139 research outputs found
Interactions of Rydberg atoms in MOTs.
No full textWe have studied the development of gases of ultra-cold Rydberg atoms in Magneto Optic Traps, and discovered that such gases exhibit a range of density-dependent phenomena. In particular, we have found that at the densities of ∼ 107 cm-3 the Rydberg atoms spontaneously evolve into long-lived high angular momentum states. These states slowly decay due to microwave background radiation over tens of milliseconds. We have numerically simulated the effects leading to such behavior, and investigated numerically the l- and n-mixing collisions of Rydberg atoms with electrons in the range of 10 meV. These calculations show that the l- and n-mixing cross-sections follow the n5 scaling law, expected from simple Stark map considerations, but also depend on the velocities of the colliding electrons, reflecting the adiabaticity of the atom-electron interactions. We have developed a novel technique of measuring the electric fields inside plasmas by using Rydberg excitation spectroscopy of embedded atoms, based on the disappearance of regions of zero oscillator strength in the presence of such fields. We have applied this technique to study the evolution of ultra-cold non-neutral plasmas excited from the MOT, and have found that it expands over 1 mus. We have simulated such an expansion by considering only Coulomb repulsion between the constituent ions, and have found that such a model is consistent with the experimental observations.PhDAtomic physicsOpticsPlasma physicsPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123772/2/3106000.pd
Global health and foreign policy.
No full textHealth has long been intertwined with the foreign policies of states. In recent years, however, global health issues have risen to the highest levels of international politics and have become accepted as legitimate issues in foreign policy. This elevated political priority is in many ways a welcome development for proponents of global health, and it has resulted in increased funding for and attention to select global health issues. However, there has been less examination of the tensions that characterize the relationship between global health and foreign policy and of the potential effects of linking global health efforts with the foreign-policy interests of states. In this paper, the authors review the relationship between global health and foreign policy by examining the roles of health across 4 major components of foreign policy: aid, trade, diplomacy, and national security. For each of these aspects of foreign policy, the authors review current and historical issues and discuss how foreign-policy interests have aided or impeded global health efforts. The increasing relevance of global health to foreign policy holds both opportunities and dangers for global efforts to improve health
Physics-Informed Extreme Theory of Functional Connections Applied to Optimal Orbit Transfer
No full textA novel and accurate physics-informed neural network method for solving differential equations, called the Extreme Theory of Functional Connections (or XTFC), is employed to solve optimal control problems. The proposed method is utilized in solving the system of differential equations resulting from the indirect method formulation of the optimal control problem, derived from the Hamiltonian function and applying the Pontryagin Maximum/Minimum Principle (PMP). The system of differential equations makes up the first order necessary conditions of the states and costates which in general produces a boundary value problem (BVPs) that is solved via X-TFC. According to the Theory of Functional Connections, the latent solutions are approximated with particular expansions, called constrained expressions. A constrained expression is a functional that both always satisfies the specified constraints and has a free-function that does not affect the specified constraints. In the X-TFC formulation, the free-function is a single-layer
NN, or more precisely, an Extreme Learning Machine (ELM). Using ELMs, the unknown coefficients appear linearly and therefore, a least-square approach (for linear problems) or an iterative least-square approach (for non-linear problems) is used to compute the unknowns by minimizing the residual of the system of differential equations. In this work, the approach is validated by solving the Feldbaum problem and optimal orbit transfer problems. It is shown the major benefit of this method is the low computational time along with comparable accuracy with respect to the state of the art methods
Trapping radioactiveRb82in an optical dipole trap and evidence of spontaneous spin polarization
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