Viscoelastic{Viscoplastic Damage Model for Asphalt Concrete

This thesis presents a continuum model for asphalt concrete incorporating non- linear viscoelasticity, viscoplasticity, mechanically-induced damage and moisture- induced damage. The Schapery single-integral viscoelastic model describes the nonlinear viscoelastic response. The viscoplastic model of Perzyna models the time- dependent permanent deformations, using a Drucker-Prager yield surface which is modified to depend on the third deviatoric stress invariant to include more complex dependence on state of stress. Mechanically-induced damage is modeled using continuum damage mechanics, using the same modified Drucker-Prager law to determine damage onset and growth. A novel moisture damage model is proposed, modeling moisture-induced damage using continuum damage mechanics; adhesive moisture- induced damage to the asphalt mastic-aggregate bond and moisture-induced cohesive damage to the asphalt mastic itself are treated separately. The analytical model is implemented numerically for three-dimensional and plane strain finite element analyses, and a series of simulations is presented to show the performance of the model and its implementation. Sensitivity studies are conducted for all model parameters and results due to various simulations corresponding to laboratory tests are presented. In addition to the continuum model, results are presented for a micromechanical model using the nonlinear-viscoelastic-viscoplastic-damage model for asphalt mastic and a linear elastic model for aggregates. Initial results are encouraging, showing the strength and stiffness of the mix as well as the failure mode varying with moisture loading. These initial results are provided as a an example of the model's robustness and suitability for modeling asphalt concrete at the mix scale

Mechanism of margination in confined flows of blood and other multicomponent suspensions

Flowing blood displays a phenomenon called margination, in which leukocytes and platelets are preferentially found near blood vessel walls, while erythrocytes are depleted from these regions. Here margination is investigated using direct hydrodynamic simulations of a binary suspension of stiff (s) and floppy (f) capsules, as well as a stochastic model that incorporates the key particle transport mechanisms in suspensions -- wall-induced hydrodynamic migration and shear-induced pair collisions. The stochastic model allows the relative importance of these two mechanisms to be directly evaluated and thereby indicates that margination, at least in the dilute case, is largely due to the differential dynamics of homogeneous (e.g. s-s) and heterogeneous (s-f) collisionsComment: 5 Pages, 4 figure

Autonomic physiological data associated with simulator discomfort

The development of a physiological monitoring capability for the Army's advanced helicopter simulator facility is reported. Additionally, preliminary physiological data is presented. Our objective was to demonstrate the sensitivity of physiological measures in this simulator to self-reported simulator sickness. The data suggested that heart period, hypergastria, and skin conductance level were more sensitive to simulator sickness than were vagal tone and normal electrogastric activity

A Ring of Warm Dust in the HD 32297 Debris Disk

We report the detection of a ring of warm dust in the edge-on disk surrounding HD 32297 with the Gemini-N/MICHELLE mid-infrared imager. Our N'-band image shows elongated structure consistent with the orientation of the scattered-light disk. The Fnu(11.2 um) = 49.9+/-2.1 mJy flux is significantly above the 28.2+/-0.6 mJy photosphere. Subtraction of the stellar point spread function reveals a bilobed structure with peaks 0.5"-0.6" from the star. An analysis of the stellar component of the SED suggests a spectral type later than A0, in contrast to commonly cited literature values. We fit three-dimensional, single-size grain models of an optically thin dust ring to our image and the SED using a Markov chain Monte Carlo algorithm in a Bayesian framework. The best-fit effective grain sizes are submicron, suggesting the same dust population is responsible for the bulk of the scattered light. The inner boundary of the warm dust is located 0.5"-0.7" (~65 AU) from the star, which is approximately cospatial with the outer boundary of the scattered-light asymmetry inward of 0.5". The addition of a separate component of larger, cooler grains that provide a portion of the 60 um flux improves both the fidelity of the model fit and consistency with the slopes of the scattered-light brightness profiles. Previous indirect estimates of the stellar age (~30 Myr) indicate the dust is composed of debris. The peak vertical optical depths in our models (~0.3-1 x 1e-2) imply that grain-grain collisions likely play a significant role in dust dynamics and evolution. Submicron grains can survive radiation pressure blow-out if they are icy and porous. Similarly, the inferred warm temperatures (130-200 K) suggest that ice sublimation may play a role in truncating the inner disk.Comment: ApJ accepted, 8 pages, 4 figure

Narrow Pass-Band Optical Filters for Space-Borne Remote Sensing Applications

Optical characterisation of 532 nm, 200 pm passband and 1064 nm, I mn passband LkD filters after exposure to proton irradiation, temperature cycling and angle tuning