Contactless determination of the efficiency of interfacial charge separation in a TiO2/phenylene vinylene polymer junction

We have used the flash-photolysis time-resolved microwave conductivity technique (TRMC) to monitor charge separation between a smooth film of anatase TiO₂ (ca 80 nm) and spin-coated layers of a dialkoxyphenylene-vinylene polymer (20–140 nm thick) on nanosecond flash-photolysis in the polymer absorption band at 544 nm. The quantum efficiency of electron injection into the TiO₂ from photons absorbed in the polymer layer can be calculated by comparing the conductivity resulting from 544 nm irradiation with that from direct band gap excitation of the anatase layer at 308 nm. The maximum efficiency per incident photon, is ca 6% for thicknesses in the range of 30–50 nm of the polymer layer. Charge separation persists well into the microsecond region.     

The prenatal diagnosis of spinal muscular atrophy

Trimethyltin (TMT) causes prominent neuronal damage and enhanced expression of neuropeptide Y in the hippocampus. We investigated expression of neuropeptide Y Y2 receptors after TMT intoxication. Markedly elevated (by 470%) concentrations of Y2 receptor mRNA were found in the suprapyramidal blade of the dentate granule cell layer after 5 days. Increases in the infrapyramidal blade were less prominent (by 198%). After 16 days, mRNA levels in both blades of the granule cell layer showed no significant difference from those in controls. Quantification of Y2 receptor-specific binding revealed no significant change at both 5 and 16 days after TMT intoxication. It is suggested, together with a previous report describing a similar increase of neuropeptide Y expression, that a transient expression of Y2 receptors in the dentate gyrus in the initial phase of TMT intoxication may be involved in mediating TMT-induced hippocampal damage.     

Frequency domain sample maximum likelihood estimation for spatially dependent parameter estimation in PDEs

The identification of the spatially dependent parameters in Partial Differential Equations (PDEs) is important in both physics and control problems. A methodology is presented to identify spatially dependent parameters from spatio-temporal measurements. Local non-rational transfer functions are derived based on three local measurements allowing for a local estimate of the parameters. A sample Maximum Likelihood Estimator (SMLE) in the frequency domain is used, because it takes noise properties into account and allows for high accuracy consistent parameter estimation. Confidence bounds on the parameters are estimated based on the noise properties of the measurements. This method is successfully applied to the simulations of a finite difference model of a parabolic PDE with piecewise constant parameters.     

Melting Apparatus for the Synthesis of Bulk ZrF4-Based Fluoride Glass

Heavy-metal fluoride glasses are currently prepared by melting of the solid fluoride precursors. We have constructed a melting facility for the synthesis of ZrF₄-based fluoride glass cullet. This stand-alone system provides a controlled (dry and reactive) atmosphere and in situ quenching of the melts. The glass is melted in a vitreous carbon crucible, which is mounted in a silica tube flow reactor. The reactor is resistively heated with a tube furnace and purged with He and SF₆ or Cl₂. It was found that of the latter two halogenating species only Cl₂ prevents effectively the formation of black inclusions in the melt (ZrF₃ and ZrF₂ particles). With this melting apparatus we have routinely melted 250-g batches of optically clear ZrF₄–BaF₂–LaF₃–AlF₃–NaF glass samples.     

Efficient infill sampling for unconstrained robust optimization problems

A novel infill sampling criterion is proposed for efficient estimation of the global robust optimum of expensive computer simulation based problems. The algorithm is especially geared towards addressing problems that are affected by uncertainties in design variables and problem parameters. The method is based on constructing metamodels using Kriging and adaptively sampling the response surface via a principle of expected improvement adapted for robust optimization. Several numerical examples and an engineering case study are used to demonstrate the ability of the algorithm to estimate the global robust optimum using a limited number of expensive function evaluations.     

Diagnostics for regression dependence in tables re-ordered by the dominant correspondence analysis solution

Correspondence analysis is an exploratory technique for analyzing the interaction in a contingency table. Tables with meaningful orders of the rows and columns may be analyzed using a model-based correspondence analysis that incorporates order constraints. However, if there exists a permutation of the rows and columns of the contingency table so that the rows are regression dependent on the columns and, vice versa, the columns are regression dependent on the rows, then both implied orders are reflected in the first dimension of the unconstrained correspondence analysis [Schriever, B.F., 1983. Scaling of order dependent categorical variables with correspondence analysis. International Statistical Review 51, 225-238]. Thus, using unconstrained correspondence analysis, we may still find that the data fit an ordinal stochastic model. Fit measures are formulated that may be used to verify whether the re-ordered contingency table is regression dependent in either the rows or columns. Using several data examples, it is shown that the fit indices may complement the usual geometric interpretation of the unconstrained correspondence analysis solution in low-dimensional space.