Onset Of Branching Research Articles

Branching, biomass distribution, and light capture efficiency in a pioneer tree, Rhus trichocarpa, in a secondary forest

Crown architecture and biomass distribution patterns were investigated in relation to branching and tree size in a pioneer species, Rhus trichocarpa Miq. (Anacardiaceae), in a Japanese secondary forest. Crown architecture changed with tree size and with branching. Crown depth and area were greater in taller trees. In addition, branched trees had crowns of greater depth, and crown area increased more rapidly with increasing height in branched trees as compared with unbranched trees. In contrast, biomass distribution to nonphotosynthetic and photosynthetic organs changed only with tree size and was similar in unbranched and branched trees of similar size. Light capture efficiency was related to neither height nor branching status for trees with heights of 1–2.5 m. Coexistence of unbranched and branched trees at the height around the onset of branching is possible because these trees realize similar biomass distribution patterns and light capture efficiencies. Individual leaf area and leaf area index increased with tree size in unbranched trees but decreased with tree size in branched trees. These results suggest that several leaf clusters of limited size are sparsely arranged in a large three-dimensional space in tall trees.

Interspecific patterns underlying variations in allometric relationship of sympatric Sterculiaceae species in a Bornean rainforest

We compared aboveground tree forms among closely related species in two genera of the Sterculiaceae (Scaphium and Heritiera) in a Bornean mixed dipterocarp forest. Two significant allometric patterns were detected: a negative correlation between the height at the onset of branching and the slope of the species-specific Cr (crown width)-D (stem diameter) allometric relationship for juveniles (D<10 cm), and a negative correlation between Hmax (observed maximum height) and the Cr-D slope. The slope of the Cr-D allometric relationship of branched trees was significantly steeper than that of monoaxial (unbranched) trees in most species. These results suggest that the branching growth habit is better adapted than the monoaxial growth habit to crown expansion, and that the morphology of short species is better adapted to crown expansion than that of tall species. We did not detected significant correlations between the height at the onset of branching and the slope of the H (height)-D allometric relationship for juvenile trees, and between Hmax and the H-D slope. In addition, the monoaxial and branched juvenile of most species did not differ significantly in the allometric slopes of the H-D relationship. Therefore, the study does not support the hypotheses that a monoaxial growth habit favors rapid height growth and that tall species have allometries better adapted to height growth.

Gene Disruption of Spred-2 Causes Dwarfism

The impact of the fibroblast growth factor receptor 3 (FGFR3)-mediated signaling pathway on bone growth has been demonstrated by various genetic approaches. Overexpression of fibroblast growth factors (FGFs), several gain-of-function mutations in the FGFR3, and constitutive activation of mitogen-activated protein kinase (MAPK) kinase (MEK1) in chondrocytes have been shown to cause dwarfism in mice by activation of the MAPK signaling pathway. To investigate the previously reported inhibitory role of Spred in the FGFR3/MAPK pathway, we generated mice with a trapped Spred-2 gene. Here we show that lack of functional Spred-2 protein in mice caused a dwarf phenotype, similar to achondroplasia, the most common form of human dwarfism. Spred-2(-/-) mice showed reduced growth and body weight, they had a shorter tibia length, and showed narrower growth plates as compared with wild-type mice. We detected promoter activity and protein expression of Spred-2 in chondrocytes, suggesting an important function of Spred-2 in chondrocytes and bone development. Stimulation of chondrocytes with different FGF concentrations showed earlier and augmented ERK phosphorylation in Spred-2(-/-) chondrocytes in comparison to Spred-2(+/+) chondrocytes. Our observations suggest a model in which loss of Spred-2 inhibits bone growth by inhibiting chondrocyte differentiation through up-regulation of the MAPK signaling pathway.

Hedgehog and Decapentaplegic instruct polarized growth of cell extensions in the Drosophila trachea.

The migration of cellular extensions is guided by signals from tissues with which they contact. Many axon guidance molecules regulate growth cone migration by directly regulating actin cytoskeletal dynamics. Secreted morphogens control global patterns of cell fate decisions during organogenesis through transcriptional regulation, and constitute another class of guidance molecules. We have investigated the guidance roles of the morphogens Hedgehog and Decapentaplegic during directed outgrowth of cytoplasmic extensions in the Drosophila trachea. A subset of tracheal terminal cells adheres to the internal surface of the epidermis and elongates cytoplasmic processes called terminal branches. Hedgehog promotes terminal branch spreading and its extension over the posterior compartment of the epidermis. Decapentaplegic, which is expressed at the onset of terminal branching, restricts dorsal extension of the terminal branch and ensures its monopolar growth. Orthogonal expression of Hedgehog and Decapentaplegic in the epidermis instructs monopolar extension of the terminal branch along the posterior compartment, thereby matching the pattern of airway growth with that of the epidermis.

A Predictive Rolling Contact Fatigue Crack Growth Model: Onset of Branching, Direction, and Growth—Role of Dry and Lubricated Conditions on Crack Patterns

Complex crack networks are initiated in rails under Rolling Contact Fatigue. This paper attempts to model the RCF crack propagation with a particular emphasis on the branching conditions and the parameters that play a role on them. The numerical tool proposed rests on the combination of the author’s RCF model, Hourlier and Pineau’s criterion for the branch prediction and experimental data and the corresponding models for fatigue crack extension that are derived from a Joint European project. Parametric studies on the influence of (i) residual stresses, (ii) both interfacial crack and wheel/rail contact frictional effects, (iii) neighboring crack are conducted to reach a better understanding of the RC crack propagation behavior and more particularly the branch conditions, i.e., the length of the primary crack prior to branch formation and the branch direction.

Syllable onsets II: three-element clusters in phonological treatment.

This study extends the application of the Sonority Sequencing Principle, as reported in J. A. Gierut (1999), to acquisition of word-initial 3-element clusters by children with functional phonological delays (ages in years;months: 3;4 to 6;3). The representational structure of 3-element clusters is complex and unusual because it consists of an s-adjunct plus a branching onset, which respectively violate and conform to the Sonority Sequencing Principle. Given the representational asymmetry, it is unclear how children might learn these clusters in treatment or whether such treatment may even be effective. Results of a single-subject staggered multiple-baseline experiment demonstrated that children learned the treated 3-element cluster in treatment but showed no further generalization to similar types of (asymmetric) onsets. Treatment of 3-element clusters did, however, result in widespread generalization to untreated singletons, including affricates. Moreover, there was differential generalization to untreated 2-element clusters, with individual differences being traced to the composition of children's singleton inventories. Theoretically, the results suggest a segmental-syllabic interface that holds predictive potential for determining the effectiveness and effects of clinical treatment as based on the notion of linguistic complexity.

A study of the morphologies and growth kinetics of three monodisperse n-alkanes: C122H246, C162H326 and C246H494

An optical and electron microscopic study has been made of three monodisperse n-alkanes crystallising as extended-chain lamellae. All showed similar morphologies at the same supercooling and the same progressive changes of texture with crystallization temperature. This is, with increasing supercooling, from a morphology composed essentially of individual lamellae arranged in parallel stacks and radiating from common nuclei through coarse, somewhat branched microstructures whose parallel stacks diverge, to finer, more-branched pseudo-spherulitic textures. Quenched, once-folded, C246 shows a random spherulitic texture with a dominant/subsidiary microstructure as for polymeric systems. The kinetics of extended-chain growth increase linearly with supercooling, as predicted by Hoffman, except for a local dip at the onset of lamellar branching. This new phenomenon occurs within one quantized state of lamellar thickness in contrast to ‘self-poisoning’ when once-folded forms give way to extended-chain crystallization. When dominant lamellae are no longer parallel but diverge, their mutual splaying angles increase with supercooling for all the three n-alkanes studied. The values are less, for the same supercooling, for the longer homologues with their thicker lamellae. This behaviour is as expected of transient ciliation due to the excess of molecular length over that of the secondary nucleus and thereby reinforces previous evidence demonstrating the responsibility of ciliation for spherulitic development in polymers.

A unified model of Proper Government

This article aims at unifying the various devices handling vowel-zero alternations in Government Phonology. Two sets of data are analysed: French schwa-zero and Czech [E]-zero alternations. It is shown that both function identically with respect to the number of consonants that surround the alternation site. The standard analysis requires four different theoretical devices in order to account for those alternations, that is Proper Government, Constituent Government, Interconstituent Government and Government-Licensing. Crucial to the standard analysis is the observation that governing domains intervening between the governor and the governee block Proper Government. I introduce an alternative account of Proper Government the main feature of which is a strict CVCV syllable structure exclusively allowing for a consecution of non-branching Onsets and non-branching Nuclei. The CVCV-analysis offers the following advantages: first, it provides a straightforward explanation for the blocking effects of intervening CCs. Second, the devices needed to account for the alternations boil down to one, that is Proper Government. In a second step, Czech [r]-[ř] alternations are discussed. I argue that what is typically assumed to be a branching Onset must be viewed as a consecution of two Onsets separated by an empty Nucleus. It follows that the model of Proper Government that capitalises on the blocking effect of governing domains such as branching Onsets is not available for Czech. Hence, if Proper Government is to be viewed as a device of UG, as is suggested by its crosslinguistic stability, there must be a unique version of Proper Government for all languages.

Effect of inhomogeneities on dynamic crack growth in an elastic solid

The role of toughness inhomogeneities on crack branching and on limiting crack growth speeds in isotropic elastic solids is analysed using a framework where the continuum is characterized by two constitutive relations; one relates stress and strain in the bulk material, the other relates the traction and separation across a specified set of cohesive surfaces. The cohesive parameters include a strength and the work of separation per unit area so that, from dimensional considerations, a characteristic length enters the formulation. Crack initiation and crack growth emerge naturally as outcomes of the imposed loading, without any ad hoc assumptions concerning crack growth or crack path selection criteria. Full transient analyses are carried out for a plane strain block with an initial central crack subject to tensile loading. The inhomogeneities have the form of spatially nonuniform distributions of cohesive strength. The amplitude, size and density of the inhomogeneities are varied. Inhomogeneities are found to promote deviations from a straight crack growth path to a wavy or zig-zag path and to lead to the onset of crack speed oscillations at a lower crack speed, but they tend to increase the amount of crack growth preceding the onset of crack branching. However, many of the main qualitative features of the crack growth behaviour, such as crack speed oscillations, crack branching and the limiting crack speed, are the same as for homogeneous solids.

Spatially Restricted Increase in Polysialic Acid Enhances Corticospinal Axon Branching Related to Target Recognition and Innervation

The polysialic acid (PSA) modification of the neural cell adhesion molecule (NCAM) has been shown to alter the responses of developing axons to their environment. We have studied the potential role of PSA in regulating the innervation of the spinal cord by corticospinal axons, which occurs by a delayed formation of collateral branches from the parent axons. Developmental changes in the distribution of PSA were examined immuno-histochemically using light and electron microscopy. Whereas NCAM is distributed along the entire pathway of rat corticospinal axons as they grow from the cortex to the spinal cord, PSA-modified NCAM does not become evident until later. When PSA becomes evident, it is restricted to the distal segment of these axons from the caudal hindbrain through the spinal cord. The increase in PSA on corticospinal axons coincides with the time that they begin to form collateral branches in the spinal cord. This unique spatiotemporal distribution of PSA suggests its involvement in corticospinal axon branching. To test this hypothesis, PSA was selectively removed by an in vivo injection of endoneuraminidase N. This treatment did not seem to interfere with the pathfinding of corticospinal axons; however, PSA removal delayed the onset of collateral branching by corticospinal axons within the spinal cord and later diminished the magnitude of branching. These findings indicate a role for PSA in the regulation of interstitial axon branching, a crucial step in the process of target recognition and innervation by corticospinal axons.

Branching of a fast crack in polymers

Crack branching in Araldited and Homalite-911 was studied using a modified Cranz-Schardin type high speed camera which provided simultaneously taken shadow patterns and specimen-focussed images. Fracture parameters including crack velocity a, stress intensity factorKd and specific crack extension resistanceR✶ were measured in the course of crack propagation. No definite critical values could be determined with one of those fracture parameters for the onset of crack branching. Instead, the productR✶a, i.e., energy per unit crack width per unit time, was found to have a critical value for the branching.

Branching of fast crack in epoxy resin.

Crack branching in epoxy (Araldite D) was studied by the method of caustics in combination with high-speed photography. Conditions for crack branching were examined using values such as crack velocity a^^·b and crack extension resistance R*b at the onset of crack branching. No characteristic critical values could be defined for R*b or a^^·b alone. Instead, it is found that the product R*b· a^^·b, i. e., dissipated energy per unit crack front and unit time, becomes constant when the crack branching occurs, and that the faster the crack, the larger the number of successful branches.

Microscopic observation of the tips of fast running cracks in PMMA

Although various theoretical models exist, little experimental data is available on the material behaviour in the ultimate vicinity of the tip of fast running cracks. Using a microscope coupled image converter camera, the tips of cracks running in PMMA (polymethylmethacrylate) at speeds between 250 m s −1 and 680 m s −1 were photographed. Due to the high aperture of the optical set-up, shadow optical effects could be greatly reduced. Thus it was possible to observe the contour of the crack flanks up to the crack tip, revealing the existence of fibrils in between the flanks. Seemingly the appearance of these fibrils is connected with the onset of crack branching. Having the crack pass a microlattice, which had been vapor deposited onto the specimen surface, the displacements around the crack tip could be determined. The recorded plastic zone is of triangular shape. Experimental results are compared with theoretical predictions.

Measuring the charges of QCD jets

We investigate the effects of perturbative branching upon the accuracy with which one can determine the charge of the underlying QCD quantum from the charge structure of a given hadronic jet. We show explicitly how at asymptoticQ 2 we lose all such charge information. We investigate these effects at current PETRA energies using the Monte Carlo program of Fox and Wolfram; and find that a reasonably accurate charge determination is still possible at these energies. We suggest the variation of the jet charge structure with multiplicity, at a given energy, as a sensitive probe of the onset of perturbative branching inside jets.

Fibrinogen-fibrin transformations characterized during the course of reaction by their intermediate structures A light scattering study in dilute solution under physiological conditions

Intermediate structures of human fibrin formed under physiological conditions were investigated by means of light scattering in the course of the polymer/network formation. Very low fibrinogen concentrations ( c = 0.03−0.13 mg/ml) were used to lower the polymerization rate, and thrombin at five concentrations (0.0085–0.04 N.I.H./ml) was used for initiation. The light scattering data were evaluated from (i) a Zimm plot, (ii) a Holtzer plot, i.e., hR θ / Kc vs. h 2, and (iii) a Kratky plot, i.e., h 2 R θ / Kc vs. h 2. In the beginning of the polymerization process rod-like structures are formed. The dimensions of the rodlike monomeric unit in the fibrin polymer are 112 × 3.9 nm and agree with the dimensions of fibrinogen, which also was found to be a thin rod of 105 ± 10 nm length and 3.9 nm diameter. The mass per unit length, obtained from the asymptote in the Holtzer plot, initially increases only slightly but for high thrombin concentrations increases steeply when a critical length of 1000 nm is exceeded. At this point also the total scattering behaviour changes considerably. The upturn in the Zimm plot and the occurrence of a maximum in the Kratky plot are clear indications for the onset of branching. At low thrombin concentrations the kink in the curve of M w/ L w against M w becomes smoothed out because of nonspecific side-by-side aggregation of fibrin strands. The results are discussed and compared with earlier findings by others, and lead to the following conclusions. (i) Fibrinogen is a polymer with some flexibility and can exist in conformations of a stretched rod 105 nm in length, a folded rod of 45 nm in length, and a banana-like conformation of 94 nm circumference. (ii) Under the conditions of the present work, fibrinogen has the thin stretched rod conformation, and has the same dimensions as the repeating unit in the fibrin polymer. (iii) After approx. 10–12 units, end-to-end aggregated monomer branching occurs. (iv) The end-to-end aggregation is promoted by the cleavage of A peptides, branching is caused by the cleavage of B peptides while side-by-side aggregation of strands is caused by nonspecific van der Waals interaction.

On fracture mirror formation in glass and polycrystalline ceramics

Abstract Specimens of one soda-lime silicate glass and three polycrystalline ceramics were fractured at room temperature and fracture-mirror radii (r) measured at the onset of crack branching or ‘hackle’. Measured radii and fracture stresses (σf) for each material obeyed the relation σf r l/2 = A, where A is a material constant. The ratio A/K ic, where K ic is the critical stress-intensity factor of a material, was, however, independent of material type. A criterion based on energy balance is presented to show that the hackles, which bound the fracture mirror, form at a fracture velocity approximately equal to one-third the elastic wave velocity in a brittle material.