11,716 research outputs found
Enhancement of entanglement in one-dimensional disordered systems
The pairwise quantum entanglement of sites in disordered electronic
one-dimensional systems (rings) is studied. We focus on the effect of diagonal
and off diagonal disorder on the concurrence between electrons on
neighbor and non neighbor sites as a function of band filling. In the
case of diagonal disorder, increasing the degree of disorder leads to a
decrease of the concurrence with respect to the ordered case. However,
off-diagonal disorder produces a surprisingly strong enhancement of
entanglement. This remarkable effect occurs near half filling, where the
concurrence becomes up to 15% larger than in the ordered system.Comment: 21 pages, 9 figure
Collective Social Capital Within a Performance-Based Management System
Local education agencies utilizing performance-based management systems as a means to improve educator effectiveness and student performance is becoming more prevalent within the United States. High-need schools are implementing these systems and endeavor to create an environment that promotes a professional learning community that improves educator quality and student achievement. This study seeks to measure the level of collective social capital generated by the implementation of one such management system, Rewarding Excellence in Instruction and Leadership, through the use of a sociological case study. Through the use of document analysis and interviews, the degree of collective social capital fostered will be sought to better understand the potential for impacting educator effectiveness
Spectral broadening of frequency combs via pulse apodization prior to nonlinear propagation
This thesis focuses on specific methods for spectrally broadening large repetition rate frequency combs using the idea that tailoring the shape of the seed pulse prior to nonlinear propagation will result in a spectrally flatter comb. A spectrally flat comb is desired for applications in optical communications, arbitrary waveform generation, and microwave photonic filtering. Three experimental setups using Fourier transform pulse shapers, Dispersion Decreasing Fiber (DDF) or Highly Nonlinear Fiber (HNLF) as the nonlinear propagation media were performed. Simulations employing the Split Step Fourier Method to solve the Nonlinear Schrödinger Equation were performed to analyze the experimental results. The first experiments employed DDF to produce a compressed pulse via Adiabatic Soliton Compression. This pulse was launched into the second stage and HNLF broadened the comb spectrum via Self Phase Modulation. A promising 130nm broadened comb spectrum was returned. The next experiments showed that, by apodizing the pulse produced by the optoelectronic frequency comb generator prior to propagation in HNLF, a flatter broadened comb spectrum was returned. These results were extended to a two-stage setup. The setup used two stages of HNLF. Sech apodization in the first stage and parabolic apodization in the second stage led to promising simulation results. With the insight gained by the simulations, experiments were performed and a flat broadened frequency comb led to applications in RF photonic filtering. An RF photonic phase filter was implemented with the comb generated as the source, and pulse compression experiments were performed
MOCCA-SURVEY database I. Accreting white dwarf binary systems in globular clusters -- IV. cataclysmic variables -- properties of bright and faint populations
We investigate here populations of cataclysmic variables (CVs) in a set of
288 globular cluster (GC) models evolved with the MOCCA code. This is by far
the largest sample of GC models ever analysed with respect to CVs. Contrary to
what has been argued for a long time, we found that dynamical destruction of
primordial CV progenitors is much stronger in GCs than dynamical formation of
CVs, and that dynamically formed CVs and CVs formed under no/weak influence of
dynamics have similar white dwarf mass distributions. In addition, we found
that, on average, the detectable CV population is predominantly composed of CVs
formed via typical common envelope phase (CEP) ( per cent), that
only per cent of all CVs in a GC is likely to be detectable, and
that core-collapsed models tend to have higher fractions of bright CVs than
non-core-collapsed ones. We also consistently show, for the first time, that
the properties of bright and faint CVs can be understood by means of the pre-CV
and CV formation rates, their properties at their formation times and cluster
half-mass relaxation times. Finally, we show that models following the initial
binary population proposed by Kroupa and set with low CEP efficiency better
reproduce the observed amount of CVs and CV candidates in NGC 6397, NGC 6752
and 47 Tuc. To progress with comparisons, the essential next step is to
properly characterize the candidates as CVs (e.g. by obtaining orbital periods
and mass ratios).Comment: 18 pages, 13 figures; accepted for publication in MNRA
Covariant Impulse Approximation for the study of the internal structure of composite particles
We present a brief review on the Impulse Approximation method to study
processes of scattering off composite particles. We first construct the model
in a non-relativistic fashion that enables us to extend the model to a
covariant Impulse Approximation, which is needed for the study of high momentum
transfer processes.Comment: 8 Page
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