Screening of polymers on selected Hawaii soils for erosion reduction and particle settling     

James A. Teo  Chittaranjan Ray  Samir A. El‐Swaify 《水文研究》2006,20(1):109-125

In recent years, high‐molecular‐weight anionic polyacrylamides (PAMs) have been tested on a variety of soils, primarily in temperate climates. However, little information is available regarding the effectiveness of PAM for preventing soil loss through runoff in tropical settings. Screening tests were performed using three negatively charged PAMs and one positively charged PAM on five Hawaii soils (two Oxisols, one Vertisol, and two Aridisols) to determine erosion loss, sediment settling, and aggregate stability. A laboratory‐scale rainfall simulator was used to apply erosive rainfall at intensities from 5 to 8·5 cm h^?1 at various PAM doses applied in both dry and solution forms. Soil detachment due to splash and runoff, as well as the runoff and percolate water volumes, were measured for initial and successive storms. The impact of PAM on particle settling and aggregate stability was also evaluated for selected soil‐treatment combinations. Among the PAMs, Superfloc A‐836 was most effective, and significantly reduced runoff and splash sediment loss for the Wahiawa Oxisol and Pakini Andisol at rates varying between 10 and 50 kg ha^?1. Reduced runoff and splash sediment loss were also noted for PAM Aerotil‐D when applied in solution form to the Wahiawa Oxisol. Significant reductions in soil loss were not noted for either the Lualualei Vertisol or the Holomua Oxisol. It is believed that the high montmorillonite content of the Lualualei Vertisol and the low cation‐exchange capacity of the Holomua Oxisol diminished the effectiveness of the various PAMs tested. The polymers were also found to enhance sediment settling of all soils and helped improve their aggregate stability. This screening study shows the potential use of PAM for tropical soils for applications such as infiltration enhancement, runoff reduction, and enhanced sedimentation of detention ponds. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Chemical abundances determined from meteor spectra: I. Ratios of the main chemical elements     

Josep M. Trigo‐Rodriguez  Jordi Llorca  Jiri Borovi ka  Juan Fabregat 《Meteoritics & planetary science》2003,38(8):1283-1294

Abstract— Relative chemical abundances of 13 meteoroids were determined by averaging the composition of the radiating gas along the fireball path that originated during their penetration into the Earth's atmosphere. Mg, Fe, Ni, Cr, Mn, and Co abundances, relative to Si, are similar to those reported for CI and CM carbonaceous chondrites and interplanetary dust particles. In contrast, relative abundances of Ca and Ti in meteor spectra indicate that these elements suffer incomplete evaporation processes. The chemical composition of all meteoroids studied in this work differs from that of 1P/Halley dust.  相似文献   

Analytical solutions of one‐dimensional infiltration before and after ponding     

Jiann‐Mou Chen  Yih‐Chi Tan  Chu‐Hui Chen 《水文研究》2003,17(4):815-822

This paper is a continuation of previous research, which obtained a convenient solution for arbitrary surface fluxes before ponding. By means of Fourier Transformation this has been extended to derive analytical solutions of a linearized Richards' equation for arbitrary input fluxes after surface saturation. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Astronomical Site Testing in Northwest of Argentina     

Pablo Recabarren  Pablo Recabarren  Mirta Mosconi  Hernán Muriel  Hernán Muriel  Diego García Lambas  Diego García Lambas  Marc Sarazin  Riccardo Giovanelli 《Astrophysics and Space Science》2004,290(3-4):409-413

We present the preliminary results of the astronomical site testing, which the group IATE of the OAC is developing in northwest of Argentine in collaboration with ESO and the Department of Astronomy of Cornell University. We show the results, which we have obtained from the analysis of GOES 8 satellite images in the 10.7 μm band, which allowed us to configurate a map of clear sky regions in an area between 23° and 28° S, and 66° 30′ and 69° W. We also comment logistical and tectonic aspects, and discuss next steps to follow in the research.  相似文献   

A warped m= 2 water maser disc in V778 Cyg?     

Natalia Babkovskaia  Juri Poutanen  Anita M. S. Richards  Ryszard Szczerba 《Monthly notices of the Royal Astronomical Society》2006,370(4):1921-1927

The silicate carbon star V778 Cyg is a source of 22-GHz water maser emission which was recently resolved by MERLIN. Observations revealed an elongated     -like structure along which the velocities of the maser features show a linear dependence on the impact parameter. This is consistent with a doubly warped   m = 2  disc observed edge-on. Water masers and silicate dust emission (detected by the Infrared Astronomical Satellite and Infrared Space Observatory ) have a common origin in O-rich material and are likely to be co-located in the disc. We propose a detailed self-consistent model of a masing gas–dust disc around a companion to the carbon star in a binary system, which allows us to estimate the companion mass of  1.7 ± 0.1 M_⊙  , the disc radius of  40 ± 3  au and the distance between companions of ∼80 au. Using a dust–gas coupling model for water masing, we calculate the maser power self-consistently, accounting for both the gas and the dust energy balances. Comparing the simulation results with the observational data, we deduce the main physical parameters of the masing disc, such as the gas and dust temperatures and their densities. We also present an analysis of the stability of the disc.  相似文献   

Peak metamorphic temperatures in type 6 ordinary chondrites: An evaluation of pyroxene and plagioclase geothermometry     

Valerie SLATER‐REYNOLDS  Harry Y. McSWEEN 《Meteoritics & planetary science》2005,40(5):745-754

Abstract— Quantifying the peak temperatures achieved during metamorphism is critical for understanding the thermal histories of ordinary chondrite parent bodies. Various geothermometers have been used to estimate equilibration temperatures for chondrites of the highest metamorphic grade (type 6), but results are inconsistent and span hundreds of degrees. Because different geothermometers and calibration models were used with different meteorites, it is unclear whether variations in peak temperatures represent actual ranges of metamorphic conditions within type 6 chondrites or differences in model calibrations. We addressed this problem by performing twopyroxene geothermometry, using QUILF95, on the same type 6 chondrites for which peak temperatures were estimated using the plagioclase geothermometer (Nakamuta and Motomura 1999). We also calculated temperatures for published pyroxene analyses from other type 6 H, L, and LL chondrites to determine the most representative peak metamorphic temperatures for ordinary chondrites. Pyroxenes record a narrow, overlapping range of temperatures in H6 (865–926 °C), L6 (812–934 °C), and LL6 (874–945 °C) chondrites. Plagioclase temperature estimates are 96–179 °C lower than pyroxenes in the same type 6 meteorites. Plagioclase estimates may not reflect peak metamorphic temperatures because chondrule glass probably recrystallized to plagioclase prior to reaching the metamorphic peak. The average temperature for H, L, and LL chondrites (～900 °C), which agrees with previously published oxygen isotope geothermometry, is at least 50 °C lower than the peak temperatures used in current asteroid thermal evolution models. This difference may require minor adjustments to thermal model calculations.  相似文献   

On the detailed magnetostratigraphy of greigite — (Smythite) mineralization,Sokolov Brown-Coal Basin,bohemia     

Miroslav Krs  Marta Krsová  Petr Pruner  Lada Kouklíková 《Studia Geophysica et Geodaetica》1991,35(4):267-284

Summary In the Middle Miocene claystones containing fossil micro-organic matter and overlying the brown-coal seams in the Jii quarry of the Sokolov Brown-Coal Basin, a strongly magnetic layer was found and subjected to detailed palaeomagnetic investigations. The principal carrier of magnetism in this bed (called Kocián's bed) is the ferrimagnetic mineralization of greigite or greigitesmythite showing pronounced metastable properties. This mineralization must be treated with caution during laboratory tests aimed at deriving palaeomagnetic directions. In Kocián's bed, about two metres thick, two zones of palaeomagnetic field transition were identified. The high degree of demagnetization achieved by using thermal stepwise procedures and a MAVACS apparatus enabled the origin of the self-reversal of remanence to be defined after heating to 360°C. The process of chemo-remanent magnetization of the authigenic greigite-(smythite) mineralization fossilizing the palaeomagnetic field was relatively fast; the transition of the palaeomagnetic field is recorded in layers not exceeding a thickness of 2 × 10^–2 m.Presented at 2nd conference on New Trends in Geomagnetism, Castle of Bechyn, Czechoslovakia, September 24–29, 1990.  相似文献   

Predicting ground-motion variations at the Turkey-flat test site,California     

J. Zahradník  J. Jech  V. Barták 《Pure and Applied Geophysics》1991,137(1-2):63-84

Results of a single group participating in an international experiment are analyzed. The experiment served to verify computational predictions of the ground-motion variations due to near-surface geological effects at a site established for that purpose by the California Department of Conservation. Based on an acceleration record at a rock location, and geotechnical model of medium, records at the other locations of a nearby sedimentary deposit were predicted. A 2-D finite-difference sensitivity analysis suggested that the lateral wave-propagation effects are negligibly small, and locally 1-D computations are sufficient for the present site. Those computations are compared with observations not available to the authors during the blind prediction. Peak accelerations, peak velocities and RMS accelerations were predicted with errors less than 159%, 114% and 62%, respectively. Maxima of the response spectra were fitted within a factor of 2. The predicted and observed Husid's plots (i.e., the normalized cumulative plots of the acceleration squared) have the correlation coefficients 0.98. The detected misfits do not show any simple relation to the instrument location, component, frequency, or time.  相似文献   

Cosmic-ray propagation in compressible turbulent media     

M. E. Katz  M. Stehlík 《Astrophysics and Space Science》1991,183(2):259-271

The influence of compressibility of media on both the statistical acceleration and the turbulent diffusion of cosmic-ray particles is investigated. The averaging over an ensemble of random velocity fields of the medium was performed in the kinetic equation. The kinetic coefficients, which are responsible for the particle acceleration, were obtained in the cases of weak and strong scattering due inhomogeneous magnetic fields.  相似文献   

A note on the problem of choosing a model of the Universe,IV     

Vladmír Skalský 《Astrophysics and Space Science》1991,181(2):313-322

The Friedmannian model of the Universe with ultra-relativistic equation of statep=–1/3 withk=0 is nondecelerative, i.e., it expands with the constant velocityv=c during the whole expanding phase of evolution of the Universe. The ultrastable nondecelerative model is the only model of the Universe which fulfills all conditions resulting from the quantum-mechanical and relativistic analysis of the Universe.  相似文献