Determination of internal scale of artificial ionospheric turbulence in direction of geomagnetic field

A 150-MHz satellite beacon is used to determine the internal scale in the direction of the geomagnetic field I₀ for the spectrum of artificial ionospheric turbulence created by the Yastreb heating facility located near Nizhny Novgorod in continuous operation at a frequency of 5.75 MHz (ordinary polarization) with effective power P·G100·150 kW. It is found that I₀ 3–4 km for transverse inhomogeneity scales I 1–2 km and I 0.7–0.9 km for I 0.5 km.Nizhny Novgorod Scientific-Research Radio-Physics Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 4, pp. 521–525, April, 1994.     

The Chiral Bag Model and properties of the πNΔ system

The effective Hamiltonian for theN system is proposed in the framework of the Chiral Bag Model (CBM). The taking into account of gluonic and pionic correctinos to the pion-nucleon coupling constantg _N and the-decay axial constantg _A leads tog _N 13·5,g _A 1·28 which are in good agreement with experimental data.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.I wish to thank Gulamov K. G., Shelest V. P. and Zinoviev G. M. for useful discussions.     

New Possibilities of Radioastronomical Diagnostics of the Jovian Magnetosphere Using the Observed Polarization of its Decameter Radio Emission

We discuss possibilities of diagnostics of the Jovian magnetosphere based on the results of measurements of the polarization characteristics of the decameter radio emission. It is shown that the essentially elliptical polarization of that radiation and its generation at frequencies near the local electron gyrofrequency opens new possibilities for radioastronomical diagnostics of the Jovian magnetosphere. The plasma distribution can be studied not only along the radiation path but also in the transverse direction, i.e., over latitudes. Moreover, since the relative position of the source and observer during a decameter noise storm is rather stable, it is possible to perform tomography of the magnetosphere (its diagnostics at different longitudes) using the planet rotation. We present the examples of diagnostics of different regions in the Jovian magnetosphere, such as sources of decameter radio emission, i.e., lower-magnetosphere regions located at a distance of about 1.5-2 R_J from the center of the planet, and the Io plasma torus located at a distance of about 6R_J from the center of the planet. It is pointed out that the number density of the magnetospheric plasma outside the Io magnetic flux tube is small (n 1 cm^-3 at the height of the gyroresonance level f_Be 30 MHz) while it is higher inside this flux tube at the same height: n 3 cm^-3. We estimate the variations in the number density of the plasma along the Io magnetic flux tube (n B, 1-1.8), determine the rate at which the integral plasma density varies over latitudes (d( n dz)/dh 2· 10³ cm^-3), and find the average number density of the plasma in the region where the radiation crosses the Io torus ( n 2· 10³ cm^-3).     

Radius,perimeter, and density profile for percolation clusters and lattice animals

Monte Carlo simulation and series expansion shows the radius of gyration of large clusters withs sites each to vary ass with0.56 in two and0.47 in three dimensions at the percolation threshold, and with(d=2)0.65 and(d=3)0.53 for random lattice animals (zero concentration). Clusters up tos=100 were used. The perimeter of random animals approaches 2.8s for larges on the simple cubic lattice. Monte Carlo simulation of the Eden process (growing animals) up tos=5,000 indicates a systematic variation of about ±0.05 for the effective exponent=(s) and thus suggests that the true asymptotic exponents may be compatible with the predictions of hyper-scaling.     

Remarks on finiteW algebras

The property of some finiteW algebras to be the commutant of a particular subalgebra of a simple Lie algebraG is used to construct realizations ofG. WhenGso(4, 2), unitary representations of the conformal and Poincaré algebras are recognized in this approach, which can be compared to the usual induced representation technics. WhenGsp(2,R) orsp(4,R), the anyonic parameter can be seen as the eigenvalue of aW generator in suchW representations ofG.Presented by P. Sorba at the 5th International Colloquium on Quantum Groups: Quantum Groups and Integrable Systems, Prague, 20–22 June 1996.P. Sorba would like to express his warm thanks to Professor estmír Burdík for the perfect organisation of the conference.     

Thickness dependence of the spin- and angle-resolved photoemission of ultrathin,epitaxial Ni(111)/W(110) layers

The thickness dependence of the magnetic band structure of ultrathin, epitaxial Ni(111)/W(110) layers has been studied by spin and angle-resolved photoemission spectroscopy. The changes of the spin-resolved photoemission intensities upon reducing the layer thickness depend strongly on the wavevector along the -L line of the Brillouin zone. The measured exchange splitting atk 1/3(-L) andk 1/2(-L) is found to be independent of the layer thickness for layers consisting of 3 or more atomic layers, while decreases rapidly with the layer thickness atk2/3(-L). This behavior is very similar to the temperature dependence of the spin-resolved photoemission spectra of bulk Ni(111) at the samek-points.     

Replica symmetry breaking in attractor neural network models

The phenomenon of replica symmetry breaking is investigated for the retrieval phases of Hopfield-type network models. The basic calculation is done for the generalized version of the standard model introduced by Horner [1] and by Perez-Vicente and Amit [2] which can exhibit low mean levels of neural activity. For a mean activity the Hopfield model is recovered. In this case, surprisingly enough, we cannot confirm the well known one step replica symmetry breaking (1RSB) result for the storage capacity which was presented by Crisanti, Amit and Gutfreund [3] ( _c ^1RSB 0.144). Rather, we find that 1RSB- and 2RSB-Ansätze yield only slightly increased capacities as compared to the replica symmetric value ( _c ^1RSB 0.138 186 and _c ^2RSB 0.138 187 compared to _c ^RS 0.137 905), significantly smaller also than the value _c ^sim =0.145±0.009 reported from simulation studies. These values still lie within the recently discovered reentrant phase [4]. We conjecture that in the infinite Parisi-scheme the reentrant behaviour disappears as is the case in the SK-spin-glass model (Parisi-Toulouse-hypothesis). The same qualitative results are obtained in the low activity range.Supported by Sonderforschungsbereich 123 Stochastische Mathematische ModelleSupported by a Heisenberg fellowship     

Spectral response of CdS with Ag,Cu, and in impurities

High-resistance (dark 10⁸ · cm) photosensitive CdS samples (light 10²–10³ · cm at saturation) were obtained from low-resistance ( 0.1 · cm) nonphotosensitive CdS single crystals by thermal diffusion of Cu, Ag, and In in vacuum at 2 · 10^–5 torr. The spectral response of impurity and pure high-resistance photosensitive single-crystal CdS samples was studied in the wavelength range from 0.35 to 3. The short-wave and long-wave limits of the spectral curves, the wavelength range of maximum photoconductivity and the forbidden band width, the depth of impurity levels, the upper edge of the impurity band, and the depth of maximum-density activation centers have been determined from the spectral curves. The results are discussed and compared with published data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 117–121, June, 1972.     

Correlated majority model

We extend the bichromatic majority model by including (one-dimensional isotropic) correlations and numerically discuss, through Monte Carlo simulations, the simple, 1/3, and 2/3 majority rules. We calculate, as functions of the concentration and correlation degree, the mean finite cluster size, and the order parameterm as well as their respective critical exponents and. We find1 regardless of the correlation degree or the type of majority. Also, a supplementary divergence of is observed at the>0 borderline.     

Asymptotic and essentially singular solutions of the Feigenbaum equation

For suitably defined largeN, we express Feigenbaum's equation as a singular Schroder functional equation whose solution is obtained using a scaling ansatz. In the limit of infiniteN certain self-consistency conditions on the scaled Schroder solution lead to an essentially singular solution of Feigenbaum's equation with a length scale factor of 0.0333 and. a limiting feigenvalue of 30.50, in agreement with Eckmann and Wittwer's value of =0.0333831... and their conjectured estimate of 30.     

Pulsations and chaos in laser-produced plasmas

A general criterion is proposed predicting the onset of chaotic behavior for parametric processes in a laser-produced plasma. The conditions when the transition to the stochastic regime occur are determined for various parametric instabilities excited when a high intensity laser interacts with a plasma. The complicated temporal structure observed in 3/2₀, 2₀, 1₀, and fast electron emission in experiments using high-intensity (I10^15–17 W/cm²), short ( _L 40–200 psec) Nd laser pulses is attributed to the reflection seeded SBS instability being driven into this regime.Lebedev Physics Institute, Leninsky Prospect 53, Moscow 117924 Russia.     

Crossover to tricritical behavior at the nematic to smecticA transition: An x-ray scattering study

We have carried out a comprehensive x-ray scattering study of the nematic to smecticA transition in the alkylbenzoate (nCB) and thiosulfate series. By changing the aliphatic chain lengthn (C _n H_2n+1) in these series, crossovers from critical to tricritical behavior are induced. We observe a smooth progression of effective exponents from the set,y1.5,v 0.80, andv 0.67 toy=1.1,v =0.6, andv =0.5 for the critical and tricritical regions respectively. In both cases the exponents are close to, but in disagreement with, values expected from current theoretical models. We conclude on an empirical basis that the varied exponents reported in the literature for other systems reflect the critical to tricritical crossover.     

Properties of MOS-structures based on anode-oxidized CdSnAs2

The properties of metal (Al, Au)-anodic oxide-CdSnAs₂ monocrystal structures are studied. It is established that MOS-structures using undoped CdSnAs₂ crystals show a high positive fixed charge in the anodic oxide (N_S 5·10¹² cm^–2) and high surface state density on the oxide-CdSnAs₂ boundary surface (N_SS 2·10¹³ cm^–2·eV^–1). In MOS-structures using diffusion-doped (copper) crystals the sign of the fixed charge is negative (N_S 10¹¹ cm^–2, N_SS 2·10¹² cm^–2·eV^–1). The latter structures show a definite photosensitivity and photomemory. The possibility of effective control of the fixed charge value within the oxide by illumination is shown. The surface state distribution over energy, time constant, and capture section is determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 90–93, September, 1982.     

Structural phase transition and internal fields in rubidium thiocyanate probed through vibrational spectroscopy

A comprehensive vibrational study of Rubidium thiocyanate (RbNCS), in the 298–448°K range reveals that the orthorhombic to tetragonal transition atT _c440°K is of order-disorder type exhibiting purely second order characteristics. A consistent order-parameter exponent 0.45±0.04 has been obtained from both Raman and IR measurements. In the Raman spectra, the appearance of sidebands in both the C–N&C–S stretching modes and their temperature dependence indicate the existence and a gradual diminution of internal electric field asT approachesT _c. These results have been discussed in the context of an anharmonic oscillator model. An activation energy (U) for the reorientational motion of NCS^– ions,U0.29±0.02 eV, has been calculated from large changes in the bandwidth (_C-N) nearT _c.     

Oxygen diffusion and dynamical disorder in high-T c superconductors: low frequency noise in superconducting tunnel junctions

The equilibrium diffusion fluctuations of oxygen concentration in HTSC are considered as a possible source of the low frequency current/voltage noise in tunnel junctions near the transition temperature in the frames of the model independent phenomenological approach. The general expression for the noise spectrum,S(), is obtained. It is shown that the noise is diffusion-like,S()^–2, and it is proportional to the square of the contact current/voltage. The noise magnitude is sharply peaked near the maximal critical temperature achievable for a given type of HTSC by an optimal oxygen doping.The noise cutoff frequency, below which it can be observed on the thermal background, has the activation like temperature dependence and is estimated to be 1s ^–1.The other possible consequences of the oxygen concentration fluctuations in HTSC are discussed.     

The magnetic behavior of CeB6: Comparison between elastic and inelastic neutron scattering,initial susceptibility and high-field magnetization

We report measurements of the elastic and inelastic neutron scattering, initial susceptibility and high-field magnetization on thoroughly prepared poly- and single crystalline samples of CeB₆. Part of these experiments have been performed at temperatures down to 60 mK and magnetic fields up to 70 kØe. Our neutron-diffraction data provide the first proof that CeB₆ is an antiferromagnet belowT _N2K as has been suggested by previous bulk experiments. The reduced value of the low-temperature magnetic moment both below and aboveT _N points to the existence of a Kondo effect of the ₇ crystal-field (CF) ground state of Ce³⁺. From the low-temperature width of the quasielastic neutron line, the Kondo temperature is inferred to beT _K3 K. The thermal variation of the initial susceptibility (forT>20K) is semiquantitatively explained invoking, besides the Kondo effect, a ₇- ₈ CF splitting of 70 K and magnetic interactions, which are about 10 times stronger between ₈ states than those between ₇ states. This large ₈- ₈ exchange interaction is also assumed to account for the most striking result of this work, i.e. the lack of any CF-transition peak up to 44 meV in our inelastic neutron-scattering spectra.     

On the existence of invariant,absolutely continuous measures

Let (, , ) be a measure space with normalized measure,f: a nonsingular transformation. We prove: there exists anf-invariant normalized measure which is absolutely continuous with respect to if and only if there exist >0, and , 0<<1, such that (E)< implies (f ^–k(E))< for allk0.     

The structure of ‘nearly’ ferroelectric RADP

X-ray scattering techniques have been used to study the structures of two crystals of Rb_1–x (NH₄) _x H₂PO₄ withx0.2, near to the boundary between ferroelectric and structural-glass behavior at low temperature. Below about 83K, both crystals develop shortrange incommensurate correlations with a wavevectorq0.13 a ^* which are presumably related to the glass properties. On cooling below 70 K, the crystal with the slightly larger NH ₄ ⁺ concentrationx, develops the ferroelectric structure in a small fraction of the crystal, while the bulk of the crystal retains the tetragonal structure. The other crystal transforms almost wholly to the ferroelectric phase. The transition to the ferroelectric structure shows considerable hysteresis on heating and cooling, and is spread over about 20 K. The transition is certainly of first order, and the spread in temperature may arise from concentration fluctuations. These results and the structure of the incommensurate modulations are compared with the predictions of a theoretical model for this system.     

Dynamical bifurcation with noise

It was shown by A. Neishtadt that dynamical bifurcation, in which the control parameter is varied with a small but finite speed , is characterized by adelay in bifurcation, here denoted _j and depending on . Here we study dynamical bifurcation, in the framework and with the language of Landau theory of phase transitions, in the presence of a Gaussian noise of strength . By numerical experiments at fixed = ₀, we study the dependence of _j on a for order parameters of dimension 3; an exact scaling relation satisfied by the equations permits us to obtain for this the behavior for general . We find that in the smallnoise regime _j() a(^–b ), while in the strong-noise regime _j() – ce(^–d); we also measure the parameters in these formulas.     

Galaxy formation just after the recombination period

A scenario of galaxy formation is outlined which is based essentially on the fact that the cosmic matter about 10⁶yr after the end of the recombination period is a general relativistic Boltzmann gas very close to equilibrium. In this scenario the observed very small inhomogeneities of the background radiation lead to very sharply edged gas clouds in the centres of the inhomogeneities. The universe between the clouds is completely swept clean of matter. If one assumes the centres of the inhomogeneities to be axially symmetric, the mass spectrum of the clouds extends from the smallest globular clusters withM 10⁵ M as the lower limit (spherical symmetry) up to the big spiral galaxies withM 10¹¹ M as the upper limit (maximal flattening). The upper limit masses are extremely thin pancakes which contract within a time interval of about 2 · 10⁹ years to the proportions of an ordinary spiral galaxy of today.