18,274 research outputs found
Investigation of compounds essential for the origin of life
Nucleic acid sequencing as a technique to determine the chemical and biological evolution of certain prokaryotic metabolic pathways is discussed. Protein in data and a microbiological organization of the prokaryotes is included
Top-mounted inlet system feasibility for transonic-supersonic fighter aircraft
The more salient findings are presented of recent top inlet performance evaluations aimed at assessing the feasibility of top-mounted inlet systems for transonic-supersonic fighter aircraft applications. Top inlet flow field and engine-inlet performance test data show the influence of key aircraft configuration variables-inlet longitudinal position, wing leading-edge extension planform area, canopy-dorsal integration, and variable incidence canards-on top inlet performance over the Mach range of 0.6 to 2.0. Top inlet performance data are compared with those or more conventional inlet/airframe integrations in an effort to assess the viability of top-mounted inlet systems relative to conventional inlet installations
A Qualitative Investigation Into the Impact of the Basketball Learning Intervention Programme (BLIP) on Disengaged Secondary School Students in the United Kingdom
This paper will evaluate the longitudinal effects of a basketball based intervention programme that targeted ten disengaged male secondary school students at a school in the Kent, England. The programme aimed to improve the behaviour and academic performance of the participants through a weekly intervention carried out by an external basketball player and coach providing academic support, mentoring and specially designed basketball sessions.
Sports interventions have been deemed to provide a positive short-term impact on young people. However, researchers have identified the need for a longitudinal approach in order to examine the effects of such interventions post involvement as supported.
This study involved five former Basketball Learning Intervention Programme (BLIP) members (with a mean age of 16.4 SD± 0.55 years) that were interviewed using semi-structured interview approach, 12 months after completing the intervention.
Interpretative Phenomenological Analysis (IPA) revealed four superordinate and eleven subordinate themes. The four superordinate themes were; ‘baseline behaviours pre-intervention’, ‘immediate outcomes of the BLIP’, ‘impact of the coach’ and ‘long standing transferable outcomes’.
The results revealed an immediate impact in comparison to the baseline behaviours of the participants pre-intervention. The data suggested that one of the most effective aspects of the programme was the positive impact of the coach on the participants. More importantly, this is the only study to report long-term improvements amongst the participants
in terms of behaviour and academics as a result of engagement in a sports based intervention
Effects of horizontal vibration on hopper flows of granular materials
The current experiments investigate the discharge of glass spheres in a planar wedge-shaped hopper (45 degree sidewalls) that is vibrated hoizontally. When the hopper is discharged without vibration, the discharge occurs as a funnel flow, with the material exiting the central region of the hopper and stagnant material along the sides. With horizontal vibration, the discharge rate increases with the velocity of vibration as compared with the discharge rate without vibration. For a certain range of acceleration parameters (20-30 Hz and accelerations greater than about 1 g), the discharge of the material occurs in an inverted-funnel pattern, with the material along the sides exiting first, followed by the material in the core; the free surface shows a peak at the center of the hopper with the free surface particles avalanching from the center toward the sides. During the deceleration phase of a vibration cycle, particles all along the trailing or low-pressure wall separate from the surface and fall under gravity for a short period before reconnecting the hopper. For lower frequencies (5 and 10 Hz), the free surface remains horizontal and the material appears to discharge uniformly from the hopper
Effects of Horizontal Vibration on Hopper Flows of Granular Material
This study experimentally examines the flow of glass spheres in a wedge-shaped hopper that is vibrated hoizontally. When the hopper is discharged without vibration, discharge occurs as a funnel flow, with the material exiting the central region of the hopper and stagnant material along the sides. With vibration, the discharge of the material occurs in reverse, with the material along the sides exiting first, followed by the material in the central region. These patterns are observed with flow visualization and high-speed photography. The study also includes measurements of the discharge rate, which increases with the amplitude of the velocity of vibration
The HI content of extremely metal-deficient blue compact dwarf galaxies
We have obtained new HI observations with the 100m Green Bank Telescope (GBT)
for a sample of 29 extremely metal-deficient star-forming Blue Compact Dwarf
(BCD) galaxies, selected from the Sloan Digital Sky Survey spectral data base
to be extremely metal-deficient (12+logO/H<7.6). Neutral hydrogen was detected
in 28 galaxies, a 97% detection rate. Combining the HI data with SDSS optical
spectra for the BCD sample and adding complementary galaxy samples from the
literature to extend the metallicity and mass ranges, we have studied how the
HI content of a galaxy varies with various global galaxian properties. There is
a clear trend of increasing gas mass fraction with decreasing metallicity, mass
and luminosity. We obtain the relation M(HI)/L(g)~L(g)^{-0.3}, in agreement
with previous studies based on samples with a smaller luminosity range. The
median gas mass fraction f(gas) for the GBT sample is equal to 0.94 while the
mean gas mass fraction is 0.90+/-0.15, with a lower limit of ~0.65. The HI
depletion time is independent of metallicity, with a large scatter around the
median value of 3.4 Gyr. The ratio of the baryonic mass to the dynamical mass
of the metal-deficient BCDs varies from 0.05 to 0.80, with a median value of
~0.2. About 65% of the BCDs in our sample have an effective yield larger than
the true yield, implying that the neutral gas envelope in BCDs is more
metal-deficient by a factor of 1.5-20, as compared to the ionized gas.Comment: 21 pages, 13 figures, accepted for publication in MNRA
Transition of Chaotic Flow in a Radially Heated Taylor-Couette System
Numerical simulations have been performed to study the stability of heated, incompressible Taylor-Couette flow for a radius ratio of 0.7 and a Prandtl number of 0.7. As Gr is increased, the Taylor cell that has the same direction of circulation as the natural convection current increases in size and the counterrotating cell becomes smaller. The flow remains axisymmetric and the average heat transfer decreases with the increase in Gr. When the cylinder is impulsively heated, the counterrotating cell vanishes and n = 1 spiral is formed for Gr = 1000. This transition marks an increase in the heat transfer due to an increase in the radial velocity component of the fluid. By slowly varying the Grashof number, the simulations demonstrate the existence of a hysteresis loop. Two different stable states with same heat transfer are found to exist at the same Grashof number. A time-delay analysis of the radial velocity and the local heat transfer coefficient time is performed to determine the dimension at two Grashof numbers. For a fixed Reynolds number of 100, the two-dimensional projection of the reconstructed attractor shows a limit cycle for Gr = −1700. The limit cycle behavior disappears at Gr = −2100, and the reconstructed attractor becomes irregular. The attractor dimension increases to about 3.2 from a value of 1 for the limit cycle case; similar values were determined for both the local heat transfer and the local radial velocity, indicating that the dynamics of the temperature variations can be inferred from that of the velocity variations
Numerical Simulations of Heat Transfer in Taylor-Couette Flow
Numerical simulations have been performed to study the effects of the gravitational and the centrifugal potentials on the stability of heated, incompressible Taylor-Couette flow. The flow is confined between two differentially heated, concentric cylinders, and the inner cylinder is allowed to rotate. The Navier-Stokes equations and the coupled energy equation are solved using a spectral method. To validate the code, comparisons are made with existing linear stability analysis and with experiments. The code is used to calculate the local and average heat transfer coefficients for a fixed Reynolds number (Re = 100) and a range of Grashof numbers. The investigation is primarily restricted to radius ratios 0.5 and 0.7 for fluids with Prandtl number of about 0.7. The variation of the local coefficients of heat transfer on the cylinder surface is investigated, and maps showing different stable states of the flow are presented. Results are also presented in terms of the equivalent conductivity, and show that heat transfer decreases with Grashof number in axisymmetric Taylor vortex flow regime, and increases with Grashof number after the flow becomes nonaxisymmetric
Soil, Plant and Livestock Interactions in Australian Tropical Savannas
This paper considers the various soil, plant and livestock interactions occurring in Australia’s wet-dry savanna rangelands. These regions are relatively intact compared to most of the world’s rangelands. However there is increasing pressure for more intensive use of the landscape, especially from pastoralism. This potentially threatens landscape health, function and productivity through reduced soil health and a loss of digestible perennial plants, especially given the low soil fertility and highly variable rainfall characteristic of these regions. There is an obvious need for understanding these impacts to devise sustainable management practices that promote soil health and viable perennial plant communities, and the restoration of soil health where required
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