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.     

Local convective heat transfer past the junction of channels of rectangular cross-section

An experimental study of the local convective heat transfer through the wall is presented in the case of an air flow past the junction of channels of a rectangular cross section. Tests for various flow-rate ratios through the two branches show that these ratios are not adequate to characterize the distribution of local heat transfer through the wall. The flow-rate through the side branch is a particularly significant parameter. Received: 2 June 1998/Accepted: 20 February 1999     

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.     

Thermally stimulated current study of the molecular movements in bone

Thermally Stimulated Current (TSC) has been used for investigating the interface and interphase in a natural composite, bone. Young adult male femoral diaphysis has been studied at different stages of demineralization by EDTA. Analysis of the fine structure of complex TSC spectra has shown that in the early stages of demineralization, dielectric relaxations are due to the hydroxyl reorientations in the mineral apatite structure. After a certain stage of demineralization, the mineral response disappears and organic matrix mobility is observed. A dissociative buffer has been used to identify collagen relaxations. The contribution of the mineral-organic interface/interphase has been isolated.     

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.