ИЗЛУЧЕНИЕ ЧЕРЕНКОВА ПРОСТРАНСТВЕННОГО З АРЯДА В ВОЛНОВОДАХ И В НЕОГР АНИЧЕННОЙ СРЕДЕ

, - e . -. , .     

ГАЛЬВАНОМАГНИТНЫИ Э ФФЕКТ В МАРГАНЕЦ-ЦИНК ОВЫХ ФЕРРИТАХ В ОКРЕСТНОС ТИ ТОЧКИ КЮРИ

. , . _c . , , . _c ; .

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The magnetoresistance in zinc-manganese ferrites in the vicinity of the Curie point

The paper describes an exact method for measuring the adiabatic and isothermal magnetoresistant effects in ferrites. It gives the results of studying the temperature dependence of the magnetoresistant effect, which is negative near the Curie point in ferrites and the temperature dependence of which has a maximum of absolute values inT _c . It is also shown that the pronounced maximum of the adiabatic magnetoresistant effect is to a certain extent caused by the magnetocaloric effect. When measuring the dependence of the magnetoresistant effect on the field strength for a temperature equal toT _c , certain small deviations from the theoretically assumed dependence were found; the influence of different factors on these deviations is discussed and a proposal for their explanation is given in analogy to the results known for metals.

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[1].

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., ., . . . , . . , . . . . .     

ВЛИЯНИЕ ПОЛНОГО ОТРА ЖЕНИЯ НА ДИАФРАГМЕ СОЛЛЕРА НА РАЗРЕШАЮШ УЮ СИЛУ РЕНТГЕНОВСКО ГО СПЕКТРОГРАФА

- - , , , . - , -.     

Asymptotic theory of multidimensional chaos

A delay-differential equationu(t)+u(t)=f(u(t–1)), 0t < , and its generalization are investigated in the limit 0, when the attractor's dimension increases infinitely. It is shown that a number of statistical characteristics are asymptotically independent of. As for the attractor, it can be regarded as a direct product ofO(1/) equivalent subattractors, their statistical characteristics being asymptotically independent of . The results enable one to predict some characteristics of the attractor with fractal dimensionD 1 for the case 1, when they are inaccessible numerically. The approach developed seems to be applicable for a wide class of spatiotemporal systems.     

По поводу связи коэрц итивной силы феррома гнетиков с внутренним напряже нием

. , ( ) qb . , . , . , . , , . . , , , . , 30 / ² 1 10 .     

ИЗУЧЕНИЕ РАДИОАКТИВ НОГО ИЗЛУЧЕНИЯ НЕЙТРОНОДЕФИЦИТНЫХ ИЗОТОПОВ Hf

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The study of radioactive radiation of neutron deficient; Hf isotopes

     

The Gelfand-Levitan equation and its application to the scattering of neutrons on protons

The Gelfand-Levitan equation for the kernelP(r, r) (withrr) is formulated and then applied for determining the scattering potential in the scattering of slow neutrons on protons (for the case when the dependence of the nuclear forces on the spins can be neglected and onlys-scattering need be considered). The potentials obtained are the same as the Bargmann ones, found by a different method.

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- P(r, r) ( rr). , ( s- ). , .

     

The electroluminescence of ZnS-Cu,Mn

The brightness waves of ZnS-Cu, Mn phosphor were investigated and it was found that their shape changes from that characteristic for copper-activated phosphors to that characteristic for manganese-activated phosphors as a function of the magnitude of the voltage applied, the length of the pulses and the temperature. In order to explain the results it is assumed that simultaneously with the mechanism of electroluminescence, accepted for ZnS-Cu (ionization of activators; recombination and radiation delayed in phase compared with voltage), there exists an immediate recombination of the Cu activators in the barriers, which is accompanied by radiation in phase with the voltage.

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ZnS-Cu, Mn

ZnS-Cu, Mn. , , , , , , , , . , , ZnS-Cu ( ; , ), : Cu , , .

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In conclusion, the authors thank Dr. M. Trlifaj for valuable discussions and M. Skala for supplying the electroluminescent phosphor of ZnS-Cu, Mn.     

Eigenfunctions of the Koch snowflake domain

We obtain non-tangential boundary estimates for the Dirichlet eigenfunctions _n and their gradients {_n } for a class of planar domains with fractal boundaries. This class includes the quasidiscs and, in particular, snowflake-type domains. When applied to the case when is the Koch snowflake domain, one of our main results states that {₁()} tends to or 0 as approaches certain types of boundary points (where ₁ > 0 denotes the ground state eigenfunction of the Dirichlet Laplacian on ). More precisely, let Ob (resp., Ac) denote the set of boundary points which are vertices of obtuse (resp., acute) angles in an inner polygonal approximation of the snowflake curve . Then given Ob (resp., Ac), we show that {₁()} (resp., 0) as tends to in within a cone based at . Moreover, we show that blowup of {₁} also occurs at all boundary points in a Cantor-type set. These results have physical relevance to the damping of waves by fractal coastlines, as pointed out by Sapovalet al. in their experiments on the Koch drum.Research partially supported by the National Science Foundation under Grant DMS-9207098.     

Dependence of energy and orientation of 90° Bloch wall on stress

The energy and orientation of a 90° Bloch wall are calculated as functions of the stress. The relative occurrence of stress in a quenched single crystal of silicon-iron is derived on the basis of the experimental distribution of the zigzag angle.

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90-

90- . . 500 kg mm^–2.

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The authors thank F. Kroupa and J. Paes for valuable remarks.     

Massive spin-two particle in a gravitational field

The spin-two particle is described by a symmetric tensorh subject to the subsidiary conditionsh = h =0. Their covariant generalization and the wave equation have been obtained directly from the Eulerian variational equations by algebraic methods only. In addition to the tensor fieldh a symmetric third-rank tensor = as well as a vector fieldA have been added, neither of which enter in the final result. The Lagrangian function is taken as a linear sum of all combinations which can be constructed from these functions, as well as terms involving the curvature tensor and its two possible contractions. Variation with respect toh , andA independently gives the Euler equations. Combining the various trace equations and choice of arbitrary constants yields the subsidiary conditions, while the Euler equations themselves give the connection between the auxiliary functions and the tensorh as well as the generalization of the wave equationD D h + 2R h -R h -R h +g R h +Rh =m ² h Finally, variation with respect tog yields the energy-momentum tensor.     

ИЗМЕНЕНИЯ ТОНКОЙ СТР УКТУРЫ МОЛОТОГО КОБА ЛТА

- , . , , - . - , , , - .     

Канал кратковременн ого силъноточного электрического разр яда

, ( 10² sec, , 10⁴ A), .

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Channel of short-time high-intensity electric discharge

By the spatial expansion of the radial cross-section of the channel of the given type of discharge (duration 10² sec and maximum intensity smaller than 10⁴ A)and by measuring some of its electrical quantities information was obtained on its channel and the influences bringing about the forming process.

     

Time production and spatial distribution of macroscopic space charges in D-C discharge plasma

It is shown for a one-dimensional approximation that, around a disturbance in the ion concentrationn ₊(x, t) in the axial direction of a cylindrical plasma, a corresponding electron distributionn _–(x, t) is established with such a large velocity that under the usual conditions of a discharge plasma this electron distribution follows the relatively slow changes in ion concentration practically without delay. Relation (24) then holds for the electron concentration, the parametersl ₁,l _D being given by Eqs. (15) and (16). As long as the disturbance of the ions isn ₊(x) 0, a space chargeq ₀(n ₊-n_–) is produced and maintained in the plasma even if the disturbance of the equilibrium state of the plasma in the initial stage was electrically neutral (i.e.n ₊(x, t=0)==n _–(x,t=0)). The dimensions of these space charges can be many orders larger than the Debye characteristic lengthl _D ; this is shown on an example of a spatially periodic curven ₊(x). The unique (quasi-stationary) expression of the electron concentrationn _– by means of the deflection of the ion concentrationn ₊(x, t) permits a considerable simplification of the solution of the problems connected with axially disturbing the homogeneous state of a plasma, sincen _–(x, t) can be eliminated from the equations of continuity of the plasma by substituting from (24), and the problem becomes that of determining the curve of the ion concentrationn ₊ from the equations modified in this way.

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, ₊(, t) - _–(, t) , . (24), l ₁ l _D (15) (16). ₊() 0, q ₀(n₊ — n_–), , (..n ₊(x,0)=_–(, 0)). () _{– +}(, t) , , . . _–(, t) n ₊ .

     

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.     

Charge Fluctuations in the Two-Dimensional One-Component Plasma

We study, via computer simulations, the fluctuations in the net electric charge in a two-dimensional, one component plasma (OCP) with uniform background charge density –e in a region inside a much larger overall neutral system. Setting e=1, this is the same as the fluctuations in N , the number of mobile particles of charge e. As expected, the distribution of N has, for large , a Gaussian form with a variance which grows only as ^||, where || is the length of the perimeter of . The properties of this system depend only on the coupling parameter =kT, which is the same as the reciprocal temperature in our units. Our simulations show that when the coupling parameter increases, ^() decreases to an asymptotic value ^()^(2)/2 which is equal (or very close) to that obtained for the corresponding variance of particles on a rigid triangular lattice. Thus, for large , the characteristic length _L=2^/ associated with charge fluctuations behaves very differently from that of the Debye length, _D1/ , which it approaches as 0. The pair correlation function of the OCP is also studied.     

БЕТАТРОННЫЕ КОЛЕБАН ИЯ В УСКОРИТЕЛЕ С ОБЩИМ ПОЛЕМ I

, . . . , , . , . , . .

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Betatron oscillations in an accelerator with a general field I

The paper gives a linear theory of equilibrium trajectories in an accelerator with a generalized magnetostatic field, the components of which are defined on a general rotation surface. Equations of motion of the particles in natural coordinates are derived with respect to the change in energy and dissipative force. A system of equilibrium trajectories is found in the general form. Conditions for the field components on the reference surface, necessary for the existence of equilibrium trajectories, for the conservation of their geometric similarities and for maintaining the constancy of the frequencies of the betatron oscillations, are derived. A condition is also derived which must be satisfied by the reference surface in order to conserve constant circular frequency of the particles. It is seen that it is not possible to find a field for an accelerator with an exactly constant circular frequency and with constant frequencies of the betatron oscillation in the relativistic energy region. An ultra-relativistic cyclotron with such properties is realizable.

     

Another Look at Just-So Solar Neutrino Oscillations

We take another look at Just-So solar neutrino oscillations, characterizing them by the energy E_/2 at which the distance-varying angle is /2, instead of by the usual m ² . The rising spectrum recently observed by SuperKamiokande is consistent with an E_/2 6–9 MeV and marginally with 48 MeV. The pp neutrinos must then be reduced to one-half the standard solar model prediction, and ⁷Be neutrinos must make up a significant part of the SAGE and GALLEX gallium signal. For E_/2 close to 9 and 48 MeV, the ⁷Be neutrinos will also show a large seasonal variation, emphasizing the importance of direct measurements of the ⁷Be neutrinos.     

The rotation of bloch walls

A Bloch wall has an integral magnetic moment which is due to the spatial distribution of the magnetic moments of the spin. The external magnetic field thus acts on the wall with a torque, which leads to the rotation of the sub-domains and therefore to deformation of the walls. A theory of this rotation is given and from it a microphysical model of the undulatory surface structure in uniaxial ferromagnets is derived. Experiments performed on magnetoplumbite single crystals fully confirm the theoretical assumptions.

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. , , . , . , , .

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Our thanks go to J. Fousek and Z. Málek who by reading this paper contributed greatly to the clarity of its presentation.