1,688 research outputs found
Direct Measurement of the Photon Statistics of a Triggered Single Photon Source
We studied intensity fluctuations of a single photon source relying on the
pulsed excitation of the fluorescence of a single molecule at room temperature.
We directly measured the Mandel parameter Q(T) over 4 orders of magnitude of
observation timescale T, by recording every photocount. On timescale of a few
excitation periods, subpoissonian statistics is clearly observed and the
probablility of two-photons events is 10 times smaller than Poissonian pulses.
On longer times, blinking in the fluorescence, due to the molecular triplet
state, produces an excess of noise.Comment: 4 pages, 3 figures, 1 table submitted to Physical Review Letter
Full counting statistics and phase diagram of a dissipative Rydberg gas
Ultra-cold gases excited to strongly interacting Rydberg states are a
promising system for quantum simulations of many-body systems. For off-resonant
excitation of such systems in the dissipative regime, highly correlated
many-body states exhibiting, among other characteristics, intermittency and
multi-modal counting distributions are expected to be created. So far,
experiments with Rydberg atoms have been carried out in the resonant,
non-dissipative regime. Here we realize a dissipative gas of rubidium Rydberg
atoms and measure its full counting statistics for both resonant and
off-resonant excitation. We find strongly bimodal counting distributions in the
off-resonant regime that are compatible with intermittency due to the
coexistence of dynamical phases. Moreover, we measure the phase diagram of the
system and find good agreement with recent theoretical predictions. Our results
pave the way towards detailed studies of many-body effects in Rydberg gases.Comment: 12 pages, 5 figure
Interaction between Experiments, Analytical Theories, and Computation
This article is a summary of a talk given at the ACS Centennial Symposium in Physical Chemistry in Philadelphia in 2008, updated with more recent studies. In keeping with the spirit of the symposium, the article is in part historical and in part a review of the newer research. The talk was divided into two parts, the first on different isotopic effects in chemistry, including the mass-independent fractionation phenomenon in gases and H/D isotope effects in enzymes, and the second on two different surface phenomena, âThe Bad and the Goodâ. The âBadâ is the fluorescence intermittency of semiconductor nanoparticles, (quantum dots, QD) being an unwanted feature in sensor applications. The âGoodâ is the âon waterâ catalysis of organic reactions, a mode of green chemistry. The possible role of Auger-type mechanisms in trapping and detrapping in the QD and hence in the formation of dark and light periods is explored. Some suggestions are made on the novel âbreakpointâ phenomenon discovered for H transfer in a thermophilic enzyme
Singularities in cascade models of the Euler equation
The formation of singularities in the three-dimensional Euler equation is
investigated. This is done by restricting the number of Fourier modes to a set
which allows only for local interactions in wave number space. Starting from an
initial large-scale energy distribution, the energy rushes towards smaller
scales, forming a universal front independent of initial conditions. The front
results in a singularity of the vorticity in finite time, and has scaling form
as function of the time difference from the singularity. Using a simplified
model, we compute the values of the exponents and the shape of the front
analytically. The results are in good agreement with numerical simulations.Comment: 33 pages (REVTeX) including eps-figures, Stylefile here.st
Hadron Multiplicities
We review results on hadron multiplicities in high energy particle
collisions. Both theory and experiment are discussed. The general procedures
used to describe particle multiplicity in Quantum Chromodynamics (QCD) are
summarized. The QCD equations for the generating functions of the multiplicity
distributions are presented both for fixed and running coupling strengths. The
mean multiplicities of gluon and quark jets, their ratio, higher moments, and
the slopes of multiplicities as a function of energy scale, are among the main
global features of multiplicity for which QCD results exist. Recent data from
high energy e+e- experiments, including results for separated quark and gluon
jets, allow rather direct tests of these results. The theoretical predictions
are generally quite successful when confronted with data. Jet and subjet
multiplicities are described. Multiplicity in limited regions of phase space is
discussed in the context of intermittency and fractality. The problem of
singularities in the generating functions is formulated. Some special features
of average multiplicities in heavy quark jets are described.Comment: 140 pages, 33 figures, version for Physics Report
Optimization Techniques for Modern Power Systems Planning, Operation and Control
Recent developments in computing, communication and improvements in optimization techniques have piqued interest in improving the current operational practices and in addressing the challenges of future power grids. This dissertation leverages these new developments for improved quasi-static analysis of power systems for applications in power system planning, operation and control.
The premise of much of the work presented in this dissertation centers around development of better mathematical modeling for optimization problems which are then used to solve current and future challenges of power grid. To this end, the models developed in this research work contributes to the area of renewable integration, demand response, power grid resilience and constrained contiguous and non-contiguous partitioning of power networks.
The emphasis of this dissertation is on finding solutions to system operator level problems in real-time. For instance, multi-period mixed integer linear programming problem for applications in demand response schemes involving more than million variables are solved to optimality in less than 20 seconds of computation time through tighter formulation. A balanced, constrained, contiguous partitioning scheme capable of partitioning 20,000 bus power system in under one minute is developed for use in time sensitive application area such as controlled islanding
A Dynamic Market Mechanism for Integration of Renewables and Demand Response
The most formidable challenge in assembling a Smart Grid is the integration of a high penetration of renewables. Demand Response, a largely promising concept, is increasingly discussed as a means to cope with the intermittent and uncertain renewables. In this paper, we propose a dynamic market mech- anism that reaches the market equilibrium through continuous negotiations between key market players. In addition to incor- porating renewables, this market mechanism also incorporates a quantitative taxonomy of demand response devices, based on the inherent magnitude, run-time, and integral constraints of demands. The dynamic market mechanism is evaluated on an IEEE 118 Bus system, a high fidelity simulation model of the Midwestern United States power grid. The results show how the proposed mechanism can be utilized to determine combinations of demand response devices in the presence of intermittent and uncertain renewables with varying levels of penetration so as to result in a desired level of Social Welfare.This work was supported in part by the National Science Foundation grants ECCS-1135815 and EFRI-1441301
High latency unmanned ground vehicle teleoperation enhancement by presentation of estimated future through video transformation
Long-distance, high latency teleoperation tasks are difficult, highly stressful for teleoperators, and prone to over-corrections, which can lead to loss of control. At higher latencies, or when teleoperating at higher vehicle speed, the situation becomes progressively worse. To explore potential solutions, this research work investigates two 2D visual feedback-based assistive interfaces (sliding-only and sliding-and-zooming windows) that apply simple but effective video transformations to enhance teleoperation. A teleoperation simulator that can replicate teleoperation scenarios affected by high and adjustable latency has been developed to explore the effectiveness of the proposed assistive interfaces. Three image comparison metrics have been used to fine-tune and optimise the proposed interfaces. An operator survey was conducted to evaluate and compare performance with and without the assistance. The survey has shown that a 900ms latency increases task completion time by up to 205% for an on-road and 147 % for an off-road driving track. Further, the overcorrection-induced oscillations increase by up to 718 % with this level of latency. The survey has shown the sliding-only video transformation reduces the task completion time by up to 25.53 %, and the sliding-and-zooming transformation reduces the task completion time by up to 21.82 %. The sliding-only interface reduces the oscillation count by up to 66.28 %, and the sliding-and-zooming interface reduces it by up to 75.58 %. The qualitative feedback from the participants also shows that both types of assistive interfaces offer better visual situational awareness, comfort, and controllability, and significantly reduce the impact of latency and intermittency on the teleoperation task
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