197,057 research outputs found
Semiempirical calculation of deep levels: divacancy in Si
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)
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
We describe the finite volume effects of CP-odd quantities, such as the
neutron electric dipole moment and the anapole moment in the -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
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
Probabilities of thunderstorm persistence at Cape Kennedy, Florid
Shuttle system ascent aerodynamic and plume heating
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
Using quantum Monte Carlo method, we study, under external magnetic fields,
the ground state phase diagram of the two-dimensional spin =1/2 dimer model
with an anisotropic intra-plane antiferromagnetic coupling. With the anisotropy
, 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 and 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
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
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
- …