К определению самопр оизволъной иамагниченности В об ласти точки кыри

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

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Negative mass cyclotron resonance maser

Physical principles, design and operation characteristics of a negative mass cyclotron resonance maser inp-type germanium are considered in this paper. The formation of anisotropic inverted distributions of negative effective mass heavy holes in strong electric and magnetic fieldsE H [001], resulting in negative conductivity in the millimetre and submillimetre wavelength ranges, is discussed. The generation is observed at 0.9 to 8mm in low compensated germanium samples with the hole concentration rangeN ₀ 2×10¹² to 2×10¹⁴ cm^–3 at low temperaturesT 25 K in electric fieldsE 40 to 350Vcm^–1. The maser frequency is tuned by the magnetic field corresponding to a cyclotron resonance frequency of carriers with an effective mass ofm _c 0.4m ₀. The spectral width of the emission in single mode operation does not exceed several megahertz. A pulse duration of 1 to 200 s and a repetition rate off _rep 1 to 200 Hz has been obtained limited by sample heating. Possibilities of improving the maser characteristics inp-Ge as well as in other A_III B_v semiconductors and the perspectives of new frequency tuning methods due to the application of uniaxial stress and magnetic field are demonstrated.     

Λ-d Scattering

A three-particle variational calculation of the cross sections and phases of elastic -d scattering in the doublet and quartet states with zero orbital angular momentum is carried out in the energy range from 0 to 20 MeV (laboratory system of coordinates). The calculation is carried out with semirealistic N-N Afnan-Tang potentials and -N potent: —N, which describe -p scattering correctly, as well as the binding energy of the hyperfragments ⁵ He, ¹³ C (within the scope of the + core model), and ³ H (considered as a three-body system).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 114–118, 1981.     

Two-frequency method for increasing the signal-to-noise ratio for nuclear quadrupole resonance14N low-frequency transitions

A method is proposed for increasing the signal-to-noise ratio during detection of NQR¹⁴N low-frequency transitions, consisting in a preliminary saturation of the _o(_–) transition before accumulation of the multiplet signals of the spin echo or induction signals, observed during the action of a series of 90 pulses on the _–(_o) transition. The gain in signal-to-noise ratio achieved by the two-frequency action is calculated theoretically, and the maximum value is found to be 3/(3 –) for _– and 3(1 + )/4 for _o. It is shown that the envelope of the induction signal for an increase in the time between the 90 pulses decreases according to one exponent for _o, while for _– and ₊ it decreases according to two exponents, and the approach to equilibrium of the system of¹⁴N nuclei is oscillatory in nature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 61–64, November, 1987.     

Der Einfluss von Mikrosegregations-Substrukturen auf die Kritische Schubspannung und den Verfestigungskoeffizient von Zinkeinkristallen

Zusammenfassung Der Einflu\ von Mikrosegregations-Substrukturen auf das plastische Verhalten von Zinkeinkristallen entspricht den allgemeinen Erwartungen in der Weise, da\ die kritische Schubspannung mit wachsender Substrukturendichte zunimmt. Der Verfestigungskoeffizient _A nimmt hingegen mit wachsender Substrukturendichte ab. Dabei wird der Verfestigungskoeffizient vom Charakter der Substruktur viel empfindlicher beeinflu\t als die kritische Schubspannung. Es wird angenommen, da\ dieser Einflu\ durch unterschiedlichen Fremdstoffgehalt zustande kommt.

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Die Autoren danken Herrn Prof. M. Valouch, der die Durchführung dieser Arbeit ermöglicht hat. Herrn P. Kratochvíl sei an dieser Stelle für zahlreiche Diskussionen aufs herzlichste gedankt.     

Infrared lattice bands of some pearls

From analysis of anisotropical lattice bands properties of 50 reflection spectra both of the CO stretching and bending bands measured from some pearl (Ca⁺⁺CO ₃ ^–– or Ca⁺⁺HCO ₃ ^–– layer) we discussed following subjects.i) Quantized properties present both in reflectivity and in energy. ii) classifications of the Optical Activity. iii) Polar distributions of the CO₃ oscillators in Ca⁺⁺CO ₃ ^–– surface mono-layer. iv) Force constants of these oscillators. v) Step variation of the dipolemoment and their influences to the degree of Optical Activity. vi) Two types of hysteresis loops of the values of Y_N (M_2Jbend ()/M_1Jstret. ()) derived from the oscillators which are at innert-state, at weak active-state and at active-state.     

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

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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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Accurate calculation of functional determinants

A dependence of the functional determinant of the operator from the family D() satisfying the condition D()=fD()+D()f on the parameter m² of infrared regularization is found in the regularization method using a generalized function.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 27–32, June, 1988.     

Parametric excitation of spherical modes in ferromagnetic spheres by perpendicular and parallel pumping

The fine structures of the threshold of subsidiary absorption and parallel pumping, observed on highly polished YIG spheres in 1975 by W. Jantz et al., are discussed with a model which uses instead of plane spin-waves the true modes regarding the shape of the sphere. These spherical modes are magnetostatic modes taking additionally the exchange interaction into account. At the closely spaced resonances of the fine structure of parallel pumping single spherical modes with angular-momentum quantum numberm=0 are excited, whereas at the resonances of subsidiary absorption pairs of spherical modes with big angular-momentum quantum numbers (|m|1000) satisfying the selection rulem+m=1 are excited. The analysis of the fine structure of subsidiary absorption shows that in regimes where the plane wave approximation predicts the excitation of spin-waves with formalk0, modes withk1.5·10⁵ cm^–1 have the lowest threshold. This discrepancy is discussed with the effect of surface pit scattering, which increases the threshold of modes withk < 2/_pit, where _pit is a typical size of the surface pits. Consequently modes withk22/_pit instead ofk0 have the lowest threshold.     

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

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К ПРОБЛЕМЕ МАГНИТНОЙ ФОКУСИРОВКИ ПУЧКОВ ЭЛЕКТРОНОВ, ЭМИТТИРО ВАННЫХ С ТЕПЛОВЫМИ СКОРОСТЯМИ

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The quantum efficiency of the internal photo-electric effect in indium antimonide

A method is described for measuring the relative quantum efficiency of the internal photo-electric effect in semi-conductors by simultaneously measuring the photo-magnetoelectric and photo-conductive effect. The results of measurements on indium antimonide are given. The quantum efficiency begins to increase if the energy of the photon exceeds 0·47 eVat room temperature. The quantum efficiency as a function of the energy of the photon is analysed on the basis of the conception of impact ionization and it is shown that a study of the structure of this curve can supply information on the, band structure of a semi-conductor in the region of high energies of electrons and holes.

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The authors thank M. Závtová and M. Vantuchová for efficient help with the measurements, K. mirous and V. Vrchovská for preparing the material, E. Antoník for critical remarks and M. Matyá and A. Müller for determining the constants of the material.     

On the electroluminescence of powdered zinc sulphide layers

The experimental study of the dependence of the electroluminescence brightness on the voltage confirms the correctness of the mechanism of electroluminescence, based on impact ionization in parts of the crystal where the electric field is concentrated. A study of the photoluminescent and electroluminescent spectra of phosphors containing two activators (copper and an element of rare earth) permits the determination of the magnitude of the volume of the crystal in which electroluminescence occurs. A study of the influence of the stored light sum on the brightness of electroluminescence and a study of the rate of growth of the variable and constant components of electroluminescence point to the fact that the excitation is transferred from the region of field concentration to the whole volume of the crystal.

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ИЗУЧЕНИЕ РАДИОАКТИВ НОГО ИЗЛУЧЕНИЯ НЕЙТРОНОДЕФИЦИТНЫХ ИЗОТОПОВ Hf

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The study of radioactive radiation of neutron deficient; Hf isotopes

     

On the asymptotic behaviour of infinite gradient systems

We consider gradient systems of infinitely many particles in one-dimensional space interacting via a positive invariant pair potential with a hard core. The main assumption is that is strictly convex within the rangeR of (whereR is a fixed number ). Under some technical conditions we prove the following theorems: Let the initial distribution be given by a translation invariant point process onR ¹. Then there exists only one extreme equilibrium state with a given intensityI() satisfyingI()R ^–1, and all ergodic initial distributions with an intensityI()R ^–1 converge weakly ast to the extreme equilibrium state with the same intensity.     

The energy of periodic surface structures in ferromagnetism

The periodic domain structures on unfavourably oriented surface layers of ferromagnetic materials were studied both experimentally and theoretically. The connection between the surface structure and the crystallographic orientation of the crystals was confirmed. All the terms contributing to the total energy of the surface layer were calculated. A general solution of the potential problem is given for arbitrary periodic distribution of the charges.

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True self-avoiding walk on critical percolation clusters and lattice animal

The statistics of true-self-avoiding walk model on two dimensional critical percolation clusters and lattice animals are studied using real-space renormalization group method. The correlation length exponents 's are found to be _TSAW ^pc 0.576 and _TSAW ^LA 0.623 respectively for the critical percolation clusters and lattice animals.     

Stationary states of an electron in the field of a hole in an ionic crystal

An approximate solution is given of the Schrödinger equation for S-states of an electron in the field of a hole, when the potential energy of the electron has the form — e²/r [1+exp (–qr].

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s- , –e²/r [1+exp (–qr].