194,709 research outputs found

    Semiempirical calculation of deep levels: divacancy in Si

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    A study of the electronic levels associated with the divacancy in silicon is reported. The extended Huckel theory is shown to reproduce the band structure of silicon. The electronic levels of the divacancy are calculated by considering a periodic array of large unit cells each containing 62 atoms; a 64 atom perfect cell with two atoms removed to form the divacancy. The results are found to be in qualitative agreement with the results of EPR and infrared absorption measurements

    Evaluation of atmospheric density models and preliminary functional specifications for the Langley Atmospheric Information Retrieval System (LAIRS)

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    This document presents the results of an extensive survey and comparative evaluation of current atmosphere and wind models for inclusion in the Langley Atmospheric Information Retrieval System (LAIRS). It includes recommended models for use in LAIRS, estimated accuracies for the recommended models, and functional specifications for the development of LAIRS

    Neutron Electric Dipole Moment at Fixed Topology

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    We describe the finite volume effects of CP-odd quantities, such as the neutron electric dipole moment and the anapole moment in the θ\theta-vacuum, under different topological sectors. We evaluate the three-point Green's functions for the electromagnetic current in a fixed non-trivial topological sector in order to extract these CP-odd observables. We discuss the role of zero modes in the CP-odd Green's function and show that, in the quenched approximation, there is a power divergence in the quark mass for CP-odd quantities at finite volume.Comment: 12 pages, revised manuscript to be publishe

    Impact of low gravity on water electrolysis operation

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    Advanced space missions will require oxygen and hydrogen utilities for several important operations including the following: (1) propulsion; (2) electrical power generation and storage; (3) environmental control and life support; (4) extravehicular activity; (5) in-space manufacturing and (6) in-space science activities. An experiment suited to a Space Shuttle standard middeck payload has been designed for the Static Feed Water Electrolysis technology which has been viewed as being capable of efficient, reliable oxygen and hydrogen generation with few subsystem components. The program included: end use design requirements, phenomena to be studied, Space Shuttle Orbiter experiment constraints, experiment design and data requirements, and test hardware requirements. The objectives are to obtain scientific and engineering data for future research and development and to focus on demonstrating and monitoring for safety of a standard middeck payload

    Thunderstorm Persistence at Cape Kennedy, Florida

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    Probabilities of thunderstorm persistence at Cape Kennedy, Florid

    Shuttle system ascent aerodynamic and plume heating

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    The shuttle program provided a challenge to the aerothermodynamicist due to the complexity of the flow field around the vehicle during ascent, since the configuration causes multiple shock interactions between the elements. Wind tunnel tests provided data for the prediction of the ascent design heating environment which involves both plume and aerodynamic heating phenomena. The approach for the heating methodology based on ground test firings and the use of the wind tunnel data to formulate the math models is discussed

    Supersolid phase in spin dimer XXZ systems under magnetic field

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    Using quantum Monte Carlo method, we study, under external magnetic fields, the ground state phase diagram of the two-dimensional spin SS=1/2 dimer model with an anisotropic intra-plane antiferromagnetic coupling. With the anisotropy 4≳Δ≳34 \gtrsim \Delta \gtrsim 3, a supersolid phase characterized by a non-uniform bose condensate density that breaks translational symmetry is found. The rich phase diagram also contains a checkerboard solid and two different types of superfluid phase formed by Sz=+1S_z=+1 and Sz=0S_z=0 spin triplets, with finite staggered magnetization in z-axis and in-plane direction, respectively. As we show, the model can be realized as a consequence of including the next nearest neighbor coupling among dimers and our results suggest that spin dimer systems may be an ideal model system to study the supersolid phase.Comment: 4 pages, 5 figure

    Aircraft adaptive learning control

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    The optimal control theory of stochastic linear systems is discussed in terms of the advantages of distributed-control systems, and the control of randomly-sampled systems. An optimal solution to longitudinal control is derived and applied to the F-8 DFBW aircraft. A randomly-sampled linear process model with additive process and noise is developed

    Feshbach resonant scattering of three fermions in one-dimensional wells

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    We study the weak-tunnelling limit for a system of cold 40K atoms trapped in a one-dimensional optical lattice close to an s-wave Feshbach resonance. We calculate the local spectrum for three atoms at one site of the lattice within a two-channel model. Our results indicate that, for this one-dimensional system, one- and two-channel models will differ close to the Feshbach resonance, although the two theories would converge in the limit of strong Feshbach coupling. We also find level crossings in the low-energy spectrum of a single well with three atoms that may lead to quantum phase transition for an optical lattice of many wells. We discuss the stability of the system to a phase with non-uniform density.Comment: 10 pages, 5 figure
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