Feasibility Demonstration of Electrostatic Precipitation at 1700°F

An experimental high-temperature, high-pressure electrostatic precipitator module has been designed, fabricated and then evaluated in a gaseous environment having the characteristics anticipated for the combustion chamber of a system for generating electric power from the incineration of municipal solid wastes.

Stable positive and negative corona discharges were established in combustion gases from the burning of methanol and air (temperature and pressure approximately 1700°F and 100 psig, respectively) without any apparent deleterious effects due to thermal ionization and/or emission. At gas conditions of about 1700°F and 50 psig, positive polarity energization of the discharge electrode appeared superior to that of negative polarity in terms of voltage level that could be applied and electrical stability.

However, precipitator performance on removal of alumina dust injected under controlled conditions with the methanol fuel, showed negative polarity to be superior to positive polarity at the selected conditions of 1650°F and 100 psig which closely correspond to those required for optimum operation of the gas turbine presently under consideration. Removal efficiencies ranging from 25% for positive polarity to as high as 87% with negative polarity were measured.

In order to check whether materials having a low ionization potential would thermally ionize to such an extent that the voltage-corona current characteristics of the precipitator would be impaired, rendering it ineffective, potassium chloride salt in solution was injected with the fuel. Results indicated that amounts of approximately one part by weight of potassium ion in 2500 to 3000 parts by weight of gas at 1700°F tripled the current measured for a given voltage when compared to non-injection.

Although a limited test program was conducted, sufficient data were obtained to allow preliminary design and sizing of larger scale units.     

Infiltration and redistribution of perchloroethylene in partially saturated, stratified porous media

Contamination of the subsurface by nonaqueous phase liquids (NAPLs) is a widespread problem. To investigate the behavior of a nonspreading, dense NAPL (DNAPL) in the vadose zone, we conducted perchloroethylene (PCE) infiltration experiments in nominally 1- and 2-dimensional (D), stratified porous media. In addition, the usefulness and limitations of a multifluid flow simulator to describe PCE infiltration and redistribution under the experimental conditions were tested. The physical simulations were conducted in a column (1-D) and a flow container (2-D) which were packed with two distinct layers of coarse-grained sand and a fine-grained sand layer in between. Volumetric water and PCE contents were determined with a fully automated dual-energy gamma radiation system. While migrating through the drier parts of the coarse-grained sand layers, PCE appeared to wet the water–air interface rather than displacing any water. In the wetter parts of the porous medium, PCE displaced water and behaved as a true nonwetting fluid. PCE showed a limited response to gradients in capillary pressure and rather high values for the volumetric PCE content were measured in the fine-grained sand layers. This was attributed to the nonspreading nature of PCE. The multifluid flow simulator appeared to predict the initial PCE movement in the vadose zone reasonably well. However, the model was not capable of predicting the final amounts of PCE retained in either the unsaturated or saturated part of the flow domain, mainly because the simulator does not consider the nonspreading flow behavior of NAPLs.     

Pigeon homing: sun compass use in the southern hemisphere

Although the sun compass of birds is based on learning the sun's arc during development, it was unclear whether birds can use the sun when its apparent movement is reversed, in particular, whether northern birds that have been introduced into the southern hemisphere can use the southern sun. To answer this question, clock-shift experiments were performed with local homing pigeons in Auckland, New Zealand (37°S). In three fast-shift tests and two slow-shift tests, the experimental birds showed deflections from the untreated controls that were the mirror images of those observed in the northern hemisphere. These results clearly show that homing pigeons in New Zealand use a sun compass that is adapted to the situation in the southern hemisphere. The learning processes establishing the compensation mechanisms thus appear to be free of constraints concerning the direction of the sun's movement. Differences from recent findings with migratory birds, where the direction of celestial rotation proved of crucial importance for establishing the migratory direction, are discussed: the differences may arise from the different orientation tasks, in particular, from the involvement of innate information in establishing the migratory direction. Received: 13 November 1997 / Accepted after revision: 28 February 1998     

Identification of duchenne muscular dystrophy genomic probe P20 constant Taq1 fragment corresponding to the EcoRV and Msp1 polymorphisms

The majority of Duchenne and Becker muscular dystrophy cases are caused by deletions observable in Southern blots with cDNA probes for the gene. When the deletion includes polymorphic probes, they may be used to determine carrier status by deletion segregation analysis: non-inheritance of parental alleles, or heterozygosity. The polymorphic genomic probe P20 is deleted in a large percentage of probands. P20 hybridizes with two constant fragments of 6.7 and 0.8 kb in Taql digests. In a number of probands, only the larger P20 Taq1 fragment is deleted. This study demonstrates that this fragment corresponds with the polymorphic EcoRV and Mspl fragments of P20. Families in which the upper Taql fragment is deleted may be screened for carrier status using non-inheritance of parental alleles or heterozygosity of P20 in EcoRV or Mspl digests.     

Crop losses: The need to quantify the effects of pests,diseases and weeds on agricultural production

Crop losses caused by pests, including rodents and birds, and by diseases and weeds, are defined, and previous studies reviewed. Information about losses is needed to monitor the effects of pests and diseases on crop production, in individual countries and worldwide, important for food policy and economic reasons; to make decisions and allocate resources on the study, management and control of pests and diseases; to stimulate action against them; to provide guidelines for research on crop improvement to prevent pest and disease attack; and as a basis for judgement on the importance of pests, diseases and weeds in relation to agriculture and the environment.The causes of such losses, why information must be up to date, and methods of assessing pests, diseases, weeds and losses are examined. The part played by losses in the development and use of economic pest and disease control action thresholds is discussed, including pest, disease, crop, climatic, economic and farmer attitude factors. The types of relation between yield and pest and disease attack are reviewed, how to measure the relation in practice, how to obtain different amounts of attack, surveys of losses, and the difficulties met in the study of losses: interaction; compensation; interplot interference; variation; and distribution. Sources of information on world losses, training and the work of the FAO are reviewed. General guidelines on crop loss assessment are given.     

Rent dissipation in a limited-access common-pool resource: Experimental evidence

This paper examines group behavior in an experimental environment designed to parallel the conditions specified in noncooperative models of limited-access common-pool resources. Using experimental methods, we investigate the strength of theoretical models which predict that users of such resources will appropriate units at a rate at which the marginal returns from appropriation are greater than the marginal appropriation costs. Our results confirm the prediction of suboptimal accrual of rents and offer evidence on the effects of increasing investment capital available to appropriators.     

An energy budget for the free-swimming and metamorphosing larvae of Balanus balanoides (Crustacea: Cirripedia)

Analysis of biochemical components and measurements of oxygen consumption rates of cypris larvae of Balanus balanoides (L.) maintained in the laboratory at 10°C for up to 5 weeks after capture shows that lipid is the primary energy reserve, although later protein is utilised. Initially, the cyprids swim freely with an oxygen consumption rate of ca. 37×10^-3 l O₂ h^-1 cyprid^-1, but within a few days the rate falls to ca. 21×10^-3 l O₂ h^-1 cyprid^-1 when they cease swimming and explore the substratum. The cost of metamorphosis was calculated both from the loss of biochemical components and oxygen consumption rates during metamorphosis; the values were 2.8×10^-2 and 3.2×10^-2 cal cyprid^-1, respectively. A budget was collated from the data on respiration and biochemical composition, whereby the energy per cyprid was partitioned into that required for essential structural components (6.8×10^-2 cal), that needed for metamorphosis (3.0×10^-2 cal) and an excess available for swimming and exploring, which in the batches studied was about 5.0×10^-2 cal. This excess is mainly derived from the utilisation of lipid reserves and is used up usually 2 1/2 to 4 weeks after capture. During these measurements, samples of cyprids were taken at weekly intervals to test the rate of settlement and success of metamorphosis. The results showed that they lose their competence to metamorphose successfully approximately at the same time (3 to 4 weeks) that the energy supply for swimming and exploration is used up.     

Origin,composition, and function of secretions from pyriform organs and internal sacs of four settling cheilo-ctenostome bryozoan larvae

Settling larvae of the bryozoans Flustrellida hispida, Flustra foliacea, Alcyonidium polycum, and Bugula neritina exhibit a common behavioral pattern. A settlement site is selected after initial exploration, and temporary attachment is accomplished with a sticky acid mucopolysaccharide secretion exuded from the pyriform organ. Permanent attachment is accomplished by acid mucopolysaccharide and protein secretions of the everted internal sac.