Oscillations of dark solitons in trapped Bose-Einstein condensates

We consider a one-dimensional defocusing Gross--Pitaevskii equation with a parabolic potential. Dark solitons oscillate near the center of the potential trap and their amplitude decays due to radiative losses (sound emission). We develop a systematic asymptotic multi-scale expansion method in the limit when the potential trap is flat. The first-order approximation predicts a uniform frequency of oscillations for the dark soliton of arbitrary amplitude. The second-order approximation predicts the nonlinear growth rate of the oscillation amplitude, which results in decay of the dark soliton. The results are compared with the previous publications and numerical computations.Comment: 13 pages, 3 figure

Evolutionary Dynamics While Trapped in Resonance: A Keplerian Binary System Perturbed by Gravitational Radiation

The method of averaging is used to investigate the phenomenon of capture into resonance for a model that describes a Keplerian binary system influenced by radiation damping and external normally incident periodic gravitational radiation. The dynamical evolution of the binary orbit while trapped in resonance is elucidated using the second order partially averaged system. This method provides a theoretical framework that can be used to explain the main evolutionary dynamics of a physical system that has been trapped in resonance.Comment: REVTEX Style, Submitte

Energy harvesting from transverse galloping

Some elastic bluff bodies under the action of a fluid flow can experience transverse galloping and lose stability if the flow velocity exceeds a critical value. For flow velocities higher than this critical value, there is an energy transfer from the flow to the body and the body develops an oscillatory motion. Usually, it is considered as an undesirable effect for civil or marine structures but here we will show that if the vibration is substantial, it can be used to extract useful energy from the surrounding flow. This paper explores analytically the potential use of transverse galloping in order to obtain energy. To this end, transverse galloping is described by a one-degree-of-freedom model where fluid forces obey the quasi-steady hypothesis. The influence of cross-section geometry and mechanical properties in the energy conversion factor is investigated

Solvent response to fluorine-atom reaction dynamics in liquid acetonitrile

Solvent restructuring and vibrational cooling follow exothermic fluorine-atom reactions in acetonitrile.</p

Nonlinear Volatility of River Flux Fluctuations

We study the spectral properties of the magnitudes of river flux increments, the volatility. The volatility series exhibits (i) strong seasonal periodicity and (ii) strongly power-law correlations for time scales less than one year. We test the nonlinear properties of the river flux increment series by randomizing its Fourier phases and find that the surrogate volatility series (i) has almost no seasonal periodicity and (ii) is weakly correlated for time scales less than one year. We quantify the degree of nonlinearity by measuring (i) the amplitude of the power spectrum at the seasonal peak and (ii) the correlation power-law exponent of the volatility series.Comment: 5 revtex pages, 6 page

Ultra-short pulses in linear and nonlinear media

We consider the evolution of ultra-short optical pulses in linear and nonlinear media. For the linear case, we first show that the initial-boundary value problem for Maxwell's equations in which a pulse is injected into a quiescent medium at the left endpoint can be approximated by a linear wave equation which can then be further reduced to the linear short-pulse equation. A rigorous proof is given that the solution of the short pulse equation stays close to the solutions of the original wave equation over the time scales expected from the multiple scales derivation of the short pulse equation. For the nonlinear case we compare the predictions of the traditional nonlinear Schr\"odinger equation (NLSE) approximation which those of the short pulse equation (SPE). We show that both equations can be derived from Maxwell's equations using the renormalization group method, thus bringing out the contrasting scales. The numerical comparison of both equations to Maxwell's equations shows clearly that as the pulse length shortens, the NLSE approximation becomes steadily less accurate while the short pulse equation provides a better and better approximation

Nuclear medium modifications of the NN interaction via quasielastic (p⃗,p⃗′\vec p,\vec p ') and (p⃗,n⃗\vec{p},\vec{n}) scattering

Within the relativistic PWIA, spin observables have been recalculated for quasielastic ($\vec p,\vec p '$) and ($\vec p,\vec n$) reactions on a $^{40}$Ca target. The incident proton energy ranges from 135 to 300 MeV while the transferred momentum is kept fixed at 1.97 fm^{-1}. In the present calculations, new Horowitz-Love--Franey relativistic NN amplitudes have been generated in order to yield improved and more quantitative spin observable values than before. The sensitivities of the various spin observables to the NN interaction parameters, such as (1) the presence of the surrounding nuclear medium, (2) a pseudoscalar versus a pseudovector interaction term, and (3) exchange effects, point to spin observables which should preferably be measured at certain laboratory proton energies, in order to test current nuclear models. This study also shows that nuclear medium effects become more important at lower proton energies ($\leq$ 200 MeV). A comparison to the limited available data indicates that the relativistic parametrization of the NN scattering amplitudes in terms of only the five Fermi invariants (the SVPAT form) is questionable.Comment: 10 pages, 6 Postscript figures, uses psfig.sty and article.sty, submitted to Phys. Rev.

A "superstorm": When moral panic and new risk discourses converge in the media

This is an Author's Accepted Manuscript of an article published in Health, Risk and Society, 15(6), 681-698, 2013, copyright Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/13698575.2013.851180.There has been a proliferation of risk discourses in recent decades but studies of these have been polarised, drawing either on moral panic or new risk frameworks to analyse journalistic discourses. This article opens the theoretical possibility that the two may co-exist and converge in the same scare. I do this by bringing together more recent developments in moral panic thesis, with new risk theory and the concept of media logic. I then apply this theoretical approach to an empirical analysis of how and with what consequences moral panic and new risk type discourses converged in the editorials of four newspaper campaigns against GM food policy in Britain in the late 1990s. The article analyses 112 editorials published between January 1998 and December 2000, supplemented with news stories where these were needed for contextual clarity. This analysis shows that not only did this novel food generate intense media and public reactions; these developed in the absence of the type of concrete details journalists usually look for in risk stories. Media logic is important in understanding how journalists were able to engage and hence how a major scare could be constructed around convergent moral panic and new risk type discourses. The result was a media ‘superstorm’ of sustained coverage in which both types of discourse converged in highly emotive mutually reinforcing ways that resonated in a highly sensitised context. The consequence was acute anxiety, social volatility and the potential for the disruption of policy and social change

vHOG, a multispecies vertebrate ontology of homologous organs groups

Motivation: Most anatomical ontologies are species-specific, whereas a framework for comparative studies is needed. We describe the vertebrate Homologous Organs Groups ontology, vHOG, used to compare expression patterns between species