Academic literature on the topic 'Microstructure Dependent Relaxation Dynamics'
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Journal articles on the topic "Microstructure Dependent Relaxation Dynamics"
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YU, Jae-Hyeong, and Chang-Whan Lee. "Study on the Time-Dependent Mechanical Behavior and Springback of Magnesium Alloy Sheet (AZ31B) in Warm Conditions." Materials 14, no. 14 (July 9, 2021): 3856. http://dx.doi.org/10.3390/ma14143856.
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In this study, the time-dependent mechanical behavior of the magnesium alloy sheet (AZ31B) was investigated through the creep and stress relaxation tests with respect to the temperature and pre-strain. The microstructure changes during creep and stress relaxation were investigated. As the tensile deformation increased in the material, twinning and dynamic recrystallization occurred, especially after the plastic instability. As a result, AZ31B showed lower resistance to creep and stress relaxation due to dynamic recrystallization. Additionally, time-dependent springback characteristics in the V- and L-bending processes concerning the holding time and different forming conditions were investigated. We analyzed changes of microstructure at each forming temperature and process. The uniaxial tensile creep test was conducted to compare the microstructures in various pre-strain conditions with those at the secondary creep stage. For the bending process, the change of the microstructure after the forming was compared to that with punch holding maintained for 1000 s after forming. Due to recrystallization, with the holding time in the die set of 60 s, the springback angle decreased by nearly 70%. Increased holding time in the die set resulted in a reduced springback angle.
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Sbrescia, Simone, Tom Engels, Evelyne Van Ruymbeke, and Michelle Seitz. "Molecular weight effects on the stress-relaxation behavior of soft thermoplastic elastomer by means of temperature scanning stress relaxation (TSSR)." Journal of Rheology 66, no. 6 (November 1, 2022): 1321–30. http://dx.doi.org/10.1122/8.0000444.
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The mechanical properties of multiblock copolymer thermoplastic elastomers (TPEs) are governed by the interplay of different reversible dynamics [e.g., hard block (HB) association and chain entanglements]. Understanding how these physical processes influence the high-temperature deformation behavior is relevant as many TPEs lose toughness with increasing temperature. Increasing molecular weight (Mw) improves their temperature resistance that is attributed to an increase in network connectivity. Indeed, longer chains are characterized by more HBs per chain and by a longer lifetime of the entanglements in the amorphous phase. Both the associating HB and disentanglement dynamics are temperature and rate dependent. To further understand the interconnected role of Mw, temperature and rate dependencies on the mechanical properties, we perform Temperature Scanning Stress Relaxation (TSSR) tests. The method consists of measuring the stress relaxation of the materials as the temperature monotonically increases, allowing us to probe the stress response as the HBs progressively disassociate due to the increase in temperature. The results show that increasing Mw improves the high-temperature relaxation behavior, allowing the material to retain more stress than its low Mw counterpart as the temperature increases. This distinction does not show itself when performing standard small strain dynamic mechanical thermal analyses. Depending on the deformation experienced before the TSSR is performed, different relaxation behaviors are observed illustrating the importance of the current microstructure in determining the mechanical properties. The TSSR approach is well-suited to benchmark the high-temperature stress-bearing properties of network-based polymers whose morphology and, hence, properties are strongly deformation dependent.
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Peng, Fan, Xiumei Zhang, Xiuming Wang, and Hao Chen. "Dynamic permeability in porous media and identification of pore fluids by using borehole Stoneley wave." Journal of Geophysics and Engineering 19, no. 3 (May 24, 2022): 336–45. http://dx.doi.org/10.1093/jge/gxac021.
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Abstract The sound field in porous media is affected by fluid flow governed by dynamic permeability. This macroscopic quantity is frequency dependent and can be connected with a relevant pore-scale estimation called the stochastic dynamic permeability (SDP) model. To further investigate the characteristics of the SDP model with different variables related to Biot relaxation frequency and envisage its potential applications in borehole acoustics, the influence of microstructures from a pore-scale image on dynamic permeability is studied. Then, the characteristics of dynamic permeability and a borehole Stoneley wave with different parameters are explored by sensitivity analysis. According to the influences of pore fluid parameters including density and viscosity, the velocity dispersion and attenuation of Stoneley waves in oil, gas and water-bearing formations are calculated. The results show that the dynamic permeability is affected by the microstructure of pores and the Biot relaxation frequency parameters have a crucial influence on the attenuation of the borehole Stoneley wave. Meanwhile, the attenuation coefficient can be used to identify the type of pore fluids. This is verified by an application to in situ acoustic logging data. The work provides a relatively comprehensive understanding of the features of the SDP dynamic permeability and indicates an approach to identify pore fluid by using a borehole Stoneley wave.
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Florêncio, Odila, Paulo Sergio Silva, Rosane Ribeiro, Javier Andres Muñoz Chaves, F. H. Sá, Fábio X. Melo, and Sandra G. Schneider. "Elastic Behavior of the Ti-13Nb-13Zr Alloy Obtained by Anelastic Spectroscopy." Defect and Diffusion Forum 283-286 (March 2009): 84–89. http://dx.doi.org/10.4028/www.scientific.net/ddf.283-286.84.
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Measurements of anelastic relaxation (internal friction and frequency) as a function of temperature were carried out in samples of Ti-13Nb-13Zr using two experimental apparatus: Flexural Vibration of the first tone of samples in Acoustic Elastometer System (Vibran Technology®) operating in a kilohertz bandwidth, and Torsional Vibration of the samples in Kê-type Torsion Pendulum operating in a hertz bandwidth. Experimental spectra of anelastic relaxation were determined in the temperature range from 300 K to 450 K for a heating rate of 1K/min under pressure of 10-5 Torr, in both apparatus. The results show a relaxation structure strongly dependent on the microstructure of the material. The dynamical elastic modulus (E) of Ti-13Nb-13Zr alloy can be determined by flexural vibrations by frequency (f) measurements (f E1/2). The anelastic relaxation spectrum of Ti-13Nb-13Zr alloy was a function of temperature obtained by torsional vibrations, not revealing the presence of interstitial solutes in solid solution in the temperature range of measurements.
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Astafurova, Elena, Anastasiya Fortuna, Evgenii Melnikov, and Sergey Astafurov. "The Effect of Strain Rate on Hydrogen-Assisted Deformation Behavior and Microstructure in AISI 316L Austenitic Stainless Steel." Materials 16, no. 8 (April 9, 2023): 2983. http://dx.doi.org/10.3390/ma16082983.
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The influence of strain rate in the interval of (10−5–10−3) 1/s on room temperature tensile behavior, dislocation arrangement, deformation mechanisms, and fracture of austenitic stainless steel AISI 316L electrochemically charged with hydrogen was investigated. Independently on strain rate, hydrogen charging provides the increase in the yield strength of the specimens due to a solid solution hardening of austenite, but it slightly influences deformation behavior and strain hardening of the steel. Simultaneously, hydrogen charging assists surface embrittlement of the specimens during straining and reduces an elongation to failure, which both are strain rate-dependent parameters. Hydrogen embrittlement index decreases with increase in strain rate, which testifies the importance of hydrogen transport with dislocations during plastic deformation. The stress–relaxation tests directly confirm the hydrogen-enhanced increase in the dislocation dynamics at low strain rates. The interaction of the hydrogen atoms with dislocations and hydrogen-associated plastic flow are discussed.
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Muhlestein, Michael B., and Michael R. Haberman. "A micromechanical approach for homogenization of elastic metamaterials with dynamic microstructure." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 472, no. 2192 (August 2016): 20160438. http://dx.doi.org/10.1098/rspa.2016.0438.
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An approximate homogenization technique is presented for generally anisotropic elastic metamaterials consisting of an elastic host material containing randomly distributed heterogeneities displaying frequency-dependent material properties. The dynamic response may arise from relaxation processes such as viscoelasticity or from dynamic microstructure. A Green's function approach is used to model elastic inhomogeneities embedded within a uniform elastic matrix as force sources that are excited by a time-varying, spatially uniform displacement field. Assuming dynamic subwavelength inhomogeneities only interact through their volume-averaged fields implies the macroscopic stress and momentum density fields are functions of both the microscopic strain and velocity fields, and may be related to the macroscopic strain and velocity fields through localization tensors. The macroscopic and microscopic fields are combined to yield a homogenization scheme that predicts the local effective stiffness, density and coupling tensors for an effective Willis-type constitutive equation. It is shown that when internal degrees of freedom of the inhomogeneities are present, Willis-type coupling becomes necessary on the macroscale. To demonstrate the utility of the homogenization technique, the effective properties of an isotropic elastic matrix material containing isotropic and anisotropic spherical inhomogeneities, isotropic spheroidal inhomogeneities and isotropic dynamic spherical inhomogeneities are presented and discussed.
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Brechtl, Jamieson, Zhong Wang, Xie Xie, Jun-Wei Qiao, and Peter K. Liaw. "Relation Between the Defect Interactions and the Serration Dynamics in a Zr-Based Bulk Metallic Glass." Applied Sciences 10, no. 11 (June 4, 2020): 3892. http://dx.doi.org/10.3390/app10113892.
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For this study, the effects of thermal annealing and compressive strain rate on the complexity of the serration behavior in a Zr-based bulk metallic glass (BMG) was investigated. Here, as-cast and thermally-annealed (300 °C, 1 week) Zr52.5Cu17.9Ni14.6Al10Ti5 BMG underwent room-temperature compression tests in the unconstrained condition at strain rates of 2 × 10−5 s−1 and 2 × 10−4 s−1. The complexity of the serrated flow was determined, using the refined composite multiscale entropy technique. Nanoindentation testing and X-ray diffraction characterization were performed to assess the changes in the microstructure and mechanical properties of the BMG that occurred during annealing. The results indicated that the BMG did not crystallize during annealing in the prescribed heating condition. Nanoindentation tests revealed that annealing led to a significant increase in the depth-dependent nanoindentation hardness and Young’s modulus, which were attributed to the structural relaxation in the glass. Furthermore, both annealing and an increased strain rate resulted in a marked enhancement in the complexity of the serrated flow during compression. It was concluded that the increase in the sample entropy with increasing strain rate is related to an increase in the number of defect interactions during the serrated flow.
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Yin, Lihong, Harold Bien, and Emilia Entcheva. "Scaffold topography alters intracellular calcium dynamics in cultured cardiomyocyte networks." American Journal of Physiology-Heart and Circulatory Physiology 287, no. 3 (September 2004): H1276—H1285. http://dx.doi.org/10.1152/ajpheart.01120.2003.
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Structural and functional changes ensue in cardiac cell networks when cells are guided by three-dimensional scaffold topography. We report enhanced synchronous pacemaking activity in association with slow diastolic rise in intracellular Ca2+ concentration ([Ca2+]i) in cell networks grown on microgrooved scaffolds. Topography-driven changes in cardiac electromechanics were characterized by the frequency dependence of [Ca2+]i in syncytial structures formed of ventricular myocytes cultured on microgrooved elastic scaffolds (G). Cells were electrically paced at 0.5–5 Hz, and [Ca2+]i was determined using microscale ratiometric (fura 2) fluorescence. Compared with flat (F) controls, the G networks exhibited elevated diastolic [Ca2+]i at higher frequencies, increased systolic [Ca2+]i across the entire frequency range, and steeper restitution of Ca2+ transient half-width ( n = 15 and 7 for G and F, respectively, P < 0.02). Significant differences in the frequency response of force-related parameters were also found, e.g., overall larger total area under the Ca2+ transients and faster adaptation of relaxation time to pacing rate ( P < 0.02). Altered [Ca2+]i dynamics were paralleled by higher occurrence of spontaneous Ca2+ release and increased sarcoplasmic reticulum load ( P < 0.02), indirectly assessed by caffeine-triggered release. Electromechanical instabilities, i.e., Ca2+ and voltage alternans, were more often observed in G samples. Taken together, these findings 1) represent some of the first functional electromechanical data for this in vitro system and 2) demonstrate direct influence of the microstructure on cardiac function and susceptibility to arrhythmias via Ca2+-dependent mechanisms. Overall, our results substantiate the idea of guiding cellular phenotype by cellular microenvironment, e.g., scaffold design in the context of tissue engineering.
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Dierdorf, Jens, Johannes Lohmar, and Gerhard Hirt. "Investigation on Hardening and Softening Behavior of Steel after Rapid Strain Rate Changes." Key Engineering Materials 716 (October 2016): 121–28. http://dx.doi.org/10.4028/www.scientific.net/kem.716.121.
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The design of industrial hot metal forming processes nowadays is mostly carried out using commercial Finite Element (FE) software codes. For precise FE simulations, reliable material properties are a crucial factor. In bulk metal forming, the most important material property is the materials flow stress, which determines the form filling and the necessary forming forces. At elevated temperatures, the flow stress of steels is determined by strain hardening, dynamic recovery and partly by dynamic recrystallization, which is dependent on strain rate and temperature. To simulate hot forming processes, which are often characterized by rapidly changing strain rates and temperatures, the flow stress is typically derived from flow curves, determined at arbitrary constant temperatures and strain rates only via linear interpolation. Hence, the materials instant reaction and relaxation behavior caused by rapid strain rate changes is not captured during simulation. To investigate the relevance of the relaxation behavior for FE simulations, trails with abrupt strain rate change are laid out and the effect on the material flow stress is analyzed in this paper. Additionally, the microstructure evolution due to the strain rate change is investigated. For this purpose, cylinder compression tests of an industrial case hardening steel are conducted at elevated temperatures and different strain rates. To analyze the influence of rapid strain rate changes, changes by one power of ten are performed at a strain of 0.3. As a reference, flow curves of the same material are determined at the initial and final constant strain rate. To investigate the microstructure evolution, compression samples are quenched at different stages, before and after the strain rate change. The results show that the flow curves after the strain rate change tend to approximate the flow curves measured for the final strain rate. However, directly after the strain rate change significant differences between the assumed instant flow stress and the real material behavior can be observed. Furthermore, it can be shown that the state of dynamic recrystallization at the time of the strain rate change influences the material response and relaxation behavior resulting in different slopes of the investigated flow curves after the strain rate change.
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Parnell, William J., and Riccardo De Pascalis. "Soft metamaterials with dynamic viscoelastic functionality tuned by pre-deformation." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2144 (March 18, 2019): 20180072. http://dx.doi.org/10.1098/rsta.2018.0072.
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The small amplitude dynamic response of materials can be tuned by employing inhomogeneous materials capable of large deformation. However, soft materials generally exhibit viscoelastic behaviour, i.e. loss and frequency-dependent effective properties. This is the case for inhomogeneous materials even in the homogenization limit when propagating wavelengths are much longer than phase lengthscales, since soft materials can possess long relaxation times. These media, possessing rich frequency-dependent behaviour over a wide range of low frequencies, can be termed metamaterials in modern terminology. The sub-class that are periodic are frequently termed soft phononic crystals although their strong dynamic behaviour usually depends on wavelengths being of the same order as the microstructure. In this paper we describe how the effective loss and storage moduli associated with longitudinal waves in thin inhomogeneous rods are tuned by pre-stress. Phases are assumed to be quasi-linearly viscoelastic, thus exhibiting time-deformation separability in their constitutive response. We illustrate however that the effective incremental response of the inhomogeneous medium does not exhibit time-deformation separability. For a range of nonlinear materials it is shown that there is strong coupling between the frequency of the small amplitude longitudinal wave and initial large deformation. This article is part of the theme issue ‘Rivlin's legacy in continuum mechanics and applied mathematics’.
Dissertations / Theses on the topic "Microstructure Dependent Relaxation Dynamics"
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Reynolds, Matthew. "Chain-length dependent rheology and relaxation dynamics in glass-forming polymers." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/22750/.
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Glassy materials differ greatly from crystalline solids; their lack of long range order makes it difficult to model their behaviour. While a lot of work has been done regarding the properties of glass-forming polymers, their exact nature is not well understood. This thesis primarily focuses on the chain-length dependence of glassy dynamics, in particular poly(methyl methacrylate) (PMMA), which is of interest due to its commercial and industrial applications. Using dielectric spectroscopy, rheology, and calorimetry, the relaxation behaviour of chain-modes and the segmental, alpha, relaxation were determined as a function of chain-length. Time-temperature superposition adequately describes the rheology data, even though decoupling between chain-modes and segmental relaxations were observed. Changes occur in the behaviour of the glass transition temperature, T_g, at the molecular weight, M, of the "dynamic bead", M_R. Relaxation times of the alpha relaxation and chain-modes of PMMA and other polymer systems collapse when renormalized by T_g, suggesting universal behaviour. This occurs when the number of correlated monomers, N_a, in the alpha relaxation corresponds to M_R. N_a was determined using modulated calorimetry and dielectric spectroscopy. A clear change in N_a was observed at M_R for less flexible PMMA and polystyrene, whereas this was less pronounced for the more flexible poly(dimethyl siloxane). This may relate to a change from intermolecular to mainly intramolecular behaviour. Furthermore, for PMMA the activation enthalpies of the alpha and beta relaxations below T_g are approximately equal at M_R, suggesting these relaxations act on similar lengthscales. The activation enthalpy of the beta relaxation also becomes M invariant for M > M_R, suggesting M_R characterises the beta relaxation. Finally, the ionic conductivity was determined for PMMA and two poly(propylene glycol) (PPG) chain-length systems. The alpha relaxation and conductivity were coupled for PPG, whereas for PMMA decoupling occurred for M > M_R. This demonstrates that polymer behaviour leads to this decoupling in PMMA. We also show that non-polymeric systems do not exhibit this decoupling behaviour.
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Koch, Federico Juan [Verfasser], Tobias [Gutachter] Brixner, Frank [Gutachter] Würthner, and Volker [Gutachter] Engel. "Structure-Dependent Ultrafast Relaxation Dynamics in Multichromophoric Systems / Federico Juan Koch. Gutachter: Tobias Brixner ; Frank Würthner ; Volker Engel." Würzburg : Universität Würzburg, 2016. http://d-nb.info/1112041516/34.
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Bonfanti, M. "REACTIONS AT SURFACES: BEYOND THE STATIC SURFACE APPROACH IN QUANTUM DYNAMICS." Doctoral thesis, Università degli Studi di Milano, 2012. http://hdl.handle.net/2434/167911.
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Thanks to the peculiar electronic properties of gas-solid interfaces, surfaces play an important role in many chemical processes. In my thesis, I considered few different reactions at surfaces and addressed the problem of their description by means of quantum dynamical methods. In particular, the focus of the work is on the inclusion of surface motion in the dynamical models. This problem is very challenging for state-of-art quantum methods, due to the unfavorable scaling with the number of degrees of freedom. To avoid this computational limit a variety of methods were adopted, ranging from a static approach in a low dimensional Time Dependent Wave Packet (TDWP) calculations to a full dynamical description of dissipation in the framework of Multi-Configuration Time-Dependent Hartree method (MCTDH).
I considered three different physical problems. The first one is the exothermic, collinearly-dominated Eley-Rideal H2 formation on graphite. In particular, I focused on the importance of the model used to describe the graphitic substrate, in light of the marked discrepancies present in available literature results. To this end, I considered the collinear reaction and computed the Potential Energy Surface (PES) for a number of different graphitic surface models using Density Functional Theory (DFT) for different dynamical regimes. I performed quantum dynamics with wave-packet techniques down to the cold collision energies relevant for the chemistry of the interstellar medium. Results show that the reactivity at moderate-to-high collision energies sensitively depends on the shape of the PES in the entrance channel, which in turn is related to the adopted surface model. At low energies I ruled out the presence of any barrier to reaction, thereby highlighting the importance of quantum reflection in limiting the reaction efficiency.
In a second part of my work, I studied the effect of lattice displacement on the interaction of H2 with the Cu(111) surface using the Specific Reaction Parameter (SRP) approach to DFT. I systematically investigated how the motion of the surface atoms affects some features of the PES, such as the dissociation barrier height and the barrier geometry corresponding to some representative reaction pathways, and the anisotropy of the potential at these geometries. This analysis allowed the identification of the surface degrees of freedom that are likely to be most relevant for H2 dissociation. In particular, I found that the lattice coordinate displacements that have the largest effect on the H2/Cu(111) DFT-SRP barrier heights and locations concern the motion of the 1st layer and 2nd layer Cu atoms in the Z direction, and motion of the 1st layer atoms in the directions parallel to the surface. Whereas the first degree of freedom mostly affects the barrier geometry, the second and third motions can lower or raise the barrier height. The latter effect cannot be described with the usual surface oscillator dynamical models employed in the past to include surface motion, and its dynamical influence on the dissociative adsorption needs to be further investigated.
In the third part of the thesis I addressed the problem of including dissipative effects in the reaction dynamics of hydrogen sticking and scattering on surfaces. I considered dissipative baths with different spectral properties and represented them with a linear chain of coupled harmonic oscillators, exploiting an equivalent effective-mode representation that has recently been developed. I studied the system dynamics with MCTDH, aiming on one hand to an accurate description of dissipation at a short time scale, and on the other hand to a simplified but qualitatively correct behavior of the long time dynamics. In this framework, I found a very useful scheme to represent the long time dynamics of the system without incurring in unwanted Poincaré's recurrences. I used this method to obtain the sticking probability of one hydrogen atom scattered by a simple one dimensional Morse potential. The methodology developed in this work is going to be extended to the more realistic problem of hydrogen sticking on graphitic surfaces.
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Thakore, Vaibhav. "Nonlinear dynamic modeling, simulation and characterization of the mesoscale neuron-electrode interface." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5529.
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Extracellular neuroelectronic interfacing has important applications in the fields of neural prosthetics, biological computation and whole-cell biosensing for drug screening and toxin detection. While the field of neuroelectronic interfacing holds great promise, the recording of high-fidelity signals from extracellular devices has long suffered from the problem of low signal-to-noise ratios and changes in signal shapes due to the presence of highly dispersive dielectric medium in the neuron-microelectrode cleft. This has made it difficult to correlate the extracellularly recorded signals with the intracellular signals recorded using conventional patch-clamp electrophysiology. For bringing about an improvement in the signal-to-noise ratio of the signals recorded on the extracellular microelectrodes and to explore strategies for engineering the neuron-electrode interface there exists a need to model, simulate and characterize the cell-sensor interface to better understand the mechanism of signal transduction across the interface. Efforts to date for modeling the neuron-electrode interface have primarily focused on the use of point or area contact linear equivalent circuit models for a description of the interface with an assumption of passive linearity for the dynamics of the interfacial medium in the cell-electrode cleft. In this dissertation, results are presented from a nonlinear dynamic characterization of the neuroelectronic junction based on Volterra-Wiener modeling which showed that the process of signal transduction at the interface may have nonlinear contributions from the interfacial medium. An optimization based study of linear equivalent circuit models for representing signals recorded at the neuron-electrode interface subsequently proved conclusively that the process of signal transduction across the interface is indeed nonlinear. Following this a theoretical framework for the extraction of the complex nonlinear material parameters of the interfacial medium like the dielectric permittivity, conductivity and diffusivity tensors based on dynamic nonlinear Volterra-Wiener modeling was developed. Within this framework, the use of Gaussian bandlimited white noise for nonlinear impedance spectroscopy was shown to offer considerable advantages over the use of sinusoidal inputs for nonlinear harmonic analysis currently employed in impedance characterization of nonlinear electrochemical systems. Signal transduction at the neuron-microelectrode interface is mediated by the interfacial medium confined to a thin cleft with thickness on the scale of 20-110 nm giving rise to Knudsen numbers (ratio of mean free path to characteristic system length) in the range of 0.015 and 0.003 for ionic electrodiffusion. At these Knudsen numbers, the continuum assumptions made in the use of Poisson-Nernst-Planck system of equations for modeling ionic electrodiffusion are not valid. Therefore, a lattice Boltzmann method (LBM) based multiphysics solver suitable for modeling ionic electrodiffusion at the mesoscale neuron-microelectrode interface was developed. Additionally, a molecular speed dependent relaxation time was proposed for use in the lattice Boltzmann equation. Such a relaxation time holds promise for enhancing the numerical stability of lattice Boltzmann algorithms as it helped recover a physically correct description of microscopic phenomena related to particle collisions governed by their local density on the lattice. Next, using this multiphysics solver simulations were carried out for the charge relaxation dynamics of an electrolytic nanocapacitor with the intention of ultimately employing it for a simulation of the capacitive coupling between the neuron and the planar microelectrode on a microelectrode array (MEA). Simulations of the charge relaxation dynamics for a step potential applied at t = 0 to the capacitor electrodes were carried out for varying conditions of electric double layer (EDL) overlap, solvent viscosity, electrode spacing and ratio of cation to anion diffusivity. For a large EDL overlap, an anomalous plasma-like collective behavior of oscillating ions at a frequency much lower than the plasma frequency of the electrolyte was observed and as such it appears to be purely an effect of nanoscale confinement. Results from these simulations are then discussed in the context of the dynamics of the interfacial medium in the neuron-microelectrode cleft. In conclusion, a synergistic approach to engineering the neuron-microelectrode interface is outlined through a use of the nonlinear dynamic modeling, simulation and characterization tools developed as part of this dissertation research.Ph.D.
Doctorate
Physics
Sciences
Physics
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Koch, Federico Juan. "Structure-Dependent Ultrafast Relaxation Dynamics in Multichromophoric Systems." Doctoral thesis, 2016. https://nbn-resolving.org/urn:nbn:de:bvb:20-opus-136306.
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Time-resolved spectroscopy allows for analyzing light-induced energy conversion and chromophore–chromophore interactions in molecular systems, which is a prerequisite in the design of new materials and for improving the efficiency of opto-electronic devices. To elucidate photo-induced dynamics of complex molecular systems, transient absorption (TA) and coherent two-dimensional (2D) spectroscopy were employed and combined with additional experimental techniques, theoretical approaches, and simulation models in this work. A systematic series of merocyanines, synthetically varied in the number of chromophores and subsitution pattern, attached to a benzene unit was investigated in cooperation with the group of Prof. Dr. Frank Würthner at the University of Würzburg. The global analysis of several TA experiments, and additional coherent 2D spectroscopy experiments, provided the basis to elaborate a relaxation scheme which was applicable for all merocyanine systems under investigation. This relaxation scheme is based on a double minimum on the excited-state potential energy surface. One of these minima is assigned to an intramolecular charge-transfer state which is stabilized in the bis- and tris-chromophoric dyes by chromphore–chromophore interactions, resulting in an increase in excited-state lifetime. Electro-optical absorption and density functional theory (DFT) calculations revealed a preferential chromophore orientation which compensates most of the dipole moment of the individual chromophores. Based on this structural assignment the conformationdependent exciton energy splitting was calculated. The linear absorption spectra of the multi-chromophoric merocyanines could be described by a combination of monomeric and excitonic spectra. Subsequently, a structurally complex polymeric squaraine dye was studied in collaboration with the research groups of Prof. Dr. Christoph Lambert and Prof. Dr. Roland Mitric at the University of Würzburg. This polymer consists of a superposition of zigzag and helix structures depending on the solvent. High-level DFT calculations confirmed the previous assignment that zigzag and helix structures can be treated as J- and H-aggregates, respectively. TA experiments revealed that in dependence on the solvent as well as the excitation energy, ultrafast energy transfer within the squaraine polymer proceeds from initially excited helix segments to zigzag segments or vice versa. Additionally, 2D spectroscopy confirmed the observed sub-picosecond dynamics. In contrast to other conjugated polymers such as MEH-PPV, which is investigated in the last chapter, ultrafast energy transfer in squaraine polymers is based on the matching of the density of states between donor and acceptor segments due to the small reorganization energy in cyanine-like chromophores. Finally, the photo-induced dynamics of the aggregated phase of the conjugated polymer MEH-PPV was investigated in cooperation with the group of Prof. Dr. Anna Köhler at the University of Bayreuth. Our collaborators had previously described the aggregation of MEH-PPV upon cooling by the formation of so-called HJ-aggregates based on exciton theory. By TA measurements and by making use of an affiliated band analysis distinct relaxation processes in the excited state and to the ground state were discriminated. By employing 2D spectroscopy the energy transfer between different conjugated segments within the aggregated polymer was resolved. The initial exciton relaxation within the aggregated phase indicates a low exciton mobility, in contrast to the subsequent energy transfer between different chromophores within several picoseconds. This work contributes by its systematic study of structure-dependent relaxation dynamics to the basic understanding of the structure-function relationship within complex molecular systems. The investigated molecular classes display a high potential to increase efficiencies of opto-electronic devices, e.g., organic solar cells, by the selective choice of the molecular morphologyZeitaufgelöste Spektroskopie ermöglicht die Untersuchung lichtinduzierter Energietransferprozesse und molekularer Wechselwirkungen. Derartige Ergebnisse bilden wiederum die Grundlage für die Entwicklung von Synthesestrategien für neuartige Materialien sowie für effizientere optoelektronische Anwendungen. Um die lichtinduzierte Dynamik komplexer molekularer Systeme aufzuklären, wurden die Techniken der transienten Absorption (TA) und der kohärenten zweidimensionalen (2D) Spektroskopie mit weiteren experimentellen Messungen sowie theoretischen Ansätzen und Simulationen kombiniert. In Kooperation mit der Forschungsgruppe von Prof. Dr. FrankWürthner an der Universität Würzburg wurde eine molekulare Serie von Merocyaninen untersucht, die sich in der Anzahl der Chromophore und dem Substitutionsmuster an einem Benzolring unterscheiden. Eine globale Analyse der TA-Experimente für die verschiedenen Moleküle der Serie sowie weitere kohärente 2D-Spektroskopie-Experimente ermöglichten es, ein Relaxationsmodell zu ermitteln, das für alle untersuchten Merocyaninsysteme anwendbar ist. Dieses Relaxationsmodell basiert auf einem doppelten Minimum in der Potentialfläche des ersten angeregten Zustands. Eines dieser Minima wurde einem intramolekularen Ladungstransferzustand zugeordnet, welcher durch die Wechselwirkung benachbarter Chromophore stabilisiert wird und dadurch einen Anstieg der Lebensdauer des angeregten Zustands bewirkt. Zusätzliche elektrooptische Absorptionsmessungen in Kombination mit Ergebnissen der Dichtefunktionaltheorie offenbarten eine bevorzugte relative Chromophororientierung, die das Dipolmoment eines einzelnen Chromophors weitestgehend kompensiert. Basierend auf dieser Strukturbestimmung wurde eine strukturabhängige Exzitonenaufspaltungsenergie ermittelt und mit der Aufspaltung in den linearen Absorptionsspektren verglichen. Die linearen Absorptionsspektren der multichromophoren Merocyanine können durch eine Kombination von monomerischen und exzitonischen Beiträgen beschrieben werden, was eine gewisse strukturelle Flexibilität erfordert. In einer weiteren Kooperation mit den Gruppen von Prof. Dr. Christoph Lambert und Prof. Dr. Roland Mitric der Universität Würzburg wurde ein strukturell komplexer, polymerer Squarainfarbstoff untersucht. Dieses Polymer besteht aus einer Superposition von Zickzack- und Helixstrukturen, welche lösungsmittelabhängig ist. Rechnungen basierend auf neuesten Methoden der Dichtefunktionaltheorie bestätigten die vorherige Zuordnung, dass Zickzack- und Helixstrukturen als J- und H-Aggregate behandelt werden können. Mittels transienter Absorption konnte ermittelt werden, dass in Abhängigkeit des Lösungsmittels sowie der Anregungsenergie ultraschneller Energietransfer innerhalb des Squarain-Polymers entweder von zunächst angeregten Helix- zu Zickzacksegmenten stattfindet oder von Zickzack- zu Helixsegmenten. Zusätzlich konnte die Subpikosekundendynamik durch die kohärente 2D-Spektroskopie bestätigt werden. Im Gegensatz zu anderen konjugierten Polymeren wie MEH-PPV, welches im letzten Kapitel dieser Arbeit behandelt wird, basiert der ultraschnelle Energietransfer in Squarainpolymeren auf dem energetischen Überlapp der Zustandsdichten von Donor- und Akzeptorsegmenten, welcher auf die geringe Reorganisationsenergie in cyaninähnlichen Farbstoffen beruht. Abschließend wurde die lichtinduzierte Dynamik der aggregierten Phase des konjugierten Polymers MEH-PPV in Kooperation mit der Gruppe von Prof. Dr. Anna Köhler von der Universität Bayreuth untersucht. Unsere Kooperationspartner hatten zuvor die Aggregation von MEH-PPV bei Abkühlung durch die Formation von sogenannten HJ-Aggregaten, welche auf der Exzitonentheorie beruhen, beschrieben. Durch transiente Absorptionsmessungen und einer zugehörigen Bandenanalyse konnte zwischen Relaxationsprozessen im angeregten Zustand und zurück zum Grundzustand unterschieden werden. Die Anwendung der kohärenten 2D-Spektroskopie ermöglichte es, Energietransferprozesse zwischen konjugierten Segmenten des aggregierten Polymers aufzuklären. Die anfängliche Exzitonenrelaxation innerhalb der aggregierten Phase deutet auf eine geringe Mobilität der Exzitonen hin, welche im Gegensatz zu den anschließenden Energietransferprozessen zwischen unterschiedlichen Chromophoren innerhalb einiger Pikosekunden steht. Diese Arbeit trägt durch eine systematische Untersuchung der strukturabhängigen Relaxationsdynamik zum grundlegenden Verständnis des Verhältnisses zwischen Struktur und Funktion von komplexen molekularen Systemen bei. Die untersuchten Molekülklassen weisen dabei ein hohes Potential auf, um durch gezielte Wahl der Morphologie zu einer Steigerung von Effizienzen in optoelektronischen Anwendungen, wie beispielsweise organischen Solarzellen, beizutragen
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Hsia, Chih-Hao. "Studies of Optically Induced Magnetization Dynamics in Colloidal Iron Oxide Nanocrystals." Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8304.
Full textAbstract:
Studying dynamics of magnetization relaxation in excited magnetic materials is
important both for understanding the rates and pathways of magnetization relaxation and
for the potential use in spin-based electronics and data storage devices in the future.
Previous studies have demonstrated that the size of nanocrystals is an important factor
for energy relaxation in quantum dots and metal nanoparticles. Since magnetization
relaxation is one of energy relaxation pathways, the size of nanocrystals may be also an
important factor for magnetization relaxation in nanoscale magnetic materials. The goal
of this study is to have a better understanding of magnetization relaxation in nanoscale
magnetic materials. In particular, we focused on the correlation between the nanocrystal
size and the rates of spin-lattice relaxation (SLR), a magnetization relaxation pathway, in
magnetic nanocrystals.
The size-dependent magnetization relaxation rate after optically induced
demagnetization in colloidal Fe3O4 nanocrystals was measured by using time-resolved
Faraday rotation (FR). Fe3O4 nanocrystals were chosen as the model system to study the correlation between the size of nanocrystals and the rates of SLR due to the wellestablished
synthetic procedure of making nanocrystals with various sizes and narrow
size dispersion. Faster SLR rates were observed in smaller Fe3O4 nanocrystals. The
results suggested the surface of nanocrystals have higher efficiency of SLR than the
interior region by using a simple model to analyze the SLR rates of Fe3O4 nanocrystals
with various sizes. Higher efficiency of SLR at the surface may be due to the stronger
spin-orbit coupling at the surface relative to the interior region. In addition to
magnetization dynamics studies, the effect of oxidation on static FR in iron oxide
nanocrystals (between Fe3O4 and y-Fe2O3) was studied. The results indicated FR signal
is linearly correlated to the strength of optical transition between Fe2 and Fe3 in Fe3O4
for a given size of nanocrystals.
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Shih-Chieh, Pu. "1. Spectroscopy and Femtosecond Dynamics on the Excited-State Proton/Charge Transfer Coupled Reaction 2. The Photophysical Properties of the Azulenylocyanine Dye, a Near-infrared Nonfluorogenic Quencher 3. Carrier Relaxation Dynamic of the II-VI Semiconductor Quantum Dot and Size-dependent of the two-photon excitation Cross-Section relation." 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-0107200612412400.
Full textBook chapters on the topic "Microstructure Dependent Relaxation Dynamics"
1
Weinelt, Martin, Anke B. Schmidt, Martin Pickel, and Markus Donath. "Spin-Dependent Relaxation of Photoexcited Electrons at Surfaces of 3d Ferromagnets." In Dynamics at Solid State Surfaces and Interfaces, 115–43. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2010. http://dx.doi.org/10.1002/9783527633418.ch6.
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Kothe, G., and C. Mayer. "Orientation and Frequency Dependent NMR Relaxation Studies of Bilayer Membranes: Characterisation of the Lipid Motions." In The Molecular Dynamics of Liquid Crystals, 519–36. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-1168-3_21.
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Lindman, Björn, Olle Söderman, and Peter Stilbs. "Microstructure and Molecular Dynamics of Surfactant Solutions: an Overview of NMR Self-Diffusion and Relaxation Studies." In Surfactants in Solution, 1–24. Boston, MA: Springer US, 1989. http://dx.doi.org/10.1007/978-1-4615-7984-7_1.
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Sabadini, Roberto, Bert Vermeersen, and Gabriele Cambiotti. "Detection of the Time-Dependent Gravity Field and Global Change." In Global Dynamics of the Earth: Applications of Viscoelastic Relaxation Theory to Solid-Earth and Planetary Geophysics, 189–224. Dordrecht: Springer Netherlands, 2016. http://dx.doi.org/10.1007/978-94-017-7552-6_5.
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Fiorani, D. "Magnetic Susceptibility Studies of Time-dependent Phenomena: Application to the Magnetic Relaxation Processes in Fine Particles and in Spin-glasses." In The Time Domain in Surface and Structural Dynamics, 391–428. Dordrecht: Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-2929-6_24.
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Colomban, Philippe, and Jean-Claude Badot. "Frequency dependent conductivity, microwave dielectric relaxation and proton dynamics." In Proton Conductors, 389–408. Cambridge University Press, 1992. http://dx.doi.org/10.1017/cbo9780511524806.026.
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Nitzan, Abraham. "Introduction To Quantum Relaxation Processes." In Chemical Dynamics in Condensed Phases. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780198529798.003.0015.
Full textAbstract:
The first question to ask about the phenomenon of relaxation is why it occurs at all. Both the Newton and the Schrödinger equations are symmetrical under time reversal: The Newton equation, dx/dt = v ; dv/dt = −∂V/∂x, implies that particles obeying this law of motion will retrace their trajectory back in time after changing the sign of both the time t and the particle velocities v. The Schrödinger equation, ∂ψ/∂t = −(i/.h) Ĥ ψ, implies that if (ψ (t) is a solution then ψ *(−t) is also one, so that observables which depend on |ψ|2 are symmetric in time. On the other hand, nature clearly evolves asymmetrically as asserted by the second law of thermodynamics. How does this asymmetry arise in a system that obeys temporal symmetry in its time evolution? Readers with background in thermodynamics and statistical mechanics have encountered the intuitive answer: Irreversibility in a system with many degrees of freedom is essentially a manifestation of the system “getting lost in phase space”:Asystem starts from a given state and evolves in time. If the number of accessible states is huge, the probability that the system will find its way back to the initial state in finite time is vanishingly small, so that an observer who monitors properties associated with the initial state will see an irreversible evolution. The question is how is this irreversible behavior manifested through the reversible equations of motion, and how does it show in the quantitative description of the time evolution. This chapter provides an introduction to this subject using the time-dependent Schrödinger equation as a starting point. Chapter 10 discusses more advanced aspects of this problem within the framework of the quantum Liouville equation and the density operator formalism.
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Zinn-Justin, Jean. "Critical dynamics and renormalization group (RG)." In Quantum Field Theory and Critical Phenomena, 875–98. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198834625.003.0036.
Full textAbstract:
Time evolution, near a phase transition in the critical domain of critical systems not far from equilibrium, using a Langevin-type evolution is studied. Typical quantities of interest are relaxation rates towards equilibrium, time-dependent correlation functions and transport coefficients. The main motivation for such a study is that, in systems in which the dynamics is local (on short time-scales, a modification of a dynamic variable has an influence only locally in space) when the correlation length becomes large, a large time-scale emerges, which characterizes the rate of time evolution. This phenomenon called critical slowing down leads to universal behaviour and scaling laws for time-dependent quantities. In contrast with the situation in static critical phenomena, there is no clean and systematic derivation of the dynamical equations governing the time evolution in the critical domain, because often the time evolution is influenced by conservation laws involving the order parameter, or other variables like energy, momentum, angular momentum, currents and so on. Indeed, the equilibrium distribution does not determine the driving force in the Langevin equation, but only the dissipative couplings are generated by the derivative of the equilibrium Hamiltonian, and directly related to the static properties. The purely dissipative Langevin equation specifically discussed, corresponding to static models like the f4 field theory and two-dimensional models. Renormalization group (RG) equations are derived, and dynamical scaling relations established.
Conference papers on the topic "Microstructure Dependent Relaxation Dynamics"
1
Shen, Jiayue, Peng Cheng, Wenting Gu, Michael Stacey, and Zhili Hao. "Stress Relaxation Measurement of Agar Using a Polymer-Based Microfluidic Device." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-66054.
Full textAbstract:
In light of the significance of the viscoelastic property of agar to cell-based tissue engineering, this paper presents the stress relaxation measurement of agar using a polymer-based microfluidic device. Comprised of a single polymer rectangular microstructure and a set of electrolyte-enabled distributed transducers, this device is capable of detecting continuous distributed static and dynamic loads. In the measurement, an agar specimen is placed on the device and a rigid probe is utilized to press the specimen against the device with a step displacement input. Consequently, the stress relaxation behavior of the specimen translates to time-dependent continuous distributed loads acting on the device and is further registered as discrete resistance changes by the device. Two agar specimens of 1% and 3% in concentration, respectively, are measured using this device; and the data analysis is conducted on the measured results to extract Young’s relaxation modulus, which is further expressed by a Prony-series representation of the Maxwell model with two exponential terms. The results demonstrate the feasibility of using this device to measure the stress relaxation behavior of soft materials.
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Feng, Yixuan, Zhipeng Pan, Xiaohong Lu, and Steven Y. Liang. "Analytical and Numerical Predictions of Machining-Induced Residual Stress in Milling of Inconel 718 Considering Dynamic Recrystallization." In ASME 2018 13th International Manufacturing Science and Engineering Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/msec2018-6386.
Full textAbstract:
A new analytical model is proposed to predict the residual stress in the milling process of Inconel 718 based upon the mechanics analysis of microstructural evolutions. The model proposes to quantify the effects of dynamic recrystallization process on the material flow stress under combined thermal-mechanical loadings in machining. Physics-based mechanistic model is applied to predict the percentage of dynamic recrystallization and the grain size as functions of the milling process parameters and materials constative attributes. The variation of grain size is expected to alter the yield stress, and such dependency relationship is applied to predict the flow stress, which is also dependent on strain, strain rate, and temperature. The time-varying trajectory of residual stress is then predicted at each milling rotation angle through the transformation from milling to equivalent orthogonal cutting, the calculation of stress distribution in loading process, and the stress change during relaxation. The results of analytical model are validated through numerical prediction. The residual stress profile predicted by proposed analytical model matches better with results from numerical model comparing with model without consideration of dynamic recrystallization, especially within subsurface area, with improved accuracy of peak compressive residual stress prediction.
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Beckerle, J. D., M. P. Casassa, E. J. Heilweil, R. R. Cavanagh, and J. C. Stephenson. "Time Dependent Studies of Vibrational Relaxation Dynamics of CO (v=1) on Metal Surfacesa." In Microphysics of Surfaces, Beams, and Adsorbates. Washington, D.C.: Optica Publishing Group, 1989. http://dx.doi.org/10.1364/msba.1989.mb3.
Full textAbstract:
Knowledge of the rates and mechanisms of vibrational relaxation of molecules adsorbed on surfaces is essential to understand the dynamics of surface processes such as sticking, desorption, and surface chemical reactions. For metallic surfaces, an important outstanding question is the role played by the bulk metal conduction electrons in the damping of adsorbate vibrations. Theoretical studies have predicted lifetimes for the stretch vibration of chemisorbed CO of less than 10 ps as a result of efficient electron hole pair damping on metal surfaces [1,2]. This lifetime is one to two orders of magnitude shorter than that expected for relaxation directly to surface phonons [3]. Experimentally, a lower limit on the vibrational T1 lifetime of ≈2 ps for CO on single crystal surfaces has been inferred from infrared absorption bandshape measurements [4,5]. However, the inability of frequency domain experiments to distinguish among the contributions to the measured bandwidth from depopulation, dephasing and inhomogeneity makes the interpretation ambiguous [6,7]. In order to clearly resolve this issue, direct measurements of the vibrational lifetimes of CO chemisorbed on metal surfaces are required.
4
Kurdila, A., and J. Li. "Relaxation Methods for Nonlinear Dynamics and Hysteresis Operators." In ASME 1999 Design Engineering Technical Conferences. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/detc99/vib-8062.
Full textAbstract:
Abstract Previous research has demonstrated that rigorous modeling and identification theory can be derived for structural dynamical models that incorporate control influence operators that are static Krasnoselskii-Pokrovskii integral hysteresis operators. Experimental evidence likewise has shown that some dynamic hysteresis models provide more accurate representations of a class of structural systems actuated by some active materials including shape memory alloys and piezoceramics. In this paper, we show that the representation of control influence operators via static hysteresis operators can be interpreted in terms of a homogeneous Young’s measure. Within this framework, we subsequently derive dynamic hysteresis operators represented in terms of Young’s measures that are parameterized in time. We show that the resulting integrodifferential equations are similar to the class of relaxed controls discussed by Warga [10], Garnkrelidze [24], and Roubicek [25]. The formulation presented here differs from that studied in [10], [24] and [25] in that the kernel of the hysteresis operator is a history dependent functional, as opposed to Caratheodory integral satisfying a growth condition. The theory presented provides representations of dynamic hysteresis operators that have provided good agreement with experimental behavior in some active materials.
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Haarer, D., and H. Maier. "Tunneling Dynamics and Spectral Diffusion in the Millikelvin Regime." In Spectral Hole-Burning and Related Spectroscopies: Science and Applications. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/shbs.1994.thd3.
Full textAbstract:
The tunneling model [1] is the theoretical basis for several anomalous and time dependent phenomena in amorphous materials, which are caused by a broad distribution of relaxation rates of the so-called two-level systems (TLS). This model has also been applied to interpret spectral diffusion in glasses and to explain the observation of time dependent spectral linewidths [2]. In terms of spectral hole-burning, the TLS dynamics leads to a logarithmic hole broadening for times larger than the minimum TLS relaxation time, while the hole widths approach a constant value for times larger than the maximum TLS relaxation time [3]. This functional dependence is caused by a hyperbolic distribution of relaxation rates; all the above described phenomena follow from the “weak coupling” model: In polymer glasses a logarithmic broadening has been found on time scales between milliseconds and days [4, 5].
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Zhu, Zimu, Daniel P. Sellan, Aydin Nabovati, and Cristina H. Amon. "Assessment of the Holland Model for Silicon Phonon-Phonon Relaxation Times Using Lattice Dynamics Calculations." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-63615.
Full textAbstract:
We assess the ability of the Holland model to accurately predict phonon-phonon relaxation times from bulk thermal conductivity values. Lattice dynamics calculations are used to obtain phonon-phonon relaxation times and thermal conductivities for temperatures ranging from 10 to 1000 K for Stillinger-Weber silicon. The Holland model is then fit to these thermal conductivities and used to predict relaxation times, which are compared to the relaxation times obtained by lattice dynamics calculations. We find that fitting the Holland model to both total and mode-dependent thermal conductivities does not result in accurate mode-dependent phonon-phonon relaxation times.
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Gerboth, M. D., and D. G. Walker. "Mode-Decay Molecular Dynamics for Frequency-Dependent Phonon Scattering Rates." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-38914.
Full textAbstract:
The thermal conductivity of crystalline materials can be determined in a statistical mechanical framework as long as phonon relaxation rates are known. Unfortunately, these quantities are difficult if not impossible to measure directly, and attempts to deduce these quantities yield gross averages not energy dependent relationships. Consequently, researchers often rely on heuristic models such as Holland’s suite of scattering rates for various phonon modes. A new molecular dynamics method was developed to estimate mode-dependent scattering rates by tracking the decay of an initially imposed standing wave. The wave vector is systematically changed and the corresponding decay is collected. Ultimately, the the thermal conductivity can be reconstructed using a Landauer formalism. The phonon scattering rates of a LJ crystal are calculated using this method. The standing wave decay approach allows scattering rates to be probed more directly than wave packet simulations, which are often used to obtain transmission coefficients.
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Xie, Xiaoliang, Robert Dunn, and John D. Simon. "Picosecond Polarization Studies of Protein Relaxation." In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1990. http://dx.doi.org/10.1364/up.1990.mc21.
Full textAbstract:
Picosecond polarization spectroscopies have been used to probe relaxation processes in heme proteins induced by ligand photodissociation. In particular, probing the N-band of myoglobin at 355 nm reveals a relaxation of several hundreds of picoseconds, over two orders of magnitude longer than the dynamics of photo-induced bond cleavage. Similar dynamics are also observed for studies in the Soret region. Time resolved linear dichroism studies confirm that the evolution of the CD signal does not arise from a change in the direction or degeneracies of the two degenerate, perpendicular transition moments of the heme. In addition, the time dependent spectral properties of the charge transfer absorption between the iron and the proximal histidine which results from photodissociation does not reveal any noticeable spectral shift on the time scale of the CD dynamics, strongly suggesting that the tilting of the proximal histidine is not causing the time dependent changes in the CD signal. These results suggest that the transient CD data is measuring a relaxation in the surrounding protein structure which is triggered by the photodissociation process.
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Sadeghian, Hamed, Johannes F. L. Goosen, Andre Bossche, Barend J. Thijsse, and Fred van Keulen. "Size-Dependent Elastic Behavior of Silicon Nanofilms: Molecular Dynamics Study." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11253.
Full textAbstract:
In this paper, the size-dependence of the elastic behavior of silicon nanofilms terminated by (100) surfaces is studied by means of molecular dynamics with the modified embedded atom method (MEAM). The results indicate that the (100) surfaces undergo 2×1 reconstruction, which significantly influences the mechanical properties of ultra-thin films. The simulations are carried out at room temperature and structural relaxation is performed. The effective Young’s modulus, in extensional mode, is determined for different thicknesses. The surface energy, surface stress and surface elasticity of layers near the surfaces (non-bulk layers) in the thin silicon films are obtained. The surface properties of nanofilms of a few layers are shown to deviate from thicker films, suggesting a size-dependence of surface parameters and, especially, surface energy. Finally, the results of a recently developed semi-continuum approach are compared with the molecular dynamics results. Below 3 nm, there is a difference between the effective Young’s modulus, calculated by the semi-continuum approach and that provided by MD, suggesting that the continuum approach can no longer provide accurate results.
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Xiao, Peng, Mitsuhiro Matsumoto, and Tomohisa Kunisawa. "Molecular Dynamics Study on Phonon Dynamics in Single-Crystal Silicon and Argon." In ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference collocated with the ASME 2007 InterPACK Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ht2007-32661.
Full textAbstract:
Modern semiconductor industry and nanotechnology have profoundly impacted the study on thermal transport in dielectric solids such as single-crystal silicon. For these heat conduction phenomena whose characteristic length and time shrink into nano scale, it is efficient to utilize phonon dynamics as a promising approach to investigate the fundamental features of heat transfer at nano scale as well as the distinguished thermal properties of nano-materials. A new computational method is proposed to explore phonon dynamics in single-crystals on the basis of classical Molecular Dynamics technique. This method utilizes the Fourier-Laplace transformation of molecular trajectory, with anharmonicity of molecular vibrations accounted in the investigation on phonon dynamics. Instantaneous mode-dependent energy of phonons and density of vibration state is obtained at each simulated time step. Mode-dependent phonon relaxation is simulated and verified with perturbation method, which gives a way to measure relaxation time of single-mode phonon. The feasibility of the proposed scheme is confirmed by a series of simulations which are carried out in this paper on 1) monatomic crystal of argon with FCC structure and 2) diatomic crystal of silicon with diamond structure, under Lennard-Jones 6-12 potential and Tersoff-1989 model, respectively.
Reports on the topic "Microstructure Dependent Relaxation Dynamics"
1
Kiv, A. E., T. I. Maximova, and V. N. Soloviev. Microstructure of the relaxed (001) Si surface. [б. в.], October 1999. http://dx.doi.org/10.31812/0564/1244.
Full textAbstract:
We have applied molecular dynamics method and semi-empirical potential [1] to obtain the realistic picture of Si surface layers relaxation. The starting configuration was taken as a parallelepiped containing 864 atoms. There were 12 layers with 72 atoms in each one. Periodic boundary conditions were used in two dimensions.
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Kiv, A. E., T. I. Maximova, and V. N. Soloviev. Microstructure of the relaxed (001) Si surface. [б. в.], December 1999. http://dx.doi.org/10.31812/0564/1245.
Full textAbstract:
We have applied molecular dynamics method and semi-empirical potential [1] to obtain the realistic picture of Si surface layers relaxation.The starting configuration was taken as a parallelepiped containing 864 atoms. There were 12 layers with 72 atoms in each one. Periodic boundary conditions were used in two dimensions. At first all atoms were in normal lattice positions. The relaxation of Si surface, which corresponds to (001) plane was investigated. MD method was applied in its standard form i.e. the equations of motion were solved by using of the central difference scheme. The time-step was 10-14s.