XPS study of carbon in electrochemical reduction products of poly(tetrafluoroethylene)

XPS spectra of reaction products of poly(tetrafluoroethylene) with lithium amalgam were studied. The primary reaction product is a mixture of LiF and elementary carbon in the sp- state in a molar ratio of 2:1. This carbon is very reactive, among others also with respect to air oxidation at room temperature leading to the formation of surface oxides with a well-defined chemical shift of the C 1s photoemission band, which can be attributed to COOH groups. The binding energy of 1s electrons in C atoms of the basic skeleton hidden in LiF is markedly higher than with other known modifications of carbon. The carbonaceous materials formed by the leaching out of LiF with water, or by the removal of LiF by melting, contain, after air oxidation, various types of surface oxides. The binding energy of C 1s photoelectrons in the resulting skeletons is comparable with that of other carbonaceous materials.     

Wärmeübertragung bei der Strömung Newton'scher Flüssigkeiten in Rohren mit SchraubeneinheitenHeat transfer to a Newtonian liquid flowing through a pipe with built-in helical elements

The effect of two types of helical elements built in a cylindrical pipe on the heat transfer intensity in a heated Newtonian liquid was investigated.The results express the dependence of the heat transfer coefficient upon flow conditions and upon physical and geometrical properties of the system examined. The resulting dimensionless equations are given in graphic form. The range of Reynolds and Prandtl numbers investigated was from 90 to 5000 and from 6 to 60, respectively.     

Artificial shortage of surface water: how can water demand management mitigate the scarcity problem?

Water demand management stresses the crucial roles of water user motivations in balancing actual water availability and competing human needs. This paper shows how the absence of such motivations influences artificial water scarcity, even in resource‐abundant countries, and how slight modifications to economic instruments (surface water charges in particular) might solve the problem. Data from the Czech Republic are used to illustrate the rationale behind the artificial scarcity problem and its solution. A model with feedback based on historical surface water abstraction data is built to simulate the impacts of different payment modification scenarios.     

Compositional characteristics and experimental burning of selected Lower Palaeozoic limestones from the Prague Basin (Barrandian area,Czech Republic) suitable for the production of natural hydraulic lime

Bulletin of Engineering Geology and the Environment - Laboratory-scale experimental burning of three facial types of Devonian limestones from the Barrandian area (Czech Republic) revealed their...     

Impacts of Climate Variables on Residential Water Consumption in the Czech Republic

The paper investigates whether there is a statistically significant impact of short-term climate variables (specifically air temperature and rainfall) on residential water consumption at two selected case sites in the Czech Republic. The analysis is based on a unique time series of daily data from 2004–2009. The statistical methods used are CART methodology and a decomposition of these time series based on a locally weighted regression method. Apart from the data analysis results, the investigation raises several methodological questions regarding the use of daily data and the scope of analysis based on such data sets.     

The potentiometric behaviour of copolymers of methacrylic acid in water-ethanol solutions

Summary The synthesis is reported of copolymers of styrene with methacrylic acid and of methyl methacrylate with methacrylic acid by radical copolymerization, of copolymers of methyl methacrylate with methacrylic acid by partial alkaline hydrolysis of poly(methyl methacrylate), and of block copolymers of styrene with methacrylic acid. Modified titration curves of all these copolymers were recorded in water and water-ethanol solutions. In a solution containing 50 mass.% ethanol, only small differences could be observed between the potentiometric behaviour of the individual copolymers and polymethacrylic acid. Also, there were no essential differences in any of the solvents used between the potentiometric behaviour of block copolymers of styrene with methacrylic acid, on the one hand, and polymethacrylic acid, on the other. On the contrary, maxima and minima were always observed on the modified titration curves of statistical copolymers with a higher content of the hydrophobic comonomer in solutions with a high water content. Thus, using the modified titration curves, it is possible to decide whether a given copolymer is of the block or statistical type.     

Simple and economic syntheses of some (Z)-7- and (Z)-9-alkenyl acetates,and of (E,Z)-7,9-dodecadien-1-yl acetate,the sex pheromone of the European grapevine moth,using aleuritic acid as a common starting material

Short syntheses of (Z)-7-dodecen-1-yl acetate, (Z)-7-tetradecen-1-yl acetate, (Z)-9-dodecen-1-yl acetate, and (Z)-9-tetradecen-1-yl acetate from 7-hydroxyheptanal and 9-oxononanoic acid precursors obtained by oxidative cleavage of easily available aleuritic acid are reported. The key step in these syntheses is a stereoselective Wittig reaction between aldehyde and alkyl-phosphonium salt. Wittig-Horner type reaction of 7-hydroxyheptanal and diethyl cyanomethylphosphonate gave the ,-unsaturated nitrile derivative which after protection of the hydroxyl group was reduced to the corresponding aldehyde. Wittig reaction of the latter, followed by acetylation, completed the synthesis of (E,Z)-7,9-dodecadien-1-yl acetate, the sex pheromone of the European grapevine mothLobesia botrana Schiff.     

Automated Sequential Injection Method for Determination of Caffeine in Coffee Drinks

An automated sequential injection analysis spectrophotometric assay for the determination of purine alkaloids in coffee drinks was developed. The sample was treated with a carrez reagent for matrix suppression followed by filtration; subsequently, alkaloids were separated from organic acids using a short C18 monolithic column (10 × 4.6 mm). The flow rate of the separation step was 10 μL s^?1 with 10% v/v of methanol as the mobile phase. The sum of alkaloids evaluated as caffeine was detected at 274 nm. The influence of the main parameters affecting the quantification of purine alkaloids was optimized. One sample analysis lasted 15 min when aspirated in triplicate. The linear range was 1–15 mg L^?1, and the determination coefficient (r ²) was 0.9969. The limit of detection and limit of quantitation were 0.128 and 0.425 mg L^?1, respectively. The repeatability evaluated as the relative standard deviation (RSD) was 3.58% (n = 12, 10 mg L^?1). Under optimal conditions, the method was successfully applied to determine purine alkaloids in different real samples including soluble coffee, coffee from an espresso machine, and brewed coffee drinks.     

Cell adhesion on modified polyethylene

Polyethylene (PE) was irradiated with 10 and 63 keV Ar⁺ ions to fluences of 1 × 10¹⁷ to 3 × 10¹⁹ m^–2 and then it was grafted with aminoacid (alanine). The changes of surface polarity, electrical conductivity, and oxygen concentration were examined on pristine, as-irradiated, and irradiated-grafted PE. The in vitro adhesion of mice fibroblasts on the modified PE was evaluated 24 hours after inoculation. It was proved that for the PE irradiated at 10 keV ion energy, the presence of chemically bound alanine increases cell adhesion and its homogenity. For PE irradiated with 63 keV ions, however, the alanine grafting leads to a reduction of the number of adhering cells. It was found that a rising surface polarity increases cell adhesion, but when its value is too high the cell adhesion starts to decrease. No correlation between electrical conductivity and cell adhesion was observed. In general, higher cell adhesion is observed on modified PE in comparison with pristine one.