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Selected AbstractsTree growth is related to light interception and wood density in two mixed dipterocarp forests of MalaysiaFUNCTIONAL ECOLOGY, Issue 3 2005D. A. KING Summary 1The development of simple predictors of tree growth is important in understanding forest dynamics. For this purpose, tree height, crown width in two perpendicular directions, trunk diameter at 1·3 m height (d.b.h.) and crown illumination index (CI) were determined for 727 pole-sized trees (8,20 cm d.b.h.) of 21 species, on forest dynamics plots at Pasoh Forest Reserve, Peninsular Malaysia and Lambir Hills National Park, Sarawak, Malaysia. A light-interception index (LI = AcrCI2, where Acr is crown area) was calculated for each tree, and wood density (stem wood dry mass/fresh volume) was estimated for each species from reported values. 2Diameter growth rates were linearly correlated with LI (mean per species r2 = 0·45, excluding substantially damaged and vine-covered trees). 3Among trees of all species, diameter growth rate was highly correlated with LI/wood density. 4Mean growth rate per species varied 10-fold among the study species, but increased linearly with mean LI/wood density ratio (r2 = 0·78), consistent with the previous pattern. 5Thus much of the variability in tree growth rates, both within and among species, can be accounted for by the simple mechanistic assumption that, within a given size class, growth is proportional to light interception/wood density. [source] Preventing crown collisions increases the crown cover and leaf area of maturing lodgepole pineJOURNAL OF ECOLOGY, Issue 3 2006SHAWN X. MENG Summary 1Crown collisions induced by tree sway are hypothesized to reduce crown closure and leaf area in maturing cold temperate forests. These declines are thought to lead to the decline in productivity when a stand ages. 2We tethered groups of lodgepole pine (Pinus contorta Dougl. Ex Loud. Var. latifolia Engelm.) trees in a web pattern at 10 m height, in four 15-m tall stands in western Alberta, Canada, to determine whether preventing crown collisions would increase crown cover and leaf area. 3The stands all had less than 65% crown closure at the beginning of study. Photographs of the canopy were taken in each control and webbed plot in 1998 and at the same point in 2004. Six years after webbing, crown cover had increased by 14.4%, compared to a 2.1% increase for the control plots. 4Webbing also resulted in significant increases in mean branch length, leaf area per branch and foliage density of individual branches from top and middle sections of the crown. Polishing of branches, caused by chronic contact with adjacent trees, was three times as common on control trees compared to webbed trees. The mean leaf area per tree was larger for the webbed trees. 5Crowns of webbed trees were more symmetrical than those of control trees. Trees from webbed plots, however, had a decline in leaf area density. The branches of control trees were typically curved upward with twigs pointed inward, making the crowns more compact compared to the outwardly expanding crowns of trees from the webbed plots. 6The fact that crowns expanded laterally after webbing, despite little change in light regime, provides strong evidence against the hypothesis that loss of crown closure in maturing stands is caused by a lack of light. 7The study indicates that the decline in crown closure and leaf area in maturing and tall stands is at least partly related to wind-induced sway of trees abrading the edges of crowns. [source] Hydrodynamics and mass transfer in a pulsed packed columnTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2000Yu Jie Abstract The hydrodynamics and mass transfer characteristics of a pulsed packed column (PPC) filled with a stainless steel super mini ring (SMR), ceramic and stainless steel Raschig rings have been studied using a 30% tributyl phosphate-kerosene (dispersed phase)/acetic acid/water (continuous phase) system. Experiments were performed in a 100 mm internal diameter column with 1.0 m height of packing. The mass transfer and axial mixing parameters were estimated simultaneously from the measured concentration profiles of two-phase based on the backflow model. It was found that pulsation has great influence on hydrodynamics and mass transfer characteristics of PPC with the SMR. Hoxp and Hox decrease significantly with pulsation, whereas flooding velocity decreases only slightly. Comparison among the three types of packing showed that the SMR has superior characteristics both in terms of capacity and mass transfer efficiency. The influence of mass transfer on characteristics of PPC was also studied. New empirical equations of characteristic velocity, Hoxand Hoxd were proposed and good agreement between calculated and experimental data was obtained. Les caractéristiques de l'hydrodynamique et du transfert de matiére dans une colonne pulsée garni (PPC) contenant des super mini-anneaux (SMR) d'acier inoxydable et des anneaux de Raschig de céramique et d'acier inoxydable (s.s.) ont été étudiées à l'aide du système 30% de phosphate de tributyl-kérosène (phase dispersée)/acide acétique/eau (phase continue). On a mené des expériences dans une colonne de 100 mm de diamètre intérieur avec une hauteur de garnissage de 1.0 m. Les paramètres de transfert de matière et de mélange axial ont été estimés simultanément à partir des profils de concentration mesurés de deux phases d'après le modèle de reflux. On a trouvé que la pulsation avait une grande influence sur les caractéristiques de l'hydrodynamique et de transfert de matière de la colonne PPC avec le SMR. Hoxp et Hox diminuent de maniére significative avec la pulsation, tandis que la vitesse d'engorgement ne diminue que Iégèrement. Une comparaison entre les trois types de garnissage montre que le SMR possède des caractéristiques supérieures à la fois en termes de capacité et d'efficacité du transfert de matière. L'influence du transfert de matière sur les caractéristiques de la colonne PPC a également été étudiée. De nouvelles équations empiriques de la vitesse caractéristique, Hox et Hoxd, sont proposées et un bon accord est obtenu entre les données calculées et les données expérhentales. [source] A critical analysis of the acceleration length and pressure profile of single-particle systems in a circulating fluidized bedASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2008Mitali Das Abstract A study was conducted to explore the hydrodynamic behaviors using both Geldart group A and B materials in a circulating fluidized bed unit consisting of fast column (riser) of 0.1016 m i.d. and 5.62 m height. The materials tested were 120 µm of the fluid catalytic cracking (FCC) catalyst, 166 µm of iron ore, 215 µm of coal and five types of sand particles, ranging in size from 300 to 622 µm. The superficial air velocity ranged between 2.01 and 4.681 m/s and solid fluxes of 12.5,50 kg/m2s. Riser static pressure profiles were measured for the FCC catalyst, coal, iron ore and sand particles. Acceleration lengths were determined from the data, and using these and other data from the literature two correlations for the acceleration length were established for Geldart's group A and B particles. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Impact of feral water buffalo and fire on growth and survival of mature savanna trees: An experimental field study in Kakadu National Park, northern AustraliaAUSTRAL ECOLOGY, Issue 6 2005PATRICIA A. WERNER Abstract The impact of feral Asian water buffalo (Bubalus bubalis) and season of fire on growth and survival of mature trees was monitored over 8 years in the eucalypt savannas of Kakadu National Park. Permanently marked plots were paired on either side of a 25-km-long buffalo-proof fence at three locations on an elevational gradient, from ridge-top to the edge of a floodplain; buffalo were removed from one side of the fence. All 750 trees ,,1.4 m height were permanently marked; survival and diameter of each tree was measured annually; 26 species were grouped into four eco-taxonomic groups. The buffalo experiment was maintained for 7 years; trees were monitored an additional year. Fires were excluded from all sites the first 3 years, allowed to occur opportunistically for 4 years and excluded for the final year. Fires were of two main types: low-intensity early dry season and high-intensity late dry season. Growth rates of trees were size-specific and positively related to diameters as exponential functions; trees grew slowest on the two ends of the gradient. Eucalypt mortality rates were 1.5 and 3 times lower than those of pantropics and of arborescent monocots, respectively, but the relative advantage was lost with fires or buffalo grazing. Without buffalo grazing, ground level biomass was 5,8 t ha,1 compared with 2,3 t ha,1, within 3 years. In buffalo-absent plots, trees grew significantly slower on the dry ridge and slope, and had higher mortality across the entire gradient, compared with trees in buffalo-present plots. At the floodplain margin, mortality of small palms was higher in buffalo-present sites, most likely due to associated heavy infestations of weeds. Low-intensity fires produced tree growth and mortality values similar to no-fire, in general, but, like buffalo, provided a ,fertilization' effect for Eucalyptus miniata and Eucalyptus tetrodonta, increasing growth in all size classes. High-intensity fires reduced growth and increased mortality of all functional groups, especially the smallest and largest (>35 cm d.b.h.) trees. When buffalo and fires were excluded in the final year, there were no differences in growth or mortality between paired sites across the environmental gradient. After 8 years, the total numbers of trees in buffalo-absent plots were only 80% of the number in buffalo-present plots, due to relatively greater recruitment of new trees in buffalo-present plots; fire-sensitive pantropics were particularly disadvantaged. Since the removal of buffalo is disadvantageous, at least over the first years, to savanna tree growth and survival due to a rebound effect of the ground-level vegetation and subsequent changes in fire-vegetation interactions, process-orientated management aimed at reducing fuel loads and competitive pressure may be required in order to return the system to a previous state. The ,footprint' of 30 years of heavy grazing by buffalo has implications for the interpretation of previous studies on fire-vegetation dynamics and for current research on vegetation change in these savannas. [source] Der Viadukt über das Tarntal bei Millau , Von den ersten Entwurfsgedanken bis zur FertigstellungBAUTECHNIK, Issue 2 2006Michel Virlogeux Prof. Dr.-Ing. Der Bau des Viadukts über das Tarntal bei Millau in Mittelfrankreich begann im Oktober 2001 und war im Dezember 2004 vollendet. Der Viadukt mit einer Gesamtlänge von 2460 m umfaßt sechs 342 m lange Hauptfelder, die an sieben Pylonen verankert sind und stellt einen bedeutenden Fortschritt im Entwurf von Schrägseilbrücken dar. Die Autobahn verläuft 270 m über dem Fluß, zwei ihrer Pfeiler sind höher als 230 m. Mit den 87 m hohen Pylonen über der Fahrbahn überragen sie den Eiffelturm. Ausgearbeitet wurden zwei Lösungen, eine in Spannbeton und eine in Stahlbauweise. The viaduct over the Tarn valley near Millau , from early design to completion. The erection of the viaduct over the Tarn valley near Millau in central France began in October 2001 and was completed in December 2004. The viaduct with an overall length of 2460 m covers six 342 m long main fields, those at seven suspension towers is embodied and represents an important progress in design of cable-stayed bridges. The motorway runs in 270 m height over the river, two of their columns are more highly than 230 m. Together with the 87 m high pylons over the roadway towers are higher then the Eiffel tower in Paris. Two solutions were prepared, one in prestressed concrete and one in steel construction method. [source] Fast Batch to Continuous Transposition: Application to the Extraction of Andrographolide from PlantsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2006L. Prat Abstract A fast development method for batch to continuous process transposition is proposed. This method is based on transient regime experiment analyses and is applied to a solid-liquid extraction. The application under consideration is the extraction of an active principle from a plant in a non-sinusoidal pulsed column. Typically, the proposed signal is composed of two different periods: firstly, a classical sinusoidal pulsation step is used to mix the liquid and solid phases in the active part of the column and allow an optimal mass transfer and, secondly, an impulsion phase, used generally for the transport of solids. The extraction is carried out in a disc and doughnut column of 54,mm diameter and 3.5,m height. Liquid and solid are flowing co-currently and downwardly. This technological improvement has been implemented to solve the difficulties due to the significant heterogeneity of the matter: one part tends to float and other to sink, which always leads to a definitive flooding in classical operations. The effects of the solid flow rate and the solvent characteristics on the hydrodynamic behavior of the column are studied. The mean residence time and the total solid holdup are calculated by using a transient regime mass balance on the experimental results. These experiments allow the identification and quantification of opposite effects of the operating parameters. Mass transfer experiments have been performed and the results fit calculated values obtained by coupling the hydrodynamic and batch extraction results. Despite the simplifications made, this validates the fast development method proposed to help batch to continuous transposition. [source] | |||||||||||||