Photodegradation of poly(vinyl esters)—I. Formation and quantitative measurement of volatile products

The high vacuum distillation technique for the analysis of photolysis products has highlighted both the extreme difficulty of removing residual solvent and the slow diffusion of photodegradation products from thin cast poly(vinyl ester) films, even at temperatures 130°C above T_g. Very long product collection periods at temperatures just below the onset of thermal degradation were used in order to obtain reliable quantitative data. The distributions of liquid-nitrogen condensable products indicated that a closer relationship exists between the photodegradation of poly(vinyl esters) and the photolysis of low molecular mass esters than previous results had suggested.     

A solvolysis model for 2-chloro-2-methyladamantane based on the linear solvation energy approach

Solvolysis/dehydrohalogenation rates of 2-chloro-2-methyladamantane (CMA) in 15 hydrogen-bond acidic and/or basic solvents are studied. The rates of reaction in these solvents have been correlated with the solvation equation developed by Kamlet, Abraham, and Taft. The linear solvation energy relationship (LSER) derived from this study is given by the following equation: log k = -5.409 + 2.219 + 2.505alpha(1) - 1.823beta(1) where , alpha(1), and beta(1) are the solvation parameters that measure the solvent dipolarity/polarizability, hydrogen-bond acidity (electrophilicity), and hydrogen-bond basicity (nucleophilicity). A high correlation coefficient (r = 0.996, SD = 0.191) was achieved. The cavity term, which includes the Hildebrand parameter for solvent cohesive energy density, delta(H), was not found to be statistically significant for this reaction substrate. The resulting equation allows calculated rates of reaction in other solvents and provides insight into the reaction pathway. In a previously reported correlation for another tertiary chloride, tert-butyl chloride (TBC), the coefficients for alpha(1) and are significantly larger and the coefficient for is statistically significant. In addition, the coefficient for beta(1) in the TBC correlation is positive, rather than negative, indicating that the transition states for TBC and CMA are significantly different. These results demonstrate why the uses of simple solvolytic correlation methods may be invalid even for comparisons of similar type substrates, e.g., tertiary chlorides. Also, these results provide confidence in the use of multiple linear regression analysis for predicting solvolytic rates in additional solvents.     

The production of artifacts during preparation of fatty acid methyl esters from fish oils,food products and pathological samples

Methyl esters were synthesized from lipid extracted by a modified Bligh and Dyer technique. The lipid was saponified and the free fatty acids methylated using boron trifluoride in methanol. Butylated hydroxytoluene (BHT; 2,6-di-tert-butyl-4-methylphenol) was added to the initial sample and to the extracted lipid prior to methyl ester synthesis. Under these conditions, the BHT was derivatized to a range of compounds, some of which can result in misinterpretation of the GC trace. Three components have been characterized by mass spectroscopy. Two of these, which eluted slightly before 16:0 on a polar column, were shown to be 2,6-di-tert-butyl-4-methoxyphenol and 2,6-di-tert-butyl-4-methoxy-methylphenol. The third component, which coeluted with 15:0 on the same column, is 2,6-di-tert-butyl-4-methoxy-5-hydroxyphenol.     

A novel laser transfer process for direct writing of electronic and sensor materials

MAPLE direct write (MAPLE DW) is a new laser-based direct-write technique which combines the basic approach employed in laser-induced forward transfer (LIFT) with the unique advantages of matrix-assisted pulsed-laser evaporation (MAPLE). MAPLE DW utilizes an optically transparent substrate coated on one side with a matrix consisting of the material to be transferred mixed with a polymer or organic binder. As in LIFT, the laser is focused through the transparent substrate onto the matrix. When a laser pulse strikes the matrix, the binder decomposes and aids the transfer of the material of interest to an acceptor substrate placed parallel to the matrix surface. MAPLE DW is a maskless deposition process which operates in air and at room temperature. Powders of Ag, BaTiO₃, SrTiO₃, and Y₃Fe₅O₁₂ with average diameters of 1 7m were transferred onto the surfaces of alumina, glass, silicon, and printed circuit board substrates. Parallel-plate and interdigitated capacitors and flat inductors were produced by MAPLE DW over Rogers RO4003 substrates. MAPLE DW was also used to transfer polymer composites for the fabrication of gas sensor chemoresistors. One such composite chemoresistor fabricated with polyepichlorohydrin/graphite was used to detect organic vapors with a sensitivity of parts per million.     

Censored regression analysis of multiclass passenger demand data subject to joint capacity constraints

In most passenger transportation systems, demand for seats is not recorded after all spaces for a particular trip have been sold out or after a booking limit has been reached. Thus historical booking data is comprised of ticketsales notdemand — a condition known as censorship of the data. Data censorship is particularly complex when there are multiple classes of demand since the demand in one class can influence the degree of censorship in another. This paper examines the problem of simultaneously estimating passenger demand models for two or more correlated classes of demand that are subject to a common capacity constraint. It is shown that theEM method of Dempster et al. [5] can be adapted to provide maximum likelihood estimates of the parameters of the demand model under these circumstances. The problem of modelling demand for airline flights is discussed as a typical example of this estimation problem. Numerical examples show that, with reasonable sample sizes, it is possible to obtain good estimates even when 75% or more of the data have been censored.     

Theory of donor states in GaP: The role of the camel's back

We present a theoretical study of the influence of the camel's back structure on the low lying excited states of the donors in GaP. Based on comparison with the observed spectrum, we conclude that the appropriate values for the parameters describing the camel's back are $\text{Δ}\text{E}\text{= 3.2}\text{meV and k}{}_{\mathrm{o}}\text{= 0.083 (}\text{a}{}_{\mathrm{o}}\text{2π}\text{)}$.     

Absorption and luminescence of the bound exciton in thallium doped silicon

We report the photoluminescence and absorption spectra of the bound exciton in Si:Tl. Four lines are observed in both spectra in contrast to three lines observed in the Al, Ga, In doped Si. The total oscillator strength is approximately 4x10^-4 continuing a trend of increasing oscillator strength with binding energy.     

Ground state energies of bound exciton for all mass ratios

We report on a calculation of the ground state energy of bound excitons using states from a model Hamiltonian and correcting the variational results by treating the difference between the model and actual Hamiltonian in second order perturbation theory. The resulting procedure is valid for all mass ratios.