4,789 research outputs found
On the Connection Between 2d Topological Gravity and the Reduced Hermitian Matrix Model
We discuss how concepts such as geodesic length and the volume of space-time
can appear in 2d topological gravity. We then construct a detailed mapping
between the reduced Hermitian matrix model and 2d topological gravity at genus
zero. This leads to a complete solution of the counting problem for planar
graphs with vertices of even coordination number. The connection between
multi-critical matrix models and multi-critical topological gravity at genus
zero is studied in some detail.Comment: 29 pages, LaTe
Stochastic integration in UMD Banach spaces
In this paper we construct a theory of stochastic integration of processes
with values in , where is a separable Hilbert space and
is a UMD Banach space (i.e., a space in which martingale differences are
unconditional). The integrator is an -cylindrical Brownian motion. Our
approach is based on a two-sided -decoupling inequality for UMD spaces due
to Garling, which is combined with the theory of stochastic integration of
-valued functions introduced recently by two of the authors.
We obtain various characterizations of the stochastic integral and prove
versions of the It\^{o} isometry, the Burkholder--Davis--Gundy inequalities,
and the representation theorem for Brownian martingales.Comment: Published at http://dx.doi.org/10.1214/009117906000001006 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Stochastic evolution equations in UMD Banach spaces
We discuss existence, uniqueness, and space-time H\"older regularity for
solutions of the parabolic stochastic evolution equation dU(t) = (AU(t) +
F(t,U(t))) dt + B(t,U(t)) dW_H(t), t\in [0,\Tend], U(0) = u_0, where
generates an analytic -semigroup on a UMD Banach space and is a
cylindrical Brownian motion with values in a Hilbert space . We prove that
if the mappings and satisfy suitable Lipschitz conditions and is
\F_0-measurable and bounded, then this problem has a unique mild solution,
which has trajectories in C^\l([0,T];\D((-A)^\theta) provided
and satisfy \l+\theta<\frac12. Various extensions of this
result are given and the results are applied to parabolic stochastic partial
differential equations.Comment: Accepted for publication in Journal of Functional Analysi
Ito's formula in UMD Banach spaces and regularity of solutions of the Zakai equation
Using the theory of stochastic integration for processes with values in a UMD
Banach space developed recently by the authors, an Ito formula is proved which
is applied to prove the existence of strong solutions for a class of stochastic
evolution equations in UMD Banach spaces. The abstract results are applied to
prove regularity in space and time of the solutions of the Zakai equation.Comment: Accepted for publication in Journal of Differential Equation
Barrier-controlled carrier transport in microcrystalline semiconducting materials: Description within a unified model
A recently developed model that unifies the ballistic and diffusive transport
mechanisms is applied in a theoretical study of carrier transport across
potential barriers at grain boundaries in microcrystalline semiconducting
materials. In the unified model, the conductance depends on the detailed
structure of the band edge profile and in a nonlinear way on the carrier mean
free path. Equilibrium band edge profiles are calculated within the trapping
model for samples made up of a linear chain of identical grains. Quantum
corrections allowing for tunneling are included in the calculation of electron
mobilities. The dependence of the mobilities on carrier mean free path, grain
length, number of grains, and temperature is examined, and appreciable
departures from the results of the thermionic-field-emission model are found.
Specifically, the unified model is applied in an analysis of Hall mobility data
for n-type microcrystalline Si thin films in the range of thermally activated
transport. Owing mainly to the effect of tunneling, potential barrier heights
derived from the data are substantially larger than the activation energies of
the Hall mobilities. The specific features of the unified model, however,
cannot be resolved within the rather large uncertainties of the analysis.Comment: REVTex, 19 pages, 9 figures; to appear in J. Appl. Phy
Primary radiotherapy in progressive optic nerve sheath meningiomas: a long-term follow-up study
Background/aims: To report the outcome of primary radiotherapy in patients with progressive optic nerve sheath meningioma (ONSM). Methods: The clinical records of all patients were reviewed in a retrospective, observational, multicentre study. Results: Thirty-four consecutive patients were included. Twenty-six women and eight men received conventional or stereotactic fractionated radiotherapy, and were followed for a median 58 (range 51–156) months. Fourteen eyes (41%) showed improved visual acuity of at least two lines on the Snellen chart. In 17 (50%) eyes, the vision stabilised, while deterioration was noted in three eyes (9%). The visual outcome was not associated with age at the time of radiotherapy (p=0.83), sex (p=0.43), visual acuity at the time of presentation (p=0.22) or type of radiotherapy (p=0.35). Optic disc swelling was associated with improved visual acuity (p<0.01) and 4/11 patients with optic atrophy also showed improvement. Long-term complications were dry eyes in five patients, cataracts in three, and mild radiation retinopathy in four. Conclusion: Primary radiotherapy for patients with ONSM is associated with long-term improvement of visual acuity and few adverse effects.Peerooz Saeed, Leo Blank, Dinesh Selva, John G. Wolbers, Peter J.C.M. Nowak, Ronald B. Geskus, Ezekiel Weis, Maarten P. Mourits, Jack Rootma
- …