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

Solvent response to fluorine-atom reaction dynamics in liquid acetonitrile

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

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.

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

Momentum-Dependent Mean Field Based Upon the Dirac-Brueckner Approach for Nuclear Matter

A momentum-dependent mean field potential, suitable for application in the transport-model description of nucleus-nucleus collisions, is derived in a microscopic way. The derivation is based upon the Bonn meson-exchange model for the nucleon-nucleon interaction and the Dirac-Brueckner approach for nuclear matter. The properties of the microscopic mean field are examined and compared with phenomenological parametrizations which are commonly used in transport-model calculations.Comment: 15 pages text (RevTex) and 4 figures (postscript in a separate uuencoded file), UI-NTH-930

Effects of temperature and ammonia flow rate on the chemical vapour deposition growth of nitrogen-doped graphene

We doped graphene in situ during synthesis from methane and ammonia on copper in a low-pressure chemical vapour deposition system, and investigated the effect of the synthesis temperature and ammonia concentration on the growth. Raman and X-ray photoelectron spectroscopy was used to investigate the quality and nitrogen content of the graphene and demonstrated that decreasing the synthesis temperature and increasing the ammonia flow rate results in an increase in the concentration of nitrogen dopants up to ca. 2.1% overall. However, concurrent scanning electron microscopy studies demonstrate that decreasing both the growth temperature from 1000 to 900 1C and increasing the N/C precursor ratio from 1/50 to 1/10 significantly decreased the growth rate by a factor of six overall. Using scanning tunnelling microscopy we show that the nitrogen was incorporated mainly in substitutional configuration, while current imaging tunnelling spectroscopy showed that the effect of the nitrogen on the density of states was visible only over a few atom distances

Complex effects of temperature on mosquito immune function

Over the last 20 years, ecological immunology has provided much insight into how environmental factors shape host immunity and host–parasite interactions. Currently, the application of this thinking to the study of mosquito immunology has been limited. Mechanistic investigations are nearly always conducted under one set of conditions, yet vectors and parasites associate in a variable world. We highlight how environmental temperature shapes cellular and humoral immune responses (melanization, phagocytosis and transcription of immune genes) in the malaria vector, Anopheles stephensi. Nitric oxide synthase expression peaked at 30°C, cecropin expression showed no main effect of temperature and humoral melanization, and phagocytosis and defensin expression peaked around 18°C. Further, immune responses did not simply scale with temperature, but showed complex interactions between temperature, time and nature of immune challenge. Thus, immune patterns observed under one set of conditions provide little basis for predicting patterns under even marginally different conditions. These quantitative and qualitative effects of temperature have largely been overlooked in vector biology but have significant implications for extrapolating natural/transgenic resistance mechanisms from laboratory to field and for the efficacy of various vector control tools

Interview with Laura Fortunato, Winner of the 2011 Gabriel W. Lasker Prize

An international jury composed of Michael Crawford (University of Kansas, USA), Dennis O\u27Rourke (University of Utah, USA), and Stephen Shennan (University College London, UK) has awarded the Gabriel Ward Lasker Prize 2011 to Dr. Laura Fortunato for her articles entitled Reconstructing the History of Residence Strategies in Indo-European–Speaking Societies and Reconstructing the History of Marriage Strategies in Indo-European–Speaking Societies considered as the best contribution to the 83rd volume of Human Biology (2011). Laura Fortunato is an Omidyar Fellow at the Santa Fe Institute in Santa Fe, New Mexico. She received her Ph.D. in anthropology from University College London in 2009; her doctoral research focused on the evolution of kinship and marriage systems. In particular, she has investigated the evolution of marriage strategies, wealth transfers at marriage, residence strategies, and inheritance strategies. Laura\u27s current research activities apply conceptual and methodological tools developed in evolutionary biology to a diverse range of topics in anthropology, from matrilineal kinship organization to cultural evolution