Showing papers by "Cranfield University published in 1993"

Groundwater nitrate dynamics in grass and poplar vegetated riparian buffer strips during the winter

Abstract: Nitate retention in riparian buffer strips is well documented in summer periods, but the potential of winter retention within these zones is poorly documented. Two sites, grass (L.), and poplar ()-vegetated riparian strips, were investigated in southern England (River Leach). Groundwater flow was via subsurface pathways within the sites, NO concentration gradients and loading rates were calculated over the winter period. Nitrate retention was found to be linearly dependent on load rate. Nitrate retention occurred at the edge of the riparian zone. This was most obvious in the poplar site where all hillslope-derived NO was absorbed within the first 5 m of flow within the riparian strip. When loading rates into the sites increased, NO absorption migrated upslope from the riparian site. The poplar-vegetated riparian zone was found to be more resilient (99% retention of NO) than the grass-vegetated riparian zone (84% retention of NO) in the winter months. It is postulated that although vegetation has no active role in retaining NO in the winter, above-ground vegetative biomass does contribute C to the soil microbacterial biomass that is engaged in NO reduction in the winter months, this accounted for the greater efficiency of the poplar vegetated site.

Dilatational bands in rubber-toughened polymers

Abstract: A theory is advanced to explain the effects of rubber particle cavitation upon the deformation and fracture of rubber-modified plastics. The criteria for cavitation in triaxially-stressed particles are first analysed using an energy-balance approach. It is shown that the volume strain in a rubber particle, its diameter and the shear modulus of the rubber are all important in determining whether void formation occurs. The effects of rubber particle cavitation on shear yielding are then discussed in the light of earlier theories of dilatational band formation in metals. A model proposed by Berg, and later developed by Gurson, is adapted to include the effects of mean stress on yielding and applied to toughened plastics. The model predicts the formation of cavitated shear bands (dilatational bands) at angles to the tensile axis that are determined by the current effective void content of the material. Band angles are calculated on the assumption that all of the rubber particles in a band undergo cavitation and the effective void content is equal to the particle volume fraction. The results are in satisfactory agreement with observations recorded in the literature on toughened plastics. The theory accounts for observed changes in the kinetics of tensile deformation in toughened nylon following cavitation and explains the effects of particle size and rubber modulus on the brittle-tough transition temperature.

Role of floodplain sediments in reducing the nitrate concentration of subsurface run‐off: A case study in the Cotswolds, UK

Abstract: Discharge of groundwater from a limestone aquifer through floodplain sediments is associated with a large decrease in the nitrate concentration of the water. Results are presented to show that only a small amount of this reduction is caused by dilution of groundwater by water already present within the floodplain sediments; most of the effect is an active reduction process, most probably biological denitrification. The nitrate reduction process appears to operate independently of surface vegetation type and tends to be focused in specific regions of the floodplain where sediments are anaerobic and carbon-rich. The results suggest that active denitrification can operate throughout the winter, when nitrate concentrations in groundwater are at their highest and that the process remains effective even during periods of maximum run-off. The results show that undrained floodplains can be used as buffer zones to protect surface waters from groundwater polluted with agriculturally derived nitrate.

Developing a ‘European’ model of human resource management

Abstract: The concept of human resource management (HRM) has been much debated in the literature. Space limitations preclude an examination of that debate here, but it is clear that the concept developed initially from work in the United States of America in the 1960s and 1970s and since then has been adopted increasingly in the academic literature, by consultancy services and in organizational terminology. The terminology spread from the USA firstly into the developed English speaking world and recently - and more partially - into Europe. Is the concept, as opposed to the terminology, applicable in Europe? This paper argues that the organizational autonomy on which the subject is propounded in the United States is not espoused in Europe. A range of subject areas in which organizations in Europe are supported/constrained by external factors are analysed, thus challenging the validity of the American model. This raises the need to consider different conceptual approaches to HRM: a new model of the concept which woul...

An X-ray diffraction study of semiconductor and metallic vanadium dioxide

Abstract: Powder diffraction data for semiconductor and metallic states of vanadium dioxide are presented. The structures are refined by Rietveld methods using a monoclinic cell (a = 5.7529A, b = 4.5263A, c = 5.3825A, β = 122.61°) and space group P21/c for the room temperature data, and a tetragonal cell (a =4.5540A, c = 2.8557A) and space group P42/mnm for data collected at 400 K. The similarity between the corresponding X-ray diffraction patterns is discussed. The transition process from the monoclinic to tetragonal phase is investigated and initial evidence for the coexistence of phases over a small temperature range is presented.

PLIF Imaging of Fuel Fraction in Practical Devices and LII Imaging of Soot

Abstract: In this paper we discuss the development and application of 2D imaging methods for the study of fuel-air mixing and the in-situ measurement of soot in flames. Fuel imaging is based on planar laser-induced fluorescence (PLIF) with pulsed UV lasers. Fuel concentrations may be estimated from the fluorescence of common fuel components or through the addition of a fluorescent species or seed. PLIF of fuel is shown to be applicable to both premixed and non-premixed combustion. The choice of fluorescent seed and the role of interfering species, such as combustion derived polyaromatic hydrocarbons (PAH) and laser-induced incandescence from soot, are discussed. The application of the method is illustrated with an example of an isothermal mixing study in a gas turbine combustor sector rig and measurements in a simple flame. The results demonstrate that PLIF can achieve high spatial resolution, circa 0.4 mm, in a combustor with dimensions of order of 400 mm. The dynamic range of the measured intensities exceeds 1500 with typical signal-to-noise ratios of better than 100:1. A major source of interference in PLIF studies of non-premixed flames is laser-induced incandescence (LII) from soot particles. We discuss the role of LII both as an interference in PLIF imaging and as an imaging method for soot volume fraction. A detailed analysis of the physics of LII is presented on a theoretical model developed. Results from the model and supporting experimental data are presented. LII images from a highly turbulent sooting flame indicate that soot structures, probably in the form of thin sheets as small as 100 μm across, are formed through vortex mixing.

Corporate Financial Strategy

Abstract: Setting the context What does the share price tell us? Linking corporate and financial strategies Corporate governance and perceived risk Making the case Financial strategy and the corporate lifecycle-Start up businesses and venture capital rowth companies: marketing focused Mature companies-to divi or not? Declining businesses-a case for euthanasia? Financial instruments: the building blocks Types of financial instrument Dividends and buybacks Transactions and operating issues-Floating a company Acquisitions mergers and selling a business Restructuring a company Management buyouts and other leveraged transactions Strategic working capital management Executive compensation International corporate finance Appendices-Review of theories of finance Valuing options and convertibles Glossary Discount and option tables

Automated feature recognition from 2D drawings

Abstract: Automated feature recognition is likely to be an essential requirement for future integrated design and manufacturing systems. Most methods which have so far been proposed use as their input a solid model which represents only the purely geometric aspects of the design information. Much research is currently in progress on the augmentation of such models with technological and other lifecycle data to give what is referred to as a product model. The presence in such a model of design feature data, in particular, may make the recognition of manufacturing features easier in the future. On the other hand, little previous work has been reported on feature recognition from 2D drawings, which is the form in which the majority of design data currently exists. The paper describes an experimental system for this purpose. It has been designed to meet the automated process-planning requirements of today rather than tomorrow, and it has been demonstrated on a range of simple prismatic machined parts.

Resource Activity Mapping: the Value Chain in Service Operations Strategy

Abstract: This explores the use of the value chain concept suggested by Porter as a tool in establishing service operations strategy. The original model has been adapted to emphasise the operational context to produce a framework for considering service delivery to meet strategic objectives. The use of the revised model for examining resource allocation using a resource activity mapping technique within a workshop environment is described.

The essence of information systems

Abstract: Setting the scene what are information systems? issues in information systems integrating information systems and business strategy identifying business advantages from information systems creating an environment for success delivering the goods marshalling the information systems social issues.

Chapman-Jouguet Deflagrations

Abstract: Two types of quasi-steady high-speed deflagration have been observed experimentally. In the first place they are reaction-waves created in, and propagating through, rough tubes and tubes that contain obstacles; in the second place they are deflagrations created from established detonations by eliminating the transverse waves from the latter’s structure. Changes in tube roughness, obstacle size and tube diameter have no significant influence on the speeds at which the deflagrations propagate. These speeds are close to sonic relative to product gases flowing out of the reaction-waves, and both classes of deflagration are observed to travel at about one-half of the corresponding Chapman-Jouguet (CJ) detonation speed. A theoretical analysis has been carried out on a configuration that consists of a plane precursor shock-wave driven by a plane CJ deflagration. Results agree very well with observations and support the idea that, at least for the duration of these observations, this combination of shock and deflagration is controlled by the energetics of the reacting mixture.

A cognitive perspective on managers' perceptions of competition

Abstract: This paper focuses on the way managers perceive their competitive environment. Within a cognitive perspective it discusses why they might group similar competitors and considers whether they are attentive to all competing firms. The literature on similarity of perceptions between managers is reviewed. Interviews amongst managers in the North Sea off‐shore oil pumps industry revealed that they made sense of competition through a categorization process. None perceived the industry in the objective manner as economists suggest. Different perceptions as to the nature of competitions were found between managers, but more homogeneous perceptions were seen between managers in the same firm than between different firms.