Showing papers by "Academy of Sciences of the Czech Republic published in 1987"

Synthesis of 9-(2-Phosphinomethoxyethyl)adenine and Related Compounds

Abstract: Alkyl 2-chloroethoxymethyl(diethoxymethyl)phosphinates VII and XIII were prepared by reaction of silyl esters of dialkoxymethylphosphinic acid with 2-chloroethyl chloromethyl ether. Adenine was alkylated with VII and XIII to give [2-(adenin-9-yl)ethoxy]methyl(diethoxymethyl)phosphinates VIII and XIV , bearing the dialkoxymethyl protecting group on the phosphorus atom. Acid hydrolysis of compounds VIII and XIV afforded 9-(2-phosphinoethoxymethyl)adenine ( X ). Alkyl dialkoxymethylphosphinates V and XI reacted with paraformaldehyde to give hydroxymethylphosphinates XV and XIX which were converted into the synthons XVI , XVII and XVIII capable of introducing a protected hydroxymethylphosphino group on a hydroxy or amino group.

Isothermal DSC method for evaluation of the kinetics of crystallization in the Ge-Sb-S glassy system

Abstract: The isothermal DSC method was used to study the crystallization kinetics of Sb2S3 in glassy (GeS2)03(Sb2S3)07 The effective activation energy of crystallization (Ea/n) was evaluated from the DSC curves using the Johnson-Mehl-Avrami transition equation

Immunocytochemical localization of RNA polymerase I in the fibrillar centers of nucleoli

Abstract: For an understanding of the functional organization of the nucleolus identification of the site of the expression of the rRNA genes is of considerable importance. Although various stages of preribosome formation have been mapped to morphologically distinct components of the nucleolus (Hadjiolov, 1985), the intranucleolar location of transcriptionally active rRNA genes has remained uncertain. From high resolution autoradiographic studies, following pulse labelling of cells with radioactive RNA precursors, it was suggested that transcription of rRNA genes takes place in the “dense fibrillar component”, and possibly also at the periphery of the “fibrillar centers” (Fakan, 1978; Thiry et al., 1985). However, using other techniques such as autoradiography with tritiated thymidine or actinomycin D, in situ-hybridization with radioactive rRNA probes and selective DNA-staining with the osmium-amine Feulgen-like reaction, DNA (including rDNA) could be detected only in the fibrillar centers (for reviews see Hernandez-Verdun, 1983; Goessens, 1984). To reconcile these seemingly contrasting results it was proposed that the fibrillar centers contain inactive rDNA in a relatively high packing density, thereby facilitating its detection, whereas the transcribed rRNA genes loop out into the surrounding dense fibrillar component (Stahl, 1982; Goessens, 1984). According to this concept the dense fibrillar component is formed by the superposition of rRNA-transcription units and newly formed rRNP material.

Unusual solutions to the Yang-Baxter equation

Abstract: The complete list of non-symmetric eight-vertex constant solutions to the Yang-Baxter equation is obtained and new solutions dependent on more than one variable are presented. The corresponding spin Hamiltonians are derived by Sutherland's method (1970).

Viscoelastic behaviour of model polyurethane networks in the main transition zone

Abstract: Starlike poly (oxypropylene) molecules (M=2630 resp. 710 g/mol), each with three OH-end-groups, are crosslinked with 4,4′-diphenylmethane diisocyanate in one stoichiometric and several nonstoichiometric reactions. Dynamic mechanical (frequency 10−4 to 102 Hz) and also some dielectric (10−2 to 106 Hz) measurements were made on these networks in a wide temperature range. The time-temperature-superposition principle was used to obtain master curves. Two large relaxation processes were detected (separated by many decades of frequency in some samples). The high frequency process seems to correspond to the glass-rubber transition in linear polymers, the low frequency process is probably due to the relaxation of “dangling chains”.

Characterization of hydrodynamic regimes in horizontal two-phase flow: Part II: Analysis of wall pressure fluctuations

Abstract: The results of a statistical analysis of wall pressure fluctuations in horizontal air-water flow are given. The effect of instrument geometry on the basic characteristics of pressure fluctuations is illustrated. Several flow regime detectors are suggested based on both the amplitude and frequency domains and the results obtained are compared with previously proposed flow regime maps.

The minipig as a model in gnotobiology.

Abstract: Due to its close physiological and morphological resemblance to man, the pig occupies an important position in biomedical research. The minipig lends itself particularly well to germfree research. It is easy to deliver, maintain, and utilize in isolators. The colostrum-free, newborn germfree piglet lacking passively obtained antibodies is of an exclusive use if distinguishing the factors of natural and adaptive immunity is needed. It fits also well in studies investigating the earliest mechanisms of antibody synthesis. Under germfree conditions, the pig has been proved an excellent model for testing the action of ionizing radiation as well as of selected bacterial strains when monoassociated. Recently, conventional pigs have been used also for studies in total or selective decontamination of the intestinal tract by antibiotics and strict isolation.

Aluminium distribution in the bulk and on the surface of Y zeolites dealuminated with SiCl4 vapour. Influence of conditions of dealumination

Abstract: Zeolites Y, dealuminated by reaction with SiCl4 at 530 and 630 K followed by washing with water, ethanol or ethanol and buffer before ammonium exchange (resulting Si/Al ratio: 3.8–10.6), have been examined using X-ray photoelectron spectroscopic measurements combined with chemical analysis. Subsequent extraction with H2Na2 EDTA allowed preferential removal of non-framework Al species which helped in the discussion of the Al location. It was found that, besides the increase of reaction temperature, the efficiency of washing (water > ethanol > ethanol and buffer) increases the Si/Al ratio both in the bulk and on the surface. Temperature increase and milder washing enhance the Al-enrichment of the surface with respect to the bulk. Non-framework Al species are responsible for the surface enrichment.

The geochemistry of mafic metavolcanics: implications for the origin of the Devonian massive sulfide deposits at Zlaté Hory, Czechoslovakia

Abstract: Mafic metavolcanic rocks in the area of the Zlate Hory massive sulfide deposits are interpreted as convergent plate-margin basalts and basaltic andesites metamorphosed to the greenschist facies. According to the major- and trace-element compositions the metabasites exhibit island-arc tholeiitic to low-K, calc-alkaline composition. Approximately 50% of samples of maifc metavolcanics studied have a salient negative anomaly of Ce in chondrite-normalized REE patterns. The Ce-depleted greenschists are thought to represent hydrothermally altered equivalents of metabasites of island-arc tholeiitic composition. The alteration was accompanied by the sulfide mineralization. That is indicated by enrichment in Ba and S together with correlation of the Ce/Ce* values and CO2 abundances in the Ce-depleted rocks. The Ce anomaly may be caused by alteraton of ore-forming, seawaterderived solutions. The occurrence of Ce-depleted greenschists supports the hypothesis of the volcanogenic origin of the ore deposits in the Zlate Hory area.

Field application of Nosema lymantriae against the gypsy moth, Lymantria dispar L.

Abstract: Nosema lymantriae (Protozoa, Microsporidia) was used in an experimental plot in oak grove for control of Lymantria dispar, with dosage 107 spores/m2 mainly on L3 in a density of 153 larvae/1000 leaves. Reductions of different instars reached 37.15% of larvae, 33.20% of pupae and 6.72% of emerging adults. The infection did not interfere with development of parasites (Tachinidae mainly), in contrary, the increasing immobilization of infected animals increased the attacks of parasites and predators. Including the number of hatching eggs in the next generation, the population was reduced by the infection to 1/10 of the control. Zusammenfassung Freilandversuche zum Einsatz von Nosema lymantriae gegen den Schwammspinner, Lymantria dispar L. Die Mikrosporidie Nosema lymantriae (Protozoa, Microsporidia) wurde auf einer Versuchsflache in einem Eichenbestand zur Bekampfung des Schwammspinners getestet. L3-Raupen wurden bei einer Besatzdichte von 153 Tieren/1000 Blattern mit einer Dosis von 107Keimen/m2 (in wassriger Suspension) behandelt. Die Reduktion der einzelnen Entwicklungsstadien erreichte bei den Raupen 37,15%, bei den Puppen 33,20% und bei den schlupfenden Faltern 6,72%. Die Erkrankung beeintrachtigte die Entwicklung von Tachinen nicht; im Gegenteil, die steigende Immobilitat befallener Tiere erleichterte die Angriffe der Parasiten und Pradatoren. Unter Berucksichtigung der Anzahl schlupfender Eier in der folgenden Generation, wurde durch die Mikrosporidien-Infektion eine Reduktion von 10% im Vergleich zur unbehandelten Kontrollpopulation bewirkt.

The Response of the Lower Ionosphere in Central and Southern Europe to Anomalous Stratospheric Conditions

Abstract: The analysis of measurements of stratospheric wind and radio wave absorption in lower ionosphere in Central Europe and southern Spain shows that the apparent difference between the response of the lower ionosphere in Central (decrease of absorption) and Southern (increase of absorption) Europe to well-developed stratospheric warmings is essentially caused by the different response of the neutral middle atmosphere (Stratosphere) to stratwarms. The periods of dominant meridional wind (much less frequent in Central Europe) are accompanied by enhanced absorption of radio waves. A decrease of absorption (weakening or break-down of the winter anomaly) appears to be observed near or after the strong stratwarm maximum in both regions.

The use of gnotobiological models for the studies of immune mechanisms.

Abstract: Germfree (GF) animals are widely used for discrimination of natural mechanisms (genetically determined) from adaptive mechanisms of immunity induced by external antigens. GF rats fed at least for first 5 days after birth with arteficial diet LNa, deficient in unsaturated fatty acids, were — in contrast to those fed with K 50 diet — deeply suppressed in humoral and cellular immune reactivities during their live. GF piglets, deprived from maternal colostrum (CF) as a source of passively transferred maternal antibody, immunized with preformed Ag/Ab complexes (HSA — anti HSA) responded according to the composition of complexes (Ab excess, equivalence, Ag excess) by low or high dose tolerance or by secondary response. Similar pictures of response were obtained in groups of presensitized GF-CF piglets by immunization with different doses of antigen. It is concluded that 3 different types of response are the result of Ag/Ab complexes acting or formed on the lymphocyte membrane and exerting stimulatory or down-regulatory signals.

Spontaneous polarization of helicoidal ferroelectric smectic C* liquid crystals

Abstract: Measurements of the spontaneous polarization of DOBAMBC in helicoidal smectic C* phase is presented. It is shown that the polarization shows an anomalous temperature dependence characterized by one square root behaviour close to Tc and by another one far from Tc. This behaviour is explained theoretically to be a consequence of a nonchiral biquadratic coupling between the polarization and the tilt of molecules in the Landau expansion of the free-energy density. Also the tilt is predicted to exhibit a (less pronounced) crossover region of the same type as the polarization within the proposed model. It is also noted that this crossover region coincides with the temperature interval where the pitch of the helix displays anomalous properties.

Magnetic properties of ErIG and approximation of isotropic exchange

Abstract: A one-ion model calculation which considers the Er3+ ion subject to the crystal field, the isotropic exchange field and the applied magnetic field is compared with the following experimental data: the easy axis direction, the transition temperature, the temperature and field dependence of the magnetization, the compensation temperature, the magnetocrystalline anisotropy and the umbrella structure of Er3+ magnetic moments in ErIG. The crystal field parameters in Y(Er)GG and ErGG are discussed and determined first. The same parameters are used for ErIG, only those of second order are allowed to vary. In spite of the isotropic exchange approximation, the experiments (except the controversial umbrella structure and anisotropy data) are well reproduced within the framework of this model. Further improvements are expected by inclusion of the anisotropy of the exchange interaction.

A simple induction anisometer

Abstract: Magnetic anisotropy of rotationally symmetric samples is measured by a simple induction method based on transverse susceptibility measurements. The sample is magnetically saturated by a d.c. field perpendicular to the axis of rotation. A small a.c. field is applied in the direction perpendicular to both the d.c. field and the axis of rotation. The transverse a.c. susceptibility is measured by a Hartshorn bridge of mutual inductance. From the transverse susceptibilities along different directions the anisotropy constants as well as the saturation magnetization can be determined.

Domain wall motion in magnetically soft metallic glasses

Abstract: The magnetic domains on the surface of amorphous alloys of the composition Fe40Ni40B20 and Fe50Ni30B20 were observed by means of the scanning electron microscope. The details of the experimental arrangement are described that enhance the s.c. type II magnetic contrast and enable us to apply a static magnetic field in the plane of the sample. The displacement of the domain walls under the influence of the applied field were measured and are discussed.

On the transferred hyperfine interaction in substituted yig

Abstract: NMR of57Fe is studied in a number of (MxY3−x) Fe5O12 garnets for small concentrations of M (M is either trivalent RE ion −Ho 3+, Gd 3+, Nd3+, Pr 3+, La 3+ or Bi 3+ ion). Beside the main resonance lines, the satellites were observed, which correspond to those Fe, in vicinity of which the impurity M is located. After correcting for the dipolar field, the field corresponding to the change of the transferred hyperfine interaction in M3+−O2−-Fe3+ vs. Y3+−O2−-Fe3+ triad was deduced from the satellites splitting. The analysis of the results indicates that the observed change in the transferred hyperfine field is mainly connected with the transfer of electrons between M3+ and Fe3+ ions and not with the local deformation around the impurity.

Characterization of hydrodynamic regimes in horizontal two-phase flow Part I: Pressure drop measurements

Abstract: A detailed flow pattern map for horizontal air—water flow was constructed using the results from pressure drop measurements in a Perspex pipe having an inside diameter of 0.05 m and a length of 5.08 m. Visual observations of flow patterns were supplemented by electrical conductivity measurements. A simple empirical pressure drop correlation is proposed which can be used in horizontal air—water flow.

Mn 3d states in photoelectron spectra from Cd1−xMnxTe

Abstract: A parametrized tight-binding model is used to describe the electronic structure of semimagnetic Cd1–xMnxTe. The density of states and the spectral density are calculated by using the coherent potential approximation. The features connected with the presence of the Mn 3d states are identified and the controversial results of angle-resolved and integrated photoemission from Cd1–xMnxTe are then explained. Mit einem parametrisierten tight-binding-Modell wird die Elektronenstruktur von semimagnetischem Cd1–xMnxTe beschrieben. Die Berechnung der Zustands- und Spektraldichte erfolgt mit Hilfe der Methode des koharenten Potentials (CPA). Die mit der Anwesenheit von Mn 3d-Zustanden verbundenen Merkmale werden identifiziert und die einander wiedersprechenden Resultate von winkelaufgelosten und integrierten Photoemissionsspektren von Cd1–xMnxTe erklart.

FMR Modes of the Bubble Domain Lattice in Garnet Films Magnetized along the Normal

Abstract: Ferromagnetic resonance experiments on films of YIG doped with Bi and varied Ga contents show three domain resonance modes in a wide range of dc fields applied normal to the film plane. A theoretical analysis is given based on the coupling of three elementary modes of hf magnetization (uniform modes in the bubbles and matrix and a non-uniform mode in the matrix which is driven by hf stray fields, in agreement with recent numerical model solutions). The results indicate principal agreement between theory and experiment (including the previous measurements where only two of the three modes are reported). Experimentelle Untersuchungen der ferromagnetischen Resonanz in Schichten von YIG mit Bi-und verschiedenem Ga-Zusatz zeigen drei Domanenresonanzmoden in einem breiten Bereich von Feldstarken im statischen Magnetfeld in der Richtung der Schichtnormale. Die theoretische Analyse berucksichtigt die Kopplung von drei elementaren Magnetisierungsmoden (homogene Moden in den Zylinderdomanen und der Matrix, und eine inhomogene Mode in der Matrix, die durch das Hochfrequenzstreufeld angeregt wird, im Einklang mit neueren numerischen Modellosungen). Die Ergebnisse zeigen prinzipielle Ubereinstimmung zwischen Theorie und Experiment (einschlieslich vorhergehender Messungen, wo nur uber zwei der drei Moden berichtet wurde).

The study of impurity levels in LEC semi-insulating GaAs:Cr samples by two-source photoconductivity measurements

Abstract: Spectral photoconductivity curves of SI GaAs:Cr crystals are measured in the extrinsic region using the two light sources method; high intensity monochromatic illumination ensures steady-state population of levels; and probe light of low intensity serves to measure corresponding photoconductivity curves. The set of obtained curves is decomposed into elementary contributions using the minimization program MINUIT. The obtained photoionization cross-sections are compared with those from absorption measurements and interpreted as transitions involving Cr2+, Cr3+, and Cr4+ ions. The influence of interaction among impurities and of internal electric field on the photoionization cross-section is discussed. [Russian Text Ignored].

On the magnetization curves of bubble lattices

Abstract: The paper presents magnetization curves of bubble lattices in garnet samples of composition (YSmLuCa)3(FeGe)5O12, in which we observed a discontinuity in the magnetization at a certain negative value of the external magnetic field applied normal to the sample surface. This points to an anomaly in the behaviour of the existing honeycomb domain structure. The proposed theoretical interpretation of this behaviour is based on the interaction of closely spaced pairs of Bloch walls.