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81.
Peter Edwards Lisa Sharma‐Wallace Tim Barnard Sandra J. Velarde Tui Warmenhoven Gerard Fitzgerald Duncan Harrison Loretta Garrett Tina Porou Pia Pohatu 《New Zealand geographer》2019,75(2):63-73
Sustainable livelihoods approaches used in international development are applied to a vulnerable New Zealand catchment. The Waiapu Catchment has a high proportion of indigenous residents, and is one of the most remote and deprived areas in the country. Linear and centralised approaches to indigenous development have failed to bring about desired changes. We identify “capitals” (social, human/political, physical, natural, financial and cultural) present in the catchment. From this assessment, we propose capital‐based holistic approaches to bring about community‐led change. The assessment and resulting approaches can be used in other vulnerable environments around the world. 相似文献
82.
A. Pedlar T. W. B. Muxlow M. A. Garrett P. Diamond K. A. Wills P. N. Wilkinson W. Alef 《Monthly notices of the Royal Astronomical Society》1999,307(4):761-768
We have used the European VLBI Network (EVN) at 18 cm to study five of the more compact radio sources in the starburst galaxy M82. The angular resolution of the observations is 15 mas, corresponding to 0.2 pc at the distance of M82. The observations reveal shells ranging in diameter from 40 to 90 mas (0.6 to 1.4 pc), although the strongest source (41.95+575) is only marginally resolved by these measurements (∼20×10 mas2 ).
We have found clear evidence for expansion in one of the shell sources (43.31+592) by re-analysing, in wide-field mode, EVN data taken in 1986. Between 1986 and 1997 this source has increased its diameter by 13.6±2 mas, corresponding to an average expansion velocity of 9850±1500 km s−1 . If we assume that the remnant is in free expansion, this is consistent with a supernova event in the early 1960s. Hence this remnant is almost certainly younger than the strongest, most compact source (41.95+575) which was known to be present in the 1960s. 41.95+575 shows no clear evidence for expansion (<4000 km s−1 ), consistent with a greater age; this is further evidence of its anomalous status. Comparison of the EVN images with earlier MERLIN data is also consistent with expansion in at least two more of the sources. We discuss the flux density variability of the compact sources in M82 and conclude that, with the exception of 41.95+575 and two transient sources, there is little evidence for significant changes in flux density of most of the remnants since the early 1980s. 相似文献
We have found clear evidence for expansion in one of the shell sources (43.31+592) by re-analysing, in wide-field mode, EVN data taken in 1986. Between 1986 and 1997 this source has increased its diameter by 13.6±2 mas, corresponding to an average expansion velocity of 9850±1500 km s
83.
Anil Kumar Mishra Masami Ohtsubo Loretta Y. Li Takahiro Higashi 《Environmental Earth Sciences》2012,65(1):21-27
As there are many correlations linking the liquid limit directly or indirectly with various engineering properties of the
soil, the accurate determination of the liquid limit is quite essential. Generally, two methods, i.e. Casagrande’s and fall
cone are adopted to determine the liquid limit of soil. Research was carried out to study the influence of the properties
of bentonite and the presence of the salt solution on the liquid limit values of soil-bentonite mixtures determined by the
Casagrande’s and fall cone methods. The results showed that irrespective of the presence of the type of bentonite or salt
solution, a higher value of the liquid limit was obtained by the Casagrande’s method as compared to the fall cone method.
However, the difference between the two methods decreased with the decrease in the liquid limit, clay fraction, specific surface
area and free swelling capacity of the bentonite present in the mixture. Similarly, the difference in the liquid limit values
obtained by both these methods is reduced with an increase in the salt concentration. 相似文献
84.
Stephen R. Parker Simon R. Poulson M. Garrett Smith Charmaine L. Weyer Kenneth M. Bates 《Aquatic Geochemistry》2010,16(1):61-84
Here we report diel (24 h) and seasonal differences in the concentration and stable carbon isotope composition of dissolved
inorganic (DIC) and organic carbon (DOC) in the Clark Fork (CFR) and Big Hole (BHR) Rivers of southwestern Montana, USA. In
the CFR, DIC concentration decreased during the daytime and increased at night while DOC showed an inverse temporal relationship;
increasing in the daytime most likely due to release of organic photosynthates and decreasing overnight due to heterotrophic
consumption. The stable isotope composition of DIC (δ13C-DIC) became enriched during the day and depleted over night and the δ13C-DOC displayed the inverse temporal pattern. Additionally, the night time molar rate of decrease in the concentration of
DOC was up to two orders of magnitude smaller than the rate of increase in the concentration of DIC indicating that oxidation
of DOC was responsible for only a small part of the increase in inorganic carbon. In the BHR, in two successive years (late
summer 2006 & 2007), the DIC displayed little diel concentration change, however, the δ13C-DIC did show a more typical diel pattern characteristic of the influences of photosynthesis and respiration indicating that
the isotopic composition of DIC can change while the concentration stays relatively constant. During 2006, a sharp night time
increase in DOC was measured; opposite to the result observed in the CFR and may be related to the night time increase in
flow and pH also observed in that year. This night time increase in DOC, flow, and pH was not observed 1 year later at approximately
the same time of year. An in-stream mesocosm chamber used during 2006 showed that the night time increase in pH and DOC did
not occur in water that was isolated from upstream or hyporheic contributions. This result suggests that a “pulse” of high
DOC and pH water was advected to the sampling site in the BHR in 2006 and a model is proposed to explain this temporal pattern. 相似文献
85.
A water-leach procedure for estimating bioaccessibility of elements in soils from transects across the United States and Canada 总被引:1,自引:1,他引:0
An objective of the North American Soil Geochemical Landscapes Project is to provide relevant data concerning bioaccessible concentrations of elements in soil to government and other institutions undertaking environmental studies. A protocol was developed that employs a 1-g soil sample agitated overnight with 40 mL of reverse-osmosis de-ionized water for 20 h, and determination of 63 elements following three steps of centrifugation by inductively coupled plasma–atomic emission spectrometry and inductively coupled plasma–mass spectrometry the following day. Statistical summaries are presented for those 48 elements (Ag, Al, As, B, Ba, Be, Br, Ca, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Ho, I, K, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, P, Pb, Pr, Rb, Re, S, Sb, Si, Sm, Sn, Sr, Tb, Ti, Tl, Tm, U, V, W, Y, Yb, Zn, Zr, and pH) for which <20% of their data were reported as below the detection limit. The resulting data set contains analyses for 161 A-horizon soils collected along two transects, one along the 38th parallel across the USA and the other from northern Manitoba to the USA–Mexico border. The spatial distribution of three selected elements (Ca, Cu, and Pb) along the two transects is discussed in this paper both as absolute amounts liberated by the leach and expressed as a percentage of the total, or near-total, amounts determined for the elements. The Ca data reflect broad trends in soil parent materials, their weathering, and subsequent soil development. Calcium concentrations are generally found to be lower in the older soils of the eastern USA. The Cu data are higher in the eastern half of the USA, correlating with soil organic C, with which it is sequestered. The Pb data exhibit little regional variability due to natural sources, but are influenced by anthropogenic sources. Based on the Pb results, the percentage water-extractable data demonstrate promise as a tool for identifying anthropogenic components. The soil–water partition (distribution) coefficients, Kds (L/kg), were determined and their relevance to estimating bioaccessible amounts of elements to soil fauna and flora is discussed. Finally, a possible link between W concentrations in human urine and water-extractable W levels in Nevada soils is discussed. 相似文献
86.
Effect of salt of various concentrations on liquid limit,and hydraulic conductivity of different soil-bentonite mixtures 总被引:1,自引:0,他引:1
Anil Kumar Mishra Masami Ohtsubo Loretta Y. Li Takahiro Higashi Junboum Park 《Environmental Geology》2009,57(5):1145-1153
Effect of the various concentrations of NaCl and CaCl2 on the four different soil-bentonite mixtures has been evaluated. The results show that the liquid limit of the mixtures
decreases with an increase in the salt concentration. Liquid limit decreased significantly with an increase in CaCl2 concentration from 0 to 0.1 N. However, a further increase in the concentration did not produce any significant decrease
in liquid limit. A quite opposite trend was observed for the NaCl solution. An increase in NaCl concentration from 0 to 0.1 N
did not produce any major decrease in the liquid limit, but a further increase in concentration from 0.1 to 1 N decreased
the liquid limit significantly. Consolidation tests were carried out on the mixtures to evaluate the effect of mineralogical
composition of the bentonite on the hydraulic conductivity (k) of the mixture in the presence of various salts concentrations. The k for any mixtures was found to be decreasing with decrease in the salt concentration. At relatively low concentration, Ca2+ had more effect on the k in comparison to the same concentration of Na+. However, at 1 N of NaCl and CaCl2 almost an equal value of k was observed. A comparison of the performance of four bentonites showed that the mixture with bentonite having highest exchangeable
sodium percentage (ESP) exhibited the lowest k when permeated with de-ionized (DI) water, however, k increased with an increase in the salt concentration. Similarly, mixture with a bentonite of lower ESP exhibited a higher
k with DI water but with the increase in the salt concentration alteration in the k, compared to all other mixtures, was relatively less. 相似文献
87.
Chris Garrett 《大气与海洋》2013,51(2):313-339
Abstract Mixing near the sloping boundaries of oceans or lakes may be a significant mechanism of diapycnal transport. The basic physics of this is reviewed, with emphasis on the reduction of the effectiveness of the process due to both reduced stratification and the restratifying secondary circulation driven by buoyancy forces. This re stratification is shown to reduce the effectiveness of intermittent mixing events as well as steady mixing. It is argued that for boundary mixing to be effective in the abyssal ocean it must extend sufficiently far from the boundary that the stratification can be maintained; this may be true for breaking bottom‐reflected internal waves. The alongslope flow implied by steady‐state boundary mixing theories is downwelling‐favourable and has a magnitude related to the thickness and other properties of the boundary layer. Mixing near a boundary may thus tend to drive a downwelling‐favourable mean circulation in the interior. If the interior circulation is imposed by other forces, the bottom boundary layer may evolve to a steady state if the interior flow is downwelling‐favourable, but if it is upwelling‐favourable initially a steady state seems unlikely and the downwelling‐favourable alongslope flow induced by the boundary mixing will tend to diffuse slowly into the interior. The nature of the solution in all these cases is sensitive to the Burger number, N2 sin2 θ/f2, where θ is the bottom slope, and to the eddy Prandtl number. 相似文献
88.
89.
Loretta Dunne Stephen A. Eales M. G. Edmunds 《Monthly notices of the Royal Astronomical Society》2003,341(2):589-598
Deep surveys in many wavebands have shown that the rate at which stars were forming was at least a factor of 10 higher at redshifts >1 than today. Heavy elements ('metals') are produced by stars, and the star formation history deduced by these surveys implies that a significant fraction of all metals in the Universe today should already exist at z ∼ 2–3 . However, only 10 per cent of the total metals expected to exist at this redshift have so far been accounted for (in damped Lyman α absorbers and the Lyman forest). In this paper, we use the results of submillimetre surveys of the local and high-redshift Universe to show that there was much more dust in galaxies in the past. We find that a large proportion of the missing metals are traced by this dust, bringing the metals implied from the star formation history and observations into agreement. We also show that the observed distribution of dust masses at high redshift can be reproduced remarkably well by a simple model for the evolution of dust in spheroids, suggesting that the descendants of the dusty galaxies found in deep submillimetre surveys are the relatively dust-free spiral bulges and ellipticals in the Universe today. 相似文献
90.
The effects of organic matter (80% humic and 15% fulvic acid) and coexistence of heavy metals (Ni, Pb and Zn) on sorption of three polycyclic aromatic hydrocarbons (PAHs)—acenaphthene, fluorene and fluoranthene—were examined for kaolinite, 60% kaolinite?+?40% sand, and 43% kaolinite?+?42% sand?+?15% bentonite. In total 108 batch sorption tests of PAHs were conducted for three types of clay mineral mixtures in six possible combinations of soil organic matter and heavy metal contents from no heavy metals and organic matter added to maximum organic matter added with spiked heavy metals. Results showed that the existence of metals increased the sorption of PAHs onto kaolinite from 4.7% for acenaphthene to 17.9% for fluoranthene. Organic matter in a kaolinite-sand-bentonite matrix could increase PAH sorption by up to 140% for fluoranthene. In all cases, increases were greater for fluoranthene, a larger PAH molecule. Heavy metals coexisting with organic matter led to enhanced sorption of PAHs compared to clay minerals without organic matter. Synergistic effects of organic matter and heavy metals on PAH sorption increments in the mixtures studied were such that the overall sorption could be 10–41% higher than that based on summation of the separate effects of metals and organics. 相似文献