INTERNAL CONSISTENCY IN MODELS OF OPTIMAL RESOURCE USE UNDER UNCERTAINTY

For several decades, economists have been concerned with the problem of optimal resource use under uncertainty. In many studies, researchers assume that prices evolve according to an exogenous stochastic process and solve the corresponding dynamic optimization problem to yield an optimal decision rule for exploitation of the resource. This study is motivated by our attempt to understand the relationship between efficiency in resource markets and optimal harvest decisions in which price is an exogenous state variable. The literature on optimal commodity storage finds that in a rational expectations equilibrium commodity prices are stationary and serially correlated. Yet recent papers on optimal timber harvesting that assume exogenous stationary prices generate harvest rules inconsistent with the price processes on which they are based. In this study, we investigate the appropriate form of the stochastic process governing prices of renewable resources. We develop a model in which timber is supplied by profit-maximizing managers with rational expectations and aggregate timber demand is subject to independent exogenous shocks. In contrast to earlier studies, prices are endogenously determined. Managers know the structure of the timber market and form expectations of future market equilibria in making optimal harvesting decisions. We show under general conditions that efficient timber prices are stationary and serially correlated. Stationarity and serial correlation are shown to arise from two sources: the occurrence of stock-outs (i.e., depletion of the inventory) and stock-dependent growth of the resource. Further, we show that prices retain these properties even in the absence of stock-outs. Simulations are used to further illustrate the analytical results. Our findings have implications for a large number of economic analyses of optimal resource use. First, our results reveal why extraction rules for renewable resources based on exogenous price specifications are internally inconsistent, even when the specification conforms to the stochastic behavior of prices generated by an efficient market. These prices arise in a particular structural environment, and if large numbers of resource managers adopt the harvesting rule, the underlying structural environment would change, and the price process would deviate from that used to derive the harvesting rule. Second, we show that there can be no gains from exploiting the stochasticity of resource prices in a rational expectations world, a finding that challenges the prescriptive policies for resource use found in many studies, including those on option values. Third, our results show that time-series analyses designed to test for the efficiency of renewable resource markets cannot distinguish prices generated in an efficient market from those generated in an inefficient market. Finally, we extend the literature on optimal storage. Previous models of commodity storage models are shown to be a special case of our model involving age-independent depreciation of the inventory.Resource /Energy Economics and Policy,

The Dynamic Behavior of Efficient Timber Prices

The problem of when to optimally harvest trees when timber prices evolve according to an exogenous stochastic process has been studied extensively in recent decades. However, little attention has been given to the appropriate form of the stochastic process for timber prices, despite the fact that the choice of a process has important effects on optimal harvesting decisions. We develop a simple theoretical model of a timber market and show that there exists a rational expectations equilibrium in which prices evolve according to a stationary ARMA(1,1) process. Simulations are used to analyze a model with a more general representation of timber stock dynamics and to demonstrate that the unconditional distribution for rational timber prices is asymmetric. Implications for the optimal harvesting literature are: 1) market efficiency provides little justification for random walk prices, 2) unit root tests, used to analyze the informational efficiency of timber markets, do not distinguish between efficient and inefficient markets, and 3) failure to recognize asymmetric disturbances in time-series analyses of historical timber prices can lead to sub-optimal harvesting rules.

Effects of Environmental Zoning on Household Sorting: Empirical Evidence and Ecological Implications

In this paper we present a preliminary analysis of whether and how spatial variation in environmental attributes affects the residential sorting of households with heterogeneous preferences. An important implication of such sorting arises if variation in preferences over environmental attributes is correlated with household activities affecting the local ecosystem, such as the replacement of native vegetation with lawns, and the removal of course woody habitat from a lake. In this case the sorting process may engender differential evolution of local ecosystems (lakes) with the same initial ecological state. The model examined in the paper has the potential to statistically examine this issue, and therefore holds promise for understanding the behavioral implications of land use policies designed to protect local ecosystems. By facilitating the grouping of different types of households onto different lakes, for instance, lakeshore zoning policies may engender differentiation in the ecological evolution of lakes beyond what would be expected from the zoning policies themselves.Environmental Economics and Policy, Land Economics/Use,

The Dynamic Effects of Open-Space Conservation Policies on Residential Development Density

Recent economic analyses emphasize that designated open-space increases the rents on neighboring residential land, and likewise, the probability of undeveloped land converting to residential uses. This paper addresses a different question: What is the effect of local open space conservation on the rate of growth in the density of existing residential land? The analysis is relevant for exurban development and also for remote lakeshore development, where shoreline development density can rapidly increase over time and open-space policies are often advocated as a way to protect ecosystems by reducing development. A discrete choice econometric model of lakeshore development is estimated with a unique parcel-level spatial-temporal dataset, using maximum simulated likelihood to account for i) the panel structure of the data, ii) unobserved spatial heterogeneity, and iii) sample selection resulting from correlated unobservables. Results indicate that, contrary to the intuition derived from the current literature, local open space conservation policies do not increase the rate of growth in residential development density, and some open space conservation policies may reduce the rate of growth in residential development density. This is consistent with land-value complementarity between local open space and parcel size. Spatially-explicit simulations at the landscape scale examine the relative effects of conservation policies on the time path of development.

Water diffusion in rat brain in vivo as detected at very large b values is multicompartmental

The diffusion-weighted signal attenuation of water in rat brain was measured with pulsed-field gradient nuclear magnetic resonance methods in a single voxel under in vivo and global ischemic conditions. The diffusion-attenuated water signal was observed in vivo at b values of 300 ms/ mu m/sup 2/ (strength of diffusion weighting) and diffusion times up to 400 ms. A series of constant diffusion time (CT) experiments with varied gradient directions and diffusion times revealed a multiexponential decay with apparent diffusion coefficients (ADC) covering two orders of magnitude from I to 0.01 mu m/sup 2//ms. In a four-exponential fit, the observed changes during global ischemia could be fully explained by changes in the relative volume fractions only with unchanged ADCs. An anisotropy of the ADC, detected at small b values, was not observed for the ADC at large b values, but for the concomitant volume fractions. An inverse Laplace Transform of the CT curves, performed with CONTIN, resulted in continuously distributed diffusion coefficients, for which the term `diffusogram' is proposed. This approach was more appropriate than a discrete exponential model with four to six components, being related to the morphology of brain tissue and its cell size distribution. On the basis of an analytical, quantitative model, it is suggested that the measured ADC at small b values reflects mainly properties of the restricting boundaries, i.e. the relative volume fractions and the extracellular tortuosity, while the intrinsic intracellular diffusion constant and the exchange time are predicted to have minor influence

Spacecraft design sensitivity for a disaster warning satellite system

A disaster warning satellite (DWS) is described for warning the general public of impending natural catastrophes. The concept is responsive to NOAA requirements and maximizes the use of ATS-6 technology. Upon completion of concept development, the study was extended to establishing the sensitivity of the DWSS spacecraft power, weight, and cost to variations in both warning and conventional communications functions. The results of this sensitivity analysis are presented

Does open space increase development?

Land-use change, spatial modeling, Land Economics/Use,

Astrobee Guest Science Interface

At the end of 2018, Astrobee will launch three free-flying robots that will navigate the entire US segment of the ISS (International Space Station) and serve as a payload facility. The mechanical and electrical interfaces are now established and several payloads are being developed. Payload Interface: Astrobee is designed to host third party guest science program payloads (GSP payloads). Some GSP payloads may be software only, such as the Zero Robotics Finals Competition, which is currently hosted on SPHERES, and which will transition to Astrobee in 2019. Several GSP payloads with custom hardware, such as the Advanced Exploration Systems (AES) Logistics Reduction and Repurposing (LRR) Project RFID reader, are already under development. These payloads will attach in the Astrobee payload bay

Diversity and Keratin Degrading Ability of Fungi Isolated from Canadian Arctic Marine Bird Feathers

We present the first records of fungi associated with feathers from seabirds and sea ducks in the Canadian Arctic and sub-Arctic. Birds sampled in Nunavut and Newfoundland (Canada) included the Common Eider (Somateria mollissima), King Eider (S. spectabilis), Black-legged Kittiwake (Rissa tridactyla), Northern Fulmar (Fulmarus glacialis), Glaucous Gull (Larus hyperboreus), Black Guillemot (Cepphus grylle), and Thick-billed Murre (Uria lomvia). In total 19 fungal species were cultured from feathers, identified using ITS rDNA barcoding, and screened for their ability to degrade keratin using a keratin azure assay. Our results indicate that 1) of the 19 isolates, 74% were ascomycetes, while the remaining 26% were basidiomycetes (yeasts); 2) 21% of the ascomycete isolates demonstrated keratinolytic activity (a known pathogenicity factor for fungi that may potentially be harmful to birds); 3) the largest number of fungi were cultured from the sampled Thick-billed Murre; and 4) based on a multiple correspondence analysis, there is some indication that both the King Eider and the Thick-billed Murre collected in the low Arctic had distinct fungal communities that were different from each other and from the other birds sampled. Although our sample sizes were small, initial trends in point (4) do demonstrate that additional study is merited to assess whether the fungal community differences are influenced by variation in the known ecologies of the avian hosts and fungi identified.Nous présentons les premiers enregistrements de champignons se rapportant aux plumes d’oiseaux et de canards de mer dans l’Arctique et la région subarctique du Canada. Parmi les oiseaux échantillonnés au Nunavut et à Terre-Neuve (Canada), notons l’eider à duvet (Somateria mollissima), l’eider à tête grise (S. spectabilis), la mouette tridactyle (Rissa tridactyla), le fulmar boréal (Fulmarus glacialis), le goéland bourgmestre (Larus hyperboreus), le guillemot à miroir (Cepphus grylle) et le guillemot de Brünnich (Uria lomvia). En tout, 19 espèces de champignons ont été prélevées à partir de plumes. Elles ont été identifiées au moyen de codes à barres ITS ADNr et examinées afin de déterminer si elles sont capables de dégrader la kératine, et ce, à l’aide d’une épreuve de dégradation de la kératine au bleu azur. Nos résultats indiquent : 1) que parmi les 19 isolats, 74 % étaient des ascomycètes et que les 26 % restants étaient des basidiomycètes (levures); 2) que 21 % des isolats d’ascomycètes ont affiché une activité kératinolytique (un facteur de pathogénicité pour les champignons, facteur susceptible de nuire aux oiseaux); 3) que le plus grand nombre de cultures de champignons a été prélevé chez le guillemot de Brünnich; et 4) que d’après une analyse de correspondance multiple, il y a une certaine indication que les échantillons de l’eider à tête grise et du guillemot de Brünnich recueillis dans le Bas-Arctique comprenaient des communautés fongiques distinctes qui différaient les unes des autres ainsi que des autres oiseaux échantillonnés. Même si la taille de nos échantillons était petite, les premières tendances ressortant du point (4) démontrent qu’il y a lieu de faire des études plus poussées afin de déterminer si les différences entre les communautés fongiques sont influencées par la variation des écologies connues des hôtes aviaires et des champignons identifiés