Near-infrared trace-gas sensors based on room-temperature diode lasers

2 monitor designed for field applications using room-temperature diode lasers are presented. Near-infrared DFB lasers operating at 1.57 μm and around 2.0 μm have been used for CO₂ measurements. At ambient concentration levels a resolution of more than two orders of magnitude has been demonstrated at 1.57 μm, at 2 μm the precision is in the order of 0.1 ppm CO₂, and for trace analysis a detection limit of 10 ppb has been obtained. The measurements demonstrate the capability of near-infrared DFB diode lasers for the precise determination of CO₂ concentrations as required for climatological, medical, or industrial applications. Received: 24 February 1998/Revised version: 27 April 1998     

Iron pentacarbonyl mediated coupling of benzyl halides to ketones under mild phase transfer conditions.

In a two-phase system (saturated aqueous calcium hydroxide, tetrabutylamnonium sulfate, dichloromethane, iron pentacarbonyl) benzyl bromides are readily carbonylated to dibenzyl ketones; α-α′ dibromoorthoxylene yields the o-quinodimethane iron tricarbonyl complex 8. It is inferred that the reactions proceed through transient generation of the tetracarbonyl ferrate dianion.     

On Perturbed Discrete Boundary Value Problems

In this paper, we study nonlinear discrete boundary value problems of the form x ( t +1)= A ( t ) x ( t )+ h ( t )+ k f ( t , x ( t ), k ) subject to Bx (0)+ Dx ( J )= u + k g ( x (0), x ( J ), k ) where k is a "small" parameter. Our main concern is the case of resonance, that is, the situation where the associated linear homogeneous boundary value problem x ( t +1)= A ( t ) x ( t ), Bx (0)+ Dx ( J )=0 admits nontrivial solutions. We establish conditions for the solvability of the nonlinear boundary value problem when k is "small". We also establish qualitative properties of these solutions.     

Poly(ester)s Containing Germanium and Silicon in the Main Chain. 1. Langmuir Monolayer Characterization

Surface characterization of poly(ester)s containing germanium (Ge) or silicon (Si) in the main chain was studied. Surface pressure‐area isotherms (π‐A) at the air/water interface were obtained by monolayer compression at constant temperature. The molecular areas from the pressure‐area isotherms were estimated for all polymers. At low surface concentrations poly(ester)s the characterization of monolayers was carried out according to the variation of the surface pressure as a function of the surface concentration; the behavior observed was described by the virial expansion development. In the semidilute region, the surface pressure variation was expressed according to the scaling laws as a power function of the surface concentration. It was found that the chemical structure of the poly(ester)s studied influences the type of the isotherms. The morphology of the monolayers was observed by Brewster angle microscopy (BAM). The molecular mechanics approach was used to obtain predictions about the local interaction energies between segments and to explain the minimum area values at the collapse point.     

Environmentally friendly synthesis of noble metal nanoparticles assisted by biodegradable dextran‐graft‐lactone copolymers

A simple “green synthesis” of noble metal nanoparticles by direct reaction between Dextran‐graft‐lactone copolymers and metal salts without the need to separately add reducing and stabilizing agents was carried out. The effects of the composition, molecular weights of copolymers and solvents on the characteristics of the nanoparticles were considered. The amphiphilic character of the copolymers seems to be an important factor in the results of the synthesis. According to the results, general correlations between experimental parameters of synthesis and characteristics of the obtained nanoparticles were established. Techniques such as, transmission electron microscopy, scanning electron microscopy, UV–visible spectroscopy, Zeta Potential, dynamic light scattering and Fourier transform Infrared Spectroscopy, were used for the characterization of the products. The results indicate the possibility of control of the characteristics of the nanostructured material. Copyright © 2014 John Wiley & Sons, Ltd.