Diffusiophoresis and electrophoresis of a charged sphere perpendicular to two plane walls.

The problem of diffusiophoretic and electrophoretic motions of a dielectric spherical particle in an electrolyte solution situated at an arbitrary position between two infinite parallel plane walls is studied theoretically in the quasisteady limit of negligible Peclet and Reynolds numbers. The applied electrolyte concentration gradient or electric field is uniform and perpendicular to the plane walls. The electric double layer at the particle surface is assumed to be thin relative to the particle radius and to the particle-wall gap widths, but the polarization effect of the diffuse ions in the double layer is incorporated. To solve the conservative equations, the general solution is constructed from the fundamental solutions in both cylindrical and spherical coordinates. The boundary conditions are enforced first at the plane walls by the Hankel transforms and then on the particle surface by a collocation technique. Numerical results for the diffusiophoretic and electrophoretic velocities of the particle relative to those of a particle under identical conditions in an unbounded solution are presented for various cases. The collocation results agree well with the approximate analytical solutions obtained by using a method of reflections. The presence of the walls can reduce or enhance the particle velocity, depending on the properties of the particle-solution system and the relative particle-wall separation distances. The boundary effects on diffusiophoresis and electrophoresis of a particle normal to two plane walls are found to be quite significant and complicated, and generally stronger than those parallel to the confining walls.

Distribution and factors associated with Salmonella enterica genotypes in a diverse population of humans and animals in Qatar using multi-locus sequence typing (MLST).

Salmonella enterica is one of the most commonly reported causes of bacterial foodborne illness around the world. Understanding the sources of this pathogen and the associated factors that exacerbate its risk to humans will help in developing risk mitigation strategies. The genetic relatedness among Salmonella isolates recovered from human gastroenteritis cases and food animals in Qatar were investigated in the hope of shedding light on these sources, their possible transmission routes, and any associated factors. A repeat cross-sectional study was conducted in which the samples and associated data were collected from both populations (gastroenteritis cases and animals). Salmonella isolates were initially analyzed using multi-locus sequence typing (MLST) to investigate the genetic diversity and clonality. The relatedness among the isolates was assessed using the minimum spanning tree (MST). Twenty-seven different sequence types (STs) were identified in this study; among them, seven were novel, including ST1695, ST1696, ST1697, ST1698, ST1699, ST1702, and ST1703. The pattern of overall ST distribution was diverse; in particular, it was revealed that ST11 and ST19 were the most common sequence types, presenting 29.5% and 11.5% within the whole population. In addition, 20 eBurst Groups (eBGs) were identified in our data, which indicates that ST11 and ST19 belonged to eBG4 and eBG1, respectively. In addition, the potential association between the putative risk factors and eBGs were evaluated. There was no significant clustering of these eBGs by season; however, a significant association was identified in terms of nationality in that Qataris were six times more likely to present with eBG1 compared to non-Qataris. In the MST analysis, four major clusters were presented, namely, ST11, ST19, ST16, and ST31. The linkages between the clusters alluded to a possible transmission route. The results of the study have provided insight into the ST distributions of S. enterica and their possible zoonotic associations in Qatar.

Translation and rotation of slightly deformed colloidal spheres experiencing slip.

The steady translation and rotation of a rigid, slightly deformed colloidal sphere in arbitrary directions in a viscous fluid are analyzed in the limit of small Reynolds number. The fluid is allowed to slip frictionally at the surface of the particle, and the Stokes equations are solved asymptotically using a method of perturbed expansions. To the second order in the small parameter characterizing the deformation of the particle from the spherical shape, the resistance problem is formulated for the general case and explicit expressions for the hydrodynamic drag force and torque exerted on the particle are obtained for the special cases of prolate and oblate spheroids. The agreement between our asymptotic results for a slip-surface spheroid and the relevant exact solutions in the literature is very good, even if the particle deformation from the spherical shape is not very small. As expected, the second-order expansions for the translational and rotational resistances in powers of the small deformation parameter make better consistency with the available exact results than the first-order expansions do. Depending on the value of the slip parameter, the hydrodynamic drag force and torque acting on a moving spheroid normalized by the corresponding values for a spherical particle with equal equatorial radius are not necessarily monotonic functions of the aspect ratio of the spheroid. Noticeable behavior of the drag force and torque is grasped in the second-order expansions; e.g., the torque exerted on a perfect-slip rotating spheroid is not necessarily zero. For a moving spheroid with a fixed aspect ratio, its normalized hydrodynamic drag force and torque decrease monotonically with an increase in the slip capability of the particle.