37,223 research outputs found
Tropical cyclone intensity change. A quantitative forecasting scheme
One to two day future tropical cyclone intensity change from both a composite and an individual case point-of-view are discussed. Tropical cyclones occurring in the Gulf of Mexico during the period 1957-1977 form the primary data source. Weather charts of the NW Atlantic were initially examined, but few differences were found between intensifying and non-intensifying cyclones. A rawinsonde composite analysis detected composite differences in the 200 mb height fields, the 850 mb temperature fields, the 200 mb zonal wind and the vertical shears of the zonal wind. The individual cyclones which make up the composite study were then separately examined using this composite case knowledge. Similar parameter differences were found in a majority of individual cases. A cyclone intensity change forecast scheme was tested against independent storm cases. Correct predictions of intensification or non-intensification could be made approximately 75% of the time
Preliminary design study - Oxidizer tank relief valve, Flox-Atlas airborne Final report
Protecting fluorine-liquid oxygen Atlas launch vehicle oxidizer tank against overpressurizatio
General N = 1 Supersymmetric Flux Vacua of (Massive) Type IIA String Theory
We derive conditions for the existence of four-dimensional \N=1
supersymmetric flux vacua of massive type IIA string theory with general
supergravity fluxes turned on. For an SU(3) singlet Killing spinor, we show
that such flux vacua exist only when the internal geometry is nearly-K\"ahler.
The geometry is not warped, all the allowed fluxes are proportional to the mass
parameter and the dilaton is fixed by a ratio of (quantized) fluxes. The
four-dimensional cosmological constant, while negative, becomes small in the
vacuum with the weak string coupling.Comment: 4 page
Use of fruit and vegetable waste as growth media in bacterial biocementation for ground improvement applications
The paper investigates the use of mixed fruit and vegetable (FV) waste to extract liquid to grow bacteria. The bacteria will be used to induce biocementation of soils and two metabolic pathways are examined. These are the ureolytic pathway and the carbonic anhydrase pathway (which absorbs CO2). The growing medium produced from fruit and vegetable waste is compared with a commercial growing medium. The results show the feasibility of using FV as a growth medium to successfully biocement soil and coal ash. A typical FV medium contains 3% total sugar and 0.302 mg/100 ml of protein. The results show that vegetable stalks and fruit peel media support the growth of both ureolytic bacteria B. licheniformis and U-1, a carbonic anhydrase-producing bacteria. The use of FV waste to grow bacteria leads to a reduction in biocementation costs for ground improvement applications
Orbital control in strained ultra-thin LaNiO/LaAlO superlattices
In pursuit of rational control of orbital polarization, we present a combined
experimental and theoretical study of single unit cell superlattices of the
correlated metal LaNiO and the band insulator LaAlO. Polarized x-ray
absorption spectra show a distinct asymmetry in the orbital response under
strain. A splitting of orbital energies consistent with octahedral distortions
is found for the case of compressive strain. In sharp contrast, for tensile
strain, no splitting is found although a strong orbital polarization is
present. Density functional theory calculations including a Hubbard U term
reveal that this asymmetry is a result of the interplay of strain and
confinement induces octahedral rotations and distortions and altered covalency
in the bonding across the interfacial Ni-O-Al apical oxygen, leading to a
charge disporportionation at the Ni sites for tensile strain.Comment: 4 pages. 5 figure
Strain-mediated metal-insulator transition in epitaxial ultra-thin films of NdNiO3
We have synthesized epitaxial NdNiO ultra-thin films in a
layer-by-layer growth mode under tensile and compressive strain on SrTiO
(001) and LaAlO (001), respectively. A combination of X-ray diffraction,
temperature dependent resistivity, and soft X-ray absorption spectroscopy has
been applied to elucidate electronic and structural properties of the samples.
In contrast to the bulk NdNiO, the metal-insulator transition under
compressive strain is found to be completely quenched, while the transition
remains under the tensile strain albeit modified from the bulk behavior.Comment: 4 pages, 4 figure
Effect of polar discontinuity on the growth of LaNiO3/LaAlO3 superlattices
We have conducted a detailed microscopic investigation of [LaNiO3(1
u.c.)/LaAlO3(1 u.c.)]N superlattices grown on (001) SrTiO3 and LaAlO3 to
explore the influence of polar mismatch on the resulting electronic and
structural properties. Our data demonstrate that the initial growth on the
non-polar SrTiO3 surface leads to a rough morphology and unusual 2+ valence of
Ni in the first LaNiO3 layer, which is not observed after growth on the polar
surface of LaAlO3. A newly devised model suggests that the polar mismatch can
be resolved if the perovskite layers grow with an excess of LaO, which also
accounts for the observed electronic, chemical, and structural effects.Comment: 3 pages, 3 figure
Silicon isotopic abundance toward evolved stars and its application for presolar grains
Galactic chemical evolution (GCE) is important for understanding the
composition of the present-day interstellar medium (ISM) and of our solar
system. In this paper, we aim to track the GCE by using the 29Si/30Si ratios in
evolved stars and tentatively relate this to presolar grain composition. We
used the APEX telescope to detect thermal SiO isotopologue emission toward four
oxygen-rich M-type stars. Together with the data retrieved from the Herschel
science archive and from the literature, we were able to obtain the 29Si/30Si
ratios for a total of 15 evolved stars inferred from their optically thin 29SiO
and 30SiO emission. These stars cover a range of masses and ages, and because
they do not significantly alter 29Si/30Si during their lifetimes, they provide
excellent probes of the ISM metallicity (or 29Si/30Si ratio) as a function of
time. The 29Si/30Si ratios inferred from the thermal SiO emission tend to be
lower toward low-mass oxygen-rich stars (e.g., down to about unity for W Hya),
and close to an interstellar or solar value of 1.5 for the higher-mass carbon
star IRC+10216 and two red supergiants. There is a tentative correlation
between the 29Si/30Si ratios and the mass-loss rates of evolved stars, where we
take the mass-loss rate as a proxy for the initial stellar mass or current
stellar age. This is consistent with the different abundance ratios found in
presolar grains. We found that older objects (up to possibly 10 Gyr old) in our
sample trace a previous, lower 29Si/30Si value of about 1. Material with this
isotopic ratio is present in two subclasses of presolar grains, providing
independent evidence of the lower ratio. Therefore, the 29Si/30Si ratio derived
from the SiO emission of evolved stars is a useful diagnostic tool for the
study of the GCE and presolar grains.Comment: 7 pages, 4 figure
Ornstein-Zernike equation and Percus-Yevick theory for molecular crystals
We derive the Ornstein-Zernike equation for molecular crystals of axially
symmetric particles and apply the Percus-Yevick approximation to this system.
The one-particle orientational distribution function has a nontrivial
dependence on the orientation and is needed as an input. Despite some
differences, the Ornstein-Zernike equation for molecular crystals has a similar
structure as for liquids. We solve both equations for hard ellipsoids on a sc
lattice. Compared to molecular liquids, the tensorial orientational correlators
exhibit less structure. However, depending on the lengths a and b of the
rotation axis and the perpendicular axes of the ellipsoids, different behavior
is found. For oblate and prolate ellipsoids with b >= 0.35 (units of the
lattice constant), damped oscillations in distinct directions of direct space
occur for some correlators. They manifest themselves in some correlators in
reciprocal space as a maximum at the Brillouin zone edge, accompanied by maxima
at the zone center for other correlators. The oscillations indicate alternating
orientational fluctuations, while the maxima at the zone center originate from
nematic-like orientational fluctuations. For a <= 2.5 and b <= 0.35, the
oscillations are weaker. For a >= 3.0 and b <= 0.35, no oscillations occur any
longer. For many of the correlators in reciprocal space, an increase of a at
fixed b leads to a divergence at the zone center q = 0, consistent with
nematic-like long range fluctuations, and for some oblate and prolate systems
with b ~< 1.0 a simultaneous tendency to divergence of few other correlators at
the zone edge is observed. Comparison with correlators from MC simulations
shows satisfactory agreement. We also obtain a phase boundary for
order-disorder transitions.Comment: 20 pages, 13 figures, submitted to Phys. Rev.
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