Electric field perturbed electron tunnelling in nonpolar organic glasses

1977 ◽  
Vol 55 (11) ◽  
pp. 2065-2079 ◽  
Author(s):  
A. J. Doheny ◽  
A. C. Albrecht
Keyword(s):  
Angular Distribution ◽  
Time Scale ◽  
Applied Field ◽  
Kinetic Equations ◽  
Quantum Mechanical ◽  
Recombination Rates ◽  
Qualitative And Quantitative ◽  
Organic Glasses ◽  
Trap Ionization ◽  
Nonpolar Organic

Isothermoluminescence (ITL) and electrophotoluminescence (EPL) resulting from electron–cation recombination are measured in a 2-methylpentane–methylcyclohexane glass. The ITL is more characteristic of quantum-mechanical tunnelling and the EPL signal is markedly stronger in this new glass than previous measurements in 3-methylpentane. Quantum-mechanical tunnelling theory is used to predict recombination rates of electrons in the potential field of a cation plus an applied field. Numerical integration of the nonhomogeneous kinetic equations resulting from a distribution of cation–electron separations leads to qualitative and quantitative predictions of the EPL signal that are observed experimentally. Fitting of the theory to experiment supports the conclusions that the angular distribution of the photoelectrons about the cations is close to isotropic, that the electrons active in ITL and EPL on the time scale of minutes are separated about 50 Å from their parent cation, and that the trap ionization potential in this nonpolar hydrocarbon glass is in the range of 0.5 to 0.7 eV.

Long-term evolution of directional spectra of wind waves modelled by DNS and kinetic equations, and comparison with airborne measurements

2021 ◽  
Author(s):  
Sergei Annenkov ◽  
Victor Shrira ◽  
Leonel Romero ◽  
Ken Melville
Keyword(s):  
Angular Distribution ◽  
Kinetic Equation ◽  
Kinetic Theory ◽  
Wind Waves ◽  
Kinetic Equations ◽  
Spectral Peak ◽  
Angular Width ◽  
Angular Structure ◽  
Airborne Measurements ◽  
Steady Growth

<p>We consider the evolution of directional spectra of waves generated by constant and changing wind, modelling it by direct numerical simulation (DNS), based on the Zakharov equation. Results are compared with numerical simulations performed with the Hasselmann kinetic equation and the generalised kinetic equation, and with airborne measurements of waves generated by offshore wind, collected during the GOTEX experiment off the coast of Mexico. Modelling is performed with wind measured during the experiment, and the initial conditions are taken as the observed spectrum at the moment when wind waves prevail over swell after the initial part of the evolution.</p><p>Directional spreading is characterised by the second moment of the normalised angular distribution function, taken at selected wavenumbers relative to the spectral peak. We show that for scales longer than the spectral peak the angular spread predicted by the DNS is close to that predicted by both kinetic equations, but it underestimates the corresponding measured value, apparently due to the presence of swell. For the spectral peak and shorter waves, the DNS shows good agreement with the data. A notable feature is the steady growth of angular width at the spectral peak with time/fetch, in contrast to nearly constant width in the kinetic equations modelling. Dependence of angular width on wavenumber is shown to be much weaker than predicted by the kinetic equations. A more detailed consideration of the angular structure at the spectral peak at large fetches shows that the kinetic equations predict an angular distribution with a well-defined peak at the central angle, while the DNS reproduces the observed angular structure, with a flat peak over a range of angles.</p><p>In order to study in detail the differences between the predictions of the DNS and the kinetic equations modelling under idealised conditions, we also perform numerical simulations for the case of constant wind forcing. As in the previous case of forcing by real wind, the most striking difference between the kinetic equations and the DNS is the steady growth with time of angular width at the spectral peak, which is demonstrated by the DNS, but is not present in the modelling with the kinetic equations. We show that while the kinetic theory, both in the case of the Hasselmann equation and the generalised kinetic equation, predicts a relatively simple shape of the spectral peak, the DNS shows a more complicated structure, with a flat top and dependence of the peak position on angle. We discuss the approximations employed in the derivation of the kinetic theory and the possible causes of the found differences of directional structure.</p>

scholarly journals Spectral evolution of weakly nonlinear random waves: kinetic description versus direct numerical simulations

2018 ◽  
Vol 844 ◽  
pp. 766-795 ◽  
Author(s):  
Sergei Y. Annenkov ◽  
Victor I. Shrira
Keyword(s):  
Time Scale ◽  
Kinetic Equations ◽  
Wave Spectra ◽  
Kinetic Description ◽  
Spectral Evolution ◽  
Short Term ◽  
Weakly Nonlinear ◽  
Term Evolution ◽  
Integral Characteristics

Kinetic equations are widely used in many branches of science to describe the evolution of random wave spectra. To examine the validity of these equations, we study numerically the long-term evolution of water wave spectra without wind input using three different models. The first model is the classical kinetic (Hasselmann) equation (KE). The second model is the generalised kinetic equation (gKE), derived employing the same statistical closure as the KE but without the assumption of quasistationarity. The third model, which we refer to as the DNS-ZE, is a direct numerical simulation algorithm based on the Zakharov integrodifferential equation, which plays the role of the primitive equation for a weakly nonlinear wave field. It does not employ any statistical assumptions. We perform a comparison of the spectral evolution of the same initial distributions without forcing, with/without a statistical closure and with/without the quasistationarity assumption. For the initial conditions, we choose two narrow-banded spectra with the same frequency distribution and different degrees of directionality. The short-term evolution ($O(10^{2})$ wave periods) of both spectra has been previously thoroughly studied experimentally and numerically using a variety of approaches. Our DNS-ZE results are validated both with existing short-term DNS by other methods and with available laboratory observations of higher-order moment (kurtosis) evolution. All three models demonstrate very close evolution of integral characteristics of the spectra, approaching with time the theoretical asymptotes of the self-similar stage of evolution. Both kinetic equations give almost identical spectral evolution, unless the spectrum is initially too narrow in angle. However, there are major differences between the DNS-ZE and gKE/KE predictions. First, the rate of angular broadening of initially narrow angular distributions is much larger for the gKE and KE than for the DNS-ZE, although the angular width does appear to tend to the same universal value at large times. Second, the shapes of the frequency spectra differ substantially (even when the nonlinearity is decreased), the DNS-ZE spectra being wider than the KE/gKE ones and having much lower spectral peaks. Third, the maximal rates of change of the spectra obtained with the DNS-ZE scale as the fourth power of nonlinearity, which corresponds to the dynamical time scale of evolution, rather than the sixth power of nonlinearity typical of the kinetic time scale exhibited by the KE. The gKE predictions fall in between. While the long-term DNS show excellent agreement with the KE predictions for integral characteristics of evolving wave spectra, the striking systematic discrepancies for a number of specific spectral characteristics call for revision of the fundamentals of the wave kinetic description.

Nonlinear electrohydrodynamics of slightly deformed oblate drops

2015 ◽  
Vol 774 ◽  
pp. 245-266 ◽  
Author(s):  
Javier A. Lanauze ◽  
Lynn M. Walker ◽  
Aditya S. Khair
Keyword(s):  
Steady State ◽  
Electric Field ◽  
Surface Charge ◽  
Time Scale ◽  
Applied Field ◽  
Major Axis ◽  
Boundary Integral ◽  
Numerical Results ◽  
Transient Deformation ◽  
Leaky Dielectric

The transient deformation of a weakly conducting (‘leaky dielectric’) drop under a uniform DC electric field is computed via an axisymmetric boundary integral method, which accounts for surface charge convection and a finite relaxation time scale over which the drop interface charges. We focus on drops that attain an ultimate oblate (major axis normal to the applied field) steady-state configuration. The computations predict that as the time scale for interfacial charging increases, a shape transition from prolate deformation (major axis parallel to the applied field) to oblate deformation occurs at intermediate times due to the slow buildup of charge at the surface of the drop. Convection of surface charge towards the equator of the drop is shown to weaken the steady-state oblate deformation. Additionally, convection results in sharp shock-like variations in surface charge density near the equator of the drop. Our numerical results are then compared with an experimental system consisting of a millimetre-sized silicone oil drop suspended in castor oil. Agreement in the transient deformation is observed between our numerical results and experimental measurements for moderate electric field strengths. This suggests that both charge relaxation and charge convection are required, in general, to quantify the time-dependent deformation of leaky dielectric drops. Importantly, accurate prediction of the observed modest deformation requires a nonlinear model. Discrepancies between our numerical calculations and experimental results arise as the field strength is increased. We believe that this is due to the observed onset of rotation and three-dimensional flow at such high electric fields in the experiments, which an axisymmetric boundary integral formulation naturally cannot capture.

scholarly journals Rapid and slow gating of veratridine-modified sodium channels in frog myelinated nerve.

1989 ◽  
Vol 93 (1) ◽  
pp. 43-65 ◽  
Author(s):  
T A Rando
Keyword(s):  
Resting State ◽  
Time Scale ◽  
Rana Pipiens ◽  
Activation Process ◽  
Na Channels ◽  
Myelinated Nerve ◽  
Qualitative And Quantitative ◽  
Related Alkaloid ◽  
Voltage Dependent ◽  
Gating Process

The properties of voltage-dependent Na channels modified by veratridine (VTD) were studied in voltage-clamped nodes of Ranvier of the frog Rana pipiens. Two modes of gating of VTD-modified channels are described. The first, occurring on a time scale of milliseconds, is shown to be the transition of channels between a modified resting state and a modified open state. There are important qualitative and quantitative differences of this gating process in nerve compared with that in muscle (Leibowitz et al., 1986). A second gating process occurring on a time scale of seconds, was originally described as a modified activation process (Ulbricht, 1969). This process is further analyzed here, and a model is presented in which the slow process represents the gating of VTD-modified channels between open and inactivated states. An expanded model is a step in the direction of unifying the known rapid and slow physiologic processes of Na channels modified by VTD and related alkaloid neurotoxins.

Tipping time of a holonomic quantum cylinder

2011 ◽  
Vol 89 (9) ◽  
pp. 903-913
Author(s):  
Mark R.A. Shegelski ◽  
Jamie Sanchez-Fortun Stoker ◽  
Ian Kellett
Keyword(s):  
Wave Function ◽  
Time Scale ◽  
Numerical Solutions ◽  
Quantum Mechanical ◽  
Length Scale ◽  
Dimensionless Form ◽  
Order Unity ◽  
Holonomic Constraints ◽  
Initial Wave ◽  
Initial Wave Function

The classical and quantum mechanical Hamiltonians for a cylinder subject to holonomic constraints are derived. The quantum mechanical Hamiltonian is simplified and cast into a dimensionless form. The tipping time of a quantum mechanical cylinder subject to gravity is calculated. Numerical solutions for an appropriate initial wave function are obtained. We find that the tipping time is given by 〈t〉tip = t0C1 exp [C2(r/r0)9], where t0 is the time scale, C1 and C2 are constants of order unity, r is the radius of the cylinder, and r0 is the length scale for the tipping. We compare our results with those found in previous works.

scholarly journals ECG Denoising Methodology using Intrinsic Time Scale Decomposition and Adaptive Switching Mean Filter

2021 ◽  
Vol 1 (2) ◽  
pp. 8-12
Author(s):  
Battula Tirumala Krishna ◽  
Putti Siva Kameswaari
Keyword(s):  
Time Scale ◽  
Signal To Noise Ratio ◽  
Software Environment ◽  
Ecg Signals ◽  
Qualitative And Quantitative ◽  
Intrinsic Time ◽  
Mean Filter ◽  
Time Scale Decomposition ◽  
Real Scenario ◽  
Qualitative And Quantitative Study

Electrocardiogram (ECG) is a widely employed tool for the analysis of cardiac disorders. A clean ECG is often desired for proper treatment of cardiac ailments. However, in the real scenario, ECG signals are corrupted with various noises during acquisition and transmission. In this article, an efficient ECG de-noising methodology using combined intrinsic time scale decomposition (ITD) and adaptive switching mean filter (ASMF) is proposed. The standard performance metric namely output SNR improvement measure the efficacy of the proposed technique at various signal to noise ratio (SNR). The proposed de-noising methodology is compared with other existing ECG de-noising approaches. A detail qualitative and quantitative study and analysis indicate that the proposed technique can be used as an effective tool for de-noising of ECG signals and hence can serve for better diagnostic in computer-based automated medical system. The performance of the proposed work is compared with existing ECG de-noising techniques namely wavelet soft thresholding based filter (DWT) [16], EMD with DWT technique [18], DWT with ADTF technique [19]. The effectiveness of the presented work has been evaluated in both qualitative and quantitative analysis. All the simulations are carried out using MATLAB software environment.

Realization of Origami-Inspired Smart Structures Using Electroactive Polymer (EAP)

2016 ◽  
Author(s):  
Saad Ahmed ◽  
Erika Arrojado ◽  
Zoubeida Ounaies
Keyword(s):  
Electric Field ◽  
Applied Field ◽  
Research Study ◽  
Active Material ◽  
Plane Motion ◽  
Electroactive Polymer ◽  
Small Ball ◽  
Qualitative And Quantitative ◽  
Paper Folding ◽  
Mechanical Actuation

Robert Lang has brought functionality to origami, the art of paper folding, by developing an extensive series of “action origami” figures. As the name suggests, these figures can perform actions and produce an output motion with the help of manual actuation, unlike traditional origami. For instance, different figures can bite, row, and fly. The goal of this research study is to adapt a few of these action origami figures put forth by Robert Lang to create ‘active’ action origami; these systems, instead of relying on manual actuation for motion, will rely on electro-mechanical actuation. This electro-mechanical actuation will be achieved through the judicious use of an electroactive polymer known as P (VDF-TrFE-CTFE) terpolymer. The terpolymer’s in-plane motion in response to an electric field is converted into bending using a unimorph configuration. This bending motion is exploited to actuate three so-called “action origami” structures: the flapping butterfly, the catapult, and the barking dog. Based on knowledge of the kinematics of the origami structures, multilayered terpolymer actuator is placed strategically on the origami figures with an aim to maximize the resulting actuation motion. In order to understand the behavior, capabilities, and limitations of the terpolymer as an active material, both qualitative and quantitative data are collected from the actuation of these three different action origami structures as a function of number of terpolymer layers, applied electric field and frequency of the applied field. The goal is to find the suitable shapes and crease patterns of the structures as well as the configurations with the terpolymer film to maximize the actuation. These three structures are tested and results show that PVDF-terpolymer is an effective actuator with ability to deform a substrate to a desired shape in the presence of an electric field: the butterfly was able to flap, the mouth of the dog was able to “bark,” and the catapult was able to launch a small ball of paper. Through experimentation, it was determined what parameters affect actuation and furthermore what values of those parameters will maximize the actuation.

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