Dissipative Chaos in Semiconductor Superlattices

We consider the motion of ballistic electrons in a miniband of a semiconductor superlattice (SSL) under the influence of an external, time-periodic electric field. We use the semi-classical balance-equation approach which incorporates elastic and inelastic scattering (as dissipation) and the self-consistent field generated by the electron motion. The coupling of electrons in the miniband to the self-consistent field produces a cooperative nonlinear oscillatory mode which, when interacting with the oscillatory external field and the intrinsic Bloch-type oscillatory mode, can lead to complicated dynamics, including dissipative chaos. For a range of values of the dissipation parameters we determine the regions in the amplitude-frequency plane of the external field in which chaos can occur. Our results suggest that for terahertz external fields of the amplitudes achieved by present-day free electron lasers, chaos may be observable in SSLs. We clarify the nature of this novel nonlinear dynamics in the superlattice-external field system by exploring analogies to the Dicke model of an ensemble of two-level atoms coupled with a resonant cavity field and to Josephson junctions.Comment: 33 pages, 8 figure

Chaetozone carpenteri, McIntosh, 1911 from the Mediterranean Sea and records of other bi-tentaculate Cirratulids

Many species of Cirratulidae have been recorded from the Mediterranean Sea since the descriptions and figures of the Naples fauna in one of the first comprehensive studies of polychaetes by delle Chiaje, 1823–3022. Chiaje, SD. 1823–30. Memorie sulla storia e notomia degli animali senza vertebre del Regno di Napoli, Vol.4, 109–214 . Napoli: Dalla stamperia de’ Fratelli Fernandes. View all references. This original publication included only multi-tentaculate cirratulids and what we would now identify as Cirriformia and Cirratulus. Since delle Chiaje's publication, 25 bi-tentaculate taxa have been recorded from the Mediterranean. During recent sampling programmes Chaetozone carpenteri McIntosh, 191155. McIntosh, WC. 1911. Notes from the Gatty Marine Laboratory, St Andrews. No. XXXII . Annals and Magazine of Natural History, Series, 8(7): 145–173. View all references, a bi-tentaculate cirratulid, has been recorded from several Mediterranean sites and is redescribed. All records of C. setosa will need to be re-examined as they may have been misidentified

Tidal inlets in the Anthropocene: geomorphology and benthic habitats of the Chioggia inlet, Venice Lagoon (Italy)

Within a multidisciplinary approach, we mapped with unprecedented detail the seafloor morphology, sediment distribution and benthic habitats of a tidal inlet which has been highly impacted by human activity. We identified an unusual habitat for lagoon environment connected to rip-rap used for jetties and hard structures and we estimated that the new pattern of flow around these hard structures caused the erosion of 430 000 m(3) of sediment in eight years