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Sample records for describe uniaxial stress

  1. Uniaxial stress control of skyrmion phase

    PubMed Central

    Nii, Y.; Nakajima, T.; Kikkawa, A.; Yamasaki, Y.; Ohishi, K.; Suzuki, J.; Taguchi, Y.; Arima, T.; Tokura, Y.; Iwasa, Y.

    2015-01-01

    Magnetic skyrmions, swirling nanometric spin textures, have been attracting increasing attention by virtue of their potential applications for future memory technology and their emergent electromagnetism. Despite a variety of theoretical proposals oriented towards skyrmion-based electronics (that is, skyrmionics), few experiments have succeeded in creating, deleting and transferring skyrmions, and the manipulation methodologies have thus far remained limited to electric, magnetic and thermal stimuli. Here, we demonstrate a new approach for skyrmion phase control based on a mechanical stress. By continuously scanning uniaxial stress at low temperatures, we can create and annihilate a skyrmion crystal in a prototypical chiral magnet MnSi. The critical stress is merely several tens of MPa, which is easily accessible using the tip of a conventional cantilever. The present results offer a new guideline even for single skyrmion control that requires neither electric nor magnetic biases and consumes extremely little energy. PMID:26460119

  2. Shallow-donor lasers in uniaxially stressed silicon

    SciTech Connect

    Kovalevsky, K. A. Zhukavin, R. Kh.; Tsyplenkov, V. V.; Shastin, V. N.; Abrosimov, N. V.; Riemann, H.; Pavlov, S. G.; Huebers, H.-W.

    2013-02-15

    The effects of the terahertz-stimulated emission of Group-V donors (phosphorus, antimony, arsenic, bismuth) in uniaxially stressed silicon, excited by CO{sub 2} laser radiation are experimentally studied. It is shown that uniaxial compressive stress of the crystal along the [100] direction increases the gain and efficiency of stimulated radiation, significantly decreasing the threshold pump intensity. The donor frequencies are measured and active transitions are identified in stressed silicon. The dependence of the residual population of active donor states on the uniaxial compressive stress along the [100] direction is theoretically estimated.

  3. Electronic processes in uniaxially stressed p-type germanium

    SciTech Connect

    Dubon, O.D. Jr.

    1996-02-01

    Effect of uniaxial stress on acceptor-related electronic processes in Ge single crystals doped with Ga, Be, and Cu were studied by Hall and photo-Hall effect measurements in conjunction with infrared spectroscopy. Stress dependence of hole lifetime in p-type Ge single crystals is used as a test for competing models of non-radiative capture of holes by acceptors. Photo-Hall effect shows that hole lifetime in Ga- and Be-doped Ge increases by over one order of magnitude with uniaxial stress at liq. He temps. Photo-Hall of Ge:Be shows a stress-induced change in the temperature dependence of hole lifetime. This is consistent with observed increase of responsivity of Ge:Ga detectors with uniaxial stress. Electronic properties of Ge:Cu are shown to change dramatically with uniaxial stress; the results provide a first explanation for the performance of uniaxially stressed, Cu-diffused Ge:Ga detectors which display a high conductivity in absence of photon signal and therefore have poor sensitivity.

  4. Uniaxially stressed Ge:Ga and Ge:Be

    SciTech Connect

    Dubon, O.D. Jr.

    1992-12-01

    The application of a large uniaxial stress to p-type Ge single crystals changes the character of both the valence band and the energy levels associated with the acceptors. Changes include the splitting of the fourfold degeneracy of the valence band top and the reduction of the ionization energy of shallow acceptors. In order to study the effect of uniaxial stress on transport properties of photoexcited holes, a variable temperature photo-Hall effect system was built in which stressed Ge:Ga and Ge:Be could be characterized. Results indicate that stress increases the lifetime and Hall mobility of photoexcited holes. These observations may help further the understanding of fundamental physical processes that affect the performance of stressed Ge photoconductors including the capture of holes by shallow acceptors.

  5. Twin Selection at the Verwey Transition Using Uniaxial Stress

    NASA Astrophysics Data System (ADS)

    Coe, R. S.; Egli, R.; Gilder, S.; Wright, J.

    2011-12-01

    Thermodynamic analysis of the effect of nonhydrostatic stress on the Verwey transition in magnetite leads to a method for how to produce an untwinned sample of the low-temperature phase. When a crystal of pure magnetite is cooled below the Verwey temperature, Tv=120-124 K for unoxidized magnetite, its electrical conductivity drops two orders of magnitude, its crystal structure changes from cubic to monoclinic, and various magnetic properties change as well. When the same crystal is heated above Tv, it transforms back to cubic symmetry with only a fraction of a degree of thermal hysteresis and regains its original shape. Microscopic twinning generally occurs during the transformation to lower symmetry, which poses problems for understanding properties of the low-temperature phase such as detailed atomic positions, cation ordering, and magnetocrystalline anisotropy and domain structure. The transformation strain deduced from the most complete X-ray diffraction studies to date distinguishes twelve monoclinic twin orientations relative to the cubic host at the transition boundary. Nonhydrostatic stress acts to change the transition temperature of some twins differently from others, and twins with higher Tv are thermodynamically favored to form over those with lower Tv. Even simple stress configurations that are relatively easy to apply, such as uniaxial compression, can be designed so as to uniquely favor a given twin orientation over all the other eleven. Thus, cooling through the transition while applying compression in the appropriate crystallographic orientation will select a particular twin from the twelve possibilities. Curiously, uniaxial stress, whether compressive or tensile, always raises Tv, whereas hydrostatic pressure lowers Tv. Moreover, the increase in Tv with uniaxial stress can be substantial, up to six times more per gigapascal than with hydrostatic pressure, and its power to discriminate between twins is also usually greater than per tesla of applied

  6. Raman study of lead zirconate titanate under uniaxial stress

    SciTech Connect

    TALLANT, DAVID R.; SIMPSON, REGINA L.; GRAZIER, J. MARK; ZEUCH, DAVID H.; OLSON, WALTER R.; TUTTLE, BRUCE A.

    2000-04-01

    The authors used micro-Raman spectroscopy to monitor the ferroelectric (FE) to antiferroelectric (AFE) phase transition in PZT ceramic bars during the application of uniaxial stress. They designed and constructed a simple loading device, which can apply sufficient uniaxial force to transform reasonably large ceramic bars while being small enough to fit on the mechanical stage of the microscope used for Raman analysis. Raman spectra of individual grains in ceramic PZT bars were obtained as the stress on the bar was increased in increments. At the same time gauges attached to the PZT bar recorded axial and lateral strains induced by the applied stress. The Raman spectra were used to calculate an FE coordinate, which is related to the fraction of FE phase present. The authors present data showing changes in the FE coordinates of individual PZT grains and correlate these changes to stress-strain data, which plot the macroscopic evolution of the FE-to-AFE transformation. Their data indicates that the FE-to-AFE transformation does not occur simultaneously for all PZT grains but that grains react individually to local conditions.

  7. Effect of uniaxial stress on gallium, beryllium, and copper-doped germanium hole population inversion lasers

    SciTech Connect

    Chamberlin, D R

    1998-05-01

    The effects of stress on germanium lasers doped with single, double, and triple acceptors have been investigated. The results can be explained quantitatively with theoretical calculations and can be attributed to specific changes in the energy levels of acceptors in germanium under stress. In contrast to previous measurements, gallium-doped Ge crystals show a decrease in lasing upon uniaxial stress. The decrease seen here is attributed to the decrease in heavy hole effective mass upon application of uniaxial stress, which results in a decreased population inversion. The discrepancy between this work and previous studies can be explained with the low compensation level of the material used here. Because the amount of ionized impurity scattering in low-compensated germanium lasers is small to begin with, the reduction in scattering with uniaxial stress does not play a significant role in changing the laser operation. Beryllium-doped germanium lasers operate based on a different mechanism of population inversion. In this material it is proposed that holes can transfer between bands by giving their energy to a neutral beryllium atom, raising the hole from the ground to a bound excited state. The free hole will then return to zero energy with some probability of entering the other band. The minimum and maximum E/B ratios for lasing change with uniaxial stress because of the change in effective mass and bound excited state energy. These limits have been calculated for the case of 300 bar [100] stress, and match very well with the observed data. This adds further credence to the proposed mechanism for population inversion in this material. In contrast to Be and Ga-doped lasers, copper-doped lasers under uniaxial stress show an increase in the range of E and B where lasing is seen. To understand this change the theoretical limits for population inversion based on both the optical phonon mechanism and the neutral acceptor mechanism have been calculated. The data are

  8. Uniaxial stress induced symmetry breaking for muon sites in Fe

    NASA Technical Reports Server (NTRS)

    Kossler, W. J.; Namkung, M.; Hitti, B.; Li, Y.; Kempton, J.; Stronach, C. E.; Goode, L. R., Jr.; Lankford, W. F.; Patterson, B. D.; Kuendig, W.

    1984-01-01

    Uniaxial stress was used on Fe single crystals to induce muon precession frequency shifts. The frequency shift for a nominally pure Fe sample at 302K was -0.34 + or - .023 MHz per 100 microstrain along the 100 magnetization axis. This corresponds to a change of magnetic field at the muon of 25.1 + to 1.6G/100 magnetic moment. For an Fe (3wt%Si) single crystal the shifts were -0.348 + or - .008 MHz/100 magnetic moment. The agreement between the shifts for Fe and Fe(3wt%Si) shows the effect to be intrinsic to iron and not strongly impurity sensitive. These shifts and their temperature dependence (1/T) are dominated by the effect of strain inducted population shifts between crystallographically equivalent, but mgnetically inequivalent sites. Their magnitudes are in good agreement ith previous theoretical predictions and by previous extrapolation from calculations on Nb and V especially if both 4T(0) and 1T sites contribute comparably.

  9. The influence of uniaxial compressive stress on the phase transitions and dielectric properties of NaNO2

    NASA Astrophysics Data System (ADS)

    Seyidov, MirHasan Yu.; Mikailzade, Faik A.; Suleymanov, Rauf A.; Bulut, Nebahat; Salehli, Ferid

    2016-06-01

    The effect of uniaxial stress on dielectric properties of sodium nitrite (NaNO2) ferroelectric has been investigated. The real part of the dielectric susceptibility was measured at the frequency of 1 kHz without and on applying compressive uniaxial stress along different crystallographic directions using a uniaxial compress meter. Extraordinary changes in the dielectric constant of NaNO2 under the influence of applied uniaxial stresses were observed for the first time. The shifts of the phase transition points Ti and Tc under the uniaxial stresses σyy and σzz were investigated. The "uniaxial pressure-temperature" phase diagram of NaNO2 was obtained from these results. The observed phenomena were interpreted on the base of the phenomenological Landau theory of phase transitions in NaNO2 by taking into account the uniaxial compressive stress effect. A best agreement between the theoretical predictions and experimental results has been revealed.

  10. A uniaxial stress capacitive dilatometer for high-resolution thermal expansion and magnetostriction under multiextreme conditions.

    PubMed

    Küchler, R; Stingl, C; Gegenwart, P

    2016-07-01

    Thermal expansion and magnetostriction are directional dependent thermodynamic quantities. For the characterization of novel quantum phases of matter, it is required to study materials under multi-extreme conditions, in particular, down to very low temperatures, in very high magnetic fields or under high pressure. We developed a miniaturized capacitive dilatometer suitable for temperatures down to 20 mK and usage in high magnetic fields, which exerts a large spring force between 40 to 75 N on the sample. This corresponds to a uniaxial stress up to 3 kbar for a sample with cross section of (0.5 mm)(2). We describe design and performance test of the dilatometer which resolves length changes with high resolution of 0.02 Å at low temperatures. The miniaturized device can be utilized in any standard cryostat, including dilution refrigerators or the commercial physical property measurement system. PMID:27475567

  11. A uniaxial stress capacitive dilatometer for high-resolution thermal expansion and magnetostriction under multiextreme conditions

    NASA Astrophysics Data System (ADS)

    Küchler, R.; Stingl, C.; Gegenwart, P.

    2016-07-01

    Thermal expansion and magnetostriction are directional dependent thermodynamic quantities. For the characterization of novel quantum phases of matter, it is required to study materials under multi-extreme conditions, in particular, down to very low temperatures, in very high magnetic fields or under high pressure. We developed a miniaturized capacitive dilatometer suitable for temperatures down to 20 mK and usage in high magnetic fields, which exerts a large spring force between 40 to 75 N on the sample. This corresponds to a uniaxial stress up to 3 kbar for a sample with cross section of (0.5 mm)2. We describe design and performance test of the dilatometer which resolves length changes with high resolution of 0.02 Å at low temperatures. The miniaturized device can be utilized in any standard cryostat, including dilution refrigerators or the commercial physical property measurement system.

  12. Effect of uniaxial tensile stress on the isomer shift of 57Fe in fcc stainless steels

    NASA Astrophysics Data System (ADS)

    Ratner, E.; Ron, M.

    1982-05-01

    The electron wave-function response to uniaxial tensile stress in fcc steels (SS310 and SS316) was investigated through the isomer shift of the Mössbauer effect. Stresses up to 12 kbar (the ultimate tensile stress is approximately 14 kbar) were applied at room temperature. The isomer shift changes linearly in these circumstances. It is concluded that, as in the case of hydrostatic pressure, the paramount factor here is the volume strain of the wave functions of 4S electrons.

  13. Effects of uniaxial stress on magnetoacoustic emission and magnetoacoustic responses in steel

    NASA Technical Reports Server (NTRS)

    Namkung, M.; Yost, W. T.; Utrata, D.; Denale, R.; Kushnick, P. W.; Grainger, J. L.

    1990-01-01

    Results of magnetoacoustic emission (MAE) and magnetoacoustic (MAC) measurements performed with an unembrittled HY-80 steel specimen are presented. The MAE measurements were obtained by applying an ac magnetic field of 20 Hz parallel to the uniaxial stress axis. The effects of tensile stress were shown to monotonically decrease the peak amplitude of the MAE burst, and they were consistent with the predicted trend based on the tensile stress-induced domain alignment. The effects of compressive stress were found to increase the peak amplitude of the MAE burst initially and to eventually decrease as the magnitude of compressive stress increased.

  14. Effect of uniaxial stress on substitutional Ni in ZnO

    NASA Astrophysics Data System (ADS)

    Lavrov, E. V.; Herklotz, F.; Kutin, Y. S.

    2013-04-01

    The influence of uniaxial stress on the electronic T13(F)→T23(F) transitions of Ni (d8) in ZnO at 4216, 4240, and 4247 cm-1 is studied. It is shown that the split pattern and polarized properties of IR absorption lines are consistent with a dynamic Jahn-Teller effect in the T23(F) state of the defect.

  15. Uniaxial Stress Dependence of the Fermi Surface of Copper.

    NASA Astrophysics Data System (ADS)

    Ruesink, Derk Willem

    Form a comprehensive experimental study of quantum oscillations in magnetostriction and torque, values have been deduced for all non-vanishing tetragonal and angular shear strain derivatives for the five principal extremal cross sections of the Fermi surface of copper, viz., the neck and belly normal to {111}, the dogsbone normal to {110} and the rosette and belly normal to {001}. It is found that the neck is most sensitive to angular shear strain, whereas the bellies are most affected by uniform dilation. For the other orbits the magnitudes of shear and dilation derivatives are comparable. The results are self consistent and agree with experimental tensile stress results of Shoenberg and Watts. Earlier magnetostriction results for the neck obtained by Aron and by Slavin can be brought into agreement with the present data by recalculating the former using the presently accepted value of the neck effective mass. The present experimental values are in reasonable agreement with theoretical values calculated by Lee, except for the tetragonal shear derivative of the {001} belly; the theoretical value is about 50% higher than the experimentally determined derivative.

  16. Cracking Process and Stress Field Evolution in Specimen Containing Combined Flaw Under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Liu, Ting; Lin, Baiquan; Yang, Wei; Zou, Quanle; Kong, Jia; Yan, Fazhi

    2016-08-01

    Hydraulic slotting, an efficient technique for underground enhanced coal bed methane (ECBM) recovery, has been widely used in China. However, its pressure relief mechanism is unclear. Thus far, only limited research has been conducted on the relationships among the mechanical properties, flaw parameters, and crack propagation patterns of coal after hydraulic slotting. In addition, because of the limitations of test methods, an in-depth information is not available for this purpose. In this work, numerical models of specimens containing combined flaws are established based on particle flow code method. Our results provide insights into the effects of flaw inclination angle on the mechanical properties, crack propagation patterns, and temporal and spatial evolution rules of stress field in specimens containing combined flaws during the loading process. Besides, based on the initiation position and underlying mechanism, three types of crack initiation modes are identified from the failure processes of specimens. Finally, the crack propagation pattern is quantitatively described by the fractal dimension, which is found to be inversely proportional to the uniaxial compressive strength and elastic modulus of the specimen. To verify the rationality of the numerical simulation results, laboratory tests were conducted and their results match well with those obtained from the numerical simulation.

  17. Ferromagnetic resonance in thin films submitted to multiaxial stress state: application of the uniaxial equivalent stress concept and experimental validation

    NASA Astrophysics Data System (ADS)

    Gueye, M.; Zighem, F.; Belmeguenai, M.; Gabor, M.; Tiusan, C.; Faurie, D.

    2016-07-01

    In this paper a unique expression of the anisotropy field induced by any multiaxial stress state in a magnetic thin film and probed by ferromagnetic resonance is derived. This analytical development has been made using the uniaxial equivalent stress concept, for which correspondances between definitions given by different authors in the literature is found. The proposed model for the anisotropy field has been applied to \\text{C}{{\\text{o}}2}\\text{FeAl} thin films (25 nm) stressed both by piezoelectric actuation (non-equi-biaxial) or by bending tests (uniaxial) and measured with a broadband ferromagnetic resonance technique. The overall exprimental data can be easily plotted on a unique graph from which the magnetostriction coefficient has been estimated.

  18. Stress-concentration factors for finite orthotropic laminates with a circular hole and uniaxial loading

    NASA Technical Reports Server (NTRS)

    Hong, C. S.; Crews, J. H., Jr.

    1979-01-01

    Stresses were calculated for finite-width orthotropic laminates with a circular hole and remote uniaxial loading using a two-dimensional finite element analysis with both uniform stress and uniform displacement boundary conditions. Five different laminates were analyzed. Computed results are presented for selected combinations of hole diameter/sheet-width ratio d/w and length-to-width ratio L/w. For small L/w values, the stress-concentration factors K sub tn were significantly different for the uniform stress and uniform displacement boundary conditions. Typically, for the uniform stress condition, the K sub tn values were much larger than for the infinite strip reference condition; however, for the uniform displacement condition, they were only slightly smaller than for this reference. The results for long strips are also presented as width correction factors. For d/w less or = 0.33, these width correction factors are nearly equal for all five laminates.

  19. Using uniaxial pseudorandom stress stimuli to develop soft tissue constitutive equations.

    PubMed

    Hoffman, Allen H; Grigg, Peter

    2002-01-01

    A nonlinear systems identification method was used to develop constitutive equations for soft tissue specimens under uniaxial tension. The constitutive equations are developed from a single test by applying a pseudorandom Gaussian (PGN) stress input to the specimen, measuring the resulting strain, and calculating the Volterra-Wiener kernels. First and second order kernels were developed for two tissues with widely different properties, rat medial collateral knee ligaments, and rat skin. These kernels were used to predict the strain response to a variety of sinusoidal stress inputs. These predicted strains were compared with the measured strain response using the normalized mean squared error (NMSE). Results showed NMSEs in the range of 0.01-0.08 provided that the magnitudes of the applied stresses were present in the original PGN stress input. Overall, the method provides a means to develop soft tissue constitutive equations that can predict both nonlinear and viscoelastic behavior over a wide range of stress inputs.

  20. Impact of [110]/(001) uniaxial stress on valence band structure and hole effective mass of silicon

    NASA Astrophysics Data System (ADS)

    Jianli, Ma; Heming, Zhang; Jianjun, Song; Guanyu, Wang; Xiaoyan, Wang; Xiaobo, Xu

    2011-02-01

    The valence band structure and hole effective mass of silicon under a uniaxial stress in (001) surface along the [110] direction were detailedly investigated in the framework of the k · p theory. The results demonstrated that the splitting energy between the top band and the second band for uniaxial compressive stress is bigger than that of the tensile one at the same stress magnitude, and of all common used crystallographic direction, such as [110], [001], [1¯10] and [100], the effective mass for the top band along [110] crystallographic direction is lower under uniaxial compressive stress compared with other stresses and crystallographic directions configurations. In view of suppressing the scattering and reducing the effective mass, the [110] crystallographic direction is most favorable to be used as transport direction of the charge carrier to enhancement mobility when a uniaxial compressive stress along [110] direction is applied. The obtained results can provide a theory reference for the design and the selective of optimum stress and crystallorgraphic direction configuration of uniaxial strained silicon devices.

  1. Cryogenic System for Neutron Scattering Experiments with In Situ Pressure Tuning Mechanism: Response of the Antiferromagnetism of URu2Si2 to Uniaxial Stress

    NASA Astrophysics Data System (ADS)

    Kawarazaki, Shuzo; Uwatoko, Yoshiya; Yokoyama, Makoto; Okita, Yuji; Tabata, Yoshikazu; Taniguchi, Toshifumi; Amitsuka, Hiroshi

    2002-10-01

    A handy insertable device to manipulate hydrostatic pressure or uniaxial stress on a sample in a cryostat for neutron scattering experiments is described. The pressure that is generated in a miniature hydraulic oil-cylinder on the top of the inserting stick is transmitted to the sample via a long piston-cylinder unit made of a thick stainless-steel tube and a fiber-reinforced plastics (FRP) rod. One can thus in situ tune the pressure or the stress on the sample without handling the pressure-cell at room temperature outside the cryostat. The device is designed to fit into the ILL-type Orange cryostat so that it can be used in many neutron scattering facilities. A newly designed uniaxial-stress cell and hydrostatic pressure cell to be used with this system are also described. The result of measurement of the hysteresis effect of uniaxial stress on the antiferromagnetism of URu2Si2 at 1.4 K is presented.

  2. Effect of uniaxial stress on the transport properties of TaSe3

    NASA Astrophysics Data System (ADS)

    Tritt, T. M.; Stillwell, E. P.; Skove, M. J.

    1986-11-01

    We have measured the effect of elastic, uniaxial stress on the resistance R, the thermoelectric power (TEP), and the superconducting transition temperature Tc of TaSe3. We find that there is a nearly discontinuous change in R and in the TEP at a stress σ of about 1.2 GPa at 20 K. In this change R increases by several orders of magnitude, while the TEP changes sign and increases by several orders of magnitude. At higher temperatures this change becomes less pronounced and occurs over a larger range of σ. We suggest that this change is due to a Fermi-surface topology change, a structural phase transition, or a charge-density-wave transition. We found no evidence for a metal-to-nonmetal transition just above the normal-superconducting transition at Tc.

  3. Uniaxial and biaxial tensile stress-stretch response of human linea alba.

    PubMed

    Cooney, Gerard M; Lake, Spencer P; Thompson, Dominic M; Castile, Ryan M; Winter, Des C; Simms, Ciaran K

    2016-10-01

    There are few studies on the stress-stretch behaviour of human linea alba, yet understanding the mechanics of this tissue is important for developing better methods of abdominal wound closure. Published data focuses mainly on porcine linea alba and for human tissue there are conflicting results and no bi-axial data available. This variability is likely due to challenges with the physical dimensions of the tissue and differences in experimental methodology. This study focussed on the tensile mechanical characterisation of the human linea alba using uniaxial and equi-load biaxial testing performed using image-based strain measurement methods. Thirteen freshly frozen human cadaveric abdominal walls were obtained and used to prepare 7 samples in both the transverse and longitudinal directions for uniaxial testing, and 13 square samples for bi-axial testing. The results showed significant anisotropy and for the equi-load biaxial tests the deformation was heavily biased in the longitudinal direction. In comparison with similar tests on porcine tissue from a previous study, it was found that the response of porcine linea alba to uniaxial loading is similar to that of human linea alba, with no statistically significant differences observed. Under biaxial loading human and porcine linea showed no statistical significance in the difference between their means in the transverse direction. However, a significant difference was observed in the longitudinal direction, and further study of the respective tissue structures is needed to better understand this result. These results provide the first data on the biaxial tensile properties of human linea alba and can aid in an improved assessment of wound closure mechanics. PMID:27367944

  4. Band offsets for biaxially and uniaxially stressed silicon-germanium layers with arbitrary substrate and channel orientations

    NASA Astrophysics Data System (ADS)

    Eneman, Geert; Roussel, Philippe; Brunco, David Paul; Collaert, Nadine; Mocuta, Anda; Thean, Aaron

    2016-08-01

    The conduction and valence band offsets between a strained silicon-germanium layer and a silicon-germanium substrate are reported for arbitrary substrate and channel crystal orientations. The offsets are calculated both for the case of biaxial stress, corresponding approximately to the stress state of a thin strained channel in a planar field-effect transistor (FET), and for uniaxial stress, which is the approximate stress state for strained channels in a FinFET configuration. Significant orientation dependence is found for the conduction band offset, overall leading to the strongest electron quantum confinement in biaxial-tensile stressed channels on {100}-oriented substrates, and uniaxial-tensile stressed channels in the ⟨100⟩ and ⟨110⟩ directions. For biaxially stressed layers on {111} substrates, the conduction band offset is significantly smaller than for {100} or {110} directions. For the valence band offset, the dependence on crystal orientation is found to be small.

  5. Frequency Shift of Polar Whispering Gallery Modes Caused by Uniaxial Stress

    NASA Astrophysics Data System (ADS)

    Wagner, H.-P.; Schmitzer, H.; Lutti, J.; Borri, P.; Langbein, W.

    2010-03-01

    Optical whispering gallery modes in small spheres -so called microcavity optical resonators- have been investigated in the past years because they are promising as single virus or single bacterium detectors and as pressure sensors for microfluidic applications. Due to high Q-factors whispering gallery modes are very sensitive to changes of the shape and the refractive index of the sphere. Both can be caused by mechanical stress. A small exerted compressive force will therefore lead to an energy shift of the resonant modes. The relationship between this energy shift and the exerted force depends on the geometry of the experimental setup. We investigated the energy shift of polar modes in polystyrene beads of 45 micron diameter applying an uniaxial force. With increasing force we find a shift to higher energy for resonator modes with different mode order n and number l. The observed results will be compared with model calculations.

  6. Uniaxial compressive stress induced nuclear quadrupole interaction at the 111Cd nucleus in n-doped silicon

    NASA Astrophysics Data System (ADS)

    Tessema, Genene

    2006-03-01

    Stress induced quadrupole interaction at the probe nucleus ( 111Cd) in silicon has been studied using the perturbed γ-γ angular correlation (PAC) method. The extra nuclear field, at the sites of the nuclei, is produced via the disturbances of the surrounding charges by the action of a uniaxial compressive stress on the samples. However, the probes situated at various lattice locations in the sample showed different responses for the same value of stress. The various lattice environments are mainly caused by the involvement of either tellurium or antimony donor atoms in the samples. As a result, the donor free substitutional probe atoms experience a finite nuclear quadrupole interaction due to the broken symmetry of the charge distribution upon uniaxial compression; those probe atoms, which form pairs with donors, exhibit a strong electric-field gradient (EFG) that appears to be pressure independent.

  7. Magnetic properties of URu{sub 2}Si{sub 2} under uniaxial stress by neutron scattering

    SciTech Connect

    Bourdarot, Frederic; Martin, Nicolas; Raymond, Stephane; Regnault, Louis-Pierre

    2011-11-01

    The aim of this study is to compare the magnetic behavior of URu{sub 2}Si{sub 2} under uniaxial stress along the a axis with the behavior under hydrostatic pressure. Both are very similar, but uniaxial stress presents a critical stress {sigma}{sub x}{sup a}[0.33(5) GPa] that is smaller than the hydrostatic critical pressure p{sub x} (0.5 GPa) where the ground state switches from a HO (hidden-order) to AF (antiferromagnetic) ground state. From these critical values and Larmor neutron diffraction, we conclude that the magnetic properties are governed by the shortest U-U distance in the plane (a lattice parameter). Under stress, the orthorhombic unit cell stays centered. A key point shown by this study is the presence of a threshold for the uniaxial stress along the a axis before the appearance of the large AF moment, which indicates no mixture of the order parameter between the HO ground state and the AF one as under hydrostatic pressure. The two most intense longitudinal magnetic excitations at Q{sub 0} =(1,0,0) and Q{sub 1} =(0.6,0,0) were measured in the HO state: the excitation at Q{sub 0} decreases in energy while the excitation at Q{sub 1} increases in energy with the uniaxial stress along the a axis. The decrease of the energy of the excitation at Q{sub 0} seems to indicate a critical energy-gap value of 1.2(1) meV at {sigma}{sub x}{sup a}. A similar value was derived from studies under hydrostatic pressure at p{sub x}.

  8. Uniaxial stress study of the ro-vibrational transitions of HD in Si

    NASA Astrophysics Data System (ADS)

    Shi, G. A.

    2005-03-01

    The vibrational spectroscopy of interstitial H2 in Si gave rise to a number of perplexing puzzles that concerned the rotational motion of the defect [1]. Most experiments were interpreted in terms of a static defect whereas theory suggested that there should be a very small barrier to rotation. The position and intensity of the HD vibrational line were also anomalous. The key to the solution of these puzzles was the discovery of a new vibrational line for HD and the recognition that certain ro- vibrational transitions are possible for HD that are not possible for the H2 or D2 homonuclear molecules in Si. H2 in Si is a nearly free rotator after all. New experiments have been performed for HD in Si in which IR spectroscopy combined with uniaxial stress has been used to confirm the assignments of the ro-vibrational transitions of HD that underpin our understanding of H2 in Si. This work is supported by NSF Grant DMR 0403641. 1. M. Stavola, E E. Chen, W.B. Fowler, G.A. Shi, Physica B 340-342, 58 (2003), and references contained therein.

  9. Occupancy of the DX center in n-Al0.32Ga0.68As under uniaxial stress

    NASA Astrophysics Data System (ADS)

    Wang, Zhiguo; Chung, Ki-woong; Miller, T.; Williamson, F.; Nathan, M. I.

    1991-05-01

    We have used the deep level transient spectroscopy signal height as a function of applied stress data and the statistics of the occupancy of the DX center to obtain the stress dependence of the thermal binding energy of the neutral DX center, EDX. We find that EDX decreases with about the same rate for uniaxial stresses along <100> and <111> directions. Our results confirm that the DX center is a highly localized center as proposed by Chadi and Chang and disagree with the model assuming the DX center being an effective mass state of the doping impurity associated with the L band.

  10. Uniaxial-stress control of spin-driven ferroelectricity in multiferroic Ba(2)CoGe(2)O(7).

    PubMed

    Nakajima, Taro; Tokunaga, Yusuke; Kocsis, Vilmos; Taguchi, Yasujiro; Tokura, Yoshinori; Arima, Taka-Hisa

    2015-02-13

    We have demonstrated that spin-driven ferroelectricity in a tetragonal multiferroic Ba(2)CoGe(2)O(7) is controlled by applying uniaxial stress. We found that the application of compressive stress along the [110] direction leads to a 45° or 135° rotation of the sublattice magnetization of the staggered antiferromagnetic order in this system. This allows the spontaneous electric polarization to appear along the c axis. The present study suggests that an application of anisotropic stress, which is the simplest way to control symmetry of matter, can induce a variety of cross-correlated phenomena in spin-driven multiferroics.

  11. Damage-based life prediction model for uniaxial low-cycle stress fatigue of super-elastic NiTi shape memory alloy microtubes

    NASA Astrophysics Data System (ADS)

    Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

    2015-08-01

    Based on the experimental observations for the uniaxial low-cycle stress fatigue failure of super-elastic NiTi shape memory alloy microtubes (Song et al 2015 Smart Mater. Struct. 24 075004) and a new definition of damage variable corresponding to the variation of accumulated dissipation energy, a phenomenological damage model is proposed to describe the damage evolution of the NiTi microtubes during cyclic loading. Then, with a failure criterion of Dc = 1, the fatigue lives of the NiTi microtubes are predicted by the damage-based model, the predicted lives are in good agreement with the experimental ones, and all of the points are located within an error band of 1.5 times.

  12. Terahertz-range spontaneous emission under the optical excitation of donors in uniaxially stressed bulk silicon and SiGe/Si heterostructures

    SciTech Connect

    Zhukavin, R. Kh. Kovalevsky, K. A.; Orlov, M. L.; Tsyplenkov, V. V.; Bekin, N. A.; Yablonskiy, A. N.; Yunin, P. A.; Pavlov, S. G.; Abrosimov, N. V.; Hübers, H.-W.; Radamson, H. H.; Shastin, V. N.

    2015-01-15

    The results of measurements of the total terahertz-range photoluminescence of Group-V donors (phosphorus, antimony, bismuth, arsenic) in bulk silicon and SiGe/Si heterostructures depending on the excitation intensity are presented. The signal of bulk silicon was also measured as a function of uniaxial stress. The results of measurement of the dependence of the spontaneous emission intensity on the uniaxial stress is in rather good agreement with theoretical calculations of the relaxation times of excited states of donors in bulk silicon. Comparative measurements of the spontaneous emission from various strained heterostructures showed that the photoluminescence signal is caused by donor-doped silicon regions.

  13. Experimental observations on uniaxial whole-life transformation ratchetting and low-cycle stress fatigue of super-elastic NiTi shape memory alloy micro-tubes

    NASA Astrophysics Data System (ADS)

    Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

    2015-07-01

    In this work, the low-cycle fatigue failure of super-elastic NiTi shape memory alloy micro-tubes with a wall thickness of 150 μm is investigated by uniaxial stress-controlled cyclic tests at human body temperature 310 K. The effects of mean stress, peak stress, and stress amplitude on the uniaxial whole-life transformation ratchetting and fatigue failure of the NiTi alloy are observed. It is concluded that the fatigue life depends significantly on the stress levels, and the extent of martensite transformation and its reverse play an important role in determining the fatigue life. High peak stress or complete martensite transformation shortens the fatigue life.

  14. Cracking and Stress-Strain Behavior of Rock-Like Material Containing Two Flaws Under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Zhao, Yanlin; Zhang, Lianyang; Wang, Weijun; Pu, Chengzhi; Wan, Wen; Tang, Jingzhou

    2016-07-01

    This paper investigates the cracking and stress-strain behavior, especially the local strain concentration near the flaw tips, of rock-like material containing two flaws. A series of uniaxial compression tests were carried out on rock-like specimens containing two flaws, with strain gauges mounted near the flaw tips to measure the local strain concentration under the uniaxial compressive loading. Four different types of cracks (wing cracks, anti-wing cracks, coplanar shear cracks and oblique shear cracks) and seven patterns of crack coalescences (T1 and T2; S1 and S2; and TS1, TS2 and TS3) are observed in the experiments. The type of crack coalescence is related to the geometry of the flaws. In general, the crack coalescence varies from the S-mode to the TS-mode and then to the T-mode with the increase of the rock bridge ligament angle. The stress-strain curves of the specimens containing two flaws are closely related to the crack development and coalescence process. The strain measurements indicate that the local tensile strain concentration below or above the pre-existing flaw tip causes wing or anti-wing cracks, while the local compressive strain concentration near the flaw tip is related to the shear crack. The measured local tensile strain shows a jump at the initiation of wing- and anti-wing cracks, reflecting the instant opening of the wing- and anti-wing crack propagating through the strain gauge. During the propagation of wing- and anti-wing cracks, the measured local tensile strain gradually increases with few jumps, implying that the opening deformation of wing- and anti-wing cracks occurs in a stable manner. The shear cracks initiate followed by a large and abrupt compressive strain jump and then quickly propagate in an unstable manner resulting in the failure of specimens.

  15. Stress distribution and lattice distortions in Nb3Sn multifilament wires under uniaxial tensile loading at 4.2 K

    NASA Astrophysics Data System (ADS)

    Scheuerlein, C.; Di Michiel, M.; Buta, F.; Seeber, B.; Senatore, C.; Flükiger, R.; Siegrist, T.; Besara, T.; Kadar, J.; Bordini, B.; Ballarino, A.; Bottura, L.

    2014-04-01

    The lattice parameter changes in three types of Nb3Sn superconducting wires during uniaxial stress-strain measurements at 4.2 K have been measured by high-energy synchrotron x-ray diffraction. The nearly-stress-free Nb3Sn lattice parameter has been determined using extracted filaments, and the elastic strain in the axial and transverse wire directions in the different wire phases has been calculated. The mechanical properties of the PIT and RRP wire are mainly determined by the properties of Nb3Sn and unreacted Nb. This is in contrast to the bronze route wire, where the matrix can carry substantial loads. In straight wires the axial Nb3Sn pre-strain is strongest in the bronze route wire, its value being smaller in the PIT and RRP wires. A strong reduction of the non-Cu elastic modulus of about 30% is observed during cool-down from ambient temperature to 4.2 K. The Nb3Sn Poisson ratio at 4.2 K measured in the untwisted bronze route wire is 0.35. The present study also shows that the process route has a strong influence on the Nb3Sn texture.

  16. Coarse-graining scheme for simulating uniaxial stress-strain response of glassy polymers through molecular dynamics.

    PubMed

    Majumder, Manoj K; S, Ramkumar; Mahajan, Dhiraj K; Basu, Sumit

    2010-01-01

    Simulation of the deformation of polymers below their glass transition through molecular dynamics provides an useful route to correlate their molecular architecture to deformation behavior. However, present computational capabilities severely restrict the time and length scales that can be simulated when detailed models of these macromolecules are used. Coarse-graining techniques for macromolecular structures intend to make bigger and longer simulations possible by grouping atoms into superatoms and devising ways of determining reasonable force fields for the superatoms in a manner that retains essential macromolecular features relevant to the process under study but jettisons unnecessary details. In this work we systematically develop a coarse-graining scheme aimed at simulating uniaxial stress-strain behavior of polymers below their glass transition. The scheme involves a two step process of obtaining the coarse grained force field parameters above glass transition. This seems to be enough to obtain "faithful" stress-strain responses after quenching to below the glass transition temperature. We apply the scheme developed to a commercially important polymer polystyrene, derive its complete force field parameters and thus demonstrate the effectiveness of the technique.

  17. Recombination luminescence in irradiated silicon-effects of uniaxial stress and temperature variations.

    NASA Technical Reports Server (NTRS)

    Jones, C. E.; Compton, W. D.

    1971-01-01

    Demonstration that luminescence in irradiated silicon consists of a spectral group between 0.80 and 1.0 eV which seems to be independent of impurities, while a lower energy group between 0.60 and 0.80 eV is seen only in pulled crystals. The small halfwidth and temperature dependence of the sharp zero-phonon lines observed in these spectra indicate that the luminescence arises from a bound-to-bound transition. A model is proposed for the transition mechanism. Stress data taken on the 0.79-eV zero-phonon line in pulled crystals can be fit by either a tetragonal 100 (in brackets) defect symmetry or by conduction-band splitting effects. It is suggested that the 0.79-eV zero-phonon line and the 0.60- to 0.80-eV spectral group arise from the EPR G-15 center. Stress data on a zero-phonon line at 0.97 eV associated with the 0.80- to 1.0-eV spectral group can be explained by a trigonal 111 (in brackets) defect. The divacancy is tentatively suggested as responsible for this luminescence spectra.

  18. Fourier-transform photoluminescence spectroscopy of excitons bound to group-III acceptors in silicon: Uniaxial stress

    NASA Astrophysics Data System (ADS)

    Karasyuk, V. A.; Thewalt, M. L. W.; An, S.; Lightowlers, E. C.

    1997-12-01

    Photoluminescence of excitons bound to Al, Ga, In, and Tl acceptors in Si crystals subjected to <001>, <111>, or <110> uniaxial stress was studied at liquid-He temperatures with 0.0025-meV spectral resolution. The deformation-potential constants of the group-III acceptors in the ground state are (in eV) b=-1.01+/-0.02, d=-3.31+/-0.06 for Al, b=-1.03+/-0.02, d=-3.10+/-0.06 for Ga, b=-0.43+/-0.01, d=-2.41+/-0.05 for In, and b=-0.30+/-0.03, d=-1.95+/-0.2 for Tl. The shear deformation-potential constant for electrons in acceptor bound excitons Ξu=8.6 eV for all group-III acceptors within an experimental error of +/-0.15 eV for Al, Ga, and In, and +/-0.8 eV for Tl. The order of the valley-orbit states in Tl bound excitons is Γ1, Γ3, Γ5 with the Γ5 energy 1.21 meV above Γ1, and 0.10 meV above Γ3. All details of the spectra including positions, relative amplitudes, and polarizations of the components have been explained on the basis of a simple model of acceptor bound excitons with holes in the J=0 state taking into account the valley-orbit splitting and the spin-orbit coupling of the electron. Significant deviations from the theoretical predictions were observed only for very small strains producing acceptor splittings comparable with the intrinsic zero-stress splitting.

  19. Cyclic hardening in copper described in terms of combined monotonic and cyclic stress-strain curves

    SciTech Connect

    Chandler, H.D. . School of Mechanical Engineering)

    1995-01-01

    Hardening of polycrystalline copper subjected to tension-compression loading cycles in the plastic region is discussed with reference to changes in flow stress determined from equations describing dislocation glide. It is suggested that hardening is as a result of the accumulation of strain on a monotonic stress-strain curve. On initial loading, the behavior is monotonic. On stress reversal, a characteristic cyclic stress-strain curve is followed until the stress reaches a value in reverse loading corresponding to the maximum attained during the preceding half cycle. Thereafter, the monotonic path is followed until strain reversal occurs at completion of the half cycle. Repetition of the process results in cyclic hardening. Steady state cyclic behavior is reached when a stress associated with the monotonic stress-strain curve is reached which is equal to the stress associated with the cyclic stress-strain curve corresponding to the imposed strain amplitude.

  20. Evaluation of in-pile and out-of-pile stress relaxation in 316L stainless steel under uniaxial loading

    NASA Astrophysics Data System (ADS)

    Kaji, Yoshiyuki; Miwa, Yukio; Tsukada, Takashi; Kikuchi, Masahiko; Kita, Satoshi; Yonekawa, Minoru; Nakano, Junichi; Tsuji, Hirokazu; Nakajima, Hajime

    2002-12-01

    Stress relaxation of tensile type specimens under fast neutron irradiation at 288 °C has been studied for 316L stainless steel (SS) in the Japan Materials Testing Reactor. In-pile stress-relaxation tests were carried out at fast neutron fluence levels of 1.3×10 24, 5.5×10 24 and 1.5×10 25 n/m 2 ( E>1 MeV). These tests were carried out at the applied total strain levels of 0.06%, 0.1%, 0.3% and 0.75%. In order to evaluate the thermal stress-relaxation behavior and to distinguish it from the irradiation induced stress-relaxation behavior, out-of-pile stress-relaxation tests were also performed at 288 °C in air using an electric furnace. This paper describes results of in-pile and out-of-pile stress-relaxation tests on 316L SS tensile specimens. These results are compared with the literature data by Foster et al. [J. Nucl. Mater. 252 (1998) 89] which were mainly obtained from bend beam specimens. Moreover, these experimental results are compared with analytical results obtained using Nagakawa's model [J. Nucl. Mater. 212-215 (1994) 541].

  1. Verification of the NIKE3D structural analysis code by comparison against the analytic solution for a spherical cavity under a far-field uniaxial stress

    SciTech Connect

    Kansa, E.J.

    1989-01-01

    The original scope of this task was to simulate the stresses and displacements of a hard rock tunnel experimental design using a suitable three-dimensional finite element code. NIKE3D was selected as a suitable code for performing these primarily approximate linearly elastic 3D analyses, but it required modifications to include initial stress, shear traction boundary condition and excavation options. During the summer of 1988, such capabilities were installed in a special version of NIKE3D. Subsequently, we verified both the LLNL's commonly used version of NIKE3D and our private modified version against the analytic solution for a spherical cavity in an elastic material deforming under a far-field uniaxial stress. We find the results produced by the unmodified and modified versions of NIKE3D to be in good agreement with the analytic solutions, except near the cavity, where the errors in the stress field are large. As can be expected from a code based on a displacement finite element formulation, the displacements are much more accurate than the stresses calculated from the 8-noded brick elements. To reduce these errors to acceptable levels, the grid must be refined further near the cavity wall. The level of grid refinement required to simulate accurately tunneling problems that do not have spatial symmetry in three dimensions using the current NIKE3D code is likely to exceed the memory capacity of the largest CRAY 1 computers at LLNL. 8 refs., 121 figs.

  2. Optical studies of the uniaxial stress-induced orbital alignment of the Cr(2+) centers in KZnF3 single crystal.

    PubMed

    Nikitin, S I; Gracheva, I N; Zverev, D G; Yusupov, R V

    2016-06-21

    Observation of an intense optical linear dichroism arising in cubic KZnF3:Cr crystal at low temperatures under uniaxial stress applied along the four-fold axis is reported. Dichroism occurs in the range of the wide vibronic absorption band corresponding to (5)Eg → (5)T2g transition of the Cr(2+) ions. Strain dependences of the dichroism value were studied at the temperatures of 2.0 K, 4.2 K, and 77 K. We associate our observations with the Jahn-Teller effect in the (5)Eg ground state of the Cr(2+) ion. The model is proposed based on a redistribution of the centers between the minima of the E⨂e problem adiabatic potential that become inequivalent under uniaxial stress applied along the four-fold axis of the crystal. It is shown that random strains in the sample have to be taken into account to achieve the quantitative agreement of the model predictions with experimental data. It is found that random strains in the studied sample originate predominantly from point defects. Obtained parameter values are inversion splitting δ = 9.2 ± 1.6 cm(-1), electron-strain coupling constant qVES = 16 500 ± 600 cm(-1), width of the random strain distribution w = (6.9 ± 0.5) ⋅ 10(-5). It is shown also that the minima of the [CrF6](4-) cluster adiabatic potential correspond to the elongated along the four-fold axes configurations. PMID:27334165

  3. Optical studies of the uniaxial stress-induced orbital alignment of the Cr2+ centers in KZnF3 single crystal

    NASA Astrophysics Data System (ADS)

    Nikitin, S. I.; Gracheva, I. N.; Zverev, D. G.; Yusupov, R. V.

    2016-06-01

    Observation of an intense optical linear dichroism arising in cubic KZnF3:Cr crystal at low temperatures under uniaxial stress applied along the four-fold axis is reported. Dichroism occurs in the range of the wide vibronic absorption band corresponding to 5Eg → 5T2g transition of the Cr2+ ions. Strain dependences of the dichroism value were studied at the temperatures of 2.0 K, 4.2 K, and 77 K. We associate our observations with the Jahn-Teller effect in the 5Eg ground state of the Cr2+ ion. The model is proposed based on a redistribution of the centers between the minima of the E⨂e problem adiabatic potential that become inequivalent under uniaxial stress applied along the four-fold axis of the crystal. It is shown that random strains in the sample have to be taken into account to achieve the quantitative agreement of the model predictions with experimental data. It is found that random strains in the studied sample originate predominantly from point defects. Obtained parameter values are inversion splitting δ = 9.2 ± 1.6 cm-1, electron-strain coupling constant qVES = 16 500 ± 600 cm-1, width of the random strain distribution w = (6.9 ± 0.5) ṡ 10-5. It is shown also that the minima of the [CrF6]4- cluster adiabatic potential correspond to the elongated along the four-fold axes configurations.

  4. Optical studies of the uniaxial stress-induced orbital alignment of the Cr(2+) centers in KZnF3 single crystal.

    PubMed

    Nikitin, S I; Gracheva, I N; Zverev, D G; Yusupov, R V

    2016-06-21

    Observation of an intense optical linear dichroism arising in cubic KZnF3:Cr crystal at low temperatures under uniaxial stress applied along the four-fold axis is reported. Dichroism occurs in the range of the wide vibronic absorption band corresponding to (5)Eg → (5)T2g transition of the Cr(2+) ions. Strain dependences of the dichroism value were studied at the temperatures of 2.0 K, 4.2 K, and 77 K. We associate our observations with the Jahn-Teller effect in the (5)Eg ground state of the Cr(2+) ion. The model is proposed based on a redistribution of the centers between the minima of the E⨂e problem adiabatic potential that become inequivalent under uniaxial stress applied along the four-fold axis of the crystal. It is shown that random strains in the sample have to be taken into account to achieve the quantitative agreement of the model predictions with experimental data. It is found that random strains in the studied sample originate predominantly from point defects. Obtained parameter values are inversion splitting δ = 9.2 ± 1.6 cm(-1), electron-strain coupling constant qVES = 16 500 ± 600 cm(-1), width of the random strain distribution w = (6.9 ± 0.5) ⋅ 10(-5). It is shown also that the minima of the [CrF6](4-) cluster adiabatic potential correspond to the elongated along the four-fold axes configurations.

  5. Magnetic property variation in carbon steel and chrome-molybdenum steel as a function of uniaxial stress noncoaxial with the magnetic field (abstract)

    SciTech Connect

    Sablik, M.J. ); Kaminski, D.A.; Jiles, D.C.; Biner, S.B. )

    1993-05-15

    Magnescope[sup 1] magnetic measurements were made on carbon steel specimens ranging from 0.1--0.8 wt %C and on chrome-molybdenum steel specimens cut from electric power plant pipes previously in service. The carbon steel specimens were heat-treated using three procedures: (1) spheroidization, (2) quenching, and (3) quench and tempering. The specimens were subjected to uniaxial tension up to 40 ksi. The inspection head was aligned so that the magnetic field was oriented at different angles with respect to the stress axis. Magnetic properties (such as coercivity and maximum differential permeability) were extracted from digitized magnetic hysteresis loop measurements. Magnetic properties were studied as a function of stress at each angle of stress-field orientation. To our knowledge, such a comprehensive study of noncoaxial stress and field effects has never been accomplished before for such a wide variety of steel specimens. Results for the various materials are presented for different orientation angles and compared to numerical results from the noncoaxial magnetomechanical hysteresis model of Sablik [ital et] [ital al].[sup 2

  6. Electro-optical effects of externally applied <100> uniaxial stress on InGaAsP 1. 3 and 1. 5. mu. m injection lasers

    SciTech Connect

    Swaminathan, V.; Parayanthal, P.; Hartman, R.L.

    1988-05-02

    The changes in the polarization of the emission, spectrum, and light-current (L-I) behavior of a 1.3 and 1.5 ..mu..m InGaAsP channeled substrate buried heterostructure laser and double-channel planar buried heterostructure laser under an external uniaxial compressive stress perpendicular to the junction were studied at room temperature. It was found that the TM emission (electric vector perpendicular to the junction) reached threshold even at a stress level of approx.1 x 10/sup 8/ dyn cm/sup -2/. For stress less than or equal to4 x 10/sup 8/ dyn cm/sup -2/, the TM emission, although reaching threshold first, was found to exist only over a limited range of currents. At high currents only TE emission (electric vector parallel to the junction) was observed. The appearance of the TE emission gave rise to nonlinear L-I characteristics. When both TM and TE emissions were seen, the former occurred at a higher energy. The limited stability of TM emission with current at low stresses is explained by invoking spectral hole burning effects which reduce the gain saturation power for TM mode than the TE mode. At high stresses greater than or equal to4 x 10/sup 8/ dyn cm/sup -2/, the increased gain for TM-polarized light ensures its stability at all currents. From our results it can be concluded that to avoid TM emission, and the associated spectral changes and nonlinear L-I characteristics, the tensile stress in the plane of the active layer should be less than 10/sup 8/ dyn cm/sup -2/.

  7. A Poroelastic Model Describing Nutrient Transport and Cell Stresses Within a Cyclically Strained Collagen Hydrogel

    PubMed Central

    Vaughan, Benjamin L.; Galie, Peter A.; Stegemann, Jan P.; Grotberg, James B.

    2013-01-01

    In the creation of engineered tissue constructs, the successful transport of nutrients and oxygen to the contained cells is a significant challenge. In highly porous scaffolds subject to cyclic strain, the mechanical deformations can induce substantial fluid pressure gradients, which affect the transport of solutes. In this article, we describe a poroelastic model to predict the solid and fluid mechanics of a highly porous hydrogel subject to cyclic strain. The model was validated by matching the predicted penetration of a bead into the hydrogel from the model with experimental observations and provides insight into nutrient transport. Additionally, the model provides estimates of the wall-shear stresses experienced by the cells embedded within the scaffold. These results provide insight into the mechanics of and convective nutrient transport within a cyclically strained hydrogel, which could lead to the improved design of engineered tissues. PMID:24209865

  8. Educational Leaders Describe a Job Too Big for One: Stress Reduction In the Midst of Leading

    ERIC Educational Resources Information Center

    Wells, Caryn M.

    2013-01-01

    This conceptual paper reviews research findings about the world of stress of principals and superintendents, focusing on the high levels of stress that the educational leaders report. The literature on occupational stress is also explored for its insights on the medical and psychological results of workplace stress and the relationship to stress…

  9. Personal and situational variables that describe coping with acute stress in competitive sport.

    PubMed

    Anshel, M H; Wells, B

    2000-08-01

    The authors examined the degree to which competitive basketball players in Australia were consistent in their cognitive appraisals and coping strategies in response to 4 types of stressful situations that they had experienced during previous basketball games as functions of perceived stress intensity. The authors predicted that both approach and avoidance coping strategies would be dependent on the type of stressful event, in accord with the transactional model. The results supported that prediction: Approach strategies were more prevalent than avoidance strategies following 3 of the 4 events. Cognitive appraisals and perceived stress intensity also strongly influenced the participants' use of coping strategies, accounting for 34% of the variance.

  10. Nonlocality in uniaxially polarizable media

    NASA Astrophysics Data System (ADS)

    Gorlach, Maxim A.; Belov, Pavel A.

    2015-08-01

    We reveal extraordinary electromagnetic properties for a general class of uniaxially polarizable media. Depending on parameters, such metamaterials may have a wide range of nontrivial shapes of isofrequency contours including lemniscate, diamond, and multiply connected curves with connectivity number reaching 5. The possibility of the dispersion engineering paves a way to more flexible manipulation of electromagnetic waves. Employing first-principles considerations we prove that uniaxially polarizable media should be described in terms of the nonlocal permittivity tensor which by no means can be reduced to local permittivity and permeability even in the long-wavelength limit. We introduce an alternative set of local material parameters including quadrupole susceptibility capable of capturing all of the second-order spatial dispersion effects.

  11. Elasticity of fibrous networks under uniaxial prestress.

    PubMed

    Vahabi, Mahsa; Sharma, Abhinav; Licup, Albert James; van Oosten, Anne S G; Galie, Peter A; Janmey, Paul A; MacKintosh, Fred C

    2016-06-14

    We present theoretical and experimental studies of the elastic response of fibrous networks subjected to uniaxial strain. Uniaxial compression or extension is applied to extracellular networks of fibrin and collagen using a shear rheometer with free water in/outflow. Both uniaxial stress and the network shear modulus are measured. Prior work [van Oosten, et al., Sci. Rep., 2015, 6, 19270] has shown softening/stiffening of these networks under compression/extension, together with a nonlinear response to shear, but the origin of such behaviour remains poorly understood. Here, we study how uniaxial strain influences the nonlinear mechanics of fibrous networks. Using a computational network model with bendable and stretchable fibres, we show that the softening/stiffening behaviour can be understood for fixed lateral boundaries in 2D and 3D networks with comparable average connectivities to the experimental extracellular networks. Moreover, we show that the onset of stiffening depends strongly on the imposed uniaxial strain. Our study highlights the importance of both uniaxial strain and boundary conditions in determining the mechanical response of hydrogels. PMID:27174568

  12. Chronic Kidney Disease Influences Multiple Systems: Describing the Relationship between Oxidative Stress, Inflammation, Kidney Damage, and Concomitant Disease

    PubMed Central

    Tucker, Patrick S.; Scanlan, Aaron T.; Dalbo, Vincent J.

    2015-01-01

    Chronic kidney disease (CKD) is characterized by increased levels of oxidative stress and inflammation. Oxidative stress and inflammation promote renal injury via damage to molecular components of the kidney. Unfortunately, relationships between inflammation and oxidative stress are cyclical in that the inflammatory processes that exist to repair radical-mediated damage may be a source of additional free radicals, resulting in further damage to renal tissue. Oxidative stress and inflammation also have the ability to become systemic, serving to injure tissues distal to the site of original insult. This review describes select mediators in the exacerbatory relationship between oxidative stress, inflammation, and CKD. This review also discusses oxidative stress, inflammation, and CKD as they pertain to the development and progression of common CKD-associated comorbidities. Lastly, the utility of several widely accessible and cost-effective lifestyle interventions and their ability to reduce oxidative stress and inflammation are discussed and recommendations for future research are provided. PMID:25861414

  13. Uniaxial Compression Experiments on Lead Zirconate Titanate 95/5-2Nb Ceramic: Evidence for an Orientation-Dependent, ''Maximum Compressive Stress'' Criterion for Onset of the Ferroelectric - Antiferroelectric Polymorphic Transformation

    SciTech Connect

    Zeuch, D.H.; Montgomery, S.T.; Holcomb, D.J.

    1999-07-26

    Some time ago we presented evidence that, under nonhydrostatic loading, the F{sub R1} {r_arrow} A{sub O} polymorphic transformation of unpoled PZT 95/5-2Nb (PNZT) ceramic began when the maximum compressive stress equaled the hydro-static pressure at which the transformation otherwise took place. Recently we showed that this simple criterion did not apply to nonhydrostatically compressed, poled ceramic. However, unpoled ceramic is isotropic, whereas poled ceramic has a preferred crystallographic orientation and is mechanically anisotropic. If we further assume that the transformation depends not only on the magnitude of the compressive stress, but also its orientation relative to some feature(s) of PNZT's crystallography, then these disparate results can be qualitatively resolved. It has long been known that this transformation can be triggered in uniaxial compression. Our modified hypothesis makes two predictions for transformation of unpoled polycrystals under uniaxial stress: (i) the transformation should begin when the maximum compressive stress, {sigma}{sub 1}, equals the hydrostatic pressure for transformation, and (ii) a steadily increasing axial stress should be required to drive the transformation.

  14. The effects of stress concentrations on reaction progress: an example from experimental growth of magnesio-aluminate spinel at corundum - periclase interfaces under uniaxial load

    NASA Astrophysics Data System (ADS)

    Jerabek, Petr; Abart, Rainer; Rybacki, Erik; Habler, Gerlinde

    2014-05-01

    The study aims to understand the reaction progress and chemical, microstructural and textural evolution of magnesio-aluminate spinel reaction rims formed at varying experimental settings (load, temperature and experiment duration). The spinel rims were grown at the contacts between periclase and corundum at temperatures of 1250°C to 1350°C and dry atmosphere, maintained by a constant argon gas flow, under uniaxial load of 0.026 and 0.26 kN per 9 mm2 of initial contact area. Single crystals of periclase with [100] and of corundum with [0001] perpendicular to the polished reaction interface as well as polycrystalline corundum were used as starting materials. Two loading procedures, immediate application of the load before heating and loading after the desired temperature had been reached, were used. An important byproduct of our experiments stemmed from the immediate application of the load, which led to deformation twinning and fracturing of corundum. This internal deformation of corundum disturbed the reaction interface and introduced loci of concentrated stress due to opening of void spaces in between the reactant crystals. Whenever cracks formed in the initial stages of an experiment, the void space opened immediately and no spinel formed along these interface segments. In the case of deformation twinning, the decreased rim thickness indicates later opening of void spaces. This is because next to twins, the reaction interface is characterized by tight physical contact on the one side and less tight contact on the other side of the twin individual. The tight contacts are characterized by enhanced reaction progress which together with the overall positive volume change of the reaction and limits on plasticity of the studied phases led to the opening of void spaces at places characterized by less tight contacts. The thickness variations are less pronounced in our high load (0.26 kN) experiments where periclase behaves plastically and to some extent reduces the

  15. Theoretical and uniaxial experimental evaluation of human annulus fibrosus degeneration.

    PubMed

    O'Connell, Grace D; Guerin, Heather L; Elliott, Dawn M

    2009-11-01

    The highly organized structure and composition of the annulus fibrosus provides the tissue with mechanical behaviors that include anisotropy and nonlinearity. Mathematical models are necessary to interpret and elucidate the meaning of directly measured mechanical properties and to understand the structure-function relationships of the tissue components, namely, the fibers and extrafibrillar matrix. This study models the annulus fibrosus as a combination of strain energy functions describing the fibers, matrix, and their interactions. The objective was to quantify the behavior of both nondegenerate and degenerate annulus fibrosus tissue using uniaxial tensile experimental data. Mechanical testing was performed with samples oriented along the circumferential, axial, and radial directions. For samples oriented along the radial direction, the toe-region modulus was 2x stiffer with degeneration. However, no other differences in measured mechanical properties were observed with degeneration. The constitutive model fit well to samples oriented along the radial and circumferential directions (R(2)> or =0.97). The fibers supported the highest proportion of stress for circumferential loading at 60%. There was a 70% decrease in the matrix contribution to stress from the toe-region to the linear-region of both the nondegenerate and degenerate tissue. The shear fiber-matrix interaction (FMI) contribution increased by 80% with degeneration in the linear-region. Samples oriented along the radial and axial direction behaved similarly under uniaxial tension (modulus=0.32 MPa versus 0.37 MPa), suggesting that uniaxial testing in the axial direction is not appropriate for quantifying the mechanics of a fiber reinforcement in the annulus. In conclusion, the structurally motivated nonlinear anisotropic hyperelastic constitutive model helps to further understand the effect of microstructural changes with degeneration, suggesting that remodeling in the subcomponents (i.e., the collagen

  16. Analysis of electromagnetic scattering by uniaxial anisotropic bispheres.

    PubMed

    Li, Zheng-Jun; Wu, Zhen-Sen; Li, Hai-Ying

    2011-02-01

    Based on the generalized multiparticle Mie theory and the Fourier transformation approach, electromagnetic (EM) scattering of two interacting homogeneous uniaxial anisotropic spheres with parallel primary optical axes is investigated. By introducing the Fourier transformation, the EM fields in the uniaxial anisotropic spheres are expanded in terms of the spherical vector wave functions. The interactive scattering coefficients and the expansion coefficients of the internal fields are derived through the continuous boundary conditions on which the interaction of the bispheres is considered. Some selected calculations on the effects of the size parameter, the uniaxial anisotropic absorbing dielectric, and the sphere separation distance are described. The backward radar cross section of two uniaxial anisotropic spheres with a complex permittivity tensor changing with the sphere separation distance is numerically studied. The authors are hopeful that the work in this paper will help provide an effective calibration for further research on the scattering characteristic of an aggregate of anisotropic spheres or other shaped anisotropic particles.

  17. Impacts of additive uniaxial strain on hole mobility in bulk Si and strained-Si p-MOSFETs

    NASA Astrophysics Data System (ADS)

    Shuo, Zhao; Lei, Guo; Jing, Wang; Jun, Xu; Zhihong, Liu

    2009-10-01

    Hole mobility changes under uniaxial and combinational stress in different directions are characterized and analyzed by applying additive mechanical uniaxial stress to bulk Si and SiGe-virtual-substrate-induced strained-Si (s-Si) p-MOSFETs (metal-oxide-semiconductor field-effect transistors) along (110) and (100) channel directions. In bulk Si, a mobility enhancement peak is found under uniaxial compressive strain in the low vertical field. The combination of (100) direction uniaxial tensile strain and substrate-induced biaxial tensile strain provides a higher mobility relative to the (110) direction, opposite to the situation in bulk Si. But the combinational strain experiences a gain loss at high field, which means that uniaxial compressive strain may still be a better choice. The mobility enhancement of SiGe-induced strained p-MOSFETs along the (110) direction under additive uniaxial tension is explained by the competition between biaxial and shear stress.

  18. Field-Induced Rheology in Uniaxial and Biaxial Fields

    SciTech Connect

    MARTIN, JAMES E.

    1999-10-22

    Steady and oscillatory shear 3-D simulations of electro- and magnetorheology in uniaxial and biaxial fields are presented, and compared to the predictions of the chain model. These large scale simulations are three dimensional, and include the effect of Brownian motion. In the absence of thermal fluctuations, the expected shear thinning viscosity is observed in steady shear, and a striped phase is seen to rapidly form in a uniaxial field, with a shear slip zone in each sheet. However, as the influence of Brownian motion increases, the fluid stress decreases, especially at lower Mason numbers, and the striped phase eventually disappears, even when the fluid stress is still high. In a biaxial field, an opposite trend is seen, where Brownian motion decreases the stress most significantly at higher Mason numbers. to account for the uniaxial steady shear data they propose a microscopic chain model of the role played by thermal fluctuations on the rheology of ER and MR fluids that delineates the regimes where an applied field can impact the fluid viscosity, and gives an analytical prediction for the thermal effect. In oscillatory shear, a striped phase again appears in uniaxial field, at strain amplitudes greater than {approx} 0.15, and the presence of a shear slip zone creates strong stress nonlinearities at low strain amplitudes. In a biaxial field, a shear slip zone is not created, and so the stress nonlinearities develop only at expected strain amplitudes. The nonlinear dynamics of these systems is shown to be in good agreement with the Kinetic Chain Model.

  19. Reduction of the piezoelectric performance in lead-free (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 piezoceramics under uniaxial compressive stress

    NASA Astrophysics Data System (ADS)

    Ehmke, Matthias C.; Daniels, John; Glaum, Julia; Hoffman, Mark; Blendell, John E.; Bowman, Keith J.

    2012-12-01

    The effect of a uniaxial compressive stress on the properties of BZT-BCT samples across the morphotropic phase boundary (MPB) is investigated using direct piezoelectric coefficient measurements. In contrast to many lead zirconate titanate compositions, the piezoelectric coefficient decreases monotonically with increasing stress and does not show an initial increase or plateau. Electrically softer rhombohedral and MPB compositions are found to be more susceptible to a decrease in piezoelectric coefficient under an increasing pre-stress than tetragonal compositions. Depoling due to ferroelastic domain switching alone, as observed by x-ray diffraction, does not explain this reduction, but instead a decreasing domain wall density is proposed to be responsible for reduced piezoelectric coefficients under increasing compressive stress. The relaxation of the piezoelectric response after complete unloading supports this proposed mechanism.

  20. Uniaxial aerodynamic attitude control of artificial satellites

    NASA Technical Reports Server (NTRS)

    Sazonov, V. V.

    1983-01-01

    Within the context of a simple mechanical model the paper examines the movement of a satellite with respect to the center of masses under conditions of uniaxial aerodynamic attitude control. The equations of motion of the satellite take account of the gravitational and restorative aerodynamic moments. It is presumed that the aerodynamic moment is much larger than the gravitational, and the motion equations contain a large parameter. A two-parameter integrated surface of these equations is constructed in the form of formal series in terms of negative powers of the large parameter, describing the oscillations and rotations of the satellite about its lengthwise axis, approximately oriented along the orbital tangent. It is proposed to treat such movements as nominal undisturbed motions of the satellite under conditions of aerodynamic attitude control. A numerical investigation is made for the above integrated surface.

  1. High temperature inelastic deformation under uniaxial loading - Theory and experiment

    NASA Technical Reports Server (NTRS)

    Chan, K. S.; Lindholm, U. S.; Bodner, S. R.; Walker, K. P.

    1989-01-01

    The elevated-temperature uniaxial inelastic deformation behavior of an Ni-base alloy, B1900 + Hf, is investigated by performing isothermal tensile, creep, cyclic, stress relaxation, and thermomechanical fatigue tests. The range of strain rates examined is from 10 to the -7th to 100 per sec, while the test temperatures range from 25 to 1093 C. This extensive constitutive data base has been used for evaluating the unified constitutive models of Bodner and Partom (1972) and of Walker (1972) which apply for the small-strain regime. Comparison of test results with independent model predictions indicates good agreement over a broad range of loading conditions, demonstrating the applicability of the unified-constitutive-equation approach for describing the strongly nonlinear and temperature-dependent response of meals under a wide range of deformation and thermal histories. Thus the results give confidence that the unified approach is an effective and efficient approach in which complex history-dependent thermoviscoplastic flow can be represented within a single inelastic strain-rate term.

  2. An Improved Correlation between Impression and Uniaxial Creep

    SciTech Connect

    Hsueh, Chun-Hway; Miranda, Pedro; Becher, Paul F

    2006-01-01

    A semiempirical correlation between impression and uniaxial creep has been established by Hyde et al. [Int. J. Mech. Sci. 35, 451 (1993) ] using finite element results for materials exhibiting general power-law creep with the stress exponent n in the range 2 {<=} n {<=} 15. Here, we derive the closed-form solution for a special case of viscoelastic materials, i.e., n = 1, subjected to impression creep and obtain the exact correlation between impression and uniaxial creep. This analytical solution serves as a checkpoint for the finite element results. We then perform finite element analyses for the general case to derive a semiempirical correlation, which agrees well with both analytical viscoelastic results and the existing experimental data. Our improved correlation agrees with the correlation of Hyde et al. for n {>=} 4, and the difference increases with decreasing n for n<4.

  3. Approaching the Limits of Strength: Measuring the Uniaxial Compressive Strength of Diamond at Small Scales.

    PubMed

    Wheeler, Jeffrey M; Raghavan, Rejin; Wehrs, Juri; Zhang, Yucheng; Erni, Rolf; Michler, Johann

    2016-01-13

    Diamond ⟨100⟩- and ⟨111⟩-oriented nanopillars were fabricated by focused ion beam (FIB) milling from synthetic single crystals and compressed using a larger diameter diamond punch. Uniaxial compressive failure was observed via fracture with a plateau in maximum stress of ∼0.25 TPa, the highest uniaxial strength yet measured. This corresponded to maximum shear stresses that converged toward 75 GPa or ∼ G/7 at small sizes, which are very close to the ultimate theoretical yield stress estimate of G/2π.

  4. Structure and properties of poly (lactic acid)/Sterculia urens uniaxial fabric biocomposites.

    PubMed

    Jayaramudu, J; Reddy, G Siva Mohan; Varaprasad, K; Sadiku, E R; Ray, S Sinha; Rajulu, A Varada

    2013-05-15

    Uniaxial cellulose fabric Sterculia urens reinforced poly (lactic acid) (PLA) matrix biocomposites were prepared by a two-roll mill. In order to assess the suitability of Sterculia fabric as reinforcement for PLA matrix, the PLA/Sterculia fabric biocomposites were prepared. Tensile parameters, such as maximum stress, Young's modulus and elongation-at-break, were determined using the Universal Testing Machine. The effect of alkali treatment and silane-coupling agent on the tensile properties of PLA-based biocomposites was studied. The results of thermogravimetric analysis show that uniaxial treatment of the fabric can improve the degradation temperature of the biocomposites. Moreover, morphological studies by scanning electron microscopy confirmed that better adhesion between the uniaxial fabric and the matrix was achieved. It was established that standard PLA resins are suitable for the manufacture of S. urens uniaxial fabric reinforced biocomposites with excellent engineering properties, useful for food packaging.

  5. Uncoupling shear and uniaxial elastic moduli of semiflexible biopolymer networks: compression-softening and stretch-stiffening

    PubMed Central

    van Oosten, Anne S. G.; Vahabi, Mahsa; Licup, Albert J.; Sharma, Abhinav; Galie, Peter A.; MacKintosh, Fred C.; Janmey, Paul A.

    2016-01-01

    Gels formed by semiflexible filaments such as most biopolymers exhibit non-linear behavior in their response to shear deformation, e.g., with a pronounced strain stiffening and negative normal stress. These negative normal stresses suggest that networks would collapse axially when subject to shear stress. This coupling of axial and shear deformations can have particularly important consequences for extracellular matrices and collagenous tissues. Although measurements of uniaxial moduli have been made on biopolymer gels, these have not directly been related to the shear response. Here, we report measurements and simulations of axial and shear stresses exerted by a range of hydrogels subjected to simultaneous uniaxial and shear strains. These studies show that, in contrast to volume-conserving linearly elastic hydrogels, the Young’s moduli of networks formed by the biopolymers are not proportional to their shear moduli and both shear and uniaxial moduli are strongly affected by even modest degrees of uniaxial strain. PMID:26758452

  6. Transport properties of armchair graphene nanoribbons under uniaxial strain: A first principles study

    NASA Astrophysics Data System (ADS)

    Van Nguyen, Chuong; Ilyasov, Victor V.; Van Hieu, Nguyen; Ngoc Hieu, Nguyen

    2016-07-01

    In this work, transport properties of armchair graphene nanoribbons (AGNRs) under uniaxial strain are considered using density functional theory. We found that carrier mobility of AGNRs depends strongly on uniaxial strain. The electron mobility of 5-AGNR is up to 38.5 ×104cm2 / V s at an elongation of 6%. However, the dependence of the effective mass of electrons and holes of AGNR on uniaxial strain can almost be described by the same function and their effective masses coincide at an elongation of 10%. The sensitivity to strain of the transport properties of AGNRs opens many ways for applications in nanoelectromechanical devices.

  7. A combined complex electrical impedance and acoustic emission study in limestone samples under uniaxial loading

    NASA Astrophysics Data System (ADS)

    Saltas, V.; Fitilis, I.; Vallianatos, F.

    2014-12-01

    In the present work, complex electrical impedance measurements in the frequency range of 10 mHz to 1 MHz were carried out in conjunction with acoustic emission monitoring in limestone samples subjected to linear and stepped-like uniaxial loading, up to ultimate failure. Cole-Cole plots of the complex impedance during the stepped loading of limestone have been used to discriminate the contributions of grains interior, grain boundaries and electrode polarization effects to the overall electrical behavior. The latter is well-described with an equivalent-circuit model which comprises components of constant phase elements and resistances in parallel connection. Electrical conductivity increases upon uniaxial loading giving rise to negative values of effective activation volume. This is a strong experimental evidence for the generation of transient electric signals recorded prior to seismic events and may be attributed to charge transfer (proton conduction) due to cracks generation and propagation as a result of the applied stress. The time-series of ac-conductivity at two distinct frequencies (10 kHz, 200 kHz) during linear loading of limestone samples exhibits a strong correlation with the acoustic emission activity obeying the same general self-similar law for critical phenomena that has been reported for the energy release before materials fracture.

  8. Uniaxial compression of suspended single and multilayer graphenes

    NASA Astrophysics Data System (ADS)

    Sgouros, A. P.; Kalosakas, G.; Galiotis, C.; Papagelis, K.

    2016-06-01

    The mechanical response of single and multiple graphene sheets under uniaxial compressive loads was studied with molecular dynamics (MD) simulations, using different semi-empirical force fields at different boundary conditions or constrains. Compressive stress-strain curves were obtained and the critical stress/strain values were derived. The MD results are compared to the linear elasticity continuum theory for loaded slabs. Concerning the length dependence of critical values, qualitatively similar behavior is observed between the theory and numerical simulations for single layer graphenes, as the critical stress/strain for buckling was found to scale to the inverse squared length. However discrepancies were noted for multilayer graphenes, where the critical buckling stress also decreased with increasing length, though at a slower rate than expected from elastic buckling analysis.

  9. Partitioned-field uniaxial holographic lenses.

    PubMed

    López, Ana M; Atencia, Jesús; Tornos, José; Quintanilla, Manuel

    2002-04-01

    The efficiency and aberration of partitioned-field uniaxial volume holographic compound lenses are theoretically and experimentally studied. These systems increase the image fields of holographic volume lenses, limited by the angular selectivity that is typical of these elements. At the same time, working with uniaxial systems has led to a decrease in aberration because two recording points (that behave as aberration-free points) are used. The extension of the image field is experimentally proved.

  10. Mie scattering by a uniaxial anisotropic sphere

    SciTech Connect

    Geng Youlin; Wu Xinbao; Li Lewei; Guan Boran

    2004-11-01

    The field solution to the electromagnetic scattering of a plane wave by a uniaxial anisotropic sphere is obtained in terms of a spherical vector wave function expansion form. Using the source-free Maxwell's equations for uniaxial anisotropic media and making the Fourier transform of the field quantities, the electromagnetic fields in the spectral domain in uniaxial anisotropic media are assumed to have a form similar to the plane wave expanded also in terms of the spherical vector wave functions. Applying the continuous boundary conditions of electromagnetic fields on the surface between the air region and uniaxial anisotropic sphere, the coefficients of transmitted fields and the scattered fields in uniaxial anisotropic media can be obtained analytically in the expansion form of vector wave eigenfunctions. Numerical results for some special cases are obtained and compared with those of the classical Lorenz-Mie theory and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach. We also present some new numerical results for the more general uniaxial dielectric material media.

  11. Mie scattering by a uniaxial anisotropic sphere.

    PubMed

    Geng, You-Lin; Wu, Xin-Bao; Li, Le-Wei; Guan, Bo-Ran

    2004-11-01

    The field solution to the electromagnetic scattering of a plane wave by a uniaxial anisotropic sphere is obtained in terms of a spherical vector wave function expansion form. Using the source-free Maxwell's equations for uniaxial anisotropic media and making the Fourier transform of the field quantities, the electromagnetic fields in the spectral domain in uniaxial anisotropic media are assumed to have a form similar to the plane wave expanded also in terms of the spherical vector wave functions. Applying the continuous boundary conditions of electromagnetic fields on the surface between the air region and uniaxial anisotropic sphere, the coefficients of transmitted fields and the scattered fields in uniaxial anisotropic media can be obtained analytically in the expansion form of vector wave eigenfunctions. Numerical results for some special cases are obtained and compared with those of the classical Lorenz-Mie theory and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach. We also present some new numerical results for the more general uniaxial dielectric material media.

  12. Method and apparatus for gripping uniaxial fibrous composite materials

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Hurwitz, F. I. (Inventor)

    1984-01-01

    A strip specimen is cut from a unidirectional strong, brittle fiber composite material, and the surfaces of both ends of the specimen are grit blasted. The specimen is then placed between metal load transfer members having grit blasted surfaces. Sufficient compressive stress is applied to the load transfer members to prevent slippage during testing at both elevated temperatures and room temperatures. The need for adhesives, load pads, and other secondary composite processing is eliminated. This gripping system was successful in tensile testing, creep rupture testing, and fatigue testing uniaxial composite materials at 316 C.

  13. The Uniaxial Tensile Response of Porous and Microcracked Ceramic Materials

    SciTech Connect

    Pandey, Amit; Shyam, Amit; Watkins, Thomas R; Lara-Curzio, Edgar; Lara-Curzio, Edgar; Stafford, Randall; Hemker, Kevin J

    2014-01-01

    The uniaxial tensile stress-strain behavior of three porous ceramic materials was determined at ambient conditions. Test specimens in the form of thin beams were obtained from the walls of diesel particulate filter honeycombs and tested using a microtesting system. A digital image correlation technique was used to obtain full-field 2D in-plane surface displacement maps during tensile loading, and in turn, the 2D strains obtained from displacement fields were used to determine the Secant modulus, Young s modulus and initial Poisson s ratio of the three porous ceramic materials. Successive unloading-reloading experiments were performed at different levels of stress to decouple the linear elastic, anelastic and inelastic response in these materials. It was found that the stress-strain response of these materials was non-linear and that the degree of nonlinearity is related to the initial microcrack density and evolution of damage in the material.

  14. Uniaxial alignment of nanoconfined columnar mesophases.

    PubMed

    Mouthuy, Pierre-Olivier; Melinte, Sorin; Geerts, Yves H; Jonas, Alain M

    2007-09-01

    By confining discotic phthalocyanines in a network of crisscrossed nanogrooves, we obtain a uniaxial alignment of the columnar mesophase. The alignment process is based on the anisotropy of interface tension between the mesophase and the nanogrooves' walls. Preferential mesophase alignment results from this nonhomogeneity combined with the anisotropy of the network cell dimensions. A simple model is proposed to explain the experimental observations.

  15. Lattice model for biaxial and uniaxial nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Sauerwein, Ricardo A.; de Oliveira, Mário J.

    2016-05-01

    We use a lattice gas model to describe the phase transitions in nematic liquid crystals. The phase diagram displays, in addition to the isotropic phase, the two uniaxial nematics, the rod-like and discotic nematics, and the biaxial nematic. Each site of the lattice has a constituent unit that takes only six orientations and is understood as being a parallelepiped brick with the three axes distinct. The possible orientations of a brick are those in which its axes are parallel to the axes of a Cartesian reference frame. The analysis of the model is performed by the use of a mean-field approximation and a Landau expansion of the free energy.

  16. Macroscopic and microscopic investigations on uniaxial ratchetting of two-phase Ti–6Al–4V alloy

    SciTech Connect

    Kang, Guozheng; Dong, Yawei; Liu, Yujie; Jiang, Han

    2014-06-01

    The uniaxial ratchetting of Ti–6Al–4V alloy with two phases (i.e., primary hexagonal close packed (HCP) α and secondary body-centered cubic (BCC) β phases) was investigated by macroscopic and microscopic experiments at room temperature. Firstly, the effects of cyclic softening/hardening feature, applied mean stress and stress amplitude on the uniaxial ratchetting of the alloy were discussed. The macroscopic investigation of Ti–6Al–4V alloy presents obvious strain-amplitude-dependent cyclic softening, as well as a three-staged evolution curve with regard to the ratchetting strain rate. The ratchetting depends greatly on the applied mean stress and stress amplitude while the ratchetting strain increases with the increasing applied mean stress and stress amplitude. Then, the evolution of dislocation patterns and deformation twinning during the uniaxial ratchetting of two-phase Ti–6Al–4V alloy were observed using transmission electron microscopy (TEM). The microscopic observation shows that deformation twinning occurs in the primary α phase and its amount increases gradually during the uniaxial ratchetting. Simultaneously, the planar dislocation evolves from discrete lines to some dislocation nets and parallel lines with the increasing number of cycles. The deformation twinning in the primary α phase is one of main contributions to the uniaxial ratchetting of Ti–6Al–4V alloy, and should be considered in the construction of corresponding constitutive model. - Highlights: • A three-staged ratchetting occurs in the stress-controlled cyclic tests of Ti–6Al–4V alloy. • Dislocation patterns change from discrete lines to nets and parallel lines. • Deformation twinning occurs during the uniaxial ratchetting. • Both dislocation slipping and twinning are the causes of ratchetting.

  17. FEM simulations of a multi stage forming process on Sandvik maraging steel 1RK91 describing the stress assisted and the strain induced martensite transformation

    NASA Astrophysics Data System (ADS)

    Post, J.; Huétink, J.; Geijselaers, H. J. M.; Voncken, R. M. J.

    2003-10-01

    Sandvik steel IRK91 combines good corrosion resistance with high strength. The steel has good deformability in austenitic conditions. This material belongs to the group of metastable austenites, so during deformation a strain-induced transformation into martensite takes place. After deformation, transformation ccontinues as a resuit of internai stresses. Depending on the heat treatment, this stress-assisted transformation is more or less atitocatalytic. Both transformations are stress-state and temperature dependent. This article presents a constitutive model for this steel, based on the macroscopic material behaviour measured by inductive measurements. Both the stress-assisted and the strain-induced transformation to martensite are incorpomted in this model. Path-dependent work hardening is also taken into account. The model is implemented in the commercial FEM code MARC for doing simulations. In the simulations thé tools are treated as rigid bodies, friction is taken into account beeause it inflnences the stress state during metal forming. The material properties after a calculation step are mapped to the next step to incorporate the cumulative effect of the transformation and work hardening during the different steps. A multi-stage metal-forming process is simulated. The process consists of different forming steps with intervals between them to simulate the waiting time between the different metal-forming steps. Results of the transformation behaviour are presented together with the shape of the product during and after metal forming. Finally, this article shows the results of the calculation in which the material transforms autocatalytic, as a resuit of a specific heat treatment.

  18. Determining Optical Axes of Uniaxial Crystals

    NASA Technical Reports Server (NTRS)

    Schock, H. J.; Regan, C. A.; Lock, J. A.

    1987-01-01

    Polarizing-microscope concept adapted for thick samples. Optical axis of crystal usually found by examining sample thinner than 1 mm between crossed polarizing plates. Frequently impractical to cut off small sample of crystal for testing, technique modified to accommodate large crystals. Ability to circumvent effect of birefringence has applications where laser beams must be transmitted through uniaxial crystals, as in laser diagnostics of contained flows in systems requiring windows for optical access.

  19. Uniaxial creep as a control on mercury intrusion capillary pressure in consolidating rock salt

    SciTech Connect

    Dewers, Thomas; Heath, Jason E.; Leigh, Christi D.

    2015-09-01

    The nature of geologic disposal of nuclear waste in salt formations requires validated and verified two - phase flow models of transport of brine and gas through intact, damaged, and consolidating crushed salt. Such models exist in oth er realms of subsurface engineering for other lithologic classes (oil and gas, carbon sequestration etc. for clastics and carbonates) but have never been experimentally validated and parameterized for salt repository scenarios or performance assessment. Mo dels for waste release scenarios in salt back - fill require phenomenological expressions for capillary pressure and relative permeability that are expected to change with degree of consolidation, and require experimental measurement to parameterize and vali date. This report describes a preliminary assessment of the influence of consolidation (i.e. volume strain or porosity) on capillary entry pressure in two phase systems using mercury injection capillary pressure (MICP). This is to both determine the potent ial usefulness of the mercury intrusion porosimetry method, but also to enable a better experimental design for these tests. Salt consolidation experiments are performed using novel titanium oedometers, or uniaxial compression cells often used in soil mech anics, using sieved run - of - mine salt from the Waste Isolation Pilot Plant (WIPP) as starting material. Twelve tests are performed with various starting amounts of brine pore saturation, with axial stresses up to 6.2 MPa (%7E900 psi) and temperatures to 90 o C. This corresponds to UFD Work Package 15SN08180211 milestone "FY:15 Transport Properties of Run - of - Mine Salt Backfill - Unconsolidated to Consolidated". Samples exposed to uniaxial compression undergo time - dependent consolidation, or creep, to various deg rees. Creep volume strain - time relations obey simple log - time behavior through the range of porosities (%7E50 to 2% as measured); creep strain rate increases with temperature and applied stress as

  20. Uniaxial strain relaxation in He{sup +} ion implanted (110) oriented SiGe layers

    SciTech Connect

    Minamisawa, R. A.; Buca, D.; Trinkaus, H.; Hollaender, B.; Mantl, S.; Destefanis, V.; Hartmann, J. M.

    2009-07-20

    Uniaxially strained (011)Si is attractive for high performance p-channel metal oxide semiconductor field effect transistor devices due to the predicted high hole mobilities. Here, we demonstrate the realization of purely uniaxially relaxed (011) SiGe virtual substrates by He{sup +} ion implantation and thermal annealing. Perfect uniaxial relaxation is evidenced by precise ion channeling angular yield scan measurements and plan view transmission electron microscopy as predicted theoretically on the basis of the layer symmetry dependent dislocation dynamics. Strikingly, misfit dislocations propagate exclusively along the [011] direction in the (011) oriented crystal and, in contrast to (100)Si, no crosshatch is formed. We describe dislocation formation and propagation inducing strain relaxation of (011)SiGe and enlighten the differences to (100) oriented SiGe on Si.

  1. A study of uniaxial tension on the superficial dermal microvasculature.

    PubMed

    Barnhill, R L; Bader, D L; Ryan, T J

    1984-05-01

    A spring-loaded apparatus was designed to apply uniaxial tension to forearm skin in 17 human subjects--10 normals, 6 psoriatics, and 1 patient with scleroderma. Simultaneously, the effects of stretching on the upper dermal vasculature were observed stereomicroscopically. Progressive changes (collapse) in the superficial microvasculature--vertical capillary loops and horizontal subpapillary plexus--with increasing tension were photographed. Force and strains were recorded at the points of disappearance of virtually all vessels. An average force of 11.9 newtons (N), accompanied by a mean strain of 10.3%, resulted in occlusion of all vessels. A much higher force (18.5 N) was necessary to occlude blood flow in the 1 patient with scleroderma. In summary, we have described a new technique for the study of mechanical forces on the blood supply of the epidermis. The data have shown that uniaxial tension has important effects on the superficial dermal microvasculature, resulting in impedance and obliteration of blood flow at relatively low magnitudes.

  2. Measuring the complex permittivity tensor of uniaxial biological materials with coplanar waveguide transmission line

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A simple and accurate technique is described for measuring the uniaxial permittivity tensor of biological materials with a coplanar waveguide transmission-line configuration. Permittivity tensor results are presented for several chicken and beef fresh meat samples at 2.45 GHz....

  3. Mechanical characterisation of porcine rectus sheath under uniaxial and biaxial tension.

    PubMed

    Lyons, Mathew; Winter, Des C; Simms, Ciaran K

    2014-06-01

    Incisional hernia development is a significant complication after laparoscopic abdominal surgery. Intra-abdominal pressure (IAP) is known to initiate the extrusion of intestines through the abdominal wall, but there is limited data on the mechanics of IAP generation and the structural properties of rectus sheath. This paper presents an explanation of the mechanics of IAP development, a study of the uniaxial and biaxial tensile properties of porcine rectus sheath, and a simple computational investigation of the tissue. Analysis using Laplace׳s law showed a circumferential stress in the abdominal wall of approx. 1.1MPa due to an IAP of 11kPa, commonly seen during coughing. Uniaxial and biaxial tensile tests were conducted on samples of porcine rectus sheath to characterise the stress-stretch responses of the tissue. Under uniaxial tension, fibre direction samples failed on average at a stress of 4.5MPa at a stretch of 1.07 while cross-fibre samples failed at a stress of 1.6MPa under a stretch of 1.29. Under equi-biaxial tension, failure occurred at 1.6MPa with the fibre direction stretching to only 1.02 while the cross-fibre direction stretched to 1.13. Uniaxial and biaxial stress-stretch plots are presented allowing detailed modelling of the tissue either in silico or in a surrogate material. An FeBio computational model of the tissue is presented using a combination of an Ogden and an exponential power law model to represent the matrix and fibres respectively. The structural properties of porcine rectus sheath have been characterised and add to the small set of human data in the literature with which it may be possible to develop methods to reduce the incidence of incisional hernia development. PMID:24725440

  4. The contribution of time-dependent stress relaxation in protein gels to the recoverable energy that is used as a tool to describe food texture

    NASA Astrophysics Data System (ADS)

    de Jong, Saskia; van Vliet, Ton; de Jongh, Harmen H. J.

    2015-11-01

    The recoverable energy (RE), defined as the ratio of the work exerted on a test specimen during compression and recovered upon subsequent decompression, has been shown to correlate to sensory profiling of protein-based food products. Understanding the mechanism determining the time-dependency of RE is primordial. This work aims to identify the protein-specific impact on the recoverable energy by stress dissipation via relaxation of (micro)structural rearrangements within protein gels. To this end, caseinate and gelatin gels are studied for their response to time-dependent mechanical deformation as they are known to develop structurally distinct network morphologies. This work shows that in gelatin gels no significant stress relaxation occurs on the seconds timescale, and consequently no time-dependency of the amount of energy stored in this material is observed. In caseinate gels, however, the energy dissipation via relaxation processes does contribute significantly to the time-dependency of reversible stored energy in the network. This can explain the obtained RE as a function of applied deformation at slow deformation rates. At faster deformation, an additional contribution to the dissipated energy is apparent, that increases with the deformation rate, which might point to the role of energy dissipation related to friction of the serum entrapped by the protein-network. This work shows that engineering strategies focused on controlling viscous flow in protein gels could be more effective to dictate the ability to elastically store energy in protein gels than routes that direct protein-specific aggregation and/or network-assembly.

  5. A computer program for predicting nonlinear uniaxial material responses using viscoplastic models

    NASA Technical Reports Server (NTRS)

    Chang, T. Y.; Thompson, R. L.

    1984-01-01

    A computer program was developed for predicting nonlinear uniaxial material responses using viscoplastic constitutive models. Four specific models, i.e., those due to Miller, Walker, Krieg-Swearengen-Rhode, and Robinson, are included. Any other unified model is easily implemented into the program in the form of subroutines. Analysis features include stress-strain cycling, creep response, stress relaxation, thermomechanical fatigue loop, or any combination of these responses. An outline is given on the theoretical background of uniaxial constitutive models, analysis procedure, and numerical integration methods for solving the nonlinear constitutive equations. In addition, a discussion on the computer program implementation is also given. Finally, seven numerical examples are included to demonstrate the versatility of the computer program developed.

  6. Tearing analysis of a new airship envelope material under uniaxial tensile load

    NASA Astrophysics Data System (ADS)

    Wang, F. X.; Xu, W.; Chen, Y. L.; Fu, G. Y.

    2016-07-01

    This paper experimentally investigated the tearing properties of a new kind of coated woven fabrics, GQ-6, made of ultra-high molecular weight polyethylene fiber. Such material can be used for the envelope materials of a stratospheric airship. First, the uniaxial tearing tests were carried out. Effects of the stretching rate, the initial crack length, and the initial crack orientation on the material's tearing tensile strength were investigated. Experimental results showed that the initial crack length and the initial crack orientation can be represented by the equivalent initial crack length while the stretching rate has a slight influence on tearing behavior of the uniaxial tensile specimens. Then analytical studies using three methods, i.e. Griffith energy theory, the stress intensity factor theory, and Thiele's empirical theory, among which, the stress intensity factor theory gives the best correlation with the test data. Finally, a 48mm threshold of the equivalent initial crack length was recommended to the envelope material in operation.

  7. Uniaxial compression test series on Bullfrog Tuff

    SciTech Connect

    Price, R H; Jones, A K; Nimick, K G

    1982-04-01

    Nineteen uniaxial compressive experiments were performed on samples of the Bullfrog Member of the Crater Flat Tuff, obtained from drillhole USW-G1 at Yucca Mountain on the Nevada Test Site. The water saturated samples were deformed at a nominal strain rate of 10{sup -5} sec{sup -1}, atmospheric pressure and room temperature. Resultant unconfined compressive strengths, axial strains to failure, Young`s moduli and Poisson`s ratios ranged from 4.63 to 153. MPa, .0028 to .0058, 2.03 to 28.9 GPa and .08 to .16, respectively.

  8. Nondestructive electromagnetic characterization of uniaxial materials

    NASA Astrophysics Data System (ADS)

    Rogers, Neil G.

    In this dissertation, a method for the simultaneous non-destructive extraction of the permittivity and permeability of a dielectric magnetic uniaxial anisotropic media is developed and several key contributions are demonstrated. The method utilizes a single fixture in which the MUT is clamped between two rectangular waveguides with 6" x 6" PEC flanges. The transmission and reflection coefficients are measured, then compared with theoretically calculated coefficients to find a least squares solution to the minimization problem. One of the key contributions of this work is the development of the total parallel plate spectral-domain Green's function by two independent methods. The Green's function is thereby shown to be correct in form and in physical meaning. A second significant contribution of this work to the scientific community is the evaluation of one of the inverse Fourier transform integrals in the complex plane. This significantly enhances the efficiency of the extraction code. A third significant contribution is the measurement of a number of uniaxial anisotropic materials, many of which were envisioned, designed and constructed in-house using 3D printing technology. The results are shown to be good in the transverse dimension, but mildly unstable in the longitudinal dimension. A secondary contribution of this work that warrants mention is the inclusion of a flexible, complete, working code for the extraction process. Although such codes have been written before, they have not been published in the literature for broader use.

  9. Quantum criticality in a uniaxial organic ferroelectric

    NASA Astrophysics Data System (ADS)

    Rowley, S. E.; Hadjimichael, M.; Ali, M. N.; Durmaz, Y. C.; Lashley, J. C.; Cava, R. J.; Scott, J. F.

    2015-10-01

    Tris-sarcosine calcium chloride (TSCC) is a highly uniaxial ferroelectric with a Curie temperature of approximately 130 K. By suppressing ferroelectricity with bromine substitution on the chlorine sites, pure single crystals were tuned through a ferroelectric quantum phase transition. The resulting quantum critical regime was investigated in detail and was found to persist up to temperatures of at least 30-40 K. The nature of long-range dipole interactions in uniaxial materials, which lead to non-analytical terms in the free-energy expansion in the polarization, predict a dielectric susceptibility varying as 1/T 3close to the quantum critical point. Rather than this, we find that the dielectric susceptibility varies as 1/T 2 as expected and observed in better known multi-axial systems. We explain this result by identifying the ultra-weak nature of the dipole moments in the TSCC family of crystals. Interestingly, we observe a shallow minimum in the inverse dielectric function at low temperatures close to the quantum critical point in paraelectric samples that may be attributed to the coupling of quantum polarization and strain fields. Finally, we present results of the heat capacity and electro-caloric effect and explain how the time dependence of the polarization in ferroelectrics and paraelectrics should be considered when making quantitative estimates of temperature changes induced by applied electric fields.

  10. Comparison of Constitutive Relationships of Tubes Established Using Uniaxial Tensile Tests and Tube Hydroforming Experiments

    NASA Astrophysics Data System (ADS)

    Li, Jing; Yang, Lianfa

    2016-08-01

    The aim of the present paper is to evaluate existing constitutive models and to fitting hardening laws of SS304 tubes for the accurate prediction of the deformation behaviors of the tubes in hydroforming. Uniaxial tensile test (UTT) and free hydro-bugling (FHB) experiments were conducted on SS304 tubes, and a hi-speed three-dimensional (3D) digital image correlation (DIC) system was applied to obtain the deformation data of the samples. Eight constitutive relationships of the tubes were then established by fitting the equivalent stress and strain data with the four existing constitutive models of Hollomon, Ghosh, Voce and Ghosh/Voce, and the fitting accuracy of the obtained constitutive relationships were analyzed and compared. The results show that Ghosh/Voce model holds the highest accuracy in describing the deformation behaviors of the tubes in UTT and FHB, followed by the Ghosh model and then the Hollomon model. The Voce model holds the lowest accuracy. A distinct discrepancy between the constitutive relationships obtained using UTT and FHB experiments are observed in present research conditions.

  11. True uniaxial compressive strengths of rock or coal specimens are independent of diameter-to-length ratios

    SciTech Connect

    Babcock, C.O.

    1991-01-01

    This paper reports that part of the compressive strength of a test specimen of rock or coal in the laboratory or a pillar in a mine comes from physical property strength and, in part, from the constraint provided by the loading stresses. Much confusion in pillar design comes from assigning the total strength change to geometry, as evidenced by the many pillar design equations with width to height as the primary variable. In tests by the U.S. Bureau of Mines, compressive strengths for cylindrical specimens of limestone, marble, sandstone, and coal were independent of the specimen test geometry when the end friction was removed. A conventional uniaxial compressive strength test between two steel platens is actually a uniaxial force and not a uniaxial stress test. The biaxial or triaxial state of stress for much of the test volume changes with the geometry of the test specimen. By removing the end friction supplied by the steel platens to the specimen, a more nearly uniaxial stress state independent of the specimen geometry is produced in the specimen. Pillar design is a constraint and physical property problem rather than a geometry problem. Roof and floor constraint are major factors in pillar design and strength.

  12. Mechanism for amorphization of boron carbide B{sub 4}C under uniaxial compression

    SciTech Connect

    Aryal, Sitaram; Rulis, Paul; Ching, W. Y.

    2011-11-01

    Boron carbide undergoes an amorphization transition under high-velocity impacts, causing it to suffer a catastrophic loss in strength. The failure mechanism is not clear and this limits the ways to improve its resistance to impact. To help uncover the failure mechanism, we used ab initio methods to carry out large-scale uniaxial compression simulations on two polytypes of stoichiometric boron carbide (B{sub 4}C), B{sub 11}C-CBC, and B{sub 12}-CCC, where B{sub 11}C or B{sub 12} is the 12-atom icosahedron and CBC or CCC is the three-atom chain. The simulations were performed on large supercells of 180 atoms. Our results indicate that the B{sub 11}C-CBC (B{sub 12}-CCC) polytype becomes amorphous at a uniaxial strain s = 0.23 (0.22) and with a maximum stress of 168 (151) GPa. In both cases, the amorphous state is the consequence of structural collapse associated with the bending of the three-atom chain. Careful analysis of the structures after amorphization shows that the B{sub 11}C and B{sub 12} icosahedra are highly distorted but still identifiable. Calculations of the elastic coefficients (C{sub ij}) at different uniaxial strains indicate that both polytypes may collapse under a much smaller shear strain (stress) than the uniaxial strain (stress). On the other hand, separate simulations of both models under hydrostatic compression up to a pressure of 180 GPa show no signs of amorphization, in agreement with experimental observation. The amorphized nature of both models is confirmed by detailed analysis of the evolution of the radial pair distribution function, total density of states, and distribution of effective charges on atoms. The electronic structure and bonding of the boron carbide structures before and after amorphization are calculated to further elucidate the mechanism of amorphization and to help form the proper rationalization of experimental observations.

  13. Infarcted rat myocardium: Data from biaxial tensile and uniaxial compressive testing and analysis of collagen fibre orientation.

    PubMed

    Sirry, Mazin S; Butler, J Ryan; Patnaik, Sourav S; Brazile, Bryn; Bertucci, Robbin; Claude, Andrew; McLaughlin, Ron; Davies, Neil H; Liao, Jun; Franz, Thomas

    2016-09-01

    Myocardial infarction was experimentally induced in rat hearts and harvested immediately, 7, 14 and 28 days after the infarction induction. Anterior wall infarct samples underwent biaxial tensile and uniaxial compressive testing. Orientation of collagen fibres was analysed following mechanical testing. In this paper, we present the tensile and compressive stress-strain raw data, the calculated tensile and compressive moduli and the measured angles of collagen orientation. The presented data is associated with the research article titled "Characterisation of the mechanical properties of infarcted myocardium in the rat under biaxial tension and uniaxial compression" (Sirry et al., 2016) [1]. PMID:27579338

  14. Phenomenological theory of uniaxial relaxor ferroelectrics

    NASA Astrophysics Data System (ADS)

    Shirokov, V. B.; Pavlenko, A. V.; Yuzyuk, Yu I.

    2016-10-01

    A phenomenological thermodynamic theory of uniaxial relaxor strontium barium niobate \\text{B}{{\\text{a}}0.5}\\text{S}{{\\text{r}}0.5}\\text{N}{{\\text{b}}2}{{\\text{O}}6} is developed using the Landau-Devonshire approach with two order parameters. The fourth-order thermodynamic potential allowed to explain the shape of the polarization hysteresis loops experimentally observed at different temperatures. We show that the broad maximum of the dielectric permittivity is not related to the phase transition and arise due to the coupling between polarization and true order parameter which has antiferroelectric nature. We found that the phase transition temperature is much higher than the maximum of the dielectric permittivity and very likely corresponds to so-called Burn’s temperature. True order parameter has no simple relation with polar modes.

  15. Unfolding of Isotactic Polypropylene under Uniaxial Stretching

    NASA Astrophysics Data System (ADS)

    Kang, Jia; Miyoshi, Toshikazu; Akihiro Kamimura, Akihiro Otsubo Collaboration

    Despite numerous investigations on polymer processing, understanding the deformation mechanisms of semicrystalline polymer under uniaxial stretching is still challenging. In this work, 13C-13C Double Quantum (DQ) NMR was applied to trace the structural evolution of 13C-labeled isotactic polypropylene (iPP) chains inside the crystallites stretched to engineering strain (e) of 21 at 100 °C. DQ NMR based on spatial proximity of 13C labeled nuclei proved conformational changes from the folded chains to the locally extended chains induced by stretching. By combining experimental findings with literature results on molecular dynamics, it was concluded that transportation of the crystalline chains plays a critical role to achieve large deformability of iPP.

  16. Phenomenological theory of uniaxial relaxor ferroelectrics.

    PubMed

    Shirokov, V B; Pavlenko, A V; Yuzyuk, Yu I

    2016-10-01

    A phenomenological thermodynamic theory of uniaxial relaxor strontium barium niobate [Formula: see text] is developed using the Landau-Devonshire approach with two order parameters. The fourth-order thermodynamic potential allowed to explain the shape of the polarization hysteresis loops experimentally observed at different temperatures. We show that the broad maximum of the dielectric permittivity is not related to the phase transition and arise due to the coupling between polarization and true order parameter which has antiferroelectric nature. We found that the phase transition temperature is much higher than the maximum of the dielectric permittivity and very likely corresponds to so-called Burn's temperature. True order parameter has no simple relation with polar modes. PMID:27485244

  17. AN ORGANOTYPIC UNIAXIAL STRAIN MODEL USING MICROFLUIDICS

    PubMed Central

    Dollé, Jean-Pierre; Morrison, Barclay; Schloss, Rene R.; Yarmush, Martin L.

    2012-01-01

    Traumatic brain injuries are the leading cause of disability each year in the US. The most common and devastating consequence is the stretching of axons caused by shear deformation that occurs during rotational acceleration of the brain during injury. The injury effects on axonal molecular and functional events are not fully characterized. We have developed a strain injury model that maintains the three dimensional cell architecture and neuronal networks found in vivo with the ability to visualize individual axons and their response to a mechanical injury. The advantage of this model is that it can apply uniaxial strains to axons that make functional connections between two organotypic slices and injury responses can be observed in real-time and over long term. This uniaxial strain model was designed to be capable of applying an array of mechanical strains at various rates of strain, thus replicating a range of modes of axonal injury. Long term culture, preservation of slice and cell orientation, and slice-slice connection on the device was demonstrated. The device has the ability to strain either individual axons or bundles of axons through the control of microchannel dimensions. The fidelity of the model was verified by observing characteristic responses to various strain injuries which included axonal beading, delayed elastic effects and breakdown in microtubules. Microtubule breakdown was shown to be dependent on the degree of the applied strain field, where maximal breakdown was observed at peak strain and minimal breakdown is observed at low strain. This strain injury model could be a powerful tool in assessing strain injury effects on functional axonal connections. PMID:23233120

  18. Comparative Analysis of Uniaxial Strain Shock Tests and Taylor Tests for Armor and Maraging Steels

    NASA Astrophysics Data System (ADS)

    Mescheryakov, Yu. I.; Zhigacheva, N. I.; Petrov, Yu. A.; Divakov, A. K.; Cline, C. F.

    2004-07-01

    High-strength constructional 38KhN3MFA steel and 02H18К9M5-BИ maraging steel were tested to determine the yield stress under dynamic loading. The 38KhN3MFA steel was used as central test material to work out the experimental technique. For both kinds of steel the results obtained in the plane shock tests under uniaxial strain condition show approximately the identical yield stress values as those obtained in Taylor tests. Cracking of maraging steel occurs along the shock-induced austenite bands where microhardness is much smaller than that for the rest of the matrix.

  19. The compliance of vascular endothelial cells (VECs) change after exposure to cyclic, uniaxial stretch

    NASA Astrophysics Data System (ADS)

    Osterday, Kathryn; Chew, Thomas; Phillip, Loury; Haga, Jason; Gomez-Gonzalez, Manuel; Del Alamo, Juan Carlos; Chien, Shu

    2012-11-01

    In vivo, VECs are exposed to both shear stress and cyclic, uniaxial stretch. It is known that VECs remodel their cytoskeleton perpendicular to stretch and parallel to shear and that cytoskeletal structure is critical to vessel function. Cytoskeletal structure must affect the magnitude and direction of the maximum and minimum shear compliance of the cytoplasm. This may provide the cell with a mechanism to tune their sensitivity to external mechanical stimuli differently along different directions, providing the flow-sensing mechanism needed for mechanotransduction. To study how cytoskeletal remodeling is correlated to changes in subcellular microrheology, we used directional particle tracking microrheology (DPTM) to calculate the shear compliance of the cytoplasm before and after exposure to cyclic, uniaxial stretch. When stretched, we find, VECs align their direction of maximum shear compliance perpendicular to stretch, their cytoplasm becomes less liquid, and the magnitude of the shear compliance along both directions of mechanical polarization decrease.

  20. Uniaxial strain-dependent magnetic and electronic properties of (Ga,Mn)As nanowires

    NASA Astrophysics Data System (ADS)

    Zhang, Chen-Hui; Xiang, Gang; Lan, Mu; Zhang, Xi

    2014-09-01

    Variations in magnetic and electronic properties as a function of uniaxial strain in wurtzite (Ga,Mn)As nanowires (NWs) grown along the [0001] direction were investigated based on density functional theory (DFT). We found that (Ga,Mn)As NWs are half-metal, and the ferromagnetic state is their stable ground state. The magnetism of the NWs is significantly affected by the strain and by the substituent position of Mn impurities. By examining charge densities near the Fermi level, we found that strain can regulate the conductive region of the NWs. More interestingly, the size of spin-down band gap of the NWs is tunable by adjusting uniaxial stress, and the NWs can be converted from indirect to direct band gap under tension.

  1. Discrete element modeling on the crack evolution behavior of brittle sandstone containing three fissures under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Yang, Sheng-Qi; Huang, Yan-Hua; Ranjith, P. G.; Jiao, Yu-Yong; Ji, Jian

    2015-12-01

    Based on experimental results of brittle, intact sandstone under uniaxial compression, the micro-parameters were firstly confirmed by adopting particle flow code (PFC^{2D}). Then, the validation of the simulated models were cross checked with the experimental results of brittle sandstone containing three parallel fissures under uniaxial compression. The simulated results agreed very well with the experimental results, including the peak strength, peak axial strain, and ultimate failure mode. Using the same micro-parameters, the numerical models containing a new geometry of three fissures are constructed to investigate the fissure angle on the fracture mechanical behavior of brittle sandstone under uniaxial compression. The strength and deformation parameters of brittle sandstone containing new three fissures are dependent to the fissure angle. With the increase of the fissure angle, the elastic modulus, the crack damage threshold, and the peak strength of brittle sandstone containing three fissures firstly increase and secondly decrease. But the peak axial strain is nonlinearly related to the fissure angle. In the entire process of deformation, the crack initiation and propagation behavior of brittle sandstone containing three fissures under uniaxial compression are investigated with respect to the fissure angle. Six different crack coalescence modes are identified for brittle sandstone containing three fissures under uniaxial compression. The influence of the fissure angle on the length of crack propagation and crack coalescence stress is evaluated. These investigated conclusions are very important for ensuring the stability and safety of rock engineering with intermittent structures.

  2. Deformation behavior of lead zirconate titanate ceramics under uniaxial compression measured by the digital image correlation method

    NASA Astrophysics Data System (ADS)

    Chen, Di; Carter, Emma; Kamlah, Marc

    2016-09-01

    The deformation behavior of lead zirconate titanate bulk ceramic specimen under uniaxial compression was monitored by the digital image correlation method and the homogeneity of the deformation was discussed. Combined with using a Sawyer-Tower circuit, the depolarization curve was also obtained. Because of the friction at both the top and bottom surfaces of the lead zirconate titanate ceramic specimen, the distribution of deformation under large uniaxial compressive stresses usually shows a barrel shape. By focusing on correspondingly selected regions of interest and calculating the values of strain components there, the barreling behavior was proved. This barreling behavior is due to elastic strains, in the first place, while the remnant strains are less affected by this phenomenon. All these findings are the experimental justifications for the selection of an aspect ratio of 3:1 for our specimens, where only the central cubic region of a specimen represents the desired purely uniaxial stress state. Only from this region, true uniaxial stress-strain results can be obtained to develop constitutive models.

  3. Edge effects on band gap energy in bilayer 2H-MoS{sub 2} under uniaxial strain

    SciTech Connect

    Dong, Liang; Wang, Jin; Dongare, Avinash M.; Namburu, Raju; O'Regan, Terrance P.; Dubey, Madan

    2015-06-28

    The potential of ultrathin MoS{sub 2} nanostructures for applications in electronic and optoelectronic devices requires a fundamental understanding in their electronic structure as a function of strain. Previous experimental and theoretical studies assume that an identical strain and/or stress state is always maintained in the top and bottom layers of a bilayer MoS{sub 2} film. In this study, a bilayer MoS{sub 2} supercell is constructed differently from the prototypical unit cell in order to investigate the layer-dependent electronic band gap energy in a bilayer MoS{sub 2} film under uniaxial mechanical deformations. The supercell contains an MoS{sub 2} bottom layer and a relatively narrower top layer (nanoribbon with free edges) as a simplified model to simulate the as-grown bilayer MoS{sub 2} flakes with free edges observed experimentally. Our results show that the two layers have different band gap energies under a tensile uniaxial strain, although they remain mutually interacting by van der Waals interactions. The deviation in their band gap energies grows from 0 to 0.42 eV as the uniaxial strain increases from 0% to 6% under both uniaxial strain and stress conditions. The deviation, however, disappears if a compressive uniaxial strain is applied. These results demonstrate that tensile uniaxial strains applied to bilayer MoS{sub 2} films can result in distinct band gap energies in the bilayer structures. Such variations need to be accounted for when analyzing strain effects on electronic properties of bilayer or multilayered 2D materials using experimental methods or in continuum models.

  4. X-Ray measurement of lattice strains in textured low carbon steel under uniaxial loading

    NASA Astrophysics Data System (ADS)

    Chang, C. H.; Koo, Y. M.

    1995-03-01

    To examine the effect of relative crystallite misorientations on the inhomogeneous deformation behavior, lattice strains in the crystallites of a textured low-carbon steel are measured by an in situ X-ray diffraction method under uniaxial loading. Internal microstresses of the crystallites are also determined from the lattice strains measured along different directions of the crystallites. The low-carbon steel has the rolling texture of orientation relationship: {211}<01Ī>, {111}<2Ī<, and {100}<011>. Different lattice stress-strain curves are obtained from the different crystallite groups, which show dissimilarity in the proportionality constant between the stress and lattice strain and the elastic limit of each crystallite group. The external elastic limit can be calculated from averaging the individual lattice yield points of each crystallite groups. Triaxial stress states are developed in the crystallites in the entire range of the elastic and plastic regions during uniaxial loading. The residual stresses of the specimen unloaded at a strain level of about 3 pet are in a biaxial stress state.

  5. The Effects of Crack Openings on Crack Initiation, Propagation and Coalescence Behavior in Rock-Like Materials Under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Cheng, Hao; Zhou, Xiaoping; Zhu, Jiang; Qian, Qihu

    2016-09-01

    This paper experimentally investigates the cracking behavior of rock-like specimens containing artificial open flaws under uniaxial compressive loads. The present experiments mainly focus on the effects of crack openings on crack propagation and coalescence behavior in rock-like materials under uniaxial compression. The real-time crack coalescence processes in the specimens with different crack openings are analyzed. The experimental results show that the crack openings significantly affect the crack initiation stresses and the crack initiation modes. The initiation stresses of wing cracks and coplanar secondary cracks decrease with increasing crack openings. However, the initiation stress of anti-wing cracks increases with increasing crack openings. Moreover, five types of crack coalescence in the specimens containing three pre-existing open flaws under uniaxial compression are observed. The effects of crack openings on the mechanical properties of rock-like materials, which include the complete axial stress-strain curves, peak stresses, peak strains and initiation stresses, are investigated in detail.

  6. Controllable strain-induced uniaxial anisotropy of Fe81Ga19 films deposited on flexible bowed-substrates

    NASA Astrophysics Data System (ADS)

    Dai, Guohong; Zhan, Qingfeng; Yang, Huali; Liu, Yiwei; Zhang, Xiaoshan; Zuo, Zhenghu; Chen, Bin; Li, Run-Wei

    2013-11-01

    We propose a convenient method to induce a uniaxial anisotropy in magnetostrictive Fe81Ga19 films grown on flexible polyethylene terephthalate (PET) substrates by bending the substrate prior to deposition. A tensile/compressive stress is induced in the Fe81Ga19 films when PET substrates are shaped from concave/convex to flat after deposition. The stressed Fe81Ga19 films exhibit a significant uniaxial magnetic anisotropy due to the internal stress arising from changes in shape of PET substrates. The easy axis is along the tensile stress direction and the coercive field along easy axis is increased with increasing the internal tensile stress. The remanence of hard axis is decreased with increasing the compressive stress, while the coercive field is almost unchanged. A modified Stoner-Wohlfarth model with considering the distribution of easy axes in polycrystalline films is used to account for the magnetic properties tuned by the strain-controlled magnetoelastic anisotropy in flexible Fe81Ga19 films. Our investigations provide a convenient way to induce uniaxial magnetic anisotropy, which is particularly important for fabricating flexible magnetoelectronic devices.

  7. Deformation micromechanisms of collagen fibrils under uniaxial tension

    PubMed Central

    Tang, Yuye; Ballarini, Roberto; Buehler, Markus J.; Eppell, Steven J.

    2010-01-01

    Collagen, an essential building block of connective tissues, possesses useful mechanical properties due to its hierarchical structure. However, little is known about the mechanical properties of collagen fibril, an intermediate structure between the collagen molecule and connective tissue. Here, we report the results of systematic molecular dynamics simulations to probe the mechanical response of initially unflawed finite size collagen fibrils subjected to uniaxial tension. The observed deformation mechanisms, associated with rupture and sliding of tropocollagen molecules, are strongly influenced by fibril length, width and cross-linking density. Fibrils containing more than approximately 10 molecules along their length and across their width behave as representative volume elements and exhibit brittle fracture. Shorter fibrils experience a more graceful ductile-like failure. An analytical model is constructed and the results of the molecular modelling are used to find curve-fitted expressions for yield stress, yield strain and fracture strain as functions of fibril structural parameters. Our results for the first time elucidate the size dependence of mechanical failure properties of collagen fibrils. The associated molecular deformation mechanisms allow the full power of traditional material and structural engineering theory to be applied to our understanding of the normal and pathological mechanical behaviours of collagenous tissues under load. PMID:19897533

  8. Uniaxial Pressure Dependence of Magnetic Order in MnSi.

    PubMed

    Chacon, A; Bauer, A; Adams, T; Rucker, F; Brandl, G; Georgii, R; Garst, M; Pfleiderer, C

    2015-12-31

    We report comprehensive small angle neutron scattering measurements complemented by ac susceptibility data of the helical order, conical phase, and Skyrmion lattice phase (SLP) in MnSi under uniaxial pressures. For all crystallographic orientations uniaxial pressure favors the phase for which a spatial modulation of the magnetization is closest to the pressure axis. Uniaxial pressures as low as 1 kbar applied perpendicular to the magnetic field axis enhance the Skyrmion lattice phase substantially, whereas the Skyrmion lattice phase is suppressed for pressure parallel to the field. Taken together we present quantitative microscopic information on how strain couples to magnetic order in the chiral magnet MnSi. PMID:26765018

  9. Describing Cognitive Structure.

    ERIC Educational Resources Information Center

    White, Richard T.

    This paper discusses questions pertinent to a definition of cognitive structure as the knowledge one possesses and the manner in which it is arranged, and considers how to select or devise methods of describing cognitive structure. The main purpose in describing cognitive structure is to see whether differences in memory (or cognitive structure)…

  10. Microstructures Resulting from Uniaxial Deformation of Magnetite

    NASA Astrophysics Data System (ADS)

    Lindquist, A. K.; Feinberg, J. M.

    2012-12-01

    Researchers rely on the magnetic record preserved in magnetite when investigating magnetic field reversals, reconstructing past tectonic plate locations, and studying changes in the strength of the earth's magnetic field. Despite the extensive use of magnetite in scientific studies, the effects of dislocations on magnetite's remanence and magnetic stability are poorly understood, yet are crucial to understanding how magnetite records and maintains past magnetic field directions and intensities. To begin to address this need, we have studied the dislocation and defect structures in magnetite that form after controlled deformation. We have also measured major hysteresis loops to investigate the changes in remanence and coercivity that result from each of these deformation events. A single magnetite octahedron was cut into roughly equal bar-shaped pieces, and each was deformed uniaxially along a <121> direction at one atmosphere using a variety of temperature and pressure conditions, each selected to fall within the dislocation glide regime. Slices were cut from each deformed bar after deformation and investigated using a transmission electron microscope to characterize the types of deformation structures resulting from each of the temperature-pressure combinations. A variety of deformation structures were observed, especially dislocations and deformation bands. Dislocations were more common in samples deformed below 875°C. Hysteresis loops were measured for each sample with a field direction perpendicular to the deformation axis. Surprisingly, there is no significant difference in the bulk coercivity of a deformed and undeformed piece of magnetite.

  11. Analysis of silicon stress/strain relationships

    NASA Technical Reports Server (NTRS)

    Dillon, O.

    1986-01-01

    Results are presented for work on stress-strain relationships in silicon ribbon. Calculations of stress fields, dislocation desities, and buckling were made; uniaxial tensile tests were made on silicon at 1150 C; and dislocation motion studies were performed.

  12. Deformation behavior of lead zirconate titanate ceramics under uniaxial compression measured by the digital image correlation method

    NASA Astrophysics Data System (ADS)

    Chen, Di; Carter, Emma; Kamlah, Marc

    2016-09-01

    The deformation behavior of lead zirconate titanate bulk ceramic specimen under uniaxial compression was monitored by the digital image correlation method and the homogeneity of the deformation was discussed. Combined with using a Sawyer–Tower circuit, the depolarization curve was also obtained. Because of the friction at both the top and bottom surfaces of the lead zirconate titanate ceramic specimen, the distribution of deformation under large uniaxial compressive stresses usually shows a barrel shape. By focusing on correspondingly selected regions of interest and calculating the values of strain components there, the barreling behavior was proved. This barreling behavior is due to elastic strains, in the first place, while the remnant strains are less affected by this phenomenon. All these findings are the experimental justifications for the selection of an aspect ratio of 3:1 for our specimens, where only the central cubic region of a specimen represents the desired purely uniaxial stress state. Only from this region, true uniaxial stress–strain results can be obtained to develop constitutive models.

  13. Inducing uniform single-crystal like orientation in natural rubber with constrained uniaxial stretch.

    PubMed

    Zhou, Weiming; Meng, Lingpu; Lu, Jie; Wang, Zhen; Zhang, Wenhua; Huang, Ningdong; Chen, Liang; Li, Liangbin

    2015-07-01

    The effect of flow on crystallization is commonly attributed to entropic reduction, which is caused by stretch and orientation of polymer chains but overlooks the role of flow on final-state free energy. With the aid of in situ synchrotron radiation wide-angle X-ray diffraction (WAXD) and a homemade constrained uniaxial tensile testing machine, polycrystals possessing single-crystal-like orientation rather than uniaxial orientation are found during the constrained stretch of natural rubber, whereas the c-axis and a-axis align in the stretch direction (SD) and constrained direction (CD), respectively. Molecular dynamics simulation shows that aligning the a-axis of crystal nuclei in CD leads to the lowest free energy increase and favors crystal nucleation. This indicates that the nomenclature of strain-induced crystallization may not fully account for the nature of flow-induced crystallization (FIC) as strain mainly emphasizes the entropic reduction of initial melt, whereas stress rather than strain plays the dominant role in crystal deformation. The current work not only contributes to a comprehensive understanding of the mechanism of flow-induced crystallization but also demonstrates the potential application of constrained uniaxial tensile stretch for the creation of functional materials containing polycrystals that possess single-crystal-like orientation.

  14. The effect of uniaxial strain on graphene nanoribbon carrier statistic.

    PubMed

    Johari, Zaharah; Ismail, Razali

    2013-01-01

    : Armchair graphene nanoribbon (AGNR) for n=3m and n=3m+1 family carrier statistic under uniaxial strain is studied by means of an analytical model based on tight binding approximation. The uniaxial strain of AGNR carrier statistic models includes the density of state, carrier concentration, and carrier velocity. From the simulation, it is found that AGNR carrier concentration has not been influenced by the uniaxial strain at low normalized Fermi energy for n=3m and n=3m+1. In addition, the carrier velocity of AGNR is mostly affected by strain at high concentration of n≈3.0×107 and 1.0 × 107 m-1 for n=3m and n=3m+1, respectively. The result obtained gives physical insight into the understanding of uniaxial strain in AGNR.

  15. Scalar Damage Variable Determined in the Uniaxial and Triaxial Compression Conditions of Sandstone Samples

    NASA Astrophysics Data System (ADS)

    Cieślik, Jerzy

    2013-03-01

    The article is based on the results of uniaxial and triaxial compression tests, performed on Wustenzeller sandstone. An overview of the possible definitions of damage variable describing the process of damage development on the basis of various hypotheses has been presented in the first part of the article. In the main part of the article the author has presented the results of laboratory investigations, where the state of damage and its changes in rock samples under uniaxial and triaxial compression conditions were being observed. Using a modified procedure of triaxial tests, a definition of damage variable, determined on the basis of changes of volumetric stiffness of an examined rock, has been developed. Damage variable defined this way, in relation to a variable determined on the basis of axial stiffness changes, points to some anisotropy effects of damage phenomenon. The results obtained from both methods have been compared whereas the relations determining the evolution of damage variable in the loading process have been established.

  16. Describe Your Favorite Teacher.

    ERIC Educational Resources Information Center

    Dill, Isaac; Dill, Vicky

    1993-01-01

    A third grader describes Ms. Gonzalez, his favorite teacher, who left to accept a more lucrative teaching assignment. Ms. Gonzalez' butterflies unit covered everything from songs about social butterflies to paintings of butterfly wings, anatomy studies, and student haiku poems and biographies. Students studied biology by growing popcorn plants…

  17. Light Self-Localization and Power-Dependent Steering in Anisotropic Dielectrics: Spatial Solitons in Uniaxial Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Alberucci, Alessandro; Assanto, Gaetano

    We discuss nonlinear propagation of light beams in anisotropic media, addressing the role of nonlocality and nonlinearity in power-dependent beam self-steering. With specific reference to spatial solitons in positive uniaxial nematic liquid crystals (i.e. nematicons), we describe soliton self-acceleration through reorientational response and nonlinear walk-off.

  18. Simple Waveforms, Simply Described

    NASA Technical Reports Server (NTRS)

    Baker, John G.

    2008-01-01

    Since the first Lazarus Project calculations, it has been frequently noted that binary black hole merger waveforms are 'simple.' In this talk we examine some of the simple features of coalescence and merger waveforms from a variety of binary configurations. We suggest an interpretation of the waveforms in terms of an implicit rotating source. This allows a coherent description, of both the inspiral waveforms, derivable from post-Newtonian(PN) calculations, and the numerically determined merger-ringdown. We focus particularly on similarities in the features of various Multipolar waveform components Generated by various systems. The late-time phase evolution of most L these waveform components are accurately described with a sinple analytic fit. We also discuss apparent relationships among phase and amplitude evolution. Taken together with PN information, the features we describe can provide an approximate analytic description full coalescence wavefoRms. complementary to other analytic waveforns approaches.

  19. A Rate-Dependent Damage Model and its Application to Uniaxial Strain

    NASA Astrophysics Data System (ADS)

    Raftenberg, Martin N.

    2005-07-01

    Our analysis is based on a damage model discussed in [1] in which the internal energy density W depends on strain E and damage κ : W(E,κ)=φ(κ)1pt1pt1ptμ1pt1pt1pt( ν1-2νEkkEll+EijEij ); μ is elastic shear modulus, ν is Poisson's ratio. The factor φ(κ)=1-( 1-φ )κκ describes degradation of elastic modulus due to damage; φmin and κmax are material constants. The system of evolution includes [ ρ^2ut^2=∇WE,;κt=-KWκ ] where K is (for now) a material constant. The above model was installed into LS-DYNA using the User Material Interface. The model was applied to a finite-element simulation of a rod under uniaxial strain, with a prescribed-velocity boundary condition at one end and a stress-free condition at the other. The resulting initial-value boundary-value problem was scaled to reveal the presence of the dimensionless group π=ρ02√(1-2ν)ρ021pt1pt1pt(1-ν)μ .( 1-φ )Kκ ^2.L.u0^2, where ρ0 is the material density, L is the length of the rod, and u0is the prescribed velocity. Solutions were obtained for a range of π values. The progression of contours of κ(x,t) was observed. [1] Grinfeld, M.A., and Wright, T.W., Metallurgical and Materials Transactions A, Vol. 35A, 2651-2661, 2004.

  20. A simple constrained uniaxial tensile apparatus for in situ investigation of film stretching processing

    NASA Astrophysics Data System (ADS)

    Meng, Lingpu; Li, Jing; Cui, Kunpeng; Chen, Xiaowei; Lin, Yuanfei; Xu, Jiali; Li, Liangbin

    2013-11-01

    A simple constrained uniaxial tensile apparatus was designed and constructed to obtain stress-strain curve during stretching and subsequent structural evolution of polymeric films. Stretch is carried out through two motor driven clamps in the machine direction and scissor-like clamps in the transverse direction keeping the sample width constant. The force information during film stretching process is recorded by a tension sensor and structural evolution can be obtained by in situ X-ray scattering technique. All parameters related to film stretching manufacturing, such as temperature, draw ratio, and stretching speed can be set independently, making the apparatus an effective method to explore the relationship between processing parameters and structure.

  1. Scaling laws and deformation mechanisms of nanoporous copper under adiabatic uniaxial strain compression

    SciTech Connect

    Yuan, Fuping Wu, Xiaolei

    2014-12-15

    A series of large-scale molecular dynamics simulations were conducted to investigate the scaling laws and the related atomistic deformation mechanisms of Cu monocrystal samples containing randomly placed nanovoids under adiabatic uniaxial strain compression. At onset of yielding, plastic deformation is accommodated by dislocations emitted from void surfaces as shear loops. The collapse of voids are observed by continuous emissions of dislocations from void surfaces and their interactions with further plastic deformation. The simulation results also suggest that the effect modulus, the yield stress and the energy aborption density of samples under uniaxial strain are linearly proportional to the relative density ρ. Moreover, the yield stress, the average flow stress and the energy aborption density of samples with the same relative density show a strong dependence on the void diameter d, expressed by exponential relations with decay coefficients much higher than -1/2. The corresponding atomistic mechanisms for scaling laws of the relative density and the void diameter were also presented. The present results should provide insights for understanding deformation mechanisms of nanoporous metals under extreme conditions.

  2. New described dermatological disorders.

    PubMed

    Gönül, Müzeyyen; Cevirgen Cemil, Bengu; Keseroglu, Havva Ozge; Kaya Akis, Havva

    2014-01-01

    Many advances in dermatology have been made in recent years. In the present review article, newly described disorders from the last six years are presented in detail. We divided these reports into different sections, including syndromes, autoinflammatory diseases, tumors, and unclassified disease. Syndromes included are "circumferential skin creases Kunze type" and "unusual type of pachyonychia congenita or a new syndrome"; autoinflammatory diseases include "chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE) syndrome," "pyoderma gangrenosum, acne, and hidradenitis suppurativa (PASH) syndrome," and "pyogenic arthritis, pyoderma gangrenosum, acne, and hidradenitis suppurativa (PAPASH) syndrome"; tumors include "acquired reactive digital fibroma," "onychocytic matricoma and onychocytic carcinoma," "infundibulocystic nail bed squamous cell carcinoma," and "acral histiocytic nodules"; unclassified disorders include "saurian papulosis," "symmetrical acrokeratoderma," "confetti-like macular atrophy," and "skin spicules," "erythema papulosa semicircularis recidivans." PMID:25243162

  3. Landau levels in uniaxially strained graphene: A geometrical approach

    SciTech Connect

    Betancur-Ocampo, Y. Cifuentes-Quintal, M.E.; Cordourier-Maruri, G.; Coss, R. de

    2015-08-15

    The effect of strain on the Landau levels (LLs) spectra in graphene is studied, using an effective Dirac-like Hamiltonian which includes the distortion in the Dirac cones, anisotropy and spatial-dependence of the Fermi velocity induced by the lattice change through a renormalized linear momentum. We propose a geometrical approach to obtain the electron’s wave-function and the LLs in graphene from the Sturm–Liouville theory, using the minimal substitution method. The coefficients of the renormalized linear momentum are fitted to the energy bands, which are obtained from a Density Functional Theory (DFT) calculation. In particular, we evaluate the case of Dirac cones with an ellipsoidal transversal section resulting from uniaxially strained graphene along the Arm-Chair (AC) and Zig-Zag (ZZ) directions. We found that uniaxial strain in graphene induces a contraction of the LLs spectra for both strain directions. Also, is evaluated the contribution of the tilting of Dirac cone axis resulting from the uniaxial deformations to the contraction of the LLs spectra. - Highlights: • The LLs in uniaxially strained graphene are found using a geometrical approach. • The energy of the LLs in function of the Dirac cone deformation is presented. • We found that uniaxial strain in graphene induces a contraction of the LLs spectra. • Contraction in LLs spectra depends on the geometrical parameters of the Dirac cone.

  4. New Described Dermatological Disorders

    PubMed Central

    Cevirgen Cemil, Bengu; Keseroglu, Havva Ozge; Kaya Akis, Havva

    2014-01-01

    Many advances in dermatology have been made in recent years. In the present review article, newly described disorders from the last six years are presented in detail. We divided these reports into different sections, including syndromes, autoinflammatory diseases, tumors, and unclassified disease. Syndromes included are “circumferential skin creases Kunze type” and “unusual type of pachyonychia congenita or a new syndrome”; autoinflammatory diseases include “chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE) syndrome,” “pyoderma gangrenosum, acne, and hidradenitis suppurativa (PASH) syndrome,” and “pyogenic arthritis, pyoderma gangrenosum, acne, and hidradenitis suppurativa (PAPASH) syndrome”; tumors include “acquired reactive digital fibroma,” “onychocytic matricoma and onychocytic carcinoma,” “infundibulocystic nail bed squamous cell carcinoma,” and “acral histiocytic nodules”; unclassified disorders include “saurian papulosis,” “symmetrical acrokeratoderma,” “confetti-like macular atrophy,” and “skin spicules,” “erythema papulosa semicircularis recidivans.” PMID:25243162

  5. True uniaxial compressive strengths of rock or coal specimens are independent of diameter-to-length ratios. Report of Investigations/1990

    SciTech Connect

    Babcock, C.O.

    1990-01-01

    Part of the compressive strength of a test specimen of rock or coal in the laboratory or a pillar in a mine comes from physical property strength and, in part, from the constraint provided by the loading stresses. Much confusion in pillar design comes from assigning the total strength change to geometry, as evidenced by the many pillar design equations with width to height as the primary variable. In tests by the U.S. Bureau of Mines, compressive strengths for cylindrical specimens of limestone, marble, sandstone, and coal were independent of the specimen test geometry when the end friction was removed. A conventional uniaxial compressive strength test between two steel platens is actually a uniaxial force and not a uniaxial stress test. The biaxial or triaxial state of stress for much of the test volume changes with the geometry of the test specimen. By removing the end friction supplied by the steel platens to the specimen, a more nearly uniaxial stress state independent of the specimen geometry is produced in the specimen. Pillar design is a constraint and physical property problem rather than a geometry problem. Roof and floor constraint are major factors in pillar design and strength.

  6. A study of the interacting electron system in stressed (001) Si MOSFETs

    NASA Astrophysics Data System (ADS)

    Lutz, J.; Kuchar, F.

    1996-11-01

    The interaction of the electrons in Si MOSFETs has been studied under uniaxial stress using quantum magnetotransport experiments (Shubnikov - de Haas and quantum Hall effect). The stress allows one to vary the relative positions of the conduction band valleys where the electron - electron interaction plays a crucial role. From the evaluation of the data we obtain the phase diagram of the population of the valleys as a function of stress and carrier density. Our results are excellently described by the theory of Takada and Ando where intervalley electron - electron interaction is taken into account.

  7. Computer-aided study of the mechanical behavior of the jaw bone fragments under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Kolmakova, Tatyana V.

    2016-08-01

    The article presents the calculated results of the mechanical behavior of simulative bone mesovolumes under uniaxial compression with their architectonics corresponding to the human jaw bone fragments. The results of the calculation show that changes in the structure and mineral content of the bone fragments can lead to the change of their prevailing deformation response. New effective parameters were introduced to reflect the character of the distribution of stresses and strains in the bone mesovolumes. Implants are to be created and selected to correspond to the offered parameters and longitudinal modulus of elasticity of bone mesovolumes in order to maintain the stress and strain state existing in bone macrovolume during the implantation and in order to avoid bone restructuring through its borderline resorption.

  8. Effects of Acoustic Emission and Energy Evolution of Rock Specimens Under the Uniaxial Cyclic Loading and Unloading Compression

    NASA Astrophysics Data System (ADS)

    Meng, Qingbin; Zhang, Mingwei; Han, Lijun; Pu, Hai; Nie, Taoyi

    2016-10-01

    Characteristics of energy accumulation, evolution, and dissipation in uniaxial cyclic loading and unloading compression of 30 sandstone rock specimens under six different loading rates were explored. Stress-strain relations and acoustic emission characteristics of the deformation and failure of rock specimens were analyzed. The densities and rates of stored energy, elastic energy, and dissipated energy under different loading rates were confirmed, and an effective approach for the equivalent energy surface was presented. The energy evolution of rock deformation and failure were revealed. It turns out that the rock deformation behavior under uniaxial cyclic loading and unloading compression remained almost unchanged compared with that of uniaxial compression. The degree of match between reloading stress-strain curves and previous unloading curves was high, thereby demonstrating the memory function of rock masses. The intensity of acoustic emission fluctuated continually during the entire cyclic process. Emissions significantly increased as the stress exceeded the unloading level. The peak of acoustic emission increased with increasing loading stress level. Relationships between energy density and axial load indicate that the rock mass possesses a certain energy storage limitation. The energy evolution of rock masses is closely related to the axial loading stress, rather than to the axial loading rate. With increasing axial loading stress, stored energy varied most rapidly, followed by that of the elastic energy, then dissipated energy. Energy accumulation dominates prior to the axial load reaching peak strength; thereafter, energy dissipation becomes dominant. The input energy causes the irreversible initiation and extension of microcracks in the rock body. Elastic energy release leads to sudden instability of rock bodies and drives rock damage.

  9. Negative Refraction in a Uniaxial Absorbent Dielectric Material

    ERIC Educational Resources Information Center

    Jen, Yi-Jun; Lakhtakia, Akhlesh; Yu, Ching-Wei; Lin, Chin-Te

    2009-01-01

    Refraction of light from an isotropic dielectric medium to an anisotropic dielectric material is a complicated phenomenon that can have several different characteristics not usually discussed in electromagnetics textbooks for undergraduate students. With a simple problem wherein the refracting material is uniaxial with its optic axis normal to the…

  10. Multiscale surface roughening of commercial purity titanium during uniaxial tension

    SciTech Connect

    Panin, Alexey; Kazachenok, Marina Kozelskaya, Anna Sinyakova, Elena; Lider, Andrey Sklyarova, Elena

    2015-10-27

    The mechanisms of the surface roughening of the titanium specimens during uniaxial tension were demonstrated. By means of optical profilometry and electron backscattered diffraction it was shown that the formation of surface roughening is a multilevel process. The correlation between the density of slip in some grains, and grain rotation, and their displacement towards the free surface was investigated.

  11. Transient Splitting of Conoscopic Isogyres of a Uniaxial Nematic

    NASA Astrophysics Data System (ADS)

    Kim, Young-Ki; Senuk, Bohdan; Tortora, Luana; Sprunt, Samuel; Lehmann, Matthias; Lavrentovich, Oleg D.

    2012-02-01

    The phase identification is often based on conoscopic observations of homeotropic cells: A uniaxial nematic produces a pattern with crossed isogyres, while the biaxial nematic shows a split of isogyres. We demonstrate that the splitting of isogyres occurs even when the material remains in the uniaxial nematic phase. In particular, in the bent core material J35, splitting of isogyres is caused by change of the temperature. The effect is transient and the isogyres return to a uniaxial (crossed) configuration after a certain time that depends on sample thickness, temperature, and rate of temperature change; the time varies from a few seconds to tens of hours. The transient splitting is caused by the temperature-induced material flow that triggers a (uniaxial) director tilt in the cell. The flows and the director tilt are demonstrated by the CARS microscopy and fluorescent confocal polarizing microscopy (FCPM). This transient effect is general and can be observed even in E7 and 5CB. The effect should be considered in textural identifications of potential biaxial nematic materials.

  12. Beam propagation through uniaxial anisotropic media: global changes in the spatial profile.

    PubMed

    Martínez-Herrero, R; Movilla, J M; Mejías, P M

    2001-08-01

    The propagation of electromagnetic beams through uniaxial anisotropic media is investigated. The Maxwell equations are solved in the paraxial limit in terms of the plane-wave spectrum associated with each Cartesian field component. Attention is focused on the global changes in the spatial structure of the beam, which are described by means of the second-order intensity moment formalism. In particular, the propagation law for the intensity moments through this kind of media is obtained. As a consequence it is inferred that it is possible to improve the beam-quality parameter by using these media.

  13. Tuning the electronic properties of boron nitride nanotube by mechanical uni-axial deformation: a DFT study

    PubMed Central

    2011-01-01

    The effect of uni-axial strain on the electronic properties of (8,0) zigzag and (5,5) armchair boron nitride nanotubes (BNNT) is addressed by density functional theory calculation. The stress-strain profiles indicate that these two BNNTS of differing types display very similar mechanical properties, but there are variations in HOMO-LUMO gaps at different strains, indicating that the electronic properties of BNNTs not only depend on uni-axial strain, but on BNNT type. The variations in nanotube geometries, partial density of states of B and N atoms, B and N charges are also discussed for (8,0) and (5,5) BNNTs at different strains. PMID:21711682

  14. Mathematical model relating uniaxial compressive behavior of manufactured sand mortar to MIP-derived pore structure parameters.

    PubMed

    Tian, Zhenghong; Bu, Jingwu

    2014-01-01

    The uniaxial compression response of manufactured sand mortars proportioned using different water-cement ratio and sand-cement ratio is examined. Pore structure parameters such as porosity, threshold diameter, mean diameter, and total amounts of macropores, as well as shape and size of micropores are quantified by using mercury intrusion porosimetry (MIP) technique. Test results indicate that strains at peak stress and compressive strength decreased with the increasing sand-cement ratio due to insufficient binders to wrap up entire sand. A compression stress-strain model of normal concrete extending to predict the stress-strain relationships of manufactured sand mortar is verified and agreed well with experimental data. Furthermore, the stress-strain model constant is found to be influenced by threshold diameter, mean diameter, shape, and size of micropores. A mathematical model relating stress-strain model constants to the relevant pore structure parameters of manufactured sand mortar is developed.

  15. Mathematical Model Relating Uniaxial Compressive Behavior of Manufactured Sand Mortar to MIP-Derived Pore Structure Parameters

    PubMed Central

    Tian, Zhenghong; Bu, Jingwu

    2014-01-01

    The uniaxial compression response of manufactured sand mortars proportioned using different water-cement ratio and sand-cement ratio is examined. Pore structure parameters such as porosity, threshold diameter, mean diameter, and total amounts of macropores, as well as shape and size of micropores are quantified by using mercury intrusion porosimetry (MIP) technique. Test results indicate that strains at peak stress and compressive strength decreased with the increasing sand-cement ratio due to insufficient binders to wrap up entire sand. A compression stress-strain model of normal concrete extending to predict the stress-strain relationships of manufactured sand mortar is verified and agreed well with experimental data. Furthermore, the stress-strain model constant is found to be influenced by threshold diameter, mean diameter, shape, and size of micropores. A mathematical model relating stress-strain model constants to the relevant pore structure parameters of manufactured sand mortar is developed. PMID:25133257

  16. Structural phase transitions in boron carbide under stress

    NASA Astrophysics Data System (ADS)

    Korotaev, P.; Pokatashkin, P.; Yanilkin, A.

    2016-01-01

    Structural transitions in boron carbide B4C under stress were studied by means of first-principles molecular dynamics in the framework of density functional theory. The behavior depends strongly on degree of non-hydrostatic stress. Under hydrostatic stress continuous bending of the three-atom C-B-C chain was observed up to 70 GPa. The presence of non-hydrostatic stress activates abrupt reversible chain bending, which is displacement of the central boron atom in the chain with the formation of weak bonds between this atom and atoms in the nearby icosahedra. Such structural change can describe a possible reversible phase transition in dynamical loading experiments. High non-hydrostatic stress achieved in uniaxial loading leads to disordering of the initial structure. The formation of carbon chains is observed as one possible transition route.

  17. Anomalous threshold reduction from <100> uniaxial strain for a low-threshold Ge laser

    NASA Astrophysics Data System (ADS)

    Sukhdeo, David S.; Kim, Yeji; Gupta, Shashank; Saraswat, Krishna C.; Dutt, Birendra Raj; Nam, Donguk

    2016-11-01

    We theoretically investigate the effect of <100> uniaxial strain on a Ge-on-Si laser. We predict a dramatic ~200x threshold reduction upon applying sufficient uniaxial tensile strain to Ge. This anomalous reduction is explained by how the topmost valence bands split and become anisotropic with uniaxial tensile strain. Approximately 3.2% uniaxial strain is required to achieve this anomalous threshold reduction for 1×1019 cm-3 n-type doping, and a complex interaction between strain and n-type doping is observed. Achieving this critical uniaxial strain level for the anomalous threshold reduction is dramatically more relevant to practical devices than realizing a direct band gap.

  18. Molecular dynamics simulations of ordering of polydimethylsiloxane under uniaxial extension

    SciTech Connect

    Lacevic, N M; Gee, R H

    2005-03-11

    Molecular dynamics simulations of a bulk melts of polydimethylsiloxane (PDMS) are utilized to study chain conformation and ordering under constant uniaxial tension. We find that large extensions induce chain ordering in the direction of applied tension. We also find that voids are created via a cavitation mechanism. This study represents a validation of the current model for PDMS and benchmark for the future study of mechanical properties of PDMS melts enriched with fillers under tension.

  19. Hyperbolic Plasmons and Topological Transitions Over Uniaxial Metasurfaces

    NASA Astrophysics Data System (ADS)

    Gomez-Diaz, J. Sebastian; Tymchenko, Mykhailo; Alù, Andrea

    2015-06-01

    We explore the unusual electromagnetic response of ultrathin anisotropic σ -near-zero uniaxial metasurfaces, demonstrating extreme topological transitions—from closed elliptical to open hyperbolic—for surface plasmon propagation, associated with a dramatic tailoring of the local density of states. The proposed metasurfaces may be implemented using nanostructured graphene monolayers and open unprecedented venues for extreme light confinement and unusual propagation and guidance, combined with large tunability via electric bias.

  20. Enhancing the toughness of regenerated silk fibroin film through uniaxial extension.

    PubMed

    Yin, Jianwei; Chen, Erqiang; Porter, David; Shao, Zhengzhong

    2010-11-01

    Films of regenerated silk fibroin (RSF) are usually brittle and weak, which prevents its wide application as a structural material. To improve the mechanical properties of RSF film, uniaxial extension under swollen conditions was employed to introduce preferred orientation of molecular chains of silk fibroin. Such a prestretching treatment resulted in the strain at break, ultimate stress, Young's modulus, and energy to break along the predrawn direction of the RSF film increasing from approximate 5%, 90 MPa, 2.7 GPa, and 2.1 kJ/kg to 35%, 169 MPa, 3.5 GPa, and 38.9 kJ/kg, respectively, which is an attractive combination of strength and toughness. The mechanism of these property enhancements was investigated using techniques such as small-angle X-ray scattering, wide-angle X-ray diffraction, atomic force microscopy, and dynamic mechanical analysis.

  1. Formulation of Macroscale Compaction Dynamics based on Mesoscale Simulations of Uniaxial Waves in Granular Explosive

    NASA Astrophysics Data System (ADS)

    Chakravarthy, Sunada; Gonthier, Keith A.

    2010-10-01

    A macroscale continuum theory for Deflagration-to-Detonation Transition (DDT) in granular explosive is generalized to account for the simultaneous existence of an arbitrary number of condensed phases. The theory assumes phase separation, and allows for flexible partitioning of dissipation between phases in a thermodynamically consistent manner. The constitutive theory is complex and requires descriptions for dissipation partition functions, relaxation rate functions, and phase-specific parameters that are not well-characterized, particularly for dynamic loading. A key focus of this study is to formulate expressions for phase-specific intergranular stresses and compaction potential energies based on mesoscale simulations of uniaxial compaction waves because of their importance to compaction induced heating and combustion. Predictions will be compared to quasi-static compaction data for granular HMX.

  2. Effect of phase symmetry on the NMR spectrum of acetonitrile oriented in a uniaxial-biaxial-uniaxial phase

    NASA Astrophysics Data System (ADS)

    Deepak, H. S. Vinay; Yelamaggad, C. V.; Khetrapal, C. L.; Ramanathan, K. V.

    2016-09-01

    We report here the measurement of the Csbnd H and the Hsbnd H dipolar couplings of the methyl group of acetonitrile oriented in the biaxial liquid crystal potassium laurate/1-decanol/water system. These parameters show large variations when measured as a function of temperature. The variations follow the symmetry of the phase as the liquid crystal goes through the sequence of uniaxial - biaxial - uniaxial phases and show a close correspondence to the phase changes that occur in the liquid crystalline solvent coinciding with the onset of biaxiality. The Hsbnd Csbnd H bond angle calculated after incorporating vibrational corrections to the dipolar couplings is discussed in terms of contributions in the case of the biaxial liquid crystal arising from vibration-rotation interaction effects.

  3. Non-destructive quantification of alignment of nanorods embedded in uniaxially stretched polymer films

    SciTech Connect

    Stoenescu, Stefan Packirisamy, Muthukumaran; Truong, Vo-Van

    2014-03-21

    Among several methods developed for uniaxial alignment of metallic nanorods for optical applications, alignment by film stretching consists in embedding the rods in a transparent thin film of thermoplastic polymer, followed by simultaneous heating and uniaxial stretching of the composite film. As to the quantification of the resulting alignment, it has been limited to statistical calculations based on microscopic examination, which is incomplete, subject to errors due to geometric distortions of the scanning electron microscope images and destructive, since it involves cutting of samples. In contrast, we present in this paper a non-destructive quantification of the average orientation of the rods, based on a probabilistic approach combined with numerical simulations of absorbance spectra and spectrometric characterization of the composite film. Assuming electromagnetically non-interacting rods, we consider the longitudinal absorbance peak of their ensemble to consist of the superposition of their individual spectra that we obtain by numerical simulation using the size and shape adapted dielectric function of the metal and the finite difference time domain method. The accuracy of the solution depends on the number of discretization intervals, the accuracy of the numerical simulations, and the accurate knowledge of the polydispersity of the rods. For the sake of concreteness, we used nanorods to describe the quantification steps but the method is equally valid for any dichroic particles.

  4. Multiple scattering of electromagnetic waves by an aggregate of uniaxial anisotropic spheres.

    PubMed

    Li, Zheng-Jun; Wu, Zhen-Sen; Shi, Yan'e; Bai, Lu; Li, Hai-Ying

    2012-01-01

    An exact analytical solution is obtained for the scattering of electromagnetic waves from a plane wave with arbitrary directions of propagation and polarization by an aggregate of interacting homogeneous uniaxial anisotropic spheres with parallel primary optical axes. The expansion coefficients of a plane wave with arbitrary directions of propagation and polarization, for both TM and TE modes, are derived in terms of spherical vector wave functions. The effects of the incident angle α and the polarization angle β on the radar cross sections (RCSs) of several types of collective uniaxial anisotropic spheres are numerically analyzed in detail. The characteristics of the forward and backward RCSs in relation to the incident wavelength are also numerically studied. Selected results on the forward and backward RCSs of several types of square arrays of SiO₂ spheres illuminated by a plane wave with different incident angles are described. The accuracy of the expansion coefficients of the incident fields is verified by comparing them with the results obtained from references when the plane wave is degenerated to a z-propagating and x- or y-polarized plane wave. The validity of the theory is also confirmed by comparing the numerical results with those provided by a CST simulation.

  5. Sensing uniaxial tensile damage in fiber-reinforced polymer composites using electrical resistance tomography

    NASA Astrophysics Data System (ADS)

    Lestari, Wahyu; Pinto, Brian; La Saponara, Valeria; Yasui, Jennifer; Loh, Kenneth J.

    2016-08-01

    This work describes the application of electrical resistance tomography (ERT) in sensing damage in fiber-reinforced polymer composites under uniaxial quasi-static tension. Damage is manifested as numerous matrix cracks which are distributed across the composite volume and which eventually coalesce into intralayer cracks. Hence, tensile damage is distributed throughout the volume, and could be more significant outside the sensor area. In this work, tensile damage of unidirectional glass fiber-reinforced polymer composites (GFRP) and plain weave carbon fiber-reinforced polymer composites (CFRP) is sensed by utilizing a spray-on nanocomposite sensor, which is then instrumented by boundary electrodes. The resistance change distribution within the sensor area is reconstructed from a series of boundary voltage measurements, and ERT is implemented using a maximum a posteriori approach and assumptions on the type of noise in the reconstruction. Results show that this technique has promise in tracking uniaxial damage in composites. The different fiber architectures (unidirectional GFRP, plain weave CFRP) give distinct features in the ERT, which are consistent with the physical behavior of the tested samples.

  6. Damage tolerance of pressurized graphite/epoxy tape cylinders under uniaxial and biaxial loading. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Priest, Stacy Marie

    1993-01-01

    The damage tolerance behavior of internally pressurized, axially slit, graphite/epoxy tape cylinders was investigated. Specifically, the effects of axial stress, structural anisotropy, and subcritical damage were considered. In addition, the limitations of a methodology which uses coupon fracture data to predict cylinder failure were explored. This predictive methodology was previously shown to be valid for quasi-isotropic fabric and tape cylinders but invalid for structurally anisotropic (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders. The effects of axial stress and structural anisotropy were assessed by testing tape cylinders with (90/0/+/-45)(sub s), (+/-45/90)(sub s), and (+/-45/0)(sub s) layups in a uniaxial test apparatus, specially designed and built for this work, and comparing the results to previous tests conducted in biaxial loading. Structural anisotropy effects were also investigated by testing cylinders with the quasi-isotropic (0/+/-45/90)(sub s) layup which is a stacking sequence variation of the previously tested (90/0/+/-45)(sub s) layup with higher D(sub 16) and D(sub 26) terms but comparable D(sub 16) and D(sub 26) to D(sub 11) ratios. All cylinders tested and used for comparison are made from AS4/3501-6 graphite/epoxy tape and have a diameter of 305 mm. Cylinder slit lengths range from 12.7 to 50.8 mm. Failure pressures are lower for the uniaxially loaded cylinders in all cases. The smallest percent failure pressure decreases are observed for the (+/-45/90)(sub s) cylinders, while the greatest such decreases are observed for the (+/-45/0)(sub s) cylinders. The relative effects of the axial stress on the cylinder failure pressures do not correlate with the degree of structural coupling. The predictive methodology is not applicable for uniaxially loaded (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders, may be applicable for uniaxially loaded (90/0/+/-45)(sub s) cylinders, and is applicable for the biaxially loaded (90/0/+/-45)(sub s) and (0

  7. Uniaxial and biaxial mechanical properties of porcine linea alba.

    PubMed

    Cooney, Gerard M; Moerman, Kevin M; Takaza, Michael; Winter, Des C; Simms, Ciaran K

    2015-01-01

    Incisional hernia is a severe complication post-laparoscopic/laparotomy surgery that is commonly associated with the linea alba. However, the few studies on the mechanical properties of the linea alba in the literature appear contradictory, possible due to challenges with the physical dimensions of samples and variations in protocol. This study focuses on the tensile mechanical characterisation of the porcine linea alba, as determined by uniaxial and equi-load biaxial testing using image-based strain measurement methods. Results show that the linea alba demonstrated a non-linear elastic, anisotropic behaviour which is often observed in biological soft tissues. The transverse direction (parallel to fibres) was found to be approximately eight times stiffer than the longitudinal (cross-fibre) direction under both uniaxial and equi-load biaxial loading. The equi-load biaxial tensile tests revealed that contraction could occur in the transverse direction despite increasing load, probably due to the anisotropy of the tissue. Optical surface marker tracking and digital image correlation methods were found to greatly improve the accuracy of stretch measurement, resulting in a 75% change in the apparent stiffness compared to using strain derived from machine cross-head displacement. Additionally, a finite element model of the experiments using a combination of an Ogden and fibre exponential power law model for the linea alba was implemented to quantify the effect of clamping and tissue dimensions (which are suboptimal for tensile testing) on the results. The preliminary model results were used to apply a correction factor to the uniaxial experimental data prior to inverse optimisation to derive best fit material parameters for the fibre reinforced Ogden model. Application of the model to the equi-load biaxial case showed some differences compared to the experimental data, suggesting a more complex anisotropic model may be necessary to capture biaxial behaviour. These

  8. Excitation energy migration in uniaxially oriented polymer films

    NASA Astrophysics Data System (ADS)

    Bojarski, P.; Kamińska, A.; Kułak, L.; Sadownik, M.

    2003-07-01

    Multistep nonradiative excitation energy transport is for the first time studied in uniaxially stretched polymer films. Concentration depolarization studies performed for 3,3 '-diethylthiacarbocyanine iodide (DTCI) for stretched (system I) and unstretched (system II) polyvinyl alcohol films (PVA) yield extremely different results. As expected, disordered system II exhibits strong concentration depolarization due to energy migration between identical fluorophores. However, for stretched films, concentration depolarization effect is much weaker and it occurs at higher dye concentrations compared to system II. This fact is mostly due to strongly modified angular distribution of dipole moments of molecules taking part in the excitation energy migration.

  9. Elastic properties of granular materials under uniaxial compaction cycles

    NASA Technical Reports Server (NTRS)

    Warren, N.; Anderson, O. L.

    1973-01-01

    Data on andesitic and basaltic sands are presented showing compressional sound velocity, density, and creep as functions of uniaxial loading through several compaction cycles. Maximum pressures over which acoustic measurements were made were in the range from 600 to 700 bars. The dynamic elastic modulus varies with pressure in a manner analogous to that of a static elastic modulus defined by small pressure perturbations on a typical compaction cycle. After several compaction cycles, two compressional elastic moduli apparently exist at low pressure (thus two modes of compressional wave propagation through the samples are indicated). The elastic moduli observations are briefly discussed in terms of a general expression for compressibility.

  10. Uniaxial indefinite material formed by helical-shaped wires

    NASA Astrophysics Data System (ADS)

    Morgado, Tiago A.; Maslovski, Stanislav I.; Silveirinha, Mário G.

    2012-06-01

    We demonstrate that a racemic array of helical-shaped metallic wires may be regarded as a local uniaxial epsilon-negative (ENG) material even when the metal conductivity is very large (e.g. in the microwave regime) and, as a result, enables strong negative refraction over a wide frequency range. Based on the negative refraction effect, we demonstrate partial focusing of p-polarized electromagnetic radiation using a planar lens formed by such a composite material. The results reported here are supported by full-wave simulations as well as by analytical calculations based on effective medium theory.

  11. Cyclic uniaxial and biaxial hardening of type 304 stainless steel modeled by the viscoplasticity theory based on overstress

    NASA Technical Reports Server (NTRS)

    Yao, David; Krempl, Erhard

    1988-01-01

    The isotropic theory of viscoplasticity based on overstress does not use a yield surface or a loading and unloading criterion. The inelastic strain rate depends on overstress, the difference between the stress and the equilibrium stress, and is assumed to be rate dependent. Special attention is paid to the modeling of elastic regions. For the modeling of cyclic hardening, such as observed in annealed Type 304 stainless steel, and additional growth law for a scalar quantity which represents the rate independent asymptotic value of the equilibrium stress is added. It is made to increase with inelastic deformation using a new scalar measure which differentiates between nonproportional and proportional loading. The theory is applied to correlate uniaxial data under two step amplitude loading including the effect of further hardening at the high amplitude and proportional and nonproportional cyclic loadings. Results are compared with corresponding experiments.

  12. Children describe life after Hurricane Andrew.

    PubMed

    Coffman, S

    1994-01-01

    Hurricane Andrew, which devastated the south Florida coast in August 1992, left over 250,000 people homeless with multiple health and social problems. This nursing study explored the experiences of 17 children, ages 5 through 12, who lived in the geographic area of storm damage. Common experiences described by the children included remembering the storm, dealing with after-effects, and reestablishing a new life. In general, children described a sense of strangeness, articulated as "life is weird" after the hurricane. In addition to stressful responses, many positive reactions were described by children in the study, revealing that the disaster also had a maturing effect.

  13. Mechanical Behavior of Gamma-Met PX under Uniaxial Loading at Elevated Temperatures and High Strain Rates

    NASA Technical Reports Server (NTRS)

    Shazly, Mostafa; Prakash, Vikas; Draper, Susan

    2005-01-01

    Gamma titanium aluminides have received considerable attention over the last decade. These alloys are known to have low density, good high temperature strength retention and good oxidation and corrosion resistance. However, poor ductility and low fracture toughness have been the key limiting factors in the full utilization of these alloys. More recently, a new generation of gamma titanium aluminide alloys, commonly referred to as Gamma-met PX, has been developed by GKSS, Germany. These alloys have been observed to have superior strength and better oxidation resistance at elevated temperatures when compared with conventional gamma titanium aluminides. The present paper discusses results of a study to understand the uniaxial mechanical behavior in both compression and tension of Gamma-Met PX at elevated temperatures and high strain rates. The compression and tensile tests are conducted using a modified split-Hopkinson bar apparatus at test temperatures ranging from room temperature to 900 C and strain rates of up to 3500/s. Under uniaxial compression, in the temperature range from room to 600 C, the flow stress is observed to be nearly independent of test temperature. However, at temperatures higher than 600 C thermal softening is observed at all strain rates with the rate of thermal softening increasing dramatically between 800 C and 900 C. The room temperature tensile tests show negligible strain-rate dependence on both yield stress and flow stress. With an increase in test temperature from room to 900 C the material shows a drop in both yield and flow stress at all levels of plastic strain. However, the measured flow stress is still higher when compared to nickel based super-alloys and other gamma titanium aluminides under similar test conditions. Also, no anomaly in yield stress is observed up to 900 C.

  14. Uniaxial pressure setup for piezoresistance and magnetoresistance measurements in Heusler materials.

    PubMed

    Bourgault, D; Porcar, L; Bruyère, C; Jacquet, P; Courtois, P

    2013-01-01

    We report on a new uniaxial pressure experimental setup for electrical resistivity measurements working in a 77 K-500 K temperature range and in a magnetic field up to 8 T. Such a continuous uniaxial pressure device enables the study of the piezoresistance and the pressure induced change in electrical properties of bulk samples. Strong influence of uniaxial pressure on transport properties is shown for Ni-Co-Mn-In Heusler single crystal material. A shift of the martensite-austenite first order transformation temperature is measured with an applied uniaxial pressure leading to an electrical resistance changed by up to 120%.

  15. Uniaxial alignment of liquid-crystalline conjugated polymers by nanoconfinement.

    PubMed

    Zheng, Zijian; Yim, Keng-Hoong; Saifullah, Mohammad S M; Welland, Mark E; Friend, Richard H; Kim, Ji-Seon; Huck, Wilhelm T S

    2007-04-01

    We demonstrate the uniaxial alignment of a liquid-crystalline conjugated polymer, poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) by means of nanoconfinement during nanoimprinting. The orientation of the conjugated backbones was parallel to the nanolines imprinted into the polymer film. Polarized UV-vis absorption and photoluminescence spectra were measured to quantify the degree of alignment, showing that the polarization ratio and uniaxial molecular order parameter were as high as 66 and 0.97, respectively. The aligned F8BT film was used as the active layer in a PLED, which resulted in polarized electroluminescence with a polarization ratio of 11. Ambipolar PFET in a top-gate configuration with aligned F8BT as the active semiconducting layer showed mobility enhancement when the chains were aligned parallel to the transport direction. Mobility anisotropies for hole and electron transport were 10-15 and 5-7, respectively, for current flow parallel and perpendicular to the alignment direction.

  16. Pseudodielectric Functions of Uniaxial Materials in Certain Symmetry Directions

    SciTech Connect

    Jellison Jr, Gerald Earle; Baba, Justin S

    2006-01-01

    The pseudodielectric function is often used to represent ellipsometric data and corresponds to the actual dielectric functions of materials when there is no surface overlayer and the material is isotropic. If a uniaxial material is oriented such that the optic axis is in the plane of incidence or is perpendicular to the plane of incidence, then the cross-polarization terms are zero and appropriate pseudodielectric functions can be determined from the ellipsometry data. We calculate the pseudodielectric functions for uniaxial crystals in three primary symmetry directions: (1) the optic axis is perpendicular to the plane of incidence, (2) the optic axis is in the plane of the sample surface and parallel to the plane of incidence, and (3) the optic axis is in the plane of the sample surface and perpendicular to the plane of incidence. These results are expanded in terms of the difference in the ordinary and extraordinary dielectric functions and compared with the approximation ofAspnes [J. Opt. Soc. Am.70, 1275 (1980)]. Comparisons are made with experimental results on oriented crystals of rutile (TiO2), and a simple procedure is presented to determine the complex dielectric function from standard ellipsometry techniques.

  17. Agitated granular rod monolayers: Tetratic or uniaxial nematic?

    NASA Astrophysics Data System (ADS)

    Mueller, Thomas; de Las Heras, Daniel; Rehberg, Ingo; Huang, Kai

    The ordering of granular rod monolayers under vertical agitations against gravity is investigated experimentally and compared quantitatively with equilibrium Monte Carlo simulations and density functional theory. At sufficiently high number density, short rods form a tetratic state and long rods form a uniaxial nematic state. The ordering transitions are found to be independent of the agitation frequency and strength, suggesting that the detailed nature of energy injection into such a nonequilibrium system does not play a crucial role. Interestingly, the length-to-width ratio at which the order changes from tetratic to uniaxial is around 7 . 3 in both experiments and simulations. This quantitative agreement indicates that, despite of driven far from thermodynamic equilibrium, agitated granular systems may share similar features with corresponding equilibrium systems. Finally, we summarize the universal and non-universal aspects between nonequilibrium granular rod and equilibrium liquid crystal systems in a state diagram. Tm and KH acknowledge the support from the DFG through Grant No. HU1939/2-1.

  18. Stress

    MedlinePlus

    ... hurt or killed. Examples include a major accident, war, assault, or a natural disaster. This type of ... stress, so you can avoid more serious health effects. NIH: National Institute of Mental Health

  19. An Approach to Model Neutron Diffraction Pattern of Uniaxial Deformed Sandstone Using Elastic Properties of Quartz

    NASA Astrophysics Data System (ADS)

    Breuer, S.; Schilling, F. R.; Mueller, B.; Scheffzuek, C.

    2015-12-01

    Mechanical properties of sedimentary rocks such as stress-strain-relations are essential for understanding dynamic processes within the Earth's crust. The measurement of in-situ lattice strain in bulk samples is possible with diffraction methods, e.g. with neutrons. The advantage of neutron diffraction is their high penetration depth, which enables to gather a statistically relevant number of grains by diffraction. The neutron time-of-flight diffraction at the strain diffractometer EPSILON which is located at the pulsed neutron source IBR-2M (JINR Dubna, RUS) enables the detection of the complete diffraction pattern up to λ = 7.1 Å (d = 5.1 Å). Uniaxial cyclic deformation experiments were carried out up to 50 MPa (three steps) on a macroscopically isotropic sandstone from Kuhbach / Lahr (Germany). The aim of the present study is to model diffraction patterns for different applied stress-levels, based on the zero-stress diffraction pattern and known elastic properties of Quartz single crystals. The as received model-predictions are compared to observations, both, in the direction of maximum stress (along the cylindric axis) and perpendicular to it. The results show that the shape of the grains has an influence on the macroscopic elastic behavior of the rock whereas the microscopic strain is affected in a different manner. The model is based on spherical quartz grains. The spheres are divided into slices. By removing some slices, the shape of sand grains is approximated. The reaction of each slice through the applied stress is modelled. Together with the relative volume of each slice and it´s elastic behavior, the diffraction pattern is predicted for different applied loads. Measured and modelled diffraction-patterns at different applied loads are in good agreement.

  20. Effect of thermal exposure on the residual stress relaxation in a hardened cylindrical sample under creep conditions

    NASA Astrophysics Data System (ADS)

    Radchenko, V. P.; Saushkin, M. N.; Tsvetkov, V. V.

    2016-05-01

    This paper describes the effect of thermal exposure (high-temperature exposure) ( T = 675°C) on the residual creep stress relaxation in a surface hardened solid cylindrical sample made of ZhS6UVI alloy. The analysis is carried out with the use of experimental data for residual stresses after micro-shot peening and exposures to temperatures equal to T = 675°C during 50, 150, and 300 h. The paper presents the technique for solving the boundary-value creep problem for the hardened cylindrical sample with the initial stress-strain state under the condition of thermal exposure. The uniaxial experimental creep curves obtained under constant stresses of 500, 530, 570, and 600 MPa are used to construct the models describing the primary and secondary stages of creep. The calculated and experimental data for the longitudinal (axial) tensor components of residual stresses are compared, and their satisfactory agreement is determined.

  1. Metallographic examinations of Type 304 stainless steel (heat 9T2796) tested in high-temperature uniaxial and multiaxial experiments

    SciTech Connect

    Swindeman, R.W.; Houck, C.W.

    1984-03-01

    The results obtained from a number of metallographic examinations of Type 304 stainless steel specimens were compiled. Samples were obtained from uniaxial and multiaxial tests covering a very broad span of temperatures and times. Special emphasis was on the identification of failure modes, cracking patterns, grain distortion, and grain-boundary microstructures. Uniaxial specimens exhibited the following sequence of failure modes with increasing temperature and time: ductile plastic tearing, ductile plastic shear, wedge cracking, and microvoid cracking. Over most of the temperature range examined (482 to 871/sup 0/C), M/sub 23/C/sub 6/ precipitated on grain boundaries at long times. Sigma phase and possibly ferrite were often present in the stressed areas at temperatures as low as 482/sup 0/C (900/sup 0/F). These metallurgical features promoted a severe loss in creep ductility at long times and low temperatures. Most multiaxial tests were performed under conditions that promoted wedge cracking. Stress gradients also favored surface crack initiation rather than bulk damage. Testing times for multiaxial tests were less than 10,000 h; hence, there was insufficient time for the development of embrittling features such as microvoids, sigma, and ferrite. Long-time multiaxial tests to failure are recommended.

  2. Pre-Peak and Post-Peak Rock Strain Characteristics During Uniaxial Compression by 3D Digital Image Correlation

    NASA Astrophysics Data System (ADS)

    Munoz, H.; Taheri, A.; Chanda, E. K.

    2016-07-01

    A non-contact optical method for strain measurement applying three-dimensional digital image correlation (3D DIC) in uniaxial compression is presented. A series of monotonic uniaxial compression tests under quasi-static loading conditions on Hawkesbury sandstone specimens were conducted. A prescribed constant lateral-strain rate to control the applied axial load in a closed-loop system allowed capturing the complete stress-strain behaviour of the rock, i.e. the pre-peak and post-peak stress-strain regimes. 3D DIC uses two digital cameras to acquire images of the undeformed and deformed shape of an object to perform image analysis and provides deformation and motion measurements. Observations showed that 3D DIC provides strains free from bedding error in contrast to strains from LVDT. Erroneous measurements due to the compliance of the compressive machine are also eliminated. Furthermore, by 3D DIC technique relatively large strains developed in the post-peak regime, in particular within localised zones, difficult to capture by bonded strain gauges, can be measured in a straight forward manner. Field of strains and eventual strain localisation in the rock surface were analysed by 3D DIC method, coupled with the respective stress levels in the rock. Field strain development in the rock samples, both in axial and shear strain domains suggested that strain localisation takes place progressively and develops at a lower rate in pre-peak regime. It is accelerated, otherwise, in post-peak regime associated with the increasing rate of strength degradation. The results show that a major failure plane, due to strain localisation, becomes noticeable only long after the peak stress took place. In addition, post-peak stress-strain behaviour was observed to be either in a form of localised strain in a shearing zone or inelastic unloading outside of the shearing zone.

  3. Two touching spherical drops in a uniaxial compressional flow: The effect of interfacial slip

    NASA Astrophysics Data System (ADS)

    Goel, Sachin; Ramachandran, Arun

    2016-05-01

    This study presents a semi-analytical solution for the problem of two touching drops with slipping interfaces pushed against each other in a uniaxial compressional flow at low capillary and Reynolds numbers. The jump in the tangential velocity at the liquid-liquid interface is modeled using the Navier slip condition. Analytical solutions of the contact force, the drop-scale stresses, and the drop-scale pressure are provided as functions of the slip coefficient (" separators=" α ) , the viscosity ratio (" separators=" κ ) , and the drop size ratio (" separators=" k ) . Since unequal drop sizes are considered, two problems are solved in the tangent sphere co-ordinate system to determine the steady state position: a pair of touching drops with its contact point at the origin of an axisymmetric straining flow, and two touching drops placed in a uniform flow parallel to the axis of symmetry of the drops. A general observation is that the effect of slip is manifested most strongly for drops whose viscosity is much greater than the suspending fluid (" separators=" κ ≫ 1 ) . For highly viscous drops, the flow and stress fields transition from those corresponding to solid particles for ακ ≪ 1, to those for inviscid drops in the limit ακ ≫ 1. The analytical expressions provided here for the contact force and the stress distributions will serve to provide the restrictions that complete the definition of the lubrication flow problem in the thin film between the two colliding drops. While the contact force that drains fluid out of the thin film is relatively unaffected by slip, the tangential stress and pressure in the near-contact region are mitigated significantly for ακ ≫ 1. The latter is expected to assist coalescence at high capillary numbers.

  4. Enhancing the operational range of piezoelectric actuators by uniaxial compressive preloading

    NASA Astrophysics Data System (ADS)

    Koruza, Jurij; Franzbach, Daniel J.; Schader, Florian; Rojas, Virginia; Webber, Kyle G.

    2015-06-01

    The influence of the uniaxial preload on the off-resonance actuation performance of piezoelectric ceramics was investigated for compressive preload values up to  -80 MPa. The study was performed on soft-type lead zirconate titanate (PZT), being the most widely used piezoelectric material. The samples were analysed using the proportional loading method, which enables the simultaneous application of electrical and mechanical loads, thereby mimicking the real operation conditions over the full stress-strain range. An increase of the blocking stress and the longitudinal piezoelectric stress coefficient was observed for all the applied preload values. The optimum properties, a blocking stress of  -56 MPa and a free strain of 0.23%, were obtained at a preload value of  -40 MPa and electric field of 2 kV mm  -  1. This represents an increase of 16% and 20%, respectively, as compared to the values obtained at the smallest preload. In addition, the maximum work output was increased by about 28%. Finally, the results obtained at the lowest preload of  -4 MPa using the proportional loading method were compared to the operational ranges determined by other methods. The comparison revealed large discrepancies between the methods, originating from the different order of the application of electrical and mechanical fields and the inherent nonlinearity of ferroelectric materials. This discrepancy results in decreased actuator performance due to impedance mismatching, demonstrating the need for accurate determination of the actuator’s operational range.

  5. Constitutive modelling of fiber-reinforced concrete under uniaxial tensile loading

    NASA Astrophysics Data System (ADS)

    Kullaa, Jyrki

    1993-01-01

    The mechanics of fiber reinforced concrete under uniaxial loading is studied. The focus is on the behavior after cracking. The interaction between the fiber and the matrix is the shear stress transfer. The stress can be elastic or frictional in nature. The bond parameters can be obtained by a simple pull-out test and theory. The load displacement curves for fibers of different lengths can be created by means of the calculated parameters. In a simple constitutive model, the main assumption is that the fibers are continuous and there exists multiple cracking in the matrix. After cracking, the fibers only carry the loading. The model uses efficiency factors in taking into account the short and randomly distributed fibers. Only the strengthening portion of the stress strain curve is analyzed. In the statistical model created, it is assumed that only one crack will develop. The theory ignores the strain of the matrix in fiber pull-out. The strain softening behavior is taken into consideration. A constitutive model which takes into account the strain softening part of the stress strain curve is developed. The crack distance and crack width are also calculated. The model takes into account one crack or multiple cracking states and different fracture mechanisms: fiber fracture or pull-out. The fibers are smooth and straight. They can be short or continuous, aligned or randomly distributed, brittle or ductile, and stiff or flexible.

  6. Ultrasonic diffraction of Bessel light beams in uniaxial gyrotropic crystals

    NASA Astrophysics Data System (ADS)

    Belyi, V. N.; Kulak, G. V.; Krokh, G. V.; Ropot, P. I.; Shakin, O. V.

    2016-09-01

    Specific features of the acousto-optic diffraction of Bessel light beams propagating in the vicinity of the optical axis of a uniaxial gyrotropic crystal have been investigated. The dependences of the diffraction efficiency on the acousto-optic interaction length, ultrasound power, and polarization state of the incident Bessel light beam have been analyzed using the coupled-wave equations and the overlap-integral method. It is shown that polarization-independent diffraction of Bessel light beams is observed in paratellurite crystals, when the Bragg diffraction efficiency is independent of the polarization state of the incident beam. The physical reason for this diffraction has been established (both theoretically and experimentally) to be simultaneous implementation of two processes of anisotropic scattering, at which the Bragg synchronism conditions are satisfied for orthogonal polarized Bessel beams with elliptical polarization.

  7. Classifying Human Leg Motions with Uniaxial Piezoelectric Gyroscopes

    PubMed Central

    Tunçel, Orkun; Altun, Kerem; Barshan, Billur

    2009-01-01

    This paper provides a comparative study on the different techniques of classifying human leg motions that are performed using two low-cost uniaxial piezoelectric gyroscopes worn on the leg. A number of feature sets, extracted from the raw inertial sensor data in different ways, are used in the classification process. The classification techniques implemented and compared in this study are: Bayesian decision making (BDM), a rule-based algorithm (RBA) or decision tree, least-squares method (LSM), k-nearest neighbor algorithm (k-NN), dynamic time warping (DTW), support vector machines (SVM), and artificial neural networks (ANN). A performance comparison of these classification techniques is provided in terms of their correct differentiation rates, confusion matrices, computational cost, and training and storage requirements. Three different cross-validation techniques are employed to validate the classifiers. The results indicate that BDM, in general, results in the highest correct classification rate with relatively small computational cost. PMID:22291521

  8. Propagation of Airy Gaussian vortex beams in uniaxial crystals

    NASA Astrophysics Data System (ADS)

    Weihao, Yu; Ruihuang, Zhao; Fu, Deng; Jiayao, Huang; Chidao, Chen; Xiangbo, Yang; Yanping, Zhao; Dongmei, Deng

    2016-04-01

    The propagation dynamics of the Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis has been investigated analytically and numerically. The propagation expression of the beams has been obtained. The propagation features of the Airy Gaussian vortex beams are shown with changes of the distribution factor and the ratio of the extraordinary refractive index to the ordinary refractive index. The correlations between the ratio and the maximum intensity value during the propagation, and its appearing distance have been investigated. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374108, 11374107, 10904041, and 11547212), the Foundation of Cultivating Outstanding Young Scholars of Guangdong Province, China, the CAS Key Laboratory of Geospace Environment, University of Science and Technology of China, the National Training Program of Innovation and Entrepreneurship for Undergraduates (Grant No. 2015093), and the Science and Technology Projects of Guangdong Province, China (Grant No. 2013B031800011).

  9. Polaron and bipolaron of uniaxially strained one dimensional zigzag ladder

    NASA Astrophysics Data System (ADS)

    Yavidov, B. Ya.

    2016-09-01

    An influence of the uniaxial strains in one dimensional zigzag ladder (1DZL) on the properties of polarons and bipolarons is considered. It is shown that strain changes all the parameters of the system, in particular, spectrum, existing bands and the masses of charge carriers. Numerical results obtained by taking into an account the Poisson effect clearly indicate that the properties of the (bi)polaronic system can be tuned via strain. Mass of bipolaron can be manipulated by the strain too which in turn leads to the way of tuning Bose-Einstein condensation temperature TBEC of bipolarons. It is shown that TBEC of bipolarons in strained 1DZL reasonably correlates with the values of critical temperature of superconductivity of certain perovskites.

  10. Propagation of Airy Gaussian vortex beams in uniaxial crystals

    NASA Astrophysics Data System (ADS)

    Weihao, Yu; Ruihuang, Zhao; Fu, Deng; Jiayao, Huang; Chidao, Chen; Xiangbo, Yang; Yanping, Zhao; Dongmei, Deng

    2016-04-01

    The propagation dynamics of the Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis has been investigated analytically and numerically. The propagation expression of the beams has been obtained. The propagation features of the Airy Gaussian vortex beams are shown with changes of the distribution factor and the ratio of the extraordinary refractive index to the ordinary refractive index. The correlations between the ratio and the maximum intensity value during the propagation, and its appearing distance have been investigated. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374108, 11374107, 10904041, and 11547212), the Foundation of Cultivating Outstanding Young Scholars of Guangdong Province, China, the CAS Key Laboratory of Geospace Environment, University of Science and Technology of China, the National Training Program of Innovation and Entrepreneurship for Undergraduates (Grant No. 2015093), and the Science and Technology Projects of Guangdong Province, China (Grant No. 2013B031800011).

  11. Programmable Extreme Pseudomagnetic Fields in Graphene by a Uniaxial Stretch.

    PubMed

    Zhu, Shuze; Stroscio, Joseph A; Li, Teng

    2015-12-11

    Many of the properties of graphene are tied to its lattice structure, allowing for tuning of charge carrier dynamics through mechanical strain. The graphene electromechanical coupling yields very large pseudomagnetic fields for small strain fields, up to hundreds of Tesla, which offer new scientific opportunities unattainable with ordinary laboratory magnets. Significant challenges exist in investigation of pseudomagnetic fields, limited by the nonplanar graphene geometries in existing demonstrations and the lack of a viable approach to controlling the distribution and intensity of the pseudomagnetic field. Here we reveal a facile and effective mechanism to achieve programmable extreme pseudomagnetic fields with uniform distributions in a planar graphene sheet over a large area by a simple uniaxial stretch. We achieve this by patterning the planar graphene geometry and graphene-based heterostructures with a shape function to engineer a desired strain gradient. Our method is geometrical, opening up new fertile opportunities of strain engineering of electronic properties of 2D materials in general.

  12. Damage mechanisms in uniaxial compression of single enamel rods.

    PubMed

    An, Bingbing; Wang, Raorao; Arola, Dwayne; Zhang, Dongsheng

    2015-02-01

    Enamel possesses a complex hierarchical structure, which bestows this tissue with unique mechanical properties. In this study, the mechanical behavior of single enamel rods was investigated under uniaxial compression. Numerical simulations were also performed using micromechanics models for individual enamel rods to identify the damage mechanisms contributing to the constitutive behavior. Experimental results showed that the single rods exhibited an elastic modulus ranging from 10~31 GPa, and that they undergo post-yield strain-hardening. The primary damage mode consisted of delamination within the assembly of mineral crystals. Results from numerical simulations suggest that strain localization within individual rods is responsible for the observed delamination, which is believed to arise from the non-uniform arrangement of mineral crystals. This mechanism was independent of mineral morphology and properties. The non-uniform crystal arrangement results in friction between crystals with different inclination angles and is believed to be responsible for the post-yield strain hardening behavior. PMID:25460920

  13. Perturbed fundamental solitons in nonlocal uniaxial nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Strinić, Aleksandra I.; Petrović, Milan S.; Aleksić, Najdan B.; Belić, Milivoj R.

    2013-01-01

    We generate perturbed fundamental solitons in three dimensional highly nonlocal uniaxial nematic liquid crystals in the presence of an externally applied bias voltage, by launching specific Gaussian beams into the liquid crystal cell. In general, launching Gaussians leads to their dispersal for low intensities and small widths, and to their instabilities for high intensities and large widths. Localized solutions in the form of well defined breathing solitons are observed only for the well defined values of the input beam intensity and width, which can be determined by a variational technique. In this case, the oscillating Gaussian beam characteristics are close to the perturbed breathing fundamental soliton solutions, with the characteristics well-predicted by the variational calculation.

  14. Scalar Casimir-Polder forces for uniaxial corrugations

    SciTech Connect

    Doebrich, Babette; DeKieviet, Maarten; Gies, Holger

    2008-12-15

    We investigate the Dirichlet-scalar equivalent of Casimir-Polder forces between an atom and a surface with arbitrary uniaxial corrugations. The complexity of the problem can be reduced to a one-dimensional Green's function equation along the corrugation which can be solved numerically. Our technique is fully nonperturbative in the height profile of the corrugation. We present explicit results for experimentally relevant sinusoidal and sawtooth corrugations. Parameterizing the deviations from the planar limit in terms of an anomalous dimension which measures the power-law deviation from the planar case, we observe up to order-one anomalous dimensions at small and intermediate scales and a universal regime at larger distances. This large-distance universality can be understood from the fact that the relevant fluctuations average over corrugation structures smaller than the atom-wall distance.

  15. Molecular dynamics simulations of uniaxial deformation of thermoplastic polyimides.

    PubMed

    Nazarychev, V M; Lyulin, A V; Larin, S V; Gurtovenko, A A; Kenny, J M; Lyulin, S V

    2016-05-01

    The results of atomistic molecular-dynamics simulations of mechanical properties of heterocyclic polymer subjected to uniaxial deformation are reported. A new amorphous thermoplastic polyimide R-BAPO with a repeat unit consisting of dianhydride 1,3-bis-(3',4,-dicarboxyphenoxy)diphenyl (dianhydride R) and diamine 4,4'-bis-(4''-aminophenoxy)diphenyloxide (diamine BAPO) was chosen for the simulations. Our primary goal was to establish the impact of various factors (sample preparation method, molecular mass, and cooling and deformation rates) on the elasticity modulus. In particular, we found that the elasticity modulus was only slightly affected by the degree of equilibration, the molecular mass and the size of the simulation box. This is most likely due to the fact that the main contribution to the elasticity modulus is from processes on scales smaller than the entanglement length. Essentially, our simulations reproduce the logarithmic dependence of the elasticity modulus on cooling and deformation rates, which is normally observed in experiments. With the use of the temperature dependence analysis of the elasticity modulus we determined the flow temperature of R-BAPO to be 580 K in line with the experimental data available. Furthermore, we found that the application of high external pressure to the polymer sample during uniaxial deformation can improve the mechanical properties of the polyimide. Overall, the results of our simulations clearly demonstrate that atomistic molecular-dynamics simulations represent a powerful and accurate tool for studying the mechanical properties of heterocyclic polymers and can therefore be useful for the virtual design of new materials, thereby supporting cost-effective synthesis and experimental research. PMID:27033967

  16. An Experimental and Numerical Study on Cracking Behavior of Brittle Sandstone Containing Two Non-coplanar Fissures Under Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Yang, Sheng-Qi; Tian, Wen-Ling; Huang, Yan-Hua; Ranjith, P. G.; Ju, Yang

    2016-04-01

    To understand the fracture mechanism in all kinds of rock engineering, it is important to investigate the fracture evolution behavior of pre-fissured rock. In this research, we conducted uniaxial compression experiments to evaluate the influence of ligament angle on the strength, deformability, and fracture coalescence behavior of rectangular prismatic specimens (80 × 160 × 30 mm) of brittle sandstone containing two non-coplanar fissures. The experimental results show that the peak strength of sandstone containing two non-coplanar fissures depends on the ligament angle, but the elastic modulus is not closely related to the ligament angle. With the increase of ligament angle, the peak strength decreased at a ligament angle of 60°, before increasing up to our maximum ligament angle of 120°. Crack initiation, propagation, and coalescence were all observed and characterized from the inner and outer tips of pre-existing non-coplanar fissures using photographic monitoring. Based on the results, the sequence of crack evolution in sandstone containing two non-coplanar fissures was analyzed in detail. In order to fully understand the crack evolution mechanism of brittle sandstone, numerical simulations using PFC2D were performed for specimens containing two non-coplanar fissures under uniaxial compression. The results are in good agreement with the experimental results. By analyzing the stress field, the crack evolution mechanism in brittle sandstone containing two non-coplanar fissures under uniaxial compression is revealed. These experimental and numerical results are expected to improve the understanding of the unstable fracture mechanism of fissured rock engineering structures.

  17. How to describe disordered structures

    PubMed Central

    Nishio, Kengo; Miyazaki, Takehide

    2016-01-01

    Disordered structures such as liquids and glasses, grains and foams, galaxies, etc. are often represented as polyhedral tilings. Characterizing the associated polyhedral tiling is a promising strategy to understand the disordered structure. However, since a variety of polyhedra are arranged in complex ways, it is challenging to describe what polyhedra are tiled in what way. Here, to solve this problem, we create the theory of how the polyhedra are tiled. We first formulate an algorithm to convert a polyhedron into a codeword that instructs how to construct the polyhedron from its building-block polygons. By generalizing the method to polyhedral tilings, we describe the arrangements of polyhedra. Our theory allows us to characterize polyhedral tilings, and thereby paves the way to study from short- to long-range order of disordered structures in a systematic way. PMID:27064833

  18. How to describe disordered structures.

    PubMed

    Nishio, Kengo; Miyazaki, Takehide

    2016-01-01

    Disordered structures such as liquids and glasses, grains and foams, galaxies, etc. are often represented as polyhedral tilings. Characterizing the associated polyhedral tiling is a promising strategy to understand the disordered structure. However, since a variety of polyhedra are arranged in complex ways, it is challenging to describe what polyhedra are tiled in what way. Here, to solve this problem, we create the theory of how the polyhedra are tiled. We first formulate an algorithm to convert a polyhedron into a codeword that instructs how to construct the polyhedron from its building-block polygons. By generalizing the method to polyhedral tilings, we describe the arrangements of polyhedra. Our theory allows us to characterize polyhedral tilings, and thereby paves the way to study from short- to long-range order of disordered structures in a systematic way. PMID:27064833

  19. Stretch calculated from grip distance accurately approximates mid-specimen stretch in large elastic arteries in uniaxial tensile tests.

    PubMed

    Tian, Lian; Henningsen, Joseph; Salick, Max R; Crone, Wendy C; Gunderson, McLean; Dailey, Seth H; Chesler, Naomi C

    2015-07-01

    The mechanical properties of vascular tissues affect hemodynamics and can alter disease progression. The uniaxial tensile test is a simple and effective method for determining the stress-strain relationship in arterial tissue ex vivo. To enable calculation of strain, stretch can be measured directly with image tracking of markers on the tissue or indirectly from the distance between the grips used to hold the specimen. While the imaging technique is generally considered more accurate, it also requires more analysis, and the grip distance method is more widely used. The purpose of this study is to compare the stretch of the testing specimen calculated from the grip distance method to that obtained from the imaging method for canine descending aortas and large proximal pulmonary arteries. Our results showed a significant difference in stretch between the two methods; however, this difference was consistently less than 2%. Therefore, the grip distance method is an accurate approximation of the stretch in large elastic arteries in the uniaxial tensile test. PMID:25881308

  20. Intergranular stress distributions in polycrystalline aggregates of irradiated stainless steel

    NASA Astrophysics Data System (ADS)

    Hure, J.; El Shawish, S.; Cizelj, L.; Tanguy, B.

    2016-08-01

    In order to predict InterGranular Stress Corrosion Cracking (IGSCC) of post-irradiated austenitic stainless steel in Light Water Reactor (LWR) environment, reliable predictions of intergranular stresses are required. Finite elements simulations have been performed on realistic polycrystalline aggregate with recently proposed physically-based crystal plasticity constitutive equations validated for neutron-irradiated austenitic stainless steel. Intergranular normal stress probability density functions are found with respect to plastic strain and irradiation level, for uniaxial loading conditions. In addition, plastic slip activity jumps at grain boundaries are also presented. Intergranular normal stress distributions describe, from a statistical point of view, the potential increase of intergranular stress with respect to the macroscopic stress due to grain-grain interactions. The distributions are shown to be well described by a master curve once rescaled by the macroscopic stress, in the range of irradiation level and strain considered in this study. The upper tail of this master curve is shown to be insensitive to free surface effect, which is relevant for IGSCC predictions, and also relatively insensitive to small perturbations in crystallographic texture, but sensitive to grain shapes.

  1. An experimental study on fracture mechanical behavior of rock-like materials containing two unparallel fissures under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Huang, Yan-Hua; Yang, Sheng-Qi; Tian, Wen-Ling; Zeng, Wei; Yu, Li-Yuan

    2016-06-01

    Strength and deformability characteristics of rock with pre-existing fissures are governed by cracking behavior. To further research the effects of pre-existing fissures on the mechanical properties and crack coalescence process, a series of uniaxial compression tests were carried out for rock-like material with two unparallel fissures. In the present study, cement, quartz sand, and water were used to fabricate a kind of brittle rock-like material cylindrical model specimen. The mechanical properties of rock-like material specimen used in this research were all in good agreement with the brittle rock materials. Two unparallel fissures (a horizontal fissure and an inclined fissure) were created by inserting steel during molding the model specimen. Then all the pre-fissured rock-like specimens were tested under uniaxial compression by a rock mechanics servo-controlled testing system. The peak strength and Young's modulus of pre-fissured specimen all first decreased and then increased when the fissure angle increased from 0° to 75°. In order to investigate the crack initiation, propagation and coalescence process, photographic monitoring was adopted to capture images during the entire deformation process. Moreover, acoustic emission (AE) monitoring technique was also used to obtain the AE evolution characteristic of pre-fissured specimen. The relationship between axial stress, AE events, and the crack coalescence process was set up: when a new crack was initiated or a crack coalescence occurred, the corresponding axial stress dropped in the axial stress-time curve and a big AE event could be observed simultaneously. Finally, the mechanism of crack propagation under microscopic observation was discussed. These experimental results are expected to increase the understanding of the strength failure behavior and the cracking mechanism of rock containing unparallel fissures.

  2. The nonlinear material properties of liver tissue determined from no-slip uniaxial compression experiments.

    PubMed

    Roan, Esra; Vemaganti, Kumar

    2007-06-01

    The mechanical response of soft tissue is commonly characterized from unconfined uniaxial compression experiments on cylindrical samples. However, friction between the sample and the compression platens is inevitable and hard to quantify. One alternative is to adhere the sample to the platens, which leads to a known no-slip boundary condition, but the resulting nonuniform state of stress in the sample makes it difficult to determine its material parameters. This paper presents an approach to extract the nonlinear material properties of soft tissue (such as liver) directly from no-slip experiments using a set of computationally determined correction factors. We assume that liver tissue is an isotropic, incompressible hyperelastic material characterized by the exponential form of strain energy function. The proposed approach is applied to data from experiments on bovine liver tissue. Results show that the apparent material properties, i.e., those determined from no-slip experiments ignoring the no-slip conditions, can differ from the true material properties by as much as 50% for the exponential material model. The proposed correction approach allows one to determine the true material parameters directly from no-slip experiments and can be easily extended to other forms of hyperelastic material models. PMID:17536913

  3. A Quasicontinuum Study of Nanovoid Collapse under Uniaxial Loading in Ta

    SciTech Connect

    Marian, J; Knap, J; Campbell, G

    2007-12-02

    The mechanisms underlying the deformation of nanovoids in Ta single crystals are analyzed when they are subjected to cyclic uniaxial deformation using numerical simulations. Boundary and cell-size effects have been mitigated by means of the Quasicontinuum (QC) method. We have considered {approx} 1 billion-atom systems containing 10.9 nm voids. Two kinds of simulations have been performed, each characterized by a different boundary condition. First, we compress the material along the nominal [0 0 1] direction, resulting in a highly symmetric configuration that results in high stresses. Second, we load the material along the high-index [{bar 4}819] direction to confine plasticity to a single slip system and break the symmetry. We find that the plastic response under these two conditions is strikingly different, the former governed by dislocation loop emission and dipole formation, while the latter is dominated by twinning. We calculate the irreversible plastic work budget derived from a loading-unloading cycle and identify the most relevant yield points. These calculations represent the first fully three-dimensional, fully non-local simulations of any body-centered cubic metal using QC.

  4. Failure Investigation for QP Steel Sheets under uniaxial and Equal-Biaxial Tension Conditions

    NASA Astrophysics Data System (ADS)

    Zou, Danqing; Li, Shuhui; He, Ji; Cui, Ronggao

    2016-08-01

    The Quenching and Partitioning (QP) steel sheet is new generation material to induce phase transformation for plasticity in forming vehicle parts. The phase transformation is strongly stress state dependent behavior in experiments, which should affect the failure timing and limit strain in forming processes. In this paper, Nakajima test with QP980 and DP1000 steel sheets under equal-biaxial loading condition is performed for failure behavior. X-ray diffraction (XRD) is adopted to obtain the volume fraction of retained austenite (fA). Digital Image Correlation (DIC) is used to record the surface strain field and its evolution during equal-biaxial tension deformation. The same level Dual Phase (DP) steel is also employed for the purpose of comparison. The results show that phase transformation in QP steel gives small impact on failure strain under equal biaxial tension condition which is contradicted with our understanding. It suggests that failure behavior under uniaxial tension of QP980 is strongly phase transformation dependent. But it shows almost independent under equal biaxial tension condition.

  5. An open-end burst test method to obtain uniaxial hoop tensile properties of fuel cladding in a hot cell

    NASA Astrophysics Data System (ADS)

    Nakatsuka, Masafumi; Aita, Makoto; Sakamoto, Kan; Higuchi, Toru

    2013-03-01

    The hoop stress-hoop strain relationship of fuel cladding is one of the essential input parameters for safety analysis of fuel rods. The three objectives of this paper were: to propose a burst test method for open-end tube specimens with the uniaxial hoop stress condition; to develop the necessary in-cell high temperature open-end burst (OEB) techniques to implement the method; and to determine the optimum specimen length for the proposed OEB test method. Silicone oil was selected as the pressurization medium, and it was sealed inside the specimens not by welding but by O-rings so that no axial tensile stress was induced in the specimens. The specimens with combined end plugs and O-rings were successfully assembled by manipulators in a hot cell, and a high temperature (⩽350 °C), high pressure (⩽100 MPa) seal was achieved. The optimum specimen length was determined by using ductile and embrittled tubes with various lengths of 30-60 mm and was found to be around 45 mm for typical BWR fuel rods. During the OEB test, internal pressure and diametral expansion were monitored to obtain the basic mechanical performance properties of the fuel cladding such as yield stress, ultimate strength, as well as the true hoop stress-hoop strain curve.

  6. Uniaxial magnetic anisotropy induced low field anomalous anisotropic magnetoresistance in manganite thin films

    NASA Astrophysics Data System (ADS)

    Liao, Zhaoliang; Huijben, Mark; Koster, Gertjan; Rijnders, Guus

    2014-09-01

    La2/3Sr1/3MnO3 films with uniaxial magnetic anisotropy were coherently grown on NdGaO3 (110) substrates. The uniaxial anisotropy has strong effect on magnetoresistance (MR). A positive MR was observed when the current is along magnetic easy axis under the current-field perpendicular geometry. In contrast, no positive MR is observed when current is along the magnetic hard axis regardless of the field direction. Our analysis indicates that the anomalous anisotropic MR effect arises from the uniaxial magnetic anisotropy caused stripe domains which contribute to strong anisotropic domain wall resistivity.

  7. Theory of third-order spectroscopic methods to extract detailed molecular orientational dynamics for planar surfaces and other uniaxial systems

    SciTech Connect

    Nishida, Jun; Fayer, Michael D.

    2014-04-14

    Functionalized organic monolayers deposited on planar two-dimensional surfaces are important systems for studying ultrafast orientational motions and structures of interfacial molecules. Several studies have successfully observed the orientational relaxation of functionalized monolayers by fluorescence depolarization experiments and recently by polarization-resolved heterodyne detected vibrational transient grating (HDTG) experiments. In this article we provide a model-independent theory to extract orientational correlation functions unique to interfacial molecules and other uniaxial systems based on polarization-resolved resonant third-order spectroscopies, such as pump-probe spectroscopy, HDTG spectroscopy, and fluorescence depolarization experiment. It will be shown (in the small beam-crossing angle limit) that five measurements are necessary to completely characterize the monolayer's motions: I{sub ∥}(t) and I{sub ⊥}(t) with the incident beams normal to the surface, I{sub ∥}(t) and I{sub ⊥}(t) with a non-zero incident angle, and a time averaged linear dichroism measurement. Once these measurements are performed, two orientational correlation functions corresponding to in-plane and out-of-plane motions are obtained. The procedure is applicable not only for monolayers on flat surfaces, but any samples with uniaxial symmetry such as uniaxial liquid crystals and aligned planar bilayers. The theory is valid regardless of the nature of the actual molecular motions on interface. We then apply the general results to wobbling-in-a-cone model, in which molecular motions are restricted to a limited range of angles. Within the context of the model, the cone angle, the tilt of the cone relative to the surface normal, and the orientational diffusion constant can be determined. The results are extended to describe analysis of experiments where the beams are not crossing in the small angle limit.

  8. Field dependent elastic anomaly in uniaxial tungsten bronze relaxors

    NASA Astrophysics Data System (ADS)

    Aftabuzzaman, Md; Dec, Jan; Kleemann, Wolfgang; Kojima, Seiji

    2016-10-01

    The electric field effects on the elastic properties of uniaxial Ca x Ba1- x Nb2O6 (x = 0.30, CBN30) single crystals were investigated using broadband Brillouin scattering spectroscopy as functions of temperature and electric field. Remarkable thermal hysteresis was observed between zero field heating and zero field cooling processes. A stretching index β = 2.05 indicates the stretched critical slowing down of polar nanoregions (PNRs). The effect of electric field along [001] direction was clearly observed. Under 1.0 kV/cm field, the alignment of nanodomains and enhancement of the long-range ferroelectric order were observed in the ferroelectric phase. In the field dependent measurement, a mixed state consisting of macrodomains induced by the electric field and nanodomains caused by the random fields was observed at 3.0 kV/cm. The mixed state persists up to 13 kV/cm because of the incomplete switching of the nanodomains to the macrodomains state. A very strong memory effect was also observed.

  9. Assembly of uniaxially aligned rare-earth-free nanomagnets

    SciTech Connect

    Balamurugan, B; Das, B; Shah, VR; Skomski, R; Li, XZ; Sellmyer, DJ

    2012-09-17

    We report HfCo7 nanoparticles with appreciable permanent-magnet properties (magnetocrystalline anisotropy K-1 approximate to 10 Mergs/cm(3), coercivity H-c approximate to 4.4 kOe, and magnetic polarization J(s) approximate to 10.9 kG at 300 K) deposited by a single-step cluster-deposition method. The direct crystalline-ordering of nanoparticles during the gas-aggregation process, without the requirement of a high-temperature thermal annealing, provides an unique opportunity to align their easy axes uniaxially by applying a magnetic field of about 5 kOe prior to deposition, and subsequently to fabricate exchange-coupled nanocomposites having J(s) as high as 16.6 kG by co-depositing soft magnetic Fe-Co. This study suggests HfCo7 as a promising rare-earth-free permanent-magnet alloy, which is important for mitigating the critical-materials aspects of rare-earth elements. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4753950

  10. Van der Waals interaction in uniaxial anisotropic media

    NASA Astrophysics Data System (ADS)

    Kornilovitch, Pavel E.

    2013-01-01

    Van der Waals interactions between flat surfaces in uniaxial anisotropic media are investigated in the nonretarded limit. The main focus is the effect of nonzero tilt between the optical axis and the surface normal on the strength of the van der Waals attraction. General expressions for the van der Waals free energy are derived using the surface mode method and the transfer-matrix formalism. To facilitate numerical calculations a temperature-dependent three-band parameterization of the dielectric tensor of the liquid crystal 5CB is developed. A solid slab immersed in a liquid crystal experiences a van der Waals torque that aligns the surface normal relative to the optical axis of the medium. The preferred orientation is different for different materials. Two solid slabs in close proximity experience a van der Waals attraction that is strongest for homeotropic alignment of the intervening liquid crystal for all the materials studied. The results have implications for the stability of plate-like colloids in liquid crystal hosts.

  11. Van der Waals interaction in uniaxial anisotropic media.

    PubMed

    Kornilovitch, Pavel E

    2013-01-23

    Van der Waals interactions between flat surfaces in uniaxial anisotropic media are investigated in the nonretarded limit. The main focus is the effect of nonzero tilt between the optical axis and the surface normal on the strength of the van der Waals attraction. General expressions for the van der Waals free energy are derived using the surface mode method and the transfer-matrix formalism. To facilitate numerical calculations a temperature-dependent three-band parameterization of the dielectric tensor of the liquid crystal 5CB is developed. A solid slab immersed in a liquid crystal experiences a van der Waals torque that aligns the surface normal relative to the optical axis of the medium. The preferred orientation is different for different materials. Two solid slabs in close proximity experience a van der Waals attraction that is strongest for homeotropic alignment of the intervening liquid crystal for all the materials studied. The results have implications for the stability of plate-like colloids in liquid crystal hosts. PMID:23234868

  12. Programmable Extreme Pseudomagnetic Fields in Graphene by a Uniaxial Stretch

    PubMed Central

    Zhu, Shuze; Stroscio, Joseph A.; Li, Teng

    2016-01-01

    Many of the properties of graphene are tied to its lattice structure, allowing for tuning of charge carrier dynamics through mechanical strain. The graphene electro-mechanical coupling yields very large pseudomagnetic fields for small strain fields, up to hundreds of Tesla, which offer new scientific opportunities unattainable with ordinary laboratory magnets. Significant challenges exist in investigation of pseudomagnetic fields, limited by the non-planar graphene geometries in existing demonstrations and the lack of a viable approach to controlling the distribution and intensity of the pseudomagnetic field. Here we reveal a facile and effective mechanism to achieve programmable extreme pseudomagnetic fields with uniform distributions in a planar graphene sheet over a large area by a simple uniaxial stretch. We achieve this by patterning the planar graphene geometry and graphene-based hetero-structures with a shape function to engineer a desired strain gradient. Our method is geometrical, opening up new fertile opportunities of strain engineering of electronic properties of 2D materials in general. PMID:26705640

  13. Monitoring contractile dermal lymphatic activity following uniaxial mechanical loading.

    PubMed

    Gray, R J; Worsley, P R; Voegeli, D; Bader, D L

    2016-09-01

    It is proposed that direct mechanical loading can impair dermal lymphatic function, contributing to the causal pathway of pressure ulcers. The present study aims to investigate the effects of loading on human dermal lymphatic vessels. Ten participants were recruited with ages ranging from 24 to 61 years. Participants had intradermal Indocyanine Green injections administrated between left finger digits. Fluorescence was imaged for 5min sequences with an infra-red camera prior to lymph vessel loading, immediately after axial loading (60mmHg) and following a recovery period. Image processing was employed to defined transient lymph packets and compare lymph function between each test phase. The results revealed that between 1-8 transient events (median=4) occurred at baseline, with a median velocity of 8.1mm/sec (range 4.1-20.1mm/sec). Immediately post-loading, there was a significant (p<0.05) reduction in velocity (median=6.4, range 2.2-13.5mm/sec), although the number of transient lymph packages varied between participants. During the recovery period the number (range 1-7) and velocity (recovery median=9.6mm/sec) of transient packets were largely restored to basal values. The present study revealed that some individuals present with impaired dermal lymphatic function immediately after uniaxial mechanical loading. More research is needed to investigate the effects of pressure and shear on lymphatic vessel patency. PMID:27245749

  14. Propagation optical quarks after an uniaxial crystal: the experiment

    NASA Astrophysics Data System (ADS)

    Egorov, Yu. A.; Konovalenko, V. L.; Zinovev, A. O.; Anischenko, P. M.; Glumova, M. V.

    2013-12-01

    There is a lots of different papers reporting about the propagation of the different types of an optical beams in a uniaxial crystals are known by that time. This beams are: Lager-Gaussian and Bessel- Gaussian beams. It is common for all this types of beams, that if propagation axis and crystal axis coincides, and accident beam had a circular polarization, are can get type spiral type degenerated umbilici, which corresponds to the charge 2 optical vortex in the orthogonal polarized beam component, generated by crystal [1] (Fig 1). This generation accurse due to total angular momentum conservation law symmetry axis of the crystal. One to the changing of the spin momentum which is associated with the beam polarization, this leads to the orbital momentum changes that associated with topological charge of formed orthogonal circular component. Double charged optical vortex could be easily perturbed by tilting beam axis with respect to the crystal axis. If the tilt angles are small (<0.1°) central umbilici splits on two lemons and the surrounding ring umbilici splits on two pairs of monster-star. The further increasing of the tilt angle leads to the topological charge of circular components becomes, equal, and additional orbital moment correspond to the beam mass center displacement.

  15. Describing ethnicity in health research.

    PubMed

    Bradby, Hannah

    2003-02-01

    Commentators have criticised the terminology used for the classification of ethnic and racialised groups in health research for a number of years. The shortcomings of fixed-response categories include the reproduction of racialised categorisations, overemphasis of homogeneity within groups and contrast between them, and failure to offer terms with which people identify and which can express complex identities. The historical injustices against black and minority groups are reflected in terminology and explicitly recognised when discussing 'race' as a social construction. The exaggeration of homogeneity within groups and contrast between them is a racialising effect of fixed classifications. Self-assigned ethnic group avoids some of these difficulties by allowing multiple affiliations to be described, but introduces the costs of processing free text. The context-dependent nature of individual ethnic identity makes comparison problematic. Researcher-assigned ethnicity can increase comparability and consistency but may be at odds with self-identity. The complexity of ethnicity itself and of its relationship with socio-economic group and racism makes proxy measures inevitably inadequate. If researchers continue to try to capture the complex and contextual detail of ethnicity, it may become clear that the general concept of ethnicity covers such a wide and specific range of experiences as to render it of limited use in making comparisons through time or across cultures.

  16. Elastic-Plastic Fracture Mechanics Analyses of Two-Dimensional and Three-Dimensional Test Specimens under Uniaxial and Biaxial Loading

    NASA Astrophysics Data System (ADS)

    Ding, Ping

    Extensive finite element analyses are performed to obtain numerical solutions of constraint parameter A for two-dimensional (2D) and three-dimensional (3D) crack geometries under both uniaxial and biaxial loading condition through a least-square fitting method. Based on the determined numerical solutions of constraint parameter A, constraint effect at crack-tip (-front) of 2D and 3D cracked specimens are analyzed under both uniaxial and biaxial loading condition. Three sets of methodologies for estimating constraint parameter A of elastic-plastic fracture mechanics are developed in the present research. They are: (1) estimating constraint parameter A by curve shape similarity, (2) predicting A values directly from the T-stress, and (3) determining parameter A based on the fully plastic solutions of A. With the obtained numerical solutions of constraint parameter A, estimate formulas for A values corresponding to the three sets of newly-developed estimate methodologies are developed for 2D and 3D cracked structures under both uniaxial and biaxial loading. It is shown that all three sets of methods can be used to predict A values with good accuracy. In the present research, it has been validated that, the obtained solutions of constraint parameter A (whether estimate methods / formulas or numerical solutions) can be utilized to predict other two commonly-used constraint parameters Q and A2 (a different normalized form of A) through the relationships between A and Q as well as A and A2.

  17. Lithography-assisted alignment control for preparation of mesoporous silica films with uniaxially oriented mesochannels.

    PubMed

    Yamauchi, Yusuke; Ishihara, Shinsuke; Suzuki, Norihiro; Wu, Kevin C W

    2014-03-01

    We report the lithography-assisted alignment control of one-dimensional (1D) mesochannels. The effectiveness on both nonionic and cationic surfactants is discussed, and a continuous film with fully uniaxially oriented mesochannels is also successfully prepared.

  18. Validation of uniaxial and triaxial accelerometers for the assessment of physical activity in preschool children

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Given the unique physical activity patterns of preschoolers, wearable electronic devices for quantitative assessment of physical activity require validation in this population. Study objective was to validate uniaxial and triaxial accelerometers in preschoolers. Room calorimetry was performed over 3...

  19. Uniaxial strain-induced mechanical and electronic property modulation of silicene

    PubMed Central

    2014-01-01

    We perform first-principles calculations of mechanical and electronic properties of silicene under uniaxial strains. Poisson's ratio and the rigidity of silicene show strong chirality dependence under large uniaxial strains. The ultimate strains of silicene with uniaxial strain are smaller than those with biaxial strain. We find that uniaxial strains induce Dirac point deviation from the high-symmetry points in the Brillouin zone and semimetal-metal transitions. Therefore, no bandgap opens under the uniaxial strain. Due to its peculiar structure and variable sp3/sp2 ratio of the chemical bond, the deviation directions of Dirac points from the high-symmetry points in the Brillouin zone and variation of Fermi velocities of silicene exhibit significant difference from those of graphene. Fermi velocities show strong anisotropy with respect to the wave vector directions and change slightly before the semimetal-metal transition. We also find that the work function of silicene increases monotonously with the increasing uniaxial strains. PACS numbers 61.46.-w; 62.20.D-; 73.22.Dj PMID:25276108

  20. The anisotropy of magnetic susceptibility of uniaxial superparamagnetic particles: Consequences for its interpretation in magnetite and maghemite bearing rocks

    NASA Astrophysics Data System (ADS)

    Lanci, Luca; Zanella, Elena

    2016-01-01

    A simple model that provides a quantitative description of the magnetic susceptibility of superparamagnetic to stable single-domain uniaxial magnetic particles can be built in the framework of the theory of stochastic resonance. This model expands that of Mullins and Tile (1973) for superparamagnetic grains by considering the dependence of superparamagnetic susceptibility on the particle orientation and thus describes the anisotropy of magnetic susceptibility (AMS) of ensembles of superparamagnetic as well as single-domain particles. The theory predicts that on the contrary of stable single domain, the maximum anisotropy of superparamagnetic particles is parallel to their easy axis and shows that the AMS of ensembles of uniaxial particle is strongly dependent on the distribution of particle grain size, coercivity, measurement temperature, and frequency. It also explains why the inverse AMS pattern expected for stable single-domain particles is rarely observed in natural samples. We use examples of well-characterized obsidian specimens to show that, as predicted by the theory, in the presence of significant superparamagnetic contributions, the maximum susceptibility axis of AMS is directed along the preferential direction of particles easy axis.

  1. Role of Molecular Structure on X-ray Diffraction in Uniaxial and Biaxial Phases of Thermotropic Liquid Crystals

    SciTech Connect

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra

    2009-04-29

    X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.

  2. Role of Molecular Structure on X-ray Diffraction in Thermotropic Uniaxial and Biaxial Nematic Liquid Crystal Phases

    SciTech Connect

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra

    2009-08-27

    X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.

  3. Graphene allotropes under extreme uniaxial strain: an ab initio theoretical study.

    PubMed

    Fthenakis, Zacharias G; Lathiotakis, Nektarios N

    2015-07-01

    Using density functional theory calculations, we study the response of three representative graphene allotropes (two pentaheptites and octagraphene) as well as graphene, to uniaxial strain up to their fracture limit. Those allotropes can be seen as distorted graphene structures formed upon periodically arranged Stone-Walles transformations. We calculate their mechanical properties (Young's modulus, Poisson's ratio, speed of sound, ultimate tensile strength and the corresponding strain), and we describe the pathways of their fracture. Finally, we study strain as a factor for the conversion of graphene into those allotropes upon Stone-Walles transformations. For specific sets of Stone-Walles transformations leading to an allotrope, we determine the strain directions and the corresponding minimum strain value, for which the allotrope is more favorable energetically than graphene. We find that the minimum strain values which favor those conversions are of the order of 9-13%. Moreover, we find that the energy barriers for the Stone-Walles transformations decrease dramatically under strain, however, they remain prohibitive for structural transitions. Thus, strain alone cannot provide a synthetic route to these allotropes, but could be a part of composite procedures for this purpose.

  4. A Numerical Method for Simulating the Microscopic Damage Evolution in Composites Under Uniaxial Transverse Tension

    NASA Astrophysics Data System (ADS)

    Zhi, Jie; Zhao, Libin; Zhang, Jianyu; Liu, Zhanli

    2016-06-01

    In this paper, a new numerical method that combines a surface-based cohesive model and extended finite element method (XFEM) without predefining the crack paths is presented to simulate the microscopic damage evolution in composites under uniaxial transverse tension. The proposed method is verified to accurately capture the crack kinking into the matrix after fiber/matrix debonding. A statistical representative volume element (SRVE) under periodic boundary conditions is used to approximate the microstructure of the composites. The interface parameters of the cohesive models are investigated, in which the initial interface stiffness has a great effect on the predictions of the fiber/matrix debonding. The detailed debonding states of SRVE with strong and weak interfaces are compared based on the surface-based and element-based cohesive models. The mechanism of damage in composites under transverse tension is described as the appearance of the interface cracks and their induced matrix micro-cracking, both of which coalesce into transversal macro-cracks. Good agreement is found between the predictions of the model and the in situ experimental observations, demonstrating the efficiency of the presented model for simulating the microscopic damage evolution in composites.

  5. Origins of asymmetric stress-strain response in phase transformations

    SciTech Connect

    Sehitoglu, H.; Gall, K.

    1997-12-31

    It has been determined that the transformation stress-strain behavior of CuZnAl and NiTi shape memory alloys is dependent on the applied stress state. The uniaxial compressive stress necessary to macroscopically trigger the transformation is approximately 34% (CuZnAl) and 26% (NiTi) larger than the required uniaxial tensile stress. For three dimensional stress states, the response of either alloy system is dependent on the directions of the dominant principal stresses along with the hydrostatic stress component of the stress state. The stress state effects are dominated by the favored growth and nucleation of more martensite plates in tension versus compression. The effect of different hydrostatic pressure levels between stress states on martensite plates volume change is considered small.

  6. Luminescent nanocrystal stress gauge

    PubMed Central

    Choi, Charina L.; Koski, Kristie J.; Olson, Andrew C. K.; Alivisatos, A. Paul

    2010-01-01

    Microscale mechanical forces can determine important outcomes ranging from the site of material fracture to stem cell fate. However, local stresses in a vast majority of systems cannot be measured due to the limitations of current techniques. In this work, we present the design and implementation of the CdSe-CdS core-shell tetrapod nanocrystal, a local stress sensor with bright luminescence readout. We calibrate the tetrapod luminescence response to stress and use the luminescence signal to report the spatial distribution of local stresses in single polyester fibers under uniaxial strain. The bright stress-dependent emission of the tetrapod, its nanoscale size, and its colloidal nature provide a unique tool that may be incorporated into a variety of micromechanical systems including materials and biological samples to quantify local stresses with high spatial resolution. PMID:21098301

  7. Dynamic properties of structural transition in iron under uniaxial compression.

    PubMed

    Shao, J L; Duan, S Q; He, A M; Qin, C S; Wang, P

    2009-06-17

    By using molecular dynamics simulations, we have successfully simulated the bcc [Formula: see text] hcp structural transition in single-crystal iron under isothermal compression along the [001] direction. The results reveal a distinct softening of C(33) and a hardening of C(31) (or C(32)) prior to the transition and an over-relaxation of the stress after transition. Above the critical stress the morphology evolution of structural transition is analyzed, which can be divided into four stages: hcp homogeneously nucleated, columnar grains formed, nuclei competed and merged, and a laminar structure formed along {110} planes. Besides, our simulations demonstrate that in mixed phases the hcp phase has negative shear stress and the potential of the hcp phase is higher than the bcc phase, and the shear stress of the system keeps a linear decrease with hcp mass fraction. The effect of temperature on the structural transition is also discussed. PMID:21693955

  8. New Magnetically Uniaxial Phases in the Samarium, Iron Binary System.

    NASA Astrophysics Data System (ADS)

    Rani, Raj

    1995-01-01

    For the first time, films magnets of binary rm Sm_5Fe_{17}, and SmFe_{12}, magnetically uniaxial phases have been sputter synthesized without any addition of a phase stabilizing third element. Perpendicular to the film plane, the room temperature saturation magnetization for highly (002) aligned film samples of SmFe_ {12} phase were measured to be 14.3 +/- 0.5 kG and the estimated anisotropy field was 130 +/- 10 kOe. X-ray diffraction studies, hysterisis loop measurements, composition measurements, and projection of moment calculations allowed to identify the SmFe_{12} phase as ThMn_{12} type tetragonal structure with a = 8.438 +/- 0.006 A, and c = 4.805 +/- 0.006 A. Film samples of this phase were synthesized by depositing the material on preheated substrates. For rm Sm_5Fe_{17} phase, the material was first deposited in amorphous form and subsequently crystallized. rm Sm_5Fe_{17 } film samples were synthesized with record high room temperature coercivity of 14.1 kOe for the two element Sm, Fe system. On nitriding rm Sm _2Fe_{17}, profound changes in magnetic properties have occurred, room temperature inplane coercivity rose from 0.75 kOe to 23 kOe. The rm Sm_2Fe_{17}N_ {x} compound retained its parent structure with the cell volume increase of ~7%. The room temperature coercivity as a function of the Sm concentration reached a maximum value of ~23 kOe at a slightly richer than stoichiometric Sm composition. High anisotropy (002) textured film samples of rm Pr(Fe_{12-y-z},Co_{y},Mo _{z})N_{x}, where y = 0-2.5, and z = 0.4-1.0 compounds were synthesized with so far the highest coercivity of 9.4 kOe. X-ray diffraction data showed that the ThMn_{12} type tetragonal structure was retained with a saturation increase in the cell volume over the first 15 minutes of nitriding time at 750 K. The coercivity reached a maximum for nitriding time of 25 minutes of nitriding time. For rm Pr_{1.04}Fe_{10.36 }Co_{1.16}Mo_{0.44}N _{x} sample measured at 293 K, perpendicular to the

  9. Uniaxial and triaxial compression tests of silicon carbide ceramics under quasi-static loading condition.

    SciTech Connect

    Brannon, Rebecca Moss; Lee, Moo Yul; Bronowski, David R.

    2005-02-01

    To establish mechanical properties and failure criteria of silicon carbide (SiC-N) ceramics, a series of quasi-static compression tests has been completed using a high-pressure vessel and a unique sample alignment jig. This report summarizes the test methods, set-up, relevant observations, and results from the constitutive experimental efforts. Results from the uniaxial and triaxial compression tests established the failure threshold for the SiC-N ceramics in terms of stress invariants (I{sub 1} and J{sub 2}) over the range 1246 < I{sub 1} < 2405. In this range, results are fitted to the following limit function (Fossum and Brannon, 2004) {radical}J{sub 2}(MPa) = a{sub 1} - a{sub 3}e -a{sub 2}(I{sub 1}/3) + a{sub 4} I{sub 1}/3, where a{sub 1} = 10181 MPa, a{sub 2} = 4.2 x 10{sup -4}, a{sub 3} = 11372 MPa, and a{sub 4} = 1.046. Combining these quasistatic triaxial compression strength measurements with existing data at higher pressures naturally results in different values for the least-squares fit to this function, appropriate over a broader pressure range. These triaxial compression tests are significant because they constitute the first successful measurements of SiC-N compressive strength under quasistatic conditions. Having an unconfined compressive strength of {approx}3800 MPa, SiC-N has been heretofore tested only under dynamic conditions to achieve a sufficiently large load to induce failure. Obtaining reliable quasi-static strength measurements has required design of a special alignment jig and load-spreader assembly, as well as redundant gages to ensure alignment. When considered in combination with existing dynamic strength measurements, these data significantly advance the characterization of pressure-dependence of strength, which is important for penetration simulations where failed regions are often at lower pressures than intact regions.

  10. Mechanical and electronic properties of monolayer and bilayer phosphorene under uniaxial and isotropic strains.

    PubMed

    Hu, Ting; Han, Yang; Dong, Jinming

    2014-11-14

    The mechanical and electronic properties of both the monolayer and bilayer phosphorenes under either isotropic or uniaxial strain have been systematically investigated using first-principles calculations. It is interesting to find that: 1) Under a large enough isotropic tensile strain, the monolayer phosphorene would lose its pucker structure and transform into a flat hexagonal plane, while two inner sublayers of the bilayer phosphorene could be bonded due to its interlayer distance contraction. 2) Under the uniaxial tensile strain along a zigzag direction, the pucker distance of each layer in the bilayer phosphorene can exhibit a specific negative Poisson's ratio. 3) The electronic properties of both the monolayer and bilayer phosphorenes are sensitive to the magnitude and direction of the applied strains. Their band gaps decrease more rapidly under isotropic compressive strain than under uniaxial strain. Also, their direct-indirect band gap transitions happen at the larger isotropic tensile strains compared with that under uniaxial strain. 4) Under the isotropic compressive strain, the bilayer phosphorene exhibits a transition from a direct-gap semiconductor to a metal. In contrast, the monolayer phosphorene initially has the direct-indirect transition and then transitions to a metal. However, under isotropic tensile strain, both the bilayer and monolayer phosphorene show the direct-indirect transition and, finally, the transition to a metal. Our numerical results may open new potential applications of phosphorene in nanoelectronics and nanomechanical devices by external isotropic strain or uniaxial strain along different directions.

  11. Creep behavior of Utah oil shale subject to uniaxial loading

    SciTech Connect

    Chong, K.P.; Dana, G.F.; Chen, J.L.

    1982-06-01

    This paper presents results of a study on the creep behavior of Utah oil shale. A Conbel Model 355 pneumatic driven testing machine is used. The set of duplicate test specimens required for creep testing were cut from a single oil shale layer using a wire saw to avoid any surface damage. A rheological model was developed for creep behavior of oil shale as a function of stress level and organic content. Data from creep testing and Fischer assay analyses were used to demonstrate correlation between various stress levels and organic contents for samples taken from the Mahogany Zone of the Parachute Creek Member in Utah's Cowboy Canyon.

  12. CaFe2As2 Under In-Plane Uniaxial Pressure

    NASA Astrophysics Data System (ADS)

    Frampton, Miles; Zieve, Rena; Dioguardi, Adam

    2014-03-01

    Many unconventional superconductors have a planar crystal structure, with a resulting two-dimensional character that favors superconductivity. They tend to have anisotropic behavior and can be very sensitive to uniaxial pressure. Since these materials often grow preferentially as platelets perpendicular to the crystalline c axis, applying in-plane pressure is challenging. We present a new setup for studying thin samples under uniaxial pressure and our results on CaFe2As2. CaFe2As2 undergoes a magnetic transition simultaneously with a tetragonal-to-orthorhombic structural transition. In-plane uniaxial pressure detwins the orthorhombic phase and accentuates the difference between the axes. We find a significant change in Ts as well as anisotropy of the in-plane resistivity that increases with pressure.

  13. Uniaxial absorbing media: conditions for refraction in the direction of the optical axis.

    PubMed

    Diñeiro, J M; Alberdi, C; Hernández, B; Sáenz, C

    2013-03-01

    When a plane wave is incident from an isotropic medium into a uniaxial transparent medium so that the ordinary wave propagates in the direction of the optical axis, the extraordinary wave will also propagate in the same direction and with the same refractive index. We will show that this is not the case when the second medium is a uniaxial absorbing material. In this work, we will state a clear and precise interpretation of the meaning of propagation in the direction of the optical axis in the case of uniaxial absorbing media. Assuming that the ordinary wave is refracted in the direction of the optical axis we will analyze the refraction of the extraordinary wave and we will compare it with the case of transparent media. The necessary conditions to have both ordinary and extraordinary waves refracted in the direction of the optical axis will be obtained.

  14. Magnetic phase transitions and monopole excitations in spin ice under uniaxial pressure: A Monte Carlo simulation

    SciTech Connect

    Xie, Y. L. Yan, Z. B.; Liu, J.-M.; Lin, L.

    2015-05-07

    In this work, we explore the spin ice model under uniaxial pressure using the Monte Carlo simulation method. For the known spin ices, the interaction correction (δ) introduced by the uniaxial pressure varies in quite a wide range from positive to negative. When δ is positive, the ground state characterized by the ferromagnetic spin chains is quite unstable, and in real materials it serves as intermediate state connecting the ice state and the long range ordered dipolar spin ice ground state. In the case of negative δ, the system relaxes from highly degenerate ice state to ordered ferromagnetic state via a first order phase transition. Furthermore, the domain walls in such ferromagnetic state are the hotbed of the excitations of magnetic monopoles, thus indicating that the uniaxial pressure can greatly increase the monopole density.

  15. Excitation energy migration between elongated fluorophores in uniaxially oriented polyvinyl alcohol films

    NASA Astrophysics Data System (ADS)

    Bojarski, P.; Gryczyński, I.; Kułak, L.; Synak, A.; Barnett, A.

    2006-11-01

    Nonradiative multistep energy migration is studied for 3,3'-diethylthiacarbocyanine iodide (DTCI) in uniaxially stretched and unstretched poly(vinyl alcohol) films. The results of fluorescence anisotropy decay measurements were found to be extremely different for unstretched and (stretched) systems. For disordered systems, fast depolarization was observed due to effective energy migration between randomly distributed fluorophores. However, for partly ordered systems, much slower depolarization was found as a result of preferential angular distribution of transition dipole moments of identical fluorophores. These results and properties of energy transport in uniaxially stretched polymer films are analyzed using the technique of Monte-Carlo simulation.

  16. Uniaxial magnetic anisotropy of quasi-one-dimensional Fe chains on Pb/Si

    SciTech Connect

    Sun, Da-li; Wang, De-yong; Du, Hai-Feng; Ning, Wei; Gao, Jian-Hua; Fang, Ya-Peng; Zhang, Xiang-Qun; Sun, Young; Cheng, Zhao-Hua; Shen, Jian

    2009-01-01

    We fabricated quasi-one-dimensional Fe chains on a 4{sup o} miscut Si (111) substrate with a Pb film as a buffer layer. The magnetic properties and morphology of Fe chains were investigated by means of scanning tunneling microscope (STM) and surface magneto-optical Kerr effect (SMOKE). STM images show that Fe chains are formed by Fe random islands along the steps of the Pb film due to step decoration. SMOKE data indicate that the Fe chains exhibit in-plane uniaxial magnetic anisotropy along the step direction. The effective in-plane uniaxial anisotropy constant at room temperature was determined by means of electron spin resonance.

  17. Strong uniaxial magnetic anisotropy in CoFe films on obliquely sputtered Ru underlayer

    SciTech Connect

    Fukuma, Y.; Lu, Z.; Fujiwara, H.; Mankey, G. J.; Butler, W. H.; Matsunuma, S.

    2009-10-01

    Co{sub 90}Fe{sub 10} films with an in-plane uniaxial magnetic anisotropy have been grown on an obliquely sputtered thin Ru underlayer. The anisotropy field can be increased up to 200 Oe. The hysteresis curves show a very high squareness in the easy axis direction and almost no hysteresis in the hard axis direction, suggesting that the induced uniaxial anisotropy is uniform throughout the films. The switching characteristics of the nanoelements fabricated from the films by e-beam lithography are also investigated. There is no degradation of the magnetic anisotropy after the annealing and lithographical process.

  18. Uniaxial crystal growth in thin film by utilizing supercooled state of mesogenic phthalocyanine

    NASA Astrophysics Data System (ADS)

    Fiderana Ramananarivo, Mihary; Higashi, Takuya; Ohmori, Masashi; Sudoh, Koichi; Fujii, Akihiko; Ozaki, Masanori

    2016-06-01

    A method of uniaxial crystal growth in wet-processed thin films of the mesogenic phthalocyanine 1,4,8,11,15,18,22,25-octahexylphthalocyanine (C6PcH2) is proposed. It consists of applying geometrically linear thermal stimulation to a supercooled state of liquid crystalline C6PcH2. The thin film showed highly ordered molecular stacking structure and uniaxial alignment over a macroscopic scale. An explanation of the crystal growth mechanism is suggested by taking into account the temperature range of crystal growth and the hysteresis property of C6PcH2 in the phase transition.

  19. Thermotropic Uniaxial and Biaxial Nematic and Smectic Phases in Bent-Core Mesogens

    SciTech Connect

    Prasad, Venna; Kang, Shin-Woong; Suresh, K.A.; Joshi, Leela; Wang, Qingbing; Kumar, Satyendra

    2010-07-20

    Two azo substituted achiral bent-core mesogens have been synthesized. Optical polarizing microscopy and synchrotron X-ray scattering studies of both compounds reveal the existence of the thermotropic uniaxial and biaxial nematic and three smectic phases at different temperatures in these single component small molecule systems. The transition from the uniaxial to biaxial nematic phase is confirmed to be second order. The transitions from the biaxial nematic to the underlying smectic phase and between the smectic phases have barely discernible heat capacity signatures and thus are also second order.

  20. Rotation method for the measurement of thickness of Z-cut uniaxial crystals

    NASA Astrophysics Data System (ADS)

    Paranin, V. D.

    2015-12-01

    An original polarization method for the measurement of thickness of Z-cut uniaxial crystals employs the transmittance measurement of the polarizer-crystal-analyzer system at different rotation angles of the crystal. The mathematical analysis of the method is based on the optics of uniaxial crystals and Jones matrices. A measurement error of no greater than ±0.6 μm is estimated using the formula of a vector sum. Z-cut crystals of congruent lithium niobate with rated thicknesses of 514 and 554 μm are used to experimentally test the method and propose practical recommendations for applications.

  1. Mechanical characterization of stomach tissue under uniaxial tensile action.

    PubMed

    Jia, Z G; Li, W; Zhou, Z R

    2015-02-26

    In this article, the tensile properties of gastric wall were investigated by using biomechanical test and theoretical analysis. The samples of porcine stomach strips from smaller and greater curvature of the stomach were cut in longitudinal and circumferential direction, respectively. The loading-unloading, stress relaxation, strain creep, tensile fracture tests were performed at mucosa-submucosa, serosa-muscle and intact layer, respectively. Results showed that the biomechanical properties of the porcine stomach depended on the layers, orientations and locations of the gastric wall and presented typical viscoelastic, nonlinear and anisotropic mechanical properties. During loading-unloading test, the stress of serosa-muscle layer in the longitudinal direction was 15-20% more than that in the circumferential direction at 12% stretch ratio, while it could reach about 40% for the intact layer and 50% for the mucosa-submucosa layer. The results of stress relaxation and strain creep showed that the variation degree was obviously faster in the circumferential direction than that in the longitudinal direction, and the ultimate residual values were also different for the different layers, orientations and locations. In the process of fracture test, the serosa-muscle layer fractured firstly followed by the mucosa-submucosa layer when the intact layer was tested, the longitudinal strips firstly began to fracture and the required stress value was about twice as much as that in the circumferential strips. The anisotropy and heterogeneity of mechanical characterization of the porcine stomach were related to its complicated geometry, structure and functions. The results would help us to understand the biomechanics of soft organ tissue.

  2. Variations of electric resistance and H2 and Rn emissions of concrete blocks under increasing uniaxial compression

    USGS Publications Warehouse

    King, C.-Y.; Luo, G.

    1990-01-01

    Electric resistance and emissions of hydrogen and radon isotopes of concrete (which is somewhat similar to fault-zone materials) under increasing uniaxial compression were continuously monitored to check whether they show any pre- and post-failure changes that may correspond to similar changes reported for earthquakes. The results show that all these parameters generally begin to increase when the applied stresses reach 20% to 90% of the corresponding failure stresses, probably due to the occurrence and growth of dilatant microcracks in the specimens. The prefailure changes have different patterns for different specimens, probably because of differences in spatial and temporal distributions of the microcracks. The resistance shows large co-failure increases, and the gas emissions show large post-failure increases. The post-failure increase of radon persists longer and stays at a higher level than that of hydrogen, suggesting a difference in the emission mechanisms for these two kinds of gases. The H2 increase may be mainly due to chemical reaction at the crack surfaces while they are fresh, whereas the Rn increases may be mainly the result of the increased emanation area of such surfaces. The results suggest that monitoring of resistivity and gas emissions may be useful for predicting earthquakes and failures of concrete structures. ?? 1990 Birkha??user Verlag.

  3. Strength Restoration of Cracked Sandstone and Coal under a Uniaxial Compression Test and Correlated Damage Source Location Based on Acoustic Emissions

    PubMed Central

    Feng, Xiaowei; Zhang, Nong; Zheng, Xigui; Pan, Dongjiang

    2015-01-01

    Underground rock masses have shown a general trend of natural balance over billions of years of ground movement. Nonetheless, man-made underground constructions disturb this balance and cause rock stability failure. Fractured rock masses are frequently encountered in underground constructions, and this study aims to restore the strength of rock masses that have experienced considerable fracturing under uniaxial compression. Coal and sandstone from a deep-buried coal mine were chosen as experimental subjects; they were crushed by uniaxial compression and then carefully restored by a chemical adhesive called MEYCO 364 with an innovative self-made device. Finally, the restored specimens were crushed once again by uniaxial compression. Axial stress, axial strain, circumferential strain, and volumetric strain data for the entire process were fully captured and are discussed here. An acoustic emission (AE) testing system was adopted to cooperate with the uniaxial compression system to provide better definitions for crack closure thresholds, crack initiation thresholds, crack damage thresholds, and three-dimensional damage source locations in intact and restored specimens. Several remarkable findings were obtained. The restoration effects of coal are considerably better than those of sandstone because the strength recovery coefficient of the former is 1.20, whereas that of the latter is 0.33, which indicates that MEYCO 364 is particularly valid for fractured rocks whose initial intact peak stress is less than that of MEYCO 364. Secondary cracked traces of restored sandstone almost follow the cracked traces of the initial intact sandstone, and the final failure is mainly caused by decoupling between the adhesive and the rock mass. However, cracked traces of restored coal only partially follow the traces of intact coal, with the final failure of the restored coal being caused by both bonding interface decoupling and self-breakage in coal. Three-dimensional damage source

  4. Strength Restoration of Cracked Sandstone and Coal under a Uniaxial Compression Test and Correlated Damage Source Location Based on Acoustic Emissions.

    PubMed

    Feng, Xiaowei; Zhang, Nong; Zheng, Xigui; Pan, Dongjiang

    2015-01-01

    Underground rock masses have shown a general trend of natural balance over billions of years of ground movement. Nonetheless, man-made underground constructions disturb this balance and cause rock stability failure. Fractured rock masses are frequently encountered in underground constructions, and this study aims to restore the strength of rock masses that have experienced considerable fracturing under uniaxial compression. Coal and sandstone from a deep-buried coal mine were chosen as experimental subjects; they were crushed by uniaxial compression and then carefully restored by a chemical adhesive called MEYCO 364 with an innovative self-made device. Finally, the restored specimens were crushed once again by uniaxial compression. Axial stress, axial strain, circumferential strain, and volumetric strain data for the entire process were fully captured and are discussed here. An acoustic emission (AE) testing system was adopted to cooperate with the uniaxial compression system to provide better definitions for crack closure thresholds, crack initiation thresholds, crack damage thresholds, and three-dimensional damage source locations in intact and restored specimens. Several remarkable findings were obtained. The restoration effects of coal are considerably better than those of sandstone because the strength recovery coefficient of the former is 1.20, whereas that of the latter is 0.33, which indicates that MEYCO 364 is particularly valid for fractured rocks whose initial intact peak stress is less than that of MEYCO 364. Secondary cracked traces of restored sandstone almost follow the cracked traces of the initial intact sandstone, and the final failure is mainly caused by decoupling between the adhesive and the rock mass. However, cracked traces of restored coal only partially follow the traces of intact coal, with the final failure of the restored coal being caused by both bonding interface decoupling and self-breakage in coal. Three-dimensional damage source

  5. Strength Restoration of Cracked Sandstone and Coal under a Uniaxial Compression Test and Correlated Damage Source Location Based on Acoustic Emissions.

    PubMed

    Feng, Xiaowei; Zhang, Nong; Zheng, Xigui; Pan, Dongjiang

    2015-01-01

    Underground rock masses have shown a general trend of natural balance over billions of years of ground movement. Nonetheless, man-made underground constructions disturb this balance and cause rock stability failure. Fractured rock masses are frequently encountered in underground constructions, and this study aims to restore the strength of rock masses that have experienced considerable fracturing under uniaxial compression. Coal and sandstone from a deep-buried coal mine were chosen as experimental subjects; they were crushed by uniaxial compression and then carefully restored by a chemical adhesive called MEYCO 364 with an innovative self-made device. Finally, the restored specimens were crushed once again by uniaxial compression. Axial stress, axial strain, circumferential strain, and volumetric strain data for the entire process were fully captured and are discussed here. An acoustic emission (AE) testing system was adopted to cooperate with the uniaxial compression system to provide better definitions for crack closure thresholds, crack initiation thresholds, crack damage thresholds, and three-dimensional damage source locations in intact and restored specimens. Several remarkable findings were obtained. The restoration effects of coal are considerably better than those of sandstone because the strength recovery coefficient of the former is 1.20, whereas that of the latter is 0.33, which indicates that MEYCO 364 is particularly valid for fractured rocks whose initial intact peak stress is less than that of MEYCO 364. Secondary cracked traces of restored sandstone almost follow the cracked traces of the initial intact sandstone, and the final failure is mainly caused by decoupling between the adhesive and the rock mass. However, cracked traces of restored coal only partially follow the traces of intact coal, with the final failure of the restored coal being caused by both bonding interface decoupling and self-breakage in coal. Three-dimensional damage source

  6. Simulations of in situ x-ray diffraction from uniaxially compressed highly textured polycrystalline targets

    SciTech Connect

    McGonegle, David Wark, Justin S.; Higginbotham, Andrew; Milathianaki, Despina; Remington, Bruce A.

    2015-08-14

    A growing number of shock compression experiments, especially those involving laser compression, are taking advantage of in situ x-ray diffraction as a tool to interrogate structure and microstructure evolution. Although these experiments are becoming increasingly sophisticated, there has been little work on exploiting the textured nature of polycrystalline targets to gain information on sample response. Here, we describe how to generate simulated x-ray diffraction patterns from materials with an arbitrary texture function subject to a general deformation gradient. We will present simulations of Debye-Scherrer x-ray diffraction from highly textured polycrystalline targets that have been subjected to uniaxial compression, as may occur under planar shock conditions. In particular, we study samples with a fibre texture, and find that the azimuthal dependence of the diffraction patterns contains information that, in principle, affords discrimination between a number of similar shock-deformation mechanisms. For certain cases, we compare our method with results obtained by taking the Fourier transform of the atomic positions calculated by classical molecular dynamics simulations. Illustrative results are presented for the shock-induced α–ϵ phase transition in iron, the α–ω transition in titanium and deformation due to twinning in tantalum that is initially preferentially textured along [001] and [011]. The simulations are relevant to experiments that can now be performed using 4th generation light sources, where single-shot x-ray diffraction patterns from crystals compressed via laser-ablation can be obtained on timescales shorter than a phonon period.

  7. Solid-state (13)C NMR and synchrotron SAXS/WAXS studies of uniaxially-oriented polyethylene.

    PubMed

    Afeworki, Mobae; Brant, Pat; Lustiger, Arnold; Norman, Alexander

    2015-11-01

    We report solid-state (13)C NMR and synchrotron wide-and small-angle X-ray scattering experiments (WAXS, SAXS) on metallocene linear low density polyethylene films (e.g., Exceed™ 1018 mLLDPE; nominally 1MI, 0.918 density ethylene-hexene metallocene copolymer) as a function of uniaxial draw ratio, λ. Combined, these experiments provide an unambiguous, quantitative molecular view of the orientation of both the crystalline and amorphous phases in the samples as a function of draw. Together with previously reported differential scanning calorimetry (DSC), gas transport measurements, transmission electron microscopy (TEM), optical birefringence, small angle X-ray scattering (SAXS) as well as other characterization techniques, this study of the state of orientation in both phases provides insight concerning the development of unusually high barrier properties of the most oriented samples (λ=10). In this work, static (non-spinning) solid-state NMR measurements indicate that in the drawn Exceed(TM) films both the crystalline and amorphous regions are highly oriented. In particular, chemical shift data show the amorphous phase is comprised increasingly of so-called "taut tie chains" (or tie chains under any state of tautness) in the mLLDPE with increasing draw ratio - the resonance lines associated with the amorphous phase shift to where the crystalline peaks are observed. In the sample with highest total draw (λ=10), virtually all of the chains in the non-crystalline region have responded and aligned in the machine (draw) direction. Both monoclinic and orthorhombic crystalline peaks are observed in high-resolution, solid-state magic-angle spinning (MAS) NMR measurements of the oriented PE films. The orientation is comparable to that obtained for ultra-high molecular weight HDPE fibers described as "ultra-oriented" in the literature. Furthermore, the presence of a monoclinic peak in cold-drawn samples suggests that there is an appreciable internal stress associated

  8. Photorealistic ray tracing of free-space invisibility cloaks made of uniaxial dielectrics.

    PubMed

    Halimeh, Jad C; Wegener, Martin

    2012-12-17

    The design rules of transformation optics generally lead to spatially inhomogeneous and anisotropic impedance-matched magneto-dielectric material distributions for, e.g., free-space invisibility cloaks. Recently, simplified anisotropic non-magnetic free-space cloaks made of a locally uniaxial dielectric material (calcite) have been realized experimentally. In a two-dimensional setting and for in-plane polarized light propagating in this plane, the cloaking performance can still be perfect for light rays. However, for general views in three dimensions, various imperfections are expected. In this paper, we study two different purely dielectric uniaxial cylindrical free-space cloaks. For one, the optic axis is along the radial direction, for the other one it is along the azimuthal direction. The azimuthal uniaxial cloak has not been suggested previously to the best of our knowledge. We visualize the cloaking performance of both by calculating photorealistic images rendered by ray tracing. Following and complementing our previous ray-tracing work, we use an equation of motion directly derived from Fermat's principle. The rendered images generally exhibit significant imperfections. This includes the obvious fact that cloaking does not work at all for horizontal or for ordinary linear polarization of light. Moreover, more subtle effects occur such as viewing-angle-dependent aberrations. However, we still find amazingly good cloaking performance for the purely dielectric azimuthal uniaxial cloak. PMID:23263067

  9. The Bloch point in uniaxial ferromagnets as a quantum mechanical object

    PubMed Central

    2014-01-01

    Quantum effects such as tunneling through pinning barrier of the Bloch Point and over-barrier reflection from the defect potential of one have been investigated in ferromagnets with uniaxial strong magnetic anisotropy. It is found that these phenomena can be appeared only in subhelium temperature range. PMID:24646347

  10. Photorealistic ray tracing of free-space invisibility cloaks made of uniaxial dielectrics.

    PubMed

    Halimeh, Jad C; Wegener, Martin

    2012-12-17

    The design rules of transformation optics generally lead to spatially inhomogeneous and anisotropic impedance-matched magneto-dielectric material distributions for, e.g., free-space invisibility cloaks. Recently, simplified anisotropic non-magnetic free-space cloaks made of a locally uniaxial dielectric material (calcite) have been realized experimentally. In a two-dimensional setting and for in-plane polarized light propagating in this plane, the cloaking performance can still be perfect for light rays. However, for general views in three dimensions, various imperfections are expected. In this paper, we study two different purely dielectric uniaxial cylindrical free-space cloaks. For one, the optic axis is along the radial direction, for the other one it is along the azimuthal direction. The azimuthal uniaxial cloak has not been suggested previously to the best of our knowledge. We visualize the cloaking performance of both by calculating photorealistic images rendered by ray tracing. Following and complementing our previous ray-tracing work, we use an equation of motion directly derived from Fermat's principle. The rendered images generally exhibit significant imperfections. This includes the obvious fact that cloaking does not work at all for horizontal or for ordinary linear polarization of light. Moreover, more subtle effects occur such as viewing-angle-dependent aberrations. However, we still find amazingly good cloaking performance for the purely dielectric azimuthal uniaxial cloak.

  11. Analysis of saturation transfer electron paramagnetic resonance spectra of a spin-labeled integral membrane protein, band 3, in terms of the uniaxial rotational diffusion model.

    PubMed Central

    Hustedt, E J; Beth, A H

    1995-01-01

    Algorithms have been developed for the calculation of saturation transfer electron paramagnetic resonance (ST-EPR) spectra of a nitroxide spin-label assuming uniaxial rotational diffusion, a model that is frequently used to describe the global rotational dynamics of large integral membrane proteins. One algorithm explicitly includes terms describing Zeeman overmodulation effects, whereas the second more rapid algorithm treats these effects approximately using modified electron spin-lattice and spin-spin relaxation times. Simulations are presented to demonstrate the sensitivity of X-band ST-EPR spectra to the rate of uniaxial rotational diffusion and the orientation of the nitroxide probe with respect to the diffusion axis. Results obtained by using the algorithms presented, which are based on the transition-rate formalism, are in close agreement with those obtained by using an eigenfunction expansion approach. The effects of various approximations used in the simulation algorithms are considered in detail. Optimizing the transition-rate formalism to model uniaxial rotational diffusion results in over an order of magnitude reduction in computation time while allowing treatment of nonaxial A- and g-tensors. The algorithms presented here are used to perform nonlinear least-squares analyses of ST-EPR spectra of the anion exchange protein of the human erythrocyte membrane, band 3, which has been affinity spin-labeled with a recently developed dihydrostilbene disulfonate derivative, [15N,2H13]-SL-H2DADS-MAL. These results suggest that all copies of band 3 present in intact erythrocytes undergo rotational diffusion about the membrane normal axis at a rate consistent with a band 3 dimer. PMID:8534811

  12. Describing Soils: Calibration Tool for Teaching Soil Rupture Resistance

    ERIC Educational Resources Information Center

    Seybold, C. A.; Harms, D. S.; Grossman, R. B.

    2009-01-01

    Rupture resistance is a measure of the strength of a soil to withstand an applied stress or resist deformation. In soil survey, during routine soil descriptions, rupture resistance is described for each horizon or layer in the soil profile. The lower portion of the rupture resistance classes are assigned based on rupture between thumb and…

  13. In situ ultra-small-angle X-ray scattering study under uniaxial stretching of colloidal crystals prepared by silica nanoparticles bearing hydrogen-bonding polymer grafts.

    PubMed

    Ishige, Ryohei; Williams, Gregory A; Higaki, Yuji; Ohta, Noboru; Sato, Masugu; Takahara, Atsushi; Guan, Zhibin

    2016-05-01

    A molded film of single-component polymer-grafted nanoparticles (SPNP), consisting of a spherical silica core and densely grafted polymer chains bearing hydrogen-bonding side groups capable of physical crosslinking, was investigated by in situ ultra-small-angle X-ray scattering (USAXS) measurement during a uniaxial stretching process. Static USAXS revealed that the molded SPNP formed a highly oriented twinned face-centered cubic (f.c.c.) lattice structure with the [11-1] plane aligned nearly parallel to the film surface in the initial state. Structural analysis of in situ USAXS using a model of uniaxial deformation induced by rearrangement of the nanoparticles revealed that the f.c.c. lattice was distorted in the stretching direction in proportion to the macroscopic strain until the strain reached 35%, and subsequently changed into other f.c.c. lattices with different orientations. The lattice distortion and structural transition behavior corresponded well to the elastic and plastic deformation regimes, respectively, observed in the stress-strain curve. The attractive interaction of the hydrogen bond is considered to form only at the top surface of the shell and then plays an effective role in cross-linking between nanoparticles. The rearrangement mechanism of the nanoparticles is well accounted for by a strong repulsive interaction between the densely grafted polymer shells of neighboring particles. PMID:27158507

  14. Orientation dependence of void growth at triple junction of grain boundaries in nanoscale tricrystal nickel film subjected to uniaxial tensile loading

    NASA Astrophysics Data System (ADS)

    Zhang, Yanqiu; Jiang, Shuyong; Zhu, Xiaoming; Sun, Dong

    2016-11-01

    Molecular dynamics simulation was performed in order to investigate the dependence of void growth on crystallographic orientation at the triple junction of grain boundaries in nanoscale tricrystal nickel film subjected to uniaxial tensile loading. The nucleation, the emission and the transmission of Shockley partial dislocations play a predominant role in the growth of void at the triple junction of grain boundaries. The orientation factors of various slip systems are calculated according to Schmid law. The slip systems activated in a grain of tricrystal nickel film basically conform to Schmid law which is completely suitable for a single crystal. The activated slip systems play an important role in plastic deformation of nanoscale tricrystal nickel film subjected to uniaxial tensile loading. The slip directions exhibit great difference among the activated slip systems such that the void is caused to be subjected to various stress conditions, which further leads to the difference in void growth among the tricrystal nickel films with different orientation distributions. It can be concluded that the grain orientation distribution has a significant influence on void growth at the triple junction of grain boundaries.

  15. Mullins effect in a filled elastomer under uniaxial tension.

    PubMed

    Maiti, A; Small, W; Gee, R H; Weisgraber, T H; Chinn, S C; Wilson, T S; Maxwell, R S

    2014-01-01

    Modulus softening and permanent set in filled polymeric materials due to cyclic loading and unloading, commonly known as the Mullins effect, can have a significant impact on their use as support cushions. A quantitative analysis of such behavior is essential to ensure the effectiveness of such materials in long-term deployment. In this work we combine existing ideas of filler-induced modulus enhancement, strain amplification, and irreversible deformation within a simple non-Gaussian constitutive model to quantitatively interpret recent measurements on a relevant PDMS-based elastomeric cushion. We find that the experimental stress-strain data is consistent with the picture that during stretching (loading) two effects take place simultaneously: (1) the physical constraints (entanglements) initially present in the polymer network get disentangled, thus leading to a gradual decrease in the effective cross-link density, and (2) the effective filler volume fraction gradually decreases with increasing strain due to the irreversible pulling out of an initially occluded volume of the soft polymer domain. PMID:24580250

  16. Mullins effect in a filled elastomer under uniaxial tension

    NASA Astrophysics Data System (ADS)

    Maiti, A.; Small, W.; Gee, R. H.; Weisgraber, T. H.; Chinn, S. C.; Wilson, T. S.; Maxwell, R. S.

    2014-01-01

    Modulus softening and permanent set in filled polymeric materials due to cyclic loading and unloading, commonly known as the Mullins effect, can have a significant impact on their use as support cushions. A quantitative analysis of such behavior is essential to ensure the effectiveness of such materials in long-term deployment. In this work we combine existing ideas of filler-induced modulus enhancement, strain amplification, and irreversible deformation within a simple non-Gaussian constitutive model to quantitatively interpret recent measurements on a relevant PDMS-based elastomeric cushion. We find that the experimental stress-strain data is consistent with the picture that during stretching (loading) two effects take place simultaneously: (1) the physical constraints (entanglements) initially present in the polymer network get disentangled, thus leading to a gradual decrease in the effective cross-link density, and (2) the effective filler volume fraction gradually decreases with increasing strain due to the irreversible pulling out of an initially occluded volume of the soft polymer domain.

  17. Mullins effect in a filled elastomer under uniaxial tension

    DOE PAGESBeta

    Maiti, A.; Small, W.; Gee, R. H.; Weisgraber, T. H.; Chinn, S. C.; Wilson, T. S.; Maxwell, R. S.

    2014-01-16

    Modulus softening and permanent set in filled polymeric materials due to cyclic loading and unloading, commonly known as the Mullins effect, can have a significant impact on their use as support cushions. The quantitative analysis of such behavior is essential to ensure the effectiveness of such materials in long-term deployment. In this work we combine existing ideas of filler-induced modulus enhancement, strain amplification, and irreversible deformation within a simple non-Gaussian constitutive model to quantitatively interpret recent measurements on a relevant PDMS-based elastomeric cushion. Also, we find that the experimental stress-strain data is consistent with the picture that during stretching (loading)more » two effects take place simultaneously: (1) the physical constraints (entanglements) initially present in the polymer network get disentangled, thus leading to a gradual decrease in the effective cross-link density, and (2) the effective filler volume fraction gradually decreases with increasing strain due to the irreversible pulling out of an initially occluded volume of the soft polymer domain.« less

  18. Mullins effect in a filled elastomer under uniaxial tension

    SciTech Connect

    Maiti, A.; Small, W.; Gee, R. H.; Weisgraber, T. H.; Chinn, S. C.; Wilson, T. S.; Maxwell, R. S.

    2014-01-16

    Modulus softening and permanent set in filled polymeric materials due to cyclic loading and unloading, commonly known as the Mullins effect, can have a significant impact on their use as support cushions. The quantitative analysis of such behavior is essential to ensure the effectiveness of such materials in long-term deployment. In this work we combine existing ideas of filler-induced modulus enhancement, strain amplification, and irreversible deformation within a simple non-Gaussian constitutive model to quantitatively interpret recent measurements on a relevant PDMS-based elastomeric cushion. Also, we find that the experimental stress-strain data is consistent with the picture that during stretching (loading) two effects take place simultaneously: (1) the physical constraints (entanglements) initially present in the polymer network get disentangled, thus leading to a gradual decrease in the effective cross-link density, and (2) the effective filler volume fraction gradually decreases with increasing strain due to the irreversible pulling out of an initially occluded volume of the soft polymer domain.

  19. A luminescent nanocrystal stress gauge

    SciTech Connect

    Choi, Charina; Koski, Kristie; Olson, Andrew; Alivisatos, Paul

    2010-10-25

    Microscale mechanical forces can determine important outcomes ranging from the site of material fracture to stem cell fate. However, local stresses in a vast majority of systems cannot be measured due to the limitations of current techniques. In this work, we present the design and implementation of the CdSe/CdS core/shell tetrapod nanocrystal, a local stress sensor with bright luminescence readout. We calibrate the tetrapod luminescence response to stress, and use the luminescence signal to report the spatial distribution of local stresses in single polyester fibers under uniaxial strain. The bright stress-dependent emission of the tetrapod, its nanoscale size, and its colloidal nature provide a unique tool that may be incorporated into a variety of micromechanical systems including materials and biological samples to quantify local stresses with high spatial resolution.

  20. Morphologic Interpretation of Rock Failure Mechanisms Under Uniaxial Compression Based on 3D Multiscale High-resolution Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Li, Gen; Liang, Zheng-Zhao; Tang, Chun-An

    2015-11-01

    Multiscale continuous lab oratory observation of the progressive failure process has become a powerful means to reveal the complex failure mechanism of rock. Correspondingly, the representative volume element (RVE)-based models, which are capable of micro/meso- to macro-scale simulations, have been proposed, for instance, the rock failure process analysis (RFPA) program. Limited by the computational bottleneck due to the RVE size, multiscale high-resolution modeling of rock failure process can hardly be implemented, especially for three-dimensional (3D) problems. In this paper, the self-developed parallel RFPA3D code is employed to investigate the failure mechanisms and various fracture morphology of laboratory-scale rectangular prism rock specimens under unconfined uniaxial compression. The specimens consist of either heterogeneous rock with low strength or relatively homogeneous rock with high strength. The numerical simulations, such as the macroscopic fracture pattern and stress-strain responses, can reproduce the well-known phenomena of physical experiments. In particular, the 3D multiscale continuum modeling is carried out to gain new insight into the morphologic interpretation of brittle failure mechanisms, which is calibrated and validated by comparing the actual laboratory experiments and field evidence. The advantages of 3D multiscale high-resolution modeling are demonstrated by comparing the failure modes against 2D numerical predictions by other models. The parallel RVE-based modeling tool in this paper can provide an alternative way to investigate the complicated failure mechanisms of rock.

  1. Microcrack closure in rocks under stress - Direct observation

    NASA Technical Reports Server (NTRS)

    Batzle, M. L.; Simmons, G.; Siegfried, R. W.

    1980-01-01

    Direct observations of the closure of microcracks in rocks under increasing stress are reported. Uniaxial stresses up to 300 bars were applied to untreated and previously heated samples of Westerly granite and Frederick diabase by a small hydraulic press which fit entirely within a scanning electron microscope. Crack closure characteristics are found to depend on crack orientation, with cracks perpendicular to the applied stress closing and those parallel tending to open, as well as crack aspect ratio, crack intersection properties, stress concentrations and surface roughness. Uniaxial and hydrostatic stress measurements are found to be strongly dependent on fracture content as observed by SEM, and the observed hysteresis in strain measurements in the first stress cycles is also related to microscopic processes

  2. Stress induced long wavelength photoconductivity in doped silicon infrared detectors

    NASA Technical Reports Server (NTRS)

    Houck, J. R.

    1982-01-01

    The long wavelength cutoff of a Si:P detector was extended to 34 microns by the application of a uniaxial stress. An unstressed Si:P photoconductive detector responds to photons of up to 28 microns wavelength. By applying a uniaxial stress to a detector along the /100/ crystal axis, the response was extended to approximately 34 microns. The /100/ axis was chosen as the stress direction because theoretical calculations predicted that such a stress extends the wavelength response more than one along the /110/ axis. These theoretical calculations were based upon fits to experimental data obtained at stresses of up to approximately kbar, and indicated that the extension in wavelength response continues to increase at much larger stresses.

  3. Geochemical changes and fracture development in Woodford Shale cores following hydrous pyrolysis under uniaxial confinement

    USGS Publications Warehouse

    Birdwell, Justin E.; Lewan, Michael D.; Miller, Michael; Baez, Luis; Beeney, Ken; Sonnenberg, Steve

    2013-01-01

    A uniaxial confinement clamp was used on Woodford Shale cores in hydrous pyrolysis experiments to study fracture development during thermal maturation. The clamp simulates overburden in that it prevents cores from expanding perpendicular to bedding fabric during the volume-increasing reactions associated with petroleum generation. Cores were cut from a slab of immature Woodford Shale and subjected to hydrous pyrolysis under confinement at 300, 330, and 365 °C for 72 hours to induce thermal maturities ranging from early bitumen to maximum expelled-oil generation. Two additional cores were used as experimental controls: (1) a confined core was saturated with water by heating it to 100 °C under hydrous pyrolysis conditions for 72 hours to use for characterization of the original rock, and (2) an unconfined core was heated at 365 °C for 72 hours to evaluate the effects of confinement on petroleum generation and expulsion. X-ray computed tomography (X-CT) imaging and other analyses identified five distinct beds within the cored interval. Using a tentative classification system, beds 1, 2, and 3 are described as dolomitic marlstone (DM) with total organic carbon (TOC) contents of 7.7, 5.8, and 7.7 wt. %, respectively; bed 4 is a cherty quartzose claystone (CQC) with TOC content of 5.5 wt. %; and bed 5 is a quartzose claystone with TOC content of 10.9 wt. %. Bed samples all had similar Rock-Eval hydrogen indices (600 ± 46 mg S2/g-TOC) and Tmax values (433 ± 2 °C), demonstrating organic matter uniformity and low thermal maturity. The X-CT scan of the core heated to 100 °C showed preexisting fractures that were nearly perpendicular to the bedding fabric primarily in the low-TOC DM bed 2 and CQC bed 4. Heating led to enhancement of preexisting fractures in the confined cores with the greatest enhancement occurring in CQC bed 4. The fractures increased in size and intensity with temperature. This is attributed to the internal pressure generated by volume

  4. Optical functions of uniaxial ZnO determined by generalized ellipsometry

    SciTech Connect

    Jellison, G.E. , Jr. and; Boatner, L.A.

    1998-08-01

    The optical functions of uniaxial ZnO have been determined using two-modulator generalized ellipsometry, where a single measurement is sufficient to determine the optical functions from appropriately aligned uniaxial crystals. Above the direct band edge ({approximately}3.3thinspeV), this technique produces the most accurate values of the optical functions of ZnO presently available, while the refractive indices determined below the direct band edge agree with minimum-deviation methods. Near the direct band edge, the optical functions are modified by the excitonic interaction with a three-dimensional critical point. The optical dielectric response functions are fit to a recent formulation by Holden {ital et al.} [Phys. Rev. B {bold 56}, 4037 (1997)]. One isotropic point in the spectrum was observed at 3.114 eV, and a near-isotropic point near 3.31{endash}3.34 eV. {copyright} {ital 1998} {ital The American Physical Society}

  5. Maier-Saupe model for a mixture of uniaxial and biaxial molecules

    NASA Astrophysics Data System (ADS)

    Nascimento, E. S.; Henriques, E. F.; Vieira, A. P.; Salinas, S. R.

    2015-12-01

    We introduce shape variations in a liquid-crystalline system by considering an elementary Maier-Saupe lattice model for a mixture of uniaxial and biaxial molecules. Shape variables are treated in the annealed (thermalized) limit. We analyze the thermodynamic properties of this system in terms of temperature T , concentration c of intrinsically biaxial molecules, and a parameter Δ associated with the degree of biaxiality of the molecules. At the mean-field level, we use standard techniques of statistical mechanics to draw global phase diagrams, which are shown to display a rich structure, including uniaxial and biaxial nematic phases, a reentrant ordered region, and many distinct multicritical points. Also, we use the formalism to write an expansion of the free energy in order to make contact with the Landau-de Gennes theory of nematic phase transitions.

  6. The influence of uniaxial prestrain on biaxial r-values in 7075-O aluminium alloy

    SciTech Connect

    Anderson, N.; Brown, D.; McMurray, R. J.; Leacock, A. G.

    2011-05-04

    Biaxial test methods have been used to determine, not only yield behaviour under biaxial conditions, but also the strain response. This paper examines the influence of uniaxial prestrain upon the biaxial r-value by extending the disc compression test procedure proposed by Barlat et al. The extension involved the use of digital image measurements of in-plane strains. The material examined was a 7075-O condition aluminium alloy. The results of the experimental programme indicated that the biaxial r-value is unaffected by uniaxial prestrain. When using the disc compression test, the mode of deformation and therefore the biaxial r-value were found to be very sensitive to the prevailing friction conditions.

  7. Deformation analysis of ferrite/pearlite banded structure under uniaxial tension using digital image correlation

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaochuan; Wang, Yong; Yang, Jia; Qiao, Zhixia; Ren, Chunhua; Chen, Cheng

    2016-10-01

    The ferrite/pearlite banded structure causes the anisotropic behavior of steel. In this paper, digital image correlation (DIC) was used to analyze the micro deformation of this microstructure under uniaxial tension. The reliability of DIC for this application was verified by a zero-deformation experiment. The results show that the performance of DIC can satisfy the requirements of the tensile deformation measurement. Then, two uniaxial tensile tests in different directions (longitudinal direction and transverse direction) were carried out and DIC was used to measure the micro deformation of the ferrite/pearlite banded structure. The measured results show that the ferrite bands undergo the main deformation in the transverse tension, which results in the relatively weaker tensile properties in the transverse direction than in the longitudinal direction. This work is useful to guide the modification of the bands morphology and extend the application scope of DIC.

  8. Optical anisotropy of uniaxially drawn and silver-dispersed polyimide films

    NASA Astrophysics Data System (ADS)

    Sawada, Takashi; Ando, Shinji; Sasaki, Shigekuni

    1999-02-01

    Distinct anisotropy in optical transmittance in the visible and near-infrared region for uniaxially drawn and silver-dispersed polyimide films was observed. The films were prepared in a one-step operation that involves thermal curing and simultaneous uniaxial drawing of poly(amic acid) (PAA) films, which were made by dissolving silver nitrate in the PAA solution at a 1:4 mol ratio. The polyimide molecular chains with a rod-like structure were oriented along the drawing direction during curing, and this orientation accompanied the generation of silver nanoparticles with elongated shapes. An anisotropy in the optical transmittance of 5:1 was obtained for a 22-μm-thick film at 850 nm with transmittance of 68% perpendicular to the drawing direction. The optical and mechanical properties of this film were retained after annealing at 300 °C for 1 h.

  9. Stable evaluation of Green's functions in cylindrically stratified regions with uniaxial anisotropic layers

    NASA Astrophysics Data System (ADS)

    Moon, H.; Donderici, B.; Teixeira, F. L.

    2016-11-01

    We present a robust algorithm for the computation of electromagnetic fields radiated by point sources (Hertzian dipoles) in cylindrically stratified media where each layer may exhibit material properties (permittivity, permeability, and conductivity) with uniaxial anisotropy. Analytical expressions are obtained based on the spectral representation of the tensor Green's function based on cylindrical Bessel and Hankel eigenfunctions, and extended for layered uniaxial media. Due to the poor scaling of these eigenfunctions for extreme arguments and/or orders, direct numerical evaluation of such expressions can produce numerical instability, i.e., underflow, overflow, and/or round-off errors under finite precision arithmetic. To circumvent these problems, we develop a numerically stable formulation through suitable rescaling of various expressions involved in the computational chain, to yield a robust algorithm for all parameter ranges. Numerical results are presented to illustrate the robustness of the formulation including cases of practical interest.

  10. Pattern formation from consistent dynamical closures of uniaxial nematic liquid crystals.

    PubMed

    Híjar, Humberto; de Hoyos, Diego Marquina; Santamaría-Holek, Iván

    2012-03-21

    Pattern formation in uniaxial polymeric liquid crystals is studied for different dynamic closure approximations. Using the principles of mesoscopic non-equilibrium thermodynamics in a mean-field approach, we derive a Fokker-Planck equation for the single-particle non-homogeneous distribution function of particle orientations and the evolution equations for the second and fourth order orientational tensor parameters. Afterwards, two dynamic closure approximations are discussed, one of them considering the relaxation of the fourth order orientational parameter and leading to a novel expression for the free-energy like function in terms of the scalar order parameter. Considering the evolution equation of the density of the system and values of the interaction parameter for which isotropic and nematic phases coexist, our analysis predicts that patterns and traveling waves can be produced in lyotropic uniaxial nematics even in the absence of external driving. PMID:22443750

  11. Mechanical properties of stanene under uniaxial and biaxial loading: A molecular dynamics study

    SciTech Connect

    Mojumder, Satyajit; Amin, Abdullah Al; Islam, Md Mahbubul

    2015-09-28

    Stanene, a graphene like two dimensional honeycomb structure of tin has attractive features in electronics application. In this study, we performed molecular dynamics simulations using modified embedded atom method potential to investigate mechanical properties of stanene. We studied the effect of temperature and strain rate on mechanical properties of α-stanene for both uniaxial and biaxial loading conditions. Our study suggests that with the increasing temperature, both the fracture strength and strain of the stanene decrease. Uniaxial loading in zigzag direction shows higher fracture strength and strain compared to the armchair direction, while no noticeable variation in the mechanical properties is observed for biaxial loading. We also found at a higher loading rate, material exhibits higher fracture strength and strain. These results will aid further investigation of stanene as a potential nano-electronics substitute.

  12. Quantum spin Hall insulator phase in monolayer WTe2 by uniaxial strain

    NASA Astrophysics Data System (ADS)

    Xiang, Hui; Xu, Bo; Liu, Jinqiu; Xia, Yidong; Lu, Haiming; Yin, Jiang; Liu, Zhiguo

    2016-09-01

    Monolayer WTe2, which is predicted to be large-gap quantum spin Hall (QSH) insulators with distorted 1T (1T') structure, attracts rapidly growing interests. However, the intrinsic semimetallic nature of the monolayer 1T'-WTe2 limits their direct applications based on QSH effect. By first-principles density functional theoretical calculations, we demonstrate a phase transition from semimetal to QSH insulator under the uniaxial strains along a and b axis in monolayer 1T'-WTe2. The electronic phase transition results from the geometric structure deformation upon the uniaxial strains. This suggests monolayer 1T'-WTe2 as a promising material for application in strain-tunable topological quantum electronics.

  13. Maier-Saupe model for a mixture of uniaxial and biaxial molecules.

    PubMed

    Nascimento, E S; Henriques, E F; Vieira, A P; Salinas, S R

    2015-12-01

    We introduce shape variations in a liquid-crystalline system by considering an elementary Maier-Saupe lattice model for a mixture of uniaxial and biaxial molecules. Shape variables are treated in the annealed (thermalized) limit. We analyze the thermodynamic properties of this system in terms of temperature T, concentration c of intrinsically biaxial molecules, and a parameter Δ associated with the degree of biaxiality of the molecules. At the mean-field level, we use standard techniques of statistical mechanics to draw global phase diagrams, which are shown to display a rich structure, including uniaxial and biaxial nematic phases, a reentrant ordered region, and many distinct multicritical points. Also, we use the formalism to write an expansion of the free energy in order to make contact with the Landau-de Gennes theory of nematic phase transitions. PMID:26764707

  14. Thermomechanical characterization of Hastelloy-X under uniaxial cyclic loading

    NASA Technical Reports Server (NTRS)

    Ellis, J. R.; Bartolotta, P. A.; Allen, G. P.; Robinson, D. N.

    1986-01-01

    In most high-temperature engineering applications, components are subjected to complex combinations of thermal and mechanical loading during service. A number of viscoplastic constitutive models were proposed which potentially can provide mathematical descriptions of material response under such conditions. Implementation of these models into large finite element codes such as MARC has already resulted in much improved inelastic analysis capability for hot-section aircraft engine components. However, a number of questions remain regarding the validity of methods adopted in characterizing these constitutive models for particular high-temperature materials. One area of concern is that the majority of experimental data available for this purpose are determined under isothermal conditions. This is in contrast to service conditions which, as noted above, almost always involve some form of thermal cycling. The obvious question arises as to whether a constitutive model characterized using an isothermal data base can adequately predict material response under thermomechanical conditions. An experimental program was initiated within the HOST program to address this particular concern. The results of the most recent isothermal and thermomechanical experiments are described.

  15. Amorphization of biperiodic domain structures in quasi-uniaxial magnetic films with a critical thickness

    NASA Astrophysics Data System (ADS)

    Arzamastseva, G. V.; Evtikhov, M. G.; Lisovskiĭ, F. V.; Mansvetova, E. G.; Temiryazeva, M. P.

    2008-08-01

    The behavior of biperiodic stripe domain structures in quasi-uniaxial magnetic films with a near-critical thickness is studied by scanning magnetic force microscopy and magnetooptical diffraction. In these films, antiphase and hybrid biperiodic domain structures are found to be absent, and the phase transitions between monoperiodic and in-phase biperiodic domain structures are shown to proceed through two-dimensional domain arrays that are amorphized in the arrangement of near-surface distortions in the domain-wall profile.

  16. Uniaxial magnetic anisotropy of rhombohedral CoCO3 crystals at T = 0 K

    NASA Astrophysics Data System (ADS)

    Men'shikov, V. V.; Rudenko, V. V.; Tugarinov, V. I.; Vorotynov, A. M.; Ovchinnikov, S. G.

    2014-03-01

    A method for calculating the contribution of exchange interaction to uniaxial anisotropy with the use of g' factors has been worked out using CoCO3 crystals as an example. The calculated contribution of dipole-dipole interactions to the anisotropy of CoCO3 is 0.93 cm-1. The sum of the contributions to the anisotropy constant of CoCO3 with the inclusion of the dipole-dipole interactions is 36.1 cm-1.

  17. Validity of uniaxial accelerometry during activities of daily living in children.

    PubMed

    Eisenmann, Joey C; Strath, Scott J; Shadrick, Danny; Rigsby, Paul; Hirsch, Nicole; Jacobson, Leigh

    2004-03-01

    The purpose of this study was to examine the validity of treadmill-based equations of two commonly used uniaxial accelerometers to estimate energy expenditure (EE) during activities of daily living in children. Twelve subjects with mean (SD) age11.4 (0.4) years engaged in a choreographed routine consisting of three activities (sweeping, bowling, and basketball) of 4min duration while wearing a Manufacturing Technology, Inc. (MTI) accelerometer, Caltrac accelerometer, and a portable gas analyzer (Cosmed K4b(2)). The equations of Trost et al. and Sallis et al. were used to convert activity counts to estimations of EE for the MTI and Caltrac, respectively. Correlation coefficients between Caltrac predictions of EE and measured EE from indirect calorimetry ranged from r=0.22 to 0.72 for individual activities. Correlations between MTI EE predictions and indirect calorimetry ranged from r=0.50 to 0.68 for individual activities. When the activities were pooled the correlations between EE from uniaxial accelerometers and EE from indirect calorimetry were moderately strong (MTI, r=0.78 and Caltrac, r=0.82). Inter-accelerometer (counts min(-1)) correlations were 0.08, -0.54, 0.63, and 0.79 for sweeping, bowling, basketball, and pooled data, respectively. The overall mean difference, or bias, and 95% confidence intervals (CI) for each uniaxial accelerometer compared to indirect calorimetry were as follows: Caltrac, bias = 2.80 (2.36, 3.24) kcal min(-1); MTI, bias = 0.88 (0.23, 1.53) kcal min(-1). Both accelerometers significantly underestimated measured EE ( P<0.05). Uniaxial accelerometers provide potential for the measurement of physical activity (PA) and EE in children. Future studies refining accelerometry predictions of PA and EE are warranted.

  18. Phase diagram of the uniaxial and biaxial soft-core Gay-Berne model

    NASA Astrophysics Data System (ADS)

    Berardi, Roberto; Lintuvuori, Juho S.; Wilson, Mark R.; Zannoni, Claudio

    2011-10-01

    Classical molecular dynamics simulations have been used to explore the phase diagrams for a family of attractive-repulsive soft-core Gay-Berne models [R. Berardi, C. Zannoni, J. S. Lintuvuori, and M. R. Wilson, J. Chem. Phys. 131, 174107 (2009)] and determine the effect of particle softness, i.e., of a moderately repulsive short-range interaction, on the order parameters and phase behaviour of model systems of uniaxial and biaxial ellipsoidal particles. We have found that isotropic, uniaxial, and biaxial nematic and smectic phases are obtained for the model. Extensive calculations of the nematic region of the phase diagram show that endowing mesogenic particles with such soft repulsive interactions affect the stability range of the nematic phases, and in the case of phase biaxiality it also shifts it to lower temperatures. For colloidal particles, stabilised by surface functionalisation, (e.g., with polymer chains), we suggest that it should be possible to tune liquid crystal behaviour to increase the range of stability of uniaxial and biaxial phases (by varying solvent quality). We calculate second virial coefficients and show that they are a useful means of characterising the change in effective softness for such systems. For thermotropic liquid crystals, the introduction of softness in the interactions between mesogens with overall biaxial shape (e.g., through appropriate conformational flexibility) could provide a pathway for the actual chemical synthesis of stable room-temperature biaxial nematics.

  19. Impact of uniaxial pressure on structural and magnetic phase transitions in electron-doped iron pnictides

    NASA Astrophysics Data System (ADS)

    Lu, Xingye; Tseng, Kuo-Feng; Keller, T.; Zhang, Wenliang; Hu, Ding; Song, Yu; Man, Haoran; Park, J. T.; Luo, Huiqian; Li, Shiliang; Nevidomskyy, Andriy H.; Dai, Pengcheng

    2016-04-01

    We use neutron resonance spin echo and Larmor diffraction to study the effect of uniaxial pressure on the tetragonal-to-orthorhombic structural (Ts) and antiferromagnetic (AF) phase transitions in iron pnictides BaFe2 -xNixAs2 (x =0 ,0.03 ,0.12 ),SrFe1.97Ni0.03As2, and BaFe2(As0.7P0.3)2. In antiferromagnetically ordered BaFe2 -xNixAs2 and SrFe1.97Ni0.03As2 with TN and Ts (TN≤Ts ), a uniaxial pressure necessary to detwin the sample also increases TN, smears out the structural transition, and induces an orthorhombic lattice distortion at all temperatures. By comparing temperature and doping dependence of the pressure induced lattice parameter changes with the elastoresistance and nematic susceptibility obtained from transport and ultrasonic measurements, we conclude that the in-plane resistivity anisotropy found in the paramagnetic state of electron underdoped iron pnictides depends sensitively on the nature of the magnetic phase transition and a strong coupling between the uniaxial pressure induced lattice distortion and electronic nematic susceptibility.

  20. Uniaxial strain-induced Kohn anomaly and electron-phonon coupling in acoustic phonons of graphene

    NASA Astrophysics Data System (ADS)

    Cifuentes-Quintal, M. E.; de la Peña-Seaman, O.; Heid, R.; de Coss, R.; Bohnen, K.-P.

    2016-08-01

    Recent advances in strain engineering at the nanoscale have shown the feasibility to modulate the properties of graphene. Although the electron-phonon (e-ph) coupling and Kohn anomalies in graphene define the phonon branches contributing to the resonance Raman scattering and are relevant to the electronic and thermal transport as a scattering source, the evolution of the e-ph coupling as a function of strain has been less studied. In this work, the Kohn anomalies and the e-ph coupling in uniaxially strained graphene along armchair and zigzag directions were studied by means of density functional perturbation theory calculations. In addition to the phonon anomaly at the transversal optical (TO) phonon branch in the K point for pristine graphene, we found that uniaxial strain induces a discontinuity in the frequency derivative of the longitudinal acoustic phonon branch. This behavior corresponds to the emergence of a Kohn anomaly, as a consequence of a strain-enhanced e-ph coupling. Thus, the present results for uniaxially strained graphene contrast with the commonly assumed view that the e-ph coupling around the K point is only present in the TO phonon branch.

  1. Preparation of uniaxial multichannel silk fibroin scaffolds for guiding primary neurons.

    PubMed

    Zhang, Qiang; Zhao, Yahong; Yan, Shuqin; Yang, Yumin; Zhao, Huijing; Li, Mingzhong; Lu, Shenzhou; Kaplan, David L

    2012-07-01

    Physical guidance cues have been exploited to stimulate neuron adhesion and neurite outgrowth. In the present study, three-dimensional (3-D) silk fibroin scaffolds with uniaxial multichannels (42-142 μm in diameter) were prepared by a directional temperature field freezing technique, followed by lyophilization. By varying the initial silk fibroin concentration, the chemical potential and quantity of free water around cylindrical ice crystals could be controlled to control the cross-section morphology of the scaffold channels. Aligned ridges also formed on the inner surface of the multichannels in parallel to the direction of the channels. In vitro, primary hippocampal neurons were seeded in these 3-D silk fibroin scaffolds with uniaxial multichannels of ∼120 μm in diameter. The morphology of the neurons was multipolar and alignment along the scaffold channels was observed. Cell-cell networks and cell-matrix interactions established by newly formed axons were observed after 7 days in culture. These neurons expressed β-III-tubulin, nerve filament and microtubule-associated protein, while glial fibrillary acidic protein immunofluorescence was barely above background. The ridges on the inner surface of the channels played a critical role in the adhesion and extension of neurons by providing continuous contact guidance. These new 3-D silk scaffolds with uniaxial multichannels provided a favorable microenvironment for the development of hippocampal neurons by guiding axonal elongation and cell migration.

  2. Dirac points and van Hove singularities of silicene under uniaxial strain

    SciTech Connect

    Lin, Xianqing; Ni, Jun

    2015-04-28

    First-principles calculations have been performed to investigate the low energy electronic properties and van Hove singularities (VHSs) of silicene under uniaxial strain. The Dirac points (DPs) persist when silicene is stretched uniaxially, while they are shifted away from the corners (K points) of the first Brillouin zone (FBZ). The relative positions of DPs with respect to the K points for silicene strained along the armchair (AC) or zigzag (ZZ) direction show opposite tendency compared with strained graphene, which is due to the larger deformation of the unit cell of strained silicene than that of strained graphene. Moreover, for silicene under AC or ZZ strain, the Fermi velocities around DPs along the positive and negative directions of the FBZ show rather significant difference. The nature of the VHS just above the Fermi energy undergoes a transition from the π* band to the σ* band for silicene under increasing AC or ZZ strain. These observations suggest uniaxial strain as an effective route to tune the electronic properties of silicene for potential applications in future electronic devices.

  3. Cellular automata to describe seismicity: A review

    NASA Astrophysics Data System (ADS)

    Jiménez, Abigail

    2013-12-01

    Cellular Automata have been used in the literature to describe seismicity. We first historically introduce Cellular Automata and provide some important definitions. Then we proceed to review the most important models, most of them being variations of the spring-block model proposed by Burridge and Knopoff, and describe the most important results obtained from them. We discuss the relation with criticality and also describe some models that try to reproduce real data.

  4. Utilization of fiber optic Bragg grating sensors in concrete columns confined with glass-fiber-reinforced plastic (GFRP) laminate under uniaxial compression test

    NASA Astrophysics Data System (ADS)

    Chan, Peter K. C.; Lau, Alan K.; Jin, Wei; Zhou, Limin

    1999-01-01

    In this paper we report of experimental studies on strain monitoring by using fiber Bragg grating sensors in concrete structures. The strain variation of the specimen under different loading conditions were monitored by the Fiber- optic Bragg grating (FBG) sensors. The FBG sensors have been pre-installed in the structure by embedding either inside the concrete specimen or at the interface between the concrete and the composites. The strain reading from the fiber grating sensor compares favorably with that obtained from the conventional strain gauge in uni-axial compression testing. The test result generally indicated that the concrete structures can be strengthened significantly by wrapping with glassfiber composites. The sensor embedded at the notch tip provides a very good indication of the health condition of the strengthened structure, especially in high stress concentration area. The strain sensitivity by using FBG sensor is 67 (mu) (epsilon) .

  5. Multistep energy migration between 3,3‧-diethyl-9-methylthiacarbocyanine iodide monomers in uniaxially oriented polymer films

    NASA Astrophysics Data System (ADS)

    Bojarski, Piotr; Gryczyński, Ignacy; Kułak, Leszek; Synak, Anna; Bharill, Shashank; Rangełowa, Simeonika; Szabelski, Mariusz

    2007-05-01

    Multistep energy migration was studied for 3,3'-diethyl-9-methylthiacarbocyanine iodide (MDTCI) in uniaxially stretched and unstretched poly(vinyl alcohol) films. At low and intermediate concentrations fluorescence anisotropy decay measurements yield completely different results for disordered and ordered systems due to strong redistribution and angular correlation of fluorophores transition moments in ordered polymer matrix. These results and other selected properties of energy transport in uniaxially stretched polymer films were analyzed using the technique of Monte-Carlo simulation.

  6. Identifying, describing, and expressing emotions after critical incidents in paramedics.

    PubMed

    Halpern, Janice; Maunder, Robert G; Schwartz, Brian; Gurevich, Maria

    2012-02-01

    For paramedics, critical incidents evoke intense emotions and may result in later psychological difficulties. We examined 2 ways to deal with emotions after critical incidents: (a) identifying emotions, and (b) describing and expressing emotions, and their association with recovery from acute stress and psychological symptoms. We surveyed 190 paramedics, examining how impaired capacity to identify and describe emotions (alexithymia) and voluntary expression of emotions during contacts with others in the first 24 hours after the incident were associated with recovery from acute stress and current symptoms of PTSD, depression, burnout, and somatization. Overall alexithymia was not associated with recovery, but the component of difficulty identifying feelings was associated with prolonged physical arousal (χ(2) = 10.1, p = .007). Overall alexithymia and all its components were associated with virtually all current symptoms (correlation coefficients .23-.38, p < .05). Voluntary emotional expression was unrelated to current symptoms. Greater emotional expression was related to greater perceived helpfulness of contacts (χ(2) = 56.8, p < .001). This suggests that identifying emotions may be important in managing occupational stress in paramedics. In contrast, voluntary emotional expression, although perceived as helpful, may not prevent symptoms. These findings may inform education for paramedics in dealing with stress.

  7. Systematically describing gross lesions in corals

    USGS Publications Warehouse

    Work, T.; Aeby, G.

    2006-01-01

    Many coral diseases are characterized based on gross descriptions and, given the lack or difficulty of applying existing laboratory tools to understanding causes of coral diseases, most new diseases will continued to be described based on appearance in the field. Unfortunately, many existing descriptions of coral disease are ambiguous or open to subjective interpretation, making comparisons between oceans problematic. One reason for this is that the process of describing lesions is often confused with that of assigning causality for the lesion. However, causality is usually something not obtained in the field and requires additional laboratory tests. Because a concise and objective morphologic description provides the foundation for a case definition of any disease, there is a need for a consistent and standardized process to describe lesions of corals that focuses on morphology. We provide a framework to systematically describe and name diseases in corals involving 4 steps: (1) naming the disease, (2) describing the lesion, (3) formulating a morphologic diagnosis and (4) formulating an etiologic diagnosis. This process focuses field investigators on describing what they see and separates the process of describing a lesion from that of inferring causality, the latter being more appropriately done using laboratory techniques.

  8. Hydrostatic, uniaxial, and triaxial compression tests on unpoled "Chem-prep" PZT 95/5-2Nb ceramic within temperature range of -55 to 75 degrees C.

    SciTech Connect

    Zeuch, David Henry; Montgomery, Stephen Tedford; Lee, Moo Yul; Hofer, John H.

    2003-10-01

    Sandia is currently developing a lead-zirconate-titanate ceramic 95/5-2Nb (or PNZT) from chemically prepared ('chem-prep') precursor powders. Previous PNZT ceramic was fabricated from the powders prepared using a 'mixed-oxide' process. The specimens of unpoled PNZT ceramic from batch HF803 were tested under hydrostatic, uniaxial, and constant stress difference loading conditions within the temperature range of -55 to 75 C and pressures to 500 MPa. The objective of this experimental study was to obtain mechanical properties and phase relationships so that the grain-scale modeling effort can develop and test its models and codes using realistic parameters. The stress-strain behavior of 'chem-prep' PNZT under different loading paths was found to be similar to that of 'mixed-oxide' PNZT. The phase transformation from ferroelectric to antiferroelectric occurs in unpoled ceramic with abrupt increase in volumetric strain of about 0.7 % when the maximum compressive stress, regardless of loading paths, equals the hydrostatic pressure at which the transformation otherwise takes place. The stress-volumetric strain relationship of the ceramic undergoing a phase transformation was analyzed quantitatively using a linear regression analysis. The pressure (P{sub T1}{sup H}) required for the onset of phase transformation with respect to temperature is represented by the best-fit line, P{sub T1}{sup H} (MPa) = 227 + 0.76 T (C). We also confirmed that increasing shear stress lowers the mean stress and the volumetric strain required to trigger phase transformation. At the lower bound (-55 C) of the tested temperature range, the phase transformation is permanent and irreversible. However, at the upper bound (75 C), the phase transformation is completely reversible as the stress causing phase transformation is removed.

  9. Venus general atmosphere circulation described by Pioneer

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The predominant weather pattern for Venus is described. Wind directions and wind velocities are given. Possible driving forces of the winds are presented and include solar heating, planetary rotation, and the greenhouse effect.

  10. Did goethe describe attention deficit hyperactivity disorder?

    PubMed

    Bonazza, Sara; Scaglione, Cesa; Poppi, Massimo; Rizzo, Giovanni

    2011-01-01

    As early as 1846, the typical symptoms of attention deficit hyperactivity disorder (ADHD) were described by Heinrich Hoffmann (1809-1894). However, in Goethe's masterpiece Faust (1832), the character of Euphorion strongly suggests ADHD diagnosis.

  11. Method of characterizing residual stress in ferromagnetic materials using a pulse histogram of acoustic emission signals

    NASA Technical Reports Server (NTRS)

    Namkung, Min (Inventor); Yost, William T. (Inventor); Kushnick, Peter W. (Inventor); Grainger, John L. (Inventor)

    1992-01-01

    The invention is a method and apparatus for characterizing residual uniaxial stress in a ferromagnetic test member by distinguishing between residual stresses resulting from positive (tension) forces and negative (compression) forces by using the distinct and known magnetoacoustic (MAC) and a magnetoacoustic emission (MAE) measurement circuit means. A switch permits the selective operation of the respective circuit means.

  12. Describing content in middle school science curricula

    NASA Astrophysics Data System (ADS)

    Schwarz-Ballard, Jennifer A.

    As researchers and designers, we intuitively recognize differences between curricula and describe them in terms of design strategy: project-based, laboratory-based, modular, traditional, and textbook, among others. We assume that practitioners recognize the differences in how each requires that students use knowledge, however these intuitive differences have not been captured or systematically described by the existing languages for describing learning goals. In this dissertation I argue that we need new ways of capturing relationships among elements of content, and propose a theory that describes some of the important differences in how students reason in differently designed curricula and activities. Educational researchers and curriculum designers have taken a variety of approaches to laying out learning goals for science. Through an analysis of existing descriptions of learning goals I argue that to describe differences in the understanding students come away with, they need to (1) be specific about the form of knowledge, (2) incorporate both the processes through which knowledge is used and its form, and (3) capture content development across a curriculum. To show the value of inquiry curricula, learning goals need to incorporate distinctions among the variety of ways we ask students to use knowledge. Here I propose the Epistemic Structures Framework as one way to describe differences in students reasoning that are not captured by existing descriptions of learning goals. The usefulness of the Epistemic Structures framework is demonstrated in the four curriculum case study examples in Part II of this work. The curricula in the case studies represent a range of content coverage, curriculum structure, and design rationale. They serve both to illustrate the Epistemic Structures analysis process and make the case that it does in fact describe learning goals in a way that captures important differences in students reasoning in differently designed curricula

  13. Residual stress measurements in carbon steel

    NASA Technical Reports Server (NTRS)

    Heyman, J. S.; Min, N.

    1986-01-01

    External dc magnetic field-induced changes in natural velocity of Rayleigh surface waves were measured in steel specimens under various stress conditions. The low field slopes of curves representing the fractional changes of natural velocity were proved to provide correct stress information in steels with different metallurgical properties. The slopes of curves under uniaxial compression, exceeding about one third of the yield stress, fell below zero in all the specimens when magnetized along the stress axis. The slopes under tension varied among different steels but remained positive in any circumstances. The stress effect was observed for both applied and residual stress. A physical interpretation of these results is given based on the stress-induced domain structure changes and the delta epsilon effect. Most importantly, it is found that the influence of detailed metallurgical properties cause only secondary effects on the obtained stress information.

  14. Development and evaluation of a device for simultaneous uniaxial compression and optical imaging of cartilage samples in vitro

    SciTech Connect

    Steinert, Marian; Kratz, Marita; Jones, David B.; Jaedicke, Volker; Hofmann, Martin R.

    2014-10-15

    In this paper, we present a system that allows imaging of cartilage tissue via optical coherence tomography (OCT) during controlled uniaxial unconfined compression of cylindrical osteochondral cores in vitro. We describe the system design and conduct a static and dynamic performance analysis. While reference measurements yield a full scale maximum deviation of 0.14% in displacement, force can be measured with a full scale standard deviation of 1.4%. The dynamic performance evaluation indicates a high accuracy in force controlled mode up to 25 Hz, but it also reveals a strong effect of variance of sample mechanical properties on the tracking performance under displacement control. In order to counterbalance these disturbances, an adaptive feed forward approach was applied which finally resulted in an improved displacement tracking accuracy up to 3 Hz. A built-in imaging probe allows on-line monitoring of the sample via OCT while being loaded in the cultivation chamber. We show that cartilage topology and defects in the tissue can be observed and demonstrate the visualization of the compression process during static mechanical loading.

  15. Quantum formalism to describe binocular rivalry.

    PubMed

    Manousakis, Efstratios

    2009-11-01

    On the basis of the general character and operation of the process of perception, a formalism is sought to mathematically describe the subjective or abstract/mental process of perception. It is shown that the formalism of orthodox quantum theory of measurement, where the observer plays a key role, is a broader mathematical foundation which can be adopted to describe the dynamics of the subjective experience. The mathematical formalism describes the psychophysical dynamics of the subjective or cognitive experience as communicated to us by the subject. Subsequently, the formalism is used to describe simple perception processes and, in particular, to describe the probability distribution of dominance duration obtained from the testimony of subjects experiencing binocular rivalry. Using this theory and parameters based on known values of neuronal oscillation frequencies and firing rates, the calculated probability distribution of dominance duration of rival states in binocular rivalry under various conditions is found to be in good agreement with available experimental data. This theory naturally explains an observed marked increase in dominance duration in binocular rivalry upon periodic interruption of stimulus and yields testable predictions for the distribution of perceptual alteration in time. PMID:19520143

  16. Sensorimotor Interference When Reasoning About Described Environments

    NASA Astrophysics Data System (ADS)

    Avraamides, Marios N.; Kyranidou, Melina-Nicole

    The influence of sensorimotor interference was examined in two experiments that compared pointing with iconic arrows and verbal responding in a task that entailed locating target-objects from imagined perspectives. Participants studied text narratives describing objects at locations around them in a remote environment and then responded to targets from memory. Results revealed only minor differences between the two response modes suggesting that bodily cues do not exert severe detrimental interference on spatial reasoning from imagined perspective when non-immediate described environments are used. The implications of the findings are discussed.

  17. Describing a Performance Improvement Specialist: The Heurist.

    ERIC Educational Resources Information Center

    Westgaard, Odin

    1997-01-01

    Describes the work of performance improvement specialists and presents a method for determining whether a particular person or position meets the job criteria. Discusses the attributes of being a heurist, or taking a holistic approach to problem solving. Lists 10 steps for a needs assessment and 30 characteristics of successful performance…

  18. How Digital Native Learners Describe Themselves

    ERIC Educational Resources Information Center

    Thompson, Penny

    2015-01-01

    Eight university students from the "digital native" generation were interviewed about the connections they saw between technology use and learning, and also their reactions to the popular press claims about their generation. Themes that emerged from the interviews were coded to show patterns in how digital natives describe themselves.…

  19. Describing Technological Paradigm Transitions: A Methodological Exploration.

    ERIC Educational Resources Information Center

    Wallace, Danny P.; Van Fleet, Connie

    1997-01-01

    Presents a humorous treatment of the "sessio taurino" (or humanistic inquiry) technique for describing changes in technological models. The fundamental tool of "sessio taurino" is a loosely-structured event known as the session, which is of indeterminate length, involves a flexible number of participants, and utilizes a preundetermined set of…

  20. Attributes of Images in Describing Tasks.

    ERIC Educational Resources Information Center

    Jorgensen, Corinne

    1998-01-01

    Report on exploratory research which investigated image attributes in a series of describing tasks. Results suggest that access to a wide range of attributes is needed to address all facets of interest and that certain classes of attributes may appear more frequently (literal objects, human form and associated attributes, color, and location).…

  1. USING TRACERS TO DESCRIBE NAPL HETEROGENEITY

    EPA Science Inventory

    Tracers are frequently used to estimate both the average travel time for water flow through the tracer swept volume and NAPL saturation. The same data can be used to develop a statistical distribution describing the hydraulic conductivity in the sept volume and a possible distri...

  2. Is the Water Heating Curve as Described?

    ERIC Educational Resources Information Center

    Riveros, H. G.; Oliva, A. I.

    2008-01-01

    We analysed the heating curve of water which is described in textbooks. An experiment combined with some simple heat transfer calculations is discussed. The theoretical behaviour can be altered by changing the conditions under which the experiment is modelled. By identifying and controlling the different parameters involved during the heating…

  3. Mechanism for the uniaxial strain dependence of the critical current in practical REBCO tapes

    NASA Astrophysics Data System (ADS)

    Osamura, Kozo; Machiya, Shutaro; Hampshire, Damian P.

    2016-06-01

    In order to elucidate the effect of uniaxial strain on the critical current of practical REBCO tapes (REBa2Cu3O7-d , RE = Y and Gd) fabricated by Superpower and SuNAM, two types of critical current measurements were carried out. In the first, the tape sample was attached directly to a universal testing machine and pulled under a tensile load. In the second, the tape was soldered to a Cu-Be springboard and then attached to the testing machine and then pushed or pulled in order to apply both tensile and compressive strains to the tape sample. An inverse parabolic behaviour was observed for the uniaxial strain dependence of the critical current of both tapes. Using synchrotron radiation, the local strain exerted on the REBCO layer was measured at room temperature under the conditions used for the two techniques for making I c measurements. On the basis of these room temperature data, the local strain exerted on the REBCO layer at 77 K was numerically evaluated. A one-dimensional chain model for current flow in the REBCO material with fractional lengths of A-domains and B-domains oriented along the uniaxial strain direction is proposed. The model can explain the parabolic strain behaviour of the critical current and shows that the strain at which the peak in I c occurs, is not only determined by pre-compression or pre-tension on the superconductor at the operating temperature, but also by the ratio of the fractional amounts of the two domains.

  4. Mechanism for the uniaxial strain dependence of the critical current in practical REBCO tapes

    NASA Astrophysics Data System (ADS)

    Osamura, Kozo; Machiya, Shutaro; Hampshire, Damian P.

    2016-06-01

    In order to elucidate the effect of uniaxial strain on the critical current of practical REBCO tapes (REBa2Cu3O7‑d , RE = Y and Gd) fabricated by Superpower and SuNAM, two types of critical current measurements were carried out. In the first, the tape sample was attached directly to a universal testing machine and pulled under a tensile load. In the second, the tape was soldered to a Cu–Be springboard and then attached to the testing machine and then pushed or pulled in order to apply both tensile and compressive strains to the tape sample. An inverse parabolic behaviour was observed for the uniaxial strain dependence of the critical current of both tapes. Using synchrotron radiation, the local strain exerted on the REBCO layer was measured at room temperature under the conditions used for the two techniques for making I c measurements. On the basis of these room temperature data, the local strain exerted on the REBCO layer at 77 K was numerically evaluated. A one-dimensional chain model for current flow in the REBCO material with fractional lengths of A-domains and B-domains oriented along the uniaxial strain direction is proposed. The model can explain the parabolic strain behaviour of the critical current and shows that the strain at which the peak in I c occurs, is not only determined by pre-compression or pre-tension on the superconductor at the operating temperature, but also by the ratio of the fractional amounts of the two domains.

  5. A Dualistic Model To Describe Computer Architectures

    NASA Astrophysics Data System (ADS)

    Nitezki, Peter; Engel, Michael

    1985-07-01

    The Dualistic Model for Computer Architecture Description uses a hierarchy of abstraction levels to describe a computer in arbitrary steps of refinement from the top of the user interface to the bottom of the gate level. In our Dualistic Model the description of an architecture may be divided into two major parts called "Concept" and "Realization". The Concept of an architecture on each level of the hierarchy is an Abstract Data Type that describes the functionality of the computer and an implementation of that data type relative to the data type of the next lower level of abstraction. The Realization on each level comprises a language describing the means of user interaction with the machine, and a processor interpreting this language in terms of the language of the lower level. The surface of each hierarchical level, the data type and the language express the behaviour of a ma-chine at this level, whereas the implementation and the processor describe the structure of the algorithms and the system. In this model the Principle of Operation maps the object and computational structure of the Concept onto the structures of the Realization. Describing a system in terms of the Dualistic Model is therefore a process of refinement starting at a mere description of behaviour and ending at a description of structure. This model has proven to be a very valuable tool in exploiting the parallelism in a problem and it is very transparent in discovering the points where par-allelism is lost in a special architecture. It has successfully been used in a project on a survey of Computer Architecture for Image Processing and Pattern Analysis in Germany.

  6. Constitutive modeling of the human Anterior Cruciate Ligament (ACL) under uniaxial loading using viscoelastic prony series and hyperelastic five parameter Mooney-Rivlin model

    NASA Astrophysics Data System (ADS)

    Chakraborty, Souvik; Mondal, Debabrata; Motalab, Mohammad

    2016-07-01

    In this present study, the stress-strain behavior of the Human Anterior Cruciate Ligament (ACL) is studied under uniaxial loads applied with various strain rates. Tensile testing of the human ACL samples requires state of the art test facilities. Furthermore, difficulty in finding human ligament for testing purpose results in very limited archival data. Nominal Stress vs. deformation gradient plots for different strain rates, as found in literature, is used to model the material behavior either as a hyperelastic or as a viscoelastic material. The well-known five parameter Mooney-Rivlin constitutivemodel for hyperelastic material and the Prony Series model for viscoelastic material are used and the objective of the analyses comprises of determining the model constants and their variation-trend with strain rates for the Human Anterior Cruciate Ligament (ACL) material using the non-linear curve fitting tool. The relationship between the model constants and strain rate, using the Hyperelastic Mooney-Rivlin model, has been obtained. The variation of the values of each coefficient with strain rates, obtained using Hyperelastic Mooney-Rivlin model are then plotted and variation of the values with strain rates are obtained for all the model constants. These plots are again fitted using the software package MATLAB and a power law relationship between the model constants and strain rates is obtained for each constant. The obtained material model for Human Anterior Cruciate Ligament (ACL) material can be implemented in any commercial finite element software package for stress analysis.

  7. Light-induced stress relief to improve flaw tolerance in network polymers

    SciTech Connect

    Long, Kevin N.; Dunn, Martin L.; Scott, Timothy F.; Turpin, Lucas P.; Qi, H. Jerry

    2010-03-15

    We demonstrate the ability to use photoactivated stress relaxation to improve flaw tolerance in network polymers. Unlike most self-healing polymers, which effectively close flaws by locally introducing healing agents (such as uncured resins), here light is used to relax elevated stresses around a flaw before it reaches a critical state, which reduces the threat that the flaw poses to the structural integrity of the material. In this study, we fabricate specimens with well-defined flaws and uniaxially stretch them to failure. By irradiating the specimens with UV light (365 nm) before failure, the nominal strain at failure is increased by 70% and the corresponding nominal stress is increased by 30% compared with nonirradiated specimens. To better understand the phenomena that occur at the multiaxial stress state at the flaw, we model the photomechanics using a recently developed finite element approach that accurately describes the light propagation, photochemistry, radical-induced network evolution, and the mechanical behavior of the material. Model predictions agree well with the experimental results and elucidate the role that photoinduced stress relaxation has on improving flaw tolerance.

  8. Ultrashort optical waveguide excitations in uniaxial silica fibers: elastic collision scenarios.

    PubMed

    Kuetche, Victor K; Youssoufa, Saliou; Kofane, Timoleon C

    2014-12-01

    In this work, we investigate the dynamics of an uniaxial silica fiber under the viewpoint of propagation of ultimately ultrashort optical waveguide channels. As a result, we unveil the existence of three typical kinds of ultrabroadband excitations whose profiles strongly depend upon their angular momenta. Looking forward to surveying their scattering features, we unearth some underlying head-on scenarios of elastic collisions. Accordingly, we address some useful and straightforward applications in nonlinear optics through secured data transmission systems, as well as laser physics and soliton theory with optical soliton dynamics.

  9. Uniaxial anisotropy and low-temperature antiferromagnetism of Mn2BO4 single crystal

    NASA Astrophysics Data System (ADS)

    Kazak, N. V.; Platunov, M. S.; Knyazev, Yu. V.; Ivanova, N. B.; Bayukov, O. A.; Vasiliev, A. D.; Bezmaternykh, L. N.; Nizhankovskii, V. I.; Gavrilkin, S. Yu.; Lamonova, K. V.; Ovchinnikov, S. G.

    2015-11-01

    The Mn2BO4 single crystals have been grown by the flux technique. A careful study of the crystal structure and magnetic properties have been carried out. The antiferromagnetic transition at TN=26 K has been traced through the dc magnetization and specific heat temperature dependences. Magnetic uniaxial anisotropy has been found with easy axis magnetization lying in the ab-plane. The obtained value of effective magnetic moment is assigned to the non-quenched orbital moment of Jahn-Teller Mn3+ ions. The discussion of magnetic properties is based on the superexchange interaction calculations.

  10. The conversion of phase structure of singular beams spreading in uniaxial crystal

    NASA Astrophysics Data System (ADS)

    Sokolenko, B.; Poletaev, D.; Rubass, A.; Volyar, A.

    2016-08-01

    The transformation of the intensity and phase of paraxial optical beams passed uniaxial crystal strictly orthogonal to the optical axis is analysed. Imbedded optical vortex in such case imputes structural disturbance to the phase and intensity distribution after anisotropic media. Considering Left and Right circular polarized components of light, we theoretically and numerically shown the dynamics of phase shaping within the rotating birefringent crystal due to anisotropic diffraction effect. Off-axial vortex experienced tangential shift at the beam component and stimulates appearance of topological pairs in vicinity of beam axis.

  11. Research of mechanics of the compact bone microvolume and porous ceramics under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Kolmakova, T. V.; Buyakova, S. P.; Kul'kov, S. N.

    2015-11-01

    The research results of the mechanics are presented and the effective mechanical characteristics under uniaxial compression of the simulative microvolume of the compact bone are defined subject to the direction of the collagen-mineral fibers, porosity and mineral content. The experimental studies of the mechanics are performed and the effective mechanical characteristics of the produced porous zirconium oxide ceramics are defined. The recommendations are developed on the selection of the ceramic samples designed to replace the fragment of the compact bone of a definite structure and mineral content.

  12. On the limits of uniaxial magnetic anisotropy tuning by a ripple surface pattern

    SciTech Connect

    Arranz, Miguel A.; Colino, Jose M.; Palomares, Francisco J.

    2014-05-14

    Ion beam patterning of a nanoscale ripple surface has emerged as a versatile method of imprinting uniaxial magnetic anisotropy (UMA) on a desired in-plane direction in magnetic films. In the case of ripple patterned thick films, dipolar interactions around the top and/or bottom interfaces are generally assumed to drive this effect following Schlömann's calculations for demagnetizing fields of an ideally sinusoidal surface [E. Schlömann, J. Appl. Phys. 41, 1617 (1970)]. We have explored the validity of his predictions and the limits of ion beam sputtering to induce UMA in a ferromagnetic system where other relevant sources of magnetic anisotropy are neglected: ripple films not displaying any evidence of volume uniaxial anisotropy and where magnetocrystalline contributions average out in a fine grain polycrystal structure. To this purpose, the surface of 100 nm cobalt films grown on flat substrates has been irradiated at fixed ion energy, fixed ion fluency but different ion densities to make the ripple pattern at the top surface with wavelength Λ and selected, large amplitudes (ω) up to 20 nm so that stray dipolar fields are enhanced, while the residual film thickness t = 35–50 nm is sufficiently large to preserve the continuous morphology in most cases. The film-substrate interface has been studied with X-ray photoemission spectroscopy depth profiles and is found that there is a graded silicon-rich cobalt silicide, presumably formed during the film growth. This graded interface is of uncertain small thickness but the range of compositions clearly makes it a magnetically dead layer. On the other hand, the ripple surface rules both the magnetic coercivity and the uniaxial anisotropy as these are found to correlate with the pattern dimensions. Remarkably, the saturation fields in the hard axis of uniaxial continuous films are measured up to values as high as 0.80 kG and obey a linear dependence on the parameter ω{sup 2}/Λ/t in quantitative agreement

  13. Buckling of an ionic polymer metal composite shell under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Shen, Linfeng; Cha, Youngsu; Shams, Adel; Porfiri, Maurizio

    2014-03-01

    In this paper, we analyze buckling of an ionic polymer metal composite (IPMC) shell subjected to uniaxial compression. A new technique is developed to fabricate tubular IPMCs using hot molding and a chemical reduction process. The short-circuit current and the mechanical deformation of the sample are recorded during the compression test. Experimental findings demonstrate that IPMC buckling can be accurately sensed via the short-circuit current, which is approximately zero during the loading phase, before exhibiting a sudden increase at the onset of the elastic instability.

  14. Uniaxial strain induced band splitting in semiconducting SrTiO3

    NASA Astrophysics Data System (ADS)

    Chang, Young Jun; Khalsa, Guru; Moreschini, Luca; Walter, Andrew L.; Bostwick, Aaron; Horn, Karsten; MacDonald, A. H.; Rotenberg, Eli

    2013-03-01

    We use angle-resolved photoemission spectroscopy to study the influence of mechanically induced uniaxial strain on the electronic structure of the oxide semiconductor SrTiO3. We observe an orbital splitting between the Ti 3dyz and 3dxy bands, which are degenerate when unperturbed. Using the k·p method, we qualitatively explain the direction and the size of the observed energy splitting. Our comprehensive understanding of band splitting explains the strain induced mobility enhancement of electron-doped SrTiO33 in terms of band degeneracy breaking and reduced interband scattering. Our approach can be extended to differently strained oxide systems.

  15. Research of mechanics of the compact bone microvolume and porous ceramics under uniaxial compression

    SciTech Connect

    Kolmakova, T. V. Buyakova, S. P. Kul’kov, S. N.

    2015-11-17

    The research results of the mechanics are presented and the effective mechanical characteristics under uniaxial compression of the simulative microvolume of the compact bone are defined subject to the direction of the collagen-mineral fibers, porosity and mineral content. The experimental studies of the mechanics are performed and the effective mechanical characteristics of the produced porous zirconium oxide ceramics are defined. The recommendations are developed on the selection of the ceramic samples designed to replace the fragment of the compact bone of a definite structure and mineral content.

  16. Features of the Amplitude-Frequency Characteristics of Electromagnetic Emission during Uniaxial Compression of Dielectric Composites

    NASA Astrophysics Data System (ADS)

    Surzhikov, V. P.; Khorsov, N. N.

    2015-04-01

    We have studied the electromagnetic emission from samples of epoxy resin filled with sand subjected to uniaxial compression. Capacitive sensor measures the electrical component of the response when excited electromagnetic emission of ultrasonic pulse using a differential amplifier. It was shown the influence of the load on the spectral signal characteristics: with increasing pressure, the formation of bands at frequencies corresponding to possibly quasi-Rayleigh waves generation. It is concluded that the use of the experimental geometry studies the main contribution to the response of electromagnetic emissions create born normal vibrations, which are damped standing waves.

  17. Evanescent wave amplification and subwavelength imaging by ultrathin uniaxial μ-near-zero material

    SciTech Connect

    Zhao, Yan

    2014-02-15

    We demonstrate strong evanescent wave amplification by a thin slab of uniaxial μ-near-zero (UMNZ) material. It is found that while retaining the same amplification effect, the slab can be made arbitrarily thin when the negative permeability along the axis of anisotropy approaches zero. Numerical results show that using a single layer of split-ring resonators (SRRs) with its thickness equal three thousandth of the incident wavelength (λ/3000), a subwavelength source distribution with λ/4 resolution can be transferred to a distance of λ/3.

  18. Effect of uniaxial deformation to 50% on the sensitization process in 316 stainless steel

    SciTech Connect

    Ramirez, L.M.; Almanza, E.; Murr, L.E. . E-mail: fekberg@utep.edu

    2004-09-15

    The effect of uniaxial deformation to 50% on the degree of sensitization (DOS) in 316 stainless steel was investigated at 625 and 670 deg. C for 5-100 h using the electrochemical potentiokinetic reactivation (EPR) test. The results showed that the deformation accelerated the sensitization/desensitization process, especially at 670 deg. C. However, the material is still sensitized after up to 100 h of aging time. Transmission electron microscopy was used to corroborate these results. The deformed material showed more carbide precipitates (Cr{sub 23}C{sub 6}) at the grain boundaries and twin intersections than did the nondeformed material.

  19. On the electrodynamics of an absorbing uniaxial nonpositive determined (indefinite) medium

    SciTech Connect

    Baranov, D. G.; Vinogradov, A. P.; Simovskii, K. R.; Nefedov, I. S.; Tret'yakov, S. A.

    2012-04-15

    It is shown that a surface plasmon, whose decay length infinitely increases as it approaches the threshold frequency, can propagate over the surface of a half-space filled with a uniaxial indefinite absorbing metamaterial. At the threshold frequency itself, a new phenomenon is observed-upon incidence of a TM-polarized wave on the absorbing material, a real Brewster angle exists, and in the case of a plate made of such a metamaterial, 'reflectionless' reflection is observed when two plane waves are incident on the plate from two sides. In the latter case, complete destructive interference of reflected and transmitted waves occurs.

  20. PNNL Stress/Strain Correlation for Zircaloy

    SciTech Connect

    Geelhood, Kenneth J.; Beyer, Carl E.; Luscher, Walter G.

    2008-07-18

    Pacific Northwest National Laboratory (PNNL) was tasked with incorporating cladding mechanical property data into the Nuclear Regulatory Commission (NRC) fuel codes, FRAPCON-31 and FRAPTRAN2, by the NRC Office of Nuclear Reactor Research. The objective of that task was to create a mechanical model that can calculate true stress, true strain, and the possible failure of the fuel rod cladding based on uniaxial test data.

  1. Combined environmental stresses

    NASA Technical Reports Server (NTRS)

    Murray, R. H.; Mccally, M.

    1973-01-01

    Tolerance levels, physiological effects, and performance degradation during simultaneous or sequential exposures to two environmental stresses, and also three or more simultaneous stresses are described. Environmental stress combinations are characterized by four descriptors: order of occurrence, duration of exposure, severity of exposure, and type of interaction. Combined stress data and facilities for combined stress study are briefly mentioned.

  2. Parameters Describing Earth Observing Remote Sensing Systems

    NASA Technical Reports Server (NTRS)

    Zanoni, Vicki; Ryan, Robert E.; Pagnutti, Mary; Davis, Bruce; Markham, Brian; Storey, Jim

    2003-01-01

    The Earth science community needs to generate consistent and standard definitions for spatial, spectral, radiometric, and geometric properties describing passive electro-optical Earth observing sensors and their products. The parameters used to describe sensors and to describe their products are often confused. In some cases, parameters for a sensor and for its products are identical; in other cases, these parameters vary widely. Sensor parameters are bound by the fundamental performance of a system, while product parameters describe what is available to the end user. Products are often resampled, edge sharpened, pan-sharpened, or compressed, and can differ drastically from the intrinsic data acquired by the sensor. Because detailed sensor performance information may not be readily available to an international science community, standardization of product parameters is of primary performance. Spatial product parameters described include Modulation Transfer Function (MTF), point spread function, line spread function, edge response, stray light, edge sharpening, aliasing, ringing, and compression effects. Spectral product parameters discussed include full width half maximum, ripple, slope edge, and out-of-band rejection. Radiometric product properties discussed include relative and absolute radiometry, noise equivalent spectral radiance, noise equivalent temperature diffenence, and signal-to-noise ratio. Geometric product properties discussed include geopositional accuracy expressed as CE90, LE90, and root mean square error. Correlated properties discussed include such parameters as band-to-band registration, which is both a spectral and a spatial property. In addition, the proliferation of staring and pushbroom sensor architectures requires new parameters to describe artifacts that are different from traditional cross-track system artifacts. A better understanding of how various system parameters affect product performance is also needed to better ascertain the

  3. CANDLE syndrome: a recently described autoinflammatory syndrome.

    PubMed

    Tüfekçi, Özlem; Bengoa, ŞebnemYilmaz; Karapinar, Tuba Hilkay; Ataseven, Eda Büke; İrken, Gülersu; Ören, Hale

    2015-05-01

    CANDLE syndrome (chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature) is a recently described autoinflammatory syndrome characterized by early onset, recurrent fever, skin lesions, and multisystemic inflammatory manifestations. Most of the patients have been shown to have mutation in PSMB8 gene. Herein, we report a 2-year-old patient with young onset recurrent fever, atypical facies, widespread skin lesions, generalized lymphadenopathy, hepatosplenomegaly, joint contractures, hypertrglyceridemia, lipodystrophy, and autoimmune hemolytic anemia. Clinical features together with the skin biopsy findings were consistent with the CANDLE syndrome. The pathogenesis and treatment of this syndrome have not been fully understood. Increased awareness of this recently described syndrome may lead to recognition of new cases and better understanding of its pathogenesis which in turn may help for development of an effective treatment. PMID:25036278

  4. Generating and Describing Affective Eye Behaviors

    NASA Astrophysics Data System (ADS)

    Mao, Xia; Li, Zheng

    The manner of a person's eye movement conveys much about nonverbal information and emotional intent beyond speech. This paper describes work on expressing emotion through eye behaviors in virtual agents based on the parameters selected from the AU-Coded facial expression database and real-time eye movement data (pupil size, blink rate and saccade). A rule-based approach to generate primary (joyful, sad, angry, afraid, disgusted and surprise) and intermediate emotions (emotions that can be represented as the mixture of two primary emotions) utilized the MPEG4 FAPs (facial animation parameters) is introduced. Meanwhile, based on our research, a scripting tool, named EEMML (Emotional Eye Movement Markup Language) that enables authors to describe and generate emotional eye movement of virtual agents, is proposed.

  5. Failure of a fiber composite lamina under three-dimensional stresses

    SciTech Connect

    DeTeresa, S J

    1999-08-31

    The efficient use of thick-section fiber composites requires a proven three-dimensional failure model. Numerous failure criteria have been proposed, but the lack of critical experimental results makes it difficult to assess the accuracy of these models. It is shown that the various predictions for failure of a lamina due to the simple state of uniaxial stress plus superposed hydrostatic pressure are disparate. These differences are sufficient to allow evaluation of failure criteria using data that has the normal scatter found for composite materials. A high-pressure test system for fiber composites is described and results for the effects of pressure on the transverse and longitudinal compression strengths of a carbon fiber/epoxy lamina are discussed. Results are compared with a few representative failure models.

  6. Commentary: describing differences--possibilities and pitfalls.

    PubMed

    Friend, Annette

    2008-01-01

    Reports of attempts to investigate, characterize, compare, and contrast those who are mentally ill fill the literature and invite controversy. It seems to be part of human nature to reestablish and define the differences between us. Creative descriptive studies continually challenge our perspective, yet they must be balanced with thoughtful consideration of possible selection bias, an understanding of how a perspective may influence a particular view, and an appreciation of statistical constraints, before describing differences as predictive risk factors.

  7. LiveDescribe: Can Amateur Describers Create High-Quality Audio Description?

    ERIC Educational Resources Information Center

    Branje, Carmen J.; Fels, Deborah I.

    2012-01-01

    Introduction: The study presented here evaluated the usability of the audio description software LiveDescribe and explored the acceptance rates of audio description created by amateur describers who used LiveDescribe to facilitate the creation of their descriptions. Methods: Twelve amateur describers with little or no previous experience with…

  8. Stress induced phase transitions in silicon

    NASA Astrophysics Data System (ADS)

    Budnitzki, M.; Kuna, M.

    2016-10-01

    Silicon has a tremendous importance as an electronic, structural and optical material. Modeling the interaction of a silicon surface with a pointed asperity at room temperature is a major step towards the understanding of various phenomena related to brittle as well as ductile regime machining of this semiconductor. If subjected to pressure or contact loading, silicon undergoes a series of stress-driven phase transitions accompanied by large volume changes. In order to understand the material's response for complex non-hydrostatic loading situations, dedicated constitutive models are required. While a significant body of literature exists for the dislocation dominated high-temperature deformation regime, the constitutive laws used for the technologically relevant rapid low-temperature loading have severe limitations, as they do not account for the relevant phase transitions. We developed a novel finite deformation constitutive model set within the framework of thermodynamics with internal variables that captures the stress induced semiconductor-to-metal (cd-Si → β-Si), metal-to-amorphous (β-Si → a-Si) as well as amorphous-to-amorphous (a-Si → hda-Si, hda-Si → a-Si) transitions. The model parameters were identified in part directly from diamond anvil cell data and in part from instrumented indentation by the solution of an inverse problem. The constitutive model was verified by successfully predicting the transformation stress under uniaxial compression and load-displacement curves for different indenters for single loading-unloading cycles as well as repeated indentation. To the authors' knowledge this is the first constitutive model that is able to adequately describe cyclic indentation in silicon.

  9. [Who really first described lesser blood circulation?].

    PubMed

    Masić, Izet; Dilić, Mirza

    2007-01-01

    Today, at least 740 years since professor and director of the Al Mansouri Hospital in Cairo Ibn al-Nafis (1210-1288), in his paper about pulse described small (pulmonary) blood circulatory system. At the most popular web search engines very often we can find its name, especially in English language. Majority of quotes about Ibn Nefis are on Arabic or Turkish language, although Ibn Nefis discovery is of world wide importance. Author Masić I. (1993) is among rare ones who in some of the indexed journals emphasized of that event, and on that debated also some authors from Great Britain and USA in the respectable magazine Annals of Internal Medicine. Citations in majority mentioning other two "describers" or "discoverers" of pulmonary blood circulation, Michael Servetus (1511-1553), physician and theologist, and William Harvey (1578-1657), which in his paper "Exercitatio anatomica de motu cordis et sanguinis in animalibus" published in 1628 described blood circulatory system. Ibn Nefis is due to its scientific work called "Second Avicenna". Some of his papers, during centuries were translated into Latin, and some published as a reprint in Arabic language. Professor Fuat Sezgin from Frankfurt published a compendium of Ibn Nefis papers in 1997. Also, Masić I. (1997) has published one monography about Ibn Nefis. Importance of Ibn Nefis epochal discovery is the fact that it is solely based on deductive impressions, because his description of the small circulation is not occurred by observation on corps during section. It is known that he did not pay attention to the Galen's theories about blood circulation. His prophecy sentence say: "If I don't know that my work will not last up to ten thousand years after me, I would not write them". Sapient sat.

  10. Describing response-event relations: Babel revisited

    PubMed Central

    Lattal, Kennon A.; Poling, Alan D.

    1981-01-01

    The terms used to describe the relations among the three components of contingencies of reinforcement and punishment include many with multiple meanings and imprecise denotation. In particular, usage of the term “contingency” and its variants and acceptance of unsubstantiated functional, rather than procedural, descriptions of response-event relations are especially troublesome in the behavior analysis literature. Clarity seems best served by restricting the term “contingency” to its generic usage and by utilizing procedural descriptions of response-event relations. PMID:22478546

  11. Young women describe the ideal physician.

    PubMed

    Clowers, Marsha

    2002-01-01

    For some, the search for the ideal care provider can be elusive. This study explored female adolescents' accounts of the ideal health care provider. One hundred fifty-seven female high school students responded to the following question: "Can you describe what the ideal doctor would be like?" Content analysis of their descriptive narratives yielded 272 references to communication competence versus 30 references to medical competence (10 references were unrelated to either communication or medical competence). Based on their responses, it is clear that while young women appreciate the importance of medical skill, it is the communicatively competent care provider that they most seek.

  12. Analysis of cooperative effects between uniaxial and torsional strains in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Najafi, Z.; Ahmadkhan Kordbacheh, A.; Afshar, M.

    2016-06-01

    The analyses of the electronic properties of a Single-Wall Carbon Nanotube (SWCN) under both uniaxial and torsional strains are presented with the main intrinsic curvature taken into account. Within tight-binding mechanism, Heyd and Charlier method is extended to cover chiral types of SWCNs using a single π- orbital model for the nanotubes. The variations of the bond lengths and the band gap as functions of chirality and the strain parameters of carbon nanotube are discussed. An improved analytical expression for the deformed geometrical structure of a SWCN with arbitrary chiral indices has been derived, and a numerical band gap analysis of a chiral type is conducted. The existence of an interference or cooperative effect between uniaxial and torsional strains on band gap of a SWCN is found. The results of our calculations show that the cooperative effects depend strongly on the chirality of SWCNs and the strain parameters, so that, in contrast to the other works, there exists some strain parameters for which the cooperative effects are not found in the armchair SWCNs. In addition, it was found that the strain parameters can be chosen to correspond to the cooperative effects in zigzag SWCNs.

  13. The role of uniaxial deformation on microstructure and dynamics of a bulk-polymerized polyurea

    NASA Astrophysics Data System (ADS)

    Runt, James; Choi, Taeyi; Fragiadakis, Daniel; Roland, C. Michael

    2011-03-01

    Polyureas, formed by the rapid reaction between isocyanates and diamines are attractive for various applications due to their outstanding mechanical properties, which can be tuned by varying component chemistry, molecular weight and stoichiometry. Polyureas synthesized from a modified methylene diphenyl diisocyanate (Isonate 143L) and polytetramethylene oxide-di-p-aminobenzoate (Versalink P1000) are widely utilized and investigated for energy absorbing applications such as impact mitigation and ballistic protection. In order to develop a more complete understanding of their mechanical response, we explore the effect of uniaxial strain on the phase separated microstructure and molecular dynamics. We utilize wide- and small-angle X-ray scattering to investigate amorphous segment and hard domain orientation and broadband dielectric spectroscopy for interrogation of the dynamics Uniaxial deformation was found to significantly perturb the phase separated microstructure and chain orientation, and result in a considerable slowing down and broadening of the polyurea soft phase segmental relaxation. This work is supported by Office of Naval Research.

  14. Axisymmetric micromechanics of elastic-perfectly plastic fibrous composites under uniaxial tension loading

    NASA Technical Reports Server (NTRS)

    Lee, Jong-Won; Allen, David H.

    1993-01-01

    The uniaxial response of a continuous fiber elastic-perfectly plastic composite is modeled herein as a two-element composite cylinder. An axisymmetric analytical micromechanics solution is obtained for the rate-independent elastic-plastic response of the two-element composite cylinder subjected to tensile loading in the fiber direction for the case wherein the core fiber is assumed to be a transversely isotropic elastic-plastic material obeying the Tsai-Hill yield criterion, with yielding simulating fiber failure. The matrix is assumed to be an isotropic elastic-plastic material obeying the Tresca yield criterion. It is found that there are three different circumstances that depend on the fiber and matrix properties: fiber yield, followed by matrix yielding; complete matrix yield, followed by fiber yielding; and partial matrix yield, followed by fiber yielding, followed by complete matrix yield. The order in which these phenomena occur is shown to have a pronounced effect on the predicted uniaxial effective composite response.

  15. Uniaxial cyclic strain enhances adipose-derived stem cell fusion with skeletal myocytes

    SciTech Connect

    Andersen, Jens Isak; Juhl, Morten; Nielsen, Thøger; Emmersen, Jeppe; Fink, Trine; Zachar, Vladimir; Pennisi, Cristian Pablo

    2014-07-25

    Highlights: • Uniaxial cyclic tensile strain (CTS) applied to ASCs alone or in coculture with myogenic precursors. • CTS promoted the formation of a highly ordered array of parallel ASCs. • Without biochemical supplements, CTS did not support advanced myogenic differentiation of ASCs. • Mechanical stimulation of cocultures boosted fusion of ASCs with skeletal myoblasts. - Abstract: Although adult muscle tissue possesses an exceptional capacity for regeneration, in the case of large defects, the restoration to original state is not possible. A well-known source for the de novo regeneration is the adipose-derived stem cells (ASCs), which can be readily isolated and have been shown to have a broad differentiation and regenerative potential. In this work, we employed uniaxial cyclic tensile strain (CTS), to mechanically stimulate human ASCs to participate in the formation skeletal myotubes in an in vitro model of myogenesis. The application of CTS for 48 h resulted in the formation of a highly ordered array of parallel ASCs, but failed to support skeletal muscle terminal differentiation. When the same stimulation paradigm was applied to cocultures with mouse skeletal muscle myoblasts, the percentage of ASCs contributing to the formation of myotubes significantly exceeded the levels reported in the literature hitherto. In perspective, the mechanical strain may be used to increase the efficiency of incorporation of ASCs in the skeletal muscles, which could be found useful in diverse traumatic or pathologic scenarios.

  16. A novel electrospinning target to improve the yield of uniaxially aligned fibers.

    PubMed

    Secasanu, Virgil P; Giardina, Christopher K; Wang, Yadong

    2009-01-01

    Electrospinning is a useful technique that can generate micro and nanometer-sized fibers. Modification of the electrospinning parameters, such as deposition target geometry, can generate uniaxially aligned fibers for use in diverse applications ranging from tissue engineering to material fabrication. For example, meshes of fibers have been shown to mimic the extracellular matrix networks for use in smooth muscle cell proliferation. Further, aligned fibers can guide neurites to grow along the direction of the fibers. Here we present a novel electrospinning deposition target that combines the benefits of two previously reported electrodes: the standard parallel electrodes and the spinning wheel with a sharpened edge. This new target design significantly improves aligned fiber yield. Specifically, the target consists of two parallel aluminum plates with sharpened edges containing a bifurcating angle of 26 degrees. Electric field computations show a larger probable area of aligned electric field vectors. This new deposition target allows fibers to deposit on a larger cross-sectional area relative to the existing parallel electrode and at least doubles the yield of uniaxially aligned fibers. Further, fiber alignment and morphology are preserved after collection from the deposition target. PMID:19562742

  17. Uniaxial strain effects on the optoelectronic properties of GaN nanowires

    NASA Astrophysics Data System (ADS)

    Xia, Sihao; Liu, Lei; Kong, Yike; Wang, Meishan

    2016-09-01

    Considering the importance of strain engineering on semiconductors, GaN nanowires under uniaxial compression deformation and stretch deformation are researched using first principle calculations with density functional theory. It is found that the deformation will destroy the stability of the nanowires except a weak stretch. The compression deformation is more difficult than the stretch deformation. Besides, the work function of the nanowires is reduced under increasing compression while that under increasing stretch is reversed. With increasing diameter, the band gaps of the nanowires gradually exhibit a linear decreasing relation as the elongation of uniaxial length of GaN nanowires. With increasing compression, the band gaps change from direct to indirect. The optical calculations exhibit a redshift for the imaginary part of dielectric function. This study demonstrates strain engineering can effectively adjust the optoelectronic characteristics of GaN nanowire. Moderate compression, which induces a lower work function with a direct band gap, can improve the photoemission performance of GaN nanowires.

  18. Optimal fine-scale structures in compliance minimization for a uniaxial load

    PubMed Central

    Kohn, Robert V.; Wirth, Benedikt

    2014-01-01

    We consider the optimization of the topology and geometry of an elastic structure O⊂R2 subjected to a fixed boundary load, i.e. we aim to minimize a weighted sum of material volume Vol(O), structure perimeter Per(O) and structure compliance Comp(O) (which is the work done by the load). As a first simple and instructive case, this paper treats the situation of an imposed uniform uniaxial tension load in two dimensions. If the weight ε of the perimeter is small, optimal geometries exhibit very fine-scale structure which cannot be resolved by numerical optimization. Instead, we prove how the minimum energy scales in ε, which involves the construction of a family of near-optimal geometries and thus provides qualitative insights. The construction is based on a classical branching procedure with some features unique to compliance minimization. The proof of the energy scaling also requires an ansatz-independent lower bound, which we derive once via a classical convex duality argument (which is restricted to two dimensions and the uniaxial load) and once via a Fourier-based refinement of the Hashin–Shtrikman bounds for the effective elastic moduli of composite materials. We also highlight the close relation to and the differences from shape optimization with a scalar PDE-constraint and a link to the pattern formation observed in intermediate states of type-I superconductors. PMID:25294972

  19. Development of an elastic cell culture substrate for a novel uniaxial tensile strain bioreactor.

    PubMed

    Moles, Matthew D; Scotchford, Colin A; Ritchie, Alastair Campbell

    2014-07-01

    Bioreactors can be used for mechanical conditioning and to investigate the mechanobiology of cells in vitro. In this study a polyurethane (PU), Chronoflex AL, was evaluated for use as a flexible cell culture substrate in a novel bioreactor capable of imparting cyclic uniaxial tensile strain to cells. PU membranes were plasma etched, across a range of operating parameters, in oxygen. Contact angle analysis and X-ray photoelectron spectroscopy showed increases in wettability and surface oxygen were related to both etching power and duration. Atomic force microscopy demonstrated that surface roughness decreased after etching at 20 W but was increased at higher powers. The etching parameters, 20 W 40 s, produced membranes with high surface oxygen content (21%), a contact angle of 66° ± 7° and reduced topographical features. Etching and protein conditioning membranes facilitated attachment, and growth to confluence within 3 days, of MG-63 osteoblasts. After 2 days with uniaxial strain (1%, 30 cycles/min, 1500 cycles/day), cellular alignment was observed perpendicular to the principal strain axis, and found to increase after 24 h. The results indicate that the membrane supports culture and strain transmission to adhered cells. PMID:23946144

  20. Development of an elastic cell culture substrate for a novel uniaxial tensile strain bioreactor

    PubMed Central

    Moles, Matthew D; Scotchford, Colin A; Ritchie, Alastair Campbell

    2014-01-01

    Bioreactors can be used for mechanical conditioning and to investigate the mechanobiology of cells in vitro. In this study a polyurethane (PU), Chronoflex AL, was evaluated for use as a flexible cell culture substrate in a novel bioreactor capable of imparting cyclic uniaxial tensile strain to cells. PU membranes were plasma etched, across a range of operating parameters, in oxygen. Contact angle analysis and X-ray photoelectron spectroscopy showed increases in wettability and surface oxygen were related to both etching power and duration. Atomic force microscopy demonstrated that surface roughness decreased after etching at 20 W but was increased at higher powers. The etching parameters, 20 W 40 s, produced membranes with high surface oxygen content (21%), a contact angle of 66° ± 7° and reduced topographical features. Etching and protein conditioning membranes facilitated attachment, and growth to confluence within 3 days, of MG-63 osteoblasts. After 2 days with uniaxial strain (1%, 30 cycles/min, 1500 cycles/day), cellular alignment was observed perpendicular to the principal strain axis, and found to increase after 24 h. The results indicate that the membrane supports culture and strain transmission to adhered cells. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 2356–2364, 2014. PMID:23946144

  1. Magnetic microstructure and magnetic properties of uniaxial itinerant ferromagnet Fe3GeTe2

    DOE PAGESBeta

    León-Brito, Neliza; Bauer, Eric Dietzgen; Ronning, Filip; Thompson, Joe David; Movshovich, Roman

    2016-08-26

    Here, magnetic force microscopy was used to observe the magnetic microstructure of Fe3GeTe2 at 4 K on the (001) surface. The surface magnetic structure consists of a two-phase domain branching pattern that is characteristic for highly uniaxial magnets in the plane perpendicular to the magnetic easy axis. The average surface magnetic domain width Ds = 1.3 μm determined from this pattern, in combination with intrinsic properties calculated from bulk magnetization data (the saturation magnetization Ms = 376 emu/cm3 and the uniaxial magnetocrystalline anisotropy constant Ku = 1.46 × 107 erg/cm3), was used to determine the following micromagnetic parameters for Fe3GeTe2more » from phenomenological models: the domain wall energy γw = 4.7 erg/cm2, the domain wall thickness δw = 2.5 nm, the exchange stiffness constant Aex = 0.95 × 10–7 erg/cm, the exchange length lex = 2.3 nm, and the critical single domain particle diameter dc = 470 nm.« less

  2. Uniaxially aligned electrospun all-cellulose nanocomposite nanofibers reinforced with cellulose nanocrystals: scaffold for tissue engineering.

    PubMed

    He, Xu; Xiao, Qiang; Lu, Canhui; Wang, Yaru; Zhang, Xiaofang; Zhao, Jiangqi; Zhang, Wei; Zhang, Ximu; Deng, Yulin

    2014-02-10

    Uniaxially aligned cellulose nanofibers with well oriented cellulose nanocrystals (CNCs) embedded were fabricated via electrospinning using a rotating drum as the collector. Scanning electron microscope (SEM) images indicated that most cellulose nanofibers were uniaxially aligned. The incorporation of CNCs into the spinning dope resulted in more uniform morphology of the electrospun cellulose/CNCs nanocomposite nanofibers (ECCNN). Polarized light microscope (PLM) and transmission electron microscope (TEM) showed that CNCs dispersed well in ECCNN nonwovens and achieved considerable orientation along the long axis direction. This unique hierarchical microstructure of ECCNN nonwovens gave rise to remarkable enhancement of their physical properties. By incorporating 20% loading (in weight) of CNCs, the tensile strength and elastic modulus of ECCNN along the fiber alignment direction were increased by 101.7 and 171.6%, respectively. Their thermal stability was significantly improved as well. In addition, the ECCNN nonwovens were assessed as potential scaffold materials for tissue engineering. It was elucidated from MTT tests that the ECCNN were essentially nontoxic to human cells. Cell culture experiments demonstrated that cells could proliferate rapidly not only on the surface but also deep inside the ECCNN. More importantly, the aligned nanofibers of ECCNN exhibited a strong effect on directing cellular organization. This feature made the scaffold particularly useful for various artificial tissues or organs, such as blood vessel, tendon, nerve, and so on, in which cell orientation was crucial for their performance.

  3. Near-field thermal radiation between homogeneous dual uniaxial electromagnetic metamaterials

    NASA Astrophysics Data System (ADS)

    Chang, Jui-Yung; Basu, Soumyadipta; Yang, Yue; Wang, Liping

    2016-06-01

    Recently, near-field thermal radiation has attracted much attention in several fields since it can exceed the Planck blackbody limit through the coupling of evanescent waves. In this work, near-field radiative heat transfer between two semi-infinite dual uniaxial electromagnetic metamaterials with two different material property sets is theoretically analyzed. The near-field radiative heat transfer is calculated using fluctuational electrodynamics incorporated with anisotropic wave optics. The underlying mechanisms, namely, magnetic hyperbolic mode, magnetic surface polariton, electrical hyperbolic mode, and electrical surface polariton, between two homogeneous dual uniaxial electromagnetic metamaterials are investigated by examining the transmission coefficient and the spectral heat flux. The effect of vacuum gap distance is also studied, which shows that the enhancement at smaller vacuum gap is mainly due to hyperbolic mode and surface plasmon polariton modes. In addition, the results show that the contribution of s-polarized waves is significant and should not be excluded due to the strong magnetic response regardless of vacuum gap distances. The fundamental understanding and insights obtained here will facilitate the finding and application of novel materials for near-field thermal radiation.

  4. Viewing zone duplication of multi-projection 3D display system using uniaxial crystal.

    PubMed

    Lee, Chang-Kun; Park, Soon-Gi; Moon, Seokil; Lee, Byoungho

    2016-04-18

    We propose a novel multiplexing technique for increasing the viewing zone of a multi-view based multi-projection 3D display system by employing double refraction in uniaxial crystal. When linearly polarized images from projector pass through the uniaxial crystal, two possible optical paths exist according to the polarization states of image. Therefore, the optical paths of the image could be changed, and the viewing zone is shifted in a lateral direction. The polarization modulation of the image from a single projection unit enables us to generate two viewing zones at different positions. For realizing full-color images at each viewing zone, a polarization-based temporal multiplexing technique is adopted with a conventional polarization switching device of liquid crystal (LC) display. Through experiments, a prototype of a ten-view multi-projection 3D display system presenting full-colored view images is implemented by combining five laser scanning projectors, an optically clear calcite (CaCO3) crystal, and an LC polarization rotator. For each time sequence of temporal multiplexing, the luminance distribution of the proposed system is measured and analyzed.

  5. Electrical transport anisotropy of uniaxial polycrystalline samples and the effective medium approximation: An application to HTS

    NASA Astrophysics Data System (ADS)

    Cruz-García, A.; Muné, P.

    2016-08-01

    In this paper we have applied the effective medium approximation (EMA) to a polycrystalline sample made up of uniaxial crystallites with similar behavior to the high critical temperature superconductors (HTS) at the normal state (σab ≫ σc). As a result the dependence of the anisotropy parameter at the level of the sample, μ =σx /σz , on orientation probability of the grains' a-axes along a certain preferential direction, γxa is obtained. The intrinsic and shape anisotropy parameters of the crystallites constitute input data. In addition, the dependence of the orientation factor, f, which has been introduced in current models on the transport properties of HTS, is calculated as a function of γxa. These results offer a tool to interpret electrical transport measurements at normal state in granular uniaxial superconducting materials with certain texture degree, by means of the correlation between microstructure and electrical transport properties. Moreover, the comparison between the model and some experimental data suggests the presence of intragranular planar defects in the polycrystalline superconductors. They may affect the measurement of paracoherent resistivity and consequently the determination of f mainly in Bi based samples.

  6. Magnetic microstructure and magnetic properties of uniaxial itinerant ferromagnet Fe3GeTe2

    NASA Astrophysics Data System (ADS)

    León-Brito, N.; Bauer, E. D.; Ronning, F.; Thompson, J. D.; Movshovich, R.

    2016-08-01

    Magnetic force microscopy was used to observe the magnetic microstructure of Fe3GeTe2 at 4 K on the (001) surface. The surface magnetic structure consists of a two-phase domain branching pattern that is characteristic for highly uniaxial magnets in the plane perpendicular to the magnetic easy axis. The average surface magnetic domain width Ds = 1.3 μm determined from this pattern, in combination with intrinsic properties calculated from bulk magnetization data (the saturation magnetization Ms = 376 emu/cm3 and the uniaxial magnetocrystalline anisotropy constant Ku = 1.46 × 107 erg/cm3), was used to determine the following micromagnetic parameters for Fe3GeTe2 from phenomenological models: the domain wall energy γw = 4.7 erg/cm2, the domain wall thickness δw = 2.5 nm, the exchange stiffness constant Aex = 0.95 × 10-7 erg/cm, the exchange length lex = 2.3 nm, and the critical single domain particle diameter dc = 470 nm.

  7. Macroscopic Mechanical Characterization of SMAs Fiber-Reinforced Hybrid Composite Under Uniaxial Loading

    NASA Astrophysics Data System (ADS)

    Lei, Hongshuai; Wang, Zhenqing; Tong, Liyong; Tang, Xiaojun

    2013-10-01

    This paper presents an experimental and theoretical investigation on the macroscopic mechanical behavior of shape memory alloys (SMAs) fiber-reinforced glass/resin composite subject to uniaxial loading at ambient temperature. A series of unidirectional SMAs reinforced composite laminates is fabricated through vacuum-assisted resin injection. Scanning electron microscopy is conducted to evaluate the interfacial cohesive quality between SMAs fiber and matrix. A theoretical model is proposed based on the SMAs phase transformation model and rule of mixture. Uniaxial tensile tests are performed to study the effects of weak interface and SMAs fiber volume fraction on the effective modulus of composite. Failure morphology of composite is discussed based on the observation using digital HF microscope. Due to the effects of phase transformation and weak interface, the overall stiffness of SMAs composite at the second stage is on average 10% lower than theoretical results. The rupture elongation of experimental result is approximately 13% higher than theoretical result. The local interfacial debonding between SMAs fiber and glass/resin matrix is the main failure mode.

  8. Using neural networks to describe tracer correlations

    NASA Astrophysics Data System (ADS)

    Lary, D. J.; Müller, M. D.; Mussa, H. Y.

    2003-11-01

    Neural networks are ideally suited to describe the spatial and temporal dependence of tracer-tracer correlations. The neural network performs well even in regions where the correlations are less compact and normally a family of correlation curves would be required. For example, the CH4-N2O correlation can be well described using a neural 5 network trained with the latitude, pressure, time of year, and CH4 volume mixing ratio (v.m.r.). In this study a neural network using Quickprop learning and one hidden layer with eight nodes was able to reproduce the CH4-N2O correlation with a correlation co-efficient of 0.9995. Such an accurate representation of tracer-tracer correlations allows more use to be made of long-term datasets to constrain chemical models. Such as the 10 dataset from the Halogen Occultation Experiment (HALOE) which has continuously observed CH4 (but not N2O) from 1991 till the present. The neural network Fortran code used is available for download

  9. Using neural networks to describe tracer correlations

    NASA Astrophysics Data System (ADS)

    Lary, D. J.; Müller, M. D.; Mussa, H. Y.

    2004-01-01

    Neural networks are ideally suited to describe the spatial and temporal dependence of tracer-tracer correlations. The neural network performs well even in regions where the correlations are less compact and normally a family of correlation curves would be required. For example, the CH4-N2O correlation can be well described using a neural network trained with the latitude, pressure, time of year, and methane volume mixing ratio (v.m.r.). In this study a neural network using Quickprop learning and one hidden layer with eight nodes was able to reproduce the CH4-N2O correlation with a correlation coefficient between simulated and training values of 0.9995. Such an accurate representation of tracer-tracer correlations allows more use to be made of long-term datasets to constrain chemical models. Such as the dataset from the Halogen Occultation Experiment (HALOE) which has continuously observed CH4 (but not N2O) from 1991 till the present. The neural network Fortran code used is available for download.

  10. Is an eclipse described in the Odyssey?

    PubMed

    Baikouzis, Constantino; Magnasco, Marcelo O

    2008-07-01

    Plutarch and Heraclitus believed a certain passage in the 20th book of the Odyssey ("Theoclymenus's prophecy") to be a poetic description of a total solar eclipse. In the late 1920s, Schoch and Neugebauer computed that the solar eclipse of 16 April 1178 B.C.E. was total over the Ionian Islands and was the only suitable eclipse in more than a century to agree with classical estimates of the decade-earlier sack of Troy around 1192-1184 B.C.E. However, much skepticism remains about whether the verses refer to this, or any, eclipse. To contribute to the issue independently of the disputed eclipse reference, we analyze other astronomical references in the Epic, without assuming the existence of an eclipse, and search for dates matching the astronomical phenomena we believe they describe. We use three overt astronomical references in the epic: to Boötes and the Pleiades, Venus, and the New Moon; we supplement them with a conjectural identification of Hermes's trip to Ogygia as relating to the motion of planet Mercury. Performing an exhaustive search of all possible dates in the span 1250-1115 B.C., we looked to match these phenomena in the order and manner that the text describes. In that period, a single date closely matches our references: 16 April 1178 B.C.E. We speculate that these references, plus the disputed eclipse reference, may refer to that specific eclipse. PMID:18577587

  11. Using Neural Networks to Describe Tracer Correlations

    NASA Technical Reports Server (NTRS)

    Lary, D. J.; Mueller, M. D.; Mussa, H. Y.

    2003-01-01

    Neural networks are ideally suited to describe the spatial and temporal dependence of tracer-tracer correlations. The neural network performs well even in regions where the correlations are less compact and normally a family of correlation curves would be required. For example, the CH4-N2O correlation can be well described using a neural network trained with the latitude, pressure, time of year, and CH4 volume mixing ratio (v.m.r.). In this study a neural network using Quickprop learning and one hidden layer with eight nodes was able to reproduce the CH4-N2O correlation with a correlation co- efficient of 0.9995. Such an accurate representation of tracer-tracer correlations allows more use to be made of long-term datasets to constrain chemical models. Such as the dataset from the Halogen Occultation Experiment (HALOE) which has continuously observed CH4, (but not N2O) from 1991 till the present. The neural network Fortran code used is available for download.

  12. Is an eclipse described in the Odyssey?

    PubMed Central

    Baikouzis, Constantino; Magnasco, Marcelo O.

    2008-01-01

    Plutarch and Heraclitus believed a certain passage in the 20th book of the Odyssey (“Theoclymenus's prophecy”) to be a poetic description of a total solar eclipse. In the late 1920s, Schoch and Neugebauer computed that the solar eclipse of 16 April 1178 B.C.E. was total over the Ionian Islands and was the only suitable eclipse in more than a century to agree with classical estimates of the decade-earlier sack of Troy around 1192–1184 B.C.E. However, much skepticism remains about whether the verses refer to this, or any, eclipse. To contribute to the issue independently of the disputed eclipse reference, we analyze other astronomical references in the Epic, without assuming the existence of an eclipse, and search for dates matching the astronomical phenomena we believe they describe. We use three overt astronomical references in the epic: to Boötes and the Pleiades, Venus, and the New Moon; we supplement them with a conjectural identification of Hermes's trip to Ogygia as relating to the motion of planet Mercury. Performing an exhaustive search of all possible dates in the span 1250–1115 B.C., we looked to match these phenomena in the order and manner that the text describes. In that period, a single date closely matches our references: 16 April 1178 B.C.E. We speculate that these references, plus the disputed eclipse reference, may refer to that specific eclipse. PMID:18577587

  13. Effect of a uniaxially deformed aerogel on the orientation of the order parameter of superfluid {sup 3}He

    SciTech Connect

    Surovtsev, E. V.

    2009-04-15

    The effect of a uniaxially deformed aerogel on the orientation of the order parameter of {sup 3}He has been analyzed with the inclusion of correlations in the positions of the particles forming the aerogel. The minimum strain for the B phase in the uniaxially stretched aerogel that can lead to the orientation of the orbital part of the order parameter different from the bulk case has been estimated. The orientational effect has been estimated for the A-like phase in the uniaxially compressed aerogel has been estimated. It has been shown that the dependence of the orientational effect on correlations in the mutual locations of the aerogel particles is stronger than that of the superconducting transition temperature.

  14. Stimulated recall interviews for describing pragmatic epistemology

    NASA Astrophysics Data System (ADS)

    Shubert, Christopher W.; Meredith, Dawn C.

    2015-12-01

    Students' epistemologies affect how and what they learn: do they believe physics is a list of equations, or a coherent and sensible description of the physical world? In order to study these epistemologies as part of curricular assessment, we adopt the resources framework, which posits that students have many productive epistemological resources that can be brought to bear as they learn physics. In previous studies, these epistemologies have been either inferred from behavior in learning contexts or probed through surveys or interviews outside of the learning context. We argue that stimulated recall interviews provide a contextually and interpretively valid method to access students' epistemologies that complement existing methods. We develop a stimulated recall interview methodology to assess a curricular intervention and find evidence that epistemological resources aptly describe student epistemologies.

  15. Describing Story Evolution from Dynamic Information Streams

    SciTech Connect

    Rose, Stuart J.; Butner, R. Scott; Cowley, Wendy E.; Gregory, Michelle L.; Walker, Julia

    2009-10-12

    Sources of streaming information, such as news syndicates, publish information continuously. Information portals and news aggregators list the latest information from around the world enabling information consumers to easily identify events in the past 24 hours. The volume and velocity of these streams causes information from prior days’ to quickly vanish despite its utility in providing an informative context for interpreting new information. Few capabilities exist to support an individual attempting to identify or understand trends and changes from streaming information over time. The burden of retaining prior information and integrating with the new is left to the skills, determination, and discipline of each individual. In this paper we present a visual analytics system for linking essential content from information streams over time into dynamic stories that develop and change over multiple days. We describe particular challenges to the analysis of streaming information and explore visual representations for showing story change and evolution over time.

  16. Describing Ecosystem Complexity through Integrated Catchment Modeling

    NASA Astrophysics Data System (ADS)

    Shope, C. L.; Tenhunen, J. D.; Peiffer, S.

    2011-12-01

    Land use and climate change have been implicated in reduced ecosystem services (ie: high quality water yield, biodiversity, and agricultural yield. The prediction of ecosystem services expected under future land use decisions and changing climate conditions has become increasingly important. Complex policy and management decisions require the integration of physical, economic, and social data over several scales to assess effects on water resources and ecology. Field-based meteorology, hydrology, soil physics, plant production, solute and sediment transport, economic, and social behavior data were measured in a South Korean catchment. A variety of models are being used to simulate plot and field scale experiments within the catchment. Results from each of the local-scale models provide identification of sensitive, local-scale parameters which are then used as inputs into a large-scale watershed model. We used the spatially distributed SWAT model to synthesize the experimental field data throughout the catchment. The approach of our study was that the range in local-scale model parameter results can be used to define the sensitivity and uncertainty in the large-scale watershed model. Further, this example shows how research can be structured for scientific results describing complex ecosystems and landscapes where cross-disciplinary linkages benefit the end result. The field-based and modeling framework described is being used to develop scenarios to examine spatial and temporal changes in land use practices and climatic effects on water quantity, water quality, and sediment transport. Development of accurate modeling scenarios requires understanding the social relationship between individual and policy driven land management practices and the value of sustainable resources to all shareholders.

  17. A geostatistical approach for describing spatial pattern in stream networks

    USGS Publications Warehouse

    Ganio, L.M.; Torgersen, C.E.; Gresswell, R.E.

    2005-01-01

    The shape and configuration of branched networks influence ecological patterns and processes. Recent investigations of network influences in riverine ecology stress the need to quantify spatial structure not only in a two-dimensional plane, but also in networks. An initial step in understanding data from stream networks is discerning non-random patterns along the network. On the other hand, data collected in the network may be spatially autocorrelated and thus not suitable for traditional statistical analyses. Here we provide a method that uses commercially available software to construct an empirical variogram to describe spatial pattern in the relative abundance of coastal cutthroat trout in headwater stream networks. We describe the mathematical and practical considerations involved in calculating a variogram using a non-Euclidean distance metric to incorporate the network pathway structure in the analysis of spatial variability, and use a non-parametric technique to ascertain if the pattern in the empirical variogram is non-random.

  18. Describing spatial pattern in stream networks: A practical approach

    USGS Publications Warehouse

    Ganio, L.M.; Torgersen, C.E.; Gresswell, R.E.

    2005-01-01

    The shape and configuration of branched networks influence ecological patterns and processes. Recent investigations of network influences in riverine ecology stress the need to quantify spatial structure not only in a two-dimensional plane, but also in networks. An initial step in understanding data from stream networks is discerning non-random patterns along the network. On the other hand, data collected in the network may be spatially autocorrelated and thus not suitable for traditional statistical analyses. Here we provide a method that uses commercially available software to construct an empirical variogram to describe spatial pattern in the relative abundance of coastal cutthroat trout in headwater stream networks. We describe the mathematical and practical considerations involved in calculating a variogram using a non-Euclidean distance metric to incorporate the network pathway structure in the analysis of spatial variability, and use a non-parametric technique to ascertain if the pattern in the empirical variogram is non-random.

  19. Dipole-exchange spin waves in nanotubes composed of uniaxial ferromagnets with "easy-plane" and "easy-axis" anisotropies

    NASA Astrophysics Data System (ADS)

    Gorobets, Yu. I.; Kulish, V. V.

    2015-07-01

    Dipole-exchange spin waves in nanotubes composed of uniaxial ferromagnets are studied. An equation for the magnetic potential of linear spin waves in uniaxial "easy plane" ferromagnets is obtained in the magnetostatic approximation taking into account magnetic dipole-dipole interactions, exchange interactions, and anisotropy effects. A solution is found for this equation and a dispersion relation for these types of spin waves is obtained. The dependence of the spin wave frequency on the total wave number is found for the case of a thin nanotube. An expression is derived for the transverse wave number spectrum.

  20. In-situ neutron diffraction of LaCoO₃ perovskite under uniaxial compression. I. Crystal structure analysis and texture development

    SciTech Connect

    Aman, Amjad; Orlovskaya, Nina; Chen, Yan; Lugovy, Mykola; Reece, Michael J.; Ma, Dong; Stoica, Alexandru D.; An, Ke

    2014-07-07

    The dynamics of texture formation, changes in crystal structure, and stress accommodation mechanisms have been studied in perovskite-type R3⁻c rhombohedral LaCoO₃ during uniaxial compression using in-situ neutron diffraction. The in-situ neutron diffraction revealed the complex crystallographic changes causing the texture formation and significant straining along certain crystallographic directions during compression, which are responsible for the appearance of hysteresis and non-linear ferroelastic deformation in the LaCoO₃ perovskite. The irreversible strain after the first loading was connected with the appearance of non-recoverable changes in the intensity ratio of certain crystallographic peaks, causing non-reversible texture formation. However, in the second loading/unloading cycle, the hysteresis loop was closed and no further irrecoverable strain appeared after deformation. The significant texture formation is responsible for an increase in the Young's modulus of LaCoO₃ at high compressive stresses, ranging from 76 GPa at the very beginning of the loading to 194 GPa at 900 MPa at the beginning of the unloading curve.

  1. In-situ neutron diffraction of LaCoO3 perovskite under uniaxial compression. I. Crystal structure analysis and texture development

    SciTech Connect

    Aman, Amjad; Chen, Yan; Lugovy, Mykola; Orlovskaya, Nina; Reece, Michael John; Ma, Dong; Stoica, Alexandru Dan; An, Ke

    2014-01-01

    The dynamics of texture formation, changes in crystal structure and stress accommodation mechanisms are studied in R3c rhombohedral LaCoO3 perovskite during in-situ uniaxial compression experiment by neutron diffraction. The neutron diffraction revealed the complex crystallographic changes causing the texture formation and significant straining along certain crystallographic directions during in-situ compression, which are responsible for the appearance of hysteresis and non-linear ferroelastic deformation in LaCoO3 perovskite. The irreversible strain after the first loading was connected with the appearance of non-recoverable changes in the intensity ratio of certain crystallographic peaks, causing non-reversible texture formation. However in the second loading/unloading cycle the hysteresis loop was closed and no irreversible strain appears after deformation. The significant texture formation is responsible for increase in the Young s modulus of LaCoO3 at high compressive loads, where the reported values of Young s modulus increase from 76 GPa measured at the very beginning of the loading to 194 GPa at 900 MPa applied compressive stress measured at the beginning of the unloading curve.

  2. Uniaxial Extensional Behavior of A--B--A Thermoplastic Elastomers: Structure-Properties Relationship and Modeling

    NASA Astrophysics Data System (ADS)

    Martinetti, Luca

    At service temperatures, A--B--A thermoplastic elastomers (TPEs) behave similarly to filled (and often entangled) B-rich rubbers since B block ends are anchored on rigid A domains. Therefore, their viscoelastic behavior is largely dictated by chain mobility of the B block rather than by microstructural order. Relating the small- and large-strain response of undiluted A--B--A triblocks to molecular parameters is a prerequisite for designing associated TPE-based systems that can meet the desired linear and nonlinear rheological criteria. This dissertation was aimed at connecting the chemical and topological structure of A--B--A TPEs with their viscoelastic properties, both in the linear and in the nonlinear regime. Since extensional deformations are relevant for the processing and often the end-use applications of thermoplastic elastomers, the behavior was investigated predominantly in uniaxial extension. The unperturbed size of polymer coils is one of the most fundamental properties in polymer physics, affecting both the thermodynamics of macromolecules and their viscoelastic properties. Literature results on poly(D,L-lactide) (PLA) unperturbed chain dimensions, plateau modulus, and critical molar mass for entanglement effect in viscosity were reviewed and discussed in the framework of the coil packing model. Self-consistency between experimental estimates of melt chain dimensions and viscoelastic properties was discussed, and the scaling behaviors predicted by the coil packing model were identified. Contrary to the widespread belief that amorphous polylactide must be intrinsically stiff, the coil packing model and accurate experimental measurements undoubtedly support the flexible nature of PLA. The apparent brittleness of PLA in mechanical testing was attributed to a potentially severe physical aging occurring at room temperature and to the limited extensibility of the PLA tube statistical segment. The linear viscoelastic response of A--B--A TPEs was first

  3. Stress echocardiography

    MedlinePlus

    Echocardiography stress test; Stress test - echocardiography; CAD - stress echocardiography; Coronary artery disease - stress echocardiography; Chest pain - stress echocardiography; Angina - stress echocardiography; ...

  4. Stress induced anisotropy in CoFeMn soft magnetic nanocomposites

    SciTech Connect

    Leary, A. M. Keylin, V.; McHenry, M. E.; Ohodnicki, P. R.

    2015-05-07

    The use of processing techniques to create magnetic anisotropy in soft magnetic materials is a well-known method to control permeability and losses. In nanocomposite materials, field annealing below the Curie temperature results in uniaxial anisotropy energies up to ∼2 kJ/m{sup 3}. Higher anisotropies up to ∼10 kJ/m{sup 3} result after annealing Fe-Si compositions under stress due to residual stress in the amorphous matrix acting on body centered cubic crystals. This work describes near zero magnetostriction Co{sub 80−x−y}Fe{sub x}Mn{sub y}Nb{sub 4}B{sub 14}Si{sub 2} soft magnetic nanocomposites, where x and y < 8 at.% with close packed crystalline grains that show stress induced anisotropies up to ∼50 kJ/m{sup 3} and improved mechanical properties with respect to Fe-Si compositions. Difference patterns measured using transmission X-ray diffraction show evidence of affine strain with respect to the stress axis.

  5. Stress induced anisotropy in CoFeMn soft magnetic nanocomposites

    SciTech Connect

    Leary, AM; Keylin, V; Ohodnicki, PR; McHenry, ME

    2015-05-07

    The use of processing techniques to create magnetic anisotropy in soft magnetic materials is a well-known method to control permeability and losses. In nanocomposite materials, field annealing below the Curie temperature results in uniaxial anisotropy energies up to similar to 2 kJ/m(3). Higher anisotropies up to similar to 10 kJ/m(3) result after annealing Fe-Si compositions under stress due to residual stress in the amorphous matrix acting on body centered cubic crystals. This work describes near zero magnetostriction Co80-x-yFexMnyNb4B14Si2 soft magnetic nanocomposites, where x and y < 8 at. % with close packed crystalline grains that show stress induced anisotropies up to similar to 50 kJ/m(3) and improved mechanical properties with respect to Fe-Si compositions. Difference patterns measured using transmission X-ray diffraction show evidence of affine strain with respect to the stress axis. (C) 2015 AIP Publishing LLC.

  6. Stress-dependent ultrasonic scattering in polycrystalline materials.

    PubMed

    Kube, Christopher M; Turner, Joseph A

    2016-02-01

    Stress-dependent elastic moduli of polycrystalline materials are used in a statistically based model for the scattering of ultrasonic waves from randomly oriented grains that are members of a stressed polycrystal. The stress is assumed to be homogeneous and can be either residual or generated from external loads. The stress-dependent elastic properties are incorporated into the definition of the differential scattering cross-section, which defines how strongly an incident wave is scattered into various directions. Nine stress-dependent differential scattering cross-sections or scattering coefficients are defined to include all possibilities of incident and scattered waves, which can be either longitudinal or (two) transverse wave types. The evaluation of the scattering coefficients considers polycrystalline aluminum that is uniaxially stressed. An analysis of the influence of incident wave propagation direction, scattering direction, frequency, and grain size on the stress-dependency of the scattering coefficients follows. Scattering coefficients for aluminum indicate that ultrasonic scattering is much more sensitive to a uniaxial stress than ultrasonic phase velocities. By developing the stress-dependent scattering properties of polycrystals, the influence of acoustoelasticity on the amplitudes of waves propagating in stressed polycrystalline materials can be better understood. This work supports the ongoing development of a technique for monitoring and measuring stresses in metallic materials. PMID:26936563

  7. Stress-dependent ultrasonic scattering in polycrystalline materials.

    PubMed

    Kube, Christopher M; Turner, Joseph A

    2016-02-01

    Stress-dependent elastic moduli of polycrystalline materials are used in a statistically based model for the scattering of ultrasonic waves from randomly oriented grains that are members of a stressed polycrystal. The stress is assumed to be homogeneous and can be either residual or generated from external loads. The stress-dependent elastic properties are incorporated into the definition of the differential scattering cross-section, which defines how strongly an incident wave is scattered into various directions. Nine stress-dependent differential scattering cross-sections or scattering coefficients are defined to include all possibilities of incident and scattered waves, which can be either longitudinal or (two) transverse wave types. The evaluation of the scattering coefficients considers polycrystalline aluminum that is uniaxially stressed. An analysis of the influence of incident wave propagation direction, scattering direction, frequency, and grain size on the stress-dependency of the scattering coefficients follows. Scattering coefficients for aluminum indicate that ultrasonic scattering is much more sensitive to a uniaxial stress than ultrasonic phase velocities. By developing the stress-dependent scattering properties of polycrystals, the influence of acoustoelasticity on the amplitudes of waves propagating in stressed polycrystalline materials can be better understood. This work supports the ongoing development of a technique for monitoring and measuring stresses in metallic materials.

  8. Thermoelectric Properties of Cu-doped Bi2Te2.85Se0.15 Prepared by Pulse-Current Sintering Under Cyclic Uniaxial Pressure

    NASA Astrophysics Data System (ADS)

    Kitagawa, Hiroyuki; Mimura, Naoki; Takimura, Kodai; Morito, Shigekazu; Kikuchi, Kotaro

    2016-03-01

    N-type Cu-doped Bi2Te2.85Se0.15 thermoelectric materials were prepared by pulse-current sintering under cyclic uniaxial pressure, and the effect of the cyclic uniaxial pressure on texture and thermoelectric properties was investigated. Cu x Bi2Te2.85Se0.15 ( x = 0-0.03) powder prepared by mechanical alloying was sintered at 673 K using pulse-current heating under 100 MPa of cyclic uniaxial pressure. X-ray diffraction patterns and electron backscattered diffraction analyses showed that the cyclic uniaxial pressure was effective for texture control. The flattened crystal grains were stacked in the thickness direction of the sintered materials and the hexagonal c-plane strongly tended to align in the direction perpendicular to the uniaxial pressure. As a result of this crystal alignment, the electrical resistivity in the direction perpendicular to the uniaxial pressure became smaller than that of equivalent samples prepared with a constant uniaxial pressure. The smaller resistivity led to a larger power factor, and the figure of merit was improved by the application of cyclic uniaxial pressure.

  9. Uniaxial compressive behavior of micro-pillars of dental enamel characterized in multiple directions.

    PubMed

    Yilmaz, Ezgi D; Jelitto, Hans; Schneider, Gerold A

    2015-04-01

    In this work, the compressive elastic modulus and failure strength values of bovine enamel at the first hierarchical level formed by hydroxyapatite (HA) nanofibers and organic matter are identified in longitudinal, transverse and oblique direction with the uniaxial micro-compression method. The elastic modulus values (∼70 GPa) measured here are within the range of results reported in the literature but these values were found surprisingly uniform in all orientations as opposed to the previous nanoindentation findings revealing anisotropic elastic properties in enamel. Failure strengths were recorded up to ∼1.7 GPa and different failure modes (such as shear, microbuckling, fiber fracture) governed by the orientation of the HA nanofibers were visualized. Structural irregularities leading to mineral contacts between the nanofibers are postulated as the main reason for the high compressive strength and direction-independent elastic behavior on enamels first hierarchical level.

  10. Tests of graphite/polyimide sandwich panels in uniaxial edgewise compression

    NASA Technical Reports Server (NTRS)

    Camarda, C. J.

    1980-01-01

    The local and general buckling behavior of graphite/polyimide sandwich panels simply supported along all four edges and loaded in uniaxial edgewise compression were investigated. Material properties of sandwich panel constituents (adhesive and facings) were determined from flatwise tension and sandwich beam flexure tests. Buckling specimens were 30.5 by 33 cm, had quasi-isotropic, symmetric facings, and a glass/polyimide honeycomb core. Core thicknesses were varied and three panels of each thickness were tested at room temperature to investigate failure modes and corresponding buckling loads. Specimens 0.635 cm thick failed by overall buckling at loads close to the analytically predicted buckling load; all other panels failed by face wrinkling. Results of the wrinkling tests indicated that several buckling formulas were unconservative and therefore not suitable for design purposes; a recommended wrinkling equation is presented.

  11. Manipulation of gap nodes by uniaxial strain in iron-based superconductors.

    PubMed

    Kang, Jian; Kemper, Alexander F; Fernandes, Rafael M

    2014-11-21

    In the iron pnictides and chalcogenides, multiple orbitals participate in the superconducting state, enabling different gap structures to be realized in distinct materials. Here we argue that the spectral weights of these orbitals can, in principle, be controlled by a tetragonal symmetry-breaking uniaxial strain, due to the enhanced nematic susceptibility of many iron-based superconductors. By investigating multiorbital microscopic models in the presence of orbital order, we show that not only Tc can be enhanced, but pairs of accidental gap nodes can be annihilated and created in the Fermi surface by an increasing external strain. We explain our results as a mixture of nearly degenerate superconducting states promoted by strain, and show that the annihilation and creation of nodes can be detected experimentally via anisotropic penetration depth measurements. Our results provide a promising framework to externally control the superconducting properties of iron-based materials. PMID:25479515

  12. Uniaxial in-plane magnetization of iron nanolayers grown within an amorphous matrix

    SciTech Connect

    Ghafari, M. Hahn, H.; Mattheis, R.; McCord, J.; Brand, R. A.; Macedo, W. A. A.

    2014-08-18

    Conversion electron Mössbauer spectroscopy is used to determine the magnetic ground state at zero magnetic field of four-monolayer thick amorphous iron layers as part of a CoFeB-Fe multilayer stack. By comparing the intensities of the magnetic hyperfine field, an easy in-plane axis of the amorphous embedded Fe layer is verified, which is collinear to the uniaxial anisotropy axis of the neighboring amorphous CoFeB. Despite the soft magnetic character of the Fe layers, external fields up to 4 T perpendicular to the film plane are insufficient to completely align the embedded Fe moments parallel to the magnetic field due to a local disorder of the magnetic moments of the Fe atoms.

  13. A unit structure Rochon prism based on the extraordinary refraction of uniaxial birefringent crystals.

    PubMed

    Wu, Wendi; Wu, Fuquan; Shi, Meng; Su, Fufang; Han, Peigao; Ma, Lili

    2013-06-01

    Based on the Fermat's principle, the universal theory of refraction and reflection of extraordinary rays (e-rays) in the uniaxial crystal is formulated. Using this theory, a new unit structure prism is designed, and its properties are studied. Based on the theoretical results, such a prism is achieved experimentally by using the Iceland crystal. In both theoretical and experimental studies, this new prism shows excellent polarization splitting performances such as big and adjustable splitting angle, comparing to the conventional Rochon prism. For the sample prism with the optical axis angle of 45°, the splitting angle reaches 19.8°in the normal incidence, and the maximum splitting angle reaches 28.44° while the incidence angle is -4°. PMID:23736569

  14. Discrete element simulation of powder compaction in cold uniaxial pressing with low pressure

    NASA Astrophysics Data System (ADS)

    Rojek, Jerzy; Nosewicz, Szymon; Jurczak, Kamila; Chmielewski, Marcin; Bochenek, Kamil; Pietrzak, Katarzyna

    2016-11-01

    This paper presents numerical studies of powder compaction in cold uniaxial pressing. The powder compaction in this work is considered as an initial stage of a hot pressing process so it is realized with relatively low pressure (up to 50 MPa). Hence the attention has been focused on the densification mechanisms at this range of pressure and models suitable for these conditions. The discrete element method employing spherical particles has been used in the numerical studies. Numerical simulations have been performed for two different contact models—the elastic Hertz-Mindlin-Deresiewicz model and the plastic Storåkers model. Numerical results have been compared with the results of laboratory tests of the die compaction of the NiAl powder. Comparisons have shown that the discrete element method is capable to represent properly the densification mechanisms by the particle rearrangement and particle deformation.

  15. Blocking temperature of interacting magnetic nanoparticles with uniaxial and cubic anisotropies from Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Russier, V.

    2016-07-01

    The low temperature behavior of densely packed interacting spherical single domain nanoparticles (MNP) is investigated by Monte Carlo simulations in the framework of an effective one spin model. The particles are distributed through a hard sphere like distribution with periodic boundary conditions and interact through the dipole dipole interaction (DDI) with an anisotropy energy including both cubic and uniaxial symmetry components. The cubic component is shown to play a sizable role on the value of the blocking temperature Tb only when the MNP easy axes are parallel to the cubic easy direction ([111] direction for a negative cubic anisotropy constant). The nature of the collective low temperature state, either ferromagnetic or spin glass like, is found to depend on the ratio of the anisotropy to the dipolar energies characterizing partly the disorder in the system.

  16. Conversion circularly polarized beam shifting optical vortices with a fractional topological charges in a uniaxial crystal

    NASA Astrophysics Data System (ADS)

    Pogrebnaya, A. O.; Halilov, S. I.; Rubass, A. F.

    2016-08-01

    In this work we have studied the distribution of a circularly polarized beam carrying the optical vortex with fractional topological charge equal to ½ in a uniaxial crystal. We have found that by increasing the angle of inclination of the beam relative to the optical axis of the crystal to α = 1.75 °, mixed dislocation movement observed wave front interference pattern to beam periphery. Experimental research has shown that when the angle α = 2 ° in the central region of the beam, we are seeing the emergence of "fork", optical vortex with a topological charge of the order of 1. The results show depolarization of the beam and the transition to the spin angular momentum of the orbital angular momentum. The intensity of the RCP and LCP component in the beam carrying the optical vortex with fractional topological charge oscillate. The total intensity of the beam as the sum of two orthogonally polarized components does not change.

  17. Engineering the quantum anomalous Hall effect in graphene with uniaxial strains

    NASA Astrophysics Data System (ADS)

    Diniz, G. S.; Guassi, M. R.; Qu, F.

    2013-12-01

    We theoretically investigate the manipulation of the quantum anomalous Hall effect (QAHE) in graphene by means of the uniaxial strain. The values of Chern number and Hall conductance demonstrate that the strained graphene in presence of Rashba spin-orbit coupling and exchange field, for vanishing intrinsic spin-orbit coupling, possesses non-trivial topological phase, which is robust against the direction and modulus of the strain. Besides, we also find that the interplay between Rashba and intrinsic spin-orbit couplings results in a topological phase transition in the strained graphene. Remarkably, as the strain strength is increased beyond approximately 7%, the critical parameters of the exchange field for triggering the quantum anomalous Hall phase transition show distinct behaviors—decrease (increase) for strains along zigzag (armchair) direction. Our findings open up a new platform for manipulation of the QAHE by an experimentally accessible strain deformation of the graphene structure, with promising application on novel quantum electronic devices with high efficiency.

  18. Phase diagrams of charged colloidal rods: Can a uniaxial charge distribution break chiral symmetry?

    NASA Astrophysics Data System (ADS)

    Drwenski, Tara; Dussi, Simone; Hermes, Michiel; Dijkstra, Marjolein; van Roij, René

    2016-03-01

    We construct phase diagrams for charged rodlike colloids within the second-virial approximation as a function of rod concentration, salt concentration, and colloidal charge. Besides the expected isotropic-nematic transition, we also find parameter regimes with a coexistence between a nematic and a second, more highly aligned nematic phase including an isotropic-nematic-nematic triple point and a nematic-nematic critical point, which can all be explained in terms of the twisting effect. We compute the Frank elastic constants to see if the twist elastic constant can become negative, which would indicate the possibility of a cholesteric phase spontaneously forming. Although the twisting effect reduces the twist elastic constant, we find that it always remains positive. In addition, we find that for finite aspect-ratio rods the twist elastic constant is also always positive, such that there is no evidence of chiral symmetry breaking due to a uniaxial charge distribution.

  19. Classification of dispersion equations for homogeneous, dielectric-magnetic, uniaxial materials.

    PubMed

    Depine, Ricardo A; Inchaussandague, Marina E; Lakhtakia, Akhlesh

    2006-04-01

    The geometric representation at a fixed frequency of the wave vector (or dispersion) surface omega(k) for lossless, homogeneous, dielectric-magnetic uniaxial materials is explored for the case when the elements of the relative permittivity and permeability tensors of the material can have any sign. Electromagnetic plane waves propagating inside the material can exhibit dispersion surfaces in the form of ellipsoids of revolution, hyperboloids of one sheet, or hyperboloids of two sheets. Furthermore, depending on the relative orientation of the optic axis, the intersections of these surfaces with fixed planes of propagation can be circles, ellipses, hyperbolas, or straight lines. The understanding obtained is used to study the reflection and refraction of electromagnetic plane waves due to a planar interface with an isotropic medium.

  20. Texture Modification in a Magnesium-Aluminum-Calcium Alloy During Uniaxial Compression

    NASA Astrophysics Data System (ADS)

    Miller, Victoria M.; Pollock, Tresa M.

    2016-04-01

    Texture evolution in an Mg-Al-Ca alloy at varied levels of alkaline earth solute content and phase fraction of coarse intermetallic particles has been examined. Elevated temperature uniaxial compression tests have been conducted on thixomolded AXJ810 material in three different initial microstructural conditions. These conditions were selected to sample a spectrum of solute content and intermetallic particle phase fraction. Solute content alters the populations of dislocations present after deformation, similar to effects observed in rare earth-containing alloys. The presence of coarse intermetallic particles promotes dynamic recrystallization at lower strains. Additionally, the combination of a fine initial grain size and coarse particles decorating the grain boundaries results in a more diffuse deformation texture by creating large orientation spreads within individual grains, promoting a further weakened recrystallized texture.

  1. Computational study to evaluate the birefringence of uniaxially oriented film of cellulose triacetate.

    PubMed

    Hayakawa, Daichi; Ueda, Kazuyoshi

    2015-01-30

    The intrinsic birefringence of a cellulose triacetate (CTA) film is evaluated using the polarizability of the monomer model of the CTA repeating unit, which is calculated using the density functional theory (DFT). Since the CTA monomer is known to have three rotational isomers, referred to as gg, gt, and tg, the intrinsic birefringence of these isomers is evaluated separately. The calculation indicates that the monomer CTA with gg and gt structures shows a negative intrinsic birefringence, whereas the monomer unit with a tg structure shows a positive intrinsic birefringence. By using these values, a model of the uniaxially elongated CTA film is constructed with a molecular dynamics simulation, and the orientation birefringence of the film model was evaluated. The result indicates that the film has negative orientation birefringence and that its value is in good agreement with experimental results. PMID:25498014

  2. Nonlinear ac stationary response and dynamic magnetic hysteresis of quantum uniaxial superparamagnets

    NASA Astrophysics Data System (ADS)

    Kalmykov, Yuri P.; Titov, Serguey V.; Coffey, William T.

    2015-11-01

    The nonlinear ac stationary response of uniaxial paramagnets and superparamagnets—nanoscale solids or clusters with spin number S ˜100-104 —in superimposed uniform ac and dc bias magnetic fields of arbitrary strength, each applied along the easy axis of magnetization, is determined by solving the evolution equation for the reduced density matrix represented as a finite set of three-term differential-recurrence relations for its diagonal matrix elements. The various harmonic components arising from the nonlinear response of the magnetization, dynamic magnetic hysteresis loops, etc., are then evaluated via matrix continued fractions indicating a pronounced dependence of the response on S arising from the quantum spin dynamics, which differ markedly from the magnetization dynamics of classical nanomagnets. In the linear response approximation, the results concur with existing solutions.

  3. Inelastic Stability Analysis Of Uniaxially Compressed Flat Rectangular Isotropic CCSS Plate

    NASA Astrophysics Data System (ADS)

    Ibearugbulem, O. M.; Eziefula, U. G.; Onwuka, D. O.

    2015-08-01

    This study investigates the inelastic stability of a thin flat rectangular isotropic plate subjected to uniform uniaxial compressive loads using Taylor-Maclaurin series formulated deflection function. The plate has clamped and simply supported edges in both characteristic directions (CCSS boundary conditions). The governing equation is derived using a deformation plasticity theory and a work principle. Values of the plate buckling coefficient are calculated for aspect ratios from 0.1 to 2.0 at intervals of 0.1. The results compared favourably with the elastic stability values and the percentage differences ranged from -0.353% to -7.427%. Therefore, the theoretical approach proposed in this study is recommended for the inelastic stability analysis of thin flat rectangular isotropic plates under uniform in-plane compression.

  4. Focusing of Gaussian beam passed under small angle to optical axis of uniaxial crystal

    NASA Astrophysics Data System (ADS)

    Ivanov, M. O.; Shostka, N. V.

    2016-07-01

    We showed both experimentally and analytically, the effect of focusing of a Gaussian beam propagated under small angle ϕ with respect to the optical axis of a uniaxial crystal, on the generation of a bottle beam. At ϕ = 0° two foci that correspond to ordinary and extraordinary parts of a beam form a closed 3D structure of a bottle beam. At this point, the beam, in the foci points, has radially and azimuthally aligned polarizations. Increasing the value of ϕ leads to dramatic changes in the intensity and polarization structure of a bottle beam. Starting from the value of ϕ = ±2° the closed 3D symmetric structure of a bottle beam breaks down. At ϕ = ±5° both beams are focused at the same transverse plane, while its polarization evolves to x- and y-linear. With a further increase in angle ϕ two foci ‘switch’ their spatial positions and move further away.

  5. Transient Microstructure of Low Hard Segment Thermoplastic Polyurethane under Uniaxial Deformation

    SciTech Connect

    Koerner,H.; Kelley, J.; Vaia, R.

    2008-01-01

    Microstructure evolution of a low hard segment (<10 mol %) thermoplastic polyurethane (LHS-TPU) has been followed by in-situ wide-angle X-ray (WAX) and small-angle X-ray scattering (SAX) with a focus on elucidating peculiar microstructural changes during uniaxial deformation ({gamma} = 1-3.5). For the LHS-TPU, the hard segments, due to their low content and chemical structure, do not crystallize but form glassy regions that act as physical cross-links. Two types of soft segment crystallites are resolved upon elongation via DSC, SAX, and WAX experiments. Phase I consists of a small amount of initial crystallites (<2%) that function similar to conventional PU hard segment domains, deforming at small uniaxial strains ({gamma} = 1-2) to a chevron-type morphology, which exhibit equatorial 4-point patterns in SAX. Phase II evolves at higher deformations ({gamma} > 2) due to strain-induced crystallization. Phase II exhibits a conventional meridional 2-point pattern along the deformation direction with lamellar crystallites aligning in the plane normal to the deformation. WAX, SAX, and DSC confirm that both phases coexist over a small strain window ({gamma} = 1.9-2.5), demonstrating the independent nature of the two crystalline phases. These findings indicate that the LHS-TPU in this study is similar to poly(butylene adipate) (PBA) in its morphological and structural behavior. This is further substantiated by NMR, which reveals that the LHS-TPU consists of 90% soft segments, which are identified as PBA via crystal structure analysis of a highly aligned fiber. The soft segments in the LHS-TPU dominate the morphology and the X-ray patterns upon deformation.

  6. Biaxial stress relaxation in glassy polymers - Polymethylmethacrylate.

    NASA Technical Reports Server (NTRS)

    Sternstein, S. S.; Ho, T. C.

    1972-01-01

    Biaxial stress relaxation studies were performed on glassy polymethylmethacrylate in combined torsion-tension strain fields using a specially designed apparatus with exceptionally high stiffness and low cross talk between the torsional and tensile load measuring transducers. It was found that at low strain levels uniaxial tension relaxation is slower than pure torsion relaxation; tensile-component relaxation rates are unaffected by the level of torsional strain; torsional-component relaxation rates decrease as tensile strain is increased; uniaxial tension relaxation rates approach the pure torsion rates at higher strains (about 2%). A phenomenological treatment is presented which shows that relaxation rates can be coupled to the strain fields in which they are observed and yet be consistent with the concepts of linear viscoelasticity and the Boltzmann superposition integral.

  7. Uniaxial anisotropy variations and the reduction of free layer coercivity in MnIr-based top spin valves

    NASA Astrophysics Data System (ADS)

    Milyaev, M. A.; Naumova, L. I.; Bannikova, N. S.; Proglyado, V. V.; Maksimova, I. K.; Kamensky, I. Y.; Ustinov, V. V.

    2015-11-01

    The effect of uniaxial anisotropy on the free layer coercivity has been studied on a MnIr-based top spin valve. Annealing and micro-patterning were applied to modify the anisotropy field. The anhysteretic magnetoresistance on magnetic field dependence has been obtained.

  8. In situ stress state and strength in mudrocks

    NASA Astrophysics Data System (ADS)

    Casey, Brendan; Germaine, John T.; Flemings, Peter B.; Fahy, Brian P.

    2016-08-01

    The stress state of mudrocks buried under uniaxial strain conditions is defined through a large number of laboratory triaxial tests performed on water-saturated resedimented mudrocks from a diverse set of geologic backgrounds. Unique relationships are found between the horizontal stresses that develop during normal uniaxial compression (given by K0NC), critical state friction angle, and shear strength during undrained loading. Tests were performed over the effective stress range of 0.1 to 100 MPa. Smectite-rich mudrocks display a more rapid reduction in shear strength with increasing effective stress, which corresponds with a more rapid increase in horizontal stresses. The relationship between horizontal stresses and critical state friction angle found in this study compares favorably with the well-known correlation of Jâky (1948), which was developed for very low stresses, even for friction angle values as low as 11°. Results for one mudrock suggest that this relationship also applies to mudrocks sheared from an unloaded (overconsolidated) state. The correlation between friction angle and K0NC is independent of the stress path applied during the compression phase of a test. This is not the case for shearing under undrained conditions, however, and the application of a stress path that produces uniaxial compression is necessary to measure a reliable shear strength. Systematic variations in K0NC and strength properties reflect an overall change in the shape and orientation of a mudrock's yield surface with effective stress level. The results of this study can aid in estimating the in situ stress state and strength properties of mudrocks, and this will have significant impact on a range of geoscience and engineering problems.

  9. Modeling of long-term fatigue damage of soft tissue with stress softening and permanent set effects

    PubMed Central

    Martin, Caitlin; Sun, Wei

    2012-01-01

    One of the major failure modes of bioprosthetic heart valves is non-calcific structural deterioration due to fatigue of the tissue leaflets. Experimental methods to characterize tissue fatigue properties are complex and time-consuming. A constitutive fatigue model that could be calibrated by isolated material tests would be ideal for investigating the effects of more complex loading conditions. However, there is a lack of tissue fatigue damage models in the literature. To address these limitations, in this study, a phenomenological constitutive model was developed to describe the stress softening and permanent set effects of tissue subjected to long-term cyclic loading. The model was used to capture characteristic uniaxial fatigue data for glutaraldehyde-treated bovine pericardium and was then implemented into finite element software. The simulated fatigue response agreed well with the experimental data and thus demonstrates feasibility of this approach. PMID:22945802

  10. Describing temperament in an ungulate: a multidimensional approach.

    PubMed

    Graunke, Katharina L; Nürnberg, Gerd; Repsilber, Dirk; Puppe, Birger; Langbein, Jan

    2013-01-01

    Studies on animal temperament have often described temperament using a one-dimensional scale, whereas theoretical framework has recently suggested two or more dimensions using terms like "valence" or "arousal" to describe these dimensions. Yet, the valence or assessment of a situation is highly individual. The aim of this study was to provide support for the multidimensional framework with experimental data originating from an economically important species (Bos taurus). We tested 361 calves at 90 days post natum (dpn) in a novel-object test. Using a principal component analysis (PCA), we condensed numerous behaviours into fewer variables to describe temperament and correlated these variables with simultaneously measured heart rate variability (HRV) data. The PCA resulted in two behavioural dimensions (principal components, PC): novel-object-related (PC 1) and exploration-activity-related (PC 2). These PCs explained 58% of the variability in our data. The animals were distributed evenly within the two behavioural dimensions independent of their sex. Calves with different scores in these PCs differed significantly in HRV, and thus in the autonomous nervous system's activity. Based on these combined behavioural and physiological data we described four distinct temperament types resulting from two behavioural dimensions: "neophobic/fearful--alert", "interested--stressed", "subdued/uninterested--calm", and "neoophilic/outgoing--alert". Additionally, 38 calves were tested at 90 and 197 dpn. Using the same PCA-model, they correlated significantly in PC 1 and tended to correlate in PC 2 between the two test ages. Of these calves, 42% expressed a similar behaviour pattern in both dimensions and 47% in one. No differences in temperament scores were found between sexes or breeds. In conclusion, we described distinct temperament types in calves based on behavioural and physiological measures emphasising the benefits of a multidimensional approach.

  11. Determination of Uniaxial Compressive Strength of Ankara Agglomerate Considering Fractal Geometry of Blocks

    NASA Astrophysics Data System (ADS)

    Coskun, Aycan; Sonmez, Harun; Ercin Kasapoglu, K.; Ozge Dinc, S.; Celal Tunusluoglu, M.

    2010-05-01

    The uniaxial compressive strength (UCS) of rock material is a crucial parameter to be used for design stages of slopes, tunnels and foundations to be constructed in/on geological medium. However, preparation of high quality cores from geological mixtures or fragmented rocks such as melanges, fault rocks, coarse pyroclastic rocks, breccias and sheared serpentinites is often extremely difficult. According to the studies performed in literature, this type of geological materials may be grouped as welded and unwelded birmocks. Success of preparation of core samples from welded bimrocks is slightly better than unwelded ones. Therefore, some studies performed on the welded bimrocks to understand the mechanical behavior of geological mixture materials composed of stronger and weaker components (Gokceoglu, 2002; Sonmez et al., 2004; Sonmez et al., 2006; Kahraman, et al., 2008). The overall strength of bimrocks are generally depends on strength contrast between blocks and matrix; types and strength of matrix; type, size, strength, shape and orientation of blocks and volumetric block proportion. In previously proposed prediction models, while UCS of unwelded bimrocks may be determined by decreasing the UCS of matrix considering the volumetric block proportion, the welded ones can be predicted by considering both UCS of matrix and blocks together (Lindquist, 1994; Lindquist and Goodman, 1994; Sonmez et al., 2006 and Sonmez et al., 2009). However, there is a few attempts were performed about the effect of blocks shape and orientation on the strength of bimrock (Linqduist, 1994 and Kahraman, et al., 2008). In this study, Ankara agglomerate, which is composed of andesite blocks and surrounded weak tuff matrix, was selected as study material. Image analyses were performed on bottom, top and side faces of cores to identify volumetric block portions. In addition to the image analyses, andesite blocks on bottom, top and side faces were digitized for determination of fractal

  12. Sandstone compaction under actively controlled uniaxial strain conditions - an experimental study on the causes of subsidence in the Dutch Wadden Area

    NASA Astrophysics Data System (ADS)

    Hol, Sander; Mossop, Antony; van der Linden, Arjan; Zuiderwijk, Pedro; Makurat, Axel; van Eijs, Rob

    2016-04-01

    In the Wadden Sea, a tidal-flat area located between the North Sea and the Dutch mainland shore, and UNESCO World Heritage site, subsidence could potentially impact the ecological system. To guide the licensing process governing gas extraction for the area by a solid understanding of the system's response to production, Nederlandse Aardolie Maatschappij (NAM) has carried out a study on the magnitudes, timing, and mechanisms of subsidence related to gas production. As part of this study program, we address the effect of production-induced reservoir compaction, using core samples from the Moddergat field located at the Wadden Sea coastline, from a depth of ~3800 m TVDSS, to assess the nature of the compaction mechanisms that operate. In this contribution, we focus on the uniaxial strain response of Permian, Aeolian sandstone to pore pressure depletion. As the majority of experiments reported in the literature are conducted under triaxial stress conditions, this data set is somewhat unique, and can help confirm the validity of micromechanical processes found for triaxial stress conditions. We report over 30 data sets of experiments carried out using 1.0 and 1.5 inch diameter plugs, sub-sampled from the extracted sandstone core material. The experiments start at in-situ conditions of pore pressure (Pf=~57 MPa), stress (Sv=~80 MPa, Sh=~67 MPa) and temperature (T up to 100 °C), and deplete to a pore pressure of 3 MPa, under actively controlled lateral constraint boundary conditions (i.e. uniaxial strain). Care was taken to systematically vary porosity and sample morphology to ensure representation of the intra-reservoir variability. Our laboratory data show that pressure-depletion results in a strain in the range of 5·10-3-1·10-2 over the total duration of the experiments of 5-12 weeks, with approximately 80% of the total strain response being close to instantaneous, and 20% developing over time. The total strain response develops during depletion as a result of

  13. Expansion of functions describing planetary surface and gravity field

    NASA Astrophysics Data System (ADS)

    Valeyev, S. G.

    1985-02-01

    The problem of description of the surface and gravity field of planets is examined using an expansion in spherical and other functions with particular consideration of the problem of expansion of lunar relief in spherical functions. The factors exerting an influence on approximating expressions can be divided into two groups. The first group includes errors generated by observational errors. Errors in the second group, generated by the mathematical description itself are stressed here. The approach used in solving the problem is statistical (regression) modeling. This approach is applied in an expansion of a function describing averaged surface relief by a number of spherical harmonics. The numerical example presented shows that the use of regression modeling makes it possible to obtain expansions with a number of terms approximately half as great as in the ordinary approach with the same or a higher descriptive accuracy. Also examined are the problems caused by the great dimensionality of the problems and the diversity of variants of initial data. The described approach gives adequate but economical models of relief and the gravity field.

  14. Uniaxial Compression Analysis and Microdeformation Characterization of Kevin Dome Anhydrite Caprock

    NASA Astrophysics Data System (ADS)

    Malenda, M. G.; Frash, L.; Carey, J. W.

    2015-12-01

    The Department of Energy currently manages the Regional Carbon Sequestration Partnership (RCSP) in efforts to develop techniques to characterize promising CO2 storage sites, efficient and durable technology for injection, and suitable regulations for future CO2 storage. Within the RCSP, the Montana State University-Bozeman led Big Sky Carbon Sequestration Project has focused on potential CO2 storage sites, including the Kevin Dome in northern Montana. The 750mi2 large dome lies along the north-southwest trending Sweetgrass Arch and is a natural CO2 reservoir with the potential to produce one million tonnes of CO2. The Project intends to extract and reinject this one million tonnes of CO2back into the water-leg of the Dome within the dolomitic, middle Duperow Formation to monitor impacts on the surrounding environment and communities. The caprock system includes extremely low porosity dolomite in the upper Duperow that is overlain by the anhydrite-dominated Potlatch caprock. Core was extracted by the Project from the Wallawein 22-1 well. Six 1"-diameter sub-samples were taken at depths of 3687 and 3689' of the 4"-diameter core in both vertical and horizontal directions. Unconfined uniaxial compression tests were conducted at room temperature using an Instron 4483 load frame with a 150kN load cell operated at a strain rate of 6.835-5mm per second. Samples were instrumented with four strain gages to record elastic moduli and characterize fracture behavior. The Potlatch anhydrite has demonstrated to be both strong and stiff with an average uniaxial compressive strength of 150.62±23.95MPa, a Young's modulus of 89.96±10.22GPa, and a Poisson's ratio of 0.32±0.05. These three variables are essential to developing geomechanical models that assess caprock responses to injection during CO2 sequestration. Petrographic characterizations of the fractured samples reveal an 80% groundmass of subeuhedral anhydrite crystals measuring 97-625μm and 20% 0.12-1mm wide veins

  15. X-ray Laue micro diffraction and neutron diffraction analysis of residual elastic strains and plastic deformation in a 1% uniaxial tensile tested nickel alloy 600 sample

    SciTech Connect

    Chao, Jing; Mark, Alison; Fuller, Marina; Barabash, Rozaliya; McIntyre, Stewart; Holt, Richard A.; Klassen, Robert; Liu, W.

    2009-01-01

    The magnitude and distribution of elastic strain for a nickel alloy 600 (A600) sample that had been subjected to uniaxial tensile stress were measured by micro Laue diffraction (MLD) and neutron diffraction techniques. For a sample that had been dimensionally strained by 1%, both MLD and neutron diffraction data indicated that the global residual elastic strain was on the order of 10{sup -4}, however the micro-diffraction data indicated considerable grain-to-grain variability amongst individual components of the residual strain tensor. A more precise comparison was done by finding those grains in the MLD map that had appropriate oriented in the specific directions matching those used in the neutron measurements and the strains were found to agree within the uncertainty. Large variations in strain values across the grains were noted during the MLD measurements which are reflected in the uncertainties. This is a possible explanation for the large uncertainty in the average strains measured from multiple grains during neutron diffraction.

  16. Use of Descartes Folium Equation for Deriving a Relation between Total Aperture of Fractures after Uniaxial Compression and Strain Parameters of Different Rocks Exhibiting Negative Total Volumetric Strains

    NASA Astrophysics Data System (ADS)

    Palchik, V.

    2014-11-01

    The axial, crack and total volumetric strains, porosity, elastic constants, crack damage stresses, uniaxial compressive strengths, as well as fracture apertures and number of fracture traces in rock samples surface after compression were defined for different chalk, basalt, dolomite, granite, limestone and sandstone samples exhibiting negative total volumetric strain at failure. It is established that the total (summed) aperture of vertical fractures obtained on the lateral surface of rock sample is related to three characteristic strain parameters: axial strain at the onset of negative total volumetric strain, axial failure strain and negative total volumetric strain at failure. The relation is based on Descartes folium equation, where the length of the loop of folium is equal to axial strain coordinate at the onset of negative total volumetric strain. This relation shows that the total aperture increases according to power law with increasing difference between axial failure strain and axial strain at the onset of negative total volumetric strain. Simultaneously, an increase in this difference leads to an increase in the value of negative total volumetric strain at failure. It is found that a direct correlation between total aperture of fractures and negative total volumetric strain at failure is relatively weak. Nevertheless, total aperture of fractures tends to increase with increasing absolute value of negative total volumetric strain at failure. It is revealed that there is no connection between the number of fracture traces and negative total volumetric strain at failure.

  17. Monitoring in situ stress/strain behaviour during plastic yielding in polymineralic rocks using neutron diffraction

    NASA Astrophysics Data System (ADS)

    Covey-Crump, S. J.; Schofield, P. F.; Stretton, I. C.; Daymond, M. R.; Knight, K. S.; Tant, J.

    2013-02-01

    Attempts to use rock deformation experiments to examine the elastic and plastic behaviour of polymineralic rocks are hampered by the fact that usually only whole sample properties can be monitored as opposed to the separate contribution of each phase. To circumvent this difficulty, room-temperature, uniaxial compression experiments were performed in a neutron beam-line on a suite of calcite + halite samples with different phase volume proportions. By collecting diffraction data during loading, the elastic strain and hence stress in each phase was determined as a function of load to bulk strains of 1-2%. In all cases, the calcite behaved elastically while the halite underwent plastic yielding. During the fully elastic part of the deformation, the composite elastic properties and the within-phase stresses are well-described both by recent shear lag models and by analyses based on Eshelby's solution for the elastic field around an ellipsoidal inclusion in a homogeneous medium. After the onset of yielding, the halite in situ stress/total strain curve may be reconstructed using the rule of mixtures. At calcite contents of greater than 30%, the in situ halite response may be significantly weaker or stronger than that obtained at lesser calcite contents. The results highlight the potential that such techniques offer for developing an explicitly experimental approach for determining the influence of microstructural variables on the mechanical properties of polymineralic rocks.

  18. Calculation of the shrinkage-induced residual stress in a viscoelastic dental restorative material

    NASA Astrophysics Data System (ADS)

    Grassia, Luigi; D'Amore, Alberto

    2013-02-01

    A procedure able to describe the curing process of a particulate composite material used in a dental restoration is developed in the ANSYS environment. The material under concern is a multifunctional methacrylate-based composite for dental restoration, activated by visible light. The model accounts for the dependence of the viscoelastic functions on temperature and degree of cure. Three geometries have been considered in the analysis that are representative of three different classes of dental restoration and mainly differ by the C (constrained)-factor, (i.e. the bounded to unbounded surface ratio). It was found that the temperature could give a necrosis in the vicinity of the tooth nerve and that the average stress at the interface between the composite and the tooth scales exponentially with the C-factor. The residual stress at the dental restoration interface is also compared with the uniaxial tensile strength of twelve commercially available composite materials: it clearly appears that the level of residual stress may overcome the strength of the composite, especially at high C-factors.

  19. High-quality uniaxial In(x)Ga(1-x)N/GaN multiple quantum well (MQW) nanowires (NWs) on Si(111) grown by metal-organic chemical vapor deposition (MOCVD) and light-emitting diode (LED) fabrication.

    PubMed

    Ra, Yong-Ho; Navamathavan, R; Park, Ji-Hyeon; Lee, Cheul-Ro

    2013-03-01

    This article describes the growth and device characteristics of vertically aligned high-quality uniaxial p-GaN/InxGa1-xN/GaN multiple quantum wells (MQW)/n-GaN nanowires (NWs) on Si(111) substrates grown by metal-organic chemical vapor deposition (MOCVD) technique. The resultant nanowires (NWs), with a diameter of 200-250 nm, have an average length of 2 μm. The feasibility of growing high-quality NWs with well-controlled indium composition MQW structure is demonstrated. These resultant NWs grown on Si(111) substrates were utilized for fabricating vertical-type light-emitting diodes (LEDs). The steep and intense photoluminescence (PL) and cathodoluminescence (CL) spectra are observed, based on the strain-free NWs on Si(111) substrates. High-resolution transmission electron microscopy (HR-TEM) analysis revealed that the MQW NWs are grown along the c-plane with uniform thickness. The current-voltage (I-V) characteristics of these NWs exhibited typical p-n junction LEDs and showed a sharp onset voltage at 2.75 V in the forward bias. The output power is linearly increased with increasing current. The result indicates that the pulsed MOCVD technique is an effective method to grow uniaxial p-GaN/InxGa1-xN/GaN MQW/n-GaN NWs on Si(111), which is more advantageous than other growth techniques, such as molecular beam epitaxy. These results suggest the uniaxial NWs are promising to allow flat-band quantum structures, which can enhance the efficiency of LEDs.

  20. Experimental Results From Stitched Composite Multi-Bay Fuselage Panels Tested Under Uni-Axial Compression

    NASA Technical Reports Server (NTRS)

    Baker, Donald J.

    2004-01-01

    The experimental results from two stitched VARTM composite panels tested under uni-axial compression loading are presented. The curved panels are divided by frames and stringers into five or six bays with a column of three bays along the compressive loading direction. The frames are supported at the ends to resist out-of-plane translation. Back-to-back strain gages are used to record the strain and displacement transducers were used to record the out-of-plane displacements. In addition a full-field measurement technique that utilizes a camera-based-stero-vision system was used to record displacements. The panels were loaded in increments to determine the first bay to buckle. Loading was discontinued at limit load and the panels were removed from the test machine for impact testing. After impacting at 20 ft-lbs to 25 ft-lbs of energy with a spherical indenter, the panels were loaded in compression until failure. Impact testing reduced the axial stiffness 4 percent and less than 1 percent. Postbuckled axial panel stiffness was 52 percent and 70 percent of the pre-buckled stiffness.

  1. Unlocking Bloch-type chirality in ultrathin magnets through uniaxial strain.

    PubMed

    Chen, Gong; N'Diaye, Alpha T; Kang, Sang Pyo; Kwon, Hee Young; Won, Changyeon; Wu, Yizheng; Qiu, Z Q; Schmid, Andreas K

    2015-01-01

    Chiral magnetic domain walls are of great interest because lifting the energetic degeneracy of left- and right-handed spin textures in magnetic domain walls enables fast current-driven domain wall propagation. Although two types of magnetic domain walls are known to exist in magnetic thin films, Bloch- and Néel-walls, up to now the stabilization of homochirality was restricted to Néel-type domain walls. Since the driving mechanism of thin-film magnetic chirality, the interfacial Dzyaloshinskii-Moriya interaction, is thought to vanish in Bloch-type walls, homochiral Bloch walls have remained elusive. Here we use real-space imaging of the spin texture in iron/nickel bilayers on tungsten to show that chiral domain walls of mixed Bloch-type and Néel-type can indeed be stabilized by adding uniaxial strain in the presence of interfacial Dzyaloshinskii-Moriya interaction. Our findings introduce Bloch-type chirality as a new spin texture, which may open up new opportunities to design spin-orbitronics devices. PMID:25798953

  2. The uniaxial compressive strength of coal: Should it be used to design pillars?

    SciTech Connect

    Mark, C.; Barton, T.

    1996-12-01

    The Bureau of Mines has recently completed a comprehensive study of coal strength. More than 4000 individual test results from over 60 scams were extracted from the literature and combined in the most complete data base of the uniaxial compressive strength of coal ever assembled. In addition, more than 100 case studies of in-mine pillar performance were available in the Analysis of Retreat Mining Pillar Stability (ARMPS) data base. Statistical analysis of this wealth of data has yielded valuable results. The data shows clearly that the {open_quotes}size effect{close_quotes} is related to coal structure. The widely-used Gaddy formula, which predicts a significant strength reduction as the specimen size is increased, was found to apply only to {open_quotes}blocky{close_quotes} coals. For friable coals, the size effect was much less pronounced or even non-existent. Case histories of failed pillars are the best available data on in situ coal strength. This study found no correlation between the ARMPS stability factor of failed pillars and coal specimen strength. Pillar design was much more reliable when a uniform coal strength was used in all case histories.

  3. X-ray scattering studies of ordered block copolymer melts during uniaxial extensional flow

    NASA Astrophysics Data System (ADS)

    Burghardt, Wesley; Mao, Ruinan; McCready, Erica

    2012-02-01

    We present the design and implementation of a new apparatus for in situ x-ray scattering studies of polymer melts during homogenous uniaxial extensional flow. The instrument is based on the commercial SER extensional flow fixture, which employs counter-rotating drums to deform a strip of polymer melt, which is incorporated into a custom-built convection oven designed to facilitate x-ray access to the sample and operation in a synchrotron environment. Here we report measurements of extensional flow-induced structural changes in a cylindrically ordered styrene-ethylene butylene-styrene triblock copolymer melt. At early stages, SAXS data reveal that the ordered microstructure deforms affinely until Hencky strains of ˜ 0.2. A global re-orientation process leads to alignment of microdomains predominantly along the stretching direction after Hencky strains of ˜ 1. Further stretching does not lead to further qualitative changes in 2-D SAXS patterns. Relaxation of both microdomain orientation and d-spacing is observed following cessation of extensional flow, albeit with different characteristic time scales. In situ x-ray scattering data are compared with off-line measurements of transient extensional viscosity, performed using the SER fixture in a rotational rheometer.

  4. Electromagnetic waves in uniaxial crystals with metallized boundaries: Mode conversion, pure reflections, and bulk polaritons

    SciTech Connect

    Alshits, V. I. Lyubimov, V. N.; Radowicz, A.

    2007-02-15

    A theory is constructed for the reflection of plane electromagnetic waves in uniaxial crystals with a positive definite permittivity tensor and an arbitrarily oriented metallized boundary. The problem is solved both for general-position orientations corresponding to three-partial reflection and for special conditions allowing two-partial reflections: mode conversions when the incident and reflected waves belong to different sheets of the refraction surface and 'pure' reflections when both waves belong to the same sheet. The space of pure reflections is shown to be formed by two types of optical-axis orientations: arbitrary directions in the plane of the crystal surface and in the plane of incidence. The configurations of the conversion surface for optically positive and negative crystals are investigated. A subspace of pure reflections that transform into one-partial bulk polaritons with the energy flux parallel to the surface at grazing incidence has been found. The domain of existence of such bulk eigenmodes is bounded by two 'lines' of solutions. These are any directions along the boundary containing the optical axis for ordinary polaritons and the direction along the projection of the optical axis onto the surface at an arbitrary orientation of the axis with respect to the boundary for extraordinary polaritons.

  5. Characterization of all the elastic, dielectric, and piezoelectric constants of uniaxially oriented poled PVDF films.

    PubMed

    Roh, Yongrae; Varadan, Vasundara V; Varadan, Vijay K

    2002-06-01

    Polyvinylidene fluoride (PVDF), a piezoelectric material, has many useful applications, for example, as sensors, transducers, and surface acoustic wave (SAW) devices. Models of performance of these devices would be useful engineering tools. However, the benefit of the model is only as accurate as the material properties used in the model. The purpose of this investigation is to measure the elastic, dielectric and piezoelectric properties over a frequency range, including the imaginary part (loss) of these properties. Measurements are difficult because poled material is available as thin films, and not all quantities can be measured in that form. All components of the elastic stiffness, dielectric tensor, and electromechanical coupling tensor are needed in the models. The material studied here is uniaxially oriented poled PVDF that has orthorhombic mm2 symmetry. Presented are the frequency dependence of all nine complex elastic constants, three complex dielectric constants, and five complex piezoelectric constants. The PVDF was produced at Raytheon Research Division, Lexington, MA. Measurements were made on thin films and on stacked, cubical samples. The elastic constants c44D and C55D, the dielectric constants epsilon11T and epsilon22T, as well as the piezoelectric constants g15 and g24 reported here have not been published before. The values were determined by ultrasonic measurements using an impedance analyzer and a least square data-fitting technique. PMID:12075977

  6. Angular momentum dynamics of a paraxial beam in a uniaxial crystal.

    PubMed

    Ciattoni, Alessandro; Cincotti, Gabriella; Palma, Claudio

    2003-03-01

    The conservation law governing the dynamics of the radiation angular momentum component along the optical axis (z axis) of a uniaxial crystal is derived from Maxwell's equations; the existence of this law is physically related to the rotational invariance of the crystal around the optical axis. Specializing the obtained general expression for the z component of the angular momentum flux to the case of a paraxial beam propagating along the optical axis, we find that the expression is the same as the corresponding one for a paraxial beam propagating in an isotropic medium of refractive index n(o) (ordinary refractive index of the crystal); besides, we show that the flux is conserved during propagation and that it decomposes into the sum of an intrinsic and an orbital contribution. Investigating their dynamics we demonstrate that they are coupled and, during propagation, an exchange between them exists. This exchange asymptotically exhibits a saturation process leading, for z--> infinity, the intrinsic part to vanish and the orbital one equates the total amount of angular momentum flux. As an example, the evolution of the intrinsic and the orbital contributions to the flux is investigated in the case of circularly polarized beams. Besides, the radiation angular momentum stored in the crystal is also investigated, in the paraxial regime, showing that it is simply given by the product of the total angular momentum flux by the time the radiation takes in passing through the crystal.

  7. Generation Behaviors of Optical Anisotropy Caused by Silver Nanoparticles Precipitated in Uniaxially Drawn Polyimide Films

    NASA Astrophysics Data System (ADS)

    Matsuda, Sho-ichi; Ando, Shinji

    2005-01-01

    The optical anisotropy generated during thermal curing and simultaneous uniaxial drawing of poly(amic acid) (PAA) films dissolving silver nitrate was investigated. The PAA was converted to polyimide (PI) during thermal curing, and silver nanoparticles were precipitated in the oriented PI films. The anisotropy in optical transmittance, i.e., the polarization characteristic, of the films strongly depended on the holding time at the final curing temperature, and a large anisotropy in transmittance with a wide wavelength region (wide-range optical anisotropy) was observed only for a film cured for the optimal holding time. During heating at the final curing temperature, silver nanoparticles were anisotropically grown and aggregated along the drawing direction, generating a significant optical anisotropy. However, additional heating induces isotropic growth, aggregation, and fusion of silver nanoparticles, resulting in the reduction in anisotropy. A numerical analysis based on the Mie theory revealed that the wide-range optical anisotropy can be generated by the anisotropies in shape and the preferential aggregation and arrays of silver nanoparticles in the drawing direction as well as the large birefringence of PI films as dielectric media.

  8. Small angle scattering methods to study porous materials under high uniaxial strain

    SciTech Connect

    Le Floch, Sylvie Balima, Félix; Pischedda, Vittoria; Legrand, Franck; San-Miguel, Alfonso

    2015-02-15

    We developed a high pressure cell for the in situ study of the porosity of solids under high uniaxial strain using neutron small angle scattering. The cell comprises a hydraulically actioned piston and a main body equipped with two single-crystal sapphire windows allowing for the neutron scattering of the sample. The sample cavity is designed to allow for a large volume variation as expected when compressing highly porous materials. We also implemented a loading protocol to adapt an existing diamond anvil cell for the study of porous materials by X-ray small angle scattering under high pressure. The two techniques are complementary as the radiation beam and the applied pressure are in one case perpendicular to each other (neutron cell) and in the other case parallel (X-ray cell). We will illustrate the use of these two techniques in the study of lamellar porous systems up to a maximum pressure of 0.1 GPa and 0.3 GPa for the neutron and X-ray cells, respectively. These devices allow obtaining information on the evolution of porosity with pressure in the pore dimension subdomain defined by the wave-numbers explored in the scattering process. The evolution with the applied load of such parameters as the fractal dimension of the pore-matrix interface or the apparent specific surface in expanded graphite and in expanded vermiculite is used to illustrate the use of the high pressure cells.

  9. K-shell spectroscopy of an independently diagnosed uniaxially expanding laser-produced aluminum plasma

    NASA Astrophysics Data System (ADS)

    Chambers, D. M.; Pinto, P. A.; Hawreliak, J.; Al'Miev, I. R.; Gouveia, A.; Sondhauss, P.; Wolfrum, E.; Wark, J. S.; Glenzer, S. H.; Lee, R. W.; Young, P. E.; Renner, O.; Marjoribanks, R. S.; Topping, S.

    2002-08-01

    We present detailed spectroscopic analysis of the primary K-shell emission lines from a uniaxially expanding laser-produced hydrogenic and heliumlike aluminum plasma. The spectroscopic measurements are found to be consistent with time-dependent hydrodynamic properties of the plasma, measured using Thomson scattering and shadowgraphy. The K-shell population kinetics code FLY with the measured hydrodynamic parameters is used to generate spectra that are compared to the experimental spectra. Excellent agreement is found between the measured and calculated spectra for a variety of experimental target widths employed to produce plasmas with different optical depths. The peak emission from the hydrogenic Lyman series is determined to be from a temporal and spatial region where the hydrodynamic parameters are essentially constant. This allows a single steady-state solution of FLY to be used to deduce the electron temperature and density, from the measured line ratios and linewidths, for comparison with the Thomson and shadowgraphy data. These measurements are found to agree well with time-dependent calculations, and provide further validation for the FLY calculations of the ionization and excitation balance for a K-shell aluminum plasma. We also discuss the possible application of this data as a benchmark for hydrodynamic simulations and ionization/excitation balance calculations.

  10. Uniaxial tension-induced fracture in gold nanowires with the dependence on size and atomic vacancies.

    PubMed

    Wang, Fenying; Dai, Yanfeng; Zhao, Jianwei; Li, Qianjin

    2014-12-01

    Atomic vacancies play an important role in the deformation and fracture processes of a metallic nanowire subjected to uniaxial tension. However, it is a great challenge to explore such evolution by experimental methods. Here, molecular dynamics simulations were used to study the deformation, fracture mechanism and mechanical character of gold nanowires with different atomic vacancies and sizes. Several valuable results were observed. Firstly, the statistical breaking position distributions showed two fracture styles of the gold nanowires. The small-sized gold nanowire exhibited a cluster rupture with disordered crystalline structures, and the breaking position appeared in the middle region, while the gold nanowire of large size exhibited an ordered slippage rupture and was apt to break at both ends. Secondly, the breaking position distribution of the large-sized gold nanowire was more sensitive to atomic vacancies than that of the small-sized gold nanowire. Thirdly, the mechanical strength could be improved by decreasing the gold nanowire size. Finally, small-sized gold nanowires had uncertain characteristics owing to the surface atom effects. PMID:25315454

  11. Effect of uniaxial strain on the electronic transport through disordered graphene p-n junctions

    NASA Astrophysics Data System (ADS)

    Deng, Min; Wang, Yong-Jian; Gang, Yu; Chen, Jian-Fei

    2016-09-01

    Using the non-equilibrium Green’s function method, we investigated theoretically the electron transport through a disordered graphene p-n junction under a perpendicular magnetic field. A uniaxial strain is applied to the graphene sheet. It is found that the conductance versus the on-site energy of the right electrode exhibits the successive step-like structure in the n-n region, however, a zero value plateau followed by the successive oscillation peaks in the p-n region. When the longitudinal or transverse strain is applied, the zero value plateau almost remains intact, while the oscillation peaks are greatly enhanced with increasing the strain strength, and depending on the orientation of the applied strain, the oscillation peaks shift towards the positive or negative energy upon increasing the strain. In the presence of the disorder, the characteristic conductance plateaus emerge at e2/h, (3/2)e2/h, etc. for the appropriate disorder strength. With the rise of the strain, the original plateau structure is destroyed, instead, the conductance exhibits new plateaus whose amplitude and position strongly depend on the strain strength and direction.

  12. Silicene nanomeshes: bandgap opening by bond symmetry breaking and uniaxial strain

    PubMed Central

    Jia, Tian-Tian; Fan, Xin-Yu; Zheng, Meng-Meng; Chen, Gang

    2016-01-01

    Based on the first-principles calculations, we have investigated in detail the bandgap opening of silicene nanomeshes. Different to the mechanism of bandgap opening induced by the sublattice equivalence breaking, the method of degenerate perturbation through breaking the bond symmetry could split the π-like bands in the inversion symmetry preserved silicene nanomeshes, resulting into the πa1 − πa2 and πz1 − πz2 band sets with sizable energy intervals. Besides the bandgap opening in the nanomeshes with Dirac point being folded to Γ point, the split energy intervals are however apart away from Fermi level to leave the semimetal nature unchanged for the other nanomeshes with Dirac points located at opposite sides of Γ point as opposite pseudo spin wave valleys. A mass bandgap could be then opened at the aid of uniaxial strain to transfer the nanomesh to be semiconducting, whose width could be continuously enlarged until reaching its maximum Emax. Moreover, the Emax could also be tuned by controlling the defect density in silicene nanomeshes. These studies could contribute to the understanding of the bandgap engineering of silicene-based nanomaterials to call for further investigations on both theory and experiment. PMID:26860967

  13. Structure Evolution of Propylene-1-Butylene Random Copolymer under Uniaxial Stretching: from Unit Cells to Lamellae

    NASA Astrophysics Data System (ADS)

    Mao, Yimin; Burger, Christian; Li, Xiaowei; Hsiao, Benjamin

    2011-03-01

    Crystallization changes of propylene-1-butylene (P-H) random copolymer with low butylene content (5.7 mol%) under uniaxial tensile deformation at high temperature (100& circ; C) was investigated using time-resolved wide- and small-angle X-ray scattering (WAXS/SAXS) techniques. Structure and preferred orientation at length scales of crystal unit cell and lamellae were investigated explicitly using 2D whole pattern analysis. γ -phase was found to be the dominant initial modification which was transformed into α -phase during stretching, forming more stable parallel packed polymer chains in the unit cell. 2D WAXS analysis enabled us to identify three orientation modes from different crystal forms, i.e., γ -phase with tilted cross- β configuration, α -phase with parallel chain packing and a-axis orientation of α -form crystals in daughter lamellae. 2D SAXS analysis based on stacking model enabled us to understand the development of the four-point pattern under deformation. We thank National Science Foundation for financial support and Derek W. Thurman and Andy H. Tsou from ExxonMobil company for providing copolymer samples.

  14. Small angle scattering methods to study porous materials under high uniaxial strain.

    PubMed

    Le Floch, Sylvie; Balima, Félix; Pischedda, Vittoria; Legrand, Franck; San-Miguel, Alfonso

    2015-02-01

    We developed a high pressure cell for the in situ study of the porosity of solids under high uniaxial strain using neutron small angle scattering. The cell comprises a hydraulically actioned piston and a main body equipped with two single-crystal sapphire windows allowing for the neutron scattering of the sample. The sample cavity is designed to allow for a large volume variation as expected when compressing highly porous materials. We also implemented a loading protocol to adapt an existing diamond anvil cell for the study of porous materials by X-ray small angle scattering under high pressure. The two techniques are complementary as the radiation beam and the applied pressure are in one case perpendicular to each other (neutron cell) and in the other case parallel (X-ray cell). We will illustrate the use of these two techniques in the study of lamellar porous systems up to a maximum pressure of 0.1 GPa and 0.3 GPa for the neutron and X-ray cells, respectively. These devices allow obtaining information on the evolution of porosity with pressure in the pore dimension subdomain defined by the wave-numbers explored in the scattering process. The evolution with the applied load of such parameters as the fractal dimension of the pore-matrix interface or the apparent specific surface in expanded graphite and in expanded vermiculite is used to illustrate the use of the high pressure cells.

  15. The polaritonic spectrum of two-dimensional photonic crystals based on uniaxial polar materials

    NASA Astrophysics Data System (ADS)

    Gómez-Urrea, H. A.; Duque, C. A.; Mora-Ramos, M. E.

    2015-11-01

    We investigate the dispersion relations of two-dimensional photonic crystals made of cylindrical rods of uniaxial polar materials that exhibit transverse phonon-polariton excitations. The rods are considered to be embedded in a dielectric background. The photonic properties are obtained with the use of the finite-difference time domain (FDTD) method and the auxiliary differential equation (ADE) technique. The anisotropy of the dielectric function is explicitly considered using an empirical approach that assigns different weights to contributions of the parallel (z) and transversal (t) polaritonic relations. The effective dielectric function is then expressed as a weighted combination of the longitudinal and transversal components: ε (ω) =αzεz (ω) +αtεt (ω) . Different sets of values of the coefficients αz and αt have been considered. The frequencies of the allowed electromagnetic modes are determined as the local maxima of the spectral analysis using a fast Fourier transform (FFT). The particular case of a square photonic crystal superlattice geometry is analyzed, and input data corresponding to phonon frequencies of wurtzite nitride semiconductors is used. It is shown that larger values of the quantity |νz,T -νt,T | are desirable if the associated dielectric anisotropy is used as a tool for tuning photonic properties in the system.

  16. Uniaxial diffusion bonding of CLAM/CLAM steels: Microstructure and mechanical performance

    NASA Astrophysics Data System (ADS)

    Zhou, Xiaosheng; Liu, Yongchang; Yu, Liming; Liu, Chenxi; Sui, Guofa; Yang, Jianguo

    2015-06-01

    By performing a two-step uniaxial diffusion bonding, the reliable joining between CLAM/CLAM steels has been attained. The microstructures at the vicinity of the joint region and in base material were respectively investigated through OM, SEM and TEM. The joint interface was integrated, and no microstructural defects were observed. In the base material, small amount of austenite is retained as thin films between martensite laths, which was suggested to be related to the compressive deformation in diffusion bonding. As a candidate structural material for the first wall in fusion energy systems, the radiation resistance of CLAM steel would be deteriorated by the retained austenite. Tensile and impact tests were carried out to assess the reliability of the joints subjected to post bond heat treatment. All the tensile specimens fractured in the base CLAM steel, meaning the good joining between CLAM steels. However, due to the low impact absorbed energy of the joints, efforts should still be made to optimize the bonding technology and the post bond heat treatment further.

  17. Periodic reversal of magneto-optic Faraday rotation on uniaxial birefringence crystal with ultrathin magnetic films

    NASA Astrophysics Data System (ADS)

    Su, C. W.; Chang, S. C.; Chang, Y. C.

    2013-07-01

    An experimental approach of inclined incidence magneto-optic Faraday effect observed in the polar plane is applied. Three samples containing ferromagnetic cobalt ultrathin films on a semiconductor zinc oxide (0001) single crystal substrate with in-plane and out-of-plane anisotropy are evaluated. Through the fine adjustment of crossed polarizers in the magneto-optic effect measurement completely recorded the detail optical and magneto-optical responses from the birefringent crystal substrate and the magnetic film, especially for the signal induced from the substrate with uniaxial optical axis. The angle dependency of interference phenomena periodically from the optical and magneto-optical responses is attributed to the birefringence even in the absence of a magnetic field. The new type of observation finds that the transmission Faraday intensity in the oblique incidence includes a combination of polarization rotations, which results from optical compensation from the substrate and magneto-optical Faraday effects from the film. The samples grown at different rates and examined by this method exhibit magnetic structure discriminations. This result can be applied in the advanced polarized-light technologies to enhance the spatial resolution of magnetic surfaces with microstructural information under various magnetic field direction.

  18. Silicene nanomeshes: bandgap opening by bond symmetry breaking and uniaxial strain.

    PubMed

    Jia, Tian-Tian; Fan, Xin-Yu; Zheng, Meng-Meng; Chen, Gang

    2016-02-10

    Based on the first-principles calculations, we have investigated in detail the bandgap opening of silicene nanomeshes. Different to the mechanism of bandgap opening induced by the sublattice equivalence breaking, the method of degenerate perturbation through breaking the bond symmetry could split the π-like bands in the inversion symmetry preserved silicene nanomeshes, resulting into the πa1 - πa2 and πz1 - πz2 band sets with sizable energy intervals. Besides the bandgap opening in the nanomeshes with Dirac point being folded to Γ point, the split energy intervals are however apart away from Fermi level to leave the semimetal nature unchanged for the other nanomeshes with Dirac points located at opposite sides of Γ point as opposite pseudo spin wave valleys. A mass bandgap could be then opened at the aid of uniaxial strain to transfer the nanomesh to be semiconducting, whose width could be continuously enlarged until reaching its maximum Emax. Moreover, the Emax could also be tuned by controlling the defect density in silicene nanomeshes. These studies could contribute to the understanding of the bandgap engineering of silicene-based nanomaterials to call for further investigations on both theory and experiment.

  19. Interlaminar stresses in composite laminates: A perturbation analysis

    NASA Technical Reports Server (NTRS)

    Hsu, P. W.; Herakovich, C. T.

    1976-01-01

    A general method of solution for an elastic balanced symmetric composite laminate subject to a uniaxial extension was developed based upon a perturbation analysis of a limiting free body containing an interfacial plane. The solution satisfies more physical requirements and boundary conditions than previous investigations, and predicts smooth continuous interlaminar stresses with no instabilities. It determines the finite maximum intensity for the interlaminar normal stress in all laminates, provides mathematical evidences for the singular stresses in angle-ply laminates, suggests the need for the experimental determination of an important problem parameter, and introduces a viable means for solving related problems of practical interest.

  20. Tensile and Microindentation Stress-Strain Curves of Al-6061

    DOE Data Explorer

    Weaver, Jordan S [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Center for Integrated Nanotechnologies (CINT); Khosravani, Ali [Georgia Inst. of Technology, Atlanta, GA (United States); Castillo, Andrew [Georgia Inst. of Technology, Atlanta, GA (United States); Kalidind, Surya R [Georgia Inst. of Technology, Atlanta, GA (United States)

    2016-07-13

    Recent spherical microindentation stress-strain protocols were developed and validated on Al-6061 (DOI: 10.1186/s40192-016-0054-3). The scaling factor between the uniaxial yield strength and the indentation yield strength was determined to be about 1.9. The microindentation stress-strain protocols were then applied to a microstructurally graded sample in an effort to extract high throughput process-property relationships. The tensile and microindentation force-displacement and stress-strain data are presented in this data set.

  1. Mathematical modeling of uniaxial mechanical properties of collagen gel scaffolds for vascular tissue engineering.

    PubMed

    Irastorza, Ramiro M; Drouin, Bernard; Blangino, Eugenia; Mantovani, Diego

    2015-01-01

    Small diameter tissue-engineered arteries improve their mechanical and functional properties when they are mechanically stimulated. Applying a suitable stress and/or strain with or without a cycle to the scaffolds and cells during the culturing process resides in our ability to generate a suitable mechanical model. Collagen gel is one of the most used scaffolds in vascular tissue engineering, mainly because it is the principal constituent of the extracellular matrix for vascular cells in human. The mechanical modeling of such a material is not a trivial task, mainly for its viscoelastic nature. Computational and experimental methods for developing a suitable model for collagen gels are of primary importance for the field. In this research, we focused on mechanical properties of collagen gels under unconfined compression. First, mechanical viscoelastic models are discussed and framed in the control system theory. Second, models are fitted using system identification. Several models are evaluated and two nonlinear models are proposed: Mooney-Rivlin inspired and Hammerstein models. The results suggest that Mooney-Rivlin and Hammerstein models succeed in describing the mechanical behavior of collagen gels for cyclic tests on scaffolds (with best fitting parameters 58.3% and 75.8%, resp.). When Akaike criterion is used, the best is the Mooney-Rivlin inspired model. PMID:25834840

  2. Mathematical modeling of uniaxial mechanical properties of collagen gel scaffolds for vascular tissue engineering.

    PubMed

    Irastorza, Ramiro M; Drouin, Bernard; Blangino, Eugenia; Mantovani, Diego

    2015-01-01

    Small diameter tissue-engineered arteries improve their mechanical and functional properties when they are mechanically stimulated. Applying a suitable stress and/or strain with or without a cycle to the scaffolds and cells during the culturing process resides in our ability to generate a suitable mechanical model. Collagen gel is one of the most used scaffolds in vascular tissue engineering, mainly because it is the principal constituent of the extracellular matrix for vascular cells in human. The mechanical modeling of such a material is not a trivial task, mainly for its viscoelastic nature. Computational and experimental methods for developing a suitable model for collagen gels are of primary importance for the field. In this research, we focused on mechanical properties of collagen gels under unconfined compression. First, mechanical viscoelastic models are discussed and framed in the control system theory. Second, models are fitted using system identification. Several models are evaluated and two nonlinear models are proposed: Mooney-Rivlin inspired and Hammerstein models. The results suggest that Mooney-Rivlin and Hammerstein models succeed in describing the mechanical behavior of collagen gels for cyclic tests on scaffolds (with best fitting parameters 58.3% and 75.8%, resp.). When Akaike criterion is used, the best is the Mooney-Rivlin inspired model.

  3. Mathematical Modeling of Uniaxial Mechanical Properties of Collagen Gel Scaffolds for Vascular Tissue Engineering

    PubMed Central

    Irastorza, Ramiro M.; Drouin, Bernard; Blangino, Eugenia; Mantovani, Diego

    2015-01-01

    Small diameter tissue-engineered arteries improve their mechanical and functional properties when they are mechanically stimulated. Applying a suitable stress and/or strain with or without a cycle to the scaffolds and cells during the culturing process resides in our ability to generate a suitable mechanical model. Collagen gel is one of the most used scaffolds in vascular tissue engineering, mainly because it is the principal constituent of the extracellular matrix for vascular cells in human. The mechanical modeling of such a material is not a trivial task, mainly for its viscoelastic nature. Computational and experimental methods for developing a suitable model for collagen gels are of primary importance for the field. In this research, we focused on mechanical properties of collagen gels under unconfined compression. First, mechanical viscoelastic models are discussed and framed in the control system theory. Second, models are fitted using system identification. Several models are evaluated and two nonlinear models are proposed: Mooney-Rivlin inspired and Hammerstein models. The results suggest that Mooney-Rivlin and Hammerstein models succeed in describing the mechanical behavior of collagen gels for cyclic tests on scaffolds (with best fitting parameters 58.3% and 75.8%, resp.). When Akaike criterion is used, the best is the Mooney-Rivlin inspired model. PMID:25834840

  4. Effect of uniaxial strain on the structural, electronic and elastic properties of orthorhombic BiMnO3

    NASA Astrophysics Data System (ADS)

    Yang, Pei; Haibin, Wu

    2015-03-01

    We study the elastic constants and electronic properties of orthorhombic BiMnO3 under uniaxial strain along the c-axis using the first-principles method. It is found that, beyond the range -0.025 < ɛ < 0.055, the predicted stiffness constants cij cannot demand the Born stability criteria and the compliance constant s44 shows abrupt changes, which accompany phase transition. In addition, the results for magnetism moments and polycrystalline properties are also reported. Additionally, under compressive strain, a band gap transition from the indirect to the direct occurs within -0.019 < ɛ < -0.018. Furthermore, the response of the band gap of orthorhombic BiMnO3 to uniaxial strain is studied.

  5. Temperature dependence of exchange bias and training effect in Co/CoO film with induced uniaxial anisotropy

    NASA Astrophysics Data System (ADS)

    Wu, R.; Fu, J. B.; Zhou, D.; Ding, S. L.; Wei, J. Z.; Zhang, Y.; Du, H. L.; Wang, C. S.; Yang, Y. C.; Yang, J. B.

    2015-06-01

    The exchange bias effect and training effect of the Co/CoO film with induced uniaxial anisotropy were investigated as functions of temperature. It was found that both effects exhibited drastic differences along the easy and the hard axes. Along the easy axis, the magnetization reversal was dominated by domain wall motion throughout the whole temperature range. However, along the hard axis, the magnetization reversal was dominated by domain wall motion and domain rotation at temperatures below and above 150 K, respectively. The crossover of the two reversal modes characterized with significant asymmetry in the hysteresis loop was observed along the hard axis at 150 K due to the interplay between the exchange and uniaxial anisotropies. Significant difference of training effect in the two directions was observed and ascribed to the differences of the duration and intensity of the interaction between ferromagnetic and antiferromagnetic spins in the two magnetization reversal modes.

  6. Isogyres - Manifestation of Spin-orbit interaction in uniaxial crystal: A closed-fringe Fourier analysis of conoscopic interference.

    PubMed

    Samlan, C T; Naik, Dinesh N; Viswanathan, Nirmal K

    2016-09-14

    Discovered in 1813, the conoscopic interference pattern observed due to light propagating through a crystal, kept between crossed polarizers, shows isochromates and isogyres, respectively containing information about the dynamic and geometric phase acquired by the beam. We propose and demonstrate a closed-fringe Fourier analysis method to disentangle the isogyres from the isochromates, leading us to the azimuthally varying geometric phase and its manifestation as isogyres. This azimuthally varying geometric phase is shown to be the underlying mechanism for the spin-to-orbital angular momentum conversion observed in a diverging optical field propagating through a z-cut uniaxial crystal. We extend the formalism to study the optical activity mediated uniaxial-to-biaxial transformation due to a weak transverse electric field applied across the crystal. Closely associated with the phase and polarization singularities of the optical field, the formalism enables us to understand crystal optics in a new way, paving the way to anticipate several emerging phenomena.

  7. Effect of Uniaxial Strain on the Structural and Magnetic Phase Transitions in BaFe2As2

    SciTech Connect

    Dhital, Chetan; Yamani, Z; Tian, W.; Zeretsky, J; Safa-Sefat, Athena; Wang, Ziqiang; Birgeneau, R. J.; Wilson, Stephen

    2012-01-01

    We report neutron scattering experiments probing the influence of uniaxial strain on both the magnetic and structural order parameters in the parent iron pnictide compound, BaFe{sub 2}As{sub 2}. Our data show that modest strain fields along the in-plane orthorhombic b axis can affect significant changes in phase behavior simultaneous to the removal of structural twinning effects. As a result, we demonstrate in BaFe{sub 2}As{sub 2} samples detwinned via uniaxial strain that the in-plane C{sub 4} symmetry is broken by both the structural lattice distortion and long-range spin ordering at temperatures far above the nominal (strain-free) phase transition temperatures. Surprising changes in the magnetic order parameter of this system under relatively small strain fields also suggest the inherent presence of magnetic domains fluctuating above the strain-free ordering temperature in this material.

  8. Effect of uniaxial strain on electrical properties of CNT-based junctionless field-effect transistor: Numerical study

    NASA Astrophysics Data System (ADS)

    Pourian, Parisa; Yousefi, Reza; Ghoreishi, Seyed Saleh

    2016-05-01

    Numerical studies on junctionless carbon nanotube field-effect transistors (JL-CNTFETs) have indicated that these devices produce more ON current than silicon junctionless transistors in comparable dimensions. Nevertheless, due to the smaller bandgap and quantum confinement effects, they provide weaker results in the OFF state. Since the change of energy bandgap is one of the effects of applying uniaxial strain on CNTs, in this paper, using non-equilibrium Green's function method (NEGF), the effects of applying strain on electrical characteristics of JL-CNTFETs, such as ION and IOFF, intrinsic delay, ION/IOFF ratio, power-delay product, unity-gain frequency, gate transconductance, and output resistance are investigated. The simulation results show that uniaxial stain, significantly alters the OFF state behavior and as a result the electrical properties of the device.

  9. Refractive indices of (NH{sub 4}){sub 2}SO{sub 4} crystals under uniaxial pressure

    SciTech Connect

    Stadnyk, V. Yo. Romanyuk, M. O.; Andrievskii, B. V.; Tuzyak, N. R.

    2009-03-15

    The effect of uniaxial pressure {sigma}{sub m} {<=} 200 bar on the spectral (300-800 nm) and temperature (300-77 K) dependences of the refractive indices of(NH{sub 4}){sub 2}SO{sub 4} crystals has been investigated. The baric dependences of the electronic polarizability, specific refraction, and parameters of the Sellmeier formula have been calculated. It is established that uniaxial pressure increases the refractive indices, mainly because of the narrowing of the band gap, increase in the oscillator density, and redshift of the UV absorption band maximum. The anomalies arising as a result of ferroelectric phase transition are related to the occurrence of spontaneous deformation and polarization (the latter is a superposition of two sublattice polarizations). The spectral and temperature dependences of the piezooptic constants are analyzed and the values of electro-optic coefficients are estimated.

  10. Isogyres - Manifestation of Spin-orbit interaction in uniaxial crystal: A closed-fringe Fourier analysis of conoscopic interference.

    PubMed

    Samlan, C T; Naik, Dinesh N; Viswanathan, Nirmal K

    2016-01-01

    Discovered in 1813, the conoscopic interference pattern observed due to light propagating through a crystal, kept between crossed polarizers, shows isochromates and isogyres, respectively containing information about the dynamic and geometric phase acquired by the beam. We propose and demonstrate a closed-fringe Fourier analysis method to disentangle the isogyres from the isochromates, leading us to the azimuthally varying geometric phase and its manifestation as isogyres. This azimuthally varying geometric phase is shown to be the underlying mechanism for the spin-to-orbital angular momentum conversion observed in a diverging optical field propagating through a z-cut uniaxial crystal. We extend the formalism to study the optical activity mediated uniaxial-to-biaxial transformation due to a weak transverse electric field applied across the crystal. Closely associated with the phase and polarization singularities of the optical field, the formalism enables us to understand crystal optics in a new way, paving the way to anticipate several emerging phenomena. PMID:27625210

  11. Isogyres – Manifestation of Spin-orbit interaction in uniaxial crystal: A closed-fringe Fourier analysis of conoscopic interference

    PubMed Central

    Samlan, C. T.; Naik, Dinesh N.; Viswanathan, Nirmal K.

    2016-01-01

    Discovered in 1813, the conoscopic interference pattern observed due to light propagating through a crystal, kept between crossed polarizers, shows isochromates and isogyres, respectively containing information about the dynamic and geometric phase acquired by the beam. We propose and demonstrate a closed-fringe Fourier analysis method to disentangle the isogyres from the isochromates, leading us to the azimuthally varying geometric phase and its manifestation as isogyres. This azimuthally varying geometric phase is shown to be the underlying mechanism for the spin-to-orbital angular momentum conversion observed in a diverging optical field propagating through a z-cut uniaxial crystal. We extend the formalism to study the optical activity mediated uniaxial-to-biaxial transformation due to a weak transverse electric field applied across the crystal. Closely associated with the phase and polarization singularities of the optical field, the formalism enables us to understand crystal optics in a new way, paving the way to anticipate several emerging phenomena. PMID:27625210

  12. SAXS/WAXS studies of flow-induced crystallization of poly(1-butene) in uniaxial extensional flow

    NASA Astrophysics Data System (ADS)

    McCready, Erica; Burghardt, Wesley

    2013-03-01

    We report studies of flow-induced crystallization of poly(1-butene) in uniaxial extensional flow. Flow was produced using an SER extensional flow fixture housed in a custom built convection oven designed to provide x-ray access for in situ studies of polymer structure using synchrotron x-ray scattering techniques. Samples were loaded into the SER fixture, heated well into the melt, and then cooled to a temperature at which quiescent crystallization would be prohibitively slow. A short interval of uniaxial extensional flow was then applied, after which simultaneous wide- and small-angle x-ray scattering (SAXS and WAXS) patterns were collected to study the phase transformation kinetics and morphology of the subsequent accelerated crystallization. The impact of both deformation rate and total applied strain on the crystallization process were examined.

  13. Complementary characterization data in support of uniaxially aligned electrospun nanocomposites based on a model PVOH-epoxy system

    PubMed Central

    Karimi, Samaneh; Staiger, Mark P.; Buunk, Neil; Fessard, Alison; Tucker, Nick

    2016-01-01

    This paper presents complementary data corresponding to characterization tests done for our research article entitled “Uniaxially aligned electrospun fibers for advanced nanocomposites based on a model PVOH-epoxy system” (Karimi et al., 2016) [1]. Poly(vinyl alcohol) and epoxy resin were selected as a model system and the effect of electrospun fiber loading on polymer properties was examined in conjunction with two manufacturing methods. A novel electrospinning technology for production of uniaxially aligned nanofiber arrays was used. A conventional wet lay-up fabrication method is compared against a novel, hybrid electrospinning–electrospraying approach. The structure and thermomechanical properties of resulting composite materials were examined using scanning electron microscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and tensile testing. For discussion of obtained results please refer to the research paper (Karimi et al., 2016) [1]. PMID:26977430

  14. Effect of uniaxial strain on the tunnel magnetoresistance of T-shaped graphene nanoribbon based spin-valve

    NASA Astrophysics Data System (ADS)

    Fouladi, A. Ahmadi

    2016-07-01

    We theoretically investigated the spin-dependent transport through a T-shaped graphene nanoribbon (TsGNR) based spin-valve consisting of armchair graphene sandwiched between two semi-infinite ferromagnetic armchair graphene nanoribbon leads in the presence of an applied uniaxial strain. Based on a tight-binding model and standard nonequilibrium Green's function technique, it is demonstrated that the tunnel magnetoresistance (TMR) for the system can be increased about 98% by tuning the uniaxial strain. Our results show that the absolute values of TMR around the zero bias voltage for compressive strain are larger than tensile strain. In addition, the TMR of the system can be nicely controlled by GNR width.

  15. Finite element implementation of Robinson's unified viscoplastic model and its application to some uniaxial and multiaxial problems

    NASA Technical Reports Server (NTRS)

    Arya, V. K.; Kaufman, A.

    1987-01-01

    A description of the finite element implementation of Robinson's unified viscoplastic model into the General Purpose Finite Element Program (MARC) is presented. To demonstrate its application, the implementation is applied to some uniaxial and multiaxial problems. A comparison of the results for the multiaxial problem of a thick internally pressurized cylinder, obtained using the finite element implementation and an analytical solution, is also presented. The excellent agreement obtained confirms the correct finite element implementation of Robinson's model.

  16. Mechanical properties of carboniferous rocks in the Upper Silesian Coal Basin under uniaxial and triaxial compression tests

    SciTech Connect

    Bukowska, M.

    2005-04-01

    Many years' studies of geological properties of rocks from the Upper Silesian Coal Basin have resulted in acquisition of a substantial data base of mechanical parameters of rocks over the total strain range. It is found that the post-peak rock properties are closely related with the peak strength and the pre-peak properties. The relationship between the uniaxial ultimate strength, elastic modulus, and drop modulus are determined.

  17. The local autocorrelation time near the surface of a system with uniaxial anisotropy in a transverse field

    NASA Astrophysics Data System (ADS)

    Korneta, W.; Pytel, Z.

    1988-07-01

    A three-dimensional semi-infinite system with strong uniaxial anisotropy ina transverse field is considered. The behaviour of the local autocorrelation time for the component of the order parameter in the direction parallel to the easy axis near the second-order phase transition for this component induced by the transverse field is given. The effect of the surface on this behaviour is discussed. The Landau approximation is used.

  18. Highly tunable magnetism in silicene doped with Cr and Fe atoms under isotropic and uniaxial tensile strain

    SciTech Connect

    Zheng, Rui; Ni, Jun; Chen, Ying

    2015-12-28

    We have investigated the magnetic properties of silicene doped with Cr and Fe atoms under isotropic and uniaxial tensile strain by the first-principles calculations. We find that Cr and Fe doped silicenes show strain-tunable magnetism. (1) The magnetism of Cr and Fe doped silicenes exhibits sharp transitions from low spin states to high spin states by a small isotropic tensile strain. Specially for Fe doped silicene, a nearly nonmagnetic state changes to a high magnetic state by a small isotropic tensile strain. (2) The magnetic moments of Fe doped silicene also show a sharp jump to ∼2 μ{sub B} at a small threshold of the uniaxial strain, and the magnetic moments of Cr doped silicene increase gradually to ∼4 μ{sub B} with the increase of uniaxial strain. (3) The electronic and magnetic properties of Cr and Fe doped silicenes are sensitive to the magnitude and direction of the external strain. The highly tunable magnetism may be applied in the spintronic devices.

  19. The effect of thermal stresses on the integrity of three built-up aircraft structures

    NASA Technical Reports Server (NTRS)

    Jenkins, J. M.

    1980-01-01

    A Mach 6 flight was simulated in order to examine heating effects on three frame/skin specimens. The specimens included: a titanium truss frame with a lockalloy skin; a stainless steel z-frame with a lockalloy skin; and a titanium z-frame with a lockalloy skin. Thermal stresses and temperature were measured on these specimens for the purpose of examining their efficiency, performance, and integrity. Measured thermal stresses were examined with respect to material yield strengths, buckling criteria, structural weight, and geometric locations. Principal thermal stresses were studied from the standpoint of uniaxial stress assumptions. Measured thermal stresses were compared to predicted values.

  20. On the in-plane uniaxial anisotropy formation by using Fe-Co-Zr-N films: A theoretical and experimental investigation

    NASA Astrophysics Data System (ADS)

    Seemann, K.; Beirle, S.; Leiste, H.

    2016-09-01

    In the present paper a simple theoretical approach for the in-plane uniaxial anisotropy evolution in thin films is introduced. In order to show, what are the conditions for a uniaxial anisotropy formation during annealing a ferromagnetic film in an external static magnetic field, a Hamiltonian, i.e., mean energy balances were established with introducing their annealing temperature dependence. At this point, a 1-dimesional chain-like arrangement of Fe and Co elements for an "isotropic" and uniaxial anisotropy state for the numerical computation was assumed. It was shown that a critical energy and annealing temperature (temperature threshold) can be attained from which a uniaxial anisotropy arises. Comparatively, calculations according to the Neél theory delivered the activation energy for inducing a uniaxial anisotropy. The experimental verification of the calculations, by using Fe40Co37Zr11N12 films which were produced by reactive magnetron sputtering, yielded the activation energy of about 250 meV. Annealing temperatures above 473 K (200 °C) enabled marked uniaxial anisotropies. This correlated with the numerical quantum mechanical estimations which yielded a critical annealing temperature of approximately 449 K (176 °C). The calculated critical energy of 243 meV was in a good agreement with the verified experiments if one assumes a short range order of at least 10 ferromagnetic atoms in line (5Fe+5Co) for computation.

  1. Role of nesprin-1 in nuclear deformation in endothelial cells under static and uniaxial stretching conditions

    SciTech Connect

    Anno, Toshiro; Sakamoto, Naoya; Sato, Masaaki

    2012-07-20

    Highlights: Black-Right-Pointing-Pointer Nesprin-1 knockdown decreases widths of nuclei in ECs under static condition. Black-Right-Pointing-Pointer Nuclear strain caused by stretching is increased by nesprin-1 knockdown in ECs. Black-Right-Pointing-Pointer We model mechanical interactions of F-actin with the nucleus in stretched cells. Black-Right-Pointing-Pointer F-actin bound to nesprin-1 may cause sustainable force transmission to the nucleus. -- Abstract: The linker of nucleus and cytoskeleton (LINC) complex, including nesprin-1, has been suggested to be crucial for many biological processes. Previous studies have shown that mutations in nesprin-1 cause abnormal cellular functions and diseases, possibly because of insufficient force transmission to the nucleus through actin filaments (F-actin) bound to nesprin-1. However, little is known regarding the mechanical interaction between the nucleus and F-actin through nesprin-1. In this study, we examined nuclear deformation behavior in nesprin-1 knocked-down endothelial cells (ECs) subjected to uniaxial stretching by evaluating nuclear strain from lateral cross-sectional images. The widths of nuclei in nesprin-1 knocked-down ECs were smaller than those in wild-type cells. In addition, nuclear strain in nesprin-1 knocked-down cells, which is considered to be compressed by the actin cortical layer, increased compared with that in wild-type cells under stretching condition. These results indicate that nesprin-1 knockdown releases the nucleus from the tension of F-actin bound to the nucleus, thereby increasing allowance for deformation before stretching, and that F-actin bound to the nucleus through nesprin-1 causes sustainable force transmission to the nucleus.

  2. Predicting the uniaxial compressive strength of cemented paste backfill from ultrasonic pulse velocity test

    NASA Astrophysics Data System (ADS)

    Yılmaz, Tekin; Ercikdi, Bayram

    2016-07-01

    The aim of this study is to investigate the predictability of the uniaxial compressive strength (UCS) of cemented paste backfill (CPB) prepared from three different tailings (Tailings T1, Tailings T2 and Tailings T3) using ultrasonic pulse velocity (UPV) test. For this purpose, 180 CPB samples with diameter × height of 5 × 10 cm (similar to NX size) prepared at different binder dosages and consistencies were subjected to the UPV and UCS tests at 7-56 days of curing periods. The effects of binder dosage and consistency on the UPV and UCS properties of CPB samples were investigated and UCS values were correlated with the corresponding UPV data. Microstructural analyses were also performed on CPB samples in order to understand the effect of microstructure (i.e. total porosity) on the UPV data. The UPV and UCSs of CPB samples increased with increasing binder dosage and reducing the consistency irrespective of the tailings type and curing periods. Changes in the mixture properties observed to have a lesser extent on the UPV properties of CPB, while, their effect on the UCS of CPB was significant. Empirical equations were produced for each mixture in order to predict the UCSs of CPB through UPV. The validity of the equations was also checked by t- and F-test. The results showed that a linear relation appeared to exist between the UPV and UCS with high correlation coefficients (r ≥ 0.79) and all models were valid by statistical analysis. Mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) analyses have revealed that the UPV properties of CPB samples were highly associated with their respective microstructural properties (i.e. total porosity). The major output of this study is that UPV test can be effectively used for a preliminary prediction of the strength of CPB.

  3. Mechanical characterization of the rat and mice skin tissues using histostructural and uniaxial data

    PubMed Central

    Karimi, Alireza; Rahmati, Seyyed Mohammadali; Navidbakhsh, Mahdi

    2015-01-01

    The skin tissue has been shown to behave like a nonlinear anisotropic material. This study was aimed to employ a constitutive fiber family equation to characterize the nonlinear anisotropic mechanical behavior of the rat and mice skin tissues in different anatomical locations, including the abdomen and back, using histostructural and uniaxial data. The rat and mice skin tissues were excised from the animals’ body and then the histological analyses were performed on each skin type to determine the mean fiber orientation angle. Afterward, the preconditioned skin tissues were subjected to a series of quasi-static axial and circumferential loads until the incidence of failure. The crucial role of fiber orientation was explicitly added into a proposed strain energy density function. The material coefficients were determined using the constrained nonlinear optimization method based on the axial and circumferential extension data of the rat and mice samples at different anatomical locations. The material coefficients of the skins were given with R2 ≥ 0.998. The results revealed a significant load-bearing capacity and stiffness of the rat abdomen compared to the rat back tissues. In addition, the mice abdomen showed a higher stiffness in the axial direction in comparison with circumferential one, while the mice back displayed its highest stiffness in the circumferential direction. The material coefficients of the rat and mice skin tissues were determined and well compared to the experimental data. The optimized fiber angles were also compared to the experimental histological data, and in all cases less than 11.85% differences were observed in both the skin tissues. PMID:25837446

  4. Yield stress and plasticity of nanostructured titanium of different purity at 300, 77, and 4.2 K

    SciTech Connect

    Tabachnikova, E. D. Bengus, V. Z.; Podol'skii, A. V.; Smirnov, S. N.; Valiev, R. Z.

    2009-11-15

    Specimens of nanostructured titanium with different dopant concentrations were prepared by intense plastic deformation via equal-channel-angular pressing. The low-temperature mechanical characteristics of the specimens subjected to active deformation under uniaxial tension and compression were studied. The yield stress and the limit uniform deformation of nanostructured and coarse-grained polycrystalline titanium were compared.

  5. Stress effects in twisted highly birefringent fibers

    NASA Astrophysics Data System (ADS)

    Wolinski, Tomasz R.

    1994-03-01

    Hydrostatic pressure and uniaxial longitudinal strain effects in twisted highly birefringent optical fibers have been investigated from the point of the Marcuse mode-coupling theory. The problem is analyzed in terms of local normal modes of the ideal fiber and in the limit of weak twist, where large linear birefringence dominates over twist effect, and therefore twist coupling between local modes is not effective. The authors present the results of birefringence measurements in highly birefringent bow-tie fibers influenced simultaneously by hydrostatic pressure up to 100 MPa and twisting the result for highly birefringent elliptical-core fibers influenced by uniaxial longitudinal strain up to 4000 (mu) (epsilon) and twisting effect. The birefringence measurement method is based on twist-induced effects and has been successfully applied in a stress environment. The experiment was conducted with a specially designed stress generating device that makes it possible to simultaneously generate various mechanical perturbations such as hydrostatic and radial pressure, axial strain and twist, allowing study of their influence on mode propagation in optical fibers. A comparison with theoretical results as well as with pervious experimental data on stress influence on the beat length parameter in highly birefringent fibers is also provided.

  6. Stress pulse phenomena

    SciTech Connect

    McGlaun, M.

    1993-08-01

    This paper is an introductory discussion of stress pulse phenomena in simple solids and fluids. Stress pulse phenomena is a very rich and complex field that has been studied by many scientists and engineers. This paper describes the behavior of stress pulses in idealized materials. Inviscid fluids and simple solids are realistic enough to illustrate the basic behavior of stress pulses. Sections 2 through 8 deal with the behavior of pressure pulses. Pressure is best thought of as the average stress at a point. Section 9 deals with shear stresses which are most important in studying solids.

  7. Osteogenic differentiation of human mesenchymal stem cells in collagen matrices: effect of uniaxial cyclic tensile strain on bone morphogenetic protein (BMP-2) mRNA expression.

    PubMed

    Sumanasinghe, Ruwan D; Bernacki, Susan H; Loboa, Elizabeth G

    2006-12-01

    Human mesenchymal stem cells (hMSCs) differentiate down an osteogenic pathway with appropriate mechanical and/or chemical stimuli. This study describes the successful culture of hMSCs in 3D collagen matrices under mechanical strain. Bone marrow-derived hMSCs were seeded in linear 3D type I collagen matrices and subjected to 0%, 10%, or 12% uniaxial cyclic tensile strain at 1 Hz for 4 h/day for 7 or 14 days. Cell viability studies indicated that hMSCs remained viable throughout the culture period irrespective of the applied strain level. Real-time RT-PCR studies indicated a significant increase in BMP-2 mRNA expression levels in hMSCs strained at 10% compared to the same day unstrained controls after both 7 and 14 days. An increase in BMP-2 was also observed in hMSCs subjected to 12% strain, but the increase was significant only in the 14-day sample. This is the first report of the culture of bone marrow-derived hMSCs in 3D collagen matrices under cyclic strain, and the first demonstration that strain alone can induce osteogenic differentiation without the addition of osteogenic supplements. Induction of bone differentiation in 3D culture is a critical step in the creation of bioengineered bone constructs. PMID:17518682

  8. Oscillations and uniaxial mechanochemical waves in a model of an active poroelastic medium: Application to deformation patterns in protoplasmic droplets of Physarum polycephalum

    NASA Astrophysics Data System (ADS)

    Alonso, Sergio; Strachauer, Ulrike; Radszuweit, Markus; Bär, Markus; Hauser, Marcus J. B.

    2016-04-01

    Self-organization in cells often manifests itself in oscillations and waves. Here, we address deformation waves in protoplasmic droplets of the plasmodial slime mould Physarum polycephalum by modelling and experiments. In particular, we extend a one-dimensional model that considered the cell as a poroelastic medium, where active tension caused mechanochemical waves that were regulated by an inhibitor (Radszuweit et al., 2013). Our extension consists of a simple, qualitative chemical reaction-diffusion model (Brusselator) that describes the regulation of the inhibitor by another biochemical species. The biochemical reaction enhances the formation of mechanochemical waves if the reaction rates and input concentrations are near or inside an oscillatory regime. The period of the waves is found to be controlled by the characteristic oscillation period, whereas their wavelength is set by mechanical parameters. The model also allows for a systematic study of the chemical activity at the onset of mechanochemical waves. We also present examples for pattern formation in protoplasmic droplets of Physarum polycephalum including global oscillations where the central region of the droplets is in antiphase to the boundary zone, as well as travelling and standing wave-like uniaxial patterns. Finally, we apply our model to reproduce these experimental results by identifying the active tension inhibitor with the intracellular calcium concentration in the Physarum droplets and by using parameter values from mechanical experiments, respectively knowledge about the properties of calcium oscillations in Physarum. The simulation results are then found to be in good agreement with the experimental observations.

  9. A comparison of stress in cracked fibrous tissue specimens with varied crack location, loading, and orientation using finite element analysis.

    PubMed

    Peloquin, John M; Elliott, Dawn M

    2016-04-01

    Cracks in fibrous soft tissue, such as intervertebral disc annulus fibrosus and knee meniscus, cause pain and compromise joint mechanics. A crack concentrates stress at its tip, making further failure and crack extension (fracture) more likely. Ex vivo mechanical testing is an important tool for studying the loading conditions required for crack extension, but prior work has shown that it is difficult to reproduce crack extension. Most prior work used edge crack specimens in uniaxial tension, with the crack 90° to the edge of the specimen. This configuration does not necessarily represent the loading conditions that cause in vivo crack extension. To find a potentially better choice for experiments aiming to reproduce crack extension, we used finite element analysis to compare, in factorial combination, (1) center crack vs. edge crack location, (2) biaxial vs. uniaxial loading, and (3) crack-fiber angles ranging from 0° to 90°. The simulated material was annulus fibrosus fibrocartilage with a single fiber family. We hypothesized that one of the simulated test cases would produce a stronger stress concentration than the commonly used uniaxially loaded 90° crack-fiber angle edge crack case. Stress concentrations were compared between cases in terms of fiber-parallel stress (representing risk of fiber rupture), fiber-perpendicular stress (representing risk of matrix rupture), and fiber shear stress (representing risk of fiber sliding). Fiber-perpendicular stress and fiber shear stress concentrations were greatest in edge crack specimens (of any crack-fiber angle) and center crack specimens with a 90° crack-fiber angle. However, unless the crack is parallel to the fiber direction, these stress components alone are insufficient to cause crack opening and extension. Fiber-parallel stress concentrations were greatest in center crack specimens with a 45° crack-fiber angle, either biaxially or uniaxially loaded. We therefore recommend that the 45° center crack case be

  10. Extended Kantorovich method for local stresses in composite laminates upon polynomial stress functions

    NASA Astrophysics Data System (ADS)

    Huang, Bin; Wang, Ji; Du, Jianke; Guo, Yan; Ma, Tingfeng; Yi, Lijun

    2016-06-01

    The extended Kantorovich method is employed to study the local stress concentrations at the vicinity of free edges in symmetrically layered composite laminates subjected to uniaxial tensile load upon polynomial stress functions. The stress fields are initially assumed by means of the Lekhnitskii stress functions under the plane strain state. Applying the principle of complementary virtual work, the coupled ordinary differential equations are obtained in which the solutions can be obtained by solving a generalized eigenvalue problem. Then an iterative procedure is established to achieve convergent stress distributions. It should be noted that the stress function based extended Kantorovich method can satisfy both the traction-free and free edge stress boundary conditions during the iterative processes. The stress components near the free edges and in the interior regions are calculated and compared with those obtained results by finite element method (FEM). The convergent stresses have good agreements with those results obtained by three dimensional (3D) FEM. For generality, various layup configurations are considered for the numerical analysis. The results show that the proposed polynomial stress function based extended Kantorovich method is accurate and efficient in predicting the local stresses in composite laminates and computationally much more efficient than the 3D FEM.

  11. Keeping Fit: Stress Relievers

    ERIC Educational Resources Information Center

    Crupi, Jeffrey

    2005-01-01

    With all the extra demands that are placed on teachers during the months of May and June, the end of the year can be an extremely stressful time. This article describes several tips for diminishing the effects of end of year stress. The following relaxation tips are described: (1) Neck and Upper Shoulder Stretch; (2) Superman Stretch; (3) Doorway…

  12. Influence of Lithophysal Geometry on the Uniaxial Compression of Tuff-Like Rock

    SciTech Connect

    Rigby, Douglas B.

    2007-06-13

    A large portion of the rock of the high-level nuclear waste repository at Yucca Mountain contains lithophysae or voids. These voids have a significant detrimental effect on the engineering properties of the rock mass and its performance. The lithophysae were formed at the time of volcanic deposition by pockets of gas trapped within the compressing and cooling pyroclastic flow material. Lithophysae vary by size, shape, and spatial frequency of occurrence. Due to the difficulties of testing actual lithophysal rock, the current mechanical property data set is limited and the numerical models of lithophysal rock are not well validated. The purpose of this task was to experimentally quantify the effect of void geometry in the mechanical compression of cubes of analog lithophysal-like rock. In this research the mechanical properties of the analog rock were systematically studied by examining various patterns of voids based on variables consisting of hole shape, size, and geometrical distribution. Each specified hole pattern was cast into 6 by 6 by 6-in. Hydro-StoneTB® specimens (produced in triplicate) and then tested under uniaxial compression. Solid Hydro-StoneTB® specimens exhibited similar mechanical properties to those estimated for rock mass solid specimens of Topopah Spring tuff. The results indicated that the compressive strength and Young’s Modulus values decrease with increasing specimen void porosity. The modulus and strength with void porosity relationships are essentially linear over the 5 to 20 percent void porosity range. When zero void porosity (solid specimen) results are added, exponential functions do not provide a good fit to the data due to a significant sensitivity of strength and modulus to the presence of macro-sized voids. From solid specimens there is roughly a 60 percent drop in strength with about 7 percent void porosity, increasing to an 80 percent drop at about 20 percent void porosity. The percent change in modulus from the solid

  13. The influence of stress state on the reorientation of hydrides in a zirconium alloy

    NASA Astrophysics Data System (ADS)

    Cinbiz, Mahmut N.; Koss, Donald A.; Motta, Arthur T.

    2016-08-01

    Hydride reorientation can occur in spent nuclear fuel cladding when subjected to a tensile hoop stress above a threshold value during cooling. Because in these circumstances the cladding is under a multiaxial stress state, the effect of stress biaxiality on the threshold stress for hydride reorientation is investigated using hydrided CWSR Zircaloy-4 sheet specimens containing ∼180 wt ppm of hydrogen and subjected to a two-cycle thermo-mechanical treatment. The study is based on especially designed specimens within which the stress biaxiality ratios range from uniaxial (σ2/σ1 = 0) to "near-equibiaxial" tension (σ2/σ1 = 0.8). The threshold stress is determined by mapping finite element calculations of the principal stresses and of the stress biaxiality ratio onto the hydride microstructure obtained after the thermo-mechanical treatment. The results show that the threshold stress (maximum principal stress) decreases from 155 to 75 MPa as the stress biaxiality increases from uniaxial to "near-equibiaxial" tension.

  14. Effects of magnetic field and pressure in magnetoelastic stress reconfigurable thin film resonators

    SciTech Connect

    Staruch, M.; Bussmann, K.; Finkel, P.; Kassner, C.; Lofland, S. E.; Fackler, S.; Takeuchi, I.; Dolabdjian, C.; Lacomb, R.

    2015-07-20

    Free-standing CoFe thin-film doubly clamped stress reconfigurable resonators were investigated as a function of magnetic field and pressure. A large uniaxial anisotropy resulting from residual uniaxial tensile stress, as revealed from magnetic hysteresis loops, leads to an easy magnetization axis aligned along the length of the beams. The quality factor of the driven resonator beams under vacuum is increased by 30 times, leading to an enhanced signal-to-noise ratio and a predicted reduction in the intrinsic magnetic noise by a factor of 6, potentially reaching as low as ∼25 pT/√Hz at 1 Torr. Stress reconfigurable sensors operating under vacuum could thus further improve the limit of detection and advance development of magnetic field sensing technology.

  15. Investigation of anisotropic photonic band gaps in three-dimensional magnetized plasma photonic crystals containing the uniaxial material

    SciTech Connect

    Zhang, Hai-Feng; Liu, Shao-Bin; Kong, Xiang-Kun

    2013-09-15

    In this paper, the dispersive properties of three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) composed of anisotropic dielectric (the uniaxial material) spheres immersed in homogeneous magnetized plasma background with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, as the Voigt effects of magnetized plasma are considered. The equations for calculating the anisotropic photonic band gaps (PBGs) in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and two flatbands regions can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field on the dispersive properties of the 3D MPPCs are investigated in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in 3D MPPCs with fcc lattices and the complete PBGs can be found compared to the conventional 3D MPPCs doped by the isotropic material. The bandwidths of PBGs can be tuned by introducing the magnetized plasma into 3D PCs containing the uniaxial material. It is also shown that the anisotropic PBGs can be manipulated by the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field, respectively. The locations of flatbands regions cannot be manipulated by any parameters except for the plasma frequency and external magnetic field. Introducing the uniaxial material can obtain the complete PBGs as the 3D MPPCs with high symmetry and also provides a way to design the tunable devices.

  16. Microfabrication and characterization of an array of dielectric elastomer actuators generating uniaxial strain to stretch individual cells

    NASA Astrophysics Data System (ADS)

    Akbari, S.; Shea, H. R.

    2012-04-01

    Cells regulate their behavior in response to mechanical strains. Cell cultures to study mechanotransuction are typically cm2 in area, far too large to monitor single cell response. We have developed an array of dielectric elastomer microactuators as a tool to study mechanotransduction of individual cells. The array consists of 72 100 µm × 200 µm electroactive polymer actuators which expand uniaxially when a voltage is applied. Single cells will be attached on each actuator to study their response to periodic mechanical strains. The device is fabricated by patterning compliant microelectrodes on both sides of a 30 µm thick polydimethylsiloxane membrane, which is bonded to a Pyrex chip with 200 µm wide trenches. Low-energy metal ion implantation is used to make stretchable electrodes and we demonstrate here the successful miniaturization of such ion-implanted electrodes. The top electrode covers the full membrane area, while the bottom electrodes are 100 µm wide parallel lines, perpendicular to the trenches. Applying a voltage between the top and bottom electrodes leads to uniaxial expansion of the membrane at the intersection of the bottom electrodes and the trenches. To characterize the in-plane strain, an array of 4 µm diameter aluminum dots is deposited on each actuator. The position of each dot is tracked, allowing displacement and strain profiles to be measured as a function of voltage. The uniaxial strain reaches 4.7% at 2.9 kV with a 0.2 s response time, sufficient to stimulate most cells with relevant biological strains and frequencies.

  17. Investigation of anisotropic photonic band gaps in three-dimensional magnetized plasma photonic crystals containing the uniaxial material

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Kong, Xiang-Kun

    2013-09-01

    In this paper, the dispersive properties of three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) composed of anisotropic dielectric (the uniaxial material) spheres immersed in homogeneous magnetized plasma background with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, as the Voigt effects of magnetized plasma are considered. The equations for calculating the anisotropic photonic band gaps (PBGs) in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and two flatbands regions can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field on the dispersive properties of the 3D MPPCs are investigated in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in 3D MPPCs with fcc lattices and the complete PBGs can be found compared to the conventional 3D MPPCs doped by the isotropic material. The bandwidths of PBGs can be tuned by introducing the magnetized plasma into 3D PCs containing the uniaxial material. It is also shown that the anisotropic PBGs can be manipulated by the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field, respectively. The locations of flatbands regions cannot be manipulated by any parameters except for the plasma frequency and external magnetic field. Introducing the uniaxial material can obtain the complete PBGs as the 3D MPPCs with high symmetry and also provides a way to design the tunable devices.

  18. The effect of intermolecular donor?acceptor energy transfer on emission anisotropy in uniaxially oriented polymer films

    NASA Astrophysics Data System (ADS)

    Sadownik, M.; Bojarski, Piotr

    2004-10-01

    Excitation energy transport between donors and acceptors is studied for uniaxially stretched and unstretched poly(vinyl) alcohol films. Donor emission anisotropy courses versus acceptor concentration as well as donor-acceptor emission anisotropy spectra occurred quite different in stretched and unstretched films. Upon donor excitation the total emission anisotropy rapidly decreases when passing from the donor to the acceptor fluorescence band in disordered systems. However, such a pronounced effect has not been found in partly ordered films. Donors and acceptors exhibit highly preferential mutual orientation in strongly ordered films resulting in the preservation of acceptor emission anisotropy.

  19. Importance of uniaxial compression for the appearance of superconductivity in NdO1-xFxBiS2

    NASA Astrophysics Data System (ADS)

    A, Omachi; T, Hiroi; J, Kajitani; O, Miura; Y, Mizuguchi

    2014-05-01

    We have investigated the crystal structure and superconducting properties of the new layered superconductor NdO1-xFxBiS2. Bulk superconductivity with a Tc above 4.5 K was observed. It was found that the Tc depended on both F concentration and crystal structure. Uniaxial compression along the c axis upon F substitution seemed to be linked with the appearance of bulk superconductivity. Furthermore, we considered that a higher Tc can be achieved when the c/a parameter was optimized in the NdO1-xFxBiS2 system.

  20. 3D numerical analysis of crack propagation of heterogeneous notched rock under uniaxial tension

    NASA Astrophysics Data System (ADS)

    Wang, S. Y.; Sloan, S. W.; Sheng, D. C.; Tang, C. A.

    2016-05-01

    Macroscopic notches play an important role in evaluating the fracture process zone (FPZ) and the strengths of a heterogeneous rock mass. Crack initiation, propagation and coalescence for unnotched, single-notched and double-notched rock specimens are numerically simulated in a 3-D numerical model (RFPA3D). A feature of the code RFPA3D is that it can numerically simulate the evolution of cracks in three-dimensional space, as well as the heterogeneity of the rock mass. For the unnotched case, special attention is given to the complete stress-strain curve and the corresponding AE events for the failure process of rock specimen. By comparing with published experimental results, the simulation results from RFPA3D are found to be satisfactory. For the single-notched case, the effect of the length and the depth of the single notch and the thickness of the specimen on the failure mode and peak stress are evaluated. The 3D FPZ is very different from that in two dimensions. For the double-notched case, the effects of the separation distance and overlap distance of the double notches, as well as influence of the homogeneity index (m) are also investigated. As the overlap distance increases, the direction of the principal tensile stress at each notch-end changes from a perpendicular direction (tensile stress field) to a nearly parallel direction (compressive stress field), which affects the evolution of the cracks from the two notches.

  1. A novel method for calculating the energy barriers for carbon diffusion in ferrite under heterogeneous stress

    NASA Astrophysics Data System (ADS)

    Tchitchekova, Deyana S.; Morthomas, Julien; Ribeiro, Fabienne; Ducher, Roland; Perez, Michel

    2014-07-01

    A novel method for accurate and efficient evaluation of the change in energy barriers for carbon diffusion in ferrite under heterogeneous stress is introduced. This method, called Linear Combination of Stress States, is based on the knowledge of the effects of simple stresses (uniaxial or shear) on these diffusion barriers. Then, it is assumed that the change in energy barriers under a complex stress can be expressed as a linear combination of these already known simple stress effects. The modifications of energy barriers by either uniaxial traction/compression and shear stress are determined by means of atomistic simulations with the Climbing Image-Nudge Elastic Band method and are stored as a set of functions. The results of this method are compared to the predictions of anisotropic elasticity theory. It is shown that, linear anisotropic elasticity fails to predict the correct energy barrier variation with stress (especially with shear stress) whereas the proposed method provides correct energy barrier variation for stresses up to ˜3 GPa. This study provides a basis for the development of multiscale models of diffusion under non-uniform stress.

  2. A novel method for calculating the energy barriers for carbon diffusion in ferrite under heterogeneous stress.

    PubMed

    Tchitchekova, Deyana S; Morthomas, Julien; Ribeiro, Fabienne; Ducher, Roland; Perez, Michel

    2014-07-21

    A novel method for accurate and efficient evaluation of the change in energy barriers for carbon diffusion in ferrite under heterogeneous stress is introduced. This method, called Linear Combination of Stress States, is based on the knowledge of the effects of simple stresses (uniaxial or shear) on these diffusion barriers. Then, it is assumed that the change in energy barriers under a complex stress can be expressed as a linear combination of these already known simple stress effects. The modifications of energy barriers by either uniaxial traction/compression and shear stress are determined by means of atomistic simulations with the Climbing Image-Nudge Elastic Band method and are stored as a set of functions. The results of this method are compared to the predictions of anisotropic elasticity theory. It is shown that, linear anisotropic elasticity fails to predict the correct energy barrier variation with stress (especially with shear stress) whereas the proposed method provides correct energy barrier variation for stresses up to ∼3 GPa. This study provides a basis for the development of multiscale models of diffusion under non-uniform stress.

  3. A novel method for calculating the energy barriers for carbon diffusion in ferrite under heterogeneous stress

    SciTech Connect

    Tchitchekova, Deyana S.; Morthomas, Julien; Perez, Michel; Ribeiro, Fabienne; Ducher, Roland

    2014-07-21

    A novel method for accurate and efficient evaluation of the change in energy barriers for carbon diffusion in ferrite under heterogeneous stress is introduced. This method, called Linear Combination of Stress States, is based on the knowledge of the effects of simple stresses (uniaxial or shear) on these diffusion barriers. Then, it is assumed that the change in energy barriers under a complex stress can be expressed as a linear combination of these already known simple stress effects. The modifications of energy barriers by either uniaxial traction/compression and shear stress are determined by means of atomistic simulations with the Climbing Image-Nudge Elastic Band method and are stored as a set of functions. The results of this method are compared to the predictions of anisotropic elasticity theory. It is shown that, linear anisotropic elasticity fails to predict the correct energy barrier variation with stress (especially with shear stress) whereas the proposed method provides correct energy barrier variation for stresses up to ∼3 GPa. This study provides a basis for the development of multiscale models of diffusion under non-uniform stress.

  4. [Stress and cognitivism].

    PubMed

    Márquez, Coral

    2004-01-01

    In this article, a brief account of the psychological sense of stress is referred. Richard Lazarus' transaccional theory is described in detail; his first transaccional cognitive theory and his last cognitive-emotional transaccional theory. Stress is also described from other points of view, such as Grenberg's emotional theory. The new construct Psychofortology is defined and some references about the principal authors are made. Psychotherapeutic possibilities from the different psychological schools mentioned are described.

  5. A prediction model for uniaxial compressive strength of deteriorated pyroclastic rocks due to freeze-thaw cycle

    NASA Astrophysics Data System (ADS)

    İnce, İsmail; Fener, Mustafa

    2016-08-01

    Either directly or indirectly, building stone is exposed to diverse atmospheric interactions depending on the seasonal conditions. Due to those interactions, objects of historic and cultural heritage, as well as modern buildings, partially or completely deteriorate. Among processes involved in rock deterioration, the freeze-thaw (F-T) cycle is one of the most important. Even though pyroclastic rocks have been used as building stone worldwide due to their easy workability, they are the building stone most affected by the F-T cycle. A historical region in Central Anatolia, Turkey, Cappadoia encompasses exceptional natural wonders characterized by fairy chimneys and unique historical and cultural heritage. Human-created caves, places of worship and houses have been dug into the pyroclastic rocks, which have in turn been used in architectural construction as building stone. Using 10 pyroclastic rock samples collected from Cappadocia, we determined the rock's index-mechanical properties to develop a statistical model for estimating percentage loss of uniaxial compressive strength a critical parameter of F-T cycle's important value. We used dry density (ρd), ultrasonic velocity (Vp), point load strengths (IS(50)), and slake-durability test indexes (Id4) values of unweathered rocks in our model, which is highly reliable (R2 = 0.84) for predetermination of percentage loss of uniaxial compressive strengths of pyroclastic rocks without requiring any F-T tests.

  6. Influence of particle shape and sample width on uniaxial compression of assembly of prolate spheroids examined by discrete element method

    NASA Astrophysics Data System (ADS)

    Parafiniuk, Piotr; Molenda, Marek; Horabik, Józef

    2014-12-01

    We use numerical simulations based on the discrete element method (DEM) to study the response of a cuboidal assembly of spherical (diameter d) or spheroidal particles to uniaxial compression. This study examines the influences of slight deviations from the spherical shape of particles or of the thickness of cuboidal samples on the packing and mechanical characteristics of the assembly. The spheroidal particles were fabricated by the multisphere method. Eight different particle shapes were considered, each with the same volume and with aspect ratios α from 1.0 to 2.5. The final vertical height and larger horizontal depth of the cuboidal deposit were 15d, whereas the thickness ranged from 1.025d to 10d. Upon increasing the assembly thickness or deviating from a spherical shape, numerical examinations by the DEM revealed clear differences in the packing structure and uniaxial compression of assemblies of spheroidal particles. The departure from a spherical shape results in intense changes in contact network, which is manifested as changes in the volume fraction, mean number of contacts per particle, and ordering of the deposits. For the more elongated particles, the pressure ratio as a function of spheroid aspect ratio reached nearly constant values regardless of the sample thickness.

  7. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19.

    PubMed

    Rowley, S E; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A T; Watts, B E; Scott, J F

    2016-05-17

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T(3), in contrast to the 1/T(2) dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T(3), i.e. with a critical exponent γ = 3. In general γ = (d + z - 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T(3).

  8. Observations of grain-boundary sliding and surface topography in an 8090 Al alloy after uniaxial and biaxial superplastic deformation

    SciTech Connect

    Chen, T.R.; Huang, J.C.

    1999-01-01

    The surface topography of an 8090 aluminum alloy was studied after uniaxial or biaxial superplastic deformation, with particular reference to grain-boundary sliding (GBS) offsets, grain rotation angles, formation of striated bands (SBs) or fibers, cavity distribution, and cavity formation mechanisms. Additionally, the contribution of GBS or grain separation to the overall strain was evaluated. Striated bands were observed and are thought to be the newly exposed faces of the grains inclined to the specimen`s surface. They were formed by sliding of grains upward and downward relative to the specimen surface. Grooves and crests inside SBs were formed from the relative motion of grain-boundary defects. Fibers were observed and are thought to be the further development of the SBs resulting from the formation of elongated cavities and grain separation. More cavitation was found in equibiaxially strained regions than in other regions subjected to approximately equivalent levels of strain. About 50 pct of the total strain was contributed to GBS in the uniaxial tensile-loaded specimens, as compared to about 30 pct in the biaxial-strained specimens. The effects of grain separation, grain rotation, and secondary GBS may be the reasons for the reduction of the observed strain contribution from GBS in biaxially strained specimens.

  9. Spectral butterfly, mixed Dirac-Schrödinger fermion behavior, and topological states in armchair uniaxial strained graphene

    NASA Astrophysics Data System (ADS)

    Roman-Taboada, Pedro; Naumis, Gerardo G.

    2014-11-01

    An exact mapping of the tight-binding Hamiltonian for a graphene nanoribbon under any armchair uniaxial strain into an effective one-dimensional system is presented. As an application, for a periodic modulation we have found a gap opening at the Fermi level and a complex fractal spectrum, akin to the Hofstadter butterfly resulting from the Harper model. The latter can be explained by the commensurability or incommensurability nature of the resulting effective potential. When compared with the zig-zag uniaxial periodic strain, the spectrum shows much bigger gaps, although in general the states have a more extended nature. For a special critical value of the strain amplitude and wavelength, a gap is open. At this critical point, the electrons behave as relativistic Dirac fermions in one direction, while, in the other direction, a nonrelativistic Schrödinger behavior is observed. Also, some topological states were observed which have the particularity of not being completely edge states since they present some amplitude in the bulk. However, these are edge states of the effective system due to a reduced dimensionality through decoupling. These states also present the fractal Chern beating observed recently in quasiperiodic systems.

  10. The Pin-Loaded Small One-Bar Specimen in Use to Determine Uniaxial and Multiaxial Creep Data

    NASA Astrophysics Data System (ADS)

    Ali, Balhassn S. M.

    2016-09-01

    Two novel small specimen creep testing techniques are presented in this paper. The pin-loaded small one-bar specimen (OBS) and the small notched specimen with four loading pins (SNS4) are designed to determine the remaining lifetime for the high-temperature components. The small OBS is suitable for use in obtaining both uniaxial creep strain and creep rupture life data and the SNS4 is designed to obtain the multiaxial behaviour using small material samples. The specimens can be made from small material samples removed from the component surface or from the heat-affected zone. The specimens can be loaded through pin connections for testing. A conversion relationship and conversion factor have been obtained and used to convert the OBS creep data to the corresponding uniaxial data. For validation two materials have been used, P92 and P91 steels at 650°C. The advantages of these testing techniques are highlighted; the recommendations for future research are also given.

  11. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19

    PubMed Central

    Rowley, S. E.; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A. T.; Watts, B. E.; Scott, J. F.

    2016-01-01

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T3, in contrast to the 1/T2 dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T3, i.e. with a critical exponent γ = 3. In general γ = (d + z – 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T3. PMID:27185343

  12. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19.

    PubMed

    Rowley, S E; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A T; Watts, B E; Scott, J F

    2016-01-01

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T(3), in contrast to the 1/T(2) dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T(3), i.e. with a critical exponent γ = 3. In general γ = (d + z - 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T(3). PMID:27185343

  13. Uniaxial ferroelectric quantum criticality in multiferroic hexaferrites BaFe12O19 and SrFe12O19

    NASA Astrophysics Data System (ADS)

    Rowley, S. E.; Chai, Yi-Sheng; Shen, Shi-Peng; Sun, Young; Jones, A. T.; Watts, B. E.; Scott, J. F.

    2016-05-01

    BaFe12O19 is a popular M-type hexaferrite with a Néel temperature of 720 K and is of enormous commercial value ($3 billion/year). It is an incipient ferroelectric with an expected ferroelectric phase transition extrapolated to lie at 6 K but suppressed due to quantum fluctuations. The theory of quantum criticality for such uniaxial ferroelectrics predicts that the temperature dependence of the electric susceptibility χ diverges as 1/T3, in contrast to the 1/T2 dependence found in pseudo-cubic materials such as SrTiO3 or KTaO3. In this paper we present evidence of the susceptibility varying as 1/T3, i.e. with a critical exponent γ = 3. In general γ = (d + z – 2)/z, where the dynamical exponent for a ferroelectric z = 1 and the dimension is increased by 1 from deff = 3 + z to deff = 4 + z due to the effect of long-range dipole interactions in uniaxial as opposed to multiaxial ferroelectrics. The electric susceptibility of the incipient ferroelectric SrFe12O19, which is slightly further from the quantum phase transition is also found to vary as 1/T3.

  14. Multiple scattering of a zero-order Bessel beam with arbitrary incidence by an aggregate of uniaxial anisotropic spheres

    NASA Astrophysics Data System (ADS)

    Li, Z. J.; Wu, Z. S.; Qu, T.; Shang, Q. C.; Bai, L.

    2016-01-01

    Based on the generalized multiparticle Mie theory, multiple scattering of an aggregate of uniaxial anisotropic spheres illuminated by a zero-order Bessel beam (ZOBB) with arbitrary propagation direction is investigated. The particle size and configuration are arbitrary. The arbitrary incident Bessel beam is expanded in terms of spherical vector wave functions (SVWFs). Utilizing the vector addition theorem of SVWFs, interactive and total scattering coefficients are derived through the continuous boundary conditions on which the interaction of the particles is considered. The accuracy of the theory and codes are verified by comparing results with those obtained for arbitrary plane wave incidence by CST simulation, and for ZOBB incidence by a numerical method. The effects of angle of incidence, pseudo-polarization angle, half-conical angle, beam center position, and permittivity tensor elements on the radar cross sections (RCSs) of several types of collective uniaxial anisotropic spheres, such as a linear chain, a 4×4×4 cube-shaped array, and other periodical structures consisting of massive spheres, are numerically analyzed. Selected results on the properties of typical particles such as TiO2, SiO2, or other particle lattices are calculated. This investigation could provide an effective test for further research on the scattering characteristics of an aggregate of anisotropic spheres by a high-order Bessel vortex beam. The results have important application in optical tweezers and particle manipulation.

  15. SAXS/WAXS studies of flow-induced crystallization of poly(1-butene) in uniaxial extensional flow

    NASA Astrophysics Data System (ADS)

    McCready, Erica; Burghardt, Wesley

    2014-03-01

    We report studies of flow-induced crystallization of poly(1-butene) in uniaxial extensional flow. Flow was produced using an SER extensional flow fixture housed in a custom built convection oven designed to provide x-ray access for in situ studies of polymer structure using synchrotron x-ray scattering techniques. Samples were loaded into the SER fixture, heated well into the melt, and then cooled to a temperature at which quiescent crystallization would be prohibitively slow. A short interval of uniaxial extensional flow was then applied, after which simultaneous wide- and small-angle x-ray scattering (SAXS and WAXS) patterns were collected to study the phase transformation kinetics and morphology of the subsequent accelerated crystallization. The degree of crystallite orientation was generally found to decrease over the course of the crystallization. WAXS measurements yielded systematically higher degrees of crystallite orientation than SAXS. Both SAXS and WAXS gave generally consistent results for the extent of crystallization, although the SAXS invariant showed a decrease at long times that is not mirrored in the WAXS data. The impact of both deformation rate and total applied strain on the crystallization process were examined.

  16. Uniaxially aligned electrospun cellulose acetate nanofibers for thin layer chromatographic screening of hydroquinone and retinoic acid adulterated in cosmetics.

    PubMed

    Tidjarat, Siripran; Winotapun, Weerapath; Opanasopit, Praneet; Ngawhirunpat, Tanasait; Rojanarata, Theerasak

    2014-11-01

    Uniaxially aligned cellulose acetate (CA) nanofibers were successfully fabricated by electrospinning and applied to use as stationary phase for thin layer chromatography. The control of alignment was achieved by using a drum collector rotating at a high speed of 6000 rpm. Spin time of 6h was used to produce the fiber thickness of about 10 μm which was adequate for good separation. Without any chemical modification after the electrospinning process, CA nanofibers could be readily devised for screening hydroquinone (HQ) and retinoic acid (RA) adulterated in cosmetics using the mobile phase consisting of 65:35:2.5 methanol/water/acetic acid. It was found that the separation run on the aligned nanofibers over a distance of 5 cm took less than 15 min which was two to three times faster than that on the non-aligned ones. On the aligned nanofibers, the masses of HQ and RA which could be visualized were 10 and 25 ng, respectively, which were two times lower than those on the non-aligned CA fibers and five times lower than those on conventional silica plates due to the appearance of darker and sharper of spots on the aligned nanofibers. Furthermore, the proposed method efficiently resolved HQ from RA and ingredients commonly found in cosmetic creams. Due to the satisfactory analytical performance, facile and inexpensive production process, uniaxially aligned electrospun CA nanofibers are promising alternative media for planar chromatography.

  17. Influence of uniaxial, biaxial and plane strain pre-straining on the dynamic tensile properties of high strength sheet steels

    NASA Astrophysics Data System (ADS)

    Larour, P.; Verleysen, P.; Bleck, W.

    2006-08-01

    The influence of pre-straining and microstructure on the dynamic properties of car body high strength steels has been investigated at room temperature. The mechanical properties of a dual phase steel DP600, a TRIP steel TRIP700 and an austenitic steel AISI 301LN2B (1.4318) have been determined performing high speed servohydraulic and split-Hopkinson bar tensile tests in the strain rate range from 0.005s-1 up to 950s-1. The pre-straining modes and levels, respectively 10% uniaxial, 10% plane strain and 5% biaxial pre-straining, have been chosen in this investigation according to industrial use. 10% plane strain pre-straining brings the highest increase of yield and tensile strength values. 5% biaxial and 10% uniaxial pre-straining have similar effect on strength properties. The austenitic steel presents a pronounced minimum for tensile strength values at around 1/s. A combination of adiabatic heating and exothermic γ to α' transformation produces some significant softening effects in the austenitic steel grade.

  18. A prediction model for uniaxial compressive strength of deteriorated pyroclastic rocks due to freeze-thaw cycle

    NASA Astrophysics Data System (ADS)

    İnce, İsmail; Fener, Mustafa

    2016-08-01

    Either directly or indirectly, building stone is exposed to diverse atmospheric interactions depending on the seasonal conditions. Due to those interactions, objects of historic and cultural heritage, as well as modern buildings, partially or completely deteriorate. Among processes involved in rock deterioration, the freeze-thaw (F-T) cycle is one of the most important. Even though pyroclastic rocks have been used as building stone worldwide due to their easy workability, they are the building stone most affected by the F-T cycle. A historical region in Central Anatolia, Turkey, Cappadoia encompasses exceptional natural wonders characterized by fairy chimneys and unique historical and cultural heritage. Human-created caves, places of worship and houses have been dug into the pyroclastic rocks, which have in turn been used in architectural construction as building stone. Using 10 pyroclastic rock samples collected from Cappadocia, we determined the rock's index-mechanical properties to develop a statistical model for estimating percentage loss of uniaxial compressive strength a critical parameter of F-T cycle's important value. We used dry density (ρd), ultrasonic velocity (Vp), point load strengths (IS(50)), and slake-durability test indexes (Id4) values of unweathered rocks in our model, which is highly reliable (R2 = 0.84) for predetermination of percentage loss of uniaxial compressive strengths of pyroclastic rocks without requiring any F-T tests.

  19. The analysis of the effect of homogeneous mechanical stress on the acoustic wave propagation in the "La3Ga5SiO14/fused silica" piezoelectric layered structure.

    PubMed

    Burkov, S I; Zolotova, O P; Sorokin, B P; Turchin, P P

    2015-01-01

    The results of computer simulation taking into account the linear and nonlinear material constants have been presented. Study of the influence of external uniaxial mechanical stress on the dispersive characteristics of elastic waves in piezoelectric structures as "La3Ga5SiO14/fused silica" has been executed. The comparison of elastic wave velocity changes under the influence of an uniaxial stress while a full set of nonlinear material constants of crystalline layer+geometric nonlinearity, or only geometric nonlinearity of the layer induced by the static deformation of a substrate, has been fulfilled.

  20. The analysis of the effect of homogeneous mechanical stress on the acoustic wave propagation in the "La3Ga5SiO14/fused silica" piezoelectric layered structure.

    PubMed

    Burkov, S I; Zolotova, O P; Sorokin, B P; Turchin, P P

    2015-01-01

    The results of computer simulation taking into account the linear and nonlinear material constants have been presented. Study of the influence of external uniaxial mechanical stress on the dispersive characteristics of elastic waves in piezoelectric structures as "La3Ga5SiO14/fused silica" has been executed. The comparison of elastic wave velocity changes under the influence of an uniaxial stress while a full set of nonlinear material constants of crystalline layer+geometric nonlinearity, or only geometric nonlinearity of the layer induced by the static deformation of a substrate, has been fulfilled. PMID:25106110

  1. The behaviour of niobium and molybdenum during uni-axial strain loading

    SciTech Connect

    Millett, J. C. F.; Cotton, M.; Bourne, N. K.; Park, N. T.; Whiteman, G.

    2014-02-21

    The mechanical response of niobium and molybdenum during one dimensional shock loading in the weak shock regime is investigated in terms of the Hugoniot elastic limit (dynamic yield) and spall (tensile) strengths. Results indicate that although both metals have high elastic limits of ca. 2 GPa, their responses are very different. Deformation in the weak shock regime in niobium is controlled by both the motion and generation of dislocations, resulting in high spall (dynamic tensile) strengths and ductility. In contrast, molybdenum has low spall strength and ductility, which suggests lower dislocation mobility in this metal. We have also shown that the strain-rate in the rising part of the shock front is related to the stress amplitude by the fourth power, as first shown by Swegle and Grady. Although we have not been able to elucidate further on the power relation, we believe that the scaling factor A is related to a materials ability to accommodate shock imposed plasticity via slip and dislocation generation. Overall, we have used arguments about the Peierls stress in body centred cubic metals to explain these results, with niobium (low Peierls stress) having a high dislocation mobility, resulting in behaviour showing some similarities to face centred cubic metals. Molybdenum, with its much higher Peierls stress has a much lower dislocation mobility, and hence lower spall strengths and ductility.

  2. Features of the uniaxial elastic deformation of X-ray-irradiated p-Si crystals

    SciTech Connect

    Pavlyk, B. V.; Lys, R. M. Didyk, R. I.; Shykorjak, J. A.

    2015-05-15

    Changes in the conductivity of p-Si single-crystals irradiated at room temperature during their mechanical compression and stress relief are studied. It is shown that irradiation is accompanied by the generation of point defects in silicon, which play the role of stoppers for dislocation motion. The effect of “radiation memory” in “electronic” silicon crystals is detected.

  3. Uniaxial strain-induced magnetic order transition from E-type to A-type in orthorhombic YMnO{sub 3} from first-principles

    SciTech Connect

    Lin, S. X.; Fang, X. G.; Zhang, A. H.; Lu, X. B.; Gao, J. W.; Gao, X. S.; Zeng, M.; Liu, J.-M.

    2014-10-28

    The spin ordering magnetic structures of orthorhombic YMnO{sub 3} subjected to uniaxial strain have been investigated using first-principles calculations based on density functional theory. On applying compressive uniaxial strain of −0.8% along the b orientation, the spin ordering magnetic structure is predicted to change from E-type to A-type antiferromagnetic orderings. The structure analysis also reveals that the uniaxial strain has a dramatic influence on the Mn-O bond lengths and Mn-O-Mn bond angles, allowing the gradual suppression of the alternation of the long and short Mn-O-Mn bonds in the ab plane. These changes present very interesting possibilities for engineering the spin ordering along with ferroelectric property in orthorhombic YMnO{sub 3}.

  4. Effect of UV-light on the uniaxial tensile properties and structure of uncoated and TiO2 coated Bombyx mori silk fibers.

    PubMed

    Aksakal, Baki; Koç, Kenan; Yargı, Önder; Tsobkallo, Katherina

    2016-01-01

    The effect of UV-light on the uniaxial tensile properties and the structure of uncoated and TiO2 coated silk fibers in the bave form by using sol-gel method was investigated with tensile testing and FT-IR/ATR spectroscopy methods after the silk filaments were exposed to UV-light with high intensity of 760W/m(2) for different times from 0.5h to 1day. It was clearly observed that TiO2 coating considerably increased the Young's modulus of the uncoated silk single filament by around 17% before the UV-irradiation. The yield point and the post yield region disappeared on the stress-strain curves of both uncoated and TiO2 coated silk filaments after UV-irradiation time higher than 1h. Except for the Young's modulus, most of the tensile characteristics of both uncoated and TiO2 coated silk filaments decreased remarkably with increasing UV-irradiation time, e.g., after 1h irradiation, although the Young's modulus slightly changed and ultimate tensile strength decreased by only around 18% and 23%, for the uncoated and TiO2 coated silk filaments, respectively; breaking extension decreased dramatically by 67% and 72%, respectively, for uncoated and TiO2 coated silk filaments. Only the Young's modulus of TiO2 coated silk filaments which can be considered as a more stable tensile characteristic became significantly higher than that of the uncoated silk filaments with increasing UV-irradiation time. After 1day irradiation, even though the uncoated silk filaments could not be tested and completely lost of their fiber properties, the TiO2 coated silk filaments showed a stress-strain curve in initial elastic region with Young's modulus of ∼13GPa which indicates considerable protective effect of TiO2 on the silk fiber structure, especially on the β-sheet microcrystals against UV-radiation. The FT-IR/ATR spectral results showed that significant photodegradation took place in not only crystalline but also amorphous regions which were deduced from the decrease in the absorbance

  5. Effect of UV-light on the uniaxial tensile properties and structure of uncoated and TiO2 coated Bombyx mori silk fibers.

    PubMed

    Aksakal, Baki; Koç, Kenan; Yargı, Önder; Tsobkallo, Katherina

    2016-01-01

    The effect of UV-light on the uniaxial tensile properties and the structure of uncoated and TiO2 coated silk fibers in the bave form by using sol-gel method was investigated with tensile testing and FT-IR/ATR spectroscopy methods after the silk filaments were exposed to UV-light with high intensity of 760W/m(2) for different times from 0.5h to 1day. It was clearly observed that TiO2 coating considerably increased the Young's modulus of the uncoated silk single filament by around 17% before the UV-irradiation. The yield point and the post yield region disappeared on the stress-strain curves of both uncoated and TiO2 coated silk filaments after UV-irradiation time higher than 1h. Except for the Young's modulus, most of the tensile characteristics of both uncoated and TiO2 coated silk filaments decreased remarkably with increasing UV-irradiation time, e.g., after 1h irradiation, although the Young's modulus slightly changed and ultimate tensile strength decreased by only around 18% and 23%, for the uncoated and TiO2 coated silk filaments, respectively; breaking extension decreased dramatically by 67% and 72%, respectively, for uncoated and TiO2 coated silk filaments. Only the Young's modulus of TiO2 coated silk filaments which can be considered as a more stable tensile characteristic became significantly higher than that of the uncoated silk filaments with increasing UV-irradiation time. After 1day irradiation, even though the uncoated silk filaments could not be tested and completely lost of their fiber properties, the TiO2 coated silk filaments showed a stress-strain curve in initial elastic region with Young's modulus of ∼13GPa which indicates considerable protective effect of TiO2 on the silk fiber structure, especially on the β-sheet microcrystals against UV-radiation. The FT-IR/ATR spectral results showed that significant photodegradation took place in not only crystalline but also amorphous regions which were deduced from the decrease in the absorbance

  6. Effect of UV-light on the uniaxial tensile properties and structure of uncoated and TiO2 coated Bombyx mori silk fibers

    NASA Astrophysics Data System (ADS)

    Aksakal, Baki; Koç, Kenan; Yargı, Önder; Tsobkallo, Katherina

    2016-01-01

    The effect of UV-light on the uniaxial tensile properties and the structure of uncoated and TiO2 coated silk fibers in the bave form by using sol-gel method was investigated with tensile testing and FT-IR/ATR spectroscopy methods after the silk filaments were exposed to UV-light with high intensity of 760 W/m2 for different times from 0.5 h to 1 day. It was clearly observed that TiO2 coating considerably increased the Young's modulus of the uncoated silk single filament by around 17% before the UV-irradiation. The yield point and the post yield region disappeared on the stress-strain curves of both uncoated and TiO2 coated silk filaments after UV-irradiation time higher than 1 h. Except for the Young's modulus, most of the tensile characteristics of both uncoated and TiO2 coated silk filaments decreased remarkably with increasing UV-irradiation time, e.g., after 1 h irradiation, although the Young's modulus slightly changed and ultimate tensile strength decreased by only around 18% and 23%, for the uncoated and TiO2 coated silk filaments, respectively; breaking extension decreased dramatically by 67% and 72%, respectively, for uncoated and TiO2 coated silk filaments. Only the Young's modulus of TiO2 coated silk filaments which can be considered as a more stable tensile characteristic became significantly higher than that of the uncoated silk filaments with increasing UV-irradiation time. After 1 day irradiation, even though the uncoated silk filaments could not be tested and completely lost of their fiber properties, the TiO2 coated silk filaments showed a stress-strain curve in initial elastic region with Young's modulus of ∼13 GPa which indicates considerable protective effect of TiO2 on the silk fiber structure, especially on the β-sheet microcrystals against UV-radiation. The FT-IR/ATR spectral results showed that significant photodegradation took place in not only crystalline but also amorphous regions which were deduced from the decrease in the absorbance

  7. Manage Stress

    MedlinePlus

    ... Manage Stress Print This Topic En español Manage Stress Browse Sections The Basics Overview Signs and Health ... and Health Effects What are the signs of stress? When people are under stress, they may feel: ...

  8. On thermal stress failure of the SNAP-19A RTG heat shield

    NASA Technical Reports Server (NTRS)

    Pitts, W. C.; Anderson, L. A.

    1974-01-01

    Results of a study on thermal stress problems in an amorphous graphite heat shield that is part of the launch-abort protect system for the SNAP-19A radio-isotope thermoelectric generators (RTG) that will be used on the Viking Mars Lander are presended. The first result is from a thermal stress analysis of a full-scale RTG heat source that failed to survive a suborbital entry flight test, possibly due to thermal stress failure. It was calculated that the maximum stress in the heat shield was only 50 percent of the ultimate strength of the material. To provide information on the stress failure criterion used for this calculation, some heat shield specimens were fractured under abort entry conditions in a plasma arc facility. It was found that in regions free of stress concentrations the POCO graphite heat shield material did fracture when the local stress reached the ultimate uniaxial stress of the material.

  9. Effect of lateral stress on the consolidation state of sediment from the Nankai Trough

    NASA Astrophysics Data System (ADS)

    Valdez, R. D., II; Kitajima, H.; Saffer, D. M.

    2015-12-01

    In order to better understand the mechanics of seismogenesis and stress state along subduction plate boundaries, the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) program has focused on drilling a transect of boreholes across the subduction zone offshore SW Japan to collect core samples and geophysical logs. One primary target of the drilling effort is a major splay fault (the "megasplay") that branches from the décollement ~55 km landward of the trench and reaches the seafloor ~30 km from the trench. Three drillsites near the tip of the megasplay sampled the same 1.24-1.65 Ma slope apron sediment section at a reference location 0.75 km seaward of the megasplay fault tip (Site C0008), at the fault tip (Site C0022), and 0.30 km landward (Site C0004) where the section is overridden by accretionary prism sediment. We report on a suite of laboratory experiments conducted on coeval core samples from the three sites, to test the hypothesis that increasing horizontal stress with proximity to the megasplay fault leads to overconsolidation. We conducted uniaxial constant rate of strain (CRS) and triaxial consolidation experiments to define consolidation state and yield behavior of the sediment, and to estimate in situ effective stress magnitudes. The consolidation state is described in terms of the over-consolidation ratio (OCR), which is the ratio of stress at yield in the experiments to the in situ vertical stress expected for normal consolidation. Values of OCR increase with proximity to the fault, with values ranging from 0.5-1 at the reference Site C0008, to 1.4-1.5 at Site C0022 at the tip of the fault, to 1.7-2.1 in the footwall of the fault at Site C0004, defining a trend of progressively increasing overconsolidation. We attribute this pattern to increasing horizontal stress as the megasplay fault is approached. Assuming that the sediment is at a critical state (i.e. on the verge of shear failure) at the tip of the

  10. DETAIL OF PLAQUE DESCRIBING LION SCULPTURES BY ROLAND HINTON PERRY, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    DETAIL OF PLAQUE DESCRIBING LION SCULPTURES BY ROLAND HINTON PERRY, NORTHWEST ABUTMENT - Connecticut Avenue Bridge, Spans Rock Creek & Potomac Parkway at Connecticut Avenue, Washington, District of Columbia, DC

  11. Anisotropic post-yield response of cancellous bone simulated by stress-strain curves of bulk equivalent structures.

    PubMed

    Tsouknidas, Alexander; Maliaris, Georgios; Savvakis, Savvas; Michailidis, Nikolaos

    2015-01-01

    During the last decade, finite element (FE) modelling has become ubiquitous in understanding complex mechanobiological phenomena, e.g. bone-implant interactions. The extensive computational effort required to achieve biorealistic results when modelling the post-yield behaviour of microstructures like cancellous bone is a major limitation of these techniques. This study describes the anisotropic biomechanical response of cancellous bone through stress-strain curves of equivalent bulk geometries. A cancellous bone segment, reverse engineered by micro computed tomography, was subjected to uniaxial compression. The material's constitutive law, obtained by nano-indentations, was considered during the simulation of the experimental process. A homodimensionally bulk geometry was employed to determine equivalent properties, resulting in a similar anisotropic response to the trabecular structure. The experimental verification of our model sustained that the obtained stress-strain curves can adequately reflect the post-yield behaviour of the sample. The introduced approach facilitates the consideration of nonlinearity and anisotropy of the tissue, while reducing the geometrical complexity of the model to a minimum. PMID:24156688

  12. Anisotropic post-yield response of cancellous bone simulated by stress-strain curves of bulk equivalent structures.

    PubMed

    Tsouknidas, Alexander; Maliaris, Georgios; Savvakis, Savvas; Michailidis, Nikolaos

    2015-01-01

    During the last decade, finite element (FE) modelling has become ubiquitous in understanding complex mechanobiological phenomena, e.g. bone-implant interactions. The extensive computational effort required to achieve biorealistic results when modelling the post-yield behaviour of microstructures like cancellous bone is a major limitation of these techniques. This study describes the anisotropic biomechanical response of cancellous bone through stress-strain curves of equivalent bulk geometries. A cancellous bone segment, reverse engineered by micro computed tomography, was subjected to uniaxial compression. The material's constitutive law, obtained by nano-indentations, was considered during the simulation of the experimental process. A homodimensionally bulk geometry was employed to determine equivalent properties, resulting in a similar anisotropic response to the trabecular structure. The experimental verification of our model sustained that the obtained stress-strain curves can adequately reflect the post-yield behaviour of the sample. The introduced approach facilitates the consideration of nonlinearity and anisotropy of the tissue, while reducing the geometrical complexity of the model to a minimum.

  13. Effect of hydrostatic pressure and uniaxial strain on the electronic structure of Pb1-xSnxTe

    DOE PAGESBeta

    Geilhufe, Matthias; Nayak, Sanjeev K.; Thomas, Stefan; Dane, Markus; Tripathi, Gouri S.; Entel, Peter; Hergert, Wolfram; Ernst, Arthur

    2015-12-09

    The electronic structure of Pb1–xSnxTe is studied by using the relativistic Korringa-Kohn-Rostoker Green function method in the framework of density functional theory. For all concentrations x, Pb1–xSnxTe is a direct semiconductor with a narrow band gap. In contrast to pure lead telluride, tin telluride shows an inverted band characteristic close to the Fermi energy. It will be shown that this particular property can be tuned, first, by alloying PbTe and SnTe and, second, by applying hydrostatic pressure or uniaxial strain. Furthermore, the magnitude of strain needed to switch between the regular and inverted band gap can be tuned by themore » alloy composition. In conclusion, there is a range of potential usage of Pb1–xSnxTe for spintronic applications.« less

  14. Crystal plasticity finite element modelling of the effect of friction on surface asperity flattening in cold uniaxial planar compression

    NASA Astrophysics Data System (ADS)

    Li, Hejie; Öchsner, Andreas; Wei, Dongbin; Ni, Guowei; Jiang, Zhengyi

    2015-12-01

    During uniaxial planar compression of annealed aluminium alloys, a novel approach to determine the surface asperity flattening (roughness Ra) is employed by analyzing the evolution of the surface's micro-texture. With an increase in compression strain, the surface asperity tends to be flattened, and strain hardening increases. Lubrication can constrain the surface asperity flattening process and hinder the progress of grain surface flattening. The development of surface texture shows an obvious dependency: under the influence of friction, the normal deformation texture component (brass orientation { 0 1 1} <1 1 2>) can be generated easily, while lubrication can hinder this texture component generation. Simulated results show a good agreement with experimental results which predicated brass orientation. However, due to the limitation of the FCC Taylor model, the other orientation components cannot be predicted.

  15. Time-resolved X-ray diffraction reveals the hidden mechanism of high piezoelectric activity in a uniaxial ferroelectric.

    PubMed

    Gorfman, Semën; Choe, Hyeokmin; Shvartsman, Vladimir V; Ziolkowski, Michael; Vogt, Marco; Strempfer, Jörg; Łukasiewicz, Tadeusz; Pietsch, Ullrich; Dec, Jan

    2015-03-01

    High piezoelectric activity of many ferroelectrics has been the focus of numerous recent studies. The structural origin of this activity remains poorly understood due to a lack of appropriate experimental techniques and mixing of different mechanisms related to ferroelectricity and ferroelasticity. Our work reports on the study of a uniaxial Sr_{0.5}Ba_{0.5}Nb_{2}O_{6} ferroelectric where the formation of regions with different spontaneous strains is ruled out by the symmetry and where the interrelation between piezoelectricity and ferroelectricity can be inspected in an isolated fashion. We performed x-ray diffraction experiments on a single crystalline sample under alternating electric field and observed an unknown hidden-in-the-bulk mechanism, which suggests that the highest piezoelectric activity is realized in the volumes where nucleation of small ferroelectric domains takes place. This new mechanism creates a novel roadmap for designing materials with enhanced piezoelectric properties.

  16. Micro- and nanodomain imaging in uniaxial ferroelectrics: Joint application of optical, confocal Raman, and piezoelectric force microscopy

    SciTech Connect

    Shur, V. Ya. Zelenovskiy, P. S.

    2014-08-14

    The application of the most effective methods of the domain visualization in model uniaxial ferroelectrics of lithium niobate (LN) and lithium tantalate (LT) family, and relaxor strontium-barium niobate (SBN) have been reviewed in this paper. We have demonstrated the synergetic effect of joint usage of optical, confocal Raman, and piezoelectric force microscopies which provide extracting of the unique information about formation of the micro- and nanodomain structures. The methods have been applied for investigation of various types of domain structures with increasing complexity: (1) periodical domain structure in LN and LT, (2) nanodomain structures in LN, LT, and SBN, (3) nanodomain structures in LN with modified surface layer, (4) dendrite domain structure in LN. The self-assembled appearance of quasi-regular nanodomain structures in highly non-equilibrium switching conditions has been considered.

  17. In-situ white beam microdiffraction study of the deformation behavior in polycrystalline magnesium alloy during uniaxial loading

    SciTech Connect

    Advanced Light Source; Tamura, Nobumichi; Lynch, P.A.; Stevenson, A.W.; Liang, D.; Parry, D.; Wilkins, S.; Madsen, I.C.; Bettles, C.; Tamura, N.; Geandier, G.

    2007-01-19

    Scanning white beam X-ray microdiffraction has been used to study the heterogeneous grain deformation in a polycrystalline Mg alloy (MgAZ31). The high spatial resolution achieved on beamline 7.3.3 at the Advanced Light Source provides a unique method to measure the elastic strain and orientation of single grains as a function of applied load. To carry out in-situmeasurements a light weight (~;;0.5kg) tensile stage, capable of providing uniaxial loads of up to 600kg, was designed to collect diffraction data on the loading and unloading cycle. In-situ observation of the deformation process provides insight about the crystallographic deformation mode via twinning and dislocation slip.

  18. Electronic and optical properties of silicene under uni-axial and bi-axial mechanical strains: A first principle study

    NASA Astrophysics Data System (ADS)

    Mohan, Brij; Kumar, Ashok; Ahluwalia, P. K.

    2014-07-01

    The uni-axial and bi-axial mechanical strain mediated electronic band structures and dielectric properties of silicene have been investigated. It is found that on applying uni- and bi-axial strains, the band gap opens for smaller strain in silicene. However, on further increase of strain beyond 8% silicene changed into metal. The ultimate tensile strength estimated is 3.4 GPa. Imaginary part of dielectric function shows that the inter-band transitions are red-shifted for uni- and bi-axial tensile strains and are blue shifted for uni- and bi-axial compressive strains. Electron energy loss (EEL) function shows that the π+σ plasmon energies are red-shifted for uni- and bi-axial strains and blue-shifted for compressive strains. The π plasmons disappears for tensile and asymmetric strains. Bi-axial asymmetric strain is found to have no influence on inter-band transitions and π+σ plasmon energies.

  19. Molecular dynamics simulations of hcp/fcc nucleation and growth in bcc iron driven by uniaxial compression.

    PubMed

    Wang, B T; Shao, J L; Zhang, G C; Li, W D; Zhang, P

    2009-12-01

    Molecular dynamics simulations have been performed to study the structural transition in bcc iron under uniaxial strain loading. We found that the transition pressures are less dependent on the crystal orientations, ∼14 GPa for [001], [011], and [111] loadings. However, the pressure interval of a mixed phase for [011] loading is much shorter than loading along other orientations. In addition, the temperature increased amplitude for [001] loading is evidently lower than other orientations. The nucleation and growth of the hcp/fcc phases, and their crystal orientation dependence, were analyzed in detail, where the atom structure was presented by the topological medium-range-order analysis. For [001] compression, the hcp structure occurs first and grows into a laminar morphology in the (011)(bcc) plane with some fcc atoms as an intermediate structure. For loading along [011] and [111] directions, both hcp and fcc structure nucleation and growth along the {110}(bcc) planes are observed; their morphology is also discussed.

  20. A trapped field of >3 T in bulk MgB2 fabricated by uniaxial hot pressing

    NASA Astrophysics Data System (ADS)

    Durrell, J. H.; Dancer, C. E. J.; Dennis, A.; Shi, Y.; Xu, Z.; Campbell, A. M.; Babu, N. Hari; Todd, R. I.; Grovenor, C. R. M.; Cardwell, D. A.

    2012-11-01

    A trapped field of over 3 T has been measured at 17.5 K in a magnetized stack of two disc-shaped bulk MgB2 superconductors of diameter 25 mm and thickness 5.4 mm. The bulk MgB2 samples were fabricated by uniaxial hot pressing, which is a readily scalable, industrial technique, to 91% of their maximum theoretical density. The macroscopic critical current density derived from the trapped field data using the Biot-Savart law is consistent with the measured local critical current density. From this we conclude that critical current density, and therefore trapped field performance, is limited by the flux pinning available in MgB2, rather than by lack of connectivity. This suggests strongly that both increasing sample size and enhancing pinning through doping will allow further increases in trapped field performance of bulk MgB2.

  1. Calculation of Dilational and Uniaxial Shear Potentials of Ge by a State-Independent Many-Body Projection Technique

    NASA Astrophysics Data System (ADS)

    Kang, Nam; Ryu, Jai; Choi, Sang

    1998-07-01

    Utilizing state-independent projection operators, we present a new optical conductivity formula for cyclotron transition in the system of electrons interacting anisotropically with phonons. The line-shape factor appearing in the conductivity tensor contains the many body effects for electrons and phonons. Applying this formula, we determine the two deformation potentials (dilation potential Ξd and uniaxial shear potential Ξu) of Ge in the quantum limit. By fitting the present theoretical values with the experimental data of Murase, Enjouji and Otsuka [J. Phys. Soc. Jpn. 29 (1970) 1248] and Kobori, Ohyama and Otsuka [J. Phys. Soc. Jpn. 59 (1990) 2141], we obtain Ξu=17.0±0.6 eV and Ξd=-10.88±0.47 eV.

  2. Analysis of transmission characteristics of doubly clad fibers with an inner cladding made of uniaxial crystal materials

    NASA Astrophysics Data System (ADS)

    Xiaoping, Zhang; Zhihong, Tan

    2002-04-01

    A doubly clad optical fiber with an inner cladding made of a uniaxial crystal material whose optical axis is parallel to the fiber axis was proposed, and exact characteristic equations of vector modes were derived. The influence of the ratio ( kcl) of the extraordinary to the ordinary ray indexes upon the waveguide dispersion was examined in detail. In view of the impossibility to deduce the expression of waveguide dispersion directly due to the complexity of the characteristic equations, a feasible approach to calculate waveguide dispersion was established. The calculated results indicate that the values of waveguide dispersion can be effectively changed through variation of kcl without changing the geometrical and optical parameters ( S and R). The influences of kcl, S and R on the propagation and cutoff characteristics of the low order modes are also analyzed.

  3. Study on Stretching Methods of Biaxially Stretched Co-polyester Film with Has Uniaxially Heat Shrinkage Properties

    NASA Astrophysics Data System (ADS)

    Haruta, Masayuki; Mukouyama, Yukinobu; Tabota, Norimi; Ito, Katsuya; Nonomura, Chisato

    Heat shrinkable film made of stretched film is widely used for decorative labels by attaching on PET bottles with heat shrinkage by steam or dry heating. Trouble cancellation in the installation process of the PET bottle is necessary. The purpose of this study is development of uniaxially heat shrinkable co-polyester film that has strength both in the machine direction (MD) and transverse direction (TD). The film production was performed using sequential biaxial stretched process that combined roll stretching with TD stretching. Cast film was processed in the order of TD stretching-Anneal 1-MD stretching-Anneal 2. As a result, the heat shrinkable film that shrunk only in MD got high tensile strength both in MD and TD. The anneal 1 temperature over Tg (Glass transition temperature) of material resin was needed to obtain the heat shrinkable film shrunk in MD after TD stretching.

  4. Time-Resolved X-Ray Diffraction Reveals the Hidden Mechanism of High Piezoelectric Activity in a Uniaxial Ferroelectric

    NASA Astrophysics Data System (ADS)

    Gorfman, Semën; Choe, Hyeokmin; Shvartsman, Vladimir V.; Ziolkowski, Michael; Vogt, Marco; Strempfer, Jörg; Łukasiewicz, Tadeusz; Pietsch, Ullrich; Dec, Jan

    2015-03-01

    High piezoelectric activity of many ferroelectrics has been the focus of numerous recent studies. The structural origin of this activity remains poorly understood due to a lack of appropriate experimental techniques and mixing of different mechanisms related to ferroelectricity and ferroelasticity. Our work reports on the study of a uniaxial Sr0.5Ba0.5Nb2O6 ferroelectric where the formation of regions with different spontaneous strains is ruled out by the symmetry and where the interrelation between piezoelectricity and ferroelectricity can be inspected in an isolated fashion. We performed x-ray diffraction experiments on a single crystalline sample under alternating electric field and observed an unknown hidden-in-the-bulk mechanism, which suggests that the highest piezoelectric activity is realized in the volumes where nucleation of small ferroelectric domains takes place. This new mechanism creates a novel roadmap for designing materials with enhanced piezoelectric properties.

  5. In-situ neutron diffraction of LaCoO{sub 3} perovskite under uniaxial compression. II. Elastic properties

    SciTech Connect

    Lugovy, Mykola; Aman, Amjad; Orlovskaya, Nina; Chen, Yan; Kuebler, Jakob; Graule, Thomas; Reece, Michael J.; Ma, Dong; Stoica, Alexandru D.; An, Ke

    2014-07-07

    Calculations of elastic constants and development of elastic anisotropy under uniaxial compression in originally isotropic polycrystalline LaCoO{sub 3} perovskite are reported. The lattice strains in individual (hkl) planes as well as average lattice strain were determined both for planes oriented perpendicular and parallel to the loading direction using in-situ neutron diffraction. Utilizing average lattice strains as well as lattice strains along the a and c crystallographic directions, an attempt was made to determine Poisson's ratio of LaCoO{sub 3}, which was then compared with that measured using an impulse excitation technique. The elastic constants were calculated and Young's moduli of LaCoO{sub 3} single crystal in different crystallographic directions were estimated.

  6. Damage evolution in uniaxial silicon carbide fiber-reinforced titanium matrix composites

    NASA Astrophysics Data System (ADS)

    Hanan, Jay Clarke

    Fiber fractures initiate damage zones ultimately determining the strength and lifetime of metal matrix composites (MMCs). The evolution of damage in a MMC comprising a row of unidirectional SiC fibers (32 vol.%) surrounded by a Ti matrix was examined using X-ray microdiffraction (gym beam size) and macrodiffraction (mm beam size). A comparison of high-energy X-ray diffraction (XRD) techniques including a powerful two-dimensional XRD method capable of obtaining powder averaged strains from a small number of grains is presented (HEmuXRD2). Using macrodiffraction, the bulk residual strain in the composite was determined against a true strain-free reference. In addition, the bulk in situ response of both the fiber reinforcement and the matrix to tensile stress was observed and compared to a three-dimensional finite element model. Using microdiffraction, multiple strain maps including both phases were collected in situ before, during, and after the application of tensile stress, providing an unprecedented detailed picture of the micromechanical behavior in the laminate metal matrix composite. Finally, the elastic axial strains were compared to predictions from a modified shear lag model, which unlike other shear lag models, considers the elastic response of both constituents. The strains showed excellent correlation with the model. The results confirmed, for the first time, both the need and validity of this new model specifically developed for large scale multifracture and damage evolution simulations of metal matrix composites. The results also provided unprecedented insight for the model, revealing the necessity of incorporating such factors as plasticity of the matrix, residual stress in the composite, and selection of the load sharing parameter. The irradiation of a small number of grains provided strain measurements comparable to a continuum mechanical state in the material. Along the fiber axes, thermal residual stresses of 740 MPa (fibers) and +350 MPa (matrix

  7. Featured Article: Temporal responses of human endothelial and smooth muscle cells exposed to uniaxial cyclic tensile strain

    PubMed Central

    Greiner, Alexandra M; Biela, Sarah A; Chen, Hao; Spatz, Joachim P

    2015-01-01

    The physiology of vascular cells depends on stimulating mechanical forces caused by pulsatile flow. Thus, mechano-transduction processes and responses of primary human endothelial cells (ECs) and smooth muscle cells (SMCs) have been studied to reveal cell-type specific differences which may contribute to vascular tissue integrity. Here, we investigate the dynamic reorientation response of ECs and SMCs cultured on elastic membranes over a range of stretch frequencies from 0.01 to 1 Hz. ECs and SMCs show different cell shape adaptation responses (reorientation) dependent on the frequency. ECs reveal a specific threshold frequency (0.01 Hz) below which no responses is detectable while the threshold frequency for SMCs could not be determined and is speculated to be above 1 Hz. Interestingly, the reorganization of the actin cytoskeleton and focal adhesions system, as well as changes in the focal adhesion area, can be observed for both cell types and is dependent on the frequency. RhoA and Rac1 activities are increased for ECs but not for SMCs upon application of a uniaxial cyclic tensile strain. Analysis of membrane protrusions revealed that the spatial protrusion activity of ECs and SMCs is independent of the application of a uniaxial cyclic tensile strain of 1 Hz while the total number of protrusions is increased for ECs only. Our study indicates differences in the reorientation response and the reaction times of the two cell types in dependence of the stretching frequency, with matching data for actin cytoskeleton, focal adhesion realignment, RhoA/Rac1 activities, and membrane protrusion activity. These are promising results which may allow cell-type specific activation of vascular cells by frequency-selective mechanical stretching. This specific activation of different vascular cell types might be helpful in improving strategies in regenerative medicine. PMID:25687334

  8. Uniaxial cyclic stretch stimulates TRPV4 to induce realignment of human embryonic stem cell-derived cardiomyocytes.

    PubMed

    Qi, Yan; Li, Zhichao; Kong, Chi-Wing; Tang, Nelson L; Huang, Yu; Li, Ronald A; Yao, Xiaoqiang

    2015-10-01

    Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) in culture are randomly organized and do not typically show directional alignment. In the present study, we used uniaxial cyclic stretch to facilitate the alignment of cultured human embryonic stem cell-derived cardiomyocytes (hESC-CMs), so that these cells can be more adult-like for potential future application in drug screening and in vitro studies of cardiac function. We then explored the functional role of mechanosensitive TRPV4 channels in cyclic stretch-induced realignment of hESC-CMs. RT-PCR, immunoblots and immunostaining detected TRPV4 expression in these cells. 4α-phorbol 12,13-didecanoate (4α-PDD), a TRPV4 agonist, elicited a cytosolic Ca(2+) ([Ca(2+)]i) rise, the effect of which was abolished by TRPV4 inhibitors RN1734 and HC067047, and a TRPV4 dominant negative construct. These results confirmed the functional presence of TRPV4 in these cells. Importantly, longitudinal stretch was found to induce a [Ca(2+)]i rise, the effect of which was inhibited by TRPV4 antagonists. Furthermore, uniaxial cyclic stretch for 2h induced realignment of hESC-CMs in the direction transverse to the direction of stretch, the effect of which was also abolished by TRPV4 antagonists. Akt phosphorylation was found to be a downstream signal of TRPV4. Taken together, these data strongly suggest endogenous TRPV4 channels as a mechanosensor, mediating cyclic stretch-induced realignment of hESC-CMs.

  9. Effects of Uniaxial and Biaxial Strain on Few-Layered Terrace Structures of MoS₂ Grown by Vapor Transport.

    PubMed

    McCreary, Amber; Ghosh, Rudresh; Amani, Matin; Wang, Jin; Duerloo, Karel-Alexander N; Sharma, Ankit; Jarvis, Karalee; Reed, Evan J; Dongare, Avinash M; Banerjee, Sanjay K; Terrones, Mauricio; Namburu, Raju R; Dubey, Madan

    2016-03-22

    One of the most fascinating properties of molybdenum disulfide (MoS2) is its ability to be subjected to large amounts of strain without experiencing degradation. The potential of MoS2 mono- and few-layers in electronics, optoelectronics, and flexible devices requires the fundamental understanding of their properties as a function of strain. While previous reports have studied mechanically exfoliated flakes, tensile strain experiments on chemical vapor deposition (CVD)-grown few-layered MoS2 have not been examined hitherto, although CVD is a state of the art synthesis technique with clear potential for scale-up processes. In this report, we used CVD-grown terrace MoS2 layers to study how the number and size of the layers affected the physical properties under uniaxial and biaxial tensile strain. Interestingly, we observed significant shifts in both the Raman in-plane mode (as high as -5.2 cm(-1)) and photoluminescence (PL) energy (as high as -88 meV) for the few-layered MoS2 under ∼1.5% applied uniaxial tensile strain when compared to monolayers and few-layers of MoS2 studied previously. We also observed slippage between the layers which resulted in a hysteresis of the Raman and PL spectra during further applications of strain. Through DFT calculations, we contended that this random layer slippage was due to defects present in CVD-grown materials. This work demonstrates that CVD-grown few-layered MoS2 is a realistic, exciting material for tuning its properties under tensile strain.

  10. Effects of Uniaxial and Biaxial Strain on Few-Layered Terrace Structures of MoS₂ Grown by Vapor Transport.

    PubMed

    McCreary, Amber; Ghosh, Rudresh; Amani, Matin; Wang, Jin; Duerloo, Karel-Alexander N; Sharma, Ankit; Jarvis, Karalee; Reed, Evan J; Dongare, Avinash M; Banerjee, Sanjay K; Terrones, Mauricio; Namburu, Raju R; Dubey, Madan

    2016-03-22

    One of the most fascinating properties of molybdenum disulfide (MoS2) is its ability to be subjected to large amounts of strain without experiencing degradation. The potential of MoS2 mono- and few-layers in electronics, optoelectronics, and flexible devices requires the fundamental understanding of their properties as a function of strain. While previous reports have studied mechanically exfoliated flakes, tensile strain experiments on chemical vapor deposition (CVD)-grown few-layered MoS2 have not been examined hitherto, although CVD is a state of the art synthesis technique with clear potential for scale-up processes. In this report, we used CVD-grown terrace MoS2 layers to study how the number and size of the layers affected the physical properties under uniaxial and biaxial tensile strain. Interestingly, we observed significant shifts in both the Raman in-plane mode (as high as -5.2 cm(-1)) and photoluminescence (PL) energy (as high as -88 meV) for the few-layered MoS2 under ∼1.5% applied uniaxial tensile strain when compared to monolayers and few-layers of MoS2 studied previously. We also observed slippage between the layers which resulted in a hysteresis of the Raman and PL spectra during further applications of strain. Through DFT calculations, we contended that this random layer slippage was due to defects present in CVD-grown materials. This work demonstrates that CVD-grown few-layered MoS2 is a realistic, exciting material for tuning its properties under tensile strain. PMID:26881920

  11. Templating α-helical poly(L-lysine)/polyanion complexes by nanostructured uniaxially oriented ultrathin polyethylene films.

    PubMed

    Keller, Thomas F; Müller, Martin; Ouyang, Wuye; Zhang, Jian-Tao; Jandt, Klaus D

    2010-12-21

    We report a templating effect of uniaxially oriented melt-drawn polyethylene (MD-PE) films on α-helical poly(L-lysine)/poly(styrenesulfonate) (α-PLL/PSS) complexes deposited by the layer-by-layer (LBL) method. The melt-drawing process induced an MD-PE fiber texture consisting of nanoscale lamellar crystals embedded in amorphous regions on the MD-PE film surface whereby the common crystallographic c axis is the PE molecular chain direction parallel to the uniaxial melt-drawing direction. The MD-PE film and the α-PLL/PSS deposit were analyzed by atomic force microscopy (AFM) and in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) using polarized light as a complementary method. Both methods revealed that α-PLL/PSS complexes adsorbed at the MD-PE surface were anisotropic and preferentially oriented perpendicular to the crystallographic c direction of the MD-PE film. Quantitatively, from AFM image analysis and ATR-FTIR dichroism of the amide II band of the α-PLL, mean cone opening angles of 12-18° for both rodlike α-PLL and the anisotropic α-PLL/PSS complexes with respect to the PE lamellae width direction were obtained. A model for the preferred alignment of α-PLL along the protruding PE lamellae is discussed, which is based on possible hydrophobic driving forces for the minimization of surface free energy at molecular and supermolecular topographic steps of the PE surface followed by electrostatic interactions between the interconnecting PSS and the α-PLL during layer-by-layer adsorption. This study elucidates the requirements and mechanisms involved in orienting biomolecules and may open up a path for designing templates to induce directed protein adsorption and cell growth by oriented polypeptide- or protein-modified PE surfaces.

  12. Crack initiation observation and local stress analysis in shear fracture tests of ultra-high strength steels

    NASA Astrophysics Data System (ADS)

    Ma, Ninshu; Takada, Kenji; Sugimoto, Nao

    2016-08-01

    To investigate the local strain and stress at the crack initiation position in shear fracture test pieces of ultra-high strength steels, a butterfly shear fracture specimen was employed. The crack initiation position and propagation direction were observed during shear fracture tests by high speed cameras and investigated through analysing the fracture surface by scanning electron microscope. Further, the finite element method was employed and the stress-triaxiality at the crack initiation position was investigated. It can be obtained that the crack initiated at the position where the stress state is close to uniaxial tensile state or plane strain state more than pure shear stress state.

  13. High-temperature, multi-atmosphere, constant stress compression creep apparatus

    NASA Astrophysics Data System (ADS)

    Carter, C. H., Jr.; Stone, C. A.; Davis, R. F.; Schaub, D. R.

    1980-10-01

    A creep apparatus is presented in which uniaxial compressive stresses, constant to within 1% for strains up to 10%, can be applied to the sample and strains can be read with an accuracy of 5 x 10 to the -7th m. Loads as great as 440 kg can be applied, and the furnace can be operated in vacuum or inert gas to 2573 K or used with a muffle tube. Data acquisition, manipulation, and plotting is computer controlled.

  14. Audio-Described Educational Materials: Ugandan Teachers' Experiences

    ERIC Educational Resources Information Center

    Wormnaes, Siri; Sellaeg, Nina

    2013-01-01

    This article describes and discusses a qualitative, descriptive, and exploratory study of how 12 visually impaired teachers in Uganda experienced audio-described educational video material for teachers and student teachers. The study is based upon interviews with these teachers and observations while they were using the material either…

  15. Necking failure and physical rupture of a molten low density polyethylene (LDPE) sample undergoing uniaxial extension

    NASA Astrophysics Data System (ADS)

    Starý, Zdeněk; Burghelea, Teodor

    2015-04-01

    A detailed experimental investigation of the deformation regimes, failure and physical rupture of a low density polyethylene (LDPE) sample undergoing extension at a constant nominal rate is presented. By combining integral measurements of the tensile forces and of the tensile stresses with the in-situ visualization of the sample within a wide range of Weissenberg numbers Wi, three distinct deformation regimes are observed. At low Wi (Wi < 10), a viscous (flowing) deformation regime characterized by a single local maximum of the tensile force (engineering stress) related to the onset of a necking instability is observed. The rupture of the sample within this regime occurs via a ductile mechanism. For intermediate values of the Weissenberg number, 10 ≤ Wi ≤ 200, a transitional deformation regime characterized by a competition between the failure behavior (via primary necking) and the stabilizing strain hardening (elastic) effects is observed. The physical rupture of the sample occurs via the emergence of secondary necks. As the Weissenberg number is further increased, Wi > 200, the strain hardening eventually wins over the necking instability and this ultimately modifies the dynamics of the physical rupture of the sample.

  16. Energy dependence of the spin excitation anisotropy in uniaxial-strained BaFe1.9Ni0.1As2

    DOE PAGESBeta

    Song, Yu; Lu, Xingye; Abernathy, Douglas L.; Tam, David W.; Niedziela, Jennifer L.; Tian, Wei; Si, Qimiao; Dai, Pengcheng; Luo, Huiqian

    2015-11-06

    In this study, we use inelastic neutron scattering to study the temperature and energy dependence of the spin excitation anisotropy in uniaxial-strained electron-doped iron pnictide BaFe1.9Ni0.1As2 near optimal superconductivity (Tc = 20K). Our work has been motivated by the observation of in-plane resistivity anisotropy in the paramagnetic tetragonal phase of electron-underdoped iron pnictides under uniaxial pressure, which has been attributed to a spin-driven Ising-nematic state or orbital ordering. Here we show that the spin excitation anisotropy, a signature of the spin-driven Ising-nematic phase, exists for energies below 60 meV in uniaxial-strained BaFe1.9Ni0.1As2. Since this energy scale is considerably larger thanmore » the energy splitting of the dxz and dyz bands of uniaxial-strained Ba(Fe1–xCox)2As2 near optimal superconductivity, spin Ising-nematic correlations are likely the driving force for the resistivity anisotropy and associated electronic nematic correlations.« less

  17. Measurement of probability distributions for internal stresses in dislocated crystals

    SciTech Connect

    Wilkinson, Angus J.; Tarleton, Edmund; Vilalta-Clemente, Arantxa; Collins, David M.; Jiang, Jun; Britton, T. Benjamin

    2014-11-03

    Here, we analyse residual stress distributions obtained from various crystal systems using high resolution electron backscatter diffraction (EBSD) measurements. Histograms showing stress probability distributions exhibit tails extending to very high stress levels. We demonstrate that these extreme stress values are consistent with the functional form that should be expected for dislocated crystals. Analysis initially developed by Groma and co-workers for X-ray line profile analysis and based on the so-called “restricted second moment of the probability distribution” can be used to estimate the total dislocation density. The generality of the results are illustrated by application to three quite different systems, namely, face centred cubic Cu deformed in uniaxial tension, a body centred cubic steel deformed to larger strain by cold rolling, and hexagonal InAlN layers grown on misfitting sapphire and silicon carbide substrates.

  18. Exact Integration Of Uniaxial Elasto-Plastic Laws For Nonlinear Structural Analysis

    SciTech Connect

    Marmo, Francesco; Rosati, Luciano; Sessa, Salvatore

    2008-07-08

    The recently formulated fiber-free approach [1,2] is used for the analytical integration of non-linear elastic and elasto-plastic normal stresses acting on beam cross sections. It is based on the subdivision of the section in suitable subdomains, which are updated during the analysis of the structural model, and the use of analytical formulas which require the constitutive law to be integrated four times as a maximum. In particular we illustrate the application of the fiber-free approach to the well known concrete model by Mander et al. [3] since its expression belongs to the set of countinous functions which do not admit a primitive. Some representative numerical tests highlight the correctness and the computational efficiency of the fiber-free approach with repsect to the traditional fiber approach, to date the only existing method to perform a non-linear sectional analysis.

  19. Electromechanical properties of high coupling single crystals under large electric drive and uniaxial compression.

    PubMed

    Amin, Ahmed

    2005-10-01

    This work investigates the 33-mode electromechanical response of relaxor-ferroelectric lead magnesium niobate-lead titanate (PMN-PT) single crystals when driven with large fields approximately 0.4 MV/m under a combined direct current (DC) field and mechanical bias similar to those used in the design of sound projectors. It demonstrates that the remarkable small signal length extensional coupling (k33 > 0.90) and other electromechanical properties of morphotropic PMN-PT single crystals prevail under large drive. The observed k33 roll-off at 42 MPa compressive stress is analyzed in terms of the recent structural data and the high-order Devonshire theory of possible ferroelectric-ferroelectric transition trajectories.

  20. Interculture: Some Concepts for Describing the Situation of Immigrants.

    ERIC Educational Resources Information Center

    Ekstrand, Lars Henric; And Others

    1981-01-01

    Attempts to find new ways of describing and analyzing dynamic interactions in country of origin, host country, and immigrant community caused by migration. Analyzes linguistic models, concept of culture, emigration psychology, and identity formation. (Author/BK)