Dynamics of Shock Probes in Driven Diffusive Systems

We study the dynamics of shock-tracking probe particles in driven diffusive systems and also in equilibrium systems. In a driven system, they induce a diverging timescale that marks the crossover between a passive scalar regime at early times and a diffusive regime at late times; a scaling form characterises this crossover. Introduction of probes into an equilibrium system gives rise to a system-wide density gradient, and the presence of even a single probe can be felt across the entire system.Comment: Accepted in Journal of Statistical Mechanics: Theory and Experimen

Conservation Laws and Integrability of a One-dimensional Model of Diffusing Dimers

We study a model of assisted diffusion of hard-core particles on a line. The model shows strongly ergodicity breaking : configuration space breaks up into an exponentially large number of disconnected sectors. We determine this sector-decomposion exactly. Within each sector the model is reducible to the simple exclusion process, and is thus equivalent to the Heisenberg model and is fully integrable. We discuss additional symmetries of the equivalent quantum Hamiltonian which relate observables in different sectors. In some sectors, the long-time decay of correlation functions is qualitatively different from that of the simple exclusion process. These decays in different sectors are deduced from an exact mapping to a model of the diffusion of hard-core random walkers with conserved spins, and are also verified numerically. We also discuss some implications of the existence of an infinity of conservation laws for a hydrodynamic description.Comment: 39 pages, with 5 eps figures, to appear in J. Stat. Phys. (March 1997

Wettability of hair using natural surfactants in presence of silver nanoparticles as additive

The adsorption of surfactant molecules and nanoparticles at the air-liquid and solid-liquid interface play an important role in reducing surface tension and interfacial tension respectively thereby increasing wetting properties to a reasonable mark. Therefore, the combination of both i.e. surfactant as well as nanoparticles in an aqueous phase can be of great interest to investigate the wettability of hair surface. Consequently, in this report, the experimental studies were conducted to study the solution behavior of acacia (natural surfactant) solutions and its wettability on hair surface in absence and presence of silver nanoparticles (Ag NPs) as additive. Natural surfactants have been chosen over synthetic one because of its biocompatibility, biodegradable, nontoxic, and nonionic natures. The nanoparticles used in this study were synthesized by chemical route from AgNO3 using NaBH4 in acacia medium where NaBH4 and acacia acts as a reducing and capping agent respectively. Moreover, insitu synthesis of silver nanoparticles (Ag NPs) using acacia was also done and performed wettability studies on hair and the obtained results was compared with the previous results. Characterizations of nanoparticles were performed with UV-Vis and FESEM to confirm the particles and its size. Physicochemical properties such as critical micellar concentration (CMC) and surface tension, contact angle, work of adhesion and surface energy of hair have been estimated and discussed. Characterization of hair surface was also done to study the surface roughness using AFM respectively

Drift and trapping in biased diffusion on disordered lattices

We reexamine the theory of transition from drift to no-drift in biased diffusion on percolation networks. We argue that for the bias field B equal to the critical value B_c, the average velocity at large times t decreases to zero as 1/log(t). For B < B_c, the time required to reach the steady-state velocity diverges as exp(const/|B_c-B|). We propose an extrapolation form that describes the behavior of average velocity as a function of time at intermediate time scales. This form is found to have a very good agreement with the results of extensive Monte Carlo simulations on a 3-dimensional site-percolation network and moderate bias.Comment: 4 pages, RevTex, 3 figures, To appear in International Journal of Modern Physics C, vol.

Driven Lattice Gases with Quenched Disorder: Exact Results and Different Macroscopic Regimes

We study the effect of quenched spatial disorder on the steady states of driven systems of interacting particles. Two sorts of models are studied: disordered drop-push processes and their generalizations, and the disordered asymmetric simple exclusion process. We write down the exact steady-state measure, and consequently a number of physical quantities explicitly, for the drop-push dynamics in any dimensions for arbitrary disorder. We find that three qualitatively different regimes of behaviour are possible in 1-$d$ disordered driven systems. In the Vanishing-Current regime, the steady-state current approaches zero in the thermodynamic limit. A system with a non-zero current can either be in the Homogeneous regime, chracterized by a single macroscopic density, or the Segregated-Density regime, with macroscopic regions of different densities. We comment on certain important constraints to be taken care of in any field theory of disordered systems.Comment: RevTex, 17pages, 18 figures included using psfig.st

Steady State and Dynamics of Driven Diffusive Systems with Quenched Disorder

We study the effect of quenched disorder on nonequilibrium systems of interacting particles, specifically, driven diffusive lattice gases with spatially disordered jump rates. The exact steady-state measure is found for a class of models evolving by drop-push dynamics, allowing several physical quantities to be calculated. Dynamical correlations are studied numerically in one dimension. We conjecture that the relevance of quenched disorder depends crucially upon the speed of the kinematic waves in the system. Time-dependent correlation functions, which monitor the dissipation of kinematic waves, behave as in pure system if the wave speed is non-zero. When the wave speed vanishes, e.g. for the disordered exclusion process close to half filling, disorder is strongly relevant and induces separation of phases with different macroscopic densities. In this case the exponent characterizing the dynamical correlation function changes.Comment: 4 pages, RevTeX, 4 eps figures included using 'psfig.sty

The Irreducible String and an Infinity of Additional Constants of Motion in a Deposition-Evaporation Model on a Line

We study a model of stochastic deposition-evaporation with recombination, of three species of dimers on a line. This model is a generalization of the model recently introduced by Barma {\it et. al.} (1993 {\it Phys. Rev. Lett.} {\bf 70} 1033) to $q\ge 3$ states per site. It has an infinite number of constants of motion, in addition to the infinity of conservation laws of the original model which are encoded as the conservation of the irreducible string. We determine the number of dynamically disconnected sectors and their sizes in this model exactly. Using the additional symmetry we construct a class of exact eigenvectors of the stochastic matrix. The autocorrelation function decays with different powers of $t$ in different sectors. We find that the spatial correlation function has an algebraic decay with exponent 3/2, in the sector corresponding to the initial state in which all sites are in the same state. The dynamical exponent is nontrivial in this sector, and we estimate it numerically by exact diagonalization of the stochastic matrix for small sizes. We find that in this case $z=2.39\pm0.05$.Comment: Some minor errors in the first version has been correcte

Strong clustering of non-interacting, passive sliders driven by a Kardar-Parisi-Zhang surface

We study the clustering of passive, non-interacting particles moving under the influence of a fluctuating field and random noise, in one dimension. The fluctuating field in our case is provided by a surface governed by the Kardar-Parisi-Zhang (KPZ) equation and the sliding particles follow the local surface slope. As the KPZ equation can be mapped to the noisy Burgers equation, the problem translates to that of passive scalars in a Burgers fluid. We study the case of particles moving in the same direction as the surface, equivalent to advection in fluid language. Monte-Carlo simulations on a discrete lattice model reveal extreme clustering of the passive particles. The resulting Strong Clustering State is defined using the scaling properties of the two point density-density correlation function. Our simulations show that the state is robust against changing the ratio of update speeds of the surface and particles. In the equilibrium limit of a stationary surface and finite noise, one obtains the Sinai model for random walkers on a random landscape. In this limit, we obtain analytic results which allow closed form expressions to be found for the quantities of interest. Surprisingly, these results for the equilibrium problem show good agreement with the results in the non-equilibrium regime.Comment: 14 pages, 9 figure

Independent Assessment of the 2018–19 fish deaths in the lower Darling

Three significant fish death events occurred in the Darling River near Menindee between December 2018 and January 2019. The three events took place within two adjacent weir pools in a 30 km reach of river between Texas Downs Station and Weir 32 (DPI NSW Fisheries, 2019). The main native fish species involved included Murray Cod, Silver Perch, Golden Perch, Bony Herring, with mortality estimates in the range of hundreds of thousands to over a million fish. Though post-event fish population sampling is yet to be conducted, we expect that these mortalities will impact populations in the lower Darling River, and perhaps beyond, for many years. These events constitute a serious ecological shock to the lower Darling and reverse positive ecological outcomes that had accrued from environmental watering programs. We have determined that fish deaths events were primarily caused by local hydrological and climatic conditions (Figure 1-1). The extreme hot and dry climate during 2018, extending into 2019, shaped the conditions that saw a large fish biomass, which had flourished since favourable spawning conditions in 2016, isolated in the weir pools around Menindee, with no means of escaping upstream or downstream. Those adverse climate conditions also shaped the subsequent algal bloom development and the strong and persistent thermal stratification of the weir pools, which created hypoxic conditions in the bottom waters of the pools. All that was needed for this to have a fatal impact on the fish was a trigger for the weir pool waters to become destratified and deprive the fish of oxygen. That trigger duly arrived with a series of sudden cool changes in the weather, with temperature drops and wind action initiating the turnover of the weir pool waters. This sudden depletion of oxygen, combined with the already high water and air temperatures, would have offered the large biomass of stressed fish no means of escape. For each fish death event, the weir pool in which the fish were trapped was bordered downstream by an impenetrable barrier (a weir) and upstream by a dry channel. Ultimately, it was the rapid transition from very favourable conditions to very adverse ones that resulted in such high numbers of fish deaths. We have also determined that the fish death events were shaped by a broader climatic, hydrologic and basin management context that placed the lower Darling River at risk of such fish deaths. The preceding six years (since 2012) had seen two high flow events that had delivered water into Menindee Lakes (2012 and 2016) and offered opportunities for substantial fish breeding and recruitment. Fish populations were further enhanced by the judicious use of environmental water. The end result was a considerable biomass of fish within the Menindee Lakes, post 2016. Outside of these high flow events there were minimal flows in the Darling River below Bourke. This period was preceded by the Millennium drought (2000-2010), during which time flows across the entire northern Murray– Darling Basin were reduced. All of the hydroclimatic evidence available indicates that the years since 2000 have been some of the driest on record, in terms of inflows into major upstream storages, combined with an increased number of extreme heat days, which would have had a major impact on water quality in remnant pools. Soon after the events, Basin government officials met and developed an action plan to respond to the crisis. Immediate actions underway include additional water quality monitoring in the lower Darling, the use of aerators and targeted fish relocations. These immediate actions are welcomed, however, the current situation remains critical – without significant inflows, further deaths of surviving fish may be expected. We consider that priorities and actions in the short-term should focus on anticipating a repeat of ‘worst-case scenario’ outcomes with responses focussed at the site scale. In addition, the Minister for Agriculture and Water Resources announced a Native Fish Management and Recovery Strategy to help manage and recover fish populations across the Basin. We consider that this provides a good opportunity to enhance native fish management and support native fish population recovery and should be developed and implemented through a genuine collaboration between governments, communities, and Traditional Owners. The strategy needs to build on existing and lapsed native fish programs across the Basin. Through our investigations, it became evident to us that, over the long-term, the extant water access arrangements in the northern Basin, as well as limitations in the river models used to plan water sharing, place the lower Darling River at a higher risk of conditions that can lead to fish deaths during droughts than has previously been anticipated. Given that we are witnessing an increasing frequency of low inflow sequences in the northern Basin, this presents a serious problem for safeguarding fish populations, and populations of other resident biota, during drought in the lower Darling. We have identified that changes to Barwon–Darling water access arrangements made by NSW just prior to the commencement of the Basin Plan in 2012 have enhanced the ability of irrigators to access water during low flow periods and during the first flow event immediately after a cease-to-flow period. Further, it appears that the river models used to develop water sharing arrangements have a tendency to overestimate streamflows during dry sequences, and hence underestimate the impacts of extractions during dry times