Showing papers by "Academy of Sciences of the Czech Republic published in 1986"

Television observations of comet Halley from Vega spacecraft

Abstract: The television system (TVS) aboard the spacecraft Vega 1 and Vega 2 observed comet Halley from 4 to 11 March 1986, and transmitted ∼1,500 images to Earth. The best images of the cometary nucleus were obtained from distances of 8,000–9,000 km. The nucleus is an irregular potato-shaped body, ∼14 × 7.5 × 7.5 km in size, which rotates with a period of 53±3 h. The surface is rather dark; the measured albedo is ∼0.04−0.01+0.02. Active emission of matter was observed on the sunlit side of the nucleus.

Propagation of light in Rb2ZnCl4-type crystals with incommensurate modulation

Abstract: Wave equation for optical waves in the incommensurate phase of Rb2ZnCl4-type crystals is solved taking into account spatial dependence of optical permittivities due to incommensurate modulation of the lattice. Using the procedure originally proposed by Golovko and Levanyuk it is shown that for the wave vectors parallel to the orthorhombic axes: a) the waves are not purely transverse, b) their amplitudes are spatially modulated and c) their velocities are changed so that corrections to refractive indices exist due to permittivity modulation. Data on birefringence of Rb2ZnCl4 are analysed and it is shown that these corrections are responsible for the jump-like changes of refractive indices at the incommensurate-ferroelectric phase transition, together with the quasi-discontinuous change of the order parameter modulus. The spatial variance of the wave amplitudes may be responsible for the possibility of SHG in the incommensurate phase whose averaged point group is centrosymmetric.

The effect of liquid silicone on the corneal endothelium in rabbits. A comparative specular microscopic and histopathologic study.

Abstract: Specular microscopic and histopathologic findings in the corneal endothelium were compared after the injection of liquid silicone into the anterior chamber of both eyes in 15 rabbits. The findings demonstrated serious damage to the endothelium in the area of contact of liquid silicone with the posterior surface of the cornea and disclosed some problems in the interpretation of specular microscopic findings. An abnormal endothelial mosaic can be probably found even in a zone of preserved intercellular borders or in a zone with a relief of the bases of extinct endothelial cells.

The second virial coefficient and an equation of state of two-dimensional fused hard-disc models

Abstract: A method for the evaluation of the second virial coefficient of two-dimensional dumbells and polyatomics and their mixtures is proposed. The method employs an exact relationship for the hard convex figure mean area; the way of calculating small differences in the mean areas of the fused hard-disc model and the corresponding hard convex figure is shown and exemplified for five models. The use of a hard convex figure equation of state for the above figures is discussed and its extension to mixtures is given.

About the luminescence properties of YAG:Nd, Ce and YAG:Nd single crystals and their relation to laser properties

Abstract: Laser excited luminescence studies of various YAG∶Nd, Ce and YAG:Nd (with an excess of yttrium) single crystals together with a testing of laser properties of rods made from the same crystals have been investigated in this paper. It was observed that laser pulse energies increase with increasing halfwidths of the luminescence spectral bands. This dependence and other observations indicate that local structure changes or Nd3+ nonequivalent centres are present in the studied crystals. Various mechanisms leading to the formation of Nd3+ nonequivalent centres are discussed and it seems that the more probable mechanism is oxygen segregation and diffusion.

Electrical and Magnetic Properties of Annealed Amorphous Fe8Ni72P10B10 at Low Temperatures

Abstract: The electrical and magnetic properties of amorphous Fe8Ni72P10B10 ribbons are strongly influenced by annealing. The temperature dependence of electrical resistivity displays a minimum, whose position and depth show a maximum at annealing temperatures lower than Tcryst ≈ 369 °C. From the measurements of magnetization and Mossbauer spectra one can infer a marked increase of the volume of ferromagnetic phase in the same range of annealing temperatures. It is supposed that the changes of the investigated properties can be explained rather by the changing magnetic order than by the direct structural influence of crystallization. Die elektrischen und magnetischen Eigenschaften von amorphen Fe8Ni72P10B10 Bandern werden durch Gluhen stark beeinflust. Der elektrische Widerstand zeigt ein ausgepragtes Maximum-verhalten der Temperatur und der Tiefe des Widerstandsminimums bei Gluhtemperaturen unterhalb von Tcryst ≈ 369 °C. Aus Magnetisierungs- und Mosbauer-Messungen wird auf ein starkes Anwachsen des Volumenanteils der ferromagnetischen Phase im gleichen Bereich der Gluhtemperaturen geschlossen. Es wird angenommen, das die Anderungen der untersuchten Eigenschaften mehr durch die sich andernde magnetische Ordnung als durch den strukturellen Einflus der Kristallisation erklart werden konnen.

Probe diagnostics op the planar magnetron discharge

Abstract: Magnetron discharge during Ti sputtering was examined by Langmuir probe. Electron densities and energies were determined at different Ar pressures, dc. powers and distances from magnetron target. Values in order of 1015m−3 and 1eV were measured even at distances up to 15 cm.

Complex polar Kerr effect spectra of magnetoplumbite

Abstract: The paper presents the complex polar Kerr effect spectra in hexagonal ferrite PbFe12O19 (magnetoplumbite) at 290 K between 2 and 5·5 eV. The spectra are compared with the corresponding spectra in Li0.5Fe2.5O4. The previously published data on optical constants of magnetoplumbite are employed to obtain the off-diagonal permittivity tensor element spectra. The effect of nonzero angle of incidence in uniaxial magnetic crystals on the observed polar Kerr effect is briefly discussed.

Twodimensional stochastic theory of crystal growth

Abstract: In the paper the twodimensional model of the stochastic theory of crystal growth is presented and used for the study of the morphology of the solidification front under different external conditions and for different rates of kinetic processes on the solidification front. The results show that the stability of the solidification front depends on the kinetic processes, which thus must be taken into account in the stability conditions.

Infrared reflectivity of BaMnF4

Abstract: The polarized reflectivity of BaMnF4 single crystals was measured in the 20–600 cm−1 range for temperatures from 10 to 300 K. The results were evaluated using Kramers-Kronig analysis to obtain the dielectric function. The number of active modes in the high temperature polar phase (T>Ti ≃250K) is in agreement with group-theoretical expectation. In the incommensurate phaseT

"Displaced nerve cells" in the human retina.

Abstract: Several kinds of nerve cells in the vertebrate retina can be found in retinal layers other that to which they belong. The present paper discusses all such cells within the human retina, as the author was able to stain them selectively using different neurohistological methods.

Study of nuclear effects in nucleon structure functions up to and beyond the kinematic limit

Abstract: An experiment on deep inelastic muon nucleon scattering in order to study the x-dependence of nucleon structure functions and their ratios over a range ofQ2=50–200 GeV2 andx= =0·4–2·0 is proposed. Such measurements performed on a number of nuclei with atomic weights from 2 to 207 provide new information for detailed studies of the EMC effect and test models explaining thex-behaviour of the nucleon structure functions and their ratios. The measurements are decisive for the proof that a quark-parton model of the nucleus describes adequately nuclear structure probed at high energies. The upgraded high luminosity BCDMS spectrometer with improved resolution in transferred energyν can be used for the measurements.

Remark on the influence of gravitation on the solidification of the binary systems

Abstract: The possible influence of the gravitation on the solidification of the binary systems in the framework of the stochastic theory is discussed. The considerations are based on the change of the kinetic parameters of the phase transformation with the change of the concentration of clusters in the melt.

Observation of $$\bar D$$ -mesons innC interactions at 40–70 GeV/c

Abstract: We have observed the production of $$\bar D^0 $$ andD − mesons in neutron carbon interactions at 40–70 GeV/c. The experiment was performed with the spectrometer BIS-2 located in the neutron beam 4N of the Serpukhov accelerator. The signals of $$\bar D$$ mesons were detected in the effective mass spectraM(K + (890)π −) andM(K +(890)π − π −). The kinematical region of detected $$\bar D$$ mesons is 30 GeV/c < pL < 60 GeV/c andp T < 1 GeV/c. For this region the partial cross sections are $$\sigma (n + C \to \bar D^0 + X)$$ . $$BR(\bar D^0 \to K^ + (890)\pi ^ - ) = (0 \cdot 9 \pm 0 \cdot 3)\mu b$$ andσ(n +C→ D − +X).BR(D − →K +(890) π−π−) = (2·1 ± 0·7) μb. The longitudinal momentum spectrum in the regionx > 0·5 can be described byF(x) ∼ (1 − x) N with $$N_{\bar D^0 } = 1 \cdot 1 \pm 0 \cdot 5 \pm 0 \cdot 4$$ and $$N_{D^ - } = 0 \cdot 8 \pm 0 \cdot 4 \pm 0 \cdot 4$$ . The transverse momentum spectra were parametrized by the exponential function dσ/dp T 2 ∼ exp (-Bp T 2 ) with $$B_{\bar D^0 } = (1 \cdot 4 \pm 0 \cdot 7)({{GeV} \mathord{\left/ {\vphantom {{GeV} c}} \right. \kern- ulldelimiterspace} c})^{ - 2} $$ and $$B_{D^ - } = (1 \cdot 7 \pm 0 \cdot 8)({{GeV} \mathord{\left/ {\vphantom {{GeV} c}} \right. \kern- ulldelimiterspace} c})^{ - 2} $$ .

Anomalies of thermal dilatation in Rb2ZnBr4 crystals

Abstract: Mise en evidence de variations discontinues des coefficients de dilatation aux temperatures de transition de phase (350 K, 190 K et 113 K)

Renormalized expansions for functional integrals: generalized coherent potential approach to lattice models

Abstract: An expansion for generating functionals (partition sums) of models expressed as lattice functional integrals with local (on-site) interactions is presented. This expansion renormalizes the standard perturbative expansion in such a way that certain its terms are summed up non-perturbatively. A non-self-consistent and a self-consistent versions of the expansion are formulated and criteria for an estimation of validity of approximations resulting from the both expansions are given. The simplest approximation being the first term of this expansion is applied to two lattice models: classicalN-component spin model and the model of non-interacting electrons in a disordered crystal. In the former model the critical temperature is calculated within 10% accuracy and in the latter, the coherent potential approximation is obtained.

A rapid means for the synthesis of aldehyde acetals

Abstract: A convenient rapid method has been proposed for the acetalization of aldehydes by ethyl orthoformate in the presence of trace amounts of perchloric acid.

Turnover of abnormal proteins in Bacillus megaterium and Saccharomyces cerevisiae: differences between in vivo and in vitro degradation.

Abstract: Degradation of abnormal proteins in Bacillus megaterium and Saccharomyces cerevisiae in vivo was compared with that in cell-free extracts. Protein degradation in vivo, when the cells were labelled with 14C-leucine during growth in the presence of ethionine, was affected by the concentration of the analogue used. Proteins synthesized in the presence of 0.2–1 mM ethionine were degraded most rapidly in both organisms. The proteolytic enzyme system of yeast degraded the analogue-containing proteins in vitro faster than the normal proteins. This holds also for proteins synthesized in the presence of 5 mM ethionine, whose degradation in vivo was impaired. The proteolytic system of B. megaterium, on the other hand, was unable in vitro to differentiate between normal and abnormal proteins. Denatured proteins underwent preferential degradation over normal and ethionine-containing proteins.

Origin of the noncubic anisotropy in Mn∶ (Y, Gd)3Fe5O12 thin films

Abstract: Thin Mn∶ YIG films exhibit a large noncubic anisotropy We show that this anisotropy may be understood on the basis of a strong Jahn-Teller effect of octahedrally coordinated Mn3+ ions The corresponding mechanism is simple — the strain caused by the film/substrate misfit orders the local Jahn-Teller distortions and, as a consequence, noncubic anisotropy appears In particular, due to the nonparallel local coordinate systems of octahedral sites, an uniaxial anisotropy is predicted also for the (111) growth plane It is pointed out that the interaction between the Jahn-Teller centres and/or their interaction with the lattice defects lower the magnitude of the anisotropy The temperature dependence of the uniaxial anisotropy was measured on the (001) and (111) oriented films using the FMR method The results are in qualitative agreement with the prediction of theory Quantitative comparison of theory with the experiment is difficult, as little is known about the distribution of the strains due to the lattice defects and about the interaction between the Jahn-Teller centres