2,623 research outputs found
Tapirs and Rhinoceroses in Captivity: An Examination of the North American Captive Populations and their Husbandry
All species of Tapiridae and Rhinocerotidae are threatened or endangered in the wild. Captive populations have been established for most of these species, but successful management has proved challenging. Effective ex situ conservation strategies, however, rely on the ability of zoological institutions to maintain and breed these endangered species. In this study, I examined the captive environment to identify the factors associated with reproduction, mortality, and health of rhinos and tapirs. Zoological institutions in the North American region that currently housed rhinos and/or tapirs were surveyed in 2003. Attaining an approximately 90% response rate, I compiled information on the following variables to describe the captive environment: number of enclosures, enclosure type, enclosure area, number of animals, public viewing, percent of walls surrounding the enclosure, enclosure substrate, topography, vegetation, mud wallows, pools, shelters, percent shade, climate, diet, feeding regime, time spent by keepers, and vaccinations. Information regarding the incidence of health problems also was obtained through the survey. Studbook data was used to obtain life history and demographic information.
Three species of tapirs [Baird\u27s (Tapirus bairdii), South American (T. terrestris), and Malay (T. indicus)] and three species of rhinos [black (Diceros bicornis), white (Ceratotherium simum), and Indian (Rhinoceros unicornis)] were included in this study. Due to the small captive population sizes, genetic and demographic Allee effects were detected. While tapirs responded similarly to their captive environment, each rhino species responded differently. Both exhibit area and completely were associated with the responses of captive tapirs and rhinos. Climate also was an influential factor for both groups of species. Other key factors included density, diet, keeper time, percent of public perimeter, and vaccinations. Complex interactions among the variables were found, including a nonlinear relationship between mean exhibit size and reproduction for black rhinos.
The results of this study can be used to improve the captive management of tapirs and rhinos. By identifying the patterns associated with successful reproduction, reduced mortality, and fewer health problems, we can move towards establishing self-sustaining populations for these species. This goal is critical for the continued husbandry and conservation of these species
Conceptual design study of advanced acoustic-composite nacelles
Conceptual studies were conducted to assess the impact of incorporating advanced technologies in the nacelles of a current wide-bodied transport and an advanced technology transport. The improvement possible in the areas of fuel consumption, flyover noise levels, airplane weight, manufacturing costs, and airplane operating cost were evaluated for short and long-duct nacelles. Use of composite structures for acoustic duct linings in the fan inlet and exhaust ducts was considered as well as for other nacelle components. For the wide-bodied transport, the use of a long-duct nacelle with an internal mixer nozzle in the primary exhaust showed significant improvement in installed specific fuel consumption and airplane direct operating costs compared to the current short-duct nacelle. The long-duct mixed-flow nacelle is expected to achieve significant reductions in jet noise during takeoff and in turbo-machinery noise during landing approach. Recommendations were made of the technology development needed to achieve the potential fuel conservation and noise reduction benefits
The mass content of the Sculptor dwarf spheroidal galaxy
We present a new determination of the mass content of the Sculptor dwarf
spheroidal galaxy, based on a novel approach which takes into account the two
distinct stellar populations present in this galaxy. This method helps to
partially break the well-known mass-anisotropy degeneracy present in the
modelling of pressure-supported stellar systems.Comment: 6 pages, 3 figures. To appear in the proceedings of IAU Symposium 254
"The Galaxy disk in a cosmological context", Copenhagen, June 200
Microbial oxidation of arsenite in a subarctic environment: diversity of arsenite oxidase genes and identification of a psychrotolerant arsenite oxidiser
Background: Arsenic is toxic to most living cells. The two soluble inorganic forms of arsenic are arsenite (+3) and arsenate (+5), with arsenite the more toxic. Prokaryotic metabolism of arsenic has been reported in both thermal and moderate environments and has been shown to be involved in the redox cycling of arsenic. No arsenic metabolism (either dissimilatory arsenate reduction or arsenite oxidation) has ever been reported in cold environments (i.e. < 10°C).
Results: Our study site is located 512 kilometres south of the Arctic Circle in the Northwest Territories, Canada in an inactive gold mine which contains mine waste water in excess of 50 mM arsenic. Several thousand tonnes of arsenic trioxide dust are stored in underground chambers and microbial biofilms grow on the chamber walls below seepage points rich in arsenite-containing solutions. We compared the arsenite oxidisers in two subsamples (which differed in arsenite concentration) collected from one biofilm. 'Species' (sequence) richness did not differ between subsamples, but the relative importance of the three identifiable clades did. An arsenite-oxidising bacterium (designated GM1) was isolated, and was shown to oxidise arsenite in the early exponential growth phase and to grow at a broad range of temperatures (4-25°C). Its arsenite oxidase was constitutively expressed and functioned over a broad temperature range.
Conclusions: The diversity of arsenite oxidisers does not significantly differ from two subsamples of a microbial biofilm that vary in arsenite concentrations. GM1 is the first psychrotolerant arsenite oxidiser to be isolated with the ability to grow below 10°C. This ability to grow at low temperatures could be harnessed for arsenic bioremediation in moderate to cold climates
Effect of Al mole fraction on carrier diffusion lengths and lifetimes in AlxGa1−xAs
The ambipolar diffusion length and carrier lifetime are measured in AlxGa1−xAs for several mole fractions in the interval 0<x<0.38. These parameters are found to have significantly higher values in the higher mole fraction samples. These increases are attributed to occupation of states in the indirect valleys, and supporting calculations are presented
Microfluidic rheology of soft colloids above and below jamming
The rheology near jamming of a suspension of soft colloidal spheres is
studied using a custom microfluidic rheometer that provides stress versus
strain rate over many decades. We find non-Newtonian behavior below the jamming
concentration and yield stress behavior above it. The data may be collapsed
onto two branches with critical scaling exponents that agree with expectations
based on Hertzian contacts and viscous drag. These results support the
conclusion that jamming is similar to a critical phase transition, but with
interaction-dependent exponents.Comment: 4 pages, experimen
Interacting Dark Matter and Dark Energy
We discuss models for the cosmological dark sector in which the energy
density of a scalar field approximates Einstein's cosmological constant and the
scalar field value determines the dark matter particle mass by a Yukawa
coupling. A model with one dark matter family can be adjusted so the
observational constraints on the cosmological parameters are close to but
different from what is predicted by the Lambda CDM model. This may be a useful
aid to judging how tightly the cosmological parameters are constrained by the
new generation of cosmological tests that depend on the theory of structure
formation. In a model with two families of dark matter particles the scalar
field may be locked to near zero mass for one family. This can suppress the
long-range scalar force in the dark sector and eliminate evolution of the
effective cosmological constant and the mass of the nonrelativistic dark matter
particles, making the model close to Lambda CDM, until the particle number
density becomes low enough to allow the scalar field to evolve. This is a
useful example of the possibility for complexity in the dark sector.Comment: 15 pages, 6 figures; added a reference and a minor correctio
Magnetic Order Beyond RKKY in the Classical Kondo Lattice
We study the Kondo lattice model of band electrons coupled to classical
spins, in three dimensions, using a combination of variational calculation and
Monte Carlo. We use the weak coupling `RKKY' window and the strong coupling
regime as benchmarks, but focus on the physically relevant intermediate
coupling regime. Even for modest electron-spin coupling the phase boundaries
move away from the RKKY results, the non interacting Fermi surface no longer
dictates magnetic order, and weak coupling `spiral' phases give way to
collinear order. We use these results to revisit the classic problem of 4f
magnetism and demonstrate how both electronic structure and coupling effects
beyond RKKY control the magnetism in these materials.Comment: 6 pages, 4 figs. Improved figures, expanded captions. To appear in
Europhys. Let
Spin-dynamic field coupling in strongly THz driven semiconductors : local inversion symmetry breaking
We study theoretically the optics in undoped direct gap semiconductors which
are strongly driven in the THz regime. We calculate the optical sideband
generation due to nonlinear mixing of the THz field and the near infrared
probe. Starting with an inversion symmetric microscopic Hamiltonian we include
the THz field nonperturbatively using non-equilibrium Green function
techniques. We find that a self induced relativistic spin-THz field coupling
locally breaks the inversion symmetry, resulting in the formation of odd
sidebands which otherwise are absent.Comment: 8 pages, 6 figure
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