Vessel-length distribution in stems of some American woody plants

1981 ◽  
Vol 59 (10) ◽  
pp. 1882-1892 ◽  
Author(s):  
Martin H. Zimmermann ◽  
Ayodeji A. Jeje
Keyword(s):  
Woody Plants ◽  
Large Diameter ◽  
Length Distribution ◽  
Vitis Labrusca ◽  
Vessel Length ◽  
Particle Penetration ◽  
Air Volume ◽  
Desk Calculator ◽  
Flow Through ◽  
Diffuse Porous

Vessel-length distributions in some trees, shrubs, and a vine have been calculated from measurements of particle penetration and of air-volume flow through the xylem. In shrubs and diffuse-porous species, longest vessels were about 1 m long, but most of them were much shorter, the largest percentage in the 0–10 cm length class. In the two ring-porous species investigated (Quercus rubra and Fraxinus americana), the longest vessels often were as long as the tree's stem, but most of them were much shorter. In the grapevine (Vitis labrusca) which has large-diameter vessels (ca. 300 μm) a small percentage of the vessels was 8 m, but most of them were less than 5 m long. In a given species, lengths of the longest vessel were quite variable, but the distribution of the short lengths was more constant. In general, vessel lengths are correlated with vessel diameters: wide vessels are longer. Even in diffuse-porous species, the slightly narrower latewood vessels are somewhat shorter than the wider early wood vessels. The method is a simplified version of that described by Skene and Balodis, but using a programmable desk calculator. It works best with diffuse-porous species in which vessels are randomly distributed in the stem, and less well in species with wide vessels, because as vessels reach the length of the stem itself, they cannot be randomly distributed.

scholarly journals A model of tight junction function in central nervous system myelinated axons

2008 ◽  
Vol 4 (4) ◽  
pp. 307-317 ◽  
Author(s):  
Alexander Gow ◽  
Jerome Devaux
Keyword(s):  
Current Flow ◽  
Large Diameter ◽  
Small Diameter ◽  
Structural Features ◽  
Axonal Membrane ◽  
Flow Through ◽  
Saltatory Conduction ◽  
Gait Abnormalities ◽  
Low Capacitance ◽  
Speed And Accuracy

The insulative properties of myelin sheaths in the central and peripheral nervous systems (CNS and PNS) are widely thought to derive from the high resistance and low capacitance of the constituent membranes. Although this view adequately accounts for myelin function in large diameter fibers, it poorly reflects the behavior of small fibers that are prominent in many regions of the CNS. Herein, we develop a computational model to more accurately represent conduction in small fibers. By incorporating structural features that, hitherto, have not been simulated, we demonstrate that myelin tight junctions (TJs) improve saltatory conduction by reducing current flow through the myelin, limiting axonal membrane depolarization and restraining the activation of ion channels beneath the myelin sheath. Accordingly, our simulations provide a novel view of myelin by which TJs minimize charging of the membrane capacitance and lower the membrane time constant to improve the speed and accuracy of transmission in small diameter fibers. This study establishes possible mechanisms whereby TJs affect conduction in the absence of overt perturbations to myelin architecture and may in part explain the tremor and gait abnormalities observed in Claudin 11-null mice.

scholarly journals Vessel-Length Distribution in Branches, Stem and Roots of Acer Rubrum L.

IAWA Journal ◽  
1982 ◽  
Vol 3 (2) ◽  
pp. 103-109 ◽  
Author(s):  
Martin H. Zimmermann ◽  
Daniel Potter
Keyword(s):  
Length Distribution ◽  
Acer Rubrum ◽  
Vessel Length

scholarly journals A semi-automated method for measuring xylem vessel length distribution

2020 ◽  
Vol 32 (4) ◽  
pp. 331-340
Author(s):  
Luciano Pereira ◽  
Marcela T. Miranda ◽  
Gabriel S. Pires ◽  
Vinícius S. Pacheco ◽  
Xinyi Guan ◽  
...  
Keyword(s):  
Length Distribution ◽  
Xylem Vessel ◽  
Vessel Length ◽  
Automated Method

A comparison of two methods for measuring vessel length in woody plants

2015 ◽  
Vol 38 (12) ◽  
pp. 2519-2526 ◽  
Author(s):  
Ruihua Pan ◽  
Jing Geng ◽  
Jing Cai ◽  
Melvin T. Tyree
Keyword(s):  
Woody Plants ◽  
Vessel Length ◽  
Measuring Vessel

scholarly journals Accessing the Influence of Hess-Murray Law on Suspension Flow through Ramified Structures

2013 ◽  
Vol 334-335 ◽  
pp. 322-328 ◽  
Author(s):  
Ana Serrenho ◽  
Antonio F. Miguel
Keyword(s):  
Fluid Flow ◽  
Turbulent Flow ◽  
Cross Section ◽  
Particle Transport ◽  
Flow Resistance ◽  
Suspension Flow ◽  
Similar Performance ◽  
Particle Penetration ◽  
Laminar And Turbulent Flow ◽  
Flow Through

The present study focuses on fluid flow and particle transport in symmetric T-shaped structures formed by tubes with circular and square cross-section. The performances of optimized structures (i.e., structures designed based on constructal allometric laws for minimum flow resistance) and not optimized structures were studied. Flow resistance and particle penetration efficiency were studied both for laminar and turbulent flow regimes, and for micrometer and submicrometer particles. Optimized structures have been proven to perform better for fluid flow but they have a similar performance for particle transport.

scholarly journals Transpulmonary passage of99mTc macroaggregated albumin in healthy humans at rest and during maximal exercise

2009 ◽  
Vol 106 (6) ◽  
pp. 1986-1992 ◽  
Author(s):  
Andrew T. Lovering ◽  
Hans C. Haverkamp ◽  
Lee M. Romer ◽  
John S. Hokanson ◽  
Marlowe W. Eldridge
Keyword(s):  
Blood Flow ◽  
Pulmonary Circulation ◽  
Maximal Exercise ◽  
Treadmill Exercise ◽  
Large Diameter ◽  
Whole Body ◽  
Separate Analysis ◽  
Healthy Humans ◽  
Macroaggregated Albumin ◽  
Flow Through

We have demonstrated that 50-μm-diameter arteriovenous pathways exist in isolated, healthy human and baboon lungs, ventilated and perfused under physiological pressures. These findings have been confirmed and extended by demonstrating the passage of 25-μm microspheres through the lungs of exercising dogs, but not at rest. Determination of blood flow through these large-diameter intrapulmonary arteriovenous pathways would be an important first step to establish a physiological role for these vessels. Currently, we sought to estimate blood flow through these arteriovenous pathways using technetium-99m (99mTc)-labeled macroaggregated albumin (MAA) in healthy humans at rest and during maximal treadmill exercise. We hypothesized that the percentage of99mTc MAA able to traverse the pulmonary circulation (%transpulmonary passage) would increase during exercise. Seven male subjects without patent foramen ovale were injected with99mTc MAA at rest on 1 day and during maximal treadmill exercise on a separate day (>6 days). Within 5 min after injection, subjects began whole body imaging in the supine position. Six of the seven subjects showed an increase in transpulmonary passage of MAA with maximal exercise. Using two separate analysis methods, percent transpulmonary passage significantly increased with exercise from baseline to absolute values of 1.2 ± 0.8% ( P = 0.008) and 1.3 ± 1.0% ( P = 0.016), respectively (means ± SD; paired t-test). We conclude that MAA may be traversing the pulmonary circulation via large-diameter intrapulmonary arteriovenous conduits in healthy humans during exercise. Recruitment of these pathways may divert blood flow away from pulmonary capillaries during exercise and compromise the lung's function as a biological filter.

Numerical Investigation Based on Orthogonal Design of Structural Parameters on Large-Diameter DTH Hammer Bit

2013 ◽  
Vol 774-776 ◽  
pp. 1442-1445
Author(s):  
Zhi Qiang Zhao ◽  
Li Jia Li ◽  
Kun Bo ◽  
Xu Sheng He ◽  
Jun Feng Chai
Keyword(s):  
Numerical Investigation ◽  
Design Method ◽  
Orthogonal Design ◽  
Structural Parameters ◽  
Large Diameter ◽  
Technical Problem ◽  
Theory Analysis ◽  
Air Volume ◽  
Orthogonal Design Method ◽  
Reverse Circulation

To achieve cutting transport with air reverse circulation in dry and shallow large-diameter holes of rock-socketed pile, and to solve the technical problem with airlift and pump reverse circulation, a large-diameter reverse circulation bit innovatively designed based on ejecting. Meanwhile, the orthogonal design method applied to explore the application feasibility of ejector theory in use of in air reverse circulation drilling. Through theory analysis, three key geometry parameters of air reverse circulation bit have proved to have direct affect on the function of cutting transport, including the diameter of nozzles (Dn), the number of nozzles (N), the angle of inclination (θs). The results have shown that reverse circulation effect of large-diameter bit designed based on ejecting is valid and stable. Further while the air volume of GQF-16 hammer bit goes to 90m3/min, a configuration of parameters with Dn=20mm, N=3, θs=35°are the most ideal parameter combinations.

scholarly journals A Neural Network Mathematical Model Design Method for Estimating Compressed Air Volume Flow through a Proportional Valve

2019 ◽  
pp. 41-49
Author(s):  
M.S. Zelenov ◽  
A.V. Chernyshev
Keyword(s):  
Neural Network ◽  
Network Model ◽  
Neural Network Model ◽  
Volume Flow ◽  
Compressed Air ◽  
Maximum Deviation ◽  
Model Design ◽  
Proportional Valve ◽  
Air Volume ◽  
Flow Through

The article describes an approach to neural network model design for simulating processes in shut-off and control pneumatic devices. This type of model can be used for a reasoned selection of components for multi-component pneumatic system configurations. As an example, the application of the proposed approach to the development of an artificial neural network to estimate the compressed air volume flow through a proportional valve is considered. The manufacturer’s catalog is used to obtain data samples. The structure of the proposed neural network model, data preprocessing for model configuration, and the selected learning algorithm are described. A computer program for compiling train and test data samples and the subsequent neural network training is developed. The results of measurements are simulated using additional, normally distributed noise with a standard deviation of 0.02. The results obtained using two mathematical models, the neural network model and the classical one, supplemented by empirical coefficients, are compared. The maximum deviation between the two models is less than 1.5 % of the maximum volume flow rate for a particular proportional valve model.

scholarly journals A Bayesian model for xylem vessel length accommodates subsampling and reveals skewed distributions in species that dominate seasonal habitats.

2016 ◽  
Vol 3 ◽  
pp. e003 ◽  
Author(s):  
Brad Oberle ◽  
Kiona Ogle ◽  
Juan Carlos Penagos Zuluaga ◽  
Jonathan Sweeney ◽  
Amy E. Zanne
Keyword(s):  
Water Stress ◽  
Sampling Error ◽  
Secondary Growth ◽  
Length Distribution ◽  
Vascular Anatomy ◽  
Woody Species ◽  
Bayesian Framework ◽  
Species Variation ◽  
Length Variation ◽  
Vessel Length

Vessel  length  is  an  important  but  understudied  dimension  of  variation  in  angiosperm  vascular  anatomy. Among other traits, vessel length mediates an important tradeoff between hydraulic efficiency and safety that could  influence  how  plants  respond  to  extreme  weather  with  climate  change.  However,  the  functional significance  of vessel length variation within individual stems is poorly known, in part because existing data analysis methods handle uncertainty in a way that makes vessel length distributions difficult to compare. We provide a solution to this problem through a hierarchical Bayesian framework for estimating vessel lengths and we demonstrate the flexibility of this method by applying it to data from serial cross sections of dye injected stems. Our approach can accelerate data collection and accommodate  associated uncertainties by statistically correcting for bias and error that result from subsampling images. We illustrate our analytical framework by estimating and comparing vessel length distributions for 21 woody species characteristic of a North American forest.  The best-fit  model  corrected  for both bias due to secondary  growth  and sampling  error  within  and among  species.  Vessel  length  estimates  from  this  model  varied  by  almost  an  order  of  magnitude  and parameters  of these  distributions  correlated  with  point  estimates  derived  from  a different,  commonly  used method. Furthermore, we show how key contrasts can be estimated with the Bayesian framework, and in doing so, we show that the shape of the vessel length distribution differed between ring- and diffuse-porous species, suggesting that within-stem vessel length variation corresponds to water stress seasonality and contributes to landscape-level  habitat segregation. Our analysis method revealed the importance of within-stem variation in vessel length, and our results complement work on between-species variation in average vessel length, further illuminating how vascular anatomy can influence woody plants’ responses to water stress.

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