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Search Results: 1 - 10 of 1336 matches for " Nikolaos Prezas "
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BMN Operators for N=1 Superconformal Yang-Mills Theories and Associated String Backgrounds
Vasilis Niarchos,Nikolaos Prezas
Physics , 2002, DOI: 10.1088/1126-6708/2003/06/015
Abstract: We study a class of near-BPS operators for a complex 2-parameter family of N=1 superconformal Yang-Mills theories that can be obtained by a Leigh-Strassler deformation of N=4 SYM theory. We identify these operators in the large N and large R-charge limit and compute their exact scaling dimensions using N=1 superspace methods. From these scaling dimensions we attempt to reverse-engineer the light-cone worldsheet theory that describes string propagation on the Penrose limit of the dual geometry.
Boundary Superstring Field Theory
Vasilis Niarchos,Nikolaos Prezas
Physics , 2001, DOI: 10.1016/S0550-3213(01)00498-9
Abstract: Using the Batalin-Vilkovisky formalism we provide a detailed analysis of the NS sector of boundary superstring field theory. We construct explicitly the relevant BV structure and derive the master action. Furthermore, we show that this action is exactly equal to the superdisk worldsheet partition function as was recently conjectured.
The Partition Function of the Two-Dimensional Black Hole Conformal Field Theory
Amihay Hanany,Nikolaos Prezas,Jan Troost
Physics , 2002, DOI: 10.1088/1126-6708/2002/04/014
Abstract: We compute the partition function of the conformal field theory on the two-dimensional euclidean black hole background using path-integral techniques. We show that the resulting spectrum is consistent with the algebraic expectations for the SL(2,R)/U(1) coset conformal field theory construction. In particular, we find confirmation for the bound on the spin of the discrete representations and we determine the density of the continuous representations. We point out the relevance of the partition function to all string theory backgrounds that include an SL(2,R)/U(1) coset factor.
Discrete Torsion, Covering Groups and Quiver Diagrams
Bo Feng,Amihay Hanany,Yang-Hui He,Nikolaos Prezas
Physics , 2000, DOI: 10.1088/1126-6708/2001/04/037
Abstract: Without recourse to the sophisticated machinery of twisted group algebras, projective character tables and explicit values of 2-cocycles, we here present a simple algorithm to study the gauge theory data of D-brane probes on a generic orbifold G with discrete torsion turned on. We show in particular that the gauge theory can be obtained with the knowledge of no more than the ordinary character tables of G and its covering group G*. Subsequently we present the quiver diagrams of certain illustrative examples of SU(3)-orbifolds which have non-trivial Schur Multipliers. The paper serves as a companion to our earlier work (arXiv:hep-th/0010023) and aims to initiate a systematic and computationally convenient study of discrete torsion.
Discrete Torsion, Non-Abelian Orbifolds and the Schur Multiplier
Bo Feng,Amihay Hanany,Yang-Hui He,Nikolaos Prezas
Physics , 2000, DOI: 10.1088/1126-6708/2001/01/033
Abstract: Armed with the explicit computation of Schur Multipliers, we offer a classification of SU(n) orbifolds for n = 2,3,4 which permit the turning on of discrete torsion. This is in response to the host of activity lately in vogue on the application of discrete torsion to D-brane orbifold theories. As a by-product, we find a hitherto unknown class of N = 1 orbifolds with non-cyclic discrete torsion group. Furthermore, we supplement the status quo ante by investigating a first example of a non-Abelian orbifold admitting discrete torsion, namely the ordinary dihedral group as a subgroup of SU(3). A comparison of the quiver theory thereof with that of its covering group, the binary dihedral group, without discrete torsion, is also performed.
Stepwise Projection: Toward Brane Setups for Generic Orbifold Singularities
Bo Feng,Amihay Hanany,Yang-Hui He,Nikolaos Prezas
Physics , 2000, DOI: 10.1088/1126-6708/2002/01/040
Abstract: The construction of brane setups for the exceptional series E6,E7,E8 of SU(2) orbifolds remains an ever-haunting conundrum. Motivated by techniques in some works by Muto on non-Abelian SU(3) orbifolds, we here provide an algorithmic outlook, a method which we call stepwise projection, that may shed some light on this puzzle. We exemplify this method, consisting of transformation rules for obtaining complex quivers and brane setups from more elementary ones, to the cases of the D-series and E6 finite subgroups of SU(2). Furthermore, we demonstrate the generality of the stepwise procedure by appealing to Frobenius' theory of Induced Representations. Our algorithm suggests the existence of generalisations of the orientifold plane in string theory.
A Computational Comparison of Basis Updating Schemes for the Simplex Algorithm on a CPU-GPU System  [PDF]
Nikolaos Ploskas, Nikolaos Samaras
American Journal of Operations Research (AJOR) , 2013, DOI: 10.4236/ajor.2013.36048

The computation of the basis inverse is the most time-consuming step in simplex type algorithms. This inverse does not have to be computed from scratch at any iteration, but updating schemes can be applied to accelerate this calculation. In this paper, we perform a computational comparison in which the basis inverse is computed with five different updating schemes. Then, we propose a parallel implementation of two updating schemes on a CPU-GPU System using MATLAB and CUDA environment. Finally, a computational study on randomly generated full dense linear programs is preented to establish the practical value of GPU-based implementation.

Letter to the Editor: Postoperative Rhinorrhea without Intraoperative Cerebrospinal Fluid Leak after Endoscopic Transnasal Transphenoidal Surgery for Pituitary Macroadenomas  [PDF]
Nikolaos Gkekas, Panagiotis Primikiris, Nikolaos Georgakoulias
Open Journal of Modern Neurosurgery (OJMN) , 2014, DOI: 10.4236/ojmn.2014.41008
Abstract: Postoperative Rhinorrhea without Intraoperative Cerebrospinal Fluid Leak after Endoscopic Transnasal Transphenoidal Surgery for Pituitary Macroadenomas
Depicting Determinants and Effects of Intimacy and Verbal Aggressiveness Target through Social Network Analysis  [PDF]
Nikolaos Hasanagas, Alexandra Bekiari
Sociology Mind (SM) , 2015, DOI: 10.4236/sm.2015.53015
Abstract: Aim of this research is to suggest determinants and effects of intimacy (including also its extreme forms such erotic relation or life-partnership), measured in term of its effect, attraction, as well as to analyze relations between attraction and verbal aggressiveness. Complete social network analysis has been conducted in a class of students of Physical Education Department, University of Thessaly (N = 53). The data were collected with standardized questionnaires. Network analysis software (Visone) as well as cross-sectional analysis (SPSS) has been implemented. The results are: Attractiveness is gender-specific, as it is connected with male students. Younger students tend to be more attractive in physical appearance and dressing. The mother’s pedagogic influence becomes evident on the attractiveness of someone for life-partnership. The academic conformity is not conducive to the development of pleasant discussions. Spending money for entertainment and impressing try to outweigh attractive physical appearance. Being aware of preference for durable erotic relation strengthens self-confidence. A companionship seems to be of socio-intellectual or of emotional-sexual nature. Attractiveness seems to lead to verbal aggression. It seems also to reduce the tendency to escape to imaginary sceneries. Physical dimension appears to be stronger than mental parameters for maintaining a durable erotic relation. The desire for life-partnership without children appears to be favored by mental elements. Verbal-aggressors search for targets without meticulously examining weaknesses and strengths on each person. Distinct types of attractiveness are also detected, corresponding to the following patterns: general sociability (“friend”) which is also connected with mild (narcissistic) exploitation, erotic relation (“erotic”) which is an autonomous value system based on superficial criteria related to appearance, focusing on communication (“distant communicable”), being an idol (“fully narcissistically exploitable”) without any reality basis, and life-long occupation of a person (“life-long exploitable”).
Suggesting Indicators of Superficiality and Purity in Verbal Aggressiveness: An Application in Adult Education Class Networks of Prison Inmates  [PDF]
Alexandra Bekiari, Nikolaos Hasanagas
Open Journal of Social Sciences (JSS) , 2016, DOI: 10.4236/jss.2016.43035
Abstract: Aim of this research is to suggest indicators, based on social network analysis, that distinguish superficial, idiosyncratic and strategic verbal aggressiveness. Two classes of an adult education school (at secondary level) in a prison have been selected as network samples (A class = 23 and B class = 12 prisoners). Complete network analysis has been applied, using standardized questionnaires. The network variables have further processed through Pearson correlation. Indicators of superficial and pure roles, particularly incremental and proportional behavior, have been applied in two forms of verbal aggressiveness (criticism and threatening). The superficial behavior (SB: outdegree of verbal aggressiveness) seems to be a quite sensitive indicator, as it presents correlations with various other relational forms of familiarity, aggressiveness and appreciation/socialization. The incremental behavior (IB: difference of received from outgoing actions) is also a sensitive indicator, revealing, however, different results. Pure aggressiveness (in terms of difference) seems to be related with quite different causes and/or occasions than the superficial aggressiveness. Incremental behavior is likely to be at first place driven by the idiosyncrasy rather than by exogenous factors and seems to constitute a completely different notion than the SB. The proportional behavior (PB: ration of outgoing to the received actions) of aggression is a quite insensitive indicator, as it depends only on a few behavioral variables. It seems to reveal a rational strategy of adaptability. Thus, it characteristically differs from the indicators of superficiality (expressing reciprocity patterns) and of the incremental aggressiveness (expressing individualism).
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