5,481 research outputs found
On the phase diagram of the Higgs SU(2) model
The Higgs SU(2) model with fixed Higgs length is usually believed to have two
different phases at high gauge coupling (\beta), separated by a line of first
order transitions but not distinuguished by any typical symmetry associated
with a local order parameter, as first proved by Fradkin and Shenker. We show
that in regions of the parameter space where it is usually supposed to be a
first order phase transition only a smooth crossover is in fact present.Comment: 6 pages, 6 figures. Talk presented at The XXVI International
Symposium on Lattice Field Theory, July 14 - 19, 2008 - Williamsburg,
Virginia, US
Exciton-Exciton transitions involving strongly bound Frenkel excitons: an ab initio approach
In pump-probe spectroscopy, two laser pulses are employed to garner dynamical
information from the sample of interest. The pump initiates the optical process
by exciting a portion of the sample from the electronic ground state to an
accessible electronic excited state, an exciton. Thereafter, the probe
interacts with the already excited sample. The change in the absorbance after
pump provides information on transitions between the excited states and their
dynamics. In this work we study these exciton-exciton transitions by means of
an ab initio real time propagation scheme based on dynamical Berry phase
formulation. The results are then analyzed taking advantage of a Fermi-golden
rule approach formulated in the excitonic basis-set and in terms of the
symmetries of the excitonic states. Using bulk LiF and 2D hBN as two prototype
materials, we discuss the selection rules for transitions involving strongly
bound Frenkel excitons, for which the hydrogen model cannot be used
Classification and Statistical Trend Analysis in Detecting Glaucomatous Visual Field Progression
Aim. To evaluate the agreement between different methods in detection of glaucomatous visual field progression using two classification-based methods and four statistical approaches based on trend analysis. Methods. This is a retrospective and longitudinal study. Twenty Caucasian patients (mean age 73.8 \ub1 13.43 years) with open-Angle glaucoma were recruited in the study. Each visual field was assessed by Humphrey Field Analyzer, program SITA standard 30-2 or 24-2 (Carl Zeiss Meditec, Inc., Dublin, CA). Full threshold strategy was also accepted for baseline tests. Progression was analyzed by using Hodapp-Parrish-Anderson classification and the Advanced Glaucoma Intervention Study visual field defect score. For the statistical analysis, linear regression (r2) was calculated for mean deviation (MD), pattern standard deviation (PSD), and visual field index (VFI), and when it was significant, each series of visual field was considered progressive. We also used Progressor to look for a significant progression of each visual field series. The agreement between methods, based on statistical analysis and classification, was evaluated using a weighted kappa statistic. Results. Thirty-eight visual field series were analyzed. The mean follow-up time was 6.2 \ub1 1.53 years (mean \ub1 standard deviation). At baseline, the mean MD was-7.34 \ub1 7.18 dB; at the end of the follow-up, the mean MD was-9.25 \ub1 8.65 dB; this difference was statistically significant (p<0.001). The agreement to detect progression was fair between all methods based on statistical analysis and classification except for PSD r2. A substantial agreement ( = 0.698 \ub1 0.126) was found between MD r2 and VFI r2. With the use of all the statistical analysis, there was a better time-saving. Conclusions. The best agreement to detect progression was found between MD r2 and VFI r2. VFI r2 showed the best agreement with all the other methods. GPA2 can help ophthalmologists to detect glaucoma progression and to help in treatment decisions. PSD r2 was the worse method to detect progression
Quantum Machines
We discuss quantum information processing machines. We start with single
purpose machines that either redistribute quantum information or identify
quantum states. We then move on to machines that can perform a number of
functions, with the function they perform being determined by a program, which
is itself a quantum state. Examples of both deterministic and probabilistic
programmable machines are given, and we conclude with a discussion of the
utility of quantum programs.Comment: To appear in Contemporary Physic
Aqueye+: a new ultrafast single photon counter for optical high time resolution astrophysics
Aqueye+ is a new ultrafast optical single photon counter, based on single
photon avalanche photodiodes (SPAD) and a 4-fold split-pupil concept. It is a
completely revisited version of its predecessor, Aqueye, successfully mounted
at the 182 cm Copernicus telescope in Asiago. Here we will present the new
technological features implemented on Aqueye+, namely a state of the art timing
system, a dedicated and optimized optical train, a high sensitivity and high
frame rate field camera and remote control, which will give Aqueye plus much
superior performances with respect to its predecessor, unparalleled by any
other existing fast photometer. The instrument will host also an optical
vorticity module to achieve high performance astronomical coronography and a
real time acquisition of atmospheric seeing unit. The present paper describes
the instrument and its first performances.Comment: Proceedings of the SPIE, Volume 9504, id. 95040C 14 pp. (2015
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