Homogenization of plasmonic crystals: seeking the epsilon-near-zero effect

By using an asymptotic analysis and numerical simulations, we derive and investigate a system of homogenized Maxwell's equations for conducting material sheets that are periodically arranged and embedded in a heterogeneous and anisotropic dielectric host. This structure is motivated by the need to design plasmonic crystals that enable the propagation of electromagnetic waves with no phase delay (epsilon-near-zero effect). Our microscopic model incorporates the surface conductivity of the two-dimensional (2D) material of each sheet and a corresponding line charge density through a line conductivity along possible edges of the sheets. Our analysis generalizes averaging principles inherent in previous Bloch-wave approaches. We investigate physical implications of our findings. In particular, we emphasize the role of the vector-valued corrector field, which expresses microscopic modes of surface waves on the 2D material. We demonstrate how our homogenization procedure may set the foundation for computational investigations of: effective optical responses of reasonably general geometries, and complicated design problems in the plasmonics of 2D materials.

Numerical analysis of weak random drift in a cline

The equilibrium state of a diffusion model for weak random genetic drift in a cline is analyzed numerically. The monoecious organism occupies an unbounded linear habitat with constant, uniform population density. Migration is homogeneous, symmetric, and independent of genotype. A single diallelic locus with a step environment is investigated in the absence of dominance and mutation. The ratio of the variance of either gene frequency to the product of the expected gene frequencies decreases monotonically to a non-zero constant. The correlation between the gene frequencies at two points decreases monotonically to zero as the separation is increased with the average position fixed; the decrease is asymptotically exponential. The correlation decreases monotonically to a positive constant depending on the separation as the average position increasingly deviates from the center of the cline with the separation fixed. The correlation also decreases monotonically to zero if one of the points is fixed and the other is moved outward in the habitat, the ultimate decrease again being exponential. All the results are parameter free. Some asymptotic formulae are derived analytically.

Embryonic-derived glial-restricted precursor cells (GRP cells) can differentiate into astrocytes and oligodendrocytes in vivo

We have isolated and characterized a unique glial-restricted precursor cell (GRP) from the embryonic spinal cord. Clonal analysis demonstrated that these cells are able to generate oligodendrocytes and two distinct type of astrocytes (type 1 and type 2) when exposed to appropriate signals in vitro. We now show that many aspects of these cells are retained in vivo. GRP cells are restricted to the glial lineage in vivo as they seem to be unable to generate neuronal phenotypes in an in vivo neurogenic environment. GRP cells survive and migrate in the neonatal and adult brain. Transplanted GRP cells differentiate into myelin-forming oligodendrocytes in a myelin-deficient background and also generate immature oligodendrocytes in the normal neonatal brain. In addition, GRP cells also consistently generated glial fibrillary protein-expressing cells in the neonatal and adult brain, a property not consistently expressed by other glial precursor cells like the O-2A/OPC cells. We suggest that the lineage restriction of GRP cells and their ability to generate both oligodendrocytes and astrocytes in vivo together with their embryonic character that allows for extensive in vitro expansion of the population makes the cell useful for clinical application.

Preventive health pamphlets in the emergency department

We conducted a prospective clinical trial to determine the effectiveness of an emergency department informational pamphlet in improving patients' compliance with recommendations that they receive Pap smears, mammograms, and a pneumococcal vaccination. Informational pamphlets were distributed to 1,000 consecutive patients who presented to a university-affiliated emergency department (ED). The pamphlet contained information stating the indications for obtaining routine Pap smears, mammograms, and a pneumococcal vaccination. Target individuals were women 18 years and older and men 65 years and older. Target patients were called approximately 2 months after their ED visits to obtain follow-up data. There were 464 target patients obtained from the 1,000 pamphlets distributed (409 female/55 male), and 68% (316) of the 464 were contacted by telephone for follow-up data. Significantly more women than men had read the pamphlet (62% vs. 8%). Of the women contacted (279), 31.9% (89) were not up to date (UTD) with Pap smears, and 11.2% (10) stated that they had scheduled an appointment for a Pap smear; 14.5% (11) of the women were not UTD with mammograms, and none had scheduled an appointment to receive care. Of the patients over age 65, 67% were not UTD with a pneumococcal vaccination, and no appointments were scheduled to obtain one. We conclude that a significant number of patients who present to this ED are in need of preventive health care. Emergency department informational pamphlets may have a role in improving Pap smear compliance. Women may be more likely then men to read informational pamphlets distributed in the ED.