Performance characteristics of a composite multivariate quality control system.

We present the results of an evaluation of the performance characteristics of a composite multivariate quality control (CMQC) system that incorporates quality control rules for univariate, multivariate, and correlation conditions. The CMQC system evaluated is designed to help analysts detect unacceptable trends and systematic error in one or more variables, unacceptable random error in one or more variables, and unacceptable changes in the correlation structure of any pair of variables. It is also designed to be tolerant of missing data, to allow analysts to reject as few as one or as many as all variables in a run, and to provide analysts with control statistics and graphics that logically relate to sources of analytical error. We show that the various components of the CMQC system have adequate statistical power to detect systematic errors, random errors, and correlation changes under the conditions likely to be encountered with multivariate analytical measurement systems: (1) a single variable with increased systematic or random error; (2) all variables or a subgroup of variables affected by a common problem that increases systematic or random error; and (3) missing data for one or more variables in a run. We also show that the power of the multivariate component of the CMQC system to detect systematic and random errors is higher than the power of an alternative multivariate test criterion.     

Efficacy of surgical treatment in traumatic central cord syndrome

BACKGROUND: Controversy surrounds the treatment of traumatic central cord syndrome (TCCS), as there are strong advocates for nonsurgical treatment for most patients. However, conservative treatment has been shown to yield a longer period of discomfort from pain and weakness in certain cases. METHODS: In a retrospective review of 114 patients presenting with acute or chronic TCCS from 1988-94, four different age groups were separately observed under different treatments. Motor and sensory recovery were assessed. RESULTS: Better results were achieved in younger patients, with or without radiographic abnormalities, and in patients with clinically correlated encroaching cord lesions who received early surgical decompression. CONCLUSIONS: Surgical intervention for TCCS must be addressed with careful clinical and radiographic survey. Removal of offending lesions in the subacute period results in significant motor and sensory improvement in short-term and long-term follow-up.     

Accelerated aging of extruded dielectric power cables. I. Controland monitoring methodology

An improved accelerated cable life test is described. Through the use of programmable logic controllers (PLCs), very precise and consistent control of the accelerated aging process has been achieved. A computer has been utilized to make continuous real-time acquisition and storage of key operating parameters possible. This precise control and monitoring methodology has permitted the study of the synergistic effects of voltage and temperature on the accelerated aging of full-sized cables in the laboratory     

Memory complaints in epilepsy: correlations with cognitive performance and neuroticism

Experimental results are presented to show that the adhesion force is the single most important limiting factor in high-resolution atomic force microscopy of DNA in air, prepared by the cytochrome-C-assisted spreading method. It is also shown that humidity plays a minor role in the control of probe force. Using a pure carbon film as the substrate to clean the AFM tip prior to imaging, it is demonstrated that 4-6 nm resolution on DNA can be routinely obtained by the atomic force microscope with commercial Si3N4 pyramid cantilevers. We also show that in organic solvents a resolution of up to 3 nm can be obtained under optimal conditions.     

A STUDY OF SUPERIMPOSED FRACTURE MODES I, II AND III ON PMMA

A test apparatus has been developed to study the fracture behaviour of engineering materials subjected to superimposed tensile and shear (Mode I and II) loads using a single edge notch specimen. Stress intensity factors were calculated using finite element analysis. Test results for PMMA are reported. Results from circumferentially notched round bar specimens, subjected to combined tension and torsion (Mode I and III) loading are also reported. The Mode I/II results are consistent with the mixed mode fracture response of a wide range of brittle materials, although there is some evidence of non-linear behaviour. The fracture behaviour for superimposed Modes I and III indicates the strong influence of non-linear deformation which causes the mixed mode toughness to be dependent on the sequence and type of loading.     

Synthesis and properties of 2,2,6,6-tetramethyl-1-(1-phenethyloxy)piperidine,an initiator for living free radical styrene polymerization

Summary An initiator for living free radical polymerization may be prepared by trapping the benzylic ethylbenzene radical with the stable 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical. The adduct, 2,2,6,6-tetramethyl-1-(1-phenethyloxy)piperidine (TMPEP), smoothly undergoes thermal fragmentation at temperatures approaching 140° C to afford an active carbon radical capable of initiating polymerization and a passive mediating nitroxyl radical to reversibly cap and preserve the propagating polymer chain.     

Cyromazine toxicity in different laboratory strains of the tobacco hornworm (Lepidoptera:Sphingidae)

Three different strains of tobacco hornworm, Manduca sexta (L.), were treated with cyromazine ingestion of cyromazine-treated artificial diet or by intrahemocoelic injection. The effect of cyromazine on larval growth and the onset and severity of poisoning symptoms were similar in the wild-type green-pigmented strain and the white-pigmented mutant. Feeding times of 4 h or greater and injected doses of 22.6 micrograms/g larva or more resulted in lower weight gains than were observed with controls. Elongation caused by exposure was evident within 12-24 h. The incidence of cuticular rupture was 55 and 67% in the dietary exposure tests and 24 and 22% in the injection tests for the green and white strains, respectively. The response of the black strain to cyromazine differed by the route of administration. Like the other strains, dietary exposure times of 4 h or greater led to smaller weight gains than in the controls. Injected doses of 2.8 micrograms/g larva or more caused a decrease in the weight gain of the treated versus controls. A smaller proportion (21%) of black larvae consuming treated diet developed cuticular ruptures, whereas injected treatments had a higher incidence (87%). The differences in the pigmentation of the white and black strains had been linked to high and low juvenile hormone titers, respectively. The greater susceptibility of the juvenile hormone-deficient black strain raises the possibility that the mode of action of cyromazine involves a hormonal component. In a separate series of experiments, the poisoning symptoms of cyromazine were attenuated or eliminated by periods of starvation of 1-3 d following exposure to the chemical. Starvation for 3 d preceding treatment attenuated but did not eliminate signs of poisoning.     

Determination of intraparticulate mass transfer coefficients via permeation measurements: theory and experimental validation

A mathematical model of mass transfer through a heterogeneous, multiphase barrier has been developed where the dispersed phase is capable of uptake of the diffusant according to a linear relationship. The model was used to describe the penetration of drugs through dispersions of permeable globules in media of known diffusional properties. Water-in-oil-in-water (W/O/W) multiple emulsions have been studied by this method. When used to analyze data obtained with a simple diffusion cell, the model allows the calculation of the mass transfer coefficient which characterizes the diffusional mass transfer across oil-water interfaces within the emulsions. The mass transfer coefficient is directly related to the drug release rate from the internal phases of multiple emulsions. Those cases where instantaneous equilibria are established or where impermeable globules are present can be treated as special limiting cases. Differential equations which express diffusant concentrations as functions of time, space, and dispersion system parameters have been solved by Laplace transformation without recourse to numerical methods. The values of the mass transfer coefficient are shown to reflect the physical characteristics of multiple emulsion systems.