The distribution of ions and their valencies in manganese ferrites II. Mn1+xFe2-xO4+y ferrites

The influence of the oxygen content on the saturation magnetic moment and the Curie temperature was studied experimentally on non-stoichiometric manganese ferrites having a varying excess of manganese. Taking into consideration the results of studying the electrical conductivity and magnetic relaxation effects, a model was elaborated for the distribution of ions in these ferrites, which starts out from the distribution of ions in stoichiometric manganese ferrite. The experimental results obtained by us and those of other authors confirm the justification of this model.

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II. Mn_1+xFe_2-xO_4+y

. , . .

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In conclusion the authors thank members of their technological department for preparing the samples and M. Mikulá for carefully carrying out the chemical analyses.     

Enhancement of conductance fluctuations in two-dimensional mesoscopic electron systems with valley structures

Conductance fluctuations are studied in twodimensional mesoscopic electron system with a two-hold valley degeneracy (n _v =2), which corresponds to the inversion layer of Si-MOSFET formed in (1,0,0) plane. It is shown that the intervalley scattering modifies conductance fluctuations depending on the ratio, Min { _c , _T }/ _v , where _v = ( – 2)/2 and _c , _T , and are, respectively, system traversal time, thermal diffusion time, intervalley scattering time and total life time of electrons. Conductance fluctuations are no longer universal and vary from G _univ 0.862·e ²/h to {ie223-5} at low temperatures even for isotropic systems. The conductance fluctuations increase with decreasing system size, increasing electron density and increasing intervalley scattering time. The effect of intervalley scattering is essentially the same as that of intersubband scattering as previously reported. At finite temperatures where _{T c} , the intervalley scattering modifies the fluctuations through the change in the energy correlation range to results in the reduction of the conductance fluctuations. In Si-MOSFET formed in (1, 1, 1) plane, wheren _v =6, more enhanced fluctuations are expected. Experimental studies are desired on theoretically predicted points.     

The motion of 90° wedge domains in BaTiO3 in an alternating electric field

The paper deals with the motion of 90° wedge domains in BaTiO₃ in an alternating field of 50 c/s. The critical field, the positional hysteresis loops with double asymmetry, the production of wedges with polarization perpendicular to the field and 180° substructure in the wedges were studied. The differences between the behaviour of the wedges and the individual 90° walls are pointed out which are caused by differences in the energy balance of these formations and by different interactions with 180° processes. The upper limit of contribution of the wedge motion to the initial permittivity is estimated. The results are discussed from the phenomenological point of view.

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90° BaTiO₃

90° BaTiO₃ , 50 Hz. , , , , , , 180° . 90° , 180° . , . .

     

The spectrum of a quasiperiodic Schrödinger operator

The spectrum (H) of the tight binding Fibonacci Hamiltonian (H _mn= _m,n+1+ _m+1,n + _m,n v(n),v(n)= ((n–1)), 1/ is the golden number) is shown to coincide with the dynamical spectrum, the set on which an infinite subsequence of traces of transfer matrices is bounded. The point spectrum is absent for any , and (H) is a Cantor set for 4. Combining this with Casdagli's earlier result, one finds that the spectrum is singular continuous for 16.On leave from the Central Research Institute for Physics, Budapest, Hungary     

The influence of oscillations on ionization in a discharge path

The paper solves the problem of gas ionization in a discharge path in a very dilute gas, where the free path of the electrons is much larger than the dimensions of the path and the transit time of the electrons between the electrodes is of the order of the period of the applied h-f voltage. It was found that for a certain ratio of the transit time of the electrons between the electrodes in the discharge path to the period of the h-f oscillation, resonance occurs when the wattless current component is zero. The electron density rises in the path and thus also the gas ionization.

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, , , . , , . , .

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In conclusion, the author would like to thank F. Benda for preparing the equipment, M. Kivánek for preparing the equipment and some of the measurements, and A. Hrdá for the measurements and for working out the case with equally large a-c and d-c voltages within the framework of her thesis.     

Energy relaxation in aϕ 4 with long range interactions

We investigate the influence of long range interactions on the relaxation behaviour of a lattice model with an on-site potential of ⁴-type and infinite range harmonic interactions. For finite number of particlesN, it is shown that the autocorrelation functions <E _n(t)E _n > of the fluctuations of the one-particle energiesE _n(t) decays exponentially. The corresponding relaxation time is proportional toN and is given by (T, N) =N₀(T). The temperature dependent time scale ₀ can explicitly be related to the dynamics of a one-particle correlator of the noninteracting system. The results are derived using Mori-Zwanzig projection formalism. The corresponding memory kernel is calculated within a mode coupling approximation and by a perturbative approach. Both results agree in leading order in 1/N. It is speculated that any interaction of range generates a timescale .     

The application of the thermodynamics of irreversible processes to welding arcs

The self-regulation of an inert gas shielded metal welding arc is dealt with briefly. A thermodynamic equation is derived for the self-regulation of such an arc.

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. .

     

О СУЩЕСТВОВАНИИ ОТРИ ЦАТЕЛЬНОГО ЯВЛЕНИЯ БАРКГАУЗЕНА

. . , . , . , . coo , 13. 5. 1954 . - .     

Hyperbolic initial-boundary-value problem for magnetic flux compression by plane liners

Based on the (relativistic) Maxwell equations with displacement current E/t, the initial-boundary-value problem for the compression of an initially homogeneous magnetic fieldB={0,B(x,t),0} between a fixed liner atx=0 and a detonation-driven liner atx=s(t) is solved analytically. By homogenizing the boundary conditions at the moving boundary, the transient electromagnetic fields are shown to be a superposition of quasistatic elliptic (E/t=0) and hyperbolic (E/t0) wave solutions. The wave equation is solved by a Fourier expansion in time-dependent eigenfunctionsf _n =f _n [nx/s(t)] for the variable region 0xs(t), where the Fourier amplitudes _n (t) are determined by coupled differential equations of second order. It is concluded that the conventional elliptic flux compression theories (E/t=0) hold approximately for nonrelativistic liner speeds , whereas the hyperbolic theory (E/t0) is valid for arbitrary liner speeds .     

A contribution to the theory of the triple crystal diffractometer

The first part of the paper gives a general equation for triple-crystal arrangement with perfect crystals on the assumption that the third crystal is rotated. It is shown that in the case of perfect crystals the shape of the reflection curve is practically independent of the vertical divergence. The case of mosaic crystals is also solved and the possibility of rotation by other than the third crystal is considered. A method is proposed for investigating the imperfection of a crystal which is different from methods used up to now. The paper is supplemented by some experimental results.

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, . , . , , . , . .

     

Elastic stress around linear dislocation in anisotropic medium

Relations are derived for the elastic stress field around a linear dislocation in an infinite medium with general anisotropy. The strongly deformed material around the core of the dislocation is cut out in the shape of an elliptic cylinder. The conditions of a free surface are used on the boundary thus formed. The calculation of the field around a crack in a crystal, the model of which was proposed by Fujita in [9], is given as an example.

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. , , , . , [9] .

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The author thanks Dr. F. Kroupa for valuable discussions and all-round help in solving the problem and Z. Hemanová for performing the numerical calculations.     

The distribution of dislocations in silicon iron single-crystals grown from the melt

The distribution of dislocations in a crystal of an Fe-4.2% Si alloy prepared from the melt is studied microscopically and, by X-ray diffraction after rendering them visible by anodic dissolving. The dislocations are also studied inside the crystal by successively grinding the surface. The density of the dislocations inside the blocks is determined by calculation from microphotos, the density of the dislocations forming the boundaries between the blocks by measuring the angles between the lattices of neighbouring blocks. It is found that the dislocations are distributed very unevenly in the crystal and most of them form complicated boundaries of blocks, similarly as with ionic crystals. The distribution of dislocations is also discussed from the point of view of their formation and conclusions are reached as to the preparation of single crystals having a smaller number of dislocations.

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Fe-Si,

- Fe-4,2%Si, , . . , , — . , , . .

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The author is indebted to Candidates of Mathematics and Physics, F. Kroupa and J. Kaczér, for careful reading and advice whereby they helped to give greater depth and accuracy to this paper. He thanks Z. Tahal and M. Honegrová for initiative shown in helping to prepare the single crystals and during exacting experimental work, and S. Kadeková for aid in adjusting the spectrometer.     

The elastic coupling between longitudinal and transversal vibrations of isotropic rods I. Rods of square and rectangular cross-section

A new approximate method for theoretically calculating longitudinal vibration frequencies of isotropic homogeneous rods of square and rectangular cross-section is given. We divide a three-dimensional longitudinal vibration into three one-dimensional ones; the coupling between the principal strains in question is assumed to be linear, similarly as in the static case of simple tension. The coupling between the deformations is realized by variable coupling parameters or depending on the order of vibrations (contrary to Rayleigh's correction where Poisson's ratio is the coupling parameter). These parameters are defined by the condition that the corresponding frequency must be minimized (stationary).Up till now Giebe and Blechschmidt [2] have given the best approximate method of calculation. The series of their calculated frequencies corresponds to the measuredones nearly as well as the frequencies calculated by us. The theory described here, however, contains a richer spectrum of frequencies and at the same time explains the frequencies measured in the range of the so-called dead zone, which is the weak point of Giebe's and Blechschmidt's theory.

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I.

. ; , . , ( , ). , ( ). [2]. , , . , , , , . . , .

     

The classical theory of nuclear spin interaction in a ferromagnet

The Hamiltonian of nuclear spin interaction in a ferromagnet is derived by the classical method, which introduces the precession of nuclear spin into the equation of motion for magnetization. From this it is shown that the interaction Hamiltonian also depends on the magnitude and sign of nuclear precession frequency _N and the damping constant of ferromagnetic resonance A. The calculation of these parameters makes the Suhl [1] quantum mechanical derivation of the Hamiltonian of nuclear spin interaction in a ferromagnet more accurate. The influence of these parameters on the relaxation timeT ₂ is also discussed and is applied to the case of cubic cobalt.

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. , _N . , [1] - . ₂ .

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In conclusion the author thanks Dr. L. Valenta for significant remarks and valuable advice on this work. He also thanks J. Kvasnica and Z. roubek for suggestive discussions.     

Сцинтилляционный сп ектрометр с сложение м импулъсов от двух кри сталлов

, . , .     

тЕОРИь И стРУктУРА тЕ МпЕРАтУРНОгО ИжОБРА жЕНИь

. , , , . .

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The theory and structure of the temperature image

The paper describes the theory of the formation of a temperature image when there are large temperature differences and introduces the concept of temperature distortion of an image. It also deals with the geometrical distortion of the temperature image by the longitudinal thermal conductivity of the receiver layer and gives a solution of the corresponding differential equation of the temperature image for the case of a general linear line test and general circular concentric test. Equations are derived for the temperature distributions of the temperature images of some optical lineated and circular test objects and their geometrical distortion due to the thermal conductivity of the receiver layer is investigated.

     

Основные соотношени я длн построения механических селект оров нейтронов

, . , , . . , , .     

ТЕМПЕРАТУРНАЯ ЗАВИС ИМОСТЬ ТЕРМОЭЛЕКТРОДВИЖУЩ ЕЙ СИЛЫ СЕРОГО ОЛОВА С ПРИМЕСЯМИ КАДМИЯ

- , - —183 —10 °.     

Change in primary extinction during decomposition of supersaturated solid solution II. Al-Cu 4% alloy-formation of G.P. zones

The change in integrated intensity of the (200) reflections of a solid solution during the formation of G.P. zones was measured and compared with the change in the character of the diffuse streaks corresponding to them. It was found that the. formation of G.P. zones does not lead to a decrease in primary extinction despite the great changes in the distribution of the copper atoms. It was shown that the formation of a precipitate accompanied by the formation of crystallographically incoherent boundaries greatly decreases the primary extinction.

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. II. 1-u 4%: [. . ]

(200) . . , . , . . , . , , , .

     

Some critical exponent inequalities for percolation

For a large class of independent (site or bond, short- or long-range) percolation models, we show the following: (1) If the percolation densityP (p) is discontinuous atp _c , then the critical exponent (defined by the divergence of expected cluster size, nP _n (p) (P _c –P)^– asp p _c ) must satisfy 2. (2) or (defined analogously to, but asp p _c ) and [P _n (p _c ) (n ^–1–1/) asn ] must satisfy, 2(1 – 1/). These inequalities for improve the previously known bound 1(Aizenman and Newman), since 2 (Aizenman and Barsky). Additionally, result 1may be useful, in standardd-dimensional percolation, for proving rigorously (ind>2) that, as expected,P _x has no discontinuity atp _c .