Radiative polarization of electrons in a strong laser wave

We reanalyze the problem of radiative polarization of electrons brought into collision with a circularly polarized strong plane wave. We present an independent analytical verification of formulae for the cross section given by D.\,Yu. Ivanov et al [Eur.\ Phys.\ J. C \textbf{36}, 127 (2004)]. By choosing the exact electron's helicity as the spin quantum number we show that the self-polarization effect exists only for the moderately relativistic electrons with energy $\gamma = E/mc^2 \lesssim 10$ and only for a non-head-on collision geometry. In these conditions polarization degree may achieve the values up to 65%, but the effective polarization time is found to be larger than 1\,s even for a high power optical or infrared laser with intensity parameter $\xi = |{\bf E}| m c^2/E_c \hbar \omega \sim 0.1$ ($E_c = m^2 c^3/e \hbar$). This makes such a polarization practically unrealizable. We also compare these results with the ones of some papers where the high degree of polarization was predicted for ultrarelativistic case. We argue that this apparent contradiction arises due to the different choice of the spin quantum numbers. In particular, the quantum numbers which provide the high polarization degree represent neither helicity nor transverse polarization, that makes the use of them inconvenient in practice.Comment: minor changes compared to v3; to appear in PR

Goodbye to Projects? ¿ A livelihoods-grounded audit of the Training for Environmental and Agricultural Management (TEAM) project in Lesotho.

Approaches to projects and development have undergone considerable change in the last decade with significant policy shifts on governance, gender, poverty eradication, and environmental issues. Most recently this has led to the adoption and promotion of the sustainable livelihood (SL) approach. The adoption of the SL approach presents challenges to development interventions including: the future of projects and programmes, and sector wide approaches (SWAPs) and direct budgetary support.This paper `A livelihoods-grounded audit of the `Training for Environmental and Agricultural Management (TEAM) project in Lesotho¿ is the eleventh in the series of project working papers.Department for International Developmen

Ripples and Shear Bands in Plowed Granular Media

Monodisperse packings of dry, air-fluidized granular media typically exist between volume fractions from $\Phi$= 0.585 to 0.64. We demonstrate that the dynamics of granular drag are sensitive to volume fraction $\Phi$ and their exists a transition in the drag force and material deformation from smooth to oscillatory at a critical volume fraction $\Phi_{c}=0.605$. By dragging a submerged steel plate (3.81 cm width, 6.98 cm depth) through $300 \mu m$ glass beads prepared at volume fractions between 0.585 to 0.635 we find that below $\Phi_{c}$ the media deformation is smooth and non-localized while above $\Phi_{c}$ media fails along distinct shear bands. At high $\Phi$ the generation of these shear bands is periodic resulting in the ripples on the surface. Work funded by The Burroughs Wellcome Fund and the Army Research Lab MAST CT

A Terradynamics of Legged Locomotion on Granular Media

The theories of aero- and hydrodynamics predict animal movement and device design in air and water through the computation of lift, drag, and thrust forces. Although models of terrestrial legged locomotion have focused on interactions with solid ground, many animals move on substrates that flow in response to intrusion. However, locomotor-ground interaction models on such flowable ground are often unavailable. We developed a force model for arbitrarily-shaped legs and bodies moving freely in granular media, and used this "terradynamics" to predict a small legged robot's locomotion on granular media using various leg shapes and stride frequencies. Our study reveals a complex but generic dependence of stresses in granular media on intruder depth, orientation, and movement direction and gives insight into the effects of leg morphology and kinematics on movement