19,217 research outputs found
Investigation of line-of-sight propagation in dense atmosphere, phase 2 Final report, Jun. 1970 - Feb. 1971
Effect of microwave absorption and decimetric radio noise in Jovian atmospheres on radio communication in 1 to 10 GHz frequency ban
Navigation in Curved Space-Time
A covariant and invariant theory of navigation in curved space-time with
respect to electromagnetic beacons is written in terms of J. L. Synge's
two-point invariant world function. Explicit equations are given for navigation
in space-time in the vicinity of the Earth in Schwarzschild coordinates and in
rotating coordinates. The restricted problem of determining an observer's
coordinate time when their spatial position is known is also considered
Significant differences in incubation times in sheep infected with bovine spongiform encephalopathy result from variation at codon 141 in the PRNP gene
The susceptibility of sheep to prion infection is linked to variation in the PRNP gene, which
encodes the prion protein. Common polymorphisms occur at codons 136, 154 and 171. Sheep
which are homozygous for the A<sub>136</sub>R<sub>154</sub>Q<sub>171</sub> allele are the most susceptible to bovine spongiform
encephalopathy (BSE). The effect of other polymorphisms on BSE susceptibility is unknown. We
orally infected ARQ/ARQ Cheviot sheep with equal amounts of BSE brain homogenate and a
range of incubation periods was observed. When we segregated sheep according to the amino
acid (L or F) encoded at codon 141 of the PRNP gene, the shortest incubation period was
observed in LL141 sheep, whilst incubation periods in FF<sub>141</sub> and LF<sub>141</sub> sheep were significantly
longer. No statistically significant differences existed in the expression of total prion protein or the
disease-associated isoform in BSE-infected sheep within each genotype subgroup. This
suggested that the amino acid encoded at codon 141 probably affects incubation times through
direct effects on protein misfolding rates
Uncertainty on coastal flood risk calculations, and how to deal with it in coastal management: case of the Belgian coastal zone
A coastal flood risk calculation estimates the damage by coastal flooding for a certain time horizon. Fivedifferent sources of uncertainty can be distinguished: unpredictability of the weather; uncertainty on theextreme value probability distribution of storm surges; unknown future values of economic growth rate,population growth rate, sea level rise rate and discount rate; limited knowledge of the behaviour of thecoastal system; limited amount of measurements about the state of the coastal system. From a preliminaryanalysis for the Belgian coastal zone it is clear that the combined effect of these different sources ofuncertainty results in a very large uncertainty on the calculated risk, namely a sigma of a factor more than10. Some important sources of uncertainty are impossible to decrease substantially by doing research ormeasurements. Therefore the only option for coastal management is to deal with these large uncertainties.It is suggested to use calculation results relatively, namely to compare scenarios of coastal management inorder to determine which scenario can best use an available budget for investment. Also it is concludedthat risk calculation results would best be compared as ratios between scenarios (in %), not as differences(in euro/year)
Quasiparticle spectrum of the cuprate BiSrCaCuO: Possible connection to the phase diagram
We previously introduced [T. Cren et al., Europhys. Lett. 52, 203 (2000)] an
energy-dependant gap function, , that fits the unusual shape of the
quasiparticle (QP) spectrum for both BiSrCaCuO and YBaCuO. A simple
anti-resonance in accounts for the pronounced QP peaks in the
density of states, at an energy , and the dip feature at a higher
energy, . Here we go a step further : our gap function is consistent
with the () phase diagram, where is the carrier density. For large QP
energies (), the total spectral gap is , where is tied to the condensation
energy. From the available data, a simple -dependance of and
is found, in particular .
These two distinct energy scales of the superconducting state are interpreted
by comparing with the normal and pseudogap states. The various forms of the QP
density of states, as well as the spectral function , are discussed
The Spectral Signature of Dust Scattering and Polarization in the Near IR to Far UV. I. Optical Depth and Geometry Effects
Spectropolarimetry from the near IR to the far UV of light scattered by dust
provides a valuable diagnostic of the dust composition, grain size distribution
and spatial distribution. To facilitate the use of this diagnostic, we present
detailed calculations of the intensity and polarization spectral signature of
light scattered by optically thin and optically thick dust in various
geometries. The polarized light radiative transfer calculations are carried out
using the adding-doubling method for a plane-parallel slab, and are extended to
an optically thick sphere by integrating over its surface. The calculations are
for the Mathis, Rumple & Nordsieck Galactic dust model, and cover the range
from 1 to 500 \AA. We find that the wavelength dependence of the
scattered light intensity provides a sensitive probe of the optical depth of
the scattering medium, while the polarization wavelength dependence provides a
probe of the grain scattering properties, which is practically independent of
optical depth. We provide a detailed set of predictions, including polarization
maps, which can be used to probe the properties of dust through imaging
spectropolarimetry in the near IR to far UV of various Galactic and
extragalactic objects. In a following paper we use the codes developed here to
provide predictions for the dependence of the intensity and polarization on
grain size distribution and composition.Comment: 29 pages + 21 figures, accepted for the Astrophysical Journal
Supplement February 2000 issue. Some revision, mostly in the introduction and
the conclusions, and a couple of correction
Mid-infrared interferometry of the massive young stellar object NGC3603 - IRS 9A
We present observations and models for one of these MYSO candidates, NGC3603
IRS 9A. Our goal is to investigate with infrared interferometry the structure
of IRS 9A on scales as small as 200AU, exploiting the fact that a cluster of O
and B stars has blown away much of the obscuring foreground dust and gas.
Observations in the N-band were carried out with the MIDI beam combiner
attached to the VLTI. Additional interferometric observations which probe the
structure of IRS 9A on larger scales were performed with an aperture mask
installed in the T-ReCS instrument of Gemini South. The spectral energy
distribution (SED) is constrained by the MIDI N-band spectrum and by data from
the Spitzer Space Telescope. Our efforts to model the structure and SED of IRS
9A range from simple geometrical models of the brightness distribution to one-
and two-dimensional radiative transfer computations. The target is resolved by
T-ReCS, with an equivalent (elliptical) Gaussian width of 330mas by 280mas
(2300 AU by 2000 AU). Despite this fact, a warm compact unresolved component
was detected by MIDI which is possibly associated with the inner regions of a
flattened dust distribution. Based on our interferometric data, no sign of
multiplicity was found on scales between about 200AU and 700AU projected
separation. A geometric model consisting of a warm (1000 K) ring (400 AU
diameter) and a cool (140 K) large envelope provides a good fit to the data. No
single model fitting all visibility and photometric data could be found, with
disk models performing better than spherical models. While the data are clearly
inconsistent with a spherical dust distribution they are insufficient to prove
the existence of a disk but rather hint at a more complex dust distribution.Comment: 8 pages, 11 figures. Accepted for publication in A&
The Baryon Content of Cosmic Structures
We make an inventory of the baryonic and gravitating mass in structures
ranging from the smallest galaxies to rich clusters of galaxies. We find that
the fraction of baryons converted to stars reaches a maximum between M500 =
1E12 and 1E13 Msun, suggesting that star formation is most efficient in bright
galaxies in groups. The fraction of baryons detected in all forms deviates
monotonically from the cosmic baryon fraction as a function of mass. On the
largest scales of clusters, most of the expected baryons are detected, while in
the smallest dwarf galaxies, fewer than 1% are detected. Where these missing
baryons reside is unclear.Comment: ApJ Letters, in pres
The effect of the application of mono-lauric acid with glycerol mono-laurate in weaned piglets, on the use of antimicrobials in sow herds
The Dutch government has obliged the pig industry to reduce the use of antimicrobials at farm level with 50% by 2013. The search for alternatives for antimicrobials and other tools which can improve the health status of the farm is intensified. One example of an alternative for antimicrobials is Daafit, a combination of lauric acid and glycerol-mono-laurate, produced by the firm Daavision B.V.
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