23,669 research outputs found
Distribution of Spectral Characteristics and the Cosmological Evolution of GRBs
We investigate the cosmological evolution of GRBs, using the total gamma ray
fluence as a measure of the burst strength. This involves an understanding of
the distributions of the spectral parameters of GRBs as well as the total
fluence distribution - both of which are subject to detector selection effects.
We present new non-parametric statistical techniques to account for these
effects, and use these methods to estimate the true distribution of the peak of
the nu F_nu spectrum, E_p, from the raw distribution. The distributions are
obtained from four channel data and therefore are rough estimates. Here, we
emphasize the methods and present qualitative results. Given its spectral
parameters, we then calculate the total fluence for each burst, and compute its
cumulative and differential distributions. We use these distributions to
estimate the cosmological rate evolution of GRBs, for three cosmological
models. Our two main conclusions are the following: 1) Given our estimates of
the spectral parameters, we find that there may exist a significant population
of high E_p bursts that are not detected by BATSE, 2) We find a GRB co-moving
rate density quite different from that of other extragalactic objects; in
particular, it is different from the recently determined star formation rate.Comment: 20 pages, including 10 postscript figures. Submitted to Ap
Implementation of the Quantum Fourier Transform
The quantum Fourier transform (QFT) has been implemented on a three bit
nuclear magnetic resonance (NMR) quantum computer, providing a first step
towards the realization of Shor's factoring and other quantum algorithms.
Implementation of the QFT is presented with fidelity measures, and state
tomography. Experimentally realizing the QFT is a clear demonstration of NMR's
ability to control quantum systems.Comment: 6 pages, 2 figure
Carrier dynamics in ion-implanted GaAs studied by simulation and observation of terahertz emission
We have studied terahertz (THz) emission from arsenic-ion implanted GaAs both
experimentally and using a three-dimensional carrier dynamics simulation. A
uniform density of vacancies was formed over the optical absorption depth of
bulk GaAs samples by performing multi-energy implantations of arsenic ions (1
and 2.4MeV) and subsequent thermal annealing. In a series of THz emission
experiments the frequency of peak THz power was found to increase significantly
from 1.4 to 2.2THz when the ion implantation dose was increased from 10^13 to
10^16 cm-3. We used a semi-classical Monte-Carlo simulation of ultra-fast
carrier dynamics to reproduce and explain these results. The effect of the
ion-induced damage was included in the simulation by considering carrier
scattering at neutral and charged impurities, as well as carrier trapping at
defect sites. Higher vacancy concentrations and shorter carrier trapping times
both contributed to shorter simulated THz pulses, the latter being more
important over experimentally realistic parameter ranges.Comment: 6 pages, 7 figure
Count Me In: The dimensions of social inclusion through culture and sport
This study was set up to examine claims made for the ability of cultural projects to promote social inclusion (cultural projects are here taken to include those incorporating sport, the arts, media, heritage and outdoor adventure). This was to be achieved primarily by collecting evidence from a sample of 14 projects selected from some 200 that had volunteered their services. The report to the government’s Social Exclusion Unit (SEU) from the Policy Action Team (PAT10) (1999)2 noted the potential. In his foreword, Chris Smith (then Secretary of State for the Department for Culture Media and Sport (DCMS)) wrote: “… art and sport can not only make a valuable contribution to delivering key outcomes of lower long term unemployment, less crime, better health and better qualifications, but can also help to develop the individual pride, community spirit and capacity for responsibility that enable communities to run regeneration programmes themselves”. Similar statements have followed from other politicians, particularly in the recent Commons debate on sport and social exclusion (22/11/01), and again in the public health debate (13/12/01). However, the PAT 10 report also came to the same conclusion as previous commentators (e.g. Glyptis, 19893; Allison & Coalter, 19964; Long & Sanderson, 19985) that there is little ‘hard’ evidence of the social benefits that accrue
Count Me In: The Dimensions of social inclusion through Culture, Media & Sport (Executive Summary)
This study was set up to examine claims made for the ability of cultural projects to promote social inclusion (cultural projects are here taken to include those incorporating sport, the arts, media, heritage and outdoor adventure). This was to be achieved primarily by collecting evidence from a sample of 14 projects selected from some 200 that had volunteered their services. The report to the government’s Social Exclusion Unit (SEU) from the Policy Action Team (PAT10) (1999) noted the potential. In his foreword, Chris Smith (then Secretary of State for the Department for Culture Media and Sport (DCMS)) wrote: “… art and sport can not only make a valuable contribution to delivering key outcomes of lower long term unemployment, less crime, better health and better qualifications, but can also help to develop the individual pride, community spirit and capacity for responsibility that enable communities to run regeneration programmes themselves”. Similar statements have followed from other politicians, particularly in the recent Commons debate on sport and social exclusion (22/11/01), and again in the public health debate (13/12/01). However, the PAT 10 report also came to the same conclusion as previous commentators (e.g. Glyptis, 19893; Allison & Coalter, 19964; Long & Sanderson, 1998) that there is little ‘hard’ evidence of the social benefits that accrue
Charge trapping in polymer transistors probed by terahertz spectroscopy and scanning probe potentiometry
Terahertz time-domain spectroscopy and scanning probe potentiometry were used
to investigate charge trapping in polymer field-effect transistors fabricated
on a silicon gate. The hole density in the transistor channel was determined
from the reduction in the transmitted terahertz radiation under an applied gate
voltage. Prolonged device operation creates an exponential decay in the
differential terahertz transmission, compatible with an increase in the density
of trapped holes in the polymer channel. Taken in combination with scanning
probe potentionmetry measurements, these results indicate that device
degradation is largely a consequence of hole trapping, rather than of changes
to the mobility of free holes in the polymer.Comment: 4 pages, 3 figure
- …