On the origin of additional peaks in the photoelectron spectra of yttrium

Ultraviolet Photoemission analysis of yttrium metal reveals well defined features far below the conduction band. In order to elucidate their origin, we have used X-ray/Ultra violet photoelectron spectroscopy together with inverse photoemission. The comparison of the spectra of clean yttrium and of H exposed yttrium suggests that these structures are most probably due to hydrogen bands, hydrogen being either in a stable surface hydride form or as subsurface H.     

A matrix method for estimating the Liapunov exponent of one-dimensional systems

Let : [0, 1][0, 1] be a piecewise monotonie expanding map. Then admits an absolutely continuous invariant measure. A result of Kosyakin and Sandler shows that can be approximated by a sequence of absolutely continuous measures _n invariant under piecewise linear Markov maps _itn. Each _itn is constructed on the inverse images of the turning points of . The easily computable measures _n are used to estimate the Liapunov exponent of . The idea of using Markov maps for estimating the Liapunov exponent is applied to both expanding and nonexpanding maps.     

Resolution of photothermal tomographic imaging of subsurface defects in metals with ray optic reconstruction

A capacitive photopyroelectric tomographic technique to obtain photothermal images of cross-sections with subsurface defects of opaque solid samples is reported. Unlike the two-dimensional projection images obtained by conventional photothermal detection methods, a tomographic scanning sequence has been used for cross-sectional imaging of subsurface features. Ray-like propagation of thermal waves is assumed in reconstructing the images. Resolution of these tomographic images with multiple features is investigated. Sensitivity of this reconstruction method to the size and shape of a single subsurface defect is also discussed.     

Study of the Anglular Structure of Emission from the Radio Galaxy 3C295 in the Decameter Wavelength Range

We present the results of observations of the angular structure of the radio source 3C295 at decameter waves using the URAN-1 and URAN-2 interferometers. It is shown that the radio image of 3C295 at these frequencies differs drastically from the structure of this object observed at higher frequencies. The simplest model of the structure of this radio galaxy, comprising one component with a Gaussian brightness distribution of angular size (7.4 ± 0.4)× (8.7± 0.4) at 25 MHz and (9.1± 0.5)× (10.6 ± 0.5) at 20 MHz, is determined. A decrease in the spectral density of the emission with decreasing frequency, observed below 50 MHz, is explained.     

How to Determine the Amplitude-Phase Structure of a 2D Optical Field and a 2D Complex Transfer Function, with the Effect of the Medium Described by Convolution

We consider the solution to the phase problem in optics in application to registration and analysis of the amplitude–phase structure of twodimensional optical fields that form or transmit images, as well as the amplitude–phase structure of transfer and spread functions of media, in which light propagates, or those of systems that form fields or images. The idea of our method is to introduce two additional modulators that visualize phase information. We consider two variants of optical schemes designed for analyzing the amplitudephase characteristics of twodimensional optical fields as well as twodimensional complex transfer and spread functions. These schemes are special because the twodimensional structure of the fields is transmitted at a distance in a disturbing medium or system and four independent twodimensional intensity distributions are to be registered in the course of processing the twodimensional fields. To solve the problem, the first additional modulation preceding the transmitting medium is introduced in the scheme. Then the spectrum of spatial frequencies is formed by the optical system. The second additional spatial modulation is applied either in the optical system plane (the first variant of the scheme) or in the plane of spatial frequencies formed by the optical system (the second variant). A separate optical system is used for registration in the plane of spatial frequencies in the first variant of the scheme and in the image plane in the second variant. The intensity distributions obtained make it possible to solve the problem.     

Methods for Attenuation of the Cross-Modulation Effects in the Wigner–Ville Distribution

We consider the characteristics of typical nonlinear distortions in the dynamical spectra of signals, obtained using the Wigner–Ville method, and discuss the existing techniques for attenuating these distortions. Certain methods are proposed to clean Wigner–Ville distributions of products of the nonlinear interaction between the signal component under study and its more powerful harmonic or pulsed components. The proposed techniques are mainly based on a preliminary linear processing (e.g., using the fast Fourier transform) and/or frequency filtering of the signal. A software package for calculating the Wigner–Ville distribution on a PC is developed. Using this package, we approved successfully the proposed algorithms for test and actual signals.     

Amplitude Profiles of Solar Type IIId Radio Bursts with Echo Components and the Global Dislocation of Their Elementary Quasi-Monochromatic Sources

We prove experimentally the possibility of direct observations of natural radio echoes on the Sun. The generally simple echo hypothesis on the origin of the time splitting in solar type IIId radio bursts sustained the crucial experimental test. These conclusions are based on both the new positional data and previous information obtained using the UTR-2 antenna system in different years since 1973.In summer 1992, we were able to register for the first time a large number of decameter type IIId bursts with pronounced echo-like components using a radioheliograph at frequencies of 20 and 25 MHz. Elementary (quasi-monochromatic) sources of the short-lived bimodal type IIId bursts were observed especially often on July 6. In this case, the time delay of the second peak, which depends on the heliolongitude of the active region, reached a maximum of about 7 s.All these double-peak bursts were localized in the central region of the solar corona, and, similar to the case of single-pulse limb type IIId bursts at a given radio frequency f, the observed elementary sources of these events appeared to be nonstationary. Such a dynamic pulsating source can radically change, at least once, its location in the celestial sphere in the field of view of a two-dimensional radio heliograph during the burst lifetime . While decaying, an echo-like burst formed rather slowly may abruptly jump from one location to another. As far as its short (3- to 4-s) steep-front precursor is concerned, its visible source behaved usually as an ephemeral sub- or ultrarelativistic object moving at a subluminal velocity over a global-scale trajectory.To all appearances, a twice-pulsing, narrow-band ( f/f 0.01) radio burst with an intensity-time profile of type IIId is generally a rather long-term ( 10-20 s) transient response of the solar atmosphere to the short-term flare of harmonic radio emission generated in the real (probably motionless and compact) source. This complex double-peak profile is due not only to the existence of a reflecting surface deep in the corona near the corresponding plasma level but also, to a considerable extent, to some opaque or semi-transparent structures located at heights of the middle corona. In particular, due to the strong influence of such structures, a coronal primary source of a bimodal burst can be seen on the Earth in some indirect rays before the solar radio echo and has the form of an additional delayed pulse.     

Detection on NMR via the anisotropy of X-rays (X-NMR-ON)

Nuclear magnetic resonance on oriented nuclei has been detected for the first time via the destruction of the anisotropy of characteristic L_x-rays. The new method can be applied to isomeric states which decay only via highly converted transitions, for which the standard NMR-ON technique — detection of NMR via the anisotropy of -rays — is not applicable. The X-NMR-ON technique has been used to measure the magnetic hyperfine splitting of^193mpt (I=1322⁺; E=149.8 keV; T_1/2= 4.3 d) to be ¦ g _NB_HF/h¦=111.3 (3) MHz. with the known hyperfine field of –1280(27) kG the magnetic moment of^193mpt is deduced to be ¦¦=0.7417(14) _N. This magnetic moment differs strongly from the known magnetic moments of the 13/2⁺ isomeric states in Hg and Pb and^195mPt.     

Analytic extrapolation inL ∞-norm: An alternative approach to “QCD Sum Rules”

In view of physical applications (especially to QCD Sum Rules), the following problem, pertaining to analytic extrapolation techniques, is studied. We are considering amplitudes, which are (real) analytic functions in the complex plane cut along=[s ₀, ). A modelF ₀(s) of the amplitude is given through the values ofF ₀(s) on some interval=[s ₂,s ₁] (withs ₁<s ₀) and the values of its discontinuity on. These values are approximate, and are supplemented by prescribed error channels, measured inL -norm (both on and). Investigating the compatibility between these data leads to an extremum problem which is solved up to a point where numerical methods can be implemented.Unité Associée au CNRS n^o040768     

Corner transfer matrices of the triangular Ising model

Recently, a new technique for investigating the zero-field, eight-vertex model on the square lattice using corner transfer matrices was suggested by Baxter. In this paper these ideas are applied to the anisotropic, ferromagnetic, triangular Ising lattice in zero field below its critical temperature. The diagonal form of the corner transfer matrix for the triangular lattice shows essentially the same structure as that for the square Ising lattice. The spontaneous magnetization can be obtained easily and agrees with that previously derived.     

A central limit theorem for the Fourth Wick power of the free lattice field

LetG _a be the free lattice field measure of massm ₀ onaZ ^d , and: _x ⁴ : be the corresponding fourth Wick power of the lattice field _x . LetgC ₀ (R ^d ),g0, be a given function anda=a(a)a satisfy: lim _a0+a=0 andaZ ^d aZ ^d . We prove that ifd3, ord=2 and lim _a0+ a|loga|²=, then satisfies the central limit theorem: there isV(a, a) with lim _a0+ V(a, a)= such that the distribution of underG _a is convergent to the standard normal distribution, asa0⁺.     

Radiation of an electric dipole located on the “Coastline”

The radiation characteristics of a vertical electrical dipole located in a narrow transition domain with a different law of impedance variation, as calculated from [4] and [5], are compared with the results in [2]. The sense of the solutions formally obtained earlier is discussed [1, 2]. The process of radiowave propagation along tracks inclined slightly to the coastline is investigated numerically.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 91–95, September, 1972.     

The multipole structure of the electromagnetic field in Friedmann space

In this article the multipole structure of sources of the electromagnetic field is investigated in an expanding universe under the assumption that the electromagnetic field itself is so small that it doesn't introduce any important distortions into the geometry of space time. It is also assumed that the radius of curvature of the universe does not depend on the time. The solutions for the multipole fields of the lower types are given in explicit form.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 34–39, August, 1973.The authors express their sincere gratitude to V. I. Rodichev for a helpful discussion of this work.     

Static and stationary axially symmetric gravitational fields of bounded sources II. solutions obtainable from Weyl's class

This paper shows that a new class of axially symmetric static electrovacuum/magnetovacuum solutions is obtainable from Weyl's class of static vacuum solutions. The new class contains an infinite set of asymptotically flat solutions (in closed form) each of which involves an arbitrary set (d, _i) of parameters. These parameters have to be interpreted as functions of massm, chargee, and higher electric/magnetic multipole moments _i of the particle. The cased = 0, _i =0 leads to the Darmois solution and the cased = 0, _i 0 leads to the results of [1]. The case d=0, e=_i=0 leads to the Schwarzschild solution, the cased 0, _i =0,e 0 leads to the Reissner-Nordström solution. To get more general examples is a lengthy but straightforward exercise.     

Identification of linear distortions in optical systems in the presence of impulsive noise

Conclusion The efficiency of the procedures described above was checked experimentally using three test images. The corresponding information technology included the stages of modeling linear blur-type distortions on a microcomputer, the superposition of impulsive noise on the image, and identification of the pulse response. The experiments confirmed the efficiency of the methods presented here.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 152–156, September, 1995.     

Spanning lengths of percolation clusters

The spanning length of a percolation cluster is defined as the difference between the maximum and minimum coordinates of the cluster with respect to some chosen direction. It is statistically related to the number size of the cluster by an exponent that differs from the iriverse dimension that would characterize a compact cluster. This exponent for large percolation clusters in simple cubic lattice sites was studied by the Monte Carlo technique, and results are presented. Previous theoretical treatments of this exponent and its relationship with other critical exponents are discussed.In the present paper we shall refer exclusively to the site percolation problem, and all our definitions will be within that context.     

Testing and Analysis of the Structure of Transmitting Media or Objects with Registration of the Field Structure in the Image Plane

A solution to the phase problem in optics is considered within the context of the registration and analysis of the amplitude–phase structure of optical nonuniformities in stationary transmitting media or in investigated objects. To solve the problem, the object or the medium is tested by radiation with a known structure. For a certain selected direction of testing, the structural change due to the interaction with the object is registered. To obtain information on the amplitudes and phases of the testing light field, an original development of the modulationspectral method put forward by the authors is used. To solve the problem, the intensity distribution is detected in the image plane both for an unmodulated field and for that subjected to an additional twodimensional modulation specially formed in the plane of spatial frequencies. The modulation should provide a visualization of the phase information contained in the light field. The intensity distributions obtained make it possible to determine the twodimensional structure of the testing field at the output of the medium or the object. In the proposed variant of the method, the testing field should not be affected in the investigated plane. The interpretation of the results is easier, since it is the image that is registered. The two intensity distributions can be registered simultaneously, provided the light beam is divided into two channels after the optical system. It is significant that the method requires no iteration procedures in solving the problem. This allows one to expect speedingup of the processing of the information and analyzing it in almost real time. Two variants of optical schemes are considered in the paper. The first one deals with media or objects with a modulation effect described by multiplication by a complex function characterizing the effect. In the second case, the effect of the object leads to redistribution of the radiation in the investigated plane and is described by the operation of convolution of the testing signal and the function characterizing the effect.     

Form of the Frequency Spectrum of Fluctuating Radiation in the Case of Interferometric Reception During Experiments on Radio Sounding of the Solar Corona

We study theoretically the profile of a spectral line of radiation which is received by an interferometer after propagation through a medium with developed turbulent structure. We derive a formula describing the resulting frequency spectrum of an initially monochromatic radiation after its propagation through a multi-scale medium with strong large-scale and weak small-scale irregularities. It is shown that the frequency spectrum observed in this case should comprise the main spectral line with Gaussian profile and wings decreasing according to a power law with index dependent on the orientation of the interferometer baseline with respect to the direction of regular drift of frozen-in irregularities of the medium. We analyze distortions of the spectral response of a very-long-baseline interferometer due to the effect of large-scale irregularities of a medium with developed turbulent structure on wideband radiation from extraterrestrial discrete radio sources. It is shown that if the amplitude fluctuations of the received radiation are weak, then the measured frequency spectrum contains information on the drift velocity and the index of the spatial spectrum of interplanetary plasma irregularities with scales from hundreds to thousands of kilometers.     

On the survival probability of a random walk in a finite lattice with a single trap

We consider the survival of a random walker in a finite lattice with periodic boundary conditions. The initial position of the random walker is uniformly distributed on the lattice with respect to the trap. We show that the survival of a random walker, U _n>, can be exactly related to the expected number of distinct sites visted on a trap-free lattice by U _n=1–S _n/N ^D (*) whereN ^D is the number of lattice points inD dimensions. We then analyze the behavior of S_n in any number of dimensions by using Tauberian methods. We find that at sufficiently long times S _n decays exponentially withn in all numbers of dimensions. InD = 1 and 2 dimensions there is an intermediate behavior which can be calculated and is valid forN ²N 1 whenD = 1 andN lnN n 1 whenD = 2. No such crossover exists when Z3. The form of (*) suggests that the single trap approximation is indeed a valid low-concentration limit for survival on an infinite lattice with a finite concentration of traps.     

Feedback-controlled two-wave coupling in reflection geometry: application to lithium niobate crystals subjected to extremely high external electric fields

An active stabilization of photorefractive two-wave coupling by means of an electronic feedback loop has been used extensively during recent years in transmission geometry. It leads to 100% diffraction efficiency and also to periodic states instead of familiar steady states. We investigate the feedback operation in the case of reflection geometry, especially for iron-doped lithium niobate (LiNbO₃:Fe) crystals. This includes formulation of the feedback equations, numerical analysis of the operation regimes for LiNbO₃ crystals, and comparison between theory and experiment, which is performed in the range of applied electric fields from 0 to 650kVcm^-1. The main findings are as follows: (i) the feedback does not lead to periodic states, (ii) it modifies the photorefractive response by introducing a frequency shift and maximizes , and (iii) there is a close relation between the enhancement of and the resonant excitation of space-charge waves predicted earlier in ferroelectric materials. PACS 42.40.Ht; 42.65.Hw