Static Relaxation Research Articles

Temperature dependent dielectric relaxation study of acetonitrile with chlorobenzene at microwave frequency using time domain reflectometry

The dielectric relaxation study of acetonitrile(ACN) with chlorobenzene(CBZ) mixture has been carried out at temperatures 15 °C, 25 °C, 35 °C and 45 °C in the frequency range of 10 MHz to 20 GHz using time domain reflectometry (TDR) for 11 different concentrations of the system. The dielectric parameters such as static dielectric constant ( ε 0) and relaxation time ( τ) have been obtained by Fourier transform and the least squares fit method. Excess properties and Kirkwood correlation factor of the mixtures have been determined. In the mixtures excess permittivity and inverse relaxation time are found to be negative. The static dielectric constants for the mixtures have been fitted with the modified Bruggeman model. The investigation shows that there is a systematic change in dielectric parameters of the system with change in concentration and temperature. The activation energies in the mixture are also determined.

The vacancy–edge dislocation interaction in fcc metals: A comparison between atomic simulations and elasticity theory

The interaction between vacancies and edge dislocations in face centered cubic metals (Al, Au, Cu, Ni) is studied at different length scales. Using empirical potentials and static relaxation, atomic simulations give us a precise description of this interaction, mostly in the case when the separation distance between both defects is small. At larger distances, elasticity theory can be used to predict this interaction. From the comparison between both approaches we obtain the minimal separation distance where elasticity applies and we estimate the degree of refinement required in the calculation. In this purpose, isotropic and anisotropic elasticity is used assuming a perfect or a dissociated edge dislocation and considering the size effect as well as the inhomogeneity interaction.

Dielectric Relaxation of Propan-1-ol with Chlorobenzene, 1,2-Dichloroethane, and Dimethylene Chloride at (288, 298, 308, and 318) K Using Time-Domain Reflectometry Technique

The values of complex permittivity of molecules containing chlorine with propan-1-ol binary mixtures have been determined over the frequency range of (0.1 to 20) GHz, at temperatures of (288, 298, 308, and 318) K, using the time-domain reflectometry (TDR) method for 11 molalities of each molecule containing chlorine with propan-1-ol system. The dielectric relaxation in these systems can be described by a single relaxation time using the Havriliak and Negami model. The static dielectric constant (ε0) and relaxation time (τ) have been obtained by fitting experimental data with the Havriliak−Negami equation.

Evidence for the existence of multiple equilibrium states in cobalt phthalocyanine tetramer: a study by dielectric spectroscopy

In any investigation, information about the molecules under consideration is very essential for tailoring their properties. Evaluation of dispersion parameters, namely optical dielectric constant, static dielectric constant, relaxation time and spreading factor, assumes significance in this context. Dielectric spectroscopy is a useful tool for estimating these parameters. Not only does it reveal details about these constants but it also gives insight into the mechanism of conduction. In this paper the evaluation of dispersion parameters of cobalt phthalocyanine tetramer in the temperature range 300–393 K is attempted using Cole–Cole plots. The temperature variation of the spreading factor indicates the existence of multiple equilibrium positions in the case of cobalt phthalocyanine tetramer. To the best of our knowledge, the evaluation of dispersion parameters for cobalt phthalocyanine tetramer is reported for the first time.

A Three-Dimensional Numerical Model for Simulating Deformation and Failure of Blocky Rock Structures

This paper presents a three-dimensional numerical model for simulation of blocky rock structures based on static relaxation approach. The proposed method utilizes static equilibrium equations to calculate the displacements of blocks, compared to Newton’s second law applied by the traditional DEM. In order to obtain displacements simultaneously, the technique of global stiffness matrix is introduced in to form the global equilibrium equations. Because large displacements come from the accumulation of small displacement increments, an iteration procedure is adopted in the calculation. A C++ program is developed based on the proposed algorithm, and an illustrative example is computed for verification.

Dielectric relaxation of dioxane-water mixtures using time domain technique

The complex permittivity of dioxane in water mixtures for various concentration and temperatures have been measured as a function of frequency between 10 MHz to 20 GHz using time domain reflectometry technique. Dielectric relaxa-tion parameters i.e. static dielectric constant and relaxation time were obtained from the complex permittivity spectra using the nonlinear least square fit method. The relaxation behaviour of these mixtures are explained by the Debye model. The Debye relaxation time of the mixture shows a maxima for the mixture with 40% of water by volume. This suggests that the tendency to form cluster between water and dioxane molecules is maximum for this mixture. The Kirkwood correlation factor, excess permittivity and Bruggeman factor have been determined at various concentration of water in dioxane.

PREDICTION OF COMPRESSIVE CREEP AND RELAXATION OF HDPE

The aim of this study is to predict the viscoelastic behaviour ofhigh density polyethylene (HDPE) used in bottles and containersfor liquid manufacturing, under compressive static long-term ofcreep and stress relaxation.

Dielectric relaxation studies of formamide-alcohol mixtures using time domain reflectometry

Dielectric relaxation studies of formamide-alcohol mixtures have been carried out for different concentrations at 303K. Time domain reflectometry (TDR) in reflection mode has been used to measure the reflection coefficient in the frequency range of 10 MHz to 10 GHz. The bilinear calibration method has been used to obtain dielectric quantities viz., static dielectric constant (ϵ0) and relaxation time (τ). The Kirkwood correlation factor and excess dielectric properties were determined and discussed to yield information on the molecular structure and dynamics of the mixture. The values of the relaxation time and the Kirkwood correlation factor decrease with increased formamide concentration in alcohol.

EFFECTS OF AN 8-WEEK STRETCHING PROGRAM ON THE PASSIVE RESISTIVE TORQUE AND STATIC STRESS-RELAXATION PROPERTIES OF THE CALF MUSCLE-TENDON UNIT OF OLDER WOMEN.

Purpose/Hypothesis: Calf muscle-tendon unit (MTU) stretching programs are used to increase dorsiflexion range of motion at the ankle. Their effects on the passive resistive torque (PRT) and static stress relaxation (SSR) properties of aged calf MTUs, however, have not been studied. The purpose of this initial study was to describe and examine the effects of an 8-week stretching program on the PRT and SSR properties of the calf MTU of older women. Number of Subjects: Thirteen women aged 65-82 years with limited active dorsiflexion RoM ≤8° participated with informed consent. Materials/Methods: After a pre-testing stretching exercise and relaxation training, a Kin-Com® dynamometer stretched the right calf MTU by moving the ankle from relaxed plantarflexion to maximal tolerated dorsiflexion (DF) and held a static (constant) stretch at the maximal DF angle for 60 seconds (s). The decline in torque during the 60s stretch was recorded while negligible surface EMG activity was monitored for the soleus, gastrocnemius and tibialis anterior muscles. The women were then randomly assigned to a group that stretched both ankles to maximal DF 10 times for 15s each, 3-times a week for 8-weeks (n=6, SG) or to a control group (n=7, CG) that did not stretch. The tests were repeated after the stretching program and descriptive statistics and ANOVA analyses were used to examine the program's influence on the maximal DF angle, the maximal tolerated PRT, and the SSR measured as the absolute torque decline and the percent torque decline (maximal PRT=100%) during the 60s static stretch. Results: The maximal passive DF angle increased for the SG from 12.3plus or minus 3.1° to 18.5plus or minus 4.37° (P=0.003), but not for the CG (test=13.6 ± 4.4°, retest=13.7 ± 5.9°). The maximal PRT increased for the SG from 16.1 ± 2.3 Nm to 26.6 ± 10.6 Nm (P=0.033), but not for the CG (test=17.5 ± s 5.3 Nm, retest=17.6 ± 4.5 Nm). The absolute torque decline increased for the SG from 2.9plus or minus 0.7 Nm to 4.1 ± 1.4 Nm, and the total percent torque decline decreased from 18.3 ± 7.3% to 15.5 ± 2.6%, but the changes were not significant. The CG showed similar test-retest values for the absolute torque decline (2.6 ± 0.7 to 2.5 ± 0.8) and the total percent torque decline (15.0 ± 2.9% to 14.0 ± 1.9%). Conclusions: The stretching program increased the maximal tolerated DF stretch angle and PRT. Although the lack of significant changes in the SSR properties was probably influenced by the small sample size, the stretching program appeared to increase the ability to sustain a greater PRT load during the 60s maximal DF stretch. The responses suggest physical adaptations in the calf MTU that increased their ability to sustain and maintain a tolerated static stretch load. Clinical Relevance: Calf MTU stretching programs for older women can increase the maximal DF angle, and also bring about the ability to withstand a maximal tolerated static stretch. The passive static adaptations may have implications for enhancing functional static and dynamic balance and ambulatory activities.

Electronic Properties of a New Layered Organic Conductor, (BEDT-TTF) 3Br( pBIB)

The electronic properties of a novel 3:1 BEDT-TTF salt were investigated by 13C-NMR measurements on a single crystal sample based on selectively 13C-enriched BEDT-TTF molecule. Static suscptibitity, Knight shift and relaxation rate were measured and a Korringa relation was confirmed. The correlation enhancement of Korringa co-efficient was found very small in comparison to the usual 2:1 BEDT-TTF salts.

Dielectric study of methyl methacrylate-alcohol mixtures by Time Domain Reflectometry at 293 K

Using picosecond Time Domain Reflectometry (TDR), dielectric relaxation studies have been carried out on binary mixtures of methyl methacrylate with 1-propanol, 1-butanol, 1-heptanol and 1-octanol for various concentrations over the frequency range from 10 MHz to 10 GHz at 293 K. The Kirkwood correlation factor and excess inverse relaxation times were determined and discussed to yield information on the molecular structure and dynamics of the mixture. The static permittivity and relaxation time decrease with an increase in the percentage of methyl methacrylate.

Transient effects in dynamic modulus measurement of silicone elastomers 1. Zero mean strain measurements

AbstractThe strain‐dependent dynamic storage modulus of a poly(dimethyl‐siloxane‐co‐methylvinyl‐siloxane‐co‐methylphenyl‐siloxane) based silicone elastomer, which is reinforced with fumed silica and crosslinked with peroxide, is investigated. The dependence of the resulting dynamic storage modulus on the duration of cycling at a particular test condition is investigated and compared to static stress relaxation measurements in the same strain range. The dynamic modulus results are shown to depend on the time of cycling at the current test conditions as well as the time of cycling at prior conditions of lower strains. The relaxation is shown to be related to the time of cycling rather than the number of cycles performed. The pattern of behavior of the relaxation of the dynamic modulus with respect to peak strain amplitude is different than that observed in a static stress relaxation test, both of which show significant nonlinear effects in strain. The observed phenomena are interpreted in terms of the role of the polymer phase on the dynamic behavior of the elastomer material. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1001–1009, 2005

Static magnetic properties and relaxation of the ternary mixed magnetic insulating systemCo1−xMnyFex−yCl2∙2H2O

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Dynamical breakdown of the Ising spin-glass order under a magnetic field

The dynamical magnetic properties of an Ising spin glass Fe$_{0.55}$Mn$_{0.45}$TiO$_3$ are studied under various magnetic fields. Having determined the temperature and static field dependent relaxation time $\tau(T;H)$ from ac magnetization measurements under a dc bias field by a general method, we first demonstrate that these data provide evidence for a spin-glass (SG) phase transition only in zero field. We next argue that the data $\tau(T;H)$ of finite $H$ can be well interpreted by the droplet theory which predicts the absence of a SG phase transition in finite fields.

Dielectric relaxation studies of higher order alcohol complexes with amines using time domain reflectometry

Dielectric relaxation study of amine–alcohol mixtures have been carried out for different concentrations at 303 K. Time Domain Reflectometry (TDR) in reflection mode has been used to measure the reflection coefficient in the frequency range of 10 MHz to 20 GHz. The bilinear calibration method has been used to obtain dielectric quantities viz., static dielectric constant ( ε 0) and relaxation time ( τ). Using these fundamental dielectric quantities the parameters like the Bruggeman factor, Kirkwood correlation factor and excess relaxation time were evaluated. The Bruggeman factor ( F BM) shows a positive deviation for pyridine [PYR] with the alcohol system and it shows a negative deviation for triethylamine [TEA] with the alcohol system. The effective Kirkwood correlation factor ( g eff) is almost unity for amines and > 1 for alcohols and their mixtures, showing parallel orientation of dipoles. The relaxation time is increasing with increasing chain length of the alcohols and it is decreasing with increasing amine concentration. The enthalpy of activation (Δ F τ ) for the dielectric relaxation is always greater than the theoretically predicted values for all the mixtures studied.

The relation between the positional specific heat and the static relaxation length:application to supercooled liquids

A general identification of the positional specific heat as the thermodynamic responsefunction associated with the static relaxation length is proposed, and a phenomenologicaldescription for the thermal dependence of the static relaxation length in supercooled liquids ispresented. Accordingly, through a phenomenological determination of the positional specificheat of supercooled liquids, we arrive at the thermal variation of the static relaxation lengthξ, which is found to vary in accordance with in the quasi-equilibrium supercooled temperature regime, whereT0 is the Vogel–Fulcher temperature and exponentν equals unity. This result to a certain degree agrees with that obtained from mean field theoryof the random-first-order transition, which suggests a power law temperature variation forξ with an apparentdivergence at T0. However, the phenomenological exponentν = 1 is higher than the corresponding mean field estimate (becoming exact in infinitedimensions), and in perfect agreement with the relaxation length exponent as obtainedfrom numerical simulations of the same models of structural glass in three spatialdimensions.

Temperature-dependent dielectric relaxation study of chlorobenzene with n-methylformamide from 10 MHz to 20 GHz

The complex permittivity spectra of chlorobenzene with n-methylformamide were determined in the frequency range of 10 MHz to 20 GHz using time domain reflectometry (TDR) in the temperature range 15 °C to 45 °C for 11 different concentrations of the system. The dielectric parameters viz. static dielectric constant ( ε 0) and relaxation time ( τ) have been obtained by the least squares fit method. Excess properties and Kirkwood correlation factor of the mixtures have been determined. For the temperature range, considered here, the permittivity and relaxation time increased with the percentage of n-methylformamide. The excess permittivity is found to be negative in the chlorobenzene-rich region and positive in the n-methylformamide-rich region. However the excess inverse relaxation time has the reverse trend. The static dielectric constants for the mixtures have been fitted with the modified Bruggeman model.

Investigation of heavily damaged ion implanted Si by atomistic simulation of Rutherford backscattering channeling spectra

Rutherford backscattering channeling (RBS-C) spectra of ion-implanted Si are simulated according to an atomistic model of radiation damage which consists of a distribution of point defects (split-〈110〉 interstitials and vacancies) structurally relaxed by empirical potentials. This model, successfully used to reproduce multiaxial spectra of lightly damaged Si, is applied here to the case of a heavily damaged sample. As a consequence of the increasing strain generated by lattice relaxation, simulations predict a superlinear trend of RBS-C disorder versus defect concentration in the range of intermediate damage density. This contrasts with the linear trend obtained by the usual description of defects as atoms randomly displaced in a rigid lattice. The new approach represents an improvement in the physical description of ion irradiation disorder within RBS-C analysis; however simulation results are found to be in less satisfactory agreement with spectra of a heavily damaged sample than with spectra of lightly damaged material. The description of damage as the result of the accumulation of simple point defects and the use of a static relaxation procedure instead of finite temperature molecular dynamics, are two possible reasons to explain the present limitations in describing the structural properties of heavily damaged, yet not completely amorphized, ion implanted Si.

Molecular dynamics study on structure and properties of liquid and amorphousAl2O3

Structure and thermodynamics properties of liquid and amorphous ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ have been investigated by Static Relaxation (SR) and Molecular Dynamics (MD) methods. Simulations were done in the basic cube under periodic boundary conditions containing 3000 ions with Born-Mayer type pair potentials. Structure of liquid and amorphous ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ models is in good agreement with experiment. The microstructure of ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ system has been analyzed through pair radial distribution functions, coordination number distributions, interatomic distances or pore distribution (for amorphous state only). Temperature dependence of the pore distribution in amorphous ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ was obtained. A thermal expansion coefficient and self-diffusion constants have been calculated. The temperature dependence of diffusion constants D in liquid ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ shows an Arrhenius law with activation energies which are close to experimental ones for liquid ${\mathrm{SiO}}_{2}$.

Molecular Dynamics Investigation of 23Na NMR Relaxation in Oligomeric DNA Aqueous Solution

An 8 ns molecular dynamics (MD) simulation has been carried out on an oligomeric DNA duplex in a minimal salt sodium aqueous solution in order to study the magnetic relaxation process of 2 3 Na. The explicit modeling of the solvent and the time length of the simulation allow study of the fast and, to some extent, the slow components of the relaxation. In agreement with experimental studies of the quadrupolar relaxation of monatomic cations in oligomeric DNA solution, the relaxation displays a multiexponential decay. According to the simulation, the slow components originate from ions directly bound to the DNA surface. The effects of the binding of the cations to DNA on the static and dynamical relaxation parameters have been studied in different binding sites either in the grooves or in the backbone. This study reveals that the quadrupolar coupling constant and the spectral densities vary largely from site to site, the fastest relaxation occurring for the ion directly bound to the minor groove. The combination of MD results with quadrupolar relaxation experimental data suggests that the occupancy of the binding sites in the minor groove of uninterrupted adenine sequences is relatively low.