7,719 research outputs found
Numerical Investigation on Flow Separation Control of Low Reynolds Number Sinusoidal Aerofoils
The paper presents a computational analysis of the characteristics of a NACA 634-
021 aerofoil incorporated with sinusoidal leading-edge protuberances at Re = 14,000.
The protuberances are characterized by an amplitude and wavelength of 12% and 50%
of the aerofoil chord length respectively. An unsteady Reynolds Average Navier Stokes
(RANS) analysis of the full-span aerofoils was carried out using Transition SST (Shear
Stress Transport) turbulence model across five different angles-of-attack (AOA).
Comparisons with previous experimental results reported good qualitative agreements
in terms of flow separation when the aerofoils are pitched at higher AOAs. Results
presented here comprised of near-wall flow visualizations of the flow separation bubble
at the peaks and troughs of the protuberances. Additionally, results indicate that the
aerofoil with leading-edge protuberances displayed distinctive wall shear streamline and
iso-contour characteristics at different span-wise positions. This implies that even at a
low Reynolds number, implementations of these leading-edge protuberances could have
positive or adverse effects on flow separation
The sleep cycle and subcortical-cortical EEG relations in the unrestrained chimpanzee
Sleep cycle and subcortical-cortical EEG relations in unrestrained chimpanze
Characterisation of the dynamical quantum state of a zero temperature Bose-Einstein condensate
We describe the quantum state of a Bose-Einstein condensate at zero
temperature. By evaluating the Q-function we show that the ground state of
Bose-Einstein condensate under the Hartree approximation is squeezed. We find
that multimode Schroedinger cat states are generated as the condensate evolves
in a ballistic expansion.Comment: 13 pages, 6 figure
Advanced rocket engine cryogenic turbopump bearing thermal model
A lumped node thermal model was developed representing the Space Shuttle Main Engine (SSME) liquid oxygen (LOX) turbopump turbine end bearings operating in a cryogenically cooled bearing tester. Bearing elements, shaft, carrier, housing, cryogen flow characteristics, friction heat, and fluid viscous energy are included in the model. Heat transfer characteristics for the regimes of forced convection boiling are modeled for liquid oxygen (LOX) and liquid nitrogen (LN2). Large temperature differences between the cryogenic fluid and baring contact surfaces require detailed nodal representation in these areas. Internal loads and friction heat are affected by temperature dependent operating clearances requiring iterations between bearing thermal and mechanical models. Analyses indicate a thermal-mechanical coupling resulting in reduced operating clearances, increased loading and heating which can contribute to premature bearing failure. Contact surfaces operate at temperatures above local saturation resulting in vapor rather than liquid in the contacts, precluding possible liquid film lubrication. Elevated temperatures can reduce lubrication, increase friction, and reduce surface hardness supporting a surface failure mode rather than subsurface fatigue
Optical carrier wave shocking: detection and dispersion
Carrier wave shocking is studied using the Pseudo-Spectral Spatial Domain
(PSSD) technique. We describe the shock detection diagnostics necessary for
this numerical study, and verify them against theoretical shocking predictions
for the dispersionless case. These predictions show Carrier Envelope Phase
(CEP) and pulse bandwidth sensitivity in the single-cycle regime. The flexible
dispersion management offered by PSSD enables us to independently control the
linear and nonlinear dispersion. Customized dispersion profiles allow us to
analyze the development of both carrier self-steepening and shocks. The results
exhibit a marked asymmetry between normal and anomalous dispersion, both in the
limits of the shocking regime and in the (near) shocked pulse waveforms.
Combining these insights, we offer some suggestions on how carrier shocking (or
at least extreme self-steepening) might be realised experimentally.Comment: 9 page
Promises and Pitfalls of Metal Imaging in Biology
A picture may speak a thousand words, but if those words fail to form a coherent sentence there is little to be learned. As cutting-edge imaging technology now provides us the tools to decipher the multitude of roles played by metals and metalloids in molecular, cellular and developmental biology, as well as health and disease, it is time to reflect on the advances made in imaging, the limitations discovered, and the future of a burgeoning field. In this Perspective, the current state-of-the-art is discussed from a self-imposed contrarian position, as we not only highlight the major advances made of the years but use them as teachable moments to zoom in on challenges that remain to be overcome. We also describe the steps being taken towards being able to paint a completely undisturbed picture of cellular metal metabolism, which is, metaphorically speaking, the Holy Grail of the discipline
Baylisascaris procyonis in raccoons (Procyon lotor) in eastern Tennessee
Raccoon (Procyon lotor) carcasses (n=118) were collected from July through December 2007 throughout eastern Tennessee. Necropsies were performed, and Baylisascaris procyonis was collected from the gastrointestinal tract of infected carcasses. Prevalence rates were determined for the overall sample population, males and females, and adults and juveniles. The sample population had a B. procyonis prevalence of 12.7%. Males and females had a prevalence of 15% and 11%, respectively; prevalence in adults and juvenile was 13% and 12.6%, respectively. There were no significant differences in prevalence rates between the different groups. Baylisascaris procyonis is an ascarid infection of raccoons that can infect humans and over 100 species of other animals. The presence of infection in raccoons, paired with the expansion of human populations in eastern Tennessee, is likely to lead to increased interactions between humans and raccoons and therefore an increased risk of human and domestic animal exposure to B. procyonis
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