scholarly journals The Influence of Dimensionality on the Rate of Diffusive Escape From an Energy Well

2012 ◽  
Vol 79 (3) ◽  
Author(s):  
L. B. Freund
Keyword(s):  
Energy Difference ◽  
Reaction Coordinate ◽  
Thermal Excitation ◽  
Energy Profile ◽  
Radial Line ◽  
First Case ◽  
Rate Of Escape ◽  
Energy Environment ◽  
Constitutive Assumption ◽  
Kinetics Of

A commonly used idealization when describing separation of a chemical bond between molecules is that of an energy well which prescribes the dependence of energy of interaction between the molecules in terms of a reaction coordinate. The energy difference between the peak to be overcome and the root of the well is the so-called activation energy, and the overall shape of the well dictates the kinetics of separation through a constitutive assumption concerning transport. An assumption tacit in this description is that the state of the bond evolves with only a single degree of freedom—the reaction coordinate—as the system explores its energy environment under random thermal excitation. In this discussion we will consider several bonds described by one and the same energy profile. The cases differ in that the energy profile varies along a line extending from the root of the well in the first case, along any radial line in a plane extending from the root of the well in a second case, and along any radial line in space extending from the root of the well in a third case. To focus the discussion we determine the statistical rate of escape of states from the well in each case, requiring that the profile of the well is the same in all three cases. It is found that the rates of escape each depend exponentially on the depth of the well but that the coefficients of the exponential vary with depth of the well differently in the three cases considered.

Dynamic Transformation of Austenite at Temperatures above the Ae3

2018 ◽  
Vol 941 ◽  
pp. 633-638
Author(s):  
John Joseph Jonas ◽  
Clodualdo Aranas Jr. ◽  
Samuel F. Rodrigues
Keyword(s):  
Electron Microscopy ◽  
Driving Force ◽  
Energy Difference ◽  
Accelerated Cooling ◽  
Free Energy Difference ◽  
Dynamic Transformation ◽  
Plate Rolling ◽  
Temperature Transformation ◽  
Mn Steel ◽  
Kinetics Of

Under loading above the Ae3 temperature, austenite transforms displacively into Widmanstätten ferrite. Here the driving force for transformation is the net softening during the phase change while the obstacle consists of the free energy difference between austenite and ferrite as well as the work of shear accommodation and dilatation during the transformation. Once the driving force is higher than the obstacle, phase transformation occurs. This phenomenon was explored here by means of the optical and electron microscopy of a C-Mn steel deformed above their transformation temperatures. Strain-temperature-transformation (STT) curves are presented that accurately quantify the amount of dynamically formed ferrite; the kinetics of retransformation are also specified in the form of appropriate TTRT diagrams. This technique can be used to improve the models for transformation on accelerated cooling in strip and plate rolling.

Diffusion Enhancement in Glassy Metals Under Non-Equilibrium Conditions

1995 ◽  
Vol 400 ◽  
Author(s):  
S. Bellini ◽  
G. Mazzone ◽  
A. Montone ◽  
M. Vittori-antisari Enea ◽  
C.R. Casaccia
Keyword(s):  
Free Volume ◽  
Growth Kinetics ◽  
Bulk Diffusion ◽  
High Energy ◽  
First Case ◽  
Diffusion Enhancement ◽  
Glass Crystal ◽  
Kinetics Of ◽  
Crystal Interface ◽  
Diffusion Properties

AbstractThe diffusion properties of a Ni-Zr metallic glass formed at the interface of a bulk diffusion couple have been studied in conditions far from a fully relaxed state. The growth kinetics of the interface film have been enhanced by both plastic deformation and high energy electron irradiation. Different results have been obtained in the two cases, since in the first case the film grows exponentially with time, while in the second case the usual square root dependence on time is observed. This behaviour has been interpreted as a consequence of the annihilation kinetics of the excess free volume introduced in the glass by the above methods. Two different mechanisms of free volume annihilation , namely exchange with a crystal vacancy at the glass-crystal interface and structural relaxation in the bulk glassy phase have been considered to be operative so that the nature of the growth kinetics has been found to depend on the mechanism predominant in each experimental condition.

Kinetics of Recycling CF/EP Composites by Thermal Excitation of Cr2O3

2019 ◽  
Vol 27 (9) ◽  
pp. 1937-1947
Author(s):  
Huanbo Cheng ◽  
Yu Sun ◽  
Ziqiang Zhou ◽  
Jie Zhang ◽  
Xin Wang ◽  
...  
Keyword(s):  
Thermal Excitation ◽  
Kinetics Of

scholarly journals Transmembrane mobility of phospholipids in sickle erythrocytes: effect of deoxygenation on diffusion and asymmetry

Blood ◽  
1991 ◽  
Vol 77 (4) ◽  
pp. 849-854 ◽  
Author(s):  
N Blumenfeld ◽  
A Zachowski ◽  
F Galacteros ◽  
Y Beuzard ◽  
PF Devaux
Keyword(s):  
Sickle Cell ◽  
Blood Cells ◽  
Cell Disease ◽  
Aminophospholipid Translocase ◽  
Outer Leaflet ◽  
First Case ◽  
Sickle Erythrocytes ◽  
Dependent Transport ◽  
The Relationship ◽  
Kinetics Of

Abstract We studied the effect of sickling on the transmembrane reorientation and distribution of phospholipids in the red blood cells of patients homozygous for sickle cell anemia (SS). To this purpose, we followed the redistribution kinetics of trace amounts of spin-labeled analogues of natural phospholipids first introduced in the membrane outer leaflet of normal or sickle erythrocytes exposed to air or nitrogen. Deoxygenation had no effect on the lipid redistribution kinetics in normal (AA) cell membranes. At atmospheric pO2, unfractionated SS cells were not different from normal cells. However, on deoxygenation inducing sickling, phosphatidylcholine passive diffusion was accelerated and the rate of the adenosine triphosphate-dependent transport of aminophospholipids was reduced, especially for phosphatidylserine. The stationary distribution of the aminophospholipids between the two leaflets was slightly less asymmetric, a phenomenon more pronounced with phosphatidylethanolamine. These changes were rapidly reversible on reoxygenation. When SS cells were separated by density, both dense and light cells exhibited the properties cited above. However, dense cells exposed to air possessed a lower aminophospholipid transport rate. These data favor the relationship between aminophospholipid translocase activity and phospholipid transmembrane asymmetry. Sickle cell disease is the first case of aminophospholipid translocase pathology.

scholarly journals Direct observation of crystallization and melting with colloids

2019 ◽  
Vol 116 (4) ◽  
pp. 1180-1184 ◽  
Author(s):  
Hyerim Hwang ◽  
David A. Weitz ◽  
Frans Spaepen
Keyword(s):  
Energy Difference ◽  
Face Centered Cubic ◽  
Limited Growth ◽  
Free Energy Difference ◽  
Precise Control ◽  
Early Computer ◽  
Face Centered ◽  
Jump Frequencies ◽  
Kinetics Of ◽  
Kinetics Of Crystal Growth

We study the kinetics of crystal growth and melting of two types of colloidal crystals: body-centered cubic (BCC) crystals and face-centered cubic (FCC) crystals. A dielectrophoretic “electric bottle” confines colloids, enabling precise control of the motion of the interface. We track the particle motion, and by introducing a structural order parameter, we measure the jump frequencies of particles to and from the crystal and determine from these the free-energy difference between the phases and the interface mobility. We find that the interface is rough in both BCC and FCC cases. Moreover, the jump frequencies correspond to those expected from the random walk of the particles, which translates to collision-limited growth in metallic systems. The mobility of the BCC interface is greater than that of the FCC interface. In addition, contrary to the prediction of some early computer simulations, we show that there is no significant asymmetry between the mobilities for crystallization and melting.

Theoretical elucidation of the energy conversion rate in organic photovoltaic cells of the fullerene nanostructure derivatives. A density functional theory study

2020 ◽  
Vol 19 (07) ◽  
pp. 2050025
Author(s):  
Nadjet Deddouche ◽  
Hafida Chemouri
Keyword(s):  
Density Functional Theory ◽  
Conversion Rate ◽  
Density Functional ◽  
Lithium Ion ◽  
Photovoltaic Cell ◽  
Energy Difference ◽  
Organic Photovoltaic ◽  
Mechanistic Study ◽  
Functional Theory ◽  
Kinetics Of

A comparative theoretical study of the kinetics of the Diels–Alder (DA) reaction between empty fullerene (C[Formula: see text]) and lithium ion encapsulated fullerene ([Formula: see text]) with 1,3 cyclohexadiene (C[Formula: see text]H[Formula: see text]) was carried out. This reaction takes place in a photovoltaic cell. The effect of the encapsulated [Formula: see text] ion on the conversion rate of solar energy into electricity has been highlighted through calculations based on the density functional theory (DFT). In addition, a static study using the global conceptual DFT indices, as part of the demonstration of the significant electrophilic power of the fullerene nanostructure, was carried out to show the effect of encapsulating the [Formula: see text] ion in this nanoparticle on the electrophilic power of Li[Formula: see text]@C[Formula: see text] and therefore on the acceleration of the reaction. The relationship between the HOMOdonor–LUMOacceptor energy difference and the DA reaction acceleration, and therefore the acceleration of light conversion (a rapid conversion implies a small gap), has been thoroughly examined. Moreover, a mechanistic study of the kinetics of the DA reaction of the fullerene involved in an organic photovoltaic cell has been carried out. In this section, a concerted synchronous mechanism with no effect of [Formula: see text] encapsulation on the synchronicity of the reaction was observed. Finally, it was revealed that Li[Formula: see text]@C[Formula: see text] reacted approximately 2466 times faster than C[Formula: see text]. Moreover, the experimental results were found in good agreement with the computer calculations.

Reaction Kinetics of Atomic chlorine on Si(100)2×1

1992 ◽  
Vol 280 ◽  
Author(s):  
Kazuhiro Karahashi ◽  
Jiro Matsuo ◽  
Kei Horiuchi
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Solid Surface ◽  
Surface Reaction ◽  
Thermal Excitation ◽  
Silicon Substrates ◽  
Chlorine Atoms ◽  
Substrate Temperatures ◽  
Kinetics Of ◽  
Atomic Chlorine

ABSTRACTThe interaction of atomic chlorine with Si(100)2×1 surfaces was studied by using chlorine atom beams. The etching reaction of silicon substrates has been observed when chlorine atoms impinged on the chlorinated surface, at substrate temperatures below 600°C. The major desorption product is SiCl2. Studies of the temperature dependence of the reaction showed that the activation energy are 0.08 eV at 0.4 ML and 0.2 eV at 0.8 ML. These extremely low activation energies suggest that the surface reaction is mainly driven by the internal energy of incident atomic chlorine instead of thermal excitation from Si(100) solid surface. Therefore chlorine atoms enter the transition state without equilibrating at the surface prior to the reaction. The reaction strongly depends on the chlorine coverage on the surface. The reaction occurred above 0.3 ML. The etching probability of the surface reached a maximum at 0.4 ML, and decreased with increasing coverage.

scholarly journals Surface Induced Crystallization in Fibre Reinforced Nylon 6,6 Composites

1992 ◽  
Vol 1 (4) ◽  
pp. 096369359200100 ◽  
Author(s):  
N Klein ◽  
G Marom
Keyword(s):  
Fibre Surface ◽  
Energy Difference ◽  
Carbon Fibres ◽  
Free Energy Difference ◽  
Difference Function ◽  
Nylon 6,6 ◽  
Aramid Fibres ◽  
Transcrystalline Layer ◽  
Kinetics Of ◽  
Induced Crystallization

The present study deals with the growth of transcrystalline layer in Nylon 6,6 reinforced with HM pitch based carbon or aramid fibres. The kinetics of transcrystalline growth is investigated quantitatively. The surface energy parameters that are derived here, can be used to define a better criterion for the nucleation of transcrystallinity from the fibre surface. The free energy difference function, Δσ, as it appears in the classical theory of heterogeneous nucleation is calculated for both aramid and HM carbon fibres.

scholarly journals Compare and contrast the reaction coordinate diagrams for chemical reactions and cytoskeletal force generators

2013 ◽  
Vol 24 (4) ◽  
pp. 433-439 ◽  
Author(s):  
Jonathan M. Scholey
Keyword(s):  
Intracellular Transport ◽  
Molecular Mechanisms ◽  
Equilibrium Constants ◽  
Reaction Coordinate ◽  
Simple Chemical ◽  
Interdisciplinary Framework ◽  
Catalyzed Reactions ◽  
Enzyme Catalyzed Reactions ◽  
Compare And Contrast ◽  
Kinetics Of

Reaction coordinate diagrams are used to relate the free energy changes that occur during the progress of chemical processes to the rate and equilibrium constants of the process. Here I briefly review the application of these diagrams to the thermodynamics and kinetics of the generation of force and motion by cytoskeletal motors and polymer ratchets as they mediate intracellular transport, organelle dynamics, cell locomotion, and cell division. To provide a familiar biochemical context for discussing these subcellular force generators, I first review the application of reaction coordinate diagrams to the mechanisms of simple chemical and enzyme-catalyzed reactions. My description of reaction coordinate diagrams of motors and polymer ratchets is simplified relative to the rigorous biophysical treatment found in many of the references that I use and cite, but I hope that the essay provides a valuable qualitative representation of the physical chemical parameters that underlie the generation of force and motility at molecular scales. In any case, I have found that this approach represents a useful interdisciplinary framework for understanding, researching, and teaching the basic molecular mechanisms by which motors contribute to fundamental cell biological processes.

scholarly journals Kinetics of the Opening and Closing of Individual Excitability-Inducing Material Channels in a Lipid Bilayer

1974 ◽  
Vol 63 (6) ◽  
pp. 707-721 ◽  
Author(s):  
Gerald Ehrenstein ◽  
Robert Blumenthal ◽  
Ramon Latorre ◽  
Harold Lecar
Keyword(s):  
Lipid Bilayers ◽  
Ionic Current ◽  
Energy Difference ◽  
Excitable Membranes ◽  
Voltage Dependent ◽  
Ion Conducting ◽  
The Many ◽  
Approach To Steady State ◽  
Opening And Closing ◽  
Kinetics Of

The kinetics of the opening and closing of individual ion-conducting channels in lipid bilayers doped with small amounts of excitability-inducing material (EIM) are determined from discrete fluctuations in ionic current. The kinetics for the approach to steady-state conductance during voltage clamp are determined for lipid bilayers containing many EIM channels. The two sets of measurements are found to be consistent, verifying that the voltage-dependent conductance of the many-channel EIM system arises from the opening and closing of individual EIM channels. The opening and closing of the channels are Poisson processes. Transition rates for these processes vary exponentially with applied potential, implying that the energy difference between the open and closed states of an EIM channel is linearly proportional to the transmembrane electric field. A model incorporating the above properties of the EIM channels predicts the observed voltage dependence of ionic conductance and conductance relaxation time, which are also characteristic of natural electrically excitable membranes.

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