Clustering and gelation of hard spheres induced by the Pickering effect

A mixture of hard-sphere particles and model emulsion droplets is studied with a Brownian dynamics simulation. We find that the addition of nonwetting emulsion droplets to a suspension of pure hard spheres can lead to both gas-liquid and fluid-solid phase separations. Furthermore, we find a stable fluid of hard-sphere clusters. The stability is due to the saturation of the attraction that occurs when the surface of the droplets is completely covered with colloidal particles. At larger emulsion droplet densities a percolation transition is observed. The resulting networks of colloidal particles show dynamical and mechanical properties typical of a colloidal gel. The results of the model are in good qualitative agreement with recent experimental findings [E. Koos and N. Willenbacher, Science 331, 897 (2011)] in a mixture of colloidal particles and two immiscible fluids.Comment: 5 figures, 5 page

Average Shortest Path Length in a Novel Small-World Network

We study a novel model of random graph which exhibits the structural characteristics of the Watts- Strogatz small-world network. The small-world network is characterized by a high level of local clustering while also having a relatively small graph diameter. The same behavior that makes the Watts-Strogatz model behave like this also makes it difficult to analyze. Our model addresses this issue, closely mimicking the same structure experimentally while following a constructive process that makes it easier to analyze mathematically. We present a bound on the average shortest path length in our new model, which we approach by looking at the two key geometric components

Activated dynamics and effective temperature in a steady state sheared glass

We conduct nonequilibrium molecular dynamics simulations to measure the shear stress, the average inherent structure energy, and the effective temperature $T_{eff}$ of a sheared model glass as a function of bath temperature $T$ and shear strain rate. For $T$ above the glass transition temperature $T_0$, the rheology approaches a Newtonian limit and $T_{eff}$ approaches $T$ as the strain rate approaches zero, while for $T<T_0$, the shear stress approaches a yield stress and $T_{eff}$ approaches a limiting value near $T_0$. In the shear-dominated regime at high $T$, high strain rate or at low $T$, we find that the shear stress and the average inherent structure energy each collapse onto a single curve as a function of $T_{eff}$. This indicates that $T_{eff}$ is controlling behavior in this regime.Comment: 4 pages, 2 figures. Revised to include additional data. Inherent structure energy results were included, and much of the shear transformation zone discussion was remove

Computer simulations of colloidal transport on a patterned magnetic substrate

We study the transport of paramagnetic colloidal particles on a patterned magnetic substrate with kinetic Monte Carlo and Brownian dynamics computer simulations. The planar substrate is decorated with point dipoles in either parallel or zigzag stripe arrangements and exposed to an additional external magnetic field that oscillates in time. For the case of parallel stripes we find that the magnitude and direction of the particle current is controlled by the tilt angle of the external magnetic field. The effect is reliably obtained in a wide range of ratios between temperature and magnetic permeability. Particle transport is achieved only when the period of oscillation of the external field is greater than a critical value. For the case of zigzag stripes a current is obtained using an oscillating external field normal to the substrate. In this case, transport is only possible in the vertex of the zigzag, giving rise to a narrow stream of particles. The magnitude and direction of the particle current are found to be controlled by a combination of the zigzag angle and the distance of the colloids from the substrate. Metropolis Monte Carlo and Brownian dynamics simulations predict results that are in good agreement with each other. Using kinetic Monte Carlo we find that at high density the particle transport is hindered by jamming.Comment: 8 pages, 9 figure

Malaria-filaria coinfection in mice makes malarial disease more severe unless filarial infection achieves patency

Coinfections are common in natural populations, and the literature suggests that helminth coinfection readily affects how the immune system manages malaria. For example, type 1–dependent control of malaria parasitemia might be impaired by the type 2 milieu of preexisting helminth infection. Alternatively, immunomodulatory effects of helminths might affect the likelihood of malarial immunopathology. Using rodent models of lymphatic filariasis (Litomosoides sigmodontis) and noncerebral malaria (clone AS Plasmodium chabaudi chabaudi), we quantified disease severity, parasitemia, and polyclonal splenic immune responses in BALB/c mice. We found that coinfected mice, particularly those that did not have microfilaremia (Mf), had more severe anemia and loss of body mass than did mice with malaria alone. Even when controlling for parasitemia, malaria was most severe in Mf coinfected mice, and this was associated with increased interferon-g responsiveness. Thus, in Mf mice, filariasis upset a delicate immunological balance in malaria infection and exacerbated malaria-induced immunopathology. Helminth infections are prevalent throughout tropical regions where malaria is transmitted [1–5]. Interactions among infections commonly alter disease severity [6, 7], and malaria-helminth coinfection can either exac

Sustainable freight: impacts of the London congestion charge and low emissions zone

This paper assesses whether two sustainability policies currently in effect in London, a congestion charge zone and a low emission zone, have affected freight operations and reduced vehicle kilometers travelled. It investigates responses by freight operators, including re-timing, re-routing, or reducing the number of trips, or replacing vehicles. Freight traffic trends from 1994 to 2012 were identified using road traffic estimates, cordon counts, and vehicle speed data and supplemented by interviews with freight industry experts and operators. Findings indicate that freight traffic increased throughout London during this timeframe, but declined in the central boroughs partly within the congestion charge zone. The congestion charge may have time-shifted some light goods trips, but most freight trips face a variety of constraints on operators’ delivery window. No evidence was found of re-routing of freight traffic or avoidance traffic around the charged zone. The low emission zone spurred higher levels of operational change than the congestion charge zone, and it was effective at spurring freight vehicle replacement. The paper also discusses freight operators’ perceptions of these policies and how they could be improved

Coarsening Dynamics of a Nonconserved Field Advected by a Uniform Shear Flow

We consider the ordering kinetics of a nonconserved scalar field advected by a uniform shear flow. Using the Ohta-Jasnow-Kawasaki approximation, modified to allow for shear-induced anisotropy, we calculate the asymptotic time dependence of the characteristic length scales, L_parallel and L_perp, that describe the growth of order parallel and perpendicular to the mean domain orientation. In space dimension d=3 we find, up to constants, L_parallel = gamma t^{3/2}, L_perp = t^{1/2}, where gamma is the shear rate, while for d = 2 we find L_parallel = gamma^{1/2} t (ln t)^{1/4}, L_perp = gamma^{-1/2}(ln t)^{-1/4} . Our predictions for d=2 can be tested by experiments on twisted nematic liquid crystals.Comment: RevTex, 4 page

Dynamics and delocalisation transition for an interface driven by a uniform shear flow

We study the effect of a uniform shear flow on an interface separating the two broken-symmetry ordered phases of a two-dimensional system with nonconserved scalar order parameter. The interface, initially flat and perpendicular to the flow, is distorted by the shear flow. We show that there is a critical shear rate, \gamma_c, proportional to 1/L^2, (where L is the system width perpendicular to the flow) below which the interface can sustain the shear. In this regime the countermotion of the interface under its curvature balances the shear flow, and the stretched interface stabilizes into a time-independent shape whose form we determine analytically. For \gamma > \gamma_c, the interface acquires a non-zero velocity, whose profile is shown to reach a time-independent limit which we determine exactly. The analytical results are checked by numerical integration of the equations of motion.Comment: 5 page

Prevention Program Sustainability and Associated Determinants: A Literature Review, Version 1.0

The Department of Homeland Security (DHS) has made millions of dollars available through the Targeted Violence and Terrorism Prevention (TVTP) Grant Program to help communities across the United States develop capabilities to combat terrorism and targeted violence. Given this investment, a key objective is ensuring the long-term impact of these programs, which depends on their sustainment beyond the initial grant. Thus, the purpose of this report is to review the relevant literature on program sustainability and discuss implications for the TVTP Grant Program. We began the review by exploring definitions of sustainability as well as similar social programming concepts, such as adaptation, scalability, and impact. Our review found no consensus definition for prevention program sustainability, suggesting the TVTP Grant Program should develop a bespoke definition guided by strategic program priorities and incorporating other social programming concepts as needed. We then examined the determinants, or factors related positively to long-term programmatic success, of sustainability. All determinants relate to capacity building at two levels: 1. Organizational (Internal). Internal organizational capacity is impacted by (a) internal stakeholder buy-in and engagement, (b) adequacy of personnel resources, particularly in terms of expertise, (c) the presence of ongoing evaluation activities to support adaptations, and (d) support from the funding agency. 2. Community (External). External community capacity is impacted by (a) external stakeholder buy-in and continued engagement beyond the initial award, and (b) the fit between the program offerings and community needs