61,748 research outputs found
A dimensional analysis of supersaturated total dissolved gas dissipation
Elevated levels of total dissolved gas (TDG) may occur downstream of dam discharges, leading to increased incidence of gas bubble disease in fish. Accelerating the dissipation of supersaturated TDG in the downstream river can mitigate this negative problem. However, developing effective mitigation techniques is hampered by limitations in present models of TDG dissipation processes. Furthermore, data useful for modelling the dissipation of supersaturated TDG through the
free surface in natural rivers are limited. Past studies indicated that the TDG dissipation process is quantitatively different from the reaeration process, and TDG behavior is quantitatively different from dissolved oxygen. However, a correct parameterization of the TDG dissipation process is still missing.
The paper presents a novel dimensional analysis of the dissipation of supersaturated TDG. This approach can provide a relationship between the TDG dissipation coefficient and some classical fluid mechanics index-numbers. This dimensional analysis considers some key parameters for the dissipation process both water and TDG properties as well as flow characteristics, including turbulence. These parameters are water kinematic viscosity, TDG molecular diffusivity and vertical turbulent diffusivity, and channel width. The application of dimensional analysis pointed out that the TDG dissipation coefficient is a function of the Schmidt number, the aspect ratio of the channel, and the shear Reynolds
number. The dimensional analysis was then verified using both field data collected in some large natural rivers and reservoirs in Sichuan and experimental data in laboratory flume at State Key Laboratory of Hydraulics and Mountain River Engineering of Sichuan University. The analysis revealed the key role of turbulence in controlling the TDG dissipation while the importance of gas/water characteristics remains still unclear and needs further investigations
Equilibrium states of the pressure function for products of matrices
Let be a non-trivial family of complex
matrices, in the sense that for any , there exists such that . Let be the pressure function of . We show
that for each , there are at most ergodic -equilibrium states of
, and each of them satisfies certain Gibbs property.Comment: 12 pages. To appear in DCD
Small-Recoil Approximation
In this review we discuss a technique to compute and to sum a class of
Feynman diagrams, and some of its applications. These are diagrams containing
one or more energetic particles that suffer very little recoil in their
interactions. When recoil is completely neglected, a decomposition formula can
be proven. This formula is a generalization of the well-known eikonal formula,
to non-abelian interactions. It expresses the amplitude as a sum of products of
irreducible amplitudes, with each irreducible amplitude being the amplitude to
emit one, or several mutually interacting, quasi-particles. For abelian
interaction a quasi-particle is nothing but the original boson, so this
decomposition formula reduces to the eikonal formula. In non-abelian situations
each quasi-particle can be made up of many bosons, though always with a total
quantum number identical to that of a single boson. This decomposition enables
certain amplitudes of all orders to be summed up into an exponential form, and
it allows subleading contributions of a certain kind, which is difficult to
reach in the usual way, to be computed. For bosonic emissions from a heavy
source with many constituents, a quasi-particle amplitude turns out to be an
amplitude in which all bosons are emitted from the same constituent. For
high-energy parton-parton scattering in the near-forward direction, the
quasi-particle turns out to be the Reggeon, and this formalism shows clearly
why gluons reggeize but photons do not. The ablility to compute subleading
terms in this formalism allows the BFKL-Pomeron amplitude to be extrapolated to
asymptotic energies, in a unitary way preserving the Froissart bound. We also
consider recoil corrections for abelian interactions in order to accommodate
the Landau-Pomeranchuk-Migdal effect.Comment: 21 pages with 4 figure
Viscoelasticity of 2D liquids quantified in a dusty plasma experiment
The viscoelasticity of two-dimensional liquids is quantified in an experiment
using a dusty plasma. An experimental method is demonstrated for measuring the
wavenumber-dependent viscosity, , which is a quantitative indicator of
viscoelasticity. Using an expression generalized here to include friction,
is computed from the transverse current autocorrelation function
(TCAF), which is found by tracking random particle motion. The TCAF exhibits an
oscillation that is a signature of elastic contributions to viscoelasticity.
Simulations of a Yukawa liquid are consistent with the experiment.Comment: 5 pages text, 3 figures, 1 supplementary material, in press Physical
Review Letters 201
Asymmetric Dark Matter and Effective Operators
In order to annihilate in the early Universe to levels well below the
measured dark matter density, asymmetric dark matter must possess large
couplings to the Standard Model. In this paper, we consider effective operators
which allow asymmetric dark matter to annihilate into quarks. In addition to a
bound from requiring sufficient annihilation, the energy scale of such
operators can be constrained by limits from direct detection and monojet
searches at colliders. We show that the allowed parameter space for these
operators is highly constrained, leading to non-trivial requirements that any
model of asymmetric dark matter must satisfy.Comment: 6 pages, 1 figure. V2 replacement: Citations added. Shading error in
Fig. 1 (L_FV panel) corrected. Addition of direct detection bounds on m_chi
<5 GeV added, minor alterations in text to reflect these change
Solid superheating observed in two-dimensional strongly-coupled dusty plasma
It is demonstrated experimentally that strongly-coupled plasma exhibits solid
superheating. A 2D suspension of microspheres in dusty plasma, initially
self-organized in a solid lattice, was heated and then cooled rapidly by
turning laser heating on and off. Particles were tracked using video
microscopy, allowing atomistic-scale observation during melting and
solidification. During rapid heating, the suspension remained in a solid
structure at temperatures above the melting point, demonstrating solid
superheating. Hysteresis diagrams did not indicate liquid supercooling in this
2D system.Comment: 9 pages text, 3 figures, in press Physical Review Letters 200
Supersymmetry and the Anomalous Anomalous Magnetic Moment of the Muon
The recently reported measurement of the muon's anomalous magnetic moment
differs from the standard model prediction by 2.6 standard deviations. We
examine the implications of this discrepancy for supersymmetry. Deviations of
the reported magnitude are generic in supersymmetric theories. Based on the new
result, we derive model-independent upper bounds on the masses of observable
supersymmetric particles. We also examine several model frameworks. The sign of
the reported deviation is as predicted in many simple models, but disfavors
anomaly-mediated supersymmetry breaking.Comment: 4 pages, 4 figures, version to appear in Phys. Rev. Let
Global behavior of cosmological dynamics with interacting Veneziano ghost
In this paper, we shall study the dynamical behavior of the universe
accelerated by the so called Veneziano ghost dark energy component locally and
globally by using the linearization and nullcline method developed in this
paper. The energy density is generalized to be proportional to the Hawking
temperature defined on the trapping horizon instead of Hubble horizon of the
Friedmann-Robertson-Walker (FRW) universe. We also give a prediction of the
fate of the universe and present the bifurcation phenomenon of the dynamical
system of the universe. It seems that the universe could be dominated by dark
energy at present in some region of the parameter space.Comment: 8 pages, 7 figures, accepted for publication in JHE
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