5,607 research outputs found
The characteristics of the flow field over the mid-upper fuselage of Lancaster P. A. 474
This note describes a series of tests conducted to determine the
characteristics of the flow field over the mid-upper fuselage of.
Lancaster P. A, 474.
The range of the tests was to include a determination of the distributions
of total head, static pressure and velocity together with
the flow directional characteristics in the pitching plane for a
number of aircraft flight configurations as listed in paragraph 1. 2.
Curves are presented in Figs. 9, 20 - 25, showing the flow directional
characteristics and the distributions of static pressure and velocity
in the region of investigation
Shock Breakout in Core-Collapse Supernovae and its Neutrino Signature
(Abridged) We present results from dynamical models of core-collapse
supernovae in one spatial dimension, employing a newly-developed Boltzmann
neutrino radiation transport algorithm, coupled to Lagrangean hydrodynamics and
a consistent high-density nuclear equation of state. We focus on shock breakout
and its neutrino signature and follow the dynamical evolution of the cores of
11 M_sun, 15 M_sun, and 20 M_sun progenitors through collapse and the first 250
milliseconds after bounce. We examine the effects on the emergent neutrino
spectra, light curves, and mix of species of artificial opacity changes, the
number of energy groups, the weak magnetism/recoil corrections, nucleon-nucleon
bremsstrahlung, neutrino-electron scattering, and the compressibility of
nuclear matter. Furthermore, we present the first high-resolution look at the
angular distribution of the neutrino radiation field both in the
semi-transparent regime and at large radii and explore the accuracy with which
our tangent-ray method tracks the free propagation of a pulse of radiation in a
near vacuum. Finally, we fold the emergent neutrino spectra with the
efficiencies and detection processes for a selection of modern underground
neutrino observatories and argue that the prompt electron-neutrino breakout
burst from the next galactic supernova is in principle observable and usefully
diagnostic of fundamental collapse/supernova behavior. Though we are not in
this study focusing on the supernova mechanism per se, our simulations support
the theoretical conclusion (already reached by others) that spherical (1D)
supernovae do not explode when good physics and transport methods are employed.Comment: 16 emulateapj pages, plus 24 postscript figures, accepted to The
Astrophysical Journal; text revised; neutrino oscillation section expanded;
Fig. 22 correcte
Science-based restoration monitoring of coastal habitats, Volume Two: Tools for monitoring coastal habitats
Healthy coastal habitats are not only important ecologically; they also support healthy coastal communities and improve the quality of people’s lives. Despite their many benefits and values, coastal habitats have been systematically modified, degraded, and destroyed throughout the United States and its protectorates beginning with European colonization in the 1600’s (Dahl 1990). As a result, many coastal habitats around the United States are in desperate need of restoration. The monitoring of restoration projects, the focus of this document, is necessary to ensure that restoration efforts are successful, to further the science, and to increase the efficiency of future restoration efforts
Temporal and spatial variability of glyoxal as observed from space
Glyoxal, CHO.CHO, is produced during the oxidation of volatile organic compounds, VOC, released by anthropogenic activities, biogenic processes and biomass burning. It has a short chemical lifetime of a few hours in the boundary layer and lower troposphere and therefore serves as an indicator and a marker of photochemical hot-spots and their response to changing atmospheric conditions around the globe. For this reason more than five years of CHO.CHO observations (2002–2007), retrieved from the radiances measured by the satellite instrument SCIAMACHY, were obtained and analyzed both temporally and spatially. The largest columns of CHO.CHO (&gt;6.10<sup>14</sup> molec cm<sup>&minus;2</sup>) are found in the tropical and sub-tropical regions, associated with high biological activity and the plumes from vegetation fires. The majority of the identified hot spots are characterized by a well-defined seasonality: the highest values being observed during the warm and dry periods as a result of the enhanced biogenic, primarily isoprene, emissions and/or biomass burning from natural or man-made fires. The regions influenced by anthropogenic pollution also encounter enhanced amounts of glyoxal. The ratio "CHO.CHO to HCHO, R<sub><I>GF</I></sub>" over the biogenically influenced photochemical hot-spots is approximately 0.045. For the studied regions, the presence of pyrogenic and anthropogenic emissions increases and decreases this number respectively. Although the 2002–2007 period of observation is limited, over the northeastern Asia a significant annual increase in CHO.CHO in addition to a seasonal cycle is reported
Inelastic scattering in ocean water and its impact on trace gas retrievals from satellite data
Over clear ocean waters, photons scattered within the water body contribute significantly to the upwelling flux. In addition to elastic scattering, inelastic Vibrational Raman Scattering (VRS) by liquid water is also playing a role and can have a strong impact on the spectral distribution of the outgoing radiance. Under clear-sky conditions, VRS has an influence on trace gas retrievals from space-borne measurements of the backscattered radiance such as from e.g. GOME (Global Ozone Monitoring Experiment). The effect is particularly important for geo-locations with small solar zenith angles and over waters with low chlorophyll concentration.<br> <br> In this study, a simple ocean reflectance model (Sathyendranath and Platt, 1998) accounting for VRS has been incorporated into a radiative transfer model. The model has been validated by comparison with measurements from a swimming-pool experiment dedicated to detect the effect of scattering within water on the outgoing radiation and also with selected data sets from GOME. The comparisons show good agreement between experimental and model data and highlight the important role of VRS.<br> <br> To evaluate the impact of VRS on trace gas retrieval, a sensitivity study was performed on synthetic data. If VRS is neglected in the data analysis, errors of more than 30% are introduced for the slant column (<i>SC</i>) of BrO over clear ocean scenarios. Exemplarily DOAS retrievals of BrO from real GOME measurements including and excluding a VRS compensation led to comparable results as in the sensitivity study, but with somewhat smaller differences between the two analyses.<br> <br> The results of this work suggest, that DOAS retrievals of atmospheric trace species from measurements of nadir viewing space-borne instruments have to take VRS scattering into account over waters with low chlorophyll concentrations, and that a simple correction term is enough to reduce the errors to an acceptable level
The cool atmospheres of the binary brown dwarf eps Indi B
We have imaged Indi B, the closest brown dwarf binary known, with
VISIR at the VLT in three narrow-band mid-infrared bandpasses located around
8.6m, 10.5m and 11.3m. We are able to spatially resolve both
components, and determine accurate mid-infrared photometry for both components
independently. In particular, our VISIR observations probe the NH feature
in the atmospheres of the cooler and warmer brown dwarfs. For the first time,
we can disentangle the contributions of the two components, and find that % our
photometry of IndiBb is in good agreement with recent ``cloud-free''
atmosphere models having an effective temperature of K.
With an assumed age of 1 Gyr for the Indi system, component Ba
agrees more with K rather than with
K, as suggested by SPITZER spectroscopic observations of
the combined Indi B system (Roellig et al., 2004). Even higher
effective temperatures appear inconsistent with our absolute photometry, as
they would imply an unphysical small size of the brown dwarf IndiBa.Comment: 4 pages, 2 figure
Instabilities in neutrino-plasma density waves
One examines the interaction and possible resonances between supernova
neutrinos and electron plasma waves. The neutrino phase space distribution and
its boundary regions are analyzed in detail. It is shown that the boundary
regions are too wide to produce non-linear resonant effects. The growth or
damping rates induced by neutrinos are always proportional to the neutrino flux
and .Comment: 9 pages, a few words modified to match PRD publicatio
Spectroscopic Constants, Abundances, and Opacities of the TiH Molecule
Using previous measurements and quantum chemical calculations to derive the
molecular properties of the TiH molecule, we obtain new values for its
ro-vibrational constants, thermochemical data, spectral line lists, line
strengths, and absorption opacities. Furthermore, we calculate the abundance of
TiH in M and L dwarf atmospheres and conclude that it is much higher than
previously thought. We find that the TiH/TiO ratio increases strongly with
decreasing metallicity, and at high temperatures can exceed unity. We suggest
that, particularly for subdwarf L and M dwarfs, spectral features of TiH near
0.52 \mic, 0.94 \mic, and in the band may be more easily measureable
than heretofore thought. The recent possible identification in the L subdwarf
2MASS J0532 of the 0.94 \mic feature of TiH is in keeping with this
expectation. We speculate that looking for TiH in other dwarfs and subdwarfs
will shed light on the distinctive titanium chemistry of the atmospheres of
substellar-mass objects and the dimmest stars.Comment: 37 pages, including 4 figures and 13 tables, accepted to the
Astrophysical Journa
Proof Theory, Transformations, and Logic Programming for Debugging Security Protocols
We define a sequent calculus to formally specify, simulate, debug and verify security protocols. In our sequents we distinguish between the current knowledge of principals and the current global state of the session. Hereby, we can describe the operational semantics of principals and of an intruder in a simple and modular way. Furthermore, using proof theoretic tools like the analysis of permutability of rules, we are able to find efficient proof strategies that we prove complete for special classes of security protocols including Needham-Schroeder. Based on the results of this preliminary analysis, we have implemented a Prolog meta-interpreter which allows for rapid prototyping and for checking safety properties of security protocols, and we have applied it for finding error traces and proving correctness of practical examples
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