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.

Numerical Analysis of Liquid Breakup and Drop Generation in Low Velocity Jets

2015 ◽  
Author(s):  
Sucharitha Rajendran ◽  
Milind A. Jog ◽  
Raj M. Manglik
Keyword(s):  
Surface Tension ◽  
Surface Tension Force ◽  
The Other ◽  
Viscous Force ◽  
Liquid Jet ◽  
Biological Applications ◽  
Liquid Stream ◽  
Low Velocity ◽  
Satellite Drops ◽  
Wide Range

Biological sprays and aerodynamically assisted bio-jets are increasingly employed in treatment of living cells and organisms for applications in regenerative medicine, tissue repair, and advanced therapeutics. The liquid used in biological applications cover a wide range of viscosities and surface tensions. Determining conditions that achieve steady and uniform drop distribution for a range of properties of the liquid jet is critical in advancing biological applications. In this study, numerical simulations of jet breakup are carried out using a modified volume of fluid (VOF) approach to capture the interface. The interplay of viscosity and surface tension is studied by varying liquid properties. Simulations show that a high viscosity jet stretches and elongates before a liquid segment detaches. Based on the thickness of the liquid thread connecting the detaching drop to the main liquid stream, two fundamentally different modes of liquid pinch off have been predicted: thick-thin and thin-thick. In the thick-thin mode, the liquid jet has a growing drop at its edge. As this drop grows in size, the liquid stream stretches till the drop is pinched off the liquid stream. In the other mode in addition to the pinch off of drops from the jet, ligaments of liquid break off. The change in the breakup mode is primarily governed by the relative magnitude of the viscous force compared to surface tension with high viscous force leading to thin-thick liquid stretching and pinch off. Thick-thin stretching is seen to produce slow moving satellite drops that merge backwards with the oncoming drop, while thin-thick stretching is noticed to result in faster satellite drops that merge forwards. On the other hand when surface tension force dominates, non-merging satellite drops are formed that move with a speed close to the primary drops.

An “Ultrafilter” in the Margo of Mature Bordered Pits?

1972 ◽  
Vol 30 ◽  
pp. 206-207
Author(s):  
I. B. Sachs ◽  
R. E. Kinney
Keyword(s):  
Surface Tension ◽  
Electron Microscope ◽  
Molecular Sieve ◽  
Pinus Strobus ◽  
Postmortem Changes ◽  
Sodium Chlorite ◽  
Bordered Pit ◽  
Pit Membrane ◽  
Bordered Pits ◽  
Surface Tension Forces

The micrographs illustrating this paper were obtained from never-dried springwood bordered pit-pairs of Pinus strobus L. Specimens were treated with acidified sodium chlorite in order to remove incrusting materials from the pit membrane. To prevent or reduce interfacial and surface tension forces and provide a view of bordered pit structure without postmortem changes, the specimens were further treated either by the critical point method of Weatherwax and Caulfield, a version of Anderson's method, or by a low temperature evaporation method using molecular sieve material at -40° C. to gently remove the alcohol, Arenberg, et al. For studying the pit membrane of bordered pit-pairs, neither technique seems to have an advantage, giving similar results.Light and electron microscope studies have established that structurally the bordered pit-pair membrane consists of a torus and a margo.

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.

Immunoferritin localization of intracellular antigens in positively stained frozen sections

1978 ◽  
Vol 36 (2) ◽  
pp. 168-169
Author(s):  
K. T. Tokuyasu
Keyword(s):  
Surface Tension ◽  
Water Surface ◽  
Thin Layers ◽  
The Other ◽  
Positive Staining ◽  
Frozen Sections ◽  
The Past ◽  
Ultrathin Frozen Sections ◽  
Definition Of

During the past investigations of immunoferritin localization of intracellular antigens in ultrathin frozen sections, we found that the degree of negative staining required to delineate u1trastructural details was often too dense for the recognition of ferritin particles. The quality of positive staining of ultrathin frozen sections, on the other hand, has generally been far inferior to that attainable in conventional plastic embedded sections, particularly in the definition of membranes. As we discussed before, a main cause of this difficulty seemed to be the vulnerability of frozen sections to the damaging effects of air-water surface tension at the time of drying of the sections.Indeed, we found that the quality of positive staining is greatly improved when positively stained frozen sections are protected against the effects of surface tension by embedding them in thin layers of mechanically stable materials at the time of drying (unpublished).

The effect of cation concentration on the nitrogen splitting constant of nitroxide free radicals

1990 ◽  
Vol 55 (10) ◽  
pp. 2377-2380
Author(s):  
Hamza A. Hussain
Keyword(s):  
Hydrogen Peroxide ◽  
Hydrogen Bonding ◽  
Free Radicals ◽  
Esr Spectroscopy ◽  
The Other ◽  
Tetraethylammonium Bromide ◽  
Splitting Constant ◽  
The One ◽  
Positively Charged ◽  
Two Equilibria

Nitroxide free radicals prepared from diethylamine, piperidine and pyrrolidine by oxidation with hydrogen peroxide were studied by ESR spectroscopy. The changes in the 14N splitting constant (aN) caused by the addition of KBr or tetraethylammonium bromide were measured in dependence on the concentration of the ions. For diethylamine nitroxide and piperidine nitroxide, the results are discussed in terms of two equilibria: the one, involving the anion, is associated with a gain or loss of hydrogen bonds to the nitroxide oxygen atom, the other is associated with the formation of solvent shared units involving the cation, which results in changes in the hydrogen bonding strenght. The large increase in the aN value in the case of pyrrolidine nitroxide is explained in terms of an interaction from one side of the positively charged N atom; the increase in aN in the case of diethylamine and piperidine nitroxides is explained in terms of interactions with both sides of the positively charged N atom.

scholarly journals Comparison of Surface Tension Models for the Volume of Fluid Method

Processes ◽  
2019 ◽  
Vol 7 (8) ◽  
pp. 542 ◽  
Author(s):  
Kurian J. Vachaparambil ◽  
Kristian Etienne Einarsrud
Keyword(s):  
Surface Tension ◽  
Multiphase Flow ◽  
Capillary Rise ◽  
Surface Tension Force ◽  
Surface Force ◽  
Parallel Plates ◽  
Time Step ◽  
Mesh Resolution ◽  
Active Research ◽  
Spurious Currents

With the increasing use of Computational Fluid Dynamics to investigate multiphase flow scenarios, modelling surface tension effects has been a topic of active research. A well known associated problem is the generation of spurious velocities (or currents), arising due to inaccuracies in calculations of the surface tension force. These spurious currents cause nonphysical flows which can adversely affect the predictive capability of these simulations. In this paper, we implement the Continuum Surface Force (CSF), Smoothed CSF and Sharp Surface Force (SSF) models in OpenFOAM. The models were validated for various multiphase flow scenarios for Capillary numbers of 10 − 3 –10. All the surface tension models provide reasonable agreement with benchmarking data for rising bubble simulations. Both CSF and SSF models successfully predicted the capillary rise between two parallel plates, but Smoothed CSF could not provide reliable results. The evolution of spurious current were studied for millimetre-sized stationary bubbles. The results shows that SSF and CSF models generate the least and most spurious currents, respectively. We also show that maximum time step, mesh resolution and the under-relaxation factor used in the simulations affect the magnitude of spurious currents.

A note on the instabilities of a horizontal shear flow with a free surface

2000 ◽  
Vol 406 ◽  
pp. 337-346 ◽  
Author(s):  
L. ENGEVIK
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Shear Flow ◽  
Velocity Profile ◽  
Froude Number ◽  
The Other ◽  
Algebraic Equations ◽  
Horizontal Shear ◽  
Analytical Treatment ◽  
Unstable Region

The instabilities of a free surface shear flow are considered, with special emphasis on the shear flow with the velocity profile U* = U*0sech2 (by*). This velocity profile, which is found to model very well the shear flow in the wake of a hydrofoil, has been focused on in previous studies, for instance by Dimas & Triantyfallou who made a purely numerical investigation of this problem, and by Longuet-Higgins who simplified the problem by approximating the velocity profile with a piecewise-linear profile to make it amenable to an analytical treatment. However, none has so far recognized that this problem in fact has a very simple solution which can be found analytically; that is, the stability boundaries, i.e. the boundaries between the stable and the unstable regions in the wavenumber (k)–Froude number (F)-plane, are given by simple algebraic equations in k and F. This applies also when surface tension is included. With no surface tension present there exist two distinct regimes of unstable waves for all values of the Froude number F > 0. If 0 < F [Lt ] 1, then one of the regimes is given by 0 < k < (1 − F2/6), the other by F−2 < k < 9F−2, which is a very extended region on the k-axis. When F [Gt ] 1 there is one small unstable region close to k = 0, i.e. 0 < k < 9/(4F2), the other unstable region being (3/2)1/2F−1 < k < 2 + 27/(8F2). When surface tension is included there may be one, two or even three distinct regimes of unstable modes depending on the value of the Froude number. For small F there is only one instability region, for intermediate values of F there are two regimes of unstable modes, and when F is large enough there are three distinct instability regions.

scholarly journals Unsteady flow induced by a withdrawal point beneath a free surface

2005 ◽  
Vol 47 (2) ◽  
pp. 185-202 ◽  
Author(s):  
T. E. Stokes ◽  
G. C. Hocking ◽  
L. K. Forbes
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Unsteady Flow ◽  
Critical Values ◽  
The Other ◽  
Withdrawal Rate ◽  
Steady Solutions

AbstractThe unsteady axisymmetric withdrawal from a fluid with a free surface through a point sink is considered. Results both with and without surface tension are included and placed in context with previous work. The results indicate that there are two critical values of withdrawal rate at which the surface is drawn directly into the outlet, one after flow initiation and the other after the flow has been established. It is shown that the larger of these values corresponds to the point at which steady solutions no longer exist.

scholarly journals Two New Polyiodides in the 4,4´-Bipyridinium Diiodide/Iodine System

2012 ◽  
Vol 67 (1) ◽  
pp. 5-10
Author(s):  
Guido J. Reiss ◽  
Martin van Megen
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Complex I ◽  
The Other ◽  
Cyclic Dimer ◽  
Water Molecules ◽  
Spectroscopic Methods ◽  
Halogen Bonds ◽  
One Dimensional ◽  
Hydroiodic Acid

The reaction of bipyridine with hydroiodic acid in the presence of iodine gave two new polyiodide-containing salts best described as 4,4´-bipyridinium bis(triiodide), C10H10N2[I3]2, 1, and bis(4,4´-bipyridinium) diiodide bis(triiodide) tris(diiodine) solvate dihydrate, (C10H10N2)2I2[I3]2 · 3 I2 ·2H2O, 2. Both compounds have been structurally characterized by crystallographic and spectroscopic methods (Raman and IR). Compound 1 is composed of I3 − anions forming one-dimensional polymers connected by interionic halogen bonds. These chains run along [101] with one crystallographically independent triiodide anion aligned and the other triiodide anion perpendicular to the chain direction. There are no classical hydrogen bonds present in 1. The structure of 2 consists of a complex I144− anion, 4,4´-bipyridinium dications and hydrogen-bonded water molecules in the ratio of 1 : 2 : 2. The I144− polyiodide anion is best described as an adduct of two iodide and two triiodide anions and three diiodine molecules. Two 4,4´-bipyridinium cations and two water molecules form a cyclic dimer through N-H· · ·O hydrogen bonds. Only weak hydrogen bonding is found between these cyclic dimers and the polyiodide anions.

A tetranuclear carbonyl fluoro rhenium(I) cluster, [Re(CO)3F]4,4H2O

1981 ◽  
Vol 34 (4) ◽  
pp. 737 ◽  
Author(s):  
E Horn ◽  
MR Snow
Keyword(s):  
Hydrogen Bonding ◽  
Title Compound ◽  
The Other ◽  
Water Molecules ◽  
Molecular Symmetry ◽  
Group 14 ◽  
Full Matrix ◽  
Abstraction Reaction ◽  
R Value ◽  
Silver Fluoride

The title compound has been prepared from Re(CO)5Br by a bromide-abstraction reaction with silver fluoride. It completes the series of known halide clusters of the type [Re(CO)3X]4 (where X = halide). The crystals are tetragonal, space group 14, with a 11.716(5), c 8.988(3) �, and Z 2. The structure was refined by full-matrix least-squares to an R value of 0.027 for 1380 observed reflections. The molecules are cubane-type clusters of Re(CO)3 groups at one set of corners interpenetrated with fluorine atoms at the other set. The clusters exhibit the molecular symmetry 43m. Each of the fluorine atoms is involved in μ3 type bridging with the rhenium atoms at an average bonding distance of 2.200(5) �. The clusters are held together by hydrogen bonding of fluoride to water molecules.

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