Analysis of the drude model in metallic films

A method, believed to be new, to simulate Drude parameters for collective oscillation of the free carriers in metallic films is proposed. Plasma resonance frequency and relaxation were simulated simultaneously from both the real and the imaginary parts of the dielectric function of a metallic film after consideration of their correlation in the Drude model. As examples, the contributions of the electrons in Ag films and of the free carriers in metallic silicide, NbSi(2) and TaSi(2), films have been studied.     

Motorcyclist fatalities and the repeal of mandatory helmet wearing laws

Previous studies had estimated that repeal of mandatory helmet wearing laws resulted in increases in the number of fatalities ranging from nearly 40% to essentially zero. This study was performed to determine more definitively the influence on motorcyclist fatalities of these repeals. After repeal, motorcyclist fatalities increased more in the states which repealed their laws than in those which did not in 24 cases out of 26, with the 95% confidence interval for the average effect being 25 +/- 6%. It is therefore concluded that repeals of mandatory helmet wearing laws for motorcyclists were followed by substantial increases in motorcyclist fatalities.     

Influence of the copper ion on aging rate of oil-paper insulation in a power transformer

To identify the influence of copper ion on the aging rate of oil-paper insulation, accelerated thermal aging experiments on oil-paper insulation were designed and performed at two significant temperatures. A set of characteristic parameters, including dissolved gases, degree of polymerisation, furfural content, water content and acid number of oil, was tested. The experiments- results reveal that copper ion has a different influence on insulation paper and oil during the aging process of the insulation system. On the one hand, it delays the degradation of insulation paper, reducing the ratio of CO₂/CO by about 11% at 80%C and by more than 50% at 130%C. On the other hand, copper ion promotes the oxidation of oil and thus accelerates the aging rate.     

Advanced Code-Division Multiplexers for Superconducting Detector Arrays

Multiplexers based on the modulation of superconducting quantum interference devices are now regularly used in multi-kilopixel arrays of superconducting detectors for astrophysics, cosmology, and materials analysis. Over the next decade, much larger arrays will be needed. These larger arrays require new modulation techniques and compact multiplexer elements that fit within each pixel. We present a new in-focal-plane code-division multiplexer that provides multiplexing elements with the required scalability. This code-division multiplexer uses compact lithographic modulation elements that simultaneously multiplex both signal outputs and superconducting transition-edge sensor (TES) detector bias voltages. It eliminates the shunt resistor used to voltage bias TES detectors, greatly reduces power dissipation, allows different dc bias voltages for each TES, and makes all elements sufficiently compact to fit inside the detector pixel area. These in-focal plane code-division multiplexers can be combined with multi-GHz readout based on superconducting microresonators to scale to even larger arrays.     

Structural, chemical, and optical properties of tin sulfide thin films as controlled by the growth temperature during co-evaporation and subsequent annealing

Tin sulfide thin films on soda-lime glass substrate were prepared by co-evaporation. This technique uses a vapor phase procedure involving chemical reactions between the precursor species evaporated simultaneously. The influence of the substrate temperature in the crystal structure and chemical composition were determined by X-ray diffraction and energy dispersive analysis of X-rays, showing that thin films crystallized in SnS, SnS₂, and Sn₂S₃ phases. Scanning electron microscope shows thin films with homogenous and uniform surface. Some of the samples were annealed to study the variation of structural, chemical, and optical properties. The variation of refractive index (n), extinction coefficient (k), and dielectric constant (ε) with wavelength and photon energy are reported. The energy band gap was calculated from optical transmittance and reflectance measurements in the range 300–1500 nm. The calculated energy band gap values were between 1.75 and 2.3 eV, depending on the phase in which crystallized the different thin films.     

Evidence for plastic deformation in the natural polycrystalline diamond,framesite

Relief-polished striations have been found within grains in polished sections of framesite, a naturally occurring polycrystalline diamond. Because the narrow zones represented by these surface striations are harder than any orientation of the matrix (as revealed by abrasion resistance) and because they etch preferentially, they have been interpreted as representing oriented deformation bands within the grains. It is concluded that the microstructure of framesite is the result of plastic deformation of diamond grains probably under conditions such that brittle fracture was inhibited.     

Effect of selective laser melting on microstructure and properties of AZ91D alloy

Selective laser melting technology is used to manufacture porous and solid AZ91D alloys. The effects of laser power and hatch spacing on the density, blowholes, microstructure and mechanical properties of AZ91D alloy are studied. The laser power and hatch spacing play a significant role in the density and blowholes of AZ91D specimens. The grains size of specimens increases from 1 μm–2 μm to 8 μm–10 μm from the bottom to the top in single molten pool. Compared with grain size of die‐casting alloy (30 μm), that of selective laser melted gets refinement. There is no significant change in microstructure in the bottom, middle and top of specimens. The micro‐hardness of AZ91D alloy, reaching up to 115.3 HV 0.1, is superior to that of die‐casting alloy (56 HV 0.1). The compression properties of porous and solid specimens reach the degree of die‐casting solid magnesium alloy. AZ91D alloy shows the potential in the application of medical biodegradable materials.     

Numerical approach to hopping conduction

A numerical method for calculation of the polarization conductivity has been developed. This approach has been applied to the correlated barrier hopping (CBH) and quantum mechanical tunnelling (QMT) models in the case of monoelectronic hops. These calculations have been performed on well-known solids such as carbon (HTT 600° C) and badly organized molybdenum and tungsten sulphides. The agreement between theory and experimental results is more satisfying than in a previous approach. The parametersW _M andN ₀ are determined for the CBH model, andN(E _F) for the QMT model.     

Order vs. Disorder: Cholesterol and Omega-3 Phospholipids Determine Biomembrane Organization

Lipid structural diversity strongly affects biomembrane chemico-physical and structural properties in addition to membrane-associated events. At high concentrations, cholesterol increases membrane order and rigidity, while polyunsaturated lipids are reported to increase disorder and flexibility. How these different tendencies balance in composite bilayers is still controversial. In this study, electron paramagnetic resonance spectroscopy, small angle neutron scattering, and neutron reflectivity were used to investigate the structural properties of cholesterol-containing lipid bilayers in the fluid state with increasing amounts of polyunsaturated omega-3 lipids. Either the hybrid 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine or the symmetric 1,2-docosahexaenoyl-sn-glycero-3-phosphocholine were added to the mixture of the naturally abundant 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine and cholesterol. Our results indicate that the hybrid and the symmetric omega-3 phospholipids affect the microscopic organization of lipid bilayers differently. Cholesterol does not segregate from polyunsaturated phospholipids and, through interactions with them, is able to suppress the formation of non-lamellar structures induced by the symmetric polyunsaturated lipid. However, this order/disorder balance leads to a bilayer whose structural organization cannot be ascribed to either a liquid ordered or to a canonical liquid disordered phase, in that it displays a very loose packing of the intermediate segments of lipid chains.