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Certain Distance (certain + distance)
Selected AbstractsComputer-generated null models as an approach to detect perceptual range in mark,re-sight studies , an example with grasshoppersECOLOGICAL ENTOMOLOGY, Issue 2 2005Silke Hein Abstract., 1. Dispersal and habitat detection are key factors for the colonisation of habitat fragments in heterogeneous landscapes. The ability to recognise a habitat from a certain distance should increase the survival chances of a dispersing individual; however, due to methodological problems there is little information on the perceptual range of most species. 2. In a field experiment, 44 individually marked grasshoppers of the species Oedipoda caerulescens (Orthoptera: Acrididae: Locustinae) were released into an unfamiliar, hostile environment at various distances from a patch of preferred habitat. 3. Whether individuals reached the habitat or not was measured, as well as the daily movement distances. The number of individuals that reached the habitat was tested against computer-generated predictions based on different underlying rules for the movement behaviour of individuals but not accounting for the ability to detect habitat from distance. 4. On the first day a significantly higher proportion of grasshoppers arrived in the habitat than predicted by any of the null models. 5. It was concluded that individuals of O. caerulescens are able to detect their preferred habitat from a distance. 6. Edge permeability was very low as none of the individuals left the habitat once they had reached it. 7. Additional analyses showed that individuals changed movement behaviour from a directed walk with great daily distances in unsuitable habitat to a walk with significantly shorter daily distances within the preferred habitat. 8. The problems that arose in the field experiment are discussed and recommendations are given for further studies. [source] The role of friction and secondary flaws on deflection and re-initiation of hydraulic fractures at orthogonal pre-existing fracturesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2006Xi Zhang SUMMARY In this study, we explore the nature of plane-strain hydraulic fracture growth in the presence of pre-existing fractures such as joints without or with secondary flaws. The 2-D plane-strain fracture studied can be taken as a cross-section through the short dimensions of an elongated 3-D fracture or as an approximate representation of the leading edge of a 3-D fracture where the edge curvature is negligible. The fluid-driven fracture intersects a pre-existing fracture to which it is initially perpendicular and is assumed not to immediately cross, but is rather deflected into the pre-existing fracture. The intersection results in branching of the fracture and associated fluid flow into the pre-existing fracture. Further growth results in opening and frictional sliding along the pre-existing fracture. Fracture propagation in an impermeable homogeneous elastic medium and fluid invasion into a pre-existing fracture are both driven by an incompressible, Newtonian fluid injected at a constant rate. The frictional stress on the surfaces of pre-existing fractures is assumed to obey the Coulomb law. The governing equations for quasi-static fluid-driven fracture growth are given and a scaling is introduced to help identify important parameters. The displacement discontinuity method and the finite difference method are employed to deal with this coupling mechanism of rock fracture and fluid flow. In order to account for fluid lag, a method for separately tracking the crack tip and the fluid front is included in the numerical model. Numerical results are obtained for internal pressure, frictional contact stresses, opening and shear displacements, and fluid lag size, as well as for fracture re-initiation from secondary flaws. After fracture intersection, the hydraulic fracture growth mode changes from tensile to shearing. This contributes to increased injection pressure and to a reduction in fracture width. In the presence of pre-existing fractures, the fluid-driven cracks can be arrested or retarded in growth rate as a result of diversion of fluid flow into and frictional sliding along the pre-existing fractures. Frictional behaviour significantly affects the ability of the fluid to enter or penetrate the pre-existing fracture only for those situations where the fluid front is within a certain distance from the intersecting point. Importantly, fluid penetration requires higher injection pressure for frictionally weak pre-existing fractures. Fracture re-initiation from secondary flaws can reduce the injection pressure, but re-initiation is suppressed by large sliding on pre-existing fractures that are frictionally weak. [source] Fluid flow and heat transfer of natural convection at a slightly inclined, upward-facing, heated plateHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2002Fumiyoshi Kimura Abstract Natural convective flows over upward-facing, inclined plates were investigated experimentally, with an emphasis on the role of opposing flows that appear over the plates inclined slightly from the horizontal line. The flow fields over the plates and the surface temperatures of the heated plates were visualized with both dye and a liquid-crystal thermometry. The results showed that both the descending and ascending flows appeared over the plates when the inclination angles of the plates were less than 15°. The two flows collided with each other at a certain distance from the plate edge, and then detached from the plate to become a thermal plume. It was found that the above distance was determined solely by the inclination angles and was independent of sizes and heat fluxes of the plates. The local heat transfer coefficients of the plates were also measured. The results showed that the heat transfer from the plate was enhanced by the occurrence of the descending flows. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(5): 362,375, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10036 [source] The nature of law as an interpretive practice and its associated modes of inquiryLEGAL STUDIES, Issue 4 2009Nathan Gibbs The paper provides a critical survey of certain methodological debates in the field of legal philosophy in order to assess their implications for legal research in general. Underpinning this survey is a concern to establish the independence and integrity of both legal practice and legal research in the light of the risks posed by preponderant forms of instrumental rationality. Thus, Brian Leiter's recent call for a ,naturalised' jurisprudence is criticised for the instrumentalist basis upon which he claims to privilege forms of legal research apparently ,continuous with' the natural and empirical social sciences. As against Leiter, it is argued that there are in fact a range of distinct but interrelated modes of legal research. In this respect, the work of HLA Hart is interpreted as an example of a distinctively theoretical mode of inquiry into law. In addition, an account of the nature of a distinctively practical mode of legal inquiry is developed from a critique of Ronald Dworkin's excessively ,theoretical' reading of the interpretive character of legal practice. A constitutive practical feature of both modes of inquiry is their capacity to take up a certain distance from any exclusive concern with instrumental or pragmatic action. [source] The gradual covering problemNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 6 2004Zvi Drezner Abstract In this paper we investigate the gradual covering problem. Within a certain distance from the facility the demand point is fully covered, and beyond another specified distance the demand point is not covered. Between these two given distances the coverage is linear in the distance from the facility. This formulation can be converted to the Weber problem by imposing a special structure on its cost function. The cost is zero (negligible) up to a certain minimum distance, and it is a constant beyond a certain maximum distance. Between these two extreme distances the cost is linear in the distance. The problem is analyzed and a branch and bound procedure is proposed for its solution. Computational results are presented. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004 [source] Numerical computation of a singular-state subarc in an economic optimal control modelOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 4 2006H. J. Oberle Abstract In this paper, optimal control problems (OCP) are considered which are characterized by a nonsmooth-state differential equation. More precisely, it is assumed that the right-hand side of the state equation is piecewise smooth and that the junction points between smooth subarcs are determined as roots of a state-dependent switching function. For this kind of OCP necessary conditions are developed. Special attention is paid to the situation that the switching function vanishes identically along a nontrivial subarc. Such subarcs, which are called singular-state subarcs, are investigated with respect to the necessary conditions and to the junction conditions. In this paper, we assume that the switching function is of first order with respect to the control. The theory is applied to an economic optimal control model due to Pohmer (Mikroökonomische Theorie der personellen Einkommens- und Vermögensverteilung. Studies in Contemporary Economics, vol. 16. Springer: Berlin, 1985), which describes the personal income distribution of a typical consumer, who wants to maximize the total utility of his lifetime by controlling the consumption, the rate of the total time used for working, and the rate of working time used for education and extended professional training. The state variables are the human capital and the capital itself. The utility function contains different parts which represent the influence of consumption, time of recreation, and human capital. Into this problem a parameter enters which describes the interest rate of capital. It is obvious that this parameter in general will differ for positive and negative values of the capital. Thus, the resulting OCP in a natural way becomes a nonsmooth one. For this problem, the necessary conditions are derived and numerical solutions are presented which are obtained by an indirect optimal control method. It turns out that for a certain distance of the positive and negative interest rate, the optimal solution contains a singular-state subarc. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||