A model for the determination of optimal electric generating system expansion patterns

Essentially constitutes a M.S. thesis in the Sloan School of Management and the Dept. of Civil EngineeringLong range electric generating capacity expansion planning requires consideration of a diverse range of issues including economic and financial evaluations, environmental protection, and overall system reliability. To determine the optimum system expansion plan, it is necessary to create a synthesis of combinations of possible technical alternatives, observe the intertemporal effects of the system along the dimensions of the problem, and choose the set of alternatives which best meets the objectives while satisfying all constraints. A system of integrated techniques and computer codes (called the Generation Expansion Model) has been formulated to evaluate the economic, environmental, and reliability aspects of regional generation expansion strategies. The computer codes comprising the model are used serially and in an iterative manner to find the set of plant and site alternatives and the corresponding plant operating histories which will minimize the total present worth of all capital, operating, and fuel costs while satisfying the demand for electricity, fuel availability, site availability, pollution limits, and reliability constraints. Prototypical versions of the three major submodels of the Generation Expansion Model exist; initial testing of the capabilities and sensitivities of the first two submodels and their interface is currently being performedNSF Contract no. GI-3493

Categorical consequence for paraconsistent logic

Includes bibliographical references (pages 149-150).Consequence relations over sets of "judgments" are defined by using "overdetermined" as well as "underdetermined" valuations. Some of these relations are shown to be categorical. And generalized soundness and completeness results are given for both multiple and single conclusion categorical consequence relations

Height-related trends in leaf xylem anatomy and shoot hydraulic characteristics in a tall conifer: safety versus efficiency in foliar water transport

• Hydraulic vulnerability of Douglas-fir (Pseudotsuga menziesii) branchlets decreases with height, allowing shoots at greater height to maintain hydraulic conductance (Kshoot) at more negative leaf water potentials (Ψl). • To determine the basis for this trend shoot hydraulic and tracheid anatomical properties of foliage from the tops of Douglas-fir trees were analysed along a height gradient from 5 to 55 m. • Values of Ψl at which Kshoot was substantially reduced, declined with height by 0.012 Mpa m−1. Maximum Kshoot was reduced by 0.082 mmol m−2 MPa−1 s−1 for every 1 m increase in height. Total tracheid lumen area per needle cross-section, hydraulic mean diameter of leaf tracheid lumens, total number of tracheids per needle cross-section and leaf tracheid length decreased with height by 18.4 μm2 m−1, 0.029 μm m−1, 0.42 m−1 and 5.3 μm m−1, respectively. Tracheid thickness-to-span ratio (tw/b)2 increased with height by 1.04 × 10–3 m−1 and pit number per tracheid decreased with height by 0.07 m−1. • Leaf anatomical adjustments that enhanced the ability to cope with vertical gradients of increasing xylem tension were attained at the expense of reduced water transport capacity and efficiency, possibly contributing to height-related decline in growth of Douglas fir.Keywords: growth limitation, hydraulic conductance, water stress, foliar anatomy, Pseudotsuga menziesii, embolismKeywords: growth limitation, hydraulic conductance, water stress, foliar anatomy, Pseudotsuga menziesii, embolis

Coordination of leaf structure and gas exchange along a height gradient in a tall conifer

The gravitational component of water potential and frictional resistance during transpiration lead to substantial reductions in leaf water potential (Ψl) near the tops of tall trees, which can influence both leaf growth and physiology. We examined the relationships between morphological features and gas exchange in foliage collected near the tops of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees of different height classes ranging from 5 to 55 m. This sampling allowed us to investigate the effects of tree height on leaf structural characteristics in the absence of potentially confounding factors such as irradiance, temperature, relative humidity and branch length. The use of cut foliage for measurement of intrinsic gas-exchange characteristics allowed identification of height-related trends without the immediate influences of path length and gravity. Stomatal density, needle length, needle width and needle area declined with increasing tree height by 0.70 mm−2 m−1, 0.20 mm m−1, 5.9 × 10−3 mm m−1 and 0.012 mm2 m−1, respectively. Needle thickness and mesophyll thickness increased with tree height by 4.8 × 10−2 mm m−1 and 0.74 μm m−1, respectively. Mesophyll conductance (gm) and CO2 assimilation in ambient [CO2] (Aamb) decreased by 1.1 mmol m−2 s−1 per m and 0.082 μmol m−2 s−1 per m increase in height, respectively. Mean reductions in gm and Aamb of foliage from 5 to 55 m were 47% and 42%, respectively. The observed trend in Aamb was associated with gm and several leaf anatomic characteristics that are likely to be determined by the prevailing vertical tension gradient during foliar development. A linear increase in foliar δ13C values with height (0.042‰ m−1) implied that relative stomatal and mesophyll limitations of photosynthesis in intact shoots increased with height. These data suggest that increasing height leads to both fixed structural constraints on leaf gas exchange and dynamic constraints related to prevailing stomatal behavior.Keywords: leaf anatomy, mesophyll resistance, photosynthesis, growth limitationKeywords: leaf anatomy, mesophyll resistance, photosynthesis, growth limitatio

Evidence for xylem embolism as a primary factor in dehydration-induced declines in leaf hydraulic conductance

Hydraulic conductance of leaves (K[subscript leaf]) typically decreases with increasing water stress and recent studies have proposed different mechanisms responsible for decreasing K[subscript leaf]. We measured K[subscript leaf] concurrently with ultrasonic acoustic emissions (UAEs) in dehydrating leaves of several species to determine whether declining K[subscript leaf] was associated with xylem embolism. In addition, we performed experiments in which the surface tension of water in the leaf xylem was reduced by using a surfactant solution. Finally, we compared the hydraulic vulnerability of entire leaves with the leaf lamina in three species. Leaf hydraulic vulnerability based on rehydration kinetics and UAE was very similar, except in Quercus garryana. However, water potentials corresponding to the initial decline in K[subscript leaf] and the onset of UAE in Q. garryana were similar. In all species tested, reducing the surface tension of water caused K[subscript leaf] to decline at less negative water potentials compared with leaves supplied with water. Microscopy revealed that as the fraction of embolized xylem increased, K[subscript leaf] declined sharply in Q. garryana. Measurements on leaf discs revealed that reductions in lamina hydraulic conductance with dehydration were not as great as those observed in intact leaves, suggesting that embolism was the primary mechanism for reductions in K[subscript leaf] during dehydration

The dynamic pipeline: hydraulic capacitance and xylem hydraulic safety in four tall conifer species

Recent work has suggested that plants differ in their relative reliance on structural avoidance of embolism versus maintenance of the xylem water column through dynamic traits such as capacitance, but we still know little about how and why species differ along this continuum. It is even less clear how or if different parts of a plant vary along this spectrum. Here we examined how traits such as hydraulic conductivity or conductance, xylem vulnerability curves, and capacitance differ in trunks, large- and small-diameter branches, and foliated shoots of four species of co-occurring conifers. We found striking similarities among species in most traits, but large differences among plant parts. Vulnerability to embolism was high in shoots, low in small- and large-diameter branches, and high again in the trunks. Safety margins, defined as the pressure causing 50% loss of hydraulic conductivity or conductance minus the midday water potential, were large in small-diameter branches, small in trunks and negative in shoots. Sapwood capacitance increased with stem diameter, and was correlated with stem vulnerability, wood density and latewood proportion. Capacitive release of water is a dynamic aspect of plant hydraulics that is integral to maintenance of long-distance water transport.This is the publisher’s final pdf. The published article is copyrighted by John Wiley & Sons Ltd. and can be found at: http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291365-3040Keywords: vulnerability curves, safety margins, hydraulic conductance, conifers, capacitanc

Users' Guides to the Medical Literature: How to Use an Article About Mortality in a Humanitarian Emergency

The accurate interpretation of mortality surveys in humanitarian crises is useful for both public health responses and security responses. Recent examples suggest that few medical personnel and researchers can accurately interpret the validity of a mortality survey in these settings. Using an example of a mortality survey from the Democratic Republic of Congo (DRC), we demonstrate important methodological considerations that readers should keep in mind when reading a mortality survey to determine the validity of the study and the applicability of the findings to their settings

Dynamics of leaf water relations components in co-occurring iso- and anisohydric conifer species

Because iso- and anisohydric species differ in stomatal regulation of the rate and magnitude of fluctuations in shoot water potential, they may be expected to show differences in the plasticity of their shoot water relations components, but explicit comparisons of this nature have rarely been made. We subjected excised shoots of co-occurring anisohydric Juniperus monosperma and isohydric Pinus edulis to pressure-volume analysis with and without prior artificial rehydration. In J. monosperma, the shoot water potential at turgor loss (Ψ[subscript TLP]) ranged from −3.4 MPa in artificially rehydrated shoots to −6.6 MPa in shoots with an initial Ψ of −5.5 MPa, whereas in P. edulis mean Ψ[subscript TLP] remained at ∼−3.0 MPa over a range of initial Ψ from −0.1 to −2.3 MPa.The shoot osmotic potential at full turgor and the bulk modulus of elasticity also declined sharply with shoot Ψ in J. monosperma, but not in P. edulis. The contrasting behaviour of J. monosperma and P. edulis reflects differences in their capacity for homeostatic regulation of turgor that may be representative of aniso- and isohydric species in general, and may also be associated with the greater capacity of J. monosperma to withstand severe drought.Keywords: osmotic potential, anisohydry, turgor, isohydry, droughtKeywords: osmotic potential, anisohydry, turgor, isohydry, drough

Expression of functional traits during seedling establishment in two populations of Pinus ponderosa from contrasting climates

First-year tree seedlings represent a particularly vulnerable life stage and successful seedling establishment is crucial for forest regeneration. We investigated the extent to which Pinus ponderosa P. & C. Lawson populations from different climate zones exhibit differential expression of functional traits that may facilitate their establishment. Seeds from two populations from sites with contrasting precipitation and temperature regimes east (PIPOdry) and west (PIPOmesic) of the Oregon Cascade mountains were sown in a common garden experiment and grown under two water availability treatments (control and drought). Aboveground biomass accumulation, vegetative phenology, xylem anatomy, plant hydraulic architecture, foliar stable carbon isotope ratios (δ13C), gas exchange and leaf water relations characteristics were measured. No treatment or population-related differences in leaf water potential were detected. At the end of the first growing season, aboveground biomass was 74 and 44% greater in PIPOmesic in the control and drought treatments, respectively. By early October, 73% of PIPOdry seedlings had formed dormant buds compared with only 15% of PIPOmesic seedlings. Stem theoretical specific conductivity, calculated from tracheid dimensions and packing density, declined from June through September and was nearly twice as high in PIPOmesic during most of the growing season, consistent with measured values of specific conductivity. Intrinsic water-use efficiency based on δ13C values was higher in PIPOdry seedlings for both treatments across all sampling dates. There was a negative relationship between values of δ13C and leaf-specific hydraulic conductivity across populations and treatments, consistent with greater stomatal constraints on gas exchange with declining seedling hydraulic capacity. Integrated growing season assimilation and stomatal conductance estimated from foliar δ13C values and photosynthetic CO2-response curves were 6 and 28% lower, respectively, in PIPOdry seedlings. Leaf water potential at the turgor loss point was 0.33 MPa more negative in PIPOdry, independent of treatment. Overall, PIPOdry seedlings exhibited more conservative behavior, suggesting reduced growth is traded off for increased resistance to drought and extreme temperatures.Keywords: gas exchange, carbon isotope discrimination, phenology, osmotic potential, hydraulic architecture, genetic variatio

Contrasting Hydraulic Strategies in Two Tropical Lianas and Their Host Trees

• Premise of the Study: Tropical liana abundance has been increasing over the past 40 yr, which has been associated with reduced rainfall. The proposed mechanism allowing lianas to thrive in dry conditions is deeper root systems than co-occurring trees, although we know very little about the fundamental hydraulic physiology of lianas. • Methods: To test the hypothesis that two abundant liana species would physiologically outperform their host tree under reduced water availability, we measured rooting depth, hydraulic properties, plant water status, and leaf gas exchange during the dry season in a seasonally dry tropical forest. We also used a model to compare water use by one of the liana species and the host tree during drought. • Key Results: All species measured were shallowly rooted. The liana species were more vulnerable to embolism than host trees and experienced water potentials that were predicted to result in substantial hydraulic losses in both leaves and stems. Water potentials measured in host trees were not negative enough to result in signifi cant hydraulic losses. Model results predicted the liana to have greater gas exchange than its host tree during drought and nondrought conditions. • Conclusions: The host tree species had a more conservative strategy for maintenance of the soil-to-leaf hydraulic pathway than the lianas it supported. The two liana species experienced embolism in stems and leaves, based on vulnerability curves and water potentials. These emboli were presumably repaired before the next morning. However, in the host tree species, reduced stomatal conductance prevented leaf or stem embolism.Keywords: Anacardium excelsum, Prionostemma aspera, Transpiration, Gas exchange, Embolism, Water relations, Drought stress, Trichostigma octandru