On preconditioning strategies for geotechnics

Iterative solvers are of increasing interest in geomechanics with the move towards 3D finite element modelling. Potentially, these methods can lead to reduced computational complexity as, unlike direct methods, they do not require the full system matrix to be assembled. In general, however, iterative solvers have not been widely adopted in geomechanics due to problems with convergence. This paper reviews the background to iterative methods for elastic and elasto-plastic material models. In some cases, existing numerical methods can be taken from research in the mathematics community. For other systems, further work is needed. The paper provides demonstrations of the capabilities of some strategies

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Growth and emigration of white shimp, Litopenaeus vannamei, in the Mar Muerto Lagoon, Southern Mexico

Microcohorts of white shrimp, Litopenaeus vannamei, were sampled with a cast net at fortnightly intervals in the Mar Muerto Lagoon, Southern Mexico. Shrimp recruited to the lagoon throughout the sampling period (January to August 1993). Mean growth rates of microcohorts ranged from 0.21 to 1.21 mm total length (TL) per day. Juvenile shrimp mainly between the sizes of 70 to 80 mm TL emigrated from the lagoon. Growth and the onset of emigration appeared to be related to water salinity

Seasonal variation of some trace metal concentrations in some fish species on stretch of River Kubanni, Zaria

In a semi-urbanized stretch of river Kubanni, Zaria, seasonal variations of some tree metals (copper, zinc and lead) in fish species (Clarias sp., Tilapia sp and Alestes sp) were investigated over a period of eight months. Water and fish were sampled monthly, pooled separately and seasonal analysis of each trace determined using atomic absorption method. The concentration of each of the elements in water higher in the dry season than during the rainy season. The dry and rainy season concentrations of copper, zinc and lead were 6.85~c10.66 mu gg super(-1)&1.45~c1.10 mu gg super(-1); 2.13~c1.68 mu gg super(-1)&0.1 5~c0.05 mu gg super(-1); and 0.52~c0.50 mu gg super(-1) & 0.31~c0.14 mu gg super(-1) respectively. Similarly, all the three accumulated more zinc and lead in the dry season than during the rainy season. Tilapia species and to some extent, Alestes species being pelagic had a higher concentration of trace metals than Clarias species which is a bottom dwelling fish Tilapia species may therefore be a better indicator species than Clarias species for monitoring trace metals in water bodies. Reasons for the observed variations in the trace metals were discusse

The Value of Monitoring Risk Averse Agents in Teams.

Vander Veen (1995) has argued that a principal has an incentive to monitor risk averse agents engaging in team production. We show that this result rests on specific informational assumptions that are not essential to team production. Moreover, under typical team environments and contract conditions there is no benefit from monitoring of individual agents, leaving only costs for the principal. We identify an additional mechanism design problem that arises in certain team settings-the principal must determine when to make information about each agent's reported ability public to the other team members.RISK ; MICROECONOMICS

WATER RIGHTS AND THEIR SIGNIFICANCE TO AGRICULTURE

Resource /Energy Economics and Policy,

EXTENSION ALTERNATIVES IN DEALING WITH EDUCATIONAL POLICY ISSUES

Teaching/Communication/Extension/Profession,

Investigation into the shear behaviour of rammed earth using shear box tests.

Scientific investigations into the structural properties of rammed earth (RE) are gaining momentum and a number of parameters (e.g. suction, particle size distribution and water content), influential on material strength and other properties, have been identified and investigated. Cement stabilisation is undergoing continued investigation, while fibrous stabilisation, also known as fibre reinforcement, is beginning to gain attention. Recent experiments have shown that the addition of fibres such as straw or wool to RE or other earthen materials can improve its flexural strength. Less attention, however, has been paid to the fracture behaviour of RE, and to its shearing behaviour. This paper presents a preliminary investigation into the shearing behaviour of stabilised and unstabilised RE reinforced with waste natural fibres. The Direct Shear Test (DST) is used to obtain peak shear stresses and displacements, from which strength parameters (φ’) and cohesion (c’) are obtained. This paper also presents some scanning electron microscope (SEM) images of these materials. The results show that wool fibres decrease the density and peak shear strength of RE. The effect of water, wool and cement content on φ’ and c’ are also discussed

Evolution of abilities to regenerate neurons in central nervous systems

This work was supported by a Kappa Kappa Gamma Graduate Fellowship Award to C. E. H. and NIH grant NS-11861 and RCDA NS-00070 to G. D. B.Neuroscienc