REDUCTION OF STATE VARIABLE DIMENSION IN STOCHASTIC DYNAMIC OPTIMIZATION MODELS WHICH USE TIME-SERIES DATA

Statistical procedures are developed for reducing the number of autonomous state variables in stochastic dynamic optimization models when these variables follow a stationary process over time. These methods essentially delete part of the information upon which decisions are based while maintaining a logically consistent model. The relatively simple linear autoregressive process as well as the general case is analyzed and the necessary formulae for practical application are derived. Several applications in agricultural economics are discussed and results presented which quantify the relative amount of information sacrificed with the reduction in number of state variables.Research Methods/ Statistical Methods,

MEASURING AND EXPLAINING THE DECLINE IN U.S. COTTON PRODUCTIVITY GROWTH

Tornquist input quantity indices were used to derive total and partial factor productivity measures for U.S. cotton across time, region, and scale. Total factor productivity for U.S. cotton increased .2 percent per year between 1974 and 1982. Partial productivity measures revealed that yield growth was about .6 percent and input use grew about .4 percent per year. Cotton enterprises in Alabama and Mississippi gained and those in the Texas High Plains lost competitive advantage relative to California. In 1982, very large (1750-5900 acres) and large (950-1749 acres) cotton enterprises were 2 percent more productive than medium-size enterprises (570-949 acres).Productivity Analysis,

ECONOMIES OF SIZE IN U.S. CROP PRODUCTION

Crop Production/Industries,

Roles, service knowledge and priorities in the provision of palliative care: a postal survey of London GPs

Objectives: To explore general practitioners' (GPs) current involvement in and attitudes towards the provision of palliative care in primary care. Methods: Postal survey of 356 London-based GPs, assessing attitudes towards palliative care provision, district nursing and specialist palliative care services, and priorities for future service development. Results: Currently, 65% of GPs were providing palliative care to patients on their list; 72% agreed or strongly agreed palliative care was a central part of their role; and 27% wanted to hand care over to specialists. Most GPs (66%) disagreed with the statement that 'palliative care is mainly district nursing (DN) work'. Many were unaware of out-of-hours DN and specialist palliative care services. Multi-variable analysis found four GP characteristics - larger practice size, more years experience as a GP, receipt of palliative care education, and current provision of palliative care - were associated with agreement that palliative care was central to a GP's role. Conclusion: A minority of NHS GPs in London would rather have no involvement in palliative care in primary care. Knowledge of current services for palliative care is generally poor among GPs. These findings highlight potential gaps in services, particularly in small practices. Specialists will need to consider these factors in working with GPs to develop primary palliative care and to enable greater access to specialist palliative care

Accurate measurement of telemetry performance

Performance of high rate telemetry stations used in the Deep Space Network is verified. Measurement techniques are discussed

Increasing security of supply by the use of a local power controller during large system disturbances

This paper describes intelligent ways in which distributed generation and local loads can be controlled during large system disturbances, using Local Power Controllers. When distributed generation is available, and a system disturbance is detected early enough, the generation can be dispatched, and its output power can be matched as closely as possible to local microgrid demand levels. Priority-based load shedding can be implemented to aid this process. In this state, the local microgrid supports the wider network by relieving the wider network of the micro-grid load. Should grid performance degrade further, the local microgrid can separate itself from the network and maintain power to the most important local loads, re-synchronising to the grid only after more normal performance is regained. Such an intelligent system would be a suitable for hospitals, data centres, or any other industrial facility where there are critical loads. The paper demonstrates the actions of such Local Power Controllers using laboratory experiments at the 10kVA scale

Does plant morphology influence fish fauna associated with seagrass meadows?

Three distinct seagrass habitats were sampled to determine whether fish assemblages differed between meadows comprising of different seagrass species with different morphological characteristics and whether plant morphology influences species assemblages. Three seagrass habitats consisting of Posidonia sinuosa, Posidonia coriacea and meadows of a mixture of P. coriacea and Heterozostera tasmanica in the Success Bank region, off the coast of Fremantle, Western Australia were selected. For each habitat, sampling was carried out using a 1m wide beam trawl over a distance of 50m at six replicated locations, on three occasions between June and September 2002. Seagrass samples were collected at each location. On each sampling, occasion a 0.025m2 quadrat was used to collect data on leaf area index (LAI), seagrass density and biomass, leaf width and length, and epiphytic algal biomass. MDS ordinations and ANOSIM showed that P. sinuosa habitats contain a significantly different composition of fish species to P. coriacea habitats (with or without H. tasmanica). Species composition was similar in P. coriacea on its own or mixed with H. tasmanica. SIMPER showed that the; differences between P. sinuosa and the P. coriacea habitats reflected the greater abundances of Stigmatopora argus, Siphonognathus radiatus and Scobinichthys granulatus, whereas Stigmatopora nigra was restricted to the P. coriacea habitats only. ANOVA demonstrated that total densities and biomass of fish and species richness were greatest in P. simwsa, while little difference occurred for those variables between the twn P. coriacea habitats. ANOVA indicated that densities of S. argus and Siphamia cephalotes did not differ between habitats, while densities of S. radiatus and S. nigra differed between P. sinuosa and the P. coriacea habitats. Densities of S. granulatus differed only between P. sinuosa and P. coriacea with H. tasmanica. Seagrass leaf density, leaf area index (LAI), leaf width, dry seagrass biomass and dry epiphytic biomass differed significantly among the three habitats, where as leaf length did not differ between these habitats. Regression analysis indicated that leaf area index influenced species richness, fish abundance and biomass, while leaf width influenced the abundance of S. argus and S. radiatus, and leaf density influenced the abundances of S. nigra and S. granulatus. BIOENV revealed that leaf width, leaf density and LAI influenced the fish composition in the seagrass meadows. Specific plant features appear to influence the fish assemblages associated with these habitats. Plant morphology also separated size-Classes of an abundant seagrass species supporting the nursery habitat theory. Artificial seagrass and live animals were used in laboratory experiments to evaluate habitat preference of the most abundant seagrass-associated fish species in the absence of predators and food, and to determine whether juvenile and/or adult-sized fish exhibit a preference for a particular seagrass morphology, corresponding to those of P. sinuosa, P. coriacea and H. tasmanica. Habitat preference experiments were conducted separately for each size class in three experimental aquaria containing artificial seagrass to simulate three different seagrass habitats. Each aquarium contained two different seagrass habitats and ten fish of the same size class. Habitat preference observations were made at hourly intervals over a 1 0-hour period. Three replicates were conducted for each experiment. The laboratory experiments showed that both juvenile and adult-sized S. argus had a strong preference towards the narrow leaves of P. coriacea and particularly H. tasmanica. However, the preference was more pronounced for the juvenile fish. Thus, seagrass morphology, specifically leaf width, appears to play a significant role in the habitat selection of S. argus. However, the ability to avoid predation is equally dependant on their body shape, size and ability to mimic their surroundings. The findings described in this study have shown that plant morphology appears to play a significant role in influencing fish faunal assemblages associated with seagrass meadows. The results of this study have clear implications for the environmental management of coastal marine ecosystems, highlighting the need to conserve seagrass meadows of different plant morphology to maintain the biodiversity of the fish assemblages in those regions

Landowner\u27s Responsibility to a Social Guest

The early common law, from which our present law has evolved, classifies persons on land into three basic categories: trespassers, licensees, and invitees. The classification determines the standard of care that is owed to these persons. The standard of care is a duty imposed upon the landowner because he is in control of his land, is presumed to know all about his land and any dangers or possible dangers that may exist, and is best able to prevent any harm to others. A social guest can fit into all three of the categories, as a trespasser, a licensee, or an invitee