3,153 research outputs found
Statistics of Pressure Fluctuations in Decaying, Isotropic Turbulence
We present results from a systematic direct-numerical simulation study of
pressure fluctuations in an unforced, incompressible, homogeneous, and
isotropic, three-dimensional turbulent fluid. At cascade completion,
isosurfaces of low pressure are found to be organised as slender filaments,
whereas the predominant isostructures appear sheet-like. We exhibit several new
results, including plots of probability distributions of the spatial
pressure-difference, the pressure-gradient norm, and the eigenvalues of the
pressure-hessian tensor. Plots of the temporal evolution of the mean
pressure-gradient norm, and the mean eigenvalues of the pressure-hessian tensor
are also exhibited. We find the statistically preferred orientations between
the eigenvectors of the pressure-hessian tensor, the pressure-gradient, the
eigenvectors of the strain-rate tensor, the vorticity, and the velocity.
Statistical properties of the non-local part of the pressure-hessian tensor are
also exhibited, for the first time. We present numerical tests (in the viscous
case) of some conjectures of Ohkitani [Phys. Fluids A {\bf 5}, 2570 (1993)] and
Ohkitani and Kishiba [Phys. Fluids {\bf 7}, 411 (1995)] concerning the
pressure-hessian and the strain-rate tensors, for the unforced, incompressible,
three-dimensional Euler equations.Comment: 10 pages, 29 figures, Accepted for publication in Physical Review
Exploring the differences between forward osmosis and reverse osmosis fouling
A comparison of alginate fouling in forward osmosis (FO) with that in reverse osmosis (RO) was made. A key experimental finding, corroborated by membrane autopsies, was that FO is essentially more prone to fouling than RO, which is opposite to a common claim in the literature where deductions on fouling are often based solely on the water flux profiles. Our theoretical analysis shows that, due to a decrease in the intensity of internal concentration polarization (ICP), and thus an increase in the effective osmotic driving force during FO fouling tests, the similarity of experimental water flux profiles for FO and RO is in accordance with there being greater fouling in FO than RO. The specific foulant resistance for FO was also found to be greater than that for RO. Possible explanations are discussed and these include the influence of reverse solute diffusion from draw solution. Whilst this explanation regarding specific foulant resistance is dependent on the draw solution properties, the finding of greater overall foulant accumulation in FO is considered to be a general finding. Additionally, the present study did not find evidence that hydraulic pressure in RO plays a critical role in foulant layer compaction. Overall this study demonstrated that although FO has higher fouling propensity, it offers superior water flux stability against fouling. For certain practical applications this resilience may be important
Scalar-tensor analysis of an exponential Lagrangian for the Gravitational Field
Within the scheme of modified gravity, an exponential Lagrangian density will
be considered, and the corresponding scalar-tensor description will be
addressed for both positive and negative values of the cosmological constant.
For negative values of the cosmological term, the potential of the scalar field
exhibits a minimum, around which scalar-field equations can be linearized. The
study of the deSitter regime shows that a comparison with the modified-gravity
description is possible in an off-shell region, i.e., in a region where the
classical equivalence between the two formulations is not fulfilled.
Furthermore, despite the negative cosmological constant, an accelerating
deSitter phase is predicted in the region where the series expansion of the
exponential term does not hold. For positive values of the cosmological
constant, the quantum regime is analyzed within the framework of Loop Quantum
Cosmology.Comment: 8 pages, 2 figures, to appear in the proceedings of'' 4th
Italian-Sino Workshop on Relativistic Astrophysics'', AIP Conference Serie
Wave fields from an off-center explosion in an embedded solid sphere
This study investigates the effects of explosions in asymmetric source regions on the excitation of seismic body waves. We give an analytic formulation for determining the wave fields from an off-center explosion in an embedded solid sphere in an elastic whole-space. As expected, this geometry generates shear as well as compressional body waves. The calculated wave fields show that the degree of shear-wave generation is determined by the asymmetry of the source region. The results are compared with the known analytic solutions of an explosion in an elastic whole-space and at the center of an elastic sphere embedded in the whole-space. The radiation patterns at different periods for different parameters of the media suggest that the asymmetry of the source region has significant effects on shorter period but has only minor effects on long periods. The long-period P-to-S wave maximum amplitude results are in agreement with that for explosions in axisymmetric cavities
Major Issues with SAP Financials in Queensland Government
This short paper reports a research project that seeks to give improved understanding of client-centered ERP lifecycle support issues in order that research, management and educational resources can be allocated and implemented effectively. The paper presents (1) the study background; (2) the research context and object; (3) the research questions and aims; (4) previous literature on major IS issues employing the Delphi method; (5) the research strategy and design; (6) progress to date; (7) expected benefits and outcomes; and (8) limitations and future research suggestions
GRB970228 and the class of GRBs with an initial spikelike emission: do they follow the Amati relation?
On the basis of the recent understanding of GRB050315 and GRB060218, we
return to GRB970228, the first Gamma-Ray Burst (GRB) with detected afterglow.
We proposed it as the prototype for a new class of GRBs with "an occasional
softer extended emission lasting tenths of seconds after an initial spikelike
emission". Detailed theoretical computation of the GRB970228 light curves in
selected energy bands for the prompt emission are presented and compared with
observational BeppoSAX data. From our analysis we conclude that GRB970228 and
likely the ones of the above mentioned new class of GRBs are "canonical GRBs"
have only one peculiarity: they exploded in a galactic environment, possibly
the halo, with a very low value of CBM density. Here we investigate how
GRB970228 unveils another peculiarity of this class of GRBs: they do not
fulfill the "Amati relation". We provide a theoretical explanation within the
fireshell model for the apparent absence of such correlation for the GRBs
belonging to this new class.Comment: 5 pages, 3 figures, in the Proceedings of the "4th Italian-Sino
Workshop on Relativistic Astrophysics", held in Pescara, Italy, July 20-28,
2007, C.L. Bianco, S.-S. Xue, Editor
Bifractality of the Devil's staircase appearing in the Burgers equation with Brownian initial velocity
It is shown that the inverse Lagrangian map for the solution of the Burgers
equation (in the inviscid limit) with Brownian initial velocity presents a
bifractality (phase transition) similar to that of the Devil's staircase for
the standard triadic Cantor set. Both heuristic and rigorous derivations are
given. It is explained why artifacts can easily mask this phenomenon in
numerical simulations.Comment: 12 pages, LaTe
A new scaling property of turbulent flows
We discuss a possible theoretical interpretation of the self scaling property
of turbulent flows (Extended Self Similarity). Our interpretation predicts
that, even in cases when ESS is not observed, a generalized self scaling, must
be observed. This prediction is checked on a number of laboratory experiments
and direct numerical simulations.Comment: Plain Latex, 1 figure available upon request to
[email protected]
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