Electrostatic waves and anomalous transport in the solar wind

In situ measurements of fluctuation spectra and particle distribution functions have now been carried out throughout interplanetary space. The link between these observations is established by theories of wave particle interaction. Linear instability analysis for the actual nonMaxwellian particle distribution functions and an examination of the velocity dependence of microscopic diffusion coefficients form the basis of such an investigation. It is described in more detail for the short wavelength, ion acoustic like turbulence which is found by linear instability analysis to correspond to the observed electrostatic fluctuations. Of the transport processes associated with these fluctuations, electron heat conduction and electron ion energy transfer are of particular importance for macroscopic solar wind expansion. These effects are studied with the aid of an anomalous transport theory. This theory (Dum, 1978 a,b) is based on the dominance of elastic scattering of electrons by fluctuations, similar to (enhanced) electron ion collisions. It has a much wider range of applicability than classical transport theory, which assumes dominance of Coulomb collisions for elastic and inelastic scattering

Bose-Einstein condensates with vortices in rotating traps

We investigate minimal energy solutions with vortices for an interacting Bose-Einstein condensate in a rotating trap. The atoms are strongly confined along the axis of rotation z, leading to an effective 2D situation in the x-y plane. We first use a simple numerical algorithm converging to local minima of energy. Inspired by the numerical results we present a variational Ansatz in the regime where the interaction energy per particle is stronger than the quantum of vibration in the harmonic trap in the x-y plane, the so-called Thomas-Fermi regime. This Ansatz allows an easy calculation of the energy of the vortices as function of the rotation frequency of the trap; it gives a physical understanding of the stabilisation of vortices by rotation of the trap and of the spatial arrangement of vortex cores. We also present analytical results concerning the possibility of detecting vortices by a time-of-flight measurement or by interference effects. In the final section we give numerical results for a 3D configuration.Comment: 15 pages, 16 figures, to be published in Eur. Phys. Jour. D; one reference update

BCS Theory for Trapped Ultracold Fermions

We develop an extension of the well-known BCS-theory to systems with trapped fermions. The theory fully includes the quantized energy levels in the trap. The key ingredient is to model the attractive interaction between two atoms by a pseudo-potential which leads to a well defined scattering problem and consequently a BCS-theory free of divergences. We present numerical results for the BCS critical temperature and the temperature dependence of the gap. They are used as a test of existing semi-classical approximations.Comment: 4 pages, 3 figures, submitted to PR

Dynamics of magnetosphere-ionosphere coupling including turbulent transport

A two dimensional two-fluid MHD model including anomalous resistivity was used to investigate the dynamics of magnetosphere-ionosphere coupling. When a field-aligned current is generated on auroral field lines, the disturbance propagates towards the ionosphere in the form of a kinetic Alfven wave. When the current exceeds a critical value, microscopic turbulence is produced, which modifies the propagation of the Alfven wave. This process is modeled by a nonlinear collision frequency, which increases with the excess of the drift velocity over the critical value. Turbulence leads to absorption and reflection of the Alfven wave, partially decoupling the generator from the ionosphere. The approach to a steady-state is strongly dependent on the presence or absence of the turbulence. The current is self-limiting, since a current in excess of critical causes a diffusion of the magnetic field perturbation and a reduction of current

Medieval Equine Medicine from Armenia

The Armenian medieval and early modern equine medicine has rarely been noticed or researched by veterinarians, historians of science, philologists, or medieval researchers. As Armenia represents both a geographical border and cultural corridor between Muslim East and Christian West, a consideration of its hippiatric texts and their integration into the general history of veterinary medicine can only lead to a deeper understanding of equine medicine from the medieval to the early modern period. They could also contribute toward tracing the paths of knowledge diffusion and transmission across political, linguistic, and religious-cultural boundaries in the time of the Crusades. The role of Armenian manuscripts bridging the traditions of equine medicine from the Muslim East and the Christian West is examined by revealing the complicated history of Armenian horse treatises that traveled the long way from Baghdad via Sis to Tbilisi

Evaporative cooling of an atomic beam

We present a theoretical analysis of the evaporative cooling of an atomic beam propagating in a magnetic guide. Cooling is provided by transverse evaporation. The atomic dynamics inside the guide is analyzed by solving the Boltzmann equation with two different approaches: an approximate analytical ansatz and a Monte-Carlo simulation. Within their domain of validity, these two methods are found to be in very good agreement with each other. They allow us to determine how the phase-space density and the flux of the beam vary along its direction of propagation. We find a significant increase for the phase-space density along the guide for realistic experimental parameters. By extrapolation, we estimate the length of the beam needed to reach quantum degeneracy.Comment: 13 pages, 7 figures, to be published in EPJ D, revised versio

Characterization and classification of soils of the Rivers State University Teaching and Research Farm, Port Harcourt, Southern Nigeria

This study was conducted to characterize and classify the soils of the Teaching and Research Farm, Rivers State University, Port Harcourt, covering 30 hectares of land area. A rigid grid soil survey method at a very detailed level (100 × 100) m² (1 ha) with two mapping units identified and delineated. Each of the mapping unit was represented by a soil profile described from the lowest end to the upper part of the profiles to avoid contamination. Soil samples were collected for laboratory analysis from the various horizons identified. The results obtained, indicated that the soils were of Inceptisols/ Cambisol order, Udepts at the suborder level, Eutrudepts Great group level and Typic Eutrudepts (subgroup level). Thus, the drainage, parent materials, climate (rainfall), and vegetation of the area along with the geologic material, formed from the sedimentary rocks that were weathered into coastal plain sands and buried under alluvium at various degrees at different locations in the study area, greatly affected the soils of Teaching and Research Farm, Rivers State University, Port Harcourt, which are primarily Inceptisols/ Cambisols