The Culicoides (Diptera: Ceratopogonidae) of Belize, Central America

The Culicoides fauna of Belize is poorly known, and until 197 4 only 3 species were recorded. Nineteen species of Culicoides from Belize were identified from six collection sites: C. barbosai Wirth & Blanton, C. crepuscularis Malloch, C. debilipalpis Lutz, C. diabolic us Hoffman, C. foxi Ortiz, C. furens (Poey), C. gabaldoni Ortiz, C. heliconiae Fox & Hoffman, C. hoffmani Fox, C. imitator Ortiz, C. insignis Lutz, C. jamaicensis Edwards, C. leopoldoi Ortiz, C. limai Barretto, C. paraensis (Goeldi), C. pifanoi Ortiz, C. pusilloides Wirth & Blanton, C. pusillus Lutz, and a new species, C. mckeeveri Brickle & Hagan is described and illustrated

Structure and Dynamics of a Phase-Separating Active Colloidal Fluid

We examine a minimal model for an active colloidal fluid in the form of self-propelled Brownian hard spheres that interact purely through excluded volume. Despite the absence of an aligning interaction, this system shows the signature behaviors of an active fluid, including anomalous number fluctuations and phase separation behavior. Using simulations and analytic modeling, we quantify the phase diagram and separation kinetics. The dense phase is a unique material that we call an active hexatic, which exhibits the structural signatures of a crystalline solid near the crystal-hexatic transition point, but the rheological and transport properties associated with a viscoelastic fluid.Comment: 5 pages, 5 figure

Large Eddy Simulation of Oscillatory Flow over a Mobile Rippled Bed using an Euler-Lagrange Approach

A volume-filtered Large-Eddy Simulation (LES) of oscillatory flow over a rippled mobile bed is conducted using an Euler-Lagrange approach. As in unsteady marine flows over sedimentary beds, the experimental data, referenced in this work for validation, shows quasi-steady state ripples in the sand bed under oscillatory flow. This work approximately reproduces this configuration with a sinusoidal pressure gradient driven flow and a sinusoidally rippled bed of particles. The LES equations, which are volume-filtered to account for the effect of the particles, are solved on an Eulerian grid, and the particles are tracked in a Lagrangian framework. In the Discrete Particle Method (DPM) used in this work, the particle collisions are handled by a soft-sphere model, and the liquid and solid phases are coupled through volume fraction and momentum exchange terms. Comparison of the numerical results to the experimental data show that the LES-DPM is capable of capturing the mesoscale features of the flow. The large scale shedding of vortices from the ripple peaks are observed in both datasets, which is reflected in the good quantitative agreement between the wall-normal flow statistics, and good qualitative agreement in ripple shape evolution. Additionally, the numerical data provides three insights into the complex interaction between the three-dimensional flow dynamics and bed morphology: (1) there is no observable distinction between reptating and saltating particle velocities, angular velocities or observed Shields parameters; (2) the potential motion of the mobile bed may create issues in the estimation of the bed shear stress used in classical models; and, (3) a helical pairing of vortices is observed, heretofore not known to have to have been identified in this type of flow configuration