Chaos in phase conjugation: physical vs numerical instabilities

Four-wave mixing equations in photorefractive media are approximated by different dynamical models and treated by different numerical methods. It is shown that the onset of instabilities and irregular behaviour in the same crystal, with a single wave mixing region, may be dependent both on the model used and the numerical method applied. Long-time irregular dynamics following from any finite-order difference schemes should be viewed with caution.     

Parallel interconnection and neural network systems employing semiconductor array technology and computer-generated holography

An experimental 16-channel parallel interconnection system able to support 100 Mbits^–1 per channel and an opto-electronic neural network operating at up to 50 Mbits^–1 have been constructed to demonstrate the potential of optics in processing systems. Both experiments operate at a wavelength of 1.5m. Components developed for these systems include arrays of InGaAs/InP MQW surface modulators for low-power electrical-to-optical conversion; InGaAs/InP for detector arrays, which are hybrid integrated with GaAs amplifier arrays; and computer-generated holograms for efficient beam splitting and to encode weights in the optical beam intensities. Each of these demonstrations has considerable scope for increasing the degree of parallelism and the operating speed. Recent modifications to the neural network enable the weights to be varied and training has been demonstrated with a novel algorithm that uses the high operating speed to advantage.     

Dipolar 31P NMR spectroscopy of crystalline inorganic phosphorus compounds.

The ability of the 90 degrees-t1-180 degrees pulse sequence to produce accurate dipole-dipole coupling information in solids is investigated. To this end, the experimental 31P spin echo decays are measured for eighteen crystalline phosphides and phosphorus chalcogenides and compared with simulations, based on the known internuclear distances in these compounds. The experimental results are generally found accurate in compounds where the dominant contribution to the dipole-dipole coupling arises from nuclei in structurally inequivalent sites with large chemical shift anisotropies. For this situation, the quantum mechanical "flip-flop" term in the dipolar Hamiltonian is suppressed and the dipole-dipole coupling is entirely heteronuclear in character. All of those compounds that do not obey this condition show accelerated spin echo decays due to a fractional contribution of the flip-flop term and possibly incomplete refocusing of chemical shift terms on the time scale of the experiment. The results confirm on an empirical basis that the spin echo NMR technique can provide accurate dipole-dipole coupling information (and thus distance distributions) in disordered solids and glasses.     

Large third-order nonlinear optical properties of C70 fullerene in the infrared regime

The nonlinear third-order optical susceptibility of C₇₀ in a toluene solution is measured for the first time by the method of degenerate four-wave mixing using 10 ns laser pulses at 1.06 m. The third-order susceptibility X _in ⁽³⁾ is 5.6×10^–12 esu for a C₇₀ toluene solution at a concentration of 0.476 g/l. The correspondent magnitude of the hyperpolarizability ₁₁₁₁ of the C₇₀ molecule is 1.2×10^–30 esu which is in a good agreement with the prediction given by the model of a free electron in a spherical box.     

Electrical activity of dislocations: Prospects for practical utilization

The electrical activity of interfacial misfit dislocations in silicon has been examined using the electron beam induced current technique (EBIC) in a scanning electron microscope. Clean misfit dislocations, i.e. no EBIC contrast, formed during high-temperature Si(Ge) chemical vapor epitaxy were studied. These defects were subsequently decorated with known metallic impurities (Au and Ni) by diffusion at 400° C to 1130° C from a back-side evaporated layer. Qualitative analysis of the electrical activity in relation to the energy levels anticipated for the clean or decorated dislocations is presented. Of particular interest is the case of defect-induced conductivity type inversion which occurred both at the top surface and at the buried dislocated interfaces of the multilayer. The prospects for using dislocations in a beneficial manner as active elements in electronic devices are discussed.     

Production properties ofD 0,D +,D *+ andD s + in 230 GeV/cπ − andK −-Cu interactions

We have studied the hadronic production of charmed mesons in the NA 32 experiment at CERN. A special trigger together with a high resolution vertex detector consisting of charge coupled devices and silicon microstrip detectors allowed the selection of very clean samples of charmed mesons. We have collected 852 fully reconstructed decays: 60D _s ⁺ →K ⁺ K ^?π⁺, 543D°→K ^?π⁺ andK ^?π⁺π^?π⁺ as well as 249D ⁺→K ^?π⁺π⁺ (or charge conjugate). 147 mesons out of our \({{D^0 } \mathord{\left/ {\vphantom {{D^0 } {\bar D^0 }}} \right. \kern-0em} {\bar D^0 }}\) sample were produced via chargedD ^* state. For all charmed mesons we determine the total production cross-section and study thex _F andp _t ² distributions.     

Isopropylation of indoline

The composition of the reaction products was ascertained, and the kinetics of the alkylation of indoline with isopropyl alcohol in 90% sulfuric acid at 60C were studied. The reactivities of indoline and its carbocyclic analogs are compared.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 920–922, July, 1991.     

Proanthocyanidins of Rhodiola semenovii

The structures of two compounds previously isolated fromRhodiola semenovii, rhodokhinoside (I) and rhodikhim (II), have been established.     

On weak and Moments Convergence of Randomly Indexed Sums

Let {X_n, n ? 1) be a sequence of independent random variables such that EX_n = a_n, E(X_n ? a_n)² = σ, n ? 1. Let {N_n, n ? 1} be a sequence of positive integer-valued random variables. Let us put In this paper we present necessary and sufficient conditions for weak and moments convergence of the sequence {(S-L_n)/s_n, n ? 1}, as n → ∞. Hermite polinomial type limit theorems are also considered. The obtained results extend the main theorem of M. Finkelstein and H. G. Tucker (1989).     

Debonding of thin external layer exerted by thermodiffusive fluxes

Summary The stress distributions in a matrix, generated by thermodiffusive fluxes, are determined for the case of a thin, inextensible membrane bonded to the bounding plane over the outer regionr (b>0, ). The problem has been reduced to solving a corresponding system of dual integral equations. There exist singularities in the distribution of contact shear stresses, namely one over square root type atr=b while a logarithmic one at the lines of jumps of temperature and/or mass diffusion.

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Ablösung einer dünner Schicht infolge thermodiffusiver Flüsse

Übersicht Es wird die sich in einer Matrix infolge thermodiffusiver Flüsse einstellende Spannungsverteilung ermittelt wobei auf einen Teil der Grenzfläche (im Bereichr (b>0, )) eine dünne und unverschiebliche Membran aufgebracht ist. Zur Lösung wird das Problem auf ein System von dualen Integralgleichungen reduziert. Die in den Kontaktschubspannungen auftretenden Singularitäten sind einerseits vom reziproken Quadratwurzeltyp am Innenrand, andererseits vom logarithmischen Typ bei Sprüngen in der Temperatur und/oder Massendiffusion.