10,970 research outputs found
Gulf stream velocity structure through combined inversion of hydrographic and acoustic Doppler data
Near-surface velocities from an acoustic Doppler instrument are used in conjunction with CTD/O2 data to produce estimates of the absolute flow field off Cape Hatteras. The data set consists of two transects across the Gulf Stream made by the R/V Endeavor cruise EN88 in August 1982. An inverse procedure is applied which makes use of both the acoustic Doppler data and property conservation constraints. Velocity sections at approximately 73 deg. W and 71 deg. W are presented with formal errors of 1-2 cm/s. The net Gulf Stream transports are estimated to be 116 + or - 2 Sv across the south leg and 161 + or - 4 Sv across the north. A Deep Western Boundary Current transport of 4 + or - 1 Sv is also estimated. While these values do not necessarily represent the mean, they are accurate estimates of the synoptic flow field in the region
Inversion of spinning sound fields
A method is presented for the reconstruction of rotating monopole source
distributions using acoustic pressures measured on a sideline parallel to the
source axis. The method requires no \textit{a priori} assumptions about the
source other than that its strength at the frequency of interest vary
sinusoidally in azimuth on the source disc so that the radiated acoustic field
is composed of a single circumferential mode. When multiple azimuthal modes are
present, the acoustic field can be decomposed into azimuthal modes and the
method applied to each mode in sequence.
The method proceeds in two stages, first finding an intermediate line source
derived from the source distribution and then inverting this line source to
find the radial variation of source strength. A far-field form of the radiation
integrals is derived, showing that the far field pressure is a band-limited
Fourier transform of the line source, establishing a limit on the quality of
source reconstruction which can be achieved using far-field measurements. The
method is applied to simulated data representing wind-tunnel testing of a
ducted rotor system (tip Mach number~0.74) and to control of noise from an
automotive cooling fan (tip Mach number~0.14), studies which have appeared in
the literature of source identification.Comment: Revised version of paper submitted to JASA; five more figures;
expanded content with more discussion of error behaviour and relation to
Nearfield Acoustical Holograph
Fracture toughness of brittle materials determined with chevron notch specimens
The use of chevron-notch specimens for determining the plane strain fracture toughness (K sub Ic) of brittle materials is discussed. Three chevron-notch specimens were investigated: short bar, short rod, and four-point-bend. The dimensionless stress intensity coefficient used in computing K sub Ic is derived for the short bar specimen from the superposition of ligament-dependent and ligament-independent solutions for the straight through crack, and also from experimental compliance calibrations. Coefficients for the four-point-bend specimen were developed by the same superposition procedure, and with additional refinement using the slice model of Bluhm. Short rod specimen stress intensity coefficients were determined only by experimental compliance calibration. Performance of the three chevron-notch specimens and their stress intensity factor relations were evaluated by tests on hot-pressed silicon nitride and sintered aluminum oxide. Results obtained with the short bar and the four-point-bend specimens on silicon nitride are in good agreement and relatively free of specimen geometry and size effects within the range investigated. Results on aluminum oxide were affected by specimen size and chevron-notch geometry, believed due to a rising crack growth resistance curve for the material. Only the results for the short bar specimen are presented in detail
Recommended from our members
Pituophis ruthveni
Number of Pages: 16Geological SciencesIntegrative Biolog
Quantum Films Adsorbed on Graphite: Third and Fourth Helium Layers
Using a path-integral Monte Carlo method for simulating superfluid quantum
films, we investigate helium layers adsorbed on a substrate consisting of
graphite plus two solid helium layers. Our results for the promotion densities
and the dependence of the superfluid density on coverage are in agreement with
experiment. We can also explain certain features of the measured heat capacity
as a function of temperature and coverage.Comment: 13 pages in the Phys. Rev. two-column format, 16 Figure
Implications of Constraints on Mass Parameters in the Higgs Sector of the Nonlinear Supersymmetric SU(5) Model
The Higgs sector of the minimal nonlinear supersymmetric SU(5) model contains
three mass parameters. Although these mass parameters are essentially free at
the electroweak scale, they might have particular values if they evolve from a
particular constraints at the GUT scale through the RG equations. By assuming a
number of simple constraints on these mass parameters at the GUT scale, we
obtain their values at the electroweak scale through the RG equations in order
to investigate the phenomenological implications. Some of them are found to be
consistent with the present experimental data.Comment: 23 pages, 10 figure
Anisakis infection in allis shad, Alosa alosa (Linnaeus, 1758), and twaite shad, Alosa fallax (Lacépède, 1803), from Western Iberian Peninsula Rivers : zoonotic and ecological implications
Acknowledgments The authors would like to thank M. N. Cueto and J.M. Antonio (ECOBIOMAR) for their excellent technical support and also Rodrigo López for making the map of the study area. We also thank the personal of the Vigo IEO, for providing information about shad captures at sea collected on the basis of national program (AMDES) included in the European Data Collection Framework (DCF) project. We are also grateful to Comandancia Naval de Tui for providing fishing data. M. Bao is supported by a PhD grant from the University of Aberdeen and also by financial support of the contract from the EU Project PARASITE (grant number 312068). This study was partially supported by a PhD grant from the Portuguese Foundation for Science and Technology (FCT) SFRH/BD/44892/2008) and partially supported by the European Regional Development Fund (ERDF) through the COMPETE—Operational Competitiveness Programme and national funds through Foundation for Science and Technology (FCT), under the project BPEst-C/MAR/ LA0015/2013. The authors thank the staff of the Station of Hydrobiology of the USC BEncoro do Con^ due their participation in the surveys. This work has been partially supported by the project 10PXIB2111059PR of the Xunta de Galicia and the project MIGRANET of the Interreg IV BSUDOE (South-West Europe) Territorial Cooperation Programme (SOE2/P2/E288). D.J. Nachón is supported by a PhD grant from the Xunta de Galicia (PRE/2011/198)Peer reviewedPostprin
Characterizing Circumgalactic Gas around Massive Ellipticals at z~0.4 - II. Physical Properties and Elemental Abundances
We present a systematic investigation of the circumgalactic medium (CGM)
within projected distances d<160 kpc of luminous red galaxies (LRGs). The
sample comprises 16 intermediate-redshift (z=0.21-0.55) LRGs of stellar mass
M_star>1e11 M_sun. Combining far-ultraviolet Cosmic Origin Spectrograph spectra
from the Hubble Space Telescope and optical echelle spectra from the ground
enables a detailed ionization analysis based on resolved component structures
of a suite of absorption transitions, including the full HI Lyman series and
various ionic metal transitions. By comparing the relative abundances of
different ions in individually-matched components, we show that cool gas (T~1e4
K) density and metallicity can vary by more than a factor of ten in in an LRG
halo. Specifically, metal-poor absorbing components with <1/10 solar
metallicity are seen in 50% of the LRG halos, while gas with solar and
super-solar metallicity is also common. These results indicate a complex
multiphase structure and poor chemical mixing in these quiescent halos. We
calculate the total surface mass density of cool gas, \Sigma_cool, by applying
the estimated ionization fraction corrections to the observed HI column
densities. The radial profile of \Sigma_cool is best-described by a projected
Einasto profile of slope \alpha=1 and scale radius r_s=48 kpc. We find that
typical LRGs at z~0.4 contain cool gas mass of M_cool= (1-2) x1e10 M_sun at
d<160 kpc (or as much as 4x1e10 M_sun at d<500 kpc), comparable to the cool CGM
mass of star-forming galaxies. Furthermore, we show that high-ionization OVI
and low-ionization absorption species exhibit distinct velocity profiles,
highlighting their different physical origins. We discuss the implications of
our findings for the origin and fate of cool gas in LRG halos.Comment: Accepted for publication in MNRAS after a minor revision. 23 pages,
14 figures, and a 29-page Appendix with 27 additional figure
- …