2,334 research outputs found
Compensatory physical education for motor impaired approved school boys.
Abstract Not Provided
Hydrogen solubility in zirconium intermetallic second phase particles
The enthalpies of solution of H in Zr binary intermetallic compounds formed
with Cu, Cr, Fe, Mo, Ni, Nb, Sn and V were calculated by means of density
functional theory simulations and compared to that of H in {\alpha}-Zr. It is
predicted that all Zr-rich phases (formed with Cu, Fe, Ni and Sn), and those
phases formed with Nb and V, offer lower energy, more stable sites for H than
{\alpha}-Zr. Conversely, Mo and Cr containing phases do not provide
preferential solution sites for H. In all cases the most stable site for H are
those that offer the highest coordination fraction of Zr atoms. Often these are
four Zr tetrahedra but not always. Implications with respect to H-trapping
properties of commonly observed ternary phases such as Zr(Cr,Fe)2, Zr2(Fe,Ni)
and Zr(Nb,Fe)2 are also discussed.Comment: manuscript accepted for publication in Journal of Nuclear Materials
(2013
Single polymer dynamics: coil-stretch transition in a random flow
By quantitative studies of statistics of polymer stretching in a random flow
and of a flow field we demonstrate that the stretching of polymer molecules in
a 3D random flow occurs rather sharply via the coil-stretch transition at the
value of the criterion close to theoretically predicted.Comment: 4 pages, 5 figure
On the need for a nonlinear subscale turbulence term in POD models as exemplified for a high Reynolds number flow over an Ahmed body
We investigate a hierarchy of eddy-viscosity terms in POD Galerkin models to
account for a large fraction of unresolved fluctuation energy. These Galerkin
methods are applied to Large Eddy Simulation data for a flow around the
vehicle-like bluff body call Ahmed body. This flow has three challenges for any
reduced-order model: a high Reynolds number, coherent structures with broadband
frequency dynamics, and meta-stable asymmetric base flow states. The Galerkin
models are found to be most accurate with modal eddy viscosities as proposed by
Rempfer & Fasel (1994). Robustness of the model solution with respect to
initial conditions, eddy viscosity values and model order is only achieved for
state-dependent eddy viscosities as proposed by Noack, Morzynski & Tadmor
(2011). Only the POD system with state-dependent modal eddy viscosities can
address all challenges of the flow characteristics. All parameters are
analytically derived from the Navier-Stokes based balance equations with the
available data. We arrive at simple general guidelines for robust and accurate
POD models which can be expected to hold for a large class of turbulent flows.Comment: Submitted to the Journal of Fluid Mechanic
Exploring the job satisfaction and organisational commitment of employees in the information technology environment
9The objective of the study was to explore the relationship between employees’ job satisfaction (as measured by the Job Satisfaction Survey) and organisational commitment (as measured on the Organisational Commitment Scale). A cross-sectional survey was conducted on a convenience sample of 86 employees at four information technology companies in South Africa. Correlational and stepwise regression analyses revealed a number of signifi cant relationships between the two variables. The fi ndings add newknowledge that can be used to improve organisational practices for the retention of valuable staff members in the information technology environment
Toward a structural understanding of turbulent drag reduction: nonlinear coherent states in viscoelastic shear flows
Nontrivial steady flows have recently been found that capture the main
structures of the turbulent buffer layer. We study the effects of polymer
addition on these "exact coherent states" (ECS) in plane Couette flow. Despite
the simplicity of the ECS flows, these effects closely mirror those observed
experimentally: Structures shift to larger length scales, wall-normal
fluctuations are suppressed while streamwise ones are enhanced, and drag is
reduced. The mechanism underlying these effects is elucidated. These results
suggest that the ECS are closely related to buffer layer turbulence.Comment: 5 pages, 3 figures, published version, Phys. Rev. Lett. 89, 208301
(2002
Small scale statistics of viscoelastic turbulence
The small scale statistics of homogeneous isotropic turbulence of dilute
polymer solutions is investigated by means of direct numerical simulations of a
simplified viscoelastic fluid model. It is found that polymers only partially
suppress the turbulent cascade below the Lumley scale, leaving a remnant energy
flux even for large elasticity. As a consequence, fluid acceleration in
viscoelastic flows is reduced with respect to Newtonian turbulence, whereas its
rescaled probability density is left unchanged. At large scales the velocity
field is found to be unaffected by the presence of polymers.Comment: 7 pages, 4 figure
The Scaling Structure of the Velocity Statistics in Atmospheric Boundary Layer
The statistical objects characterizing turbulence in real turbulent flows
differ from those of the ideal homogeneous isotropic model.They
containcontributions from various 2d and 3d aspects, and from the superposition
ofinhomogeneous and anisotropic contributions. We employ the recently
introduceddecomposition of statistical tensor objects into irreducible
representations of theSO(3) symmetry group (characterized by and
indices), to disentangle someof these contributions, separating the universal
and the asymptotic from the specific aspects of the flow. The different
contributions transform differently under rotations and so form a complete
basis in which to represent the tensor objects under study. The experimental
data arerecorded with hot-wire probes placed at various heights in the
atmospheric surfacelayer. Time series data from single probes and from pairs of
probes are analyzed to compute the amplitudes and exponents of different
contributions to the second order statistical objects characterized by ,
and . The analysis shows the need to make a careful distinction
between long-lived quasi 2d turbulent motions (close to the ground) and
relatively short-lived 3d motions. We demonstrate that the leading scaling
exponents in the three leading sectors () appear to be different
butuniversal, independent of the positions of the probe, and the large
scaleproperties. The measured values of the exponent are , and .
We present theoretical arguments for the values of these exponents usingthe
Clebsch representation of the Euler equations; neglecting anomalous
corrections, the values obtained are 2/3, 1 and 4/3 respectively.Comment: PRE, submitted. RevTex, 38 pages, 8 figures included . Online (HTML)
version of this paper is avaliable at http://lvov.weizmann.ac.il
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