The Experts below are selected from a list of 302181 Experts worldwide ranked by ideXlab platform
Mary C. Boyce - One of the best experts on this subject based on the ideXlab platform.
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Large strain time-Dependent Behavior of filled elastomers
Mechanics of Materials, 2000Co-Authors: J.s. Bergström, Mary C. BoyceAbstract:Abstract The stress–strain Behavior of elastomeric materials is known to be rate-Dependent and to exhibit hysteresis upon cyclic loading. Although these features of the rubbery constitutive response are well-recognized and important to its function, few models attempt to quantify these aspects of response. Experiments have acted to isolate the time-Dependent and long term equilibrium components of the stress–strain Behavior (Bergstrom, J.S., Boyce, M.C., 1998. J. Mech. Phys. Solids 46, 931–954). These data formed the foundation of a constitutive model for the time-Dependent, hysteretic stress–strain Behavior of elastomers where the Behavior is decomposed into an equilibrium molecular network acting in parallel with a rate-Dependent network (cf. loc. cit.). In this paper, the Bergstrom and Boyce constitutive model is extended to specifically account for the effect of filler particles such as carbon black on the time-Dependent, hysteretic stress–strain Behavior. The influence of filler particles is found to be well-modeled by amplification of scalar equivalent values of the stretch and the shear stress thus providing effective measures of matrix stretch and matrix shear stress. The amplification factor is Dependent on the volume fraction and distribution of filler particles; three-dimensional stochastic micromechanical models are presented and verify the proposed amplification of stretch and stress. A direct comparison between the new model and experimental data for two series of filled elastomers (a chloroprene rubber series and a natural rubber series) indicates that the new model framework successfully captures the observed Behavior. The success of the model implies that the effects of filler particles on the equilibrium, rate and hysteresis Behavior of elastomers mainly requires a treatment of the composite nature of the microstructure and not micro-level concepts such as alteration of mobility or effective crosslinking density of the elastomeric phase of the material.
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constitutive modeling of the large strain time Dependent Behavior of elastomers
Journal of The Mechanics and Physics of Solids, 1998Co-Authors: J.s. Bergström, Mary C. BoyceAbstract:Abstract The mechanical Behavior of elastomeric materials is known to be rate-Dependent and to exhibit hysteresis upon cyclic loading. Although these features of the rubbery constitutive response are well-recognized and important to its function, few models attempt to quantify these aspects of response perhaps due to the complex nature of the Behavior and its apparent inconsistency with regard to current reasonably successful models of rubber elasticity. In this paper a detailed experimental investigation probing the material response of carbon black filled Chloroprene rubber subjected to different time-Dependent strain histories is presented. Some of the key observations from the experiments are: (1) both filled and unfilled elastomers show significant amounts of hysteresis during cyclic loading; (2) the amount of carbon black particles does not strongly influence the normalized amount of hysteresis; (3) both filled and unfilled elastomers are strain-rate Dependent and the rate dependence is higher during the uploading than during the unloading; (4) at fixed strain, the stress is observed to approach the same equilibrium level with relaxation time whether loading or unloading. Based on the experimental data a new constitutive model has been developed. The foundation of the model is that the mechanical Behavior can be decomposed into two parts: an equilibrium network corresponding to the state that is approached in long time stress relaxation tests; and a second network capturing the non-linear rate-Dependent deviation from the equilibrium state. The time-dependence of the second network is further assumed to be governed by the reptational motion of molecules having the ability to significantly change conformation and thereby relaxing the overall stress state. By comparing the predictions from the proposed three-dimensional constitutive model with experimental data for uniaxial compression and plane strain compression we conclude that the constitutive model predicts rate-dependence and relaxation Behavior well.
Daniel Blankschtein - One of the best experts on this subject based on the ideXlab platform.
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understanding the ph Dependent Behavior of graphene oxide aqueous solutions a comparative experimental and molecular dynamics simulation study
Langmuir, 2012Co-Authors: Chihjen Shih, Richa Sharma, Michael S Strano, Daniel BlankschteinAbstract:Understanding the pH-Dependent Behavior of graphene oxide (GO) aqueous solutions is important to the production of assembled GO or reduced GO films for electronic, optical, and biological applications. We have carried out a comparative experimental and molecular dynamics (MD) simulation study to uncover the mechanisms behind the aggregation and the surface activity of GO at different pH values. At low pH, the carboxyl groups are protonated such that the GO sheets become less hydrophilic and form aggregates. MD simulations further suggest that the aggregates exhibit a GO–water–GO sandwichlike structure and as a result are stable in water instead of precipitating. However, at high pH, the deprotonated carboxyl groups are very hydrophilic such that individual GO sheets prefer to dissolve in bulk water like a regular salt. The GO aggregates formed at low pH are found to be surface-active and do not exhibit characteristic features of surfactant micelles. Our findings suggest that GO does not behave like conven...
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understanding the ph Dependent Behavior of graphene oxide aqueous solutions a comparative experimental and molecular dynamics simulation study
Langmuir, 2012Co-Authors: Chihjen Shih, Richa Sharma, Michael S Strano, Shangchao Lin, Daniel BlankschteinAbstract:Understanding the pH-Dependent Behavior of graphene oxide (GO) aqueous solutions is important to the production of assembled GO or reduced GO films for electronic, optical, and biological applications. We have carried out a comparative experimental and molecular dynamics (MD) simulation study to uncover the mechanisms behind the aggregation and the surface activity of GO at different pH values. At low pH, the carboxyl groups are protonated such that the GO sheets become less hydrophilic and form aggregates. MD simulations further suggest that the aggregates exhibit a GO-water-GO sandwichlike structure and as a result are stable in water instead of precipitating. However, at high pH, the deprotonated carboxyl groups are very hydrophilic such that individual GO sheets prefer to dissolve in bulk water like a regular salt. The GO aggregates formed at low pH are found to be surface-active and do not exhibit characteristic features of surfactant micelles. Our findings suggest that GO does not behave like conventional surfactants in pH 1 and 14 aqueous solutions. The molecular-level understanding of the solution Behavior of GO presented here can facilitate and improve the experimental techniques used to synthesize and sort large, uniform GO dispersions in a solution phase.
J.s. Bergström - One of the best experts on this subject based on the ideXlab platform.
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Large strain time-Dependent Behavior of filled elastomers
Mechanics of Materials, 2000Co-Authors: J.s. Bergström, Mary C. BoyceAbstract:Abstract The stress–strain Behavior of elastomeric materials is known to be rate-Dependent and to exhibit hysteresis upon cyclic loading. Although these features of the rubbery constitutive response are well-recognized and important to its function, few models attempt to quantify these aspects of response. Experiments have acted to isolate the time-Dependent and long term equilibrium components of the stress–strain Behavior (Bergstrom, J.S., Boyce, M.C., 1998. J. Mech. Phys. Solids 46, 931–954). These data formed the foundation of a constitutive model for the time-Dependent, hysteretic stress–strain Behavior of elastomers where the Behavior is decomposed into an equilibrium molecular network acting in parallel with a rate-Dependent network (cf. loc. cit.). In this paper, the Bergstrom and Boyce constitutive model is extended to specifically account for the effect of filler particles such as carbon black on the time-Dependent, hysteretic stress–strain Behavior. The influence of filler particles is found to be well-modeled by amplification of scalar equivalent values of the stretch and the shear stress thus providing effective measures of matrix stretch and matrix shear stress. The amplification factor is Dependent on the volume fraction and distribution of filler particles; three-dimensional stochastic micromechanical models are presented and verify the proposed amplification of stretch and stress. A direct comparison between the new model and experimental data for two series of filled elastomers (a chloroprene rubber series and a natural rubber series) indicates that the new model framework successfully captures the observed Behavior. The success of the model implies that the effects of filler particles on the equilibrium, rate and hysteresis Behavior of elastomers mainly requires a treatment of the composite nature of the microstructure and not micro-level concepts such as alteration of mobility or effective crosslinking density of the elastomeric phase of the material.
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constitutive modeling of the large strain time Dependent Behavior of elastomers
Journal of The Mechanics and Physics of Solids, 1998Co-Authors: J.s. Bergström, Mary C. BoyceAbstract:Abstract The mechanical Behavior of elastomeric materials is known to be rate-Dependent and to exhibit hysteresis upon cyclic loading. Although these features of the rubbery constitutive response are well-recognized and important to its function, few models attempt to quantify these aspects of response perhaps due to the complex nature of the Behavior and its apparent inconsistency with regard to current reasonably successful models of rubber elasticity. In this paper a detailed experimental investigation probing the material response of carbon black filled Chloroprene rubber subjected to different time-Dependent strain histories is presented. Some of the key observations from the experiments are: (1) both filled and unfilled elastomers show significant amounts of hysteresis during cyclic loading; (2) the amount of carbon black particles does not strongly influence the normalized amount of hysteresis; (3) both filled and unfilled elastomers are strain-rate Dependent and the rate dependence is higher during the uploading than during the unloading; (4) at fixed strain, the stress is observed to approach the same equilibrium level with relaxation time whether loading or unloading. Based on the experimental data a new constitutive model has been developed. The foundation of the model is that the mechanical Behavior can be decomposed into two parts: an equilibrium network corresponding to the state that is approached in long time stress relaxation tests; and a second network capturing the non-linear rate-Dependent deviation from the equilibrium state. The time-dependence of the second network is further assumed to be governed by the reptational motion of molecules having the ability to significantly change conformation and thereby relaxing the overall stress state. By comparing the predictions from the proposed three-dimensional constitutive model with experimental data for uniaxial compression and plane strain compression we conclude that the constitutive model predicts rate-dependence and relaxation Behavior well.
Chihjen Shih - One of the best experts on this subject based on the ideXlab platform.
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understanding the ph Dependent Behavior of graphene oxide aqueous solutions a comparative experimental and molecular dynamics simulation study
Langmuir, 2012Co-Authors: Chihjen Shih, Richa Sharma, Michael S Strano, Daniel BlankschteinAbstract:Understanding the pH-Dependent Behavior of graphene oxide (GO) aqueous solutions is important to the production of assembled GO or reduced GO films for electronic, optical, and biological applications. We have carried out a comparative experimental and molecular dynamics (MD) simulation study to uncover the mechanisms behind the aggregation and the surface activity of GO at different pH values. At low pH, the carboxyl groups are protonated such that the GO sheets become less hydrophilic and form aggregates. MD simulations further suggest that the aggregates exhibit a GO–water–GO sandwichlike structure and as a result are stable in water instead of precipitating. However, at high pH, the deprotonated carboxyl groups are very hydrophilic such that individual GO sheets prefer to dissolve in bulk water like a regular salt. The GO aggregates formed at low pH are found to be surface-active and do not exhibit characteristic features of surfactant micelles. Our findings suggest that GO does not behave like conven...
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understanding the ph Dependent Behavior of graphene oxide aqueous solutions a comparative experimental and molecular dynamics simulation study
Langmuir, 2012Co-Authors: Chihjen Shih, Richa Sharma, Michael S Strano, Shangchao Lin, Daniel BlankschteinAbstract:Understanding the pH-Dependent Behavior of graphene oxide (GO) aqueous solutions is important to the production of assembled GO or reduced GO films for electronic, optical, and biological applications. We have carried out a comparative experimental and molecular dynamics (MD) simulation study to uncover the mechanisms behind the aggregation and the surface activity of GO at different pH values. At low pH, the carboxyl groups are protonated such that the GO sheets become less hydrophilic and form aggregates. MD simulations further suggest that the aggregates exhibit a GO-water-GO sandwichlike structure and as a result are stable in water instead of precipitating. However, at high pH, the deprotonated carboxyl groups are very hydrophilic such that individual GO sheets prefer to dissolve in bulk water like a regular salt. The GO aggregates formed at low pH are found to be surface-active and do not exhibit characteristic features of surfactant micelles. Our findings suggest that GO does not behave like conventional surfactants in pH 1 and 14 aqueous solutions. The molecular-level understanding of the solution Behavior of GO presented here can facilitate and improve the experimental techniques used to synthesize and sort large, uniform GO dispersions in a solution phase.
Tom Hindmarsh Sten - One of the best experts on this subject based on the ideXlab platform.
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parallel processing by cortical inhibition enables context Dependent Behavior
Nature Neuroscience, 2017Co-Authors: Kishore V Kuchibhotla, Jonathan V Gill, Grace W Lindsay, Eleni S Papadoyannis, Rachel E Field, Tom Hindmarsh StenAbstract:Physical features of sensory stimuli are fixed, but sensory perception is context Dependent. The precise mechanisms that govern contextual modulation remain unknown. Here, we trained mice to switch between two contexts: passively listening to pure tones and performing a recognition task for the same stimuli. Two-photon imaging showed that many excitatory neurons in auditory cortex were suppressed during Behavior, while some cells became more active. Whole-cell recordings showed that excitatory inputs were affected only modestly by context, but inhibition was more sensitive, with PV+, SOM+, and VIP+ interneurons balancing inhibition and disinhibition within the network. Cholinergic modulation was involved in context switching, with cholinergic axons increasing activity during Behavior and directly depolarizing inhibitory cells. Network modeling captured these findings, but only when modulation coincidently drove all three interneuron subtypes, ruling out either inhibition or disinhibition alone as sole mechanism for active engagement. Parallel processing of cholinergic modulation by cortical interneurons therefore enables context-Dependent Behavior.
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parallel processing by cortical inhibition enables context Dependent Behavior
Nature Neuroscience, 2017Co-Authors: Kishore V Kuchibhotla, Jonathan V Gill, Grace W Lindsay, Eleni S Papadoyannis, Rachel E Field, Tom Hindmarsh StenAbstract:Animals have a remarkable ability to adjust their Behavioral response to the same stimulus based on the immediate Behavioral context. The authors show that the nucleus basalis broadcasts a contextual signal to the auditory cortex that is then translated by inhibitory networks to regulate excitatory neuronal output and Behavior.
