Boundary conditions and renormalized stress-energy tensor on a Poincar\'e patch of AdS2\textrm{AdS}_2

Quantum field theory on anti-de Sitter spacetime requires the introduction of boundary conditions at its conformal boundary, due essentially to the absence of global hyperbolicity. Here we calculate the renormalized stress-energy tensor $T_{\mu\nu}$ for a scalar field $\phi$ on the Poincar\'e patch of $\text{AdS}_2$ and study how it depends on those boundary conditions. We show that, except for the Dirichlet and Neumann cases, the boundary conditions break the maximal $\textrm{AdS}$ invariance. As a result, $\langle\phi^2\rangle$ acquires a space dependence and $\langle T_{\mu\nu}\rangle$ is no longer proportional to the metric. When the physical quantities are expanded in a parameter $\beta$ which characterizes the boundary conditions (with $\beta=0$ corresponding to Dirichlet and $\beta=\infty$ corresponding to Neumann), the singularity of the Green's function is entirely subtracted at zeroth order in $\beta$. As a result, the contribution of nontrivial boundary conditions to the stress-energy tensor is free of singular terms.Comment: 7 pages. Minor Correction. Matches published versio

Transparent Dynamic reconfiguration for CORBA

Distributed systems with high availability requirements have to support some form of dynamic reconfiguration. This means that they must provide the ability to be maintained or upgraded without being taken off-line. Building a distributed system that allows dynamic reconfiguration is very intrusive to the overall design of the system, and generally requires special skills from both the client and server side application developers. There is an opportunity to provide support for dynamic reconfiguration at the object middleware level of distributed systems, and create a dynamic reconfiguration transparency to application developers. We propose a Dynamic Reconfiguration Service for CORBA that allows the reconfiguration of a running system with maximum transparency for both client and server side developers. We describe the architecture, a prototype implementation, and some preliminary test result

Access networks for mobility: a techno-economic model for broadband access technologies

The two main challenges for the access networks are the increasing bandwidth demand and mobility trends. The "triple play" services required (Internet, telephone and TV services) lead to a great increase in bandwidth demand. However, the existing access networks are not able to support this increase, and the capacity to delivery broadband services remain as a challenge ("last mile problem"). The access network remains a bottleneck in terms of the bandwidth and service quality it affords the end user. Besides the bandwidth, other great challenge to access networks is the mobility and the user need to have internet access anywhere and anytime. Then, the increasing demand of "quad-play" (also known as quadruple-play) services, including video, voice, data and mobility, have created new challenges to the modern broadband wireless/wired access networks. This document proposes a techno-economic model to support the new requirements of fixed and nomadic users

Game theoretic modeling of NGANs: impact of retail and wholesale services price variation

The increasing demand for broadband access leads operators to upgrade the existing access infrastructures (or building new access network). Broadband access networks require higher investments (especially passive infrastructures such as trenches/ducts and base station towers/masts), and before making any decision it is important to analyze all solutions. The selection of the best solution requires understanding the technical possibilities and limitations of the different access technologies, as well as understanding the costs of building and operating the networks. This study analyzes the effect of asymmetric retail and wholesale prices on operators’ NPV, profit, consumer surplus, welfare, retail market, wholesale market, and so on. For that, we propose a tehno-economic model complemented by a theoretic-game model. This tool identifies all the essential costs of building (and operating) access networks, and performs a detailed analysis and comparison of the different solutions in various scenarios. Communities, operators/service providers, and regulators can use this tool to compare different technological solutions, forecast deployment costs, compare diferente scenarios, and so on, and help them in making deployment (or regulatory) decisions. The game-theory analyses give a better understanding of the competition and its effect on the business case scenarios’ economic results

Infrastructure sharing as an opportunity to promote competition in local access networks

Telecom infrastructures are facing unprecedented challenges, with increasing demands on network capacity. Today, network operators must determine how to expand the existing access network infrastructure into networks capable of satisfying the user’s requirements. Thus, in this context, providers need to identify the technological solutions that enable them to profitably serve customers and support future needs. However, the identification of the “best” solution is a difficult task. Although the cost of bandwidth in the active layer has reduced significantly (and continually) in recent years, the cost of the civil works—such as digging and trenching—represents a major barrier for operators to deploy NGA infrastructure. Duct is a critical part of the next-generation access networks, and its sharing would reduce or eliminate this capital cost and this barrier to entry. The aim of this paper is to provide a better understanding of the economics of broadband access networks technologies (wireline and wireless), their role in the deployment of several services in different regions, and the development of competition in the access networks

Diversidade de artrópodes terrestres em dois tipos de culturas frutícolas na ilha Terceira, Açores: os predadores generalistas e himenópteros parasitóides (Hymenoptera, Parasitica)

I Congresso de Fruticultura e Viticultura. Angra do Heroísmo 17-19 Abril 2008.Trabalho de investigação desenvolvido no projecto INTERFRUTA II, financiado pelo programa INTERREG III-B."[…]. Neste trabalho abordou-se a diversidade de artrópodes terrestres em três pomares pertencentes a dois tipos de culturas frutícolas. Pretendeu-se conhecer a riqueza específica dos predadores generalistas, com relevância na ordem Araneae, assim como a diversidade de himenópteros parasitóides (Hymenoptera, Parasitica) em três pomares de dois tipos de culturas frutícolas, e determinar a presença de possíveis himenópteros parasitóides da mosca-do-mediterrâneo (Ceratitis capitata Wiedemann) (Diptera, Thephritidae) e do bichado-da-castanha (Cydia splendana (Hübner)) (Lepidoptera, Troticidae), dependendo da cultura em estudo.

Stochastic Nature of Physical Parameterizations in Ensemble Prediction: A Stochastic Convection Approach

Abstract In this paper it is argued that ensemble prediction systems can be devised in such a way that physical parameterizations of subgrid-scale motions are utilized in a stochastic manner, rather than in a deterministic way as is typically done. This can be achieved within the context of current physical parameterization schemes in weather and climate prediction models. Parameterizations are typically used to predict the evolution of grid-mean quantities because of unresolved subgrid-scale processes. However, parameterizations can also provide estimates of higher moments that could be used to constrain the random determination of the future state of a certain variable. The general equations used to estimate the variance of a generic variable are briefly discussed, and a simplified algorithm for a stochastic moist convection parameterization is proposed as a preliminary attempt. Results from the implementation of this stochastic convection scheme in the Navy Operational Global Atmospheric Prediction System (NOGAPS) ensemble are presented. It is shown that this method is able to generate substantial tropical perturbations that grow and "migrate" to the midlatitudes as forecast time progresses while moving from the small scales where the perturbations are forced to the larger synoptic scales. This stochastic convection method is able to produce substantial ensemble spread in the Tropics when compared with results from ensembles created from initial-condition perturbations. Although smaller, there is still a sizeable impact of the stochastic convection method in terms of ensemble spread in the extratropics. Preliminary simulations with initial-condition and stochastic convection perturbations together in the same ensemble system show a promising increase in ensemble spread and a decrease in the number of outliers in the Tropics

Robot orientation with histograms on MSL

One of the most important tasks on robot soccer is localization. The team robots should self-localize on the 18 x 12 meters soccer field. Since a few years ago the soccer field has increased and the corner posts were removed and that increased the localization task complexity. One important aspect to take care for a proper localization is to find out the robot orientation. This paper proposes a new technique to calculate the robot orientation. The proposed method consists of using a histogram of white-green transitions (to detect the lines on the field) to know the robot orientation. This technique does not take much computational time and proves to be very reliable.(undefined

Topological low-temperature limit of Z(2) spin-gauge theory in three dimensions

We study Z(2) lattice gauge theory on triangulations of a compact 3-manifold. We reformulate the theory algebraically, describing it in terms of the structure constants of a bidimensional vector space H equipped with algebra and coalgebra structures, and prove that in the low-temperature limit H reduces to a Hopf Algebra, in which case the theory becomes equivalent to a topological field theory. The degeneracy of the ground state is shown to be a topological invariant. This fact is used to compute the zeroth- and first-order terms in the low-temperature expansion of Z for arbitrary triangulations. In finite temperatures, the algebraic reformulation gives rise to new duality relations among classical spin models, related to changes of basis of H.Comment: 10 pages, no figure