Wave dynamics in random, absorptive or laseractive media

We consider the behavior of light propagating in dielectrically disordered and energetically nonconservative material. Disorder and energy nonconservation can be dealt with via the use of the mathematical formalism commonly known as the Keldysh technique. We derive in the Keldysh formalism a field theory of light propagation in disordered, nonconservative media. This field theoretical formulation is commonly known as the nonlinear sigma model. We also show how to calculate physical quantities like correlation functions from the sigma model, and how a source term can be included in the action of the field theory. We apply the derived field theory to the calculation of full counting statistics. We derive a generating functional for the cumulants of energy transmitted through a weakly nonconservative one-dimensional disordered system. We find fluctuations of transmittance which is in accordance to Dorokhov’s distribution of transmission coefficients. Our numerical results also agree quantitatively with previous diagrammatic results of low order cumulants. We apply the field theoretical formalism to random lasing. We calculate the photonic distribution function. We find that the distribution function obeys a nonlocal Fisher equation. Finally we consider the effect of the vector nature of light on wave properties, specifically whether polarization increases or decreases the propensity of light waves in disordered dielectric media to become localized (Anderson localization).We map the light polarization to a “pseudospin” degree of freedom which we then treat with techniques adapted from classical studies of electronic spin. We find that the polarization of light waves does in fact contribution to a diminished probability of return to the origin, the value of which determines of course the ease for the occurrence of Anderson localization

Central engine afterglow of Gamma-ray Bursts

Before 2004, nearly all GRB afterglow data could be understood in the context of the external shocks model. This situation has changed in the past two years, when it became clear that some afterglow components should be attributed to the activity of the central engine; i.e., the {\it central engine afterglow}. We review here the afterglow emission that is directly related to the GRB central engine. Such an interpretation proposed by Katz, Piran & Sari, peculiar in pre-{\it Swift} era, has become generally accepted now.Comment: 4 pages including 1 figure. Presented at the conference "Astrophysics of Compact Objects" (July 1-7, 2007; Huangshan, China

Heavy Metal Emission Characteristics of Urban Road Runoff

Pavement runoff sampling points were set up on the main roads of Chengdu city. Six rainfall-runoff events from July to September in 2017 were sampled by synchronous observation of rainfall, runoff and pollution. The concentration changes of copper, lead, zinc, chromium and cadmium in the runoff process were monitored, and the pollution emission regularity and initial scouring effect were studied. The results show that the emission regularity of pavement runoff pollution is closely related to rainfall characteristics and pollutant occurrence, and the concentration of dissolved heavy metals reaches its peak at the initial stage of runoff. The peak time of particulate heavy metal concentration lagged slightly behind that of rainfall intensity. There is a big difference between the strength of initial scouring degree and dissolved heavy metals the stronger the initial scouring degree of total heavy metals, the weaker the dissolved heavy metals. Reducing pavement runoff in the early stage of rainfall is an effective means to control heavy metal pollution

Enhanced heat transport in thermal convection with suspensions of rod-like expandable particles

Thermal convection of fluid is a more efficient way than diffusion to carry heat from hot sources to cold places. Here, we experimentally study the Rayleigh–Bénard convection of aqueous glycerol solution in a cubic cell with suspensions of rod-like particles made of polydimethylsiloxane. The particles are inertial due to their large thermal expansion coefficient and finite sizes. The thermal expansion coefficient of the particles is three times larger than that of the background fluid. This contrast makes the suspended particles lighter than the local fluid in hot regions and heavier in cold regions. The heat transport is enhanced at relatively large Rayleigh number ( Ra ) but reduced at small Ra . We demonstrate that the increase of Nusselt number arises from the particle–boundary layer interactions: the particles act as ‘active’ mixers of the flow and temperature fields across the boundary layers

Molecular dynamics simulation of persistent slip bands formation in nickel-base superalloys

Persistent slip band (PSB) is an important and typical microstructure generated during fatigue crack initiation. Intensive work has been done to investigate the mechanisms of the formation of persistent slip bands since the 1950s when Wadsworth[1] observed the fatigue fracture in copper. Simulations have indicated that PSBs formation during fatigue crack initiation is related to the dislocation driving force and interaction. In this paper, a molecular dynamics (MD) simulation associated with embedded atom model (EAM) is applied to the PSBs formation in nickel-base superalloys with different microstructure and temperature under tensiletensile loadings. Five MD models with different microstructure (pure γ phase and γ/γ′ phase), grain orientation ([1 0 0][0 1 0][0 0 1] and [1 1 1][1 ¯ 0 1][1 2 ¯ 1]) and simulation temperature (300 K, 600 K, 900 K) were built up in these simulations. Our results indicated that within the γ phase by massive dislocations, pile-up and propagation which can penetrate the grain. Also, it is found that the temperature will affect the material fatigue performance and blur PSBs appearance. The simulation results are in strong agreement with published experimental test result. This simulation is based on the work[2]. The highlights of the article include: 1) investigation of the PSB formation via molecular dynamics simulation with three different parameters, 2) conduct of a new deformation and velocity combination controlled simulation for the PSB formation, 3) high-performance computing of PSB formation, and 4) systematic analysis of the PSB formation at the atomic scale in which the dislocation plays a critical role