9,068 research outputs found
Black Holes in Six-dimensional Conformal Gravity
We study conformally-invariant theories of gravity in six dimensions. In four
dimensions, there is a unique such theory that is polynomial in the curvature
and its derivatives, namely Weyl-squared, and furthermore all solutions of
Einstein gravity are also solutions of the conformal theory. By contrast, in
six dimensions there are three independent conformally-invariant polynomial
terms one could consider. There is a unique linear combination (up to overall
scale) for which Einstein metrics are also solutions, and this specific theory
forms the focus of our attention in this paper. We reduce the equations of
motion for the most general spherically-symmetric black hole to a single
5th-order differential equation. We obtain the general solution in the form of
an infinite series, characterised by 5 independent parameters, and we show how
a finite 3-parameter truncation reduces to the already known Schwarzschild-AdS
metric and its conformal scaling. We derive general results for the
thermodynamics and the first law for the full 5-parameter solutions. We also
investigate solutions in extended theories coupled to conformally-invariant
matter, and in addition we derive some general results for conserved charges in
cubic-curvature theories in arbitrary dimensions.Comment: 28 pages. References adde
An Deformation of Gauged STU Supergravity
Four-dimensional gauged STU supergravity is a consistent
truncation of the standard gauged supergravity in which
just the four gauge fields in the Cartan subgroup of are
retained. One of these is the graviphoton in the supergravity
multiplet and the other three lie in three vector multiplets. In this paper we
carry out the analogous consistent truncation of the newly-discovered family of
-deformed gauged supergravities, thereby obtaining
a family of -deformed STU gauged supergravities. Unlike in some other
truncations of the deformed supergravity that have been
considered, here the scalar potential of the deformed STU theory is independent
of the parameter. However, it enters in the scalar couplings in the
gauge-field kinetic terms, and it is non-trivial because of the minimal
couplings of the fermion fields to the gauge potentials. We discuss the
supersymmetry transformation rules in the -deformed supergravities, and
present some examples of black hole solutions.Comment: 31 pages. Derivation of the range of \omega corrected; discussion of
supersymmetry of solutions extended, and a reference adde
AdS Dyonic Black Hole and its Thermodynamics
We obtain spherically-symmetric and -symmetric dyonic black holes that
are asymptotic to anti-de Sitter space-time (AdS), which are solutions in
maximal gauged four-dimensional supergravity, with just one of the U(1) fields
carrying both the electric and magnetic charges . We study the
thermodynamics, and find that the usually-expected first law does not hold
unless P=0, Q=0 or P=Q. For general values of the charges, we find that the
first law requires a modification with a new pair of thermodynamic conjugate
variables. We show that they describe the scalar hair that breaks some of the
asymptotic AdS symmetries.Comment: 21 pages, typos corrected, discussion of Euclidean action adde
AIDing Contraception: HIV and Recent Trends in Abortion Rates
Since the onset of HIV/AIDS awareness in the early 1980s, much attention has centered around the substantial negative effects of the disease throughout the world. This paper provides evidence of a secondary effect the disease has had on sexual behavior in the United States. Using a difference-in-differences estimation framework and state level data, we show that the perceived threat of HIV resulted in a drop in unwanted pregnancies, as demonstrated by a lower incidence of abortions. Our results suggest that each additional reported case of HIV per 1,000 individuals resulted in 85.5 fewer abortions per 1,000 live births.
How Tsinghua Became a World Class Research University: A Case Study on the Impact of Rankings on a Chinese Higher Education Institution
Today’s global knowledge economy has highlighted the need for the comparison of higher education quality. This need has been largely met by international university rankings. Although it is widely recognized that no one ranking system is completely objective, higher education stakeholders across the world still take rankings’ results seriously. Rankings, thereby, exert a great deal of influence on higher education institutions. Ranking affects higher education through various approaches. In a variety of practical manifestations, the idea of building a “world-class” university has been widely adopted by national governments that urgently want to improve competitiveness in the globalized knowledge economy. Chinese universities (in this thesis, China, or Chinese, refers to mainland China) have been steadily climbing up international rankings over the last decade. The extraordinary achievement has its roots in the initiative of establishing “world-class” universities. This study explored the actual course of events through which a Chinese university raises its statures in global rankings. By using an exploratory case study research design, the study attempted to answer the question about how a Chinese university became a world-class research university according to the global ranking systems. The findings revealed that an antiquated university has the potential to update to a high-quality modern research institution within a short period of time if talents, resources, and governance mechanism are adequately aligned
Development of engineering design tools to help reduce apple bruising
A large percentage of apples are wasted each year due to damage such as bruising. The apple journey from orchard to supermarket is very complex and apples are subjected to a variety of static and dynamic loads that could result in this damage occurring. The main aim of this work was to carry out numerical modelling to develop a design tool that can be used to optimise the design of harvesting and sorting equipment and packaging media to reduce the likelihood of apple bruise formation resulting from impact loads. An experimental study, along with analytical calculations, varying apple drop heights and counterface material properties, were used to provide data to validate the numerical modelling. Good correlation was seen between the models and experiments and this approach combined with previous work on static modelling should provide a comprehensive design tool for reducing the likelihood of apple bruising occurring
Theoretical and experimental design of an alternative system to 2 x 2 MIMO for LTE over 60 km directly modulated RoF link
Relay nodes (RN) are used as an important structure to extend the coverage of the Third Generation Partnership Program’s Long Term Evolution (3GPP-LTE). The promising technology as the interface between eNodeB (eNB) and RN is radio-over-fibre (RoF), due to its longer span transmission capability. In this paper, we propose an alternative technique to 2×2 multiple-input and multiple-output (MIMO) in LTE structure for transmission over 60 km directly modulated RoF link by introducing frequency division multiplexing (FDM) for orthogonal FDM (OFDM). The system is demonstrated theoretically and experimentally. In the baseband, quadrature phase shift keying (QPSK), 16-quadrature amplitude modulation (QAM) and 64-QAM are considered as the single carrier modulations (SCM) according to the LTE standard. The system degradation pattern is identical between the theoretical and experimental system, thus proving the accuracy of the theoretical system design. The real time QPSK, 16-QAM and 64-QAM system achieved an average EVM of 5.84%, 5.90% and 5.97%, respectively for 2 GHz and 2.6 GHz bands. These resultant EVMs are below the 8% 3GPP-LTE EVM requirement
Choices, Expectations, and Experiences of UB International Students
This study examines the choices, expectations, and experiences of the international students who currently study at the University of Bridgeport. The paper can serve as the background for future research and may provide some references to improve internationalization at the University of Bridgeport. The research also intends to examine the role of policies and regional socio-economy in international student mobility from the perspective of UB and to have an in-depth understanding on the sheer trend of international students mobility
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