A Three-Dimensional Finite Element Analysis of Heat Transfer in the Forearm

The finite element method was used to analyze heat transfer within a section of the forearm while exposed to different ambient conditions and with different metabolic states. The three-dimensional model accounts for the different material properties of bone, muscle and blood and incorporates a single artery-vein pair for counter-current heat exchange. The geometry of the model was developed from anatomical cross-sectional images of the forearm. The model was used to determine the effects or rest vs. exercise, free vs. forced surface convection and 0 degrees C vs. -20 degrees C external temperatures. The results of the model were compared to experimental data and the model exhibits qualitatively correct behaviour. This model can be used to study hyperthermia, burns and cryogenic freezing of tissue.     

Taxonomic Notes on Some Australian Ostracods with Description of New Species

The following ostracods from Australian inland waters are described: Limnocythere mowbrayensis Chapman, 1914, Limnocythere porphyretica sp.n. Zonocypretta kalimna gen. et sp.n. Diacypris spinosa sp.n. D. dictyote sp.n. D. phoxe sp.n. The taxonomic position of each of the genera mentioned above is discussed and all the Australian Diacypris species are reviewed. Ecological data for some of these species are also provided     

Lakes of south-western Uganda

The vegetation of Lake Bunyonyi, a high altitude lake in Kigezi, S.W. Uganda, is described. The lake had two distinct plant communities. In the shallow sheltered bays and inflows extensive floating swamps of Cyperus papyrus L. and Cladium janiaicen. se Cranz. existed. On the steep, exposed shores there was only a narrow band of vegetation, dominated by firmly rooted Phragmites australis (Cav.) Steud., usually with papyrus behind. Floating-leaved Potamogeton and Nymphaea sometimes occurred outside the emergent species, and submerged species, including Ceratophyllum demersum L. grew down to 8 m. The pattern of vegetation, and the contribution of floating islands to the distribution of plants in the lake is discussed. Susceptibility to fragmentation, and distribution by wind are thought to be major factors governing the pattern. Oxygen proflies measured at the fringe of swamps indicated that the swamps did not cause appreciable deoxygenation of the water.     

Co‐limitation of photosynthetic capacity by nitrogen and phosphorus in West Africa woodlands

Photosynthetic leaf traits were determined for savanna and forest ecosystems in West Africa, spanning a large range in precipitation. Standardized major axis fits revealed important differences between our data and reported global relationships. Especially for sites in the drier areas, plants showed higher photosynthetic rates for a given N or P when compared with relationships from the global data set. The best multiple regression for the pooled data set estimated V_cmax and J_max from N_DW and S. However, the best regression for different vegetation types varied, suggesting that the scaling of photosynthesis with leaf traits changed with vegetation types. A new model is presented representing independent constraints by N and P on photosynthesis, which can be evaluated with or without interactions with S. It assumes that limitation of photosynthesis will result from the least abundant nutrient, thereby being less sensitive to the allocation of the non‐limiting nutrient to non‐photosynthetic pools. The model predicts an optimum proportionality for N and P, which is distinct for V_cmax and J_max and inversely proportional to S. Initial tests showed the model to predict V_cmax and J_max successfully for other tropical forests characterized by a range of different foliar N and P concentrations.     

The Cellular Pathway of Short-distance Transfer of Photosynthates and Potassium in the Elongating Stem ofPhaseolus vulgarisL. A Physiological Assessment

Plasmolytic disruption of plasmodesmata interconnecting metaphloemsieve element-companion cell complexes with small and largephloem parenchyma cells in the elongating region of internode2 ofPhaseolus vulgarisL. seedlings did not affect accumulationof phloem-imported¹⁴C-photosynthates and⁸⁶rubidium. The membrane-impermeantdye, 5(6) carboxyfluorescein, loaded into leaf phloem as themembrane-permeant diacetate ester, was found not to move radiallyout of the importing sieve elements in the internode elongationregion. In contrast, the apoplasmic tracer, Calcuofluor White,rapidly moved laterally throughout all tissues of the elongationzone. Hexoses, sucrose and potassium were identified as themain osmotica in internode apoplasmic sap. Label asymmetry in[¹⁴C](fructosyl)sucrose was retained on accumulation by excisedstem segments. Uptake of [¹⁴C]sucrose and⁸⁶rubidium by stemsegments exhibited saturation kinetics. Sucrose uptake was inhibitedby the slowly penetrating sulphydryl reagent, para-chloromercuribenzenesulphonicacid.In vitrorates of sucrose uptake, at apoplasmic concentrations,corresponded to its predictedin vivorate of delivery to thestem ground tissues from mature sieve elements when respiratorylosses were assumed to be confined to the stem phloem. For potassium,the total delivery rate could be accounted for by itsin vitrorateof uptake. Overall, it was concluded that radial transport,in the elongation zone of internode 2 ofPhaseolus vulgarisL.seedlings, follows an apoplasmic route from mature sieve elementsto stem ground tissues.Copyright 1998 Annals of Botany Company PhaseoluLes vulgaris, apoplasm, elongating stem, French bean, photosynthates, potassium, radial transfer, symplasm.     

Inter‐regional comparison of land‐use effects on stream metabolism

1. Rates of whole‐system metabolism (production and respiration) are fundamental indicators of ecosystem structure and function. Although first‐order, proximal controls are well understood, assessments of the interactions between proximal controls and distal controls, such as land use and geographic region, are lacking. Thus, the influence of land use on stream metabolism across geographic regions is unknown. Further, there is limited understanding of how land use may alter variability in ecosystem metabolism across regions. 2. Stream metabolism was measured in nine streams in each of eight regions (n = 72) across the United States and Puerto Rico. In each region, three streams were selected from a range of three land uses: agriculturally influenced, urban‐influenced, and reference streams. Stream metabolism was estimated from diel changes in dissolved oxygen concentrations in each stream reach with correction for reaeration and groundwater input. 3. Gross primary production (GPP) was highest in regions with little riparian vegetation (sagebrush steppe in Wyoming, desert shrub in Arizona/New Mexico) and lowest in forested regions (North Carolina, Oregon). In contrast, ecosystem respiration (ER) varied both within and among regions. Reference streams had significantly lower rates of GPP than urban or agriculturally influenced streams. 4. GPP was positively correlated with photosynthetically active radiation and autotrophic biomass. Multiple regression models compared using Akaike’s information criterion (AIC) indicated GPP increased with water column ammonium and the fraction of the catchment in urban and reference land‐use categories. Multiple regression models also identified velocity, temperature, nitrate, ammonium, dissolved organic carbon, GPP, coarse benthic organic matter, fine benthic organic matter and the fraction of all land‐use categories in the catchment as regulators of ER. 5. Structural equation modelling indicated significant distal as well as proximal control pathways including a direct effect of land‐use on GPP as well as SRP, DIN, and PAR effects on GPP; GPP effects on autotrophic biomass, organic matter, and ER; and organic matter effects on ER. 6. Overall, consideration of the data separated by land‐use categories showed reduced inter‐regional variability in rates of metabolism, indicating that the influence of agricultural and urban land use can obscure regional differences in stream metabolism.