13,010 research outputs found
On possible lower bounds for the direct detection rate of SUSY Dark Matter
One can expect accessible lower bounds for dark matter detection rate due to
restrictions on masses of the SUSY-partners. To explore this correlation one
needs a new-generation large-mass detector. The absolute lower bound for
detection rate can naturally be due to spin-dependent interaction. Aimed at
detecting dark matter with sensitivity higher than event/day/kg an
experiment should have a non-zero-spin target. Perhaps, the best is to create a
GENIUS-like detector with both Ge-73 (high spin) and Ge-76 nuclei.Comment: latex, 5 pages, 3 figures. Talk given at the III International
Conference on Non-accelerator New Physics (NANP'01), Dubna, 19--23 June, 200
Model-independent Limits from Spin-dependent WIMP Dark Matter Experiments
Spin-dependent WIMP searches have traditionally presented results within an
odd group approximation and by suppressing one of the spin-dependent
interaction cross sections. We here elaborate on a model-independent analysis
in which spin-dependent interactions with both protons and neutrons are
simultaneously considered. Within this approach, equivalent current limits on
the WIMP-nucleon interaction at WIMP mass of 50 GeV/c are either
pb, pb or ,
depending on the choice of cross section or coupling strength
representation. These limits become less restrictive for either larger or
smaller masses; they are less restrictive than those from the traditional odd
group approximation regardless of WIMP mass. Combination of experimental
results are seen to produce significantly more restrictive limits than those
obtained from any single experiment. Experiments traditionally considered
spin-independent are moreover found to severely limit the spin-dependent phase
space. The extension of this analysis to the case of positive signal
experiments is explored.Comment: 12 pages, 12 figures, submitted to Phys. Rev.
Bias Dependence and Electrical Breakdown of Small Diameter Single-Walled Carbon Nanotubes
The electronic breakdown and the bias dependence of the conductance have been
investigated for a large number of catalytic chemical vapor deposition (CCVD)
grown single-walled carbon nanotubes (SWCNTs) with very small diameters. The
convenient fabrication of thousands of properly contacted SWCNTs was possible
by growth on electrode structures and subsequent electroless palladium
deposition. Almost all of the measured SWCNTs showed at least weak gate
dependence at room temperature. Large differences in the conductance and
breakdown behavior have been found for "normal" semiconducting SWCNTs and small
band-gap semiconducting (SGS) SWCNTs.Comment: submitted to Journal of Applied Physic
On the direct search for spin-dependent WIMP interactions
We examine the current directions in the search for spin-dependent dark
matter. We discover that, with few exceptions, the search activity is
concentrated towards constraints on the WIMP-neutron spin coupling, with
significantly less impact in the WIMP-proton sector. We review the situation of
those experiments with WIMP-proton spin sensitivity, toward identifying those
capable of reestablishing the balance.Comment: 7 pages, 4 figure
Dynamical Evolution of Boson Stars II: Excited States and Self-Interacting Fields
The dynamical evolution of self-gravitating scalar field configurations in
numerical relativity is studied. The previous analysis on ground state boson
stars of non-interacting fields is extended to excited states and to fields
with self couplings.
Self couplings can significantly change the physical dimensions of boson
stars, making them much more astrophysically interesting (e.g., having mass of
order 0.1 solar mass). The stable () and unstable () branches of
equilibrium configurations of boson stars of self-interacting fields are
studied; their behavior under perturbations and their quasi-normal oscillation
frequencies are determined and compared to the non-interacting case.
Excited states of boson stars with and without self-couplings are studied and
compared. Excited states also have equilibrium configurations with and
branch structures; both branches are intrinsically unstable under a generic
perturbation but have very different instability time scales. We carried out a
detailed study of the instability time scales of these configurations. It is
found that highly excited states spontaneously decay through a cascade of
intermediate states similar to atomic transitions.Comment: 16 pages+ 13 figures . All figures are available at
http://wugrav.wustl.edu/Paper
Sub 20 nm Short Channel Carbon Nanotube Transistors
Carbon nanotube field-effect transistors with sub 20 nm long channels and
on/off current ratios of > 1000000 are demonstrated. Individual single-walled
carbon nanotubes with diameters ranging from 0.7 nm to 1.1 nm grown from
structured catalytic islands using chemical vapor deposition at 700 degree
Celsius form the channels. Electron beam lithography and a combination of HSQ,
calix[6]arene and PMMA e-beam resists were used to structure the short channels
and source and drain regions. The nanotube transistors display on-currents in
excess of 15 microA for drain-source biases of only 0.4 Volt.Comment: Nano Letters in pres
A custom designed density estimation method for light transport
We present a new Monte Carlo method for solving the global illumination problem in environments with general geometry descriptions and light emission and scattering properties. Current Monte Carlo global illumination algorithms are based on generic density estimation techniques that do not take into account any knowledge about the nature of the data points --- light and potential particle hit points --- from which a global illumination solution is to be reconstructed. We propose a novel estimator, especially designed for solving linear integral equations such as the rendering equation. The resulting single-pass global illumination algorithm promises to combine the flexibility and robustness of bi-directional path tracing with the efficiency of algorithms such as photon mapping
Fast Face Detector Training Using Tailored Views
Face detection is an important task in computer vision and often serves as the first step for a variety of applications. State-of-the-art approaches use efficient learning algorithms and train on large amounts of manually labeled imagery. Acquiring appropriate training images, however, is very time-consuming and does not guarantee that the collected training data is representative in terms of data variability. Moreover, available data sets are often acquired under con-trolled settings, restricting, for example, scene illumination or 3D head pose to a narrow range. This paper takes a look into the automated generation of adaptive training samples from a 3D morphable face model. Using statistical insights, the tailored training data guarantees full data variability and is enriched by arbitrary facial attributes such as age or body weight. Moreover, it can automatically adapt to environmental constraints, such as illumination or viewing angle of recorded video footage from surveillance cameras. We use the tailored imagery to train a new many-core imple-mentation of Viola Jones ’ AdaBoost object detection frame-work. The new implementation is not only faster but also enables the use of multiple feature channels such as color features at training time. In our experiments we trained seven view-dependent face detectors and evaluate these on the Face Detection Data Set and Benchmark (FDDB). Our experiments show that the use of tailored training imagery outperforms state-of-the-art approaches on this challenging dataset. 1
Dynamical evolution of boson stars in Brans-Dicke theory
We study the dynamics of a self-gravitating scalar field solitonic object
(boson star) in the Jordan-Brans-Dicke (BD) theory of gravity. We show
dynamical processes of this system such as (i) black hole formation of
perturbed equilibrium configuration on an unstable branch; (ii) migration of
perturbed equilibrium configuration from the unstable branch to stable branch;
(iii) transition from excited state to a ground state. We find that the
dynamical behavior of boson stars in BD theory is quite similar to that in
general relativity (GR), with comparable scalar wave emission. We also
demonstrate the formation of a stable boson star from a Gaussian scalar field
packet with flat gravitational scalar field initial data. This suggests that
boson stars can be formed in the BD theory in much the same way as in GR.Comment: 13 pages by RevTeX, epsf.sty, 16 figures, comments added, refs
updated, to appear in Phys. Rev.
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