Anomalous Elastic Behavior in hcp- and Sm-Type Dysprosium
Tschauner, Oliver; Grubor-Urosevic, Ognjen; Dera, Przemyslaw; Mulcahy, Sean R.
2012-04-11
The compression behavior of elemental dysprosium in the hcp- and the Sm-type phases has been examined under hydrostatic pressure. Sm-type Dy has been found about 1% denser than the hcp phase. This increase in density is due to c-axis contraction in Sm-type Dy, whereas the a-axis even expands compared with the hcp-phase. Both the hcp- and the Sm-type phases show an inversion in the pressure derivative of the c/a ratio. For hcp-Dy this inversion is very sharp with minimal c/a at 2.5 GPa. At the same pressure, the compression behavior of hcp-Dy changes abruptly from dominantly c-axis compression to almost isotropic compression with slightly softer S{sub 11}. The bulk modulus increases at this point by a factor of {approx}2. Both hcp- and Sm-type Dy exhibit a crossover from highly anisotropic compression mostly along the c-axis to almost isotropic compression. We discuss these anomalies with respect to a possible Lifshitz transition and structural soft modes.
Mohan, Priyanka; Goldbart, Paul M; Narayanan, Rajesh; Toner, John; Vojta, Thomas
2010-08-20
We show that layered quenched randomness in planar magnets leads to an unusual intermediate phase between the conventional ferromagnetic low-temperature and paramagnetic high-temperature phases. In this intermediate phase, which is part of the Griffiths region, the spin-wave stiffness perpendicular to the random layers displays anomalous scaling behavior, with a continuously variable anomalous exponent, while the magnetization and the stiffness parallel to the layers both remain finite. Analogous results hold for superfluids and superconductors. We study the two phase transitions into the anomalous elastic phase, and we discuss the universality of these results, and implications of finite sample size as well as possible experiments. PMID:20868107
Anomalous bubble propagation in elastic tubes
NASA Astrophysics Data System (ADS)
Heap, Alexandra; Juel, Anne
2008-08-01
Airway reopening is an important physiological event, as exemplified by the first breath of an infant that inflates highly collapsed airways by driving a finger of air through its fluid-filled lungs. Whereas fundamental models of airway reopening predict the steady propagation of only one type of bubble with a characteristic rounded tip, our experiments reveal a surprising selection of novel bubbles with counterintuitive shapes that reopen strongly collapsed, liquid-filled elastic tubes. Our multiple bubbles are associated with a discontinuous relationship between bubble pressure and speed that sets exciting challenges for modelers.
Anomalous Flexural Behaviors of Microtubules
Liu, Xiaojing; Zhou, Youhe; Gao, Huajian; Wang, Jizeng
2012-01-01
Apparent controversies exist on whether the persistence length of microtubules depends on its contour length. This issue is particularly challenging from a theoretical point of view due to the tubular structure and strongly anisotropic material property of microtubules. Here we adopt a higher order continuum orthotropic thin shell model to study the flexural behavior of microtubules. Our model overcomes some key limitations of a recent study based on a simplified anisotropic shell model and results in a closed-form solution for the contour-length-dependent persistence length of microtubules, with predictions in excellent agreement with experimental measurements. By studying the ratio between their contour and persistence lengths, we find that microtubules with length at ∼1.5 μm show the lowest flexural rigidity, whereas those with length at ∼15 μm show the highest flexural rigidity. This finding may provide an important theoretical basis for understanding the mechanical structure of mitotic spindles during cell division. Further analysis on the buckling of microtubules indicates that the critical buckling load becomes insensitive to the tube length for relatively short microtubules, in drastic contrast to the classical Euler buckling. These rich flexural behaviors of microtubules are of profound implication for many biological functions and biomimetic molecular devices. PMID:22768935
Anomalous human behavior detection: an adaptive approach
NASA Astrophysics Data System (ADS)
van Leeuwen, Coen; Halma, Arvid; Schutte, Klamer
2013-05-01
Detection of anomalies (outliers or abnormal instances) is an important element in a range of applications such as fault, fraud, suspicious behavior detection and knowledge discovery. In this article we propose a new method for anomaly detection and performed tested its ability to detect anomalous behavior in videos from DARPA's Mind's Eye program, containing a variety of human activities. In this semi-unsupervised task a set of normal instances is provided for training, after which unknown abnormal behavior has to be detected in a test set. The features extracted from the video data have high dimensionality, are sparse and inhomogeneously distributed in the feature space making it a challenging task. Given these characteristics a distance-based method is preferred, but choosing a threshold to classify instances as (ab)normal is non-trivial. Our novel aproach, the Adaptive Outlier Distance (AOD) is able to detect outliers in these conditions based on local distance ratios. The underlying assumption is that the local maximum distance between labeled examples is a good indicator of the variation in that neighborhood, and therefore a local threshold will result in more robust outlier detection. We compare our method to existing state-of-art methods such as the Local Outlier Factor (LOF) and the Local Distance-based Outlier Factor (LDOF). The results of the experiments show that our novel approach improves the quality of the anomaly detection.
Crystal Structure Anisotropy Explains Anomalous Elastic Properties of Metal Nanorods
NASA Astrophysics Data System (ADS)
Goupalov, Serguei
2014-03-01
It is demonstrated that the frequency of the extensional vibrational mode of a nanorod made of an elastically anisotropic crystalline material deviates widely from the predictions of the theories based on the analysis of the long-wavelength limit. The dispersion relation for the fundamental extensional mode of a gold rod grown in the [ 100 ] direction is calculated and found to be in an excellent agreement with experimental data obtained from the transient optical absorption measurements on gold nanorods.[1] This explains an anomaly in the elastic properties of nanorods which was previously attributed to a 26% decrease in Young's modulus for nanorods compared to its bulk value.
Anomalous incident-angle and elliptical-polarization rotation of an elastically refracted P-wave
Fa, Lin; Fa, Yuxiao; Zhang, Yandong; Ding, Pengfei; Gong, Jiamin; Li, Guohui; Li, Lijun; Tang, Shaojie; Zhao, Meishan
2015-01-01
We report a newly discovered anomalous incident-angle of an elastically refracted P-wave, arising from a P-wave impinging on an interface between two VTI media with strong anisotropy. This anomalous incident-angle is found to be located in the post-critical incident-angle region corresponding to a refracted P-wave. Invoking Snell’s law for a refracted P-wave provides two distinctive solutions before and after the anomalous incident-angle. For an inhomogeneously refracted and elliptically polarized P-wave at the anomalous incident-angle, its rotational direction experiences an acute variation, from left-hand elliptical to right-hand elliptical polarization. The new findings provide us an enhanced understanding of acoustical-wave scattering and lead potentially to widespread and novel applications. PMID:26244284
Effects of elastic anisotropy on mechanical behavior of intermetallic compounds
Yoo, M.H.
1991-01-01
Fundamental aspects of the deformation and fracture behavior of ordered intermetallic compounds are examined within the framework of linear anisotropic elasticity theory of dislocations and cracks. The orientation dependence and the tension/compression asymmetry of yield stress are explained in terms of the anisotropic coupling effect of non-glide stresses to the glide strain. The anomalous yield behavior is related to the disparity (edge/screw) of dislocation mobility and the critical stress required for the dislocation multiplication mechanism of Frank-Read type. The slip-twin conjugate relationship, extensive faulting, and pseudo-twinning (martensitic transformation) at a crack tip can be enhanced also by the anisotropic coupling effect, which may lead to transformation toughening of shear type.
Measurements of anomalous elastic scattering of 59.54-keV photons
Baraldi, C.; Casnati, E.; Tartari, A.; Andreis, M.; Singh, B.
1996-12-01
Coherent scattering cross sections of 59.54-keV photons on target foils of {sup 64}Gd, {sup 66}Dy, {sup 68}Er, {sup 70}Yb, {sup 72}Hf, and {sup 73}Ta at 60{degree}, 90{degree}, and 120{degree} have been measured to provide information on the region of {ital K} anomalous elastic scattering. The results are compared with the values calculated by the second perturbative order {ital S} matrix and by two procedures based on the form-factor approximation corrected by the anomalous scattering factors. Agreement of the {ital S} matrix values is very satisfactory, on the whole, and that of the values given by the form-factor approximations is fairly good. {copyright} {ital 1996 The American Physical Society.}
Long-lived anomalous thermal diffusion induced by elastic cell membranes on nearby particles
NASA Astrophysics Data System (ADS)
Daddi-Moussa-Ider, Abdallah; Guckenberger, Achim; Gekle, Stephan
2016-01-01
The physical approach of a small particle (virus, medical drug) to the cell membrane represents the crucial first step before active internalization and is governed by thermal diffusion. Using a fully analytical theory we show that the stretching and bending of the elastic membrane by the approaching particle induces a memory in the system, which leads to anomalous diffusion, even though the particle is immersed in a purely Newtonian liquid. For typical cell membranes the transient subdiffusive regime extends beyond 10 ms and can enhance residence times and possibly binding rates up to 50%. Our analytical predictions are validated by numerical simulations.
Anomalous behavior of LEED beam intensity during annealing
NASA Astrophysics Data System (ADS)
Fu, Tsu-Yi; Liu, T. F.; Su, C. W.; Shern, C. S.; Chen, R. H.
2000-10-01
Low-energy electron diffraction was used to study the annealing effects of 1 ML Ag on the ultra-thin-film Co/Pt (111). The behavior of the specular beam intensity versus temperature is anomalous. Besides the normal Debye-Waller effect, a bend occurs at 550 K, and a dramatic increase occurs at a higher temperature. A corresponding study by Auger electron spectroscopy and ultraviolet photoelectron spectroscopy indicates that the bend results from the Co inter-diffusion. The anomalous increase indicates that a more stable state forms at a higher temperature. The Co coverage plays an important role in determining the turning temperature. Possible mechanisms are discussed.
Asymptotic behavior of the supremum tail probability for anomalous diffusions
NASA Astrophysics Data System (ADS)
Michna, Zbigniew
2008-01-01
In this paper we investigate asymptotic behavior of the tail probability for subordinated self-similar processes with regularly varying tail probability. We show that the tail probability of the one-dimensional distributions and the supremum tail probability are regularly varying with the pre-factor depending on the moments of the subordinating process. We can apply our result to the so-called anomalous diffusion.
Anomalous elastic scattering of x-ray photon by an atom with an open shell
NASA Astrophysics Data System (ADS)
Hopersky, A. N.; Petrov, I. D.; Nadolinsky, A. M.; Yavna, V. A.; Koneev, R. V.
2004-08-01
In the non-relativistic approximation for the wavefunctions of the one-electron states and in the dipole approximation for the scattering amplitude the effect of relaxation of atomic shells in the field of core vacancies, multiplet splitting, Auger and radiative vacancy decays and virtual processes of one-photon double excitation/ionization from the atomic ground state on the differential cross section of anomalous elastic scattering of the linearly polarized x-ray photon by the copper atom near its 1s-shell ionization threshold are studied. The results of calculations are found to be in agreement with the high-precision synchrotron radiation experiment by Arp et al (1993 J. Phys. B: At. Mol. Opt. Phys. 26 4381).
Anomalous mechanical behavior and crack growth of oxide glasses
NASA Astrophysics Data System (ADS)
Seaman, Jared Hilliard
This thesis is concerned with analytically describing anomalous mechanical behaviors of glass. A new slow crack growth model is presented that considers a semi-elliptical crack in a cylindrical glass rod subjected to 4-point bending that is both loaded statically and under a time-dependent load. This model is used to explain a suppression of the loading-rate dependency of ion-exchanged strengthened glass. The stress relaxation behavior of an ion-exchanged strengthened glass is then analyzed in view of a newly observed water-assisted surface stress relaxation mechanism. By making refinements to a time-dependent Maxwell material model for stress buildup and relaxation, the anomalous subsurface compressive stress peak in ion-exchanged strengthened glass is explained. The notion of water-assisted stress relaxation is extended to the crack tip, where high tensile stresses exist. A toughening effect has historically been observed for cracks aged at subcritical stress intensity factors, where crack tip stress relaxation is hypothesized. A simple fracture mechanics model is developed that estimates a shielding stress intensity factor that is then superimposed with the far-field stress intensity factor. The model is used to estimate anomalous "restart" times for aged cracks. The same model predicts a non-linear crack growth rate for cracks loaded near the static fatigue limit. Double cantilever beam slow crack growth experiments were performed and new slow crack growth data for soda-lime silicate glass was collected. Interpretation of this new experimental slow crack growth data suggests that the origin of the static fatigue limit in glass is due to water-assisted stress relaxation. This thesis combines a number of studies that offer a new unified understanding of historical anomalous mechanical behaviors of glass. These anomalies are interpreted as simply the consequence of slow crack growth and water-assisted surface stress relaxation.
Anomalous Elasticity of 4He Films at the Quantum Phase Transition
NASA Astrophysics Data System (ADS)
Shirahama, Keiya; Takahashi, Daisuke; Kogure, Takayuki; Yoshimura, Hitomi; Higashino, Rama
4 He films on solid substrates exhibit a quantum phase transition between localized (nonsuperfluid) and superfluid states by changing coverage n. We have made torsional oscillator (TO) studies for 4He films adsorbed on nanoporous glasses. A TO with localized films showed an apparent ''supersolid'' behavior, an increase in TO frequency f with broad peak in Q-1. Combining with FEM analyses for TO's with different designs, we conclude that the behavior results from the softening of adsorbed 4He films at high temperatures. The features in f and Q-1 are fitted well to a Debye-like activation with a distributed energy gap Δ, so the elasticity is accounted by thermal excitation of localized atoms to an ''extended'' state. As the critical coverage nc approaches the gap decreases to zero with a powerlaw Δ ~(n -nc) 1 . 2 . Assuming that the 4He chemical potential μ (n) is located in the middle of the gap, we can estimate the elastic constant κ-1 =n2 ∂μ / ∂n . The elasticity agrees with shear moduli of 4He films obtained from the FEM analysis within factor of three. The energetics proposed from the elastic behavior naturally explains other properties of He films adsorbed on disordered substrates.
Hard elastic scattering in QCD: Leading behavior
Botts, J.F.
1989-01-01
The author derives the asymptotic behavior of elastic meson-meson and baryon-baryon scattering at high energy and large angle t/s {approximately} O(1). The results organize both Sudakov and nonleading logarithmic corrections to independent (Landshoff) scatterings of valence quarks. He shows how to separate these contributions systematically from single scattering contributions, in a manner which suggests that the complete amplitudes should be computable perturbatively down to the dimensional counting power, in terms of hadronic wave functions. In the final chapter, the perturbative asymptotic amplitude and differential cross section for elastic pion-pion scattering is calculated numerically. For various choices of pion wave function and running coupling, the onset of power law behavior, d{sigma}/dt {approximately} s{sup {minus}5.8}, was observed. The dependence in d{sigma}/dt on the cutoff in gluon momentum, chosen to be O({Lambda}{sub QCD}/Q), was observed to be sharp for ln(s/1GeV{sup 2}) less than 1. Very small oscillations in d{sigma}/dt appear in physically realizable energies, but these are cutoff dependent, and their interpretation unclear. Higher twist effects were estimated to be roughly {approximately}15% for 2 < ln(s/1GeV{sup 2}) < 10.
Possible Implications of Anomalous Shock Wave Behavior for Laser Fusion
NASA Astrophysics Data System (ADS)
Bates, Jason W.; Montgomery, David C.
1997-11-01
In ``normal'' materials, shocks are compressive because of the inequality (partial^2p / partial V^2)_s> 0, which is, however, not dictated by thermodynamics.(e.g.), Ya. B. Zel'dovich and Yu. P. Raizer, ``Physics of Shock Waves and High-Temperature Hydrodynamic Phenomena,'' (N.Y., Academic Press, 1967), Vol I, pp. 67-69; Vol II, pp. 750-762. In ``anomalous'' materials, the inequality may go the other way, and exotic phenomena result: rarefactive shocks, spreading compressive pulses, and shock wave ``splitting'' or instability.^2,(N. M. Kuznetsov, Sov. Phys. JETP 61), 275 (1985). Materials tend to behave ``anomalously'' in the vicinities of phase transitions. Shock-imploded DT fusion fuels will experience a variety of phase transitions, including melting, vaporization, molecular dissociation, and ionization. Imperfectly explored gas-dynamic problems may require attention to each case. For example, in the shock Hugoniot measurements of Da Silva et al. [Phys. Rev. Lett. 78, 483 (1997)], the high-pressure part of Fig. 4b suggests the possibility of ``anomalous'' behavior.
NASA Astrophysics Data System (ADS)
Chen, Ting; Gwanmesia, Gabriel D.; Wang, Xuebing; Zou, Yongtao; Liebermann, Robert C.; Michaut, Chloé; Li, Baosheng
2015-02-01
Compressional and shear wave velocities of coesite have been measured using ultrasonic interferometry in a multi-anvil apparatus up to 12.6 GPa at room temperature for the first time. While the P wave velocity increases continuously with pressure, the S wave exhibits an anomalous softening and the velocity decreases continuously with pressure. Finite strain analysis of the data yielded KS0 = 103.6 (4) GPa, G0 = 61.6 (2) GPa and K0‧ = 2.9 (1), G0‧ = 0.3 (1) for the bulk and shear moduli and their pressure derivatives, respectively. The anomalous elastic behavior of coesite results in large velocity and impedance contrasts across the coesite-stishovite transition, reaching ˜39% and ˜48% for P and S wave velocity contrasts, and ˜70% and 78% for P and S wave impedance contrasts, respectively, at pressure ˜8 GPa, with P and S wave velocity perturbations showing no apparent dependence on depths (i.e., dln V (P or S) / dh ˜ 0) within 8-12 GPa. These unusually large contrasts and depth independent characteristics render the transition between the two silica polymorphs one of the most plausible candidates for the cause of the seismically observed X-discontinuity. The current P and S wave velocity perturbation dependences on the SiO2 content, d (ln VP) / d (SiO2) ˜ 0.43 (wt%)-1 and d (ln VS) / d (SiO2) ˜ 0.60 (wt%)-1, can serve as a geophysical probe to track ancient subducted eclogite materials to gain insights on the geodynamics of the mantle.
Anomalous behavior of 2+ excitations around 132Sn
NASA Astrophysics Data System (ADS)
Terasaki, J.; Engel, J.; Nazarewicz, W.; Stoitsov, M.
2002-11-01
In certain neutron-rich Te isotopes, a decrease in the energy of the first excited 2+ state is accompanied by a decrease in the E2 strength to that state from the ground state, contradicting simple systematics and general intuition about quadrupole collectivity. We use a separable quadrupole-plus-pairing Hamiltonian and the quasiparticle random phase approximation to calculate energies, B(E2,0+-->2+) strengths, and g factors for the lowest 2+ states near 132Sn (Z>=50). We trace the anomalous behavior in the Te isotopes to a reduced neutron pairing above the N=82 magic gap.
Anomalous elastic buckling of layered crystalline materials in the absence of structure slenderness
NASA Astrophysics Data System (ADS)
Ren, Manrui; Liu, Yilun; Zhe Liu, Jefferson; Wang, Lifeng; Zheng, Quanshui
2016-03-01
Layered crystalline materials, such as graphene, boron nitride, tungsten sulfate, phosphorene, etc., have attracted enormous attentions, due to their unique crystal structures and superior mechanical, thermal, and physical properties. Making use of mechanical buckling is a promising route to control their structural morphology and thus tune their physical properties, giving rise to many novel applications. In this paper, we employ molecular dynamics (MD) simulations and theoretical modeling to study the compressive buckling of a column made of layered crystalline materials with the crystal layers parallel to the compressive direction. We find that the mechanical buckling of the layered crystalline materials exhibits two anomalous and counter-intuitive features as approaching the zero slenderness ratio. First, the critical buckling strain εcr has a finite value that is much lower than the material's elastic limit strain. A continuum mechanics model (by homogenizing the layered materials) is proposed for the εcr, which agrees well with the results of MD simulations. We find that the εcr solely depends on elastic constants without any structural dimension, which appears to be an intrinsic material property and thus is defined as intrinsic buckling strain (IBS), εcrIBS , in this paper. Second, below a certain nanoscale length, l0, in the compressive direction (e.g., about 20 nm for graphite), the critical buckling strain εcr shows a size effect, i.e., increasing as the column length L decreases. To account for the size effect, inspired by our recently developed multi-beam shear model (Liu et al., 2011), a bending energy term of individual crystal layer is introduced in our continuum model. The theoretical model of εcr agrees well with the size effects observed in MD simulations. This study could lay a ground for engineering layered crystalline materials in various nano-materials and nano-devices via mechanical buckling.
Anomalous elastic scattering of x-ray photons by a neon-like ion
NASA Astrophysics Data System (ADS)
Hopersky, A. N.; Nadolinsky, A. M.; Dzuba, D. V.; Yavna, V. A.
2005-05-01
In the non-relativistic approximation for the wavefunctions of the one-electron states and in the dipole approximation for the scattering amplitude, the effect of radial monopole rearrangement of electron shells within the field of a vacancy and of the processes of one-photon double excitation/ionization on the absolute values and the shapes of the differential cross sections of anomalous non-zero-angle elastic scattering of linearly polarized x-ray photons by the Ne atom and by the neon-like Si4+ and Ar8+ ions in the vicinity of K- and KL23-ionization thresholds is studied. The results of calculations for the Ne atom were found to be in agreement with the high-precision synchrotron radiation experiments by Coreno et al (1999 Phys. Rev. A 59 2494; K-ionization threshold) and by Avaldi et al (1996 J. Phys. B: At. Mol. Opt. Phys. 29 L737; KL23-ionization threshold). The results of calculations for the Si4+ and Ar8+ ions are predictions.
Anomalous Ion Charge State Behavior In Interplanetary Coronal Mass Ejections
NASA Astrophysics Data System (ADS)
Kocher, M.; Lepri, S. T.; Landi, E.; Zhao, L.
2015-12-01
A recent analysis of solar wind charge state composition measurements from the ACE/SWICS instrument showed that the expected correlation between the frozen-in values of the O7/O6 and C6/C5 ratios was violated in ~5% of the slow solar wind in the 1998-2011 period (Zhao et al. 2015). In this work we determine that such anomalous behavior is also found in over 40% of Interplanetary Coronal Mass Ejections (ICMEs), as identified by Richardson and Cane (2010). An analysis of the plasma composition during these events reveals significant depletions in densities of fully stripped ions of Carbon, Oxygen, and Nitrogen. We argue that these events are indicators of ICME plasma acceleration via magnetic reconnection near the freeze-in region of Carbon and Oxygen above the solar corona.
Anomalous behavior of water inside the SecY translocon.
Capponi, Sara; Heyden, Matthias; Bondar, Ana-Nicoleta; Tobias, Douglas J; White, Stephen H
2015-07-21
The heterotrimeric SecY translocon complex is required for the cotranslational assembly of membrane proteins in bacteria and archaea. The insertion of transmembrane (TM) segments during nascent-chain passage through the translocon is generally viewed as a simple partitioning process between the water-filled translocon and membrane lipid bilayer, suggesting that partitioning is driven by the hydrophobic effect. Indeed, the apparent free energy of partitioning of unnatural aliphatic amino acids on TM segments is proportional to accessible surface area, which is a hallmark of the hydrophobic effect [Öjemalm K, et al. (2011) Proc Natl Acad Sci USA 108(31):E359-E364]. However, the apparent partitioning solvation parameter is less than one-half the value expected for simple bulk partitioning, suggesting that the water in the translocon departs from bulk behavior. To examine the state of water in a SecY translocon complex embedded in a lipid bilayer, we carried out all-atom molecular-dynamics simulations of the Pyrococcus furiosus SecYE, which was determined to be in a "primed" open state [Egea PF, Stroud RM (2010) Proc Natl Acad Sci USA 107(40):17182-17187]. Remarkably, SecYE remained in this state throughout our 450-ns simulation. Water molecules within SecY exhibited anomalous diffusion, had highly retarded rotational dynamics, and aligned their dipoles along the SecY transmembrane axis. The translocon is therefore not a simple water-filled pore, which raises the question of how anomalous water behavior affects the mechanism of translocon function and, more generally, the partitioning of hydrophobic molecules. Because large water-filled cavities are found in many membrane proteins, our findings may have broader implications. PMID:26139523
Anomalous behavior of water inside the SecY translocon
Capponi, Sara; Heyden, Matthias; Bondar, Ana-Nicoleta; Tobias, Douglas J.; White, Stephen H.
2015-01-01
The heterotrimeric SecY translocon complex is required for the cotranslational assembly of membrane proteins in bacteria and archaea. The insertion of transmembrane (TM) segments during nascent-chain passage through the translocon is generally viewed as a simple partitioning process between the water-filled translocon and membrane lipid bilayer, suggesting that partitioning is driven by the hydrophobic effect. Indeed, the apparent free energy of partitioning of unnatural aliphatic amino acids on TM segments is proportional to accessible surface area, which is a hallmark of the hydrophobic effect [Öjemalm K, et al. (2011) Proc Natl Acad Sci USA 108(31):E359–E364]. However, the apparent partitioning solvation parameter is less than one-half the value expected for simple bulk partitioning, suggesting that the water in the translocon departs from bulk behavior. To examine the state of water in a SecY translocon complex embedded in a lipid bilayer, we carried out all-atom molecular-dynamics simulations of the Pyrococcus furiosus SecYE, which was determined to be in a “primed” open state [Egea PF, Stroud RM (2010) Proc Natl Acad Sci USA 107(40):17182–17187]. Remarkably, SecYE remained in this state throughout our 450-ns simulation. Water molecules within SecY exhibited anomalous diffusion, had highly retarded rotational dynamics, and aligned their dipoles along the SecY transmembrane axis. The translocon is therefore not a simple water-filled pore, which raises the question of how anomalous water behavior affects the mechanism of translocon function and, more generally, the partitioning of hydrophobic molecules. Because large water-filled cavities are found in many membrane proteins, our findings may have broader implications. PMID:26139523
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.
What Determines Different Anomalous Transport Behavior in Different Porous Media?
NASA Astrophysics Data System (ADS)
Bijeljic, B.; Raeini, A.; Mostaghimi, P.; Blunt, M. J.
2012-12-01
Solute transport in porous media is of importance in many scientific fields and applications, notably in contaminant migration in subsurface hydrology, geological storage of carbon-dioxide, packed bed reactors and chromatography in chemical engineering, and tracer studies in enhanced oil recovery. The non-Fickian nature of dispersive processes in heterogeneous media has been demonstrated experimentally from pore to field scales. However, the exact relationship between structure, velocity field and transport has not been fully understood. We study and explain the origin of non-Fickian transport behavior as a function of pore-scale heterogeneity by simulating flow and transport directly on micro-CT images of pore space of the media with increasing pore-scale complexity: beadpack, Bentheimer sandstone and Portland limestone. The Navier-Stokes equations are solved to compute the flow field and the streamline method is used to transport particles by advection, while the random walk method is used for diffusion. The connectivity of the fast flow paths for beadpack, Bentheimer sandstone and Portland carbonate is presented in Figs.1a-c. We show how computed propagators (concentration vs. displacement) for beadpack, sandstone and carbonate depend on the spread in the velocity distribution. A narrow velocity distribution in the beadpack leads to the least anomalous behaviour where the propagators rapidly become Gaussian (Fig.1d); the wider velocity distribution in the sandstone gives rise to a small immobile concentration peak, and a large secondary mobile peak moving at approximately the average flow speed (Fig.1e); in the carbonate with the widest velocity distribution the stagnant concentration peak is persistent, while the emergence of a smaller secondary mobile peak is observed, leading to a highly anomalous behavior (Fig.1f). This defines different generic nature of transport in the three media and quantifies the effect of pore structure on transport. Moreover, the
Elhandi, S.; Taj, S.; Attaourti, Y.; Manaut, B.; Oufni, L.
2010-04-15
The effect of the electron's anomalous magnetic moment on the relativistic electronic dressing for the process of electron-hydrogen atom elastic collisions is investigated. We consider a laser field with circular polarization and various electric field strengths. The Dirac-Volkov states taking into account this anomaly are used to describe the process in the first order of perturbation theory. The correlation between the terms coming from this anomaly and the electric field strength gives rise to the strong dependence of the spinor part of the differential cross section (DCS) with respect to these terms. A detailed study has been devoted to the nonrelativistic regime as well as the moderate relativistic regime. Some aspects of this dependence as well as the dynamical behavior of the DCS in the relativistic regime have been addressed.
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.
Investigation of Anomalous Behavior in Metallic-Based Materials Under Compressive Loading
NASA Technical Reports Server (NTRS)
Gil, Christopher M.; Lissenden, Cliff J.; Lerch, Bradley A.
1998-01-01
An anomalous material response has been observed under the action of applied compressive loads in fibrous SiC/Ti (both Ti-6242 and Ti-15-3 alloys) and the monolithic nickel-base alloy IN-718 in the aged condition. The observed behavior is an increase, rather than a decrease, in the instantaneous Young's modulus with increasing load. This increase is small, but can be significant in yield surface determination tests, where an equivalent offset strain on the order of 10 micron(1 x 10(exp -6) m/m) is being used. Stiffening has been quantified by calculating offset strains from the linear elastic loading line. The offset strains associated with stiffening during compressive loading are positive and of the same order as the target offset strains in yield surface determination tests. At this time we do not have a reasonable explanation for this response nor can we identify a deformation mechanism that might cause it. On the other hand, we are not convinced that it is an artifact of the experimental procedure because a number of issues have been identified and seemingly ruled out. In fact, stiffening appears to be temperature dependent, since it decreases as the temperature increases.
Asymptotic Behavior of Anomalous Diffusions Driven by alpha -Stable Noise
NASA Astrophysics Data System (ADS)
Michna, Z.
2008-08-01
In this paper we discuss decomposition principle for alpha -stable Lévy processes. We investigate asymptotic properties of components and stochastic integrals driven by such processes providing an important class of anomalous diffusions. We consider two case studies with integrands being fractional Brownian motion and gamma process.
Elastic-plastic behavior of non-woven fibrous mats
NASA Astrophysics Data System (ADS)
Silberstein, Meredith N.; Pai, Chia-Ling; Rutledge, Gregory C.; Boyce, Mary C.
2012-02-01
Electrospinning is a novel method for creating non-woven polymer mats that have high surface area and high porosity. These attributes make them ideal candidates for multifunctional composites. Understanding the mechanical properties as a function of fiber properties and mat microstructure can aid in designing these composites. Further, a constitutive model which captures the membrane stress-strain behavior as a function of fiber properties and the geometry of the fibrous network would be a powerful design tool. Here, mats electrospun from amorphous polyamide are used as a model system. The elastic-plastic behavior of single fibers are obtained in tensile tests. Uniaxial monotonic and cyclic tensile tests are conducted on non-woven mats. The mat exhibits elastic-plastic stress-strain behavior. The transverse strain behavior provides important complementary data, showing a negligible initial Poisson's ratio followed by a transverse:axial strain ratio greater than -1:1 after an axial strain of 0.02. A triangulated framework has been developed to emulate the fibrous network structure of the mat. The micromechanically based model incorporates the elastic-plastic behavior of single fibers into a macroscopic membrane model of the mat. This representative volume element based model is shown to capture the uniaxial elastic-plastic response of the mat under monotonic and cyclic loading. The initial modulus and yield stress of the mat are governed by the fiber properties, the network geometry, and the network density. The transverse strain behavior is linked to discrete deformation mechanisms of the fibrous mat structure including fiber alignment, fiber bending, and network consolidation. The model is further validated in comparison to experiments under different constrained axial loading conditions and found to capture the constraint effect on stiffness, yield, post-yield hardening, and post-yield transverse strain behavior. Due to the direct connection between
Anomalous behavior of 1/f noise in graphene near the charge neutrality point
NASA Astrophysics Data System (ADS)
Takeshita, Shunpei; Matsuo, Sadashige; Tanaka, Takahiro; Nakaharai, Shu; Tsukagoshi, Kazuhito; Moriyama, Takahiro; Ono, Teruo; Arakawa, Tomonori; Kobayashi, Kensuke
2016-03-01
We investigate the noise in single layer graphene devices from equilibrium to far-from equilibrium and found that the 1/f noise shows an anomalous dependence on the source-drain bias voltage (VSD). While the Hooge's relation is not the case around the charge neutrality point, we found that it is recovered at very low VSD region. We propose that the depinning of the electron-hole puddles is induced at finite VSD, which may explain this anomalous noise behavior.
Model for the elastic behavior near intermartensitic transitions
NASA Astrophysics Data System (ADS)
Dai, Liyang; Cullen, James; Wuttig, Manfred
2005-05-01
Transitions between different martensitic states have been observed in Ni0.50Mn0.284Ga0.216 using elastic constant measurements. In this paper, we develop a model to explain the reentrant behavior based on a Landau expansion of the free energy in strain space. Here, we assume that the coefficient of the third-order term as well as the second-order term has significant temperature dependence. This assumption results in a C' versus temperature in good agreement with observation. The model and possible modifications to it are discussed and compared to the elastic constant data.
Anomalous postcritical refraction behavior for certain transversely isotropic media
Fa, L.; Brown, R.L.; Castagna, J.P.
2006-01-01
Snell's law at the boundary between two transversely isotropic media with a vertical axis of symmetry (VTI media) can be solved by setting up a fourth order polynomial for the sine of the reflection/transmission angles. This approach reveals the possible presence of an anomalous postcritical angle for certain transversely isotropic media. There are thus possibly three incident angle regimes for the reflection/refraction of longitudinal or transverse waves incident upon a VTI medium: precritical, postcritical/preanomalous, and postanomalous. The anomalous angle occurs for certain strongly anisotropic media where the required root to the phase velocity equation must be switched in order to obey Snell's law. The reflection/transmission coefficients, polarization directions, and the phase velocity are all affected by both the anisotropy and the incident angle. The incident critical angles are also effected by the anisotropy. ?? 2006 Acoustical Society of America.
Degree-strength correlation reveals anomalous trading behavior.
Sun, Xiao-Qian; Shen, Hua-Wei; Cheng, Xue-Qi; Wang, Zhao-Yang
2012-01-01
Manipulation is an important issue for both developed and emerging stock markets. Many efforts have been made to detect manipulation in stock markets. However, it is still an open problem to identify the fraudulent traders, especially when they collude with each other. In this paper, we focus on the problem of identifying the anomalous traders using the transaction data of eight manipulated stocks and forty-four non-manipulated stocks during a one-year period. By analyzing the trading networks of stocks, we find that the trading networks of manipulated stocks exhibit significantly higher degree-strength correlation than the trading networks of non-manipulated stocks and the randomized trading networks. We further propose a method to detect anomalous traders of manipulated stocks based on statistical significance analysis of degree-strength correlation. Experimental results demonstrate that our method is effective at distinguishing the manipulated stocks from non-manipulated ones. Our method outperforms the traditional weight-threshold method at identifying the anomalous traders in manipulated stocks. More importantly, our method is difficult to be fooled by colluded traders. PMID:23082114
Degree-Strength Correlation Reveals Anomalous Trading Behavior
Sun, Xiao-Qian; Shen, Hua-Wei; Cheng, Xue-Qi; Wang, Zhao-Yang
2012-01-01
Manipulation is an important issue for both developed and emerging stock markets. Many efforts have been made to detect manipulation in stock markets. However, it is still an open problem to identify the fraudulent traders, especially when they collude with each other. In this paper, we focus on the problem of identifying the anomalous traders using the transaction data of eight manipulated stocks and forty-four non-manipulated stocks during a one-year period. By analyzing the trading networks of stocks, we find that the trading networks of manipulated stocks exhibit significantly higher degree-strength correlation than the trading networks of non-manipulated stocks and the randomized trading networks. We further propose a method to detect anomalous traders of manipulated stocks based on statistical significance analysis of degree-strength correlation. Experimental results demonstrate that our method is effective at distinguishing the manipulated stocks from non-manipulated ones. Our method outperforms the traditional weight-threshold method at identifying the anomalous traders in manipulated stocks. More importantly, our method is difficult to be fooled by colluded traders. PMID:23082114
Anomalous magnetic behavior at the graphene/Co interface
Mandal, Sumit; Saha, Shyamal K.
2014-07-14
An intensive theoretical study on the interaction between graphene and transition metal atom has been carried out; however, its experimental verification is still lacking. To explore the theoretical prediction of antiferromagnetic coupling due to charge transfer between graphene and cobalt, epitaxial layer of cobalt is grown on graphene surface. Predicted antiferromagnetic interaction with Neel temperature (T{sub N} ∼ 32 K) which anomalously shifts to higher temperature (34 K) and becomes more prominent under application of magnetic field of 1 T is reported. Lowering of magnetoresistance as a consequence of this antiferromagnetic coupling at the interface is also observed.
Subdiffusion in an external potential: Anomalous effects hiding behind normal behavior
NASA Astrophysics Data System (ADS)
Fedotov, Sergei; Korabel, Nickolay
2015-04-01
We propose a model of subdiffusion in which an external force is acting on a particle at all times not only at the moment of jump. The implication of this assumption is the dependence of the random trapping time on the force with the dramatic change of particles behavior compared to the standard continuous time random walk model in the long time limit. Constant force leads to the transition from non-ergodic subdiffusion to ergodic diffusive behavior. However, we show this behavior remains anomalous in a sense that the diffusion coefficient depends on the external force and on the anomalous exponent. For quadratic potential we find that the system remains non-ergodic. The anomalous exponent in this case defines not only the speed of convergence but also the stationary distribution which is different from standard Boltzmann equilibrium.
Elastic/viscoplastic behavior of fiber-reinforced thermoplastic composites
NASA Technical Reports Server (NTRS)
Wang, C.; Sun, C. T.; Gates, T. S.
1990-01-01
An elastic/viscoplastic constitutive model was used to characterize the nonlinear and rate dependent behavior of a continuous fiber-reinforced thermoplastic composite. This model was incorporated into a finite element program for the analysis of laminated plates and shells. Details on the finite element formulation with the proposed constitutive model were presented. The numerical results were compared with experimental data for uniaxial tension and three-point bending tests of (+ or - 45 deg)3s APC-2 laminates.
Dynamically strained ferroelastics: Statistical behavior in elastic and plastic regimes
NASA Astrophysics Data System (ADS)
Ding, X.; Lookman, T.; Zhao, Z.; Saxena, A.; Sun, J.; Salje, E. K. H.
2013-03-01
The dynamic evolution in ferroelastic crystals under external shear is explored by computer simulation of a two-dimensional model. The characteristic geometrical patterns obtained during shear deformation include dynamic tweed in the elastic regime as well as interpenetrating needle domains in the plastic regime. As a result, the statistics of jerk energy differ in the elastic and plastic regimes. In the elastic regime the distributions of jerk energy are sensitive to temperature and initial configurations. However, in the plastic regime the jerk distributions are rather robust and do not depend much on the details of the configurations, although the geometrical pattern formed after yield is strongly influenced by the elastic constants of the materials and the configurations we used. Specifically, for all geometrical configurations we studied, the energy distribution of jerks shows a power-law noise pattern P(E)˜E-(γ-1)(γ-1=1.3-2) at low temperatures and a Vogel-Fulcher distribution P(E) ˜ exp-(E/E0) at high temperatures. More complex behavior occurs at the crossover between these two regimes where our simulated jerk distributions are very well described by a generalized Poisson distributions P(E)˜E-(γ-1) exp-(E/E0)n with n = 0.4-0.5 and γ-1 ≈ 0 (Kohlrausch law). The geometrical mechanisms for the evolution of the ferroelastic microstructure under strain deformation remain similar in all thermal regimes, whereas their thermodynamic behavior differs dramatically: on heating, from power-law statistics via the Kohlrausch law to a Vogel-Fulcher law. There is hence no simple way to predict the local evolution of the twin microstructure from just the observed statistical behavior of a ferroelastic crystal. It is shown that the Poisson distribution is a convenient way to describe the crossover behavior contained in all the experimental data without recourse to specific scaling functions or temperature-dependent cutoff lengths.
Abnormal Elastic and Vibrational Behaviors of Magnetite at High Pressures
Lin, Jung-Fu; Wu, Junjie; Zhu, Jie; Mao, Zhu; Said, Ayman H.; Leu, Bogdan M.; Cheng, Jinguang; Uwatoko, Yoshiya; Jin, Changqing; Zhou, Jianshi
2014-01-01
Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe2+-Fe3+-Fe2+ ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature. PMID:25186916
Abnormal Elastic and Vibrational Behaviors of Magnetite at High Pressures
NASA Astrophysics Data System (ADS)
Lin, Jung-Fu; Wu, Junjie; Zhu, Jie; Mao, Zhu; Said, Ayman H.; Leu, Bogdan M.; Cheng, Jinguang; Uwatoko, Yoshiya; Jin, Changqing; Zhou, Jianshi
2014-09-01
Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe2+-Fe3+-Fe2+ ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature.
Abnormal elastic and vibrational behaviors of magnetite at high pressures.
Lin, Jung-Fu; Wu, Junjie; Zhu, Jie; Mao, Zhu; Said, Ayman H; Leu, Bogdan M; Cheng, Jinguang; Uwatoko, Yoshiya; Jin, Changqing; Zhou, Jianshi
2014-01-01
Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe(2+)-Fe(3+)-Fe(2+) ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature. PMID:25186916
Evolution of anomalous Hall behavior in thin Pt/Co/Pt trilayers
NASA Astrophysics Data System (ADS)
Sun, Niu-yi; Zhang, Yan-qing; Che, Wen-ru; Shan, Rong; Zhu, Zhen-gang
2016-05-01
In this work, through controlling spin scattering mechanisms, anomalous Hall behaviors exhibit a series of evolutions in thin Pt/Co/Pt trilayers. The shape of Hall resistivity over longitudinal resistivity (ρAH /ρxx versus ρxx) curve turns from bending to linear and then bending again in most trilayers. This kind of evolution cannot be explained by the conventional linear scaling of anomalous Hall effect. It should be ascribed to the contribution of spin-phonon skew scattering. Our research may help to understand spin scattering behavior in low-dimensional systems more deeply and build a proper synergy between theory and experiment on the research of anomalous Hall effect.
NASA Astrophysics Data System (ADS)
Hopersky, A. N.; Yavna, V. A.; Popov, V. A.
1997-11-01
Within the non-relativistic approximation the effect of radial monopole rearrangement of electron shells within the field of a vacancy and of the processes of one-photon double excitation - ionization on the differential cross section of anomalous non-zero-angle elastic scattering of linearly polarized x-ray photons by the Xe atom in the region of its 1s-shell ionization threshold is studied. Theoretical results for the anomalous dispersion region of scattering demonstrate a strong dependence of the cross section value on the approximation used.
NASA Astrophysics Data System (ADS)
Renaud, G.; Le Bas, P.; Ten Cate, J. A.; Ulrich, T. J.; Carey, J. W.; Han, J.; Darling, T. W.; Johnson, P. A.
2011-12-01
Unraveling the physics of the earthquake source, reliable sequestration of CO2, predicting wellbore breakout in oil and gas reservoirs, monitoring thermal damage to rock in nuclear waste storage, and probing cement integrity require new approaches to material characterization and imaging. The elastic nonlinear material response is extremely promising in this regard. A persistent problem has been the direct relation between elastic nonlinearity and mechanical damage, because a reliable physics-based theory does not yet exist; however, recent work in medical nonlinear acoustics has led to an experimental breakthrough in measuring material nonlinear response. The breakthrough, termed Dynamic Acousto-Elasticity Testing (e.g., Renaud et al, 2008), has significant implication to development of a physics based theory, and thus ultimately to our ability to directly relate nonlinear material behavior to damage. The method provides the means to dynamically study the velocity-pressure and attenuation-pressure behaviors through the full wave cycle in contrast to most methods that measure average response (e.g., Nonlinear Resonance Ultrasound Spectroscopy [e.g., Guyer and Johnson, 2009]). The method relies on exciting a sample with a low frequency vibration in order to cycle it through stress-strain multiple times. Simultaneously, a high frequency ultrasonic source applies pulses and the change in wavespeed as a function of the low frequency stress is measured. In crystalline rock, we expect that the elastic nonlinearity arises from the microcracks and dislocations contained within individual crystals. In contrast, sandstones, limestones and other sedimentary rocks may have other origin(s) of elastic nonlinearity that are currently under debate. Thus we can use a crystalline sample as a point of reference from which to extrapolate to other sources of nonlinear mechanisms. We report results from our preliminary studies applying a number of room-dry rock samples of differing rock
Elastic response and phase behavior in binary liquid crystal mixtures.
Sidky, Hythem; Whitmer, Jonathan K
2016-05-11
Utilizing density-of-states simulations, we perform a full mapping of the phase behavior and elastic responses of binary liquid crystalline mixtures represented by the multicomponent Lebwohl-Lasher model. Our techniques are able to characterize the complete phase diagram, including nematic-nematic phase separation predicted by mean-field theories, but previously not observed in simulations. Mapping this phase diagram permits detailed study of elastic properties across the miscible nematic region. Importantly, we observe for the first time local phase separation and disordering driven by the application of small linear perturbations near the transition temperature and more significantly through nonlinear stresses. These findings are of key importance in systems of blended nematics which contain particulate inclusions, or are otherwise confined. PMID:27093188
Anomalous elastic behaviour of hydrous sanidine megacrysts from the Eifel, Germany
NASA Astrophysics Data System (ADS)
Schreuer, Jürgen; Demtröder, Kathrin; Sondergeld, Peter; Dehn, Sara
2010-05-01
Sanidine megacrystals from Volkesfeld (Riedener Kessel, East Eifel volcanic field) are well known for their fast irreversible changes of optical properties at moderately high annealing temperatures (starting from 750°C) [1]. These unique optical effects are probably related to fast changes of the Al/Si-order, the origin of which is not yet understood. Polarised infrared spectra and NMR studies indicate a relatively high amount of water (about 200 wt-ppm) in the Eifel sanidines compared to low-sanidine crystals from Madagascar (~ 1 wt-ppm) [2,3] possessing no unusual optical properties at high temperatures. In order to clarify the role of water for the observed anomalies, we investigated the elastic properties of sanidine megacrystals from four different eruptive centres (Essingen, Kerpen, Rockeskyll, Volkesfeld) of the quarternary volcanic fields of the Eifel between room temperature and 1100°C with the aid of resonant ultrasound spectroscopy (RUS). Low-sanidine from Madagascar served as a reference. The Eifel sanidine megacrystals are all very similar in respect to their chemical and structural properties. The chemical composition NaxK1-xAlSi3O8 as obtained by EMPA varies between x = 0.15 (east Eifel volcanic field) and 0.27 (west Eifel volcanic field) with up to 2 at-% celsian and less than 0.02 at-% anorthite. High-resolution DSC and thermogravimetric measurements revealed an irreversible weight loss at about 950°C which corresponds to about 250 wt-ppm H2O. Single crystal structure analyses yielded 2t1 ≈ 0.58 for the Al-occupation of the t1 tetrahedral position indicating nearly fully disordered high-sanidines. For comparison, the potassium-rich low-sanidines from Madagascar are characterised by 2t1 = 0.69. The temperature evolution of the elastic constants of 'dry' Madagascar sanidine is monotonic and fully reversible in successive runs. However, at about 890°C a small peak appears in the ultrasound attenuation above a slowly rising background. In
Anomalous swimming behavior of bacteria in nematic liquid crystals
NASA Astrophysics Data System (ADS)
Sokolov, Andrey; Zhou, Shuang; Lavrentovich, Oleg; Aranson, Igor
2015-03-01
Flagellated bacteria stop swimming in isotropic media of viscosity higher than 0.06kgm-1s-1. However, Bacillus Subtilis slows down by only about 30% in a nematic chromonic liquid crystal (CLC, 14wt% DSCG in water), where the anisotropic viscosity can be as high as 6kgm-1s-1. The bacteria velocity (Vb) is linear with the flagella rotation frequency. The phase velocity of the flagella Vf ~ 2Vb in LC, as compared to Vf ~ 10Vb in water. The flow generated by the bacteria is localized along the bacterial body axis, decaying slowly over tens of micrometers along, but rapidly over a few micrometers across this axis. The concentrated flow grants the bacteria new ability to carry cargo particles in LC, ability not seen in their habitat isotropic media. We attribute these anomalous features to the anisotropy of viscosity of the CLC, namely, the viscosities of splay and twist is hundreds times higher than that of bend deformation, which provides extra boost of swimming efficiency and enables the bacteria swim at considerable speed in a viscous medium. Our findings can potentially lead to applications such as particle transportation in microfluidic devices. A.S and I.A are supported by the US DOE, Office of Science, BES, Materials Science and Engineering Division. S.Z. and O.D.L are supported by NSF DMR 1104850, DMS-1434185.
Anomalous rheological behavior of long glass fiber reinforced polypropylene
NASA Astrophysics Data System (ADS)
Kim, Dong Hak; Lee, Young Sil; Son, Younggon
2012-12-01
Dynamic rheological properties of PP-based long glass fiber-reinforced thermoplastics (LFT) were investigated. Weight fractions of the glass fibers investigated in the present study ranged from 0.15 to 0.5, which are higher than those of previous studies. We observed very abnormal rheological behavior. Complex viscosity (η*) of the LFT increased with the glass fiber content up to 40 wt. %. However, the η* with a weight fraction of 0.5 is observed to be lower than that of LFT with a weight fraction of 0.4 in spite of higher glass fiber content. From various experiments, we found that this abnormal behavior is analogous to the rheological behavior of a lyotropic liquid crystalline polymer solution and concluded that the abnormal rheological behavior for the LFT is attributed to the formation of a liquid crystal- like structure at high concentrations of long glass fibers.
Elastic Behavior of pr Substituted Y-123 Superconducting Materials
NASA Astrophysics Data System (ADS)
Dole, B. N.; Purushotham, Y.; Reddy, P. Venugopal; Shah, S. S.
The longitudinal (Vl) and shear (Vs) wave velocities of Praseodymium substituted YB2Cu3O7-δ high temperature superconductors were determined at room temperature by the pulse transmission technique. The values of Young's (E), rigidity (n) and bulk (k) moduli have been corrected to zero porosity. The zero porous corrected values of the elastic moduli are found to increase with increasing Praseodymium concentration. A linear relationship between the Debye temperature (θD) and average sound velocity (Vm) has also been observed and the behavior is explained qualitatively.
Suppressing Anomalous Localized Waffle Behavior in Least Squares Wavefront Reconstructors
Gavel, D
2002-10-08
A major difficulty with wavefront slope sensors is their insensitivity to certain phase aberration patterns, the classic example being the waffle pattern in the Fried sampling geometry. As the number of degrees of freedom in AO systems grows larger, the possibility of troublesome waffle-like behavior over localized portions of the aperture is becoming evident. Reconstructor matrices have associated with them, either explicitly or implicitly, an orthogonal mode space over which they operate, called the singular mode space. If not properly preconditioned, the reconstructor's mode set can consist almost entirely of modes that each have some localized waffle-like behavior. In this paper we analyze the behavior of least-squares reconstructors with regard to their mode spaces. We introduce a new technique that is successful in producing a mode space that segregates the waffle-like behavior into a few ''high order'' modes, which can then be projected out of the reconstructor matrix. This technique can be adapted so as to remove any specific modes that are undesirable in the final reconstructor (such as piston, tip, and tilt for example) as well as suppress (the more nebulously defined) localized waffle behavior.
Anomalous bond length behavior and a new solid phase of bromine under pressure
Wu, Min; Tse, John S.; Pan, Yuanming
2016-01-01
The behavior of diatomic molecular solids under pressure have attracted great interest and been extensively studied. Under ambient pressure, the structure of bromine is known to be a molecular phase (phase I). With increasing pressure, it transforms into an incommensurate phase (phase V) before eventually to a monoatomic phase (phase II). However, between phases I and V, the interatomic distance was found to first increase with pressure and then decreased abruptly. This anomalous bond length behavior is accompanied by the splitting of the Raman bands. These phenomena have not been resolved. Here we suggest a new solid phase that explains the Raman spectra. Furthermore, the anomalous bond length behavior is found to be the result of subtle second neighbor intermolecular interactions and is an intrinsic property of bromine in molecular phases. PMID:27156710
Anomalous bond length behavior and a new solid phase of bromine under pressure.
Wu, Min; Tse, John S; Pan, Yuanming
2016-01-01
The behavior of diatomic molecular solids under pressure have attracted great interest and been extensively studied. Under ambient pressure, the structure of bromine is known to be a molecular phase (phase I). With increasing pressure, it transforms into an incommensurate phase (phase V) before eventually to a monoatomic phase (phase II). However, between phases I and V, the interatomic distance was found to first increase with pressure and then decreased abruptly. This anomalous bond length behavior is accompanied by the splitting of the Raman bands. These phenomena have not been resolved. Here we suggest a new solid phase that explains the Raman spectra. Furthermore, the anomalous bond length behavior is found to be the result of subtle second neighbor intermolecular interactions and is an intrinsic property of bromine in molecular phases. PMID:27156710
Anomalous bond length behavior and a new solid phase of bromine under pressure
NASA Astrophysics Data System (ADS)
Wu, Min; Tse, John S.; Pan, Yuanming
2016-05-01
The behavior of diatomic molecular solids under pressure have attracted great interest and been extensively studied. Under ambient pressure, the structure of bromine is known to be a molecular phase (phase I). With increasing pressure, it transforms into an incommensurate phase (phase V) before eventually to a monoatomic phase (phase II). However, between phases I and V, the interatomic distance was found to first increase with pressure and then decreased abruptly. This anomalous bond length behavior is accompanied by the splitting of the Raman bands. These phenomena have not been resolved. Here we suggest a new solid phase that explains the Raman spectra. Furthermore, the anomalous bond length behavior is found to be the result of subtle second neighbor intermolecular interactions and is an intrinsic property of bromine in molecular phases.
Anomalous compression behavior of germanium during phase transformation
Yan, Xiaozhi; Tan, Dayong; Ren, Xiangting; Yang, Wenge E-mail: duanweihe@scu.edu.cn; He, Duanwei E-mail: duanweihe@scu.edu.cn; Mao, Ho-Kwang
2015-04-27
In this article, we present the abnormal compression and plastic behavior of germanium during the pressure-induced cubic diamond to β-tin structure transition. Between 8.6 GPa and 13.8 GPa, in which pressure range both phases are co-existing, first softening and followed by hardening for both phases were observed via synchrotron x-ray diffraction and Raman spectroscopy. These unusual behaviors can be interpreted as the volume misfit between different phases. Following Eshelby, the strain energy density reaches the maximum in the middle of the transition zone, where the switch happens from softening to hardening. Insight into these mechanical properties during phase transformation is relevant for the understanding of plasticity and compressibility of crystal materials when different phases coexist during a phase transition.
Pentamodal behaviors and acoustic bandgaps of asymmetric pentamode elastic metamaterials
NASA Astrophysics Data System (ADS)
Huang, Yan; Lu, Xuegang; Liang, Gongying; Xu, Zhuo
2016-04-01
The asymmetric pentamode metamaterial structure which is built by connecting double-cones with different cross-section shapes (regular triangle, square, pentagon and hexagon) to form diamond lattice is proposed in this paper. Then its phonon band structure is calculated by finite-element method (FEM), and its pentamodal behaviors and acoustic bandgaps are studied in detail. Results show that in the process of adjusting geometrical parameters, the asymmetric case performs similar pentamodal behaviors [ratio of bulk modulus to shear modulus B/G and single-mode bandgap (SBG)] with the symmetric cases. And the asymmetric case not only remains the intrinsic complete bandgap (CBG) of mode 12-13 like symmetric cases, but also opens new and wide CBG of mode 10-11 and mode 14-15 for appropriate parameters. Therefore, introducing structural asymmetry should be an effective way to open CBG in pentamode elastic metamaterials.
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.
Explanation of Anomalous Behavior Observed in Impedance Eduction Techniques Using Measured Data
NASA Technical Reports Server (NTRS)
Watson, Willie R.; Jones, Michael G.
2010-01-01
Several enhancements that improve the accuracy and robustness of an impedance eduction technique that use an automatic optimizer are presented. These enhancements are then used to launch an intensive investigation into the cause of anomalous behavior that occurs for a small number of test conditions. This anomalous behavior is investigated for both a hardwall insert and a conventional liner. The primary conclusions of the study are that: (1) for the hard wall insert, the anomalies are due to narrow peaks in the objective function, (2) For the conventional liner, the anomalies are due to the presence of an extremely flat objective function, and (3) the anomalies appear to be triggered by inconsistencies between the duct propagation model and the measured data. At high frequencies, the duct propagation model may need to include the effects of higher-order duct modes, whereas at low frequencies, the effects of the mean boundary layer may have to be included.
Anomalous Thermal Behavior in Microcalorimeter Gamma-Ray Detectors
Horansky, Robert D.; Beall, James A.; Irwin, Kent D.; Ullom, Joel N.
2009-12-16
Improving the resolution of gamma-ray detectors is important for many fields, including determinations of the Lamb shift in atoms with high atomic numbers, nuclear treaty verification, and environmental monitoring. High-purity germanium detectors are currently the tool of choice for precision gamma-ray spectroscopy. The resolution of these detectors is limited to about 500 eV full-width-at-half-maximum at 100 keV by Fano statistics. In comparison, low-temperature microcalorimeters can provide over an order of magnitude improvement in photon resolution. For instance, a gamma-ray microcalorimeter has achieved 25 eV FWHM resolution at 103 keV. These calorimeters consist of two components, a bulk absorber to stop incident gamma rays and a thermometer made from a thin film electrically biased in the superconducting-to-normal phase transition, called a Transition Edge Sensor, or TES. The standard absorber is bulk, superconducting tin. While tin has historically been the best performing absorber, pulse decays in Sn devices are much slower than predicted. We have begun a systematic study of absorber behavior in order to assess and improve response times. This study leverages two capabilities: the ability to microfabricate highly uniform arrays of gamma-ray detectors and the ability to read out many detectors in a single cool-down using SQUID multiplexer circuits. Here, we present two experiments to identify the source of thermal time constants. The first involves varying properties of the Sn absorber including purity, vendor, and crystal grain size. The second examines the role of the other elements in the microcalorimeter assembly.
Mechanical behavior and elastic properties of prestrained columnar ice
NASA Astrophysics Data System (ADS)
Snyder, Scott Aaron
Experiments on columnar-grained ice at --10 °C reveal changes to its mechanical behavior and elastic properties due to compressive prestrain. Laboratory-grown (152-mm cube) specimens of freshwater and saline ice were prestrained under uniaxial across-column compression (to levels from epsilon p = 0.003 to epsilonp = 0.20, at constant strain rates in the ductile regime) and then reloaded, again under uniaxial across-column compression (at rates from 1x10--6 s--1 to 3 x 10--2s--1). Prestrain caused solid-state recrystallization as well as damage in the form of non-propagating microcracks. These microstructural changes were quantified by analysis of thin sections. Elastic properties in across-column directions, both parallel (x1) and perpendicular ( x2) to the initial loading direction, were obtained from P-wave and S-wave ultrasonic velocities. As a result (and depending on the level) of the prestrain imparted in both materials, Young's modulus E was reduced by as much as 30%; the ductile-to-brittle (D--B) transition strain rate epsilon D/B was increased up to a factor of 3 to 10; and the ductile behavior with respect to loading along a direction within the horizontal ( x1-x2) plane of the parent ice sheet changed from isotropic to anisotropic. As the prestrain rate approached the nominal D--B transition rate of initially undamaged material, the magnitudes of prestrain effects on elastic compliance increased. The shift in the D--B transition, on the other hand, was less sensitive to the prestrain rate. The results are interpreted within the framework of a recent model that predicts the transition strain rate based on the micromechanical boundary between creep and fracture processes. Prestrain primarily affected certain parameters in the model, specifically the power-law creep coefficient B (more so than the creep exponent n), Young's modulus E and, by extension, the fracture toughness KIc. The physical implications of these effects are discussed.
Anomalous scaling behavior and surface roughening in molecular thin-film deposition
Yim, S.; Jones, T. S.
2006-04-15
The thin film growth dynamics of a molecular semiconductor, free-base phthalocyanine (H{sub 2}Pc), deposited by organic molecular beam deposition, has been studied by atomic force microscopy (AFM) and height difference correlation function (HDCF) analysis. The measured dynamic scaling components ({alpha}{sub loc}=0.61{+-}0.12, {beta}=1.02{+-}0.08, and 1/z=0.72{+-}0.13) are consistent with rapid surface roughening and anomalous scaling behavior. A detailed analysis of AFM images and simple growth models suggest that this behavior arises from the pronounced upward growth of crystalline H{sub 2}Pc mounds during the initial stages of thin film growth.
Chatterjee, Achintya K.; Nandy, Nilmadhab; Bari, Md. Washimul; Choudhury, Asit K.
2010-10-20
The anomalous behavior of D-layer preparation time of the ionosphere are observed only before, during and after the earthquakes, which took place in the neighbouring region by monitoring the Very Low Frequency (VLF) signal using Gyrator II loop antenna. The anomalies were also observed in the sunrise terminator times during seismically active days. These anomalous behavior may be due to the Lithosphere-Ionosphere coupling. These anomalies may be a precursor of earthquake.
Anomalous behaviors of Wyrtki Jets in the equatorial Indian Ocean during 2013
Duan, Yongliang; Liu, Lin; Han, Guoqing; Liu, Hongwei; Yu, Weidong; Yang, Guang; Wang, Huiwu; Wang, Haiyuan; Liu, Yanliang; Zahid; Waheed, Hussain
2016-01-01
In-situ measurement of the upper ocean velocity discloses significant abnormal behaviors of two Wyrtki Jets (WJs) respectively in boreal spring and fall, over the tropical Indian Ocean in 2013. The two WJs both occurred within upper 130 m depth and persisted more than one month. The exceptional spring jet in May was unusually stronger than its counterpart in fall, which is clearly against the previous understanding. Furthermore, the fall WJ in 2013 unexpectedly peaked in December, one month later than its climatology. Data analysis and numerical experiments illustrate that the anomalous changes in the equatorial zonal wind, associated with the strong intra-seasonal oscillation events, are most likely the primary reason for such anomalous WJs activities. PMID:27436723
Anomalous behaviors of Wyrtki Jets in the equatorial Indian Ocean during 2013
NASA Astrophysics Data System (ADS)
Duan, Yongliang; Liu, Lin; Han, Guoqing; Liu, Hongwei; Yu, Weidong; Yang, Guang; Wang, Huiwu; Wang, Haiyuan; Liu, Yanliang; Zahid; Waheed, Hussain
2016-07-01
In-situ measurement of the upper ocean velocity discloses significant abnormal behaviors of two Wyrtki Jets (WJs) respectively in boreal spring and fall, over the tropical Indian Ocean in 2013. The two WJs both occurred within upper 130 m depth and persisted more than one month. The exceptional spring jet in May was unusually stronger than its counterpart in fall, which is clearly against the previous understanding. Furthermore, the fall WJ in 2013 unexpectedly peaked in December, one month later than its climatology. Data analysis and numerical experiments illustrate that the anomalous changes in the equatorial zonal wind, associated with the strong intra-seasonal oscillation events, are most likely the primary reason for such anomalous WJs activities.
Anomalous behaviors of Wyrtki Jets in the equatorial Indian Ocean during 2013.
Duan, Yongliang; Liu, Lin; Han, Guoqing; Liu, Hongwei; Yu, Weidong; Yang, Guang; Wang, Huiwu; Wang, Haiyuan; Liu, Yanliang; Zahid; Waheed, Hussain
2016-01-01
In-situ measurement of the upper ocean velocity discloses significant abnormal behaviors of two Wyrtki Jets (WJs) respectively in boreal spring and fall, over the tropical Indian Ocean in 2013. The two WJs both occurred within upper 130 m depth and persisted more than one month. The exceptional spring jet in May was unusually stronger than its counterpart in fall, which is clearly against the previous understanding. Furthermore, the fall WJ in 2013 unexpectedly peaked in December, one month later than its climatology. Data analysis and numerical experiments illustrate that the anomalous changes in the equatorial zonal wind, associated with the strong intra-seasonal oscillation events, are most likely the primary reason for such anomalous WJs activities. PMID:27436723
Novel negative Poisson's ratio behavior induced by an elastic instability
NASA Astrophysics Data System (ADS)
Bertoldi, Katia; Reis, Pedro; Willshaw, Stephen; Mullin, Tom
2010-03-01
When materials are compressed along a particular axis they are most commonly observed to expand in directions orthogonal to the applied load. The property that characterizes this behavior is the Poisson's ratio which is defined as the ratio between the negative transverse and longitudinal strains. Materials with a negative Poisson's ratio will contract in the transverse direction when compressed and demonstration of practical examples is relatively recent. A significant challenge in the fabrication of auxetic materials is that it usually involves embedding structures with intricate geometries within a host matrix. As such, the manufacturing process has been a bottleneck in the practical development towards applications. Here we exploit elastic instabilities to create novel effects within materials with periodic microstructure and we show that they may lead to negative Poisson's ratio behavior for the 2D periodic structures i.e. it only occurs under compression. The uncomplicated manufacturing process of the samples together with the robustness of the observed phenomena suggests that this may form the basis of a practical method for constructing planar auxetic materials over a wide range of length-scales.
NASA Astrophysics Data System (ADS)
Hopersky, A. N.; Novikov, S. A.; Chuvenkov, V. V.
2002-04-01
The absolute values and shape of differential cross-section of the process of the anomalous elastic scattering for non-zero angle are investigated within non-relativistic approximation for linearly polarized X-ray radiation scattered by multicharged atomic ions Ne 6+ in the range of the ionization threshold of 1 s-shell. The many-particle effects of radial rearrangement of electron shells in the field of an inner 1 s-vacancy and the effect of vacancy stabilization are taken into account. The results of the work are predictions.
Anomalous glass transition behavior of SBR-Al2O3 nanocomposites at small filler concentrations
NASA Astrophysics Data System (ADS)
Sushko, Rymma; Filimon, Marlena; Dannert, Rick; Elens, Patrick; Sanctuary, Roland; Baller, Jörg
2014-10-01
Elastomers filled with hard nanoparticles are of great technical importance for the rubber industry. In general, fillers improve mechanical properties of polymer materials, e.g. elastic moduli, tensile strength etc. The smaller the size of the particles, the larger is the interface where interactions between polymer molecules and fillers can generate new properties. Using temperature-modulated differential scanning calorimetry and dynamic mechanical analysis, we investigated the properties of pure styrene-butadiene rubber (SBR) and SBR/alumina nanoparticles. Beside a reinforcement effect seen in the complex elastic moduli, small amounts of nanoparticles of about 2 wt% interestingly lead to an acceleration of the relaxation modes responsible for the thermal glass transition. This leads to a minimum in the glass transition temperature as a function of nanoparticle content in the vicinity of this critical concentration. The frequency dependent elastic moduli are used to discuss the possible reduction of the entanglement of rubber molecules as one cause for this unexpected behavior.
Investigation of Sludge Batch 3 (Macrobatch 4) Glass Sample Anomalous Behavior
Bannochie, C. J.; Bibler, N. E.; Peeler, D. K.
2005-08-15
Two Defense Waste Processing Facility (DWPF) glass samples from Sludge Batch 3 (SB3) (Macrobatch 4) were received by the Savannah River National Laboratory (SRNL) on February 23, 2005. One sample, S02244, was designated for the Product Consistency Test (PCT) and elemental and radionuclide analyses. The second sample, S02247, was designated for archival storage. The samples were pulled from the melter pour stream during the feeding of Melter Feed Tank (MFT) Batch 308 and therefore roughly correspond to feed from Slurry Mix Evaporator (SME) Batches 306-308. During the course of preparing sample S02244 for PCT and other analyses two observations were made which were characterized as ''unusual'' or anomalous behavior relative to historical observations of glasses prepared for the PCT. These observations ultimately led to a series of scoping tests in order to determine more about the nature of the behavior and possible mechanisms. The first observation was the behavior of the ground glass fraction (-100 +200 mesh) for PCT analysis when contacted with deionized water during the washing phase of the PCT procedure. The behavior was analogous to that of an organic compound in the presence of water: clumping, floating on the water surface, and crawling up the beaker walls. In other words, the glass sample did not ''wet'' normally, displaying a hydrophobic behavior in water. This had never been seen before in 18 years SRNL PCT tests on either radioactive or non-radioactive glasses. Typical glass behavior is largely to settle to the bottom of the water filled beaker, though there may be suspended fines which result in some cloudiness to the wash water. The typical appearance is analogous to wetting sand. The second observation was the presence of faint black rings at the initial and final solution levels in the Teflon vessels used for the mixed acid digestion of S02244 glass conducted for compositional analysis. The digestion is composed of two stages, and at both the
Anomalous photoconductive behavior of a single InAs nanowire photodetector
Li, Junshuai; Yan, Xin; Sun, Fukuan; Zhang, Xia Ren, Xiaomin
2015-12-28
We report on a bare InAs nanowire photodetector which exhibits an anomalous photoconductive behavior. Under low-power illumination, the current is smaller than the dark current, and monotonously decreases as the excitation power increases. When the excitation power is high enough, the current starts to increase normally. The phenomenon is attributed to different electron mobilities in the “core” and “shell” of a relatively thick nanowire originating from the surface effect, which result in a quickly dropped “core current” and slowly increased “shell current” under illumination.
Investigation of Anomalous Sputtering Behavior of a Ga-In Target
NASA Astrophysics Data System (ADS)
Nunn, Dale R.; Weathers, D. L.; Burns, L. R.; Kadam, P.; Li, S.
2006-12-01
Nonstoichiometric sputtering has been studied for decades, in part because of its potential role in modifying the composition of materials in the inner Solar System. Sputtering of multi-component materials typically results in lighter atoms/isotopes sputtering at average angles closer to the target normal than heavier atoms/isotopes in the absence of chemical influences, but Ga-In may not adhere to this. There is a hint of experimental evidence that the isotopes of Ga sputtered from this target exhibit the opposite behavior. We present computer simulation results that also suggest this anomalous behavior, and discuss a new experiment we are conducting to probe this behavior in more detail. In the experiment, material sputtered by Ar+ is collected on carbon foil, which is analyzed after collection to determine the angular distribution of sputtered material. Analysis of the collector foils utilizes two techniques, SIMS (Secondary Ion Mass Spectrometry) and RBS (Rutherford Backscattering Spectrometry).
Anomalous anisotropic compression behavior of superconducting CrAs under high pressure
Yu, Zhenhai; Wu, Wei; Hu, Qingyang; Zhao, Jinggeng; Li, Chunyu; Yang, Ke; Cheng, Jinguang; Luo, Jianlin; Wang, Lin; Mao, Ho-kwang
2015-01-01
CrAs was observed to possess the bulk superconductivity under high-pressure conditions. To understand the superconducting mechanism and explore the correlation between the structure and superconductivity, the high-pressure structural evolution of CrAs was investigated using the angle-dispersive X-ray diffraction (XRD) method. The structure of CrAs remains stable up to 1.8 GPa, whereas the lattice parameters exhibit anomalous compression behaviors. With increasing pressure, the lattice parameters a and c both demonstrate a nonmonotonic change, and the lattice parameter b undergoes a rapid contraction at ∼0.18−0.35 GPa, which suggests that a pressure-induced isostructural phase transition occurs in CrAs. Above the phase transition pressure, the axial compressibilities of CrAs present remarkable anisotropy. A schematic band model was used to address the anomalous compression behavior of CrAs. The present results shed light on the structural and related electronic responses to high pressure, which play a key role toward understanding the superconductivity of CrAs. PMID:26627230
NASA Astrophysics Data System (ADS)
Shabbir, G.; Kojima, S.
2014-03-01
The acoustic phonon mode anomalies in the paraelectric phase of tetragonal and rhombohedral (1 - x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 single crystals were systematically investigated by Brillouin light scattering measurements. The inverse relaxation time in the paraelectric phase of both crystals showed a stretched-type slowing-down temperature dependence approaching the structural phase transition temperature (T_{\\text{C}}) instead of a normal critical slowing-down. The observed anomalous part of the elastic constant (c_{11}) in the paraelectric phase of the tetragonal crystal in the vicinity of T_{\\text{C}} , exhibited a log(T-T_{0}/T_{0}) -type dependence in the temperature range from T_{\\text{C}} to \\sim T_{\\text{C}}+80\\ ^\\circ \\text{C} . On the other hand, the elastic constant of the rhombohedral ferroelectric crystal exhibited a deviation from such a temperature dependence. This was attributed to the interaction of acoustic phonon modes with strong polarization fluctuations and elastic deformation arising from the complex dynamics of polar nanoregions.
Anomalous ion-channeling behavior across the superconducting transition in high-T(sub c) materials
NASA Astrophysics Data System (ADS)
Rehn, L. E.; Sharma, R. P.; Baldo, P. M.; Liu, J. Z.
1989-07-01
Axial channeling scans with minimum RBS yields of less than or = 2 percent were obtained for 1.5 MeV He-4 ions incident along the c-axis in YBa2Cu3O(7-delta) and ErBa2Cu3O(7-delta) single crystals. Large variations in the FWHM of the (001) channeling dip were observed for temperatures between 30 and 300 K. An abrupt, (approx.) 8 percent increase was measured as the temperature was lowered through the superconducting transition T(sub c); the rela tive increase across T(sub c) in the width of the axial dip was even larger for angles of incidence less than the critical angle. A simple analytical procedure for polyatomic materials yields isotropic, average thermal vibrational amplitudes that agree well with considerably less precise neutron powder diffraction results on sintered samples. The individual contribution to the angular channeling dip from the row of Er and Ba atoms parallel to the c-axis can be isolated in the RBS scans of the Er compound. This separation reveals normal (Debye-type) behavior for atoms in the Er-Ba row, demonstrating that the anomalous changes are due solely to atomic displacements in the Cu-O row. Finally, x ray studies using specimens with different O stoichiometries reveal that the anomalous change in the FWHM shifts in temperature in direct proportion to the change in T(sub c).
Liu, Haozhe; Wang, Luhong; Xiao, Xianghui; De Carlo, Francesco; Feng, Ji; Mao, Ho-kwang; Hemley, Russell J.
2008-01-01
The high-pressure behavior of amorphous selenium has been investigated with time-resolved diamond anvil cell synchrotron x-ray diffraction and computed microtomography techniques. A two-step dynamic crystallization process is observed in which the monoclinic phase crystallized from the amorphous selenium and gradually converted to the trigonal phase, thereby explaining previously observed anomalous changes in electrical conductivity of the material under pressure. The crystallization of this elemental system involves local topological fluctuations and results in an unusual pressure-induced volume expansion. The metastability of the phases involved in the transition accounts for this phenomenon. The results demonstrate the use of pressure to control and directly monitor the relative densities and energetics of phases to create new phases from highly metastable states. The microtomographic technique developed here represents a method for determination of the equations of state of amorphous materials at extreme pressures and temperatures. PMID:18768800
Theory of the anomalous critical behavior for the smectic-A -hexatic transition
NASA Astrophysics Data System (ADS)
Kats, E. I.; Lebedev, V. V.; Muratov, A. R.
2016-06-01
We propose a theoretical explanation for the long-standing problem of the anomalous critical behavior of the heat capacity near the smectic-A -hexatic phase transition. Experiments find a large specific heat critical exponent α =0.5 -0.7 , which is inconsistent with a small negative value α ≈-0.01 expected for the three-dimensional X Y universality class. We show that most of the observed features can be explained by treating simultaneously fluctuations of the hexatic orientational and translational (positional) order parameters. Assuming that the translational correlation length ξt r is much larger than the hexatic correlation length ξh, we calculate the temperature dependence of the heat capacity in the critical region near the smectic-A -hexatic phase transition. Our results are in quantitative agreement with the calorimetric experimental data.
Theory of the anomalous critical behavior for the smectic-A-hexatic transition.
Kats, E I; Lebedev, V V; Muratov, A R
2016-06-01
We propose a theoretical explanation for the long-standing problem of the anomalous critical behavior of the heat capacity near the smectic-A-hexatic phase transition. Experiments find a large specific heat critical exponent α=0.5-0.7, which is inconsistent with a small negative value α≈-0.01 expected for the three-dimensional XY universality class. We show that most of the observed features can be explained by treating simultaneously fluctuations of the hexatic orientational and translational (positional) order parameters. Assuming that the translational correlation length ξ_{tr} is much larger than the hexatic correlation length ξ_{h}, we calculate the temperature dependence of the heat capacity in the critical region near the smectic-A-hexatic phase transition. Our results are in quantitative agreement with the calorimetric experimental data. PMID:27415334
Anomalous pressure behavior of tangential modes in single-wall carbon nanotubes
NASA Astrophysics Data System (ADS)
Yang, Wei; Wang, Ru-Zhi; Wang, Yu-Fang; Song, Xue-Mei; Wang, Bo; Yan, Hui
2007-07-01
Using molecular-dynamics simulations and the force-constant model, we have studied the Raman-active tangential modes (TMs) of a (10,0) single-wall carbon nanotube under hydrostatic pressure. With increasing pressure, the atomic motions in the three TMs present obvious diversities. The pressure derivative of E1g , A1g , and E2g mode frequencies shows an increased value (dωE1g/dP>0) , a constant value (dωA1g/dP˜0) , and a negative value (dωE2g/dP<0) above 5.3GPa , respectively. The intrinsic characteristics of TMs consumedly help us understand the essence of the experimental T band of CNT. The anomalous pressure behavior of the TM frequencies may originate from the tube symmetry alteration from D10h to D2h then to C2h .
Anomalous Behavior of 2+ Excitations of Tellurium Isotopes around N = 82
NASA Astrophysics Data System (ADS)
Terasaki, J.; Engel, J.; Nazarewicz, W.; Stoitsov, M.
2003-10-01
In certain neutron-rich Te isotopes, a decrease in the energy of the first excited 2+ state is accompanied by a decrease in the E2 strength to that state from the ground state, contradicting simple systematics and general intuition about quadrupole collectivity. We use a separable quadrupole-plus-pairing Hamiltonian and the quasiparticle random phase approximation to calculate energies, B(E2,0+ → 2+) strengths, and g factors for the lowest 2+ states near 132Sn (Z ≥ 50). We trace the anomalous behavior in the Te isotopes to a reduced neutron pairing above the N = 82 magic gap. In addition, we briefly discuss the magicity of 68Ni.
Anomalous behavior of the energy gap in the one-dimensional quantum XY model.
Okuyama, Manaka; Yamanaka, Yuuki; Nishimori, Hidetoshi; Rams, Marek M
2015-11-01
We reexamine the well-studied one-dimensional spin-1/2 XY model to reveal its nontrivial energy spectrum, in particular the energy gap between the ground state and the first excited state. In the case of the isotropic XY model, the XX model, the gap behaves very irregularly as a function of the system size at a second order transition point. This is in stark contrast to the usual power-law decay of the gap and is reminiscent of the similar behavior at the first order phase transition in the infinite-range quantum XY model. The gap also shows nontrivial oscillatory behavior for the phase transitions in the anisotropic model in the incommensurate phase. We observe a close relation between this anomalous behavior of the gap and the correlation functions. These results, those for the isotropic case in particular, are important from the viewpoint of quantum annealing where the efficiency of computation is strongly affected by the size dependence of the energy gap. PMID:26651656
Decoupling Nonclassical Nonlinear Behavior of Elastic Wave Types
NASA Astrophysics Data System (ADS)
Remillieux, Marcel C.; Guyer, Robert A.; Payan, Cédric; Ulrich, T. J.
2016-03-01
In this Letter, the tensorial nature of the nonequilibrium dynamics in nonlinear mesoscopic elastic materials is evidenced via multimode resonance experiments. In these experiments the dynamic response, including the spatial variations of velocities and strains, is carefully monitored while the sample is vibrated in a purely longitudinal or a purely torsional mode. By analogy with the fact that such experiments can decouple the elements of the linear elastic tensor, we demonstrate that the parameters quantifying the nonequilibrium dynamics of the material differ substantially for a compressional wave and for a shear wave. This result could lead to further understanding of the nonlinear mechanical phenomena that arise in natural systems as well as to the design and engineering of nonlinear acoustic metamaterials.
Decoupling Nonclassical Nonlinear Behavior of Elastic Wave Types.
Remillieux, Marcel C; Guyer, Robert A; Payan, Cédric; Ulrich, T J
2016-03-18
In this Letter, the tensorial nature of the nonequilibrium dynamics in nonlinear mesoscopic elastic materials is evidenced via multimode resonance experiments. In these experiments the dynamic response, including the spatial variations of velocities and strains, is carefully monitored while the sample is vibrated in a purely longitudinal or a purely torsional mode. By analogy with the fact that such experiments can decouple the elements of the linear elastic tensor, we demonstrate that the parameters quantifying the nonequilibrium dynamics of the material differ substantially for a compressional wave and for a shear wave. This result could lead to further understanding of the nonlinear mechanical phenomena that arise in natural systems as well as to the design and engineering of nonlinear acoustic metamaterials. PMID:27035309
Transverse surface mechanical behavior and modified elastic modulus for charged nanostructures
NASA Astrophysics Data System (ADS)
Zhu, Linli; Zheng, Xiaojing
2008-09-01
The reversible surface stretch often emerges from the Hellman-Feynman forces exerted on the charged surfaces, leading to the change of the surface stress. A generalized surface elasticity theory is formulated, which allows one to analyze the transverse surface mechanical behavior. The involved transverse surface elastic constants are determined by an efficient method based on analyzing the process of molecular-dynamics simulation for surface elasticity. Our approach provides a framework with which the direct relation between the in-plane surface stress and the transverse surface elastic deformation is addressed in the presence of the surface charges. We also find the significant modification in the elastic modulus of nanostructures due to the existence of the transverse component of surface stress and strain arisen from the surface charges.
Nonlinear elastic behavior of phantom materials for elastography.
Pavan, Theo Z; Madsen, Ernest L; Frank, Gary R; Adilton O Carneiro, Antonio; Hall, Timothy J
2010-05-01
The development of phantom materials for elasticity imaging is reported in this paper. These materials were specifically designed to provide nonlinear stress/strain relationship that can be controlled independently of the small strain shear modulus of the material. The materials are mixtures of agar and gelatin gels. Oil droplet dispersions in these materials provide further control of the small strain shear modulus and the nonlinear parameter of the material. Since these materials are mostly water, they are assumed to be incompressible under typical experimental conditions in elasticity imaging. The Veronda-Westman model for strain energy density provided a good fit to all materials used in this study. Materials with a constant gelatin concentration (3.0% dry weight) but varying agar concentration (0.6-2.8% dry weight) demonstrated the same power law relationship between elastic modulus and agar concentration found for pure agar (1.89 +/- 0.02), consistent with percolation theory, and provided a consistent nonlinearity parameter of 4.5 +/- 0.3. The insights provided by this study will form the basis for stable elastography phantoms with stiffness and nonlinear stress/strain relationships in the background that differ from those in the target. PMID:20400811
Mazel, Vincent; Busignies, Virginie; Diarra, Harona; Tchoreloff, Pierre
2013-11-01
The elastic properties of pharmaceutical powders and compacts are of great interest to understand the complex phenomena that occur during and after the tableting process. The elastic recovery after compression is known to be linked with adverse phenomena such as capping or delamination of tablets. Classically, the elastic behavior is modeled using linear elasticity and is characterized using only Young's modulus (E), often by using a value extrapolated at zero porosity. In this work, four pharmaceutical products were studied. The elastic behavior of compacts obtained using a large range of applied pressure was characterized. First, it was found more suitable to use apparent elastic moduli than extrapolations at zero porosity. Then, the results indicate that there was not always a good correlation between the values of Young's modulus and the actual elastic recovery of the compacts. Poisson's ratio (v), which differs from one product to another and is porosity-dependent, must be taken into account. Finally, the bulk modulus (K), which combines E and v, was shown to be well correlated with the elastic recovery of the compacts and can be considered as a relevant parameter to characterize the elastic behavior of pharmaceutical compacts. PMID:23963744
A-thermal elastic behavior of silicate glasses
NASA Astrophysics Data System (ADS)
Rabia, Mohammed Kamel; Degioanni, Simon; Martinet, Christine; Le Brusq, Jacques; Champagnon, Bernard; Vouagner, Dominique
2016-02-01
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 Si4+ ions by Al3+ 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
Modular correction method of bending elastic modulus based on sliding behavior of contact point
NASA Astrophysics Data System (ADS)
Ma, Zhichao; Zhao, Hongwei; Zhang, Qixun; Liu, Changyi
2015-08-01
During the three-point bending test, the sliding behavior of the contact point between the specimen and supports was observed, the sliding behavior was verified to affect the measurements of both deflection and span length, which directly affect the calculation of the bending elastic modulus. Based on the Hertz formula to calculate the elastic contact deformation and the theoretical calculation of the sliding behavior of the contact point, a theoretical model to precisely describe the deflection and span length as a function of bending load was established. Moreover, a modular correction method of bending elastic modulus was proposed, via the comparison between the corrected elastic modulus of three materials (H63 copper-zinc alloy, AZ31B magnesium alloy and 2026 aluminum alloy) and the standard modulus obtained from standard uniaxial tensile tests, the universal feasibility of the proposed correction method was verified. Also, the ratio of corrected to raw elastic modulus presented a monotonically decreasing tendency as the raw elastic modulus of materials increased.
NASA Astrophysics Data System (ADS)
Martelloni, Gianluca; Bagnoli, Franco
2016-04-01
In the past three decades, fractional and fractal calculus (that is, calculus of derivatives and integral of any arbitrary real or complex order) appeared to be an important tool for its applications in many fields of science and engineering. This theory allows to face, analytically and/or numerically, fractional differential equations and fractional partial differential equations. In particular, one of the several applications deals with anomalous diffusion processes. The latter phenomena can be clearly described from the statistical viewpoint. Indeed, in various complex systems, the diffusion processes usually no longer follow Gaussian statistics, and thus Fick's second law fails to describe the related transport behavior. In particular, one observes deviations from the linear time dependence of the mean squared displacement ⟨x2(t)⟩ ∝ t, (1) which is characteristic of Brownian motion, i.e., a direct consequence of the central limit theorem and the Markovian nature of the underlying stochastic process [1-17]. Instead, anomalous diffusion is found in a wide diversity of systems and its feature is the non-linear growth of the mean squared displacement over time. Especially the power-law pattern, with exponent γ different from 1 ⟨ ⟩ x2(t) ∝ tγ, (2) characterizes many systems [18, 19], but a variety of other rules, such as a logarithmic time dependence, exist [20]. The anomalous diffusion, as expressed in Eq. (2) is connected with the breakdown of the central limit theorem, caused by either broad distributions or long-range correlations, e.g., the extreme statistics and the power law distributions, typical of the self-organized criticality [42, 43]. Instead, anomalous diffusion rests on the validity of the Levy-Gnedenko generalized central limit theorem [21-23]. Particularly, broad spatial jumps or waiting time distributions lead to non-Gaussian distribution and non-Markovian time evolution of the system. Anomalous diffusion has been known since
Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2
NASA Astrophysics Data System (ADS)
Sefat, Athena S.; Li, Li; Cao, Huibo B.; McGuire, Michael A.; Sales, Brian; Custelcean, Radu; Parker, David S.
2016-02-01
Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe2As2 (TN = Ts = 133 K) increase for x = 0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bond distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (TN = Ts = 131 K), and this is due to charge doping. We illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism.
Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2
Sefat, Athena S.; Li, Li; Cao, Huibo B.; McGuire, Michael A.; Sales, Brian; Custelcean, Radu; Parker, David S.
2016-02-12
Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe2As2 (TN = Ts = 133 K) increase for x = 0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bondmore » distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (TN = Ts = 131 K), and this is due to charge doping. Finally, we illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism.« less
Anomalous magneto-elastic and charge doping effects in thallium-doped BaFe2As2
Sefat, Athena S.; Li, Li; Cao, Huibo B.; McGuire, Michael A.; Sales, Brian; Custelcean, Radu; Parker, David S.
2016-01-01
Within the BaFe2As2 crystal lattice, we partially substitute thallium for barium and report the effects of interlayer coupling in Ba1-xTlxFe2As2 crystals. We demonstrate the unusual effects of magneto-elastic coupling and charge doping in this iron-arsenide material, whereby Néel temperature rises with small x, and then falls with additional x. Specifically, we find that Néel and structural transitions in BaFe2As2 (TN = Ts = 133 K) increase for x = 0.05 (TN = 138 K, Ts = 140 K) from magnetization, heat capacity, resistivity, and neutron diffraction measurements. Evidence from single crystal X-ray diffraction and first principles calculations attributes the stronger magnetism in x = 0.05 to magneto-elastic coupling related to the shorter intraplanar Fe-Fe bond distance. With further thallium substitution, the transition temperatures decrease for x = 0.09 (TN = Ts = 131 K), and this is due to charge doping. We illustrate that small changes related to 3d transition-metal state can have profound effects on magnetism. PMID:26867821
Petrova, A. E.; Krasnorussky, V. N.; Stishov, S. M.
2010-09-15
Measurements of the sound velocities in a single crystal of FeSi were performed in the temperature range 4-300 K. Elastic constants C{sub 11} and C{sub 44} deviate from a quasiharmonic behavior at high temperature; on the other hand, elastic constants C{sub 12} increases anomalously in the entire temperature range, indicating a change in the electron structure of this material.
SmartFoams with magneto-sensitive elastic behavior
NASA Astrophysics Data System (ADS)
Sorrentino, Luigi; D'Auria, Marco; Davino, Daniele; Visone, Ciro; Iannace, Salvatore
2014-05-01
Polymeric foams with embedded magnetic particles can be considered as a new class of lightweight systems that could lead to relevant industrial applications both for their enhanced directional (anisotropic) mechanical properties and for their sensitivity to magnetic field that can be used to actively control their elastic modulus. A new polyurethane (PU)/magnetosensitive particles composite foam (SmartFoam) was prepared by applying a magnetic field during its in situ polymerization/foaming process. A chain-like structure of magneto-sensitive particles was induced along the magnetic field lines, in turn controlling the degree of both structural anisotropy and functional properties without affecting the foam cellular morphology. The anisotropic distribution of magnetic particles in the SmartFoam imparted the capability to real-time control its structural properties under working conditions.
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.
Anomalous behavior in the magneto-optics of a gapped topological insulator
NASA Astrophysics Data System (ADS)
Tabert, C. J.; Carbotte, J. P.
2015-12-01
The Dirac fermions at the surface of a topological insulator can be gapped by introducing magnetic dopants. Alternatively, in an ultrathin slab with thickness on the order of the extent of the surface states, both the top and bottom surface states acquire a common gap value (Δ ) but with opposite sign. In a topological insulator, the dominant piece of the Hamiltonian (H ̂) is of a relativistic nature. A subdominant nonrelativistic piece is also present and, in an external magnetic field (B ) applied perpendicular to the surface, the N =0 Landau level is no longer at zero energy but is shifted to positive energy by the Schrödinger magnetic energy. When a gap is present, it further shifts this level down by -Δ for positive Δ and up by |Δ | for a negative gap. This has important consequences for the magneto-optical properties of such systems. In particular, at charge neutrality, the lowest energy transition displays anomalous nonmonotonic behavior as a function of B in both its position in energy and its optical spectral weight. The gap can also have a profound impact on the spectral weight of the interband lines and on corresponding structures in the real part of the dynamical Hall conductivity. Conversely, the interband background in zero field remains unchanged by the nonrelativistic term in H ̂ (although its onset frequency is modified).
Fraiman, Daniel; Chialvo, Dante R.
2012-01-01
The study of spontaneous fluctuations of brain activity, often referred as brain noise, is getting increasing attention in functional magnetic resonance imaging (fMRI) studies. Despite important efforts, much of the statistical properties of such fluctuations remain largely unknown. This work scrutinizes these fluctuations looking at specific statistical properties which are relevant to clarify its dynamical origins. Here, three statistical features which clearly differentiate brain data from naive expectations for random processes are uncovered: First, the variance of the fMRI mean signal as a function of the number of averaged voxels remains constant across a wide range of observed clusters sizes. Second, the anomalous behavior of the variance is originated by bursts of synchronized activity across regions, regardless of their widely different sizes. Finally, the correlation length (i.e., the length at which the correlation strength between two regions vanishes) as well as mutual information diverges with the cluster's size considered, such that arbitrarily large clusters exhibit the same collective dynamics than smaller ones. These three properties are known to be exclusive of complex systems exhibiting critical dynamics, where the spatio-temporal dynamics show these peculiar type of fluctuations. Thus, these findings are fully consistent with previous reports of brain critical dynamics, and are relevant for the interpretation of the role of fluctuations and variability in brain function in health and disease. PMID:22934058
NASA Astrophysics Data System (ADS)
Martelloni, Gianluca; Bagnoli, Franco
2016-04-01
In the past three decades, fractional and fractal calculus (that is, calculus of derivatives and integral of any arbitrary real or complex order) appeared to be an important tool for its applications in many fields of science and engineering. This theory allows to face, analytically and/or numerically, fractional differential equations and fractional partial differential equations. In particular, one of the several applications deals with anomalous diffusion processes. The latter phenomena can be clearly described from the statistical viewpoint. Indeed, in various complex systems, the diffusion processes usually no longer follow Gaussian statistics, and thus Fick's second law fails to describe the related transport behavior. In particular, one observes deviations from the linear time dependence of the mean squared displacement ⟨x2(t)⟩ ∝ t, (1) which is characteristic of Brownian motion, i.e., a direct consequence of the central limit theorem and the Markovian nature of the underlying stochastic process [1-17]. Instead, anomalous diffusion is found in a wide diversity of systems and its feature is the non-linear growth of the mean squared displacement over time. Especially the power-law pattern, with exponent γ different from 1 ⟨ ⟩ x2(t) ∝ tγ, (2) characterizes many systems [18, 19], but a variety of other rules, such as a logarithmic time dependence, exist [20]. The anomalous diffusion, as expressed in Eq. (2) is connected with the breakdown of the central limit theorem, caused by either broad distributions or long-range correlations, e.g., the extreme statistics and the power law distributions, typical of the self-organized criticality [42, 43]. Instead, anomalous diffusion rests on the validity of the Levy-Gnedenko generalized central limit theorem [21-23]. Particularly, broad spatial jumps or waiting time distributions lead to non-Gaussian distribution and non-Markovian time evolution of the system. Anomalous diffusion has been known since
NASA Astrophysics Data System (ADS)
Vacek, George; Sherrill, C. David; Yamaguchi, Yukio; Schaefer, Henry F., III
1996-02-01
P. Dupré, R. Jost, M. Lombardi, P. G. Green, E. Abramson, and R. W. Field have observed anomalous behavior of the anticrossing density in the Zeeman anticrossing (ZAC) spectra of gas phase Ã 1Au acetylene in the 42 200 to 45 300 cm-1 energy range. To best explain this result, they hypothesize a large singlet-triplet coupling due to the existence of a linear isomerization barrier connecting a triplet-excited cis- and trans-acetylene in the vicinity of the studied energy range (˜45 500 cm-1). Theoretically such a linear stationary point, however, must have two different degenerate bending vibrational frequencies which are either imaginary or exactly zero. Neither case has yet been experimentally detected. Here, we have studied the two lowest-lying linear triplet-excited-state stationary points of acetylene, 3Σ+u and 3Δu, to see if they fit Dupré et al.'s hypothesis. We have completed geometry optimization and harmonic vibrational frequency analysis using complete-active-space self-consistent field (CASSCF) wave functions as well as determined energy points at those geometries using the second-order configuration interaction (SOCI) method. Harmonic vibrational analyses of both stationary points reveal two different doubly degenerate vibrational modes with imaginary vibrational frequencies (or negative force constants) indicating that they are indeed saddle points with a Hessian index of four. At the DZP SOCI//CASSCF level of theory with zero-point vibrational energy (ZPVE) correction, the 3Σ+u stationary point lies 35 840 cm-1 above the ground state of acetylene. This is much too low in energy to contribute to the ZAC spectral anomaly. At the same level of theory with ZPVE correction, the 3Δu stationary point lies 44 940 cm-1 above the ground state consistent with Dupré et al.'s hypothesis. Several solutions to the anomalous ZAC spectra are discussed. We propose that the anomaly may also be due to coupling with a nearly linear structure on the T3 surface of
Petalite under pressure: Elastic behavior and phase stability
Ross, Nancy L.; Zhao, Jing; Slebodnick, Carla; Spencer, Elinor C.; Chakoumakos, Bryan C.
2015-04-01
The lithium aluminosilicate mineral petalite (LiAlSi4O10) has been studied using high-pressure single-crystal X-ray diffraction (HP-XRD) up to 5 GPa. Petalite undergoes two pressure-induced first-order phase transitions, never reported in the literature, at ca. 1.5 and 2.5 GPa. The first of these transforms the low-pressure α-phase of petalite (P2/c) to an intermediate β-phase that then fully converts to the high-pressure β-phase at ca. 2.5 GPa. The α→β transition is isomorphic and is associated with a commensurate modulation that triples the unit cell volume. Analysis of the HP-XRD data show that although the fundamental features of the petalite structure are retained throughmore » this transition, there are subtle alterations in the internal structure of the silicate double-layers in the β-phase relative to the α-phase. Measurement of the unit cell parameters of petalite as a function of pressure, and fitting of the data with 3rd order Birch-Murnaghan equations of state, has provided revised elastic constants for petalite. The bulk moduli of the α and β-phases are 49(1) and 35(3) GPa, respectively. These values indicate that the compressibility of the- phase of petalite lies between the alkali feldpsars and alkali feldspathoids, whereas the β-phase has a compressibility more comparable with layered silicates. Structure analysis has shown that the compression of the -phase is facilitated by the rigid body movement of the Si2O7 units from which the silicate double-layers are constructed.« less
Petalite under pressure: Elastic behavior and phase stability
Ross, Nancy L.; Zhao, Jing; Slebodnick, Carla; Spencer, Elinor C.; Chakoumakos, Bryan C.
2015-04-01
The lithium aluminosilicate mineral petalite (LiAlSi_{4}O_{10}) has been studied using high-pressure single-crystal X-ray diffraction (HP-XRD) up to 5 GPa. Petalite undergoes two pressure-induced first-order phase transitions, never reported in the literature, at ca. 1.5 and 2.5 GPa. The first of these transforms the low-pressure α-phase of petalite (P2/c) to an intermediate β-phase that then fully converts to the high-pressure β-phase at ca. 2.5 GPa. The α→β transition is isomorphic and is associated with a commensurate modulation that triples the unit cell volume. Analysis of the HP-XRD data show that although the fundamental features of the petalite structure are retained through this transition, there are subtle alterations in the internal structure of the silicate double-layers in the β-phase relative to the α-phase. Measurement of the unit cell parameters of petalite as a function of pressure, and fitting of the data with 3rd order Birch-Murnaghan equations of state, has provided revised elastic constants for petalite. The bulk moduli of the α and β-phases are 49(1) and 35(3) GPa, respectively. These values indicate that the compressibility of the- phase of petalite lies between the alkali feldpsars and alkali feldspathoids, whereas the β-phase has a compressibility more comparable with layered silicates. Structure analysis has shown that the compression of the -phase is facilitated by the rigid body movement of the Si_{2}O_{7} units from which the silicate double-layers are constructed.
Analysis of nonlinear elastic behavior in miniature pneumatic artificial muscles
NASA Astrophysics Data System (ADS)
Hocking, Erica G.; Wereley, Norman M.
2013-01-01
Pneumatic artificial muscles (PAMs) are well known for their excellent actuator characteristics, including high specific work, specific power, and power density. Recent research has focused on miniaturizing this pneumatic actuator technology in order to develop PAMs for use in small-scale mechanical systems, such as those found in robotic or aerospace applications. The first step in implementing these miniature PAMs was to design and characterize the actuator. To that end, this study presents the manufacturing process, experimental characterization, and analytical modeling of PAMs with millimeter-scale diameters. A fabrication method was developed to consistently produce low-cost, high performance, miniature PAMs using commercially available materials. The quasi-static behavior of these PAMs was determined through experimentation on a single actuator with an active length of 39.16 mm (1.54 in) and a diameter of 4.13 mm (0.1625 in). Testing revealed the PAM’s full evolution of force with displacement for operating pressures ranging from 207 to 552 kPa (30-80 psi in 10 psi increments), as well as the blocked force and free contraction at each pressure. Three key nonlinear phenomena were observed: nonlinear PAM stiffness, hysteresis of the force versus displacement response for a given pressure, and a pressure deadband. To address the analysis of the nonlinear response of these miniature PAMs, a nonlinear stress versus strain model, a hysteresis model, and a pressure bias are introduced into a previously developed force balance analysis. Parameters of these nonlinear model refinements are identified from the measured force versus displacement data. This improved nonlinear force balance model is shown to capture the full actuation behavior of the miniature PAMs at each operating pressure and reconstruct miniature PAM response with much more accuracy than previously possible.
NASA Astrophysics Data System (ADS)
Clark, Alisha N.; Lesher, Charles E.; Jacobsen, Steven D.; Wang, Yanbin
2016-06-01
Independent measurements of the volumetric and elastic properties of Columbia River basalt glass were made up to 5.5 GPa by high-pressure X-ray microtomography and GHz-ultrasonic interferometry, respectively. The Columbia River basalt displays P and S wave velocity minima at 4.5 and 5 GPa, respectively, violating Birch's law. These data constrain the pressure dependence of the density and elastic moduli at high pressure, which cannot be modeled through usual equations of state nor determined by stepwise integrating the bulk sound velocity as is common practice. We propose a systematic variation in compression behavior of silicate glasses that is dependent on the degree of polymerization and arises from the flexibility of the aluminosilicate network. This behavior likely persists into the liquid state for basaltic melts resulting in weak pressure dependence for P wave velocities perhaps to depths of the transition zone. Modeling the effect of partial melt on P wave velocity reductions suggests that melt fraction determined by seismic velocity variations may be significantly overestimated in the crust and upper mantle.
Thongyothee, Chawis Chucheepsakul, Somchai
2013-12-28
This paper is concerned with postbuckling behaviors of nanorods subjected to an end concentrated load. One end of the nanorod is clamped while the other end is fixed to a support that can slide in the slot. The governing equation is developed from static equilibrium and geometrical conditions by using the exact curvature corresponding to the elastica theory. The nonlocal elasticity, the effect of surface stress, and their combined effects are taken into account in Euler–Bernoulli beam theory. Differential equations in this problem can be solved numerically by using the shooting-optimization technique for the postbuckling loads and the buckled configurations. The results show that nanorods with the nonlocal elasticity effect undergo increasingly large deformation while the effect of surface stress in combination with nonlocal elasticity decreases the deflection of nanorods under the same postbuckling load.
NASA Astrophysics Data System (ADS)
Ludwig, Ryan M.; Moore, David T.
2014-06-01
Using matrix isolation FTIR, we have observed the formation of anionic copper carbonyl complexes [Cu(CO)n]- (n=1-3) following co-deposition of Cu- and counter-cations (Ar+ or Kr+) into argon matrices doped with CO. When the deposition is carried out at 20 K, weak bands corresponding to the neutral copper carbonyl complexes Cu(CO)n (n=1-3) are also observed, and these grow in steadily as the matrix is annealed up to 30 K. This is in contrast to what is observed at 10 K (c.f. ISMS 2014 abstract #P631), where no appreciable neutral bands are observed, and indicates that some neutralization occurs during the formation of the complexes in the 20 K matrix. In addition, sharp peaks not previously observed grow in around the anionic bands upon annealing to 30 K; this is somewhat odd, since annealing typically simplifies the spectra of matrix samples as kinetically trapped metastable species relax to more stable forms. In this case, higher-resolution (0.125 wn) spectra reveal considerable new fine structure, with 5 and 20 peaks appearing in the regions of the mono- and tricarbonyl anions, respectively, each of which nominally has but a single IR-active CO-stretching mode. These new features are tentatively assigned (at least in part) to electric-field-induced splitting arising from long-range interactions with cationic species in the matrix. A second anomalous feature of these spectra is that, upon photodetachment, several new bands are observed in the region of the neutral copper carbonyl species. Upon annealing these bands then disappear, with concomitant growth of the expected neutral bands. This behavior raises the exciting possibility that these transient bands represent metastable "vertical detachment products", where the neutral species has been kinetically trapped by the matrix in the geometry of the anion. Evidence supporting this interpretation will be presented. Funding support from NSF CAREER Award CHE-0955637 is gratefully acknowledged Ryan M. Ludwig and David
Quasi-static analysis of elastic behavior for some systems having higher fracture densities.
Berryman, J.G.; Aydin, A.
2009-10-15
Elastic behavior of geomechanical systems with interacting (but not intersecting) fractures is treated using generalizations of the Backus and the Schoenberg-Muir methods for analyzing layered systems whose layers are intrinsically anisotropic due to locally aligned fractures. By permitting the axis of symmetry of the locally anisotropic compliance matrix for individual layers to differ from that of the layering direction, we derive analytical formulas for interacting fractured regions with arbitrary orientations to each other. This procedure provides a systematic tool for studying how contiguous, but not yet intersecting, fractured domains interact, and provides a direct (though approximate) means of predicting when and how such interactions lead to more dramatic weakening effects and ultimately to failure of these complicated systems. The method permits decomposition of the system elastic behavior into specific eigenmodes that can all be analyzed, and provides a better understanding about which of these specific modes are expected to be most important to the evolving failure process.
NASA Astrophysics Data System (ADS)
Rovang, D. C.; Bruner, N.; Johnston, M. D.; Madrid, E. A.; Maenchen, J. E.; Oliver, B. V.; Portillo, S.; Welch, D. R.
2008-09-01
The immersed-Bz diode is being developed as a high-brightness, flash x-ray radiography source at Sandia National Laboratories. This diode is a foil-less electron-beam diode with a long, thin, needlelike cathode which is inserted into the bore of a solenoid. The solenoidal magnetic field guides the electron beam emitted from the cathode to the anode while maintaining a small beam radius. The electron beam strikes a thin, high-atomic-number anode and produces forward-directed bremsstrahlung. In addition, electron beam heating of the anode produces surface plasmas allowing ion emission. Two different operating regimes for this diode have been identified: A nominal operating regime where the total diode current is characterized as classically bipolar with stable impedance [see D. C. Rovang et al., Phys. Plasmas 14, 113107 (2007)] and an anomalous operating regime characterized by a rapid impedance collapse where the total diode current greatly exceeds the bipolar limit. The operating regimes are approximately separated by cathode diameters greater than 3mm for the nominal regime and less than 3mm for the anomalous impedance collapse regime. Results from a comprehensive series of experiments conducted at 4-5MV characterizing the transition from this nominal operating regime to the anomalous operating regime as the cathode diameter is reduced are presented. Results from experiments investigating the effects of anode-cathode gap, anode material, and cryogenic modification of the anode surface are also presented. Although these investigations were unsuccessful in completely mitigating the anomalous behavior, insight gained from these experiments has elucidated several key physics issues that are discussed.
NASA Astrophysics Data System (ADS)
Amar, El Hadji Bouya; Clamond, Didier; Fraysse, Nathalie; Rajchenbach, Jean
2009-06-01
In order to specify the mechanical behavior of grain piles, we investigate the response of a non-cohesive bidimensional packing of cylinders submitted to a point load. By means of image processing, we have an accurate access to the individual grain displacements in the reversible regime. The measured displacement field deviates unambiguously from the predictions of Continuum Elasticity. The data reveal a partial agreement with the diffusive models of Harr (1966) or of Coppersmith et al. (1996).
NASA Astrophysics Data System (ADS)
Jiang, Shao-Long; Li, Xu-Jing; Liu, Yi-Wei; Chen, Xi; Liu, Qian-Qian; Han, Gang; Yang, Guang; Wang, Dong-Wei; Zhang, Jing-Yan; Teng, Jiao; Yu, Guang-Hua
2016-01-01
The effect of annealing on the anomalous Hall effect (AHE) in perpendicular Co/Pt multilayers sandwiched by HfO2 layers has been studied. It was found that thermally stable AHE features can be obtained in perpendicular Co/Pt multilayers with the introduction of two Co/HfO2 interfaces, leading to the improvement of the skew scattering contribution to the AHE after annealing. On the contrary, thermally stable AHE behavior cannot be observed in Co/Pt multilayers sandwiched by Pt layers or MgO layers because of Co-Pt interdiffusion during annealing.
Elastic-plastic behavior of a semicircular frame being pressed against a rigid plane
NASA Astrophysics Data System (ADS)
Zhang, X. W.; Yang, J. L.; Yu, T. X.
2008-08-01
As a simplified structural model, a semicircular frame is used to study the crashworthiness behavior of an aircraft fuselage. The quasi-static large elastic-plastic deformation of a semicircular frame in the process of its being pressed against a rigid ground is analyzed. First, based on the linear elastic assumption, the quasi-static large deformation contact process of the frame can be divided into three phases, i.e., point contact, line contact and post-buckling. By means of a shooting method, the relations between the displacement and contact force as well as the distribution of bending moment in the three phases are obtained. Then, by assuming an elastic, perfectly-plastic moment-curvature relationship for the semi-circular frame, the contact process is analyzed in detail to reveal the plastic collapse mechanism, the traveling of plastic hinge and the force-displacement relationship. In order to verify the analysis, a preliminary experiment was conducted, in which two types of half rings with clamped ends were pressed by a rigid plate. In addition, a numerical simulation is also conducted by employing ABAQUS to analyze both rectangular cross-sectional beam and I-beam. Finally, the theoretical predictions are compared with the experimental results and numerical solutions, showing that the elastic-plastic analysis can predict the contact process very well.
NASA Astrophysics Data System (ADS)
Li, B.; Zhang, P.; Fu, Q. Q.; Li, X. F.; Zhao, X.; Song, X. L.
2014-08-01
Load-displacement responses and ultimate strength of polyhedral graphite particles (PGPs) undergoing in situ nano-compression at ambient temperature have been studied. The dynamic responses of PGPs to uniaxial loads exhibit a typical nonlinear elastic behavior for graphitic nanomaterials. Based on the analysis of stress-strain relationship, the intrinsic strength is slightly larger than actual ultimate strength, indicating the mechanical properties influenced by the initial defects in PGPs. For a given case, compressive Young's modulus E and third-order elastic modulus D achieve to 12.8 GPa and -13.9 GPa, respectively. Weibull probability analysis confirmed its broad range of structural defects inside PGPs and mechanical properties are sensitive to initial defects. The values of ultimate strength of tested PGPs with diameter of 150-400 nm fall within 2-4.5 GPa, which are in the range between shear elastic modulus C44 of turbo-g (minimum) and C44 of hex-g (maximum) in the literature. The deformation and failure mechanisms are discussed and rationalized in terms of structural factors and elastic moduli of perfect graphite crystals.
NASA Astrophysics Data System (ADS)
Riveiro, Maria; Falkman, Göran; Ziemke, Tom; Kronhamn, Thomas
2009-05-01
The goal of visual analytical tools is to support the analytical reasoning process, maximizing human perceptual, understanding and reasoning capabilities in complex and dynamic situations. Visual analytics software must be built upon an understanding of the reasoning process, since it must provide appropriate interactions that allow a true discourse with the information. In order to deepen our understanding of the human analytical process and guide developers in the creation of more efficient anomaly detection systems, this paper investigates how is the human analytical process of detecting and identifying anomalous behavior in maritime traffic data. The main focus of this work is to capture the entire analysis process that an analyst goes through, from the raw data to the detection and identification of anomalous behavior. Three different sources are used in this study: a literature survey of the science of analytical reasoning, requirements specified by experts from organizations with interest in port security and user field studies conducted in different marine surveillance control centers. Furthermore, this study elaborates on how to support the human analytical process using data mining, visualization and interaction methods. The contribution of this paper is twofold: (1) within visual analytics, contribute to the science of analytical reasoning with practical understanding of users tasks in order to develop a taxonomy of interactions that support the analytical reasoning process and (2) within anomaly detection, facilitate the design of future anomaly detector systems when fully automatic approaches are not viable and human participation is needed.
Berryman, James G.; Grechka, Vladimir
2006-07-08
A model study on fractured systems was performed using aconcept that treats isotropic cracked systems as ensembles of crackedgrains by analogy to isotropic polycrystalline elastic media. Theapproach has two advantages: (a) Averaging performed is ensembleaveraging, thus avoiding the criticism legitimately leveled at mosteffective medium theories of quasistatic elastic behavior for crackedmedia based on volume concentrations of inclusions. Since crack effectsare largely independent of the volume they occupy in the composite, sucha non-volume-based method offers an appealingly simple modelingalternative. (b) The second advantage is that both polycrystals andfractured media are stiffer than might otherwise be expected, due tonatural bridging effects of the strong components. These same effectshave also often been interpreted as crack-crack screening inhigh-crack-density fractured media, but there is no inherent conflictbetween these two interpretations of this phenomenon. Results of thestudy are somewhat mixed. The spread in elastic constants observed in aset of numerical experiments is found to be very comparable to the spreadin values contained between the Reuss and Voigt bounds for thepolycrystal model. However, computed Hashin-Shtrikman bounds are much tootight to be in agreement with the numerical data, showing thatpolycrystals of cracked grains tend to violate some implicit assumptionsof the Hashin-Shtrikman bounding approach. However, the self-consistentestimates obtained for the random polycrystal model are nevertheless verygood estimators of the observed average behavior.
Analytical modeling of elastic-plastic wave behavior near grain boundaries in crystalline materials
Loomis, Eric; Greenfield, Scott; Luo, Shengnian; Swift, Damian; Peralta, Pedro
2009-01-01
It is well known that changes in material properties across an interface will produce differences in the behavior of reflected and transmitted waves. This is seen frequently in planar impact experiments, and to a lesser extent, oblique impacts. In anisotropic elastic materials, wave behavior as a function of direction is usually accomplished with the aid of velocity surfaces, a graphical method for predicting wave scattering configurations. They have expanded this method to account for inelastic deformation due to crystal plasticity. The set of derived equations could not be put into a characteristic form, but instead led to an implicit problem. to overcome this difficulty an algorithm was developed to search the parameters space defined by a wave normal vector, particle velocity vector, and a wave speed. A solution was said to exist when a set from this parameter space satisfied the governing vector equation. Using this technique they can predict the anisotropic elastic-plastic velocity surfaces and grain boundary scattering configuration for crystalline materials undergoing deformation by slip. Specifically, they have calculated the configuration of scattered elastic-plastic waves in anisotropic NiAl for an incident compressional wave propagating along a <111> direction and contacting a 45 degree inclined grain boundary and found that large amplitude transmitted waves exist owing to the fact that the wave surface geometry forces it to propagate near the zero Schmid factor direction <100>.
Kollu, Pratap E-mail: anirmalagrace@vit.ac.in; Prathapani, Sateesh; Varaprasadarao, Eswara K.; Mallick, Sudhanshu; Bahadur, D. E-mail: anirmalagrace@vit.ac.in; Santosh, Chella; Grace, Andrews Nirmala E-mail: anirmalagrace@vit.ac.in
2014-08-04
Magnetic Reduced Graphene Oxide-Nickel/NiFe{sub 2}O{sub 4} (RGO-Ni/NF) nanocomposite has been synthesized by one pot solvothermal method. Respective phase formations and their purities in the composite are confirmed by High Resolution Transmission Electron Microscope and X Ray Diffraction, respectively. For the RGO-Ni/NF composite material finite-size effects lead to the anomalous magnetic behavior, which is corroborated in temperature and field dependent magnetization curves. Here, we are reporting the behavior of higher magnetization values for Zero Field Cooled condition to that of Field Cooled for the RGO-Ni/NF nanocomposite. Also, the observed negative and positive moments in Hysteresis loops at relatively smaller applied fields (100 Oe and 200 Oe) are explained on the basis of surface spin disorder.
Constitutive acoustic-emission elastic-stress behavior of magnesium alloy
NASA Technical Reports Server (NTRS)
Williams, J. H., Jr.; Emerson, G. P.
1977-01-01
Repeated laoding and unloading of a magnesium alloy below the macroscopic yield stress result in continuous acoustic emissions which are generally repeatable for a given specimen and which are reproducible between different specimens having the same load history. An acoustic emission Bauschinger strain model is proposed to describe the unloading emission behavior. For the limited range of stress examined, loading and unloading stress delays of the order of 50 MN/sq m are observed, and they appear to be dependent upon the direction of loading, the stress rate, and the stress history. The stress delay is hypothesized to be the manifestation of an effective friction stress. The existence of acoustic emission elastic stress constitutive relations is concluded, which provides support for a previously proposed concept for the monitoring of elastic stresses by acoustic emission.
Elastic and Anelastic Behavior of TBCs Sprayed at High-Deposition Rates
NASA Astrophysics Data System (ADS)
Valarezo, A.; Dwivedi, G.; Sampath, S.; Musalek, R.; Matejicek, J.
2015-01-01
Coatings sprayed at high-deposition rates often result in stiff, dense, and highly stressed coatings. The high deposition temperature at which the coatings are formed is responsible for these characteristics. In this paper, TBCs were sprayed at high-deposition rates, increasing the tensile quenching stresses beyond the threshold of crack opening during spraying. Dense structures were observed within a pass, in the presence of micro and macro defects specifically horizontal cracks within interpasses and vertical segmentation cracks. Mechanical properties, mainly the elastic and anelastic behavior of TBCs were significantly affected by the strain accommodation and friction occurring within intersplats and interpass interfaces. The strain tolerance obtained in as-sprayed conditions decreased as the microstructure and defects sintered during high-temperature heat cycles. The non-linearity degree decreased while the elastic modulus of the various coatings increased to a maximum value.
NASA Astrophysics Data System (ADS)
Wang, Huiming
2014-04-01
An exact solution is obtained for multilayered pyroelectric cylindrical (MPC) actuators with weakly conducting interfaces subjected to thermo-electro-mechanical loading. The outer surface of the composite cylindrical actuator is supported by a Winkler-type elastic foundation. At the interface, all the thermal and mechanical quantities as well as the normal electric displacement are assumed to be continuous but the electric potential is discontinuous. The temperature fields are obtained by the transfer matrix method and the piezothermoelastic fields are developed by the state space method combined with the Cayley-Hamilton theorem. Numerical results are presented graphically to show the effects of the elastic foundation, interfacial parameters and heat transfer coefficient on the piezothermoelastic behavior of MPC actuators.
The elastic precursor behavior of tantalum under dynamic loading, its implications and modeling.
Ding, Jow-Lian
2010-03-01
When elastic-plastic materials, such as metals, are subjected to moderately high strain rates or dynamic loadings, the plastic stress wave trails behind the elastic wave because of its slower wave speed. Due to the inherent time-dependent nature of the plastic deformation, the elastic precursor generally loads the material to a metastable elastic state at a stres level that is higher than the static strength of the material. This metastable state gradually relaxes to the equilibrium state and the relaxation results in the so-called precursor decay. In a recent work by Asay et al. (J. Appl. Phys., 2009), the inelastic response of annealed and cold-rolled pure polycrystalline tantalum at intermediate strain rates ({approx} 106/sec) was experimentally characterized with ramp wave loading. It was found that the precursor of the annealed tantalum showed little decay over a propagation distance of 6 mm even though the peak precursor stress was well above the static strength of the mateiral. The precursor for the cold-rolled sample was more dispersive and did not exhibit the characteristics depicted by the annealed samples. In this study, a constitutive model based on the concept of dislocation motion and generation was developed to gain insights into this somewhat unusual precursor behavior, particularly for the annealed samples, and the possible underlying deformation mechanisms for tantalum. Despite its simplicity, the model worked quite well for both the annealed and cold-rolled materials. The tantalum studied here essentially exhibits strong rate sensitivity and this behavior is modeled through the low dislocation density and the strong stress dependence of the dislocation velocity. Both of these contributions may be related to the low mobility of the screw dislocations in bcc metals. This low mobility may result from its extended, three-dimensional core structure.
NASA Technical Reports Server (NTRS)
Plaut, Jeffrey J.; Saunders, R. Stephen; Stofan, E. R.; Kirk, R. L.; Schaber, G. G.; Soderblom, L. A.; Ford, P. G.; Pettengill, G. H.; Campbell, D. B.; Stacy, N. J. S.
1992-01-01
Magellan observations indicate that many venusian impact craters have associated surfaces, typically lower in backscatter and emissivity than the surroundings, that extend up to hundreds of kilometers to the west of craters, in parabolic planforms. During Magellan's second mapping cycle, a number of these parabolic features were imaged for a second time, under a different viewing geometry. In some cases, the SAR backscatter appearance of portions of the parabolic features was quite different in the two datasets. We present a description and preliminary interpretations of the anomalous appearance of these features as observed during Magellan's first and second mapping cycles.
Elastic behavior of porcine coronary artery tissue under uniaxial and equibiaxial tension.
Lally, C; Reid, A J; Prendergast, P J
2004-10-01
The aim of this study was to characterize the nonlinear anisotropic elastic behavior of healthy porcine coronary arteries under uniaxial and equibiaxial tension. Porcine coronary tissue was chosen for its availability and similarity to human arterial tissue. A biaxial test device previously used to test human femoral arterial tissue samples (Prendergast, P. J., C. Lally, S. Daly, A. J. Reid, T. C. Lee, D. Quinn, and F. Dolan. ASME J. Biomech. Eng., Vol. 125, pp. 692-699, 2003) was further developed to test porcine coronary tissue specimens. The device applies an equal force to the four sides of a square specimen and therefore creates a biaxial stretch that demonstrates the anisotropy of arterial tissue. The nonlinear elastic behavior was marked in both uniaxial and biaxial tests. The tissue demonstrated higher stiffness in the circumferential direction in four out of eight cases subjected to biaxial tension. Even though anisotropy is demonstrated it is proposed that an isotropic hyperelastic model may adequately represent the properties of an artery, provided that an axial stretch is applied to the vessel to simulate the in vivo longitudinal tethering on the vessel. Isotropic hyperelastic models based on the Mooney-Rivlin constitutive equation were derived from the test data by averaging the longitudinal and circumferential equibiaxial data. Three different hyperelastic models were established to represent the test specimens that exhibited a high stiffness, an average stiffness, and a low stiffness response; these three models allow the analyst to account for the variability in the arterial tissue mechanical properties. These models, which take account of the nonlinear elastic behavior of coronary tissue, may be implemented in finite element models and used to carry out preclinical tests of intravascular devices. The errors associated with the hyperelastic models when fitting to both the uniaxial and equibiaxial data for the low stiffness, average stiffness, and
A cool supergiant with anomalous behavior of the 2800 Mg II doublet
NASA Technical Reports Server (NTRS)
Gurzadian, G. A.; Rustambekian, S. S.; Kondo, Y.; Perez, Mario R.; Terzian, Yervant
1991-01-01
The IUE ultraviolet spectrum for a supergiant of type G Ia, HD 135345, is obtained for the wavelength region 2000-3000 A. In the spectrum, the continuum as well as the feature of the Mg II doublet at 2800 A is found to be anomalous. The observed level of continuum increases toward short wavelengths to 2000 A, verifying that this supergiant is actually a binary system with a hot companion. The anomalies in the magnesium doublet are the complete absence of the chromospheric emission and the very small equivalent width of the doublet absorption: the equivalent width is 4 A, which is 7.5 times smaller than that for a typical G5 star. The main parameters of the binary system are obtained, namely, spectral classes, effective temperatures, ratio of radii, and visible magnitudes.
Alves, Viviane S; Pimenta, Daniel C; Sattlegger, Evelyn; Castilho, Beatriz A
2004-01-30
Gir2 is an uncharacterized protein of Saccharomyces cerevisiae, containing a RWD/GI domain. In this work, we report the biophysical characterization of Gir2. His-tagged Gir2, expressed and purified from Escherichia coli, showed an abnormally slow migration on SDS-PAGE. The yeast expressed protein behaves similarly. Using mass spectrometry and peptide mass fingerprinting we demonstrated that the protein has the expected molecular mass (34kDa). EDC modification of carboxylate groups reverted the anomalous migration on SDS-PAGE. Size exclusion chromatography showed that Gir2 has a Stokes radius larger than expected. Gir2 is thermostable and lacks extensive structure, as determined by CD analysis. Based on these findings, we suggest that Gir2 is a representative of the growing group of "natively unfolded" proteins. PMID:14715270
Looney, B.B.; Scott, M.T.
1988-12-31
Recent field and laboratory data have confirmed that apparent dispersivity is a function of the flow distance of the measurement. This scale effect is not consistent with classical advection dispersion modeling often used to describe the transport of solutes in saturated porous media. Many investigators attribute this anomalous behavior to the fact that the spreading of solute is actually the result of the heterogeneity of subsurface materials and the wide distribution of flow paths and velocities available in such systems. An analysis using straightforward analytical equations confirms this hypothesis. An analytical equation based on a flow variance approach matches available field data when a variance description of approximately 0.4 is employed. Also, current field data provide a basis for statistical selection of the variance parameter based on the level of concern related to the resulting calculated concentration. While the advection dispersion approach often yielded reasonable predictions, continued development of statistical and stochastic techniques will provide more defendable and mechanistically descriptive models.
Riley, M.A.; Petters, T.; Shick, J.; Archer, D.E.; Doering, J.; Holcomb, J.W.; Johns, G.D.; Johnson, T.D.; Tekyi-Mensah, O.N.; Tabor, S.L.; Womble, P.C.; Wood, V.A. ); Baktash, C.; Halbert, M.L.; Hensley, D.C.; Lee, I.Y. ); Charity, R.J.; Sarantites, D.G.; Wittmer, L.L. ); Simpson, J. )
1993-02-01
A highly deformed rotational band has been observed in the odd-odd nucleus [sup 136]Pm. This band sheds important new light on the anomalous behavior of the dynamical moments of inertia of rotational bands previously observed in the Ce-Nd-Sm [ital A][similar to]135 superdeformed region which has been a theoretical puzzle for several years.
NASA Astrophysics Data System (ADS)
Ullrich, Angela; Schranz, Wilfried; Miletich, Ronald
2009-12-01
The high-pressure behavior of the lattice elasticity of spodumene, LiAlSi2O6, was studied by static compression in a diamond-anvil cell up to 9.3 GPa. Investigations by means of single-crystal XRD and Raman spectroscopy within the hydrostatic limits of the pressure medium focus on the pressure ranges around ~3.2 and ~7.7 GPa, which have been reported previously to comprise two independent structural phase transitions. While our measurements confirm the well-established first-order C2/ c- P21/ c transformation at 3.19 GPa (with 1.2% volume discontinuity and a hysteresis between 0.02 and 0.06 GPa), both unit-cell dimensions and the spectral changes observed in high-pressure Raman spectra give no evidence for structural changes related to a second phase transition. Monoclinic lattice parameters and unit-cell volumes at in total 59 different pressure points have been used to re-calculate the lattice-related properties of spontaneous strain, volume strain, and the bulk moduli as a function of pressure across the transition. A modified Landau free energy expansion in terms of a one component order parameter has been developed and tested against these experimentally determined data. The Landau solution provides a much better reproduction of the observed anomalies than any equation-of-state fit to data sets truncated below and above P tr, thus giving Landau parameters of K 0 = 138.3(2) GPa, K' = 7.46(5), λ V = 33.6(2) GPa, a = 0.486(3), b = -29.4(6) GPa and c = 551(11) GPa.
NASA Astrophysics Data System (ADS)
Ghadiri, Majid; Soltanpour, Mahdi; Yazdi, Ali; Safi, Mohsen
2016-05-01
Free transverse vibration of a size-dependent cracked functionally graded (FG) Timoshenko nanobeam resting on a polymer elastic foundation is investigated in the present study. Also, all of the surface effects: surface density, surface elasticity and residual surface tension are studied. Moreover, satisfying the balance condition between the nanobeam and its surfaces was discussed. According to the power-law distribution, it is supposed that the material properties of the FG nanobeam are varying continuously across the thickness. Considering the small-scale effect, the Eringen's nonlocal theory is used; accounting the effect of polymer elastic foundation, the Winkler model is proposed. For this purpose, the equations of motion of the FG Timoshenko nanobeam and boundary conditions are obtained using Hamilton's principle. To find the analytical solutions for equations of motion of the FG nanobeam, the separation of variables method is employed. Two cases of boundary conditions, i.e., simply supported-simply supported (SS) and clamped-clamped (CC) are investigated in the present work. Numerical results are demonstrating a good agreement between the results of the present study and some available cases in the literature. The emphasis of the present study is on investigating the effect of various parameters such as crack severity, crack position, gradient index, mode number, nonlocal parameter, elastic foundation parameter and nanobeam length. It is clearly revealed that the vibrational behavior of a FG nanobeam is depending significantly on these effects. Also, these numerical results can be serving as benchmarks for future studies of FG nanobeams.
Anomalous critical behavior in the polymer collapse transition of three-dimensional lattice trails.
Bedini, Andrea; Owczarek, Aleksander L; Prellberg, Thomas
2012-07-01
Trails (bond-avoiding walks) provide an alternative lattice model of polymers to self-avoiding walks, and adding self-interaction at multiply visited sites gives a model of polymer collapse. Recently a two-dimensional model (triangular lattice) where doubly and triply visited sites are given different weights was shown to display a rich phase diagram with first- and second-order collapse separated by a multicritical point. A kinetic growth process of trails (KGTs) was conjectured to map precisely to this multicritical point. Two types of low-temperature phases, a globule phase and a maximally dense phase, were encountered. Here we investigate the collapse properties of a similar extended model of interacting lattice trails on the simple cubic lattice with separate weights for doubly and triply visited sites. Again we find first- and second-order collapse transitions dependent on the relative sizes of the doubly and triply visited energies. However, we find no evidence of a low-temperature maximally dense phase with only the globular phase in existence. Intriguingly, when the ratio of the energies is precisely that which separates the first-order from the second-order regions anomalous finite-size scaling appears. At the finite-size location of the rounded transition clear evidence exists for a first-order transition that persists in the thermodynamic limit. This location moves as the length increases, with its limit apparently at the point that maps to a KGT. However, if one fixes the temperature to sit at exactly this KGT point, then only a critical point can be deduced from the data. The resolution of this apparent contradiction lies in the breaking of crossover scaling and the difference in the shift and transition width (crossover) exponents. PMID:23005384
Buckling Behavior of Long Anisotropic Plates Subjected to Elastically Restrained Thermal Expansion
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.
2002-01-01
An approach for synthesizing buckling results for, and behavior of, thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and elastically restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexurally anisotropic plates that are subjected to combined mechanical loads and is based on useful nondimensional parameters. In addition, stiffness-weighted laminate thermal-expansion parameters and compliance coefficients are derived that are used to determine critical temperatures in terms of physically intuitive mechanical-buckling coefficients. The effects of membrane orthotropy and membrane anisotropy are included in the general formulation. Many results are presented for some common laminates that are intended to facilitate a structural designer's transition to the use of generic buckling design curves. Several curves that illustrate the fundamental parameters used in the analysis are presented, for nine contemporary material systems, that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of generic design curves. The analysis approach and generic results indicate the effects and characteristics of elastically restrained laminate thermal expansion or contraction, membrane orthotropy and anisotropy, and flexural orthotropy and anisotropy in a very general and unifying manner.
NASA Technical Reports Server (NTRS)
Librescu, Liviu
1990-01-01
Within this research project, the following topics were studied: (1) foundation of the refined theory of flat cross-ply laminated composite flat and curved panels as well as their static and dynamic response analysis; (2) foundation of a geometrically-nonlinear shear-deformable theory of composite laminated flat panels including the effect of initial geometric imperfections and its application in the postbuckling analysis; (3) the study of the dynamic response of shear deformable elastic laminated composite panels to deterministic time-dependent external excitations as the sonic boom and explosive blast type-loadings; (4) the study of the dynamic response of shear deformable elastic laminated composite panels to random excitation as e.g. the one produced by a jet noise or by any time-dependent external excitation whose characteristics are expressed in a statistical sense; and (5) the dynamic stability of fiber-reinforced composite flat panels whose materials (due to e.g. an ambient high temperature field) exhibit a time-dependent physical behavior.
Akpinar, Erol; Reis, Dennys; Figueiredo Neto, Antonio M
2014-05-19
A novel quaternary lyotropic liquid-crystalline mixture of dodecyltrimethylammonium bromide (DDTMABr)/sodium bromide/1-dodecanol/water, presenting the biaxial nematic phase (NB ) in addition to two uniaxial discotic (ND) and calamitic (NC) nematic ones, was synthesized. The partial phase diagram of this new mixture was constructed as a function of the DDTMABr molar-fraction concentration. The phase transitions from uniaxial to biaxial nematic phases were studied by means of the temperature dependence of the optical birefringence. In a particular region of the phase diagram, anomalous behavior was observed in the crossover from N-B to N+b: the contrast of the conoscopic fringes, which allows the birefringence measurements, almost vanishes, and the sample loses its alignment. This behavior, which was not observed before in lyotropics, was interpreted as a decrease in the mean diamagnetic susceptibility anisotropy (Δχ) of the sample, which was related to the shape anisotropy of the micelles. Small-angle X-ray scattering measurements were performed to evaluate the micellar shape anisotropy; these revealed that this mixture presented a smaller shape anisotropy than those of other lyotropic micellar systems presenting the NB phase. PMID:24692308
Anomalous phase separation behavior of gel-derived soda-silica glasses
NASA Technical Reports Server (NTRS)
Neilson, G. F.; Weinberg, M. C.
1982-01-01
The effects of retained bound hydroxyl groups on amorphous immiscibility behavior and on the kinetics of phase separation were studied in glasses containing from 10 to 19 percent sodium oxide preparaed by the gel process. Differences in behavior as functions of preliminary thermal treatment of the gel precursor and of melting conditions were studied, employing IR spectroscopy, SAXS and WAXD to monitor the variation in glass microstructure. Both the initial gel treatment and the OH concentration in the prepared glasses were found to affect the immiscibility temperatures, and the magnitude of the maximum temperature increase was also a function of the sodium oxide concentration. It is suggested that the variation in thermodynamic behavior may be caused by the structural arrangement attained by the OH groups during the gel condensation process, which in turn affects the extent of hydrogen bonding to nonbridging oxygen ions.
Homogenized In-Plane Elastic-Viscoplastic Behavior of Long Fiber-Reinforced Laminates
NASA Astrophysics Data System (ADS)
Matsuda, Tetsuya; Ohno, Nobutada; Tanaka, Hiroki; Shimizu, Toshihiro
In this work, the homogenized elastic-viscoplastic behavior of long fiber-reinforced laminates under in-plane loading is predicted by taking into account the microscopic structure and stacking sequence of laminae. A homogenization theory of nonlinear time-dependent composites is applied to such laminates, leading to the macroscopic rate-type constitutive equation of laminates and the evolution equations of microscopic and average stresses in each lamina. The macroscopic constitutive equation is shown to have a stiffness tensor and a stress relaxation function which are evaluated explicitly in terms of the microscopic structure and stacking sequence of laminae. The established theory is then verified by performing in-plane uniaxial tensile tests of unidirectional, cross-ply, and quasi-isotropic carbon fiber/epoxy laminates. It is thus shown that the theory predicts successfully the anisotropic viscoplasticity of unidirectional and cross-ply laminates and the negligible viscoplasticity of quasi-isotropic laminates.
Theory of buckling and post-buckling behavior of elastic structures
NASA Technical Reports Server (NTRS)
Budiansky, B.
1974-01-01
The present paper provides a unified, general presentation of the basic theory of the buckling and post-buckling behavior of elastic structures in a form suitable for application to a wide variety of special problems. The notation of functional analysis is used for this purpose. Before the general analysis, simple conceptual models are used to elucidate the basic concepts of bifurcation buckling, snap buckling, imperfection sensitivity, load-shortening relations, and stability. The energy approach, the virtual-work approach, and mode interaction are discussed. The derivations and results are applicable to continua and finite-dimensional systems. The virtual-work and energy approaches are given separate treatments, but their equivalence is made explicit. The basic concepts of stability occupy a secondary position in the present approach.
Post-buckling behavior of a beam-column on a nonlinear elastic foundation with a gap
NASA Technical Reports Server (NTRS)
Kuznetsov, E. N.; Johns, T. G.
1980-01-01
The structural behavior of an elastic beam-column placed with a gap between two nonlinearity elastic layers each resting on a rigid foundation was examined. The beam-column was laterally supported at both ends and subjected to a uniform transverse load and axial compression. Its slenderness was such that the axial compressive force exceeds the amount that would be necessary to buckle it as a simple supported column. The elastic layers were represented by an elastic foundation with a strongly nonlinear specific reaction taken as a rapidly increasing function of the layer compression. The analytical model developed simulated the entire pattern of the deflection and stress state including layer and end support reactions, under gradually increasing axial force.
Gama, S.; de Campos, A.; Coelho, A. A.; Alves, C. S.; Ren, Y.; Garcia, F.; Brown, D. E.; da Silva, L. M.; Magnus, A.; Carvalho, G.; Gandra, G. C.; dos Santos, A. O.; Cardoso, L. P.; von Ranke, P. J.; X-Ray Science Division; Univ. Federal de Sao Paulo; Unv. Estadual de Champinas; Univ. Estadual de Maringa Lab. Nacional de Luz Sincrotron; Northern Univ.; Univ. de Estado do Rio de Janerio
2009-01-01
First order phase transitions for materials with exotic properties are usually believed to happen at fixed values of the intensive parameters (such as pressure, temperature, etc.) characterizing their properties. It is also considered that the extensive properties of the phases (such as entropy, volume, etc.) have discontinuities at the transition point, but that for each phase the intensive parameters remain constant during the transition. These features are a hallmark for systems described by two thermodynamic degrees of freedom. In this work it is shown that first order phase transitions must be understood in the broader framework of thermodynamic systems described by three or more degrees of freedom. This means that the transitions occur along intervals of the intensive parameters, that the properties of the phases coexisting during the transition may show peculiar behaviors characteristic of each system, and that a generalized Clausius-Clapeyron equation must be obeyed. These features for the magnetic case are confirmed, and it is shown that experimental calorimetric data agree well with the magnetic Clausius-Clapeyron equation for MnAs. An estimate for the point in the temperature-field plane where the first order magnetic transition turns to a second order one is obtained (the critical parameters) for MnAs and Gd{sub 5}Ge{sub 2}Si{sub 2} compounds. Anomalous behavior of the volumes of the coexisting phases during the magnetic first order transition is measured, and it is shown that the anomalies for the individual phases are hidden in the behavior of the global properties as the volume.
NASA Astrophysics Data System (ADS)
Goad, M. R.; Korista, K. T.; De Rosa, G.; Kriss, G. A.; Edelson, R.; Barth, A. J.; Ferland, G. J.; Kochanek, C. S.; Netzer, H.; Peterson, B. M.; Bentz, M. C.; Bisogni, S.; Crenshaw, D. M.; Denney, K. D.; Ely, J.; Fausnaugh, M. M.; Grier, C. J.; Gupta, A.; Horne, K. D.; Kaastra, J.; Pancoast, A.; Pei, L.; Pogge, R. W.; Skielboe, A.; Starkey, D.; Vestergaard, M.; Zu, Y.; Anderson, M. D.; Arévalo, P.; Bazhaw, C.; Borman, G. A.; Boroson, T. A.; Bottorff, M. C.; Brandt, W. N.; Breeveld, A. A.; Brewer, B. J.; Cackett, E. M.; Carini, M. T.; Croxall, K. V.; Dalla Bontà, E.; De Lorenzo-Cáceres, A.; Dietrich, M.; Efimova, N. V.; Evans, P. A.; Filippenko, A. V.; Flatland, K.; Gehrels, N.; Geier, S.; Gelbord, J. M.; Gonzalez, L.; Gorjian, V.; Grupe, D.; Hall, P. B.; Hicks, S.; Horenstein, D.; Hutchison, T.; Im, M.; Jensen, J. J.; Joner, M. D.; Jones, J.; Kaspi, S.; Kelly, B. C.; Kennea, J. A.; Kim, M.; Kim, S. C.; Klimanov, S. A.; Lee, J. C.; Leonard, D. C.; Lira, P.; MacInnis, F.; Manne-Nicholas, E. R.; Mathur, S.; McHardy, I. M.; Montouri, C.; Musso, R.; Nazarov, S. V.; Norris, R. P.; Nousek, J. A.; Okhmat, D. N.; Papadakis, I.; Parks, J. R.; Pott, J.-U.; Rafter, S. E.; Rix, H.-W.; Saylor, D. A.; Schimoia, J. S.; Schnülle, K.; Sergeev, S. G.; Siegel, M.; Spencer, M.; Sung, H.-I.; Teems, K. G.; Treu, T.; Turner, C. S.; Uttley, P.; Villforth, C.; Weiss, Y.; Woo, J.-H.; Yan, H.; Young, S.; Zheng, W.-K.
2016-06-01
During an intensive Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV monitoring campaign of the Seyfert 1 galaxy NGC 5548 performed from 2014 February to July, the normally highly correlated far UV continuum and broad emission line variations decorrelated for ∼60–70 days, starting ∼75 days after the first HST/COS observation. Following this anomalous state, the flux and variability of the broad emission lines returned to a more normal state. This transient behavior, characterized by significant deficits in flux and equivalent width of the strong broad UV emission lines, is the first of its kind to be unambiguously identified in an active galactic nucleus reverberation mapping campaign. The largest corresponding emission line flux deficits occurred for the high ionization, collisionally excited lines C iv and Si iv(+O iv]), and also He ii(+O iii]), while the anomaly in Lyα was substantially smaller. This pattern of behavior indicates a depletion in the flux of photons with {E}{{ph}}\\gt 54 {{eV}} relative to those near 13.6 eV. We suggest two plausible mechanisms for the observed behavior: (i) temporary obscuration of the ionizing continuum incident upon broad line region (BLR) clouds by a moving veil of material lying between the inner accretion disk and inner (BLR), perhaps resulting from an episodic ejection of material from the disk, or (ii) a temporary change in the intrinsic ionizing continuum spectral energy distribution resulting in a deficit of ionizing photons with energies >54 eV, possibly due to a transient restructuring of the Comptonizing atmosphere above the disk. Current evidence appears to favor the latter explanation.
Anomalous magnetotransport behavior in Fe-doped MnNiGe alloys
NASA Astrophysics Data System (ADS)
Dutta, P.; Pramanick, S.; Singh, Vijay; Major, Dan Thomas; Das, D.; Chatterjee, S.
2016-04-01
The electrical dc transport properties of hexagonal magnetic equiatomic alloys of nominal composition Mn1 -xFexNiGe (x =0.2 and0.25 ) have been investigated experimentally as well as theoretically using first-principles electronic structure calculations. Thermal hysteresis in the magnetization data indicates that the alloys undergo a first-order martensitic transition. Both the alloys show unusual nonmetallic resistivity behavior and a noticeable amount of training effect in resistivity when thermally cycled through the first-order martensitic transition. We observe moderate negative magnetoresistance (˜-11.5 % for 150 kOe) at 5 K (well below the martensitic transition temperature) associated with clear virgin line effect for both the alloys. We have adapted different flavors of density functional theory approach to understand the experimentally observed nonmetallic transport behavior.
NASA Astrophysics Data System (ADS)
Korman, M. S.; Duong, D. V.; Kalsbeck, A. E.
2015-10-01
An apparatus (SPO), designed to study flexural vibrations of a soil loaded plate, consists of a thin circular elastic clamped plate (and cylindrical wall) supporting a vertical soil column. A small magnet attached to the center of the plate is driven by a rigid AC coil (located coaxially below the plate) to complete the electrodynamic soil plate oscillator SPO design. The frequency dependent mechanical impedance Zmech (force / particle velocity, at the plate's center) is inversely proportional to the electrical motional impedance Zmot. Measurements of Zmot are made using the complex output to input response of a Wheatstone bridge that has an identical coil element in one of its legs. Near resonance, measurements of Zmot (with no soil) before and after a slight point mass loading at the center help determine effective mass, spring, damping and coupling constant parameters of the system. "Tuning curve" behavior of real{ Zmot } and imaginary{ Zmot } at successively higher vibration amplitudes of dry sifted masonry sand are measured. They exhibit a decrease "softening" in resonance frequency along with a decrease in the quality Q factor. In soil surface vibration measurements a bilinear hysteresis model predicts the tuning curve shape for this nonlinear mesoscopic elastic SPO behavior - which also models the soil vibration over an actual plastic "inert" VS 1.6 buried landmine. Experiments are performed where a buried 1m cube concrete block supports a 12 inch deep by 30 inch by 30 inch concrete soil box for burying a VS 1.6 in dry sifted masonry sand for on-the-mine and off-the-mine soil vibration experiments. The backbone curve (a plot of the peak amplitude vs. corresponding resonant frequency from a family of tuning curves) exhibits mostly linear behavior for "on target" soil surface vibration measurements of the buried VS 1.6 or drum-like mine simulants for relatively low particle velocities of the soil. Backbone curves for "on target" measurements exhibit
Zhang, Haiwa; Ke, Feng; Li, Yan; Wang, Li; Liu, Cailong; Zeng, Yi; Yao, Mingguang; Han, Yonghao; Ma, Yanzhang; Gao, Chunxiao
2015-01-01
The interface effect is one of the most important factors that strongly affect the structural transformations and the properties of nano-/submicro-crystals under pressure. However, characterization of the granular boundary changes in materials is always challenging. Here, using tetrakaidecahedral Zn2SnO4 microcrystals as an example, we employed alternating current impedance, X-ray diffraction methods and transmission electron microscopy to elucidate the effect of the interface on the structure and electrical transport behavior of the Zn2SnO4 material under pressure. We clearly show that grain refinement of the initial microcrystals into nanocrystals (approximately 5 nm) occurs at above 12.5 GPa and is characterized by an anomalous resistance variation without a structural phase transition. A new phase transition pathway from the cubic to hexagonal structure occurs at approximately 29.8 GPa in Zn2SnO4. The unexpected grain refinement may explain the new structural transition in Zn2SnO4, which is different from the previous theoretical prediction. Our results provide new insights into the link between the structural transition, interface changes and electrical transport properties of Zn2SnO4. PMID:26399167
NASA Astrophysics Data System (ADS)
Wakisaka, Yuki; Uemura, Yohei; Yokoyama, Toshihiko; Asakura, Hiroyuki; Morimoto, Hiroyuki; Tabuchi, Masao; Ohshima, Daiki; Kato, Takeshi; Iwata, Satoshi
2015-11-01
The metamagnetic transition in FeRh thin films has been investigated via temperature-dependent x-ray-absorption fine-structure spectroscopy in order to gain correlations between magnetization and local electronic and geometric structures. According to the Fe and Rh K -edge x-ray-absorption near-edge structure (XANES), strong hybridization between Fe and Rh was revealed to exist. This Fe-Rh hybridization was observed to decrease during the phase transition from the antiferromagnetic (AFM) to ferromagnetic (FM) phases from the systematic change in the Fe K -edge XANES. In addition, only the Debye-Waller factor of the Fe-Fe pair in the AFM phase was observed to be considerably enhanced when compared with that in the FM phase, which was ascribed to local structural fluctuation inherent in the AFM phase. By considering the different features of the exchange interactions in Fe-Rh and Fe-Fe, this anomalous behavior is interpreted as being consistent with the recent theoretical study proposing the local fluctuations of spin and structure. Therefore, we consider that the local spin and Fe-Fe distance fluctuations play an important role in driving the metamagnetic transition, whereas the Fe-Rh hybridization correlates with the static stability of each magnetic phase.
Carrado, K.A.; Thiyagarajan, P.; Winans, R.E.; Song, Kang
1997-09-01
The authors have exploited anomalous small angle x-ray scattering (ASAXS) to monitor the solvation behavior of Cu(II), Er(III) and Yb(III) ions within the interlayers of the natural aluminosilicate clay mineral montmorillonite. The ASAXS technique can reveal the distribution of specific metallic species within a heterogeneous and disordered matrix. The variations of signal intensity as a function of absorption energy were monitored for all of the metal-clays as a function of hydration. Two different hydration levels were probed: as prepared at ambient conditions, or so-called {open_quotes}dry{close_quotes} powders, and {open_quotes}wet{close_quotes} pastes. ASAXS intensities should increase with absorption energy if the metal ion is associated with the interlayer solvent (water in this case), and decrease if the metal ion is associated with the solid matrix. The results show that: (1) Cu(II) is solvated within the interlayers of the wet sample, as expected, and (2) Er(III) and Yb(III) decrease in ASAXS intensity with increased hydration. This latter result was not expected and there is speculation that these ions have associated as hydrolyzed products with the clay surface. The basic principles underlying SAXS and ASAXS will also be presented in this paper.
Anomalous behavior of LiF:Mg,Cu,P (TLD100H) irradiated with electron beams
NASA Astrophysics Data System (ADS)
Triolo, A.; Brai, M.; Bartolotta, A.; Marrale, M.
2006-12-01
Thermoluminescent dosimeters of LiF:Mg,Cu,P (TLD100H) were exposed to 60Co γ-ray, protons, high energy electrons and the glow curves were analyzed. We observed an unusual behavior of the TL response of dosimeters to 7 and 14 MeV electron beam. In fact the relative amplitude between two of the five peaks (2° and 3° peaks) assumes values smaller than the unity for doses up to 5 Gy and values greater than the unity for doses equal to or greater than 10 Gy. A possible explanation of this behavior is given adopting a model of the formation of the peaks 2° and 3° and examining the different ways of energy release in matter for each beam. To perform this analysis we deconvoluted the glow curve adopting general order kinetic (GOK) equation for the description of the peak shape, determining the number of peaks and their trapping parameter (E,s,n0).
Elastic behavior and pressure-induced structure evolution of topaz up to 45 GPa
NASA Astrophysics Data System (ADS)
Gatta, G. D.; Morgenroth, W.; Dera, P.; Petitgirard, S.; Liermann, H.-P.
2014-09-01
The behavior of a natural topaz, Al2.00Si1.05O4.00(OH0.26F1.75), has been investigated by means of in situ single-crystal synchrotron X-ray diffraction up to 45 GPa. No phase transition or change in the compressional regime has been observed within the pressure-range investigated. The compressional behavior was described with a third-order Birch-Murnaghan equation of state (III-BM-EoS). The III-BM-EoS parameters, simultaneously refined using the data weighted by the uncertainties in P and V, are as follows: K V = 158(4) GPa and K V ' = 3.3(3). The confidence ellipse at 68.3 % (Δχ2 = 2.30, 1σ) was calculated starting from the variance-covariance matrix of K V and K' obtained from the III-BM-EoS least-square procedure. The ellipse is elongated with a negative slope, indicating a negative correlation of the parameters K V and K V ', with K V = 158 ± 6 GPa and K V ' = 3.3 ± 4. A linearized III-BM-EoS was used to obtain the axial-EoS parameters (at room- P), yielding: K( a) = 146(5) GPa [ β a = 1/(3 K( a)) = 0.00228(6) GPa-1] and K'( a) = 4.6(3) for the a-axis; K( b) = 220(4) GPa [ β b = 0.00152(4) GPa-1] and K'( b) = 2.6(3) for the b-axis; K( c) = 132(4) GPa [ β c = 0.00252(7) GPa-1] and K'( c) = 3.3(3) for the c-axis. The elastic anisotropy of topaz at room- P can be expressed as: K( a): K( b): K( c) = 1.10:1.67:1.00 ( β a: β b: β c = 1.50:1.00:1.66). A series of structure refinements have been performed based on the intensity data collected at high pressure, showing that the P-induced structure evolution at the atomic scale is mainly represented by polyhedral compression along with inter-polyhedral tilting. A comparative analysis of the elastic behavior and P/ T-stability of topaz polymorphs and "phase egg" (i.e., AlSiO3OH) is carried out.
Acoustic probing of elastic behavior and damage in weakly cemented granular media
NASA Astrophysics Data System (ADS)
Langlois, V.; Jia, X.
2014-02-01
We investigate the elastic behavior and damage of weakly cemented granular media under external load with ultrasound. The cementation controlled experiments are performed by freezing the capillary liquid at the bead contact in a dense glass or polymeric [poly(methyl methacrylate)] bead pack wet by tetradecane of volume fraction ϕ = 0.1%-4%. When the pendular rings are solidified, an abrupt increase by a factor of 2 in the compressional wave velocity is observed. We interpret the data in terms of effective medium models in which the contact stiffnesses are derived by either a bonded contact model [P. J. Digby, J. Appl. Mech. 48, 803 (1981), 10.1115/1.3157738] or a cemented contact model [J. Dvorkin, A. Nur, and H. Yin, Mech. Mater. 18, 351 (1994), 10.1016/0167-6636(94)90044-2]. The former fails to quantitatively account for the results with a soft cement relative to the grain, whereas the latter considering the mechanical properties of the cement does apply. Moreover, we monitor the irreversible behavior of the cemented granular packs under moderate uniaxial loading (<1.3 MPa) with the correlation method of ultrasound scattering. The damage of the cemented materials is accompanied by a compressional wave velocity decrease up to 60%, likely due to the fractures induced at the grain-cement interfaces.
Acoustic probing of elastic behavior and damage in weakly cemented granular media.
Langlois, V; Jia, X
2014-02-01
We investigate the elastic behavior and damage of weakly cemented granular media under external load with ultrasound. The cementation controlled experiments are performed by freezing the capillary liquid at the bead contact in a dense glass or polymeric [poly(methyl methacrylate)] bead pack wet by tetradecane of volume fraction ϕ = 0.1%-4%. When the pendular rings are solidified, an abrupt increase by a factor of 2 in the compressional wave velocity is observed. We interpret the data in terms of effective medium models in which the contact stiffnesses are derived by either a bonded contact model [P. J. Digby, J. Appl. Mech. 48, 803 (1981)] or a cemented contact model [J. Dvorkin, A. Nur, and H. Yin, Mech. Mater. 18, 351 (1994)]. The former fails to quantitatively account for the results with a soft cement relative to the grain, whereas the latter considering the mechanical properties of the cement does apply. Moreover, we monitor the irreversible behavior of the cemented granular packs under moderate uniaxial loading (1.3 MPa) with the correlation method of ultrasound scattering. The damage of the cemented materials is accompanied by a compressional wave velocity decrease up to 60%, likely due to the fractures induced at the grain-cement interfaces. PMID:25353594
NASA Astrophysics Data System (ADS)
Barbati, Alexander; Robisson, Agathe; Dussan, Elizabeth; McKinley, Gareth
2015-11-01
The transport of particle-laden viscoelastic suspensions is routine in several industrial and natural systems. Many applications, such as hydraulic fracturing in the oilfield, require the successive (and occasionally simultaneous) flow and placement or rigid particles, commonly known as proppant. Hydraulically-generated fractures are routinely less than 6 particle diameters in width. We investigate the flow of viscoelastic particle-laden suspensions in microfabricated geometries mimicking hydraulically-generated fractures under a variety of dynamic conditions to illustrate the interaction between inertia, elasticity, and geometry on particle behavior during flow. We characterize the flow in these model geometries with a combination of streakline imaging, particle image velocimetry, and direct imaging of model proppant particles embedded in the flow. We accompany these small-scale measurements with macro-scale interrogation of fluid rheology by measuring material functions of the working fluid in under shear and extension. These material functions are used in concert with imposed flow conditions and imaging results to identify dominant transport mechanisms on the channel and particle scale, which indicate overall system behavior.
Structural and elastic properties of fcc/fcc metallic multilayers: A molecular-dynamics study
NASA Astrophysics Data System (ADS)
Tȩcza, Grzegorz W.
1992-12-01
Interplanar and intraplanar spacings as well as the elastic constants of fcc/fcc metallic multilayers stacked along [001] were determined via variable-cell molecular-dynamics simulation in (HtN) and (EhN) ensembles at room temperature. Qualitative differences in the structural and elastic properties of the multilayers, simulated using various 12-6 Lennard-Jones potentials, were observed. The anomalous behavior of the elastic constants and the biaxial modulus was linked to the modulation wavelength dependence of various structural parameters. The importance of the fluctuation contributions for the calculation of the full elastic constants is demonstrated.
Application of CFD to Explain Anomalous Stall Behavior of the SSME Flowmeter
NASA Technical Reports Server (NTRS)
Ascoli, E.; Clever, W.; Hadid, A.; Lynch, E. D.; Stewart, M.; Lee, K.
1999-01-01
The Space Shuttle Main Engine (SSME) Fuel Flowmeter is located in the duct between the low and high pressure fuel turbopumps. In the flowmeter the rotation rate of a 4-blade rotor positioned downstream of two flow straighteners is employed to measure the engine fuel flow rate and thereby control the engine mixture ratio via the engine controller. Hence, inaccurate operation of the flowmeter could have serious consequences for SSME engine operation and performance, forcing, for example, tanking of extra fuel to allow for inaccurate flowmeter measurement. Since the current flight flowmeter configuration was incorporated into the SSME in the early eighties, some anomalies in flowmeter behavior have been observed. The initial flowmeter incorporated an "egg crate" design for the two flow straighteners which turn the duct flow to make it more uniform and parallel after it has come out of the 90 degree bend just upstream of the flowmeter.
Electron energy-loss spectroscopy of anomalous plutonium behavior in nuclear waste materials.
Buck, Edgar C; Finn, Patricia A; Bates, John K
2004-01-01
Plutonium-enriched layer has been observed in corroded spent uranium oxide fuel (CSNF). These Pu-enriched regions were examined with analytical transmission electron microscopy combined with electron energy-loss spectroscopy (EELS). The enriched region also contained U, Am, Ru, Zr, but only minor enrichment of rare earth elements. The Pu, possibly as Pu(V) according to EELS measurements, was dispersed within re-precipitated uranium oxide (identified as U3O8) nano-crystals between U(VI) secondary phases and the CSNF surface. The U, Pu, and Am enrichment was observed in the corrosion products with tests on different nuclear fuels. This may have implications for the long-term behavior of CSNF under storage in a geologic waste repository. Furthermore, there may be an increased potential for the generation of Pu-bearing colloids from this type of weathered CSNF. PMID:15003610
Electron Energy-loss Spectroscopy of Anomalous Plutonium Behavior in Nuclear Waste Materials
Buck, Edgar C.; Finn, patricia A.; Bates, John K.
2004-06-01
Plutonium-enriched layer has been observed in corroded spent uranium oxide fuel (CSNF). These Pu-enriched regions were examined with analytical transmission electron microscopy combined with electron energy-loss spectroscopy. The enriched region also contained U, Am, Ru, Zr, but only minor enrichment of rare earth elements. The Pu, possibly as Pu(V) according to EELS measurements, was dispersed within re-precipitated uranium oxide (identified as U3O8) nano-crystals between U(VI) secondary phases and the CSNF surface. The U, Pu, and Am enrichment was observed in the corrosion products with tests on different nuclear fuels. This may have implications for the long-term behavior of CSNF under storage in a geologic waste repository. Furthermore, there may be an increased potential for the generation of Pu-bearing colloids from this type of weathered CSNF.
Mallamace, Francesco; Corsaro, Carmelo; Stanley, H. Eugene
2012-01-01
The density maximum of water dominates the thermodynamics of the system under ambient conditions, is strongly P-dependent, and disappears at a crossover pressure Pcross ~ 1.8 kbar. We study this variable across a wide area of the T–P phase diagram. We consider old and new data of both the isothermal compressibility KT(T, P) and the coefficient of thermal expansion αP(T, P). We observe that KT(T) shows a minimum at T* ~ 315±5 K for all the studied pressures. We find the behavior of αP to also be surprising: all the αP(T) curves measured at different P cross at T*. The experimental data show a “singular and universal expansivity point” at T* ~ 315 K and αP(T*) ≃ 0.44 10−3 K−1. Unlike other water singularities, we find this temperature to be thermodynamically consistent in the relationship connecting the two response functions. PMID:23251779
Anomalous phonon behavior of carbon nanotubes: First-order influence of external load
NASA Astrophysics Data System (ADS)
Aghaei, Amin; Dayal, Kaushik; Elliott, Ryan S.
2013-01-01
External loads typically have an indirect influence on phonon curves, i.e., they influence the phonon curves by changing the state about which linearization is performed. In this paper, we show that in nanotubes, the axial load has a direct first-order influence on the long-wavelength behavior of the transverse acoustic (TA) mode. In particular, when the tube is force-free, the TA mode frequencies vary quadratically with wave number and have curvature (second derivative) proportional to the square-root of the nanotube's bending stiffness. When the tube has non-zero external force, the TA mode frequencies vary linearly with wave number and have slope proportional to the square-root of the axial force. Therefore, the TA phonon curves—and associated transport properties—are not material properties but rather can be directly tuned by external loads. In addition, we show that the out-of-plane shear deformation does not contribute to this mode and the unusual properties of the TA mode are exclusively due to bending. Our calculations consist of 3 parts: First, we use a linear chain of atoms as an illustrative example that can be solved in close-form; second, we use our recently developed symmetry-adapted phonon analysis method to present direct numerical evidence; and finally, we present a simple mechanical model that captures the essential physics of the geometric nonlinearity in slender nanotubes that couples the axial load directly to the phonon curves. We also compute the density of states and show the significant effect of the external load.
Jeong, Sung In; Kim, Byung-Soo; Kang, Sun Woong; Kwon, Jae Hyun; Lee, Young Moo; Kim, Soo Hyun; Kim, Young Ha
2004-12-01
Tubular scaffolds were fabricated from very elastic poly(L-lactide-co-epsilon-caprolactone) (PLCL, 50:50). The scaffolds were seeded with smooth muscle cells (SMCs) and implanted in nude mice to investigate the tissue compatibility and in vivo degradation behavior. Histological examination of all the implants with haematoxylin and eosin staining, masson trichrome staining, SM alpha-actin antibody, and CM-DiI labeling confirmed that the regular morphology and biofunction of the SMCs seeded and the expression of the vascular smooth muscle matrices in PLCL scaffolds. The implanted PLCL scaffolds displayed a slow degradation on time, where caprolactone units were faster degraded than lactide did. This could be explained by the fact that amorphous regions composed of mainly CL moieties degraded earlier than hard domains where most of the LA units were located. From these results, the scaffolds applied in this study were found to exhibit excellent tissue compatibility to SMCs and might be very useful for vascular tissue engineering. PMID:15183608
NASA Astrophysics Data System (ADS)
Hopersky, A. N.; Yavna, V. A.; Novikov, S. A.; Chuvenkov, V. V.
2000-06-01
The differential cross section and dispersional correction for the real part of the elastic scattering amplitude of an x-ray photon by a molybdenum atom in the energy range of the ionization threshold of the 1s-shell is calculated in the non-relativistic approximation. The effect of the rearrangement of electron shells of the atomic residues in the field of the virtual 1s-vacancy is taken into account. The processes of one-photon multiple excitation/ionization of the ground state is also considered. Good agreement with the results of existing experiments is obtained.
Stokes, Ian A F; Laible, Jeffrey P; Gardner-Morse, Mack G; Costi, John J; Iatridis, James C
2011-01-01
Intervertebral disks support compressive forces because of their elastic stiffness as well as the fluid pressures resulting from poroelasticity and the osmotic (swelling) effects. Analytical methods can quantify the relative contributions, but only if correct material properties are used. To identify appropriate tissue properties, an experimental study and finite element analytical simulation of poroelastic and osmotic behavior of intervertebral disks were combined to refine published values of disk and endplate properties to optimize model fit to experimental data. Experimentally, nine human intervertebral disks with adjacent hemi-vertebrae were immersed sequentially in saline baths having concentrations of 0.015, 0.15, and 1.5 M and the loss of compressive force at constant height (force relaxation) was recorded over several hours after equilibration to a 300-N compressive force. Amplitude and time constant terms in exponential force-time curve-fits for experimental and finite element analytical simulations were compared. These experiments and finite element analyses provided data dependent on poroelastic and osmotic properties of the disk tissues. The sensitivities of the model to alterations in tissue material properties were used to obtain refined values of five key material parameters. The relaxation of the force in the three bath concentrations was exponential in form, expressed as mean compressive force loss of 48.7, 55.0, and 140 N, respectively, with time constants of 1.73, 2.78, and 3.40 h. This behavior was analytically well represented by a model having poroelastic and osmotic tissue properties with published tissue properties adjusted by multiplying factors between 0.55 and 2.6. Force relaxation and time constants from the analytical simulations were most sensitive to values of fixed charge density and endplate porosity. PMID:20711754
Multiscale, structure-based modeling for the elastic mechanical behavior of arterial walls.
Stylianopoulos, Triantafyllos; Barocas, Victor H
2007-08-01
Passive elastic behavior of arterial wall remains difficult to model. Although phenomenological and structural models exist, the question of how the three-dimensional network structure of the collagen in the artery determines its mechanical properties is still open. A model is presented that incorporates a collagen network as well as the noncollagenous material that comprise the artery. The collagen architecture is represented as a network of interconnected fibers, and a neo-Hookean constitutive equation is used to describe the contribution of the noncollagenous matrix. The model is multiscale in that volume-averaging theory is applied to the collagen network, and it is structural in that parameters of the microstructure of the collagen network were considered instead of a macroscopic constitutive law. The computational results provided a good fit to published experimental data for decellularized porcine carotid arteries. The model predicted increased circumferential compliance for increased axial stretch, consistent with previously published reports, and a relatively small sensitivity to open angle. Even at large extensions, the model predicted that the noncollagenous matrix would be in compression, preventing collapse of the collagen network. The incorporation of fiber-fiber interactions led to an accurate model of artery wall behavior with relatively few parameters. The counterintuitive result that the noncollagenous component is in compression during extension and inflation of the tissue suggests that the collagen is important even at small strains, with the noncollagenous components supporting the network, but not resisting the load directly. More accurate representation of the microstructure of the artery wall is needed to explore this issue further. PMID:17655483
NASA Astrophysics Data System (ADS)
Ikeya, Motoji; Matsumoto, Hiroshi; Huang, Qing-Hua
1998-05-01
Alignment of silkworms and fish, observed as seismic anomalous animal behavior (SAAB) prior to the Kobe earthquake, were duplicated in a laboratory by applying a pulsed electric field assuming SAAB as electrophysiological responses to the stimuli of seismic electric signals (SES). The animals became aligned perpendicularly to the field direction since their skeletal muscle had a higher resistivity perpendicular to the field direction than parallel to it. An electromagnetic model of a fault is proposed in which dipolar charges, ±q are generated due to the change of seismic stress, σ(t). From a mathematical model, dq/dt=-α(dσ/dt) - q/ɛρ, where α is the charge generation constant like a piezoelectric coefficient, ɛ, the dielectric constant and ρ, the resistivity of bedrock granite. A fault having a length 2a and a displacement or rock rupture time τ, during which the stress is changed, gives pulsed dipolar charge surface densities, +q(t, x) and -q(t, x+2a), or an apparent electric dipole moment of P(t)=2aQ(t)=2aAq(t)=aM 0[ɛρ/(τ-ɛρ)](e-1/τ-e-1/σρ) using the earthquake moment M 0. The fault displacement, D, its initial velocity, D‧ and the stress drop, Δσ give τ=D/D‧=(Δσ/σ 0)(α/β). The field fintensity, F, and seismic current density at a fault zone, J were calculated as F=q/ɛ and J=F/ρ‧ using ρ‧ of water as to give J=0.1-1 A/m2 sufficient to cause SAAB experimentally. The near-field ultra low frequency (ULF) waves generated by P(t) give SES reciprocally proportional to the distance R.
Elastic behavior of zymogen granule membranes in response to changes in pH and pCa.
Miyamoto, S; Fujime, S
1990-01-01
In the process of secretion, the membrane of secretory granules is expected to change its elastic behavior. Elastic modulus of the membrane of zymogen granules, prepared from the rat pancreas acinar cell, was measured by an osmotic swelling method. The elastic modulus of the granule membrane at pCa 8 reduced from the maximal value of 230 dyn/cm at pH 6.0 to almost zero at pH 7.5. In a cytosol of an acinar cell, calcium ions play an important role as a second messenger in secretion. The elastic modulus of the granule membrane reduced in a sigmoidal fashion at pCa between 7.0 and 6.0. This range of pCa corresponds to a physiological rise of free Ca2+ concentrations in the cell cytosol when stimulated by external secretagogues. Reduction of the elastic modulus indicates that the state of the granule membrane switches to a more flexible one in which the granule is easy to appose to the cell plasma membrane and then swell as a final step of exocytosis. PMID:2306504
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.
NASA Astrophysics Data System (ADS)
Schiemer, Jason; Spalek, Leszek J.; Saxena, Siddharth S.; Panagopoulos, Christos; Katsufuji, Takuro; Bussmann-Holder, Annette; Köhler, Jürgen; Carpenter, Michael A.
2016-02-01
Magnetoelectric coupling phenomena in EuTiO3 are of considerable fundamental interest and are also understood to be key to reported multiferroic behavior in strained films, which exhibit distinctly different properties to the bulk. Here, the magnetoelastic coupling of EuTiO3 is investigated by resonant ultrasound spectroscopy with in situ applied magnetic field and stress as a function of temperature ranging from temperatures above the structural transition temperature T s to below the antiferromagnetic ordering temperature T n. One single crystal and two polycrystalline samples are investigated and compared to each other. Both paramagnetic and diamagnetic transducer carriers are used, allowing an examination of the effect of both stress and magnetic field on the behavior of the sample. The properties are reported in constant field/variable temperature and in constant temperature/variable field mode where substantial differences between both data sets are observed. In addition, elastic and magnetic poling at high fields and stresses at low temperature has been performed in order to trace the history dependence of the elastic constants. Four different temperature regions are identified, characterized by unusual elastic responses. The low-temperature phase diagram has been explored and found to exhibit rich complexity. The data evidence a considerable relaxation of elastic constants at high temperatures, but with little effect from magnetic field alone above 20 K, in addition to the known low-temperature coupling.
NASA Astrophysics Data System (ADS)
Schmidt, Martin Jeffrey
The goal of this dissertation was to experimentally investigate the high rate and high pressure mechanical response of a mortar and concrete mix and use or develop a constitutive model able to describe the observed behavior. Triaxial compression tests at a strain rate of 10-6/ s, and for confining pressures ranging from 0 to 0.5 GPa were conducted. Dynamic tests in the range 60/s to about 160/s under both unconfined and confined conditions were conducted using the University of Florida's 7.62 cin diameter split Hopkinson pressure bar (SHPB). The data obtained in such tests allowed the quantification of the combined effects of confining pressure and strain rate on the deformation and strength of the materials. For mortar, dilatancy has been observed at high levels of the principal stress difference for both dynamic and quasi-static conditions. The unconfined dynamic compressive strengths are approximately double those of the quasi-static compressive strengths. Most of the confined SHPB mortar specimens showed very little damage post-test other than some chipping around the top edges, most likely due to localized tensile effects. For the concrete selected for this research. WES5000, quasi-static hydrostatic tests conducted up to a pressure of 0.5 GPa allowed for the accurate determination of the dependence of the bulk modulus on pressure and the correct estimation of the material's compaction properties when subjected to pressures in the range encountered in dynamic events. For confined quasi-static conditions, the material exhibited hardening behavior up to failure. Both compressibility and dilatancy regimes of the volumetric behavior were observed, the dilatancy threshold being highly dependent on the level of confinement. The unconfined dynamic strength is as high as 1.5 times the quasi-static strength, the material generally exhibiting far more cracking under similar loading conditions than was observed in mortar. The confined dynamic tests showed similar stress
Application of the pair torque interaction potential to simulate the elastic behavior of SLMoS2
NASA Astrophysics Data System (ADS)
Berinskii, I. E.; Panchenko, A. Yu; Podolskaya, E. A.
2016-05-01
This paper is devoted to the application of the pair torque interaction potential for the simulation of the elastic behavior of a promising two-dimensional material: single layer molybdenium disulphide (SLMoS2). It is demonstrated that both Mo-Mo and S-S interactions can be regarded as pair force interactions with sufficient accuracy. Using both experimental and calculated numerically elastic moduli, and also the phonon spectrum available in the literature, the parameters of the Morse potential are determined for Mo-Mo and S-S bonds, and the parameters of the pair torque potential are obtained for the Mo-S bond. As a result, a combination of force and torque pair potentials is proposed, which allows for the correct modelling of SLMoS2 mechanical behavior.
NASA Technical Reports Server (NTRS)
Rubinstein, Robert; Auslender, Aaron H.
1999-01-01
The decay of anomalous effects on shock waves in weakly ionized gases following plasma generator extinction has been measured in the anticipation that the decay time must correlate well with the relaxation time of the mechanism responsible for the anomalous effects. When the relaxation times cannot be measured directly, they are inferred theoretically, usually assuming that the initial state is nearly in thermal equilibrium. In this paper, it is demonstrated that relaxation from any steady state far from equilibrium, including the state of a weakly ionized gas, can proceed much more slowly than arguments based on relaxation from near equilibrium states might suggest. This result justifies a more careful analysis of the relaxation times in weakly ionized gases and suggests that although the experimental measurements of relaxation times did not lead to an unambiguous conclusion, this approach to understanding the anomalous effects may warrant further investigation.
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.
Numerical modeling of the behavior of an elastic capsule in a microchannel flow: The initial motion
NASA Astrophysics Data System (ADS)
Ma, Gang; Hua, Jinsong; Li, Hua
2009-04-01
The initial motion of two-dimensional capsule in microchannel flow just after release is investigated in this paper by a numerical simulation method, which combines the finite volume method with the front tracking technique. The capsule is modeled as liquid medium enclosed by a thin membrane, for which linear elastic properties are taken into consideration. Three kinds of initial capsule shapes (circle, ellipse, and biconcave) and three initial positions (center-line, near-center, and near-wall positions) are considered in the simulations. Off-center capsules (the near-center and near-wall capsules) experience tilting and membrane tank-treading, and migrate laterally while they move with the fluid flow. After initial rapid tilting, the circular and elliptic near-wall capsules reach quasistationary tilt orientation, while the biconcave near-wall capsules experience steady change in tilt orientation with time. Lateral movements of the capsules indicate the existence of lift effect causing the capsule to move away from the wall. Lift velocities, the velocity components along the transverse direction, of the circular near-wall capsules decrease as they approach the centerline, while those of the elliptic and biconcave near-wall capsules do not show this trend, which might result from the short range of the simulation time. In general, the capsule with higher membrane dilation modulus has lower lift velocity, showing the effect of capsule deformability on the capsule behavior. Both tank-treading and lift velocities are 1-2 orders lower than the capsule translational velocity. For the circular and biconcave capsules, no matter the center-line or off-center capsules, hematocrit ratio increases with the membrane dilation modulus, namely, the capsule moving velocity decreases with the increasing dilation modulus, while the elliptic capsules with nondimensional membrane dilation moduli of 2500 and 500 show inverse trend in some time range. A preliminary study is carried out
NASA Astrophysics Data System (ADS)
Weise, Michael J.; Costa, Daniel P.; Kudela, Raphael M.
2006-11-01
During the highly anomalous conditions in early 2005, characterized by increased water temperatures and decreased productivity, male California sea lions adopted previously undocumented foraging behaviors. We investigated the movement and spatially explicit foraging behavior of males using satellite-linked data loggers and compared foraging behavior and effort between 2003-2004 and 2004-2005. Males foraged almost exclusively over the continental shelf during short trips in 2003-2004, while during anomalous conditions in 2004-2005 they altered their foraging effort by spending more time at sea and venturing up to 450 km offshore. Foraging trips in 2004-2005 were more than twice the distance and three times the duration of trips during 2003-2004. Our data indicated that the effects of climatic shifts during 2005 extended beyond the physical oceanography and lower trophic levels, to an apex predator; providing insight into the plasticity of foraging behavior and movement patterns of sea lions as they respond to environmental perturbations.
Lapas, Luciano C.; Ferreira, Rogelma M. S.; Rubí, J. Miguel; Oliveira, Fernando A.
2015-03-14
We analyze the temperature relaxation phenomena of systems in contact with a thermal reservoir that undergoes a non-Markovian diffusion process. From a generalized Langevin equation, we show that the temperature is governed by a law of cooling of the Newton’s law type in which the relaxation time depends on the velocity autocorrelation and is then characterized by the memory function. The analysis of the temperature decay reveals the existence of an anomalous cooling in which the temperature may oscillate. Despite this anomalous behavior, we show that the variation of entropy remains always positive in accordance with the second law of thermodynamics.
NASA Astrophysics Data System (ADS)
Lapas, Luciano C.; Ferreira, Rogelma M. S.; Rubí, J. Miguel; Oliveira, Fernando A.
2015-03-01
We analyze the temperature relaxation phenomena of systems in contact with a thermal reservoir that undergoes a non-Markovian diffusion process. From a generalized Langevin equation, we show that the temperature is governed by a law of cooling of the Newton's law type in which the relaxation time depends on the velocity autocorrelation and is then characterized by the memory function. The analysis of the temperature decay reveals the existence of an anomalous cooling in which the temperature may oscillate. Despite this anomalous behavior, we show that the variation of entropy remains always positive in accordance with the second law of thermodynamics.
Lapas, Luciano C; Ferreira, Rogelma M S; Rubí, J Miguel; Oliveira, Fernando A
2015-03-14
We analyze the temperature relaxation phenomena of systems in contact with a thermal reservoir that undergoes a non-Markovian diffusion process. From a generalized Langevin equation, we show that the temperature is governed by a law of cooling of the Newton's law type in which the relaxation time depends on the velocity autocorrelation and is then characterized by the memory function. The analysis of the temperature decay reveals the existence of an anomalous cooling in which the temperature may oscillate. Despite this anomalous behavior, we show that the variation of entropy remains always positive in accordance with the second law of thermodynamics. PMID:25770525
NASA Astrophysics Data System (ADS)
Phani, K. K.; Sanyal, Dipayan
2008-04-01
A novel procedure for the estimation of the elastic properties of the sintered and compacted metal powders from the ultrasonic velocities of the green compact alone has been proposed in this article. The methodology has been validated for sintered iron powder and copper powder compacts as well as for consolidated silver powder compacts of various processing histories, powder sizes, and pore morphology. The predicted elastic moduli, including the derived modulus (Poisson’s ratio), are found to be in reasonably good agreement with the measured data reported in the literature. The proposed method can be developed as a potent tool for the quantitative nondestructive evaluation (QNDE) of powder metallurgy products.
Elastic behavior of Bi2Se3 2D nanosheets grown by van der Waals epitaxy
NASA Astrophysics Data System (ADS)
Yan, Haoming; Vajner, Cooper; Kuhlman, Michael; Guo, Lingling; Li, Lin; Araujo, Paulo T.; Wang, Hung-Ta
2016-07-01
Elastic properties of bismuth selenite (Bi2Se3) two-dimensional (2D) nanosheets were investigated using atomic force microscope (AFM) nanoindentations. Bi2Se3 2D nanosheets were synthesized by van der Waals epitaxy and subsequently transferred on SiO2/Si substrates containing pre-fabricated hole arrays. The suspension of 2D nanosheets was confirmed via the distinct optical contrast characteristics and AFM. In nanoindentations, the correlation between a point force load and the elastic response in the deformation depth was found being thickness-dependent, between 7 and 12 quintuple layers. The Young's modulus, E = 17.86-25.45 GPa (fitted value = 20.67 GPa), and the pretension, T = 0.0218-0.0417 N/m, acquired according to the bending plate regime are consistent with ones from the stretching membrane regime. Furthermore, these Bi2Se3 2D nanosheets could elastically endure a 4.0%-8.3% strain before being ruptured with AFM tips. Compliant and robust elastic properties of Bi2Se3 2D nanosheets, as observed, provide a feasible way for exploring the topological phase transition.
Delella, Flávia Karina; Felisbino, Sérgio Luis
2010-10-01
Doxazosin (DOX), an α-adrenoceptor antagonist, induces the relaxation of smooth muscle cell tonus and reduces the clinical symptoms of benign prostatic hyperplasia (BPH). However, the effects of DOX in the prostate stromal microenvironment are not fully known. In a previous study, we showed that DOX treatment for 30 days increased deposition of collagen fibers in the three rat prostatic lobes. Herein, we investigated the effects of DOX on stromal cell ultrastructure and elastic fiber deposition. Adult Wistar rats were treated with DOX (25 mg/kg/day); and the ventral, dorsal, and anterior prostates were excised at 30 days of treatment. The prostatic lobes were submitted to histochemical and stereological-morphometric analyze and transmission electron microscopy (TEM). Histochemical staining plus stereological analysis of the elastic fiber system showed that DOX-treated prostatic lobes presented more elaunin and elastic fibers than controls, mainly in the ventral lobe. Ultrastructural analysis showed that fibroblasts and smooth muscle cells from DOX-treated prostates presented active synthetic phenotypes, evidenced by enlarged rough endoplasmic reticulum and Golgi apparatus cisterns, and confirmed the observation of thickened elaunin fibers. Our findings suggest that, under α-adrenergic blockade by DOX, the fibroblasts become more active and smooth muscle cells shift from a predominantly contractile to a more synthetic phenotype. The deposition of collagen and elastic system fibers in the prostatic stroma may counterbalance the absence of smooth muscle tone during α-blockers treatment. PMID:20155861
Robertson, Benjamin D.; Sawicki, Gregory S.
2015-01-01
In terrestrial locomotion, there is a missing link between observed spring-like limb mechanics and the physiological systems driving their emergence. Previous modeling and experimental studies of bouncing gait (e.g., walking, running, hopping) identified muscle-tendon interactions that cycle large amounts of energy in series tendon as a source of elastic limb behavior. The neural, biomechanical, and environmental origins of these tuned mechanics, however, have remained elusive. To examine the dynamic interplay between these factors, we developed an experimental platform comprised of a feedback-controlled servo-motor coupled to a biological muscle-tendon. Our novel motor controller mimicked in vivo inertial/gravitational loading experienced by muscles during terrestrial locomotion, and rhythmic patterns of muscle activation were applied via stimulation of intact nerve. This approach was based on classical workloop studies, but avoided predetermined patterns of muscle strain and activation—constraints not imposed during real-world locomotion. Our unconstrained approach to position control allowed observation of emergent muscle-tendon mechanics resulting from dynamic interaction of neural control, active muscle, and system material/inertial properties. This study demonstrated that, despite the complex nonlinear nature of musculotendon systems, cyclic muscle contractions at the passive natural frequency of the underlying biomechanical system yielded maximal forces and fractions of mechanical work recovered from previously stored elastic energy in series-compliant tissues. By matching movement frequency to the natural frequency of the passive biomechanical system (i.e., resonance tuning), muscle-tendon interactions resulting in spring-like behavior emerged naturally, without closed-loop neural control. This conceptual framework may explain the basis for elastic limb behavior during terrestrial locomotion. PMID:26460038
Robertson, Benjamin D; Sawicki, Gregory S
2015-10-27
In terrestrial locomotion, there is a missing link between observed spring-like limb mechanics and the physiological systems driving their emergence. Previous modeling and experimental studies of bouncing gait (e.g., walking, running, hopping) identified muscle-tendon interactions that cycle large amounts of energy in series tendon as a source of elastic limb behavior. The neural, biomechanical, and environmental origins of these tuned mechanics, however, have remained elusive. To examine the dynamic interplay between these factors, we developed an experimental platform comprised of a feedback-controlled servo-motor coupled to a biological muscle-tendon. Our novel motor controller mimicked in vivo inertial/gravitational loading experienced by muscles during terrestrial locomotion, and rhythmic patterns of muscle activation were applied via stimulation of intact nerve. This approach was based on classical workloop studies, but avoided predetermined patterns of muscle strain and activation-constraints not imposed during real-world locomotion. Our unconstrained approach to position control allowed observation of emergent muscle-tendon mechanics resulting from dynamic interaction of neural control, active muscle, and system material/inertial properties. This study demonstrated that, despite the complex nonlinear nature of musculotendon systems, cyclic muscle contractions at the passive natural frequency of the underlying biomechanical system yielded maximal forces and fractions of mechanical work recovered from previously stored elastic energy in series-compliant tissues. By matching movement frequency to the natural frequency of the passive biomechanical system (i.e., resonance tuning), muscle-tendon interactions resulting in spring-like behavior emerged naturally, without closed-loop neural control. This conceptual framework may explain the basis for elastic limb behavior during terrestrial locomotion. PMID:26460038
NASA Astrophysics Data System (ADS)
Zheng, Shanfu
In order to provide a better understanding on the mechanical properties of composite materials, a dual homogenization and finite-element study is carried out in this thesis to examine the elastic stiffness and elastoplastic behavior of a fiber-reinforced composite containing either ductile interphase or interfacial cracks. In the case of interphase, circular fibers are examined. In the other case of interfacial cracks, the fibers are taken to be with elliptic cross-section to demonstrate the influence of the fiber shape. The influence of interphase is studied by the generalized self-consistent model and by finite element method (FEM) with NASTRAN. Both the traction specified boundary and displacement specified boundary conditions are carried out to determine their influence on the elastoplastic behaviors of the fiber-reinforced composite. The propagation of plastic zone in both the interphase and the ductile matrix, and stress distribution in the interphase are also vividly demonstrated. A fictitious fiber model is adopted to mimic the effect of double debonding on composites. Based on this model, the elastic stiffness of elliptic fiber-reinforced composites is obtained directly by the homogenization method, and its elastoplastic behavior is further studied by use of the concept of secant moduli and an energy-based effective stress which is evaluated by a field fluctuation method. The finite element method is carried out by ANSYS to check the accuracy of the homogenization theory and to find out its associated debonding range in practice. The local stress and deformation behavior of the composite are also given by FEM as the complementary to the homogenization theory. The single debonding is performed also by FEM to compare its influence with that of the double debonding. A new model to investigate the effect of single debonding on the effective elastic moduli is developed based on the elasticity solution of a circular cylinder with an interface crack. The solution
NASA Astrophysics Data System (ADS)
Liu, Chu; Pollard, David D.; Shi, Bin
2013-01-01
Analytical solutions of elastic properties and failure modes of a two-dimensional close-packed discrete element model are proposed. Based on the assumption of small deformation, the conversion formulas between five inter-particle parameters of the lattice model and rock mechanical properties were derived. Using the formulas, the inter-particle parameters can be determined by Young's modulus (E), Poisson's ratio (v), tensile strength (Tu), compressive strength (Cu), and coefficient of intrinsic friction (μi). The lattice defined by the parameters simulates the elastic and failure behaviors of rocks and crystals and therefore can be used to investigate the initiation and development of geological structures quantitatively. Furthermore, the solutions also provide a theoretical basis for the calibration of parameters of random discrete assemblies. The model of quartz was used as an example to validate the formulas and test the errors. The simulated results show that E and v converge to theoretical values when particle number increases. These elastic properties are almost constant when the magnitude of strain is lower than 10-3. The simulated Tu and Cu of a single three-element unit are also consistent with the formulas. However, due to the boundary effects and stress concentrations, Tu and Cu of lattices with multiple units are lower than the values predicted by the formulas. Therefore, greater Tu and Cu can be used in the formulas to counteract this effect. The model is applicable to the simulation of complicated structures that involve deformation and failure at different scales.
NASA Astrophysics Data System (ADS)
Garg, Sandeep Kumar; Cuerno, Rodolfo; Kanjilal, Dinakar; Som, Tapobrata
2016-06-01
We have studied the early stage dynamics of ripple patterns on Si surfaces, in the fluence range of 1-3 × 1018 ions cm-2, as induced by medium energy Ar+-ion irradiation at room temperature. Under our experimental conditions, the ripple evolution is found to be in the linear regime, while a clear decreasing trend in the ripple wavelength is observed up to a certain time (fluence). Numerical simulations of a continuum model of ion-sputtered surfaces suggest that this anomalous behavior is due to the relaxation of the surface features of the experimental pristine surface during the initial stage of pattern formation. The observation of this hitherto unobserved behavior of the ripple wavelength seems to have been enabled by the use of medium energy ions, where the ripple wavelengths are found to be order(s) of magnitude larger than those at lower ion energies.
Spin-glass behavior and anomalous magnetoresistance in ferromagnetic Ge{sub 1-x}Fe{sub x}Te epilayer
Liu, Jindong; Cheng, Xiaomin Tong, Fei; Miao, Xiangshui
2014-07-28
We report that the Ge{sub 1-x}Fe{sub x}Te thin film exhibits spin-glass behavior when the Fe concentration increases to 0.08. A large bifurcation between the zero-field cooling and field cooling temperature-dependent magnetization was observed. The hysteresis loops after zero-field cooling and field cooling show an exchange bias effect. A time-dependent thermoremanent magnetization follows power-law decay, which confirms the existence of spin glass. The anomalous magnetotranport properties present a further evidence for spin-glass behavior and give a freezing temperature T{sub g} ∼ 5 K in the Ge{sub 0.92}Fe{sub 0.08}Te thin film.
NASA Technical Reports Server (NTRS)
2007-01-01
In this composite image of spiral galaxy M106 (NGC 4258), optical data from the Digitized Sky Survey is shown as yellow, radio data from the Very Large Array appears as purple, X-ray data from Chandra is coded blue, and infrared data from the Spitzer Space Telescope appears red. Two anomalous arms, which aren't visible at optical wavelengths, appear as purple and blue emission.
Rubber and gel origami: visco- and poro-elastic behavior of folded structures
NASA Astrophysics Data System (ADS)
Evans, Arthur; Bende, Nakul; Na, Junhee; Hayward, Ryan; Santangelo, Christian
2014-11-01
The Japanese art of origami is rapidly becoming a platform for material design, as researchers develop systematic methods to exploit the purely geometric rules that allow paper to folded without stretching. Since any thin sheet couples mechanics strongly to geometry, origami provides a natural template for generating length-scale independent structures from a variety of different materials. In this talk I discuss some of the implications of using polymeric sheets and shells over many length scales to create folded materials with tunable shapes and properties. These implications include visco-elastic snap-through transitions and poro-elastically driven micro origami. In each case, mechanical response, dynamics, and reversible folding is tuned through a combination of geometry and constitutive properties, demonstrating the efficacy of using origami principles for designing functional materials.
Universality and scaling behavior of injected power in elastic turbulence in wormlike micellar gel.
Majumdar, Sayantan; Sood, A K
2011-07-01
We study the statistical properties of spatially averaged global injected power fluctuations for Taylor-Couette flow of a wormlike micellar gel formed by surfactant cetyltrimethylammonium tosylate. At sufficiently high Weissenberg numbers the shear rate, and hence the injected power p(t), at a constant applied stress shows large irregular fluctuations in time. The nature of the probability distribution function (PDF) of p(t) and the power-law decay of its power spectrum are very similar to that observed in recent studies of elastic turbulence for polymer solutions. Remarkably, these non-Gaussian PDFs can be well described by a universal, large deviation functional form given by the generalized Gumbel distribution observed in the context of spatially averaged global measures in diverse classes of highly correlated systems. We show by in situ rheology and polarized light scattering experiments that in the elastic turbulent regime the flow is spatially smooth but random in time, in agreement with a recent hypothesis for elastic turbulence. PMID:21867248
Elastic Behavior and Phase Stability of the β1-AgZn Alloy
NASA Astrophysics Data System (ADS)
Matsuo, Yoshie; Suzuki, Toshiharu; Nagasawa, Akira
1980-10-01
To elucidate the dynamical mechanism of the β1 to \\zeta transition the elastic constants of metastable β1 phase of Ag-Zn alloys containing 46.5 and 48.5 at.% Zn are measured in the range between room temperature and the β1 to \\zeta transition temperature using an ultrasonic pulse-echo overlapping method. The elastic constants CL[110]{=}(C11{+}C12{+}2C44)/2 and C44 decrease linearly with increasing temperature up to 340 K and then fall more rapidly on further heating. On the other hand, C11 decreases linearly on heating up to 340 K and then increases at higher temperatures. Furthermore, CL[111]{=}(C11{+}2C12{+}4C44)/3 which is mainly related to the β1 to \\zeta transition mechanism decreases rapidly above 340 K. These elastic constants show a characteristic temperature hysteresis with heating and cooling. Based on the obtained results, we discuss the transition mechanism and stability of the β1 phase.
NASA Astrophysics Data System (ADS)
Chen, Yunxia; Dorgan, Brian L.; McIlroy, David N.; Eric Aston, D.
2006-11-01
Nanomechanical bending behavior and elastic modulus of silver nanowires (65-140nm∅) suspended across silicon microchannels were investigated using digital pulsed force mode (DPFM) atomic force microscopy through coincident imaging and force profiling. Deflection profiles analyzed off-line demonstrate the role of bending nanowire shape and symmetry in experimentally determining boundary conditions, eliminating the need to rely on isolated midpoint bending measurements and the usual assumptions for supported-end behavior. Elastic moduli for as-prepared silver nanowires ranged from 80.4±5.3to96.4±12.8GPa, which met or exceeded the literature values for bulk silver. The calculated moduli were based on classic modeling, both with one-dimensional analytical solutions and three-dimensional finite element analysis. Modeling results indicate that the classic models are accurate as long as the boundary conditions are not arbitrarily assumed but directly confirmed by data analysis. DPFM also facilitated the experimental determination of sample gauge lengths from images and bending profiles.
NASA Astrophysics Data System (ADS)
Zhen, Tiejun
Dislocation-based deformation in crystalline solids is almost always plastic. Once dislocations are generated they entangle and render the process irreversible. In our recent work we show that this does not apply to a new class of materials, best characterized as kinking nonlinear elastic (KNE) solids. KNE solids include the MAX phases, mica, graphite, boron nitride, so called nonlinear mesoscopic elastic (NME) solids discussed in geological literature and most probably ice. The MAX phases are a new class of layered machinable ternary carbides and nitrides, with the chemical formula M n+1AXn, where M is an early transition metal, A is an A-group element (mostly IIIA and IVA) and X is C or N. The compressive loading-unloading stress-strain curves of KNE solids in the elastic regime outline nonlinear, fully reversible, reproducible, rate-independent, closed hysteresis loops whose shape and extent of energy dissipated are strongly influenced by grain size with the energy dissipated being significantly larger in the coarse-grained material. This unique property is attributed to the formation and annihilation of incipient kink bands (IKBs), defined to be thin plates of sheared material bounded by opposite walls of dislocations. As long as the dislocation walls remain attached, the response is fully reversible. Furthermore, because the dislocations are confined to the basal planes work hardening does not occur and the dislocations can move reversibly over relatively large distances. This kind of dislocation motion renders KNE solids potentially high damping material. The loss factor for Ti3SiC2, a prime member of KNE solids, is higher than most woods, and comparable to polypropylene and nylon. At higher temperatures or stress, since the IKB dissociate and coalesce to form regular irreversible kink bands. The close hystesis loops are open, the response is strain-rate dependent, and cyclic hardening is observed even at 1200°C.
The elastic and yield behavior of polyethylene tubes subjected to biaxial loadings
NASA Technical Reports Server (NTRS)
Tuttle, M. E.; Semeliss, M.; Wong, R.
1992-01-01
The elastic and yield response of extruded thin-walled high-density polyethylene tubes with a density in the range of 0.961 to 0.964 gm/cu cm was investigated. Material properties in the axial and hoop directions were measured, and the tubes were found to be mildly transversely isotropic. The yield response was pressure sensitive, and was well predicted using the pressure-modified Hill criterion using a compressive to tensile yield strength ratio of 1:12.
NASA Astrophysics Data System (ADS)
Akimoto, Takuma; Yamamoto, Eiji
2016-06-01
We consider the Langevin equation with dichotomously fluctuating diffusivity, where the diffusion coefficient changes dichotomously over time, in order to study fluctuations of time-averaged observables in temporally heterogeneous diffusion processes. We find that the time-averaged mean-square displacement (TMSD) can be represented by the occupation time of a state in the asymptotic limit of the measurement time and hence occupation time statistics is a powerful tool for calculating the TMSD in the model. We show that the TMSD increases linearly with time (normal diffusion) but the time-averaged diffusion coefficients are intrinsically random when the mean sojourn time for one of the states diverges, i.e., intrinsic nonequilibrium processes. Thus, we find that temporally heterogeneous environments provide anomalous fluctuations of time-averaged diffusivity, which have relevance to large fluctuations of the diffusion coefficients obtained by single-particle-tracking trajectories in experiments.
NASA Astrophysics Data System (ADS)
Ridgway, Sam P.; Hooley, Chris A.
2015-06-01
We analyze the low-energy physics of nearly ferromagnetic metals in two spatial dimensions using the functional renormalization group technique. We find a new low-energy fixed point, at which the fermionic (electronlike) excitations are non-Fermi-liquid (zf=13 /10 ) and the magnetic fluctuations exhibit an anomalous Landau damping whose rate vanishes as Γq˜|q |3 /5 in the low-|q | limit. We discuss this renormalization of the Landau-damping exponent, which is the major novel prediction of our work, and highlight the possible link between that renormalization and neutron-scattering data on UGe2 and related compounds. Implications of our analysis for YFe2Al10 are also discussed.
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.
Leoni, Fabio; Franzese, Giancarlo
2014-11-07
Confinement can modify the dynamics, the thermodynamics, and the structural properties of liquid water, the prototypical anomalous liquid. By considering a generic model for anomalous liquids, suitable for describing solutions of globular proteins, colloids, or liquid metals, we study by molecular dynamics simulations the effect that an attractive wall with structure and a repulsive wall without structure have on the phases, the crystal nucleation, and the dynamics of the fluid. We find that at low temperatures the large density of the attractive wall induces a high-density, high-energy structure in the first layer (“templating” effect). In turn, the first layer induces a “molding” effect on the second layer determining a structure with reduced energy and density, closer to the average density of the system. This low-density, low-energy structure propagates further through the layers by templating effect and can involve all the existing layers at the lowest temperatures investigated. Therefore, although the high-density, high-energy structure does not self-reproduce further than the first layer, the structured wall can have a long-range influence thanks to a sequence of templating, molding, and templating effects through the layers. We find that the walls also have an influence on the dynamics of the liquid, with a stronger effect near the attractive wall. In particular, we observe that the dynamics is largely heterogeneous (i) among the layers, as a consequence of the sequence of structures caused by the walls presence, and (ii) within the same layer, due to superdiffusive liquid veins within a frozen matrix of particles near the walls at low temperature and high density. Hence, the partial freezing of the first layer does not correspond necessarily to an effective reduction of the channel's section in terms of transport properties, as suggested by other authors.
Elastic-Plastic Behavior of U6Nb under Ramp Wave Loading
Hayes, D. B.; Gray, G. T. III; Hixson, R. S.; Hall, C. A.
2006-07-28
When uranium-niobium (6 wt.%) alloy is shock loaded, the expected elastic precursor is absent. A prior model attributed this absence to shear-induced twinning and the concomitant shear stress reduction that prevented the shocked material from reaching the plastic yield point. In the present study, carefully prepared U6Nb was subjected to shock loading to verify the adequacy of the prior model. Other samples were loaded with a ramp pressure pulse with strain rate large enough so that significant twinning would not occur during the experiment. Backward integration analyses of these latter experiments' back surface motion give stress-strain loading paths in U6Nb that suggest ordinary elastic-plastic flow. Some of the U6Nb was pre-strained by cold rolling in an effort to further ensure that twinning did not affect wave propagation. Shock and ramp loadings yielded similar results to the baseline material except, as expected, they are consistent with a higher yield stress and twinning shear stress threshold.
Analysis of the biomechanical behavior of short implants: The photo-elasticity method.
Pellizzer, Eduardo Piza; de Mello, Caroline Cantieri; Santiago Junior, Joel Ferreira; de Souza Batista, Victor Eduardo; de Faria Almeida, Daniel Augusto; Verri, Fellippo Ramos
2015-10-01
The aim of this study was to analyze the stress distribution of short implants supporting single unit or splinted crowns by the photo-elasticity method. Four photo-elastic models were produced: A (3.75×7 mm); B (3.75×7 mm, 3.75×7 mm and 3.75×7 mm); C (3.75×10 mm, 3.75×7 mm and 3.75×7 mm); D (3.75×13 mm, 3.75×7 mm and 3.75×7 mm). The prostheses were made with Ni-Cr alloy. A load of 100 N in the axial and oblique directions was applied, totaling 380 applications, individually capturing their images in each model. The data were randomized and analyzed qualitatively and quantitatively by 2 examiners. The oblique loading was significantly more damaging. The increase in length was favorable for stress distribution (p<0.05). The splinting was beneficial for the transmission of stresses mainly (p<0.05). The splinting of the crowns, as well as increasing the length of the first implant and axial loading was most beneficial in the stress distribution. Short splinted implants behaved better than single unit implants. Increasing of the length of the first implant significantly improved the stress distribution in all analyzed situations. PMID:26117754
Anomalous field-induced magnetoresistance behavior in Pr0.5Sr0.5MnO3 at low temperatures
NASA Astrophysics Data System (ADS)
Kumar, Dhirendra; Shahee, Aga; Rawat, Rajeev; Lalla, N. P.
2012-06-01
Low-temperature (LT) XRD and magnetoresistance (MR) have been studied in the single phase polycrystalline Pr0.5Sr0.5MnO3 with space-group I4/mcm. The resistance-vs-temperature (R-T) variation at zero-field show a broad paramagnetic to ferromagnetic metallic (FMM) transition at Tc ˜ 240K and it further undergoes FMM to antiferromagnetic insulating (AFMI) transition at TN ˜ 90K with a broad hysteresis indicates a disorder broadened first order phase transition (FOPT). The zero-field cooled (ZFC) MR at 5K shows an open loop with virgin curve lying outside the envelope curve. This anomalous behavior vanishes with increasing temperature. This has been attributed to field-induced transformation of AFMI to FMM phase, which remains arrested down to zero magnetic field at 5K.
Lu, Jinwen; Zhao, Yongqing; Niu, Hongzhi; Zhang, Yusheng; Du, Yuzhou; Zhang, Wei; Huo, Wangtu
2016-05-01
The present study is to investigate the microstructural characteristics, electrochemical corrosion behavior and elasticity properties of Ti-6Al-xFe alloys with Fe addition for biomedical application, and Ti-6Al-4V alloy with two-phase (α+β) microstructure is also studied as a comparison. Microstructural characterization reveals that the phase and crystal structure are sensitive to the Fe content. Ti-6Al alloy displays feather-like hexagonal α phase, and Ti-6Al-1Fe exhibits coarse lath structure of hexagonal α phase and a small amount of β phase. Ti-6Al-2Fe and Ti-6Al-4Fe alloys are dominated by elongated, equiaxed α phase and retained β phase, but the size of α phase particle in Ti-6Al-4Fe alloy is much smaller than that in Ti-6Al-2Fe alloy. The corrosion resistance of these alloys is determined in SBF solution at 37 °C. It is found that the alloys spontaneously form a passive oxide film on their surface after immersion for 500 s, and then they are stable for polarizations up to 0 VSCE. In comparison with Ti-6Al and Ti-6Al-4V alloys, Ti-6Al-xFe alloys exhibit better corrosion resistance with lower anodic current densities, larger polarization resistances and higher open-circuit potentials. The passive layers show stable characteristics, and the wide frequency ranges displaying capacitive characteristics occur for high iron contents. Elasticity experiments are performed to evaluate the elasticity property at room temperature. Ti-6Al-4Fe alloy has the lowest Young's modulus (112 GPa) and exhibits the highest strength/modulus ratios as large as 8.6, which is similar to that of c.p. Ti (8.5). These characteristics of Ti-6Al-xFe alloys form the basis of a great potential to be used as biomedical implantation materials. PMID:26952395
Anomalous magneto-structural behavior of MnBi explained: a path towards an improved permanent magnet
Zarkevich, Nikolay A.; Wang, Lin-Lin; Johnson, Duane D.
2014-03-04
Low-temperature MnBi (hexagonal NiAs phase) exhibits anomalies in the lattice constants (a, c) and bulk elastic modulus (B) below 100 K, spin reorientation and magnetic susceptibility maximum near 90 K, and, importantly for high-temperature magnetic applications, an increasing coercivity (unique to MnBi) above 180 K. We calculate the total energy and magneto-anisotropy energy (MAE) versus (a, c) using DFT+U methods. We reproduce and explain all the above anomalies. We predict that coercivity and MAE increase due to increasing a, suggesting means to improve MnBi permanent magnets.
Anomalous magneto-structural behavior of MnBi explained: A path towards an improved permanent magnet
Zarkevich, NA; Wang, LL; Johnson, DD
2014-03-01
Low-temperature MnBi (hexagonal NiAs phase) exhibits anomalies in the lattice constants (a, c) and bulk elastic modulus (B) below 100 K, spin reorientation and magnetic susceptibility maximum near 90 K, and, importantly for high-temperature magnetic applications, an increasing coercivity (unique to MnBi) above 180 K. We calculate the total energy and magneto-anisotropy energy (MAE) versus (a, c) using DFT+U methods. We reproduce and explain all the above anomalies. We predict that coercivity and MAE increase due to increasing a, suggesting means to improve MnBi permanent magnets. (C) 2014 Author(s).
NASA Technical Reports Server (NTRS)
Nemeth, Michael P.
2004-01-01
An approach for synthesizing buckling results for thin balanced and unbalanced symmetric laminates that are subjected to uniform heating or cooling and elastically restrained against thermal expansion or contraction is presented. This approach uses a nondimensional analysis for infinitely long, flexural anisotropic plates that are subjected to combined mechanical loads. In addition, stiffness-weighted laminate thermal-expansion parameters and compliance coefficients are derived that are used to determine critical temperatures in terms of physically intuitive mechanical-buckling coefficients. Many results are presented for some common laminates that are intended to facilitate a structural designer s transition to the use of the generic buckling design curves. Several curves that illustrate the fundamental parameters used in the analysis are presented, for nine contemporary material systems, that provide physical insight into the buckling response in addition to providing useful design data. Examples are presented that demonstrate the use of the generic design curves.
NASA Astrophysics Data System (ADS)
Shafiei, Navvab; Kazemi, Mohammad; Ghadiri, Majid
2016-08-01
This study is concerned with the small-scale effect on the nonlinear flapwise bending vibration of rotating cantilever and propped cantilever nanobeams. Euler-Bernoulli beam theory is used to model the nanobeam with nonlinearity. Nonlinear strain-displacement relations are employed to account for geometric nonlinearity of the system. The axial forces are modeled as the true spatial and thermal variations due to the rotation. Hamilton's principle is used to derive the nonlinear governing equation and nonlocal nonlinear boundary conditions based on Eringen's nonlocal elasticity theory. Finally, the differential quadrature method is used in conjunction with the direct iterative method to derive the nonlinear vibration frequencies of the nanobeam. The effects of the angular velocity, nonlocal small-scale parameter, temperature change and nonlinear amplitude on nonlinear vibration of the rotary nanobeam are discussed. The results of this work can be used in nanosensors, nanomotors, nanoturbines and NEMS applications.
Elastic behavior of methyltrimethoxysilane based aerogels reinforced with tri-isocyanate.
Nguyen, Bao Chau N; Meador, Mary Ann B; Medoro, Alexandra; Arendt, Victoria; Randall, Jason; McCorkle, Linda; Shonkwiler, Brian
2010-05-01
The elastic properties and/or flexibility of polymer reinforced silica aerogels having methyltrimethoxysilane (MTMS) and bis(trimethoxysilylpropyl)amine (BTMSPA) making up the silica structure are examined. The dipropylamine spacer from BTMSPA is used both to provide a flexible linking group in the silica structure, and as a reactive site via its secondary amine for reaction with a tri-isocyanate, Desmodur N3300A. The tri-isocyanate provides an extended degree of branching or reinforcement, resulting in increased compressive strength of the aerogel monoliths while the overall flexibility arising from the underlying silica structure is maintained. The compressive moduli of the reinforced aerogel monoliths in this study range from 0.001 to 158 MPa. Interestingly, formulations across this entire range of modulus recover nearly all of their length after two compressions to 25% strain. Differences in pore structure of the aerogels due to processing conditions and solvent are also discussed. PMID:20426430
Structural behavior of two-cell composite rotor blades with elastic couplings
NASA Astrophysics Data System (ADS)
Chandra, Ramesh; Chopra, Inderjit
1991-09-01
This paper presents an analytical-cum-experimental study of the structural response of composite rotor blades with elastic couplings. Vlasov theory is expanded to analyze two-cell composite rotor blades made out of general composite laminates including the transverse shear deformation of the cross-section. Variation of shear stiffness along the countour of the section is included in the warping function. In order to validate this analysis, two-cell graphite-epoxy composite blades with extension-torsion coupling were fabricated using matched-die molding technique. These blades were tested under tip bending and torsional loads, and their structural response in terms of bending slope and twist was measured with a laser optical system. Good correlation between theory and experiment is achieved.
Modeling the effective elastic behavior of a transversely cracked laminated composite
Thomas, D.J.; Wetherhold, R.C.
1998-01-01
The solution for the stress state present in the vicinity of transverse matrix cracks within a composite laminate is typically obtained by assuming a regular crack spacing geometry for the problem and applying a shear-lag analysis. In order to explore the validity of this underlying assumption, the probability density function for the location of the next transverse matrix crack within a crack bounded region is examined. The regular crack spacing assumption is shown to be reasonable from an engineering point of view. Continuing with this assumption, a generalized shear-lag model for multilayer, off-axis laminates subjected to full in-plane loads is developed. This model is used to quantitatively evaluate the effective elastic properties of the damaged material. The results are applicable to materials such as ceramic matrix or polymer matrix unidirectional fiber systems where damage in the form of transverse matrix cracks arises.
Visentin, Adam F; Panzer, Matthew J
2012-06-27
Harnessing the many favorable properties of ionic liquids in a solid electrolyte thin film form is desirable for a host of electrical energy storage applications, including electrochemical double layer capacitors. Using a cross-linked polymer matrix to provide structural support, freestanding ionogel materials can be achieved with a wide range of polymer weight fractions. Compression testing and impedance spectroscopy have been used to characterize the mechanical and electrical responses of ionogels containing between 4.9 and 44.7 wt % poly(ethylene glycol) diacrylate. Although the elastic modulus of these solid electrolyte materials is observed to vary by more than 4 orders of magnitude within the composition range studied, concomitant changes in gel ionic conductivity and double layer capacitance were much less dramatic. PMID:22583832
Elastic behavior and platelet retraction in low- and high-density fibrin gels.
Wufsus, Adam R; Rana, Kuldeepsinh; Brown, Andrea; Dorgan, John R; Liberatore, Matthew W; Neeves, Keith B
2015-01-01
Fibrin is a biopolymer that gives thrombi the mechanical strength to withstand the forces imparted on them by blood flow. Importantly, fibrin is highly extensible, but strain hardens at low deformation rates. The density of fibrin in clots, especially arterial clots, is higher than that in gels made at plasma concentrations of fibrinogen (3-10 mg/mL), where most rheology studies have been conducted. Our objective in this study was to measure and characterize the elastic regimes of low (3-10 mg/mL) and high (30-100 mg/mL) density fibrin gels using shear and extensional rheology. Confocal microscopy of the gels shows that fiber density increases with fibrinogen concentration. At low strains, fibrin gels act as thermal networks independent of fibrinogen concentration. Within the low-strain regime, one can predict the mesh size of fibrin gels by the elastic modulus using semiflexible polymer theory. Significantly, this provides a link between gel mechanics and interstitial fluid flow. At moderate strains, we find that low-density fibrin gels act as nonaffine mechanical networks and transition to affine mechanical networks with increasing strains within the moderate regime, whereas high-density fibrin gels only act as affine mechanical networks. At high strains, the backbone of individual fibrin fibers stretches for all fibrin gels. Platelets can retract low-density gels by >80% of their initial volumes, but retraction is attenuated in high-density fibrin gels and with decreasing platelet density. Taken together, these results show that the nature of fibrin deformation is a strong function of fibrin fiber density, which has ramifications for the growth, embolization, and lysis of thrombi. PMID:25564864
Elastic Behavior and Platelet Retraction in Low- and High-Density Fibrin Gels
Wufsus, Adam R.; Rana, Kuldeepsinh; Brown, Andrea; Dorgan, John R.; Liberatore, Matthew W.; Neeves, Keith B.
2015-01-01
Fibrin is a biopolymer that gives thrombi the mechanical strength to withstand the forces imparted on them by blood flow. Importantly, fibrin is highly extensible, but strain hardens at low deformation rates. The density of fibrin in clots, especially arterial clots, is higher than that in gels made at plasma concentrations of fibrinogen (3–10 mg/mL), where most rheology studies have been conducted. Our objective in this study was to measure and characterize the elastic regimes of low (3–10 mg/mL) and high (30–100 mg/mL) density fibrin gels using shear and extensional rheology. Confocal microscopy of the gels shows that fiber density increases with fibrinogen concentration. At low strains, fibrin gels act as thermal networks independent of fibrinogen concentration. Within the low-strain regime, one can predict the mesh size of fibrin gels by the elastic modulus using semiflexible polymer theory. Significantly, this provides a link between gel mechanics and interstitial fluid flow. At moderate strains, we find that low-density fibrin gels act as nonaffine mechanical networks and transition to affine mechanical networks with increasing strains within the moderate regime, whereas high-density fibrin gels only act as affine mechanical networks. At high strains, the backbone of individual fibrin fibers stretches for all fibrin gels. Platelets can retract low-density gels by >80% of their initial volumes, but retraction is attenuated in high-density fibrin gels and with decreasing platelet density. Taken together, these results show that the nature of fibrin deformation is a strong function of fibrin fiber density, which has ramifications for the growth, embolization, and lysis of thrombi. PMID:25564864
NASA Astrophysics Data System (ADS)
Carneiro, V. H.; Capela, P.; Teixeira, J. C.; Teixeira, S.; Cerqueira, F.; Macedo, F.; Ribas, L.; Soares, D.
2016-06-01
The impact in the elastic behavior and internal friction, caused by the introduction of Copper layers in Glass-Fiber/Epoxy Resin composites and temperature effects, were studied and evaluated recurring to Dynamic Mechanical Analysis. It is shown that the introduction of Copper layers increases the storage modulus of the composites and delays their glass transition temperature, however, it allows a faster transformation. Additionally, it is concluded that the introduction of Copper layers elevates the internal friction during the glass transition phase by the inversion of the deformation mechanism due to thermal expansion and increase in the Poisson's ratio of the epoxy resin to a value near 0.5 where its deformation is approximately isochoric. This increase in damping capacity is relevant in application with cyclic fatigue and mechanical vibration.
NASA Astrophysics Data System (ADS)
Gupta, M. K.; Mittal, R.; Chaplot, S. L.; Rols, S.
2014-03-01
We report a comparative study of the dynamics of Cu2O, Ag2O, and Au2O (i.e., M2O with M = Au, Ag, and Cu) using first principle calculations based on the density functional theory. Here, for the first time, we show that the nature of chemical bonding and open space in the unit cell are directly related to the magnitude of thermal expansion coefficient. A good match between the calculated phonon density of states and that derived from inelastic neutron scattering measurements is obtained for Cu2O and Ag2O. The calculated thermal expansions of Ag2O and Cu2O are negative, in agreement with available experimental data, while it is found to be positive for Au2O. We identify the low energy phonon modes responsible for this anomalous thermal expansion. We further calculate the charge density in the three compounds and find that the magnitude of the ionic character of the Ag2O, Cu2O, and Au2O crystals is in decreasing order, with an Au-O bond of covalent nature strongly rigidifying the Au4O tetrahedral units. The nature of the chemical bonding is also found to be an important ingredient to understand the large shift of the phonon frequencies of these solids with pressure and temperature. In particular, the quartic component of the anharmonic term in the crystal potential is able to account for the temperature dependence of the phonon modes.
Elastic behavior of silica/poly(dimethylsiloxane) nanocomposites: nano-size effects
NASA Astrophysics Data System (ADS)
Ibrahim, I. A. M.; Zikry, A. A. F.; Sharaf, M. A.; Mark, J. E.; Jacob, K.; Jasiuk, I. M.; Tannenbaumn, R.
2012-09-01
Elastomeric materials require the incorporation of reinforcing fillers in order to improve their mechanical properties. The enhancement of properties is very much dependent on the size and any surface modification of the reinforcing agent. It is widely accepted that the reinforcement effects are primarily due to molecular interactions of the polymeric matrix and the filler inclusions and it involves both chemical and physical interactions. Herein, we have incorporated silica nano fillers (Stober silica) into poly (dimethylsiloxane) (PDMS) elastomeric networks. The mechanical and swelling properties of the networks were investigated as a function of filler sizes (50, 130, and 170 nm), volume fraction of the filler inclusions, and surface treatment of the particles by were analyzed to give the Mooney-Rivlin constants 2C1 and 2C2. These properties were found to be dependent on the size of the nano inclusions. Thus, a nano size phenomenon had been discerned and was one of the highlights of this investigation. This phenomenon was largely attributed to the high specific surface area of the nano fillers used that leads to significant increase in the interfacial interactions. Also, and as would be expected, the properties of the polymeric networks filled with unmodified particles were different than those obtained for the polymeric networks filled with surface-modified particles. This has been primarily attributed to changes in the surface properties, and as would be expected, the elastic properties of the networks were thus shown to be strongly dependent on type and concentration.
Structural behavior of two-cell composite rotor blades with elastic couplings
NASA Astrophysics Data System (ADS)
Chandra, Ramesh; Chopra, Inderjit
1992-12-01
This paper presents an analytical-cum-experimental study of the structural response of composite rotor blades with elastic couplings. Vlasov theory is expanded to analyze two-cell composite rotor blades made out of general composite laminates including the transverse shear deformation of the cross section. Variation of shear stiffness along the contour of the section is included in the warping function. To validate this analysis, two-cell graphite-epoxy composite blades with extension-torsion coupling were fabricated using a matched-die molding technique. These blades were tested under tip bending and torsional loads, and their structural response in terms of bending slope and twist was measured with a laser optical system. Good correlation between theory and experiment was achieved. Axial force-induced twist rate of the order of 10 deg/m length due to a 4.45-kN force can be realized in extension-torsion coupled blades with a hygrothermally stable lay-up for potential applications in the design of tilt rotors.
NASA Astrophysics Data System (ADS)
Yu, N.; Zhang, H. Q.; Jia, H. M.; Zhang, S. T.; Ruan, M.; Yang, F.; Wu, Z. D.; Xu, X. X.; Bai, C. L.
2010-07-01
The elastic scattering angular distributions of the weakly bound 9Be projectile from 208Pb and 209Bi have been measured for 14 beam energies near the threshold from 37 to 50 MeV. The parameters of the optical potential are extracted by means of phenomenological optical model analysis with PTOLEMY. Both of the systems show unusual potential behavior in the vicinity of the Coulomb barrier that the strength of the imaginary (absorptive) part of the potential is increasing (rather than decreasing) with decreasing energy, which is quite different from the results of some previous reports. This unusual threshold phenomenon indicates that the breakup channel is strongly coupled with the elastic channel and has obvious effects on the optical potential. The analyses also show that high precision elastic scattering angular distributions, especially those below the Coulomb barrier, are very important for extracting correct threshold behavior of the optical potential.
Huang, Guoliang; Song, Fei; Wang, Xiaodong
2010-01-01
Elastic waves, especially guided waves, generated by a piezoelectric actuator/sensor network, have shown great potential for on-line health monitoring of advanced aerospace, nuclear, and automotive structures in recent decades. Piezoelectric materials can function as both actuators and sensors in these applications due to wide bandwidth, quick response and low costs. One of the most fundamental issues surrounding the effective use of piezoelectric actuators is the quantitative evaluation of the resulting elastic wave propagation by considering the coupled piezo-elastodynamic behavior between the actuator and the host medium. Accurate characterization of the local interfacial stress distribution between the actuator and the host medium is the key issue for the problem. This paper presents a review of the development of analytical, numerical and hybrid approaches for modeling of the coupled piezo-elastodynamic behavior. The resulting elastic wave propagation for structural health monitoring is also summarized. PMID:22319319
NASA Astrophysics Data System (ADS)
Xu, Guangjing; Han, Peng; Huang, Qinghua; Hattori, Katsumi; Febriani, Febty; Yamaguchi, Hiroki
2013-11-01
There have been many reports on ultra-low-frequency (ULF) electromagnetic phenomena associated with earthquakes in a very wide frequency range. In this study, unusual behaviors of geomagnetic diurnal variations prior to the 2011 off the Pacific coast of Tohoku earthquake (Mw9.0) have been reported. Ratios of diurnal variation range between the target station Esashi (ESA) which is about 135 km from the epicenter and the remote reference station Kakioka (KAK) about 302 km distant to the epicenter have been computed. The results of 10-day running mean of the ratios showed a clear anomaly exceeding the statistical threshold in the vertical component about 2 months before the mega event. This anomaly is unique over a 3-year background, and the further stochastic test indicates that this anomaly is unlikely a random anomaly, which is highly suggestive of correlation with the mega event. The original records of geomagnetic fields of the ESA station also exhibit continuous anomalous behaviors for about 10 days in the vertical component approximate 2 months prior to the Mw9.0 earthquake.
NASA Astrophysics Data System (ADS)
Han, P.; Hattori, K.; Huang, Q.; Xu, G.
2013-12-01
There have been many reports on ultra-low-frequency (ULF) electromagnetic phenomena associated with earthquakes in a very wide frequency range. In this study, unusual behaviors of geomagnetic diurnal variations prior to the 2011 off the Pacific coast of Tohoku earthquake (Mw9.0) have been reported. Ratios of diurnal variation range between the target station Esashi (ESA) which is about 135 km from the epicenter and the remote reference station Kakioka (KAK) about 302 km distant to the epicenter have been computed. The results of 10-day running mean of the ratios showed a clear anomaly exceeding the statistical threshold in the vertical component about 2 months before the mega event. This anomaly is unique over a three-year background, and the further statistical test indicates that this anomaly is unlikely a random anomaly, which is highly suggestive of correlation with the mega event. The original records of geomagnetic fields of the ESA station also exhibits continuous anomalous behaviors for about 10 days in the vertical component approximate two months prior to the Mw 9.0 earthquake.
NASA Astrophysics Data System (ADS)
Nakatsuji, Satoru
2008-03-01
Among metallic magnets on geometrical frustrated lattices, the pyrochlore oxide Pr2Ir2O7 is unique for its metallic spin liquid behavior ootnotetextS. Nakatsuji, Y. Machida, Y. Maeno, T. Tayama, T. Sakakibara, J. v. Duijn, L. Balicas, J. N. Millican, R. T. Macaluso, and Julia Y. Chan, Phys. Rev. Lett. 96, 087204 (2006)., and unconventional Hall transport phenomena ootnotetextY. Machida, S. Nakatsuji, Y. Maeno, T. Tayama, T. Sakakibara, and S. Onoda, Phys. Rev. Lett. 98, 057203 (2007).. Despite the Weiss temperature T^* = 20 K deu to the RKKY interaction, Pr2Ir2O7 exhibits no magnetic long range order, but spin freezing at a very low temperature ˜120 mK. Instead, the Kondo effect, including lnT dependence in the resistivity, emerges and leads to partial screening of the 4f-moments below T^*. Moreover, the underscreened 4f- moments show spin-liquid behavior below a renormalized energy scale of θw˜1.7 K. Interestingly, in this spin-liquidlike paramagnetic regime, the Hall resistivity ρxy becomes largely enhanced, and shows behavior far different from anomalous Hall effects (AHE) due to the spin- orbit coupling observed in ordinary magnetic conductors. We discuss the origin of the metallic spin liquid behavior and unconventional AHE in terms of the spin chirality due to the non-coplanar texture of the <111> Ising-like Pr moments. This work is based on the collaboration with Y. Machida, T. Tayama, T. Sakakibara (ISSP, Univ.of Tokyo), Y. Maeno (Kyoto Univ.), S. Onoda (RIKEN, Tokyo), C. Broholm (Johns Hopkins Univ.), C. Stock and J. van Duijn (ISIS), L. Balicas (NHMFL), Jung Young Cho, and Julia Y. Chan (Louisiana State Univ.).
Nonlinear response of plain concrete shear walls with elastic-damaging behavior
Yazdani, S.; Schreyer, H.L.
1997-02-01
This report summarizes the theoretical and computational efforts on the modeling of small scale shear walls. Small scale shear walls are used extensively in the study of shear wall behavior because the construction and testing of full size walls are rather expensive. A finite element code is developed which incorporates nonlinear constitutive relations of damage mechanics. The program is used to obtain nonlinear load-deformation curves and to address the initial loss of stiffness due to shrinkage cracking. The program can also be used to monitor the continuous degradation of the fundamental frequency due to progressive damage.
Kaluza, Dawid; Adamiak, Wojciech; Kalwarczyk, Tomasz; Sozanski, Krzysztof; Opallo, Marcin; Jönsson-Niedziolka, Martin
2013-12-23
We have investigated the oxidation of ferrocene at a flowing organic solvent|aqueous electrolyte|solid electrode junction in a microfluidic setup using cyclic voltammetry and fluorescent laser scanning confocal microscopy. At low flow rates the oxidation current decreases with increasing flow, contrary to the Levich equation, but at higher flow rates the current increases linearly with the cube root of the flow rate. This behavior is explained using a simple model postulating a smallest effective width of the three-phase junction, which after fitting to the data comes to be ca. 20 μm. The fluorescence microscopy reveals mixing of the two phases close to the PDMS cover, but the liquid|liquid junction is stable close to the glass support. This study shows the importance of the solid|liquid|liquid junctions for the behavior of multiphase systems under microfluidic conditions. PMID:24328179
Fickian dispersion is anomalous
Cushman, John H.; O’Malley, Dan
2015-06-22
The thesis put forward here is that the occurrence of Fickian dispersion in geophysical settings is a rare event and consequently should be labeled as anomalous. What people classically call anomalous is really the norm. In a Lagrangian setting, a process with mean square displacement which is proportional to time is generally labeled as Fickian dispersion. With a number of counter examples we show why this definition is fraught with difficulty. In a related discussion, we show an infinite second moment does not necessarily imply the process is super dispersive. By employing a rigorous mathematical definition of Fickian dispersion we illustrate why it is so hard to find a Fickian process. We go on to employ a number of renormalization group approaches to classify non-Fickian dispersive behavior. Scaling laws for the probability density function for a dispersive process, the distribution for the first passage times, the mean first passage time, and the finite-size Lyapunov exponent are presented for fixed points of both deterministic and stochastic renormalization group operators. The fixed points of the renormalization group operators are p-self-similar processes. A generalized renormalization group operator is introduced whose fixed points form a set of generalized self-similar processes. Finally, power-law clocks are introduced to examine multi-scaling behavior. Several examples of these ideas are presented and discussed.
Fickian dispersion is anomalous
Cushman, John H.; O’Malley, Dan
2015-06-22
The thesis put forward here is that the occurrence of Fickian dispersion in geophysical settings is a rare event and consequently should be labeled as anomalous. What people classically call anomalous is really the norm. In a Lagrangian setting, a process with mean square displacement which is proportional to time is generally labeled as Fickian dispersion. With a number of counter examples we show why this definition is fraught with difficulty. In a related discussion, we show an infinite second moment does not necessarily imply the process is super dispersive. By employing a rigorous mathematical definition of Fickian dispersion wemore » illustrate why it is so hard to find a Fickian process. We go on to employ a number of renormalization group approaches to classify non-Fickian dispersive behavior. Scaling laws for the probability density function for a dispersive process, the distribution for the first passage times, the mean first passage time, and the finite-size Lyapunov exponent are presented for fixed points of both deterministic and stochastic renormalization group operators. The fixed points of the renormalization group operators are p-self-similar processes. A generalized renormalization group operator is introduced whose fixed points form a set of generalized self-similar processes. Finally, power-law clocks are introduced to examine multi-scaling behavior. Several examples of these ideas are presented and discussed.« less
NASA Astrophysics Data System (ADS)
Crunteanu, Aurelian; Fabert, Marc; Cornette, Julie; Colas, Maggy; Orlianges, Jean-Christophe; Bessaudou, Annie; Cosset, Françoise
2014-03-01
We present the vanadium dioxide (VO2) thin films deposition using e-beam evaporation of a vanadium target under oxygen atmosphere on different substrates (sapphire, Si, SiO2/Si…) and we focus on their electrical and optical properties variations as the material undergoes a metal-insulator transition under thermal and electrical stimuli. The phase transition induces extremely abrupt changes in the electronic and optical properties of the material: the electrical resistivity increases up to 5 orders of magnitude while the optical properties (transmission, reflection, refractive index) are drastically modified. We present the integration of these films in simple planar optical devices and we demonstrate electrical-activated optical modulators for visible-infrared signals with high discrimination between the two states. We will highlight a peculiar behavior of the VO2 material in the infrared and far infrared regions (2- 20 μm), namely its anomalous emissivity change under thermal- end electrical activation (negative differential emittance phenomenon) with potential applications in active coatings for thermal regulation, optical limiting or camouflage coatings.
Anomalous magnetic behavior in the transition metal ions doped Cu{sub 2}O flower-like nanostructures
Ahmed, Asar; Gajbhiye, Namdeo S.
2011-01-15
Cuprous oxide (Cu{sub 2}O) flower-like nanostructures doped with various metal ions i.e. Fe, Co, Ni and Mn have been synthesized by an organic phase solution method. The powder X-ray diffraction study clearly reveals them as single phase simple cubic cuprite lattice. Study of their magnetic properties have shown that these doped samples are ferromagnetic in nature; however, no such property was observed for the undoped Cu{sub 2}O sample. The magnitude of the ferromagnetic behavior was found to be dependent on the dopant metal ions amount, which increased consistently with its increase. As total magnetic moment contribution of the doped metal ions calculated was insignificant, it is believed to have originated from the induced magnetic moments at cation deficiency sites in the material, created possibly due to the disturbance of the crystal lattice by the dopant ions. The existence of the defects has been supported by photoluminescence spectra of the doped samples. -- Graphical abstract: Room temperature ferromagnetic behavior was observed in the Cu{sub 2}O nanoflowers doped with Fe, Co, Ni and Mn ions. Cation deficiencies formed due to dopant ions were possibly responsible for ferromagnetism. Display Omitted
Elastic constants at low temperatures - Recent measurements on technological materials at NBS
NASA Technical Reports Server (NTRS)
Ledbetter, H. M.
1978-01-01
Solid-state low-temperature elastic properties have been experimentally studied at the NBS Cryogenic Division for four years. Most studies were between room temperature and liquid-helium temperature; some were only to liquid-nitrogen temperature. Two dynamic (high-frequency) experimental methods were used, pulse-echo and resonance, resulting in adiabatic elastic constants. The present paper reviews these studies for 47 technological materials - metals, alloys, and composites. The elastic constants primarily discussed are Young's modulus, the shear modulus, the bulk modulus (reciprocal compressibility), and Poisson's ratio. A summary table is presented to show which base metals tend to exhibit regular, irregular, or anomalous behavior in their elastic constant/temperature curves.
Hosseinzadeh, M; Ghoreishi, M; Narooei, K
2016-06-01
In this study, the hyperelastic models of demineralized and deproteinized bovine cortical femur bone were investigated and appropriate models were developed. Using uniaxial compression test data, the strain energy versus stretch was calculated and the appropriate hyperelastic strain energy functions were fitted on data in order to calculate the material parameters. To obtain the mechanical behavior in other loading conditions, the hyperelastic strain energy equations were investigated for pure shear and equi-biaxial tension loadings. The results showed the Mooney-Rivlin and Ogden models cannot predict the mechanical response of demineralized and deproteinized bovine cortical femur bone accurately, while the general exponential-exponential and general exponential-power law models have a good agreement with the experimental results. To investigate the sensitivity of the hyperelastic models, a variation of 10% in material parameters was performed and the results indicated an acceptable stability for the general exponential-exponential and general exponential-power law models. Finally, the uniaxial tension and compression of cortical femur bone were studied using the finite element method in VUMAT user subroutine of ABAQUS software and the computed stress-stretch curves were shown a good agreement with the experimental data. PMID:26953961
Micromorphic homogenization of a porous medium: elastic behavior and quasi-brittle damage
NASA Astrophysics Data System (ADS)
Hütter, Geralf; Mühlich, Uwe; Kuna, Meinhard
2015-11-01
Today it is well known that the classical Cauchy continuum theory is insufficient to describe the deformation behavior of solids if gradients occur over distances which are comparable to the microstructure of the material. This becomes crucial e.g., for small specimens or during localization of deformation induced by material degradation (damage). Higher-order continuum approaches like micromorphic theories are established to address such problems. However, such theories require the formulation of respective constitutive laws, which account for the microstructural interactions. Especially in damage mechanics such laws are mostly formulated in a purely heuristic way, which leads to physical and numerical problems. In the present contribution, the fully micromorphic constitutive law for a porous medium is obtained in closed form by homogenization based on the minimal boundary conditions concept. It is shown that this model describes size effects of porous media like foams adequately. The model is extended toward quasi-brittle damage overcoming the physical and numerical limitations of purely heuristic approaches.
NASA Astrophysics Data System (ADS)
Brazhkin, V. V.; Katayama, Y.; Kanzaki, M.; Kondrin, M. V.; Lyapin, A. G.
2011-09-01
It is known that a number of compressed melts undergo structural phase transitions. Data on the structural changes at high pressures in chalcogenides (AsS, As2S3) and oxide (B2O3) melts with a network structure have been reviewed. Viscosity is one of the fundamental physical properties of a liquid. For various melts, it varies in a very wide range. Structural transformations in melts induce the corresponding changes in all physical properties, in particular viscosity. The measurements of the viscosity of a number of melts at high pressures and temperatures by the radiographic method have been reported. Changes in the viscosity by several orders of magnitude have been detected when the pressure is varied by several gigapascals. The diffusion mechanism in network-structure melts at various pressures has been analyzed. The prediction of the behavior of the viscosity of various melts at superhigh pressures is of high importance for the physics of glass transition, geophysics, and materials science.
Schwartz, Joshua J; Huth, Kenneth; Hunce, Raymond; Lentine, Brandon
2010-06-15
Research has demonstrated that certain midbrain neurons of anurans 'count' interpulse intervals (IPIs). Some neurons fire after exposure to fewer intervals than do others. Counting can be reset to zero if an IPI falls outside the cell's tolerance range. We tested female gray treefrogs for behavioral correlates of these neural response patterns using phonotaxis tests in order to gain a better understanding of the mechanistic bases of female responses to calls. For example, previous work demonstrated females often prefer longer to shorter pulsed advertisement calls, even when the former occur at lower rates. Call attractiveness can also be reduced when pulse duration and timing have been manipulated experimentally or disrupted by acoustic interference. In this study, female responses were consistent with neural data, emphasizing the importance of IPIs. Females discriminated in favor of calls with normal interpulse timing relative to those in which a single IPI was too long or too short. Our data suggest that neural resetting of interval counting by inappropriate intervals may more strongly influence females than reduced firing in response to such intervals on an individual basis. Data also suggest a transition point between 125 ms and 175 ms at which an interval between pulse strings is treated as an interval between calls. PMID:20511520
NASA Astrophysics Data System (ADS)
Hu, Bin; Kieweg, Sarah
2011-11-01
Many complex fluids of interest exhibit viscoelastic hehavior. Polymeric drug delivery vehicles, such as anti-HIV topical microbicides, are among these fluids. For the optimal design of microbicides, the combined effect of shear-thinning and elastic behavior on the gravity-driven spreading of viscoelastic fluids is studied. We develop a 2D model to simulate the fluids spreading down an incline using ANSYS POLYFLOW software package. Arbitrary Lagrangian-Eulerian (ALE) method combined with Lagrangian remeshing is applied to track the moving free surface of fluids during spreading. Adaptive meshing method is used to generate high quality mesh for the remeshing process. Based on an elastic viscous split stress (EVSS) approach, several differential viscoelastic constitutive models are studied to investigate the combined effect of shear-thinning and elastic behavior. Mesh convergence test and constant volume check are studied to verify the new model. Moreover, the new model with zero elasticity is compared with previous studies of Newtonian and power-law fluids.
NASA Technical Reports Server (NTRS)
Roth, Don J.; Deguire, Mark R.; Dolhert, Leonard E.
1991-01-01
Ultrasonic velocity measurement techniques were used to evaluate the effects of oxidation and reduction on the elastic properties, global microstructure and oxygen content of the YBa2Cu3O(7-x) ceramic superconductor for samples ranging from 70 to 90 pct. of theoretical density. Bulk density, velocity, and elastic modulus generally increased with increasing oxygen content upon oxidation, and this behavior was reversible. Velocity image patterns were similar after oxidation and reduction treatments for a 90 pct. dense sample, although the velocity value at any given point on the sample was changed following the treatments. The unchanging pattern correlated with destructive measurements showing that the spatial pore distribution (fraction and size) was not measurably altered after the treatments. Changes in superconducting behavior, crystal structure, and grain structure were observed consistent with changes in oxygen content.
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.
Anomalously large anisotropic magnetoresistance in a perovskite manganite
Li, Run-Wei; Wang, Huabing; Wang, Xuewen; Yu, X. Z.; Matsui, Y.; Cheng, Zhao-Hua; Shen, Bao-Gen; Plummer, E. Ward; Zhang, Jiandi
2009-01-01
The signature of correlated electron materials (CEMs) is the coupling between spin, charge, orbital and lattice resulting in exotic functionality. This complexity is directly responsible for their tunability. We demonstrate here that the broken symmetry, through cubic to orthorhombic distortion in the lattice structure in a prototype manganite single crystal, La0.69Ca0.31MnO3, leads to an anisotropic magneto-elastic response to an external field, and consequently to remarkable magneto-transport behavior. An anomalous anisotropic magnetoresistance (AMR) effect occurs close to the metal-insulator transition (MIT) in the system, showing a direct correlation with the anisotropic field-tuned MIT in the system and can be understood by means of a simple phenomenological model. A small crystalline anisotropy stimulates a “colossal” AMR near the MIT phase boundary of the system, thus revealing the intimate interplay between magneto- and electronic-crystalline couplings. PMID:19706504
Yangui, A; Pillet, S; Mlayah, A; Lusson, A; Bouchez, G; Triki, S; Abid, Y; Boukheddaden, K
2015-12-14
Optical and structural properties of the organic-inorganic hybrid perovskite-type (C6H11NH3)2[PbI4] (abbreviated as C6PbI4) were investigated using optical absorption, photoluminescence (PL), and x-ray diffraction measurements. Room temperature, optical absorption measurements, performed on spin-coated films of C6PbI4, revealed two absorption bands at 2.44 and 3.21 eV. Upon 325 nm (3.815 eV) laser irradiation, strong green PL emission peaks were observed at 2.41 eV (P1) and 2.24 eV (P2) and assigned to free and localized excitons, respectively. The exciton binding energy was estimated at 356 meV. At low temperature, two additional emission bands were detected at 2.366 eV (P3) and a large band (LB) at 1.97 eV. The former appeared only below 40 K and the latter emerged below 130 K. The thermal dependence of the PL spectra revealed an abnormal behavior accompanied by singularities in the peak positions and intensities at 40 and 130 K. X-ray diffraction studies performed on powder and single crystals as a function of temperature evidenced significant changes of the interlayer spacing at 50 K and ∼138 K. Around 138 K, a commensurate to incommensurate structural phase transition occurred on cooling. It involves a symmetry breaking leading to a distortion of the PbI6 octahedron. The resulting incommensurate spatial modulation of the Pb-I distances (and Pb-I-Pb angles) causes a spatial modulation of the band gap, which is at the origin of the emergence of the LB below ∼130 K and the anomalous behavior of the position of P1 below 130 K. The change of the interlayer spacing in the 40-50 K range may in turn be related to the significant decrease of the intensity of P2 and the maximum emission of the LB. These results underline the intricate character of the structural and the PL properties of the hybrid perovskites; understanding such properties should benefit to the design of optoelectronic devices with targeted properties. PMID:26671368
NASA Astrophysics Data System (ADS)
Yangui, A.; Pillet, S.; Mlayah, A.; Lusson, A.; Bouchez, G.; Triki, S.; Abid, Y.; Boukheddaden, K.
2015-12-01
Optical and structural properties of the organic-inorganic hybrid perovskite-type (C6H11NH3)2[PbI4] (abbreviated as C6PbI4) were investigated using optical absorption, photoluminescence (PL), and x-ray diffraction measurements. Room temperature, optical absorption measurements, performed on spin-coated films of C6PbI4, revealed two absorption bands at 2.44 and 3.21 eV. Upon 325 nm (3.815 eV) laser irradiation, strong green PL emission peaks were observed at 2.41 eV (P1) and 2.24 eV (P2) and assigned to free and localized excitons, respectively. The exciton binding energy was estimated at 356 meV. At low temperature, two additional emission bands were detected at 2.366 eV (P3) and a large band (LB) at 1.97 eV. The former appeared only below 40 K and the latter emerged below 130 K. The thermal dependence of the PL spectra revealed an abnormal behavior accompanied by singularities in the peak positions and intensities at 40 and 130 K. X-ray diffraction studies performed on powder and single crystals as a function of temperature evidenced significant changes of the interlayer spacing at 50 K and ˜138 K. Around 138 K, a commensurate to incommensurate structural phase transition occurred on cooling. It involves a symmetry breaking leading to a distortion of the PbI6 octahedron. The resulting incommensurate spatial modulation of the Pb-I distances (and Pb-I-Pb angles) causes a spatial modulation of the band gap, which is at the origin of the emergence of the LB below ˜130 K and the anomalous behavior of the position of P1 below 130 K. The change of the interlayer spacing in the 40-50 K range may in turn be related to the significant decrease of the intensity of P2 and the maximum emission of the LB. These results underline the intricate character of the structural and the PL properties of the hybrid perovskites; understanding such properties should benefit to the design of optoelectronic devices with targeted properties.
Yangui, A.; Pillet, S.; Mlayah, A.; Lusson, A.; Bouchez, G.; Boukheddaden, K. E-mail: kbo@physique.uvsq.fr; Triki, S.; Abid, Y. E-mail: kbo@physique.uvsq.fr
2015-12-14
Optical and structural properties of the organic-inorganic hybrid perovskite-type (C{sub 6}H{sub 11}NH{sub 3}){sub 2}[PbI{sub 4}] (abbreviated as C{sub 6}PbI{sub 4}) were investigated using optical absorption, photoluminescence (PL), and x-ray diffraction measurements. Room temperature, optical absorption measurements, performed on spin-coated films of C{sub 6}PbI{sub 4}, revealed two absorption bands at 2.44 and 3.21 eV. Upon 325 nm (3.815 eV) laser irradiation, strong green PL emission peaks were observed at 2.41 eV (P1) and 2.24 eV (P2) and assigned to free and localized excitons, respectively. The exciton binding energy was estimated at 356 meV. At low temperature, two additional emission bands were detected at 2.366 eV (P3) and a large band (LB) at 1.97 eV. The former appeared only below 40 K and the latter emerged below 130 K. The thermal dependence of the PL spectra revealed an abnormal behavior accompanied by singularities in the peak positions and intensities at 40 and 130 K. X-ray diffraction studies performed on powder and single crystals as a function of temperature evidenced significant changes of the interlayer spacing at 50 K and ∼138 K. Around 138 K, a commensurate to incommensurate structural phase transition occurred on cooling. It involves a symmetry breaking leading to a distortion of the PbI{sub 6} octahedron. The resulting incommensurate spatial modulation of the Pb–I distances (and Pb–I–Pb angles) causes a spatial modulation of the band gap, which is at the origin of the emergence of the LB below ∼130 K and the anomalous behavior of the position of P1 below 130 K. The change of the interlayer spacing in the 40-50 K range may in turn be related to the significant decrease of the intensity of P2 and the maximum emission of the LB. These results underline the intricate character of the structural and the PL properties of the hybrid perovskites; understanding such properties should benefit to the design of optoelectronic devices with
Siegel, D. P.; Kozlov, M. M.
2004-01-01
The energy of intermediates in fusion of phospholipid bilayers is sensitive to \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\bar {{\\kappa}}}_{{\\mathrm{m}}},\\end{equation*}\\end{document} the saddle splay (Gaussian curvature) elastic modulus of the lipid monolayers. The value \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\bar {{\\kappa}}}_{{\\mathrm{m}}}\\end{equation*}\\end{document} is also important in understanding the stability of inverted cubic (QII) and rhombohedral (R) phases relative to the lamellar (Lα) and inverted hexagonal (HII) phases in phospholipids. However, \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\bar {{\\kappa}}}_{{\\mathrm{m}}}\\end{equation*}\\end{document} cannot be measured directly. It was previously measured by observing changes in QII phase lattice dimensions as a function of water content. Here we use observations of the phase behavior of N-mono-methylated dioleoylphosphatidylethanolamine (DOPE-Me) to determine \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\bar {{\\kappa}}}_{{\\mathrm{m}}}.\\end{equation*}\\end{document} At the temperature of the Lα/QII phase transition, TQ, the partial energies of the two phases are equal, and we can express \\documentclass[12pt
Li, Qian; Matula, Thomas J; Tu, Juan; Guo, Xiasheng; Zhang, Dong
2013-02-21
It has been accepted that the dynamic responses of ultrasound contrast agent (UCA) microbubbles will be significantly affected by the encapsulating shell properties (e.g., shell elasticity and viscosity). In this work, a new model is proposed to describe the complicated rheological behaviors in an encapsulating shell of UCA microbubbles by applying the nonlinear 'Cross law' to the shell viscous term in the Marmottant model. The proposed new model was verified by fitting the dynamic responses of UCAs measured with either a high-speed optical imaging system or a light scattering system. The comparison results between the measured radius-time curves and the numerical simulations demonstrate that the 'compression-only' behavior of UCAs can be successfully simulated with the new model. Then, the shell elastic and viscous coefficients of SonoVue microbubbles were evaluated based on the new model simulations, and compared to the results obtained from some existing UCA models. The results confirm the capability of the current model for reducing the dependence of bubble shell parameters on the initial bubble radius, which indicates that the current model might be more comprehensive to describe the complex rheological nature (e.g., 'shear-thinning' and 'strain-softening') in encapsulating shells of UCA microbubbles by taking into account the nonlinear changes of both shell elasticity and shell viscosity. PMID:23339902
Breakup threshold anomaly in the elastic scattering of {sup 6}Li on {sup 27}Al
Figueira, J. M.; Niello, J. O. Fernandez; Abriola, D.; Arazi, A.; Capurro, O. A.; Barbara, E. de; Marti, G. V.; Heimann, D. Martinez; Negri, A. E.; Pacheco, A. J.; Padron, I.; Gomes, P. R. S.; Lubian, J.; Correa, T.; Paes, B.
2007-01-15
Elastic scattering of the weakly bound {sup 6}Li on {sup 27}Al was measured at near-barrier energies. The data analysis was performed using a Woods-Saxon shape optical potential and also using the double-folding Sao Paulo potential. The results show the presence of the breakup threshold anomaly (BTA), an anomalous behavior when compared with the scattering of tightly bound nuclei. This behavior is attributed to a repulsive polarization potential produced by the coupling to the continuum breakup states.
Elastic anomalies in Fe-Cr alloys.
Zhang, Hualei; Wang, Guisheng; Punkkinen, Marko P J; Hertzman, Staffan; Johansson, Börje; Vitos, Levente
2013-05-15
Using ab initio alloy theory, we determine the elastic parameters of ferromagnetic and paramagnetic Fe(1-c)Cr(c) (0 ≤ c ≤ 1) alloys in the body centered cubic crystallographic phase. Comparison with the experimental data demonstrates that the employed theoretical approach accurately describes the observed composition dependence of the polycrystalline elastic moduli. The predicted single-crystal elastic constants follow complex anomalous trends, which are shown to originate from the interplay between magnetic and chemical effects. The nonmonotonic composition dependence of the elastic parameters has marked implications on the micro-mechanical properties of ferrite stainless steels. PMID:23604218
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
Zaoui, Ali
2012-02-15
The present work relates to the study of structural and elastic properties of Tobermorite 11 A as a function of external pressure and composition in terms of calcium to silicon ratio. Basing on the lattice dynamics method, the main aim of this work is precisely to shed light, for the first time, on the high pressure structural phase transition in Tobermorite 11 A and the possible correlation with some elastic quantities. In order to check the transferability of the potentials used we have, additionally, performed a single calculation based on the density functional theory (DFT) for a pressure of 15 GPa in the case of Ca/Si = 1. The variation of the unit cell parameters with pressure indicates that Tobermorite 11 A undergoes a structural instability around 15 GPa along b-axis and around 20 GPa along a-axis which is confirmed from our calculations of X-Rays diffraction patterns at various pressure values. We have also observed the anisotropic character of the Tobermorite structure for both cases (Ca/Si = 1 and Ca/Si = 0.83). Our results show that around 20 GPa an important change appears in the elastic behaviour of Tobermorite. As pressure increases the calculated elastic quantities for Ca/Si = 1 became closer to those evaluated for Ca/Si = 0.83, which may stimulate further experimental and theoretical research on the matter.
Barczak, T.M.; Burton, W.S.
1987-01-01
Longwall-roof behavior is characterized by strata displacements in both the face-to-waste (horizontal) and roof-to-floor (vertical) directions. The roof-support structure provides resistance to this motion by translation of these displacements into vertical and horizontal support loading. Observations indicate that the shield reacts with both a vertical and horizontal force to uniaxial convergence (displacement). However, there are different magnitudes depending on whether the displacement is vertical or horizontal. This makes it possible to use supports as monitors of strata activity and loading. The Bureau of Mines examined this behavior using a linear elastic model of the support structure with two degrees of freedom. Vertical and horizontal load reactions were related to associated displacement actions of the strata. This was done by determining the stiffness of the shield under controlled vertical and horizontal displacement motions in the Bureau's mine roof simulator. The report provides example predictions of strata convergence and isolation of horizontal support loading due to vertical roof convergence using the linear elastic shield model. The report also examines efforts to determine strata behavior by direct measurement of support displacement.
NASA Astrophysics Data System (ADS)
Takahashi, Masahiko; Yui, Hiroharu; Ikezoe, Yasuhiro; Sawada, Tsuguo
2004-05-01
Dynamic behavior of water-in-oil microemulsions at the oil/water interface was investigated using the quasi-elastic laser scattering method. We observed an anomalous rebound behavior of interfacial tension γ induced by collapses of microemulsions and adsorptions of AOT molecules at the interface. γ rapidly decreased and reached a minimum value (5.5 mN/m) at about 500 s after the preparation of the interface, and then increased gradually for about 2000 s to the equilibrium value (8.0 mN/m). We considered the mechanism of the rebound behavior in terms of transient change in interfacial thickness induced by the collapses of AOT microemulsions.
Effect of Zn2+ substitution and zero porosity correction on elastic behavior of CoFe2O4
NASA Astrophysics Data System (ADS)
Modi, K. B.; Dulera, S. V.; Vasoya, N. H.; Raval, P. Y.; Pansara, P. R.; Saija, K. G.; Jadhav, K. M.
2016-05-01
Polycrystalline spinel ferrite system, ZnxCo1-xFe2O4 (x = 0.0-0.6), was synthesized by solid state reaction route. The effect of Zn2+ substitutions on zero porosity corrected elastic constants has been investigated. The unexpected weakening in mechanical strength/elastic stiffness of the ferrites is not only due to substitution of Zn2+ ions, that do not contribute to the active bond formation and increase inter ionic distances, but mainly due to anisotropic thermal stress induced occurrence and development of micro-cracks as well as oxygen vacant sites in the samples with Zn2+ substitution. The bulk modulus to rigidity modulus ratio, ((K0/G0) ˜ 2.0), indicates the ductile nature of ferrite compositions.
NASA Technical Reports Server (NTRS)
Morris, D. H.; Simonds, R. A.
1983-01-01
The influence of elevated and cryogenic temperatures on the elastic moduli and fracture strengths of several C6000/PMR-15 and C6000/NR-15082 laminates was measured. Tests were conducted at -157 C, 24 C, and 316 C (-250 F, 75 F, and 600 F). Both notched and unnotched laminates were tested. The average stress failure criterion was used to predict the fracture strength of quasi-isotropic notched laminates.
NASA Astrophysics Data System (ADS)
Ziegenhain, Gerolf; Hartmaier, Alexander; Urbassek, Herbert M.
2009-09-01
Molecular-dynamics simulation can give atomistic information on the processes occurring in nanoindentation experiments. In particular, the nucleation of dislocation loops, their growth, interaction and motion can be studied. We investigate how realistic the interatomic potentials underlying the simulations have to be in order to describe these complex processes. Specifically we investigate nanoindentation into a Cu single crystal. We compare simulations based on a realistic many-body interaction potential of the embedded-atom-method type with two simple pair potentials, a Lennard-Jones and a Morse potential. We find that qualitatively many aspects of nanoindentation are fairly well reproduced by the simple pair potentials: elastic regime, critical stress and indentation depth for yielding, dependence on the crystal orientation, and even the level of the hardness. The quantitative deficits of the pair potential predictions can be traced back: (i) to the fact that the pair potentials are unable in principle to model the elastic anisotropy of cubic crystals and (ii) as the major drawback of pair potentials we identify the gross underestimation of the stable stacking fault energy. As a consequence these potentials predict the formation of too large dislocation loops, the too rapid expansion of partials, too little cross slip and in consequence a severe overestimation of work hardening.
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.
NASA Astrophysics Data System (ADS)
Gautam, Subodh K.; Gautam, Naina; Singh, R. G.; Ojha, S.; Shukla, D. K.; Singh, Fouran
2015-12-01
The effect of Niobium doping and size of crystallites on highly transparent nano-crystalline Niobium doped Titanium Dioxide (NTO) thin films with stable anatase phase are reported. The Nb doping concentration is varied within the solubility limit in TiO2 lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb+5 in the TiO2 lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR) spectra of films with small size crystallites shows stiffening of about 4 cm-1 for the Eg(1) mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B1g mode exhibits a large anomalous softening of 20 cm-1 with asymmetrical broadening; which was not reported for the case of pure TiO2 crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb5+ doping induced reduction of Ti4+ ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phonon dynamics by performing the near edge x-ray absorption fine structure (NEXAFS) and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively.
NASA Astrophysics Data System (ADS)
Vainshtein, Arkady
2011-04-01
Anomalous quark triangles with one axial and two vector currents are studied in special kinematics when one of the vector currents carries a soft momentum. According to the Adler-Bardeen theorem the anomalous longitudinal part of the triangle is not renormalized in the chiral limit. We show that perturbative corrections the transversal part of the triangle is also absent. This nonrenormalization, in difference with the longitudinal part, holds on only perturbatively.
Analytical solutions for anomalous dispersion transport
NASA Astrophysics Data System (ADS)
O'Malley, D.; Vesselinov, V. V.
2014-06-01
Groundwater flow and transport often occur in a highly heterogeneous environment (potentially heterogeneous at multiple spatial scales) and is impacted by geochemical reactions, advection, diffusion, and other pore scale processes. All these factors can give rise to large-scale anomalous dispersive behavior that can make complex model representation and prediction of plume concentrations challenging due to difficulties unraveling all the complexities associated with the governing processes, flow medium, and their parameters. An alternative is to use upscaled stochastic models of anomalous dispersion, and this is the approach used here. Within a probabilistic framework, we derive a number of analytical solutions for several anomalous dispersion models. The anomalous dispersion models are allowed to be either non-Gaussian (α-stable Lévy), correlated, or nonstationary from the Lagrangian perspective. A global sensitivity analysis is performed to gain a greater understanding of the extent to which uncertainty in the parameters associated with the anomalous behavior can be narrowed by examining concentration measurements from a network of monitoring wells and to demonstrate the computational speed of the solutions. The developed analytical solutions are encoded and available for use in the open source computational framework MADS (http://mads.lanl.gov).
Eliazar, Iddo; Klafter, Joseph
2011-09-15
Brownian motion is widely considered the quintessential model of diffusion processes-the most elemental random transport processes in Science and Engineering. Yet so, examples of diffusion processes displaying highly non-Brownian statistics-commonly termed 'Anomalous Diffusion' processes-are omnipresent both in the natural sciences and in engineered systems. The scientific interest in Anomalous Diffusion and its applications is growing exponentially in the recent years. In this Paper we review the key statistics of Anomalous Diffusion processes: sub-diffusion and super-diffusion, long-range dependence and the Joseph effect, Levy statistics and the Noah effect, and 1/f noise. We further present a theoretical model-generalizing the Einstein-Smoluchowski diffusion model-which provides a unified explanation for the prevalence of Anomalous Diffusion statistics. Our model shows that what is commonly perceived as 'anomalous' is in effect ubiquitous. - Highlights: > The article provides an overview of Anomalous Diffusion (AD) statistics. > The Einstein-Smoluchowski diffusion model is extended and generalized. > The generalized model universally generates AD statistics. > A unified 'universal macroscopic explanation' for AD statistics is established. > AD statistics are shown to be fundamentally connected to robustness.
Lee, Sooyeol; Wang, H; Gharghouri, Michael; Nayyeri, G.; Woo, Wan; Shin, E; Wu, Peidong; Poole, W. J.; Wu, Wei; An, Ke
2014-01-01
In situ neutron diffraction and elastic viscoplastic self-consistent (EVPSC) modeling have been employed to understand the deformation mechanisms of the loading unloading process under uniaxial tension in a solid-solution-strengthened extruded Mg 9 wt.% Al alloy. The initial texture measured by neutron diffraction shows that the {00.2} basal planes in most grains are tilted around 20 30 from the extrusion axis, indicating that basal slip should be easily activated in a majority of grains under tension. Non-linear stress strain responses are observed during unloading and reloading after the material is fully plastically deformed under tension. In situ neutron diffraction measurements have also demonstrated the non-linear behavior of lattice strains during unloading and reloading, revealing that load redistribution continuously occurs between soft and hard grain orientations. The predicted macroscopic stress strain curve and the lattice strain evolution by the EVPSC model are in good agreement with the experimental data. The EVPSC model provides the relative activities of the available slip and twinning modes, as well as the elastic and plastic strains of the various grain families. It is suggested that the non-linear phenomena in the macroscopic stress strain responses and microscopic lattice strains during unloading and reloading are due to plastic deformation by the operation of basal a slip in the soft grain orientations (e.g. {10.1}, {11.2} and {10.2} grain families).
NASA Astrophysics Data System (ADS)
Fiore, Carlos E.; Szortyka, Marcia M.; Barbosa, Marcia C.; Henriques, Vera B.
2009-10-01
The Bell-Lavis model for liquid water is investigated through numerical simulations. The lattice-gas model on a triangular lattice presents orientational states and is known to present a highly bonded low density phase and a loosely bonded high density phase. We show that the model liquid-liquid transition is continuous, in contradiction with mean-field results on the Husimi cactus and from the cluster variational method. We define an order parameter which allows interpretation of the transition as an order-disorder transition of the bond network. Our results indicate that the order-disorder transition is in the Ising universality class. Previous proposal of an Ehrenfest second order transition is discarded. A detailed investigation of anomalous properties has also been undertaken. The line of density maxima in the HDL phase is stabilized by fluctuations, absent in the mean-field solution.