Optically injected laser system: characterization of chaos, bifurcation, and control

A single mode semiconductor laser subjected to optical injection, described by a set of three coupled nonlinear ordinary differential equations, exhibiting chaos is considered. By means of a recurrence analysis, quantification of the strange attractor is made. Analytical studies of the system using asymptotic averaging technique, derive certain conditions describing the prediction of 1-->2 bifurcation, which have subsequently been verified on numerical simulation. Furthermore, the locus of points on the parameter phase space representing Hopf bifurcation has been derived. The problem of control of chaos by a new procedure based on adaptive stabilization is also addressed. The results of such control are shown explicitly. Though this analysis deals with a very specific set of equations, the overall features that come out of the study remains valid for almost all laser systems.     

First close-to-threshold measurement of the analysing power A y in the reaction \vec pp \rightarrow pp\eta

At the internal facility COSY-11 a first measurement of the reaction near the production threshold has been performed. Results for the analysing power will be presented and a comparison with one-meson exchange models will be discussed.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.40.Vv Vector-meson dominance - 13.60.Le Meson production - 13.88. + e Polarization in interactions and scattering - 24.70. + s Polarization phenomena in reactions     

The3He(α,γ)7Be reaction and the solar neutrino problem

The capture reaction³He(α,γ)⁷Be has been investigated in the energy range ofE _c.m. =107 to 1,266 keV. The⁴He or³He beams of up to 300 μA particle current were incident on³He or⁴He gas targets, respectively. The gas target systems were all of the windowless and recirculating type. Excitation functions have been obtained with the use of an extended-static gas target, while the measurements ofγ-ray angular distributions involved a quasi-point supersonic jet system. The determination of absolute cross sections has been carried out with both types of gas target systems. Theγ-ray yields in the³He(α,γ)⁷Be reaction were detected using 80 cm³ Ge(Li) detectors. The data lead to a zero-energy intercept of the astrophysicalS(E) factor ofS(0)=0.30±0.03 keV-b. This result reduces the calculated solar neutrino rate by a factor of 1.76.     

A characterization of the circle group via uniqueness of roots

It was shown in Bíró et al. (2001) [7] that every cyclic subgroup C of the circle group T admits a characterizing sequence (un) of integers in the sense that unx→0 for some x∈T iff x∈C. More generally, for a subgroup H of a topological (abelian) group G one can define:

(a)

g(H) to be the set of all elements x of G such that unx→0 in G for all sequences (un) of integers such that unh→0 in G for all h∈H;

(b)

H to be g-closed if H=g(H).

We show then that an infinite compact abelian group G has all its cyclic subgroups g-closed iff G≅T.     

Synthesis by pulsed laser ablation in Ar and SERS activity of silver thin films with controlled nanostructure

Thin silver films were deposited by pulsed laser ablation in a controlled Ar atmosphere and their SERS activity was investigated. The samples were grown at Ar pressures between 10 and 70 Pa and at different laser pulse numbers. Other deposition parameters such as laser fluence, target to substrate distance and substrate temperature were kept fixed at 2.0 J/cm², 35 mm and 297 K. Film morphologies were investigated by scanning and transmission electron microscopies (SEM, TEM). Surface features range from isolated nearly spherical nanoparticles to larger islands with smoothed edges. Cluster growth is favored by plume confinement induced by background gas. After landing on the substrate clusters start to aggregate giving rise to larger structures as long as the deposition goes on. Such a path of film growth allows controlling the surface morphology as a function of laser pulse number and Ar pressure. These two easy-to-manage process parameters control the number density and the average size of the as-deposited nanoparticles. We investigated the influence of substrate morphologies on their surface enhanced Raman scattering properties. Raman measurements were performed after soaking the samples in rhodamine 6G aqueous solutions over the concentration range between 1.0 × 10⁻⁴ and 5.0 × 10⁻⁸ M. The sensitivity of the film SERS activity on the surface features is put into evidence.     

Generalized and projective synchronization in modulated time-delayed systems

In this Letter, we propose a method for generalized and projective synchronization in modulated time-delayed systems using nonlinear active control. Sufficient condition for generalized synchronization is calculated analytically by Krasovskii-Lyapunov stability theory. The validity of the proposed algorithm has been confirmed by simulation results. The proposed method helps to find the explicit form of the functional relation between the synchronized variables, for which very few formulations are known at the present moment. Both usual and lag-anticipatory cases can be treated on the same footing.     

Synthesis of Highly Emissive Fluorophores Based on Multiply Stacked Anthracene Arrangement

Newly designed fluorophore systems with feather-like structures were constructed by connecting bisanthracene building units via a concise reaction sequence of bromination, etherification, and desilylation. Spectroscopic characterizations revealed that all of the fluorophore systems achieved high light absorptivity and high emission efficiency by preventing closely spaced anthracene chromophores from mutual interactions to reduce concomitant energy loss by fluorescence quenching. The application of fluorophore systems for the preparation of light-harvesting dyad materials has successfully demonstrated their potential utility as versatile photofunctional tools.