Grid oscillators

Loading a two-dimensional grid with active devices offers a means of combining the power of solid-state oscillators in the microwave and millimeter-wave range. The grid structure allows a large number of negative resistance devices to be combined. This approach is attractive because the active devices do not require an external locking signal, and the combining is done in free space. In addition, the loaded grid is a planar structure amenable to monolithic integration. Measurements on a 25-MESFET grid at 9.7 GHz show power-combining and frequencylocking without an external locking signal, with an ERP of 37 W. Experimental far-field patterns agree with theoretical results obtained using reciprocity.     

Reflex oscillators

Acta physica Academiae Scientiarum Hungaricae - Comparing the mechanism of reflex klystron and Barkhausen-Kurz oscillators, we found them principally to be the same. Both are feed-back oscillators,...     

Fibonacci oscillators

We discuss the properties of oscillators whose spectrum is given by a generalized Fibonacci sequence. The properties include: invariance under the unitary quantum group, generalized angular momentum, coherent states and difference calculus, relativistic interpretation.     

Deformed supersymmetric oscillators

We construct and discuss the Fock-space representation and the number operator for a deformed supersymmetric oscillator with “peculiar” statistics. We suggest a possible generalization to multimode deformed oscillators.     

Dissipative hydrodynamic oscillators

Summary The oscillatory motion of a liquid-liquid interface induced by the Marangoni effect,i.e. the variation of surface tension with the concentration of a surfactant, is described as the harmonic oscillation of the surfactant concentration at the interface. Then, at vanishing damping, threshold values and parameter regions for sustainedlongitudinal (Marangoni-Lucassen) waves are given in terms of the transport coefficients of the two liquids. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Self-interacting one-dimensional oscillators

Energy eigenvalues and 〈x ²〉 _n for the oscillators having potential energyV(x)=(ω ² x ²/2)+λ<x ^2r >x ^2s have been determined for various values ofλ, r, s andn using renormalized hypervirial-Padé scheme. In general, the results show an improvement over the findings of earlier workers. Variation of the evaluated quantities and of the renormalization parameter withλ, r, s andn has been discussed. In addition, this potential has been employed as an illustrative example of the applicability of alternative formalism of perturbation theory developed by Kim and Sukhatme (J. Phys. A25 647 (1992)).     

Dissipative hydrodynamic oscillators

Summary New theoretical predictions concerning overstability of viscoelastic fluids are given in terms of the Prandtl number and the ratio of viscoelastic relaxation to thermal diffusion times.

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Riassunto Si danno nuove previsioni teoriche che riguardano la sovrastabilità di fluidi viscoelastici nei termini del numero di Prandtl e del rapporto tra il rilassamento viscoelastico e i tempi di diffusione termica.

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Резюме Предлагаются новые теоретические предсказания, касающиеся устойчивости упруговязких жидкостей. Предложенный подход основан на числе Прандтля и отношении времени упруговязкой релаксации к времени термодиффузии.

     

Dissipative hydrodynamic oscillators

Summary Suitable transformations are used to convert the two-component Lorenz model for double-diffusion, Soret-driven convection and the laser with saturable absorber into either a Duffing oscillator equation or a system of two coupled Duffing oscillators. Then we discuss the range of parameter values where complete integration is possible.     

Pseudo-Hermitian generalized Dirac oscillators

We study generalized Dirac oscillators with complex interactions in (1+1)$(1+1)$ dimensions. It is shown that for the choice of interactions considered here, the Dirac Hamiltonians are η$\eta$-pseudo-Hermitian with respect to certain metric operators η$\eta$. Exact solutions for the generalized Dirac oscillator for some choices of the interactions have also been obtained. It is also shown that generalized Dirac oscillators can be identified with an anti-Jaynes–Cummings-type model and by spin flipping they can also be identified with a Jaynes–Cummings-type model.     

Millimeter wave self-mixing oscillators

Self-oscillating mixers in both dielectric and waveguide cavities have veen investigated in the 60 GHz frequency range. The deveces consist of negative resistance diodes of GaAs and InP material coupled to waveguide cavities or high resistivity dielectric cavities such as silicon or Al₂O₃. Experimental measurements show that these devices have a sensitivity in the order of –80 dBm with the intermediate frequency at 60 MHz and an IF bandwidth of 120 MHz. Applications are suggested based on minimum detectable signal and RF power capabilities for systems requiring small size and low cost.     

Femtosecond optical parametric oscillators

Development of femtosecond optical parametric oscillators (OPO) began a decade ago and has followed the technological progress in lasers and nonlinear crystals. There exist now such OPOs operating in the near or mid-infrared as well as in the visible. In this paper, we give an overview of the existing performances and of the prospects of this very active field.     

Submillimeter backward wave oscillators

NASA Lewis Research Center is engaged in a program to develop a series of backward wave oscillators (BWO's) for the frequency range 500 to 2000 GHz. Generically BWO's are electron beam traveling wave tubes operating in a dispersive regime in which the group velocity and the phase velocity of the induced electromagnetic wave are in opposite directions. The oscillation frequency of a BWO is controlled by the electron beam velocity (anode voltage).Such tubes because of their frequency tunability, phase locking capability, and large bandwidth are ideal local oscillators for heterdyne receiver/spectrometers.The design of the BWO's will be discussed with emphasis on the etched slow wave structure, zero compression electron beam, long life cathode, and moderate operating voltages.     

Soliton Raman fibre-ring oscillators

Results are presented on the operation and optimization of soliton Raman fibre-ring lasers using a c.w. mode-locked Nd-YAG laser at 1.32m as the source of 100 ps pump pulses. Various lengths of standard single-mode silica fibre were used, and tunable pulses as short as 100 fs generated.On leave from Departamento de Fisica, Universidade Federal de Alagoas, Maceio, 57000-AL, Brazil     

Anti-synchronization of chaotic oscillators

We have observed anti-synchronization phenomena in coupled identical chaotic oscillators. Anti-synchronization can be characterized by the vanishing of the sum of relevant variables. We have qualitatively analyzed its base mechanism by using the dynamics of the difference and the sum of the relevant variables in coupled chaotic oscillators. Near the threshold of the synchronization and anti-synchronization transition, we have obtained the novel characteristic relation.     

Nanosecond optical parametric oscillators

The main characteristics of nanosecond OPOs are presented: nonlinear crystals, tunability ranges, output energies, phase-matching conditions. A semianalytical model and a completely numerical model are described. They point out the importance of the complex intensity distribution that appears in the transverse planes of the output pulses. Techniques to improve the spectral and spatial quality of the output beams such as intracavity Fabry–Pérot filters or unstable cavity are detailed. Finally a modelisation and experimental results about intracavity OPO are presented.