Evaluation of Carboxen carbon molecular sieves for trapping replacement chlorofluorocarbons

A method has been developed for trapping and preconcentrating the very volatile replacement chlorofluorocarbons (hydrofluorocarbons and hydrochlorofluorocarbons) using microtraps filled with Carboxen, a carbon molecular sieve type material, without the need for extensive cryotrapping using liquid nitrogen. We present here the adsorption characteristics of four Carboxen materials, Carboxen 569, 1000, 1001, and 1002, used to trap a range of replacement chlorofluorocarbons varying in boiling point from −48.4 to −9.8°C. The application of these traps for the automated analysis of trace gases in atmospheric and environmental chemistry could prove extremely useful.     

TheA 1-and the ϕ-meson in QCD

Recently we used a method of stable analytic extrapolation to test whether strictly local duality between the asymptotic and the resonance region, which is believed to be valid in QCD, appears already at the present stage of QCD calculations. Probing the QCD ?-amplitude, we found a prominent bump structure in the resonance region, i.e. a rather direct evidence for the validity of local duality. In the present paper we confirm and extend this result by giving two further applications, theA ₁-meson and the ?-meson. While we do not meet theA ₁, as was to be expected since other sum rules can not separate it from the continuum, too, the extrapolation of the ?-amplitude leads to an enormous bump. Comparing this ?-bump with our ?-bump, we recover at least qualitatively the real proportions.     

Stochastic resonance in perspective

Summary We outline the historical development of stochastic resonance (SR), a phenomenon in which the signal and/or the signal-to-noise ratio in a nonlinear system increase with increasing intensity of noise. We discuss basic theoretical ideas explaining and describing SR, and we review some revealing experimental data that place SR within the wider context of statistical physics. We emphasize the close relationship of SR to some effects that are well known in condensed-matter physics. Paper presented at the International Workshop ?Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing and Related Phenomena?, Elba, 5–10 June 1994.     

Effect of transverse object position on the reconstructed image of an aperture-limited in-line hologram

It is experimentally demonstrated that the image resolution from an in-line Fraunhofer hologram degrades appreciably when the centre of the diffraction pattern from a 5-bar resolution target is located asymmetrically in the hologram aperture. This effect is confirmed and analysed using calculated and experimentally measured images from holograms of a one-dimensional wire. Increasing asymmetry results in an increasing error in the measured linewidth, and a reduction of image resolution. A simple model based on average fringe contrast is used to predict this decrease in resolution with transverse object position.     

A flower-like Ising model. Thermodynamic properties

We consider a flower-like Ising model, in which there are some additional bonds (in the “flower-core”) compared to a pure Ising chain. To understand the behaviour of this system and particularly the competition between ferromagnetic (usual) bonds along the chain and antiferromagnetic (additional) bonds across the chain, we study analytically and iteratively the main thermodynamic quantities. Very interesting is, in the zero-field and zero-temperature limit, the behaviour of the magnetization and the susceptibility, closely related to the ground state configurations and their degeneracies. This degeneracy explains the existence of non-zero entropy at zero temperature, in our results. Also, this model could be useful for the experimental investigations in studying the saturation curves for the enzyme kinetics or the melting curves for DNA-denaturation in some flower-like configurations.     

A theory of spin fluctuations in the refractory compounds VN and NbN

We calculate the spin fluctuation spectra of VN and NbN in the relevant frequency- and wave vector regime. Significant quantitative differences between the dynamical spin susceptibilities of both substances are found. While in the case of VN their amplitudes are large, especially towards the Brillouin zone boundary and for frequencies below 1 eV, enhancement effects in NbN are of minor importance.     

Evaluation of atomic fluorescence, absorption and emission techniques for the determination of mercury

Summary Atomic fluorescence (AFS), absorption (AAS) and emission (AES) systems were evaluated for the determination of inorganic mercury. Identical vapour generation and amalgamation procedures were used to permit direct comparison of the performance of a commercial long-path AAS instrument to laboratory constructed non-dispersive AFS as well as He-MIP based AES instruments. Instrumental noise-limited detection limits (LOD) were 0.94, 2.4, 2.8 pg for AAS, AES and AFS techniques, respectively. Methodological LOD's were found to be blank controlled and similar for all three instruments, viz. 9, 25 and 16 pg for AAS, AFS and AES, respectively. All three systems produced accurate results at the low ng/l concentration, as verified by the analysis of a certified river water reference material (NRCC ORMS-1).