, the DGR instability only occurs in a finite window of chemical potentials from above Lambda_QCD to mu_critical = exp(gamma ln^2 Nc + O(ln Nc ln ln Nc))Lambda_QCD, where gamma = 0.02173. Our analysis shows that, at least in the perturbative regime, the instability occurs only at extremely large Nc, Nc > 1000 Nf, where Nf is the number of flavors. We conclude that the DGR instability is not likely to occur in QCD with three colors, where the ground state is expected to be a color superconductor. We speculate on possible structure of the ground state of finite-density QCD with very large Nc.Comment: 13 pages, 5 figures, 3 figures drawn using PicTe

A kinetic study of the photolysis of tris(2,4-pentanedionato)cobalt(III) and bis(2,4-pentanedionato)cobalt(II) in chloroform

Under 254nm irradiation in chloroform, Co(acac)3 (Hacac = 2,4-pentanedione) is converted to Co(acac)2 and then to CoCl2. The metal complex is the primary photoactive species in the photoreduction of Co(acac)3, but the photosubstitution of Co(acac)2 appears to occur primarily through absorption of light by the solvent, followed by a chain reaction in which chlorine atoms displace pentanedionyl radicals. The photosubstitution rate law is complex, and the apparent quantum yield (based on total light absorbed) varies with incident light intensity and Co(acac)2 concentration, reaching values as high as 16 under the conditions of this study. Referred only to the light absorbed by CHCL3, the highest quantum yield measured was 150. An observed partial inverse dependence of the photosubstitution rate on the initial concentration of Co(acac)2 is explained in terms of a mechanism in which the pentanedione product competes with Co(acac)2 for an intermediate

An Analysis of the Search Spaces for Generate and Validate Patch Generation Systems

We present the first systematic analysis of the characteristics of patch search spaces for automatic patch generation systems. We analyze the search spaces of two current state-of-the-art systems, SPR and Prophet, with 16 different search space configurations. Our results are derived from an analysis of 1104 different search spaces and 768 patch generation executions. Together these experiments consumed over 9000 hours of CPU time on Amazon EC2. The analysis shows that 1) correct patches are sparse in the search spaces (typically at most one correct patch per search space per defect), 2) incorrect patches that nevertheless pass all of the test cases in the validation test suite are typically orders of magnitude more abundant, and 3) leveraging information other than the test suite is therefore critical for enabling the system to successfully isolate correct patches. We also characterize a key tradeoff in the structure of the search spaces. Larger and richer search spaces that contain correct patches for more defects can actually cause systems to find fewer, not more, correct patches. We identify two reasons for this phenomenon: 1) increased validation times because of the presence of more candidate patches and 2) more incorrect patches that pass the test suite and block the discovery of correct patches. These fundamental properties, which are all characterized for the first time in this paper, help explain why past systems often fail to generate correct patches and help identify challenges, opportunities, and productive future directions for the field

Logic Programming for Finding Models in the Logics of Knowledge and its Applications: A Case Study

The logics of knowledge are modal logics that have been shown to be effective in representing and reasoning about knowledge in multi-agent domains. Relatively few computational frameworks for dealing with computation of models and useful transformations in logics of knowledge (e.g., to support multi-agent planning with knowledge actions and degrees of visibility) have been proposed. This paper explores the use of logic programming (LP) to encode interesting forms of logics of knowledge and compute Kripke models. The LP modeling is expanded with useful operators on Kripke structures, to support multi-agent planning in the presence of both world-altering and knowledge actions. This results in the first ever implementation of a planner for this type of complex multi-agent domains.Comment: 16 pages, 1 figure, International Conference on Logic Programming 201

Traversable wormhole in the deformed Ho\v{r}ava-Lifshitz gravity

Asymptotically flat wormhole solutions are found in the deformed Ho\v{r}ava-Lifshitz gravity. It turns out that higher curvature terms can not play the role of exotic matters which are crucial to form a traversable wormhole, and external exotic sources are still needed. In particular, the exotic matter behaves like phantom energy if Kehagias-Sfetsos vacuum is considered outside the wormhole. Interestingly, the spherically symmetric setting makes the matter and the higher curvature contribution satisfy four-dimensional conservation of energy in the covariant form.Comment: 13 pages, 2 figures, version published in Phys. Rev.