Homogeneous nucleation rate measurements of 1-butanol in helium: a comparative study of a thermal diffusion cloud chamber and a laminar flow diffusion chamber

Isothermal homogeneous nucleation rates of 1-butanol were measured both in a thermal diffusion cloud chamber and in a laminar flow diffusion chamber built recently at the Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Prague, Czech Republic. The chosen system 1-butanol-helium can be studied reasonably well in both devices, in the overlapping range of temperatures. The results were compared with those found in the literature and those measured by Lihavainen in a laminar flow diffusion chamber of a similar design. The same isotherms measured with the thermal diffusion cloud chamber occur at highest saturation ratios of the three devices. Isotherms measured with the two laminar flow diffusion chambers are reasonably close together; the measurements by Lihavainen occur at lowest saturation ratios. The temperature dependences observed were similar in all three devices. The molecular content of critical clusters was calculated using the nucleation theorem and compared with the Kelvin equation. Both laminar flow diffusion chambers provided very similar sizes slightly above the Kelvin equation, whereas the thermal diffusion cloud chamber suggests critical cluster sizes significantly smaller. The results found elsewhere in the literature were in reasonable agreement with our results.     

A note on the largest empty rectangle problem

We consider the following problem: given a rectangle containingn points, find the largest perimeter subrectangle whose sides are parallel to those of the original rectangle, whose aspect ratio is below a given bound, and which does not contain any of the given points. Chazelle, Drysdale and Lee have studied a variant of this problem with areas as the quantity to be maximized. They gave anO(nlog³ n) algorithm for that problem. We adopt a similar divide-and-conquer approach and are able to use the simpler properties of the perimeter measure to obtain anO(nlog² n) algorithm for our problem.The work of the first author was supported by the Academy of Finland and that of the second by the Natural Sciences and Engineering Research Council of Canada Grant No. A-5692.     

Determination of antimony in geochemical samples by graphite furnace atomic absorption spectrometry using different matrix modifiers

Determination of antimony by graphite furnace atomic absorption spectrometry using five different matrix modifiers, viz. nitric acid, copper, nickel, molybdenum and palladium, together with L'vov platform was studied. Without matrix modification, antimony was lost in a 1.2-M HCl solution when the thermal pretreatment temperature exceeded 700°C. By using 1.4 M HNO₃ or $\text{1μg}\text{20μl}$ copper solution the thermal pretreatment temperature could be increased up to 900°C. The matrix modification with $\text{2μg}\text{20μl}$ palladium, $\text{4μg}\text{20μl}$ molybdenum, or $\text{20μg}\text{20μl}$ nickel allowed the use of 1300°C as the pretreatment temperature. The best results were obtained with palladium when its concentration exceeded $\text{0.8μg}\text{20μl}$. Chemical interferences were studied with standard solutions spiked with different metal chlorides. The severe interference caused by iron chloride was avoided with ascorbic acid (2.5 %, $\text{w}\text{v}$). The method was tested on some geochemical reference samples.     

A novel particle sampling system for physico-chemical and toxicological characterization of emissions

Several studies have shown that combustion-derived fine particles cause adverse health effects. Previous toxicological studies on combustion-derived fine particles have rarely involved multiple endpoints and a detailed characterization of chemical composition. In this study, we developed a novel particle sampling system for toxicological and chemical characterization (PSTC), consisting of the Dekati Gravimetric Impactor (DGI) and a porous tube diluter. Physico-chemical and toxicological properties of the particles emitted from various combustion sources were evaluated in two measurement campaigns. First, the DGI was compared with the High-Volume Cascade Impactor (HVCI) and to the Dekati Low-Pressure Impactor (DLPI), using the same dilution system and the same sampling conditions. Only small differences were observed in the mass size distributions, total particulate matter (PM), and particulate matter with diameter smaller than 1 um (PM(1)) concentrations and geometric mass mean diameters (GMMD) between these three impactors. Second, the PSTC was compared with the HVCI sampling system, which has been optimal for collection of particulate samples for toxicological and chemical analyses. Differences were observed in the mass size distributions, total PM and PM(1) emissions, and GMMDs, probably due to the different sampling and dilution methods as well as different sampling substrates which affected the behavior of semi-volatile and volatile organic compounds. However, no significant differences were detected in the in vitro measurements of cytotoxicity between the samples collected with the PSTC and the HVCI systems. In measurements of genotoxicity, significant differences between the two sampling systems were seen only with the particles emitted from the sauna stove. In conclusion, due to compact size, PSTC is an applicable method for use in particle sampling as part of the toxicological and chemical characterization of particulate emissions from different combustion sources. It offers some advantages compared to the previously used high-volume sampling methods including compactness for field measurements, simple preparation of sample substrates and high extraction efficiency.     

On s-Reflexive Spaces and Continuous Selections

This paper deals with the s-reflexive spaces introduced by Yang and Zhao. The authors prove that every s-reflexive Hausdorff space is zero-dimensional, and indicate a close relationship between the theory of s-reflexive spaces and that of continuous selections. Several examples relating to s-reflexivity are given.     

Heavy Metal Accumulation in Woodland Moss (Pleurozium Schreberi) in the Area Around a Chromium Opencast Mine at Kemi,and in the Area Around the Ferrochrome and Stainless Steel Works at Tornio,Northern Finland

Abstract

Woodland moss (Pleurozium schreberi) samples were collected at 52 sampling sites around a chromium opencast mine and around a ferrochrome and stainless steels works. The samples were dried, homogenized and digested with a mixture of concentrated nitric and perchloric acids. The Cr, Ni and Zn concentrations in the moss samples were determined by FAAS in order to clarify the aerial distribution of heavy metals from both the opencast chromium mine and the ferrochrome and stainless steel works. This study, carried out in 2000, compares the heavy metal (Cr, Ni, Zn) concentrations in mosses to the results of previous studies in 1995 and in 1990. According to the results, the average Ni concentrations (mean) in mosses have increased since 1990 along with increased Ni emissions from point sources, but the average Cr concentrations (mean) in mosses have increased despite the decrease in Cr emissions from point sources have decreased. The results have been discussed from various point of view, as well as depicted out the low deposition of Zn on mosses.     

Rapid estimation of chemical kinetics by implicit calibration. II

This study continues the development of a method, implicit calibration, for estimating kinetic parameters from on-line measurements of batch reactions. The basic idea of implicit calibration is to combine non-linear parameter estimation with the calibration of measured spectra with concentrations calculated by an assumed kinetic model. A new example is studied, an esterification reaction with a rather complicated kinetic mechanism, where activities, instead of concentrations, and NIR spectra are used as measurements. The emphasis in the study is on estimating the uncertainty of the kinetic parameters. Two approaches, linearization and bootstrap, are applied. In the case studied, the two approaches give closely similar estimates of the uncertainty. As well, a new way is introduced to control the rigidity of the implicit calibration, based on minimizing the lack of fit of the model. It is also shown that ‘mixed implicit calibration’, i.e. implicit calibration combined with a few off-line calibrated concentrations, greatly enhances the identifiability of the kinetic model. Copyright © 2003 John Wiley & Sons, Ltd.