Pervaporation by a continuous membrane column

The possibility and applicability of the continuous membrane column concept to the membrane separation process of pervaporation has been demonstrated. It shows that a mixture of two or more liquids can be separated to a high degree without cascading several stages of individual pervaporation units. The degree of enrichment is unlimited in a continuous membrane column while a maximum limit exists in a conventional pervaporator. This new concept of membrane operation has been shown previously to give enhanced separations in gaseous systems without the expense and complexity of a multi-staged cascade.

The permeabilities of silicone rubber to ethanol—water and isopropanol—water mixtures were determined at 25 and 40°C as a function of concentration. Separation experiments were carried out in small membrane columns. Included were instances in which feed mixtures just below the azeotrope (because of the small size of the experimental column) were enriched beyond the normal azeotropic composition (0.89 mole fraction ethanol) on a continuous basis. Feed compositions at other levels were also investigated; for example, a feed at 0.50 mole fraction ethanol was continuously separated into two streams at 0.69 and 0.12 mole fraction ethanol Finally, a mathematical analysis has been developed which adequately describes capillary membrane pervaporation within a continuous membrane column configuration.     

A modified assay for cholinesterase

A radioisotopic assay for cholinesterase activity is described, which was developed by combining parts of existing systems. Easily used microliter volumes are employed. Labeled acetylcholine and acetate are separated by liquid cation-exchange chromatography. The method is sensitive, rapid, and easy to perform.     

Structure-activity analysis of the purine binding site of human liver glycogen phosphorylase

Human liver glycogen phosphorylase (HLGP) catalyzes the breakdown of glycogen to maintain serum glucose levels and is a therapeutic target for diabetes. HLGP is regulated by multiple interacting allosteric sites, each of which is a potential drug binding site. We used surface plasmon resonance (SPR) to screen for compounds that bind to the purine allosteric inhibitor site. We determined the affinities of a series of compounds and solved the crystal structures of three representative ligands with K(D) values from 17-550 microM. The crystal structures reveal that the affinities are partly determined by ligand-specific water-mediated hydrogen bonds and side chain movements. These effects could not be predicted; both crystallographic and SPR studies were required to understand the important features of binding and together provide a basis for the design of new allosteric inhibitors targeting this site.     

Steady state dislocation motion via molecular dynamics

Nonequilibrium molecular dynamics is applied to the generation and steady propagation of edge dislocations. “Normal” propagation at about one-third the longitudinal sound speed, transonic propagation at nine-tenths that speed, climb, and multiplication are all observed.     

Chaos and irreversibility in simple model systems

The multifractal link between chaotic time-reversible mechanics and thermodynamic irreversibility is illustrated for three simple chaotic model systems: the Baker Map, the Galton Board, and many-body color conductivity. By scaling time, or the momenta, or the driving forces, it can be shown that the dissipative nature of the three thermostated model systems has analogs in conservative Hamiltonian and Lagrangian mechanics. Links between the microscopic nonequilibrium Lyapunov spectra and macroscopic thermodynamic dissipation are also pointed out. (c) 1998 American Institute of Physics.     

Taking stock of the occupational safety and health challenges of nanotechnology: 2000–2015

Engineered nanomaterials significantly entered commerce at the beginning of the 21st century. Concerns about serious potential health effects of nanomaterials were widespread. Now, approximately 15 years later, it is worthwhile to take stock of research and efforts to protect nanomaterial workers from potential risks of adverse health effects. This article provides and examines timelines for major functional areas (toxicology, metrology, exposure assessment, engineering controls and personal protective equipment, risk assessment, risk management, medical surveillance, and epidemiology) to identify significant contributions to worker safety and health. The occupational safety and health field has responded effectively to identify gaps in knowledge and practice, but further research is warranted and is described. There is now a greater, if imperfect, understanding of the mechanisms underlying nanoparticle toxicology, hazards to workers, and appropriate controls for nanomaterials, but unified analytical standards and exposure characterization methods are still lacking. The development of control-banding and similar strategies has compensated for incomplete data on exposure and risk, but it is unknown how widely such approaches are being adopted. Although the importance of epidemiologic studies and medical surveillance is recognized, implementation has been slowed by logistical issues. Responsible development of nanotechnology requires protection of workers at all stages of the technological life cycle. In each of the functional areas assessed, progress has been made, but more is required.     

Momentum transport from nonlinear mode coupling of magnetic fluctuations

A cause of observed anomalous plasma momentum transport in a reversed-field pinch is determined experimentally. Magnetohydrodynamic theory predicts that nonlinear interactions involving triplets of tearing modes produce internal torques that redistribute momentum. Evidence for the nonlinear torque is acquired by detecting the correlation of momentum redistribution with the mode triplets, with the elimination of one of the modes in the triplet, and with the external driving of one of the modes.