443 research outputs found
Precision Primordial He Measurement with CMB Experiments
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) are
two major pillars of cosmology. Standard BBN accurately predicts the primordial
light element abundances (He, D, He and Li), depending on one
parameter, the baryon density. Light element observations are used as a
baryometers. The CMB anisotropies also contain information about the content of
the universe which allows an important consistency check on the Big Bang model.
In addition CMB observations now have sufficient accuracy to not only determine
the total baryon density, but also resolve its principal constituents, H and
He. We present a global analysis of all recent CMB data, with special
emphasis on the concordance with BBN theory and light element observations. We
find and
(fraction of baryon mass as He) using CMB data alone, in agreement with
He abundance observations. With this concordance established we show that
the inclusion of BBN theory priors significantly reduces the volume of
parameter space. In this case, we find
and . We also find that the inclusion of deuterium
abundance observations reduces the and ranges by a factor
of 2. Further light element observations and CMB anisotropy experiments
will refine this concordance and sharpen BBN and the CMB as tools for precision
cosmology.Comment: 7 pages, 3 color figures made minor changes to bring inline with
journal versio
A taxonomic and phylogenetic revision of Penicillium section Aspergilloides
AbstractSpecies belonging to Penicillium section Aspergilloides have a world-wide distribution with P. glabrum, P. spinulosum and P. thomii the most well-known species of this section. These species occur commonly and can be isolated from many substrates including soil, food, bark and indoor environments. The taxonomy of these species has been investigated several times using various techniques, but species delimitation remains difficult. In the present study, 349 strains belonging to section Aspergilloides were subjected to multilocus molecular phylogenetic analyses using partial ÎČ-tubulin (BenA), calmodulin (CaM) and RNA polymerase II second largest subunit (RPB2) sequences. Section Aspergilloides is subdivided into 12 clades and 51 species. Twenty-five species are described here as new and P. yezoense, a species originally described without a Latin diagnosis, is validated. Species belonging to section Aspergilloides are phenotypically similar and most have monoverticillate conidiophores and grow moderately or quickly on agar media. The most important characters to distinguish these species were colony sizes on agar media, growth at 30 °C, ornamentation and shape of conidia, sclerotium production and stipe roughness
High-speed >90% quantum-efficiency p-i-n photodiodes with a resonance wavelength adjustable in the 795-835 nm range
We report GaAs/AlGaAs-based high-speed, high-efficiency, resonant cavity enhanced p-i-n photodiodes. The devices were fabricated by using a microwave-compatible fabrication process. By using a postprocess recess etch, we tuned the resonance wavelength from 835 to 795 nm while keeping the peak efficiencies above 90%. The maximum quantum efficiency was 92% at a resonance wavelength of 823 nm. The photodiode had an experimental setup-limited temporal response of 12 ps. When the system response is deconvolved, the 3 dB bandwidth corresponds to 50 GHz, which is in good agreement with our theoretical calculations. © 1999 American Institute of Physics
Taxonomy, nomenclature and phylogeny of three cladosporium-like hyphomycetes, Sorocybe resinae, Seifertia azaleae and the Hormoconis anamorph of Amorphotheca resinae
Using morphological characters, cultural characters, large subunit and
internal transcribed spacer rDNA (ITS) sequences, and provisions of the
International Code of Botanical Nomenclature, this paper attempts to resolve
the taxonomic and nomenclatural confusion surrounding three species of
cladosporium-like hyphomycetes. The type specimen of Hormodendrum
resinae, the basis for the use of the epithet resinae for the
creosote fungus {either as Hormoconis resinae or Cladosporium
resinae) represents the mononematous synanamorph of the synnematous,
resinicolous fungus Sorocybe resinae. The phylogenetic relationships
of the creosote fungus, which is the anamorph of Amorphotheca
resinae, are with the family Myxotrichaceae, whereas S.
resinae is related to Capronia (Chaetothyriales,
Herpotrichiellaceae). Our data support the segregation of
Pycnostysanus azaleae, the cause of bud blast of rhododendrons, in
the recently described anamorph genus Seifertia, distinct from
Sorocybe; this species is related to the Dothideomycetes but
its exact phylogenetic placement is uncertain. To formally stabilize the name
of the anamorph of the creosote fungus, conservation of Hormodendrum
resinae with a new holotype should be considered. The paraphyly of the
family Myxotrichaceae with the Amorphothecaceae suggested by
ITS sequences should be confirmed with additional genes
Dust Devil Tracks
Dust devils that leave dark- or light-toned tracks are common on Mars and they can also be found on the Earthâs surface. Dust devil tracks (hereinafter DDTs) are ephemeral surface features with mostly sub-annual lifetimes. Regarding their size, DDT widths can range between âŒ1 m and âŒ1 km, depending on the diameter of dust devil that created the track, and DDT lengths range from a few tens of meters to several kilometers, limited by the duration and horizontal ground speed of dust devils. DDTs can be classified into three main types based on their morphology and albedo in contrast to their surroundings; all are found on both planets: (a) dark continuous DDTs, (b) dark cycloidal DDTs, and (c) bright DDTs. Dark continuous DDTs are the most common type on Mars. They are characterized by their relatively homogenous and continuous low albedo surface tracks. Based on terrestrial and martian in situ studies, these DDTs most likely form when surficial dust layers are removed to expose larger-grained substrate material (coarse sands of â„500 ÎŒm in diameter). The exposure of larger-grained materials changes the photometric properties of the surface; hence leading to lower albedo tracks because grain size is photometrically inversely proportional to the surface reflectance. However, although not observed so far, compositional differences (i.e., color differences) might also lead to albedo contrasts when dust is removed to expose substrate materials with mineralogical differences. For dark continuous DDTs, albedo drop measurements are around 2.5 % in the wavelength range of 550â850 nm on Mars and around 0.5 % in the wavelength range from 300â1100 nm on Earth. The removal of an equivalent layer thickness around 1 ÎŒm is sufficient for the formation of visible dark continuous DDTs on Mars and Earth. The next type of DDTs, dark cycloidal DDTs, are characterized by their low albedo pattern of overlapping scallops. Terrestrial in situ studies imply that they are formed when sand-sized material that is eroded from the outer vortex area of a dust devil is redeposited in annular patterns in the central vortex region. This type of DDT can also be found in on Mars in orbital image data, and although in situ studies are lacking, terrestrial analog studies, laboratory work, and numerical modeling suggest they have the same formation mechanism as those on Earth. Finally, bright DDTs are characterized by their continuous track pattern and high albedo compared to their undisturbed surroundings. They are found on both planets, but to date they have only been analyzed in situ on Earth. Here, the destruction of aggregates of dust, silt and sand by dust devils leads to smooth surfaces in contrast to the undisturbed rough surfaces surrounding the track. The resulting change in photometric properties occurs because the smoother surfaces have a higher reflectance compared to the surrounding rough surface, leading to bright DDTs. On Mars, the destruction of surficial dust-aggregates may also lead to bright DDTs. However, higher reflective surfaces may be produced by other formation mechanisms, such as dust compaction by passing dust devils, as this may also cause changes in photometric properties. On Mars, DDTs in general are found at all elevations and on a global scale, except on the permanent polar caps. DDT maximum areal densities occur during spring and summer in both hemispheres produced by an increase in dust devil activity caused by maximum insolation. Regionally, dust devil densities vary spatially likely controlled by changes in dust cover thicknesses and substrate materials. This variability makes it difficult to infer dust devil activity from DDT frequencies. Furthermore, only a fraction of dust devils leave tracks. However, DDTs can be used as proxies for dust devil lifetimes and wind directions and speeds, and they can also be used to predict lander or rover solar panel clearing events. Overall, the high DDT frequency in many areas on Mars leads to drastic albedo changes that affect large-scale weather patterns
The Sensitivity of Ligo to a Stochastic Background, and its Dependance on the Detector Orientations
We analyze the sensitivity of a network of interferometer gravitational-wave
detectors to the gravitational-wave stochastic background, and derive the
dependence of this sensitivity on the orientations of the detector arms. We
build on and extend the recent work of Christensen, but our conclusion for the
optimal choice of orientations of a pair of detectors differs from his. For a
pair of detectors (such as LIGO) that subtends an angle at the center of the
earth of \,\alt 70^\circ, we find that the optimal configuration is for each
detector to have its arms make an angle of (modulo ) with
the arc of the great circle that joins them. For detectors that are farther
separated, each detector should instead have one arm aligned with this arc. We
also describe in detail the optimal data-analysis algorithm for searching for
the stochastic background with a detector network, which is implicit in earlier
work of Michelson. The LIGO pair of detectors will be separated by . The minimum detectable stochastic energy-density for these
detectors with their currently planned orientations is greater than
what it would be if the orientations were optimal.Comment: 56 pages, 10 figures, Caltech preprint GRP-347, submitted to Phys Rev
D, uses revtex macro
Growth capacity of thermotolerant campylobacters in culture media supplemented with pig and cow blood
Detector Description and Performance for the First Coincidence Observations between LIGO and GEO
For 17 days in August and September 2002, the LIGO and GEO interferometer
gravitational wave detectors were operated in coincidence to produce their
first data for scientific analysis. Although the detectors were still far from
their design sensitivity levels, the data can be used to place better upper
limits on the flux of gravitational waves incident on the earth than previous
direct measurements. This paper describes the instruments and the data in some
detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial
change
Search for Gravitational Waves from Primordial Black Hole Binary Coalescences in the Galactic Halo
We use data from the second science run of the LIGO gravitational-wave
detectors to search for the gravitational waves from primordial black hole
(PBH) binary coalescence with component masses in the range 0.2--.
The analysis requires a signal to be found in the data from both LIGO
observatories, according to a set of coincidence criteria. No inspiral signals
were found. Assuming a spherical halo with core radius 5 kpc extending to 50
kpc containing non-spinning black holes with masses in the range 0.2--, we place an observational upper limit on the rate of PBH coalescence
of 63 per year per Milky Way halo (MWH) with 90% confidence.Comment: 7 pages, 4 figures, to be submitted to Phys. Rev.
A Pre-Landing Assessment of Regolith Properties at the InSight Landing Site
This article discusses relevant physical properties of the regolith at the Mars InSight landing site as understood prior to landing of the spacecraft. InSight will land in the northern lowland plains of Mars, close to the equator, where the regolith is estimated to be â„3--5 m thick. These investigations of physical properties have relied on data collected from Mars orbital measurements, previously collected lander and rover data, results of studies of data and samples from Apollo lunar missions, laboratory measurements on regolith simulants, and theoretical studies. The investigations include changes in properties with depth and temperature. Mechanical properties investigated include density, grain-size distribution, cohesion, and angle of internal friction. Thermophysical properties include thermal inertia, surface emissivity and albedo, thermal conductivity and diffusivity, and specific heat. Regolith elastic properties not only include parameters that control seismic wave velocities in the immediate vicinity of the Insight lander but also coupling of the lander and other potential noise sources to the InSight broadband seismometer. The related properties include Poissonâs ratio, P- and S-wave velocities, Youngâs modulus, and seismic attenuation. Finally, mass diffusivity was investigated to estimate gas movements in the regolith driven by atmospheric pressure changes. Physical properties presented here are all to some degree speculative. However, they form a basis for interpretation of the early data to be returned from the InSight mission.Additional co-authors: Nick Teanby and Sharon Keda
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