26,855 research outputs found
Study of Apollo water impact. Volume 6 - User's manual - Interaction Final report
Computer program for hydroelastic responses of flexible shells of revolution during axially symmetric impact into incompressible fluids as in Apollo water impac
Crystallization and preliminary X-ray analysis of the sporulation factor SpoIIAA in its native and phosphorylated forms
Sporulation in Bacillus begins with an asymmetric cell division producing two progeny with identical chromosomes but different developmental fates. As such, it is a simple example of cellular differentiation. The establishment of cell type is controlled by a series of alternate RNA polymerase sigma subunits. The first compartment-specific sigma factor is sigma (F), whose activity is controlled by SpoIIAB, an anti-sigma factor, and SpoIIAA, an anti-sigma factor antagonist which is phosphorylated by the kinase activity of SpoIIAB. Here, the preliminary crystallographic analysis of SpoIIAA and phosphorylated SpoIIAA from B. sphaericus in forms suitable for high-resolution structure determination are reported
Hosts & distribution of Rocky Mountain wood ticks (Dermacentor andersoni) at a tick focus in British Columbia rangeland
In a study of a Rocky Mountain wood tick (RMWT) population, <i>Eutamias amoenus</i> and <i>Peromyscus maniculatus</i> were the hosts most frequently trapped. Of these <i>E. amoenus</i> carried the greater number of immature RMWT. RMWT were also found in decreasing order of abundance on the following larger rodents: <i>Marmota flaviventris</i>, <i>Neotoma cinerea</i>, and <i>Tamiasciurus hudsonicus</i>. Of 3 areas sampled in and near the tick focus in 1967, most of the ticks were found on the uppermost steep and rocky, shrubby area, while the fewest were taken on a less steep grassy slope with few rocks. Sherman traps were the most efficient of 7 types tested in 1967 for capturing small mammals.In both 1967 and 1968, larvae were most abundant on rodents in July, and scarce or absent from September to June. In 1968, trapping rodents from March to October revealed a major increase in nymph numbers in April and May, and a smaller rise in August and early September. In 1967, CO, as dry ice attracted only a few adult and nymphal ticks, when placed on and near the trap lines and rodent burrows. The number of unfed adult ticks/100 m<sup>2</sup>, recorded by flagging on and near the trap lines, declined each year in 1968 to 1970. In addition to RMWT, a few <i>Ixodes kingi</i> and <i>I. marmotae</i> were collected from mustelids and rodents
The decay of highly excited open strings
The decay rates of leading edge Regge trajectory states are calculated for very high level number in open bosonic string theories, ignoring tachyon final states. The optical theorem simplifies the analysis while enabling identification of the different mass level decay channels. The main result is that (in four dimensions) the greatest single channel is the emission of a single photon and a state of the next mass level down. A simple asymptotic formula for arbitrarily high level number is given for this process. Also calculated is the total decay rate exactly up to N=100. It shows little variation over this range but appears to decrease for larger N. The formalism is checked in examples and the decay rate of the first excited level calculated for open superstring theories. The calculation may also have implications for high spin meson resonances
A Possible Formation Scenario for Dwarf Spheroidal Galaxies - II: A Parameter Study
Dwarf spheroidal (dSph) galaxies are considered the basic building blocks of
the galaxy formation process in the LCDM (Lambda Cold Dark Matter) hierarchical
cosmological model. These galaxies are believed to be the most dark matter (DM)
dominated systems known, have the lowest stellar content, and are poor in gas.
Many theories attempt to explain the formation of dSph galaxies resorting to
the fact that these galaxies are mainly found orbiting large galaxies or
invoking other mechanisms of interactions. Here we show the full set of
simulation as an extension of our fiducial model, where we study the formation
of classical dSph galaxies in isolation by dissolving star clusters within the
DM halo of the dwarf galaxy. In our parameter survey we adopt cored and cusped
DM halo profiles and consider different numbers of dissolving star clusters. We
investigate the dependency of observable quantities with different masses and
scale-lengths of the DM halo and different star formation efficiencies (SFE).
We find that our proposed scenario explains many features of the classical dSph
galaxies of the Milky Way, like their morphology and their dynamics. We see
trends how the surface brightness and the scale-length of the luminous
component vary with the parameters of our simulations. We also identify how
irregularities in their shape, i.e. clumpiness and ellipticity vary in our
simulations. In velocity space, we identify the parameters leading to flat
velocity dispersions curves. We recognize kinematically cold substructures in
velocity space, named fossil remnants and stemming from our unique initial
conditions, which alter the expected results. These streaming motions are
considered as a key feature for future observation with high resolution to
validate our scenario.Comment: 23 pages, 9 figures, 4 Tables, accepted for publication in MNRA
Synchrotron Polarization at High Galactic Latitude
We present preliminary results from mapping the high-latitude Galactic
polarization with the Effelsberg Telescope at 21 cm. Structures on the
resulting maps are mostly on the scale of several degrees. The results show
detection of polarization over most of the field, at the level of tens of
percent of the synchrotron emission. The evidence of more structure in Stokes Q
and U rather than in suggests the existence of Faraday
rotation.Comment: To be published in the proceedings of "The Cosmic Microwave
Background and its Polarization", New Astronomy Reviews, (eds. S. Hanany and
K.A. Olive
NICMOS and VLBA observations of the gravitational lens system B1933+503
NICMOS observations of the complex gravitational lens system B1933+503 reveal
infrared counterparts to two of the inverted spectrum radio images. The
infrared images have arc-like structures. The corresponding radio images are
also detected in a VLBA map made at 1.7 GHz with a resolution of 6 mas. We fail
to detect two of the four inverted radio spectrum components with the VLBA even
though they are clearly visible in a MERLIN map at the same frequency at a
different epoch. The absence of these two components could be due to rapid
variability on a time-scale less than the time delay, or to broadening of the
images during propagation of the radio waves through the ISM of the lensing
galaxy to an extent that they fall below the surface brightness detectability
threshold of the VLBA observations. The failure to detect the same two images
with NICMOS is probably due to extinction in the ISM of the lensing galaxy.Comment: 5 pages, 4 figures, submitted to MNRA
Gravitational lensing statistics with extragalactic surveys. II. Analysis of the Jodrell Bank-VLA Astrometric Survey
We present constraints on the cosmological constant from
gravitational lensing statistics of the Jodrell Bank-VLA Astrometric Survey
(JVAS). Although this is the largest gravitational lens survey which has been
analysed, cosmological constraints are only comparable to those from optical
surveys. This is due to the fact that the median source redshifts of JVAS are
lower, which leads to both relatively fewer lenses in the survey and a weaker
dependence on the cosmological parameters. Although more approximations have to
be made than is the case for optical surveys, the consistency of the results
with those from optical gravitational lens surveys and other cosmological tests
indicate that this is not a major source of uncertainty in the results.
However, joint constraints from a combination of radio and optical data are
much tighter. Thus, a similar analysis of the much larger Cosmic Lens All-Sky
Survey should provide even tighter constraints on the cosmological constant,
especially when combined with data from optical lens surveys.
At 95% confidence, our lower and upper limits on ,
using the JVAS lensing statistics information alone, are respectively -2.69 and
0.68. For a flat universe, these correspond to lower and upper limits on
\lambda_{0} of respectively -0.85 and 0.84. Using the combination of JVAS
lensing statistics and lensing statistics from the literature as discussed in
Quast & Helbig (Paper I) the corresponding values are
-1.78 and 0.27. For a flat universe, these correspond to lower and upper limits
on of respectively -0.39 and 0.64.Comment: LaTeX, 9 pages, 18 PostScript files in 6 figures. Paper version
available on request. Data available from
http://gladia.astro.rug.nl:8000/ceres/data_from_papers/papers.htm
Arctic marine climate of the early nineteenth century
The climate of the early nineteenth century is likely to have been significantly cooler than that of today, as it was a period of low solar activity (the Dalton minimum) and followed a series of large volcanic eruptions. Proxy reconstructions of the temperature of the period do not agree well on the size of the temperature change, so other observational records from the period are particularly valuable. Weather observations have been extracted from the reports of the noted whaling captain William Scoresby Jr., and from the records of a series of Royal Navy expeditions to the Arctic, preserved in the UK National Archives. They demonstrate that marine climate in 1810 - 1825 was marked by consistently cold summers, with abundant sea-ice. But although the period was significantly colder than the modern average, there was considerable variability: in the Greenland Sea the summers following the Tambora eruption (1816 and 1817) were noticeably warmer, and had less sea-ice coverage, than the years immediately preceding them; and the sea-ice coverage in Lancaster Sound in 1819 and 1820 was low even by modern standards. © 2010 Author(s)
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