41,916 research outputs found
Compact modes in quasi one dimensional coupled magnetic oscillators
In this work we study analytically and numerically the spectrum and
localization properties of three quasi-one-dimensional (ribbons) split-ring
resonator arrays which possess magnetic flatbands, namely, the stub, Lieb and
kagome lattices, and how their spectra is affected by the presence of
perturbations that break the delicate geometrical interference needed for a
magnetic flatband to exist. We find that the Stub and Lieb ribbons are stable
against the three types of perturbations considered here, while the kagome
ribbon is, in general, unstable. When losses are incorporated, all flatbands
remain dispersionless but become complex, with the kagome ribbon exhibiting the
highest loss rate.Comment: 11 pages, 15 figure
Cluster of galaxies around seven radio-loud QSOs at 1<z<1.6: K-band images
We have conducted a NIR study of the environments of seven radio-loud quasars
at redshifts 1<z<1.6. In present paper we describe deep band images
obtained for the fields of ~6X6 arcmin around the quasars with 3
limiting magnitudes of K~20.5. These fields were previously studied using deep
B and R band images (Sanchez & Gonzalez-Serrano 1999). Using together optical
and NIR data, it has been found a significant excess of galaxies which
optical-NIR colours, luminosity, spatial scale, and number of galaxies are
compatible with clusters at the redshift of the quasar.
We have selected a sample of cluster candidates analyzing the R-K vs. K
diagram. A ~25% of the candidates present red optical-NIR colours and an
ultraviolet excess. This population has been also found in clusters around
quasars at the same redshifts (Tanaka et al. 2000; Haines et al. 2001). These
galaxies seem to follow a mixed evolution: a main passive evolution plus late
starformation processes. The quasars do not inhabit the core of the clusters,
being found in the outer regions. This result agrees with the hypothesis that
the origin/feeding mechanism of the nuclear activity were merging processes.
The quasars inhabit the region were a collision is most probably to produce a
merger.Comment: 15 pages. A&A, accepted for publishin
Ocean waves near Hurricane Josephine from SIR-B
Radar images of ocean surface waves near hurricane Josephine were acquired with the Shuttle Imaging Radar-B (SIR-B) system on October 12, 1984. Fast Fourier transform analyses of the images were performed along most of the 600-km image track. These data reveal the presence of at least two dominant wave systems which undergo significant spatial variations in wavelength and direction
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