Acoustic models and sonar systems     

Porter  M.B. 《Oceanic Engineering, IEEE Journal of》1993,18(4):425-437

The basic types of acoustic models are reviewed. These include ray models, spectral integral models, normal mode models, parabolic equation modeling, and 3-D acoustic modeling. Their application to conventional sonar simulation problems is demonstrated. Examples of their use in more advanced signal processing applications are presented  相似文献   

Upper crust attenuation in the Basin and Range Province of Sonora,Mexico     

Castro  Raúl R.  Villalobos-Escobar  Gina P. 《Journal of Seismology》2021,25(5):1241-1249

Journal of Seismology - We estimated the S-wave quality factor Q(f) of the upper crust in northeastern Sonora, Mexico, using a two-layer model. The first layer of the model has a thickness of 1 km,...  相似文献   

Organochlorine contaminant exposure and associations with hematological and humoral immune functional assays with dam age as a factor in free-ranging northern fur seal pups (Callorhinus ursinus)     

Beckmen KB  Blake JE  Ylitalo GM  Stott JL  O'Hara TM 《Marine pollution bulletin》2003,46(5):594-606

Potential effects of organochlorine contaminant (OC) exposure on humoral immune function and health of free-ranging northern fur seals were investigated. Forty-two "neonates" were captured for blood sample collection and re-sampled as "pups" 29-51 days later. OCs were extracted from whole blood to identify polychlorinated biphenyl congeners and chlorinated pesticides by high performance liquid chromatography. Humoral immune function was assessed by antibody responses to vaccination and immunoglobulin concentrations. Additional health status indicators included leukocyte counts and haptoglobin concentrations. Mean OC concentrations were higher in neonates than at recapture. Neonates of young dams had higher mean OC concentrations than neonates of older dams. A higher proportion of old dam's pups developed a twofold or greater increase in antigen-specific antibodies compared to young dam's pups. Higher OC exposure and poor immune responses in first-born pups may indicate a higher risk of secondary morbidity and mortality than pups of multiparous dams.  相似文献   

Dust motions in quasi-statically charged binary asteroid systems     

Jared M. Maruskin  Julie Bellerose  Macken Wong  Lara Mitchell  David Richardson  Douglas Mathews  Tri Nguyen  Usha Ganeshalingam  Gina Ma 《Celestial Mechanics and Dynamical Astronomy》2013,115(3):281-298

In this paper, we discuss dust motion and investigate possible mass transfer of charged particles in a binary asteroid system, in which the asteroids are electrically charged due to solar radiation. The surface potential of the asteroids is assumed to be a piecewise function, with positive potential on the sunlit half and negative potential on the shadow half. We derive the nonautonomous equations of motion for charged particles and an analytic representation for their lofting conditions. Particle trajectories and temporary relative equilibria are examined in relation to their moving forbidden regions, a concept we define and discuss. Finally, we use a Monte Carlo simulation for a case study on mass transfer and loss rates between the asteroids.  相似文献   

Suzaku observations of charge exchange emission from solar system objects     

Y. Ezoe  R. Fujimoto  N.Y. Yamasaki  K. Mitsuda  T. Ohashi  K. Ishikawa  S. Oishi  Y. Miyoshi  N. Terada  Y. Futaana  F.S. Porter  G.V. Brown 《Astronomische Nachrichten》2012,333(4):319-323

Recent results of charge exchange emission from solar system objects observed with the Japanese Suzaku satellite are reviewed. Suzaku is of great importance to investigate diffuse X‐ray emission like the charge exchange from planetary exospheres and comets. The Suzaku studies of Earth's exosphere, Martian exosphere, Jupiter's aurorae, and comets are overviewed (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Solar wind charge exchange and local hot bubble X‐ray emission with the DXL sounding rocket experiment     

M. Galeazzi  M.R. Collier  T. Cravens  D. Koutroumpa  K.D. Kuntz  S. Lepri  D. McCammon  F. S. Porter  K. Prasai  I. Robertson  S. Snowden  N.E. Thomas  Y. Uprety 《Astronomische Nachrichten》2012,333(4):383-387

The Diffuse X‐ray emission from the Local Galaxy (DXL) sounding rocket is a NASA approved mission with a scheduled first launch in December 2012. Its goal is to identify and separate the X‐ray emission of the solar wind charge exchange (SWCX) from that of the local hot bubble (LHB) to improve our understanding of both. To separate the SWCX contribution from the LHB, DXL will use the SWCX signature due to the helium focusing cone at l = 185°, b = –18°. DXL uses large area proportional counters, with an area of 1000 cm² and grasp of about 10 cm² sr both in the 1/4 and 3/4 keV bands. Thanks to the large grasp, DXL will achieve in a 5‐minute flight what cannot be achieved by current and future X‐ray satellites (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

AXIOM: Advanced X‐ray imaging of the magnetosheath     

S. Sembay  G. Branduardi‐Raymont  J.P. Eastwood  D.G. Sibeck  A. Abbey  P. Brown  J.A. Carter  C.M. Carr  C. Forsyth  D. Kataria  S. Kemble  S. Milan  C.J. Owen  A.M. Read  L. Peacocke  C.S. Arridge  A.J. Coates  M.R. Collier  S.W.H. Cowley  A.N. Fazakerley  G. Fraser  G.H. Jones  R. Lallement  M. Lester  F.S. Porter  T. Yeoman 《Astronomische Nachrichten》2012,333(4):388-392

AXIOM (Advanced X‐ray Imaging Of the Magnetosphere) is a concept mission which aims to explain how the Earth's magnetosphere responds to the changing impact of the solar wind using a unique method never attempted before; performing wide‐field soft X‐ray imaging and spectroscopy of the magnetosheath, magnetopause and bow shock at high spatial and temporal resolution. Global imaging of these regions is possible because of the solar wind charge exchange (SWCX) process which produces elevated soft X‐ray emission from the interaction of high charge‐state solar wind ions with primarily neutral hydrogen in the Earth's exosphere and near‐interplanetary space (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Discharge responses associated with rapid snow cover ablation events in the Susquehanna and Wabash River basins     

Zachary J. Suriano  Gina R. Henderson  Daniel J. Leathers 《自然地理学》2020,41(1):70-82

ABSTRACT

In the mid-latitudes, snow plays a critical role in regional hydroclimate, with snow ablation variability in ephemeral regions representing an area of essential research. Due to a lack of historical snow-water-equivalent data in the eastern United States, recent research has substituted daily snow depth changes for ablation. These studies, however, do not explicitly examine if such a substitution yields a snowmelt hydrological signal, an important component of water resource management. As such, this study evaluates if ablation events, as defined as a daily snow depth decrease, subsequently result in increased river discharge within two similarly sized watersheds in the eastern United States: the Wabash and Susquehanna River basins. For both basins, >75% of snow ablation events resulted in a positive river discharge response (increase in discharge) at a 3-day lag. Furthermore, results show a significant and positive relationship between ablation event frequency and seasonal discharge response, such that an increase (decrease) in seasonal snow ablation event frequency yields an increase (decrease) in associated seasonal river discharge at a 3-day lag. These relationships indicate that inter-diurnal decreases in snow depth do carry hydrological implications, adding confidence that such a definition of ablation is appropriate for climatological applications.  相似文献   

Microearthquakes near the eastern end of St Paul's Fracture Zone     

T. J. G. Francis  I. T. Porter  R. C. Lilwall 《Geophysical Journal International》1978,53(2):201-217

Summary . Four ocean-bottom seismographs were deployed near the eastern end of the St Paul's Fracture Zone in 1974 December. Microearthquakes were observed both along the fracture zone and in the median valley of the Mid-Atlantic Ridge. Seventy-six of them have been located and reliable depths obtained for 51. The range of depths observed suggests that the thickness of the lithosphere close to the ridge axis is 7 km. The absence of earthquakes on the ridge axis between 1 and 5 km depth may be the result of a highly cracked crust and thus indicates the depth to which hydrothermal fluids penetrate.  相似文献   

Reconstruction of climatic and environmental changes in NW Romania during the early part of the last deglaciation (15,000–13,600 cal yr BP)     

Barbara Wohlfarth  Gina Hannon  Angelica Feurdean  Lucretia Ghergari  Bogdan P. Onac  Gran Possnert 《Quaternary Science Reviews》2001,20(18):3

High resolution pollen, plant macrofossil, charcoal, mineral magnetic and sedimentary analyses, combined with AMS ¹⁴C measurements, were performed on multiple sediment sequences along a transect through the former crater lake Preluca iganului in northwestern Romania in order to reconstruct the climatic and environmental changes during the early part of the Last Termination. Lake sediments started to accumulate at 14,700 cal yr BP. Initially the upland vegetation consisted of an open forest with mainly Betula and Salix and few Pinus sp., but from 14,500 cal yr BP onwards, Pinus mugo, P. sylvestris and Populus and later on also Larix became established around the lake. Between 14,150 and 13,950 cal yr BP, Pinus cembra seems to have replaced P. mugo and P. sylvestris. At 13,950 cal yr BP the tree cover increased and Picea appeared for the first time, together with Pinus cembra, P. mugo and Larix. From 13,750 cal yr BP onwards, a Picea forest developed around the site. Based on the combined proxy data the following climatic development may be inferred: 14,700–14,500 cal yr BP, cooler and wet/humid; 14,500–14,400 cal yr BP: gradually warmer temperatures, wet/humid with dry summers; 14,400–14,320 cal yr BP: warm and dry; 14,320–14,150 cal yr BP: cooler and wet/humid; 14,150–14,100 cal yr BP: warm and dry; 14,100–13,850 cal yr BP: warmer and wet/humid; <13,850 cal yr BP: warm and dry. The tentative correlation of this development with the North Atlantic region assumes that the period >14,700 cal yr could correspond to GS-2a, the time span between 14,700 and 14,320 to GI-1e, the phase between 14,320 and 14,150 cal yr BP to GI-1d and the time frame between 14,150 and 13,600 cal yr BP to the lower part of GI-1c.  相似文献