A note on formulas for localized failure of frictional materials in compression and biaxial loading modes     

Matthias Lambrecht  Christian Miehe 《国际地质力学数值与分析法杂志》2001,25(10):955-971

The paper investigates aspects of the localization analysis of frictional materials. We derive closed formulas and diagrams for the inclination angle of critical discontinuity surfaces which develop in homogeneous compression and biaxial loading tests. The localization analysis is based on a Drucker–Prager‐type elastoplastic hardening model for non‐associated plastic flow at small strains, which we represent in spectral form. For this type of constitutive model, general analytical formulas for the so‐called critical hardening modulus and the inclination angle of critical discontinuity surfaces are derived for the plane strain case. The subsequent treatment then specializes these formulas for the analysis of compression and biaxial loading modes. The key contribution here is a detailed analysis of plane strain deformation modes where the localized failure occurs after subsequent plastic flow. The derived formulas and diagrams can be applied to the checking of an accompanying localization analysis of frictional materials in finite‐element computations. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Dissolved noble gases in the porewater of lacustrine sediments as palaeolimnological proxies     

Kuno M. Strassmann  Matthias S. Brennwald  Frank Peeters 《Geochimica et cosmochimica acta》2005,69(7):1665-1674

This paper presents results from the numerical modelling of the transport of atmospheric noble gases (He, Ne, Ar, Kr, Xe), tritiated water and ³He produced by radioactive decay of ³H, in unconsolidated lacustrine sediment. Two case studies are discussed: (1) the evolution of ³H and ³He concentrations in the sediment porewater of Lake Zug (Switzerland) from 1953 up to the present; and (2) the response of dissolved atmospheric noble gas concentrations in the sediment porewater of a subtropical lake to an abrupt climatic change that occurred some 10 kyr before the present. (1) Modelled ³H and ³He porewater concentrations are compared with recent data from Lake Zug. An estimate of the effective diffusion coefficients in the sediment porewater is derived using an original approach which is also applicable also to lakes for which the historical ³H and ³He concentrations in the water column are unknown. (2) The air/water partitioning of atmospheric noble gases is sensitive to water temperature and salinity, and thus provides a mechanism by which these environmental variables are recorded in the concentrations of atmospheric noble gases in lakes. We investigate the feasibility of using noble gas concentrations in the porewater of lacustrine sediments as a proxy for palaeoenvironmental conditions in lakes. Numerical modelling shows that heavy noble gases in sediment porewater, because of their comparatively small diffusion coefficients and the strong temperature sensitivity of their equilibrium concentrations, can preserve concentrations corresponding to past lake temperatures over times on the order of 10 kyr. Noble gas analysis of sediment porewaters therefore promises to yield valuable quantitative information on the past environmental states of lakes.  相似文献   

Glacial geomorphology and ice ages in Tibet and the surrounding mountains   总被引：1，自引：0，他引：1  

Matthias  Kuhle 《Island Arc》2005,14(4):346-367

Abstract   Since 1973 new data have been obtained on the maximum extent of glaciation in High Asia. Evidence for an ice sheet covering Tibet during the last glacial period means a radical rethinking about glaciation in the northern hemisphere. The ice sheet's subtropical latitude, vast size (2.4 million km²) and high elevation (6000 m a.s.l.) are supposed to have resulted in a substantial, albedo-induced cooling of the Earth's atmosphere and the disruption of summer monsoon circulation. Moraines were found to reach down to 460 m a.s.l. on the southern flank of the Himalayas and to 2300 m a.s.l. on the northern slope of the Tibetan Plateau, in the Qilian Shan region. On the northern slopes of the Karakoram, Aghil and Kuen-Lun Mountains, moraines occur as far down as 1900 m a.s.l. In southern Tibet, radiographic analyses of erratics suggest a former ice thickness of at least 1200 m. Glacial polish and roches moutonnées in the Himalayas and Karakoram suggest former glaciers as thick as 1200–2700 m. On the basis of this evidence, a 1100–1600-m lower equilibrium line has been reconstructed, resulting in an ice sheet of 2.4 million km², covering almost all of Tibet. Radiometric ages, obtained by different methods, classify this glaciation as isotope stage 3–2 in age (Würmian, the last glacial period, ca  60 000–18 000 years ago).  相似文献   

Assessment of Discharge through a Dike Breach and Simulation of Flood Wave Propagation   总被引：2，自引：0，他引：2  

Paul Kamrath  Markus Disse  Matthias Hammer  Jürgen Köngeter 《Natural Hazards》2006,38(1-2):63-78

This paper presents a simple and fast method to calculate flow through a dike breach. The approach was based on two-dimensional numerical simulations of idealized dike breakages at straight river-sections. As a result, computation of discharge through a breach can be achieved by use of the new developed formula (denoted as dike break formula). Furthermore, a methodology that combines one-dimensional hydrodynamic modelling, the dike break formula and a simple GIS-based method to estimate inundation areas is described. This fast and easy-to-handle tool can be utilized for near real-time forecasting or evacuation decisions. Detailed predictions were made for a number of flood and dike break scenarios at the River Rhine to prove the accuracy of the new method compared with two-dimensional numerical models.  相似文献   

Fluid inclusions in apatite from Jacupiranga calcite carbonatites: Evidence for a fluid-stratified carbonatite magma chamber     

Alessandra Costanzo  Kathryn Ruth Moore  Frances Wall  Martin Feely 《Lithos》2006,91(1-4):208-228

Carbonatites of the Jacupiranga alkaline–carbonatite complex in São Paulo State, Brazil, were used to investigate mineral–fluid interaction in a carbonatite magma chamber because apatite showed a marked discontinuity between primary fluid inclusion-rich cores and fluid inclusion-poor rims. Sylvite and burbankite, apatite, pyrite, chalcopyrite and ilmenite are the common phases occurring as trapped solids within primary fluid inclusions and reflect the general assemblage of the carbonatite. The apatite cores had higher Sr and REE concentrations than apatite rims, due to the presence of fluid inclusions into which these elements partitioned. A positive cerium anomaly was observed in both the core and rim of apatite crystals because oxidised Ce⁴⁺ partitioned into the magma. The combined evidence from apatite chemistry, fluid inclusion distribution and fluid composition was used to test the hypotheses that the limit of fluid inclusion occurrence within apatite crystals arises from: (1) generation of a separate fluid phase; (2) utilization of all available fluid during the first stage of crystallization; (3) removal of crystals from fluid-rich magma to fluid-poor magma; (4) an increase in the growth rate of apatite; or (5) escape of the fluids from the rim of the apatite after crystallization. The findings are consistent with fractionation and crystal settling of a carbonatite assemblage in a fluid-stratified magma chamber. Secondary fluid inclusions were trapped during a hydrothermal event that precipitated an assemblage of anhedral crystals: strontianite, carbocernaite, barytocalcite, barite and norsethite, pyrophanite, magnesian siderite and baddeleyite, ancylite-(Ce), monazite-(Ce) and allanite. The Sr- and REE-rich nature of the secondary assemblage, and lack of a positive cerium anomaly indicate that hydrothermal fluids have a similar source to the primary magma and are related to a later carbonatite intrusion.  相似文献   

Earthquake activity related to seismic cycles in a model for a heterogeneous strike-slip fault   总被引：1，自引：0，他引：1  

Gert Zller  Sebastian Hainzl  Yehuda Ben-Zion  Matthias Holschneider 《Tectonophysics》2006,423(1-4):137

We investigate the evolution of seismicity within large earthquake cycles in a model of a discrete strike-slip fault in elastic solid. The model dynamics is governed by realistic boundary conditions consisting of constant velocity motion of regions around the fault, static/kinetic friction and dislocation creep along the fault, and 3D elastic stress transfer. The fault consists of brittle parts which fail during earthquakes and undergo small creep deformation between events, and aseismic creep cells which are characterized by high ongoing creep motion. This mixture of brittle and creep cells is found to generate realistic aftershock sequences which follow the modified Omori law and scale with the mainshock size. Furthermore, we find that the distribution of interevent times of the simulated earthquakes is in good agreement with observations. The temporal occurrence, however, is magnitude-dependent; in particular, the small events are clustered in time, whereas the largest earthquakes occur quasiperiodically. Averaging the seismicity before several large earthquakes, we observe an increase of activity and a broadening scaling range of magnitudes when the time of the next mainshock is approached. These results are characteristics of a critical point behavior. The presence of critical point dynamics is further supported by the evolution of the stress field in the model, which is compatible with the observation of accelerating moment release in natural fault systems.  相似文献   

Validation of a field filtration technique for characterization of suspended particulate matter from freshwater. Part II. Minor, trace and ultra trace elements     

Fredrik dman  Thomas Ruth  Ilia Rodushkin  Christer Pontr 《Applied Geochemistry》2006,21(12):2112-2134

A field filtration method for the concentration and separation of suspended particulate matter (SPM) from freshwater systems and the subsequent determination of minor, trace and ultra trace elements (As, Ba, Be, Cd, Co, Cr, Cs, Cu, Ga, Hf, Mo, Nb, Ni, Pb, Rb, Sb, Sc, Sn, Sr, Ta, Th, Tl, U, V, W, Zn and Zr) is validated with respect to detection limits, precision and bias. The validation comprises the whole procedure including filtration, sample digestion and instrumental analysis. The method includes two digestion procedures (microwave acid digestion and alkali fusion) in combination with inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). Total concentrations of these 27 trace and minor elements have been determined in suspended particulate matter (SPM) from lake and river water with low levels of suspended solids (<2 mg L⁻¹ DW), and a wide range of element concentrations. The precision of the method including filtration, digestion and instrumental determination ranges between 8% and 18% RSD for most elements on a dry weight basis. Higher recovery after acid digestion is found for some elements, probably because of volatilization or retention losses in the fusion procedure. Other elements show higher recovery after fusion, which is explained by more efficient decomposition of refractory mineral phases relative to the non-total acid digestion. Non-detectable concentrations of some elements are reported due to small differences between blank filter levels and the amounts of elements present on the filters after sampling. The method limits of detection range between 0.7 ng and 2.65 μg, as estimated from the blank filter samples. These detection limits are 10–550 times higher compared to the corresponding instrumental limits of detection. The accuracy and bias of the overall analytical procedure was assessed from replicate analysis of certified reference materials. A critical evaluation of the instrumental capabilities of the ICP-QMS instrumentation in comparison with a double focusing sector field plasma mass spectrometry technique (ICP-SFMS) is also included. It was found that a modified microwave acid digestion procedure in combination with ICP-SFMS could replace ICP-AES determinations and fusion digestions for most of the investigated elements. Guidelines and limitations for this time- and labour- efficient procedure, offering accurate results for the majority of elements studied are discussed.  相似文献   

The Greenland Ice Core Chronology 2005, 15–42 ka. Part 2: comparison to other records     

Anders Svensson  Katrine K. Andersen  Matthias Bigler  Henrik B. Clausen  Dorthe Dahl-Jensen  Siwan M. Davies  Sigfus J. Johnsen  Raimund Muscheler  Sune O. Rasmussen  Regine Rthlisberger  Jrgen Peder Steffensen  Bo.M. Vinther 《Quaternary Science Reviews》2006,25(23-24):3258

A new Greenland Ice Core Chronology (GICC05) based on multi-parameter counting of annual layers has been obtained for the last 42 ka. Here we compare the glacial part of the new time scale, which is based entirely on records from the NorthGRIP ice core, to existing time scales and reference horizons covering the same period. These include the GRIP and NorthGRIP modelled time scales, the Meese-Sowers GISP2 counted time scale, the Shackleton–Fairbanks GRIP time scale (SFCP04) based on ¹⁴C calibration of a marine core, the Hulu Cave record, three volcanic reference horizons, and the Laschamp geomagnetic excursion event occurring around Greenland Interstadial 10. GICC05 is generally in good long-term agreement with the existing Greenland ice core chronologies and with the Hulu Cave record, but on shorter time scales there are significant discrepancies. Around the Last Glacial Maximum there is a more than 1 ka age difference between GICC05 and SFCP04 and a more than 0.5 ka discrepancy in the same direction between GICC05 and the age of a recently identified tephra layer in the NorthGRIP ice core. Both SFCP04 and the tephra age are based on ¹⁴C-dated marine cores and fixed marine reservoir ages. For the Laschamp event, GICC05 agrees with a recent independent dating within the uncertainties.  相似文献   

Shields for the starship Enterprise     

Ruth Bamford  Robert Bingham  Mike Hapgood 《Astronomy& Geophysics》2007,48(6):6.18-6.23

Ruth Bamford, Robert Bingham and Mike Hapgood discuss the physics behind shielding spacecraft from solar and cosmic radiation with mini-magnetospheres.  相似文献   

Kiglapait geochemistry VI: Oxygen isotopes     

Ruth I. Kalamarides 《Geochimica et cosmochimica acta》1984,48(9):1827-1836

The Kiglapait layered intrusion is the first major intrusion found to have all whole rock and calculated liquid δ¹⁸O values close to a normal uncontaminated gabbroic value of 6.0. The intrusion experienced no detectable oxygen isotope exchange with its surrounding rocks and cooling of the magma was conductive. The δ¹⁸O values of average whole rocks vary smoothly from 6.0 at the base of the Lower Zone to 6.3 at the top of the Upper Zone. The calculated liquid δ¹⁸O values lie practically superimposed on the whole rock trend. The whole-rock data and the modelled δ¹⁸O of the magma and cumulates rigorously demonstrate that the effect of incoming cumulus phases such as magnetite and augite on the δ¹⁸O of the liquid and rocks during fractional crystallization is negligible. The cancelling effects of complementary modal variations among the mafic mineral phases and feldspar, keep the δ¹⁸O of the whole rocks constant to within ±0.1 %.. The minor change in δ¹⁸O that does occur with fractionation is consistent with the enrichment of residual liquids in feldspar component and the increasing fractionation factor δ Liquid-Fsp with falling temperature.The δ¹⁸O values of the country rocks bracket the estimated δ¹⁸O of the Kiglapait magma. Modelling with oxygen isotopes indicates that contamination of the intrusion, indicated by published radiogenic Sr and Nd isotopic data, was minor. The most probable contaminant had δ¹⁸O?7.7 and the contamination most likely occurred at >99% solidified. Subsolidus oxygen isotope exchange with an external source appears to have been very minor.  相似文献