2,234 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
Development of âRL Plusâ: winter wheat variety performance in relation to site characteristics (HGCA Project Report No. 365)
This project developed RL Plus, an augmented version of the Recommended Lists for Cereals and Oilseeds, published by the HGCA on CD and the internet (http://www.hgca.com) to provide the cereals and oilseeds industry with means of interrogating and analysing data from HGCA-funded variety trials. Given that RL Plus is fully documented and published in electronic form, it is not described further here. This report is confined to additional research analysing relative variety performance of winter wheat in terms of site
characteristics.
A spreadsheet was constructed of treated yields of winter wheat from 43 varieties across 506 trials (Recommended List, National List or BSPB trials) in the UK from harvests during 1992-2002. This included site information collected from the trials, and supplemented with the site location (OS coordinates), soil types, meteorological data and drought index derived during the project. Complete, or nearcomplete, data existed for 249 trials from harvests during 1993-2003. These data were used to investigate
factors associated with site variation in variety yields.
Data-mining techniques were used to identify site variables that explained variation in variety yields between sites. This information was used to build models to describe and predict patterns of variety variability due to site differences. Variation in variety yields could be modelled in terms of overall variety differences (43% variety variation accounted for), and variety interactions with large-scale trend due to geographic location (general climate, 16%), small-scale location trend specific to years (micro-climates, 14%), expected site yield (2%), late sown crops (crops sown on/after 30 October, 0.4%), sites with sandy or shallow soil (0.5%), sites with low soil K index (0.4%), differences between years (4.5%), differences between sites (unexplained by site variables, 2%), and other unexplained variation (18%). Further investigation suggested that other site variables, such as previous cropping, might also influence variety variability but that the relationship was local (differed between regions).
The results of the statistical analysis can be used to optimise use of the âVarieties on your Farmâ module of RL Plus. In general, geographic location appears to be the most important site variable influencing variation in variety yields across the UK. However, for particular varieties, the expected site yield, soil type or soil K index may be equally important
First Record of the Plains Minnow, Hybognathus placitus, in Canada
Seven Plains Minnows, Hybognathus placitus, Family Cyprinidae, were collected on 11 June 2003 from Morgan Creek, in Grasslands National Park, Saskatchewan, Canada. This collection is the first record of the species in Canada and extends the northern distribution limit of the species. Of 95 Hybognathus spp. collected at the site, only eight specimens were retained for positive identification because of the uncertain status of two conspecifics, the Western Silvery Minnow, H. argyritis, and the Brassy Minnow, H. hankinsoni, in Saskatchewan. Our findings should stimulate additional sampling to assess the identification and status of Hybognathus spp. in southwestern Saskatchewan. Accurate field identification of Hybognathus spp. remains an issue and collection of all specimens is recommended to accurately identify members within the genus
N, P and K budgets for crop rotations on nine organic farms in the UK
On organic farms, where the importation of materials to build/maintain soil fertility is restricted, it is important that a balance between inputs and outputs of nutrients is achieved to ensure both short-term productivity and long-term sustainability. This paper considers different approaches to nutrient budgeting on organic farms and evaluates the sources of bias in the measurements and/or estimates of the nutrient inputs and outputs. The paper collates 88 nutrient budgets compiled at the farm scale in 9 temperate countries. All the nitrogen (N) budgets showed an N surplus (average 83.2 kg N ha-1 year-1). The efficiency of N use, defined as outputs/inputs, was highest (0.9) and lowest (0.2) in arable and beef systems respectively. The phosphorus (P) and potassium (K) budgets showed both surpluses and deficits (average 3.6 kg P ha-1 year-1, 14.2 kg K ha-1 year-1) with horticultural systems showing large surpluses resulting from purchased manure. The estimation of N fixation and quantities of nutrients in purchased manures may introduce significant errors in nutrient budgets. Overall, the data illustrate the diversity of management systems in place on organic farms, and suggest that used together with soil analysis, nutrient budgets are a useful tool for improving the long-term sustainability of organic systems
NICMOS Observations of the Pre-Main-Sequence Planetary Debris System HD 98800
Spectral energy distributions (SEDs) from 0.4 to 4.7 microns are presented
for the two principal stellar components of HD~98800, A and B. The third major
component, an extensive planetary debris system (PDS), emits > 20% of the
luminosity of star B in a blackbody SED at 164 +/- 5K extending from mid-IR to
millimeter-wavelengths. At 0.95 microns a preliminary upper limit of < 0.06 is
obtained for the ratio of reflected light to the total from star B. This result
limits the albedo of the PDS to < 0.3. Values are presented for the
temperature, luminosity, and radius of each major systemic component.
Remarkable similarities are found between the PDS and the interplanetary debris
system around the Sun as it could have appeared a few million years after its
formation.Comment: LaTeX, 9 pages with 1 encapsulated postscript figure and one
specially formatted Table which is rendered as a postscript file and included
as a figure. Accepted for publication in Astrophysical Journal Letter
Sub-millimeter images of a dusty Kuiper belt around eta Corvi
We present sub-millimeter and mid-infrared images of the circumstellar disk
around the nearby F2V star eta Corvi. The disk is resolved at 850um with a size
of ~100AU. At 450um the emission is found to be extended at all position
angles, with significant elongation along a position angle of 130+-10deg; at
the highest resolution (9.3") this emission is resolved into two peaks which
are to within the uncertainties offset symmetrically from the star at 100AU
projected separation. Modeling the appearance of emission from a narrow ring in
the sub-mm images shows the observed structure cannot be caused by an edge-on
or face-on axisymmetric ring; the observations are consistent with a ring of
radius 150+-20AU seen at 45+-25deg inclination. More face-on orientations are
possible if the dust distribution includes two clumps similar to Vega; we show
how such a clumpy structure could arise from the migration over 25Myr of a
Neptune mass planet from 80-105AU. The inner 100AU of the system appears
relatively empty of sub-mm emitting dust, indicating that this region may have
been cleared by the formation of planets, but the disk emission spectrum shows
that IRAS detected an additional hot component with a characteristic
temperature of 370+-60K (implying a distance of 1-2AU). At 11.9um we found the
emission to be unresolved with no background sources which could be
contaminating the fluxes measured by IRAS. The age of this star is estimated to
be ~1Gyr. It is very unusual for such an old main sequence star to exhibit
significant mid-IR emission. The proximity of this source makes it a perfect
candidate for further study from optical to mm wavelengths to determine the
distribution of its dust.Comment: 22 pages, 4 figures. Scheduled for publication in ApJ 10 February
2005 issu
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
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A sulfated glycoprotein synthesized by Sertoli cells and by epididymal cells is a component of the sperm membrane
We report here the purification, partial characterization and immunofluorescent localization of a dimeric acidic glycoprotein (DAG-protein) secreted by cultures of Sertoli cells of rat testes. Partially purified protein was obtained after chromatography over Sepharose 4B under conditions which favored a soluble, nonaggregated form of the protein. Rechromatography over the same column under reducing conditions yielded very pure monomers of 41,000 daltons and 29,000 daltons. Antibodies were prepared against the mixed monomers and used to immunoprecipitate proteins in spent medium from cultures incubated with [35S] methionine, 35SO4 = or tunicamycin. DAG-protein and another protein (Band 4, 70,000 daltons) were coprecipitated by the antiserum and all contained 35SO4 = in their structures. It was shown by Western blotting that the antiserum cross-reacted very weakly with Band 4 protein. The DAG-protein polypeptides secreted in the presence of tunicamycin were assumed to lack N-glycosylation and exhibited apparent molecular weights of 27,000 and 21,000 daltons. Immunoprecipitations of media from organ cultures of testis and epididymis yielded DAG-protein of slightly lower molecular weight than the protein secreted in Sertoli cell cultures. Indirect immunofluorescence of DAG-protein in paraffin sections of testis and epididymis revealed that the protein was concentrated in the cytoplasm of Sertoli cells, on the stereocilia of epididymal principal cells, in the cytoplasm of epididymal halo cells, and was associated with late spermatids and mature sperm. Sperm were specifically labeled on the acrosome, at the neck, and on the endpiece of the tail. No enzymatic or structural function has been ascribed to DAG-protein as yet, but the protein must play a pivotal role in spermatogenesis because it is secreted by both the testis and epididymis and becomes an integral component of sperm
The Quantum Transverse Field Ising Model on an Infinite Tree from Matrix Product States
We give a generalization to an infinite tree geometry of Vidal's infinite
time-evolving block decimation (iTEBD) algorithm for simulating an infinite
line of quantum spins. We numerically investigate the quantum Ising model in a
transverse field on the Bethe lattice using the Matrix Product State ansatz. We
observe a second order phase transition, with certain key differences from the
transverse field Ising model on an infinite spin chain. We also investigate a
transverse field Ising model with a specific longitudinal field. When the
transverse field is turned off, this model has a highly degenerate ground state
as opposed to the pure Ising model whose ground state is only doubly
degenerate.Comment: 28 pages, 23 figures, PDFlate
The Papoose Flat Pluton of eastern California: a reassessment of its emplacement history in the light of new microstructural and crystallographic fabric observations
One of the most outstanding apparent examples in N America of a forcibly emplaced pluton is the Papoose Flat Pluton of eastern California. Sideways expansion of this granitic pluton, during emplacement into a series of Cambrian shelf strata, has been regarded by early workers as resulting in the observed intense crystal plastic deformation of the pluton's mylonitic border facies and surrounding country rocks. This deformation is evidenced by up to 90% thinning of individual stratigraphic layers within the pluton's metamorphic aureole, although such intense penetrative deformation of the country rocks is not observed outside the aureole. Previously published quartz c-axis fabrics associated with this deformation (and presented on projection planes oriented perpendicular to lineation) were interpreted as being symmetrical with respect to foliation and lineation, implying almost coaxial deformation histories. Such fabrics could be interpreted as indicating that the pluton evolved by "ballooningâ as a result of new magma being intruded into its core during emplacement. However, a major problem with applying the strict ballooning model to the Papoose Flat Pluton is that while oblate strains would be expected to develop in association with a ballooning mechanism, the mylonitic rocks of this elongate WNW-ESE-trending pluton and its aureole are characterised by both a strongly developed foliation, which is concordant with the pluton's margin, and an intense, NW-SE trending, shallow plunging stretching lineation. Previously published fabrics from the Papoose Flat Pluton and its metamorphic aureole have been rotated on to a projection plane oriented parallel to lineation and perpendicular to foliation. Examination of the fabrics in this projection plane has revealed that they are in fact dominantly asymmetric, and that a constant sense of asymmetry is detected across the pluton, suggesting a consistent (top-to-the-SE) shear-sense. This new interpretation is strongly supported by microstructural and petrofabric analysis of additional L-S tectonites collected, during recent fieldwork, from both the aureole and quartz veins within the pluton's gneissic border facies. Thus mylonite formation around the Papoose Flat Pluton could have involved large-scale consistently oriented translation and associated shearing, rather than passive "blister-likeâ coaxial deformation associated with pluton ballooning. It should be noted that mylonitic deformation is restricted to the western half of the pluton, features indicative of a more "permittedâ emplacement mechanism being found in the eastern portion of the pluton. The detected top-to-the-SE shear-sense could be interpreted as indicating that the granitic material forming the western part of the pluton was forcibly intruded in a northwestward direction from the pluton source as a nearly solidified wedge beneath a static cover of sedimentary rocks. Alternatively, the detected shear sense could also be interpreted as indicating SE-directed thrusting of the cover rocks over the underlying pluton, the western margin of the pluton suffering intense mylonitic deformation, while the eastern margin was located in a "stress-shadowâ region. If this alternative interpretation is correct, then the deformation temperatures indicated by the pattern of quartz c-axis fabrics dictate that thrusting must either be synchronous with pluton emplacement, or at least have commenced during the early stages of pluton coolin
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