Thermal effects in collision-free infrared multiphoton absorption by SF6 and CF3Br

An opto-thermal molecular beam study has been carried out to investigate the multiple-photon laser excitation of SF₆ and CF₃Br. The molecular beam was produced by means of a supersonic expansion through a nozzle at variable temperature. The opto-thermal signal was measured by means of a high-sensitivity superconducting bolometer. The multiple-photon excitation of SF₆ has been measured as a function of the initial ro-vibrational population of the molecule. The experimental results have been compared with both previously published data of molecular beam and gas cell experiments and theoretical calculations. A satisfactory agreement has been found between some of our experimental results and the theoretical spectra obtained by means of the heat-bath feed-back model.     

Avoided-crossing-based liquid-crystal photonic-bandgap notch filter

We demonstrate a highly tunable deep notch filter realized in a liquid-crystal photonic-bandgap (LCPBG) fiber. The filter is realized without inducing a long-period grating in the fiber but simply by filling a solid-core photonic-crystal fiber with a liquid crystal and exploiting avoided crossings within the bandgap of the LCPBG fiber. The filter is demonstrated experimentally and investigated using numerical simulations. A high degree of tuning of the spectral position of the deep notch is also demonstrated.     

On a Recent Proposal of Faster than Light Quantum Communication

In a recent paper, A.Y. Shiekh has discussed an experimental set-up which, in his opinion, should make possible faster-than-light communication using the collapse of the quantum wave function. Contrary to the many proposals which have been presented in the past, he does not resort to an entangled state of two systems but he works with a single particle in a superposition of two states—corresponding to its propagation in opposite directions—one of which goes through an appropriate interferometer. The possibility for an observer near the interferometer to introduce or not, at his free will, a phase shifter along one of the paths should allow to change instantaneously the probability of finding the particle in the far-away region corresponding to the other state of the superposition and, correspondingly, to change the intensity of a beam of particles reaching a distant observer. In this paper we show a flaw in the argument: once more, as it has been proved in full generality a long time ago, the process of wave packet reduction cannot be used for superluminal communication.     

Determination of Mercury with a Miniature Sensor for Point-of-care Testing

In developing countries, subsistence gold mining entails mixing metallic mercury with crushed sediments to extract gold. In this approach, the gold−mercury amalgam is heated to evaporate mercury and obtain gold. Thus, the highly volatile mercury can be absorbed through inhalation, resulting in adverse health effects. Urinalysis can be used to detect mercury, which is excreted in urine and feces, and correlate exposure with toxic effects. The current gold standard analytical methods are based on fluorescence or inductively coupled plasma mass spectrometry methods, but are expensive, time consuming, and are not easily accessible in countries where testing is needed. In this work, we report on a miniature electrochemical sensor that can rapidly detect mercury in urine at levels well below the US Biological Exposure Index (BEI) limit of 50 ppb (μg/L). The sensor is based on a thin-film gold electrode and anodic stripping voltammetry electroanalytical approach. The sensor successfully detected mercury at trace levels in urine, with a limit of detection of ∼15 ppb Hg in the linear range of 20–80 ppb. With the low-cost disposable sensors and portable instrumentation, it is well suited for point-of-care applications.     

Multiple light-harvesting II polypeptides from maize mesophyll chloroplasts are distinct gene products.

The major light-harvesting complex of photosystem II in higher plants is known as LHCII. It is composed of a number of chlorophyll-binding proteins sharing epitopes with each other. The number of apoproteins resolved by fully denaturing sodium dodecylsulfate polyacrylamide gel electrophoresis varies in different species. In order to know if this heterogeneity is caused by the expression of a number of homologous genes or if it is the product of post-translational modifications, we have resolved the six major apoproteins of Zea mays LHCII. Each protein is purified to homogeneity, subjected to direct protein sequencing and the sequences compared with those deduced from lhcb genes in maize and other organisms. All of the six proteins are distinct gene products, since they show differences in their primary structure. Three apoproteins are identified as products of type I lhcb genes and one each as type II and type III gene products. A sixth protein does not fit the requirements for any of the lhcb genes so far cloned and is therefore probably the product of an lhcb gene type not yet described. Our results clearly show that the major source of LHCII protein heterogeneity is the expression of many lhcb genes. Fractionation of maize LHCII by non-denaturing flat-bed isoelectric focusing resolves at least five major isoforms showing distinct differences in their polypeptide composition and also differing in their spectroscopic properties, thus suggesting that individual Lhcb gene products have distinct pigment-binding properties.     

Phase behavior and some calorimetric and physical properties of diurethanes from perfluoropolyether macromonomers

Density and calorimetric measurements have been carried out on copolymeric perfluoropolyethers of molecular weight ranging between 500 and 4700, terminated at both chain ends either with  CH₂OH or ethylurethane groups. Samples of the second series are models for perfluoropolyethers based polyurethanes. Density measurements point out that the terminal alcoholic group brings about a negative excess volume, which increases with decreasing the molecular weight; a lower excess volume is found for urethane‐terminated molecules. Calorimetric traces, T_g, and Δc_p at T_g show that alcoholic‐terminated molecules are amorphous and one phase systems, while urethane‐terminated compounds are crystalline; phase separation is observed for this last series when the molecular weight of the fluorinated segment is larger than 1000. The trend of T_g with molecular weight is discussed for one‐ and two‐phase systems in the light of current theories for the glass transition. The decrease of the melting point with increasing the molecular weight for the urethane series can be described by the Flory equation for random copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1609–1622, 1999