Gaussian model for localized translational motion: application to incoherent neutron scattering

A simple model based on Gaussian statistics, aimed at describing localized diffusive translational motion in one, two, and three dimensions is presented and used to calculate the corresponding incoherent neutron scattering laws. In the time domain, these laws are closed form mathematical functions. In the frequency domain, some of these laws can be expressed as an infinite series depending on one single index. Owing to this relative simplicity, such a model can advantageously replace previous models such as diffusion on a segment, inside a circle and inside a sphere with an impermeable surface, to analyze neutron quasielastic scattering data associated with molecular motions in confined media. It may also be more realistic when the confinement is defined by soft, ill-defined boundaries.     

Autonomous gel/enzyme oscillator fueled by glucose: Preliminary evidence for oscillations

A novel prototype gel oscillator that functions by dissipating the chemical energy of glucose by an enzyme-mediated reaction is proposed. The product of the reaction modulates the degree of swelling and hence the permeability of a poly(N-isopropylacrylamide-co-methacrylic acid) gel membrane which in turn regulates the flow of substrate to the enzyme. No external energy is required aside from the chemical energy of glucose present externally at constant concentration. A negative chemomechanical feedback loop is established which, coupled with hysteresis in the membrane permeability characteristics, produces pulsing oscillations. In this study, we introduce a simple model which provides guidelines for experimental design, and report preliminary experimental evidence for oscillation. Application of this prototype system to the episodic delivery of drugs and hormones is envisaged. (c) 1999 American Institute of Physics.     

One-pot synthesis of pentacyclic diamines from quinolines by a new Zn/AcOH-promoted cascade reaction

A simple and efficient method for the one-pot synthesis of pentacyclic diamines from quinolines is described. It involves a new Zn/AcOH-promoted cascade reaction, in which two C[bond]C bonds and four to five stereogenic centers are established under mild conditions. The regiochemistry of the dimerization and cyclization step is governed by substituent effects, allowing access to a head-to-head (2, 3) or head-to-tail skeleton (4, 5).     

New methodology for acridine synthesis using a rhodium-catalyzed benzannulation

A new methodology for the synthesis of acridine derivatives is disclosed. The starting materials are commercially available quinolines, which can be converted, via five high efficient steps, in a key quinoline intermediate substituted with a TBS-protected-enol-ether and an internal alkyne. The key and last step is a rhodium-catalyzed benzannulation of the quinoline intermediate yielding the desired poly-substituted acridines derivatives.     

Determination of niacin in infant formula by solid-phase extraction and anion-exchange liquid chromatography.

A peer-verified, solid-phase extraction (SPE)/anion exchange liquid chromatographic method is presented for the determination of niacin in milk-based and soy-based infant formula. Analysis is in 3 steps: test sample digestion, extraction/cleanup, and liquid chromatography (LC). Digestion uses a standard AOAC digestion procedure that involves autoclaving at 121 degrees C for 45 min in (1 + 1) H2SO4 to free endogenous niacin from protein and to convert added niacinamide to niacin. The digest solution is adjusted to pH 6.5 with 7.5M NaOH. Acidification to pH <1.0 with (1 + 1) H2SO4 precipitates the protein. The clarified solution is then filtered, and the filtrate is brought to volume. SPE of niacin is accomplished by passing an aliquot of the digest solution through an aromatic sulfonic acid-SPE (ArSCX-SPE) column. After the column is washed with methanol and water to remove extraneous material, the niacin is eluted with 0.25M sodium acetate/acetic acid buffer at pH 5.6. An anion-exchange polystyrene-divinylbenzene column with 0.1 M sodium acetate/acetic acid buffer at pH 4.0 is used for LC. Niacin is determined by UV detection at 260 nm. A standard curve is prepared by passing known amounts of niacin through the ArSCX-SPE columns used for niacin extraction. The following values for x and relative standard deviation (RSD) were obtained for National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1846 Infant Formula with a certified value for niacin of 63.3 +/- 7.6 microg/g: Submitting laboratory.-- x = 59.7 +/- 4.0 microg/g; RSD = >6.7%; confidence interval (CI) = +/- 1.4 microg/g; n = 27. Peer laboratory.--x = 56.6 +/- 6.6 microg/g; RSD = >11.7%; CI =+/- 4.1 microg/g; n = 8.     

Laser beam scattering effects in non-absorbent inhomogenous polymers

In this paper a numerical model for laser beam scattering in the semi-transparent polymers is presented, using a Monte Carlo algorithm and the Mie theory. The algorithm correctly accounts for the independent multiply-scattered light. We describe the algorithm, present a number of important parameters that account in the welding process, and explicitly show how the algorithm can be used to estimate the laser beam intensity both inside the semi-transparent component and at the welding interface and the beam widening. For the model validation an experimental bench test has been realized and some results from two test cases are presented.     

Electroactuation of fluid using topographical wetting transitions

The complex morphologies of liquids on topographically structured substrates are exploited for liquid actuation in open microchannels. The liquid is either confined in prefabricated grooves, thus forming elongated filaments, or gathers in macroscopic drops without invading the grooves, depending on conditions. Using the electrowetting effect, we can reversibly switch between these two states. The length of the filaments is sensitive to the ionic content of the liquid and can be described quantitatively with an electrical model considering the voltage drop along the groove.