A conceptual model of light coupling by pillar diffraction gratings

Diffractivestructures such as pillar gratings are a promising way of coupling light into or out of thin semiconductor devices, for applications in thin film solar cells and light-emitting diodes. In this paper we show that the diffuse transmittance behavior of pillar gratings can be understood using the concept of grating mode interference and that the optimum heights of the grating and an estimate of the optimum period can be predicted with the effective index method. Furthermore, the method also gives good results for structures outside the range for which it was derived, including circular pillars and quasiperiodic structures. We also show that pillar gratings offer substantially improved performance over groove gratings for thin film silicon solar cells.One of the authors K.R.C. acknowledges the support of an Australian Research Council fellowship. The Centre of Excellence for Advanced Silicon Photovoltaics and Photonics is supported by the Australian Research Council

Microprobe Analysis of Element Distribution in Rabbit and Dog Erythrocytes as Examples of High and Low Potassium Cells

The concentrations of Na, Mg, P, S, Cl, K and Fe were determined by microprobe in near 100% hematocrit suspensions of rabbit and dog erythrocytes prepared by freezing and drying. These cells are representative, respectively, of high potassium, low sodium, and high sodium, low potassium cells. Water contents of the cells were the same, as were, approximately, the levels of Cl, S and Fe. Rabbit P was nearly double that of the dog. For the rabbit, the cell Na/K ratio was 0.21 and for the dog 15.4, illustrating the major diffusible electrolyte difference between these two types of cell. The rabbit erythrocytes showed an apparent negative immobile charge density of 95 meq/kg of cell water and the dog 56 meq/kg cell water, a distinct difference. Serum electrolytes in the two species are exactly comparable (Standard Tables). Ionic distribution in these cell types was treated by the Gibbs-Duhem equation representing two heterogeneous systems in thermodynamic equilibrium with the blood serum. Factors to be considered are: (1) the composition of the erythrocyte and its net immobile charge; (2) the physicochemical properties of the individual ions (charge, ionic radius, hydration energy, standard chemical potential); (3) the dielectric constant of the dispersion medium (in this case, water); and (4) the binding constants of the ions. The hypothesis of active transport (the sodium-potassium pump) is specifically rejected as an explanation of ionic differences

Microprobe Analysis of Element Distribution in Bovine Extracellular Matrices and Muscle

The concentrations of some essential elements, Na, K, P, S and Cl were determined by microprobe analysis in bovine extracellular matrices of cartilage, tendon and elastic tissue (ligamentum nuchae) and in muscle cells. The values for the different tissues were compared and related to the blood electrolyte concentrations. Among the connective tissues the highest Na and lowest Cl values were found for cartilage which bears a high negative charge. The lowest concentrations of these elements occurred in elastic tissue which is relatively non-polar. In the three extracellular matrices sodium levels exceeded potassium. In myofibers potassium was the major cation at 30 times the blood value and about 3 times the concentration of sodium. Chlorine values were around 0.4 that of blood. Sulfur and phosphorus are components of the tissue macromolecules. The negative charge on the extracellular matrices is a function of carboxyl and sulfate radicals. In the myofiber this property is largely attributable to carboxyl and phosphate groups. Differences in potassium-sodium distribution in cells and extracellular matrices are attributed partly to the microtrabecular lattice and to the ordered state of cell water. In general the element concentrations and selective distribution can be related to the chemical composition and organization of the tissue, the net immobile charge, the nature of the dispersion medium (water) and changes in its dielectric constant, and to the physico-chemical properties of the individual ions

Letter to the Editor by M.B. Engel and H.R. Catchpole Relating to: Can We See Living Structures in the Cell [by G.N. Ling, Scanning Microscopy Vol. 6, p. 405-450 (1992)] and Reply by G.N. Ling

Dear Editor, As workers in the field of ionic equilibrium in extracellular matrices and cells, and as contributors to this Journal of papers supporting an alternative explanation to that represented by the dominant schools of active transport (ionic pumps), we are surprised by the statement of Ling (1992, p. 449) which appears to limit published criticism of those schools to himself and A.S. Troshin. By an odd coincidence, our abstract (Catchpole et al., 1951) on the distribution of potassium and sodium through selective action of the cations with ground substance and water appeared simultaneously with that of Ling (1951): Tentative hypothesis for selective ionic accumulation in muscle cells . We have also published papers and monographs since that distant time. So much, at least, for longevity

Feline hypersomatotropism and acromegaly tumorigenesis: a potential role for the AIP gene

Acromegaly in humans is usually sporadic, however up to 20% of familial isolated pituitary adenomas are caused by germline sequence variants of the aryl-hydrocarbon-receptor interacting protein (AIP) gene. Feline acromegaly has similarities to human acromegalic families with AIP mutations. The aim of this study was to sequence the feline AIP gene, identify sequence variants and compare the AIP gene sequence between feline acromegalic and control cats, and in acromegalic siblings. The feline AIP gene was amplified through PCR using whole blood genomic DNA from 10 acromegalic and 10 control cats, and 3 sibling pairs affected by acromegaly. PCR products were sequenced and compared with the published predicted feline AIP gene. A single nonsynonymous SNP was identified in exon 1 (AIP:c.9T > G) of two acromegalic cats and none of the control cats, as well as both members of one sibling pair. The region of this SNP is considered essential for the interaction of the AIP protein with its receptor. This sequence variant has not previously been reported in humans. Two additional synonymous sequence variants were identified (AIP:c.481C > T and AIP:c.826C > T). This is the first molecular study to investigate a potential genetic cause of feline acromegaly and identified a nonsynonymous AIP single nucleotide polymorphism in 20% of the acromegalic cat population evaluated, as well as in one of the sibling pairs evaluated

Surface plasmon enhanced silicon solar cells

Thin-film solar cells have the potential to significantly decrease the cost of photovoltaics. Light trapping is particularly critical in such thin-film crystalline silicon solar cells in order to increase light absorption and hence cell efficiency. In this article we investigate the suitability of localized surface plasmons on silvernanoparticles for enhancing the absorbance of silicon solar cells. We find that surface plasmons can increase the spectral response of thin-film cells over almost the entire solar spectrum. At wavelengths close to the band gap of Si we observe a significant enhancement of the absorption for both thin-film and wafer-based structures. We report a sevenfold enhancement for wafer-based cells at λ=1200 nm and up to 16-fold enhancement at λ=1050 nm for 1.25 μm thin silicon-on-insulator (SOI) cells, and compare the results with a theoretical dipole-waveguide model. We also report a close to 12-fold enhancement in the electroluminescence from ultrathin SOI light-emitting diodes and investigate the effect of varying the particle size on that enhancement.S. Pillai would like to acknowledge the UNSW Faculty of Engineering Research Scholarship. K.R. Catchpole acknowledges the support of an Australian Research Council fellowship

Extension\u27s Role in Preparing Youth for the Workforce: A Challenge to Extension Professionals

During the first decade of the 21st century, much as been written about the knowledge economy, implications for work, and concerns about a widening gap between the skills employers need and the capabilities of employees. An intentional focus on workforce preparation will improve the impact of 4-H programming by more clearly demonstrating a return on investment to stakeholders, better preparing future leaders for the workforce and life, and helping fill a gap for employers. A call to action and five questions (e.g., Why 21st century skills? ) are presented with initial thought from the authors

The Detectability of Pair-Production Supernovae at z < 6

Nonrotating, zero metallicity stars with initial masses 140 < M < 260 solar masses are expected to end their lives as pair-production supernovae (PPSNe), in which an electron-positron pair-production instability triggers explosive nuclear burning. Interest in such stars has been rekindled by recent theoretical studies that suggest primordial molecular clouds preferentially form stars with these masses. Since metal enrichment is a local process, the resulting PPSNe could occur over a broad range of redshifts, in pockets of metal-free gas. Using the implicit hydrodynamics code KEPLER, we have calculated a set of PPSN light curves that addresses the theoretical uncertainties and allows us to assess observational strategies for finding these objects at intermediate redshifts. The peak luminosities of typical PPSNe are only slightly greater than those of Type Ia, but they remain bright much longer (~ 1 year) and have hydrogen lines. Ongoing supernova searches may soon be able to limit the contribution of these very massive stars to < 1% of the total star formation rate density out to z=2 which already provides useful constraints for theoretical models. The planned Joint Dark Energy Mission satellite will be able to extend these limits out to z=6.Comment: 12 pages, 6 figures, ApJ in press; slightly revised version, a few typos correcte

The effect of dielectric spacer thickness on surface plasmon enhanced solar cells for front and rear side depositions

The excitation of surface plasmons on metallic nanoparticles has the potential to significantly improve the performance of solar cells, in particular thin-film structures. In this article, we investigate the effect of the dielectric spacer layer thickness on the photocurrent enhancement of 2 μm thick, thin-film poly-Si on glass solar cells, due to random arrays of self-assembled Ag nanoparticlesdeposited on the front or the rear of the cells. We report a strong asymmetry in the external quantum efficiency (EQE) of the cell for front and rear located particles for different spacer thicknesses, which is attributed to differences in the scattering behavior of the nanoparticles. We find that for random arrays, with spectrally broad scattering resonances, the strength of the driving field and the coupling efficiency are more important for light trapping than the resonance wavelength. For particles located on the front of the cells it is desirable to have a thin dielectric spacer layer to enhance the scattering from the Ag nanoparticles. Additionally, light trapping provided by the random sized particles on the front can overcome suppression of light transmitted in the visible wavelength regions for thin layers of Si, to result in overall EQE enhancements. However, for particles deposited on the rear it is more beneficial to have the particles as close to the Si substrate as possible to increase both the scattering and the coupling efficiency.K.R.C. acknowledges the support of an Australian Research Council fellowship and the EU FP7 PRIMA project

Constraining the Nature of the Galactic Center X-ray Source Population

We searched for infrared counterparts to the cluster of X-ray point sources discovered by Chandra in the Galactic Center Region (GCR). While the sources could be white dwarfs, neutron stars, or black holes accreting from stellar companions, their X-ray properties are consistent with magnetic Cataclysmic Variables, or High Mass X-ray Binaries (HMXB) at low accretion-rates. A direct way to decide between these possibilities and hence between alternative formation scenarios is to measure or constrain the luminosity distribution of the companions. Using infrared (J, H, K, Br-gamma) imaging, we searched for counterparts corresponding to typical HMXB secondaries: spectral type B0V with K<15 at the GCR. We found no significant excess of bright stars in Chandra error circles, indicating that HMXBs are not the dominant X-ray source population, and account for fewer than 10% of the hardest X-ray sources.Comment: 4 pages, 3 figures, 1 table, accepted in ApJ Letters for publicatio