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921.
This paper presents results of meticulous laboratory testing and numerical simulations on the effect of reinforcement on the
low-strain stiffness and bearing capacity of shallow foundations on dry sand. The effect of the location and the number of
reinforcement layers is studied in the laboratory, whereas numerical simulations are used to study the reinforcement-foundation
interaction. Laboratory tests show an increase of 100, 200, and 275% not only in bearing capacity but also in low-strain stiffness
(linear load–displacement behaviour) of a square foundation when one, two, and three layers of reinforcement are used, respectively.
The specimen preparation technique is found to be crucial for the repeatability and reliability of the laboratory results
(less than 5% variability). Numerical simulations demonstrate that if reinforcements are placed up to a depth of one footing
width (B) below the foundation, better re-distribution of the load to deeper layers is achieved, thus reducing the stresses and strains
underneath the foundation. Numerical simulations and experimental results clearly identify a critical zone between 0.3 and
0.5B, where maximum benefits not only on the bearing capacity but also on the low-strain stiffness of the foundation are obtained.
Therefore, soil reinforcement can also be used to reduce low-strain vibrations of foundations. 相似文献
922.
We report on the use of X-ray diffractometry under controlled conditions of temperature and relative humidity (RH-XRD) for
the investigation of NaCl deliquescence in the pore space of glass filter frits, which were used as model substrates. The
study confirms that RH-XRD is an appropriate experimental technique for the in situ observation of phase transformation in
porous materials. It is used for an investigation of both the deliquescence kinetics and the deliquescence humidity within
pores of different median pore diameter. Several major influences affecting deliquescence rates in the pore space close to
the surface of a porous material are discussed. It appears that quite short-term variation of ambient relative humidity, e.g.,
typical daily fluctuations, might induce damaging deliquescence–crystallization cycles within the pore space of building materials.
In agreement with theoretical considerations it was found that confinement of NaCl crystals in pores with median diameters
in the range 1.4–70 μm does not affect the deliquescence humidity of the salt. 相似文献
923.
Julien Berger Olivier Féménias Nicolas Coussaert Jean-Claude C. Mercier Daniel Demaiffe 《Contributions to Mineralogy and Petrology》2007,153(5):557-575
Ultramafic and mafic xenoliths of magmatic origin, sampled in the Beaunit vent (northern French Massif Central), derive from
the Permian (257 Ma) Beaunit layered complex (BLC) that was emplaced at the crust-mantle transition zone (∼1 GPa). These plutonic
xenoliths are linked to a single fractional crystallisation process in four steps: peridotitic cumulates; websteritic cumulates;
Al-rich mafic cumulates (plagioclase, pyroxenes, garnet, amphibole and spinel) and finally low-Al mafic cumulates. This sequence
of cumulates can be related to the compositional evolution of hydrous Mg basaltic magma that evolved to high-Al basalt and
finally to andesitic basalt. Sr and Nd isotopic compositions confirm the co-genetic character of the various magmatic xenoliths
and argue for an enriched upper mantle source comparable to present mantle wedges above subduction zones. LILE, LREE and Pb
enrichment are a common feature of all xenoliths and argue for an enriched sub-alkaline transitional parental magma. The existence
of a Permian magma chamber at 30 km depth suggests that the low-velocity zone observed locally beneath the Moho probably does
not represent an anomalous mantle but rather a sequence of mafic/ultramafic cumulates with densities close to those of mantle
rocks. 相似文献
924.
W. N. Mussel E. Murad J. D. Fabris W. S. Moreira J. B. S. Barbosa C. C. Murta W. P. Abrahão J. W. V. De Mello V. K. Garg 《Physics and Chemistry of Minerals》2007,34(6):383-387
We studied a chalcopyrite from a Cu ore deposit in Rio Grande do Sul, Brazil, by Mössbauer spectroscopy at room temperature and 110 K. Supporting methods to check for sample purity and to characterize further sample properties were slow-scanning X-ray powder diffraction and optical and microprobe analyses of polished sections of selected grains. Chemical analyses obtained using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer showed the sample to consist of homogeneous and essentially stoichiometric chalcopyrite (CuFeS2). Mössbauer spectra taken at both the above temperatures consist of asymmetric magnetically ordered patterns with unequal intensities of the line pairs 1–6 and 2–5, pointing to the existence of non-equivalent or multiple Fe sites. Least-squares fittings evidenced that the resonance intensity ratio of subspectrum with lower quadrupole shift (indicative of a more symmetric environment) to that with higher shift is 69:31, at room temperature, and 68:32, at 110 K. Rietveld refinement of the XRD data indicates the existence of tetragonal [a = 0.52855(1) and c = 1.0412(1) nm] and cubic [a 0 = 0.5273(2) nm] modifications in a proportion of 74:26, in good agreement with the Mössbauer data. The saturation magnetization of the sample was 32.7 J/(T kg), confirming the oxidation state of Fe as trivalent and pointing to little to no spin canting. 相似文献
925.
Jan Pleuger Sybille Roller Jens M. Walter Ekkehard Jansen Nikolaus Froitzheim 《International Journal of Earth Sciences》2007,96(2):229-252
The boundary zone between two Penninic nappes, the eclogite-facies to ultrahigh-pressure Zermatt-Saas zone in the footwall
and the blueschist-facies Combin zone in the hanging wall, has been interpreted previously as a major normal fault reflecting
synorogenic crustal extension. Quartz textures of mylonites from this fault were measured using neutron diffraction. Together
with structural field observations, the data allow a refined reconstruction of the kinematic evolution of the Pennine nappes.
The main results are: (1) the contact is not a normal fault but a major thrust towards northwest which was only later overprinted
by southeast-directed normal faulting; (2) exhumation of the footwall rocks did not occur during crustal extension but during
crustal shortening; (3) the Sesia-Dent Blanche nappe system originated from a continental fragment (Cervinia) in the Alpine
Tethys ocean, and the Combin zone ophiolites from the ocean basin southeast of Cervinia; (4) out-of-sequence thrusting played
a major role in the tectonic evolution of the Penninic nappes.
An erratum to this article can be found at 相似文献
926.
In this study, the relationship between fluorine in drinking water and that in urine of urban residents in China is assessed. Fluorine concentrations in tap water and those in urine show a good correlation with a linear regression coefficient of 0. 9798, indicating that the fluorine concentrations in big cities under investigation are extremely low, and the main source of fluorine is tap water. The weather effect on the intake amount of fluorine is also discussed. When air temperature is above 15℃, people would intake more fluorine through drinking water with the rise of air temperature. When temperature is below 15℃, no remarkable relationship is observed between air temperature and the intake amount of fluorine. This phenomenon indicates that the main source of fluorine in China is tap water instead of foodstuff. 相似文献
927.
Phosphorus Sorption Dynamics of Hawaii’s Coastal Wetlands 总被引:2,自引:0,他引:2
While phosphorus (P) sorption has been studied in Hawaii’s terrestrial soils, P sorption dynamics have yet to be investigated
in coastal wetlands. In other coastal zones, wetlands have been shown to sorb P and act as P sinks at the land–sea interface.
Thus, the objectives of this study were to examine variance in the P sorption index (PSI) within wetlands along hydrologic
gradients and among wetlands of different types and to identify soil properties that best explain variability in the PSI.
Forty wetlands on five islands were sampled and P sorption and related properties were measured. Phosphorus sorption index
values ranged from −16.4–1,732.5. Hydrologic zone (within sites) and surface water salinity (among sites) accounted for significant
proportions of the variance in the PSI. While texture, pH, and carbon content were found to be important predictors of PSI,
the highest correlations were found for oxalate-extractable iron. 相似文献
928.
929.
Pakama Queenscious Siyongwana 《GeoJournal》2009,74(4):293-310
The demise of South African Apartheid Planning in 1994 and subsequent lost of Umtata’s capital status when the Transkei was
subsumed into the new Eastern Cape Province resulted in the major political transformation of the Transkei state. Central
to the post-apartheid transformation was restructuring of Transkei bureaucracy which at the time of South Africa’s independence
in 1994 displayed abnormalities. This paper documents the restructuring of the Transkei bureaucracy focusing on Umtata since
1994. The study has brought to the forefront the following facts: Firstly, that at the time of the Transkei merger into South
Africa, employment in the government was ‘booming’ and to greater extent it was affected by Umtata’s role—being the capital
city of the pseudo-Transkei state. Secondly, the post 1994-political transformation of the Transkei Bantustan impacted negatively
on Umtata’s employment notably the civil service sector by ‘squeezing’ it during the early years of democracy (1994–2000).
Thirdly, since 2001, with Umtata serving as the major urban centre of both King Sabata Local Municipality and OR Tambo District
Municipality, employment in the civil service and municipality has been revitalized. 相似文献
930.
Transparent exopolymer particle (TEP) distributions were examined in North Carolina’s Neuse River Estuary (NRE) over a 1-year
period, and experiments were conducted to examine controls upon TEP formation. TEP-carbon averaged 16% of the total organic
carbon pool in the NRE. From May to early August 2007, TEP ranged from 805 to 1,801 μg xanthan gum (XG) L−1. A large phytoplankton bloom peaked in early August and then subsequently declined. Within 2 weeks of the bloom’s peak, TEP
concentrations increased to >3,500 μg XG L−1 and remained elevated through mid-December. Decreasing water temperatures and enhanced retention due to drought conditions
in Fall 2007 likely aided in the persistence of TEP concentrations during this timeframe. Thereafter, TEP decreased coincident
with increased river flow and flushing of the estuary that began in January 2008, and TEP remained low (ranging from 991 to
1,712 μg XG L−1) until the end of April 2008. TEP was positively correlated with salinity, suggesting that cation availability (which co-varies
with salinity and stabilizes the structural integrity of TEP) may play a role in estuarine TEP formation. In two cation addition
experiments using water from the mesohaline region, TEP concentrations tended to be higher in treatments with vs. without
cations added. Statistically significant relationships were also found between in situ TEP concentrations and pH, mixing,
and temperature, suggesting that a complex suite of environmental parameters affect TEP formation and its distribution in
estuaries. 相似文献