In this paper we present the first results on emission in metamaterial. We show how the specific properties of metallic composite material can modify the emission of an embedded source. We show that under proper conditions the energy radiated by a source embedded in a slab of metamaterial will be concentrated in a narrow cone in the surrounding media. An experimental demonstration of this effect is given in the microwave domain, and the constructed antenna has a directivity equivalent to the best reported results with photonic-crystal-based antennas but using a completely different physical principle [B. Temelkuaran, J. Appl. Phys. 87, 603 (2000)]].

Abstract. Over 20 global ocean tide models have been developed since 1994, primarily as a consequence of analysis of the precise altimetric measurements from TOPEX/POSEIDON and as a result of parallel developments in numerical tidal modeling and data assimilation. This paper provides an accuracy assessment of 10 such tide models and discusses their benefits in many fields including geodesy, oceanography, and geophysics. A variety of tests indicate that all these tide models agree within 2-3 cm in the deep ocean, and they represent a significant improvement over the classical Schwiderski 1980 model by approximately 5 cm rms. As a result, two tide models were selected for the reprocessing of TOPEX/POSEIDON Geophysical Data Records in late 1995. Current ocean tide models allow an improved observation of deep ocean surface dynamic topography using satellite altimetry. Other significant contributions include theft applications in an improved orbit computation for TOPEX/POSEIDON and other geodetic satellites, to yield accurate predictions of Earth rotation excitations and improved estimates of ocean loading corrections for geodetic observatories, and to allow better separation of astronomical tides from phenomena with meteorological and geophysical origins. The largest differences between these tide models occur in shallow waters, indicating that the current models are still problematic in these areas. Future improvement of global tide models is anticipated with additional high-quality altimeter data and with advances in numerical techniques to assimilate data into high-resolution hydrodynamic models.

An atlas of the main components of the tides has been produced on the basis of a finite element hydrodynamic model, with the aim of offering the scientific community, using satellite altimetric data, a prediction of the tidal contribution to sea surface height variations under the ground tracks of the satellites that is totally independent of altimetric measurements. The geographic coverage of the simulations only excludes, temporarily, some marginal seas like the Bay of Fundy. But the design of the model, based on a nonlinear formulation of the shallow water equations, could enable the simulations to be extended to these very singular areas. On the other hand, the Arctic Basin and the Antarctic Circumpolar Basin have been fully resolved, including the under‐ice shelf areas of the Weddell Sea and the Ross Sea. Eight constituents, M2, S2, N2, K2, 2N2, K1, O1, and Q1 have been simulated. Five secondary constituents: Mu2, Nu2, L2, T2, and P1, required to insure a priori correct predictions, have been deduced by admittance. The accuracy and precision of these solutions have been estimated by reference to the harmonic constituents data set available from analysis of the entire collection of pelagic, plateau and coastal observations made to date, and archived by International Association for Physical Sciences of the Oceans and International Hydrographie Bureau. Over the deep oceans, these solutions fit the observations to within a few centimeters for the larger components: M2, S2, K1, O1, and a few millimeters for the others, in RMS maximum difference to a standard set of 78 ground truth stations. Over the shelves, the differences are larger, because of the increase in amplitude of the tidal waves, but the flexibility offered by the finite element technique to refine the discretization mesh of the model over the shallow seas enables detailed cotidal maps to be produced along the coasts. One zoom on South Georgia Island, in the South Atlantic Ocean, is presented as an illustration. Finally, the performances of the tidal predictions made on the basis of this new set of solutions was tested by looking at the residual RMS differences at the crossover points of sea level measurements supplied by the TOPEX/POSEIDON mission, when using these predictions. This test provided confirmation of most of the conclusions already drawn on the basis of the previous comparisons with in situ tide gauge data.

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We design and analyze the performance of cooperative search strategies for unmanned aerial vehicles (UAVs) searching for moving, possibly evading, targets in a hazardous environment. Rather than engaging in independent sensing missions, the sensing agents (UAVs with sensors) "work together" by arranging themselves into a flight configuration that optimizes their integrated sensing capability. If a UAV is shot down by enemy fire, the team adapts by reconfiguring its topology to optimally continue the mission with the surviving assets. We present a cooperative search methodology that integrates the multiple agents into an advantageous formation that distinctively enhances the sensing and detection operations of the system while minimizing the transmission of excessive control information for adaptation of the team's topology. After analyzing our strategy to determine the performance tradeoff between search time and number of UAVs employed, we present an algorithm that selects the minimum number of UAVs to deploy in order to meet a targeted search time within probabilistic guarantees.