Uncertainty limits for the macroscopic elastic moduli of random polycrystalline aggregates
NASA Astrophysics Data System (ADS)
Chinh, Pham Duc
2000-08-01
Practical polycrystalline aggregates are expected to have macroscopic properties that depend upon the properties of constituent crystals and the aggregate geometry. Since that microgeometry is usually random, there will be some uncertainty in the observed macroscopic behavior of the aggregates. The general shape-independent upper and lower estimates for those uncertainty intervals for the elastic moduli of completely random polycrystals are constructed from the minimum energy and complementary energy principles. Applications to aggregates of cubic crystals are presented.
On the scatter ranges for the elastic moduli of random aggregates of general anisotropic crystals
NASA Astrophysics Data System (ADS)
Chinh, Pham Duc
2011-02-01
A randomly inhomogeneous material may have macroscopic properties (elasticity, conductivity) scattered over some uncertainty intervals, despite the idealistic uniqueness assumption of homogenization theory. Based on minimum energy principles and certain statistical isotropy-symmetry hypotheses, our partly third-order bounds on the effective properties of random polycrystals are expected to estimate those scatter ranges. Explicit expressions are given and calculated for the elastic moduli of the random aggregates of some known monoclinic and triclinic crystals, which yield results in agreement with those calculated for higher-symmetry crystals: the moduli are determinable within an accuracy of two or three significant digits in most cases. It is shown, however, that with some real-world exotic crystals the bounds may fall far apart, and further theoretical and experimental studies on them deserve attention.
Measuring Moduli Of Elasticity At High Temperatures
NASA Technical Reports Server (NTRS)
Wolfenden, Alan
1993-01-01
Shorter, squatter specimens and higher frequencies used in ultrasonic measurement technique. Improved version of piezo-electric ultrasonic composite oscillator technique used to measure moduli of elasticity of solid materials at high temperatures.
Elastic moduli of pyrope rich garnets
NASA Astrophysics Data System (ADS)
Pandey, B. K.; Pandey, A. K.; Singh, C. K.
2013-06-01
The elastic properties of minerals depend on its composition, crystal structure, temperature and level of defects. The elastic parameters are important for the interpretation of the structure and composition of the garnet rich family. In present work we have calculated the elastic moduli such as isothermal bulk modulus, Young's modulus and Shear modulus over a wide range of temperature from 300 K to 1000 K by using Birch EOS and Poirrier Tarantola equation of state. The obtained results are compared with the experimental results obtained by measuring the elastic moduli of single crystal. The calculated results show that the logarithmic isothermal EOS does not cooperate well with experimental results.
Polycrystalline gamma plutonium's elastic moduli versus temperature
Migliori, Albert; Betts, J; Trugman, A; Mielke, C H; Mitchell, J N; Ramos, M; Stroe, I
2009-01-01
Resonant ultrasound spectroscopy was used to measure the elastic properties of pure polycrystalline {sup 239}Pu in the {gamma} phase. Shear and longitudinal elastic moduli were measured simultaneously and the bulk modulus was computed from them. A smooth, linear, and large decrease of all elastic moduli with increasing temperature was observed. They calculated the Poisson ratio and found that it increases from 0.242 at 519 K to 0.252 at 571 K. These measurements on extremely well characterized pure Pu are in agreement with other reported results where overlap occurs.
Multidimensional Contact Moduli of Elastically Anisotropic Solids
Gao, Yanfei; Pharr, George Mathews
2007-01-01
Effective moduli of elastically anisotropic solids under normal and tangential contacts are derived using the Stroh formalism and the two dimensional Fourier transform. Each Fourier component corresponds to a plane field in the plane spanned by the surface normal and a wavevector, the solution of which only involves an algebraic eigenvalue problem. Exact solutions are obtained for indenters described by parabolae of revolution, which are found to be a good approximation for arbitrary axisymmetric indenters.
Elastic fields and moduli in defected graphene.
Dettori, Riccardo; Cadelano, Emiliano; Colombo, Luciano
2012-03-14
By means of tight-binding atomistic simulations we study a family of native defects in graphene which have recently been detected experimentally. Their formation energy is found to be as large as several electronvolts, consistent with the empirical evidence of high crystalline quality in most graphene samples. Defects, especially if associated with bond reconstructions, induce sizable deformation and stress fields with a spatial distribution closely related to their actual symmetry. The description of such fields proposed here is believed to be useful for the unambiguous characterization of images obtained by electron microscopy. We also argue that they define the basin of mutual interaction between two nearby defects. Finally, we provide evidence that defects differently affect the linear elastic moduli of monolayer graphene. In general, both the Young modulus and the Poisson ratio are decreased, but their dependence upon the defect surface density is remarkably more pronounced for vacancy-like than for number-like defects.
Resonant Acoustic Determination of Complex Elastic Moduli
NASA Technical Reports Server (NTRS)
Brown, David A.; Garrett, Steven L.
1991-01-01
A simple, inexpensive, yet accurate method for measuring the dynamic complex modulus of elasticity is described. Using a 'free-free' bar selectively excited in three independent vibrational modes, the shear modulus is obtained by measuring the frequency of the torsional resonant mode and the Young's modulus is determined from measurement of either the longitudinal or flexural mode. The damping properties are obtained by measuring the quality factor (Q) for each mode. The Q is inversely proportional to the loss tangent. The viscoelastic behavior of the sample can be obtained by tracking a particular resonant mode (and thus a particular modulus) using a phase locked loop (PLL) and by changing the temperature of the sample. The change in the damping properties is obtained by measuring the in-phase amplitude of the PLL which is proportional to the Q of the material. The real and imaginary parts or the complex modulus can be obtained continuously as a function of parameters such as temperature, pressure, or humidity. For homogeneous and isotropic samples only two independent moduli are needed in order to characterize the complete set of elastic constants, thus, values can be obtained for the dynamic Poisson's ratio, bulk modulus, Lame constants, etc.
Spatial Distributions of Local Elastic Moduli Near the Jamming Transition
NASA Astrophysics Data System (ADS)
Mizuno, Hideyuki; Silbert, Leonardo E.; Sperl, Matthias
2016-02-01
Recent progress on studies of the nanoscale mechanical responses in disordered systems has highlighted a strong degree of heterogeneity in the elastic moduli. In this contribution, using computer simulations, we study the elastic heterogeneities in athermal amorphous solids—composed of isotropic static sphere packings—near the jamming transition. We employ techniques based on linear response methods that are amenable to experimentation. We find that the local elastic moduli are randomly distributed in space and are described by Gaussian probability distributions, thereby lacking any significant spatial correlations, that persist all the way down to the transition point. However, the shear modulus fluctuations grow as the jamming threshold is approached, which is characterized by a new power-law scaling. Through this diverging behavior we are able to identify a characteristic length scale, associated with shear modulus heterogeneities, that distinguishes between bulk and local elastic responses.
Structures and Elastic Moduli of Polymer Nanocomposite Thin Films
NASA Astrophysics Data System (ADS)
Yuan, Hongyi; Karim, Alamgir; University of Akron Team
2014-03-01
Polymeric thin films generally possess unique mechanical and thermal properties due to confinement. In this study we investigated structures and elastic moduli of polymer nanocomposite thin films, which can potentially find wide applications in diverse areas such as in coating, permeation and separation. Conventional thermoplastics (PS, PMMA) and biopolymers (PLA, PCL) were chosen as polymer matrices. Various types of nanoparticles were used including nanoclay, fullerene and functionalized inorganic particles. Samples were prepared by solvent-mixing followed by spin-coating or flow-coating. Film structures were characterized using X-ray scattering and transmission electron microscopy. Elastic moduli were measured by strain-induced elastic buckling instability for mechanical measurements (SIEBIMM), and a strengthening effect was found in certain systems due to strong interaction between polymers and nanoparticles. The effects of polymer structure, nanoparticle addition and film thickness on elastic modulus will be discussed and compared with bulk materials.
Spatial Distributions of Local Elastic Moduli Near the Jamming Transition.
Mizuno, Hideyuki; Silbert, Leonardo E; Sperl, Matthias
2016-02-12
Recent progress on studies of the nanoscale mechanical responses in disordered systems has highlighted a strong degree of heterogeneity in the elastic moduli. In this contribution, using computer simulations, we study the elastic heterogeneities in athermal amorphous solids--composed of isotropic static sphere packings--near the jamming transition. We employ techniques based on linear response methods that are amenable to experimentation. We find that the local elastic moduli are randomly distributed in space and are described by Gaussian probability distributions, thereby lacking any significant spatial correlations, that persist all the way down to the transition point. However, the shear modulus fluctuations grow as the jamming threshold is approached, which is characterized by a new power-law scaling. Through this diverging behavior we are able to identify a characteristic length scale, associated with shear modulus heterogeneities, that distinguishes between bulk and local elastic responses. PMID:26919018
Computation of graphene elastic moduli at low temperature
Zubko, I. Yu. Kochurov, V. I.
2015-10-27
Finding the values of parameters for the simplest Mie’s family potentials is performed in order to estimate elastic moduli of graphene monolayers using lattice statics approach. The coincidence criterion of the experimentally determined Poisson’s ratio with the estimated value is taken in order to select dimensionless power parameters of the Mie-type potential. It allowed obtaining more precise estimation of elastic properties in comparison with variety of other potentials for carbon atoms in graphene monolayer.
Strain fluctuations and elastic moduli in disordered solids
NASA Astrophysics Data System (ADS)
Sussman, Daniel M.; Schoenholz, Samuel S.; Xu, Ye; Still, Tim; Yodh, A. G.; Liu, Andrea J.
2015-08-01
Recently there has been a surge in interest in using video-microscopy techniques to infer the local mechanical properties of disordered solids. One common approach is to minimize the difference between particle vibrational displacements in a local coarse-graining volume and the displacements that would result from a best-fit affine deformation. Effective moduli are then inferred under the assumption that the components of this best-fit affine deformation tensor have a Boltzmann distribution. In this paper, we combine theoretical arguments with experimental and simulation data to demonstrate that the above does not reveal information about the true elastic moduli of jammed packings and colloidal glasses.
Dynamics and elasticity of fire ant aggregations
NASA Astrophysics Data System (ADS)
Fernandez-Nieves, Alberto; Tennenbaum, Michael; Liu, Zhongyang; Hu, David
2015-03-01
Fire ants, Solenopsis invicta, form aggregations that are able to drip and spread like simple liquids, but that can also store energy and maintain a shape like elastic solids. They are an active material where the constituent particles constantly transform chemical energy into work. We find that fire ant aggregations shear thin and exhibit a stress cutoff below which they are able to oppose the applied stress. In the linear regime, the dynamics is fractal-like with both storage and shear moduli that overlap for over three orders of magnitude and that are power law with frequency. This dynamic behavior, characteristic of polymer gels and the gelation point, gives way to a predominantly elastic regime at higher ant densities. In comparison, dead ants are always solid-like.
Elastic Moduli of Vortex Lattices within Nonlocal London Model
NASA Astrophysics Data System (ADS)
Miranović, P.; Kogan, V. G.
2001-09-01
Vortex lattice (VL) elastic response is analyzed within the nonlocal London model which holds for high- κ clean superconductors. The squash modulus vanishes at the field H□ where VL undergoes a square-to-rhombus transition. For H>H□, where the square VL is stable, the rotation modulus turns zero at H = Hr, indicating VL instability to rotations. The shear modulus depends on the shear direction; the dependence is strong in the vicinity of H□ where the square VL is soft with respect to the shear along [110]. The H dependences of the moduli are evaluated for LuNi2B2C.
Variation of elastic moduli of clays with humidity
NASA Astrophysics Data System (ADS)
Kuila, U.; Prasad, M.
2012-12-01
The elastic moduli of clays are highly variable. The reported values of elastic moduli of clays in the literature provide a large range: ranging from 0.15 GPa to 400 GPa. One of the many probable reasons for this variation is different external experimental environments leading to varied amounts of cations and bound water in the interlayers. The clay structure is affected by the kind of water associated with it: free water and bound water, the water in the interlayer. Smectite and mixed-layered illite-smectite (I-S) are capable of retaining significant electrostatic bound water in excess of 200C and can rapidly adsorb moisture from the air depending upon the humidity conditions. These can lead to the variation in their elastic properties. Prior experimental studies of acoustic velocity measurement in compacted clay pellets showed comparable trends (Figure 1) but different velocities for same reported porosity. This can be attributed to the humidity difference in the lab ambient conditions where the measurements were made. Molecular simulation studies on montmorillonite clays shows similar dependence of Young's Modulus on the hydration state of the clays (Pal Bathija 2009). In this paper, we studied the effect of humidity on the elastic properties of compacted pellets of Na-montmorillonite. This can be achieved by placing the Na-montmorillonite pellets in bell jars containing different saturated salt solutions. These salt solutions are used as a standard for relative humidity measurements. Figure 2 shows an experimental set-up used to the experiment. We will present the results of the variation of elastic properties of clays with varying humidity conditions. Preliminary results suggest that acoustic velocities through the compacted Na-montmorillonite pellet depend on the humidity conditions. The varying amount of interlayer clay-bound water and capillary condensation of water in small micropores in clays with varying humidity conditions resulted in the change in the
Dynamic elastic moduli during isotropic densification of initially granular media
NASA Astrophysics Data System (ADS)
Vasseur, Jérémie; Wadsworth, Fabian B.; Lavallée, Yan; Dingwell, Donald B.
2016-03-01
The elastic properties of homogeneous, isotropic materials are well constrained. However, in heterogeneous and evolving materials, these essential properties are less well-explored. During sintering of volcanic ash particles by viscous processes as well as during compaction and cementation of sediments, microstructure and porosity undergo changes that affect bulk dynamic elastic properties. Here using a model system of glass particles as an analogue for initially granular rock-forming materials, we have determined porosity and P-wave velocity during densification. Using these results, we test models for the kinetics of densification and the resultant evolution of the elastic properties to derive a quantitative description of the coupling between the kinetics of isotropic densification and the evolving dynamic elastic moduli. We demonstrate the power of the resultant model on a wide range of data for non-coherent sediments as well as sedimentary and volcanic rocks. We propose that such constraints be viewed as an essential ingredient of time-dependent models for the deformation of evolving materials in volcanoes and sedimentary basins.
Effect of micromorphological development on the elastic moduli of fly ash-lime stabilized bentonite
Baykal, G.I.
1987-01-01
The mineralogical and micromorphological changes occurring in fly ash-lime stabilized bentonite were observed and related to changes in elastic moduli of the stabilized mixture. Compacted fly ash, fly ash-lime, bentonite-lime, bentonite-fly ash, and bentonite-fly ash-lime mixtures were prepared and cured at 23C and 50C, for 1, 28, 90 and 180 days. The development of microstructure and cementitous crystals were observed by a scanning electron microscope, and energy dispersive spectrum analyzer and a X-ray diffractometer. The elastic moduli and strengths were obtained from unconsolidated undrained triaxial and unconfined compressive strength tests. The physical test results were compared with changes observed by scanning electron microscopy and X-ray diffraction. CSH gel Type I, II and III, ettringite, afwillite and tetracalcium aluminate thirteen hydrate crystals were identified in the cured specimens. The elastic modulus of the fly ash-lime stabilized bentonite was higher than the untreated bentonite and the increase in elastic modulus corresponded to the curing times when new cementitious crystals were observed. Acicular crystals (CSH Type I and II) and ettringite crystals spanned the pores and increased the contact points where blocky aggregates of equant crystals (CSH III) engulfed the fly ash grains providing support. The compressive strength increased, and the strain at a failure decreased resulting in an increase in the elastic modulus. Some fly ash grains providing support for montmorillonite aggregates dissolved and created weak spots in the matrix, causing a decrease in elastic modulus at longer curing periods. At 50C curing temperature the same cementitious crystals were observed as at 23C. However, the rate of the reactions increased considerably.
Elastic moduli of nanocrystalline binary Al alloys with Fe, Co, Ti, Mg and Pb alloying elements
NASA Astrophysics Data System (ADS)
Babicheva, Rita I.; Bachurin, Dmitry V.; Dmitriev, Sergey V.; Zhang, Ying; Kok, Shaw Wei; Bai, Lichun; Zhou, Kun
2016-05-01
The paper studies the elastic moduli of nanocrystalline (NC) Al and NC binary Al-X alloys (X is Fe, Co, Ti, Mg or Pb) by using molecular dynamics simulations. X atoms in the alloys are either segregated to grain boundaries (GBs) or distributed randomly as in disordered solid solution. At 0 K, the rigidity of the alloys increases with decrease in atomic radii of the alloying elements. An addition of Fe, Co or Ti to the NC Al leads to increase in the Young's E and shear μ moduli, while an alloying with Pb decreases them. The elastic moduli of the alloys depend on a distribution of the alloying elements. The alloys with the random distribution of Fe or Ti demonstrate larger E and μ than those for the corresponding alloys with GB segregations, while the rigidity of the Al-Co alloy is higher for the case of the GB segregations. The moduli E and μ for polycrystalline aggregates of Al and Al-X alloys with randomly distributed X atoms are estimated based on the elastic constants of corresponding single-crystals according to the Voigt-Reuss-Hill approximation, which neglects the contribution of GBs to the rigidity. The results show that GBs in NC materials noticeably reduce their rigidity. Furthermore, the temperature dependence of μ for the NC Al-X alloys is analyzed. Only the Al-Co alloy with GB segregations shows the decrease in μ to the lowest extent in the temperature range of 0-600 K in comparison with the NC pure Al.
Elastic Moduli of Vortex Lattices within Nonlocal London Model
Miranovic, P.; Kogan, V. G.
2001-09-24
Vortex lattice (VL) elastic response is analyzed within the nonlocal London model which holds for high-{kappa} clean superconductors. The squash modulus vanishes at the field H{sub (open square)} where VL undergoes a square-to-rhombus transition. For H>H{sub (open square)}, where the square VL is stable, the rotation modulus turns zero at H=H{sub r} , indicating VL instability to rotations. The shear modulus depends on the shear direction; the dependence is strong in the vicinity of H{sub (open square)} where the square VL is soft with respect to the shear along [110] . The H dependences of the moduli are evaluated for LuNi{sub 2}B {sub 2}C .
An ultrasonic method for studying elastic moduli as a function of temperature
NASA Technical Reports Server (NTRS)
Peterson, R. G.
1969-01-01
Ultrasonic method is used to determine the elastic moduli of materials used in components of high-temperature nuclear reactors. An ultrasonic, pulse-echo technique determines the velocity of sound waves propogating in a heated region of rod-shaped specimens. From these velocities, the elastic moduli are calculated.
Elastic moduli and vibrational modes in jammed particulate packings
NASA Astrophysics Data System (ADS)
Mizuno, Hideyuki; Saitoh, Kuniyasu; Silbert, Leonardo E.
2016-06-01
When we elastically impose a homogeneous, affine deformation on amorphous solids, they also undergo an inhomogeneous, nonaffine deformation, which can have a crucial impact on the overall elastic response. To correctly understand the elastic modulus M , it is therefore necessary to take into account not only the affine modulus MA, but also the nonaffine modulus MN that arises from the nonaffine deformation. In the present work, we study the bulk (M =K ) and shear (M =G ) moduli in static jammed particulate packings over a range of packing fractions φ . The affine MA is determined essentially by the static structural arrangement of particles, whereas the nonaffine MN is related to the vibrational eigenmodes. We elucidate the contribution of each vibrational mode to the nonaffine MN through a modal decomposition of the displacement and force fields. In the vicinity of the (un)jamming transition φc, the vibrational density of states g (ω ) shows a plateau in the intermediate-frequency regime above a characteristic frequency ω*. We illustrate that this unusual feature apparent in g (ω ) is reflected in the behavior of MN: As φ →φc , where ω*→0 , those modes for ω <ω* contribute less and less, while contributions from those for ω >ω* approach a constant value which results in MN to approach a critical value MN c, as MN-MN c˜ω* . At φc itself, the bulk modulus attains a finite value Kc=KA c-KN c>0 , such that KN c has a value that remains below KA c. In contrast, for the critical shear modulus Gc, GN c and GA c approach the same value so that the total value becomes exactly zero, Gc=GA c-GN c=0 . We explore what features of the configurational and vibrational properties cause such a distinction between K and G , allowing us to validate analytical expressions for their critical values.
Watt, J.P.; Peselnick, L.
1980-01-01
Bounds on the effective elastic moduli of randomly oriented aggregates of hexagonal, trigonal, and tetragonal crystals are derived using the variational principles of Hashin and Shtrikman. The bounds are considerably narrower than the widely used Voigt and Reuss bounds. The Voigt-Reuss-Hill average lies within the Hashin-Shtrikman bounds in nearly all cases. Previous bounds of Peselnick and Meister are shown to be special cases of the present results.
NASA Astrophysics Data System (ADS)
Fleischmann, J. A.; Drugan, W. J.; Plesha, M. E.
2013-07-01
We derive the macroscopic elastic moduli of a statistically isotropic particulate aggregate material via the homogenization methods of Voigt (1928) (kinematic hypothesis), Reuss (1929) (static hypothesis), and Hershey (1954) and Kröner (1958) (self-consistent hypothesis), originally developed to treat crystalline materials, from the directionally averaged elastic moduli of three regular cubic packings of uniform spheres. We determine analytical expressions for these macroscopic elastic moduli in terms of the (linearized) elastic inter-particle contact stiffnesses on the microscale under the three homogenization assumptions for the three cubic packings (simple, body-centered, and face-centered), assuming no particle rotation. To test these results and those in the literature, we perform numerical simulations using the discrete element method (DEM) to measure the overall elastic moduli of large samples of randomly packed uniform spheres with constant normal and tangential contact stiffnesses (linear spring model). The beauty of DEM is that simulations can be run with particle rotation either prohibited or unrestrained. In this first part of our two-part series of papers, we perform DEM simulations with particle rotation prohibited, and we compare these results with our theoretical results that assumed no particle rotation. We show that the self-consistent homogenization assumption applied to the locally body-centered cubic (BCC) packing most accurately predicts the measured values of the overall elastic moduli obtained from the DEM simulations, in particular Poisson's ratio. Our new analytical self-consistent results lead to significantly better predictions of Poisson's ratio than all prior published theoretical results. Moreover, our results are based on a direct micromechanics analysis of specific geometrical packings of uniform spheres, in contrast to all prior theoretical analyses, which were based on difficult-to-verify hypotheses involving overall inter
Universal behavior of changes in elastic moduli of hot compressed oxide glasses
NASA Astrophysics Data System (ADS)
Svenson, Mouritz N.; Guerette, Michael; Huang, Liping; Lönnroth, Nadja; Mauro, John C.; Rzoska, Sylwester J.; Bockowski, Michal; Smedskjaer, Morten M.
2016-05-01
The elastic moduli of glasses are important for numerous applications, but predicting them based on their chemical composition and forming history remains a great challenge. In this study, we investigate the relationship between densification and changes in elastic moduli as a result of isostatic compression up to 1 GPa of various oxide compositions at elevated temperature (so-called hot compression). An approximately linear relationship is observed between the relative changes in density and elastic moduli across a variety of glass families, although these glasses exhibit a diverse range of structural responses during compression owing to their dramatically different chemistries.
Elastic moduli and vibrational modes in jammed particulate packings.
Mizuno, Hideyuki; Saitoh, Kuniyasu; Silbert, Leonardo E
2016-06-01
When we elastically impose a homogeneous, affine deformation on amorphous solids, they also undergo an inhomogeneous, nonaffine deformation, which can have a crucial impact on the overall elastic response. To correctly understand the elastic modulus M, it is therefore necessary to take into account not only the affine modulus M_{A}, but also the nonaffine modulus M_{N} that arises from the nonaffine deformation. In the present work, we study the bulk (M=K) and shear (M=G) moduli in static jammed particulate packings over a range of packing fractions φ. The affine M_{A} is determined essentially by the static structural arrangement of particles, whereas the nonaffine M_{N} is related to the vibrational eigenmodes. We elucidate the contribution of each vibrational mode to the nonaffine M_{N} through a modal decomposition of the displacement and force fields. In the vicinity of the (un)jamming transition φ_{c}, the vibrational density of states g(ω) shows a plateau in the intermediate-frequency regime above a characteristic frequency ω^{*}. We illustrate that this unusual feature apparent in g(ω) is reflected in the behavior of M_{N}: As φ→φ_{c}, where ω^{*}→0, those modes for ω<ω^{*} contribute less and less, while contributions from those for ω>ω^{*} approach a constant value which results in M_{N} to approach a critical value M_{Nc}, as M_{N}-M_{Nc}∼ω^{*}. At φ_{c} itself, the bulk modulus attains a finite value K_{c}=K_{Ac}-K_{Nc}>0, such that K_{Nc} has a value that remains below K_{Ac}. In contrast, for the critical shear modulus G_{c}, G_{Nc} and G_{Ac} approach the same value so that the total value becomes exactly zero, G_{c}=G_{Ac}-G_{Nc}=0. We explore what features of the configurational and vibrational properties cause such a distinction between K and G, allowing us to validate analytical expressions for their critical values. PMID:27415345
QUANTITATIVE NON-DESTRUCTIVE EVALUATION (QNDE) OF THE ELASTIC MODULI OF POROUS TIAL ALLOYS
Yeheskel, O.
2008-02-28
The elastic moduli of {gamma}-TiA1 were studied in porous samples consolidated by various techniques e.g. cold isostatic pressing (CIP), pressure-less sintering, or hot isostatic pressing (HIP). Porosity linearly affects the dynamic elastic moduli of samples. The results indicate that the sound wave velocities and the elastic moduli affected by the processing route and depend not only on the attained density but also on the consolidation temperature. In this paper we show that there is linear correlation between the shear and the longitudinal sound velocities in porous TiA1. This opens the way to use a single sound velocity as a tool for quantitative non-destructive evaluation (QNDE) of porous TiA1 alloys. Here we demonstrate the applicability of an equation derived from the elastic theory and used previously for porous cubic metals.
Equivalent orthotropic elastic moduli identification method for laminated electrical steel sheets
NASA Astrophysics Data System (ADS)
Saito, Akira; Nishikawa, Yasunari; Yamasaki, Shintaro; Fujita, Kikuo; Kawamoto, Atsushi; Kuroishi, Masakatsu; Nakai, Hideo
2016-05-01
In this paper, a combined numerical-experimental methodology for the identification of elastic moduli of orthotropic media is presented. Special attention is given to the laminated electrical steel sheets, which are modeled as orthotropic media with nine independent engineering elastic moduli. The elastic moduli are determined specifically for use with finite element vibration analyses. We propose a three-step methodology based on a conventional nonlinear least squares fit between measured and computed natural frequencies. The methodology consists of: (1) successive augmentations of the objective function by increasing the number of modes, (2) initial condition updates, and (3) appropriate selection of the natural frequencies based on their sensitivities on the elastic moduli. Using the results of numerical experiments, it is shown that the proposed method achieves more accurate converged solution than a conventional approach. Finally, the proposed method is applied to measured natural frequencies and mode shapes of the laminated electrical steel sheets. It is shown that the method can successfully identify the orthotropic elastic moduli that can reproduce the measured natural frequencies and frequency response functions by using finite element analyses with a reasonable accuracy.
Probing asthenospheric density, temperature, and elastic moduli below the western United States.
Ito, Takeo; Simons, Mark
2011-05-20
Periodic ocean tides continually provide a cyclic load on Earth's surface, the response to which can be exploited to provide new insights into Earth's interior structure. We used geodetic observations of surface displacements induced by ocean tidal loads to constrain a depth-dependent model for the crust and uppermost mantle that provides independent estimates of density and elastic moduli below the western United States and nearby offshore regions. Our observations require strong gradients in both density and elastic shear moduli at the top and bottom of the asthenosphere but no discrete structural discontinuity at a depth of 220 kilometers. The model indicates that the asthenosphere has a low-density anomaly of ~50 kilograms per cubic meter; a temperature anomaly of ~300°C can simultaneously explain this density anomaly and inferred colocated minima in elastic moduli. PMID:21493821
NASA Astrophysics Data System (ADS)
Chatterjee, Avik P.
2008-03-01
A model is developed for the elastic moduli of networks composed of transversely isotropic elongated particles characterized by aspect ratio polydispersity. An effective medium approach is employed to integrate our treatment of elastic fiber networks with results from (i) the Mori-Tanaka model for dispersions of transversely isotropic inclusions and from (ii) percolation theory, and to describe fiber-reinforced nanocomposites. Model calculations are presented for the dependences of composite moduli on particle aspect ratios, volume fractions, and polydispersities, and on anisotropy in the fiber stiffness tensor.
Elasticity theory equations and fracture condition for materials of varying moduli
Oleinikov, A.I.
1986-11-01
Many massive rocks and composite materials belong to the class of materials of varying moduli with definite distinct deformation and strength properties under tension and compression. The results of experiments indicate that the difference between the properties of materials of different moduli is not limited to tension and compression cases but can also appear clearly for any change in the form of the state of stress. Elasticity theory equations are constructed here to describe the strain of materials of varying moduli as well as the dependence of the strength properties on the form of the state of strain. Tests were done on coal, limestone, diabase and cement and results are shown. Using the dependencies obtained, Poisson's ratio and the elastic modulus can be calculated for these rocks. The equations and conditions of fracture proposed, are written in a simple invariant form.
Bönisch, Matthias; Calin, Mariana; van Humbeeck, Jan; Skrotzki, Werner; Eckert, Jürgen
2015-03-01
While the current research focus in the search for biocompatible low-modulus alloys is set on β-type Ti-based materials, the potential of fully martensitic Ti-based alloys remains largely unexplored. In this work, the influence of composition and pre-straining on the elastic properties of martensitic binary Ti-Nb alloys was studied. Additionally, the phase formation was compared in the as-cast versus the quenched state. The elastic moduli and hardness of the studied martensitic alloys are at a minimum of 16wt.% Nb and peak between 23.5 and 28.5wt.% Nb. The uniaxial deformation behavior of the alloys used is characterized by the absence of distinct yield points. Monotonic and cyclic (hysteretic) loading-unloading experiments were used to study the influence of Nb-content and pre-straining on the elastic moduli. Such experiments were also utilized to assess the recoverable elastic and anelastic deformations as well as hysteretic energy losses. Particular attention has been paid to the separation of non-linear elastic from anelastic strains, which govern the stress and strain limits to which a material can be loaded without deforming it plastically. It is shown that slight pre-straining of martensitic Ti-Nb alloys can lead to considerable reductions in their elastic moduli as well as increases in their total reversible strains.
Temperature Dependent Elastic moduli of Lead-Telluride based Thermoelectric Materials
Ren, Fei; Case, Eldon D; Ni, Jennifer E.; Timm, Edward J; Lara-Curzio, Edgar; Kanatzidis, Mercouri G.; Trejo, Rosa M; Lin, Chia-Her
2009-01-01
In the open literature, reports of mechanical properties are limited for semiconducting thermoelectric materials, including the temperature dependence of the elastic moduli. In this study, for both cast ingots and hot pressed billets of Ag-, Sb-, Sn-, and S- doped PbTe thermoelectric materials, Resonant Ultrasound Spectroscopy (RUS) was utilized to determine the temperature dependence of elastic moduli including Young's modulus, shear modulus, and Poisson's ratio. This study is the first to determine the temperature-dependent elastic moduli for these PbTe based thermoelectrics and among the few determinations of elasticity of any thermoelectric material for temperatures above 300 K. The Young s modulus and Poisson s ratio measured from room temperature to 773 K during heating and cooling agreed well. Also, the observed Young s modulus, E, versus temperature, T, relationship E(T) = E0(1 bT) is consistent with predictions for materials in the range well above the Debye temperature. A nanoindentation study of Young s modulus on the specimen faces showed that both the cast and hot pressed specimens were approximately elastically isotropic.
Determination of Elastic Moduli of Fiber-Resin Composites Using an Impulse Excitation Technique
NASA Technical Reports Server (NTRS)
Viens, Michael J.; Johnson, Jeffrey J.
1996-01-01
The elastic moduli of graphite/epoxy and graphite/cyanate ester composite specimens with various laminate lay-ups was determined using an impulse excitation/acoustic resonance technique and compared to those determined using traditional strain gauge and extensometer techniques. The stiffness results were also compared to those predicted from laminate theory using uniaxial properties. The specimen stiffnesses interrogated ranged from 12 to 30 Msi. The impulse excitation technique was found to be a relatively quick and accurate method for determining elastic moduli with minimal specimen preparation and no requirement for mechanical loading frames. The results of this investigation showed good correlation between the elastic modulus determined using the impulse excitation technique, strain gauge and extensometer techniques, and modulus predicted from laminate theory. The flexural stiffness determined using the impulse excitation was in good agreement with that predicted from laminate theory. The impulse excitation/acoustic resonance interrogation technique has potential as a quality control test.
Effective elastic constants of polycrystalline aggregates
NASA Astrophysics Data System (ADS)
Bonilla, Luis L.
A METHOD is presented for the determination of the effective elastic constants of a transversely isotropic aggregate of weakly anisotropic crystallites with cubic symmetry. The results obtained generalize those given in the literature for the second and third order elastic constants. In addition, the second moments and the binary angular correlations of the second order stiffnesses are obtained. It is also explained how these moments can be used to find the two-point correlations of the elastic constants.
Pressure derivatives of elastic moduli of fused quartz to 10 kb
Peselnick, L.; Meister, R.; Wilson, W.H.
1967-01-01
Measurements of the longitudinal and shear moduli were made on fused quartz to 10 kb at 24??5??C. The anomalous behavior of the bulk modulus K at low pressure, ???K ???P 0, at higher pressures. The pressure derivative of the rigidity modulus ???G ???P remains constant and negative for the pressure range covered. A 15-kb hydrostatic pressure vessel is described for use with ultrasonic pulse instrumentation for precise measurements of elastic moduli and density changes with pressure. The placing of the transducer outside the pressure medium, and the use of C-ring pressure seals result in ease of operation and simplicity of design. ?? 1967.
Elastic Moduli Inheritance and Weakest Link in Bulk Metallic Glasses
Stoica, Alexandru Dan; Wang, Xun-Li; Lu, Z.P.; Clausen, Bjorn; Brown, Donald
2012-01-01
We show that a variety of bulk metallic glasses (BMGs) inherit their Young s modulus and shear modulus from the solvent components. This is attributed to preferential straining of locally solvent-rich configurations among tightly bonded atomic clusters, which constitute the weakest link in an amorphous structure. This aspect of inhomogeneous deformation, also revealed by our in-situ neutron diffraction studies of an elastically deformed BMG, suggests a scenario of rubber-like viscoelasticity owing to a hierarchy of atomic bonds in BMGs.
Zel, I. Yu.; Ivankina, T. I.; Levin, D. M.; Lokajicek, T.
2015-07-15
The velocities of elastic waves with quasi-longitudinal and quasi-transverse polarizations in a spherical rock sample have been measured. The experimental values of velocities are used to calculate 21 elastic moduli of the sample. For comparison, the effective elastic properties of the sample are simulated based on the data on the crystallographic textures of rock-forming minerals obtained by neutron diffraction. It is shown that the largest discrepancy between the model predictions and experimental velocity values is observed for transversely polarized waves.
Proposed moduli of dry rock and their application to predicting elastic velocities of sandstones
Lee, Myung W.
2005-01-01
Velocities of water-saturated isotropic sandstones under low frequency can be modeled using the Biot-Gassmann theory if the moduli of dry rocks are known. On the basis of effective medium theory by Kuster and Toksoz, bulk and shear moduli of dry sandstone are proposed. These moduli are related to each other through a consolidation parameter and provide a new way to calculate elastic velocities. Because this parameter depends on differential pressure and the degree of consolidation, the proposed moduli can be used to calculate elastic velocities of sedimentary rocks under different in-place conditions by varying the consolidation parameter. This theory predicts that the ratio of P-wave to S-wave velocity (Vp/Vs) of a dry rock decreases as differential pressure increases and porosity decreases. This pattern of behavior is similar to that of water-saturated sedimentary rocks. If microcracks are present in sandstones, the velocity ratio usually increases as differential pressure increases. This implies that this theory is optimal for sandstones having intergranular porosities. Even though the accurate behavior of the consolidation parameter with respect to differential pressure or the degree of consolidation is not known, this theory presents a new way to predict S-wave velocity from P-wave velocity and porosity and to calculate elastic velocities of gas-hydrate-bearing sediments. For given properties of sandstones such as bulk and shear moduli of matrix, only the consolidation parameter affects velocities, and this parameter can be estimated directly from the measurements; thus, the prediction of S-wave velocity is accurate, reflecting in-place conditions.
Elastic Moduli and Damping of Vibrational Modes of Aluminum/Silicon Carbide Composite Beams
NASA Technical Reports Server (NTRS)
Leidecker, Henning
1996-01-01
Elastic and shear moduli were determined for two aluminum matrix composites containing 20 and 40 volume percent discontinuous silicon carbide, respectively, using transverse, longitudinal, and torsional vibrational modes of specimens prepared as thin beams. These moduli are consistent with those determined from stress-strain measurements. The damping factors for these modes were also determined. Thermal properties are used to show that part of the damping of transverse modes is caused by the transverse thermal currents discussed by C. Zener (thermo-elastic damping); this damping is frequency-dependent with a maximum damping factor of approximately 0.002. The remaining damping is frequency-independent, and has roughly similar values in transverse, longitudinal, and torsional modes: approximately 0.0001.
Changes in the elastic moduli of C-S-H due to presence of interlaminar cations
NASA Astrophysics Data System (ADS)
Mejia, Shirley; Hoyos, Bibian
2016-03-01
A set of models of calcium silicate hydrate (C-S-H) with alkali cations in the interlaminar layer, various calcium/silicon ratios, and each with a density of 2.4 g cm-3 is presented. Using molecular simulation techniques, the objective was to study how the Young’s, bulk, and shear modulus, as well as the Poisson’s ratio changed due to the presence of monovalent ions. The effect of density on the elastic moduli was neglected, thus the NVT ensemble was used. Comparing the different simulation cells, it was found that models with sodium and potassium ions in the structure and an alkali/silicon ratio of 0.18 showed negative effects on the elastic moduli of C-S-H. This could be mainly ascribed to the shielding effect of the alkali on the interlaminar interactions that contribute to the cohesion between the layers of C-S-H.
Elastic Moduli of Nanoparticle-Polymer Composite Thin Films via Buckling on Elastomeric Substrates
NASA Astrophysics Data System (ADS)
Yuan, Hongyi; Karim, Alamgir; University of Akron Team
2011-03-01
Polymeric thin films find applications in diverse areas such as coatings, barriers and packaging. The dispersion of nanoparticles into the films was proven to be an effective method to generate tunable properties, particularly mechanical strength. However, there are very few methods for mechanical characterization of the composite thin films with high accuracy. In this study, nanometric polystyrene and polyvinyl alcohol films with uniformly dispersed cobalt and Cloisite nanoparticles at varying concentrations were synthesized via flow-coating and then transferred to crosslinked polydimethylsiloxane (PDMS) flexible substrates. The technique of Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) was employed to determine the elastic moduli of the films, which were calculated from the buckling patterns generated by applying compressive stresses. Results on moduli of films as a function of the concentrations of nanoparticles and the thicknesses of the composite films will be presented. *Corresponding author: alamgir@uakron.edu
Ultrasonic measurement of the moduli of elasticity of refractory materials at high temperatures
NASA Astrophysics Data System (ADS)
Fargeot, D.; Gault, C.; Platon, F.
1980-02-01
A method of ultrasonic measurement of moduli of elasticity of refractory materials up to temperatures of the order of 2000 K is described. The use of magnetostrictive transducers allows operation in the 150-350 kHz frequency range of filamentary test samples with a diameter of about 2 mm and a length of 40-50 mm. Two practical examples are considered, for alpha alumina and for gamma alumina obtained by plasma torch projection.
Ren, Fei; Case, Eldon D; Sootsman, Joseph; Kanatzidis, Mercouri G.; Kong, Huijun; Uher, Ctirad; Lara-Curzio, Edgar; Trejo, Rosa M
2008-01-01
The thermoelectric material PbTe has been used in a wide variety of power generator applications. However, there is limited mechanical property data available for PbTe for temperatures above room temperature. This paper reports dynamic elastic moduli measured via resonant ultrasound spectroscopy on undoped and PbI2-doped polycrystalline PbTe between room temperature and 773 K; in addition, the room temperature carrier concentration was measured by a Hall effect experiment. The Young s modulus and shear modulus of PbTe decreased linearly with temperature above room temperature, while the Poisson s ratio exhibited either monotonic increase or decrease with temperature. The Young s modulus and shear modulus values obtained during heating and cooling agreed to within 1%. The dynamic elastic moduli data obtained in this study compared well in general with literature data. The difference observed between the current study and other literature studies is explained in terms of the carrier concentration effect on elastic moduli.
Elastic properties of dry clay mineral aggregates, suspensions and sandstones
NASA Astrophysics Data System (ADS)
Vanorio, Tiziana; Prasad, Manika; Nur, Amos
2003-10-01
The presence of clay minerals can alter the elastic behaviour of rocks significantly. Although clay minerals are common in sedimentary formations and seismic measurements are our main tools for studying subsurface lithologies, measurements of elastic properties of clay minerals have proven difficult. Theoretical values for the bulk modulus of clay are reported between 20 and 50 GPa. The only published experimental measurement of Young's modulus in a clay mineral using atomic force acoustic microscopy (AFAM) gave a much lower value of 6.2 GPa. This study has concentrated on using independent experimental methods to measure the elastic moduli of clay minerals as functions of pressure and saturation. First, ultrasonic P- and S-wave velocities were measured as functions of hydrostatic pressure in cold-pressed clay aggregates with porosity and grain density ranging from 4 to 43 per cent and 2.13 to 2.83 g cm-3, respectively. In the second experiment, P- and S-wave velocities in clay powders were measured under uniaxial stresses compaction. In the third experiment, P-wave velocity and attenuation in a kaolinite-water suspension with clay concentrations between 0 and 60 per cent were measured at ambient conditions. Our elastic moduli measurements of kaolinite, montmorillonite and smectite are consistent for all experiments and with reported AFAM measurements on a nanometre scale. The bulk modulus values of the solid clay phase (Ks) lie between 6 and 12 GPa and shear (μs) modulus values vary between 4 and 6 GPa. A comparison is made between the accuracy of velocity prediction in shaley sandstones and clay-water and clay-sand mixtures using the values measured in this study and those from theoretical models. Using Ks= 12 GPa and μs= 6 GPa from this study, the models give a much better prediction both of experimental velocity reduction due to increase in clay content in sandstones and velocity measurements in a kaolinite-water suspension.
Soft-materials elastic and shear moduli measurement using piezoelectric cantilevers
NASA Astrophysics Data System (ADS)
Markidou, Anna; Shih, Wan Y.; Shih, Wei-Heng
2005-06-01
We have developed a soft-material elastic modulus and shear modulus sensor using piezoelectric cantilevers. A piezoelectric cantilever is consisted of a highly piezoelectric layer, e.g., lead-zirconate-titanate bonded to a nonpiezoelectric layer, e.g., stainless steel. Applying an electric field in the thickness direction causes a piezoelectric cantilever to bend, generating an axial displacement or force. When a piezoelectric cantilever is in contact with an object, this electric field-generated axial displacement is reduced due to the resistance by the object. With a proper design of the piezoelectric cantilever's geometry, its axial displacements with and without contacting the object could be accurately measured. From these measurements the elastic modulus of the object can be deduced. In this study, we tailored the piezoelectric cantilevers for measuring the elastic and shear moduli of tissue-like soft materials with forces in the submilli Newton to milliNewton range. Elastic moduli and shear moduli of soft materials were measured using piezoelectric cantilevers with a straight tip and an L-shaped tip, respectively. Using gelatin and commercial rubber material as model soft tissues, we showed that a piezoelectric cantilever 1.5-2cm long could measure the elastic modulus and the shear modulus of a small soft material sample (1-3mm wide) in the small strain range (<1%). For samples 5mm high, the resultant compressive (shear) strains were less than 0.5% (1%). The measurements were validated by (1) comparing the measured Young's modulus of the commercial rubber sample with its known value and (2) by measuring both the Young's modulus and shear modulus on the samples and confirming the thus deduced Poisson's ratios with the separately measured Poisson's ratios.
Measurements of Elastic Moduli of Silicone Gel Substrates with a Microfluidic Device
Gutierrez, Edgar; Groisman, Alex
2011-01-01
Thin layers of gels with mechanical properties mimicking animal tissues are widely used to study the rigidity sensing of adherent animal cells and to measure forces applied by cells to their substrate with traction force microscopy. The gels are usually based on polyacrylamide and their elastic modulus is measured with an atomic force microscope (AFM). Here we present a simple microfluidic device that generates high shear stresses in a laminar flow above a gel-coated substrate and apply the device to gels with elastic moduli in a range from 0.4 to 300 kPa that are all prepared by mixing two components of a transparent commercial silicone Sylgard 184. The elastic modulus is measured by tracking beads on the gel surface under a wide-field fluorescence microscope without any other specialized equipment. The measurements have small and simple to estimate errors and their results are confirmed by conventional tensile tests. A master curve is obtained relating the mixing ratios of the two components of Sylgard 184 with the resulting elastic moduli of the gels. The rigidity of the silicone gels is less susceptible to effects from drying, swelling, and aging than polyacrylamide gels and can be easily coated with fluorescent tracer particles and with molecules promoting cellular adhesion. This work can lead to broader use of silicone gels in the cell biology laboratory and to improved repeatability and accuracy of cell traction force microscopy and rigidity sensing experiments. PMID:21980487
Measurements of elastic moduli of silicone gel substrates with a microfluidic device.
Gutierrez, Edgar; Groisman, Alex
2011-01-01
Thin layers of gels with mechanical properties mimicking animal tissues are widely used to study the rigidity sensing of adherent animal cells and to measure forces applied by cells to their substrate with traction force microscopy. The gels are usually based on polyacrylamide and their elastic modulus is measured with an atomic force microscope (AFM). Here we present a simple microfluidic device that generates high shear stresses in a laminar flow above a gel-coated substrate and apply the device to gels with elastic moduli in a range from 0.4 to 300 kPa that are all prepared by mixing two components of a transparent commercial silicone Sylgard 184. The elastic modulus is measured by tracking beads on the gel surface under a wide-field fluorescence microscope without any other specialized equipment. The measurements have small and simple to estimate errors and their results are confirmed by conventional tensile tests. A master curve is obtained relating the mixing ratios of the two components of Sylgard 184 with the resulting elastic moduli of the gels. The rigidity of the silicone gels is less susceptible to effects from drying, swelling, and aging than polyacrylamide gels and can be easily coated with fluorescent tracer particles and with molecules promoting cellular adhesion. This work can lead to broader use of silicone gels in the cell biology laboratory and to improved repeatability and accuracy of cell traction force microscopy and rigidity sensing experiments.
Temperature Coefficients of the Elastic Moduli and Dissipation in B2 Martensites
NASA Astrophysics Data System (ADS)
Darling, Timothy; Migliori, Albert; Thoma, Dan; Hugo, Richard; Freibert, Franz; Louca, Despina
2000-03-01
We have measured the temperature dependence of the elastic moduli and the internal friction of the B2 structure martensites NiTi, Ni_0.62Al_0.38, and AuZn using Resonant Ultrasound Spectroscopy (RUS). In the high temperature austenite phase the moduli show an anomalous positive temperature coefficient, and below the martensite transition the materials display a high dissipation which seems glass-like. We believe that the fundamental shear instability of the body-centered phase and subtle disorder in the martensite phase are responsible for these behaviors. We have also carried out neutron PDF, transport and TEM measurements to detect the subtle structural effects which are producing the anomalies in the ultrasound data.
Dynamic elastic moduli in magnetic gels: Normal modes and linear response.
Pessot, Giorgio; Löwen, Hartmut; Menzel, Andreas M
2016-09-14
In the perspective of developing smart hybrid materials with customized features, ferrogels and magnetorheological elastomers allow a synergy of elasticity and magnetism. The interplay between elastic and magnetic properties gives rise to a unique reversible control of the material behavior by applying an external magnetic field. Albeit few works have been performed on the time-dependent properties so far, understanding the dynamic behavior is the key to model many practical situations, e.g., applications as vibration absorbers. Here we present a way to calculate the frequency-dependent elastic moduli based on the decomposition of the linear response to an external stress in normal modes. We use a minimal three-dimensional dipole-spring model to theoretically describe the magnetic and elastic interactions on the mesoscopic level. Specifically, the magnetic particles carry permanent magnetic dipole moments and are spatially arranged in a prescribed way, before they are linked by elastic springs. An external magnetic field aligns the magnetic moments. On the one hand, we study regular lattice-like particle arrangements to compare with previous results in the literature. On the other hand, we calculate the dynamic elastic moduli for irregular, more realistic particle distributions. Our approach measures the tunability of the linear dynamic response as a function of the particle arrangement, the system orientation with respect to the external magnetic field, as well as the magnitude of the magnetic interaction between the particles. The strength of the present approach is that it explicitly connects the relaxational modes of the system with the rheological properties as well as with the internal rearrangement of the particles in the sample, providing new insight into the dynamics of these remarkable materials. PMID:27634276
Dynamic elastic moduli in magnetic gels: Normal modes and linear response
NASA Astrophysics Data System (ADS)
Pessot, Giorgio; Löwen, Hartmut; Menzel, Andreas M.
2016-09-01
In the perspective of developing smart hybrid materials with customized features, ferrogels and magnetorheological elastomers allow a synergy of elasticity and magnetism. The interplay between elastic and magnetic properties gives rise to a unique reversible control of the material behavior by applying an external magnetic field. Albeit few works have been performed on the time-dependent properties so far, understanding the dynamic behavior is the key to model many practical situations, e.g., applications as vibration absorbers. Here we present a way to calculate the frequency-dependent elastic moduli based on the decomposition of the linear response to an external stress in normal modes. We use a minimal three-dimensional dipole-spring model to theoretically describe the magnetic and elastic interactions on the mesoscopic level. Specifically, the magnetic particles carry permanent magnetic dipole moments and are spatially arranged in a prescribed way, before they are linked by elastic springs. An external magnetic field aligns the magnetic moments. On the one hand, we study regular lattice-like particle arrangements to compare with previous results in the literature. On the other hand, we calculate the dynamic elastic moduli for irregular, more realistic particle distributions. Our approach measures the tunability of the linear dynamic response as a function of the particle arrangement, the system orientation with respect to the external magnetic field, as well as the magnitude of the magnetic interaction between the particles. The strength of the present approach is that it explicitly connects the relaxational modes of the system with the rheological properties as well as with the internal rearrangement of the particles in the sample, providing new insight into the dynamics of these remarkable materials.
NASA Astrophysics Data System (ADS)
Ghosh, G.
2015-08-01
A comprehensive computational study of elastic properties of cementite (Fe3C) and its alloyed counterparts (M3C (M = Al, Co, Cr, Cu, Fe, Hf, Mn, Mo, Nb, Ni, Si, Ta, Ti, V, W, Zr, Cr2FeC and CrFe2C) having the crystal structure of Fe3C is carried out employing electronic density-functional theory (DFT), all-electron PAW pseudopotentials and the generalized gradient approximation for the exchange-correlation energy (GGA). Specifically, as a part of our systematic study of cohesive properties of solids and in the spirit of materials genome, following properties are calculated: (i) single-crystal elastic constants, Cij, of above M3Cs; (ii) anisotropies of bulk, Young's and shear moduli, and Poisson's ratio based on calculated Cijs, demonstrating their extreme anisotropies; (iii) isotropic (polycrystalline) elastic moduli (bulk, shear, Young's moduli and Poisson's ratio) of M3Cs by homogenization of calculated Cijs; and (iv) acoustic Debye temperature, θD, of M3Cs based on calculated Cijs. We provide a critical appraisal of available data of polycrystalline elastic properties of alloyed cementite. Calculated single crystal properties may be incorporated in anisotropic constitutive models to develop and test microstructure-processing-property-performance links in multi-phase materials where cementite is a constituent phase.
NASA Technical Reports Server (NTRS)
Sachse, W.; Ruoff, A. L.
1974-01-01
The propagation of ultrasonic pulses in pyrophyllite specimens was studied to determine the effect of specimen precompression on the measured elastic moduli. Measurements were made at room pressure and, for the precompressed specimens, to pressures of 3 kbar. Pyrophyllite was found to be elastically anisotropic, apparently the result of the fabric present in our material. The room pressure adiabatic bulk modulus as measured on specimens made of isostatically compacted powered pyrophyllite was determined to be 96.1 kbar. The wave speeds of ultrasonic pulses in pyrophyllite were found to decrease with increasing specimen precompression. A limiting value of precompression was found, above which no further decrease in wave speed was observed. For the shear wave speeds this occurs at 10 kbar while for the longitudinal wave at 25 kbar. In the limit, the shear waves propagate 20% slower than in the unprecompressed samples; for the longitudinal wave the difference is 30%.
NASA Astrophysics Data System (ADS)
Yuan, Hongyi; Marszalek-Kempke, Jolanta; Verma, Prateek; Karim, Alamgir
2012-02-01
Mechanical properties are important for the long term durability of polymeric thin films. Unfortunately, there are very few methods for mechanical characterization of sub-micron thin films with high accuracy and repeatability. The technique of Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) was employed to determine the elastic moduli of nanocomposite and blend films, which were calculated from the buckling patterns generated by applying compressive stresses. In this study, polylactic acid (PLA) / Cloisite 30B nanocomposite thin films and polycaprolactone (PCL) / PLA blend thin films were prepared via spin-coating and then transferred to crosslinked polydimethylsiloxane (PDMS) flexible substrates. Results showed the strengthening effect of Cloisite 30B on PLA systems. The effect of nanoparticle concentrations and the influences of crystallinity and phase separation of blends will be presented.
NASA Astrophysics Data System (ADS)
Ji, Xiang-Ying; Cao, Yan-Ping; Feng, Xi-Qiao
2010-06-01
We investigate the stiffening effect of graphene sheets dispersed in polymer nanocomposites using the Mori-Tanaka micromechanics method. The effective elastic moduli of graphene sheet-reinforced composites are first predicted by assuming that all the graphene sheets are either aligned or randomly oriented in the polymer matrix while maintaining their platelet-like shape. It is shown that a very low content of graphene sheets can considerably enhance the effective stiffness of the composite. The superiority of graphene sheets as a kind of reinforcement is further verified by a comparison with carbon nanotubes, another promising nanofiller in polymer composites. In addition, we analyze several critical physical mechanisms that may affect the reinforcing effects, including the agglomeration, stacking-up and rolling-up of graphene sheets. The results reveal the extent to which these factors will negatively influence the elastic moduli of graphene sheet-reinforced nanocomposites. This theoretical study may help to understand the relevant experimental results and facilitate the mechanical characterization and optimal synthesis of these kinds of novel and highly promising nanocomposites.
Electrostatic and electrokinetic contributions to the elastic moduli of a driven membrane
NASA Astrophysics Data System (ADS)
Lacoste, D.; Menon, G. I.; Bazant, M. Z.; Joanny, J. F.
2009-03-01
We discuss the electrostatic contribution to the elastic moduli of a cell or artificial membrane placed in an electrolyte and driven by a DC electric field. The field drives ion currents across the membrane, through specific channels, pumps or natural pores. In steady state, charges accumulate in the Debye layers close to the membrane, modifying the membrane elastic moduli. We first study a model of a membrane of zero thickness, later generalizing this treatment to allow for a finite thickness and finite dielectric constant. Our results clarify and extend the results presented by D. Lacoste, M. Cosentino Lagomarsino, and J.F. Joanny (EPL 77, 18006 (2007)), by providing a physical explanation for a destabilizing term proportional to k ⊥ 3 in the fluctuation spectrum, which we relate to a nonlinear (E2) electrokinetic effect called induced-charge electro-osmosis (ICEO). Recent studies of ICEO have focused on electrodes and polarizable particles, where an applied bulk field is perturbed by capacitive charging of the double layer and drives the flow along the field axis toward surface protrusions; in contrast, we predict “reverse” ICEO flows around driven membranes, due to curvature-induced tangential fields within a nonequilibrium double layer, which hydrodynamically enhance protrusions. We also consider the effect of incorporating the dynamics of a spatially dependent concentration field for the ion channels.
Effect of TeO 2 on the elastic moduli of sodium borate glasses
NASA Astrophysics Data System (ADS)
Saddeek, Yasser B.; Latif, Lamia. Abd El
2004-05-01
Sodium borate glass containing tellurite as Te xNa 2-2 xB 4-4 xO 7-5 x with x=0, 0.05, 0.15, 0.25 and 0.35 have been prepared by rapid quenching. Ultrasonic velocity (both longitudinal and shear) measurements have been made using a transducer operated at the fundamental frequency of 4 MHz at room temperature. The density was measured by the conventional Archimedes method. The elastic moduli, the Debye temperature, Poisson's ratio, and the parameters derived from the Makishima-Mackenzie model and the bond compression model have been obtained as a function of TeO 2 content. The monotonic decrease in the velocities and the elastic moduli, and the increase in the ring diameter and the ratio Kbc/ Ke as a function of TeO 2 modifier content reveals the loose packing structure, which is attributed to the increase in the molar volume and the reduction in the vibrations of the borate lattice. The observed results confirm that the addition of TeO 2 changes the rigid character of Na 2B 4O 7 to a matrix of ionic behaviour bonds (NBOs). This is due to the creation of more and more discontinuities and defects in the glasses, thus breaking down the borax structure.
NASA Astrophysics Data System (ADS)
Saxena, Nishank; Mavko, Gary
2016-03-01
Estimation of elastic rock moduli using 2D plane strain computations from thin sections has several numerical and analytical advantages over using 3D rock images, including faster computation, smaller memory requirements, and the availability of cheap thin sections. These advantages, however, must be weighed against the estimation accuracy of 3D rock properties from thin sections. We present a new method for predicting elastic properties of natural rocks using thin sections. Our method is based on a simple power-law transform that correlates computed 2D thin section moduli and the corresponding 3D rock moduli. The validity of this transform is established using a dataset comprised of FEM-computed elastic moduli of rock samples from various geologic formations, including Fontainebleau sandstone, Berea sandstone, Bituminous sand, and Grossmont carbonate. We note that using the power-law transform with a power-law coefficient between 0.4-0.6 contains 2D moduli to 3D moduli transformations for all rocks that are considered in this study. We also find that reliable estimates of P-wave (Vp) and S-wave velocity (Vs) trends can be obtained using 2D thin sections.
Compositional dependence of elastic moduli for transition-metal oxide spinels
NASA Astrophysics Data System (ADS)
Reichmann, H. J.; Jacobsen, S. D.; Boffa Ballaran, T.
2012-12-01
Spinel phases (AB2O4) are common non-silicate oxides in the Earth's crust and upper mantle. A characteristic of this mineral group is the ability to host a wide range of transition metals. Here we summarize the influence of transition metals (Fe, Zn, and Mn) on the pressure dependence of elastic moduli of related spinels (magnetite, gahnite, and franklinite) using GHz-ultrasonic interferometry. Measurements were carried out up to 10 GPa in diamond-anvil cells using hydrostatic pressure media. Transition metals with unfilled 3d orbitals strongly influence the elastic properties of spinels. Franklinite (Zn,Mn)Fe2O4 and magnetite Fe3O4 with transition metals on both A and B cation sites exhibit pressure-induced mode softening of C44, whereas C44 of gahnite(ZnAl2O4) and spinel (MgAl2O4) exhibit positive pressure derivatives of the shear moduli. Spinels with two transition elements tend to undergo phase changes at a lower pressure than those with none or only one transition metal. Along the Mn-Zn solid solution, the variation of moduli with composition is non-linear, and a mid-range franklinite composition studied here shows a minimum in C44 compared with either end-member: MnFe2O 4 or ZnFe2O4. In general, the linear variation of sound velocity with density (Birch's Law) is followed by spinels, however spinels containing only one or no transition metals follow a distinct slope from those containing transition metals on both A and B sites. The Cauchy relation, 0.5(C12 - C44) = P is fulfilled by spinels with only one or no transition metals, suggesting that that Coulomb interactions dominate. Spinels with two transition metals fail to meet the Cauchy relation, indicating strong directional dependence and covalent character of bonding. The bonding character of transition metals is crucial to understanding the elastic behavior of natural and synthetic spinel solid solutions containing transition metals.
van Oosten, Anne S. G.; Vahabi, Mahsa; Licup, Albert J.; Sharma, Abhinav; Galie, Peter A.; MacKintosh, Fred C.; Janmey, Paul A.
2016-01-01
Gels formed by semiflexible filaments such as most biopolymers exhibit non-linear behavior in their response to shear deformation, e.g., with a pronounced strain stiffening and negative normal stress. These negative normal stresses suggest that networks would collapse axially when subject to shear stress. This coupling of axial and shear deformations can have particularly important consequences for extracellular matrices and collagenous tissues. Although measurements of uniaxial moduli have been made on biopolymer gels, these have not directly been related to the shear response. Here, we report measurements and simulations of axial and shear stresses exerted by a range of hydrogels subjected to simultaneous uniaxial and shear strains. These studies show that, in contrast to volume-conserving linearly elastic hydrogels, the Young’s moduli of networks formed by the biopolymers are not proportional to their shear moduli and both shear and uniaxial moduli are strongly affected by even modest degrees of uniaxial strain. PMID:26758452
Mapping elasticity moduli of atherosclerotic plaque in situ via atomic force microscopy.
Tracqui, Philippe; Broisat, Alexis; Toczek, Jackub; Mesnier, Nicolas; Ohayon, Jacques; Riou, Laurent
2011-04-01
Several studies have suggested that evolving mechanical stresses and strains drive atherosclerotic plaque development and vulnerability. Especially, stress distribution in the plaque fibrous capsule is an important determinant for the risk of vulnerable plaque rupture. Knowledge of the stiffness of atherosclerotic plaque components is therefore of critical importance. In this work, force mapping experiments using atomic force microscopy (AFM) were conducted in apolipoprotein E-deficient (ApoE(-/-)) mouse, which represents the most widely used experimental model for studying mechanisms underlying the development of atherosclerotic lesions. To obtain the elastic material properties of fibrous caps and lipidic cores of atherosclerotic plaques, serial cross-sections of aortic arch lesions were probed at different sites. Atherosclerotic plaque sub-structures were subdivided into cellular fibrotic, hypocellular fibrotic and lipidic rich areas according to histological staining. Hertz's contact mechanics were used to determine elasticity (Young's) moduli that were related to the underlying histological plaque structure. Cellular fibrotic regions exhibit a mean Young modulus of 10.4±5.7kPa. Hypocellular fibrous caps were almost six-times stiffer, with average modulus value of 59.4±47.4kPa, locally rising up to ∼250kPa. Lipid rich areas exhibit a rather large range of Young's moduli, with average value of 5.5±3.5kPa. Such precise quantification of plaque stiffness heterogeneity will allow investigators to have prospectively a better monitoring of atherosclerotic disease evolution, including arterial wall remodeling and plaque rupture, in response to mechanical constraints imposed by vascular shear stress and blood pressure.
Ghosh, G.
2015-08-15
A comprehensive computational study of elastic properties of cementite (Fe{sub 3}C) and its alloyed counterparts (M{sub 3}C (M = Al, Co, Cr, Cu, Fe, Hf, Mn, Mo, Nb, Ni, Si, Ta, Ti, V, W, Zr, Cr{sub 2}FeC and CrFe{sub 2}C) having the crystal structure of Fe{sub 3}C is carried out employing electronic density-functional theory (DFT), all-electron PAW pseudopotentials and the generalized gradient approximation for the exchange-correlation energy (GGA). Specifically, as a part of our systematic study of cohesive properties of solids and in the spirit of materials genome, following properties are calculated: (i) single-crystal elastic constants, C{sub ij}, of above M{sub 3}Cs; (ii) anisotropies of bulk, Young’s and shear moduli, and Poisson’s ratio based on calculated C{sub ij}s, demonstrating their extreme anisotropies; (iii) isotropic (polycrystalline) elastic moduli (bulk, shear, Young’s moduli and Poisson’s ratio) of M{sub 3}Cs by homogenization of calculated C{sub ij}s; and (iv) acoustic Debye temperature, θ{sub D}, of M{sub 3}Cs based on calculated C{sub ij}s. We provide a critical appraisal of available data of polycrystalline elastic properties of alloyed cementite. Calculated single crystal properties may be incorporated in anisotropic constitutive models to develop and test microstructure-processing-property-performance links in multi-phase materials where cementite is a constituent phase.
Aggregation-structure-elasticity relationship of gels
NASA Astrophysics Data System (ADS)
Ma, Hang-Shing
Aerogel is a mesoporous, low-density material which is desirable for applications like thermal insulation and low-k interlayer dielectric. However, its lack of mechanical integrity hinders its development. Experiments have shown that aerogels exhibit a scaling relationship E ∝ rho m between modulus E and density rho, with the exponent m usually between 3 and 4. The objective of the dissertation is to use computer modeling to understand how the random aggregation process accounts for the fractal structure and the compliant nature of aerogels. Model gels were created by the diffusion-limited cluster-cluster aggregation (DLCA), which simulates random aggregation leading to the sol-gel transition. Then each resulting structure was modeled as an elastic beam network and numerically compressed using the finite element method (FEM). Analyses showed that the DLCA gels reproduced the scaling relationship after trimming the non-contributive dangling branches from the mechanically efficient looped networks. The dangling bond deflection (DEF) model was therefore developed to model the random rotational movement of the dangling branches and the subsequent loop structure formation. Model gels with extensive loops and negligible dangling branches were simulated by combining the DLCA and DEF models. Representation of the aerogel networks by the DLCADEF models was validated for the resemblance of the fractal geometry and elastic behavior. The lack of mechanical integrity in aerogels is a natural consequence of the random aggregation and the resulting fractal structure. Fractal clusters are created in the early stage of aggregation, each of which is characterized by a dense core and sparse perimeter. These clusters grow in size until they percolate at the gel point by knitting together at the perimeters. The gel structure possesses a "blob-and-link" architecture, with the blobs representing the rigid cores of the fractal clusters, and the links corresponding to the tenuous chains
Temperature- and thickness-dependent elastic moduli of polymer thin films
2011-01-01
The mechanical properties of polymer ultrathin films are usually different from those of their counterparts in bulk. Understanding the effect of thickness on the mechanical properties of these films is crucial for their applications. However, it is a great challenge to measure their elastic modulus experimentally with in situ heating. In this study, a thermodynamic model for temperature- (T) and thickness (h)-dependent elastic moduli of polymer thin films Ef(T,h) is developed with verification by the reported experimental data on polystyrene (PS) thin films. For the PS thin films on a passivated substrate, Ef(T,h) decreases with the decreasing film thickness, when h is less than 60 nm at ambient temperature. However, the onset thickness (h*), at which thickness Ef(T,h) deviates from the bulk value, can be modulated by T. h* becomes larger at higher T because of the depression of the quenching depth, which determines the thickness of the surface layer δ. PMID:21711747
Preparation and elastic moduli of germanate glass containing lead and bismuth.
Sidek, Hj A A; Bahari, Hamid R; Halimah, Mohamed K; Yunus, Wan M M
2012-01-01
This paper reports the rapid melt quenching technique preparation for the new family of bismuth-lead germanate glass (BPG) systems in the form of (GeO(2))(60)-(PbO)(40-) (x)-(½Bi(2)O(3))(x) where x = 0 to 40 mol%. Their densities with respect of Bi(2)O(3) concentration were determined using Archimedes' method with acetone as a floatation medium. The current experimental data are compared with those of bismuth lead borate (B(2)O(3))(20)-(PbO)(80-) (x)-(Bi(2)O(3))(x). The elastic properties of BPG were studied using the ultrasonic pulse-echo technique where both longitudinal and transverse sound wave velocities have been measured in each glass samples at a frequency of 15 MHz and at room temperature. Experimental data shows that all the physical parameters of BPG including density and molar volume, both longitudinal and transverse velocities increase linearly with increasing of Bi(2)O(3) content in the germanate glass network. Their elastic moduli such as longitudinal, shear and Young's also increase linearly with addition of Bi(2)O(3) but the bulk modulus did not. The Poisson's ratio and fractal dimensionality are also found to vary linearly with the Bi(2)O(3) concentration. PMID:22606000
Elastic moduli of rock glasses under pressure to 8 kilobars and geophysical implications.
Meister, R.; Robertson, E.C.; Werke, R.W.; Raspet, R.
1980-01-01
Shear and longitudinal velocities were measured by the ultrasonic phase comparison method as a function of pressure to 8 kbar on synthetic glasses of basalt, andesite, rhyolite, and quartz composition and on natural obsidian. Velocities of most of the glasses decrease anomalously with pressure, but increasingly more-normal behavior occurs with decrease in SiO2 content. The pressure derivatives of rigidity and bulk modulus increase linearly, from -3.39 to -0.26 and from -5.91 to +2.09, respectively, with decrease in SiO2 content from 100 to 49%. The change from negative to positive in the pressure derivatives of both moduli and observed at Poisson's ratio of about 0.25 is consitent with the Smyth model for the anomalous elastic behavior of glass. If the temperature in the upper mantle is about 1500oC, tholeiitic basalt would be molten in accordance with the partial melt explanation for the low-velocity zone; at 1300oC and below, basalt would be in the glassy state, especially if more felsic than tholeiite. -Authors
Efstathiou, C.; Boyce, D.E.; Park, J.-S.; Lienert, U.; Dawson, P.R.; Miller, M.P.
2010-11-30
This paper presents a method - based on high-energy synchrotron X-ray diffraction data and a crystal-based finite element simulation formulation - for understanding grain scale deformation behavior within a polycrystalline aggregate. We illustrate this method by using it to determine the single-crystal elastic moduli of {beta}21s, a body-centered cubic titanium alloy. We employed a polycrystalline sample. Using in situ loading and high-energy X-rays at the Advanced Photon Source beamline 1-ID-C, we measured components of the lattice strain tensor from four individual grains embedded within a polycrystalline specimen. We implemented an optimization routine that minimized the difference between the experiment and simulation lattice strains. Sensitivity coefficients needed in the optimization routine are generated numerically using the finite element model. The elastic moduli that we computed for the {beta}21s are C{sub 11} = 110 GPa, C{sub 12} = 74 GPa and C{sub 44} = 89 GPa. The resulting Zener anisotropic ratio is A = 5.
NASA Astrophysics Data System (ADS)
de Jong, Maarten; Chen, Wei; Notestine, Randy; Persson, Kristin; Ceder, Gerbrand; Jain, Anubhav; Asta, Mark; Gamst, Anthony
2016-10-01
Materials scientists increasingly employ machine or statistical learning (SL) techniques to accelerate materials discovery and design. Such pursuits benefit from pooling training data across, and thus being able to generalize predictions over, k-nary compounds of diverse chemistries and structures. This work presents a SL framework that addresses challenges in materials science applications, where datasets are diverse but of modest size, and extreme values are often of interest. Our advances include the application of power or Hölder means to construct descriptors that generalize over chemistry and crystal structure, and the incorporation of multivariate local regression within a gradient boosting framework. The approach is demonstrated by developing SL models to predict bulk and shear moduli (K and G, respectively) for polycrystalline inorganic compounds, using 1,940 compounds from a growing database of calculated elastic moduli for metals, semiconductors and insulators. The usefulness of the models is illustrated by screening for superhard materials.
de Jong, Maarten; Chen, Wei; Notestine, Randy; Persson, Kristin; Ceder, Gerbrand; Jain, Anubhav; Asta, Mark; Gamst, Anthony
2016-01-01
Materials scientists increasingly employ machine or statistical learning (SL) techniques to accelerate materials discovery and design. Such pursuits benefit from pooling training data across, and thus being able to generalize predictions over, k-nary compounds of diverse chemistries and structures. This work presents a SL framework that addresses challenges in materials science applications, where datasets are diverse but of modest size, and extreme values are often of interest. Our advances include the application of power or Hölder means to construct descriptors that generalize over chemistry and crystal structure, and the incorporation of multivariate local regression within a gradient boosting framework. The approach is demonstrated by developing SL models to predict bulk and shear moduli (K and G, respectively) for polycrystalline inorganic compounds, using 1,940 compounds from a growing database of calculated elastic moduli for metals, semiconductors and insulators. The usefulness of the models is illustrated by screening for superhard materials. PMID:27694824
NASA Astrophysics Data System (ADS)
Zhang, R. F.; Lin, Z. J.; Zhao, Y. S.; Veprek, S.
2011-03-01
Using first-principles calculations, we show that, in spite of its relatively low shear modulus, boron suboxide (B6O) is superhard because of its high shear strength of ⩾38 GPa which originates from three-dimensional covalently bonded network of B12 icosahedral units connected by boron and oxygen atoms. We further demonstrate that the high shear resistance of B6O is related to strong B-B covalent bonds that connect the B12 units. These results challenge the concept of design intrinsically superhard materials based on high elastic moduli only.
Determination of the dynamic elastic constants of recycled aggregate concrete
NASA Astrophysics Data System (ADS)
Tsoumani, A. A.; Barkoula, N.-M.; Matikas, T. E.
2015-03-01
Nowadays, construction and demolition waste constitutes a major portion of the total solid waste production in the world. Due to both environmental and economical reasons, an increasing interest concerning the use of recycled aggregate to replace aggregate from natural sources is generated. This paper presents an investigation on the properties of recycled aggregate concrete. Concrete mixes are prepared using recycled aggregates at a substitution level between 0 and 100% of the total coarse aggregate. The influence of this replacement on strengthened concrete's properties is being investigated. The properties estimated are: density and dynamic modulus of elasticity at the age of both 7 and 28 days. Also, flexural strength of 28 days specimens is estimated. The determination of the dynamic elastic modulus was made using the ultrasonic pulse velocity method. The results reveal that the existence of recycled aggregates affects the properties of concrete negatively; however, in low levels of substitution the influence of using recycled aggregates is almost negligible. Concluding, the controlled use of recycled aggregates in concrete production may help solve a vital environmental issue apart from being a solution to the problem of inadequate concrete aggregates.
Lavrentyev, A I; Rokhlin, S I
2001-04-01
An ultrasonic method proposed by us for determination of the complete set of acoustical and geometrical properties of a thin isotropic layer between semispaces (J. Acoust. Soc. Am. 102 (1997) 3467) is extended to determination of the properties of a coating on a thin plate. The method allows simultaneous determination of the coating thickness, density, elastic moduli and attenuation (longitudinal and shear) from normal and oblique incidence reflection (transmission) frequency spectra. Reflection (transmission) from the coated plate is represented as a function of six nondimensional parameters of the coating which are determined from two experimentally measured spectra: one at normal and one at oblique incidence. The introduction of the set of nondimensional parameters allows one to transform the reconstruction process from one search in a six-dimensional space to two searches in three-dimensional spaces (one search for normal incidence and one for oblique). Thickness, density, and longitudinal and shear elastic moduli of the coating are calculated from the nondimensional parameters determined. The sensitivity of the method to individual properties and its stability against experimental noise are studied and the inversion algorithm is accordingly optimized. An example of the method and experimental measurement for comparison is given for a polypropylene coating on a steel foil.
Improved rigorous bounds on the effective elastic moduli of a composite material
NASA Astrophysics Data System (ADS)
Kantor, Y.; Bergman, D. J.
A NEW METHOD for deriving rigorous bounds on the effective elastic constants of a composite material is presented and used to derive a number of known as well as some new bounds. The new approach is based on a presentation of those constants as a sum of simple poles. The locations and strengths of the poles are treated as variational parameters, while different kinds of available information are translated into constraints on these parameters. Our new results include an extension of the range of validity of the Hashin-Shtrikman bounds to the case of composites made of isotropic materials but with an arbitrary microgeometry. We also use information on the effective elastic constants of one composite in order to obtain improved bounds on the effective elastic constants of another composite with the same or a similar microgeometry.
Chen, Haihua; Peng, Fang; Mao, Ho-kwang; Shen, Guoyin; Liermann, Hanns-Peter; Li, Zuo; Shu, Jinfu
2010-07-23
The high pressure behavior of titanium nitride (TiN) was investigated using synchrotron radial x-ray diffraction (RXRD) under nonhydrostatic compression up to 45.4 GPa in a diamond-anvil cell. We obtained the hydrostatic compression equation of state of TiN. Fitting to the third-order Birch-Murnaghan equation of state, the bulk modulus derived from nonhydrostatic compression data varies from 232 to 353 GPa, depending on angle {Psi}, the orientation of the diffraction planes with respect to the loading axis. The RXRD data obtained at {Psi} = 54.7{sup o} yield a bulk modulus K{sub 0} = 282 {+-} 9 GPa with pressure derivative K{prime}{sub 0} fixed at 4. We have analyzed the deformation mechanisms by analyzing the (111), (200), (220), (311), and (222) peaks in the x-ray diffraction under pressures. The ratio of uniaxial stress component to shear modulus t/G ranges from 0.007-0.027 at the pressure of 6.4-45.4 GPa. It was found that the TiN sample could support a maximum uniaxial stress component t of 8.6 GPa, when it started to yield at 45.4 GPa under uniaxial compression. And the aggregate elastic moduli of TiN at high pressure were determined from the synchrotron RXRD measurements.
Roch, T; Cui, J; Kratz, K; Lendlein, A; Jung, F
2012-01-01
The need for engineered devices to treat cardiovascular diseases is increasing due to an aging population and a changing lifestyle. Soft poly(n-butyl acrylate) (cPnBA) networks were recently described as polymer networks with adjustable mechanical properties and suggested as soft substrates for cells, which could potentially be used for cardiovascular implants. Vascular prostheses designed to be implanted in arteries should have an elasticity similar to blood vessels (elastic modulus at body temperature between 100 and 1200 kPa). Therefore, cPnBA networks with E-moduli of 250 kPa (cPnBA0250) and 1100 kPa (cPnBA1100) were developed. Recently, it was shown that both materials were non-cytotoxic for murin fibroblasts, human primary endothelial cells and human monocytes. However, before such newly developed polymers can be used in vivo, it has to be assured that the sterilized materials have a very low endotoxin load to avoid an unspecific activation of the immune system, which otherwise might cause local or systemic inflammatory responses and could lead to severe pathologies. In this study we investigated the immuno-compatibility of sterilized cPnBA0250 and cPnBA1100 with the help of an immuno-competent macrophage cell line as well as with whole human blood.
Elastometry of deflated capsules: elastic moduli from shape and wrinkle analysis.
Knoche, Sebastian; Vella, Dominic; Aumaitre, Elodie; Degen, Patrick; Rehage, Heinz; Cicuta, Pietro; Kierfeld, Jan
2013-10-01
Elastic capsules, prepared from droplets or bubbles attached to a capillary (as in a pendant drop tensiometer), can be deflated by suction through the capillary. We study this deflation and show that a combined analysis of the shape and wrinkling characteristics enables us to determine the elastic properties in situ. Shape contours are analyzed and fitted using shape equations derived from nonlinear membrane-shell theory to give the elastic modulus, Poisson ratio and stress distribution of the membrane. We include wrinkles, which generically form upon deflation, within the shape analysis. Measuring the wavelength of wrinkles and using the calculated stress distribution gives the bending stiffness of the membrane. We compare this method with previous approaches using the Laplace-Young equation and illustrate the method on two very different capsule materials: polymerized octadecyltrichlorosilane (OTS) capsules and hydrophobin (HFBII) coated bubbles. Our results are in agreement with the available rheological data. For hydrophobin coated bubbles, the method reveals an interesting nonlinear behavior consistent with the hydrophobin molecules having a rigid core surrounded by a softer shell.
Elastometry of deflated capsules: elastic moduli from shape and wrinkle analysis.
Knoche, Sebastian; Vella, Dominic; Aumaitre, Elodie; Degen, Patrick; Rehage, Heinz; Cicuta, Pietro; Kierfeld, Jan
2013-10-01
Elastic capsules, prepared from droplets or bubbles attached to a capillary (as in a pendant drop tensiometer), can be deflated by suction through the capillary. We study this deflation and show that a combined analysis of the shape and wrinkling characteristics enables us to determine the elastic properties in situ. Shape contours are analyzed and fitted using shape equations derived from nonlinear membrane-shell theory to give the elastic modulus, Poisson ratio and stress distribution of the membrane. We include wrinkles, which generically form upon deflation, within the shape analysis. Measuring the wavelength of wrinkles and using the calculated stress distribution gives the bending stiffness of the membrane. We compare this method with previous approaches using the Laplace-Young equation and illustrate the method on two very different capsule materials: polymerized octadecyltrichlorosilane (OTS) capsules and hydrophobin (HFBII) coated bubbles. Our results are in agreement with the available rheological data. For hydrophobin coated bubbles, the method reveals an interesting nonlinear behavior consistent with the hydrophobin molecules having a rigid core surrounded by a softer shell. PMID:24015876
NASA Astrophysics Data System (ADS)
Uhlemann, S.; Hagedorn, S.; Dashwood, B.; Maurer, H.; Gunn, D.; Dijkstra, T.; Chambers, J.
2016-11-01
In the broad spectrum of natural hazards, landslides in particular are capable of changing the landscape and causing significant human and economic losses. Detailed site investigations form an important component in the landslide risk mitigation and disaster risk reduction process. These investigations usually rely on surface observations, discrete sampling of the subsurface, and laboratory testing to examine properties that are deemed representative of entire slopes. Often this requires extensive interpolations and results in large uncertainties. To compliment and extend these approaches, we present a study from an active landslide in a Lias Group clay slope, North Yorkshire, UK, examining combined P- and S-wave seismic refraction tomography (SRT) as a means of providing subsurface volumetric imaging of geotechnical proxies. The distributions of seismic wave velocities determined from SRT at the study site indicated zones with higher porosity and fissure density that are interpreted to represent the extent and depth of mass movements and weathered bedrock zones. Distinguishing the lithological units was facilitated by deriving the Poisson's ratio from the SRT data as saturated clay and partially saturated sandy silts showed distinctively different Poisson's ratios. Shear and Young's moduli derived from the SRT data revealed the weak nature of the materials in active parts of the landslide (i.e. 25 kPa and 100 kPa respectively). The SRT results are consistent with intrusive (i.e. cone penetration tests), laboratory, and additional geoelectrical data from this site. This study shows that SRT forms a cost-effective method that can significantly reduce uncertainties in the conceptual ground model of geotechnical and hydrological conditions that govern landslide dynamics.
Polycrystalline elastic moduli of a high-entropy alloy at cryogenic temperatures
Haglund, A.; Koehler, M.; Catoor, D.; George, E. P.; Keppens, V.
2014-12-05
A FCC high-entropy alloy (HEA) that exhibits strong temperature dependence of strength at low homologous temperatures in sharp contrast to pure FCC metals like Ni that show weak temperature dependence is CrMnCoFeNi. In order to understand this behavior, elastic constants were determined as a function of temperature. From 300 K down to 55 K, the shear modulus (G) of the HEA changes by only 8%, increasing from 80 to 86 GPa. Moreover, this temperature dependence is weaker than that of FCC Ni, whose G increases by 12% (81–91 GPa). Therefore, the uncharacteristic temperature-dependence of the strength of the HEA is not due to the temperature dependence of its shear modulus.
Polycrystalline elastic moduli of a high-entropy alloy at cryogenic temperatures
Haglund, A.; Koehler, M.; Catoor, D.; George, E. P.; Keppens, V.
2014-12-05
A FCC high-entropy alloy (HEA) that exhibits strong temperature dependence of strength at low homologous temperatures in sharp contrast to pure FCC metals like Ni that show weak temperature dependence is CrMnCoFeNi. In order to understand this behavior, elastic constants were determined as a function of temperature. From 300 K down to 55 K, the shear modulus (G) of the HEA changes by only 8%, increasing from 80 to 86 GPa. Moreover, this temperature dependence is weaker than that of FCC Ni, whose G increases by 12% (81–91 GPa). Therefore, the uncharacteristic temperature-dependence of the strength of the HEA ismore » not due to the temperature dependence of its shear modulus.« less
Cell model and elastic moduli of disordered solids - Low temperature limit
NASA Technical Reports Server (NTRS)
Peng, S. T. J.; Landel, R. F.; Moacanin, J.; Simha, Robert; Papazoglou, Elisabeth
1987-01-01
The cell theory has been previously employed to compute the equation of state of a disordered condensed system. It is now generalized to include anisotropic stresses. The condition of affine deformation is adopted, transforming an orginally spherical into an ellipsoidal cell. With a Lennard-Jones n-m potential between nonbonded centers, the formal expression for the deformational free energy is derived. It is to be evaluated in the limit of the linear elastic range. Since the bulk modulus in this limit is already known, it is convenient to consider a uniaxial deformation. To begin with, restrictions are made to the low-temperature limit in the absence of entropy contributions. Young's modulus and Poisson's ratio then follow.
Elastic Moduli of Pyrolytic Boron Nitride Measured Using 3-Point Bending and Ultrasonic Testing
NASA Technical Reports Server (NTRS)
Kaforey, M. L.; Deeb, C. W.; Matthiesen, D. H.; Roth, D. J.
1999-01-01
Three-point bending and ultrasonic testing were performed on a flat plate of PBN. In the bending experiment, the deformation mechanism was believed to be shear between the pyrolytic layers, which yielded a shear modulus, c (sub 44), of 2.60 plus or minus .31 GPa. Calculations based on the longitudinal and shear wave velocity measurements yielded values of 0.341 plus or minus 0.006 for Poisson's ratio, 10.34 plus or minus .30 GPa for the elastic modulus (c (sub 33)), and 3.85 plus or minus 0.02 GPa for the shear modulus (c (sub 44)). Since free basal dislocations have been reported to affect the value of c (sub 44) found using ultrasonic methods, the value from the bending experiment was assumed to be the more accurate value.
Pride, Steven R.; Berryman, James G.
2009-01-05
An analysis is presented to show how it is possible for unconsolidated granular packings to obey overall non-Hertzian pressure dependence due to the imperfect and random spatial arrangements of the grains in these packs. With imperfect arrangement, some gaps that remain between grains can be closed by strains applied to the grain packing. As these gaps are closed, former rattler grains become jammed and new stress-bearing contacts are created that increase the elastic stiffness of the packing. By allowing for such a mechanism, detailed analytical expressions are obtained for increases in bulk modulus of a random packing of grains with increasing stress and strain. Only isotropic stress and strain are considered in this analysis. The model is shown to give a favorable fit to laboratory data on variations in bulk modulus due to variations in applied pressure for bead packs.
Thayer, Patrick S; Verbridge, Scott S; Dahlgren, Linda A; Kakar, Sanjeev; Guelcher, Scott A; Goldstein, Aaron S
2016-08-01
Electrospun microfibers are attractive for the engineering of oriented tissues because they present instructive topographic and mechanical cues to cells. However, high-density microfiber networks are too cell-impermeable for most tissue applications. Alternatively, the distribution of sparse microfibers within a three-dimensional hydrogel could present instructive cues to guide cell organization while not inhibiting cell behavior. In this study, thin (∼5 fibers thick) layers of aligned microfibers (0.7 μm) were embedded within collagen hydrogels containing mesenchymal stem cells (MSCs), cultured for up to 14 days, and assayed for expression of ligament markers and imaged for cell organization. These microfibers were generated through the electrospinning of polycaprolactone (PCL), poly(ester-urethane) (PEUR), or a 75/25 PEUR/PCL blend to produce microfiber networks with elastic moduli of 31, 15, and 5.6 MPa, respectively. MSCs in composites containing 5.6 MPa fibers exhibited increased expression of the ligament marker scleraxis and the contractile phenotype marker α-smooth muscle actin versus the stiffer fiber composites. Additionally, cells within the 5.6 MPa microfiber composites were more oriented compared to cells within the 15 and 31 MPa microfiber composites. Together, these data indicate that the mechanical properties of microfiber/collagen composites can be tuned for the engineering of ligament and other target tissues. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1894-1901, 2016.
NASA Astrophysics Data System (ADS)
Taghizadeh, K.; Kumar, N.; Magnanimo, V.; Luding, S.
2015-09-01
Understanding the mechanical stiffness of closely packed, dense granular systems is of interest in many fields, such as soil mechanics, material science and physics. The main difficulty arises due to discreteness and disorder in granular materials at the microscopic scale which requires a multi-scale approach. The Discrete Element Method (DEM) is a powerful tool to inspect the influence of the microscopic contact properties of its individual constituents on the bulk behavior of granular assemblies. In this study, the isotropic deformation mode of polydisperse packings of frictionless and frictional spheres are modeled by using DEM, to investigate the effective stiffness of the granular assembly. At various volume fractions, for every sample, we determine the stress and fabric incremental response that result from the application of strain-probes. As we are interested first in the reversible, elastic response, the amplitude of the applied perturbations has to be small enough to avoid opening and closing of too many contacts, which would lead to irreversible rearrangements in the sample. Counterintuitively, with increasing inter-particle contact friction, the bulk modulus decreases systematically with the coefficient of friction for samples with the same volume fraction. We explain this by the difference in microstructure (isotropic fabric) the samples get when compressed to the same density.
Laplanche, G.; Gadaud, P.; Horst, O.; Otto, F.; Eggeler, G.; George, E.
2014-11-15
The equiatomic CoCrFeMnNi alloy is now regarded as a model face-centered cubic single-phase high-entropy alloy. Consequently, determination of its intrinsic properties such as the temperature dependencies of elastic moduli and thermal expansion coefficient are important to improve understanding of this new class of material. Lastly, these temperature dependencies were measured over a large temperature range (200–1270 K) in this study.
NASA Technical Reports Server (NTRS)
Wolfenden, A.; Lastrapes, G.; Duggan, M. B.; Raj, S. V.
1991-01-01
Young's and shear moduli and damping were measured for as-cast polycrystalline LiF-(22 mol pct)CaF2 eutectic specimens as a function of temperature using the piezoelectric ultrasonic composite oscillator technique. The shear modulus decreased with increasing temperature from about 40 GPa at 295 K to about 30 GPa at 1000 K, while the Young modulus decreased from about 115 GPa at 295 K to about 35 GPa at 900 K. These values are compared with those derived from the rule of mixtures using elastic moduli data for LiF and CaF2 single crystals. It is shown that, while the shear modulus data agree reasonably well with the predicted trend, there is a large discrepancy between the theoretical calculations and the Young modulus values, where this disagreement increases with increasing temperature.
High Elastic Moduli of a 54Al2O3-46Ta2O5 Glass Fabricated via Containerless Processing
NASA Astrophysics Data System (ADS)
Rosales-Sosa, Gustavo A.; Masuno, Atsunobu; Higo, Yuji; Inoue, Hiroyuki; Yanaba, Yutaka; Mizoguchi, Teruyasu; Umada, Takumi; Okamura, Kohei; Kato, Katsuyoshi; Watanabe, Yasuhiro
2015-10-01
Glasses with high elastic moduli have been in demand for many years because the thickness of such glasses can be reduced while maintaining its strength. Moreover, thinner and lighter glasses are desired for the fabrication of windows in buildings and cars, cover glasses for smart-phones and substrates in Thin-Film Transistor (TFT) displays. In this work, we report a 54Al2O3-46Ta2O5 glass fabricated by aerodynamic levitation which possesses one of the highest elastic moduli and hardness for oxide glasses also displaying excellent optical properties. The glass was colorless and transparent in the visible region, and its refractive index nd was as high as 1.94. The measured Young’s modulus and Vickers hardness were 158.3 GPa and 9.1 GPa, respectively, which are comparable to the previously reported highest values for oxide glasses. Analysis made using 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy revealed the presence of a significantly large fraction of high-coordinated Al in addition to four-coordinated Al in the glass. The high elastic modulus and hardness are attributed to both the large cationic field strength of Ta5+ ions and the large dissociation energies per unit volume of Al2O3 and Ta2O5.
High Elastic Moduli of a 54Al2O3-46Ta2O5 Glass Fabricated via Containerless Processing.
Rosales-Sosa, Gustavo A; Masuno, Atsunobu; Higo, Yuji; Inoue, Hiroyuki; Yanaba, Yutaka; Mizoguchi, Teruyasu; Umada, Takumi; Okamura, Kohei; Kato, Katsuyoshi; Watanabe, Yasuhiro
2015-01-01
Glasses with high elastic moduli have been in demand for many years because the thickness of such glasses can be reduced while maintaining its strength. Moreover, thinner and lighter glasses are desired for the fabrication of windows in buildings and cars, cover glasses for smart-phones and substrates in Thin-Film Transistor (TFT) displays. In this work, we report a 54Al2O3-46Ta2O5 glass fabricated by aerodynamic levitation which possesses one of the highest elastic moduli and hardness for oxide glasses also displaying excellent optical properties. The glass was colorless and transparent in the visible region, and its refractive index nd was as high as 1.94. The measured Young's modulus and Vickers hardness were 158.3 GPa and 9.1 GPa, respectively, which are comparable to the previously reported highest values for oxide glasses. Analysis made using (27)Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy revealed the presence of a significantly large fraction of high-coordinated Al in addition to four-coordinated Al in the glass. The high elastic modulus and hardness are attributed to both the large cationic field strength of Ta(5+) ions and the large dissociation energies per unit volume of Al2O3 and Ta2O5. PMID:26468639
High Elastic Moduli of a 54Al2O3-46Ta2O5 Glass Fabricated via Containerless Processing
Rosales-Sosa, Gustavo A.; Masuno, Atsunobu; Higo, Yuji; Inoue, Hiroyuki; Yanaba, Yutaka; Mizoguchi, Teruyasu; Umada, Takumi; Okamura, Kohei; Kato, Katsuyoshi; Watanabe, Yasuhiro
2015-01-01
Glasses with high elastic moduli have been in demand for many years because the thickness of such glasses can be reduced while maintaining its strength. Moreover, thinner and lighter glasses are desired for the fabrication of windows in buildings and cars, cover glasses for smart-phones and substrates in Thin-Film Transistor (TFT) displays. In this work, we report a 54Al2O3-46Ta2O5 glass fabricated by aerodynamic levitation which possesses one of the highest elastic moduli and hardness for oxide glasses also displaying excellent optical properties. The glass was colorless and transparent in the visible region, and its refractive index nd was as high as 1.94. The measured Young’s modulus and Vickers hardness were 158.3 GPa and 9.1 GPa, respectively, which are comparable to the previously reported highest values for oxide glasses. Analysis made using 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy revealed the presence of a significantly large fraction of high-coordinated Al in addition to four-coordinated Al in the glass. The high elastic modulus and hardness are attributed to both the large cationic field strength of Ta5+ ions and the large dissociation energies per unit volume of Al2O3 and Ta2O5. PMID:26468639
Basaruddin, Khairul Salleh; Takano, Naoki; Nakano, Takayoshi
2015-01-01
An assessment of the mechanical properties of trabecular bone is important in determining the fracture risk of human bones. Many uncertainty factors contribute to the dispersion of the estimated mechanical properties of trabecular bone. This study was undertaken in order to propose a computational scheme that will be able to predict the effective apparent elastic moduli of trabecular bone considering the uncertainties that are primarily caused by image-based modelling and trabecular stiffness orientation. The effect of image-based modelling which focused on the connectivity was also investigated. A stochastic multi-scale method using a first-order perturbation-based and asymptotic homogenisation theory was applied to formulate the stochastically apparent elastic properties of trabecular bone. The effective apparent elastic modulus was predicted with the introduction of a coefficient factor to represent the variation of bone characteristics due to inter-individual differences. The mean value of the predicted effective apparent Young's modulus in principal axis was found at approximately 460 MPa for respective 15.24% of bone volume fraction, and this is in good agreement with other experimental results. The proposed method may provide a reference for the reliable evaluation of the prediction of the apparent elastic properties of trabecular bone.
Ni, Jennifer E; Case, Eldon D; Hogan, Timophy P.; Trejo, Rosa M; Lara-Curzio, Edgar; Kanatzidis, Mercouri G.
2013-01-01
Twenty-six (Pb0.95Sn0.05Te)0.92(PbS)0.08 0.055% PbI2 SiC nanoparticle (SiCnp) composite thermoelectric specimens were either hot pressed or pulsed electric current sintered (PECS). Bloating (a thermally induced increase in porosity, P, for as-densified specimens) was observed during annealing at temperatures >603 K for hot-pressed specimens and PECS-processed specimens from wet milled powders, but in contrast seven out of seven specimens densified by PECS from dry milled powders showed no observable bloating following annealing at temperatures up to 936 K. In this study, bloating in the specimens was accessed via thermal annealing induced changes in (i) porosity measured by scanning electron microscopy on fractured specimen surfaces, (ii) specimen volume and (iii) elastic moduli. The moduli were measured by resonant ultrasound spectroscopy. SiCnp additions (1 3.5 vol.%) changed the fracture mode from intergranular to transgranular, inhibited grain growth, and limited bloating in the wet milled PECS specimens. Inhibition of bloating likely occurs due to cleaning of contamination from powder particle surfaces via PECS processing which has been reported previously in the literature.
Hamed, E; Novitskaya, E; Li, J; Chen, P-Y; Jasiuk, I; McKittrick, J
2012-03-01
A theoretical experimentally based multi-scale model of the elastic response of cortical bone is presented. It portrays the hierarchical structure of bone as a composite with interpenetrating biopolymers (collagen and non-collagenous proteins) and minerals (hydroxyapatite), together with void spaces (porosity). The model involves a bottom-up approach and employs micromechanics and classical lamination theories of composite materials. Experiments on cortical bone samples from bovine femur include completely demineralized and deproteinized bones as well as untreated bone samples. Porosity and microstructure are characterized using optical and scanning electron microscopy, and micro-computed tomography. Compression testing is used to measure longitudinal and transverse elastic moduli of all three bone types. The characterization of structure and properties of these three bone states provides a deeper understanding of the contributions of the individual components of bone to its elastic response and allows fine tuning of modeling assumptions. Very good agreement is found between theoretical modeling and compression testing results, confirming the validity of the interpretation of bone as an interpenetrating composite material.
Thompson, T.W.; Kelkar, S.M.; Gray, K.E.
1983-02-01
The behavior of Berea sandstone and Leuders limestone under atmospheric and elevated pore pressures is reported. The porosity and the permeability changes, along with the static and dynamic moduli for these rocks have been determined under various conditions. The existing theoretical background pertinent to the study is reviewed along with the previous experimental work. The detailed descriptions and the discussions on the experimental procedure involved and the equipment utilized are presented. A discussion on the sources of experimental errors is included. It also includes the error propagation equations and relevant discussions on the data acquisition and analysis. The findings are summarized together with a discussion of the results. The conclusions drawn from these results are included. The bulk of the data acquired and the results computed from it are presented.
Migliori, Albert; Söderlind, Per; Landa, Alexander; Freibert, Franz J.; Maiorov, Boris; Ramshaw, B. J.; Betts, Jon B.
2016-01-01
The electronic and thermodynamic complexity of plutonium has resisted a fundamental understanding for this important elemental metal. A critical test of any theory is the unusual softening of the bulk modulus with increasing temperature, a result that is counterintuitive because no or very little change in the atomic volume is observed upon heating. This unexpected behavior has in the past been attributed to competing but never-observed electronic states with different bonding properties similar to the scenario with magnetic states in Invar alloys. Using the recent observation of plutonium dynamic magnetism, we construct a theory for plutonium that agrees with relevant measurements by using density-functional-theory (DFT) calculations with no free parameters to compute the effect of longitudinal spin fluctuations on the temperature dependence of the bulk moduli in δ-Pu. We show that the softening with temperature can be understood in terms of a continuous distribution of thermally activated spin fluctuations. PMID:27647904
NASA Astrophysics Data System (ADS)
Samani, Abbas; Zubovits, Judit; Plewes, Donald
2007-03-01
Understanding and quantifying the mechanical properties of breast tissues has been a subject of interest for the past two decades. This has been motivated in part by interest in modelling soft tissue response for surgery planning and virtual-reality-based surgical training. Interpreting elastography images for diagnostic purposes also requires a sound understanding of normal and pathological tissue mechanical properties. Reliable data on tissue elastic properties are very limited and those which are available tend to be inconsistent, in part as a result of measurement methodology. We have developed specialized techniques to measure tissue elasticity of breast normal tissues and tumour specimens and applied them to 169 fresh ex vivo breast tissue samples including fat and fibroglandular tissue as well as a range of benign and malignant breast tumour types. Results show that, under small deformation conditions, the elastic modulus of normal breast fat and fibroglandular tissues are similar while fibroadenomas were approximately twice the stiffness. Fibrocystic disease and malignant tumours exhibited a 3-6-fold increased stiffness with high-grade invasive ductal carcinoma exhibiting up to a 13-fold increase in stiffness compared to fibrogalndular tissue. A statistical analysis showed that differences between the elastic modulus of the majority of those tissues were statistically significant. Implications for the specificity advantages of elastography are reviewed.
NASA Astrophysics Data System (ADS)
Fan, D.; Mao, Z.; Lin, J.; Yang, J.
2013-12-01
Brillouin light scattering (BLS) is the inelastic scattering of monochromatic laser light by phonons in the GHz frequency range [1]. BLS spectroscopy can be used to measure sound velocities traveling along certain directions of a single crystal through the frequency shifts of the scattered light from the acoustic phonons [1]. Over the past few decades, BLS spectroscopy has been widely used to measure the velocities of acoustic waves for a wide range of Earth's materials, in which the full elastic constants were derived from the measured compressional (VP) and shear wave (VS) velocities. However, the VP velocities of minerals normally overlap with the shear-wave velocities of diamonds in Brillouin measurements approximately above 25 GPa [2-5] such that only VS of minerals can be measured experimentally. Theoretical models have showed that the shear-wave velocities of minerals also carry necessary information to invert the full elastic tensors [2], although previous studies at high pressures have focused on measuring velocities within the principle planes of the crystals. This leads to a strong trade-off among individual Cij, preventing the derivation of the full elastic tensors from the VS velocities alone [3-5]. In this study, we have come up with an elastic model to overcome this problem by finding a suitable crystallographic plane that has optimized VS-VP interactions in the elastic tensors. Using MgO, spinel and zoisite as test samples, we have used measured VP/VS or VS velocities of these crystals using BLS spectroscopy to derive their full elastic tensors. This new approach sheds lights on future high-pressure elasticity studies relevant to materials the Earth's deep interior. 1. Sinogeikin, S.V., Bass, J.D., Phys. Earth Planet. Inter., 120, 43 (2000). 2. Every, A. G., Phys. Rev. B., 22, 1746, (1980) 3. Marquardt, H., Speziale, S., Reichmann, H.J., Frost, D.J., and Schilling, F.R., Earth Planet. Sci. Lett., 287, 345 (2009). 4. Marquardt, H., Speziale, S
Moreno-Flores, Susana; Benitez, Rafael; Vivanco, María dM; Toca-Herrera, José Luis
2010-11-01
In this work we present a unified method to study the mechanical properties of cells using the atomic force microscope. Stress relaxation and creep compliance measurements permitted us to determine, the relaxation times, the Young moduli and the viscosity of breast cancer cells (MCF-7). The results show that the mechanical behaviour of MCF-7 cells responds to a two-layered model of similar elasticity but differing viscosity. Treatment of MCF-7 cells with an actin-depolymerising agent results in an overall decrease in both cell elasticity and viscosity, however to a different extent for each layer. The layer that undergoes the smaller decrease (36-38%) is assigned to the cell membrane/cortex while the layer that experiences the larger decrease (70-80%) is attributed to the cell cytoplasm. The combination of the method presented in this work, together with the approach based on stress relaxation microscopy (Moreno-Flores et al 2010 J. Biomech. 43 349-54), constitutes a unique AFM-based experimental framework to study cell mechanics. This methodology can also be extended to study the mechanical properties of biomaterials in general.
Helgerud, M.B.; Waite, W.F.; Kirby, S.H.; Nur, A.
2009-01-01
We used ultrasonic pulse transmission to measure compressional, P, and shear, S, wave speeds in laboratory-formed polycrystalline ice Ih, si methane hydrate, and sll methane-ethane hydrate. From the wave speed's linear dependence on temperature and pressure and from the sample's calculated density, we derived expressions for bulk, shear, and compressional wave moduli and Poisson's ratio from -20 to 15??C and 22.4 to 32.8 MPa for ice Ih, -20 to 15??C and 30.5 to 97.7 MPa for si methane hydrate, and -20 to 10??C and 30.5 to 91.6 MPa for sll methane-ethane hydrate. All three materials had comparable P and S wave speeds and decreasing shear wave speeds with increasing applied pressure. Each material also showed evidence of rapid intergranular bonding, with a corresponding increase in wave speed, in response to pauses in sample deformation. There were also key differences. Resistance to uniaxial compaction, indicated by the pressure required to compact initially porous samples, was significantly lower for ice Ih than for either hydrate. The ice Ih shear modulus decreased with increasing pressure, in contrast to the increase measured in both hydrates ?? 2009.
NASA Astrophysics Data System (ADS)
Guillot, François M.; Trivett, D. H.
2011-07-01
Two independent systems to measure the dynamic complex Young's and bulk moduli of viscoelastic materials as a function of temperature and hydrostatic pressure are described. In the Young's modulus system, a bar-shaped sample is adhered to a piezoelectric shaker and mounted vertically inside an air-filled pressure vessel. Data are obtained using both the traditional resonant approach and a wave-speed technique. In the bulk modulus system, the compressibility of a sample of arbitrary shape immersed in Castor oil and placed inside a pressure chamber is measured. Data can be obtained at frequencies typically ranging from 50 Hz to 5 kHz, at temperatures comprised between -2 and 50 °C and under hydrostatic pressures ranging from 0 to 2 MPa (Young's), or 6.5 MPa (bulk). Typical data obtained with both systems are presented, and it is shown how these data can be combined to completely characterize the elasticity of the material under investigation. In particular, they can be used to obtain experimental values of the complex Poisson's ratio, whose accurate measurement is otherwise quite challenging to perform directly. As an example, the magnitude and loss tangent of Poisson's ratio are presented for a nearly incompressible rubber.
Holten-Andersen, Niels; Harrington, Matthew J.; Birkedal, Henrik; Lee, Bruce P.; Messersmith, Phillip B.; Lee, Ka Yee C.; Waite, J. Herbert
2011-01-01
Growing evidence supports a critical role of metal-ligand coordination in many attributes of biological materials including adhesion, self-assembly, toughness, and hardness without mineralization [Rubin DJ, Miserez A, Waite JH (2010) Advances in Insect Physiology: Insect Integument and Color, eds Jérôme C, Stephen JS (Academic Press, London), pp 75–133]. Coordination between Fe and catechol ligands has recently been correlated to the hardness and high extensibility of the cuticle of mussel byssal threads and proposed to endow self-healing properties [Harrington MJ, Masic A, Holten-Andersen N, Waite JH, Fratzl P (2010) Science 328:216–220]. Inspired by the pH jump experienced by proteins during maturation of a mussel byssus secretion, we have developed a simple method to control catechol-Fe3+ interpolymer cross-linking via pH. The resonance Raman signature of catechol-Fe3+ cross-linked polymer gels at high pH was similar to that from native mussel thread cuticle and the gels displayed elastic moduli (G′) that approach covalently cross-linked gels as well as self-healing properties. PMID:21278337
A Note on Aggregate Price-Level Elasticity and Supply-Side Shocks.
ERIC Educational Resources Information Center
Findlay, David W.
1995-01-01
Investigates factors that influence the short-run and long-run effects of supply-side shocks on aggregate income and tax revenues. Concludes that the long-run relationship between tax revenues and the tax rate is completely independent of price-level elasticity. (CFR)
Touchette, Brant W; Marcus, Sarah E; Adams, Emily C
2014-03-28
Bulk modulus of elasticity (ɛ), depicting the flexibility of plant tissues, is recognized as an important component in maintaining internal water balance. Elevated ɛ and comparatively low osmotic potential (Ψπ) may work in concert to effectively maintain vital cellular water content. This concept, termed the 'cell water conservation hypothesis', may foster tolerance for lower soil-water potentials in plants while minimizing cell dehydration and shrinkage. Therefore, the accumulation of solutes in marine plants, causing decreases in Ψπ, play an important role in plant-water relations and likely works with higher ɛ to achieve favourable cell volumes. While it is generally held that plants residing in marine systems have higher leaf tissue ɛ, to our knowledge no study has specifically addressed this notion in aquatic and wetland plants residing in marine and freshwater systems. Therefore, we compared ɛ and Ψπ in leaf tissues of 38 freshwater, coastal and marine plant species using data collected in our laboratory, with additional values from the literature. Overall, 8 of the 10 highest ɛ values were observed in marine plants, and 20 of the lowest 25 ɛ values were recorded in freshwater plants. As expected, marine plants often had lower Ψπ, wherein the majority of marine plants were below -1.0 MPa and the majority of freshwater plants were above -1.0 MPa. While there were no differences among habitat type and symplastic water content (θsym), we did observe higher θsym in shrubs when compared with graminoids, and believe that the comparatively low θsym observed in aquatic grasses may be attributed to their tendency to develop aerenchyma that hold apoplastic water. These results, with few exceptions, support the premise that leaf tissues of plants acclimated to marine environments tend to have higher ɛ and lower Ψπ, and agree with the general tenets of the cell water conservation hypothesis.
Xia, J.; Xu, Y.; Miller, R.D.; Chen, C.
2006-01-01
A Gibson half-space model (a non-layered Earth model) has the shear modulus varying linearly with depth in an inhomogeneous elastic half-space. In a half-space of sedimentary granular soil under a geostatic state of initial stress, the density and the Poisson's ratio do not vary considerably with depth. In such an Earth body, the dynamic shear modulus is the parameter that mainly affects the dispersion of propagating waves. We have estimated shear-wave velocities in the compressible Gibson half-space by inverting Rayleigh-wave phase velocities. An analytical dispersion law of Rayleigh-type waves in a compressible Gibson half-space is given in an algebraic form, which makes our inversion process extremely simple and fast. The convergence of the weighted damping solution is guaranteed through selection of the damping factor using the Levenberg-Marquardt method. Calculation efficiency is achieved by reconstructing a weighted damping solution using singular value decomposition techniques. The main advantage of this algorithm is that only three parameters define the compressible Gibson half-space model. Theoretically, to determine the model by the inversion, only three Rayleigh-wave phase velocities at different frequencies are required. This is useful in practice where Rayleigh-wave energy is only developed in a limited frequency range or at certain frequencies as data acquired at manmade structures such as dams and levees. Two real examples are presented and verified by borehole S-wave velocity measurements. The results of these real examples are also compared with the results of the layered-Earth model. ?? Springer 2006.
Touchette, Brant W.; Marcus, Sarah E.; Adams, Emily C.
2014-01-01
Bulk modulus of elasticity (ɛ), depicting the flexibility of plant tissues, is recognized as an important component in maintaining internal water balance. Elevated ɛ and comparatively low osmotic potential (Ψπ) may work in concert to effectively maintain vital cellular water content. This concept, termed the ‘cell water conservation hypothesis’, may foster tolerance for lower soil-water potentials in plants while minimizing cell dehydration and shrinkage. Therefore, the accumulation of solutes in marine plants, causing decreases in Ψπ, play an important role in plant–water relations and likely works with higher ɛ to achieve favourable cell volumes. While it is generally held that plants residing in marine systems have higher leaf tissue ɛ, to our knowledge no study has specifically addressed this notion in aquatic and wetland plants residing in marine and freshwater systems. Therefore, we compared ɛ and Ψπ in leaf tissues of 38 freshwater, coastal and marine plant species using data collected in our laboratory, with additional values from the literature. Overall, 8 of the 10 highest ɛ values were observed in marine plants, and 20 of the lowest 25 ɛ values were recorded in freshwater plants. As expected, marine plants often had lower Ψπ, wherein the majority of marine plants were below −1.0 MPa and the majority of freshwater plants were above −1.0 MPa. While there were no differences among habitat type and symplastic water content (θsym), we did observe higher θsym in shrubs when compared with graminoids, and believe that the comparatively low θsym observed in aquatic grasses may be attributed to their tendency to develop aerenchyma that hold apoplastic water. These results, with few exceptions, support the premise that leaf tissues of plants acclimated to marine environments tend to have higher ɛ and lower Ψπ, and agree with the general tenets of the cell water conservation hypothesis. PMID:24876296
Page, L.; Heard, H.C.
1981-03-17
Young's modulus (E), bulk modulus (K), and the coefficient of thermal linear expansion (..cap alpha..) have been determined for Climax quartz monzonite to 500/sup 0/C and pressures (P) to 55 MPa and for Sudbury gabbro to 300/sup 0/C and 55 MPa. For each rock, both E and K decreased with T and increased with P in a nonlinear manner. In the monzonite, E and K decreased by up to 60% as P decreased from 55.2 to 6.9 MPa isothermally, while the gabbro indicated a decrease up to 70% over the same pressure range. As T increased isobarically, E and K for the monzonite decreased by up to a factor of approx. 80% from 19 to 500/sup 0/C. The moduli of the gabbro decreased by as much as 70% from 19 to 300/sup 0/C. ..cap alpha.. for the monzonite increased with T and decreased with P in a nonmonotonic fashion, with most measured values for ..cap alpha.. greater than values calculated for the crack-free aggregate. Depending on P, ..cap alpha.. in the monzonite increased from 8 to 11.10/sup -6/ /sup 0/C/sup -1/ at 40/sup 0/C to 22 to 25.10/sup -6/C/sup -1/ at 475/sup 0/C. For the gabbro, ..cap alpha.. also generally decreased with increasing P. Values ranged from 6 to 11.10/sup -6/ /sup 0/C/sup -1/, showing a nonlinear trend and very little net increas over the T range from 19 to 300/sup 0/C. Calculated permeability of these rocks based on the ..cap alpha.. determinations indicated that permeabilities may increase by up to a factor of 3 over the temperature interval 19 to 300/sup 0/C, and the permeability of the monzonite is inferred to increase by up to a factor of 8 by 500/sup 0/C. In both rocks, most measurements are consistent with microcracks controlling the thermoelastic response by opening with T and closing with sigma and P.
ERIC Educational Resources Information Center
Kyer, Ben L.; Maggs, Gary E.
1995-01-01
Utilizes two-dimensional price and output graphs to demonstrate the way that the price-level elasticity of aggregate demand affects alternative monetary policy rules designed to cope with random aggregate supply shocks. Includes graphs illustrating price-level, real Gross Domestic Product (GDP), nominal GDP, and nominal money supply targeting.…
Mechanics of fire ant aggregations
NASA Astrophysics Data System (ADS)
Tennenbaum, Michael; Liu, Zhongyang; Hu, David; Fernandez-Nieves, Alberto
2016-01-01
Fire ants link their bodies to form aggregations; these can adopt a variety of structures, they can drip and spread, or withstand applied loads. Here, by using oscillatory rheology, we show that fire ant aggregations are viscoelastic. We find that, at the lowest ant densities probed and in the linear regime, the elastic and viscous moduli are essentially identical over the spanned frequency range, which highlights the absence of a dominant mode of structural relaxation. As ant density increases, the elastic modulus rises, which we interpret by alluding to ant crowding and subsequent jamming. When deformed beyond the linear regime, the aggregation flows, exhibiting shear-thinning behaviour with a stress load that is comparable to the maximum load the aggregation can withstand before individual ants are torn apart. Our findings illustrate the rich, collective mechanical behaviour that can arise in aggregations of active, interacting building blocks.
Mechanics of fire ant aggregations.
Tennenbaum, Michael; Liu, Zhongyang; Hu, David; Fernandez-Nieves, Alberto
2016-01-01
Fire ants link their bodies to form aggregations; these can adopt a variety of structures, they can drip and spread, or withstand applied loads. Here, by using oscillatory rheology, we show that fire ant aggregations are viscoelastic. We find that, at the lowest ant densities probed and in the linear regime, the elastic and viscous moduli are essentially identical over the spanned frequency range, which highlights the absence of a dominant mode of structural relaxation. As ant density increases, the elastic modulus rises, which we interpret by alluding to ant crowding and subsequent jamming. When deformed beyond the linear regime, the aggregation flows, exhibiting shear-thinning behaviour with a stress load that is comparable to the maximum load the aggregation can withstand before individual ants are torn apart. Our findings illustrate the rich, collective mechanical behaviour that can arise in aggregations of active, interacting building blocks. PMID:26501413
Peselnick, L.; Meister, R.
1965-01-01
Variational principles of anisotropic elasticity have been applied to aggregates of randomly oriented pure-phase polycrystals having hexagonal symmetry and trigonal symmetry. The bounds of the effective elastic moduli obtained in this way show a considerable improvement over the bounds obtained by means of the Voigt and Reuss assumptions. The Hill average is found to be in most cases a good approximation when compared to the bounds found from the variational method. The new bounds reduce in their limits to the Voigt and Reuss values. ?? 1965 The American Institute of Physics.
NASA Astrophysics Data System (ADS)
Zerr, Andreas; Chigarev, Nikolay; Bourguille, Judith; Tetard, Florent; Brinza, Ovidiu; Nikitin, Sergey; Lomonosov, Alexey; Gusev, Vitalyi
2013-06-01
Bulk and shear moduli (B0 and G0) of the dense polycrystalline oxygen bearing c-Zr3N4 and η-Ta2N3 were determined from the laser ultrasonic (LU) measurements on highly porous samples having the volume fraction porosity of 0.23 and 0.18, respectively. Dense samples of these high-pressure (HP) materials are today not available due to their very high hardness and absence of a densification procedure. Combining the LU data with a numerical analysis of the sample porosity, the ``true'' isotropic moduli were determined to be B0 = 217(20) GPa and G0 = 163(9) GPa, for c-Zr3N4, and B0 = 281(15) GPa and G0 = 123(2) GPa, for η-Ta2N3. For both HP-nitrides the B0 values agree with those obtained earlier via the HP compression measurements in a diamond anvil cell. Also, the self-healing behavior of η-Ta2N3 by mechanical polishing was confirmed by two independent methods. Finally, the results obtained for η-Ta2N3 via the LU method were compared with our nanoindentation measurements. The high G0 value of c-Zr3N4 suggests that this material could vie with γ-Si3N4 for the rank of the third hardest material after diamond and c-BN. Supported by the Agence Nationale de la Recherche (France).
Variational method of determining effective moduli of polycrystals with tetragonal symmetry
Meister, R.; Peselnick, L.
1966-01-01
Variational principles have been applied to aggregates of randomly oriented pure-phase polycrystals having tetragonal symmetry. The bounds of the effective elastic moduli obtained in this way show a substantial improvement over the bounds obtained by means of the Voigt and Reuss assumptions. The Hill average is found to be a good approximation in most cases when compared to the bounds found from the variational method. The new bounds reduce in their limits to the Voigt and Reuss values. ?? 1966 The American Institute of Physics.
Structure and elastic properties of boron suboxide at 240 GPa
NASA Astrophysics Data System (ADS)
Lu, Y. P.; He, D. W.
2009-04-01
Structure and elastic properties of boron suboxide at high pressure have been investigated using generalized gradient approximation within the plane-wave pseudopotential density functional theory. The elastic constants are calculated using the finite strain method. The pressure dependences of lattice parameters, elastic constants, aggregate elastic moduli, and sound velocities of boron suboxide are predicted. It is found that the most stable structure of hcp boron suboxide at zero pressure corresponds to the ratio c /a of about 2.274 and the equilibrium lattice parameters a0 and c0 are about 5.331 and 12.124 Å, respectively. The high-pressure elastic constants indicate that boron suboxide is mechanically stable up to 368 GPa. The pressure dependence of the calculated normalized volume and the aggregate elastic moduli agree well with the recent experimental results. The sound velocities along different directions for the structure of boron suboxide are obtained. It shows that the velocities of the shear wave decrease as pressure increases but those of all the longitudinal waves increase with pressure. Moreover, the azimuthal anisotropy of the compression and shear aggregate wave velocities for different pressures are predicted. They change behavior with increasing pressure around 87 GPa because of an electronic topological transition. A refined analysis has been made to reveal the high pressure elastic anisotropy in boron suboxide.
El-Hachemi, Zoubir; Balaban, Teodor Silviu; Campos, J Lourdes; Cespedes, Sergio; Crusats, Joaquim; Escudero, Carlos; Kamma-Lorger, Christina S; Llorens, Joan; Malfois, Marc; Mitchell, Geoffrey R; Tojeira, Ana P; Ribó, Josep M
2016-07-01
The J aggregates of 4-sulfonatophenyl meso-substituted porphyrins are non-covalent polymers obtained by self-assembly that form nanoparticles of different morphologies. In the case of high aspect-ratio nanoparticles (bilayered ribbons and monolayered nanotubes), shear hydrodynamic forces may modify their shape and size, as observed by peak force microscopy, transmission electron microscopy of frozen solutions, small-angle X-ray scattering measurements in a disk-plate rotational cell, and cone-plate rotational viscometry. These nanoparticles either show elastic or plastic behaviour: there is plasticity in the ribbons obtained upon nanotube collapse on solid/air interfaces and in viscous concentrated nanotube solutions, whereas elasticity occurs in the case of dilute nanotube solutions. Sonication and strong shear hydrodynamic forces lead to the breaking of the monolayered nanotubes into small particles, which then associate into large colloidal particles. PMID:27238461
NASA Astrophysics Data System (ADS)
Braun, Christopher
2012-09-01
This thesis is concerned with the application of operadic methods, particularly modular operads, to questions arising in the study of moduli spaces of surfaces as well as applications to the study of homotopy algebras and new constructions of 'quantum invariants' of manifolds inspired by ideas originating from physics. We consider the extension of classical 2-dimensional topological quantum field theories to Klein topological quantum field theories which allow unorientable surfaces. We generalise open topological conformal field theories to open Klein topological conformal field theories and consider various related moduli spaces, in particular deducing a Mobius graph decomposition of the moduli spaces of Klein surfaces, analogous to the ribbon graph decomposition of the moduli spaces of Riemann surfaces. We also begin a study, in generality, of quantum homotopy algebras, which arise as 'higher genus' versions of classical homotopy algebras. In particular we study the problem of quantum lifting. We consider applications to understanding invariants of manifolds arising in the quantisation of Chern-Simons field theory.
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.
Johnston, A.M.
2000-10-09
The moduli used in RSA (see [5]) can be generated by many different sources. The generator of that modulus (assuming a single entity generates the modulus) knows its factorization. They would have the ability to forge signatures or break any system based on this moduli. If a moduli and the RSA parameters associated with it were generated by a reputable source, the system would have higher value than if the parameters were generated by an unknown entity. So for tracking, security, confidence and financial reasons it would be beneficial to know who the generator of the RSA modulus was. This is where digital marking comes in. An RSA modulus ia digitally marked, or digitally trade marked, if the generator and other identifying features of the modulus (such as its intended user, the version number, etc.) can be identified and possibly verified by the modulus itself. The basic concept of digitally marking an RSA modulus would be to fix the upper bits of the modulus to this tag. Thus anyone who sees the public modulus can tell who generated the modulus and who the generator believes the intended user/owner of the modulus is.
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.
Nonlinear elastic properties of particulate composites
NASA Astrophysics Data System (ADS)
Chen, Yi-Chao; Jiang, Xiaohu
1993-07-01
A METHOD of computing effective elastic moduli of isotropic nonlinear composites is developed by using a perturbation scheme. It is demonstrated that only solutions from linear elasticity are needed in computing higher order moduli. As an application of the method, particulate composites of nonlinear elastic materials are analysed.
Investigation of metal and ceramic-matrix composites moduli: Experiment and theory
Liaw, P.K.; Miriyala, N.; Yu, N.; Hsu, D.K.; Saini, V.; Jeong, H.
1996-05-01
The elastic behavior of metal and ceramic-matrix composites were characterized by ultrasonic techniques. While an immersion ultrasonic technique was used to measure the stiffness moduli of silicon carbide (SiC) particulate reinforced aluminium metal-matrix composites, a dry-coupling method was used to determine the elastic constants of woven Nicalon{trademark} fiber reinforced SiC ceramic-matrix composites. A unified micromechanics model was developed to predict the elastic moduli of these composites from the knowledge of their constituent elastic constants. The model quantitatively predicted the effects of microstructural characteristics, such as the reinforcement content and porosity in the material, on the elastic moduli of the composite systems studied. The predicted moduli were in good agreement with the experimental results for both the particulate reinforced metal-matrix composites and woven fiber reinforced ceramic-matrix composites.
Static and Dynamic Moduli of Malm Carbonate: A Poroelastic Correlation
NASA Astrophysics Data System (ADS)
Hassanzadegan, Alireza; Guérizec, Romain; Reinsch, Thomas; Blöcher, Guido; Zimmermann, Günter; Milsch, Harald
2016-08-01
The static and poroelastic moduli of a porous rock, e.g., the drained bulk modulus, can be derived from stress-strain curves in rock mechanical tests, and the dynamic moduli, e.g., dynamic Poisson's ratio, can be determined by acoustic velocity and bulk density measurements. As static and dynamic elastic moduli are different, a correlation is often required to populate geomechanical models. A novel poroelastic approach is introduced to correlate static and dynamic bulk moduli of outcrop analogues samples, representative of Upper-Malm reservoir rock in the Molasse basin, southwestern Germany. Drained and unjacketed poroelastic experiments were performed at two different temperature levels (30 and 60°C). For correlating the static and dynamic elastic moduli, a drained acoustic velocity ratio is introduced, corresponding to the drained Poisson's ratio in poroelasticity. The strength of poroelastic coupling, i.e., the product of Biot and Skempton coefficients here, was the key parameter. The value of this parameter decreased with increasing effective pressure by about 56 ~% from 0.51 at 3 MPa to 0.22 at 73 MPa. In contrast, the maximum change in P- and S-wave velocities was only 3 % in this pressure range. This correlation approach can be used in characterizing underground reservoirs, and can be employed to relate seismicity and geomechanics (seismo-mechanics).
Improved Indentation Test for Measuring Nonlinear Elasticity
NASA Technical Reports Server (NTRS)
Eldridge, Jeffrey I.
2004-01-01
A cylindrical-punch indentation technique has been developed as a means of measuring the nonlinear elastic responses of materials -- more specifically, for measuring the moduli of elasticity of materials in cases in which these moduli vary with applied loads. This technique offers no advantage for characterizing materials that exhibit purely linear elastic responses (constant moduli of elasticity, independent of applied loads). However, the technique offers a significant advantage for characterizing such important materials as plasma-sprayed thermal-barrier coatings, which, in cyclic loading, exhibit nonlinear elasticity with hysteresis related to compaction and sliding within their microstructures.
Quiver structure of heterotic moduli
NASA Astrophysics Data System (ADS)
He, Yang-Hui; Lee, Seung-Joo
2012-11-01
We analyse the vector bundle moduli arising from generic heterotic compactifications from the point of view of quiver representations. Phenomena such as stability walls, crossing between chambers of supersymmetry, splitting of non-Abelian bundles and dynamic generation of D-terms are succinctly encoded into finite quivers. By studying the Poincaré polynomial of the quiver moduli space using the Reineke formula, we can learn about such useful concepts as Donaldson-Thomas invariants, instanton transitions and supersymmetry breaking.
NASA Astrophysics Data System (ADS)
Holec, D.; Tasnádi, F.; Wagner, P.; Friák, M.; Neugebauer, J.; Mayrhofer, P. H.; Keckes, J.
2014-11-01
Despite the fast development of computational material modeling, the theoretical description of macroscopic elastic properties of textured polycrystalline aggregates starting from basic principles remains a challenging task. In this study we use a supercell-based approach to obtain the elastic properties of a random solid solution cubic Zr1 -xAlxN system as a function of the metallic sublattice composition and texture descriptors. The employed special quasirandom structures are optimized not only with respect to short-range-order parameters, but also to make the three cubic directions [1 0 0 ] , [0 1 0 ] , and [0 0 1 ] as similar as possible. In this way, only a small spread of elastic constant tensor components is achieved and an optimum trade-off between modeling of chemical disorder and computational limits regarding the supercell size and calculational time is proposed. The single-crystal elastic constants are shown to vary smoothly with composition, yielding x ≈0.5 an alloy constitution with an almost isotropic response. Consequently, polycrystals with this composition are suggested to have Young's modulus independent of the actual microstructure. This is indeed confirmed by explicit calculations of polycrystal elastic properties, both within the isotropic aggregate limit and with fiber textures with various orientations and sharpness. It turns out that for low AlN mole fractions, the spread of the possible Young's modulus data caused by the texture variation can be larger than 100 GPa. Consequently, our discussion of Young's modulus data of cubic Zr1 -xAlxN contains also the evaluation of the texture typical for thin films.
On a new compactification of moduli of vector bundles on a surface. IV: Nonreduced moduli
Timofeeva, Nadezda V
2013-01-31
The construction of a nonreduced projective moduli scheme of semistable admissible pairs is performed. We establish the connection of this moduli scheme with the reduced moduli scheme constructed in the previous article and prove that the nonreduced moduli scheme contains an open subscheme which is isomorphic to a moduli scheme of semistable vector bundles. Bibliography: 10 titles.
Moduli mediation without moduli-induced gravitino problem
NASA Astrophysics Data System (ADS)
Akita, Kensuke; Kobayashi, Tatsuo; Oikawa, Akane; Otsuka, Hajime
2016-05-01
We study the moduli-induced gravitino problem within the framework of the phenomenologically attractive mirage mediations. The huge amount of gravitino generated by the moduli decay can be successfully diluted by introducing an extra light modulus field which does not induce the supersymmetry breaking. Since the lifetime of extra modulus field becomes longer than usually considered modulus field, our proposed mechanism is applied to both the low- and high-scale supersymmetry breaking scenarios. We also point out that such an extra modulus field appears in the flux compactification of type II string theory.
High-pressure elastic properties of cubic Ir2P from ab initio calculations
NASA Astrophysics Data System (ADS)
Sun, Xiao-Wei; Bioud, Nadhira; Fu, Zhi-Jian; Wei, Xiao-Ping; Song, Ting; Li, Zheng-Wei
2016-10-01
A study of the high-pressure elastic properties of new synthetic Ir2P in the anti-fluorite structure is conducted using ab initio calculations based on density functional theory. The elastic constants C11, C12 and C44 for the cubic Ir2P are obtained by the stress-strain method and the elastic stability calculations under pressure indicate that it is stable at least 100 GPa. Additionally, the electronic density of states, the aggregate elastic moduli, that is bulk modulus, shear modulus, and Young's modulus along with the Debye temperature, Poisson's ratio, and elastic anisotropy factor are all successfully obtained. Moreover, the pressure dependence of the longitudinal and shear wave velocities in three different directions [100], [110], and [111] for Ir2P are also predicted for the first time.
Zhang, Tongfeng; Thomson, Murray J
2016-02-01
An improved data analysis approach has been developed for the combined laser extinction and two-angle elastic light scattering diagnostics to relate the various measured optical cross sections to soot aggregate properties. The performance of the proposed approach is assessed using the comprehensive dataset of Santoro ethylene-air co-flow diffusion flame. Compared to previously reported studies, the proposed approach can be applied to a wider range of soot sources by removing the assumption made to the scattering regime or moment ratio of aggregate size distribution. The proposed approach also considers the contribution of scattering to extinction in determining the soot volume fraction, and this contribution is shown to increase as soot aggregate size becomes larger. The sensitivity of the calculation to the assumed parameters of the approach is examined and discussed. The mean radius of gyration of soot aggregates and the ratio of scattering intensities at the two measurement angles are shown to be independent of soot refractive index and are therefore recommended for soot model validation purposes. PMID:26836101
Stabilization of moduli by fluxes
Behrndt, Klaus
2004-12-10
In order to fix the moduli, non-trivial fluxes might the essential input. We summarize different aspects of compactifications in the presence of fluxes, as there is the relation to generalized Scherk-Schwarz reductions and gauged supergravity but also the description of flux-deformed geometries in terms of G-structures and intrinsic torsion.
Simple torsion test for shear moduli determination of orthotropic composites
NASA Technical Reports Server (NTRS)
Sumsion, H. T.; Rajapakse, Y. D. S.
1978-01-01
By means of torsion tests performed on test specimens of the same material having a minimum of two different cross sections (flat sheet of different widths), the effective in-plane (G13) and out-of-plane (G23) shear moduli were determined for two composite materials of uniaxial and angleply fiber orientations. Test specimens were 16 plies (nominal 2 mm) thick, 100 mm in length, and in widths of 6.3, 9.5, 12.5, and 15.8 mm. Torsion tests were run under controlled deflection (constant angle of twist) using an electrohydraulic servocontrolled test system. In-plane and out-of-plane shear moduli were calculated from an equation derived in the theory of elasticity which relates applied torque, the torsional angle of twist, the specimen width/thickness ratio, and the ratio of the two shear moduli G13/G23. Results demonstrate that torsional shear moduli, G23 as well as G13, can be determined by simple torsion tests of flat specimens of rectangular cross section. Neither the uniaxial nor angleply composite material were transversely isotropic.
Readily fiberizable glasses having a high modulus of elasticity
NASA Technical Reports Server (NTRS)
Bacon, J. F.
1970-01-01
New glass compositions yield composites having higher moduli of elasticity and specific moduli of elasticity than commercially available glasses. Over a reasonable temperature range the glasses have a viscosity of about 20,000 poises. They consist of silica, alumina, magnesia, and beryllia, plus at least one uncommon oxide.
Elastic module of superhard rhenium diboride
Koehler, Michael R.; Keppens, Veerle; Sales, Brian C; Jin, Rongying; Mandrus, David
2009-01-01
The elastic moduli of polycrystalline rhenium diboride are measured as a function of temperature between 5 and 325 K. The room temperature results show that ReB{sub 2} has very high values for both the bulk and shear modulus, confirming the incompressible and superhard nature of this material. With decreasing temperature, the moduli increase, with a hint of softening below 50 K.
Variational bounds on the effective moduli of anisotropic composites
NASA Astrophysics Data System (ADS)
Milton, Graeme W.; Kohn, Robert V.
THE VRITIONAL inequalities of Hashin and Shtrikman are transformed to a simple and concise form. They are used to bound the effective conductivity tensor σ∗ of an anisotropic composite made from an arbitrary number of possibly anisotropic phases, and to bound the effective elasticity tensor C∗ of an anisotropic mixture of two well-ordered isotropic materials. The bounds depend on the conductivities and elastic moduli of the components and their respective volume fractions. When the components are isotropic the conductivity bounds, which constrain the eigenvalues of σ∗, include those previously obtained by Hashin and Shtrikman, Murat and Tartar, and Lurie and Cherkaev. Our approach can also be used in the context of linear elasticity to derive bounds on C∗ for composites comprised of an arbitrary number of anisotropic phases. For two-component composites our bounds are tighter than those obtained by Kantor and Bergman and by Francfort and Murat, and are attained by sequentially layered laminate materials.
Ke, Y.; Ortola, S.; Beaucour, A.L.; Dumontet, H.
2010-11-15
An approach which combines both experimental techniques and micromechanical modelling is developed in order to characterise the elastic behaviour of lightweight aggregate concretes (LWAC). More than three hundred LWAC specimens with various lightweight aggregate types (5) of several volume ratios and three different mortar matrices (normal, HP, VHP) are tested. The modelling is based on iterative homogenisation process and includes the ITZ specificities experimentally observed with scanning electron microscopy (SEM). In agreement with experimental measurements, the effects of mix design parameters as well as of the interfacial transition zone (ITZ) on concrete mechanical performances are quantitatively analysed. Confrontations with experimental results allow identifying the elastic moduli of LWA which are difficult to determine experimentally. Whereas the traditional empirical formulas are not sufficiently precise, predictions of LWAC elastic behaviours computed with the micromechanical models appear in good agreement with experimental measurements.
NASA Astrophysics Data System (ADS)
Duffy, T. S.
2013-12-01
The single-crystal elastic stiffness tensor fully characterizes the anisotropic elastic response of minerals. An understanding of how such elastic properties vary with pressure, temperature, structure, and composition are needed to interpret seismic data for the Earth. Additionally, elastic moduli are important for understanding many solid-state phenomena including mechanical stability, interatomic interactions, material strength, compressibility, and phase transition mechanisms. A database of single-crystal elastic properties of minerals and related phases is being assembled. This dataset currently incorporates over 400 sets of elastic constant measurements on more than 270 separate phases. In addition to compiling the individual elastic stiffnesses, the database also allows calculation of a variety of additional properties including anisotropy factors, bulk and linear compressibilities, and stability criteria, as well as evaluation of aggregate properties including bounds and averages of bulk, shear, Young's modulus, Poisson's ratio and elastic wave speeds. Extensions of the database to include high pressure and high temperature data as well as theoretical calculations are being planned. Examples of application of this database to geophysical problems will be highlighted. Specific applications to be discussed include: 1) variation of elastic anisotropy with pressure for mantle and crustal minerals; 2) evaluation of elasticity data for pyroxenes revealing major structural and chemical controls on elasticity as well as remaining ambiguities and uncertainties.
A new approach to monopole moduli spaces
NASA Astrophysics Data System (ADS)
Nash, Oliver
2007-07-01
We introduce a new way to study both Euclidean and hyperbolic monopole moduli spaces. The idea is to apply Kodaira's deformation theory to the spectral curve in an appropriate ambient space. Using this we are able to recover the usual hyperkähler structure on the Euclidean monopole moduli space and to identify a new type of geometry on the hyperbolic monopole moduli space.
Anisotropy in Packing Structure and Elasticity of Sintered Spherical Particles
NASA Astrophysics Data System (ADS)
Kato, Hiroshi; Matsunaga, Chikako; Kurashige, Michio; Imai, Kazuwo
By computer simulation, we estimated macroscopic elastic moduli of sintered equal-sized spherical particles. The simulation is composed of sequential accumulation of spheres and structural analysis of a “random network of 6-degree-freedom springs”, which is a mechanical model of “sintered particles”. From the examination of statistical characteristics of the random packings of spheres, we discovered that their packing structure is affected by gravity; more precisely, line segments connecting the centers of spheres in contact lie more frequently around the direction of 45° from the vertical (gravity) line, although they are uniformly distributed about the vertical line. This non-uniform zenithal frequency-distribution of segments makes, in turn, the sintered aggregates transversely isotropic in elasticity: Young's modulus in the vertical direction is roughly 17% larger than that in the horizontal direction. Our additional experiments using sintered glass-beads saturated with water support the simulated anisotropy.
The moduli and gravitino (non)-problems in models with strongly stabilized moduli
Evans, Jason L.; Olive, Keith A.; Garcia, Marcos A.G. E-mail: garciagarcia@physics.umn.edu
2014-03-01
In gravity mediated models and in particular in models with strongly stabilized moduli, there is a natural hierarchy between gaugino masses, the gravitino mass and moduli masses: m{sub 1/2} << m{sub 3/2} << m{sub φ}. Given this hierarchy, we show that 1) moduli problems associated with excess entropy production from moduli decay and 2) problems associated with moduli/gravitino decays to neutralinos are non-existent. Placed in an inflationary context, we show that the amplitude of moduli oscillations are severely limited by strong stabilization. Moduli oscillations may then never come to dominate the energy density of the Universe. As a consequence, moduli decay to gravitinos and their subsequent decay to neutralinos need not overpopulate the cold dark matter density.
Young's Moduli of Cold and Vacuum Plasma Sprayed Metallic Coatings
NASA Technical Reports Server (NTRS)
Raj, S. V.; Pawlik, R.; Loewenthal, W.
2009-01-01
Monolithic metallic copper alloy and NiCrAlY coatings were fabricated by either the cold spray (CS) or the vacuum plasma spray (VPS) deposition processes. Dynamic elastic modulus property measurements were conducted on these monolithic coating specimens between 300 K and 1273 K using the impulse excitation technique. The Young's moduli decreased almost linearly with increasing temperature at all temperatures except in the case of the CS Cu-23%Cr-5%Al and VPS NiCrAlY, where deviations from linearity were observed above a critical temperature. It was observed that the Young's moduli for VPS Cu-8%Cr were larger than literature data compiled for Cu. The addition of 1%Al to Cu- 8%Cr significantly increased its Young's modulus by 12 to 17% presumably due to a solid solution effect. Comparisons of the Young s moduli data between two different measurements on the same CS Cu- 23%Cr-5%Al specimen revealed that the values measured in the first run were about 10% higher than those in the second run. It is suggested that this observation is due to annealing of the initial cold work microstructure resulting form the cold spray deposition process.
Anisotropic elastic and vibrational properties of Ru2B3 and Os2B3: a first-principles investigation
NASA Astrophysics Data System (ADS)
Ozisik, Haci; Deligoz, Engin; Surucu, Gokhan; Bogaz Ozisik, Havva
2016-07-01
The structural, mechanical and lattice dynamical properties of Ru2B3 and Os2B3 have been investigated by using a first-principles method based on the density functional theory within the generalized gradient approximation. The single crystal elastic constants are numerically estimated using strain–stress approach. The polycrystalline aggregate elastic parameters are calculated from the single elastic constants via the Voigt–Reuss–Hill approximations. Subsequently, the ductility and brittleness are characterized with the estimation from Pugh’s rule (B/G) and Cauchy pressure. Additionally, the Debye temperature is calculated from the average elastic wave velocity obtained from bulk and shear moduli. The calculated parameters are consistent with the previous experimental and theoretical data. These borides are both mechanically and dynamically stable in the considered structure.
Moduli of monopole walls and amoebas
NASA Astrophysics Data System (ADS)
Cherkis, Sergey A.; Ward, Richard S.
2012-05-01
We study doubly-periodic monopoles, also called monopole walls, determining their spectral data and computing the dimensions of their moduli spaces. Using spectral data we identify the moduli, and compare our results with a perturbative analysis. We also identify an SL(2, {Z}) action on monopole walls, in which the S transformation corresponds to the Nahm transform.
String moduli stabilization at the conifold
NASA Astrophysics Data System (ADS)
Blumenhagen, Ralph; Herschmann, Daniela; Wolf, Florian
2016-08-01
We study moduli stabilization for type IIB orientifolds compactified on Calabi-Yau threefolds in the region close to conifold singularities in the complex structure moduli space. The form of the periods implies new phenomena like exponential mass hierarchies even in the regime of negligible warping. Integrating out the heavy conic complex structure modulus leads to an effective flux induced potential for the axio-dilaton and the remaining complex structure moduli containing exponentially suppressed terms that imitate non-perturbative effects. It is shown that this scenario can be naturally combined with the large volume scenario so that all moduli are dynamically stabilized in the dilute flux regime. As an application of this moduli stabilization scheme, a string inspired model of aligned inflation is designed that features a parametrically controlled hierarchy of mass scales.
Elastic constant versus temperature behavior of three hardened maraging steels
NASA Technical Reports Server (NTRS)
Ledbetter, H. M.; Austin, M. W.
1985-01-01
Elastic constants of three maraging steels were determined by measuring ultrasonic velocities. Annealed steels show slightly lower bulk moduli and considerably lower shear moduli than hardened steels. All the elastic constants (Young's modulus, shear modulus, bulk modulus and Poisson's ratio) show regular temperature behavior between 76 and 400 K. Young's modulus and the shear modulus increase with increasing yield strength, but the bulk modulus and Poisson's ratio are relatively unchanged. Elastic anisotropy is quite small.
Measurements of Young's and shear moduli of rail steel at elevated temperatures.
Bao, Yuanye; Zhang, Haifeng; Ahmadi, Mehdi; Karim, Md Afzalul; Felix Wu, H
2014-03-01
The design and modelling of the buckling effect of Continuous Welded Rail (CWR) requires accurate material constants, especially at elevated temperatures. However, such material constants have rarely been found in literature. In this article, the Young's moduli and shear moduli of rail steel at elevated temperatures are determined by a new sonic resonance method developed in our group. A network analyser is used to excite a sample hanged inside a furnace through a simple tweeter type speaker. The vibration signal is picked up by a Polytec OFV-5000 Laser Vibrometer and then transferred back to the network analyser. Resonance frequencies in both the flexural and torsional modes are measured, and the Young's moduli and shear moduli are determined through the measured resonant frequencies. To validate the measured elastic constants, the measurements have been repeated by using the classic sonic resonance method. The comparisons of obtained moduli from the two methods show an excellent consistency of the results. In addition, the material elastic constants measured are validated by an ultrasound test based on a pulse-echo method and compared with previous published results at room temperature. The measured material data provides an invaluable reference for the design of CWR to avoid detrimental buckling failure.
Moduli Space of Non-Abelian Vortices
NASA Astrophysics Data System (ADS)
Eto, Minoru; Isozumi, Youichi; Nitta, Muneto; Ohashi, Keisuke; Sakai, Norisuke
2006-04-01
We completely determine the moduli space MN,k of k vortices in U(N) gauge theory with N Higgs fields in the fundamental representation. Its open subset for separated vortices is found as the symmetric product (C×CPN-1)k/Sk. Orbifold singularities of this space correspond to coincident vortices and are resolved resulting in a smooth moduli manifold. The relation to Kähler quotient construction is discussed.
Moduli stabilization in stringy ISS models
Nakayama, Yu; Nakayama, Yu; Yamazaki, Masahito; Yanagida, T.T.
2007-09-28
We present a stringy realization of the ISS metastable SUSY breaking model with moduli stabilization. The mass moduli of the ISS model is stabilized by gauging of a U(1) symmetry and its D-term potential. The SUSY is broken both by F-terms and D-terms. It is possible to obtain de Sitter vacua with a vanishingly small cosmological constant by an appropriate fine-tuning of flux parameters.
Hard tissue as a composite material. I - Bounds on the elastic behavior.
NASA Technical Reports Server (NTRS)
Katz, J. L.
1971-01-01
Recent determination of the elastic moduli of hydroxyapatite by ultrasonic methods permits a re-examination of the Voigt or parallel model of the elastic behavior of bone, as a two phase composite material. It is shown that such a model alone cannot be used to describe the behavior of bone. Correlative data on the elastic moduli of dentin, enamel and various bone samples indicate the existence of a nonlinear dependence of elastic moduli on composition of hard tissue. Several composite models are used to calculate the bounds on the elastic behavior of these tissues. The limitations of these models are described, and experiments to obtain additional critical data are discussed.
NASA Technical Reports Server (NTRS)
Aboudi, Jacob
2000-01-01
The micromechanical generalized method of cells model is employed for the prediction of the effective moduli of electro-magneto-thermo-elastic composites. These include the effective elastic, piezoelectric, piezomagnetic, dielectric, magnetic permeability, electromagnetic coupling moduli, as well as the effective thermal expansion coefficients and the associated pyroelectric and pyromagnetic constants. Results are given for fibrous and periodically bilaminated composites.
Zhou, Shuang; Neupane, Krishna; Nastishin, Yuriy A; Baldwin, Alan R; Shiyanovskii, Sergij V; Lavrentovich, Oleg D; Sprunt, Samuel
2014-09-14
Using dynamic light scattering, we study orientational fluctuation modes in the nematic phase of a self-assembled lyotropic chromonic liquid crystal (LCLC) disodium cromoglycate and measure the Frank elastic moduli and viscosity coefficients. The elastic moduli of splay (K1) and bend (K3) are in the order of 10 pN while the twist modulus (K2) is an order of magnitude smaller. The splay constant K1 and the ratio K1/K3 both increase substantially as the temperature T decreases, which we attribute to the elongation of the chromonic aggregates at lower temperatures. The bend viscosity is comparable to that of thermotropic liquid crystals, while the splay and twist viscosities are several orders of magnitude larger. The temperature dependence of bend viscosity is weak. The splay and twist viscosities change exponentially with the temperature. In addition to the director modes, the fluctuation spectrum reveals an additional mode that is attributed to diffusion of structural defects in the column-like aggregates.
Mazer, N A; Schurtenberg, P; Carey, M C; Preisig, R; Weigand, K; Känzig, W
1984-04-24
Using quasi-elastic light scattering ( QLS ), we have characterized the macromolecular components in hepatic bile obtained from the dog and compared these results with data from model bile solutions containing the bile salt (BS) sodium taurocholate (TC), egg lecithin (L), and cholesterol (Ch). Native bile samples were obtained by direct catheterization of the common bile duct in a previously cholecystectomized dog fitted with a Thomas duodenal cannula. Hepatic bile was sampled during three secretory states: (A) unstimulated "fasting" bile, (B) "stimulated" secretion during an intravenous TC infusion, and (C) "secretin-stimulated" secretion. All three samples had comparable molar ratios of L/BS (0.21 +/- 0.03) and Ch/L (0.027 +/- 0.006) but differed in the total lipid concentration (BS + L + Ch): (A) 13.1 +/- 0.8, (B) 6.7 +/- 0.8, and (C) 3.0 +/- 0.4 g/dL. From the QLS autocorrelation functions measured on samples B and C, three macromolecular components (denoted 1 alpha, 1 beta, and 2) were resolved. Component 1 alpha (hydrodynamic radius R1 alpha = 10 +/- 2 A) is comparable in size to the micellar aggregates of model systems. Component 1 beta (R1 beta = 67 +/- 7 A) appears to reflect an average of biliary proteins. Component 2 (R2 = 650 +/- 15 A) is a trace component whose size and sedimentation behavior are compatible with those of the canalicular membrane vesicles postulated to be present in bile [ Godfrey , P. P., Warner, M. J., & Coleman , R. (1981) Biochem. J. 196, 11]. Serial dilution of the B and C bile samples with Tris buffer (0.15 M NaCl, pH 8.0) showed a remarkable similarity in the behavior of the 1 alpha component as compared to the mean hydrodynamic radius Rh of similarly diluted model bile solutions. When a critical dilution factor, d gamma, is reached, Rh increases abruptly from approximately 30 to approximately 400 A. Above a second dilution factor, d alpha, it then decreases to a value of approximately 150 A. Similar results were obtained on
Elasticity of iron-bearing olivine polymorphs investigated by first principles
NASA Astrophysics Data System (ADS)
Núñez Valdez, Maribel; Yu, Yonggang; Wentzcovitch, Renata
2011-03-01
We calculate by first principles the effect of iron on the high pressure-temperature elasticity of olivine polymorphs: α -phase (olivine), β -phase (wadsleyite) and γ -phase (ringwoodite), the major constituents of the Earth's upper mantle and transition zone (TZ). We combine the LDA, the quasiharmonic approximation, and a model vibrational density of states for the solid solution to calculate the full elastic tensor Cij , bulk (K) and shear (G) moduli of (Mg 0.875 Fe 0.125)2 Si O4 . Comparison with experimental data at ambient conditions validates our results. In the pressure and temperature range of the upper mantle and TZ we study single crystal wave propagation anisotropy and polarization anisotropy in aggregates with preferred orientation. Research supported by NSF EAR-1019853 and EAR-0810272. Computations were performed at the Minnesota Supercomputing Institute.
NASA Astrophysics Data System (ADS)
Kyaw, S. T.; Sun, W.; Becker, A. A.
2015-02-01
Physical mechanisms at different length scales have to be taken into account while predicting the overall failure of nuclear graphite structures of advanced gas cooled graphite reactors. In this paper, the effect of composition of meso graphite phases and porosity on the aggregate elastic properties is predicted using the Eshelby homogenisation method. Results indicate an overall decrease in elastic modulus with an increase in porosity. Subsequently, the moduli at different porosity levels are used to predict the critical strain energy release rates for crack propagation of graphite, and fracture behaviour is studied using compact tension and four point bending tests. Compared to flexural strength at zero porosity level, significant reduction in strength of up to 80% at 30% porosity level is observed. Evolution of flexural strength due to porosity is also compared against available experimental values of graphite from UK nuclear plants.
Accidental Kähler moduli inflation
Maharana, Anshuman; Rummel, Markus; Sumitomo, Yoske
2015-09-14
We study a model of accidental inflation in type IIB string theory where inflation occurs near the inflection point of a small Kähler modulus. A racetrack structure helps to alleviate the known concern that string-loop corrections may spoil Kähler Moduli Inflation unless having a significant suppression via the string coupling or a special brane setup. Also, the hierarchy of gauge group ranks required for the separation between moduli stabilization and inflationary dynamics is relaxed. The relaxation becomes more significant when we use the recently proposed D-term generated racetrack model.
Elasticity of plagioclase feldspars
NASA Astrophysics Data System (ADS)
Brown, J. Michael; Angel, Ross J.; Ross, Nancy L.
2016-02-01
Elastic properties are reported for eight plagioclase feldspars that span compositions from albite (NaSi3AlO8) to anorthite (CaSi2Al2O8). Surface acoustic wave velocities measured using Impulsive Stimulated Light Scattering and compliance sums from high-pressure X-ray compression studies accurately determine all 21 components of the elasticity tensor for these triclinic minerals. The overall pattern of elasticity and the changes in individual elastic components with composition can be rationalized on the basis of the evolution of crystal structures and chemistry across this solid-solution join. All plagioclase feldspars have high elastic anisotropy; a* (the direction perpendicular to the b and c axes) is the softest direction by a factor of 3 in albite. From albite to anorthite the stiffness of this direction undergoes the greatest change, increasing twofold. Small discontinuities in the elastic components, inferred to occur between the three plagioclase phases with distinct symmetry (C1>¯, I1>¯, and P1>¯), appear consistent with the nature of the underlying conformation of the framework-linked tetrahedra and the associated structural changes. Measured body wave velocities of plagioclase-rich rocks, reported over the last five decades, are consistent with calculated Hill-averaged velocities using the current moduli. This confirms long-standing speculation that previously reported elastic moduli for plagioclase feldspars are systematically in error. The current results provide greater assurance that the seismic structure of the middle and lower crusts can be accurately estimated on the basis of specified mineral modes, chemistry, and fabric.
Pre-Stressed Viscoelastic Composites: Effective Incremental Moduli and Band-Gap Tuning
Parnell, William J.
2010-09-30
We study viscoelastic wave propagation along pre-stressed nonlinear elastic composite bars. In the pre-stressed state we derive explicit forms for the effective incremental storage and loss moduli with dependence on the pre-stress. We also derive a dispersion relation for the effective wavenumber in the case of arbitrary frequency, hence permitting a study of viscoelastic band-gap tuning via pre-stress.
An Approach to Calculate Mineralś Bulk Moduli KS from Chemical Composition and Density ρ
NASA Astrophysics Data System (ADS)
Breuer, S.; Schilling, F. R.; Mueller, B.; Drüppel, K.
2015-12-01
The elastic properties of minerals are fundamental parameters for technical and geotechnical applications and an important research topic towards a better understanding of the Earth's interior. Published elastic properties, chemical composition, and density data of 86 minerals (total of 258 data including properties of minerals at various p, T conditions) were collected into a database. It was used to test different hypotheses about relationships between these properties (e.g. water content in minerals and their Poisson's ratio). Furthermore, a scheme to model the average elastic properties, i.e. the bulk modulus KS, based on mineral density and composition was developed. Birch's law, a linearity between density ρ and wave velocity (e.g. vp.), is frequently used in seismic and seismology to derive density of the Earth's interior from seismic velocities. Applying the compiled mineral data contradicts the use of a simple velocity-density relation (e.g. Gardneŕs relation, 1974). The presented model-approach to estimate the mineralś bulk moduli Ks (as Voigt-Reuss-Hill average) is based on the idea of pressure-temperature (p-T) dependent ionś bulk moduli. Using a multi-exponential regression to ascertain the ionś bulk moduli and by applying an exponential scaling with density ρ, their bulk moduli could be modelled. As a result, > 88 % of the 258 bulk moduli data are predicted with an uncertainty of < 20 % compared to published values. Compared to other models (e.g. Anderson et al. 1970 and Anderson & Nafe 1965), the here presented approach to model the bulk moduli only requires the density ρ and chemical composition of the mineral and is not limited to a specific group of minerals, composition, or structure. In addition to this, by using the pressure and temperature dependent density ρ(p, T), it is possible to predict bulk moduli for varying p-T conditions. References:Gardner, G.H.F, Gardner, L.W. and Gregory, A.R. (1974). Geophysics, 39, No. 6, 770
NASA Astrophysics Data System (ADS)
Yin, Changyong
In this thesis, we study the geometry of the moduli space and the Teichmuller space of Calabi-Yau manifolds, which mainly involves the following two aspects: the (locally, globally) Hermitian symmetric property of the Teichmuller space and the first Chern form of the moduli space with the Weil-Petersson and Hodge metrics. In the first part, we define the notation of quantum correction for the Teichmuller space T of Calabi-Yau manifolds. Under the assumption of vanishing of weak quantum correction, we prove that the Teichmuller space, with the Weil-Petersson metric, is a locally symmetric space. For Calabi-Yau threefolds, we show that the vanishing of strong quantum correction is equivalent to that the image of the Teichmuller space under the period map is an open submanifold of a globally Hermitian symmetric space W of the same dimension as T. Finally, for Hyperkahler manifolds of dimension 2n ≥ 4, we find globally defined families of (2, 0) and (2n, 0)-classes over the Teichmuller space of polarized Hyperkahler manifolds. In the second part, we prove that the first Chern form of the moduli space of polarized Calabi-Yau manifolds, with the Hodge metric or the Weil-Petersson metric, represents the first Chern class of the canonical extensions of the tangent bundle to the compactification of the moduli space with normal crossing divisors.
Prediction of elastic properties for polymer-particle nanocomposites exhibiting an interphase.
Deng, Fei; Van Vliet, Krystyn J
2011-04-22
Particle-polymer nanocomposites often exhibit mechanical properties described poorly by micromechanical models that include only the particle and matrix phases. Existence of an interfacial region between the particle and matrix, or interphase, has been posited and indirectly demonstrated to account for this effect. Here, we present a straightforward analytical approach to estimate effective elastic properties of composites comprising particles encapsulated by an interphase of finite thickness and distinct elastic properties. This explicit solution can treat nanocomposites that comprise either physically isolated nanoparticles or agglomerates of such nanoparticles; the same framework can also treat physically isolated nanoparticle aggregates or agglomerates of such aggregates. We find that the predicted elastic moduli agree with experiments for three types of particle-polymer nanocomposites, and that the predicted interphase thickness and stiffness of carbon black-rubber nanocomposites are consistent with measured values. Finally, we discuss the relative influence of the particle-polymer interphase thickness and stiffness to identify maximum possible changes in the macroscale elastic properties of such materials. PMID:21393814
Elastic properties of granular materials under uniaxial compaction cycles
NASA Technical Reports Server (NTRS)
Warren, N.; Anderson, O. L.
1973-01-01
Data on andesitic and basaltic sands are presented showing compressional sound velocity, density, and creep as functions of uniaxial loading through several compaction cycles. Maximum pressures over which acoustic measurements were made were in the range from 600 to 700 bars. The dynamic elastic modulus varies with pressure in a manner analogous to that of a static elastic modulus defined by small pressure perturbations on a typical compaction cycle. After several compaction cycles, two compressional elastic moduli apparently exist at low pressure (thus two modes of compressional wave propagation through the samples are indicated). The elastic moduli observations are briefly discussed in terms of a general expression for compressibility.
Moduli of Vortices and Grassmann Manifolds
NASA Astrophysics Data System (ADS)
Biswas, Indranil; Romão, Nuno M.
2013-05-01
We use the framework of Quot schemes to give a novel description of the moduli spaces of stable n-pairs, also interpreted as gauged vortices on a closed Riemann surface Σ with target {Mat_{r × n}({C})}, where n ≥ r. We then show that these moduli spaces embed canonically into certain Grassmann manifolds, and thus obtain natural Kähler metrics of Fubini-Study type. These spaces are smooth at least in the local case r = n. For abelian local vortices we prove that, if a certain "quantization" condition is satisfied, the embedding can be chosen in such a way that the induced Fubini-Study structure realizes the Kähler class of the usual L 2 metric of gauged vortices.
Elasticity and structure of mantle pyroxenes
NASA Astrophysics Data System (ADS)
Bass, J. D.; Zhang, J. S.; Sang, L.; Reynard, B.; Montagnac, G.; Dera, P. K.
2012-12-01
The elastic properties of both natural orthoenstatite and natural diopside have been determined at high pressures to over 14 GPa at room temperature by Brillouin spectroscopy. Single crystals of Fe-bearing orthoenstatite from San Carlos, AZ were used in one part of the study. The sound velocity data display a pronounced change in elastic character upon cold compression to above 12 GPa. There is an abrupt change in velocity anisotropy above that pressure. Single-crystal X-ray structure refinements, performed at the GSECARS beamline, Sector 13 of the APS, demonstrate that orthoenstatite transforms to a new high-pressure phase with space group P21/c (HPCEN2), with the transition pressure bracketed to be between about 10-14 GPa (JS Zhang et al., 2012). No evidence of a structure with C2/c space group was observed. Raman spectroscopy was used to explore the compositional dependence of the transition pressure and structure of the high-pressure phase. Single crystals of nearly pure Mg end-member OPX, a high-alumina sample, and an Fe-rich sample were examined. We find that Al and Fe both effect the transition pressure, but that the high-pressure phase is still P21/c HPCEN2 in all cases. The single-crystal elasticity diopside was measured to transition zone pressures using Brillouin spectroscopy. A very dense high-quality velocity data set was obtained, from which the single-crystal elastic moduli as a function of pressure were obtained. Results for the aggregate bulk elastic properties are in very good agreement with polycrystalline acoustic measurements of Li and Neuville. This is a case where the results of single-crystal Brillouin and polycrystalline acoustic measurements give highly consistent results. Li, B.S., and Neuville, D.R. (2010) Elasticity of diopside to 8 GPa and 1073 K and implications for the upper mantle. Physics of the Earth and Planetary Interiors, 183(3-4), 398-403. Zhang, JS, P Dera, and JD Bass (2012) A new high-pressure phase transition in natural Fe
BCFT moduli space in level truncation
NASA Astrophysics Data System (ADS)
Kudrna, Matěj; Maccaferri, Carlo
2016-04-01
We propose a new non-perturbative method to search for marginal deformations in level truncated open string field theory. Instead of studying the flatness of the effective potential for the marginal field (which is not expected to give a one-to-one parametrization of the BCFT moduli space), we identify a new non-universal branch of the tachyon potential which, from known analytic examples, is expected to parametrize the marginal flow in a much larger region of the BCFT moduli space. By a level 18 computation in Siegel gauge we find an increasingly flat effective potential in the non-universal sector, connected to the perturbative vacuum and we confirm that the coefficient of the marginal field ( λ SFT) has a maximum compatible with the value where the solutions stop existing in the standard Sen-Zwiebach approach. At the maximal reachable level the effective potential still deviates from flatness for large values of the tachyon, but the Ellwood invariants stay close to the correct BCFT values on the whole branch and the full periodic moduli space of the cosine deformation is covered.
Universal Elasticity and Fluctuations of Nematic Gels
NASA Astrophysics Data System (ADS)
Xing, Xiangjun; Radzihovsky, Leo
2003-04-01
We study elasticity of spontaneously orientationally ordered amorphous solids, characterized by a vanishing transverse shear modulus, as realized by nematic elastomers and gels. We show that local heterogeneities and elastic nonlinearities conspire to lead to anomalous nonlocal universal elasticity controlled by a nontrivial infrared fixed point. Namely, such solids are characterized by universal shear and bending moduli that, respectively, vanish and diverge at long scales, are universally incompressible, and exhibit a universal negative Poisson ratio and a non-Hookean elasticity down to arbitrarily low strains. Based on expansion about five dimensions, we argue that the nematic order is stable to thermal fluctuation and local heterogeneities down to dlc<3.
Elastic properties of gamma-Pu by resonant ultrasound spectroscopy
Migliori, Albert; Betts, J; Trugman, A; Mielke, C H; Mitchell, J N; Ramos, M; Stroe, I
2009-01-01
Despite intense experimental and theoretical work on Pu, there is still little understanding of the strange properties of this metal. We used resonant ultrasound spectroscopy method to investigate the elastic properties of pure polycrystalline Pu at high temperatures. Shear and longitudinal elastic moduli of the {gamma}-phase of Pu were determined simultaneously and the bulk modulus was computed from them. A smooth linear and large decrease of all elastic moduli with increasing temperature was observed. We calculated the Poisson ratio and found that it increases from 0.242 at 519K to 0.252 at 571K.
Elastic-wave velocity in marine sediments with gas hydrates: Effective medium modeling
Helgerud, M.B.; Dvorkin, J.; Nur, A.; Sakai, A.; Collett, T.
1999-01-01
We offer a first-principle-based effective medium model for elastic-wave velocity in unconsolidated, high porosity, ocean bottom sediments containing gas hydrate. The dry sediment frame elastic constants depend on porosity, elastic moduli of the solid phase, and effective pressure. Elastic moduli of saturated sediment are calculated from those of the dry frame using Gassmann's equation. To model the effect of gas hydrate on sediment elastic moduli we use two separate assumptions: (a) hydrate modifies the pore fluid elastic properties without affecting the frame; (b) hydrate becomes a component of the solid phase, modifying the elasticity of the frame. The goal of the modeling is to predict the amount of hydrate in sediments from sonic or seismic velocity data. We apply the model to sonic and VSP data from ODP Hole 995 and obtain hydrate concentration estimates from assumption (b) consistent with estimates obtained from resistivity, chlorinity and evolved gas data. Copyright 1999 by the American Geophysical Union.
Asymptotic estimates on scatter ranges for elastic properties of completely random polycrystals
NASA Astrophysics Data System (ADS)
Chinh, Pham Duc
2003-06-01
One observes that the shape and crystalline orientations of the anisotropic grains in a completely random polycrystal are uncorrelated, hence the polycrystal appears (we say, nearly) macroscopically homogeneous and isotropic, and has relatively (almost) definite macroscopic elastic properties. However, because of the polycrystalline irregular microgeometry, the macroscopic properties of the aggregate may be not unique (even in principle and for the large representative element limit), and the macroscopic homogeneity and isotropy hypotheses for it may be not exact (but approximate with some accuracy). With these statements we abandon the conventional strict uniqueness and exactness viewpoint and, in fact, adopt weaker but perhaps more realistic hypotheses that allow for small uncertainties. Our upper and lower bounds on elastic moduli of random polycrystals, though based on (approximate) statistical isotropy and symmetry hypotheses, can still provide asymptotic estimates on possible ranges for the properties of the aggregates with certain accuracy, provided the intervals between bounds are sufficiently small. The formal bounds are used to derive explicit estimates for the aggregates of tetragonal crystals (classes 4, 4¯,4/m ). The numerical results appear reliable, as the stated asymptotic condition is met.
Characterization of the Nonlinear Elastic Properties of Graphite/Epoxy Composites Using Ultrasound
NASA Technical Reports Server (NTRS)
Prosser, William H.; Green, Robert E., Jr.
1990-01-01
The normalized change in ultrasonic "natural" velocity as a function of stress and temperature was measured in a unidirectional laminate of T300/5208 graphite/epoxy composite using a pulsed phase locked loop ultrasonic interferometer. These measurements were used together with the linear (second order) elastic moduli to calculate some of the nonlinear (third order) moduli of this material.
Permutation combinatorics of worldsheet moduli space
NASA Astrophysics Data System (ADS)
Freidel, Laurent; Garner, David; Ramgoolam, Sanjaye
2015-06-01
Light-cone string diagrams have been used to reproduce the orbifold Euler characteristic of moduli spaces of punctured Riemann surfaces at low genus and with few punctures. Nakamura studied the meromorphic differential introduced by Giddings and Wolpert to characterize light-cone diagrams and introduced a class of graphs related to this differential. These Nakamura graphs were used to parametrize the cells in a light-cone cell decomposition of moduli space. We develop links between Nakamura graphs and realizations of the worldsheet as branched covers. This leads to a development of the combinatorics of Nakamura graphs in terms of permutation tuples. For certain classes of cells, including those of the top dimension, there is a simple relation to Belyi maps, which allows us to use results from Hermitian and complex matrix models to give analytic formulas for the counting of cells at an arbitrarily high genus. For the most general cells, we develop a new equivalence relation on Hurwitz classes which organizes the cells and allows efficient enumeration of Nakamura graphs using the group theory software gap.
Elastic properties of sub-stoichiometric nitrogen ion implanted silicon
NASA Astrophysics Data System (ADS)
Sarmanova, M. F.; Karl, H.; Mändl, S.; Hirsch, D.; Mayr, S. G.; Rauschenbach, B.
2015-04-01
Elastic properties of sub-stoichiometric nitrogen implanted silicon were measured with nanometer-resolution using contact resonance atomic force microscopy (CR-AFM) as function of ion fluence and post-annealing conditions. The determined range of indentation moduli was between 100 and 180 GPa depending on the annealing duration and nitrogen content. The high indentation moduli can be explained by formation of Si-N bonds, as verified by X-ray photoelectron spectroscopy.
Moduli stabilization and the pattern of sparticle spectra
Choi, Kiwoon
2008-11-23
We discuss the pattern of low energy sparticle spectra which appears in some class of moduli stabilization scenario. In case that light moduli are stabilized by non-perturbative effects encoded in the superpotential and a phenomenologically viable de Sitter vacuum is obtained by a sequestered supersymmetry breaking sector, the anomaly-mediated soft terms become comparable to the moduli-mediated ones, leading to a quite distinctive pattern of low energy spacticle masses dubbed the mirage mediation pattern. We also discuss low energy sparticle masses in more general mixed-mediation scenario which includes a comparable size of gauge mediation in addition to the moduli and anomaly mediations.
The elastic energy of damaged rocks
NASA Astrophysics Data System (ADS)
Hamiel, Y.; Lyakhovsky, V.; Ben-Zion, Y.
2009-12-01
Crustal rocks are typically treated as linear elastic material with constant elastic moduli. This assumption is appropriate for rock with relatively low damage, associated with low concentration of cracks and flaws, and under relatively small strains. However, laboratory and field data indicate that rocks subjected to sufficiently high loads exhibit clear deviations from linear behavior. In general, nonlinear stress-strain relationships of rocks can be approximated by including higher-order terms of the strain tensor in the elastic energy expression (e.g., the Murnaghan model). Such models are successful for calculating rock deformation under high confining pressure. However, values of the third (higher order) Murnaghan moduli estimated from acoustic experiments are one to two orders of magnitude above the expected values of the same moduli estimated from the stress-strain relations in quasi-static rock-mechanics experiments. The Murnaghan model also fails to reproduce an abrupt change in the elastic moduli when deformation changes from compression to tension. Such behavior was observed in laboratory experiments with rocks, concrete, and composite brittle material samples. Bi-linear elastic models with abrupt change of the moduli under stress reversal were suggested based on acoustic experiments ("clapping" nonlinearity) and in continuum damage mechanics (unilateral damage model). Here we present a theoretical basis for general second-order nonlinear expression of the elastic potential. We then show that a simplified version of the general nonlinear model is consistent with bi-linear elastic behavior and accounts for non-linearity even under small strains. We apply the simplified nonlinear model to various laboratory observations, including quasi-static modeling of rocks and composite material with different effective moduli under tension and compression; rock dilation under shear; stress- and damage-induced seismic wave anisotropy observed during cycling load of
NASA Astrophysics Data System (ADS)
Růžek, M.; Sedlák, P.; Seiner, H.; Landa, M.
2011-01-01
This paper deals with determination of in-plane elastic constants of thin layers deposited on substrates. Modified resonant ultrasound spectroscopy is used to measure resonant spectra before and after layer deposition . These two spectra are compared and changes in the position of the resonant peaks are associated with layer properties. It is shown that for thin layers either the elastic moduli or the surface mass density can be determined, providing the complementary information (the surface mass density for the determination of the moduli, the elastic moduli for the determination of the surface mass density) is known. As an experimental demonstration of this approach, the elastic moduli of diamond-like-carbon film deposited on a silicon substrate and the surface mass density of a thin spray paint on a silicon substrate are determined.
Elastic properties of functionalized carbon nanotubes.
Milowska, Karolina Z; Majewski, Jacek A
2013-09-14
We study the effects of covalent functionalization of single wall carbon nanotubes (CNT) on their elastic properties. We consider simple organic molecules -NH, -NH2, -CH2, -CH3, -OH attached to CNTs' surface at various densities. The studies are based on the first principles calculations in the framework of density functional theory. We have determined the changes in the geometry and the elastic moduli of the functionalized CNTs as a function of the density of adsorbed molecules. It turns out that elastic moduli diminish with increasing concentration of adsorbents, however, the functionalized CNTs remain strong enough to be suitable for reinforcement of composites. The strongest effect is observed for CNTs functionalized with -CH2 radical, where the Young's modulus of the functionalized system is 30% smaller than in the pristine CNTs.
Macione, J; Depaula, C A; Guzelsu, N; Kotha, S P
2010-07-01
Previous studies indicate that changes in the longitudinal elastic properties of bone due to changes in mineral content are related to the longitudinal strength of bone tissue. Changes in mineral content are expected to affect bone tissue mechanical properties along all directions, albeit to different extents. However, changes in tissue mechanical properties along the different directions are expected to be correlated to one another. In this study, we investigate if radial, circumferential, and longitudinal moduli are related in bone tissue with varying mineral content. Plexiform bovine femoral bone samples were treated in fluoride ion solutions for a period of 3 and 12 days to obtain bones with 20% and 32% lower effective mineral contents. Transmission ultrasound velocities were obtained in the radial, circumferential, and longitudinal axes of bone and combined with measured densities to obtain corresponding tensorial moduli. Results indicate that moduli decreased with fluoride ion treatments and were significantly correlated to one another (r(2) radial vs. longitudinal = 0.80, r(2) circumferential vs. longitudinal = 0.90, r(2) radial vs. circumferential = 0.85). Densities calculated from using ultrasound parameters, acoustic impedance and transmission velocities, were moderately correlated to those measured by the Archimedes principle (r(2)=0.54, p<0.01). These results suggest that radial and circumferential ultrasound measurements could be used to determine the longitudinal properties of bone and that ultrasound may not be able to predict in vitro densities of bones containing unbonded mineral. PMID:20416555
Matrix Models, Monopoles and Modified Moduli
NASA Astrophysics Data System (ADS)
Erlich, Joshua; Hong, Sungho; Unsal, Mithat
2004-09-01
Motivated by the Dijkgraaf-Vafa correspondence, we consider the matrix model duals of Script N = 1 supersymmetric SU(Nc) gauge theories with Nf flavors. We demonstrate via the matrix model solutions a relation between vacua of theories with different numbers of colors and flavors. This relation is due to an Script N = 2 nonrenormalization theorem which is inherited by these Script N = 1 theories. Specializing to the case Nf = Nc, the simplest theory containing baryons, we demonstrate that the explicit matrix model predictions for the locations on the Coulomb branch at which monopoles condense are consistent with the quantum modified constraints on the moduli in the theory. The matrix model solutions include the case that baryons obtain vacuum expectation values. In specific cases we check explicitly that these results are also consistent with the factorization of corresponding Seiberg-Witten curves. Certain results are easily understood in terms of M5-brane constructions of these gauge theories.
Nonlinear and heterogeneous elasticity of multiply-crosslinked biopolymer networks
NASA Astrophysics Data System (ADS)
Amuasi, H. E.; Heussinger, C.; Vink, R. L. C.; Zippelius, A.
2015-08-01
We simulate randomly crosslinked networks of biopolymers, characterizing linear and nonlinear elasticity under different loading conditions (uniaxial extension, simple shear, and pure shear). Under uniaxial extension, and upon entering the nonlinear regime, the network switches from a dilatant to contractile response. Analogously, under isochoric conditions (pure shear), the normal stresses change their sign. Both effects are readily explained with a generic weakly nonlinear elasticity theory. The elastic moduli display an intermediate super-stiffening regime, where moduli increase much stronger with applied stress σ than predicted by the force-extension relation of a single wormlike-chain ({G}{wlc}∼ {σ }3/2). We interpret this super-stiffening regime in terms of the reorientation of filaments with the maximum tensile direction of the deformation field. A simple model for the reorientation response gives an exponential stiffening, G∼ {{{e}}}σ , in qualitative agreement with our data. The heterogeneous, anisotropic structure of the network is reflected in correspondingly heterogeneous and anisotropic elastic properties. We provide a coarse-graining scheme to quantify the local anisotropy, the fluctuations of the elastic moduli, and the local stresses as a function of coarse-graining length. Heterogeneities of the elastic moduli are strongly correlated with the local density and increase with applied strain.
A new approach to the cosmological moduli problem
NASA Astrophysics Data System (ADS)
Dienes, Keith R.; Kost, Jeff; Thomas, Brooks
2016-06-01
A generic byproduct of many theories beyond the Standard Model is the appearance of light scalar fields known as moduli. These moduli should be copiously produced in the early universe but have dangerously long lifetimes, leading to their excessive domination of the late-time energy density - an issue known as the "cosmological moduli problem". In this talk, we discuss a number of new effects which have direct relevance for the cosmological moduli problem and which, depending on circumstances, can either unexpectedly amerliorate it or worsen it, often by many orders of magnitude. As described more fully in Ref. [1], these effects arise in theories containing multiple moduli which mix amongst themselves in the presence of a mass-generating phase transition.
Elasticity of the Rod-Shaped Gram-Negative Eubacteria
NASA Astrophysics Data System (ADS)
Boulbitch, A.; Quinn, B.; Pink, D.
2000-12-01
We report a theoretical calculation of the elasticity of the peptidoglycan network, the only stress-bearing part of rod-shaped Gram-negative eubacteria. The peptidoglycan network consists of elastic peptides and inextensible glycan strands, and it has been proposed that the latter form zigzag filaments along the circumference of the cylindrical bacterial shell. The zigzag geometry of the glycan strands gives rise to nonlinear elastic behavior. The four elastic moduli of the peptidoglycan network depend on its stressed state. For a bacterium under physiological conditions the elasticity is proportional to the bacterial turgor pressure. Our results are in good agreement with recent measurements.
Single-crystal elasticity of the deep-mantle magnesite at high pressure and temperature
NASA Astrophysics Data System (ADS)
Yang, Jing; Mao, Zhu; Lin, Jung-Fu; Prakapenka, Vitali B.
2014-04-01
Magnesite (MgCO3) is considered to be a major candidate carbon host in the Earth's mantle, and has been found to exist as an accessory mineral in carbonated peridotite and eclogite. Studying the thermal elastic properties of magnesite under relevant pressure-temperature conditions of the upper mantle is thus important for our understanding of the deep-carbon storage in the Earth's interior. Here we have measured the single-crystal elasticity of a natural magnesite using in situ Brillouin spectroscopy and X-ray diffraction in a diamond anvil cell up to 14 GPa at room temperature and up to 750 K at ambient pressure, respectively. Using the third-order Eulerian finite-strain equations to model the elasticity data, we have derived the aggregate adiabatic bulk, KS0, and shear moduli, G0, at ambient conditions: KS0=114.7 (±1.3) GPa and G0=69.9 (±0.6) GPa. The pressure derivatives of the bulk and shear moduli at 300 K are (∂KS/∂P)T=4.82 (±0.10) and (∂G/∂P)T=1.75 (±0.10), respectively, while their temperature derivatives at ambient pressure are (∂Ks/∂T)P=-24.0 (±0.2) MPa/K and (∂G/∂T)P=-14.8 (±0.7) MPa/K. Based on the thermal elastic modeling of the measured elastic constants along an expected normal upper-mantle geotherm and a cold subducting slab, magnesite exhibits compressional wave (VP) anisotropy of approximately 46-49% and shear wave (VS) splitting of 37-41% that are much larger than those of major constituent minerals in the Earth's upper mantle including olivine, pyroxene, and garnet. The modeled aggregate VP and VS velocity in moderately carbonated peridotite and eclogite containing approximately 10 wt.% magnesite (approximately 5 wt.% CO2) show minimal effects of magnesite on the seismic profiles of these rock assemblages at upper mantle conditions, suggesting that the presence of magnesite is likely difficult to be detected seismically. However, due to its unusually high VP and VS anisotropies, magnesite with strong preferred orientations
Elastic Properties of Mantle Minerals
NASA Astrophysics Data System (ADS)
Duffy, T. S.; Stan, C. V.
2012-12-01
The most direct information about the interior structure of the Earth comes from seismic wave velocities. Interpretation of seismic data requires an understanding of how sound velocities and elastic properties of minerals vary with pressure, temperature, crystal structure, and composition as well as the role of anelasticity, melts, etc. More generally, elastic moduli are important for understanding many solid-state phenomena including mechanical stability, interatomic interactions, material strength, compressibility, and phase transition mechanisms. The database of mineral elasticity measurements has been growing rapidly in recent years. In this work, we report initial results of an ongoing survey of our current knowledge of mineral elasticity at both ambient conditions and high pressures and temperatures. The analysis is selective, emphasizing single crystal measurements but also incorporating polycrystalline measurements and volume compression data as appropriate. The goal is to synthesize our current understanding of mineral elasticity in terms of structure and composition, and to identify the major remaining needs for experimental and theoretical work. Clinopyroxenes (Cpx) provide an example of our approach. A wide range of clinopyroxene compositions are found geologically and Mg-, Ca-, and Na-rich clinopyroxenes are expected to be important components in the upper mantle. The single-crystal elastic properties of a number of endmember Cpx compositions have been measured and these exhibit a range of ~25% in shear velocity. Those with monovalent cations (spodumene, jadeite) in the M2 site exhibit the highest velocities while Fe-rich (hendenbergit, acmite) compositions have the lowest velocities. The effects on velocity due to a wide range of chemical substitutions can be defined, but there are important discrepancies and omissions in the database. New measurements of omphacites, intermediate diopside-hedenbergite compositions, aegerine/acmite, augite, etc. are
Marquez, J. Pablo; Elson, Elliot L.; Genin, Guy M.
2010-01-01
While much is known about the subcellular structures responsible for the mechanical functioning of a contractile fibroblast, debate exists about how these components combine to endow a cell with its form and mechanical function. We present an analysis of mechanical characterization experiments performed on bio-artificial tissue constructs, which we believe serve as a more realistic testing environment than two-dimensional cell culture. These model tissues capture many features of real tissues with the advantage that they can be engineered to model different physiological and pathological characteristics. We study here a model tissue consisting of reconstituted type I collagen and varying concentrations of activated contractile fibroblasts that is relevant to modelling different stages of wound healing. We applied this system to assess how cell and extracellular matrix (ECM) mechanics vary with cell concentration. Short-term and long-term moduli of the ECM were estimated through analytical and numerical analysis of two-phase elastic solids containing cell-shaped voids. The relative properties of cells were then deduced from the results of numerical analyses of two-phase elastic solids containing mechanically isotropic cells of varying modulus. With increasing cell concentration, the short-term and long-term tangent moduli of the reconstituted collagen ECM increased sharply from a baseline value, while those of the cells decreased monotonically. PMID:20047943
AFM Investigation of Liquid-Filled Polymer Microcapsules Elasticity.
Sarrazin, Baptiste; Tsapis, Nicolas; Mousnier, Ludivine; Taulier, Nicolas; Urbach, Wladimir; Guenoun, Patrick
2016-05-10
Elasticity of polymer microcapsules (MCs) filled with a liquid fluorinated core is studied by atomic force microscopy (AFM). Accurately characterized spherical tips are employed to obtain the Young's moduli of MCs having four different shell thicknesses. We show that those moduli are effective ones because the samples are composites. The strong decrease of the effective MC elasticity (from 3.0 to 0.1 GPa) as the shell thickness decreases (from 200 to 10 nm) is analyzed using a novel numerical approach. This model describes the evolution of the elasticity of a coated half-space according to the contact radius, the thickness of the film, and the elastic moduli of bulk materials. This numerical model is consistent with the experimental data and allows simulating the elastic behavior of MCs at high frequencies (5 MHz). While the quasi-static elasticity of the MCs is found to be very dependent on the shell thickness, the high frequency (5 MHz) elastic behavior of the core leads to a stable behavior of the MCs (from 2.5 to 3 GPa according to the shell thickness). Finally, the effect of thermal annealing on the MCs elasticity is investigated. The Young's modulus is found to decrease because of the reduction of the shell thickness due to the loss of the polymer. PMID:27058449
Stretch Moduli of Ribonucleotide Embedded Short DNAs
NASA Astrophysics Data System (ADS)
Chiu, Hsiang-Chih; Koh, Kyung Duk; Riedo, Elisa; Storici, Francesca
2013-03-01
Understanding the mechanical properties of DNA is essential to comprehending the dynamics of many cellular functions. DNA deformations are involved in many mechanisms when genetic information needs to be stored and used. In addition, recent studies have found that Ribonucleotides (rNMPs) are among the most common non-standard nucleotides present in DNA. The presences of rNMPs in DNA might cause mutation, fragility or genotoxicity of chromosome but how they influence the structure and mechanical properties of DNA remains unclear. By means of Atomic Force Microscopy (AFM) based single molecule spectroscopy, we measure the stretch moduli of double stranded DNAs (dsDNA) with 30 base pairs and 5 equally embedded rNMPs. The dsDNAs are anchored on gold substrate via thiol chemistry, while the AFM tip is used to pick up and stretch the dsDNA from its free end through biotin-streptavidin bonding. Our preliminary results indicate that the inclusion of rNMPs in dsDNA might significantly change its stretch modulus, which might be important in some biological processes.
Explicitly broken supersymmetry with exactly massless moduli
NASA Astrophysics Data System (ADS)
Dong, Xi; Freedman, Daniel Z.; Zhao, Yue
2016-06-01
The AdS/CFT correspondence is applied to an analogue of the little hierarchy problem in three-dimensional supersymmetric theories. The bulk is governed by a super-gravity theory in which a U(1) × U(1) R-symmetry is gauged by Chern-Simons fields. The bulk theory is deformed by a boundary term quadratic in the gauge fields. It breaks SUSY completely and sources an exactly marginal operator in the dual CFT. SUSY breaking is communicated by gauge interactions to bulk scalar fields and their spinor superpartners. The bulk-to-boundary propagator of the Chern-Simons fields is a total derivative with respect to the bulk coordinates. Integration by parts and the Ward identity permit evaluation of SUSY breaking effects to all orders in the strength of the deformation. The R-charges of scalars and spinors differ so large SUSY breaking mass shifts are generated. Masses of R-neutral particles such as scalar moduli are not shifted to any order in the deformation strength, despite the fact that they may couple to R-charged fields running in loops. We also obtain a universal deformation formula for correlation functions under an exactly marginal deformation by a product of holomorphic and anti-holomorphic U(1) currents.
Anoop Krishnan, N. M. Ghosh, Debraj
2014-02-14
The elastic behavior of single-walled boron nitride nanotubes is studied under axial and torsional loading. Molecular dynamics simulation is carried out with a tersoff potential for modeling the interatomic interactions. Different chiral configurations with similar diameter are considered to study the effect of chirality on the elastic and shear moduli. Furthermore, the effects of tube length on elastic modulus are also studied by considering different aspects ratios. It is observed that both elastic and shear moduli depend upon the chirality of a nanotube. For aspect ratios less than 15, the elastic modulus reduces monotonically with an increase in the chiral angle. For chiral nanotubes, the torsional response shows a dependence on the direction of loading. The difference between the shear moduli against and along the chiral twist directions is maximum for chiral angle of 15°, and zero for zigzag (0°) and armchair (30°) configurations.
Elastic Anomalies in Orbital-Degenerate Frustrated Spinel CoV2O4
NASA Astrophysics Data System (ADS)
Watanabe, Tadataka; Yamada, Shogo; Koborinai, Rui; Katsufuji, Takuro
Ultrasound velocity measurements were performed on a single crystal of the orbital-degenerate frustrated spinel CoV2O4 in all the symmetrically-independent elastic moduli of the cubic crystal. The measurements of temperature dependence of the elastic moduli observed discontinuous elastic anomalies due to a ferrimagnetic transition at TC = 165 K and another phase transition at T* = 50 K. Additionally, the measurements observed anomalous temperature dependence of the elastic moduli, specifically, non-monotonic temperature dependence in the magnetically-ordered phase below TC, and magnetic-field-sensitive elastic softening with decreasing temperature in the paramagnetic phase above TC. These anomalous temperature variations below and above TC should be driven by the coupling of lattice to magnetic excitations.
Computation of elastic properties of 3D digital cores from the Longmaxi shale
NASA Astrophysics Data System (ADS)
Zhang, Wen-Hui; Fu, Li-Yun; Zhang, Yan; Jin, Wei-Jun
2016-06-01
The dependence of elastic moduli of shales on the mineralogy and microstructure of shales is important for the prediction of sweet spots and shale gas production. Based on 3D digital images of the microstructure of Longmaxi black shale samples using X-ray CT, we built detailed 3D digital images of cores with porosity properties and mineral contents. Next, we used finite-element (FE) methods to derive the elastic properties of the samples. The FE method can accurately model the shale mineralogy. Particular attention is paid to the derived elastic properties and their dependence on porosity and kerogen. The elastic moduli generally decrease with increasing porosity and kerogen, and there is a critical porosity (0.75) and kerogen content (ca. ≤3%) over which the elastic moduli decrease rapidly and slowly, respectively. The derived elastic moduli of gas- and oil-saturated digital cores differ little probably because of the low porosity (4.5%) of the Longmaxi black shale. Clearly, the numerical experiments demonstrated the feasibility of combining microstructure images of shale samples with elastic moduli calculations to predict shale properties.
Moduli inflation in five-dimensional supergravity models
Abe, Hiroyuki; Otsuka, Hajime E-mail: hajime.13.gologo@akane.waseda.jp
2014-11-01
We propose a simple but effective mechanism to realize an inflationary early universe consistent with the observed WMAP, Planck and/or BICEP2 data, which would be incorporated in various supersymmetric models of elementary particles constructed in the (effective) five-dimensional spacetime. In our scenario, the inflaton field is identified with one of the moduli appearing when the fifth direction is compactified, and a successful cosmological inflation without the so-called η problem can be achieved by a very simple moduli stabilization potential. We also discuss the related particle cosmology during and (just) after the inflation, such as the (no) cosmological moduli problem.
Moduli stabilization and flavor structure in 5D SUGRA with multi moduli
Abe, Hiroyuki; Sakamura, Yutaka
2008-11-23
We investigate 5-dimensional supergravity on S{sup 1}/Z{sub 2} with a physical Z{sub 2}-odd vector multiplet, which yields an additional modulus other than the radion. We find additional terms in the 4-dimensional effective theory that are peculiar to the multi moduli case. Such terms can make the soft masses are non-tachyonic and almost flavor-universal at tree-level, in contrast to the single modulus case. This provides a new possibility to solve the SUSY flavor problem.
Moduli spaces of cold holographic matter
NASA Astrophysics Data System (ADS)
Ammon, Martin; Jensen, Kristan; Kim, Keun-Young; Laia, João N.; O'Bannon, Andy
2012-11-01
We use holography to study (3 + 1)-dimensional {N}=4 supersymmetric Yang-Mills theory with gauge group SU( N c ), in the large- N c and large-coupling limits, coupled to a single massless ( n + 1)-dimensional hypermultiplet in the fundamental representation of SU( N c ), with n = 3, 2, 1. In particular, we study zero-temperature states with a nonzero baryon number charge density, which we call holographic matter. We demonstrate that a moduli space of such states exists in these theories, specifically a Higgs branch parameterized by the expectation values of scalar operators bilinear in the hypermultiplet scalars. At a generic point on the Higgs branch, the R-symmetry and gauge group are spontaneously broken to subgroups. Our holographic calculation consists of introducing a single probe D p-brane into AdS 5 × {{{S}}^5} , with p = 2 n + 1 = 7, 5, 3, introducing an electric flux of the D p-brane worldvolume U(1) gauge field, and then obtaining explicit solutions for the worldvolume fields dual to the scalar operators that parameterize the Higgs branch. In all three cases, we can express these solutions as non-singular self-dual U(1) instantons in a four-dimensional space with a metric determined by the electric flux. We speculate on the possibility that the existence of Higgs branches may point the way to a counting of the microstates producing a nonzero entropy in holographic matter. Additionally, we speculate on the possible classification of zero-temperature, nonzero-density states described holographically by probe D-branes with worldvolume electric flux.
Local structure controls the nonaffine shear and bulk moduli of disordered solids.
Schlegel, M; Brujic, J; Terentjev, E M; Zaccone, A
2016-01-01
Paradigmatic model systems, which are used to study the mechanical response of matter, are random networks of point-atoms, random sphere packings, or simple crystal lattices; all of these models assume central-force interactions between particles/atoms. Each of these models differs in the spatial arrangement and the correlations among particles. In turn, this is reflected in the widely different behaviours of the shear (G) and compression (K) elastic moduli. The relation between the macroscopic elasticity as encoded in G, K and their ratio, and the microscopic lattice structure/order, is not understood. We provide a quantitative analytical connection between the local orientational order and the elasticity in model amorphous solids with different internal microstructure, focusing on the two opposite limits of packings (strong excluded-volume) and networks (no excluded-volume). The theory predicts that, in packings, the local orientational order due to excluded-volume causes less nonaffinity (less softness or larger stiffness) under compression than under shear. This leads to lower values of G/K, a well-documented phenomenon which was lacking a microscopic explanation. The theory also provides an excellent one-parameter description of the elasticity of compressed emulsions in comparison with experimental data over a broad range of packing fractions.
Local structure controls the nonaffine shear and bulk moduli of disordered solids
NASA Astrophysics Data System (ADS)
Schlegel, M.; Brujic, J.; Terentjev, E. M.; Zaccone, A.
2016-01-01
Paradigmatic model systems, which are used to study the mechanical response of matter, are random networks of point-atoms, random sphere packings, or simple crystal lattices; all of these models assume central-force interactions between particles/atoms. Each of these models differs in the spatial arrangement and the correlations among particles. In turn, this is reflected in the widely different behaviours of the shear (G) and compression (K) elastic moduli. The relation between the macroscopic elasticity as encoded in G, K and their ratio, and the microscopic lattice structure/order, is not understood. We provide a quantitative analytical connection between the local orientational order and the elasticity in model amorphous solids with different internal microstructure, focusing on the two opposite limits of packings (strong excluded-volume) and networks (no excluded-volume). The theory predicts that, in packings, the local orientational order due to excluded-volume causes less nonaffinity (less softness or larger stiffness) under compression than under shear. This leads to lower values of G/K, a well-documented phenomenon which was lacking a microscopic explanation. The theory also provides an excellent one-parameter description of the elasticity of compressed emulsions in comparison with experimental data over a broad range of packing fractions.
Bounds on scalar masses in theories of moduli stabilization
NASA Astrophysics Data System (ADS)
Acharya, Bobby Samir; Kane, Gordon; Kuflik, Eric
2014-04-01
In recent years it has been realized that pre-BBN decays of moduli can be a significant source of dark matter production, giving a "nonthermal WIMP miracle" and substantially reduced fine-tuning in cosmological axion physics. We study moduli masses and sharpen the claim that moduli dominated the pre-BBN universe. We conjecture that in any string theory with stabilized moduli there will be at least one modulus field whose mass is of order (or less than) the gravitino mass. Cosmology then generically requires the gravitino mass not be less than about 30 TeV and the cosmological history of the universe is nonthermal prior to BBN. Stable LSP's produced in these decays can account for the observed dark matter if they are "wino-like." We briefly consider implications for the LHC, rare decays, and dark matter direct detection and point out that these results could prove challenging for models attempting to realize gauge mediation in string theory.
Moduli spaces of sheaves on K3 surfaces
NASA Astrophysics Data System (ADS)
Sawon, Justin
2016-11-01
In this survey article we describe moduli spaces of simple, stable, and semistable sheaves on K3 surfaces, following the work of Mukai, O'Grady, Huybrechts, Yoshioka, and others. We also describe some recent developments, including applications to the study of Chow rings of K3 surfaces, determination of the ample and nef cones of irreducible holomorphic symplectic manifolds, and moduli spaces of Bridgeland stable complexes of sheaves.
The Kodaira dimension of the moduli of K3 surfaces
NASA Astrophysics Data System (ADS)
Gritsenko, V. A.; Hulek, K.; Sankaran, G. K.
2007-05-01
The moduli space of polarised K3 surfaces of degree 2d is a quasi-projective variety of dimension 19. For general d very little has been known about the Kodaira dimension of these varieties. In this paper we present an almost complete solution to this problem. Our main result says that this moduli space is of general type for d>61 and for d=46,50,54,58,60.
Stabilizing all geometric moduli in heterotic Calabi-Yau vacua
Anderson, Lara B.; Ovrut, Burt; Gray, James; Lukas, Andre
2011-05-15
We propose a scenario to stabilize all geometric moduli--that is, the complex structure, Kaehler moduli, and the dilaton--in smooth heterotic Calabi-Yau compactifications without Neveu-Schwarz three-form flux. This is accomplished using the gauge bundle required in any heterotic compactification, whose perturbative effects on the moduli are combined with nonperturbative corrections. We argue that, for appropriate gauge bundles, all complex structure and a large number of other moduli can be perturbatively stabilized--in the most restrictive case, leaving only one combination of Kaehler moduli and the dilaton as a flat direction. At this stage, the remaining moduli space consists of Minkowski vacua. That is, the perturbative superpotential vanishes in the vacuum without the necessity to fine-tune flux. Finally, we incorporate nonperturbative effects such as gaugino condensation and/or instantons. These are strongly constrained by the anomalous U(1) symmetries, which arise from the required bundle constructions. We present a specific example, with a consistent choice of nonperturbative effects, where all remaining flat directions are stabilized in an anti-de Sitter vacuum.
Stabilizing all geometric moduli in heterotic Calabi-Yau vacua
Anderson, Lara B.; Gray, James; Lukas, Andre; Ovrut, Burt
2011-05-27
We propose a scenario to stabilize all geometric moduli - that is, the complex structure, Kähler moduli and the dilaton - in smooth heterotic Calabi-Yau compactifications without Neveu-Schwarz three-form flux. This is accomplished using the gauge bundle required in any heterotic compactification, whose perturbative effects on the moduli are combined with non-perturbative corrections. We argue that, for appropriate gauge bundles, all complex structure and a large number of other moduli can be perturbatively stabilized - in the most restrictive case, leaving only one combination of Kähler moduli and the dilaton as a flat direction. At this stage, the remaining moduli space consists of Minkowski vacua. That is, the perturbative superpotential vanishes in the vacuum without the necessity to fine-tune flux. Finally, we incorporate non-perturbative effects such as gaugino condensation and/or instantons. These are strongly constrained by the anomalous U(1) symmetries which arise from the required bundle constructions. We present a specific example, with a consistent choice of non-perturbative effects, where all remaining flat directions are stabilized in an AdS vacuum.
Introduction to physical properties and elasticity models: Chapter 20
Dvorkin, Jack; Helgerud, Michael B.; Waite, William F.; Kirby, Stephen H.; Nur, Amos
2003-01-01
Estimating the in situ methane hydrate volume from seismic surveys requires knowledge of the rock physics relations between wave speeds and elastic moduli in hydrate/sediment mixtures. The elastic moduli of hydrate/sediment mixtures depend on the elastic properties of the individual sedimentary particles and the manner in which they are arranged. In this chapter, we present some rock physics data currently available from literature. The unreferenced values in Table I were not measured directly, but were derived from other values in Tables I and II using standard relationships between elastic properties for homogeneous, isotropic material. These derivations allow us to extend the list of physical property estimates, but at the expense of introducing uncertainties due to combining property values measured under different physical conditions. This is most apparent in the case of structure II (sII) hydrate for which very few physical properties have been measured under identical conditions.
Stabilized fiber-reinforced pavement base course with recycled aggregate
NASA Astrophysics Data System (ADS)
Sobhan, Khaled
This study evaluates the benefits to be gained by using a composite highway base course material consisting of recycled crushed concrete aggregate, portland cement, fly ash, and a modest amount of reinforcing fibers. The primary objectives of this research were to (a) quantify the improvement that is obtained by adding fibers to a lean concrete composite (made from recycled aggregate and low quantities of Portland cement and/or fly ash), (b) evaluate the mechanical behavior of such a composite base course material under both static and repeated loads, and (c) utilize the laboratory-determined properties with a mechanistic design method to assess the potential advantages. The split tensile strength of a stabilized recycled aggregate base course material was found to be exponentially related to the compacted dry density of the mix. A lean mix containing 4% cement and 4% fly ash (by weight) develops sufficient unconfined compressive, split tensile, and flexural strengths to be used as a high quality stabilized base course. The addition of 4% (by weight) of hooked-end steel fibers significantly enhances the post-peak load-deformation response of the composite in both indirect tension and static flexure. The flexural fatigue behavior of the 4% cement-4% fly ash mix is comparable to all commonly used stabilized materials, including regular concrete; the inclusion of 4% hooked-end fibers to this mix significantly improves its resistance to fatigue failure. The resilient moduli of stabilized recycled aggregate in flexure are comparable to the values obtained for traditional soil-cement mixes. In general, the fibers are effective in retarding the rate of fatigue damage accumulation, which is quantified in terms of a damage index defined by an energy-based approach. The thickness design curves for a stabilized recycled aggregate base course, as developed by using an elastic layer approach, is shown to be in close agreement with a theoretical model (based on Westergaard
Goda, Ibrahim; Ganghoffer, Jean-François
2015-11-01
The purpose of this paper is to develop a homogeneous, orthotropic couple-stress continuum model as a substitute of the 3D periodic heterogeneous cellular solid model of vertebral trabecular bone. Vertebral trabecular bone is modeled as a porous material with an idealized periodic structure made of 3D open cubic cells, which is effectively orthotropic. The chosen architecture is based on studies of samples taken from the central part of vertebral bodies. The effective properties are obtained based on the response of the representative volume element under prescribed boundary conditions. Mixed boundary conditions comprising both traction and displacement boundary conditions are applied on the structure boundaries. In this contribution, the effective mechanical constants of the effective couple-stress continuum are deduced by an equivalent strain energy method. The characteristic lengths for bending and torsion are identified from the resulting homogenized orthotropic moduli. We conduct this study computationally using a finite element approach. Vertebral trabecular bone is modeled either as a cellular solid or as a two-phase material consisting of bone tissue (stiff phase) forming a trabecular network, and a surrounding soft tissue referring to the bone marrow present in the pores. Both the bone tissue forming the network and the pores are assumed to be homogeneous linear elastic, and isotropic media. The scale effects on the predicted couple stress moduli of these networks are investigated by varying the size of the bone specimens over which the boundary conditions are applied. The analysis using mixed boundary conditions gives results that are independent of unit cell size when computing the first couple stress tensor, while it is dependent on the cell size as to the second couple stress tensor moduli. This study provides overall guidance on how the size of the trabecular specimen influence couple stresses elastic moduli of cellular materials, with focus on bones
Wang, Huabin; Zhou, Xingfei; An, Hongjie; Sun, Jielin; Zhang, Yi; Hu, Jun
2008-08-01
Individual xanthan molecules were prepared on highly oriented pyrolytic graphite surface with a modified spin-casting technique. Then the radial compression elasticity of single xanthan molecules was investigated by vibrating scanning polarization force microscopy. The effective elastic moduli of xanthan molecules are estimated to be approximately 20-100 MPa under loads below 0.4 nN. PMID:19049142
Price and Income Elasticities of Iranian Exports
NASA Astrophysics Data System (ADS)
Atrkar Roshan, Sedigheh
This study investigates the export demand elasticities at the aggregate and disaggregated levels over the period 1977 to 2001 for Iran. By utilizing an export demand model and using time series techniques that account for the nonstationarity in the data, the price and income elasticities of demand are estimated by commodity class. As the elasticities of demand for various categories of exports are different, while they are crucial for policy determination. Based upon the estimated results, price and income elasticities are almost similar to those obtained in earlier studies in the case of developing countries. The main findings of this paper demonstrate that, price elasticities are smaller than -1 for all exports categories, whereas the income elasticities are found to be greater than one. The results also suggested, the income elasticities of industrial goods are higher compared to other export categories, while the lower elasticities are found in primary exports. The price and income elasticity estimates have also good statistical properties.
Complete Elastic Tensor through the First-Order Transformation in U2Rh3Si5
NASA Astrophysics Data System (ADS)
Leisure, R. G.; Kern, S.; Drymiotis, F. R.; Ledbetter, H.; Migliori, A.; Mydosh, J. A.
2005-08-01
The complete elastic tensor of U2Rh3Si5 has been determined over the temperature range of 5 300 K, including the dramatic first-order transition to an antiferromagnetic state at 25.5 K. Sharp upward steps in the elastic moduli as the temperature is decreased through the transition reveal the first-order nature of the phase change. In the antiferromagnetic state the temperature dependence of the elastic moduli scales with the square of the ordered moment on the uranium ion, demonstrating strong spin-lattice coupling. The temperature dependence of the moduli well above the transition indicates coupling of the ultrasonic waves to the crystal electric field levels of the uranium ion where the lowest state is a singlet. The elastic constant data suggest that the first-order phase change is magnetically driven by a bootstrap mechanism involving the ground state singlet and a magnetically active crystal electric field level.
NASA Astrophysics Data System (ADS)
Patrício, P.; Almeida, P. L.; Portela, R.; Sobral, R. G.; Grilo, I. R.; Cidade, T.; Leal, C. R.
2014-08-01
The activity of growing living bacteria was investigated using real-time and in situ rheology—in stationary and oscillatory shear. Two different strains of the human pathogen Staphylococcus aureus—strain COL and its isogenic cell wall autolysis mutant, RUSAL9—were considered in this work. For low bacteria density, strain COL forms small clusters, while the mutant, presenting deficient cell separation, forms irregular larger aggregates. In the early stages of growth, when subjected to a stationary shear, the viscosity of the cultures of both strains increases with the population of cells. As the bacteria reach the exponential phase of growth, the viscosity of the cultures of the two strains follows different and rich behaviors, with no counterpart in the optical density or in the population's colony-forming units measurements. While the viscosity of strain COL culture keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the population stabilizes, the viscosity of the mutant strain culture decreases steeply, still in the exponential phase, remains constant for some time, and increases again, reaching a constant plateau at a maximum value for the late phase of growth. These complex viscoelastic behaviors, which were observed to be shear-stress-dependent, are a consequence of two coupled effects: the cell density continuous increase and its changing interacting properties. The viscous and elastic moduli of strain COL culture, obtained with oscillatory shear, exhibit power-law behaviors whose exponents are dependent on the bacteria growth stage. The viscous and elastic moduli of the mutant culture have complex behaviors, emerging from the different relaxation times that are associated with the large molecules of the medium and the self-organized structures of bacteria. Nevertheless, these behaviors reflect the bacteria growth stage.
Stabilizing all geometric moduli in heterotic Calabi-Yau vacua
Anderson, Lara B.; Gray, James; Lukas, Andre; Ovrut, Burt
2011-05-27
We propose a scenario to stabilize all geometric moduli - that is, the complex structure, Kähler moduli and the dilaton - in smooth heterotic Calabi-Yau compactifications without Neveu-Schwarz three-form flux. This is accomplished using the gauge bundle required in any heterotic compactification, whose perturbative effects on the moduli are combined with non-perturbative corrections. We argue that, for appropriate gauge bundles, all complex structure and a large number of other moduli can be perturbatively stabilized - in the most restrictive case, leaving only one combination of Kähler moduli and the dilaton as a flat direction. At this stage, the remaining modulimore » space consists of Minkowski vacua. That is, the perturbative superpotential vanishes in the vacuum without the necessity to fine-tune flux. Finally, we incorporate non-perturbative effects such as gaugino condensation and/or instantons. These are strongly constrained by the anomalous U(1) symmetries which arise from the required bundle constructions. We present a specific example, with a consistent choice of non-perturbative effects, where all remaining flat directions are stabilized in an AdS vacuum.« less
Moduli vacuum misalignment and precise predictions in string inflation
NASA Astrophysics Data System (ADS)
Cicoli, Michele; Dutta, Koushik; Maharana, Anshuman; Quevedo, Fernando
2016-08-01
The predictions for all the cosmological observables of any inflationary model depend on the number of e-foldings which is sensitive to the post-inflationary history of the universe. In string models the generic presence of light moduli leads to a late-time period of matter domination which lowers the required number of e-foldings and, in turn, modifies the exact predictions of any inflationary model. In this paper we compute exactly the shift of the number of e-foldings in Kähler moduli inflation which is determined by the magnitude of the moduli initial displacement caused by vacuum misalignment and the moduli decay rates. We find that the preferred number of e-foldings gets reduced from 50 to 45, causing a modification of the spectral index at the percent level. Our results illustrate the importance of understanding the full post-inflationary evolution of the universe in order to derive precise predictions in string inflation. To perform this task it is crucial to work in a setting where there is good control over moduli stabilisation.
Universal elasticity and fluctuations of nematic gels.
Xing, Xiangjun; Radzihovsky, Leo
2003-04-25
We study elasticity of spontaneously orientationally ordered amorphous solids, characterized by a vanishing transverse shear modulus, as realized by nematic elastomers and gels. We show that local heterogeneities and elastic nonlinearities conspire to lead to anomalous nonlocal universal elasticity controlled by a nontrivial infrared fixed point. Namely, such solids are characterized by universal shear and bending moduli that, respectively, vanish and diverge at long scales, are universally incompressible, and exhibit a universal negative Poisson ratio and a non-Hookean elasticity down to arbitrarily low strains. Based on expansion about five dimensions, we argue that the nematic order is stable to thermal fluctuation and local heterogeneities down to d(lc)<3. PMID:12732018
Universal elasticity and fluctuations of nematic gels
NASA Astrophysics Data System (ADS)
Xing, Xiangjun; Radzihovsky, Leo
2003-03-01
We study elasticity of spontaneously orientationally-ordered amorphous solids, characterized by a vanishing transverse shear modulus, as realized for example by nematic elastomers and gels. We show that local heterogeneities and elastic nonlinearities conspire to lead to anomalous nonlocal universal elasticity controlled by a nontrivial infared fixed point. Namely, at long scales, such solids are characterized by universal shear and bending moduli that, respectively, vanish and diverge at long scales, are universally incompressible and exhibit universal negative Poisson ratio and a non-Hookean elasticity down to arbitrarily low strains. Based on expansion about five dimensions, we argue that the nematic order is stable to thermal fluctuation and local hetergeneities down to d_lc < 3.
NASA Astrophysics Data System (ADS)
Blake, O. O.; Faulkner, D. R.
2016-04-01
Elastic properties are key parameters during the deformation of rocks. They can be measured statically or dynamically, but the two measurements are often different. In this study, the static and dynamic bulk moduli (Kstatic and Kdynamic) were measured at varying effective stress for dry and fluid-saturated Westerly granite with controlled fracture densities under isotropic and differential stress states. Isotropic fracturing of different densities was induced in samples by thermal treatment to 250, 450, 650, and 850°C. Results show that fluid saturation does not greatly affect static moduli but increases dynamic moduli. Under isotropic loading, high fracture density and/or low effective pressure results in a low Kstatic/Kdynamic ratio. For dry conditions Kstatic/Kdynamic approaches 1 at low fracture densities when the effective pressure is high, consistent with previous studies. Stress-induced anisotropy exists under differential stress state that greatly affects Kstatic compared to Kdynamic. As a result, the Kstatic/Kdynamic ratio is higher than that for the isotropic stress state and approaches 1 with increasing axial loading. The effect of stress-induced anisotropy increases with increasing fracture density. A key omission in previous studies comparing static and dynamic properties is that anisotropy has not been considered. The standard methods for measuring static elastic properties, such as Poisson's ratio, Young's and shear modulus, involve subjecting the sample to a differential stress state that promotes anisotropy. Our results show that stress-induced anisotropy resulting from differential stress state is a major contributor to the difference between static and dynamic elasticity and is dominant with high fracture density.
Linear elastic behavior of dry soap foams
Kraynik, A.M.; Reinelt, D.A.
1996-08-10
Linear elastic constants are computed for three dry foams that have crystal symmetry, bubbles with equal volume V, and films with uniform surface tension T. The Kelvin, Williams, and Weaire-Phelan foams contain one, two, and eight bubbles in the unit cell, respectively. All three foams have 14-sided bubbles, but these tetrakaidecahedra have different topology; the Weaire-Phelan foam also contains pentagonal dodecahedra. In addition to the bulk modulus for volume compression, the authors calculate two shear moduli for the Kelvin and Weaire-Phelan foams, which have cubic symmetry, and four shear moduli for the Williams foam, which has tetragonal symmetry. The Williams foam has five elastic constants, not six, because the stress remains isotropic for uniform expansion; this is not guaranteed by symmetry alone. The two shear moduli for the Weaire-Phelan foam differ by less than 5%. The other two foams exhibit much greater elastic anisotropy; their shear moduli differ by a factor of 2. An effective isotropic shear modulus {bar G}, which represents the response averaged over all orientations, is evaluated for each foam. Scaled by T/V{sup 1/3}, {bar G} is 0.8070, 0.7955, and 0.8684 for the Kelvin, Williams, and Weaire-Phelan foams, respectively. When extrapolated to the dry limit, the shear modulus data of Princen and Kiss (for concentrated oil-in-water emulsions with polydisperse drop-size distributions) fall within the range of the calculations. The Surface Evolver program, developed by Brakke, was used to compute minimal surfaces for the dry foams. Also reported for each undeformed foam are various geometric constants relating to interfacial energy density, cell edge length, and bubble pressure.
NASA Astrophysics Data System (ADS)
Ziółkowski, Andrzej
2016-09-01
An apparatus of micromechanics is used to isolate the key ingredients entering macroscopic Gibbs free energy function of a shape memory alloy (SMA) material. A new self-equilibrated eigenstrains influence moduli (SEIM) method is developed for consistent estimation of effective (macroscopic) thermostatic properties of solid materials, which in microscale can be regarded as amalgams of n-phase linear thermoelastic component materials with eigenstrains. The SEIM satisfy the self-consistency conditions, following from elastic reciprocity (Betti) theorem. The method allowed expressing macroscopic coherency energy and elastic complementary energy terms present in the general form of macroscopic Gibbs free energy of SMA materials in the form of semilinear and semiquadratic functions of the phase composition. Consistent SEIM estimates of elastic complementary energy, coherency energy and phase transformation strains corresponding to classical Reuss and Voigt conjectures are explicitly specified. The Voigt explicit relations served as inspiration for working out an original engineering practice-oriented semiexperimental SEIM estimates. They are especially conveniently applicable for an isotropic aggregate (composite) composed of a mixture of n isotropic phases. Using experimental data for NiTi alloy and adopting conjecture that it can be treated as an isotropic aggregate of two isotropic phases, it is shown that the NiTi coherency energy and macroscopic phase strain are practically not influenced by the difference in values of austenite and martensite elastic constants. It is shown that existence of nonzero fluctuating part of phase microeigenstrains field is responsible for building up of so-called stored energy of coherency, which is accumulated in pure martensitic phase after full completion of phase transition. Experimental data for NiTi alloy show that the stored coherency energy cannot be neglected as it considerably influences the characteristic phase transition
Structural, elastic, electronic and optical properties of KAlQ2 (Q = Se, Te): A DFT study
NASA Astrophysics Data System (ADS)
Benmakhlouf, A.; Bentabet, A.; Bouhemadou, A.; Maabed, S.; Khenata, R.; Bin-Omran, S.
2015-10-01
First-principles calculations in the framework of density functional theory have been conducted to explore the structural, elastic, electronic and optical properties of two layered ternary compounds chalcogenides of aluminum KAlSe2 and KAlTe2. We have calculated all of the equilibrium structural parameters; the lattice parameters (a, b and c), angle β and twenty three internal atomic coordinates. The obtained results are in excellent agreement with the available experimental data. We have predicted the single-crystal elastic constants Cij of the title materials using stress-strain approach and then derived the elastic moduli of the polycrystalline aggregates and related properties via the Voigt-Reuss-Hill approximations. The band structure and density of states diagrams have been calculated and analyzed. Both compounds demonstrate semiconducting behavior with direct band gap. The linear optical properties, namely the frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity and energy-loss function, have been calculated and analyzed in a wide energy range up to 20 eV.
Cosmological moduli problem, supersymmetry breaking, and stability in postinflationary cosmology
NASA Astrophysics Data System (ADS)
Banks, T.; Berkooz, M.; Steinhardt, P. J.
1995-07-01
We review scenarios that have been proposed to solve the cosmological problem caused by moduli in string theory, the postmodern Polonyi problem (PPP). In particular, we discuss the difficulties encountered by the apparently ``trivial'' solution of this problem, in which moduli masses are assumed to arise from nonperturbative, SUSY-preserving, dynamics at a scale higher than that of SUSY breaking. This suggests a powerful cosmological vacuum selection principle in superstring theory. However, we argue that if one eschews the possibility of cancellations between different exponentials of the inverse string coupling, the mechanism described above cannot stabilize the dilaton. Thus, even if supersymmetric dynamics gives mass to the other moduli in string theory, the dilaton mass must be generated by SUSY breaking, and dilaton domination of the energy density of the Universe cannot be avoided. We conclude that the only proposal for solving the PPP that works is the intermediate scale inflation scenario of Randall and Thomas. However, we point out that all extant models have ignored unavoidably large inhomogeneities in the cosmological moduli density at very early times, and speculate that the effects associated with nonlinear gravitational collapse of these inhomogeneities may serve as an efficient mechanism for converting moduli into ordinary matter. As an important by-product of this investigation we show that in a postinflationary universe minima of the effective potential with a negative cosmological constant are not stationary points of the classical equations of scalar field cosmology. Instead, such points lead to catastrophic gravitational collapse of that part of the Universe which is attracted to them. Thus postinflationary cosmology dynamically chooses non-negative values of the cosmological constant. This implies that supersymmetry must be broken in any sensible inflationary cosmology. We suggest that further study of the cosmology of moduli will lead to
CP violation and moduli stabilization in heterotic models
Giedt, Joel
2002-04-01
The role of moduli stabilization in predictions for CP violation is examined in the context of four-dimensional effective supergravity models obtained from the weakly coupled heterotic string. They point out that while stabilization of compactification moduli has been studied extensively, the determination of background values for other scalar by dynamical means has not been subjected to the same degree of scrutiny. These other complex scalars are important potential sources of CP violation and they show in a simple model how their background values (including complex phases) may be determined from the minimization of the supergravity scalar potential, subject to the constraint of vanishing cosmological constant.
Ultrasonic measurement of the elastic properties of ultra-high performance concrete (UHPC)
NASA Astrophysics Data System (ADS)
Washer, Glenn; Fuchs, Paul; Rezai, Ali; Ghasemi, Hamid
2005-05-01
This paper discusses research to develop ultrasonic methods for materials characterization of an innovative new material known as Reactive Powder Concrete (RPC). Also known as Ultra-high performance concrete (UHPC), this relatively new material has been proposed for the construction of civil structures. UHPC mix designs typically include no aggregates larger than sand, and include steel fibers 0.2 mm in diameter and 12 mm in length. These steel fibers increase the strength and toughness of the UHPC significantly relative to more traditional concretes. Compressive strengths of 200 to 800 MPa have been achieved with UHPC, compared with maximum compressive strength of 50 to 100 MPa for more traditional concrete materials. Young"s modulus of 50 to 60 GPa are common for UHPC. However, the curing methods employed have a significant influence on the strength and modulus of UHPC. This paper reports on the development of ultrasonic methods for monitoring the elastic properties of UHPC under a series of curing scenarios. Ultrasonic velocity measurements are used to estimate the bulk elastic modulus of UHPC and results are compared with traditional, destructive methods. Measurements of shear moduli and Poisson's ratio based on ultrasonic velocity are also reported. The potential for the development of quality control techniques for the future implementation of UHPC is discussed.
Tepordei, V.V.
1995-01-01
Part of the 1994 Industrial Minerals Review. The production, consumption, and applications of construction aggregates are reviewed. In 1994, the production of construction aggregates, which includes crushed stone and construction sand and gravel combined, increased 7.7 percent to 2.14 Gt compared with the previous year. These record production levels are mostly a result of funding for highway construction work provided by the Intermodal Surface Transportation Efficiency Act of 1991. Demand is expected to increase for construction aggregates in 1995.
Mesoscale elastic properties of marine sponge spicules.
Zhang, Yaqi; Reed, Bryan W; Chung, Frank R; Koski, Kristie J
2016-01-01
Marine sponge spicules are silicate fibers with an unusual combination of fracture toughness and optical light propagation properties due to their micro- and nano-scale hierarchical structure. We present optical measurements of the elastic properties of Tethya aurantia and Euplectella aspergillum marine sponge spicules using non-invasive Brillouin and Raman laser light scattering, thus probing the hierarchical structure on two very different scales. On the scale of single bonds, as probed by Raman scattering, the spicules resemble a combination of pure silica and mixed organic content. On the mesoscopic scale probed by Brillouin scattering, we show that while some properties (Young's moduli, shear moduli, one of the anisotropic Poisson ratios and refractive index) are nearly the same as those of artificial optical fiber, other properties (uniaxial moduli, bulk modulus and a distinctive anisotropic Poisson ratio) are significantly smaller. Thus this natural composite of largely isotropic materials yields anisotropic elastic properties on the mesoscale. We show that the spicules' optical waveguide properties lead to pronounced spontaneous Brillouin backscattering, a process related to the stimulated Brillouin backscattering process well known in artificial glass fibers. These measurements provide a clearer picture of the interplay of flexibility, strength, and material microstructure for future functional biomimicry.
Mesoscale elastic properties of marine sponge spicules.
Zhang, Yaqi; Reed, Bryan W; Chung, Frank R; Koski, Kristie J
2016-01-01
Marine sponge spicules are silicate fibers with an unusual combination of fracture toughness and optical light propagation properties due to their micro- and nano-scale hierarchical structure. We present optical measurements of the elastic properties of Tethya aurantia and Euplectella aspergillum marine sponge spicules using non-invasive Brillouin and Raman laser light scattering, thus probing the hierarchical structure on two very different scales. On the scale of single bonds, as probed by Raman scattering, the spicules resemble a combination of pure silica and mixed organic content. On the mesoscopic scale probed by Brillouin scattering, we show that while some properties (Young's moduli, shear moduli, one of the anisotropic Poisson ratios and refractive index) are nearly the same as those of artificial optical fiber, other properties (uniaxial moduli, bulk modulus and a distinctive anisotropic Poisson ratio) are significantly smaller. Thus this natural composite of largely isotropic materials yields anisotropic elastic properties on the mesoscale. We show that the spicules' optical waveguide properties lead to pronounced spontaneous Brillouin backscattering, a process related to the stimulated Brillouin backscattering process well known in artificial glass fibers. These measurements provide a clearer picture of the interplay of flexibility, strength, and material microstructure for future functional biomimicry. PMID:26672719
Elastic behavior of a two-dimensional crystal near melting.
von Grünberg, H H; Keim, P; Zahn, K; Maret, G
2004-12-17
Using positional data from video microscopy, we determine the elastic moduli of two-dimensional colloidal crystals as a function of temperature. The moduli are extracted from the wave-vector-dependent normal-mode spring constants in the limit q-->0 and are compared to the renormalized Young's modulus of the Kosterlitz-Thouless-Halperin-Nelson-Young theory. An essential element of this theory is the universal prediction that Young's modulus must approach 16 pi at the melting temperature. This is indeed observed in our experiment.
On the possibility of large axion moduli spaces
Rudelius, Tom
2015-04-01
We study the diameters of axion moduli spaces, focusing primarily on type IIB compactifications on Calabi-Yau three-folds. In this case, we derive a stringent bound on the diameter in the large volume region of parameter space for Calabi-Yaus with simplicial Kähler cone. This bound can be violated by Calabi-Yaus with non-simplicial Kähler cones, but additional contributions are introduced to the effective action which can restrict the field range accessible to the axions. We perform a statistical analysis of simulated moduli spaces, finding in all cases that these additional contributions restrict the diameter so that these moduli spaces are no more likely to yield successful inflation than those with simplicial Kähler cone or with far fewer axions. Further heuristic arguments for axions in other corners of the duality web suggest that the difficulty observed in [1] of finding an axion decay constant parametrically larger than M{sub p} applies not only to individual axions, but to the diagonals of axion moduli space as well. This observation is shown to follow from the weak gravity conjecture of [2], so it likely applies not only to axions in string theory, but also to axions in any consistent theory of quantum gravity.
Supersymmetry breaking due to moduli stabilization in string theory
NASA Astrophysics Data System (ADS)
Linde, Andrei; Mambrini, Yann; Olive, Keith A.
2012-03-01
We consider the phenomenological consequences of fixing compactification moduli. In the simplest Kachru-Kallosh-Linde-Trivedi constructions, stabilization of internal dimensions is rather soft: weak scale masses for moduli are generated, and are of order mσ˜m3/2. As a consequence one obtains a pattern of soft supersymmetry breaking masses found in gravity and/or anomaly mediated supersymmetry breaking (AMSB) models. These models may lead to destabilization of internal dimensions in the early universe, unless the Hubble constant during inflation is very small. Fortunately, strong stabilization of compactified dimensions can be achieved by a proper choice of the superpotential (e.g., in the Kallosh-Linde model with a racetrack superpotential). This allows for a solution of the cosmological moduli problem and for a successful implementation of inflation in supergravity. We show that strong moduli stabilization leads to a very distinct pattern of soft supersymmetry breaking masses. In general, we find that soft scalar masses remain of order the gravitino mass, while gaugino masses nearly vanish at the tree level; i.e., they are of order m3/22/mσ. Radiative corrections generate contributions to gaugino masses reminiscent of AMSB models and a decoupled spectrum of scalars reminiscent of split supersymmetry. This requires a relatively large gravitino mass [˜O(100)TeV], resolving the cosmological gravitino problem and problems with tachyonic staus in AMSB models.
On the possibility of large axion moduli spaces
Rudelius, Tom
2015-04-28
We study the diameters of axion moduli spaces, focusing primarily on type IIB compactifications on Calabi-Yau three-folds. In this case, we derive a stringent bound on the diameter in the large volume region of parameter space for Calabi-Yaus with simplicial Kähler cone. This bound can be violated by Calabi-Yaus with non-simplicial Kähler cones, but additional contributions are introduced to the effective action which can restrict the field range accessible to the axions. We perform a statistical analysis of simulated moduli spaces, finding in all cases that these additional contributions restrict the diameter so that these moduli spaces are no more likely to yield successful inflation than those with simplicial Kähler cone or with far fewer axions. Further heuristic arguments for axions in other corners of the duality web suggest that the difficulty observed in http://dx.doi.org/10.1088/1475-7516/2003/06/001 of finding an axion decay constant parametrically larger than M{sub p} applies not only to individual axions, but to the diagonals of axion moduli space as well. This observation is shown to follow from the weak gravity conjecture of http://dx.doi.org/10.1088/1126-6708/2007/06/060, so it likely applies not only to axions in string theory, but also to axions in any consistent theory of quantum gravity.
NASA Astrophysics Data System (ADS)
Ettouhami, A. M.; Saunders, Karl; Radzihovsky, L.; Toner, John
2005-06-01
We study the elasticity, fluctuations, and pinning of a putative spontaneous vortex solid in ferromagnetic superconductors. Using a rigorous thermodynamic argument, we show that in the idealized case of vanishing crystalline pinning anisotropy the long-wavelength tilt modulus of such a vortex solid vanishes identically, as guaranteed by the underlying rotational invariance. The vanishing of the tilt modulus means that, to lowest order, the associated tension elasticity is replaced by the softer, curvature elasticity. The effect of this is to make the spontaneous vortex solid qualitatively more susceptible to the disordering effects of thermal fluctuations and random pinning. We study these effects, taking into account the nonlinear elasticity, that, in three dimensions, is important at sufficiently long length scales, and showing that a “columnar elastic glass” phase of vortices results. This phase is controlled by a previously unstudied zero-temperature fixed point, and it is characterized by elastic moduli that have universal strong wave-vector dependence out to arbitrarily long length scales, leading to non-Hookean elasticity. We argue that, although translationally disordered for weak disorder, the columnar elastic glass is stable against the proliferation of dislocations and is, therefore, a topologically ordered elastic glass. As a result, the phenomenology of the spontaneous vortex state of isotropic magnetic superconductors differs qualitatively from a conventional, external-field-induced mixed state. For example, for weak external fields H , the magnetic induction scales universally like B(H)˜B(0)+cHα , with α≈0.72 .
Elastic constants of Transversely Isotropically Porous (TIP) materials
Tuchinskii, L.I.; Kalimova, N.L.
1994-11-01
The authors derive formulas describing the dependence of the elastic characteristics of multicapillary materials on the capillary porosity. The investigated materials are classified as transversely isotropic, and the anisotropy in their properties is the result of the directionality of the capillary pores. Analysis of the dependences obtained has shown that the elasticity moduli of these materials may be calculated using formulas suggested for reinforced materials, in which the elastic constants of the fibers are assumed to be equal to zero. The authors derive a relation between the Poisson`s ratios and the capillary porosity.
Single-Crystal Elasticity of Ettringite at ambient conditions
NASA Astrophysics Data System (ADS)
Speziale, S.; Jiang, F.; Mao, Z.; Monteiro, P. J.; Wenk, H.; Duffy, T. S.; Schilling, F.
2006-12-01
Ettringite, [Ca6Al2 (SO4)3 (OH)12^{.}26H2O] is a natural trigonal sulfate and one of the most relevant crystalline components of Portland cement. It is both a primary crystalline product during cement paste consolidation and a secondary phase which develops during concrete degradation. Even though the understanding of the mechanical properties of cement paste and of consolidated concrete is a longstanding problem of engineering and materials science, we still have a poor knowledge of the physical properties of ettringite. This makes it difficult to develop quantitative models able to predict the behavior and properties of such a complex multi-component system. We have now determined the single-crystal elastic constants of natural ettringite by Brillouin spectroscopy at ambient conditions. Brillouin scattering was measured along 54 different directions from two 2 mm size platelets of approximate orientation (001) and (100) prepared from a large single crystal of ettringite from South Africa. The six non-zero single-crystal elastic constants of this trigonal mineral are: C11 = 35.1(1) GPa, C12 = 21.9(1) GPa, C13 = 20.0(5) GPa, C14 = 0.6(2) GPa, C_{33 = 55(1) GPa, C44 = 11.0(2) GPa. The Hill average of the aggregate bulk and shear modulus are 27.3(9) GPa and 9.9(1) GPa respectively, more than 35 percent smaller than the moduli of gypsum. Ettringite possesses a large elastic anisotropy, with a difference of 50 percent between the Young's modulus along the stiff c- axis and the a- axis. The rigidity in planes containing the c- axis is 40 percent higher than in the basal plane. The pattern of elastic anisotropy in ettringite is directly connected to its crystallographic structure and to its external morphology. In fact, stiff chains of [Al(OH) 6]^{3-} octahedra alternating with triplets of Ca2+ in eight-fold coordination run parallel to the c- axis. Development of secondary fibrous ettringite elongated parallel to c- axis might play a major role as a mechanism for
Moduli effective action in warped brane-world compactifications
NASA Astrophysics Data System (ADS)
Garriga, Jaume; Pujolàs, Oriol; Tanaka, Takahiro
2003-04-01
We consider a class of 5D brane-world solutions with a power-law warp factor a(y)~yq, and bulk dilaton with profile /φ~lny, where /y is the proper distance in the extra dimension. This class includes the heterotic M-theory brane-world of [Phys. Rev. D 59 (1999) 086001, and ] and the Randall-Sundrum (RS) model as a limiting case. In general, there are two moduli fields y+/-, corresponding to the ``positions'' of two branes (which live at the fixed points of an orbifold compactification). Classically, the moduli are massless, due to a scaling symmetry of the action. However, in the absence of supersymmetry, they develop an effective potential at one loop. Local terms proportional to K+/-4, where K+/-=q/y+/- is the local curvature scale at the location of the corresponding brane, are needed in order to remove the divergences in the effective potential. Such terms break the scaling symmetry and hence they may act as stabilizers for the moduli. When the branes are very close to each other, the effective potential induced by massless bulk fields behaves like V~d-4, where /d is the separation between branes. When the branes are widely separated, the potentials for each one of the moduli generically develop a ``Coleman-Weinberg''-type behaviour of the form a4(y+/-)K+/-4ln(K+/-/μ+/-), where μ+/- are renormalization scales. In the RS case, the bulk geometry is AdS and K+/- are equal to a constant, independent of the position of the branes, so these terms do not contribute to the mass of the moduli. However, for generic warp factor, they provide a simple stabilization mechanism. For /q>~10, the observed hierarchy can be naturally generated by this potential, giving the lightest modulus a mass of order m-<~TeV.
NASA Astrophysics Data System (ADS)
Watanabe, Tadataka; Hara, Shigeo; Ikeda, Shin-Ichi; Tomiyasu, Keisuke
2011-07-01
Ultrasound velocity measurements of the orbitally frustrated spinel GeCo2O4 reveal unique elastic anomalies within the antiferromagnetic phase. Temperature dependence of shear moduli exhibits a minimum within the antiferromagnetic phase, suggesting the coupling of shear acoustic phonons to molecular spin-orbit excitations. Magnetic-field dependence of elastic moduli exhibits diplike anomalies, being interpreted as magnetic-field-induced metamagnetic and structural transitions. These elastic anomalies suggest that the survival of geometrical frustration, and the interplay of spin, orbital, and lattice degrees of freedom evoke a set of phenomena in the antiferromagnetic phase.
Zubko, I. Yu. Kochurov, V. I.
2015-10-27
For the aim of the crystal temperature control the computational-statistical approach to studying thermo-mechanical properties for finite sized crystals is presented. The approach is based on the combination of the high-performance computational techniques and statistical analysis of the crystal response on external thermo-mechanical actions for specimens with the statistically small amount of atoms (for instance, nanoparticles). The heat motion of atoms is imitated in the statics approach by including the independent degrees of freedom for atoms connected with their oscillations. We obtained that under heating, graphene material response is nonsymmetric.
Modeling and measurement of tissue elastic moduli using optical coherence elastography
NASA Astrophysics Data System (ADS)
Liang, Xing; Oldenburg, Amy L.; Crecea, Vasilica; Kalyanam, Sureshkumar; Insana, Michael F.; Boppart, Stephen A.
2008-02-01
Mechanical forces play crucial roles in tissue growth, patterning and development. To understand the role of mechanical stimuli, biomechanical properties are of great importance, as well as our ability to measure biomechanical properties of developing and engineered tissues. To enable these measurements, a novel non-invasive, micron-scale and high-speed Optical Coherence Elastography (OCE) system has been developed utilizing a titanium:sapphire based spectral-domain Optical Coherence Tomography (OCT) system and a mechanical wave driver. This system provides axial resolution of 3 microns, transverse resolution of 13 microns, and an acquisition rate as high as 25,000 lines per second. External lowfrequency vibrations are applied to the samples in the system. Step and sinusoidal steady-state responses are obtained to first characterize the OCE system and then characterize samples. Experimental results of M-mode OCE on silicone phantoms and human breast tissues are obtained, which correspond to biomechanical models developed for this analysis. Quantified results from the OCE system correspond directly with results from an indentation method from a commercial. With micron-scale resolution and a high-speed acquisition rate, our OCE system also has the potential to rapidly measure dynamic 3-D tissue biomechanical properties.
Versaevel, Marie; Grevesse, Thomas; Riaz, Maryam; Lantoine, Joséphine; Gabriele, Sylvain
2014-01-01
This protocol describes a simple method to deposit protein micropatterns over a wide range of culture substrate stiffness (three orders of magnitude) by using two complementary polymeric substrates. In the first part, we introduce a novel polyacrylamide hydrogel, called hydroxy-polyacrylamide (PAAm), that permits to surmount the intrinsically nonadhesive properties of polyacrylamide with minimal requirements in cost or expertize. We present a protocol for tuning easily the rigidity of "soft" hydroxy-PAAm hydrogels between ~0.5 and 50 kPa and a micropatterning method to locally deposit protein micropatterns on these hydrogels. In a second part, we describe a protocol for tuning the rigidity of "stiff" silicone elastomers between ~100 and 1000 kPa and printing efficiently proteins from the extracellular matrix. Finally, we investigate the effect of the matrix rigidity on the nucleus of primary endothelial cells by tuning the rigidity of both polymeric substrates. We envision that the complementarity of these two polymeric substrates, combined with an efficient microprinting technique, can be further developed in the future as a powerful mechanobiology platform to investigate in vitro the effect of mechanotransduction cues on cellular functions, gene expression, and stem cell differentiation.
NASA Technical Reports Server (NTRS)
Abdul-Aziz, Ali; Kalluri, Sreeramesh
1991-01-01
The temperature-dependent engineering elastic constants of a directionally solidified nickel-base superalloy were estimated from the single-crystal elastic constants of nickel and MAR-MOO2 superalloy by using Wells' method. In this method, the directionally solidified (columnar-grained) nickel-base superalloy was modeled as a transversely isotropic material, and the five independent elastic constants of the transversely isotropic material were determined from the three independent elastic constants of a cubic single crystal. Solidification for both the single crystals and the directionally solidified superalloy was assumed to be along the (001) direction. Temperature-dependent Young's moduli in longitudinal and transverse directions, shear moduli, and Poisson's ratios were tabulated for the directionally solidified nickel-base superalloy. These engineering elastic constants could be used as input for performing finite element structural analysis of directionally solidified turbine engine components.
Elastic properties of alkali-feldspars
NASA Astrophysics Data System (ADS)
Waeselmann, N.; Brown, J.; Angel, R. J.; Ross, N.; Kaminsky, W.
2013-12-01
New measurements of single crystal elastic moduli for a suite of the alkali feldspars are reported. In order to interpret Earth's seismic structure, knowledge of the elastic properties of constituent minerals is essential. The elasticity of feldspar minerals, despite being the most abundant phase in Earth's crust (estimated to be more than 60%), were previously poorly characterized. All prior seismic and petrologic studies have utilized 50-year-old results, of questionable quality, based on 1-bar measurements on pseudo-single crystals. Alkali-feldspars present a large experimental challenge associated with their structural complexity. In the K-end member (KAlSi3O8) the symmetry is governed by Al/Si ordering, in the Na-end member (NaAlSi3O8) the symmetry is governed by whether or not there is a displacive collapse of the framework independent of the Al/Si ordering. K-feldspars exhibit monoclinic (C2/m) symmetry (necessitating determination of 13 elastic moduli) if disordered and triclinic (C-1) symmetry (21 elastic moduli) if ordered. Exsolution of Na-rich and K-rich phases is ubiquitous in natural samples, making it difficult to find suitable single phase and untwinned samples for study. The small single domain samples selected for this study were previously characterized by x-ray diffraction and microprobe analysis to ensure adequate sample quality. Surface wave velocities were measured on oriented surfaces of natural and synthetic single crystals using impulsively stimulated light scattering. A surface corrugation with a spacing of about 2 microns was impulsively created by the overlap of 100 ps infrared light pulses. The time evolution of the stimulated standing elastic waves was detected by measuring the intensity of diffraction from the surface corrugation of a variably delayed probe pulse. This method allows accurate (better than 0.2%) determination of velocities on samples smaller than 100 microns. The combination of measured surface wave velocities and
Langer, W.H.; Tepordei, V.V.; Bolen, W.P.
2000-01-01
Construction aggregates consist primarily of crushed stone and construction sand and gravel. Total estimated production of construction aggregates increased in 1999 by about 2% to 2.39 Gt (2.64 billion st) compared with 1998. This record production level continued an expansion that began in 1992. By commodities, crushed stone production increased 3.3%, while sand and gravel production increased by about 0.5%.
Tepordei, V.V.
1994-01-01
Part of a special section on industrial minerals in 1993. The 1993 production of construction aggregates increased 6.3 percent over the 1992 figure, to reach 2.01 Gt. This represents the highest estimated annual production of combined crushed stone and construction sand and gravel ever recorded in the U.S. The outlook for construction aggregates and the issues facing the industry are discussed.
The moduli space of superconformal instantons in sigma models
Monastyrsky, M.I. ); Natanzon, S.M. )
1991-06-21
In this paper, an approach to instantons in supersymmetrical 2-dimensional sigma models is discussed. In this approach superinstantons are characterized as the superconformal maps of a physical space into the isotopic (target) space. The authors consider a special case of the supersphere with punctures. New topological invariants as the number of the so-called fermionic points appear in this case. The authors also analyze the structure of the moduli space of superinstantons within this framework.
On natural inflation and moduli stabilisation in string theory
NASA Astrophysics Data System (ADS)
Palti, Eran
2015-10-01
Natural inflation relies on the existence of an axion decay constant which is super-Planckian. In string theory only sub-Planckian axion decay constants have been found in any controlled regime. However in field theory it is possible to generate an enhanced super-Planckian decay constant by an appropriate aligned mixing between axions with individual sub-Planckian decay constants. We study the possibility of such a mechanism in string theory. In particular we construct a new realisation of an alignment scenario in type IIA string theory compactifications on a Calabi-Yau where the alignment is induced through fluxes. Within field theory the original decay constants are taken to be independent of the parameters which induce the alignment. In string theory however they are moduli dependent quantities and so interact gravitationally with the physics responsible for the mixing. We show that this gravitational effect of the fluxes on the moduli can precisely cancel any enhancement of the effective decay constant. This censorship of an effective super-Planckian decay constant depends on detailed properties of Calabi-Yau moduli spaces and occurs for all the examples and classes that we study. We expand these results to a general superpotential assuming only that the axion superpartners are fixed supersymmetrically and are able to show for a large class of Calabi-Yau manifolds, but not all, that the cancellation effect occurs and is independent of the superpotential. We also study simple models where the moduli are fixed non-supersymmetrically and find that similar cancellation behaviour can emerge. Finally we make some comments on a possible generalisation to axion monodromy inflation models.
TOPICAL REVIEW: Inverse problems in elasticity
NASA Astrophysics Data System (ADS)
Bonnet, Marc; Constantinescu, Andrei
2005-04-01
This review is devoted to some inverse problems arising in the context of linear elasticity, namely the identification of distributions of elastic moduli, model parameters or buried objects such as cracks. These inverse problems are considered mainly for three-dimensional elastic media under equilibrium or dynamical conditions, and also for thin elastic plates. The main goal is to overview some recent results, in an effort to bridge the gap between studies of a mathematical nature and problems defined from engineering practice. Accordingly, emphasis is given to formulations and solution techniques which are well suited to general-purpose numerical methods for solving elasticity problems on complex configurations, in particular the finite element method and the boundary element method. An underlying thread of the discussion is the fact that useful tools for the formulation, analysis and solution of inverse problems arising in linear elasticity, namely the reciprocity gap and the error in constitutive equation, stem from variational and virtual work principles, i.e., fundamental principles governing the mechanics of deformable solid continua. In addition, the virtual work principle is shown to be instrumental for establishing computationally efficient formulae for parameter or geometrical sensitivity, based on the adjoint solution method. Sensitivity formulae are presented for various situations, especially in connection with contact mechanics, cavity and crack shape perturbations, thus enriching the already extensive known repertoire of such results. Finally, the concept of topological derivative and its implementation for the identification of cavities or inclusions are expounded.
Koike, J. ); Okamoto, P.R.; Rehn, L.E. ); Meshii, M. . Dept. of Materials Science and Engineering)
1990-09-01
In an attempt to correlate the shear instability mechanism with empirical criteria for irradiation-induced amorphization, shear moduli of an A{sub 3}B-type fcc crystal were calculated as a function of the chemical long range order parameter (S) using a Morse potential. The shear moduli were found to decrease with decreasing S. When the depth and the curvature of the A-B potential were changed while keeping the A-A and B-B potentials constant, the magnitude of the decrease in shear moduli is greater for deeper and narrower A-B potentials. The present results indicate that a shear instability should occur more readily in compounds with larger ordering energy and larger elastic moduli. These results agree with the reported empirical criteria for irradiation-induced amorphization, therefore providing further support for the shear instability mechanism for solid-state amorphization. 9 refs., 3 figs.
Measurement of Elastic Modulus of Collagen Type I Single Fiber.
Dutov, Pavel; Antipova, Olga; Varma, Sameer; Orgel, Joseph P R O; Schieber, Jay D
2016-01-01
Collagen fibers are the main components of the extra cellular matrix and the primary contributors to the mechanical properties of tissues. Here we report a novel approach to measure the longitudinal component of the elastic moduli of biological fibers under conditions close to those found in vivo and apply it to type I collagen from rat tail tendon. This approach combines optical tweezers, atomic force microscopy, and exploits Euler-Bernoulli elasticity theory for data analysis. This approach also avoids drying for measurements or visualization, since samples are freshly extracted. Importantly, strains are kept below 0.5%, which appear consistent with the linear elastic regime. We find, surprisingly, that the longitudinal elastic modulus of type I collagen cannot be represented by a single quantity but rather is a distribution that is broader than the uncertainty of our experimental technique. The longitudinal component of the single-fiber elastic modulus is between 100 MPa and 360 MPa for samples extracted from different rats and/or different parts of a single tail. Variations are also observed in the fibril-bundle/fibril diameter with an average of 325±40 nm. Since bending forces depend on the diameter to the fourth power, this variation in diameter is important for estimating the range of elastic moduli. The remaining variations in the modulus may be due to differences in composition of the fibril-bundles, or the extent of the proteoglycans constituting fibril-bundles, or that some single fibrils may be of fibril-bundle size.
Cell elasticity with altered cytoskeletal architectures across multiple cell types.
Grady, Martha E; Composto, Russell J; Eckmann, David M
2016-08-01
The cytoskeleton is primarily responsible for providing structural support, localization and transport of organelles, and intracellular trafficking. The structural support is supplied by actin filaments, microtubules, and intermediate filaments, which contribute to overall cell elasticity to varying degrees. We evaluate cell elasticity in five different cell types with drug-induced cytoskeletal derangements to probe how actin filaments and microtubules contribute to cell elasticity and whether it is conserved across cell type. Specifically, we measure elastic stiffness in primary chondrocytes, fibroblasts, endothelial cells (HUVEC), hepatocellular carcinoma cells (HUH-7), and fibrosarcoma cells (HT 1080) subjected to two cytoskeletal destabilizers: cytochalasin D and nocodazole, which disrupt actin and microtubule polymerization, respectively. Elastic stiffness is measured by atomic force microscopy (AFM) and the disruption of the cytoskeleton is confirmed using fluorescence microscopy. The two cancer cell lines showed significantly reduced elastic moduli values (~0.5kPa) when compared to the three healthy cell lines (~2kPa). Non-cancer cells whose actin filaments were disrupted using cytochalasin D showed a decrease of 60-80% in moduli values compared to untreated cells of the same origin, whereas the nocodazole-treated cells showed no change in elasticity. Overall, we demonstrate actin filaments contribute more to elastic stiffness than microtubules but this result is cell type dependent. Cancer cells behaved differently, exhibiting increased stiffness as well as stiffness variability when subjected to nocodazole. We show that disruption of microtubule dynamics affects cancer cell elasticity, suggesting therapeutic drugs targeting microtubules be monitored for significant elastic changes. PMID:26874250
High-pressure single-crystal elasticity study of CO{sub 2} across phase I-III transition
Zhang, Jin S. Bass, Jay D.; Shieh, Sean R.; Dera, Przemyslaw; Prakapenka, Vitali
2014-04-07
Sound velocities and elastic moduli of solid single-crystal CO{sub 2} were measured at pressures up to 11.7(3) GPa by Brillouin spectroscopy. The aggregate adiabatic bulk modulus (K{sub S}), shear modulus (G), and their pressure derivatives for CO{sub 2} Phase I are K{sub S0} = 3.4(6) GPa, G{sub 0} = 1.8(2) GPa, (dK{sub S}/dP){sub 0} = 7.8(3), (dG/dP){sub 0} = 2.5(1), (d{sup 2}K{sub S}/dP{sup 2}){sub 0} = −0.23(3) GPa{sup −1}, and (d{sup 2}G/dP{sup 2}){sub 0} = −0.10(1) GPa{sup −1}. A small increase of elastic properties was observed between 9.8(1) and 10.5(3) GPa, in agreement with the CO{sub 2} I-III transition pressure determined from previous x-ray diffraction experiments. Above the transition pressure P{sub T}, we observed a mixture dominated by CO{sub 2}-I, with minor CO{sub 2}-III. The CO{sub 2}-I + III mixture shows slightly increased sound velocities compared to pure CO{sub 2}-I. Elastic anisotropy calculated from the single-crystal elasticity tensor exhibits a decrease with pressure beginning at 7.9(1) GPa, which is lower than P{sub T}. Our results coincide with recent X-ray Raman observations, suggesting that a pressure-induced electronic transition is related to local structural and optical changes.
Surface effect on the elastic behavior of static bending nanowires.
He, Jin; Lilley, Carmen M
2008-07-01
The surface effect from surface stress and surface elasticity on the elastic behavior of nanowires in static bending is incorporated into Euler-Bernoulli beam theory via the Young-Laplace equation. Explicit solutions are presented to study the dependence of the surface effect on the overall Young's modulus of nanowires for three different boundary conditions: cantilever, simply supported, and fixed-fixed. The solutions indicate that the cantilever nanowires behave as softer materials when deflected while the other structures behave like stiffer materials as the nanowire cross-sectional size decreases for positive surface stresses. These solutions agree with size dependent nanowire overall Young's moduli observed from static bending tests by other researchers. This study also discusses possible reasons for variations of nanowire overall Young's moduli observed.
Surface effect on the elastic behavior of static bending nanowires.
He, Jin; Lilley, Carmen M
2008-07-01
The surface effect from surface stress and surface elasticity on the elastic behavior of nanowires in static bending is incorporated into Euler-Bernoulli beam theory via the Young-Laplace equation. Explicit solutions are presented to study the dependence of the surface effect on the overall Young's modulus of nanowires for three different boundary conditions: cantilever, simply supported, and fixed-fixed. The solutions indicate that the cantilever nanowires behave as softer materials when deflected while the other structures behave like stiffer materials as the nanowire cross-sectional size decreases for positive surface stresses. These solutions agree with size dependent nanowire overall Young's moduli observed from static bending tests by other researchers. This study also discusses possible reasons for variations of nanowire overall Young's moduli observed. PMID:18510370
The Single-Crystal Elasticity of Yttria (Y2O3) to High Temperature
NASA Technical Reports Server (NTRS)
Kriven, Waltraud M.; Palko, James W.; Sinogeikin, Stanislav V.; Bass, Jay D.; Sayir, Ali; Levine, Stanley R. (Technical Monitor)
2000-01-01
The single-crystal elastic moduli of yttria have been measured by Brillouin spectroscopy up to 1200 C. The room temperature values obtained are C11 = 223.6 +/- 0.6 GPa, C44 = 74.6 +/- 0.5 GPa, and C12 = 112.4 +/- 1.0 GPa. The resulting bulk and (Voigt-Reuss-Hill) shear moduli are K = 149.5 +/- 1.0 GPa and G(sub VRH) = 66.3 +/- 0.8 GPa, respectively. These agree much more closely with experimental values reported for polycrystalline samples than do previous single-crystal measurements. Linear least squares regressions to the variation of bulk and shear moduli with temperature result in derivatives of dK/dT = -17 +/- 2 MPa/degC and dG(sub VRH)/dT = -8 +/- 2 MPa/degC. Elastic anisotropy was found to remain essentially constant over the temperature range studied.
Elastic Properties of Rolled Uranium -- 10 wt.% Molybdenum Nuclear Fuel Foils
D. W. Brown; D. J. Alexander; K. D. Clarke; B. Clausen; M. A. Okuniewski; T. A. Sisneros
2013-11-01
In situ neutron diffraction data was collected during elastic loading of rolled foils of uranium-10 wt.% molybdenum bonded to a thin layer of zirconium. Lattice parameters were ascertained from the diffraction patterns to determine the elastic strain and, subsequently, the elastic moduli and Poisson’s ratio in the rolling and transverse directions. The foil was found to be elastically isotropic in the rolling plane with an effective modulus of 86 + / - 3 GPa and a Poisson’s ratio 0.39 + / - 0.04.
Elasticity of hcp cobalt at high pressure and temperature: a quasi-harmonic case
Antonangeli, D; Krisch, M; Farber, D L; Ruddle, D G; Fiquet, G
2007-11-30
We performed high-resolution inelastic x-ray scattering measurements on a single crystal of hcp cobalt at simultaneous high pressure and high temperature, deriving 4 of the 5 independent elements of the elastic tensor. Our experiments indicate that the elasticity of hcp-Co is well described within the frame of a quasi-harmonic approximation and that anharmonic high-temperature effects on the elastic moduli, sound velocities and elastic anisotropy are minimal at constant density. These results support the validity of the Birch's law and represent an important benchmark for ab initio thermal lattice dynamics and molecular-dynamics simulations.
Elastic-plastic analysis of the toroidal field coil inner leg of the compact ignition tokamak
Horie, T.
1987-07-01
Elastic-plastic analyses were made for the inner leg of the Compact Ignition Tokamak toroidal field (TF) coil, which is made of copper-Inconel composite material. From the result of the elastic-plastic analysis, the effective Young's moduli of the inner leg were determined by the analytical equations. These Young's moduli are useful for the three-dimensional, elastic, overall TF coil analysis. Comparison among the results of the baseline design (R = 1.324 m), the bucked pressless design, the 1.527-m major radius design, and the 1.6-m major radius design was also made, based on the elastic-plastic TF coil inner leg analyses.
Single-Crystal Elastic Constants of Yttria (Y2O3) Measured to High Temperatures
NASA Technical Reports Server (NTRS)
Sayir, Ali; Palko, James W.; Kriven, Waltraud M.; Sinogeikin, Sergey V.; Bass, Jay D.
2001-01-01
Yttria, or yttrium sesquioxide (Y2O3), has been considered for use in nuclear applications and has gained interest relatively recently for use in infrared optics. Single crystals of yttria have been grown successfully at the NASA Glenn Research Center using a laser-heated float zone technique in a fiber and rod. Such samples allow measurement of the single-crystal elastic properties, and these measurements provide useful property data for the design of components using single crystals. They also yield information as to what degree the elastic properties of yttria ceramics are a result of the intrinsic properties of the yttria crystal in comparison to characteristics that may depend on processing, such as microstructure and intergranular phases, which are common in sintered yttria. The single-crystal elastic moduli are valuable for designing such optical components. In particular, the temperature derivatives of elastic moduli allow the dimensional changes due to heating under physical constraints, as well as acoustic excitation, to be determined. The single-crystal elastic moduli of yttria were measured by Brillouin spectroscopy up to 1200 C. The room-temperature values obtained were C(sub 11) = 223.6 + 0.6 GPa, C(sub 44) = 74.6 + 0.5 GPa, and C(sub 12) = 112.4 + 1.0 GPa. The resulting bulk and (Voigt-Reuss-Hill) shear moduli were K = 149.5 + 1.0 GPa and G(sub VRH) = 66.3 + 0.8 GPa, respectively. Linear least-squares regressions to the variation of bulk and shear moduli with temperature resulted in derivatives of dK/dT = -17 + 2 MPa/C and dG(sub VRH)/dT = -8 + 2 MPa/ C. Elastic anisotropy was found to remain essentially constant over the temperature range studied.
Electroweak vacuum stabilized by moduli during/after inflation
NASA Astrophysics Data System (ADS)
Ema, Yohei; Mukaida, Kyohei; Nakayama, Kazunori
2016-10-01
It is known that the present electroweak vacuum is likely to be metastable and it may lead to a serious instability during/after inflation. We propose a simple solution to the problem of vacuum instability during/after inflation. If there is a moduli field which has Planck-suppressed interactions with the standard model fields, the Higgs quartic coupling in the early universe naturally takes a different value from the present one. A slight change of the quartic coupling in the early universe makes the Higgs potential absolutely stable and hence we are free from the vacuum instability during/after inflation.
New results of intersection numbers on moduli spaces of curves.
Liu, Kefeng; Xu, Hao
2007-08-28
We present a series of results we obtained recently about the intersection numbers of tautological classes on moduli spaces of curves, including a simple formula of the n-point functions for Witten's tau classes, an effective recursion formula to compute higher Weil-Petersson volumes, several new recursion formulae of intersection numbers and our proof of a conjecture of Itzykson and Zuber concerning denominators of intersection numbers. We also present Virasoro and KdV properties of generating functions of general mixed kappa and psi intersections. PMID:17702863
Dynamic Young's moduli of space materials at low temperatures
NASA Astrophysics Data System (ADS)
Zhang, Z.; Zhao, L. Z.; Tu, Z. H.; Zhang, P. Q.
Using vibration analysis methods, the dynamic mechanical properties of space materials at low temperatures (from 4.2 to 300 K) are studied in this paper. System identification techniques in the time domain are used to identify the dynamic parameters of the space materials Ti-5Al-2.5Sn extra-low-interstitial (ELI) alloy and Al-2.5Li-1.3Cu-0.9Mg-0.13Zr (Al-Li) alloy. The dynamic Young's moduli of these materials are calculated using the basic natural frequencies at different temperatures.
An Inverse Problem Approach for Elasticity Imaging through Vibroacoustics
Aguilo, Miguel A.; Brigham, J. C.; Aquino, W.; Fatemi, M.
2011-01-01
A new methodology for estimating the spatial distribution of elastic moduli using the steady-state dynamic response of solids immersed in fluids is presented. The technique relies on the ensuing acoustic pressure field from a remotely excited solid to inversely estimate the spatial distribution of Young’s modulus. This work proposes the use of Gaussian radial basis functions (GRBF) to represent the spatial variation of elastic moduli. GRBF are shown to possess the advantage of representing smooth functions with quasi-compact support, and can efficiently represent elastic moduli distributions such as those that occur in soft biological tissue in the presence of tumors. The direct problem consists of a coupled acoustic-structure interaction boundary value problem solved in the frequency domain using the finite element method. The inverse problem is cast as an optimization problem in which the objective function is defined as a measure of discrepancy between an experimentally measured response and a finite element representation of the system. Non-gradient based optimization algorithms in combination with a divide and conquer strategy are used to solve the resulting optimization problem. The feasibility of the proposed approach is demonstrated through a series of numerical and a physical experiment. For comparison purposes, the surface velocity response was also used for the inverse characterization as the measured response in place of the acoustic pressure. PMID:20335092
Nonlinear elasticity, fluctuations and heterogeneity of nematic elastomers
NASA Astrophysics Data System (ADS)
Xing, Xiangjun; Radzihovsky, Leo
2008-01-01
Liquid crystal elastomers realize a fascinating new form of soft matter that is a composite of a conventional crosslinked polymer gel (rubber) and a liquid crystal. These solid liquid crystal amalgams, quite similarly to their (conventional, fluid) liquid crystal counterparts, can spontaneously partially break translational and/or orientational symmetries, accompanied by novel soft Goldstone modes. As a consequence, these materials can exhibit unconventional elasticity characterized by symmetry-enforced vanishing of some elastic moduli. Thus, a proper description of such solids requires an essential modification of the classical elasticity theory. In this work, we develop a rotationally invariant, nonlinear theory of elasticity for the nematic phase of ideal liquid crystal elastomers. We show that it is characterized by soft modes, corresponding to a combination of long wavelength shear deformations of the solid network and rotations of the nematic director field. We study thermal fluctuations of these soft modes in the presence of network heterogeneities and show that they lead to a large variety of anomalous elastic properties, such as singular length-scale dependent shear elastic moduli, a divergent elastic constant for splay distortion of the nematic director, long-scale incompressibility, universal Poisson ratios and a nonlinear stress-strain relation for arbitrary small strains. These long-scale elastic properties are universal, controlled by a nontrivial zero-temperature fixed point and constitute a qualitative breakdown of the classical elasticity theory in nematic elastomers. Thus, nematic elastomers realize a stable "critical phase", characterized by universal power-law correlations, akin to a critical point of a continuous phase transition, but extending over an entire phase.
Precisely predicting and designing the elasticity of metallic glasses
Liu, Z. Q. E-mail: zhfzhang@imr.ac.cn; Wang, R. F.; Qu, R. T.; Zhang, Z. F. E-mail: zhfzhang@imr.ac.cn
2014-05-28
We reveal that the elastic moduli of metallic glasses (MGs) invariably vary in a much steeper manner than that predicted by the conventional “rule of mixtures” in individual alloy systems. Such deviations are proved to originate fundamentally from their disordered atomic structures and intrinsic local heterogeneities. By treating the MGs as atomic-level dual phase hybrids, we further propose universal relations to be capable of precisely predicting and designing the elastic constants of MGs. This may contribute to the development of MGs with intended properties and behaviors, and allow new understandings on the structures and properties as well as their relationships in MGs.
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
Thermal fluctuations and anomalous elasticity of homogeneous nematic elastomers
NASA Astrophysics Data System (ADS)
Xing, X.; Radzihovsky, L.
2003-03-01
We present a unified formulation of a rotationally invariant nonlinear elasticity for a variety of spontaneously anisotropic phases, and use it to study thermal fluctuations in nematic elastomers and spontaneously anisotropic gels. We find that in a thermodynamic limit homogeneous nematic elastomers are universally incompressible, are characterized by a universal ratio of shear moduli, and exhibit an anomalous elasticity controlled by a nontrivial low-temperature fixed-point perturbative in D = 3 - epsilon dimensions. In three dimensions, we make predictions that are asymptotically exact.
Cosserat elasticity of negative Poisson’s ratio foam: experiment
NASA Astrophysics Data System (ADS)
Rueger, Zach; Lakes, Roderic S.
2016-05-01
Negative Poisson’s ratio polymer foams derived from reticulated open cell foams exhibit large size effects in torsion and bending. Effective moduli increase as diameter decreases in contrast to the prediction of classical elasticity. Size effects of this sort are predicted by Cosserat (micropolar) elasticity in which points can rotate as well as translate and distributed moments are incorporated. The Cosserat coupling number N was about twice as large as that of as-received foam, leading to strong effects. The torsion characteristic length {{\\ell }}{{t}} was similar. Cosserat effects are known to enhance toughness and immunity from stress concentration.
Precisely predicting and designing the elasticity of metallic glasses
NASA Astrophysics Data System (ADS)
Liu, Z. Q.; Wang, R. F.; Qu, R. T.; Zhang, Z. F.
2014-05-01
We reveal that the elastic moduli of metallic glasses (MGs) invariably vary in a much steeper manner than that predicted by the conventional "rule of mixtures" in individual alloy systems. Such deviations are proved to originate fundamentally from their disordered atomic structures and intrinsic local heterogeneities. By treating the MGs as atomic-level dual phase hybrids, we further propose universal relations to be capable of precisely predicting and designing the elastic constants of MGs. This may contribute to the development of MGs with intended properties and behaviors, and allow new understandings on the structures and properties as well as their relationships in MGs.
Flow-induced aggregation of colloidal particles in viscoelastic fluids
NASA Astrophysics Data System (ADS)
Xie, Donglin; Qiao, Greg G.; Dunstan, Dave E.
2016-08-01
The flow-induced aggregation of dilute colloidal polystyrene nanoparticles suspended in Newtonian and viscoelastic solutions is reported. A rheo-optical method has been used to detect real-time aggregation processes via measuring optical absorption or scattering in a quartz Couette cell. The observed absorbance decreases over time are attributed to the flow-induced coagulation. Numerical simulations show that the aggregation processes still follow the Smoluchowski coagulation equation in a revised version. Suspensions in a series of media are studied to evaluate the effect of the media rheological properties on the particle aggregation. The data shows that elasticity reduces the aggregation while the solution viscosity enhances the aggregation processes.
Saleh, Tarik A.; Farrow, Adam M.; Freibert, Franz J.
2012-06-06
Samples of {alpha} plutonium were fabricated at the Los Alamos National Laboratory's Plutonium Facility. Cylindrical samples were machined from cast pucks. Precision immersion density and resonant ultrasound spectroscopy (RUS) measurements were completed on 27 new samples, yielding elastic moduli measurements. Mechanical tests were performed in compression yielding stress-strain curves as a function of rate, temperature and phase.
Elasticity of the Sm1-xYxS alloy Based on Ultrasonic Measurements
NASA Astrophysics Data System (ADS)
Soboleva, EG; Igisheva, AL; Wojciechowski, KW
2016-08-01
The elastic moduli, sound velocities, Gruneisen parameter, Poisson's ratios and brittleness-plasticity criterion ratios are studied for the Sm1-xYxS alloys. Their dependence on the concentration of alloy components including a valence transition from semiconductors into the metal phase is presented. Auxeticity (negative Poisson's ratio) is found for some concentrations.
Modeling Pseudo-elastic Behavior of Springback
NASA Astrophysics Data System (ADS)
Xia, Z. Cedric
2005-08-01
One of the principal foundations of mathematical theory of conventional plasticity for rate-independent metals is that there exists a well-defined yield surface in stress space for any material point under deformation. A material point can undergo further plastic deformation if the applied stresses are beyond current yield surface which is generally referred as "plastic loading". On the other hand, if the applied stress state falls within or on the yield surface, the metal will deform elastically only and is said to be undergoing "elastic unloading". Although it has been always recognized throughout the history of development of plasticity theory that there is indeed inelastic deformation accompanying elastic unloading, which leads to metal's hysteresis behavior, its effects were thought to be negligible and were largely ignored in the mathematical treatment. Recently there have been renewed interests in the study of unloading behavior of sheet metals upon large plastic deformation and its implications on springback prediction. Springback is essentially an elastic recovery process of a formed sheet metal blank when it is released from the forming dies. Its magnitude depends on the stress states and compliances of the deformed sheet metal if no further plastic loading occurs during the relaxation process. Therefore the accurate determination of material compliances during springback and its effective incorporation into simulation software are important aspects for springback calculation. Some of the studies suggest that the unloading curve might deviate from linearity, and suggestions were made that a reduced elastic modulus be used for springback simulation. The aim of this study is NOT to take a position on the debate of whether elastic moduli are changed during sheet metal forming process. Instead we propose an approach of modeling observed psuedoelastic behavior within the context of mathematical theory of plasticity, where elastic moduli are treated to be
Area Expansivity Moduli of Regenerating Plant Protoplast Cell Walls Exposed to Shear Flows
NASA Astrophysics Data System (ADS)
Fujimura, Yuu; Iino, Masaaki; Watanabe, Ugai
2005-05-01
To control the elasticity of the plant cell wall, protoplasts isolated from cultured Catharanthus roseus cells were regenerated in shear flows of 115 s-1 (high shear) and 19.2 s-1 (low shear, as a control). The surface area expansivity modulus and the surface breaking strength of these regenerating protoplasts were measured by a micropipette aspiration technique. Cell wall synthesis was also measured using a cell wall-specific fluorescent dye. High shear exposure for 3 h doubled both the surface area modulus and breaking strength observed under low shear, significantly decreased cell wall synthesis, and roughly quadrupled the moduli of the cell wall. Based on the cell wall synthesis data, we estimated the three-dimensional modulus of the cell wall to be 4.1± 1.2 GPa for the high shear, and 0.35± 0.2 GPa for the low shear condition, using the surface area expansivity modulus divided by the cell wall thickness, which is identical with the Young’s modulus divided by 2(1-σ), where σ is Poisson's ratio. We concluded that high shear exposure considerably strengthens the newly synthesized cell wall.
Quiver theories for moduli spaces of classical group nilpotent orbits
NASA Astrophysics Data System (ADS)
Hanany, Amihay; Kalveks, Rudolph
2016-06-01
We approach the topic of Classical group nilpotent orbits from the perspective of the moduli spaces of quivers, described in terms of Hilbert series and generating functions. We review the established Higgs and Coulomb branch quiver theory constructions for A series nilpotent orbits. We present systematic constructions for BCD series nilpotent orbits on the Higgs branches of quiver theories defined by canonical partitions; this paper collects earlier work into a systematic framework, filling in gaps and providing a complete treatment. We find new Coulomb branch constructions for above minimal nilpotent orbits, including some based upon twisted affine Dynkin diagrams. We also discuss aspects of 3 d mirror symmetry between these Higgs and Coulomb branch constructions and explore dualities and other relationships, such as HyperKähler quotients, between quivers. We analyse all Classical group nilpotent orbit moduli spaces up to rank 4 by giving their unrefined Hilbert series and the Highest Weight Generating functions for their decompositions into characters of irreducible representations and/or Hall Littlewood polynomials.
Non-Gaussian Error Distributions of LMC Distance Moduli Measurements
NASA Astrophysics Data System (ADS)
Crandall, Sara; Ratra, Bharat
2015-12-01
We construct error distributions for a compilation of 232 Large Magellanic Cloud (LMC) distance moduli values from de Grijs et al. that give an LMC distance modulus of (m - M)0 = 18.49 ± 0.13 mag (median and 1σ symmetrized error). Central estimates found from weighted mean and median statistics are used to construct the error distributions. The weighted mean error distribution is non-Gaussian—flatter and broader than Gaussian—with more (less) probability in the tails (center) than is predicted by a Gaussian distribution; this could be the consequence of unaccounted-for systematic uncertainties. The median statistics error distribution, which does not make use of the individual measurement errors, is also non-Gaussian—more peaked than Gaussian—with less (more) probability in the tails (center) than is predicted by a Gaussian distribution; this could be the consequence of publication bias and/or the non-independence of the measurements. We also construct the error distributions of 247 SMC distance moduli values from de Grijs & Bono. We find a central estimate of {(m-M)}0=18.94+/- 0.14 mag (median and 1σ symmetrized error), and similar probabilities for the error distributions.
Simple torsion test for shear moduli determination of orthotropic composites
NASA Technical Reports Server (NTRS)
Sumsion, H. T.; Rajapakse, Y. D. S.
1978-01-01
The shear moduli G13 and G23 for two different composites (AS/3501 and T300/5209) of uniaxial and cross-ply fiber orientations were determined by torsion testing of flat specimens of rectangular cross section. Torsion tests were run under controlled angle of twist in an electro-hydraulic servo-controlled test system. Both laser and potentiometer methods of measuring the angle of twist were used. The in-plane shear modulus was calculated with a formula for transversally isotropic materials and a formula for orthotropic materials, while the out-of-plane shear modulus was calculated from the orthotropic material formula. Neither the uniaxial nor the angle-ply composite materials studied were transversely isotropic. The degree of anisotropy for the angle-ply materials was several times greater than that of the uniaxial composites. For specimens of uniaxial fiber orientation, the in-plane shear moduli could be calculated to a good approximation by using the isotropic formula and test machine deflection data.
Moduli stabilisation with nilpotent goldstino: vacuum structure and SUSY breaking
NASA Astrophysics Data System (ADS)
Aparicio, Luis; Quevedo, Fernando; Valandro, Roberto
2016-03-01
We study the effective field theory of KKLT and LVS moduli stabilisation scenarios coupled to an anti-D3-brane at the tip of a warped throat. We describe the presence of the anti-brane in terms of a nilpotent goldstino superfield in a supersymmetric effective field theory. The introduction of this superfield produces a term that can lead to a de Sitter minimum. We fix the Kähler moduli dependence of the nilpotent field couplings by matching this term with the anti-D3-brane uplifting contribution. The main result of this paper is the computation, within this EFT, of the soft supersymmetry breaking terms in both KKLT and LVS for matter living on D3-brane (leaving the D7-brane analysis to an appendix). A handful of distinct phenomenological scenarios emerge that could have low energy implications, most of them having a split spectrum of soft masses. Some cosmological and phenomenological properties of these models are discussed. We also check that the attraction between the D3-brane and the anti-D3-brane does not affect the leading contribution to the soft masses and does not destabilise the system.
Nelson, T.I.; Bolen, W.P.
2007-01-01
Construction aggregates, primarily stone, sand and gravel, are recovered from widespread naturally occurring mineral deposits and processed for use primarily in the construction industry. They are mined, crushed, sorted by size and sold loose or combined with portland cement or asphaltic cement to make concrete products to build roads, houses, buildings, and other structures. Much smaller quantities are used in agriculture, cement manufacture, chemical and metallurgical processes, glass production and many other products.
Tepordei, V.V.
1996-01-01
Part of the Annual Commodities Review 1995. Production of construction aggregates such as crushed stone and construction sand and gravel showed a marginal increase in 1995. Most of the 1995 increases were due to funding for highway construction work. The major areas of concern to the industry included issues relating to wetlands classification and the classification of crystalline silica as a probable human carcinogen. Despite this, an increase in demand is anticipated for 1996.
Tepordei, V.V.
1993-01-01
Part of a special section on the market performance of industrial minerals in 1992. Production of construction aggregates increased by 4.6 percent in 1992. This increase was due, in part, to the increased funding for transportation and infrastructure projects. The U.S. produced about 1.05 Gt of crushed stone and an estimated 734 Mt of construction sand and gravel in 1992. Demand is expected to increase by about 5 percent in 1993.
NASA Astrophysics Data System (ADS)
Soledad Antonel, P.; Jorge, Guillermo; Perez, Oscar E.; Butera, Alejandro; Gabriela Leyva, A.; Martín Negri, R.
2011-08-01
Magnetic elastic structured composites were prepared by using CoFe2O4 ferromagnetic and superparamagnetic nanoparticles as fillers in polydimethylsiloxane (PDMS) matrixes, which were cured in the presence of a uniform magnetic field. Cobalt-iron oxide nanoparticles of three different average sizes (between 2 and 12 nm) were synthesized and characterized. The smallest nanoparticles presented superparamagnetic behavior, with a blocking temperature of approximately 75 K, while larger particles are already blocked at room temperature. Macroscopically structured-anisotropic PDMS-CoFe2O4 composites were obtained when curing the dispersion of the nanoparticles in the presence of a uniform magnetic field (0.3 T). The formation of the particle's chains (needles) orientated in the direction of the magnetic field was observed only when loading with the larger magnetically blocked nanoparticles. The SEM images show that the needles are formed by groups of nanoparticles which retain their original average size. The Young's moduli of the structured composites are four times larger when measured along the oriented needles than in the perpendicular direction. Magnetization (VSM) and ferromagnetic resonance curves of the structured composites were determined as a function of the relative orientation between the needles and the probe field. The remanence magnetization was 30% higher when measured parallel to the needles, while the coercive field remains isotropic. These observations are discussed in terms of the individual nanoparticle's properties and its aggregation in the composites.
Soap Bubble Elasticity: Analysis and Correlation with Foam Stability
NASA Astrophysics Data System (ADS)
Karakashev, S. I.; Tsekov, R.; Manev, E. D.; Nguyen, A. V.
2010-05-01
A correlation between the elastic modulus of soap bubble and the foam stability was found. A model system was chosen: a soap bubble stabilized by simple nonionic surfactant tetraethylene glycol octyl ether (C8E4) and 10^-5 M NaCl. The Elastic moduli were determined by periodical expansion and shrinking of foam bubbles with frequency of 0.1 Hz and volumetric amplitude of 2 mm 3. The film tension was monitored via commercial profile analysis tensiometer (Sinterface Technologies, GmbH). The elastic moduli of foam bubbles versus surfactant concentration in the range of 2x10^-3 - 10^-2 M were obtained. In addition, the theory of Lucassen and van den Tempel for the elastic modulus of single liquid/air interface at given frequency was exploited as well. The bulk diffusion coefficient of the surfactant molecules is unknown parameter through the adsorption frequency in this theory. Hence, a fitting procedure (with one free parameter) was conducted matching experimental and theoretical data. The value of the bulk diffusion coefficient of C8E4 obtained was 5.1x10^-11 m^2/s, which is an order of magnitude lower value than what is expected for. The foam was generated by shaking method and left to decay. A correlation between the elastic modulus and foam life time upon surfactant concentration was found.
Haycraft, James J
2009-12-01
The acoustic phonons of the epsilon polymorph of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo [5.5.0.0(5,9).0(3,11)] dodecane (epsilon-CL-20) have been studied using Brillouin scattering spectroscopy. Analysis of the acoustic phonon velocities allowed determination of the complete stiffness tensor for this energetic material. The results are compared to a theoretical determination of the epsilon-CL-20 elastic constants, bulk moduli, and shear moduli. The observed ordering of elastic constants, C(22)>C(33)>C(11), is noted to be different from other nitramine energetic materials. Finally, the elasticity of epsilon-CL-20 is compared to recently published reports on cyclotrimethylene trinitramine's (RDX) elasticity and the beta polymorph of cyclotetramethylene tetranitramine's (beta-HMX) elasticity. PMID:19968345
NASA Astrophysics Data System (ADS)
Haycraft, James J.
2009-12-01
The acoustic phonons of the epsilon polymorph of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo [5.5.0.05,9.03,11] dodecane (ɛ-CL-20) have been studied using Brillouin scattering spectroscopy. Analysis of the acoustic phonon velocities allowed determination of the complete stiffness tensor for this energetic material. The results are compared to a theoretical determination of the ɛ-CL-20 elastic constants, bulk moduli, and shear moduli. The observed ordering of elastic constants, C22>C33>C11, is noted to be different from other nitramine energetic materials. Finally, the elasticity of ɛ-CL-20 is compared to recently published reports on cyclotrimethylene trinitramine's (RDX) elasticity and the beta polymorph of cyclotetramethylene tetranitramine's (β-HMX) elasticity.
Impact of Hydration Media on Ex Vivo Corneal Elasticity Measurements
Dias, Janice; Ziebarth, Noël M.
2014-01-01
Objectives To determine the effect of hydration media on ex vivo corneal elasticity. Methods Experiments were conducted on forty porcine eyes retrieved from an abattoir (10 eyes each for PBS, BSS, Optisol, 15% Dextran). The epithelium was removed and the cornea was excised with an intact scleral rim and placed in 20% Dextran overnight to restore its physiological thickness. For each hydration media, corneas were evenly divided into two groups: one with an intact scleral rim and the other without. Corneas were mounted onto a custom chamber and immersed in a hydration medium for elasticity testing. While in each medium, corneal elasticity measurements were performed for 2 hours: at 5-minute intervals for the first 30 minutes and then 15-minute intervals for the remaining 90 minutes. Elasticity testing was performed using nanoindentation with spherical indenters and Young’s modulus was calculated using the Hertz model. Thickness measurements were taken before and after elasticity testing. Results The percentage change in corneal thickness and elasticity was calculated for each hydration media group. BSS, PBS, and Optisol showed an increase in thickness and Young’s moduli for corneas with and without an intact scleral rim. 15% Dextran exhibited a dehydrating effect on corneal thickness and provided stable maintenance of corneal elasticity for both groups. Conclusions Hydration media affects the stability of corneal thickness and elasticity measurements over time. 15% Dextran was most effective in maintaining corneal hydration and elasticity, followed by Optisol. PMID:25603443
Single-Crystal Elasticity of Earth Materials: An Appraisal
NASA Astrophysics Data System (ADS)
Duffy, T. S.
2015-12-01
The elastic properties of minerals are of central importance for interpreting seismic data for the Earth's crust, mantle, and core. Mineral elasticity data also have more general applications towards understanding equations of state, phase equilibria, interatomic forces, material strength, and phase transitions. The singe-crystal elastic properties are the most generally useful as they provide complete information on the anisotropy of elastic moduli (e.g. Poisson's ratio, Young's modulus), sound velocities, and compressibility. Measurement of the full set of single-crystal elastic properties remains challenging especially for lower symmetry crystals. In this talk, I present an overview of our current understanding of single-crystal elasticity based on a newly constructed database of single-crystal elastic properties. At ambient conditions the full elastic tensor of about 150 minerals have now been measured, along with about another 60 related compounds that are not formally minerals. About two-thirds of the measured minerals are oxides or silicates. A limitation of the existing database is that only about 10% of the measurements are on crystals of monoclinic or triclinic symmetry, while these two systems account for about 40% of known minerals. Additionally, only a smaller subset of minerals have been examined at high pressure or temperature conditions. Several applications of the database will be presented emphasizing trends in elastic anisotropy. The pyroxenes will be used as an illustrative example.
A novel method to determine the elastic modulus of extremely soft materials.
Stirling, Tamás; Zrínyi, Miklós
2015-06-01
Determination of the elastic moduli of extremely soft materials that may deform under their own weight is a rather difficult experimental task. A new method has been elaborated by means of which the elastic modulus of such materials can be determined. This method is generally applicable to all soft materials with purely neo-Hookean elastic deformation behaviour with elastic moduli lower than 1 kPa. Our novel method utilises the self-deformation of pendent gel cylinders under gravity. When suspended, the material at the very top bears the weight of the entire gel cylinder, but that at the bottom carries no load at all. Due to the non-uniform stress distribution along the gel sample both the stress and the resulting strain show position dependence. The cross-sectional area of the material is lowest at the top of the sample and gradually increases towards its bottom. The equilibrium geometry of the pendant gel is used to evaluate the elastic modulus. Experimental data obtained by the proposed new method were compared to the results obtained from underwater measurements. The parameters affecting the measurement uncertainty were studied by a Pareto analysis of a series of adaptive Monte Carlo simulations. It has been shown that our method provides an easily achievable method to provide an accurate determination of the elastic modulus of extremely soft matter typically applicable for moduli below 1 kPa.
A novel method to determine the elastic modulus of extremely soft materials.
Stirling, Tamás; Zrínyi, Miklós
2015-06-01
Determination of the elastic moduli of extremely soft materials that may deform under their own weight is a rather difficult experimental task. A new method has been elaborated by means of which the elastic modulus of such materials can be determined. This method is generally applicable to all soft materials with purely neo-Hookean elastic deformation behaviour with elastic moduli lower than 1 kPa. Our novel method utilises the self-deformation of pendent gel cylinders under gravity. When suspended, the material at the very top bears the weight of the entire gel cylinder, but that at the bottom carries no load at all. Due to the non-uniform stress distribution along the gel sample both the stress and the resulting strain show position dependence. The cross-sectional area of the material is lowest at the top of the sample and gradually increases towards its bottom. The equilibrium geometry of the pendant gel is used to evaluate the elastic modulus. Experimental data obtained by the proposed new method were compared to the results obtained from underwater measurements. The parameters affecting the measurement uncertainty were studied by a Pareto analysis of a series of adaptive Monte Carlo simulations. It has been shown that our method provides an easily achievable method to provide an accurate determination of the elastic modulus of extremely soft matter typically applicable for moduli below 1 kPa. PMID:25873419
Sharp estimates for the moduli of continuity of metric projections onto weakly convex sets
NASA Astrophysics Data System (ADS)
Ivanov, G. E.
2015-08-01
We study the dependence of metric projections on the following three parameters: the point projected, the set to which we are projecting, and the norm (generally speaking, non-symmetric) that determines the metric. We obtain sharp estimates for the moduli of continuity of metric projections onto convex and weakly convex sets in Banach spaces. We also estimate these moduli in terms of the moduli of convexity and smoothness of the space (or the quasi-ball).
NASA Astrophysics Data System (ADS)
Song, Yongjia; Hu, Hengshan; Rudnicki, John W.
2016-07-01
Grain-scale local fluid flow is an important loss mechanism for attenuating waves in cracked fluid-saturated poroelastic rocks. In this study, a dynamic elastic modulus model is developed to quantify local flow effect on wave attenuation and velocity dispersion in porous isotropic rocks. The Eshelby transform technique, inclusion-based effective medium model (the Mori-Tanaka scheme), fluid dynamics and mass conservation principle are combined to analyze pore-fluid pressure relaxation and its influences on overall elastic properties. The derivation gives fully analytic, frequency-dependent effective bulk and shear moduli of a fluid-saturated porous rock. It is shown that the derived bulk and shear moduli rigorously satisfy the Biot-Gassmann relationship of poroelasticity in the low-frequency limit, while they are consistent with isolated-pore effective medium theory in the high-frequency limit. In particular, a simplified model is proposed to quantify the squirt-flow dispersion for frequencies lower than stiff-pore relaxation frequency. The main advantage of the proposed model over previous models is its ability to predict the dispersion due to squirt flow between pores and cracks with distributed aspect ratio instead of flow in a simply conceptual double-porosity structure. Independent input parameters include pore aspect ratio distribution, fluid bulk modulus and viscosity, and bulk and shear moduli of the solid grain. Physical assumptions made in this model include (1) pores are inter-connected and (2) crack thickness is smaller than the viscous skin depth. This study is restricted to linear elastic, well-consolidated granular rocks.
On a new compactification of moduli of vector bundles on a surface. III: Functorial approach
Timofeeva, Nadezhda V
2011-03-31
A new compactification for the scheme of moduli for Gieseker-stable vector bundles with prescribed Hilbert polynomial on the smooth projective polarized surface (S,L) is constructed. We work over the field k=k-bar of characteristic zero. Families of locally free sheaves on the surface S are completed with locally free sheaves on schemes which are modifications of S. The Gieseker-Maruyama moduli space has a birational morphism onto the new moduli space. We propose the functor for families of pairs 'polarized scheme-vector bundle' with moduli space of such type. Bibliography: 16 titles.
Structure and elastic properties of smectic liquid crystalline elastomer films.
Stannarius, R; Köhler, R; Dietrich, U; Lösche, M; Tolksdorf, C; Zentel, R
2002-04-01
Mechanical measurements, x-ray investigations, and optical microscopy are employed to characterize the interplay of chemical composition, network topology, and elastic response of smectic liquid crystalline elastomers (LCEs) in various mesophases. Macroscopically ordered elastomer films of submicrometer thicknesses were prepared by cross linking freely suspended smectic polymer films. The cross-linked material preserves the mesomorphism and phase transitions of the precursor polymer. The elastic response of the smectic LCE is entropic, and the corresponding elastic moduli are of the order of MPa. In the tilted ferroelectric smectic-C* phase, the network structure plays an important role. Due to the coupling of elastic network deformations to the orientation of the mesogenic groups in interlayer cross-linked materials (mesogenic cross-linker units), the stress-strain characteristics is found to differ qualitatively from that in the other phases.
Polysoaps: Configurations and Elasticity
NASA Astrophysics Data System (ADS)
Halperin, A.
1997-03-01
Simple polymers are very long, flexible, linear molecules. Amphiphiles, soaps, are small molecules comprising of a part that prefers water over oil and a part that prefers oil over water. By combining the two we arrive at an interesting, little explored, class of materials: Polysoaps. These comprise of a water soluble backbone incorporating, at intervals, covalently bound amphiphilic monomers. In water, the polymerised amphiphiles aggregate into self assembled units known as micelles. This induces a dramatic modification of the spatial configurations of the polymers. What were featureless random coils now exhibit intramolecular, hierachial self organisation. Due to this self organisation it is necessary to modify the paradigms describing the large scale behaviour of these polymers: Their configurations, dimensions and elasticity. Understanding the behaviour of these polymers is of practical interest because of their wide range of industrial applications, ranging from cosmetics to paper coating. It is of fundamental interest because polysoaps are characterised by a rugged free energy landscape that is reminiscent of complex systems such as proteins and glasses. The talk concerns theoretical arguments regarding the following issues: (i) The design parameters that govern the spatial configurations of the polysoaps, (ii) The interaction between polysoaps and free amphiphiles, (iii) The effect of the intramolecular self organisation on the elasticity of the chains.
Bolen, W.P.; Tepordei, V.V.
2001-01-01
The estimated production during 2000 of construction aggregates, crushed stone, and construction sand and gravel increased by about 2.6% to 2.7 Gt (3 billion st), compared with 1999. The expansion that started in 1992 continued with record production levels for the ninth consecutive year. By commodity, construction sand and gravel production increased by 4.5% to 1.16 Gt (1.28 billion st), while crushed stone production increased by 1.3% to 1.56 Gt (1.72 billion st).
NASA Astrophysics Data System (ADS)
Rosa, Angelika D.; Sanchez-Valle, Carmen; Wang, Jingyun; Saikia, Ashima
2015-06-01
Seismic anomalies in the vicinity of cold slabs, including low velocity zones and enhanced seismic shear wave splitting have been commonly attributed to the presence of hydrated slab material. The dense hydrous magnesium silicate (DHMS) superhydrous phase B (ShyB, Mg10Si3H4O18) is considered an important water carrier to transition zone depth due to its large pressure stability and abundance (up to 20 vol.%) in hydrous peridotites. To interpret the observed seismic anomalies in terms of hydration and to assess the role of ShyB in deep water recycling, we have investigated the sound velocities and single-crystal elasticity of ShyB to pressures of 17.5 GPa at ambient temperature by Brillouin scattering spectroscopy in diamond anvil cells. The Voigt-Reuss-Hill averages for the adiabatic bulk moduli KS, shear moduli μ and their pressure derivatives yield KS = 150(2) GPa, μ = 99(1) GPa, (∂KS/∂P) = 4.7(2) and (∂μ/∂P) = 1.44(5). The aggregate compressional and shear wave velocities of ShyB at transition zone pressures are comparable to those of hydrous iron-bearing ringwoodite but are significantly lower than anhydrous phases in peridotites. The calculated velocity contrast between dry and ShyB-bearing hydrous peridotite (containing 1.2 wt.% of water) indicate that 17 vol.% of ShyB decreases both compressional VP and shear VS wave velocities by at most 2.5% at transition zone depths. Our results, combined with data for the deformation mechanisms of ShyB, indicate that ShyB aggregates develop strong textures under down-dip compression regime and yield a maximum shear wave splitting of 1.1% in the plane perpendicular to the compression axis at 17.5 GPa. Although ShyB in hydrous subducted peridotite would reduce its seismic velocities, the splitting geometry VSV > VSH generated by ShyB fabrics in peridotite is incompatible with the pattern observed in Tonga and Sangihe, and would require the contribution of other phases to be explained. Textured phase D is a
Unusually Large Young's Moduli of Amino Acid Molecular Crystals.
Azuri, Ido; Meirzadeh, Elena; Ehre, David; Cohen, Sidney R; Rappe, Andrew M; Lahav, Meir; Lubomirsky, Igor; Kronik, Leeor
2015-11-01
Young's moduli of selected amino acid molecular crystals were studied both experimentally and computationally using nanoindentation and dispersion-corrected density functional theory. The Young modulus is found to be strongly facet-dependent, with some facets exhibiting exceptionally high values (as large as 44 GPa). The magnitude of Young's modulus is strongly correlated with the relative orientation between the underlying hydrogen-bonding network and the measured facet. Furthermore, we show computationally that the Young modulus can be as large as 70-90 GPa if facets perpendicular to the primary direction of the hydrogen-bonding network can be stabilized. This value is remarkably high for a molecular solid and suggests the design of hydrogen-bond networks as a route for rational design of ultra-stiff molecular solids.
Dynamics of moduli and gaugino condensates in an expanding universe
Papineau, Chloé; Ramos-Sánchez, Saúl; Postma, Marieke E-mail: mpostma@nikhef.nl
2010-02-01
We study dynamical moduli stabilization driven by gaugino condensation in supergravity. In the presence of background radiation, there exists a region of initial conditions leading to successful stabilization. We point out that most of the allowed region corresponds to initial Hubble rate H close to the scale of condensation Λ, which is the natural cutoff of the effective theory. We first show that including the condensate dynamics sets a strong bound on the initial conditions. We then find that (complete) decoupling of the condensate happens at H about two orders of magnitude below Λ. This bound implies that in the usual scenario with the condensate integrated out, only the vicinity of the minimum leads to stabilization. Finally, we discuss the effects of thermal corrections.
Heavy tails in Calabi-Yau moduli spaces
NASA Astrophysics Data System (ADS)
Long, Cody; McAllister, Liam; McGuirk, Paul
2014-10-01
We study the statistics of the metric on Kähler moduli space in compactifications of string theory on Calabi-Yau hypersurfaces in toric varieties. We find striking hierarchies in the eigenvalues of the metric and of the Riemann curvature contribution to the Hessian matrix: both spectra display heavy tails. The curvature contribution to the Hessian is non-positive, suggesting a reduced probability of metastability compared to cases in which the derivatives of the Kähler potential are uncorrelated. To facilitate our analysis, we have developed a novel triangulation algorithm that allows efficient study of hypersurfaces with h 1,1 as large as 25, which is difficult using algorithms internal to pack-ages such as Sage. Our results serve as input for statistical studies of the vacuum structure in flux compactifications, and of the distribution of axion decay constants in string theory.
The Moduli Space of Asymptotically Cylindrical Calabi-Yau Manifolds
NASA Astrophysics Data System (ADS)
Conlon, Ronan J.; Mazzeo, Rafe; Rochon, Frédéric
2015-09-01
We prove that the deformation theory of compactifiable asymptotically cylindrical Calabi-Yau manifolds is unobstructed. This relies on a detailed study of the Dolbeault-Hodge theory and its description in terms of the cohomology of the compactification. We also show that these Calabi-Yau metrics admit a polyhomogeneous expansion at infinity, a result that we extend to asymptotically conical Calabi-Yau metrics as well. We then study the moduli space of Calabi-Yau deformations that fix the complex structure at infinity. There is a Weil-Petersson metric on this space, which we show is Kähler. By proving a local families L 2-index theorem, we exhibit its Kähler form as a multiple of the curvature of a certain determinant line bundle.
Aggregate breakdown of nanoparticulate titania
NASA Astrophysics Data System (ADS)
Venugopal, Navin
Six nanosized titanium dioxide powders synthesized from a sulfate process were investigated. The targeted end-use of this powder was for a de-NOx catalyst honeycomb monolith. Alteration of synthesis parameters had resulted principally in differences in soluble ion level and specific surface area of the powders. The goal of this investigation was to understand the role of synthesis parameters in the aggregation behavior of these powders. Investigation via scanning electron microscopy of the powders revealed three different aggregation iterations at specific length scales. Secondary and higher order aggregate strength was investigated via oscillatory stress rheometry as a means of simulating shear conditions encountered during extrusion. G' and G'' were measured as a function of the applied oscillatory stress. Oscillatory rheometry indicated a strong variation as a function of the sulfate level of the particles in the viscoelastic yield strengths. Powder yield stresses ranged from 3.0 Pa to 24.0 Pa of oscillatory stress. Compaction curves to 750 MPa found strong similarities in extrapolated yield point of stage I and II compaction for each of the powders (at approximately 500 MPa) suggesting that the variation in sulfate was greatest above the primary aggregate level. Scanning electron microscopy of samples at different states of shear in oscillatory rheometry confirmed the variation in the linear elastic region and the viscous flow regime. A technique of this investigation was to approach aggregation via a novel perspective: aggregates are distinguished as being loose open structures that are highly disordered and stochastic in nature. The methodology used was to investigate the shear stresses required to rupture the various aggregation stages encountered and investigate the attempt to realign the now free-flowing constituents comprising the aggregate into a denser configuration. Mercury porosimetry was utilized to measure the pore size of the compact resulting from
Torus action on the moduli spaces of torsion plane sheaves of multiplicity four
NASA Astrophysics Data System (ADS)
Choi, Jinwon; Maican, Mario
2014-09-01
We describe the torus fixed locus of the moduli space of stable sheaves with Hilbert polynomial 4m+1 on P2. We determine the torus representation of the tangent spaces at the fixed points, which leads to the computation of the Betti and Hodge numbers of the moduli space.
Kähler classes on universal moduli spaces and volumina of Quot spaces
NASA Astrophysics Data System (ADS)
Okonek, Christian; Teleman, Andrei
2015-10-01
We study canonical Kähler metrics on moduli spaces of stable oriented pairs in a very general framework, and we prove a universal formula expressing the Kähler class of such a moduli space in terms of characteristic classes of the universal bundle. We use these results to compute the volumina of certain Quot spaces.
Elastic constants of Pinus radiata D. Don by means of ultrasound transmission techniques
NASA Astrophysics Data System (ADS)
Baradit, Erik; Fuentealba, Cecillia
2001-08-01
This work consists in applying the crystals theory and mechanical waves propagation in wood. The wood when is considered as a body of orthotropic symmetry satisfies Hooke's law in its tensor form. Therefore, from the dynamical point of view the elastic constant are expressed by means of Christoffel's equation and can be determined using the ultrasound wave propagation of different polarization through wood. To obtain the constants is necessary the measurement of longitudinal and shear waves in different directions. The experiment results show that in some cases the exact shear wave velocities are very difficult to measure due to waves superposition . In this work the elastic constants (three moduli of elasticity and three shear moduli) Pinus radiata D. Don growing in Chile by ultrasound trasmission techniques are estimated.
Multi-scale imaging and elastic simulation of carbonates
NASA Astrophysics Data System (ADS)
Faisal, Titly Farhana; Awedalkarim, Ahmed; Jouini, Mohamed Soufiane; Jouiad, Mustapha; Chevalier, Sylvie; Sassi, Mohamed
2016-05-01
Digital Rock Physics (DRP) is an emerging technology that can be used to generate high quality, fast and cost effective special core analysis (SCAL) properties compared to conventional experimental techniques and modeling techniques. The primary workflow of DRP conssits of three elements: 1) image the rock sample using high resolution 3D scanning techniques (e.g. micro CT, FIB/SEM), 2) process and digitize the images by segmenting the pore and matrix phases 3) simulate the desired physical properties of the rocks such as elastic moduli and velocities of wave propagation. A Finite Element Method based algorithm, that discretizes the basic Hooke's Law equation of linear elasticity and solves it numerically using a fast conjugate gradient solver, developed by Garboczi and Day [1] is used for mechanical and elastic property simulations. This elastic algorithm works directly on the digital images by treating each pixel as an element. The images are assumed to have periodic constant-strain boundary condition. The bulk and shear moduli of the different phases are required inputs. For standard 1.5" diameter cores however the Micro-CT scanning reoslution (around 40 μm) does not reveal smaller micro- and nano- pores beyond the resolution. This results in an unresolved "microporous" phase, the moduli of which is uncertain. Knackstedt et al. [2] assigned effective elastic moduli to the microporous phase based on self-consistent theory (which gives good estimation of velocities for well cemented granular media). Jouini et al. [3] segmented the core plug CT scan image into three phases and assumed that micro porous phase is represented by a sub-extracted micro plug (which too was scanned using Micro-CT). Currently the elastic numerical simulations based on CT-images alone largely overpredict the bulk, shear and Young's modulus when compared to laboratory acoustic tests of the same rocks. For greater accuracy of numerical simulation prediction, better estimates of moduli inputs
Nonuniform elastic properties of macromolecules and effect of prestrain on their continuum nature.
Aggarwal, Ankush; May, Eric R; Brooks, Charles L; Klug, William S
2016-01-01
Many experimental and theoretical methods have been developed to calculate the coarse-grained continuum elastic properties of macromolecules. However, all of those methods assume uniform elastic properties. Following the continuum mechanics framework, we present a systematic way of calculating the nonuniform effective elastic properties from atomic thermal fluctuations obtained from molecular dynamics simulation at any coarse-grained scale using a potential of the mean-force approach. We present the results for a mutant of Sesbania mosaic virus capsid, where we calculate the elastic moduli at different scales and observe an apparent problem with the chosen reference configuration in some cases. We present a possible explanation using an elastic network model, where inducing random prestrain results in a similar behavior. This phenomenon provides a novel insight into the continuum nature of macromolecules and defines the limits on details that the elasticity theory can capture. Further investigation into prestrains could elucidate important aspects of conformational dynamics of macromolecules.
Replica treatment of the effective elastic behavior of a composite
NASA Astrophysics Data System (ADS)
Parcollet, O.; Barthelémy, M.; Zérah, G.
1996-02-01
We use the replica trick and a variational method to determine the effective elastic coefficients of a disordered composite. We obtain for them a self-consistent formula, which is satisfactory from the points of view of low disorder and low dilution expansions. When the bulk moduli K and the shear moduli μ are such that K>~2μ, it satisfies Hashin-Shtrikman bounds and is close to the usual effective-medium approximation. In the case K>~2μ, we observe a deviation of Hashin-Shtrikman bounds which can be understood by analogy with an equivalent one-dimensional problem. Finally, this calculation allows us to derive the rigidity threshold pr for any dimension d.
WE-E-9A-01: Ultrasound Elasticity
Emelianov, S; Hall, T; Bouchard, R
2014-06-15
Principles and techniques of ultrasound-based elasticity imaging will be presented, including quasistatic strain imaging, shear wave elasticity imaging, and their implementations in available systems. Deeper exploration of quasistatic methods, including elastic relaxation, and their applications, advantages, artifacts and limitations will be discussed. Transient elastography based on progressive and standing shear waves will be explained in more depth, along with applications, advantages, artifacts and limitations, as will measurement of complex elastic moduli. Comparisons will be made between ultrasound radiation force techniques, MR elastography, and the simple A mode plus mechanical plunger technique. Progress in efforts, such as that by the Quantitative Imaging Biomarkers Alliance, to reduce the differences in the elastic modulus reported by different commercial systems will be explained. Dr. Hall is on an Advisory Board for Siemens Ultrasound and has a research collaboration with them, including joint funding by R01CA140271 for nonlinear elasticity imaging. Learning Objectives: Be reminded of the long history of palpation of tissue elasticity for critical medical diagnosis and the relatively recent advances to be able to image tissue strain in response to an applied force. Understand the differences between shear wave speed elasticity measurement and imaging and understand the factors affecting measurement and image frame repletion rates. Understand shear wave propagation effects that can affect measurements, such as essentially lack of propagation in fluids and boundary effects, so important in thin layers. Know characteristics of available elasticity imaging phantoms, their uses and limitations. Understand thermal and cavitational limitations affecting radiation force-based shear wave imaging. Have learning and references adequate to for you to use in teaching elasticity imaging to residents and technologists. Be able to explain how elasticity measurement
Quantitative microstructure characterization and elastic properties upscaling of carbonate rocks
NASA Astrophysics Data System (ADS)
Vialle, Stephanie; Lebedev, Maxim
2016-04-01
Most Rock Physics models commonly used to predict elastic properties rely on a very simplified representation of the pore and grains geometry. Initially developed for siliclastic rocks, they do not apply easily and/or with as much success, to rocks with more complicated microstructure such as carbonates, which exhibit complex relationships between geophysical attributes and rock properties, such as P-wave velocity versus porosity. Furthermore, until recently, most microstructure imaging techniques such as optical microscopy, SEM, X-ray micro-CT, etc., only give a qualitative description of the pore and grain arrangement. Nano-indentation technique is a method that gives quantitative information by mean of local (micrometer size) measurements of elastic moduli. We used this technique to obtain 300 μm * 300 μm maps of Young's moduli (around 1000 data points) of two microporous carbonates of same mineralogy but of two different microstructures. As the size of the indenter tip is much smaller than the characteristic length of the heterogeneities in microstructure, the distribution of the Young's moduli can be deconvolved into its component parts (i.e. phases). SEM imaging of the same areas than the ones mapped by nano-indentation shows correlations between type of micrite and phases of different mean Young's modulus: tight micrites exhibiting a higher Young's modulus (up to 64 GPa) than microporous micrites (as low as 9 GPa). We then investigate different ways to upscale the measurements in order to get the effective bulk and shear moduli, from simply using volume fractions of the different phases, classical Hashin-Shrikman bounds, and Hill average; to using micro-CT imaging and analysis combined with rock physics models. Though more work is still needed to render nano-indentation technique a robust method for rock physics, both on the theory behind and on the upscaling of the measurements, these results that use nano-indentation method in a statistical way are very
Roulette inflation with Kaehler moduli and their axions
Bond, J. Richard; Kofman, Lev; Prokushkin, Sergey; Vaudrevange, Pascal M.
2007-06-15
We study 2-field inflation models based on the 'large-volume' flux compactification of type IIB string theory. The role of the inflaton is played by a Kaehler modulus {tau} corresponding to a 4-cycle volume and its axionic partner {theta}. The freedom associated with the choice of Calabi-Yau manifold and the nonperturbative effects defining the potential V({tau},{theta}) and kinetic parameters of the moduli brings an unavoidable statistical element to theory prior probabilities within the low-energy landscape. The further randomness of ({tau},{theta}) initial conditions allows for a large ensemble of trajectories. Features in the ensemble of histories include 'roulette trajectories', with long-lasting inflations in the direction of the rolling axion, enhanced in the number of e-foldings over those restricted to lie in the {tau}-trough. Asymptotic flatness of the potential makes possible an eternal stochastic self-reproducing inflation. A wide variety of potentials and inflaton trajectories agree with the cosmic microwave background and large scale structure data. In particular, the observed scalar tilt with weak or no running can be achieved in spite of a nearly critical de Sitter deceleration parameter and consequently a low gravity wave power relative to the scalar curvature power.
Roulette inflation with Kähler moduli and their axions
NASA Astrophysics Data System (ADS)
Bond, J. Richard; Kofman, Lev; Prokushkin, Sergey; Vaudrevange, Pascal M.
2007-06-01
We study 2-field inflation models based on the “large-volume” flux compactification of type IIB string theory. The role of the inflaton is played by a Kähler modulus τ corresponding to a 4-cycle volume and its axionic partner θ. The freedom associated with the choice of Calabi-Yau manifold and the nonperturbative effects defining the potential V(τ,θ) and kinetic parameters of the moduli brings an unavoidable statistical element to theory prior probabilities within the low-energy landscape. The further randomness of (τ,θ) initial conditions allows for a large ensemble of trajectories. Features in the ensemble of histories include “roulette trajectories,” with long-lasting inflations in the direction of the rolling axion, enhanced in the number of e-foldings over those restricted to lie in the τ-trough. Asymptotic flatness of the potential makes possible an eternal stochastic self-reproducing inflation. A wide variety of potentials and inflaton trajectories agree with the cosmic microwave background and large scale structure data. In particular, the observed scalar tilt with weak or no running can be achieved in spite of a nearly critical de Sitter deceleration parameter and consequently a low gravity wave power relative to the scalar curvature power.
Framed BPS states, moduli dynamics, and wall-crossing
NASA Astrophysics Data System (ADS)
Lee, Sungjay; Yi, Piljin
2011-04-01
We formulate supersymmetric low energy dynamics for BPS dyons in strongly-coupled N = 2 Seiberg-Witten theories, and derive wall-crossing formulae thereof. For BPS states made up of a heavy core state and n probe (halo) dyons around it, we derive a reliable supersymmetric moduli dynamics with 3 n bosonic coordinates and 4 n fermionic superpartners. Attractive interactions are captured via a set of supersymmetric potential terms, whose detail depends only on the charges and the special Kähler data of the underlying N = 2 theories. The small parameters that control the approximation are not electric couplings but the mass ratio between the core and the probe, as well as the distance to the marginal stability wall where the central charges of the probe and of the core align. Quantizing the dynamics, we construct BPS bound states and derive the primitive and the semi-primitive wall-crossing formulae from the first principle. We speculate on applications to line operators and Darboux coordinates, and also about extension to supergravity setting.
Explaining the electroweak scale and stabilizing moduli in M theory
Acharya, Bobby S.; Bobkov, Konstantin; Kane, Gordon L.; Kumar, Piyush; Shao Jing
2007-12-15
In a recent paper [B. Acharya, K. Bobkov, G. Kane, P. Kumar, and D. Vaman, Phys. Rev. Lett. 97, 191601 (2006).] it was shown that in fluxless M theory vacua with at least two hidden sectors undergoing strong gauge dynamics and a particular form of the Kaehler potential, all moduli are stabilized by the effective potential and a stable hierarchy is generated, consistent with standard gauge unification. This paper explains the results of [B. Acharya, K. Bobkov, G. Kane, P. Kumar, and D. Vaman, Phys. Rev. Lett. 97, 191601 (2006).] in more detail and generalizes them, finding an essentially unique de Sitter vacuum under reasonable conditions. One of the main phenomenological consequences is a prediction which emerges from this entire class of vacua: namely, gaugino masses are significantly suppressed relative to the gravitino mass. We also present evidence that, for those vacua in which the vacuum energy is small, the gravitino mass, which sets all the superpartner masses, is automatically in the TeV-100 TeV range.
Elastic properties of Pu metal and Pu-Ga alloys
NASA Astrophysics Data System (ADS)
Söderlind, Per; Landa, Alex; Klepeis, J. E.; Suzuki, Y.; Migliori, A.
2010-06-01
We present elastic properties, theoretical and experimental, of Pu metal and Pu-Ga (δ) alloys together with ab initio equilibrium equation of state for these systems. For the theoretical treatment we employ density-functional theory in conjunction with spin-orbit coupling and orbital polarization for the metal and coherent-potential approximation for the alloys. Pu and Pu-Ga alloys are also investigated experimentally using resonant ultrasound spectroscopy. We show that orbital correlations become more important proceeding from α→β→γ plutonium, thus suggesting increasing f -electron correlation and a corresponding softening of the elastic moduli. For the δ-Pu-Ga alloys we find a softening with larger Ga content, i.e., atomic volume, bulk modulus, and elastic constants imply a weakened chemical bonding with addition of Ga. Our measurements confirm qualitatively the theory but uncertainties remain when comparing the model with experiments.
Moduli-space dynamics of noncommutative abelian sigma-model solitons
NASA Astrophysics Data System (ADS)
Klawunn, Michael; Lechtenfeld, Olaf; Petersen, Stefan
2006-06-01
In the noncommutative (Moyal) plane, we relate exact U(1) sigma-model solitons to generic scalar-field solitons for an infinitely stiff potential. The static k-lump moduli space Bbb Ck/Sk features a natural Kähler metric induced from an embedding Grassmannian. The moduli-space dynamics is blind against adding a WZW-like term to the sigma-model action and thus also applies to the integrable U(1) Ward model. For the latter's two-soliton motion we compare the exact field configurations with their supposed moduli-space approximations. Surprisingly, the two do not match, which questions the adiabatic method for noncommutative solitons.
Shear moduli in bcc-fcc structure transition of colloidal crystals.
Zhou, Hongwei; Xu, Shenghua; Sun, Zhiwei; Zhu, Ruzeng
2015-10-14
Shear moduli variation in the metastable-stable structure transition of charged colloidal crystals was investigated by the combination techniques of torsional resonance spectroscopy and reflection spectrometer. Modulus of the system increases with the proceeding of the transition process and it finally reaches the maximum value at the end of the transition. For colloidal crystals in stable state, the experimental moduli show good consistence with theoretical expectations. However, in the transition process, the moduli are much smaller than theoretical ones and this can be chalked up to crystalline imperfection in the transition state.
Measurement of Elastic Modulus of Collagen Type I Single Fiber.
Dutov, Pavel; Antipova, Olga; Varma, Sameer; Orgel, Joseph P R O; Schieber, Jay D
2016-01-01
Collagen fibers are the main components of the extra cellular matrix and the primary contributors to the mechanical properties of tissues. Here we report a novel approach to measure the longitudinal component of the elastic moduli of biological fibers under conditions close to those found in vivo and apply it to type I collagen from rat tail tendon. This approach combines optical tweezers, atomic force microscopy, and exploits Euler-Bernoulli elasticity theory for data analysis. This approach also avoids drying for measurements or visualization, since samples are freshly extracted. Importantly, strains are kept below 0.5%, which appear consistent with the linear elastic regime. We find, surprisingly, that the longitudinal elastic modulus of type I collagen cannot be represented by a single quantity but rather is a distribution that is broader than the uncertainty of our experimental technique. The longitudinal component of the single-fiber elastic modulus is between 100 MPa and 360 MPa for samples extracted from different rats and/or different parts of a single tail. Variations are also observed in the fibril-bundle/fibril diameter with an average of 325±40 nm. Since bending forces depend on the diameter to the fourth power, this variation in diameter is important for estimating the range of elastic moduli. The remaining variations in the modulus may be due to differences in composition of the fibril-bundles, or the extent of the proteoglycans constituting fibril-bundles, or that some single fibrils may be of fibril-bundle size. PMID:26800120
Determination of the elastic modulus of snow via acoustic measurements
NASA Astrophysics Data System (ADS)
Gerling, Bastian; van Herwijnen, Alec; Löwe, Henning
2016-04-01
The elastic modulus of snow is a key quantity from the viewpoint of avalanche research and forecasting, snow engineering or materials science in general. Since it is a fundamental property, many measurements have been reported in the literature. Due to differences in measurement methods, there is a lot of variation in the reported values. Especially values derived via computer tomography (CT) based numerical calculations using finite element methods are not corresponding to the results of other methods. The central issue is that CT based moduli are purely elastic whereas other methods may include viscoelastic deformation. In order to avoid this discrepancy we derived the elastic modulus of snow via wave propagation measurements and compared our results with CT based calculations. We measured the arrival times of acoustic pulses propagating through the snow samples to determine the P-wave velocity and in turn derive the elastic modulus along the direction of wave propagation. We performed a series of laboratory experiments to derive the P-wave modulus of snow in relation to density. The P-wave modulus ranged from 10 to 280 MPa for a snow density between 150 and 370 kg/m^3;. The moduli derived from the acoustic measurements correlated well with the CT-based values and both exhibited a power law trend over the entire density range. Encouraged by these results we used the acoustic method to investigate the temporal evolution of the elastic modulus. The rate of increase was very close to values mentioned in literature on the sintering rate of snow. Overall, our results are a first but important step towards a new measurement method to attain the elastic properties of snow.
Structure, stability and elasticity of DNA nanotubes.
Joshi, Himanshu; Dwaraknath, Anjan; Maiti, Prabal K
2015-01-14
DNA nanotubes are tubular structures composed of DNA crossover molecules. We present a bottom up approach for the construction and characterization of these structures. Various possible topologies of nanotubes are constructed such as 6-helix, 8-helix and tri-tubes with different sequences and lengths. We have used fully atomistic molecular dynamics simulations to study the structure, stability and elasticity of these structures. Several nanosecond long MD simulations give the microscopic details about DNA nanotubes. Based on the structural analysis of simulation data, we show that 6-helix nanotubes are stable and maintain their tubular structure; while 8-helix nanotubes are flattened to stabilize themselves. We also comment on the sequence dependence and the effect of overhangs. These structures are approximately four times more rigid having a stretch modulus of ∼4000 pN compared to the stretch modulus of 1000 pN of a DNA double helix molecule of the same length and sequence. The stretch moduli of these nanotubes are also three times larger than those of PX/JX crossover DNA molecules which have stretch moduli in the range of 1500-2000 pN. The calculated persistence length is in the range of a few microns which is close to the reported experimental results on certain classes of DNA nanotubes.
Environmental bias and elastic curves on surfaces
NASA Astrophysics Data System (ADS)
Guven, Jemal; María Valencia, Dulce; Vázquez-Montejo, Pablo
2014-09-01
The behavior of an elastic curve bound to a surface will reflect the geometry of its environment. This may occur in an obvious way: the curve may deform freely along directions tangent to the surface, but not along the surface normal. However, even if the energy itself is symmetric in the curve's geodesic and normal curvatures, which control these modes, very distinct roles are played by the two. If the elastic curve binds preferentially on one side, or is itself assembled on the surface, not only would one expect the bending moduli associated with the two modes to differ, binding along specific directions, reflected in spontaneous values of these curvatures, may be favored. The shape equations describing the equilibrium states of a surface curve described by an elastic energy accommodating environmental factors will be identified by adapting the method of Lagrange multipliers to the Darboux frame associated with the curve. The forces transmitted to the surface along the surface normal will be determined. Features associated with a number of different energies, both of physical relevance and of mathematical interest, are described. The conservation laws associated with trajectories on surface geometries exhibiting continuous symmetries are also examined.
NASA Astrophysics Data System (ADS)
Perreard, I. M.; Pattison, A. J.; Doyley, M.; McGarry, M. D. J.; Barani, Z.; Van Houten, E. E.; Weaver, J. B.; Paulsen, K. D.
2010-11-01
The mechanical model commonly used in magnetic resonance elastography (MRE) is linear elasticity. However, soft tissue may exhibit frequency- and direction-dependent (FDD) shear moduli in response to an induced excitation causing a purely linear elastic model to provide an inaccurate image reconstruction of its mechanical properties. The goal of this study was to characterize the effects of reconstructing FDD data using a linear elastic inversion (LEI) algorithm. Linear and FDD phantoms were manufactured and LEI images were obtained from time-harmonic MRE acquisitions with variations in frequency and driving signal amplitude. LEI responses to artificially imposed uniform phase shifts in the displacement data from both purely linear elastic and FDD phantoms were also evaluated. Of the variety of FDD phantoms considered, LEI appeared to tolerate viscoelastic data-model mismatch better than deviations caused by poroelastic and anisotropic mechanical properties in terms of visual image contrast. However, the estimated shear modulus values were substantially incorrect relative to independent mechanical measurements even in the successful viscoelastic cases and the variations in mean values with changes in experimental conditions associated with uniform phase shifts, driving signal frequency and amplitude were unpredictable. Overall, use of LEI to reconstruct data acquired in phantoms with FDD material properties provided biased results under the best conditions and significant artifacts in the worst cases. These findings suggest that the success with which LEI is applied to MRE data in tissue will depend on the underlying mechanical characteristics of the tissues and/or organs systems of clinical interest.
NASA Astrophysics Data System (ADS)
Li, Tao; Zeng, Kaiyang
2014-01-01
The macroscopic mechanical properties of the abalone shell have been studied extensively in the literature, but the in situ nanoscale elasticity of various micro-constituents in the shell have not been characterized and reported yet. In this study, the nanoscale elasticity mappings including different micro-constituents in abalone shell were observed by using the Contact Resonance Force Microscopy (CR-FM) technique. CR-FM is one of the advanced scanning probe microscopy techniques that is able to quantify the local elastic moduli of various materials in a non-destructive manner. Instead of an average value, an elasticity mapping that reveals the nanoscale variations of elastic moduli with location can be extracted and correlated with the topography of the structure. Therefore in this study, by adopting the CR-FM technique that is incorporated with the band excitation technique, the elasticity variations of the abalone shell caused by different micro-constituents and crystal orientations are reported, and the elasticity values of the aragonite and calcite nanograins are quantified.The macroscopic mechanical properties of the abalone shell have been studied extensively in the literature, but the in situ nanoscale elasticity of various micro-constituents in the shell have not been characterized and reported yet. In this study, the nanoscale elasticity mappings including different micro-constituents in abalone shell were observed by using the Contact Resonance Force Microscopy (CR-FM) technique. CR-FM is one of the advanced scanning probe microscopy techniques that is able to quantify the local elastic moduli of various materials in a non-destructive manner. Instead of an average value, an elasticity mapping that reveals the nanoscale variations of elastic moduli with location can be extracted and correlated with the topography of the structure. Therefore in this study, by adopting the CR-FM technique that is incorporated with the band excitation technique, the
Yuan, Hongyi; Singh, Gurpreet; Raghavan, Dharmaraj; Al-Enizi, Abdullah M; Elzatahry, Ahmed; Karim, Alamgir
2014-08-27
Structure-interaction-mechanical property correlation in bionanocomposite thin films is an area of growing interest for research and application areas from barrier to molecular transport to UV blocking layers for polymer solar cells to dielectric properties modification. Here we study flow coated ultrathin to thin films (70-150 nm) of clay bionanocomposites to understand the nanoparticle dispersion and its effect on nanomechanical properties. Binary and ternary thin film systems of polylactide (PLA), polycaprolactone (PCL), and Cloisite 30B (C30B) clay platelets were investigated. While C30B was only partially intercalated by PLA, it was almost completely intercalated by PCL due to strong hydrogen bonding. In addition, the dispersion of C30B improved continuously and linearly with increasing PCL content in homogeneously cast blended PLA:PCL. GIWAXS confirmed that the intercalated clay platelets in PLA and PCL were dominantly oriented parallel to the substrate. The method of strain induced elastic buckling instability for mechanical measurements (SIEBIMM) showed that pure PLA and PCL had in-plane modulus unchanged from bulk values for this range of ultrathin-thin films. In PLA/C30B nanocomposite thin films, the in-plane elastic modulus rapidly increased by up to 26% with 2 wt % C30B, but saturated thereafter up to 10 wt % C30B forming C30B aggregates. On the other hand, the in-plane elastic modulus of PCL/C30B thin films increased linearly by up to 43% with 10 wt % C30B due to the higher interaction driven dispersion, results that were shown to fit well with the Halpin-Tsai model. We conclude that the different strengthening behavior came from different interaction driven dispersion states of C30B in polymer matrices, governed by their molecular structures. PMID:25062299
Numerical Weil-Petersson metrics on moduli spaces of Calabi-Yau manifolds
NASA Astrophysics Data System (ADS)
Keller, Julien; Lukic, Sergio
2015-06-01
We introduce a simple and very fast algorithm to compute Weil-Petersson metrics on moduli spaces of Calabi-Yau varieties. Additionally, we introduce a second algorithm to approximate the same metric using Donaldson's quantization link between infinite and finite dimensional Geometric Invariant Theoretical (GIT) quotients that describe moduli spaces of varieties. Although this second algorithm is slower and more sophisticated, it can also be used to compute similar metrics on other moduli spaces (e.g. moduli spaces of vector bundles on Calabi-Yau varieties). We study the convergence properties of both algorithms and provide explicit computer implementations using a family of Calabi-Yau quintic hypersurfaces in P4. Also, we include discussions on: the existing methods that are used to compute this class of metrics, the background material that we use to build our algorithms, and how to extend the second algorithm to the vector bundle case.
Compositional dependence of Young's moduli for amorphous FeCo-SiO{sub 2} thin films
Zhang, L.; Xie, J. L.; Deng, L. J.; Guo, Q.; Zhu, Z. W.; Bi, L.
2011-04-01
Systematic force-deflection measurements with microcantilevers and a combinatorial-deposition method have been used to investigate the Young's moduli of amorphous composite FeCo-SiO{sub 2} thin films as a function of film composition, with high compositional resolution. It is found that the modulus decreases monotonically with increasing FeCo content. Such a trend can be explained in terms of the metalloid atoms having a significant effect on the Young's moduli of metal-metalloid composites, which is associated with the strong chemical interaction between the metalloid and themetallic atoms rather than that between the metallic components themselves. This work provides an efficient and effective method to study the moduli of magnetic thin films over a largecomposition coverage, and to compare the relative magnitudes of moduli for differentcompositions at high compositional resolution.
Young's moduli of surface-bound liposomes by atomic force microscopy force measurements.
Brochu, Heïdi; Vermette, Patrick
2008-03-01
Mechanical properties of layers of intact liposomes attached by specific interactions on solid surfaces were studied by atomic force microscopy (AFM) force measurements. Force-distance measurements using colloidal probe tips were obtained over liposome layers and used to calculate Young's moduli by using the Hertz contact theory. A classical Hertz model and a modified Hertz one have been used to extract Young's moduli from AFM force curves. The modified model, proposed by Dimitriadis, is correcting for the finite sample thickness since Hertz's classical model is assuming that the sample is infinitely thick. Values for Young's moduli of 40 and 8 kPa have been obtained using the Hertz model for one and three layers of intact liposomes, respectively. Young's moduli of approximately 3 kPa have been obtained using the corrected Hertz model for both one and three layers of surface-bound liposomes. Compression work performed by the colloidal probe to compress these liposome layers has also been calculated.
Bubbles attenuate elastic waves at seismic frequencies
NASA Astrophysics Data System (ADS)
Tisato, Nicola; Quintal, Beatriz; Chapman, Samuel; Podladchikov, Yury; Burg, Jean-Pierre
2016-04-01
The vertical migration of multiphase fluids in the crust can cause hazardous events such as eruptions, explosions, pollution and earthquakes. Although seismic tomography could potentially provide a detailed image of such fluid-saturated regions, the interpretation of the tomographic signals is often controversial and fails in providing a conclusive map of the subsurface saturation. Seismic tomography should be improved considering seismic wave attenuation (1/Q) and the dispersive elastic moduli which allow accounting for the energy lost by the propagating elastic wave. In particular, in saturated media a significant portion of the energy carried by the propagating wave is dissipated by the wave-induced-fluid-flow and the wave-induced-gas-exsolution-dissolution (WIGED) mechanisms. The WIGED mechanism describes how a propagating wave modifies the thermodynamic equillibrium between different fluid phases causing the exsolution and the dissolution of the gas in the liquid, which in turn causes a significant frequency dependent 1/Q and moduli dispersion. The WIGED theory was initially postulated for bubbly magmas but only recently was extended to bubbly water and experimentally demonstrated. Here we report these theory and laboratory experiments. Specifically, we present i) attenuation measurements performed by means of the Broad Band Attenuation Vessel on porous media saturated with water and different gases, and ii) numerical experiments validating the laboratory observations. Finally, we will extend the theory to fluids and to pressure-temperature conditions which are typical of phreatomagmatic and hydrocarbon domains and we will compare the propagation of seismic waves in bubble-free and bubble-bearing subsurface domains. With the present contribution we extend the knowledge about attenuation in rocks which are saturated with multiphase fluid demonstrating that the WIGED mechanism could be extremely important to image subsurface gas plumes.
A-thermal elastic behavior of silicate glasses.
Rabia, Mohammed Kamel; Degioanni, Simon; Martinet, Christine; Le Brusq, Jacques; Champagnon, Bernard; Vouagner, Dominique
2016-02-24
Depending on the composition of silicate glasses, their elastic moduli can increase or decrease as function of the temperature. Studying the Brillouin frequency shift of these glasses versus temperature allows the a-thermal composition corresponding to an intermediate glass to be determined. In an intermediate glass, the elastic moduli are independent of the temperature over a large temperature range. For sodium alumino-silicate glasses, the a-thermal composition is close to the albite glass (NaAlSi3O8). The structural origin of this property is studied by in situ high temperature Raman scattering. The structure of the intermediate albite glass and of silica are compared at different temperatures between room temperature and 600 °C. When the temperature increases, it is shown that the high frequency shift of the main band at 440 cm(-1) in silica is a consequence of the cristobalite-like alpha-beta transformation of 6-membered rings. This effect is stronger in silica than bond elongation (anharmonic effects). As a consequence, the elastic moduli of silica increase as the temperature increases. In the albite glass, the substitution of 25% of Si(4+) ions by Al(3+) and Na(+) ions decreases the proportion of SiO2 6-membered rings responsible for the silica anomaly. The effects of the silica anomaly balance the anharmonicity in albite glass and give rise to an intermediate a-thermal glass. Different networks, formers or modifiers, can be added to produce different a-thermal glasses with useful mechanical or chemical properties.
A-thermal elastic behavior of silicate glasses.
Rabia, Mohammed Kamel; Degioanni, Simon; Martinet, Christine; Le Brusq, Jacques; Champagnon, Bernard; Vouagner, Dominique
2016-02-24
Depending on the composition of silicate glasses, their elastic moduli can increase or decrease as function of the temperature. Studying the Brillouin frequency shift of these glasses versus temperature allows the a-thermal composition corresponding to an intermediate glass to be determined. In an intermediate glass, the elastic moduli are independent of the temperature over a large temperature range. For sodium alumino-silicate glasses, the a-thermal composition is close to the albite glass (NaAlSi3O8). The structural origin of this property is studied by in situ high temperature Raman scattering. The structure of the intermediate albite glass and of silica are compared at different temperatures between room temperature and 600 °C. When the temperature increases, it is shown that the high frequency shift of the main band at 440 cm(-1) in silica is a consequence of the cristobalite-like alpha-beta transformation of 6-membered rings. This effect is stronger in silica than bond elongation (anharmonic effects). As a consequence, the elastic moduli of silica increase as the temperature increases. In the albite glass, the substitution of 25% of Si(4+) ions by Al(3+) and Na(+) ions decreases the proportion of SiO2 6-membered rings responsible for the silica anomaly. The effects of the silica anomaly balance the anharmonicity in albite glass and give rise to an intermediate a-thermal glass. Different networks, formers or modifiers, can be added to produce different a-thermal glasses with useful mechanical or chemical properties. PMID:26815634
Parnell, William J; Vu, M B; Grimal, Q; Naili, S
2012-07-01
We compare theoretical predictions of the effective elastic moduli of cortical bone at both the meso- and macroscales. We consider the efficacy of three alternative approaches: the method of asymptotic homogenization, the Mori-Tanaka scheme and the Hashin-Rosen bounds. The methods concur for specific engineering moduli such as the axial Young's modulus but can vary for others. In a past study, the effect of porosity alone on mesoscopic properties of cortical bone was considered, taking the matrix to be isotropic. Here, we consider the additional influence of the transverse isotropy of the matrix. We make the point that micromechanical approaches can be used in two alternative ways to predict either the macroscopic (size of cortical bone sample) or mesoscopic (in between micro- and macroscales) effective moduli, depending upon the choice of representative volume element size. It is widely accepted that the mesoscale behaviour is an important aspect of the mechanical behaviour of bone but models incorporating its effect have started to appear only relatively recently. Before this only macroscopic behaviour was addressed. Comparisons are drawn with experimental data and simulations from the literature for macroscale predictions with particularly good agreement in the case of dry bone. Finally, we show how predictions of the effective mesoscopic elastic moduli can be made which retain dependence on the well-known porosity gradient across the thickness of cortical bone.
Parnell, William J; Vu, M B; Grimal, Q; Naili, S
2012-07-01
We compare theoretical predictions of the effective elastic moduli of cortical bone at both the meso- and macroscales. We consider the efficacy of three alternative approaches: the method of asymptotic homogenization, the Mori-Tanaka scheme and the Hashin-Rosen bounds. The methods concur for specific engineering moduli such as the axial Young's modulus but can vary for others. In a past study, the effect of porosity alone on mesoscopic properties of cortical bone was considered, taking the matrix to be isotropic. Here, we consider the additional influence of the transverse isotropy of the matrix. We make the point that micromechanical approaches can be used in two alternative ways to predict either the macroscopic (size of cortical bone sample) or mesoscopic (in between micro- and macroscales) effective moduli, depending upon the choice of representative volume element size. It is widely accepted that the mesoscale behaviour is an important aspect of the mechanical behaviour of bone but models incorporating its effect have started to appear only relatively recently. Before this only macroscopic behaviour was addressed. Comparisons are drawn with experimental data and simulations from the literature for macroscale predictions with particularly good agreement in the case of dry bone. Finally, we show how predictions of the effective mesoscopic elastic moduli can be made which retain dependence on the well-known porosity gradient across the thickness of cortical bone. PMID:22109098
Engineering a Fibrocartilage Spectrum Through Modulation of Aggregate Redifferentiation
Murphy, Meghan K.; Masters, Taylor E.; Hu, Jerry C.; Athanasiou, Kyriacos A.
2015-01-01
Expanded costochondral cells provide a clinically relevant cell source for engineering both fibrous and hyaline articular cartilage. Expanding chondrocytes in monolayer results in a shift toward a proliferative, fibroblastic phenotype. Three-dimensional aggregate culture may, however, be used to recover chondrogenic matrix production. This study sought to engineer a spectrum of fibrous to hyaline neocartilage from a single cell source by varying the duration of three-dimensional culture following expansion. In third passage porcine costochondral cells, the effects of aggregate culture duration were assessed after 0, 8, 11, 14, and 21 days of aggregate culture and after 4 subsequent weeks of neocartilage formation. Varying the duration of aggregate redifferentiation generated a spectrum of fibrous to hyaline neocartilage. Within 8 days of aggregation, proliferation ceased, and collagen and glycosaminoglycan production increased, compared with monolayer cells. In self-assembled neocartilage, type II to I collagen ratio increased with increasing aggregate duration, yet glycosaminoglycan content varied minimally. Notably, 14 days of aggregate redifferentiation increased collagen content by 25%, tensile modulus by over 110%, and compressive moduli by over 50%, compared with tissue formed in the absence of redifferentiation. A spectrum of fibrous to hyaline cartilage was generated using a single, clinically relevant cell source, improving the translational potential of engineered cartilage. PMID:24380383
Elasticity of interfacial rafts of hard particles with soft shells.
Knoche, Sebastian; Kierfeld, Jan
2015-05-19
We study an elasticity model for compressed protein monolayers or particle rafts at a liquid interface. Based on the microscopic view of hard-core particles with soft shells, a bead-spring model is formulated and analyzed in terms of continuum elasticity theory. The theory can be applied, for example, to hydrophobin-coated air-water interfaces or, more generally, to liquid interfaces coated with an adsorbed monolayer of interacting hard-core particles. We derive constitutive relations for such particle rafts and describe the buckling of compressed planar liquid interfaces as well as their apparent Poisson ratio. We also use the constitutive relations to obtain shape equations for pendant or buoyant capsules attached to a capillary, and to compute deflated shapes of such capsules. A comparison with capsules obeying the usual Hookean elasticity (without hard cores) reveals that the hard cores trigger capsule wrinkling. Furthermore, it is shown that a shape analysis of deflated capsules with hard-core/soft-shell elasticity gives apparent elastic moduli which can be much higher than the original values if Hookean elasticity is assumed.
Elasticity of interfacial rafts of hard particles with soft shells.
Knoche, Sebastian; Kierfeld, Jan
2015-05-19
We study an elasticity model for compressed protein monolayers or particle rafts at a liquid interface. Based on the microscopic view of hard-core particles with soft shells, a bead-spring model is formulated and analyzed in terms of continuum elasticity theory. The theory can be applied, for example, to hydrophobin-coated air-water interfaces or, more generally, to liquid interfaces coated with an adsorbed monolayer of interacting hard-core particles. We derive constitutive relations for such particle rafts and describe the buckling of compressed planar liquid interfaces as well as their apparent Poisson ratio. We also use the constitutive relations to obtain shape equations for pendant or buoyant capsules attached to a capillary, and to compute deflated shapes of such capsules. A comparison with capsules obeying the usual Hookean elasticity (without hard cores) reveals that the hard cores trigger capsule wrinkling. Furthermore, it is shown that a shape analysis of deflated capsules with hard-core/soft-shell elasticity gives apparent elastic moduli which can be much higher than the original values if Hookean elasticity is assumed. PMID:25901364
On dynamic and elastic stability of group IIIB metal carbides: Ab-initio calculations
NASA Astrophysics Data System (ADS)
Sahoo, B. D.; Mukherjee, D.; Joshi, K. D.; Gupta, Satish C.
2012-06-01
The elastic and dynamic stabilities of IIIB metal carbides in NaCl (B1 phase) type fcc structure have been investigated at zero pressure by first-principles calculations using the plane-wave pseudopotential method. The analysis of elastic moduli and phonon dispersion relations in ScC and YC suggest that the B1 phase is stable both elastically as well as dynamically at zero pressure. In contrast, for LaC, we find that the shear elastic modulus C' (=(C11-C12)/2) is negative at zero pressure and also the phonon frequencies in various directions of the Brillouin zone are imaginary, indicative of elastic as well as dynamic instability of B1 phase at zero pressure in this compound.
Using dynamic holography for studying the elastic properties of solids
NASA Astrophysics Data System (ADS)
Kamshilin, A. A.; Oliva, A.; Moreno, E.
1990-06-01
The elastic properties of several well-known materials (aluminum, duralumin, steel, and PVC) were investigated using an automatic holographic interferometer with a photorefractive electrooptical titanium sillenite crystal (Bi12TiO20). The Young's moduli determined by this method are in good agreement with the values from reference tables. The method is characterized by high reliability and does not require the use of expensive vibration isolation equipment since the reliability of holographic interferograms depends on the adaptability of the crystals to changing external conditions.
NASA Astrophysics Data System (ADS)
Bernabe, Y.; Evans, J.
2012-12-01
In a previous work we investigated stress transfer in a pair of grain contacts undergoing pressure solution (PS) creep, showed that stress transfer resulted in a significant decrease in overall strain rate, and concluded that PS creep rates of a randomly packed granular aggregate should be affected by packing evolution and the formation of new contacts during creep. To test these conclusions further, we are numerically simulating the "elastic" hydrostatic compression of a random pack of spheres, using a numerical method similar to that of Cundall and Strack [1979]. We assumed that the spheres were frictionless (i.e., spheres in contact only interacted through normal forces) and that the contact forces obeyed the non-linear Digby [1981] model. In order to determine the PS creep compression of the sphere pack subjected to a constant confining pressure pc, we calculated the thicknesses of the dissolved layers at each individual grain contact during a small time increment and, from these, the overall deformation of the sphere pack. We used an analytical expression discussed in our previous paper and originating from Lehner and Leroy [2004]. During these simulations, we also computed the mean coordination number of the grain contact z, the effective bulk modulus K of the sphere pack and others parameters characterizing the topological and mechanical properties of the sphere assembly. Our results show strong non-linear increase of z and K with pc during "elastic" compression and, with time, during PS creep. The packing rearrangements associated with PS creep produce complex time dependence of the overall deformation ɛ(t). We observed a regular transition from ɛ∝t^3/4 at early times (i.e., less than 0.1 years) and ɛ∝t^1/3 at late times (i.e., more than 1000 years). Cundall, P.A., and O.D.L. Strack (1979), A discrete numerical model for granular assemblies, Geotech., 29, 47-65. Digby, P.J. (1981), The effective elastic moduli of porous rocks, J. Appl. Mech., 48, 803
NASA Astrophysics Data System (ADS)
Penta, Raimondo; Gerisch, Alf
2016-08-01
The classical asymptotic homogenization approach for linear elastic composites with discontinuous material properties is considered as a starting point. The sharp length scale separation between the fine periodic structure and the whole material formally leads to anisotropic elastic-type balance equations on the coarse scale, where the arising fourth rank operator is to be computed solving single periodic cell problems on the fine scale. After revisiting the derivation of the problem, which here explicitly points out how the discontinuity in the individual constituents' elastic coefficients translates into stress jump interface conditions for the cell problems, we prove that the gradient of the cell problem solution is minor symmetric and that its cell average is zero. This property holds for perfect interfaces only (i.e., when the elastic displacement is continuous across the composite's interface) and can be used to assess the accuracy of the computed numerical solutions. These facts are further exploited, together with the individual constituents' elastic coefficients and the specific form of the cell problems, to prove a theorem that characterizes the fourth rank operator appearing in the coarse-scale elastic-type balance equations as a composite material effective elasticity tensor. We both recover known facts, such as minor and major symmetries and positive definiteness, and establish new facts concerning the Voigt and Reuss bounds. The latter are shown for the first time without assuming any equivalence between coarse and fine-scale energies (Hill's condition), which, in contrast to the case of representative volume elements, does not identically hold in the context of asymptotic homogenization. We conclude with instructive three-dimensional numerical simulations of a soft elastic matrix with an embedded cubic stiffer inclusion to show the profile of the physically relevant elastic moduli (Young's and shear moduli) and Poisson's ratio at increasing (up to
Scaling Behavior and Strain Dependence of In-Plane Elastic Properties of Graphene.
Los, J H; Fasolino, A; Katsnelson, M I
2016-01-01
We show by atomistic simulations that, in the thermodynamic limit, the in-plane elastic moduli of graphene at finite temperature vanish with system size L as a power law L(-η(u)) with η(u)≃0.325, in agreement with the membrane theory. We provide explicit expressions for the size and strain dependence of graphene's elastic moduli, allowing comparison to experimental data. Our results explain the recently experimentally observed increase of the Young modulus by more than a factor of 2 for a tensile strain of only a few per mill. The difference of a factor of 2 between the measured asymptotic value of the Young modulus for tensilely strained systems and the value from ab initio calculations remains, however, unsolved. We also discuss the asymptotic behavior of the Poisson ratio, for which our simulations disagree with the predictions of the self-consistent screening approximation.
Effective-medium theory of elastic waves in random networks of rods.
Katz, J I; Hoffman, J J; Conradi, M S; Miller, J G
2012-06-01
We formulate an effective medium (mean field) theory of a material consisting of randomly distributed nodes connected by straight slender rods, hinged at the nodes. Defining wavelength-dependent effective elastic moduli, we calculate both the static moduli and the dispersion relations of ultrasonic longitudinal and transverse elastic waves. At finite wave vector k the waves are dispersive, with phase and group velocities decreasing with increasing wave vector. These results are directly applicable to networks with empty pore space. They also describe the solid matrix in two-component (Biot) theories of fluid-filled porous media. We suggest the possibility of low density materials with higher ratios of stiffness and strength to density than those of foams, aerogels, or trabecular bone.
NASA Astrophysics Data System (ADS)
Gavrilyuk, A. P.; Karpov, S. V.
2009-09-01
Optical nonlinearities in aggregates of nanoparticles formed in silver hydrosols (SHs) are studied under pico- and nanosecond pulsed laser excitation. The dependence of the nonlinear refractive index n 2 on the degree of hydrosol aggregation is studied experimentally at the wavelength λ=1.064 μm. It is found that n 2 changes sign when the degree of hydrosol aggregation is increased. Various physical effects occurring in resonant domains of the aggregates are analyzed using a simple physical model of two bound silver nanoparticles. The theory takes into account thermal, elastic, electrostatic, and light-induced effects. Experimental results are discussed in the context of this theory.
Evaluation of Fracture in Concrete with Recycled Aggregate by Acoustic Emission
NASA Astrophysics Data System (ADS)
Nishibata, Sayaka; Watanabe, Takeshi; Hashimoro, Chikanori; Kohno, Kiyoshi
This research revealed fracture behavior of concrete in using recycled aggregates by Acoustic Emission as one of the Non-destructive Inspection. The phenomenon of acoustic emission (AE) is the propagation of elastic waves generated from a source, known as a micro-crack in an elastic material. There were taken to use low-treated recycled aggregate, crushed returned ready mixed concrete for aggregate and normal aggregate. Examination measured AE under the uniaxial compression test. The condition of load is repeated loading. As a result, fracture behavior due to low treated recycled aggregate was detected by AE. It is clarified that AE of concrete with low treated recycled aggregate appeared in low stress level. It has been understood that difference of aggregates becomes clear from Kaiser effect in repeated loading. In relation between RA value and average frequency, it has been understood the adhesion properties of the cement paste in recycled aggregate are appreciable.
NASA Astrophysics Data System (ADS)
Ali, M. A.; Roknuzzaman, M.; Nasir, M. T.; Islam, A. K. M. A.; Naqib, S. H.
2016-04-01
The elastic, electronic, and optical properties of Cu3MTe4 (M = Nb, Ta) are investigated for the first time using the density-functional formalism. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. Different elastic moduli are calculated. The Born criteria for mechanical stability are found to be fulfilled from the estimated values of the elastic moduli, Cij. The band structure and the electronic energy density of states (EDOS) are also determined. The band structure calculations show semiconducting behavior for both the compounds. The theoretically calculated values of the band gaps are found to be strongly dependent on the nature of the functional representing the exchange correlations. Technologically significant optical parameters (e.g., dielectric function, refractive index, absorption coefficient, optical conductivity, reflectivity, and loss function) have been determined. Important conclusions are drawn based on the theoretical findings.
Luczynski, Krzysztof W; Brynk, Tomasz; Ostrowska, Barbara; Swieszkowski, Wojciech; Reihsner, Roland; Hellmich, Christian
2013-01-01
This paper is concerned with reliable and physically sound elasticity determination of rapid-prototyped tissue engineering scaffolds made of poly-L-lactide (PLLA), with and without small portions of tricalcium phosphate (TCP) inclusions. At the level of overall scaffolds, that is, that of several millimeters, multiple uniaxial loading-unloading (quasistatic) tests were performed, giving access to the scaffolds' Young's moduli, through stress-strain characteristics during unloading. In addition, acoustic tests with 0.05 MHz frequency delivered an independent access to elastic properties, in terms of the normal components of the scaffolds' stiffness tensors. The latter strongly correlate, in a linear fashion, with the Young's moduli from the unloading tests, revealing porosity independence of Poisson's ratio. The magnitude of the latter is in full agreement with literature data on polymers. Both of these facts underline that both ultrasound tests and quasistatic unloading tests reliably provide the elastic properties of tissue engineering scaffolds.
Poonacha, Seema; Salagundi, Basavaraj; Rupesh, P L.; Raghavan, Rohit
2013-01-01
Objectives: To evaluate and compare the flexural strength and the elastic moduli of three provisional crown materials (methyl methacrylate based autopolymerized resin, bis acryl composite based autopolymerized resin and urethane dimethacrylate based light polymerized resin) after storing in artificial saliva and testing at intervals of 24 hours and 7 days. Study design: A metal master mould with four slots of dimensions 25x2x2 mm was fabricated to obtain samples of standard dimensions. A total of 135 specimens were thus obtained with 45 each of three provisional materials. Further 15 samples of each group were tested after storing for one hour at room temperature and again at intervals of 24 hours and 7 days after storing in artificial saliva. Three point flexural tests were carried out in the universal testing machine to calculate the flexural strength and the elastic modulus. The changes were calculated and data was analyzed with Fisher’s test and ANOVA. Results: The flexural strength of the methyl methacrylate resin reduced significantly while bis-acrylic composite resin showed a significant increase in its flexural strength after storing in artificial saliva for 24 hours and the values of both remained constant thereafter. Contrary to these findings, light polymerized resin showed a significant decrease in flexural strength after storing in artificial saliva for 24 hours and then significantly increased in flexural strength after 7 days. However the changes in the values for elastic modulus of respective materials were statistically insignificant. Conclusion: Methacrylate based autopolymerizing resin showed the highest flexural strength and elastic moduli after fabrication and after storing in artificial saliva and for 24 hours and 7 days. Bis-acrylic composite resin showed the least flexural strength and elastic moduli. Key words:Provisional restorations, interim restorations, Methyl Methacrylate, composite restoration, flexural strength, elastic moduli
Theoretical prediction of structural and elastic behavior of AlRu under pressure: A FP-LAPW study
NASA Astrophysics Data System (ADS)
Jain, Ekta; Pagare, Gitanjali; Devi, Hansa; Sanyal, S. P.
2015-06-01
Using full potential linearized augmented plane wave (FP-LAPW) method, the structural and elastic properties of AlRu intermetallic compound have been determined within the framework of density functional theory (DFT). The exchange correlation potential is used for generalized gradient approximations in the scheme of Perdew-Burke-Ernzerhof (GGA-PBE), Wu-Cohen (GGA-WC) and Perdew et. al. (GGA-PBEsol). Furthermore we have analyzed the trend of elastic constants (C11, C12 and C44) and elastic moduli (B, G and E) under variable pressure.
NASA Astrophysics Data System (ADS)
M, Shakil; Muhammad, Zafar; Shabbir, Ahmed; Muhammad Raza-ur-rehman, Hashmi; M, A. Choudhary; T, Iqbal
2016-07-01
The plane wave pseudo-potential method was used to investigate the structural, electronic, and elastic properties of CdSe1‑x Te x in the zinc blende phase. It is observed that the electronic properties are improved considerably by using LDA+U as compared to the LDA approach. The calculated lattice constants and bulk moduli are also comparable to the experimental results. The cohesive energies for pure CdSe and CdTe binary and their mixed alloys are calculated. The second-order elastic constants are also calculated by the Lagrangian theory of elasticity. The elastic properties show that the studied material has a ductile nature.
Aligned natural inflation and moduli stabilization from anomalous U(1) gauge symmetries
NASA Astrophysics Data System (ADS)
Li, Tianjun; Li, Zhijin; Nanopoulos, Dimitri V.
2014-11-01
To obtain natural inflation with large tensor-to-scalar ratio in string framework, we need a special moduli stabilization mechanism which can separate the masses of real and imaginary components of Kähler moduli at different scales, and achieve a trans-Planckian axion decay constant from sub-Planckian axion decay constants. In this work, we stabilize the matter fields by F-terms and the real components of Kähler moduli by D-terms of two anomalous U(1)X × U(1)A symmetries strongly at high scales, while the corresponding axions remain light due to their independence on the Fayet-Iliopoulos (FI) term in moduli stabilization. The racetrack-type axion superpotential is obtained from gaugino condensations of the hidden gauge symmetries SU(n)×SU(m) with massive matter fields in the bi-fundamental respresentations. The axion alignment via Kim-Nilles-Pelroso (KNP) mechanism corresponds to an approximate S 2 exchange symmetry of two Kähler moduli in our model, and a slightly S 2 symmetry breaking leads to the natural inflation with super-Planckian decay constant.
Moduli Dark Matter and the Search for Its Decay Line using Suzaku X-Ray Telescope
NASA Technical Reports Server (NTRS)
Kusenko, Alexander; Loewenstein, Michael; Yanagida, Tsutomu T.
2013-01-01
Light scalar fields called moduli arise from a variety of different models involving supersymmetry and/or string theory; thus their existence is a generic prediction of leading theories for physics beyond the standard model. They also present a formidable, long-standing problem for cosmology. We argue that an anthropic solution to the moduli problem exists in the case of small moduli masses and that it automatically leads to dark matter in the form of moduli. The recent discovery of the 125 GeV Higgs boson implies a lower bound on the moduli mass of about a keV. This form of dark matter is consistent with the observed properties of structure formation, and it is amenable to detection with the help of x-ray telescopes. We present the results of a search for such dark matter particles using spectra extracted from the first deep x-ray observations of the Draco and Ursa Minor dwarf spheroidal galaxies, which are darkmatter- dominated systems with extreme mass-to-light ratios and low intrinsic backgrounds. No emission line is positively detected, and we set new constraints on the relevant new physics.
Shear elastic modulus estimation from indentation and SDUV on gelatin phantoms
Amador, Carolina; Urban, Matthew W.; Chen, Shigao; Chen, Qingshan; An, Kai-Nan; Greenleaf, James F.
2011-01-01
Tissue mechanical properties such as elasticity are linked to tissue pathology state. Several groups have proposed shear wave propagation speed to quantify tissue mechanical properties. It is well known that biological tissues are viscoelastic materials; therefore velocity dispersion resulting from material viscoelasticity is expected. A method called Shearwave Dispersion Ultrasound Vibrometry (SDUV) can be used to quantify tissue viscoelasticity by measuring dispersion of shear wave propagation speed. However, there is not a gold standard method for validation. In this study we present an independent validation method of shear elastic modulus estimation by SDUV in 3 gelatin phantoms of differing stiffness. In addition, the indentation measurements are compared to estimates of elasticity derived from shear wave group velocities. The shear elastic moduli from indentation were 1.16, 3.40 and 5.6 kPa for a 7, 10 and 15% gelatin phantom respectively. SDUV measurements were 1.61, 3.57 and 5.37 kPa for the gelatin phantoms respectively. Shear elastic moduli derived from shear wave group velocities were 1.78, 5.2 and 7.18 kPa for the gelatin phantoms respectively. The shear elastic modulus estimated from the SDUV, matched the elastic modulus measured by indentation. On the other hand, shear elastic modulus estimated by group velocity did not agree with indentation test estimations. These results suggest that shear elastic modulus estimation by group velocity will be bias when the medium being investigated is dispersive. Therefore a rheological model should be used in order to estimate mechanical properties of viscoelastic materials. PMID:21317078
NASA Astrophysics Data System (ADS)
Belomestnykh, V. N.; Tesleva, E. P.
2012-10-01
Based on the known experimental data on the rigidity constants c ij ( x) of single crystals of samarium monosulfide solid solutions (alloys) with yttrium, lanthanum, and thulium impurities, their anisotropic and isotropic acoustic (sound velocities), elastic (elasticity moduli and Poisson's ratios), and anharmonic (Grüneisen parameters) properties are investigated. Anomalous behavior of these characteristics at isostructural electron phase transitions in the examined mixed systems in the intermediate valence state is discussed.
Thermal elasticity of Fe- and Al-bearing and -free MgSiO3-perovskite
NASA Astrophysics Data System (ADS)
Shukla, G.; Wu, Z.; Wentzcovitch, R. M.
2013-12-01
We present a thorough analysis of the thermal elastic properties of iron- and aluminum-bearing and -free MgSiO3-perovskite. Results from different first principles methods are compared to experimental data available and results for elastic moduli and velocities are analyzed at lower mantle conditions. Velocity heterogeneity produced by temperature variations and variation of aluminum and iron content are carefully examined and contrasted. This analysis is essential for improving understanding of the constitution of Earth's lower mantle. Research supported by NSF awards EAR-1319361, -1019853, and -0810272.
Stabilizing electrodeposition in elastic solid electrolytes containing immobilized anions.
Tikekar, Mukul D; Archer, Lynden A; Koch, Donald L
2016-07-01
Ion transport-driven instabilities in electrodeposition of metals that lead to morphological instabilities and dendrites are receiving renewed attention because mitigation strategies are needed for improving rechargeability and safety of lithium batteries. The growth rate of these morphological instabilities can be slowed by immobilizing a fraction of anions within the electrolyte to reduce the electric field at the metal electrode. We analyze the role of elastic deformation of the solid electrolyte with immobilized anions and present theory combining the roles of separator elasticity and modified transport to evaluate the factors affecting the stability of planar deposition over a wide range of current densities. We find that stable electrodeposition can be easily achieved even at relatively high current densities in electrolytes/separators with moderate polymer-like mechanical moduli, provided a small fraction of anions are immobilized in the separator. PMID:27453943
Stabilizing electrodeposition in elastic solid electrolytes containing immobilized anions
Tikekar, Mukul D.; Archer, Lynden A.; Koch, Donald L.
2016-01-01
Ion transport–driven instabilities in electrodeposition of metals that lead to morphological instabilities and dendrites are receiving renewed attention because mitigation strategies are needed for improving rechargeability and safety of lithium batteries. The growth rate of these morphological instabilities can be slowed by immobilizing a fraction of anions within the electrolyte to reduce the electric field at the metal electrode. We analyze the role of elastic deformation of the solid electrolyte with immobilized anions and present theory combining the roles of separator elasticity and modified transport to evaluate the factors affecting the stability of planar deposition over a wide range of current densities. We find that stable electrodeposition can be easily achieved even at relatively high current densities in electrolytes/separators with moderate polymer-like mechanical moduli, provided a small fraction of anions are immobilized in the separator. PMID:27453943
Stabilizing electrodeposition in elastic solid electrolytes containing immobilized anions.
Tikekar, Mukul D; Archer, Lynden A; Koch, Donald L
2016-07-01
Ion transport-driven instabilities in electrodeposition of metals that lead to morphological instabilities and dendrites are receiving renewed attention because mitigation strategies are needed for improving rechargeability and safety of lithium batteries. The growth rate of these morphological instabilities can be slowed by immobilizing a fraction of anions within the electrolyte to reduce the electric field at the metal electrode. We analyze the role of elastic deformation of the solid electrolyte with immobilized anions and present theory combining the roles of separator elasticity and modified transport to evaluate the factors affecting the stability of planar deposition over a wide range of current densities. We find that stable electrodeposition can be easily achieved even at relatively high current densities in electrolytes/separators with moderate polymer-like mechanical moduli, provided a small fraction of anions are immobilized in the separator.
Elastic properties of silver borate glasses doped with praseodymium oxide
Gowda, G. V. Jagadeesha; Eraiah, B.
2014-04-24
A series of glasses xPr{sub 6}O{sub 11−}(35−x) Ag{sub 2}O−65B{sub 2}O{sub 3} with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5 mol % were synthesized by melt quenching technique. Longitudinal and shear ultrasonic velocity were measured at 5 MHz frequency and at room temperature. Elastic moduli, Poisson's ratio and Debye temperature have been calculated from the measured density and ultrasonic velocity at room temperature. The experimental results indicate that the elastic constants depend upon the composition of the glasses. The role of the Pr{sub 6}O{sub 11} inside the glass network was discussed.
Structural mechanics and helical geometry of thin elastic composites.
Wada, Hirofumi
2016-09-21
Helices are ubiquitous in nature, and helical shape transition is often observed in residually stressed bodies, such as composites, wherein materials with different mechanical properties are glued firmly together to form a whole body. Inspired by a variety of biological examples, the basic physical mechanism responsible for the emergence of twisting and bending in such thin composite structures has been extensively studied. Here, we propose a simplified analytical model wherein a slender membrane tube undergoes a helical transition driven by the contraction of an elastic ribbon bound to the membrane surface. We analytically predict the curvature and twist of an emergent helix as functions of differential strains and elastic moduli, which are confirmed by our numerical simulations. Our results may help understand shapes observed in different biological systems, such as spiral bacteria, and could be applied to novel designs of soft machines and robots.
Structural mechanics and helical geometry of thin elastic composites.
Wada, Hirofumi
2016-09-21
Helices are ubiquitous in nature, and helical shape transition is often observed in residually stressed bodies, such as composites, wherein materials with different mechanical properties are glued firmly together to form a whole body. Inspired by a variety of biological examples, the basic physical mechanism responsible for the emergence of twisting and bending in such thin composite structures has been extensively studied. Here, we propose a simplified analytical model wherein a slender membrane tube undergoes a helical transition driven by the contraction of an elastic ribbon bound to the membrane surface. We analytically predict the curvature and twist of an emergent helix as functions of differential strains and elastic moduli, which are confirmed by our numerical simulations. Our results may help understand shapes observed in different biological systems, such as spiral bacteria, and could be applied to novel designs of soft machines and robots. PMID:27510457
Electroactive superelongation of carbon nanotube aggregates in liquid crystal medium.
Jeong, Seok Jin; Park, Kyung Ah; Jeong, Seok Ho; Jeong, Hee Jin; An, Kay Hyeok; Nah, Chang Woon; Pribat, Didier; Lee, Seung Hee; Lee, Young Hee
2007-08-01
We report an effect of superelongation of carbon nanotube (CNT) aggregates driven by the electric field in a liquid crystal (LC) medium. The CNT aggregates started to elongate above a certain threshold field and sustained the elongation up to nearly 400% in the linear region with a large electroactive constant of 70 (V/microm)-1. The original morphology of the CNT aggregates was restored upon removal of the field. The elongation was fully reversible below a certain breakdown field, irrespective of the nematic or isotropic phase of the LC medium. The overall process involved (i) the alignment of CNT aggregates to increase the dipole energy of aggregates in the presence of the bias voltage, (ii) stretching of the CNTs by sliding-out from the bundles, and (iii) the entropic elasticity that restores the randomly entangled CNT network of the original aggregates after suppression of the bias voltage.
Flow-induced aggregation of colloidal particles in viscoelastic fluids.
Xie, Donglin; Qiao, Greg G; Dunstan, Dave E
2016-08-01
The flow-induced aggregation of dilute colloidal polystyrene nanoparticles suspended in Newtonian and viscoelastic solutions is reported. A rheo-optical method has been used to detect real-time aggregation processes via measuring optical absorption or scattering in a quartz Couette cell. The observed absorbance decreases over time are attributed to the flow-induced coagulation. Numerical simulations show that the aggregation processes still follow the Smoluchowski coagulation equation in a revised version. Suspensions in a series of media are studied to evaluate the effect of the media rheological properties on the particle aggregation. The data shows that elasticity reduces the aggregation while the solution viscosity enhances the aggregation processes. PMID:27627363
High-temperature elasticity of iron-bearing olivines
NASA Astrophysics Data System (ADS)
Isaak, Donald G.
1992-02-01
The first high-temperature data on the nine adiabatic elastic moduli for iron-bearing olivine are reported. These measurements are on two single-crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 K. The two specimens contain 8 and 9 modal percent fayalite, which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability. The rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of CO and CO2 gas. A small increase (˜1-2 GPa) in the adiabatic bulk modulus of each specimen, over that of end-member forsterite, was found. The data are high quality to extreme temperatures, with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens. Neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli, which is in contrast to published forsterite data. The temperature derivatives of the isotropic bulk modulus KS are (-1.69, -1.80) × 10-2 GPa K-1 for the two olivine specimens, and the shear modulus G derivatives are (-1.38, -1.36) × 10-2 GPa K-1. These derivatives are only slightly larger in magnitude than |(∂KS/∂T)P| = 1.56 × 10-2 and |(∂G/∂T)P| = 1.30 × 10-2 GPa K-1 found previously for iron-bearing olivine over a very small temperature range. There are also no significant differences between the temperature derivatives found here and the average derivatives of end-member forsterite from data retrieved over a slightly larger temperature range. Several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high-pressure phases in Earth's transition zone. One result from these systematics related to the seismic velocities in the Earth, and especially the shear wave velocities, is that an olivine content of less than 50% is implied at the 400
Crosslinked Polymer Lamellae with Tunable Elasticity & Stability
NASA Astrophysics Data System (ADS)
Discher, Dennis; Bermudez, Harry; Hammer, Daniel; Bates, Frank; Discher, Bohdana
2001-03-01
Polymerization of self-assembled block copolymers has long been viewed as an effective means of locking in nanostructure but very little information exists on end-point properties. To address this issue, amphiphilic diblocks were used to make micron-size vesicles in water with subsequent crosslinking within the membrane. Massive crosslinking of polyethyleneoxide-polybutadiene (EO26-BD46) leads to surface wrinkles and other solid-like elastic characteristics in a membrane with a core that is less than 10 nm thick. Vesicles prove stable in chloroform, retaining their contents, and can also be dehydrated and rehydrated without membrane permeation, implying a defect-free surface many microns squared in area. Mechanically, the extensively crosslinked membranes exhibit elastic moduli consistent with crosslinking between close-packed neighbors and can also withstand lateral stresses of 1000 Atm orders of magnitude higher than any natural lipid membrane. However, bond dilution by tunable addition of the non-crosslinkable analog polyethyleneoxide-polyethylethylene (EO40-EE37) destabilizes the membrane in a manner consistent with rigidity percolation through a novel multi-layer stack of two-dimensional lattices.
Colloidal aggregation and dynamics in anisotropic fluids
Mondiot, Frédéric; Botet, Robert; Snabre, Patrick; Mondain-Monval, Olivier; Loudet, Jean-Christophe
2014-01-01
We present experiments and numerical simulations to investigate the collective behavior of submicrometer-sized particles immersed in a nematic micellar solution. We use latex spheres with diameters ranging from 190 to 780 nm and study their aggregation properties due to the interplay of the various colloidal forces at work in the system. We found that the morphology of aggregates strongly depends on the particle size, with evidence for two distinct regimes: the biggest inclusions clump together within minutes into either compact clusters or V-like structures that are completely consistent with attractive elastic interactions. On the contrary, the smallest particles form chains elongated along the nematic axis, within comparable timescales. In this regime, Monte Carlo simulations, based on a modified diffusion-limited cluster aggregation model, strongly suggest that the anisotropic rotational Brownian motion of the clusters combined with short-range depletion interactions dominate the system coarsening; elastic interactions no longer prevail. The simulations reproduce the sharp transition between the two regimes on increasing the particle size. We provide reasonable estimates to interpret our data and propose a likely scenario for colloidal aggregation. These results emphasize the growing importance of the diffusion of species at suboptical-wavelength scales and raise a number of fundamental issues. PMID:24715727
Thermodynamics of Protein Aggregation
NASA Astrophysics Data System (ADS)
Osborne, Kenneth L.; Barz, Bogdan; Bachmann, Michael; Strodel, Birgit
Amyloid protein aggregation characterizes many neurodegenerative disorders, including Alzheimer's, Parkinson's, and Creutz- feldt-Jakob disease. Evidence suggests that amyloid aggregates may share similar aggregation pathways, implying simulation of full-length amyloid proteins is not necessary for understanding amyloid formation. In this study we simulate GNNQQNY, the N-terminal prion-determining domain of the yeast protein Sup35 to investigate the thermodynamics of structural transitions during aggregation. We use a coarse-grained model with replica-exchange molecular dynamics to investigate the association of 3-, 6-, and 12-chain GNNQQNY systems and we determine the aggregation pathway by studying aggregation states of GN- NQQNY. We find that the aggregation of the hydrophilic GNNQQNY sequence is mainly driven by H-bond formation, leading to the formation of /3-sheets from the very beginning of the assembly process. Condensation (aggregation) and ordering take place simultaneously, which is underpinned by the occurrence of a single heat capacity peak only.
Age-Related Differences in Muscle Shear Moduli in the Lower Extremity.
Akagi, Ryota; Yamashita, Yota; Ueyasu, Yuta
2015-11-01
This study investigated the age-related differences in shear moduli of the rectus femoris muscle (RF), the lateral head of the gastrocnemius muscle (LG) and the soleus muscle (SOL) using shear wave ultrasound elastography. Thirty-one young individuals and 49 elderly individuals volunteered for this study. The shear modulus of RF was determined at 50% of the thigh length, and those of LG and SOL were determined at 30% of the lower leg length. RF and LG shear moduli were significantly higher in young individuals than in elderly individuals, but there was no age-related difference in SOL shear modulus. From the standpoint of an index reflecting muscle mechanical properties, it is suggested that the lower muscle shear moduli of RF and LG are the reason for the decreased explosive muscle strength in the lower extremity and the increased risk of falls for elderly individuals.
The confined compressive strengths and Young's moduli of three American coals
NASA Astrophysics Data System (ADS)
Costantino, Marc; Trettenero, Stan
1983-01-01
We report the confined compression strengths and Young's moduli of coal and roof rock from the Upper Freeport seam, Lucerne No. 6 Mine, Homer City, Pennsylvania, the Lower Kittanning seam, Kitt No. 1 Mine, Phillipi, West Virginia, and the Soldier Canyon seam, Soldier Canyon Mine, Price, Utah. A total of 210 tests to failure in biaxial compression were performed at confining pressures of 0.1, 3.0, and 10.0 MPa. The strengths increase by a factor of 2-3 over the confining pressure range, while the Young's moduli are about constant. Standard deviations are 10-30% of the mean, emphasizing the need to do many tests. Failure in all three coals is brittle, progressing from dilational to multiplane shear to single-plane shear on increasing confining pressure. Strengths and moduli could not be correlated with such macroscopic inhomogeneities as large cracks, voids, and compositional changes.
Moduli spaces of stable bundles on Calabi-Yau varieties and Donaldson-Thomas invariants
NASA Astrophysics Data System (ADS)
Costa, L.
2011-11-01
Let Y be a smooth Calabi-Yau hypersurface of P1×P where P stands for a Pd-bundle over P1. We will prove that for many ample line bundles L and certain Chern characters c, the moduli space M(c) (resp. ML(c)) of L-Gieseker semistable (resp. L-stable ) rank two torsion free sheaves (resp. vector bundles) on Y with Chern character c are smooth and irreducible and we will compute its dimension. Moreover, we will prove that both moduli spaces coincide. As a byproduct of the geometrical description of these moduli spaces, we will compute the Donaldson-Thomas invariants of some Calabi-Yau 3-folds.
Strain rate, temperature, and humidity on strength and moduli of a graphite/epoxy composite
NASA Technical Reports Server (NTRS)
Lifshitz, J. M.
1981-01-01
Results of an experimental study of the influence of strain rate, temperature and humidity on the mechanical behavior of a graphite/epoxy fiber composite are presented. Three principal strengths (longitudinal, transverse and shear) and four basic moduli (E1, E2, G12 and U12) of a unidirectional graphite/epoxy composite were followed as a function of strain rate, temperature and humidity. Each test was performed at a constant tensile strain rate in an environmental chamber providing simultaneous temperature and humidity control. Prior to testing, specimens were given a moisture preconditioning treatment at 60 C. Values for the matrix dominated moduli and strength were significantly influenced by both environmental and rate parameters, whereas the fiber dominated moduli were not. However, the longitudinal strength was significantly influenced by temperature and moisture content. A qualitative explanation for these observations is presented.
Elastic constants of monocrystal iron from 3 to 500 K
NASA Astrophysics Data System (ADS)
Adams, J. J.; Agosta, D. S.; Leisure, R. G.; Ledbetter, H.
2006-12-01
Resonant ultrasound spectroscopy was used to measure the monocrystal elastic constants of iron over a temperature range of 3-500K. All the moduli behave normally as a function of temperature and are well described by the semiempirical Einstein-oscillator model. Values at 300K are bulk modulus=166.2±0.9GPa; shear constant C'=(C11-C12)/2=48.15±0.9GPa; shear constant C44=115.87±0.17GPa. The Poisson ratio (ν100) is 0.3679±0.0005. Representation surfaces of Young's and torsion moduli are presented. The Debye temperature (θD) is 476.3K as calculated from 3K measured elastic constants. A thermodynamic Grüneisen parameter γth=1.65 is calculated. The temperature dependence of the internal friction associated with C' is very different from that associated with C44. Possible reasons for this difference are suggested.
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.
Yegingil, Hakki; Shih, Wan Y; Shih, Wei-Heng
2007-11-01
We have experimentally investigated the depth sensitivity limit of a piezoelectric cantilever tissue elastic modulus sensor and simultaneously determined the elastic modulus and the depth of a tumor directly. Using model tissues consisting of bottom-supported modeling clay inclusions of various depths in a gelatin matrix, we empirically determined that the depth sensitivity limit of a piezoelectric cantilever sensor was twice the linear dimension of the indentation area (or the cantilever width). Knowing the depth sensitivity limit of the individual cantilever sensor as input and treating a model tissue that has the gelatin matrix on top and the modeling clay inclusion at the bottom as two springs in series, we showed that the elastic moduli and depths of the hard inclusions could be simultaneously determined with the elastic modulus profiles measured by two cantilevers with different widths as input.
Elastic anisotropy and shear-induced atomistic deformation of tetragonal silicon carbon nitride
Yan, Haiyan; Zhang, Meiguang; Zhao, Yaru; Zhou, Xinchun; Wei, Qun
2014-07-14
First-principles calculations are employed to provide a fundamental understanding of the structural features, elastic anisotropy, shear-induced atomistic deformation behaviors, and its electronic origin of the recently proposed superhard t-SiCN. According to the dependences of the elastic modulus on different crystal directions, the t-SiCN exhibits a well-pronounced elastic anisotropy which may impose certain limitations and restrictions on its applications. The further mechanical calculations demonstrated that t-SiCN shows lower elastic moduli and ideal shear strength than those of typical hard substances of TiN and TiC, suggesting that it cannot be intrinsically superhard as claimed in the recent works. We find that the failure modes of t-SiCN at the atomic level during shear deformation can be attributed to the breaking of C-C bonds through the bonding evolution and electronic localization analyses.
Supersymmetry breaking, moduli stabilization, and hidden U(1) breaking in M theory
Acharya, Bobby S.; Torabian, Mahdi
2011-06-15
We calculate and explore the moduli potential for M theory compactified on G{sub 2}-manifolds in which the superpotential is dominated by a single membrane instanton term plus one from an asymptotically free hidden sector gauge interaction. We show that all moduli can be stabilized and that hidden sector gauge symmetries can be Higgsed at a high scale. We then compute the spectrum of superpartner masses at the grand unified theory scale and evolve it to the electroweak scale. We find a spectrum which is very similar to the G{sub 2}-minimal supersymmetric standard model with light gauginos - accessible at the LHC - and a neutral wino dark matter candidate.
The geometry of the light-cone cell decomposition of moduli space
NASA Astrophysics Data System (ADS)
Garner, David; Ramgoolam, Sanjaye
2015-11-01
The moduli space of Riemann surfaces with at least two punctures can be decomposed into a cell complex by using a particular family of ribbon graphs called Nakamura graphs. We distinguish the moduli space with all punctures labelled from that with a single labelled puncture. In both cases, we describe a cell decomposition where the cells are parametrised by graphs or equivalence classes of finite sequences (tuples) of permutations. Each cell is a convex polytope defined by a system of linear equations and inequalities relating light-cone string parameters, quotiented by the automorphism group of the graph. We give explicit examples of the cell decomposition at low genus with few punctures.
The geometry of the light-cone cell decomposition of moduli space
Garner, David Ramgoolam, Sanjaye
2015-11-15
The moduli space of Riemann surfaces with at least two punctures can be decomposed into a cell complex by using a particular family of ribbon graphs called Nakamura graphs. We distinguish the moduli space with all punctures labelled from that with a single labelled puncture. In both cases, we describe a cell decomposition where the cells are parametrised by graphs or equivalence classes of finite sequences (tuples) of permutations. Each cell is a convex polytope defined by a system of linear equations and inequalities relating light-cone string parameters, quotiented by the automorphism group of the graph. We give explicit examples of the cell decomposition at low genus with few punctures.
Gravitational particle production in massive chaotic inflation and the moduli problem.
de Haro, Jaume; Elizalde, Emilio
2012-02-10
Particle production from vacuum fluctuations during inflation is briefly revisited. The moduli problem occurring with light particles produced at the end of inflation is addressed, namely, the fact that some results are in disagreement with nucleosynthesis constrains. A universal solution to this problem is found which leads to reasonable reheating temperatures in all cases. It invokes the assumption that, immediately after inflation, the moduli evolve like nonrelativistic matter. The assumption is justified in the context of massive chaotic inflation where, at the end of inflation, the Universe evolves as if it were matter dominated.
Gravitational particle production in massive chaotic inflation and the moduli problem.
de Haro, Jaume; Elizalde, Emilio
2012-02-10
Particle production from vacuum fluctuations during inflation is briefly revisited. The moduli problem occurring with light particles produced at the end of inflation is addressed, namely, the fact that some results are in disagreement with nucleosynthesis constrains. A universal solution to this problem is found which leads to reasonable reheating temperatures in all cases. It invokes the assumption that, immediately after inflation, the moduli evolve like nonrelativistic matter. The assumption is justified in the context of massive chaotic inflation where, at the end of inflation, the Universe evolves as if it were matter dominated. PMID:22401053
Elastic properties of amorphous thin films studied by Rayleigh waves
Schwarz, R.B.; Rubin, J.B.
1993-08-01
Physical vapor deposition in ultra-high vacuum was used to co-deposit nickel and zirconium onto quartz single crystals and grow amorphous Ni{sub 1-x}Zr{sub x} (0.1 < x < 0.87) thin film. A high-resolution surface acoustic wave technique was developed for in situ measurement of film shear moduli. The modulus has narrow maxima at x = 0. 17, 0.22, 0.43, 0.5, 0.63, and 0.72, reflecting short-range ordering and formation of aggregates in amorphous phase. It is proposed that the aggregates correspond to polytetrahedral atom arrangements limited in size by geometrical frustration.
The Effect of Iron on the Elastic Properties of Ringwoodite at High Pressure
Higo,Y.; Inoue, T.; Li, B.; Irifune, T.; Liebermann, R.
2006-01-01
Elastic wave velocities of ringwoodite with compositions of Mg2SiO4, (Mg0.8Fe0.2)2SiO4 and (Mg0.5Fe0.5)2SiO4 have been measured to address the effect of iron on the elastic properties of silicate spinel under high pressure. Ultrasonic measurements on specimens produced by hot-pressing at about 19 GPa and at 1200 C were conducted at pressures up to 14 GPa at room temperature in a multianvil apparatus. Pressure was estimated from a relationship between the travel time in an Al2O3 buffer rod and the pressure estimated from in situ X-ray diffraction measurements. Thus, measured bulk modulus (K) of ringwoodite slightly increases with increasing iron content, while the pressure derivative of the bulk modulus remains virtually the same (K' = 4.4 for XFe = Fe/(Fe + Mg) = 0-0.5). In contrast, the shear modulus (G) decreases significantly with increasing iron content, while the pressure derivative of the shear modulus slightly decreases or remains almost unchanged (G' = 1.4-1.0 for XFe = 0-0.5). The effects of iron content on the elastic moduli are somewhat different from those of an earlier study using Brillion scattering method, but are consistent with the elastic moduli of the Fe2SiO4 end-member measured in a piston-cylinder apparatus using ultrasonic interferometry. The effects of iron on the elastic moduli of ringwoodite are described as K = 184(1) + 16(1)XFe (GPa) and G = 124(2) - 45(3)XFe (GPa), by combining the present and earlier results based on the ultrasonic interferometry at high pressure. The present result suggests that the temperature anomalies, rather than the variations of iron content in ringwoodite, are more likely causes for the observed variations in seismic velocities in the mantle transition region.
Metaconcrete: Engineered aggregates for enhanced dynamic performance
NASA Astrophysics Data System (ADS)
Mitchell, Stephanie J.
This work presents the development and investigation of a new type of concrete for the attenuation of waves induced by dynamic excitation. Recent progress in the field of metamaterials science has led to a range of novel composites which display unusual properties when interacting with electromagnetic, acoustic, and elastic waves. A new structural metamaterial with enhanced properties for dynamic loading applications is presented, which is named metaconcrete. In this new composite material the standard stone and gravel aggregates of regular concrete are replaced with spherical engineered inclusions. Each metaconcrete aggregate has a layered structure, consisting of a heavy core and a thin compliant outer coating. This structure allows for resonance at or near the eigenfrequencies of the inclusions, and the aggregates can be tuned so that resonant oscillations will be activated by particular frequencies of an applied dynamic loading. The activation of resonance within the aggregates causes the overall system to exhibit negative effective mass, which leads to attenuation of the applied wave motion. To investigate the behavior of metaconcrete slabs under a variety of different loading conditions a finite element slab model containing a periodic array of aggregates is utilized. The frequency dependent nature of metaconcrete is investigated by considering the transmission of wave energy through a slab, which indicates the presence of large attenuation bands near the resonant frequencies of the aggregates. Applying a blast wave loading to both an elastic slab and a slab model that incorporates the fracture characteristics of the mortar matrix reveals that a significant portion of the supplied energy can be absorbed by aggregates which are activated by the chosen blast wave profile. The transfer of energy from the mortar matrix to the metaconcrete aggregates leads to a significant reduction in the maximum longitudinal stress, greatly improving the ability of the material
Determining the frequency dependence of elastic properties of fractured rocks
NASA Astrophysics Data System (ADS)
Ahrens, Benedikt; Renner, Jörg
2016-04-01
In the brittle crust, rocks often contain joints or faults on various length scales that have a profound effect on fluid flow and heat transport, as well as on the elastic properties of rocks. Improving the understanding of the effect of fractures and the role of stress state and heterogeneity along the fractures on elastic properties of rocks is potentially important for the characterization of deep geothermal reservoirs. Seismic surveys, typically covering a frequency range of about 1 to 1000 Hz, are a valuable tool to investigate fractured rocks but the extraction of fracture properties remains difficult. The elementary frequency-dependent interaction between fractured rock matrix and viscous pore fluids and the resulting effects on wave propagation require well-founded dispersion analyses of heterogeneous rocks. In this laboratory study, we investigate the stress dependence of the effective elastic properties of fractured reservoir rocks over a broad frequency range. To assess the effect of faults on the effective elastic properties, we performed cyclic axial loading tests on intact and fractured samples of Solnhofen limestone and Padang granodiorite. The samples contained an idealized fault, which was created by stacking two sample discs on top of each other that experienced various surface treatments to vary their roughness. The dynamic loading tests were conducted with frequencies up to 10 Hz and amplitudes reaching 10% of the statically applied stress. Simultaneously, P- and S-wave measurements were performed in the ultrasonic frequency range (above 100 kHz) with a total of 16 sensors, whose positioning above and below the samples guarantees a wide range of transmission and reflection angles. Preliminary results of static and dynamic elastic properties of intact Padang granodiorite show a pronounced increase in Young's moduli and Poisson's ratio with increasing axial stress. Stress relaxation is accompanied by a decrease of the modulus and the Poisson
Elastically Decoupling Dark Matter.
Kuflik, Eric; Perelstein, Maxim; Lorier, Nicolas Rey-Le; Tsai, Yu-Dai
2016-06-01
We present a novel dark matter candidate, an elastically decoupling relic, which is a cold thermal relic whose present abundance is determined by the cross section of its elastic scattering on standard model particles. The dark matter candidate is predicted to have a mass ranging from a few to a few hundred MeV, and an elastic scattering cross section with electrons, photons and/or neutrinos in the 10^{-3}-1 fb range. PMID:27314712
Elastically Decoupling Dark Matter.
Kuflik, Eric; Perelstein, Maxim; Lorier, Nicolas Rey-Le; Tsai, Yu-Dai
2016-06-01
We present a novel dark matter candidate, an elastically decoupling relic, which is a cold thermal relic whose present abundance is determined by the cross section of its elastic scattering on standard model particles. The dark matter candidate is predicted to have a mass ranging from a few to a few hundred MeV, and an elastic scattering cross section with electrons, photons and/or neutrinos in the 10^{-3}-1 fb range.
NASA Astrophysics Data System (ADS)
Stølen, Svein; Trønnes, Reidar G.
2007-09-01
The thermodynamic properties of perovskite (pv) and post-perovskite (ppv) of CaIrO 3 are derived from total energy calculations using density functional theory. Negative molar volume and enthalpy changes of 0.40 cm 3 mol -1 and 11.8 kJ mol -1 for the pv to ppv transition at 0 K stabilize ppv at low temperatures and high-pressures. Vibrational entropies calculated in the harmonic approximation, using the direct method, favour pv with increasing temperatures (105.5 J K -1 mol -1 for pv versus 99.2 J K -1 mol -1 for ppv at 298 K). A main reason for the lower entropy of post-perovskite compared to perovskite is probably related to constraints on certain vibrational modes imposed by edge-sharing of octahedra in post-perovskite. The Clapeyron slope of the pv-ppv phase boundary is deduced from the calculated enthalpy and volume of transition in conjunction with an experimental transition temperature. The resulting d p/d T of 18 MPa K -1 is in good agreement with experimental determinations reported in literature. The high-pressure properties were calculated from the variation of the total energy with volume using the Murnaghan (M) and the Birch-Murnaghan (B-M) equations-of-state. The two methods give the same values for the bulk modulus but somewhat different values for the pressure derivative of the bulk modulus: K0 = 178 GPa and K0=2.8 (M) and 3.3 (B-M) for pv compared to K0 = 164 GPa and K0=3.9 (M) and 4.0 (B-M) for ppv. By holding K0 for pv fixed at 4.0, K0 is reduced to 172 GPa. The bulk moduli at zero pressure were also derived through calculation of the elastic constants giving K0 = 172 GPa for pv compared to K0 = 157 GPa for ppv. In order to compare the changes in the bulk and shear moduli across the pv-ppv phase transition, also the shear moduli were derived from the elastic constants. Whereas the bulk modulus decreases by about 9% from perovskite to post-perovskite, the shear modulus increases by about 15% across the transition. The elastic parameters obtained
Darling, T.; Migliori, A.; Armstrong, P.E.; Vaidya, R.; Scherer, C.; Lowe, T.
1997-09-01
We have measured the temperature dependence of the elastic constants of the 51XX series steels [gear steels] for a range of phases. At RT the normalized steel (pearlite) has the highest value of the moduli, the bainite phase the next highest, and martensite the lowest. Extrapolation of the austenite suggests that at RT austenite has lower moduli than martensite. For all the grades and phases of steels examined, the behavior of the elastic constants is similar: a curve could be drawn for each of the moduli from all the phases and all the grades would not deviate by more than {+-}4%. The normalized phase (100% pearlite in 5180) is stable up to 900 C. Bainite is stable up to 500 C. Martensite starts to change above 150 C as it tempers or strain relieves; once this is complete, the martensite moduli increase to similar values to bainite. Extrapolations are discussed. Behavior in lower carbon steels (5140, 5120) should conform to above; there is no explanation for the anomalous behavior of the quenched 5120 steel.
Erba, A. Mahmoud, A.; Dovesi, R.; Belmonte, D.
2014-03-28
A computational strategy is devised for the accurate ab initio simulation of elastic properties of crystalline materials under pressure. The proposed scheme, based on the evaluation of the analytical stress tensor and on the automated computation of pressure-dependent elastic stiffness constants, is implemented in the CRYSTAL solid state quantum-chemical program. Elastic constants and related properties (bulk, shear and Young moduli, directional seismic wave velocities, elastic anisotropy index, Poisson's ratio, etc.) can be computed for crystals of any space group of symmetry. We apply such a technique to the study of high-pressure elastic properties of three silicate garnet end-members (namely, pyrope, grossular, and andradite) which are of great geophysical interest, being among the most important rock-forming minerals. The reliability of this theoretical approach is proved by comparing with available experimental measurements. The description of high-pressure properties provided by several equations of state is also critically discussed.
Fernique-type inequalities and moduli of continuity for anisotropic Gaussian random fields.
Meerschaert, Mark M; Wang, Wensheng; Xiao, Yimin
2012-08-01
This paper is concerned with sample path properties of anisotropic Gaussian random fields. We establish Fernique-type inequalities and utilize them to study the global and local moduli of continuity for anisotropic Gaussian random fields. Applications to fractional Brownian sheets and to the solutions of stochastic partial differential equations are investigated.
Fernique-type inequalities and moduli of continuity for anisotropic Gaussian random fields
Meerschaert, Mark M.; Wang, Wensheng; Xiao, Yimin
2013-01-01
This paper is concerned with sample path properties of anisotropic Gaussian random fields. We establish Fernique-type inequalities and utilize them to study the global and local moduli of continuity for anisotropic Gaussian random fields. Applications to fractional Brownian sheets and to the solutions of stochastic partial differential equations are investigated. PMID:24825922
Stanimirova, Rumyana D; Gurkov, Theodor D; Kralchevsky, Peter A; Balashev, Konstantin T; Stoyanov, Simeon D; Pelan, Eddie G
2013-05-21
Here, we combine experiments with Langmuir trough and atomic force microscopy (AFM) to investigate the reasons for the special properties of layers from the protein HFBII hydrophobin spread on the air-water interface. The hydrophobin interfacial layers possess the highest surface dilatational and shear elastic moduli among all investigated proteins. The AFM images show that the spread HFBII layers are rather inhomogeneous, (i.e., they contain voids, monolayer and multilayer domains). A continuous compression of the layer leads to filling the voids and transformation of a part of the monolayer into a trilayer. The trilayer appears in the form of large surface domains, which can be formed by folding and subduction of parts from the initial monolayer. The trilayer appears also in the form of numerous submicrometer spots, which can be obtained by forcing protein molecules out of the monolayer and their self-assembly into adjacent pimples. Such structures are formed because not only the hydrophobic parts, but also the hydrophilic parts of the HFBII molecules can adhere to each other in the water medium. If a hydrophobin layer is subjected to oscillations, its elasticity considerably increases, up to 500 mN/m, which can be explained with compaction. The relaxation of the layer's tension after expansion or compression follows the same relatively simple law, which refers to two-dimensional diffusion of protein aggregates within the layer. The characteristic diffusion time after compression is longer than after expansion, which can be explained with the impedence of diffusion in the more compact interfacial layer. The results shed light on the relation between the mesoscopic structure of hydrophobin interfacial layers and their unique mechanical properties that find applications for the production of foams and emulsions of extraordinary stability; for the immobilization of functional molecules at surfaces, and as coating agents for surface modification.
Alpha-plutonium's low-temperature elastic constants
NASA Astrophysics Data System (ADS)
Betts, J. B.; Migliori, A.; Ledbetter, H.; Dooley, D.; Miller, D. A.
2006-03-01
Using resonant-ultrasound spectroscopy, we measured alpha-plutonium's polycrystal elastic constants between 18 and 344 K. All elastic constants -- bulk, shear, extension, longitudinal moduli and Poisson ratio -- behave smoothly during cooling, indicating no significant phase transition: electronic, magnetic, or structural. Both principal elastic constants (bulk and shear) increase about 30% upon cooling from 300 to 0 K, a large change among metals, which we attribute to 5f-electron delocalization. From the low-temperature elastic constants, we computed that the Debye temperature equals 205 K, exceeding significantly most previous estimates. From the bulk-modulus/temperature slope dB/dT, we computed that the Gruneisen parameter equals 5.1, intermediate among previous estimates using other approaches. Alpha-plutonium shows an unusually high shear-modulus/bulk-modulus ratio G/B, thus a low Poisson ratio: 0.18. Within 0.5%, the Poisson ratio shows temperature invariance; its small negative slope being opposite expectation. Again, we attribute this exceptional behavior to 5f-electron localization.
Ancestrally high elastic modulus of gecko setal beta-keratin.
Peattie, Anne M; Majidi, Carmel; Corder, Andrew; Full, Robert J
2007-12-22
Typical bulk adhesives are characterized by soft, tacky materials with elastic moduli well below 1MPa. Geckos possess subdigital adhesives composed mostly of beta-keratin, a relatively stiff material. Biological adhesives like those of geckos have inspired empirical and modelling research which predicts that even stiff materials can be effective adhesives if they take on a fibrillar form. The molecular structure of beta-keratin is highly conserved across birds and reptiles, suggesting that material properties of gecko setae should be similar to that of beta-keratin previously measured in birds, but this has yet to be established. We used a resonance technique to measure elastic bending modulus in two species of gecko from disparate habitats. We found no significant difference in elastic modulus between Gekko gecko (1.6 GPa +/- 0.15s.e.; n=24 setae) and Ptyodactylus hasselquistii (1.4 GPa +/- 0.15s.e.; n=24 setae). If the elastic modulus of setal keratin is conserved across species, it would suggest a design constraint that must be compensated for structurally, and possibly explain the remarkable variation in gecko adhesive morphology.
Peng, Qing; De, Suvranu
2014-10-21
Silicane is a fully hydrogenated silicene-a counterpart of graphene-having promising applications in hydrogen storage with capacities larger than 6 wt%. Knowledge of its elastic limit is critical in its applications as well as tailoring its electronic properties by strain. Here we investigate the mechanical response of silicane to various strains using first-principles calculations based on density functional theory. We illustrate that non-linear elastic behavior is prominent in two-dimensional nanomaterials as opposed to bulk materials. The elastic limits defined by ultimate tensile strains are 0.22, 0.28, and 0.25 along armchair, zigzag, and biaxial directions, respectively, an increase of 29%, 33%, and 24% respectively in reference to silicene. The in-plane stiffness and Poisson ratio are reduced by a factor of 16% and 26%, respectively. However, hydrogenation/dehydrogenation has little effect on its ultimate tensile strengths. We obtained high order elastic constants for a rigorous continuum description of the nonlinear elastic response. The limitation of second, third, fourth, and fifth order elastic constants are in the strain range of 0.02, 0.08, and 0.13, and 0.21, respectively. The pressure effect on the second order elastic constants and Poisson's ratio were predicted from the third order elastic constants. Our results could provide a safe guide for promising applications and strain-engineering the functions and properties of silicane monolayers. PMID:25190587
Elastic properties of minerals
Aleksandrov, K.S.; Prodaivoda, G.T.
1993-09-01
Investigations of the elastic properties of the main rock-forming minerals were begun by T.V. Ryzhova and K.S. Aleksandrov over 30 years ago on the initiative of B.P. Belikov. At the time, information on the elasticity of single crystals in general, and especially of minerals, was very scanty. In the surveys of that time there was information on the elasticity of 20 or 30 minerals. These, as a rule, did not include the main rock-forming minerals; silicates were represented only by garnets, quartz, topaz, tourmaline, zircon, beryl, and staurolite, which are often found in nature in the form of large and fairly high-quality crystals. Then and even much later it was still necessary to prove a supposition which now seems obvious: The elastic properties of rocks, and hence the velocities of elastic (seismic) waves in the earth`s crust, are primarily determined by the elastic characteristics of the minerals composing these rocks. Proof of this assertion, with rare exceptions of mono-mineralic rocks (marble, quartzite, etc.) cannot be obtained without information on the elasticities of a sufficiently large number of minerals, primarily framework, layer, and chain silicates which constitute the basis of most rocks. This also served as the starting point and main problem of the undertakings of Aleksandrov, Ryzhova, and Belikov - systematic investigations of the elastic properties of minerals and then of various rocks. 108 refs., 7 tabs.
NASA Astrophysics Data System (ADS)
Davis, R. O.; Selvadurai, A. P. S.
1996-04-01
This book concisely examines the use of elasticity in solving geotechnical engineering problems. In a highly illustrated and user-friendly format, it provides a thorough grounding in the linear theory of elasticity and an understanding of the applications. The first two chapters present a basic framework of the theory of elasticity and describe test procedures for the determination of elastic parameters for soils. Chapters 3 and 4 present the fundamental solutions of Boussinesque, Kelvin, and Mindlin, and use these to formulate solutions to problems of practical interest in geotechnical engineering. The book concludes with a sequence of appendices designed to provide the interested student with details of elasticity theory that are peripheral to the main text. Each chapter concludes with a set of questions for the student to answer. The book is appropriate for upper level students in civil engineering and engineering geology.
Cross-type optical separation of elastic oblate capsules in a uniform flow
Chang, Cheong Bong; Sung, Hyung Jin; Huang, Wei-Xi
2015-01-21
The dynamic behavior of an elastic capsule with an initially oblate spheroidal shape during cross-type optical separation was numerically investigated. The penalty immersed boundary method was adopted for the fluid-membrane interaction, and the optical force calculation was conducted by using the ray optics method including the ray-surface intersection algorithm. The oblate elastic capsule of b/a = 0.5 with different surface Young's moduli and different initial inclination angles was considered. The oblate capsule with higher surface Young's moduli was less deformed, and was more migrated for each initial inclination angle. Unlike the oblate rigid particle, the initially inclined capsules with moderate inclination angles were similarly migrated since the oblate elastic capsule was deformed during rotation near the laser beam axis. The oblate capsules can be separated according to the surface Young's modulus, except for nearly non-inclined capsules. As the fluid velocity decreased, the migration distance increased. The maximum deformation parameter was insensitive to the fluid velocity. Furthermore, a new dimensionless number (S{sub ec}) was introduced to predict the migration distance of the oblate elastic capsule.
Hardrock Elastic Physical Properties: Birch's Seismic Parameter Revisited
NASA Astrophysics Data System (ADS)
Wu, M.; Milkereit, B.
2014-12-01
Identifying rock composition and properties is imperative in a variety of fields including geotechnical engineering, mining, and petroleum exploration, in order to accurately make any petrophysical calculations. Density is, in particular, an important parameter that allows us to differentiate between lithologies and estimate or calculate other petrophysical properties. It is well established that compressional and shear wave velocities of common crystalline rocks increase with increasing densities (i.e. the Birch and Nafe-Drake relationships). Conventional empirical relations do not take into account S-wave velocity. Physical properties of Fe-oxides and massive sulfides, however, differ significantly from the empirical velocity-density relationships. Currently, acquiring in-situ density data is challenging and problematic, and therefore, developing an approximation for density based on seismic wave velocity and elastic moduli would be beneficial. With the goal of finding other possible or better relationships between density and the elastic moduli, a database of density, P-wave velocity, S-wave velocity, bulk modulus, shear modulus, Young's modulus, and Poisson's ratio was compiled based on a multitude of lab samples. The database is comprised of isotropic, non-porous metamorphic rock. Multi-parameter cross plots of the various elastic parameters have been analyzed in order to find a suitable parameter combination that reduces high density outliers. As expected, the P-wave velocity to S-wave velocity ratios show no correlation with density. However, Birch's seismic parameter, along with the bulk modulus, shows promise in providing a link between observed compressional and shear wave velocities and rock densities, including massive sulfides and Fe-oxides.
Proton Nucleus Elastic Scattering Data.
1993-08-18
Version 00 The Proton Nucleus Elastic Scattering Data file PNESD contains the numerical data and the related bibliography for the differential elastic cross sections, polarization and integral nonelastic cross sections for elastic proton-nucleus scattering.
Sun, Qicheng; Jin, Feng; Wang, Guangqian; Song, Shixiong; Zhang, Guohua
2015-01-01
Mesoscopic structures form in dense granular materials due to the self-organisation of the constituent particles. These structures have internal structural degrees of freedom in addition to the translational degree of freedom. The resultant granular elasticity, which exhibits intrinsic variations and inevitable relaxation, is a key quantity that accounts for macroscopic solid- or fluid-like properties and the transitions between them. In this work, we propose a potential energy landscape (PEL) with local stable basins and low elastic energy barriers to analyse the nature of granular elasticity. A function for the elastic energy density is proposed for stable states and is further calibrated with ultrasonic measurements. Fluctuations in the elastic energy due to the evolution of internal structures are proposed to describe a so-called configuration temperature Tc as a counterpart of the classical kinetic granular temperature Tk that is attributed to the translational degrees of freedom. The two granular temperatures are chosen as the state variables, and a fundamental equation is established to develop non-equilibrium thermodynamics for granular materials. Due to the relatively low elastic energy barrier in the PEL, granular elasticity relaxes more under common mechanical loadings, and a simple model based on mean-field theory is developed to account for this behaviour. PMID:25951049
Effect of Hydration on the Single-crystal Elasticity of Fe-bearing Wadsleyite to 12 GPa
Z Mao; S Jacobsen; D Frost; C McCammon; E Hauri; T Duffy
2011-12-31
The single-crystal elastic properties of Fe-bearing wadsleyite with 1.93 wt% H{sub 2}O (Mg{sub 1.634}Fe{sub 0.202}H{sub 0.305}SiO{sub 4}) have been determined by Brillouin scattering. At ambient conditions, the aggregate bulk and shear moduli (K{sub S0}, G{sub 0}) of this wadsleyite are 156.2(5) and 98.0(3) GPa, respectively. Compared to the corresponding anhydrous wadsleyite, 1.93 wt% H{sub 2}O lowers K{sub S0} and G{sub 0} by 8.1% and 9.3%, respectively. High-pressure measurements up to 12 GPa show that the pressure derivative of the bulk modulus, K'{sub S0} = 4.8(1), is similar to that of the anhydrous Fe-wadsleyite with reported values of 4.6-4.74, but the addition of H{sub 2}O increases the pressure derivative of the shear modulus, G{sub 0}' from 1.5(1) to 1.9(1). This contrasts with the G{sub 0}' of Fe-free wadsleyite, which is the same within uncertainty for the hydrous and anhydrous phases. As a result, both the compressional- and shear-wave velocities (v{sub P}, v{sub S}) of hydrous Fe-bearing wadsleyite are about 200({+-}24) m/s slower than anhydrous Fe-bearing wadsleyite at transition zone pressures.
ERIC Educational Resources Information Center
Liffen, C. L.; Hunter, M.
1980-01-01
Described is a school project to investigate aggregations in flatworms which may be influenced by light intensity, temperature, and some form of chemical stimulus released by already aggregating flatworms. Such investigations could be adopted to suit many educational levels of science laboratory activities. (DS)
Elastic membranes in confinement
NASA Astrophysics Data System (ADS)
Bostwick, Joshua; Miksis, Michael; Davis, Stephen
2014-11-01
An elastic membrane stretched between two walls takes a shape defined by its length and the volume of fluid it encloses. Many biological structures, such as cells, mitochondria and DNA, have finer internal structure in which a membrane (or elastic member) is geometrically ``confined'' by another object. We study the shape stability of elastic membranes in a ``confining'' box and introduce repulsive van der Waals forces to prevent the membrane from intersecting the wall. We aim to define the parameter space associated with mitochondria-like deformations. We compare the confined to `unconfined' solutions and show how the structure and stability of the membrane shapes changes with the system parameters.
Elastic properties of nanowires
NASA Astrophysics Data System (ADS)
da Fonseca, Alexandre F.; Malta, C. P.; Galva~O, Douglas S.
2006-05-01
We present a model to study Young's modulus and Poisson's ratio of the composite material of amorphous nanowires. It is an extension of the model derived by two of us [da Fonseca and Galva~o, Phys. Rev. Lett. 92, 175502 (2004)] to study the elastic properties of amorphous nanosprings. The model is based on twisting and tensioning a straight nanowire and we propose an experimental setup to obtain the elastic parameters of the nanowire. We used the Kirchhoff rod model to obtain the expressions for the elastic constants of the nanowire.
Polynomial approximations of a class of stochastic multiscale elasticity problems
NASA Astrophysics Data System (ADS)
Hoang, Viet Ha; Nguyen, Thanh Chung; Xia, Bingxing
2016-06-01
We consider a class of elasticity equations in {mathbb{R}^d} whose elastic moduli depend on n separated microscopic scales. The moduli are random and expressed as a linear expansion of a countable sequence of random variables which are independently and identically uniformly distributed in a compact interval. The multiscale Hellinger-Reissner mixed problem that allows for computing the stress directly and the multiscale mixed problem with a penalty term for nearly incompressible isotropic materials are considered. The stochastic problems are studied via deterministic problems that depend on a countable number of real parameters which represent the probabilistic law of the stochastic equations. We study the multiscale homogenized problems that contain all the macroscopic and microscopic information. The solutions of these multiscale homogenized problems are written as generalized polynomial chaos (gpc) expansions. We approximate these solutions by semidiscrete Galerkin approximating problems that project into the spaces of functions with only a finite number of N gpc modes. Assuming summability properties for the coefficients of the elastic moduli's expansion, we deduce bounds and summability properties for the solutions' gpc expansion coefficients. These bounds imply explicit rates of convergence in terms of N when the gpc modes used for the Galerkin approximation are chosen to correspond to the best N terms in the gpc expansion. For the mixed problem with a penalty term for nearly incompressible materials, we show that the rate of convergence for the best N term approximation is independent of the Lamé constants' ratio when it goes to {infty}. Correctors for the homogenization problem are deduced. From these we establish correctors for the solutions of the parametric multiscale problems in terms of the semidiscrete Galerkin approximations. For two-scale problems, an explicit homogenization error which is uniform with respect to the parameters is deduced. Together
Bayon, A.; Varade, A.; Gascon, F.
1997-04-01
An experimental method is proposed for the elastic characterization of an isotropic material based upon the vibration natural frequencies recorded by means of a single assembly and experiment. Speckle heterodyne optic interferometry is applied to detect the tangential component of the vibration at a point. The sample is a slender rod excited through a broad-spectrum percussion, where the vibration recorded is a superposition of the transverse and torsional natural modes. Spectral analysis of the vibration allows the identification of the transverse and torsional natural frequencies. This is followed by calculation of the elastic moduli. {copyright} {ital 1997 Acoustical Society of America.}
Elastic properties of sand-peat moss mixtures from ultrasonic measurements
Trombino, C N
1998-09-02
Effective remediation of an environmental site requires extensive knowledge of the geologic setting, as well as the amount and distribution of contaminants. Seismic investigations provide a means to examine the subsurface with minimum disturbance, Laboratory measurements are needed to interpret field data. In this experiment, laboratory tests were performed to characterize manufactured soil samples in terms of their elastic properties. The soil samples consisted of small (mass) percentages (1 to 20 percent) of peat moss mixed with pure quartz sand. Sand was chosen as the major component because its elastic properties are well known except at the lowest pressures. The ultrasonic pulse transmission technique was used to collect elastic wave velocity data. These data were analyzed and mathematically processed to calculate the other elastic properties such as the modulus of elasticity. This experiment demonstrates that seismic data are affected by the amount~of peat moss added to pure sand samples. Elastic wave velocities, velocity gradients, and elastic moduli vary with pressure and peat moss amounts. In particular, ultrasonic response changes dramatically when pore space fills with peat. With some further investigation, the information gathered in this experiment could be applied to seismic field research.
Mechanism of Resilin Elasticity
Qin, Guokui; Hu, Xiao; Cebe, Peggy; Kaplan, David L.
2012-01-01
Resilin is critical in the flight and jumping systems of insects as a polymeric rubber-like protein with outstanding elasticity. However, insight into the underlying molecular mechanisms responsible for resilin elasticity remains undefined. Here we report the structure and function of resilin from Drosophila CG15920. A reversible beta-turn transition was identified in the peptide encoded by exon III and for full length resilin during energy input and release, features that correlate to the rapid deformation of resilin during functions in vivo. Micellar structures and nano-porous patterns formed after beta-turn structures were present via changes in either the thermal or mechanical inputs. A model is proposed to explain the super elasticity and energy conversion mechanisms of resilin, providing important insight into structure-function relationships for this protein. Further, this model offers a view of elastomeric proteins in general where beta-turn related structures serve as fundamental units of the structure and elasticity. PMID:22893127
Fixing All Moduli for M-Theory on K3xK3
Aspinwall, Paul S.; Kallosh, Renata; /Stanford U., Phys. Dept.
2005-06-15
We analyze M-theory compactified on K3 x K3 with fluxes preserving half the supersymmetry and its F-theory limit, which is dual to an orientifold of the type IIB string on K3 x (T{sup 2}/Z{sub 2}). The geometry of attractive K3 surfaces plays a significant role in the analysis. We prove that the number of choices for the K3 surfaces is finite and we show how they can be completely classified. We list the possibilities in one case. We then study the instanton effects and see that they will generically fix all of the moduli. We also discuss situations where the instanton effects might not fix all the moduli.
N = 2 gauge theories, instanton moduli spaces and geometric representation theory
NASA Astrophysics Data System (ADS)
Szabo, Richard J.
2016-11-01
We survey some of the AGT relations between N = 2 gauge theories in four dimensions and geometric representations of symmetry algebras of two-dimensional conformal field theory on the equivariant cohomology of their instanton moduli spaces. We treat the cases of gauge theories on both flat space and ALE spaces in some detail, and with emphasis on the implications arising from embedding them into supersymmetric theories in six dimensions. Along the way we construct new toric noncommutative ALE spaces using the general theory of complex algebraic deformations of toric varieties, and indicate how to generalize the construction of instanton moduli spaces. We also compute the equivariant partition functions of topologically twisted six-dimensional Yang-Mills theory with maximal supersymmetry in a general Ω-background, and use the construction to obtain novel reductions to theories in four dimensions.
Stebner, A. P.; Brown, D. W.; Brinson, L. C.
2013-05-27
Polycrystalline, monoclinic nickel-titanium specimens were subjected to tensile and compressive deformations while neutron diffraction spectra were recorded in situ. Using these data, orientation-specific and macroscopic Young's moduli are determined from analysis of linear-elastic deformation exhibited by 13 unique orientations of monoclinic lattices and their relationships to each macroscopic stress and strain. Five of 13 elastic compliance constants are also identified: s{sub 11} = 1.15, s{sub 15} = -1.10, s{sub 22} = 1.34, s{sub 33} = 1.06, s{sub 35} = -1.54, all Multiplication-Sign 10{sup -2} GPa{sup -1}. Through these results, recent atomistic calculations of monoclinic nickel-titanium elastic constants are validated.
An inclusion in one of two joined isotropic elastic half-spaces
NASA Astrophysics Data System (ADS)
Walpole, L. J.
1997-10-01
Two dissimilar, homogeneous and istropic, elastic half-spaces are bonded together over thier infinite plane of contract. An arbitrarily shaped finite part of one of them (an inclusion) tends spontaneously to undergo a unifrom infinitesimal strain, but, as it remains attached to and restrained by the surrounding material, an equilibrated state of stress and strain is established everywhere instead. By adopting a convenient expression for the fundamental field of a point force, we transformed inclusion. For a general shape of the inclussion and for particular spherical and finite cylindrical shapes in detail, we consider the evaluation of the elastic strain energy, especially of the interaction term which depends on the location of the inclusion and both pairs of elastic moduli, and which is of great significance in physical applications.
Ab initio investigations of the elastic properties of chlorates and perchlorates
NASA Astrophysics Data System (ADS)
Korabel'nikov, D. V.; Zhuravlev, Yu. N.
2016-06-01
Elastic properties of NaClO3, KClO3, LiClO4, NaClO4, and KClO4 have been investigated from first principles by the method of linear combination of atomic orbitals in the gradient approximation of the density functional theory using CRYSTAL software. The elastic constants and moduli, hardness, Poisson's ratio, and the anisotropy parameters have been calculated. The velocities of sound, the Debye temperature, the thermal conductivity, and the Grüneisen parameter have been estimated. It has been found that these compounds are mechanically stable, anisotropic, and ductile materials. The dependences of their elastic parameters on the atomic number of the cation have been calculated. The obtained results are in good agreement with the available experimental data.
From Process Modeling to Elastic Property Prediction for Long-Fiber Injection-Molded Thermoplastics
Nguyen, Ba Nghiep; Kunc, Vlastimil; Frame, Barbara J.; Phelps, Jay; Tucker III, Charles L.; Bapanapalli, Satish K.; Holbery, James D.; Smith, Mark T.
2007-09-13
This paper presents an experimental-modeling approach to predict the elastic properties of long-fiber injection-molded thermoplastics (LFTs). The approach accounts for fiber length and orientation distributions in LFTs. LFT samples were injection-molded for the study, and fiber length and orientation distributions were measured at different locations for use in the computation of the composite properties. The current fiber orientation model was assessed to determine its capability to predict fiber orientation in LFTs. Predicted fiber orientations for the studied LFT samples were also used in the calculation of the elastic properties of these samples, and the predicted overall moduli were then compared with the experimental results. The elastic property prediction was based on the Eshelby-Mori-Tanaka method combined with the orientation averaging technique. The predictions reasonably agree with the experimental LFT data
Finite-element formulations for problems of large elastic-plastic deformation
NASA Technical Reports Server (NTRS)
Mcmeeking, R. M.; Rice, J. R.
1975-01-01
An Eulerian finite element formulation is presented for problems of large elastic-plastic flow. The method is based on Hill's variational principle for incremental deformations, and is ideally suited to isotropically hardening Prandtl-Reuss materials. Further, the formulation is given in a manner which allows any conventional finite element program, for 'small strain' elastic-plastic analysis, to be simply and rigorously adapted to problems involving arbitrary amounts of deformation and arbitrary levels of stress in comparison to plastic deformation moduli. The method is applied to a necking bifurcation analysis of a bar in plane-strain tension. The paper closes with a unified general formulation of finite element equations, both Lagrangian and Eulerian, for large deformations, with arbitrary choice of the conjugate stress and strain measures. Further, a discussion is given of other proposed formulations for elastic-plastic finite element analysis at large strain, and the inadequacies of some of these are commented upon.
Thermodynamics of viscous flow and elasticity of glass forming liquids in the glass transition range
NASA Astrophysics Data System (ADS)
Rouxel, T.
2011-11-01
The elastic moduli of glasses from different chemical systems, including oxide, chalcogenide, oxynitride, and metallic, were investigated through the glass transition (Tg), typically from 0.4 to 1.3 Tg. These data were used to interpret the temperature sensitivity of the shear viscosity coefficient obtained on the same materials. The relevant Gibbs free activation energy was estimated from the apparent heat of flow by means of the temperature dependence of the shear elastic modulus. The activation entropy associated with the viscous flow was also derived and was found to correlate with the fragile versus strong character of the glass forming liquids. Finally, the physicochemistry of the flow process was described on the basis of the glass network de-structuration which shows up through the temperature dependence of Poisson's ratio, and an expression for the shear viscosity coefficient is proposed which is chiefly based on the high temperature elastic behavior.
NASA Astrophysics Data System (ADS)
Quilliet, Catherine; Quemeneur, François; Marmottant, Philippe; Imhof, Arnout; Pépin-Donat, Brigitte; van Blaaderen, Alfons
2010-03-01
The deflation of elastic spherical surfaces has been numerically investigated, and show very different types of deformations according the range of elastic parameters, some of them being quantitatively explained through simple calculations. This allows to retrieve various shapes observed on hollow shells (from colloidal to centimeter scale), on lipid vesicles, or on some biological objects. The extension of this process to other geometries allows to modelize vegetal objects such as the ultrafast trap of carnivorous plants.
Bonds, bands and elasticity of smithsonite rock
NASA Astrophysics Data System (ADS)
Bouibes, A.; Zaoui, A.; Tunega, D.
2013-07-01
The objective here is to spread out in detail the various fundamental state properties of smithsonite rock (ZnCO3) for which the most intrinsic quantities remain still unknown. First-principles electronic structure calculations based on the density functional theory with the pseudopotential method were performed using diverse functionals. A number of mechanical quantities were evaluated such as bulk modulus, elastic constants, Young's and shear moduli, and transversal and longitudinal sound velocities (VS and VP). Fitting the compression data of smithsonite to the third-order Birch-Murnaghan equation of state gives a bulk modulus of 124.17 GPa, which reflects an important rigidity compared to the other carbonates. The analysis of the band structure reveals a band-gap energy of 3.36 eV that is close enough to some semiconductors rather than insulators. Finally the chemical bonding was analyzed through the electronic charge density of the total contributions of the valence bands. A pronounced charge transfer was observed towards the carbonate ion, indicating thereby the ionic character of ZnCO3.
Metaconcrete: designed aggregates to enhance dynamic performance
NASA Astrophysics Data System (ADS)
Mitchell, Stephanie J.; Pandolfi, Anna; Ortiz, Michael
2014-04-01
We propose a new type of concrete for the attenuation of elastic waves induced by dynamic excitation. In this metamaterial, which we call metaconcrete, the stone, sand, and gravel aggregates of standard concrete are replaced with spherical inclusions consisting of a heavy metal core coated with a soft outer layer. These engineered aggregates can be tuned so that particular frequencies of a propagating blast wave will activate resonant oscillations of the heavy mass within the inclusions. The resonant behavior causes the system to exhibit negative effective mass, and this interaction between the wave motion and the resonant aggregates results in the attenuation of the applied dynamic loading. We introduce the concept of negative mass by deriving the effective momentum mass for the system and we define the geometrical and material parameters for the design of resonant aggregates. We develop finite element models for the analysis of metaconcrete behavior, defining a section of slab containing a periodic arrangement of inclusions. By computing the energy histories for the system when subject to a blast load, we show that there is a transfer of energy between the inclusions and the surrounding mortar. The inclusions are able to absorb a significant portion of the applied energy, resulting in a reduction in the amount of stress carried by the mortar phase and greatly improving the ability of the material to resist damage under explosive dynamic loading.
Gauge theory dynamics and Kähler potential for Calabi-Yau complex moduli
NASA Astrophysics Data System (ADS)
Doroud, Nima; Gomis, Jaume
2013-12-01
We compute the exact two-sphere partition function and matrix of two-point functions of operators in the chiral ring with their complex conjugates in two-dimensional supersymmetric gauge theories. For gauge theories that flow in the infrared to a CalabiYau nonlinear sigma model, these renormalization group invariant observables determine the exact Kähler potential and associated Zamolodchikov metric in the complex structure moduli space of the Calabi-Yau manifold.
Elastic Collisions and Gravity
NASA Astrophysics Data System (ADS)
Ball, Steven
2009-04-01
Elastic collisions are fascinating demonstrations of conservation principles. The mediating force must be conservative in an elastic collision. Truly elastic collisions take place only when the objects in collision do not touch, e.g. magnetic bumpers on low friction carts. This requires that we define a collision as a momentum transfer. Elastic collisions in 1-D can be solved in general and the implications are quite remarkable. For example, a heavy object moving initially towards a light object followed by an elastic collision results in a final velocity of the light object greater than either initial velocity. This is easily demonstrated with low friction carts. Gravitational elastic collisions involving a light spacecraft and an extremely massive body like a moon or planet can be approximated as 1-D collisions, such as the ``free return'' trajectory of Apollo 13 around the moon. The most fascinating gravitational collisions involve the gravitational slingshot effect used to boost spacecraft velocities. The maximum gravitational slingshot effect occurs when approaching a nearly 1-D collision, revealing that the spacecraft can be boosted to greater than twice the planet velocity, enabling the spacecraft to travel much further away from the Sun.
In search of a corrected prescription drug elasticity estimate: a meta-regression approach.
Gemmill, Marin C; Costa-Font, Joan; McGuire, Alistair
2007-06-01
An understanding of the relationship between cost sharing and drug consumption depends on consistent and unbiased price elasticity estimates. However, there is wide heterogeneity among studies, which constrains the applicability of elasticity estimates for empirical purposes and policy simulation. This paper attempts to provide a corrected measure of the drug price elasticity by employing meta-regression analysis (MRA). The results indicate that the elasticity estimates are significantly different from zero, and the corrected elasticity is -0.209 when the results are made robust to heteroskedasticity and clustering of observations. Elasticity values are higher when the study was published in an economic journal, when the study employed a greater number of observations, and when the study used aggregate data. Elasticity estimates are lower when the institutional setting was a tax-based health insurance system.
Lemoine, Martin; Martin, Jerome; Yokoyama, Jun'ichi
2009-12-15
We set constraints on moduli cosmology from the production of dark matter - radiation and baryon -radiation isocurvature fluctuations through modulus decay, assuming the modulus remains light during inflation. We find that the moduli problem becomes worse at the perturbative level as a significant part of the parameter space m{sub {sigma}} (modulus mass) - {sigma}{sub inf} (modulus vacuum expectation value at the end of inflation) is constrained by the nonobservation of significant isocurvature fluctuations. We discuss in detail the evolution of the modulus vacuum expectation value and perturbations, in particular, the consequences of Hubble scale corrections to the modulus potential, and the stochastic motion of the modulus during inflation. We show, in particular, that a high modulus mass scale m{sub {sigma}} > or approx. 100 TeV, which allows the modulus to evade big bang nucleosynthesis constraints is strongly constrained at the perturbative level. We find that generically, solving the moduli problem requires the inflationary scale to be much smaller than 10{sup 13} GeV.
Scattering and sequestering of blow-up moduli in local string models
NASA Astrophysics Data System (ADS)
Conlon, Joseph P.; Witkowski, Lukas T.
2011-12-01
We study the scattering and sequestering of blow-up fields - either local to or distant from a visible matter sector - through a CFT computation of the dependence of physical Yukawa couplings on the blow-up moduli. For a visible sector of D3-branes on orbifold singularities we compute the disk correlator left< {tau_s^{{(1)}}tau_s^{{(2)}}...tau_s^{{(n)}}ψ ψ φ } rightrangle between orbifold blow-up moduli and matter Yukawa couplings. For n = 1 we determine the full quantum and classical correlator. This result has the correct factorisation onto lower 3-point functions and also passes numerous other consistency checks. For n > 1 we show that the structure of picture-changing applied to the twist operators establishes the sequestering of distant blow-up moduli at disk level to all orders in α'. We explain how these results are relevant to suppressing soft terms to scales parametrically below the gravitino mass. By giving vevs to the blow-up fields we can move into the smooth limit and thereby derive CFT results for the smooth Swiss-cheese Calabi-Yaus that appear in the Large Volume Scenario.
Guessasma, S; Oyen, M
2016-01-14
Remarkable mechanical performance of biological tissues is explained by a hierarchical fibrous structure. Designing materials that have similar properties is challenging because of the need to assess complex deformation mechanisms. In order to shed more light on architectural possibilities of biopolymer fibrous networks, we propose a numerical study that relates the fibre arrangement to the elastic modulus of a gelatin scaffold obtained using electrospinning. The adopted approach is based on the virtual designing of scaffolds using all possible combinations of Euler angles that define fibre orientations including preferable alignment. The generated networks are converted into a finite element model and the predicted elastic behaviour is examined. Predictions show that the fibre alignment achieved experimentally in biopolymer fibrous networks is for most of the fibres exhibiting an orthotropic behaviour. Some particular combinations of Euler angles allow transverse isotropic architectures while only limited cases are isotropic. A large sensitivity of Young's moduli to Euler angles is achieved describing multiple scenarios of independent anisotropic behaviours. An anisotropy ratio of the elastic behaviour is suggested based on a suitable combination of elastic moduli. Such a ratio exhibits a wide variation depending on individual and coupled effects of Euler angles. The finite element model predicts 2D, 3D and 4D maps representing all possible configurations of fibre alignment and their consequences on elastic behaviour. The predicted fibre orientation representing the observed anisotropic behaviour of electrospun gelatin networks demonstrates unbalanced contributions of in-plane and out-of plane fibres for a large range of processing conditions.
Langer, William H.; Drew, Lawrence J.; Sachs, J.S.
2004-01-01
This book is designed to help you understand our aggregate resources-their importance, where they come from, how they are processed for our use, the environmental concerns related to their mining and processing, how those concerns are addressed, and the policies and regulations designed to safeguard workers, neighbors, and the environment from the negative impacts of aggregate mining. We hope this understanding will help prepare you to be involved in decisions that need to be made-individually and as a society-to be good stewards of our aggregate resources and our living planet.
Effect of a hypergravity environment on cortical bone elasticity in rats
NASA Technical Reports Server (NTRS)
Kohles, S. S.; Bowers, J. R.; Vailas, A. C.; Vanderby, R. Jr
1996-01-01
There is considerable interest in determining whether hypergravity can be used as a countermeasure for microgravity-induced bone loss. This study was conducted on 20 immature male rats in order to investigate possible elastic adaptations of cortical bone in rapidly growing rats exposed to chronic hypergravity. Ten rats were continuously centrifuged for 14 days at twice gravitational acceleration (2G) on a 12.75 foot radius centrifuge and 10 rats concurrently acted as stationary controls. The effect of hypergravity on the elastic characteristics of cortical bone was quantified via ultrasonic wave propagation. Propagation velocities of longitudinal and shear waves were measured through cubic cortical specimens from the posterior femoral diaphyses. Density was measured with an Archimedes' technique. The orthotropic elastic properties were calculated and used to compare the difference between groups. Results showed an average increase in both the Young's moduli (Eii, + 2.2%) and shear moduli (Gij, + 4.3%) with a statistically significant increase only in G12 (+15.7%, P = 0.046). The ratio of transverse to axial strain (Poisson's ratio, nuij) demonstrated statistically significant changes in nu12, nu21, nu13, and nu31 (P < 0.05). These findings suggest that although slight elastic changes were incurred via a hypergravity environment, the treatment level or duration in this study do not dramatically perturb the normal elastic behavior of cortical bone and that dramatic biomechanical differences noted in previous studies were due more to structural changes than material elasticity changes. Hypergravity applied post facto to a microgravity environment would offer further illucidation of this method as treatment for a degenerative spaceflight experience.
Protein Colloidal Aggregation Project
NASA Technical Reports Server (NTRS)
Oliva-Buisson, Yvette J. (Compiler)
2014-01-01
To investigate the pathways and kinetics of protein aggregation to allow accurate predictive modeling of the process and evaluation of potential inhibitors to prevalent diseases including cataract formation, chronic traumatic encephalopathy, Alzheimer's Disease, Parkinson's Disease and others.
Elastic constants of beryllium: a first-principles investigation.
Dal Corso, Andrea
2016-02-24
We apply several recently introduced projector-augmented wave, ultrasoft, and norm-conserving pseudopotentials (PPs) to the calculation of the elastic constants of beryllium and compare the results with previous theory and experiments. We discuss how the elastic constants depend on the Brillouin zone integration, the PP type, and the exchange and correlation functional. We find that although in percentage terms the elastic constants of beryllium depend on the PPs more than the crystal parameters or the bulk moduli, the differences between the local density approximation (LDA) and the Perdew, Burke, and Ernzerhof (PBE) generalized-gradient approximation are larger than the PP differences. The LDA overestimates compared to experiments, while the PBE values are higher than those of experiments but show a much better agreement. The PBEsol functional gives values that are slightly higher than those from PBE, with differences comparable to the PP uncertainty. We propose a simple formula to rationalize the internal relaxations in hexagonal close-packed crystals and show that Be relaxations are in reasonable agreement with this formula. The effects of internal relaxations on the values of C11 and C12 amount to a few per cent of C11, but up to 50% of C12. PMID:26809146
Critical behaviour in the nonlinear elastic response of hydrogels.
Dennison, M; Jaspers, M; Kouwer, P H J; Storm, C; Rowan, A E; MacKintosh, F C
2016-08-17
In this paper we study the elastic response of synthetic hydrogels to an applied shear stress. The hydrogels studied here have previously been shown to mimic the behaviour of biopolymer networks when they are sufficiently far above the gel point. We show that near the gel point they exhibit an elastic response that is consistent with the predicted critical behaviour of networks near or below the isostatic point of marginal stability. This point separates rigid and floppy states, distinguished by the presence or absence of finite linear elastic moduli. Recent theoretical work has also focused on the response of such networks to finite or large deformations, both near and below the isostatic point. Despite this interest, experimental evidence for the existence of criticality in such networks has been lacking. Using computer simulations, we identify critical signatures in the mechanical response of sub-isostatic networks as a function of applied shear stress. We also present experimental evidence consistent with these predictions. Furthermore, our results show the existence of two distinct critical regimes, one of which arises from the nonlinear stretch response of semi-flexible polymers.
Critical behaviour in the nonlinear elastic response of hydrogels.
Dennison, M; Jaspers, M; Kouwer, P H J; Storm, C; Rowan, A E; MacKintosh, F C
2016-08-17
In this paper we study the elastic response of synthetic hydrogels to an applied shear stress. The hydrogels studied here have previously been shown to mimic the behaviour of biopolymer networks when they are sufficiently far above the gel point. We show that near the gel point they exhibit an elastic response that is consistent with the predicted critical behaviour of networks near or below the isostatic point of marginal stability. This point separates rigid and floppy states, distinguished by the presence or absence of finite linear elastic moduli. Recent theoretical work has also focused on the response of such networks to finite or large deformations, both near and below the isostatic point. Despite this interest, experimental evidence for the existence of criticality in such networks has been lacking. Using computer simulations, we identify critical signatures in the mechanical response of sub-isostatic networks as a function of applied shear stress. We also present experimental evidence consistent with these predictions. Furthermore, our results show the existence of two distinct critical regimes, one of which arises from the nonlinear stretch response of semi-flexible polymers. PMID:27464595
Cell aggregation and sedimentation.
Davis, R H
1995-01-01
The aggregation of cells into clumps or flocs has been exploited for decades in such applications as biological wastewater treatment, beer brewing, antibiotic fermentation, and enhanced sedimentation to aid in cell recovery or retention. More recent research has included the use of cell aggregation and sedimentation to selectively separate subpopulations of cells. Potential biotechnological applications include overcoming contamination, maintaining plasmid-bearing cells in continuous fermentors, and selectively removing nonviable hybridoma cells from perfusion cultures.
Lubrication properties of protein aggregate dispersions in a soft contact.
Chojnicka, Agnieszka; de Jong, Saskia; de Kruif, Cornelus G; Visschers, Ronald W
2008-02-27
The lubrication, rheological, and molecular properties of two different protein aggregate dispersions were compared: globular aggregates of whey protein isolate (WPI) and fibrillar aggregates of ovalbumin from egg white. These dispersions are models for the lubricating fluid that is present between the tongue and the palate when consuming liquid or gelled products. To simulate oral conditions, a commercial tribometer was modified so that soft rubber surfaces could be used. This allowed us to measure friction at low contact pressures similar to those present between the tongue and palate. Clear correlations were observed between the measured friction coefficients and specific properties of the lubricating fluid such as protein concentration and aggregate size and shape. Furthermore, surface properties like elasticity, surface-surface interactions, and surface roughness had a significant effect on the friction under conditions that are relevant for texture perception. We conclude that in vitro measurements at low contact pressure provide valuable information for understanding and controlling food properties that modulate oral friction.
Wald, Michael J; Magland, Jeremy F; Rajapakse, Chamith S; Bhagat, Yusuf A; Wehrli, Felix W
2012-08-01
The relationship between fabric (a measure of structural anisotropy) and elastic properties of trabecular bone was examined by invoking morphology and homogenization theory on the basis of micromagnetic resonance images from the distal tibia in specimens (N = 30) and human subjects (N = 16) acquired at a 160 × 160 × 160 μm(3) voxel size. The fabric tensor was mapped in 7.5 × 7.5 × 7.5 mm(3) cubic subvolumes by a three-dimensional mean-intercept-length method. Elastic constants (three Young's and three shear moduli) were derived from linear microfinite element simulations of three-dimensional grayscale bone volume fraction-mapped images. In the specimen data, moduli fit power laws of bone volume fraction (bone volume/total volume) for all three test directions and subvolumes (R(2) = 0.92-0.98) with exponents ranging from 1.3 to 1.8. Weaker linear relationships were found for the in vivo data because of a narrower range in bone volume/total volume. When pooling the data for all test directions and subvolumes, bone volume/total volume predicted elastic moduli less well in the specimens (mean R(2) = 0.74) and not at all in vivo. A model of bone volume/total volume and fabric was highly predictive of microfinite element-derived Young's moduli: mean R(2) s of 0.98 and 0.82 (in vivo). The results show that fabric, an important predictor of bone mechanical properties, can be assessed in the limited resolution and signal-to-noise ratio regime of micromagnetic resonance images.
Elasticity of polymeric nanocolloidal particles
Riest, Jonas; Athanasopoulou, Labrini; Egorov, Sergei A.; Likos, Christos N.; Ziherl, Primož
2015-01-01
Softness is an essential mechanical feature of macromolecular particles such as polymer-grafted nanocolloids, polyelectrolyte networks, cross-linked microgels as well as block copolymer and dendrimer micelles. Elasticity of individual particles directly controls their swelling, wetting, and adsorption behaviour, their aggregation and self-assembly as well as structural and rheological properties of suspensions. Here we use numerical simulations and self-consistent field theory to study the deformation behaviour of a single spherical polymer brush upon diametral compression. We observe a universal response, which is rationalised using scaling arguments and interpreted in terms of two coarse-grained models. At small and intermediate compressions the deformation can be accurately reproduced by modelling the brush as a liquid drop, whereas at large compressions the brush behaves as a soft ball. Applicable far beyond the pairwise-additive small-strain regime, the models may be used to describe microelasticity of nanocolloids in severe confinement including dense disordered and crystalline phases. PMID:26522242
Elastic Properties of the Solid Electrolyte Li7La3Zr2O12 (LLZO)
Yu, Seungho; Schmidt, Robert D.; Garcia-mendez, Regina; Herbert, Erik G.; Dudney, Nancy J.; Wolfenstine, Jeff; Sakamoto, Jeff; Seigel, Donald
2015-12-16
The oxide known as LLZO, with nominal composition Li_{7}La_{3}Zr_{2}O_{12}, is a promising solid electrolyte for Li-based batteries due to its high Li-ion conductivity and chemical stability with respect to lithium. Solid electrolytes may also enable the use of metallic Li anodes by serving as a physical barrier that suppresses dendrite initiation and propagation during cycling. Prior linear elasticity models of the Li electrode/solid electrolyte interface suggest that the stability of this interface is highly dependent on the elastic properties of the solid separator. For example, dendritic suppression is predicted to be enhanced as the electrolyte s shear modulus increases. In the present study a combination of first-principles calculations, acoustic impulse excitation measurements, and nanoindentation experiments are used to determine the elastic constants and moduli for highconductivity LLZO compositions based on Al and Ta doping. The calculated and measured isotropic shear moduli are in good agreement and fall within the range of 56-61 GPa. These values are an order of magnitude larger than that for Li metal and far exceed the minimum value ( 8.5 GPa) believed to be necessary to suppress dendrite initiation. These data suggest that LLZO exhibits sufficient stiffness to warrant additional development as a solid electrolyte for Li batteries.
Elastic Properties of the Solid Electrolyte Li7La3Zr2O12 (LLZO)
Yu, Seungho; Schmidt, Robert D.; Garcia-mendez, Regina; Herbert, Erik G.; Dudney, Nancy J.; Wolfenstine, Jeff; Sakamoto, Jeff; Seigel, Donald
2015-12-16
The oxide known as LLZO, with nominal composition Li7La3Zr2O12, is a promising solid electrolyte for Li-based batteries due to its high Li-ion conductivity and chemical stability with respect to lithium. Solid electrolytes may also enable the use of metallic Li anodes by serving as a physical barrier that suppresses dendrite initiation and propagation during cycling. Prior linear elasticity models of the Li electrode/solid electrolyte interface suggest that the stability of this interface is highly dependent on the elastic properties of the solid separator. For example, dendritic suppression is predicted to be enhanced as the electrolyte s shear modulus increases. Inmore » the present study a combination of first-principles calculations, acoustic impulse excitation measurements, and nanoindentation experiments are used to determine the elastic constants and moduli for highconductivity LLZO compositions based on Al and Ta doping. The calculated and measured isotropic shear moduli are in good agreement and fall within the range of 56-61 GPa. These values are an order of magnitude larger than that for Li metal and far exceed the minimum value ( 8.5 GPa) believed to be necessary to suppress dendrite initiation. These data suggest that LLZO exhibits sufficient stiffness to warrant additional development as a solid electrolyte for Li batteries.« less
Elastic membranes in confinement.
Bostwick, J B; Miksis, M J; Davis, S H
2016-07-01
An elastic membrane stretched between two walls takes a shape defined by its length and the volume of fluid it encloses. Many biological structures, such as cells, mitochondria and coiled DNA, have fine internal structure in which a membrane (or elastic member) is geometrically 'confined' by another object. Here, the two-dimensional shape of an elastic membrane in a 'confining' box is studied by introducing a repulsive confinement pressure that prevents the membrane from intersecting the wall. The stage is set by contrasting confined and unconfined solutions. Continuation methods are then used to compute response diagrams, from which we identify the particular membrane mechanics that generate mitochondria-like shapes. Large confinement pressures yield complex response diagrams with secondary bifurcations and multiple turning points where modal identities may change. Regions in parameter space where such behaviour occurs are then mapped. PMID:27440257
Elastic anisotropy of crystals
NASA Astrophysics Data System (ADS)
Kube, Christopher M.
2016-09-01
An anisotropy index seeks to quantify how directionally dependent the properties of a system are. In this article, the focus is on quantifying the elastic anisotropy of crystalline materials. Previous elastic anisotropy indices are reviewed and their shortcomings discussed. A new scalar log-Euclidean anisotropy measure AL is proposed, which overcomes these deficiencies. It is based on a distance measure in a log-Euclidean space applied to fourth-rank elastic tensors. AL is an absolute measure of anisotropy where the limiting case of perfect isotropy yields zero. It is a universal measure of anisotropy applicable to all crystalline materials. Specific examples of strong anisotropy are highlighted. A supplementary material (ftp://ftp.aip.org/epaps/aip_advances/E-AAIDBI-6-041609) provides an anisotropy table giving the values of AL for 2,176 crystallite compounds.
Sewell, T. D.; Bedrov, D.; Menikoff, Ralph; Smith, G. D.
2001-01-01
Atomistic molecular dynamics simulations have been used to calculate isothermal elastic properties for {beta}-, {alpha}-, and {delta}-HMX. The complete elastic tensor for each polymorph was determined at room temperature and pressure via analysis of microscopic strain fluctuations using formalism due to Rahman and Parrinello [J. Chem. Phys. 76,2662 (1982)]. Additionally, the isothermal compression curve was computed for {beta}-HMX for 0 {le} p {le} 10.6 GPa; the bulk modulus K and its pressure derivative K{prime} were obtained from two fitting forms employed previously in experimental studies of the {beta}-HMX equation of state. Overall, the results indicate good agreement between the bulk modulus predicted from the measured and calculated compression curves. The bulk modulus determined directly from the elastic tensor of {beta}-HMX is in significant disagreement with the compression curve-based results. The explanation for this discrepancy is an area of current research.
NASA Astrophysics Data System (ADS)
Yu, Betty; Kang, Soo-Young; Akthakul, Ariya; Ramadurai, Nithin; Pilkenton, Morgan; Patel, Alpesh; Nashat, Amir; Anderson, Daniel G.; Sakamoto, Fernanda H.; Gilchrest, Barbara A.; Anderson, R. Rox; Langer, Robert
2016-08-01
We report the synthesis and application of an elastic, wearable crosslinked polymer layer (XPL) that mimics the properties of normal, youthful skin. XPL is made of a tunable polysiloxane-based material that can be engineered with specific elasticity, contractility, adhesion, tensile strength and occlusivity. XPL can be topically applied, rapidly curing at the skin interface without the need for heat- or light-mediated activation. In a pilot human study, we examined the performance of a prototype XPL that has a tensile modulus matching normal skin responses at low strain (<40%), and that withstands elongations exceeding 250%, elastically recoiling with minimal strain-energy loss on repeated deformation. The application of XPL to the herniated lower eyelid fat pads of 12 subjects resulted in an average 2-grade decrease in herniation appearance in a 5-point severity scale. The XPL platform may offer advanced solutions to compromised skin barrier function, pharmaceutical delivery and wound dressings.
Zacharias, Mario; Paul, Indranil; Garst, Markus
2015-07-10
We discuss elastic instabilities of the atomic crystal lattice at zero temperature. Because of long-range shear forces of the solid, at such transitions the phonon velocities vanish, if at all, only along certain crystallographic directions, and, consequently, the critical phonon fluctuations are suppressed to a lower dimensional manifold and governed by a Gaussian fixed point. In the case of symmetry-breaking elastic transitions, a characteristic critical phonon thermodynamics arises that is found, e.g., to violate Debye's T(3) law for the specific heat. We point out that quantum critical elasticity is triggered whenever a critical soft mode couples linearly to the strain tensor. In particular, this is relevant for the electronic Ising-nematic quantum phase transition in a tetragonal crystal as discussed in the context of certain cuprates, ruthenates, and iron-based superconductors. PMID:26207483
Norris, Andrew N.
2014-01-01
We consider a periodic lattice structure in d=2 or 3 dimensions with unit cell comprising Z thin elastic members emanating from a similarly situated central node. A general theoretical approach provides an algebraic formula for the effective elasticity of such frameworks. The method yields the effective cubic elastic constants for three-dimensional space-filling lattices with Z=4, 6, 8, 12 and 14, the last being the ‘stiffest’ lattice proposed by Gurtner & Durand (Gurtner & Durand 2014 Proc. R. Soc. A 470, 20130611. (doi:10.1098/rspa.2013.0611)). The analytical expressions provide explicit formulae for the effective properties of pentamode materials, both isotropic and anisotropic, obtained from the general formulation in the stretch-dominated limit for Z=d+1. PMID:25484608
Yu, Betty; Kang, Soo-Young; Akthakul, Ariya; Ramadurai, Nithin; Pilkenton, Morgan; Patel, Alpesh; Nashat, Amir; Anderson, Daniel G; Sakamoto, Fernanda H; Gilchrest, Barbara A; Anderson, R Rox; Langer, Robert
2016-08-01
We report the synthesis and application of an elastic, wearable crosslinked polymer layer (XPL) that mimics the properties of normal, youthful skin. XPL is made of a tunable polysiloxane-based material that can be engineered with specific elasticity, contractility, adhesion, tensile strength and occlusivity. XPL can be topically applied, rapidly curing at the skin interface without the need for heat- or light-mediated activation. In a pilot human study, we examined the performance of a prototype XPL that has a tensile modulus matching normal skin responses at low strain (<40%), and that withstands elongations exceeding 250%, elastically recoiling with minimal strain-energy loss on repeated deformation. The application of XPL to the herniated lower eyelid fat pads of 12 subjects resulted in an average 2-grade decrease in herniation appearance in a 5-point severity scale. The XPL platform may offer advanced solutions to compromised skin barrier function, pharmaceutical delivery and wound dressings. PMID:27159017
Peselnick, L.; Robie, R.A.
1962-01-01
The recent measurements of the elastic constants of calcite by Reddy and Subrahmanyam (1960) disagree with the values obtained independently by Voigt (1910) and Bhimasenachar (1945). The present authors, using an ultrasonic pulse technique at 3 Mc and 25??C, determined the elastic constants of calcite using the exact equations governing the wave velocities in the single crystal. The results are C11=13.7, C33=8.11, C44=3.50, C12=4.82, C13=5.68, and C14=-2.00, in units of 1011 dyncm2. Independent checks of several of the elastic constants were made employing other directions and polarizations of the wave velocities. With the exception of C13, these values substantially agree with the data of Voigt and Bhimasenachar. ?? 1962 The American Institute of Physics.
Mechanics of elastic networks.
Norris, Andrew N
2014-12-01
We consider a periodic lattice structure in d=2 or 3 dimensions with unit cell comprising Z thin elastic members emanating from a similarly situated central node. A general theoretical approach provides an algebraic formula for the effective elasticity of such frameworks. The method yields the effective cubic elastic constants for three-dimensional space-filling lattices with Z=4, 6, 8, 12 and 14, the last being the 'stiffest' lattice proposed by Gurtner & Durand (Gurtner & Durand 2014 Proc. R. Soc. A470, 20130611. (doi:10.1098/rspa.2013.0611)). The analytical expressions provide explicit formulae for the effective properties of pentamode materials, both isotropic and anisotropic, obtained from the general formulation in the stretch-dominated limit for Z=d+1.
Effect of chain length and unsaturation on elasticity of lipid bilayers.
Rawicz, W; Olbrich, K C; McIntosh, T; Needham, D; Evans, E
2000-01-01
Micropipette pressurization of giant bilayer vesicles was used to measure both elastic bending k(c) and area stretch K(A) moduli of fluid-phase phosphatidylcholine (PC) membranes. Twelve diacyl PCs were chosen: eight with two 18 carbon chains and degrees of unsaturation from one double bond (C18:1/0, C18:0/1) to six double bonds per lipid (diC18:3), two with short saturated carbon chains (diC13:0, diC14:0), and two with long unsaturated carbon chains (diC20:4, diC22:1). Bending moduli were derived from measurements of apparent expansion in vesicle surface area under very low tensions (0.001-0.5 mN/m), which is dominated by smoothing of thermal bending undulations. Area stretch moduli were obtained from measurements of vesicle surface expansion under high tensions (>0.5 mN/m), which involve an increase in area per molecule and a small-but important-contribution from smoothing of residual thermal undulations. The direct stretch moduli varied little (< +/-10%) with either chain unsaturation or length about a mean of 243 mN/m. On the other hand, the bending moduli of saturated/monounsaturated chain PCs increased progressively with chain length from 0.56 x 10(-19) J for diC13:0 to 1.2 x 10(-19) J for diC22:1. However, quite unexpectedly for longer chains, the bending moduli dropped precipitously to approximately 0.4 x 10(-19) J when two or more cis double bonds were present in a chain (C18:0/2, diC18:2, diC18:3, diC20:4). Given nearly constant area stretch moduli, the variations in bending rigidity with chain length and polyunsaturation implied significant variations in thickness. To test this hypothesis, peak-to-peak headgroup thicknesses h(pp) of bilayers were obtained from x-ray diffraction of multibilayer arrays at controlled relative humidities. For saturated/monounsaturated chain bilayers, the distances h(pp) increased smoothly from diC13:0 to diC22:1 as expected. Moreover, the distances and elastic properties correlated well with a polymer brush model of the
Fibronectin Aggregation and Assembly
Ohashi, Tomoo; Erickson, Harold P.
2011-01-01
The mechanism of fibronectin (FN) assembly and the self-association sites are still unclear and contradictory, although the N-terminal 70-kDa region (I1–9) is commonly accepted as one of the assembly sites. We previously found that I1–9 binds to superfibronectin, which is an artificial FN aggregate induced by anastellin. In the present study, we found that I1–9 bound to the aggregate formed by anastellin and a small FN fragment, III1–2. An engineered disulfide bond in III2, which stabilizes folding, inhibited aggregation, but a disulfide bond in III1 did not. A gelatin precipitation assay showed that I1–9 did not interact with anastellin, III1, III2, III1–2, or several III1–2 mutants including III1–2KADA. (In contrast to previous studies, we found that the III1–2KADA mutant was identical in conformation to wild-type III1–2.) Because I1–9 only bound to the aggregate and the unfolding of III2 played a role in aggregation, we generated a III2 domain that was destabilized by deletion of the G strand. This mutant bound I1–9 as shown by the gelatin precipitation assay and fluorescence resonance energy transfer analysis, and it inhibited FN matrix assembly when added to cell culture. Next, we introduced disulfide mutations into full-length FN. Three disulfide locks in III2, III3, and III11 were required to dramatically reduce anastellin-induced aggregation. When we tested the disulfide mutants in cell culture, only the disulfide bond in III2 reduced the FN matrix. These results suggest that the unfolding of III2 is one of the key factors for FN aggregation and assembly. PMID:21949131
Thermo-elastic behavior of deformed woven fabric composites at elevated temperatures: Part 1
Vu-Khanh, T.; Liu, B.
1994-12-31
This paper presents the results of a study on the effects of temperature on the thermo-elastic properties of woven fabric composites. The thermo-mechanical behavior of woven fabric composites is characterized by a laminate composed of four fictional unidirectional plies, called the sub-plies model. The model allows determination of the thermo-elastic properties of deformed fabric composites (non-orthogonal structure) and direct use of layered shell elements in finite element codes. A special procedure is also proposed to measure the fiber undulation effect and to predict the on-axis thermo-elastic coefficients of the equivalent constituent plies. The thermo-elastic behavior at elevated temperature was investigated on graphite/epoxy fabric composites. Experimental measurements were carried out from 23 C to 177 C. The results revealed that the equivalent thermal expansion coefficients of the sub-plies remain almost constant over a wide range of temperature. However, the equivalent elastic moduli and Poison`s ratio of the sub-plies vary nonlinearly with temperature. Semiempirical equations based on the experimental data were also developed to predict the equivalent on-axis thermo-elastic properties of the fictional constituent plies in the sub-plies model as a function of temperature.
Theoretical study of atomic structure and elastic properties of branched silicon nanowires.
Sorokin, Pavel B; Kvashnin, Alexander G; Kvashnin, Dmitry G; Filicheva, Julia A; Avramov, Pavel V; Fedorov, Alexander S; Chernozatonskii, Leonid A
2010-05-25
The atomic structure and elastic properties of Y-shaped silicon nanowires of "fork"- and "bough"-types were theoretically studied, and effective Young moduli were calculated using Tersoff interatomic potential. The oscillation of fork Y-type branched nanowires with various branch lengths and diameters was studied. In the final stages of the bending, the formation of new bonds between different parts of the wires was observed. It was found that the stiffness of the nanowires is comparable with the stiffness of Y-shaped carbon nanotubes.
A first principle study of the pressure dependent elastic properties of monazite LaPO4
NASA Astrophysics Data System (ADS)
Ali, Kawsar; Arya, A.; Ghosh, P. S.; Dey, G. K.
2016-05-01
DFT based ab-initio simulations have been performed to study the effect of pressure on the elastic properties of monazite LaPO4 which is a promising host material for immobilization of high level nuclear waste. The phase is found to be stable up to 30 GPa. The calculated polycrystalline bulk, shear and Young moduli show an increasing trend as a function of pressure. The ductility and anisotropy in shear modulus of the material have been found to increase with pressure; whilethe bulk modulus anisotropy decreases with pressure.
Measurement of elastic modulus and ultrasonic wave velocity by piezoelectric resonator
NASA Astrophysics Data System (ADS)
Erhart, Jiří
2015-01-01
A piezoelectric ceramic resonator is used for the ‘electrical’ measurement of elastic properties, i.e. Young’s modulus and ultrasonic wave velocity in metallic materials. Piezoelectric response is precisely calculated for the piezoelectric ceramic ring fixed at the end of a metallic rod. The piezoelectric ring serves as both an actuator as well as a sensor. The experimental setup and method of measurement using higher overtones is explained in detail and practically demonstrated for a set of different metallic materials. Young’s moduli and ultrasonic wave velocities are measured within 3% relative error. The presented method is suitable for an advanced engineering class or physics laboratory training.
Measuring the elastic properties of living cells with atomic force microscopy indentation.
Mackay, Joanna L; Kumar, Sanjay
2013-01-01
Atomic force microscopy (AFM) is a powerful and versatile tool for probing the mechanical properties of biological samples. This chapter describes the procedures for using AFM indentation to measure the elastic moduli of living cells. We include step-by-step instructions for cantilever calibration and data acquisition using a combined AFM/optical microscope system, as well as a detailed protocol for data analysis. Our protocol is written specifically for the BioScope™ Catalyst™ AFM system (Bruker AXS Inc.); however, most of the general concepts can be readily translated to other commercial systems.
Transverse vibrations of a circular plate carrying an elastically mounted mass
NASA Astrophysics Data System (ADS)
Avalos, D. R.; Larrondo, H. A.; Laura, P. A. A.
1994-10-01
An exact solution of the title problem is rather difficult to obtain. On the other hand, it is not advantageous from a practical viewpoint if one wishes to take into account several parameters that come into play: flexibility of rotational and translational properties at the plate edge; elastic moduli of the plate material; concentrated mass/total plate mass, etc. In view of these considerations an approximate, yet quite accurate solution is obtained by using the optimized Rayleigh-Ritz method and polynomial co-ordinate functions which satisfy identically the governing boundary conditions. Only axisymmetric modes are considered in the present investigation.
Elastic modulus measurements of LDEF glasses and glass-ceramics using a speckle technique
NASA Technical Reports Server (NTRS)
Wiedlocher, D. E.; Kinser, D. L.
1992-01-01
Elastic moduli of five glass types and the glass-ceramic Zerodur, exposed to a near-earth orbit environment on the Long Duration Exposure Facility (LDEF), were compared to that of unexposed samples. A double exposure speckle photography technique utilizing 633 nm laser light was used in the production of the speckle pattern. Subsequent illumination of a double exposed negative using the same wavelength radiation produces Young's fringes from which the in-plane displacements are measured. Stresses imposed by compressive loading produced measurable strains in the glasses and glass-ceramic.
Henager, Charles H.; Nguyen, Ba Nghiep; Kurtz, Richard J.; Roosendaal, Timothy J.; Borlaug, Brennan A.; Ferraris, Monica; Ventrella, Andrea; Katoh, Yutai
2015-03-01
The use of SiC and SiC-composites in fission or fusion environments requires joining methods for assembling systems. The international fusion community designed miniature torsion specimens for joint testing and irradiation in test reactors with limited irradiation volumes. These torsion specimens fail out-of-plane when joints are strong and when elastic moduli are within a certain range compared to SiC, which causes difficulties in determining shear strengths for joints or for comparing unirradiated and irradiated joints. A finite element damage model was developed that indicates fracture is likely to occur within the joined pieces to cause out-of-plane failures for miniature torsion specimens when a certain modulus and strength ratio between the joint material and the joined material exists. The model was extended to treat elastic-plastic joints such as SiC/epoxy and steel/epoxy joints tested as validation of the specimen design.
NASA Astrophysics Data System (ADS)
van Otterloo, Jozua; Cruden, Alexander R.
2016-06-01
Gelatine is a viscoelastic polymer that has been employed widely in geological analogue experiments to study processes related to the elastic behaviour of rocks such as tensile fracturing, seismicity and magma intrusion. However, the elastic domain of this material has not yet been clearly defined by rheological tests. Here we describe the rheology and define the elastic domain of 250 bloom/20 mesh pigskin gelatine at concentrations ≤ 10 wt.% and temperatures of 5-25 °C; however, these results are strongly comparable with gelatine of 245-260 bloom. New equations are given for the shear and elastic moduli in relationship to temperature and gelatine concentration. It is found that at concentrations ≤ 3 wt.% the tested gelatine is best described by a rheological model composed of a combination of Kelvin-Voight and Maxwell elements and, therefore, is not suitable to model elastic behaviour in geological analogue experiments. At higher concentrations it is best described by a simpler viscoelastic model comprising a single Maxwell element. In order to ensure that geological analogue experiments remain within the elastic domain where the elastic component is far greater than the viscous component, strain rates should range between 0.1 and 10 s- 1 and temperature values should be < 15 °C. With a Poisson's ratio of ~ 0.45 for concentrations > 3 wt.% analogue experiments using gelatine approximate the elastic behaviour of natural rocks more closely than previously assumed.
Acquired disorders of elastic tissue: Part II. decreased elastic tissue.
Lewis, Kevan G; Bercovitch, Lionel; Dill, Sara W; Robinson-Bostom, Leslie
2004-08-01
Elastic fibers in the extracellular matrix are integral components of dermal connective tissue. The resilience and elasticity required for normal structure and function of the skin are attributable to the network of elastic tissue. Advances in our understanding of elastic tissue physiology provide a foundation for studying the pathogenesis of elastic tissue disorders. Many acquired disorders are nevertheless poorly understood owing to the paucity of reported cases. Several acquired disorders in which loss of dermal elastic tissue produces prominent clinical and histopathologic features have recently been described, including middermal elastolysis, papular elastorrhexis, and pseudoxanthoma-like papillary dermal elastolysis, which must be differentiated from more well-known disorders such as anetoderma, acquired cutis laxa, and acrokeratoelastoidosis. Learning objective At the conclusion of this learning activity, participants should have an understanding of the similarities and differences between acquired disorders of elastic tissue that are characterized by a loss of elastic tissue.
ERIC Educational Resources Information Center
Gordon, Warren B.
2006-01-01
This paper examines the elasticity of demand, and shows that geometrically, it may be interpreted as the ratio of two simple distances along the tangent line: the distance from the point on the curve to the x-intercept to the distance from the point on the curve to the y-intercept. It also shows that total revenue is maximized at the transition…
Elastic and Inelastic Collisions
ERIC Educational Resources Information Center
Gluck, Paul
2010-01-01
There have been two articles in this journal that described a pair of collision carts used to demonstrate vividly the difference between elastic and inelastic collisions. One cart had a series of washers that were mounted rigidly on a rigid wooden framework, the other had washers mounted on rubber bands stretched across a framework. The rigidly…
ERIC Educational Resources Information Center
Cocco, Alberto; Masin, Sergio Cesare
2010-01-01
Participants estimated the imagined elongation of a spring while they were imagining that a load was stretching the spring. This elongation turned out to be a multiplicative function of spring length and load weight--a cognitive law analogous to Hooke's law of elasticity. Participants also estimated the total imagined elongation of springs joined…
Hydrodynamic Elastic Magneto Plastic
1985-02-01
The HEMP code solves the conservation equations of two-dimensional elastic-plastic flow, in plane x-y coordinates or in cylindrical symmetry around the x-axis. Provisions for calculation of fixed boundaries, free surfaces, pistons, and boundary slide planes have been included, along with other special conditions.
Moduli stabilization, F-term uplifting, and soft supersymmetry breaking terms
Abe, Hiroyuki; Higaki, Tetsutaro; Kobayashi, Tatsuo; Omura, Yuji
2007-01-15
We study moduli stabilization with F-term uplifting. As a source of uplifting F-term, we consider spontaneous supersymmetry breaking models, e.g. the Polonyi model and the Intriligator-Seiberg-Shih model. We analyze potential minima by requiring almost vanishing vacuum energy and evaluate the size of modulus F-term. We also study soft SUSY-breaking terms. In our scenario, the mirage mediation is dominant in gaugino masses. Scalar masses can be comparable with gaugino masses or much heavier, depending on couplings with spontaneous supersymmetry breaking sector.
NASA Astrophysics Data System (ADS)
Lee, Scott; Richards, Zachary
2015-03-01
The section modulus of a bone is a measure of its ability to resist bending torques. Carnivorous dinosaurs presumably had strong arm bones to hold struggling prey during hunting. Some theropods are believed to have become herbivorous and such animals would not have needed such strong arms. In this work, the section moduli of the humerus bones of bipedal theropod dinosaurs (from Microvenator celer to Tyrannosaurus rex) are studied to determine the maximum bending loads their arms could withstand. The results show that bending strength is not of uniform importance to these magnificent animals. The predatory theropods had strong arms for use in hunting. In contrast, the herbivorous dinosaurs had weaker arms.
Moduli stabilization in type II Calabi-Yau compactifications at finite temperature
NASA Astrophysics Data System (ADS)
Liu, Lihui; Partouche, Hervé
2012-11-01
We consider the type II superstring compactified on Calabi-Yau threefolds, at finite temperature. The latter is implemented at the string level by a free action on the Euclidean time circle. We show that all Kähler and complex structure moduli involved in the gauge theories geometrically engineered in the vicinity of singular loci are lifted by the stringy thermal effective potential. The analysis is based on the effective gauged super-gravity at low energy, without integrating out the non-perturbative BPS states becoming massless at the singular loci. The universal form of the action in the weak coupling regime and at low enough temperature is determined in two cases. Namely, the conifold locus, as well as a locus where the internal space develops a genus- g curve of A N -1 singularities, thus realizing an SU( N ) gauge theory coupled to g hypermultiplets in the adjoint. In general, we argue that the favored points of stabilization sit at the intersection of several such loci. As a result, the entire vector multiplet moduli space is expected to be lifted, together with hypermultiplet moduli. The scalars are dynamically stabilized during the cosmological evolution induced by the back-reaction of the thermal effective potential on the originally static background. When the universe expands and the temperature T drops, the scalars converge to minima, with damped oscillations. Moreover, they store an energy density that scales as T 4, which never dominates over radiation. The reason for this is that the mass they acquire at one-loop is of order the temperature scale, which is time-dependent rather than constant. As an example, we analyze the type IIA compactification on a hy-persurface {P}_{{( {1,1,2,2,6} )}}^4 [12], with Hodge numbers h 11 = 2 and h 12 = 128. In this case, both Kähler moduli are stabilized at a point, where the internal space develops a node and an enhanced SU(2) gauge theory coupled to 2 adjoint hypermultiplets. This shows that in the dual thermal
Measuring the complex moduli of materials by using the double pendulum system
NASA Astrophysics Data System (ADS)
Casimir, J. B.; Vinh, T.
2012-03-01
A interesting double pendulum system permits evaluating complex moduli (Young and shear) without independent excitation and transducers. This instrument was described at France in 1934 by Le Rolland and Sorin in Etude d' une méthode utilisant le couplage entre deux systèmes oscillants pour la détermination de la résistance mécanique des constructions et la mesure des modules d' élasticité, scientific and technical publications of the Air Force Ministry, no. 47, 1934. This device is revisited and improved in order to make it applicable to measurements of viscoelastic materials.
Wilson, C.; Swan, C.
2007-07-01
New technology carried out at Tufts University and the University of Massachusetts on synthetic lightweight aggregate has created material from various qualities of fly ash from coal-fired power plants for use in different engineered applications. In pilot scale manufacturing tests an 'SLA' containing 80% fly ash and 20% mixed plastic waste from packaging was produced by 'dry blending' mixed plastic with high carbon fly ash. A trial run was completed to produce concrete masonry unit (CMU) blocks at a full-scale facility. It has been shown that SLA can be used as a partial substitution of a traditional stone aggregate in hot asphalt mix. 1 fig., 2 photos.
Frequency dependent elastic impedance inversion for interstratified dispersive elastic parameters
NASA Astrophysics Data System (ADS)
Zong, Zhaoyun; Yin, Xingyao; Wu, Guochen
2016-08-01
The elastic impedance equation is extended to frequency dependent elastic impedance equation by taking partial derivative to frequency. With this equation as the forward solver, a practical frequency dependent elastic impedance inversion approach is presented to implement the estimation of the interstratified dispersive elastic parameters which makes full use of the frequency information of elastic impedances. Three main steps are included in this approach. Firstly, the elastic Bayesian inversion is implemented for the estimation of elastic impedances from different incident angle. Secondly, with those estimated elastic impedances, their variations are used to estimate P-wave velocity and S-wave velocity. Finally, with the prior elastic impedance and P-wave and S-wave velocity information, the frequency dependent elastic variation with incident angle inversion is presented for the estimation of the interstratified elastic parameters. With this approach, the interstratified elastic parameters rather than the interface information can be estimated, making easier the interpretation of frequency dependent seismic attributes. The model examples illustrate the feasibility and stability of the proposed method in P-wave velocity dispersion and S-wave velocity dispersion estimation. The field data example validates the possibility and efficiency in hydrocarbon indication of the estimated P-wave velocity dispersion and S-wave velocity dispersion.
Wang Weihua
2011-09-01
We study the similarity and correlations between relaxations and plastic deformation in metallic glasses (MGs) and MG-forming liquids. It is shown that the microscope plastic events, the initiation and formation of shear bands, and the mechanical yield in MGs where the atomic sites are topologically unstable induced by applied stress, can be treated as the glass to supercooled liquid state transition induced by external shear stress. On the other hand, the glass transition, the primary and secondary relaxations, plastic deformation and yield can be attributed to the free volume increase induced flow, and the flow can be modeled as the activated hopping between the inherent states in the potential energy landscape. We then propose an extended elastic model to describe the flow based on the energy landscape theory. That is, the flow activation energy density is linear proportional to the instantaneous elastic moduli, and the activation energy density {rho}{sub E} is determined to be a simple expression of {rho}{sub E}=(10/11)G+(1/11)K. The model indicates that both shear and bulk moduli are critical parameters accounting for both the homogeneous and inhomogeneous flows in MGs and MG-forming liquids. The elastic model is experimentally certified. We show that the elastic perspectives offers a simple scenario for the flow in MGs and MG-forming liquids and are suggestive for understanding the glass transition, plastic deformation, and nature and characteristics of MGs.
Donaldson, F E; Pankaj, P; Cooper, D M L; Thomas, C D L; Clement, J G; Simpson, A H R W
2011-06-01
Homogenized elastic properties are often assumed for macro-finite element (FE) models used in orthopaedic biomechanics. The accuracy of material property assignments may have a strong effect on the ability of these models to make accurate predictions. For cortical bone, most macro-scale FE models assume isotropic elastic material behaviour and do not include variation of material properties due to bone micro-architecture. The first aim of the present study was to evaluate the variation of apparent-level (homogenized) orthotropic elastic constants of cortical bone with age and indices of bone micro-architecture. Considerable age-dependent differences in porosity were noted across the cortical thickness in previous research. The second aim of the study was to quantify the resulting differences in elastic constants between the periosteum and endosteum. Specimens were taken from the anterior femoral midshaft of 27 female donors (age 53.4 +/- 23.6 years) and micro-FE (gFE) analysis was used to derive orthotropic elastic constants. The variation of orthotropic elastic constants (Young's moduli, shear moduli, and Poisson's ratios) with various cortical bone micro-architectural indices was investigated. The ratio of canal volume to tissue volume, Ca.V/TV, analogous to porosity, was found to be the strongest predictor (r2(ave) = 0.958) of the elastic constants. Age was less predictive (r2(ave) = 0.385) than Ca.V/TV. Elastic anisotropy increased with increasing Ca.V/TV, leading to lower elastic moduli in the transverse, typically less frequently loaded, directions. Increased Ca.V/TV led to a more substantial reduction in elastic constants at the endosteal aspect than at the periosteal aspect. The results are expected to be most applicable in similar midshaft locations of long bones; specific analysis of other sites would be necessary to evaluate elastic properties elsewhere. It was concluded that Ca.V/TV was the most predictive of cortical bone elastic constants and that
Mukharjee, Bibhuti Bhusan; Barai, Sudhirkumar V
2015-06-01
The present work addresses the development of novel construction materials utilising commercial grade nano-silica and recycled aggregates retrieved from construction and demolition waste. For this, experimental work has been carried out to examine the influence of nano-silica and recycled aggregates on compressive strength, modulus of elasticity, water absorption, density and volume of voids of concrete. Fully natural and recycled aggregate concrete mixes are designed by replacing cement with three levels (0.75%, 1.5% and 3%) of nano-silica. The results of the present investigation depict that improvement in early days compressive strength is achieved with the incorporation of nano-silica in addition to the restoration of reduction in compressive strength of recycled aggregate concrete mixes caused owing to the replacement of natural aggregates by recycled aggregates. Moreover, the increase in water absorption and volume of voids with a reduction of bulk density was detected with the incorporation of recycled aggregates in place of natural aggregates. However, enhancement in density and reduction in water absorption and volume of voids of recycled aggregate concrete resulted from the addition of nano-silica. In addition, the results of the study reveal that nano-silica has no significant effect on elastic modulus of concrete. PMID:25986048
Mukharjee, Bibhuti Bhusan; Barai, Sudhirkumar V
2015-06-01
The present work addresses the development of novel construction materials utilising commercial grade nano-silica and recycled aggregates retrieved from construction and demolition waste. For this, experimental work has been carried out to examine the influence of nano-silica and recycled aggregates on compressive strength, modulus of elasticity, water absorption, density and volume of voids of concrete. Fully natural and recycled aggregate concrete mixes are designed by replacing cement with three levels (0.75%, 1.5% and 3%) of nano-silica. The results of the present investigation depict that improvement in early days compressive strength is achieved with the incorporation of nano-silica in addition to the restoration of reduction in compressive strength of recycled aggregate concrete mixes caused owing to the replacement of natural aggregates by recycled aggregates. Moreover, the increase in water absorption and volume of voids with a reduction of bulk density was detected with the incorporation of recycled aggregates in place of natural aggregates. However, enhancement in density and reduction in water absorption and volume of voids of recycled aggregate concrete resulted from the addition of nano-silica. In addition, the results of the study reveal that nano-silica has no significant effect on elastic modulus of concrete.
Spreading and spontaneous motility of multicellular aggregates on soft substrates
NASA Astrophysics Data System (ADS)
Brochard-Wyart, Françoise
2013-03-01
We first describe the biomechanics of multicellular aggregates, a model system for tissues and tumors. We first characterize the tissue mechanical properties (surface tension, elasticity, viscosity) by a new pipette aspiration technique. The aggregate exhibits a viscoelastic response but, unlike an inert fluid, we observe aggregate reinforcement with pressure, which for a narrow range of pressures results in pulsed contractions or shivering. We interpret this reinforcement as a mechanosensitive active response of the acto-myosin cortex. Such an active behavior has previously been found to cause tissue pulsation during dorsal closure of Drosophila embryo. We then describe the spreading of aggregates on rigid glass substrates, varying both intercellular and substrate adhesion. We find both partial and complete wetting regimes. For the dynamics, we find a universal spreading law at short time, analogous to that of a viscoelastic drop. At long time, we observe, for strong substrate adhesion, a precursor film spreading around the aggregate. Depending on aggregate cohesion, this precursor film can be a dense cellular monolayer (liquid state) or consist of individual cells escaping from the aggregate body (gas state). The transition from liquid to gas state appears also to be present in the progression of a tumor from noninvasive to metastatic, known as the epithelial-mesenchymal transition. Finally, we describe the effect of the substrate rigidity on the phase diagram of wetting. On soft gels decorated with fibronectin and strongly cohesive aggregates, we have observed a wetting transition induced by the substrate rigidity: on ultra soft gels, below an elastic modulus Ec the aggregates do not spread, whereas above Ec we observe a precursor film expending with a diffusive law. The diffusion coefficient D(E) present a maximum for E =Em. A maximum of mobility versus the substrate rigidity had also been observed for single cells. Near Em, we observe a new phenomenon: a cell
Aggregates, broccoli and cauliflower
NASA Astrophysics Data System (ADS)
Grey, Francois; Kjems, Jørgen K.
1989-09-01
Naturally grown structures with fractal characters like broccoli and cauliflower are discussed and compared with DLA-type aggregates. It is suggested that the branching density can be used to characterize the growth process and an experimental method to determine this parameter is proposed.
Molecular dynamics simulations of the straining of nanoparticle chain aggregates: the case of copper
NASA Astrophysics Data System (ADS)
Dalis, Adamos; Friedlander, Sheldon K.
2005-07-01
Previous studies in our laboratory have shown that individual nanoparticle chain aggregates (NCAs) exhibit unusual mechanical behaviour when under strain inside the transmission electron microscope. NCAs made of various materials (e.g. carbon, metal oxides and metals) were strained by as much as 100% under tension. The nanoparticles that compose the chains were 5-10 nm in diameter and the chains of the order of 1 µm in length. Such aggregates are of technological importance in the manufacture of nanocomposite materials (e.g. rubber), aggregate break-up (e.g. sampling diesel emissions) and chemical-mechanical planarization. The goal of this study was to simulate the mechanical behaviour of chain aggregates with morphological properties similar to those of technological interest. Molecular dynamics (MD) and energy minimization computer simulations are employed to investigate, at the atomic scale, the behaviour of short nanoparticle aggregates under strain and to obtain quantitative information on the forces involved in aggregate straining and fracturing. The interaction potential used is that of copper obtained with the embedded atom method (EAM). Two seven-nanoparticle aggregates are studied, one linear and the other kinked. The seven nanoparticles in both aggregates are single crystals and about 2.5 nm in diameter each. The aggregates are strained along their longest dimension, to the breaking point, at strain rates spanning from 2.5 × 107 to 8.0 × 108 s-1 (MD simulations). The linear aggregate yield strain is about 0.1. The kinked aggregate elastic limit is also about 0.1, but only one-third of the stress develops along the straining direction compared to the linear aggregate. The kinked aggregate breaks at a strain of about 0.5, five times higher than the breaking strain of the linear aggregate. The ability of the kinked aggregate to straighten through combined nanoparticle interface sliding and rotation accounts for the extra strain accommodation. Simulation
Dalis, Adamos; Friedlander, Sheldon K
2005-07-01
Previous studies in our laboratory have shown that individual nanoparticle chain aggregates (NCAs) exhibit unusual mechanical behaviour when under strain inside the transmission electron microscope. NCAs made of various materials (e.g. carbon, metal oxides and metals) were strained by as much as 100% under tension. The nanoparticles that compose the chains were 5-10 nm in diameter and the chains of the order of 1 µm in length. Such aggregates are of technological importance in the manufacture of nanocomposite materials (e.g. rubber), aggregate break-up (e.g. sampling diesel emissions) and chemical-mechanical planarization. The goal of this study was to simulate the mechanical behaviour of chain aggregates with morphological properties similar to those of technological interest. Molecular dynamics (MD) and energy minimization computer simulations are employed to investigate, at the atomic scale, the behaviour of short nanoparticle aggregates under strain and to obtain quantitative information on the forces involved in aggregate straining and fracturing. The interaction potential used is that of copper obtained with the embedded atom method (EAM). Two seven-nanoparticle aggregates are studied, one linear and the other kinked. The seven nanoparticles in both aggregates are single crystals and about 2.5 nm in diameter each. The aggregates are strained along their longest dimension, to the breaking point, at strain rates spanning from 2.5 × 10(7) to 8.0 × 10(8) s(-1) (MD simulations). The linear aggregate yield strain is about 0.1. The kinked aggregate elastic limit is also about 0.1, but only one-third of the stress develops along the straining direction compared to the linear aggregate. The kinked aggregate breaks at a strain of about 0.5, five times higher than the breaking strain of the linear aggregate. The ability of the kinked aggregate to straighten through combined nanoparticle interface sliding and rotation accounts for the extra strain accommodation
Moduli of curve families and (quasi-)conformality of power-law entropies
NASA Astrophysics Data System (ADS)
Kalogeropoulos, Nikos
2016-03-01
We present aspects of the moduli of curve families on a metric measure space which may prove useful in calculating, or in providing bounds to, non-additive entropies having a power-law functional form. We use as paradigmatic cases the calculations of the moduli of curve families for a cylinder and for an annulus in ℝn. The underlying motivation for these studies is that the definitions and some properties of the modulus of a curve family resembles those of the Tsallis entropy, when the latter is seen from a micro-canonical viewpoint. We comment on the origin of the conjectured invariance of the Tsallis entropy under Möbius transformations of the non-extensive (entropic) parameter. Needing techniques applicable to both locally Euclidean and fractal classes of spaces, we examine the behavior of the Tsallis functional, via the modulus, under quasi-conformal maps. We comment on properties of such maps and their possible significance for the dynamical foundations of power-law entropies.
Ultrasonic determination of Young's moduli of the coat and core materials of a drug tablet.
Akseli, Ilgaz; Becker, Douglas C; Cetinkaya, Cetin
2009-03-31
Many modern tablet presses have system controls that monitor the force exerted to compress the solid oral dosage forms; however this data provides only limited information about the mechanical state of the tablet due to various process and materials uncertainties. A contact pulse/echo ultrasonic scheme is presented for the determination of the local Young's moduli of the coat and the core materials of enteric-coated and monolayer coated tablets. The Young's modulus of a material compacted into solid dosage can be related to its mechanical hardness and, consequently, its dissolution rate. In the current approach, short ultrasonic pulses are generated by the active element of a delay line transducer and are launched into the tablet. The waveforms reflected from the tablet coat-core interface are captured by the same transducer and are processed for determining the reflection and transmission coefficients of the interface from partially overlapping echoes. The Young's moduli of the coat and the core materials are then extracted from these coefficients. The results are compared to those obtained by an air-coupled acoustic excitation study, and good agreement is found. The described measurement technique provides greater insight into the local physical properties of the solid oral dosage form and, as a result, has the potential to provide better hardness-related performance predictability of compacts. PMID:19059326
Consistent decoupling of heavy scalars and moduli in N=1 supergravity
NASA Astrophysics Data System (ADS)
Achúcarro, Ana; Hardeman, Sjoerd; Sousa, Kepa
2008-11-01
We consider the conditions for integrating out heavy chiral fields and moduli in N=1 supergravity, subject to two explicit requirements. First, the expectation values of the heavy fields should be unaffected by low energy phenomena. Second, the low energy effective action should be described by N=1 supergravity. This leads to a working definition of decoupling in N=1 supergravity that is different from the usual condition of gravitational strength couplings between sectors, and that is the relevant one for inflation with moduli stabilization, where some light fields (the inflaton) can have long excursions in field space. It is also important for finding de Sitter vacua in flux compactifications such as LARGE volume and Kachru-Kallosh-Linde-Trivedi (KKLT) scenarios, since failure of the decoupling condition invalidates the implicit assumption that the stabilization and uplifting potentials have a low energy supergravity description. We derive a sufficient condition for supersymmetric decoupling, namely, that the Kähler invariant function G=K+log|W|2 is of the form G=L(light,H(heavy)) with H and L arbitrary functions, which includes the particular case G=L(light)+H(heavy). The consistency condition does not hold in general for the ansatz K=K(light)+K(heavy), W=W(light)+W(heavy) and we discuss under what circumstances it does hold.
Physics of cell elasticity, shape and adhesion
NASA Astrophysics Data System (ADS)
Safran, S. A.; Gov, N.; Nicolas, A.; Schwarz, U. S.; Tlusty, T.
2005-07-01
We review recent theoretical work that analyzes experimental measurements of the shape, fluctuations and adhesion properties of biological cells. Particular emphasis is placed on the role of the cytoskeleton and cell elasticity and we contrast the shape and adhesion of elastic cells with fluid-filled vesicles. In red blood cells (RBC), the cytoskeleton consists of a two-dimensional network of spectrin proteins. Our analysis of the wavevector and frequency dependence of the fluctuation spectrum of RBC indicates that the spectrin network acts as a confining potential that reduces the fluctuations of the lipid bilayer membrane. However, since the cytoskeleton is only sparsely connected to the bilayer, one cannot regard the composite cytoskeleton-membrane as a polymerized object with a shear modulus. The sensitivity of RBC fluctuations and shapes to ATP concentration may reflect topological defects induced in the cytoskeleton network by ATP. The shapes of cells that adhere to a substrate are strongly determined by the cytoskeletal elasticity that can be varied experimentally by drugs that depolymerize the cytoskeleton. This leads to a tension-driven retraction of the cell body and a pearling instability of the resulting ray-like protrusions. Recent experiments have shown that adhering cells exert polarized forces on substrates. The interactions of such “force dipoles” in either bulk gels or on surfaces can be used to predict the nature of self-assembly of cell aggregates and may be important in the formation of artificial tissues. Finally, we note that cell adhesion strongly depends on the forces exerted on the adhesion sites by the tension of the cytoskeleton. The size and shape of the adhesion regions are strongly modified as the tension is varied and we present an elastic model that relates this tension to deformations that induce the recruitment of new molecules to the adhesion region. In all these examples, cell shape and adhesion differ from vesicle shape and
Thermal expansion and elastic anisotropy in single crystal Al2O3 and SiC reinforcements
NASA Technical Reports Server (NTRS)
Salem, Jonathan A.; Li, Zhuang; Bradt, Richard C.
1994-01-01
In single crystal form, SiC and Al2O3 are attractive reinforcing components for high temperature composites. In this study, the axial coefficients of thermal expansion and single crystal elastic constants of SiC and Al2O3 were used to determine their coefficients of thermal expansion and Young's moduli as a function of crystallographic orientation and temperature. SiC and Al2O3 exhibit a strong variation of Young's modulus with orientation; however, their moduli and anisotropies are weak functions of temperature below 1000 C. The coefficients of thermal expansion exhibit significant temperature dependence, and that of the non-cubic Al2O3 is also a function of crystallographic orientation.
Yong, Ee Hou; Nelson, David R; Mahadevan, L
2013-10-25
On microscopic scales, the crystallinity of flexible tethered or cross-linked membranes determines their mechanical response. We show that by controlling the type, number, and distribution of defects on a spherical elastic shell, it is possible to direct the morphology of these structures. Our numerical simulations show that by deflating a crystalline shell with defects, we can create elastic shell analogs of the classical platonic solids. These morphologies arise via a sharp buckling transition from the sphere which is strongly hysteretic in loading or unloading. We construct a minimal Landau theory for the transition using quadratic and cubic invariants of the spherical harmonic modes. Our approach suggests methods to engineer shape into soft spherical shells using a frozen defect topology.
Hudetz, A G; Monos, E
1981-01-01
Three-dimensional quasi-static mechanical measurements were carried out on cylindrical segments of the dog carotid and iliac arteries for determination of the passive anisotropic elastic properties of the vessel wall. On the basis of passive characteristics of outer diameter vs. intraluminal pressure, and axial extending force vs. intraluminal pressure, picked up at various fixed initial vascular length values, the incremental Young moduli and poisson ratios of the vessel wall were calculated in the 0--33 kPa (0--250 mm Hg) pressure range. The strain energy function of the arteries was approximated by polynomial and exponential models. We found that an exponential energy function with 4-parameters gives more accurate results than the 7- or 12-parameter polynomial functions. According to the results the axial modulus reaches higher values than the tangential and radial moduli at a low tangential stretch level, while at high tangential stretch the tangential modulus is the highest in both carotid and iliac arteries. After elevation of the initial tangential stretch the increase in the tangential modulus is the most pronounced, while the values of radial and axial moduli increased less. A change in the initial axial stretch influences the axial and radial moduli to a similar extent, but has no substantial effect on the value of the tangential modulus. The values of corresponding poisson ratios depend in a similar way on the initial deformation state. The different behaviour of the two Poisson ratios characterizing the mechanical coupling between tangential and axial directions, indicates that the structural coupling between the two main directions is asymmetrical. It is assumed that this property of the passive vascular structure can be explained by the network arrangement of collagen fibres in the vessel wall.
Asare-Asher, Samuel; Connor, Jason N; Sedev, Rossen
2015-07-01
Liquid marbles are liquid droplets covered densely with small particles. They exhibit hydrophobic properties even on hydrophilic surfaces and this behaviour is closely related to the Cassie wetting state and the phenomenon of superhydrophobicity. Typical liquid marbles are of millimetre size but their properties are analogous to smaller capsules and droplets of Pickering emulsions. We study water marbles covered with an uneven multilayer of polyethylene particles. Their elastic properties were assessed under quasi-static conditions. The liquid marbles are highly elastic and can sustain a reversible deformation of up to 30%. The spring constant is of the same order of magnitude as that for bare water droplets. Therefore the elasticity of the liquid marble is provided mainly by the liquid menisci between the particles. Upon further compression, the spring constant increases up to the point of breakage. This increase may be due to capillary attraction acting across the emerging cracks in the particle coating. The stress-strain curve for liquid marbles is similar to that obtained with liquid-filled microcapsules. A mechanical scaling description proposed for capsules is qualitatively applicable for liquid marbles. The exact mechanical role of the multilayer particle network remains elusive.
NASA Astrophysics Data System (ADS)
Dremin, I. M.
2013-01-01
Colliding high-energy hadrons either produce new particles or scatter elastically with their quantum numbers conserved and no other particles produced. We consider the latter case here. Although inelastic processes dominate at high energies, elastic scattering contributes considerably (18-25%) to the total cross section. Its share first decreases and then increases at higher energies. Small-angle scattering prevails at all energies. Some characteristic features can be seen that provide information on the geometrical structure of the colliding particles and the relevant dynamical mechanisms. The steep Gaussian peak at small angles is followed by the exponential (Orear) regime with some shoulders and dips, and then by a power-law decrease. Results from various theoretical approaches are compared with experimental data. Phenomenological models claiming to describe this process are reviewed. The unitarity condition predicts an exponential fall for the differential cross section with an additional substructure to occur exactly between the low momentum transfer diffraction cone and a power-law, hard parton scattering regime under high momentum transfer. Data on the interference of the Coulomb and nuclear parts of amplitudes at extremely small angles provide the value of the real part of the forward scattering amplitude. The real part of the elastic scattering amplitude and the contribution of inelastic processes to the imaginary part of this amplitude (the so-called overlap function) are also discussed. Problems related to the scaling behavior of the differential cross section are considered. The power-law regime at highest momentum transfer is briefly described.
NASA Astrophysics Data System (ADS)
Shukla, Pramod
2011-01-01
In the context of Type IIB compactified on a large volume Swiss-Cheese orientifold in the presence of a mobile space-time filling D3-brane and stacks of fluxed D7-branes wrapping the "big" divisor Σ B of a Swiss-Cheese Calabi Yau in WCP 4[1, 1, 1, 6, 9], we explore various implications of moduli dynamics and discuss their couplings and decay into MSSM (-like) matter fields early in the history of universe to reach thermal equilibrium. Like finite temperature effects in O'KKLT, we observe that the local minimum of zero-temperature effective scalar potential is stable against any finite temperature corrections (up to two-loops) in large volume scenarios as well. Also we find that moduli are heavy enough to avoid any cosmological moduli problem.
Karp-Boss, Lee; Gueta, Rachel; Rousso, Itay
2014-01-01
Unique features of diatoms are their intricate cell covers (frustules) made out of hydrated, amorphous silica. The frustule defines and maintains cell shape and protects cells against grazers and pathogens, yet it must allow for cell expansion during growth and division. Other siliceous structures have also evolved in some chain-forming species as means for holding neighboring cells together. Characterization and quantification of mechanical properties of these structures are crucial for the understanding of the relationship between form and function in diatoms, but thus far only a handful of studies have addressed this issue. We conducted micro-indentation experiments, using atomic force microscopy (AFM), to examine local variations in elastic (Young's) moduli of cells and linking structures in the marine, chain-forming diatom Lithodesmium undulatum. Using a fluorescent tracer that is incorporated into new cell wall components we tested the hypothesis that new siliceous structures differ in elastic modulus from their older counterparts. Results show that the local elastic modulus is a highly dynamic property. Elastic modulus of stained regions was significantly lower than that of unstained regions, suggesting that newly formed cell wall components are generally softer than the ones inherited from the parent cells. This study provides the first evidence of differentiation in local elastic properties in the course of the cell cycle. Hardening of newly formed regions may involve incorporation of additional, possibly organic, material but further studies are needed to elucidate the processes that regulate mechanical properties of the frustule during the cell cycle. PMID:25337801
Dong, Juncai; Zhu, Hailiang; Chen, Dongliang
2015-01-01
As a fundamental property of pressure-induced amorphization (PIA) in ice and ice-like materials (notably α-quartz), the occurrence of mechanical instability can be related to violation of Born criteria for elasticity. The most outstanding elastic feature of α-quartz before PIA has been experimentally reported to be the linear softening of shear modulus C44, which was proposed to trigger the transition through Born criteria B3. However, by using density-functional theory, we surprisingly found that both C44 and C66 in α-quartz exhibit strong nonlinearity under compression and the Born criteria B3 vanishes dominated by stiffening of C14, instead of by decreasing of C44. Further studies of archetypal quartz homeotypes (GeO2 and AlPO4) repeatedly reproduced the same elastic-hardening-driven mechanical instability, suggesting a universal feature of this family of crystals and challenging the long-standing idea that negative pressure derivatives of individual elastic moduli can be interpreted as the precursor effect to an intrinsic structural instability preceding PIA. The implications of this elastic anomaly in relation to the dispersive softening of the lowest acoustic branch and the possible transformation mechanism were also discussed. PMID:26099720
Dong, Juncai; Zhu, Hailiang; Chen, Dongliang
2015-01-01
As a fundamental property of pressure-induced amorphization (PIA) in ice and ice-like materials (notably α-quartz), the occurrence of mechanical instability can be related to violation of Born criteria for elasticity. The most outstanding elastic feature of α-quartz before PIA has been experimentally reported to be the linear softening of shear modulus C44, which was proposed to trigger the transition through Born criteria B3. However, by using density-functional theory, we surprisingly found that both C44 and C66 in α-quartz exhibit strong nonlinearity under compression and the Born criteria B3 vanishes dominated by stiffening of C14, instead of by decreasing of C44. Further studies of archetypal quartz homeotypes (GeO2 and AlPO4) repeatedly reproduced the same elastic-hardening-driven mechanical instability, suggesting a universal feature of this family of crystals and challenging the long-standing idea that negative pressure derivatives of individual elastic moduli can be interpreted as the precursor effect to an intrinsic structural instability preceding PIA. The implications of this elastic anomaly in relation to the dispersive softening of the lowest acoustic branch and the possible transformation mechanism were also discussed. PMID:26099720
Dong, Juncai; Zhu, Hailiang; Chen, Dongliang
2015-06-23
As a fundamental property of pressure-induced amorphization (PIA) in ice and ice-like materials (notably α-quartz), the occurrence of mechanical instability can be related to violation of Born criteria for elasticity. The most outstanding elastic feature of α-quartz before PIA has been experimentally reported to be the linear softening of shear modulus C44, which was proposed to trigger the transition through Born criteria B3. However, by using density-functional theory, we surprisingly found that both C44 and C66 in α-quartz exhibit strong nonlinearity under compression and the Born criteria B3 vanishes dominated by stiffening of C14, instead of by decreasing of C44. Further studies of archetypal quartz homeotypes (GeO2 and AlPO4) repeatedly reproduced the same elastic-hardening-driven mechanical instability, suggesting a universal feature of this family of crystals and challenging the long-standing idea that negative pressure derivatives of individual elastic moduli can be interpreted as the precursor effect to an intrinsic structural instability preceding PIA. The implications of this elastic anomaly in relation to the dispersive softening of the lowest acoustic branch and the possible transformation mechanism were also discussed.
Karp-Boss, Lee; Gueta, Rachel; Rousso, Itay
2014-01-01
Unique features of diatoms are their intricate cell covers (frustules) made out of hydrated, amorphous silica. The frustule defines and maintains cell shape and protects cells against grazers and pathogens, yet it must allow for cell expansion during growth and division. Other siliceous structures have also evolved in some chain-forming species as means for holding neighboring cells together. Characterization and quantification of mechanical properties of these structures are crucial for the understanding of the relationship between form and function in diatoms, but thus far only a handful of studies have addressed this issue. We conducted micro-indentation experiments, using atomic force microscopy (AFM), to examine local variations in elastic (Young's) moduli of cells and linking structures in the marine, chain-forming diatom Lithodesmium undulatum. Using a fluorescent tracer that is incorporated into new cell wall components we tested the hypothesis that new siliceous structures differ in elastic modulus from their older counterparts. Results show that the local elastic modulus is a highly dynamic property. Elastic modulus of stained regions was significantly lower than that of unstained regions, suggesting that newly formed cell wall components are generally softer than the ones inherited from the parent cells. This study provides the first evidence of differentiation in local elastic properties in the course of the cell cycle. Hardening of newly formed regions may involve incorporation of additional, possibly organic, material but further studies are needed to elucidate the processes that regulate mechanical properties of the frustule during the cell cycle.
Anselmo, Aaron C; Zhang, Mengwen; Kumar, Sunny; Vogus, Douglas R; Menegatti, Stefano; Helgeson, Matthew E; Mitragotri, Samir
2015-03-24
The impact of physical and chemical modifications of nanoparticles on their biological function has been systemically investigated and exploited to improve their circulation and targeting. However, the impact of nanoparticles' flexibility (i.e., elastic modulus) on their function has been explored to a far lesser extent, and the potential benefits of tuning nanoparticle elasticity are not clear. Here, we describe a method to synthesize polyethylene glycol (PEG)-based hydrogel nanoparticles of uniform size (200 nm) with elastic moduli ranging from 0.255 to 3000 kPa. These particles are used to investigate the role of particle elasticity on key functions including blood circulation time, biodistribution, antibody-mediated targeting, endocytosis, and phagocytosis. Our results demonstrate that softer nanoparticles (10 kPa) offer enhanced circulation and subsequently enhanced targeting compared to harder nanoparticles (3000 kPa) in vivo. Furthermore, in vitro experiments show that softer nanoparticles exhibit significantly reduced cellular uptake in immune cells (J774 macrophages), endothelial cells (bEnd.3), and cancer cells (4T1). Tuning nanoparticle elasticity potentially offers a method to improve the biological fate of nanoparticles by offering enhanced circulation, reduced immune system uptake, and improved targeting.
NASA Astrophysics Data System (ADS)
Abramovich, A.
2012-12-01
Cermets is a ceramic-metal composite usually produced by sintering a precompacted mixture of the initial powders. These composite materials were created for industrial applications to produce engineering structures possessing a high strength, thermal stability and resistance to aggressive media. In the present work elastic properties of cermets samples, obtained by sintering of corundum (α-Al2O3) and stainless steel powders were investigated in dependence on steel concentration 5 - 35% wt. and on temperature of sintering in vacuum 1400-1700°C. It was stated that values of elastic moduli are in complex dependence on concentration and temperature, reach maxima at steel concentration 15 - 20% wt. and increase with sintering temperature rise. In the work also the results of cermets microstructure researches and discussion of these results are presented. The results are discussed from stand view of ultrasound propagation through medium having grain boundaries which influence on the physical properties of composite.
Finite element formulations for problems of large elastic-plastic deformation
NASA Technical Reports Server (NTRS)
Mcmeeking, R. M.; Rice, J. R.
1974-01-01
An Eulerian finite element formulation is presented for problems of large elastic-plastic flow. The method is based on Hill's variational principle for incremental deformations, and is suited to isotropically hardening Prandtl-Reuss materials. The formulation is given in a manner which allows any conventional finite element program, for "small strain" elasticplastic analysis, to be simply and rigorously adapted to problems involving arbitrary amounts of deformation and arbitrary levels of stress in comparison to plastic deformation moduli. The method is applied to a necking bifurcation analysis of a bar in plane-strain tension. A unified general formulation of finite element equations, both Lagrangian and Eulerian, for large deformations, with arbitrary choice of the conjugate stress and strain measures, and a discussion is given of other proposed formulations for elastic-plastic finite element analysis at large strain.
Two-vortex interactions and elastic constants in type II superconductors
Miesenboeck, H.M.
1984-07-01
The elastic energy of a distorted flux-line lattice is calculated on the basis of a two-vortex interaction. Such a description is completely sufficient throughout the whole induction range between the upper and lower critical fields H/sub c//sub 1/ and H/sub c//sub 2/. Therefore it is possible to calculate all elastic moduli from a common potential consisting of two parts, one of a combined ''electromagnetic London type,'' the other based on the core overlap of the flux lines. The results are highly nonlocal and are in agreement with previous calculations of Brandt, but are modified near H/sub c//sub 1/ for small k (the ratio between the penetration depth and the coherence length).
ELEMENTARY APPROACH TO SELF-ASSEMBLY AND ELASTIC PROPERTIES OF RANDOM COPOLYMERS
S. M. CHITANVIS
2000-10-01
The authors have mapped the physics of a system of random copolymers onto a time-dependent density functional-type field theory using techniques of functional integration. Time in the theory is merely a label for the location of a given monomer along the extent of a flexible chain. We derive heuristically within this approach a non-local constraint which prevents segments on chains in the system from straying too far from each other, and leads to self-assembly. The structure factor is then computed in a straightforward fashion. The long wave-length limit of the structure factor is used to obtain the elastic modulus of the network. It is shown that there is a surprising competition between the degree of micro-phase separation and the elastic moduli of the system.
Time-dependent behaviour of high performance concrete: influence of coarse aggregate characteristics
NASA Astrophysics Data System (ADS)
Makani, A.; Vidal, T.; Pons, G.; Escadeillas, G.
2010-06-01
This paper examines the influence of coarse aggregate characteristics on the time-dependent deformations of High Performances Concretes (HPC). Four concretes made using the same cement paste but incorporating different types of aggregate (rolled siliceous gravel, crushed granite, crushed limestone and crushed siliceous gravels) were studied in order to investigate the effect of aggregate properties on the compressive strength, modulus of elasticity, shrinkage and creep. The results indicate that the aggregate type has a significant effect on creep and shrinkage deformations of HPC. An influence of the shape of aggregate on time-dependent deformations has also been observed. On the basis of these results, long-term behaviour seems to be correlated to the characteristics of the Interfacial Transition Zone (ITZ) strongly depending on the mineralogical nature and properties of aggregates. The experimental results are compared with the values calculated using the current Eurocode 2 model in order to assess the accuracy of the predictions.
Shear wave elasticity imaging of cervical lymph nodes.
Bhatia, Kunwar S S; Cho, Carmen C M; Tong, Cina S L; Yuen, Edmund H Y; Ahuja, Anil T
2012-02-01
A pilot study of real-time shear wave ultrasound elastography (SWE) for cervical lymphadenopathy in routine clinical practice was conducted on 55 nodes undergoing conventional ultrasound (US) with US-guided needle aspiration for cytology. Elastic moduli of stiffest regions in nodes were measured on colour-coded elastograms, which were correlated with cytology. Malignant nodes (n = 31, 56.4%) were stiffer (median 25.0 kPa, range 6.9-278.9 kPa) than benign nodes (median 21.4 kPa, range 8.9-30.2 kPa) (p = 0.008, Mann Whitney U test). A cut-off of 30.2 kPa attained highest accuracy of 61.8%, corresponding to 41.9% sensitivity, 100% specificity and 0.77 area under the receiver operating characteristic curve. Qualitatively, elastograms of benign nodes were homogeneously soft; malignant nodes were homogeneously soft or markedly heterogeneous with some including regions lacking elasticity signal. SWE is feasible for neck nodes. It appears unsuitable for cancer screening but may detect a subset of malignant nodes. The cause of spatial heterogeneity of malignant nodes on SWE is yet to be established.
Elastic velocities of partially gas-saturated unconsolidated sediments
Lee, M.W.
2004-01-01
Fluid in sediments significantly affects elastic properties of sediments and gas in the pore space can be identified by a marked reduction of P-wave velocity or a decrease of Poisson's ratio. The elastic properties of gas-saturated sediments can be predicted by the classical Biot-Gassmann theory (BGT). However, parameters for the BGT such as the Biot coefficient or moduli of dry frame of unconsolidated and high porosity sediments are not readily available. Dependence of velocities on differential pressure or porosity for partially gas-saturated sediments is formulated using properties derived from velocities of water-saturated sediments. Laboratory samples for unconsolidated and consolidated sediments and well log data acquired for unconsolidated marine sediments agree well with the predictions. However, because the P-wave velocity depends highly on how the gas is saturated in the pore space such as uniform or patch, the amounts of gas estimated from the P-wave velocity contains high uncertainty. The modeled Vp/Vs ratio of partially gas-saturated sediment using the patch distribution is usually greater than 1.6, whereas the ratio modeled assuming a uniform distribution is about 1.6. Thus, Poisson's ratio or Vp/Vs ratio may be used to differentiate patch from uniform saturation, but differences between various models of patch saturation cannot be easily identified. ?? 2004 Elsevier Ltd. All rights reserved.
Elasticity of Wadsleyite at 12 GPa1073K
W Liu; J Kung; B Li; N Nishiyama; Y Wang
2011-12-31
Elasticity of (Mg{sub 0.87}Fe{sub 0.13}){sub 2}SiO{sub 4} wadsleyite has been measured at simultaneous high pressure and high temperature to 12 GPa and 1073 K using ultrasonic interferometry in conjunction with synchrotron X-radiation. The elastic moduli and their pressure and temperature derivatives are precisely determined using pressure-standard-free third-order and fourth-order finite strain equations. Combined with previous thermoelastic data on olivine, the density, velocity and acoustic impedance contrasts between {alpha}- and {beta}-(Mg{sub 0.9}Fe{sub 0.1}){sub 2}SiO{sub 4} at 410-km depth are calculated along a 1673 K adiabatic geotherm. Both the third- and fourth-order finite strain equation fitting results give estimation of {approx}33-58% olivine content in the upper mantle to account for a seismic discontinuity of {approx}5% velocity jumps, and 8.5% (P wave) and 11.1% (S wave) impedance jumps at 410 km depth.
Characterization of nuclear graphite elastic properties using laser ultrasonic methods
Zeng, Fan W; Han, Karen; Olasov, Lauren R; Gallego, Nidia C; Contescu, Cristian I; Spicer, James B
2015-01-01
Laser ultrasonic methods have been used to characterize the elastic behaviors of commercially-available and legacy nuclear graphites. Since ultrasonic techniques are sensitive to various aspects of graphite microstructure including preferred grain orientation, microcrack orientation and porosity, laser ultrasonics is a candidate technique for monitoring graphite degradation and structural integrity in environments expected in high-temperature, gas-cooled nuclear reactors. Aspects of materials texture can be assessed by studying ultrasonic wavespeeds as a function of propagation direction and polarization. Shear wave birefringence measurements, in particular, can be used to evaluate elastic anisotropy. In this work, laser ultrasonic measurements of graphite moduli have been made to provide insight into the relationship between the microstructures and the macroscopic stiffnesses of these materials. In particular, laser ultrasonic measurements have been made using laser line sources to produce shear waves with specific polarizations. By varying the line orientation relative to the sample, shear wave birefringence measurements have been recorded. Results from shear wave birefringence measurements show that an isostatically molded graphite, such as PCIB, behaves isotropically, while an extruded graphite, such as H-451, displays significant ultrasonic texture. Graphites have complicated microstructures that depend on the manufacturing processes used, and ultrasonic texture in these materials could originate from grain orientation and preferred microcrack alignment. Effects on material isotropy due to service related microstructural changes are possible and the ultimate aim of this work is to determine the degree to which these changes can be assessed nondestructively using laser ultrasonics measurements
Elasticity dominated surface segregation of small molecules in polymer mixtures
NASA Astrophysics Data System (ADS)
Croce, Salvatore; Krawczyk, Jaroslaw; McLeish, Tom; Chakrabarti, Buddhapriya
When a binary polymer mixture with mobile components is left to equilibrate, the low molecular weight component migrates to the free surface. A balance between loss of translational entropy and gain in surface energy dictates the equilibrium partitioning ratio and the migrant fraction. Despite its ubiquity and several theoretical and experimental investigations, the phenomenon is not fully understood. Further, methods by which migration can be controlled are in its nascent stage of development. We propose a new phenomenological free energy functional that incorporates the elasticity of bulk polymer mixtures (reticulated networks and gels) and show (using mean field and self-consistent field theories) that the migrant fraction decreases with increasing the bulk modulus of the system. Further, a wetting transition observed otherwise for large values of miscibility parameter and polymerization index can be avoided by increasing the elastic modulus of the system. Estimated values of moduli (for the effect to be observable) are akin to those of rubbery polymers. Our work paves the way for controlling surface migration in complex industrial formulations with polymeric ingredients where this effect leads to decreased product stability and performance.
Asymptotic analysis of mathematical models for elastic composite media
NASA Astrophysics Data System (ADS)
Serkov, S. K.
The main subject of the thesis is the asymptotic analysis of models in mechanics of composite materials. It is based on the extension of the theory of the Polya-Szego tensors to the problems of homogenization and fracture. Such a technique allows one to obtain an asymptotic solution to a problem where most of numerical algorithms fail due to the presence of a singular perturbation. As a result of this work, a number of interesting effects have been found in optimization of composites and inverse problems of crack-inclusion interaction. Chapter 1 is an introductory chapter that contains the main definitions and bibliographical remarks. In Chapter 2 the Polya-Szego dipole tensors are employed for analysis of plane elasticity problems in non-homogeneous media. Classes of equivalence for defects (cavities and rigid inclusions) are specified for the Laplace and Navier operators: composite materials with defects of the same class have the same effective elastic moduli. Explicit asymptotic formulae for the effective compliance matrices of dilute composites are obtained. The problem of the optimal cavity shape is analyzed in Chapter 3. The analysis uses the Polya-Szego tensors calculated in Chapter 2. A new type of structure which is optimal for shear loading has been found. Properties of the optimal cavity are described. The crack-inclusion interaction problem considered in Chapter 4 has been solved by the asymptotic methods. An analysis of crack trajectories is performed in Chapter 5 for different types of defects and interface conditions. The algorithm employs the Polya-Szego tensors as integral characteristics describing the defect. Comparison with experimental data (Ceramic Centre, Bologna) is presented. In Chapter 6 we use the method of compound asymptotic expansions to treat the homogenization problem for thin-walled composites. The technique of boundary layer fields is employed to derive the junction condition in the region connecting thin walls. The asymptotic
Structural, electronic and elastic properties of the cubic CaTiO{sub 3} under pressure: A DFT study
Tariq, Saad Ahmed, Afaq; Tariq, Samar; Saad, Saher
2015-07-15
Using highly accurate FP-LAPW method with GGA approximation structural, electronic and elastic properties of cubic CaTiO{sub 3} have been calculated from 0-120 GPa range of pressure. It is observed that lattice constant, bond length and anisotropy factor decrease with increase in pressure. Also the brittle nature and indirect band-gap of the compound become ductile and direct band-gap respectively at 120 GPa. Moduli of elasticity, density of the material, Debye temperature and wave elastic wave velocities increase with increase in pressure. Spin dependent DOS’s plots show invariant anti-ferromagnetic nature of the compound under pressure. Our calculated results are in good agreement with available theoretical and experimental results.
NASA Astrophysics Data System (ADS)
Zhu, Zun-Lue; Fu, Hong-Zhi; Sun, Jin-Feng; Liu, Yu-Fang; Shi, De-Heng; Xu, Guo-Liang
2009-08-01
The first-principles plane-wave pseudopotential method using the generalized gradient approximation within the framework of density functional theory is applied to anaylse the equilibrium lattice parameters, six independent elastic constants, bulk moduli, thermal expansions and heat capacities of MoSi2. The quasi-harmonic Debye model, using a set of total energy versus cell volume obtained with the plane-wave pseudopotential method, is applied to the study of the elastic properties, thermodynamic properties and vibrational effects. The calculated zero pressure elastic constants are in overall good agreement with the experimental data. The calculated heat capacities and the thermal expansions agree well with the observed values under ambient conditions and those calculated by others. The results show that the temperature has hardly any effect under high pressure.
NASA Astrophysics Data System (ADS)
Sobol', O. V.
2016-09-01
The dependence of elastic moduli for different directions on the nonstoichiometry with respect to carbon atoms in octahedral interstices of face-centered cubic crystalline lattice is established for the first time for metastable tungsten carbide (β-WC1- x phase). It is shown that with decreasing content of carbon atoms in the tungsten carbide lattice it is compressed, which is accompanied by the growth of the contribution of metallic component, thus determining higher density of the coating material and change of elastic characteristics for different crystallographic directions. This makes it possible to obtain carbide coatings with the required ratio of elastic constants via corresponding technological regimes, which is especially important in formation of coatings with predominant crystallite growth orientation.
Lugovy, Mykola; Aman, Amjad; Orlovskaya, Nina; Chen, Yan; Kuebler, Jakob; Graule, Thomas; Reece, Michael J.; Ma, Dong; Stoica, Alexandru D.; An, Ke
2014-07-07
Calculations of elastic constants and development of elastic anisotropy under uniaxial compression in originally isotropic polycrystalline LaCoO{sub 3} perovskite are reported. The lattice strains in individual (hkl) planes as well as average lattice strain were determined both for planes oriented perpendicular and parallel to the loading direction using in-situ neutron diffraction. Utilizing average lattice strains as well as lattice strains along the a and c crystallographic directions, an attempt was made to determine Poisson's ratio of LaCoO{sub 3}, which was then compared with that measured using an impulse excitation technique. The elastic constants were calculated and Young's moduli of LaCoO{sub 3} single crystal in different crystallographic directions were estimated.
NASA Technical Reports Server (NTRS)
Sheu, Y. C.; Fu, L. S.
1982-01-01
The extended method of equivalent inclusion developed is applied to study the specific wave problems of the transmission of elastic waves in an infinite medium containing a layer of inhomogeneity, and of the scattering of elastic waves in an infinite medium containing a perfect spherical inhomogeneity. The eigenstrains are expanded as a geometric series and the method of integration for the inhomogeneous Helmholtz operator given by Fu and Mura is adopted. The results obtained by using a limited number of terms in the eigenstrain expansion are compared with exact solutions for the layer problem and for a perfect sphere. Two parameters are singled out for this comparison: the ratio of elastic moduli, and the ratio of the mass densities. General trends for three different situations are shown.
Henager, Charles H.; Nguyen, Ba Nghiep; Kurtz, Richard J.; Ferraris, Monica; Katoh, Yutai
2015-06-30
The international fusion community designed miniature torsion specimens for joint testing and irradiation in test reactors with limited irradiation volumes since SiC and SiC-composites used in fission or fusion environments require joining methods for assembling systems. Torsion specimens fail out-of-plane when joints are strong and when elastic moduli are comparable to SiC, which causes difficulties in determining shear strengths for many joints or for comparing unirradiated and irradiated joints. A finite element damage model was developed to treat elastic joints such as SiC/Ti3SiC2+SiC and elastic-plastic joints such as SiC/epoxy and steel/epoxy. The model uses constitutive shear data and is validated using epoxy joint data. The elastic model indicates fracture is likely to occur within the joined pieces to cause out-of-plane failures for miniature torsion specimens when a certain modulus and strength ratio between the joint material and the joined material exists. Lower modulus epoxy joints always fail in plane and provide good model validation.
Cultural Heritage Content Re-Use: An Aggregators's Point of View
NASA Astrophysics Data System (ADS)
Gavrilis, D.; Ioannides, M.; Theofanous, E.
2015-08-01
This paper introduces a use case of re-using aggregated and enriched metadata for the tourism creative industry. The MORe aggregation and enrichment framework is presented along with an example for enriching cultural heritage objects harvested from a number of Omeka repositories. The enriched content is then published both to the EU Digital Library Europeana (http://www.europeana.eu) and to an Elastic Search component that feeds a portal aimed at providing tourists with interesting information.
NASA Astrophysics Data System (ADS)
Xu, C.; Li, Q.; Liu, C. M.; Duan, M. Y.; Wang, H. K.
2016-05-01
First-principles calculations are employed to investigate the structural and elastic properties, formation enthalpies and chemical bonding features as well as hardness values of chromium tetraboride (CrB4) with different structures. The lattice parameters, Poisson’s ratio and B/G ratio are also derived. Our calculations indicate that the orthorhombic structure with Pnnm symmetry is the most energetically stable one for CrB4. Except for WB4P63/mmc structure with imaginary frequencies, another six new structures are investigated through the full phonon dispersion calculations. Their mechanical and thermodynamic stabilities are also studied by calculating the elastic constants and formation enthalpies. Our calculations show that the thermodynamic stabilities of all these CrB4 phases can be enhanced under high pressure. The large shear moduli, Young’s moduli and hardness values indicate that these CrB4 phases are potential hard materials. Analyses of the densities of states (DOSs) and electron localization functions (ELFs) provide further understandings of the chemical and physical properties of these CrB4 phases. It is observed that the large occupations and high strengths of the B-B covalent bonds are important for the stabilities, incompressibility and hardnesses of these CrB4 phases.
Hansen, Hendrik H.G.; Richards, Michael S.; Doyley, Marvin M.; de Korte, Chris L.
2013-01-01
Atherosclerotic plaque rupture can initiate stroke or myocardial infarction. Lipid-rich plaques with thin fibrous caps have a higher risk to rupture than fibrotic plaques. Elastic moduli differ for lipid-rich and fibrous tissue and can be reconstructed using tissue displacements estimated from intravascular ultrasound radiofrequency (RF) data acquisitions. This study investigated if modulus reconstruction is possible for noninvasive RF acquisitions of vessels in transverse imaging planes using an iterative 2D cross-correlation based displacement estimation algorithm. Furthermore, since it is known that displacements can be improved by compounding of displacements estimated at various beam steering angles, we compared the performance of the modulus reconstruction with and without compounding. For the comparison, simulated and experimental RF data were generated of various vessel-mimicking phantoms. Reconstruction errors were less than 10%, which seems adequate for distinguishing lipid-rich from fibrous tissue. Compounding outperformed single-angle reconstruction: the interquartile range of the reconstructed moduli for the various homogeneous phantom layers was approximately two times smaller. Additionally, the estimated lateral displacements were a factor of 2–3 better matched to the displacements corresponding to the reconstructed modulus distribution. Thus, noninvasive elastic modulus reconstruction is possible for transverse vessel cross sections using this cross-correlation method and is more accurate with compounding. PMID:23478602
Hansen, Hendrik H G; Richards, Michael S; Doyley, Marvin M; de Korte, Chris L
2013-01-01
Atherosclerotic plaque rupture can initiate stroke or myocardial infarction. Lipid-rich plaques with thin fibrous caps have a higher risk to rupture than fibrotic plaques. Elastic moduli differ for lipid-rich and fibrous tissue and can be reconstructed using tissue displacements estimated from intravascular ultrasound radiofrequency (RF) data acquisitions. This study investigated if modulus reconstruction is possible for noninvasive RF acquisitions of vessels in transverse imaging planes using an iterative 2D cross-correlation based displacement estimation algorithm. Furthermore, since it is known that displacements can be improved by compounding of displacements estimated at various beam steering angles, we compared the performance of the modulus reconstruction with and without compounding. For the comparison, simulated and experimental RF data were generated of various vessel-mimicking phantoms. Reconstruction errors were less than 10%, which seems adequate for distinguishing lipid-rich from fibrous tissue. Compounding outperformed single-angle reconstruction: the interquartile range of the reconstructed moduli for the various homogeneous phantom layers was approximately two times smaller. Additionally, the estimated lateral displacements were a factor of 2-3 better matched to the displacements corresponding to the reconstructed modulus distribution. Thus, noninvasive elastic modulus reconstruction is possible for transverse vessel cross sections using this cross-correlation method and is more accurate with compounding.