Experimental characterization of the impact of temperature and humidity on the breakdown of soil water repellency in sandy soils and composts          下载免费PDF全文

Amii Whelan  Cedric Kechavarzi  Frederic Coulon  Stefan H. Doerr 《水文研究》2015,29(8):2065-2073

Soil water repellency is a widespread phenomenon with the capacity to alter hydrological and geomorphological processes. Water repellency decays with time, and the consequences are only of concern during the timescale at which the water repellency persists. This study aimed to characterize the influence of temperature and humidity on the breakdown of water repellency. Apparent contact angle measurements were carried out on samples consisting of sand treated with stearic acid as well as naturally repellent dune sands and composts. Temperature and humidity were controlled using a cooled incubator and a purpose designed enclosed box in which humidity could be raised or lowered. Results showed the contact angle of the stearic‐acid‐treated sands decayed with time and that there was a significant increase with stearic acid concentration. For all samples, the decay in apparent contact angle could be described with a continuous breakdown model. The stearic‐acid‐treated sands showed a significant increase in contact angle with relative humidity at a temperature of 10 and 20 °C. These differences diminished with increasing temperature. Similar results were seen for the dune sands and composts. Despite the influence of temperature and humidity on contact angles, there was no significant change in the rate at which the contact angle decayed in any sample. Absolute humidity was found to provide a more relevant indicator than relative humidity when assessing the influence of humidity on repellency over a range of temperatures. The contact angle initially increased with absolute humidity before plateauing owing to the confounding effect of temperature. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Comparison of 4D tomographic mapping versus thin-shell approximation for ionospheric delay corrections for single-frequency GPS receivers over North America   总被引：1，自引：1，他引：0  

Damien J. Allain  Cathryn N. Mitchell 《GPS Solutions》2010,14(3):279-291

The majority of navigation satellite receivers operate on a single frequency. They compensate for the ionospheric delay using either an ionospheric model which typically only corrects for 50% of the delay or a thin-shell map of the ionosphere. A 4D tomographic imaging technique is used to map the free electron density over the full-height of the ionosphere above North America during autumn 2003. The navigation solutions computed using correction based upon the thin-shell and the full-height maps are compared in this paper. The maps are used to calculate the excess propagation delay on the L1 frequency experienced by GPS receivers at selected locations across North America. The excess delay is applied to correct the single-frequency pseudorange observations at each location, and the improvements to the resulting positioning are calculated. It is shown that the thin-shell and full-height maps perform almost as well as a dual-frequency carrier-smoothed benchmark and for most receivers better than the unfiltered dual-frequency benchmark. The full-height corrections perform well and are considerably better than thin-shell corrections under extreme storm conditions.  相似文献   

Stress changes induced at neighbouring faults by the June 2000 earthquakes,South Iceland Seismic Zone     

Romain Plateaux  Jacques Angelier  Françoise Bergerat  Frederic Cappa  Ragnar Stefánsson 《地学学报》2010,22(2):79-86

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Intensity measures for probabilistic assessment of non‐structural components acceleration demand          下载免费PDF全文

Marco De Biasio  Stephane Grange  Frederic Dufour  Frederic Allain  Ilie Petre‐Lazar 《地震工程与结构动力学》2015,44(13):2261-2280

A fundamental issue in the framework of seismic probabilistic risk analysis is the choice of ground motion intensity measures (IMs). Based on the floor response spectrum method, the present contribution focuses on the ability of IMs to predict non‐structural components (NSCs) horizontal acceleration demand. A large panel of IMs is examined and a new IM, namely equipment relative average spectral acceleration (E‐ASA_R), is proposed for the purpose of NSCs acceleration demand prediction. The IMs efficiency and sufficiency comparisons are based on (i) the use of a large dataset of recorded earthquake ground motions; (ii) numerical analyses performed on three‐dimensional numerical models, representing actual structural wall and frame buildings; and (iii) systematic statistical analysis of the results. From the comparative study, the herein introduced E‐ASA_R shows high efficiency with respect to the estimation of maximum floor response spectra ordinates. Such efficiency is particularly remarkable in the case of structural wall buildings. Besides, the sufficiency and the simple formulation allowing the use of existing ground motion prediction models make the E‐ASA_R a promising IMs for seismic probabilistic risk assessment. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Multiple time-scale modelling of the circulation in Torres Strait—Australia     

Frederic Saint-Cast 《Continental Shelf Research》2008

Ocean circulation influences nearly all aspects of the marine ecosystem. This study describes the water circulation patterns on time scales from hours to years across Torres Strait and adjacent gulfs and seas, including the north of the Great Barrier Reef. The tridimensional circulation model incorporated realistic atmospheric and oceanographic forcing, including winds, waves, tides, and large-scale regional circulation taken from global model outputs. Simulations covered a hindcast period of 8 years (i.e. 01/03/1997–31/12/2004), allowing the tidal, seasonal, and interannual flow characteristics to be investigated. Results indicated that the most energetic current patterns in Torres Strait were strongly dominated by the barotropic tide and its spring-neap cycle. However, longer-term flow through the strait was mainly controlled by prevailing winds. A dominant westward drift developed in summer over the southeasterly trade winds season, which then weakened and reversed in winter over the northwesterly monsoon winds season. The seasonal flow through Torres Strait was strongly connected to the circulation in the north of the Great Barrier Reef, but showed little connectivity with the coastal circulation in the Gulf of Papua. Interannual variability in Torres Strait was highest during the monsoon period, reflecting variability in wind forcing including the timing of the monsoon. The characteristics of the circulation were also discussed in relation to fine sediment transport. Turbidity level in Torres Strait is expected to peak at the end of the monsoon, while it is likely to be at a low at the end of the trade season, eventually leading to a critically low bottom light level which constitutes a severe risk of seagrass dieback.  相似文献   

High resolution simulation of the South Asian monsoon using a variable resolution global climate model   总被引：2，自引：1，他引：1  

T. P Sabin  R. Krishnan  Josefine Ghattas  Sebastien Denvil  Jean-Louis Dufresne  Frederic Hourdin  Terray Pascal 《Climate Dynamics》2013,41(1):173-194

This study examines the feasibility of using a variable resolution global general circulation model (GCM), with telescopic zooming and enhanced resolution (~35 km) over South Asia, to better understand regional aspects of the South Asian monsoon rainfall distribution and the interactions between monsoon circulation and precipitation. For this purpose, two sets of ten member realizations are produced with and without zooming using the LMDZ (Laboratoire Meteorologie Dynamique and Z stands for zoom) GCM. The simulations without zoom correspond to a uniform 1° × 1° grid with the same total number of grid points as in the zoom version. So the grid of the zoomed simulations is finer inside the region of interest but coarser outside. The use of these finer and coarser resolution ensemble members allows us to examine the impact of resolution on the overall quality of the simulated regional monsoon fields. It is found that the monsoon simulation with high-resolution zooming greatly improves the representation of the southwesterly monsoon flow and the heavy precipitation along the narrow orography of the Western Ghats, the northeastern mountain slopes and northern Bay of Bengal (BOB). A realistic Monsoon Trough (MT) is also noticed in the zoomed simulation, together with remarkable improvements in representing the associated precipitation and circulation features, as well as the large-scale organization of meso-scale convective systems over the MT region. Additionally, a more reasonable simulation of the monsoon synoptic disturbances (lows and disturbances) along the MT is noted in the high-resolution zoomed simulation. On the other hand, the no-zoom version has limitations in capturing the depressions and their movement, so that the MT zone is relatively dry in this case. Overall, the results from this work demonstrate the usefulness of the high-resolution variable resolution LMDZ model in realistically capturing the interactions among the monsoon large-scale dynamics, the synoptic systems and the meso-scale convective systems, which are essential elements of the South Asian monsoon system.  相似文献   

Geophysical and Geoarchaeological Investigations at Aganoa Beach,American Samoa: An Early Archaeological Site in Western Polynesia     

Frederic B. Pearl  William A. Sauck 《Geoarchaeology》2014,29(6):462-476

Archaeological investigations at Aganoa, a coastal site in American Samoa, western Polynesia, revealed a marine resources exploitation base for the early inhabitants of the island. A series of 19 radiocarbon age determinations indicates the principal period of site utilization began no later than 570 B.C., and probably earlier, and lasted for about 300 years. This site is squarely in the phase identified by previous scholars as “ancestral Polynesian.” Geophysical survey in the form of long, shore‐perpendicular transects showed the accretionary history of this beach and ridge area. Surprisingly, it revealed that the earlier ridges were directly below the modern ridge (i.e., progradation of this geomorphic feature had not occurred). The survey revealed a buried paleosol with little or no disturbance, which yielded a well‐preserved assemblage of plain and decorated ceramics, stone artifacts, fishhooks, and archaeofauna. No evidence of archaeological continuity was seen between the end of the terminal Lapita occupation and the later reoccupation of the site after about A.D. 700. This study demonstrates the utility and feasibility of using ground‐penetrating radar for the discovery of deeply buried coastal sites.  相似文献   

High-resolution spectroscopy of ROSAT-discovered weak-line T Tauri stars near Lupus     

R. Wichmann  E. Covino  J. M. Alcalá  J. Krautter  S. Allain  P. H. Hauschildt 《Monthly notices of the Royal Astronomical Society》1999,307(4):909-918

We present high-resolution optical echelle spectroscopy for a large fraction of the Li-rich late-type stars recently discovered in the vicinity of the Lupus dark clouds. Our results confirm the high Li  i   λ 6708 equivalent widths previously estimated from medium-resolution spectra, thus adding strength to the conclusion that the large majority of these stars are still in the pre-main-sequence phase of their evolution, contrary to claims from other authors that many of them might be zero-age main-sequence stars. We present a statistical approach to derive a mean distance for the sample, and find that it is consistent with, or slightly lower than, the Hipparcos distance of the Lupus star-forming region. The radial velocities measured for part of these stars are consistent with those observed for the Lupus star-forming region, while stars outside the dark clouds show a mean difference of the order of 3 km s⁻¹. The projected rotational velocities show a lack of slow rotators, which is interpreted as a consequence of the X-ray selection of the sample. The Li-rich stars in Lupus studied in this work yield a fairly 'clean' sample of very young stars, while in other star-forming regions a larger fraction of older zero-age main-sequence stars has been found among ROSAT -discovered Li-rich stars. We argue that this fact reflects the relation of these stars with the Gould Belt.  相似文献   

An assessment of the use of stabilized coal and oil ash for construction of artificial fishing reefs: Comparison of fishes observed on small ash and concrete reefs   总被引：2，自引：0，他引：2  

Frederic E. Vose  Walter G. Nelson   《Marine pollution bulletin》1998,36(12):980-988

Fishes present on small artificial reefs located 2 km off the central east coast of Florida (USA) were surveyed to determine the acceptability of using stabilized oil and coal ash residue as a component material in construction of artificial fishing reefs. Species richness was not significantly different over 2.5 yr on stabilized oil and coal ash reefs compared to concrete control reefs. Of 19 species tested for significant differences in mean abundance, lane snapper was observed at significantly higher mean abundances on fossil-fuel ash reefs (stabilized oil ash/coal fly ash), while three reef species (hairy blenny, porkfish and gray snapper) were significantly more common on concrete control reefs. Further study is needed to determine whether contaminants (Cu, V, Ni and Zn) from stabilized ash blocks can cause abundance differences for some fishes. Plausible alternate explanations for the differences in mean abundance include both interspecific interactions (competition and predation) and differences in the attraction or retention of fish among reef replicates due to slight variations in reef dimensions.  相似文献   

The Cepheid period–luminosity zero-point from radial velocities and Hipparcos proper motions     

Michael Feast  Frederic Pont  & Patricia Whitelock 《Monthly notices of the Royal Astronomical Society》1998,298(2):L43-L44

A value for the zero-point (ρ) of the Cepheid period–luminosity relation, <  M _V  >= 2.81 log P  + ρ, is deduced by comparing the value of the Oort constant, A , derived from radial velocities with that derived from Hipparcos proper motions. We find in this way that ρ =−1.47 ± 0.13, in excellent agreement with the value derived from Hipparcos trigonometrical parallaxes, ρ = −1.43 ± 0.10, by Feast &38; Catchpole in a recent paper.  相似文献