36 research outputs found
A mathematical model for assessment of material requirements for cable supported bridges: implications for conceptual design
No full textRecent technological developments have led to improvements in the strengths of materials, such as the steel and wire ropes used in the construction of cable supported bridges. This, combined with technological advancements in construction, has encouraged the design of structures with increasing spans, leaving the question of material and environmental costs behind. This paper presents a refined
mathematical model for the assessment of relative material costs of the supporting structures for
cable-stayed and cable suspension bridges. The proposed model is more accurate than the ones published to date in that it includes the self weight of the cables and the pylons. Comparisons of material requirements for each type of bridge are carried out across a range of span/dip ratios. The basis of comparison is the assumption that each structure is made of the same material (steel) and
carries an identical design load, q, exerted by the deck. Calculations are confined to a centre span of a three-span bridge, with the size of the span ranging from 500 m to 3000 m. Results show that the optimum span/dip ratio, which minimises material usage, is 3 for a cable-stayed (harp type) bridge, and 5 for a suspension structure. The inclusion of the self weight of cable in the analysis imposes limits on either the span, or span/dip ratio. This effect is quantified and discussed with reference to
the longest cable-supported bridges in the world completed to date and planned in the future
Microplasma light tiles: thin sheet lamps for general illumination
No full textFlat, thin and lightweight lamps providing spatially uniform and dimmable illumination from active areas as large as 400 cm2 are being developed for general illumination and specialty applications. Comprising an array of low-temperature, nonequilibrium microplasmas driven by a dielectric barrier structure and operating at pressures of typically 400–700 Torr, these lamps have a packaged thickness <4 mm and yet produce luminance values beyond 26 000 cd m−2 with a luminous efficacy approaching 30 lm W−1. Third generation lamps, presently in limited production, offer a correlated colour temperature in the 3000–4100 K interval and a colour rendering index of 80. Current lamps employ Xe2 (λ ∼ 172 nm) as the primary emitter photoexciting a mixture of phosphors, and the pressure dependence of the wavelength-integrated fluorescence from the electronically excited dimer has been investigated with a vacuum ultraviolet spectrometer. In contrast to other promising lighting technologies, the decline in luminous efficacy of microplasma lamps with increasing power delivered to the lamp is small. For a 6 × 6 inch2 (∼225 cm2) lamp, efficacy falls <16% when the radiant output (luminance) is raised from 2000 cd m−2 to > 10 000 cd m−2.</jats:p
Environmental packaging
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The food packaging industry is a £300bn global industry growing at a rate of 12% per year and increasingly favouring polymer or polymer-based materials. This generates 58m tonnes of "plastic" packaging waste annually in the EU and poses significant challenges for management given existing legislative constraints and increasing concerns surrounding the environmental impacts. The government, consumers, food retailers and pressure groups are all driving the demand for biodegradable packaging from renewable resources that can be disposed of with reduced impacts to the environment. Green Peace has devised a pyramid classification system of "Poisonous Plastics", which ranks plastics in terms of their harmfulness to the environment. They are campaigning against the use of oil-based materials and advocating the take up of biodegradable materials.
The market for biodegradable food packaging is expanding rapidly but is still in its early stages of development and has not reached a critical mass to achieve significant market penetration. This is predominantly due to a lack of suitable materials that meet all environmental, functional and economical requirements. Whilst the long-term solution requires continued efforts in materials research and development, in the shorter term, changing working practices can abate the environmental impact of the industry.
This research project tackled the challenge of environmental packaging from several
directions:
A novel starch-based material was developed that would fill the current gap in the food packaging market and facilitate recovery of the used materials by home composting.
Using the sponsoring organisation as a case study, it was proved that by changing working practices by increasing rework and re-processing waste material for use in lower grade applications, both manufacturing costs and environmental impact can be reduced, thus benefiting both industry and the environment.
A Life Cycle Assessment of selected biopolymers and oil-based polymers confirmed Green Peace's damning view of PVC and highlighted the need to develop biopolymers further. A domestic composting study of a range of commercially available "biodegradable" polymer materials revealed that a number of biodegradable packaging materials may typically biodegrade well in industrial high-temperature composting systems but fail to biodegrade under a low-temperature home composting environment and thus alerted the potential pitfall in waste management of some biodegradable polymers.Pactiv Europe; Engineering and Physical Sciences Research Council (EPSRC
Crop production during the first course of an organic crop rotation trial in Denmark
No full textThree factors are included in a factorial field experiment: 1) fraction of grass-clover and pulses in the rotation (crop rotation), 2) catch crop (with or without catch crop), and 3) manure (with or without animal manure). Manure is applied as slurry in rates corresponding to 40 % of the nitrogen demand. Grain yields for three sites and three years of the experiment are presented for two four-course rotations. One rotation has a green-manure crop, which is replaced by winter wheat in the other rotation.
The use of manure significantly increased grain yield of the cereal crops in most cases. The positive effects of the catch crops were mainly observed in the spring cereals. The largest rotation yields were obtained in the crop rotation without a green manure crop. The positive effect of a green manure crop could not substitute for the yield decrease from leaving 25% of the area out of produc-tio
Recent developments in the fabrication and performance of low-cost microplasma lighting tiles
No full textOpen windrow composting of polymers: An investigation into the rate of degradation of polyethylene
No full textThe compostability of degradable polymers under open windrow composting conditions is explored within this paper. Areas for consideration were the use of, and impacts of, degradable polyethylene (PE) sacks on the composting process and the quality of the finished compost product. These factors were investigated through polymer weight loss over the composting process, the amount of polymer residue and chemical contaminants in the finished compost product, the windrow temperature profiles and a bioassay to establish plant growth and germination levels using the final compost product. This trial also included a comparative study of the weight loss under composting conditions of two different types of ‘degradable’ polymer sacks currently on the European market: PE and a starch based product. Statistical analysis of the windrow temperature profiles has led to the development of a model, which can help to predict the expected trends in the temperature profiles of open compost windrows where the organic waste is kerbside collected using a degradable PE sack
Whole-rotation dry matter and nitrogen grain yields from the first course of an organic farming crop rotation experiment
No full textThe possibilities for increasing total grain yield in organic cereal production through manipulation of crop rotation design were investigated in a field experiment on different soil types in Denmark from 1997 to 2000. Three experimental factors were included in the experiment in a factorial design: 1) proportion of grass-clover and pulses in the rotation, 2) catch crop (with and without), and 3) manure (with and without). Three four-course rotations were compared. Two of the rotations had one year of grass-clover as a green manure crop, either followed by spring wheat or by winter wheat. The grass-clover was replaced by winter cereals in the third rotation. Animal manure was applied as slurry in rates corresponding to 40% of the nitrogen (N) demand of the cereal crops.
Rotational grain yields of the cereal and pulse crops were calculated by summing yields for each plot over the four years in the rotation. The rotational yields were affected by all experimental factors (rotation, manure and catch crop). However, the largest effects on both dry matter and N yields were caused by differences between sites caused by differences in soils, climate and cropping history. The rotation without a green manure crop produced the greatest total yield. Dry matter and N yields in this rotation were about 10% higher than in the rotation with a grass-clover ley in one year of four. Therefore, the yield benefits from the grass-clover ley could not compensate for the yield reduction as a result of leaving 25% of the rotation out of production. There were no differences in dry matter and N yields in grains between the rotations, where either spring or winter cereals followed the grass-clover ley. The N use efficiency for ammonium-N in the applied manure corresponded to that obtained from N in commercial fertilizer. There were only very small yield benefits from the use of catch crops. However, this may change over time as fertility builds up in the system with catch crops
Optimization of multistage depressed collectors.
No full textRandom walk and genetic algorithm techniques have been implemented in a 3-D collector simulation code to automate the design optimization of multistage depressed collectors. An axisymmetric four-stage collector and an asymmetric two-stage collector have been optimized following both approaches. Procedures for the implementation of these methods in any suitable code and simulated performance of the collectors are demonstrated. The results show significant improvement in the collector performances due to optimization. A comparison between the optimum collector performances that were obtained using these methods has also been carried out
