251,171 research outputs found
String Representation for the 't Hooft Loop Average in the Abelian Higgs Model
Making use of the duality transformation, we derive in the Londons' limit of
the Abelian Higgs Model string representation for the 't Hooft loop average
defined on the string world-sheet, which yields the values of two coefficient
functions parametrizing the bilocal correlator of the dual field strength
tensors. The asymptotic behaviours of these functions agree with the ones
obtained within the Method of Vacuum Correlators in QCD in the lowest order of
perturbation theory. We demonstrate that the bilocal approximation to the
Method of Vacuum Correlators is an exact result in the Londons' limit, i.e. all
the higher cumulants in this limit vanish. We also show that at large
distances, apart from the integration over metrics, the obtained string
effective theory (which in this case reduces to the nonlinear massive axionic
sigma model) coincides with the low-energy limit of the dual version of 4D
compact QED, the so-called Universal Confining String Theory. We derive string
tension of the Nambu-Goto term and the coupling constant of the rigidity term
for the obtained string effective theory and demonstrate that the latter one is
always negative, which means the stability of strings, while the positiveness
of the former is confirmed by the present lattice data. These data enable us to
find the Higgs boson charge and the vacuum expectation value of the Higgs
field, which model QCD best of all. We also study dynamics of the weight factor
of the obtained string representation for the 't Hooft average in the loop
space. In conclusion, we obtain string representation for the partition
function of the correlators of an arbitrary number of Higgs currents, by virtue
of which we rederive the structure of the bilocal correlator of the dual field
strength tensors, which yields the surface term in the string effective action.Comment: 11 pages, LaTeX, no figures, references are adde
Experiences and issues for environmental science sensor network deployments
Sensor network research is a large and growing area of academic effort, examining technological and deployment issues in the area of environmental monitoring. These technologies are used by environmental engineers and scientists to monitor a multiplicity of environments and services, and, specific to this paper, energy and water supplied to the built environment. Although the technology is developed by Computer Science specialists, the use and deployment is traditionally performed by environmental engineers. This paper examines deployment from the perspectives of environmental engineers and scientists and asks what computer scientists can do to improve the process. The paper uses a case study to demonstrate the agile operation of WSNs within the Cloud Computing infrastructure, and thus the demand-driven, collaboration-intense paradigm of Digital Ecosystems in Complex Environments
Evaluation of Skylab photography for water resources, San Luis Valley, Colorado
The author has identified the following significant results. Skylab S190A photography used in a stereo mode is sufficient for defining the drainage divides and drainage patterns at the regional level. This data, combined with geologic information, define the boundaries and distribution of ground water recharge and discharge areas within the basin
Experiences and issues for environmental engineering sensor network deployments
Sensor network research is a large and growing area of academic effort, examining technological and deployment issues in the area of environmental monitoring. These technologies are used by environmental engineers and scientists to monitor a multiplicity of environments and services, and, specific to this paper, energy and water supplied to the built environment. Although the technology is developed by Computer Science specialists, the use and deployment is traditionally performed by environmental engineers. This paper examines deployment from the perspectives of environmental engineers and scientists and asks what computer scientists can do to improve the process. The paper uses a case study to demonstrate the agile operation of WSNs within the Cloud Computing infrastructure, and thus the demand-driven, collaboration-intense paradigm of Digital Ecosystems in Complex Environments
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Scalable grid resource allocation for scientific workflows using hybrid metaheuristics
Grid infrastructure is a valuable tool for scientific users, but it is characterized by a high level of complexity which makes it difficult for them to quantify their requirements and allocate resources. In this paper, we show that resource trading is a viable and scalable approach for scientific users to consume resources. We propose the use of Grid resource bundles to specify supply and demand combined with a hybrid metaheuristic method to determine the allocation of resources in a market-based approach. We evaluate this through the application domain of scientific workflow execution on the Grid
Monitoring Challenges and Approaches for P2P File-Sharing Systems
Since the release of Napster in 1999, P2P file-sharing has enjoyed a dramatic rise in popularity. A 2000 study by Plonka on the University of Wisconsin campus network found that file-sharing accounted for a comparable volume of traffic to HTTP, while a 2002 study by Saroiu et al. on the University of Washington campus network found that file-sharing accounted for more than treble the volume of Web traffic observed, thus affirming the significance of P2P in the context of Internet traffic. Empirical studies of P2P traffic are essential for supporting the design of next-generation P2P systems, informing the provisioning of network infrastructure and underpinning the policing of P2P systems. The latter is of particular significance as P2P file-sharing systems have been implicated in supporting criminal behaviour including copyright infringement and the distribution of illegal pornograph
Extending sensor networks into the cloud using Amazon web services
Sensor networks provide a method of collecting environmental data for use in a variety of distributed applications. However, to date, limited support has been provided for the development of integrated environmental monitoring and modeling applications. Specifically, environmental dynamism makes it difficult to provide computational resources that are sufficient to deal with changing environmental conditions. This paper argues that the Cloud Computing model is a good fit with the dynamic computational requirements of environmental monitoring and modeling. We demonstrate that Amazon EC2 can meet the dynamic computational needs of environmental applications. We also demonstrate that EC2 can be integrated with existing sensor network technologies to offer an end-to-end environmental monitoring and modeling solution
Dirty quantum Hall ferromagnets and quantum Hall spin glasses
We study quantum Hall ferromagnets in the presence of a random electrostatic
impurity potential, within the framework of a classical non-linear sigma model.
We discuss the behaviour of the system using a heuristic picture for the
competition between exchange and screening, and test our conclusions with
extensive numerical simulations. We obtain a phase diagram for the system as a
function of disorder strength and deviation of the average Landau level filling
factor from unity. Screening of an impurity potential requires distortions of
the spin configuration. In the absence of Zeeman coupling there is a
disorder-driven, zero-temperature phase transition from a ferromagnet at weak
disorder and small deviation from integer filling to a spin glass at stronger
disorder or large charge deviation. We characterise the spin glass phase in
terms of its magnetic and charge response, as well as its ac conductivity.Comment: 12 pages, 6 figures, REVTEX
Dynamics of thermalisation in small Hubbard-model systems
We study numerically the thermalisation and temporal evolution of the reduced
density matrix for a two-site subsystem of a fermionic Hubbard model prepared
far from equilibrium at a definite energy. Even for very small systems near
quantum degeneracy, the subsystem can reach a steady state resembling
equilibrium. This occurs for a non-perturbative coupling between the subsystem
and the rest of the lattice where relaxation to equilibrium is Gaussian in
time, in sharp contrast to perturbative results. We find similar results for
random couplings, suggesting such behaviour is generic for small systems.Comment: 4 pages, 5 figure
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