Branching Parameters Research Articles

Cover cropping and novel pesticide usage in the management of pests of hot pepper ( Capsicum chinense)

In a bid to develop technologies that serve grower needs for economic management of pests and diseases of hot pepper (scotch bonnet) while protecting public health and the environment, a study to assess the potential of cover cropping and/or less-risk pesticide usage in the management of pests and diseases of hot pepper was conducted for two consecutive seasons in Uganda. A split-plot randomized complete block design with three replications was used with cropping system (main plots) and pesticide treatment (sub-plots) as the factors. There were two cropping systems: the hot pepper þ cowpea system vs. a hot pepper monocrop and five pesticide treatment options: (i) prophylactic treatment of plots at transplanting with granular carbofuran; (ii) weekly sprays of a neem-based formulation; (iii) combination of the prophylactic carbofuran treatment and neem; (iv) sulphur sprays at 10-day intervals (season 2 only); and (v) the untreated control. Data were collected on population dynamics of aphids, whiteflies, thrips, mites, nematodes and on plant performance parameters of branching and fruit weight. Results indicated that the hot pepper þ cowpea system greatly lowered infestations of aphids and nematodes on hot pepper, but did not decrease thrips and whiteflies; and brought about a yield penalty on hot pepper. Prophylactic applications of carbofuran and/or sprays of a neem-based formulation lowered populations of aphids and whiteflies on hot pepper to varying extents; and increased yield of pepper.

Earthquake Patterns in Diverse Tectonic Zones of the Globe

We extend existing branching models for earthquake occurrences by incorporating potentially important estimates of tectonic deformation and by allowing the parameters in the models to vary across different tectonic regimes. We partition the Earth’s surface into five regimes: trenches (including subduction zones and oceanic convergent boundaries and earthquakes in outer rise or overriding plate); fast spreading ridges and oceanic transforms; slow spreading ridges and transforms; active continental zones, and plate interiors (everything not included in the previous categories). Our purpose is to specialize the models to give them the greatest possible predictive power for use in earthquake forecasts. We expected the parameters of the branching models to be significantly different in the various tectonic regimes, because earlier studies (Bird and Kagan in Bull Seismol Soc Am 94(6):2380–2399, 2004) found that the magnitude limits and other parameters differed between similar categories. We compiled subsets of the CMT and PDE earthquake catalogs corresponding to each tectonic regime, and optimized the parameters for each, and for the whole Earth, using a maximum likelihood procedure. We also analyzed branching models for California and Nevada using regional catalogs. Our estimates of parameters that can be compared to those of other models were consistent with published results. Examples include the proportion of triggered earthquakes and the exponent describing the temporal decay of triggered earthquakes. We also estimated epicentral location uncertainty and rupture zone size and our results are consistent with independent estimates. Contrary to our expectation, we found no dramatic differences in the branching parameters for the various tectonic regimes. We did find some modest differences between regimes that were robust under changes in earthquake catalog and lower magnitude threshold. Subduction zones have the highest earthquake rates, the largest upper magnitude limit, and the highest proportion of triggered events. Fast spreading ridges have the smallest upper magnitude limit and the lowest proportion of triggered events. The statistical significance of these variations cannot be assessed until methods are developed for estimating confidence limits reliably. Some results apparently depend on arbitrary decisions adopted in the analysis. For example, the proportion of triggered events decreases as the lower magnitude limit is increased, possibly because our procedure for assigning independence probability favors larger earthquakes. In some tests we censored earthquakes occurring near and just after a previous event, to account for the fact that most such earthquakes will be missing from the catalog. Fortunately the branching model parameters were hardly affected, suggesting that the inability to measure immediate aftershocks does not cause a serious estimation bias. We compare our branching model with the ETAS model and discuss the differences in the models parametrization and the results of earthquake catalogs analysis.

Random cross-linked poly(styrene- co-maleic anhydride): Characterization of cross-linking intermediates by size exclusion chromatography

The cross-linking reaction of poly(styrene- co-maleic anhydride) (SMA) with ethylene glycol (EG) was monitored using size exclusion chromatography. On-line viscosity and static light scattering detection provided [ η] and R g for structural analysis of the cross-linking intermediates. With increasing reaction time a decrease of the expansion exponent α of the Kuhn–Mark–Houwink–Sakurada relationship was observed. A change from coiled structures to spherical molecules during the cross-linking reaction was confirmed by analyzing the fractal dimensions of the molecules after different reaction times. The calculation of the branching parameters g and g′ revealed the formation of contracted branched molecules. The connection of SMA chains by EG leads to a contraction of the polymers with increasing molecular weight.

Geometric Variability of the Abdominal Aorta and Its Major Peripheral Branches

Vessel geometry determines blood flow dynamics and plays a crucial role in the pathogenesis of vascular disease. In vivo assessment of three-dimensional (3D) vessel anatomy is vital to improve the realism of arterial flow model geometries and investigate factors associated with the localisation of atherosclerosis. The quantification of vascular geometry is also particularly important for the proper design and preclinical testing of endovascular devices used to treat peripheral arterial disease. The purpose of this study was to quantitatively evaluate the intersubject variability of 3D branching and curvature of the abdominal aorta and its major peripheral arteries. Contrast-enhanced renal MRA scans of healthy abdominal vessels obtained in 12 subjects (8 men, 4 women mean age 49 years, range 27-84 years) were segmented, and smoothed centerlines were determined as descriptors of arterial geometry. Robust techniques were employed to characterise non-planar vessel curvature, arterial taper, and 3D branching parameters. Noticeable 3D curvature and tapering were quantified for the proximal anterior visceral and renal branches. Mean 3D branching angles of 63.5+/-10.1 degrees and 73.1+/-6.8 degrees were established for the right and left renal arteries, respectively. Angles describing the ostial position and initial trajectory of the renal arteries confirmed the antero-lateral origin and direction of the right and the more lateral orientation of the left. The anterior visceral branches emerged predominantly from the left side of the anterior aortic wall. Branching parameters determined at the aortic bifurcation demonstrated mild asymmetry and non-planarity at this location. In summary, the results from this study address the scarcity of available in vivo 3D quantitative geometric data relating to the abdominal vasculature and reflect the geometric variability in living subjects.

A model of the formation of branched polymethyl methacrylates

A model of formation of macromolecules in the form of a crown of a tree was suggested to describe the character of branching and architecture of branched macromolecules synthesized by radical copolymerization of a monomer with a bifunctional monomer-branching agent in the presence of a chain transfer agent. The branch representing a polymer chain with included branching agent units was accepted as the main structural element of macromolecules. Model parameters were determined from the kinetic characteristics of copolymerization, such as reagent ratio and growth rate and chain transfer constants. Branching and architecture parameters of branched polymethyl methacrylates synthesized at various monomer: branching agent: chain transfer agent ratios were calculated

Subsampling effects in neuronal avalanche distributions recorded in vivo

BackgroundMany systems in nature are characterized by complex behaviour where large cascades of events, or avalanches, unpredictably alternate with periods of little activity. Snow avalanches are an example. Often the size distribution f(s) of a system's avalanches follows a power law, and the branching parameter sigma, the average number of events triggered by a single preceding event, is unity. A power law for f(s), and sigma = 1, are hallmark features of self-organized critical (SOC) systems, and both have been found for neuronal activity in vitro. Therefore, and since SOC systems and neuronal activity both show large variability, long-term stability and memory capabilities, SOC has been proposed to govern neuronal dynamics in vivo. Testing this hypothesis is difficult because neuronal activity is spatially or temporally subsampled, while theories of SOC systems assume full sampling. To close this gap, we investigated how subsampling affects f(s) and sigma by imposing subsampling on three different SOC models. We then compared f(s) and sigma of the subsampled models with those of multielectrode local field potential (LFP) activity recorded in three macaque monkeys performing a short term memory task.ResultsNeither the LFP nor the subsampled SOC models showed a power law for f(s). Both, f(s) and sigma, depended sensitively on the subsampling geometry and the dynamics of the model. Only one of the SOC models, the Abelian Sandpile Model, exhibited f(s) and sigma similar to those calculated from LFP activity.ConclusionSince subsampling can prevent the observation of the characteristic power law and sigma in SOC systems, misclassifications of critical systems as sub- or supercritical are possible. Nevertheless, the system specific scaling of f(s) and sigma under subsampling conditions may prove useful to select physiologically motivated models of brain function. Models that better reproduce f(s) and sigma calculated from the physiological recordings may be selected over alternatives.

Effect of Tail Architecture on Self-Assembly of Amphiphiles for Polymeric Micelles

Brownian dynamics simulations were carried out to explore the self-assembly of amphiphilic copolymers composed of a linear hydrophilic head and a hydrophobic tail with different architectures. In order to investigate the effect of architecture of hydrophobic tail on self-assembling behavior, these architectures of linear, branched, starlike, and dendritic tails were selected for comparison, and the branching parameter of the tail was employed to characterize the tail architectures. The critical micelle concentration (cmc), dynamics of aggregation, aggregate distribution, gyration radius distribution, density profiles of micelle, shape anisotropy, and thermal stability were examined for the four typical types of copolymers. The calculated results reveal that the self-assembly of linear tail copolymer has the lowest cmc, and the consequently formed polymeric micelles have narrow dispersion and greater aggregate size, and the micelle is closer to spherical shape. It was found that the cmc is inversely proportional to the branching parameter. Linear tail aggregates in solution to form polymeric micelles with higher physical stability, compared to other architectures of tail. The size of polymeric micelle increases with the increase of the branching parameter of the tail, and it exhibits an exponential relationship with the branching parameter. In addition, the micelles formed from copolymers with a high branching parameter of the tail were found to have higher thermal stability. This work provides useful information on designing self-assembling systems for preparing polymeric micelles applied to drug delivery.

Determination of scission, crosslinking and branching parameters of electron beam irradiated methacrylate–acrylamide copolymer

The aim of this work was to investigate the impact of electron beam irradiation at different dose rates on the molecular structure of linear methacrylate–acrylamide copolymer. In the first part, the radiation chemical yields of scission ( G s) and crosslinking ( G x ) have been determined after irradiation for various initial molecular weights CL1 (40 000 g/mol), CL2 (90 000 g/mol) and CL3 (425 000 g/mol). Based on this calculation, solvent (ethanol) was found to increase the impact of irradiation especially at low concentration of copolymer. In the second part, the presence of branching in samples before and after e-beam irradiation was explored, and branching calculation was performed.

Multivariate analysis of Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) Venus Express nightside and limb observations

Spectral signatures measured by Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on the nightside and at the limb of Venus are analyzed with Independent Component Analysis. A methodology has been set up to minimize instrumental effects and to interpret the results on the basis of studies of the most common situations in the data set. The main spectral components commonly retrieved on the nightside include the bulk signal modulated by atmospheric opacity variations, photometric variations in the long‐wavelength atmospheric windows, a branching parameter describing particle size variations, and O2 emission at 1.26 and 1.58 μm. Faint atmospheric windows are detected at 1.51, 1.55, 1.78, and 1.82 μm for the first time. The polar vortex structure is outlined, with two main circular areas made of many concentric rings with alternating particle sizes. Discrete clouds about 100 km across are observed in low opacity conditions. High‐altitude, warm clouds are tentatively observed from the polar vortex down to 55°S. At the limb, the two signatures of CO2 nonlocal thermodynamic equilibrium emission are directly mapped, and the thermal structure of the cloud layers and upper atmosphere is apparent. Surface emission is detected with a spatial resolution limited by atmosphere blurring, reaching ∼35 km in exceptional conditions. Horizontal offsets indicate that the radiation propagates mostly vertically, consistent with the large optical depth and vertical extent of the cloud layer. Intense scattering is suspected to take place at the bottom of the atmosphere, at least in the southern plains.

Synthesis and Dilute Solution Properties of Well-Defined H-Shaped Polybutadienes

A novel and advantageous approach to synthesis of H-shaped polybutadienes (H-PBd) is reported. The synthetic strategy employs classical anionic polymerization using high-vacuum techniques and utilizes a difunctional linking agent 4-(dichloromethylsilyl)diphenylethylene (DCMSDPE). The synthesis involves (a) growing a living PBd chain using s-BuLi as initiator in benzene at room temperature, (b) titration of DCMSDPE with living PBdLi, (c) addition of s-BuLi to activate the double bond of DPE, (d) subsequent addition of butadiene to generate a living “1/2 H”, which has two arms and half of the final cross-bar, and (e) finally coupling the two “1/2 H” molecules with dichlorodimethylsilane to produce an H-PBd, which has two arms attached to each end of the cross-bar. The weight-average molecular weight, number-average molecular weight, molecular weight distribution, intrinsic viscosity, and radius of gyration were characterized by multidetector size exclusion chromatography (SEC) coupled with a refractive index detector, a two-angle (15° and 90°) light scattering detector, and a Viscotek differential viscometer in tetrahydrofuran at 40 °C. The H-PBds showed narrow and symmetrical molecular weight distributions (polydispersity indices, PDI = 1.03−1.06). Furthermore, the use of light scattering detectors showed that there were no detectable high molecular weight, more highly branched components present in these materials. This is an important advantage of this novel approach over previous synthetic routes to H-polymers. The values of the branching parameters g (0.58−0.77) and g′ (0.60−0.75) in the thermodynamically good solvent, tetrahydrofuran, are consistent with values reported previously by Roovers and Toporowski for H polystyrenes in the good solvent toluene. Effects of architecture on the branching parameters are elucidated.

Branched and Functionalized Polybutadienes by a Facile Two‐Step Synthesis

AbstractAnionic polymerization was used to prepare silane‐endfunctionalized polybutadiene macromonomers with different molecular weights ranging from 9 000 to 34 000 g · mol−1. These were polymerized by a hydrosilylation reaction in bulk to obtain branched polymers, using Karstedt's catalyst. Surprisingly, the addition of monofunctional silanes during the polymerization showed only a minimal effect concerning the degree of polymerization. Furthermore, it was possible to introduce a variety of functional silanes without increasing the overall number of reaction steps by a convenient AB2 + A type “pseudocopolymerization” method. All branched polymers were analyzed by SEC, SEC‐MALLS, SEC‐viscosimetry. 1H NMR spectroscopy, and DSC concerning their branching ratio. The branching parameters for the branched polymers exhibited similar characteristics as for hyperbranched polymers obtained from conventional AB2 monomers. Detailed kinetic studies showed that the polymerization occurred very rapidly in comparison to the hydrosilylation polymerization of classical AB2 type carbosilane monomers.magnified image

Characterization of Polymer Architectures by Multidetection Size Exclusion Chromatography

AbstractSummary: This paper discusses the analysis of star‐branched and dendritic polyisobutylenes (PIBs) using branching parameters based on radii of gyration Rg,z and hydrodynamic radii Rh,z. Rg,z and Rh,z were measured by Size Exclusion Chromatography equipped with a Wyatt Technology Viscostar viscometer (VIS), a Wyatt Optilab DSP RI detector, a Wyatt DAWN EOS 18 angle Multiangle Light Scattering (MALS) detector and a Wyatt Quasi‐elastic Light Scattering QELS detector. Branching parameters were calculated from these measurements and compared with those computed for these architectures.

Homeostasis of neuronal avalanches during postnatal cortex development in vitro

Cortical networks in vivo and in vitro are spontaneously active in the absence of inputs, generating highly variable bursts of neuronal activity separated by up to seconds of quiescence. Previous measurements in adult rat cortex revealed an intriguing underlying organization of these dynamics, termed neuronal avalanches, which is indicative of a critical network state. Here we demonstrate that neuronal avalanches persist throughout development in cortical slice cultures from newborn rats. More specifically, we find that in spite of large variations of average rate in activity, spontaneous bursts occur with power-law distributed sizes (exponent −1.5) and a critical branching parameter close to 1. Our findings suggest that cortical networks homeostatically regulate a critical state during postnatal maturation.

Synthesis and characterization of arborescent (hyperbranched) polyisobutylenes from the 4‐(1,2‐oxirane‐isopropyl)styrene inimer

AbstractThe synthesis of the novel inimer (initiator‐monomer) 4‐(1,2‐oxirane‐isopropyl)styrene EPOIM and the copolymerization of this inimer with isobutylene (IB) to form arborescent polyisobutylene (PIB) is described. Polymerizations were accomplished by use of TiCl4 coinitiator and the effect of reaction conditions was investigated. Size exclusion chromatography (SEC) was used demonstrate EPOIM incorporation across the whole molecular weight distribution. The average number of branch points (B) per chain measured by use of selective link destruction increased with increasing EPOIM/IB ratio and decreased with [TiCl4]. Large scale polymerizations were carried out based on results from small scale polymerizations. Architecture analysis carried out through use of branching parameters based on the radii of gyration Rg and hydrodynamic radii Rh measured by multidetector SEC corroborated the proposed arborescent architecture. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5847–5856, 2007

Methods for Three-Dimensional Geometric Characterization of the Arterial Vasculature

Complex vascular anatomy often affects endovascular procedural outcome. Accurate quantitative assessment of three-dimensional (3D) in-vivo arterial morphology is therefore vital for endovascular device design, and preoperative planning of percutaneous interventions. The aim of this work was to establish geometric parameters describing arterial branch origin, trajectory, and vessel curvature in 3D space that eliminate the errors implicit in planar measurements. 3D branching parameters at visceral and aortic bifurcation sites, as well as arterial tortuosity were determined from vessel centerlines derived from magnetic resonance angiography data for three subjects. Errors in coronal measurements of 3D branching angles for the right and left renal arteries were 3.1 +/- 3.4 degrees and 7.5 +/- 3.7 degrees , respectively. Distortion of the anterior visceral branching angles from sagittal measurements was less pronounced. Asymmetry in branching and planarity of the common iliac arteries was observed at aortic bifurcations. The renal arteries possessed considerably greater 3D curvature than the abdominal aorta and common iliac vessels with mean average values of 0.114 +/- 0.015 and 0.070 +/- 0.019 mm(-1) for the left and right, respectively. In conclusion, planar projections misrepresented branch trajectory, vessel length, and tortuosity proving the importance of 3D geometric characterization for possible applications in planning of endovascular interventional procedures and providing parameters for endovascular device design.

Optimal design of microfluidic networks using biologically inspired principles

From the earliest of times, Man has sought to replicate ideas that have evolved naturally in plants and animals. Understanding and extracting these “natural” design strategies has opened up a whole new field of research known as biomimetics. Designs formulated using biologically inspired principles range from novel surface treatments that mimic physiological processes to geometrical optimization for improving the performance of a system. In this paper, we will show how biomimetic principles based on the laws that govern biological vascular trees can be used to design artificial microfluidic distribution systems. The study focuses specifically on microfluidic manifolds composed of constant-depth rectangular- or trapezoidal-sectioned channels, as these geometries can readily be fabricated using standard micro-fabrication techniques. We will show that it is possible to introduce a prescribed element of flow control into the system by carefully selecting the branching parameter that governs the change in channel dimension at each bifurcation.

Determination of the molecular characteristics of commercial polyethylenes with different architectures and the relation with the melt flow index

AbstractThe molecular weight distribution curves of several commercial polyethylene samples were evaluated by high‐temperature gel permeation chromatography with two detectors (a refractive‐index detector and a viscometer) to determine the molecular sizes and architectures (branching). The polymer samples included high‐ and low‐density polyethylenes with different molecular weight distributions (wide, medium, unimodal, and bimodal) from nine producers. The results were tested against the melt flow index and zero‐shear melt viscosity to find correlations. The data for high‐density polyethylene correlated well with the molecular weight, whereas the data for low‐density polyethylene did not correlate. However, when the weight‐average molecular weight was corrected by the branching parameter and a factor form, all the polyethylene samples fit a single equation. These results indicate that the melt flow index is dependent not only on the molecular weight but also on the molecular shape, including branching. The relation accounted for samples of different resin producers, molecular weights (65,000–638,000), and polydispersities (2.9–20). The use of the branching parameter for the correction of the molecular weight allowed the correlation of these parameters despite differences in the technologies, molecular weights, and molecular architectures. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1572–1578, 2007

Vector-Tensor and Vector-Vector Decay Amplitude Analysis ofB0→φK*0

We perform an amplitude analysis of the decays B0→ϕK2*(1430)0, ϕK*(892)0, and ϕ(Kπ)S−wave0 with a sample of about 384×106 BB¯ pairs recorded with the BABAR detector. The fractions of longitudinal polarization fL of the vector-tensor and vector-vector decay modes are measured to be 0.853−0.069+0.061±0.036 and 0.506±0.040±0.015, respectively. Overall, twelve parameters are measured for the vector-vector decay and seven parameters for the vector-tensor decay, including the branching fractions and parameters sensitive to CP violation.Received 24 October 2006DOI:https://doi.org/10.1103/PhysRevLett.98.051801©2007 American Physical Society

Ontogenetic trends in the morphological features of main stem annual shoots of Pinus pinaster (Pinaceae)

Phase change refers to the transition between juvenile and adult vegetative phases. The study of trees throughout their entire life span requires retrospective analyses and validates the use of a chronosequence by sequencing observations at different and successive stages. The main axis growth pattern of 62 maritime pines (Pinus pinaster) selected in a chronosequence of three stands consisting of 8-, 22-, and 48-yr-old trees was analyzed retrospectively. Comparison of measured features (length, number of axillary products, reproductive organs) at common ages from the three stands supported the validity of using these data to form a continuous chronosequence. Endogenous trends in tree development are revealed free from variability due to annual growth conditions. Two main phases of development corresponding respectively to the juvenile vegetative and adult reproductive stages were identified, and the transition between both occurred in 9-yr-old trees. The relevance of these two phases and more generally the notion of phase changes are discussed in light of observed trends in the values of studied growth and branching parameters that may either show gradual variations (such as length of annual shoot) or a distinctive expression in one or the other phase (such as presence of female cones).

A VEGF 165-induced phenotypic switch from increased vessel density to increased vessel diameter and increased endothelial NOS activity

Although vascular endothelial growth factor-165 (VEGF 165) regulates numerous angiogenic cellular activities, its complex effects on vascular morphology are not highly quantified. By fractal-based, multiparametric branching analysis of 2D vascular pattern in the quail chorioallantoic membrane (CAM), we report that vessel density increased maximally at lower VEGF concentrations, but that vessel diameter and activity of endothelial nitric oxide synthase (eNOS) increased maximally at higher VEGF concentrations. Following exogenous application of human VEGF 165 to the CAM at embryonic day 7, vessel density and diameter were measured after 24 h at arterial end points by the fractal dimension ( D f) and generational branching parameters for vessel area density ( A v), vessel length density ( L v) and vessel diameter ( D v) using the computer code VESGEN. The VEGF-dependent phenotypic switch from normal vessels displaying increased vessel density to abnormal, dilated vessels typical of tumor vasculature and other pathologies resulted from an approximate threefold increase in VEGF concentration (1.25 to 5 μg/CAM) and correlated positively with increased eNOS activity. Relative to control specimens, eNOS activity increased maximally to 60% following VEGF treatment at 5 μg/CAM, compared to 10% at 1.25 μg/CAM, and was accompanied by no significant change in activity of inducible NOS. In summary, VEGF 165 induced a phenotypic switch from increased vessel density associated with low VEGF concentration, to increased vessel diameter and increased eNOS activity at high VEGF concentration.