Comparison of Two Year Classes of Hybrid Grass Carp and Grass Carp for Aquatic Plant Control

Two year classes of grass carp and F, hybrids resulting from bighead carp male x grass carp female were compared at various stocking densities for aquatic plant control. One and two year old grass carp exhibited higher survival rates and better growth rates than the same age hybrid grass carp. The presence of grass carp or hybrid grass carp decreased both Secchi disc transparencies and dissolved oxygen values. Grass carp had a greater negative effect upon these measurements because they removed the vegetation quicker than the hybrid grass carp. These apparent detrimental effects on water quality are necessary trade-offs for vegetation removal by any method. Grass carp and hybrid grass carp utilized Chara sp., Potamogeton pectinatus, Hydrodicton sp., Rhizoclonia sp., and Pithophora sp. Two year old hybrid grass carp required approximately twice as much time as the same age grass carp to eliminate dense growths of the vegetation listed above. One year old hybrid grass carp were slightly less effective than one year old grass carp at controlling these same plant species. However, it was extremely difficult for one or two year old hybrid grass carp to totally eliminate dense growths of these plant species except at high stocking densities. The use of mean vegetation heights to indirectly measure total plant biomass was unacceptable whenever unpreferred floating plant species were present. The hybrid grass carp appeared to be a poor alternative biological control for nuisance aquatic vegetation when compared directly to the grass carp

The WorkPlace distributed processing environment

Real time control problems require robust, high performance solutions. Distributed computing can offer high performance through parallelism and robustness through redundancy. Unfortunately, implementing distributed systems with these characteristics places a significant burden on the applications programmers. Goddard Code 522 has developed WorkPlace to alleviate this burden. WorkPlace is a small, portable, embeddable network interface which automates message routing, failure detection, and re-configuration in response to failures in distributed systems. This paper describes the design and use of WorkPlace, and its application in the construction of a distributed blackboard system

An application of machine learning to the organization of institutional software repositories

Software reuse has become a major goal in the development of space systems, as a recent NASA-wide workshop on the subject made clear. The Data Systems Technology Division of Goddard Space Flight Center has been working on tools and techniques for promoting reuse, in particular in the development of satellite ground support software. One of these tools is the Experiment in Libraries via Incremental Schemata and Cobweb (ElvisC). ElvisC applies machine learning to the problem of organizing a reusable software component library for efficient and reliable retrieval. In this paper we describe the background factors that have motivated this work, present the design of the system, and evaluate the results of its application

Balancing Incentives: The Tension Between Basic and Applied Research

This paper presents empirical evidence that the intensity of research workers' incentives for the distinct tasks of basic and applied research are positively associated with each other. We relate this finding to the prediction of the theoretical literature that when effort is multi-dimensional, firms will balance' the provision of incentives; when incentives are strong along one dimension, firms will set high-powered incentives for effort along other dimensions which compete for the worker's effort and attention (Holmstrom and Milgrom, 1991). We test for this effect in the context of pharmaceutical research using detailed data on individual research programs financed by private firms. Consistent with the complementarity hypothesis, we find strong evidence that firms who provide strong promotion-based incentives for individuals to invest in fundamental or basic' research also provide more intense incentives for success in applied research through the capital budgeting process. The intensity of these bonus' incentives is weaker in firms who use a more centralized research budgeting process. We interpret this latter finding as providing support for theories which emphasize substitutability between contractible and non-contractible signals of effort (Baker, Gibbons, and Murphy, 1994).

Unsaturated fatty acid regulation of cytochrome P450 expression via a CAR-dependent pathway.

The liver is responsible for key metabolic functions, including control of normal homoeostasis in response to diet and xenobiotic metabolism/detoxification. We have shown previously that inactivation of the hepatic cytochrome P450 system through conditional deletion of POR (P450 oxidoreductase) induces hepatic steatosis, liver growth and P450 expression. We have exploited a new conditional model of POR deletion to investigate the mechanism underlying these changes. We demonstrate that P450 induction, liver growth and hepatic triacylglycerol (triglyceride) homoeostasis are intimately linked and provide evidence that the observed phenotypes result from hepatic accumulation of unsaturated fatty acids, which mediate these phenotypes by activation of the nuclear receptor CAR (constitutive androstane receptor) and, to a lesser degree, PXR (pregnane X receptor). To our knowledge this is the first direct evidence that P450s play a major role in controlling unsaturated fatty acid homoeostasis via CAR. The regulation of P450s involved in xenobiotic metabolism by this mechanism has potentially significant implications for individual responses to drugs and environmental chemicals