41,963 research outputs found
Streakline flow visualization of discrete-hole film cooling with normal, slanted, and compound angle injection
Film injection from discrete holes in a three-row, staggered array with five-diameter spacing was studied for three hole angles: (1) normal, (2) slanted 30 deg to the surface in the direction of the main stream, and (3) slanted 30 deg to the surface and 45 deg laterally to the main stream. The ratio of the boundary layer thickness-to-hole diameter and Reynolds number were typical of gas-turbine film-cooling applications. Detailed streaklines showing the turbulent motion of the injected air were obtained by photographing very small neutrally buoyant, helium-filled soap bubbles which follow the flow field
Flow visualization of discrete hole film cooling for gas turbine applications
Film injection from discrete holes in a three row staggered array with 5-diameter spacing is studied. The boundary layer thickness-to-hole diameter ratio and Reynolds number are typical of gas turbine film cooling applications. Two different injection locations are studied to evaluate the effect of boundary layer thickness on film penetration and mixing. Detailed streaklines showing the turbulent motion of the injected air are obtained by photographing neutrally buoyant helium filled soap bubbles which follow the flow field. The bubble streaklines passing downstream injection locations are clearly identifiable and can be traced back to their origin. Visualization of surface temperature patterns obtained from infrared photographs of a similar film cooled surface are also included
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Fe isotopic composition of Martian meteorites and some terrestrial analogues
We report Fe isotopic composition of seven martian meteorites and other terrestrial materials that may be considered Martian analogues
Gaussian ellipsoid model for confined polymer systems
Polymer systems in slab geometries are studied on the basis of the recently
presented Gaussian Ellipsoid Model [J. Chem. Phys. 114, 7655 (2001)].The
potential of the confining walls has an exponential shape. For homogeneous
systems in thermodynamic equilibrium we discuss density, orientation and
deformation profiles of the polymers close to the walls. For strongly
segregated mixtures of polymer components A and B equilibrium profiles are
studied near a planar interface separating A and B rich regions. Spinodal
decomposition processes of the mixtures in the presence of neutral walls show
upon strong confinement an increase of the lateral size of A and B rich domains
and a slowing down of the demixing kinetics. These findings are in agreement
with predictions from time dependent Ginzburg--Landau theory. In the case,
where one wall periodically favors one of the two mixture components over the
other, different equilibrium structures emerge and lead to different kinetic
pathways of spinodal decomposition processes in such systems.Comment: 18 pages, 16 figures, submitted to J. Chem. Phy
Regional technical workshop, Lusaka, Zambia. 17-19 Jun 2008. Workshop report
The WorldFish Center and FAO are implementing a regional programme entitled "Fisheries and HIV/AIDS in Africa; investing in sustainable solutions", funded by the Swedish International Development Cooperation Agency (Sida) and the Norwegian Ministry of Foreign Affairs. The main purpose of the workshop was to bring together partners on the programme to share ideas and current research proposals, to strengthen these research proposals by taking into account cross cutting issues such as ethics and gender, and to determine arrangements for ongoing collaborative support.Fisheries, AIDS, Public health, HIV, Nutritive value
The effect of the quasar H1821+643 on the surrounding intracluster medium: revealing the underlying cooling flow
We present a detailed study of the thermodynamic properties of the
intracluster medium of the only low redshift galaxy cluster to contain a highly
luminous quasar, H1821+643. The cluster is a highly massive, strong cool core
cluster. We find that the ICM entropy around the quasar is significantly lower
than that of other similarly massive strong cool core clusters within the
central 80 kpc, and that the entropy lies significantly below the extrapolated
baseline entropy profile from hierarchical structure formation. By comparing
the scaled temperature profile with those of other strong cool core clusters of
similar total mass, we see that the entropy deficiency is due to the central
temperature being significantly lower. This suggests that the presence of the
quasar in the core of H1821+643 has had a dramatic cooling effect on the
intracluster medium around it. We find that, if the quasar was brighter in the
past, Compton cooling by radiation from the quasar may have caused the low
entropy and temperature levels in the ICM around the quasar. Curiously, the
gradients of the steep central temperature and entropy decline are in
reasonable agreement with the profiles expected for a constant pressure cooling
flow. It is possible that the system has been locked into a Compton cooled
feedback cycle which prevents energy release from the black hole heating the
gas sufficiently to switch it off, leading to the formation of a huge (~3x10^10
solar mass) supermassive black hole.Comment: 8 pages, 10 figures. Accepted for publication in MNRA
An excess of damped Lyman alpha galaxies near QSOs
We present a sample of 33 damped Lyman alpha systems (DLAs) discovered in the
Sloan Digital Sky Survey (SDSS) whose absorption redshifts (z_abs) are within
6000 km/s of the QSO's systemic redshift (z_sys). Our sample is based on 731
2.5 < z_sys < 4.5 non-broad-absorption-line (non-BAL) QSOs from Data Release 3
(DR3) of the SDSS. We estimate that our search is ~100 % complete for absorbers
with N(HI) >= 2e20 cm^-2. The derived number density of DLAs per unit redshift,
n(z), within v < 6000 km/s is higher (3.5 sigma significance) by almost a
factor of 2 than that of intervening absorbers observed in the SDSS DR3, i.e.
there is evidence for an overdensity of galaxies near the QSOs. This provides a
physical motivation for excluding DLAs at small velocity separations in surveys
of intervening 'field' DLAs. In addition, we find that the overdensity of
proximate DLAs is independent of the radio-loudness of the QSO, consistent with
the environments of radio-loud and radio-quiet QSOs being similar.Comment: Accepted for publication in MNRAS (13 pages, 6 figures
Optimal integral force feedback and structured PI tracking control : application for objective lens positioner
Peer reviewedPostprin
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