Stochastic user equilibrium assignment with elastic demand

It is well-known that, in deterministic user equilibrium assignment, it is straightforward to allow for elastic demand. The research described in this paper sets out to show that the same is true for stochastic user equilibrium assignment with elastic demand (SUEED). It presents a new objective function for SUEED, and a simple solution algorithm that can be implemented by only a minor modification to existing assignment software. A numerical example illustrates the working of the algorith

Horticultural Growing Media and Plant Nutrition (a)

End of Project ReportThis publication reports on four different studies under the overall title: (1)The effect of type and rate of controlled release fertiliser on the performance of hardy nursery stock in containers; (2) Analysis of substrates containing controlled release fertilisers; (3)The effect of water quality and rate of lime on the growth of nursery stock plants in peat; (4)Effect of suSCon Green on the growth of nursery stock plantsEuropean Union Structural Funds (EAGGF

Effect of Peat Grade, Irrigation System and Nutrition on the Production of Nursery Stock in Closed Systems

End of Project ReportContainerised nursery stock plants in Ireland are almost exclusively produced in peat growing media using controlled release fertilisers and are irrigated by means of overhead spraylines with the drainage water going to waste. Concern about nutrient pollution and the need to use water and nutrients more efficiently may lead in the future to regulations about capturing and re-cycling drainage water. This would particularly apply where nutrients are incorporated in the irrigation as in liquid feeding or where hard water is being acidified to neutralise bicarbonate. These experiments were started to study the performance of nursery stock plants in closed systems and to compare ebb and flood and capillary irrigation with overhead spraylines. A comparison of a liquid feeding regime as against the use of controlled release fertilisers was also included. The use of fractionated peat allows peat substrates with a wide range of physical properties to be prepared by using graded fractions or blends. It was thought desirable to include these in the experiments as there may well be interactions between irrigation systems and substrate propertiesEuropean Union Structural Funds (EAGGF

ALE Defeasible Description Logic

One of Semantic Web strengths is the ability to address incomplete knowledge. However, at present, it cannot handle incomplete knowledge directly. Also, it cannot handle non-monotonic reasoning. In this paper, we extend ALE Defeasible Description Logic with existential quantifier, i.e., ALE Defeasible Description Logic. Also, we modify some parts of the logic, resulting in an increasing efficiency in its reasoning

Closures and fairness in the semantics of programming logic

AbstractWe use the notions of closures and fair chaotic iterations to give a semantics to logic programs. The relationships between the semantics of individual rules and the semantics of the whole program are established and an application to parallel processing is mentioned. A chaotic fixed point theorem is given, which carries the non-determinism inherent to resolution. Finally, we introduce a general definition of finite failure and the concept of fair SLD resolution, and show that this procedure is sound and strongly complete with respect to both success and finite failure, thus extending a result of Apt and Van Emden (1982)

The use of tensiometers to control the irrigation of nursery stock in containers.

End of Project ReportThe use of digital tensiometers to control the irrigation of nursery stock in containers was studied over a three year period. Over this time the tensiometers performed satisfactorily and successfully automated the irrigation of the plants. The results indicate the feasibility of using them to control nursery stock irrigation under Irish conditions. An irrigation tension of 50 hPa to trigger an irrigation period resulted in larger plants than those grown under drier regimes with irrigation tensions of 100 and 200 hPa. Measurements of stomatal resistance indicated that the plants in the drier regimes were growing under greater moisture stress. The drier regimes reduced the number of irrigations and also the overall usage of water. They reduced plant size but did not impair plant appearance. It may be possible to use this approach in the future to control plant growth. There was no difference in performance between plants gown with ebb and flood irrigation and those irrigated via overhead spraylines. The ebb and flood system gave a considerable reduction in water use.European Union Structural Funds (EAGGF

Economic aspects of the production and marketing of hardy nursery stock

End of Project ReportA census of the Nursery Stock industry, carried out in autumn 1997, valued the sales of plants produced by the industry in 1996 at £18.8m. In the period since a previous census in 1994 field production of nursery stock expanded by 17% while the production of container plants shifted towards the greater use of protected cultivation. Employment in the industry rose by 28% to 912 full time equivalent jobs. Kildare was predominant in the production of containerised plants while Tipperary was the most important county for field production. Together, these two counties produced nearly half the value of the industry. Together with Cork, Dublin, Kilkenny and Wicklow they accounted for three quarters of the value of the industry. The industry was concentrated in that the largest 10% of the nurseries produced 59% of the value of the industry. As nursery size increased, the value of sales output per person rose sharply. Larger nurseries were also more productive per unit area. Exports were valued at £3.45m and imports at £2.22m. The main lines exported were ornamental shrubs followed by liners and deciduous trees. Two thirds of the exports were destined for Great Britain with the remainder going to Northern Ireland. Exporting was even more concentrated than production with the largest 10% of the nurseries providing 83% of the exports. The main imports were deciduous trees and liners. Two thirds of the imports originated from the continent and the remainder were from Great Britain. Small nurseries reported that capital and profitability were the principal factors limiting expansion of their nurseries. Larger nurseries however placed the availability of suitable staff as the main limiting factor. The most common difficulty reported by exporters was the cost of transport and a number of problems relating to the difficulties that individual nurseries or small groups have in supplying a large, discerning and relatively distant market. This underlined the need for increased co-ordination and co-operation in the future

The Irish Hardy Nursery Stock Industry: Recent Trends and Competitive Position.

End of Project ReportTh Irish Hardy Nursery Stock (HNS) industry has grown considerably in recent times. For the industry to maintain this level of growth it must remain competitive, particularly relative to the UK and the Netherlands, Ireland's main trading partners for HNS. Consequently, the objectives of this research were to (i) establish the size and value of the Irish HNS industry in 1999/2000, and (ii) examine the relative competitiveness of the Irish HNS industry, using profitability and value as indicators of competitiveness. A census of the Irish HNS industry was carried out between September 2000 and June 2001 to establish the size and value of the industry. The results of the census showed that the net value of plants produced on Irish nurseries amounted to €30.6m in 1999, an increase of €6.8m from €23.4m at the last census in 1996. In the same period the total area devoted to HNS production also increased from 391 ha in 1997 to 465ha in 1999. Kildare remains the most important county in the industry in terms of value because of the large area devoted to outdoor containerised production and production under protection. In terms of competitiveness, unpaid labour (imputed) had a significant effect on profitability levels for the three countries. When an imputed charge for unpaid labour was included in the analysis, the UK and Ireland had relatively higher Net Nursery Income (NNI) than the Netherlands. However, when the imputed charge for unpaid labour was excluded from the analysis, Ireland and the Netherlands had relatively higher NNI values than the UK. Firm size and mechanisation levels, were examined as possible sources of inter-firm variations in costs of production and profits. Economies of scale appeared to be evident as nursery size increased from `small' to `medium' and dissipated as nursery size increased from `medium' to `large'. This indicated that the minimum economic size for HNS production appeared to be relatively low. Based on the observed relationship between labour productivity and mechanisation levels, it is possible to infer that future mechanisation of the Irish industry may provide a partial solution to labour availability problems. Although the Irish HNS industry showed a competitive cost advantage, the low added value content of the Irish product is not a reassuring sign for the industry. The research revealed that the competitive potential of the industry in the Netherlands, based on relative value-added properties, was ahead of the Irish and UK industries. However, the Netherlands has not fully succeeded in converting this potential into competitive performance in the Irish market for HNS. The Irish HNS industry remains the largest supplier of HNS to the domestic market, although HNS available from the Netherlands was seen as given better value. In order for the Irish industry to remain competitive in the future the competitive strategies which the industry adopts must be re-evaluated. Distinct market segments were observed in the Irish market, which offers potential for a focused competitive strategy, which may suit smaller specialist producers. The critical buying criteria identified and subsequent relative performance of the Irish industry should provide the information, which is required for a competitive strategy of differentiation

Optimising Nutrition Of Containerised Nursery Stock

End of Project ReportIrish peat, used as a growing medium in horticulture, tends to have a higher state of decomposition and a higher potential buffering capacity than some of the younger peats from Scandinavian or Baltic countries. Particularly where hard water, with high bicarbonate content, is used for irrigation this could be an important property in giving the peat greater stability with respect to pH levels throughout the cropping period. It may also influence the optimum rate of lime to be applied to adjust the pH prior to cropping. The effect of peat type on the performance of nursery stock plants, Azalea and Hebe in 2-litre containers, was studied when irrigated with both soft and hard water and with different rates of lime in the peat growing medium. When irrigated with hard water, the rate of pH increase was less with relatively decomposed Irish peat than with younger Baltic peats. Using Irish peat, a rate of dolomitic lime addition to the peat of 4 kg/m3 was best for Hebe when irrigated with soft water. Irrigating with hard water the lime rate could vary between 2 and 4 kg/m3 without affecting plant performance. With the Baltic peats, increasing the rate of lime addition above 2 kg/m3 tended to reduce growth of Hebe. Azalea gave better results when irrigated with soft water. In hard water areas therefore it is advisable, if possible, to collect rain water from a greenhouse roof for irrigation purposes. A zero rate of lime gave inferior results with Azalea. With hard water a rate of 1 kg/m3 was optimum. With soft water this could be increased to 2 kg/m3 without damage. New formulations of the controlled release fertiliser (CRF) have been introduced recently. An experiment was carried out to evaluate the CRFs available in Ireland for the production of containerised nursery stock over a 12 month period. The effect of rate of CRF was also studied. Experiments were also located in the Colleges of Horticulture in Warrenstown and Kildalton. All the CRFs in these experiments produced acceptable results in terms of plant performance. There were differences between the CRFs but these were not consistent between the experiments. The vigorous species Lonicera pileata and Escallonia macrantha responed positively to rates of CRF up to 8 kg/m3. The conifer, Thuja plicata gave no response to rates above 6 kg/m3. In an experiment over two seasons using 20 nursery stock species, a liquid feeding system resulted in heavier plants of most species than did one based on a controlled release fertiliser.European Union Structural Funds (EAGGF