29,308 research outputs found

    Sub-femtosecond electron bunches created by direct laser acceleration in a laser wakefield accelerator with ionization injection

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    In this work, we will show through three-dimensional particle-in-cell simulations that direct laser acceleration in laser a wakefield accelerator can generate sub-femtosecond electron bunches. Two simulations were done with two laser pulse durations, such that the shortest laser pulse occupies only a fraction of the first bubble, whereas the longer pulse fills the entire first bubble. In the latter case, as the trapped electrons moved forward and interacted with the high intensity region of the laser pulse, micro-bunching occurred naturally, producing 0.5 fs electron bunches. This is not observed in the short pulse simulation.Comment: AAC 201

    Barriers to accessing psychological treatment for medium to high risk male young offenders

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    Within the young offender population, rates of personality disorder and mood disorders are considerably higher than both the general and adult offender population. Despite this high level of need and high risk of harm, psychological services within prisons are widely underutilized. Little is known about the barriers to accessing treatment for young offenders. This study investigated barriers to accessing psychological treatment for male young offenders detained in a UK prison. There were 128 participants, aged 18–21. A cross-sectional design compared self-reported barriers and psychological distress for Black and Minority Ethnic (BME) and White young offenders not accessing treatment, as well as those who were. A preference for self-reliance, a lack of trust in the prison system, lengthy waiting times and a general reluctance to talk about emotions were the most commonly cited barriers. BME young offenders not engaged in treatment reported significantly more barriers to accessing treatment than BME young offenders who were engaged in treatment, but both BME groups had equal levels of psychological distress. There was no significant difference between BME and White young offenders in the number of barriers reported, including stigma barriers. Future research should evaluate interventions to increase access for this marginalised population

    Distributed lag models for hydrological data

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    The distributed lag model (DLM), used most prominently in air pollution studies, finds application wherever the effect of a covariate is delayed and distributed through time. We explore the use of modified formulations of DLMs to provide flexible varying-coeficient models with smoothness constraints, applicable in any setting in which lagged covariates are regressed on a time-dependent response. The models are applied to simulated flow and rainfall data and to flow data from a Scottish mountain river, with particular emphasis on approximating the relationship between environmental covariates and flow regimes in order to detect the influence of unobserved processes. It was found that under certain rainfall conditions some of the variability in the influence of rainfall on flow arises through a complex interaction between antecedent ground wetness and the time-delay in rainfall. The models are able to identify subtle changes in rainfall response, particularly in the location of peak influence in the lag structure and offer a computationally attractive approach for fitting DLMs

    Contrasts between Equilibrium and Non-equilibrium Steady States: Computer Aided Discoveries in Simple Lattice Gases

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    A century ago, the foundations of equilibrium statistical mechanics were laid. For a system in equilibrium with a thermal bath, much is understood through the Boltzmann factor, exp{-H[C]/kT}, for the probability of finding the system in any microscopic configuration C. In contrast, apart from some special cases, little is known about the corresponding probabilities, if the same system is in contact with more than one reservoir of energy, so that, even in stationary states, there is a constant energy flux through our system. These non-equilibrium steady states display many surprising properties. In particular, even the simplest generalization of the Ising model offers a wealth of unexpected phenomena. Mostly discovered through Monte Carlo simulations, some of the novel properties are understood while many remain unexplained. A brief review and some recent results will be presented, highlighting the sharp contrasts between the equilibrium Ising system and this non-equilibrium counterpart.Comment: 9 pages, 3 figure
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