4,095 research outputs found
Fission-induced plasmas
The possibility of creating a plasma from fission fragments, and to utilize the energy of the particles to create population inversion that would lead to laser action is investigated. An investigation was made of various laser materials which could be used for nuclear-pumped lasing. The most likely candidate for a fissioning material in the gaseous form is uranium hexafluoride - UF6, and experiments were performed to investigate materials that would be compatible with it. One of the central problems in understanding a fission-induced plasma is to obtain a model of the electron behavior, and some preliminary calculations are presented. In particular, the rates of various processes are discussed. A simple intuitive model of the electron energy distribution function is also shown. The results were useful for considering a mathematical model of a nuclear-pumped laser. Next a theoretical model of a (3)He-Ar nuclear-pumped laser is presented. The theory showed good qualitative agreement with the experimental results
Extracting New Physics from the CMB
We review how initial state effects generically yield an oscillatory
component in the primordial power spectrum of inflationary density
perturbations. These oscillatory corrections parametrize unknown new physics at
a scale and are potentially observable if the ratio is
sufficiently large. We clarify to what extent present and future CMB data
analysis can distinguish between the different proposals for initial state
corrections.Comment: Invited talk by B. Greene at the XXII Texas Symposium on Relativistic
Astrophysics, Stanford University, 13-17 December 2004, (TSRA04-0001), 8
pages, LaTeX, some references added, added paragraph at the end of section 2
and an extra note added after the conclusions regarding modifications to the
large k power spectra deduced from galaxy survey
Recommended from our members
Semiparametric Nonlinear Panel Data Models with Measurement Error
This paper develops identification and estimation of the parameters of a nonlinear semi-parametric panel data model with mismeasured variables as well as the corresponding average partial effects using only three periods of data. The past observables are used as instruments to control the measurement error problem, and the time averages of perfectly observed variables are used to restrict the unobserved individual-specific effect by a correlated random effects specification. The proposed approach relies on the Fourier transforms of several conditional expectations of observable variables. We estimate the model via the semi-parametric sieve minimum distance estimator. The finite-sample properties of the estimator are investigated through Monte Carlo simulations. We use our method to estimate the effect of the wage rate on labor supply using PSID data
Observing the Geometry of Warped Compactification via Cosmic Inflation
Using DBI inflation as an example, we demonstrate that the detailed geometry
of warped compactification can leave an imprint on the cosmic microwave
background (CMB). We compute CMB observables for DBI inflation in a generic
class of warped throats and find that the results (such as the sign of the tilt
of the scalar perturbations and its running) depend sensitively on the precise
shape of the warp factor. In particular, we analyze the warped deformed
conifold and find that the results can differ from those of other warped
geometries, even when these geometries approximate well the exact metric of the
warped deformed conifold.Comment: 4 pages, 3 figures. v2: References and clarifications adde
Good rotations
Numerical integrations in celestial mechanics often involve the repeated
computation of a rotation with a constant angle. A direct evaluation of these
rotations yields a linear drift of the distance to the origin. This is due to
roundoff in the representation of the sine s and cosine c of the angle theta.
In a computer, one generally gets c^2 + s^2 1, resulting in a mapping that
is slightly contracting or expanding. In the present paper we present a method
to find pairs of representable real numbers s and c such that c^2 + s^2 is as
close to 1 as possible. We show that this results in a drastic decrease of the
systematic error, making it negligible compared to the random error of other
operations. We also verify that this approach gives good results in a realistic
celestial mechanics integration.Comment: 24 pages, 3 figure
Studies of new media radiation induced laser
Various lasants were investigated especially, 2-iodohepafluoropropane (i-C3F7I) for the direct solar pumped lasers. Optical pumping of iodine laser was achieved using a small flashlamp. Using i-C3F7I as a laser gain medium, threshold inversion density, small signal gain, and laser performance at the elevated temperature were measured. The experimental results and analysis are presented. The iodine laser kinetics of the C3F7I and IBr system were numerically simulated. The concept of a direct solar-pumped laser amplifier using (i-C3F7I) as the laser material was evaluated and several kinetic coefficients for i-C3F7I laser system were reexamined. The results are discussed
Convex Rank Tests and Semigraphoids
Convex rank tests are partitions of the symmetric group which have desirable
geometric properties. The statistical tests defined by such partitions involve
counting all permutations in the equivalence classes. Each class consists of
the linear extensions of a partially ordered set specified by data. Our methods
refine existing rank tests of non-parametric statistics, such as the sign test
and the runs test, and are useful for exploratory analysis of ordinal data. We
establish a bijection between convex rank tests and probabilistic conditional
independence structures known as semigraphoids. The subclass of submodular rank
tests is derived from faces of the cone of submodular functions, or from
Minkowski summands of the permutohedron. We enumerate all small instances of
such rank tests. Of particular interest are graphical tests, which correspond
to both graphical models and to graph associahedra
- …