63,287 research outputs found
A Methodology for Engineering Collaborative and ad-hoc Mobile Applications using SyD Middleware
Today’s web applications are more collaborative and utilize standard and ubiquitous Internet protocols. We have earlier developed System on Mobile Devices (SyD) middleware to rapidly develop and deploy collaborative applications over heterogeneous and possibly mobile devices hosting web objects. In this paper, we present the software engineering methodology for developing SyD-enabled web applications and illustrate it through a case study on two representative applications: (i) a calendar of meeting application, which is a collaborative application and (ii) a travel application which is an ad-hoc collaborative application. SyD-enabled web objects allow us to create a collaborative application rapidly with limited coding effort. In this case study, the modular software architecture allowed us to hide the inherent heterogeneity among devices, data stores, and networks by presenting a uniform and persistent object view of mobile objects interacting through XML/SOAP requests and responses. The performance results we obtained show that the application scales well as we increase the group size and adapts well within the constraints of mobile devices
Some properties of the model of a superconductor with pair hopping and magnetic interactions at half-filling
We present our preliminary studies of an effective model of a superconductor
with short coherence length involving magnetic interactions. The Hamiltonian
considered consists of (i) the effective on-site interaction U, (ii) the
intersite magnetic exchange interactions (Jz, Jxy) between nearest-neighbors
and (iii) the intersite charge exchange term I, determining the hopping of
electron pairs between nearest-neighbor sites. In the analysis of the phase
diagrams and thermodynamic properties of this model for half-filling (n=1) we
have adopted the variational approach, which treats the on-site interaction
term exactly and the intersite interactions within the mean-field
approximation. One finds that the system considered can exhibit very
interesting multicritical behaviors (including tricritical, critical-end and
bicritical points) caused by the competition between magnetism and
superconductivity, even for n=1. Our investigations show that, depending on the
values of interaction parameters, the system at half-filling can exhibit three
homogeneous phases: superconducting (SS), (anti-)ferromagnetic (F) and
nonordered (NO). The transitions between ordered phases (SS, F) and the NO
phase can be first order as well as second order ones, whereas SS-F transition
is first order one. Temperature dependencies of the order parameters and
thermodynamic properties of the system at the sequence of transitions: SS-F-NO
with increasing temperature for J/I=0.3, U/I0 = 0.69 and n=1 are also
presented.Comment: 5 pages, 3 figures, presented at 15th National School of
Superconductivity - 100 years of superconductivity, Kazimierz Dolny, Poland,
October 9 - 13, 2011; final version, pdf-ReVTeX, corrected typo
Lattice thermal conductivity of disordered binary alloys : a formulation
We present here a formulation for the calculation of the configuration
averaged lattice thermal conductivity in random alloys. Our formulation is
based on the augmented-space theorem, introduced by one of us, combined with a
generalized diagrammatic technique. The diagrammatic approach simplifies the
problem of including effects of disorder corrections to a great extent. The
approach allows us to obtain an expression for the effective heat current in
case of disordered alloys, which in turn is used in a Kubo-Greenwood type
formula for the thermal conductivity. We show that disorder scattering
renormalizes the phonon propagators as well as the heat currents. The
corrections to the current terms have been shown to be related to the
self-energy of the propagators. We also study the effect of vertex corrections
in a simplified ladder diagram approximation. A mode dependent diffusivity
and then a total thermal diffusivity averaged over different modes
are defined. Schemes for implementing the said formalism are discussed. A few
initial numerical results on the frequency and temperature dependence of
lattice thermal conductivity are presented for NiPd alloy and are also compared
with experiment. We also display numerical results on the frequency dependence
of thermal diffusivity averaged over modes.Comment: 16 pages, 17 figure
Fluctuations and the role of collision duration in reaction-diffusion systems
In a reaction-diffusion system, fluctuations in both diffusion and reaction
events, have important effects on the steady-state statistics of the system.
Here, we argue through extensive lattice simulations, mean-field type
arguments, and the Doi-Peliti formalism that the collision duration statistics
-- i.e., the time two particles stay together in a lattice site -- plays a
leading role in determining the steady state of the system. We obtain
approximate expressions for the average densities of the chemical species and
for the critical diffusion coefficient required to sustain the reaction
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