Photodegradation of Reactive Black 5, Direct Red 28 and Direct Yellow 12 using UV, UV/H(2)O(2) and UV/H(2)O(2)/Fe(2+): a comparative study

The photodegradation of three commercially available dyestuffs (C.I. Reactive Black 5, C.I. RB5, C.I. Direct Yellow 12, C.I. DY12, and C.I. Direct Red 28, C.I. DR28) by UV, UV/H(2)O(2) and UV/H(2)O(2)/Fe(II) processes was investigated in a laboratory-scale batch photoreactor equipped with an 16W immersed-type low-pressure mercury vapour lamp. The experimental results were assessed in terms of absorbance and total organic carbon (TOC) reduction. The initial concentration was kept constant at 100 mg l(-1) for all dyes. Initial results showed that, color removal efficiencies by UV or H(2)O(2) alone were negligible for all dyes. Almost complete disappearance of C.I. RB5 (99%) and DY12 (98%) in UV/H(2)O(2) process was possible to achieve after 60 min of irradiation. The maximum color removal efficiency of C.I. DR28 after 60 min of irradiation, however, was only 40% and reached a maximum value of 70% after 120 min of irradiation. Corresponding mineralization efficiencies were 50, 55 and 7-12%, respectively. The addition of Fe(II) to the system, so-called the photo-Fenton process, greatly enhanced the color removal, the efficiencies being 98, 88 and 85% for C.I. RB5, C.I. DY12 and C.I. DR28 only after 5 min of irradiation. Corresponding mineralization efficiencies were 98% for 45 min irradiation, 100% for 60 min irradiation and 98% for 90 min irradiation, respectively. However, marginal benefit was less significant in the higher range of both H(2)O(2) and Fe(II). Furthermore, decreases in both decolorization and mineralization were observed at higher concentrations of oxidant and catalyst due to the scavenging effect of excess H(2)O(2) and OH radicals. The degradation of all dyes was found to follow first-order reaction kinetics.     

Molal volumes of somen-Fatty acids and their methyl and ethyl esters

The densities of some pure methyl and ethyl esters ofn-fatty acids were determined at temperatures between 10° to 80°C. The molal volumes of these esters and the long-chain fatty acids were correlated with temperature and chainlength. The reciprocals of the average methylene contribution at long-chain and the end group contribution to the molal volumes were found to be linear functions of the temperature. With the introduction of a correction term to account for mutual interaction of the end groups, three equations, one for each of the esters and the acids, were developed. These equations were used to calculate the molal values of the acids with carbon numbers up to 30 and up to 20 for the esters at temperatures ranging from 10° to 100°C. Excellent agreements were obtained between the molal volumes calculated by the equations and those obtained from the literature and experimental data.     

Development of New Volatile Organic Compound (VOC) Exposure Metrics and their Relationship to “Sick Building Syndrome” Symptoms

Abstract Occupants of office buildings are exposed to low concentrations of complex mixtures of volatile organic compounds (VOCs) that encompass a number of chemical classes and a broad range of irritancies. “Sick building syndrome” (SBS) is suspected to be related to these exposures. Using data from 22 office areas in 12 California buildings, seven VOC exposure metrics were developed and their ability to predict self-reported SBS irritant symptoms of office workers was tested. The VOC metrics were each evaluated in a multivariate logistic regression analysis model adjusted for other risk factors or confounders. Total VOCs and most of the other metrics were not statistically significant predictors of symptoms in crude or adjusted analyses. Two metrics were developed using principal components (PC) analysis on subsets of the 39 VOCs. The Irritancy/PC metric was the most statistically significant predictor of adjusted irritant symptoms. The irritant potencies of individual compounds, highly correlated nature of indoor VOC mixtures, and probable presence of potent, but unmeasured, VOCs were variously factored into this metric. These results, which for the first time show a link between low level VOC exposures from specific types of indoor sources to SBS symptoms, require confirmation using data sets from other buildings.     

Coupled-mode equations for pulse switching in parallel waveguides

The coupled-mode equations that describe the switching dynamics of optical pulses in two parallel waveguides are derived. These equations differ from the conventional ones in having extra coupling terms that arise from the dispersion properties of the coupling coefficient. It is shown that the coupling-coefficient dispersion can cause pulse distortion or even pulse breakup and in general produces much more significant effects than the group-velocity dispersion     

卫星电视接收技术的现状及其发展趋势

本文综述了卫星电视接收技术的国内外现状,简要地概括了它的十个发展方向,其发展的最终目标是要进入家庭.在技术开发和市场开拓上都是具有光明前途的.     

SAXS experiments on voids in gel-spun polyethylene fibres

The morphology and properties of extracted gel-spun polyethylene fibres depend on the spinning conditions. The main structures in the extracted fibre are shish-kebabs and lamellae. Equatorial small-angle X-ray scattering (SAXS) experiments show that the former structure is very porous due to the presence of lamellar overgrowth preventing a close package of the backbone fibrils, whereas the latter structure is relatively dense. After hot-drawing, due to melting/recrystallization, both structures are transformed on a 100 nm scale into a dense structure consisting of shish-kebabs or fibrils containing a void volume fraction of about 1%, as revealed by the scattering power of equatorial SAXS experiments. Moreover, a slight decrease of the equatorial intensity especially at the smallest angles after treating the hot-drawn fibres with paraffin oil, points to a small contribution of multiple scattering to the equatorial scattering. This implies the presence of a superstructure of not too closely packed macrofibrils. SAXS measurements of strained ultra-high-strength polyethylene fibres show that no or very little void formation is involved in the fracture mechanism. Most probably this is due to the (partly) fibrillar structure.