羟氨苄青霉素引起大疱性类天疱疮样疹

Much has been written about theory and practice in the law, and the tension between practitioners and theorists. Judges do not cite theoretical articles often; they rarely "apply" theories to particular cases. These arguments are not revisited. Instead the Essay explores the working and interaction of theory and practice, practitioners and theorists. The Essay starts with a story about solving a legal issue using our intellectual tools - theory, practice, and their progenies: experience and "gut." Next the Essay elaborates on the nature of theory, practice, experience and "gut." The third part of the Essay discusses theories that are helpful to practitioners and those that are less helpful. The Essay concludes that practitioners theorize, and theorists practice. They use these intellectual tools differently because the goals and orientations of theorists and practitioners, and the constraints under which they act, differ. Theory, practice, experience and "gut" help us think, remember, decide and create. They complement each other like the two sides of the same coin: distinct but inseparable.

Of Theory and Practice

Elements Of X Ray Diffraction

The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.

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VALIDITY OF CUBIC LAW FOR FLUID FLOW IN A DEFORMABLE ROCK FRACTURE - eScholarship

Positive ions that are available in soils absorb on grain surfaces. The total sum of cations that can be absorbed bij a soil/sediment at a certain PH is defined by the cation-exchange capacity (CEC, in meq g-1: mol equivalents per gram). The uptake of cations is an important parameter in agriculture and the larger the CEC, the more cations can be absorbed to the soil. The CEC depends highly on the pH of soil and sediments, where the CEC decreases with decreasing PH (increasing acidity). The exchange of ions on sediments occurs commonly fast on geological time scales, but the kinetics of adsorption in natural environments is still poorly understood. The strength of the bonding between the cations and the sediments varies from weak Van der Waals bondings (physical adsorption) to strong chemical bonds. The CEC is widely used for agricultural assessment because it is a measure of general soil fertility as well as an indicator of structural stability because CED is capabel of enhancing development of shrinkage cracks. The list below shows the CEC for different types of minerals. The data indicate that the CEC can vary over 2 orders of magnitude for various types of , minerals and can vary one order of magnitude within one soil type. Cation exchange capacity for different types of sediment (Eisma, 1992; Locher and de Bakker, 1990):

Cation exchange capacity.

Quarried rock fragments (ballast) constitute one of the most commonly used construction materials in railway engineering practice. Ballast is subjected to high stress levels as well as being always exposed to environmental changes. Unsatisfactory performance of railway tracks is often associated with the loss of cross level, track profile and track alignment. The in situ condition and the engineering behavior of ballast are also important aspects governing the stability and performance of a given railway track structure. This paper presents the findings of a series of isotropically consolidated, triaxial compression tests on two modeled fractions of uniformly graded latite basalt, which is currently being used by the Railway Services Authority (RSA) of New South Wales, Australia, in the construction of new railway tracks. These tests form part of an extended research program sponsored by RSA to study the stress-strain relationships, strength properties and degradation characteristics of various types of railway ballast. The program is associated with the necessity of upgrading railway tracks for the looming Olympics in 2000. Large-scale triaxial equipment has been employed during the testing program, which is formulated to provide specific geotechnical information on the shear strength and the angle of internal friction of ballast as a function of the particle size distribution. The effect of maximum principal stress ratio on the deformation and degradation of ballast is also studied. Nonlinear relationships are developed to describe appropriately the variation of shear strength, angle of internal friction, dilation rate and degree of particle crushing at different confining pressures and principal stress ratios.

https://ro.uow.edu.au/cgi/viewcontent.cgi?article=1207&context=engpapers

Shear Behavior of Railway Ballast Based on Large-Scale Triaxial Tests

Ballast plays a vital role in transmitting and distributing train wheel loads to the underlying sub-ballast and subgrade. Bearing capacity of track, train speed, riding quality and passenger comfort all depend on the stability of ballast through mechanical interlocking of particles. Ballast attrition and breakage occur progressively under heavy cyc

Advanced Rail Geotechnology - Ballasted Track

Traditional railway foundations or substructures have become increasingly overloaded in recent years, owing to the introduction of faster and heavier trains. A lack of substructure re-engineering has resulted in maintenance cycles becoming more frequent and increasingly expensive. Two significant problems arising from increasing axle loads are differential track settlement and ballast degradation. One potential method of enhancing the substructure is to manipulate the level of ballast confinement. To investigate this possibility, a series of high-frequency cyclic triaxial tests has been conducted to examine the effects of confining pressure and deviator stress magnitude on ballast deformation (permanent and resilient) and degradation. Experimental results indicate that, for each deviator stress considered, an 'optimum' range of confining pressures exists such that degradation is minimised. This range was found to vary from 15–65 kPa for a maximum deviator stress of 230 kPa to 50–140 kPa when deviatoric st...

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Effect of confining pressure on ballast degradation and deformation under cyclic triaxial loading

Traditional railway foundations or substructures have become increasingly overloaded in recent years due to the introduction of faster and heavier trains. A lack of substructure re-engineering has resulted in maintenance cycles becoming more frequent and increasingly expensive. Two significant problems arising from increasing axle loads are differential track settlement and ballast degradation. One potential method of enhancing the substructure is by manipulating the level of ballast confinement. To investigate this possibility, a series of high frequency cyclic triaxial tests have been conducted to examine the effects of confining pressure and

/pdf/effect-of-confining-pressure-on-the-degradation-of-ballast-5lu84v893i.pdf

Effect of confining pressure on the degradation of ballast under cyclic loading

This study describes the behavior of embankments stabilized with prefabricated vertical drains installed in soft clay foundations, based on several fully instrumented case histories selected from T...

Buddhima Indraratna

Papers

Shear Behavior of Railway Ballast Based on Large-Scale Triaxial Tests

Advanced Rail Geotechnology - Ballasted Track

Effect of confining pressure on ballast degradation and deformation under cyclic triaxial loading

Effect of confining pressure on the degradation of ballast under cyclic loading

Numerical modeling of vertical drains with smear and well resistance installed in soft clay