Size effect of Ruderman-Kittel-Kasuya-Yosida interaction mediated by electrons in nanoribbons

We calculated the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the magnetic impurities mediated by electrons in nanoribbons. It was shown that the RKKY interaction is strongly dependent on the width of the nanoribbon and the transverse positions of the impurities. The transverse confinement of electrons is responsible for the above size effect of the RKKY interaction. It provides a potential way to control the RKKY interaction by changing nanostructure geometry

P−v{\cal P}-v Criticality in Gauged Supergravities

AdS black holes show richer transition behaviors in extended phase space by assuming the cosmological constant and its conjugate quantity to behave like thermodynamic pressure and thermodynamic volume. We study the extended thermodynamics of charged dilatonic AdS black holes in a class of Einstein-Maxwell-dilaton theories that can be embedded in gauged supergravities in various dimensions. We find that the transition behaviors of higher dimensional dilatonic AdS black holes are different from the four dimensional counterparts, and new transition behaviors emerges in higher dimensions. First, there exists standard Van der Waals transition only in a five dimensional dilatonic AdS black hole with two equal charges. Second, there emerge a new phase transition branch in negative pressure region in six and seven dimensional dilatonic black holes with two equal charges. Third, there emerge transition behaviors in higher dimensional black hole with single charge cases, which are absent in four dimensions.Comment: Latex, 18 pages, 8 figures; published versio

The Contribution of Celebrity Endorsement to University student’s buying behavior in developing countries: A case study of Zimbabwean university students.

This study focused on evaluating the contribution of celebrity endorsement to University student’s buying behaviour in developing countries and this was achieved through the phenomenological philosophy and a case study design. The sample was made up of 100 respondents. Questionnaires and focus group discussions were used to collect data from the respondents. The results obtained from the study show that celebrity endorsement has a positive influence on university student’s buying behaviour. Results from the study also show that celebrities hold power to influence consumer perception and life style choices. Furthermore, it was established that celebrity endorsement positively contributes to sales, brand awareness of the brand. The study findings also show that domestic celebrities from Zimbabwe are not trusted by consumers due to their bad behaviour such as drug abuse. Hence, it was concluded that celebrity endorsement is a powerful advertising tool which positively contributes to consumer buying behaviour but however in implementing celebrity endorsement in developing countries careful evaluation of the endorser has to be taken before the strategy is fully implemented. Therefore, the study recommends that the match up hypothesis model approach and international celebrities should be used by companies in developing countries in order to enhance their marketing skills and sales Keywords: celebrity, endorsement, consumer perception, brand awareness, consumer buying behavior,      marketing, domestic celebrity DOI: 10.7176/JMCR/72-06 Publication date:October 31st 202

The Impact of E-Commerce on the Performance of Logistic Service Providers in Ghana

Since the introduction of information technology in the late 90’s, e-commerce and logistics have gained weight throughout the world. Ghana has experienced the arithmetic growth of e-commerce since the 21st century. Although, majority of Third-Party Logistic companies are from Europe and USA (FedEx, DHL, UPS, etc), there have been the introduction and development of some local 3PL (OMA Ghana Ltd, McDan Shipping, etc.). The research’s had the main objectives were to: (1) explore the inventory management model practiced by the e-commerce companies in Ghana; and (2) assess the impact of e-commerce on the performance of logistic service providers in Ghana. The study concluded that: Almost 85% of e-commerce companies in Ghana preferred Jointly Managed Model. Also, there was positive correlation between e-commerce and the performance of logistic service providers in Ghana.  The study further recommended that; the Government of Ghana should help in providing credible housing addressing system to enhance local home-to-home delivery of goods and services; and the e-commerce companies should work hand in hand to enable online payment system on their platform by providing SSL securities and Data Protection services. Keywords: E-commerce, Logistics service providers, E-commerce in Ghana. DOI: 10.7176/JESD/11-10-04 Publication date:May 31st 202

Discrete gradient structure of a second-order variable-step method for nonlinear integro-differential models

The discrete gradient structure and the positive definiteness of discrete fractional integrals or derivatives are fundamental to the numerical stability in long-time simulation of nonlinear integro-differential models. We build up a discrete gradient structure for a class of second-order variable-step approximations of fractional Riemann-Liouville integral and fractional Caputo derivative. Then certain variational energy dissipation laws at discrete levels of the corresponding variable-step Crank-Nicolson type methods are established for time-fractional Allen-Cahn and time-fractional Klein-Gordon type models. They are shown to be asymptotically compatible with the associated energy laws of the classical Allen-Cahn and Klein-Gordon equations in the associated fractional order limits.Numerical examples together with an adaptive time-stepping procedure are provided to demonstrate the effectiveness of our second-order methods.Comment: 25 pages, 16 figures, 2 table

Properties of gapped systems in AdS/BCFT

We study the conductivities and entanglement structures of two different holographic gapped systems at zero density in the presence of boundaries within AdS/BCFT. The first gapped system is described by the Einstein-scalar gravity and the second one is the dual of AdS soliton geometry. We show that in both these two systems the bulk and boundary conductivities along the spatial direction of the boundary of BCFT are trivial. For the first system, when we increase the size of the subsystem the renormalized entanglement entropy is always non-negative and monotonically decreasing with discontinuous, or continuous, or smooth behavior, depending on the effective tension of the brane. While for the AdS soliton with a boundary, the renormalized entanglement entropy only exhibits a discontinuous drop when we increase the size of the subsystem.Comment: 36 pages, 17 figures, published versio

Internal structure of hairy rotating black holes in three dimensions

We construct hairy rotating black hole solutions in three dimensional Einstein gravity coupled to a complex scalar field. When we turn on a real and uniform source on the dual CFT, the black hole is stationary with two Killing vectors and we show that there is no inner horizon for the black hole and the system evolves smoothly into a Kasner universe. When we turn on a complex and periodic driving source on the dual CFT with a phase velocity equal to the angular velocity of the black hole, we have a time-dependent black hole with only one Killing vector. We show that inside the black hole, after a rapid collapse of the Einstein-Rosen bridge, oscillations of the scalar field follow. Then the system evolves into the Kasner epoch with possible Kasner inversion, which occurs in most of the parameter regimes. In both cases, one of the metric fields obeys a simple relation between its value at the horizon and in the Kasner epoch.Comment: 35 pages, 14 figure