4,869 research outputs found
Microlensing and Variability in the Bulge of M31
For the past five seasons, the Angstrom Project, an international
microlensing collaboration, has been making observations of the central bulge
of M31, the Andromeda galaxy, searching for microlensing events. This thesis
describes the work that has been done to develop an automatic candidate
selection pipeline which enables lensing candidates to be found even if they
are blended with periodic variable baseline, something which has never been
attempted before in the same way. As a by-product of this process, many
variable stars are found and their properties are investigated and
characterised. The results of the investigations to date are presented. The
final selection of microlensing candidates selected from the most recent
Angstrom lightcurve data set is shown, and a separate more detailed
investigation into one particularly interesting microlensing candidate of very
short duration is described.Comment: PhD Thesis, Astrophysics Research Institute, Liverpool John Moores
University, accepted Jan 11th 2010- 319 page
Experiment K-6-06. Morphometric and EM analyses of tibial epiphyseal plates from Cosmos 1887 rats
Light and electron microscopy studies were carried out on decalcified tibial epiphyseal plates of rats flown aboard Cosmos 1887 (12.5d flight plus 53.5h recovery). Analysis of variance showed that the proliferative zone of flight animals was significantly higher than that of synchronous controls, while the hypertrophic/calcification zone was significantly reduced. Flight animals had more cells than synchronous controls in the proliferative zone, and less in the hypertrophic/calcification region. The total number of cells, however, was significantly higher in flight animals. No differences were found for perimeter or shape factor of growth plates, but area was significantly lower in flight animals in comparison to synchronous controls. Collagen fibrils in flight animals were shorter and wider than in synchronous controls. The time required for a cell to cycle through the growth plate is 2 to 3 days, so most of the cells and matrix present were formed after the animals had returned to 1 g, and probably represent stages of recovery from microgravity exposure, which in itself is an interesting question
Systems, interactions and macrotheory
A significant proportion of early HCI research was guided by one very clear vision: that the existing theory base in psychology and cognitive science could be developed to yield engineering tools for use in the interdisciplinary context of HCI design. While interface technologies and heuristic methods for behavioral evaluation have rapidly advanced in both capability and breadth of application, progress toward deeper theory has been modest, and some now believe it to be unnecessary. A case is presented for developing new forms of theory, based around generic “systems of interactors.” An overlapping, layered structure of macro- and microtheories could then serve an explanatory role, and could also bind together contributions from the different disciplines. Novel routes to formalizing and applying such theories provide a host of interesting and tractable problems for future basic research in HCI
A study of the stress wave factor technique for evaluation of composite materials
The acousto-ultrasonic approach for nondestructive evaluation provides a measurement procedure for quantifying the integrated effect of globally distributed damage characteristic of fiber reinforced composite materials. The evaluation procedure provides a stress wave factor that correlates closely with several material performance parameters. The procedure was investigated for a variety of materials including advanced composites, hybrid structure bonds, adhesive bonds, wood products, and wire rope. The research program focused primarily on development of fundamental understanding and applications advancements of acousto-ultrasonics for materials characterization. This involves characterization of materials for which detection, location, and identification of imperfections cannot at present be analyzed satisfactorily with mechanical performance prediction models. In addition to presenting definitive studies on application potentials, the understanding of the acousto-ultrasonic method as applied to advanced composites is reviewed
Surface nano-patterning through styrene adsorption on Si(100)
We present an ab initio study of the structural and electronic properties of
styrene molecules adsorbed on the dimerized Si(100) surface at different
coverages, ranging from the single-molecule to the full monolayer. The
adsorption mechanism primarily involves the vinyl group via a [2+2]
cycloaddition process that leads to the formation of covalent Si-C bonds and a
local surface derelaxation, while it leaves the phenyl group almost
unperturbed. The investigation of the functionalized surface as a function of
the coverage (e.g. 0.5 -- 1 ML) and of the substrate reconstruction reveals two
major effects. The first results from Si dimer-vinyl interaction and concerns
the controlled variation of the energy bandgap of the interface. The second is
associated to phenyl-phenyl interactions, which gives rise to a regular pattern
of electronic wires at surface, stemming from the pi-pi coupling. These
findings suggest a rationale for tailoring the surface nano-patterning of the
surface, in a controlled way.Comment: 19 pages (preprint), 4 figures, supplementary materia
Study of effects of fuel properties in turbine-powered business aircraft
Increased interest in research and technology concerning aviation turbine fuels and their properties was prompted by recent changes in the supply and demand situation of these fuels. The most obvious change is the rapid increase in fuel price. For commercial airplanes, fuel costs now approach 50 percent of the direct operating costs. In addition, there were occasional local supply disruptions and gradual shifts in delivered values of certain fuel properties. Dwindling petroleum reserves and the politically sensitive nature of the major world suppliers make the continuation of these trends likely. A summary of the principal findings, and conclusions are presented. Much of the material, especially the tables and graphs, is considered in greater detail later. The economic analysis and examination of operational considerations are described. Because some of the assumptions on which the economic analysis is founded are not easily verified, the sensitivity of the analysis to alternates for these assumptions is examined. The data base on which the analyses are founded is defined in a set of appendices
Equidistribution of Heegner Points and Ternary Quadratic Forms
We prove new equidistribution results for Galois orbits of Heegner points
with respect to reduction maps at inert primes. The arguments are based on two
different techniques: primitive representations of integers by quadratic forms
and distribution relations for Heegner points. Our results generalize one of
the equidistribution theorems established by Cornut and Vatsal in the sense
that we allow both the fundamental discriminant and the conductor to grow.
Moreover, for fixed fundamental discriminant and variable conductor, we deduce
an effective surjectivity theorem for the reduction map from Heegner points to
supersingular points at a fixed inert prime. Our results are applicable to the
setting considered by Kolyvagin in the construction of the Heegner points Euler
system
Currents, Torques, and Polarization Factors in Magnetic Tunnel Junctions
Application of Bardeen's tunneling theory to magnetic tunnel junctions having
a general degree of atomic disorder reveals the close relationship between
magneto-conduction and voltage-driven pseudo-torque, as well as the thickness
dependence of tunnel-polarization factors. Among the results: 1) The torque
generally varies as sin theta at constant applied voltage. 2) Whenever
polarization factors are well defined, the voltage-driven torque on each moment
is uniquely proportional to the polarization factor of the other magnet. 3) At
finite applied voltage, this relation predicts significant voltage-asymmetry in
the torque. For one sign of voltage the torque remains substantial even when
the magnetoconductance is greatly diminished. 4) A broadly defined junction
model, called ideal middle, allows for atomic disorder within the magnets and
F/I interface regions. In this model, the spin dependence of a state-weighting
factor proportional to the sum over general state index of evaluated within the
(e.g. vacuum) barrier generalizes the local state density in previous theories
of the tunnel-polarization factor. 5) For small applied voltage,
tunnel-polarization factors remain legitimate up to first order in the inverse
thickness of the ideal middle. An algebraic formula describes the first-order
corrections to polarization factors in terms of newly defined lateral
auto-correllation scales.Comment: This version no. 3 is thoroughly revised for clarity. Just a few
notations and equations are changed, and references completed. No change in
results. 17 pages including 4 figure
Correlated Quantum Transport of Density Wave Electrons
Recently observed Aharonov-Bohm quantum interference of period h/2e in charge
density wave rings strongly suggest that correlated density wave electron
transport is a cooperative quantum phenomenon. The picture discussed here
posits that quantum solitons nucleate and transport current above a Coulomb
blockade threshold field. We propose a field-dependent tunneling matrix element
and use the Schrodinger equation, viewed as an emergent classical equation as
in Feynman's treatment of Josephson tunneling, to compute the evolving
macrostate amplitudes, finding excellent quantitative agreement with voltage
oscillations and current-voltage characteristics in NbSe3. A proposed phase
diagram shows the conditions favoring soliton nucleation versus classical
depinning. (Published in Phys. Rev. Lett. 108, 036404 (2012).)Comment: 9 pages, 4 figures, (5 pages & 3 figures for main article), includes
Supplemental Material with 1 figure. Published version: Physical Review
Letters, vol. 108, p. 036404 (2012
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