Anisotropic diffusion in confined colloidal dispersions: The evanescent diffusivity

We employ an analogy to traditional dynamic light scattering to describe the inhomogeneous and anisotropic diffusion of colloid particles near a solid boundary measured via evanescent wave dynamic light scattering. Following this approach, we generate new expressions for the short-time self- and collective diffusivities of colloidal dispersions with arbitrary volume fraction. We use these expressions in combination with accelerated Stokesian dynamics simulations to calculate the diffusivities in the limit of large and small scattering wave numbers for evanescent penetration depths ranging from four particle radii to one-fifth of a particle radius and volume fractions from 10% to 40%. We show that at high volume fractions, and larger penetration depths, the boundaries have little effect on the dynamics of the suspension parallel to the wall since, to a first approximation, the boundary acts hydrodynamically much as another nearby particle. However, near and normal to the wall, the diffusivity shows a strong dependence on penetration depth for all volume fractions. This is due to the lubrication interactions between the particles and the boundary as the particle moves relative to the wall. These results are novel and comprehensive with respect to the range of penetration depth and volume fraction and provide a complete determination of the effect of hydrodynamic interactions on colloidal diffusion adjacent to a rigid boundary

Simulation of hydrodynamically interacting particles near a no-slip boundary

The dynamics of spherical particles near a single plane wall are computed using an extension of the Stokesian dynamics method that includes long-range many-body and pairwise lubrication interactions between the spheres and the wall in Stokes flow. Extra care is taken to ensure that the mobility and resistance tensors are symmetric, positive, and definite—something which is ineluctable for particles in low-Reynolds-number flows. We discuss why two previous simulation methods for particles near a plane wall, one using multipole expansions and the other using the Rotne-Prager tensor, fail to produce symmetric resistance and mobility tensors. Additionally, we offer some insight on how the Stokesian dynamics paradigm might be extended to study the dynamics of particles in any confining geometry

Particle motion between parallel walls: Hydrodynamics and simulation

The low-Reynolds-number motion of a single spherical particle between parallel walls is determined from the exact reflection of the velocity field generated by multipoles of the force density on the particle’s surface. A grand mobility tensor is constructed and couples these force multipoles to moments of the velocity field in the fluid surrounding the particle. Every element of the grand mobility tensor is a finite, ordered sum of inverse powers of the distance between the walls. These new expressions are used in a set of Stokesian dynamics simulations to calculate the translational and rotational velocities of a particle settling between parallel walls and the Brownian drift force on a particle diffusing between the walls. The Einstein correction to the Newtonian viscosity of a dilute suspension that accounts for the change in stress distribution due to the presence of the channel walls is determined. It is proposed how the method and results can be extended to computations involving many particles and periodic simulations of suspensions in confined geometries

Anti-transgender discrimination and oppression in New York City and San Francisco during the Gay Liberation Movement, 1965-1975

Transgender and gender non-conforming people in San Francisco and New York City were oppressed in many ways during the 1960s and 1970s. Due to employment discrimination, many were homeless and worked as prostitutes. While living on the streets, transgender and gender non-conforming people frequently faced arrest and police harassment due to laws against cross-dressing and solicitation. Transgender and gender non-conforming people were also oftentimes the victims of hate crimes. Even gay liberation activists oppressed transgender and gender non-conforming people. They did this by excluding transgender and gender non-conforming people from gay liberation organizations and refusing to support transgender causes. Despite the obstacles they faced, many transgender and gender non-conforming people of San Francisco and New York City carried out some of the most fearless activist efforts of the gay liberation era

Mapping systemic risk: critical degree and failures distribution in financial networks

The 2008 financial crisis illustrated the need for a thorough, functional understanding of systemic risk in strongly interconnected financial structures. Dynamic processes on complex networks being intrinsically difficult, most recent studies of this problem have relied on numerical simulations. Here we report analytical results in a network model of interbank lending based on directly relevant financial parameters, such as interest rates and leverage ratios. Using a mean-field approach, we obtain a closed-form formula for the "critical degree", viz. the number of creditors per bank below which an individual shock can propagate throughout the network. We relate the failures distribution (probability that a single shock induces $F$ failures) to the degree distribution (probability that a bank has $k$ creditors), showing in particular that the former is fat-tailed whenever the latter is. Our criterion for the onset of contagion turns out to be isomorphic to the condition for cooperation to evolve on graphs and social networks, as recently formulated in evolutionary game theory. This remarkable connection supports recent calls for a methodological rapprochement between finance and ecology.Comment: 19 pages, 4 figure

Japanese Agricultural Policy Studies : the State of the Field

With Trans-Pacifi c Partnership (TPP) negotiations ongoing, agriculture is at the centre of public policy debates in Japan. Japan’s protectionist agricultural policy has been examined from a number of perspectives, including political economy and political science. This paper presents an analytical overviewof the most important strands in the previous literature, and also of several recent studies which offer fresh insights into the determinants of Japan’s agricultural policy. The paper draws together these various strands to create a more complete picture of current academic approaches to agricultural policy in Japan,and highlights the most fertile areas for future research

Examining Migration Flows Across Kentucky\u27s Counties

The state of Kentucky is home to many rural counties which experience high levels of outward migration due to their relatively unfavorable economic conditions. While migration trends nationally have begun to plateau, migration flows from county to county show a much more volatile story. This study will examine the relationship between economic opportunity and migration flow estimates in Kentucky’s counties through a multiple regression approach with the response variable being annual migration flow estimates, with multiple predictor variables showing the economic composition of the county. Variables used in this regression include annual unemployment rates, educational attainment levels, county poverty rates, and the percentage of a county’s population that is of the prime working age, 25-54. Based on the results of this regression, it was determined that there are a few counties in Kentucky that despite relatively unfavorable economic conditions, have been able to stem the flow of outward migration and either maintain their existing working population, or attract new citizens to their county. At the heart of this research is the question of why some of these counties have been more successful than others in retaining their young people despite these existing economic hardships. Due to this finding, interviews with public officials, organizations, and agencies associated with these “bright spot” counties were conducted and the results of these interviews were used to highlight the strategies used by these counties to stem the flow of outward migration, while also providing other county, state, and national leaders with recommendations based on the success stories of these few Kentucky counties

An examination of the applicability of hydrotalcite for removing oxalate anions from Bayer process solutions

Hydrotalcite and thermally activated hydrotalcites were examined for their potential as methods for the removal of oxalate anions from Bayer Process liquors. Hydrotalcite was prepared and characterised by a number of methods, including X-ray diffraction, thermogravimetric analysis, nitrogen adsorption analysis and vibrational spectroscopy. Thermally activated hydrotalcites were prepared by a low temperature method and characterised using X-ray diffraction, nitrogen adsorption analysis and vibrational spectroscopy. Oxalate intercalated hydrotalcite was prepared by two methods and analysed with X-ray diffraction and for the first time thermogravimetric analysis, Raman spectroscopy and infrared emission spectroscopy. The adsorption of oxalate anions by hydrotalcite and thermally activated hydrotalcite was tested in a range of solutions using both batch and kinetic adsorption models