243 research outputs found
Scaling Cosmologies from Duality Twisted Compactifications
Oscillating moduli fields can support a cosmological scaling solution in the
presence of a perfect fluid when the scalar field potential satisfies
appropriate conditions. We examine when such conditions arise in
higher-dimensional, non-linear sigma-models that are reduced to four dimensions
under a generalized Scherk-Schwarz compactification. We show explicitly that
scaling behaviour is possible when the higher-dimensional action exhibits a
global SL(n,R) or O(2,2) symmetry. These underlying symmetries can be exploited
to generate non-trivial scaling solutions when the moduli fields have
non-canonical kinetic energy. We also consider the compactification of
eleven-dimensional vacuum Einstein gravity on an elliptic twisted torus.Comment: 21 pages, 3 figure
Beta, Dipole and Noncommutative Deformations of M-theory Backgrounds with One or More Parameters
We construct new M-theory solutions starting from those that contain 5 U(1)
isometries. We do this by reducing along one of the 5-torus directions, then
T-dualizing via the action of an O(4,4) matrix and lifting back to
11-dimensions. The particular T-duality transformation is a sequence of O(2,2)
transformations embedded in O(4,4), where the action of each O(2,2) gives a
Lunin-Maldacena deformation in 10-dimensions. We find general formulas for the
metric and 4-form field of single and multiparameter deformed solutions, when
the 4-form of the initial 11-dimensional background has at most one leg along
the 5-torus. All the deformation terms in the new solutions are given in terms
of subdeterminants of a 5x5 matrix, which represents the metric on the 5-torus.
We apply these results to several M-theory backgrounds of the type AdS_r x
X^{11-r}. By appropriate choices of the T-duality and reduction directions we
obtain analogues of beta, dipole and noncommutative deformations. We also
provide formulas for backgrounds with only 3 or 4 U(1) isometries and study a
case, for which our assumption for the 4-form field is violated.Comment: v2:minor corrections, v3:small improvements, v4:conclusions expanded,
to appear in Class. Quant. Gra
RESTful API Testing Methodologies: Rationale, Challenges, and Solution Directions
Service-oriented architecture has evolved to be the backbone for large-scale integration between different applications and platforms. This concept has led to today's reality of cloud services. Many of the major business platforms are providing their services to end-users and other companies as well. Companies are crafting ways to allow other businesses fast service integration and to get on board quickly in the market. REST (representational state transfer) has emerged as the standard protocol for implementing and consuming these services, which are called RESTful application programming interfaces (APIs). As the internal details of the RESTful APIs are not completely available during consumption, thorough testing has been a major challenge. Any unprecedented change in the APIs can cause the major failure of service operations, which can cause an organization to face both financial and trust losses. Research efforts have been made to alleviate testing challenges by introducing different frameworks and auto-generating unit test approaches. However, there is still a lack of an overview of the state-of-the-art in RESTful API testing. As such, the objective of this article is to identify, analyze, and synthesize the studies that have been performed related to RESTful APIs' testing methodologies and unit test generation. With this perspective, a systematic literature review (SLR) study was conducted. In total, 16 papers were retrieved and included based on study selection criteria for in-depth analysis. This SLR discusses and categorizes different problems and solutions related to RESTful APIs' testing and unit test generation. 2022 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This research was partially funded by the Norwegian University of Science and Technology, Norway for the support of Open Access fund.Scopus2-s2.0-8512988348
Software defect prediction: do different classifiers find the same defects?
Open Access: This article is distributed under the terms of the Creative Commons Attribution 4.0 International License CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.During the last 10 years, hundreds of different defect prediction models have been published. The performance of the classifiers used in these models is reported to be similar with models rarely performing above the predictive performance ceiling of about 80% recall. We investigate the individual defects that four classifiers predict and analyse the level of prediction uncertainty produced by these classifiers. We perform a sensitivity analysis to compare the performance of Random Forest, Naïve Bayes, RPart and SVM classifiers when predicting defects in NASA, open source and commercial datasets. The defect predictions that each classifier makes is captured in a confusion matrix and the prediction uncertainty of each classifier is compared. Despite similar predictive performance values for these four classifiers, each detects different sets of defects. Some classifiers are more consistent in predicting defects than others. Our results confirm that a unique subset of defects can be detected by specific classifiers. However, while some classifiers are consistent in the predictions they make, other classifiers vary in their predictions. Given our results, we conclude that classifier ensembles with decision-making strategies not based on majority voting are likely to perform best in defect prediction.Peer reviewedFinal Published versio
Strings on the deformed T^{1,1}: giant magnon and single spike solutions
In this paper we find giant magnon and single spike string solutions in a
sector of the gamma-deformed conifold. We examine the dispersion relations and
find a behavior analogous to the undeformed case. The transcendental functional
relations between the conserved charges are shifted by certain gamma-dependent
term. The latter is proportional to the total momentum and thus qualitatively
different from known cases.Comment: 35 pages, no figure
Compactifications with S-Duality Twists
We consider generalised Scherk Schwarz reductions of supergravity and
superstring theories with twists by electromagnetic dualities that are
symmetries of the equations of motion but not of the action, such as the
S-duality of D=4, N=4 super-Yang-Mills coupled to supergravity. The reduction
cannot be done on the action itself, but must be done either on the field
equations or on a duality invariant form of the action, such as one in the
doubled formalism in which potentials are introduced for both electric and
magnetic fields. The resulting theory in odd-dimensions has massive form fields
satisfying a self-duality condition . We construct such theories
in D=3,5,7.Comment: Latex, 26 pages. References adde
A Massive S-duality in 4 dimensions
We reduce the Type IIA supergravity theory with a generalized Scherk-Schwarz
ansatz that exploits the scaling symmetry of the dilaton, the metric and the NS
2-form field. The resulting theory is a new massive, gauged supergravity theory
in four dimensions with a massive 2-form field and a massive 1-form field. We
show that this theory is S-dual to a theory with a massive vector field and a
massive 2-form field, which are dual to the massive 2-form and 1-form fields in
the original theory, respectively. The S-dual theory is shown to arise from a
Scherk-Schwarz reduction of the heterotic theory. Hence we establish a massive,
S-duality type relation between the IIA theory and the heterotic theory in four
dimensions. We also show that the Lagrangian for the new four dimensional
theory can be put in the most general form of a D=4, N=4 gauged Lagrangian
found by Schon and Weidner, in which (part of) the SL(2) group has been gauged.Comment: 20 pages, references adde
Lectures on Nongeometric Flux Compactifications
These notes present a pedagogical review of nongeometric flux
compactifications. We begin by reviewing well-known geometric flux
compactifications in Type II string theory, and argue that one must include
nongeometric "fluxes" in order to have a superpotential which is invariant
under T-duality. Additionally, we discuss some elementary aspects of the
worldsheet description of nongeometric backgrounds. This review is based on
lectures given at the 2007 RTN Winter School at CERN.Comment: 31 pages, JHEP
Semi-classical Strings in Sasaki-Einstein Manifolds
We find point-like and classical string solutions on the AdS_5 x X^5, where
X^5 are the 5-dimensional Sasaki-Einstein manifolds Ypq and Lpqr. The number of
acceptable solutions is limited drastically in order to satisfy the constraints
on the parameters and coordinates of the manifolds. The energy of the solutions
depends on the parameters of the Sasaki-Einstein manifolds and on the conserved
momenta transcendentally. A discussion on BPS solutions is presented as well.Comment: 34 pages, 9 figure
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