Biaxial test simulations using a packing of polygonal particles   总被引：1，自引：0，他引：1  

A. A. Peña  A. Lizcano  F. Alonso‐Marroquin  H. J. Herrmann 《国际地质力学数值与分析法杂志》2008,32(2):143-160

The mechanical response of cohesionless granular materials under monotonic loading is studied by performing molecular dynamic simulations. The diversity of shapes of soil grains is modelled by using randomly generated convex polygons as granular particles. Results of the biaxial test obtained for dense and loose media show that samples achieve the same void ratio at large strains independent of their initial density state. This limit state resembles the so‐called critical state of soil mechanics, except for some stress fluctuations, which remain for large deformations. These fluctuations are studied at the micro‐mechanical level, by following the evolution of the co‐ordination number, force chains and the fraction of the sliding contacts of the sample. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Rate constants for the reactions of the NO3 radical with HCOOH/HCOO− and CH3COOH/CH3COO− in aqueous solution between 278 and 328 K     

M. Exner  H. Herrmann  R. Zellner 《Journal of Atmospheric Chemistry》1994,18(4):359-378

The kinetics of the aqueous phase reactions of NO₃ radicals with HCOOH/HCOO^– and CH₃COOH/CH₃COO^– have been investigated using a laser photolysis/long-path laser absorption technique. NO₃ was produced via excimer laser photolysis of peroxodisulfate anions (S₂O ₈ ^2– ) at 351 nm followed by the reactions of sulfate radicals (SO ₄ ^– ) with excess nitrate. The time-resolved detection of NO₃ was achieved by long-path laser absorption at 632.8 nm. For the reactions of NO₃ with formic acid (1) and formate (2) rate coefficients ofk ₁=(3.3±1.0)×10⁵ l mol^–1 s^–1 andk ₂=(5.0±0.4)×10⁷ l mol^–1 s^–1 were found atT=298 K andI=0.19 mol/l. The following Arrhenius expressions were derived:k ₁(T)=(3.4±0.3)×10¹⁰ exp[–(3400±600)/T] l mol^–1 s^–1 andk ₂(T)=(8.2±0.8)×10¹⁰ exp[–(2200±700)/T] l mol^–1 s^–1. The rate coefficients for the reactions of NO₃ with acetic acid (3) and acetate (4) atT=298 K andI=0.19 mol/l were determined as:k ₃=(1.3±0.3)×10⁴ l mol^–1 s^–1 andk ₄=(2.3±0.4)×10⁶ l mol^–1 s^–1. The temperature dependences for these reactions are described by:k ₃(T)=(4.9±0.5)×10⁹ exp[–(3800±700)/T] l mol^–1 s^–1 andk ₄(T)=(1.0±0.2)×10¹² exp[–(3800±1200)/T] l mol^–1 s^–1. The differences in reactivity of the anions HCOO^– and CH₃COO^– compared to their corresponding acids HCOOH and CH₃COOH are explained by the higher reactivity of NO₃ in charge transfer processes compared to H atom abstraction. From a comparison of NO₃ reactions with various droplets constituents it is concluded that the reaction of NO₃ with HCOO^– may present a dominant loss reaction of NO₃ in atmospheric droplets.  相似文献   

Aluminium species distribution during mixing of acid coal and slate mine drainage with neutral stream waters     

Reimer Herrmann  Isolde Baumgartner 《International Journal of Earth Sciences》1992,81(3):759-767

We measured the spatial variation of aluminium concentrations and computed its species distribution before and during mixing of acid mine drainage containing waters with near neutral receiving waters. Acid mine drainage was collected from the Loquitz Creek, Thuringia, Germany, and Garvey Creek, Westland, New Zealand, which drain slate mine workings and coal mine workings, resp. The acidneutralizing capacity (ANC) of the receiving streams and the mixing with waters having low Al-concentrations cause a decrease of aluminium concentrations below the confluence. Depending on volumes and ANCs involved, the content of free Al and sulphate bound Al decreases after mixing in favour of organic and hydroxide bound Al. In addition, below the junction of the Loquitz Creek and the Aue Creek with its high ANC, we observe the precipitation of aluminium hydroxides and Al hydroxysulphates.

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Zusammenfassung Wir haben die räumliche Änderung der Aluminiumkonzentrationen vor und nach der Mischung von Flußwasser, versauert durch Bergwerksabwässer, mit nahezu neutralem Wasser der Vorfluter gemessen und haben dazu die Speziesverteilung berechnet. Saure Bergwerksabwässer sickern aus Halden eines Schiefertagebaus in Thüringen in die Loquitz ebenso wie aus Halden eines Kohletagebaus in den Garvey Creek, Westland, Neuseeland. Die Säuren-Neutralisierungskapazität der Vorfluter und die Mischung mit Al-armem Wasser bewirken eine Abnahme der Aluminiumkonzentrationen nach dem Zusammenfluß. In Abhängigkeit von beteiligten Abflüssen und Säuren-Neutralisierungskapazitäten nimmt der Gehalt an freiem Aluminium und sulfatgebundenem Aluminium nach der Mischung zugunsten von organisch- und hydroxy-gebundenem Aluminium ab. Ferner beobachten wir unterhalb des Zusammenflusses von Loquitz und Aue, der eine hohe Säuren-Neutralisierungskapazität eigen ist, eine Ausfällung von Aluminiumhydroxyden und Aluminiumhydroxysulfaten.

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Résumé Nous avons mesuré la variation spatiale de la teneur en Al et calculé la distribution de ses différentes formes dans deux cours d'eau différents, qui reçoivent des eaux acides venant de mines situées sur leur cours. Ces mesures ont été faites d'une part sur le cours du Loquitz (Thuringe-Allemagne) qui reçoit des aux acides venant d'une mine d'ardoise et d'autre part sur le cours du Garvey (Westland - Nouvelle Zélande) qui reçoit les eaux d'une mine de charbon. Pour chaque cours d'eau, les mesures ont été faites en amont de la source d'apport, puis en aval, c'est-à-dire après le mélange avec les eaux acides. La capacité de neutralisation des acides (ANC) des eaux des cours d'eau récepteurs et la basse teneur en Al des eaux d'apport provoquent une diminution de la teneur en Al après le mélange. Dans une mesure liée aux volumes en jeu et à l'ANC, la teneur en Al libre et en Al lié au sulfate diminue près le mélange au profit de l'Al lié soit à des substances organiques, soit à des hydroxydes. De plus, en aval du confluent du Loquitz et de l'Aue, rivière à ANC élevé, nous observons la précipitation d'hydroxydes d'Al et d'hydroxisulfates d'Al.

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Tectonic relation between northeastern China and the Korean peninsula revealed by interpretation of GRACE satellite gravity data   总被引：2，自引：0，他引：2  

Sungchan Choi  Chang-Whan Oh  Herrmann Luehr 《Gondwana Research》2006,9(1-2):62

The major continental blocks in northeastern Asia are the North China block and the South China block, which have collided starting from the Korean peninsula. Geologic and geophysical interpretations reveal a well defined suture zone in northeastern China from Qinling through Dabie to Jiaodong. The discovery of high-pressure metamorphic rocks in the Hongseong area of the Korean peninsula, prominent evidence for the collision zone, indicates extension of the collision zone in northeastern China into the Korean peninsula. Interpretation of the GRACE satellite gravity dataset shows two prominent structural boundaries in the Yellow Sea. One extends from the Jiaodong Belt in eastern China to the Imjingang Belt in the Korean peninsula. The other extends from near Nanjing, eastern China, to Hongseong. Tectonic movement in or near the suture zone may be responsible for seismic activity in the western Korean peninsula and the development of the Yellow Sea sedimentary basin.  相似文献   

Ground motion scaling in the Marmara region, Turkey   总被引：1，自引：0，他引：1  

A. Akinci  L. Malagnini  R. B. Herrmann  R. Gok  M. B. Sørensen 《Geophysical Journal International》2006,166(2):635-651

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Luxury Tourism and Regional Economic Development in Mexico   总被引：1，自引：0，他引：1  

Ludger Brenner  Adrin Guillermo Aguilar 《The Professional geographer》2002,54(4):500-520

This article argues that little attention has been paid to the territorial and socioeconomic impact of consumer–service globalization on Third World countries. It specifically examines the economic role of tourism in Mexico and its limited effect on the country's regional development. Despite governmental support in order to enhance economic growth, currency receipts, and employment, tourism contributes less than 5 percent to the gross domestic product, and the majority of tourism–related jobs are precarious and low–skilled. The promotion of luxury resorts in coastal areas has led to highly concentrated and fast–growing enclaves of mainly foreign investment. However, this strategy has failed to stimulate productive links between tourist centers and their hinterlands and has led to large–scale urbanization characterized by a considerable lack of basic services for the resident population.  相似文献   

Wind velocity and sand transport on a barchan dune   总被引：2，自引：0，他引：2  

G. Sauermann  J. S. Andrade  Jr.  L. P. Maia  U. M. S. Costa  A. D. Araújo  H. J. Herrmann 《Geomorphology》2003,54(3-4):245-255

We present measurements of wind velocity and sand flux performed on the windward side of a large barchan dune in Jericoacoara, northeastern Brazil. From the measured profile, we calculate the air shear stress using an analytical approximation and treat the problem of flow separation by an heuristic model. We find that the results from this approach agree well with our field data. Moreover, using the calculated shear velocity, we predict the sand flux according to well-known equilibrium relations and with a phenomenological continuum saltation model that includes saturation transients and thus allows for nonequilibrium conditions. Based on the field data and theoretical predicted results, we indicate the principal differences between saturated and nonsaturated sand flux models. Finally, we show that the measured dune moves with invariant shape and predict its velocity from our data and calculations.  相似文献   

Modelling transverse dunes     

Veit Schwmmle  Hans Herrmann 《地球表面变化过程与地形》2004,29(6):769-784

Transverse dunes appear in regions of mainly unidirectional wind and high sand availability. A dune model is extended to two‐dimensional calculation of the shear stress. It is applied to simulate dynamics and morphology of three‐dimensional transverse dunes. In the simulations they seem to reach translational invariance and do not stop growing. Hence, simulations of two‐dimensional dune ?elds have been performed. Characteristic laws were found for the time evolution of transverse dunes. Bagnold's law of the dune velocity is modi?ed and reproduced. The interaction between transverse dunes led to the interesting conclusion that small dunes can travel over bigger ones. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Tourmalinites from the Eastern Sierras Pampeanas, Argentina     

S. M. Tourn  C. J. Herrmann  S. Ametrano  M. K. de Brodtkorb   《Ore Geology Reviews》2004,24(3-4):229

In the eastern Sierras Pampeanas, Central Argentina, tourmalinites and coticules are found in close association with stratabound scheelite deposits in metamorphic terranes. In Sierra Grande (Agua de Ramón and Ambul districts) and Sierra de Altautina, tourmalinites are associated with stratabound scheelite deposits related to orthoamphibolites. In the Pampa del Tamboreo area, tourmalinites are located in biotite schists stratigraphically related to acid to intermediate metavolcanic rocks and scheelite-bearing quartzites.The mineral chemistry and boron isotopic compositions of tourmalinite-hosted and vein-hosted tourmalines are investigated. Overall, the tourmalines belong to the dravite-schorl series and are generally aluminous; Fe/(Fe+Mg) ranges from 0.33 to 0.85, Al/(Al+Fe+Mg) from 0.66 to 0.76 and the amount of X-site vacancy (0.12–0.48) indicates significant foitite components. Their boron isotopic compositions (δ¹¹B) are from −24.0‰ to−15.0‰.Similar mineral chemistries and boron isotopic values for tourmaline in tourmalinites related to stratabound scheelite mineralisation and in tungsten-bearing quartz veins suggest a common source for the boron and probably the tungsten. The field, chemical and isotopic relationships are consistent with tungsten and boron in quartz-vein deposits being remobilised from stratabound scheelite and tourmalinite, dominantly by liquid-state transfer associated with regional shear zones. Tungsten and boron in the original sedimentary sequence (now meta-exhalites) are ascribed to volcanogenic exhalations.  相似文献   

Urban planning and tsunami impact mitigation in Chile after February 27, 2010     

Marie Geraldine Herrmann Lunecke 《Natural Hazards》2015,79(3):1591-1620

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