Maximum variance unimodal distributions

A new sufficient condition for the variance of a unimodal distribution in ?a, b? to have the least upper bound $\text{(b ? a)}{}^2\text{12}$ is derived. This condition is more general than the condition found by Jacobson (1969). A new proof that the least upper bound for all unimodal distributions in ?a, b? is $\text{(b ? a)}{}^2\text{9}$ is also given. These results are used to construct a new estimator of the variance of such distributions.     

Determination of non-volatile N-nitrosamines in baby bottle rubber nipples and pacifiers by high-performance liquid chromatography-thermal energy analysis

A method is described for the determination of non-volatile N-nitrosamines in baby bottle rubber nipples and pacifiers. It consists of extraction of the sample with dichloromethane in the presence of ascorbyl palmitate (an inhibitor of artifactual formation of nitrosamines), clean-up on silica or basic alumina, and final analysis by high-performance liquid chromatography-thermal energy analysis, a technique which is highly specific for N-nitroso compounds. The method worked well for the determination of four rubber-related non-volatile nitrosamines, namely, N-nitrosomethylphenylamine, N-nitrosoethylphenylamine, N-nitrosodicyclohexylamine, and N-nitrosodibenzylamine (recoveries from spiked samples greater than 80%; detection limit, ca. 5 micrograms/kg for each). Eighteen out of twenty four samples analyzed were found to contain varying levels (mean, 41 micrograms/kg; range, 8-146 micrograms/kg) of N-nitrosodibenzylamine. The identity of the compound was confirmed by gas chromatography-thermal energy analysis as well as by gas chromatography-mass spectrometry analyses.     

Independence Distribution Preserving Covariance Structures for the Multivariate Linear Model

Consider the multivariate linear model for the random matrixY_n×pMN(XB, VΣ), whereBis the parameter matrix,Xis a model matrix, not necessarily of full rank, andVΣ is annp×nppositive-definite dispersion matrix. This paper presents sufficient conditions on the positive-definite matrixVsuch that the statistics for testingH₀: CB=0vsH_a: CB≠0have the same distribution as under the i.i.d. covariance structureIΣ.     

Furan precursors in food: a model study and development of a simple headspace method for determination of furan

Furan was previously detected in foods that had undergone thermal treatment. Because furan is now classified as a possible human carcinogen, a model system was developed to investigate the origins of furan. Also, a simple, rapid isotope dilution (d4-furan) headspace method was developed to measure furan. Two pathways of furan formation have been identified in the model systems tested so far. The first is the oxidation of polyunsaturated fatty acids at elevated temperatures, and the second is linked to the decomposition of ascorbic acid derivatives. The analytical procedure, based on the use of a 50 microL injection (from the headspace of a 1.5 mL vial containing 0.5 mL water) into the split/splitless injection port of a gas chromatograph/mass spectrometer (electron ionization, selected-ion monitoring), showed linearity in the 10-1000 ng/g range with a limit of detection of 1 ng/g.     

Accounting for diffuse layer ions in triple-layer models

The triple-layer model is one of the most widely used surface complexation models for adsorption on mineral surfaces. In current implementations, the accounting of ions in the diffuse layer may be neglected, resulting in a charge imbalance in the modeled solution as well as errors in mass balance, particularly in low ionic strength solutions when mineral-specific surface area is large. This paper introduces an internally consistent scheme for modeling diffuse layer ions in the triple-layer model. Model calculations illustrate the difference between the proposed and previous implementations using an idealized example. The guarantee of charge balance on both sides of the interface assures that pH is accurately modeled. This may be important in reactive transport simulations, such as modeling adsorption in low ionic strength variable charge soil solutions.     

Correlations betweenT c andn s/m * (carrier density/ effective mass) in high-T c and organic superconductors

We update our muon spin relaxation studies of the magnetic field penetration depth which show the correlations betweenT _c and the relaxation rate σ αn _s/m ^* (carrier density/effective mass) of hole-doped high-T _c cuprate superconductors (La₂, Sr₃)CuO₄, YBa₂Cu₃O₇ (Y_1−xPr_x)Ba₂Cu₃O₇, and other double and triple layer systems. These studies are extended to the organic superconductor (BEDT-TTF)₂Cu(NCS)₂.