102 research outputs found
Optimal quality of exceptional points for the Lebesgue density theorem
In spite of the Lebesgue density theorem, there is a positive such
that, for every non-trivial measurable set of real numbers, there is a
point at which both the lower densities of and of the complement of are
at least . The problem of determining the supremum of possible values
of this was studied in a paper of V. I. Kolyada, as well as in some
recent papers. We solve this problem in the present work.Comment: 45 page
Residue Formulas for the Large k Asymptotics of Witten's Invariants of Seifert Manifolds. The Case of SU(2)
We derive the large k asymptotics of the surgery formula for SU(2) Witten's
invariants of general Seifert manifolds. The contributions of connected
components of the moduli space of flat connections are identified. The
contributions of irreducible connections are presented in a residue form. This
form is similar to the one used by A. Szenes, L. Jeffrey and F. Kirwan. This
similarity allows us to express the contributions of irreducible connections in
terms of intersection numbers on their moduli spaces.Comment: 39 pages, no figures, LaTe
On Witten multiple zeta-functions associated with semisimple Lie algebras IV
In our previous work, we established the theory of multi-variable Witten
zeta-functions, which are called the zeta-functions of root systems. We have
already considered the cases of types , , , and . In
this paper, we consider the case of -type. We define certain analogues of
Bernoulli polynomials of -type and study the generating functions of them
to determine the coefficients of Witten's volume formulas of -type. Next
we consider the meromorphic continuation of the zeta-function of -type and
determine its possible singularities. Finally, by using our previous method, we
give explicit functional relations for them which include Witten's volume
formulas.Comment: 22 pag
(0,2) Deformations of Linear Sigma Models
We study (0,2) deformations of a (2,2) supersymmetric gauged linear sigma
model for a Calabi-Yau hypersurface in a Fano toric variety. In the non-linear
sigma model these correspond to some of the holomorphic deformations of the
tangent bundle on the hypersurface. Combinatorial formulas are given for the
number of these deformations, and we show that these numbers are exchanged by
mirror symmetry in a subclass of the models.Comment: 35 pages; uses xy-fig; typos fixed, acknowledgments adde
Comparative study on the uniform energy deposition achievable via optimized plasmonic nanoresonator distributions
Plasmonic nanoresonators of core-shell composition and nanorod shape were
optimized to tune their absorption cross-section maximum to the central
wavelength of a short pulse. Their distribution along a pulse-length scaled
target was optimized to maximize the absorptance with the criterion of minimal
absorption difference in between neighbouring layers. Successive approximation
of layer distributions made it possible to ensure almost uniform deposited
energy distribution up until the maximal overlap of two counter-propagating
pulses. Based on the larger absorptance and smaller uncertainty in absorptance
and energy distribution core-shell nanoresonators override the nanorods.
However, optimization of both nanoresonator distributions has potential
applications, where efficient and uniform energy deposition is crucial,
including phase transitions and even fusion
Crater formation by fast ions: comparison of experiment with Molecular Dynamics simulations
An incident fast ion in the electronic stopping regime produces a track of
excitations which can lead to particle ejection and cratering. Molecular
Dynamics simulations of the evolution of the deposited energy were used to
study the resulting crater morphology as a function of the excitation density
in a cylindrical track for large angle of incidence with respect to the surface
normal. Surprisingly, the overall behavior is shown to be similar to that seen
in the experimental data for crater formation in polymers. However, the
simulations give greater insight into the cratering process. The threshold for
crater formation occurs when the excitation density approaches the cohesive
energy density, and a crater rim is formed at about six times that energy
density. The crater length scales roughly as the square root of the electronic
stopping power, and the crater width and depth seem to saturate for the largest
energy densities considered here. The number of ejected particles, the
sputtering yield, is shown to be much smaller than simple estimates based on
crater size unless the full crater morphology is considered. Therefore, crater
size can not easily be used to estimate the sputtering yield.Comment: LaTeX, 7 pages, 5 EPS figures. For related figures/movies, see:
http://dirac.ms.virginia.edu/~emb3t/craters/craters.html New version uploaded
5/16/01, with minor text changes + new figure
Parametric Polyhedra with at least Lattice Points: Their Semigroup Structure and the k-Frobenius Problem
Given an integral matrix , the well-studied affine semigroup
\mbox{ Sg} (A)=\{ b : Ax=b, \ x \in {\mathbb Z}^n, x \geq 0\} can be
stratified by the number of lattice points inside the parametric polyhedra
. Such families of parametric polyhedra appear in
many areas of combinatorics, convex geometry, algebra and number theory. The
key themes of this paper are: (1) A structure theory that characterizes
precisely the subset \mbox{ Sg}_{\geq k}(A) of all vectors b \in \mbox{
Sg}(A) such that has at least solutions. We
demonstrate that this set is finitely generated, it is a union of translated
copies of a semigroup which can be computed explicitly via Hilbert bases
computations. Related results can be derived for those right-hand-side vectors
for which has exactly solutions or fewer
than solutions. (2) A computational complexity theory. We show that, when
, are fixed natural numbers, one can compute in polynomial time an
encoding of \mbox{ Sg}_{\geq k}(A) as a multivariate generating function,
using a short sum of rational functions. As a consequence, one can identify all
right-hand-side vectors of bounded norm that have at least solutions. (3)
Applications and computation for the -Frobenius numbers. Using Generating
functions we prove that for fixed the -Frobenius number can be
computed in polynomial time. This generalizes a well-known result for by
R. Kannan. Using some adaptation of dynamic programming we show some practical
computations of -Frobenius numbers and their relatives
Creation of multiple nanodots by single ions
In the challenging search for tools that are able to modify surfaces on the
nanometer scale, heavy ions with energies of several 10 MeV are becoming more
and more attractive. In contrast to slow ions where nuclear stopping is
important and the energy is dissipated into a large volume in the crystal, in
the high energy regime the stopping is due to electronic excitations only.
Because of the extremely local (< 1 nm) energy deposition with densities of up
to 10E19 W/cm^2, nanoscaled hillocks can be created under normal incidence.
Usually, each nanodot is due to the impact of a single ion and the dots are
randomly distributed. We demonstrate that multiple periodically spaced dots
separated by a few 10 nanometers can be created by a single ion if the sample
is irradiated under grazing angles of incidence. By varying this angle the
number of dots can be controlled.Comment: 12 pages, 6 figure
Laser Wake Field Collider
Recently NAno-Plasmonic, Laser Inertial Fusion Experiments (NAPLIFE) were proposed, as an improved way to achieve laser driven fusion. The improvement is the combination of two basic research discoveries: (i) the possibility of detonations on space-time hyper-surfaces with time-like normal (i.e. simultaneous detonation in a whole volume) and (ii) to increase this volume to the whole target, by regulating the laser light absorption using nanoshells or nanorods as antennas. These principles can be realized in a one dimensional configuration, in the simplest way with two opposing laser beams as in particle colliders. Such, opposing laser beam experiments were also performed recently. Here we study the consequences of the Laser Wake Field Acceleration (LWFA) if we experience it in a colliding laser beam set-up. These studies can be applied to laser driven fusion, but also to other rapid phase transition, combustion, or ignition studies in other materials.publishedVersio
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