Comparison Of Tenax And Carbotrap For VOC Sampling In Indoor Air

The most important features of Tenax and Carbotrap, solid sorbents used widely for sampling organic pollutants in air, have been tested under the conditions requested for surveys in indoor spaces and for determinations of VOC emitted from indoor sources by chamber experiments. The performances of samplers, tested with 10 nonpolar and polar (mostly lipophilic) hydrocarbons, present as vapours in 0.5 to 2.0 litre air samples, include: (a) accuracy and reproducibility of the measured concentration, (b) background or “blank” of samplers, (c) stability upon storage (at ambient and below ambient temperatures) of clean samplers and of samplers loaded with VOC, and (d) performance stability after several sampling desorption cycles. The results fulfil the requirements for both adsorbents, though each presents some different drawbacks. In particular (a) Tenax samplers show a “blank” (90 percentile) of 16 ng of benzene and 5 ng of toluene, Carbotrap samplers roughly twice as much; (b) the samplers may be stored for one month either before or after use and (c) they may withstand many cycles without discernible deterioration.     

Röntgenbeugungsuntersuchungen zur Restaustenitumwandlung

Röntgenbeugungsuntersuchungen zur Ermittlung des Restaustenitgehaltes in martensitischem Gußeisen in Abhängigkeit von der Anlaßdauer bei 400 und 500 °C. Zusammenhang zwischen der Änderung der Halbwertsbreite der (220)-Beugungslinie des Restaustenits und dessen Umwandlungsgeschwindigkeit. Ansatz zur Erklärung dieses Zusammenhanges.     

Influence of substrate absorption on the optical and geometrical characterization of thin dielectric films

The role played by a glass substrate on the accurate determination of the optical constants and the thickness of a thin dielectric film deposited on it, when well-known envelope methods are used, is discussed. Analytical expressions for the two envelopes of the optical transmission spectra corresponding to film. with both uniform and nonuniform thicknesses are derived, assuming the substrate to be a weakly absorbing layer. It is shown that accurate determination of the refractive index and the film thickness is notably improved when the absorption of the substrate is considered. The analytical expressions for the upper and lower envelope, are used to characterize optically and geometrically both uniform and nonuniform amorphous chalcogenide films. The results obtained are compared with those derived by use of expressions for the envelopes that neglect the substrate absorption. The comparison shows that overestimated refractive indexes and underestimated thicknesses are obtained when the conventional approach, in which the substrate absorption is neglected, is used.     

Measurements of the corneal birefringence with a liquid-crystal imaging polariscope

An imaging polariscope has been used to analyze the spatially resolved polarization properties of living human corneas. The apparatus is a modified double-pass setup, incorporating a liquid-crystal modulator in the analyzer pathway. Keeping the incident polarization state fixed (first passage), we recorded a series of three images of the pupil's plane corresponding to independent polarization states of the analyzer unit. Azimuth and retardation at each point of the cornea were calculated from those images. Results show that the magnitude of retardation increases along the radius toward the periphery of the cornea. Left-right eye symmetry in retardation was also found. Maps of azimuth indicate that the direction of the corneal slow axis is nasally downward.     

Hydrolytic and enzymatic degradations of physically crosslinked hydrogels prepared from PLA/PEO/PLA triblock copolymers

Degradable copolymers were synthesized by ring opening polymerization of lactide in the presence of poly(ethylene glycol) (PEG), using CaH₂ as a biocompatible initiator. The resulting PLA/PEO/PLA triblock copolymers were dissolved in a biocompatible solvent, namely tetraglycol. Physically crosslinked hydrogels were then prepared by introducing small amounts of water into the thus obtained solutions. Hydrolytic degradation of the highly swollen hydrogels was realized in 0.13 M pH=7.4 phosphate buffer, while the enzymatic degradation was carried out in 0.05 M pH=8.6 Tris buffer containing a PLA-degrading enzyme, proteinase K. In both cases, degradation was initially very fast with dramatic weight loss. The LA/EO ratio of the remaining material increased rapidly, in agreement with the release of PEO-rich segments. In a second phase, the degradation rate slowed down. The presence of proteinase K strongly accelerated the degradation rate of the hydrogels, indicating that the enzyme was able to penetrate inside and attack the PLA domains which constituted nanometric nodes in the gel network.     

KINETIC CHARACTERISTICS OF A BATCH ADSORBER OR AN ION EXCHANGE DEVICE OPERATED UNDER NONISOTHERMAL CONDITIONS

A model was formulated for a batch adsorber or ion exchange device with heat generation inside the bulk liquid due to mixing or electrical heating and due to heat of adsorption. Internal and external particle mass and heat transfer gradients and heat transfer through the vessel wall were included. The effective diffusion coefficient was taken to be temperature dependent. Numerical calculations (by orthogonal collocation) give conditions for the existence of intra particle nonisothermity and show the effect of mixing and process temperature on adsorption kinetics.     

A Configurable Architecture for the Wavelet Packet Transform

The standard Wavelet Transform (WT) has a wide range of applications, from signal analysis to image or video compression and communications. Most of these applications would be benefited if the transform provided good spectral and temporal resolution in arbitrary regions of the time-frequency plane. This flexible choice of the time-frequency tiling is provided by the Wavelet Packet Transform (WPT). Though many VLSI architectures have been proposed for the WT in the literature, it is not the case for the WPT. We present both word-serial and word-parallel real-time pipelined architectures capable of computing a complete WPT binary tree, but which are easily configurable to compute any required WPT subtree.     

Magnetic resonance in Hallevorden-Spatz disease

The Hallevorden-Spatz disease should be suspected in children or young people with motor, pyramidal or extrapyramidal symptomatology and deterioration of superior functions specially upon the existence of family history. Pathognomonic diagnosis may only be obtained by necropsy but magnetic resonance images, although not pathognomic, are sufficiently characteristics to strongly support the diagnosis. Four cases of Hallevorden-Spatz disease are presented with special emphasis on the MR images characteristic of this disease.     

振兴我国天然气工业研究报告之一——振兴天然气工业必须走社会主义商品经济的道路

我国天然气工业的发展与国民经济的需要不相适应,虽然可以提出许多原因,而根本原因是没有真正承认天然气工业也是社会主义商品经济的一个产业部门,没有给予天然气企业以真正的商品生产者、经营者的地位。振兴天然气工业,必须走商品经济的道路。