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Energy-changing electron-hydrogen atom collisions are crucial to regulating the energy balance in astrophysical and laboratory plasmas and are relevant to the formation of stellar atmospheres, recombination in H II clouds, primordial recombination, three-body recombination, and heating in ultracold and fusion plasmas. Computational modeling of electron-hydrogen collision has been attempted through quantum mechanical scattering state-to-state calculations of transitions involving low-lying energy levels in hydrogen (with principal quantum number n < 7) and at large principal quantum numbers using classical trajectory techniques. Analytical expressions are proposed that interpolate the current quantum mechanical and classical trajectory results for electron-hydrogen scattering in the entire range of energy levels for nearly the entire temperature range of interest in astrophysical environments. An asymptotic expression for the Born cross section is interpolated with a modified expression previously derived for electron-hydrogen scattering in the Rydberg regime using classical trajectory Monte Carlo simulations. The derived formula is compared to existing numerical data for transitions involving low principal quantum numbers, and the dependence of the deviations on temperature is discussed. [ABSTRACT FROM AUTHOR]

Collisions between electrically charged particles and neutral atoms are central for understanding the dynamics of neutral gases and plasmas in a variety of physical situations of terrestrial and astronomical interest. Specifically, redistribution of angular momentum states within the degenerate shell of highly excited Rydberg atoms occurs efficiently in distant collisions with ions. This process is crucial in establishing the validity of the local thermal equilibrium assumption and may also play a role in determining a precise ionization fraction in primordial recombination. We provide an accurate expression for the non-perturbative rate coefficient of collisions between protons and H(nl) ending in a final state H(nl'), with n being the principal quantum number and l, l' the initial and final angular momentum quantum numbers, respectively. The validity of this result is confirmed by results of classical trajectory Monte Carlo simulations. Previous results, obtained by Pengelly and Seaton only for dipole-allowed transitions l ͛ l ± 1, overestimate the l-changing collisional rate coefficients approximately by a factor of six, and the physical origin of this overestimation is discussed. [ABSTRACT FROM AUTHOR]

We describe an experimental setup designed to produce ultracold trapped gas clouds of fermionic 6Li and bosonic 87Rb. This combination of alkali metals has the potential to reach deeper Fermi degeneracy with respect to other mixtures since it allows for improved heat capacity matching which optimizes sympathetic cooling efficiency. Atomic beams of the two species are independently produced and then decelerated by Zeeman slowers. The slowed atoms are collected into a magneto-optical trap and then transferred into a quadrupole magnetic trap. An ultracold Fermi gas with temperature in the 10−3 T F range should be attainable through selective confinement of the two species via a properly detuned laser beam focused in the center of the magnetic trap. [ABSTRACT FROM AUTHOR]

In recent years, a fluid dynamics phenomenon has been observed that shows interesting analogies with several quantum mechanical ones. Under specific experimental conditions, a liquid droplet released on a vibrating liquid persists in jumping, forming a localized wave-particle, and its behaviour resembles that of a de Broglie wave-particle. In this paper we discuss a simplified model for this phenomenon and the results of numerical fluid dynamics simulations implemented on the basis of the model. In spite of the relevant simplifying assumptions of our approach, we observe that a wave-droplet coupling is obtained and the droplet travels at nearly constant velocity, as it is observed in experiments. This suggests that the model describes the basic features of the phenomenon well, and that the simulation could be used to introduce undergraduate students to the study of quantum mechanics. [ABSTRACT FROM AUTHOR]