33,776 research outputs found
Optimal Estimates for the Electric Field in Two-Dimensions
The purpose of this paper is to set out optimal gradient estimates for
solutions to the isotropic conductivity problem in the presence of adjacent
conductivity inclusions as the distance between the inclusions goes to zero and
their conductivities degenerate. This difficult question arises in the study of
composite media. Frequently in composites, the inclusions are very closely
spaced and may even touch. It is quite important from a practical point of view
to know whether the electric field (the gradient of the potential) can be
arbitrarily large as the inclusions get closer to each other or to the boundary
of the background medium.
In this paper, we establish both upper and lower bounds on the electric field
in the case where two circular conductivity inclusions are very close but not
touching. We also obtain such bounds when a circular inclusion is very close to
the boundary of a circular domain which contains the inclusion. The novelty of
these estimates, which improve and make complete our earlier results published
in Math. Ann., is that they give an optimal information about the blow-up of
the electric field as the conductivities of the inclusions degenerate.Comment: 26 page
Modulation of the Curie Temperature in Ferromagnetic/Ferroelectric Hybrid Double Quantum Wells
We propose a ferromagnetic/ferroelectric hybrid double quantum well
structure, and present an investigation of the Curie temperature (Tc)
modulation in this quantum structure. The combined effects of applied electric
fields and spontaneous electric polarization are considered for a system that
consists of a Mn \delta-doped well, a barrier, and a p-type ferroelectric well.
We calculate the change in the envelope functions of carriers at the lowest
energy sub-band, resulting from applied electric fields and switching the
dipole polarization. By reversing the depolarizing field, we can achieve two
different ferromagnetic transition temperatures of the ferromagnetic quantum
well in a fixed applied electric field. The Curie temperature strongly depends
on the position of the Mn \delta-doped layer and the polarization strength of
the ferroelectric well.Comment: 9 pages, 5 figures, to be published in Phys. Rev. B (2006) minor
revision: One of the line types is changed in Fig.
State space collapse and diffusion approximation for a network operating under a fair bandwidth sharing policy
We consider a connection-level model of Internet congestion control,
introduced by Massouli\'{e} and Roberts [Telecommunication Systems 15 (2000)
185--201], that represents the randomly varying number of flows present in a
network. Here, bandwidth is shared fairly among elastic document transfers
according to a weighted -fair bandwidth sharing policy introduced by Mo
and Walrand [IEEE/ACM Transactions on Networking 8 (2000) 556--567] []. Assuming Poisson arrivals and exponentially distributed document
sizes, we focus on the heavy traffic regime in which the average load placed on
each resource is approximately equal to its capacity. A fluid model (or
functional law of large numbers approximation) for this stochastic model was
derived and analyzed in a prior work [Ann. Appl. Probab. 14 (2004) 1055--1083]
by two of the authors. Here, we use the long-time behavior of the solutions of
the fluid model established in that paper to derive a property called
multiplicative state space collapse, which, loosely speaking, shows that in
diffusion scale, the flow count process for the stochastic model can be
approximately recovered as a continuous lifting of the workload process.Comment: Published in at http://dx.doi.org/10.1214/08-AAP591 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Solid particle erosion of environmental barrier coatings and ceramic matrix composites
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PHS48 Cost-Effectiveness Analysis of Tolvaptan for Hyponatreamia in South Korea
Lanz, AlfredoPla general de la part frontal de dona ajaguda sobre un suport en forma de llit o
taula. Va ser donada per l'autor, Alfredo Lanz, i simbolitza
el mar Mediterrani. Feta en tres planxes d'acer retallades de colors vius: verd, vermell i groc
Precessing Jet and Large Dust Grains in the V380 Ori NE Star-forming Region
The V380 Ori NE bipolar outflow was imaged in the SiO and CO J = 1 - 0 lines,
and dense cores in L1641 were observed in the 2.0-0.89 mm continuum. The highly
collimated SiO jet shows point-symmetric oscillation patterns in both position
and velocity, which suggests that the jet axis is precessing and the driving
source may belong to a non-coplanar binary system. By considering the position
and velocity variabilities together, accurate jet parameters were derived. The
protostellar system is viewed nearly edge-on, and the jet has a flow speed of
35 km/s and a precession period of 1600 years. The CO outflow length gives a
dynamical timescale of 6300 years, and the protostar must be extremely young.
The inferred binary separation of 6-70 au implies that this protobinary system
may have been formed through the disk instability process. The continuum
spectra of L1641 dense cores indicate that the emission comes from dust, and
the fits with modified blackbody functions give emissivity power indices of
beta = 0.3-2.2. The emissivity index shows a positive correlation with the
molecular line width, but no strong correlation with bolometric luminosity or
temperature. V380 Ori NE has a particularly low value of beta = 0.3, which
tentatively suggests the presence of millimeter-sized dust grains. Because the
dust growth takes millions of years, much longer than the protostellar age,
this core may have produced large grains in the starless core stage. HH 34 MMS
and HH 147 MMS also have low emissivity indices.Comment: To appear in the Astrophysical Journal Supplement Serie
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