19,723 research outputs found
The effects of deviate internal representations in the optimal model of the human operator
Some of the issues and equations involved in predicting closed-loop man machine performance for situations in which the human operators' knowledge of the system and/or environment are imperfect are presented and discussed. Several examples to demonstrate some of the effects to be expected when such is the case are then given
General Relativistic Radiative Transfer
We present a general method to calculate radiative transfer including
scattering in the continuum as well as in lines in spherically symmetric
systems that are influenced by the effects of general relativity (GR). We
utilize a comoving wavelength ansatz that allows to resolve spectral lines
throughout the atmosphere. The used numerical solution is an operator splitting
(OS) technique that uses a characteristic formal solution. The bending of
photon paths and the wavelength shifts due to the effects of GR are fully taken
into account, as is the treatment of image generation in a curved spacetime. We
describe the algorithm we use and demonstrate the effects of GR on the
radiative transport of a two level atom line in a neutron star like atmosphere
for various combinations of continuous and line scattering coefficients. In
addition, we present grey continuum models and discuss the effects of different
scattering albedos on the emergent spectra and the determination of effective
temperatures and radii of neutron star atmospheres
Type II Supernovae: Model Light Curves and Standard Candle Relationships
A survey of Type II supernovae explosion models has been carried out to
determine how their light curves and spectra vary with their mass, metallicity,
and explosion energy. The presupernova models are taken from a recent survey of
massive stellar evolution at solar metallicity supplemented by new calculations
at subsolar metallicity. Explosions are simulated by the motion of a piston
near the edge of the iron core and the resulting light curves and spectra are
calculated using full multi-wavelength radiation transport. Formulae are
developed that describe approximately how the model observables (light curve
luminosity and duration) scale with the progenitor mass, explosion energy, and
radioactive nucleosynthesis. Comparison with observational data shows that the
explosion energy of typical supernovae (as measured by kinetic energy at
infinity) varies by nearly an order of magnitude -- from 0.5 to 4.0 x 10^51
ergs, with a typical value of ~0.9 x 10^51 ergs. Despite the large variation,
the models exhibit a tight relationship between luminosity and expansion
velocity, similar to that previously employed empirically to make SNe IIP
standardized candles. This relation is explained by the simple behavior of
hydrogen recombination in the supernova envelope, but we find a sensitivity to
progenitor metallicity and mass that could lead to systematic errors.
Additional correlations between light curve luminosity, duration, and color
might enable the use of SNe IIP to obtain distances accurate to ~20% using only
photometric data.Comment: 12 pages, ApJ in pres
High-overtone Bulk-Acoustic Resonator gravimetric sensitivity: towards wideband acoustic spectroscopy
In the context of direct detection sensors with compact dimensions, we
investigate the gravimetric sensitivity of High-overtone Bulk Acoustic
Resonators, through modeling of their acoustic characteristics and experiment.
The high frequency characterizing such devices is expected to induce a
significant effect when the acoustic field boundary conditions are modified by
a thin adlayer. Furthermore, the multimode spectral characteristics is
considered for wideband acoustic spectroscopy of the adlayer, once the
gravimetric sensitivity dependence of the various overtones is established.
Finally, means of improving the gravimetric sensitivity by confining the
acoustic field in a low acoustic-impedance layer is theoretically established.Comment: 9 pages, 10 figures in J. Appl. Phys. 201
Sensitivity of a highâelevation rocky mountain watershed to altered climate and CO2
We explored the hydrologic and ecological responses of a headwater mountain catchment, Loch Vale watershed, to climate change and doubling of atmospheric CO2 scenarios using the Regional HydroâEcological Simulation System (RHESSys). A slight (2°C) cooling, comparable to conditions observed over the past 40 years, led to greater snowpack and slightly less runoff, evaporation, transpiration, and plant productivity. An increase of 2°C yielded the opposite response, but model output for an increase of 4°C showed dramatic changes in timing of hydrologic responses. The snowpack was reduced by 50%, and runoff and soil water increased and occurred 4â5 weeks earlier with 4°C warming. Alpine tundra photosynthetic rates responded more to warmer and wetter conditions than subalpine forest, but subalpine forest showed a greater response to doubling of atmospheric CO2 than tundra. Even though water use efficiency increased with the double CO2 scenario, this had little effect on basinâwide runoff because the catchment is largely unvegetated. Changes in winter and spring climate conditions were more important to hydrologic and vegetation dynamics than changes that occurred during summer
Non-LTE treatment of molecules in the photospheres of cool stars
We present a technique to treat systems with very many levels, like
molecules, in non-LTE. This method is based on a superlevel formalism coupled
with rate operator splitting. Superlevels consist of many individual levels
that are assumed to be in LTE relative to each other. The usage of superlevels
reduces the dimensionality of the rate equations dramatically and, thereby,
makes the problem computationally more easily treatable. Our superlevel
formalism retains maximum accuracy by using direct opacity sampling (dOS) when
calculating the radiative transitions and the opacities. We developed this
method in order to treat molecules in cool dwarf model calculations in non-LTE.
Cool dwarfs have low electron densities and a radiation field that is far from
a black body radiation field, both properties may invalidate the conditions for
the common LTE approximation. Therefore, the most important opacity sources,
the molecules, need to be treated in non-LTE. As a case study we applied our
method to carbon monoxide. We find that our method gives accurate results since
the conditions for the superlevel method are very well met for molecules. Due
to very high collisional cross sections with hydrogen, and the high densities
of H_2 the population of CO itself shows no significant deviation from LTE.Comment: AASTeX v50, 35 pages including 12 figures, accepted by Ap
Atmospheric Analysis of the M/L- and M/T-Dwarf Binary Systems LHS 102 and Gliese 229
We present 0.9-2.5um spectroscopy with R~800 and 1.12-1.22um spectroscopy
with R~5800 for the M dwarfs Gl 229A and LHS 102A, and for the L dwarf LHS
102B. We also report IZJHKL' photometry for both components of the LHS 102
system, and L' photometry for Gl 229A. The data are combined with previously
published spectroscopy and photometry to produce flux distributions for each
component of the kinematically old disk M/L-dwarf binary system LHS 102 and the
kinematically young disk M/T-dwarf binary system Gliese 229. The data are
analyzed using synthetic spectra generated by the latest "AMES-dusty" and
"AMES-cond" models by Allard & Hauschildt. Although the models are not able to
reproduce the overall slope of the infrared flux distribution of the L dwarf,
most likely due to the treatment of dust in the photosphere, the data for the M
dwarfs and the T dwarf are well matched. We find that the Gl 229 system is
metal-poor despite having kinematics of the young disk, and that the LHS 102
system has solar metallicity. The observed luminosities and derived
temperatures and gravities are consistent with evolutionary model predictions
if the Gl 229 system is very young (age ~30 Myr) with masses (A,B) of
(0.38,>0.007)M(sun), and the LHS 102 system is older, aged 1-10 Gyr with masses
(A,B) of (0.19,0.07)M(sun).Comment: 29 pages incl. 13 figures and 5 tables;; accepted for publication in
MNRA
Beyond Worst-Case Analysis for Joins with Minesweeper
We describe a new algorithm, Minesweeper, that is able to satisfy stronger
runtime guarantees than previous join algorithms (colloquially, `beyond
worst-case guarantees') for data in indexed search trees. Our first
contribution is developing a framework to measure this stronger notion of
complexity, which we call {\it certificate complexity}, that extends notions of
Barbay et al. and Demaine et al.; a certificate is a set of propositional
formulae that certifies that the output is correct. This notion captures a
natural class of join algorithms. In addition, the certificate allows us to
define a strictly stronger notion of runtime complexity than traditional
worst-case guarantees. Our second contribution is to develop a dichotomy
theorem for the certificate-based notion of complexity. Roughly, we show that
Minesweeper evaluates -acyclic queries in time linear in the certificate
plus the output size, while for any -cyclic query there is some instance
that takes superlinear time in the certificate (and for which the output is no
larger than the certificate size). We also extend our certificate-complexity
analysis to queries with bounded treewidth and the triangle query.Comment: [This is the full version of our PODS'2014 paper.
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