Polarization switching and induced birefringence in InGaAsP multiple quantum wells at 1.5 mu m

We analyze the 1.5mum wavelength operation of a room temperature polarization switch based on electron spin dynamics in InGaAsP multiple quantum wells. An unexpected difference in response for left and right circularly polarized pump light in pump-probe measurements was discovered and determined to be caused by an excess carrier induced birefringence. Transient polarization rotation and ellipticity were measured as a function of time delay. (C) 2002 American Institute of Physics.</p

Three-dimensional spatiotemporal optical solitons in nonlocal nonlinear media

We demonstrate the existence of stable three-dimensional spatiotemporal solitons (STSs) in media with a nonlocal cubic nonlinearity. Fundamental (nonspinning) STSs forming one-parameter families are stable if their propagation constant exceeds a certain critical value, that is inversely proportional to the range of nonlocality of nonlinear response. All spinning three-dimensional STSs are found to be unstable.Comment: 14 pages, 6 figures, accepted to PRE, Rapid Communication

Metastabilnost α-stabilnih jezgri bogatih neutroni!vla

Cluster radioactivities of nuclei far from beta-stability line in the neutron-rich region, where a-decay is not allowed, have been systematically studied within analytical superasymmetric fission model. Input mass tables calculated by various authors were used to determine the released energy. Half-lives shorter than 1030 seconds have been estimated for very neutron-rich parent nuclei with atomic numbers form 57 to 86. The emitted clusters are also proton-deficient nuclei, as for example 22O, 46S, 50Ar, 76Fe, 78Ni, etc.Sistematski je istraživana radioaktivnost atomskih jezgri s emisijom nukleonskih grozdova u području bogatom neutronima izvan linije beta stabilnosti, koristeći analitički supersimetrijski fisijski model. U određivanju oslobođene energije upotrebljavane su masene tablice različitih autora. Za jezgre bogate neutronima s atomskim brojevima između 57 i 86 procijenjena su vremena poluraspada na manje od 10 30 s. Emitirani grozdovi su također jezgre siromašne protonima, kao na primjer 2 20, 4 6S, 50Ar, 7 6Fe, 7 8Ni itd

Stable three-dimensional spinning optical solitons supported by competing quadratic and cubic nonlinearities

We show that the quadratic interaction of fundamental and second harmonics in a bulk dispersive medium, combined with self-defocusing cubic nonlinearity, give rise to completely localized spatiotemporal solitons (vortex tori) with vorticity s=1. There is no threshold necessary for the existence of these solitons. They are found to be stable against small perturbations if their energy exceeds a certain critical value, so that the stability domain occupies about 10% of the existence region of the solitons. We also demonstrate that the s=1 solitons are stable against very strong perturbations initially added to them. However, on the contrary to spatial vortex solitons in the same model, the spatiotemporal solitons with s=2 are never stable.Comment: latex text, 10 ps and 2 jpg figures; Physical Review E, in pres

Collisions between counter-rotating solitary vortices in the three-dimensional Ginzburg-Landau equation

We report results of collisions between coaxial vortex solitons with topological charges ±S in the complex cubic-quintic Ginzburg-Landau equation. With the increase of the collision momentum, merger of the vortices into one or two dipole or quadrupole clusters of fundamental solitons (for S=1 and 2, respectively) is followed by the appearance of pairs of counter-rotating “unfinished vortices,” in combination with a soliton cluster or without it. Finally, the collisions become elastic. The clusters generated by the collisions are very robust, while the “unfinished vortices,” eventually split into soliton pairs

On the existence and stability of three-dimensional solitons and vortices in optics and BoseEinstein condensate: occurence of swallowtail bifurcations

Abstract. We give an overview of recent results in the area of three-dimensional nonspinning and spinning solitons in some selected models in optics and Bose-Einstein condensate (BEC). We concentrate on the existence and stability of these multiple dimensional localized structures and we reveal the occurence of two cuspidal points in the Hamiltonian (BEC energy) versus soliton norm diagram, resulting in a generic swallowtail bifurcation

Stochastic epidemic-type model with enhanced connectivity: exact solution

We present an exact analytical solution to a one-dimensional model of the Susceptible-Infected-Recovered (SIR) epidemic type, with infection rates dependent on nearest-neighbor occupations. We use a quantum mechanical approach, transforming the master equation via a quantum spin operator formulation. We calculate exactly the time-dependent density of infected, recovered and susceptible populations for random initial conditions, and compare our results with a low connectivity SIR model reported by Schuetz et al.. Our results compare well to those of previous work, validating the model as a useful tool for additional and extended studies in this important area. Our model also provides exact solutions for the n-point correlation functions, and can be extended to more complex epidemic type models

Two-dimensional solitons with hidden and explicit vorticity in bimodal cubic-quintic media

We demonstrate that two-dimensional two-component bright solitons of an annular shape, carrying vorticities $(m,\pm m)$ in the components, may be stable in media with the cubic-quintic nonlinearity, including the \textit{hidden-vorticity} (HV) solitons of the type $(m,-m)$, whose net vorticity is zero. Stability regions for the vortices of both $(m,\pm m)$ types are identified for $m=1$, 2, and 3, by dint of the calculation of stability eigenvalues, and in direct simulations. A novel feature found in the study of the HV solitons is that their stability intervals never reach the (cutoff) point at which the bright vortex carries over into a dark one, hence dark HV solitons can never be stable, contrarily to the bright ones. In addition to the well-known symmetry-breaking (\textit{external}) instability, which splits the ring soliton into a set of fragments flying away in tangential directions, we report two new scenarios of the development of weak instabilities specific to the HV solitons. One features \textit{charge flipping}, with the two components exchanging the angular momentum and periodically reversing the sign of their spins. The composite soliton does not split in this case, therefore we identify such instability as an \textit{intrinsic} one. Eventually, the soliton splits, as weak radiation loss drives it across the border of the ordinary strong (external) instability. Another scenario proceeds through separation of the vortex cores in the two components, each individual core moving toward the outer edge of the annular soliton. After expulsion of the cores, there remains a zero-vorticity breather with persistent internal vibrations.Comment: 10 pages, 11 figure