1,939 research outputs found
Discovery of Reflection Nebulosity Around Five Vega-like Stars
Coronagraphic optical observations of six Vega-like stars reveal reflection
nebulosities, five of which were previously unknown. The nebulosities
illuminated by HD 4881, HD 23362, HD 23680, HD 26676, and HD 49662 resemble
that of the Pleiades, indicating an interstellar origin for dust grains. The
reflection nebulosity around HD 123160 has a double-arm morphology, but no
disk-like feature is seen as close as 2.5 arcsec from the star in K-band
adaptive optics data. We demonstrate that uniform density dust clouds
surrounding HD 23362, HD 23680 and HD 123160 can account for the observed
12-100 micron spectral energy distributions. For HD 4881, HD 26676, and HD
49662 an additional emission source, such as from a circumstellar disk or
non-equilibrium grain heating, is required to fit the 12-25 micron data. These
results indicate that in some cases, particularly for Vega-like stars located
beyond the Local Bubble (>100 pc), the dust responsible for excess thermal
emission may originate from the interstellar medium rather than from a
planetary debris system.Comment: The Astrophysical Journal, in press for March, 2002 (32 pages, 13
figures
Bacteriological Profile of Palm Oil Sale Sites in Selected Markets in Kaduna State, Nigeria
The bacteriological profile of palm oil sale sites in selected markets in Kaduna state, Nigeria were evaluated using standard techniques by collecting a (60) soil samples. Aside from bacteriological profile, pH, moisture content, temperature and lipase activity analyzed. The soil samples had pH that ranged from acidic to neutral (3.0-8.00) which indicates the presence of hydrolytic enzymes. Microorganisms isolated from soil samples palm oil sale sites were screened from their lipase producing ability. A total of (10) ten bacteria belonging to the genera Bacillus, Streptococcus, Lactobacillus, Streptobacillus, Micrococcus, Staphylococcus and Pseudomonas. The lipolytic activity of the bacteria when screened on solid agar ranged for 1.1 to 3.2cm, 2.3-3.7cm, 2.3-6.7cm at 24, 48 and 72hours respectively while that of fungal species ranged from 0.6 to12cm, 0.3-1.5cm and 1.1-1. 7cm at 3,7,14 days of incubation respectively. Exo-enzyme was produced from the various species screened for lipolytic activities. The study shows that Bacillus subtilis and Trichoderma spp. had high potential
The Coronal X-ray Spectrum of the Multiple Weak-Lined T Tauri Star System HD 98800
We present high-resolution X-ray spectra of the multiple (hierarchical
quadruple) weak-lined T Tauri star system HD 98800, obtained with the High
Energy Transmission Gratings Spectrograph (HETGS) aboard the Chandra X-ray
Observatory (CXO). In the zeroth-order CXO/HETGS X-ray image, both principle
binary components of HD 98800 (A and B, separation 0.8'') are detected;
component A was observed to flare during the observation. The infrared excess
(dust disk) component, HD 98800B, is a factor ~4 fainter in X-rays than the
apparently ``diskless'' HD 98800A, in quiescence. The line ratios of He-like
species (e.g., Ne IX, O VII) in the HD 98800A spectrum indicate that the
X-ray-emitting plasma around HD 98800 is in a typical coronal density regime
(log n <~ 11). We conclude that the dominant X-ray-emitting component(s) of HD
98800 is (are) coronally active. The sharp spectral differences between HD
98800 and the classical T Tauri star TW Hya demonstrate the potential utility
of high-resolution X-ray spectroscopy in providing diagnostics of pre-main
sequence accretion processes.Comment: 11 pages, 5 figures; to appear in the Astrophysical Journal (Letters
A Keplerian Disk around the Herbig Ae star HD169142
We present Submillimeter Array observations of the Herbig Ae star HD169142 in
1.3 millimeter continuum emission and 12CO J=2-1 line emission at 1.5 arcsecond
resolution that reveal a circumstellar disk. The continuum emission is centered
on the star position and resolved, and provides a mass estimate of about 0.02
solar masses for the disk. The CO images show patterns in position and velocity
that are well matched by a disk in Keplerian rotation with low inclination to
the line-of-sight. We use radiative transfer calculations based on a flared,
passive disk model to constrain the disk parameters by comparison to the
spectral line emission. The derived disk radius is 235 AU, and the inclination
is 13 degrees. The model also necessitates modest depletion of the CO
molecules, similar to that found in Keplerian disks around T Tauri stars.Comment: 10 pages, 2 figures, accepted by A
Finite Element Analysis for Stress-Strain Parameter of Projectile Impeded Glass Fibre Reinforced Polyester (Gfrp) Composites
For the treatment of progressive damage, spatial discretization is required so that numerical techniques such as the finite element method or finite difference method would be advantageous. Finite element and finite difference techniques have also been applied to impact problems because they are more versatile at modeling boundary conditions and local phenomena such as stresses and strain under a point load. This paper investigates the stress-strain magnitude on body amour composites of glass fibre reinforced polyester (GFRP), when hit with ogival and conical nosed projectiles through the application of finite element analysis using ANSYS software version 10.1. The finite element result of the plain stress analysis shows that the composite is stronger in the longitudinal direction. This is supported by the fact that the maximum stress of 328.125MPa was recorded in the X direction while the maximum stress of 57.726MPa was recorded in the Y direction. The analysis also indicates that the maximum influence of the stress was experienced around the incident hole and the minimum at the exterior boarders of the samples. Keywords: Finite Element, Plain Stress Analysis, Projectiles, ANSYS Software, Body Amour, Fibre Reinforcement
Tropomyosin 2.1 collaborates with fibronectin to promote TGF-β1-induced contraction of human lung fibroblasts
Many lung diseases are characterized by fibrosis, leading to impaired tissue patency and reduced lung function. Development of fibrotic tissue depends on two-way interaction between the cells and the extra-cellular matrix (ECM). Concentration-dependent increased stiffening of the ECM is sensed by the cells, which in turn increases intracellular contraction and pulling on the matrix causing matrix reorganization and further stiffening. It is generally accepted that the inflammatory cytokine growth factor β1 (TGF-β1) is a major driver of lung fibrosis through the stimulation of ECM production. However, TGF-β1 also regulates the expression of members of the tropomyosin (Tm) family of actin associating proteins that mediate ECM reorganization through intracellular-generated forces. Thus, TGF-β1 may mediate the bi-directional signaling between cells and the ECM that promotes tissue fibrosis. Using combinations of cytokine stimulation, mRNA, protein profiling and cellular contractility assays with human lung fibroblasts, we show that concomitant induction of key Tm isoforms and ECM by TGF-β1, significantly accelerates fibrotic phenotypes. Knocking down Tpm2.1 reduces fibroblast-mediated collagen gel contraction. Collectively, the data suggest combined ECM secretion and actin cytoskeleton contractility primes the tissue for enhanced fibrosis. Our study suggests that Tms are at the nexus of inflammation and tissue stiffening. Small molecules targeting specific Tm isoforms have recently been designed; thus targeting Tpm2.1 may represent a novel therapeutic target in lung fibrosis
Evidence of reproductive isolation confirms that Apis andreniformis (Smith, 1858) is a separate species from sympatric Apis florea (Fabricius, 1787).
The species Apis andreniformis (Smith, 1858), the small dwarf honey bee of South-east Asia, is recognized as a valid biological species. This recognition is based on distinctive endophallus characteristics in comparison with sympatric Apis florea (Fabricius, 1787). Additionally, scanning electron microscope images of drone basitarsi are presented, as are preliminary comparisons of wing venation
Spitzer/IRS spectroscopy of high mass precursors to planetary nebulae
We present Spitzer/IRS observations of a small sample of heavily obscured
IRAS sources displaying both the infrared and OH maser emission characteristic
of OH/IR stars on the asymptotic giant branch (AGB), but also radio continuum
emission typical of ionized planetary nebulae (PNe), the so-called OHPNe. Our
observations show that their mid-infrared spectra are dominated by the
simultaneous presence of strong and broad amorphous silicate absorption
features together with crystalline silicate features, originated in their
O-rich circumstellar shells. Out of the five sources observed, three of them
are clearly non-variable at infrared wavelengths, confirming their post-AGB
status, while the remaining two still show strong photometric fluctuations, and
may still have not yet departed from the AGB. One of the non-variable sources
in the sample, IRAS 17393-2727, displays a strong [Ne II] nebular emission at
12.8 microns, indicating that the ionization of its central region has already
started. This suggests a rapid evolution from the AGB to the PN stage. We
propose that these heavily obscured OHPNe represent the population of high mass
precursors to PNe in our Galaxy.Comment: To appear in The Astrophysical Journal Letters (scheduled in the 2007
September 1 issue
Indigenous knowledges and development: a postcolonial caution
As a result of the failure of formal top-down development, there has recently been increased interest in the possibilities of drawing upon the indigenous knowledges of those in the communities involved, in an attempt to produce more effective development strategies. The concept of indigenous knowledge calls for the inclusion of local voices and priorities, and promises empowerment through ownership of the process. However, there has been little critical examination of the ways in which indigenous knowledges have been included in the development process. Drawing upon postcolonial theory, this article suggests that indigenous knowledges are often drawn into development by both theorists and development institutions in a very limited way, failing to engage with other ways of perceiving development, and thus missing the possibility of devising more challenging alternatives
- …