A technique for investigating the Faraday effect in pulsed magnetic fields

A technique for measuring the Faraday effect is described which enables measurements to be made in strong fields; such investigations are usually hard to perform. The technique has an adequate sensitivity and accuracy.In conclusion, we express our sincere gratitude to Corresponding Member of the Academy of Sciences of the USSR, B.I. Verkin for his interest and assistance.     

A further contribution to the theory of the transient hot-wire technique for thermal conductivity measurements

We study the density of states of a one-dimensional tightbinding electron model with random hopping elements. The Hamiltonian is $\text{H = -∑}{}_{\mathrm{i}}\text{J}{}_{\mathrm{<mtext>i+</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{(a}{}^{\mathrm{+}}{}_{\mathrm{i}}\text{a}{}_{\mathrm{i+1}}\text{+a}{}^{\mathrm{+}}{}_{\mathrm{i+1}}\text{a}{}_{\mathrm{i}}\text{)}$, where the $\text{J}{}_{\mathrm{<mtext>i+</mtext><mtext>1</mtext><mtext>2</mtext>}}$'s are independent identically distributed random variables. It is proved that the single particle density of states D(E) diverges near E = 0 as $\text{1}\text{|(E}\text{log}{}^3\text{|E|)|}$.     

Scanning technique for investigating optical fibre dispersion

Differential mode delay measurements have been performed, both for step-index and for graded-index fibres, using a sinusoidally modulated optical source. From a differential mode delay measurement, it is possible to get all the information on the fibre baseband response with or without the effect of skew rays, and in particular of leaky rays. A theoretical model of mode coupling is developed and is used for computing the baseband response for fibres where mode coupling is not negligible.     

A contribution to the theory of the C–V technique for the evaluation of carrier-concentration profiles in semiconductors

An extension of the previously developed theory (the integral capacitance technique (ICT)) for the evaluation of the carrier-concentration profile in semiconductors is presented. It is shown that there is a possibility to determine the space-charge density at the edge of a depletion layer straightforwardly from experiment, without additional calculation procedures. This gives a sufficient advantage of the method proposed against those previously developed owing to excluding from the consideration the whole range of the C–V data, which are necessary for the ICT or DCT (differential capacitance technique) implementation. The method is based on the combination of a traditional C–V differential capacitance measurement and the measurement of the proper capacitance (integral capacitance) performed separately and at the same value of the applied voltage. PACS 84.37.+g;61.72.Tt;73.40.Ty;73.40.Vz;61.72.Ss;81.70.Jb     

Spontaneous Raman scattering: a useful tool for investigating the afterglow of nanosecond scale discharges in air

Nanosecond scale discharges are considered an interesting way for assisting combustion by enhancing either flame stabilization or ignition. Better understanding of energy deposit and radical species production processes is still required under pressure conditions normally encountered in combustion. The purpose of the present paper is to show that spontaneous Raman scattering, seldom used to investigate nanosecond pulsed discharges, is a useful measurement method for investigating the energy deposit of these discharges. The advantage of spontaneous Raman scattering is described by analyzing N₂ and O₂ spectra during the post-discharge of a filamentary nanosecond air discharge under atmospheric pressure, using phase-locked average spectra. The main advantages of spontaneous Raman scattering measurements are that they allow line-wise probing of different species with the same experimental setup and the determination of vibrational distribution by comparison with theoretical modeling over a wide range of vibrational levels (from v=0 to v=20 for N₂). The model proposed takes into account the high level of vibrational excitation and the strong non-equilibrium observed, allowing the characterization of the vibrational relaxation over the complete post-discharge duration. Although the rotational structure is not resolved, the rotational temperature and thus translational temperature are determined with a moderate uncertainty for T above 500 K.     

A contribution to the linear magnetoresistance problem

It is shown that semi-classical transport theory provides an extremely accurate prediction of the limiting high field transverse magnetoresistivities of the compensated metals Cd, Pb and W. These results invalidate those theoretical models based on scattering effects which have been proposed to explain the linear term in the magnetoresistivities of K, Al and In. We argue that the only remaining viable models are those based on the effects of sample imperfections and inhomogeneities.     

A contribution to the theory of X-ray monochromators

The characteristic function is introduced, describing completely the monochromating effect of monochromating units. Expressions for this function are presented for monochromating units frequently used. An example of computation for Johansson's unit shows the conditions in a special case. The curves indicating the shift of the wavelength centroid of monochromated radiation for crystals of different perfection allow conclusions to be drawn about the influence of the alignment of the crystal on precision measurements of lattice constants. The experiments verify the suggested model. The computations for a given experimental arrangement permit a simple determination of the effective breadth of the reflection curve, if a distance of two suitably chosen diffraction lines of a polycrystalline specimen is measured. Finally, it was found experimentally that a small elastic bending does not essentially alter the reflection curve of highly elastic and imperfect crystals unless macroscopic distortions are present.

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The author is deeply grateful to Prof. A. Kochanovská for her encouraging interest and wishes to express his thanks to Z. Hemanová for her careful computations.     

A contribution to the determination of optical constants

A method is described for determining optical constants by means of a computer on the basis of intensity measurements and the computed results for a weakly absorbing substance in the form of a thin film are used to demonstrate the multiplevaluedness of the transmission-reflection measuring method.     

A contribution to the problem of effective particle-hole interactions

Various effects arising in nuclear-structure calculations and leading all to a renormalisation of the nucleon-nucleon interaction are reviewed. A new treatment is proposed for the renormalisation due to mixing of the particle-hole subspace and then particle ?n hole (n=2, 3, 4 etc.) subspaces.     

A contribution to the characterization of laser-hardened steel surfaces

The article deals with the possibility to characterize the laser heat-treatment of steel surface by means of X-ray diffraction and microhardness measurements. For tensometric analysis the X-ray one-tilt method with no reference substance was used. It is shown that hardened surface layers of the carbon steel are affected by compressions reaching in the middle of the laser beam track up to ≈ 350 MPa. The microhardness increased by as much as 350 %. Presented at the 6th Joint Seminar “Development of Materials Science in Research and Education”, Karlštejn, Czech Republic, 17–19 September 1996. This research is a part of the research project supported by Grant Agency of the Czech Republic (Grant No. 106/95/0080).     

A contribution to the theory of some photographic effects

The increase in sensitivity of a photographic layer by pre-illumination, the Clayden effect and the Villard effect are explained as special cases of the influence of multiple exposure on a sensitive layer. It is shown that the known fact can be explained by the theory of the intermittent effect which is based on the assumption of the inertia of electron processes in AgBr crystals.     

A contribution to the domain structure of iron whiskers

The paper contains an interpretation of the domain patterns found on iron whiskers. An explanation of the closure structure at the end of a whisker grown in the [111] direction is given on the basis of a quantitative analysis. Structures, which form on whiskers strained by axial pressure and bending, are also dealt with. The results are in good agreement with experiment.

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A contribution to the systematics of stochastic volatility models

We systematically compare several classes of stochastic volatility models of stock market fluctuations. We show that the long-time return distribution is either Gaussian or develops a power-law tail, while the short-time return distribution has generically a stretched-exponential form, but can also assume an algebraic decay, in the family of models which we call “GARCH” type. The intermediate regime is found in the exponential Ornstein-Uhlenbeck process. We also calculate the decay of the autocorrelation function of volatility.