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1.
The temperature (T) evolution of the barium carbonate (BaCO3) structure was studied using Rietveld structure refinements based on synchrotron X-ray diffraction and a powdered synthetic
sample. BaCO3 transforms from an orthorhombic, Pmcn, α phase to a trigonal, R3m, β phase at 811°C. The orthorhombic BaCO3 structure is isotypic with aragonite, CaCO3. In trigonal R3m BaCO3, the CO3 group occupies one orientation and shows no rotational disorder. The average <Ba–O> distances increase while the <C–O> distances
decrease linearly with T in the orthorhombic phase. After the 811°C phase transition, the <Ba–O> distances increase while C–O distances decrease.
There is also a significant volume change of 2.8% at the phase transition. 相似文献
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3.
The seasonal variation of foliar δ13C values in Sabina przewalskii Kom. and Sabina chinensis (Lin.) Ant. was measured. The relationships between foliar δ13C values and branch δ13C values as well as environmental factors (monthly total precipitation, monthly average air temperature, monthly average soil
temperature, monthly total solar duration, relative humidity, atmospheric pressure, vapor pressure, wind speed and potential
evaporation) were investigated. The results showed that the foliar δ13C values were negatively correlated with air pressure, and positively correlated with air temperature, precipitation, vapor
pressure, potential evaporation, solar duration, wind speed and soil temperature. No significant relationship between δ13C values and relative humidity was detected. This demonstrates that the foliar δ13C of Sabina is a successful empirical indictor of these meteorological factors within the usual range of C3 whole-leaf δ13C values. Furthermore, the δ13C signature of leaf tissue is similar to that of wood tissue and the responses of δ13C values in S.
przewalskii Kom. to environmental factors are also relatively stronger than that of S. chinensis (Lin.) Ant. These results provided strong evidence that it is feasible to extract climatic information from tree-ring δ13C series and S.
przewalskii Kom. is a dendroclimatologically promising tree species. 相似文献
4.
Gerald R. North 《GeoJournal》2007,70(1):27-31
An Inconvenient Truth provides an opportunity to examine the differences between scientific statements and the mixed statements made by politicians.
The Gore movie is a powerful example of the latter. There are some inaccuracies and exaggerations in the film, but on the
whole it represents mainstream scientific views on global warming. This essay looks into the state of the art of climate change
research including its scientific underpinnings. Climate science is in a state of ‘normal science’ as discussed by Kuhn. There
is a large body of scientists who are adherents to the paradigm and there does not appear to be any serious alternative at
this time. 相似文献
5.
Durgesh C Rai 《Journal of Earth System Science》2003,112(3):421-429
The current designs of supporting structures of elevated water tanks are extremely vulnerable under lateral forces due to
an earthquake and the Bhuj earthquake provided another illustration when a great many water tank stagings suffered damage
and a few collapsed. The more popular shaft type stagings suffer from poor ductility of thin shell sections besides low redundancy
and toughness whereas framed stagings consist of weak members and poor brace-column joints. A strength analysis of a few damaged
shaft type stagings clearly shows that all of them either met or exceeded the strength requirements of IS:1893-1984, however,
they were all found deficient when compared with requirements of the International Building Code. IS:1893-1984 is unjustifiably
low for these systems which do not have the advantage of ductility and redundancy and are currently being underestimated at
least by a factor of 3 and need an upward revision of forces immediately. 相似文献
6.
Ali Bouafia 《Geotechnical and Geological Engineering》2007,25(3):283-301
Lateral load-deflection behaviour of single piles is often analysed in practice on the basis of methods of load-transfer P–Y curves. The paper is aimed at presenting the results of the interpretation of five full-scale horizontal loading tests of
single instrumented piles in two sandy soils, in order to define the parameters of P–Y curves, namely the initial lateral reaction modulus and the lateral soil resistance, in correlation with the pressuremeter
test parameters. P–Y curve parameters were found varying as a power of lateral pile/soil stiffness, on the basis of which hyperbolic P–Y curves in sand were proposed. The predictive capabilities of the proposed P–Y curves were assessed by predicting the soil/pile response in full-scale tests as well as in centrifuge tests and a very good
agreement was found between the computed deflections and bending moments, and the measured ones. Small-sized database of full-scale
pile loading tests in sand was built and a comparative study of some commonly used P–Y curve methods was undertaken. Moreover, it was shown that the load-deflection curves of these test piles may be normalised
in a practical form for an approximate evaluation of pile deflection in a preliminary stage of pile design. At last, a parametric
study undertaken on the basis of the proposed P–Y curves showed the significant influence of the lateral pile/soil stiffness on the non-linear load-deflection response. 相似文献
7.
John W. Nielsen-Gammon 《GeoJournal》2007,70(1):21-26
The movie An Inconvenient Truth is a powerful portrayal of global warming and its impacts. The main scientific argument presented in the movie is for the
most part consistent with the weight of scientific evidence, but with some of the main points needing updating, correction,
or qualification. The detailed argument relies almost entirely on past and current evidence and neglects almost all information
that can be gained from computer models, perhaps because such information would be difficult for a lay audience to grasp,
believe, or connect with emotionally. This places an undue weight on current events as signs of ongoing climate change: some
such events are apparently not related at all to climate change, while for other specific events the role of global warming
is difficult or impossible to establish. 相似文献
8.
The propagation of plane waves in an anisotropic elastic medium possessing monoclinic symmetry is discussed. The expressions
for the phase velocity ofqP andqSV waves propagating in the plane of elastic symmetry are obtained in terms of the direction cosines of the propagation vector.
It is shown that, in general,qP waves are not longitudinal andqSV waves are not transverse. Pure longitudinal and pure transverse waves can propagate only in certain specific directions.
Closed-form expressions for the reflection coefficients ofqP andqSV waves incident at the free surface of a homogeneous monoclinic elastic half-space are obtained. These expressions are used
for studying numerically the variation of the reflection coefficients with the angle of incidence. The present analysis corrects
some fundamental errors appearing in recent papers on the subject. 相似文献
9.
Lukáš Ackerman Jiří Zachariáš Marta Pudilová 《International Journal of Earth Sciences》2007,96(4):623-638
Fluid inclusions, mineral thermometry and stable isotope data from two types of mineralogically and texturally contrasting
pegmatites, barren ones and lithium ones, from the Moldanubian Zone of the Bohemian Massif were studied in order to constrain
P–T conditions of their emplacement, subsolidus hydrothermal evolution and to estimate composition of the early exsolved fluid
and that of the parental melt. Despite the fact that the lithium pegmatites are abundant throughout the crystalline units
of the Bohemian Massif, data similar to this paper have not been published yet. The studied pegmatites are hosted by iron-rich
calcic skarn bodies. This specific setting allowed scavenging of calcium, fluorine and some other elements from the host rocks
into the pegmatitic melts and post-magmatic fluids. Such contamination process was important namely in the case of barren
pegmatites, as can be deduced from the variation in anorthite contents in plagioclase and from the presence of fluorite, hornblende
(with F content) or garnet in the contact zones of pegmatite dykes. Fluid inclusions were studied mostly in quartz, but also
in fluorite, titanite and apatite. Early aqueous–carbonic and late aqueous fluids were identified in both pegmatite types.
The P–T conditions of crystallization as well as the detailed composition of exsolved magmatic fluid, however, particularly differ.
The magmatic fluids associated with barren pegmatites correspond to H2O–CO2 low salinity fluids, composition of which evolved from 20 to 23 to <5 mol% CO2, and from 2 to 4–6 mol% NaCl eq. Sudden decrease in the CO2 content of the post-magmatic fluids (<5 mol% CO2) seems to coincide with the enrichment of the fluid in calcium (from the contamination process) and resulted in precipitation
of calcites (frequently found as trapped solid phases in fluid inclusions). The fluids associated with lithium pegmatites
are more complex (H2O–CO2/N2–H3BO3–NaCl). The CO2 content of early exsolved fluid is 26–20 mol% CO2 and remains the same in the next fluid generation. The main difference between the magmatic and the first post-magmatic fluids
is the presence of 7–9 wt% of H3BO3 (identified as daughter mineral sassolite) in the former. The second post-magmatic fluids are again CO2-poor (∼4 mol%) and more saline (∼4 mol% NaCl eq.). The composition of exsolved fluid was further used to constrain volatile
composition and content of the parental melts. Finally, P–T conditions of pegmatite crystallization are constrained: 600–640°C and 420–580 MPa for the barren pegmatites and 500–570°C
and 310–430 MPa for the lithium pegmatite. While the emplacement of the former occurred in thermal equilibrium with the Moldanubian
host rock environment, the emplacement of the later suggests substantial thermal disequilibrium. 相似文献
10.
For a common, widespread, and familiar plant,Phragmites australis engenders an enormous level of scientific controversy and emotional conflict. In parts of the world,Phragmites is an important component of healthy ecosystems and an integral (if now minor) contributor to human economies. In other places
it is an invading, unfriendly, and ugly weed. To some scientists and environmentalists,Phragmites is an indicator of and key factor in landscape degradation and habitat deterioration. To others, it is a valiant remnant
of nature, providing a relatively rich ecology where there might otherwise be only barren and eroding ground. Our review of
the literature leads us to conclude thatPhragmites is simply a biological entity. It is not inherently good or bad, since its evolution, biology, and ecology do not give it
a value. The controversy overPhragmites, its role in the ecosystem, and the need for and intensity of management efforts are all artifacts of human perspectives.
Effective, consistent management decisions (for either control or enhancement ofPhragmites) can only be made on the basis of site-specific scientific findings, a consideration of technologies with their needed level-of-effort,
and explicit exposition of the human values driving the management options. We present a simple decision model to illustrate
the interaction of these management components forPhragmites in the environment. 相似文献
11.
Jason E. Tanner 《Estuaries and Coasts》2007,30(4):601-606
The European green crab (Carcinus maenas) is a highly successful marine invader, having established populations in a number of areas outside its natural range in
the last 100 years. In South Australia,C. maenas can be abundant on intertidal mud flats, which are used by juveniles of the native blue swimmer crab (Portunus pelagicus) and could have the potential to cause substantial negative effects on this species. The influence of adult blue and green
crabs on habitat selection by juvenile blue crabs was tested to determine if they responded to both predators in a similar
fashion. The presence of predators did not influence habitat selection by juvenile blue crabs in either laboratory or field
experiments, but juvenile behavior in the selected habitat did differ between the two adult species. Many more crabs buried
themselves beneath the substrate when adult conspecifics were present than when adult green crabs were present. Burying in
the presence of adult green crabs was no more frequent than when predators were absent. It remains to be determined if this
makes juvenile blue crabs more vulnerable to predation by green crabs than by adults of their own species, or if the difference
in response is because green crabs pose a different or lesser threat. 相似文献
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13.
The objective of this study is to demonstrate the basic characteristics of Bacillus SP3 and evaluate its effect on different crude oils. Strain SP3 is a motile, gram-positive, spore-producing rod that was isolated from a reservoir of the Shengli oil field in East China. The cells of strain SP3 grew at high temperatures up to 58℃ at the pH range of 5.5–8.5. Strain SP3 grew facultatively and could use different organic substrates, and produce some metabolites such as 4-hydroxy-4-methyl-2-pentanone, methyl-2-nitrogen benzene and 1, 2-benzenedicarboxylic acid bis ester. Laboratory studies have demonstrated that the strain converted and degraded different components and changed the physical and chemical properties of crude oils. Strain SP3 degraded crude oil and the growth of bacteria on crude oil resulted in loss of aromatic hydrocarbons, resins and asphaltenes. The bioconversion of crude oils would lead to an enrichment in lighter hydrocarbons and an overall redistribution of saturate hydrocarbons. The interactions of microorganisms with crude oils are variable, depending on the microbial species and the chemical compositions of crude oils. 相似文献
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15.
N. A. Gashkina 《Geochemistry International》2018,56(10):1016-1027
16.
Seasonal variation patterns of aboveground and belowground biomass, net primary production, and nutrient accumulation were
assessed inAtriplex portulacoides L. andLimoniastrum monopetalum (L.) Boiss. in Castro Marim salt marsh, Portugal. Sampling was conducted for five periods during 2001–2002 (autumn, winter,
spring, summer, and autumn). This study indicates that both species have a clear seasonal variation pattern for both aboveground
and belowground biomass. Mean live biomass was 2516 g m−2 yr−1 forL. monopetalum and 598 g m−2 yr−1 forA. portulacoides. Peak living biomass, in spring for both species, was three times greater in the former, 3502 g m−2 yr−1, than in the latter, 1077 g m−2 yr−1. For both the Smalley (Groenendijk 1984) and Weigert and Evans (1964) methods, productivity ofL. monopetalum (2917 and 3635 g m−2 yr−1, respectively) was greater than that ofA. portulacoides (1002 and 1615 g m−2 yr−1, respectively). Belowground biomass ofL. monopetalum was 1.7 times greater than that ofA. portulacoides. In spite of this, the root:shoot ratio forA. monopetalum to aerial components. Leaf area index was similar for both species, but specific leaf area ofA. portulacoides was twice that ofL. monopetalum. The greatest nutrient contents were found in leaves. Leaf nitrogen content was maximum in summer for both species (14.6
mg g−1 forA. portulacoides and 15.5 mg g−1 forL. monopetalum). Leaf phosphorus concentration was minimum in summer (1.1 mg g−1 inA. portulacoides and 1.2 mg g−1 inL. monopetalum). Leaf potassium contents inA. portulacoides were around three times greater than inL. monopetalum. Leaf calcium contents inL. monopetalum were three times greater than inA. portulacoides. There was a pronounced seasonal variation of calcium content in the former, while in the latter no clear variation was registered.
Both species exhibited a decrease in magnesium leaf contents in the summer period. Mangamese content inL. monopetalum leaves was tenfold that inA. portulacoides. Seasonal patterns of nutrient contents inA. portulacoides andL. monopetalum suggest that availability of these elements was not a limiting factor to biomass production. 相似文献
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18.
Martin T. O’Connell Travis D. Shepherd Ann M. U. O’Connell Ransom A. Myers 《Estuaries and Coasts》2007,30(4):567-574
We analyzed historic and current fishery independent data to determine if the abundance of two apex predators, bull sharks
(Carcharhinus leucas) and alligator gar (Atractosteus spatula), in Lake Pontchartrain had changed significantly over the last half century. Lake Pontchartrain is an environmentally degraded
oligohaline estuary in southeastern Louisiana that has experienced considerable changes in fish assemblage composition over
this interval. Using gillnet, beach seine, and trawl data collected during three time periods (1953–1955, 1977–1978, and 1996–2005),
we analyzed trends in abundance forC. leucas andA. spatula using generalized linear models with a negative binomial error structure and a log link. Lake Pontchartrain data were divided
into four spatial locations (northwest, northeast, southwest, southeast) since each region represents a unique combination
of anthropogenic and natural influences that could affect catches. For each species and gear type, we produced log-likelihood
profiles for the instantaneous rate of change in relative abundance through time. Raw catches were generally lower for both
species in the later surveys.C. leucas were not captured in beach seines since the 1950s andA. spatula were rarely captured in trawls or seines since the 1970s. Likelihood profiles of changes in abundance forC. leucas andA. spatula showed very large declines in both species since 1953.C. leucas declined by 98.6% (95% CI: 73.4–99.9%) in gillnets and became functionally extirpated in beach seines with a decline of 99.9%
(95% CI: 23–99.9%). Among all gears,C. leucas declined by the same rate as in gillnets. The decline inA. spatula was also large with a decrease of 98.6% (95% CI: 73.4–99.9%) in beach seines and a decline of 99.2% (95% CI: 54.8–99.9%)
in trawls since 1953. Catches ofA. spatula in gillnets did not show a significant change over the study period. The continued decline of these two apex predators could
seriously affect efforts to restore this degraded estuarine ecosystem. 相似文献
19.