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371.
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373.
Wesley E. LeMasurier Sung Hi Choi Y. Kawachi Samuel B. Mukasa N. W. Rogers 《Contributions to Mineralogy and Petrology》2011,162(6):1175-1199
The Marie Byrd Land province includes 18 large (up to 1,800 km3) central volcanoes distributed across an active volcano-tectonic dome. The typical volcano structure consists of a basal
1,000–5,000 m of basanite surmounted by trachyte and subordinate intermediate rocks, plus phonolite, or pantellerite, or comendite.
The volumes of felsic sections are large (~30–700 km3), but these rocks probably make up <10% of volcanic rock in the province. This paper describes pantellerite volcanoes in
the Ames and Flood Ranges, which include a large and varied suite of these iron-rich, silica-poor rhyolites. Isotopic and
trace element data, maintenance of isotopic equilibrium throughout the basalt-felsic range, and the results of modeling, all
exclude significant crustal contamination and point to fractional crystallization as the process that controls magmatic evolution.
The most unusual feature of these volcanoes is the apparent need to derive pantellerites from basanite, the long interval
of fractionation at the base of the lithosphere and crust, involving kaersutite as the key phase in developing pantellerite,
and a plumbing system that permitted coeval eruption of pantellerite and phonolite from the same edifice. Peralkalinity most
likely developed in upper crustal reservoirs during the final 4–5% of magmatic history, by fractionating a high proportion
of plagioclase under low pH2O. Mantle plume activity appears to drive doming and volcanism. This, a stationary plate, and continental lithospheric structure
seem to provide an optimal environment for the evolution of a diverse, large volume suite of felsic rocks by fractional crystallization. 相似文献
374.
Patric Lindahl Ryuji Asami Paul Worsfold Min-Seok Choi 《Geochimica et cosmochimica acta》2011,75(5):1346-1356
The Pu isotopes, 239Pu and 240Pu, were determined in annually-banded skeletons of an accurately dated (1943-1999) modern coral (Porites lobata) from Guam Island to identify historical Pu sources to the tropical Northwest Pacific Ocean. Activity concentrations of 239+240Pu and 240Pu/239Pu atom ratios were determined in the dated coral bands using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Close-in fallout from the former US Pacific Proving Grounds (PPG) in the Marshall Islands and global fallout were identified as the two main sources. The Guam site was dominated by PPG close-in fallout in the 1950s, with an average 240Pu/239Pu atom ratio of 0.315 ± 0.005. In addition, a higher 240Pu/239Pu atom ratio (0.456 ± 0.020) was observed that could be attributed to fallout from the “Ivy Mike” thermonuclear detonation in 1952. The atom ratio decreased in the 1960s and 1970s due to increase in the global fallout with a low 240Pu/239Pu atom ratio (∼0.18). Recent coral bands (1981-1999) are dominated by the transport of remobilised Pu, with high 240Pu/239Pu atom ratios, from the Marshall Islands to Guam Island along the North Equatorial Current (NEC). This remobilised Pu was estimated to comprise 69% of the total Pu in the recent coral bands, although its contribution was variable over time. 相似文献
375.
Numerical simulation of vertical ground heat exchangers: Intermittent operation in unsaturated soil conditions 总被引:1,自引:0,他引:1
The effect of varying the thermal properties of inhomogeneous unsaturated soil on the intermittent operation of a vertical ground heat exchanger (GHE) was simulated by a conjugate heat transfer simulation using a transient conductive heat transfer model. A three-phase soil model was used to introduce soil properties that vary with depth. The performance during the first few hours was significantly different from that of an analytical infinite line source model that assumes steady-state borehole conditions, although relatively good agreement was obtained thereafter. Unsaturated soil conditions afforded a 40% lower mean heat exchange rate than saturated conditions. This demonstrates the importance of considering unsaturated conditions in the design and performance evaluation of GHEs. 相似文献
376.
Biochar application in a tropical,agricultural region: A plot scale study in Tamil Nadu,India 总被引:1,自引:0,他引:1
A plot-scale evaluation of biochar application to agricultural soils was conducted in Tirunelveli, Tamil Nadu, India, to investigate the potential of biochar to improve soil fertility and moisture content. Biochar feedstocks need to be sustainably sourced: several locally available feedstocks (rice husk, cassia stems, palm leaves and sawdust) were analysed as proposed soil amendments so that no single biomass material is depleted to maintain biochar addition. The biochars from different biomass feedstock contained >20% C and were high in macro- and micronutrients. The results suggest that an application rate of 6.6 metric tonnes ha?1 cassia biochar was enough to initiate C-accumulation, which is reflected in an increase in OM and a net reduction in soil bulk density. 相似文献
377.
Like any other coal, the highly heterogeneous nature of brown coal can sometimes make it difficult to interpret the results
of laboratory experiments. More homogeneous samples with properties reproducible in the laboratory would provide significant
advantage, especially in understanding the effects of various factors in the properties of coal. An attempt was made to develop
reconstituted coal (RC) samples in the laboratory through an extensive material development and laboratory testing programme.
The latter consisted of mainly uniaxial compression tests. The main objective in developing the RC material is to use it in
future research on CO2 sequestration in unmineable coal seams. A highly homogeneous coal sample would make it much easier to identify, for example,
the effect of CO2 sorption on the mechanical, flow and transport properties of coal. Uniaxial compression tests were conducted on some brown
coal samples to determine the approximate mechanical properties. The results revealed an average uniaxial compressive strength
of 1.46 MPa, an average elastic modulus of 77.43 MPa and a Poisson’s ratio of 0.16. The measured properties were used as a
reference for the development of RC samples. An extensive laboratory experimental programme was conducted to develop RC samples
with the desirable mechanical properties. Portland cement was used as the cementing agent for the RC. Different variables
such as percentage of cement, water content, compaction load and curing time were taken into account when developing RC samples.
Uniaxial compression tests were carried out to ensure that the RC samples were reasonably homogeneous and the properties were
similar to those of natural coal. Percentages of cement by weight of coal such as 4, 6 and 8% were attempted and a 4% cement
mix with 50% water was considered most suitable for the RC samples. Average compressive strength of 0.8 MPa (28-day strength)
and an average elastic modulus of 34 MPa were achieved for the RC samples. Further efforts at improvement would involve better
matching of the uniaxial compressive strength and elastic modulus of RC samples with the natural coal samples. 相似文献
378.
This paper is concerned with the robust control synthesis of autonomous underwater vehicle(AUV) for general path following maneuvers.First,we present maneuvering kinematics and vehicle dynamics in a unified framework.Based on H∞ loop-shaping procedure,the 2-DOF autopilot controller has been presented to enhance stability and path tracking.By use of model reduction,the high-order control system is reduced to one with reasonable order,and further the scaled low-order controller has been analyzed in both the frequency and the time domains.Finally,it is shown that the autopilot control system provides robust performance and stability against prescribed levels of uncertainty. 相似文献
379.
Fugacity of CO2 (fCO2), temperature, salinity, nutrients, and chlorophyll-a were measured in the surface waters of southwestern East Sea/Japan Sea in July 2005. Surface waters were divided into three
waters based on hydrographic characteristics: the water with moderate sea surface temperature (SST) and high sea surface salinity
(SSS) located east of the front (East water); the water with high SST and moderate SSS located west of the front (West water);
and the water with low SST and SSS located in the middle part of the study area (Middle water). High fCO2 larger than 420 μatm were found in the West water. In the Middle water, CO2 was undersaturated with respect to the atmosphere, with values between 246 and 380 μatm. Moderate fCO2 values ranging from 370 to 420 μatm were observed in the East water. For the East and West waters, estimates of temperature
dependency of fCO2 (12.6 and 15.1 μatm °C−1, respectively) were rather similar to a theoretical value, indicating that SST is likely to be a major factor controlling
the surface fCO2 distribution in these two regions. In the Middle water, however, the estimated temperature dependence was somewhat lower
than the theoretical value, and relatively high concentrations of surface chlorophyll-a coincided with the low surface fCO2, implying that biological uptake may considerably affect the fCO2 distribution. The net sea-to-air CO2 flux of the study area was estimated to be 0.30±4.81 mmol m−2 day−1 in summer, 2005. 相似文献
380.
Woo Chun Lee Soon-Oh Kim James Ranville Seong-Taek Yun Sun Hee Choi 《Environmental Earth Sciences》2014,71(8):3307-3318
Arsenic(V), as the arsenate (AsO4 3?) ion and its conjugate acids, has a strong affinity on Fe, Mn, and Al (oxyhydr)oxides and clay minerals. Removal of arsenate from aqueous solution by poorly crystalline ferrihydrite (hydrous ferric oxide) via a combination of macroscopic (equilibria and kinetics of sorption) and X-ray absorption spectroscopic studies was investigated. The removal of arsenate significantly decreased with increasing pH and sorption maxima of approximately 1.994 mmol/g (0.192 molAs/molFe) were achieved at pH 2.0. The Langmuir isotherm is most appropriate for arsenate sorption over the wide range of pH, indicating that arsenate sorption preferentially takes place at relatively homogenous and monolayer sites rather than heterogeneous and multilayer surfaces. The kinetic study demonstrated that arsenate sorption onto 2-line ferrihydrite is considerably fast, and sorption equilibrium was achieved within the reaction time of 2 h. X-ray absorption near-edge structure spectroscopy indicates no change in oxidation state of arsenate following interaction with the ferrihydrite surfaces. Extended X-ray absorption fine structure spectroscopy supports the efficient removal of arsenate by the 2-line ferrihydrite through the formation of highly stable inner-sphere surface complexes, such as bidentate binuclear corner-sharing (2C) and bidentate mononuclear edge-sharing (2E) complexes. 相似文献