bluuebunny/crossref_metadata_2025 huggingface dataset:
Inertial Effects on Void Growth in Porous Viscoplastic Materials
Authors: Tong W. , Ravichandran G.
Published: February 2008

The present work examines the inertial effects on void growth in viscoplastic materials which have been largely neglected in analyses of dynamic crack growth and spallation phenomena using existing continuum porous material models. The dynamic void growth in porous materials is investigated by analyzing the finite deformation of an elastic/viscoplastic spherical shell under intense hydrostatic tensile loading. Under typical dynamic loading conditions, inertia is found to have a strong stabilizing effect on void growth process and consequently to delay coalescence even when the high rate-sensitivity of materials at very high strain rates is taken into account. Effects of strain hardening and thermal softening are found to be relatively small. Approximate relations are suggested to incorporate inertial effects and rate sensitivity of matrix materials into the porous viscoplastic material constitutive models for dynamic ductile fracture analyses for certain loading conditions.
Damage-Coupled Creep Mechanics and its Structural Analysis Principle
Authors: Zeng Pan , Sun X. F.
Published: February 2008

Continuum damage mechanics (CDM) is considered as a general method to treat the progressive deterioration of materials and structures in the framework of continuum mechanics. The damage-coupled creep mechanics based on CDM is discussed in the paper first, including the description of effective stress concept and the expression of all field equations in creep. The general formulation of a constitutive relation is presented after simplifying treatment for the sake of the modeling of creep damage problem in computational mechanics. The parametric variational principle (PVP) developed from the idea of optimal theory is introduced to establish the numerical principle of structural analysis for damage-coupled creep mechanics, including both the associated potential variational principle and the corresponding FEM formulations. The possibility of applying the principle presented by this paper to the life and damage prediction of structural components is finally illustrated by some examples on creep experiments for three kinds of materials.
Diffusion Rate for Stress in Orthotropic Materials
Authors: Mate̤milo̤la S. A. , Stronge W. J. , Durban D.
Published: February 2008

Axial rates of diffusion of the symmetrical state of stress caused by equal but opposed normal forces acting on opposite sides of an indefinitely long strip or plate, are examined in the context of orthotropic elastic materials. To obtain the stress components for this boundary value problem, the imposed surface tractions are represented by a Fourier integral. At distances larger than one quarter of the thickness, the normal stress on the middle surface is closely represented by the sum of eigenfunctions for this problem, up to, and including the first complex eigenfunction as well as its conjugate. Each eigenfunction is a product of exponentially decreasing and oscillatory terms. The exponential term is more significant for determining the rate of diffusion of stress in materials with a large ratio of axial to transverse Young’s moduli Ex/Ey ⩾ 3; this term shows a strong dependence on the ratio of transverse Young’s modulus to shear modulus Ey/G.
Three-Dimensional Viscous Flows Between Concentric Cylinders Executing Axially Variable Oscillations: A Hybrid Spectral/Finite Difference Solution
Authors: Mateescu D. , Paidoussis M. P. , Sim W.-G.
Published: February 2008

A hybrid spectral/finite difference method is developed in this paper for the analysis of three-dimensional unsteady viscous flows between concentric cylinders subjected to fully developed laminar flow and executing transverse oscillations. This method uses a partial spectral collocation approach, based on spectral expansions of the flow parameters in the transverse coordinates and time, in conjunction with a finite difference discretization of the axial derivatives. The finite difference discretization uses central differencing for the diffusion derivatives and a mixed central-upwind differencing for the convective derivatives, in terms of the local mesh Reynolds number. This mixed scheme can be used with coarser as well as finer axial mesh spacings, enhancing the computational efficiency. The hybrid spectral/finite difference method efficiently reduces the problem to a block-tridiagonal matrix inversion, avoiding the numerical difficulties otherwise encountered in a complete three-dimensional spectral-collocation approach. This method is used to compute the unsteady fluid-dynamic forces, the real and imaginary parts of which are related, respectively, to the added-mass and viscous-damping coefficients. A parametric investigation is conducted to determine the influence of the Reynolds and oscillatory Reynolds (or Stokes) numbers on the axial variation of the real and imaginary components of the unsteady forces. A semi-analytical method is also developed for the validation of the hybrid spectral method, in the absence of previous accurate solutions or experimental results for this problem. Good agreement is found between these very different methods, within the applicability domain of the semi-analytical method.
Thermohydrodynamic Analysis of Process-Liquid Hydrostatic Journal Bearings in Turbulent Regime, Part II: Numerical Solution and Results
Authors: Yang Zhou , San Andres L. , Childs D. W.
Published: February 2008

A finite difference scheme is implemented to solve the nonlinear differential equations describing the turbulent bulk-flow on the film lands of a hydrostatic journal bearing (HJB). A Newton-Raphson scheme is used to update the recess pressures and to satisfy the mass continuity requirement at each bearing recess. Comparisons of numerical predictions from the thermohydrodynamic (THD) model with experimental measurements of mass flow rate, fluid temperature, and static stiffness coefficient from a LH2 test HJB article show very good agreement. In particular, the exit temperature of the bearing is lower than the supply temperature; i.e., the liquid temperature decreases along the bearing length. Similar values of direct stiffness and damping coefficients are predicted by the adiabatic THD model and other considering isothermal flow characteristics. However, the THD model predicts lower cross-coupled stiffness and whirl frequency ratio (WFR < 0.5). The results show that for the application presented, the LH2 hydrostatic bearing is more stable than previously thought.
Analysis of Linear Nonconservative Vibrations
Authors: Ma F. , Caughey T. K.
Published: February 2008

The coefficients of a linear nonconservative system are arbitrary matrices lacking the usual properties of symmetry and definiteness. Classical modal analysis is extended in this paper so as to apply to systems with nonsymmetric coefficients. The extension utilizes equivalence transformations and does not require conversion of the equations of motion to first-order forms. Compared with the state-space approach, the generalized modal analysis can offer substantial reduction in computational effort and ample physical insight.
On the Inverse Problem of Rectangular Plates Subjected to Elastic Impact, Part I: Method Development and Numerical Verification
Authors: Yen Ching-Shih , Wu Enboa
Published: February 2008

A method to identify both the impact location and the transverse impact force history from the strain responses at certain points on a rectangular plate is presented. The governing equations of the plate were obtained by applying the Reissner-Mindlin plate theory and the Rayleigh-Ritz method. The strain response was related to the impact force by solving the above equations using the eigenmode expansion method. A mutuality relationship among any pairs of strain responses was used to find the impact location without knowing in advance the impact force history. The force history was subsequently determined after the impact location was identified. The conjugate gradient method was adopted to search for the optimal impact location as well as the force history. Numerical verification was performed using randomly generated impact locations and force histories to simulate impact events. The excellent agreement showed the effectiveness and the validity of the proposed method.
Vibration of Stress-Free Hollow Cylinders of Arbitrary Cross Section
Authors: Liew K. M. , Hung K. C. , Lim M. K.
Published: February 2008

A three-dimensional elasticity solution to the vibrations of stress-free hollow cylinders of arbitrary cross section is presented. The natural frequencies and deformed mode shapes of these cylinders are obtained via a three-dimensional displacement-based energy formulation. The technique is applied specifically to the parametric investigation of hollow cylinders of different cross sections and sizes. It is found that the cross-sectional property of the cylinder has significant effects on the normal mode responses, particularly, on the transverse bending modes. By varying the length-to-width ratio of these elastic cylinders, interesting results demonstrating the dependence of frequencies on the length of the cylinder have been concluded.
Three-Dimensional Rigid-Body Collisions With Multiple Contact Points
Authors: Marghitu D. B. , Hurmuzlu Y.
Published: February 2008

This article deals with three-dimensional collisions of rigid, kinematic chains with an external surface while in contact with other surfaces. We concentrate on a special class of kinematic chain problems where there are multiple contact points during the impact process. A differential formulation based algorithm is used to obtain solutions that utilize the kinematic, kinetic, and the energetic definitions of the coefficient of restitution. Planar and spatial collisions of a three-link chain with two contact points are numerically studied to compare the outcomes predicted by each approach. Particular emphasis is placed on the relation between the post and pre-impact energies, slippage and rebounds at the contact points, and differences among planar and nearly planar three-dimensional solutions.
On the Instability Mechanisms of a Disk Rotating Close to a Rigid Surface
Authors: Huang F. Y. , Mote C. D.
Published: February 2008

The instability mechanisms of a rotating disk, coupled to a rigid surface through a viscous fluid film at the interface, are investigated analytically. The fluid in the film is driven circumferentially by the viscous shear, and it flows outwards radially under centrifugal forces. The circumferential flow component creates an equivalent viscous damping rotating at one half the disk rotation speed. This film damping dissipates all backward traveling waves where the undamped wave speeds are greater than one half the disk rotation speed. The radial flow component creates a nonsymmetric stiffness in the disk-film system that energizes any wave mode at rotation speeds above its flutter speed. Instabilities in the disk-film system are of two types. A rotating damping instability is caused by the rotating film damping at rotation speeds above a critical value that is less than the flutter speed. A combination instability is caused by the combined effect of the film stiffness and damping at rotation speeds above a threshold that is greater than the flutter speed. The maximum rotation speed of stable disk vibration is bounded above by the lowest onset speed of rotating damping instability. This speed limit is predicted for two wall enclosure designs. The maximum stable rotation speed of a 5.25-inch diameter flexible, memory disk, separated from a rigid surface by a viscous air film, is shown to be more than 15 times greater than the maximum speed of the disk without the air film.
Equilibrium Displacement and Stress Distribution in a Two-Dimensional, Axially Moving Web Under Transverse Loading
Authors: Lin C. C. , Mote C. D.
Published: February 2008

Von Karman nonlinear plate equations are modified to describe the motion of a wide, axially moving web with small flexural stiffness under transverse loading. The model can represent a paper web or plastic sheet under some conditions. Closed-form solutions to two nonlinear, coupled equations governing the transverse displacement and stress function probably do not exist. The transverse forces arising from the bending stiffness are much smaller than those arising from the applied axial tension except near the edges of the web. This opens the possibility that boundary layer and singular perturbation theories can be used to model the bending forces near the edges of the web when determining the equilibrium solution and stress distribution. The present analysis is applied to two examples: (I) a web deflecting under its own uniformly distributed weight; (II) a web deflecting under a transverse load whose distribution is described by the product of sine functions in the axial and width directions. Membrane theory and linear plate theory solutions are used to characterize the importance of the web deformation solutions.
Thermal Stresses in a Multilayered Anisotropic Medium With Interface Thermal Resistance
Authors: Chen T. C. , Jang H. I.
Published: February 2008

This note is concerned with thermoelastic analysis of a multilayered anisotropic medium under the state of generalized plane deformation with interlayer thermal contact resistance. The powerful flexibility/stiffness matrix method is adopted here to obtain the complete solution of the entire layered medium by introducing the thermal and mechanical boundary and layer interface conditions including interlayer imperfect thermal contact conditions. As a numerical illustration, the effects of interlayer thermal resistance on the distributions of temperatures and thermal stresses in a laminated anisotropic slab subjected to a uniform surface temperature rise are presented.
Spores of Frankia strain HFPCcl3 nodulate Casuarina equisetifolia after passage through the digestive tracts of captive parakeets (Melopsittacus undulatus)
Authors: Burleigh Stephen H. , Dawson Jeffrey O.
Published: February 2008

Spores of Frankia strain HFPCcl3 nodulated Casuarina equisetifolia after passage through the digestive tracts of captive parakeets (Melopsittacus undulatus). Parakeets excreted infectious fecal material from 6 to 72 h after ingesting food inoculated with Frankia spores. Air desiccation of spore-containing fecal material reduced its infectious capacity by approximately 90%. Hyphal filaments of this strain lost most of their infectious capacity after passage through parakeet digestive tracts. These results indicate that it is possible for spores of Frankia to survive passage through the digestive tracts of birds, thereby predisposing them to avian dispersal. Key words: actinorhizal plants, Casuarina, Frankia, nodulation, parakeets, spores.
Ecotypic variation ofGremmeniella abietinain northern Europe: disease patterns reflected by DNA variation
Authors: Hellgren M. , Högberg N.
Published: February 2008

Genetic variation in Gremmeniella abietina isolated from Pinus sylvestris, Pinus contorta, and Picea abies in southern and northern Fennoscandia was studied with arbitrary primed polymerase chain reaction. Fennoscandian G. abietina isolates were clearly separated into two ecotypically distinct groups based on their amplified banding patterns. Analysis of variance based on amplified fragments, AMOVA, and principal component analysis confirmed the separation of the isolates into the two groups. One group contained isolates associated with a disease syndrome affecting young trees covered by deep snow during winter in northern Fennoscandia. The second group of isolates was found on trees between 15 and 40 years old, scattered throughout the crowns. It occurs throughout Fennoscandia but is most frequent in the southern parts. No size polymorphism was found in fragments resulting after restriction enzyme digestion of internal transcribed spacer and intergenic spacer regions of nuclear ribosomal DNA. An estimate of gene flow between populations calculated based on amplified band frequencies, FST, indicated that there was restricted genetic exchange between populations of the two groups of isolates. Key words: Gremmeniella abietina, arbitrary primed polymerase chain reaction, genetic variation, ecotypes, ribosomal DNA.
Condensed tannins in sainfoin. II. Occurrence and changes during leaf development
Authors: Lees G. L. , Gruber M. Y. , Suttill N. H.
Published: February 2008

A histological study examined condensed tannin (CT) formation in plant tissue samples taken from the meristematic area of very young sainfoin (Onobrychis viciifolia Scop.) seedlings and from leaflets sampled at various stages of development in mature plants growing in the greenhouse. Light and electron microscopy revealed no CT in the seedling meristem and leaf primordia, but CTs were seen very early in leaf development forming first in the vacuoles of discrete cells of the abaxial subepidermal layer when the leaflets were recognizable, but still folded. Immature leaflets collected from the growing point of a mature sainfoin plant show similar CT formation with the abaxial cell vacuoles filled with CT when the new leaves have reached the 90°-fold stage. As the leaflets unfold and mature, CTs begin to appear in the vacuoles of small, but discrete cells in the adaxial subepidermal layer while the tannin-containing cells in the abaxial subepidermal layer begin to lose CT. The CT continues to increase in the adaxial layer until typical enlarged tannin idioblasts or sacs are observed at full leaflet expansion and maturity. By this stage, the vacuoles in the abaxial layer are almost empty. In senescing leaflet samples collected from the leaf rachis attached to the last and second to last node near the base of the plant, the cells in both subepidermal layers have lost the majority of the CT that was originally formed. At senescence all tannin-containing cells appear as empty shells. We speculate that a finite amount of CT is formed in the two subepidermal layers of new leaves at different stages of early leaf development, does not increase during the mature phase, and is catabolized in older leaves and during senescence. Key words: condensed tannins, sainfoin, Onobrychis viciifolia, leaf development.
Anther, ovule, seed, and nucellar embryo development inCitrus sinensiscv. Valencia
Authors: Koltunow Anna M. , Soltys Kathleen , Nito Nobumasa , McClure Stuart
Published: February 2008

'Valencia' orange, a commercially important cultivar of Citrus, forms polyembryonic seeds by an apomictic process called nucellar embryony in which many embryos initiate directly from nucellar cells surrounding the sexual embryo sac. We observed anther, ovule, seed, and fruit development in relation to nucellar embryo development in seeds and unfertilized ovules of 'Valencia'. Pollination and fertilization are required to set fruit in 'Valencia', and low seed set was found to be related to defects in both male and female gametogenesis. Nucellar embryo initial cells were evident histologically in ovules of flowers just prior to anthesis. However, in vitro culture of ovules from flowers at different prepollination stages showed that embryos could develop from ovules cultured as early as the binucleate stage of megagametogenesis in which nucellar initial cells were absent histologically. During fruit development, the timing and sequence of the early events of nucellar embryo formation were synchronous in seeds and unfertilized ovules, indicating a co-ordinated control of embryo development in spatially and developmentally distinct structures. In both developing seeds and unfertilized ovules, embryo initial cells first formed thick walls, which isolated them from surrounding maternal tissue. In later stages, the cell walls thinned in some initial cells and embryogenesis became asynchronous. Cleavage of embryogénie cells coincided with degenerative processes linked to embryo sac expansion in seeds and to a previously unreported, localized degeneration in the central portion of the nucellus in unfertilized ovules. Some initial cells never divided. Nucellar embryo development was restricted to the central portion of unfertilized ovules and to the micropylar region of seeds. Only fertilized ovules had the capacity to form mature polyembryonic seeds. In unfertilized ovules a specialized vascular structure formed linking developing embryos to the chalazal vasculature of the ovule. Embryo development arrested at the globular stage in unfertilized ovules and the integuments differentiated to form a seed coat. The timing of reproductive events described was linked to floral and fruit morphological characteristics to facilitate molecular characterization of nucellar embryogenesis and seed formation in this cultivar. Key words: Citrus, nucellar embryony, seed, ovule, apomixis.
Immunolocalization of a proteinase of the sap-staining fungus Ophiostoma piceae using antibodies to proteinase K
Authors: Hoffert C. , Gharibian S. , Breuil C. , Brown D. L.
Published: February 2008

Polyclonal antibodies were raised against proteinase K and were used to immunolocalize the major extracellular proteinase of the sap-staining fungus Ophiostoma piceae (Münch) H. and P. Sydow. Immunodot blotting showed that the IgG antibodies recognized both enzymes but reacted more strongly with proteinase K than with the O. piceae proteinase. Immunogold labelling and transmission electron microscopy revealed that the O. piceae proteinase was localized in the cell walls of O. piceae grown either in liquid media or wood. Key words: Ophiostoma piceae, proteinase, immunogold labelling, transmission electron microscopy, antibody, proteinase K.
Mating system and distribution of enzyme genetic variation in bracken (Pteridium aquilinum)
Authors: Korpelainen Helena
Published: February 2008

An allozyme study of populations of bracken, Pteridium aquilinum, revealed very low rates of intragametophytic selfing, on average 0.046, despite potential hermaphroditism and selfing of the gametophytes. The average number of genotypes per population was only 3.0 and mean heterozygosity equalled 0.015. Several populations consisted of only one genotype. The level of genetic divergence among populations was considerable. The mean value of the differentiation among populations (FST) was high (0.307) and the gene flow values were low, equalling 0.52 and 0.23 depending on the method of estimation. It is suggested that the life history of P. aquilinum, characterized by variable rates of spore production, vegetative reproduction, and the inefficiency of gametophyte growth and reproduction in established bracken stands, promotes genetic differentiation between populations. Key words: bracken, Pteridophyta, genetic variation, gene flow, mating systems.
The effects of smut (Ustilago destruens) on seed production, dormancy, and viability in fall panicum (Panicum dichotomiflorum)
Authors: Govinthasamy Thevaki , Cavers Paul B.
Published: February 2008

Fall panicum (Panicum dichotomiflorum var. geniculatum), an abundant annual weed in southwestern Ontario, suffers large seed losses from the smut Ustilago destruens. From 19 to 83% of plants were infected in three sites surveyed. Some infected plants were completely sterile, but others produced small numbers of viable seeds. Most of these seeds did not give rise to smut-infected plants if they were not exposed to smut teliospores in the soil over winter. Compared with seeds from uninfected plants, those from infected plants had lower percent viability and weaker dormancy. When seeds from either infected or uninfected plants were mixed with smut teliospores over winter, 39% of the resulting plants were smut infected, compared with less than 1% of plants from seeds overwintered without smut teliospores. Seeds mixed with smut teliospores over winter did not lose viability, but some of them were slower to germinate the following spring. Key words: smut, fall panicum, seed viability, seed dormancy, germination, Ustilago destruens, Panicum dichotomiflorum.
Composition of prairie plant communities on productive versus unproductive sites in wet and dry years
Authors: Piper Jon K.
Published: February 2008

A natural productivity gradient was used to test questions about plant species composition, diversity, and sensitivity to environmental change of prairie vegetation within the tallgrass region. From 1986 to 1992 I monitored seasonal net aboveground production and species composition at four sites with soils that differed in texture and percent organic matter, pH, and concentrations of NH4, total N, K, Ca, Mg, and SO4. Four years of the survey featured above normal precipitation and 3 were drought years. August standing crop averaged 566 ± 307, 419 ± 143, 268 ± 158, and 232 ± 148 g ∙ m−2at the four sites. Production generally increased with soil fertility (i.e., percent organic matter, total N, and K) and precipitation. The two more productive sites featured higher percentages of grass biomass, but legumes were rare. The site with the lowest soil N supported the consistently highest legume biomass and lowest grass biomass among sites. The least productive site displayed the highest percentage of composites. Species evenness, but not richness, was inversely related to August biomass for all sites. There were significant differences in production across years, as well as in percentages of grass, legume, and composite biomass. Total plot richness ranged from 24 to 40 species sampled per year at site 2 to 51 –53 species at site 4, and tended to decline in the dry year 1989. Poor soils, although less productive overall, appear to prevent dominance by tall grasses and thereby maintain relatively more diverse spring and summer floras. Increased light availability near the soil surface probably enables the persistence of low-growing plants. Evenness, but not richness, varied among sites. The patterns of plant community composition have implications for restoration ecology as well as the design of prairielike perennial grain mixtures. Key words: diversity, evenness, plant community, prairie, soil type, variability.
Particle regularity on thylakoid fracture faces is influenced by storage conditions
Authors: Semenova Galina A.
Published: February 2008

Specific temperature, storage times, and medium composition enable initiation of regular arrays of intramembranous particles on the exoplasmic fracture face during prolonged storage of isolated chloroplasts at 4 °C, producing about 2 – 10 regular arrays with 2 – 30 particles in each array, with a period of about 36 nm, oriented in 1 – 4 directions. The particle sizes do not change throughout the time of storage (1 – 4 weeks). The second type of particle regularity arises during prolonged storage of chloroplasts in greater than 1 M sucrose at −18 °C. Rounded areas of small particles tightly packed into paracrystalline arrays are found among less densely packed particles. The density of small particles is 4700 particles/μm2, and the mean size is 11 nm, whereas the particle density of the background is 1600 particles/μm2with a mean particle size of 13 nm compared with 1200 particles/μm2and mean size 16 nm in fresh chloroplasts. Based on the reduction of particle sizes and manner of packing on the fracture face, it is proposed that the small particles are a light-harvesting complex, separate from photosystem II and aggregated into paracrystalline arrays. The thylakoid lipids may participate in formation of particle regularity. Key words: thylakoid membrane, freeze fracture, particle regularity, low temperatures.
The cost of reproduction to the clonal herb Asarum canadense (wild ginger)
Authors: Muir Angela M.
Published: February 2008

The cost of reproduction to the clonal understorey herb Asarum canadense (wild ginger) was examined by measuring subsequent growth and storage. All connected vegetative rhizome was controlled and fully measured. Three important aspects of reproductive effort were addressed: (i) the effect of sexual reproduction on subsequent storage and growth of fragments, (ii) the effect of asexual reproduction on subsequent storage and growth of fragments, and (iii) a comparison to determine the least costly method of reproduction. It was found that sexual reproduction in wild ginger has an energy cost that diverts energy from storage and growth. Asexual reproduction represents neither a net energy cost nor gain to the fragment and is the least costly mode of reproduction to wild ginger. Key words: Asarum canadense, reproduction, rhizome, clonal.
An experimental and theoretical evaluation of a floor truss system
Authors: Monforton Gerard R. , Temple Murray C. , Wolf Gerhard W. H.
Published: February 2008

Floor joists consisting of 38 × 89 mm top and bottom chords connected by galvanized steel V webs are often used in the construction of low-rise buildings where long spans are required. An experimental and theoretical program was undertaken to evaluate the performance of such joists when used in conjunction with plywood sheathing attached to the top chord to form a truss floor system. A finite-element analysis procedure for sandwich beams with faces of unequal thickness was adapted in order to predict the load-deflection curves of full-scale floor systems. The experimental program involved the testing of double-block shear specimens to determine the modulus of rigidity of the core, shear specimens to evaluate the performance of the adhesive, and four floor sections to evaluate the performance of the floor system when subjected to uniformly distributed loads. The results indicate that a modulus of rigidity can be determined from the double-block shear specimens, the adhesive performed well under a variety of environmental conditions, the sand wich beam analysis can be used to predict the load-deflection curve of the truss floor system, and the floors performed well when subjected to uniformly distributed loads. Key words: adhesive, floors, floor joists, floor trusses, metal V webs, timber.
SEXTANG : système expert d'aide à l'exploitation des stations d'épuration par étangs aérés facultatifs
Authors: Gagnon J. , Sérodes J. B. , Simian G.
Published: February 2008

When completed, the actual program of municipal wastewater abatment of Quebec will comprise, among many treatment stations, approximately 400 facultative aerated lagoons. This type of station needs some supervision to maintain a good performance. Failure to adequately supervise the process could result in partly treated waters, not meeting environmental regulations, being released, SEXTANG is a prototype of expert system developed to assist operators of these stations in their every day duties and to identify the causes of misfunctions and propose solutions. Four different functions are available: (i) diagnosis and solutions to identified problems, (ii) data record and processing of current parameters, (iii) sludge management, and (iv) information on environmental regulations, SEXTANG presents also a user friendly interface with functions like an explanation of questions asked by the system, a dictionary of wastewater treatment terminology, and the access, at any time during a consultation, to the values and answers given by the operator since the beginning of the consultation. Key words: expert system, wastewater treatment, facultative aerated lagoons, computer-assisted operation.
Distribution of methylisothiocyanate and chloropicrin in boles or roots of Douglas-fir trees
Authors: Morrell Jeffery J. , Forsyth Paul G. , Thies Walt G.
Published: February 2008

The distribution of the fumigants methylisothiocyanate (MITC), Vorlex, and chloropicrin, used to control Phellinusweirii (Murr.) Gilb., was assessed 10 years after application to sites near the bases of living Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco). MITC was detected up to 8 m above the original application site, and fumigants were present at the highest levels near the pith of the tree. MITC was detectable as far as 2.1 m down the roots in trees treated with the largest dosage, and Vorlex was detectable 1.5 m from the application site. Levels of chloropicrin were generally greater than levels of MITC or Vorlex, but chloropicrin was detected only up to 3 m above the application site; lower water solubility probably accounted for the restricted diffusion of this chemical. The results indicate that fumigants can diffuse for considerable distances through Douglas-fir boles and roots. Further studies are underway to establish the efficacy of the concentrations measured in these trees.
Genetic parameters and age–age correlations in a clonally replicated test of black spruce after 10 years
Authors: Mullin T.J. , Park Y.S.
Published: February 2008

Height growth at 10 years from striking was assessed for clonally replicated full-sib black spruce (Piceamariana (Mill.) B.S.P) families tested at three locations in central Nova Scotia. Variance components were interpreted according to an additive–dominance–epistasis genetic model and used to derive comparative estimates of gain from various selection and deployment strategies. Field performance at 5 and 10 years was compared with that of the original ortets and families growing in a 25-week greenhouse study, by means of phenotypic and genetic correlation, and rank-change analyses. Between age 5 and 10, the additive portion of the total genetic variance for height decreased from 66 to 38%, while the dominance portion increased from less than 3 to 13%, and the epistatic portion from 31 to almost 49%. As a consequence, narrow-sense heritability estimates were lower at age 10 and gain estimates also decreased, particularly for those strategies that capture gain primarily from additive effects. Although correlations between field performance and early growth measurements were generally poor, the strongest were found at the half-sib level; full-sib correlations were somewhat weaker and those between clone means and early ortet performance were small and not statistically significant. The strongest age–age correlations were those that involved family mean seedling weight in the greenhouse. Family rankings based on early oven-dry biomass production also showed the most consistent agreement with ranking after 5 and 10 years of field testing, although the analyses suggest that effective early selection is probably limited to culling the worst 25% of the families based on biomass. Genotype–environment interactions were statistically significant, although these were limited to only 2% of the phenotypic variance in height growth; furthermore, strong genetic correlations between environments suggested that these interactions have little impact on selection efficiency.
Fertilizing and mulching influence on the performance of four native woody species suitable for revegetation in subarctic Quebec
Authors: Houle Gilles , Babeux Patrice
Published: February 2008

Two plantations were established in the village of Whapmagoostui-Kuujjuaraapik to determine the effects of two types of fertilizer (fast or slow release) and two types of mulch (plastic or organic) on native woody species growth and survival in subarctic Quebec. In the first plantation, the species tested were Salixplanifolia Pursh, Alnuscrispa (Ait.) Pursh, Piceaglauca (Moench) Voss, and Pinusbanksiana Lamb. Four growing seasons after planting, cuttings of S. planifolia had the highest survival of all four species (96% in control plots) and a very good growth (4.8 mm and 5.7 cm growth in diameter and height, respectively). The performance of A. crispa was also very good (77% survival in control plots; 5.1 mm and 7.5 cm growth in diameter and height, respectively), while Piceaglauca (17% survival in control plots; 0.6 mm and −9.0 cm growth in diameter and height, respectively) and Pinusbanksiana (31% survival in control plots; 2.4 mm and 5.7 cm growth in diameter and height, respectively) performance was poor. The application of a slow-release fertilizer enhanced plant growth of all four species, but reduced the survival of A. crispa, particularly when a plastic mulch was used. Otherwise, mulching had no significant effect on either growth or survival of any of the other species. In the second plantation, established on a more exposed site, the survival of S. planifolia was lower (77% in control plots) than in the first plantation, and the application of a fast-release fertilizer there had a negative effect on plant growth. These latter results appear to be related to freezing injuries and winter killing of vegetative buds. Organic mulching did not influence plant growth on this second site, but the utilization of Alnus wood chips increased the survival of S. planifolia cuttings. We recommend the use of S. planifolia and also of A. crispa for revegetation purposes in subarctic Quebec. Application of a slow-release fertilizer can increase plant growth, but should not be combined with the use of plastic mulches, as plant survival is then negatively affected.
Modeling the diameter and locational distribution of branches within the crowns of loblolly pine trees in unthinned plantations
Authors: Doruska Paul F. , Burkhart Harold E.
Published: February 2008

Crown structure for 9- to 30-year-old loblolly pine (Pinustaeda L.) trees in unthinned plantations was quantified via analysis of branch diameters and location, both along and around the bole, using data from 68 trees. The trees ranged in size from 11.1 to 31.6 cm in diameter at breast height and from 8.30 to 25.67 m in total height, and were growing in Piedmont and Atlantic Coastal Plain stands. Three equations were used to describe the diameter distribution of branches. Circular statistics were used to examine branching patterns around the bole. A system of two equations was developed to predict the total number of branches within a crown. A series of three equations was used to describe the mean of and range in diameters within a whorl. Attempts at modeling the height above ground to branches (whorls) were unsuccessful; therefore, equal height growth per year was assumed and whorls were placed within each year of growth in concordance with the literature. Similarly, predicting the number of branches within a whorl of a certain height was difficult, and overall percentages were employed. Analysis of branch azimuths on a whole-tree basis indicated that a uniform, or regular, distribution was appropriate (and not a "circular normal" distribution). Finally, circular correlation was used to analyze rotational patterns within and between whorls, and a strong positive correlation was found for consecutive whorls of the same number of branches. From this study it was concluded that modeling crown structure is difficult, with much variation occurring among trees.
Growth, photosynthesis, and herbicide tolerance of genetically modified hybrid poplar
Authors: Donahue Raymon A. , Davis Tim D. , Michler Charles H. , Riemenschneider Don E. , Carter Doug R. , Marquardt Paula E. , Sankhla Narendra , Sankhla Daksha , Haissig Bruce E. , Isebrands J.G.
Published: February 2008

Hybrid poplar clone NC–5339 (Populusalba × Populusgrandidentata cv. Crandon) was genetically modified for glyphosate (N-(phosphonomethyl)glycine) tolerance by Agrobacterium-mediated transformation with genetic constructs (pPMG 85/587 and pCGN 1107) that included the mutant aroA gene for 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase (EC 2.5.1.19) and the neomycin phosphotransferase selectable marker gene. pCGN 1107 also harbored the coding sequence for a chloroplast transit peptide and the CaMV 35S promoter fused to the mutant aroA gene. Transformants were selected for kanamycin tolerance, and integration of the aroA gene was verified by Southern blot analysis. Cuttings of NC-5339 and the derived transformants were rooted and grown in glasshouses at separate locations, with maximum photosynthetic photon flux density of 1600 and 750 μmol•m−2•s−1. Productivity was assessed by growth studies and photosynthesis measurements at both locations. Glyphosate tolerance was tested by (i) measurement of chlorophyll concentration in herbicide-treated leaf discs and (ii) whole-plant spray tests. Plants transformed with construct pCGN 1107 were the most herbicide tolerant. Perhaps high-level expression of the aroA gene by the CaMV 35S promoter, transport of mutant EPSP synthase into the chloroplasts, or both facilitated glyphosate tolerance. Plants grown at higher photosynthetic photon flux densities (1600 vs. 750 μmol•m−2•s−1) had significantly higher maximum net photosynthesis (19.8 vs. 16.2 μmol•m−2•s−1) and more biomass accumulation (47.6 vs. 33.7 g). However, there were no significant differences between NC-5339 and transformants within location for net photosynthesis or any growth parameter. Genetic modification of hybrid poplar NC-5339 for glyphosate tolerance did not adversely affect plant productivity at either location.
Boron deficiency in eucalypt plantations in China
Authors: Dell B. , Malajczuk N.
Published: February 2008

Boron deficiency is identified as one of the more important causes of poor stem form and malformed leaves in plantations of Eucalyptusglobulus in Yunnan Province, and of Eucalyptusgrandis, Eucalyptustereticornis, and Eucalyptusurophylla in Guandong Province. Symptoms of B deficiency in E. globulus were rolled and malformed leaves, stem dieback, and a prostrate form. In E. urophylla, leaf margins became chlorotic then necrotic, leaves turned brittle and corky, shoots died back, and the upper stem nodes were enlarged supporting numerous short-lived axillary shoots. In E. grandis, stem dieback was preceded by the basipetal accumulation of anthocyanin in leaves. Boron-deficient E. tereticornis leaves developed marginal and interveinal chlorosis and recurved margins. Depressed foliar B concentrations were associated with visible symptoms. In E. globulus, the mean B concentration in young leaves of healthy trees was 31 mg/kg dry matter compared with 10 mg/kg in prostrate trees. Symptoms did not appear in E. globulus trees supplied with B fertilizer at planting. Normal shoot growth was restored in E. urophylla by the addition of B to the soil.
Nitrogen mineralization and decomposition in forest floors in adjacent plantations of western red cedar, western hemlock, and Douglas-fir
Authors: Prescott C.E. , Preston C.M.
Published: February 2008

To determine if western red cedar (Thujaplicata Donn) litter contributes to low N availability in cedar–hemlock forests, we measured concentrations of N and rates of net N mineralization in forest floors from single-species plantations of cedar, western hemlock (Tsugaheterophylla (Raf.) Sarg.), and Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) on the same site in coastal British Columbia. Concentrations of total and extractable N and rates of net N mineralization during laboratory incubations were lowest in the cedar forest floor and highest in Douglas-fir. Less C was mineralized in the cedar forest floor during incubation, and the amount of N mineralized per unit C was least in cedar. Rates of mass loss of foliar litter of the three species were similar during the first 50 weeks of a 70-week laboratory incubation, but cedar lost mass more quickly during the final 20 weeks. Rates of net N mineralization in the forest floors were significantly correlated with the initial percent N, C/N, % Klason lignin, and lignin/N of foliar litter. Foliar litter of cedar had lower concentrations of N and greater proportions of alkyl C (based on 13C NMR spectroscopy) than Douglas-fir litter. These characteristics of cedar litter may contribute to low N availability in cedar–hemlock forest floors. Concentrations of alkyl C (waxes and cutin) may be better than lignin for predicting rates of mass loss and N mineralization from litter.
Breast-height relative density and radial growth in mature jack pine (Pinusbanksiana) for 38 years after thinning
Authors: Barbour R. James , Fayle David C.F. , Chauret Gilles , Cook Jean , Karsh Marianne B. , Ran Shikun
Published: February 2008

Sawlogs are in short supply in northern Ontario, and thinning has been suggested as one way to improve the situation. The only rotation-age jack pine (Pinusbanksiana Lamb.) thinning trial in the region was examined to assess how commercial thinning influenced wood quality. This report covers an unreplicated trial of a 65-year chronology of pith to bark relative densities and growth rates based on X-ray densitometry of breast-height increment cores taken from trees on two thinned plots (average spacing 2.6 and 3.4 m) and an unthinned control (average spacing 1.7 m). The trees on the treatment plots responded to thinning by producing wood with significantly lower relative density than those on the control plot. This trend continued much longer than reported for other pines and could negatively affect pulp yield or mechanical properties of lumber. Enhanced earlywood growth caused a drop in the proportion of latewood that resulted in the decline in density. Thinning may have improved moisture availability during the early and middle season and encouraged earlywood growth. Density and growth rate differences became apparent soon after treatment. Early, rapid, and inexpensive estimates of the product potential of younger thinning trials are possible using the techniques demonstrated here.
The differential sensitivity of red pine and quaking aspen to competition
Authors: Puettmann Klaus J. , Reich Peter B.
Published: February 2008

Growth of red pine (Pinusresinosa Ait.) and quaking aspen (Populustremuloides Michx.) target trees with varying degrees of competition by neighboring aspen was measured in a 7-year-old clearcut in northeastern Minnesota. Competitive conditions were measured using indices of resource availability (percent open sky) and neighborhood stand density. Three-year diameter growth of target trees was reduced by more than 50% in both species because of competition from neighboring quaking aspen. The last 2 year's height growth was also reduced by approximately 30% for both species. The relationship between growth and percent open sky was convex for red pine and concave for quaking aspen, potentially indicating a greater sensitivity in aspen to any reduction below optimal resource availability. Competition reduced crown size in both species, but self-pruning occurred only in quaking aspen. Needle and leaf size were not affected by competition, but red pine needle density was lower in highly competitive environments. Red pine had a higher specific gravity when growing under competition, partially offsetting the reduction in wood volume.
Relations between tree-ring widths, climate, and annual area burned in the boreal forest of Alberta
Authors: Larsen C.P.S. , MacDonald G.M.
Published: February 2008

Ring-width chronologies from three white spruce (Piceaglauca (Moench) Voss) and two jack pine (Pinusbanksiana Lamb.) sites in the boreal forest of northern Alberta were constructed to determine whether they could provide proxy records of monthly weather, summer fire weather, and the annual area burned by wildfires in Wood Buffalo National Park. All but one of the standard and residual chronologies exhibited significant positive correlations with June precipitation in the growth year, and all but three of the chronologies exhibited positive correlations with precipitation in June, July, or August of the previous year. Three of the residual chronologies also exhibited negative correlations with June temperature in the growth year. Four of the standard and residual chronologies exhibited significant correlations with the Seasonal Severity Rating fire weather variable from Fort Smith, N.W.T. Four of the standard chronologies and three of the residual chronologies exhibited significant correlations with the annual area burned in Wood Buffalo National Park. Significant correlations were also found for some of the standard and residual chronologies with fire weather and annual area burned in the previous year. These results suggest that ring widths and annual area burned in this portion of the boreal forest are sensitive to similar weather conditions. Tree-ring records may therefore provide a useful means of examining decadal to centennial length relations between climate and annual area burned in the boreal forest.