Showing papers by "University of Leeds published in 1977"

On the Formation of Travel Demand Models and Economic Evaluation Measures of User Benefit

Abstract: This paper examines a variety of issues within the context of two main themes: the formation of travel demand models and economic evaluation measures which are mutually consistent within a theory of rational choice; and a consideration of the structure of models which are representations of the trip decision process over several dimensions: location, mode, and route. Random utility theory is invoked to explore both the role and properties of composite costs or index prices in the ‘recursive’ approach to the structuring of travel choice models, and their significance in the economic evaluation problem. It is shown that the specification of these costs must be made very precisely, with respect to the demand model form chosen, in order to retain the underlying assumption that the traveller is an optimal decisionmaker. It is argued that the structure of ‘simultaneous’ models currently in use is inconsistent with the form of utility function assumed to generate those models. Furthermore, it is shown that the ‘...

Storage of elastic strain energy in muscle and other tissues

Abstract: Storage of strain energy in elastic materials has important roles in mammal running, insect jumping and insect flight. The elastic materials involved include muscle in every case, but only in insect flight is the proportion of the energy stored in the muscle substantial.

A monohydroxylated metabolite of tamoxifen with potent antioestrogenic activity

Abstract: The oestrogenic and antioestrogenic properties of tamoxifen and its monohydroxylated (monohydroxytamoxifen) and dihydroxylated (dihydroxytamoxifen) metabolites have been investigated in the immature rat. Whether administered orally or subcutaneously, monohydroxytamoxifen was more active than tamoxifen as an antioestrogen. Dihydroxytamoxifen was less active than tamoxifen as an antioestrogen, but this derivative alone was unable to induce a uterotrophic response. Both metabolites of tamoxifen were potent inhibitors of the binding of [3H]oestradiol to oestrogen receptors in vitro. It is possible that the metabolites play a supportive role in the antioestrogenic activity of tamoxifen. The potent activity of monohydroxytamoxifen in vivo and in vitro suggests that this compound could be an important new tool for the subcellular investigation of oestrogenic and antioestrogenic events.

On Time Versus Space

Abstract: It is shown that every deterministic multitape Turing machine of time complexity t(n) can be simulated by a deterministic Turing machine of tape complexity t(n)/logt(n). Consequently, for tape constructable t(n), the class of languages recognizable by multitape Turing machines of time complexity t(n) is strictly contained in the class of languages recognized by Turing machines of tape complexity t(n). In particular the context-sensitive languages cannot be recognized in linear time by deterministic multitape Turing machines.

The development of endomycorrhizal root systems: i. spread of infection and growth‐promoting effects with four species of vesicular‐arbuscular endophyte

Abstract: SUMMARY Four vesicular-arbuscular endophytes were inoculated into onions cultured in soil in a growth chamber. Dry weight, root length, infected root length, phosphorus content and quantity of external mycelium were measured at intervals. Three endophytes produced similar hyphal inflows, growth increments and external mycelium. One endophyte produced no growth increase in the host, and had little external mycelium and slow increase in percentage infection.

Isothermal Elastohydrodynamic Lubrication of Point Contacts: Part IV—Starvation Results

Abstract: The influence of lubricant starvation on minimum film thickness was investigated by moving the inlet boundary closer to the contact center. The following expression was derived for the dimensionless inlet distance at the boundary between the fully flooded and starved conditions: m* = 1 + 3.06 ((R/b)(R/b)H) to the power 0.58, where R is the effective radius of curvature, b is the semiminor axis of the contact ellipse, and H is the central film thickness for fully flooded conditions. A corresponding expression was also given based on the minimum film thickness for fully flooded conditions. Therefore, for m m*, starvation occurs and, for m m*, a fully flooded condition exists. Two other expressions were also derived for the central and minimum film thicknesses for a starved condition. Contour plots of the pressure and the film thickness in and around the contact are shown for the fully flooded and starved lubricating conditions, from which the film thickness was observed to decrease substantially as starvation increases.

Influence of the Level of Nitrate Nutrition on Ion Uptake and Assimilation, Organic Acid Accumulation, and Cation-Anion Balance in Whole Tomato Plants

Abstract: Tomato plants ( Lycopersicon esculentum L. var. Ailsa Craig) were grown in water culture in nutrient solution in a series of 10 increasing levels of nitrate nutrition. Using whole plant data derived from analytical and yield data of individual plant parts, the fate of anion charge arising from increased NO 3 assimilation was followed in its distribution between organic anion accumulation in the plant and OH − efflux into the nutrient solution as calculated by excess anion over cation uptake. With increasing NO 3 nutrition the bulk of the anion charge appeared as organic anion accumulation in the plants. OH − efflux at a maximum accounted for only 20% of the anion charge shift. The major organic anion accumulated in response to nitrate assimilation was malate. The increase in organic anion accumulation was paralleled by an increase in cation concentration (K + , Ca 2+ , Mg 2+ , Na + ). Total inorganic anion levels (NO 3 − , SO 4 2− , H 2 PO 4 − , Cl − ) were relatively constant. The effect of increasing NO 3 nutrition in stimulating organic anion accumulation was much more pronounced in the tops than in the roots. It is suggested that increasing the level of NO 3 nutrition to tomato plants stimulates cation uptake and translocation as counter-ions are required to accompany NO 3 − ions to the upper plant parts, the major site of NO 3 reduction. On NO 3 reduction, the resulting stoichiometric accumulation of organic anions is balanced by the cations originally accompanying NO 3 − ions. Organic anions and cations are largely retained in the upper plant parts. The results suggest that only a small fraction of the total K absorbed by the roots can be translocated downward from the leaves to the roots in the phloem sap. The possible extent of K recirculation is thus low.

Supramolecular structure of a high‐modulus polyaromatic fiber (Kevlar 49)

Abstract: The supramolecular organization of the aromatic polyamide fiber Kevlar 49 has been studied using a combination of electron diffraction and electron microscope dark-field image techniques. The dark-field images derived using selected reflections from longitudinal sections exhibit axial banding of two main types having periodicities of 500 and 250 nm. Careful analysis, including tilting experiments, conclusively shows that the supramolecular architecture of these fibers consists of a system of sheets regularly pleated along their long axes and arranged radially.

Allometry of the limbs of antelopes (Bovidae)

Abstract: The principal bones, muscles and tendons in the legs of seven species of antelope of varying size have been measured, and aliometric equations have been derived. Some data published by Sachs (1967) have also been analysed. Most of the exponents of the aliometric equations agree well with McMahon's (1973, 1975a) theory of elastic similarity: lengths are approximately proportional to (mass)0˙25, diameters to (mass)0˙375 and cross-sectional areas to (mass)0˙75. However, some of the exponents for diameters and areas in the hind leg are significantly different from those predicted by the theory. The results are discussed in conjunction with previously published data on fast galloping. It is shown that maximum stresses in bones, muscles and tendons are probably more or less independent of body mass in antelopes galloping at their maximum speed. The tensile stresses in the tibia and humerus approach the tensile yield strength of bone. The total work which is done by the muscles in each stride at maximum speed and the energy saved by elastic storage are probably more or less proportional to body mass. The deviations of some of the allometric exponents for diameter from the expected value of 0middot;375 are partially explained.

Some Physiological Aspects of Copper and Zinc Tolerance in Agrostis tenuis Sibth.: Cell Elongation and Membrane Damage

Abstract: Three clones of Agrostis tenuis Sibth. were studied with respect to the effects of Zn and Cu on the growth of root segments excised from the zone of cell elongation. Elongation growth in segments from a Cu-tolerant and a Zn-tolerant clone was inhibited to a lesser extent by Cu and Zn respectively than was the growth of a clone which was not tolerant to these metals. Concentrations of Cua+ which inhibited root growth also caused leakage of K+ from the cells but toxic concentrations of Zn2+ did not induce K+ leakage. Copper induced a higher rate of K+ leakage at 25 than at 0 °C. The implications of these results for the site of the toxic effects of Zn and Cu and the nature of the resistance mechanisms are discussed.

Vascular and glomerular changes in the ageing kidney.

Abstract: Glomerular size, shape and number were examined in 44 human kidneys obtained at necropsy. Intrarenal vascular appearances were assessed histologically and by post-mortem angiography. The mean cross-sectional area of glomeruli varied nearly three-fold and glomerular number varied more than three-fold when kidneys from different adult subjects were compared but kidneys from the same subject resembled one another in glomerular size and number. A significant negative correlation existed in the adult between glomerular number and dimensions. Glomerular numbers in the few immature kidneys studied were similar to those in adult kidneys but glomeruli were smaller. Glomerular numbers tended to decline as age and severity of age-related vascular changes increased but correlation was poor. The possibility remains that glomerular involution in the senescent kidney occurs independently of events in the vessels. In men, but not in women, totally hyalinised glomeruli were observed more frequently with increasing age but their presence did not appear to be related to the degree of vascular change. In the senescent kidney, glomerular lobulations tended to disappear. This, together with glomerular loss, must result in a reduction in the area available for filtration. Assessments of total glomerular surface area should take account of glomerular shape and dimensions as well as numbers.

Intracranial pressure changes in neurosurgical patients during hypotension induced with sodium nitroprusside or trimetaphan.

Abstract: Intracranial pressure has been measured in 45 patients undergoing neurosurgery during the induction of deliberate hypotension using either sodium nitroprusside or trimetaphan. A statistically significant increase in intracranial pressure (ICP) occurred during the early stages of the infusion of nitroprusside in normocapnic patients. A non-significant increase in ICP was obtained in hypocapnic patients. The mean ICP increased from 6.3 mm Hg to 11.7 mm Hg when the arterial pressure was reduced slightly, but the response in individual patients varied widely (range -1.6 mm Hg to +20.9 mm Hg). When the arterial pressure (BP) had decreased to 70% of the value existing before infusion of nitroprusside, mean ICP returned to control values and thereafter decreased with further reductions in BP. In patients rendered hypotensive with trimetaphan, there was no change in mean ICP but two patients showed moderate increases (+9.3 mm Hg and +5.7 mm Hg). The mechanism of the increase in ICP with nitroprusside is thought to be expansion of the intracranial blood volume as a result of cerebral vasodilatation. Trimetaphan does not usually produce ICP changes except when intracranial compression is severe, for in these circumstances a small change in intracranial blood volume consequent upon autoregulation may trigger an increase in ICP.

Breeding site specificity in the domestic species of Drosophila

Abstract: The emergences of domestic Drosophila species from fruits and vegetables in a market are analysed by partitioning the species diversity. Confidence limits are determined for the components of diversity.

Annual fluctuations in the recruitment of Patella vulgata L.

Abstract: In an attempt to identify the causes of the natural population fluctuations on British rocky coasts, an exploratory programme on the recruitment fluctuations of certain ‘key species’ has been operating for several years. The choice of species and the emphasis upon their recruitment have been discussed elsewhere (Lewis, 1976) and were justified as the most economical means of gaining the ability to (a) ‘explain’ major changes in the general character of rocky shore communities, and (b) make predictions about natural events against which to detect regional or temporal consequences of man-made changes in water quality. Mussels, barnacles and limpets are being studied but it is the last with which most interpretative progress appears to have been made, and this paper is concerned solely with Patella vulgata L. It is, however, essentially a preliminary report in a continuing study and it illustrates the practical and interpretative problems inherent in formulating and substantiating hypotheses in this type of work.

Analysis of fields and inductances in air-cored and iron-cored synchronous machines

Abstract: A consequence of the projected trend in turbine-generator design towards large airgaps, airgap windings without slots, and superconducting windings, is a progressive change in the nature of the machine from `iron-cored' to `air-cored'. A general analysis of fields and winding inductances that is applicable to all configurations is presented. The underlying unity of the various types is brought out, and particular attention is given to a comparison of the conventional design and the fully air-cored (superconducting) machine. In a companion paper the comparative design and performance analysis of air-cored and iron-cored synchronous machines is discussed.

Defensible Space: A Theoretical and Empirical Appraisal:

Abstract: The assertion that where crimes take place is to a large extent determined by physical lay-out has been made forcibly by Oscar Newman in 'Defensible Space', where particular attention is given to t...

An algorithm for determining all extreme points of a convex polytope

Abstract: An algorithm for determining all the extreme points of a convex polytope associated with a set of linear constraints, via the computation of basic feasible solutions to the constraints, is presented. The algorithm is based on the product-form revised simplex method and as such can be readily linked onto standard linear programming codes. Applications of such an algorithm are reviewed and limited computational experience given.