77 research outputs found
Onsager reciprocity in premelting solids
The diffusive motion of foreign particles dispersed in a premelting solid is analyzed within the framework of irreversible thermodynamics. We determine the mass diffusion coefficient, thermal diffusion coefficient and Soret coefficient of the particles in the dilute limit, and find good agreement with experimental data. In contrast to liquid suspensions, the unique nature of premelting solids allows us to derive an expression for the Dufour coefficient and independently verify the Onsager reciprocal relation coupling diffusion to the flow of heat
Dynamics of colloidal particles in ice
We use X-ray Photon Correlation Spectroscopy (XPCS) to probe the dynamics of colloidal particles in polycrystalline ice. During freezing, the dendritic ice morphology and rejection of particles from the ice created regions of high-particle-density, where some of the colloids were forced into contact and formed disordered aggregates. We find that the particles in these high density regions underwent ballistic motion coupled with both stretched and compressed exponential decays of the intensity autocorrelation function, and that the particles’ characteristic velocity increased with temperature. We explain this behavior in terms of ice grain boundary migration
The Ursinus Weekly, April 3, 1916
Male Glee Club in home concert • 46th anniversary of Zwing Society • Varsity nine wins in opening game • Schaff prize essay: The toll of the European war • Christian organizations • Resolutions • College directoryhttps://digitalcommons.ursinus.edu/weekly/2624/thumbnail.jp
Axisymmetric viscous gravity currents flowing over a porous medium
We study the axisymmetric propagation of a viscous gravity current over a
deep porous medium into which it also drains. A model for the propagation and
drainage of the current is developed and solved numerically in the case of
constant input from a point source. In this case, a steady state is possible in
which drainage balances the input, and we present analytical expressions for
the resulting steady profile and radial extent. We demonstrate good agreement
between our experiments, which use a bed of vertically aligned tubes as the
porous medium, and the theoretically predicted evolution and steady state.
However, analogous experiments using glass beads as the porous medium exhibit a
variety of unexpected behaviours, including overshoot of the steady-state
radius and subsequent retreat, thus highlighting the importance of the porous
medium geometry and permeability structure in these systems.Comment: 11 pages, 6 figures, 1 tabl
The Behavior of Granular Materials under Cyclic Shear
The design and development of a parallel plate shear cell for the study of
large scale shear flows in granular materials is presented. The parallel plate
geometry allows for shear studies without the effects of curvature found in the
more common Couette experiments. A system of independently movable slats
creates a well with side walls that deform in response to the motions of grains
within the pack. This allows for true parallel plate shear with minimal
interference from the containing geometry. The motions of the side walls also
allow for a direct measurement of the velocity profile across the granular
pack. Results are presented for applying this system to the study of transients
in granular shear and for shear-induced crystallization. Initial shear profiles
are found to vary from packing to packing, ranging from a linear profile across
the entire system to an exponential decay with a width of approximately 6 bead
diameters. As the system is sheared, the velocity profile becomes much sharper,
resembling an exponential decay with a width of roughly 3 bead diameters.
Further shearing produces velocity profiles which can no longer be fit to an
exponential decay, but are better represented as a Gaussian decay or error
function profile. Cyclic shear is found to produce large scale ordering of the
granular pack, which has a profound impact on the shear profile. There exist
periods of time in which there is slipping between layers as well as periods of
time in which the layered particles lock together resulting in very little
relative motion.Comment: 10 pages including 12 figure
Sensitivity of the stress response function to packing preparation
A granular assembly composed of a collection of identical grains may pack
under different microscopic configurations with microscopic features that are
sensitive to the preparation history. A given configuration may also change in
response to external actions such as compression, shearing etc. We show using a
mechanical response function method developed experimentally and numerically,
that the macroscopic stress profiles are strongly dependent on these
preparation procedures. These results were obtained for both two and three
dimensions. The method reveals that, under a given preparation history, the
macroscopic symmetries of the granular material is affected and in most cases
significant departures from isotropy should be observed. This suggests a new
path toward a non-intrusive test of granular material constitutive properties.Comment: 15 pages, 11 figures, some numerical data corrected, to appear in J.
Phys. Cond. Mat. special issue on Granular Materials (M. Nicodemi Editor
Stress response inside perturbed particle assemblies
The effect of structural disorder on the stress response inside three
dimensional particle assemblies is studied using computer simulations of
frictionless sphere packings. Upon applying a localised, perturbative force
within the packings, the resulting {\it Green's} function response is mapped
inside the different assemblies, thus providing an explicit view as to how the
imposed perturbation is transmitted through the packing. In weakly disordered
arrays, the resulting transmission of forces is of the double-peak variety, but
with peak widths scaling linearly with distance from the source of the
perturbation. This behaviour is consistent with an anisotropic elasticity
response profile. Increasing the disorder distorts the response function until
a single-peak response is obtained for fully disordered packings consistent
with an isotropic description.Comment: 8 pages, 7 figure captions To appear in Granular Matte
Structure of nanoparticles embedded in micellar polycrystals
We investigate by scattering techniques the structure of water-based soft
composite materials comprising a crystal made of Pluronic block-copolymer
micelles arranged in a face-centered cubic lattice and a small amount (at most
2% by volume) of silica nanoparticles, of size comparable to that of the
micelles. The copolymer is thermosensitive: it is hydrophilic and fully
dissolved in water at low temperature (T ~ 0{\deg}C), and self-assembles into
micelles at room temperature, where the block-copolymer is amphiphilic. We use
contrast matching small-angle neuron scattering experiments to probe
independently the structure of the nanoparticles and that of the polymer. We
find that the nanoparticles do not perturb the crystalline order. In addition,
a structure peak is measured for the silica nanoparticles dispersed in the
polycrystalline samples. This implies that the samples are spatially
heterogeneous and comprise, without macroscopic phase separation, silica-poor
and silica-rich regions. We show that the nanoparticle concentration in the
silica-rich regions is about tenfold the average concentration. These regions
are grain boundaries between crystallites, where nanoparticles concentrate, as
shown by static light scattering and by light microscopy imaging of the
samples. We show that the temperature rate at which the sample is prepared
strongly influence the segregation of the nanoparticles in the
grain-boundaries.Comment: accepted for publication in Langmui
The receptor tyrosine kinase EphB4 is overexpressed in ovarian cancer, provides survival signals and predicts poor outcome
EphB4 is a member of the largest family of transmembrane receptor tyrosine kinases and plays critical roles in axonal pathfinding and blood vessel maturation. We wanted to determine the biological role of EphB4 in ovarian cancer. We studied the expression of EphB4 in seven normal ovarian specimens and 85 invasive ovarian carcinomas by immunohistochemistry. EphB4 expression was largely absent in normal ovarian surface epithelium, but was expressed in 86% of ovarian cancers. EphB4 expression was significantly associated with advanced stage of disease and the presence of ascites. Overexpression of EphB4 predicted poor survival in both univariate and multivariate analyses. We also studied the biological significance of EphB4 expression in ovarian tumour cells lines in vitro and in vivo. All five malignant ovarian tumour cell lines tested expressed higher levels of EphB4 compared with the two benign cell lines. Treatment of malignant, but not benign, ovarian tumour cell lines with progesterone, but not oestrogen, led to a 90% reduction in EphB4 levels that was associated with 50% reduction in cell survival. Inhibition of EphB4 expression by specific siRNA or antisense oligonucleotides significantly inhibited tumour cell viability by inducing apoptosis via activation of caspase-8, and also inhibited tumour cell invasion and migration. Furthermore, EphB4 antisense significantly inhibited growth of ovarian tumour xenografts and tumour microvasculature in vivo. Inhibition of EphB4 may hence have prognostic and therapeutic utility in ovarian carcinoma
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