The effect of normal stiffness on the shear resistance of rock     

Leonard Obert  B. T. Brady  Frank W. Schmechel 《Rock Mechanics and Rock Engineering》1976,8(2):57-72

The Effect of Normal Stiffness on the Shear Resistance of RockThis paper presents the theory and design of a shear machine whose normal stiffness could be varied by four orders of magnitude. Experimental techniques, testing procedures, and special equipment designed by the Bureau of Mines for determining the effect of normal stiffness on the shear stress-normal displacement behavior of intact and prepared joint surfaces of both hard (granite) and soft (sandstone) rock under constant shear displacement rate are described. Experimental results are presented which show that the effect of increasing the normal stiffness on either intact rock or fractured surfaces is to provide increased normal confinement. Increased normal confinement results in an increased shear strength for rock. Engineering significance of this result is discussed.  相似文献   

Morphotectonic analysis of the Hazara arc region of the Himalayas, north Pakistan and northwest India     

Vivien Gornitz  Leonard Seeber   《Tectonophysics》1981,74(3-4)

In the Hazara arc region of northern Pakistan, some of the active basements structures buried below a thick, detached sedimentary layer are inferred from the distribution of lineaments and the drainage patterns, as viewed in Landsat satellite imagery and from river profiles.A prominent set of NW-trending lineaments seen on satellite imagery, coincides approximately with the southwest or updip side of the Indus—Kohistan seismic zone (IKSZ) —the most active basement structure of the region, even though this structure is buried beneath and decoupled from a 12 km thick sedimentary layer. The IKSZ has been interpreted as an extension of the Himalayan Basement Thrust, and is also associated with a prominent topographic “step”.Knickpoints on major rivers in the region lie on or north of the IKSZ. All Indus River tributaries, examined north of the IKSZ, show prominent knickpoints, while two tributaries draining south of the IKSZ have no knickpoints. These results suggest ongoing uplift above and north of the IKSZ, and are consistent with the tectonic model obtained from the seismic data.Another prominent lineament set is detected along the north—south section of the Indus River. This set is probably related to the Indus River horst—anticline and associated reentrant.One of the two highest lineament concentrations occurs at the intersection between the NW-trending IKSZ lineament and the N-trending Indus River lineament. The other is along the west bank of the Indus Valley, 25 km north of Tarbela Dam.A topographic ridge (Swabi—Nowshera ridge) appears to be forming along the west side of the Indus River, in the Peshawar Basin. The rising ridge is ponding the Kabul River upstream of Nowshera, where the drainage is braided.  相似文献   

Morphology of the Weddell Sea and southwest Indian Ocean     

Dr. G. Leonard Johnson  Prof. Jean-René Vanney  Anders Elverhøi  John L. LaBrecque 《Ocean Dynamics》1981,34(6):263-272

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DISCUSSION OF "Monitoring Well Installation, Purging, and Sampling Techniques-Part 1: Conceptualizations," by Joseph F. Keely and Kwasi Boateng, May-June 1987 issue, v. 25, no. 3, pp. 300–313     

Leonard A. Wood  S. S. Papadopulos 《Ground water》1988,26(1):87-88

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Regional Geography*     

Leonard Guelke 《The Professional geographer》1977,29(1):1-7

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Travel patterns and challenges of physically disabled persons in Nigeria     

Leonard Sitji Bombom  Ibrahim Abdullahi 《GeoJournal》2016,81(4):519-533

The physically disabled persons represent a special group of the transportation disadvantaged who have suffered many deprivations. The study explores the travel patterns and some of the challenges being encountered by the physically disabled in Jos, Nigeria. Using the questionnaire and focus group discussion methods, the study found that the respondents are of low social and economic statuses. Walking, with enormous time and energy costs, is the most common means of travel among the group. Commercial vehicle drivers apparently hardly attend to the transportation needs of the group even when they can afford the fare. The physically disabled persons view this “injustice” as a reflection of a whole gamut of perceived discriminatory policies of the “able” society to isolate and disempower them. There is therefore a deep-seated feeling of resentment among the physically disabled towards society’s perceived apathy, marginalization and discrimination that manifest even in access to transportation. They believe that the social and physical environments are deliberately hostile to them. Any plans to alleviate the transportation problems of the disabled and integrate them into the mainstream of the economic and social activities of the larger society should address, fundamentally, these perceived marginalization and injustices.  相似文献   

Holocene Vegetation Dynamics, Fire History, Lake Level and Climate Change in the Kootenay Valley, Southeastern British Columbia, Canada     

Douglas J. Hallett  Leonard V. Hills 《Journal of Paleolimnology》2006,35(2):351-371

The environmental history of the Kootenay Valley in the southern Canadian Rockies was reconstructed using lake sediment from Dog Lake, British Columbia, and compared to other paleoenvironmental studies in the region to understand how vegetation dynamics and fire regimes responded to climate change during the Holocene. A pollen-based vegetation reconstruction indicates five periods of vegetation change. At 10,300 cal yr B.P. Pinus-Juniperus parkland colonized the valley and by 7600 cal yr B.P. was replaced by mixed stands of Pinus, Picea and Pseudotsuga/Larix. Fire frequencies increased to their Holocene maximums during the 8200–4000 cal yr B.P. period. From 5500–4500 cal yr B.P. Pseudotsuga/Larix reached its maximum extent in the Kootenay Valley under a more frequent fire regime. At 5000 cal yr B.P. Picea and Abies began to expand in the area and by 4500 cal yr B.P. the forest shifted to a closed montane spruce forest type with dramatically reduced fire frequency. The shift to less frequent forest fires after 4500 cal yr B.P., along with a moisterPicea – dominated closed forest, corresponds to Neoglacial advances in the Canadian Rockies and Coast Mountains. Fire intervals after 4000 cal yr B.P. are significantly longer than the shorter fire intervals of the early to mid Holocene. A return to drier, more open forest condition occurs between 2400–1200 cal yr B.P. with a slight increase in fire activity and summer drought events. Lower lake levels inferred by charophyte accumulation rates during the 2400–1200 cal yr B.P. interval support this moisture regime shift. An abrupt shift toPicea dominated forest occurred from 1200–1000 cal yr B.P. and a final period of wet-closed forest cover reaches its maximum extent from 700–150 cal yr B.P. that appears to be a response to Little Ice Age cooling. Present forests are within their natural range of variability but are predicted to shift again to a drier more open structure with increased Pseudotsuga/Larix cover. More frequent stand replacing fires and increased area burned likely will accompany this change due to continued global warming.  相似文献   

The response of moving radiometers     

L. P. Herrington  R. E. Leonard  J. E. Hamilton  G. M. Heisler 《Boundary-Layer Meteorology》1972,2(4):395-405

The output of a radiometer passing over a field of varying emittance or reflectance will not, in general, provide a faithful reproduction of the variations. The space-weighted averaging effect of the radiometer's hemispherical view plus the distortion produced by the first-order response of the radiometer sensor will result in low-pass filtering of the data. By means of a simplified model of the moving radiometer system, this paper provides guidelines for the interpretation of information from such systems. Faithful reproduction requires instruments with a fast time constant, operating close to the surface with a relatively slow speed of translation.  相似文献   

Validation of model improvements for the GISS GCM     

José A. Marengo  Leonard M. Druyan 《Climate Dynamics》1994,10(3):163-179

The general circulation model of the NASA/Goddard Institute for Space Studies (GISS GCM) was designed primarily for global climate change and climate sensitivity applications. The modelling group at GISS has developed new and more physically appropriate parameterizations of meteorological/hydrological processes which are being validated in an effort to improve the performance of the Model II version of the GISS GCM. This study discusses some preliminary evaluations of this testing based on multiple-year simulations at 4° latitude by 5° longitude horizontal resolution. These runs individually incorporate new formulations of the planetary boundary layer (PBL), the moist cumulus convection scheme and the ground hydrology and compare results using B-grid and C-grid numerics. The new PBL produces a realistically stronger tropical surface circulation, while the new cumulus scheme generates more realistic distributions of tropical convection and moisture. The main impact of the more sophisticated ground hydrology model is to increase surface air temperatures. Improvements in modelled sea level pressure and rainfall features by the C-grid are somewhat offset by increases in speed excesses at the cores of the summer hemisphere westerly jets. Each modelling innovation targeted a different aspect of the climate not adequately represented by Model II. However, since the various modelling changes were tested individually, the present evaluation could not demonstrate many dramatic improvements in the simulated climates. This documentation of impacts should, however, serve as a benchmark for the validation of future simulations of the GISS GCM that combine all of the modelling improvements.  相似文献   

The partitioning of nitrogen oxides in the lower Arctic troposphere during spring 1988     

Jan W. Bottenheim  Leonard A. Barrie  Elliot Atlas 《Journal of Atmospheric Chemistry》1993,17(1):15-27

Surface observations of several nitrogen oxides in the Canadian high Arctic during the period March-April 1988 are reported. These include data on NO₂, the inorganic nitrates HNO₃ and particulate nitrate, and the organic nitrates PAN and C₃–C₇ alkyl-nitrates. It is found that the organic nitrates make up 70–80% of the sum of the measured nitrogen oxides. Based on concurrently measured sulphur oxides, the period of observation was divided into two halves with the first half representing less polluted, more aged air than the second. The preponderance of the organic nitrates was less in the first period than the second. In contrast, there was little difference in the inorganic nitrates and NO₂ concentrations. The dominant inorganic nitrate shifted from particulate nitrate in the first period towards gaseous HNO₃ in the second. No correlation between the nitrates (inorganic or organic) and O₃ was observed; although some indication of a positive correlation between NO₂ and O₃ has been reported earlier (Bottenheimet al., 1990). Possible explanations for these observations are proposed. A survey of other potential nitrogen oxides that may be present in the Arctic air but not measured in these experiments suggests that the nitrogen oxides not measured here constitute a minor fraction of the total reactive nitrogen (NO _y ).Paper submitted to the 7th International Symposium of the Commission for Atmospheric Chemistry and Global Pollution on the Chemistry of the Global Atmosphere held in Chamrousse, France, from 5 to 11 September 1990.  相似文献