The water relations of hemlock (Tsuga canadensis). V. The localization of resistances to bulk water flow

1975 ◽  
Vol 53 (10) ◽  
pp. 1078-1084 ◽  
Author(s):  
M. T. Tyree ◽  
C. Caldwell ◽  
J. Dainty
Keyword(s):  
Activation Energy ◽  
Water Flow ◽  
Water Exchange ◽  
Careful Analysis ◽  
Bulk Water ◽  
Exponential Process ◽  
Measurable Amount ◽  
Pressure Bomb ◽  
Overall Resistance ◽  
Kinetics Of

The pressure-bomb technique has been used to measure the kinetics of water exchange while a plant enclosed in a pressure bomb evolves from one equilibrium balance pressure to another. In earlier studies two observations were made. (1) The kinetics of water exchange appeared to be described by an exponential process in which three populations of cells exchange water with apoplast independently of each other. (2) The temperature dependence of the tempo of water exchange yielded an activation energy of 25.9 ± 0.6 × 103 J/mol, which is higher than the activation energy for laminar flow of water in pipes (= 17 × 103 J/mol). These results have been repeated and a more careful analysis has been conducted involving infiltration of air spaces in leaves with water and the selective removal of the leaves. It now appears that the xylem network up to (but not including) the leaves contributes about two thirds of the resistance to water flow in whole shoots 15 to 40 g in fresh weight. Presumably leaves near the cut basal end of the shoot experience a smaller xylem resistance than leaves near the apex. The kinetics of water exchange from water in the air spaces of infiltrated shoots indicates that there is a barrier at the air–water interface of leaves that equals the normal shoot resistance to bulk water flow. The activation energy for water flow through the xylem alone was measured to be about 17 × 103 J/mol. Although the leaves contribute a measurable amount to the overall resistance to water flow, the mathematical description of the system is much more complicated than previously supposed.

The water relations of hemlock (Tsuga canadensis). II. The kinetics of water exchange between the symplast and apoplast

1973 ◽  
Vol 51 (8) ◽  
pp. 1481-1489 ◽  
Author(s):  
M. T. Tyree ◽  
J. Dainty
Keyword(s):  
Water Exchange ◽  
Turgor Pressure ◽  
Experimental Studies ◽  
Tsuga Canadensis ◽  
Rate Of Change ◽  
Cell Constant ◽  
Exponential Process ◽  
Pressure Increment ◽  
Pressure Bomb ◽  
Kinetics Of

We present a theoretical analysis of the events that occur while a plant enclosed in a pressure bomb evolves from one equilibrium balancing pressure to another. The initial rate of efflux from any one cell in response to a pressure increment of ΔP equals (ALp)i ΔP, where (ALp)i is the surface area times hydraulic conductivity of the cell's semipermeable membrane(s). If the volume changes and pressure increment are small, the cell will approach equilibrium exponentially. The half time of the exponential process is governed by (ALp)iki, where ki is the cell constant (= the combined rate of change of osmotic and turgor pressure with the volume expressed from the cell). Experimental studies of the kinetics of water exchange between the symplast and apoplast of hemock (Tsuga canadensis) shoots in a pressure bomb reveal that the cells collectively behave as though they fall into three distinct populations which approach equilibrium with different half times.

The water relations of hemlock (Tsuga canadensis). III. The temperature dependence of water exchange in a pressure bomb

1973 ◽  
Vol 51 (8) ◽  
pp. 1537-1543 ◽  
Author(s):  
M. T. Tyree ◽  
M. Benis ◽  
J. Dainty
Keyword(s):  
Activation Energy ◽  
Temperature Dependence ◽  
Water Exchange ◽  
Membrane Resistance ◽  
Tsuga Canadensis ◽  
Rate Equations ◽  
Rate Theory ◽  
Water Permeation ◽  
Pressure Bomb ◽  
Extracellular Resistance

The pressure-bomb technique has been used to measure the temperature dependence of water exchange between the apoplast and symplast of hemlock (Tsuga canadensis) shoots. By applying the Arrhenius rate theory, the activation energy for water exchange in the whole shoot equals 25.9 + 0.6 × 103 J per mole. A theory is proposed on the basis of the Arrhenius rate equations which allows us to predict the relative magnitudes of the membrane resistance, Rm, and the extracellular resistance, Rx, to water permeation. On the basis of our calculations, we believe Rm is at least one-quarter of Rx and may even exceed Rx, but more work needs to be done to be sure.

Application of model-free kinetic analysis methods to dehydration of a HEU-type zeolite rich tuff from Turkey

Clay Minerals ◽  
2015 ◽  
Vol 50 (1) ◽  
pp. 77-90
Author(s):  
Güler Narin
Keyword(s):  
Activation Energy ◽  
Bulk Water ◽  
Single Step ◽  
Heating Rates ◽  
Temperature Range ◽  
Dehydration Rate ◽  
Model Free ◽  
Thermogravimetric Data ◽  
Type Zeolite ◽  
Kinetics Of

AbstractNon-isothermal dehydration kinetics of a heulandite-type zeolite-rich tuff from Turkey was investigated using thermogravimetric data recorded at three different heating rates (5, 10 and 20°C/min) under nitrogen flow. Isoconversional model-free methods gave a constant activation energy over the temperature range 30–200°C suggesting that the dehydration is a single-step process within this temperature range. The apparent activation energy was determined as: 34.54±1.18, 30.99±1.14 and 27.79±1.42 kJ/mol by the Flynn–Wall–Ozawa, the Kissinger–Akahira–Sunose and the Friedman methods, respectively. The activation energy values determined were less than the activation energy for vaporization of bulk water, indicating control of the dehydration rate by diffusion of water within this temperature range.

Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

1982 ◽  
Vol 47 (7) ◽  
pp. 1780-1786 ◽  
Author(s):  
Rostislav Kudláček ◽  
Jan Lokoč
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Liquid Phase ◽  
Ionizing Radiation ◽  
Oxide Catalyst ◽  
Absorbed Dose ◽  
Hydrogenation Rate ◽  
Solution Composition ◽  
Mixed Catalyst ◽  
Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

On the use of Ozawa/Flynn/Wall method to determine aging activation energy for elastomers

2021 ◽  
pp. 009524432110203
Author(s):  
Sudhir Bafna
Keyword(s):  
Mechanical Properties ◽  
Activation Energy ◽  
Weight Loss ◽  
Oxygen Consumption ◽  
Dwell Time ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Degradation Mechanism ◽  
Kinetics Of ◽  
Wall Method

It is often necessary to assess the effect of aging at room temperature over years/decades for hardware containing elastomeric components such as oring seals or shock isolators. In order to determine this effect, accelerated oven aging at elevated temperatures is pursued. When doing so, it is vital that the degradation mechanism still be representative of that prevalent at room temperature. This places an upper limit on the elevated oven temperature, which in turn, increases the dwell time in the oven. As a result, the oven dwell time can run into months, if not years, something that is not realistically feasible due to resource/schedule constraints in industry. Measuring activation energy (Ea) of elastomer aging by test methods such as tensile strength or elongation, compression set, modulus, oxygen consumption, etc. is expensive and time consuming. Use of kinetics of weight loss by ThermoGravimetric Analysis (TGA) using the Ozawa/Flynn/Wall method per ASTM E1641 is an attractive option (especially due to the availability of commercial instrumentation with software to make the required measurements and calculations) and is widely used. There is no fundamental scientific reason why the kinetics of weight loss at elevated temperatures should correlate to the kinetics of loss of mechanical properties over years/decades at room temperature. Ea obtained by high temperature weight loss is almost always significantly higher than that obtained by measurements of mechanical properties or oxygen consumption over extended periods at much lower temperatures. In this paper, data on five different elastomer types (butyl, nitrile, EPDM, polychloroprene and fluorocarbon) are presented to prove that point. Thus, use of Ea determined by weight loss by TGA tends to give unrealistically high values, which in turn, will lead to incorrectly high predictions of storage life at room temperature.

scholarly journals Fluoride Leaching of Titanium from Ti-Bearing Electric Furnace Slag in [NH4+]-[F−] Solution

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1176
Author(s):  
Fuqiang Zheng ◽  
Yufeng Guo ◽  
Feng Chen ◽  
Shuai Wang ◽  
Jinlai Zhang ◽  
...  
Keyword(s):  
Activation Energy ◽  
Electric Furnace ◽  
Kinetic Equations ◽  
Surface Chemical ◽  
Leaching Rate ◽  
Surface Chemical Reaction ◽  
Mechanism And Kinetics ◽  
Semi Empirical ◽  
Kinetics Of ◽  
Furnace Slag

The effects of F− concentration, leaching temperature, and time on the Ti leaching from Ti-bearing electric furnace slag (TEFS) by [NH4+]-[F−] solution leaching process was investigated to reveal the leaching mechanism and kinetics of titanium. The results indicated that the Ti leaching rate obviously increased with the increase of leaching temperature and F− concentration. The kinetic equation of Ti leaching was obtained, and the activation energy was 52.30 kJ/mol. The fitting results of kinetic equations and calculated values of activation energy both indicated that the leaching rate of TEFS was controlled by surface chemical reaction. The semi-empirical kinetics equation was consistent with the real experimental results, with a correlation coefficient (R2) of 0.996. The Ti leaching rate reached 92.83% after leaching at 90 °C for 20 min with F− concentration of 14 mol/L and [NH4+]/[F−] ratio of 0.4. The leaching rates of Si, Fe, V, Mn, and Cr were 94.03%, 7.24%, 5.36%, 4.54%, and 1.73%, respectively. The Ca, Mg, and Al elements were converted to (NH4)3AlF6 and CaMg2Al2F12 in the residue, which can transform into stable oxides and fluorides after pyro-hydrolyzing and calcinating.

scholarly journals A Study of the Impact of Graphite on the Kinetics of SPS in Nano- and Submicron WC-10%Co Powder Compositions

Ceramics ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 331-363
Author(s):  
Eugeniy Lantcev ◽  
Aleksey Nokhrin ◽  
Nataliya Malekhonova ◽  
Maksim Boldin ◽  
Vladimir Chuvil'deev ◽  
...  
Keyword(s):  
Activation Energy ◽  
Solid Phase ◽  
Continuous Heating ◽  
Diffusion Creep ◽  
Hard Alloys ◽  
Fine Grained ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
The Impact ◽  
Kinetics Of

This study investigates the impact of carbon on the kinetics of the spark plasma sintering (SPS) of nano- and submicron powders WC-10wt.%Co. Carbon, in the form of graphite, was introduced into powders by mixing. The activation energy of solid-phase sintering was determined for the conditions of isothermal and continuous heating. It has been demonstrated that increasing the carbon content leads to a decrease in the fraction of η-phase particles and a shift of the shrinkage curve towards lower heating temperatures. It has been established that increasing the graphite content in nano- and submicron powders has no significant effect on the SPS activation energy for “mid-range” heating temperatures, QS(I). The value of QS(I) is close to the activation energy of grain-boundary diffusion in cobalt. It has been demonstrated that increasing the content of graphite leads to a significant decrease in the SPS activation energy, QS(II), for “higher-range” heating temperatures due to lower concentration of tungsten atoms in cobalt-based γ-phase. It has been established that the sintering kinetics of fine-grained WC-Co hard alloys is limited by the intensity of diffusion creep of cobalt (Coble creep).

Vulcanization of Elastomers. 23. The Chemical Kinetics of Vulcanization Reactions and The Physical Properties of The Vulcanizates. I

1960 ◽  
Vol 33 (2) ◽  
pp. 335-341
Author(s):  
Walter Scheele ◽  
Karl-Heinz Hillmer
Keyword(s):  
Activation Energy ◽  
Physical Properties ◽  
Chemical Kinetics ◽  
Kcal Mole ◽  
First Order ◽  
Equilibrium Swelling ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization ◽  
Limiting Value ◽  
Good Agreement

Abstract As a complement to earlier investigations, and in order to examine more closely the connection between the chemical kinetics and the changes with vulcanization time of the physical properties in the case of vulcanization reactions, we used thiuram vulcanizations as an example, and concerned ourselves with the dependence of stress values (moduli) at different degrees of elongation and different vulcanization temperatures. We found: 1. Stress values attain a limiting value, dependent on the degree of elongation, but independent of the vulcanization temperature at constant elongation. 2. The rise in stress values with the vulcanization time is characterized by an initial delay, which, however, is practically nonexistent at higher temperatures. 3. The kinetics of the increase in stress values with vulcanization time are both qualitatively and quantitatively in accord with the dependence of the reciprocal equilibrium swelling on the vulcanization time; both processes, after a retardation, go according to the first order law and at the same rate. 4. From the temperature dependence of the rate constants of reciprocal equilibrium swelling, as well as of the increase in stress, an activation energy of 22 kcal/mole can be calculated, in good agreement with the activation energy of dithiocarbamate formation in thiuram vulcanizations.

Magnetic Properties, Nanostructure, and Ordering Kinetics of Nb Additive FePtCu Films

2010 ◽  
Vol 638-642 ◽  
pp. 1743-1748
Author(s):  
G.J. Chen ◽  
Y.H. Shih ◽  
Jason S.C. Jang ◽  
S.R. Jian ◽  
P.H. Tsai ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Activation Energy ◽  
Magnetic Properties ◽  
Heating Rates ◽  
Fept Alloy ◽  
Ordering Kinetics ◽  
Nb Content ◽  
Kinetics Of ◽  
Nb Addition ◽  
Microstructure And Magnetic Properties

In this study,the (FePt)94-xCu6Nbx (x=0, 2.87, 4.52, 5.67) alloy films were prepared by co-sputtering. The effects of Nb addition content and heat treatment on the microstructure and magnetic properties of the polycrystalline FePtCu films are reported. Our previous experiments showed that the ordering temperature of the (FePt)94Cu6 films reduced to 320 °C, which is much lower than that of the FePt alloy. However, the grain growth after heat treatment limited the practical application in recording media. By adding the Nb content in the (FePt)94Cu6 film, the grain sizes of the films can be adjusted from 50 to 18nm, even for the films annealed at temperature as high as 600°C. DSC traces of as-deposited disorder films at different heating rates, to evaluate the crystallization of the order phase, revealed that the addition of Nb enhanced the activation energy of ordering from 87 kJ/mol to 288 kJ/mol for the (FePt)94-xCu6Nbx (x=0 and 2.87, respectively) films. The reduction of the grain size and the corresponding increase in the activation energy of the Fe-Pt-Cu-Nb films might result from the precipitation of the Nb atoms around the ordering FePt phase. The (FePt)94-xCu6Nbx (x=2.87) film showed a coercive force of 13.4 kOe and the magnetization of 687 emu/cc.

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