Permeability and structure of the wood of Sitka spruce

1970 ◽  
Vol 175 (1039) ◽  
pp. 149-166 ◽  
Keyword(s):  
Sitka Spruce ◽  
Basic Fuchsin ◽  
Flow Paths ◽  
Membrane Pores ◽  
Pit Membrane ◽  
Bordered Pits ◽  
In Series ◽  
Flow Through ◽  
Conifer Wood ◽  
Tangential Directions

The gaseous permeability of dry Sitka spruce sapwood in the longitudinal and tangential directions has been measured at various mean pressures between 1 and 700 mmHg. From these measurements it has been shown that both the tracheid lumina and the pores in the mem­branes of the bordered pits make significant contributions to the total resistance to longitudinal fluid flow through the wood, and the number and equivalent radii of the conducting tracheid lumina and the pit membrane pores have been derived. The conducting tracheids have been observed directly by examination of transverse wood sections, after staining the flow -paths with reduced basic fuchsin solution. The conducting tracheids were found mainly in the latewood and their radii and number were in agreement with the values derived from permeability measurements. Direct carbon replicas of bordered pit membranes have been examined in the electron microscope. Unaspirated, i. e. conducting bordered pits were found only in the latewood region and the size and number of the pores in the latewood pit membranes were in agreement with values derived from permeability measurements, which predicted about 250 pit membrane pores of radius 0.14 μ m in series with each conducting tracheid lumen. The effect of a possible distribution of pore size on the results is considered, and the significance of this work in relation to previous work on the gaseous permeability of conifer wood is discussed.

The dimensions and number of pit membrane pores in conifer wood

1969 ◽  
Vol 172 (1027) ◽  
pp. 137-151 ◽  
Keyword(s):  
Average Pore Size ◽  
Longitudinal Direction ◽  
Average Pore ◽  
Flow Equations ◽  
Pore Sizes ◽  
Membrane Pores ◽  
Pit Membrane ◽  
Flow Through ◽  
Average Size ◽  
Conifer Wood

A method is described which allows the determination of the average size, and the average number pertracheid, of the pit membrane pores through which fluids can pass in the longitudinal direction along oven-dried conifer wood. This consists in the observation of flow rates through the wood, in turn, of a non-polar liquid ( n -hexane) and of a gas (air) at low pressure. Preliminary tests with Millipore filters of known porosity show that the method is sufficiently reliable to give pore sizes with acceptable accuracy, and reasons are given to expect the flow equations derived to be applicable to flow through wood. For all species examined the radii of the pores are larger for sap wood than for heartwood. They vary with species, ranging from 0.34 µ m ( Larix leptolepis , heartwood) to (exceptionally among the species examined) 2.75 µ m ( L. leptolepis sapwood) with an average of about 0.8 µ m. The average number of pores per tracheid varies with species but is always of the order of unity. This is lower than was expected; it is, however, in harmony with other recent work and indicates a widespread aspiration of pits during drying. The precise meaning of the average pore size determined by the present methods depends on the distribution of pore sizes in a specimen and this is examined. The method used makes the assumption implicit in all previous work, that the resistance to flow resides entirely in the pit membrane. It is shown that, if the figure of unity means literally that each tracheid in a specimen possesses one open spore, this assumption is valid. If, however, only a few tracheids are available for flow, with correspondingly a greater number of open pores pertracheid, then this assumption cannot be accepted. Further work is necessary to determine the number of tracheids involved. /

scholarly journals The aspiration of bordered pits in conifer wood

1972 ◽  
Vol 181 (1065) ◽  
pp. 395-406 ◽  
Keyword(s):  
Surface Tension ◽  
Hydrogen Bonding ◽  
Pinus Sylvestris ◽  
Growth Ring ◽  
Surface Tension Force ◽  
The Other ◽  
Liquid Meniscus ◽  
Pit Membrane ◽  
Bordered Pits ◽  
Conifer Wood

The variation of tension in a radial strand of a bordered pit membrane during drying has been derived theoretically from two approaches. One considers the mechanical extension of the strand, while the other considers the surface tension force caused by an annular liquid meniscus in the pit chamber. The tension has been calculated for pits in earlywood, in latewood and in regions near the earlywood-latewood boundary of a single growth ring in Pinus sylvestris L., using experimentally observed typical values for pit dimensions. The occurrence of aspiration of earlywood but not of latewood pits in air-seasoned wood is correctly predicted by the analysis, which also predicts that, contrary to accepted theory, earlywood pit membranes should be displaced and brought into contact with the pit border irrespective of the liquid present during drying. It is shown that this must involve considerable creep in the radial strands. Permanent aspiration must only occur when the liquid promotes bonding between the membrane and the border, and the probability that this is hydrogen bonding is discussed.

INTERVESSEL PIT MEMBRANE THICKNESS AS A KEY DETERMINANT OF EMBOLISM RESISTANCE IN ANGIOSPERM XYLEM

IAWA Journal ◽  
2016 ◽  
Vol 37 (2) ◽  
pp. 152-171 ◽  
Author(s):  
Shan Li ◽  
Frederic Lens ◽  
Susana Espino ◽  
Zohreh Karimi ◽  
Matthias Klepsch ◽  
...  
Keyword(s):  
Cellulose Microfibrils ◽  
Spatial Density ◽  
Functional Explanation ◽  
Membrane Thickness ◽  
Membrane Pores ◽  
Transmission Electron ◽  
Pit Membrane ◽  
Bordered Pits ◽  
Angiosperm Species ◽  
Embolism Resistance

Pit membranes in bordered pits between neighbouring vessels play a major role in the entry of air-water menisci from an embolised vessel into a water-filled vessel (i.e., air-seeding). Here, we investigate intervessel pit membrane thickness (TPM) and embolism resistance (P50, i.e., the water potential corresponding to 50% loss of hydraulic conductivity) across a broad range of woody angiosperm species. Data on TPM and double intervessel wall thickness (TVW) were compiled based on electron and light microscopy. Fresh material that was directly fixated for transmission electron microscopy (TEM) was investigated for 71 species, while non-fresh samples were frozen, stored in alcohol, or air dried prior to TEM preparation for an additional 60 species. TPM and P50 were based on novel observations and literature. A strong correlation between TPM and P50 was found for measurements based on freshly fixated material (r = 0.78, P >0.01, n = 37), and between TPM and TVW (r = 0.79, P >0.01, n = 59), while a slightly weaker relationship occurred between TVW and P50 (r = 0.40, P >0.01, n = 34). However, non-fresh samples showed no correlation between TPM and P50, and between TPM and TVW. Intervessel pit membranes in non-fresh samples were c.28% thinner and more electron dense than fresh samples. Our findings demonstrate that TPM measured on freshly fixated material provides one of the strongest wood anatomical correlates of droughtinduced embolism resistance in angiosperms. Assuming that cellulose microfibrils show an equal spatial density, TPM is suggested to affect the length and the shape of intervessel pit membrane pores, but not the actual pore size. Moreover, the shrinking effect observed for TPM after dehydration and frost is associated with an increase in microfibril density and porosity, which may provide a functional explanation for embolism fatigue.

Comparison of Aerobic and Anoxic-Aerobic Digestion of Waste Activated Sludge

1985 ◽  
Vol 17 (8) ◽  
pp. 1475-1478 ◽  
Author(s):  
A P. C. Warner ◽  
G. A. Ekama ◽  
G v. R. Marais
Keyword(s):  
Experimental Data ◽  
Activated Sludge ◽  
Waste Activated Sludge ◽  
Activated Sludge Process ◽  
Cycle Times ◽  
Waste Sludge ◽  
Volatile Solids ◽  
In Series ◽  
Flow Through ◽  
Theoretical Simulations

The laboratory scale experimental investigation comprised a 6 day sludge age activated sludge process, the waste sludge of which was fed to a number of digesters operated as follows: single reactor flow through digesters at 4 or 6 days sludge age, under aerobic and anoxic-aerobic conditions (with 1,5 and 4 h cycle times) and 3-in-series flow through aerobic digesters each at 4 days sludge age; all digesters were fed draw-and-fill wise once per day. The general kinetic model for the aerobic activated sludge process set out by Dold et al., (1980) and extended to the anoxic-aerobic process by van Haandel et al., (1981) simulated accurately all the experimental data (Figs 1 to 4) without the need for adjusting the kinetic constants. Both theoretical simulations and experimental data indicate that (i) the rate of volatile solids destruction is not affected by the incorporation of anoxic cycles and (ii) the specific denitrification rate is independent of sludge age and is K4T = 0,046(l,029)(T-20) mgNO3-N/(mg active VSS. d) i.e. about 2/3 of that in the secondary anoxic of the single sludge activated sludge stystem. An important consequence of (i) and (ii) above is that denitrification can be integrated easily in the steady state digester model of Marais and Ekama (1976) and used for design (Warner et al., 1983).

Instability Modes of Two-Phase Flows in a Mixing-Layer Microdevice

2001 ◽  
Author(s):  
Tak For Yu ◽  
Sylvanus Yuk Kwan Lee ◽  
Yitshak Zohar ◽  
Man Wong
Keyword(s):  
Gas Flow ◽  
Mixing Layer ◽  
Fluid Flows ◽  
Two Phase Flows ◽  
Two Phase ◽  
Pressure Distributions ◽  
Instability Modes ◽  
In Series ◽  
Mass Flow Rates ◽  
Flow Through

Abstract Extensive development of biomedical and chemical analytic microdevices involves microscale fluid flows. Merging of fluid streams is expected to be a key feature in such devices. An integrated microsystem consisting of merging microchannels and distributed pressure microsensors has been designed and characterized to study this phenomenon on a microscale. The two narrow, uniform and identical channels merged smoothly into a wide, straight and uniform channel downstream of a splitter plate. All of the devices were fabricated using standard micromachining techniques. Mass flow rates and pressure distributions were measured for single-phase gas flow in order to characterize the device. The experimental results indicated that the flow developed when both inlets were connected together to the gas source could be modeled as gas flow through a straight and uniform microchannel. The flow through a single branch while the other was blocked, however, could be modeled as gas flow through a pair of microchannels in series. Flow visualizations of two-phase flows have been conducted when driving liquid and gas through the inlet channels. Several instability modes of the gas/liquid interface have been observed as a function of the pressure difference between the two streams at the merging location.

scholarly journals Computing water flow through complex landscapes – Part 2: Finding hierarchies in depressions and morphological segmentations

2020 ◽  
Vol 8 (2) ◽  
pp. 431-445
Author(s):  
Richard Barnes ◽  
Kerry L. Callaghan ◽  
Andrew D. Wickert
Keyword(s):  
Water Flow ◽  
Hydrological Modeling ◽  
Dynamic Models ◽  
Terrain Analysis ◽  
Flow Paths ◽  
Topographic Complexity ◽  
Morphological Segmentation ◽  
Surface Water Flow ◽  
Digital Elevation ◽  
Flow Through

Abstract. Depressions – inwardly draining regions of digital elevation models – present difficulties for terrain analysis and hydrological modeling. Analogous “depressions” also arise in image processing and morphological segmentation, where they may represent noise, features of interest, or both. Here we provide a new data structure – the depression hierarchy – that captures the full topologic and topographic complexity of depressions in a region. We treat depressions as networks in a way that is analogous to surface-water flow paths, in which individual sub-depressions merge together to form meta-depressions in a process that continues until they begin to drain externally. This hierarchy can be used to selectively fill or breach depressions or to accelerate dynamic models of hydrological flow. Complete, well-commented, open-source code and correctness tests are available on GitHub and Zenodo.

scholarly journals Testing for ion-mediated enhancement of the hydraulic conductance of the leaf xylem in diverse angiosperms

2017 ◽  
Vol 4 ◽  
pp. e004 ◽  
Author(s):  
Christine Scoffoni ◽  
Grace John ◽  
Herve Cochard ◽  
Lawren Sack
Keyword(s):  
Water Solution ◽  
Pure Water ◽  
Xylem Sap ◽  
Hydraulic Conductance ◽  
Membrane Pores ◽  
Whole Plant ◽  
Pit Membrane ◽  
Major Bottleneck ◽  
The Difference ◽  
Xylem Conduits

Replacing ultra-pure water solution with ion solution closer to the composition of natural xylem sap increases stem hydraulic conductance by up to 58%, likely due to changes in electroviscosity in the pit membrane pores. This effect has been proposed to contribute to the control of plant hydraulic and stomatal conductance and potentially to influence on carbon balance during dehydration. However, this effect has never been directly tested for leaf xylem, which constitutes a major bottleneck in the whole plant. We tested for an ion-mediated increase in the hydraulic conductance of the leaf xylem (Kx) for seven species diverse in phylogeny and drought tolerance. Across species, no significant changes in Kx were observed between 0 and 15 mM KCl. We further tested for an effect of ion solution during measurements of Kx vulnerability to dehydration in Quercus agrifolia and found no significant impact. These results for leaf xylem contrast with the often strong ion effect reported for stems, and we suggest several hypotheses to account for the difference, relating to the structure of xylem conduits across vein orders, and the ultrastructure of leaf xylem pores. A negligible ion response in leaves would weaken xylem sap ion-mediated control of plant hydraulic conductance, facilitating modeling of whole plant hydraulic behavior and its influence on productivity.

Function and three-dimensional structure of intervessel pit membranes in angiosperms: a review

IAWA Journal ◽  
2019 ◽  
Vol 40 (4) ◽  
pp. 673-702 ◽  
Author(s):  
Lucian Kaack ◽  
Clemens M. Altaner ◽  
Cora Carmesin ◽  
Ana Diaz ◽  
Mirko Holler ◽  
...  
Keyword(s):  
Water Transport ◽  
Three Dimensional ◽  
Cellulose Microfibrils ◽  
Dimensional Structure ◽  
High Porosity ◽  
Dynamic Surface ◽  
Three Dimensional Structure ◽  
Pit Membrane ◽  
Bordered Pits ◽  
20 Nm

ABSTRACTPit membranes in bordered pits of tracheary elements of angiosperm xylem represent primary cell walls that undergo structural and chemical modifications, not only during cell death but also during and after their role as safety valves for water transport between conduits. Cellulose microfibrils, which are typically grouped in aggregates with a diameter between 20 to 30 nm, make up their main component. While it is clear that pectins and hemicellulose are removed from immature pit membranes during hydrolysis, recent observations of amphiphilic lipids and proteins associated with pit membranes raise important questions about drought-induced embolism formation and spread via air-seeding from gas-filled conduits. Indeed, mechanisms behind air-seeding remain poorly understood, which is due in part to little attention paid to the three-dimensional structure of pit membranes in earlier studies. Based on perfusion experiments and modelling, pore constrictions in fibrous pit membranes are estimated to be well below 50 nm, and typically smaller than 20 nm. Together with the low dynamic surface tensions of amphiphilic lipids at air-water interfaces in pit membranes, 5 to 20 nm pore constrictions are in line with the observed xylem water potentials values that generally induce spread of embolism. Moreover, pit membranes appear to show ideal porous medium properties for sap flow to promote hydraulic efficiency and safety due to their very high porosity (pore volume fraction), with highly interconnected, non-tortuous pore pathways, and the occurrence of multiple pore constrictions within a single pore. This three-dimensional view of pit membranes as mesoporous media may explain the relationship between pit membrane thickness and embolism resistance, but is largely incompatible with earlier, two-dimensional views on air-seeding. It is hypothesised that pit membranes enable water transport under negative pressure by producing stable, surfactant coated nanobubbles while preventing the entry of large bubbles that would cause embolism.

The mechanism of flow of gases through coniferous wood

1971 ◽  
Vol 177 (1047) ◽  
pp. 197-223 ◽  
Keyword(s):  
Gas Flow ◽  
Strong Support ◽  
Quadratic Function ◽  
Linear Functions ◽  
Modern Theory ◽  
Specific Flow ◽  
Permeability Constant ◽  
Bordered Pits ◽  
Flow Through ◽  
Coniferous Wood

The mechanism of flow of gases through coniferous wood has been examined and found to follow the viscous/slip régime. According to the general theory the specific flow K of a gas in this régime is a linear function of its mean pressure p̅. For coniferous wood, however, we have found that K is a quadratic function of p̅ approximating to a linear one at high enough values of p̅ . It is shown that this is because K is the sum of two linear functions of p̅ , k 1 and k 2 such that 1/ K = 1/ k 1 + 1/ k 2 where k 1 is believed to be the flow through the tracheids alone and k 2 the flow through the bordered pits. It is shown that the permeability constant for viscous flow K v calculated from gas flow is applicable to liquids so that liquid flow can be predicted from gas flow data. With some species the observed flow rate of a liquid differs greatly from the predicted value. Evidence has been obtained that this is because the torus and margo fibrils of the bordered pit are readily displaced by the surface tension and momentum forces developed on them by a liquid causing radical and erratic changes in permeability. Approximate values for the ‘diameter̕ of the smaller flow path have been calculated from the ratio of the viscous to the slip component of flow of k 2 . These were found to be about 1.4 to 1.7 μ m. This is the same order of size as the distances between the torus and the interior of the border of the pit and indicates that it is the geometry of this part of the structure, rather than that of the margo, that controls flow. These results provide strong support for the modern theory of pit structure based on electron microscope photographs.

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