Electronic speckle pattern interferometry using optical fibers

Initial experiments using electronic speckle pattern interferometry with fiberoptic imaging and illumination are described.     

A kinetic study of the reaction of fluorine atoms with CH3F,CH3Cl,CH3Br,CF2H2, CO,CF3H,CF3CHCl2, CF3CH2F,CHF2CHF2, CF2ClCH3, CHF2CH3, and CF3CF2H at 295 ± 2 K

A variety of relative and absolute techniques have been used to measure the reactivity of fluorine atoms with a series of halogenated organic compounds and CO. The following rate constants were derived, in units of cm³ molecule^?1 s^?1: CH₃F, (3.7 ± 0.8) × 10^?11, CH₃Cl, (3.3 ± 0.7) × 10^?11; CH₃Br, (3.0 ± 0.7) × 10^?11; CF₂H₂, (4.3 ± 0.9) × 10^?12; CO, (5.5 ± 1.0) × 10^?13 (in 700 torr total pressure of N₂ diluent); CF₃H, (1.4 ± 0.4) × 10^?13; CF₃CCl₂H (HCFC-123), (1.2 ± 0.4) × 10^?12; CF₃CFH₂ (HFC-134a), (1.3 ± 0.3) × 10^?12, CHF₂CHF₂ (HFC-134), (1.0 ± 0.3) × 10^?12; CF₂ClCH₃ (HCFC-42b), (3.9 ± 0.9) × 10^?12, CF₂HCH₃ (HFC-152a), (1.7 ± 0.4) × 10^?11; and CF₃CF₂H (HFC-125), (3.5 ± 0.8) × 10^?13. Quoted errors are statistical uncertainties (2σ). For rate constants derived using relative rate techniques, an additional uncertainty has been added to account for potential systematic errors in the reference rate constants used. Experiments were performed at 295 ± 2 K. Results are discussed with respect to the previous literature data and to the interpretation of laboratory studies of the atmospheric chemistry of HCFCs and HFCs. © 1993 John Wiley & Sons, Inc.     

Aporism: Uncertainty about mathematics

Neither absolutism nor aposteriorism have questioned the progressive elements associated with the applications and the social functions of mathematical knowledge. Aporism raises this question by discussing the thesis of the formatting power of mathematics. This thesis unites linguistic relativism applied to mathematics and the idea that technology is a structuring principle in society. We are no longer surrounded by “nature”, instead we live in a techno-nature. Mathematical abstractions can be projected outside the sphere of mathematics, and in this way they modulate and eventually constitute fundamental categories of techno-nature. The Vico paradox expresses the difficulties of specifying the nature and function of technological actions. We are not even able to grasp and to understand what we have ourselves constructed. A critique cannot be guaranteed by scientific (or mathematical) thinking itself. Critique becomes a much more complex activity including reflections on technological actions. A crifique includes ethical considerations, and therefore a critique of mathematics is also ethical.     

Terahertz spectroscopy for rubber production testing

The interest in new test methods for rubber production has been growing rapidly over the past years. Recent developments in production planning aim to minimize storage times, and hence limit the time available for process control between production steps. New additives such as silica and carbon nanotubes allow for significant improvements in the material quality. Both developments demand new approaches to control the production process where established methods do not work satisfactorily. In this study, we have investigated the capability of terahertz time-domain spectroscopy as a new tool for rubber production testing. Offline measurements of different material families show a strong contrast in the terahertz refractive index. Inline measurements during elastomer extrusion allow for monitoring production processes and the duration of purposely induced material changes in the extruder. This technique helps to improve the quality of the materials and to minimize waste.     

Characterizing R-duality in Banach spaces

R-duals of certain sequences in Hilbert spaces were introduced by Casazza, Kutyniok and Lammers in 2004 and later generalized to Banach spaces by Xiao and Zhu. In this paper we provide some characterizations of R-dual sequences in Banach spaces.     

Inhibition of Ps formation in benzene and cyclohexane by CH3Cl and CH3Br. Correlation to radiation chemistry results

Positron-annihilation lifetime spectra have been measured for mixtures of CH₃Cl and CH₃Br in cyclohexane and of CH₃Cl in benzene. The ortho-positronium (Ps) yield decreased monotonically from 38% and 43% in cyclohexane and benzene respectively to 11% in pure CH₃Cl and 6% in pure CH₃Br. The strength of the inhibition of Ps formation by CH₃Br was ten times that of CH₃Cl in cyclohexane, because the CH₃Br^? anion debrominates rapidly, while CH₃Cl^? is long-lived (= 30 ns) compared to the maximum time of Ps formation of 400–500 ps. as shown in radiation chemistry. The positron can pick off the electron from the CH₃X^? anions to form Ps. while it forms a bound state with the halides. X^?. CH₃Cl was a roughly three times weaker Ps inhibitor in benzene than in cyclohexane, which shows that CH₃Cl^? does not dechlorinate in times comparable to or shorter than 400–500 ps in benzene. An improved model for the explanation of Ps formation in mixtures, where the Ps yield versus electron scavenger concentration has a minimum, is proposed and discussed.     

Solvated positron chemistry competitive positron reactions with halide ions in water

It is shown by means of the angular correlation technique that the binding of positrons to halides is strongly influenced by solvation effects. For aqueous solutions we find increasing values for the binding energies between the halide and the positron with increasing mass of the halide. This is contrary to the calculations of Cade and Farazdel for the vacuum case.     

Book reviews

Structural Chemistry -