30,096 research outputs found
Performance evaluation of a class of systematic, rate (M-1)/M, convolutional codes
The implementation and performance evaluation are described for a class of rate (M-1)/M, systematic, convolutional codes being decoded with a simple majority logic decoder. The encoding logic appends one parity bit for each PCM telemetry word. It is shown that over the critical range of received PCM telemetry signal-to-noise ratios, this coding procedure produces a net coding gain of from 1.5 to 2.5 db relative to an equal power transmission of uncoded PCM telemetry. Being a low-redundancy systematic code, it is possible to process this data without convolutional decoding with a small rate loss penalty of about 0.5 db
Oscillations in the Primordial Bispectrum: Mode Expansion
We consider the presence of oscillations in the primordial bispectrum,
inspired by three different cosmological models; features in the primordial
potential, resonant type non-Gaussianities and deviation from the standard
Bunch Davies vacuum. In order to put constraints on their bispectra, a logical
first step is to put these into factorized form which can be achieved via the
recently proposed method of polynomial basis expansion on the tetrahedral
domain. We investigate the viability of such an expansion for the oscillatory
bispectra and find that one needs an increasing number of orthonormal mode
functions to achieve significant correlation between the expansion and the
original spectrum as a function of their frequency. To reduce the number of
modes required, we propose a basis consisting of Fourier functions
orthonormalized on the tetrahedral domain. We show that the use of Fourier mode
functions instead of polynomial mode functions can lead to the necessary
factorizability with the use of only 1/5 of the total number of modes required
to reconstruct the bispectra with polynomial mode functions. Moreover, from an
observational perspective, the expansion has unique signatures depending on the
orientation of the oscillation due to a resonance effect between the mode
functions and the original spectrum. This effect opens the possibility to
extract informa- tion about both the frequency of the bispectrum as well as its
shape while considering only a limited number of modes. The resonance effect is
independent of the phase of the reconstructed bispectrum suggesting Fourier
mode extraction could be an efficient way to detect oscillatory bispectra in
the data.Comment: 17 pages, 12 figures. Matches published versio
An Evaluation of the effects of DC\u27s voucher program on public school achievement and racial integration after one year
This study evaluates the initial effect Washington D.C.\u27s Opportunity Scholarship Program (OPS) on the academic performance of public schools and its effects on the opportunities District students have to attend integrated schools. OPS is a federally sponsored school voucher program that provides vouchers worth up to $7,500 for an estimated 1,800 to 2,000 students in the District of Columbia. Students can use the scholarships to pay tuition at participating private schools in the District. The pilot program is designed to last for 5 years
Collisional Aspects of Bosonic and Fermionic Dipoles in Quasi-Two-Dimensional Confining Geometries
Fundamental aspects of ultracold collisions between identical bosonic or
fermionic dipoles are studied under quasi-two-dimensional (Q2D) confinement. In
the strongly dipolar regime, bosonic and fermion species are found to share
important collisional properties as a result of the confining geometry, which
suppresses the inelastic rates irrespective of the quantum statistics obeyed. A
potential negative is that the confinement causes dipole-dipole resonances to
be extremely narrow, which could make it difficult to explore Q2D dipolar gases
with tunable interactions. Such properties are shown to be universal, and a
simple WKB model reproduces most of our numerical results. In order to shed
light on the many-body behavior of dipolar gases in Q2D we have analyzed the
scattering amplitude and developed an energy-analytic form of the
pseudopotentials for dipoles. For specific values of the dipolar interaction,
the pseudopotential coefficient can be tuned to arbitrarily large values,
indicating the possibility of realizing Q2D dipolar gases with tunable
interactions.Comment: 4.1 pages, 3 figure
The Effect of Milwaukee’s Parental Choice Program on Student Achievement in Milwaukee Public Schools
This paper examines evidence on the “systemic effects” of expanding school choice in Milwaukee, Wisconsin. Milwaukee is home to one of the nation’s largest and longest-running school choice programs. If there are systemic effects from expanding school choice we should be able to see them in Milwaukee. This paper also introduces a novel method for analyzing systemic effects. Taking full advantage of student-level data, we develop a new measure of those effects based on the extent of voucher options that each student has each year. The idea behind this measure is that school systems face greater competitive pressure to serve students well when students have more options to leave. This type of measure might be useful for future analyses of systemic effects. Using this new approach, we find that students fare better academically when they have more options from Milwaukee’s voucher program. The effects are modest in magnitude, but they are robust to multiple specifications of the model
Classical {\it vs.}\ Landau-Ginzburg Geometry of Compactification
We consider superstring compactifications where both the classical
description, in terms of a Calabi-Yau manifold, and also the quantum theory is
known in terms of a Landau-Ginzburg orbifold model. In particular, we study
(smooth) Calabi-Yau examples in which there are obstructions to parametrizing
all of the complex structure cohomology by polynomial deformations thus
requiring the analysis based on exact and spectral sequences. General arguments
ensure that the Landau-Ginzburg chiral ring copes with such a situation by
having a nontrivial contribution from twisted sectors. Beyond the expected
final agreement between the mathematical and physical approaches, we find a
direct correspondence between the analysis of each, thus giving a more complete
mathematical understanding of twisted sectors. Furthermore, this approach shows
that physical reasoning based upon spectral flow arguments for determining the
spectrum of Landau-Ginzburg orbifold models finds direct mathematical
justification in Koszul complex calculations and also that careful point- field
analysis continues to recover suprisingly much of the stringy features.Comment: 14
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