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Abstract: The Rainbow massif, an oceanic core complex located in a nontransform discontinuity on the Mid‐Atlantic Ridge (36°N), is notable for hosting high‐temperature hydrothermal discharge through ultramafic rocks. Here we report results from a 9 month microearthquake survey conducted with a network of 13 ocean bottom seismometers deployed on and around the Rainbow massif as part of the MARINER experiment in 2013–2014. High rates (~300 per day) of low‐magnitude (average ML ~ 0.5) microearthquakes were detected beneath the massif. The hypocenters do not cluster along deeply penetrating fault surfaces and do not exhibit mainshock/aftershock sequences, supporting the hypothesis that the faulting associated with the exhumation of the massif is currently inactive. Instead, the hypocenters demarcate a diffuse zone of continuous, low‐magnitude deformation at relatively shallow (< ~3 km) depths beneath the massif, sandwiched in between the seafloor and seismic reflectors interpreted to be magmatic sills driving hydrothermal convection. Most of the seismicity is located in regions where seismic refraction data indicate serpentinized ultramafic host rock, and although the seismic network we deployed was not capable of constraining the focal mechanism of most events, our analysis suggests that serpentinization may play an important role in microearthquake generation at the Rainbow massif. [ABSTRACT FROM AUTHOR]

In this work is reported an experimental and numerical investigation of magnetic resonator antennas (MRA) of magnetic the alloy BaxSr1-xFe12O19 obtained in a new procedure in the solid-state method. The experimental and theoretical characteristics of the antenna like return loss, bandwidth, input impedance, and radiation patterns are in good agreement. Numerical validation is done, taking into account the air gaps between the dielectric resonator and the metallic conductors. Frequency response bandwidth in the range of 9–10% was obtained for frequency operation around 4 GHz. The alloys BaxSr1-xFe12O19 showed a dielectric constant around 8, with loss in the range 10-2–10-3. The temperature coefficient of resonant frequency (τf) was also measured for magnetic alloys BaxSr1-xFe12O19. The values obtained were in the range of 44.90–87.83 ppm/°C. These results obtained confirm the potential use of those materials for small dielectric MRA. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 452–458, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24931 [ABSTRACT FROM AUTHOR]

In this paper we did a study of the dielectric properties: capacitance (C), dielectric permittivity(ε), electric modulus(M) and dielectric loss(tangα)) in the radio-frequency(RF) and microwave (MW) frequency range as a function of temperature and the temperature coefficient of capacitance (TCC) of the composites [Pb(Fe1/2Nb1/2)O3(PFN)]Z–[CrYFe2−YO3(CRFO)]100−Z where Z = 0, 10, 50, 90 and 100%. The compounds were prepared by the powder-sintering and the X-ray diffraction (XRD) was used in this study using the Rietveld procedure. The X-ray analysis shows that PFN phase is tetragonal where the CRFO phase belongs to a trigonal structure. The capacitance, dielectric permittivity, electric modulus and loss were studied in the frequency range of 100 Hz to 1GHz and temperature range of 25–100 °C. The values of TCC for all the samples are presenting positive values. The study of the electric modulus (M) as a function of frequency and temperature lead to the measurement of the activation energy (Eac), which is directed linked to the relaxation process associated to the interfacial polarization effect in the samples. The study of the electrical properties in the RF and MW range of frequencies is important in view of possible applications of these composites as future components in RF and MW circuits. [ABSTRACT FROM AUTHOR]

The M-type barium hexaferrite Ba x Sr1− x Fe12O19 (where 0 < x < 1) alloys were prepared by a new ceramic procedure. The samples were studied using X-ray diffraction and Rietveld analysis, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, infrared and Mössbauer spectroscopy. The X-ray analysis indicates that the all the samples present a hexagonal structure. The IR spectra showed three main absorption bands in range of 400–600 cm−1 corresponding to SFO100 and BFO100. The Mössbauer spectra showed a superposition of five subspectra associated with the five sites of the iron ion, which in the ferric state. The SEM studies showed that the hexaferrites presented grains that varied in the range of 260–305 nm. The dielectric properties: dielectric constant ( ε′) and dielectric loss (tg δ) were measured at room temperature in the frequency range from 100 Hz to 40 MHz. The samples present a nonlinear behavior for the dielectric constant at 100 Hz, 1 kHz and 1 MHz. The dielectric constant is not following the linear mixing rule for the samples. The structural, dielectric and magnetic properties of the composite barium hexaferrite phases were discussed in view of applications as a material for permanent magnets, high density magnetic recording and microwave devices. [ABSTRACT FROM AUTHOR]

A study of the structural characteristics of the composites [Pb(Fe0.5Nb0.5)O3(PFN)] x -[Cr0.75Fe1.25O3(CRFO)]100− x ( x = 0 (CRFO100), 10, 50, 90, 100) was performed in this work. The compounds PFN100 and CRFO100 were prepared by conventional solid-state method and investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and 57Fe Mössbauer Spectroscopy techniques. The X-ray analysis shows that PFN100 is tetragonal and the CRFO100 phase has a trigonal symmetry. The refinement of all the composites was also performed and discussed in this paper. The Mössbauer spectrum for the composite samples shows a paramagnetic doublet and a sextet probably assigned to a magnetic phase associated to Fe+3. For the sample PFN100, only a magnetic field of 49.5 T (isomer shift (δ) = 0.21 mm/s) was detected. For the composite sample, the δ and Δ are typical of Fe ions at sites of octahedral coordination. [ABSTRACT FROM AUTHOR]

The probe-feed cylindrical dielectric resonator antennas (DRA) based on a new magnetodielectric composites Cr0.75Fe1.25O3 (CRFO)/Fe0.5Cu0.75Ti0.75O3 (FCTO) are investigated. The experimental and theoretical characteristics of the antenna like return loss, bandwidth, input impedance, and radiation patterns are in good agreement. Numerical validation is done, tacking into account the air gaps between the dielectric resonator and the metallic conductors. Frequency response bandwidth in the range of 6.6–11.8% was obtained for frequency operation around 4 GHz. The CRFO-FCTO present a dielectric constant in the range of 8–13 with loss around 10-3. To summarize, the performance of a cylindrical DRA based in a new matrix CRFO/FCTO was examined. These measurements confirm the potential use of such materials for small DRA. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 409–413, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22160 [ABSTRACT FROM AUTHOR]

Presents seismological data that constrain the three-dimensional velocity structure beneath the Axial volcano on the Juan de Fuca mid-ocean ridge. Formation of the Axial volcano; Seismic-travel time prediction; Low-velocity anomaly under the caldera.

Six sonic booms, generated by F-4 aircraft under steady flight at a range of altitudes (610-6100 m) and Mach numbers (1.07-1.26), were measured just above the air/sea interface, and at five depths in the water column. The measurements were made with a vertical hydrophone array suspended from a small spar buoy at the sea surface, and telemetered to a nearby research vessel. The sonic boom pressure amplitude decays exponentially with depth, and the signal fades into the ambient noise field by 30-50 m, depending on the strength of the boom at the sea surface. Low-frequency components of the boom waveform penetrate significantly deeper than high frequencies. Frequencies greater than 20 Hz are difficult to observe at depths greater than about 10 m. Underwater sonic boom pressure measurements exhibit excellent agreement with predictions from analytical theory, despite the assumption of a flat air/sea interface. Significant scattering of the sonic boom signal by the rough ocean surface is not detected. Real ocean conditions appear to exert a negligible effect on the penetration of sonic booms into the ocean unless steady vehicle speeds exceed Mach 3, when the boom incidence angle is sufficient to cause scattering on realistic open ocean surfaces. © 2000 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

The effect of atmosphere-induced rounding on the loudness of sonic boom waveforms is investigated. Waveforms with varying degrees of roundness representative of measured flight test data are considered. Simple equations are developed by which the perceived loudness and C-weighted sound exposure levels of these sonic booms can be calculated directly from their waveform parameters. This method shows excellent agreement with more complex loudness calculations (e.g., by Johnson and Robinson) as well as the full C-weighted sound exposure level calculation. A new set of flight test data is used to correlate shock strength with rise time. The results are compared to a semi-empirical model proposed by Dr. Kenneth Plotkin from earlier work. [ABSTRACT FROM AUTHOR]