An interpretation of the changes in demographic behaviour at a sub-national level using spatial measures in post-socialist countries: A case study of the Czech Republic and Slovakia

The transformation of fertility and family behaviour in post-socialist countries was quick and the changes were striking. An account of the changes is the subject of dispute and the mechanisms have still not been explained in a fully satisfying manner. Relatively little attention has been paid to the changes in spatial aspects concerning the broadening of changes in family behaviour. The aim of this paper is to answer the question as to whether changes spread stochastically in post-socialist countries or if there are obvious spatial patterns. The study tries to answer the questions whether there are any cores of changes which may be understood as innovations, if there is any spatial clustering and if the extent is hierarchically arranged.     

Computer-access security systems using keystroke dynamics

An approach to securing access to computer systems is described. By performing real-time measurements of the time durations between the keystrokes when a password is entered and using pattern-recognition algorithms, three online recognition systems were devised and tested. Two types of passwords were considered: phrases and individual names. A fixed phrase was used in the identification system. Individual names were used as a password in the verification system and in the overall recognition system. All three systems were tested and evaluated. The identification system used 10 volunteers and gave an indecision error of 1.2%. The verification system used 26 volunteers and gave an error of 8.1% in rejecting valid users and an error of 2.8% in accepting invalid users. The overall recognition system used 32 volunteers and gave an error of 3.1% in rejecting valid users and an error of 0.5% in accepting invalid users     

Membranes based on poly(styrene-N-phenylmaleimide)/poly(2,6-dimethyl-1,4-phenylene oxide) blends

Blend membranes were prepared by casting chloroform solutions of mixtures of styrene-N-phenylmaleimide copolymer containing ca. 10 mol % imide units with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), and their phase behavior was evaluated. At a content of 20% PPO, the membranes were homogeneous; those having 40 or more % PPO exhibited phase separation. Membranes made of the parent polymers and their blends were tested in the pervaporation of aqueous ethanol solutions; permeabilities to oxygen, nitrogen, and carbon dioxide were also determined. The pervaporation characteristics and gas transport properties are discussed considering the interactions of polymer chains and the phase structure of the membranes. © 1995 John Wiley & Sons, Inc.     

Estimation of thermodynamic quality of the solvent from the concentration effect in gel permeation chromatography of polymers

Dependences of the elution volume, V_e, on the concentration of the injected polystyrene (PS), c, in gel chromatography with inorganic carriers were studied in various single and binary eluents. It was found that the dependence of V_e on c is approximately linear in the region of low concentrations and its slope depends on the thermodynamic quality of the eluent. This relationship is more pronounced for higher molecular weights. Correlation for the slope k with the limiting viscosity numbers [η] proposed earlier in the literature is not valid for thermodynamically poor eluents; however, a correlation was found for all the eluents employed between k and the product A₂M, where A₂ is the second virial coefficient of polymer in solution. This supports the interpretation of the concentration effect in gel chromatography of polymers as a consequence of the decreasing effective hydrodynamic volume of coils with increasing concentration. The link between the empirically found correlation of k with A₂M and the existing theory of the concentration effect in g.p.c. was examined. Comparison of the virial coefficients determined from the slope k for PS in various eluents with the literature data showed that gel chromatography could yield a rapid estimate of the value A₂. As has been shown by an analysis of the concentration effect on the distribution coefficient K the concentration effect leads to the formation of a non-linear isotherm and to the asymmetrical peak shapes. In the range of very low concentrations, deviations from the linear dependence of V_e on c can be expected as a result of both the sorption effect and the thermodynamic partition of the solute.     

Contribution of adsorption and partition to the separation mechanism in gel chromatography on inorganic carriers

Gel permeation chromatography (GPC) calibration curves log hydrodynamic volume versus elution volumes were obtained from a series of single and mixed eluents for polystyrene on inorganic carriers. The observed calibration shifts were interpreted as a result of adsorption and partition effects on elution volume V_e. Secondary contributions to the separation mechanism can be qualitatively described by means of thermodynamic relations from liquid adsorption (LSC) and liquid partition (LLC) chromatography using the solubility parameters of the eluents. The universal calibration procedure based on the hydrodynamic volume of the coils is directly applicable only for systems in which adsorption and partition is approximately the same.     

Reactive polymers,XXXVII. An investigation of the internal structure of polymeric sorbents based on poly(2,3-epoxypropyl methacrylate-co-ethylene dimethacrylate)

The internal structure of polymeric sorbents based on 2,3-epoxypropyl methacrylateethylene dimethacrylate was investigated by means of mercury porosimetry and by employing the sorption method. The results were confronted with characteristic chromatographic data and helped to elucidate the relationships existing between the internal structure of copolymers and their chromatographic properties.     

Chitosan–Oligo(silsesquioxane) Blend Membranes: Preparation, Morphology, and Diffusion Permeability

Preparation of the blend chitosan (CHI) membranes containing polyhedral oligomeric silsesquioxane (POSS) derivatives was investigated. POSS derivatives such as (3-aminopropyl)isobutyl-POSS (amino-POSS), [2-(3,4-epoxycyclohexyl)ethyl]isobutyl-POSS (epoxy-POSS), and octa(tetramethylammonium)-POSS were used. The blend CHI–amino-POSS membranes were predicted to be the most porous due to having the weakest interactions between the components in the blends. The CHI–epoxy-POSS blend membranes were assumed to be more dense owing to chemical binding of the chitosan amino groups with the epoxy groups of POSS. Studies of membrane morphology and diffusion permeability support these predictions.     

A real-time optical image projection system for electron microscopy

The Hughes liquid crystal light valve has been coupled to a transmission electron microscope using a fibre optics plate and transmission phosphor. This system makes it possible to reconstruct in real time, electron images in coherent or incoherent light of arbitrary intensity outside the vacuum. The experimental results reported are used to estimate the design parameters of an on-line coherent optical diffractometer for high resolution work.     

Polymers with reactive p-phenylene diamine groups

Suspension copolymers of N-ethyl-N-(2-methacroylethyl)-p-phenylenediamine (AMBD) and 2-hydroxyethyl-methacrylate (HEMA) were prepared and the copolymerization conditions were determined. The reactive copolymers contain a theoretical number of reactive groups capable of reacting with low-moleculare weight compounds. A change in the porous character of the copolymer has no influence on its reactivity.