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1.
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   

2.
The reflection and transmission phenomena of elastic waves incident at a corrugated interface between two dissimilar fibre‐reinforced elastic half‐spaces have been analysed. Using Rayleigh method of approximation, the expressions of the reflection and transmission coefficients are obtained in closed form for the plane interface as well as for the first order approximation of the periodic interface ζ = d cos px. All these reflection and transmission coefficients of regular and irregular waves are found to be the functions of angle of incidence and elastic parameters of the media. Moreover, the coefficients of irregularly reflected and transmitted waves are found to be proportional to the amplitude of the corrugated interface and are functions of the frequency of the incident wave. Numerical computations have been performed for a specific model to compute these coefficients and results obtained are shown graphically. The results of Singh and Singh (Sadhana 2004; 29 :249–257) and Ben‐Menahem and Singh (Seismic Waves and Sources. Springer: New York) have been derived from our analysis as particular cases. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

3.
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   

4.
Lucinid bivalves dominate the infauna of tropical seagrass sediments. While the effect of seagrass on lucinids has been studied, the reverse effect has largely been ignored. Lucinids can alter porewater chemistry (i.e., increase porewater nutrients by suspension feeding and decrease porewater sulfides by oxygen introduction and bacterial oxidation), which can potentially change seagrass productivity and growth morphology. To observe correlations between porewater chemistry and lucinid presence, a field survey and laboratory microcosm experiment were conducted. Survey sampling sites with lucinids had significantly lower sulfide and higher ammonium concentrations than sampling sites without lucinids. There was no difference in phosphate concentration among sampling sites. Both lucinid species used in the microcosm experiment (Ctena orbiculata andLucinesca nassula) significantly lowered sulfide concentrations in the sediment porewater. Microcosm and field survey results were incorporated into a sulfide budget. In seagrass sediments, lucinids remove 2–16% of the total sulfide produced. Sulfide is a major stressor to both plants and animals in Florida Bay sediments; this removal may be important to maintaining seagrass productivity and health. Oxygen introduction into sediments byC. orbiculata was estimated in a dye experiment.C. orbiculata were added to small tubes containing sieved mud and incubated in a bath of seawater with a Rhodamine WT. Rhodamine WT accumulation in the sediment was measured. A first order estimate showed that oxygen introduction can account for less than 5% ofC. orbiculata sulfide removal.  相似文献   

5.
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   

6.
Rhizedra lutosa (Hübner) (Lepidoptera: Noctuidae), native to Europe, was first found in North America in 1988 in southern New Jersey. The insect is reported to cause serious damage toPhragmites australis in the Netherlands, but it now appears to be relatively unimportant throughout central Europe. We are investigating this insect as part of an effort to characterize existing natural enemies ofP. australis in North America toward a goal of biological control of this invasive plant. We trapped adults ofR. lutosa with blacklights in Rhode Island, Massachusetts, Connecticut, New York, Delaware, and Maryland; we also found it in Ohio and Pennsylvania.R. lutosa larvae feed in stems and rhizomes ofP. australis growing in dry sites. Based uponR. lutosa damage surveys andP. australis biomass measurements, we have determined that this insect does cause a reduction of plant growth in some sites, however, because of low moth densities, this effect is small. Despite spreading rapidly,R. lutosa densities do not appear to be increasing at sites we have investigated, and this insect does not currently appear to have much of an impact uponP. australis in North America.  相似文献   

7.
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   

8.
Quantifying the relative value ofPhragmites australis andSpartina alterniflora habitat is important to evaluate the benefits and risks of different attempts to addressPhragmites expansion on the U.S. eastern seaboard. Two contrasting approaches commonly used to restore tidal marsh habitats invaded byPhragmites communities involve sprayingPhragmites with herbicide only when its coverage of a particular marsh area is near or close to 100%. Alternatively, after the first application, herbicide is annually applied on any surviving patches ofPhragmites present in a mosaic of other marsh vegetation. A model is introduced to evaluate the relative habitat value of these control regimes, here termed the Intermittent and Continuous. Compared to the Intermittent approach, the area of herbicide application in the Continuous approach is higher in the first 6 yr, but lower the reafter. The cumulative gain in habitat quality after 20 yr in either approach is sensitive to the presumed relative values ofPhragmites versusSpartina habitat, and may even be negative if they are nearly equal. Annual applications of herbicide to patches ofPhragmites appears to generate more habitat value and with less herbicide than occasional applications whenPhragmites cover is at is maximum.  相似文献   

9.
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   

10.
The invasion of North American tidal marshes byPhragmites australis, or common reed, is a large-scale ecological problem that has been primarily studied at small spatial scales. Previous local-scale studies have provided evidence that the expansion ofPhragmites is facilitated by disturbance and increased nitrogen (N) associated with agricultural and urban-suburban (developed) land uses along wetland-upland borders. We tested the generality of previous findings across a larger spatial scale and wider range of environmental conditions in Chesapeake Bay, the largest estuarine ecosystem in the USA. We sampled 90 tidal wetlands nested within 30 distinct subestuarine watersheds and examined the relationship between land use andPhragmites abundance and foliar N, an indicator of nitrogen availability. We estimated land use adjacent to wetland borders and within subestuary watersheds and explored the importance of spatial proximity by weighting land use by its distance from the wetland border or subestuary shoreline, respectively. Regression tree and changepoint analyses revealed thatPhragmites abundance sharply increased in almost every wetland where development adjacent to borders exceeded 15%. Where development was <15% but natural land cover at the near the subestuary shoreline was low (<∼35%),Phragmites was abundant, suggesting that wetlands in highly modified watersheds also were susceptible to invasion, regardless of land use adjacent to wetlands.Phragmites foliar N was markedly elevated in watersheds with >14–22% shoreline development, the same level of development that corresponded to high levels of invasion. Our results suggest that development near wetlands is at least partially responsible for patterns of invasion across Chesapeake Bay. Larger-scale phenomena, such as nitrogen pollution at the watershed-subestuary scale, also may be facilitating invasion. Urbanization near coastlines appears to play an important role in the invasion success ofPhragmites in coastal wetlands of Chesapeake Bay and probably much of eastern North America.  相似文献   

11.
The seismic anisotropy of the mantle is studied based on the data of S and ScS waves from earthquakes occurred in the mantle transition zone over the period of 2007–2013 and recorded by seismic stations in the continental margin of Asia, on Sakhalin Island, and in the southern part of the Kamchatka Peninsula. The measurements of the azimuths of polarization of the fast S and ScS waves in the continental margin of Asia show that they are predominantly oriented in the E–SE directions. Based on the distribution of the shear wave splitting parameters, the symmetry of the medium can be described in terms of a transversely isotropic model with a horizontal symmetry axis and may correspond to horizontal flow in the upper mantle beneath the Amur Plate. The fast azimuths of polarization of ScS wave, which were determined to be of N–NE directions in the northern area of Sakhalin Island and in the continental part of Asia, may correspond to an inclined flow under the conditions of oblique subduction and complex geometry of the downgoing Pacific Plate. In the south of the Kamchatka Peninsula, the S- and ScS-wave azimuths of polarization from the M 8.4 Sea of Okhotsk earthquake are determined to be oriented along the direction of the Pacific Plate motion. The fast-S-wave azimuths of polarization from the aftershocks of the Sea of Okhotsk earthquake and from other large events of 2008–2009 are determined to be nearly parallel to the motion trend of the Pacific Plate, but orthogonal to it for the events of 2008–2009. On the basis of the distribution of azimuths of polarization of the fast S waves, the symmetry of the medium can be described in terms of a transversely isotropic model with the symmetry axis inclined orthogonally to the plane of downgoing plate and oriented westward orthogonally to the trench strike.  相似文献   

12.
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   

13.
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   

14.
In a pre-stressed anisotropic elastic medium, three types of quasi-waves propagate along an arbitrary direction. In general, none of the waves is truly longitudinal. The present study finds the specific directions in a pre-stressed anisotropic elastic medium along which longitudinal waves may propagate. This paper demonstrates how the propagation of longitudinal waves is affected by various pre-stresses present in the medium. The study establishes the explicit expressions defining the existence and propagation of longitudinal waves in pre-stressed anisotropic elastic medium. These expressions involve not only the direction and elastic stiffness of the medium, but also the pre-stresses present in the medium. Changes in conditions for the existence of longitudinal waves in orthotropic, monoclinic and triclinic anisotropies are discussed in detail. The most important part of the paper is a practical aspect suggested to calculate the specific directions for the existence of longitudinal waves in pre-stressed anisotropic elastic medium. In this approach, only those parameters are used that can be observed by the receiver in a geophysical experiment of wave propagation. The existence of longitudinal waves has been shown graphically using a numerical example for three types of anisotropic symmetries in elastic medium.  相似文献   

15.
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   

16.
This note reports an unknown trophic interaction between a mammalian herbivore, the capybara (Hydrochaeris hydrochaeris), and the seagrassRuppia maritima (wigeongrass) and compares the feeding behavior of capybaras to other seagrass grazers. Observations were made in Spring 2002 in the Barra Grande, a small, shallow, moderately stratified, bar-built estuary at Ilha Grande, Rio de Janeiro State, southeast Brazil. The activities of the capybaras were investigated and grazing impacts were quantified in situ. The capybaras were observed feeding onR. maritima during the day and aquatic feeding alternated with periods of feeding on land.R. maritima was the only submerged aquatic vegetation to be consumed by the capybaras. The feeding activity of the capybaras on wige ongrass consisted of alternately diving down to theR. maritima then surfacing; the capybaras spent a significantly greater amount of time under water. In the area where the capybaras foraged 18.1% of the seagrass meadow showed recent grazing scars. Vegetation of recently and not recently grazed areas were compared. Grazing scars, which were slightly elongated, were not completely devoid ofR. maritima but presented reduced standing crop: canopy height, shoot density, and shoot, rhizome, and root biomass were reduced in grazed areas. The grazing patterns observed in capybaras resembled those previously reported in the sirenia, mammals that include two seagrass-eating species.  相似文献   

17.
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   

18.
 Cation tracer diffusion coefficients, DMe *, for Me=Fe, Mn, Co and Ti, were measured using radioactive isotopes in the spinel solid solution (Ti x Fe 1−x )3−δO4 as a function of the oxygen activity. Experiments were performed at different cationic compositions (x=0, 0.1, 0.2 and 0.3) at 1100, 1200, 1300 and 1400 °C. The oxygen activity dependence of all data for DMe * at constant temperature and cationic composition can be described by equations of the type DMe *=D∘ Me[V]. CV·a O2 2/3+DMe[I] ∘·a O2 −2/3·DMe[V] ∘ and DMe[I] ∘ are constants and CV is a factor of the order of unity which decreases with increasing δ. All log DMe * vs. loga O2 curves obtained for different values of x and for different temperatures go through a minimum due to a change in the type of point defects dominating the cation diffusion with oxygen activity. Cation vacancies prevail for the cation diffusion at high oxygen activities while cation interstitials become dominant at low oxygen activities. At constant values of x, DMe[V] ∘ decreases with increasing temperature while DMe[I] ∘ increases.  相似文献   

19.
The burrowing crab,Chasmagnathus granulatus, is the dominant benthic macroinvertebrate of southwest Atlantic salt marshes and tidal flats, having strong ecosystem engineering effects by direct and indirect effects on soil, vegetation, invertebrates, fishes, and birds. Vegetation structure is a main component for bird habitat selection, since greater habitat complexity generates higher niche diversity. This environmental complexity can be modified by species interactions or disturbance events (i.e., by crabs), in turn modifying the associated community. The bird species of salt marshes of the southwest Atlantic are highly dependent on these ecosystems. We assessed the effects of the burrowing crab on the structure of the cordgrass,Spartina densiflora, marshes, and how these changes affected the composition and diversity of birds. This study was conducted at the Mar Chiquita Coastal Lagoon, Argentina (37°40′S, 57°23′W).S. densiflora marshes were classified within three categories: marshes without burrowing crabs, marshes with low burrow densities, and marshes with high burrow densities. We made vegetation and bird surveys during spring beforeS. densiflora produce seeds and in summer when seeds are abundant. We also manipulated inflorescence (i.e., spike) density (a variable affected by crabs) to assess the effect on bird habitat use. The highest inflorescence density ofS. densiflora and highest bird diversity were recorded at low burrow densities. Cover and height ofS. densiflora were negatively correlated with burrow density. The number of bird species and the number of red-capped wren-spinetail,Spartonoica maluroides, were negatively related with cover and height ofS. densiflora. Experiments confirmed that granivorous species used areas with higher spike densities, a variable related to crab burrow density. Burrowing crabs directly and indirectly affect the cover, height, spike density, and morphologic characteristic of seeds ofS. densiflora marshes. These effects indirectly affect the bird community that uses these marshes, being negatively related toS. maluroides and total bird abundance, and positively related to bird diversity.  相似文献   

20.
This paper presents evaluation of cation distributions from diffraction data collected at high T, P, and is an extension of the spinel structure modelling procedure by Lavina et al. (2002). Optimised cation-to-oxygen distances are modified for thermal expansion and compressibility at T and P of interest following Hazen and Prewitt (1977) and Hazen and Yang (1999). The procedure is applied to literature data concerning hercynite, spinel s.s., Zn aluminate, Zn ferrite, magnetite and the (Fe3O4)1– x (MgAl2O4) x join. Calculated cation distribution is strongly affected by standard deviations in cell parameters and oxygen coordinates. The underestimated values often reported in the literature for powder profile refinements may strongly affect the cation distribution; however, if standard deviations are increased to physically realistic values, consistent results are obtained. For P up to 10 GPa, reasonable evaluations of cation distribution are obtained for spinel s.s., Zn aluminate and magnetite, whereas for Zn ferrite they are limited to 1.8 GPa. For P beyond 10 GPa, compressibility cannot be assumed to be linear; the relationship between cell parameter and pressure is well-defined, but the inaccuracy of oxygen coordinate prevents simple modelling of bond distances with pressure.  相似文献   

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