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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A new rigorous upper bound for the inverse critical temperature of the two-dimensional Coulomb gas

In this paper we show how to improve the recent result _c 17.2 on the inverse critical temperature for the two-dimensional Coulomb gas at low density to get the following upper bound: _c 16.     

Renormalization group equations with several length scales and crossover scaling functions for axial anisotropy

The critical behaviour of axially anisotropicn-vector models is characterized by two distinct length scales, the correlation lengths and for the easy and hard axes. In order to handle the full range of anisotropics from to partial differential renormalization group equations are derived, depending on and . The anisotropicX-Y model is studied in detail near four dimensions. The crossover scaling functions for the susceptibilities are calculated to first order in=4–d. Two distinct crossover regions are found for weak and dominant anisotropy, respectively.     

МОДЕЛИРОВАНИЕ ЭЛЕКТ РОННО-ОПТИЧЕСКИХ СИС ТЕМ С ОСЕВОЙ СИММЕТРИЕЙ П РИ ПОМОЩИ СЕТИ СОПРОТИВЛЕНИЙ

The paper explains the theory of modelling electrostatic fields by a resistance network. The conditions, which the resistance network must satisfy, are derived and the question of modelling electrodes of different shapes is solved. The finished network and the results obtained on it when modelling a jet for a linear h-f accelerator of electrons are described. Particular attention is paid to the influence of a space charge, the modelling of which is an advantage of this method.

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Photo-luminescence and growth defects in ZnS: Cu monocrystals

The paper describes microscopic investigation into the spectral distribution of photo-luminescence and its polarization on hexagonal ZnS monocrystals in relation to the structural defects of such crystals. These observations, as well as birefringent observations, show that the values of the birefringence and the degree of polarization in different stripes of the same crystal are the same within the limits of observational errors.

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ZnS: Cu

ZnS . , , , .

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In conclusion the author would like to thank K. Pátek, L. Souková and M. Mokonová for providing the monocrystals and for fruitful discussions.     

Zur Labyrinthstruktur bei Martensit

Ohne Zusammenfassung

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Magnetic relaxation spectrum of ferrites Mn x Fe3−x O4+γ

The initial permeability disaccommodation in ferritesMn _x Fe₃–xO₄₊ , 0·5x1, was studied in a temperature range around –200°C to +180°C. Four separate bands were found in the relaxation spectrum of these ferrites.

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Mn _x Fe_3–x O₄₊

Mn _x Fe_3–x O₄₊ , 0,5x1, –200°C +180°C. .

     

Electrodynamics of moving particles

A consistent relativistic theory of the classical Maxwell field interacting with classical, charged, point-like particles is proposed. The theory is derived from a classical soliton-like model of an extended particle. An approximation procedure for such a model is developed, which leads to an already renormalized formula for the total four-momentum of the system composed of fields and particles. Conservation of this quantity leads to a theory which is universal (i.e. does not depend upon a specific model we start with) and which may be regarded as a simple and necessary completion of special relativity. The renormalization method proposed here may be considered as a realization of Einstein's idea of deriving equations of motion from field equations. It is shown that the Dirac's 3-dots equation does not describe a fundamental law of physics, but only a specific family of solutions of our theory, corresponding to a specific choice of the field initial data.     

Основные соотношени я длн построения механических селект оров нейтронов

, . , , . . , , .     

Die Integralbeziehungen bei der stationären laminaren Strömung mit geschlossenen Stromlinien in annähernd kreisförmigen Gebieten

Zusammenfassung Für die statioäre lineare ebene Strömung mit geschlossenen Stromlinien bei einer großen Reynoldsschen Zahl in annähernd kreisförmigen Gebieten werden zwei Integralbeziehungen (5) und (9) abgeleitet. Nach der ersten von diesen ist das Integral der Reibungskraft entlang der Grenze des Strömungsgebiets direkt proportional der Länge dieser Grenze und der Größe der Rotation der Geschwindigkeit im Kern der Strömung. Aus der zweiten Beziehung geht hervor: Das Volumen der in der Zeiteinheit den Schnitt der Rezirkulationsgrenzschicht durchfließenden Flüssigkeit ist direkt proportional dem Integral entlang der Gebietsgrenze aus der Differenz der Quadrate der Strömungsgeschwindigkeit an der Grenze des Kerns und der Geschwindigkeit an der Gebietsgrenze und umgekehrt proportional der Größe der Geschwindigkeitsrotation im Kern und der Länge der Gebietsgrenze.

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(5) (9). . : , , .

     

Über den Einfluss von Stickstopf auf die Exoelektronenemission von Germanium

Zusammenfassung Es wurde der Einfluß eines Bombardements mit Stickstoffionen vor der Erregung untersucht und gezeigt, daß die Stiekstoffatome eine große Rolle bei der Entstehung des Emissionsmaximums bei 150° spielen.

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, 150°C.

     

Nonlinear two-photon interaction in a strong magnetic field

Sections of nonlinear photon-photon scattering processes and merger of photons in the nucleus (Ze) (Ze) in a strong magnetic field are computed by using a developed two-dimensional formalism. Closed expressions are obtained for the sections with a graphical illustration of the results and they are compared with the case of no external fields.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 16–19, June, 1988.     

К В. Ч. НАГРЕВУ РАЗРЕЖЕННОЙ ПЛАЗМЫ

[2]. . , . , . . . .     

Эффективностъ сцинт илляционных счетчик ов для быстрых нейтроно в

, ZnS(Ag) . ZnS(Ag) . Po-Be, Ra-Be Li(d, n), C(d, n), N(d, n), Be(d, n). -, Co⁶⁰, Cs¹³⁷ Ra, , -, Li(p, ). , .     

Current distributions in a two-dimensional random-resistor network

The current and logarithm-of-the-current distributionsn(i) andn(ln i) on bond diluted two-dimensional random-resistor networks at the percolation threshold are studied by a modified transfer matrix method. Thek th moment (–9k8) of n(ln i) i.e., ln i&^k, is found to scale with the linear sizeL as (InL)^(k). The exponents (k) are not inconsistent with the recent theoretical prediction (k)=k, with deviations which may be attributed to severe finitesize effects. For small currents, ln n(y)–, yielding information on the threshold below which the multifractality of (i) breaks down. Our numerical results for the moments of the currents are consistent with other available results.     

The basic equations of the dynamics of the continuous distribution of dislocations II. Interpretation of general theory

The basic equations of the dynamics of the continuous distribution of dislocations analogical to Maxwell equations are derived in a series of papers [I, II, III]. The analogy of the elastic and electromagnetic fields is analyzed. In part [II] a physical interpretation is given of the tensors of stress and distortion and expressions are considered for the energy density of the elastic field of the dislocations. The basic equations are generalized for the case of a non-zero Poisson ratio and a finite body. A detailed interpretation is given of the tensor components of dislocation current density.

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II.

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The van der Waals limit for classical systems

For a -dimensional system of particles with the two-body potentialq(r)+ ^v K(r) and density , it is proved under fairly weak conditions onq andK that the canonical pressure (, ) and chemical potential (, ) tend to definite limits when 0. The limiting functions are absolutely continuous and are given in terms of the derivative of the limiting free energy density which was found in Part I.     

ПОЛЕ ПЕРЕМЕННОГО ДИП ОЛЯ В НЕОДНОРОДНОМ ПОЛУПРОСТРАНСТВЕ

, . , ₁, ₂. - .     

Standpoint cosmology

An unorthodox cosmology is based on a notion of standpoint, distinguishing past from future, realized through Hilbert-space representation of the complex conformai group for 3+1spacetime and associated coherent states. Physical (approximate) symmetry attaches to eight-parameter complex Poincaré displacements, interpretable as growth of standpoint age (one parameter), boost of matter energy-momentum in standpoint rest frame (three parameters) and displacement of matter location in a compact U(1)O(4)/O(3) spacetime attached to standpoint (four parameters). An initial condition (at big bang) is characterized by a huge dimensionless parameter that breaks dilation invariance. Four major length scales are recognized, called Planck, particle, lab, and Hubble, with separations controlled by ; all physical concepts, including spacetime, depend on wideness of scale separation.     

The influence of successive asymmetrical magnetization reversal on the magnetic state of open samples

A study is made of the influence of successive asymmetrical magnetization reversal on the magnetic state of open samples, where the macroscopic demagnetization field has a significant effect during magnetization reversal and leads to a sort of rotation of the asymmetrical loops performed one after another. This effect is similar to reptation, which was studied experimentally by Nguyen van Dang [1–4] and theoretically explained by Néel [5, 6]. The quantitative expression of the rotation of asymmetrical loops in open samples as a function of the number of loops and amplitude of the disymmetry is similar to that with the reptation effect.

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In conclusion the authors thank Dr. L. Valenta, C. Sc., and Z. Málek, C. Sc., for valuable discussions.