Surface changes on crystalline stones due to salt crystallisation   总被引：1，自引：0，他引：1  

Patricia Vázquez  Ana Luque  Francisco J. Alonso  Carlota M. Grossi 《Environmental Earth Sciences》2013,69(4):1237-1248

This study assesses the changes on the surface of crystalline stones due to salt crystallisation. Efflorescence was forced to grow on the surface of granite and marbles through 60 cycles of salt crystallisation with sodium sulphate. Changes on surface roughness, gloss and colour were measured every 15 cycles and the specimens were examined with naked eye and SEM. Sodium sulphate produces damage which depends on mineral composition. Results show that granites experience a mechanical decay with an increase in roughness. Peaks of mica can be observed on the surface and cracks widen and grow deeper. Colour and gloss do not show any significant change, although gloss decreases with an increase in surface roughness. In marbles, the decay is mainly chemical. Surface roughness increases due to dissolution of the calcite. White marbles exhibit yellowing. Gloss decreases during the first cycles—as grain boundaries become more visible—but tends to regain almost its initial value as the number of cycles increases. In this case, gloss does not show any relation with surface roughness.  相似文献   

Measurement of soluble reactive phosphorus concentration profiles and fluxes in river-bed sediments using DET gel probes   总被引：3，自引：0，他引：3  

Helen P. Jarvie  Robert J.G. Mortimer  Elizabeth J. Palmer-Felgate  Katherine St. Quinton  Sarah A. Harman  Patricia Carbo 《Journal of Hydrology》2008,350(3-4):261-273

DET (diffusive equilibrium in thin films) gel probes were used for sampling river-bed sediment porewaters, to characterise in situ soluble reactive phosphorus (SRP) concentration profiles and fluxes. DET probes were deployed in three contrasting rural streams: (1) a headwater ‘pristine’ stream, with minimal P inputs from low intensity grassland and no point sources, (2) an intensively cultivated arable catchment, and (3) a stream subject to high P loadings from sewage effluent and intensive arable farming. The DET results showed highly enriched porewater SRP concentrations of between ca. 400 and 5000 μg-P l⁻¹ in the sewage-impacted stream. In contrast, the arable and pristine streams had porewater SRP concentrations <70 μg-P l⁻¹ and <20 μg-P l⁻¹, respectively. Porewater SRP concentration profiles in both the sewage-impacted and arable-impacted streams showed well-defined vertical structure, indicating internal sources and sinks of SRP within the sediment. However, there was little variability in porewater SRP concentrations in the pristine stream. The DET porewater profiles indicated net diffusion of SRP (a) from the overlying river water into the surface sediment and (b) from subsurface sediment upwards towards the sediment–water interface. A mass balance for the sewage-impacted site showed that the influx of SRP into the surface sediments from the overlying river water was small (ca. 1% of the daily river SRP load). The DET results indicated that, in the arable and sewage-impacted streams, the surface ‘cap’ of fine sediment may play an important role in inhibiting upward movement of SRP from subsurface porewaters into the overlying river water, under steady-state, low-flow conditions.  相似文献   

A heat perturbation flow meter for application in soft sediments     

Richard B. Greswell  Michael S. Riley  Patricia Fernandes Alves  John H. Tellam 《Journal of Hydrology》2009,370(1-4):73-82

A prototype flow meter has been developed, based upon the heat perturbation principle, to monitor groundwater specific discharge in soft sediments. The device is designed for use in spatially intensive, long-term monitoring campaigns in remote or inconvenient locations, and is cheap, robust and capable of being logged automatically. The results of the laboratory tests indicate that the heat perturbation principle is suitable for determining the magnitude of specific discharge to a degree of accuracy that would be useful in practical applications in dynamic groundwater systems with rapidly changing flows of approximately 1 md⁻¹ or more and that the groundwater flow direction can generally be determined to a high level of precision. The accuracy and reliability of the estimates of specific discharge have been shown to depend strongly upon the geometrical precision of manufacture and the quality of the temperature monitoring system. These factors become most significant in the estimation of lower flows and further investigation is required to determine the detection limit of the device. Specific discharge estimates have been shown to be insensitive to dispersivity values appropriate to the scale of the device. Unlike the majority of heat perturbation devices, calibration is unnecessary.  相似文献   

Source process of very-long-period events accompanying long-period signals at Cotopaxi Volcano,Ecuador     

Indira Molina  Hiroyuki Kumagai  Alexander García-Aristizábal  Masaru Nakano  Patricia Mothes 《Journal of Volcanology and Geothermal Research》2008

Renewed seismic activity of Cotopaxi, Ecuador, began in January 2001 with the increased number of long-period (LP) events, followed by a swarm of volcano-tectonic (VT) earthquakes in November 2001. In late June 2002, the activity of very-long-period (VLP) (2 s) events accompanying LP (0.5–1 s) signals began beneath the volcano. The VLP waveform was characterized by an impulsive signature, which was accompanied by the LP signal showing non-harmonic oscillations. We observed temporal changes of both the VLP and LP signals from the beginning until September 2003: The VLP signal gradually disappeared and the LP signal characterized by decaying harmonic oscillations became dominant. Assuming possible source geometries, we applied a waveform inversion method to the observed waveforms of the largest VLP event. Our inversion and particle motion analyses point to volumetric changes of a sub-vertical crack as the VLP source, which is located at a depth of 2–3 km beneath the northeastern flank. The spectral analysis of the decaying harmonic oscillations of LP events shows frequencies between 2.0 and 3.5 Hz, with quality factors significantly above 100. The increased VT activity and deformation data suggest an intrusion of magma beneath the volcano. A release of gases with small magma particles may have repetitively occurred due to the pressurization, which was caused by sustained bubble growth at the magma ceiling. The released particle-laden gases opened a crack above the magma system and triggered the resonance of the crack. We interpret the VLP and LP events as the gas-release process and the resonance of the crack, respectively.  相似文献   

Seasonal variation in di-nitrogen fluxes and associated processes (denitrification, anammox and nitrogen fixation) in sediment subject to shellfish farming influences     

Laura Minjeaud  Valerie D. Michotey  Nicole Garcia  Patricia C. Bonin 《Aquatic Sciences - Research Across Boundaries》2009,71(4):425-435

Seasonal patterns of di-nitrogen fluxes together with denitrification, anammox, and N-fixation rates were studied in sediment in an area subject to strong human pressure via waste water, tributaries and shellfish farming in the Mediterranean Sea (Carteau Cove, NW area of the Gulf of Lion). Ammonium concentration demonstrated no seasonal variation, however, a large increase in its concentration was observed over a 10 years period due to intense biodeposition of organic matter. In contrast, nitrate concentration demonstrated no seasonal or long-term (10 years) variation. The main processes affecting di-nitrogen flux magnitudes were denitrification and N-fixation. Anammox was only detected occasionally, nevertheless it represented at times up to 39% of the N₂-flux. Nitrate reducing processes were variable and denitrification showed a 20-fold increase over the past 10 years and might actually have reached its potential maximal activity. Rates of N₂ production (denitrification and anammox) were generally higher than those of N-fixation, leading to elimination of nitrogen from the ecosystem.  相似文献   

ESR dating of dental enamel from Middle Palaeolithic levels at Lazaret Cave,France     

Véronique Michel  Guanjun Shen  Patricia Valensi  Henry de Lumley 《Quaternary Geochronology》2009,4(3):233-240

ESR dating was carried out on Cervus elaphus tooth enamel samples from the depositional sequence of Lazaret Cave, Nice, France. The deposits contain Anteneandertal hominid fossils associated with abundant lithic artefacts and faunal remains. Three samples from the Mousterian occupations in complex CIII (Fouille d'entrée) yielded early uptake (EU) ages between 108 and 125 ka and linear uptake (LU) ages between 133 and 160 ka. Seven samples from the Acheulian levels in the upper part of the complex CII (Fouille d'entrée and Fouille centre) gave EU ages between 113 and 165 ka and LU ages between 147 and 210 ka, with weighted means at 131 ± 7 and 165 ± 9 ka, respectively. The results of six enamel samples from the lower Acheulian levels at Locus VIII, another place in the cave, were discarded because of their decreasing tendency with depth. The US–ESR combination method was also applied and the CSUS–ESR dates were calculated using the ESR-DATA program. Altogether, the data suggest that the Lazaret Acheulian and Mousterian occupations were rapidly formed during OIS 6.  相似文献   

Mira kinematics from Hipparcos data: a Galactic bar to beyond the Solar circle     

Michael W. Feast  Patricia A. Whitelock 《Monthly notices of the Royal Astronomical Society》2000,317(2):460-487

The space motions of Mira variables are derived from radial velocities, Hipparcos proper motions and a period–luminosity relation. The previously known dependence of Mira kinematics on the period of pulsation is confirmed and refined. In addition, it is found that Miras with periods in the range 145–200 d in the general Solar neighbourhood have a net radial outward motion from the Galactic Centre of 75±18 km s⁻¹. This, together with a lag behind the circular velocity of Galactic rotation of 98±19 km s⁻¹, is interpreted as evidence for an elongation of their orbits, with their major axes aligned at an angle of ∼17° with the Sun–Galactic Centre line, towards positive Galactic longitudes. This concentration seems to be a continuation to the Solar circle and beyond of the bar-like structure of the Galactic bulge, with the orbits of some local Miras probably penetrating into the bulge. These conclusions are not sensitive to the distance scale adopted. A further analysis is given of the short-period (SP) red group of Miras discussed in companion papers in this series. In Appendix A the mean radial velocities and other data for 842 oxygen-rich Mira-like variables are tabulated. These velocities were derived from published optical and radio observations.  相似文献   

Economics, ethics, and climate policy: framing the debate     

Richard B. Howarth  Patricia A. Monahan 《Global and Planetary Change》1996,11(4):187-199

This paper examines the economic and ethical dimensions of climate policy in light of existing knowledge of the impacts of global warming and the costs of greenhouse gas emissions abatement. We find that the criterion of economic efficiency, operationalized through cost-benefit analysis, is ill-equipped to cope with the pervasive uncertainties and issues of intergenerational fairness that characterize climate change. In contrast, the concept of sustainable development—that today's policies should ensure that future generations enjoy life opportunities undiminished relative to the present—is a normative criterion that explicitly addresses the uncertainties and distributional aspects of global environmental change. If one interprets the sustainability criterion to imply that it is morally wrong to impose catastrophic risks on unborn generations when reducing those risks would not noticeably diminish the quality of life of existing persons, a case can be made for significant steps to reduce greenhouse gas emissions.  相似文献   

Characterization of the bivalve ultrafiltration barrier: What pollutants pass through?     

M.Patricia Morse  Edgar Meyhofer  William E. Robinson 《Marine environmental research》1988,24(1-4)

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The provenance of Australian uranium ore concentrates by elemental and isotopic analysis     

Elizabeth Keegan  Stephan Richter  Ian Kelly  Henri Wong  Patricia Gadd  Heinz Kuehn  Adolfo Alonso-Munoz 《Applied Geochemistry》2008

Elemental and isotopic ratio analyses of U ore concentrate samples, from the 3 operating U mining facilities in Australia, were carried out to determine if significant variations exist between their products, thereby allowing the U ore concentrate’s origin to be identified. Elemental analyses were conducted using inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence spectrometry (XRF). Lead isotope ratios were measured using ICP-MS and U isotope analyses were conducted using thermal ionisation mass spectrometry (TIMS). Minute quantities of sample, such as that obtained from a swipe, were also examined for elemental concentrations using secondary ion mass spectrometry (SIMS). The results of multivariate statistical analysis show clear patterns in the trace elemental composition of the processed U ores, indicating that it is possible to use this feature as a unique identifier of an Australian U ore concentrate’s source. Secondary ion mass spectrometry analyses also allow individual particles to be differentiated using this ‘fingerprinting’ technique. Isotope ratios determined using TIMS reveal that there is a significant difference in the n(²³⁴U)/n(²³⁸U) isotope ratio between the U ore concentrate from each mine.  相似文献