Showing papers by "Academy of Sciences of the Czech Republic published in 1968"

The preparation of thin layers of Ge and Si by chemical hydrogen plasma transport

Abstract: It has been proved that the transport of Ge and Si in hydrogen plasma takes place under certain conditions. The transport is probably carried on by volatile hydrides of Ge and Si which are formed during the interaction of hydrogen plasma and the respective semiconductor. The semiconductor layers prepared by this method are compact and well adhesive to the substrate. When deposited on glass they had a polycrystalline structure.

Transition in swollen polymer networks induced by intramolecular condensation

Abstract: It is predicted that the net repulsion between the segments of a polymer network and a poor solvent can cause a phase transition marked by a sudden change in the degree of swelling. This is analogous to the “coil–globule” transition recently predicted by Ptitsyn to occur for a macromolecule in solution. The critical conditions for the transition. as well as phase diagrams, are calculated for the gel in free swelling and under uniaxial tension, which facilitates the transition. The transition depends on the gel being formed of chains crosslinked while greatly swollen by a diluent and also having a high degree of crosslinking. It is concluded that it would be difficult to attain the conditions necessary for the transition in the free-swelling case, but that it should be possible for gel under tension.

Studies on the conformation of protonated DNA.

Abstract: Experiments were made to demonstrate the predominant protonation effects and structural changes of the ordered double helical DNA structure and denatured state of DNA. Spectrophotometric titrations performed at different wavelengths indicate that cytosine can be protonated in the DNA double helical molecule to a high extent without breakdown of the secondary structure. With DNA heat-denatured under severe conditions the protonation of cytosine can be measured at 280, 295, and 300 mμ: the apparent pK value obtained was ∼4.6. The protonated double helical conformation of the DNA molecule differs from the unprotonated state, which follows from the decrease of the thermal stability and from changes in the ORD curves. The ORD of a GC-rich DNA indicates a novel Cotton effect with positive rotations at ∼260 mμ in 0.02M KCl below pH 4.0 to pH 3.3. The occurrence of the new peak parallels the extent of protonated cytosine measured by the spectrophotometric titrations. It is concluded that the protonated cytosine in the double helical structure is responsible for the difference between the protonated DNA conformation and the native state at neutral pH.

Preparation of solid solutions of deuterated triglycine sulphate and concentration dependence of some of their ferroelectric properties

Abstract: A number of ferroelectric solid solutions (N[H, D]2CH2COO[H, D])3[H, D]2SO4 have been prepared in the concentration range of the initial components of 0 to 94·2%. Moreover, the parameters of the Curie-Weiss law have been measured as a function of the concentration of the initial components. The course of the phase transition position and of the Curie constant as a function of the concentration is discussed by means of Janovec's thermodynamic theory of ferroelectric solid solutions. Mixed crystals cannot be classified as perfect solid solutions, but their behaviour may be expressed by regular approximation.

Dislocations in an inhomogeneous anisotropic medium

Abstract: The general expressions for the stress field of a dislocation situated near a welded, slipping and free boundary are derived employing the method of Fourier transformations. As an example the stress field of a screw dislocation near a simple type of welded boundary is explicitly given.

Cannibalism and Predation by Aphids

Abstract: APHIDS are usually regarded as feeding exclusively on plant sap which they ingest through stylet-like mouth parts, but they have occasionally been seen to feed on animal food. During feeding on a turgid plant, they do not have to suck but depend chiefly on the pressure of the sap for ingestion. They can, however, suck through artificial membranes on food that is under negligible pressure. This communication collates records of cannibalism and predation among aphids.

Study on a new soft denture liner of the Sofdent type.

Abstract: It has been shown that the admixture of diacetins in the capacity of a diluent in the polymerization of hydrophilic poly(ethyleneglycol methacrylate) gels improves the properties of products used as soft denture liners, especially by inhibiting the volume changes caused by swelling, and by improving the mechanical properties of gels as well as the strength of bond between the gel and the basic material of the prosthesis.

Defect structure of hydrogen-reduced BaTiO3 with additions of Fe, Co and Ni

Abstract: A discussion is presented of the possibilities of trapping an electron set free by hydrogen reduction in BaTiO3 crystals without and with additions of Fe, Co and Ni It is proved with the aid of the absorption spectra of reduced BaTiO3 measured in the visible region, and of a theoretical calculation of the energy gain accompanying electron trapping that the preferred reduction is that of Fe, Co and Ni ions to divalent ones The minimum hydrogen reduction temperature at which a band at 2·5 to 4 μ is initiated, belonging — as our results indicate — to Ti3+ in a certain configuration of the defect oxygen octahedron, was calculated from chemical analysis data of BaTiO3 monocrystals and also verified experimentally

Static Volumetric Methods for Determination of Absorbed Amount of Gases on Clean Solid Surfaces

Abstract: The amount of gas adsorbed on the surface of solids is one of the fundamental data of adsorption studies. The amount adsorbed can be determined either from pressure changes within a certain constant volume–volumetric determination–or more directly from the change of weight of a solid substance (adsorbent)–weight determination–in a static or flow apparatus.

Heat flow in the Upper Silesian coal basin

Abstract: The paper presents results of heat flow measurements made in 6 deep bores in the Czechoslovakian part of the Upper Silesian coal basin. The heat flow measured was in the range from 1.74 to 1.87 μcal/cm2s. The undisturbed period before the temperature measurement in the bore is discussed and results of repeated temperature measurements carried out 0.1, 1,5 and 36 days after cessation of drilling in one of the bores NP-522, are also given. Although the temperature in the bore still differs considerably from equilibrium, it is possible to determine the temperature gradient with an accuracy better than 5% as soon as 5 days after drilling was finished.

Cyclo- and Cyclized Diene Polymers. XVIII. Microstructure and Mechanism of Cyclopolymerization of Isoprene and Butadiene with C2H5AlCl2 + TiCl4 Catalyst

Abstract: The polymerization of isoprene and butadiene with an ethylaluminum dichloride-titanum tetrachloride catalyst system yields ladder polymers containing fused cyclic structures. Cyclopolymers prepared in n-heptane are generally insoluble powders, while cyclopolymers prepared in aromatic solvents are soluble even when the molecular weight exceeds 1 × 106. In cyclopolyisoprene two phenyl groups are incorporated into the polymer structure per 100 monomer units, independent of molecular weight from 1 × 104 to 2 × 106, while cyclopolybutadiene contains as many as 7–9 phenyl groups per 100 monomer units. The cyclopolymers contain residual unsaturation, 10–40% of which is cycloalkenyl, and methyl groups. Indirect evidence indicates that cyclopolyisoprene may have a perhydrophenanthrene structure. The proposed polymerization mechanism involves cation-radical initiation and propagation. An activated monomer cation radical results from a one-electron transfer from monomer to an electron acceptor species produ...

The influence of neutral gas temperature on the parameters of ionization waves in neon

Abstract: In the present paper, the influence of cooling down the neutral gas to a temperature of 77°K on the parameters of ionization waves excited in the positive column of a d. c. glow discharge in neon is studied. After the cooling, the group velocity, phase velocity, frequency and relaxation time of the waves of varietyp decreased and they increased in case of varietiesr ands. The results of measurements were compared to the lifetime of metastable atoms in the case of thep-wave, and to that of atomic ions in the case of ther-wave. The variations of lifetime with temperature correspond to the variations of relaxation times of the waves; the lifetime of metastable atoms is 5 to 7 times longer, the lifetime of atomic ions agrees with the relaxation time fairly well.

Synthetic analogues of oxytocin: an approach to problems of hormone action

Abstract: Synthetic organic chemistry has in recent years become a recognized participant in the study of hormone action. Although the synthetic approach is capable of yielding copious information about the relation between chemical structure and biological activity and thereby, in principle, it can aid in exploring the molecular basis of hormone action, the results obtained by this approach are by no means unambiguous. For one thing, the great conformational flexibility of peptide chains makes it difficult to estimate the overall effect of a change in chemical structure on the topochemistry of the molecule in that conformation which it adopts in its interaction with a particular receptor site. Furthermore, the complexity of biological systems capable of showing a response to the hormones or their analogues is such that this response cannot, as yet, be confidently interpreted in terms of molecular interactions. A generalized scheme of hormonal regulation in the intact organism is shown in figure 5; an exogenously introduced hormonal peptide will bypass the stages of biosynthesis and release (though it might conceivably operate feedback mechanisms where these exist), but its behaviour in each subsequent stage of the system will be affected by its chemical and physical properties. Any change in the structure of the peptide is therefore likely to modify its interactions at several or all of these stages and the change in overt response will represent the complex results of these modified interactions. To some extent the effect on the individual stages can be distinguished by working with biological preparations of varying complexity, from the whole organism to isolated tissues; but even the simplest tissue preparations are still biochemically very complicated systems in which the receptor molecules have yet to be identified. On the other hand, any stage of the whole process of hormonal regulation is a fair target for attempts to achieve modified biological properties by structural variations, and this paper will be concerned with illustrating these possibilities, using examples from our work on neurohypophysial hormone analogues. Quite early in this work it was found that modification of the isoleucine sidechain (figure 6a) in sequence position 3 of oxytocin led to a considerable decrease of the uterotonic activity in vitro (as of most other biological effects). The shape of the dose-response relations, which were parallel to those for oxytocin over a range of conditions, indicated that it was the 'affinity' for the receptor which was reduced. A comparison of the side-chain structures in this series of analogues showed that this decrease in binding to the receptors could not be explained merely by steric hindrance due to additional or 'misplaced' groups (as, for example, in the