Dynamic linear viscoelastic properties and extensional failure of asphalt binders
NASA Astrophysics Data System (ADS)
Ruan, Yonghong
Billions of dollars are spent annually in USA to maintain old pavements that are badly cracked. In order to reduce this expenditure, it is desirable to have criteria for selecting asphalts with superior cracking resistance that will provide pavements with longer durability. Literature reports indicate that the ductility of binders recovered from asphalt pavements correlates with cracking failure. However, ductility measurement is a time and material consuming process, and subject to reproducibility difficulties, as are all failure tests. In addition, ductility measurement does not belong to the currently used Superpave(TM) specification. Correlations between ductility and dynamic viscoelastic properties (measured with the dynamic shear rheometer, DSR), which are much easier and faster to perform and may be included into the Superpave(TM) system, are studied for both straight and modified binders. Ductility correlates quite well with G'/(eta '/G') for conventional asphalt binders aged at different conditions, especially when ductility is below 10 cm. However, for modified asphalts, there is no universal correlation between ductility and G'/(eta'/G'), even in the low ductility region. As far as the asphalt binder in pavement is concerned, the loss due to oxidative aging of its ductility is an important reason for pavement cracking. Polymer modification modifies the rheological and oxidative hardening properties of asphalt binders. The effect of polymeric modifiers on various properties of asphalt binders was investigated. Modifiers studied were diblock poly (styrene-b-butadiene) rubber (SBR), triblock poly (styrene-b-butadiene-b-styrene) (SBS), and tire rubber. Polymer modified binders have a lower hardening and oxidation rate than their corresponding base asphalts. In addition, modified binders have lower hardening susceptibility compared with their base materials and in some cases the results can be dramatic. Polymer modification improves asphalt binders' shear
NASA Astrophysics Data System (ADS)
Pottier, Basile; Talini, Laurence; Frétigny, Christian
2012-02-01
We present a new optical method to measure the linear viscoelastic properties of materials, ranging from complex fluids to soft solids, within a large frequency range (about 0.1--10^4 Hz). The surface fluctuation specular reflection technique is based on the measurement of the thermal fluctuations of the free surfaces of materials at which a laser beam is specularly reflected. The propagation of the thermal surface waves depends on the surface tension, density, and complex viscoelastic modulus of the material. For known surface tension and density, we show that the frequency dependent elastic and loss moduli can be deduced from the fluctuation spectrum. Using a viscoelastic solid (a cross-linked PDMS), which linear viscoelastic properties are known in a large frequency range from rheometric measurements and the time--temperature superposition principle, we show that there is a good agreement between the rheological characterization provided by rheometric and fluctuation measurements. We also present measurements conducted with complex fluids that are supramolecular polymer solutions. The agreement with other low frequency and high frequency rheological measurements is again very good, and we discuss the sensitivity of the technique to surface viscoelasticity.
Stephanou, Pavlos S; Mavrantzas, Vlasis G
2014-06-01
We present a hierarchical computational methodology which permits the accurate prediction of the linear viscoelastic properties of entangled polymer melts directly from the chemical structure, chemical composition, and molecular architecture of the constituent chains. The method entails three steps: execution of long molecular dynamics simulations with moderately entangled polymer melts, self-consistent mapping of the accumulated trajectories onto a tube model and parameterization or fine-tuning of the model on the basis of detailed simulation data, and use of the modified tube model to predict the linear viscoelastic properties of significantly higher molecular weight (MW) melts of the same polymer. Predictions are reported for the zero-shear-rate viscosity η0 and the spectra of storage G'(ω) and loss G″(ω) moduli for several mono and bidisperse cis- and trans-1,4 polybutadiene melts as well as for their MW dependence, and are found to be in remarkable agreement with experimentally measured rheological data. PMID:24908037
NASA Astrophysics Data System (ADS)
Stephanou, Pavlos S.; Mavrantzas, Vlasis G.
2014-06-01
We present a hierarchical computational methodology which permits the accurate prediction of the linear viscoelastic properties of entangled polymer melts directly from the chemical structure, chemical composition, and molecular architecture of the constituent chains. The method entails three steps: execution of long molecular dynamics simulations with moderately entangled polymer melts, self-consistent mapping of the accumulated trajectories onto a tube model and parameterization or fine-tuning of the model on the basis of detailed simulation data, and use of the modified tube model to predict the linear viscoelastic properties of significantly higher molecular weight (MW) melts of the same polymer. Predictions are reported for the zero-shear-rate viscosity η0 and the spectra of storage G'(ω) and loss G″(ω) moduli for several mono and bidisperse cis- and trans-1,4 polybutadiene melts as well as for their MW dependence, and are found to be in remarkable agreement with experimentally measured rheological data.
Quasi-linear viscoelastic properties of the human medial patello-femoral ligament.
Criscenti, G; De Maria, C; Sebastiani, E; Tei, M; Placella, G; Speziali, A; Vozzi, G; Cerulli, G
2015-12-16
The evaluation of viscoelastic properties of human medial patello-femoral ligament is fundamental to understand its physiological function and contribution as stabilizer for the selection of the methods of repair and reconstruction and for the development of scaffolds with adequate mechanical properties. In this work, 12 human specimens were tested to evaluate the time- and history-dependent non linear viscoelastic properties of human medial patello-femoral ligament using the quasi-linear viscoelastic (QLV) theory formulated by Fung et al. (1972) and modified by Abramowitch and Woo (2004). The five constant of the QLV theory, used to describe the instantaneous elastic response and the reduced relaxation function on stress relaxation experiments, were successfully evaluated. It was found that the constant A was 1.21±0.96MPa and the dimensionless constant B was 26.03±4.16. The magnitude of viscous response, the constant C, was 0.11±0.02 and the initial and late relaxation time constants τ1 and τ2 were 6.32±1.76s and 903.47±504.73s respectively. The total stress relaxation was 32.7±4.7%. To validate our results, the obtained constants were used to evaluate peak stresses from a cyclic stress relaxation test on three different specimens. The theoretically predicted values fit the experimental ones demonstrating that the QLV theory could be used to evaluate the viscoelastic properties of the human medial patello-femoral ligament.
Chen, J.S.; Tsai, C.J. . Dept. of Civil Engineering)
1999-08-01
This article evaluates the effects of linear viscoelastic properties of asphalt on pavement rutting and fatigue cracking. The parameters in the binder specification recently developed by the Strategic Highway Research Program (SHRP) were also compared for pavement performance. Two studies were conducted for asphalt-aggregate mixes. The first study was the wheel tracking test to evaluate the rutting of mixes containing three asphalts. The second study was a detailed field study of the effects of binder properties on the pavement performance of eight different sections. Results of both investigations indicated that SHRP parameters were not sufficient indicators for predicting the rutting and fatigue cracking of pavements. The discrepancies between performance data and existing parameters of the binder mainly resulted from the inherited assumptions made during the specification development, that is, stress- or strain-controlled mode and traffic loading frequency. In order to directly relate the linear viscoelastic properties of asphalt binders to pavement performance, calculating the dissipated energy per traffic cycle, W[sub d], became imperative. Fundamental derivation of W[sub d] was developed in this study. Results indicated that W[sub d] could predict the rutting and fatigue cracking of pavements reasonably well, This study, proposed the dissipated energy, W[sub d], as the single parameter for evaluating pavement rutting and fatigue cracking.
NASA Astrophysics Data System (ADS)
Karim, Mir; Indei, Tsutomu; Schieber, Jay D.; Khare, Rajesh
2016-01-01
Particle rheology is used to extract the linear viscoelastic properties of an entangled polymer melt from molecular dynamics simulations. The motion of a stiff, approximately spherical particle is tracked in both passive and active modes. We demonstrate that the dynamic modulus of the melt can be extracted under certain limitations using this technique. As shown before for unentangled chains [Karim et al., Phys. Rev. E 86, 051501 (2012), 10.1103/PhysRevE.86.051501], the frequency range of applicability is substantially expanded when both particle and medium inertia are properly accounted for by using our inertial version of the generalized Stokes-Einstein relation (IGSER). The system used here introduces an entanglement length dT, in addition to those length scales already relevant: monomer bead size d , probe size R , polymer radius of gyration Rg, simulation box size L , shear wave penetration length Δ , and wave period Λ . Previously, we demonstrated a number of restrictions necessary to obtain the relevant fluid properties: continuum approximation breaks down when d ≳Λ ; medium inertia is important and IGSER is required when R ≳Λ ; and the probe should not experience hydrodynamic interaction with its periodic images, L ≳Δ . These restrictions are also observed here. A simple scaling argument for entangled polymers shows that the simulation box size must scale with polymer molecular weight as Mw3. Continuum analysis requires the existence of an added mass to the probe particle from the entrained medium but was not observed in the earlier work for unentangled chains. We confirm here that this added mass is necessary only when the thickness LS of the shell around the particle that contains the added mass, LS>d . We also demonstrate that the IGSER can be used to predict particle displacement over a given timescale from knowledge of medium viscoelasticity; such ability will be of interest for designing nanoparticle-based drug delivery.
Viscoelastic Properties of Networks
NASA Astrophysics Data System (ADS)
Gündüz, Güngör
A network was characterized by its viscoelastic properties. The viscoelastic property indicates the deformations or changes in the shape and in the internal structure during the evolution of a network. The change in the direction of motion was taken as elastic deformation and the change in the vertical direction as viscous deformation. These deformations were related to the change of geometry of internal structure and of shape. Thus it was possible to characterize a network by its storage and loss moduli. The change of the structure of a network during its evolution changes also its entropy. However entropy depends on the number of microstates of an already existing framework. As examples, two different systems (i) New York Stock Exchange and (ii) a melody were studied for their viscoelastic properties. The change of viscous property was compared with the change of different types of entropies such as configurational entropy, crossing entropy, and topological entropy. This last entropy was introduced and explained in the text. It was found out that there is no direct correspondence between the increase of entropy and the increase of viscous property of a network although they sometimes correlate with each other.
Dynamics of gas bubbles in viscoelastic fluids. I. Linear viscoelasticity
Allen; Roy
2000-06-01
The nonlinear oscillations of spherical gas bubbles in linear viscoelastic fluids are studied. A novel approach is implemented to derive a governing system of nonlinear ordinary differential equations. The linear Maxwell and Jeffreys models are chosen as the fluid constitutive equations. An advantage of this new formulation is that, when compared with previous approaches, it facilitates perturbation methods and numerical investigations. Analytical solutions are obtained using a multiple scale perturbation method and compared with the Newtonian results for various Deborah numbers. Numerical analysis of the full equations supports the perturbation analysis, and further reveals significant differences between the viscoelastic and Newtonian cases. Differences in the oscillation phase and harmonic structure characterize some of the viscoelastic effects. Subharmonic excitations at particular fluid parameters lead to a discrete group modulation of the radial excursions; this appears to be a unique, previously undiscovered phenomenon. Implications for medical ultrasound applications are discussed in light of these current findings.
Viscoelastic properties of ferrofluids.
Chirikov, D N; Fedotov, S P; Iskakova, L Yu; Zubarev, A Yu
2010-11-01
The paper deals with theoretical study of non linear viscoelastic phenomena in ferrofluids placed in magnetic field. Our attention is focused on the study of nonstationary flow and Maxwell-like relaxation of the macroscopical viscous stress after alternation of the shear rate. We propose that these phenomena can be explained by finite rate of evolution of chainlike aggregates, consisting of the ferrofluid particles. Statistical model of the chains growth-disintegration is suggested. In this model the chain-single particle mechanism of the chains evolution is considered, the effects of the chain-chain interaction are ignored. The proposed model allows us to estimate the time-dependent function of distribution over number of particles in the chain. Having determined this function and using methods of hydromechanics of ferrofluids with chainlike aggregates, we have studied evolution of the ferrofluid viscosity after stepwise alternation of the fluid shear rate. The estimated time of relaxation is in a reasonable agreement with experimental results. Thus, our analysis shows that the observed macroscopical viscoelastic phenomena in ferrofluids can be provided by evolution of the chain ensemble. PMID:21230477
Local linear viscoelasticity of confined fluids
NASA Astrophysics Data System (ADS)
Hansen, J. S.; Daivis, P. J.; Todd, B. D.
2007-04-01
In this paper the authors propose a novel method to study the local linear viscoelasticity of fluids confined between two walls. The method is based on the linear constitutive equation and provides details about the real and imaginary parts of the local complex viscosity. They apply the method to a simple atomic fluid undergoing zero mean oscillatory flow using nonequilibrium molecular dynamics simulations. The method shows that the viscoelastic properties of the fluid exhibit dramatic spatial changes near the wall-fluid boundary due to the high density in this region. It is also shown that the real part of the viscosity converges to the frequency dependent local shear viscosity sufficiently far away from the wall. This also provides valuable information about the transport properties in the fluid, in general. The viscosity is compared with predictions from the local average density model. The two methods disagree in that the local average density model predicts larger viscosity variations near the wall-fluid boundary than what is observed through the method presented here.
A Thermodynamic Theory Of Solid Viscoelasticity. Part 1: Linear Viscoelasticity.
NASA Technical Reports Server (NTRS)
Freed, Alan D.; Leonov, Arkady I.
2002-01-01
The present series of three consecutive papers develops a general theory for linear and finite solid viscoelasticity. Because the most important object for nonlinear studies are rubber-like materials, the general approach is specified in a form convenient for solving problems important for many industries that involve rubber-like materials. General linear and nonlinear theories for non-isothermal deformations of viscoelastic solids are developed based on the quasi-linear approach of non-equilibrium thermodynamics. In this, the first paper of the series, we analyze non-isothermal linear viscoelasticity, which is applicable in a range of small strains not only to all synthetic polymers and bio-polymers but also to some non-polymeric materials. Although the linear case seems to be well developed, there still are some reasons to implement a thermodynamic derivation of constitutive equations for solid-like, non-isothermal, linear viscoelasticity. The most important is the thermodynamic modeling of thermo-rheological complexity , i.e. different temperature dependences of relaxation parameters in various parts of relaxation spectrum. A special structure of interaction matrices is established for different physical mechanisms contributed to the normal relaxation modes. This structure seems to be in accord with observations, and creates a simple mathematical framework for both continuum and molecular theories of the thermo-rheological complex relaxation phenomena. Finally, a unified approach is briefly discussed that, in principle, allows combining both the long time (discrete) and short time (continuous) descriptions of relaxation behaviors for polymers in the rubbery and glassy regions.
Viscoelastic properties of cellular polypropylene ferroelectrets
NASA Astrophysics Data System (ADS)
Gaal, Mate; Bovtun, Viktor; Stark, Wolfgang; Erhard, Anton; Yakymenko, Yuriy; Kreutzbruck, Marc
2016-03-01
Viscoelastic properties of cellular polypropylene ferroelectrets (PP FEs) were studied at low frequencies (0.3-33 Hz) by dynamic mechanical analysis and at high frequencies (250 kHz) by laser Doppler vibrometry. Relaxation behavior of the in-plane Young's modulus ( Y11 ' ˜ 1500 MPa at room temperature) was observed and attributed to the viscoelastic response of polypropylene matrix. The out-of-plane Young's modulus is very small ( Y33 ' ≈ 0.1 MPa) at low frequencies, frequency- and stress-dependent, evidencing nonlinear viscoelastic response of PP FEs. The high-frequency mechanical response of PP FEs is shown to be linear viscoelastic with Y33 ' ≈ 0.8 MPa. It is described by thickness vibration mode and modeled as a damped harmonic oscillator with one degree of freedom. Frequency dependence of Y33 * in the large dynamic strain regime is described by the broad Cole-Cole relaxation with a mean frequency in kHz range attributed to the dynamics of the air flow between partially closed air-filled voids in PP FEs. Switching-off the relaxation contribution causes dynamic crossover from the nonlinear viscoelastic regime at low frequencies to the linear viscoelastic regime at high frequencies. In the small strain regime, contribution of the air flow seems to be insignificant and the power-law response, attributed to the mechanics of polypropylene cell walls and closed air voids, dominates in a broad frequency range. Mechanical relaxation caused by the air flow mechanism takes place in the sound and ultrasound frequency range (10 Hz-1 MHz) and, therefore, should be taken into account in ultrasonic applications of the PP FEs deal with strong exciting or receiving signals.
Hickey, Robert J.; Gillard, Timothy M.; Lodge, Timothy P.; Bates, Frank S.
2015-08-28
Rheological evidence of composition fluctuations in disordered diblock copolymers near the order disorder transition (ODT) has been documented in the literature over the past three decades, characterized by a failure of time–temperature superposition (tTS) to reduce linear dynamic mechanical spectroscopy (DMS) data in the terminal viscoelastic regime to a temperature-independent form. However, for some materials, most notably poly(styrene-b-isoprene) (PS–PI), no signature of these rheological features has been found. We present small-angle X-ray scattering (SAXS) results on symmetric poly(cyclohexylethylene-b-ethylene) (PCHE–PE) diblock copolymers that confirm the presence of fluctuations in the disordered state and DMS measurements that also show no sign of the features ascribed to composition fluctuations. Assessment of DMS results published on five different diblock copolymer systems leads us to conclude that the effects of composition fluctuations can be masked by highly asymmetric block dynamics, thereby resolving a long-standing disagreement in the literature and reinforcing the importance of mechanical contrast in understanding the dynamics of ordered and disordered block polymers.
Viscoelastic properties of oat ß-glucan-rich aqueous dispersions
Technology Transfer Automated Retrieval System (TEKTRAN)
C-trim is a healthy food product containing the dietary of soluble fiber ß-glucan. The suspension of C-trim in water is a hydrocolloid biopolymer. The linear and non-linear rheological properties for suspensions of C-trim biopolymers were investigated. The linear viscoelastic behaviors for C-trim...
Nonlinear viscoelastic properties of long-chain randomly branched polybutadiene
Kasehagen, L.J.; Macosko, C.W.
1996-12-31
The presence of long-chain random branching in polymer melts is known to have a large effect on a material`s viscoelastic properties. A hydrosilation reaction between near-monodisperse polybutadiene and a small difunctional crosslinker was used to produce polymer with well characterized random branching for rheological study. Although, previous work has characterized the branching, molecular weight distribution and linear viscoelastic properties of the system, non-linear properties are often of more importance in processing and will be reported on in this work. The shear behavior of a series of polybutadienes of varying branching content were investigated using start-up of steady shear and step shear measurements. Transient uniaxial extensional measurements were also made using a fiber-windup technique on a commercial shear rheometer. Results will be presented by comparison with the linear viscoelastic results and non-linear constitutive equations. Particular emphasis will be placed on changes in the damping function as branching content increases.
Viscoelastic properties of levan polysaccharides
NASA Astrophysics Data System (ADS)
Noll, Kenneth; Rende, Deniz; Ozisik, Rahmi; Toksoy-Oner, Ebru
2014-03-01
Levan is a naturally occurring polysaccharide that is composed of β-D-fructofuranose units with β(2-6) linkages between fructose rings. It is synthesized by the action of a secreted levansucrase (EC 2.4.1.10) that converts sucrose into the levan externally (exopolysaccharide). Levan is a homopolysaccharide that is non-toxic, water soluble,, and has anti-tumor activity and low immunological response. Therefore, levan presents great potential to be used as a novel functional biopolymer in foods, feeds, cosmetics, pharmaceutical and chemical industries. Despite these favorable properties, levan has a moderately low mechanical properties and poor film forming capability. In the current study, the agglomeration behavior of levan in water and in saline solutions was investigated at 298 and 310 K by dynamic light scattering and transmission electron microscopy (TEM). The viscoelastic properties of neat and oxidized levan films were studied via nanoindentation experiments in the quasi-static and dynamic modes The material is partially based upon work supported by NSF under Grant Nos. 1200270 and 1003574, and TUBITAK 111M232.
Semi-analytical computation of displacement in linear viscoelastic materials
NASA Astrophysics Data System (ADS)
Spinu, S.; Gradinaru, D.
2015-11-01
Prediction of mechanical contact performance based on elastic models is not accurate in case of viscoelastic materials; however, a closed-form description of the viscoelastic contact has yet to be found. This paper aims to advance a semi-analytical method for computation of displacement induced in viscoelastic materials by arbitrary surface tractions, as a prerequisite to a semi-analytical solution for the viscoelastic contact problem. The newly advanced model is expected to provide greater generality, allowing for arbitrary contact geometry and / or arbitrary loading history. While time-independent equations in the purely elastic model can be treated numerically by imposing a spatial discretization only, a viscoelastic constitutive law requires supplementary temporal discretization capable of simulating the memory effect specific to viscoelastic materials. By deriving new influence coefficients, computation of displacement induced in a viscoelastic material by a known but otherwise arbitrary history of surface tractions can be achieved via superposition authorized by the Boltzmann superposition theory applicable in the frame of linear viscoelasticity.
Viscoelastic properties of semiflexible filamentous bacteriophage fd.
Schmidt, F G; Hinner, B; Sackmann, E; Tang, J X
2000-10-01
The cytoskeletal protein filament F-actin has been treated in a number of recent studies as a model physical system for semiflexible filaments. In this work, we studied the viscoelastic properties of entangled solutions of the filamentous bacteriophage fd as an alternative to F-actin with similar physical parameters. We present both microrheometric and macrorheometric measurements of the viscoelastic storage and loss moduli, G'(f ) and G"(f ), respectively, in a frequency range 0.01
Linear Viscoelasticity and Swelling of Polyelectrolyte Complex Coacervates
NASA Astrophysics Data System (ADS)
Hamad, Fawzi; Colby, Ralph
2012-02-01
The addition of near equimolar amounts of poly(diallyldimethylammonium chloride) to poly(isobutylene-alt-maleate sodium), results in formation of a polyelectrolyte complex coacervate. Zeta-potential titrations conclude that these PE-complexes are nearly charge-neutral. Swelling and rheological properties are studied at different salt concentrations in the surrounding solution. The enhanced swelling observed at high salt concentration suggests the system behaves like a polyampholyte gel, and weaker swelling at very low salt concentrations implies polyelectrolyte gel behavior. Linear viscoelastic oscillatory shear measurements indicate that the coacervates are viscoelastic liquids and that increasing ionic strength of the medium weakens the electrostatic interactions between charged units, lowering the relaxation time and viscosity. We use the time-salt superposition idea recently proposed by Spruijt, et al., allowing us to construct master curves for these soft materials. Similar swelling properties observed when varying molecular weights. Rheological measurements reveal that PE-complexes with increasing molecular weight polyelectrolytes form a network with higher crosslink density, suggesting time-molecular weight superposition idea.
Viscoelastic properties of vis-breaking polypropylenes
NASA Astrophysics Data System (ADS)
Nobile, Maria Rossella; Moad, Graeme; Habsuda, Jana; Li, Guoxin; Nichols, Lance; Dagley, Ian; Simon, George P.
2015-12-01
In this work hydrogen peroxide is used as a green initiator to cause scissioning of polypropylene (PP) with water as the only by-product replacing the organic peroxides that are usually used. The rheological properties of a commercial polypropylene and of the scissioned samples are determined by dynamic rheology and an inversion procedure for converting the linear viscoelastic data into molar mass distribution has been adopted. The results presented show that the molar mass distribution of the PP polymer is narrowed on scissioning. The process is found to produce polymers similar in molecular architecture and behavior to organic peroxide cleaved materials, the results of which are given as a comparison in this work.
Viscoelastic properties of 3-D braided PEEK/graphite composites
Hu, Jian-Ni.
1992-01-01
In this study, 3-D braided PEEK/AS4 graphite composites were performed and processed to investigate the viscoelastic behavior of this new system. These manufactured composites were characterized to determine their fiber volume fractions and matrix crystallinity indices using matrix digestion and wide angle x-ray diffraction. After physical characterization, the mechanical response of these composites were evaluated at various temperatures. Experimental results from tensile measurements were compared to an established fabric geometry model (FGM). This model predicts tensile modules based upon fiber and matrix properties, fiber volume fraction, and braiding angle. Model predictions and experimental results are given here, and are in good agreement with each other. In order to study the time-dependent mechanical properties of these 3-D braided composites, their stress relaxation, creep and dynamic mechanical properties were evaluated. These results were then compared to a new composite model. This model combined a Quasi/linear Viscoelastic Model (QVM) for the viscoelastic behavior of PEEK with the FGM approach to predict the viscoelastic behavior of 3-D PEEK composites. The experimental stress relaxation and creep results are in good agreement with the QVM-FGM analysis. Thus, the QVM-FGM approach was used to accurately correlate these viscoelastic properties of 3-D braided PEEK/graphite composites. Through wider use and testing, this QVM/FGM approach may be used to increase our understanding and perhaps facilitate the design of composite structures.
Viscoelastic properties of the normal human bladder.
Andersson, S; Kronström, A; Bjerle, P
1989-01-01
Continuous and stepwise cystometry were performed through suprapubic catheters in 12 healthy young subjects in order to assess passive viscoelastic variables of the normal human bladder during the collection phase. Elastic contants increased non-linearly with bladder distension. Relative elastic modulus and relaxation time of the bladder wall increased or tended to increase with bladder distension and infusion rate. There was considerable interindividual variation in all variables suggesting that discrimination between normal and abnormal bladder wall viscoelasticity may be difficult in routine clinical practice.
HAMMERAND,DANIEL C.; KAPANIA,RAKESH K.
2000-05-01
A triangular flat shell element for large deformation analysis of linear viscoelastic laminated composites is presented. Hygrothermorheologically simple materials are considered for which a change in the hygrothermal environment results in a horizontal shifting of the relaxation moduli curves on a log time scale, in addition to the usual hygrothermal loads. Recurrence relations are developed and implemented for the evaluation of the viscoelastic memory loads. The nonlinear deformation process is computed using an incremental/iterative approach with the Newton-Raphson Method used to find the incremental displacements in each step. The presented numerical examples consider the large deformation and stability of linear viscoelastic structures under deformation-independent mechanical loads, deformation-dependent pressure loads, and thermal loads. Unlike elastic structures that have a single critical load value associated with a given snapping of buckling instability phenomenon, viscoelastic structures will usually exhibit a particular instability for a range of applied loads over a range of critical times. Both creep buckling and snap-through examples are presented here. In some cases, viscoelastic results are also obtained using the quasielastic method in which load-history effects are ignored, and time-varying viscoelastic properties are simply used in a series of elastic problems. The presented numerical examples demonstrate the capability and accuracy of the formulation.
Viscoelastic modelling of tennis ball properties
NASA Astrophysics Data System (ADS)
Sissler, L.; Jones, R.; Leaney, P. G.; Harland, A.
2010-06-01
An explicit finite element (FE) tennis ball model which illustrates the effects of the viscoelastic materials of a tennis ball on ball deformation and bounce during normal impacts is presented. A tennis ball is composed of a rubber core and a fabric cover comprised of a wool-nylon mix which exhibit non-linear strain rate properties during high velocity impacts. The rubber core model was developed and validated using low strain rate tensile tests on rubber samples as well as high velocity normal impacts of pressurised cores at velocities ranging from 15 m/s to 50 m/s. The impacts were recorded using a high speed video (HSV) camera to determine deformation, impact time and coefficient of restitution (COR). The material properties of the core model were tuned to match the HSV results. A two component anisotropic fabric model was created which included artificial Rayleigh damping to account for hysteresis effects, and the core model 'tuning' process was used to refine the cloth layer. The ball model's parameters were in good agreement with experimental data at all velocities for both cores and complete balls, and a time sequenced comparison of HSV ball motion and FE model confirmed the validity of the model.
Molecular and structural analysis of viscoelastic properties
NASA Astrophysics Data System (ADS)
Yapp, Rebecca D.; Kalyanam, Sureshkumar; Insana, Michael F.
2007-03-01
Elasticity imaging is emerging as an important tool for breast cancer detection and monitoring of treatment. Viscoelastic image contrast in breast lesions is generated by disease specific processes that modify the molecular structure of connective tissues. We showed previously that gelatin hydrogels exhibit mechanical behavior similar to native collagen found in breast tissue and therefore are suitable as phantoms for elasticity imaging. This paper summarizes our study of the viscoelastic properties of hydrogels designed to discover molecular-scale sources of elasticity image contrast.
Anisotropy of bituminous mixture in the linear viscoelastic domain
NASA Astrophysics Data System (ADS)
Di Benedetto, Hervé; Sauzéat, Cédric; Clec'h, Pauline
2016-08-01
Some anisotropic properties in the linear viscoelastic domain of bituminous mixtures compacted with a French LPC wheel compactor are highlighted in this paper. Bituminous mixture is generally considered as isotropic even if the compaction process on road or in laboratory induces anisotropic properties. Tension-compression complex modulus tests have been performed on parallelepipedic specimens in two directions: (i) direction of compactor wheel movement (direction I, which is horizontal) and (ii) direction of compaction (direction II, which is vertical). These tests consist in measuring sinusoidal axial and lateral strains as well as sinusoidal axial stress, when sinusoidal axial loading is applied on the specimen. Different loading frequencies and temperatures are applied. Two complex moduli, EI ^{*} and E_{II}^{*}, and four complex Poisson's ratios, ν_{{II-I}}^{*}, ν_{{III-I}}^{*}, ν_{{I-II}}^{*} and ν_{{III-II}}^{*}, were obtained. The vertical direction appears softer than the other ones for the highest frequencies. There are very few differences between the two directions I and II for parameters concerning viscous effects (phase angles φ(EI) and φ(E_{II}), and shift factors). The four Poisson's ratios reveal anisotropic properties but rheological tensor can be considered as symmetric when considering very similar values obtained for the two measured parameters (I-II and II-I)
Viscoelastic properties of laryngeal posturing muscles
NASA Astrophysics Data System (ADS)
Alipour, Fariborz; Hunter, Eric; Titze, Ingo
2003-10-01
Viscoelastic properties of canine laryngeal muscles were measured in a series of in vitro experiments. Laryngeal posturing that controls vocal fold length and adduction/abduction is an essential component of the voice production. The dynamics of posturing depends on the viscoelastic and physiological properties of the laryngeal muscles. The time-dependent and nonlinear behaviors of these tissues are also crucial in the voice production and pitch control theories. The lack of information on some of these muscles such as posterior cricoarytenoid muscle (PCA), lateral cricoarytenoid muscle (LCA), and intraarytenoid muscle (IA) was the major incentive for this study. Samples of PCA and LCA muscles were made from canine larynges and mounted on a dual-servo system (Ergometer) as described in our previous works. Two sets of experiments were conducted on each muscle, a 1-Hz stretch and release experiment that provides stress-strain data and a stress relaxation test. Data from these muscles were fitted to viscoelastic models and Young's modulus and viscoelastic constants are obtained for each muscle. Preliminary data indicates that elastics properties of these muscles are similar to those of thyroarytenoid and cricothyroid muscles. The relaxation response of these muscles also shows some similarity to other laryngeal muscles in terms of time constants.
Chan, Roger W; Rodriguez, Maritza L
2008-08-01
Previous studies reporting the linear viscoelastic shear properties of the human vocal fold cover or mucosa have been based on torsional rheometry, with measurements limited to low audio frequencies, up to around 80 Hz. This paper describes the design and validation of a custom-built, controlled-strain, linear, simple-shear rheometer system capable of direct empirical measurements of viscoelastic shear properties at phonatory frequencies. A tissue specimen was subjected to simple shear between two parallel, rigid acrylic plates, with a linear motor creating a translational sinusoidal displacement of the specimen via the upper plate, and the lower plate transmitting the harmonic shear force resulting from the viscoelastic response of the specimen. The displacement of the specimen was measured by a linear variable differential transformer whereas the shear force was detected by a piezoelectric transducer. The frequency response characteristics of these system components were assessed by vibration experiments with accelerometers. Measurements of the viscoelastic shear moduli (G' and G") of a standard ANSI S2.21 polyurethane material and those of human vocal fold cover specimens were made, along with estimation of the system signal and noise levels. Preliminary results showed that the rheometer can provide valid and reliable rheometric data of vocal fold lamina propria specimens at frequencies of up to around 250 Hz, well into the phonatory range. PMID:18681608
Chan, Roger W.; Rodriguez, Maritza L.
2008-01-01
Previous studies reporting the linear viscoelastic shear properties of the human vocal fold cover or mucosa have been based on torsional rheometry, with measurements limited to low audio frequencies, up to around 80 Hz. This paper describes the design and validation of a custom-built, controlled-strain, linear, simple-shear rheometer system capable of direct empirical measurements of viscoelastic shear properties at phonatory frequencies. A tissue specimen was subjected to simple shear between two parallel, rigid acrylic plates, with a linear motor creating a translational sinusoidal displacement of the specimen via the upper plate, and the lower plate transmitting the harmonic shear force resulting from the viscoelastic response of the specimen. The displacement of the specimen was measured by a linear variable differential transformer whereas the shear force was detected by a piezoelectric transducer. The frequency response characteristics of these system components were assessed by vibration experiments with accelerometers. Measurements of the viscoelastic shear moduli (G′ and G″) of a standard ANSI S2.21 polyurethane material and those of human vocal fold cover specimens were made, along with estimation of the system signal and noise levels. Preliminary results showed that the rheometer can provide valid and reliable rheometric data of vocal fold lamina propria specimens at frequencies of up to around 250 Hz, well into the phonatory range. PMID:18681608
Linear viscoelastic behaviour of oil-in-water food emulsions stabilised by tuna-protein isolates.
Ruiz-Márquez, D; Partal, P; Franco, Jm; Gallegos, C
2013-02-01
This work deals with the manufacture of oil-in-water food emulsions stabilised by tuna proteins. The influence of protein and oil concentrations on the linear viscoelastic properties and microstructure of these emulsions was analysed. Stable emulsions with suitable linear viscoelastic response and microstructural characteristics were formulated with 70 wt.% oil and, at least, 0.25 wt.% tuna protein. Similarly, emulsions with oil concentrations between 45 and 70 wt.% were prepared using 0.50 wt.% protein. All these emulsions showed a predominantly elastic response in the linear viscoelastic region and a well-developed plateau region in its mechanical spectrum. Rheological and droplet size distribution results pointed out an extensive droplet flocculation, due to interactions among emulsifier molecules located at the oil-water interface of adjacent droplets. As a result, the linear viscoelastic behaviour was controlled by protein-protein interactions, allowing the use of the plateau modulus to successfully normalise both the storage and loss moduli as a function of frequency onto a master curve, irrespective of the selected emulsion formulation. PMID:23239763
Quasi-linear viscoelastic characterization of human hip ligaments.
Kemper, Andrew R; McNally, Craig; Smith, Byron; Duma, Stefan M
2007-01-01
The object of this study was to develop a quasi-linear viscoelastic model for the iliofemoral and ischiofemoral hip ligaments. In order to accomplish this, a total of 56 axial tension tests were performed on 8 bone-ligament-bone specimens prepared from 4 fresh frozen male cadavers. Each specimen went through a battery of 7 tests including a series of step-and-hold tests and load-and-unload ramp tests. The bone-ligament-bone specimens were situated so that the load from a servo-hydraulic Material Testing System would be applied on the long axis of each ligament. The reduced relaxation data was fit to a two exponential damping function while the instantaneous elastic response was fit to a power-law function. These two constituents were then combined to create a single constitutive equation for each ligament. The quasi-linear viscoelastic model presented in this study can be used to improve the biofidelity of computational models of the human hip. PMID:17487102
Viscoelastic properties of isolated collagen fibrils.
Shen, Zhilei Liu; Kahn, Harold; Ballarini, Roberto; Eppell, Steven J
2011-06-22
Understanding the viscoelastic behavior of collagenous tissues with complex hierarchical structures requires knowledge of the properties at each structural level. Whole tissues have been studied extensively, but less is known about the mechanical behavior at the submicron, fibrillar level. Using a microelectromechanical systems platform, in vitro coupled creep and stress relaxation tests were performed on collagen fibrils isolated from the sea cucumber dermis. Stress-strain-time data indicate that isolated fibrils exhibit viscoelastic behavior that could be fitted using the Maxwell-Weichert model. The fibrils showed an elastic modulus of 123 ± 46 MPa. The time-dependent behavior was well fit using the two-time-constant Maxwell-Weichert model with a fast time response of 7 ± 2 s and a slow time response of 102 ± 5 s. The fibrillar relaxation time was smaller than literature values for tissue-level relaxation time, suggesting that tissue relaxation is dominated by noncollagenous components (e.g., proteoglycans). Each specimen was tested three times, and the only statistically significant difference found was that the elastic modulus is larger in the first test than in the subsequent two tests, indicating that viscous properties of collagen fibrils are not sensitive to the history of previous tests.
Viscoelastic Properties of Isolated Collagen Fibrils
Shen, Zhilei Liu; Kahn, Harold; Ballarini, Roberto; Eppell, Steven J.
2011-01-01
Understanding the viscoelastic behavior of collagenous tissues with complex hierarchical structures requires knowledge of the properties at each structural level. Whole tissues have been studied extensively, but less is known about the mechanical behavior at the submicron, fibrillar level. Using a microelectromechanical systems platform, in vitro coupled creep and stress relaxation tests were performed on collagen fibrils isolated from the sea cucumber dermis. Stress-strain-time data indicate that isolated fibrils exhibit viscoelastic behavior that could be fitted using the Maxwell-Weichert model. The fibrils showed an elastic modulus of 123 ± 46 MPa. The time-dependent behavior was well fit using the two-time-constant Maxwell-Weichert model with a fast time response of 7 ± 2 s and a slow time response of 102 ± 5 s. The fibrillar relaxation time was smaller than literature values for tissue-level relaxation time, suggesting that tissue relaxation is dominated by noncollagenous components (e.g., proteoglycans). Each specimen was tested three times, and the only statistically significant difference found was that the elastic modulus is larger in the first test than in the subsequent two tests, indicating that viscous properties of collagen fibrils are not sensitive to the history of previous tests. PMID:21689535
Viscoelastic properties of actin-coated membranes
NASA Astrophysics Data System (ADS)
Helfer, E.; Harlepp, S.; Bourdieu, L.; Robert, J.; Mackintosh, F. C.; Chatenay, D.
2001-02-01
In living cells, cytoskeletal filaments interact with the plasma membrane to form structures that play a key role in cell shape and mechanical properties. To study the interaction between these basic components, we designed an in vitro self-assembled network of actin filaments attached to the outer surface of giant unilamellar vesicles. Optical tweezers and single-particle tracking experiments are used to study the rich dynamics of these actin-coated membranes (ACM). We show that microrheology studies can be carried out on such an individual microscopic object. The principle of the experiment consists in measuring the thermally excited position fluctuations of a probe bead attached biochemically to the membrane. We propose a model that relates the power spectrum of these thermal fluctuations to the viscoelastic properties of the membrane. The presence of the actin network modifies strongly the membrane dynamics with respect to a fluid, lipid bilayer one. It induces first a finite (ω=0) two-dimensional (2D) shear modulus G02D~0.5 to 5 μN/m in the membrane plane. Moreover, the frequency dependence at high frequency of the shear modulus [G'2D(f )~f0.85+/-0.07] and of the bending modulus (κACM(f)~f0.55+/-0.21) demonstrate the viscoelastic behavior of the composite membrane. These results are consistent with a common exponent of 0.75 for both moduli as expected from our model and from prior measurements on actin solutions.
Linear viscoelasticity of a polystyrene-polyisoprene bicontinuous microemulsion
NASA Astrophysics Data System (ADS)
Brinker, Kristin; Burghardt, Wesley
2004-03-01
Polymer bicontinuous microemulsions are disordered phases in which two immiscible homopolymers are emulsified by a diblock copolymer which stabilizes the interface between A-rich and B-rich domains. Many examples have been found in symmetric ternary A, B, A-B blends, in which the microemulsion phase is found between regimes of an ordered lamellar phase at high copolymer concentration and macroscopic 2- or 3-phase coexistence at low copolymer concentration. The convoluted, interpenetrating morphology of these phases and high specific interfacial area leads to complex viscoelastic behavior, even when the constituent homopolymers are essentially Newtonian. To date, only one such system (based on polyethylethylene-PDMS) has been subjected to extensive rheological investigation. Many of the interesting qualitative and quantitiative phenomena in this system were attributed to large viscosity mismatch between the homopolymers due to their difference in glass transition temperature. Here we consider a microemulsion system based on polystyrene and polyisoprene. This system should similarly exhibit large viscosity contrast, and thus serves as a model to investigate the universality of the phenomena previously documented. Rheology, optical microscopy and x-ray scattering have been used to map out the phase behavior in this system. Here we will report on linear viscoelastic data collected as a function of temperature in the microemulsion regime.
Viscoelastic properties of actin-coated membranes.
Helfer, E; Harlepp, S; Bourdieu, L; Robert, J; MacKintosh, F C; Chatenay, D
2001-02-01
In living cells, cytoskeletal filaments interact with the plasma membrane to form structures that play a key role in cell shape and mechanical properties. To study the interaction between these basic components, we designed an in vitro self-assembled network of actin filaments attached to the outer surface of giant unilamellar vesicles. Optical tweezers and single-particle tracking experiments are used to study the rich dynamics of these actin-coated membranes (ACM). We show that microrheology studies can be carried out on such an individual microscopic object. The principle of the experiment consists in measuring the thermally excited position fluctuations of a probe bead attached biochemically to the membrane. We propose a model that relates the power spectrum of these thermal fluctuations to the viscoelastic properties of the membrane. The presence of the actin network modifies strongly the membrane dynamics with respect to a fluid, lipid bilayer one. It induces first a finite (omega=0) two-dimensional (2D) shear modulus G(0)(2D) approximately 0.5 to 5 microN/m in the membrane plane. Moreover, the frequency dependence at high frequency of the shear modulus [G(')(2D)(f ) approximately f(0.85+/-0.07)] and of the bending modulus (kappa(ACM)(f) approximately f(0.55+/-0.21)) demonstrate the viscoelastic behavior of the composite membrane. These results are consistent with a common exponent of 0.75 for both moduli as expected from our model and from prior measurements on actin solutions.
Measurement of the linear viscoelastic behavior of antimisting kerosene
NASA Technical Reports Server (NTRS)
Ferry, J. D.
1983-01-01
Measurements of dynamic viscoelastic properties in very small oscillating shear deformations was made on solutions of a jet fuel, Jet A, containing an antimisting polymeric additive, FM-9. A few measurements were also made on solutions of FM-9 in a mixed solvent of mineral oil, Tetralin, and 0-terphenyl. Two samples of FM-9 had approximate number-average molecular weights of 12,000,000 and 8,100,000 as deduced from analysis of the measurements. The ranges of variables were 2.42 to 4.03 g/1 in concentration (0.3 to 0.5% by weight), 1 to 35 in temperature, 1.3 to 9.4 cp in solvent viscosity, and 103 to 6100 Hz in frequency. Measurements in the Jet A solvent were made both with and without a modifying carrier. The results were compared with the Zimm theory and the viscoelastic behavior was found to resemble rather closely that of ordinary non-polar polymers in theta solvents. The relation of the results to the antithixotropic behavior of such solutions a high shear rates is discussed in terms of intramolecular and intermolecular interactions.
Viscoelastic properties of mineralized alginate hydrogel beads.
Olderøy, Magnus O; Xie, Minli; Andreassen, Jens-Petter; Strand, Berit L; Zhang, Zhibing; Sikorski, Pawel
2012-07-01
Alginate hydrogels have applications in biomedicine, ranging from delivery of cells and growth factors to wound management aids. However, they are mechanically soft and have shown little potential for the use in bone tissue engineering. Here, the viscoelastic properties of alginate hydrogel beads mineralized with calcium phosphate, both by a counter-diffusion (CD) and an enzymatic approach, are characterized by a micro-manipulation technique and mathematical modeling. Fabricated hydrogel materials have low mineral content (below 3 % of the total hydrogel mass, which corresponds to mineral content of up to 60 % of the dry mass) and low dry mass content (<5 %). For all samples compression and hold (relaxation after compression) data was collected and analyzed. The apparent Young's modulus of the mineralized beads was estimated by the Hertz model (compression data) and was shown to increase up to threefold upon mineralization. The enzymatically mineralized beads showed higher apparent Young's modulus compared to the ones mineralized by CD, even though the mineral content of the former was lower. Full compression-relaxation force-time profiles were analyzed using viscoelastic model. From this analysis, infinite and instantaneous Young's moduli were determined. Similarly, enzymatic mineralized beads, showed higher instantaneous and infinite Young's modulus, even if the degree of mineralization is lower then that achieved for CD method. This leads to the conclusion that both the degree of mineralization and the spatial distribution of mineral are important for the mechanical performance of the composite beads, which is in analogy to highly structured mineralized tissues found in many organisms.
Interconversion of linearly viscoelastic material functions expressed as Prony series: a closure
NASA Astrophysics Data System (ADS)
Luk-Cyr, Jacques; Crochon, Thibaut; Li, Chun; Lévesque, Martin
2013-02-01
Interconversion of viscoelastic material functions is a longstanding problem that has received attention since the 1950s. There is currently no accepted methodology for interconverting viscoelastic material functions due to the lack of stability and accuracy of the existing methods. This paper presents a new exact, analytical interconversion method for linearly viscoelastic material functions expressed as Prony series. The new algorithm relies on the equations of the thermodynamics of irreversible processes used for defining linearly viscoelastic constitutive theories. As a result, interconversion is made possible for unidimensional and tridimensional materials for arbitrary material symmetry. The algorithm has been tested over a broad range of cases and was found to deliver accurate interconversion in all cases. Based on its accuracy and stability, the authors believe that their algorithm provides a closure to the interconversion of linearly viscoelastic constitutive theories expressed with Prony series.
NASA Astrophysics Data System (ADS)
Musa, A. B.
2015-05-01
The study is about impact of a short elastic rod (or slug) on a stationary semi-infinite viscoelastic rod. The viscoelastic materials are modeled as standard linear solid which involve three material parameters and the motion is treated as one-dimensional. We first establish the governing equations pertaining to the impact of viscoelastic materials subject to certain boundary conditions for the case when an elastic slug moving at a speed V impacts a semi-infinite stationary viscoelastic rod. The objective is to validate the numerical results of stresses and velocities at the interface following wave transmissions and reflections in the slug after the impact using viscoelastic discontinuity. If the stress at the interface becomes tensile and the velocity changes its sign, then the slug and the rod part company. If the stress at the interface is compressive after the impact, the slug and the rod remain in contact. After modelling the impact and solve the governing system of partial differential equations in the Laplace transform domain, we invert the Laplace transformed solution numerically to obtain the stresses and velocities at the interface for several viscosity time constants and ratios of acoustic impedances. In inverting the Laplace transformed equations, we used the complex inversion formula because there is a branch cut and infinitely many poles within the Bromwich contour. In the viscoelastic discontinuity analysis, we look at the moving discontinuities in stress and velocity using the impulse-momentum relation and kinematical condition of compatibility. Finally, we discussed the relationship of the stresses and velocities using numeric and the validated stresses and velocities using viscoelastic discontinuity analysis.
Evaluating the Viscoelastic Properties of Tissue from Laser Speckle Fluctuations
Hajjarian, Zeinab; Nadkarni, Seemantini K.
2012-01-01
Most pathological conditions such as atherosclerosis, cancer, neurodegenerative, and orthopedic disorders are accompanied with alterations in tissue viscoelasticity. Laser Speckle Rheology (LSR) is a novel optical technology that provides the invaluable potential for mechanical assessment of tissue in situ. In LSR, the specimen is illuminated with coherent light and the time constant of speckle fluctuations, τ, is measured using a high speed camera. Prior work indicates that τ is closely correlated with tissue microstructure and composition. Here, we investigate the relationship between LSR measurements of τ and sample mechanical properties defined by the viscoelastic modulus, G*. Phantoms and tissue samples over a broad range of viscoelastic properties are evaluated using LSR and conventional mechanical testing. Results demonstrate a strong correlation between τ and |G*| for both phantom (r = 0.79, p <0.0001) and tissue (r = 0.88, p<0.0001) specimens, establishing the unique capability of LSR in characterizing tissue viscoelasticity. PMID:22428085
Constitutive modeling of the aging viscoelastic properties of portland cement paste
NASA Astrophysics Data System (ADS)
Grasley, Zachary C.; Lange, David A.
2007-12-01
Analytical approaches for modeling aging viscoelastic behavior of concrete include the time-shift approach (analogous to time-temperature superposition), the solidification theory, and the dissolution-precipitation approach. The aging viscoelastic properties of concrete are generally attributed solely to the cement paste phase since the aggregates are typically linear elastic. In this study, the aging viscoelastic behavior of four different cement pastes has been measured and modeled according to both the time-shift approach and the solidification theory. The inability of each individual model to fully characterize the aging viscoelastic response of the materials provides insight into the mechanisms for aging of the viscoelastic properties of cement paste and concrete. A model that considers aging due to solidification in combination with inherent aging of the cement paste gel (modeled using the time-shift approach) more accurately predicted the aging viscoelastic behavior of portland cement paste than either the solidification or time-shift approaches independently. The results provide evidence that solidification and other intrinsic gel aging mechanisms are concurrently active in the aging process of cementitious materials.
Linear viscoelastic limits of asphalt concrete at low and intermediate temperatures
NASA Astrophysics Data System (ADS)
Mehta, Yusuf A.
valid for mixtures similar to the ones tested in this study. Different envelopes should be used in the case of mixtures containing a very soft or a very stiff polymer modified binder. At 4°C, the typical values of stresses and material properties of mixtures fell within the linear viscoelastic region, considering the typical shear creep compliance values at loading times and stresses experienced in the field. However, typical values at 20°C fell within a region in which some, but not all of the mixtures tested in this study behaved linearly. It is known that the behavior of asphalt concrete mixture changes from linear to nonlinear, depending on the temperature and loading conditions. However, this study is the first of its kind in which both the proportionality and the superposition condition were evaluated. The experimental design and the analysis procedures presented in this study can be applied to similar experiments that may be conducted in the future to evaluate linearity of different types of asphalt concrete mixtures.
Analyzing and improving viscoelastic properties of high density polyethylene
NASA Astrophysics Data System (ADS)
Ahmed, Reaj Uddin
2011-12-01
High Density Polyethylene (HDPE) is closely packed, less branched polyethylene having higher mechanical properties, chemical resistance, and heat resistance than Low Density Polyentylene (LDPE). Better properties and cost effectiveness make it an important raw material over LDPE in packaging industries. Stacked containers made of HDPE experience static loading and deformation strain during their storage period in a warehouse. As HDPE is a viscoelastic material, dimensional stability of stacked HDPE containers depends on time dependent properties such as creep and stress relaxation. Now, light weighting is a driving force in packaging industries, which results in lower production costs but performance of the product becomes a challenge. Proper understanding of the viscoelastic properties of HDPE, with relevant FE simulation can facilitate improved designs. This research involves understanding and improving viscoelastic properties, creep behavior, and stress relaxation of HDPE. Different approaches were carried out to meet the objectives. Organic filler CaCO3 was added to HDPE at increasing weight fractions and corresponding property changes were investigated. Annealing heat treatments were also carried out for potential property improvements. The effect of ageing was also investigated on both annealed and non annealed HDPE. The related performance of different water bottles against squeeze pressure was also characterized. Both approaches, incorporation of CaCO3 and annealing, showed improvements in the properties of HDPE over neat HDPE. This research aids finding the optimum solution for improving viscoelastic properties, stress relaxation, and creep behavior of HDPE in manufacturing.
Lundkvist, A.; Lilleodden, E.; Sickhaus, W.; Kinney, J.; Pruitt, L.; Balooch, M.
1998-02-09
Using an Atomic Force Microscope with an attachment for indentation, we have measured local, in vitro mechanical properties of healthy femoral artery tissue held in saline solution. The elastic modulus (34. 3 kPa) and viscoelastic response ({tau}sub{epsilon} {equals} 16.9 s and {tau}sub{sigma} {equals} 29.3 s) of the unstretched,intimal vessel wall have been determined using Sneddon theory and a three element model(standard linear solid) for viscoelastic materials. The procedures necessary to employ the indenting attachment to detect elastic moduli in the kPa range in liquid are described.
Viscoelastic properties of high solids softwood kraft black liquors
Zaman, A.A.; Fricke, A.L. . Dept. of Chemical Engineering)
1995-01-01
The linear viscoelastic functions of several softwood slash pine kraft black liquors from a two level, four variable factorially designed pulping experiment were determined for solids concentrations from 65% to 81% and temperatures from 40 to 85 C. At high solids and lower temperatures, black liquors behave like un-cross-linked polymers.The exact level of dynamic viscosity and storage modulus at any given condition is dependent upon the solids composition which will vary from liquor to liquor. The linear viscoelastic functions were described using Cross and Carreau-Yasuda models. Superposition principles developed for polymer melts and concentrated polymer solutions were applied to obtain reduced correlations for dynamic viscosity and storage modulus. The data for dynamic viscosity were shifted over the whole range of temperature, solids concentrations, and frequency, and a single curve for dynamic viscosity behavior of every liquor was obtained. The data for storage modulus did not superimpose into a single curve for the effects of solids concentration. The reduced correlations were used to estimate the viscoelasticity of the liquors near normal firing conditions and found that black liquors will not have any problem in droplet formation for concentrations up to 81% solids and temperatures above 120 C. The viscometric and linear viscoelastic functions of black liquors were compared (Cox-Merz rule), and it was shown that at sufficiently low shear rates and frequencies both shear viscosity and the magnitude of the complex viscosity approach zero shear rate viscosity.
On the modal decoupling of linear mechanical systems with frequency-dependent viscoelastic behavior
NASA Astrophysics Data System (ADS)
Mastroddi, Franco; Calore, Paolo
2016-03-01
Linear Multi-Degree of Freedom (MDOF) mechanical systems having frequency-dependent viscoelastic behaviors are often studied and modelled in frequency or Laplace domains. Indeed, once this modelling process is carried out, it is not generally possible to reduce the obtained MDOF damped mechanical system to a set of uncoupled damped modal oscillators apart from some special cases. In this paper a general procedure has been proposed to transform a coupled linear mechanical system having frequency-dependent viscoelastic characteristics to a set of independent damped modal oscillators. The procedure is based on a linear co-ordinate transformation procedure using matrices in real field only. The approach is exact and based on the solution of one associated eigenproblem for the case of linearly viscous damping. In the general case of frequency-dependent viscoelastic materials, the approach includes an iterative procedure solving local eigenproblems.Some numerical results are reported to show the capabilities of the proposed approach.
Valdez-Jasso, Daniela; Bia, Daniel; Zócalo, Yanina; Armentano, Ricardo L.; Haider, Mansoor A.; Olufsen, Mette S.
2013-01-01
A better understanding of the biomechanical properties of the arterial wall provides important insight into arterial vascular biology under normal (healthy) and pathological conditions. This insight has potential to improve tracking of disease progression and to aid in vascular graft design and implementation. In this study, we use linear and nonlinear viscoelastic models to predict biomechanical properties of the thoracic descending aorta and the carotid artery under ex vivo and in vivo conditions in ovine and human arteries. Models analyzed include a four-parameter (linear) Kelvin viscoelastic model and two five-parameter nonlinear viscoelastic models (an arctangent and a sigmoid model) that relate changes in arterial blood pressure to the vessel cross-sectional area (via estimation of vessel strain). These models were developed using the framework of Quasilinear Viscoelasticity (QLV) theory and were validated using measurements from the thoracic descending aorta and the carotid artery obtained from human and ovine arteries. In vivo measurements were obtained from ten ovine aortas and ten human carotid arteries. Ex vivo measurements (from both locations) were made in eleven male Merino sheep. Biomechanical properties were obtained through constrained estimation of model parameters. To further investigate the parameter estimates we computed standard errors and confidence intervals and we used analysis of variance to compare results within and between groups. Overall, our results indicate that optimal model selection depends on the arterial type. Results showed that for the thoracic descending aorta (under both experimental conditions) the best predictions were obtained with the nonlinear sigmoid model, while under healthy physiological pressure loading the carotid arteries nonlinear stiffening with increasing pressure is negligible, and consequently, the linear (Kelvin) viscoelastic model better describes the pressure-area dynamics in this vessel. Results
Hohne, Danial N; Younger, John G; Solomon, Michael J
2009-07-01
We introduce a flexible microfluidic device to characterize the mechanical properties of soft viscoelastic solids such as bacterial biofilms. In the device, stress is imposed on a test specimen by the application of a fixed pressure to a thin, flexible poly(dimethyl siloxane) (PDMS) membrane that is in contact with the specimen. The stress is applied by pressurizing a microfabricated air channel located above the test area. The strain resulting from the applied stress is quantified by measuring the membrane deflection with a confocal laser scanning microscope. The deflection is governed by the viscoelastic properties of the PDMS membrane and of the test specimen. The relative contributions of the membrane and test material to the measured deformation are quantified by comparing a finite element analysis with an independent (control) measurement of the PDMS membrane mechanical properties. The flexible microfluidic rheometer was used to characterize both the steady-state elastic modulus and the transient strain recoil of two soft materials: gellan gums and bacterial biofilms. The measured linear elastic moduli and viscoelastic relaxation times of gellan gum solutions were in good agreement with the results of conventional mechanical rheometry. The linear Young's moduli of biofilms of Staphylococcus epidermidis and Klebsiella pneumoniae, which could not be measured using conventional methods, were found to be 3.2 and 1.1 kPa, respectively, and the relaxation time of the S. epidermidis biofilm was 13.8 s. Additionally, strain hardening was observed in all the biofilms studied. Finally, design parameters and detection limits of the method show that the device is capable of characterizing soft viscoelastic solids with elastic moduli in the range of 102-105 Pa. The flexible microfluidic rheometer addresses the need for mechanical property characterization of soft viscoelastic solids common in fields such as biomaterials, food, and consumer products. It requires only 200 p
Hohne, Danial N.; Younger, John G.; Solomon, Michael J.
2009-01-01
We introduce a flexible microfluidic device to characterize the mechanical properties of soft viscoelastic solids such as bacterial biofilms. In the device, stress is imposed on a test specimen by application of a fixed pressure to a thin, flexible poly(dimethyl siloxane) (PDMS) membrane that is in contact with the specimen. The stress is applied by pressurizing a microfabricated air channel located above the test area. The strain resulting from the applied stress is quantified by measuring the membrane deflection with a confocal laser-scanning microscope. The deflection is governed by the viscoelastic properties of the PDMS membrane and of the test specimen. The relative contributions of the membrane and test material to the measured deformation are quantified by comparing a finite element analysis and an independent (control) measurement of the PDMS membrane mechanical properties. The flexible microfluidic rheometer was used to characterize both the steady-state elastic modulus and transient strain recoil of two soft materials: gellan gums and bacterial biofilms. The measured linear elastic moduli and viscoelastic relaxation times of gellan gum solutions were in good agreement with the results of conventional mechanical rheometry. The linear Young’s moduli of biofilms of Staphylococcus epidermidis and Klebsiella pneumoniae, which could not be measured using conventional methods, were found to be 3.2 kPa and 1.1 kPa, respectively, and the relaxation time of the S. epidermidis biofilm was 13.8 s. Additionally, strain hardening was observed in all the biofilms studied. Finally, design parameters and detection limits of the method show that the device is capable of characterizing soft viscoelastic solids with elastic moduli in the range of 102 – 105 Pa. The flexible microfluidic rheometer addresses a need for mechanical property characterization of soft viscoelastic solids common in fields such as biomaterials, food and consumer products. It requires only ~ 200 p
Hohne, Danial N; Younger, John G; Solomon, Michael J
2009-07-01
We introduce a flexible microfluidic device to characterize the mechanical properties of soft viscoelastic solids such as bacterial biofilms. In the device, stress is imposed on a test specimen by the application of a fixed pressure to a thin, flexible poly(dimethyl siloxane) (PDMS) membrane that is in contact with the specimen. The stress is applied by pressurizing a microfabricated air channel located above the test area. The strain resulting from the applied stress is quantified by measuring the membrane deflection with a confocal laser scanning microscope. The deflection is governed by the viscoelastic properties of the PDMS membrane and of the test specimen. The relative contributions of the membrane and test material to the measured deformation are quantified by comparing a finite element analysis with an independent (control) measurement of the PDMS membrane mechanical properties. The flexible microfluidic rheometer was used to characterize both the steady-state elastic modulus and the transient strain recoil of two soft materials: gellan gums and bacterial biofilms. The measured linear elastic moduli and viscoelastic relaxation times of gellan gum solutions were in good agreement with the results of conventional mechanical rheometry. The linear Young's moduli of biofilms of Staphylococcus epidermidis and Klebsiella pneumoniae, which could not be measured using conventional methods, were found to be 3.2 and 1.1 kPa, respectively, and the relaxation time of the S. epidermidis biofilm was 13.8 s. Additionally, strain hardening was observed in all the biofilms studied. Finally, design parameters and detection limits of the method show that the device is capable of characterizing soft viscoelastic solids with elastic moduli in the range of 102-105 Pa. The flexible microfluidic rheometer addresses the need for mechanical property characterization of soft viscoelastic solids common in fields such as biomaterials, food, and consumer products. It requires only 200 p
Fractional characteristic times and dissipated energy in fractional linear viscoelasticity
NASA Astrophysics Data System (ADS)
Colinas-Armijo, Natalia; Di Paola, Mario; Pinnola, Francesco P.
2016-08-01
In fractional viscoelasticity the stress-strain relation is a differential equation with non-integer operators (derivative or integral). Such constitutive law is able to describe the mechanical behavior of several materials, but when fractional operators appear, the elastic and the viscous contribution are inseparable and the characteristic times (relaxation and retardation time) cannot be defined. This paper aims to provide an approach to separate the elastic and the viscous phase in the fractional stress-strain relation with the aid of an equivalent classical model (Kelvin-Voigt or Maxwell). For such equivalent model the parameters are selected by an optimization procedure. Once the parameters of the equivalent model are defined, characteristic times of fractional viscoelasticity are readily defined as ratio between viscosity and stiffness. In the numerical applications, three kinds of different excitations are considered, that is, harmonic, periodic, and pseudo-stochastic. It is shown that, for any periodic excitation, the equivalent models have some important features: (i) the dissipated energy per cycle at steady-state coincides with the Staverman-Schwarzl formulation of the fractional model, (ii) the elastic and the viscous coefficients of the equivalent model are strictly related to the storage and the loss modulus, respectively.
The analytical representation of viscoelastic material properties using optimization techniques
NASA Astrophysics Data System (ADS)
Hill, S. A.
1993-02-01
This report presents a technique to model viscoelastic material properties with a function of the form of the Prony series. Generally, the method employed to determine the function constants requires assuming values for the exponential constants of the function and then resolving the remaining constants through linear least-squares techniques. The technique presented here allows all the constants to be analytically determined through optimization techniques. This technique is employed in a computer program named PRONY and makes use of commercially available optimization tool developed by VMA Engineering, Inc. The PRONY program was utilized to compare the technique against previously determined models for solid rocket motor TP-H1148 propellant and V747-75 Viton fluoroelastomer. In both cases, the optimization technique generated functions that modeled the test data with at least an order of magnitude better correlation. This technique has demonstrated the capability to use small or large data sets and to use data sets that have uniformly or nonuniformly spaced data pairs. The reduction of experimental data to accurate mathematical models is a vital part of most scientific and engineering research. This technique of regression through optimization can be applied to other mathematical models that are difficult to fit to experimental data through traditional regression techniques.
Viscoelastic and optical properties of four different PDMS polymers
NASA Astrophysics Data System (ADS)
Deguchi, Shinji; Hotta, Junya; Yokoyama, Sho; Matsui, Tsubasa S.
2015-09-01
Polydimethylsiloxane (PDMS) is the most commonly used silicone elastomer with a wide range of applications including microfluidics and microcontact printing. Various types of PDMS are currently available, and their bulk material properties have been extensively investigated. However, because the properties are rarely compared in a single study, it is often unclear whether the large disparity of the reported data is attributable to the difference in methodology or to their intrinsic characteristics. Here we report on viscoelastic properties and optical properties of four different PDMS polymers, i.e. Sylgard-184, CY52-276, SIM-360, and KE-1606. Our results show that all the PDMSs are highly elastic rather than viscoelastic at the standard base/curing agent ratios, and their quantified elastic modulus, refractive index, and optical cleanness are similar but distinct in magnitude.
A new device for measuring the viscoelastic properties of hydrated matrix gels.
Parsons, Jeffrey W; Coger, Robin N
2002-04-01
Determinations of the viscoelastic properties of extracellular matrices (ECMs) are becoming increasingly important for accurate predictive modeling of biological systems. Since the interactions of the cells with the ECM and surrounding fluid (e.g., blood, media) each affect cell behavior; it is advantageous to evaluate the ECM's material properties in the presence of the hydrating fluid. Conventional rheometry methods evaluate the bulk material properties of gel materials while displacing the hydrating liquid film. Such systems are therefore nonideal for testing materials such as ECMs, whose properties change with dehydration. The new patent pending, piezoelectrically actuated linear rheometer is designed to eliminate this problem. It uses a single cantilever to apply an oscillating load to the gel and to sense the gel's deflection. Composed of two thin film piezopolymer layers, the cantilever uses one layer as the actuator, and the second piezopolymer layer to measure the lateral movement of its attached probe. The viscoelastic nature of the ECM adds stiffness and damping to the system, resulting in the attenuation and phase shift of the sensor's output voltage. From these parameters, the ECM's shear storage and loss moduli are then determined. Initial tests on the BioMatrix I and type I collagen ECMs reveal that the first prototype of the piezoelectrically actuated linear rheometer is capable of accurately determining the trend and order of magnitude of an ECM's viscoelastic properties. In this paper, details of the rheometer's design and operating principles are described. PMID:12002123
Vibration of visco-elastic rectangular plate with linearly thickness variations in both directions
NASA Astrophysics Data System (ADS)
Gupta, A. K.; Khanna, A.
2007-04-01
The analysis presented here is to study the effect of linear thickness variations in both directions on vibration of visco-elastic rectangular plate having clamped boundary conditions on all the four edges. Using the separation of variables method, the governing differential equation has been solved for vibration of visco-elastic rectangular plate. An approximate but quite convenient frequency equation is derived by using Rayleigh-Ritz technique with a two-term deflection function. Logarithmic decrement, time period and deflection at different points for the first two modes of vibration are calculated for various values of taper constants and aspect ratio.
Non-linear dynamics of viscoelastic liquid trilayers subjected to an electric field
NASA Astrophysics Data System (ADS)
Karapetsas, George; Bontozoglou, Vasilis
2014-11-01
The scope of this work is to investigate the non-linear dynamics of the electro-hydrodynamic instability of a trilayer of immiscible liquids. We consider the case of a polymer film which is separated from the top electrode by two viscous fluids. We develop a computational model and carry out 2D numerical simulations fully accounting for the flow and electric field in all phases. For the numerical solution of the governing equations we employ the mixed finite element method combined with a quasi-elliptic mesh generation scheme which is capable of following the large deformations of the liquid-liquid interface. We model the viscoelastic behavior using the Phan-Thien and Tanner (PTT) constitutive equation taking fully into account the non-linear elastic effects as well as a varying shear and extensional viscosity. We perform a thorough parametric study and investigate the influence of the electric properties of fluids, applied voltage and various rheological parameters. The authors acknowledge the support by the General Secretariat of Research and Technology of Greece under the action ``Supporting Postdoctoral Researchers'' (Grant Number PE8/906), co-funded by the European Social Fund and National Resources.
Dynamic viscoelastic properties of vinyl polysiloxane denture soft lining materials.
Abe, Y; Taji, T; Hiasa, K; Tsuga, K; Akagawa, Y
2009-12-01
The aim of this study was to investigate the dynamic viscoelastic properties of seven commercially available vinyl polysiloxane denture soft lining materials. Five rectangular specimens (2 x 10 x 30 mm) were prepared from each material. The complex modulus E* (MPa) and loss tangent (tan delta) of each specimen were determined with a non-resonance forced vibration method using an automatic dynamic viscoelastometer at 1 Hz after 1 day of dry storage, and after 1, 30, 60, 90 and 180 days of wet storage at 37 degrees C. All data were analysed using one-way anova and Bonferroni/Dunn's test for multiple comparisons with a significance level of P < 0.01. All materials varied widely in terms of viscoelasticities and showed both an increase in E* and a decrease in tan delta at 1 Hz after the 1-day wet storage. After 60 days of wet storage, both E* and tan delta did not change significantly. The stiffer materials (>30% filler content) with high E* values (>2.00 MPa) showed elastic behaviour with tan delta values of around 0.03. The softer materials (6% filler content) with high tan delta values (initial value > 0.10) showed viscous behaviour and were easily affected by water absorption after the 1-day wet storage. It can be concluded that for the proper selection of vinyl polysiloxane denture soft lining materials, it is very important to evaluate the viscoelastic properties after 60 days of wet storage. PMID:19840358
Teller, Sean S; Farran, Alexandra J E; Xiao, Longxi; Jiao, Tong; Duncan, Randall L; Clifton, Rodney J; Jia, Xinqiao
2012-10-01
The biomechanical function of the vocal folds (VFs) depends on their viscoelastic properties. Many conditions can lead to VF scarring that compromises voice function and quality. To identify candidate replacement materials, the structure, composition, and mechanical properties of native tissues need to be understood at phonation frequencies. Previously, the authors developed the torsional wave experiment (TWE), a stress-wave-based experiment to determine the linear viscoelastic shear properties of small, soft samples. Here, the viscoelastic properties of porcine and human VFs were measured over a frequency range of 10-200 Hz. The TWE utilizes resonance phenomena to determine viscoelastic properties; therefore, the specimen test frequency is determined by the sample size and material properties. Viscoelastic moduli are reported at resonance frequencies. Structure and composition of the tissues were determined by histology and immunochemistry. Porcine data from the TWE are separated into two groups: a young group, consisting of fetal and newborn pigs, and an adult group, consisting of 6-9-month olds and 2+-year olds. Adult tissues had an average storage modulus of 2309±1394 Pa and a loss tangent of 0.38±0.10 at frequencies of 36-200 Hz. The VFs of young pigs were significantly more compliant, with a storage modulus of 394±142 Pa and a loss tangent of 0.40±0.14 between 14 and 30 Hz. No gender dependence was observed. Histological staining showed that adult porcine tissues had a more organized, layered structure than the fetal tissues, with a thicker epithelium and a more structured lamina propria. Elastin fibers in fetal VF tissues were immature compared to those in adult tissues. Together, these structural changes in the tissues most likely contributed to the change in viscoelastic properties. Adult human VF tissues, recovered postmortem from adult patients with a history of smoking or disease, had an average storage modulus of 756±439 Pa and a loss tangent of 0
Commisso, Maria S; Martínez-Reina, Javier; Mayo, Juana; Domínguez, Jaime
2013-02-01
The main objectives of this work are: (a) to introduce an algorithm for adjusting the quasi-linear viscoelastic model to fit a material using a stress relaxation test and (b) to validate a protocol for performing such tests in temporomandibular joint discs. This algorithm is intended for fitting the Prony series coefficients and the hyperelastic constants of the quasi-linear viscoelastic model by considering that the relaxation test is performed with an initial ramp loading at a certain rate. This algorithm was validated before being applied to achieve the second objective. Generally, the complete three-dimensional formulation of the quasi-linear viscoelastic model is very complex. Therefore, it is necessary to design an experimental test to ensure a simple stress state, such as uniaxial compression to facilitate obtaining the viscoelastic properties. This work provides some recommendations about the experimental setup, which are important to follow, as an inadequate setup could produce a stress state far from uniaxial, thus, distorting the material constants determined from the experiment. The test considered is a stress relaxation test using unconfined compression performed in cylindrical specimens extracted from temporomandibular joint discs. To validate the experimental protocol, the test was numerically simulated using finite-element modelling. The disc was arbitrarily assigned a set of quasi-linear viscoelastic constants (c1) in the finite-element model. Another set of constants (c2) was obtained by fitting the results of the simulated test with the proposed algorithm. The deviation of constants c2 from constants c1 measures how far the stresses are from the uniaxial state. The effects of the following features of the experimental setup on this deviation have been analysed: (a) the friction coefficient between the compression plates and the specimen (which should be as low as possible); (b) the portion of the specimen glued to the compression plates (smaller
Relationships between tissue composition and viscoelastic properties in human trabecular bone.
Ojanen, X; Isaksson, H; Töyräs, J; Turunen, M J; Malo, M K H; Halvari, A; Jurvelin, J S
2015-01-21
Trabecular bone is a metabolically active tissue with a high surface to volume ratio. It exhibits viscoelastic properties that may change during aging. Changes in bone properties due to altered metabolism are sensitively revealed in trabecular bone. However, the relationships between material composition and viscoelastic properties of bone, and their changes during aging have not yet been elucidated. In this study, trabecular bone samples from the femoral neck of male cadavers (n=21) aged 17-82 years were collected and the tissue level composition and its associations with the tissue viscoelastic properties were evaluated by using Raman microspectroscopy and nanoindentation, respectively. For composition, collagen content, mineralization, carbonate substitution and mineral crystallinity were evaluated. The calculated mechanical properties included reduced modulus (Er), hardness (H) and the creep parameters (E1, E2, η1and η2), as obtained by fitting the experimental data to the Burgers model. The results indicated that the creep parameters, E1, E2, η1and η2, were linearly correlated with mineral crystallinity (r=0.769-0.924, p<0.001). Creep time constant (η2/E2) tended to increase with crystallinity (r=0.422, p=0.057). With age, the mineralization decreased (r=-0.587, p=0.005) while the carbonate substitution increased (r=0.728, p<0.001). Age showed no significant associations with nanoindentation parameters. The present findings suggest that, at the tissue-level, the viscoelastic properties of trabecular bone are related to the changes in characteristics of bone mineral. This association may be independent of human age.
Characterization of Viscoelastic Properties of Polymeric Materials Through Nanoindentation
NASA Technical Reports Server (NTRS)
Odegard, G. M.; Bandorawalla, T.; Herring, H. M.; Gates, T. S.
2003-01-01
Nanoindentation is used to determine the dynamic viscoelastic properties of six polymer materials. It is shown that varying the harmonic frequency of the nanoindentation does not have any significant effect on the measured storage and loss moduli of the polymers. Agreement is found between these results and data from DMA testing of the same materials. Varying the harmonic amplitude of the nanoindentation does not have a significant effect on the measured properties of the high performance resins, however, the storage modulus of the polyethylene decreases as the harmonic amplitude increases. Measured storage and loss moduli are also shown to depend on the density of the polyethylene.
Zheng, Y P; Mak, A F
1999-06-01
A manual indentation protocol was established to assess the quasi-linear viscoelastic (QLV) properties of lower limb soft tissues. The QLV parameters were extracted using a curve-fitting procedure on the experimental indentation data. The load-indentation responses were obtained using an ultrasound indentation apparatus with a hand-held pen-sized probe. Limb soft tissues at four sites of eight normal young subjects were tested in three body postures. Four QLV model parameters were extracted from the experimental data. The initial modulus E0 ranged from 0.22 kPa to 58.4 kPa. The nonlinear factor E1 ranged from 21.7 kPa to 547 kPa. The time constant tau ranged from 0.05 s to 8.93 s. The time-dependent materials parameter alpha ranged from 0.029 to 0.277. Large variations of the parameters were noted among subjects, sites, and postures.
Cortes, Daniel H; Suydam, Stephen M; Silbernagel, Karin Grävare; Buchanan, Thomas S; Elliott, Dawn M
2015-06-01
Viscoelastic mechanical properties are frequently altered after tendon injuries and during recovery. Therefore, non-invasive measurements of shear viscoelastic properties may help evaluate tendon recovery and compare the effectiveness of different therapies. The objectives of this study were to describe an elastography method for measuring localized viscoelastic properties of tendons and to discuss the initial results in healthy and injured human Achilles and semitendinosus tendons. The technique used an external actuator to generate the shear waves in the tendon at different frequencies and plane wave imaging to measure shear wave displacements. For each of the excitation frequencies, maps of direction-specific wave speeds were calculated using local frequency estimation. Maps of viscoelastic properties were obtained using a pixel-wise curve fit of wave speed and frequency. The method was validated by comparing measurements of wave speed in agarose gels with those obtained using magnetic resonance elastography. Measurements in human healthy Achilles tendons revealed a pronounced increase in wave speed as a function of frequency, which highlights the importance of tendon viscoelasticity. Additionally, the viscoelastic properties of the Achilles tendon were larger than those reported for other tissues. Measurements in a tendinopathic Achilles tendon indicated that it is feasible to quantify local viscoelastic properties. Similarly, measurement in the semitendinosus tendon revealed substantial differences in viscoelastic properties between the healthy and contralateral tendons. Consequently, this technique has the potential to evaluate localized changes in tendon viscoelastic properties caused by injury and during recovery in a clinical setting.
Age-dependence of intracranial viscoelastic properties in living rats.
Shulyakov, Alexander V; Cenkowski, Stefan S; Buist, Richard J; Del Bigio, Marc R
2011-04-01
To explore the effect of maturation on intracranial mechanical properties, viscoelastic parameters were determined in 44 live rats at ages 1-2, 10-12, 21, 56-70, and 180 days using instrumented indentation. With the dura mater intact, the apparent modulus of elasticity, the indentation modulus, and viscous behavior were measured in vivo, as well as 1 h after death. In a separate group of 25 rats, brain water, and protein content were determined. A significant increase of the elastic and indentation moduli beginning at 10-12 days after birth and continuing to 180 days was observed. The creep behavior decreased in the postnatal period and stabilized at 21 days. Changes in intracranial biomechanical properties corresponded to a gradual decrease of brain water, and an increase in total protein content, including glial fibrillary acidic protein, myelin basic protein, and neurofilament light chain. Elastic properties were not significantly different comparing the live and dead states. However, there were significant postmortem changes in viscous behavior. Viscoelastic properties of living rat intracranial contents are shown to be age dependent, reflecting the physical and biochemical changes during postnatal development. This may be important for understanding why young and mature brains respond differently in situations of brain trauma and hydrocephalus.
NASA Astrophysics Data System (ADS)
Chakraborty, Debadi; Sader, John E.
2015-05-01
Simple bulk liquids such as water are commonly assumed to be Newtonian. While this assumption holds widely, the fluid-structure interaction of mechanical devices at nanometer scales can probe the intrinsic molecular relaxation processes in a surrounding liquid. This was recently demonstrated through measurement of the high frequency (20 GHz) linear mechanical vibrations of bipyramidal nanoparticles in simple liquids [Pelton et al., "Viscoelastic flows in simple liquids generated by vibrating nanostructures," Phys. Rev. Lett. 111, 244502 (2013)]. In this article, we review and critically assess the available constitutive equations for compressible viscoelastic flows in their linear limits—such models are required for analysis of the above-mentioned measurements. We show that previous models, with the exception of a very recent proposal, do not reproduce the required response at high frequency. We explain the physical origin of this recent model and show that it recovers all required features of a linear viscoelastic flow. This constitutive equation thus provides a rigorous foundation for the analysis of vibrating nanostructures in simple liquids. The utility of this model is demonstrated by solving the fluid-structure interaction of two common problems: (1) a sphere executing radial oscillations in liquid, which depends strongly on the liquid compressibility and (2) the extensional mode vibration of bipyramidal nanoparticles in liquid, where the effects of liquid compressibility are negligible. This highlights the importance of shear and compressional relaxation processes, as a function of flow geometry, and the impact of the shear and bulk viscosities on nanometer scale flows.
NASA Astrophysics Data System (ADS)
Joo, Sung-Jun; Park, Buhm; Kim, Do-Hyoung; Kwak, Dong-Ok; Song, In-Sang; Park, Junhong; Kim, Hak-Sung
2015-03-01
Woven glass fabric/BT (bismaleimide triazine) composite laminate (BT core), copper (Cu), and photoimageable solder resist (PSR) are the most widely used materials for semiconductors in electronic devices. Among these materials, BT core and PSR contain polymeric materials that exhibit viscoelastic behavior. For this reason, these materials are considered to have time- and temperature-dependent moduli during warpage analysis. However, the thin geometry of multilayer printed circuit board (PCB) film makes it difficult to identify viscoelastic characteristics. In this work, a vibration test method was proposed for measuring the viscoelastic properties of a multilayer PCB film at different temperatures. The beam-shaped specimens, composed of a BT core, Cu laminated on a BT core, and PSR and Cu laminated on a BT core, were used in the vibration test. The frequency-dependent variation of the complex bending stiffness was determined using a transfer function method. The storage modulus (E‧) of the BT core, Cu, and PSR as a function of temperature and frequency were obtained, and their temperature-dependent variation was identified. The obtained properties were fitted using a viscoelastic model for the BT core and the PSR, and a linear elastic model for the Cu. Warpage of a line pattern specimen due to temperature variation was measured using a shadow Moiré analysis and compared to predictions using a finite element model. The results provide information on the mechanism of warpage, especially warpage due to temperature-dependent variation in viscoelastic properties.
Solares, Santiago D
2014-01-01
This paper presents computational simulations of single-mode and bimodal atomic force microscopy (AFM) with particular focus on the viscoelastic interactions occurring during tip-sample impact. The surface is modeled by using a standard linear solid model, which is the simplest system that can reproduce creep compliance and stress relaxation, which are fundamental behaviors exhibited by viscoelastic surfaces. The relaxation of the surface in combination with the complexities of bimodal tip-sample impacts gives rise to unique dynamic behaviors that have important consequences with regards to the acquisition of quantitative relationships between the sample properties and the AFM observables. The physics of the tip-sample interactions and its effect on the observables are illustrated and discussed, and a brief research outlook on viscoelasticity measurement with intermittent-contact AFM is provided.
Dynamic viscoelastic properties of experimental silicone soft lining materials.
Santawisuk, Wallapat; Kanchanavasita, Widchaya; Sirisinha, Chakrit; Harnirattisai, Choltacha
2010-08-01
The purpose of this study was to evaluate the dynamic viscoelastic properties of experimental silicone soft lining materials, Silastic MDX 4-4210 reinforced with silica fillers. Storage modulus (E'), loss modulus (E") and damping factor (tan delta) were determined using a dynamic mechanical analyzer under a deformation strain level of 0.27% at test frequency and a temperature range of 1 Hz and 0 to 60 degrees C, respectively. The degree of silica dispersion was also studied using a field emission scanning electron microscopy (FE-SEM). One-way ANOVA and Tukey's HSD test results indicated that the prepared silicone elastomers provided a significantly greater damping factor, but less storage modulus than GC Reline Soft and Tokuyama Sofreliner Tough (p<0.001). The storage moduli, loss moduli and damping factor of the experimental silicone elastomers increased with increasing amounts of fumed silica. In conclusion, the experimental silicone elastomers revealed acceptable dynamic viscoelastic properties to be used as denture soft lining materials.
Li, Yan; Deng, Jianxin; Zhou, Jun; Li, Xueen
2016-11-01
Corresponding to pre-puncture and post-puncture insertion, elastic and viscoelastic mechanical properties of brain tissues on the implanting trajectory of sub-thalamic nucleus stimulation are investigated, respectively. Elastic mechanical properties in pre-puncture are investigated through pre-puncture needle insertion experiments using whole porcine brains. A linear polynomial and a second order polynomial are fitted to the average insertion force in pre-puncture. The Young's modulus in pre-puncture is calculated from the slope of the two fittings. Viscoelastic mechanical properties of brain tissues in post-puncture insertion are investigated through indentation stress relaxation tests for six interested regions along a planned trajectory. A linear viscoelastic model with a Prony series approximation is fitted to the average load trace of each region using Boltzmann hereditary integral. Shear relaxation moduli of each region are calculated using the parameters of the Prony series approximation. The results show that, in pre-puncture insertion, needle force almost increases linearly with needle displacement. Both fitting lines can perfectly fit the average insertion force. The Young's moduli calculated from the slope of the two fittings are worthy of trust to model linearly or nonlinearly instantaneous elastic responses of brain tissues, respectively. In post-puncture insertion, both region and time significantly affect the viscoelastic behaviors. Six tested regions can be classified into three categories in stiffness. Shear relaxation moduli decay dramatically in short time scales but equilibrium is never truly achieved. The regional and temporal viscoelastic mechanical properties in post-puncture insertion are valuable for guiding probe insertion into each region on the implanting trajectory. PMID:27646405
Li, Yan; Deng, Jianxin; Zhou, Jun; Li, Xueen
2016-11-01
Corresponding to pre-puncture and post-puncture insertion, elastic and viscoelastic mechanical properties of brain tissues on the implanting trajectory of sub-thalamic nucleus stimulation are investigated, respectively. Elastic mechanical properties in pre-puncture are investigated through pre-puncture needle insertion experiments using whole porcine brains. A linear polynomial and a second order polynomial are fitted to the average insertion force in pre-puncture. The Young's modulus in pre-puncture is calculated from the slope of the two fittings. Viscoelastic mechanical properties of brain tissues in post-puncture insertion are investigated through indentation stress relaxation tests for six interested regions along a planned trajectory. A linear viscoelastic model with a Prony series approximation is fitted to the average load trace of each region using Boltzmann hereditary integral. Shear relaxation moduli of each region are calculated using the parameters of the Prony series approximation. The results show that, in pre-puncture insertion, needle force almost increases linearly with needle displacement. Both fitting lines can perfectly fit the average insertion force. The Young's moduli calculated from the slope of the two fittings are worthy of trust to model linearly or nonlinearly instantaneous elastic responses of brain tissues, respectively. In post-puncture insertion, both region and time significantly affect the viscoelastic behaviors. Six tested regions can be classified into three categories in stiffness. Shear relaxation moduli decay dramatically in short time scales but equilibrium is never truly achieved. The regional and temporal viscoelastic mechanical properties in post-puncture insertion are valuable for guiding probe insertion into each region on the implanting trajectory.
Linear oscillation of gas bubbles in a viscoelastic material under ultrasound irradiation
Hamaguchi, Fumiya; Ando, Keita
2015-11-15
Acoustically forced oscillation of spherical gas bubbles in a viscoelastic material is studied through comparisons between experiments and linear theory. An experimental setup has been designed to visualize bubble dynamics in gelatin gels using a high-speed camera. A spherical gas bubble is created by focusing an infrared laser pulse into (gas-supersaturated) gelatin gels. The bubble radius (up to 150 μm) under mechanical equilibrium is controlled by gradual mass transfer of gases across the bubble interface. The linearized bubble dynamics are studied from the observation of spherical bubble oscillation driven by low-intensity, planar ultrasound driven at 28 kHz. It follows from the experiment for an isolated bubble that the frequency response in its volumetric oscillation was shifted to the high frequency side and its peak was suppressed as the gelatin concentration increases. The measurement is fitted to the linearized Rayleigh–Plesset equation coupled with the Voigt constitutive equation that models the behavior of linear viscoelastic solids; the fitting yields good agreement by tuning unknown values of the viscosity and rigidity, indicating that more complex phenomena including shear thinning, stress relaxation, and retardation do not play an important role for the small-amplitude oscillations. Moreover, the cases for bubble-bubble and bubble-wall systems are studied. The observed interaction effect on the linearized dynamics can be explained as well by a set of the Rayleigh–Plesset equations coupled through acoustic radiation among these systems. This suggests that this experimental setup can be applied to validate the model of bubble dynamics with more complex configuration such as a cloud of bubbles in viscoelastic materials.
Linear oscillation of gas bubbles in a viscoelastic material under ultrasound irradiation
NASA Astrophysics Data System (ADS)
Hamaguchi, Fumiya; Ando, Keita
2015-11-01
Acoustically forced oscillation of spherical gas bubbles in a viscoelastic material is studied through comparisons between experiments and linear theory. An experimental setup has been designed to visualize bubble dynamics in gelatin gels using a high-speed camera. A spherical gas bubble is created by focusing an infrared laser pulse into (gas-supersaturated) gelatin gels. The bubble radius (up to 150 μm) under mechanical equilibrium is controlled by gradual mass transfer of gases across the bubble interface. The linearized bubble dynamics are studied from the observation of spherical bubble oscillation driven by low-intensity, planar ultrasound driven at 28 kHz. It follows from the experiment for an isolated bubble that the frequency response in its volumetric oscillation was shifted to the high frequency side and its peak was suppressed as the gelatin concentration increases. The measurement is fitted to the linearized Rayleigh-Plesset equation coupled with the Voigt constitutive equation that models the behavior of linear viscoelastic solids; the fitting yields good agreement by tuning unknown values of the viscosity and rigidity, indicating that more complex phenomena including shear thinning, stress relaxation, and retardation do not play an important role for the small-amplitude oscillations. Moreover, the cases for bubble-bubble and bubble-wall systems are studied. The observed interaction effect on the linearized dynamics can be explained as well by a set of the Rayleigh-Plesset equations coupled through acoustic radiation among these systems. This suggests that this experimental setup can be applied to validate the model of bubble dynamics with more complex configuration such as a cloud of bubbles in viscoelastic materials.
Viscoelastic properties of model segments of collagen molecules.
Gautieri, Alfonso; Vesentini, Simone; Redaelli, Alberto; Buehler, Markus J
2012-03-01
Collagen is the prime construction material in vertebrate biology, determining the mechanical behavior of connective tissues such as tendon, bone and skin. Despite extensive efforts in the investigation of the origin of collagen unique mechanical properties, a deep understanding of the relationship between molecular structure and mechanical properties remains elusive, hindered by the complex hierarchical structure of collagen-based tissues. In particular, although extensive studies of viscoelastic properties have been pursued at the macroscopic (fiber/tissue) level, fewer investigations have been performed at the smaller scales, including in particular collagen molecules and fibrils. These scales are, however, important for a complete understanding of the role of collagen as an important constituent in the extracellular matrix. Here, using an atomistic modeling approach, we perform in silico creep tests of a collagen-like peptide, monitoring the strain-time response for different values of applied external load. The results show that individual collagen molecules exhibit a nonlinear viscoelastic behavior, with a Young's modulus increasing from 6 to 16GPa (for strains up to 20%), a viscosity of 3.84.±0.38Pa·s, and a relaxation time in the range of 0.24-0.64ns. The single molecule viscosity, for the first time reported here, is several orders of magnitude lower than the viscosity found for larger-scale single collagen fibrils, suggesting that the viscous behavior of collagen fibrils and fibers involves additional mechanisms, such as molecular sliding between collagen molecules within the fibril or the effect of relaxation of larger volumes of solvent. Based on our molecular modeling results we propose a simple structural model that describes collagen tissue as a hierarchical structure, providing a bottom-up description of elastic and viscous properties form the properties of the tissue basic building blocks. PMID:22204879
NASA Astrophysics Data System (ADS)
Hanyga, Andrzej
2014-09-01
Dispersion, attenuation and wavefronts in a class of linear viscoelastic media proposed by Strick and Mainardi (Geophys J R Astr Soc 69:415-429, 1982) and a related class of models due to Lomnitz, Jeffreys and Strick are studied by a new method due to the author. Unlike the previously studied explicit models of relaxation modulus or creep compliance, these two classes support propagation of discontinuities. Due to an extension made by Strick, either of these two classes of models comprise both viscoelastic solids and fluids. We also discuss the Andrade viscoelastic media. The Andrade media do not support discontinuity waves and exhibit the pedestal effect.
Non-Newtonian and Viscoelastic Properties of Lava Flows
NASA Astrophysics Data System (ADS)
Bagdassarov, N. S.
2004-12-01
Lava flow models require an in-depth knowledge of the rheological properties of lava. Previous measurements have shown that, at typical eruption temperatures, lavas are non-Newtonian. The reasons for this include the formation and destruction of crystal networks and bubble deformation during shear. The effects of bubbles are investigated experimentally in this contribution using analogue fluids with bubble concentrations <20%. The shear-thinning behaviour of bubbly liquids noted by previous workers is shown to be dependent on the previous shearing history of the fluid. This thixotropic behaviour, which was investigated using a rotational vane viscometer, is caused by delayed bubble deformation and recovery when subjected to changes in shear stress. A rotational vane viscometer and torsional deformation apparatus were used to investigate the rheological properties of bubbly liquids and foams in order to determine a viscoelastic transition. These experiments have shown that the foams tested are viscoelastic power law fluids with a yield strength. Non-Newtonian properties and yield strength of foams are shown to be a probable cause of accelerating flow fragmentation in tube flow experiments on expanding foams. The flow of a bubbly fluid through a narrowing conduit may cause a pulsating regime of a flow due to periodic slip and slip-free boundary conditions near the walls of a conduit. Slip boundary conditions can lead to instability in viscoelastic shear flow causing short wavelength fluctuations at high shear rates. This mechanism may also take place during explosive volcanic eruptions. The frequency and amplitude of oscillation shear affect the structure of lavas which are thixotropic non-Newtonian liquids. The frequency dependent structure of lavas can be identified via frequency hysteresis and time-evolution of internal friction and viscosity. The rheological properties of basaltic lavas from Etna, Hawai'i and Vesuvius have been investigated at temperatures
Aging-related differences in chondrocyte viscoelastic properties.
Steklov, Nikolai; Srivastava, Ajay; Sung, K L P; Chen, Peter C; Lotz, Martin K; D'Lima, Darryl D
2009-06-01
The biomechanical properties of articular cartilage change profoundly with aging. These changes have been linked with increased potential for cartilage degeneration and osteoarthritis. However, less is known about the change in biomechanical properties of chondrocytes with increasing age. Cell stiffness can affect mechanotransduction pathways and may alter cell function. We measured aging-related changes in the biomechanical properties of chondrocytes. Human chondrocytes were isolated from knee articular cartilage within 48 hours after death or from osteochondral specimens obtained from knee arthroplasty. Cells were divided into two age groups: between 18 and 35 years (18 - 35); and greater than 55 years (55+) of age. The 55+ group was further subdivided based on visual grade of osteoarthritis: normal (N) or osteoarthritic (OA). The viscoelastic properties of the cell were measured using the previously described micropipette cell aspiration technique. The equilibrium modulus, instantaneous modulus, and apparent viscosity were significantly higher in the 55+ year age group than in the 18 - 35 age group. On the other hand, no differences were found in the equilibrium modulus, instantaneous modulus, or apparent viscosity between the N and OA groups. The increase in cell stiffness can be attributed to altered mechanical properties of the cell membrane, the cytoplasm, or the cytoskeleton. Increased stiffness has been reported in osteoarthritic chondrocytes, which in turn has been attributed to the actin cytoskeleton. A similar mechanism may be responsible for our finding of increased stiffness in aging chondrocytes. With advancing age, changes in the biomechanical properties of the cell could alter molecular and biochemical responses.
Nanoscale viscoelastic properties and adhesion of polydimethylsiloxane for tissue engineering
NASA Astrophysics Data System (ADS)
Chen, J.; Wright, K. E.; Birch, M. A.
2014-02-01
It has shown that altering crosslink density of biopolymers will regulate the morphology of Mesenchymal Stem Cells (MSCs) and the subsequent MSCs differentiation. These observations have been found in a wide range of biopolymers. However, a recent work published in Nature Materials has revealed that MSCs morphology and differentiation was unaffected by crosslink density of polydimethylsiloxane (PDMS), which remains elusive. To understand such unusual behaviour, we use nanoindentation tests and modelling to characterize viscoelastic properties and surface adhesion of PDMS with different base:crosslink ratio varied from 50:1 (50D) to 10:1 (10D). It has shown that lower crosslink density leads to lower elastic moduli. Despite lower nanoindentation elastic moduli, PDMS with lowest crosslink density has higher local surface adhesion which would affect cell-biomaterials interactions. This work suggests that surface adhesion is likely another important physical cue to regulate cell-biomaterials interactions. [Figure not available: see fulltext.
Duan, Wangping; Wei, Lei; Zhang, Juntao; Hao, Yongzhuang; Li, Chunjiang; Li, Hao; Li, Qi; Zhang, Quanyou; Chen, Weiyi; Wei, Xiaochun
2011-12-01
The cytoskeleton network is believed to play an important role in the biomechanical properties of the chondrocyte. Ours and other laboratories have demonstrated that chondrocytes exhibit a viscoelastic solid creep behavior in vitro and that viscoelastic properties decrease in osteoarthritic chondrocytes. In this study, we aimed to understand whether the alteration of viscoelastic properties is associated with changes in cytoskeleton components of ageing chondrocytes from rabbit knee articular cartilage. Three age groups were used for this study: young (2-months-old, N=23), adult (8-months-old, N=23), and old (31-months-old, N=23) rabbit groups. Cartilage structure and proteoglycan and type II collagen content were determined by H&E and Toluidine Blue staining, and type II collagen antibody. The detailed structure of the chondrocytes in all groups was visualized using transmission electron microscopy (TEM). Chondrocytes were isolated from full-thickness knee cartilage of rabbits from all groups and their viscoelastic properties were quantified within 2 hours of isolation using a micropipette aspiration technique combined with a standard linear viscoelastic solid model. The components and network of the cytoskeleton within the cells were analyzed by laser scanning confocal microscopy (LSCM) with immunofluorescence staining as well as real time PCR and western blotting. With ageing, articular cartilage contained less chondrocytes and less proteoglycans and type II collagen. TEM observations showed that the cell membranes were not clearly defined, organelles were fewer and the nuclei were deformed or shrunk in the old cells compared with the young and adult cells. In suspension, chondrocytes from all three age groups showed significant viscoelastic creep behavior, but the deformation rate and amplitude of old chondrocytes were increased under the same negative pressure when compared to young and adult chondrocytes. Viscoelastic properties of the old cells, including
Peterson, Brandon W; Busscher, Henk J; Sharma, Prashant K; van der Mei, Henny C
2012-01-01
Centrifugal compaction causes changes in the surface properties of bacterial cells. It has been shown previously that the surface properties of planktonic cells change with increasing centrifugal compaction. This study aimed to analyze the influences of centrifugal compaction and environmental conditions on the visco-elastic properties of oral biofilms. Biofilms were grown out of a layer of initially adhering streptococci, actinomyces or a combination of these. Different uni-axial deformations were induced on the biofilms and the load relaxations were measured over time. Linear-Regression-Analysis demonstrated that both the centrifugation coefficient for streptococci and induced deformation influenced the percentage relaxation. Centrifugal compaction significantly influenced relaxation only upon compression of the outermost 20% of the biofilm (p < 0.05), whereas biofilm composition became influential when 50% deformation was induced, invoking re-arrangement of the bacteria in deeper biofilm structures. In summary, the effects of centrifugal compaction of initially adhering, centrifuged bacteria extend to the visco-elastic properties of biofilms, indicating that the initial bacterial layer influences the structure of the entire biofilm.
Computational Analysis of Viscoelastic Properties of Crosslinked Actin Networks
Kim, Taeyoon; Hwang, Wonmuk; Lee, Hyungsuk; Kamm, Roger D.
2009-01-01
Mechanical force plays an important role in the physiology of eukaryotic cells whose dominant structural constituent is the actin cytoskeleton composed mainly of actin and actin crosslinking proteins (ACPs). Thus, knowledge of rheological properties of actin networks is crucial for understanding the mechanics and processes of cells. We used Brownian dynamics simulations to study the viscoelasticity of crosslinked actin networks. Two methods were employed, bulk rheology and segment-tracking rheology, where the former measures the stress in response to an applied shear strain, and the latter analyzes thermal fluctuations of individual actin segments of the network. It was demonstrated that the storage shear modulus (G′) increases more by the addition of ACPs that form orthogonal crosslinks than by those that form parallel bundles. In networks with orthogonal crosslinks, as crosslink density increases, the power law exponent of G′ as a function of the oscillation frequency decreases from 0.75, which reflects the transverse thermal motion of actin filaments, to near zero at low frequency. Under increasing prestrain, the network becomes more elastic, and three regimes of behavior are observed, each dominated by different mechanisms: bending of actin filaments, bending of ACPs, and at the highest prestrain tested (55%), stretching of actin filaments and ACPs. In the last case, only a small portion of actin filaments connected via highly stressed ACPs support the strain. We thus introduce the concept of a ‘supportive framework,’ as a subset of the full network, which is responsible for high elasticity. Notably, entropic effects due to thermal fluctuations appear to be important only at relatively low prestrains and when the average crosslinking distance is comparable to or greater than the persistence length of the filament. Taken together, our results suggest that viscoelasticity of the actin network is attributable to different mechanisms depending on the amount
Computational analysis of viscoelastic properties of crosslinked actin networks.
Kim, Taeyoon; Hwang, Wonmuk; Lee, Hyungsuk; Kamm, Roger D
2009-07-01
Mechanical force plays an important role in the physiology of eukaryotic cells whose dominant structural constituent is the actin cytoskeleton composed mainly of actin and actin crosslinking proteins (ACPs). Thus, knowledge of rheological properties of actin networks is crucial for understanding the mechanics and processes of cells. We used Brownian dynamics simulations to study the viscoelasticity of crosslinked actin networks. Two methods were employed, bulk rheology and segment-tracking rheology, where the former measures the stress in response to an applied shear strain, and the latter analyzes thermal fluctuations of individual actin segments of the network. It was demonstrated that the storage shear modulus (G') increases more by the addition of ACPs that form orthogonal crosslinks than by those that form parallel bundles. In networks with orthogonal crosslinks, as crosslink density increases, the power law exponent of G' as a function of the oscillation frequency decreases from 0.75, which reflects the transverse thermal motion of actin filaments, to near zero at low frequency. Under increasing prestrain, the network becomes more elastic, and three regimes of behavior are observed, each dominated by different mechanisms: bending of actin filaments, bending of ACPs, and at the highest prestrain tested (55%), stretching of actin filaments and ACPs. In the last case, only a small portion of actin filaments connected via highly stressed ACPs support the strain. We thus introduce the concept of a 'supportive framework,' as a subset of the full network, which is responsible for high elasticity. Notably, entropic effects due to thermal fluctuations appear to be important only at relatively low prestrains and when the average crosslinking distance is comparable to or greater than the persistence length of the filament. Taken together, our results suggest that viscoelasticity of the actin network is attributable to different mechanisms depending on the amount of
Non-linear analysis and the design of Pumpkin Balloons: stress, stability and viscoelasticity
NASA Astrophysics Data System (ADS)
Rand, J. L.; Wakefield, D. S.
Tensys have a long-established background in the shape generation and load analysis of architectural stressed membrane structures Founded upon their inTENS finite element analysis suite these activities have broadened to encompass lighter than air structures such as aerostats hybrid air-vehicles and stratospheric balloons Winzen Engineering couple many years of practical balloon design and fabrication experience with both academic and practical knowledge of the characterisation of the non-linear viscoelastic response of the polymeric films typically used for high-altitude scientific balloons Both companies have provided consulting services to the NASA Ultra Long Duration Balloon ULDB Program Early implementations of pumpkin balloons have shown problems of geometric instability characterised by improper deployment and these difficulties have been reproduced numerically using inTENS The solution lies in both the shapes of the membrane lobes and also the need to generate a biaxial stress field in order to mobilise in-plane shear stiffness Balloons undergo significant temperature and pressure variations in flight The different thermal characteristics between tendons and film can lead to significant meridional stress Fabrication tolerances can lead to significant local hoop stress concentrations particularly adjacent to the base and apex end fittings The non-linear viscoelastic response of the envelope film acts positively to help dissipate stress concentrations However creep over time may produce lobe geometry variations that may
NASA Astrophysics Data System (ADS)
Weigand, William; Messmore, Ashley; Anderson, Rae
The sea annelid, Chaetopterus Variopedatus, secretes a bioluminescent mucus that also exhibits complex viscoelastic properties. The constituents of the mucus are relatively unknown but it does play an important role in the development of the worms' parchment-like housing tubes. In order to determine how and why this mucus can exhibit material properties ranging from fluidity to rigidity we perform microrheology experiments. We determine the microscale viscoelastic properties by using optical tweezers to produce small oscillations in the mucus which allow us to determine both the linear storage and loss moduli (G',G'') along with the viscosity of the fluid. By varying the size of the microspheres (2-10 µm) and oscillation amplitude (.5-10 µm) we are able to determine the dominant intrinsic length scales of the molecular mesh comprising the mucus. By varying the oscillation frequency (1-15Hz) we determine the crossover frequency at which G' surpasses G'', to quantify the longest relaxation time of the mesh network. Initial results show a strong dependence on bead size which indicate that the dominant entanglement lengthscale of the mucus mesh is ~5 um. Microspheres of this size exhibit a wide variety of stress responses in different regions of the mucus demonstrating the substantial microscale heterogeneity of the mucus. We carry out measurements on a population of worms of varying size and age to determine mucus variability between worms.
Parrales, Miguel A; Fernandez, Juan M; Perez-Saborid, Miguel; Kopechek, Jonathan A; Porter, Tyrone M
2014-09-01
The acoustic attenuation spectrum of lipid-coated microbubble suspensions was measured in order to characterize the linear acoustic behavior of ultrasound contrast agents. For that purpose, microbubbles samples were generated with a very narrow size distribution by using microfluidics techniques. A performance as good as optical characterization techniques of single microbubbles was achieved using this method. Compared to polydispersions (i.e., contrast agents used clinically), monodisperse contrast agents have a narrower attenuation spectrum, which presents a maximum peak at a frequency value corresponding to the average single bubble resonance frequency. The low polydispersity index of the samples made the estimation of the lipid viscoelastic properties more accurate since, as previously reported, the shell linear parameters may change with the equilibrium bubble radius. The results showed the great advantage of dealing with monodisperse populations rather than polydisperse populations for the acoustic characterization of ultrasound contrast agents. PMID:25190383
Viscoelastic Properties of Poly[(butylene succinate)-co-adipate] Nanocomposites.
Al-Thabaiti, Shaeel A; Ray, Suprakas Sinha; Basahell, Sulaiman Nassir; Mokhtar, Mohamed
2015-03-01
This article reports the viscoelastic properties of poly[(butylene succinate)-co-adipate] (PBSA) nanocomposites. The nanocomposites of PBSA with various loadings of organically modified clay were prepared by melt-mixing in a batch-mixer. The solid and melt-state viscoelastic properties of neat PBSA and various nanocomposites were studied in detail. The dynamic mechanical studies demonstrated an increase in the storage modulus of PBSA matrix with organoclay loading. Melt-state rheological properties were found to be modified with organoclay loading changing from liquid-like, to gel-like and then viscoelastic solid-like. Such changes in viscoelastic properties along with the improvements in thermomechanical properties are expected to open opportunities for the use of PBSA extending its applications from the classical field of packaging to new niches such as tissue-engineering. PMID:26413658
Nonlinear viscoelastic properties of tissue assessed by ultrasound.
Sinkus, Ralph; Bercoff, Jeremy; Tanter, Mickaël; Gennisson, Jean-Luc; El-Khoury, Carl; Servois, Vincent; Tardivon, Anne; Fink, Mathias
2006-11-01
A technique to assess qualitatively the presence of higher-order viscoelastic parameters is presented. Low-frequency, monochromatic elastic waves are emitted into the material via an external vibrator. The resulting steady-state motion is detected in real time via an ultra fast ultrasound system using classical, one-dimensional (1-D) ultrasound speckle correlation for motion estimation. Total data acquisition lasts only for about 250 ms. The spectrum of the temporal displacement data at each image point is used for analysis. The presence of nonlinear effects is detected by inspection of the ratio of the second harmonics amplitude with respect to the total amplitude summed up to the second harmonic. Results from a polyacrylamide-based phantom indicate a linear response (i.e., the absence of higher harmonics) for this type of material at 65 Hz mechanical vibration frequency and about 100 microm amplitude. A lesion, artificially created by injection of glutaraldehyde into a beef specimen, shows the development of higher harmonics at the location of injection as a function of time. The presence of upper harmonics is clearly evident at the location of a malignant lesion within a mastectomy.
Nonlinear viscoelastic properties of tissue assessed by ultrasound.
Sinkus, Ralph; Bercoff, Jeremy; Tanter, Mickaël; Gennisson, Jean-Luc; El-Khoury, Carl; Servois, Vincent; Tardivon, Anne; Fink, Mathias
2006-11-01
A technique to assess qualitatively the presence of higher-order viscoelastic parameters is presented. Low-frequency, monochromatic elastic waves are emitted into the material via an external vibrator. The resulting steady-state motion is detected in real time via an ultra fast ultrasound system using classical, one-dimensional (1-D) ultrasound speckle correlation for motion estimation. Total data acquisition lasts only for about 250 ms. The spectrum of the temporal displacement data at each image point is used for analysis. The presence of nonlinear effects is detected by inspection of the ratio of the second harmonics amplitude with respect to the total amplitude summed up to the second harmonic. Results from a polyacrylamide-based phantom indicate a linear response (i.e., the absence of higher harmonics) for this type of material at 65 Hz mechanical vibration frequency and about 100 microm amplitude. A lesion, artificially created by injection of glutaraldehyde into a beef specimen, shows the development of higher harmonics at the location of injection as a function of time. The presence of upper harmonics is clearly evident at the location of a malignant lesion within a mastectomy. PMID:17091837
Interrogating the viscoelastic properties of tissue using viscoelastic response (VISR) ultrasound
NASA Astrophysics Data System (ADS)
Selzo, Mallory Renee
Affecting approximately 1 in 3,500 newborn males, Duchenne muscular dystrophy (DMD) is one of the most common lethal genetic disorders in humans. Boys with DMD suffer progressive loss of muscle strength and function, leading to wheelchair dependence, cardiac and respiratory compromise, and death during young adulthood. There are currently no treatments that can halt or reverse the disease progression, and translating prospective treatments into clinical trials has been delayed by inadequate outcome measures. Current outcome measures, such as functional and muscle strength assessments, lack sensitivity to individual muscles, require subjective effort of the child, and are impacted by normal childhood growth and development. The goal of this research is to develop Viscoelastic Response (VisR) ultrasound which can be used to delineate compositional changes in muscle associated with DMD. In VisR, acoustic radiation force (ARF) is used to produce small, localized displacements within the muscle. Using conventional ultrasound to track the motion, the displacement response of the tissue can be evaluated against a mechanical model. In order to develop signal processing techniques and assess mechanical models, finite element method simulations are used to model the response of a viscoelastic material to ARF excitations. Results are then presented demonstrating VisR differentiation of viscoelastic changes with progressive dystrophic degeneration in a dog model of DMD. Finally, clinical feasibility of VisR imaging is demonstrated in two boys with DMD.
Physical aging effects on the compressive linear viscoelastic creep of IM7/K3B composite
NASA Technical Reports Server (NTRS)
Veazie, David R.; Gates, Thomas S.
1995-01-01
An experimental study was undertaken to establish the viscoelastic behavior of 1M7/K3B composite in compression at elevated temperature. Creep compliance, strain recovery and the effects of physical aging on the time dependent response was measured for uniaxial loading at several isothermal conditions below the glass transition temperature (T(g)). The IM7/K3B composite is a graphite reinforced thermoplastic polyimide with a T(g) of approximately 240 C. In a composite, the two matrix dominated compliance terms associated with time dependent behavior occur in the transverse and shear directions. Linear viscoelasticity was used to characterize the creep/recovery behavior and superposition techniques were used to establish the physical aging related material constants. Creep strain was converted to compliance and measured as a function of test time and aging time. Results included creep compliance master curves, physical aging shift factors and shift rates. The description of the unique experimental techniques required for compressive testing is also given.
Comparative study of viscoelastic properties using virgin yogurt
Dimonte, G.; Nelson, D.; Weaver, S.; Schneider, M.; Flower-Maudlin, E.; Gore, R.; Baumgardner, J.R.; Sahota, M.S.
1998-07-01
We describe six different tests used to obtain a consistent set of viscoelastic properties for yogurt. Prior to yield, the shear modulus {mu} and viscosity {eta} are measured nondestructively using the speed and damping of elastic waves. Although new to foodstuffs, this technique has been applied to diverse materials from metals to the earth{close_quote}s crust. The resultant shear modulus agrees with {mu}{approximately}E/3 for incompressible materials, where the Young{close_quote}s modulus E is obtained from a stress{endash}strain curve in compression. The tensile yield stress {tau}{sub o} is measured in compression and tension, with good agreement. The conventional vane and cone/plate rheometers measured a shear stress yield {tau}{sub os}{approximately}{tau}{sub o}/{radical} (3) , as expected theoretically, but the inferred {open_quotes}apparent{close_quotes} viscosity from the cone/plate rheometer is much larger than the wave measurement due to the finite yield ({tau}{sub os}{ne}0). Finally, we inverted an open container of yogurt for 10{sup 6} s{gt}{eta}/{mu} and observed no motion. This demonstrates unequivocally that yogurt possesses a finite yield stress rather than a large viscosity. We present a constitutive model with a pre-yield viscosity to describe the damping of the elastic waves and use a simulation code to describe yielding in complex geometry. {copyright} {ital 1998 Society of Rheology.}
NASA Astrophysics Data System (ADS)
Iwaoka, Nobuyuki; Hagita, Katsumi; Takano, Hiroshi
2014-03-01
On the basis of relaxation mode analysis (RMA), we present an efficient method to estimate the linear viscoelasticity of polymer melts in a molecular dynamics (MD) simulation. Slow relaxation phenomena appeared in polymer melts cause a problem that a calculation of the stress relaxation function in MD simulations, especially in the terminal time region, requires large computational efforts. Relaxation mode analysis is a method that systematically extracts slow relaxation modes and rates of the polymer chain from the time correlation of its conformations. We show the computational cost may be drastically reduced by combining a direct calculation of the stress relaxation function based on the Green-Kubo formula with the relaxation rates spectra estimated by RMA. N. I. acknowledges the Graduate School Doctoral Student Aid Program from Keio University.
Siviello, Ciro; Greco, Francesco; Larobina, Domenico
2015-08-14
The mechanical behaviour of ionically cross-linked alginate gels is investigated here in detail. To determine the range of linear response of the materials, uniaxial, unconfined compression and torsional deformation experiments are performed, obtaining both the stress-strain and the viscoelastic behaviour of the gels. On-line measurements of the radii of the cylindrical gel samples in these experiments are also reported. The linearity range in the gel mechanical response is found to be rather limited, up to 6% strain, at most, contrary to more optimistic conclusions usually reported in the literature. We confirm the presence of a stress-diffusion coupling phenomenon in our alginates, i.e., the migration of water from/into the gels in response to the applied deformation. A phenomenon of inner (constitutive) relaxation of the network component of the gels is also clearly identified, and observed to occur, in parallel with solvent diffusion, upon compression. At sufficiently longer times after a deformation step, syneresis is always observed, with concomitant nonstandard viscoelastic effects, such as the growth of a normal force in torsion, and a size dependent decay of the longitudinal force in compression. We applied a two-fluid model, recently developed by two of the present authors [D. Larobina and F. Greco, J. Chem. Phys., 2012, 136(13), 134904], to simulate the relaxation tests upon torsional and compressive deformations, and to fit our own experiments. The model is found to well describe the coupling between constitutive relaxation and diffusion, and to reproduce the available force and radii data before the advent of syneresis.
High Frequency Measurements of Viscoelastic Properties of Hydrogels for Vocal Fold Regeneration.
Jiao, T; Farran, A; Jia, X; Clifton, R J
2009-01-01
This report describes a torsional wave experiment used to measure the viscoelastic properties of vocal fold tissues and soft materials over the range of phonation frequencies. A thin cylindrical sample is mounted between two hexagonal plates. The assembly is enclosed in an environmental chamber to maintain the temperature and relative humidity at in vivo conditions. The bottom plate is subjected to small oscillations by means of a galvanometer driven by a frequency generator that steps through a sequence of frequencies. At each frequency, measured rotations of the top and bottom plates are used to determine the ratio of the amplitudes of the rotations of the two plates. Comparisons of the frequency dependence of this ratio with that predicted for torsional waves in a linear viscoelastic material allows the storage modulus and the loss angle, in shear, to be calculated by a best-fit procedure. Experimental results are presented for hydrogels that are being examined as potential materials for vocal fold regeneration. PMID:20300451
Viscoelastic properties of graphene-based epoxy resins
NASA Astrophysics Data System (ADS)
Nobile, Maria Rossella; Fierro, Annalisa; Rosolia, Salvatore; Raimondo, Marialuigia; Lafdi, Khalid; Guadagno, Liberata
2015-12-01
In this paper the viscoelastic properties of an epoxy resin filled with graphene-based nanoparticles have been investigated in the liquid state, before curing, by means of a rotational rheometer equipped with a parallel plate geometry. Exfoliated graphite was prepared using traditional acid intercalation followed by a sudden treatment at high temperature (900°C). The percentage of exfoliated graphite was found to be 56%. The epoxy matrix was prepared by mixing a tetrafunctional precursor with a reactive diluent which produces a significant decrease in the viscosity of the epoxy precursor so that the dispersion step of nanofillers in the matrix can easily occur. The hardener agent, the 4,4-diaminodiphenyl sulfone (DDS), was added at a stoichiometric concentration with respect to all the epoxy rings. The inclusion of the partially exfoliated graphite (pEG) in the formulated epoxy mixture significantly modifies the rheological behaviour of the mixture itself. The epoxy mixture, indeed, shows a Newtonian behaviour while, at 3 wt % pEG content, the complex viscosity of the nanocomposite clearly shows a shear thinning behaviour with η* values much higher at the lower frequencies. The increase in complex viscosity with the increasing of the partially exfoliated graphite content was mostly caused by a dramatic increase in the storage modulus. All the graphene-based epoxy mixtures were cured by a two-stage curing cycles: a first isothermal stage was carried out at the lower temperature of 125°C for 1 hour while the second isothermal stage was performed at the higher temperature of 200°C for 3 hours. The mechanical properties of the cured nanocomposites show high values in the storage modulus and glass transition temperature.
A multiscale model for predicting the viscoelastic properties of asphalt concrete
NASA Astrophysics Data System (ADS)
Garcia Cucalon, Lorena; Rahmani, Eisa; Little, Dallas N.; Allen, David H.
2016-08-01
It is well known that the accurate prediction of long term performance of asphalt concrete pavement requires modeling to account for viscoelasticity within the mastic. However, accounting for viscoelasticity can be costly when the material properties are measured at the scale of asphalt concrete. This is due to the fact that the material testing protocols must be performed recursively for each mixture considered for use in the final design.
NASA Astrophysics Data System (ADS)
Wang, Jing; Hosoda, Masaki; Tshikudi, Diane M.; Nadkarni, Seemantini K.
2016-03-01
A number of disease conditions including coronary atherosclerosis, peripheral artery disease and gastro-intestinal malignancies are associated with alterations in tissue mechanical properties. Laser speckle rheology (LSR) has been demonstrated to provide important information on tissue mechanical properties by analyzing the time scale of temporal speckle intensity fluctuations, which serves as an index of tissue viscoelasticity. In order to measure the mechanical properties of luminal organs in vivo, LSR must be conducted via a miniature endoscope or catheter. Here we demonstrate the capability of an omni-directional LSR catheter to quantify tissue mechanical properties over the entire luminal circumference without the need for rotational motion. Retracting the catheter using a motor-drive assembly enables the reconstruction of cylindrical maps of tissue mechanical properties. The performance of the LSR catheter is tested using a luminal phantom with mechanical moduli that vary in both circumferential and longitudinal directions. 2D cylindrical maps of phantom viscoelastic properties are reconstructed over four quadrants of the coronary circumference simultaneously during catheter pullback. The reconstructed cylindrical maps of the decorrelation time constants easily distinguish the different gel components of the phantom with different viscoelastic moduli. The average values of decorrelation times calculated for each gel component of the phantom show a strong correspondence with the viscoelastic moduli measured via standard mechanical rheometry. These results highlight the capability for cylindrical mapping of tissue viscoelastic properties using LSR in luminal organs using a miniature catheter, thus opening the opportunity for improved diagnosis of several disease conditions.
NASA Astrophysics Data System (ADS)
Schmitt, D. R.; Wang, Z.; Wang, F.; Wang, R.
2015-12-01
Currently the moduli and velocities of rocks at seismic frequencies are usually measured by the strain-stress method in lab. However, such measurements require well-designed equipment and skilled technicians, which greatly hinders the experimental investigation on the elastic and visco-elastic properties of rocks at seismic frequencies. We attempt to model the dynamic moduli of porous rocks saturated with viscous fluid at seismic frequencies on core scale using the strain-stress method, aiming to provide a complement to real core measurements in lab. First, we build 2D geometrical models containing the pore structure information of porous rocks based on the digital images (such as thin section, SEM, CT, etc.) of real rocks. Then we assume the rock frames are linearly elastic, and use the standard Maxwell spring-dash pot model to describe the visco-elastic properties of pore fluids. Boundary conditions are set according to the strain-stress method; and the displacement field is calculated using the finite element method (FEM). We numerically test the effects of fluid viscosity, frequency, and pore structure on the visco-elastic properties based on the calculation results. In our modeling, the viscosity of the pore fluid ranges from 103mPas to 109mPas; and the frequency varies from 5Hz to 500Hz. The preliminary results indicate that the saturated rock behaves stiffer and shows larger phase lag between stress and strain when the viscosity of the pore fluid and (or) the frequency increase.
NASA Astrophysics Data System (ADS)
Vu, Q. H.; Brenner, R.; Castelnau, O.; Moulinec, H.; Suquet, P.
2012-03-01
The correspondence principle is customarily used with the Laplace-Carson transform technique to tackle the homogenization of linear viscoelastic heterogeneous media. The main drawback of this method lies in the fact that the whole stress and strain histories have to be considered to compute the mechanical response of the material during a given macroscopic loading. Following a remark of Mandel (1966 Mécanique des Milieux Continus(Paris, France: Gauthier-Villars)), Ricaud and Masson (2009 Int. J. Solids Struct. 46 1599-1606) have shown the equivalence between the collocation method used to invert Laplace-Carson transforms and an internal variables formulation. In this paper, this new method is developed for the case of polycrystalline materials with general anisotropic properties for local and macroscopic behavior. Applications are provided for the case of constitutive relations accounting for glide of dislocations on particular slip systems. It is shown that the method yields accurate results that perfectly match the standard collocation method and reference full-field results obtained with a FFT numerical scheme. The formulation is then extended to the case of time- and strain-dependent viscous properties, leading to the incremental collocation method (ICM) that can be solved efficiently by a step-by-step procedure. Specifically, the introduction of isotropic and kinematic hardening at the slip system scale is considered.
NASA Technical Reports Server (NTRS)
Gupta, K. K.; Akyuz, F. A.; Heer, E.
1972-01-01
This program, an extension of the linear equilibrium problem solver ELAS, is an updated and extended version of its earlier form (written in FORTRAN 2 for the IBM 7094 computer). A synchronized material property concept utilizing incremental time steps and the finite element matrix displacement approach has been adopted for the current analysis. A special option enables employment of constant time steps in the logarithmic scale, thereby reducing computational efforts resulting from accumulative material memory effects. A wide variety of structures with elastic or viscoelastic material properties can be analyzed by VISCEL. The program is written in FORTRAN 5 language for the Univac 1108 computer operating under the EXEC 8 system. Dynamic storage allocation is automatically effected by the program, and the user may request up to 195K core memory in a 260K Univac 1108/EXEC 8 machine. The physical program VISCEL, consisting of about 7200 instructions, has four distinct links (segments), and the compiled program occupies a maximum of about 11700 words decimal of core storage.
Nguyen, Nhung; Shao, Yue; Wineman, Alan; Fu, Jianping; Waas, Anthony
2016-07-01
Breast cancer cells (MCF-7 and MCF-10A) are studied through indentation with spherical borosilicate glass particles in atomic force microscopy (AFM) contact mode in fluid. Their mechanical properties are obtained by analyzing the recorded reaction force-time response. The analysis is based on comparing experimental data with predictions from finite element (FE) simulation. Here, FE modeling is employed to simulate the AFM indentation experiment which is neither a displacement nor a force controlled test. This approach is expected to overcome many underlying problems of the widely used models such as Hertz contact model due to its capability to capture the contact behaviors between the spherical indentor and the cell, account for cell geometry, and incorporate with large strain theory. In this work, a non-linear viscoelastic (NLV) model in which the viscoelastic part is described by Prony series terms is used for the constitutive model of the cells. The time-dependent material parameters are extracted through an inverse analysis with the use of a surrogate model based on a Kriging estimator. The purpose is to automatically extract the NLV properties of the cells with a more efficient process compared to the iterative inverse technique that has been mostly applied in the literature. The method also allows the use of FE modeling in the analysis of a large amount of experimental data. The NLV parameters are compared between MCF-7 and MCF-10A and MCF-10A treated and untreated with the drug Cytochalasin D to examine the possibility of using relaxation properties as biomarkers for distinguishing these types of breast cancer cells. The comparisons indicate that malignant cells (MCF-7) are softer and exhibit more relaxation than benign cells (MCF-10A). Disrupting the cytoskeleton using the drug Cytochalasin D also results in a larger amount of relaxation in the cell's response. In addition, relaxation properties indicate larger differences as compared to the elastic moduli
NASA Astrophysics Data System (ADS)
LEMERLE, P.
2002-02-01
Wave propagation methods allow the deduction of the viscoelastic damping properties of materials from the waveform pattern of a transitory wave: the wave profile is recorded at two travel distances in a thin bar made of the medium studied. In the case of linear viscoelasticity, the characteristics of the material are deduced directly from the transfer function of the two pulses measured. From a theoretical point of view, these methods are of great interest as they bridge a gap between vibratory methods and ultrasonic methods, allowing results to be obtained in a frequency range covering one and a half to two decades in the audiometric range (20 Hz-20 kHz). However, they have not been used much in industrial applications due to the difficulty and cost involved in producing samples in the form of bars. This study shows how this type of method can be adapted to measuring the viscoelastic properties of damping materials using reduced size and common shaped samples such as end-stop buffers.
Changes in the texture and viscoelastic properties of bread containing rice porridge during storage.
Tsai, Chia-Ling; Sugiyama, Junichi; Shibata, Mario; Kokawa, Mito; Fujita, Kaori; Tsuta, Mizuki; Nabetani, Hiroshi; Araki, Tetsuya
2012-01-01
The objective of this study was to investigate the effects of rice porridge on the texture and viscoelastic properties of bread during storage. Three types of bread, wheat flour bread, 15% rice flour bread, and 15% rice porridge bread, were prepared. After baking and storing the bread for 24 h, 48 h, and 72 h at room temperature, we measured the texture and viscoelastic properties of the bread crumbs by texture profile analysis (TPA) and creep test. The 15% rice porridge bread showed a significantly higher specific volume and maintained softer crumbs than the other two types (p<0.05). It also had a slightly stickier texture than the others. It can be concluded that rice porridge improves the specific volume, texture, and viscoelastic properties of bread crumbs during storage.
Elastic and viscoelastic properties of α iron at high temperatures
NASA Astrophysics Data System (ADS)
Isaak, Donald G.; Masuda, Koji
1995-09-01
Recent experiments done at low driving frequencies suggest that a large degree of dispersion exists in the measured value of the shear modulus, μ, of α iron at high temperature. Discrepancies between values for μ from ultrasonic measurements and those from low-frequency torsional measurements have been interpreted in terms of viscoelastic relaxation. However, the ultrasonic data are not in agreement with one another, and the degree of dispersion is not accurately known. We present new high-temperature data for the elastic moduli of single-crystal iron (α phase). The elastic moduli were measured using the rectangular parallelepiped resonance method (0.27-0.59 MHz) from room temperature to 925 K. Our data show that the difference in μ at high temperature between ultrasonic-based measurements and low-frequency (1 Hz) torsional measurements is only 14 GPa, rather than 29 GPa, as inferred from previous analyses. Thus the possible effects of viscoelastic relaxation are reduced but not eliminated. We find no dispersion in measurements for μ of α iron when considering frequencies ranging from 0.27 to 70 MHz and discuss the possibility that significant viscoelastic effects on measurements of μ at high temperature are limited to frequencies below 3 Hz.
Impact of leg lengthening on viscoelastic properties of the deep fascia
Wang, Hai-Qiang; Wei, Yi-Yong; Wu, Zi-Xiang; Luo, Zhuo-Jing
2009-01-01
Background Despite the morphological alterations of the deep fascia subjected to leg lengthening have been investigated in cellular and extracellular aspects, the impact of leg lengthening on viscoelastic properties of the deep fascia remains largely unknown. This study aimed to address the changes of viscoelastic properties of the deep fascia during leg lengthening using uniaxial tensile test. Methods Animal model of leg lengthening was established in New Zealand white rabbits. Distraction was initiated at a rate of 1 mm/day and 2 mm/day in two steps, and preceded until increases of 10% and 20% in the initial length of tibia had been achieved. The deep fascia specimens of 30 mm × 10 mm were clamped with the Instron 1122 tensile tester at room temperature with a constant tensile rate of 5 mm/min. After 5 load-download tensile tests had been performed, the specimens were elongated until rupture. The load-displacement curves were automatically generated. Results The normal deep fascia showed typical viscoelastic rule of collagenous tissues. Each experimental group of the deep fascia after leg lengthening kept the properties. The curves of the deep fascia at a rate of 1 mm/day with 20% increase in tibia length were the closest to those of normal deep fascia. The ultimate tension strength and the strain at rupture on average of normal deep fascia were 2.69 N (8.97 mN/mm2) and 14.11%, respectively. The increases in ultimate tension strength and strain at rupture of the deep fascia after leg lengthening were statistically significant. Conclusion The deep fascia subjected to leg lengthening exhibits viscoelastic properties as collagenous tissues without lengthening other than increased strain and strength. Notwithstanding different lengthening schemes result in varied viscoelastic properties changes, the most comparable viscoelastic properties to be demonstrated are under the scheme of a distraction rate of 1 mm/day and 20% increase in tibia length. PMID:19698092
NASA Astrophysics Data System (ADS)
Tsamopoulos, John; Karapetsas, George
2013-11-01
It is well known that during extrusion of viscoelastic fluids various flow instabilities may arise resulting in a distorted free surface. In order to investigate the factors generating these instabilities we perform a linear stability analysis at zero Reynolds number around the steady solution of the cylindrical or planar stick-slip flow for a viscoelastic fluid following the PTT model. The stick-slip flow is an important special case of the extrudate swell problem, since the latter reduces to it in the limit of infinite surface tension. We will show that the flow becomes unstable as the Weissenberg number increases above a critical value, due to a Hopf bifurcation suggesting that the flow will become periodic in time. Both the critical value of the Weissenberg number and the frequency of the instability depend strongly on the rheological parameters of the viscoelastic model. The elasticity alone can be responsible for the appearance of instabilities in the extrusion process of viscoelastic fluids and the often used assumptions of wall slip or compressibility, although they might be present, are not required. Finally, the mechanisms that produce these instabilities are examined through energy analysis of the disturbance flow. The authors would like to acknowledge the financial support by the General Secretariat of Research and Technology of Greece under the Action ``Supporting Postdoctoral Researchers'' (Grant No: PE8/906), and under the ``Excellence Program'' (Grant No: 1918)
On the use of a loudspeaker for measuring the viscoelastic properties of sound absorbing materials.
Doutres, Olivier; Dauchez, Nicolas; Génevaux, Jean-Michel; Lemarquand, Guy
2008-12-01
This paper investigates the feasibility to use an electrodynamic loudspeaker to determine viscoelastic properties of sound-absorbing materials in the audible frequency range. The loudspeaker compresses the porous sample in a cavity, and a measurement of its electrical impedance allows one to determine the mechanical impedance of the sample: no additional sensors are required. Viscoelastic properties of the material are then estimated by inverting a 1D Biot model. The method is applied to two sound-absorbing materials (glass wool and polymer foam). Results are in good agreement with the classical compression quasistatic method.
Effect of Matrix on Cardiomyocyte Viscoelastic Properties in 2D Culture
Deitch, Sandra; Gao, Bruce Z.; Dean, Delphine
2012-01-01
Cardiomyocyte phenotype changes significantly in 2D culture systems depending on the substrate composition and organization. Given the variety of substrates that are used both for basic cardiac cell culture studies and for regenerative medicine applications, there is a critical need to understand how the different matrices influence cardiac cell mechanics. In the current study, the mechanical properties of neonatal rat cardiomyocytes cultured in a subconfluent layer upon aligned and unaligned collagen and fibronectin matrices were assessed over a two week period using atomic force microscopy. The elastic modulus was estimated by fitting the Hertz model to force curve data and the percent relaxation was determined from stress relaxation curves. The Quasilinear Viscoelastic (QLV) and Standard Linear Solid (SLS) models were fit to the stress relaxation data. Cardiomyocyte cellular mechanical properties were found to be highly dependent on matrix composition and organization as well as time in culture. It was observed that the cells stiffened and relaxed less over the first 3 to 5 days in culture before reaching a plateau in their mechanical properties. After day 5, cells on aligned matrices were stiffer than cells on unaligned matrices and cells on fibronectin matrices were stiffer than cells on collagen matrices. No such significant trends in percent relaxation measurements were observed but the QLV model fit the data very well. These results were correlated with observed changes in cellular structure associated with culture on the different substrates and analyzed for cell-to-cell variability. PMID:23285736
Sun Hongxiang; Zhang Shuyi; Xu Baiqiang
2011-04-01
Taking account of the viscoelasticity of materials, the pulsed laser generation of surface acoustic waves in coating-substrate systems has been investigated quantitatively by using the finite element method. The displacement spectra of the surface acoustic waves have been calculated in frequency domain for different coating-substrate systems, in which the viscoelastic properties of the coatings and substrates are considered separately. Meanwhile, the temporal displacement waveforms have been obtained by applying inverse fast Fourier transforms. The numerical results of the normal surface displacements are presented for different configurations: a single plate, a slow coating on a fast substrate, and a fast coating on a slow substrate. The influences of the viscoelastic properties of the coating and the substrate on the attenuation of the surface acoustic waves have been studied. In addition, the influence of the coating thickness on the attenuation of the surface acoustic waves has been also investigated in detail.
NASA Astrophysics Data System (ADS)
Wakefield, David
approach to stress and stability analysis inherent in inTENS, and focuses in particular on: Implementation of an alternative application of the Incremental Schapery Rand (ISR) representation of the non-linear visco-elastic response of the polyethylene balloon film. This is based upon the relaxation modulus, rather than the creep compliance, and as such fits more efficiently into the Dynamic Relaxation analysis procedure used within inTENS. Comparisons of results between the two approaches are given. Verification of the material model by comparison with material tests. Verification of the application to pumpkin balloon structures by comparison with scale model tests. Application of inTENS with ISR to time-stepping analyses of a balloon flight including diurnal variations of temperature and pressure. This includes the demonstration of a method for checking the likely hood of overall instability developing at any particular time in the flight as both balloon geometry and film properties change due to visco-elastic effects.
Viscoelastic properties of elastomeric materials for O-ring applications
NASA Technical Reports Server (NTRS)
Bower, Mark V.
1989-01-01
Redesign of the Space Shuttle Solid Rocket Booster necessitated re-evaluation of the material used in the field joint O-ring seals. This research project was established to determine the viscoelastic characteristics of five candidate materials. The five materials are: two fluorocarbon compounds, two nitrile compounds, and a silicon compound. The materials were tested in a uniaxial compression test to determine the characteristic relaxation functions. These tests were performed at five different temperatures. A master material curve was developed for each material from the experimental data. The results of this study are compared to tensile relaxation tests. Application of these results to the design analysis is discussed in detail.
Canetta, Elisabetta; Duperray, Alain; Leyrat, Anne; Verdier, Claude
2005-01-01
Cell adhesive and rheological properties play a very important role in cell transmigration through the endothelial barrier, in particular in the case of inflammation (leukocytes) or cancer metastasis (cancer cells). In order to characterize cell viscoelastic properties, we have designed a force spectrometer (AFM) which can stretch cells thereby allowing measurement of their rheological properties. This custom-made force spectrometer allows two different visualizations, one lateral and one from below. It allows investigation of the effects of rheology involved during cell stretching. To test the ability of our system to characterize such viscoelastic properties, ICAM-1 transfected CHO cells were analyzed. Two forms of ICAM-1 were tested; wild type ICAM-1, which can interact with the cytoskeleton, and a mutant form which lacks the cytoplasmic domain, and is unable to associate with the cytoskeleton. Stretching experiments carried out on these cells show the formation of long filaments. Using a previous model of filament elongation, we could determine the viscoelastic properties of a single cell. As expected, different viscoelastic components were found between the wild type and the mutant, which reveal that the presence of interactions between ICAM-1 and the cytoskeleton increases the stiffness of the cell. PMID:16308464
Technology Transfer Automated Retrieval System (TEKTRAN)
The influence of jet-cooking Prowashonupana barley flour on total phenolic contents, antioxidant activities, water holding capacities, and viscoelastic properties was studied. Barley flour was jet-cooked without or with pH adjustment at 7, 9, or 11. Generally, the free phenolic content and antioxi...
NASA Technical Reports Server (NTRS)
1997-01-01
The bibliography contains citations concerning analytical techniques using constitutive equations, applied to materials under stress. The properties explored with these techniques include viscoelasticity, thermoelasticity, and plasticity. While many of the references are general as to material type, most refer to specific metals or composites, or to specific shapes, such as flat plate or spherical vessels.
Ferrando Chavez, Diana Lila; Nejidat, Ali; Herzberg, Moshe
2016-09-01
The role of the viscoelastic properties of biofouling layers in their removal from the membrane was studied. Model fouling layers of extracellular polymeric substances (EPS) originated from microbial biofilms of Pseudomonas aeruginosa PAO1 differentially expressing the Psl polysaccharide were used for controlled washing experiments of fouled RO membranes. In parallel, adsorption experiments and viscoelastic modeling of the EPS layers were conducted in a quartz crystal microbalance with dissipation (QCM-D). During the washing stage, as shear rate was elevated, significant differences in permeate flux recovery between the three different EPS layers were observed. According to the amount of organic carbon remained on the membrane after washing, the magnitude of Psl production provides elevated resistance of the EPS layer to shear stress. The highest flux recovery during the washing stage was observed for the EPS with no Psl. Psl was shown to elevate the layer's shear modulus and shear viscosity but had no effect on the EPS adhesion to the polyamide surface. We conclude that EPS retain on the membrane as a result of the layer viscoelastic properties. These results highlight an important relation between washing efficiency of fouling layers from membranes and their viscoelastic properties, in addition to their adhesion properties. PMID:27404109
Ferrando Chavez, Diana Lila; Nejidat, Ali; Herzberg, Moshe
2016-09-01
The role of the viscoelastic properties of biofouling layers in their removal from the membrane was studied. Model fouling layers of extracellular polymeric substances (EPS) originated from microbial biofilms of Pseudomonas aeruginosa PAO1 differentially expressing the Psl polysaccharide were used for controlled washing experiments of fouled RO membranes. In parallel, adsorption experiments and viscoelastic modeling of the EPS layers were conducted in a quartz crystal microbalance with dissipation (QCM-D). During the washing stage, as shear rate was elevated, significant differences in permeate flux recovery between the three different EPS layers were observed. According to the amount of organic carbon remained on the membrane after washing, the magnitude of Psl production provides elevated resistance of the EPS layer to shear stress. The highest flux recovery during the washing stage was observed for the EPS with no Psl. Psl was shown to elevate the layer's shear modulus and shear viscosity but had no effect on the EPS adhesion to the polyamide surface. We conclude that EPS retain on the membrane as a result of the layer viscoelastic properties. These results highlight an important relation between washing efficiency of fouling layers from membranes and their viscoelastic properties, in addition to their adhesion properties.
Importance of Viscoelastic Property Measurement of a New Hydrogel for Health Care
NASA Astrophysics Data System (ADS)
Roy, Niladri; Saha, Nabanita; Kitano, Takeshi; Saha, Petr
2009-07-01
A simple technology based new hydrogel "PVP-CMC-BA" has been prepared by the scientists of Tomas Bata University in Zlin, Czech Republic. Its swelling property (in presence of water, human blood and different pH), antimicrobial property (in presence of skin infection causing agents like: Staphylococcus aureus; bacteria and Candida albicans; fungi) and viscoelastic properties such as storage modulus (G'), loss modulus (G") and complex viscosity (η*) were investigated at room temperature (25-28° C) which demonstrate that PVP-CMC-BA hydrogel is maintaining requisite properties for health care application, specially as a wound dressing material. The elasticity and antimicrobial property of PVP-CMC-BA is directly correlated with percentage of boric acid, an antiseptic agent. The consequential values of viscoelastic properties of the hydrogel (before drying) enable us to understand its specific flexible condition to apply on the surface of human body.
NASA Astrophysics Data System (ADS)
Resapu, Rajeswara Reddy
The most common approaches to determining mechanical material properties of materials are tension and compression tests. However, tension and compression testing cannot be implemented under certain loading conditions (immovable object, not enough space to hold object for testing, etc). Similarly, tensile and compression testing cannot be performed on certain types of materials (delicate, bulk, non-machinable, those that cannot be separated from a larger structure, etc). For such cases, other material testing methods need to be implemented. Indentation testing is one such method; this approach is often non-destructive and can be used to characterize regions that are not compatible with other testing methods. However, indentation testing typically leads to force-displacement data as opposed to the direct stress-strain data normally used for the mechanical characterization of materials; this data needs to be analyzed using a suitable approach to determine the associated material properties. As such, methods to establish material properties from force-displacement indentation data need to be identified. In this work, a finite element approach using parameter optimization is developed to determine the mechanical properties from the experimental indentation data. Polymers and tissues tend to have time-dependent mechanical behavior; this means that their mechanical response under load changes with time. This dissertation seeks to characterize the properties of these materials using indentation testing under the assumption that they are linear viscoelastic. An example of a material of interest is the polymer poly vinyl chloride (PVC) that is used as the insulation of some aircraft wiring. Changes in the mechanical properties of this material over years of service can indicate degradation and a potential hazard to continued use. To investigate the validity of using indentation testing to monitor polymer insulation degradation, PVC film and PVC-insulated aircraft wiring are
Hayot, Céline M; Forouzesh, Elham; Goel, Ashwani; Avramova, Zoya; Turner, Joseph A
2012-04-01
Plant development results from controlled cell divisions, structural modifications, and reorganizations of the cell wall. Thereby, regulation of cell wall behaviour takes place at multiple length scales involving compositional and architectural aspects in addition to various developmental and/or environmental factors. The physical properties of the primary wall are largely determined by the nature of the complex polymer network, which exhibits time-dependent behaviour representative of viscoelastic materials. Here, a dynamic nanoindentation technique is used to measure the time-dependent response and the viscoelastic behaviour of the cell wall in single living cells at a micron or sub-micron scale. With this approach, significant changes in storage (stiffness) and loss (loss of energy) moduli are captured among the tested cells. The results reveal hitherto unknown differences in the viscoelastic parameters of the walls of same-age similarly positioned cells of the Arabidopsis ecotypes (Col 0 and Ws 2). The technique is also shown to be sensitive enough to detect changes in cell wall properties in cells deficient in the activity of the chromatin modifier ATX1. Extensive computational modelling of the experimental measurements (i.e. modelling the cell as a viscoelastic pressure vessel) is used to analyse the influence of the wall thickness, as well as the turgor pressure, at the positions of our measurements. By combining the nanoDMA technique with finite element simulations quantifiable measurements of the viscoelastic properties of plant cell walls are achieved. Such techniques are expected to find broader applications in quantifying the influence of genetic, biological, and environmental factors on the nanoscale mechanical properties of the cell wall.
Viscoelastic properties of erythrocyte membranes in high-frequency electric fields
NASA Astrophysics Data System (ADS)
Engelhardt, H.; Gaub, H.; Sackmann, E.
1984-01-01
The high deformability of erythrocytes which is essential for their transport through the capillaries depends critically on their discoid shape and on the elasticity of the plasma membrane, which may be determined by interactions of the cytoskeleton, the lipid/protein leaflet and the glycocalyx. Although techniques exist for measurement of the static elastic properties of erythrocytes, the cells are continuously deformed in vivo, the stress varying within periods of a few seconds. Thus dynamic elastic behaviour is essential for their physiological function. We present here a novel means of measuring the dynamic elastic constants of the red cell based on the transient deformation of individual cells in an inhomogeneous high-frequency (HF) electric field. By microscopy it is possible to record cellular elongations as small as 200 nm occurring within time scales of 1 ms. A main advantage is that the cellular response is linear and thus can be more readily interpreted theoretically. We have observed a creep function consisting of two exponentials with response times of 0.1 s and 1 s, which can be described in terms of a simple viscoelastic model. A remarkable temperature dependence of the membrane elasticity between 25 °C and 15 °C is observed for freshly drawn cells but not for trypsinized ones.
Subcritical dyke propagation in a host rock with temperature-dependent viscoelastic properties
NASA Astrophysics Data System (ADS)
Chen, Zuan; Jin, Z.-H.
2011-09-01
In this paper, we examine the effects of temperature-dependent viscoelastic properties of the host rock on the subcritical growth of a dyke from a magma chamber. A theoretical relationship between the velocity of subcritical dyke growth and dyke length is established using a perturbation solution of stress intensity factor at the dyke tip and a viscoelastic crack growth theory in which the temperature-dependent creep properties are taken into account. The temperature field around the dyke is calculated using an analytic solution. The numerical results for a dyke subcritically propagating from a magma chamber indicate that while the general dyke growth characteristics are similar to those with constant creep properties, the subcritical dyke growth velocity is increased by an order of magnitude by considering the temperature dependence of the creep properties. Hence, the subcritical growth duration before the dyke reaches the unstable growth state is significantly shortened.
NASA Astrophysics Data System (ADS)
Posnansky, Oleg
2016-09-01
The measuring of viscoelastic response is widely used for revealing information about soft matter and biological tissue noninvasively. This information encodes intrinsic dynamic correlations and depends on relations between macroscopic viscoelasticity and structure at the mesoscopic scale. Here we show numerically that the frequency dependent dynamical shear moduli distinguish between the mesoscopic architectural complexities and sensitive to the Euclidean dimensionality. Our approach enables the explanation of two- and three-dimensional viscoelastic experiments by objectively choosing and modeling the most relevant architectural features such as the concentration of compounds and intra-model hierarchical characteristics of physical parameters. Current work provides a link between the macroscopical effective viscoelastic properties to viscoelastic constants and network geometry on the mesoscale. Besides of this we also pay attention to the analytical properties of generalized susceptibility function of considered constitutive model accounting principles of causality.
Lyotropic chromonic liquid crystals: From viscoelastic properties to living liquid crystals
NASA Astrophysics Data System (ADS)
Zhou, Shuang
Lyotropic chromonic liquid crystal (LCLC) represents a broad range of molecules, from organic dyes and drugs to DNA, that self-assemble into linear aggregates in water through face-to-face stacking. These linear aggregates of high aspect ratio are capable of orientational order, forming, for example nematic phase. Since the microscopic properties (such as length) of the chromonic aggregates are results of subtle balance between energy and entropy, the macroscopic viscoelastic properties of the nematic media are sensitive to change of external factors. In the first part of this thesis, by using dynamic light scattering and magnetic Frederiks transition techniques, we study the Frank elastic moduli and viscosity coefficients of LCLC disodium cromoglycate (DSCG) and sunset yellow (SSY) as functions of concentration c , temperature T and ionic contents. The elastic moduli of splay (K1) and bend (K3) are in the order of 10pN, about 10 times larger than the twist modulus (K2). The splay modulus K1 and the ratio K1/K3 both increase substantially as T decreases or c increases, which we attribute to the elongation of linear aggregates at lower T or higher c . The bend viscosity is comparable to that of thermotropic liquid crystals, while the splay and twist viscosities are several orders of magnitude larger, changing exponentially with T . Additional ionic additives into the system influence the viscoelastic properties of these systems in a dramatic and versatile way. For example, monovalent salt NaCl decreases bend modulus K3 and increases twist viscosity, while an elevated pH decreases all the parameters. We attribute these features to the ion-induced changes in length and flexibility of building units of LCLC, the chromonic aggregates, a property not found in conventional thermotropic and lyotropic liquid crystals form by covalently bound units of fixed length. The second part of the thesis studies a new active bio-mechanical hybrid system called living liquid crystal
Visco-Elastic Properties of Sodium Hyaluronate Solutions
NASA Astrophysics Data System (ADS)
Kulicke, Werner-Michael; Meyer, Fabian; Bingöl, Ali Ö.; Lohmann, Derek
2008-07-01
Sodium Hyaluronate (NaHA) is a member of the glycosaminoglycans and is present in the human organism as part of the synovial fluid and the vitreous body. HA is mainly commercialized as sodium or potassium salt. It can be extracted from cockscombs or can be produced by bacterial fermentation ensuring a low protein content. Because of its natural origin and toxicological harmlessness, NaHA is used to a great extent for pharmaceutical and cosmetic products. In medical applications, NaHA is already being used as a component of flushing and stabilizing fluids in the treatment of eye cataract and as a surrogate for natural synovial fluid. Another growing domain in the commercial utilization of NaHA is the field of skin care products like dermal fillers or moisturizers. In this spectrum, NaHA is used in dilute over semidilute up to concentrated (0
Jan, Yih-Kuen; Lung, Chi-Wen; Cuaderes, Elena; Rong, Daqian; Boyce, Kari
2013-01-01
Diabetic foot ulcers are one of the most serious complications associated with diabetes mellitus. Current research studies have demonstrated that biomechanical alterations of the diabetic foot contribute to the development of foot ulcers. However, the changes of soft tissue biomechanical properties associated with diabetes and its influences on the development of diabetic foot ulcers have not been investigated. The purpose of this study was to investigate the effect of diabetes on the biomechanical properties of plantar soft tissues and the relationship between biomechanical properties and plantar pressure distributions. We used the ultrasound indentation tests to measure force-deformation relationships of plantar soft tissues and calculate the effective Young's modulus and quasi-linear viscoelastic parameters to quantify biomechanical properties of plantar soft tissues. We also measured plantar pressures to calculate peak plantar pressure and plantar pressure gradient. Our results showed that diabetics had a significantly greater effective Young's modulus and initial modulus of quasi-linear viscoelasticity compared to non-diabetics. The plantar pressure gradient and biomechanical properties were significantly correlated. Our findings indicate that diabetes is linked to an increase in viscoelasticity of plantar soft tissues that may contribute to a higher peak plantar pressure and plantar pressure gradient in the diabetic foot.
Protsenko, Iu L; Kobelev, A V; Lukin, O N; Balakin, A A; Smoliuk, L T
2009-07-01
Peculiarities of viscoelastic behavior of rabbit papillary muscle in passive state are studied by transversal versus longitudinal deformation curves, stress-strain and hysteresis curves, and stress relaxation curves under ramp stretching. The papillary muscle was chosen because of mostly longitudinal orientation of fibers and its elongated shape, which both make it as an appropriate model for uniaxial tests. The problem of evaluation of connective tissue protein structures and intracellular matrix contribution into the properties under consideration is solved by using the maceration method to remove intracellular structures. The different contribution of intracellular and extracellular protein features into total properties of a papillary muscle leads to nonlinearity of myocardial viscoelastic properties, such as the increase of differential elastic module and relaxation time with deformation.
NASA Astrophysics Data System (ADS)
Fincan, Mustafa
Polydimethylsiloxane (PDMS) mechanical properties were measured using custom-built compression test device. PDMS elastic modulus can be varied with the elastomer base to the curing agent ratio, i.e. by changing the cross-linking density. PDMS samples with different crosslink density in terms of their elastic modulus were measured. In this project the PDMS samples with the base/curing agent ratio ranging from 5:1 to 20:1 were tested. The elastic modulus varied with the amount of the crosslinker, and ranged from 0.8 MPa to 4.44 MPa. The compression device was modified by adding digital displacement gauges to measure the lateral strain of the sample, which allowed obtaining the true stress-strain data. Since the unloading behavior was different than the loading behavior of the viscoelastic PDMS, it was utilized to asses viscoelastic properties of the polymer. The thesis describes a simple method for measuring mechanical properties of soft polymeric materials.
NASA Astrophysics Data System (ADS)
Yuan, K. Y.; Yuan, W.; Ju, J. W.; Yang, J. M.; Kao, W.; Carlson, L.
2013-04-01
As asphalt pavements age and deteriorate, recurring pothole repair failures and propagating alligator cracks in the asphalt pavements have become a serious issue to our daily life and resulted in high repairing costs for pavement and vehicles. To solve this urgent issue, pothole repair materials with superior durability and long service life are needed. In the present work, revolutionary pothole patching materials with high toughness, high fatigue resistance that are reinforced with nano-molecular resins have been developed to enhance their resistance to traffic loads and service life of repaired potholes. In particular, DCPD resin (dicyclopentadiene, C10H12) with a Rhuthinium-based catalyst is employed to develop controlled properties that are compatible with aggregates and asphalt binders. In this paper, a multi-level numerical micromechanics-based model is developed to predict the viscoelastic properties and dynamic moduli of these innovative nano-molecular resin reinforced pothole patching materials. Irregular coarse aggregates in the finite element analysis are modeled as randomly-dispersed multi-layers coated particles. The effective properties of asphalt mastic, which consists of fine aggregates, tar, cured DCPD and air voids are theoretically estimated by the homogenization technique of micromechanics in conjunction with the elastic-viscoelastic correspondence principle. Numerical predictions of homogenized viscoelastic properties and dynamic moduli are demonstrated.
NASA Astrophysics Data System (ADS)
Rebelo, L. M.; de Sousa, J. S.; Mendes Filho, J.; Radmacher, M.
2013-02-01
The viscoelastic properties of human kidney cell lines from different tumor types (carcinoma (A-498) and adenocarcinoma (ACHN)) are compared to a non-tumorigenic cell line (RC-124). Our methodology is based on the mapping of viscoelastic properties (elasticity modulus E and apparent viscosity η) over the surface of tens of individual cells with atomic force microscopy (AFM). The viscoelastic properties are averaged over datasets as large as 15000 data points per cell line. We also propose a model to estimate the apparent viscosity of soft materials using the hysteresis observed in conventional AFM deflection-displacement curves, without any modification to the standard AFM apparatus. The comparison of the three cell lines show that the non-tumorigenic cells are less deformable and more viscous than cancerous cells, and that cancer cell lines have distinctive viscoelastic properties. In particular, we obtained that ERC-124 > EA-498 > EACHN and ηRC-124 > ηA-498 > ηACHN.
NASA Astrophysics Data System (ADS)
Price, Carey Daniel
Homogenous polymer materials, such as bulk polyester or high-density polyethylene (HDPE), are not commonly associated with armor materials in their raw, unmodified form due to their poor performance at typical ballistic impact velocities. However, projectile penetrations into homogenous polymeric materials have been shown to correlate strongly to the highly temperature-dependent viscoelastic properties such as elastic storage modulus and loss modulus. Ballistic trials conducted at room temperature showed that these two parameters statistically account for a large percentage of the variation in ballistic performance between different polymers. The purpose of this study is to determine the correlation of viscoelastic properties to ballistic resistance when the temperature of the polymer targets is altered above and below room temperature. The ultimate goal is to use these data to determine which materials would perform best against ultra-high velocity impacts, such as the case of micrometeoroid impacts with spacecraft.
Custom-Built Optical Tweezers for Locally Probing the Viscoelastic Properties of Cancer Cells
NASA Astrophysics Data System (ADS)
Tavano, Federica; Bonin, Serena; Pinato, Giulietta; Stanta, Giorgio; Cojoc, Dan
2011-07-01
We report a home built optical tweezers setup to investigate the mechanism of the membrane tether formation from single cells in vitro. Using an optically trapped microbead as probe, we have determined the force-elongation curve during tether formation and extracted several parameters characterizing the viscoelastic behavior of the cell membrane: tether stiffness, force, and viscosity. Breast cancer MDA-MB-231 cells have been studied in two different conditions, at room and physiological temperatures, showing a strong temperature dependence of the visoelastic properties of the cell membrane. To get detailed inside information about the tether formation mechanism we have extended the analysis of the force-elongation curves fitting them with a Kelvin model. These preliminary results are part of a larger project of whose goal is to compare the viscoelastic properties of several types of cancer cell lines, characterized by different aggressiveness and metastatic potential.
Measurement of Viscoelastic Properties of Condensed Matter using Magnetic Resonance Elastography
NASA Astrophysics Data System (ADS)
Gruwel, Marco L. H.; Latta, Peter; Matwiy, Brendon; Sboto-Frankenstein, Uta; Gervai, Patricia; Tomanek, Boguslaw
2010-01-01
Magnetic resonance elastography (MRE) is a phase contrast technique that provides a non-invasive means of evaluating the viscoelastic properties of soft condensed matter. This has a profound bio-medical significance as it allows for the virtual palpation of areas of the body usually not accessible to the hands of a medical practitioner, such as the brain. Applications of MRE are not restricted to bio-medical applications, however, the viscoelastic properties of prepackaged food products can also non-invasively be determined. Here we describe the design and use of a modular MRE acoustic actuator that can be used for experiments ranging from the human brain to pre-packaged food products. The unique feature of the used actuator design is its simplicity and flexibility, which allows easy reconfiguration.
NASA Astrophysics Data System (ADS)
Erdel, Fabian; Baum, Michael; Rippe, Karsten
2015-02-01
The eukaryotic cell nucleus harbours the DNA genome that is organized in a dynamic chromatin network and embedded in a viscous crowded fluid. This environment directly affects enzymatic reactions and target search processes that access the DNA sequence information. However, its physical properties as a reaction medium are poorly understood. Here, we exploit mobility measurements of differently sized inert green fluorescent tracer proteins to characterize the viscoelastic properties of the nuclear interior of a living human cell. We find that it resembles a viscous fluid on small and large scales but appears viscoelastic on intermediate scales that change with protein size. Our results are consistent with simulations of diffusion through polymers and suggest that chromatin forms a random obstacle network rather than a self-similar structure with fixed fractal dimensions. By calculating how long molecules remember their previous position in dependence on their size, we evaluate how the nuclear environment affects search processes of chromatin targets.
NASA Technical Reports Server (NTRS)
1996-01-01
The bibliography contains citations concerning analytical techniques using constitutive equations, applied to materials under stress. The properties explored with these techniques include viscoelasticity, thermoelasticity, and plasticity. While many of the references are general as to material type, most refer to specific metals or composites, or to specific shapes, such as flat plate or spherical vessels. (Contains 50-250 citations and includes a subject term index and title list.)
Measurement of instantaneous viscoelastic properties by impedance-frequency curve of the ventricle.
Koiwa, Y; Hashiguchi, R; Ohyama, T; Isoyama, S; Satoh, S; Suzuki, H; Takishima, T
1986-04-01
We developed a method for estimating the instantaneous viscoelastic properties of the left ventricle (LV). This impedance-curve method is based on the instantaneous impedance-frequency curve of the left ventricle generated by a rapidly oscillating mechanical impulse applied to the epicardial surface of the heart. The theoretical basis of the method and experimentally obtained instantaneous impedance-frequency curves were examined to evaluate the validity of our basic assumptions. Using these impedance-curve data, we calculated the instantaneous viscoelastic properties of the LV during the cardiac cycle. The impedance curve shows a configuration that is almost the same as the theoretical curve based on the assumption that an RCL (R, resistor; C, capacitor; L, inductor) parallel circuit is the electrical analog for the LV. The impedance curve varied moment by moment during the development of instantaneous LV pressure. The elastic and viscous coefficients, calculated from the impedance curve, increased with increase of LV pressure. We concluded that the impedance-curve method can delineate the instantaneous viscoelastic properties of the ventricle (especially of the ventricular myocardium).
The viscoelastic properties of the vitreous humor measured using an optically trapped local probe
NASA Astrophysics Data System (ADS)
Watts, Fiona; Tan, Lay Ean; Tassieri, Manlio; McAlinden, Niall; Wilson, Clive G.; Girkin, John M.; Wright, Amanda J.
2011-10-01
We present results demonstrating for the first time that an optically trapped bead can be used as a local probe to measure the variation in the viscoelastic properties of the vitreous humor of a rabbit eye. The Brownian motion of the optically trapped bead was monitored on a fast CCD camera on the millisecond timescale. Analysis of the bead trajectory provides local information about the viscoelastic properties of the medium surrounding the particle. Previous, bulk, methods for measuring the viscoelastic properties of the vitreous destroy the sample and allow only a single averaged measurement to be taken per eye. Whereas, with our approach, we were able to observe local behaviour typical of non-Newtonian and gel-like materials, along with the homogenous and in-homogeneous nature of different regions of the dissected vitreous humor. The motivation behind these measurements is to gain a better understanding of the structure of the vitreous humor in order to design effective drug delivery techniques. In particular, we are interested in methods for delivering drug to the retina of the eye in order to treat sight threatening diseases such as age related macular degeneration.
Feng, Y.; Clayton, E.H.; Chang, Y.; Okamoto, R.J.; Bayly, P.V.
2013-01-01
Characterization of the dynamic mechanical behavior of brain tissue is essential for understanding and simulating the mechanisms of traumatic brain injury (TBI). Changes in mechanical properties may also reflect changes in the brain due to aging or disease. In this study, we used magnetic resonance elastography (MRE) to measure the viscoelastic properties of ferret brain tissue in vivo. Three-dimensional (3D) displacement fields were acquired during wave propagation in the brain induced by harmonic excitation of the skull at 400 Hz, 600 Hz and 800 Hz. Shear waves with wavelengths on the order of millimeters were clearly visible in the displacement field, in strain fields, and in the curl of displacement field (which contains no contributions from longitudinal waves). Viscoelastic parameters (storage and loss moduli) governing dynamic shear deformation were estimated in gray and white matter for these excitation frequencies. To characterize the reproducibility of measurements, two ferrets were studied on three different dates each. Estimated viscoelastic properties of white matter in the ferret brain were generally similar to those of gray matter and consistent between animals and scan dates. In both tissue types G′ increased from approximately 3 kPa at 400 Hz to 7 kPa at 800 Hz and G″ increased from approximately 1 kPa at 400 Hz to 2 kPa at 800 Hz. These measurements of shear wave propagation in the ferret brain can be used to both parameterize and validate finite element models of brain biomechanics. PMID:23352648
Cartagena, Alexander; Raman, Arvind
2014-03-01
The measurement of viscoelasticity of cells in physiological environments with high spatio-temporal resolution is a key goal in cell mechanobiology. Traditionally only the elastic properties have been measured from quasi-static force-distance curves using the atomic force microscope (AFM). Recently, dynamic AFM-based methods have been proposed to map the local in vitro viscoelastic properties of living cells with nanoscale resolution. However, the differences in viscoelastic properties estimated from such dynamic and traditional quasi-static techniques are poorly understood. In this work we quantitatively reconstruct the local force and dissipation gradients (viscoelasticity) on live fibroblast cells in buffer solutions using Lorentz force excited cantilevers and present a careful comparison between mechanical properties (local stiffness and damping) extracted using dynamic and quasi-static force spectroscopy methods. The results highlight the dependence of measured viscoelastic properties on both the frequency at which the chosen technique operates as well as the interactions with subcellular components beyond certain indentation depth, both of which are responsible for differences between the viscoelasticity property maps acquired using the dynamic AFM method against the quasi-static measurements.
Electro-optic and viscoelastic properties of a ferroelectric liquid crystalline binary mixture
NASA Astrophysics Data System (ADS)
Dardas, Dorota
2016-04-01
This study describes the properties of a binary liquid crystalline mixture composed of commercially available materials, Ce-3 (4-(n-hexyloxy phenyl)-1-(2-fuethyl butyl) biphenyl-4-carboxylate) and Ce-8 (4-(2-methylbutyl) phenyl-4-n-octylbiphenyl-4-carboxylate), in a weight ratio of 50:50. Both compounds show polymesomorphism and ferroelectric properties within a relatively wide temperature range. Taken separately, each compound has its advantages and disadvantages from the technical point of view. The influence of temperature on the electro-optical and viscoelastic properties of the produced binary mixture is investigated in this paper.
Transient vibration of thin viscoelastic orthotropic plates
NASA Astrophysics Data System (ADS)
Soukup, J.; Valeš, F.; Volek, J.; Skočilas, J.
2011-02-01
This article deals with solutions of transient vibration of a rectangular viscoelastic orthotropic thin 2D plate for particular deformation models according to Flügge and Timoshenko-Mindlin. The linear model, a general standard viscoelastic body, of the rheologic properties of a viscoelastic material was applied. The time and coordinate curves of the basic quantities displacement, rotation, velocity, stress and deformation are compared. The results obtained by an approximate analytic method are compared with numerical results for 3D plate generated by FEM application and with experimental investigation.
Soft viscoelastic properties of nuclear actin age oocytes due to gravitational creep.
Feric, Marina; Broedersz, Chase P; Brangwynne, Clifford P
2015-11-18
The actin cytoskeleton helps maintain structural organization within living cells. In large X. laevis oocytes, gravity becomes a dominant force and is countered by a nuclear actin network that prevents liquid-like nuclear bodies from immediate sedimentation and coalescence. However, nuclear actin's mechanical properties, and how they facilitate the stabilization of nuclear bodies, remain unknown. Using active microrheology, we find that nuclear actin forms a weak viscoelastic network, with a modulus of roughly 0.1 Pa. Embedded probe particles subjected to a constant force exhibit continuous displacement, due to viscoelastic creep. Gravitational forces also cause creep displacement of nuclear bodies, resulting in their asymmetric nuclear distribution. Thus, nuclear actin does not indefinitely support the emulsion of nuclear bodies, but only kinetically stabilizes them by slowing down gravitational creep to ~2 months. This is similar to the viability time of large oocytes, suggesting gravitational creep ages oocytes, with fatal consequences on long timescales.
Soft viscoelastic properties of nuclear actin age oocytes due to gravitational creep.
Feric, Marina; Broedersz, Chase P; Brangwynne, Clifford P
2015-01-01
The actin cytoskeleton helps maintain structural organization within living cells. In large X. laevis oocytes, gravity becomes a dominant force and is countered by a nuclear actin network that prevents liquid-like nuclear bodies from immediate sedimentation and coalescence. However, nuclear actin's mechanical properties, and how they facilitate the stabilization of nuclear bodies, remain unknown. Using active microrheology, we find that nuclear actin forms a weak viscoelastic network, with a modulus of roughly 0.1 Pa. Embedded probe particles subjected to a constant force exhibit continuous displacement, due to viscoelastic creep. Gravitational forces also cause creep displacement of nuclear bodies, resulting in their asymmetric nuclear distribution. Thus, nuclear actin does not indefinitely support the emulsion of nuclear bodies, but only kinetically stabilizes them by slowing down gravitational creep to ~2 months. This is similar to the viability time of large oocytes, suggesting gravitational creep ages oocytes, with fatal consequences on long timescales. PMID:26577186
Soft viscoelastic properties of nuclear actin age oocytes due to gravitational creep
Feric, Marina; Broedersz, Chase P.; Brangwynne, Clifford P.
2015-01-01
The actin cytoskeleton helps maintain structural organization within living cells. In large X. laevis oocytes, gravity becomes a dominant force and is countered by a nuclear actin network that prevents liquid-like nuclear bodies from immediate sedimentation and coalescence. However, nuclear actin’s mechanical properties, and how they facilitate the stabilization of nuclear bodies, remain unknown. Using active microrheology, we find that nuclear actin forms a weak viscoelastic network, with a modulus of roughly 0.1 Pa. Embedded probe particles subjected to a constant force exhibit continuous displacement, due to viscoelastic creep. Gravitational forces also cause creep displacement of nuclear bodies, resulting in their asymmetric nuclear distribution. Thus, nuclear actin does not indefinitely support the emulsion of nuclear bodies, but only kinetically stabilizes them by slowing down gravitational creep to ~2 months. This is similar to the viability time of large oocytes, suggesting gravitational creep ages oocytes, with fatal consequences on long timescales. PMID:26577186
Mahross, Hamada Zaki; Baroudi, Kusai
2015-01-01
Objective: The objective was to investigate the effect of silver nanoparticles (AgNPs) incorporation on viscoelastic properties of acrylic resin denture base material. Materials and Methods: A total of 20 specimens (60 × 10 × 2 mm) of heat cured acrylic resin were constructed and divided into four groups (five for each), according to the concentration of AgNPs (1%, 2%, and 5% vol.) which incorporated into the liquid of acrylic resin material and one group without additives (control group). The dynamic viscoelastic test for the test specimens was performed using the computerized material testing system. The resulting deflection curves were analyzed by material testing software NEXYGEN MT. Results: The 5% nanoparticles of silver (NAg) had significantly highest mean storage modulus E’ and loss tangent Tan δ values followed by 2% NAg (P < 0.05). For 1% nanosilver incorporation (group B), there were no statistically significant differences in storage modulus E’, lost modulus E” or loss tangent Tan δ with other groups (P > 0.05). Conclusion: The AgNPs incorporation within the acrylic denture base material can improve its viscoelastic properties. PMID:26038651
NASA Technical Reports Server (NTRS)
Gutierrez-Lemini, Danton; McCool, Alex (Technical Monitor)
2001-01-01
A method is developed to establish the J-resistance function for an isotropic linear viscoelastic solid of constant Poisson's ratio using the single-specimen technique with constant-rate test data. The method is based on the fact that, for a test specimen of fixed crack size under constant rate, the initiation J-integral may be established from the crack size itself, the actual external load and load-point displacement at growth initiation, and the relaxation modulus of the viscoelastic solid, without knowledge of the complete test record. Since crack size alone, of the required data, would be unknown at each point of the load-vs-load-point displacement curve of a single-specimen test, an expression is derived to estimate it. With it, the physical J-integral at each point of the test record may be established. Because of its basis on single-specimen testing, not only does the method not require the use of multiple specimens with differing initial crack sizes, but avoids the need for tracking crack growth as well.
Rheological Properties of Viscoelastic Drops on Superamphiphobic Substrates.
Harrold, Victoria C; Paven, Maxime; Vollmer, Doris; Sharp, James S
2016-04-26
The rheological properties of microliter sized drops of polymer solutions were investigated using measurements of their mechanical vibrational response. Drops were suspended on superamphiphobic substrates and vibrated by the application of a short mechanical impulse. Surface vibrations were monitored by refracting laser light through the drops and focusing the refracted light onto the surface of a photodiode. Time dependent variations in the photodiode output were Fourier transformed to obtain the frequency and spectral width of the mechanical resonances of the drops. These quantities were related to the frequency dependent shear storage and loss moduli (G' and G″, respectively) using a simple theoretical model. The resulting rheological properties were found to be in agreement with microrheology measurements of the same solutions. Drop vibration therefore provides a fast and accurate method of quantifying the rheological properties of single drops.
NASA Astrophysics Data System (ADS)
Noll, Kenneth; Wong, Maranda; Evke, Erin; Rende, Deniz; Ozisik, Rahmi
2014-03-01
Polycarbonate, PC, and poly(methyl methacrylate), PMMA, are economic alternatives to glass mainly die to their mecahnical and optical properties. The uses of PC and PMMA can be expanded if their impact response and scratch resistance are improved. Carbon nanotubes are known to increase the toughness of PMMA and improve its resistance impact forces. In the current study, the viscoelastic properties of PC, PMMA and their nanocomposites were investigated via nanoindentation experiments. Stress relaxation experiments were performed under various loading rates._ The material is partially based upon work supported by NSF under Grant Nos. 1200270 and 1003574.
Viscoelastic Properties and Morphology of Mumio-based Medicated Hydrogels
NASA Astrophysics Data System (ADS)
Zandraa, Oyunchimeg; Jelínková, Lenka; Roy, Niladri; Sáha, Tomáš; Kitano, Takeshi; Saha, Nabanita
2011-07-01
Novel medicated hydrogels were prepared (by moist heat treatment) with PVA, agar, mumio, mare's milk (MM), seabuckthorn oil (SB oil) and salicylic acid (SA) for wound dressing/healing application. Scanning electron micrographs (SEM) show highly porous structure of these hydrogels. The swelling behaviour of the hydrogels in physiological solution displays remarkable liquid absorption property. The knowledge obtained from rheological investigations of these-systems may be highly useful for the characterization of the newly developed topical formulations. In the present study, an oscillation frequency sweep test was used for the evaluation of storage modulus (G'), loss modulus (G″), and complex viscosity (η*) of five different formulations, over an angular frequency range from 0.1 to 100 rad.s-1. The influence of healing agents and swelling effect on the rheological properties of mumio-based medicated hydrogels was investigated to judge its application on uneven surface of body.
Tomaiuolo, Giovanna; Rusciano, Giulia; Caserta, Sergio; Carciati, Antonio; Carnovale, Vincenzo; Abete, Pasquale; Sasso, Antonio; Guido, Stefano
2014-01-01
In cystic fibrosis (CF) patients airways mucus shows an increased viscoelasticity due to the concentration of high molecular weight components. Such mucus thickening eventually leads to bacterial overgrowth and prevents mucus clearance. The altered rheological behavior of mucus results in chronic lung infection and inflammation, which causes most of the cases of morbidity and mortality, although the cystic fibrosis complications affect other organs as well. Here, we present a quantitative study on the correlation between cystic fibrosis mucus viscoelasticity and patients clinical status. In particular, a new diagnostic parameter based on the correlation between CF sputum viscoelastic properties and the severity of the disease, expressed in terms of FEV1 and bacterial colonization, was developed. By using principal component analysis, we show that the types of colonization and FEV1 classes are significantly correlated to the elastic modulus, and that the latter can be used for CF severity classification with a high predictive efficiency (88%). The data presented here show that the elastic modulus of airways mucus, given the high predictive efficiency, could be used as a new clinical parameter in the prognostic evaluation of cystic fibrosis.
Even-Tzur, Nurit; Weisz, Ety; Hirsch-Falk, Yifat; Gefen, Amit
2006-01-01
Modern sport shoes are designed to attenuate mechanical stress waves, mainly through deformation of the viscoelastic midsole which is typically made of ethylene vinyl acetate (EVA) foam. Shock absorption is obtained by flow of air through interconnected air cells in the EVA during shoe deformation under body-weight. However, when the shoe is overused and air cells collapse or thickness of the EVA is reduced, shock absorption capacity may be affected, and this may contribute to running injuries. Using lumped system and finite element models, we studied heel pad stresses and strains during heel-strike in running, considering the viscoelastic constitutive behavior of both the heel pad and EVA midsole. In particular, we simulated wear cases of the EVA, manifested in the modeling by reduced foam thickness, increased elastic stiffness, and shorter stress relaxation with respect to new shoe conditions. Simulations showed that heel pad stresses and strains were sensitive to viscous damping of the EVA. Wear of the EVA consistently increased heel pad stresses, and reduced EVA thickness was the most influential factor, e.g., for a 50% reduction in thickness, peak heel pad stress increased by 19%. We conclude that modeling of the heel-shoe interaction should consider the viscoelastic properties of the tissue and shoe components, and the age of the studied shoe.
Viscoelastic properties of human arteries. Methodology and preliminary results.
Rosset, E; Brunet, C; Rieu, R; Rolland, P; Pellissier, J F; Magnan, P E; Foulon, P; Drizenko, A; Laude, M; Branchereau, A; Friggi, A
1996-01-01
In order to study the biomechanical properties of the arterial wall and to compare arteries with different histologic structures, we designed a device that allows testing of arterial segments under near-physiologic conditions. A hydrodynamic generator simulates systolo-diastolic pressures in an open loop. An intraarterial pressure sensor and a sonomicrometer connected to two piezoelectric crystals placed in diametric opposition on the arterial wall allow computer calculation of compliance, stiffness, midwall radial arterial stress, Young modulus, and incremental modulus for a given arterial segment at a given pressure setting. Seven healthy common carotid artery (CCA) segments and seven healthy (superficial) femoral artery (FA) segments were studied immediately after removal from brain-dead donors between the ages of 18 and 35 years. Histologic examination was performed to determine the density of elastic fibers in the arterial wall. Hysteresis was observed in all segments regardless of pressure settings. Compliance was greater and modulus values and stiffness were lower in CCA than in FA. No evidence of structural change was noted after testing in the circulation loop. These preliminary results open the way to a wide variety of applications for our hydrodynamic circulation loop. Experiments will be undertaken to compare the mechanical properties of arteries before and after cryopreservation.
Viscoelastic properties of kenaf reinforced unsaturated polyester composites
NASA Astrophysics Data System (ADS)
Osman, Ekhlas A.; Mutasher, Saad A.
2014-03-01
In order to quantify the effect of temperature on the mechanical and dynamic properties of kenaf fiber unsaturated polyester composites, formulations containing 10 wt.% to 40 wt.% kenaf fiber were produced and tested at two representative temperatures of 30°C and 50°C. Dynamic mechanical analysis was performed, to obtain the strain and creep compliance for kenaf composites at various styrene concentrations. It is possible to obtain creep curves at different temperature levels which can be shifted along the time axis to generate a single curve known as a master curve. This technique is known as the time-temperature superposition principle. Shift factors conformed to a William-Landel-Ferry (WLF) equation. However, more long term creep data was needed in order to further validate the applicability of time-temperature superposition principle (TTSP) to this material. The primary creep strain model was fitted to 60 min creep data. The resulting equation was then extrapolated to 5.5 days; the creep strain model of power-law was successfully used to predict the long-term creep behavior of natural fiber/thermoset composites.
Theoretical and experimental studies on viscoelastic properties of erythrocyte membrane.
Chien, S; Sung, K L; Skalak, R; Usami, S; Tözeren, A
1978-01-01
The deformation of a portion of erythrocyte during aspirational entry into a micropipette has been analyzed on the basis of a constant area deformation of an infinite plane membrane into a cylindrical tube. Consideration of the equilibrium of the membrane at the tip of the pipette has generated the relation between the aspirated length and the dimensionless time during deformational entry as well as during relaxation after the removal of aspiration pressure. Experimental studies on deformation and relaxation of normal human erythrocytes were performed with the use of micropipettes and a video dimension analyzer which allowed the continuous recording of the time-courses. The deformation consisted of an initial rapid phase with a membrane viscosity (range 0.6 x 10(-4) to 4 x 10(-4) dyn.s/cm) varying inversely with the degree of deformation and a later slow phase with a high membrane viscosity (mean 2.06 x 10(-2) dyn.s/cm) which was not correlated with the degree of deformation. The membrane viscosity of the recovery phase after 20 s of deformation (mean 5.44 x 10(-4) dyn.s/cm) was also independent of the degree of deformation. When determined after a short period of deformation (e.g., 2 s), however, membrane viscosity of the recovery phase became lower and agreed with that of the deformation phase. These results suggest that the rheological properties of the membrane can undergo dynamic changes depending on the extent and duration of deformation, reflecting molecular rearrangement in response to membrane strain. PMID:728524
NASA Astrophysics Data System (ADS)
Phan, See-Eng; Li, Min; Russel, William B.; Zhu, Jixiang; Chaikin, Paul M.; Lant, Chris T.
1999-08-01
We present measurements of the high-frequency shear modulus and dynamic viscosity for nonaqueous hard sphere colloidal crystals both in normal and microgravity environments. All experiments were performed on a multipurpose PHaSE instrument. For the rheological measurements, we detect the resonant response to oscillatory forcing with a dynamic light scattering scheme. The resonant response for colloidal crystals formed in normal and microgravity environments was similar, indicating that the bulk rheological properties are unaffected by differing crystal structure and crystallite size within the experimental error. Our high-frequency shear modulus seems reasonable, lying close to Frenkel and Ladd's predictions [Phys. Rev. Lett. 59, 1169 (1987)] for the static modulus of hard sphere crystals. Our high-frequency dynamic viscosity, on the other hand, seems high, exceeding Shikata and Pearson [J. Rheol. 38, 601 (1994)] and van der Werff et al.'s measurements [Phys. Rev. A 39, 795 (1989)] on the high-frequency dynamic viscosity for metastable fluids. The measurements are in the linear regime for the shear modulus but may not be for the dynamic viscosity as Frith et al. [Powder Technol. 51, 27 (1987)] report that the dynamic viscosity passes through a maximum with strain amplitude.
NASA Astrophysics Data System (ADS)
Musa, Abu Bakar
2013-09-01
The study is about impact of a short elastic rod(or slug) on a stationary semi-infinite viscoelastic rod. The viscoelastic materials are modeled as standard linear solid which involve three material parameters and the motion is treated as one-dimensional. We first establish the governing equations pertaining to the impact of viscoelastic materials subject to certain boundary conditions for the case when an elastic slug moving at a speed V impacts a semi-infinite stationary viscoelastic rod. The objective is to predict stresses and velocities at the interface following wave transmissions and reflections in the slug after the impact using viscoelastic discontinuity. If the stress at the interface becomes tensile and the velocity changes its sign, then the slug and the rod part company. If the stress at the interface is compressive after the impact, the slug and the rod remain in contact. In the process of predicting the stress and velocity of wave propagation using viscoelastic discontinuity, the Z-effective which is the effective ratio of acoustic impedance plays important role. It can be shown that effective ratio of acoustic impedance can help us to determine whether the slug and the rod move together or part company after the impact. After modeling the impact and solve the governing system of partial differential equations in the Laplace transform domain. We invert the Laplace transformed solution numerically to obtain the stresses and velocities at the interface for several viscosity time constants and ratios of acoustic impedances. In inverting the Laplace transformed equations, we used the complex inversion formula because there is a branch cut and infinitely many poles within the Bromwich contour. In the discontinuity analysis, we look at the moving discontinuities in stress and velocity using the impulse-momentum relation and kinematical condition of compatibility. Finally, we discussed the relationship of the stresses and velocities using numeric and the
NASA Astrophysics Data System (ADS)
Zhang, Wei; Yu, YongLiang; Tong, BingGang
2014-01-01
For attaining the optimized locomotory performance of swimming fishes, both the passive visco-elastic properties of the fish body and the mechanical behavior of the active muscles should coordinate with the fish body's undulatory motion pattern. However, it is difficult to directly measure the visco-elastic constitutive relation and the muscular mechanical performance in vivo. In the present paper, a new approach based on the continuous beam model for steady swimming fish is proposed to predict the fish body's visco-elastic properties and the related muscle mechanical behavior in vivo. Given the lateral travelling-wave-like movement as the input condition, the required muscle force and the energy consumption are functions of the fish body's visco-elastic parameters, i.e. the Young's modulus E and the viscosity coefficient µ in the Kelvin model. After investigating the variations of the propagating speed of the required muscle force with the fish body's visco-elastic parameters, we analyze the impacts of the visco-elastic properties on the energy efficiencies, including the energy utilization ratios of each element of the kinematic chain in fish swimming and the overall efficiency. Under the constraints of reasonable wave speed of muscle activation and the physiological feasibility, the optimal design of the passive visco-elastic properties can be predicted aiming at maximizing the overall efficiency. The analysis is based on the small-amplitude steady swimming of the carangiform swimmer, with typical Reynolds number varying from 2.5×104 to 2.5×105, and the present results show that the non-dimensional Young's modulus is 112±34, and the non-dimensional viscosity coefficient is 13 approximately. In the present estimated ranges, the overall efficiency of the swimming fish is insensitive to the viscosity, and its magnitude is about 0.11±0.02, in the predicted range given by previous study.
Corneal Viscoelastic Properties from Finite-Element Analysis of In Vivo Air-Puff Deformation
Kling, Sabine; Bekesi, Nandor; Dorronsoro, Carlos; Pascual, Daniel; Marcos, Susana
2014-01-01
Biomechanical properties are an excellent health marker of biological tissues, however they are challenging to be measured in-vivo. Non-invasive approaches to assess tissue biomechanics have been suggested, but there is a clear need for more accurate techniques for diagnosis, surgical guidance and treatment evaluation. Recently air-puff systems have been developed to study the dynamic tissue response, nevertheless the experimental geometrical observations lack from an analysis that addresses specifically the inherent dynamic properties. In this study a viscoelastic finite element model was built that predicts the experimental corneal deformation response to an air-puff for different conditions. A sensitivity analysis reveals significant contributions to corneal deformation of intraocular pressure and corneal thickness, besides corneal biomechanical properties. The results show the capability of dynamic imaging to reveal inherent biomechanical properties in vivo. Estimates of corneal biomechanical parameters will contribute to the basic understanding of corneal structure, shape and integrity and increase the predictability of corneal surgery. PMID:25121496
Viscoelastic properties of the nematode Caenorhabditis elegans, a self-similar, shear-thinning worm.
Backholm, Matilda; Ryu, William S; Dalnoki-Veress, Kari
2013-03-19
Undulatory motion is common to many creatures across many scales, from sperm to snakes. These organisms must push off against their external environment, such as a viscous medium, grains of sand, or a high-friction surface; additionally they must work to bend their own body. A full understanding of undulatory motion, and locomotion in general, requires the characterization of the material properties of the animal itself. The material properties of the model organism Caenorhabditis elegans were studied with a micromechanical experiment used to carry out a three-point bending measurement of the worm. Worms at various developmental stages (including dauer) were measured and different positions along the worm were probed. From these experiments we calculated the viscoelastic properties of the worm, including the effective spring constant and damping coefficient of bending. C. elegans moves by propagating sinusoidal waves along its body. Whereas previous viscoelastic approaches to describe the undulatory motion have used a Kelvin-Voigt model, where the elastic and viscous components are connected in parallel, our measurements show that the Maxwell model, where the elastic and viscous components are in series, is more appropriate. The viscous component of the worm was shown to be consistent with a non-Newtonian, shear-thinning fluid. We find that as the worm matures it is well described as a self-similar elastic object with a shear-thinning damping term and a stiffness that becomes smaller as one approaches the tail. PMID:23460699
Hettich, Mike; Jacob, Karl; Ristow, Oliver; Schubert, Martin; Bruchhausen, Axel; Gusev, Vitalyi; Dekorsy, Thomas
2016-09-16
We investigate the viscoelastic properties of confined molecular nano-layers by time resolved optical pump-probe measurements. Access to the elastic properties is provided by the damping time of acoustic eigenmodes of thin metal films deposited on the molecular nano-layers which show a strong dependence on the molecular layer thickness and on the acoustic eigen-mode frequencies. An analytical model including the viscoelastic properties of the molecular layer allows us to obtain the longitudinal sound velocity as well as the acoustic absorption coefficient of the layer. Our experiments and theoretical analysis indicate for the first time that the molecular nano-layers are much more viscous than elastic in the investigated frequency range from 50 to 120 GHz and thus show pronounced acoustic absorption. The longitudinal acoustic wavenumber has nearly equal real and imaginary parts, both increasing proportional to the square root of the frequency. Thus, both acoustic velocity and acoustic absorption are proportional to the square root of frequency and the propagation of compressional/dilatational acoustic waves in the investigated nano-layers is of the diffusional type, similar to the propagation of shear waves in viscous liquids and thermal waves in solids.
Hettich, Mike; Jacob, Karl; Ristow, Oliver; Schubert, Martin; Bruchhausen, Axel; Gusev, Vitalyi; Dekorsy, Thomas
2016-01-01
We investigate the viscoelastic properties of confined molecular nano-layers by time resolved optical pump-probe measurements. Access to the elastic properties is provided by the damping time of acoustic eigenmodes of thin metal films deposited on the molecular nano-layers which show a strong dependence on the molecular layer thickness and on the acoustic eigen-mode frequencies. An analytical model including the viscoelastic properties of the molecular layer allows us to obtain the longitudinal sound velocity as well as the acoustic absorption coefficient of the layer. Our experiments and theoretical analysis indicate for the first time that the molecular nano-layers are much more viscous than elastic in the investigated frequency range from 50 to 120 GHz and thus show pronounced acoustic absorption. The longitudinal acoustic wavenumber has nearly equal real and imaginary parts, both increasing proportional to the square root of the frequency. Thus, both acoustic velocity and acoustic absorption are proportional to the square root of frequency and the propagation of compressional/dilatational acoustic waves in the investigated nano-layers is of the diffusional type, similar to the propagation of shear waves in viscous liquids and thermal waves in solids. PMID:27633351
Influence of the Viscoelastic Properties of the Polyimide Dielectric Coating on the Wafer Warpage
NASA Astrophysics Data System (ADS)
Zhu, Chunsheng; Ning, Wenguo; Xu, Gaowei; Luo, Le
2014-09-01
Polyimide is widely used as the dielectric material in wafer level packaging. One potential problem with its application is the warpage and stress generated in the curing process. This paper investigated the material properties of polyimide and its influence on the wafer warpage. The viscoelastic properties of polyimide film were measured and a mathematical model of the properties was developed. Finite element analysis of the wafer warpage was performed and this indicates that the viscoelastic material model gave the best prediction. To better understand the causation of the warpage, curvature evolution of the polyimide-coated silicon wafer during its curing process was measured by a multi-beam optical sensor system. It was found that the warpage was mainly induced by the coefficient of thermal expansion mismatch and that the cure shrinkage of polyimide had little effect. Additionally, the effect of the cooling rate on the wafer warpage was also studied. Both simulation and experiment results showed that a slower cooling rate in the temperature range around the glass transition temperature ( T g) of polyimide will help to reduce the final wafer warpage.
Hettich, Mike; Jacob, Karl; Ristow, Oliver; Schubert, Martin; Bruchhausen, Axel; Gusev, Vitalyi; Dekorsy, Thomas
2016-01-01
We investigate the viscoelastic properties of confined molecular nano-layers by time resolved optical pump-probe measurements. Access to the elastic properties is provided by the damping time of acoustic eigenmodes of thin metal films deposited on the molecular nano-layers which show a strong dependence on the molecular layer thickness and on the acoustic eigen-mode frequencies. An analytical model including the viscoelastic properties of the molecular layer allows us to obtain the longitudinal sound velocity as well as the acoustic absorption coefficient of the layer. Our experiments and theoretical analysis indicate for the first time that the molecular nano-layers are much more viscous than elastic in the investigated frequency range from 50 to 120 GHz and thus show pronounced acoustic absorption. The longitudinal acoustic wavenumber has nearly equal real and imaginary parts, both increasing proportional to the square root of the frequency. Thus, both acoustic velocity and acoustic absorption are proportional to the square root of frequency and the propagation of compressional/dilatational acoustic waves in the investigated nano-layers is of the diffusional type, similar to the propagation of shear waves in viscous liquids and thermal waves in solids. PMID:27633351
NASA Astrophysics Data System (ADS)
Karim, Mir; Kohale, Swapnil C.; Indei, Tsutomu; Schieber, Jay D.; Khare, Rajesh
2012-11-01
We present a technique for the determination of viscoelastic properties of a medium by tracking the motion of an embedded probe particle by using molecular dynamics simulations. The approach involves the analysis of the simulated particle motion by continuum theory; it is shown to work in both passive and active modes. We demonstrate that, for passive rheology, an analysis based on the generalized Stokes-Einstein relationship is not adequate to obtain the values of the viscoelastic moduli over the frequency range studied. For both passive and active modes, it is necessary to account for the medium and particle inertia when analyzing the particle motion. For a polymer melt system consisting of short chains, the values calculated from the proposed approach are in good quantitative agreement with previous literature results that were obtained using completely different simulation approaches. The proposed particle rheology simulation technique is general and could provide insight into the characterization of the mechanical properties in biological systems, such as cellular environments and polymeric systems, such as thin films and nanocomposites that exhibit spatial variation in properties over the nanoscale.
NASA Astrophysics Data System (ADS)
Hettich, Mike; Jacob, Karl; Ristow, Oliver; Schubert, Martin; Bruchhausen, Axel; Gusev, Vitalyi; Dekorsy, Thomas
2016-09-01
We investigate the viscoelastic properties of confined molecular nano-layers by time resolved optical pump-probe measurements. Access to the elastic properties is provided by the damping time of acoustic eigenmodes of thin metal films deposited on the molecular nano-layers which show a strong dependence on the molecular layer thickness and on the acoustic eigen-mode frequencies. An analytical model including the viscoelastic properties of the molecular layer allows us to obtain the longitudinal sound velocity as well as the acoustic absorption coefficient of the layer. Our experiments and theoretical analysis indicate for the first time that the molecular nano-layers are much more viscous than elastic in the investigated frequency range from 50 to 120 GHz and thus show pronounced acoustic absorption. The longitudinal acoustic wavenumber has nearly equal real and imaginary parts, both increasing proportional to the square root of the frequency. Thus, both acoustic velocity and acoustic absorption are proportional to the square root of frequency and the propagation of compressional/dilatational acoustic waves in the investigated nano-layers is of the diffusional type, similar to the propagation of shear waves in viscous liquids and thermal waves in solids.
Suydam, Stephen M; Soulas, Elizabeth M; Elliott, Dawn M; Silbernagel, Karin Gravare; Buchanan, Thomas S; Cortes, Daniel H
2015-06-01
Changes in tendon viscoelastic properties are observed after injuries and during healing as a product of altered composition and structure. Continuous Shear Wave Elastography is a new technique measuring viscoelastic properties of soft tissues using external shear waves. Tendon has not been studied with this technique, therefore, the aims of this study were to establish the range of shear and viscosity moduli in healthy Achilles tendons, determine bilateral differences of these parameters and explore correlations of viscoelasticity to plantar flexion strength and tendon area. Continuous Shear Wave Elastography was performed over the free portion of both Achilles tendons from 29 subjects. Isometric plantar flexion strength and cross sectional area were measured. The average shear and viscous moduli was 83.2 kPa and 141.0 Pa-s, respectively. No correlations existed between the shear or viscous modulus and area or strength. This indicates that viscoelastic properties can be considered novel, independent biomarkers. The shear and viscosity moduli were bilaterally equivalent (p = 0.013, 0.017) which allows determining pathologies through side-to-side deviations. The average bilateral coefficient of variation was 7.2% and 9.4% for shear and viscosity modulus, respectively. The viscoelastic properties of the Achilles tendon may provide an unbiased, non-subjective rating system of tendon recovery and optimizing treatment strategies.
Suydam, Stephen M.; Soulas, Elizabeth M.; Elliott, Dawn M.; Silbernagel, Karin Gravare; Buchanan, Thomas S.; Cortes, Daniel H.
2015-01-01
Changes in tendon viscoelastic properties are observed after injuries and during healing as a product of altered composition and structure. Continuous Shear Wave Elastography is a new technique measuring viscoelastic properties of soft tissues using external shear waves. Tendon has not been studied with this technique, therefore, the aims of this study were to establish the range of shear and viscosity moduli in healthy Achilles tendons, determine bilateral differences of these parameters and explore correlations of viscoelasticity to plantar flexion strength and tendon area. Continuous Shear Wave Elastography was performed over the free portion of both Achilles tendons from 29 subjects. Isometric plantar flexion strength and cross sectional area were measured. The average shear and viscous moduli was 83.2kPa and 141.0Pa-s, respectively. No correlations existed between the shear or viscous modulus and area or strength. This indicates that viscoelastic properties can be considered novel, independent biomarkers. The shear and viscosity moduli were bilaterally equivalent (p=0.013,0.017) which allows determining pathologies through side-to-side deviations. The average bilateral coefficient of variation was 7.2% and 9.4% for shear and viscosity modulus, respectively. The viscoelastic properties of the Achilles tendon may provide an unbiased, non-subjective rating system of tendon recovery and optimizing treatment strategies. PMID:25882209
Abramowitch, Steven D; Woo, Savio L
2004-02-01
The quasi-linear viscoelastic (QLV) theory proposed by Fung (1972) has been frequently used to model the nonlinear time- and history-dependent viscoelastic behavior of many soft tissues. It is common to use five constants to describe the instantaneous elastic response (constants A and B) and reduced relaxation function (constants C, tau 1, and tau 2) on experiments with finite ramp times followed by stress relaxation to equilibrium. However, a limitation is that the theory is based on a step change in strain which is not possible to perform experimentally. Accounting for this limitation may result in regression algorithms that converge poorly and yield nonunique solutions with highly variable constants, especially for long ramp times (Kwan et al. 1993). The goal of the present study was to introduce an improved approach to obtain the constants for QLV theory that converges to a unique solution with minimal variability. Six goat femur-medial collateral ligament-tibia complexes were subjected to a uniaxial tension test (ramp time of 18.4 s) followed by one hour of stress relaxation. The convoluted QLV constitutive equation was simultaneously curve-fit to the ramping and relaxation portions of the data (r2 > 0.99). Confidence intervals of the constants were generated from a bootstrapping analysis and revealed that constants were distributed within 1% of their median values. For validation, the determined constants were used to predict peak stresses from a separate cyclic stress relaxation test with averaged errors across all specimens measuring less than 6.3 +/- 6.0% of the experimental values. For comparison, an analysis that assumed an instantaneous ramp time was also performed and the constants obtained for the two approaches were compared. Significant differences were observed for constants B, C, tau 1, and tau 2, with tau 1 differing by an order of magnitude. By taking into account the ramping phase of the experiment, the approach allows for viscoelastic
NASA Astrophysics Data System (ADS)
Yamasaki, Tadashi; Houseman, Gregory; Hamling, Ian; Postek, Elek
2010-05-01
We have developed a new parallelized 3-D numerical code, OREGANO_VE, for the solution of the general visco-elastic problem in a rectangular block domain. The mechanical equilibrium equation is solved using the finite element method for a (non-)linear Maxwell visco-elastic rheology. Time-dependent displacement and/or traction boundary conditions can be applied. Matrix assembly is based on a tetrahedral element defined by 4 vertex nodes and 6 nodes located at the midpoints of the edges, and within which displacement is described by a quadratic interpolation function. For evaluating viscoelastic relaxation, an explicit time-stepping algorithm (Zienkiewicz and Cormeau, Int. J. Num. Meth. Eng., 8, 821-845, 1974) is employed. We test the accurate implementation of the OREGANO_VE by comparing numerical and analytic (or semi-analytic half-space) solutions to different problems in a range of applications: (1) equilibration of stress in a constant density layer after gravity is switched on at t = 0 tests the implementation of spatially variable viscosity and non-Newtonian viscosity; (2) displacement of the welded interface between two blocks of differing viscosity tests the implementation of viscosity discontinuities, (3) displacement of the upper surface of a layer under applied normal load tests the implementation of time-dependent surface tractions (4) visco-elastic response to dyke intrusion (compared with the solution in a half-space) tests the implementation of all aspects. In each case, the accuracy of the code is validated subject to use of a sufficiently small time step, providing assurance that the OREGANO_VE code can be applied to a range of visco-elastic relaxation processes in three dimensions, including post-seismic deformation and post-glacial uplift. The OREGANO_VE code includes a capability for representation of prescribed fault slip on an internal fault. The surface displacement associated with large earthquakes can be detected by some geodetic observations
NASA Astrophysics Data System (ADS)
Dakshinamurthy, Devika; Gupta, Srinivasa
2016-06-01
Fused Deposition Modelling (FDM) is a fast growing Rapid Prototyping (RP) technology due to its ability to build parts having complex geometrical shape in reasonable time period. The quality of built parts depends on many process variables. In this study, the influence of three FDM process parameters namely, slice height, raster angle and raster width on viscoelastic properties of Acrylonitrile Butadiene Styrene (ABS) RP-specimen is studied. Statistically designed experiments have been conducted for finding the optimum process parameter setting for enhancing the storage modulus. Dynamic Mechanical Analysis has been used to understand the viscoelastic properties at various parameter settings. At the optimal parameter setting the storage modulus and loss modulus of the ABS-RP specimen was 1008 and 259.9 MPa respectively. The relative percentage contribution of slice height and raster width on the viscoelastic properties of the FDM-RP components was found to be 55 and 31 % respectively.
Barnhill, Eric; Kennedy, Paul; Hammer, Steven; van Beek, Edwin J R; Brown, Colin; Roberts, Neil
2013-12-01
Skeletal muscle viscoelastic properties reflect muscle microstructure and neuromuscular activation. Elastographic methods, including magnetic resonance elastography, have been used to characterize muscle viscoelastic properties in terms of region of interest (ROI) measurements. The present study extended this approach to create thresholded pixel-by-pixel maps of viscoelastic properties of skeletal muscle during rest and knee extension in eleven subjects. ROI measurements were taken for individual quadricep muscles and the quadriceps region as a whole, and the viscoelastic parameter map pixels were statistically tested at positive false discovery rate q ≤ 0.25. ROI measurements showed significant (p ≤ 0.05) increase in storage modulus (G') and loss modulus (G″), with G″ increasing more than G', in agreement with previous findings. The q-value maps further identified the vastus intermedius as the primary driver of this change, with greater G″/G' increase than surrounding regions. Additionally, a cluster of significant decrease in G″/G' was found in the region of vastus lateralis below the fulcrum point of the lift. Viscoelastic parameter mapping of contracted muscle allows new insight into the relationship between physiology, neuromuscular activation, and human performance.
Zhang, Jing; Tian, Jiabin; Ta, Na; Huang, Xinsheng; Rao, Zhushi
2016-08-01
Finite element method was employed in this study to analyze the change in performance of implantable hearing devices due to the consideration of soft tissues' viscoelasticity. An integrated finite element model of human ear including the external ear, middle ear and inner ear was first developed via reverse engineering and analyzed by acoustic-structure-fluid coupling. Viscoelastic properties of soft tissues in the middle ear were taken into consideration in this model. The model-derived dynamic responses including middle ear and cochlea functions showed a better agreement with experimental data at high frequencies above 3000 Hz than the Rayleigh-type damping. On this basis, a coupled finite element model consisting of the human ear and a piezoelectric actuator attached to the long process of incus was further constructed. Based on the electromechanical coupling analysis, equivalent sound pressure and power consumption of the actuator corresponding to viscoelasticity and Rayleigh damping were calculated using this model. The analytical results showed that the implant performance of the actuator evaluated using a finite element model considering viscoelastic properties gives a lower output above about 3 kHz than does Rayleigh damping model. Finite element model considering viscoelastic properties was more accurate to numerically evaluate implantable hearing devices. PMID:27276992
Modeling and Testing of the Viscoelastic Properties of a Graphite Nanoplatelet/Epoxy Composite
NASA Technical Reports Server (NTRS)
Odegard, Gregory M.; Gates, Thomas S.
2005-01-01
In order to facilitate the interpretation of experimental data, a micromechanical modeling procedure is developed to predict the viscoelastic properties of a graphite nanoplatelet/epoxy composite as a function of volume fraction and nanoplatelet diameter. The predicted storage and loss moduli for the composite are compared to measured values from the same material using three test methods; Dynamical Mechanical Analysis, nanoindentation, and quasi-static tensile tests. In most cases, the model and experiments indicate that for increasing volume fractions of nanoplatelets, both the storage and loss moduli increase. Also, the results indicate that for nanoplatelet sizes above 15 microns, nanoindentation is capable of measuring properties of individual constituents of a composite system. Comparison of the predicted values to the measured data helps illustrate the relative similarities and differences between the bulk and local measurement techniques.
Age-associated alterations in viscoelastic properties of canine aortic strips.
Yin, F C; Spurgeon, H A; Kallman, C H
1983-10-01
Many studies have delineated the changes in the elastic properties of arterial tissue as a function of age. Despite the fact that viscoelasticity is a prominent feature of these tissues, there is little information or characterization of age-associated changes in viscoelastic properties, over a wide range of smooth muscle activation, particularly in nonhuman tissue where atherosclerosis is not a confounding factor. In the present study, using small sinusoidal length perturbations, we determined the dynamic stiffness properties across a wide range of lengths (stretch ratios from 100 to 135%) and frequencies (from 0.25 to 35 Hz) in strips excised from ascending and descending aortas from six young (2 to 4-year-old) and 12 senescent (10- to 13-year-old) beagles. Studies were performed with the smooth muscle fully activated with calcium and norepinephrine, as well as fully inactivated with cyanide, iodoacetate, and dinitrophenol. There was a cubic nonlinear dependence of stiffness modulus on length only in senescent tissue and, surprisingly, little frequency dependence in tissue of either age. Compared to the young aortas, the three-dimensional surface representing the dependence of stiffness modulus on length and frequency from both the ascending and descending regions of aged aortas was displaced higher on the stiffness axis both with the muscle fully activated and inactivated. This age difference was accentuated at longer lengths. The phase lag between force and length was greater in the young vs. the old strips only in the activated, ascending aortic tissue. We found no age differences in the content of elastin, collagen, or in the collagen/elastin ratio, to account for these mechanical property differences.(ABSTRACT TRUNCATED AT 250 WORDS)
Viscoelastic properties of bovine orbital connective tissue and fat: constitutive models.
Yoo, Lawrence; Gupta, Vijay; Lee, Choongyeop; Kavehpore, Pirouz; Demer, Joseph L
2011-12-01
Reported mechanical properties of orbital connective tissue and fat have been too sparse to model strain-stress relationships underlying biomechanical interactions in strabismus. We performed rheological tests to develop a multi-mode upper convected Maxwell (UCM) model of these tissues under shear loading. From 20 fresh bovine orbits, 30 samples of connective tissue were taken from rectus pulley regions and 30 samples of fatty tissues from the posterior orbit. Additional samples were defatted to determine connective tissue weight proportion, which was verified histologically. Mechanical testing in shear employed a triborheometer to perform: strain sweeps at 0.5-2.0 Hz; shear stress relaxation with 1% strain; viscometry at 0.01-0.5 s(-1) strain rate; and shear oscillation at 1% strain. Average connective tissue weight proportion was 98% for predominantly connective tissue and 76% for fatty tissue. Connective tissue specimens reached a long-term relaxation modulus of 668 Pa after 1,500 s, while corresponding values for fatty tissue specimens were 290 Pa and 1,100 s. Shear stress magnitude for connective tissue exceeded that of fatty tissue by five-fold. Based on these data, we developed a multi-mode UCM model with variable viscosities and time constants, and a damped hyperelastic response that accurately described measured properties of both connective and fatty tissues. Model parameters differed significantly between the two tissues. Viscoelastic properties of predominantly connective orbital tissues under shear loading differ markedly from properties of orbital fat, but both are accurately reflected using UCM models. These viscoelastic models will facilitate realistic global modeling of EOM behavior in binocular alignment and strabismus.
Viscoelastic properties of bovine orbital connective tissue and fat: constitutive models
Yoo, Lawrence; Gupta, Vijay; Lee, Choongyeop; Kavehpore, Pirouz
2012-01-01
Reported mechanical properties of orbital connective tissue and fat have been too sparse to model strain–stress relationships underlying biomechanical interactions in strabismus. We performed rheological tests to develop a multi-mode upper convected Maxwell (UCM) model of these tissues under shear loading. From 20 fresh bovine orbits, 30 samples of connective tissue were taken from rectus pulley regions and 30 samples of fatty tissues from the posterior orbit. Additional samples were defatted to determine connective tissue weight proportion, which was verified histologically. Mechanical testing in shear employed a triborheometer to perform: strain sweeps at 0.5–2.0 Hz; shear stress relaxation with 1% strain; viscometry at 0.01–0.5 s−1 strain rate; and shear oscillation at 1% strain. Average connective tissue weight proportion was 98% for predominantly connective tissue and 76% for fatty tissue. Connective tissue specimens reached a long-term relaxation modulus of 668 Pa after 1,500 s, while corresponding values for fatty tissue specimens were 290 Pa and 1,100 s. Shear stress magnitude for connective tissue exceeded that of fatty tissue by five-fold. Based on these data, we developed a multimode UCM model with variable viscosities and time constants, and a damped hyperelastic response that accurately described measured properties of both connective and fatty tissues. Model parameters differed significantly between the two tissues. Viscoelastic properties of predominantly connective orbital tissues under shear loading differ markedly from properties of orbital fat, but both are accurately reflected using UCM models. These viscoelastic models will facilitate realistic global modeling of EOM behavior in binocular alignment and strabismus. PMID:21207094
Technology Transfer Automated Retrieval System (TEKTRAN)
The nutrient and energy demand of sexual maturation in many fish cultivars causes structural change to key contractile proteins and thereby, affects fillet firmness. Thermal denaturation and viscoelastic properties of white muscle from diploid (2N; fertile) and triploid (3N; sterile) female rainbow...
Stojković, Biljana; Sretenovic, Simon; Dogsa, Iztok; Poberaj, Igor; Stopar, David
2015-02-01
We studied the viscoelastic properties of homogeneous and inhomogeneous levan-DNA mixtures using optical tweezers and a rotational rheometer. Levan and DNA are important components of the extracellular matrix of bacterial biofilms. Their viscoelastic properties influence the mechanical as well as molecular-transport properties of biofilm. Both macro- and microrheology measurements in homogeneous levan-DNA mixtures revealed pseudoplastic behavior. When the concentration of DNA reached a critical value, levan started to aggregate, forming clusters of a few microns in size. Microrheology using optical tweezers enabled us to measure local viscoelastic properties within the clusters as well as in the DNA phase surrounding the levan aggregates. In phase-separated levan-DNA mixtures, the results of macro- and microrheology differed significantly. The local viscosity and elasticity of levan increased, whereas the local viscosity of DNA decreased. On the other hand, the results of bulk viscosity measurements suggest that levan clusters do not interact strongly with DNA. Upon treatment with DNase, levan aggregates dispersed. These results demonstrate the advantages of microrheological measurements compared to bulk viscoelastic measurements when the materials under investigation are complex and inhomogeneous, as is often the case in biological samples.
McConney, Michael E; Schaber, Clemens F; Julian, Michael D; Barth, Friedrich G; Tsukruk, Vladimir V
2007-12-22
Atomic force microscopy (AFM) and surface force spectroscopy were applied in live spiders to their joint pad material located distal of the metatarsal lyriform organs, which are highly sensitive vibration sensors. The surface topography of the material is sufficiently smooth to probe the local nanomechanical properties with nanometre elastic deflections. Nanoscale loads were applied in the proximad direction on the distal joint region simulating the natural stimulus situation. The force curves obtained indicate the presence of a soft, liquid-like epicuticular layer (20-40 nm thick) above the pad material, which has much higher stiffness. The Young modulus of the pad material is close to 15 MPa at low frequencies, but increases rapidly with increasing frequencies approximately above 30 Hz to approximately 70 MPa at 112 Hz. The adhesive forces drop sharply by about 40% in the same frequency range. The strong frequency dependence of the elastic modulus indicates the viscoelastic nature of the pad material, its glass transition temperature being close to room temperature (25 +/- 2 degrees C) and, therefore, to its maximized energy absorption from low-frequency mechanical stimuli. These viscoelastic properties of the cuticular pad are suggested to be at least partly responsible for the high-pass characteristics of the vibration sensor's physiological properties demonstrated earlier.
Houston, Jack E.; Grest, Gary Stephen; Moore, Nathan W.; Feibelman, Peter J.
2010-09-01
This report summarizes the work completed under the Laboratory Directed Research and Development (LDRD) project 10-0973 of the same title. Understanding the molecular origin of the no-slip boundary condition remains vitally important for understanding molecular transport in biological, environmental and energy-related processes, with broad technological implications. Moreover, the viscoelastic properties of fluids in nanoconfinement or near surfaces are not well-understood. We have critically reviewed progress in this area, evaluated key experimental and theoretical methods, and made unique and important discoveries addressing these and related scientific questions. Thematically, the discoveries include insight into the orientation of water molecules on metal surfaces, the premelting of ice, the nucleation of water and alcohol vapors between surface asperities and the lubricity of these molecules when confined inside nanopores, the influence of water nucleation on adhesion to salts and silicates, and the growth and superplasticity of NaCl nanowires.
Effect of an accelerated aging protocol on viscoelastic properties of UHMWPE.
Lewis, Gladius
2002-01-01
The values of two viscoelastic properties (storage modulus and loss angle) of four sets of ultra-high-molecular-weight polyethylene specimens were obtained. Two sets comprised specimens that had been sterilized (using gamma radiation in air or ethylene oxide gas) while the other two sets comprised specimens that were sterilized and then exposed to an accelerated aging protocol that, in the literature, has been proposed as simulating 5 years of real-time shelf aging. An analysis of the present results from the four specimen sets and those obtained, in a previous study by the present author, on specimens machined from real-time shelf aged tibial inserts suggests that the claim made for the accelerated aging protocol may be conservative.
Viscoelastic properties of stiff joints: a new approach in analyzing joint contracture.
Akai, M; Shirasaki, Y; Tateishi, T
1993-01-01
The purpose of this study was to analyze the joint stiffness after immobilization in a rat's lower extremity model. Rat knee joints were surgically immobilized in a full flexed position for periods of up to 7 weeks with or without intra-articular intervention. The biomechanical analysis was assessed by measuring the bone-joint-bone sample as a cantilever. Measurement was performed with (a) knee flexion angle with gravity, (b) fast Fourier transform analysis of time-dependent mechanical noise with random frequencies, and (c) dynamic stiffness and loss tangent with sinusoidal vibration at a certain frequency. The results showed that the conventional static mechanical test could not detect the intraarticular changes of the whole knee joint. The measurement of the viscoelastic properties covering wide frequencies revealed that an accurate change occurred. PMID:8369728
Sharma, Vaibhav; Patel, Nimesha; Kohli, Nupur; Ravindran, Nivedita; Hook, Lilian; Mason, Chris; García-Gareta, Elena
2016-01-01
Dermal scaffolds promote healing of debilitating skin injuries caused by burns and chronic skin conditions. Currently available products present disadvantages and therefore, there is still a clinical need for developing new dermal substitutes. This study aimed at comparing the viscoelastic, physical and bio-degradable properties of two dermal scaffolds, the collagen-based and clinically well established Integra(®) and a novel fibrin-based dermal scaffold developed at our laboratory called Smart Matrix(®), to further evaluate our previous published findings that suggested a higher influx of cells, reduced wound contraction and less scarring for Smart Matrix(®) when used in vivo. Rheological results showed that Integra(®) (G' = 313.74 kPa) is mechanically stronger than Smart Matrix(®) (G' = 8.26 kPa), due to the presence of the silicone backing layer in Integra(®). Micro-pores were observed on both dermal scaffolds, although nano-pores as well as densely packed nano-fibres were only observed for Smart Matrix(®). Average surface roughness was higher for Smart Matrix(®) (Sa = 114.776 nm) than for Integra(®) (Sa = 75.565 nm). Both scaffolds possess a highly porous structure (80-90%) and display a range of pore micro-sizes that represent the actual in vivo scenario. In vitro proteolytic bio-degradation suggested that Smart Matrix(®) would degrade faster upon implantation in vivo than Integra(®). For both scaffolds, the enzymatic digestion occurs via bulk degradation. These observed differences could affect cell behaviour on both scaffolds. Our results suggest that fine-tuning of scaffolds' viscoelastic, physical and bio-degradable properties can maximise cell behaviour in terms of attachment, proliferation and infiltration, which are essential for tissue repair. PMID:27586397
Brands, Dave W A; Bovendeerd, Peter H M; Wismans, Jac S H M
2002-11-01
In current Finite Element (FE) head models, brain tissue is commonly assumed to display linear viscoelastic material behaviour. However, brain tissue behaves like a non-linear viscoelastic solid for shear strains above 1%. The main objective of this study was to study the effect of non-linear material behaviour on the predicted brain response. We used a non-linear viscoelastic constitutive model, developed on the basis of experimental shear data presented elsewere. First we tested the numerical implementation of the constitutive model by simulating the response of a silicone gel (Sylgard 572 A&B) filled cylindrical cup, subjected to a transient rotational acceleration. The experimental results could be reproduced within 9%. Subsequently, the effect of non-linear material modelling on computed brain response was investigated in an existing three-dimensional head model subjected to an eccentric rotation. At the applied external load strains in the brain were approximately ten times larger than was expected on the basis of published data. This is probably caused by the values of the shear moduli applied in the model. These are at least a factor of ten lower than the ones used in head models in literature but comparable to material data in recent literature. Non-linear material behaviour was found to influence the levels of predicted strains (+20%) and stresses (-11%) but not their temporal and spatial distribution. The pressure response was independent of non-linear material behaviour. In fact it could be predicted by the equilibrium of momentum, and thus it is independent of the choice of the brain constitutive model.
Effects of multiwall carbon nanotubes on viscoelastic properties of magnetorheological elastomers
NASA Astrophysics Data System (ADS)
Aziz, Siti Aishah Abdul; Amri Mazlan, Saiful; Intan Nik Ismail, Nik; Ubaidillah, U.; Choi, Seung-Bok; Khairi, Muntaz Hana Ahmad; Azhani Yunus, Nurul
2016-07-01
The effect of different types of multiwall carbon nanotubes (MWCNTs) on the morphological, magnetic and viscoelastic properties of magnetorheological elastomers (MREs) are studied in this work. A series of natural rubber MRE are prepared by adding MWCNTs as a new additive in MRE. Effects of functionalized MWCNT namely carboxylated MWCNT (COOH-MWCNT) and hydroxylated MWCNT (OH-MWCNT) on the rheological properties of MREs are investigated and the pristine MWCNTs is referred as a control. Epoxidised palm oil (EPO) is used as a medium to disperse carbonyl iron particle (CIP) and sonicate the MWCNTs. Morphological and magnetic properties of MREs are characterized by field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM), respectively. Rheological properties under different magnetic field are evaluated by using parallel plate rheometer. From the results obtained, FESEM images indicate that COOH-MWCNT and CIP have better compatibility which leads to the formation of interconnected network in the matrix. In addition, by adding functionalized COOH-MWCNT, it is shown that the saturation magnetization is 5% higher than the pristine MWCNTs. It is also found that with the addition of COOH-MWCNT, the magnetic properties are improved parallel with enhancement of MR effect particularly at low strain amplitude. It is finally shown that the use of EPO also can contribute to the enhancement of MR performance.
Morphology, absorptivity and viscoelastic properties of mineralized PVP-CMC hydrogel
NASA Astrophysics Data System (ADS)
Saha, Nabanita; Shah, Rushita; Vyroubal, Radek; Kitano, Takeshi; Saha, Petr
2013-04-01
A simple liquid diffusion mineralization technique was applied for the incorporation of calcium carbonate (CaCO3) in PVP-CMC hydrogel. The hydrogel was prepared 6.5 mm thick to achieve around 1 mm thick sample after mineralization of hydrogel matrix with calcite. The calcite crystals were round shaped and organized as building blocks inside the porous three dimensional cross linked structure of the PVP-CMC hydrogel. The present study was designed to evaluate the properties of mineralized (calcite) hydrogel with respect to freshly prepared hydrogel and those swelled in water (H2O) after drying. The viscoelastic properties of swelled and mineralized samples were reported though the dry PVP-CMC hydrogel were swelled and mineralized with calcite until 150 min. It is observed that there is not much difference in elastic property of fresh and 60 min mineralized hydrogels but the values of elastic property are decreased in the case of swelled hydrogels. It is interesting that in case of swelled samples the values of complex viscosity (η*) are increased with the increase of swelling time after 90 min but in case of calcite hydrogel the values (η*) are gradually decreased with the increase of time.
NASA Technical Reports Server (NTRS)
Roberts, Gary D; Malarik, Diane C.; Robaidek, Jerrold O.
1991-01-01
Viscoelastic properties of the addition cured polyimide, PMR-15, were studied using dynamic mechanical and stress relaxation tests. For temperatures below the glass transition temperature, T sub g, the dynamic mechanical properties measured using a temperature scan rate of 10 C/min were strongly affected by the presence of absorbed moisture in the resin. Dynamic mechanical properties measured as a function of time during an isothermal hold provided an indication of chemical changes occurring in the resin. For temperatures above (T sub g + 20 C), the storage modulus increased continuously as a function of time indicating that additional crosslinking is occurring in the resin. Because of these changes in chemical structures, the stress relaxation modulus could not be measured over any useful time interval for temperatures above T sub g. For temperatures below T sub g, dynamic mechanical properties appeared to be unaffected by chemical changes for times exceeding 1 hr. Since the duration of the stress relaxation tests was less than 1 hr, the stress relaxation modulus could be measured. As long as the moisture content of the resin was less than 2 pct, stress relaxation curves measured at different temperatures could be superimposed using horizontal shifts along the log(time) axis with only small shifts along the vertical axis.
Viscoelastic Properties of Differentiating Blood Cells Are Fate- and Function-Dependent
Ekpenyong, Andrew E.; Whyte, Graeme; Chalut, Kevin; Pagliara, Stefano; Lautenschläger, Franziska; Fiddler, Christine; Paschke, Stephan; Keyser, Ulrich F.; Chilvers, Edwin R.; Guck, Jochen
2012-01-01
Although cellular mechanical properties are known to alter during stem cell differentiation, understanding of the functional relevance of such alterations is incomplete. Here, we show that during the course of differentiation of human myeloid precursor cells into three different lineages, the cells alter their viscoelastic properties, measured using an optical stretcher, to suit their ultimate fate and function. Myeloid cells circulating in blood have to be advected through constrictions in blood vessels, engendering the need for compliance at short time-scales (
Effect of accelerated aging on the viscoelastic properties of a medical grade silicone.
Mahomed, Aziza; Hukins, David W L; Kukureka, Stephen N
2015-01-01
The viscoelastic properties of cylinders (diameter 5 mm, height 2.2 ± 0.2 mm) of Nagor silicone elastomer of medium hardness, were investigated before and after the specimens had undergone accelerated aging in saline solution at 70°C for 38, 76 and 114 days (to simulate aging at 37°C, for 1, 2 and 3 years, respectively). All sets of specimens were immersed in physiological saline solution at 37°C during testing and the properties were measured using dynamic mechanical analysis (DMA). A sinusoidal cyclic compression of 40 N ± 5 N was applied over a frequency range, f, of 0.02-25 Hz. Values of the storage, E', and loss, E″, moduli were found to depend on f; the dependence of E' or E″ on the logarithm (base 10) of f was represented by a second-order polynomial. After accelerated aging, the E' and E″ values did not increase significantly (p<0.05). Furthermore, scanning electron microscopy (SEM) showed that accelerated aging did not affect the surface morphology of silicone. Attenuated total reflectance Fourier transform infra-red spectroscopy (ATR-FTIR) showed that accelerated aging had a negligible effect on the surface chemical structures of the material. Differential scanning calorimetry (DSC) showed no changes to the bulk properties of silicone, following accelerated aging.
Viscoelastic properties of collagen-adhesive composites under water-saturated and dry conditions.
Singh, Viraj; Misra, Anil; Parthasarathy, Ranganathan; Ye, Qiang; Spencer, Paulette
2015-02-01
To investigate the time- and rate-dependent mechanical properties of collagen-adhesive composites, creep and monotonic experiments are performed under dry and wet conditions. The composites are prepared by infiltration of dentin adhesive into a demineralized bovine dentin. Experimental results show that for small stress level under dry conditions, both the composite and the neat adhesive have similar behavior. On the other hand, in wet conditions, the composites are significantly soft and weak compared to the neat adhesives. The behavior in the wet condition is found to be affected by the hydrophilicity of both the adhesive and the collagen. As the adhesive-collagen composites are a part of the complex construct that forms the adhesive-dentin interface, their presence will affect the overall performance of the restoration. We find that Kelvin-Voigt model with at least four elements is required to fit the creep compliance data, indicating that the adhesive-collagen composites are complex polymers with several characteristic time scales whose mechanical behavior will be significantly affected by loading rates and frequencies. Such mechanical properties have not been investigated widely for these types of materials. The derived model provides an additional advantage that it can be exploited to extract other viscoelastic properties which are, generally, time consuming to obtain experimentally. The calibrated model is utilized to obtain stress relaxation function, frequency-dependent storage and loss modulus, and rate-dependent elastic modulus.
Viscoelastic Properties of Collagen-Adhesive Composites under Water Saturated and Dry Conditions
Singh, Viraj; Misra, Anil; Parthasarathy, Ranganathan; Ye, Qiang; Spencer, Paulette
2014-01-01
To investigate the time and rate dependent mechanical properties of collagen-adhesive composites, creep and monotonic experiments are performed under dry and wet conditions. The composites are prepared by infiltration of dentin adhesive into a demineralized bovine dentin. Experimental results show that for small stress level under dry conditions, both the composite and neat adhesive have similar behavior. On the other hand, in wet conditions, the composites are significantly soft and weak compared to the neat adhesives. The behavior in the wet condition is found to be affected by the hydrophilicity of both the adhesive and collagen. Since the adhesive-collagen composites area part of the complex construct that forms the adhesive-dentin interface, their presence will affect the overall performance of the restoration. We find that Kelvin-Voigt model with at least 4-elements is required to fit the creep compliance data, indicating that the adhesive-collagen composites are complex polymers with several characteristics time-scales whose mechanical behavior will be significantly affected by loading rates and frequencies. Such mechanical properties have not been investigated widely for these types of materials. The derived model provides an additional advantage that it can be exploited to extract other viscoelastic properties which are, generally, time consuming to obtain experimentally. The calibrated model is utilized to obtain stress relaxation function, frequency-dependent storage and loss modulus, and rate dependent elastic modulus. PMID:24753362
Dutta, Amit K; Nayak, Arpan; Belfort, Georges
2008-08-01
The real-time changes in viscoelasticity of adsorbed poly(L-lysine) (PLL) and adsorbed histone (lysine rich fraction) due to cross-linking by glutaraldehyde and corresponding release of associated water were investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D) and attenuated total reflection Fourier transform infrared spectroscopy (ATR/FTIR). The kinetics of PLL and histone adsorption were measured through changes in mass adsorbed onto a gold-coated quartz surface from changes in frequency and dissipation and using the Voigt viscoelastic model. Prior to cross-linking, the shear viscosity and shear modulus of the adsorbed PLL layer were approximately 3.0 x 10(-3) Pas and approximately 2.5 x 10(5) Pa, respectively, while after cross-linking, they increased to approximately 17.5 x 10(-3) Pas and approximately 2.5 x 10(6) Pa, respectively. For the adsorbed histone layer, shear viscosity and shear modulus increased modestly from approximately 1.3 x 10(-3) to approximately 2.0 x 10(-3) Pas and from approximately 1.2 x 10(4) to approximately 1.6 x 10(4) Pa, respectively. The adsorbed mass estimated from the Sauerbrey equation (perfectly elastic) and the Voigt viscoelastic model differ appreciably prior to cross-linking whereas after cross-linking they converged. This is because trapped water molecules were released during cross-linking. This was confirmed experimentally via ATR/FTIR measurements. The variation in viscoelastic properties increased substantially after cross-linking presumably due to fluctuation of the randomly cross-linked network structure. An increase in fluctuation of the viscoelastic properties and the loss of imbibed water could be used as a signature of the formation of a cross-linked network and the amount of cross-linking, respectively. PMID:18508070
Jiao, Tong; Clifton, Rodney J; Converse, Gabriel L; Hopkins, Richard A
2012-02-01
In the development of tissue-engineered heart valves based on allograft decellularized extracellular matrix scaffolds, the material properties of the implant should be ideally comparable to the native semilunar valves. This investigation of the viscoelastic properties of the three functional aortic/pulmonary valve tissues (leaflets, sinus wall, and great vessel wall) was undertaken to establish normative values for fresh samples of human valves and to compare these properties after various steps in creating scaffolds for subsequent bioreactor-based seeding protocols. Torsional wave methods were used to measure the viscoelastic properties. Since preclinical surgical implant validation studies require relevant animal models, the tests reported here also include results for three pairs of both ovine and baboon aortic and pulmonary valves. For human aortic valves, four cryopreserved valves were compared with four decellularized scaffolds. Because of organ and heart valve transplant scarcity for pulmonary valves, only three cryopreserved and two decellularized pulmonary valves were tested. Leaflets are relatively soft. Loss angles are similar for all tissue samples. Regardless of species, the decellularization process used in this study has little effect on viscoelastic properties.
A micromechanical approach to elastic and viscoelastic properties of fiber reinforced concrete
Pasa Dutra, V.F.; Maghous, S. Campos Filho, A.; Pacheco, A.R.
2010-03-15
Some aspects of the constitutive behavior of fiber reinforced concrete (FRC) are investigated within a micromechanical framework. Special emphasis is put on the prediction of creep of such materials. The linear elastic behavior is first examined by implementation of a Mori-Tanaka homogenization scheme. The micromechanical predictions for the overall stiffness prove to be very close to finite element solutions obtained from the numerical analysis of a representative elementary volume of FRC modeled as a randomly heterogeneous medium. The validation of the micromechanical concepts based on comparison with a set of experiments, shows remarkable predictive capabilities of the micromechanical representation. The second part of the paper is devoted to non-ageing viscoelasticity of FRC. Adopting a Zener model for the behavior of the concrete matrix and making use of the correspondence principle, the homogenized relaxation moduli are derived analytically. The validity of the model is established by mean of comparison with available experiment measurements of creep strain of steel fiber reinforced concrete under compressive load. Finally, the model predictions are compared to those derived from analytical models formulated within a one-dimensional setting.
Ahn, Kyung Hyun; Lim, Sanghyuk; Kum, Kee Yeon; Chang, Seok Woo
2015-01-01
Preheating of dental composites improves their flowability, facilitating successful restorations. However, the flowability of dental composites is affected not only by temperature but also by the deformation conditions. In the present work, the effects of various deformation conditions upon the viscoelastic properties of a preheated dental composite were studied. The rheological properties of Z350 dental composites at 25, 45, and 60°C were measured by a strain-controlled rheometer. When a low strain (0.03%) was applied, the preheated composite exhibited greater shear storage modulus (G') and complex viscosity (η*) than a room-temperature composite. Oppositely, when a high strain (50%) was applied, G' and η* of a preheated composite were lower than those of a room-temperature composite. Preheating of dental composites might be helpful in clinical practice both to increase the slumping resistance when minimal manipulation is used (e.g., during the build-up of a missing cusp tip) and to increase flowability when manipulation entailing high shear strain is applied (e.g., when uncured composite resin is spread on a dentin surface).
Yang, Jun; Han, Chun-Rui; Duan, Jiu-Fang; Xu, Feng; Sun, Run-Cang
2013-04-24
The preparation and mechanical properties of elastomeric nanocomposite hydrogels consisting of cellulose nanocrystals (CNCs) and poly(ethylene glycol) (PEG) are reported. The aqueous nanocomposite CNC/PEG precursor solutions covalently cross-linked through a one-stage photocross-linking process. The mechanical properties of nanocomposite hydrogels, including Young's modulus (E), fracture stress (σ), and fracture strain (ε), were measured as a function of CNC volume fraction (φCNC, 0.2-1.8%, v/v) within polymeric matrix. It was found that the homogeneously dispersed nanocomposite hydrogels can be prepared with φCNC being less than 1.5%, whereas the heterogeneous nanocomposite hydrogels were obtained with φCNC being higher than 1.5%. The nanocomposite hydrogels exhibited higher strengths and flexibilities when compared with neat PEG hydrogels, where the modulus, fracture stress, and fracture strain enhanced by a factor of 3.48, 5, and 3.28, respectively, over the matrix material alone at 1.2% v/v CNC loading. Oscillatory shear data indicated the CNC-PEG nanocomposite hydrogels were more viscous than the neat PEG hydrogels and were efficient at energy dissipation due to the reversible interactions between CNC and PEG polymer chains. It was proposed that the strong gel viscoelastic behavior and the mechanical reinforcement were related to "filler network", where the temporary interactions between CNC and PEG interfered with the covalent cross-links of PEG. PMID:23534336
An acoustic wave biosensor for probing the viscoelastic properties of living cells
NASA Astrophysics Data System (ADS)
Li, Fang; Wang, James H.-C.; Wang, Qing-Ming
2006-05-01
The thickness shear mode (TSM) resonator attached with living cells has been shown to be an effective functional biosensing device to monitor the process of cell adhesion to a surface. In this study, we first monitored the dynamic process of cell attachment and spreading as a function of cell seeding densities. Based on the steady state of cell adhesion to the substrate, a multilayer sensor structure model including a quartz substrate, a cell-substrate interfacial layer and a cell layer was constructed. The thickness of cell-substrate interfacial layer and the viscoelastic properties of human skin fibroblasts (HSF) were then determined by fitting experimental results with the theoretical model. It has been obtained that the thickness of the cell-substrate interfacial layer is 60-80 nm, and the elastic module and viscosity of cell layers are about 13 KPa and 3-4 mPa's respectively. These results are in a good agreement with those measured by other techniques, such as magnetic bead microrheometry, atomic force microscopy (AFM) and Surface Plasmon Resonance Microscopy (SPRM). In addition, knowing that the actin cytoskeleton is important for the mechanical properties of living cells, we investigated the motional resistance change caused by the disruption of actin cytoskeleton induced by fungal toxin Cytochalasin D in the human skin fibroblasts. The results indeed indicate the direct correlation between resistance changes and the disruption of actin cytoskeleton, which are again consistent with the results observed by fluorescence images.
Preparation and characterization of herbal creams for improvement of skin viscoelastic properties.
Ahshawat, M S; Saraf, S; Saraf, S
2008-06-01
The aim of this study was to formulate and evaluate herbal cosmetic creams for their improvement of skin viscoelastic and hydration properties. The cosmetic cream formulations were designed by using ethanolic extracts of Glycyrriza glabra, Curcuma longa (roots), seeds of Psorolea corlifolia, Cassia tora, Areca catechu, Punica granatum, fruits of Embelica officinale, leaves of Centella asiatica, dried bark of Cinnamon zeylanicum and fresh gel of Aloe vera in varied concentrations (0.12-0.9%w/w) and characterized using physicochemical and physiological measurements. The ethanolic extracts of herbs were incorporated in a cream base that is prepared by a phase inversion emulsification technique. The cream base was prepared by utilizing oil of Prunus amagdalus, Sesamum indicum, honey, cetyl alcohol, stearic acid, polysorbate monoleate, sorbitan monostearate, propylene glycol and glycerin. Physicochemical assessments and microbiological testing were completed for all formulations according to the methods of the Indian Standard Bureau. The studies were carried out for 6 weeks on normal subjects (6 males and 12 females, between 22 and 50 years) on the back of their volar forearm for evaluation of viscoelastic properties in terms of extensibility via a suction measurement, firmness using laboratory fabricated instruments such as ball bouncing and skin hydration using electric (resistance) measurement methods. The physicochemical parameters of formulations CAA1-CAA6, i.e. pH, acid value, saponification value, viscosity, spreadability, layer thickness microbial count and skin sensitivity were found to be in the range of 5.01 +/- 0.4-6.07 +/- 0.6, 3.3-5.1 +/- 0.2, 20-32, 5900-6755 cps, 60-99%, 25-50 mum, 31-46 colony-forming units (CFU) and a 0-1 erythema score. The formulations, CAA4 and CAA5, showed an increase in percentage extensibility (32.27 +/- 1.7% and 29.89 +/- 1.64%, respectively), firmness (28.86 +/- 0.86% and 29.89 +/- 2.8%, respectively) and improved skin
RLC model of visco-elastic properties of the chest wall
NASA Astrophysics Data System (ADS)
Aliverti, Andrea; Ferrigno, Giancarlo
1996-04-01
The quantification of the visco-elastic properties (resistance (R), inertia (L) and compliance (C)) of the different chest wall compartments (pulmonary rib cage,diaphragmatic rib cage and abdomen) is important to study the status of the passive components of the respiratory system, particularly in selected pathologies. Applying the viscoelastic-electrical analogy to the chest wall, we used an identification method in order to estimate the R, L and C parameters of the different parts of the chest, basing on different models; the input and output measured data were constituted by the volume variations of the different chest wall compartments and by the nasal pressure during controlled intermittent positive pressure ventilation by nasal mask, while the parameters of the system (R, L and C of the different compartments) were to be estimated. Volumes were measured with a new method, recently validated, based on an opto-electronic motion analyzer, able to compute with high accuracy and null invasivity the absolute values and the time variations of the volumes of each of the three compartments. The estimation of the R, L and C parameters has been based on a least-squared criterion, and the minimization has been based on a robustified iterative Gauss-Newton algorithm. The validation of the estimation procedure (fitting) has ben performed computing the percentage root mean square value of the error between the output real data and the output estimated data. The method has been applied to 2 healthy subjects. Also preliminary results have been obtained from 20 subjects affected by neuromuscular diseases (Duchenne Muscular Dystrophy (DMD) and Spinal Muscle Atrophy (SMA)). The results show that: (a) the best-fitting electrical models of the respiratory system are made up by one or three parallel RLC branches supplied by a voltage generator (so considering inertial properties, particularly in the abdominal compartment, and not considering patient/machine connection); (b) there
NASA Astrophysics Data System (ADS)
Conway, Heather; Rende, Deniz; Ozisik, Rahmi
2013-03-01
Poly(methyl methacrylate), PMMA, has been used as an economic alternative to glass and polycarbonate in differing situations because of its lightweight, shatter resistance, and ease of processability. The uses of PMMA can be expanded if its weakness to impact force and its scratch resistance are improved. In the current study, viscoelastic properties of silica nanoparticle filled PMMA were investigated via nanoindentation experiments. Silica nanoparticles are known to increase the toughness of PMMA. In the current study, silica nanoparticles were chemically modified with fluorinated alkanes to alter nanofiller-polymer interactions. Results show that viscoelastic properties are strongly affected by silica surface chemistry and silica concentration. This work was partially supported by NSF CMMI-1200270 and DUE-1003574
Biswas, Arnab; Dubey, Mrigendra; Mukhopadhyay, Sujay; Kumar, Ashish; Pandey, Daya Shankar
2016-03-28
Progelator complex Zn-TRPA-2 undergoes Cl(-) triggered gelation to afford ZTP2G, while Zn-TRPA-2 capped Au-NPs under similar conditions gave another gel GNZTP2G which also represents a rare nano-composite metallogel. When Zn-TRPA-2 was triggered by Cl(-) and NO3(-) simultaneously, crystals of demetalated species NA-TRPA-2 grew inside the ZTP2G matrix. Interestingly, GNZTP2G exhibits superior viscoelastic properties over ZTP2G.
NASA Astrophysics Data System (ADS)
Fleitout, L.; Garaud, J.; Cailletaud, G.; Vigny, C.; Simons, W. J.; Ambrosius, B. A.; Trisirisatayawong, I.; Satirapod, C.; Geotecdi Song
2011-12-01
The giant seism of Aceh (december 2004),followed by the Nias and Bengkulu earthquakes, broke a large portion of the boundary between the Indian ocean and the Sunda block. For the first time in history, the deformations associated with a very large earthquake can be followed by GPS, in particular by the SEAMERGE (far-field) and SUGAR (near-field) GPS networks. A 3D finite element code (Zebulon-Zset) is used to model both the cosismic and the postseismic deformations. The modeled zone is a large portion of spherical shell around Sumatra extanding over more than 60 degrees in latitude and longitude and from the Earth's surface to the core-mantle boundary. The mesh is refined close to the subduction zone. First, the inverted cosismic displacements on the subduction plane are inverted for and provide a very good fit to the GPS data for the three seisms. The observed postseismic displacements, non-dimensionalized by the cosismic displacements, present three very different patterns as function of time: For GPS stations in the far-field, the total horizontal post-seismic displacement after 4 years is as large as the cosismic displacement. The velocities vary slowly over 4 years. A large subsidence affects Thailand and Malaysia. In the near-field, the postseismic displacement reaches only some 15% of the cosismic displacement and it levels off after 2 years. In the middle-field (south-west coast of Sumatra), the postseismic displacement also levels-off with time but more slowly and it reaches more than 30% of the cosismic displacement after four years. In order to fit these three distinct displacement patterns, we need to invoke both viscoelastic deformation in the asthenosphere and a low-viscosity wedge: Neither the vertical subsidence nor the amplitude of the far-field horizontal velocities could be explained by postseismic sliding on the subduction interface. The low viscosity wedge permits to explain the large middle-field velocities. The viscoelastic properties of the
Safouane, M; Miller, R; Möhwald, H
2005-12-01
A capillary wave technique was used to study the viscoelastic properties of floating polyelectrolyte multilayers of (PSS/PAH)(n) at the air-water interface. Oppositely charged polyelectrolyte layers were adsorbed onto two different Langmuir monolayers, either the lipid dimethyldioctadecylammonium bromide (DODAB) or the block copolymer poly(styrene-b-sodium acrylate) (PS-b-PAA). The results allow to propose a schematic representation of the multilayers in three zones: Zone I as a precursor, representing the adhesion between the Langmuir monolayer and the bulk polyelectrolyte multilayer. Zone II forms a bulk or core zone of the multilayer. Zone III as an outer zone in direct contact with the aqueous phase. The results show an increase of the elasticity after the formation of four polyelectrolyte layers accompanied by an apparent negative viscosity. This behaviour was interpreted as a translation of elasticity dominance from zone I to zone II. The Young modulus of seven layers was in the same order of magnitude as observed for planar polyelectrolyte multilayer films.
Effect of age and exercise on the viscoelastic properties of rat tail tendon.
LaCroix, Andrew S; Duenwald-Kuehl, Sarah E; Brickson, Stacey; Akins, Tiffany L; Diffee, Gary; Aiken, Judd; Vanderby, Ray; Lakes, Roderic S
2013-06-01
Tendon mechanical properties are thought to degrade during aging but improve with exercise. A remaining question is whether exercise in aged animals provides sufficient regenerative, systemic stimulus to restore younger mechanical behaviors. Herein we address that question with tail tendons from aged and exercised rats, which would be subject to systemic effects but not direct loading from the exercise regimen. Twenty-four month old rats underwent one of three treadmill exercise training protocols for 12 months: sedentary (walking at 0° incline for 5 min/day), moderate (running at 0° incline for 30 min/day), or high (running at 4° incline for 30 min/day). A group of 9 month old rats were used to provide an adult control, while a group of 3 month old rats provided a young control. Tendons were harvested at sacrifice and mechanically tested. Results show significant age-dependent differences in modulus, ultimate stress, relaxation rate, and percent relaxation. Relaxation rate was strain-dependent, consistent with nonlinear superposition or Schapery models but not with quasilinear viscoelasticity (QLV). Trends in exercise data suggest that with exercise, tendons assume the elastic character of younger rats (lower elastic modulus and ultimate stress).
NASA Astrophysics Data System (ADS)
Worametrachanon, Srivilai; Apichartsrangkoon, Arunee
2014-10-01
This study investigated how pressure (500, 600 MPa/20 min) altered the viscoelastic characteristics and phytochemical properties of germinated and non-germinated purple-rice drinks in comparison with pasteurization. Accordingly, color parameters, storage and loss moduli, anthocyanin content, γ-oryzanol, γ-aminobutyric acid (GABA), total phenolic compounds and 2,2-diphenyl-1-picrylthydrazyl (DPPH) capacity of the processed drinks were determined. The finding showed that germinated and pressurized rice drink had lower Browning Index than the non-germinated and pasteurized rice drink. The plots of storage and loss moduli for processed rice drinks indicated that time of pressurization had greater impact on gel structural modification than the level of pressure used. The phytochemicals, including total phenolics, and DPPH capacity in pressurized rice drinks retained higher quantity than those in pasteurized drink, despite less treatment effects on anthocyanin. On the contrary, both γ-oryzanol and GABA were found in high amounts in germinated rice drink with little variation among processing effects.
Szopinski, Daniel; Luinstra, Gerrit A
2016-11-20
The industrial relevant nonlinear viscoelastic properties of aqueous carboxymethyl hydroxypropyl guar gum (CMHPG) and non-ionic hydroxypropyl guar gum (HPG) solutions between semi-dilute and concentrated solution state were investigated by large amplitude oscillatory shear flow (LAOS). Aqueous CMHPG and HPG solutions enter the nonlinear flow regime at deformations γ0>100%. The nonlinear stress waveforms were analyzed by FT-rheology and orthogonal stress decomposition along the MITlaos framework. A rheological fingerprint is generated (Pipkin space) showing that the guar gum derivative solutions undergo a shear-thinning at high strains, which is preceded by a thickening above a minimum strain rate at intermediate strains. The influence and breakup of superstructures/aggregates gives a "rheological fingerprint", a function of the applied deformation and time scale (Pipkin space). A characteristic process time was found that scales exponentially with the overlap parameter with an exponent of 4/2, and is proposed to represent the relaxation process of the superstructure in solution. PMID:27561501
Cell adaptation to a physiologically relevant ECM mimic with different viscoelastic properties
Ghosh, Kaustabh; Pan, Zhi; Guan, E; Ge, Shouren; Liu, Yajie; Nakamura, Toshio; Ren, Xiang-Dong; Rafailovich, Miriam; Clark, Richard A.F.
2009-01-01
To successfully induce tissue repair or regeneration in vivo, bioengineered constructs must possess both optimal bioactivity and mechanical strength. This is because cell interaction with the extracellular matrix (ECM) produces two different but concurrent signaling mechanisms: ligation-induced signaling, which depends on ECM biological stimuli, and traction-induced signaling, which depends on ECM mechanical stimuli. In this report, we provide a fundamental understanding of how alterations in mechanical stimuli alone, produced by varying the viscoelastic properties of our bioengineered construct, modulate phenotypic behavior at the whole-cell level. Using a physiologically-relevant ECM mimic composed of hyaluronan and fibronectin, we found that adult human dermal fibroblasts modify their mechanical response in order to match substrate stiffness. More specifically, the cells on stiffer substrates had higher modulus and a more stretched and organized actin cytoskeleton (and vice versa), which translated into larger traction forces exerted on the substrate. This modulation of cellular mechanics had contrasting effects on migration and proliferation, where cells migrated faster on softer substrates while proliferating preferentially on the stiffer ones. These findings implicate substrate rigidity as a critical design parameter in the development of bioengineered constructs aimed at eliciting maximal cell and tissue function. PMID:17049594
Gutman, Jenia; Kaufman, Yair; Kawahara, Kazuyoshi; Walker, Sharon L; Freger, Viatcheslav; Herzberg, Moshe
2014-06-01
Bacterial outer membrane components play a critical role in bacteria-surface interactions (adhesion and repulsion). Sphingomonas species (spp.) differ from other Gram-negative bacteria in that they lack lipopolysaccharides (LPSs) in their outer membrane. Instead, Sphingomonas spp. outer membrane consists of glycosphingolipids (GSLs). To delineate the properties of the outer membrane of Sphingomonas spp. and to explain the adhesion of these cells to surfaces, we employed a single-component-based approach of comparing GSL vesicles to LPS vesicles. This is the first study to report the formation of vesicles containing 100% GSL. Significant physicochemical differences between GSL and LPS vesicles are reported. Composition-dependent vesicle adherence to different surfaces using quartz crystal microbalance with dissipation monitoring (QCM-D) technology was observed, where higher GSL content resulted in higher mass accumulation on the sensor. Additionally, the presence of 10% GSL and above was found to promote the relative rigidity of the vesicle obtaining viscoelastic ratio of 30-70% higher than that of pure LPS vesicles.
Nano confinement effects on dynamic and viscoelastic properties of Selenium Films
NASA Astrophysics Data System (ADS)
Yoon, Heedong; McKenna, Gregory
2015-03-01
In current study, we use a novel nano bubble inflation technique to study nano confinement effects on the dynamic and viscoelastic properties of physical vapor deposited Selenium films. Film thicknesses ranged from 60 to 260 nm. Creep experiments were performed for the temperatures ranging from Tg,macroscopic-14 °C to Tg,\\ macroscopic + 19 °C. Time temperature superposition and time thickness superposition were applied to create reduced creep curves, and those were compared with macroscopic data [J. Non-Cryst. Solids. 2002, 307, 790-801]. The results showed that the time temperature superposition was applicable in the glassy relaxation regime to the steady-state plateau regime. However in the long time response of the creep compliance, time thickness superposition failed due to the thickness dependence on the steady-state plateau. It was observed that the steady state compliance increased with film thickness. The thickness dependence on the plateau stiffening followed a power law of DPlateau ~ h2.46, which is greater than observed in organic polymers where the exponents observed range from 0.83 to 2.0 [Macromolecules. 2012, 45 (5), 2453-2459]. National Science Foundation Grant No. CHE 1112416 and John R. Bradford Endowment at Texas Tech
Kazemirad, Siavash; K. Heris, Hossein; Mongeau, Luc
2013-01-01
A characterization method based on Rayleigh wave propagation was developed for the quantification of the frequency-dependent viscoelastic properties of soft materials at high frequencies; i.e., up to 4 kHz. Planar harmonic surface waves were produced on the surface of silicone rubber samples. The phase and amplitude of the propagating waves were measured at different locations along the propagation direction, which allowed the calculation of the complex Rayleigh wavenumbers at each excitation frequency using a transfer function method. An inverse wave propagation problem was then solved to obtain the complex shear/elastic moduli from the measured wavenumbers. In a separate, related investigation, dynamic indentation tests using atomic force microscopy (AFM) were performed at frequencies up to 300 Hz. No systematic verification study is available for the AFM-based method, which can be used when the dimensions of the test samples are too small for other existing testing methods. The results obtained from the Rayleigh wave propagation and AFM-based indentation methods were compared with those from a well-established method, which involves the generation of standing longitudinal compression waves in rod-shaped test specimens. The results were cross validated and qualitatively confirmed theoretical expectations presented in the literature for the frequency-dependence of polymers. PMID:23654420
NASA Astrophysics Data System (ADS)
Itoh, Shintaro; Fukuzawa, Kenji; Hamamoto, Yuya; Zhang, Hedong
2010-08-01
We measured the temperature dependence of the viscoelastic properties of a liquid polymer confined and sheared within a nanometer-sized gap. In the viscoelastic measurements, we used the fiber wobbling method, a highly sensitive method that we have developed for measuring shear forces. As a liquid sample, we used the fluoropolyether lubricant Fomblin Zdol4000. Our experimental results showed that the temperature dependence of the viscosity was well expressed by the well-known Andrade equation, even in the confined state. The activation enthalpy was calculated by assuming that Eyring's theory of viscosity holds for gaps of a width ranging from 100 nm down to a few nanometers. We observed a significant decrease in the activation enthalpy for gaps smaller than 10 nm. Elasticity, which only appeared for confinement in gaps smaller than 10 nm, roughly decreased with increasing temperature.
Viscoelastic properties of individual glial cells and neurons in the CNS
Lu, Yun-Bi; Franze, Kristian; Seifert, Gerald; Steinhäuser, Christian; Kirchhoff, Frank; Wolburg, Hartwig; Guck, Jochen; Janmey, Paul; Wei, Er-Qing; Käs, Josef; Reichenbach, Andreas
2006-01-01
One hundred fifty years ago glial cells were discovered as a second, non-neuronal, cell type in the central nervous system. To ascribe a function to these new, enigmatic cells, it was suggested that they either glue the neurons together (the Greek word “γλια” means “glue”) or provide a robust scaffold for them (“support cells”). Although both speculations are still widely accepted, they would actually require quite different mechanical cell properties, and neither one has ever been confirmed experimentally. We investigated the biomechanics of CNS tissue and acutely isolated individual neurons and glial cells from mammalian brain (hippocampus) and retina. Scanning force microscopy, bulk rheology, and optically induced deformation were used to determine their viscoelastic characteristics. We found that (i) in all CNS cells the elastic behavior dominates over the viscous behavior, (ii) in distinct cell compartments, such as soma and cell processes, the mechanical properties differ, most likely because of the unequal local distribution of cell organelles, (iii) in comparison to most other eukaryotic cells, both neurons and glial cells are very soft (“rubber elastic”), and (iv) intriguingly, glial cells are even softer than their neighboring neurons. Our results indicate that glial cells can neither serve as structural support cells (as they are too soft) nor as glue (because restoring forces are dominant) for neurons. Nevertheless, from a structural perspective they might act as soft, compliant embedding for neurons, protecting them in case of mechanical trauma, and also as a soft substrate required for neurite growth and facilitating neuronal plasticity. PMID:17093050
Solares, Santiago D
2016-01-01
Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip-sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surface as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young's modulus. Relevant cases are discussed for single- and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip-sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. A multifrequency AFM simulation tool based on the above sample model is provided as supporting information. PMID:27335746
Solares, Santiago D.
2016-04-15
Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip-sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surfacemore » as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young's modulus. Relevant cases are discussed for single-and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip-sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. As a result, a multifrequency AFM simulation tool based on the above sample model is provided as supporting information.« less
Solares, Santiago D
2016-01-01
Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip-sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surface as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young's modulus. Relevant cases are discussed for single- and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip-sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. A multifrequency AFM simulation tool based on the above sample model is provided as supporting information.
2016-01-01
Summary Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip–sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surface as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young’s modulus. Relevant cases are discussed for single- and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip–sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. A multifrequency AFM simulation tool based on the above sample model is provided as supporting information. PMID:27335746
Mechanical Signal Filtering by Viscoelastic Properties of Cuticle in a Wandering Spider
NASA Astrophysics Data System (ADS)
McConney, Michael E.; Schaber, Clemens; Julian, Michael; Humphrey, Joseph A. C.; Barth, Friedrich; Tsukruk, Vladimir V.
2009-03-01
As recently found, in mechano-sensors of wandering spiders (Cupiennius salei) viscoelastic materials are important in signal filtering. We used atomic force microscopy to probe the time dependent mechanical behavior of these materials in live animals. We measured Young's modulus of a rubbery material located between a vibration receptor and the stimulus source. Earlier electrophysiological studies had demonstrated that the strain needed to elicit a sensory response (action potential) increased drastically as stimulus frequencies went below 10 Hz. Our surface force spectroscopy data similarly indicated a significant decrease in stiffness of the cuticular material and therefore less efficient energy transmission due to viscoelastic effects, as the frequency dropped to around 10 Hz. The stimulus transmitting cuticular material is acting as a high-pass filter for the mechanical stimulus on its way to the strain receptors. Again our results indicate that viscoelastic mechanical signal filtering is an important tool for arthropods to specifically respond to biologically relevant stimulus patterns.
Effect of carbamazepine on viscoelastic properties and hot melt extrudability of Soluplus ®.
Gupta, Simerdeep Singh; Parikh, Tapan; Meena, Anuprabha K; Mahajan, Nidhi; Vitez, Imre; Serajuddin, Abu T M
2015-01-15
The purpose of this study was to apply viscoelastic properties of polymer and drug-polymer mixtures to determine processing conditions for the preparation of amorphous solid dispersion by melt extrusion. A poorly water-soluble drug, carbamazepine (CBZ), was mixed with Soluplus(®) as the carrier. Torque analysis using a melt extruder was performed at 10, 20 and 30% w/w drug concentrations and the effect of barrel temperature was studied. Viscosity of the mixtures either at fixed temperatures with different angular frequencies or as a function of temperature with the same frequency was studied using a rheometer. The viscosity of Soluplus(®) and the torque exerted on the twin screws decreased with the increase in CBZ concentration. The viscosity versus temperature plots for different CBZ concentrations were parallel to each other, without the drug melting transition, indicating complete drug-polymer miscibility. Thus, the drug-polymer mixtures could be extruded at temperature as low as 140°C with 10% w/w drug load, 135°C with 20% w/w drug and 125°C with 30% w/w drug, which were, respectively, ∼ 50°C, 55°C and 65°C below the melting point of 191°C for CBZ. The differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) analyses of the binary mixtures extruded at 125-150°C showed absence of crystalline drug. A systematic study of miscibility and extrudability of drug-polymer mixtures by rheological and torque analysis as a function of temperature will help formulators select optimal melt extrusion processing conditions to develop solid dispersions. PMID:25448585
NASA Astrophysics Data System (ADS)
Patankar, Kshitish A.; Dillard, David A.; Case, Scott W.; Ellis, Michael W.; Lai, Yeh-Hung; Budinski, Michael K.; Gittleman, Craig S.
2008-09-01
When a proton exchange membrane (PEM) based fuel cell is placed in service, hygrothermal stresses develop within the membrane and vary widely with internal operating environment. These hygrothermal stresses associated with hygral contraction and expansion at the operating conditions are believed to be critical in membrane mechanical integrity and durability. Understanding and accurately modeling the viscoelastic constitutive properties of a PEM is important for making hygrothermal stress predictions in the cyclic temperature and humidity environment of operating fuel cells. The tensile stress relaxation moduli of a commercially available PEM, Gore-Select® 57, were obtained over a range of humidities and temperatures. These tests were performed using TA Instruments 2980 and Q800 dynamic mechanical analyzers (DMA), which are capable of applying specified tensile loading conditions on small membrane samples at a given temperature. A special humidity chamber was built in the form of a cup that encloses tension clamps of the DMA. The chamber was inserted in the heating furnace of the DMA and connected to a gas humidification unit by means of plastic tubing through a slot in the chamber. Stress relaxation data over a temperature range of 40 90°C and relative humidity range of 30 90% were obtained. Thermal and hygral master curves were constructed using thermal and hygral shift factors and were used to form a hygrothermal master curve using the time temperature moisture superposition principle. The master curve was also constructed independently using just one shift factor. The hygrothermal master curve was fitted with a 10-term Prony series for use in finite element software. The hygrothermal master curve was then validated using longer term tests. The relaxation modulus from longer term data matches well with the hygrothermal master curve. The long term test showed a plateau at longer times, suggesting an equilibrium modulus.
Orgad, Oded; Oren, Yoram; Walker, Sharon L; Herzberg, Moshe
2011-08-01
Among various functions, extracellular polymeric substances (EPS) provide microbial biofilms with mechanical stability and affect initial cell attachment, the first stage in the biofilm formation process. The role of alginate, an abundant polysaccharide in Pseudomonas aeruginosa biofilms, in the viscoelastic properties and adhesion kinetics of EPS was analyzed using a quartz crystal microbalance with dissipation (QCM-D) monitoring technology. EPS was extracted from two P. aeruginosa biofilms, a wild type strain, PAO1, and a mucoid strain, PAOmucA22 that over-expresses alginate production. The higher alginate content in the EPS originating from the mucoid biofilms was clearly shown to increase both the rate and the extent of attachment of the EPS, as well as the layer's thickness. Also, the presence of calcium and elevated ionic strength increased the thickness of the EPS layer. Dynamic light scattering (DLS) showed that the presence of calcium and elevated ionic strength induced intermolecular attractive interactions in the mucoid EPS molecules. For the wild type EPS, in the presence of calcium, an elevated shift in the distribution of the diffusion coefficients was observed with DLS due to a more compacted conformation of the EPS molecules. Moreover, the alginate over-expression effect on EPS adherence was compared to the effect of alginate over-expression on P. aeruginosa cell attachment. In a parallel plate flow cell, under similar hydraulic and aquatic conditions as those applied for the EPS adsorption tests in the QCM-D flow cell, reduced adherence of the mucoid strain was clearly observed compared to the wild type isogenic bacteria. The results suggest that alginate contributes to steric hindrance and shielding of cell surface features and adhesins that are known to promote cell attachment.
Effect of carbamazepine on viscoelastic properties and hot melt extrudability of Soluplus ®.
Gupta, Simerdeep Singh; Parikh, Tapan; Meena, Anuprabha K; Mahajan, Nidhi; Vitez, Imre; Serajuddin, Abu T M
2015-01-15
The purpose of this study was to apply viscoelastic properties of polymer and drug-polymer mixtures to determine processing conditions for the preparation of amorphous solid dispersion by melt extrusion. A poorly water-soluble drug, carbamazepine (CBZ), was mixed with Soluplus(®) as the carrier. Torque analysis using a melt extruder was performed at 10, 20 and 30% w/w drug concentrations and the effect of barrel temperature was studied. Viscosity of the mixtures either at fixed temperatures with different angular frequencies or as a function of temperature with the same frequency was studied using a rheometer. The viscosity of Soluplus(®) and the torque exerted on the twin screws decreased with the increase in CBZ concentration. The viscosity versus temperature plots for different CBZ concentrations were parallel to each other, without the drug melting transition, indicating complete drug-polymer miscibility. Thus, the drug-polymer mixtures could be extruded at temperature as low as 140°C with 10% w/w drug load, 135°C with 20% w/w drug and 125°C with 30% w/w drug, which were, respectively, ∼ 50°C, 55°C and 65°C below the melting point of 191°C for CBZ. The differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) analyses of the binary mixtures extruded at 125-150°C showed absence of crystalline drug. A systematic study of miscibility and extrudability of drug-polymer mixtures by rheological and torque analysis as a function of temperature will help formulators select optimal melt extrusion processing conditions to develop solid dispersions.
NASA Technical Reports Server (NTRS)
Stroud, Jason D.; Baicu, Catalin F.; Barnes, Mary A.; Spinale, Francis G.; Zile, Michael R.
2002-01-01
To determine whether and to what extent one component of the extracellular matrix, fibrillar collagen, contributes causally to abnormalities in viscoelasticity, collagen was acutely degraded by activation of endogenous matrix metalloproteinases (MMPs) with the serine protease plasmin. Papillary muscles were isolated from normal cats and cats with right ventricular pressure overload hypertrophy (POH) induced by pulmonary artery banding. Plasmin treatment caused MMP activation, collagen degradation, decreased the elastic stiffness constant, and decreased the viscosity constant in both normal and POH muscles. Thus, whereas many mechanisms may contribute to the abnormalities in myocardial viscoelasticity in the POH myocardium, changes in fibrillar collagen appear to play a predominant role.
Nonlinear Viscoelastic Characterization of the Porcine Spinal Cord
Shetye, Snehal; Troyer, Kevin; Streijger, Femke; Lee, Jae H. T.; Kwon, Brian K.; Cripton, Peter; Puttlitz, Christian M.
2014-01-01
Although quasi-static and quasi-linear viscoelastic properties of the spinal cord have been reported previously, there are no published studies that have investigated the fully (strain-dependent) nonlinear viscoelastic properties of the spinal cord. In this study, stress relaxation experiments and dynamic cycling were performed on six fresh porcine lumbar cord specimens to examine their viscoelastic mechanical properties. The stress relaxation data were fitted to a modified superposition formulation and a novel finite ramp time correction technique was applied. The parameters obtained from this fitting methodology were used to predict the average dynamic cyclic viscoelastic behavior of the porcine cord. The data indicate that the porcine spinal cord exhibited fully nonlinear viscoelastic behavior. The average weighted RMSE for a Heaviside ramp fit was 2.8kPa, which was significantly greater (p < 0.001) than that of the nonlinear (comprehensive viscoelastic characterization (CVC) method) fit (0.365kPa). Further, the nonlinear mechanical parameters obtained were able to accurately predict the dynamic behavior, thus exemplifying the reliability of the obtained nonlinear parameters. These parameters will be important for future studies investigating various damage mechanisms of the spinal cord and studies developing high resolution finite elements models of the spine. PMID:24211612
ERIC Educational Resources Information Center
Dave, Eshan V.
2009-01-01
Asphalt concrete pavements are inherently graded viscoelastic structures. Oxidative aging of asphalt binder and temperature cycling due to climatic conditions being the major cause of non-homogeneity. Current pavement analysis and simulation procedures dwell on the use of layered approach to account for these non-homogeneities. The conventional…
Viscoelastic properties of a bio-hydrogel produced from soybean oil
Technology Transfer Automated Retrieval System (TEKTRAN)
Hydrogels are a class of viscoelastic materials that have many biomedical utilization potentials, such as drug delivery, wound care product, breast implant materials, and tissue engineering, etc. Hydrogels produced from biopolymers and/or natural sources have particular advantages in vivo applicati...
Water sorption, viscoelastic, and optical properties of thin NafionRTM films
NASA Astrophysics Data System (ADS)
Petrina, Stephanie Ann
The hydrogen fuel cell industry continues to make strides in terms of improving device efficiency and performance, yet ion transport within the catalyst layer is not well understood. Thin ionomer films coating the catalytic particles are responsible for proton transport throughout the catalytic layer, yet the basic physical properties of these thin films, which interact with the catalyst surface, are widely unknown. Fundamentally, the material properties of thin polymer films are known to deviate from thick, free-standing membranes composed of the same material based on their interfacial interactions. The work in this dissertation seeks to uncover the properties of thin NafionRTM films to begin to understand their role in catalyst layer performance. By identifying the influence of processing conditions, polymer--substrate interaction, and thickness on water uptake characteristics of thin Nafion RTM films, the proton and oxygen transport parameters that are most relevant to performance in the catalyst layer can be understood. Since the hydration of NafionRTM is relevant for its proton conduction and performance in a fuel cell, water sorption of substrate--supported NafionRTM thin films was characterized via the change in sample mass and thickness as the relative humidity (RH) of the sample environment was varied. Monolithic thin NafionRTM films were characterized for a variety of sample preparation conditions and substrates to identify how processing conditions and other sample parameters may affect water uptake. Spin cast NafionRTM films exhibited low density and refractive index for very thin films due to the higher relative void fraction induced by rapid film formation. The density of hydrated films was observed to decrease beyond the volume additivity limit as RH increased, and the relationship between density and refractive index was confirmed with the Lorentz-Lorenz relationship. The complex refractive indices (N = n + ik) of substrate--supported Nafion RTM
NASA Astrophysics Data System (ADS)
Ribierre, Jean-Charles; Mager, Loiec; Fort, Alain F.; Mery, Stephane
2002-12-01
In photorefractive guest-host polymers, fast orientational dynamics of push-pull chromophores are needed to obtain the so-called orientational enhancement as well as high performances. For this purpose, a better understanding of the relationships between viscoelastic properties of polymers and orientational processes of chromophores is now essential for the optimization and the development of new efficient photorefractive polymers. In the present investigation, the orientational dynamics of the chromophores are probed in details by dielectric spectroscopy, second-harmonic generation and ellipsometric techniques, in various doped polymers. The materials are based on a polyvinylcarbazole plasticized with N-ethyl carbazole, a polysiloxane functionnalized with a carbazole pendant, as well as polystyrenes with different average macromolecular weights. The temperature-dependencies of their dielectric and electro-optic responses provide information on the rotational mobility of the chromophores at a microscopic scale. These data are directly compared to the temperature-dependence of the viscoelastic properties, characterized at a macroscopic level by shear compliance measurements. The analysis reveals the strong coupling between the orientational processes of the chromophores and the polymer chain dynamics. The effects of other physical parameters (applied voltage magnitude, amount of plasticizer, average molecular weight of the polymer host) on the orientational dynamics of chromophores are also investigated in order to describe the mechanical interactions between the chromophores and the polymer host. Finally, a new way of optimization for photorefractive polymeric material properties is suggested.
Characterization of viscoelastic properties of molybdenum disulphide filled polyamide by indentation
NASA Astrophysics Data System (ADS)
Stan, Felicia; Fetecau, Catalin
2013-05-01
In this paper, the creep behavior of molybdenum disulphide (MoS2) filled polyamide 66 composite was investigated through sharp indentation at room temperature. Two types of indentation creep test, the 3-step indentation test, and the 5-step indentation test were considered in order to explore whether the measured creep response is mainly viscoelastic or includes a significant contribution from the plastic deformation developed during the loading phase. The experimental indentation creep data were analyzed within an analytical framework based on the hereditary integral operator for the ramp creep and a viscoelastic-plastic (VEP) model in order to determine the indentation creep compliance function including the short- and long-time modulus. The equivalent shear modulus calculated from the creep compliance function was compared to the indentation plane strain modulus derived from the initial slope of the unloading curve in order to investigate the validity of the Oliver and Pharr method.
Linear and nonlinear mechanical properties of a series of epoxy resins
NASA Technical Reports Server (NTRS)
Curliss, D. B.; Caruthers, J. M.
1987-01-01
The linear viscoelastic properties have been measured for a series of bisphenol-A-based epoxy resins cured with the diamine DDS. The linear viscoelastic master curves were constructed via time-temperature superposition of frequency dependent G-prime and G-double-prime isotherms. The G-double-prime master curves exhibited two sub-Tg transitions. Superposition of isotherms in the glass-to-rubber transition (i.e., alpha) and the beta transition at -60 C was achieved by simple horizontal shifts in the log frequency axis; however, in the region between alpha and beta, superposition could not be effected by simple horizontal shifts along the log frequency axis. The different temperature dependency of the alpha and beta relaxation mechanisms causes a complex response of G-double-prime in the so called alpha-prime region. A novel numerical procedure has been developed to extract the complete relaxation spectra and its temperature dependence from the G-prime and G-double-prime isothermal data in the alpha-prime region.
Tanaka, Reina; Saito, Tsuguyuki; Hänninen, Tuomas; Ono, Yuko; Hakalahti, Minna; Tammelin, Tekla; Isogai, Akira
2016-06-13
We report the viscoelastic properties of core-shell-structured, hemicellulose-rich nanofibrillated cellulose (NFC) in dispersion and wet-film states. The hemicellulose-rich NFC (hemicellulose neutral sugars 23%, carboxylate 0.2 mmol g(-1)), prepared from Japanese persimmons, had a core crystallite thickness of 2.3 nm and unit fibril thickness of 4.2 nm. A carboxylate-rich NFC (hemicellulose neutral sugars 7%, carboxylate 0.9 mmol g(-1)) with crystallite and fibril widths of 2.5 and 3.3 nm, respectively, was used as a reference. The solid-concentration dependencies of the storage moduli of gel-like water dispersions of the hemicellulose-rich NFC were weaker than those of carboxylate-rich NFC, and the dispersions were loosely flocculated even at high salt concentrations and low pH values. The viscoelastic properties of wet NFC films were similar to those of their dispersions; the hemicellulose-rich NFC films were significantly less sensitive to salt concentration and pH and were soft and swollen at high salt concentrations and low pH values. PMID:27142723
Viscoelasticity of silica gels
Scherer, G.W.
1995-12-01
The response of silica gels to mechanical loads depends on the properties of the solid phase and the permeability of the network. Understanding this behavior is essential for modeling of stresses developed during drying or heating of gels. The permeability and the mechanical properties are readily determined from a simple beam-bending experiment, by measuring the load relaxation that occurs at constant deflection. Load decay results from movement of the liquid within the network; in addition, there may be viscoelastic relaxation of the network itself. Silica gel is viscoelastic in chemically aggressive media, but in inert liquids (such as ethanol or acetone) it is elastic. Experiments show that the viscoelastic relaxation time decreases as the concentration and pH of the water in the pore liquid increase. During drying, the permeability decreases and the viscosity increases, both exhibiting a power-law dependence on density of the gel network.
NASA Astrophysics Data System (ADS)
Soltani, T.; Fouzai, M.; Dhaoudi, H.; Marcerou, J. P.; Othman, T.
2016-06-01
Some chiral series with benzoate cores (CnHH, CnF3 and CnF2) are reported. These series (hydrogenous, monofluoro-substituted in positions 2 and 3 of the first phenyl ring near the chiral chain) display very rich polymorphism, including SmC*, SmC*α, SmC*FI1, SmC*FI2 and SmC*A phases. Based on the theoretical Hammaneh-Taylor model, we analyze phase diagrams and physical properties, including spontaneous polarization, transverse dipole moment and torsion of the studied compounds. This description offers an insight into the factors that affect the stability of the intermediate smectic phases. The effect of fluoro substitution on the visco-elastic properties is investigated.
Donahue, T L; Gregersen, C; Hull, M L; Howell, S M
2001-04-01
Due to ready availability, decreased cost, and freedom from transmissible diseases in humans such as hepatitis and AIDS, it would be advantageous to use tendon grafts from farm animals as a substitute for human tendon grafts in in vitro experiments aimed at improving the outcome of anterior cruciate ligament (ACL) reconstructive surgery. Thus the objective of this study was to determine whether an anterior cruciate ligament (ACL) graft composed of two loops of bovine common digital extensor tendon has the same viscoelastic, structural, and material properties as a graft composed of a double loop of semitendinosus and gracilis tendons from humans. To satisfy this objective, grafts were constructed from each tissue source. The cross-sectional area was measured using an area micrometer, and each graft was then pulled using a materials testing system while submerged in a saline bath. Using two groups of tendon grafts (n = 10), viscoelastic tests were conducted over a three-day period during which a constant displacement load relaxation test was followed by a constant amplitude, cyclic load creep test (first day), a constant load creep test (second day), and an incremental cyclic load creep test (third day). Load-to-failure tests were performed on two different groups of grafts (n = 8). When the viscoelastic behavior was compared, there were no significant differences in the rate of load decay or the final load (relaxation test) and rates of displacement increase or final displacements (creep tests) (p > 0.115). To compare both the structural and material properties in the toe region (i.e., < 250 N) of the load-elongation curve, the tangent stiffness and modulus functions were computed from parameters used in an exponential model fit to the load (stress)-elongation (strain) data. Although one of the two parameters in the functions was different statistically, this difference translated into a difference of only 0.03 mm in displacement at 250 N of load. In the linear
Stability analysis on a set of calcium-regulated viscoelastic equations
NASA Astrophysics Data System (ADS)
Trainor, L. E. H.; Goodwin, B. C.
1986-05-01
In recent years some progress has been made in modelling pattern formation and morphogenesis in biological systems in terms of calcium ion regulation of the viscoelastic properties of the cellular cortex. In this paper, linear stability analysis is used on a set of calcium-regulated viscoelastic equations derived by Goodwin and Trainor [5] for the 3-dimensional medium appropriate to regeneration phenomena in the single celled alga Acetabularia mediterranea. The nature of the instabilities is discussed and it is shown how complex patterns arise naturally from the cross-terms linking viscoelastic strain to calcium concentration and concentration gradients.
Stability analysis on a set of calcium-regulated viscoelastic equations
NASA Astrophysics Data System (ADS)
Trainor, L. E. H.; Goodwin, B. C.
1986-08-01
In recent years some progress has been made in modelling pattern formation and morphogenesis in biological systems in terms of calcium ion regulation of the viscoelastic properties of the cellular cortex. In this paper, linear stability analysis is used on a set of calcium-regulated viscoelastic equations derived by Goodwin and Trainor [5] for the 3-dimensional medium appropriate to regeneration phenomena in the single celled alga Acetabularia mediterranea. The nature of the instabilities is discussed and it is shown how complex patterns arise naturally from the cross-terms linking viscoelastic strain to calcium concentration and concentration gradients.
Mrozek, Randy A; Leighliter, Brad; Gold, Christopher S; Beringer, Ian R; Yu, Jian H; VanLandingham, Mark R; Moy, Paul; Foster, Mark H; Lenhart, Joseph L
2015-04-01
The fundamental material response of a viscoelastic material when impacted by a ballistic projectile has important implication for the defense, law enforcement, and medical communities particularly for the evaluation of protective systems. In this paper, we systematically vary the modulus and toughness of a synthetic polymer gel to determine their respective influence on the velocity-dependent penetration of a spherical projectile. The polymer gels were characterized using tensile, compression, and rheological testing taking special care to address the unique challenges associated with obtaining high fidelity mechanical data on highly conformal materials. The depth of penetration data was accurately described using the elastic Froude number for viscoelastic gels ranging in Young's modulus from ~60 to 630 kPa. The minimum velocity of penetration was determined to scale with the gel toughness divided by the gel modulus, a qualitative estimate for the zone of deformation size scale upon impact. We anticipate that this work will provide insight into the critical material factors that control ballistic penetration behavior in soft materials and aid in the design and development of new ballistic testing media.
Mrozek, Randy A; Leighliter, Brad; Gold, Christopher S; Beringer, Ian R; Yu, Jian H; VanLandingham, Mark R; Moy, Paul; Foster, Mark H; Lenhart, Joseph L
2015-04-01
The fundamental material response of a viscoelastic material when impacted by a ballistic projectile has important implication for the defense, law enforcement, and medical communities particularly for the evaluation of protective systems. In this paper, we systematically vary the modulus and toughness of a synthetic polymer gel to determine their respective influence on the velocity-dependent penetration of a spherical projectile. The polymer gels were characterized using tensile, compression, and rheological testing taking special care to address the unique challenges associated with obtaining high fidelity mechanical data on highly conformal materials. The depth of penetration data was accurately described using the elastic Froude number for viscoelastic gels ranging in Young's modulus from ~60 to 630 kPa. The minimum velocity of penetration was determined to scale with the gel toughness divided by the gel modulus, a qualitative estimate for the zone of deformation size scale upon impact. We anticipate that this work will provide insight into the critical material factors that control ballistic penetration behavior in soft materials and aid in the design and development of new ballistic testing media. PMID:25637822
Textural and cooking properties and viscoelastic changes on heating and cooling of Balkan cheeses.
Guinee, T P; Pudja, P; Miočinović, J; Wiley, J; Mullins, C M
2015-11-01
The growth in food service and prepared consumer foods has led to increasing demand for cheese with customized textural and cooking characteristics. The current study evaluated Kačkavalj, Kačkavalj Krstaš, and Trappist cheeses procured from manufacturing plants in Serbia for texture profile characteristics, flow and extensibility of the heated cheese, and changes in viscoelasticity characteristics during heating and cooling. Measured viscoelastic parameters included elastic modulus, G', loss modulus, G″, and loss tangent, LT (G″/G'). The melting temperature and congealing temperature were defined as the temperature at which LT=1 during heating from 25 to 90°C and on cooling from 90 to 25°C. The maximum LT during heating was as an index of the maximum fluidity of the molten cheese. Significant variation was noted for the extent of flow and extensibility of the heated cheeses, with no trend of cheese type. As a group, the Kačkavalj cheeses had relatively high levels of salt-in-moisture and pH 4.6-soluble N and low protein-to-fat ratio and levels of αs1-CN (f24-199). They fractured during compression to 75%; had relatively low values of cohesiveness, chewiness, and springiness; melted at ~70 to 90°C; reached maximum LT at 90°C; and congealed at 58 to 63°C. Conversely, the Kačkavalj Krstaš and Trappist cheeses had low levels of primary proteolysis and salt-in-moisture content and a high protein-to-fat ratio. They did not fracture during compression, had high values for cohesiveness and chewiness, melted at lower temperatures (56-62°C), attained maximum fluidity at a lower temperature (72-78°C), and congealed at 54 to 69°C. There was a hysteretic dependence of G' and LT on temperature for all cheeses, with the LT during cooling being higher than that during heating, and G' during cooling being lower or higher than the equivalent values during heating depending on the cheese type. Monitoring the dynamic changes in viscoelasticity during heating and
Textural and cooking properties and viscoelastic changes on heating and cooling of Balkan cheeses.
Guinee, T P; Pudja, P; Miočinović, J; Wiley, J; Mullins, C M
2015-11-01
The growth in food service and prepared consumer foods has led to increasing demand for cheese with customized textural and cooking characteristics. The current study evaluated Kačkavalj, Kačkavalj Krstaš, and Trappist cheeses procured from manufacturing plants in Serbia for texture profile characteristics, flow and extensibility of the heated cheese, and changes in viscoelasticity characteristics during heating and cooling. Measured viscoelastic parameters included elastic modulus, G', loss modulus, G″, and loss tangent, LT (G″/G'). The melting temperature and congealing temperature were defined as the temperature at which LT=1 during heating from 25 to 90°C and on cooling from 90 to 25°C. The maximum LT during heating was as an index of the maximum fluidity of the molten cheese. Significant variation was noted for the extent of flow and extensibility of the heated cheeses, with no trend of cheese type. As a group, the Kačkavalj cheeses had relatively high levels of salt-in-moisture and pH 4.6-soluble N and low protein-to-fat ratio and levels of αs1-CN (f24-199). They fractured during compression to 75%; had relatively low values of cohesiveness, chewiness, and springiness; melted at ~70 to 90°C; reached maximum LT at 90°C; and congealed at 58 to 63°C. Conversely, the Kačkavalj Krstaš and Trappist cheeses had low levels of primary proteolysis and salt-in-moisture content and a high protein-to-fat ratio. They did not fracture during compression, had high values for cohesiveness and chewiness, melted at lower temperatures (56-62°C), attained maximum fluidity at a lower temperature (72-78°C), and congealed at 54 to 69°C. There was a hysteretic dependence of G' and LT on temperature for all cheeses, with the LT during cooling being higher than that during heating, and G' during cooling being lower or higher than the equivalent values during heating depending on the cheese type. Monitoring the dynamic changes in viscoelasticity during heating and
Amid, Bahareh Tabatabaee; Mirhosseini, Hamed
2012-09-01
The aim of the present study was to investigate the effects of different purification and drying methods on the viscoelastic behaviour and rheological properties of durian seed gum. The results indicated that the purified gum A (using isopropanol and ethanol) and D (using hydrochloric acid and ethanol) showed the highest and lowest viscosity, respectively. Four drying techniques included oven drying (105 °C), freeze drying, spray drying and vacuum oven drying. In the present work, all purified gums exhibited more elastic (gel-like) behaviour than the viscous (liquid-like) behaviour (G″
Mapping viscoelastic properties of healthy and pathological red blood cells at the nanoscale level
NASA Astrophysics Data System (ADS)
Ciasca, G.; Papi, M.; di Claudio, S.; Chiarpotto, M.; Palmieri, V.; Maulucci, G.; Nocca, G.; Rossi, C.; de Spirito, M.
2015-10-01
In order to pass through the microcirculation, red blood cells (RBCs) need to undergo extensive deformations and to recover the original shape. This extreme deformability is altered by various pathological conditions. On the other hand, an altered RBC deformability can have major effects on blood flow and can lead to pathological implications. The study of the viscoelastic response of red blood cells to mechanical stimuli is crucial to fully understand deformability changes under pathological conditions. However, the typical erythrocyte biconcave shape hints to a complex and intrinsically heterogeneous mechanical response that must be investigated by using probes at the nanoscale level. In this work, the local viscoelastic behaviour of healthy and pathological red blood cells was probed by Atomic Force Microscopy (AFM). Our results clearly show that the RBC stiffness is not spatially homogeneous, suggesting a strong correlation with the erythrocyte biconcave shape. Moreover, our nanoscale mapping highlights the key role played by viscous forces, demonstrating that RBCs do not behave as pure elastic bodies. The fundamental role played by viscous forces is further strengthened by the comparison between healthy and pathological (diabetes mellitus) RBCs. It is well known that pathological RBCs are usually stiffer than the healthy ones. Our measures unveil a more complex scenario according to which the difference between normal and pathological red blood cells does not merely lie in their stiffness but also in a different dynamical response to external stimuli that is governed by viscous forces.In order to pass through the microcirculation, red blood cells (RBCs) need to undergo extensive deformations and to recover the original shape. This extreme deformability is altered by various pathological conditions. On the other hand, an altered RBC deformability can have major effects on blood flow and can lead to pathological implications. The study of the viscoelastic
Zhang, Sipei; Lee, Keun Hyung; Sun, Jingru; Frisbie, C. Daniel; Lodge, Timothy P.
2013-03-07
The viscoelastic properties and ionic conductivity of ion gels based on the self-assembly of a poly(styrene-b-ethylene oxide-b-styrene) (SOS) triblock copolymer (M{sub n,S} = 3 kDa, M{sub n,O} = 35 kDa) in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMI][TFSA]) were investigated over the composition range of 10-50 wt % SOS and the temperature range of 25-160 C. The poly(styrene) (PS) end-blocks associate into micelles, whereas the poly(ethylene oxide) (PEO) midblocks are well-solvated by this ionic liquid. The ion gel with 10 wt % SOS melts at 54 C, with the longest relaxation time exhibiting a similar temperature dependence to that of the viscosity of bulk PS. However, the actual values of the gel relaxation time are more than 4 orders of magnitude larger than the relaxation time of bulk PS. This is attributed to the thermodynamic penalty of pulling PS end-blocks through the PEO/[EMI][TFSA] matrix. Ion gels with 20-50 wt % SOS do not melt and show two plateaus in the storage modulus over the temperature and frequency ranges measured. The one at higher frequencies is that of an entangled network of PEO strands with PS cross-links; the modulus displays a quadratic dependence on polymer weight fraction and agrees with the prediction of linear viscoelastic theory assuming half of the PEO chains are elastically effective. The frequency that separates the two plateaus, {omega}{sub c}, reflects the time scale of PS end-block pull-out. The other plateau at lower frequencies is that of a congested micelle solution with PS cores and PEO coronas, which has a power law dependence on domain spacing similar to diblock melts. The ionic conductivity of the ion gels is compared to PEO homopolymer solutions at similar polymer concentrations; the conductivity is reduced by a factor of 2.1 or less, decreases with increasing PS volume fraction, and follows predictions based on a simple obstruction model. Our collective results allow the formulation
Viscoelasticity of hyaluronic acid-gelatin hydrogels for vocal fold tissue engineering.
Kazemirad, Siavash; Heris, Hossein K; Mongeau, Luc
2016-02-01
Crosslinked injectable hyaluronic acid (HA)-gelatin (Ge) hydrogels have remarkable viscoelastic and biological properties for vocal fold tissue engineering. Patient-specific tuning of the viscoelastic properties of this injectable biomaterial could improve tissue regeneration. The frequency-dependent viscoelasticity of crosslinked HA-Ge hydrogels was measured as a function of the concentration of HA, Ge, and crosslinker. Synthetic extracellular matrix hydrogels were fabricated using thiol-modified HA and Ge, and crosslinked by poly(ethylene glycol) diacrylate. A recently developed characterization method based on Rayleigh wave propagation was used to quantify the frequency-dependent viscoelastic properties of these hydrogels, including shear storage and loss moduli, over a broad frequency range; that is, from 40 to 4000 Hz. The viscoelastic properties of the hydrogels increased with frequency. The storage and loss moduli values and the rate of increase with frequency varied with the concentrations of the constituents. The range of the viscoelastic properties of the hydrogels was within that of human vocal fold tissue obtained from in vivo and ex vivo measurements. Frequency-dependent parametric relations were obtained using a linear least-squares regression. The results are useful to better fine-tune the storage and loss moduli of HA-Ge hydrogels by varying the concentrations of the constituents for use in patient-specific treatments.
Kiss, Miklos Z.; Daniels, Matthew J.; Varghese, Tomy
2009-01-01
The viscoelastic characteristics of thermal lesions in ex vivo animal liver are investigated in this paper. Characterization of the moduli of thermal lesions prepared at several temperatures will provide additional information for the elastographic monitoring of radio frequency ablation of hepatic tumors. In this study, the frequency-dependent complex modulus of thermal lesions prepared at temperatures ranging from 60–90 °C over a frequency range from 0.1–50 Hz are presented. Lesions were prepared using either radio frequency ablation or double immersion boiling. It was found that both the magnitude and phase of the modulus increase with frequency, a behavior that has been noted in the literature. A new result reported shows that the modulus dependence on temperature reveals a local maximum around 70–75 °C corresponding to the temperature at which tissue has released most of its water content. The modulus values at temperatures higher than 70 °C continued to increase, but the extent of increase depend on animal species and other factors. PMID:19362313
NASA Astrophysics Data System (ADS)
Traore, N.; Le Pourhiet, L.; Frelat, J.; Rolandone, F.; Meyer, B.
2012-04-01
The screw dislocation model (Weertman & Weertman, 1966) gives the horizontal displacement u as a function of the vertical distance d to the dislocation, the horizontal distance x and the slip s on each side of the dislocation. u = - (s/π) arctan(x/d) Savage and Burford (1973) interpreted this model in terms of horizontal displacement across a strike slip fault which is locked down to depth d, s being the plate velocity. Because of its simplicity and because the arctangent shape well represents the displacement that can be measured around most of the major strike slip faults, this model is commonly used to match geodetic data. We present numerical simulations that have been made with the software CASTEM, a finite element code for structural and mechanical modeling. The models are rectangular boxes that have elastic or viscoelastic properties, and three different kinds of conditions are applied on the boundaries of the domain that may have an impact on the localization of the displacement near the fault plane. The first boundary condition imposes the displacement under the plate, this case has been chosen because of its similarity to the Weertman's screw dislocation model. The second boundary condition imposes the displacement in the front, it corresponds to an extrusion. For the third boundary condition, the displacement is imposed laterally and simulates the general plate motion that drags the domain on both sides. We found that the displacement at the free surface does not fit an arctangent in all cases. If a perfectly elastic, homogeneous domain is used, only the first two types of boundary conditions lead to a displacement field resembling the geodetic data. This is awkward since the third kind of boundary conditions seems to be geologically the more relevant one. We then introduced local rheological modifications to reduce locally the equivalent elastic plate thickness in the vicinity of the fault. This is achieved by introducing a viscoelastic relaxation in
NASA Astrophysics Data System (ADS)
Fittipaldi, Mauro; Rodriguez, Luis A.; Grace, Landon R.
2015-05-01
The decrease in glass transition temperature and change in creep compliance due to water diffusion in a biocompatible thermoplastic elastomer was studied and quantified. Knowledge of the mechanical and viscoelastic performance of the styrene-isobutylene-styrene block (SIBS) copolymer is important to determine the feasibility of certain in-vivo applications. Furthermore, the deterioration in these types of properties due to the plasticizing effect of water must be well understood for long term usage. Samples were formed with an injection molding press and fully dried prior to immersion in distilled water at 37°C. Water diffusion kinetics were studied for four different SIBS copolymers of varying molecular weight and styrene content by measuring weight changes as a function of time. These gravimetric diffusion studies showed an inverse relationship between diffusivity and styrene content and molecular weight for the first thousand hours of immersion. Measurements of storage modulus, loss modulus, tangent delta, strain recovery and creep compliance were performed using a dynamic mechanical analyzer for the high molecular weight, high styrene content SIBS version at different absorbed water contents. A measurable and nearly linear decrease of the glass transition temperature and creep recovery with respect to water content was observed for the samples tested even at relatively low water content: an increase in water content of 0.27% correlated to a decrease of 4°C in glass transition temperature while a 0.16% weight increase corresponded to a 12.5% decrease in creep recovery. These quantified material properties restrict the use of SIBS in certain implantable operations that undergo cyclic strains, and in sterilization techniques that require high temperatures. As such, they are important to understand in order to determine the viability of in vivo usage of this biocompatible polymer.
Viscoelasticity measurements inside liposomes
NASA Astrophysics Data System (ADS)
Zhang, Shu; Gibson, Lachlan; Preece, Daryl; Nieminen, Timo A.; Rubinsztein-Dunlop, Halina
2014-09-01
Microrheology, the study of the behavior of fluids on the microscopic scale, has been and continues to be one of the most important subjects that can be applied to characterize the behavior of biological fluids. It is extremely difficult to make rapid measurement of the viscoelastic properties of the interior of living cells. Liposomes are widely used as model system for studying different aspects of cell biology. We propose to develop a microrheometer, based on real-time control of optical tweezers, in order to investigate the viscoelastic properties of the fluid inside liposomes. This will give greater understanding of the viscoelastic properties of the fluids inside cells. In our experiment, the liposomes are prepared by different methods to find out both a better way to make GUVs and achieve efficient encapsulation of particle. By rotating the vaterite inside a liposome via spin angular momentum, the optical torque can be measured by measuring the change of polarization of the transmitted light, which allows the direct measurement of viscous drag torque since the optical torque is balanced by the viscous drag. We present an initial feasibility demonstration of trapping and manipulation of a microscopic vaterite inside the liposome. The applied method is simple and can be extended to sensing within the living cells.
Iannitti, Tommaso; Bingöl, Ali Ö; Rottigni, Valentina; Palmieri, Beniamino
2013-11-18
Nowadays there is an increased demand for safe and effective volume enhancing fillers to achieve soft tissue augmentation in order to overcome tissue defects and aging-associated skin changes. In the present study we characterized the rheological and biological properties of Variofill(®), a new highly viscoelastic hyaluronic acid gel, by investigating the local effects following subcutaneous implantation in the rat to detect the host-tissue reactions and biodegradation over 18 months. We also investigated, for the first time, the application of Variofill(®) in esthetic and restorative surgery in two medical case reports. In the first case report we successfully performed Variofill(®) treatment to improve facial scars in a patient previously involved in a car crash. In the second case report we carried out a novel procedure involving a high-dose (1000 ml) injection of Variofill(®) into the dermis and subcutis of the abdominal quadrants in order to allow a classic reconstructive procedure of the abdominal wall in a patient presenting a wide incisional hernia.
Kawakami, Masaru; Byrne, Katherine; Khatri, Bhavin; McLeish, Tom C B; Radford, Sheena E; Smith, D Alastair
2004-10-12
We report on single molecule measurements of the viscoelastic properties of the polysaccharide dextran using a new approach which involves acquiring the power spectral density of the thermal noise of an atomic force microscope cantilever while holding the single molecule of interest under force-clamp conditions. The attractiveness of this approach when compared with techniques which use forced oscillations under constant loading rate conditions is that it is a near-equilibrium measure of mechanical response which provides a more relevant probe of thermally driven biomolecular dynamics. Using a simple harmonic oscillator model of the cantilever-molecule system and by subtracting the response of the free cantilever taking into account hydrodynamic effects, the effective damping zetamol and elastic constant kmol of a single molecule are obtained. The molecular elasticity measured by this new technique shows a dependence on applied force that reflects the chair-boat conformational transition of the pyranose rings of the dextran molecule which is in good agreement with values obtained directly from the gradient of a conventional constant loading rate force-extension curve. The molecular damping is also seen to follow a nontrivial dependence on loading which we suggest indicates that it is internal friction and not work done on the solvent that is the dominant dissipative process. PMID:15461521
Viscoelasticity of mono- and polydisperse inverse ferrofluids.
Saldivar-Guerrero, Ruben; Richter, Reinhard; Rehberg, Ingo; Aksel, Nuri; Heymann, Lutz; Rodriguez-Fernández, Oliverio S
2006-08-28
We report on measurements of a magnetorheological model fluid created by dispersing nonmagnetic microparticles of polystyrene in a commercial ferrofluid. The linear viscoelastic properties as a function of magnetic field strength, particle size, and particle size distribution are studied by oscillatory measurements. We compare the results with a magnetostatic theory proposed by De Gans et al. [Phys. Rev. E 60, 4518 (1999)] for the case of gap spanning chains of particles. We observe these chain structures via a long distance microscope. For monodisperse particles we find good agreement of the measured storage modulus with theory, even for an extended range, where the linear magnetization law is no longer strictly valid. Moreover we compare for the first time results for mono- and polydisperse particles. For the latter, we observe an enhanced storage modulus in the linear regime of the magnetization. PMID:16965057
Viscoelasticity of reversibly crosslinked networks of semiflexible polymers.
Plagge, Jan; Fischer, Andreas; Heussinger, Claus
2016-06-01
We present a theoretical framework for the linear and nonlinear viscoelastic properties of reversibly crosslinked networks of semiflexible polymers. In contrast to affine models where network strain couples to the polymer end-to-end distance, in our model strain rather serves to locally distort the network structure. This induces bending modes in the polymer filaments, the properties of which are slaved to the surrounding network structure. Specifically, we investigate the frequency-dependent linear rheology, in particular in combination with crosslink binding-unbinding processes. We also develop schematic extensions to describe the nonlinear response during creep measurements as well as during constant strain-rate ramps. PMID:27415312
Viscoelasticity of reversibly crosslinked networks of semiflexible polymers
NASA Astrophysics Data System (ADS)
Plagge, Jan; Fischer, Andreas; Heussinger, Claus
2016-06-01
We present a theoretical framework for the linear and nonlinear viscoelastic properties of reversibly crosslinked networks of semiflexible polymers. In contrast to affine models where network strain couples to the polymer end-to-end distance, in our model strain rather serves to locally distort the network structure. This induces bending modes in the polymer filaments, the properties of which are slaved to the surrounding network structure. Specifically, we investigate the frequency-dependent linear rheology, in particular in combination with crosslink binding-unbinding processes. We also develop schematic extensions to describe the nonlinear response during creep measurements as well as during constant strain-rate ramps.
Viscoelastic properties of kenaf bast fiber in relation to stem age
Technology Transfer Automated Retrieval System (TEKTRAN)
Natural fibers traditionally used for cordage are proving valuable for advanced industrial applications due in part to beneficial physical and chemical properties, but also because they are a renewable and biodegradable resource. Kenaf (Hibiscus cannabinus L., Malvaceae) produces high yields of lig...
Technology Transfer Automated Retrieval System (TEKTRAN)
Hydrogels have been widely studied due to their potential application in drug delivery systems as they are capable of forming aggregates in aqueous solutions. Hydrogels formed from biopolymers or natural sources have special advantages because of their biodegradable and biocompatible properties. I...
Linear and nonlinear magnetic properties of ferrofluids
NASA Astrophysics Data System (ADS)
Szalai, I.; Nagy, S.; Dietrich, S.
2015-10-01
Within a high-magnetic-field approximation, employing Ruelle's algebraic perturbation theory, a field-dependent free-energy expression is proposed which allows one to determine the magnetic properties of ferrofluids modeled as dipolar hard-sphere systems. We compare the ensuing magnetization curves, following from this free energy, with those obtained by Ivanov and Kuznetsova [Phys. Rev. E 64, 041405 (2001), 10.1103/PhysRevE.64.041405] as well as with new corresponding Monte Carlo simulation data. Based on the power-series expansion of the magnetization, a closed expression for the magnetization is also proposed, which is a high-density extension of the corresponding equation of Ivanov and Kuznetsova. From both magnetization equations the zero-field susceptibility expression due to Tani et al. [Mol. Phys. 48, 863 (1983), 10.1080/00268978300100621] can be obtained, which is in good agreement with our MC simulation results. From the closed expression for the magnetization the second-order nonlinear magnetic susceptibility is also derived, which shows fair agreement with the corresponding MC simulation data.
Linear and nonlinear magnetic properties of ferrofluids.
Szalai, I; Nagy, S; Dietrich, S
2015-10-01
Within a high-magnetic-field approximation, employing Ruelle's algebraic perturbation theory, a field-dependent free-energy expression is proposed which allows one to determine the magnetic properties of ferrofluids modeled as dipolar hard-sphere systems. We compare the ensuing magnetization curves, following from this free energy, with those obtained by Ivanov and Kuznetsova [Phys. Rev. E 64, 041405 (2001)] as well as with new corresponding Monte Carlo simulation data. Based on the power-series expansion of the magnetization, a closed expression for the magnetization is also proposed, which is a high-density extension of the corresponding equation of Ivanov and Kuznetsova. From both magnetization equations the zero-field susceptibility expression due to Tani et al. [Mol. Phys. 48, 863 (1983)] can be obtained, which is in good agreement with our MC simulation results. From the closed expression for the magnetization the second-order nonlinear magnetic susceptibility is also derived, which shows fair agreement with the corresponding MC simulation data. PMID:26565247
Viscoelastic and aging characteristics of polymers
Feng, W W
1984-04-01
This paper concerns the time dependent mechanical properties for incompressible polymer-like materials subjected to finite deformations. There are two parts: the viscoelastic effects and the aging characteristics. A method for determining these mechanical properties is presented in detail.
Investigation of mechanisms of viscoelastic behavior of collagen molecule.
Ghodsi, Hossein; Darvish, Kurosh
2015-11-01
Unique mechanical properties of collagen molecule make it one of the most important and abundant proteins in animals. Many tissues such as connective tissues rely on these properties to function properly. In the past decade, molecular dynamics (MD) simulations have been used extensively to study the mechanical behavior of molecules. For collagen, MD simulations were primarily used to determine its elastic properties. In this study, constant force steered MD simulations were used to perform creep tests on collagen molecule segments. The mechanical behavior of the segments, with lengths of approximately 20 (1X), 38 (2X), 74 (4X), and 290 nm (16X), was characterized using a quasi-linear model to describe the observed viscoelastic responses. To investigate the mechanisms of the viscoelastic behavior, hydrogen bonds (H-bonds) rupture/formation time history of the segments were analyzed and it was shown that the formation growth rate of H-bonds in the system is correlated with the creep growth rate of the segment (β=2.41βH). In addition, a linear relationship between H-bonds formation growth rate and the length of the segment was quantified. Based on these findings, a general viscoelastic model was developed and verified here, using the smallest segment as a building block, the viscoelastic properties of larger segments could be predicted. In addition, the effect of temperature control methods on the mechanical properties were studied, and it was shown that application of Langevin Dynamics had adverse effect on these properties while the Lowe-Anderson method was shown to be more appropriate for this application. This study provides information that is essential for multi-scale modeling of collagen fibrils using a bottom-up approach.
Viscoelasticity Studies for Chrome-Free Leather
Technology Transfer Automated Retrieval System (TEKTRAN)
Chrome-free leather such as glutaraldehyde-tanned leather behaves very differently from chrome-tanned leather. Information regarding its viscoelasticity has not been reported. Hysteresis and stress relaxation are two essential properties associated with viscoelasticity. We have designed a cyclic ...
NASA Astrophysics Data System (ADS)
Traore, N.; Le Pourhiet, L.; Frelat, J.; Meyer, B.; Rolandone, F.
2011-12-01
The screw dislocation model (Weertman & Weertman, 1966) gives the horizontal displacement u as a function of the vertical distance d to the dislocation, the horizontal distance x and the slip s on each side of the dislocation. (Eq. 1) u = (s/π) arctan(x/d) Savage and Burford (1973) interpreted this model in terms of horizontal displacement across a strike slip fault which is locked down to depth d, s being the plate velocity. Because of its simplicity (only two parameters used and the solution being independent of elastic properties) this model has become very popular and is commonly used to match geodetic data and infer the size of locked patches of active strike slip faults such as the San Andreas Fault. The plane section where the geodetic u is measured is the Earth's surface, which behaves as a free surface. Yet, originally in the screw dislocation model, the half space above the dislocation is infinite and therefore, on the horizontal section where Eq. 1 is verified, the state of stress is radically different to the one that occurs at the surface of earth. In order to evaluate the error generated by this approximation, numerical simulations have been tested with the software CASTEM, a finite element code for structural and mechanical modelling. We find that the displacement at the free surface fits an arctangent as in Eq. 1 but with an effective locking depth d about twice smaller than the one we input in the numerical model. It remains that the arctangent shape well represents the displacement that can be measured around most strike slip faults. For that purpose, we present various physical models, using elastic or viscoelastic properties and several kinds of boundary conditions, that may have an impact on the localization of the displacement. We set three different kinds of imposed displacement, at the front, underneath or on the lateral sides of the domain. The first type of boundary conditions corresponds to an oceanic transform set up where the
Influence of TESG layer viscoelasticity on the imaging properties of microlenses
NASA Astrophysics Data System (ADS)
Vasiljević, Darko; Murić, Branka; Pantelić, Dejan; Panić, Bratimir
2012-05-01
Microlenses were produced by the irradiation of a layer of tot'hema and eosin sensitized gelatin (TESG) with laser light (second harmonic Nd:YAG, 532 nm). For this research, eight microlenses were written on a dog-bone-shaped TESG layer. After production, microlenses were uniaxially stretched on a tensile testing machine. Each microlens had different amounts of strain (0, 30, 60, 80, 120, 140, 180 and 240% strain). The influence of TESG layer extensibility on the imaging properties of microlenses was characterized by calculating the root mean square wavefront aberration, the modulation transfer function and the geometrical spot diagram. All microlenses had very good imaging properties and the microlens with 0% strain had diffraction-limited performance.
Multiscale Modeling Approach toward the Prediction of Viscoelastic Properties of Polymers.
Maurel, G; Schnell, B; Goujon, F; Couty, M; Malfreyt, P
2012-11-13
We report a multiscale modeling approach to study static and dynamical properties of polymer melts at large time and length scales. We use a bottom-up approach consisting of deriving coarse-grained models from an atomistic description of the polymer melt. We use the iterative Boltzmann inversion (IBI) procedure and a pressure-correction function to map the thermodynamic conditions of the atomistic configurations. The coarse-grained models are incorporated in the dissipative particle dynamics (DPD) method. The thermodynamic, structural, and dynamical properties of the cis-1,4-polybutadiene melt are very well reproduced by the coarse-grained DPD models with a significative computational gain. We complete this study by addressing the challenging question of the investigation of the shear modulus evolution. As expected from experiments, the stress correlation functions show behaviors that are dependent on the molecular weights defining unentangled and weakly entangled polymer melts. PMID:26605616
Yang, Jun; Han, ChunRui
2016-09-28
With inspiration from the concept of natural dynamic materials, binary-component composite hydrogels with excellent mechanical properties and recovery capability were prepared from the cellulose nanocrystal (CNC) skeleton reinforced covalently cross-linked polyacrylamide (PAAm) networks. The hierarchical skeleton obtained by freeze-drying of CNC aqueous suspension was directly impregnated into acrylamide (AAm) monomer solution, and in situ polymerization occurred in the presence of hydrophilic cross-linker PEGDA575. Under stress, hydrogen bonds at the interface between CNC and PAAm as well as inside the CNC skeleton acted as sacrificial bonds to dissipate energy, while the covalently cross-linked PAAm chains bind the network together by providing adhesion to CNC and thereby suppress the catastrophic craze propagation. The above synergistic effects of the CNC skeleton and the elastic PAAm network enabled the composite hydrogels to withstand up to 181 kPa of tensile stress, 1.01 MPa of compressive strength, and 1392% elongation at break with the fracture energy as high as 2.82 kJ/m(2). Moreover, the hydrogels recovered more than 70% elasticity after eight loading-unloading cycles, revealing excellent fatigue resistance. The depth-sensing instrumentation by indentation test corroborated that the CNC skeleton contributed simultaneous improvements in hardness and elasticity by as much as 500% in comparison with the properties of the pristine PAAm hydrogels. This elegant strategy by using the CNC skeleton as a reinforcing template offers a new perspective for the fabrication of robust hydrogels with exceptional mechanical properties that may be important for biomedical applications where high strength is required, such as scaffolds for tissue engineering.
Yang, Jun; Han, ChunRui
2016-09-28
With inspiration from the concept of natural dynamic materials, binary-component composite hydrogels with excellent mechanical properties and recovery capability were prepared from the cellulose nanocrystal (CNC) skeleton reinforced covalently cross-linked polyacrylamide (PAAm) networks. The hierarchical skeleton obtained by freeze-drying of CNC aqueous suspension was directly impregnated into acrylamide (AAm) monomer solution, and in situ polymerization occurred in the presence of hydrophilic cross-linker PEGDA575. Under stress, hydrogen bonds at the interface between CNC and PAAm as well as inside the CNC skeleton acted as sacrificial bonds to dissipate energy, while the covalently cross-linked PAAm chains bind the network together by providing adhesion to CNC and thereby suppress the catastrophic craze propagation. The above synergistic effects of the CNC skeleton and the elastic PAAm network enabled the composite hydrogels to withstand up to 181 kPa of tensile stress, 1.01 MPa of compressive strength, and 1392% elongation at break with the fracture energy as high as 2.82 kJ/m(2). Moreover, the hydrogels recovered more than 70% elasticity after eight loading-unloading cycles, revealing excellent fatigue resistance. The depth-sensing instrumentation by indentation test corroborated that the CNC skeleton contributed simultaneous improvements in hardness and elasticity by as much as 500% in comparison with the properties of the pristine PAAm hydrogels. This elegant strategy by using the CNC skeleton as a reinforcing template offers a new perspective for the fabrication of robust hydrogels with exceptional mechanical properties that may be important for biomedical applications where high strength is required, such as scaffolds for tissue engineering. PMID:27606621
Ultrasonic characterization of changes in viscoelastic properties of epoxy during cure
NASA Technical Reports Server (NTRS)
Winfree, W. P.; Parker, F. R.
1985-01-01
A technique for using the longitudinal velocity (LV) of an ultrasonic wave to monitor the extent of cross linking (CL) during the cure of thermosetting resins is described. The method was developed by monitoring the rate of change in LV during the cure of a bisphenol-A epoxy resin with an amine adduct. The experiment included variations in the temperature and stoichiometry in order to express the rate of change in terms of the reaction kinetics. The pulse-echo method was used with a single transducer operating at 20 MHz. Numerical models were defined to account for the acoustic response of a single layer, the attenuation and the reflection coefficient. A linear relationship was observed between the inverse of the temperature and the log of the rate of change in the velocity, supporting the theory that the velocity could be used to monitor the extent of the cross-linking reaction. An activation energy of 11.9 kcal/mole was calculated for the mixture being investigated.
Rodell, Christopher B.; MacArthur, John W.; Dorsey, Shauna M.; Wade, Ryan J.; Wang, Leo L.; Woo, Y. Joseph
2015-01-01
Clinical percutaneous delivery of synthetically engineered hydrogels remains limited due to challenges posed by crosslinking kinetics – too fast leads to delivery failure, too slow limits material retention. To overcome this challenge, we exploit supramolecular assembly to localize hydrogels at the injection site and introduce subsequent covalent crosslinking to control final material properties. Supramolecular gels were designed through the separate pendant modifications of hyaluronic acid (HA) by the guest-host pair cyclodextrin and adamantane, enabling shear-thinning injection and high target site retention (>98%). Secondary covalent crosslinking occurred via addition of thiols and Michael-acceptors (i.e., methacrylates, acrylates, vinyl sulfones) on HA and increased hydrogel moduli (E=25.0±4.5kPa) and stability (>3.5 fold in vivo at 28 days). Application of the dual-crosslinking hydrogel to a myocardial infarct model showed improved outcomes relative to untreated and supramolecular hydrogel alone controls, demonstrating its potential in a range of applications where the precise delivery of hydrogels with tunable properties is desired. PMID:26526097
Viscoelastic and Mechanical Properties of Thermoset PMR-type Polyimide-Clay Nanocomposites
NASA Technical Reports Server (NTRS)
Abdalla, Mohamed O.; Dean, Derrick; Campbell, Sandi
2002-01-01
High temperature thermoset polyimide-clay nanocomposites were prepared by blending 2.5 and 5 wt% of an unmodified Na(+-) montmorillonite (PGV) and two organically modified FGV (PGVCl0COOH, PGVC12) with a methanol solution of PMR-15 precursor. The methanol facilitated the dispersal of the unmodified clay. Dynamic mechanical analysis results showed a significant increase in the thermomechanical properties (E' and E") of 2.5 wt% clay loaded nanocomposites in comparison with the neat polyimide. Higher glass transition temperatures were observed for 2.5 wt% nanocomposites compared to the neat polyimide. Flexural properties measurements for the 2.5 wt% nanocomposites showed a significant improvement in the modulus and strength, with no loss in elongation. This trend was not observed for the 5 wt% nanocomposites. An improvement in the CTE was observed for the PGV/PMR-15 nanocomposites, while a decrease was observed for the organically modified samples. This was attributed to potential variations in the interface caused by modifier degradation.
Silicon-induced changes in viscoelastic properties of sorghum root cell walls.
Hattori, Taiichiro; Inanaga, Shinobu; Tanimoto, Eiichi; Lux, Alexander; Luxová, Miroslava; Sugimoto, Yukihiro
2003-07-01
Silicon is deposited in the endodermal tissue in sorghum (Sorghum bicolor L. Moench) roots. Its deposition is thought to protect vascular tissues in the stele against invasion by parasites and drying soil via hardening of endodermal cells. We studied the silicon-induced changes in mechanical properties of cell walls to clarify the role of silicon in sorghum root. Sorghum seedlings were grown in nutrient solution with or without silicon. The mechanical properties of cell walls were measured in three separated root zones: basal, apical and subapical. Silicon treatment decreased cell-wall extensibility in the basal zone of isolated stele tissues covered by endodermal inner tangential walls. The silicon-induced hardening of cell walls was also measured with increases in elastic moduli (E) and viscosity coefficients (eta). These results provided new evidence that silicon deposition might protect the stele as a mechanical barrier by hardening the cell walls of stele and endodermal tissues. In contrast to the basal zone, silicon treatment increased cell-wall extensibility in the apical and subapical zones with concomitant decrease in E and eta. Simultaneously, silicon promoted root elongation. When root elongation is promoted by silicon, one of the causal factors maybe the silicon-enhanced extensibility of cell walls in the growing zone.
Atomic force microscopy imaging of viscoelastic properties in toughened polypropylene resins
NASA Astrophysics Data System (ADS)
Nysten, Bernard; Legras, Roger; Costa, Jean-Louis
1995-11-01
The bulk morphology of two toughened polypropylene/(ethylene propylene)copolymer resins (PP/EP) presenting different impact resistances has been studied by means of different atomic force microscopy techniques: contact atomic force microscopy, lateral force microscopy (LFM), and force modulation microscopy (FMM). The three techniques reveal two different morphologies as observed in transmission electronic microscopy. In LFM, a higher friction force is observed on the rubbery phase which has the lower Young's modulus confirming the relationship between friction force and elastic properties. In force modulation, the elastic moduli is found to be much lower on the EP nodules in both resins. FMM also reveals that the difference of viscous response between the PP matrix and the EP nodules is much lower in the resin which is less impact resistant.
A new fast and unsynchronized method for MRI of viscoelastic properties of soft tissues.
Lewa, C J; Roth, M; Nicol, L; Franconi, J M; de Certaines, J D
2000-11-01
Quantitative measurement of mechanical properties of biologic tissues may have several applications for diagnosis or biomechanic modeling in sports medicine, traumatology, or computer-guided surgery. The magnetic resonance imaging (MRI) methods previously tested for these applications all required synchronization between MRI acquisition pulses and the mechanical stimulation. A new unsynchronized method operating with no prior knowledge of intensity, direction, and frequency of the mechanical waves is proposed. A specifically modified SPAMM (SPAtial Modulation of Magnetization) sequence has been used, operating on a 0.2-T MRI system. The experimental results obtained on test objects fit well with theoretical calculations. The new proposed method is very fast (a less than 5-second acquisition time) for routine clinical use. PMID:11050651
[Assessment of the viscoelastic properties of biological membranes by measurements on bilayers].
Pasechnik, V I; Gianik, T
1978-01-01
The frequency characteristic of the complex Young modulus along the normal to surface is measured for the bilayer lipid membranes (BLM). For egg lecithin membranes the absolute value of the modulus (formula: see text) rises from 4.10(6) to 10(8) dyn/cm2 (n-decane) and from 10(8) to 10(9) dyn/cm2 (n-hexadecane) with the frequency change from 20 Hz to 15 000 Hz depending on different membrane solvents. (formula: see text) also rises several times if cholesterol is added or lipid hydrocarbon chains are longer or more saturated. If the solvent--n-hexadecane is freezed out in the region of 14 degrees C,(formula: see text) increases up to 10(10) dyn/cm2. The loss angle is measured and real and imaginary parts of (formula: see text) are determined. (formula: see text) posesses the relaxtion times spectrum in the range 10(-5)--10(-3) s. The conclusion is made that biological membranes like BLM have polymer properties, their (formula: see text) values may achieve 10(10) dyn/cm2 and the relaxation times are greater than 10(-3) s.
Changes in viscoelastic properties of rat lung parenchymal strips with maturation.
Tanaka, R; Ludwig, M S
1999-12-01
The lung extracellular matrix changes rapidly with maturation. To further our understanding of the mechanisms underlying lung tissue mechanics, we studied age-related changes in mechanical properties in lung parenchymal strips from baby (10-15 days old), young ( approximately 3 wk old), and adult ( approximately 8 wk old) rats. Subpleural strips were cut and suspended in a fluid-filled organ bath. One end of the strip was attached to a force transducer and the other to a servo-controlled lever arm. Measurements of force (F) and length (L) were recorded during sinusoidal oscillations of various amplitudes and frequencies. Resistance modulus (R) and elastance modulus (E) were estimated by fitting the equation of motion to changes in stress (T) and stretch ratio (lambda). Hysteresivity (eta) was calculated as follows: eta = (R/E)2pif, where f is frequency. Slow-cycling T-lambda curves were measured by applying a constant slow length change. Finally, quasi-static T-lambda curves were measured as stress was increased from 0 to 6 kPa and back to 0 kPa in stepwise increments. Our results showed that lung tissue from immature rats was stiffer and less hysteretic than tissue from more mature animals. In addition, tissue from baby animals behaved in a manner compatible with an increased vulnerability to plastic change.
Impact of Simulated Microgravity on Cytoskeleton and Viscoelastic Properties of Endothelial Cell
NASA Astrophysics Data System (ADS)
Janmaleki, M.; Pachenari, M.; Seyedpour, S. M.; Shahghadami, R.; Sanati-Nezhad, A.
2016-09-01
This study focused on the effects of simulated microgravity (s-μg) on mechanical properties, major cytoskeleton biopolymers, and morphology of endothelial cells (ECs). The structural and functional integrity of ECs are vital to regulate vascular homeostasis and prevent atherosclerosis. Furthermore, these highly gravity sensitive cells play a key role in pathogenesis of many diseases. In this research, impacts of s-μg on mechanical behavior of human umbilical vein endothelial cells were investigated by utilizing a three-dimensional random positioning machine (3D-RPM). Results revealed a considerable drop in cell stiffness and viscosity after 24 hrs of being subjected to weightlessness. Cortical rigidity experienced relatively immediate and significant decline comparing to the stiffness of whole cell body. The cells became rounded in morphology while western blot analysis showed reduction of the main cytoskeletal components. Moreover, fluorescence staining confirmed disorganization of both actin filaments and microtubules (MTs). The results were compared statistically among test and control groups and it was concluded that s-μg led to a significant alteration in mechanical behavior of ECs due to remodeling of cell cytoskeleton.
Dynamic viscoelastic properties of processed soft denture liners: Part II--Effect of aging.
Wagner, W C; Kawano, F; Dootz, E R; Koran, A
1995-09-01
The proper functioning of soft denture liners depends to a great extent on their mechanical properties. As with many polymers these materials are affected by aging. Twelve soft denture liners were processed by a laboratory according to the manufacturers' directions. Five specimens of each material were tested without aging. Five additional specimens of each material were subjected to 900 hours of accelerated aging in a Weather-Ometer instrument. These were tested with a dynamic viscoelastometer at three frequencies and two temperatures, and data for 37 degrees C and 1 Hz was obtained. Two of the ethyl methacrylate resins demonstrated the largest increases in storage (E') and loss moduli (E") after aging. These materials also showed the greatest overall E' and E". One denture liner material exhibited 673% and 488% increases in E' and E", and other materials showed smaller increases. The effects of aging on the damping factor (tan delta) were varied and five materials showed increased tan delta. Only two ethyl methacrylate resins developed lower tan delta. All the silicone and polyphosphazine rubbers showed small changes after aging and had the lowest tan delta values. Significance of differences between materials and treatments was tested with ANOVA, Scheffé intervals, and t-tests at a = 0.05. The ethyl methacrylate soft denture liners were affected the most by accelerated aging, and the silicones and polyphosphazine were least affected. The ethyl methacrylate resins also had the greatest values of E', E", and tan delta after aging.
Impact of Simulated Microgravity on Cytoskeleton and Viscoelastic Properties of Endothelial Cell
Janmaleki, M.; Pachenari, M.; Seyedpour, S. M.; Shahghadami, R.; Sanati-Nezhad, A.
2016-01-01
This study focused on the effects of simulated microgravity (s-μg) on mechanical properties, major cytoskeleton biopolymers, and morphology of endothelial cells (ECs). The structural and functional integrity of ECs are vital to regulate vascular homeostasis and prevent atherosclerosis. Furthermore, these highly gravity sensitive cells play a key role in pathogenesis of many diseases. In this research, impacts of s-μg on mechanical behavior of human umbilical vein endothelial cells were investigated by utilizing a three-dimensional random positioning machine (3D-RPM). Results revealed a considerable drop in cell stiffness and viscosity after 24 hrs of being subjected to weightlessness. Cortical rigidity experienced relatively immediate and significant decline comparing to the stiffness of whole cell body. The cells became rounded in morphology while western blot analysis showed reduction of the main cytoskeletal components. Moreover, fluorescence staining confirmed disorganization of both actin filaments and microtubules (MTs). The results were compared statistically among test and control groups and it was concluded that s-μg led to a significant alteration in mechanical behavior of ECs due to remodeling of cell cytoskeleton. PMID:27581365
Viscoelastic properties and nanoscale structures of composite oligopeptide-polysaccharide hydrogels.
Hyland, Laura L; Taraban, Marc B; Feng, Yue; Hammouda, Boualem; Yu, Y Bruce
2012-03-01
Biocompatible and biodegradable peptide hydrogels are drawing increasing attention as prospective materials for human soft tissue repair and replacement. To improve the rather unfavorable mechanical properties of our pure peptide hydrogels, in this work we examined the possibility of creating a double hydrogel network. This network was created by means of the coassembly of mutually attractive, but self-repulsive oligopeptides within an already-existing fibrous network formed by the charged, biocompatible polysaccharides chitosan, alginate, and chondroitin. Using dynamic oscillatory rheology experiments, it was found that the coassembly of the peptides within the existing polysaccharide network resulted in a less stiff material as compared to the pure peptide networks (the elastic modulus G' decreased from 90 to 10 kPa). However, these composite oligopeptide-polysaccharide hydrogels were characterized by a greater resistance to deformation (the yield strain γ grew from 4 to 100%). Small-angle neutron scattering (SANS) was used to study the 2D cross-sectional shapes of the fibers, their dimensional characteristics, and the mesh sizes of the fibrous networks. Differences in material structures found with SANS experiments confirmed rheology data, showing that incorporation of the peptides dramatically changed the morphology of the polysaccharide network. The resulting fibers were structurally very similar to those forming the pure peptide networks, but formed less stiff gels because of their markedly greater mesh sizes. Together, these findings suggest an approach for the development of highly deformation-resistant biomaterials. PMID:21994046
Maier, Timo; Haraszti, Tamás
2015-01-01
Filamentous actin is one of the most important cytoskeletal elements. Not only is it responsible for the elastic properties of many cell types, but it also plays a vital role in cellular adhesion and motility. Understanding the bundling kinetics of actin filaments is important in the formation of various cytoskeletal structures, such as filopodia and stress fibers. Utilizing a unique pillar-structured microfluidic device, we investigated the time dependence of bundling kinetics of pillar supported free-standing actin filaments. Microparticles attached to the filaments allowed the measurement of thermal motion, and we found that bundling takes place at lower concentrations than previously found in 3-dimensional actin gels, i.e. actin filaments formed bundles in the presence of 5-12 mM of magnesium chloride in a time-dependent manner. The filaments also displayed long term stability for up to hours after removing the magnesium ions from the buffer, which suggests that there is an extensive hysteresis between cation induced crosslinking and decrosslinking.
Maier, Timo; Haraszti, Tamás
2015-01-01
Filamentous actin is one of the most important cytoskeletal elements. Not only is it responsible for the elastic properties of many cell types, but it also plays a vital role in cellular adhesion and motility. Understanding the bundling kinetics of actin filaments is important in the formation of various cytoskeletal structures, such as filopodia and stress fibers. Utilizing a unique pillar-structured microfluidic device, we investigated the time dependence of bundling kinetics of pillar supported free-standing actin filaments. Microparticles attached to the filaments allowed the measurement of thermal motion, and we found that bundling takes place at lower concentrations than previously found in 3-dimensional actin gels, i.e. actin filaments formed bundles in the presence of 5–12 mM of magnesium chloride in a time-dependent manner. The filaments also displayed long term stability for up to hours after removing the magnesium ions from the buffer, which suggests that there is an extensive hysteresis between cation induced crosslinking and decrosslinking. PMID:26322783
Effects of racing and gender on viscoelastic properties of horse blood.
Wood, S C; Fedde, M R
1997-02-01
Splenic contraction in racing horses increases the hematocrit (hct), thereby increasing blood viscosity. We tested as to whether racing also affects the elastic properties of blood. Mares and geldings were studied for thus purpose. After racing, there was: (i) an increased erythrocyte count independent of gender and race distance (0.32 to 1.7 km): (ii) an increased mean erythrocyte volume in both sexes; (iii) an increased heterogeneity of RBC size in both sexes; (iv) an increased plasma fibrinogen concentration and erythrocyte sedimentation rate in both sexes; and (v) an increased elastic yield stress (EYS). When corrected to a constant hct of 65%, the blood of mares, but not geldings, had increased EYS after racing. Gender differences in fibrinogen response (p = 0.72) did not account for this and the mechanism is not known. Since EYS is analogous to the point at which ketchup starts to flow from a bottle, its increase could be deleterious in vascular beds characterized by pulsatile flow, e.g. the coronary circulation. PMID:9108630
Impact of Simulated Microgravity on Cytoskeleton and Viscoelastic Properties of Endothelial Cell.
Janmaleki, M; Pachenari, M; Seyedpour, S M; Shahghadami, R; Sanati-Nezhad, A
2016-01-01
This study focused on the effects of simulated microgravity (s-μg) on mechanical properties, major cytoskeleton biopolymers, and morphology of endothelial cells (ECs). The structural and functional integrity of ECs are vital to regulate vascular homeostasis and prevent atherosclerosis. Furthermore, these highly gravity sensitive cells play a key role in pathogenesis of many diseases. In this research, impacts of s-μg on mechanical behavior of human umbilical vein endothelial cells were investigated by utilizing a three-dimensional random positioning machine (3D-RPM). Results revealed a considerable drop in cell stiffness and viscosity after 24 hrs of being subjected to weightlessness. Cortical rigidity experienced relatively immediate and significant decline comparing to the stiffness of whole cell body. The cells became rounded in morphology while western blot analysis showed reduction of the main cytoskeletal components. Moreover, fluorescence staining confirmed disorganization of both actin filaments and microtubules (MTs). The results were compared statistically among test and control groups and it was concluded that s-μg led to a significant alteration in mechanical behavior of ECs due to remodeling of cell cytoskeleton. PMID:27581365
Dynamic viscoelastic models of human skin using optical elastography
Kearney, Steven P.; Khan, Altaf; Dai, Zoujun; Royston, Thomas J.
2015-01-01
A novel technique for measuring in vivo human skin viscoelastic properties using optical elastography has been developed. The technique uses geometrically focused surface (GFS) waves that allow for wide bandwidth measurements of the wave field. An analytical solution for the case of a radiating annular disk surface source was fit to experimentally measured GFS waves, enabling an estimate of the frequency-dependent surface wavenumber, which can then be related to the dynamic shear modulus. Several viscoelastic models were then fit to the dynamic shear modulus dispersion curve. Viscoelastic models were evaluated based on their overall quality of fit and variability amongst healthy volunteers. An Ecoflex phantom was used to validate the procedure and results by comparison to similar studies using the same type of phantom. For skin results, it was found that the “α” parameters from the fractional models had the least variability, with coefficients of variability of 0.15, and 0.16. The best fitting models were the standard linear solid, and the fractional Voigt, with a mean fit correlation coefficient, R2, of 0.93, 0.89, respectively. This study has demonstrated the efficacy of this new method, and with larger studies the viscoelastic skin models could be used to identify various skin diseases and their response to treatment. PMID:26305137
Dynamic viscoelastic models of human skin using optical elastography.
Kearney, Steven P; Khan, Altaf; Dai, Zoujun; Royston, Thomas J
2015-09-01
A novel technique for measuring in vivo human skin viscoelastic properties using optical elastography has been developed. The technique uses geometrically focused surface (GFS) waves that allow for wide bandwidth measurements of the wave field. An analytical solution for the case of a radiating annular disk surface source was fit to experimentally measured GFS waves, enabling an estimate of the frequency-dependent surface wavenumber, which can then be related to the dynamic shear modulus. Several viscoelastic models were then fit to the dynamic shear modulus dispersion curve. Viscoelastic models were evaluated based on their overall quality of fit and variability amongst healthy volunteers. An Ecoflex phantom was used to validate the procedure and results by comparison to similar studies using the same type of phantom. For skin results, it was found that the 'α' parameters from the fractional models had the least variability, with coefficients of variability of 0.15, and 0.16. The best fitting models were the standard linear solid, and the fractional Voigt, with a mean fit correlation coefficient, R(2), of 0.93, 0.89, respectively. This study has demonstrated the efficacy of this new method, and with larger studies the viscoelastic skin models could be used to identify various skin diseases and their response to treatment. PMID:26305137
Predicting nonlinear properties of metamaterials from the linear response.
O'Brien, Kevin; Suchowski, Haim; Rho, Junsuk; Salandrino, Alessandro; Kante, Boubacar; Yin, Xiaobo; Zhang, Xiang
2015-04-01
The discovery of optical second harmonic generation in 1961 started modern nonlinear optics. Soon after, R. C. Miller found empirically that the nonlinear susceptibility could be predicted from the linear susceptibilities. This important relation, known as Miller's Rule, allows a rapid determination of nonlinear susceptibilities from linear properties. In recent years, metamaterials, artificial materials that exhibit intriguing linear optical properties not found in natural materials, have shown novel nonlinear properties such as phase-mismatch-free nonlinear generation, new quasi-phase matching capabilities and large nonlinear susceptibilities. However, the understanding of nonlinear metamaterials is still in its infancy, with no general conclusion on the relationship between linear and nonlinear properties. The key question is then whether one can determine the nonlinear behaviour of these artificial materials from their exotic linear behaviour. Here, we show that the nonlinear oscillator model does not apply in general to nonlinear metamaterials. We show, instead, that it is possible to predict the relative nonlinear susceptibility of large classes of metamaterials using a more comprehensive nonlinear scattering theory, which allows efficient design of metamaterials with strong nonlinearity for important applications such as coherent Raman sensing, entangled photon generation and frequency conversion.
Swimming & Propulsion in Viscoelastic Media
NASA Astrophysics Data System (ADS)
Arratia, Paulo
2012-02-01
Many microorganisms have evolved within complex fluids, which include soil, intestinal fluid, and mucus. The material properties or rheology of such fluids can strongly affect an organism's swimming behavior. A major challenge is to understand the mechanism of propulsion in media that exhibit both solid- and fluid-like behavior, such as viscoelastic fluids. In this talk, we present experiments that explore the swimming behavior of biological organisms and artificial particles in viscoelastic media. The organism is the nematode Caenorhabditis elegans, a roundworm widely used for biological research that swims by generating traveling waves along its body. Overall, we find that fluid elasticity hinders self-propulsion compared to Newtonian fluids due to the enhanced resistance to flow near hyperbolic points for viscoelastic fluids. As fluid elasticity increases, the nematode's propulsion speed decreases. These results are consistent with recent theoretical models for undulating sheets and cylinders. In order to gain further understanding on propulsion in viscoelastic media, we perform experiments with simple reciprocal artificial `swimmers' (magnetic dumbbell particles) in polymeric and micellar solutions. We find that self-propulsion is possible in viscoelastic media even if the motion is reciprocal.
Squirming propulsion in viscoelastic fluids
NASA Astrophysics Data System (ADS)
de Corato, Marco; Greco, Francesco; Maffettone, Pier Luca
2015-11-01
The locomotion of organisms in Newtonian fluids at low-Reynolds numbers displays very different features from that at large Reynolds numbers; indeed, in this regime the viscous forces are dominant over the inertial ones and propulsion is possible only with non-time-reversible swimming strokes. In many situations of biological interest, however, small organisms are propelling themselves through non-Newtonian fluids such as mucus or biofilms, which display highly viscoelastic properties. Fluid viscoelasticity affects in a complex way both the micro-organisms' swimming velocity and dissipated power, possibly affecting their collective behavior. In our work, we employ the so called ``squirmer'' model to study the motion of spherical ciliated organisms in a viscoelastic fluid. We derive analytical formulas for the squirmer swimming velocity and dissipated power that show a complex interplay between the fluid constitutive behavior and the propulsion mechanism.
NASA Astrophysics Data System (ADS)
Yang, Pengliang; Brossier, Romain; Métivier, Ludovic; Virieux, Jean
2016-07-01
In this paper we study 3D multiparameter full waveform inversion (FWI) in viscoelastic media based on the generalized Maxwell/Zener body (GMB/GZB) including arbitrary number of attenuation mechanisms. We present a frequency-domain energy analysis to establish the stability condition of a full anisotropic viscoelastic system, according to zero-valued boundary condition and the elastic-viscoelastic correspondence principle: the real-valued stiffness matrix becomes a complex-valued one in Fourier domain when seismic attenuation is taken into account. We develop a least-squares optimization approach to linearly relate the quality factor with the anelastic coefficients by estimating a set of constants which are independent of the spatial coordinates, which supplies an explicit incorporation of the parameter Q in the general viscoelastic wave equation. By introducing the Lagrangian multipliers into the matrix expression of the wave equation with implicit time integration, we build a systematic formulation of multiparameter full waveform inversion for full anisotropic viscoelastic wave equation, while the equivalent form of the state and adjoint equation with explicit time integration is available to be resolved efficiently. In particular, this formulation lays the foundation for the inversion of the parameter Q in the time domain with full anisotropic viscoelastic properties. In the 3D isotropic viscoelastic settings, the anelastic coefficients and the quality factors using bulk and shear moduli parameterization can be related to the counterparts using P- and S- velocity. Gradients with respect to any other parameter of interest can be found by chain rule. Pioneering numerical validations as well as the real applications of this most generic framework will be carried out to disclose the potential of viscoelastic FWI when adequate high performance computing resources and the field data are available.
NASA Astrophysics Data System (ADS)
Yang, Pengliang; Brossier, Romain; Métivier, Ludovic; Virieux, Jean
2016-10-01
In this paper, we study 3-D multiparameter full waveform inversion (FWI) in viscoelastic media based on the generalized Maxwell/Zener body including arbitrary number of attenuation mechanisms. We present a frequency-domain energy analysis to establish the stability condition of a full anisotropic viscoelastic system, according to zero-valued boundary condition and the elastic-viscoelastic correspondence principle: the real-valued stiffness matrix becomes a complex-valued one in Fourier domain when seismic attenuation is taken into account. We develop a least-squares optimization approach to linearly relate the quality factor with the anelastic coefficients by estimating a set of constants which are independent of the spatial coordinates, which supplies an explicit incorporation of the parameter Q in the general viscoelastic wave equation. By introducing the Lagrangian multipliers into the matrix expression of the wave equation with implicit time integration, we build a systematic formulation of multiparameter FWI for full anisotropic viscoelastic wave equation, while the equivalent form of the state and adjoint equation with explicit time integration is available to be resolved efficiently. In particular, this formulation lays the foundation for the inversion of the parameter Q in the time domain with full anisotropic viscoelastic properties. In the 3-D isotropic viscoelastic settings, the anelastic coefficients and the quality factors using bulk and shear moduli parametrization can be related to the counterparts using P and S velocity. Gradients with respect to any other parameter of interest can be found by chain rule. Pioneering numerical validations as well as the real applications of this most generic framework will be carried out to disclose the potential of viscoelastic FWI when adequate high-performance computing resources and the field data are available.
Relativistic viscoelastic fluid mechanics
Fukuma, Masafumi; Sakatani, Yuho
2011-08-15
A detailed study is carried out for the relativistic theory of viscoelasticity which was recently constructed on the basis of Onsager's linear nonequilibrium thermodynamics. After rederiving the theory using a local argument with the entropy current, we show that this theory universally reduces to the standard relativistic Navier-Stokes fluid mechanics in the long time limit. Since effects of elasticity are taken into account, the dynamics at short time scales is modified from that given by the Navier-Stokes equations, so that acausal problems intrinsic to relativistic Navier-Stokes fluids are significantly remedied. We in particular show that the wave equations for the propagation of disturbance around a hydrostatic equilibrium in Minkowski space-time become symmetric hyperbolic for some range of parameters, so that the model is free of acausality problems. This observation suggests that the relativistic viscoelastic model with such parameters can be regarded as a causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting parameters to various values, this theory can treat a wide variety of materials including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus we expect the theory to be the most universal description of single-component relativistic continuum materials. We also show that the presence of strains and the corresponding change in temperature are naturally unified through the Tolman law in a generally covariant description of continuum mechanics.
Relativistic viscoelastic fluid mechanics.
Fukuma, Masafumi; Sakatani, Yuho
2011-08-01
A detailed study is carried out for the relativistic theory of viscoelasticity which was recently constructed on the basis of Onsager's linear nonequilibrium thermodynamics. After rederiving the theory using a local argument with the entropy current, we show that this theory universally reduces to the standard relativistic Navier-Stokes fluid mechanics in the long time limit. Since effects of elasticity are taken into account, the dynamics at short time scales is modified from that given by the Navier-Stokes equations, so that acausal problems intrinsic to relativistic Navier-Stokes fluids are significantly remedied. We in particular show that the wave equations for the propagation of disturbance around a hydrostatic equilibrium in Minkowski space-time become symmetric hyperbolic for some range of parameters, so that the model is free of acausality problems. This observation suggests that the relativistic viscoelastic model with such parameters can be regarded as a causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting parameters to various values, this theory can treat a wide variety of materials including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus we expect the theory to be the most universal description of single-component relativistic continuum materials. We also show that the presence of strains and the corresponding change in temperature are naturally unified through the Tolman law in a generally covariant description of continuum mechanics.
Linear contrail and contrail cirrus properties determined from satellite data
NASA Astrophysics Data System (ADS)
Minnis, Patrick; Bedka, Sarah T.; Duda, David P.; Bedka, Kristopher M.; Chee, Thad; Ayers, J. Kirk; Palikonda, Rabindra; Spangenberg, Douglas A.; Khlopenkov, Konstantin V.; Boeke, Robyn
2013-06-01
properties of contrail cirrus clouds are retrieved through analysis of Terra and Aqua Moderate Resolution Imaging Spectroradiometer data for 21 cases of spreading linear contrails. For these cases, contrail cirrus enhanced the linear contrail coverage by factors of 2.4-7.6 depending on the contrail mask sensitivity. In dense air traffic areas, linear contrail detection sensitivity is apparently reduced when older contrails overlap and thus is likely diminished during the afternoon. The mean optical depths and effective particle sizes of the contrail cirrus were 2-3 times and 20% greater, respectively, than the corresponding values retrieved for the adjacent linear contrails. When contrails form below, in, or above existing cirrus clouds, the column cloud optical depth is increased and particle size is decreased. Thus, even without increased cirrus coverage, contrails will affect the radiation balance. These results should be valuable for refining model characterizations of contrail cirrus needed to fully assess the climate impacts of contrails.
Lakshmanan, Ramji S; Efremov, Vitaly; O'Donnell, James S; Killard, Anthony J
2016-09-01
The coagulation of blood plasma in response to activation with a range of tissue factor (TF) concentrations was studied with a quartz crystal microbalance (QCM), where frequency and half width at half maximum (bandwidth) values measured from the conductance spectrum near resonant frequency were used. Continuous measurement of bandwidth along with the frequency allows for an understanding of the dissipative nature of the forming viscoelastic clot, thus providing information on the complex kinetics of the viscoelastic changes occurring during the clot formation process. Using a mathematical model, these changes in frequency and bandwidth have been used to derive novel QCM parameters of effective elasticity, effective mass density and rigidity factor of the viscoelastic layer. The responses of QCM were compared with those from thromboelastography (TEG) under identical conditions. It was demonstrated that the nature of the clot formed, as determined from the QCM parameters, was highly dependent on the rate of clot formation resulting from the TF concentration used for activation. These parameters could also be related to physical clot characteristics such as fibrin fibre diameter and fibre density, as determined by scanning electron microscopic image analysis. The maximum amplitude (MA) as measured by TEG, which purports to relate to clot strength, was unable to detect these differences. PMID:27311950
Fractional calculus in viscoelasticity: An experimental study
NASA Astrophysics Data System (ADS)
Meral, F. C.; Royston, T. J.; Magin, R.
2010-04-01
Viscoelastic properties of soft biological tissues provide information that may be useful in medical diagnosis. Noninvasive elasticity imaging techniques, such as Magnetic Resonance Elastography (MRE), reconstruct viscoelastic material properties from dynamic displacement images. The reconstruction algorithms employed in these techniques assume a certain viscoelastic material model and the results are sensitive to the model chosen. Developing a better model for the viscoelasticity of soft tissue-like materials could improve the diagnostic capability of MRE. The well known "integer derivative" viscoelastic models of Voigt and Kelvin, and variations of them, cannot represent the more complicated rate dependency of material behavior of biological tissues over a broad spectral range. Recently the "fractional derivative" models have been investigated by a number of researchers. Fractional order models approximate the viscoelastic material behavior of materials through the corresponding fractional differential equations. This paper focuses on the tissue mimicking materials CF-11 and gelatin, and compares fractional and integer order models to describe their behavior under harmonic mechanical loading. Specifically, Rayleigh (surface) waves on CF-11 and gelatin phantoms are studied, experimentally and theoretically, in order to develop an independent test bed for assessing viscoelastic material models that will ultimately be used in MRE reconstruction algorithms.
Viscoelastic behavior of discrete human collagen fibrils.
Svensson, René B; Hassenkam, Tue; Hansen, Philip; Peter Magnusson, S
2010-01-01
Whole tendon and fibril bundles display viscoelastic behavior, but to the best of our knowledge this property has not been directly measured in single human tendon fibrils. In the present work an atomic force microscopy (AFM) approach was used for tensile testing of two human patellar tendon fibrils. Fibrils were obtained from intact human fascicles, without any pre-treatment besides frozen storage. In the dry state a single isolated fibril was anchored to a substrate using epoxy glue, and the end of the fibril was glued on to an AFM cantilever for tensile testing. In phosphate buffered saline, cyclic testing was performed in the pre-yield region at different strain rates, and the elastic response was determined by a stepwise stress relaxation test. The elastic stress-strain response corresponded to a second-order polynomial fit, while the viscous response showed a linear dependence on the strain. The slope of the viscous response showed a strain rate dependence corresponding to a power function of powers 0.242 and 0.168 for the two patellar tendon fibrils, respectively. In conclusion, the present work provides direct evidence of viscoelastic behavior at the single fibril level, which has not been previously measured. PMID:19878908
Non-linear optical titanyl arsenates: Crystal growth and properties
NASA Astrophysics Data System (ADS)
Nordborg, Jenni Eva Louise
Crystals are appreciated not only for their appearance, but also for their unique physical properties which are utilized by the photonic industry in appliances that we come across every day. An important part of enabling the technical use of optical devices is the manufacture of crystals. This dissertation deals with a specific group of materials called the potassium titanyl phosphate (KIP) family, known for their non-linear optical and ferroelectric properties. The isomorphs vary in their linear optical and dielectric properties, which can be tuned to optimize device performance by forming solid solutions of the different materials. Titanyl arsenates have a wide range of near-infrared transmission which makes them useful for tunable infrared lasers. The isomorphs examined in the present work were primarily RbTiOASO4 (RTA) and CsTiOAsO4 (CTA) together with the mixtures RbxCs 1-xTiOAsO4 (RCTA). Large-scale crystals were grown by top seeding solution growth utilizing a three-zone furnace with excellent temperature control. Sufficiently slow cooling and constant upward lifting produced crystals with large volumes useable for technical applications. Optical quality RTA crystals up to 10 x 12 x 20 mm were grown. The greater difficulty in obtaining good crystals of CTA led to the use of mixed RCTA materials. The mixing of rubidium and cesium in RCTA is more favorable to crystal growth than the single components in pure RTA and CTA. Mixed crystals are rubidium-enriched and contain only 20-30% of the cesium concentration in the flux. The cesium atoms show a preference for the larger cation site. The network structure is very little affected by the cation substitution; consequently, the non-linear optical properties of the Rb-rich isomorphic mixtures of RTA and CTA can be expected to remain intact. Crystallographic methods utilizing conventional X-ray tubes, synchrotron radiation and neutron diffraction have been employed to investigate the properties of the atomic
Kumar, P Arun; Pushpadass, Heartwin A; Franklin, Magdaline Eljeeva Emerald; Simha, H V Vikram; Nath, B Surendra
2016-10-01
The influence of enzymatic hydrolysis of starch on the pasting properties of barnyard millet was studied using a rheometer. The effects of blending hydrolyzed barnyard millet wort with milk at different ratios (0:1, 1:1, 1:1.5 and 1:2) on flow and viscoelastic behavior were investigated. From the pasting curves, it was evident that enzymatically-hydrolyzed starch did not exhibit typical pasting characteristics expected of normal starch. The Herschel-Bulkley model fitted well to the flow behaviour data, with coefficient of determination (R(2)) ranging from 0.942 to 0.988. All milk-wort blends demonstrated varying degree of shear thinning with flow behavior index (n) ranging from 0.252 to 0.647. Stress-strain data revealed that 1:1 blend of milk to wort had the highest storage modulus (7.09-20.06Pa) and an elastically-dominant behavior (phase angle <45°) over the tested frequency range. The crossover point of G' and G" shifted to higher frequencies with increasing wort content. From the flow and viscoelastic behavior, it was concluded that the 1:1 blend of milk to wort would have least phase separation and better flowability during spray drying.
Linear and nonlinear optical properties of chalcogenide microstructured optical fibers
NASA Astrophysics Data System (ADS)
Trolès, Johann; Brilland, Laurent; Caillaud, Celine; Renversez, Gilles; Mechin, David; Adam, Jean-Luc
2015-03-01
Chalcogenide glasses are known for their large transparency in the mid-infrared and their high linear refractive index (>2). They present also a high non-linear coefficient (n2), 100 to 1000 times larger than for silica, depending on the composition. we have developed a casting method to prepare the microstructured chalcogenide preform. This method allows optical losses as low as 0.4 dB/m at 1.55 µm and less than 0.05 dB/m in the mid IR. Various chalcogenide MOFs operating in the IR range has been fabricated in order to associate the high non-linear properties of these glasses and the original MOF properties. For example, small core fibers have been drawn to enhance the non linearities for telecom applications such as signal regeneration and generation of supercontinuum sources. On another hand, in the 3-12 µm window, single mode fibers and exposed core fibers have been realized for Gaussian beams propagation and sensors applications respectively.
Anisotropic linear elastic properties of fractal-like composites.
Carpinteri, Alberto; Cornetti, Pietro; Pugno, Nicola; Sapora, Alberto
2010-11-01
In this work, the anisotropic linear elastic properties of two-phase composite materials, made up of square inclusions embedded in a matrix, are investigated. The inclusions present a fractal hierarchical distribution and are supposed to have the same Poisson's ratio as the matrix but a different Young's modulus. The effective elastic moduli of the medium are computed at each fractal iteration by coupling a position-space renormalization-group technique with a finite element analysis. The study allows to obtain and generalize some fundamental properties of fractal composite materials. PMID:21230552
Response properties of pigeon otolith afferents to linear acceleration
NASA Technical Reports Server (NTRS)
Si, X.; Angelaki, D. E.; Dickman, J. D.
1997-01-01
In the present study, the sensitivity to sinusoidal linear accelerations in the plane of the utricular macula was tested in afferents. The head orientation relative to the translation axis was varied in order to determine the head position that elicited the maximal and minimal responses for each afferent. The response gain and phase values obtained to 0.5-Hz and 2-Hz linear acceleration stimuli were then plotted as a function of head orientation and a modified cosine function was fit to the data. From the best-fit cosine function, the predicted head orientations that would produce the maximal and minimal response gains were estimated. The estimated maximum response gains to linear acceleration in the utricular plane for the afferents varied between 75 and 1420 spikes s-1 g-1. The mean maximal gains for all afferents to 0.5-Hz and 2-Hz sinusoidal linear acceleration stimuli were 282 and 367 spikes s-1 g-1, respectively. The minimal response gains were essentially zero for most units. The response phases always led linear acceleration and remained constant for each afferent, regardless of head orientation. These response characteristics indicate that otolith afferents are cosine tuned and behave as one-dimensional linear accelerometers. The directions of maximal sensitivity to linear acceleration for the afferents varied throughout the plane of the utricle; however, most vectors were directed out of the opposite ear near the interaural axis. The response dynamics of the afferents were tested using stimulus frequencies ranging between 0.25 Hz and 10 Hz (0.1 g peak acceleration). Across stimulus frequencies, most afferents had increasing gains and constant phase values. These dynamic properties for individual afferents were fit with a simple transfer function that included three parameters: a mechanical time constant, a gain constant, and a fractional order distributed adaptation operator.
Viscoelastic analyses of launch vehicle components
Chi, J.K.; Lin, S.R.
1995-12-31
Current analysis techniques for solid rocket propellant, and insulation used in space launch vehicles, have several shortcomings. The simplest linear elastic analysis method ignores the inherent viscoelastic behavior of these materials entirely. The relaxation modulus method commonly used to simulate time-dependent effects ignores the past loading history, while the rigorous viscoelastic finite-element analysis is often expensive and impractical. The response of viscoelastic materials is often characterized by the time-dependent relaxation moduli obtained from uniaxial relaxation tests. Since the relaxation moduli are functions of elapsed time, the viscoelastic analysis is not only dependent on the current stress or strain state but also the full loading history. As a preliminary step towards developing a procedure which will yield reasonably conservative results for analyzing the structural response of solid rocket motors, an equivalent-modulus approach was developed. To demonstrate its application, a viscoelastic thick-walled cylindrical material, confined by a stiff steel case and under an internal pressure condition, was analyzed using (1) the equivalent-modulus elastic quasi-static method, (2) an exact viscoelastic closed-form solution, and (3) the viscoelastic finite-element program. A combination of two springs and one viscous damper is used to represent the viscoelastic material with parameters obtained from stress-relaxation tests. The equivalent modulus is derived based on an accumulated quasi-static stress/strain state. The exact closed-form solution is obtained by the Laplace Transform method. The ABAQUS program is then used for the viscoelastic finite-element solution, where the loading-rate dependent moduli is represented by a Prony series expansion of the relaxation modulus. Additional analyses were performed for two space launch solid rocket motors for the purpose of comparing results from the equivalent-modulus approach and the ABAQUS program.
Linear Properties of Numerical Schemes for the Shallow Water Equations
NASA Astrophysics Data System (ADS)
Eldred, C.; Randall, D. A.
2013-12-01
The shallow water equations provide a useful analogue of fully compressible Euler equations since they have similar conservation laws, many of the same types of waves and a similar (quasi-) balanced state. There has been extensive work exploring the linear properties (balanced states and propagating modes) of various schemes for the shallow water equations on uniform grids, but comparatively little work for non-uniform grids (especially in the case of finite difference and finite volume methods). With the simplifications associated with uniform grids, analytic results for the dispersion relationship and other linear properties can be obtained. However, such grids are not necessarily representative of the actual grids used in dynamical cores on the sphere. Using the Atmospheric Dynamical Core Testbed (ADCoT) built on top of Morphe, the linear properties of various popular finite-difference and finite-volume schemes are examined on both uniform and non-uniform grids (such as the cubed sphere, triangular geodesic and hexagonal-pentagonal geodesic grids).
Theory of reciprocating contact for viscoelastic solids
NASA Astrophysics Data System (ADS)
Putignano, Carmine; Carbone, Giuseppe; Dini, Daniele
2016-04-01
A theory of reciprocating contacts for linear viscoelastic materials is presented. Results are discussed for the case of a rigid sphere sinusoidally driven in sliding contact with a viscoelastic half-space. Depending on the size of the contact, the frequency and amplitude of the reciprocating motion, and on the relaxation time of the viscoelastic body, we establish that the contact behavior may range from the steady-state viscoelastic solution, in which traction forces always oppose the direction of the sliding rigid punch, to a more elaborate trend, which is due to the strong interaction between different regions of the path covered during the reciprocating motion. Practical implications span a number of applications, ranging from seismic engineering to biotechnology.
Grant, Colin A; Alfouzan, Abdulrahman; Gough, Tim; Twigg, Peter C; Coates, Phil D
2013-01-01
Visco-elastic behaviour at the nano-level of a commonly used polymer (PET) is characterised using atomic force microscopy (AFM) at a range of temperatures. The modulus, indentation creep and relaxation time of the PET film (thickness=100 μm) is highly sensitive to temperature over an experimental temperature range of 22-175°C. The analysis showed a 40-fold increase in the amount of indentation creep on raising the temperature from 22°C to 100°C, with the most rapid rise occurring above the glass-to-rubber transition temperature (T(g)=77.1°C). At higher temperatures, close to the crystallisation temperature (T(c)=134.7°C), the indentation creep reduced to levels similar to those at temperatures below T(g). The calculated relaxation time showed a similar temperature dependence, rising from 0.6s below T(g) to 1.2s between T(g) and T(c) and falling back to 0.6s above T(c). Whereas, the recorded modulus of the thick polymer film decreases above T(g), subsequently increasing near T(c). These visco-elastic parameters are obtained via mechanical modelling of the creep curves and are correlated to the thermal phase changes that occur in PET, as revealed by differential scanning calorimetry (DSC). PMID:22750040
Linear and Branched PEIs (Polyethylenimines) and Their Property Space
Lungu, Claudiu N.; Diudea, Mircea V.; Putz, Mihai V.; Grudziński, Ireneusz P.
2016-01-01
A chemical property space defines the adaptability of a molecule to changing conditions and its interaction with other molecular systems determining a pharmacological response. Within a congeneric molecular series (compounds with the same derivatization algorithm and thus the same brute formula) the chemical properties vary in a monotonic manner, i.e., congeneric compounds share the same chemical property space. The chemical property space is a key component in molecular design, where some building blocks are functionalized, i.e., derivatized, and eventually self-assembled in more complex systems, such as enzyme-ligand systems, of which (physico-chemical) properties/bioactivity may be predicted by QSPR/QSAR (quantitative structure-property/activity relationship) studies. The system structure is determined by the binding type (temporal/permanent; electrostatic/covalent) and is reflected in its local electronic (and/or magnetic) properties. Such nano-systems play the role of molecular devices, important in nano-medicine. In the present article, the behavior of polyethylenimine (PEI) macromolecules (linear LPEI and branched BPEI, respectively) with respect to the glucose oxidase enzyme GOx is described in terms of their (interacting) energy, geometry and topology, in an attempt to find the best shape and size of PEIs to be useful for a chosen (nanochemistry) purpose. PMID:27089324
Linear and Branched PEIs (Polyethylenimines) and Their Property Space.
Lungu, Claudiu N; Diudea, Mircea V; Putz, Mihai V; Grudziński, Ireneusz P
2016-04-13
A chemical property space defines the adaptability of a molecule to changing conditions and its interaction with other molecular systems determining a pharmacological response. Within a congeneric molecular series (compounds with the same derivatization algorithm and thus the same brute formula) the chemical properties vary in a monotonic manner, i.e., congeneric compounds share the same chemical property space. The chemical property space is a key component in molecular design, where some building blocks are functionalized, i.e., derivatized, and eventually self-assembled in more complex systems, such as enzyme-ligand systems, of which (physico-chemical) properties/bioactivity may be predicted by QSPR/QSAR (quantitative structure-property/activity relationship) studies. The system structure is determined by the binding type (temporal/permanent; electrostatic/covalent) and is reflected in its local electronic (and/or magnetic) properties. Such nano-systems play the role of molecular devices, important in nano-medicine. In the present article, the behavior of polyethylenimine (PEI) macromolecules (linear LPEI and branched BPEI, respectively) with respect to the glucose oxidase enzyme GOx is described in terms of their (interacting) energy, geometry and topology, in an attempt to find the best shape and size of PEIs to be useful for a chosen (nanochemistry) purpose.
Linear and Branched PEIs (Polyethylenimines) and Their Property Space.
Lungu, Claudiu N; Diudea, Mircea V; Putz, Mihai V; Grudziński, Ireneusz P
2016-01-01
A chemical property space defines the adaptability of a molecule to changing conditions and its interaction with other molecular systems determining a pharmacological response. Within a congeneric molecular series (compounds with the same derivatization algorithm and thus the same brute formula) the chemical properties vary in a monotonic manner, i.e., congeneric compounds share the same chemical property space. The chemical property space is a key component in molecular design, where some building blocks are functionalized, i.e., derivatized, and eventually self-assembled in more complex systems, such as enzyme-ligand systems, of which (physico-chemical) properties/bioactivity may be predicted by QSPR/QSAR (quantitative structure-property/activity relationship) studies. The system structure is determined by the binding type (temporal/permanent; electrostatic/covalent) and is reflected in its local electronic (and/or magnetic) properties. Such nano-systems play the role of molecular devices, important in nano-medicine. In the present article, the behavior of polyethylenimine (PEI) macromolecules (linear LPEI and branched BPEI, respectively) with respect to the glucose oxidase enzyme GOx is described in terms of their (interacting) energy, geometry and topology, in an attempt to find the best shape and size of PEIs to be useful for a chosen (nanochemistry) purpose. PMID:27089324
A Thermodynamic Theory of Solid Viscoelasticity. Part II:; Nonlinear Thermo-viscoelasticity
NASA Technical Reports Server (NTRS)
Freed, Alan D.; Leonov, Arkady I.; Gray, Hugh R. (Technical Monitor)
2002-01-01
This paper, second in the series of three papers, develops a general, nonlinear, non-isothermal, compressible theory for finite rubber viscoelasticity and specifies it in a form convenient for solving problems important to the rubber, tire, automobile, and air-space industries, among others. Based on the quasi-linear approach of non-equilibrium thermodynamics, a general nonlinear theory of differential type has been developed for arbitrary non-isothermal deformations of viscoelastic solids. In this theory, the constitutive equations were presented as the sum of a rubber elastic (equilibrium) and a liquid type viscoelastic (non-equilibrium) terms. These equations have then been simplified using several modeling and simplicity arguments.
Crustal deformation, the earthquake cycle, and models of viscoelastic flow in the asthenosphere
NASA Technical Reports Server (NTRS)
Cohen, S. C.; Kramer, M. J.
1983-01-01
The crustal deformation patterns associated with the earthquake cycle can depend strongly on the rheological properties of subcrustal material. Substantial deviations from the simple patterns for a uniformly elastic earth are expected when viscoelastic flow of subcrustal material is considered. The detailed description of the deformation pattern and in particular the surface displacements, displacement rates, strains, and strain rates depend on the structure and geometry of the material near the seismogenic zone. The origin of some of these differences are resolved by analyzing several different linear viscoelastic models with a common finite element computational technique. The models involve strike-slip faulting and include a thin channel asthenosphere model, a model with a varying thickness lithosphere, and a model with a viscoelastic inclusion below the brittle slip plane. The calculations reveal that the surface deformation pattern is most sensitive to the rheology of the material that lies below the slip plane in a volume whose extent is a few times the fault depth. If this material is viscoelastic, the surface deformation pattern resembles that of an elastic layer lying over a viscoelastic half-space. When the thickness or breath of the viscoelastic material is less than a few times the fault depth, then the surface deformation pattern is altered and geodetic measurements are potentially useful for studying the details of subsurface geometry and structure. Distinguishing among the various models is best accomplished by making geodetic measurements not only near the fault but out to distances equal to several times the fault depth. This is where the model differences are greatest; these differences will be most readily detected shortly after an earthquake when viscoelastic effects are most pronounced.
Thin film dynamics of viscoelastic fluids
NASA Astrophysics Data System (ADS)
Lebon, Luc; Limat, Laurent
2012-11-01
We present here viscoelastic fluids in thin film flows, such as liquid bells or liquid curtains. The viscoelastic property of the liquids exhibits specific dynamics in such flows. In the case of bells, the elastic strength tends to extend the bell size for example. In the case of curtain flows, original behaviour of holes are observed with specific growth mechanism for bubbles trapped in the flow.
Linear elastic properties derivation from microstructures representative of transport parameters.
Hoang, Minh Tan; Bonnet, Guy; Tuan Luu, Hoang; Perrot, Camille
2014-06-01
It is shown that three-dimensional periodic unit cells (3D PUC) representative of transport parameters involved in the description of long wavelength acoustic wave propagation and dissipation through real foam samples may also be used as a standpoint to estimate their macroscopic linear elastic properties. Application of the model yields quantitative agreement between numerical homogenization results, available literature data, and experiments. Key contributions of this work include recognizing the importance of membranes and properties of the base material for the physics of elasticity. The results of this paper demonstrate that a 3D PUC may be used to understand and predict not only the sound absorbing properties of porous materials but also their transmission loss, which is critical for sound insulation problems. PMID:24907783
NASA Astrophysics Data System (ADS)
Deng, R.; Davies, P.; Bajaj, A. K.
2003-05-01
A hereditary model and a fractional derivative model for the dynamic properties of flexible polyurethane foams used in automotive seat cushions are presented. Non-linear elastic and linear viscoelastic properties are incorporated into these two models. A polynomial function of compression is used to represent the non-linear elastic behavior. The viscoelastic property is modelled by a hereditary integral with a relaxation kernel consisting of two exponential terms in the hereditary model and by a fractional derivative term in the fractional derivative model. The foam is used as the only viscoelastic component in a foam-mass system undergoing uniaxial compression. One-term harmonic balance solutions are developed to approximate the steady state response of the foam-mass system to the harmonic base excitation. System identification procedures based on the direct non-linear optimization and a sub-optimal method are formulated to estimate the material parameters. The effects of the choice of the cost function, frequency resolution of data and imperfections in experiments are discussed. The system identification procedures are also applied to experimental data from a foam-mass system. The performances of the two models for data at different compression and input excitation levels are compared, and modifications to the structure of the fractional derivative model are briefly explored. The role of the viscous damping term in both types of model is discussed.
Maazouz, A.; Sautereau, H.; Gerard, J.F. . Lab. des Materiaux Macromoleculaires)
1993-10-20
The deformation and fracture behaviors of hybrid-particulate epoxy composites have been examined. These materials were based on a DGEBA/DDA matrix with various volume fractions of glass beads and different rubber contents. Young's modulus, yield stress, dynamic mechanical spectra, and fracture energy have been determined at room temperature. The Kerner model fits well the Young's modulus for the hybrid complexes with various glass bead contents. The analysis of the relaxation peak recorded from viscoelastic measurements allow us to discuss the influence of the introduction of the glass beads on the mobility of macromolecular chains and the characteristics of the rubber-separated phase. The fracture energy displays a strong improvement and synergism effect due to the presence of both kinds of particles. The toughening mechanisms were discussed.
Pseudospectral modeling and dispersion analysis of Rayleigh waves in viscoelastic media
Zhang, K.; Luo, Y.; Xia, J.; Chen, C.
2011-01-01
Multichannel Analysis of Surface Waves (MASW) is one of the most widely used techniques in environmental and engineering geophysics to determine shear-wave velocities and dynamic properties, which is based on the elastic layered system theory. Wave propagation in the Earth, however, has been recognized as viscoelastic and the propagation of Rayleigh waves presents substantial differences in viscoelastic media as compared with elastic media. Therefore, it is necessary to carry out numerical simulation and dispersion analysis of Rayleigh waves in viscoelastic media to better understand Rayleigh-wave behaviors in the real world. We apply a pseudospectral method to the calculation of the spatial derivatives using a Chebyshev difference operator in the vertical direction and a Fourier difference operator in the horizontal direction based on the velocity-stress elastodynamic equations and relations of linear viscoelastic solids. This approach stretches the spatial discrete grid to have a minimum grid size near the free surface so that high accuracy and resolution are achieved at the free surface, which allows an effective incorporation of the free surface boundary conditions since the Chebyshev method is nonperiodic. We first use an elastic homogeneous half-space model to demonstrate the accuracy of the pseudospectral method comparing with the analytical solution, and verify the correctness of the numerical modeling results for a viscoelastic half-space comparing the phase velocities of Rayleigh wave between the theoretical values and the dispersive image generated by high-resolution linear Radon transform. We then simulate three types of two-layer models to analyze dispersive-energy characteristics for near-surface applications. Results demonstrate that the phase velocity of Rayleigh waves in viscoelastic media is relatively higher than in elastic media and the fundamental mode increases by 10-16% when the frequency is above 10. Hz due to the velocity dispersion of P
Amid, Bahareh Tabatabaee; Mirhosseini, Hamed
2012-01-01
In recent years, the demand for a natural plant-based polymer with potential functions from plant sources has increased considerably. The main objective of the current study was to study the effect of chemical extraction conditions on the rheological and functional properties of the heteropolysaccharide/protein biopolymer from durian (Durio zibethinus) seed. The efficiency of different extraction conditions was determined by assessing the extraction yield, protein content, solubility, rheological properties and viscoelastic behavior of the natural polymer from durian seed. The present study revealed that the soaking process had a more significant (p < 0.05) effect than the decolorizing process on the rheological and functional properties of the natural polymer. The considerable changes in the rheological and functional properties of the natural polymer could be due to the significant (p < 0.05) effect of the chemical extraction variables on the protein fraction present in the molecular structure of the natural polymer from durian seed. The natural polymer from durian seed had a more elastic (or gel like) behavior compared to the viscous (liquid like) behavior at low frequency. The present study revealed that the natural heteropolysaccharide/protein polymer from durian seed had a relatively low solubility ranging from 9.1% to 36.0%. This might be due to the presence of impurities, insoluble matter and large particles present in the chemical structure of the natural polymer from durian seed. PMID:23203099
Cochrane, Alexander P.; Merrett, Craig G.; Hilton, Harry H.
2014-12-10
The advent of new structural concepts employing composites in primary load carrying aerospace structures in UAVs, MAVs, Boeing 787s, Airbus A380s, etc., necessitates the inclusion of flexibility as well as viscoelasticity in static structural and aero-viscoelastic analyses. Differences and similarities between aeroelasticity and aero-viscoelasticity have been investigated in [2]. An investigation is undertaken as to the dependence and sensitivity of aerodynamic and stability derivatives to elastic and viscoelastic structural flexibility and as to time dependent flight and maneuver velocities. Longitudinal, lateral and directional stabilities are investigated. It has been a well established fact that elastic lifting surfaces are subject to loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings one of the critical static parameters is the velocity at which control reversal takes place (V{sub REV}{sup E}). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds V{sub REV<}{sup ≧}V{sub REV}{sup E}, but furthermore does so in time at 0 < t{sub REV} ≤ ∞. The influence of the twin effects of viscoelastic and elastic materials and of variable flight velocities on longitudinal, lateral, directional and spin stabilities are also investigated. It has been a well established fact that elastic lifting surfaces are subject to loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are here extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings the critical parameter is the velocity at
NASA Astrophysics Data System (ADS)
Cochrane, Alexander P.; Merrett, Craig G.; Hilton, Harry H.
2014-12-01
The advent of new structural concepts employing composites in primary load carrying aerospace structures in UAVs, MAVs, Boeing 787s, Airbus A380s, etc., necessitates the inclusion of flexibility as well as viscoelasticity in static structural and aero-viscoelastic analyses. Differences and similarities between aeroelasticity and aero-viscoelasticity have been investigated in [2]. An investigation is undertaken as to the dependence and sensitivity of aerodynamic and stability derivatives to elastic and viscoelastic structural flexibility and as to time dependent flight and maneuver velocities. Longitudinal, lateral and directional stabilities are investigated. It has been a well established fact that elastic lifting surfaces are subject to loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings one of the critical static parameters is the velocity at which control reversal takes place (VREVE). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds VREV<≧VREVE, but furthermore does so in time at 0 < tREV ≤ ∞. The influence of the twin effects of viscoelastic and elastic materials and of variable flight velocities on longitudinal, lateral, directional and spin stabilities are also investigated. It has been a well established fact that elastic lifting surfaces are subject to loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are here extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings the critical parameter is the velocity at which control reversal takes place (VREVE
Silver, Frederick H; Ebrahimi, Ali; Snowhill, Patrick B
2002-01-01
We have studied the strain rate dependence of incremental stress-strain curves of self-assembled type I collagen fibers in an effort to understand the molecular phenomena that contribute to the macroscopic mechanical behavior of tendons. Results of viscoelastic tests at strain rates between 10% and 1000% per min suggest that the slope of the elastic stress-strain curve is to a first approximation independent of strain rate while the slope of the viscous stress-strain curve increases with increased strain rate. After correction of the slope of the viscous stress-strain curve for the changes in strain rate, it is observed that the apparent viscosity decreases with increased strain rate. It is concluded that the approximate strain rate independence of the elastic spring constant of collagen is consistent with the spring-like behavior of the 12 flexible regions that make up the collagen D-period. These regions are poor in the rigid amino acid residues proline and hydroxyproline. In contrast, the thixotropy of collagen is consistent with the slippage of subfibrillar subunits during tensile deformation. It is hypothesized that at high strain rates subfibrillar subunits appear to "hydroplane" by each other on a layer of loosely bound water. PMID:12685863
NASA Technical Reports Server (NTRS)
Nicholson, Lee M.; Whitley, Karen S.; Gates, Thomas S.
2001-01-01
Mechanical testing of the elastic and viscoelastic response of an advanced thermoplastic polyimide (LaRC-SI) with known variations in molecular weight was performed over a range of temperatures below the glass transition temperature. The notched tensile strength was shown to be a strong function of both molecular weight and temperature, whereas stiffness was only a strong function of temperature. A critical molecular weight was observed to occur at a weight average molecular weight of M, approx. 22,000 g/mol below which, the notched tensile strength decreases rapidly. This critical molecular weight transition is temperature-independent. Low, molecular weight materials tended to fail in a brittle manner, whereas high molecular weight materials exhibited ductile failure. Furthermore, low molecular weight materials have increased creep compliance and creep compliance rate, and are more sensitive to temperature than the high molecular weight materials. At long timescales (less than 1100 hours) physical aging serves to significantly decrease the creep compliance and creep rate of all the materials tested. Low molecular weight materials are less influenced by the effects of physical aging.
Environmental and viscoelastic effects on stresses in adhesive joints
Palazotto, A.N.; Birman, V.
1995-04-01
This paper considers the state of the art in several important areas of research on adhesively bonded joints. The paper reviews the studies dealing with environmental and viscoelastic effects on stresses in adhesive joints. Environmental factors that affect stresses include temperature and moisture. These factors are analyzed and practical examples that illustrate their impact on adhesives are given for the solid-rocket motor, which is a structural component paramount to the U.S. space program. The paper deals with viscoelastic effects on adhesive joints, and a number of viscoelastic models used in the analysis of viscoelastic materials, including adhesives, are reviewed. The use of the solid-rocket motor as an example characterizes the circumstances where viscoelastic properties of adhesive layers are essential. Close attention is paid to the fractional derivative model of Bagley and Torvik, which may be a good candidate for an analytical study of adhesive joints. Finally, existing studies on viscoelastic adhesive joints are considered. 54 refs.
Viscoelastic material inversion using Sierra-SD and ROL
Walsh, Timothy; Aquino, Wilkins; Ridzal, Denis; Kouri, Drew Philip; van Bloemen Waanders, Bart Gustaaf; Urbina, Angel
2014-11-01
In this report we derive frequency-domain methods for inverse characterization of the constitutive parameters of viscoelastic materials. The inverse problem is cast in a PDE-constrained optimization framework with efficient computation of gradients and Hessian vector products through matrix free operations. The abstract optimization operators for first and second derivatives are derived from first principles. Various methods from the Rapid Optimization Library (ROL) are tested on the viscoelastic inversion problem. The methods described herein are applied to compute the viscoelastic bulk and shear moduli of a foam block model, which was recently used in experimental testing for viscoelastic property characterization.
NASA Astrophysics Data System (ADS)
Ribeiro, Eduardo Afonso; Pereira, Jucélio Tomás; Alberto Bavastri, Carlos
2015-09-01
One of the major reasons for inserting damping into bearings is that rotating machines are often requested in critical functioning conditions having sometimes to function under dynamic instability or close to critical speeds. Hydrodynamic and magnetic bearings have usually been used for this purpose, but they present limitations regarding costs and operation, rendering the use of viscoelastic supports a feasible solution for vibration control in rotating machines. Most papers in the area use simple analytic or single degree of freedom models for the rotor as well as classic mechanical models of linear viscoelasticity for the support - like Maxwell, Kelvin-Voigt, Zenner, four-element, GHM models and even frequency independent models - but they lack the accuracy of fractional models in a large range of frequency and temperature regarding the same number of coefficients. Even in those works, the need to consider the addition of degrees of freedom to the support is evident. However, so far no paper has been published focusing on a methodology to determine the optimal constructive form for any viscoelastic support in which the rotor is discretized by finite elements associated to an accurate model for characterizing the viscoelastic material. In general, the support is meant to be a simple isolation system, and the fact the stiffness matrix is complex and frequency-temperature dependent - due to its viscoelastic properties - forces the traditional methods to require an extremely long computing time, thus rendering them too time consuming in an optimization environment. The present work presents a robust methodology based mainly on generalized equivalent parameters (GEP) - for an optimal design of viscoelastic supports for rotating machinery - aiming at minimizing the unbalance frequency response of the system using a hybrid optimization technique (genetic algorithms and Nelder-Mead method). The rotor is modeled based on the finite element method using Timoshenko's thick
RF properties of periodic accelerating structures for linear colliders
Wang, J.W.
1989-07-01
With the advent of the SLAC electron-positron linear collider (SLC) in the 100 GeV center-of-mass energy range, research and development work on even higher energy machines of this type has started in several laboratories in the United States, Europe, the Soviet Union and Japan. These linear colliders appear to provide the only promising approach to studying e/sup /plus//e/sup /minus// physics at center-of-mass energies approaching 1 TeV. This thesis concerns itself with the study of radio frequency properties of periodic accelerating structures for linear colliders and their interaction with bunched beams. The topics that have been investigated are: experimental measurements of the energy loss of single bunches to longitudinal modes in two types of structures, using an equivalent signal on a coaxial wire to simulate the beam; a method of canceling the energy spread created within a single bunch by longitudinal wakefields, through appropriate shaping of the longitudinal charge distribution of the bunch; derivation of the complete transient beam-loading equation for a train of bunches passing through a constant-gradient accelerator section, with application to the calculation and minimization of multi-bunch energy spread; detailed study of field emission and radio frequency breakdown in disk-loaded structures at S-, C- and X-band frequencies under extremely high-gradient conditions, with special attention to thermal effects, radiation, sparking, emission of gases, surface damage through explosive emission and its possible control through RF-gas processing. 53 refs., 49 figs., 9 tabs.
Viscoelastic cationic polymers containing the urethane linkage
NASA Technical Reports Server (NTRS)
Rembaum, A. (Inventor)
1972-01-01
A method for the synthesis and manufacturing of elastomeric compositions and articles containing quaternary nitrogen centers and condensation residues along the polymeric backbone of the centers is presented. Linear and cross-linked straight chain and block polymers having a wide damping temperature range were synthesized. Formulae for the viscoelastic cationic polymers are presented.
Linear dispersion properties of ring velocity distribution functions
Vandas, Marek
2015-06-15
Linear properties of ring velocity distribution functions are investigated. The dispersion tensor in a form similar to the case of a Maxwellian distribution function, but for a general distribution function separable in velocities, is presented. Analytical forms of the dispersion tensor are derived for two cases of ring velocity distribution functions: one obtained from physical arguments and one for the usual, ad hoc ring distribution. The analytical expressions involve generalized hypergeometric, Kampé de Fériet functions of two arguments. For a set of plasma parameters, the two ring distribution functions are compared. At the parallel propagation with respect to the ambient magnetic field, the two ring distributions give the same results identical to the corresponding bi-Maxwellian distribution. At oblique propagation, the two ring distributions give similar results only for strong instabilities, whereas for weak growth rates their predictions are significantly different; the two ring distributions have different marginal stability conditions.
Linear processes in high dimensions: Phase space and critical properties
NASA Astrophysics Data System (ADS)
Mastromatteo, Iacopo; Bacry, Emmanuel; Muzy, Jean-François
2015-04-01
In this work we investigate the generic properties of a stochastic linear model in the regime of high dimensionality. We consider in particular the vector autoregressive (VAR) model and the multivariate Hawkes process. We analyze both deterministic and random versions of these models, showing the existence of a stable phase and an unstable phase. We find that along the transition region separating the two regimes the correlations of the process decay slowly, and we characterize the conditions under which these slow correlations are expected to become power laws. We check our findings with numerical simulations showing remarkable agreement with our predictions. We finally argue that real systems with a strong degree of self-interaction are naturally characterized by this type of slow relaxation of the correlations.
Omari, Eenas A; Varghese, Tomy; Kliewer, Mark A; Harter, Josephine; Hartenbach, Ellen M
2015-07-16
Ultrasound elastography is envisioned as an optional modality to augment standard ultrasound B-mode imaging and is a promising technique to aid in detecting uterine masses which cause abnormal uterine bleeding in both pre- and post-menopausal women. In order to determine the effectiveness of strain imaging, mechanical testing to establish the elastic contrast between normal uterine tissue and stiffer masses such as leiomyomas (fibroids) and between softer pathologies such as uterine cancer and adenomyosis has to be performed. In this paper, we evaluate the stiffness of normal uterine tissue, leiomyomas, and endometrial cancers using a EnduraTEC ElectroForce (ELF) system. We quantify the viscoelastic characteristics of uterine tissue and associated pathologies globally by using two mechanical testing approaches, namely a dynamic and a quasi-static (ramp testing) approach. For dynamic testing, 21 samples obtained from 18 patients were tested. The testing frequencies were set to 1, 10, 20, and 30 Hz. We also report on stiffness variations with pre-compression from 1% to 6% for testing at 2%, 3%, and 4% strain amplitude. Our results show that human uterine tissue stiffness is both dependent on percent pre-compression and testing frequencies. For ramp testing, 20 samples obtained from 14 patients were used. A constant strain rate of 0.1% was applied and comparable results to dynamic testing were obtained. The mean modulus contrast at 2% amplitude between normal uterine tissue (the background) and leiomyomas was 2.29 and 2.17, and between the background and cancer was 0.47 and 0.39 for dynamic and ramp testing, respectively.
Yamamoto, Takahiro; Yoshida, Masaru
2012-06-01
We investigated viscoelastic and photoresponsive properties of the microparticle/liquid-crystal (LC) composite gels. The mechanical strength of the colloidal gels can be widely tuned by varying particle concentrations. With increasing particle concentration, a storage modulus of the particle/LC composite gels increased and reached over 10(4) Pa, showing good self-supporting ability. We demonstrated for the first time that the particle/LC composite gels exhibited rapid and repetitive recovery of the mechanical strength after large-amplitude oscillatory breakdown. In addition, photoresponsive properties of the composite gels were investigated by the cis-trans photoisomerization of the azobenzene compound doped into the host LCs. The photochemical gel-sol transition could be repeatedly induced by changing the phase structure of the host LCs between nematic and isotropic, using the photoisomerization. The particle/LC composite gels can be applied to optically healable materials by the site-selective gel-sol transition based on the photochemical modulation of the phase structures of the host LCs.
Jones, David S; Laverty, Thomas P; Morris, Caoimhe; Andrews, Gavin P
2016-08-01
Poly(methylvinylether-co-maleic acid) (PMVE/MA) is commonly used as a component of pharmaceutical platforms, principally to enhance interactions with biological substrates (mucoadhesion). However, the limited knowledge on the rheological properties of this polymer and their relationships with mucoadhesion has negated the biomedical use of this polymer as a mono-component platform. This study presents a comprehensive study of the rheological properties of aqueous PMVE/MA platforms and defines their relationships with mucoadhesion using multiple regression analysis. Using dilute solution viscometry the intrinsic viscosities of un-neutralised PMVE/MA and PMVE/MA neutralised using NaOH or TEA were 22.32±0.89dLg(-1), 274.80±1.94dLg(-1) and 416.49±2.21dLg(-1) illustrating greater polymer chain expansion following neutralisation using Triethylamine (TEA). PMVE/MA platforms exhibited shear-thinning properties. Increasing polymer concentration increased the consistencies, zero shear rate (ZSR) viscosities (determined from flow rheometry), storage and loss moduli, dynamic viscosities (defined using oscillatory analysis) and mucoadhesive properties, yet decreased the loss tangents of the neutralised polymer platforms. TEA neutralised systems possessed significantly and substantially greater consistencies, ZSR and dynamic viscosities, storage and loss moduli, mucoadhesion and lower loss tangents than their NaOH counterparts. Multiple regression analysis enabled identification of the dominant role of polymer viscoelasticity on mucoadhesion (r>0.98). The mucoadhesive properties of PMVE/MA platforms were considerable and were greater than those of other platforms that have successfully been shown to enhance in vivo retention when applied to the oral cavity, indicating a positive role for PMVE/MA mono-component platforms for pharmaceutical and biomedical applications. PMID:27085044
Viscoelastic characterization of soft biological materials
NASA Astrophysics Data System (ADS)
Nayar, Vinod Timothy
Progressive and irreversible retinal diseases are among the primary causes of blindness in the United States, attacking the cells in the eye that transform environmental light into neural signals for the optic pathway. Medical implants designed to restore visual function to afflicted patients can cause mechanical stress and ultimately damage to the host tissues. Research shows that an accurate understanding of the mechanical properties of the biological tissues can reduce damage and lead to designs with improved safety and efficacy. Prior studies on the mechanical properties of biological tissues show characterization of these materials can be affected by environmental, length-scale, time, mounting, stiffness, size, viscoelastic, and methodological conditions. Using porcine sclera tissue, the effects of environmental, time, and mounting conditions are evaluated when using nanoindentation. Quasi-static tests are used to measure reduced modulus during extended exposure to phosphate-buffered saline (PBS), as well as the chemical and mechanical analysis of mounting the sample to a solid substrate using cyanoacrylate. The less destructive nature of nanoindentation tests allows for variance of tests within a single sample to be compared to the variance between samples. The results indicate that the environmental, time, and mounting conditions can be controlled for using modified nanoindentation procedures for biological samples and are in line with averages modulus values from previous studies but with increased precision. By using the quasi-static and dynamic characterization capabilities of the nanoindentation setup, the additional stiffness and viscoelastic variables are measured. Different quasi-static control methods were evaluated along with maximum load parameters and produced no significant difference in reported reduced modulus values. Dynamic characterization tests varied frequency and quasi-static load, showing that the agar could be modeled as a linearly
Electrical analogous in viscoelasticity
NASA Astrophysics Data System (ADS)
Ala, Guido; Di Paola, Mario; Francomano, Elisa; Li, Yan; Pinnola, Francesco P.
2014-07-01
In this paper, electrical analogous models of fractional hereditary materials are introduced. Based on recent works by the authors, mechanical models of materials viscoelasticity behavior are firstly approached by using fractional mathematical operators. Viscoelastic models have elastic and viscous components which are obtained by combining springs and dashpots. Various arrangements of these elements can be used, and all of these viscoelastic models can be equivalently modeled as electrical circuits, where the spring and dashpot are analogous to the capacitance and resistance, respectively. The proposed models are validated by using modal analysis. Moreover, a comparison with numerical experiments based on finite difference time domain method shows that, for long time simulations, the correct time behavior can be obtained only with modal analysis. The use of electrical analogous in viscoelasticity can better reveal the real behavior of fractional hereditary materials.
String-merging of meso- viscoelastic droplets
NASA Astrophysics Data System (ADS)
Xu, Yuanze; Xu, Jianmao
2007-03-01
Great challenge exists in the multi-scale rheological modeling of immiscible polyblends with non-linear morphology changes, including viscoelastic drop break-up and collapse. A new type mechanism of merging and coalescence, called string-merging of meso- viscoelastic droplets was described and analyzed. By iterative stretching and relaxation in a four-roll mill rheometer, one droplet containing high molar mass PIB (polyisobutene), was separated into two droplets connected by a string in a dumbbell shape suspending in polydimethylsiloxane (PDMS) medium. In quiescent state, the string pulled the two spheres merging closer and collapsed into one spherical drop finally. The process exhibits interesting features, different from capillary breakup mechanism. By adding the viscoelasticity of the systems to the force balance of Laplace force and viscous drag, the phenomenon may be well analyzed. The necessity to involve the microscopic consideration of the highly oriented entangled state are discussed.
Numerical solution methods for viscoelastic orthotropic materials
NASA Technical Reports Server (NTRS)
Gramoll, K. C.; Dillard, D. A.; Brinson, H. F.
1988-01-01
Numerical solution methods for viscoelastic orthotropic materials, specifically fiber reinforced composite materials, are examined. The methods include classical lamination theory using time increments, direction solution of the Volterra Integral, Zienkiewicz's linear Prony series method, and a new method called Nonlinear Differential Equation Method (NDEM) which uses a nonlinear Prony series. The criteria used for comparison of the various methods include the stability of the solution technique, time step size stability, computer solution time length, and computer memory storage. The Volterra Integral allowed the implementation of higher order solution techniques but had difficulties solving singular and weakly singular compliance function. The Zienkiewicz solution technique, which requires the viscoelastic response to be modeled by a Prony series, works well for linear viscoelastic isotropic materials and small time steps. The new method, NDEM, uses a modified Prony series which allows nonlinear stress effects to be included and can be used with orthotropic nonlinear viscoelastic materials. The NDEM technique is shown to be accurate and stable for both linear and nonlinear conditions with minimal computer time.
Substructure synthesis methods for viscoelastic structures
NASA Astrophysics Data System (ADS)
Qian, Duan
1993-09-01
Viscoelastic damping models are necessary for accurate dynamic analysis of flexible aerospace structures. The method of substructure synthesis is extended to systems with general linear viscoelastic damping. The stationary variational principles for discrete symmetric and nonsymmetric viscoelastic systems are first developed in parallel for the time, Laplace, and frequency domain. The corresponding substructure synthesis methods are then formulated. On the basis of the Rayleigh-Ritz method, each substructure is represented by a set of admissible trial vectors. Real trial vectors, such as eigenvectors and Lanczos vectors of the corresponding undamped substructure as well as Ritz vectors obtained by spatial discretization of simple functions, are recommended. The geometric compatibility between substructures can be approximated by a weighted residual method, and the traditional state space formulation is avoided. The effort involved in the reduction process is almost independent of the complexity of viscoelastic models. Beam and plate examples are presented to illustrate the effectiveness of the substructure synthesis method in terms of reducing the size of final equations to obtain accurate solutions of eigenvalues, frequency responses, and transient responses for viscoelastic symmetric systems.
Collective motion of microswimmers in viscoelastic fluids
NASA Astrophysics Data System (ADS)
Li, Gaojin; Ardekani, Arezoo
2015-11-01
The dynamics of suspension of self-propelled microorganisms show fascinating hydrodynamic phenomena, such as, large scale swarming motion, locally correlated motion, enhanced particle diffusion, and enhanced fluid mixing. Even though many studies have been conducted in a Newtonian fluid, the collective motion of microorganisms in non-Newtonian fluids is less understood. The non-Newtonian fluid rheological properties, such as viscoelasticity and shear-dependent viscosity in saliva, mucus and biofilm, significantly affect the swimming properties and hydrodynamic interaction of microorganisms. In this work, we use direct numerical simulation to investigate the collective motion of rod-like swimmers in viscoelastic fluids. Two swimming types, pusher and puller, are investigated. The background viscoelastic fluid is modeled using an Oldroyd-B constitutive equation. This work is supported by NSF CBET-1445955 and Indiana CTSI TR001108.
Accurate Determination of Torsion and Pure Bending Moment for Viscoelastic Measurements
NASA Astrophysics Data System (ADS)
Wang, Yun-Che; Ko, Chih-Chin; Shiau, Li-Ming
Measurements of time-dependent material properties in the context of linear viscoelasticity, at a given frequency and temperature, require accurate determination of both loading and deformation that are subjected to the testing materials. A pendulum-type viscoelastic spectroscopy is developed to experimentally measure loss tangent and the magnitude of dynamic modulus of solid materials. The mechanical system of the device is based on the behavior of the cantilever beam, and torsion and pure bending moment are generated from the interaction between a permanent magnet and the Helmholtz coils. The strength of the magnetic interactions may be determined with a material with known mechanical properties, such as aluminum 6061T4 alloy. The sensitivity of the torque measurement is on the order of one micro N-m level. With the high accurate torque measurement and deformation detection from a laser-based displacement measurement system, viscoelastic properties of materials can be experimentally measured in different frequency regimes. Sinusoidal driving signals are adopted for measuring complex modulus in the sub-resonant regime, and dc bias driving for creep tests in the low frequency limit. At structural resonant frequencies, the full-width-at-half-maximum (FWHM) method or Lorentzian curve fitting method is adopted to extract material properties. The completion of determining material properties in the wide frequency spectrum may help to identify the deformation mechanisms of the material and to create better models for simulation work.
Gupta, Anupam; Sbragaglia, Mauro
2016-01-01
The effects of viscoelasticity on the dynamics and break-up of fluid threads in microfluidic T-junctions are investigated using numerical simulations of dilute polymer solutions at changing the Capillary number (Ca), i.e. at changing the balance between the viscous forces and the surface tension at the interface, up to Ca ≈ 3×10(-2). A Navier-Stokes (NS) description of the solvent based on the lattice Boltzmann models (LBM) is here coupled to constitutive equations for finite extensible non-linear elastic dumbbells with the closure proposed by Peterlin (FENE-P model). We present the results of three-dimensional simulations in a range of Ca which is broad enough to characterize all the three characteristic mechanisms of break-up in the confined T-junction, i.e. squeezing, dripping and jetting regimes. The various model parameters of the FENE-P constitutive equations, including the polymer relaxation time τP and the finite extensibility parameter L2, are changed to provide quantitative details on how the dynamics and break-up properties are affected by viscoelasticity. We will analyze cases with Droplet Viscoelasticity (DV), where viscoelastic properties are confined in the dispersed (d) phase, as well as cases with Matrix Viscoelasticity (MV), where viscoelastic properties are confined in the continuous (c) phase. Moderate flow-rate ratios Q ≈ O(1) of the two phases are considered in the present study. Overall, we find that the effects are more pronounced in the case with MV, as the flow driving the break-up process upstream of the emerging thread can be sensibly perturbed by the polymer stresses. PMID:26810396
Ferrari, Marco; Sorrentino, Roberto; Zarone, Fernando; Apicella, Davide; Aversa, Raffaella; Apicella, Antonio
2008-07-01
The study aimed at estimating the effect of insertion length of posts with composite restorations on stress and strain distributions in central incisors and surrounding bone. The typical, average geometries were generated in a FEA environment. Dentin was considered as an elastic orthotropic material, and periodontal ligament was coupled with nonlinear viscoelastic mechanical properties. The model was then validated with experimental data on displacement of incisors from published literature. Three post lengths were investigated in this study: root insertion of 5, 7, and 9 mm. For control, a sound incisor model was generated. Then, a tearing load of 50 N was applied to both sound tooth and simulation models. Post restorations did not seem to affect the strain distribution in bone when compared to the control. All simulated post restorations affected incisor biomechanics and reduced the root's deforming capability, while the composite crowns underwent a higher degree of deformation than the sound crown. No differences could be noticed in incisor stress and strain. As for the influence of post length, it was not shown to affect the biomechanics of restored teeth. PMID:18833761
Labouesse, Céline; Gabella, Chiara; Meister, Jean-Jacques; Vianay, Benoît; Verkhovsky, Alexander B.
2016-01-01
Actin-myosin filament bundles (stress fibers) are critical for tension generation and cell shape, but their mechanical properties are difficult to access. Here we propose a novel approach to probe individual peripheral stress fibers in living cells through a microsurgically generated opening in the cytoplasm. By applying large deformations with a soft cantilever we were able to fully characterize the mechanical response of the fibers and evaluate their tension, extensibility, elastic and viscous properties. PMID:27025817
Rheology of human blood plasma: viscoelastic versus Newtonian behavior.
Brust, M; Schaefer, C; Doerr, R; Pan, L; Garcia, M; Arratia, P E; Wagner, C
2013-02-15
We investigate the rheological characteristics of human blood plasma in shear and elongational flows. While we can confirm a Newtonian behavior in shear flow within experimental resolution, we find a viscoelastic behavior of blood plasma in the pure extensional flow of a capillary breakup rheometer. The influence of the viscoelasticity of blood plasma on capillary blood flow is tested in a microfluidic device with a contraction-expansion geometry. Differential pressure measurements revealed that the plasma has a pronounced flow resistance compared to that of pure water. Supplementary measurements indicate that the viscoelasticity of the plasma might even lead to viscoelastic instabilities under certain conditions. Our findings show that the viscoelastic properties of plasma should not be ignored in future studies on blood flow.
Inertial effects in the response of viscous and viscoelastic fluids.
Liverpool, T B; MacKintosh, F C
2005-11-11
We consider the effect of inertia on the high frequency response of a general linear viscoelastic material to local deformations. We calculate the displacement response and correlation functions for points separated by a distance r. The effects of inertia and incompressibility lead to anticorrelations in the correlation or response functions, which become more pronounced for more elastic materials. Furthermore, the stress propagation in viscoelastic media is no longer diffusive, as for simple liquids.
A detailed viscoelastic characterization of the P17 and adult rat brain.
Elkin, Benjamin S; Ilankovan, Ashok I; Morrison, Barclay
2011-11-01
Brain is a morphologically and mechanically heterogeneous organ. Although rat brain is commonly used as an experimental neurophysiological model for various in vivo biomechanical studies, little is known about its regional viscoelastic properties. To address this issue, we have generated viscoelastic mechanical property data for specific anatomical regions of the P17 and adult rat brain. These ages are commonly used in rat experimental models. We measured mechanical properties of both white and gray matter regions in coronal slices with a custom-designed microindentation device performing stress-relaxation indentations to 10% effective strain. Shear moduli calculated for short (100?ms), intermediate (1?sec), and long (20?sec) time points, ranged from ?1?kPa for short term moduli to ?0.4?kPa for long term moduli. Both age and anatomic region were significant factors affecting the time-dependent shear modulus. White matter regions and regions of the cerebellum were much more compliant than those of the hippocampus, cortex, and thalamus. Linear viscoelastic models (Prony series, continuous phase lag, and a power law model) were fit to the time-dependent shear modulus data. All models fit the data equally with no significant differences between them (F-test; p>0.05). The F-test was also used to statistically determine that a Prony series with three time-dependent parameters accurately fit the data with no added benefit from additional terms. The age- and region-dependent rat brain viscoelastic properties presented here will help inform future biomechanical models of the rat brain with specific and accurate regional mechanical property data. PMID:21341982
A robust algorithm for the contact of viscoelastic materials
NASA Astrophysics Data System (ADS)
Spinu, S.; Cerlinca, D.
2016-08-01
Existing solutions for the contact problem involving viscoelastic materials often require numerical differentiation and integration, as well as resolution of transcendental equations, which can raise convergence issues. The algorithm advanced in this paper can tackle the contact behaviour of the viscoelastic materials without any convergence problems, for arbitrary contact geometry, arbitrary loading programs and complex constitutive models of linear viscoelasticity. An updated algorithm for the elastic frictionless contact, coupled with a semi-analytical method for the computation of viscoelastic displacement, is employed to solve the viscoelastic contact problem at a series of small time increments. The number of equations in the linear system resulting from the geometrical condition of deformation is set by the number of cells in the contact area, which is a priori unknown. A trial-and-error approach is implemented, resulting in a series of linear systems which are solved on evolving contact areas, until static equilibrium equations and complementarity conditions are fully satisfied for every cell in the computational domain. At any iteration, cells with negative pressure are excluded from the contact area, while cells with negative gap (i.e. cells where the contacting bodies are predicted to overlap) are reincluded. The solution is found when pressure is stabilized in relation to the imposed normal load. This robust algorithm is expected to solve a large variety of contact problems involving viscoelastic materials.
Analysis of a delayed fracture criterion for lifetime prediction of viscoelastic polymer materials
NASA Astrophysics Data System (ADS)
Guedes, Rui Miranda
2012-08-01
In this work a multi-axial yield/failure model for viscoelastic/plastic materials is applied, which was developed by Naghdi and Murch (in J. Appl. Mech. 30:321-328, 1963) and later extended and refined by Crochet (in J. Appl. Mech. 33:327-334, 1966), to predict long-term creep rupture of polymers. The criterion defines a function, which depends on time, the viscoelastic properties and applied stress, to establish an empirical law with creep yield (fracture). In this work a linear relationship is proposed, defined as a time-dependent failure criterion, which can be applied for extrapolation purposes. A comparative analysis using energy-based failure criteria is performed. It is proved, for the polymers considered in this study, that the proposed time-dependent failure criterion holds for long times. Experimental data are used to illustrate the applicability of this time-dependent failure criterion.
Transient dynamics of a colloidal particle driven through a viscoelastic fluid
NASA Astrophysics Data System (ADS)
Ruben Gomez-Solano, Juan; Bechinger, Clemens
2015-10-01
We study the transient motion of a colloidal particle actively dragged by an optical trap through different viscoelastic fluids (wormlike micelles, polymer solutions, and entangled λ-phage DNA). We observe that, after sudden removal of the moving trap, the particle recoils due to the recovery of the deformed fluid microstructure. We find that the transient dynamics of the particle proceeds via a double-exponential relaxation, whose relaxation times remain independent of the initial particle velocity whereas their amplitudes strongly depend on it. While the fastest relaxation mirrors the viscous damping of the particle by the solvent, the slow relaxation results from the recovery of the strained viscoelastic matrix. We show that this transient information, which has no counterpart in Newtonian fluids, can be exploited to investigate linear and nonlinear rheological properties of the embedding fluid, thus providing a novel method to perform transient rheology at the micron-scale.
On the linear properties of the nonlinear radiative transfer problem
NASA Astrophysics Data System (ADS)
Pikichyan, H. V.
2016-11-01
In this report, we further expose the assertions made in nonlinear problem of reflection/transmission of radiation from a scattering/absorbing one-dimensional anisotropic medium of finite geometrical thickness, when both of its boundaries are illuminated by intense monochromatic radiative beams. The new conceptual element of well-defined, so-called, linear images is noteworthy. They admit a probabilistic interpretation. In the framework of nonlinear problem of reflection/transmission of radiation, we derive solution which is similar to linear case. That is, the solution is reduced to the linear combination of linear images. By virtue of the physical meaning, these functions describe the reflectivity and transmittance of the medium for a single photon or their beam of unit intensity, incident on one of the boundaries of the layer. Thereby the medium in real regime is still under the bilateral illumination by external exciting radiation of arbitrary intensity. To determine the linear images, we exploit three well known methods of (i) adding of layers, (ii) its limiting form, described by differential equations of invariant imbedding, and (iii) a transition to the, so-called, functional equations of the "Ambartsumyan's complete invariance".
McConney, Michael E.; Schaber, Clemens F.; Julian, Michael D.; Eberhardt, William C.; Humphrey, Joseph A.C.; Barth, Friedrich G.; Tsukruk, Vladimir V.
2009-01-01
The micromechanical properties of spider air flow hair sensilla (trichobothria) were characterized with nanometre resolution using surface force spectroscopy (SFS) under conditions of different constant deflection angular velocities (rad s−1) for hairs 900–950 μm long prior to shortening for measurement purposes. In the range of angular velocities examined (4×10−4−2.6×10−1 rad s−1), the torque T (Nm) resisting hair motion and its time rate of change (Nm s−1) were found to vary with deflection velocity according to power functions. In this range of angular velocities, the motion of the hair is most accurately captured by a three-parameter solid model, which numerically describes the properties of the hair suspension. A fit of the three-parameter model (3p) to the experimental data yielded the two torsional restoring parameters, S 3p=2.91×10−11 Nm rad−1 and =2.77×10−11 Nm rad−1 and the damping parameter R 3p=1.46×10−12 Nm s rad−1. For angular velocities larger than 0.05 rad s−1, which are common under natural conditions, a more accurate angular momentum equation was found to be given by a two-parameter Kelvin solid model. For this case, the multiple regression fit yielded S 2p=4.89×10−11 Nm rad−1 and R 2p=2.83×10−14 Nm s rad−1 for the model parameters. While the two-parameter model has been used extensively in earlier work primarily at high hair angular velocities, to correctly capture the motion of the hair at both low and high angular velocities it is necessary to employ the three-parameter model. It is suggested that the viscoelastic mechanical properties of the hair suspension work to promote the phasic response behaviour of the sensilla. PMID:19091682
Shin, Duk; Koike, Yasuharu
2013-01-01
To understand the mechanism of neural motor control, it is important to clarify how the central nervous system organizes the coordination of redundant muscles. Previous studies suggested that muscle activity for step-tracking wrist movements are optimized so as to reduce total effort or end-point variance under neural noise. However, since the muscle dynamics were assumed as a simple linear system, some characteristic patterns of experimental EMG were not seen in the simulated muscle activity of the previous studies. The biological muscle is known to have dynamic properties in which its elasticity and viscosity depend on activation level. The motor control system is supposed to consider the viscoelasticity of the muscles when generating motor command signals. In this study, we present a computational motor control model that can control a musculoskeletal system with nonlinear dynamics. We applied the model to step-tracking wrist movements actuated by five muscles with dynamic viscoelastic properties. To solve the motor redundancy, we designed the control model to generate motor commands that maximize end-point accuracy under signal-dependent noise, while minimizing the squared sum of them. Here, we demonstrate that the muscle activity simulated by our model exhibits spatiotemporal features of experimentally observed muscle activity of human and nonhuman primates. In addition, we show that the movement trajectories resulting from the simulated muscle activity resemble experimentally observed trajectories. These results suggest that, by utilizing inherent viscoelastic properties of the muscles, the neural system may optimize muscle activity to improve motor performance. PMID:23324321
Parametric vibrations and stability of viscoelastic shells
NASA Astrophysics Data System (ADS)
Ilyasov, M. H.
2010-05-01
The problem of dynamic stability of viscoelastic extremely shallow and circular cylindrical shells with any hereditary properties, including time-dependence of Poisson’s ratio, are reduced to the investigation of stability of the zero solution of an ordinary integro-differential equation with variable coefficients. Using the Laplace integral transform, an integro-differential equation is reduced to the new integro-differential one of which the main part coincides with the damped Hill equation and the integral part is proportional to the product of two small parameters. Changing this equation for the system of two linear equations of the first order and using the averaging method, the monodromy matrix of the obtained system is constructed. Considering the absolute value of the eigen-values of monodromy matrix is greater than unit, the condition for instability of zero solution is obtained in the three-dimensional space of parameters corresponding to the frequency, viscosity and amplitude of external action. Analysis of form and size of instability domains is carried out.
Frequency Response of Synthetic Vocal Fold Models with Linear and Nonlinear Material Properties
ERIC Educational Resources Information Center
Shaw, Stephanie M.; Thomson, Scott L.; Dromey, Christopher; Smith, Simeon
2012-01-01
Purpose: The purpose of this study was to create synthetic vocal fold models with nonlinear stress-strain properties and to investigate the effect of linear versus nonlinear material properties on fundamental frequency (F[subscript 0]) during anterior-posterior stretching. Method: Three materially linear and 3 materially nonlinear models were…
Lembré, Pierre; Di Martino, Patrick; Vendrely, Charlotte
2014-01-01
The bacterial biofilm is a complex environment of cells, which secrete a matrix made of various components, mainly polysaccharides and proteins. An understanding of the precise role of these components in the stability and dynamics of biofilm architecture would be a great advantage for the improvement of anti-biofilm strategies. Here, artificial biofilm matrices made of polysaccharides and auto-assembled peptides were designed, and the influence of bacterial amyloid proteins on the mechanical properties of the biofilm matrix was studied. The model polysaccharides methylcellulose and alginate and peptides derived from the amyloid proteins curli and FapC found in biofilms of Enterobacteriaceae and Pseudomonas, respectively, were used. Rheological measurements showed that the amyloid peptides do not prevent the gelation of the polysaccharides but influence deformation of the matrices under shear stress and modify the gel elastic response. Hence the secretion of amyloids could be for the biofilm a way of adapting to environmental changes. PMID:24592895
Park, Hyung-seok; Gong, Myoung-Seon; Park, Jeong-Hui; Moon, Sung-Il; Wall, Ivan B; Kim, Hae-Won; Lee, Jae Ho; Knowles, Jonathan C
2013-11-01
As a way to modify both the physical and biological properties of a highly elastic and degradable polyurethane (PU), silk fibroin (SF) was blended with the PU at differing ratios. With increasing SF content, the tensile strength decreased as did the strain at break; the stiffness increased to around 35 MPa for the highest silk content. C2C12 (a mouse myoblast cell line) cells were used for in vitro experiments and showed significantly improved cell responses with increasing SF content. With increasing SF content the number of non-adherent cells was reduced at both 4 and 8h compared to the sample with the lowest SF content. In addition, muscle marker genes were upregulated compared to the sample containing no SF, and in particular sarcomeric actin and α-actin. PMID:23892141
Viscoelastic coupling of nanoelectromechanical resonators.
Simonson, Robert Joseph; Staton, Alan W.
2009-09-01
This report summarizes work to date on a new collaboration between Sandia National Laboratories and the California Institute of Technology (Caltech) to utilize nanoelectromechanical resonators designed at Caltech as platforms to measure the mechanical properties of polymeric materials at length scales on the order of 10-50 nm. Caltech has succeeded in reproducibly building cantilever resonators having major dimensions on the order of 2-5 microns. These devices are fabricated in pairs, with free ends separated by reproducible gaps having dimensions on the order of 10-50 nm. By controlled placement of materials that bridge the very small gap between resonators, the mechanical devices become coupled through the test material, and the transmission of energy between the devices can be monitored. This should allow for measurements of viscoelastic properties of polymeric materials at high frequency over short distances. Our work to date has been directed toward establishing this measurement capability at Sandia.
Polarization properties of linearly polarized parabolic scaling Bessel beams
NASA Astrophysics Data System (ADS)
Guo, Mengwen; Zhao, Daomu
2016-10-01
The intensity profiles for the dominant polarization, cross polarization, and longitudinal components of modified parabolic scaling Bessel beams with linear polarization are investigated theoretically. The transverse intensity distributions of the three electric components are intimately connected to the topological charge. In particular, the intensity patterns of the cross polarization and longitudinal components near the apodization plane reflect the sign of the topological charge.
Martiel, Isabelle; Sagalowicz, Laurent; Mezzenga, Raffaele
2014-09-01
Upon the addition of minute quantities of water into a phosphatidylcholine (PC) solution in certain organic solvents, PC micelles elongate into giant reverse wormlike micelles that entangle and form highly viscous microemulsions, called lecithin organogels. We investigated the microrheological properties of concentrated PC-cyclohexane reverse wormlike micellar systems by diffusive wave spectroscopy (DWS) in apolar medium, combined with bulk shear rheology. We applied DWS to our oil-continuous system by using hydrophobic poly(hydroxystearic acid)-grafted PMMA particles as monodisperse tracer particles. Relevant parameters such as the micellar scission energy and persistence length were extracted from the microrheology data and interpreted according to the sphere-to-rod-to-sphere structural transition. On the basis of these quantities, we calculated the bending and saddle-splay moduli of the PC-covered water-cyclohexane interface. This approach represents a new method for the quantitative estimation of these fundamental parameters, which are thought to underpin the self-assembly of surfactants.
NASA Astrophysics Data System (ADS)
Kimble, L. D.; Fakirov, S.; Bhattacharyya, D.
2015-05-01
Microfibrillar composites (MFCs) from petrochemical-derived polymers have been investigated for several years and the technique can result in significant improvements in mechanical properties when compared with the neat matrix material of the respective composite. The current work applies the technique to biodegradable, biocompatible polymers for potential applications in bioabsorbable medical devices. MFCs were prepared from melt blended poly(L-lactic acid) (PLLA) and poly(glycolic acid) (PGA) via cold drawing then compression molding of extruded yarn. These MFCs were shown to have higher Young's moduli than that of neat PLLA but for load-bearing applications the creep characteristics are of interest. The MFC sheets resulting from compression molding were subjected to tensile relaxation tests at 37°C in the fiber orientation direction. Specimens were also tested via dynamic mechanical thermal analysis (DMTA). Neat PLLA specimens were subjected to the same tests for comparison. Results indicate that at 37°C PLLA/PGA MFCs exhibit lower creep resistance than that of neat PLLA due to the more rapid relaxation of stress observed. DMTA results elucidate the loss modulus changes in PLLA/PGA MFCs which occur as the material approaches the glass transition temperature of PGA (˜45°C).
Benhamou, Karima; Dufresne, Alain; Magnin, Albert; Mortha, Gérard; Kaddami, Hamid
2014-01-01
The main objective of the present study was to control and optimize the preparation of nanofibrillated cellulose (NFC) from the date palm tree by monitoring the oxidation time (degree of oxidation) of the pristine cellulose and the number of cycles through the homogenizer. The oxidation was monitored by TEMPO (1-oxo-2,2,6,6-tétraméthylpipyridine 1-oxyle) mediated oxidation. Evidence of the successful isolation of NFC was given by FE-SEM observation revealing fibrils with a width in the range 20-30nm, depending of the oxidation time. The evolution of the transparency of the aqueous NFC suspension and carboxylic content according to the degree of oxidation and number of cycles were also analyzed by UV-vis transmittance, Fourier-transform infrared spectroscopy (FT-IR), conductimetry, and X-ray diffraction analysis. A significant NFC length reduction occurred during the TEMPO-mediated oxidation. The rheological properties of NFC suspensions were characterized as function of the oxidation time. Dynamic rheology showed that the aqueous suspension behavior changed from liquid to gel depending on the concentration. The highest concentration studied was 1wt% and the modulus reached 1MPa which was higher than for non-oxidized NFC. An explanation of the gel structure evolution with the oxidation time applied to the NFC (NFC length) was proposed. The gel structure evolves from an entanglement-governed gel structure to an immobilized water molecule-governed one.
Gupta, Simerdeep Singh; Solanki, Nayan; Serajuddin, Abu T M
2016-02-01
Most cellulosic polymers cannot be used as carriers for preparing solid dispersion of drugs by hot melt extrusion (HME) due to their high melt viscosity and thermal degradation at high processing temperatures. Three HME-grade hydroxypropyl methylcelluloses, namely Affinisol™ HPMC HME 15 cP, Affinisol™ HPMC HME 100 cP, and Affinisol™ HPMC HME 4 M, have recently been introduced by The Dow Chemical Co. to enable the preparation of solid dispersion at lower and more acceptable processing temperatures. In the present investigation, physicochemical properties of the new polymers relevant to HME were determined and compared with that of Kollidon(®) VA 64. Powder X-ray diffraction (PXRD), modulated differential scanning calorimetry (mDSC), thermogravimetric analysis (TGA), moisture sorption, rheology, and torque analysis by melt extrusion were applied. PXRD and mDSC showed that the Affinisol™ polymers were amorphous in nature. According to TGA, the onset of degradation for all polymers was >220°C. The Affinisol™ polymers exhibited less hygroscopicity than Kollidon(®) VA 64 and another HPMC polymer, Methocel™ K100LV. The complex viscosity profiles of the Affinisol™ polymers as a function of temperature were similar. The viscosity of the Affinisol™ polymers was highly sensitive to the shear rate applied, and unlike Kollidon(®) VA 64, the viscosity decreased drastically when the angular frequency was increased. Because of the very high shear rate encountered during melt extrusion, Affinisol™ polymers showed capability of being extruded at larger windows of processing temperatures as compared to that of Kollidon(®) VA 64. PMID:26511936
Gupta, Simerdeep Singh; Solanki, Nayan; Serajuddin, Abu T M
2016-02-01
Most cellulosic polymers cannot be used as carriers for preparing solid dispersion of drugs by hot melt extrusion (HME) due to their high melt viscosity and thermal degradation at high processing temperatures. Three HME-grade hydroxypropyl methylcelluloses, namely Affinisol™ HPMC HME 15 cP, Affinisol™ HPMC HME 100 cP, and Affinisol™ HPMC HME 4 M, have recently been introduced by The Dow Chemical Co. to enable the preparation of solid dispersion at lower and more acceptable processing temperatures. In the present investigation, physicochemical properties of the new polymers relevant to HME were determined and compared with that of Kollidon(®) VA 64. Powder X-ray diffraction (PXRD), modulated differential scanning calorimetry (mDSC), thermogravimetric analysis (TGA), moisture sorption, rheology, and torque analysis by melt extrusion were applied. PXRD and mDSC showed that the Affinisol™ polymers were amorphous in nature. According to TGA, the onset of degradation for all polymers was >220°C. The Affinisol™ polymers exhibited less hygroscopicity than Kollidon(®) VA 64 and another HPMC polymer, Methocel™ K100LV. The complex viscosity profiles of the Affinisol™ polymers as a function of temperature were similar. The viscosity of the Affinisol™ polymers was highly sensitive to the shear rate applied, and unlike Kollidon(®) VA 64, the viscosity decreased drastically when the angular frequency was increased. Because of the very high shear rate encountered during melt extrusion, Affinisol™ polymers showed capability of being extruded at larger windows of processing temperatures as compared to that of Kollidon(®) VA 64.
Nonlinear Viscoelastic Mechanics of Cross-linked Rubbers
NASA Technical Reports Server (NTRS)
Freed, Alan D.; Leonov, Arkady I.; Gray, Hugh R. (Technical Monitor)
2002-01-01
The paper develops a general theory for finite rubber viscoelasticity, and specifies it in the form, convenient for solving problems important for rubber, tire and space industries. Based on the quasi-linear approach of non-equilibrium thermodynamics, a general nonlinear theory has been developed for arbitrary nonisothermal deformations of viscoelastic solids. In this theory, the constitutive equations are presented as the sum of known equilibrium (rubber elastic) and non-equilibrium (liquid polymer viscoelastic) terms. These equations are then simplified using several modeling arguments. Stability constraints for the proposed constitutive equations are also discussed. It is shown that only strong ellipticity criteria are applicable for assessing stability of the equations governing viscoelastic solids.
Afterslip Distribution of Large Earthquakes Using Viscoelastic Media
NASA Astrophysics Data System (ADS)
Sato, T.; Higuchi, H.
2009-12-01
One of important parameters in simulations of earthquake generation is frictional properties of faults. To investigate the frictional properties, many authors studied coseismic slip and afterslip distribution of large plate interface earthquakes using coseismic and post seismic surface deformation by GPS data. Most of these studies used elastic media to get afterslip distribution. However, the effect of viscoelastic relaxation at the asthenosphere is important on post seismic surface deformation (Matsu’ura and Sato, GJI, 1989; Sato and Matsu’ura, GJI, 1992). Therefore, the studies using elastic media did not estimate correct afterslip distribution because they forced the cause of surface deformation on only afterslips at plate interface. We estimate afterslip distribution of large interplate earthquakes using viscoelastic media. We consider not only viscoelastic responses of coseismic slip but also viscoelastic responses of afterslips. Because many studies suggested that the magnitude of afterslips was comparable to that of coseismic slip, viscoelastic responses of afterslips can not be negligible. Therefore, surface displacement data include viscoelastic response of coseismic slip, viscoelastic response of afterslips which occurred just after coseismic period to just before the present, and elastic response of the present afterslip. We estimate afterslip distribution for the 2003 Tokachi-oki earthquake, Hokkaido, Japan using GPS data by GSI, Japan. We use CAMP model (Hashimoto et al, PAGEOPH, 2004) as a plate interface between the Pacific plate and the North American plate. The viscoelastic results show clearer that afterslips distribute on areaes where the coseismic slip does not occur. The viscoelastic results also show that the afterslips concentrate deeper parts of the plate interface at the eastern adjoining area of the 2003 Tokachi-oki earthquake.
Rheological regional properties of brain tissue studied under cyclic creep/ recovery shear stresses
NASA Astrophysics Data System (ADS)
Boudjema, F.; Lounis, M.; Khelidj, B.; Bessai, N.
2015-04-01
The rheological properties of brain tissue were studied by repeated creep-recovery shear tests under static conditions for different regions. Corpus callosum CC, Thalamus Th and Corona radiata CR. Non-linear viscoelastic model was also proposed to characterize the transient/steady states of shear creep results. From the creep-recovery data it was obvious that the brain tissues show high regional anisotropy. However. the both samples exhibit fluid viscoelastic properties in the first shear stress cycle of 100 Pa, while this behaviour evolutes to solid viscoelastic with cyclic effect.
Viscoelasticity evaluation of rubber by surface reflection of supersonic wave.
Omata, Nobuaki; Suga, Takahiro; Furusawa, Hirokazu; Urabe, Shinichi; Kondo, Takeru; Ni, Qing-Qing
2006-12-22
The main characteristic of rubber is a viscoelasticity. So it is important to research the characteristic of the viscoelasticity of the high frequency band for the friction between a rubber material and the hard one with roughness, for instance, the tire and the road. As for the measurement of the viscoelasticity of rubber, DMA (dynamic mechanical analysis) is general. However, some problems are pointed out to the measurement of the high frequency band by DMA. Then, we evaluated the viscoelasticity characteristic by the supersonic wave measurement. However, attenuation of rubber is large, and when the viscoelasticity is measured by the supersonic wave therefore, it is inconvenient and limited in a past method by means of bottom reflection. In this report, we tried the viscoelasticity evaluation by the method of using complex surface reflection coefficient and we compared with the friction coefficient under wide-range friction velocity. As a result, some relationships had been found for two properties. We report the result that character of viscoelasticity of rubber was comparable to friction coefficient.
Dynamic wetting of viscoelastic droplets
NASA Astrophysics Data System (ADS)
Wang, Yuli; Minh, Do-Quang; Amberg, Gustav
2015-10-01
We conduct numerical experiments on spreading of viscoelastic droplets on a flat surface. Our work considers a Giesekus fluid characterized by a shear-thinning viscosity and an Oldroyd-B fluid, which is close to a Boger fluid with constant viscosity. Our results qualitatively agree with experimental observations in that both shear thinning and elasticity enhances contact line motion, and that the contact line motion of the Boger fluid obeys the Tanner-Voinov-Hoffman relation. Excluding inertia, the spreading speed shows strong dependence on rheological properties, such as the viscosity ratio between the solvent and the polymer suspension, and the polymeric relaxation time. We also discuss how elasticity can affect contact line motion. The molecular migration theory proposed in the literature is not able to explain the agreement between our simulations and experimental results.
Dynamic wetting of viscoelastic droplets.
Wang, Yuli; Minh, Do-Quang; Amberg, Gustav
2015-10-01
We conduct numerical experiments on spreading of viscoelastic droplets on a flat surface. Our work considers a Giesekus fluid characterized by a shear-thinning viscosity and an Oldroyd-B fluid, which is close to a Boger fluid with constant viscosity. Our results qualitatively agree with experimental observations in that both shear thinning and elasticity enhances contact line motion, and that the contact line motion of the Boger fluid obeys the Tanner-Voinov-Hoffman relation. Excluding inertia, the spreading speed shows strong dependence on rheological properties, such as the viscosity ratio between the solvent and the polymer suspension, and the polymeric relaxation time. We also discuss how elasticity can affect contact line motion. The molecular migration theory proposed in the literature is not able to explain the agreement between our simulations and experimental results. PMID:26565327
A Viscoelastic Constitutive Law For FRP Materials
NASA Astrophysics Data System (ADS)
Ascione, Luigi; Berardi, Valentino Paolo; D'Aponte, Anna
2011-09-01
The present study deals with the long-term behavior of fiber-reinforced polymer (FRP) materials in civil engineering. More specifically, the authors propose a mechanical model capable of predicting the viscoelastic behavior of FRP laminates in the field of linear viscoelasticity, starting from that of the matrix material and fiber. The model is closely connected with the low FRP stress levels in civil engineering applications. The model is based on a micromechanical approach which assumes that there is a perfect adhesion between the matrix and fiber. The long-term behavior of the phases is described through a four-parameter rheological law. A validation of the model has also been developed by matching the predicted behavior with an experimental one available in the literature.
PROPERTIES OF INTERSTELLAR TURBULENCE FROM GRADIENTS OF LINEAR POLARIZATION MAPS
Burkhart, Blakesley; Lazarian, A.; Gaensler, B. M.
2012-04-20
Faraday rotation of linearly polarized radio signals provides a very sensitive probe of fluctuations in the interstellar magnetic field and ionized gas density resulting from magnetohydrodynamic (MHD) turbulence. We used a set of statistical tools to analyze images of the spatial gradient of linearly polarized radio emission (|{nabla}P|) for both observational data from a test image of the Southern Galactic Plane Survey (SGPS) and isothermal three-dimensional simulations of MHD turbulence. Visually, in both observations and simulations, a complex network of filamentary structures is seen. Our analysis shows that the filaments in |{nabla}P| can be produced both by interacting shocks and random fluctuations characterizing the non-differentiable field of MHD turbulence. The latter dominates for subsonic turbulence, while the former is only present in supersonic turbulence. We show that supersonic and subsonic turbulence exhibit different distributions as well as different morphologies in the maps of |{nabla}P|. Particularly, filaments produced by shocks show a characteristic 'double jump' profile at the sites of shock fronts resulting from delta function-like increases in the density and/or magnetic field, while those produced by subsonic turbulence show a single jump profile. In order to quantitatively characterize these differences, we use the topology tool known as the genus curve as well as the probability distribution function moments of the image distribution. We find that higher values for the moments correspond to cases of |{nabla}P| with larger sonic Mach numbers. The genus analysis of the supersonic simulations of |{nabla}P| reveals a 'swiss cheese' topology, while the subsonic cases have characteristics of a 'clump' topology. Based on the analysis of the genus and the higher order moments, the SGPS test region data have a distribution and morphology that match subsonic- to transonic-type turbulence, which confirms what is now expected for the warm ionized
Properties of Interstellar Turbulence from Gradients of Linear Polarization Maps
NASA Astrophysics Data System (ADS)
Burkhart, Blakesley; Lazarian, A.; Gaensler, B. M.
2012-04-01
Faraday rotation of linearly polarized radio signals provides a very sensitive probe of fluctuations in the interstellar magnetic field and ionized gas density resulting from magnetohydrodynamic (MHD) turbulence. We used a set of statistical tools to analyze images of the spatial gradient of linearly polarized radio emission (|∇P|) for both observational data from a test image of the Southern Galactic Plane Survey (SGPS) and isothermal three-dimensional simulations of MHD turbulence. Visually, in both observations and simulations, a complex network of filamentary structures is seen. Our analysis shows that the filaments in |∇P| can be produced both by interacting shocks and random fluctuations characterizing the non-differentiable field of MHD turbulence. The latter dominates for subsonic turbulence, while the former is only present in supersonic turbulence. We show that supersonic and subsonic turbulence exhibit different distributions as well as different morphologies in the maps of |∇P|. Particularly, filaments produced by shocks show a characteristic "double jump" profile at the sites of shock fronts resulting from delta function-like increases in the density and/or magnetic field, while those produced by subsonic turbulence show a single jump profile. In order to quantitatively characterize these differences, we use the topology tool known as the genus curve as well as the probability distribution function moments of the image distribution. We find that higher values for the moments correspond to cases of |∇P| with larger sonic Mach numbers. The genus analysis of the supersonic simulations of |∇P| reveals a "swiss cheese" topology, while the subsonic cases have characteristics of a "clump" topology. Based on the analysis of the genus and the higher order moments, the SGPS test region data have a distribution and morphology that match subsonic- to transonic-type turbulence, which confirms what is now expected for the warm ionized medium.
Modeling Electrically Active Viscoelastic Membranes
Roy, Sitikantha; Brownell, William E.; Spector, Alexander A.
2012-01-01
The membrane protein prestin is native to the cochlear outer hair cell that is crucial to the ear's amplification and frequency selectivity throughout the whole acoustic frequency range. The outer hair cell exhibits interrelated dimensional changes, force generation, and electric charge transfer. Cells transfected with prestin acquire unique active properties similar to those in the native cell that have also been useful in understanding the process. Here we propose a model describing the major electromechanical features of such active membranes. The model derived from thermodynamic principles is in the form of integral relationships between the history of voltage and membrane resultants as independent variables and the charge density and strains as dependent variables. The proposed model is applied to the analysis of an active force produced by the outer hair cell in response to a harmonic electric field. Our analysis reveals the mechanism of the outer hair cell active (isometric) force having an almost constant amplitude and phase up to 80 kHz. We found that the frequency-invariance of the force is a result of interplay between the electrical filtering associated with prestin and power law viscoelasticity of the surrounding membrane. Paradoxically, the membrane viscoelasticity boosts the force balancing the electrical filtering effect. We also consider various modes of electromechanical coupling in membrane with prestin associated with mechanical perturbations in the cell. We consider pressure or strains applied step-wise or at a constant rate and compute the time course of the resulting electric charge. The results obtained here are important for the analysis of electromechanical properties of membranes, cells, and biological materials as well as for a better understanding of the mechanism of hearing and the role of the protein prestin in this mechanism. PMID:22701528
Ciambella, J; Paolone, A; Vidoli, S
2014-09-01
We report about the experimental identification of viscoelastic constitutive models for frequencies ranging within 0-10Hz. Dynamic moduli data are fitted forseveral materials of interest to medical applications: liver tissue (Chatelin et al., 2011), bioadhesive gel (Andrews et al., 2005), spleen tissue (Nicolle et al., 2012) and synthetic elastomer (Osanaiye, 1996). These materials actually represent a rather wide class of soft viscoelastic materials which are usually subjected to low frequencies deformations. We also provide prescriptions for the correct extrapolation of the material behavior at higher frequencies. Indeed, while experimental tests are more easily carried out at low frequency, the identified viscoelastic models are often used outside the frequency range of the actual test. We consider two different classes of models according to their relaxation function: Debye models, whose kernel decays exponentially fast, and fractional models, including Cole-Cole, Davidson-Cole, Nutting and Havriliak-Negami, characterized by a slower decay rate of the material memory. Candidate constitutive models are hence rated according to the accurateness of the identification and to their robustness to extrapolation. It is shown that all kernels whose decay rate is too fast lead to a poor fitting and high errors when the material behavior is extrapolated to broader frequency ranges.
NASA Astrophysics Data System (ADS)
Grizzuti, Nino; Pasquino, Rossana
2008-07-01
The rheology of non-Brownian, inertialess rigid spheres suspended in viscoelastic fluids was investigated in the dilute and semi-dilute regimes (volume fractions up to 10%), where interparticle interactions become increasingly relevant. PMMA spherical particles were suspended in viscoelastic Polydimethylsiloxanes (PDMS). A Newtonian fluid (Polyisobutilene, PIB) was also used as a reference system. As expected, both the viscosity and the viscoelastic moduli increased with increasing solid volume fraction. The rheological parameters showed a simple scaling behaviour when their normalized values (with respect to the pure fluid) were considered. Viscosity and moduli were found to be independent upon shear rate and frequency, respectively. Following Batchelor's approach for non-dilute Newtonian suspensions, a second order polynomial dependency for the rheological properties was assumed. While the Newtonian reference fluid was found to obey well Batchelor's theoretical predictions, the viscoelastic suspensions showed more pronounced deviations from the linear dilute behavior, resulting in a second order polynomial coefficient substantially larger than that predicted by Batchelor for Newtonian systems. It was also found that the same concentration dependence was followed by both elastic and loss modulus.
Viscoelastic Mapping of Living Cell Interiors
NASA Astrophysics Data System (ADS)
Heinrich, Doris; Sackmann, Erich; Koehler, Jana; Gerisch, Guenther
2004-03-01
We performed spatially resolved mapping of the viscoelastic properties of the cytoplasm of living cell interiors. A magnetic tweezer was applied as a local probe for the investigation of active and passive transport inside the slime mold cells Dictyostelium discoideum. Fluorescence labeled components, i.e. the microtubulins, the endoplasmatic reticulum or the core, allow for the determination of the interaction of the magnetic probes with the cytoplasm. By comparing the trajectories of the magnetic beads in the presence of an external magnetic force and in the absence of an external force, we can measure the viscosity at any given position within the cell. These experiments show that the cytoplasm consists of soft pathways (yield stress less or equal 10 Pa) and hard pathways (yield stress less or equal 500 Pa). Selective actin, myosin II or microtubulin network removal in the living cells allows for the determination of the influence of these cell parts on the viscoelastic properties.
Linear and NLO properties of an organic single crystal
NASA Astrophysics Data System (ADS)
Rajesh Kumara, P. C.; Ravindrachary, V.; Janardhana, K.; Poojary, Boja; Manjunath, K. B.; Umesh, G.
2012-06-01
Organic compound of 1-(4-methoxyphenyl)-3-(2-methoxy 5-bromophenyl)prop-2-en-1-one [MMBPP] with molecular formula C16H11BrO3 was synthesized using Schmidt condensation method. A FT-IR spectrum was recorded to identify the various functional groups present in the compound. The single crystals were grown using slow evaporation solution growth technique. The high quality transparent crystals up to a size 10×7×5 mm3 are obtained with in fifteen days. UV-Visible spectrum reveals that the crystal is transparent in the entire visible region. The single crystal XRD study shows that the compound crystallizes in orthorhombic crystal system with a space group P212121 and the observed cell parameters are a =7.6095(13) Å, b =13.049(2) Å, c = 15.525(3) Å, Volume 1541.6(5) Å3. The third order Nonlinearity was confirmed by Z-scan technique and non-linear parameters were determined.
Linear center-of-mass dynamics emerge from non-linear leg-spring properties in human hopping.
Riese, Sebastian; Seyfarth, Andre; Grimmer, Sten
2013-09-01
Given the almost linear relationship between ground-reaction force and leg length, bouncy gaits are commonly described using spring-mass models with constant leg-spring parameters. In biological systems, however, spring-like properties of limbs may change over time. Therefore, it was investigated how much variation of leg-spring parameters is present during vertical human hopping. In order to do so, rest-length and stiffness profiles were estimated from ground-reaction forces and center-of-mass dynamics measured in human hopping. Trials included five hopping frequencies ranging from 1.2 to 3.6 Hz. Results show that, even though stiffness and rest length vary during stance, for most frequencies the center-of-mass dynamics still resemble those of a linear spring-mass hopper. Rest-length and stiffness profiles differ for slow and fast hopping. Furthermore, at 1.2 Hz two distinct control schemes were observed.
Wang, Yuxiang; Marshall, Kara L; Baba, Yoshichika; Lumpkin, Ellen A; Gerling, Gregory J
2015-01-01
Although the skin's mechanical properties are well characterized in tension, little work has been done in compression. Here, the viscoelastic properties of a population of mouse skin specimens (139 samples from 36 mice, aged 5 to 34 weeks) were characterized upon varying specimen thickness, as well as strain level and rate. Over the population, we observed the skin's viscoelasticity to be quite variable, yet found systematic correlation of residual stress ratio with skin thickness and strain, and of relaxation time constants with strain rates. In particular, as specimen thickness ranged from 211 to 671 μm, we observed significant variation in both quasi-linear viscoelasticity (QLV) parameters, the relaxation time constant (τ1 = 0.19 ± 0.10 s) and steady-state residual stress ratio (G∞ = 0.28 ± 0.13). Moreover, when τ1 was decoupled and fixed, we observed that G∞ positively correlated with skin thickness. Second, as steady-state stretch was increased (λ∞ from 0.22 to 0.81), we observed significant variation in both QLV parameters (τ1 = 0.26 ± 0.14 s, G∞ = 0.47 ± 0.17), and when τ1 was fixed, G∞ positively correlated with stretch level. Third, as strain rate was increased from 0.06 to 22.88 s-1, the median time constant τ1 varied from 1.90 to 0.31 s, and thereby negatively correlated with strain rate. These findings indicate that the natural range of specimen thickness, as well as experimental controls of compression level and rate, significantly influence measurements of skin viscoelasticity.
Wang, Yuxiang; Marshall, Kara L.; Baba, Yoshichika; Lumpkin, Ellen A.; Gerling, Gregory J.
2015-01-01
Although the skin’s mechanical properties are well characterized in tension, little work has been done in compression. Here, the viscoelastic properties of a population of mouse skin specimens (139 samples from 36 mice, aged 5 to 34 weeks) were characterized upon varying specimen thickness, as well as strain level and rate. Over the population, we observed the skin’s viscoelasticity to be quite variable, yet found systematic correlation of residual stress ratio with skin thickness and strain, and of relaxation time constants with strain rates. In particular, as specimen thickness ranged from 211 to 671 μm, we observed significant variation in both quasi-linear viscoelasticity (QLV) parameters, the relaxation time constant (τ1 = 0.19 ± 0.10 s) and steady-state residual stress ratio (G∞ = 0.28 ± 0.13). Moreover, when τ1 was decoupled and fixed, we observed that G∞ positively correlated with skin thickness. Second, as steady-state stretch was increased (λ∞ from 0.22 to 0.81), we observed significant variation in both QLV parameters (τ1 = 0.26 ± 0.14 s, G∞ = 0.47 ± 0.17), and when τ1 was fixed, G∞ positively correlated with stretch level. Third, as strain rate was increased from 0.06 to 22.88 s−1, the median time constant τ1 varied from 1.90 to 0.31 s, and thereby negatively correlated with strain rate. These findings indicate that the natural range of specimen thickness, as well as experimental controls of compression level and rate, significantly influence measurements of skin viscoelasticity. PMID:25803703
Dynamic testing of regional viscoelastic behavior of canine sclera
Palko, Joel R.; Pan, Xueliang; Liu, Jun
2011-01-01
Intraocular pressure (IOP) fluctuations have gained recent clinical interest and thus warrant an understanding of how the sclera responds to dynamic mechanical insults. The objective of this study was to characterize the regional dynamic viscoelastic properties of canine sclera under physiological cyclic loadings. Scleral strips were excised from the anterior, equatorial, and posterior sclera in ten canine eyes. The dimensions of each strip were measured using a high resolution ultrasound imaging system. The strips were tested in a humidity chamber at approximately 37°C using a Rheometrics Systems Analyzer. A cyclic strain input (0.25%, 1 Hz) was applied to the strips, superimposed upon pre-stresses corresponding to an IOP of 15, 25, and 45 mmHg. The cyclic stress output was recorded and the dynamic properties were calculated based on linear viscoelasticity. Uniaxial tensile tests were also performed on the same samples and the results were compared to those reported for human eyes. The results showed that the sclera’s resistance to dynamic loading increased significantly while the damping capability decreased significantly with increasing pre-stresses for all regions of sclera (P<0.001). Anterior sclera appeared to have a significantly higher damping capability than equatorial and posterior sclera (P=0.003 and 0.018, respectively). The secant modulus from uniaxial tensile tests showed a decreasing trend from anterior to posterior sclera, displaying a similar pattern as in the human eye. In conclusion, all scleral regions in the canine eyes exhibited an increased ability to resist and a decreased ability to dampen cyclic stress insults at increasing prestress (i.e., increasing steady-state IOP). The regional variation of the dynamic properties differed from those of uniaxial tensile tests. Dynamic testing may provide useful information to better understand the mechanical behavior of the sclera in response to dynamic IOP. PMID:21983041
Ferromagnetic viscoelastic liquid crystalline materials
NASA Astrophysics Data System (ADS)
Schlesier, Cristina; Shibaev, Petr; McDonald, Scott
2012-02-01
Novel ferromagnetic liquid crystalline materials were designed by mixing ferromagnetic nanoparticles with glass forming oligomers and low molar mass liquid crystals. The matrix in which nanoparticles are embedded is highly viscous that reduces aggregation of nanoparticles and stabilizes the whole composition. Mechanical and optical properties of the composite material are studied in the broad range of nanoparticle concentrations. The mechanical properties of the viscoelastic composite material resemble those of chemically crosslinked elastomers (elasticity and reversibility of deformations). The optical properties of ferromagnetic cholesteric materials are discussed in detail. It is shown that application of magnetic field leads to the shift of the selective reflection band of the cholesteric material and dramatically change its color. Theoretical model is suggested to account for the observed effects; physical properties of the novel materials and liquid crystalline elastomers are compared and discussed. [1] P.V. Shibaev, C. Schlesier, R. Uhrlass, S. Woodward, E. Hanelt, Liquid Crystals, 37, 1601 (2010) [2] P.V. Shibaev, R. Uhrlass, S. Woodward, C. Schlesier, Md R. Ali, E. Hanelt, Liquid Crystals, 37, 587 (2010)
NASA Astrophysics Data System (ADS)
Haldar, Samadyuti
2016-04-01
The stability of thin electrically conducting viscoelastic fluid film flowing down on a non-conducting inclined plane in the presence of electromagnetic field is investigated under induction-free approximation. Surface evolution equation is derived by long-wave expansion method. The stabilizing role of Hartman number M (magnetic field) and the destabilizing role of the viscoelastic property {\\varGamma} and the electric parameter E on such fluid film are established through the linear stability analysis of the surface evolution equation. Investigation shows that at small values of Hartman number ( M), the influence of electric parameter ( E) on the viscoelastic parameter {(\\varGamma)} is insignificant, while for large values of M, E introduces more destabilizing effect at low values of {\\varGamma} than that at high values of {\\varGamma }. An interesting result also perceived from our analysis is that the stabilizing effect of Hartman number ( M) is decreasing with the increase of the values of {\\varGamma} and E, even it gives destabilizing effect after a certain high value of the electric field depending on the high value of {\\varGamma}. The weakly nonlinear study reveals that the increase of {\\varGamma} decreases the explosive and subcritical unstable zones but increases the supercritical stable zone keeping the unconditional zone almost constant.
Metal colloids and quantum dots: linear and nonlinear optical properties
Henderson, Don O.
1997-05-12
Nanophase materials have found a wide application in a variety of technological areas which include ultrafast optical switching high density information storage and retrieval, electronics, and catalysts, to mention a few. Nanocrystal science has also drawn considerable interest from the fundamental perspective engaging physicists, chemists, and material scientists into this area of rapidly expanding and challenging research. Basic questions concerning how matter evolves from atomic like behavior to molecular and onto bulk lie at the center nanocrystal research. In addition, because of the high surface to volume ratio of the nanocrystals, the interaction potential between a nanocrystal and its surrounding environment becomes an important issue in determining its properties. While significant progress has been made in nanocrystal research, there are many problems concerned with their fabrication. In particular, the difficulty of incorporating nanocrystals into a matrix that is appropriate for ultimate device development has hindered some aspects of nanocrystal research. Ion implantation is a method that is now established as a technique for fabricating metal and semiconductor nanocrystals. It is highly versatile in that one may select nearly any host material for incorporating the nanocrystals of interest. The flexibility of being able to select the host matrix is also interesting from the point of view that it opens the opportunity to investigate matrix-nanocrystal interactions. We summarize in the following sections results on metal and semiconductor nanocrystals formed by ion implantation into dielectric hosts.
Linear and Nonlinear Ultrasonic Properties of Granular Soils
Bonner, B.; Berge, P.A.; Aracne-Ruddle, C.M.; Bertete-Auguirre, H.; Wildenschild, D.; Trombino, C.N.; Hardy, E.
2000-04-20
The ultrasonic pulse transmission method (100-500 kHz) was adapted to measure compressional (P) and shear (S) wave velocities for synthetic soils fabricated from quartz-clay and quartz-peat mixtures. Velocities were determined as samples were loaded by small (up to 0.1 MPa) uniaxial stress to determine how stress at grain contacts affects ave amplitudes, velocities, and frequency content. Samples were fabricated from quartz sand mixed with either a swelling clay or peat (natural cellulose). P velocities in these dry synthetic soil samples were low, ranging from about 230 to 430 m/s for pure sand, about 91 to 420 m/s for sand-peat mixtures, and about 230 to 470 m/s for dry sand-clay mixtures. S velocities were about half of the P velocity in most cases, about 130 to 250 m/s for pure sand, about 75-220 m/s for sand-peat mixtures, and about 88-220 m/s for dry sand-clay mixtures. These experiments demonstrate that P and S velocities are sensitive to the amount and type of admixed second phase at low concentrations. They found that dramatic increases in all velocities occur with small uniaxial loads, indicating strong nonlinearity of the acoustic properties. Composition and grain packing contribute to the mechanical response at grain contacts and the nonlinear response at low stresses.
Model Checking Linear-Time Properties of Probabilistic Systems
NASA Astrophysics Data System (ADS)
Baier, Christel; Größer, Marcus; Ciesinski, Frank
This chapter is about the verification of Markov decision processes (MDPs) which incorporate one of the fundamental models for reasoning about probabilistic and nondeterministic phenomena in reactive systems. MDPs have their roots in the field of operations research and are nowadays used in a wide variety of areas including verification, robotics, planning, controlling, reinforcement learning, economics and semantics of randomized systems. Furthermore, MDPs served as the basis for the introduction of probabilistic automata which are related to weighted automata. We describe the use of MDPs as an operational model for randomized systems, e.g., systems that employ randomized algorithms, multi-agent systems or systems with unreliable components or surroundings. In this context we outline the theory of verifying ω-regular properties of such operational models. As an integral part of this theory we use ω-automata, i.e., finite-state automata over finite alphabets that accept languages of infinite words. Additionally, basic concepts of important reduction techniques are sketched, namely partial order reduction of MDPs and quotient system reduction of the numerical problem that arises in the verification of MDPs. Furthermore we present several undecidability and decidability results for the controller synthesis problem for partially observable MDPs.
Viscoelastic Effects on Spraying and Fragmentation of Polymeric Solutions
NASA Astrophysics Data System (ADS)
Keshavarz, Bavand; McKinley, Gareth; Houze, Eric; Moore, John; Koerner, Michael; MIT, Mech., Eng., Dept. Team; Axalta Coating Systems Team
2013-11-01
The addition of small amounts of polymer to Newtonian fluids can inhibit the spray process, but the physical reasons behind these effects are still unclear. To explore this phenomenon, model viscoelastic fluids composed of very dilute solutions of polyethylene oxide are tested in a variety of fragmentation processes including air-assisted atomization, jet impact fragmentation, drop impact, and rotary atomization. Spray image analysis shows that when the fluid viscoelasticity is increased the average particle diameter and Sauter Mean Diameter both show a systematic increase before reaching an asymptotic plateau value. As observed for Newtonian fluids, the droplet size distributions are still well described by a Gamma distribution but the addition of viscoelasticity shifts the distribution to smaller values of n, corresponding to a broader size distribution. A linear stability analysis indicates that the effects of fluid viscoelasticity are more pronounced in the final stage of ligament formation than in the initial stages of atomization. The linear analysis can predict the observed trends in the mean droplet sizes; however, the shift in the size distributions seems to rise from the nonlinear dynamics of the stretched viscoelastic ligaments close to break up.
Viscoelasticity of Human Blood
Thurston, G. B.
1972-01-01
Measurements made for oscillatory flow of blood in circular tubes show that blood possesses elastic properties which make consideration of its viscous properties alone inadequate. Results are for a frequency of 10 Hz while varying the amplitude of the velocity gradient for red blood cells in plasma at concentrations ranging from 0 to 100% apparent hematocrit. For velocity gradients less than 1-2 sec-1 both the viscous and elastic components of the shearing stress are linearly related to the gradient. For hematocrits above 20% the elastic component of the complex coefficient of viscosity increases with hematocrit approximately to the third power while the viscous component increases exponentially. Oscillatory flow measurements at very low hematocrits, when extrapolated to zero cell concentration, give the intrinsic viscosity of the average individual isolated red cell. The viscous part of this is found to be 1.7 which is compared with theoretical values from the rigid ellipsoid model for which the minimum possible value is 2.5. This difference is attributed to cell deformability. With increasing velocity gradient nonlinear properties develop. The viscous component of the complex viscosity becomes of the order of the steady flow viscosity at high gradients while the elastic component tends to decrease in inverse proportion to the gradient. Thus, the elastic component of the oscillatory stress tends to saturate, this tendency appearing at the approximate level of the yield stress. PMID:5056964
Viscoelastic response of fibroblasts to tension transmitted through adherens junctions.
Ragsdale, G K; Phelps, J; Luby-Phelps, K
1997-01-01
Cytoplasmic deformation was monitored by observing the displacements of 200-nm green fluorescent beads microinjected into the cytoplasm of Swiss 3T3 fibroblasts. We noted a novel protrusion of nonruffling cell margins that was accompanied by axial flow of beads and cytoplasmic vesicles as far as 50 microm behind the protruding plasma membrane. Fluorescent analog cytochemistry and immunofluorescence localization of F-actin, alpha-actinin, N-cadherin, and beta-catenin showed that the protruding margins of deforming cells were mechanically coupled to neighboring cells by adherens junctions. Observations suggested that protrusion resulted from passive linear deformation in response to tensile stress exerted by centripetal contraction of the neighboring cell. The time dependence of cytoplasmic strain calculated from the displacements of beads and vesicles was fit quantitatively by a Kelvin-Voight model for a viscoelastic solid with a mean limiting strain of 0.58 and a mean strain rate of 4.3 x 10(-3) s(-1). In rare instances, the deforming cell and its neighbor spontaneously became uncoupled, and recoil of the protruding margin was observed. The time dependence of strain during recoil also fit a Kelvin-Voight model with similar parameters, suggesting that the kinetics of deformation primarily reflect the mechanical properties of the deformed cell rather than the contractile properties of its neighbor. The existence of mechanical coupling between adjacent fibroblasts through adherens junctions and the viscoelastic responses of cells to tension transmitted directly from cell to cell are factors that must be taken into account to fully understand the role of fibroblasts in such biological processes as wound closure and extracellular matrix remodeling during tissue development. Images FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 PMID:9370474
Probing of polymer surfaces in the viscoelastic regime.
Chyasnavichyus, Marius; Young, Seth L; Tsukruk, Vladimir V
2014-09-01
In this Feature Article, we discussed the experimental and modeling methods and analyzed the limitations of the surface probing of nanomechanical properties of polymeric and biological materials in static and dynamic regimes with atomic force microscopy (AFM), which are widely utilized currently. To facilitate such measurements with minimized ambiguities, in this study we present a combined method to evaluate the viscoelastic properties of compliant polymeric materials. We collected force-distance data in the static regime for a benchmark polymer material (poly(n-butyl methacrylate)) with an easily accessible glass-transition temperature (about 25 °C) at different loading rates and different temperatures across the glassy state, glass-transition region, and rubbery state. For this analysis, we exploited a Johnson-modified Sneddon's approach in a combination with the standard linear solid model. Critical experimental steps suggested for robust probing are (i) the use of a tip with a well-characterized parabolic shape, (ii) probing in a liquid environment in order to reduce jump-in phenomenon, and (iii) minute indentations to ensure the absence of plastic deformation. Whereas the standard Sneddon's model generates quantitatively adequate elastic modulus values below and above the glass transition, this traditional approach can significantly underestimate actual modulus values in the vicinity of the glass-transition region (15 °C above or below Tg), with major deviations occurring at the loss tangent peak. The analysis of the experimental data with Sneddon's model for the elastic region (glassy and rubbery states) and Johnson's model for the viscoelastic region allowed for the restoration of the universal master curve and the evaluation of the storage modulus, loss modulus, loss tangent, relaxation times, and activation energies of the polymer surface across the glass-transition region and at relevant loading rates.
Hydrodynamics and heat transfer in a laminar flow of viscoelastic fluid in a flat slot channel
NASA Astrophysics Data System (ADS)
Ananyev, D. V.; Halitova, G. R.; Vachagina, E. K.
2015-01-01
Results of the numerical study of hydrodynamics and heat transfer in a laminar flow of viscoelastic fluid in a flat slot channel are presented in the present paper. The model of nonlinear viscoelastic fluid of Phan-Thien—Tanner is used to describe the viscoelastic properties of fluid. The solution to the stated problem by software package "COMSOL Multiphysics" is considered. The method of solution is verified, and results are compared with data of the other authors. It is determined that in the flow of viscoelastic fluid in a flat slot channel, the maximal contribution of heating due to dissipation is approximately 7-8 %.
The viscoelasticity of curing thermosets
Adolf, D.; Martin, J.E.
1990-01-01
As a crosslinking polymer cures, dramatic changes in molecular architecture occur. These structural changes in turn affect the viscoelastic behavior of the material. At a critical extent of reaction (the gel point), the polymer undergoes a transition from a viscous liquid to an elastic solid. We have monitored the evolution of structure and viscoelasticity in an epoxy encapsulant used at Sandia, the diglycidyl ether of Bisphenol A (BADGE) cured with diethanolamine (DEA). The structure evolves according to percolation theory, and the viscoelasticity evolves according to out dynamic scaling theory for branched polymers. 7 refs., 4 figs.
VISCOELASTIC MODELS OF TIDALLY HEATED EXOMOONS
Dobos, Vera; Turner, Edwin L.
2015-05-01
Tidal heating of exomoons may play a key role in their habitability, since the elevated temperature can melt the ice on the body even without significant solar radiation. The possibility of life has been intensely studied on solar system moons such as Europa or Enceladus where the surface ice layer covers a tidally heated water ocean. Tidal forces may be even stronger in extrasolar systems, depending on the properties of the moon and its orbit. To study the tidally heated surface temperature of exomoons, we used a viscoelastic model for the first time. This model is more realistic than the widely used, so-called fixed Q models because it takes into account the temperature dependence of the tidal heat flux and the melting of the inner material. Using this model, we introduced the circumplanetary Tidal Temperate Zone (TTZ), which strongly depends on the orbital period of the moon and less on its radius. We compared the results with the fixed Q model and investigated the statistical volume of the TTZ using both models. We have found that the viscoelastic model predicts 2.8 times more exomoons in the TTZ with orbital periods between 0.1 and 3.5 days than the fixed Q model for plausible distributions of physical and orbital parameters. The viscoelastic model provides more promising results in terms of habitability because the inner melting of the body moderates the surface temperature, acting like a thermostat.
Viscoelastic Models of Tidally Heated Exomoons
NASA Astrophysics Data System (ADS)
Dobos, Vera; Turner, Edwin L.
2015-05-01
Tidal heating of exomoons may play a key role in their habitability, since the elevated temperature can melt the ice on the body even without significant solar radiation. The possibility of life has been intensely studied on solar system moons such as Europa or Enceladus where the surface ice layer covers a tidally heated water ocean. Tidal forces may be even stronger in extrasolar systems, depending on the properties of the moon and its orbit. To study the tidally heated surface temperature of exomoons, we used a viscoelastic model for the first time. This model is more realistic than the widely used, so-called fixed Q models because it takes into account the temperature dependence of the tidal heat flux and the melting of the inner material. Using this model, we introduced the circumplanetary Tidal Temperate Zone (TTZ), which strongly depends on the orbital period of the moon and less on its radius. We compared the results with the fixed Q model and investigated the statistical volume of the TTZ using both models. We have found that the viscoelastic model predicts 2.8 times more exomoons in the TTZ with orbital periods between 0.1 and 3.5 days than the fixed Q model for plausible distributions of physical and orbital parameters. The viscoelastic model provides more promising results in terms of habitability because the inner melting of the body moderates the surface temperature, acting like a thermostat.
Weakly nonlinear instability of planar viscoelastic sheets
NASA Astrophysics Data System (ADS)
Wang, Chen; Yang, Li-jun; Xie, Luo; Chen, Pi-min
2015-01-01
A second-order weakly nonlinear analysis has been made of the temporal instability for the linear sinuous mode of two-dimensional planar viscoelastic liquid sheets moving in an inviscid gas. The convected Jeffreys models including the corotational Jeffreys model, Oldroyd A model, and the Oldroyd B model are considered as the rheology model of the viscoelastic fluid of the sheet. The solution for the second-order gas-to-liquid interface displacement has been derived, and the temporal evolution leading to the breakup has been shown. The second-order interface displacement of the linear sinuous mode is varicose, which causes the sheet to fragment into ligaments. First-order constitutive relations of the three rheology models become identical after linearization, so the linear instability results are also the same. For the second-order weakly nonlinear instability, the second-order constitutive relation varies among the corotational Jeffreys model, Oldroyd A model, and the Oldroyd B model, but although they have different disturbance pressures, their disturbance velocities and interface displacements are the same, and therefore, the sheets of the corotational Jeffreys fluid, Oldroyd A fluid, and the Oldroyd B fluid have the same instability behavior characterized by the wave profile and breakup time. The reason for the identical instability behavior is that the effect of different codeformations of the corotational frame, covariant frame, and the contravariant frame is counteracted by the corresponding change in the second-order disturbance pressure, leaving no influence on the second-order velocity. At wavenumbers with maximum instabilities, an increase in the elasticity, or a reduction of the deformation retardation time, leads to a larger linear temporal growth rate, greater second-order disturbance amplitude, and shorter breakup time, thereby enhancing instability. The mechanism of linear instability has been examined using an energy approach, which shows that the
Hilton, Harry H.
2008-02-15
Protocols are developed for formulating optimal viscoelastic designer functionally graded materials tailored to best respond to prescribed loading and boundary conditions. In essence, an inverse approach is adopted where material properties instead of structures per se are designed and then distributed throughout structural elements. The final measure of viscoelastic material efficacy is expressed in terms of failure probabilities vs. survival time000.
Nonlinear viscoelastic characterization of polycarbonate
NASA Technical Reports Server (NTRS)
Caplan, E. S.; Brinson, H. F.
1982-01-01
Uniaxial tensile creep and recovery data from polycarbonate at six temperatures and six stress levels are analyzed for nonlinear viscoelastic constitutive modeling. A theory to account for combined effects of two or more accelerating factors is presented.
Instability of viscoelastic compound jets
NASA Astrophysics Data System (ADS)
Ye, Han-Yu; Yang, Li-Jun; Fu, Qing-Fei
2016-04-01
This paper investigates the axisymmetric instability of a viscoelastic compound jet, for which the constitutive relation is described by the Oldroyd B model. It is found that a viscoelastic compound jet is more unstable than a Newtonian compound jet, regardless of whether the viscoelastic compound jet is inner-Newtonian-outer-viscoelastic, inner-viscoelastic-outer-Newtonian, or fully viscoelastic. It is also found that an increase in the stress relaxation time of the inner or outer fluid renders the jet more unstable, while an increase in the time constant ratio makes the jet less unstable. An analysis of the energy budget of the destabilization process is performed, in which a formulation using the relative rate of change of energy is adopted. The formulation is observed to provide a quantitative analysis of the contribution of each physical factor (e.g., release of surface energy and viscous dissipation) to the temporal growth rate. The energy analysis reveals the mechanisms of various trends in the temporal growth rate, including not only how the growth rate changes with the parameters, but also how the growth rate changes with the wavenumber. The phenomenon of the dispersion relation presenting two local maxima, which occurred in previous research, is explained by the present energy analysis.
Frequency Response of Synthetic Vocal Fold Models with Linear and Nonlinear Material Properties
Shaw, Stephanie M.; Thomson, Scott L.; Dromey, Christopher; Smith, Simeon
2014-01-01
Purpose The purpose of this study was to create synthetic vocal fold models with nonlinear stress-strain properties and to investigate the effect of linear versus nonlinear material properties on fundamental frequency during anterior-posterior stretching. Method Three materially linear and three materially nonlinear models were created and stretched up to 10 mm in 1 mm increments. Phonation onset pressure (Pon) and fundamental frequency (F0) at Pon were recorded for each length. Measurements were repeated as the models were relaxed in 1 mm increments back to their resting lengths, and tensile tests were conducted to determine the stress-strain responses of linear versus nonlinear models. Results Nonlinear models demonstrated a more substantial frequency response than did linear models and a more predictable pattern of F0 increase with respect to increasing length (although range was inconsistent across models). Pon generally increased with increasing vocal fold length for nonlinear models, whereas for linear models, Pon decreased with increasing length. Conclusions Nonlinear synthetic models appear to more accurately represent the human vocal folds than linear models, especially with respect to F0 response. PMID:22271874
Nonlinear Dynamics in Viscoelastic Jets
NASA Astrophysics Data System (ADS)
Majmudar, Trushant; Varagnat, Matthieu; McKinley, Gareth
2008-11-01
Instabilities in free surface continuous jets of non-Newtonian fluids, although relevant for many industrial processes, remain poorly understood in terms of fundamental fluid dynamics. Inviscid, and viscous Newtonian jets have been studied in considerable detail, both theoretically and experimentally. Instability in viscous jets leads to regular periodic coiling of the jet, which exhibits a non-trivial frequency dependence with the height of the fall. Here we present a systematic study of the effect of viscoelasticity on the dynamics of continuous jets of worm-like micellar surfactant solutions of varying viscosities and elasticities. We observe complex nonlinear spatio-temporal dynamics of the jet, and uncover a transition from periodic to quasi-periodic to a multi-frequency, broad-spectrum dynamics. Beyond this regime, the jet dynamics smoothly crosses over to exhibit the ``leaping shampoo'' or the Kaye effect. We examine different dynamical regimes in terms of scaling variables, which depend on the geometry (dimensionless height), kinematics (dimensionless flow rate), and the fluid properties (elasto-gravity number) and present a regime map of the dynamics of the jet in terms of these dimensionless variables.
Nonlinear Dynamics in Viscoelastic Jets
NASA Astrophysics Data System (ADS)
Majmudar, Trushant; Varagnat, Matthieu; McKinley, Gareth
2009-03-01
Instabilities in free surface continuous jets of non-Newtonian fluids, although relevant for many industrial processes, remain poorly understood in terms of fundamental fluid dynamics. Inviscid, and viscous Newtonian jets have been studied in considerable detail, both theoretically and experimentally. Instability in viscous jets leads to regular periodic coiling of the jet, which exhibits a non-trivial frequency dependence with the height of the fall. Here we present a systematic study of the effect of viscoelasticity on the dynamics of continuous jets of worm-like micellar surfactant solutions of varying viscosities and elasticities. We observe complex nonlinear spatio-temporal dynamics of the jet, and uncover a transition from periodic to quasi-periodic to a multi-frequency, broad-spectrum dynamics. Beyond this regime, the jet dynamics smoothly crosses over to exhibit the ``leaping shampoo'' or the Kaye effect. We examine different dynamical regimes in terms of scaling variables, which depend on the geometry (dimensionless height), kinematics (dimensionless flow rate), and the fluid properties (elasto-gravity number) and present a regime map of the dynamics of the jet in terms of these dimensionless variables.
Nonlinear viscoelastic characterization of polymer materials using a dynamic-mechanical methodology
NASA Technical Reports Server (NTRS)
Strganac, Thomas W.; Payne, Debbie Flowers; Biskup, Bruce A.; Letton, Alan
1995-01-01
Polymer materials retrieved from LDEF exhibit nonlinear constitutive behavior; thus the authors present a method to characterize nonlinear viscoelastic behavior using measurements from dynamic (oscillatory) mechanical tests. Frequency-derived measurements are transformed into time-domain properties providing the capability to predict long term material performance without a lengthy experimentation program. Results are presented for thin-film high-performance polymer materials used in the fabrication of high-altitude scientific balloons. Predictions based upon a linear test and analysis approach are shown to deteriorate for moderate to high stress levels expected for extended applications. Tests verify that nonlinear viscoelastic response is induced by large stresses. Hence, an approach is developed in which the stress-dependent behavior is examined in a manner analogous to modeling temperature-dependent behavior with time-temperature correspondence and superposition principles. The development leads to time-stress correspondence and superposition of measurements obtained through dynamic mechanical tests. Predictions of material behavior using measurements based upon linear and nonlinear approaches are compared with experimental results obtained from traditional creep tests. Excellent agreement is shown for the nonlinear model.
NASA Technical Reports Server (NTRS)
Cohen, S. C.
1979-01-01
A model of viscoelastic deformations associated with earthquakes is presented. A strike-slip fault is represented by a rectangular dislocation in a viscoelastic layer (lithosphere) lying over a viscoelastic half-space (asthenosphere). Deformations occur on three time scales. The initial response is governed by the instantaneous elastic properties of the earth. A slower response is associated with viscoelastic relaxation of the lithosphere and a yet slower response is due to viscoelastic relaxation of the asthenosphere. The major conceptual contribution is the inclusion of lithospheric viscoelastic properties into a dislocation model of earthquake related deformations and stresses. Numerical calculations using typical fault parameters reveal that the postseismic displacements and strains are small compared to the coseismic ones near the fault, but become significant further away. Moreover, the directional sense of the deformations attributable to the elastic response, the lithospheric viscoelastic softening, and the asthenospheric viscoelastic flow may differ and depend on location and model details. The results and theoretical arguments suggest that the stress changes accompanying lithospheric relaxation may also be in a different sense than and be larger than the strain changes.
Stress Boundary layer Development in Planar flow of Viscoelastic Fluids
NASA Astrophysics Data System (ADS)
Ashrafi, Nariman; Mohamadali, Meysam
2015-11-01
Two-dimensional steady planar creeping flow of the nonlinear viscoelastic Upper Convected Maxwell (UCM) fluid along a flat plate is analyzed for high Weissenberg numbers, Wi. The viscoelastic boundary layer, formed in a thin region closer to the wall in which the relaxation terms are recovered. By means of similarity transformations the non-linear momentum and constitutive equations in each layer transform into a system of highly nonlinear coupled ordinary differential equations. The proper similarity variable is found that asymptotically matches each two adjacent layers. The numerical simulation shows that at the outer layer, the velocity profile changes linearly with the similarity variable meaning that no velocity boundary layer is developed. In general, the boundary layer is formed in all three stress components in different fashions. The stress boundary layer divides the flow into two separate regions of viscoelastic and elastic flows, in addition to the top outer flow. The viscoelastic region is completely bounded in two directions (x and y) for horizontal normal stress, Txx, and shear stress, Txy. Finally it is observed that the stress boundary layer for vertical stress, Tyy, is formed only in x direction.
Application of linear response theory to magnetotransport properties of dense plasmas.
Adams, J R; Reinholz, H; Redmer, R
2010-03-01
Linear response theory, as developed within the Zubarev formalism, is a quantum statistical approach for describing systems out of but close to equilibrium, which has been successfully applied to a wide variety of plasmas in an external electric field and/or containing a temperature gradient. We present here an extension of linear response theory to include the effects of an external magnetic field. General expressions for the complete set of relevant transport properties are given. In particular, the Hall effect and the influence of a magnetic field on the dc electrical conductivity are discussed. Low-density limits including electron-electron scattering are presented as well as results for arbitrary degeneracy.
Application of linear response theory to magnetotransport properties of dense plasmas
Adams, J. R.; Redmer, R.; Reinholz, H.
2010-03-15
Linear response theory, as developed within the Zubarev formalism, is a quantum statistical approach for describing systems out of but close to equilibrium, which has been successfully applied to a wide variety of plasmas in an external electric field and/or containing a temperature gradient. We present here an extension of linear response theory to include the effects of an external magnetic field. General expressions for the complete set of relevant transport properties are given. In particular, the Hall effect and the influence of a magnetic field on the dc electrical conductivity are discussed. Low-density limits including electron-electron scattering are presented as well as results for arbitrary degeneracy.
NASA Astrophysics Data System (ADS)
Boutelier, D.; Cruden, A.; Saumur, B.
2016-05-01
Analogue models often require that materials with specific physical properties be engineered to satisfy scaling conditions. To achieve this goal we investigate the rheology of aqueous solutions of Natrosol 250 HH, a rheology modifier employed in various industries to thicken viscous solutions. We report the rheological properties as functions of the concentration and temperature and discuss the advantages and limitations of these materials in view of their use in analogue modelling experiments. The solutions are linear visco-elastic for low stresses (or strain-rates), becoming shear-thinning for larger stresses. For the typically slow analogue experiments of tectonics, the solutions can be considered linear visco-elastic with a Maxwell relaxation time much smaller than the characteristic observation time. This simplification is even more appropriate when the solutions are employed at temperatures higher than 20 °C, since the solutions then display a behaviour that is more viscous, less elastic at the same shear-rate, while the Newtonian viscosity reduces and the shear-rate limit between Newtonian and shear-thinning behaviours increases. The Newtonian viscosity is shown to increase non-linearly with concentration and decrease non-linearly with temperature. With concentrations between 0 and 3% and temperature between 20 and 40 °C, the viscosity varied between 10-1 and 4000 Pa s, while the density remained close to the density of water. Natrosol 250 HH thus offers the possibility to control the viscosity of a solution without significantly affecting the density, thereby facilitating the design and setup of analogue experiments.
Dynamics of a polymer in an active and viscoelastic bath
NASA Astrophysics Data System (ADS)
Vandebroek, Hans; Vanderzande, Carlo
2015-12-01
We study the dynamics of an ideal polymer chain in a viscoelastic medium and in the presence of active forces. The motion of the center of mass and of individual monomers is calculated. On time scales that are comparable to the persistence time of the active forces, monomers can move superdiffusively, while on larger time scales subdiffusive behavior occurs. The difference between this subdiffusion and that in the absence of active forces is quantified. We show that the polymer swells in response to active processes and determine how this swelling depends on the viscoelastic properties of the environment. Our results are compared to recent experiments on the motion of chromosomal loci in bacteria.
Viscoelastic mechanisms of aortic baroreceptor resetting to hypotension and to hypertension.
Xavier-Neto, J; Moreira, E D; Krieger, E M
1996-10-01
Viscoelastic and electrophysiological mechanisms have been implicated in the resetting of baroreceptors in hypertension, but resetting in response to hypotension has been less studied. To evaluate the temporal relationship between viscoelastic mechanisms and acute resetting, we examined the "in vivo" behavior of aortic caliber and aortic baroreceptor activity during step changes in pressure. Fifteen-minute hemorrhage in Wistar rats produced stable hypotension (30 mmHg) and viscoelastic contraction (111 +/- 14.2 microns systolic caliber; P < 0.01). Integrated aortic activity fell to 19.8 +/- 3.9% of control (P < 0.001) after 3 s of hypotension but recovered to 64 +/- 4.1% 15 min later (P < 0.01 from 3 s). Recovery of baroreceptor activity was linearly correlated to viscoelastic contraction (r = 0.963; P < 0.0001). Thirty-minute phenylephrine infusion (1.0-4.0 micrograms/min) produced stable hypertension (30 mmHg) and viscoelastic dilation (211 +/- 37.0 microns systolic caliber). Integrated aortic activity increased to 218.0 +/- 18% of control values (P < 0.001) 30 s after hypertension and was reduced to 164.0 +/- 12.0% (P < 0.001 from 3 s) within 30 min. Reduction of baroreceptor activity correlated linearly with viscoelastic relaxation (r = 0.963; P < 0.0001). The results indicate that in the in vivo rat aorta, viscoelastic mechanisms parallel and may contribute to the baroreceptor resetting during hypotension and hypertension.
Linear and nonlinear optical properties of hybrid metallic–dielectric plasmonic nanoantennas
Hentschel, Mario; Metzger, Bernd; Knabe, Bastian
2016-01-01
Summary We study the linear and nonlinear optical properties of hybrid metallic–dielectric plasmonic gap nanoantennas. Using a two-step-aligned electron beam lithography process, we demonstrate the ability to selectively and reproducibly fill the gap region of nanoantennas with dielectric nanoparticles made of lithium niobate (LiNbO3) with high efficiency. The linear optical properties of the antennas are modified due to the large refractive index of the material. This leads to a change in the coupling strength as well as an increase of the effective refractive index of the surrounding. The combination of these two effects causes a red- or blue-shift of the plasmonic modes, respectively. We find that the nonlinear optical properties of the combined system are only modified in the range of one order of magnitude. The observed changes in our experiments in the nonlinear emission can be traced to the changed dielectric environment and thus the modified linear optical properties. The intrinsic nonlinearity of the dielectric used is in fact small when compared to the nonlinearity of the metallic part of the hybrid antennas. Thus, the nonlinear signals generated by the antenna itself are dominant in our experiments. We demonstrate that the well-known nonlinear response of bulk dielectric materials cannot always straightforwardly be used to boost the nonlinear response of nanoscale antenna systems. Our results significantly deepen the understanding of these interesting hybrid systems and offer important guidelines for the design of nanoscale, nonlinear light sources. PMID:26925359
Linear and nonlinear optical properties of hybrid metallic-dielectric plasmonic nanoantennas.
Hentschel, Mario; Metzger, Bernd; Knabe, Bastian; Buse, Karsten; Giessen, Harald
2016-01-01
We study the linear and nonlinear optical properties of hybrid metallic-dielectric plasmonic gap nanoantennas. Using a two-step-aligned electron beam lithography process, we demonstrate the ability to selectively and reproducibly fill the gap region of nanoantennas with dielectric nanoparticles made of lithium niobate (LiNbO3) with high efficiency. The linear optical properties of the antennas are modified due to the large refractive index of the material. This leads to a change in the coupling strength as well as an increase of the effective refractive index of the surrounding. The combination of these two effects causes a red- or blue-shift of the plasmonic modes, respectively. We find that the nonlinear optical properties of the combined system are only modified in the range of one order of magnitude. The observed changes in our experiments in the nonlinear emission can be traced to the changed dielectric environment and thus the modified linear optical properties. The intrinsic nonlinearity of the dielectric used is in fact small when compared to the nonlinearity of the metallic part of the hybrid antennas. Thus, the nonlinear signals generated by the antenna itself are dominant in our experiments. We demonstrate that the well-known nonlinear response of bulk dielectric materials cannot always straightforwardly be used to boost the nonlinear response of nanoscale antenna systems. Our results significantly deepen the understanding of these interesting hybrid systems and offer important guidelines for the design of nanoscale, nonlinear light sources. PMID:26925359
NASA Astrophysics Data System (ADS)
Kent, James; Holdaway, Daniel
2015-04-01
Data assimilation is one of the most common inverse problems encountered in geophysical models. One of the leading techniques used for data assimilation in numerical weather prediction is four dimensional variational data assimilation (4DVAR). In 4DVAR the tangent linear and adjoint versions of the nonlinear model are used to perform a minimization with time dependent observations. In order for the minimization to perform well requires a certain degree of linearity in both the underlying equations and numerical methods used to solve them. Advection is central to the underlying equations used for numerical weather prediction, as well as many other geophysical models. From the advection of momentum, temperature and moisture to passive tracers such as smoke from wildfires, accurate transport is paramount. Over recent decades much effort has been directed toward the development of positive definite, non-oscillatory, mass conserving advection schemes. These schemes are capable of giving excellent representation of transport, but by definition introduce nonlinearity into equations that are otherwise quite linear. One such example is the flux limited piecewise parabolic method (PPM) used in NASA's Goddard Earth Observing System version 5 (GEOS-5), which can perform very poorly when linearized. With a view to an optimal representation of transport in the linear versions of atmospheric models and 4DVAR we analyse the performance of a number of different linear and nonlinear advection schemes. The schemes are analysed using a one dimensional case study, a passive tracer in GEOS-5 experiment and using the full linearized version of GEOS-5. Using the three studies it is shown that higher order linear schemes provide the best representation of the transport of perturbations and sensitivities. In certain situations the nonlinear schemes give the best performance but are subject to issues. It is also shown that many of the desirable properties of the nonlinear schemes are
Reusable antifouling viscoelastic adhesive with an elastic skin.
Patil, Sandip; Malasi, Abhinav; Majumder, Abhijit; Ghatak, Animangsu; Sharma, Ashutosh
2012-01-10
Although the viscoelasticity or tackiness of a pressure-sensitive adhesive gives it strength owing to energy dissipation during peeling, it also renders it nonreusable because of structural changes such as the formation of fibrils, cohesive failure, and fouling. However, an elastic layer has good structural integrity and cohesive strength but low adhesive energy. We demonstrate an effective composite adhesive in which a soft viscoelastic bulk layer is imbedded in a largely elastic thin skin layer. The composite layer is able to meet the conflicting demands of the high peel strength comparable to the viscoelastic core and the structural integrity, reusability, and antifouling properties of the elastic skin. Our model adhesive is made of poly(dimethylsiloxane), where its core and skin are created by varying the cross-linking percentage from 2 to 10%. PMID:22201420
Local viscoelasticity of living cells measured by rotational magnetic spectroscopy
NASA Astrophysics Data System (ADS)
Berret, J.-F.
2016-01-01
When submitted to a magnetic field, micron-size wires with superparamagnetic properties behave as embedded rheometers and represent interesting sensors for microrheology. Here we use rotational magnetic spectroscopy to measure the shear viscosity of the cytoplasm of living cells. We address the question of whether the cytoplasm is a viscoelastic liquid or an elastic gel. The main result of the study is the observation of a rotational instability between a synchronous and an asynchronous regime of rotation, found for murine fibroblasts and human cancer cells. For wires of susceptibility 3.6, the transition occurs in the range 0.01-1 rad s-1. The determination of the shear viscosity (10-100 Pa s) and elastic modulus (5-20 Pa) confirms the viscoelastic character of the cytoplasm. In contrast to earlier studies, it is concluded that the interior of living cells can be described as a viscoelastic liquid, and not as an elastic gel.
Reusable antifouling viscoelastic adhesive with an elastic skin.
Patil, Sandip; Malasi, Abhinav; Majumder, Abhijit; Ghatak, Animangsu; Sharma, Ashutosh
2012-01-10
Although the viscoelasticity or tackiness of a pressure-sensitive adhesive gives it strength owing to energy dissipation during peeling, it also renders it nonreusable because of structural changes such as the formation of fibrils, cohesive failure, and fouling. However, an elastic layer has good structural integrity and cohesive strength but low adhesive energy. We demonstrate an effective composite adhesive in which a soft viscoelastic bulk layer is imbedded in a largely elastic thin skin layer. The composite layer is able to meet the conflicting demands of the high peel strength comparable to the viscoelastic core and the structural integrity, reusability, and antifouling properties of the elastic skin. Our model adhesive is made of poly(dimethylsiloxane), where its core and skin are created by varying the cross-linking percentage from 2 to 10%.
Fractional modeling of Pasternak-type viscoelastic foundation
NASA Astrophysics Data System (ADS)
Cai, Wei; Chen, Wen; Xu, Wenxiang
2016-06-01
In this paper, we propose a fractional Pasternak-type foundation model to characterize the time-dependent properties of the viscoelastic foundation. With varying fractional orders, the proposed model can govern the traditional Winkler model, Pasternak model, and viscoelastic model. We take the four-edge simply supported rectangular thin plate as an example to analyze the viscoelastic foundation reaction, and obtain the solution of the new governing equation. Theoretical results show that the fractional order has a dramatic influence on the deflection and bending moment. It can be further concluded that the softer foundation will become more time-dependent. Subsequently, the difference between fractional Pasternak-type and Winkler foundation model is presented in this work. The existence of constrained boundary is found to definitely affect deflection and bending moment. Such phenomenon, known as the wall effect, is deeply discussed.
Effect of Viscoelasticity of Vessel Walls on Pulse Wave
NASA Astrophysics Data System (ADS)
Saito, Masashi; Yamamoto, Yuya; Matsukawa, Mami; Watanabe, Yoshiaki; Furuya, Mio; Asada, Takaaki
2010-07-01
The pulse wave comes from the displacement of surface skin and is composed of incident and reflected waves. Since the properties of the reflected wave change considerably owing to the viscoelasticity of the vessel walls, the analysis of the reflected wave is considered to be useful for evaluating arterial stiffness; thereby, appropriate estimation of the incident wave is important for separating the pulse wave. Here, the incident wave is generated by a forward wave, which is the intravascular pressure caused by blood flow. In the former analysis, we assumed the blood vessel as an elastic tube and estimated the forward wave from the blood flow velocity waveform. In this study, we used a viscoelastic model to estimate a more appropriate forward wave. In this estimation, we used viscoelastic properties similar to those of bovine aorta, human aorta, or human artery. The estimated forward waves showed that the difference in the viscous properties of vessel walls causes minimal changes in the forward waves, which were also similar to that estimated using the elastic model. The result tells us that the elastic model is acceptable and useful for the estimation of forward wave, incident wave, and reflected wave, which enables the simple evaluation of the viscoelastic properties of vessel walls.
Cutting edge science: Laser surgery illuminates viscoelasticity of merotelic kinetochores
Cabello, Simon
2016-01-01
Increasing evidence in eukaryotic cells suggests that mechanical forces are essential for building a robust mitotic apparatus and correcting inappropriate chromosome attachments. In this issue, Cojoc et al. (2016. J. Cell Biol., http://dx.doi.org/10.1083/jcb.201506011) use laser microsurgery in vivo to measure and study the viscoelastic properties of kinetochores. PMID:27002164
Cutting edge science: Laser surgery illuminates viscoelasticity of merotelic kinetochores.
Cabello, Simon; Gachet, Yannick; Tournier, Sylvie
2016-03-28
Increasing evidence in eukaryotic cells suggests that mechanical forces are essential for building a robust mitotic apparatus and correcting inappropriate chromosome attachments. In this issue, Cojoc et al. (2016. J. Cell Biol., http://dx.doi.org/10.1083/jcb.201506011) use laser microsurgery in vivo to measure and study the viscoelastic properties of kinetochores.
Viscoelastic Taylor-Couette instability as analog of the magnetorotational instability
NASA Astrophysics Data System (ADS)
Bai, Yang; Crumeyrolle, Olivier; Mutabazi, Innocent
2015-09-01
A linear stability analysis and an experimental study of a viscoelastic Taylor-Couette flow corotating in the Keplerian ratio allow us to elucidate the analogy between the viscoelastic instability and the magnetorotational instability (MRI). A generalized Rayleigh criterion allows us to determine the potentially unstable zone to pure-elasticity-driven perturbations. Experiments with a viscoelastic polymer solution yield four modes: one pure-elasticity mode and three elastorotational instability (ERI) modes that represent the MRI-analog modes. The destabilization by the polymer viscosity is evidenced for the ERI modes.
Linear and nonlinear quantitative structure-property relationship modelling of skin permeability.
Khajeh, A; Modarress, H
2014-01-01
In this work, quantitative structure-property relationship (QSPR) models were developed to estimate skin permeability based on theoretically derived molecular descriptors and a diverse set of experimental data. The newly developed method combining modified particle swarm optimization (MPSO) and multiple linear regression (MLR) was used to select important descriptors and develop the linear model using a training set of 225 compounds. The adaptive neuro-fuzzy inference system (ANFIS) was used as an efficient nonlinear method to correlate the selected descriptors with experimental skin permeability data (log Kp). The linear and nonlinear models were assessed by internal and external validation. The obtained models with three descriptors show good predictive ability for the test set, with coefficients of determination for the MPSO-MLR and ANFIS models equal to 0.874 and 0.890, respectively. The QSPR study suggests that hydrophobicity (encoded as log P) is the most important factor in transdermal penetration. PMID:24090175
Two-phase viscoelastic jetting
Yu, J-D; Sakai, S.; Sethian, J.A.
2008-12-10
A coupled finite difference algorithm on rectangular grids is developed for viscoelastic ink ejection simulations. The ink is modeled by the Oldroyd-B viscoelastic fluid model. The coupled algorithm seamlessly incorporates several things: (1) a coupled level set-projection method for incompressible immiscible two-phase fluid flows; (2) a higher-order Godunov type algorithm for the convection terms in the momentum and level set equations; (3) a simple first-order upwind algorithm for the convection term in the viscoelastic stress equations; (4) central difference approximations for viscosity, surface tension, and upper-convected derivative terms; and (5) an equivalent circuit model to calculate the inflow pressure (or flow rate) from dynamic voltage.
NASA Astrophysics Data System (ADS)
Duda, D. P.; Minnis, P.; Chee, T.; Khlopenkov, K. V.; Bedka, S. T.
2015-12-01
Observation of linear contrail cirrus coverage and retrieval of their optical properties are valuable data for validating atmospheric climate models that represent contrail formation explicitly. These data can reduce our uncertainty of the regional effects of contrail-generated cirrus on global radiative forcing, and thus improve our estimation of the impact of aviation on climate change. We continue our work to create a multi-year climatology of the physical properties of linear contrails from multi-spectral satellite observations. We use an automated contrail detection algorithm (CDA) to determine the coverage of linear persistent contrails over the Northern Hemisphere during 2012. The contrail detection algorithm is a modified form of the Mannstein et al. (1999) method, and uses several channels from thermal infrared MODIS data to reduce the occurrence of false positive detections. Global aircraft emissions waypoint data provided by FAA allow comparison of detected contrails with commercial aircraft flight tracks. A pixel-level product based on the advected flight tracks defined by the waypoint data and U-V wind component profiles from the NASA GMAO MERRA reanalyses has been developed to assign a confidence of contrail detection for the contrail mask. To account for possible contrail cirrus missed by the CDA, a post-processing method based on the assumption that pixels adjacent to detected linear contrails will have radiative signatures similar to those of the detected contrails is applied to the Northern Hemisphere data. Results from MODIS measurements during 2012 will be presented, representing a near-global climatology of contrail coverage. Linear contrail coverage will be compared with coverage estimates determined previously from 2006 MODIS data and with maps of potential persistent contrail formation derived from MERRA reanalysis data for both 2006 and 2012. In addition, contrail physical properties such as optical depth and particle size derived from the
Electronic transport properties of linear nC20 (n ≤ 5) oligomers: Theoretical investigation
NASA Astrophysics Data System (ADS)
Javan, Masoud Bezi
2015-03-01
We have used extended Huckel tight binding (EHTB) method considering Landauer-Buttiker formalism for investigating the electronic transport properties in linear nC20 (n ≤ 5) oligomers sandwiched between two Au (111) electrodes. We have presented the I-V and conductance characteristics of the nC20 oligomers and also their dependences to the oligomer structural properties. It was found that the zero bias conductance of the energetically favorable nC20 oligomers increases with growth of their length and the I-V characteristic remains almost linear at low bias voltages (up to 0.2 V). Some quantities such as transmission spectrum and electronic structure of nC20 oligomers are discussed in the context. The results can be used for developing electronic nanodevices based on fullerenes.
Linear and Nonlinear Optical Properties in Spherical Quantum Dots: Generalized Hulthén Potential
NASA Astrophysics Data System (ADS)
Onyeaju, M. C.; Idiodi, J. O. A.; Ikot, A. N.; Solaimani, M.; Hassanabadi, H.
2016-09-01
In this work, we studied the optical properties of spherical quantum dots confined in Hulthén potential with the appropriate centrifugal term included. The approximate solution of the bound state and wave functions were obtained from the Schrödinger wave equation by applying the factorization method. Also, we have used the density matrix formalism to investigate the linear and third-order nonlinear absorption coefficient and refractive index changes.
Spintronic and transport properties of linear atomic strings of transition metals (Fe, Co, Ni)
NASA Astrophysics Data System (ADS)
Tyagi, Neha; Jaiswal, Neeraj K.; Srivastava, Pankaj
2016-05-01
In the present work, first-principles investigations have been performed to study the spintronic and transport properties of linear atomic strings of Fe, Co and Ni. The structural stabilities of the considered strings were compared on the basis of binding energies which revealed that all the strings are energetically feasible to be achieved. Further, all the considered strings are found to be ferromagnetic and the observed magnetic moment ranges from 1.38 to 1.71 μB. The observed transport properties and high spin polarization points towards their potential for nano interconnects and spintronic applications.
Evaluation of frequency dependent non-linear optical property using long-range correction method
NASA Astrophysics Data System (ADS)
Yokoi, Yukina; Ishimaru, Hiroki; Kamiya, Muneaki; Sekino, Hideo
2015-02-01
We for the first time performed a systematic evaluation of dynamic second hyperpolarizabilities corresponding to all the third-order Nonlinear Optical (NLO) processes using Time Dependent Density Functional Theory (TDDFT) with exchange functional corrected for long-range interaction. We develop a program system which quantitatively evaluate the frequency dependent non-linear optical property of molecules, and apply to the polyene molecules of different lengths. The dispersion curves obtained for each NLO processes have divergence at the frequency corresponding to the one predicted by Sum Over State (SOS) interpretation of the property.
Durand, Grégory; Prosak, Robert A.; Han, Yongbin; Ortial, Stéphanie; Rockenbauer, Antal; Pucci, Bernard; Villamena, Frederick A.
2009-01-01
Nitrone spin traps have been employed as pharmacological agent against neurodegenerative diseases and ischemia-reperfusion induced injury. The structure-activity relationship was explored for the two types of nitrones, i.e., cyclic (DMPO) and linear (PBN), which are conjugated to a fluorinated amphiphilic carrier (FAC) for their cytoprotective properties against hydrogen peroxide (H2O2), 3-morpholinosynonimine hydrochloride (SIN-1) and 4-hydroxynonenal (HNE) induced cell death on bovine aortic endothelial cells. The compound FAMPO was synthesized and characterized, and its physical-chemical and spin trapping properties were explored. Cytotoxicity and cytoprotective properties of various nitrones either conjugated and non-conjugated to FAC (i.e., AMPO, FAMPO, PBN and FAPBN) were assessed using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium (MTT) reduction assay. Results show that of all the nitrones tested, FAPBN is the most protective against H2O2, but FAMPO and to a lesser extent its unconjugated form, AMPO, are more protective against SIN-1 induced cytotoxicity. However, none of the nitrones used protect the cells from HNE-induced cell death. The difference in the cytoprotective properties observed between the cyclic and linear nitrones may arise from the differences in their intrinsic antioxidant properties and localization in the cell. PMID:19678661
Xu, Wen-Sheng; Freed, Karl F
2015-07-14
The lattice cluster theory (LCT) for semiflexible linear telechelic melts, developed in Paper I, is applied to examine the influence of chain stiffness on the average degree of self-assembly and the basic thermodynamic properties of linear telechelic polymer melts. Our calculations imply that chain stiffness promotes self-assembly of linear telechelic polymer melts that assemble on cooling when either polymer volume fraction ϕ or temperature T is high, but opposes self-assembly when both ϕ and T are sufficiently low. This allows us to identify a boundary line in the ϕ-T plane that separates two regions of qualitatively different influence of chain stiffness on self-assembly. The enthalpy and entropy of self-assembly are usually treated as adjustable parameters in classical Flory-Huggins type theories for the equilibrium self-assembly of polymers, but they are demonstrated here to strongly depend on chain stiffness. Moreover, illustrative calculations for the dependence of the entropy density of linear telechelic polymer melts on chain stiffness demonstrate the importance of including semiflexibility within the LCT when exploring the nature of glass formation in models of linear telechelic polymer melts.
NASA Astrophysics Data System (ADS)
Xu, Wen-Sheng; Freed, Karl F.
2015-07-01
The lattice cluster theory (LCT) for semiflexible linear telechelic melts, developed in Paper I, is applied to examine the influence of chain stiffness on the average degree of self-assembly and the basic thermodynamic properties of linear telechelic polymer melts. Our calculations imply that chain stiffness promotes self-assembly of linear telechelic polymer melts that assemble on cooling when either polymer volume fraction ϕ or temperature T is high, but opposes self-assembly when both ϕ and T are sufficiently low. This allows us to identify a boundary line in the ϕ-T plane that separates two regions of qualitatively different influence of chain stiffness on self-assembly. The enthalpy and entropy of self-assembly are usually treated as adjustable parameters in classical Flory-Huggins type theories for the equilibrium self-assembly of polymers, but they are demonstrated here to strongly depend on chain stiffness. Moreover, illustrative calculations for the dependence of the entropy density of linear telechelic polymer melts on chain stiffness demonstrate the importance of including semiflexibility within the LCT when exploring the nature of glass formation in models of linear telechelic polymer melts.
Xu, Wen-Sheng; Freed, Karl F.
2015-07-14
The lattice cluster theory (LCT) for semiflexible linear telechelic melts, developed in Paper I, is applied to examine the influence of chain stiffness on the average degree of self-assembly and the basic thermodynamic properties of linear telechelic polymer melts. Our calculations imply that chain stiffness promotes self-assembly of linear telechelic polymer melts that assemble on cooling when either polymer volume fraction ϕ or temperature T is high, but opposes self-assembly when both ϕ and T are sufficiently low. This allows us to identify a boundary line in the ϕ-T plane that separates two regions of qualitatively different influence of chain stiffness on self-assembly. The enthalpy and entropy of self-assembly are usually treated as adjustable parameters in classical Flory-Huggins type theories for the equilibrium self-assembly of polymers, but they are demonstrated here to strongly depend on chain stiffness. Moreover, illustrative calculations for the dependence of the entropy density of linear telechelic polymer melts on chain stiffness demonstrate the importance of including semiflexibility within the LCT when exploring the nature of glass formation in models of linear telechelic polymer melts.
Viscoelastic struts for vibration mitigation of FORTE
Maly, J.R.; Butler, T.A.
1996-05-01
FORTE is a small satellite being developed by Los Alamos National Laboratory (LANL) and Sandia National Laboratories Albuquerque (SNLA). It will be placed into orbit via a Pegasus launch in 1996. Testing a full-scale engineering model of the structure using the proto-qualification, system-level vibration spectrum indicated that acceleration levels caused by structural resonances exceed component levels to which certain sensitive components had previously been qualified. Viscoelastic struts were designed to reduce response levels associated with these resonances by increasing the level of damping in key structural modes of the spacecraft. Four identical shear-lap struts were fabricated ad installed between the two primary equipment decks. The struts were designed using a system finite element model (FEM) of the spacecraft, a component FEM of the strut, and measured viscoelastic properties. Direct complex stiffness testing was performed to characterize the frequency-dependent behavior of the struts, and these measured properties (shear modulus and loss factor) were used to represent the struts in the spacecraft model. System-level tests were repeated with the struts installed and the response power spectral densities at critical component locations were reduced by as much as 10 dB in the frequency range of interest.
Viscoelastic struts for vibration mitigation of FORTE
NASA Astrophysics Data System (ADS)
Maly, Joseph R.; Butler, Thomas A.
1996-05-01
FORTE is a small satellite being developed by Los Alamos National Laboratory (LANL) and Sandia National Laboratories Albuquerque (SNLA). It will be placed into orbit via a Pegasus launch in 1996. Testing a full-scale engineering model of the structure using the proto- qualification, system-level vibration spectrum indicated that acceleration levels caused by structural resonances exceed component levels to which certain sensitive components had previously been qualified. Viscoelastic struts were designed to reduce response levels associated with these resonances by increasing the level of damping in key structural modes of the spacecraft. Four identical shear-lap struts were fabricated and installed between the two primary equipment decks. The struts were designed using a system finite element model (FEM) of the spacecraft, a component FEM of the strut, and measured viscoelastic properties. Direct complex stiffness testing was performed to characterize the frequency-dependent behavior of the struts, and these measured properties (shear modulus and loss factor) were used to represent the struts in the spacecraft model. System-level tests were repeated with the struts installed and the response power spectral densities at critical component locations were reduced by as much as 10 dB in the frequency range of interest.
A Computational Study of Viscoelastic Effects on Drop Dynamics in Microchannels
NASA Astrophysics Data System (ADS)
Izbassarov, Daulet; Muradoglu, Metin
2013-11-01
A front-tracking method is developed and applied to study effects of viscoelasticity on drop dynamics in microchannels. The FENE-CR and Oldroyd-B models are employed to model the viscoelasticity. The viscoelastic model equations are solved fully coupled with the flow equations. An explicit semi-analytical time integration scheme is used for the viscoelastic model equations at low Deborah numbers and a log-conformation is used to alleviate the well-known difficulties at high Deborah numbers. The log-conformation is found to be stable and very robust for a wide range of Deborah numbers. The method is first validated for the benchmark single-phase viscoelastic flow through an axisymmetric channel with a 4:1 constriction and the results are found to be in a good agreement with earlier computational simulations. The algorithm is then used to study fluid dynamics of buoyancy-driven viscoelastic two-phase systems in a capillary tube. Extensive computations are performed to examine the effects of confinement and rheological properties of the phases on drop mobility and deformation. Finally, the method is applied to study the motion and deformation of a viscoelastic droplet in a pressure driven axisymmetric contraction/expansion micro-channel. Key Words:Viscoelastic fluid,FENE model. This work is supported by the Scientific and Technical Research Council of Turkey (TUBITAK), Grant No. 112M181.
Adeyeye, Moji Christianah; Jain, Ashwinkumar C; Ghorab, Mohamed K M; Reilly, William J
2002-01-01
The purpose of this study was to examine the viscoelastic properties of topical creams containing various concentrations of microcrystalline cellulose and sodium carboxymethyl cellulose (Avicel(R) CL-611) as a stabilizer. Avicel CL-611 was used at 4 different levels (1%, 2%, 4%, and 6% dispersion) to prepare topical creams, and hydrocortisone acetate was used as a model drug. The viscoelastic properties such as loss modulus (G"), storage modulus (G'), and loss tangent (tan delta) of these creams were measured using a TA Instruments AR 1000 Rheometer and compared to a commercially available formulation. Continuous flow test to determine the yield stress and thixotropic behavior, and dynamic mechanical tests for determining the linear viscosity time sweep data, were performed. Drug release from the various formulations was studied using an Enhancer TM Cell assembly. Formulations containing 1% and 2% Avicel CL-611 had relative viscosity, yield stress, and thixotropic values that were similar to those of the commercial formulation. The elastic modulus (G') of the 1% and 2% formulation was relatively high and did not cross the loss modulus (G"), indicating that the gels were strong. In the commercial formulation, G' increased after preshearing and broke down after 600 seconds. The strain sweep tests showed that for all formulations containing Avicel CL-611, the G' was above G" with a good distance between them. The gel strength and the predominance of G' can be ranked 6% > 4% > 2%. The strain profiles for the 1% and 2% formulations were similar to those of the commercial formulation. The delta values for the 1% and 2% formulations were similar, and the formulations containing 4% Avicel CL-611 had lower delta values, indicating greater elasticity. Drug release from the commercial preparation was fastest compared to the formulations prepared using Avicel CL-611, a correlation with the viscoelastic properties. It was found that viscoelastic data, especially the strain
Viscoelasticity of biofilms and their recalcitrance to mechanical and chemical challenges
Peterson, Brandon W.; He, Yan; Ren, Yijin; Zerdoum, Aidan; Libera, Matthew R.; Sharma, Prashant K.; van Winkelhoff, Arie-Jan; Neut, Danielle; Stoodley, Paul; van der Mei, Henny C.; Busscher, Henk J.
2015-01-01
We summarize different studies describing mechanisms through which bacteria in a biofilm mode of growth resist mechanical and chemical challenges. Acknowledging previous microscopic work describing voids and channels in biofilms that govern a biofilms response to such challenges, we advocate a more quantitative approach that builds on the relation between structure and composition of materials with their viscoelastic properties. Biofilms possess features of both viscoelastic solids and liquids, like skin or blood, and stress relaxation of biofilms has been found to be a corollary of their structure and composition, including the EPS matrix and bacterial interactions. Review of the literature on viscoelastic properties of biofilms in ancient and modern environments as well as of infectious biofilms reveals that the viscoelastic properties of a biofilm relate with antimicrobial penetration in a biofilm. In addition, also the removal of biofilm from surfaces appears governed by the viscoelasticity of a biofilm. Herewith, it is established that the viscoelasticity of biofilms, as a corollary of structure and composition, performs a role in their protection against mechanical and chemical challenges. Pathways are discussed to make biofilms more susceptible to antimicrobials by intervening with their viscoelasticity, as a quantifiable expression of their structure and composition. PMID:25725015
Prediction of the Viscoelastic Bulk Modulus
NASA Astrophysics Data System (ADS)
Guo, Jiaxi; Simon, Sindee
2010-03-01
The bulk and shear viscoelastic responses for several materials appear to arise from the same molecular mechanisms at short times, i.e., Andrade creep where the KWW beta parameter is approximately 0.3. If this is indeed the case, prediction and placement of the bulk viscoelastic response can be made simply by knowing the limiting elastic and rubbery bulk moduli and the viscoelastic shear response. The proposed methodology, which uses only easily measured functions, is considerably less time- and labor-intensive than direct measurement of the viscoelastic bulk modulus. Here we investigate this hypothesis and compare the calculated viscoelastic bulk responses for several materials to existing data in the literature.
Nonlinear Viscoelastic Stress Transfer As a Possible Aftershock Triggering Mechanism
NASA Astrophysics Data System (ADS)
Zhang, X.; Shcherbakov, R.
2014-12-01
The earthquake dynamics can be modelled by employing the spring-block system [Burridge and Knopoff, 1967]. In this approach the earthquake fault is modelled by an array of blocks coupling the loading plate and the lower plate. The dynamics of the system is governed by the system of equations of motion for each block. It is possible to map this system into a cellular automata model, where the stress acting on each block is increased in each time step, and the failing process (frictional slip) is described by stress transfer rules [Olami et al, 1992]. The OFC model produces a power-law distribution for avalanche statistics but it is not capable of producing robust aftershock sequences which follow Omori's law.We propose a nonlinear viscoelastic stress transfer mechanism in the aftershock triggering. In a basic spring-block model setting, we introduce the nonlinear viscoelastic stress transfer between neighbouring blocks, as well as between blocks and the top loading plate. The shear stress of the viscous component is a power-law function of the velocity gradient with an exponent smaller or greater than 1 for the nonlinear viscoelasticity, or 1 for the linear case. The stress transfer function of this nonlinear viscoelastic model has a power-law time-dependent form. It features an instantaneous stress transmission triggering an instantaneous avalanche, which is the same as the original spring-block model; and a power-law relaxation term, which could trigger further aftershocks. We incorporate this nonlinear viscoelasticity mechanism in a lattice cellular automata model. The model could exhibit both the Gutenberg-Richter scaling for the frequency-magnitude distribution and a power-law time decay of aftershocks, which is in accordance with Omori's law. Our study suggests that the stress transfer function may play an important role in the aftershock triggering. We have found that the time decay curve of aftershocks is affected by the shape of the stress transfer function
Viscoelastic behaviour of pumpkin balloons
NASA Astrophysics Data System (ADS)
Gerngross, T.; Xu, Y.; Pellegrino, S.
2008-11-01
The lobes of the NASA ULDB pumpkin-shaped super-pressure balloons are made of a thin polymeric film that shows considerable time-dependent behaviour. A nonlinear viscoelastic model based on experimental measurements has been recently established for this film. This paper presents a simulation of the viscoelastic behaviour of ULDB balloons with the finite element software ABAQUS. First, the standard viscoelastic modelling capabilities available in ABAQUS are examined, but are found of limited accuracy even for the case of simple uniaxial creep tests on ULDB films. Then, a nonlinear viscoelastic constitutive model is implemented by means of a user-defined subroutine. This approach is verified by means of biaxial creep experiments on pressurized cylinders and is found to be accurate provided that the film anisotropy is also included in the model. A preliminary set of predictions for a single lobe of a ULDB is presented at the end of the paper. It indicates that time-dependent effects in a balloon structure can lead to significant stress redistribution and large increases in the transverse strains in the lobes.
Standing shear waves in anisotropic viscoelastic media
NASA Astrophysics Data System (ADS)
Krit, T.; Golubkova, I.; Andreev, V.
2015-10-01
We studied standing shear waves in anisotropic resonator represented by a rectangular parallelepiped (layer) fixed without slipping between two wooden plates of finite mass. The viscoelastic layer with edges of 70 mm × 40 mm × 15 mm was made of a rubber-like polymer plastisol with rubber bands inside. The bands were placed vertical between the top and the bottom plate. Mechanical properties of the plastisol itself were carefully measured previously. It was found that plastisol shows a cubic nonlinear behavior, i.e. the stress-strain curve could be represented as: σ = μɛ + βμɛ3, where ɛ stands for shear strain and σ is an applied shear stress. The value of shear modulus μ depends on frequency and was found to be several kilopascals which is common for such soft solids. Nonlinear parameter β is frequency dependent too and varies in range from tenths to unity at 1-100 Hz frequency range, decreasing with frequency growth. Stretching the rubber bands inside the layer leads to change of elastic properties in resonator. Such effect could be noticed due to frequency response of the resonator. The numerical model of the resonator was based on finite elements method (FEM) and performed in MatLab. The resonator was cut in hundreds of right triangular prisms. Each prism was provided with viscoelastic properties of the layer except for the top prisms provided with the wooden plate properties and the prisms at the site of the rubber bands provided with the rubber properties. The boundary conditions on each prism satisfied the requirements that resonator is inseparable and all its boundaries but bottom are free. The bottom boundary was set to move horizontally with constant acceleration amplitude. It was shown numerically that the resonator shows anisotropic behavior expressed in different frequency response to oscillations applied to a bottom boundary in different directions.
Viscoelasticity of brain corpus callosum in biaxial tension
NASA Astrophysics Data System (ADS)
Labus, Kevin M.; Puttlitz, Christian M.
2016-11-01
Computational models of the brain rely on accurate constitutive relationships to model the viscoelastic behavior of brain tissue. Current viscoelastic models have been derived from experiments conducted in a single direction at a time and therefore lack information on the effects of multiaxial loading. It is also unclear if the time-dependent behavior of brain tissue is dependent on either strain magnitude or the direction of loading when subjected to tensile stresses. Therefore, biaxial stress relaxation and cyclic experiments were conducted on corpus callosum tissue isolated from fresh ovine brains. Results demonstrated the relaxation behavior to be independent of strain magnitude, and a quasi-linear viscoelastic (QLV) model was able to accurately fit the experimental data. Also, an isotropic reduced relaxation tensor was sufficient to model the stress-relaxation in both the axonal and transverse directions. The QLV model was fitted to the averaged stress relaxation tests at five strain magnitudes while using the measured strain history from the experiments. The resulting model was able to accurately predict the stresses from cyclic tests at two strain magnitudes. In addition to deriving a constitutive model from the averaged experimental data, each specimen was fitted separately and the resulting distributions of the model parameters were reported and used in a probabilistic analysis to determine the probability distribution of model predictions and the sensitivity of the model to the variance of the parameters. These results can be used to improve the viscoelastic constitutive models used in computational studies of the brain.
Post-seismic relaxation theory on laterally heterogeneous viscoelastic model
Pollitz, F.F.
2003-01-01
Investigation was carried out into the problem of relaxation of a laterally heterogeneous viscoelastic Earth following an impulsive moment release event. The formal solution utilizes a semi-analytic solution for post-seismic deformation on a laterally homogeneous Earth constructed from viscoelastic normal modes, followed by application of mode coupling theory to derive the response on the aspherical Earth. The solution is constructed in the Laplace transform domain using the correspondence principle and is valid for any linear constitutive relationship between stress and strain. The specific implementation described in this paper is a semi-analytic discretization method which assumes isotropic elastic structure and a Maxwell constitutive relation. It accounts for viscoelastic-gravitational coupling under lateral variations in elastic parameters and viscosity. For a given viscoelastic structure and minimum wavelength scale, the computational effort involved with the numerical algorithm is proportional to the volume of the laterally heterogeneous region. Examples are presented of the calculation of post-seismic relaxation with a shallow, laterally heterogeneous volume following synthetic impulsive seismic events, and they illustrate the potentially large effect of regional 3-D heterogeneities on regional deformation patterns.
Viscoelasticity of colloidal polycrystals doped with impurities
NASA Astrophysics Data System (ADS)
Louhichi, Ameur; Tamborini, Elisa; Oberdisse, Julian; Cipelletti, Luca; Ramos, Laurence
2015-09-01
We investigate how the microstructure of a colloidal polycrystal influences its linear visco-elasticity. We use thermosensitive copolymer micelles that arrange in water in a cubic crystalline lattice, yielding a colloidal polycrystal. The polycrystal is doped with a small amount of nanoparticles, of size comparable to that of the micelles, which behave as impurities and thus partially segregate in the grain boundaries. We show that the shear elastic modulus only depends on the packing of the micelles and varies neither with the presence of nanoparticles nor with the crystal microstructure. By contrast, we find that the loss modulus is strongly affected by the presence of nanoparticles. A comparison between rheology data and small-angle neutron-scattering data suggests that the loss modulus is dictated by the total amount of nanoparticles in the grain boundaries, which in turn depends on the sample microstructure.
Viscoelasticity of colloidal polycrystals doped with impurities.
Louhichi, Ameur; Tamborini, Elisa; Oberdisse, Julian; Cipelletti, Luca; Ramos, Laurence
2015-09-01
We investigate how the microstructure of a colloidal polycrystal influences its linear visco-elasticity. We use thermosensitive copolymer micelles that arrange in water in a cubic crystalline lattice, yielding a colloidal polycrystal. The polycrystal is doped with a small amount of nanoparticles, of size comparable to that of the micelles, which behave as impurities and thus partially segregate in the grain boundaries. We show that the shear elastic modulus only depends on the packing of the micelles and varies neither with the presence of nanoparticles nor with the crystal microstructure. By contrast, we find that the loss modulus is strongly affected by the presence of nanoparticles. A comparison between rheology data and small-angle neutron-scattering data suggests that the loss modulus is dictated by the total amount of nanoparticles in the grain boundaries, which in turn depends on the sample microstructure. PMID:26465473
Origins of viscoelastic dissipation in self-assembled organic monolayers
Shinn, N.D.; Michalske, T.A.
1998-04-01
Although self-assembled monolayers (SAMs) are promising candidates for interfacial lubricants in micro-electromechanical systems, the relationship between the monolayer structure and its viscoelastic properties is not understood. Using Acoustic Wave Damping (AWD), the authors have measured the complex shear modulus of linear alkane thiol monolayers, HS(CH{sub 2}){sub n{minus}1}CH{sub 3} denoted as C{sub n}, on Au(111)-textured substrates. The AWD technique measures the elastic energy storage and dissipative loss within a SAM adsorbed onto the electrodes of a quartz crystal microbalance. For C{sub 12}, C{sub 14} and C{sub 18} SAMs, the storage modulus increases with alkane chain length, but the loss modulus exhibits no systematic correlation. To investigate the origins of energy dissipation, the authors used a new, high-sensitivity oscillator circuit to simultaneously monitor the adsorption kinetics and acoustic damping during monolayer growth from the gas phase. For both C{sub 9} and C{sub 12} thiols, the dissipation in the growing monolayer can be correlated with distinct two-dimensional fluid phases and the nucleation and growth of condensed-phase islands.
Stochastic system identification of skin properties: linear and wiener static nonlinear methods.
Chen, Yi; Hunter, Ian W
2012-10-01
Wiener static nonlinear system identification was used to study the linear dynamics and static nonlinearities in the response of skin and underlying tissue under indentation in vivo. A device capable of measuring the dynamic mechanical properties of bulk skin tissue was developed and it incorporates a custom-built Lorentz force actuator that measures the dynamic compliance between the input force (<12 N) and the output displacement (<20 mm). A simple linear stochastic system identification technique produced a variance accounted for (VAF) of 75-81% and Wiener static nonlinear techniques increased the VAF by 5%. Localized linear techniques increased the VAF to 85-95% with longer tests. Indentation experiments were conducted on 16 test subjects to determine device sensitivity and repeatability. Using the device, the coefficient of variation of test metrics was found to be as low as 2% for a single test location. The measured tissue stiffness was 300 N/m near the surface and 4.5 kN/m for high compression. The damping ranged from 5 to 23 N s/m. The bulk skin properties were also shown to vary significantly with gender and body mass index. The device and techniques used in this research can be applied to consumer product analysis, medical diagnosis and tissue research.
NASA Astrophysics Data System (ADS)
Alfi, V.; Cristelli, M.; Pietronero, L.; Zaccaria, A.
2009-02-01
We present a detailed study of the statistical properties of the Agent Based Model introduced in paper I [Eur. Phys. J. B, DOI: 10.1140/epjb/e2009-00028-4] and of its generalization to the multiplicative dynamics. The aim of the model is to consider the minimal elements for the understanding of the origin of the stylized facts and their self-organization. The key elements are fundamentalist agents, chartist agents, herding dynamics and price behavior. The first two elements correspond to the competition between stability and instability tendencies in the market. The herding behavior governs the possibility of the agents to change strategy and it is a crucial element of this class of models. We consider a linear approximation for the price dynamics which permits a simple interpretation of the model dynamics and, for many properties, it is possible to derive analytical results. The generalized non linear dynamics results to be extremely more sensible to the parameter space and much more difficult to analyze and control. The main results for the nature and self-organization of the stylized facts are, however, very similar in the two cases. The main peculiarity of the non linear dynamics is an enhancement of the fluctuations and a more marked evidence of the stylized facts. We will also discuss some modifications of the model to introduce more realistic elements with respect to the real markets.
NASA Astrophysics Data System (ADS)
Xin, Fu-Long; Bai, Xian-Xu; Qian, Li-Jun
2016-10-01
Magnetorheological elastomers (MREs), a smart composite, exhibit dual characteristics of both MR materials and particle reinforced composites, i.e., the viscoelasticity of MREs depends on external magnetic field as well as strain amplitude and excitation frequency. In this article, the principle of a frequency-, amplitude-, and magneto-dependent linear dynamic viscoelastic model for isotropic MREs is proposed and investigated. The viscoelasticity of MREs is divided into frequency- and amplitude-dependent mechanical viscoelasticity and frequency-, amplitude-, and magneto-dependent magnetic viscoelasticity. Based on the microstructures of ferrous particles and matrix, the relationships between mechanical shear modulus corresponding to the mechanical viscoelasticity and strain amplitude and excitation frequency are obtained. The relationships between magnetic shear modulus corresponding to the magnetic viscoelasticity with strain amplitude, excitation frequency, and further external magnetic field are derived using the magneto-elastic theory. The influence of magnetic saturation on the MR effect is also considered. The dynamic characteristics of a fabricated isotropic MRE sample under different strain amplitudes, excitation frequencies and external magnetic fields are tested. The parameters of the proposed model are identified with the experimental data and the theoretical expressions of shear storage modulus and shear loss modulus of the MRE sample are obtained. In the light of the theoretical expressions, the loss factors of the MRE sample under different loading conditions are analyzed and compared with the test results to evaluate the effectiveness of the proposed model.
Viscoelasticity and shear thinning of nanoconfined water.
Kapoor, Karan; Amandeep; Patil, Shivprasad
2014-01-01
Understanding flow properties and phase behavior of water confined to nanometer-sized pores and slits is central to a wide range of problems in science, such as percolation in geology, lubrication of future nano-machines, self-assembly and interactions of biomolecules, and transport through porous media in filtration processes. Experiments with different techniques in the past have reported that viscosity of nanoconfined water increases, decreases, or remains close to bulk water. Here we show that water confined to less than 20-nm-thick films exhibits both viscoelasticity and shear thinning. Typically viscoelasticity and shear thinning appear due to shearing of complex non-Newtonian mixtures possessing a slowly relaxing microstructure. The shear response of nanoconfined water in a range of shear frequencies (5 to 25 KHz) reveals that relaxation time diverges with reducing film thickness. It suggests that slow relaxation under confinement possibly arises due to existence of a critical point with respect to slit width. This criticality is similar to the capillary condensation in porous media.
Viscoelastic Flow Modelling for Polymer Flooding
NASA Astrophysics Data System (ADS)
de, Shauvik; Padding, Johan; Peters, Frank; Kuipers, Hans; Multi-scale Modelling of Multi-phase Flows Team
2015-11-01
Polymer liquids are used in the oil industry to improve the volumetric sweep and displacement efficiency of oil from a reservoir. Surprisingly, it is not only the viscosity but also the elasticity of the displacing fluid that determine the displacement efficiency. The main aim of our work is to obtain a fundamental understanding of the effect of fluid elasticity, by developing an advanced computer simulation methodology for the flow of non-Newtonian fluids through porous media. We simulate a 3D unsteady viscoelastic flow through a converging diverging geometry of realistic pore dimension using computational fluid dynamics (CFD).The primitive variables velocity, pressure and extra stresses are used in the formulation of models. The viscoelastic stress part is formulated using a FENE-P type of constitutive equation, which can predict both shear and elongational stress properties during this flow. A Direct Numerical Simulation (DNS) approach using Finite volume method (FVM) with staggered grid has been applied. A novel second order Immersed boundary method (IBM) has been incorporated to mimic porous media. The effect of rheological parameters on flow characteristics has also been studied. The simulations provide an insight into 3D flow asymmetry at higher Deborah numbers. Micro-Particle Image Velocimetry experiments are carried out to obtain further insights. These simulations present, for the first time, a detailed computational study of the effects of fluid elasticity on the imbibition of an oil phase.
Viscoelastic damping in crystalline composites and alloys
NASA Astrophysics Data System (ADS)
Ranganathan, Raghavan; Ozisik, Rahmi; Keblinski, Pawel
We use molecular dynamics simulations to study viscoelastic behavior of model Lennard-Jones (LJ) crystalline composites subject to an oscillatory shear deformation. The two crystals, namely a soft and a stiff phase, individually show highly elastic behavior and a very small loss modulus. On the other hand, when the stiff phase is included within the soft matrix as a sphere, the composite exhibits significant viscoelastic damping and a large phase shift between stress and strain. In fact, the maximum loss modulus in these model composites was found to be about 20 times greater than that given by the theoretical Hashin-Shtrikman upper bound. We attribute this behavior to the fact that in composites shear strain is highly inhomogeneous and mostly accommodated by the soft phase, corroborated by frequency-dependent Grüneisen parameter analysis. Interestingly, the frequency at which the damping is greatest scales with the microstructural length scale of the composite. Finally, a critical comparison between damping properties of these composites with ordered and disordered alloys and superlattice structures is made.
Linear and nonlinear optical properties of gold nanoparticle-Eu oxide composite thin films
NASA Astrophysics Data System (ADS)
Henari, F. Z.; Dakhel, A. A.
2008-08-01
In this work, nanogold particles incorporated onto europium oxide films at levels of 4% and 7% were fabricated by a vacuum evaporation technique on glass and silicon substrates held at 200 °C. Samples were investigated by x-ray diffraction and linear and nonlinear optical absorption. The linear optical absorption data were measured in the UV-visible-near infrared spectral regions and from these data the energy gap and the surface plasmon resonance were determined. The third order nonlinear optical properties of the nanogold particles incorporated onto europium oxide films were measured using the Z-scan technique. Nonlinear absorption and refraction were performed using a continuous wave laser at 633 nm. A large value of third order nonlinearities was obtained with the samples.
A generalized hydrodynamic model for acoustic mode stability in viscoelastic plasma fluid
NASA Astrophysics Data System (ADS)
Borah, B.; Haloi, A.; Karmakar, P. K.
2016-05-01
In this paper a generalized hydrodynamic (GH) model to investigate acoustic-mode excitation and stability in simplified strongly coupled bi-component plasma is proposed. The goal is centered in seeing the viscoelasticity-influences on the instability properties. The dispersive and nondispersive features are methodologically explored followed by numerical illustrations. It is seen that, unlike usual plasma acoustic mode, here the mode stability is drastically modified due to the considered viscoelastic effects contributed from both the electronic and ionic fluids. For example, it is found that there exists an excitation threshold value on angular wavenumber, K ≈3 in the K-space on the Debye scale, beyond which only dispersive characteristic features prevail. Further, it is demonstrated that the viscoelastic relaxation time plays a stabilizing influential role on the wave dynamics. In contrast, it is just opposite for the effective viscoelastic relaxation effect. Consistency with the usual viscoelasticity-free situations, with and without plasma approximation taken into account, is also established and explained. It is identified and conjectured that the plasma fluid viscoelasticity acts as unavoidable dispersive agency in attributing several new characteristics to acoustic wave excitation and propagation. The analysis is also exploited to derive a quantitative glimpse on the various basic properties and dimensionless numbers of the viscoelastic plasma. Finally, extended implications of our results tentative to different cosmic, space and astrophysical situations, amid the entailed facts and faults, are highlighted together with indicated future directions.
Jiménez-Sánchez, Arturo; Isunza-Manrique, Itzel; Ramos-Ortiz, Gabriel; Rodríguez-Romero, Jesús; Farfán, Norberto; Santillan, Rosa
2016-06-30
Design parameters derived from structure-property relationships play a very important role in the development of efficient molecular-based functional materials with optical properties. Here, we report on the linear and nonlinear optical properties of a fluorene-derived dipolar system (DS) and its octupolar analogue (OS), in which donor and acceptor groups are connected by a phenylacetylene linkage, as a strategy to increase the number of delocalized electrons in the π-conjugated system. The optical nonlinear response was analyzed in detail by experimental and theoretical methods, showing that, in the octupolar system OS, the dipolar effects induced a strong two-photon absorption process whose magnitude is as large as 2210 GM at infrared wavelengths. Solvatochromism studies were implemented to obtain further insight on the charge transfer process. We found that the triple bond plays a fundamental role in the linear and nonlinear optical responses. The strong solvatochromism behavior in DS and OS was analyzed by using four empirical solvent scales, namely Lippert-Mataga, Kamlet-Taft, Catalán, and the recently proposed scale of Laurence et al., finding consistent results of strong solvent polarizability and viscosity dependence. Finally, the role of the acceptor groups was further studied by synthesizing the analogous compound 2DS, having no acceptor group.
Jiménez-Sánchez, Arturo; Isunza-Manrique, Itzel; Ramos-Ortiz, Gabriel; Rodríguez-Romero, Jesús; Farfán, Norberto; Santillan, Rosa
2016-06-30
Design parameters derived from structure-property relationships play a very important role in the development of efficient molecular-based functional materials with optical properties. Here, we report on the linear and nonlinear optical properties of a fluorene-derived dipolar system (DS) and its octupolar analogue (OS), in which donor and acceptor groups are connected by a phenylacetylene linkage, as a strategy to increase the number of delocalized electrons in the π-conjugated system. The optical nonlinear response was analyzed in detail by experimental and theoretical methods, showing that, in the octupolar system OS, the dipolar effects induced a strong two-photon absorption process whose magnitude is as large as 2210 GM at infrared wavelengths. Solvatochromism studies were implemented to obtain further insight on the charge transfer process. We found that the triple bond plays a fundamental role in the linear and nonlinear optical responses. The strong solvatochromism behavior in DS and OS was analyzed by using four empirical solvent scales, namely Lippert-Mataga, Kamlet-Taft, Catalán, and the recently proposed scale of Laurence et al., finding consistent results of strong solvent polarizability and viscosity dependence. Finally, the role of the acceptor groups was further studied by synthesizing the analogous compound 2DS, having no acceptor group. PMID:27281172
Effect of Sb addition on linear and non-linear optical properties of amorphous Ge-Se-Sn thin films
NASA Astrophysics Data System (ADS)
Sharma, Navjeet; Sharma, Surbhi; Sarin, Amit; Kumar, Rajesh
2016-01-01
Optical characterization of amorphous thin films of Ge20Sn10Se70-xSbx (x = 0, 3, 6, 9, 12, 15) has been carried out. Thin films were deposited onto pre cleaned glass substrates using thermal evaporation technique. Transmission spectra of the films were recorded, for normal incidence, in range 400-2400 nm. Refractive index of the films was calculated using the envelope method by Swanepoel. Dispersion analysis has been carried out using single effective oscillator model. Other optical constants such as absorption coefficients, extinction coefficients have also been evaluated. Tauc plots were used to evaluate the optical band gap. The refractive index has been found to be increasing while the band gap decreases with increasing Sb concentration. The observed optical behavior of the films has been explained using chemical bond approach. Cohesive energy is found to be decreasing in the present work, which reflects that bond strength decreases with the increasing content of Sb. Non-linear optical parameters (i.e. n2 and χ(3)) have been derived from linear optical parameters (i.e. n, k, Eg). Observed changes in linear and non-linear parameters have been reported in this study.
Uniqueness of the interior plane strain time-harmonic viscoelastic inverse problem
NASA Astrophysics Data System (ADS)
Zhang, Yixiao; Barbone, Paul E.; Harari, Isaac; Oberai, Assad A.
2016-07-01
Elasticity imaging has emerged as a promising medical imaging technique with applications in the detection, diagnosis and treatment monitoring of several types of disease. In elasticity imaging measured displacement fields are used to generate images of elastic parameters of tissue by solving an inverse problem. When the tissue excitation, and the resulting tissue motion is time-harmonic, elasticity imaging can be extended to image the viscoelastic properties of the tissue. This leads to an inverse problem for the complex-valued shear modulus at a given frequency. In this manuscript we have considered the uniqueness of this inverse problem for an incompressible, isotropic linear viscoelastic solid in a state of plane strain. For a single measured displacement field we conclude that the solution is infinite dimensional, and the data required to render it unique is determined by the measured strain field. In contrast, for two independent displacement fields such that the principal directions of the resulting strain fields are different, the space of possible solutions is eight dimensional, and given additional data, like the value of the shear modulus at four locations, or over a calibration region, we may determine the shear modulus everywhere. We have also considered simple analytical examples that verify these results and offer additional insights. The results derived in this paper may be used as guidelines by the practitioners of elasticity imaging in designing more robust and accurate imaging protocols.
López-Guerra, Enrique A; Solares, Santiago D
2014-01-01
We examine different approaches to model viscoelasticity within atomic force microscopy (AFM) simulation. Our study ranges from very simple linear spring-dashpot models to more sophisticated nonlinear systems that are able to reproduce fundamental properties of viscoelastic surfaces, including creep, stress relaxation and the presence of multiple relaxation times. Some of the models examined have been previously used in AFM simulation, but their applicability to different situations has not yet been examined in detail. The behavior of each model is analyzed here in terms of force-distance curves, dissipated energy and any inherent unphysical artifacts. We focus in this paper on single-eigenmode tip-sample impacts, but the models and results can also be useful in the context of multifrequency AFM, in which the tip trajectories are very complex and there is a wider range of sample deformation frequencies (descriptions of tip-sample model behaviors in the context of multifrequency AFM require detailed studies and are beyond the scope of this work).
Free vibrations of a taut cable with a general viscoelastic damper modeled by fractional derivatives
NASA Astrophysics Data System (ADS)
Sun, Limin; Chen, Lin
2015-01-01
This study extends dynamic understanding of a taut cable with a viscous damper at arbitrary location to that with a general linear viscoelastic (VE) damper portrayed by a five-parameter fractional derivative model (FDM). The FDM is able to describe a generalized relationship between force and deformation of viscoelastic dampers (material) in a wide frequency range, which can simulate a practical damper including its support condition or a secondary tie between neighboring cables. Free vibrations of the passively controlled cable system have then been formulated analytically through complex modal analysis. For the restricted case that the FDM is installed close to one cable anchorage, asymptotic solutions for the system complex frequency and modal damping are presented; explicit formulas have also been derived to determine the maximal attainable damping and corresponding optimum FDM parameters, based on which effects of frequency-dependent damper properties are appreciated. Considering the FDM located at arbitrary location, the three distinct regimes of frequency evolutions observed for a cable with a viscous damper have been generalized to that with a VE damper; also, new characteristics of the regime diagram and the frequency evolution in each regime are observed.
Reynolds, Jacob G.
2013-01-11
Partial molar properties are the changes occurring when the fraction of one component is varied while the fractions of all other component mole fractions change proportionally. They have many practical and theoretical applications in chemical thermodynamics. Partial molar properties of chemical mixtures are difficult to measure because the component mole fractions must sum to one, so a change in fraction of one component must be offset with a change in one or more other components. Given that more than one component fraction is changing at a time, it is difficult to assign a change in measured response to a change in a single component. In this study, the Component Slope Linear Model (CSLM), a model previously published in the statistics literature, is shown to have coefficients that correspond to the intensive partial molar properties. If a measured property is plotted against the mole fraction of a component while keeping the proportions of all other components constant, the slope at any given point on a graph of this curve is the partial molar property for that constituent. Actually plotting this graph has been used to determine partial molar properties for many years. The CSLM directly includes this slope in a model that predicts properties as a function of the component mole fractions. This model is demonstrated by applying it to the constant pressure heat capacity data from the NaOH-NaAl(OH{sub 4}H{sub 2}O system, a system that simplifies Hanford nuclear waste. The partial molar properties of H{sub 2}O, NaOH, and NaAl(OH){sub 4} are determined. The equivalence of the CSLM and the graphical method is verified by comparing results detennined by the two methods. The CSLM model has been previously used to predict the liquidus temperature of spinel crystals precipitated from Hanford waste glass. Those model coefficients are re-interpreted here as the partial molar spinel liquidus temperature of the glass components.
NASA Technical Reports Server (NTRS)
Gawronski, W.
2004-01-01
Wind gusts are the main disturbances that depreciate tracking precision of microwave antennas and radiotelescopes. The linear-quadratic-Gaussian (LQG) controllers - as compared with the proportional-and-integral (PI) controllers significantly improve the tracking precision in wind disturbances. However, their properties have not been satisfactorily understood; consequently, their tuning is a trial-and-error process. A control engineer has two tools to tune an LQG controller: the choice of coordinate system of the controller model and the selection of weights of the LQG performance index. This article analyzes properties of an open- and closed-loop antenna. It shows that the proper choice of coordinates of the open-loop model simplifies the shaping of the closed-loop performance. The closed-loop properties are influenced by the LQG weights. The article shows the impact of the weights on the antenna closed-loop bandwidth, disturbance rejection properties, and antenna acceleration. The bandwidth and the disturbance rejection characterize the antenna performance, while the acceleration represents the performance limit set by the antenna hardware (motors). The article presents the controller tuning procedure, based on the coordinate selection and the weight properties. The procedure rationally shapes the closed-loop performance, as an alternative to the trial-and-error approach.
Elastic and viscoelastic characterization of mouse oocytes using micropipette indentation.
Liu, Xinyu; Shi, Jiayi; Zong, Zong; Wan, Kai-Tak; Sun, Yu
2012-10-01
This paper reports the first quantitative comparison study of elastic and viscoelastic properties of oocytes from young and aged mice. A force measurement technique, including a poly(dimethylsiloxane) (PDMS) cell holding device and a sub-pixel computer vision tracking algorithm, is utilized for measuring forces applied to an oocyte and resultant cell deformations in real time during oocyte manipulation. To characterize elastic and viscoelastic properties of the oocytes, a stress-relaxation indentation test is performed. A two-step, large-deformation mechanical model is developed to extract the mechanical properties of the oocytes from the measured force-deformation data. The experimental results demonstrate that the aged oocytes are significantly softer (instantaneous modulus: 2.2 vs. 5.2 kPa in young oocytes) but more viscous (relaxation time: 4.1 vs. 2.3 s in young oocytes) than the young oocytes.
Elastic and viscoelastic characterization of mouse oocytes using micropipette indentation.
Liu, Xinyu; Shi, Jiayi; Zong, Zong; Wan, Kai-Tak; Sun, Yu
2012-10-01
This paper reports the first quantitative comparison study of elastic and viscoelastic properties of oocytes from young and aged mice. A force measurement technique, including a poly(dimethylsiloxane) (PDMS) cell holding device and a sub-pixel computer vision tracking algorithm, is utilized for measuring forces applied to an oocyte and resultant cell deformations in real time during oocyte manipulation. To characterize elastic and viscoelastic properties of the oocytes, a stress-relaxation indentation test is performed. A two-step, large-deformation mechanical model is developed to extract the mechanical properties of the oocytes from the measured force-deformation data. The experimental results demonstrate that the aged oocytes are significantly softer (instantaneous modulus: 2.2 vs. 5.2 kPa in young oocytes) but more viscous (relaxation time: 4.1 vs. 2.3 s in young oocytes) than the young oocytes. PMID:22644532
Johnson, Paul A; Tencate, James A; Le Bas, Pierre-Yves; Guyer, Robert; Vu, Cung Khac; Skelt, Christopher
2013-11-05
In some aspects of the disclosure, a method and an apparatus is disclosed for investigating material surrounding the borehole. The method includes generating a first low frequency acoustic wave within the borehole, wherein the first low frequency acoustic wave induces a linear and a nonlinear response in one or more features in the material that are substantially perpendicular to a radius of the borehole; directing a first sequence of high frequency pulses in a direction perpendicularly with respect to the longitudinal axis of the borehole into the material contemporaneously with the first acoustic wave; and receiving one or more second high frequency pulses at one or more receivers positionable in the borehole produced by an interaction between the first sequence of high frequency pulses and the one or more features undergoing linear and nonlinear elastic distortion due to the first low frequency acoustic wave to investigate the material surrounding the borehole.
Wu, Heng-Qing; Sun, Shi-Ling; Zhong, Rong-Lin; Xu, Hong-Liang; Su, Zhong-Min
2012-11-01
In the present work, Li@porphyrins and their derivatives were designed in order to explore the effect of dehydrogenation/hydrogenation on linear and nonlinear optical properties. Their stable structures were obtained by the M06-2X method. Moreover, the M06-2X method showed that dehydrogenation/hydrogenation has greatly influences polarizabilities (α₀ values) and hyperpolarizabilities (β(tot) and γ(tot) values): α₀ values ranged from 331 to 389 au, β(tot) values from 0 to 2465 au, and γ(tot) values from -21.2 × 10⁴ to 21.4 × 10⁴ au. This new knowledge of the effect of dehydrogenation/hydrogenation on nonlinear optical properties may prove beneficial to the design and development of high-performance porphyrin materials. PMID:22722697
Preparation, linear and NLO properties of DNA-CTMA-SBE complexes
NASA Astrophysics Data System (ADS)
Manea, Ana-Maria; Rau, Ileana; Kajzar, Francois; Meghea, Aurelia
2013-10-01
Synthesis of deoxyribonucleic acid (DNA) - was cetyltrimethylammonium (CTMA) - sea buckthorn extract (SBE) at different concentrations is decribed. The complexes were processed into good optical quality thin films by spin coating on different substrates such as: glass, silica and ITO covered glass substrates. SBE contains many bioactive substances that can be used in the treatment of several diseases, such as cardiovascular disease, cancer, and acute mountain sickness. The obtained thin films were characterized for their spectroscopic, fluorescent, linear and nonlinear optical properties as function of SBE concentration. The third-order nonlinear optical (NLO) properties of thin films were determined by the optical third-harmonic generation technique at 1 064.2 nm fundamental wavelength.
Synthesis, crystal growth and studies on non-linear optical property of new chalcones
NASA Astrophysics Data System (ADS)
Sarojini, B. K.; Narayana, B.; Ashalatha, B. V.; Indira, J.; Lobo, K. G.
2006-09-01
The synthesis, crystal growth and non-linear optical (NLO) property of new chalcone derivatives are reported. 4-Propyloxy and 4-butoxy benzaldehydes were made to under go Claisen-Schmidt condensation with 4-methoxy, 4-nitro and 4-phenoxy acetophenones to form corresponding chalcones. The newly synthesized compounds were characterized by analytical and spectral data. The Second harmonic generation (SHG) efficiency of these compounds was measured by powder technique using Nd:YAG laser. Among tested compounds three chalcones showed NLO property. The chalcone 1-(4-methoxyphenyl)-3-(4-propyloxy phenyl)-2-propen-1-one exhibited SHG conversion efficiency 2.7 times that of urea. The bulk crystal of 1-(4-methoxyphenyl)-3-(4-butoxyphenyl)-2-propen-1-one (crystal size 65×28×15 mm 3) was grown by slow-evaporation technique from acetone. Microhardness of the crystal was tested by Vicker's microhardness method.
Self-consistent modeling of visco-elastic polycrystals: Application to irradiation creep and growth
NASA Astrophysics Data System (ADS)
Turner, P. A.; Tomé, C. N.
1993-07-01
w EPRESENT a model that permits the simulation of the transient response of polycrystalline aggregates to externally imposed loads and temperature gradients. The mechanical response of the constitutive grains includes elastic, Newtonian (linearly viscous), thermal and growth terms. The formulation explicitly accounts for the anisotropy in the elastic, creep, thermal and growth properties of both grains and polycrystals, and describes the time evolution of the overall visco-elastic moduli and of the internal stresses. It also provides, as limit cases, the correct overall elastic, thermal, creep and growth moduli of the polycrystal. The model is applied to analyse the characteristics of irradiation creep and growth in reactor tubes subjected to hydrostatic pressure. The influence of texture, grain anisotropy, grain shape and thermal stresses over the predicted polycrystal response, and expecially over the transient regime, is analysed in detail.
NASA Astrophysics Data System (ADS)
Lhuissier, Henri; Néel, Baptiste; Limat, Laurent
2014-11-01
A jet of a Newtonian liquid impacting onto a wall at right angle spreads as a thin liquid sheet which preserves the radial symmetry of the jet. We observe that for a viscoelastic jet (solution of polyethylene glycol in water) this symmetry can break: close to the wall, the jet cross-section is faceted and radial steady liquid films (membranes) form, which connect the cross-section vertices to the sheet. The number of membranes increases with increasing viscoelastic relaxation time of the solution, but also with increasing jet velocity and decreasing distance from the jet nozzle to the wall. A mechanism for this surprising destabilization of the jet, which develops perpendicularly to the direction expected for a buckling mechanism, is presented that explains these dependences. The large-scale consequences of the jet destabilization on the sheet spreading and fragmentation, which show through the faceting of hydraulic jumps and suspended (Savart) sheets, will also be discussed.
Probing the linear and nonlinear optical properties of nitrogen-substituted carbon nanotube.
Sun, Shi-Ling; Hu, Yang-Yang; Xu, Hong-Liang; Su, Zhong-Min; Hao, Li-Zhu
2012-07-01
In view of their intriguing structural and electrical properties, the linear and nonlinear optical (NLO) responses of six carbon nanotube (CNT) molecules substituted by nitrogen atoms at one end have been explored by using the CAM-B3LYP method. Molecules 1, 2 and 3 were obtained by increasing the lengths of the CNTs, and 1-Li, 2-Li and 3-Li were constructed by doping one Li atom into the N-substituted end of 1, 2 and 3 (mentioned above), respectively. Two effective approaches have been proposed to increase nonlinear optical properties(NLO): increasing the length of the CNT as well as doping one Li atom into the N-substituted end. The results show that both the linear polarizabilities (α(0)) and nonlinear first hyperpolarizabilities (β(tot)) values increase with increasing the lengths of the CNTs: 188 of 1 < 307 of 2 < 453 of 3 for α(0) and 477 of 1 < 2654 of 2 < 3906 au of 3 for β(tot). Significantly, compared with the non-doped CNTs, the β(tot) values are remarkably enhanced by doping one Li atom into the N-substituted end: 477 of 1 < 23258 of 1-Li, 2654 of 2 < 37244 of 2-Li, and 3906 of 3 < 72004 au of 3-Li. Moreover, the β(vec) values show a similar trend to the β(tot) values. Our results may be beneficial to experimentalists in exploring high-performance nonlinear optical materials based on CNT.
NASA Astrophysics Data System (ADS)
Yamanaka, Kota; Hirata, Shinnosuke; Hachiya, Hiroyuki
2016-07-01
Ultrasonic distance measurement for obstacles has been recently applied in automobiles. The pulse–echo method based on the transmission of an ultrasonic pulse and time-of-flight (TOF) determination of the reflected echo is one of the typical methods of ultrasonic distance measurement. Improvement of the signal-to-noise ratio (SNR) of the echo and the avoidance of crosstalk between ultrasonic sensors in the pulse–echo method are required in automotive measurement. The SNR of the reflected echo and the resolution of the TOF are improved by the employment of pulse compression using a maximum-length sequence (M-sequence), which is one of the binary pseudorandom sequences generated from a linear feedback shift register (LFSR). Crosstalk is avoided by using transmitted signals coded by different M-sequences generated from different LFSRs. In the case of lower-order M-sequences, however, the number of measurement channels corresponding to the pattern of the LFSR is not enough. In this paper, pulse compression using linear-frequency-modulated (LFM) signals coded by M-sequences has been proposed. The coding of LFM signals by the same M-sequence can produce different transmitted signals and increase the number of measurement channels. In the proposed method, however, the truncation noise in autocorrelation functions and the interference noise in cross-correlation functions degrade the SNRs of received echoes. Therefore, autocorrelation properties and cross-correlation properties in all patterns of combinations of coded LFM signals are evaluated.
NASA Astrophysics Data System (ADS)
Yamanaka, Kota; Hirata, Shinnosuke; Hachiya, Hiroyuki
2016-07-01
Ultrasonic distance measurement for obstacles has been recently applied in automobiles. The pulse-echo method based on the transmission of an ultrasonic pulse and time-of-flight (TOF) determination of the reflected echo is one of the typical methods of ultrasonic distance measurement. Improvement of the signal-to-noise ratio (SNR) of the echo and the avoidance of crosstalk between ultrasonic sensors in the pulse-echo method are required in automotive measurement. The SNR of the reflected echo and the resolution of the TOF are improved by the employment of pulse compression using a maximum-length sequence (M-sequence), which is one of the binary pseudorandom sequences generated from a linear feedback shift register (LFSR). Crosstalk is avoided by using transmitted signals coded by different M-sequences generated from different LFSRs. In the case of lower-order M-sequences, however, the number of measurement channels corresponding to the pattern of the LFSR is not enough. In this paper, pulse compression using linear-frequency-modulated (LFM) signals coded by M-sequences has been proposed. The coding of LFM signals by the same M-sequence can produce different transmitted signals and increase the number of measurement channels. In the proposed method, however, the truncation noise in autocorrelation functions and the interference noise in cross-correlation functions degrade the SNRs of received echoes. Therefore, autocorrelation properties and cross-correlation properties in all patterns of combinations of coded LFM signals are evaluated.
Properties of Linear Contrails Detected in 2012 Northern Hemisphere MODIS Imagery
NASA Technical Reports Server (NTRS)
Duda, David P.; Chee, Thad; Khlopenkov, Konstantin; Bedka, Sarah; Spangenberg, Doug; Minnis, Patrick
2015-01-01
Observation of linear contrail cirrus coverage and retrieval of their optical properties are valuable data for validating atmospheric climate models that represent contrail formation explicitly. These data can reduce our uncertainty of the regional effects of contrail-generated cirrus on global radiative forcing, and thus improve our estimation of the impact of commercial aviation on climate change. We use an automated contrail detection algorithm (CDA) to determine the coverage of linear persistent contrails over the Northern Hemisphere during 2012. The contrail detection algorithm is a modified form of the Mannstein et al. (1999) method, and uses several channels from thermal infrared MODIS data to reduce the occurrence of false positive detections. A set of contrail masks of varying sensitivity is produced to define the potential range of uncertainty in contrail coverage estimated by the CDA. Global aircraft emissions waypoint data provided by FAA allow comparison of detected contrails with commercial aircraft flight tracks. A pixel-level product based on the advected flight tracks defined by the waypoint data and U-V wind component profiles from the NASA GMAO GEOS-4 reanalysis has been developed to assign a confidence of contrail detection for the contrail mask. To account for possible contrail cirrus missed by the CDA, a post-processing method based on the assumption that pixels adjacent to detected linear contrails will have radiative signatures similar to those of the detected contrails is applied to the Northern Hemisphere data. Results from several months of MODIS observations during 2012 will be presented, representing a near-global climatology of contrail coverage. Linear contrail coverage will be compared with coverage estimates determined previously from 2006 MODIS data.
Linear and nonlinear optical properties of Sb-doped GeSe2 thin films
NASA Astrophysics Data System (ADS)
Zhang, Zhen-Ying; Chen, Fen; Lu, Shun-Bin; Wang, Yong-Hui; Shen, Xiang; Dai, Shi-Xun; Nie, Qiu-Hua
2015-06-01
Sb-doped GeSe2 chalcogenide thin films are prepared by the magnetron co-sputtering method. The linear optical properties of as-deposited films are derived by analyzing transmission spectra. The refractive index rises and the optical band gap decreases from 2.08 eV to 1.41 eV with increasing the Sb content. X-ray photoelectron spectra further confirm the formation of a covalent Sb-Se bond. The third-order nonlinear optical properties of thin films are investigated under femtosecond laser excitation at 800 nm. The results show that the third-order nonlinear optical properties are enhanced with increasing the concentration of Sb. The nonlinear refraction indices of these thin films are measured to be on the order of 10-18 m2/W with a positive sign and the nonlinear absorption coefficients are obtained to be on the order of 10-10 m/W. These excellent properties indicate that Sb-doped Ge-Se films have a good prospect in the applications of nonlinear optical devices. Project supported by the National Key Basic Research Program of China (Grant No. 2012CB722703), the National Natural Science Foundation of China (Grant No. 61377061), the Young Leaders of Academic Climbing Project of the Education Department of Zhejiang Province, China (Grant No. pd2013092), the Program for Innovative Research Team of Ningbo City, China (Grant No. 2009B217), and the K. C. Wong Magna Fund in Ningbo University, China.
NASA Astrophysics Data System (ADS)
Liu, M.; Wang, Y.; Ren, J.
2015-04-01
Viscoelastic dampers are one of popular vibration mitigation devices applied to tall buildings to reduce seismic and wind-induced vibiration. In this paper，a new kind of viscoelastic-wall damper, which could be installed at the shearwall location of high-rising buildings, is proposed to enhance the energy disspation ability. The seismic resistance behaviors of one tall building installed with the viscoelastic-wall dampers are investigated by numerical analysis. The mechanical property testing of the viscoelastic-wall damper is carried to investigate its performance parameter under various exciting frequency and strain amplitude. According to the testing results, a mathematical model of viscoelastic - wall damper is modeled based on Kelvin model. On the basis of a 36-floor frame-shear wall structure and using the finite element software ABAQUS, two finite element models of the high-rising building with and without viscoelastic-wall dampers are set up. Elasto-plastic time-history analysis is used to compare the seismic performance of the two structures subjected to the frequently and rarely earthquakes. It is proved that the seismic response of the structure is mitigated effectively when it is equipped with viscoelastic-wall dampers.
Dynamics of contracting viscoelastic filaments
NASA Astrophysics Data System (ADS)
Harris, Michael; Appathurai, Santosh; Bhat, Pradeep; Basaran, Osman
2009-11-01
Satellite drops are detrimental to many industrial applications involving the formation of viscoelastic drops including inkjet printing, DNA microarraying, and printing of flexible solar cells. The precursor to these satellite drops is a slender liquid filament that connects an about-to-form drop to the rest of the liquid in the nozzle. Once a filament is formed, it contracts due to surface tension. A filament may undergo further breakup during recoil. Whereas the contraction of Newtonian filaments in a passive ambient fluid is well understood (Schulkes 1996 and Notz and Basaran 2004), the contraction dynamics of viscoelastic filaments remains largely unexplored and is addressed in this presentation. Here the filament shape is idealized as an axisymmetric fluid cylinder terminated by hemispherical end-caps, and the conformation tensor formalism (Pasquali & Scriven 2002) is used to model the viscoelasticity. The dynamics of contracting filaments are then analyzed by means of both a well-benchmarked two-dimensional finite element algorithm (Notz et al. 2001, Chen et al. 2002) and a one-dimensional slender-jet algorithm (Padgett et al. 1996). Regions of the parameter space are identified where recoiling filaments give rise to either a single satellite drop or multiple satellites.
Self-gravitational instability in magnetized finitely conducting viscoelastic fluid
NASA Astrophysics Data System (ADS)
Prajapati, R. P.; Chhajlani, R. K.
2013-04-01
The linear self-gravitational instability of finitely conducting, magnetized viscoelastic fluid is investigated using the modified generalized hydrodynamic (GH) model. A general dispersion relation is obtained with the help of linearized perturbation equations using the normal mode analysis and it is discussed for longitudinal and transverse modes of propagation. In longitudinal propagation, we find that Alfven mode is uncoupled with the gravitating mode. The Jeans criterion of instability is determined which depends upon shear viscosity and bulk viscosity while it is independent of magnetic field. The viscoelastic effects modify the fundamental Jeans criterion of gravitational instability. In transverse mode of propagation, the Alfven mode couples with the acoustic mode, compressional viscoelastic mode and gravitating mode. The growth rate of Jeans instability is compared in weakly coupled plasma (WCP) and strongly coupled plasma (SCP) which is larger for SCP in both the modes of propagations. The presence of finite electrical resistivity removes the effect of magnetic field in the condition of Jeans instability and expression of critical Jeans wavenumber. It is found that Mach number and shear viscosity has stabilizing while finite electrical resistivity has destabilizing influence on the growth rate of Jeans instability.
Unsteady boundary-layer flow over jerked plate moving in a free stream of viscoelastic fluid.
Munawar, Sufian; Mehmood, Ahmer; Ali, Asif; Saleem, Najma
2014-01-01
This study aims to investigate the unsteady boundary-layer flow of a viscoelastic non-Newtonian fluid over a flat surface. The plate is suddenly jerked to move with uniform velocity in a uniform stream of non-Newtonian fluid. Purely analytic solution to governing nonlinear equation is obtained. The solution is highly accurate and valid for all values of the dimensionless time 0 ≤ τ < ∞. Flow properties of the viscoelastic fluid are discussed through graphs. PMID:24892060
Unsteady Boundary-Layer Flow over Jerked Plate Moving in a Free Stream of Viscoelastic Fluid
Mehmood, Ahmer; Ali, Asif; Saleem, Najma
2014-01-01
This study aims to investigate the unsteady boundary-layer flow of a viscoelastic non-Newtonian fluid over a flat surface. The plate is suddenly jerked to move with uniform velocity in a uniform stream of non-Newtonian fluid. Purely analytic solution to governing nonlinear equation is obtained. The solution is highly accurate and valid for all values of the dimensionless time 0 ≤ τ < ∞. Flow properties of the viscoelastic fluid are discussed through graphs. PMID:24892060
Collective dynamics of sperm in viscoelastic fluid
NASA Astrophysics Data System (ADS)
Tung, Chih-Kuan; Harvey, Benedict B.; Fiore, Alyssa G.; Ardon, Florencia; Suarez, Susan S.; Wu, Mingming
Collective dynamics in biology is an interesting subject for physicists, in part because of its close relations to emergent behaviors in condensed matter, such as phase separation and criticality. However, the emergence of order is often less drastic in systems composed of the living cells, sometimes due to the natural variability among individual organisms. Here, using bull sperm as a model system, we demonstrate that the cells migrate collectively in viscoelastic fluids, exhibiting behavior similar to ``flocking''. This collectiveness is greatly reduced in similarly viscous Newtonian fluids, suggesting that the cell-cell interaction is primarily a result of the elastic property or the memory effect of the fluids, instead of pure hydrodynamic interactions. Unlike bacterial swarming, this collectiveness does not require a change in phenotype of the cells; therefore, it is a better model system for physicists. Supported by NIH grant 1R01HD070038.
Viscoelasticity of nano-alumina dispersions
Rand, B.; Fries, R.
1996-06-01
The flow and viscoelastic properties of electrostatically stabilized nano-alumina dispersions have been studied as a function of ionic strength and volume fraction of solids. At low ionic strength the suspensions were deflocculated and showed a transition from viscous to elastic behavior as the solid content increased associated with the onset of double layer interpenetration. The phase transition was progressively shifted to higher solids fractions with increasing ionic strength. At higher ionic strength, above the critical coagulation concentration, the suspensions formed attractive networks characterized by high elasticity. Two independent methods of estimating the effective radius of electrostatically stabilized {open_quotes}soft{close_quotes} particles, a{sub eff}, are presented based on phase angle data and a modified Dougherty-Krieger equation. The results suggest that a{sub eff} is not constant for a given system but changes with both solids fraction and ionic strength.
Estimation of viscoelastic parameters in Prony series from shear wave propagation
NASA Astrophysics Data System (ADS)
Jung, Jae-Wook; Hong, Jung-Wuk; Lee, Hyoung-Ki; Choi, Kiwan
2016-06-01
When acquiring accurate ultrasonic images, we must precisely estimate the mechanical properties of the soft tissue. This study investigates and estimates the viscoelastic properties of the tissue by analyzing shear waves generated through an acoustic radiation force. The shear waves are sourced from a localized pushing force acting for a certain duration, and the generated waves travel horizontally. The wave velocities depend on the mechanical properties of the tissue such as the shear modulus and viscoelastic properties; therefore, we can inversely calculate the properties of the tissue through parametric studies.
A Numerical Model of Viscoelastic Flow in Microchannels
Trebotich, D; Colella, P; Miller, G; Liepmann, D
2002-11-14
The authors present a numerical method to model non-Newtonian, viscoelastic flow at the microscale. The equations of motion are the incompressible Navier-Stokes equations coupled with the Oldroyd-B constitutive equation. This constitutive equation is chosen to model a Boger fluid which is representative of complex biological solutions exhibiting elastic behavior due to macromolecules in the solution (e.g., DNA solution). The numerical approach is a projection method to impose the incompressibility constraint and a Lax-Wendroff method to predict velocities and stresses while recovering both viscous and elastic limits. The method is second-order accurate in space and time, free-stream preserving, has a time step constraint determined by the advective CFL condition, and requires the solution of only well-behaved linear systems amenable to the use of fast iterative methods. They demonstrate the method for viscoelastic incompressible flow in simple microchannels (2D) and microducts (3D).
Wall-mode instability in plane shear flow of viscoelastic fluid over a deformable solid.
Chokshi, Paresh; Bhade, Piyush; Kumaran, V
2015-02-01
The linear stability analysis of a plane Couette flow of an Oldroyd-B viscoelastic fluid past a flexible solid medium is carried out to investigate the role of polymer addition in the stability behavior. The system consists of a viscoelastic fluid layer of thickness R, density ρ, viscosity η, relaxation time λ, and retardation time βλ flowing past a linear elastic solid medium of thickness HR, density ρ, and shear modulus G. The emphasis is on the high-Reynolds-number wall-mode instability, which has recently been shown in experiments to destabilize the laminar flow of Newtonian fluids in soft-walled tubes and channels at a significantly lower Reynolds number than that for flows in rigid conduits. For Newtonian fluids, the linear stability studies have shown that the wall modes become unstable when flow Reynolds number exceeds a certain critical value Re(c) which scales as Σ(3/4), where Reynolds number Re=ρVR/η,V is the top-plate velocity, and dimensionless parameter Σ=ρGR(2)/η(2) characterizes the fluid-solid system. For high-Reynolds-number flow, the addition of polymer tends to decrease the critical Reynolds number in comparison to that for the Newtonian fluid, indicating a destabilizing role for fluid viscoelasticity. Numerical calculations show that the critical Reynolds number could be decreased by up to a factor of 10 by the addition of small amount of polymer. The critical Reynolds number follows the same scaling Re(c)∼Σ(3/4) as the wall modes for a Newtonian fluid for very high Reynolds number. However, for moderate Reynolds number, there exists a narrow region in β-H parametric space, corresponding to very dilute polymer solution (0.9≲β<1) and thin solids (H≲1.1), in which the addition of polymer tends to increase the critical Reynolds number in comparison to the Newtonian fluid. Thus, Reynolds number and polymer properties can be tailored to either increase or decrease the critical Reynolds number for unstable modes, thus providing
Wall-mode instability in plane shear flow of viscoelastic fluid over a deformable solid
NASA Astrophysics Data System (ADS)
Chokshi, Paresh; Bhade, Piyush; Kumaran, V.
2015-02-01
The linear stability analysis of a plane Couette flow of an Oldroyd-B viscoelastic fluid past a flexible solid medium is carried out to investigate the role of polymer addition in the stability behavior. The system consists of a viscoelastic fluid layer of thickness R , density ρ , viscosity η , relaxation time λ , and retardation time β λ flowing past a linear elastic solid medium of thickness H R , density ρ , and shear modulus G . The emphasis is on the high-Reynolds-number wall-mode instability, which has recently been shown in experiments to destabilize the laminar flow of Newtonian fluids in soft-walled tubes and channels at a significantly lower Reynolds number than that for flows in rigid conduits. For Newtonian fluids, the linear stability studies have shown that the wall modes become unstable when flow Reynolds number exceeds a certain critical value Rec which scales as Σ3 /4, where Reynolds number Re =ρ V R /η ,V is the top-plate velocity, and dimensionless parameter Σ =ρ G R2/η2 characterizes the fluid-solid system. For high-Reynolds-number flow, the addition of polymer tends to decrease the critical Reynolds number in comparison to that for the Newtonian fluid, indicating a destabilizing role for fluid viscoelasticity. Numerical calculations show that the critical Reynolds number could be decreased by up to a factor of 10 by the addition of small amount of polymer. The critical Reynolds number follows the same scaling Rec˜Σ3 /4 as the wall modes for a Newtonian fluid for very high Reynolds number. However, for moderate Reynolds number, there exists a narrow region in β -H parametric space, corresponding to very dilute polymer solution (0.9 ≲β <1 ) and thin solids (H ≲1.1 ) , in which the addition of polymer tends to increase the critical Reynolds number in comparison to the Newtonian fluid. Thus, Reynolds number and polymer properties can be tailored to either increase or decrease the critical Reynolds number for unstable modes
Wall-mode instability in plane shear flow of viscoelastic fluid over a deformable solid.
Chokshi, Paresh; Bhade, Piyush; Kumaran, V
2015-02-01
The linear stability analysis of a plane Couette flow of an Oldroyd-B viscoelastic fluid past a flexible solid medium is carried out to investigate the role of polymer addition in the stability behavior. The system consists of a viscoelastic fluid layer of thickness R, density ρ, viscosity η, relaxation time λ, and retardation time βλ flowing past a linear elastic solid medium of thickness HR, density ρ, and shear modulus G. The emphasis is on the high-Reynolds-number wall-mode instability, which has recently been shown in experiments to destabilize the laminar flow of Newtonian fluids in soft-walled tubes and channels at a significantly lower Reynolds number than that for flows in rigid conduits. For Newtonian fluids, the linear stability studies have shown that the wall modes become unstable when flow Reynolds number exceeds a certain critical value Re(c) which scales as Σ(3/4), where Reynolds number Re=ρVR/η,V is the top-plate velocity, and dimensionless parameter Σ=ρGR(2)/η(2) characterizes the fluid-solid system. For high-Reynolds-number flow, the addition of polymer tends to decrease the critical Reynolds number in comparison to that for the Newtonian fluid, indicating a destabilizing role for fluid viscoelasticity. Numerical calculations show that the critical Reynolds number could be decreased by up to a factor of 10 by the addition of small amount of polymer. The critical Reynolds number follows the same scaling Re(c)∼Σ(3/4) as the wall modes for a Newtonian fluid for very high Reynolds number. However, for moderate Reynolds number, there exists a narrow region in β-H parametric space, corresponding to very dilute polymer solution (0.9≲β<1) and thin solids (H≲1.1), in which the addition of polymer tends to increase the critical Reynolds number in comparison to the Newtonian fluid. Thus, Reynolds number and polymer properties can be tailored to either increase or decrease the critical Reynolds number for unstable modes, thus providing
Magnetomotive nanoparticle transducers for optical rheology of viscoelastic materials.
Crecea, Vasilica; Oldenburg, Amy L; Liang, Xing; Ralston, Tyler S; Boppart, Stephen A
2009-12-01
The availability of a real-time non-destructive modality to interrogate the mechanical properties of viscoelastic materials would facilitate many new investigations. We introduce a new optical method for measuring elastic properties of samples which employs magnetite nanoparticles as perturbative agents. Magnetic nanoparticles distributed in silicone-based samples are displaced upon probing with a small external magnetic field gradient and depth-resolved optical coherence phase shifts allow for the tracking of scatterers in the sample with nanometer-scale sensitivity. The scatterers undergo underdamped oscillations when the magnetic field is applied step-wise, allowing for the measurement of the natural frequencies of oscillation of the samples. Validation of the measurements is accomplished using a commercial indentation apparatus to determine the elastic moduli of the samples. This real-time non-destructive technique constitutes a novel way of probing the natural frequencies of viscoelastic materials in which magnetic nanoparticles can be introduced.
Assessing the influence of viscoelastic stress change globally
NASA Astrophysics Data System (ADS)
Sunbul, Fatih; Nalbant, Suleyman; Steacy, Sandy; Parsons, Thomas
2014-05-01
viscoelastic properties of the lower crust and mantle are reversed. The comparison between these two cases allows us to assess the influence of the post-seismic viscoelastic stress change globally. Additionally, our approach allows more complete of the relationship between the global earthquake rate and the stress change.
Banquet-Terán, Julio; Johnson-Restrepo, Boris; Hernández-Morelo, Alveiro; Ropero, Jorge; Fontalvo-Gomez, Miriam; Romañach, Rodolfo J
2016-07-01
A nondestructive and faster methodology to quantify mechanical properties of polypropylene (PP) pellets, obtained from an industrial plant, was developed with Raman spectroscopy. Raman spectra data were obtained from several types of samples such as homopolymer PP, random ethylene-propylene copolymer, and impact ethylene-propylene copolymer. Multivariate calibration models were developed by relating the changes in the Raman spectra to mechanical properties determined by ASTM tests (Young's traction modulus, tensile strength at yield, elongation at yield on traction, and flexural modulus at 1% secant). Several strategies were evaluated to build robust models including the use of preprocessing methods (baseline correction, vector normalization, de-trending, and standard normal variate), selecting the best subset of wavelengths to model property response and discarding irrelevant variables by applying genetic algorithm (GA). Linear multivariable models were investigated such as partial least square regression (PLS) and PLS with genetic algorithm (GA-PLS) while nonlinear models were implemented with artificial neural network (ANN) preceded by GA (GA-ANN). The best multivariate calibration models were obtained when a combination of genetic algorithms and artificial neural network were used on Raman spectral data with relative standard errors (%RSE) from 0.17 to 0.41 for training and 0.42 to 0.88% validation data sets. PMID:27287847
Microstructure development in viscoelastic fluid systems
NASA Astrophysics Data System (ADS)
Li, Huaping
This thesis deals with the mechanisms of microstructure development in polymer blends. Much work has been performed on the breakup process of immiscible systems where the dispersed phase is suspended inside another matrix. The fluids used were polymer melts or model viscoelastic fluids, and the processing flows were model shear flow or processing flows seen in industry. It is found that in industrial extruders or batch mixers, the morphology of the dispersed polymer evolves from pellets to films, and subsequently to fibers and particles. In this thesis, it is demonstrated based on force analysis that the in-situ graft reactive compatibilization facilitates breakup of the dispersed phase by suppressing slip at the interface of the dispersed phase and matrix phase. The morphology development of polymer blends in industrial mixers was simulated by performing experiments of model viscoelastic drop deformation and breakup under shear flow. Two distinct modes of drop deformation and breakup were observed. Namely, viscoelastic drops can elongate and breakup either in (1) the flow direction or (2) the vorticity direction. The first normal stress difference N1 plays a decisive role in the conditions and modes of drop breakup. Drop size is an important factor which determines to a great extent the mode of drop breakup and the critical point when the drop breakup mechanism changes. Small drops break along the vorticity direction, whereas large drops break in the flow direction. A dramatic change in the critical shear rate was found when going from one breakup mode to another. Polymer melts processed under shear flow present different morphology development mechanisms: films, fibers, vorticity elongation and surface instability. The mechanisms depend greatly on the rheological properties of both the dispersed and matrix phases, namely the viscosity ratio and elasticity ratio. High viscosity ratio and high elasticity ratio result elongation of the dispersed phase in the
Linear and nonlinear properties of the ULF waves driven by ring-beam distribution functions
NASA Technical Reports Server (NTRS)
Killen, K.; Omidi, N.; Krauss-Varban, D.; Karimabadi, H.
1995-01-01
The problem of the exitation of obliquely propagating magnetosonic waves which can steepen up (also known as shocklets) is considered. Shocklets have been observed upstream of the Earth's bow shock and at comets Giacobini-Zinner and Grigg-Skjellerup. Linear theory as well as two-dimensional (2-D) hybrid (fluid electrons, particle ions) simulations are used to determine the properties of waves generated by ring-beam velocity distributions in great detail. The effects of both proton and oxygen ring-beams are considered. The study of instabilities excited by a proton ring-beam is relevant to the region upstream of the Earth's bow shock, whereas the oxygen ring-beam corresponds to cometary ions picked up by the solar wind. Linear theory has shown that for a ring-beam, four instabilities are found, one on the nonresonant mode, one on the Alfven mode, and two along the magnetosonic/whistler branch. The relative growth rate of these instabilities is a sensitive function of parameters. Although one of the magnetosonic instabilities has maximum growth along the magnetic field, the other has maximum growth in oblique directions. We have studied the competition of these instabilities in the nonlinear regime using 2-D simulations. As in the linear limit, the nonlinear results are a function of beam density and distribution function. By performing the simulations as both initial value and driven systems, we have found that the outcome of the simulations can vary, suggesting that the latter type simulations is needed to address the observations. A general conclusion of the simulation results is that field-aligned beams do not result in the formation of shocklets, whereas ring-beam distributions can.
Age dependent changes of arterial wall viscoelasticity.
Antonov, P; Antonova, M; Nikolova, N; Antonova, N; Vlaskovska, M; Kasakov, L
2008-01-01
Viscoelastic characteristics (VEC) of old rat aorta (Wistar, 10 months) were obtained by sinusoidal excitation of intraluminal pressure (p) in cylindrical arterial preparations. The pressure excitation frequency (f(exc)) was swept in the range 3-30 Hz up and down at several mean-pressure levels while response volume oscillations were recorded and resonance curves were plotted. Natural frequency (f(0)), dynamic modulus of elasticity (E') and coefficient of viscosity (beta) were estimated from resonance curves and the dependences of VEC on p were drawn. The results showed that f(0) decreased linearly with p whereas our previous data for young rat aorta (Wistar, 4 months) showed independence of f(0) on p. E' increased nonlinearly with p with the values being higher in comparison to young rat aorta. This means stiffening of rat aorta with age in accordance with the known literature data. beta-values increased linearly with p being higher in comparison to young rat aorta, demonstrative of raised intrinsic friction in the wall. VEC values were higher at decreasing f(exc) suggesting that the direction of excitation sweeping also determines the arterial wall biomechanical behaviour. It could be concluded that blood vessels VEC worsen with age, which endangers the arterial wall integrity, especially at higher intraluminal pressure.
Linear electro-optic properties of YCa4O(BO3)3
NASA Astrophysics Data System (ADS)
Adams, J. J.; Ebbers, C. A.
2003-08-01
We have characterized the effective linear electro-optic coefficients of YCa4O(BO3)3 (YCOB) relative to KH2PO4 and KD2PO4 at 632.8 nm. We measured a maximum reff value of 10.8 +/- 1.4 pm/V for YCOB in a transverse electric field configuration for propagation along the X or the α dielectric axis, with the electric field applied along the Z or the γ dielectric axis. We also found effective coefficients of 10.7 +/- 1.0 and 3.4 +/- 0.4 pm/V for YCOB in longitudinal configurations. The remaining values of reff for various transverse applied voltages were found to be less than 3 pm/V. The excellent thermomechanical properties of this crystal, coupled with moderate electro-optic coefficients, make YCOB and its isomorphs potential candidates for use as high-average-power electro-optic switches.
Some new progress on the light absorption properties of linear alkyl benzene solvent
NASA Astrophysics Data System (ADS)
Yu, Guang-You; Cao, De-Wen; Huang, Ai-Zhong; Yu, Lei; Loh, Chang-Wei; Wang, Wen-Wen; Qian, Zhi-Qiang; Yang, Hai-Bo; Huang, Huang; Xu, Zong-Qiang; Zhu, Xue-Yuan; Xu, Bin; Qi, Ming
2016-01-01
Linear alkyl benzene (LAB) will be used as the solvent in a liquid scintillator mixture for the JUNO antineutrino experiment. Its light absorption properties should therefore be understood prior to its effective use in the experiment. Attenuation length measurements at a light wavelength of 430 nm have been performed on samples of LAB prepared for the JUNO experiment. Inorganic impurities in LAB have also been studied for their possibilities of light absorption in our wavelength of interest. In view of a tentative plan by the JUNO collaboration to utilize neutron capture with hydrogen in the detector, we also present in this work a preliminary study on the carbon-hydrogen ratio and the attenuation length of the samples. Supported by China Ministry of Science and Technology(2013CB834300)
NASA Astrophysics Data System (ADS)
Larson, Ronald; Heo, Youngsuk
2008-03-01
We examine the validity of the de Gennes ``blob'' concept in predicting linear and nonlinear rheological properties of semidilute polystyrene solutions in tricresyl phosphate (TCP). At a fixed value of rescaled concentration c/ce where ce is the entanglement concentration, below a critical value of around 2.0 for our polystyrene/TCP solutions, linear and nonlinear rheological functions superimpose after the modulus and the frequency (or shear rate) of each solution are respectively normalized with the concentration-dependent plateau modulus and the equilibration time obtained from the de Gennes scaling relationships using the literature value of the solvent-quality exponent 0.53. However, once the polymer volume fraction exceeds the ``swelling volume fraction, above which the polymer takes on a random walk configuration on all length scales even in a good solvent, this universal scaling breaks down and the polymer conformation appears to be governed by Colby-Rubinstein's scaling laws for theta solutions. We estimate that all polybutadiene solutions in phenyl octane (a good solvent) from the work of Colby et al. are above the swelling concentration and can be scaled using theta solvent scaling laws for concentrations ranging all the way up to the melt, showing universal behavior of melts and solutions above the swelling concentration.
Moon, Jin Seok; Shin, So Yeon; Choi, Hye Sun; Joo, Wooha; Cho, Seung Kee; Li, Ling; Kang, Jung-Hyun; Kim, Tae-Jip; Han, Nam Soo
2015-10-20
This study was conducted to investigate the prebiotic effects of linear arabino-oligosaccharides (LAOS) and debranched (linear) sugar beet arabinan (LAR) for the development of new prebiotics. LAOS were prepared from LAR by enzymatic hydrolysis with endo-arabinanase from Bacillus licheniformis, followed by removal of the arabinose fraction by incubation with resting cells of Leuconostoc mesenteroides. The resulting LAOS contained DP2 (28.7%), DP3 (49.9%), DP4 (20.1%), and DP5 (1.16%). A standardized digestibility test showed that LAOS and LAR were not digestible. Individual cultures of 24 strains of gastrointestinal bacteria showed that LAOS and LAR stimulated growth of Lactobacillus brevis, Bifidobacterium longum, and Bacteroides fragilis. In vitro batch fermentation using human fecal samples showed that LAOS had higher bifidogenic properties than LAR; LAOS increased the population of bifidobacteria which produced short-chain fatty acids (SCFAs). LAOS was fermented slowly compared to fructo-oligosaccharides and this may permit SCFA production in the distal colon. This study demonstrates that LAOS prepared from LAR are promising dietary substrates for improvement of human intestinal health.
Rayleigh-Taylor instability in non-uniform magnetized rotating strongly coupled viscoelastic fluid
NASA Astrophysics Data System (ADS)
Prajapati, R. P.
2016-02-01
The Rayleigh-Taylor instability (RTI) in an incompressible strongly coupled viscoelastic fluid is investigated considering the effects of inhomogeneous magnetic field, density gradient, and uniform rotation. The generalized hydrodynamic equations have been formulated, and linear dispersion relation is derived taking appropriate density and magnetic field profiles for the considered system. The gravity induced stable and unstable configurations of RTI are analyzed in hydrodynamic and kinetic limits. In the kinetic limit, shear wave modified dispersion relation and the condition of RTI are derived in terms of magnetic-viscoelastic Mach number and viscoelastic Froude number. The criteria of RTI and critical wavenumber for the growth of RTI to be unstable are estimated numerically for white dwarf and inertial confinement fusion target. It is observed that magnetic field, rotation, and viscoelastic effects play a significant role in the suppression of RTI in these systems. The stabilizing influence of magnetic field, rotation, and magnetic-viscoelastic Mach number while the destabilizing influence of viscoelastic Froude on the growth rate of RTI number is observed graphically. The growth rate of RTI decreases faster in kinetic limit as compared to the hydrodynamic limit.
Two-dimensional time-domain finite-difference modeling for viscoelastic seismic wave propagation
NASA Astrophysics Data System (ADS)
Fan, Na; Zhao, Lian-Feng; Xie, Xiao-Bi; Ge, Zengxi; Yao, Zhen-Xing
2016-09-01
Real Earth media are not perfectly elastic. Instead, they attenuate propagating mechanical waves. This anelastic phenomenon in wave propagation can be modeled by a viscoelastic mechanical model consisting of several standard linear solids. Using this viscoelastic model, we approximate a constant Q over a frequency band of interest. We use a four-element viscoelastic model with a trade-off between accuracy and computational costs to incorporate Q into 2-D time-domain first-order velocity-stress wave equations. To improve the computational efficiency, we limit the Q in the model to a list of discrete values between 2 and 1000. The related stress and strain relaxation times that characterize the viscoelastic model are pre-calculated and stored in a database for use by the finite-difference calculation. A viscoelastic finite-difference scheme that is second order in time and fourth order in space is developed based on the MacCormack algorithm. The new method is validated by comparing the numerical result with analytical solutions that are calculated using the generalized reflection/transmission coefficient method. The synthetic seismograms exhibit greater than 95 per cent consistency in a two-layer viscoelastic model. The dispersion generated from the simulation is consistent with the Kolsky-Futterman dispersion relationship.
2D time-domain finite-difference modeling for viscoelastic seismic wave propagation
NASA Astrophysics Data System (ADS)
Fan, Na; Zhao, Lian-Feng; Xie, Xiao-Bi; Ge, Zengxi; Yao, Zhen-Xing
2016-07-01
Real Earth media are not perfectly elastic. Instead, they attenuate propagating mechanic