Assessment of rigid overlying strata failure in face mining   总被引：2，自引：0，他引：2  

Eva Jiránková 《Central European Journal of Geosciences》2010,2(4):524-530

The method of overlying strata failure assessment of extracted seams is based upon the simultaneous assessment of surface subsidence and seismic activity, considering the spatiatemporal progress of mining, depending on the character of the rock mass. The rigid overlying strata failure assessment results in finding whether a failure of the firm overlying rocks occurred or whether a strutting arch was formed over the mined-out area. The practical importance of the overlying strata failure assessment consists in determining the size of the mined-out area at which the com-plete failure of the rigid overlying strata occurred and in the assessment of the current stress condition of the overlying strata failure. The assessment method is applicable in deep mine workings where thick coal seams are being mined by means of the method of longwall mining with controlled caving. The results of this method are used to amend contemporary known methods of rock-burst protection, namely (regarding the use of surface measurements for the evaluation) in overlying strata areas.  相似文献   

Late Quaternary glacial and deglacial history of eastern Vestfirdir,Iceland using cosmogenic isotope (36Cl) exposure ages and marine cores     

Sarah M. Principato  slaug Geirsdttir  Gudrún Eva Jhannsdttir  John T. Andrews 《第四纪科学杂志》2006,21(3):271-285

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On the Interpretation of Orthonormal Coordinates for Compositional Data   总被引：1，自引：0，他引：1  

Eva Fišerová  Karel Hron 《Mathematical Geosciences》2011,43(4):455-468

The simplex with the Aitchison geometry is a natural sample space for compositional data, that is, observations carrying only relative information (especially proportions, percentages, etc., often occurring in the geosciences). For this reason, standard statistical methods that rely on Euclidean structure of the real space cannot be used directly for statistical analysis. At first, compositional data need to be expressed in coordinates of an orthonormal basis on the simplex (with respect to the Aitchison geometry). The mathematical interpretation of the orthonormal coordinates is derived from the procedure by which they are constructed (called sequential binary partition), and they act as balances between groups of compositional parts. The goal of this paper is to describe the covariance structure of coordinates and, consequently, to provide a complementary interpretation based on log-ratios of parts of the original composition. It must be noted that, in a composition, the ratios themselves contain all the relevant information. The possibilities as well as the limitations of this approach are demonstrated through illustrative examples.  相似文献   

Coastal inshore waters in the NW Mediterranean: Physicochemical and biological characterization and management implications     

Eva Flo  Esther Garcés  Marta Manzanera  Jordi Camp 《Estuarine, Coastal and Shelf Science》2011

The physicochemical and biological characteristics of coastal waters form a gradient extending from land to ocean. In the Mediterranean this gradient is particularly large, due to the sea’s weak tides. Within coastal waters, those waters in contact with land are called coastal inshore waters (CIW), defined herein as between 0 and 200 m from the shoreline. Here we present the first physicochemical and biological characterization of CIW of the NW Mediterranean Sea. This case study is based on 19 years of data collected from coastal inshore (CIW; 0–200 m), nearshore (CNW; 200–1500 m), and offshore (COW; >1500 m) waters of the Catalan coast. Analyses of these data showed that the physicochemical and biological characteristics of CIW differ significantly from those of CNW and COW due to: (1) significantly higher concentrations of dissolved inorganic nutrients (nitrate = 11.07 μM, nitrite = 0.52 μM, ammonium = 6.43 μM, phosphate = 0.92 μM, silicates = 5.99 μM) and chlorophyll-a (=2.42 μg/L) in CIW than in either CNW or COW (in some cases up to one order of magnitude); (2) a greater variability of dissolved inorganic nutrients and chlorophyll-a in CIW than in CNW and COW, and (3) the presence of a mostly urban population and the effects of river inflows as a primary source of CIW variability but with minimal impact on CNW or COW. In addition, the risk of eutrophication was found to be highest in CIW, placing human and environmental interests at greater risk than in the outermost coastal waters. The results highlight the importance of considering the distinctive physicochemical and biological properties of CIW in future coastal waters studies. This is of major importance in assessments of eutrophication and coastal water quality, not only to identify the pressure–impact relationships but also to allow the timely detection of local environmental problems and thus avoid endangering the unique communities of CIW and ensuring the sustainability of human activities. In conclusion, CIW characterization is essential to integrate coastal zone management.  相似文献   

The effects of brine disposal on a subtidal meiofauna community     

Rodrigo Riera  Fernando Tuya  Alicia Sacramento  Eva Ramos  Myriam Rodríguez  Óscar Monterroso 《Estuarine, Coastal and Shelf Science》2011

Desalination plants generate notable (>1,000 s m³) quantities of hypersaline brine which potentially affect the biological communities in the receiving area. We assessed whether proximity to a brine discharge point located off Gran Canaria (Canary Islands, eastern Atlantic) altered patterns in the abundance and assemblage structure of subtidal, soft-bottom, meiofauna. Samples were collected twice (May 2008 and January 2009) at 0, 15 and 30 m away from the brine discharge point, corresponding to a change in salinity from 45 to 36. Proximity to the brine discharge point affected overall meiofaunal abundances: lowest abundances were observed at 0 m (64.55 ± 39.86 ind 10 cm⁻², mean ± SD) than at 15 (210.49 ± 121.01 ind 10 cm⁻²) and 30 m (361.88 ± 102.64 ind 10 cm⁻²) away from the brine discharge point. This pattern was particularly notable for the most conspicuous meiofaunal groups: nematodes and copepods, and meiofaunal assemblage structure also differed with varying proximity to the brine discharge point. Although multivariate techniques identified changes in salinity as a relevant driver of patterns in meiofaunal assemblage structure with varying proximity to the brine outfall, a shift in particle size composition between May 2008 and January 2009 also contributed to explain differences in meiofaunal abundances and assemblage structure with varying proximity to the brine discharge point. Hence, meiofauna can be considered a suitable tool to monitor environmental impacts derived from the discharge of hypersaline effluents on subtidal, soft-bottom, assemblages if potential confounding drivers, i.e. here temporal changes in particle size composition, are accounted for to avoid possible confusing interpretations.  相似文献   

On the origin of the radial mass density profile of the Galactic halo globular cluster system     

Geneviève Parmentier †  Eva K. Grebel 《Monthly notices of the Royal Astronomical Society》2005,359(2):615-623

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Cosmological constant and the flat rotation curves of galaxies     

Eva Gessner 《Astrophysics and Space Science》1992,194(2):197-205

It is shown that Einstein's cosmological constant can explain of the flat rotation curves of spiral galaxies.  相似文献   

Trace metals in sediment cores from Deception and Penguin Islands (South Shetland Islands, Antarctica)     

Guerra R  Fetter E  Ceschim LM  Martins CC 《Marine pollution bulletin》2011,62(11):2571-2575

This paper presents information on the levels of trace elements in sediments collected at Deception and Penguin Islands and tracks the sources of natural and anthropogenic inputs of metals into this sub-Antarctic region. The results suggest that natural processes, such as volcanic activity, hydrothermal processes and sediment transport, are more important than anthropogenic inputs in accounting for the metal concentrations measured in sediments at Deception Island. The higher levels of trace metals recorded in sediments at Penguin Island seem to reflect the composition of the source rocks of the island, which are dominated by the olivine-basalt group. Our findings show that human activities in the study areas may contribute to negligible levels of trace metals associated with anthropogenic inputs (e.g., Cr and Zn) in sediments, and these results can be used in the future as background levels related to low anthropogenic impacts.  相似文献   

Tree-ring dates on two pre-Little Ice Age advances in Glacier Bay National Park and Preserve, Alaska, USA     

Gregory C. Wiles  Daniel E. Lawson  Eva Lyon  Nicholas Wiesenberg  R.D. D'Arrigo 《Quaternary Research》2011,76(2):190-195

Two interstadial tree ring-width chronologies from Geikie Inlet, Glacier Bay Southeast, Alaska were built from 40 logs. One of these chronologies has been calendar dated to AD 224–999 (775 yr) crossdating with a living ring-width chronology from Prince William Sound, Alaska. Trees in this chronology were likely killed through inundation by sediments and meltwater from the advancing Geikie Glacier and its tributaries ca. AD 850. The earlier tree-ring chronology spans 545 yr and is a floating ring-width series tied to radiocarbon ages of about 3000 cal yr BP. This tree-ring work indicates two intervals of glacial expansion by the Geikie Glacier system toward the main trunk glacier in Glacier Bay between 3400 and 3000 cal yr BP and again about AD 850. The timing of both expansions is consistent with patterns of ice advance at tidewater glaciers in other parts of Alaska and British Columbia about the same time, and with a relative sea-level history from just outside Glacier Bay in Icy Strait. This emerging tree-ring dated history builds on previous radiocarbon-based glacial histories and is the first study to use tree-ring dating to assign calendar dates to glacial activity for Glacier Bay.  相似文献   

DFT study of Rb-TFA structure after high-pressure action     

Eva Scholtzová 《Physics and Chemistry of Minerals》2011,38(10):819-824

The pressure-induced A-B phase transition of synthetic Rb-tetra-ferri-annite (Rb-TFA) mica was studied theoretically by means of Density Functional Theory (DFT) method. The calculations show that Rb-TFA keeps a Franzini A-type structure up to at least 5.39 GPa of pressure, whereas at higher pressure, it transforms to a Franzini B-type structure. The negative value of the tetrahedral rotation angle α = −4.68° has appeared at 5.56 GPa of calculated pressure. This result is in a relatively good agreement with experimentally estimated phase transition area in the range of 3.36−3.84 GPa. The energy difference between the A and B structures is very small (ΔE = 8 kJ/mol). The detailed analysis of the optimized structural data shows minimal changes in the structure of Rb-TFA after the pressure-induced phase transition.  相似文献