8,022 research outputs found
On subsets of S^n whose (n + 1)-point subsets are contained in open hemispheres
We investigate the nature of subsets of spheres which satisfy a tameness condition associated with the Bieri–Groves FPm-conjecture. We find that there is a natural polyhedrality in the case of n-tame subsets of an (n − 1)-sphere. In the case n = 3 we establish a strong polyhedrality condition for certain maximal open 3-tame sets. Many examples are included
Biomass production and nitrogen dynamics in an integrated aquaculture/agriculture system
A combined aquaculture/agriculture system that brings together the three major components of a Controlled Ecological Life Support System (CELSS) - biomass production, biomass processing, and waste recycling - was developed to evaluate ecological processes and hardware requirements necessary to assess the feasibility of and define design criteria for integration into the Kennedy Space Center (KSC) Breadboard Project. The system consists of a 1 square meter plant growth area, a 500 liter fish culture tank, and computerized monitoring and control hardware. Nutrients in the hydrophonic solution were derived from fish metabolites and fish food leachate. In five months of continuous operation, 27.0 kg of lettuce tops, 39.9 kg of roots and biofilm, and 6.6 kg of fish (wet weights) were produced with 12.7 kg of fish food input. Based on dry weights, a biomass conversion index of 0.52 was achieved. A nitrogen budget was derived to determine partitioning of nitrogen within various compartments of the system. Accumulating nitrogen in the hypoponic solution indicated a need to enlarge the plant growth area, potentially increasing the biomass production and improving the biomass conversion index
Continuous hydroponic wheat production using a recirculating system
Continuous crop production, where plants of various ages are growing simultaneously in a single recirculating nutrient solution, is a possible alternative to batch production in a Controlled Ecological Life Support System. A study was conducted at John F. Kennedy Space Center where 8 trays (0.24 sq m per tray) of Triticum aestivum L. Yecora Rojo were grown simultaneously in a growth chamber at 23 C, 65 percent relative humidity, 1000 ppm CO2, continuous light, with a continuous flow, thin film nutrient delivery system. The same modified Hoagland nutrient solution was recirculated through the plant trays from an 80 L reservoir throughout the study. It was maintained by periodic addition of water and nutrients based on chemical analyses of the solution. The study was conducted for 216 days, during which 24 trays of wheat were consecutively planted (one every 9 days), 16 of which were grown to maturity and harvested. The remaining 8 trays were harvested on day 216. Grain yields averaged 520 g m(exp -2), and had an average edible biomass of 32 percent. Consecutive yields were unaffected by nutrient solution age. It was concluded that continual wheat production will work in this system over an extended period of time. Certain micronutrient deficiencies and toxicities posed problems and must be addressed in future continuous production systems
Flow pattern transition accompanied with sudden growth of flow resistance in two-dimensional curvilinear viscoelastic flows
We find three types of steady solutions and remarkable flow pattern
transitions between them in a two-dimensional wavy-walled channel for low to
moderate Reynolds (Re) and Weissenberg (Wi) numbers using direct numerical
simulations with spectral element method. The solutions are called
"convective", "transition", and "elastic" in ascending order of Wi. In the
convective region in the Re-Wi parameter space, the convective effect and the
pressure gradient balance on average. As Wi increases, the elastic effect
becomes suddenly comparable and the first transition sets in. Through the
transition, a separation vortex disappears and a jet flow induced close to the
wall by the viscoelasticity moves into the bulk; The viscous drag significantly
drops and the elastic wall friction rises sharply. This transition is caused by
an elastic force in the streamwise direction due to the competition of the
convective and elastic effects. In the transition region, the convective and
elastic effects balance. When the elastic effect dominates the convective
effect, the second transition occurs but it is relatively moderate. The second
one seems to be governed by so-called Weissenberg effect. These transitions are
not sensitive to driving forces. By the scaling analysis, it is shown that the
stress component is proportional to the Reynolds number on the boundary of the
first transition in the Re-Wi space. This scaling coincides well with the
numerical result.Comment: 33pages, 23figures, submitted to Physical Review
Registration of retinal images from Public Health by minimising an error between vessels using an affine model with radial distortions
In order to estimate a registration model of eye fundus images made of an
affinity and two radial distortions, we introduce an estimation criterion based
on an error between the vessels. In [1], we estimated this model by minimising
the error between characteristics points. In this paper, the detected vessels
are selected using the circle and ellipse equations of the overlap area
boundaries deduced from our model. Our method successfully registers 96 % of
the 271 pairs in a Public Health dataset acquired mostly with different
cameras. This is better than our previous method [1] and better than three
other state-of-the-art methods. On a publicly available dataset, ours still
better register the images than the reference method
Observational Prospects for Afterglows of Short Duration Gamma-ray Bursts
If the efficiency for producing -rays is the same in short duration
(\siml 2 s) Gamma-Ray Bursts (GRBs) as in long duration GRBs, then the
average kinetic energy of short GRBs must be times less than that of
long GRBs. Assuming further that the relativistic shocks in short and long
duration GRBs have similar parameters, we show that the afterglows of short
GRBs will be on average 10--40 times dimmer than those of long GRBs. We find
that the afterglow of a typical short GRB will be below the detection limit
(\siml 10 \microJy) of searches at radio frequencies. The afterglow would be
difficult to observe also in the optical, where we predict R \simg 23 a few
hours after the burst. The radio and optical afterglow would be even fainter if
short GRBs occur in a low-density medium, as expected in NS-NS and NS-BH merger
models. The best prospects for detecting short-GRB afterglows are with early
(\siml 1 day) observations in X-rays.Comment: 5 pages, 2 figures, submitted to ApJ lette
Objects that Sound
In this paper our objectives are, first, networks that can embed audio and
visual inputs into a common space that is suitable for cross-modal retrieval;
and second, a network that can localize the object that sounds in an image,
given the audio signal. We achieve both these objectives by training from
unlabelled video using only audio-visual correspondence (AVC) as the objective
function. This is a form of cross-modal self-supervision from video.
To this end, we design new network architectures that can be trained for
cross-modal retrieval and localizing the sound source in an image, by using the
AVC task. We make the following contributions: (i) show that audio and visual
embeddings can be learnt that enable both within-mode (e.g. audio-to-audio) and
between-mode retrieval; (ii) explore various architectures for the AVC task,
including those for the visual stream that ingest a single image, or multiple
images, or a single image and multi-frame optical flow; (iii) show that the
semantic object that sounds within an image can be localized (using only the
sound, no motion or flow information); and (iv) give a cautionary tale on how
to avoid undesirable shortcuts in the data preparation.Comment: Appears in: European Conference on Computer Vision (ECCV) 201
The Rapidly Fading Optical Afterglow of GRB 980519
GRB 980519 had the most rapidly fading of the well-documented GRB afterglows,
consistent with t^{-2.05 +/- 0.04} in BVRI as well as in X-rays during the two
days in which observations were made. We report VRI observations from the MDM
1.3m and WIYN 3.5m telescopes, and we synthesize an optical spectrum from all
of the available photometry. The optical spectrum alone is well fitted by a
power law of the form nu^{-1.20 +/- 0.25}, with some of the uncertainty due to
the significant Galactic reddening in this direction. The optical and X-ray
spectra together are adequately fitted by a single power law nu^{-1.05 +/-
0.10}. This combination of steep temporal decay and flat broad-band spectrum
places a severe strain on the simplest afterglow models involving spherical
blast waves in a homogeneous medium. Instead, the rapid observed temporal decay
is more consistent with models of expansion into a medium of density n(r)
proportional to r^{-2}, or with predictions of the evolution of a jet after it
slows down and spreads laterally. The jet model would relax the energy
requirements on some of the more extreme GRBs, of which GRB 980519 is likely to
be an example because of its large gamma-ray fluence and faint host galaxy.Comment: 13 pages, submitted to ApJ Letter
The radius and mass of the subgiant star bet Hyi from interferometry and asteroseismology
We have used the Sydney University Stellar Interferometer (SUSI) to measure
the angular diameter of beta Hydri. This star is a nearby G2 subgiant whose
mean density was recently measured with high precision using asteroseismology.
We determine the radius and effective temperature of the star to be
1.814+/-0.017 R_sun (0.9%) and 5872+/-44 K (0.7%) respectively. By combining
this value with the mean density, as estimated from asteroseismology, we make a
direct estimate of the stellar mass. We find a value of 1.07+/-0.03 M_sun
(2.8%), which agrees with published estimates based on fitting in the H-R
diagram, but has much higher precision. These results place valuable
constraints on theoretical models of beta Hyi and its oscillation frequencies.Comment: 3 figures, 3 tables, to appear in MNRAS Letter
Variable maternal nutrition and growth hormone treatment in the second quarter of pregnancy in pigs alter semitendinosus muscle in adolescent progeny
Maternal nutrition and growth hormone (GH) treatment during early- to mid-pregnancy can each alter the subsequent growth and differentiation of muscle in progeny. We have investigated the effects of varying maternal nutrition and maternal treatment with porcine (p) GH during the second quarter of pregnancy in gilts on semitendinosus muscle cross-sectional area and fibre composition of progeny, and relationships between maternal and progeny measures and progeny muscularity. Fifty-three Large White×Landrace gilts, pregnant to Large White×Duroc boars, were fed either 2·2 kg (about 35 % ad libitum intake) or 3·0 kg commercial ration (13·5 MJ digestible energy, 150 g crude protein (N×6·25)/kg DM)/d and injected with 0, 4 or 8 mg pGH/d from day 25 to 50 of pregnancy, then all were fed 2·2 kg/d for the remainder of pregnancy. The higher maternal feed allowance from day 25 to 50 of pregnancy increased the densities of total and secondary fibres and the secondary:primary fibre ratio in semitendinosus muscles of their female progeny at 61 d of age postnatally. The densities of secondary and total muscle fibres in semitendinosus muscles of progeny were predicted by maternal weight before treatment and maternal plasma insulin-like growth factor-II during treatment. Maternal pGH treatment from day 25 to day 50 of pregnancy did not alter fibre densities, but increased the cross-sectional area of the semitendinosus muscle; this may be partially explained by increased maternal plasma glucose. Thus, maternal nutrition and pGH treatment during the second quarter of pregnancy in pigs independently alter muscle characteristics in progeny.Kathryn L. Gatford, Jason E. Ekert, Karina Blackmore, Miles J. De Blasio, Jodie M. Boyce, Julie A. Owens, Roger G. Campbell and Phillip C. Owen
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