2,497 research outputs found
Centaur AC-8 Postflight Guidance Analysis
Centaur AC-8 postflight guidance and control analysi
Pilot interaction with automated airborne decision making systems
An investigation was made of interaction between a human pilot and automated on-board decision making systems. Research was initiated on the topic of pilot problem solving in automated and semi-automated flight management systems and attempts were made to develop a model of human decision making in a multi-task situation. A study was made of allocation of responsibility between human and computer, and discussed were various pilot performance parameters with varying degrees of automation. Optimal allocation of responsibility between human and computer was considered and some theoretical results found in the literature were presented. The pilot as a problem solver was discussed. Finally the design of displays, controls, procedures, and computer aids for problem solving tasks in automated and semi-automated systems was considered
Indistinguishability and Interference in the Coherent Control of Atomic and Molecular Processes
The subtle and fundamental issue of indistinguishability and interference
between independent pathways to the same target state is examined in the
context of coherent control of atomic and molecular processes, with emphasis
placed on possible "which-way" information due to quantum entanglement
established in the quantum dynamics. Because quantum interference between
independent pathways to the same target state occurs only when the independent
pathways are indistinguishable, it is first shown that creating useful
coherence (as defined in the paper) between nondegenerate states of a molecule
for subsequent quantum interference manipulation cannot be achieved by
collisions between atoms or molecules that are prepared in momentum and energy
eigenstates. Coherence can, however, be transferred from light fields to atoms
or molecules. Using a particular coherent control scenario, it is shown that
this coherence transfer and the subsequent coherent phase control can be
readily realized by the most classical states of light, i.e., coherent states
of light. It is further demonstrated that quantum states of light may suppress
the extent of phase-sensitive coherent control by leaking out some which-way
information while "incoherent interference control" scenarios proposed in the
literature have automatically ensured the indistinguishability of multiple
excitation pathways. The possibility of quantum coherence in photodissociation
product states is also understood in terms of the disentanglement between
photodissociation fragments. Results offer deeper insights into quantum
coherence generation in atomic and molecular processes.Comment: 26 pages, based on one Chapter from first author's Ph.D thesis in
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Laparoscopic Approach for Metachronous Cecal and Sigmoid Volvulus
This report indicates that laparoscopic techniques may be a safe approach for acute colonic volvulus
Vitamins A & D Inhibit the Growth of Mycobacteria in Radiometric Culture
The role of vitamins in the combat of disease is usually conceptualized as acting by modulating the immune response of an infected, eukaryotic host. We hypothesized that some vitamins may directly influence the growth of prokaryotes, particularly mycobacteria. complex).Vitamins A and D cause dose-dependent inhibition of all three mycobacterial species studied. Vitamin A is consistently more inhibitory than vitamin D. The vitamin A precursor, β-carotene, is not inhibitory, whereas three vitamin A metabolites cause inhibition. Vitamin K has no effect. Vitamin E causes negligible inhibition in a single strain.We show that vitamin A, its metabolites Retinyl acetate, Retinoic acid and 13-cis Retinoic acid and vitamin D directly inhibit mycobacterial growth in culture. These data are compatible with the hypothesis that complementing the immune response of multicellular organisms, vitamins A and D may have heretofore unproven, unrecognized, independent and probable synergistic, direct antimycobacterial inhibitory activity
Quantum mechanics explained
The physical motivation for the mathematical formalism of quantum mechanics
is made clear and compelling by starting from an obvious fact - essentially,
the stability of matter - and inquiring into its preconditions: what does it
take to make this fact possible?Comment: 29 pages, 5 figures. v2: revised in response to referee comment
Transitive and Gallai colorings
A Gallai coloring of the complete graph is an edge-coloring with no rainbow
triangle. This concept first appeared in the study of comparability graphs and
anti-Ramsey theory. We introduce a transitive analogue for acyclic directed
graphs, and generalize both notions to Coxeter systems, matroids and
commutative algebras.
It is shown that for any finite matroid (or oriented matroid), the maximal
number of colors is equal to the matroid rank. This generalizes a result of
Erd\H{o}s-Simonovits-S\'os for complete graphs. The number of Gallai (or
transitive) colorings of the matroid that use at most colors is a
polynomial in . Also, for any acyclic oriented matroid, represented over the
real numbers, the number of transitive colorings using at most 2 colors is
equal to the number of chambers in the dual hyperplane arrangement.
We count Gallai and transitive colorings of the root system of type A using
the maximal number of colors, and show that, when equipped with a natural
descent set map, the resulting quasisymmetric function is symmetric and
Schur-positive.Comment: 31 pages, 5 figure
Towards More Accurate Molecular Dynamics Calculation of Thermal Conductivity. Case Study: GaN Bulk Crystals
Significant differences exist among literature for thermal conductivity of
various systems computed using molecular dynamics simulation. In some cases,
unphysical results, for example, negative thermal conductivity, have been
found. Using GaN as an example case and the direct non-equilibrium method,
extensive molecular dynamics simulations and Monte Carlo analysis of the
results have been carried out to quantify the uncertainty level of the
molecular dynamics methods and to identify the conditions that can yield
sufficiently accurate calculations of thermal conductivity. We found that the
errors of the calculations are mainly due to the statistical thermal
fluctuations. Extrapolating results to the limit of an infinite-size system
tend to magnify the errors and occasionally lead to unphysical results. The
error in bulk estimates can be reduced by performing longer time averages using
properly selected systems over a range of sample lengths. If the errors in the
conductivity estimates associated with each of the sample lengths are kept
below a certain threshold, the likelihood of obtaining unphysical bulk values
becomes insignificant. Using a Monte-Carlo approach developed here, we have
determined the probability distributions for the bulk thermal conductivities
obtained using the direct method. We also have observed a nonlinear effect that
can become a source of significant errors. For the extremely accurate results
presented here, we predict a [0001] GaN thermal conductivity of 185 at 300 K, 102 at 500 K, and 74
at 800 K. Using the insights obtained in the work, we have achieved a
corresponding error level (standard deviation) for the bulk (infinite sample
length) GaN thermal conductivity of less than 10 , 5 , and 15 at 300 K, 500 K, and 800 K respectively
Teaching and understanding of quantum interpretations in modern physics courses
Just as expert physicists vary in their personal stances on interpretation in
quantum mechanics, instructors vary on whether and how to teach interpretations
of quantum phenomena in introductory modern physics courses. In this paper, we
document variations in instructional approaches with respect to interpretation
in two similar modern physics courses recently taught at the University of
Colorado, and examine associated impacts on student perspectives regarding
quantum physics. We find students are more likely to prefer realist
interpretations of quantum-mechanical systems when instructors are less
explicit in addressing student ontologies. We also observe contextual
variations in student beliefs about quantum systems, indicating that
instructors who choose to address questions of ontology in quantum mechanics
should do so explicitly across a range of topics.Comment: 18 pages, references, plus 2 pages supplemental materials. 8 figures.
PACS: 01.40.Fk, 03.65.-
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