Momentum-Transfer to and Elementary-Excitations of a Bose-Einstein Condensate by a Time-Dependent Optical Potential

We present results of calculations on Bose-Einstein condensed $^{87}$Rb atoms subjected to a moving standing-wave light-potential of the form $V_L(z,t) = V_0(t) \cos(q z-\omega t)$. We calculate the mean-field dynamics (the order paramter) of the condensate and determine the resulting condensate momentum in the $z$ direction, $P_z(q,\omega,V_0,t_p)$, where $V_0$ is the peak optical potential strength and $t_p$ is the pulse duration. Although the local density approximation for the Bogoliubov excitation spectral distribution is a good approximation for very low optical intensities, long pulse duration and sufficiently large values of the wavevector $q$ of the light-potential, for small $q$, short duration pulses, or for not-so-low intensities, the local density perturbative description of the excitation spectrum breaks down badly, as shown by our results.Comment: 8 pages, 7 figure

Gender streaming and prior achievement in high school science and mathematics

Girls choose advanced matriculation electives in science and mathematics almost as frequently as boys, in Israel, but are very much under-represented in physics and computer science, and over-represented in biology and chemistry. We test the hypothesis that these patterns stem from differences in mathematical ability. Administrative data on two half-cohorts of Israeli eighth-grade students in Hebrew-language schools links standardized test scores in mathematics, science, Hebrew and English to their subsequent choice of matriculation electives. It shows that the gendered choices they make remain largely intact after conditioning on prior test scores, indicating that these choices are not driven by differences in perceived mathematical ability, or by boys’ comparative advantage in mathematics. Moreover, girls who choose matriculation electives in physics and computer science score higher than boys, on average. Girls and boys react differently to early signals of mathematical and verbal ability; and girls are less adversely affected by socioeconomic disadvantage

Dynamics of condensation and evaporation: Effect of inter-drop spacing

When studying the condensation of vapor to liquid drops on solid hydrophobic surfaces the volume of drops V is found to increase linearly with time, $V\propto t$. Constant-contact-angle evaporation studies showed that drop volumes decrease according to $V\propto t^{3/2}$. Since both processes are diffusion limited, one would expect the same kinetics. Here, we demonstrate experimentally, theoretically and by finite-element simulations that the spacing between condensing or evaporating drops affects the growth. The volume of single, isolated drops changes according to $V\propto t^{3/2}$. For a dense array of drops each individual drop will grow or shrink linearly, $V\propto t$