Channelized coplanar waveguide pin-diode switches

Three different types of p-i-n diode, reflective CPW switches are presented. The first two switches are the series and the shunt mounted diode switches. Each has achieved greater than 15 dB of isolation over a broad bandwidth. The third switch is a narrow band, high isolation switched filter which has achieved 19 dB of isolation. Equivalent circuits and measured performance for each switch is presented

A numerical study of wave-current interaction in the bottom boundary layer

In the present work, a numerical wave-current flume has been developed, based on a standard k-εmodel. The numerical flume was 12.86m in length, with a numerical beach at one end of the flume. The Volume of Fluid (VOF) method was used to capture the free surface in the flume. The velocity profile obtained at the test section from the numerical simulation has then been compared with experimental data and good agreement found. Periodic velocities in the bottom boundary layer have been obtained which agree well with the experimental data. The model provides an insight to the changes in bed shear stress time histories that characterise wave current interaction

Extreme wave groups in a wave flume: Controlled generation and breaking onset

Extreme waves in random seas are usually breaking or close to breaking. Understanding the kinematics and evolution of such waves is important for determining loads on offshore structures. Controlled repeatable generation of realistic breaking waves in wave flume experiments is a difficult but important task. It is rather easy to generate an arbitrary breaking wave, but to the authors’ knowledge there is no methodology for accurate generation of a wave group with a pre-defined spectrum related to a modelled sea state with spilling breaking at a prescribed position. Such waves can be used to model extreme breaking waves in a random sea and their interaction with structures. This paper offers such a methodology. The key feature of the method is the application of an iterative focussing procedure to a linearised amplitude spectrum rather than to a full nonlinear spectrum. The linearised spectrum is obtained using a harmonics separation technique and the general derivation of the method is given for an arbitrary number of components. The procedure is applied to generate focussed wave groups with amplitudes increased in small steps until local crest breaking occurs. As a result, the highest non-breaking waves and weakly breaking waves are generated for otherwise identical conditions. The methodology is applied for four different wave spectra of the same peak frequency: JONSWAP, Pierson-Moskowitz, wide and narrow band Gaussian. It is found that steepness of the limiting breaking wave depends strongly on the choice of wave group spectrum. The results demonstrate that neglecting spectral properties of design waves may lead to misrepresentation of their breaking behaviour

Experimental Generation of Focusing Wave Groups on Following and Adverse-Sheared Currents in a Wave-Current Flume

Focused waves are often used in physical and numerical studies as a representative condition for extreme waves or as a means to generate very steep and breaking waves at a prescribed location in space and time. They have also been combined with depth-varying currents in investigations of incipient wave breaking, wave breaking–induced energy dissipation, and wave–current induced loads on marine structures. A focused wave is created when all the components in a transient wave group come into phase. In the past, linear wave theory and iterative methodologies coupled with the linear Doppler-shifted dispersion relationship have been suggested to account for the presence of a current and achieve the required phase and amplitude focusing. In the majority of cases, linear or constant steepness spectra are used, which, compared to measured or theoretical spectra like the Joint North Sea Wave Project (JONSWAP), Gaussian, and Pierson-Moskowitz (PM) can be termed unrealistic. The effectiveness of these methodologies also decreases as the nonlinearity increases; therefore, in most studies, either weakly nonlinear conditions are used or the focus location is determined empirically. Here, an iterative methodology is suggested that can focus waves of any height at a predetermined temporal and spatial location even for wave groups propagating on a strong following or adverse current. An experimental apparatus developed to generate relatively stable sheared velocity profiles is also described. The depth-varying profile of the resulting currents diverges from that of classical wind-driven currents and comes closer to profiles measured in field sites important for the deployment of, for instance, tidal and wind energy converters. The methodology is successfully applied to wave groups traveling on still water, following, and adverse currents, and the results presented refer to linear, weakly nonlinear, and strongly nonlinear–focused waves generated for a range of realistic target spectra. The capability to generate wave groups with the same amplitude spectrum at a fixed location for a variety of flow conditions—still water, following, and adverse sheared currents—is also illustrated

Experimental investigations on channelized coplanar waveguide

A new variant of coplanar waveguide (CPW) which was termed channelized coplanar waveguide (CCPW) is presented. Measured propagation characteristics for CCPW such as epsilon(eff) and unloaded Q as a function of geometrical parameters and frequency are presented. The measured and modeled epsilon(eff) are also compared. Equivalent circuit model element values are presented for a CCPW open circuit and a CCPW right angle bend. A CCPW matched T-junction, matched 1:3 junction, and a novel coax-to-CCPW in-phase, N-way, radial power divider are also demonstrated

Channelized coplanar waveguide: Discontinuities, junctions, and propagation characteristics

A new variant of CPW which has been termed channelized CPW, CCPW, is presented. Measured and computed propagation characteristics are presented. Lumped equivalent circuit element values for a CCPW open circuit and right angle bend have been obtained. CCPW power divider junctions and a coax-to-CCPW in-phase, radial power divider are also presented

Coming to America: Multiple Origins of New World Geckos

Geckos in the Western Hemisphere provide an excellent model to study faunal assembly at a continental scale. We generated a time-calibrated phylogeny, including exemplars of all New World gecko genera, to produce a biogeographic scenario for the New World geckos. Patterns of New World gecko origins are consistent with almost every biogeographic scenario utilized by a terrestrial vertebrate with different New World lineages showing evidence of vicariance, dispersal via temporary land bridge, overseas dispersal, or anthropogenic introductions. We also recovered a strong relationship between clade age and species diversity, with older New World lineages having more species than more recently arrived lineages. Our data provide the first phylogenetic hypothesis for all New World geckos and highlight the intricate origins and ongoing organization of continental faunas. The phylogenetic and biogeographical hypotheses presented here provide an historical framework to further pursue research on the diversification and assembly of the New World herpetofauna

Geodetic, teleseismic, and strong motion constraints on slip from recent southern Peru subduction zone earthquakes

We use seismic and geodetic data both jointly and separately to constrain coseismic slip from the 12 November 1996 M_w 7.7 and 23 June 2001 M_w 8.5 southern Peru subduction zone earthquakes, as well as two large aftershocks following the 2001 earthquake on 26 June and 7 July 2001. We use all available data in our inversions: GPS, interferometric synthetic aperture radar (InSAR) from the ERS-1, ERS-2, JERS, and RADARSAT-1 satellites, and seismic data from teleseismic and strong motion stations. Our two-dimensional slip models derived from only teleseismic body waves from South American subduction zone earthquakes with M_w > 7.5 do not reliably predict available geodetic data. In particular, we find significant differences in the distribution of slip for the 2001 earthquake from models that use only seismic (teleseismic and two strong motion stations) or geodetic (InSAR and GPS) data. The differences might be related to postseismic deformation or, more likely, the different sensitivities of the teleseismic and geodetic data to coseismic rupture properties. The earthquakes studied here follow the pattern of earthquake directivity along the coast of western South America, north of 5°S, earthquakes rupture to the north; south of about 12°S, directivity is southerly; and in between, earthquakes are bilateral. The predicted deformation at the Arequipa GPS station from the seismic-only slip model for the 7 July 2001 aftershock is not consistent with significant preseismic motion