Photon statistics and dynamics of Fluorescence Resonance Energy Transfer

We report high time-resolution measurements of photon statistics from pairs of dye molecules coupled by fluorescence resonance energy transfer (FRET). In addition to quantum-optical photon antibunching, we observe photon bunching on a timescale of several nanoseconds. We show by numerical simulation that configuration fluctuations in the coupled fluorophore system could account for minor deviations of our data from predictions of basic Forster theory. With further characterization we believe that FRET photon statistics could provide a unique tool for studying DNA mechanics on timescales from 10^-9 to 10^-3 s.Comment: 4 pages, 4 figures, submitted to Physical Review Letter

Universality of residence-time distributions in non-adiabatic stochastic resonance

We present mathematically rigorous expressions for the residence-time and first-passage-time distributions of a periodically forced Brownian particle in a bistable potential. For a broad range of forcing frequencies and amplitudes, the distributions are close to periodically modulated exponential ones. Remarkably, the periodic modulations are governed by universal functions, depending on a single parameter related to the forcing period. The behaviour of the distributions and their moments is analysed, in particular in the low- and high-frequency limits.Comment: 8 pages, 1 figure New version includes distinction between first-passage-time and residence-time distribution

Relating the Cosmological Constant and Supersymmetry Breaking in Warped Compactifications of IIB String Theory

It has been suggested that the observed value of the cosmological constant is related to the supersymmetry breaking scale M_{susy} through the formula Lambda \sim M_p^4 (M_{susy}/M_p)^8. We point out that a similar relation naturally arises in the codimension two solutions of warped space-time varying compactifications of string theory in which non-isotropic stringy moduli induce a small but positive cosmological constant.Comment: 7 pages, LaTeX, references added and minor changes made, (v3) map between deSitter and global cosmic brane solutions clarified, supersymmetry breaking discussion improved and references adde

Bubbling solutions, entropy enhancement and the fuzzball proposal

In this short note we explain the main idea of the work done in arXiv:0804.4487[hep-th] and arXiv:0812.2942[hep-th]. We present a family of black hole microstates, the bubbling solutions. We then explain how supertubes placed in such backgrounds have their entropy enhanced by the presence of the background dipole charges. This indicates this could account for a large amount in the entropy of the three charge black hole.Comment: 2 pages, contribution to the Cargese 2008 proceedings: Theory and Particle Physics: the LHC perspective and beyon

Metastability in Interacting Nonlinear Stochastic Differential Equations II: Large-N Behaviour

We consider the dynamics of a periodic chain of N coupled overdamped particles under the influence of noise, in the limit of large N. Each particle is subjected to a bistable local potential, to a linear coupling with its nearest neighbours, and to an independent source of white noise. For strong coupling (of the order N^2), the system synchronises, in the sense that all oscillators assume almost the same position in their respective local potential most of the time. In a previous paper, we showed that the transition from strong to weak coupling involves a sequence of symmetry-breaking bifurcations of the system's stationary configurations, and analysed in particular the behaviour for coupling intensities slightly below the synchronisation threshold, for arbitrary N. Here we describe the behaviour for any positive coupling intensity \gamma of order N^2, provided the particle number N is sufficiently large (as a function of \gamma/N^2). In particular, we determine the transition time between synchronised states, as well as the shape of the "critical droplet", to leading order in 1/N. Our techniques involve the control of the exact number of periodic orbits of a near-integrable twist map, allowing us to give a detailed description of the system's potential landscape, in which the metastable behaviour is encoded

The GAINS Model for Greenhouse Gases - Version 1.0: Carbon Dioxide (CO2)

Many of the traditional air pollutants and greenhouse gases have common sources, offering a cost-effective potential for simultaneous improvements of traditional air pollution problems and climate change. A methodology has been developed to extend the RAINS integrated assessment model to explore synergies and trade-offs between the control of greenhouse gases and air pollution. With this extension, the GAINS (GHG-Air pollution INteraction and Synergies) model will allow the assessment of emission control costs for the six greenhouse gases covered under the Kyoto Protocol (CO2, CH4, N2O and the three F-gases) together with the emissions of air pollutants SO2, NOx, VOC, NH3 and PM. This report describes the first implementation (Version 1.0) of the model extension model to incorporate CO2 emissions. GAINS Version 1.0 assesses 230 options for reducing CO2 emissions from the various source categories, both through structural changes in the energy system (fuel substitution, energy efficiency improvements) and through end-of-pipe measures (e.g., carbon capture). GAINS quantifies for 43 countries/regions in Europe country-specific application potentials of the various options in the different sectors of the economy, and estimates the societal resource costs of these measures. Mitigation potentials are estimated in relation to an exogenous baseline projection that is considered to reflect current planning, and are derived from a comparison of scenario results for a range of carbon prices obtained from energy models. A critical element of the GAINS assessment refers to the assumptions on CO2 mitigation measures for which negative life cycle costs are calculated. There are a number of options for which the accumulated (and discounted over time) cost savings from reduced energy consumption outweigh their investments, even if private interest rates are used. If the construction of the baseline projection assumes a cost-effectiveness rationale, such measures would be autonomously adopted by the economic actors, even in the absence of any CO2 mitigation interest. In practice, however, it can be observed that various market imperfections impede the autonomous penetration. Due to the substantial CO2 mitigation potential that is associated with such negative cost options, projections of future CO2 emissions and even more of the available CO2 mitigation potentials are highly sensitive towards assumptions on their autonomous penetration rates occurring in the baseline projection. Assuming that all negative cost measures would form an integral part of the Energy Outlook developed in 2003 by the Directorate General for Energy and Transport of the European Commission that has been developed with a cost-minimizing energy model, CO2 emissions in Europe would approach 1990 levels in 2020, even in absence of any specific climate policy. Beyond that, GAINS estimates for 2020 an additional reduction potential of 20 percent. With full application of all mitigation measures contained in the GAINS database, the power sector could reduce its CO2 emissions by 550 Mt, the transport sector by 400 Mt, industry by 190 Mt, and the residential and commercial sector by 50 Mt below the baseline projection. Total costs of all these measures would amount to approximately 90 billion Euro/year

Risk factors for criminal recidivism - a prospective follow-up study in prisoners with substance abuse

Background: Substance use in general has been shown to predict criminal recidivism. The present study aimed to examine potential predictors of criminal recidivism, including substance-specific substance use patterns, in prisoners with substance use. Methods: A cohort of prisoners with substance use problems (N = 4,152) were assessed with the Addiction Severity Index (ASI) in the Swedish criminal justice system. Clients were followed for an average of 2.7 years. Criminal recidivism was defined as any return to the criminal justice system. Results: During follow-up, 69 percent (n = 2,862) returned to the criminal justice system. Recidivism was associated with amphetamine and heroin use, with an additive risk for injectors, and with polysubstance use. Also, recidivism was negatively associated with alcohol, other opioids than heroin/methadone and with hallucinogenic drugs, and positively associated with previous psychiatric in-patient treatment, violent behaviour, and with a shorter index sentence. Associations remained when controlling for type of crime. Conclusions: Even when controlling for type and severity of crime, and for psychiatric problems, risk of criminal relapse was increased by substance use variables, including amphetamine, heroin and polysubstance use, and an additional risk was shown for injection drug users. These findings have implications for the need for substance abuse treatment after release from prison

Stochastic resonance for nonequilibrium systems

Stochastic resonance (SR) is a prominent phenomenon in many natural and engineered noisy systems, whereby the response to a periodic forcing is greatly amplified when the intensity of the noise is tuned to within a specific range of values. We propose here a general mathematical framework based on large deviation theory and, specifically, on the theory of quasipotentials, for describing SR in noisy N -dimensional nonequilibrium systems possessing two metastable states and undergoing a periodically modulated forcing. The drift and the volatility fields of the equations of motion can be fairly general, and the competing attractors of the deterministic dynamics and the edge state living on the basin boundary can, in principle, feature chaotic dynamics. Similarly, the perturbation field of the forcing can be fairly general. Our approach is able to recover as special cases the classical results previously presented in the literature for systems obeying detailed balance and allows for expressing the parameters describing SR and the statistics of residence times in the two-state approximation in terms of the unperturbed drift field, the volatility field, and the perturbation field. We clarify which specific properties of the forcing are relevant for amplifying or suppressing SR in a system and classify forcings according to classes of equivalence. Our results indicate a route for a detailed understanding of SR in rather general systems

Beyond the Fokker-Planck equation: Pathwise control of noisy bistable systems

We introduce a new method, allowing to describe slowly time-dependent Langevin equations through the behaviour of individual paths. This approach yields considerably more information than the computation of the probability density. The main idea is to show that for sufficiently small noise intensity and slow time dependence, the vast majority of paths remain in small space-time sets, typically in the neighbourhood of potential wells. The size of these sets often has a power-law dependence on the small parameters, with universal exponents. The overall probability of exceptional paths is exponentially small, with an exponent also showing power-law behaviour. The results cover time spans up to the maximal Kramers time of the system. We apply our method to three phenomena characteristic for bistable systems: stochastic resonance, dynamical hysteresis and bifurcation delay, where it yields precise bounds on transition probabilities, and the distribution of hysteresis areas and first-exit times. We also discuss the effect of coloured noise.Comment: 37 pages, 11 figure