The Behaviour Of Cosmological Models With Varying-G

We provide a detailed analysis of Friedmann-Robertson-Walker universes in a wide range of scalar-tensor theories of gravity. We apply solution-generating methods to three parametrised classes of scalar-tensor theory which lead naturally to general relativity in the weak-field limit. We restrict the parameters which specify these theories by the requirements imposed by the weak-field tests of gravitation theories in the solar system and by the requirement that viable cosmological solutions be obtained. We construct a range of exact solutions for open, closed, and flat isotropic universes containing matter with equation of state $p\leq \frac{1}{3}\rho$ and in vacuum. We study the range of early and late-time behaviours displayed, examine when there is a `bounce' at early times, and expansion maxima in closed models.Comment: 58 pages LaTeX, 6 postscript figures, uses eps

Stable Inflationary Dissipative Cosmologies

The stability of the de Sitter era of cosmic expansion in spatially curved homogeneous isotropic universes is studied. The source of the gravitational field is an imperfect fluid such that the parameters that characterize it may change with time. In this way we extend our previous analysis for spatially-flat spaces as well as the work of Barrow.Comment: 13 pages, LaTeX 2.09, 1 figure. To be published in International Journal of Modern Physics

Environmental Impact Assessment and Investment under Uncertainty. An Application to Power Grid Interconnection

We consider a firm that must undergo a costly and time-consuming regulatory process before making an irreversible, lagged investment whose value varies randomly. We analyze two cases: regulatory approval is valid forever or it expires after some time. We apply our model to Hydro-Québec's project of building a 1250 megawatts interconnection with Ontario. We find that the firm may start the regulatory process earlier if regulatory approval is valid long enough or if uncertainty is high enough; it postpones it otherwise. When to start the regulatory process and when to invest depend on the duration of the regulatory green light.Regulation, uncertainty, irreversibility, real options, interconnections

Environmental Impact Assessment and Investment under Uncertainty. An Application to Power Grid Interconnection.

We consider a firm that must undergo a costly and time-consuming regulatory process before making an irreversible, lagged investment whose value varies randomly. We analyze two cases: regulatory approval is valid forever or it expires after some time. We apply our model to Hydro-Québec's project of building a 1250 megawatts interconnection with Ontario. We find that the firm may start the regulatory process earlier if regulatory approval is valid long enough or if uncertainty is high enough; it postpones it otherwise. When to start the reglulatory process and when to invest depend on the duration of the regulatory green light.Regulation, uncertainty, irreversibility, real options; interconnections

Cohort aggregation modelling for complex forest stands: Spruce-aspen mixtures in British Columbia

Mixed-species growth models are needed as a synthesis of ecological knowledge and for guiding forest management. Individual-tree models have been commonly used, but the difficulties of reliably scaling from the individual to the stand level are often underestimated. Emergent properties and statistical issues limit their effectiveness. A more holistic modelling of aggregates at the whole stand level is a potentially attractive alternative. This work explores methodology for developing biologically consistent dynamic mixture models where the state is described by aggregate stand-level variables for species or age/size cohorts. The methods are demonstrated and tested with a two-cohort model for spruce-aspen mixtures named SAM. The models combine single-species submodels and submodels for resource partitioning among the cohorts. The partitioning allows for differences in competitive strength among species and size classes, and for complementarity effects. Height growth reduction in suppressed cohorts is also modelled. SAM fits well the available data, and exhibits behaviors consistent with current ecological knowledge. The general framework can be applied to any number of cohorts, and should be useful as a basis for modelling other mixed-species or uneven-aged stands.Comment: Accepted manuscript, to appear in Ecological Modellin

Dynamic-error analysis of digital and combined analog-digital computer systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68553/2/10.1177_003754976600600408.pd

Environmental Impact Assessment and Investment under Uncertainty: An Application to Power Grid Interconnection

We consider a firm that must undergo a costly and time-consuming regulatory process before making an irreversible, lagged investment whose value varies randomly. We analyze two cases: regulatory approval is valid forever or it expires after some time. We apply our model to Hydro Québec's project of building a 1250 megawatts interconnection with Ontario. We find that the firm may start the regulatory process earlier if regulatory approval is valid long enough or if uncertainty is high enough; it postpones it otherwise. When to start the regulatory process and when to invest depend on the duration of the regulatory green light. Nous considérons une firme qui doit se soumettre à un processus réglementaire long et coûteux avant de réaliser un investissement irréversible. La valeur de cet investissement est aléatoire et un délai de mise en service est nécessaire. Nous analysons deux cas : l'approbation réglementaire est toujours valide ou elle a une durée finie. Nous appliquons notre modèle à un projet d'Hydro Québec : la construction d'une interconnexion de 1250 mégawatts avec l'Ontario. Nous montrons que la firme débute le processus réglementaire plus tôt si l'approbation réglementaire est suffisamment longue ou si l'incertitude est assez élevée; autrement elle le retarde. Ces décisions dépendent aussi de la durée de l'approbation réglementaire.regulation, uncertainty, irreversibility, real options, interconnections, réglementation, incertitude, irréversibilité, options réelles, interconnexions