2,254 research outputs found
Subresultants in multiple roots: an extremal case
We provide explicit formulae for the coefficients of the order-d polynomial
subresultant of (x-\alpha)^m and (x-\beta)^n with respect to the set of
Bernstein polynomials \{(x-\alpha)^j(x-\beta)^{d-j}, \, 0\le j\le d\}. They are
given by hypergeometric expressions arising from determinants of binomial
Hankel matrices.Comment: 18 pages, uses elsart. Revised version accepted for publication at
Linear Algebra and its Application
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
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
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
Lack of analgesic efficacy in female rats of\ud the commonly recommended oral dose of\ud buprenorphine
Previous work in our laboratory showed that the recommended oral dose of buprenorphine (0.5 mg/kg) was not as effective\ud
as the standard therapeutic subcutaneous dose for postoperative analgesia in male Long-Evans (hooded) and Sprague-Dawley (albino) rats. The aim of the current study was to extend this analysis to female rats. We measured the pain threshold in adult female rats in diestrus or proestrus before and 30 and 60 min after oral buprenorphine (0.5 mg/kg,), the standard subcutaneous dose of buprenorphine (0.05 mg/kg), or vehicle only (1 ml/kg each orally and subcutaneously). Female rats showed an increased pain threshold (analgesia) after subcutaneous buprenorphine but no change in pain threshold after either oral buprenorphine or vehicle only. Estrous cycle stage (proestrus versus diestrus) did not affect the analgesic effects of buprenorphine, but rats in proestrus showed significantly lower pain thresholds (less tolerance to pain) than did those in diestrus. These results show that the oral dose of buprenorphine recommended for postoperative analgesic care does not induce significant analgesia in female rats and therefore is not as effective as the standard subcutaneous dose
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
A double-lined spectroscopic orbit for the young star HD 34700
We report high-resolution spectroscopic observations of the young star HD
34700, which confirm it to be a double-lined spectroscopic binary. We derive an
accurate orbital solution with a period of 23.4877 +/- 0.0013 days and an
eccentricity of e = 0.2501 +/- 0.0068. The stars are found to be of similar
mass (M2/M1 = 0.987 +/- 0.014) and luminosity. We derive also the effective
temperatures (5900 K and 5800 K) and projected rotational velocities (28 km/s
and 22 km/s) of the components. These values of v sin i are much higher than
expected for main-sequence stars of similar spectral type (G0), and are not due
to tidal synchronization. We discuss also the indicators of youth available for
the object. Although there is considerable evidence that the system is young
--strong infrared excess, X-ray emission, Li I 6708 absorption (0.17 Angstroms
equivalent width), H alpha emission (0.6 Angstroms), rapid rotation-- the
precise age cannot yet be established because the distance is unknown.Comment: 17 pages, including 2 figures and 2 tables. Accepted for publication
in AJ, to appear in February 200
Dense medium machine processing method for palm kernel/ shell separation
A machine processing method for the separation of cracked palm kernel from the shells using dense medium is presented. Cracked palm kernel is a mixture of kernels, broken shells, dusts and other impurities. In order to produce quality palm kernel oil, clean palm kernel nuts must be used, therefore the need for the separation of the palm kernel nuts from the shells. Several methods are used in the separation. The handpicking method yields good quality kernels but the method is slow, laborious and unsuitable for large scale productions. Salt solution method is unsuitable because of acidity of concentrated solution of salt used which affects the palm kernel as well as the quality of the oil produced. The clay suspension method is time consuming, laborious and cumbersome. The limitations of the above-stated methods of separation gave rise to the need for alternative methods of separation. A machine processing method using dense medium, a separator, a shell collector and a kernel collector was proposed. A machine was developed which produced kernels that contain 6.5% moisture content, 51% fat, 8.9% protein, 7% free fatty acid and 1.9% ash content. The kernels from the machine separation method were compared with the kernels produced by the other methods. The results revealed that the kernels obtained by hand picking method contains 7% moisture content, 52% fat, 9% protein, 7% free fatty acid and 2% ash content. The ones obtained using salt solution bath method contain 6% moisture content, 45% fat, 8% protein, 4.5% free fatty acid and 1.7% ash content. The ones obtained using conventional clay bath method contain 8% moisture content, 48% fat, 8.5% protein, 5.5% free fatty acid and 1.8% ash content. From the results obtained, the dense medium separation and clay suspension methods provide a better and cleaner means of palm kernel nut and shell separation because of the low moisture content and high fat, protein and ash contents among the methods of separation used.Keywords: Palm Kernel, Shell, Separation, Machine Processing Method, Dense Mediu
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