Inversion for Range-Dependent Sediment Compressional-Wave-Speed Profiles From Modal Dispersion Data     

Rajan  S. D. Becker  K. M. 《Oceanic Engineering, IEEE Journal of》2010,35(1):43-58

A perturbative inversion method for estimating sediment compressional-wave-speed profiles from modal travel-time data is extended to include range-dependent environments. The procedure entails dividing a region into range-independent sections and obtaining estimates of the sediment properties for each region. Inversion results obtained using synthetic data show that range-dependent properties can be obtained if an experiment is designed to include multiple source/receiver combinations. This approach is applied to field data collected during the 2006 Shallow Water Experiment (SW06). The sediment compressional-wave-speed profiles resulting from analysis of the field data are evaluated by comparing acoustic fields predicted based on the inversion to acoustic fields measured during a different experiment conducted in the same region. The model is also compared to seismic reflection survey data collected during SW06. Resolution and variance estimated for the inversion results are also presented.   相似文献   

First results from the Gauribidanur Radio heliograph     

K. R. Subramanian  R. Ramesh  M. S. Sundara Rajan  Ch. V. Sastry 《Astrophysics and Space Science》1996,243(1):259-262

Observations of the Sun at two frequencies (51 and 77 MHz) using the East-West arm of the Gauribidanur Radio heliograph are presented.  相似文献   

Erratum to: Effect of the variation in the lower tropospheric temperature on the wind onset of the Indian summer monsoon   总被引：1，自引：0，他引：1  

Kenji Taniguchi  Devaraj Rajan  Toshio Koike 《Meteorology and Atmospheric Physics》2010,106(3-4):227-227

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⁴⁰Ar-³⁹Ar chronology of isolated phases from Bununu and Malvern howardites     

R.S. Rajan  J.C. Huneke  S.P. Smith  G.J. Wasserburg 《Earth and Planetary Science Letters》1975,27(2):181-190

High resolution⁴⁰Ar-³⁹Ar age spectra have been measured on plagioclase and glass from two howardites. Both the plagioclase and glass from the gas-rich Bununu howardite show well-defined age plateaux, yielding distinct ages of 4.42 ± 0.04 and 4.24 ± 0.05 AE, respectively. These age patterns are rather well behaved and are interpreted as representing the distinct times of formation of plagioclase from igneous processes and of glass fragments produced by impact on the meteorite body. The release pattern for the glass from the heavily shocked Malvern howardite is undulating at low and intermediate temperatures but does have a high-temperature plateau. Its age spectrum indicates little apparent diffusion loss, but rather an extensive redistribution of either⁴⁰Ar during the shock event or of³⁹Ar during the neutron irradiation or both. The total K-Ar age of Malvern glass is 3.64 ± 0.04 AE and the high-temperature plateau is 3.73 ± 0.05 AE. The age spectrum of the Malvern plagioclase has an intermediate temperature “plateau” at 3.80 AE that represents 20% of the total⁴⁰Ar content and increases towards a high-temperature plateau at 4.29 ± 0.04 AE containing 26% of the total gas release. It seems likely that the event which formed the Malvern glass also reset part of the plagioclase. The distinct histories observed for the different phases of these howardites are consistent with their formation from a regolith. The present results along with similar young ages for igneous clasts from Kapoeta clearly show that the regoliths were extant on the parent bodies of howardites and that they were subjected to violent impact events at least as recently as 3.7 AE ago.  相似文献   

Evidence for²⁴⁴Pu fission tracks in hibonites from Murchison carbonaceous chondrite     

R.S. Rajan  A.S. Tamhane 《Earth and Planetary Science Letters》1982,58(1):129-135

We have developed a technique for revealing nuclear tracks in the mineral hibonite (CaAl₁₂O₁₉), found in the refractory inclusions from carbonaceous chondrites. The tracks in hibonitesfrom Murchison carbonaous chondrite are dominated by fission tracks from²⁴⁴Pu (constituting more than 90% of the total). The measured uranium contents in these crystals range from 1.2 to 62 ppb. We deduce that the average value for the²⁴⁴Pu/²³⁸U ratio in most of the Murchison hibonites at the time of track retention is0.022 ± 0.011.  相似文献   

Mechanical shredding of water hyacinth (<Emphasis Type="Italic">Eichhornia crassipes</Emphasis>): Effects on water quality in the Sacramento-San Joaquin River Delta,California     

Ben K. Greenfield  Geoffrey S. Siemering  Joy C. Andrews  Michael Rajan  Stephen P. Andrews  David F. Spencer 《Estuaries and Coasts》2007,30(4):627-640

Management actions to control invasive aquatic species can have significant ecosystem-scale effects. We evaluated the water chemistry and nutrient effects of mechanical shredding to control water hyacinth (Eichhornia crassipes) in an agricultural slough and a tidal wetland on the Sacramento-San Joaquin River Delta, California. Shredding was conducted with two types of shredder boats in fall of 2003 and another boat in spring of 2004. Shredding measurably affected water quality, but specific effects varied as a function of shredding site and season. Significant increases were observed for total Kjeldahl nitrogen and total phosphorus for all experiments. Dissolved oxygen effects varied by site, decreasing after shredding at the agricultural slough but increasing at the tidal wetland. The increase in dissolved oxygen likely resulted from tidal incursions from the adjacent river. A year-long time series of dissolved oxygen data indicated a negative relationship between hyacinth abundance and dissolved oxygen concentrations. Hyacinth contained similar tissue concentrations of mercury to underlying sediments, suggesting that plant harvesting could aid mercury remediation efforts. Simple mass calculations indicated that Delta-wide shredding operations could cause between 0.1% and 9.6% increases in the overall abundance of carbon, nitrogen, and phosphorus in the Delta water column. Results suggest that local effects of management actions to control invasive aquatic plants will vary widely as a function of site-specific hydrology, but that estuary-wide effects would be limited.  相似文献   

Development of probability distributions for urban hydrologic model parameters and a Monte Carlo analysis of model sensitivity          下载免费PDF全文

James Knighton  Eric White  Edward Lennon  Rajesh Rajan 《水文研究》2014,28(19):5131-5139

This paper proposes an approach to estimating the uncertainty related to EPA Storm Water Management Model model parameters, percentage routed (P_R) and saturated hydraulic conductivity (K_sat), which are used to calculate stormwater runoff volumes. The methodology proposed in this paper addresses uncertainty through the development of probability distributions for urban hydrologic parameters through extensive calibration to observed flow data in the Philadelphia collection system. The established probability distributions are then applied to the Philadelphia Southeast district model through a Monte Carlo approach to estimate the uncertainty in prediction of combined sewer overflow volumes as related to hydrologic model parameter estimation. Understanding urban hydrology is critical to defining urban water resource problems. A variety of land use types within Philadelphia coupled with a history of cut and fill have resulted in a patchwork of urban fill and native soils. The complexity of urban hydrology can make model parameter estimation and defining model uncertainty a difficult task. The development of probability distributions for hydrologic parameters applied through Monte Carlo simulations provided a significant improvement in estimating model uncertainty over traditional model sensitivity analysis. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Multi-path arrival estimates using simulated annealing: applicationto crosshole tomography experiment     

Blackowiak  A.D. Rajan  S.D. 《Oceanic Engineering, IEEE Journal of》1995,20(3):157-165

In the analysis of crosshole tomography data, the first step is to estimate the arrival time and amplitude of the multi-path arrivals which comprise the received signal. Normally algorithms such as matched filter are used to determine the arrival times. However, when the bandwidth of the signal is small, this method cannot resolve closely spaced arrivals. We, therefore, investigate the performance of a simulated annealing algorithm in estimating the amplitude scaling factors and delay times of the separate arrivals in a signal composed of closely spaced arrivals with added noise. The algorithm is applied to field data collected during a crosshole tomography experiment conducted in sea ice  相似文献   

ROEDDERITE IN THE QINGZHEN (EH3) CHONDRITE     

E.R. Rambaldi  R.S. Rajan  R.M. Housley 《Meteoritics & planetary science》1986,21(1):141-149

The rare mineral roedderite, (Na_1.09 K_0.89 Ca_0.02)_2.00 (Mg_4.71 Fe_0.27)_4.98 (Si_11.80 Al_0.09)_11.89 O₃₀ has been found in accessory amounts in the highly unequilibrated enstatite chondrite, Qingzhen. It occurs in association with minor amounts of albite and SiO₂ as inclusions within the metal or sulfide phases of metal-sulfide assemblages. The roedderite crystals are connected through oxide and silicate veins to the surrounding matrix. The presence of glass coated vesicles on the surface of the assemblages strongly suggests that roedderite originated in the presence of a fluid phase, presumably during post-accretional planetary processes.  相似文献   

GALLIUM-BEARING SPHALERITE IN A METAL-SULFIDE NODULE OF THE QINGZHEN (EH3) CHONDRITE     

E.R. Rambaldi  R.S. Rajan  R.M. Housley  D. Wang 《Meteoritics & planetary science》1986,21(1):23-31

The Qingzhen (EH3) chondrite contains a population of spheroidal metal-sulfide nodules, which display textural evidence of reheating and melting. Evidence of metal sulfuration is also present, suggesting replacement of metal by sulfide during melting. This process has led to the nucleation of perryite along metal-sulfide interfaces. Gallium-bearing sphalerite and a Cu-sulfide of composition intermediate between chalcopyrite and cubanite occur as inclusions within the metal of some nodules. Other phases present are: kamacite, troilite, Ga-free sphalerite, niningerite, perryite, schreibersite, oldhamite, Cr-sulfide (minerals A and B), djerfisherite, SiO₂, albite and enstatite. The Ga-bearing sphalerite may have formed by injection of molten sulfide droplets into the metal followed by subsolidus diffusion of Ga from the metal into the sulfide. The latter may occur because of Ga supersaturation in the metal during progressive sulfuration and its decreased affinity for the metal phase during cooling below the taenite-kamacite transition point.  相似文献