2,125 research outputs found
A study to define meteorological uses and performance requirements for the Synchronous Earth Observatory Satellite
The potential meteorological uses of the Synchronous Earth Observatory Satellite (SEOS) were studied for detecting and predicting hazards to life, property, or the quality of the environment. Mesoscale meteorological phenonmena, and the observations requirements for SEOS are discussed along with the sensor parameters
Sterigmatocystin production by Aspergillus nidulans
Sterigmatocystin (ST), a mycotoxin with the molecular formula C18 H12 O6, is reported from seven genera of fungi, including 22 species of Aspergillus (Cole and Cox 1981 Handbook of Toxic Fungal Metabolites, Academic Press pp 67-93)
Pod Yield Comparison of Pure-Line Peanut Selections Simultaneously Developed from Georgia and Zimbabwe Breeding Programs
Crosses were made between two widely grown U.S. peanut (Arachis hypogaea L.) cultivars, ‘Florunner’ and Florigiant’, and two genotypes adapted to growing conditions on the plateau of tropical Africa, ‘Makulu Red’ and 486 GKP. F2 seed populations were equally divided between Georgia and Zimbabwe. Subsequently, pedigree selection was practised simultaneously at both locations in the early segregating generations. The highest yielding pureline selections were then interchanged, and combined yield evaluations were determined over three growing seasons at each location.
‘Florunner’, ‘Florigiant’, and the Georgia pureline selections tested at the Georgia location had significantly higher pod yields than ‘Makulu Red’, 486 GKP, and the Zimbabwe selections. Conversely, the mean yield of the Zimbabwe selections tested m Zimbabwe was significantly higher than that of the Georgia selections. Thus, the breeding environment under which selection is conducted among cross populations strongly influences the yield adaptability of selected peanut genotype
The Nature of SN 1961V
The nature of SN 1961V has been uncertain. Its peculiar optical light curve
and slow expansion velocity are similar to those of super-outbursts of luminous
blue variables (LBVs), but its nonthermal radio spectral index and declining
radio luminosity are consistent with decades-old supernovae (SNe). We have
obtained Hubble Space Telescope STIS images and spectra of the stars in the
vicinity of SN 1961V, and find Object 7 identified by Filippenko et al. to be
the closest to the optical and radio positions of SN 1961V. Object 7 is the
only point source detected in our STIS spectra and only its H-alpha emission is
detected; it cannot be the SN or its remnant because of the absence of
forbidden lines. While the H-alpha line profile of Object 7 is remarkably
similar to that of eta Car, the blue color (similar to an A2Ib supergiant) and
lack of appreciable variability are unlike known post-outburst LBVs. We have
also obtained Very Long Baseline Array (VLBA) observations of SN 1961V at 18
cm. The non-detection of SN 1961V places a lower limit on the size of the
radio-emitting region, 7.6 mas or 0.34 pc, which implies an average expansion
velocity in excess of 4,400 km/s, much higher than the optical expansion
velocity measured in 1961. We conclude the following: (1) A SN occurred in the
vicinity of SN 1961V a few decades ago. (2) If the SN 1961V light maximum
originates from a giant eruption of a massive star, Object 7 is the most
probable candidate for the survivor, but its blue color and lack of significant
variability are different from a post-outburst eta Car. (3) The radio SN and
Object 7 could be physically associated with each other through a binary
system. (4) Object 7 needs to be monitored to determine its nature and
relationship to SN 1961V.Comment: 16 pages, 3 figures, accepted by the Astronomical Journal for the
2004 May issu
Absolute-Magnitude Distributions and Light Curves of Stripped-Envelope Supernovae
The absolute visual magnitudes of three Type IIb, 11 Type Ib and 13 Type Ic
supernovae (collectively known as stripped-envelope supernovae) are studied by
collecting data on the apparent magnitude, distance, and interstellar
extinction of each event. Weighted and unweighted mean absolute magnitudes of
the combined sample as well as various subsets of the sample are reported. The
limited sample size and the considerable uncertainties, especially those
associated with extinction in the host galaxies, prevent firm conclusions
regarding differences between the absolute magnitudes of supernovae of Type Ib
and Ic, and regarding the existence of separate groups of overluminous and
normal-luminosity stripped-envelope supernovae. The spectroscopic
characteristics of the events of the sample are considered. Three of the four
overluminous events are known to have had unusual spectra. Most but not all of
the normal luminosity events had typical spectra. Light curves of
stripped-envelope supernovae are collected and compared. Because SN 1994I in
M51 was very well observed it often is regarded as the prototypical Type Ic
supernova, but it has the fastest light curve in the sample. Light curves are
modeled by means of a simple analytical technique that, combined with a
constraint on E/M from spectroscopy, yields internally consistent values of
ejected mass, kinetic energy, and nickel mass.Comment: 39 pages, 14 figures, 7 tables; Accepted to A
C-axis Raman spectra of a normal plane-chain bilayer cuprate and the pseudogap
We investigate the Raman spectra in the geometry where both incident and
scattered photon polarizations are parallel to the -direction, for a
plane-chain bilayer coupled via a single-particle tunneling . The
Raman vertex is derived in the tight-binding limit and in the absence of
Coulomb screening, the Raman intensity can be separated into intraband
() and interband () transitions. In the
small- limit, the interband part dominates and a pseudogap will appear
as it does in the conductivity. Coulomb interactions bring in a two-particle
coupling and result in the breakdown of intra- and interband separation.
Nevertheless, when is small, the Coulomb screening () has little effect on the intensity to which the unscreened
interband transitions contribute most. In general, the total Raman spectra are
strongly dependent on the magnitude of .Comment: 23 pages, 6 figures, submitted to Phys. Rev.
Optical sum in Nearly Antiferromagnetic Fermi Liquid Model
We calculate the optical sum (OS) and the kinetic energy (KE) for a tight
binding band in the Nearly Antiferromagnetic Fermi Liquid (NAFFL) model which
has had some success in describing the electronic structure of the high
cuprates. The interactions among electrons due to the exchange of spin
fluctuations profoundly change the probability of occupation of states of momentum {\bf k} and spin which is the
central quantity in the calculations of OS and KE. Normal and superconducting
states are considered as a function of temperature. Both integrals are found to
depend importantly on interactions and an independent electron model is
inadequate.Comment: 9 Pages, 5 Figures Accepted for publication in Phys. Rev.
Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydro Models
We have performed detailed NLTE spectral synthesis modeling of 2 types of 1-D
hydro models: the very highly parameterized deflagration model W7, and two
delayed detonation models. We find that overall both models do about equally
well at fitting well observed SNe Ia near to maximum light. However, the Si II
6150 feature of W7 is systematically too fast, whereas for the delayed
detonation models it is also somewhat too fast, but significantly better than
that of W7. We find that a parameterized mixed model does the best job of
reproducing the Si II 6150 line near maximum light and we study the differences
in the models that lead to better fits to normal SNe Ia. We discuss what is
required of a hydro model to fit the spectra of observed SNe Ia near maximum
light.Comment: 29 pages, 14 figures, ApJ, in pres
Effect of anisotropy on universal transport in unconventional superconductors
We investigate the universal electronic transport for a mixed
+s-wave superconductor in the presence of an anisotropic
elliptical Fermi surface. Similar to the universal low-temperature transport
predicted in a -wave superconductor with a circular Fermi surface,
anisotropic universal features are found in the low-temperature microwave
conductivity, and thermal conductivity in the anisotropic system. The effects
of anisotropy on the penetration depth, impurity induced suppression, and
the zero-frequency density of states are also considered. While a small amount
of anisotropy can lead to a strong suppression of the effective scattering rate
and hence the density of states at zero frequency, experimental data suggests
that large effects are restored by a negative -component gap admixture.Comment: 8 page
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