Fichtner On Density-Gradient Modeling of Tunneling Through Insulators

Abstract — The density gradient model (DG) is tested for its ability to describe tunneling currents through thin insulating barriers. Simulations of single barriers (MOS diodes, MOS-FETs) and double barriers show the limitations of the DG model. As a reference the Schrödinger-Bardeen method is taken. ‘Resonant tunneling ’ in the density gradient model turns out to be an artifact related to large density differences in the semiconductor regions. I

Thermal-expansion-derived lattice instability in La₂CuO₄

We present results for the thermal expansion, α(T), of both polycrystalline and single crystalline La2CuO4. Our results demonstrate the existence of an anomaly in α(T) aroundT=35 K which is clearly intrinsic and most likely due to a lattice instability

Variability in Quartz Exposure in the Construction Industry: Implications for Assessing Exposure-Response Relations

The aims of this study were to determine implications of inter- and intraindividual variation in exposure to respirable (quartz) dust and of heterogeneity in dust characteristics for epidemiologic research in construction workers. Full-shift personal measurements (n = 67) from 34 construction workers were collected. The between-worker and day-to-day variances of quartz and respirable dust exposure were estimated using mixed models. Heterogeneity in dust characteristics was evaluated by electron microscopic analysis and electron spin resonance. A grouping strategy based on job title resulted in a 2- and 3.5-fold reduction in expected attenuation of a hypothetical exposure-response relation for respirable dust and quartz exposure, respectively, compared to an individual based approach. Material worked on explained most of the between-worker variance in respirable dust and quartz exposure. However, for risk assessment in epidemiology, grouping workers based on the materials they work on is not practical. Microscopic characterization of dust samples showed large quantities of aluminum silicates and large quantities of smaller particles, resulting in a D50 between 1 and 2 μ m. For risk analysis, job title can be used to create exposure groups, although error is introduced by the heterogeneity of dust produced by different construction workers activities and by the nonuniformity of exposure groups. A grouping scheme based on materials worked on would be superior, for both exposure and risk assessment, but is not practical when assessing past exposure. In dust from construction sites, factors are present that are capable of influencing the toxicological potency

Variability in Quartz Exposure in the Construction Industry: Implications for Assessing Exposure-Response Relations

The aims of this study were to determine implications of inter- and intraindividual variation in exposure to respirable (quartz) dust and of heterogeneity in dust characteristics for epidemiologic research in construction workers. Full-shift personal measurements (n = 67) from 34 construction workers were collected. The between-worker and day-to-day variances of quartz and respirable dust exposure were estimated using mixed models. Heterogeneity in dust characteristics was evaluated by electron microscopic analysis and electron spin resonance. A grouping strategy based on job title resulted in a 2- and 3.5-fold reduction in expected attenuation of a hypothetical exposure-response relation for respirable dust and quartz exposure, respectively, compared to an individual based approach. Material worked on explained most of the between-worker variance in respirable dust and quartz exposure. However, for risk assessment in epidemiology, grouping workers based on the materials they work on is not practical. Microscopic characterization of dust samples showed large quantities of aluminum silicates and large quantities of smaller particles, resulting in a D50 between 1 and 2 μ m. For risk analysis, job title can be used to create exposure groups, although error is introduced by the heterogeneity of dust produced by different construction workers activities and by the nonuniformity of exposure groups. A grouping scheme based on materials worked on would be superior, for both exposure and risk assessment, but is not practical when assessing past exposure. In dust from construction sites, factors are present that are capable of influencing the toxicological potency

Polymer Thin Films on Patterned Si Surfaces

The propagation of roughness from a patterned silicon surface by polymer thin films was measured as a function of film thickness, time, and surface interaction using atomic force microscopy and synchrotron X-ray reflection. In the presence of an interacting surface, the decay length of the surface modulation was much longer than that observed in simple liquids. By measuring the time dependence of the surface corrugation amplitude, we were able to extract a surface diffusion coefficient by applying a modified version of the Mullins theory for surface diffusion in crystalline solids. The measured diffusion coefficients were an order of magnitude smaller than in the bulk, and scaled as 1/M3/2, in agreement with previous SIMS results. The results are interpreted in terms of surface interactions confining polymer chains over distances larger than the radii of gyration