• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 928
  • 670
  • 368
  • 42
  • 17
  • 7
  • 6
  • 4
  • 2
  • 1
  • Tagged with
  • 3453
  • 1162
  • 667
  • 562
  • 513
  • 512
  • 505
  • 504
  • 504
  • 475
  • 451
  • 371
  • 364
  • 269
  • 238
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Studies of the physical and economic effects of flooding in an agricultural area in south west Scotland

McDonald, A. T. January 1975 (has links)
No description available.

The role of prescribed burning moorland mangement in the Peak District

Harris, Michael Patrick Kevin January 2011 (has links)
The overall aim of this thesis was to develop a better understanding of the role of prescribed burning in moorland management within the Peak District National Park. These moorlands are dominated by heather (Calluna vulgaris (L.) Hull). Prescribed burning is a management tool that used routinely to manage moorland vegetation for grouse and sheep production. The aim is to remove the above-ground foliage and allow the Calluna to resprout from the burned stems. Normally such prescribed burning is done on a rotational matrix, and the aim is to provide a continual supply of moorland vegetation in different stages. This thesis attempted to answer the following questions: (a)How degraded are the moorlands in the Peak District, and does prescribed burning affect species density and restoration potential? (b) What are the environmental factors that influence the response of the plant communities, and how do the constituent species respond after prescribed fire?) (c) Does prescribed burning affect soil chemical properties? (d) What factors affect biomass reduction in prescribed fires on upland moorland? (e) What changes in above-ground biomass, carbon and nitrogen occur during this burning The context for this work is that British moors are high-priority habitats for conservation and it is increasingly recognized that they provide important ecosystem services (carbon accounting, water provision). A combination of field survey and experiments was used. A chronosequence study carried out on five replicate moors showed the vegetation was severely depauperate relative to the species that might be expected in pristine moorland vegetation. Moreover, the seed bank was also depauperate and propagules must be added to restore them. There was an increase in species richness immediately following prescribed burning with a subsequent decline with time. Multivariate analysis produced two gradients, a continuum from relatively lichen-rich vegetation to a graminoid-dominated one, and (b) a post-fire growth response of the Calluna. Calluna was the only species to show increasing growth after burning; all other species were reduced in the oldest vegetation. A similar study of soil properties showed that prescribed burning had a limited effect; some chemical properties changed with the burn-recovery cycle. In order to develop an improved method of prescribed burning the relationship between fire severity and both fire characteristics and environmental variables was assessed experimentally. The results were inconclusive but suggest that the burns with the highest temperatures were flash fires whereas the burns with the lower residence times were smouldering fires that probably converted more biomass to charcoal). A study of prescribed burns showed that the loss of biomass during prescribed burning was very variable and this almost certainly reflected a range of environmental and management factors. The burning method used in the Peak District is designed to minimize biomass loss and it was demonstrated that in some burns this was very successful. The accumulation of above-ground biomass was measured after burning and the oldest stands had much greater biomass values than literature ones and no sign of an asymptote at 50 years.

A multi-objective bi-level optimisation model of agricultural policy in Scotland

Konstantinos, V. January 2007 (has links)
Agricultural policy analysis can be visualised as a multiple objective hierarchical optimisation problem whereby sequential non-cooperative interactions between policy makers and farmers take place. The objectives and choices of policy makers will almost always diverge from the objectives and choices of farmers. This thesis shows how multi-objective genetic algorithms (MOGA) in conjunction with mathematical programming can be used for solving this type of problem. A positive mathematical programming (PMP) model is developed to capture the production choices of farmers, and its objective function parameters are estimated using the method of generalised maximum entropy. The PMP model is nested in, and controlled by, a MOGA which captures the process of multi-objective optimisation of policy decisions. The approach is illustrated using a case study taken from Scottish agricultural systems, where several socio-economic and environmental objectives for policy making are considered. Five types of policy instruments are examined: the current single payment scheme, a multi-payment scheme based on land use, an input taxation, a regulatory scheme and, a combination of the last three. For a selection of scenarios alternative Pareto-optimal solutions are discovered and tradeoffs between policy objectives are presented along with their associated production patterns. Two lines of conclusions are drawn: (1) the performance of the method suggests that it is well suited to dealing with real world applications of policy optimisation and, (2) the current agricultural policy may be sub-optimal in relation to most of the policy objectives examined; more effective policies are possible for Scottish agriculture.

Modelling mechanisms of change in crop populations

Partner, P. L. R. January 1995 (has links)
Computer-based simulation models of changes occurring within crop population when subjected to agents of phenotypic change, have been developed for use on commonly available personal computer equipment. As an underlying developmental principle, the models have been designed as general-case, mechanistic, stochastic models, in contrast to the predominantly empirically-derived, system-specific, deterministic (predictive) models currently available. A modelling methodology has evolved, to develop portable simulation models, written in high-level, general purpose code, allowing for use, modification and continued development by biologists with little requirement for computer programming expertise. The initial subject of these modelling activities was the simulation of the effects of selection and other agents of genetic change in crop populations, resulting in the computer model, PSELECT. Output from PSELECT, specifically phenotypic and genotypic response to phenotypic truncation selection, conformed to expectation, as defined by results from established analogue modelling work. Validation of the model by comparison of output with the results from an experimental-scale plant breeding exercise was less conclusive, and, owing to the fact that the genetic basis of the phenotypic characters used in the selection programme was insufficiently defined, the validation exercise provided only broad qualitative agreement with the model output. By virtue of the predominantly subjective nature of plant breeding programmes, the development of PSELECT resulted in a model of theoretical interest, but with little current practical application. Modelling techniques from the development of the PSELECT model were applied to the simulation of plant disease epidemics, where the modelled system is well characterised, and simulation modelling is an area of active research. The model SATSUMA, simulating the spatial and temporal development of diseases within crop populations, was developed. The model generates output which conforms to current epidemiological theory, and is compatible with contemporary methods of temporal and spatial analysis of crop disease epidemics. Temporal disease progress in the simulations was accurately described by variations of a generalised logistic model. Analysis of the spatial pattern of simulated epidemics by frequency distribution fitting or distance class methods was found to give good qualitative agreement with observed biological systems.

Molecular farming : production of pharmaceuticals in transgenic tobacco

Ahmad, Kafeel January 2011 (has links)
Molecular farming is an experimental application of biotechnology to modify crops in order to produce proteins and chemicals for medicinal and commercial interests. The vast majority in the developing world cannot afford the high cost of therapeutics produced by existing methods. We not only need to produce new therapeutics but also need to produce cheaper versions of the existing ones. Molecular farming could offer a viable option for this growing need for biopharmaceuticals. Part of the thesis deals with investigating ways to produce DesB30 form of human insulin in transgenic tobacco. The human insulin was synthesized in vitro as strep-tag II-mini-insulin fusion protein. Expression of mini-insulin by transgenic tobacco was confirmed by RT-PCR, western blotting and ELISA. However, sufficient levels of purified insulin could not be obtained to carry out further functional assays. Strategies for increasing the yield of insulin by transgenic tobacco are discussed and further increases in yield would need to be developed for this to become a viable and cost effective source of this important pharmaceutical. The second part of the thesis describes the production of a recombinant microbial polysaccharide in tobacco. Seven type 2 pneumococcal polysaccharide biosynthetic genes were expressed in a single tobacco plant, utilizing the plant Kex2 (Kexin protease 2) like protease system for multiple gene expression. Expression of these genes in transgenic tobacco was confirmed by RT-PCR and western blotting. Correct processing of the expressed proteins by the Kex2 protease system was confirmed. However, In planta production of type 2 polysaccharide could not be confirmed mainly as a result of high background from the wild type plant polysaccharide extracts. Strategies to overcome these issues are described. The usefulness of Kex2 protease system for multiple gene expression and metabolic pathways engineering is also discussed.

The Mobilisation and Transport of Sediments, Colloids and Phosphorous from Improved Temperate Grassland

Bilotta, Gary Stuart January 2008 (has links)
No description available.

Design, simulation and optimisation of a chimney-dependent direct-mode solar crop dryer (CDSCD)

Afriyie, John Kwasi January 2007 (has links)
No description available.

The drying of ryegrass seeds in deep layers

Nellist, M. E. January 1974 (has links)
Preservation of quality is the primary consideration in the drying of grass seed. Quality may be lost through destruction of seed viability and contamination by mould. Both result from the establishment, within the drying bed, of undesirable temperature and moisture conditions generated by the interaction of the seed and drying air. The work was based on the assumption that such moisture and temperature changes could be calculated from a knowledge of the heat and mass transfer properties of the seed and air, and that it would be possible to proceed from this physical framework to the calculation and imposition of biological restraints upon the selection of drying conditions. Experimental work was carried out with a large and a small seeded strain of ryegrass of similar shape and structure. For each strain, potential germination was expressed as a function of moisture content at threshing. Apparatus was developed for determining exposed layer drying curves at a wide range of air conditions and numerical procedures were developed for fitting the data to alternative diffusion equations. The fitted constants were expressed as functions of drying air temperature, humidity and seed initial moisture content. Effects on germination were expressed as functions of drying air temperature, exposure time and potential germination. A mathematical model of the drying process was programmed in FORTRAN and used the exposed layer constants to predict moisture and temperature changes in deep beds subjected to fluctuating inlet air conditions. The model was stable, economical in computing time and gave reasonable overall agreement with experimental deep bed results. Consistent over-cptimism of the. drying time predictions was identified with cumulative error in temperature changes. Possible revisions of the basic equations pose problems of integration beyond the scope of the present work.

The properties of ensiled crops and the design of silos

Wood, Jonathan G. M. January 1970 (has links)
The primary aim of the programme of research described in this thesis was to develop a method of calculating the pressures of ensiled materials for use in the design of silos. I have given in Chapter I the detailed records of the filling and unloading of a number of silos. Chapter 2 includes a literature survey and, the results of-my own field work on'the measurement of pressures wall strains and silage temperatures. Chapter 3 is concerned with the measurement of the properties of concrete silo staves and proposes quality standards, Chapter 4 reviews in detail the available information on the physical and biological properties of ensiled grain including my research on the varilations in grain density with pressure, moisture content and time. Chapter 5 similarily reviews the data on the, properties of ensiled grass and forage, including my research on the densities of these materials under the wide variety of conditions encountered in silos, I have used the results of my field and laboratory work and published material to develop in Chapter 6 a finite lamina calculation method for determining the pressures in and the capacities of silos, This enables the field conditions (with wide varlations in the maturity and moisture content of layers) to be simulated in detail and the optimum filling technique to be calculated. It also enables the filling rate required to limit overheating for given crop conditions to be determined.

Spray formation processes within agricultural flat fan nozzles

Zhou, Quanbao January 1996 (has links)
No description available.

Page generated in 0.0423 seconds