Differential equations governing slip-induced pore-pressure fluctuations in a water-saturated granular medium

Macroscopic frictional slip in water-saturated granular media occurs commonly during landsliding, surface faulting, and intense bedload transport. A mathematical model of dynamic pore-pressure fluctuations that accompany and influence such sliding is derived here by both inductive and deductive methods. The inductive derivation shows how the governing differential equations represent the physics of the steadily sliding array of cylindrical fiberglass rods investigated experimentally by Iverson and LaHusen (1989). The deductive derivation shows how the same equations result from a novel application of Biot's (1956) dynamic mixture theory to macroscopic deformation. The model consists of two linear differential equations and five initial and boundary conditions that govern solid displacements and pore-water pressures. Solid displacements and water pressures are strongly coupled, in part through a boundary condition that ensures mass conservation during irreversible pore deformation that occurs along the bumpy slip surface. Feedback between this deformation and the pore-pressure field may yield complex system responses. The dual derivations of the model help explicate key assumptions. For example, the model requires that the dimensionless parameterB, defined here through normalization of Biot's equations, is much larger than one. This indicates that solid-fluid coupling forces are dominated by viscous rather than inertial effects. A tabulation of physical and kinematic variables for the rod-array experiments of Iverson and LaHusen and for various geologic phenomena shows that the model assumptions commonly are satisfied. A subsequent paper will describe model tests against experimental data.     

Geometrical Properties of Galaxy Clusters

Empirical and analytical procedures are developed to determine the morphological properties of galaxy clusters. The apparent orientations and shapes are obtainted in two dimensional space while the direction towards the cluster pole is found in three dimensional space. These properties were determined for three Abell clusters and found to be strongly related. This revised version was published online in July 2006 with corrections to the Cover Date.     

Flood hydrograph estimation from arid catchment morphology

Data on performance of a geomorphologic rainfall-runoff model in simulating observed flash flood hydrographs in 32 arid catchments have been analysed. The catchments, which are located in the southwest region of Saudi Arabia, vary in their size, slope of land, and characteristics of soils, and are in zones of different rainstorm characteristics. The sensitivity of the model accuracy with various catchment and rainfall characteristics has been investigated. Size, followed by rate of infiltration and slope of land, are the most effective catchment characteristics affecting the accuracy. In addition, the accuracy varies with spatial and temporal rainfall variation, total rainfall depth, and length of the dry period between two successive rainstorms over catchment. It is sensitive to temporal rainfall variation more than spatial rainfall variation, and to the dry period more than total rainfall depth. Generally, the model did not display an accuracy approaching that of the observations, especially in simulating peak flowrates in large size infiltrating catchments having high temporal rainstorm variation. Guidelines on the best use of the model in arid catchments were proposed.     

ON THE MARINE CILIATE, Pseudocohnilembus hargisi(PROTOZOA, CILIOPHORA, SCUTICOCILIATIDA) WITH COMPARISON OF ITS RELATED SPECIES

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A Comparison Between Near-Infrared And Visible Imaging Of The Inner Coma Of Comet Hale-Bopp At Perihelion

We present a comparison between images of comet C/1995 O1 (Hale-Bopp) obtained from 12 March to 9 May 1997, with two telescopes of the Observatorio del Teide (IAC, Tenerife, Spain) in visible (Johnson-V filter) and three near-infrared narrowband filters (Brγ (2.166 μm), CO (2.295 μm), and K_con (2.260 μm)). No significant differences are observed between the images in the three near-infrared bands suggesting that any CO emission is very weak, or produced by an extended flat source. We do not find evidence for the existence of an additional infrared component due to emission by warm dust, or to dust grains of diverse composition and/or size. Visible and infrared images of the same rotational phase look almost identical, supporting the view that the observed jets and shells are mainly dust structures. This revised version was published online in July 2006 with corrections to the Cover Date.     

BOOK REVIEWS

Book Reviewed in this article: Hillslope Processes. Binghamton Symposia in Geomorphology International Series: 16. Athol D. Abrahams , ed. The Atlas of Central America and the Caribbean. The Diagram Group . The Cultural Atlas of Islam. Isma'il R. al Faruqi and Lois Lamaya'al Faruqi . Atlas of Israel Contemporary Africa: Development, Culture and the State. Morag Bell . Fundamentals of Physical Geography. David Briggs and Peter Smithson . The Bicentennial Census: New Directions for Methodology in 1990. Constance F. Citro and Michael L. Cohen , eds . World Patterns of Modern Urban Change: Essays in Honor of Chauncy D. Harris. Michael P. Conzen , ed . New Directions for Agriculture and Agricultural Research: Neglected Dimensions and Emerging Alternatives. Kenneth A. Dahlberg , ed . Water Resources Atlas of Florida. E.A. Fernald and D.J. Patton , eds . Landscape Ecology. R.T.T. Forman and M. Godron . The Myth of the North American City: Continentalism Challenged. Michael Goldberg and John Mercer . The Permafrost Environment. Stuart A. Harris . Climate and Circulation of the Tropics. Stefan Hastenrath . The Island of South Georgia. Robert Headland . The Making of Urban Europe, 1000-1950. Paul M. Hohenberg and Lynn Hollen Lees . Bombay in Transition: The Growth and Social Ecology of a Colonial City, 1889–1980. Meera Kosambi . Plant Closings; Public or Private Choices? Richard B. McKenzie , ed . Malaysia: Tradition, Modernity and Islam. R.S. Milne and Diane K. Mauzy . Technology on the Frontier: Mining in Old Ontario. Dianne Newell . The Maritime Political Boundaries of the World. J.R.V. Prescott . Tall Office Buildings in the United States. James W. Pygman and Richard Kateley (Real Estate Research Corporation). Technology, Regions, and Policy. John Rees , ed . The United States and the Regional Organization of Asia and the Pacific: 1965-1985. W.W. Rostow . Renewable Energy: Progress, Prospects. Stephen W. Sawyer Wisconsin Foundations. Gwen Schultz . Dwelling, Place and Environment: Towards a Phenomenology of Person and World. David Seamon and Robert Mugerauer , eds . Power and Place: Canadian Urban Development in the North American Context. Gilbert A. Stelter and Alan F.J. Artibise , eds . Small Firms in Regional Economic Development: Britain, Ireland and the United States. D. J. Storey , ed . Mathematical Methods in Human Geography and Planning. A. G. Wilson and R. J. Bennett . El Niño North: Niño Effects on the Eastern Subarctic Pacific Ocean. W. S. Wooster and D. L. Fluharty , eds . The Soviet Iron and Steel Industry. Craig ZumBrunnen and Jeffrey Osleeb .     

Numerical Investigation of the Galactic Problem by Computing Families of Periodic Solutions

The galactic dynamical system expressed by a third-order axisymmetric polynomial potential is investigated numerically by computing periodic solutions. We define as Sthe compact set of initial conditions generating bounded motions, and as S ^p , with S ^p ? S, the countable set of all initial conditions generating periodic solutions. Then, we consider the subsets S _s ^p and S _a ^p of S ^p , where S _s ^p ∪ S _a ^p = S ^p , S _s ^p S _a ^p = Ø, the first of which corresponds to symmetric periodic solutions, and the second to asymmetric solutions. Then, we approximate the set S _s ^p , leaving treatment of the set S _a ^p of asymmetric solutions for a future publication. The set S _s ^p is known to be dense in S (‘Last Geometric Theorem of Poincar;’, Birkhoff, 1913). Using a computer programme capable to locate all elements of the set S _s ^p that generate symmetric periodic solutions that re-enter after intersecting the axis of symmetry from 1 to ntimes. The results of the approximation of S _s ^p in the total domain and in the sample sub-domains of zooming, we present in graphical form as family curves in the (x, C) plane. The solutions located with the largest periods re-enter after 440 galaxy revolutions while the families calculated fully (initial conditions, period, energy, stability co-efficient) include solutions that re-enter after 340 galaxy revolutions. To advance further the approximation of the set S _s ^p thus obtained, we applied the same procedure inside eight sub-domains of the domain Sinto which we ‘zoomed’ through selection of finer search steps and double maximum periods. The family curves thus calculated presented in the (x, C) plane do not intersect anywhere in some sub-domains and their pattern resembles that of laminar flow. In other sub-domains, however, we found family curves from which branching families emanate. The concepts of completeand non-completeapproximation of S _s ^p in sub-domains of laminar and sub-domains with branching family curves, respectively, is introduced. Also, the concept of basic family of order1, 2, ..., n, are defined. The morphology of individual periodic solutions of all families is investigated, and the types of envelopes found are described. The approximate set S _s ^p was also checked by computing Poincar; sections for energy values corresponding to the mean energy range of the eight sub-domains of zooming mentioned above. These sections show that most parts of the compact domain in Sgenerating non-periodic but bounded solutions correspond to with well-shaped tori that intersect the x-axis, a fact that implies that dominant to exclusive type of periodic solutions are the symmetric ones with two normal crossings of this axis. The presence of non-symmetric periodic solutions as well as of chaotic regions is encountered. All calculations reported here were performed using the variable step R-K 8th-order direct integration and setting the allowable energy variation Δ C= |C _start? C _end| < 10^?13. The output, consisting of many thousands of families and their properties (initial conditions, morphology, stability, etc.), is stored in a directory entitled ‘Atlas of the Symmetric Periodic Solution of the Galactic Motion Problem’.     

The Spin Axis Position of C/1995 O1 (Hale–Bopp)

Monitoring of the near-nucleus activity of C/1995 O1 (Hale-Bopp) began in Teide Observatory in August 1995. During 1996 the comet was observed on 72 nights between March 26 and November 13. A permanent fan structure was observed towards the north during the whole period of observation. The position angle of the axis of this fan was measured and its variations with time were used to determine the position of the North Pole of the cometary nucleus. This revised version was published online in July 2006 with corrections to the Cover Date.     

三维激光扫描技术与断层面形貌量化分析在基岩区古地震研究中的应用

由于对第四纪地层的严重依赖,传统古地震探槽研究方法在基岩区难以发挥作用,导致无法获取基岩区断层的强震活动历史。本研究以山西地堑系的交城断裂为目标断裂,以断裂北段2处基岩断层面为研究对象,通过三维激光扫描技术获取基岩断层面高精度形貌,基于变差函数法结合滑动窗口操作量化断层表面形貌特征,开展在基岩区提取断裂古地震信息的实例研究。结果显示,2处基岩断层面的形貌在高度上具有明显的分段特征,指示了断层面在地震事件作用下的分段出露过程。这种断层面形貌分段特征可以用来识别古地震事件和同震位移量。在思西村基岩断层面上,识别出由老到新的3次古地震事件,同震倾滑位移量依次为2.0 m、1.9 m和2.3 m,在上兰镇基岩断层面上,识别出由老到新的3次古地震事件,同震倾滑位移量依次为1.4 m、2.5 m和2.0 m,指示了交城断裂北、中段具有产生同震位移量大于2 m、震级大于7.5级的破裂型地震的能力。上述研究成果表明,基于三维激光扫描和形貌量化分析方法开展基岩断层面古地震研究,可以准确而高效地识别古地震事件次数和同震位移量,扩展古地震的研究对象,拓宽古地震的研究空间。在未来的研究中,可以适时地开展宇宙成因核素测年以测定断层面的暴露年龄,获得发震年代,给予地震序列年龄框架。     

Analysis of rill step–pool morphology and its comparison with stream case

In this paper, the morphology of step–pool features is analysed using rill measurements and literature data for streams. Close-range photogrammetry was used to carry out ground measurements on rills with step–pool units, shaped on a plot having slope equal to 14, 15, 22, 24 and 26%. Data were used to compare the relationships between H/L, in which H is the step height and L is the step length, and the mean gradient of the step–pool sequence, S_m, for streams or the slope of the step–pool unit, S, for rills. The relationship of H/L against S_m is widely used to test the occurrence of the maximum flow resistance condition in streams, which is associated with the range 1 ≤ (H/L)/S_m ≤ 2. Further analyses were carried out to compare both the formation process and the profile of the pool in rills with those related to streams. Moreover, for a single rill channel, an analysis of flow characteristics expressed in terms of Darcy–Weisbach friction factor and Froude number was developed. The results allowed us to state: (i) the relationships of H/L versus S_m and S are quite similar and the steepness ratio for streams, (H/L)/S_m, and for rills, (H/L)/S, generally ranges from 1 to 2; (ii) the formation process and the profile of the pool in rills are not consistent with those occurring in streams; (iii) in the rills, the longitudinal size of the pool is dominant with respect to the maximum scour depth; (iv) the presence of a sequence of step–pool units within a rill segment noticeably increases flow resistance compared to segments with a flat bed; (v) the Froude number of the flow over the sequence of step–pool units in rills is slightly below the range of 0.8–1 corresponding to the maximum flow resistance in step–pool units.