Extremely high wall-shear stress events in a turbulent boundary layer

Science.gov (United States)

Pan, Chong; Kwon, Yongseok

2018-04-01

The present work studies the fluctuating characteristics of the streamwise wall-shear stress in a DNS of a turbulent boundary layer at Re τ =1500 from a structural view. The two-dimensional field of the fluctuating friction velocity u‧ τ (x,z) is decomposed into the large- and small-scale components via a recently proposed scale separation algorithm, Quasi-bivariate Variational Mode Decomposition (QB-VMD). Both components are found to be dominated by streak-like structures, which can be regarded as the wall signature of the inner-layer streaks and the outer-layer LSMs, respectively. Extreme positive/negative wall-shear stress fluctuation events are detected in the large-scale component. The former’s occurrence frequency is nearly one order of magnitude higher than the latter; therefore, they contribute a significant portion of the long tail of the wall-shear stress distribution. Both two-point correlations and conditional averages show that these extreme positive wall-shear stress events are embedded in the large-scale positive u‧ τ streaks. They seem to be formed by near-wall ‘splatting’ process, which are related to strong finger-like sweeping (Q4) events originated from the outer-layer positive LSMs.

High performance experiments in JT-60U reversed shear discharges

International Nuclear Information System (INIS)

Fujita, T.; Kamada, Y.; Ishida, S.

2001-01-01

The operation of JT-60U reversed shear discharges has been extended to a high plasma current, low-q regime keeping a large radius of the internal transport barrier (ITB) and the record value of equivalent fusion multiplication factor in JT-60U, Q DT eq =1.25, has been achieved at 2.6 MA. Operational schemes to reach the low-q regime with good reproducibility have been developed. The reduction of Z eff was obtained in the newly installed W-shaped pumped divertor. The beta limit in the low-q min regime, which limited the performance of L-mode edge discharges, has been improved in H-mode edge discharges with a broader pressure profile, which was obtained by power flow control with ITB degradation. Sustainment of ITB and improved confinement for 5.5 seconds has been demonstrated in an ELMy H reversed shear discharge. (author)

The Role of Axisymmetric Reconnection Events in JET Discharges with Extreme Shear Reversal

Energy Technology Data Exchange (ETDEWEB)

B.C. Stratton; J.A. Breslau; R.V. Budny; S.C. Jardin; W. Park; H.R. Strauss; L.E. Zakharov; B. Alper; V. Drozdov; N.C. Hawkes; S. Reyes-Cortes; and Contributors to the EFDA-JET Work Programme

2001-12-03

Injection of Lower Hybrid Heating and Current Drive into the current ramp-up phase of Joint European Torus (JET) discharges can produce extremely reversed q-profiles characterized by a core region of very small or zero current density (within Motional Stark Effect diagnostic measurement errors) and q(subscript min) > 1. T(subscript e)-profiles show sawtooth-like collapses and the presence of an internal transport barrier. Accurate equilibrium reconstructions of these discharges are obtained using the ESC code, which was recently extended to allow equilibrium reconstructions in which a free boundary solver determines the plasma boundary and a fixed boundary solver provides the magnetic geometry and current density profile. The core current density does not appear to go negative, although current diffusion calculations indicate that sufficient non-inductive current drive to cause this is present. This is explained by nonlinear resistive MHD simulations in toroidal geometry which predict that these discharges undergo n=0 reconnection events (axisymmetric sawteeth) that redistribute the current to hold the core current density near zero.

Stationary magnetic shear reversal during Lower Hybrid experiments in Tore Supra

International Nuclear Information System (INIS)

Litaudon, X.; Arslanbekov, R.; Hoang, G.T.; Joffrin, E.; Kazarian-Vibert, F.; Moreau, D.; Peysson, Y.; Bibet, P.

1996-01-01

Stable and stationary states with hollow current density profiles have been achieved with Lower Hybrid Current Drive (LHCD) during Lower Hybrid (LH) wave accessibility experiments. By analysing the bounded propagation domain in phase space which naturally limits the central penetration and absorption of the waves, off-axis LH power deposition has been realized in a reproducible manner. The resulting current density profile modifications have led to a global confinement enhancement attributed to the formation of an internal 'transport barrier' in the central reversed shear region where the electron thermal diffusivity is reduced to its neoclassical collisional level. The multiple-pass LH wave propagation in the weak Landau damping and reversed magnetic shear regime is also investigated in the framework of a statistical theory and the experimental validation of this theory is discussed. (author)

Synergistic effects of the safety factor and shear flows on development of internal transport barriers in reversed shear plasmas

International Nuclear Information System (INIS)

Wang, A.K.; Dong, J.Q.; Qu, W.X.; Qiu, X.M.

2002-01-01

A new suppression mechanism of turbulent transport, characteristic of the synergism between safety factor and shear flows, is proposed to explain the internal transport barriers (ITBs) observed in neutral-beam-heated tokamak discharges with reversed magnetic shear. It is shown that the evolution of turbulent transport with the strength of the suppression mechanism reproduces the basic features of the formation and development of ITBs observed in experiments. In addition, the present analyses predict the possibility of global ion and electron heat transport barriers

The roles of electric field shear and Shafranov shift in sustaining high confinement in enhanced reversed shear plasmas on the TFTR tokamak

International Nuclear Information System (INIS)

Synakowski, E.J.; Beer, M.A.

1997-02-01

The relaxation of core transport barriers in TFTR Enhanced Reversed Shear plasmas has been studied by varying the radial electric field using different applied torques from neutral beam injection. Transport rates and fluctuations remain low over a wide range of radial electric field shear, but increase when the local E x B shearing rates are driven below a threshold comparable to the fastest linear growth rates of the dominant instabilities. Shafranov-shift-induced stabilization alone is not able to sustain enhanced confinement

Active control of internal transport barrier and confinement database in JT-60U reversed shear plasma

Energy Technology Data Exchange (ETDEWEB)

Sakamoto, Yoshiteru; Takizuka, Tomonori; Shirai, Hiroshi; Fujita, Takaaki; Kamada, Yutaka; Ide, Shunsuke; Fukuda, Takeshi; Koide, Yoshihiko [Japan Atomic Energy Research Inst., Naka, Ibaraki (Japan). Naka Fusion Research Establishment

2001-07-01

Active control of internal transport barrier (ITB) and confinement properties of plasma with ITB have been studied in reversed shear plasmas. Modifications of the radial electric field (E{sub r}) profile by changing the combination of tangential neutral beams can control the ITB strength, where the contribution to E{sub r} from the toroidal rotation plays an important role. The ITB confinement database of reversed shear plasmas has been constructed. Stored energy is strongly correlated with poloidal magnetic field at the ITB foot. (author)

Suppressing Electron Turbulence and Triggering Internal Transport Barriers with Reversed Magnetic Shear in the National Spherical Torus Experiment

Science.gov (United States)

Peterson, Jayson Luc

2011-10-01

Observations in the National Spherical Torus Experiment (NSTX) have found electron temperature gradients that greatly exceed the linear threshold for the onset for electron temperature gradient-driven (ETG) turbulence. These discharges, deemed electron internal transport barriers (e-ITBs), coincide with a reversal in the shear of the magnetic field and with a reduction in electron-scale density fluctuations, qualitatively consistent with earlier gyrokinetic predictions. To investigate this phenomenon further, we numerically model electron turbulence in NSTX reversed-shear plasmas using the gyrokinetic turbulence code GYRO. These first-of-a-kind nonlinear gyrokinetic simulations of NSTX e-ITBs confirm that reversing the magnetic shear can allow the plasma to reach electron temperature gradients well beyond the critical gradient for the linear onset of instability. This effect is very strong, with the nonlinear threshold for significant transport approaching three times the linear critical gradient in some cases, in contrast with moderate shear cases, which can drive significant ETG turbulence at much lower gradients. In addition to the experimental implications of this upshifted nonlinear critical gradient, we explore the behavior of ETG turbulence during reversed shear discharges. This work is supported by the SciDAC Center for the Study of Plasma Microturbulence, DOE Contract DE-AC02-09CH11466, and used the resources of NCCS at ORNL and NERSC at LBNL. M. Ono et al., Nucl. Fusion 40, 557 (2000).

Analytic, two fluid, field reversed configuration equilibrium with sheared rotation

International Nuclear Information System (INIS)

Sobehart, J.R.

1989-01-01

A two fluid model is used to derive an analytical equilibrium for elongated field reversed configurations containing shear in both the electron and ion velocity profiles. Like some semiempirical models used previously, the analytical expressions obtained provide a satisfactory fit to the experimental results for all radii with a few key parameters. The present results reduce to the rigid rotor model and the infinite conductivity case for a specific choice of the parameters

Behaviour of C-shaped angle shear connectors under monotonic and fully reversed cyclic loading: An experimental study

International Nuclear Information System (INIS)

Shariati, Mahdi; Ramli Sulong, N.H.; Suhatril, Meldi; Shariati, Ali; Arabnejad Khanouki, M.M.; Sinaei, Hamid

2012-01-01

Highlights: ► C-shaped angle connectors show 8.8–33.1% strength degradation under cyclic loading. ► Connector fracture type of failure was experienced in C-shaped angle shear connectors. ► In push-out samples, more cracking was observed in those slabs with longer angles. ► C-shaped angle connectors show good behaviour in terms of the ultimate shear capacity. ► C-shaped angle connectors did not fulfil the requirements for ductility criteria. -- Abstract: This paper presents an evaluation of the structural behaviour of C-shaped angle shear connectors in composite beams, suitable for transferring shear force in composite structures. The results of the experimental programme, including eight push-out tests, are presented and discussed. The results include resistance, strength degradation, ductility, and failure modes of C-shaped angle shear connectors, under monotonic and fully reversed cyclic loading. The results show that connector fracture type of failure was experienced in C-shaped angle connectors and after the failure, more cracking was observed in those slabs with longer angles. On top of that, by comparing the shear resistance of C-shaped angle shear connectors under monotonic and cyclic loading, these connectors showed 8.8–33.1% strength degradation, under fully reversed cyclic loading. Furthermore, it was concluded that the mentioned shear connector shows a proper behaviour, in terms of the ultimate shear capacity, but it does not satisfy the ductility criteria, imposed by the Eurocode 4, to perform a plastic distribution of the shear force between different connectors along the beam length.

Discontinuity model for internal transport barrier formation in reversed magnetic shear plasmas

International Nuclear Information System (INIS)

Kishimoto, Y.; Kim, J-Y.; Horton, W.; Tajima, T.; LeBrun, M.J.

2001-01-01

To aid in understanding the internal transport barrier (ITB) being formed in reversed magnetic shear experiments, in addition to the well known shear flow effect, we point out an important nonlocal effect and/or finite size effect which comes from the complex behavior of the nonlocal mode over a finite radial region around the minimum q(safety factor)-surface. The nonlocal mode changes its structure depending on the sign of the magnetic shear and due to this fact, the nonlocal modes are weakly excited across the q min -surface. This leads to a discontinuity or gap which disconnects the phase relation in the global wave structure across the q min -surface. Once such a discontinuity (or gap) is formed, transport suppression occurs and therefore a transport barrier can be expected near the q min -surface. We confirm the existence of this discontinuity using a toroidal particle simulation. (author)

Memory-induced sign reversals of the spatial cross-correlation for particles in viscoelastic shear flows

International Nuclear Information System (INIS)

Sauga, Ako; Laas, Katrin; Mankin, Romi

2015-01-01

Highlights: • Cross-correlation (CC) of coordinates of particles in viscoelastic shear flows is discussed. • Expressions for CC functions subjected to both internal and external noises are presented. • Impact of internal and external noises on CC functions are compared. • Memory-induced reentrant sign reversals of the spatial cross-moment are established. - Abstract: The behavior of shear-induced cross-correlation functions between particle fluctuations along orthogonal directions in the shear plane for harmonically trapped Brownian particles in a viscoelastic shear flow is studied. A generalized Langevin equation with a power-law-type memory kernel is used to model the complex structure of the viscoelastic media. Interaction with fluctuations of environmental parameters is modeled by a multiplicative white Gaussian noise, by an internal fractional Gaussian noise, and by an additive external white noise. It is shown that the presence of a memory has a profound effect on the behavior of the cross-correlation functions. Particularly, memory-induced reentrant sign reversals of the spatial cross-moment between orthogonal random displacements of a particle are established, i.e., an increase of the memory exponent can cause the sign reversal from positive to negative, but by a further increase of the memory exponent a reentrant transition from negative to positive values appears. Similarities and differences between the behavior of the models with additive internal and external noises are considered. It is shown that additive external and internal noises cause qualitatively different dependencies of the cross-correlation functions on the time lag. The occurrence of energetic instability due to the influence of multiplicative noise is also discussed.

Characteristics of internal transport barrier in JT-60U reversed shear plasmas

International Nuclear Information System (INIS)

Sakamoto, Y.; Kamada, Y.; Ide, S.; Fujita, T.; Shirai, H.; Takizuka, T.; Koide, Y.; Fukuda, T.; Oikawa, T.; Suzuki, T.; Shinohara, K.; Yoshino, R.

2001-01-01

Characteristics of internal transport barrier (ITB) structure are studied and the active ITB control has been developed in JT-60U reversed shear plasmas. The following results are found. Outward propagation of the ITB with steep T i gradient is limited to the minimum safety factor location (ρ qmin ). However the ITB with reduced T i gradient can move to the outside of ρ qmin . Lower boundary of ITB width is proportional to the ion poloidal gyroradius at the ITB center. Furthermore the demonstration of the active control of the ITB strength based on the modification of the radial electric field shear profile is successfully performed by the toroidal momentum injection in different directions or the increase of heating power by neutral beams. (author)

The effect of toroidal plasma rotation on low-frequency reversed shear Alfven eigenmodes in tokamaks

NARCIS (Netherlands)

Haverkort, J. W.

2012-01-01

The influence of toroidal plasma rotation on the existence of reversed shear Alfven eigenmodes (RSAEs) near their minimum frequency is investigated analytically. An existence condition is derived showing that a radially decreasing kinetic energy density is unfavourable for the existence of RSAEs.

Intrinsic Rotation and Momentum Transport in Reversed Shear Plasmas with Internal Transport Barriers

Science.gov (United States)

Jhang, Hogun; Kim, S. S.; Diamond, P. H.

2010-11-01

The intrinsic rotation in fusion plasmas is believed to be generated via the residual stress without external momentum input. The physical mechanism responsible for the generation and transport of intrinsic rotation in L- and H-mode tokamak plasmas has been studied extensively. However, it is noted that the physics of intrinsic rotation generation and its relationship to the formation of internal transport barriers (ITBs) in reversed shear (RS) tokamak plasmas have not been explored in detail, which is the main subject in the present work. A global gyrofluid code TRB is used for this study. It is found that the large intrinsic rotation (˜10-30% of the ion sound speed depending on ITB characteristics) is generated near the ITB region and propagates into the core. The intrinsic rotation increases linearly as the temperature gradient at ITB position increases, albeit not indefinitely. Key parameters related to the symmetry breaking, such as turbulent intensity and its gradient, the flux surface averaged parallel wavenumber are evaluated dynamically during the ITB formation. The role of reversed shear and the q-profile curvature is presented in relation to the symmetry breaking mechanism in RS plasmas.

Analytical reverse time migration: An innovation in imaging of infrastructures using ultrasonic shear waves.

Science.gov (United States)

Asadollahi, Aziz; Khazanovich, Lev

2018-04-11

The emergence of ultrasonic dry point contact (DPC) transducers that emit horizontal shear waves has enabled efficient collection of high-quality data in the context of a nondestructive evaluation of concrete structures. This offers an opportunity to improve the quality of evaluation by adapting advanced imaging techniques. Reverse time migration (RTM) is a simulation-based reconstruction technique that offers advantages over conventional methods, such as the synthetic aperture focusing technique. RTM is capable of imaging boundaries and interfaces with steep slopes and the bottom boundaries of inclusions and defects. However, this imaging technique requires a massive amount of memory and its computation cost is high. In this study, both bottlenecks of the RTM are resolved when shear transducers are used for data acquisition. An analytical approach was developed to obtain the source and receiver wavefields needed for imaging using reverse time migration. It is shown that the proposed analytical approach not only eliminates the high memory demand, but also drastically reduces the computation time from days to minutes. Copyright © 2018 Elsevier B.V. All rights reserved.

Discontinuity model for internal transport barrier formation in reversed magnetic shear plasmas

International Nuclear Information System (INIS)

Kishimoto, Y.; Dettrick, S.A.; Li, J.Q.; Shirai, S.; Kim, J.Y.; Horton, W.; Tajima, T.; LeBrun, M.J.

2000-01-01

It is becoming clear that tokamak anomalous transport is dominated by radially extended non-local modes which originate from strong toroidal coupling of rational surfaces in non-uniform plasmas. To aid in understanding the internal transport barrier (ITB) formed in reversed magnetic shear experiments, in addition to the well known shear flow effect, the article points out an important non-local effect and/or finite size effect which comes from the complex behaviour of the mode over a finite radial region around the minimum q (safety factor) surface. The non-local mode, which is characterized by its radial extent and the degree of tilting in the poloidal direction (Δr, θ 0 ), changes its structure depending on the sign of the magnetic shear, and as a result such modes are weakly excited across the q min surface. This leads to a discontinuity or gap which disconnects the phase relation in the global wave structure across the q min surface. Once such a discontinuity (or gap) is formed, transport suppression occurs and therefore a transport barrier can be expected near the q min surface. The existence of this discontinuity is confirmed through use of a toroidal particle simulation. It is also shown that whether such a discontinuity is efficiently established depends on the presence of the radial electric field and the related plasma shear flow. (author)

Toroidal plasmoid generation via extreme hydrodynamic shear.

Science.gov (United States)

Gharib, Morteza; Mendoza, Sean; Rosenfeld, Moshe; Beizai, Masoud; Alves Pereira, Francisco J

2017-11-28

Saint Elmo's fire and lightning are two known forms of naturally occurring atmospheric pressure plasmas. As a technology, nonthermal plasmas are induced from artificially created electromagnetic or electrostatic fields. Here we report the observation of arguably a unique case of a naturally formed such plasma, created in air at room temperature without external electromagnetic action, by impinging a high-speed microjet of deionized water on a dielectric solid surface. We demonstrate that tribo-electrification from extreme and focused hydrodynamic shear is the driving mechanism for the generation of energetic free electrons. Air ionization results in a plasma that, unlike the general family, is topologically well defined in the form of a coherent toroidal structure. Possibly confined through its self-induced electromagnetic field, this plasmoid is shown to emit strong luminescence and discrete-frequency radio waves. Our experimental study suggests the discovery of a unique platform to support experimentation in low-temperature plasma science. Copyright © 2017 the Author(s). Published by PNAS.

Microstructural Origins of Nonlinear Response in Associating Polymers under Oscillatory Shear

Directory of Open Access Journals (Sweden)

Mark A. Wilson

2017-10-01

Full Text Available The response of associating polymers with oscillatory shear is studied through large-scale simulations. A hybrid molecular dynamics (MD, Monte Carlo (MC algorithm is employed. Polymer chains are modeled as a coarse-grained bead-spring system. Functionalized end groups, at both ends of the polymer chains, can form reversible bonds according to MC rules. Stress-strain curves show nonlinearities indicated by a non-ellipsoidal shape. We consider two types of nonlinearities. Type I occurs at a strain amplitude much larger than one, type II at a frequency at which the elastic storage modulus dominates the viscous loss modulus. In this last case, the network topology resembles that of the system at rest. The reversible bonds are broken and chains stretch when the system moves away from the zero-strain position. For type I, the chains relax and the number of reversible bonds peaks when the system is near an extreme of the motion. During the movement to the other extreme of the cycle, first a stress overshoot occurs, then a yield accompanied by shear-banding. Finally, the network restructures. Interestingly, the system periodically restores bonds between the same associating groups. Even though major restructuring occurs, the system remembers previous network topologies.

ExB flow shear and enhanced confinement in the Madison Symmetric Torus reversed-field pinch

International Nuclear Information System (INIS)

Chapman, B.E.; Almagri, A.F.; Anderson, J.K.; Chiang, C.; Craig, D.; Fiksel, G.; Lanier, N.E.; Prager, S.C.; Sarff, J.S.; Stoneking, M.R.; Terry, P.W.

1998-01-01

Strong ExB flow shear occurs in the edge of three types of enhanced confinement discharge in the Madison Symmetric Torus [Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch. Measurements in standard (low confinement) discharges indicate that global magnetic fluctuations drive particle and energy transport in the plasma core, while electrostatic fluctuations drive particle transport in the plasma edge. This paper explores possible contributions of ExB flow shear to the reduction of both the magnetic and electrostatic fluctuations and, thus, the improved confinement. In one case, shear in the ExB flow occurs when the edge plasma is biased. Biased discharges exhibit changes in the edge electrostatic fluctuations and improved particle confinement. In two other cases, the flow shear emerges (1) when auxiliary current is driven in the edge and (2) spontaneously, following sawtooth crashes. Both edge electrostatic and global magnetic fluctuations are reduced in these discharges, and both particle and energy confinement improve. copyright 1998 American Institute of Physics

Phase contrast imaging measurements of reversed shear Alfvén eigenmodes during sawteeth in Alcator C-Moda)

Science.gov (United States)

Edlund, E. M.; Porkolab, M.; Kramer, G. J.; Lin, L.; Lin, Y.; Wukitch, S. J.

2009-05-01

Reversed shear Alfvén eigenmodes (RSAEs) have been observed with the phase contrast imaging diagnostic and Mirnov coils during the sawtooth cycle in Alcator C-mod [M. Greenwald et al., Nucl. Fusion 45, S109 (2005)] plasmas with minority ion-cyclotron resonance heating. Both down-chirping RSAEs and up-chirping RSAEs have been observed during the sawtooth cycle. Experimental measurements of the spatial structure of the RSAEs are compared to theoretical models based on the code NOVA [C. Z. Cheng and M. S. Chance, J. Comput. Phys. 71, 124 (1987)] and used to derive constraints on the q profile. It is shown that the observed RSAEs can be understood by assuming a reversed shear q profile (up chirping) or a q profile with a local maximum (down chirping) with q ≈1.

Martensite shear phase reversion-induced nanograined/ultrafine-grained Fe-16Cr-10Ni alloy: The effect of interstitial alloying elements and degree of austenite stability on phase reversion

Energy Technology Data Exchange (ETDEWEB)

Misra, R.D.K., E-mail: dmisra@louisiana.edu [Center for Structural and Functional Materials, University of Louisiana at Lafayette, Madison Hall Room 217, P.O. Box 44130, Lafayette, LA 70504-1430 (United States); Zhang, Z.; Venkatasurya, P.K.C. [Center for Structural and Functional Materials, University of Louisiana at Lafayette, Madison Hall Room 217, P.O. Box 44130, Lafayette, LA 70504-1430 (United States); Somani, M.C.; Karjalainen, L.P. [Department of Mechanical Engineering, University of Oulu, P.O. Box 4200, Oulu 90014 (Finland)

2010-11-15

Research highlights: {yields} Development of a novel process involving phase-reversion annealing process. {yields} Austensite stability strongly influences development of nanograined structure. {yields} Interstitial elements influence microstructural evolution during annealing. - Abstract: We describe here an electron microscopy study of microstructural evolution associated with martensitic shear phase reversion-induced nanograined/ultrafine-grained (NG/UFG) structure in an experimental Fe-16Cr-10Ni alloy with very low interstitial content. The primary objective is to understand and obtain fundamental insights on the influence of degree of austenite stability (Fe-16Cr-10Ni, 301LN, and 301 have different austenite stability index) and interstitial elements (carbon and nitrogen) in terms of phase reversion process, microstructural evolution during reversion annealing, and temperature-time annealing sequence. A relative comparison of Fe-16Cr-10Ni alloy with 301LN and 301 austenitic stainless steels indicated that phase reversion in Fe-16Cr-10Ni occurred by shear mechanism, which is similar to that observed for 301, but is different from the diffusional mechanism in 301LN steel. While the phase reversion in the experimental Fe-16Cr-10Ni alloy and 301 austenitic stainless steel occurred by shear mechanism, there were fundamental differences between these two alloys. The reversed strain-free austenite grains in Fe-16Cr-10Ni alloy were characterized by nearly same crystallographic orientation, where as in 301 steel there was evidence of break-up of martensite laths during reversion annealing resulting in several regions of misoriented austenite grains in 301 steel. Furthermore, a higher phase reversion annealing temperature range (800-900 deg. C) was required to obtain a fully NG/UFG structure of grain size 200-600 nm. The difference in the phase reversion and the temperature-time sequence in the three stages is explained in terms of Gibbs free energy change that

Resistive instabilities in reversed shear discharges and wall stabilization on JT-60U

International Nuclear Information System (INIS)

Takeji, S.; Tokuda, S.; Fujita, T.; Suzuki, T.; Isayama, A.; Ide, S.; Ishii, Y.; Kamada, Y.; Koide, Y.; Matsumoto, T.; Oikawa, T.; Ozeki, T.; Sakamoto, Y.

2001-01-01

Resistive instabilities and wall stabilization of ideal low toroidal mode number, n, kink modes are investigated in JT-60U reversed shear discharges. Resistive interchange modes with n=1 are found to appear in reversed shear discharges with large pressure gradient at the normalized beta, β N , of about unity or even lower. The resistive interchange modes appear as intermittent burst-like magnetohydrodynamic (MHD) activities and higher n≤3 modes are observed occasionally in higher β N regime. No clear degradation of the plasma stored energy is observed by the resistive interchange modes themselves. It is also found that resistive interchange modes can lead to major collapse owing to a coupling with tearing modes at the outer mode rational surface over the minimum safety factor. Stability analysis revealed that stability parameter of tearing modes, Δ' , at the outer mode rational surface is affected by the free-boundary condition. The result is consistent with the experimental evidence that major collapse tends to occur when plasma edge safety factor, q*, is near integer values. Stabilization of ideal low n kink modes by the JT-60U wall is demonstrated. Magnetohydrodynamic perturbations that are attributed to resistive wall modes are observed followed by major collapse in wall-stabilized discharges. (author)

Local transport barrier formation and relaxation in reverse-shear plasmas on the TFTR tokamak

International Nuclear Information System (INIS)

Synakowski, E.J.; Beer, M.A.

1997-02-01

The roles of turbulence stabilization by sheared E x B flow and Shafranov-shift gradients are examined for TFTR. Enhanced Reverse-Shear plasmas. Both effects in combination provide the basis of a positive-feedback model that predicts reinforced turbulence suppression with increasing pressure gradient. Local fluctuation behavior at the onset of ERS confinement is consistent with this framework. The power required for transitions into the ERS regime are lower when high power neutral beams are applied earlier in the current profile evolution, consistent with the suggestion that both effects play a role. Separation of the roles of E x B and Shafranov shift effects was performed by varying the E x B shear through changes in the toroidal velocity with nearly-steady-state pressure profiles. Transport and fluctuation levels increase only when E x B shearing rates are driven below a critical value that is comparable to the fastest linear growth rates of the dominant instabilities. While a turbulence suppression criterion that involves the ratio of shearing to linear growth rates is in accord with many of these results, the existence of hidden dependencies of the criterion is suggested in experiments where the toroidal field was varied. The forward transition into the ERS regime has also been examined in strongly rotating plasmas. The power threshold is higher with unidirectional injection than with balanced injection

The effect of toroidal plasma rotation on low-frequency reversed shear Alfvén eigenmodes in tokamaks

NARCIS (Netherlands)

J.W. Haverkort (Willem)

2012-01-01

htmlabstractThe influence of toroidal plasma rotation on the existence of reversed shear Alfvén eigenmodes (RSAEs) near their minimum frequency is investigated analytically. An existence condition is derived showing that a radially decreasing kinetic energy density is unfavourable for the existence

Some features of the disruption instability in reversed shear TFTR plasmas

International Nuclear Information System (INIS)

Semenov, I.B.; Mirnov, S.V.; McGuire, K.M.

1999-01-01

The behaviour of MHD perturbations before and during disruptions in TFTR reversed shear plasmas with q min ∼ 2 was analysed. In the q min region, tearing modes, wavelike modes, and mixed tearing plus wavelike modes are followed by disruption. Sometimes a helical snake (helix) appears at the X point of the q min island. The local outward electron energy transport near the X point can be explained by the development of 'positive' magnetic islands (islands with positive current perturbations). It is proposed that the disruption is initiated when the X point of the magnetic islands coincides in one toroidal position near the torus equator. (author)

Gyrofluid Simulations of Intrinsic Rotation Generation in Reversed Shear Plasmas with Internal Transport Barriers

Science.gov (United States)

Jhang, Hogun; Kim, S. S.; Kwon, J. M.; Terzolo, L.; Kim, J. Y.; Diamond, P. H.

2010-11-01

It is accepted that the intrinsic rotation is generated via the residual stress, which is non-diffusive components of the turbulent Reynolds stress, without external momentum input. The physics leading to the onset of intrinsic rotation in L- and H- mode plasmas have been elucidated elsewhere. However, the physics responsible for the generation and transport of the intrinsic rotation and its relationship to the formation of internal transport barriers (ITBs) in reversed shear (RS) plasmas have not been explored in detail, which is the main subject in the present work. The revised version of the global gyrofluid code TRB is used for this study. It is found that the large intrinsic rotation (˜10-30% of the ion sound speed depending on ITB characteristics) is generated near the ITB region and propagates into the core. The intrinsic rotation increases linearly as the temperature gradient at ITB position increases, albeit not indefinitely. Key parameters related to the symmetry breaking, such as turbulent intensity and its gradient, the flux surface averaged parallel wavenumber are evaluated dynamically during the ITB formation. In particular, the role of reversed shear and the q-profile curvature is presented in relation to the symmetry breaking in RS plasmas.

Biofouling of reverse-osmosis membranes under different shear rates during tertiary wastewater desalination: microbial community composition.

Science.gov (United States)

Al Ashhab, Ashraf; Gillor, Osnat; Herzberg, Moshe

2014-12-15

We investigated the influence of feed-water shear rate during reverse-osmosis (RO) desalination on biofouling with respect to microbial community composition developed on the membrane surface. The RO membrane biofilm's microbial community profile was elucidated during desalination of tertiary wastewater effluent in a flat-sheet lab-scale system operated under high (555.6 s(-1)), medium (370.4 s(-1)), or low (185.2 s(-1)) shear rates, corresponding to average velocities of 27.8, 18.5, and 9.3 cm s(-1), respectively. Bacterial diversity was highest when medium shear was applied (Shannon-Weaver diversity index H' = 4.30 ± 0.04) compared to RO-membrane biofilm developed under lower and higher shear rates (H' = 3.80 ± 0.26 and H' = 3.42 ± 0.38, respectively). At the medium shear rate, RO-membrane biofilms were dominated by Betaproteobacteria, whereas under lower and higher shear rates, the biofilms were dominated by Alpha- and Gamma- Proteobacteria, and the latter biofilms also contained Deltaproteobacteria. Bacterial abundance on the RO membrane was higher at low and medium shear rates compared to the high shear rate: 8.97 × 10(8) ± 1.03 × 10(3), 4.70 × 10(8) ± 1.70 × 10(3) and 5.72 × 10(6) ± 2.09 × 10(3) copy number per cm(2), respectively. Interestingly, at the high shear rate, the RO-membrane biofilm's bacterial community consisted mainly of populations known to excrete high amounts of extracellular polymeric substances. Our results suggest that the RO-membrane biofilm's community composition, structure and abundance differ in accordance with applied shear rate. These results shed new light on the biofouling phenomenon and are important for further development of antibiofouling strategies for RO membranes. Copyright © 2014 Elsevier Ltd. All rights reserved.

Reinforced concrete membrane elements subjected to reversed cyclic in-plane shear stress

International Nuclear Information System (INIS)

Ohmori, N.; Tsubota, H.; Inoue, N.; Watanabe, S.; Kurihara, K.

1987-01-01

The response of reinforced concrete elements subjected to reversed cyclic in-plane shear stresses can be predicted by an analytical model, which considers equilibrium, compatibility and stress-strain relationships including hysteresis loop of unloading and reloading stages all expressed in terms of average stresses and average strains. The analytical results show that the dominant hysteretic behaviours in regard to decrease of stiffness during unloading, successive slip phenomena and restoration of compressive stiffness at the reloading stages are well simulated analytically. The results agree quite well with the observed behaviours. As for the envelope curve of the hysteretic response there remain the discrepancies that the stiffness and ultimate strength are a bit larger than the observed results, especially in the case of a panel with a large reinforcement ratio. Such descrepancies are also found in the predicted results of monotonic loading and more precise studies are necessary to evaluate more accurate envelope curves under not only reversed cyclic loading but also monotonic loading. (orig./HP)

Anomalous Beam-Ion Loss in TFTR Reversed Magnetic Shear Plasmas

International Nuclear Information System (INIS)

Ruskov, E.; Bell, M.; Budny, R.V.; McCune, D.C.; Medley, S.S.; Redi, M.H.; Scott, S.; Synakowski, E.J.; Goeler, S. von; White, R.B.; Zweben, S.J.

1999-01-01

Anomalous beam-ion loss has been observed in an experiment with short tritium beam pulses injected into deuterium-beam-heated Tokamak Fusion Test Reactor plasmas (P NBI =15 MW) with reversed magnetic shear (RS). Comparisons of the measured total 14thinspthinspMeV neutron emission, the neutron flux along eight radial locations, and the perpendicular plasma stored energy with predictions from an extensive set of TRANSP simulations suggest that about 40% beam power is lost on a time scale much shorter than the tritium beam pulse length Δt=70 ms. In contrast with recent results [K. Tobita et al., Nucl.Fusion 37, 1583 (1997)] from RS experiments at JT-60U, we were not able to show conclusively that magnetic field ripple is responsible for this anomaly. copyright 1999 The American Physical Society

Measurements of the eigenfunction of reversed shear Alfvén eigenmodes that sweep downward in frequency

International Nuclear Information System (INIS)

Heidbrink, W. W.; Austin, M. E.; Spong, D. A.; Tobias, B. J.; Van Zeeland, M. A.

2013-01-01

Reversed shear Alfvén eigenmodes (RSAEs) usually sweep upward in frequency when the minimum value of the safety factor q min decreases in time. On rare occasions, RSAEs sweep downward prior to the upward sweep. Electron cyclotron emission measurements show that the radial eigenfunction during the downsweeping phase is similar to the eigenfunction of normal, upsweeping RSAEs

Intrinsic torque reversals induced by magnetic shear effects on the turbulence spectrum in tokamak plasmas

Energy Technology Data Exchange (ETDEWEB)

Lu, Z. X.; Tynan, G. [Center for Energy Research and Department of Mechanical and Aerospace Engineering, University of California at San Diego, San Diego, California 92093 (United States); Center for Momentum Transport and Flow Organization and Center for Astrophysics and Space Science, University of California, San Diego, California 92093 (United States); Wang, W. X.; Ethier, S. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540 (United States); Diamond, P. H. [Center for Momentum Transport and Flow Organization and Center for Astrophysics and Space Science, University of California, San Diego, California 92093 (United States); Gao, C.; Rice, J. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2015-05-15

Intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. This work focuses on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear (s{sup ^}) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak s{sup ^}. Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak s{sup ^} discharges and that the value of s{sup ^}{sub crit} is consistent with the experimental results s{sup ^}{sub crit}{sup exp}≈0.2∼0.3 [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. The consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak s{sup ^} and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive s{sup ^}.

Shear Resistance Variations in Experimentally Sheared Mudstone Granules: A Possible Shear-Thinning and Thixotropic Mechanism

Science.gov (United States)

Hu, Wei; Xu, Qiang; Wang, Gonghui; Scaringi, Gianvito; Mcsaveney, Mauri; Hicher, Pierre-Yves

2017-11-01

We present results of ring shear frictional resistance for mudstone granules of different size obtained from a landslide shear zone. Little rate dependency of shear resistance was observed in sand-sized granules in any wet or dry test, while saturated gravel-sized granules exhibited significant and abrupt reversible rate-weakening (from μ = 0.6 to 0.05) at about 2 mm/s. Repeating resistance variations occurred also under constant shear displacement rate. Mudstone granules generate mud as they are crushed and softened. Shear-thinning and thixotropic behavior of the mud can explain the observed behavior: with the viscosity decreasing, the mud can flow through the coarser soil pores and migrate out from the shear zone. This brings new granules into contact which produces new mud. Thus, the process can start over. Similarities between experimental shear zones and those of some landslides in mudstone suggest that the observed behavior may play a role in some landslide kinematics.

Off-axis sawteeth and double-tearing reconnection in reversed magnetic shear plasmas in TFTR

International Nuclear Information System (INIS)

Chang, Z.; Park, W.; Fredrickson, E.D.

1996-06-01

Off-axis sawteeth are often observed in reversed magnetic shear plasmas when the minimum safety factor q is near or below 2. Fluctuations with m/n = 2/1 (m and n are the poloidal and toroidal mode numbers) appear before and after the crashes. Detailed comparison has been made between the measured T e profile evolution during the crash and a nonlinear numerical magnetohydrodynamics (MHD) simulation. The good agreement between the observation and simulation indicates that the off-axis sawteeth are due to a double-tearing magnetic reconnection process

Shear zones between rock units with no relative movement

DEFF Research Database (Denmark)

Koyi, H.; Schmeling, H.; Burchardt, S.

2012-01-01

, elongated bodies (vertical plates or horizontal rod-like bodies) produce tabular shear zones. Unlike conventional shear zones across which shear indicators ideally display consistent symmetries, shear indicators on either sides of the shear zone reported here show reverse kinematics. Thus profiles exhibit...... by progressive extension and (perhaps) where slabs of subducted oceanic lithosphere delaminate from the continental crust and sink into the asthenosphere. We also argue that such shear zones may be more common than they have been given the credit for and may be responsible for some of the kinematic reversals...

Evolution of thermal ion transport barriers in reversed shear/ optimised shear plasmas

International Nuclear Information System (INIS)

Voitsekhovitch, I.; Garbet, X.; Moreau, D.; Bush, C.E.; Budny, R.V.; Gohil, P.; Kinsey, J.E.; Talyor, T.S.; Litaudon, X.

2001-01-01

The effects of the magnetic and ExB rotation shears on the thermal ion transport in advanced tokamak scenarios are analyzed through the predictive modelling of the evolution of internal transport barriers. Such a modelling is performed with an experimentally validated L-mode thermal diffusivity completed with a semi-empirical shear correction which is based on simple theoretical arguments from turbulence studies. A multi-machine test of the model on relevant discharges from the ITER Data Base (TFTR, DIII-D and JET) is presented. (author)

Sheared flow layer formation in tokamak plasmas with reversed magnetic shear

International Nuclear Information System (INIS)

Dong, J.Q.; Long, Y.X.; Mou, Z.Z.; Zhang, J.H.; Li, J.Q.

2005-01-01

Sheared flow layer (SFL) formation due to magnetic energy release through tearing-reconnections in tokamak plasmas is investigated. The characteristics of the SFLs created in the development of double tearing mode, mediated by electron viscosity in configurations with non-monotonic safety factor q profiles and, therefore, two rational flux surfaces of same q value, are analyzed in detail as an example. Quasi-linear simulations demonstrate that the sheared flows induced by the mode have desirable characteristics (lying at the boundaries of the magnetic islands), and sufficient levels required for internal transport barrier (ITB) formation. A possible correlation of the SFLs with experimental observations, that double transport barrier structures are preferentially formed in proximity of the two rational surfaces, is also proffered. (author)

Phenomenological Analysis of the Kinematic Hardening of HSLA and IF Steels Using Reverse Simple Shear Tests

International Nuclear Information System (INIS)

Aouafi, A.; Bouvier, S.; Gasperini, M.; Lemoine, X.; Bouaziz, O.

2007-01-01

Reverse simple shear tests are used to analyse the Bauschinger effect and the evolution of the kinematic hardening for a wide range of equivalent von Mises strain [0.025 - 0.3]. This work is carried out on two high strength low-alloyed steels. In order to investigate the effect of the precipitates on the macroscopic behaviour, a ferritic mild steel is used as a reference. Different phenomenological descriptions of the back-stress tensor are examined in order to analyse their ability to describe the experimental behaviour

Shear zones between rock units with no relative movement

DEFF Research Database (Denmark)

Koyi, Hemin; Schmeling, Harro; Burchardt, Steffi

2013-01-01

Shear zones are normally viewed as relatively narrow deformation zones that accommodate relative displacement between two "blocks" that have moved past each other in opposite directions. This study reports localized zones of shear between adjacent blocks that have not moved past each other. Such ...... given credit for and may be responsible for some reverse kinematics reported in shear zones....... or wakes, elongated bodies (vertical plates or horizontal rod-like bodies) produce tabular shear zones or wakes. Unlike conventional shear zones across which shear indicators usually display consistent symmetries, shear indicators on either side of the shear zone or wake reported here show reverse...... kinematics. Thus profiles exhibit shear zones with opposed senses of movement across their center-lines or -planes.We have used field observations and results from analytical and numerical models to suggest that examples of wakes are the transit paths that develop where denser blocks sink within salt...

Sustainment of high confinement in JT-60U reversed shear plasmas

International Nuclear Information System (INIS)

Fujita, T.; Kamada, Y.; Ide, S.; Takeji, S.; Sakamoto, Y.; Isayama, A.; Suzuki, T.; Oikawa, T.; Fukuda, T.

2001-01-01

confinement is achieved owing to strong internal transport barriers (ITBs), are reported. In a high current plasma with an L-mode edge, deuterium-tritium-equivalent fusion power gain, Q DT eq =0.5 was sustained for 0.8 s (∼ energy confinement time) by adjusting plasma beta precisely using feedback control of stored energy. In a high triangularity plasma with an ELMy H-mode edge, the shrinkage of reversed shear region was suppressed and quasi steady sustainment of high confinement was achieved by raising the poloidal beta and enhancing the bootstrap current peaked at the ITB layer. High bootstrap current fraction (∼80%) was obtained in a high q regime (q 95 ∼9), which leaded to full non-inductive current drive condition. The normalized beta (β N ) of ∼ 2 and H-factor of H 89 ∼3.5 (HH 98y2 ∼2.2) were sustained for 2.7 s (∼ 6 times energy confinement time). (author)

Perturbative transport experiments in JET low or reverse magnetic shear plasmas

Energy Technology Data Exchange (ETDEWEB)

Mantica, P. [Istituto di Fisica del Plasma, EURATOM-ENEA-CNR Association, Milan (Italy); Gorini, G. [Istituto di Fisica del Plasma, EURATOM-ENEA-CNR Association, Milan (Italy); INFM, Department of Physics, University of Milano-Bicocca, Milan (Italy); Imbeaux, F. [Association Euratom-CEA, CEA Cadarache, St. Paul-lez-Durance (France)] (and others)

2002-10-01

Perturbative transport experiments have been performed in JET low or reverse magnetic shear plasmas either in conditions of fully developed internal transport barrier (ITB) or during a phase where an ITB was not observed. Transient peripheral cooling was induced either by laser ablation or by shallow pellet injection, and the ensuing travelling cold pulse was used to probe the plasma transport in the electron and, for the first time, also in the ion channel. Cold pulses travelling through ITBs are observed to erode the ITB outer part, but, if the inner ITB portion survives, it strongly damps the propagating wave. The result is discussed in the context of proposed possible pictures for ITB formation. In the absence of an ITB, the cold pulse shows a fast propagation in the outer plasma half, which is consistent with a region of stiff transport, while in the inner half it slows down but shows the peculiar feature of amplitude growing while propagating. The data are powerful tests for the validation of theoretical transport models. (author)

Extremely low-frequency magnetic fields can impair spermatogenesis recovery after reversible testicular damage induced by heat.

Science.gov (United States)

Tenorio, Bruno Mendes; Ferreira Filho, Moisés Bonifacio Alves; Jimenez, George Chaves; de Morais, Rosana Nogueira; Peixoto, Christina Alves; Nogueira, Romildo de Albuquerque; da Silva Junior, Valdemiro Amaro

2014-06-01

Male infertility is often related to reproductive age couples experiencing fertility-related issues. Men may have fertility problems associated with reversible testicular damage. Considering that men have been increasingly exposed to extremely low-frequency magnetic fields generated by the production, distribution and use of electricity, this study analyzed whether 60 Hz and 1 mT magnetic field exposure may impair spermatogenesis recovery after reversible testicular damage induced by heat shock using rats as an experimental model. Adult male rats were subjected to a single testicular heat shock (HS, 43 °C for 12 min) and then exposed to the magnetic field for 15, 30 and 60 d after HS. Magnetic field exposure during the spermatogenesis recovery induced changes in testis components volume, cell ultrastructure and histomorphometrical parameters. Control animals had a reestablished and active spermatogenesis at 60 d after heat shock, while animals exposed to magnetic field still showed extensive testicular degeneration. Magnetic field exposure did not change the plasma testosterone. In conclusion, extremely low-frequency magnetic field may be harmful to fertility recovery in males affected by reversible testicular damage.

Modelling of shear effects on thermal and particle transport in advanced Tokamak scenarios

International Nuclear Information System (INIS)

Moreau, D.; Voitsekhovitch, I.; Baker, D.R.

1999-01-01

Evolution of thermal and particle internal transport barriers (ITBs) is studied by modelling the time-dependent energy and particle balance in DIII-D plasmas with reversed magnetic shear configurations and in JET discharges with monotonic or slightly reversed q-profiles and large ExB rotation shear. Simulations are performed with semi-empirical models for anomalous diffusion and particle pinch. Stabilizing effects of magnetic and ExB rotation shears are included in anomalous particle and heat diffusivity. Shear effects on particle and thermal transport are compared. Improved particle and energy confinement with the formation of an internal transport barrier (ITB) has been produced in DIII-D plasmas during current ramp-up accompanied with neutral beam injection (NBI). These plasmas are characterized by strong reversed magnetic shear and large ExB rotation shear which provide the reduction of anomalous fluxes. The formation of ITB's in the optimized shear (OS) JET scenario starts with strong NBI heating in a target plasma with a flat or slightly reversed q-profile pre-formed during current ramp-up with ion cyclotron resonance heating (ICRH). Our paper presents the modelling of particle and thermal transport for these scenarios. (authors)

Role of the current density profile on drift wave stability in internal transport barrier reversed magnetic shear experiments at JET and Tore Supra

Energy Technology Data Exchange (ETDEWEB)

Fourment, C; Hoang, G T; Eriksson, L-G; Garbet, X; Litaudon, X; Tresset, G [EURATOM-CEA Association, CEA/DSM/DRFC, CEA Cadarache, 13108 St Paul-lez-Durance (France)

2003-03-01

The role of the current density profile on drift wave stability is investigated using a linear electrostatic gyro-kinetic code. The growth rates are shown to have a linear dependence on the normalized temperature gradients above a certain threshold. A parametric study of the threshold shows a dramatic stabilizing effect of negative magnetic shear, especially for large scale instabilities. A set of handy formulae fitting the threshold as a function of the magnetic shear and the safety factor is proposed. Analysis of reversed magnetic shear discharges with internal transport barrier (ITB) in JET shows that ion ITBs can be triggered by the negative magnetic shear in the core of the plasma. Subsequently, the increase of the ExB shearing rate allows for the expansion of the ITB, despite the increase of the linear growth rates due to the temperature gradient peaking. In the case of the electron ITB obtained in the Tore Supra LHEP mode, the central increase of the confinement is associated with the stabilization of large scale trapped electron modes by the negative magnetic shear effect, whereas the steep electron temperature gradient destabilizes the small scale electron temperature gradient modes, which prevent the electron heat transport to reach neoclassical levels.

Dynamic behavior of transport in normal and reversed shear plasmas with internal barriers in JT-60U

International Nuclear Information System (INIS)

Neudatchin, Sergi V.; Takizuka, Tomonori; Shirai, Hiroshi; Fujita, Takaaki; Isayama, Akihiko; Kamada, Yutaka; Koide, Yoshihiko

2001-12-01

Transport evolution in normal shear (NrS) and reversed shear (RS) JT-60U tokamak plasmas with internal transport barrier (ITB) is described as a combination of various fast and slow time scale processes. Abrupt in time (ms time scale) and wide in space (∼0.3 of minor radius) variations of electron and ion heat diffusivities χ e,i (δχ e,i ), which are called ITB-events and seen as simultaneous rise and decay of electron and ion temperatures in two spatial zones, are found for weak ITBs in both NrS and RS plasmas. Profiles of δχ e in RS plasmas with strong ITBs are usually localized near ITB foot inside smaller space region. The maximum of the heat flux variation is located near position of the minimum of safety factor in various RS plasmas, and variation is extended in positive shear region. Inward and outward heat pulse propagations created by the jump of χ e and the sawtooth-like crash are analyzed. Small values of χ e and the absence of heat pinch are found inside strong ITBs. Another non-local abrupt variations of χ e inside most of the plasma volume, including significant part of weak ITB inside RS zone of RS plasmas, are seen at the ELM-induced H-L transition and the L-H recovery. (author)

Escape patterns due to ergodic magnetic limiters in tokamaks with reversed magnetic shear

International Nuclear Information System (INIS)

Roberto, M.; Da Silva, E.C.; Caldas, I.L.; Viana, R.L.

2004-01-01

In this work we study the ergodic magnetic limiters (EML) action on field lines from the point of view of a chaotic scattering process, considering the so-called exit basins, or sets of points in the chaotic region which originate field lines hitting the wall in some specified region. We divide the tokamak wall into three areas of equal poloidal angular length, corresponding to different exits for a chaotic field line. In order to obtain the exit basins we used a grid chosen inside a small rectangle which comprises a representative part of the chaotic region near the wall. Thus, exit basins were obtained for a tokamak wall with reversed magnetic shear. The no-twist mapping describes the perturbed magnetic field lines with two chains of magnetic islands and chaotic field lines in their vicinity. For a perturbing resonant magnetic field with a fixed helicity, the observed escape pattern changes with the perturbation intensity. (authors)

Physics of strong internal transport barriers in JT-60U reversed-magnetic-shear plasmas

Energy Technology Data Exchange (ETDEWEB)

Hayashi, N; Takizuka, T; Sakamoto, Y; Fujita, T; Kamada, Y; Ide, S; Koide, Y [Japan Atomic Energy Agency, 801-1 Mukouyama, Naka, Ibaraki 311-0193 (Japan)

2006-05-15

The physics of strong internal transport barriers (ITBs) in JT-60U reversed-magnetic-shear (RS) plasmas has been studied through the modelling on the 1.5 dimensional transport simulation. The key physics to produce two scalings on the basis of the JT-60U box-type ITB database are identified. As for the scaling for the narrow ITB width proportional to the ion poloidal gyroradius, the following three physics are important: (1) the sharp reduction of the anomalous transport below the neoclassical level in the RS region, (2) the autonomous formation of pressure and current profiles through the neoclassical transport and the bootstrap current and (3) the large difference between the neoclassical transport and the anomalous transport in the normal-shear region. As for the scaling for the energy confinement inside ITB ({epsilon}{sub f}{beta}{sub p,core} {approx} 0.25, where {epsilon}{sub f} is the inverse aspect ratio at the ITB foot and {beta}{sub p,core} is the core poloidal beta value), the value of 0.25 is found to be a saturation value due to the MHD equilibrium. The value of {epsilon}{sub f}{beta}{sub p,core} reaches the saturation value, when the box-type ITB is formed in the strong RS plasma with a large asymmetry of the poloidal magnetic field, regardless of the details of the transport and the non-inductively driven current.

Hydrodynamic of a deformed bubble in linear shear flow

International Nuclear Information System (INIS)

Adoua, S.R.

2007-07-01

This work is devoted to the study of an oblate spheroidal bubble of prescribed shape set fixed in a linear shear flow using direct numerical simulation. The three dimensional Navier-Stokes equations are solved in orthogonal curvilinear coordinates using a finite volume method. The bubble response is studied over a wide range of the aspect ratio (1-2.7), the bubble Reynolds number (50-2000) and the non-dimensional shear rate (0.-1.2). The numerical simulations shows that the shear flow imposes a plane symmetry of the wake whatever the parameters of the flow. The trailing vorticity is organized into two anti-symmetrical counter rotating tubes with a sign imposed by the competition of two mechanisms (the Lighthill mechanism and the instability of the wake). Whatever the Reynolds number, the lift coefficient reaches the analytical value obtained in an inviscid, weakly sheared flow corresponding to a lift force oriented in the same direction as that of a spherical bubble. For moderate Reynolds numbers, the direction of the lift force reverses when the bubble aspect ratio is large enough as observed in experiments. This reversal occurs for aspect ratios larger than 2.225 and is found to be directly linked to the sign of the trailing vorticity which is concentrated within two counter-rotating threads which propel the bubble in a direction depending of their sign of rotation. The behavior of the drag does not revel any significant effect induced by the wake structure and follows a quadratic increase with the shear rate. Finally, the torque experienced by the bubble also reverses for the same conditions inducing the reversal of the lift force. By varying the orientation of the bubble in the shear flow, a stable equilibrium position is found corresponding to a weak angle between the small axis of the bubble and the flow direction. (author)

Fusion performance analysis of plasmas with reversed magnetic shear in the Tokamak Fusion Test Reactor

International Nuclear Information System (INIS)

Ruskov, E.; Bell, M.; Budny, R.V.; McCune, D.C.; Medley, S.S.; Nazikian, R.; Synakowski, E.J.; Goeler, S. von; White, R.B.; Zweben, S.J.

1999-01-01

A case for substantial loss of fast ions degrading the performance of tokamak fusion test reactor plasmas [Phys. Plasmas 2, 2176 (1995)] with reversed magnetic shear (RS) is presented. The principal evidence is obtained from an experiment with short (40 - 70 ms) tritium beam pulses injected into deuterium beam heated RS plasmas [Phys. Rev. Lett. 82, 924 (1999)]. Modeling of this experiment indicates that up to 40% beam power is lost on a time scale much shorter than the beam - ion slowing down time. Critical parameters which connect modeling and experiment are: The total 14 MeV neutron emission, its radial profile, and the transverse stored energy. The fusion performance of some plasmas with internal transport barriers is further deteriorated by impurity accumulation in the plasma core. copyright 1999 American Institute of Physics

Analysis of the Shear Behavior of Stubby Y-Type Perfobond Rib Shear Connectors for a Composite Frame Structure.

Science.gov (United States)

Kim, Sang-Hyo; Kim, Kun-Soo; Lee, Do-Hoon; Park, Jun-Seung; Han, Oneil

2017-11-22

Shear connectors are used in steel beam-concrete slabs of composite frame and bridge structures to transfer shear force according to design loads. The existing Y-type perfobond rib shear connectors are designed for girder slabs of composite bridges. Therefore, the rib and transverse rebars of the conventional Y-type perfobond rib shear connectors are extremely large for the composite frames of building structures. Thus, this paper proposes stubby Y-type perfobond rib shear connectors, redefining the existing connectors, for composite frames of building structures; these were used to perform push-out tests. These shear connectors have relatively small ribs compared to the conventional Y-type perfobond rib shear connectors. To confirm the shear resistance of these stubby shear connectors, we performed an experiment by using transverse rebars D13 and D16. The results indicate that these shear connectors have suitable shear strength and ductility for application in composite frame structures. The shear strengths obtained using D13 and D16 were not significantly different. However, the ductility of the shear connectors with D16 was 45.1% higher than that of the shear connectors with D13.

Displacement-length scaling of brittle faults in ductile shear.

Science.gov (United States)

Grasemann, Bernhard; Exner, Ulrike; Tschegg, Cornelius

2011-11-01

Within a low-grade ductile shear zone, we investigated exceptionally well exposed brittle faults, which accumulated antithetic slip and rotated into the shearing direction. The foliation planes of the mylonitic host rock intersect the faults approximately at their centre and exhibit ductile reverse drag. Three types of brittle faults can be distinguished: (i) Faults developing on pre-existing K-feldspar/mica veins that are oblique to the shear direction. These faults have triclinic flanking structures. (ii) Wing cracks opening as mode I fractures at the tips of the triclinic flanking structures, perpendicular to the shear direction. These cracks are reactivated as faults with antithetic shear, extend from the parent K-feldspar/mica veins and form a complex linked flanking structure system. (iii) Joints forming perpendicular to the shearing direction are deformed to form monoclinic flanking structures. Triclinic and monoclinic flanking structures record elliptical displacement-distance profiles with steep displacement gradients at the fault tips by ductile flow in the host rocks, resulting in reverse drag of the foliation planes. These structures record one of the greatest maximum displacement/length ratios reported from natural fault structures. These exceptionally high ratios can be explained by localized antithetic displacement along brittle slip surfaces, which did not propagate during their rotation during surrounding ductile flow.

Displacement–length scaling of brittle faults in ductile shear

Science.gov (United States)

Grasemann, Bernhard; Exner, Ulrike; Tschegg, Cornelius

2011-01-01

Within a low-grade ductile shear zone, we investigated exceptionally well exposed brittle faults, which accumulated antithetic slip and rotated into the shearing direction. The foliation planes of the mylonitic host rock intersect the faults approximately at their centre and exhibit ductile reverse drag. Three types of brittle faults can be distinguished: (i) Faults developing on pre-existing K-feldspar/mica veins that are oblique to the shear direction. These faults have triclinic flanking structures. (ii) Wing cracks opening as mode I fractures at the tips of the triclinic flanking structures, perpendicular to the shear direction. These cracks are reactivated as faults with antithetic shear, extend from the parent K-feldspar/mica veins and form a complex linked flanking structure system. (iii) Joints forming perpendicular to the shearing direction are deformed to form monoclinic flanking structures. Triclinic and monoclinic flanking structures record elliptical displacement–distance profiles with steep displacement gradients at the fault tips by ductile flow in the host rocks, resulting in reverse drag of the foliation planes. These structures record one of the greatest maximum displacement/length ratios reported from natural fault structures. These exceptionally high ratios can be explained by localized antithetic displacement along brittle slip surfaces, which did not propagate during their rotation during surrounding ductile flow. PMID:26806996

Origins of the anomalous stress behavior in charged colloidal suspensions under shear.

Science.gov (United States)

Kumar, Amit; Higdon, Jonathan J L

2010-11-01

Numerical simulations are conducted to determine microstructure and rheology of sheared suspensions of charged colloidal particles at a volume fraction of ϕ=0.33. Over broad ranges of repulsive force strength F0 and Péclet number Pe, dynamic simulations show coexistence of ordered and disordered stable states with the state dependent on the initial condition. In contrast to the common view, at low shear rates, the disordered phase exhibits a lower viscosity (μ(r)) than the ordered phase, while this behavior is reversed at higher shear rates. Analysis shows the stress reversal is associated with different shear induced microstructural distortions in the ordered and disordered systems. Viscosity vs shear rate data over a wide range of F0 and Pe collapses well upon rescaling with the long-time self-diffusivity. Shear thinning viscosity in the ordered phase scaled as μ(r)∼Pe(-0.81) at low shear rates. The microstructural dynamics revealed in these studies explains the anomalous behavior and hysteresis loops in stress data reported in the literature.

Squatting-Related Tibiofemoral Shear Reaction Forces and a Biomechanical Rationale for Femoral Component Loosening

Directory of Open Access Journals (Sweden)

Ashvin Thambyah

2014-01-01

Full Text Available Previous gait studies on squatting have described a rapid reversal in the direction of the tibiofemoral joint shear reaction force when going into a full weight-bearing deep knee flexion squat. The effects of such a shear reversal have not been considered with regard to the loading demand on knee implants in patients whose activities of daily living require frequent squatting. In this paper, the shear reversal effect is discussed and simulated in a finite element knee implant-bone model, to evaluate the possible biomechanical significance of this effect on femoral component loosening of high flexion implants as reported in the literature. The analysis shows that one of the effects of the shear reversal was a switch between large compressive and large tensile principal strains, from knee extension to flexion, respectively, in the region of the anterior flange of the femoral component. Together with the known material limits of cement and bone, this large mismatch in strains as a function of knee position provides new insight into how and why knee implants may fail in patients who perform frequent squatting.

Reversible Watermarking Using Prediction-Error Expansion and Extreme Learning Machine

Directory of Open Access Journals (Sweden)

Guangyong Gao

2015-01-01

Full Text Available Currently, the research for reversible watermarking focuses on the decreasing of image distortion. Aiming at this issue, this paper presents an improvement method to lower the embedding distortion based on the prediction-error expansion (PE technique. Firstly, the extreme learning machine (ELM with good generalization ability is utilized to enhance the prediction accuracy for image pixel value during the watermarking embedding, and the lower prediction error results in the reduction of image distortion. Moreover, an optimization operation for strengthening the performance of ELM is taken to further lessen the embedding distortion. With two popular predictors, that is, median edge detector (MED predictor and gradient-adjusted predictor (GAP, the experimental results for the classical images and Kodak image set indicate that the proposed scheme achieves improvement for the lowering of image distortion compared with the classical PE scheme proposed by Thodi et al. and outperforms the improvement method presented by Coltuc and other existing approaches.

MHD instabilities leading to disruption in JT-60U reversed shear plasmas

International Nuclear Information System (INIS)

Takechi, M.; Fujita, T.; Ishii, Y.; Ozeki, T.; Suzuki, T.; Isayama, A.

2005-01-01

High performance reversed shear discharges with strong internal transport barrier (ITB) and flat pressure profile in the plasma core region disrupt frequently even with low beta. We analyzed MHD instabilities leading to low beta disruption with measuring fluctuations and current profile with MSE measurement. We mainly observed two type of disruptions. One is the disruption without precursor at q surf ∼integer. The other is the disruption with n=1 precursor of γ>10 ms. The poloidal mode number of the n=1 mode is equal to outermost integer of q. The n=1 mode exist from peripheral region to ITB layer or peripheral region and ITB and the phase is 180 degree different between them. To explain these characteristics of disruption, we introduce the simple model such as, disruption occurs when the both MHD instabilities at plasma surface and at safety factor being equal to surface mode are unstable. This simple model can explain almost all observed disruption by two process. One is the surface mode triggered disruption, which occurs when q surf change, corresponding q surface at ITB layer change discretely. The other is the internal mode triggered disruption, which occurs when corresponding q surface become unstable gradually. (author)

Large shear deformation of particle gels studied by Brownian Dynamics simulations

NARCIS (Netherlands)

Rzepiela, A.A.; Opheusden, van J.H.J.; Vliet, van T.

2004-01-01

Brownian Dynamics (BD) simulations have been performed to study structure and rheology of particle gels under large shear deformation. The model incorporates soft spherical particles, and reversible flexible bond formation. Two different methods of shear deformation are discussed, namely affine and

Gyrokinetic global analysis of ion temperature gradient driven mode in reversed shear tokamaks

International Nuclear Information System (INIS)

Idomura, Y.; Tokuda, S.; Kishimoto, Y.

2003-01-01

A new toroidal gyrokinetic particle code has been developed to study the ion temperature gradient driven (ITG) turbulence in reactor relevant tokamak parameters. We use a new method based on a canonical Maxwellian distribution F CM (P φ , ε, μ), which is defined by three constants of motion in the axisymmetric toroidal system, the canonical angular momentum P φ , the energy ε, and the magnetic moment μ. A quasi-ballooning representation enables linear and nonlinear high-m,n global calculations with a good numerical convergence. Conservation properties are improved by using the optimized loading method. From comprehensive linear global analyses over a wide range of an unstable toroidal mode number spectrum (n=0∼100) in large tokamak parameters (a/ρ ti =320∼460), properties of the ITG modes in reversed shear tokamaks are discussed. In the nonlinear simulation, it is found that a new method based on F CM can simulate a zonal flow damping correctly, and spurious zonal flow oscillations, which are observed in a conventional method based on a local Maxwellian distribution F LM (ψ, ε, μ), do not appear in the nonlinear regime. (author)

Inplane shear capacity of reinforced composite masonry block walls

International Nuclear Information System (INIS)

White, W.H.; Tseng, W.S.

1981-01-01

The objective of this paper is to describe a test program performed to determine the inplane shear capacity, stiffness and ductility of composite masonry walls subjected to earthquake type loadings. Specimens were simultaneously subjected to a range of compressive loads to simulate dead load; and inplane shear loads with full load reversal to simulate the earthquake cycling load. The influence of horizontal and vertical reinforcing steel percentages on the inplane shear capacity, stiffness and ductility was also investigated. (orig./HP)

Experimental Study of Reversed Shear Alfven Eigenmodes During The Current Ramp In The Alcator C-Mod Tokamak

International Nuclear Information System (INIS)

Edlund, E.M.; Porkolab, M.; Kramer, G.J.; Lin, L.; Lin, Y.; Tsuji, N.; Wukitch, S.J.

2010-01-01

Experiments conducted in the Alcator C-Mod tokamak at MIT have explored the physics of reversed shear Alfven eigenmodes (RSAEs) during the current ramp. The frequency evolution of the RSAEs throughout the current ramp provides a constraint on the evolution of q min , a result which is important in transport modeling and for comparison with other diagnostics which directly measure the magnetic field line structure. Additionally, a scaling of the RSAE minimum frequency with the sound speed is used to derive a measure of the adiabatic index, a measure of the plasma compressibility. This scaling bounds the adiabatic index at 1.40 ± 0.15 used in MHD models and supports the kinetic calculation of separate electron and ion compressibilities with an ion adiabatic index close to 7/4.

Extreme reversed sexual dichromatism in a bird without sex role reversal.

Science.gov (United States)

Heinsohn, Robert; Legge, Sarah; Endler, John A

2005-07-22

Brilliant plumage is typical of male birds, reflecting differential enhancement of male traits when females are the limiting sex. Brighter females are thought to evolve exclusively in response to sex role reversal. The striking reversed plumage dichromatism of Eclectus roratus parrots does not fit this pattern. We quantify plumage color in this species and show that very different selection pressures are acting on males and females. Male plumage reflects a compromise between the conflicting requirements for camouflage from predators while foraging and conspicuousness during display. Females are liberated from the need for camouflage but compete for rare nest hollows.

Overview of the ARIES-RS reversed-shear tokamak power plant study

International Nuclear Information System (INIS)

Najmabadi, F.; Billone, M.C.

1997-01-01

The ARIES-RS tokamak is a conceptual, D-T-burning 1000 MWe power plant. As with earlier ARIES design studies, the final design of ARIES-RS was obtained in a self-consistent manner using the best available physics and engineering models. Detailed analyses of individual systems together with system interfaces and interactions were incorporated into the ARIES systems code in order to assure self-consistency and to optimize towards the lowest cost system. The ARIES-RS design operates with a reversed-shear plasma and employs a moderate aspect ratio (A=4.0). The plasma current is relatively low (I p =11.32 MA) and bootstrap current fraction is high (f BC =0.88). Consequently, the auxiliary power required for RF current drive is relatively low (∝80 MW). At the same time, the average toroidal beta is high (β=5%), providing power densities near practical engineering limits (the peak neutron wall loading is 5.7 MW m -2 ). The toroidal-field (TF) coil system is designed with relatively 'conventional' materials (Nb 3 Sn and NbTi conductor with 316SS structures), and is operated at a design limit of ∝16 T at the coil in order to optimize the design point. The ARIES-RS design uses a self-cooled lithium blanket with vanadium alloy as the structural material. The V-alloy has low activation, low afterheat, high temperature capability and can handle high heat flux. A self-cooled liquid lithium blanket is simple, and with the development of an insulating coating, has low operating pressure. Also, this blanket gives excellent neutronics performance. Detailed analysis has been performed to minimize the cost and maximize the performance of the blanket and shield. (orig.)

The Cora Lake Shear Zone: Strain Localization in an Ultramylonitic, Deep Crustal Shear Zone, Athabasca Granulite Terrain, Western Churchill Province, Canada

Science.gov (United States)

Regan, S.; Williams, M. L.; Mahan, K. H.; Orlandini, O. F.; Jercinovic, M. J.; Leslie, S. R.; Holland, M.

2012-12-01

Ultramylonitic shear zones typically involve intense strain localization, and when developed over large regions can introduce considerable heterogeneity into the crust. The Cora Lake shear zone (CLsz) displays several 10's to 100's of meters-wide zones of ultramylonite distributed throughout its full 3-5 km mylonitized width. Detailed mapping, petrography, thermobarometry, and in-situ monazite geochronology suggest that it formed during the waning phases of granulite grade metamorphism and deformation, within one of North America's largest exposures of polydeformed lower continental crust. Anastomosing zones of ultramylonite contain recrystallized grain-sizes approaching the micron scale and might appear to suggest lower temperature mylonitization. However, feldspar and even clinopyroxene are dynamically recrystallized, and quantitative thermobarometry of syn-deformational assemblages indicate high P and T conditions ranging from 0.9 -10.6 GPa and 775-850 °C. Even at these high T's, dynamic recovery and recrystallization were extremely limited. Rocks with low modal quartz have extremely small equilibrium volumes. This is likely the result of inefficient diffusion, which is further supported by the unannealed nature of the crystals. Local carbonate veins suggests that H2O poor, CO2 rich conditions may have aided in the preservation of fine grain sizes, and may have inhibited dynamic recovery and recrystallization. The Cora Lake shear zone is interpreted to have been relatively strong and to have hardened during progressive deformation. Garnet is commonly fractured perpendicular to host rock fabric, and statically replaced by both biotite and muscovite. Pseudotachylite, with the same sense of shear, occurs in several ultramylonitized mafic granulites. Thus, cataclasis and frictional melt are interpreted to have been produced in the lower continental crust, not during later reactivation. We suggest that strengthening of rheologically stiffer lithologies led to

SHEAR ACCELERATION IN EXPANDING FLOWS

Energy Technology Data Exchange (ETDEWEB)

Rieger, F. M. [ZAH, Institut für Theoretische Astrophysik, Universität Heidelberg, Philosophenweg 12, D-69120 Heidelberg (Germany); Duffy, P., E-mail: frank.rieger@mpi-hd.mpg.de, E-mail: peter.duffy@ucd.ie [University College Dublin, Belfield, Dublin 4 (Ireland)

2016-12-10

Shear flows are naturally expected to occur in astrophysical environments and potential sites of continuous non-thermal Fermi-type particle acceleration. Here we investigate the efficiency of expanding relativistic outflows to facilitate the acceleration of energetic charged particles to higher energies. To this end, the gradual shear acceleration coefficient is derived based on an analytical treatment. The results are applied to the context of the relativistic jets from active galactic nuclei. The inferred acceleration timescale is investigated for a variety of conical flow profiles (i.e., power law, Gaussian, Fermi–Dirac) and compared to the relevant radiative and non-radiative loss timescales. The results exemplify that relativistic shear flows are capable of boosting cosmic-rays to extreme energies. Efficient electron acceleration, on the other hand, requires weak magnetic fields and may thus be accompanied by a delayed onset of particle energization and affect the overall jet appearance (e.g., core, ridge line, and limb-brightening).

Drift reversal capability in helical systems

International Nuclear Information System (INIS)

Yokoyama, M.; Itoh, K.; Okamura, S.

2002-10-01

The maximum-J (J is the second adiabatic invariant) capability, i.e., the drift reversal capability, is examined in quasi-axisymmetric (QAS) stellarators and quasi-poloidally symmetric (QPS) stellarators as a possible mechanism for turbulent transport suppression. Due to the existence of non-axisymmetry of the magnetic field strength in QAS configurations, a local maximum of J is created to cause the drift reversal. The increase of magnetic shear in finite beta equilibria also has favorable effect in realizing the drift reversal. The radial variation of the uniform magnetic field component plays a crucial role for the drift reversal in a QPS configuration. Thus, the drift reversal capability and its external controllability are demonstrated for QAS and QPS stellarators, by which the impact of magnetic configuration on turbulent transport can be studied in experiments. (author)

Drift reversal capability in helical systems

International Nuclear Information System (INIS)

Yokoyama, M.; Itoh, K.; Okamura, S.; Matsuoka, K.; Nakajima, N.; Itoh, S.-I.; Neilson, G.H.; Zarnstorff, M.C.; Rewoldt, G.

2003-01-01

The maximum-J (J is the second adiabatic invariant) capability, i.e., the drift reversal capability, is examined in quasi-axisymmetric (QAS) stellarators and quasi-poloidally symmetric (QPS) stellarators as a possible mechanism for turbulent transport suppression. Due to the existence of non-axisymmetry of the magnetic field strength in QAS configurations, a local maximum of J is created to cause the drift reversal. The increase of magnetic shear in finite beta equilibria also has favorable effect in realizing the drift reversal. The radial variation of the uniform magnetic field component plays a crucial role for the drift reversal in a QPS configuration. Thus, the drift reversal capability and its external controllability are demonstrated for QAS and QPS stellarators, by which the impact of magnetic configuration on turbulent transport can be studied in experiments. (author)

A study on plate anchor detailing systems of shear re-bar

International Nuclear Information System (INIS)

Tsurumaki, S.; Ujiie, K.; Nishikawa, T.; Kitayama, K.

1995-01-01

For shell walls and base slabs in reactor buildings, besides a large amount of main bars, numerous shear re-bars have been employed to resist to out-of-plane force. As a result , detailing work involving shear re-bar is extremely involved. For example, the employed re-bar anchor method differs from the ordinary methods in which, a end of shear re-bar with 135-degrees hook or with anchor plate type and another re-bar end with 90-degrees hook are used. However the structural characteristics in members using shear re-bar of the bolt-mounted anchor plate have not yet been examined. A test was performed to confirm the effects of anchor methods for shear re-bars on shearing behavior of members. This paper describes the test plan, method and results. (author). 12 figs., 7 tabs

Negative snakes in JET: evidence for negative shear

International Nuclear Information System (INIS)

Gill, R.D.; Alper, B.; Edwards, A.W.

1994-01-01

The signature of the negative snakes from the soft X-ray cameras is very similar to the more usual snakes except that the localised region of the snake has, compared with its surroundings, decreased rather than increased emission. Circumstances where negative snakes have been seen are reviewed. The negative snake appears as a region of increased resistance and of increased impurity density. The relationship between the shear and the current perturbation is shown, and it seem probable that the magnetic shear is reversed at the point of the negative snake, i.e. that q is decreasing with radius. 6 refs., 6 figs

Negative snakes in JET: evidence for negative shear

Energy Technology Data Exchange (ETDEWEB)

Gill, R D; Alper, B; Edwards, A W [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Pearson, D [Reading Univ. (United Kingdom)

1994-07-01

The signature of the negative snakes from the soft X-ray cameras is very similar to the more usual snakes except that the localised region of the snake has, compared with its surroundings, decreased rather than increased emission. Circumstances where negative snakes have been seen are reviewed. The negative snake appears as a region of increased resistance and of increased impurity density. The relationship between the shear and the current perturbation is shown, and it seem probable that the magnetic shear is reversed at the point of the negative snake, i.e. that q is decreasing with radius. 6 refs., 6 figs.

The brittle-viscous-plastic evolution of shear bands in the South Armorican Shear Zone

Science.gov (United States)

Bukovská, Zita; Jeřábek, Petr; Morales, Luiz F. G.; Lexa, Ondrej; Milke, Ralf

2014-05-01

Shear bands are microscale shear zones that obliquely crosscut an existing anisotropy such as a foliation. The resulting S-C fabrics are characterized by angles lower than 45° and the C plane parallel to shear zone boundaries. The S-C fabrics typically occur in granitoids deformed at greenschist facies conditions in the vicinity of major shear zones. Despite their long recognition, mechanical reasons for localization of deformation into shear bands and their evolution is still poorly understood. In this work we focus on microscale characterization of the shear bands in the South Armorican Shear Zone, where the S-C fabrics were first recognized by Berthé et al. (1979). The initiation of shear bands in the right-lateral South Armorican Shear Zone is associated with the occurrence of microcracks crosscutting the recrystallized quartz aggregates that define the S fabric. In more advanced stages of shear band evolution, newly formed dominant K-feldspar, together with plagioclase, muscovite and chlorite occur in the microcracks, and the shear bands start to widen. K-feldspar replaces quartz by progressively bulging into the grain boundaries of recrystallized quartz grains, leading to disintegration of quartz aggregates and formation of fine-grained multiphase matrix mixture. The late stages of shear band development are marked by interconnection of fine-grained white mica into a band that crosscuts the original shear band matrix. In its extremity, the shear band widening may lead to the formation of ultramylonites. With the increasing proportion of shear band matrix from ~1% to ~12%, the angular relationship between S and C fabrics increases from ~30° to ~40°. The matrix phases within shear bands show differences in chemical composition related to distinct evolutionary stages of shear band formation. The chemical evolution is well documented in K-feldspar, where the albite component is highest in porphyroclasts within S fabric, lower in the newly formed grains within

Evaluation of Shear Resisting Capacity of a Prestressed Concrete Containment Building with Steel or Polyamide Fiber Reinforcement

International Nuclear Information System (INIS)

Choun, Youngsun; Park, Junhee

2014-01-01

Conventional reinforced concrete (RC) members generally show a rapid deterioration in shear resisting mechanisms under a reversed cyclic load. However, the use of high-performance fiber-reinforced cement composites provides excellent damage tolerance under large displacement reversals compared with regular concrete. Previous experimental studies have indicated that the use of fibers in conventional RC can enhance the structural and functional performance of prestressed concrete containment buildings (PCCBs) in nuclear power plants. This study evaluates the shear resisting capacity for a PCCB constructed using steel fiber reinforced concrete (SFRC) or polyamide fiber reinforced concrete (PFRC). The effects of steel and polyamide fibers on the shear performance of a PCCB were investigated. It was revealed that steel fibers are more effective to enhance the shear resisting capacity of a PCCB than polyamide fibers. The ductility and energy dissipation increase significantly in fiber reinforced PCCBs

Evaluation of Shear Resisting Capacity of a Prestressed Concrete Containment Building with Steel or Polyamide Fiber Reinforcement

Energy Technology Data Exchange (ETDEWEB)

Choun, Youngsun; Park, Junhee [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2014-05-15

Conventional reinforced concrete (RC) members generally show a rapid deterioration in shear resisting mechanisms under a reversed cyclic load. However, the use of high-performance fiber-reinforced cement composites provides excellent damage tolerance under large displacement reversals compared with regular concrete. Previous experimental studies have indicated that the use of fibers in conventional RC can enhance the structural and functional performance of prestressed concrete containment buildings (PCCBs) in nuclear power plants. This study evaluates the shear resisting capacity for a PCCB constructed using steel fiber reinforced concrete (SFRC) or polyamide fiber reinforced concrete (PFRC). The effects of steel and polyamide fibers on the shear performance of a PCCB were investigated. It was revealed that steel fibers are more effective to enhance the shear resisting capacity of a PCCB than polyamide fibers. The ductility and energy dissipation increase significantly in fiber reinforced PCCBs.

Designing shear-thinning

Science.gov (United States)

Nelson, Arif Z.; Ewoldt, Randy H.

2017-11-01

Design in fluid mechanics often focuses on optimizing geometry (airfoils, surface textures, microfluid channels), but here we focus on designing fluids themselves. The dramatically shear-thinning ``yield-stress fluid'' is currently the most utilized non-Newtonian fluid phenomenon. These rheologically complex materials, which undergo a reversible transition from solid-like to liquid-like fluid flow, are utilized in pedestrian products such as paint and toothpaste, but also in emerging applications like direct-write 3D printing. We present a paradigm for yield-stress fluid design that considers constitutive model representation, material property databases, available predictive scaling laws, and the many ways to achieve a yield stress fluid, flipping the typical structure-to-rheology analysis to become the inverse: rheology-to-structure with multiple possible materials as solutions. We describe case studies of 3D printing inks and other flow scenarios where designed shear-thinning enables performance remarkably beyond that of Newtonian fluids. This work was supported by Wm. Wrigley Jr. Company and the National Science Foundation under Grant No. CMMI-1463203.

Spatial extreme value analysis to project extremes of large-scale indicators for severe weather.

Science.gov (United States)

Gilleland, Eric; Brown, Barbara G; Ammann, Caspar M

2013-09-01

Concurrently high values of the maximum potential wind speed of updrafts ( W max ) and 0-6 km wind shear (Shear) have been found to represent conducive environments for severe weather, which subsequently provides a way to study severe weather in future climates. Here, we employ a model for the product of these variables (WmSh) from the National Center for Atmospheric Research/United States National Center for Environmental Prediction reanalysis over North America conditioned on their having extreme energy in the spatial field in order to project the predominant spatial patterns of WmSh. The approach is based on the Heffernan and Tawn conditional extreme value model. Results suggest that this technique estimates the spatial behavior of WmSh well, which allows for exploring possible changes in the patterns over time. While the model enables a method for inferring the uncertainty in the patterns, such analysis is difficult with the currently available inference approach. A variation of the method is also explored to investigate how this type of model might be used to qualitatively understand how the spatial patterns of WmSh correspond to extreme river flow events. A case study for river flows from three rivers in northwestern Tennessee is studied, and it is found that advection of WmSh from the Gulf of Mexico prevails while elsewhere, WmSh is generally very low during such extreme events. © 2013 The Authors. Environmetrics published by JohnWiley & Sons, Ltd.

Simulation of lower hybrid current drive in enhanced reversed shear plasmas in the tokamak fusion test reactor using the lower hybrid simulation code

International Nuclear Information System (INIS)

Kaita, R.; Bernabei, S.; Budny, R.

1996-01-01

The Enhanced Reversed Shear (ERS) mode has already shown great potential for improving the performance of the Tokamak Fusion Test Reactor (TFTR) and other devices. Sustaining the ERS, however, remains an outstanding problem. Lower hybrid (LH) current drive is a possible method for modifying the current profile and controlling its time evolution. To predict its effectiveness in TFTR, the Lower Hybrid Simulation Code (LSC) model is used in the TRANSP code and the Tokamak Simulation Code (TSC). Among the results from the simulations are the following. (1) Single-pass absorption is expected in TFTR ERS plasmas. The simulations show that the LH current follows isotherms of the electron temperature. The ability to control the location of the minimum in the q profile (q min ) has been demonstrated by varying the phase velocity of the launched LH waves and observing the change in the damping location. (2) LH current drive can been used to sustain the q min location. The tendency of qmin to drift inward, as the inductive current diffuses during the formation phase of the reversed shear discharge, is prevented by the LH current driven at a fixed radial location. If this results in an expanded plasma volume with improved confinement as high power neutral beam injection is applied, the high bootstrap currents induced during this phase can then maintain the larger qmin radius. (3) There should be no LH wave damping on energetic beam particles. The values of perpendicular index of refraction in the calculations never exceed about 20, while ions at TFR injection energies are resonant with waves having values closer to 100. Other issues being addressed in the study include the LH current drive efficiency in the presence of high bootstrap currents, and the effect of fast electron diffusion on LH current localization

Two-fluid and nonlinear effects of tearing and pressure-driven resistive modes in reversed field pinches

International Nuclear Information System (INIS)

Mirnov, V.V.

2002-01-01

Large-scale tearing instabilities have long been considered to underlie transport and dynamo processes in the reversed field pinch (RFP). The vast majority of theoretical and computational RFP work has focused on pressureless, single-fluid MHD in cylindrical plasmas driven solely by a toroidal electric field. We report results of five investigations covering two-fluid dynamos, toroidal nonlinear MHD computation, nonlinear computation of Oscillating Field Current Drive (OFCD), the effect of shear flow on tearing instability, and the effect of pressure on resistive instability. The key findings are: (1) two-fluid dynamo arising from the Hall term is much larger than the standard MHD dynamo present in a single-fluid treatment, (2) geometric coupling from toroidicity precludes the occurrence of laminar single helicity states, except for nonreversed plasmas, (3) OFCD, a form of AC helicity injection, can sustain the RFP plasma current, although magnetic fluctuations are enhanced, (4) edge shear flow can destabilize the edge resonant m=0 modes, which occur as spikes in experiment, and (5) pressure driven modes are resistive at low beta, only becoming ideal at extremely high beta. (author)

An Innovative Adaptive Pushover Procedure Based on Storey Shear

International Nuclear Information System (INIS)

Shakeri, Kazem; Shayanfar, Mohsen A.

2008-01-01

Since the conventional pushover analyses are unable to consider the effect of the higher modes and progressive variation in dynamic properties, recent years have witnessed the development of some advanced adaptive pushover methods. However in these methods, using the quadratic combination rules to combine the modal forces result in a positive value in load pattern at all storeys and the reversal sign of the modes is removed; consequently these methods do not have a major advantage over their non-adaptive counterparts. Herein an innovative adaptive pushover method based on storey shear is proposed which can take into account the reversal signs in higher modes. In each storey the applied load pattern is derived from the storey shear profile; consequently, the sign of the applied loads in consecutive steps could be changed. Accuracy of the proposed procedure is examined by applying it to a 20-storey steel building. It illustrates a good estimation of the peak response in inelastic phase

Effects of low central fuelling on density and ion temperature profiles in reversed shear plasmas on JT-60U

Energy Technology Data Exchange (ETDEWEB)

Takenaga, H; Ide, S; Sakamoto, Y; Fujita, T [Japan Atomic Energy Agency, Naka Ibaraki 311-0193 (Japan)], E-mail: takenaga.hidenobu@jaea.go.jp

2008-07-15

Effects of low central fuelling on density and ion temperature profiles have been investigated using negative ion based neutral beam injection and electron cyclotron heating (ECH) in reversed shear plasmas on JT-60U. Strong internal transport barrier (ITB) was maintained in density and ion temperature profiles, when central fuelling was decreased by switching positive ion based neutral beam injection to ECH after the strong ITB formation. Similar density and ion temperature ITBs were formed for the low and high central fuelling cases during the plasma current ramp-up phase. Strong correlation between the density gradient and the ion temperature gradient was observed, indicating that particle transport and ion thermal transport are strongly coupled or the density gradient assists the ion temperature ITB formation through suppression of drift wave instabilities such as ion temperature gradient mode. These results support that the density and ion temperature ITBs can be formed under reactor relevant conditions.

Effects of low central fuelling on density and ion temperature profiles in reversed shear plasmas on JT-60U

Science.gov (United States)

Takenaga, H.; Ide, S.; Sakamoto, Y.; Fujita, T.; JT-60 Team

2008-07-01

Effects of low central fuelling on density and ion temperature profiles have been investigated using negative ion based neutral beam injection and electron cyclotron heating (ECH) in reversed shear plasmas on JT-60U. Strong internal transport barrier (ITB) was maintained in density and ion temperature profiles, when central fuelling was decreased by switching positive ion based neutral beam injection to ECH after the strong ITB formation. Similar density and ion temperature ITBs were formed for the low and high central fuelling cases during the plasma current ramp-up phase. Strong correlation between the density gradient and the ion temperature gradient was observed, indicating that particle transport and ion thermal transport are strongly coupled or the density gradient assists the ion temperature ITB formation through suppression of drift wave instabilities such as ion temperature gradient mode. These results support that the density and ion temperature ITBs can be formed under reactor relevant conditions.

Interchange stability of noncircular reversed field pinches

International Nuclear Information System (INIS)

Skinner, D.A.; Prager, S.C.; Todd, A.M.M.

1987-08-01

Interchange (Mercier) stability of toroidal reversed-field-pinch plasmas with noncircular cross-section is evaluated numerically. Marginally stable pressure profiles and beta values are produced. Most shapes, such as indented or vertically elongated, reduce stability by making the net magnetic curvature of the poloidal-field-dominated plasmas yet worse than that of the circle. Horizontally elongated plasmas slightly enhance stability beyond that of the circle as a result of increased shear produced by toroidicity. Such shear enhancement by the toroidal shift of magnetic surfaces might be exploited for future, more comprehensive studies

Brownian dynamics simulations of an order-disorder transition in sheared sterically stabilized colloidal suspensions

International Nuclear Information System (INIS)

Rigos, A.A.; Wilemski, G.

1992-01-01

The shear thinning behavior of a sterically stabilized nonaqueous colloidal suspension was investigated using nonequilibrium Brownian dynamics simulations of systems with 108 and 256 particles. At a volume fraction of 0.4, the suspension is thixotropic: it has a reversible shear thinning transition from a disordered state to an ordered, lamellar state with triangularly packed strings of particles. The time scale for the transition is set by the free particle diffusion constant. For the smaller system, the transition occurs gradually with increasing shear rate. For the larger system, the transition is sharp and discontinuous shear thinning is found. 34 refs., 9 figs., 1 tab

Development of Flexible Extremities Protection utilizing Shear Thickening Fluid/Fabric Composites

Science.gov (United States)

2012-01-19

The influence of Interparticle Interactions and Hydrodynamic Forces on Shear Thickening in Concentrated Colloidal Dispersions and Slurries 10...Armor Using Fumed SiO2 Nanoparticles Dispersed into Polyethylene Glycol (PEG) through Sonic Cavitation , NSTI-Nanotech 2006. 2006/05/07 00:00:00...for a wide variety of suspensions such as clay–water [17], calcium carbonate–water [18], polystyrene spheres in silicon oil [19], iron particles in

Hydrodynamic of a deformed bubble in linear shear flow; Hydrodynamique d'une bulle deformee dans un ecoulement cisaille

Energy Technology Data Exchange (ETDEWEB)

Adoua, S.R

2007-07-15

This work is devoted to the study of an oblate spheroidal bubble of prescribed shape set fixed in a linear shear flow using direct numerical simulation. The three dimensional Navier-Stokes equations are solved in orthogonal curvilinear coordinates using a finite volume method. The bubble response is studied over a wide range of the aspect ratio (1-2.7), the bubble Reynolds number (50-2000) and the non-dimensional shear rate (0.-1.2). The numerical simulations shows that the shear flow imposes a plane symmetry of the wake whatever the parameters of the flow. The trailing vorticity is organized into two anti-symmetrical counter rotating tubes with a sign imposed by the competition of two mechanisms (the Lighthill mechanism and the instability of the wake). Whatever the Reynolds number, the lift coefficient reaches the analytical value obtained in an inviscid, weakly sheared flow corresponding to a lift force oriented in the same direction as that of a spherical bubble. For moderate Reynolds numbers, the direction of the lift force reverses when the bubble aspect ratio is large enough as observed in experiments. This reversal occurs for aspect ratios larger than 2.225 and is found to be directly linked to the sign of the trailing vorticity which is concentrated within two counter-rotating threads which propel the bubble in a direction depending of their sign of rotation. The behavior of the drag does not revel any significant effect induced by the wake structure and follows a quadratic increase with the shear rate. Finally, the torque experienced by the bubble also reverses for the same conditions inducing the reversal of the lift force. By varying the orientation of the bubble in the shear flow, a stable equilibrium position is found corresponding to a weak angle between the small axis of the bubble and the flow direction. (author)

Origin of the Sheared Magnetic Fields that Erupt in Flares and Coronal Mass Ejections

Science.gov (United States)

Moore, Ronald L.; Sterling, Alphonse C.

2006-01-01

From a search of the Yohkoh/SXT whole-Sun movie in the years 2000 and 2001, we found 37 flare-arcade events for which there were full-disk magnetograms from SOHO/MDI, coronagraph movies from SOHO/LASCO, and before and after full-disk chromospheric images from SOHOBIT and/or from ground-based observatories. For each event, the observations show or strongly imply that the flare arcade was produced in the usual way by the eruption of sheared core field (as a flux rope) from along the neutral line inside a mature bipolar magnetic arcade. Two-thirds (25) of these arcades had the normal leading-trailing magnetic polarity arrangement of the active regions in the hemisphere of the arcade, but the other third (12) had reversed polarity, their leading flux being the trailing-polarity remnant of one or more old active regions and their trailing flux being the leading-polarity remnant of one or more other old active regions. From these observations, we conclude: (1) The sheared core field in a reversed-polarity arcade must be formed by processes in and above the photosphere, not by the emergence of a twisted flux rope bodily from below the photosphere. (2) The sheared core fields in the normal-polarity arcades were basically the same as those in the reversed-polarity arcades: both showed similar sigmoidal form and produced similar explosions (similar flares and CMEs). (3) Hence, the sheared core fields in normal-polarity mature arcades are likely formed mainly by the same processes as in reversed-polarity arcades. (4) These processes should be discernible in high-resolution magnetogram sequences and movies of the photosphere, chromosphere, and corona such those to come from Solar-B

Experimental Research on Boundary Shear Stress in Typical Meandering Channel

Science.gov (United States)

Chen, Kai-hua; Xia, Yun-feng; Zhang, Shi-zhao; Wen, Yun-cheng; Xu, Hua

2018-06-01

A novel instrument named Micro-Electro-Mechanical System (MEMS) flexible hot-film shear stress sensor was used to study the boundary shear stress distribution in the generalized natural meandering open channel, and the mean sidewall shear stress distribution along the meandering channel, and the lateral boundary shear stress distribution in the typical cross-section of the meandering channel was analysed. Based on the measurement of the boundary shear stress, a semi-empirical semi-theoretical computing approach of the boundary shear stress was derived including the effects of the secondary flow, sidewall roughness factor, eddy viscosity and the additional Reynolds stress, and more importantly, for the first time, it combined the effects of the cross-section central angle and the Reynolds number into the expressions. Afterwards, a comparison between the previous research and this study was developed. Following the result, we found that the semi-empirical semi-theoretical boundary shear stress distribution algorithm can predict the boundary shear stress distribution precisely. Finally, a single factor analysis was conducted on the relationship between the average sidewall shear stress on the convex and concave bank and the flow rate, water depth, slope ratio, or the cross-section central angle of the open channel bend. The functional relationship with each of the above factors was established, and then the distance from the location of the extreme sidewall shear stress to the bottom of the open channel was deduced based on the statistical theory.

Effects of extreme wind shear on aeroelastic modal damping of wind turbines

DEFF Research Database (Denmark)

Skjoldan, P.F.; Hansen, Morten Hartvig

2013-01-01

Wind shear is an important contributor to fatigue loads on wind turbines. Because it causes an azimuthal variation in angle of attack, it can also affect aerodynamic damping. In this paper, a linearized model of a wind turbine, based on the nonlinear aeroelastic code BHawC, is used to investigate...

Extremely rapid directional change during Matuyama-Brunhes geomagnetic polarity reversal

Science.gov (United States)

Sagnotti, Leonardo; Scardia, Giancarlo; Giaccio, Biagio; Liddicoat, Joseph C.; Nomade, Sebastien; Renne, Paul R.; Sprain, Courtney J.

2014-11-01

We report a palaeomagnetic investigation of the last full geomagnetic field reversal, the Matuyama-Brunhes (M-B) transition, as preserved in a continuous sequence of exposed lacustrine sediments in the Apennines of Central Italy. The palaeomagnetic record provides the most direct evidence for the tempo of transitional field behaviour yet obtained for the M-B transition. 40Ar/39Ar dating of tephra layers bracketing the M-B transition provides high-accuracy age constraints and indicates a mean sediment accumulation rate of about 0.2 mm yr-1 during the transition. Two relative palaeointensity (RPI) minima are present in the M-B transition. During the terminus of the upper RPI minimum, a directional change of about 180 ° occurred at an extremely fast rate, estimated to be less than 2 ° per year, with no intermediate virtual geomagnetic poles (VGPs) documented during the transit from the southern to northern hemisphere. Thus, the entry into the Brunhes Normal Chron as represented by the palaeomagnetic directions and VGPs developed in a time interval comparable to the duration of an average human life, which is an order of magnitude more rapid than suggested by current models. The reported investigation therefore provides high-resolution integrated palaeomagnetic and radioisotopic data that document the fine details of the anatomy and tempo of the M-B transition in Central Italy that in turn are crucial for a better understanding of Earth's magnetic field, and for the development of more sophisticated models that are able to describe its global structure and behaviour.

Reconnection During Periods of Large IMF By Producing Shear Instabilities at the Dayside Convection Reversal Boundary

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Qamar, S.; Clauer, C. R.; Hartinger, M.; Xu, Z.

2017-12-01

During periods of large interplanetary magnetic field (IMF) By component and small negative Bz (GSM Coordinates), the ionospheric polar electric potential system is distorted so as to produce large east-west convection shears across local noon. Past research has shown examples of ULF waves with periods of approximately 10 - 20 minutes observed at this convection shear by the Greenland west coast chain of magnetometers. Past work has shown examples of these waves and associated them with conditions in the solar wind and IMF, particularly periods of large IMF By component. Here we report the results of a search of several years of solar wind data to identify periods when the IMF By component is large and the magnetometer chains along the 40-degree magnetic meridian (Greenland west coast and conjugate Antarctic chains) are within a few hours of local noon. We test here the hypothesis that large IMF By reconnection leads to large convection shears across local noon that generate ULF waves through, presumably, a shear instability such as Kelvin-Helmholtz.

Role of low order rational q-values in the ITB events in JT-60U reverse shear plasmas

International Nuclear Information System (INIS)

Neudatchin, S.V.; Takizuka, T.; Hayashi, N.; Isayama, A.; Shirai, H.; Fujita, T.; Kamada, Y.; Koide, Y.; Suzuki, T.

2004-01-01

Non-local confinement bifurcations inside and around internal transport barriers (ITBs) with a ms timescale (ITB events) have previously been found in JT-60U reverse shear (RS) and high-β p plasmas. ITB events are observed as the simultaneous rise and decay of T e in two zones. They are created by an abrupt non-local reduction (or increase) of heat flux inside 30-40% of the minor radius. Under sufficient neutral beam power P nbi (above ∼8 MW for the 1.2-1.5 MA/3.8 T pulses described below), ITB events were previously detected at various q min values. However, the role of q min equal to 3.5, 3, 2.5, 2 is not obvious for ITB formation. In this paper, we focus on new features of ITB evolution near low-order-rational values of q min . The formation of a stronger ITB and its further splitting into two radially separated ITBs is described. These ITBs are located in both positive and negative shear zones of a plasma with L-mode edge. The similarity of space-time evolution of T e and T i at sufficient power is highlighted (even when the variation is significant and complicated in space and time). Within error-bars, ITB splitting occurs as q min passes through 2.5. The similarity of space-time evolution of T e and T i suggests a similarity in the qualitative behaviour of electron and ion heat diffusivities in time and space. The temporal formation of an ITB in the zone with small positive shear, while q min passes through 3 (after periodical improvements and degradations via ITB events with 8 ms period) in H-mode, with P nbi = 8 MW, is described. At lower powers, ITB events are observed only near rational values of q min . In weak RS shots with P nbi = 4 MW, transport is reduced via ITB events during 0.08 s at q min = 3.5, and repetitive short-term phases of reduced transport are observed as q min passes through 3. The behaviour of T i looks different. The difference in T e and T i evolution, which was detected regularly under low power, probably indicates a decoupling

Interaction between the Stress Phase Angle (SPA and the Oscillatory Shear Index (OSI Affects Endothelial Cell Gene Expression.

Directory of Open Access Journals (Sweden)

Ronny Amaya

Full Text Available Hemodynamic forces play an important role in the non-uniform distribution of atherosclerotic lesions. Endothelial cells are exposed simultaneously to fluid wall shear stress (WSS and solid circumferential stress (CS. Due to variations in impedance (global factors and geometric complexities (local factors in the arterial circulation a time lag arises between these two forces that can be characterized by the temporal phase angle between CS and WSS (stress phase angle-SPA. Asynchronous flows (SPA close to -180° that are most prominent in coronary arteries have been associated with localization of atherosclerosis. Reversing oscillatory flows characterized by an oscillatory shear index (OSI that is great than zero are also associated with atherosclerosis localization. In this study we examined the relationship between asynchronous flows and reversing flows in altering the expression of 37 genes relevant to atherosclerosis development. In the case of reversing oscillatory flow, we observed that the asynchronous condition upregulated 8 genes compared to synchronous hemodynamics, most of them proatherogenic. Upregulation of the pro-inflammatory transcription factor NFκB p65 was confirmed by western blot, and nuclear translocation of NFκB p65 was confirmed by immunofluorescence staining. A comparative study between non-reversing flow and reversing flow found that in the case of synchronous hemodynamics, reversing flow altered the expression of 11 genes, while in the case of asynchronous hemodynamics, reversing flow altered the expression of 17 genes. Reversing flow significantly upregulated protein expression of NFκB p65 for both synchronous and asynchronous conditions. Nuclear translocation of NFκB p65 was confirmed for synchronous and asynchronous conditions in the presence of flow reversal. These data suggest that asynchronous hemodynamics and reversing flow can elicit proatherogenic responses in endothelial cells compared to synchronous

Strength and stiffness of uniaxially tensioned reinforced concrete panels subjected to membrane shear. Technical report

International Nuclear Information System (INIS)

Hilmy, S.I.; White, R.N.; Gergely, P.

1982-06-01

This report presents experimental and analytical results on internal pressurization effects and seismic shear effects in a concrete containment vessel that is cracked by tension in one direction only. The experimental program, which was restricted to 6 in. thick flat specimens with two-way reinforcement, included establishment of (a) extensional stiffness for uniaxially tensioned specimens stressed to 0.6fy, and (b) shear strength and stiffness of these cracked specimens with tension levels ranging from 0 to 0.9fy; values were about 10 to 15 percent higher than in similar biaxially tensioned specimens. Eleven (11) specimens were tested (6 in monotonic shear and 5 in reversing cyclic shear)

Combined shearing interferometer and hartmann wavefront sensor

International Nuclear Information System (INIS)

Hutchin, R. A.

1985-01-01

A sensitive wavefront sensor combining attributes of both a Hartmann type of wavefront sensor and an AC shearing interferometer type of wavefront sensor. An incident wavefront, the slope of which is to be detected, is focussed to first and second focal points at which first and second diffraction gratings are positioned to shear and modulate the wavefront, which then diverges therefrom. The diffraction patterns of the first and second gratings are positioned substantially orthogonal to each other to shear the wavefront in two directions to produce two dimensional wavefront slope data for the AC shearing interferometer portion of the wavefront sensor. First and second dividing optical systems are positioned in the two diverging wavefronts to divide the sheared wavefront into an array of subapertures and also to focus the wavefront in each subaperture to a focal point. A quadrant detector is provided for each subaperture to detect the position of the focal point therein, which provides a first indication, in the manner of a Hartmann wavefront sensor, of the local wavefront slope in each subaperture. The total radiation in each subaperture, as modulated by the diffraction grating, is also detected by the quadrant detector which produces a modulated output signal representative thereof, the phase of which relative to modulation by the diffraction grating provides a second indication of the local wavefront slope in each subaperture, in the manner of an AC shearing interferometer wavefront sensor. The data from both types of sensors is then combined by long term averaging thereof to provide an extremely sensitive wavefront sensor

Shear melting and high temperature embrittlement: theory and application to machining titanium.

Science.gov (United States)

Healy, Con; Koch, Sascha; Siemers, Carsten; Mukherji, Debashis; Ackland, Graeme J

2015-04-24

We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.

Yield of reversible colloidal gels during flow start-up: release from kinetic arrest.

Science.gov (United States)

Johnson, Lilian C; Landrum, Benjamin J; Zia, Roseanna N

2018-06-05

Yield of colloidal gels during start-up of shear flow is characterized by an overshoot in shear stress that accompanies changes in network structure. Prior studies of yield of reversible colloidal gels undergoing strong flow model the overshoot as the point at which network rupture permits fluidization. However, yield under weak flow, which is of interest in many biological and industrial fluids shows no such disintegration. The mechanics of reversible gels are influenced by bond strength and durability, where ongoing rupture and re-formation impart aging that deepens kinetic arrest [Zia et al., J. Rheol., 2014, 58, 1121], suggesting that yield be viewed as release from kinetic arrest. To explore this idea, we study reversible colloidal gels during start-up of shear flow via dynamic simulation, connecting rheological yield to detailed measurements of structure, bond dynamics, and potential energy. We find that pre-yield stress grows temporally with the changing roles of microscopic transport processes: early time behavior is set by Brownian diffusion; later, advective displacements permit relative particle motion that stretches bonds and stores energy. Stress accumulates in stretched, oriented bonds until yield, which is a tipping point to energy release, and is passed with a fully intact network, where the loss of very few bonds enables relaxation of many, easing glassy arrest. This is immediately followed by a reversal to growth in potential energy during bulk plastic deformation and condensation into larger particle domains, supporting the view that yield is an activated release from kinetic arrest. The continued condensation of dense domains and shrinkage of network surfaces, along with a decrease in the potential energy, permit the gel to evolve toward more complete phase separation, supporting our view that yield of weakly sheared gels is a 'non-equilibrium phase transition'. Our findings may be particularly useful for industrial or other coatings, where weak

Shear Elasticity and Shear Viscosity Imaging in Soft Tissue

Science.gov (United States)

Yang, Yiqun

In this thesis, a new approach is introduced that provides estimates of shear elasticity and shear viscosity using time-domain measurements of shear waves in viscoelastic media. Simulations of shear wave particle displacements induced by an acoustic radiation force are accelerated significantly by a GPU. The acoustic radiation force is first calculated using the fast near field method (FNM) and the angular spectrum approach (ASA). The shear waves induced by the acoustic radiation force are then simulated in elastic and viscoelastic media using Green's functions. A parallel algorithm is developed to perform these calculations on a GPU, where the shear wave particle displacements at different observation points are calculated in parallel. The resulting speed increase enables rapid evaluation of shear waves at discrete points, in 2D planes, and for push beams with different spatial samplings and for different values of the f-number (f/#). The results of these simulations show that push beams with smaller f/# require a higher spatial sampling rate. The significant amount of acceleration achieved by this approach suggests that shear wave simulations with the Green's function approach are ideally suited for high-performance GPUs. Shear wave elasticity imaging determines the mechanical parameters of soft tissue by analyzing measured shear waves induced by an acoustic radiation force. To estimate the shear elasticity value, the widely used time-of-flight method calculates the correlation between shear wave particle velocities at adjacent lateral observation points. Although this method provides accurate estimates of the shear elasticity in purely elastic media, our experience suggests that the time-of-flight (TOF) method consistently overestimates the shear elasticity values in viscoelastic media because the combined effects of diffraction, attenuation, and dispersion are not considered. To address this problem, we have developed an approach that directly accounts for all

Shear machines

International Nuclear Information System (INIS)

Astill, M.; Sunderland, A.; Waine, M.G.

1980-01-01

A shear machine for irradiated nuclear fuel elements has a replaceable shear assembly comprising a fuel element support block, a shear blade support and a clamp assembly which hold the fuel element to be sheared in contact with the support block. A first clamp member contacts the fuel element remote from the shear blade and a second clamp member contacts the fuel element adjacent the shear blade and is advanced towards the support block during shearing to compensate for any compression of the fuel element caused by the shear blade (U.K.)

Intra-Continental Deformation by Mid-Crustal Shearing and Doming in a Cenozoic Compressive Setting Along the Ailao Shan-Red River Shear Zone

Science.gov (United States)

Zhang, B.

2016-12-01

Large-scale lateral strike-slip shear zones have been a key point in the debate about the deformation mechanisms of Asia in response to the India-Asia collision. The exhumed gneiss has been attributed to lateral strike-slip shear zone. This hypothesis has been challenged by recent discoveries indicating that a contractional doming deformation prior to the initiation of lateral strike-slip shearing. The Cenozoic Xuelong Shan antiformal dome is located at the northern segment of the Ailao Shan-Red River shear zone. Subhorizontal foliation in the gneiss core are recognized, representing a broad top-to-NE shear initiated under amphibolite facies conditions and propagated into greenschist facies in the mantling schist and strike-slip shear zone. Quartz CPOs and opening angles of crossed girdle fabrics in quartz suggest that the deformation temperatures increased with increasing structural depth from 300-500 °C in the mantling schist to ≥650 °C in the gneissic core. This trend is mirrored by variations in the metamorphic grade of the syn-kinematic mineral assemblages and microstructures, which ranges from garnet + amphibole + biotite + sillimanite + rutite + feldspar in the core to garnet + staurolite + biotite + epidote + muscovite within the limb units. Five-stage deformation is identified: (1) a broad top-to-NE shear in the subhorizontal level (D1); (2) opposing reverse-sense shear along the two schist limbs of the dome during contraction-related doming (D2-D3); (3) sinistral strike-slip shearing within the eastern limb (D4); and (4) extensional deformation (D5). The antiformal dome formation had been roughly coeval with top-to-NE ductile shearing in the mid-crust at 32 Ma or earlier. The geometries of the antiformal dome in the Xuelong Shan dome are similar to those associated with the antiform in the Dai Nui Con Voi, Diancang Shan and Ailao Shan zones. It is likely that the complex massifs, which define a regional linear gneiss dome zone in Cenozoic intra

Rational Calibration of Four IEC 61400-1 Extreme External Conditions

DEFF Research Database (Denmark)

Larsen, Gunner Chr.; Hansen, Kurt Schaldemose

2008-01-01

Based on a set of asymptotic statistical models on closed form this paper presents a rational and consistent calibration of four extreme external conditions defined in the International Electrotechnical Commission (IEC) 61400-1 standard: extreme operating gust, extreme wind shear, extreme coheren...... and proposed specifications of the magnitudes of the extreme external wind conditions are highlighted and discussed using an illustrative example based on two selected terrain types. Copyright © 2008 John Wiley & Sons, Ltd....... gust with direction change and extreme wind direction change. These four extreme external conditions are used in the definition of six of the IEC 61400-1 ultimate load cases. The statistical models are based on simple and easily accessible mean wind speed and turbulence characteristics...

Magnetic reversals from planetary dynamo waves.

Science.gov (United States)

Sheyko, Andrey; Finlay, Christopher C; Jackson, Andrew

2016-11-24

A striking feature of many natural dynamos is their ability to undergo polarity reversals. The best documented example is Earth's magnetic field, which has reversed hundreds of times during its history. The origin of geomagnetic polarity reversals lies in a magnetohydrodynamic process that takes place in Earth's core, but the precise mechanism is debated. The majority of numerical geodynamo simulations that exhibit reversals operate in a regime in which the viscosity of the fluid remains important, and in which the dynamo mechanism primarily involves stretching and twisting of field lines by columnar convection. Here we present an example of another class of reversing-geodynamo model, which operates in a regime of comparatively low viscosity and high magnetic diffusivity. This class does not fit into the paradigm of reversal regimes that are dictated by the value of the local Rossby number (the ratio of advection to Coriolis force). Instead, stretching of the magnetic field by a strong shear in the east-west flow near the imaginary cylinder just touching the inner core and parallel to the axis of rotation is crucial to the reversal mechanism in our models, which involves a process akin to kinematic dynamo waves. Because our results are relevant in a regime of low viscosity and high magnetic diffusivity, and with geophysically appropriate boundary conditions, this form of dynamo wave may also be involved in geomagnetic reversals.

Reverse Saphenous Conduit Flap in 19 Dogs and 1 Cat.

Science.gov (United States)

Cavalcanti, Jacqueline V J; Barry, Sabrina L; Lanz, Otto I; Barnes, Katherine; Coutin, Julia V

2018-05-14

The purpose of this retrospective study was to report the outcomes of 19 dogs and 1 cat undergoing reverse saphenous conduit flap between 1999 and 2016. Reverse saphenous conduit flap was used to treat traumatic wounds and wounds resulting from tumor excision in the hind limb; the majority of cases had medial shearing injuries. All animals had complete flap survival. In five animals (20%), minor donor site dehiscence occurred, which did not require surgery. Other postoperative complications included signs of severe venous congestion in one dog. Reverse saphenous conduit flap is a useful technique to repair skin defects of the distal hind limb.

Constraining the reversing and non-reversing modes of the geodynamo. New insights from magnetostratigraphy.

Science.gov (United States)

Gallet, Y.; Pavlov, V.; Shatsillo, A.; Hulot, G.

2015-12-01

Constraining the evolution in the geomagnetic reversal frequency over hundreds of million years is not a trivial matter. Beyond the fact that there are long periods without reversals, known as superchrons, and periods with many reversals, the way the reversal frequency changes through time during reversing periods is still debated. A smooth evolution or a succession of stationary segments have both been suggested to account for the geomagnetic polarity time scale since the Middle-Late Jurassic. Sudden changes from a reversing mode to a non-reversing mode of the geodynamo may also well have happened, the switch between the two modes having then possibly been controlled by the thermal conditions at the core-mantle boundary. There is, nevertheless, a growing set of magnetostratigraphic data, which could help decipher a proper interpretation of the reversal history, in particular in the early Paleozoic and even during the Precambrian. Although yielding a fragmentary record, these data reveal the occurrence of both additional superchrons and periods characterized by extremely high, not to say extraordinary, magnetic reversal frequencies. In this talk, we will present a synthesis of these data, mainly obtained from Siberia, and discuss their implication for the magnetic reversal behavior over the past billion years.

Thermal conductivity of graphene nanoribbons under shear deformation: A molecular dynamics simulation

Science.gov (United States)

Zhang, Chao; Hao, Xiao-Li; Wang, Cui-Xia; Wei, Ning; Rabczuk, Timon

2017-01-01

Tensile strain and compress strain can greatly affect the thermal conductivity of graphene nanoribbons (GNRs). However, the effect of GNRs under shear strain, which is also one of the main strain effect, has not been studied systematically yet. In this work, we employ reverse nonequilibrium molecular dynamics (RNEMD) to the systematical study of the thermal conductivity of GNRs (with model size of 4 nm × 15 nm) under the shear strain. Our studies show that the thermal conductivity of GNRs is not sensitive to the shear strain, and the thermal conductivity decreases only 12–16% before the pristine structure is broken. Furthermore, the phonon frequency and the change of the micro-structure of GNRs, such as band angel and bond length, are analyzed to explore the tendency of thermal conductivity. The results show that the main influence of shear strain is on the in-plane phonon density of states (PDOS), whose G band (higher frequency peaks) moved to the low frequency, thus the thermal conductivity is decreased. The unique thermal properties of GNRs under shear strains suggest their great potentials for graphene nanodevices and great potentials in the thermal managements and thermoelectric applications. PMID:28120921

Shearing-induced asymmetry in entorhinal grid cells.

Science.gov (United States)

Stensola, Tor; Stensola, Hanne; Moser, May-Britt; Moser, Edvard I

2015-02-12

Grid cells are neurons with periodic spatial receptive fields (grids) that tile two-dimensional space in a hexagonal pattern. To provide useful information about location, grids must be stably anchored to an external reference frame. The mechanisms underlying this anchoring process have remained elusive. Here we show in differently sized familiar square enclosures that the axes of the grids are offset from the walls by an angle that minimizes symmetry with the borders of the environment. This rotational offset is invariably accompanied by an elliptic distortion of the grid pattern. Reversing the ellipticity analytically by a shearing transformation removes the angular offset. This, together with the near-absence of rotation in novel environments, suggests that the rotation emerges through non-coaxial strain as a function of experience. The systematic relationship between rotation and distortion of the grid pattern points to shear forces arising from anchoring to specific geometric reference points as key elements of the mechanism for alignment of grid patterns to the external world.

Effects of cooling rate on particle rearrangement statistics: Rapidly cooled glasses are more ductile and less reversible.

Science.gov (United States)

Fan, Meng; Wang, Minglei; Zhang, Kai; Liu, Yanhui; Schroers, Jan; Shattuck, Mark D; O'Hern, Corey S

2017-02-01

Amorphous solids, such as metallic, polymeric, and colloidal glasses, display complex spatiotemporal response to applied deformations. In contrast to crystalline solids, during loading, amorphous solids exhibit a smooth crossover from elastic response to plastic flow. In this study, we investigate the mechanical response of binary Lennard-Jones glasses to athermal, quasistatic pure shear as a function of the cooling rate used to prepare them. We find several key results concerning the connection between strain-induced particle rearrangements and mechanical response. We show that the energy loss per strain dU_{loss}/dγ caused by particle rearrangements for more rapidly cooled glasses is larger than that for slowly cooled glasses. We also find that the cumulative energy loss U_{loss} can be used to predict the ductility of glasses even in the putative linear regime of stress versus strain. U_{loss} increases (and the ratio of shear to bulk moduli decreases) with increasing cooling rate, indicating enhanced ductility. In addition, we characterized the degree of reversibility of particle motion during a single shear cycle. We find that irreversible particle motion occurs even in the linear regime of stress versus strain. However, slowly cooled glasses, which undergo smaller rearrangements, are more reversible during a single shear cycle than rapidly cooled glasses. Thus, we show that more ductile glasses are also less reversible.

EFFECT OF ION ∇ B DRIFT DIRECTION ON TURBULENCE FLOW AND FLOW SHEAR

International Nuclear Information System (INIS)

FENZI, C; McKEE, G.R; BURRELL, K.H; CARLSTROM, T.N; FONCK, R.J; GROEBNER, R.J

2003-01-01

The divertor magnetic geometry has a significant effect on the poloidal flow and resulting flow shear of turbulence in the outer region of L-mode tokamak plasmas, as determined via two-dimensional measurements of density fluctuations with Beam Emission Spectroscopy on DIII-D. Plasmas with similar parameters, except that in one case the ion (del)B drift points towards the divertor X-point (lower single-null, LSN), and in the other case, the ion (del)B drift points away from the divertor X-point (upper single-null, USN), are compared. Inside of r/a=0.9, the turbulence characteristics (amplitude, flow direction, correlation lengths) are similar in both cases, while near r/a=0.92, a dramatic reversal of the poloidal flow of turbulence relative to the core flow direction is observed in plasmas with the ion (del)B drift pointing towards the divertor X-point. No such flow reversal is observed in plasmas with the ion (del)B drift pointing away from the divertor X-point. This poloidal flow reversal results in a significantly larger local shear in the poloidal turbulence flow velocity in plasmas with the ion (del)B drift pointing towards the divertor X-point. Additionally, these plasmas locally exhibit significant dispersion, with two distinct and counter-propagating turbulence modes. Likewise, the radial correlation length of the turbulence is reduced in these plasmas, consistent with biorthogonal decomposition measurements of dominant turbulence structures. The naturally occurring turbulence flow shear in these LSN plasmas may facilitate the LH transition that occurs at an input power of roughly one-half to one-third that of corresponding plasmas with the ion (del)B drift pointing away from the X-point

Extreme emulsification: formation and structure of nanoemulsions

Directory of Open Access Journals (Sweden)

T.G.Mason

2006-01-01

Full Text Available Nanoemulsions are metastable dispersions of nanodroplets of one liquid that have been ruptured by shear in another immiscible liquid. The ruptured droplets are stabilized against subsequent coalescence by a surfactant. Because the nanodroplets do not form spontaneously, as they can in lyotropic ``microemulsion'' phases, the structure of nanoemulsions is primarily dependent on the history of the applied shear stresses relative to the interfacial restoring stresses. By applying extremely high shear rates and controlling the composition of the emulsion, we have been able to rupture microscale droplets down to diameters as small as 30 nm in a microfluidic process that yields bulk quantities suitable for commercial production. Following ultracentrifugal fractionation to make the droplets uniform, we study the structure of these emulsions using small angle neutron scattering (SANS at dilute and concentrated volume fractions. We contrast the structure of a concentrated nanoemulsion with the structure factor of hard spheres at a similar volume fraction.

Electromagnetic transport components and sheared flows in drift-Alfven turbulence

DEFF Research Database (Denmark)

Naulin, V.

2003-01-01

Results from three-dimensional numerical simulations of drift-Alfven turbulence in a toroidal geometry with sheared magnetic field are presented. The simulations show a relation between self-generated poloidal shear flows and magnetic field perturbations. For large values of the plasma beta we ob...... with a folded Gaussian, while the PDFs of the spatially averaged transport are in good agreement with an extreme value distribution. (C) 2003 American Institute of Physics....... related to magnetic flutter is proposed. The characteristics of the ExB flux are investigated using probability density distribution functions (PDFs). Although they are not Gaussian, no signs of algebraic tails in the PDFs are observed. The PDFs of the pointwise transport are found to agree well...

Study on the crystallographic orientation relationship and formation mechanism of reversed austenite in economical Cr12 super martensitic stainless steel

International Nuclear Information System (INIS)

Ye, Dong; Li, Shaohong; Li, Jun; Jiang, Wen; Su, Jie; Zhao, Kunyu

2015-01-01

Effect of carbides and crystallographic orientation relationship on the formation mechanism of reversed austenite of economical Cr12 super martensitic stainless steel (SMSS) has been investigated mainly by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results indicate that the M_2_3C_6 precipitation and the formation of the reversed austenite have the interaction effect during tempering process in SMSS. The reversed austenite forms intensively at the sub-block boundary and the lath boundary within a misorientation range of 0–60°. M_2_3C_6 has the same crystallographic orientation relationship with reversed austenite. There are two different kinds of formation modes for reversed austenite. One is a nondiffusional shear reversion; the other is a diffusion transformation. Both are strictly limited by crystallographic orientation relationship. The austenite variants are limited to two kinds within one packet and five kinds within one prior austenite grain. - Highlights: • Reversed austenite forms at martensite boundaries with misorientation of 0–60° • M_2_3C_6 precipitation and reversed austenite formation have the interaction effect. • Two austenite variants with different orientations can be formed inside a packet. • Two reversed austenite formation modes: shear reversion; diffusion transformation

Study on the crystallographic orientation relationship and formation mechanism of reversed austenite in economical Cr12 super martensitic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Ye, Dong; Li, Shaohong; Li, Jun; Jiang, Wen [Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China); Su, Jie [Institute for Structural Materials, Central Iron and Steel Research Institute, Beijing 100081 (China); Zhao, Kunyu, E-mail: kyzhaoy@sina.com [Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China)

2015-11-15

Effect of carbides and crystallographic orientation relationship on the formation mechanism of reversed austenite of economical Cr12 super martensitic stainless steel (SMSS) has been investigated mainly by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results indicate that the M{sub 23}C{sub 6} precipitation and the formation of the reversed austenite have the interaction effect during tempering process in SMSS. The reversed austenite forms intensively at the sub-block boundary and the lath boundary within a misorientation range of 0–60°. M{sub 23}C{sub 6} has the same crystallographic orientation relationship with reversed austenite. There are two different kinds of formation modes for reversed austenite. One is a nondiffusional shear reversion; the other is a diffusion transformation. Both are strictly limited by crystallographic orientation relationship. The austenite variants are limited to two kinds within one packet and five kinds within one prior austenite grain. - Highlights: • Reversed austenite forms at martensite boundaries with misorientation of 0–60° • M{sub 23}C{sub 6} precipitation and reversed austenite formation have the interaction effect. • Two austenite variants with different orientations can be formed inside a packet. • Two reversed austenite formation modes: shear reversion; diffusion transformation.

Study on shear properties of coral sand under cyclic simple shear condition

Science.gov (United States)

Ji, Wendong; Zhang, Yuting; Jin, Yafei

2018-05-01

In recent years, the ocean development in our country urgently needs to be accelerated. The construction of artificial coral reefs has become an important development direction. In this paper, experimental studies of simple shear and cyclic simple shear of coral sand are carried out, and the shear properties and particle breakage of coral sand are analyzed. The results show that the coral sand samples show an overall shear failure in the simple shear test, which is more accurate and effective for studying the particle breakage. The shear displacement corresponding to the peak shear stress of the simple shear test is significantly larger than that corresponding to the peak shear stress of the direct shear test. The degree of particle breakage caused by the simple shear test is significantly related to the normal stress level. The particle breakage of coral sand after the cyclic simple shear test obviously increases compared with that of the simple shear test, and universal particle breakage occurs within the whole particle size range. The increasing of the cycle-index under cyclic simple shear test results in continuous compacting of the sample, so that the envelope curve of peak shearing force increases with the accumulated shear displacement.

Highly Viscoelastic Reverse Wormlike Micellar Systems from a Mixture of Lecithin, Polyglycerol Fatty Acid Monoesters, and an Oil.

Science.gov (United States)

Hashizaki, Kaname; Imai, Miko; Yako, Shuhei; Tsusaka, Hitomi; Sakanishi, Yuichi; Saito, Yoshihiro; Fujii, Makiko

2017-09-01

We report new lecithin reverse wormlike micelles with high viscoelasticity formed using lecithin/polyglycerol fatty acid monoester (PGLFA)/oil systems. In this study, the influence of the amphiphilicity (i.e., hydrophile-lipophile balance, HLB) of PGLFA on the phase behavior and rheological properties of reverse wormlike micelles was investigated in detail. PGLFAs with degrees of polymerization of polyglycerol varying between 6-40 and constituent fatty acids with chains between 6-18 carbon atoms long were used. Partial phase diagrams of the lecithin/PGLFA/n-decane systems indicated that the appropriate PGLFA could change the lecithin/oil solution into a highly viscoelastic solution comprising reverse wormlike micelles. Rheological measurements showed that all systems that formed reverse wormlike micelles exhibited an unusual phenomenon called "shear-thickening". Furthermore, reverse wormlike micelles grew as the PGLFA concentration increased and the zero-shear viscosity (η 0 ) of the solution rapidly increased. Our results indicate that the magnitude of the maximum η 0 depends on the degree of polymerization of the constituent polyglycerol in the PGLFA, while the size of the reverse micellar region and the highly viscous region in the phase diagram depends on the HLB value of the PGLFA.

Shear strength of non-shear reinforced concrete elements

DEFF Research Database (Denmark)

Hoang, Cao linh

1997-01-01

The paper deals with the plastic shear strength of non shear reinforced T-beams.The influence of an un-reinforced flange on the shear capacity is investigated by considering a failure mechanism involving crack sliding in the web and a kind of membrane action over an effective width of the flange...

Development of Test Method for Simple Shear and Prediction of Hardening Behavior Considering the Branchings Effect

International Nuclear Information System (INIS)

Kim, Dongwook; Bang, Sungsik; Kim, Minsoo; Lee, Hyungyil; Kim, Naksoo

2013-01-01

In this study we establish a process to predict hardening behavior considering the Branchings effect for zircaloy-4 sheets. When a metal is compressed after tension in forming, the yield strength decreases. For this reason, the Branchings effect should be considered in FE simulations of spring-back. We suggested a suitable specimen size and a method for determining the optimum tightening torque for simple shear tests. Shear stress-strain curves are obtained for five materials. We developed a method to convert the shear load-displacement curve to the effective stress-strain curve with Fea. We simulated the simple shear forward/reverse test using the combined isotropic/kinematic hardening model. We also investigated the change of the load-displacement curve by varying the hardening coefficients. We determined the hardening coefficients so that they follow the hardening behavior of zircaloy-4 in experiments

Development of Test Method for Simple Shear and Prediction of Hardening Behavior Considering the Branchings Effect

Energy Technology Data Exchange (ETDEWEB)

Kim, Dongwook; Bang, Sungsik; Kim, Minsoo; Lee, Hyungyil; Kim, Naksoo [Sogang Univ., Seoul (Korea, Republic of)

2013-10-15

In this study we establish a process to predict hardening behavior considering the Branchings effect for zircaloy-4 sheets. When a metal is compressed after tension in forming, the yield strength decreases. For this reason, the Branchings effect should be considered in FE simulations of spring-back. We suggested a suitable specimen size and a method for determining the optimum tightening torque for simple shear tests. Shear stress-strain curves are obtained for five materials. We developed a method to convert the shear load-displacement curve to the effective stress-strain curve with Fea. We simulated the simple shear forward/reverse test using the combined isotropic/kinematic hardening model. We also investigated the change of the load-displacement curve by varying the hardening coefficients. We determined the hardening coefficients so that they follow the hardening behavior of zircaloy-4 in experiments.

Fluctuation reduction and enhanced confinement in the MST reversed-field pinch

International Nuclear Information System (INIS)

Chapman, B.E.

1997-10-01

Plasmas with a factor of ≥3 improvement in energy confinement have been achieved in the MST reversed-field pinch (RFP). These plasmas occur spontaneously, following sawtooth crashes, subject to constraints on, eg, toroidal magnetic field reversal and wall conditioning. Possible contributors to the improved confinement include a reduction of core-resonant, global magnetic fluctuations and a reduction of electrostatic fluctuations over the entire plasma edge. One feature of these plasmas is a region of strong ExB flow shear in the edge. Never before observed in conjunction with enhanced confinement in the RFP, such shear is common in enhanced confinement discharges in tokamaks and stellarators. Another feature of these plasmas is a new type of discrete dynamo event. Like sawtooth crashes, a common form of discrete dynamo, these events correspond to bursts of edge parallel current. The reduction of electrostatic fluctuations in these plasmas occurs within and beyond the region of strong ExB flow shear, similar to what is observed in tokamaks and stellarators. However, the reductions in the MST include fluctuations whose correlation lengths are larger than the width of the shear region. The reduction of the global magnetic fluctuations is most likely due to flattening of the μ=μ 0 rvec J· rvec B/B 2 profile. Flattening can occur, eg, due to the new type of discrete dynamo event and reduced edge resistivity. Enhanced confinement plasmas are also achieved in the MST when auxiliary current is applied to flatten the μ profile and reduce magnetic fluctuations. Unexpectedly, these plasmas also exhibit a region (broader than in the case above) of strong ExB flow shear in the edge, an edge-wide reduction of electrostatic fluctuations, and the new type of discrete dynamo event. Auxiliary current drive has historically been viewed as the principal route to fusion reactor viability for the RFP

Suppressing electron turbulence and triggering internal transport barriers with reversed magnetic shear in the National Spherical Torus Experiment

Energy Technology Data Exchange (ETDEWEB)

Peterson, J. L. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Bell, R.; Guttenfelder, W.; Hammett, G. W.; Kaye, S. M.; LeBlanc, B.; Mikkelsen, D. R. [Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Candy, J. [General Atomics, San Diego, California 92186 (United States); Smith, D. R. [Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Yuh, H. Y. [Nova Photonics Inc., Princeton, New Jersey 08540 (United States)

2012-05-15

The National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)] can achieve high electron plasma confinement regimes that are super-critically unstable to the electron temperature gradient driven (ETG) instability. These plasmas, dubbed electron internal transport barriers (e-ITBs), occur when the magnetic shear becomes strongly negative. Using the gyrokinetic code GYRO [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)], the first nonlinear ETG simulations of NSTX e-ITB plasmas reinforce this observation. Local simulations identify a strongly upshifted nonlinear critical gradient for thermal transport that depends on magnetic shear. Global simulations show e-ITB formation can occur when the magnetic shear becomes strongly negative. While the ETG-driven thermal flux at the outer edge of the barrier is large enough to be experimentally relevant, the turbulence cannot propagate past the barrier into the plasma interior.

FLUID EVOLUTION AND MINERAL REACTIONS DURING SHEAR ZONE FORMATION AT NUSFJORD, LOFOTEN, NORWAY (Invited)

Science.gov (United States)

Kullerud, K.

2009-12-01

At Nusfjord in Lofoten, Norway, three 0.3 - 3 m thick shear zones occur in a gabbro-anorthosite. During deformation, the shear zones were infiltrated by a hydrous fluid enriched in Cl. In the central parts of the shear zones, fluid-rock interaction resulted in complete break-down of the primary mafic silicates. Complete hydration of these minerals to Cl-free amphibole and biotite suggests that the hydrous fluid was present in excess during deformation in these parts of the shear zones. Along the margins of the shear zones, however, the igneous mafic silicates (Cpx, Bt, Opx) were only partly overgrown by hydrous minerals. Here, Cl-enriched minerals (Amph, Bt, Scp, Ap) can be observed. Amphibole shows compositions covering the range 0.1 - 4.0 wt % Cl within single thin sections. Mineral textures and extreme compositional variations of the Cl-bearing minerals indicate large chemical gradients of the fluid phase. Relics of primary mafic silicates and compositionally zoned reaction coronas around primary mafic silicates suggest that the free fluid was totally consumed before the alteration of the primary phases were completed. The extreme variations in the Cl-content of amphibole are inferred to monitor a gradual desiccation of the Cl-bearing grain-boundary fluid during fluid-mineral reactions accordingly: 1) The first amphibole that formed during the reactions principally extracted water from the fluid, resulting in a slight increase in the Cl content of the fluid. 2) Continued amphibole-forming reactions resulted in gradual consumption of the free fluid phase, principally by extracting water from the fluid, resulting in an increase in its Cl-content. Higher Cl-content of the fluid resulted in higher Cl-content of the equilibrium amphibole. 3) The most Cl-enriched amphibole (4 wt % Cl) formed in equilibrium with the last volumes of the grain-boundary fluid, which had evolved to a highly saline solution. Mineral reactions within a 1-2 thick zone of the host rock along

Seismic Behaviour of Composite Steel Fibre Reinforced Concrete Shear Walls

Science.gov (United States)

Boita, Ioana-Emanuela; Dan, Daniel; Stoian, Valeriu

2017-10-01

In this paper is presented an experimental study conducted at the “Politehnica” University of Timisoara, Romania. This study provides results from a comprehensive experimental investigation on the behaviour of composite steel fibre reinforced concrete shear walls (CSFRCW) with partially or totally encased profiles. Two experimental composite steel fibre reinforced concrete walls (CSFRCW) and, as a reference specimen, a typical reinforced concrete shear wall (RCW), (without structural reinforcement), were fabricated and tested under constant vertical load and quasi-static reversed cyclic lateral loads, in displacement control. The tests were performed until failure. The tested specimens were designed as 1:3 scale steel-concrete composite elements, representing a three storeys and one bay element from the base of a lateral resisting system made by shear walls. Configuration/arrangement of steel profiles in cross section were varied within the specimens. The main objective of this research consisted in identifying innovative solutions for composite steel-concrete shear walls with enhanced performance, as steel fibre reinforced concrete which was used in order to replace traditional reinforced concrete. A first conclusion was that replacing traditional reinforcement with steel fibre changes the failure mode of the elements, as from a flexural mode, in case of element RCW, to a shear failure mode for CSFRCW. The maximum lateral force had almost similar values but test results indicated an improvement in cracking response, and a decrease in ductility. The addition of steel fibres in the concrete mixture can lead to an increase of the initial cracking force, and can change the sudden opening of a crack in a more stable process.

Sheared-flow induced confinement transition in a linear magnetized plasma

Science.gov (United States)

Zhou, S.; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Carter, T. A.; Vincena, S.; Friedman, B.; Schaffner, D.

2012-01-01

A magnetized plasma cylinder (12 cm in diameter) is induced by an annular shape obstacle at the Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)]. Sheared azimuthal flow is driven at the edge of the plasma cylinder through edge biasing. Strong fluctuations of density and potential (δn /n~eδφ/kTe~0.5) are observed at the plasma edge, accompanied by a large density gradient (Ln=|∇lnn |-1~2cm) and shearing rate (γ ~300kHz). Edge turbulence and cross-field transport are modified by changing the bias voltage (Vbias) on the obstacle and the axial magnetic field (Bz) strength. In cases with low Vbias and large Bz, improved plasma confinement is observed, along with steeper edge density gradients. The radially sheared flow induced by E ×B drift dramatically changes the cross-phase between density and potential fluctuations, which causes the wave-induced particle flux to reverse its direction across the shear layer. In cases with higher bias voltage or smaller Bz, large radial transport and rapid depletion of the central plasma density are observed. Two-dimensional cross-correlation measurement shows that a mode with azimuthal mode number m =1 and large radial correlation length dominates the outward transport in these cases. Linear analysis based on a two-fluid Braginskii model suggests that the fluctuations are driven by both density gradient (drift wave like) and flow shear (Kelvin-Helmholtz like) at the plasma edge.

Sheared-flow induced confinement transition in a linear magnetized plasma

International Nuclear Information System (INIS)

Zhou, S.; Heidbrink, W. W.; Boehmer, H.; McWilliams, R.; Carter, T. A.; Vincena, S.; Friedman, B.; Schaffner, D.

2012-01-01

A magnetized plasma cylinder (12 cm in diameter) is induced by an annular shape obstacle at the Large Plasma Device [W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991)]. Sheared azimuthal flow is driven at the edge of the plasma cylinder through edge biasing. Strong fluctuations of density and potential (δn/n∼eδφ/kT e ∼0.5) are observed at the plasma edge, accompanied by a large density gradient (L n =∇lnn -1 ∼2cm) and shearing rate (γ∼300kHz). Edge turbulence and cross-field transport are modified by changing the bias voltage (V bias ) on the obstacle and the axial magnetic field (B z ) strength. In cases with low V bias and large B z , improved plasma confinement is observed, along with steeper edge density gradients. The radially sheared flow induced by ExB drift dramatically changes the cross-phase between density and potential fluctuations, which causes the wave-induced particle flux to reverse its direction across the shear layer. In cases with higher bias voltage or smaller B z , large radial transport and rapid depletion of the central plasma density are observed. Two-dimensional cross-correlation measurement shows that a mode with azimuthal mode number m=1 and large radial correlation length dominates the outward transport in these cases. Linear analysis based on a two-fluid Braginskii model suggests that the fluctuations are driven by both density gradient (drift wave like) and flow shear (Kelvin-Helmholtz like) at the plasma edge.

Flooding and flow reversal of two-phase annular flow

International Nuclear Information System (INIS)

Asahi, Y.

1978-01-01

The flooding and flow reversal conditions of two-phase annular flow are mathematically defined in terms of a characteristic function representing a force balance. Sufficiently below the flooding point in counter-current flow, the interface is smooth and the characteristic equation reduces to the Nusselt relationship. Just below flooding point and above the flow reversal point in cocurrent flow, the interface is 'wavy', so that the interfacial shear effect plays an important role. The theoretical analysis is compared with experimental results by others. It is suggested that the various length effects which have been experimentally observed may be accounted for by the spatial variation of the droplet entrainment. (Auth.)

Structure of high and low shear-stress events in a turbulent boundary layer

Science.gov (United States)

Gomit, G.; de Kat, R.; Ganapathisubramani, B.

2018-01-01

Simultaneous particle image velocimetry (PIV) and wall-shear-stress sensor measurements were performed to study structures associated with shear-stress events in a flat plate turbulent boundary layer at a Reynolds number Reτ≈4000 . The PIV field of view covers 8 δ (where δ is the boundary layer thickness) along the streamwise direction and captures the entire boundary layer in the wall-normal direction. Simultaneously, wall-shear-stress measurements that capture the large-scale fluctuations were taken using a spanwise array of hot-film skin-friction sensors (spanning 2 δ ). Based on this combination of measurements, the organization of the conditional wall-normal and streamwise velocity fluctuations (u and v ) and of the Reynolds shear stress (-u v ) can be extracted. Conditional averages of the velocity field are computed by dividing the histogram of the large-scale wall-shear-stress fluctuations into four quartiles, each containing 25% of the occurrences. The conditional events corresponding to the extreme quartiles of the histogram (positive and negative) predominantly contribute to a change of velocity profile associated with the large structures and in the modulation of the small scales. A detailed examination of the Reynolds shear-stress contribution related to each of the four quartiles shows that the flow above a low wall-shear-stress event carries a larger amount of Reynolds shear stress than the other quartiles. The contribution of the small and large scales to this observation is discussed based on a scale decomposition of the velocity field.

Experimental study of shear rate dependence in perpetually sheared granular matter

Science.gov (United States)

Liu, Sophie Yang; Guillard, François; Marks, Benjy; Rognon, Pierre; Einav, Itai

2017-06-01

We study the shear behaviour of various granular materials by conducting novel perpetual simple shear experiments over four orders of magnitude of relatively low shear rates. The newly developed experimental apparatus employed is called "3D Stadium Shear Device" which is an extended version of the 2D Stadium Shear Device [1]. This device is able to provide a non-radial dependent perpetual shear flow and a nearly linear velocity profile between two oppositely moving shear walls. Using this device, we are able to test a large variety of granular materials. Here, we demonstrate the applicability of the device on glass beads (diameter 1 mm, 3 mm, and 14 mm) and rice. We particularly focus on studying these materials at very low inertial number I ranging from 10-6 to 10-2. We find that, within this range of I, the friction coefficient μ of glass beads has no shear rate dependence. A particularly appealing observation comes from testing rice, where the attainment of critical state develops under much longer duration than in other materials. Initially during shear we find a value of μ similar to that found for glass beads, but with time this value decreases gradually towards the asymptotic critical state value. The reason, we believe, lies in the fact that rice grains are strongly elongated; hence the time to achieve the stable μ is primarily controlled by the time for particles to align themselves with respect to the shear walls. Furthermore, the initial packing conditions of samples also plays a role in the evolution of μ when the shear strain is small, but that impact will eventually be erased after sufficient shear strain.

Pulsatility Index as a Diagnostic Parameter of Reciprocating Wall Shear Stress Parameters in Physiological Pulsating Waveforms.

Directory of Open Access Journals (Sweden)

Idit Avrahami

Full Text Available Arterial wall shear stress (WSS parameters are widely used for prediction of the initiation and development of atherosclerosis and arterial pathologies. Traditional clinical evaluation of arterial condition relies on correlations of WSS parameters with average flow rate (Q and heart rate (HR measurements. We show that for pulsating flow waveforms in a straight tube with flow reversals that lead to significant reciprocating WSS, the measurements of HR and Q are not sufficient for prediction of WSS parameters. Therefore, we suggest adding a third quantity-known as the pulsatility index (PI-which is defined as the peak-to-peak flow rate amplitude normalized by Q. We examine several pulsating flow waveforms with and without flow reversals using a simulation of a Womersley model in a straight rigid tube and validate the simulations through experimental study using particle image velocimetry (PIV. The results indicate that clinically relevant WSS parameters such as the percentage of negative WSS (P[%], oscillating shear index (OSI and the ratio of minimum to maximum shear stress rates (min/max, are better predicted when the PI is used in conjunction with HR and Q. Therefore, we propose to use PI as an additional and essential diagnostic quantity for improved predictability of the reciprocating WSS.

The Effect of a Shear Flow on the Uptake of LDL and Ac-LDL by Cultured Vascular Endothelial Cells

Science.gov (United States)

Niwa, Koichi; Karino, Takeshi

The effects of a shear flow on the uptake of fluorescence-labeled low-density lipoprotein (DiI-LDL), acetylated LDL (DiI-Ac-LDL), and lucifer yellow (LY; a tracer of fluid-phase endocytosis) by cultured bovine aortic ECs were studied using a rotating-disk shearing apparatus. It was found that 2hours’ exposure of ECs to a laminar shear flow that imposed ECs an area-mean shear stress of 10dynes/cm2 caused an increase in the uptake of DiI-LDL and LY. By contrast, the uptake of DiI-Ac-LDL was decreased by exposure of the ECs to a shear flow. Addition of dextran sulfate (DS), a competitive inhibitor of scavenger receptors, reversed the effect of a shear flow on the uptake of DiI-Ac-LDL, resulting in an increase by the imposition of a shear flow, while the uptake of DiI-LDL and LY remained unaffected. It was concluded that a shear flow promotes the endocytosis of DiI-LDL and LY by ECs, but suppresses the uptake of DiI-Ac-LDL by ECs by inhibiting scavenger receptor-mediated endocytosis.

Experimental study of shear rate dependence in perpetually sheared granular matter

Directory of Open Access Journals (Sweden)

Liu Sophie Yang

2017-01-01

Full Text Available We study the shear behaviour of various granular materials by conducting novel perpetual simple shear experiments over four orders of magnitude of relatively low shear rates. The newly developed experimental apparatus employed is called “3D Stadium Shear Device” which is an extended version of the 2D Stadium Shear Device [1]. This device is able to provide a non-radial dependent perpetual shear flow and a nearly linear velocity profile between two oppositely moving shear walls. Using this device, we are able to test a large variety of granular materials. Here, we demonstrate the applicability of the device on glass beads (diameter 1 mm, 3 mm, and 14 mm and rice. We particularly focus on studying these materials at very low inertial number I ranging from 10−6 to 10−2. We find that, within this range of I, the friction coefficient μ of glass beads has no shear rate dependence. A particularly appealing observation comes from testing rice, where the attainment of critical state develops under much longer duration than in other materials. Initially during shear we find a value of μ similar to that found for glass beads, but with time this value decreases gradually towards the asymptotic critical state value. The reason, we believe, lies in the fact that rice grains are strongly elongated; hence the time to achieve the stable μ is primarily controlled by the time for particles to align themselves with respect to the shear walls. Furthermore, the initial packing conditions of samples also plays a role in the evolution of μ when the shear strain is small, but that impact will eventually be erased after sufficient shear strain.

Characteristics of Asperity Damage and Its Influence on the Shear Behavior of Granite Joints

Science.gov (United States)

Meng, Fanzhen; Zhou, Hui; Wang, Zaiquan; Zhang, Chuanqing; Li, Shaojun; Zhang, Liming; Kong, Liang

2018-02-01

Surface roughness significantly affects the shear behavior of rock joints; thus, studies on the asperity damage characteristics and its influence on the shear behavior of joints are extremely important. In this paper, shear tests were conducted on tensile granite joints; asperity damage was evaluated based on acoustic emission (AE) events; and the influence of asperity damage on joint shear behavior was analyzed. The results indicated that the total AE events tended to increase with normal stress. In addition, the asperity damage initiation shear stress, which is defined as the transition point from slow growth to rapid growth in the cumulative events curve, was approximately 0.485 of the peak shear strength regardless of the normal stress. Moreover, 63-85% of the AE events were generated after the peak shear stress, indicating that most of the damage occurred in this stage. Both the dilation and the total AE events decreased with shear cycles because of the damage inflicted on asperities during the previous shear cycle. Two stages were observed in the normal displacement curves under low normal stress, whereas three stages (compression, dilation and compression again) were observed at a higher normal stress; the second compression stage may be caused by tensile failure outside the shear plane. The magnitude of the normal stress and the state of asperity are two important factors controlling the post-peak stress drop and stick-slip of granite joints. Serious deterioration of asperities will stop stick-slip from recurring under the same normal stress because the ability to accumulate energy is decreased. The AE b-value increases with the number of shear cycles, indicating that the stress concentration inside the fault plane is reduced because of asperity damage; thus, the potential for dynamic disasters, such as fault-slip rockbursts, will be decreased.

Temperature-dependent residual shear strength characteristics of smectite-rich landslide soils

Science.gov (United States)

Shibasaki, Tatsuya; Matsuura, Sumio; Okamoto, Takashi

2015-04-01

On gentle clayey slopes in weathered argillaceous rock areas, there exist many landslides which repeatedly reactivate with slow movement. The slip surface soils of these landslides are sometimes composed dominantly of swelling clay mineral (smectite) which is well known to show extremely low residual friction angle. From field data monitored at landslide sites in Japan, it has become clear that some landslides with relatively shallow slip surface begin to move and become active in late autumn or early winter every year. In such cases, the triggering mechanisms of landslides have not been understood well enough, because landslide initiation and movement are not always clearly linked with rises in pore water pressures (ground water levels). In this study, we focus on the influence of seasonal variation in ground temperature on slope stability and have investigated the effect of temperature on the shear strength of slip surface soils. Undisturbed soil samples were collected by boring from the Busuno landslide in Japan. We performed box shear experiments on undisturbed slip surface soils at low temperature ranges (approximately 5-25 °C). XRD analysis revealed that these soils contain high fraction of smectite. Slickensided slip surface within test specimen was coincided with the shearing plane of the shear box and shear displacement was applied precisely along the localized slip surface. Experiments were performed under slow shearing rate condition (0.005mm/min) and the results showed that shear strength decreased with decreasing temperature. Temperature effect was rather significant on frictional angle than on cohesion. Ring shear experiments were also performed on normally-consolidated remoulded samples. Under residual strength condition, temperature-change experiments (cooling-event tests) ranging approximately from 5 to 25 °C were performed on smectite-rich landslide soils and commercial bentonites. As well as the results by box shear test, shear weakening

A new Class of Extremal Composites

DEFF Research Database (Denmark)

Sigmund, Ole

2000-01-01

microstructure belonging to the new class of composites has maximum bulk modulus and lower shear modulus than any previously known composite. Inspiration for the new composite class comes from a numerical topology design procedure which solves the inverse homogenization problem of distributing two isotropic......The paper presents a new class of two-phase isotropic composites with extremal bulk modulus. The new class consists of micro geometrics for which exact solutions can be proven and their bulk moduli are shown to coincide with the Hashin-Shtrikman bounds. The results hold for two and three dimensions...... and for both well- and non-well-ordered isotropic constituent phases. The new class of composites constitutes an alternative to the three previously known extremal composite classes: finite rank laminates, composite sphere assemblages and Vigdergauz microstructures. An isotropic honeycomb-like hexagonal...

Wind Shear and the Strength of Severe Convective Phenomena—Preliminary Results from Poland in 2011–2015

Directory of Open Access Journals (Sweden)

Wojciech Pilorz

2016-10-01

Full Text Available Severe convective phenomena cause significant loss in the economy and, primarily, casualties. Therefore, it is essential to forecast such extreme events to avoid or minimize the negative consequences. Wind shear provides an updraft-downdraft separation in the convective cell, which extends the cell lifetime. Wind shears between a few different air layers have been examined in all damaging convective cases in Poland, taken from the European Severe Weather Database between 2011 and 2015, in order to find their values and patterns according to the intensity of this phenomenon. Each severe weather report was assigned wind shear values from the nearest sounding station, and subsequently the presented summary was made. It was found that wind shear values differ between the given phenomena and their intensity. This regularity is particularly visible in shears containing 0 km wind. The highest shears occur within wind reports. Lower values are associated with hail reports. An important difference between weak and F1+ tornadoes was found in most of the wind shears. Severe phenomena probability within 0–6 km and 0–1 km shears show different patterns according to the phenomena and their intensity. This finding has its application in severe weather forecasting.

Shear thinning and shear thickening of a confined suspension of vesicles

Science.gov (United States)

Nait Ouhra, A.; Farutin, A.; Aouane, O.; Ez-Zahraouy, H.; Benyoussef, A.; Misbah, C.

2018-01-01

Widely regarded as an interesting model system for studying flow properties of blood, vesicles are closed membranes of phospholipids that mimic the cytoplasmic membranes of red blood cells. In this study we analyze the rheology of a suspension of vesicles in a confined geometry: the suspension, bound by two planar rigid walls on each side, is subject to a shear flow. Flow properties are then analyzed as a function of shear rate γ ˙, the concentration of the suspension ϕ , and the viscosity contrast λ =ηin/ηout , where ηin and ηout are the fluid viscosities of the inner and outer fluids, respectively. We find that the apparent (or effective viscosity) of the suspension exhibits both shear thinning (decreasing viscosity with shear rate) or shear thickening (increasing viscosity with shear rate) in the same concentration range. The shear thinning or thickening behaviors appear as subtle phenomena, dependant on viscosity contrast λ . We provide physical arguments on the origins of these behaviors.

Thermal electron transport in regimes with low and negative magnetic shear in Tore Supra

International Nuclear Information System (INIS)

Voitsekhovitch, I.; Litaudon, X.; Moreau, D.; Aniel, T.; Becoulet, A.; Erba, M.; Joffrin, E.; Kazarian-Vibert, F.; Peysson, Y.

1997-01-01

The magnetic shear effect on thermal electron transport is studied in a large variety of non-inductive plasmas in Tore Supra. An improved confinement in the region of low and negative shear was observed and quantified with an exponential dependence on the magnetic shear (Litaudon, et al., Fusion Energy 1996 (Proc. 16th Int. Conf. Montreal, 1996), Vol. 1, IAEA, Vienna (1997) 669). This is interpreted as a consequence of a decoupling of the global modes (Romanelli and Zonca, Phys. Fluids B 5 (1993) 4081) that are thought to be responsible for anomalous transport. This dependence is proposed in order to complete the Bohm-like L mode local electron thermal diffusivity so as to describe the transition from Bohm-like to gyroBohm transport in the plasma core. The good agreement between the predictive simulations of the different Tore Supra regimes (hot core lower hybrid enhanced performance, reversed shear plasmas and combined lower hybrid current drive and fast wave electron heating) and experimental data provides a basis for extrapolation of this magnetic shear dependence in the local transport coefficients to future machines. As an example, a scenario for non-inductive current profile optimization and control in ITER is presented. (author)

Expression, purification, crystallization and preliminary X-ray analysis of eCGP123, an extremely stable monomeric green fluorescent protein with reversible photoswitching properties

International Nuclear Information System (INIS)

Don Paul, Craig; Traore, Daouda A. K.; Byres, Emma; Rossjohn, Jamie; Devenish, Rodney J.; Kiss, Csaba; Bradbury, Andrew; Wilce, Matthew C. J.; Prescott, Mark

2011-01-01

eCGP123, an extremely stable GFP with photoswitching properties, has been expressed, purified and crystallized. A diffraction data set has been collected at 2.10 Å resolution. Enhanced consensus green protein variant 123 (eCGP123) is an extremely thermostable green fluorescent protein (GFP) that exhibits useful negative reversible photoswitching properties. eCGP123 was derived by the application of both a consensus engineering approach and a recursive evolutionary process. Diffraction-quality crystals of recombinant eCGP123 were obtained by the hanging-drop vapour-diffusion method using PEG 3350 as the precipitant. The eCGP123 crystal diffracted X-rays to 2.10 Å resolution. The data were indexed in space group P1, with unit-cell parameters a = 74.63, b = 75.38, c = 84.51 Å, α = 90.96, β = 89.92, γ = 104.03°. The Matthews coefficient (V M = 2.26 Å 3 Da −1 ) and a solvent content of 46% indicated that the asymmetric unit contained eight eCGP123 molecules

The cation-controlled and hydrogen bond-mediated shear-thickening behaviour of a tree-fern isolated polysaccharide.

Science.gov (United States)

Wee, May S M; Matia-Merino, Lara; Goh, Kelvin K T

2015-10-05

The shear-thickening rheological behaviour (between 5 and 20s(-1)) of a 5% (w/w) viscoelastic gum extracted from the fronds of the native New Zealand black tree fern or mamaku in Māori was further explored by manipulating the salt content. The freeze-dried mamaku gum contained a high mineral content and sugars which upon removal via dialysis, resulted in the loss of shear thickening. However, this loss was reversible by the addition of salts to the dialysed dispersion. The mechanism of shear-thickening behaviour was therefore hypothesised to be due to shear-induced transition of intra- to intermolecular hydrogen bonding, promoted by the screening effect of cations. Mono-, di- and trivalent salts, i.e. Na(+), K(+), N(CH3)4(+), Ca(2+), Mg(2+), Al(3+) and La(3+) at concentrations between 0.001 and 1.0M were tested to support the hypothesis as well as to demonstrate the sensitivity of the biopolymer to cation valency and concentrations. The cation valency and concentration were crucial factors in determining: (i) zero-shear viscosity, (ii) critical shear rate, γ˙c (or shear rate at the onset of shear-thickening) and (iii) the extent of shear-thickening of the solution. For mono- and divalent cations these parameters were similar at equivalent ionic strengths and fairly independent of the cation type. Trivalent cations (La(3+)) however caused precipitation of the gum in the concentration range of 0.005-0.05 M but clear dispersions were obtained above 0.05 M. Copyright © 2015 Elsevier Ltd. All rights reserved.

Shear stress induced by an interstitial level of slow flow increases the osteogenic differentiation of mesenchymal stem cells through TAZ activation.

Directory of Open Access Journals (Sweden)

Kyung Min Kim

Full Text Available Shear stress activates cellular signaling involved in cellular proliferation, differentiation, and migration. However, the mechanisms of mesenchymal stem cell (MSC differentiation under interstitial flow are not fully understood. Here, we show the increased osteogenic differentiation of MSCs under exposure to constant, extremely low shear stress created by osmotic pressure-induced flow in a microfluidic chip. The interstitial level of shear stress in the proposed microfluidic system stimulated nuclear localization of TAZ (transcriptional coactivator with PDZ-binding motif, a transcriptional modulator of MSCs, activated TAZ target genes such as CTGF and Cyr61, and induced osteogenic differentiation. TAZ-depleted cells showed defects in shear stress-induced osteogenic differentiation. In shear stress induced cellular signaling, Rho signaling pathway was important forthe nuclear localization of TAZ. Taken together, these results suggest that TAZ is an important mediator of interstitial flow-driven shear stress signaling in osteoblast differentiation of MSCs.

Rotational stability of a long field-reversed configuration

International Nuclear Information System (INIS)

Barnes, D. C.; Steinhauer, L. C.

2014-01-01

Rotationally driven modes of long systems with dominantly axial magnetic field are considered. We apply the incompressible model and order axial wavenumber small. A recently developed gyro-viscous model is incorporated. A one-dimensional equilibrium is assumed, but radial profiles are arbitrary. The dominant toroidal (azimuthal) mode numbers ℓ=1 and ℓ=2 modes are examined for a variety of non-reversed (B) and reversed profiles. Previous results for both systems with rigid rotor equilibria are reproduced. New results are obtained by incorporation of finite axial wavenumber and by relaxing the assumption of rigid electron and ion rotation. It is shown that the frequently troublesome ℓ=2 field reversed configuration (FRC) mode is not strongly affected by ion kinetic effects (in contrast to non-reversed cases) and is likely stabilized experimentally only by finite length effects. It is also shown that the ℓ=1 wobble mode has a complicated behavior and is affected by a variety of configuration and profile effects. The rotationally driven ℓ=1 wobble is completely stabilized by strong rotational shear, which is anticipated to be active in high performance FRC experiments. Thus, observed wobble modes in these systems are likely not driven by rotation alone

Rotational stability of a long field-reversed configuration

Energy Technology Data Exchange (ETDEWEB)

Barnes, D. C., E-mail: coronadocon@msn.com; Steinhauer, L. C. [Tri Alpha Energy, Rancho Santa Margarita, California 92688 (United States)

2014-02-15

Rotationally driven modes of long systems with dominantly axial magnetic field are considered. We apply the incompressible model and order axial wavenumber small. A recently developed gyro-viscous model is incorporated. A one-dimensional equilibrium is assumed, but radial profiles are arbitrary. The dominant toroidal (azimuthal) mode numbers ℓ=1 and ℓ=2 modes are examined for a variety of non-reversed (B) and reversed profiles. Previous results for both systems with rigid rotor equilibria are reproduced. New results are obtained by incorporation of finite axial wavenumber and by relaxing the assumption of rigid electron and ion rotation. It is shown that the frequently troublesome ℓ=2 field reversed configuration (FRC) mode is not strongly affected by ion kinetic effects (in contrast to non-reversed cases) and is likely stabilized experimentally only by finite length effects. It is also shown that the ℓ=1 wobble mode has a complicated behavior and is affected by a variety of configuration and profile effects. The rotationally driven ℓ=1 wobble is completely stabilized by strong rotational shear, which is anticipated to be active in high performance FRC experiments. Thus, observed wobble modes in these systems are likely not driven by rotation alone.

Reversed-Field Pinch plasma model

International Nuclear Information System (INIS)

Miley, G.H.; Nebel, R.A.; Moses, R.W.

1979-01-01

The stability of a Reversed-Field Pinch (RFP) is strongly dependent on the plasma profile and the confining sheared magnetic field. Magnetic diffusion and thermal transport produce changing conditions of stability. Despite the limited understanding of RFP transport, modelling is important to predict general trends and to study possible field programming options. To study the ZT-40 experiment and to predict the performance of future RFP reactors, a one-dimensional transport code has been developed. This code includes a linear, ideal MHD stability check based on an energy principle. The transport section integrates plasma profiles forward in time while the stability section periodically checks the stability of the evolving plasma profile

Rotation profile flattening and toroidal flow shear reversal due to the coupling of magnetic islands in tokamaks

Energy Technology Data Exchange (ETDEWEB)

Tobias, B.; Grierson, B. A.; Okabayashi, M. [Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States); Chen, M.; Domier, C. W.; Luhmann, N. C.; Muscatello, C. M. [University of California at Davis, Davis, California 95616 (United States); Classen, I. G. J. [Dutch Institute for Fundamental Fusion Energy Research, DIFFER, Rhinjuizen (Netherlands); Fitzpatrick, R. [University of Texas at Austin, Austin, Texas 78705 (United States); Olofsson, K. E. J.; Paz-Soldan, C. [General Atomics, San Diego, California 92121 (United States)

2016-05-15

The electromagnetic coupling of helical modes, even those having different toroidal mode numbers, modifies the distribution of toroidal angular momentum in tokamak discharges. This can have deleterious effects on other transport channels as well as on magnetohydrodynamic (MHD) stability and disruptivity. At low levels of externally injected momentum, the coupling of core-localized modes initiates a chain of events, whereby flattening of the core rotation profile inside successive rational surfaces leads to the onset of a large m/n = 2/1 tearing mode and locked-mode disruption. With increased torque from neutral beam injection, neoclassical tearing modes in the core may phase-lock to each other without locking to external fields or structures that are stationary in the laboratory frame. The dynamic processes observed in these cases are in general agreement with theory, and detailed diagnosis allows for momentum transport analysis to be performed, revealing a significant torque density that peaks near the 2/1 rational surface. However, as the coupled rational surfaces are brought closer together by reducing q{sub 95}, additional momentum transport in excess of that required to attain a phase-locked state is sometimes observed. Rather than maintaining zero differential rotation (as is predicted to be dynamically stable by single-fluid, resistive MHD theory), these discharges develop hollow toroidal plasma fluid rotation profiles with reversed plasma flow shear in the region between the m/n = 3/2 and 2/1 islands. The additional forces expressed in this state are not readily accounted for, and therefore, analysis of these data highlights the impact of mode coupling on torque balance and the challenges associated with predicting the rotation dynamics of a fusion reactor—a key issue for ITER.

An Exit for the Human Product: A Comparative Study of Extreme Literature

Directory of Open Access Journals (Sweden)

Amelia Ying Qin

2014-04-01

Full Text Available This paper examines from a comparative perspective six novels telling stories of extreme life experiences set in both Western and oriental cultures. The paper argues that in these extreme cases, the characters, subjected to absolute power domination, lose their individual identities and are transformed into “human products.” Their struggles for power will always remain futile unless they find a way to reverse the power relationships they are trapped in. Such a reversal allows the hope of an exit for the “human products” to escape the hopeless situation of perpetuated social, sexual, and mental enslavement.

Current-driven instabilities of the kinetic shear Alfven wave: Application to reversed field pinches and spheromaks

International Nuclear Information System (INIS)

Meyerhofer, D.D.; Perkins, F.W.

1984-01-01

The kinetic Alfven wave is studied in a cylindrical force-free plasma with self-consistent magnetic fields. This equilibrium represents a reversed field pinch or a spheromak. The stability of the wave is found to depend on the ratio of the electron drift velocity to the Alfven velocity. This ratio varies inversely with the square root of the plasma line density. The critical line density using the Spitzer--Harm electron distribution function is found for reversed field pinches with deuterium plasmas to be approximately 2 x 10 18 and is 5 x 10 17 m -1 in spheromaks with hydrogen plasmas. The critical line density is in reasonable agreement with experimental data for reversed field pinches

Current driven instabilities of the kinetic shear Alfven wave: application to reversed field pinches and spheromaks

International Nuclear Information System (INIS)

Meyerhofer, D.D.; Perkins, F.W.

1984-04-01

The kinetic Alfven wave is studied in a cylindrical force-free plasma with self-consistent magnetic fields. This equilibrium represents a reversed field pinch or a spheromak. The stability of the wave is found to depend on the ratio of the electron drift velocity to the Alfven velocity. This ratio varies inversely with the square root of the plasma line density. The critical line density using the Spitzer-Harm electron distribution function is found for reversed field pinches with deuterium plasmas to be approximately 2 x 10 18 m -1 and is 5 x 10 17 m -1 in spheromaks with hydrogen plasmas. The critical line density is in reasonable agreement with experimental data for reversed field pinches

Effect of alkali–silica reaction on the shear strength of reinforced concrete structural members. A numerical and statistical study

Energy Technology Data Exchange (ETDEWEB)

Saouma, Victor E.; Hariri-Ardebili, Mohammad Amin [Department of Civil Engineering, University of Colorado, Boulder, CO 80305 (United States); Le Pape, Yann, E-mail: lepapeym@ornl.gov [Oak Ridge National Laboratory, One Bethel Valley Road, Oak Ridge, TN 37831 (United States); Balaji, Rajagopalan [Department of Civil Engineering, University of Colorado, Boulder, CO 80305 (United States)

2016-12-15

Highlights: • Alkali–silica reaction (ASR) affects reinforced structures shear strength. • Statistical analysis indicates large scattering of post-ASR strength losses/gains. • Competitive structural and materials mechanisms affect the residual shear strength. - Abstract: The residual structural shear resistance of concrete members without shear reinforcement and subject to alkali–aggregate reaction (ASR) is investigated by finite element analysis. A parametric numerical study of 648 analyses considering various structural members’ geometries, boundary conditions, ASR-induced losses of materials properties, ASR expansions and reinforcement ratios is conducted. As a result of competitive mechanisms (e.g., ASR-induced prestressing caused by the longitudinal reinforcement) and loss of concrete materials properties, important scatter in terms of gain or loss of shear strength is observed: about 50% of the studied configurations lead to a degradation of structural performance. The range of variation in terms of post-ASR shear resistance is extremely scattered, in particular, when ASR results in out-of-plane expansion only. Influencing factors are derived by two methods: (i) visual inspection of boxplots and probability distributions, and (ii) information criteria within multiple-linear regression analysis.

Shear strength of non-shear reinforced concrete elements

DEFF Research Database (Denmark)

Hoang, Cao linh

1997-01-01

The paper deals with the shear strength of prestressed hollow-core slabs determined by the theory of plasticity. Two failure mechanisms are considered in order to derive the solutions.In the case of sliding failure in a diagonal crack, the shear strength is determined by means of the crack sliding...

Shear-mode Crack Initiation Behavior in the Martensitic and Bainitic Microstructures

Directory of Open Access Journals (Sweden)

Wada Kentaro

2018-01-01

Full Text Available Fully reversed torsional fatigue tests were conducted to elucidate the behaviour of shear-mode crack initiation and propagation in one martensitic and two bainitic steels. The relationship between the crack initiation site and microstructure was investigated by means of an electron backscatter diffraction (EBSD technique. From the S-N diagram, two notable results were obtained: (i the shear-mode crack was initiated on the prior austenitic grain boundary in martensitic steel, while in bainitic steels, the crack was initiated along the {110} plane; one of the slip planes of bcc metals, and (ii the torsional fatigue limit of lower bainitic steel with finer grains was 60 MPa higher than that of upper bainitic steel with coarser grains even though the hardnesses were nearly equivalent. The mechanism determining the torsional fatigue strength in these steels is discussed from the viewpoint of microstructure morphology.

MHD shear flows with non-constant transverse magnetic field

International Nuclear Information System (INIS)

Núñez, Manuel

2012-01-01

Viscous conducting flows parallel to a fixed plate are studied. In contrast with the Hartmann setting, the problem is not linearized near a fixed transverse magnetic field, although the field tends to be transversal far from the wall. While general solutions may be formally obtained for all cases, their behavior is far more clear when the magnetic Prandtl number equals one. We consider two different instances: a fixed magnetic field at the wall, or an insulating sheet. The evolution of the flow and the magnetic field both near the plate and far from it are detailed, analyzing the possibility of reverse flow and instability of the solutions. -- Highlights: ► A conducting shear flow does not leave a transverse magnetic field invariant. ► Solutions are found for all cases, but these are more useful when kinetic and magnetic diffusivities coincide. ► Dirichlet and Neumann conditions on the magnetic field are studied. ► Reverse flow, and eventual instability, are possible.

Continuous shear - a method for studying material elements passing a stationary shear plane

DEFF Research Database (Denmark)

Lindegren, Maria; Wiwe, Birgitte; Wanheim, Tarras

2003-01-01

circumferential groove. Normally shear in metal forming processes is of another nature, namely where the material elements move through a stationary shear zone, often of small width. In this paper a method enabling the simulation of this situation is presented. A tool for continuous shear has beeen manufactured...... and tested with AlMgSil and copper. The sheared material has thereafter been tested n plane strain compression with different orientation concerning the angle between the shear plane and the compression direction....

Kansas Department of Transportation column expert : ultimate shear capacity of circular columns using the simplified modified compression field theory.

Science.gov (United States)

2015-09-01

The importance of the analysis of circular columns to accurately predict their ultimate confined : capacity under shear-flexure-axial force interaction domain is recognized in light of the extreme load event : imposed by the current American Associat...

Dual shear plate power processor packaging design. [for Solar Electric Propulsion spacecraft

Science.gov (United States)

Franzon, A. O.; Fredrickson, C. D.; Ross, R. G.

1975-01-01

The use of solar electric propulsion (SEP) for spacecraft primary propulsion imposes an extreme range of operational and environmental design requirements associated with the diversity of missions for which solar electric primary propulsion is advantageous. One SEP element which is particularly sensitive to these environmental extremes is the power processor unit (PPU) which powers and controls the electric ion thruster. An improved power processor thermal-mechanical packaging approach, referred to as dual shear plate packaging, has been designed to accommodate these different requirements with minimum change to the power processor design. Details of this packaging design are presented together with test results obtained from thermal-vacuum and structural-vibration tests conducted with prototype hardware.

Analysis of extreme wind events at Høvsøre and the effect on wind turbine loads

DEFF Research Database (Denmark)

Hannesdóttir, Ásta; Kelly, Mark C.; Mann, Jakob

used to simulate wind turbine response in time domain. The simulations are made for the DTU 10 MW reference wind turbine. Load analysis shows that the maximum tilt moment on the tower yaw bearing correlates well with the wind shear of the measurements. When these loads are compared with the extreme...... wind shear load case of the IEC standards, it is seen that they are of similar magnitude and in one case even higher....

Initial reversed-field pinch experiments on ZT-40 and recent advances in RFP theory

International Nuclear Information System (INIS)

Baker, D.A.; Buchenauer, C.J.; Burkhardt, L.C.

1980-01-01

The ZT-40 reversed-field pinch (RFP) has been operated in several modes: (1) without reversed toroidal field, (2) with self reversal, and (3) with aided reversal. An analytic ohmic heating and ignition model both confirm and provide guidance for transport codes. Nondissipative formation schemes have been analyzed and ideal MHD stable evolution and burn scenarios have been found. Particle and fluid simulations have produced qualitative agreement with respect to the nonlinear behavior of m = 0 resistive g-modes. Helical ohmic reversed field states are produced by a 2-D dynamical simulation, and nonlinear analytic work describes the final state. A fast resistive MHD code for linear stability has clarified the relations between several kinds of resistive instabilities. Ballooning modes and g-modes in systems with arbitrary magnetic shear including resistivity and viscosity, have been studied in a unified treatment with growth rate vs wavenumber showing the existence of important cutoffs

Separate structure of two branches of sheared slab ηi mode and effects of plasma rotation shear in weak magnetic shear region

International Nuclear Information System (INIS)

Jiquan Li; Kishimoto, Y.; Tuda, T.

2000-01-01

The separate structure of two branches of the sheared slab η i mode near the minimum-q magnetic surface is analysed and the effects of plasma rotation shears are considered in the weak magnetic shear region. Results show that the separation condition depends on the non-monotonous q profile and the deviation of rational surface from the minimum-q surface. Furthermore, it is found that the diamagnetic rotation shear may suppress the perturbation of the sheared slab η i mode at one side of the minimum-q surface, the poloidal rotation shear from the sheared E-vector x B-vector flow has a similar role to the slab mode structure when it possesses a direction same as the diamagnetic shear. A plausible interrelation between the separate structures of the two branches of the sheared slab mode and the discontinuity or gap of the radially global structure of the drift wave near the minimum-q surface observed in the toroidal particle simulation (Kishimoto Y et al 1998 Plasma Phys. Control. Fusion 40 A663) is discussed. It seems to support such a viewpoint: the double or/and global branches of the sheared slab η i mode near the minimum-q surface may become a bridge to connect the radially global structures of the drift wave at two sides of the minimum-q surface and the discontinuity may originate from the separate structures of these slab modes for a flatter q profile. (author)

Suppression of plasma turbulence during optimised shear configurations in JET

International Nuclear Information System (INIS)

Conway, G.D.; Borba, D.N.; Alper, B.

1999-08-01

Density turbulence suppression is observed in the internal transport barrier (ITB) region of JET discharges with optimised magnetic shear. The suppression occurs in two stages. First, low frequency turbulence is reduced across the plasma core by a toroidal velocity shear generated by intense auxiliary heating. Then when the ITB forms, high frequency turbulence is reduced locally within the steep pressure gradient region of the ITB, consistent with the effects of enhanced E x B poloidal shear. The turbulence suppression is correlated with reduced plasma transport and improved fusion performance. Much effort has been spent in recent years in developing alternative scenarios for operating tokamak fusion reactors. One particular scenario involves reversing or reducing the central magnetic shear to form an internal transport barrier (ITB). The result is reduced plasma core energy transport and enhanced fusion performance. It is believed that ITBs may be formed through a combination of E x B velocity shear and magnetic shear stabilisation of plasma turbulence and instabilities. In this Letter we present results from JET optimised shear discharges showing that turbulence suppression during ITB formation occurs in two stages. First low frequency turbulence is reduced across the plasma core, coinciding with a region of strong toroidal velocity shear; then high frequency turbulence is locally suppressed around the ITB region, consistent with enhanced pressure gradient driven E x B poloidal shear. The measurements were made using a system of X-mode reflectometers consisting of two, dual-channel toroidal correlation reflectometers at 75 GHz (covering plasma outboard edge) and 105 GHz (core and inboard edge), and a 92-96 GHz swept frequency radial correlation reflectometer (plasma core). Reflectometry is a powerful tool for measuring density fluctuations. The highly localised reflection of the microwave beam gives excellent spatial localisation. Measurements can be made

Functional Polymer Opals and Porous Materials by Shear-Induced Assembly of Tailor-Made Particles.

Science.gov (United States)

Gallei, Markus

2018-02-01

Photonic band-gap materials attract enormous attention as potential candidates for a steadily increasing variety of applications. Based on the preparation of easily scalable monodisperse colloids, such optically attractive photonic materials can be prepared by an inexpensive and convenient bottom-up process. Artificial polymer opals can be prepared by shear-induced assembly of core/shell particles, yielding reversibly stretch-tunable materials with intriguing structural colors. This feature article highlights recent developments of core/shell particle design and shear-induced opal formation with focus on the combination of hard and soft materials as well as crosslinking strategies. Structure formation of opal materials relies on both the tailored core/shell architecture and the parameters for polymer processing. The emphasis of this feature article is on elucidating the particle design and incorporation of addressable moieties, i.e., stimuli-responsive polymers as well as elaborated crosslinking strategies for the preparation of smart (inverse) opal films, inorganic/organic opals, and ceramic precursors by shear-induced ordering. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shear Capacity of C-Shaped and L-Shaped Angle Shear Connectors.

Directory of Open Access Journals (Sweden)

Farzad Tahmasbi

Full Text Available This paper investigates the behaviour of C-shaped and L-shaped angle shear connectors embedded in solid concrete slabs. An effective finite element model is proposed to simulate the push out tests of these shear connectors that encompass nonlinear material behaviour, large displacement and damage plasticity. The finite element models are validated against test results. Parametric studies using this nonlinear model are performed to investigate the variations in concrete strength and connector dimensions. The finite element analyses also confirm the test results that increasing the length of shear connector increases their shear strength proportionately. It is observed that the maximum stress in L-shaped angle connectors takes place in the weld attachment to the beam, whereas in the C-shaped angle connectors, it is in the attached leg. The location of maximum concrete compressive damage is rendered in each case. Finally, a new equation for prediction of the shear capacity of C-shaped angle connectors is proposed.

Shear Capacity of C-Shaped and L-Shaped Angle Shear Connectors

Science.gov (United States)

Tahmasbi, Farzad; Maleki, Shervin; Shariati, Mahdi; Ramli Sulong, N. H.; Tahir, M. M.

2016-01-01

This paper investigates the behaviour of C-shaped and L-shaped angle shear connectors embedded in solid concrete slabs. An effective finite element model is proposed to simulate the push out tests of these shear connectors that encompass nonlinear material behaviour, large displacement and damage plasticity. The finite element models are validated against test results. Parametric studies using this nonlinear model are performed to investigate the variations in concrete strength and connector dimensions. The finite element analyses also confirm the test results that increasing the length of shear connector increases their shear strength proportionately. It is observed that the maximum stress in L-shaped angle connectors takes place in the weld attachment to the beam, whereas in the C-shaped angle connectors, it is in the attached leg. The location of maximum concrete compressive damage is rendered in each case. Finally, a new equation for prediction of the shear capacity of C-shaped angle connectors is proposed. PMID:27478894

Quantified Mechanical Properties of the Deltoid Muscle Using the Shear Wave Elastography: Potential Implications for Reverse Shoulder Arthroplasty.

Directory of Open Access Journals (Sweden)

Taku Hatta

Full Text Available The deltoid muscle plays a critical role in the biomechanics of shoulders undergoing reverse shoulder arthroplasty (RSA. However, both pre- and postoperative assessment of the deltoid muscle quality still remains challenging. The purposes of this study were to establish a novel methodology of shear wave elastography (SWE to quantify the mechanical properties of the deltoid muscle, and to investigate the reliability of this technique using cadaveric shoulders for the purpose of RSA. Eight fresh-frozen cadaveric shoulders were obtained. The deltoid muscles were divided into 5 segments (A1, A2, M, P1 and P2 according to the muscle fiber orientation and SWE values were measured for each segment. Intra- and inter-observer reliability was evaluated using intraclass correlation coefficient (ICC. To measure the response of muscle tension during RSA, the humeral shaft was osteotomized and subsequently elongated by an external fixator (intact to 15 mm elongation. SWE of the deltoid muscle was measured under each stretch condition. Intra- and inter-observer reliability of SWE measurements for all regions showed 0.761-0.963 and 0.718-0.947 for ICC(2,1. Especially, SWE measurements for segments A2 and M presented satisfactory repeatability. Elongated deltoid muscles by the external fixator showed a progressive increase in passive stiffness for all muscular segments. Especially, SWE outcomes of segments A2 and M reliably showed an exponential growth upon stretching (R2 = 0.558 and 0.593. Segmental measurements using SWE could be reliably and feasibly used to quantitatively assess the mechanical properties of the deltoid muscle, especially in the anterior and middle portions. This novel technique based on the anatomical features may provide helpful information of the deltoid muscle properties during treatment of RSA.

Bayesian decision and mixture models for AE monitoring of steel-concrete composite shear walls

Science.gov (United States)

Farhidzadeh, Alireza; Epackachi, Siamak; Salamone, Salvatore; Whittaker, Andrew S.

2015-11-01

This paper presents an approach based on an acoustic emission technique for the health monitoring of steel-concrete (SC) composite shear walls. SC composite walls consist of plain (unreinforced) concrete sandwiched between steel faceplates. Although the use of SC system construction has been studied extensively for nearly 20 years, little-to-no attention has been devoted to the development of structural health monitoring techniques for the inspection of damage of the concrete behind the steel plates. In this work an unsupervised pattern recognition algorithm based on probability theory is proposed to assess the soundness of the concrete infill, and eventually provide a diagnosis of the SC wall’s health. The approach is validated through an experimental study on a large-scale SC shear wall subjected to a displacement controlled reversed cyclic loading.

Plasticity Approach to Shear Design

DEFF Research Database (Denmark)

Hoang, Cao Linh; Nielsen, Mogens Peter

1998-01-01

The paper presents some plastic models for shear design of reinforced concrete beams. Distinction is made between two shear failure modes, namely web crushing and crack sliding. The first mentioned mode is met in beams with large shear reinforcement degrees. The mode of crack sliding is met in non......-shear reinforced beams as well as in lightly shear reinforced beams. For such beams the shear strength is determined by the recently developed crack sliding model. This model is based upon the hypothesis that cracks can be transformed into yield lines, which have lower sliding resistance than yield lines formed...... in uncracked concrete. Good agree between theory and tests has been found.Keywords: dsign, plasticity, reinforced concrete, reinforcement, shear, web crushing....

Turbulence suppression by E x B shear in JET optimized shear pulses

International Nuclear Information System (INIS)

Beer, M.A.; Budny, R.V.; Challis, C.D.; Conway, G.

2000-01-01

The authors calculate microinstability growth rates in JET optimized shear plasmas with a comprehensive gyrofluid model, including sheared E x B flows, trapped electrons, and all dominant ion species in realistic magnetic geometry. They find good correlation between E x B shear suppression of microinstabilities and both the formation and collapse of the internal transport barrier

Shear Strains, Strain Rates and Temperature Changes in Adiabatic Shear Bands

Science.gov (United States)

1980-05-01

X14A. It has been found that when bainitic and martensitic steels are sheared adiabatically, a layer of material within ths shear zone is altezed and...Sooiety for Metals, Metals Park, Ohio, 1978, pp. 148-0. 21 TABLE II SOLID-STATE TRANSFORMATIONS IN BAINITIC STEEL TRANSFORMATION TRANSFORMATION...shear, thermoplastic, plasticity, plastic deformation, armor, steel IL AnSRACT ( -=nba asoa.tm a naeoesM iN faity by bleak n bet/2972 Experiments

Mechanical characteristics under monotonic and cyclic simple shear of spark plasma sintered ultrafine-grained nickel

International Nuclear Information System (INIS)

Dirras, G.; Bouvier, S.; Gubicza, J.; Hasni, B.; Szilagyi, T.

2009-01-01

The present work focuses on understanding the mechanical behavior of bulk ultrafine-grained nickel specimens processed by spark plasma sintering of high purity nickel nanopowder and subsequently deformed under large amplitude monotonic simple shear tests and strain-controlled cyclic simple shear tests at room temperature. During cyclic tests, the samples were deformed up to an accumulated von Mises strain of about ε VM = 0.75 (the flow stress was in the 650-700 MPa range), which is extremely high in comparison with the low tensile/compression ductility of this class of materials at quasi-static conditions. The underlying physical mechanisms were investigated by electron microscopy and X-ray diffraction profile analysis. Lattice dislocation-based plasticity leading to cell formation and dislocation interactions with twin boundaries contributed to the work-hardening of these materials. The large amount of plastic strain that has been reached during the shear tests highlights intrinsic mechanical characteristics of the ultrafine-grained nickel studied here.

Mechanical characteristics under monotonic and cyclic simple shear of spark plasma sintered ultrafine-grained nickel

Energy Technology Data Exchange (ETDEWEB)

Dirras, G., E-mail: dirras@univ-paris13.fr [LPMTM - CNRS, Institut Galilee, Universite Paris 13, 99 Avenue J.B. Clement, 93430 Villetaneuse (France); Bouvier, S. [LPMTM - CNRS, Institut Galilee, Universite Paris 13, 99 Avenue J.B. Clement, 93430 Villetaneuse (France); Gubicza, J. [Department of Materials Physics, Eoetvoes Lorand University, P.O.B. 32, Budapest H-1518 (Hungary); Hasni, B. [LPMTM - CNRS, Institut Galilee, Universite Paris 13, 99 Avenue J.B. Clement, 93430 Villetaneuse (France); Szilagyi, T. [Department of Materials Physics, Eoetvoes Lorand University, P.O.B. 32, Budapest H-1518 (Hungary)

2009-11-25

The present work focuses on understanding the mechanical behavior of bulk ultrafine-grained nickel specimens processed by spark plasma sintering of high purity nickel nanopowder and subsequently deformed under large amplitude monotonic simple shear tests and strain-controlled cyclic simple shear tests at room temperature. During cyclic tests, the samples were deformed up to an accumulated von Mises strain of about {epsilon}{sub VM} = 0.75 (the flow stress was in the 650-700 MPa range), which is extremely high in comparison with the low tensile/compression ductility of this class of materials at quasi-static conditions. The underlying physical mechanisms were investigated by electron microscopy and X-ray diffraction profile analysis. Lattice dislocation-based plasticity leading to cell formation and dislocation interactions with twin boundaries contributed to the work-hardening of these materials. The large amount of plastic strain that has been reached during the shear tests highlights intrinsic mechanical characteristics of the ultrafine-grained nickel studied here.

Relative viscosity of emulsions in simple shear flow: Temperature, shear rate, and interfacial tension dependence

Energy Technology Data Exchange (ETDEWEB)

Choi, Se Bin; Lee, Joon Sang [Dept. of Mechanical Engineering, Yonsei Unversity, Seoul (Korea, Republic of)

2015-08-15

We simulate an emulsion system under simple shear rates to analyze its rheological characteristics using the lattice Boltzmann method (LBM). We calculate the relative viscosity of an emulsion under a simple shear flow along with changes in temperature, shear rate, and surfactant concentration. The relative viscosity of emulsions decreased with an increase in temperature. We observed the shear-thinning phenomena, which is responsible for the inverse proportion between the shear rate and viscosity. An increase in the interfacial tension caused a decrease in the relative viscosity of the decane-in-water emulsion because the increased deformation caused by the decreased interfacial tension significantly influenced the wall shear stress.

Gravo-Aeroelastic Scaling for Extreme-Scale Wind Turbines

Energy Technology Data Exchange (ETDEWEB)

Fingersh, Lee J [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Loth, Eric [University of Virginia; Kaminski, Meghan [University of Virginia; Qin, Chao [University of Virginia; Griffith, D. Todd [Sandia National Laboratories

2017-06-09

A scaling methodology is described in the present paper for extreme-scale wind turbines (rated at 10 MW or more) that allow their sub-scale turbines to capture their key blade dynamics and aeroelastic deflections. For extreme-scale turbines, such deflections and dynamics can be substantial and are primarily driven by centrifugal, thrust and gravity forces as well as the net torque. Each of these are in turn a function of various wind conditions, including turbulence levels that cause shear, veer, and gust loads. The 13.2 MW rated SNL100-03 rotor design, having a blade length of 100-meters, is herein scaled to the CART3 wind turbine at NREL using 25% geometric scaling and blade mass and wind speed scaled by gravo-aeroelastic constraints. In order to mimic the ultralight structure on the advanced concept extreme-scale design the scaling results indicate that the gravo-aeroelastically scaled blades for the CART3 are be three times lighter and 25% longer than the current CART3 blades. A benefit of this scaling approach is that the scaled wind speeds needed for testing are reduced (in this case by a factor of two), allowing testing under extreme gust conditions to be much more easily achieved. Most importantly, this scaling approach can investigate extreme-scale concepts including dynamic behaviors and aeroelastic deflections (including flutter) at an extremely small fraction of the full-scale cost.

Shear banding, discontinuous shear thickening, and rheological phase transitions in athermally sheared frictionless disks

Science.gov (United States)

Vâgberg, Daniel; Olsson, Peter; Teitel, S.

2017-05-01

We report on numerical simulations of simple models of athermal, bidisperse, soft-core, massive disks in two dimensions, as a function of packing fraction ϕ , inelasticity of collisions as measured by a parameter Q , and applied uniform shear strain rate γ ˙. Our particles have contact interactions consisting of normally directed elastic repulsion and viscous dissipation, as well as tangentially directed viscous dissipation, but no interparticle Coulombic friction. Mapping the phase diagram in the (ϕ ,Q ) plane for small γ ˙, we find a sharp first-order rheological phase transition from a region with Bagnoldian rheology to a region with Newtonian rheology, and show that the system is always Newtonian at jamming. We consider the rotational motion of particles and demonstrate the crucial importance that the coupling between rotational and translational degrees of freedom has on the phase structure at small Q (strongly inelastic collisions). At small Q , we show that, upon increasing γ ˙, the sharp Bagnoldian-to-Newtonian transition becomes a coexistence region of finite width in the (ϕ ,γ ˙) plane, with coexisting Bagnoldian and Newtonian shear bands. Crossing this coexistence region by increasing γ ˙ at fixed ϕ , we find that discontinuous shear thickening can result if γ ˙ is varied too rapidly for the system to relax to the shear-banded steady state corresponding to the instantaneous value of γ ˙.

Magnetohydrodynamic effects of current profile control in reversed field pinches

International Nuclear Information System (INIS)

Sovinec, C.R.; Prager, S.C.

1999-01-01

Linear and non-linear MHD computations are used to investigate reversed field pinch configurations with magnetic fluctuations reduced through current profile control. Simulations with reduced ohmic drive and moderate auxiliary current drive, represented generically with an electron force term, applied locally in radius near the plasma edge show magnetic fluctuation energies that are orders of magnitude smaller than those in simulations without profile control. The core of the improved configurations has reduced magnetic shear and closed flux surfaces in some cases, and reversal is sustained through the auxiliary current drive. Modes resonant near the edge may become unstable with auxiliary drive, but their saturation levels can be controlled. The space of auxiliary drive parameters is explored, and the ill effects of deviating far from optimal conditions is demonstrated in non-linear simulations. (author)

Comparison of direct shear and simple shear responses of municipal solid waste in USA

KAUST Repository

Fei, Xunchang; Zekkos, Dimitrios

2017-01-01

Although large-size simple shear (SS) testing of municipal solid waste (MSW) may arguably provide a more realistic estimate of the shear strength (τ ) of MSW than the most commonly used direct shear (DS) testing, a systematic comparison between

Radiologic Findings of Reversed Intestinal Rotation in Adults: 3 Cases Report

International Nuclear Information System (INIS)

Baek, Hyeon Seok; Cho, Jae Ho; Chang, Jay Chun; Kim, Jae Woon; Kim, Kum Rae; Park, Won Kyu; Kim, Jong Yeol

2009-01-01

Most anomalies of intestinal rotation are detected during the postneonatal period. In adults, the diagnosis and treatment of patients with a congenital anomaly of the midgut can be difficult because of their extremely rarity. Based on embryology, anomalies of intestinal rotation can be divided into non-rotation, reversed rotation and malrotation. Reversed rotation of the midgut is the rarest of all anomalies of intestinal rotation. Although this anomaly is rare, it can be diagnosed by a detailed knowledge of embryology and anatomy. We report three adult patients with reversed intestinal rotation and review the embryology, clinical presentation and radiographic findings of this disorder

Semiconductor laser shearing interferometer

International Nuclear Information System (INIS)

Ming Hai; Li Ming; Chen Nong; Xie Jiaping

1988-03-01

The application of semiconductor laser on grating shearing interferometry is studied experimentally in the present paper. The method measuring the coherence of semiconductor laser beam by ion etching double frequency grating is proposed. The experimental result of lens aberration with semiconductor laser shearing interferometer is given. Talbot shearing interferometry of semiconductor laser is also described. (author). 2 refs, 9 figs

Austenitic Reversion of Cryo-rolled Ti-Stabilized Austenitic Stainless Steel: High-Resolution EBSD Investigation

Science.gov (United States)

Tiamiyu, A. A.; Odeshi, A. G.; Szpunar, J. A.

2018-02-01

In this study, AISI 321 austenitic stainless steel (ASS) was cryo-rolled and subsequently annealed at 650 and 800 °C to reverse BCC α'-martensite to FCC γ-austenite. The texture evolution associated with the reversion at the selected temperatures was investigated using high-resolution EBSD. After the reversion, TiC precipitates were observed to be more stable in 650 °C-annealed specimens than those reversed at 800 °C. {110} texture was mainly developed in specimens subjected to both annealing temperatures. However, specimens reversed at 650 °C have stronger texture than those annealed at 800 °C, even at the higher annealing time. The strong intensity of {110} texture component is attributed to the ability of AISI 321 ASS to memorize the crystallographic orientation of the deformed austenite, a phenomenon termed texture memory. The development of weaker texture in 800 °C-annealed specimens is attributed to the residual strain relief in grains, dissolution of grain boundary precipitates, and an increase in atomic migration along the grain boundaries. Based on the observed features of the reversed austenite grains and estimation from an existing model, it is suspected that the austenite reversion at 650 and 800 °C undergone diffusional and martensitic shear reversion, respectively.

Comparison of direct shear and simple shear responses of municipal solid waste in USA

KAUST Repository

Fei, Xunchang

2017-10-25

Although large-size simple shear (SS) testing of municipal solid waste (MSW) may arguably provide a more realistic estimate of the shear strength (τ ) of MSW than the most commonly used direct shear (DS) testing, a systematic comparison between the shear responses of MSW obtained from the two testing methods is lacking. In this study, a large-size shear device was used to test identical MSW specimens sampled in USA in DS and SS. Eight DS tests and 11 SS tests were conducted at vertical effective stresses of 50–500 kPa. The stress–displacement response of MSW in SS testing was hyperbolic and a maximum shear stress was reached, whereas a maximum shear stress was not reached in most DS tests. The τ, effective friction angle (ϕ ′) and cohesion (c ′) of MSW were obtained from DS and SS tests by using a displacement failure criterion of 40 mm. τ in SS testing was found to be equal to or lower than τ in DS testing with ratios of τ between 73 and 101%. SS testing resulted in higher ϕ ′ but lower c ′ than DS testing. The shear strength parameters were lower than those obtained in previous studies from DS tests at 55 mm displacement.

Experimental investigations into the shear behavior of self-compacting RC beams with and without shear reinforcement

Directory of Open Access Journals (Sweden)

Ammar N. HANOON

2014-12-01

Full Text Available Self-compacting concrete (SCC is a new generation of high-performance concrete, known for its excellent deformability and high resistance to segregation and bleeding. Nonetheless, SCC may be incapable of resisting shear because the shear resistance mechanisms of this concrete are uncertain, especially the aggregate interlock mechanism. This uncertainty is attributed to the fact that SCC contains a smaller amount of coarse aggregates than normal concrete (NC does. This study focuses on the shear strength of self-compacting reinforced concrete (RC beams with and without shear reinforcement. A total of 16 RC beam specimens was manufactured and tested in terms of shear span-to-depth ratio and flexural and shear reinforcement ratio. The test results were compared with those of the shear design equations developed by ACI, BS, CAN and NZ codes. Results show that an increase in web reinforcement enhanced cracking strength and ultimate load. Shear-tension failure was the control failure in all tested beams.

Confocal microscopy of colloidal dispersions in shear flow using a counter-rotating cone-plate shear cell

International Nuclear Information System (INIS)

Derks, Didi; Wisman, Hans; Blaaderen, Alfons van; Imhof, Arnout

2004-01-01

We report on novel possibilities for studying colloidal suspensions in a steady shear field in real space. Fluorescence confocal microscopy is combined with the use of a counter-rotating cone-plate shear cell. This allows imaging of individual particles in the bulk of a sheared suspension in a stationary plane. Moreover, this plane of zero velocity can be moved in the velocity gradient direction while keeping the shear rate constant. The colloidal system under study consists of rhodamine labelled PMMA spheres in a nearly density and refractive index matched mixture of cyclohexylbromide and cis-decalin. We show measured flow profiles in both the fluid and the crystalline phase and find indications for shear banding in the case of a sheared crystal. Furthermore, we show that, thanks to the counter-rotating principle of the cone-plate shear cell, a layer of particles in the bulk of a sheared crystalline suspension can be imaged for a prolonged time, with the result that their positions can be tracked

XIAP reverses various functional activities of FRNK in endothelial cells

International Nuclear Information System (INIS)

Ahn, Sunyoung; Kim, Hyun Jeong; Chi, Sung-Gil; Park, Heonyong

2012-01-01

Highlights: ► FRNK domain is recruited into focal adhesion (FA), controlling endothelial cell adhesion. ► XIAP binds the FRNK domain of FAK. ► XIAP inhibits recruitment of FRNK into Fas and FRNK-promoted cell adhesion. ► XIAP plays a key role in vascular functions of FRNK or FRNK domain-mediated vascular functions of FAK. -- Abstract: In endothelial cells, focal adhesion kinase (FAK) regulates cell proliferation, migration, adhesion, and shear-stimulated activation of MAPK. We recently found that FAK is recruited into focal adhesion (FA) sites through interactions with XIAP (X-chromosome linked inhibitor of apoptosis protein) and activated by Src kinase in response to shear stress. In this study, we examined which domain(s) of FAK is(are) important for various vascular functions such as FA recruiting, XIAP-binding and shear stress-stimulated ERK activation. Through a series of experiments, we determined that the FRNK domain is recruited into FA sites and promotes endothelial cell adhesion. Interestingly, XIAP knockdown was shown to reduce FA recruitment of FRNK and the cell adhesive effect of FRNK. In addition, we found that XIAP interacts with FRNK, suggesting cross-talk between XIAP and FRNK. We also demonstrated that FRNK inhibits endothelial cell migration and shear-stimulated ERK activation. These inhibitory effects of FRNK were reversed by XIAP knockdown. Taken together, we can conclude that XIAP plays a key role in vascular functions of FRNK or FRNK domain-mediated vascular functions of FAK.

Excited waves in shear layers

Science.gov (United States)

Bechert, D. W.

1982-01-01

The generation of instability waves in free shear layers is investigated. The model assumes an infinitesimally thin shear layer shed from a semi-infinite plate which is exposed to sound excitation. The acoustical shear layer excitation by a source further away from the plate edge in the downstream direction is very weak while upstream from the plate edge the excitation is relatively efficient. A special solution is given for the source at the plate edge. The theory is then extended to two streams on both sides of the shear layer having different velocities and densities. Furthermore, the excitation of a shear layer in a channel is calculated. A reference quantity is found for the magnitude of the excited instability waves. For a comparison with measurements, numerical computations of the velocity field outside the shear layer were carried out.

Mechanism of shallow disrupted slide induced by extreme rainfall

Science.gov (United States)

Igwe, O.; Fukuoka, H.

2010-12-01

On July 16, 2010, extreme rainfall attacked western Japan and it caused very intense rainfall in Shobara city, Hiroshima prefecture, Japan. This rainfall induced hundreds of shallow disrupted slides and many of those became debris flows. One of this debris flows attacked a house standing in front of the exit of a channel, and claimed a resident’s life. Western Japan had repeatedly similar disasters in the past. Last event took place from July 19 to 26, 2009, when western Japan had a severe rainstorms and caused floods and landslides. Most of the landslides are debris slide - debris flows. Most devastated case took place in Hofu city, Japan. On July 21, extremely intense rainstorm caused numerous debris flows and mud flows in the hillslopes. Some of the debris flows destroyed residential houses and home for elderly people, and finally killed 14 residents. One of the unusual feature of both disaster was that landslides are distributed in very narrow area. In the 2010 Shobara city disaster, all of the landslides were distributed in 5 km x 3 km, and in the 2009 Hofu city disaster, most devastated zone of landslides were 10 km x 5 km. Rain radars of Meteorological Agency of Government of Japan detected the intense rainfall, however, the spatial resolution is usually larger than 5 km and the disaster area is too small to predict landslides nor issue warning. Furthermore, it was found that the growth rate of baby clouds was very quick. The geology of both areas are rhyolite (Shobara) and granite (Hofu), so the areal assessment of landslide hazard should be prepared before those intense rainfall will come. As for the Hofu city case, it was proved that debris flows took place in the high precipitation area and covered by covered by weathered granite sands and silts which is called “masa". This sands has been proved susceptible against landslides under extreme rainfall conditions. However, the transition from slide - debris flow process is not well revealed, except

Structure of sheared and rotating turbulence: Multiscale statistics of Lagrangian and Eulerian accelerations and passive scalar dynamics.

Science.gov (United States)

Jacobitz, Frank G; Schneider, Kai; Bos, Wouter J T; Farge, Marie

2016-01-01

The acceleration statistics of sheared and rotating homogeneous turbulence are studied using direct numerical simulation results. The statistical properties of Lagrangian and Eulerian accelerations are considered together with the influence of the rotation to shear ratio, as well as the scale dependence of their statistics. The probability density functions (pdfs) of both Lagrangian and Eulerian accelerations show a strong and similar dependence on the rotation to shear ratio. The variance and flatness of both accelerations are analyzed and the extreme values of the Eulerian acceleration are observed to be above those of the Lagrangian acceleration. For strong rotation it is observed that flatness yields values close to three, corresponding to Gaussian-like behavior, and for moderate and vanishing rotation the flatness increases. Furthermore, the Lagrangian and Eulerian accelerations are shown to be strongly correlated for strong rotation due to a reduced nonlinear term in this case. A wavelet-based scale-dependent analysis shows that the flatness of both Eulerian and Lagrangian accelerations increases as scale decreases, which provides evidence for intermittent behavior. For strong rotation the Eulerian acceleration is even more intermittent than the Lagrangian acceleration, while the opposite result is obtained for moderate rotation. Moreover, the dynamics of a passive scalar with gradient production in the direction of the mean velocity gradient is analyzed and the influence of the rotation to shear ratio is studied. Concerning the concentration of a passive scalar spread by the flow, the pdf of its Eulerian time rate of change presents higher extreme values than those of its Lagrangian time rate of change. This suggests that the Eulerian time rate of change of scalar concentration is mainly due to advection, while its Lagrangian counterpart is only due to gradient production and viscous dissipation.

Shear strength of non-shear reinforced concrete elements

DEFF Research Database (Denmark)

Hoang, Cao linh

1997-01-01

is based upon the hypothesis that cracks can be transformed into yield lines, which have lower sliding resistance than yield lines formed in uncracked concrete.Proposals have been made on how the derived standard solutions may be applied to more complicated cases, such as continuous beams, beams......The report deals with the shear strength of statically indeterminate reinforced concrete beams without shear reinforcement. Solutions for a number of beams with different load and support conditions have been derived by means of the crack sliding model developed by Jin- Ping Zhang.This model...

Experiments on sheet metal shearing

OpenAIRE

Gustafsson, Emil

2013-01-01

Within the sheet metal industry, different shear cutting technologies are commonly used in several processing steps, e.g. in cut to length lines, slitting lines, end cropping etc. Shearing has speed and cost advantages over competing cutting methods like laser and plasma cutting, but involves large forces on the equipment and large strains in the sheet material.Numerical models to predict forces and sheared edge geometry for different sheet metal grades and different shear parameter set-ups a...

Experimental observation of shear thickening oscillation

DEFF Research Database (Denmark)

Nagahiro, Shin-ichiro; Nakanishi, Hiizu; Mitarai, Namiko

2013-01-01

We report experimental observations of the shear thickening oscillation, i.e. the spontaneous macroscopic oscillation in the shear flow of severe shear thickening fluid. Using a density-matched starch-water mixture, in the cylindrical shear flow of a few centimeters flow width, we observed...

Shear behaviour of reinforced phyllite concrete beams

International Nuclear Information System (INIS)

Adom-Asamoah, Mark; Owusu Afrifa, Russell

2013-01-01

Highlights: ► Phyllite concrete beams often exhibited shear with anchorage bond failure. ► Different shear design provisions for reinforced phyllite beams are compared. ► Predicted shear capacity of phyllite beams must be modified by a reduction factor. -- Abstract: The shear behaviour of concrete beams made from phyllite aggregates subjected to monotonic and cyclic loading is reported. First diagonal shear crack load of beams with and without shear reinforcement was between 42–58% and 42–92% of the failure loads respectively. The phyllite concrete beams without shear links had lower post-diagonal cracking shear resistance compared to corresponding phyllite beams with shear links. As a result of hysteretic energy dissipation, limited cyclic loading affected the stiffness, strength and deformation of the phyllite beams with shear reinforcement. Generally, beams with and without shear reinforcement showed anchorage bond failure in addition to the shear failure due to high stress concentration near the supports. The ACI, BS and EC codes are conservative for the prediction of phyllite concrete beams without shear reinforcement but they all overestimate the shear strength of phyllite concrete beams with shear reinforcement. It is recommended that the predicted shear capacity of phyllite beams reinforced with steel stirrups be modified by a reduction factor of 0.7 in order to specify a high enough safety factor on their ultimate strength. It is also recommended that susceptibility of phyllite concrete beams to undergo anchorage bond failure is averted in design by the provision of greater anchorage lengths than usually permitted.

Viscosity of nanoconfined polyamide-6,6 oligomers: atomistic reverse nonequilibrium molecular dynamics simulation.

Science.gov (United States)

Eslami, Hossein; Müller-Plathe, Florian

2010-01-14

Our new simulation scheme in isosurface-isothermal-isobaric ensemble [Eslami, H.; Mozaffari, F.; Moghadasi, J.; Müller-Plathe, F. J. Chem. Phys. 2008, 129, 194702], developed to simulate confined fluids in equilibrium with bulk, is applied to simulate polyamide-6,6 oligomers confined between graphite surfaces. The reverse nonequilibrium molecular dynamics simulation technique is employed to shear the graphite surfaces. In this work, six confined systems, with different surface separations, as well as the bulk fluid are simulated. Our results show a viscosity increase with respect to the bulk fluid, with decreasing distance between surfaces. Also, the calculated viscosities of the confined systems show an oscillatory behavior with maxima corresponding to well-formed layers between the surfaces. We observe a substantial slip at the surfaces, with the slip length depending on the shear rate and on the slit width. The slip length and the slip velocity show oscillatory behavior with out-of-phase oscillations with respect to the solvation force oscillations. Moreover, the temperature difference between coldest and hottest parts of the simulation box depends on the shear rate and on the layering effect (solvation force oscillations). An analysis of oligomer deformation under flow shows preferential alignment of oligomers parallel to the surfaces with increasing shear rate.

To determine the slow shearing rate for consolidation drained shear box tests

Science.gov (United States)

Jamalludin, Damanhuri; Ahmad, Azura; Nordin, Mohd Mustaqim Mohd; Hashim, Mohamad Zain; Ibrahim, Anas; Ahmad, Fauziah

2017-08-01

Slope failures always occur in Malaysia especially during the rainy seasons. They cause damage to properties and fatalities. In this study, a total of 24 one dimensional consolidation tests were carried out on soil samples taken from 16 slope failures in Penang Island and in Baling, Kedah. The slope failures in Penang Island are within the granitic residual soil while in Baling, Kedah they are situated within the sedimentary residual soil. Most of the disturbed soil samples were taken at 100mm depth from the existing soil surface while some soil samples were also taken at 400, 700 and 1000mm depths from the existing soil surface. They were immediately placed in 2 layers of plastic bag to prevent moisture loss. Field bulk density tests were also carried out at all the locations where soil samples were taken. The field bulk density results were later used to re-compact the soil samples for the consolidation tests. The objective of the research is to determine the slow shearing rate to be used in consolidated drained shear box for residual soils taken from slope failures so that the effective shear strength parameters can be determined. One dimensional consolidation tests were used to determine the slow shearing rate. The slow shearing rate found in this study to be used in the consolidated drained shear box tests especially for Northern Malaysian residual soils was 0.286mm/minute.

Reverse gyrase functions in genome integrity maintenance by protecting DNA breaks in vivo

DEFF Research Database (Denmark)

Han, Wenyuan; Feng, Xu; She, Qunxin

2017-01-01

Reverse gyrase introduces positive supercoils to circular DNA and is implicated in genome stability maintenance in thermophiles. The extremely thermophilic crenarchaeon Sulfolobus encodes two reverse gyrase proteins, TopR1 (topoisomerase reverse gyrase 1) and TopR2, whose functions in thermophilic...... and subsequent DNA degradation. The former occurred immediately after drug treatment, leading to chromosomal DNA degradation that concurred with TopR1 degradation, followed by chromatin protein degradation and DNA-less cell formation. To gain a further insight into TopR1 function, the expression of the enzyme...

Anomalous shear wave delays and surface wave velocities at Yellowstone Caldera, Wyoming

International Nuclear Information System (INIS)

Daniel, R.G.; Boore, D.M.

1982-01-01

To investigate the effects of a geothermal area on the propagation of intermediate-period (1--30 s) teleseismic body waves and surface waves, a specially designed portable seismograph system was operated in Yellowstone Caldera, Wyoming. Travel time residuals, relative to a station outside the caldera, of up to 2 s for compressional phases are in agreement with short-period residuals for P phases measured by other investigators. Travel time delays for shear arrivals in the intermediate-period band range from 2 to 9 s and decrease with increasing dT/dΔ. Measured Rayleigh wave phase velocities are extremely low, ranging from 3.2 km/s at 27-s period to 2.0 km/s at 7-s period; the estimated uncertainty associated with these values is 15%. We propose a model for compressional and shear velocities and Poisson's ratio beneath the Yellowstone caldera which fits the teleseismic body and surface wave data: it consists of a highly anomalous crust with an average shear velocity of 3.0 km/s overlying an upper mantle with average velocity of 4.1 km/s. The high average value of Poisson's ratio in the crust (0.34) suggests the presence of fluids there; Poisson's ratio in the mantle between 40 and approximately 200 km is more nearly normal (0.29) than in the crust. A discrepancy between normal values of Poisson's ratio in the crust calculated from short-period data and high values calculated from teleseismic data can be resolved by postulating a viscoelastic crustal model with frequency-dependent shear velocity and attenuation

Sheared Electroconvective Instability

Science.gov (United States)

Kwak, Rhokyun; Pham, Van Sang; Lim, Kiang Meng; Han, Jongyoon

2012-11-01

Recently, ion concentration polarization (ICP) and related phenomena draw attention from physicists, due to its importance in understanding electrochemical systems. Researchers have been actively studying, but the complexity of this multiscale, multiphysics phenomenon has been limitation for gaining a detailed picture. Here, we consider electroconvective(EC) instability initiated by ICP under pressure-driven flow, a scenario often found in electrochemical desalinations. Combining scaling analysis, experiment, and numerical modeling, we reveal unique behaviors of sheared EC: unidirectional vortex structures, its size selection and vortex propagation. Selected by balancing the external pressure gradient and the electric body force, which generates Hagen-Poiseuille(HP) flow and vortical EC, the dimensionless EC thickness scales as (φ2 /UHP)1/3. The pressure-driven flow(or shear) suppresses unfavorably-directed vortices, and simultaneously pushes favorably-directed vortices with constant speed, which is linearly proportional to the total shear of HP flow. This is the first systematic characterization of sheared EC, which has significant implications on the optimization of electrodialysis and other electrochemical systems.

Fifty years of shear zones

Science.gov (United States)

Graham, Rodney

2017-04-01

We are here, of course, because 1967 saw the publication of John Ramsay's famous book. Two years later a memorable field trip from Imperial College to the Outer Hebrides saw John on a bleak headland on the coast of North Uist where a relatively undeformed metadolerite within Lewisian (Precambrian) gneisses contained ductile shear zones with metamorphic fabrics in amphibolite facies. One particular outcrop was very special - a shear zone cutting otherwise completely isotropic, undeformed metadolerite, with an incremental foliation starting to develop at 45° to the deformation zone, and increasing in intensity as it approached the shear direction. Here was proof of the process of simple shear under ductile metamorphic conditions - the principles of simple shear outlined in John Ramsay's 1967 book clearly visible in nature, and verified by Ramsay's mathematical proofs in the eventual paper (Ramsay and Graham, 1970). Later work on the Lewisian on the mainland of Scotland, in South Harris, in Africa, and elsewhere applied Ramsay's simple shear principles more liberally, more imprecisely and on larger scale than at Caisteal Odair, but in retrospect it documented what seems now to be the generality of mid and lower crustal deformation. Deep seismic reflection data show us that on passive margins hyper-stretched continental crust (whether or not cloaked by Seaward Dipping Reflectors) seems to have collapsed onto the mantle. Crustal faults mostly sole out at or above the mantle - so the Moho is a detachment- an 'outer marginal detachment', if you like, and, of course, it must be a ductile shear. On non-volcanic margins this shear zone forms the first formed ocean floor before true sea floor spreading gets going to create real oceanic crust. Gianreto Manatschal, Marcel Lemoine and others realised that the serpentinites described in parts of the Alps are exposed remnants of this ductile shear zone. Associated ophicalcite breccias tell of sea floor exposure, while high

High strength semi-active energy absorbers using shear- and mixedmode operation at high shear rates

Science.gov (United States)

Becnel, Andrew C.

This body of research expands the design space of semi-active energy absorbers for shock isolation and crash safety by investigating and characterizing magnetorheological fluids (MRFs) at high shear rates ( > 25,000 1/s) under shear and mixed-mode operation. Magnetorheological energy absorbers (MREAs) work well as adaptive isolators due to their ability to quickly and controllably adjust to changes in system mass or impact speed while providing fail-safe operation. However, typical linear stroking MREAs using pressure-driven flows have been shown to exhibit reduced controllability as impact speed (shear rate) increases. The objective of this work is to develop MREAs that improve controllability at high shear rates by using pure shear and mixed shear-squeeze modes of operation, and to present the fundamental theory and models of MR fluids under these conditions. A proof of concept instrument verified that the MR effect persists in shear mode devices at shear rates corresponding to low speed impacts. This instrument, a concentric cylinder Searle cell magnetorheometer, was then used to characterize three commercially available MRFs across a wide range of shear rates, applied magnetic fields, and temperatures. Characterization results are presented both as flow curves according to established practice, and as an alternate nondimensionalized analysis based on Mason number. The Mason number plots show that, with appropriate correction coefficients for operating temperature, the varied flow curve data can be collapsed to a single master curve. This work represents the first shear mode characterization of MRFs at shear rates over 10 times greater than available with commercial rheometers, as well as the first validation of Mason number analysis to high shear rate flows in MRFs. Using the results from the magnetorheometer, a full scale rotary vane MREA was developed as part of the Lightweight Magnetorheological Energy Absorber System (LMEAS) for an SH-60 Seahawk helicopter

Shear thickening in suspensions: the lubricated-to-frictional contact scenario

Science.gov (United States)

Morris, Jeffrey

2017-11-01

Suspensions of solid particles in viscous liquids can vary from low-viscosity liquids to wet granular materials or soft solids depending on the solids loading and the forces acting between particles. When the particles are very concentrated, these mixtures are ''dense suspensions.'' Dense suspensions often exhibit shear thickening, an increase in apparent viscosity as the shear rate is increased. In its most extreme form, order of magnitude increases in viscosity over such a narrow range in shear rate occur that the term discontinuous shear thickening (DST) is applied. DST is particularly striking as it occurs in the relatively simple case of nearly hard spheres in a Newtonian liquid, and is found to take place for submicron particles in colloidal dispersions to much larger particle corn starch dispersions. We focus on simulations of a recently developed ``lubricated-to-frictional'' rheology in which the interplay of viscous lubrication, repulsive surface forces, and contact friction between particle surfaces provides a scenario to explain DST. Our simulation method brings together elements of the discrete-element method from granular flow with a simplified Stokesian Dynamics, and can rationalize not only the abrupt change in properties with imposed shear rate (or shear stress), but also the magnitude of the change. The large change in properties is associated with the breakdown of lubricating films between particles, with activation of Coulomb friction between particles. The rate dependence is caused by the shearing forces driving particles to contact, overwhelming conservative repulsive forces between surfaces; the repulsive forces are representative of colloidal stabilization by surface charge or steric effects, e.g. due to adsorbed polymer. The results of simulation are compared to developments by other groups, including a number of experimental studies and a theory incorporating the same basic elements as the simulation. The comparison to experiments of the

Shear flow over a plane wall with an axisymmetric cavity or a circular orifice of finite thickness

International Nuclear Information System (INIS)

Pozrikidis, C.

1994-01-01

Shear flow over a plane wall that contains an axisymmetric depression or pore is studied using a new boundary integral method which is suitable for computing three-dimensional Stokes flow within axisymmetric domains. Numerical results are presented for cavities in the shape of a section of a sphere or a circular cylinder of finite length, and for a family of pores or orifices with finite thickness. The results illustrate the distribution of shear stresses over the plane wall and inside the cavities or pores. It is found that in most cases, the distribution of shear stresses over the plane wall, around the depressions, is well approximated with that for flow over an orifice of infinitesimal thickness for which an exact solution is available. The kinematic structure of the flow is discussed with reference to eddy formation and three-dimensional flow reversal. It is shown that the thickness of a circular orifice or depth of a pore play an important role in determining the kinematical structure of the flow underneath the orifice in the lower half-space

Direct numerical simulations of premixed autoignition in compressible uniformly-sheared turbulence

Science.gov (United States)

Towery, Colin; Darragh, Ryan; Poludnenko, Alexei; Hamlington, Peter

2017-11-01

High-speed combustion systems, such as scramjet engines, operate at high temperatures and pressures, extremely short combustor residence times, very high rates of shear stress, and intense turbulent mixing. As a result, the reacting flow can be premixed and have highly-compressible turbulence fluctuations. We investigate the effects of compressible turbulence on the ignition delay time, heat-release-rate (HRR) intermittency, and mode of autoignition of premixed Hydrogen-air fuel in uniformly-sheared turbulence using new three-dimensional direct numerical simulations with a multi-step chemistry mechanism. We analyze autoignition in both the Eulerian and Lagrangian reference frames at eight different turbulence Mach numbers, Mat , spanning the quasi-isentropic, linear thermodynamic, and nonlinear compressibility regimes, with eddy shocklets appearing in the nonlinear regime. Results are compared to our previous study of premixed autoignition in isotropic turbulence at the same Mat and with a single-step reaction mechanism. This previous study found large decreases in delay times and large increases in HRR intermittency between the linear and nonlinear compressibility regimes and that detonation waves could form in both regimes.

A Piezoelectric Shear Stress Sensor

Science.gov (United States)

Kim, Taeyang; Saini, Aditya; Kim, Jinwook; Gopalarathnam, Ashok; Zhu, Yong; Palmieri, Frank L.; Wohl, Christopher J.; Jiang, Xiaoning

2016-01-01

In this paper, a piezoelectric sensor with a floating element was developed for shear stress measurement. The piezoelectric sensor was designed to detect the pure shear stress suppressing effects of normal stress generated from the vortex lift-up by applying opposite poling vectors to the: piezoelectric elements. The sensor was first calibrated in the lab by applying shear forces and it showed high sensitivity to shear stress (=91.3 +/- 2.1 pC/Pa) due to the high piezoelectric coefficients of PMN-33%PT (d31=-1330 pC/N). The sensor also showed almost no sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the device. The usable frequency range of the sensor is 0-800 Hz. Keywords: Piezoelectric sensor, shear stress, floating element, electromechanical symmetry

The dynamics of a shear band

Science.gov (United States)

Giarola, Diana; Capuani, Domenico; Bigoni, Davide

2018-03-01

A shear band of finite length, formed inside a ductile material at a certain stage of a continued homogeneous strain, provides a dynamic perturbation to an incident wave field, which strongly influences the dynamics of the material and affects its path to failure. The investigation of this perturbation is presented for a ductile metal, with reference to the incremental mechanics of a material obeying the J2-deformation theory of plasticity (a special form of prestressed, elastic, anisotropic, and incompressible solid). The treatment originates from the derivation of integral representations relating the incremental mechanical fields at every point of the medium to the incremental displacement jump across the shear band faces, generated by an impinging wave. The boundary integral equations (under the plane strain assumption) are numerically approached through a collocation technique, which keeps into account the singularity at the shear band tips and permits the analysis of an incident wave impinging a shear band. It is shown that the presence of the shear band induces a resonance, visible in the incremental displacement field and in the stress intensity factor at the shear band tips, which promotes shear band growth. Moreover, the waves scattered by the shear band are shown to generate a fine texture of vibrations, parallel to the shear band line and propagating at a long distance from it, but leaving a sort of conical shadow zone, which emanates from the tips of the shear band.

Nonlinear stability research on the hydraulic system of double-side rolling shear

Science.gov (United States)

Wang, Jun; Huang, Qingxue; An, Gaocheng; Qi, Qisong; Sun, Binyu

2015-10-01

This paper researches the stability of the nonlinear system taking the hydraulic system of double-side rolling shear as an example. The hydraulic system of double-side rolling shear uses unsymmetrical electro-hydraulic proportional servo valve to control the cylinder with single piston rod, which can make best use of the space and reduce reversing shock. It is a typical nonlinear structure. The nonlinear state-space equations of the unsymmetrical valve controlling cylinder system are built first, and the second Lyapunov method is used to evaluate its stability. Second, the software AMEsim is applied to simulate the nonlinear system, and the results indicate that the system is stable. At last, the experimental results show that the system unsymmetrical valve controlling the cylinder with single piston rod is stable and conforms to what is deduced by theoretical analysis and simulation. The construction and application of Lyapunov function not only provide the theoretical basis for using of unsymmetrical valve controlling cylinder with single piston rod but also develop a new thought for nonlinear stability evaluation.

Simulations of Granular Particles Under Cyclic Shear

Science.gov (United States)

Royer, John; Chaikin, Paul

2012-02-01

We perform molecular dynamics (MD) simulations of spherical grains subjected to cyclic, quasi-static shear in a 3D parallelepiped shear cell. This virtual shear cell is constructed out of rough, bumpy walls in order to minimize wall-induced ordering and has an open top surface to allow the packing to readily dilate or compact. Using a standard routine for MD simulations of frictional grains, we simulate over 1000 shear cycles, measuring grain displacements, the local packing density and changes in the contact network. Varying the shear amplitude and the friction coefficient between grains, we map out a phase diagram for the different types of behavior exhibited by these sheared grains. With low friction and high enough shear, the grains can spontaneously order into densely packed crystals. With low shear and increasing friction the packing remains disordered, yet the grains arrange themselves into configurations which exhibit limit cycles where all grains return to the same position after each full shear cycle. At higher shear and friction there is a transition to a diffusive state, where grains continue rearrange and move throughout the shear cell.

CAT LIDAR wind shear studies

Science.gov (United States)

Goff, R. W.

1978-01-01

The studies considered the major meteorological factors producing wind shear, methods to define and classify wind shear in terms significant from an aircraft perturbation standpoint, the significance of sensor location and scan geometry on the detection and measurement of wind shear, and the tradeoffs involved in sensor performance such as range/velocity resolution, update frequency and data averaging interval.

Estimation of in-situ stresses in concrete members using polarized ultrasonic shear waves

Science.gov (United States)

Chen, Andrew; Schumacher, Thomas

2014-02-01

Ultrasonic testing is commonly used to detect flaws, estimate geometries, and characterize properties of materials and structures. Acoustoelasticity refers to the dependency of stress wave velocity with applied stresses and is a phenomenon that has been known by geophysicists since the 1960s. A way to capitalize on this effect for concrete applications is by using ultrasonic shear waves which are particularly sensitive to applied stresses when polarized in the direction of the applied stress. The authors conducted an experiment on a 150 mm (6 in.) diameter concrete cylinder specimen with a length of 305 mm (12 in.) that was loaded in discrete load steps to failure. At each load step two ultrasonic shear waves were transmitted through the specimen, one with the polarization perpendicular and the other transverse to the applied stress. The velocity difference between the two sets of polarized shear waves was found to correlate with the applied stress in the specimen. Two potential applications for this methodology include estimation of stresses in pre-stressed concrete bridge girders and investigation of load redistribution in structural support elements after extreme events. This paper introduces the background of the methodology, presents an analysis of the collected data, and discusses the relationship between the recorded signals and the applied stress.

Time-Reversal Generation of Rogue Waves

Science.gov (United States)

Chabchoub, Amin; Fink, Mathias

2014-03-01

The formation of extreme localizations in nonlinear dispersive media can be explained and described within the framework of nonlinear evolution equations, such as the nonlinear Schrödinger equation (NLS). Within the class of exact NLS breather solutions on a finite background, which describe the modulational instability of monochromatic wave trains, the hierarchy of rational solutions localized in both time and space is considered to provide appropriate prototypes to model rogue wave dynamics. Here, we use the time-reversal invariance of the NLS to propose and experimentally demonstrate a new approach to constructing strongly nonlinear localized waves focused in both time and space. The potential applications of this time-reversal approach include remote sensing and motivated analogous experimental analysis in other nonlinear dispersive media, such as optics, Bose-Einstein condensates, and plasma, where the wave motion dynamics is governed by the NLS.

Shear flow effect on ion temperature gradient vortices in plasmas with sheared magnetic field

DEFF Research Database (Denmark)

Chakrabarti, N.; Juul Rasmussen, J.

1999-01-01

The effect of velocity shear on ion temperature gradient (ITG) driven vortices in a nonuniform plasma in a curved, sheared magnetic field is investigated. In absence of parallel ion dynamics, vortex solutions for the ITG mode are studied analytically. It is shown that under certain conditions...... and ultimately lead to a dominating monopolar form. The effects of magnetic shear indicate it may destroy these structures. (C) 1999 American Institute of Physics....

Friction of Shear-Fracture Zones

Science.gov (United States)

Riikilä, T. I.; Pylväinen, J. I.; Åström, J.

2017-12-01

A shear fracture of brittle solids under compression undergoes a substantial evolution from the initial microcracking to a fully formed powder-filled shear zone. Experiments covering the entire process are relatively easy to conduct, but they are very difficult to investigate in detail. Numerically, the large strain limit has remained a challenge. An efficient simulation model and a custom-made experimental device are employed to test to what extent a shear fracture alone is sufficient to drive material to spontaneous self-lubrication. A "weak shear zone" is an important concept in geology, and a large number of explanations, specific for tectonic conditions, have been proposed. We demonstrate here that weak shear zones are far more general, and that their emergence only demands that a microscopic, i.e., fragment-scale, stress relaxation mechanism develops during the fracture process.

Graphene-Based Reversible Nano-Switch/Sensor Schottky Diode

Science.gov (United States)

Miranda, Felix A.; Meador, Michael A.; Theofylaktos, Onoufrios; Pinto, Nicholas J.; Mueller, Carl H.; Santos-Perez, Javier

2010-01-01

This proof-of-concept device consists of a thin film of graphene deposited on an electrodized doped silicon wafer. The graphene film acts as a conductive path between a gold electrode deposited on top of a silicon dioxide layer and the reversible side of the silicon wafer, so as to form a Schottky diode. By virtue of the two-dimensional nature of graphene, this device has extreme sensitivity to different gaseous species, thereby serving as a building block for a volatile species sensor, with the attribute of having reversibility properties. That is, the sensor cycles between active and passive sensing states in response to the presence or absence of the gaseous species.

The rheology of shear thickening fluid (STF) and the dynamic performance of an STF-filled damper

International Nuclear Information System (INIS)

Zhang, X Z; Li, W H; Gong, X L

2008-01-01

This paper presents a study of the rheological properties of shear thickening fluid (STF) and its application as a damper. The STF samples, with different weight fractions, were prepared by dispersing nanosized silica particles in a solvent. By using a parallel-plate rheometer, both steady-state and dynamic experiments were carried out to investigate the rheological properties of STFs. Experimental results indicated that these suspensions show an abrupt increase in complex viscosity beyond a critical dynamic shear rate, as well as this increase being reversible. Working with the fabricated STF materials, a prototype damper was fabricated and its dynamic performances were experimentally evaluated. An equivalent linear model through effective elastic stiffness and viscous damping was developed to address both the damping and the stiffness capabilities of the damper. Also, a mathematical model was developed to investigate working mechanisms of STF-based devices

Shear stiffness in nanolaminar Ti3SiC2 challenges ab initio calculations

International Nuclear Information System (INIS)

Kisi, E H; Zhang, J F; Kirstein, O; Riley, D P; Styles, M J; Paradowska, A M

2010-01-01

Nanolaminates such as the M n+1 AX n (MAX) phases are a material class with ab initio derived elasticity tensors published for over 250 compounds. We have for the first time experimentally determined the full elasticity tensor of the archetype MAX phase, Ti 3 SiC 2 , using polycrystalline samples and in situ neutron diffraction. The experimental elastic constants show extreme shear stiffness, with c 44 more than five times greater than expected for an isotropic material. Such shear stiffness is quite rare in hexagonal materials and strongly contradicts the predictions of all published MAX phase elastic constants derived from ab initio calculations. It is concluded that second order properties such as elastic moduli derived from ab initio calculations require careful experimental verification. The diffraction technique used currently provides the only method of verification for the elasticity tensor for the majority of new materials where single crystals are not available. (fast track communication)

Reverse ray tracing for transformation optics.

Science.gov (United States)

Hu, Chia-Yu; Lin, Chun-Hung

2015-06-29

Ray tracing is an important technique for predicting optical system performance. In the field of transformation optics, the Hamiltonian equations of motion for ray tracing are well known. The numerical solutions to the Hamiltonian equations of motion are affected by the complexities of the inhomogeneous and anisotropic indices of the optical device. Based on our knowledge, no previous work has been conducted on ray tracing for transformation optics with extreme inhomogeneity and anisotropicity. In this study, we present the use of 3D reverse ray tracing in transformation optics. The reverse ray tracing is derived from Fermat's principle based on a sweeping method instead of finding the full solution to ordinary differential equations. The sweeping method is employed to obtain the eikonal function. The wave vectors are then obtained from the gradient of that eikonal function map in the transformed space to acquire the illuminance. Because only the rays in the points of interest have to be traced, the reverse ray tracing provides an efficient approach to investigate the illuminance of a system. This approach is useful in any form of transformation optics where the material property tensor is a symmetric positive definite matrix. The performance and analysis of three transformation optics with inhomogeneous and anisotropic indices are explored. The ray trajectories and illuminances in these demonstration cases are successfully solved by the proposed reverse ray tracing method.

Magnetorheological dampers in shear mode

International Nuclear Information System (INIS)

Wereley, N M; Cho, J U; Choi, Y T; Choi, S B

2008-01-01

In this study, three types of shear mode damper using magnetorheological (MR) fluids are theoretically analyzed: linear, rotary drum, and rotary disk dampers. The damping performance of these shear mode MR dampers is characterized in terms of the damping coefficient, which is the ratio of the equivalent viscous damping at field-on status to the damping at field-off status. For these three types of shear mode MR damper, the damping coefficient or dynamic range is derived using three different constitutive models: the Bingham–plastic, biviscous, and Herschel–Bulkley models. The impact of constitutive behavior on shear mode MR dampers is theoretically presented and compared

Investigation on cold-drawn gold bonding wire with serial and reverse-direction drawing

International Nuclear Information System (INIS)

Cho, Jae-Hyung; Rollett, A.D.; Cho, J.-S.; Park, Y.-J.; Park, S.-H.; Oh, K.H.

2006-01-01

Gold bonding wires have been manufactured through multiple drawing steps with serial and reverse-direction drawing. The texture and microstructure of the gold bonding wires were characterized with X-ray diffraction and EBSD and compared with the predictions of finite element (FE) simulation. Initial fiber decreases during drawing and is replaced by fiber. The oriented grains are concentrated in the center and surface regions, whereas the oriented grains are located throughout the cross-section of the wire. Regions near the surface often exhibit the complex textures. A simplified forward and backward drawing process was modeled by FE analysis with ABAQUS/Standard TM . The simple two-step drawing process results in severe variation in shear strain under the surface and displays the opposite behavior in the shear components of the deformation gradient. The texture evolution was predicted using the deformation gradient calculated in the FE simulations together with a model of polycrystal plasticity. The and fibers are predicted to develop in the center part of the wire where homogeneous deformation occurs. The regions near the surface that experience repeated shear strain exhibit complex textures that deviate from the standard and fibers. The {1 1 2} and {1 1 1} components are prevalent in the higher shear strain regions. The variations of the anisotropic elastic directional moduli with position were also calculated

IMAGE ANALYSIS FOR MODELLING SHEAR BEHAVIOUR

Directory of Open Access Journals (Sweden)

Philippe Lopez

2011-05-01

Full Text Available Through laboratory research performed over the past ten years, many of the critical links between fracture characteristics and hydromechanical and mechanical behaviour have been made for individual fractures. One of the remaining challenges at the laboratory scale is to directly link fracture morphology of shear behaviour with changes in stress and shear direction. A series of laboratory experiments were performed on cement mortar replicas of a granite sample with a natural fracture perpendicular to the axis of the core. Results show that there is a strong relationship between the fracture's geometry and its mechanical behaviour under shear stress and the resulting damage. Image analysis, geostatistical, stereological and directional data techniques are applied in combination to experimental data. The results highlight the role of geometric characteristics of the fracture surfaces (surface roughness, size, shape, locations and orientations of asperities to be damaged in shear behaviour. A notable improvement in shear understanding is that shear behaviour is controlled by the apparent dip in the shear direction of elementary facets forming the fracture.

Design and implementation of a shearing apparatus for the experimental study of shear displacement in rocks

Science.gov (United States)

Moore, Johnathan; Crandall, Dustin; Gill, Magdalena; Brown, Sarah; Tennant, Bryan

2018-04-01

Fluid flow in the subsurface is not well understood in the context of "impermeable" geologic media. This is especially true of formations that have undergone significant stress fluctuations due to injection or withdrawal of fluids that alters the localized pressure regime. When the pressure regime is altered, these formations, which are often already fractured, move via shear to reduce the imbalance in the stress state. While this process is known to happen, the evolution of these fractures and their effects on fluid transport are still relatively unknown. Numerous simulation and several experimental studies have been performed that characterize the relationship between shearing and permeability in fractures; while many of these studies utilize measurements of fluid flow or the starting and ending geometries of the fracture to characterize shear, they do not characterize the intermediate stages during shear. We present an experimental apparatus based on slight modifications to a commonly available Hassler core holder that allows for shearing of rocks, while measuring the hydraulic and mechanical changes to geomaterials during intermediate steps. The core holder modification employs the use of semi-circular end caps and structural supports for the confining membrane that allow for free movement of the sheared material while preventing membrane collapse. By integrating this modified core holder with a computed tomography scanner, we show a new methodology for understanding the interdependent behavior between fracture structure and flow properties during intermediate steps in shearing. We include a case study of this device function which is shown here through shearing of a fractured shale core and simultaneous observation of the mechanical changes and evolution of the hydraulic properties during shearing.

Mean wall-shear stress measurements using the micro-pillar shear-stress sensor MPS3

International Nuclear Information System (INIS)

Große, S; Schröder, W

2008-01-01

A new sensor to measure the mean turbulent wall-shear stress in turbulent flows is described. The wall-shear stress sensor MPS 3 has been tested in a well-defined fully developed turbulent pipe flow at Reynolds numbers Re b based on the bulk velocity U b and the pipe diameter D in the range of Re b = 10 000–20 000. The results demonstrate a convincing agreement of the mean wall-shear stress obtained with the new sensor technique with analytical and experimental results from the literature. The sensor device consists of a flexible micro-pillar that extends from the wall into the viscous sublayer. Bending due to the exerting fluid forces, the pillar-tip deflection serves as a measure for the local wall-shear stress. The sensor concept, calibration techniques, the achievable accuracy and error estimates, the fields of application and the sensor limits will be discussed. Furthermore, a first estimate of the pillar dynamic response will be derived showing the potential of the sensor to also measure the turbulent fluctuating wall-shear stress

Microstructural evolution of a model, shear-banding micellar solution during shear startup and cessation.

Science.gov (United States)

López-Barrón, Carlos R; Gurnon, A Kate; Eberle, Aaron P R; Porcar, Lionel; Wagner, Norman J

2014-04-01

We present direct measurements of the evolution of the segmental-level microstructure of a stable shear-banding polymerlike micelle solution during flow startup and cessation in the plane of flow. These measurements provide a definitive, quantitative microstructural understanding of the stages observed during flow startup: an initial elastic response with limited alignment that yields with a large stress overshoot to a homogeneous flow with associated micellar alignment that persists for approximately three relaxation times. This transient is followed by a shear (kink) band formation with a flow-aligned low-viscosity band that exhibits shear-induced concentration fluctuations and coexists with a nearly isotropic band of homogenous, highly viscoelastic micellar solution. Stable, steady banding flow is achieved only after approximately two reptation times. Flow cessation from this shear-banded state is also found to be nontrivial, exhibiting an initial fast relaxation with only minor structural relaxation, followed by a slower relaxation of the aligned micellar fluid with the equilibrium fluid's characteristic relaxation time. These measurements resolve a controversy in the literature surrounding the mechanism of shear banding in entangled wormlike micelles and, by means of comparison to existing literature, provide further insights into the mechanisms driving shear-banding instabilities in related systems. The methods and instrumentation described should find broad use in exploring complex fluid rheology and testing microstructure-based constitutive equations.

Inductive shearing of drilling pipe

Science.gov (United States)

Ludtka, Gerard M.; Wilgen, John; Kisner, Roger; Mcintyre, Timothy

2016-04-19

Induction shearing may be used to cut a drillpipe at an undersea well. Electromagnetic rings may be built into a blow-out preventer (BOP) at the seafloor. The electromagnetic rings create a magnetic field through the drillpipe and may transfer sufficient energy to change the state of the metal drillpipe to shear the drillpipe. After shearing the drillpipe, the drillpipe may be sealed to prevent further leakage of well contents.

Non-homogeneous flow profiles in sheared bacterial suspensions

Science.gov (United States)

Samanta, Devranjan; Cheng, Xiang

Bacterial suspensions under shear exhibit interesting rheological behaviors including the remarkable ``superfluidic'' state with vanishing viscosity at low shear rates. Theoretical studies have shown that such ``superfluidic'' state is linked with non-homogeneous shear flows, which are induced by coupling between nematic order of active fluids and hydrodynamics of shear flows. However, although bulk rheology of bacterial suspensions has been experimentally studied, shear profiles within bacterial suspensions have not been explored so far. Here, we experimentally investigate the flow behaviors of E. coli suspensions under planar oscillatory shear. Using confocal microscopy and PIV, we measure velocity profiles across gap between two shear plates. We find that with increasing shear rates, high-concentration bacterial suspensions exhibit an array of non-homogeneous flow behaviors like yield-stress flows and shear banding. We show that these non-homogeneous flows are due to collective motion of bacterial suspensions. The phase diagram of sheared bacterial suspensions is systematically mapped as functions of shear rates an bacterial concentrations. Our experiments provide new insights into rheology of bacterial suspensions and shed light on shear induced dynamics of active fluids. Chemical Engineering and Material Science department.

Exponential Shear Flow of Linear, Entangled Polymeric Liquids

DEFF Research Database (Denmark)

Neergaard, Jesper; Park, Kyungho; Venerus, David C.

2000-01-01

A previously proposed reptation model is used to interpret exponential shear flow data taken on an entangled polystyrenesolution. Both shear and normal stress measurements are made during exponential shear using mechanical means. The model iscapable of explaining all trends seen in the data......, and suggests a novel analysis of the data. This analysis demonstrates thatexponential shearing flow is no more capable of stretching polymer chains than is inception of steady shear at comparableinstantaneous shear rates. In fact, all exponential shear flow stresses measured are bounded quantitatively...

Far-from-equilibrium sheared colloidal liquids: Disentangling relaxation, advection, and shear-induced diffusion

KAUST Repository

Lin, Neil Y. C.

2013-12-01

Using high-speed confocal microscopy, we measure the particle positions in a colloidal suspension under large-amplitude oscillatory shear. Using the particle positions, we quantify the in situ anisotropy of the pair-correlation function, a measure of the Brownian stress. From these data we find two distinct types of responses as the system crosses over from equilibrium to far-from-equilibrium states. The first is a nonlinear amplitude saturation that arises from shear-induced advection, while the second is a linear frequency saturation due to competition between suspension relaxation and shear rate. In spite of their different underlying mechanisms, we show that all the data can be scaled onto a master curve that spans the equilibrium and far-from-equilibrium regimes, linking small-amplitude oscillatory to continuous shear. This observation illustrates a colloidal analog of the Cox-Merz rule and its microscopic underpinning. Brownian dynamics simulations show that interparticle interactions are sufficient for generating both experimentally observed saturations. © 2013 American Physical Society.

Far-from-equilibrium sheared colloidal liquids: Disentangling relaxation, advection, and shear-induced diffusion

KAUST Repository

Lin, Neil Y. C.; Goyal, Sushmit; Cheng, Xiang; Zia, Roseanna N.; Escobedo, Fernando A.; Cohen, Itai

2013-01-01

Using high-speed confocal microscopy, we measure the particle positions in a colloidal suspension under large-amplitude oscillatory shear. Using the particle positions, we quantify the in situ anisotropy of the pair-correlation function, a measure of the Brownian stress. From these data we find two distinct types of responses as the system crosses over from equilibrium to far-from-equilibrium states. The first is a nonlinear amplitude saturation that arises from shear-induced advection, while the second is a linear frequency saturation due to competition between suspension relaxation and shear rate. In spite of their different underlying mechanisms, we show that all the data can be scaled onto a master curve that spans the equilibrium and far-from-equilibrium regimes, linking small-amplitude oscillatory to continuous shear. This observation illustrates a colloidal analog of the Cox-Merz rule and its microscopic underpinning. Brownian dynamics simulations show that interparticle interactions are sufficient for generating both experimentally observed saturations. © 2013 American Physical Society.

Study of shear thickening behavior in colloidal suspensions

Directory of Open Access Journals (Sweden)

N Maleki Jirsaraee

2015-01-01

Full Text Available We studied the shear thickening behavior of the nano silica suspension (silica nanoparticles 12 nm in size suspended in ethylene glycol under steady shear. The critical shear rate for transition into shear thickening phase was determined at different concentrations and temperatures. The effect of temperature and concentration was studied on the shear thickening behavior. In silica suspension, it was observed that all the samples had a transition into shear thickening phase and also by increasing the temperature, critical shear rate increased and viscosity decreased. Our observations showed that movement in silica suspension was Brownian and temperature could cause a delay in transition into shear thickening phase. Yet, we observed that increasing the concentration would decrease critical shear rate and increase viscosity. Increasing temperature increased Brownian forces and increasing concentration increased hydrodynamic forces, confirming the contrast between these two forces for transition into shear thickening phase for the suspensions containing nano particles

Onset of shear thinning in glassy liquids: Shear-induced small reduction of effective density.

Science.gov (United States)

Furukawa, Akira

2017-01-01

We propose a simple mechanism for describing the onset of shear thinning in a high-density glassy liquid. In a shear flow, along the compression axis, the overlap between neighboring particles is more enhanced than that at equilibrium, meaning that the "effective" size is reduced along this axis. On the other hand, along the extension axis perpendicular to the compression axis, the average structural configurations are stretched, but it does not indicate the expansion of the "effective" size itself. This asymmetric shear flow effect for particles results in a small reduction of the "effective" density. Because, in glass-forming liquids, the structural relaxation time τ_{α} strongly depends on the density ρ, even a very small reduction of the effective density should lead to a significant decrease of the relaxation time under shear flow. We predict that the crossover shear rate from Newtonian to non-Newtonian flow behaviors is given by γ[over ̇]_{c}=[ρ(∂τ_{α}/∂ρ)]^{-1}, which can be much smaller than 1/τ_{α} near the glass transition point. It is shown that this prediction is consistent with the results of molecular dynamics simulations.

Effect of Boundary Condition on the Shear Behaviour of Rock Joints in the Direct Shear Test

Science.gov (United States)

Bahaaddini, M.

2017-05-01

The common method for determination of the mechanical properties of the rock joints is the direct shear test. This paper aims to study the effect of boundary condition on the results of direct shear tests. Experimental studies undertaken in this research showed that the peak shear strength is mostly overestimated. This problem is more pronounced for steep asperities and under high normal stresses. Investigation of the failure mode of these samples showed that tensile cracks are generated at the boundary of sample close to the specimen holders and propagated inside the intact materials. In order to discover the reason of observed failure mechanism in experiments, the direct shear test was simulated using PFC2D. Results of numerical models showed that the gap zone size between the upper and lower specimen holders has a significant effect on the shear mechanism. For the high gap size, stresses concentrate at the vicinity of the tips of specimen holders and result in generation and propagation of tensile cracks inside the intact material. However, by reducing the gap size, stresses are concentrated on asperities, and damage of specimen at its boundary is not observed. Results of this paper show that understanding the shear mechanism of rock joints is an essential step prior to interpreting the results of direct shear tests.

Dilatancy of Shear Transformations in a Colloidal Glass

Science.gov (United States)

Lu, Y. Z.; Jiang, M. Q.; Lu, X.; Qin, Z. X.; Huang, Y. J.; Shen, J.

2018-01-01

Shear transformations, as fundamental rearrangement events operating in local regions, hold the key of plastic flow of amorphous solids. Despite their importance, the dynamic features of shear transformations are far from clear, which is the focus of the present study. Here, we use a colloidal glass under shear as the prototype to directly observe the shear-transformation events in real space. By tracing the colloidal-particle rearrangements, we quantitatively determine two basic properties of shear transformations: local shear strain and dilatation (or free volume). It is revealed that the local free volume undergoes a significantly temporary increase prior to shear transformations, eventually leading to a jump of local shear strain. We clearly demonstrate that shear transformations have no memory of the initial free volume of local regions. Instead, their emergence strongly depends on the dilatancy ability of these local regions, i.e., the dynamic creation of free volume. More specifically, the particles processing the high dilatancy ability directly participate in subsequent shear transformations. These results experimentally enrich Argon's statement about the dilatancy nature of shear transformations and also shed insight into the structural origin of amorphous plasticity.

Rheometry-PIV of shear-thickening wormlike micelles.

Science.gov (United States)

Marín-Santibañez, Benjamín M; Pérez-Gonzalez, José; de Vargas, Lourdes; Rodríguez-Gonzalez, Francisco; Huelsz, Guadalupe

2006-04-25

The shear-thickening behavior of an equimolar semidilute aqueous solution of 40 mM/L cetylpyridinium chloride and sodium salicylate was studied in this work by using a combined method of rheometry and particle image velocimetry (PIV). Experiments were conducted at 27.5 degrees C with Couette, vane-bob, and capillary rheometers in order to explore a wide shear stress range as well as the effect of boundary conditions and time of flow on the creation and destruction of shear-induced structures (SIS). The use of the combined method of capillary rheometry with PIV allowed the detection of fast spatial and temporal variations in the flow kinematics, which are related to the shear-thickening behavior and the dynamics of the SIS but are not distinguished by pure rheometrical measurements. A rich-in-details flow curve was found for this solution, which includes five different regimes. Namely, at very low shear rates a Newtonian behavior was found, followed by a shear thinning one in the second regime. In the third, shear banding was observed, which served as a precursor of the SIS and shear-thickening. The fourth and fifth regimes in the flow curve were separated by a spurtlike behavior, and they clearly evidenced the existence of shear-thickening accompanied by stick-slip oscillations at the wall of the rheometer, which subsequently produced variations in the shear rate under shear stress controlled flow. Such a stick-slip phenomenon prevailed up to the highest shear stresses used in this work and was reflected in asymmetric velocity profiles with spatial and temporal variations linked to the dynamics of creation and breakage of the SIS. The presence of apparent slip at the wall of the rheometer provides an energy release mechanism which leads to breakage of the SIS, followed by their further reformation during the stick part of the cycles. In addition, PIV measurements allowed the detection of apparent slip at the wall, as well as mechanical failures in the bulk of the

Demonstration of high performance negative central magnetic shear discharges on the DIII-D tokamak

International Nuclear Information System (INIS)

Rice, B.W.; Burrell, K.H.; Lao, L.L.

1996-01-01

Reliable operation of discharges with negative central magnetic shear has led to significant increases in plasma performance and reactivity in both low confinement, L-mode, and high confinement, H-mode, regimes in the DIII-D tokamak. Using neutral beam injection early in the initial current ramp, a large range of negative shear discharges have been produced with durations lasting up to 3.2 s. The total non- inductive current (beam plus bootstrap) ranges from 50% to 80% in these discharges. In the region of shear reversal, significant peaking of the toroidal rotation [f φ ∼ 30-60 kHz] and ion temperature [T i (0) ∼ 15-22 keV] profiles are observed. In high power discharges with an L-mode edge, peaked density profiles are also observed. Confinement enhancement factors up to H ≡ τ E /τ ITER-89P ∼ 2.5 with an L-mode edge, and H ∼ 3.3 in an Edge Localized Mode (ELM)-free H-mode, are obtained. Transport analysis shows both ion thermal diffusivity and particle diffusivity to be near or below standard neoclassical values in the core. Large pressure peaking in L- mode leads to high disruptivity with Β N ≡ Β T /(I/aB) ≤ 2.3, while broader pressure profiles in H- mode gives low disruptivity with Β N ≤ 4.2

Terminal Investment Strategies and Male Mate choice: Extreme Tests of Bateman.

Science.gov (United States)

Andrade, Maydianne C B; Kasumovic, Michael M

2005-11-01

Bateman's principle predicts the intensity of sexual selection depends on rates of increase of fecundity with mating success for each sex (Bateman slopes). The sex with the steeper increase (usually males) is under more intense sexual selection and is expected to compete for access to the sex under less intense sexual selection (usually females). Under Bateman and modern refinements of his ideas, differences in parental investment are key to defining Bateman slopes and thus sex roles. Other theories predict sex differences in mating investment, or any expenditures that reduce male potential reproductive rate, can also control sex roles. We focus on sexual behaviour in systems where males have low paternal investment but frequently mate only once in their lifetimes, after which they are often killed by the female. Mating effort (=terminal investment) is high for these males, and many forms of investment theory might predict sex role reversal. We find no qualitative evidence for sex role reversal in a sample of spiders that show this extreme male investment pattern. We also present new data for terminally-investing redback spiders (Latrodectus hasselti). Bateman slopes are relatively steep for male redbacks, and, as predicted by Bateman, there is little evidence for role reversal. Instead, males are competitive and show limited choosiness despite wide variation in female reproductive value. This study supports the proposal that high male mating investment coupled with low parental investment may predispose males to choosiness but will not lead to role reversal. We support the utility of using Bateman slopes to predict sex roles, even in systems with extreme male mating investment.

Behavior of Tilted Angle Shear Connectors

Science.gov (United States)

Khorramian, Koosha; Maleki, Shervin; Shariati, Mahdi; Ramli Sulong, N. H.

2015-01-01

According to recent researches, angle shear connectors are appropriate to transfer longitudinal shear forces across the steel-concrete interface. Angle steel profile has been used in different positions as L-shaped or C-shaped shear connectors. The application of angle shear connectors in tilted positions is of interest in this study. This study investigates the behaviour of tilted-shaped angle shear connectors under monotonic loading using experimental push out tests. Eight push-out specimens are tested to investigate the effects of different angle parameters on the ultimate load capacity of connectors. Two different tilted angles of 112.5 and 135 degrees between the angle leg and steel beam are considered. In addition, angle sizes and lengths are varied. Two different failure modes were observed consisting of concrete crushing-splitting and connector fracture. By increasing the size of connector, the maximum load increased for most cases. In general, the 135 degrees tilted angle shear connectors have a higher strength and stiffness than the 112.5 degrees type. PMID:26642193

Behavior of Tilted Angle Shear Connectors.

Directory of Open Access Journals (Sweden)

Koosha Khorramian

Full Text Available According to recent researches, angle shear connectors are appropriate to transfer longitudinal shear forces across the steel-concrete interface. Angle steel profile has been used in different positions as L-shaped or C-shaped shear connectors. The application of angle shear connectors in tilted positions is of interest in this study. This study investigates the behaviour of tilted-shaped angle shear connectors under monotonic loading using experimental push out tests. Eight push-out specimens are tested to investigate the effects of different angle parameters on the ultimate load capacity of connectors. Two different tilted angles of 112.5 and 135 degrees between the angle leg and steel beam are considered. In addition, angle sizes and lengths are varied. Two different failure modes were observed consisting of concrete crushing-splitting and connector fracture. By increasing the size of connector, the maximum load increased for most cases. In general, the 135 degrees tilted angle shear connectors have a higher strength and stiffness than the 112.5 degrees type.

Periodic Viscous Shear Heating Instability in Fine-Grained Shear Zones: Possible Mechanism for Intermediate Depth Earthquakes and Slow Earthquakes?

Science.gov (United States)

Kelemen, P. B.; Hirth, G.

2004-12-01

Localized ductile shear zones with widths of cm to m are observed in exposures of Earth's shallow mantle (e.g., Kelemen & Dick JGR 95; Vissers et al. Tectonophys 95) and dredged from oceanic fracture zones (e.g., Jaroslow et al. Tectonophys 96). These are mylonitic (grain size 10 to 100 microns) and record mineral cooling temperatures from 1100 to 600 C. Pseudotachylites in a mantle shear zone show that shear heating temperatures can exceed the mantle solidus (e.g., Obata & Karato Tectonophys 95). Simple shear, recrystallization, and grain boundary sliding all decrease the spacing between pyroxenes, so olivine grain growth at lower stress is inhibited; thus, once formed, these shear zones do not "heal" on geological time scales. Reasoning that grain-size sensitive creep will be localized within these shear zones, rather than host rocks (grain size 1 to 10 mm), and inspired by the work of Whitehead & Gans (GJRAS 74), we thought these might undergo repeated shear heating instabilities. In this view, as elastic stress increases, the shear zone weakens via shear heating; rapid deformation of the weak shear zone releases most stored elastic stress; lower stress and strain rate coupled with diffusion of heat into host rocks leads to cooling and strengthening, after which the cycle repeats. We constructed a simple numerical model incorporating olivine flow laws for dislocation creep, diffusion creep, grain boundary sliding, and low T plasticity. We assumed that viscous deformation remains localized in shear zones, surrounded by host rocks undergoing elastic deformation. We fixed the velocity along one side of an elastic half space, and calculated stress due to elastic strain. This stress drives viscous deformation in a shear zone of specified width. Shear heating and thermal diffusion control temperature evolution in the shear zone and host rocks. A maximum of 1400 C (where substantial melting of peridotite would occur) is imposed. Grain size evolves during dislocation

Effects of ExB velocity shear and magnetic shear on turbulence and transport in magnetic confinement devices

International Nuclear Information System (INIS)

Burrell, K.H.

1996-11-01

One of the scientific success stories of fusion research over the past decade is the development of the ExB shear stabilization model to explain the formation of transport barriers in magnetic confinement devices. This model was originally developed to explain the transport barrier formed at the plasma edge in tokamaks after the L (low) to H (high) transition. This concept has the universality needed to explain the edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines. More recently, this model has been applied to explain the further confinement improvement from H (high)-mode to VH (very high)-mode seen in some tokamaks, where the edge transport barrier becomes wider. Most recently, this paradigm has been applied to the core transport barriers formed in plasmas with negative or low magnetic shear in the plasma core. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to a higher energy state with reduced turbulence and transport when an additional source of free energy is applied to it. The transport decrease that is associated with ExB velocity shear effects also has significant practical consequences for fusion research. The fundamental physics involved in transport reduction is the effect of ExB shear on the growth, radial extent and phase correlation of turbulent eddies in the plasma. The same fundamental transport reduction process can be operational in various portions of the plasma because there are a number ways to change the radial electric field Er. An important theme in this area is the synergistic effect of ExB velocity shear and magnetic shear. Although the ExB velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of ExB velocity shear and facilitate turbulence stabilization

Low-rise shear wall failure modes

International Nuclear Information System (INIS)

Farrar, C.R.; Hashimoto, P.S.; Reed, J.W.

1991-01-01

A summary of the data that are available concerning the structural response of low-rise shear walls is presented. This data will be used to address two failure modes associated with the shear wall structures. First, data concerning the seismic capacity of the shear walls with emphasis on excessive deformations that can cause equipment failure are examined. Second, data concerning the dynamic properties of shear walls (stiffness and damping) that are necessary to compute the seismic inputs to attached equipment are summarized. This case addresses the failure of equipment when the structure remains functional. 23 refs

Chirality-specific lift forces of helix under shear flows: Helix perpendicular to shear plane.

Science.gov (United States)

Zhang, Qi-Yi

2017-02-01

Chiral objects in shear flow experience a chirality-specific lift force. Shear flows past helices in a low Reynolds number regime were studied using slender-body theory. The chirality-specific lift forces in the vorticity direction experienced by helices are dominated by a set of helix geometry parameters: helix radius, pitch length, number of turns, and helix phase angle. Its analytical formula is given. The chirality-specific forces are the physical reasons for the chiral separation of helices in shear flow. Our results are well supported by the latest experimental observations. © 2016 Wiley Periodicals, Inc.

Modeling combined tension-shear failure of ductile materials

International Nuclear Information System (INIS)

Partom, Y

2014-01-01

Failure of ductile materials is usually expressed in terms of effective plastic strain. Ductile materials can fail by two different failure modes, shear failure and tensile failure. Under dynamic loading shear failure has to do with shear localization and formation of adiabatic shear bands. In these bands plastic strain rate is very high, dissipative heating is extensive, and shear strength is lost. Shear localization starts at a certain value of effective plastic strain, when thermal softening overcomes strain hardening. Shear failure is therefore represented in terms of effective plastic strain. On the other hand, tensile failure comes about by void growth under tension. For voids in a tension field there is a threshold state of the remote field for which voids grow spontaneously (cavitation), and the material there fails. Cavitation depends on the remote field stress components and on the flow stress. In this way failure in tension is related to shear strength and to failure in shear. Here we first evaluate the cavitation threshold for different remote field situations, using 2D numerical simulations with a hydro code. We then use the results to compute examples of rate dependent tension-shear failure of a ductile material.

Role of E x B Shear and Magnetic Shear in the Formation of Transport Barriers in DIII-D

International Nuclear Information System (INIS)

Burrell, K.H.

2005-01-01

Development of the E x B shear stabilization model to explain the formation of transport barriers in magnetic confinement devices is a major achievement of fusion research. This concept has the universality needed to explain the H-mode edge transport barriers seen in limiter and divertor tokamaks, stellarators, and mirror machines; the broader edge transport barrier seen in VH-mode plasmas; and the core transport barriers formed in tokamaks with low or negative magnetic shear. These examples of confinement improvement are of considerable physical interest; it is not often that a system self-organizes to reduce transport when an additional source of free energy is applied to it. The transport decrease associated with E x B velocity shear is also of great practical benefit to fusion research. The fundamental physics involved in transport reduction is the effect of E x B shear on the growth, radial extent, and phase correlation of turbulent eddies in the plasma. The same basic transport reduction process can be operational in various portions of the plasma because there are a number of ways to change the radial electric field E r . An important theme in this area is the synergistic effect of E x B velocity shear and magnetic shear. Although the E x B velocity shear appears to have an effect on broader classes of microturbulence, magnetic shear can mitigate some potentially harmful effects of E x B velocity shear and facilitate turbulence stabilization. The experimental results on DIII-D and other devices are generally consistent with the basic theoretical models

Wall Shear Stress Estimation of Thoracic Aortic Aneurysm Using Computational Fluid Dynamics

Directory of Open Access Journals (Sweden)

J. Febina

2018-01-01

Full Text Available An attempt has been made to evaluate the effects of wall shear stress (WSS on thoracic aortic aneurysm (TAA using Computational Fluid Dynamics (CFD. Aneurysm is an excessive localized swelling of the arterial wall due to many physiological factors and it may rupture causing shock or sudden death. The existing imaging modalities such as MRI and CT assist in the visualization of anomalies in internal organs. However, the expected dynamic behaviour of arterial bulge under stressed condition can only be effectively evaluated through mathematical modelling. In this work, a 3D aneurysm model is reconstructed from the CT scan slices and eventually the model is imported to Star CCM+ (Siemens, USA for intensive CFD analysis. The domain is discretized using polyhedral mesh with prism layers to capture the weakening boundary more accurately. When there is flow reversal in TAA as seen in the velocity vector plot, there is a chance of cell damage causing clots. This is because of the shear created in the system due to the flow pattern. It is observed from the proposed mathematical modelling that the deteriorating WSS is an indicator for possible rupture and its value oscillates over a cardiac cycle as well as over different stress conditions. In this model, the vortex formation pattern and flow reversals are also captured. The non-Newtonian model, including a pulsatile flow instead of a steady average flow, does not overpredict the WSS (15.29 Pa compared to 16 Pa for the Newtonian model. Although in a cycle the flow behaviour is laminar-turbulent-laminar (LTL, utilizing the non-Newtonian model along with LTL model also overpredicted the WSS with a value of 20.1 Pa. The numerical study presented here provides good insight of TAA using a systematic approach to numerical modelling and analysis.

Focusing of Shear Shock Waves

Science.gov (United States)

Giammarinaro, Bruno; Espíndola, David; Coulouvrat, François; Pinton, Gianmarco

2018-01-01

Focusing is a ubiquitous way to transform waves. Recently, a new type of shock wave has been observed experimentally with high-frame-rate ultrasound: shear shock waves in soft solids. These strongly nonlinear waves are characterized by a high Mach number, because the shear wave velocity is much slower, by 3 orders of magnitude, than the longitudinal wave velocity. Furthermore, these waves have a unique cubic nonlinearity which generates only odd harmonics. Unlike longitudinal waves for which only compressional shocks are possible, shear waves exhibit cubic nonlinearities which can generate positive and negative shocks. Here we present the experimental observation of shear shock wave focusing, generated by the vertical motion of a solid cylinder section embedded in a soft gelatin-graphite phantom to induce linearly vertically polarized motion. Raw ultrasound data from high-frame-rate (7692 images per second) acquisitions in combination with algorithms that are tuned to detect small displacements (approximately 1 μ m ) are used to generate quantitative movies of gel motion. The features of shear shock wave focusing are analyzed by comparing experimental observations with numerical simulations of a retarded-time elastodynamic equation with cubic nonlinearities and empirical attenuation laws for soft solids.

Hysteretic Models Considering Axial-Shear-Flexure Interaction

Science.gov (United States)

Ceresa, Paola; Negrisoli, Giorgio

2017-10-01

Most of the existing numerical models implemented in finite element (FE) software, at the current state of the art, are not capable to describe, with enough reliability, the interaction between axial, shear and flexural actions under cyclic loading (e.g. seismic actions), neglecting crucial effects for predicting the nature of the collapse of reinforced concrete (RC) structural elements. Just a few existing 3D volume models or fibre beam models can lead to a quite accurate response, but they are still computationally inefficient for typical applications in earthquake engineering and also characterized by very complex formulation. Thus, discrete models with lumped plasticity hinges may be the preferred choice for modelling the hysteretic behaviour due to cyclic loading conditions, in particular with reference to its implementation in a commercial software package. These considerations lead to this research work focused on the development of a model for RC beam-column elements able to consider degradation effects and interaction between the actions under cyclic loading conditions. In order to develop a model for a general 3D discrete hinge element able to take into account the axial-shear-flexural interaction, it is necessary to provide an implementation which involves a corrector-predictor iterative scheme. Furthermore, a reliable constitutive model based on damage plasticity theory is formulated and implemented for its numerical validation. Aim of this research work is to provide the formulation of a numerical model, which will allow implementation within a FE software package for nonlinear cyclic analysis of RC structural members. The developed model accounts for stiffness degradation effect and stiffness recovery for loading reversal.

Least-squares wave-front reconstruction of Shack-Hartmann sensors and shearing interferometers using multigrid techniques

International Nuclear Information System (INIS)

Baker, K.L.

2005-01-01

This article details a multigrid algorithm that is suitable for least-squares wave-front reconstruction of Shack-Hartmann and shearing interferometer wave-front sensors. The algorithm detailed in this article is shown to scale with the number of subapertures in the same fashion as fast Fourier transform techniques, making it suitable for use in applications requiring a large number of subapertures and high Strehl ratio systems such as for high spatial frequency characterization of high-density plasmas, optics metrology, and multiconjugate and extreme adaptive optics systems

Direct Shear Behavior of Fiber Reinforced Concrete Elements

Directory of Open Access Journals (Sweden)

Hussein Al-Quraishi

2018-01-01

Full Text Available Improving the accuracy of load-deformation behavior, failure mode, and ultimate load capacity for reinforced concrete members subjected to in-plane loadings such as corbels, wall to foundation connections and panels need shear strength behavior to be included. Shear design in reinforced concrete structures depends on crack width, crack slippage and roughness of the surface of cracks. This paper illustrates results of an experimental investigation conducted to investigate the direct shear strength of fiber normal strength concrete (NSC and reactive powder concrete (RPC. The tests were performed along a pre-selected shear plane in concrete members named push-off specimens. The effectiveness of concrete compressive strength, volume fraction of steel fiber, and shear reinforcement ratio on shear transfer capacity were considered in this study. Furthermore, failure modes, shear stress-slip behavior, and shear stress-crack width behavior were also presented in this study. Tests’ results showed that volume fraction of steel fiber and compressive strength of concrete in NSC and RPC play a major role in improving the shear strength of concrete. As expectedly, due to dowel action, the shear reinforcement is the predominant factor in resisting the shear stress. The shear failure of NSC and RPC has the sudden mode of failure (brittle failure with the approximately linear behavior of shear stress-slip relationship till failure. Using RPC instead of NSC with the same amount of steel fibers in constructing the push-off specimen result in high shear strength. In NSC, shear strength influenced by the three major factors; crack surface friction, aggregate interlock and steel fiber content if present. Whereas, RPC has only steel fiber and cracks surface friction influencing the shear strength. Due to cementitious nature of RPC in comparisons with NSC, the RPC specimen shows greater cracks width. It is observed that the Mattock model gives very satisfactory

A comprehensive study on rotation reversal in KSTAR: experimental observations and modelling

Science.gov (United States)

Na, D. H.; Na, Yong-Su; Angioni, C.; Yang, S. M.; Kwon, J. M.; Jhang, Hogun; Camenen, Y.; Lee, S. G.; Shi, Y. J.; Ko, W. H.; Lee, J. A.; Hahm, T. S.; KSTAR Team

2017-12-01

Dedicated experiments have been performed in KSTAR Ohmic plasmas to investigate the detailed physics of the rotation reversal phenomena. Here we adapt the more general definition of rotation reversal, a large change of the intrinsic toroidal rotation gradient produced by minor changes in the control parameters (Camenen et al 2017 Plasma Phys. Control. Fusion 59 034001), which is commonly observed in KSTAR regardless of the operating conditions. The two main phenomenological features of the rotation reversal are the normalized toroidal rotation gradient ({{u}\\prime} ) change in the gradient region and the existence of an anchor point. For the KSTAR Ohmic plasma database including the experiment results up to the 2016 experimental campaign, both features were investigated. First, the observations show that the locations of the gradient and the anchor point region are dependent on {{q}95} . Second, a strong dependence of {{u}\\prime} on {νeff} is clearly observed in the gradient region, whereas the dependence on R/{{L}{{Ti}}} , R/{{L}{{Te}}} , and R/{{L}{{ne}}} is unclear considering the usual variation of the normalized gradient length in KSTAR. The experimental observations were compared against several theoretical models. The rotation reversal might not occur due to the transition of the dominant turbulence from the trapped electron mode to the ion temperature gradient mode or the neoclassical equilibrium effect in KSTAR. Instead, it seems that the profile shearing effects associated with a finite ballooning tilting well reproduce the experimental observations of both the gradient region and the anchor point; the difference seems to be related to the magnetic shear and the q value. Further analysis implies that the increase of {{u}\\prime} in the gradient region with the increase of the collisionality would occur when the reduction of the momentum diffusivity is comparatively larger than the reduction of the residual stress. It is supported by the perturbative

Origins of Shear Jamming for Frictional Grains

Science.gov (United States)

Wang, Dong; Zheng, Hu; Ren, Jie; Dijksman, Joshua; Bares, Jonathan; Behringer, Robert

2016-11-01

Granular systems have been shown to be able to behave like solids, under shear, even when their densities are below the critical packing fraction for frictionless isotropic jamming. To understand such a phenomena, called shear jamming, the question we address here is: how does shear bring a system from a unjammed state to a jammed state, where the coordination number, Z, is no less than 3, the isotropic jamming point for frictional grains? Since Z can be used to distinguish jammed states from unjammed ones, it is vital to understand how shear increases Z. We here propose a set of three particles in contact, denoted as a trimer, as the basic unit to characterize the deformation of the system. Trimers, stabilized by inter-grain friction, fail under a certain amount of shear and bend to make extra contacts to regain stability. By defining a projection operator of the opening angle of the trimer to the compression direction in the shear, O, we see a systematically linear decrease of this quantity with respect to shear strain, demonstrating the bending of trimers as expected. In addition, the average change of O from one shear step to the next shows a good collapse when plotted against Z, indicating a universal behavior in the process of shear jamming. We acknowledge support from NSF DMR1206351, NASA NNX15AD38G, the William M. Keck Foundation and a RT-MRSEC Fellowship.

Crosswind Shear Gradient Affect on Wake Vortices

Science.gov (United States)

Proctor, Fred H.; Ahmad, Nashat N.

2011-01-01

Parametric simulations with a Large Eddy Simulation (LES) model are used to explore the influence of crosswind shear on aircraft wake vortices. Previous studies based on field measurements, laboratory experiments, as well as LES, have shown that the vertical gradient of crosswind shear, i.e. the second vertical derivative of the environmental crosswind, can influence wake vortex transport. The presence of nonlinear vertical shear of the crosswind velocity can reduce the descent rate, causing a wake vortex pair to tilt and change in its lateral separation. The LES parametric studies confirm that the vertical gradient of crosswind shear does influence vortex trajectories. The parametric results also show that vortex decay from the effects of shear are complex since the crosswind shear, along with the vertical gradient of crosswind shear, can affect whether the lateral separation between wake vortices is increased or decreased. If the separation is decreased, the vortex linking time is decreased, and a more rapid decay of wake vortex circulation occurs. If the separation is increased, the time to link is increased, and at least one of the vortices of the vortex pair may have a longer life time than in the case without shear. In some cases, the wake vortices may never link.

Sheared-root inocula of vesicular-arbuscular mycorrhizal fungi.

Science.gov (United States)

Sylvia, D M; Jarstfer, A G

1992-01-01

For efficient handling, vesicular-arbuscular mycorrhizal fungi should be processed into small and uniform inocula; however, processing can reduce the inoculum density. In this article we describe the preparation and use of sheared-root inocula of Glomus spp. in which inoculum densities were increased during processing. Our objectives were to determine inoculum viability and density after shearing and to ascertain if the sheared inocula could be pelletized or used with a gel carrier. Root samples were harvested from aeroponic cultures, blotted dry, cut into 1-cm lengths, and sheared in a food processor for up to 80 s. After shearing, the inoculum was washed over sieves, and the propagule density in each fraction was determined. Sheared inocula were also encapsulated in carrageenan or used in a gel carrier. Shearing aeroponically produced root inocula reduced particle size. Propagule density increased with decreasing size fraction down to a size of 63 mum, after which propagule density decreased. The weighted-average propagule density of the inoculum was 135,380 propagules g (dry weight) of sheared root material. Sheared roots were encapsulated successfully in carrageenan, and the gel served as an effective carrier. Aeroponic root inoculum was stored dry at 4 degrees C for 23 months without significant reduction in propagule density; however, this material was not appropriate for shearing. Moist roots, useful for shearing, began to lose propagule density after 1 month of storage. Shearing proved to be an excellent method to prepare viable root inocula of small and uniform size, allowing for more efficient and effective use of limited inoculum supplies.

Imaging Shear Strength Along Subduction Faults

Science.gov (United States)

Bletery, Quentin; Thomas, Amanda M.; Rempel, Alan W.; Hardebeck, Jeanne L.

2017-11-01

Subduction faults accumulate stress during long periods of time and release this stress suddenly, during earthquakes, when it reaches a threshold. This threshold, the shear strength, controls the occurrence and magnitude of earthquakes. We consider a 3-D model to derive an analytical expression for how the shear strength depends on the fault geometry, the convergence obliquity, frictional properties, and the stress field orientation. We then use estimates of these different parameters in Japan to infer the distribution of shear strength along a subduction fault. We show that the 2011 Mw9.0 Tohoku earthquake ruptured a fault portion characterized by unusually small variations in static shear strength. This observation is consistent with the hypothesis that large earthquakes preferentially rupture regions with relatively homogeneous shear strength. With increasing constraints on the different parameters at play, our approach could, in the future, help identify favorable locations for large earthquakes.

Imaging shear strength along subduction faults

Science.gov (United States)

Bletery, Quentin; Thomas, Amanda M.; Rempel, Alan W.; Hardebeck, Jeanne L.

2017-01-01

Subduction faults accumulate stress during long periods of time and release this stress suddenly, during earthquakes, when it reaches a threshold. This threshold, the shear strength, controls the occurrence and magnitude of earthquakes. We consider a 3-D model to derive an analytical expression for how the shear strength depends on the fault geometry, the convergence obliquity, frictional properties, and the stress field orientation. We then use estimates of these different parameters in Japan to infer the distribution of shear strength along a subduction fault. We show that the 2011 Mw9.0 Tohoku earthquake ruptured a fault portion characterized by unusually small variations in static shear strength. This observation is consistent with the hypothesis that large earthquakes preferentially rupture regions with relatively homogeneous shear strength. With increasing constraints on the different parameters at play, our approach could, in the future, help identify favorable locations for large earthquakes.

Coronal Polarization of Pseudostreamers and the Solar Polar Field Reversal

Science.gov (United States)

Rachmeler, L. A.; Guennou, C.; Seaton, D. B.; Gibson, S. E.; Auchere, F.

2016-01-01

The reversal of the solar polar magnetic field is notoriously hard to pin down due to the extreme viewing angle of the pole. In Cycle 24, the southern polar field reversal can be pinpointed with high accuracy due to a large-scale pseudostreamer that formed over the pole and persisted for approximately a year. We tracked the size and shape of this structure with multiple observations and analysis techniques including PROBA2/SWAP EUV images, AIA EUV images, CoMP polarization data, and 3D tomographic reconstructions. We find that the heliospheric field reversed polarity in February 2014, whereas in the photosphere, the last vestiges of the previous polar field polarity remained until March 2015. We present here the evolution of the structure and describe its identification in the Fe XII 1074nm coronal emission line, sensitive to the Hanle effect in the corona.

Wave induced extreme hull girder loads on containerships

DEFF Research Database (Denmark)

Jensen, Jørgen Juncher; Pedersen, Preben Terndrup; Shi, Bill

2009-01-01

This paper provides simple but rational procedures for prediction of extreme wave – induced sectional hull girder forces with reasonable engineering accuracy. The procedures take into account main ship hull characteristics such as: length, breadth, draught, block coefficient, bow flare coefficient......, forward speed and hull flexibility. The vertical hull girder loads are evaluated for specific operational profiles. Firstly a quadratic strip theory is presented which can give separate predictions for the hogging and sagging bending moments and shear forces and for hull girder loads. Then this procedure...... is based on rational methods it can be applied for novel single hull ship types not presently covered by the rules of the classification societies or to account for specific operational profiles....

Differentiating benign from malignant solid breast masses: value of shear wave elastography according to lesion stiffness combined with greyscale ultrasound according to BI-RADS classification.

Science.gov (United States)

Evans, A; Whelehan, P; Thomson, K; Brauer, K; Jordan, L; Purdie, C; McLean, D; Baker, L; Vinnicombe, S; Thompson, A

2012-07-10

The aim of this study was to assess the performance of shear wave elastography combined with BI-RADS classification of greyscale ultrasound images for benign/malignant differentiation in a large group of patients. One hundred and seventy-five consecutive patients with solid breast masses on routine ultrasonography undergoing percutaneous biopsy had the greyscale findings classified according to the American College of Radiology BI-RADS. The mean elasticity values from four shear wave images were obtained. For mean elasticity vs greyscale BI-RADS, the performance results against histology were sensitivity: 95% vs 95%, specificity: 77% vs 69%, Positive Predictive Value (PPV): 88% vs 84%, Negative Predictive Value (NPV): 90% vs 91%, and accuracy: 89% vs 86% (all P>0.05). The results for the combination (positive result from either modality counted as malignant) were sensitivity 100%, specificity 61%, PPV 82%, NPV 100%, and accuracy 86%. The combination of BI-RADS greyscale and shear wave elastography yielded superior sensitivity to BI-RADS alone (P=0.03) or shear wave alone (P=0.03). The NPV was superior in combination compared with either alone (BI-RADS P=0.01 and shear wave P=0.02). Together, BI-RADS assessment of greyscale ultrasound images and shear wave ultrasound elastography are extremely sensitive for detection of malignancy.

Statistics on Near Wall Structures and Shear Stress Distribution from 3D Holographic Measurement.

Science.gov (United States)

Sheng, J.; Malkiel, E.; Katz, J.

2007-11-01

Digital Holographic Microscopy performs 3D velocity measurement in the near-wall region of a turbulent boundary layer in a square channel over a smooth wall at Reτ=1,400. Resolution of ˜1μm over a sample volume of 1.5x2x1.5mm (x^+=50, y^+=60, z^+=50) is sufficient for resolving buffer layer and lower log layer structures, and for measuring instantaneous wall shear stress distributions from velocity gradients in the viscous sublayer. Results, based on 700 instantaneous realizations, provide detailed statistics on the spatial distribution of both wall stress components along with characteristic flow structures. Conditional sampling based on maxima and minima of wall shear stresses, as well as examination of instantaneous flow structures, lead to development of a conceptual model for a characteristic flow phenomenon that seems to generating extreme stress events. This structure develops as an initially spanwise vortex element rises away from the surface, due to local disturbance, causing a local stress minimum. Due to increasing velocity with elevation, this element bends downstream, forming a pair of inclined streamwise vortices, aligned at 45^0 to freestream, with ejection-like flow between them. Entrainment of high streamwise momentum on the outer sides of this vortex pair generates streamwise shear stress maxima, 70 δν downstream, which are displaced laterally by 35 δν from the local minimum.

Predicting Shear Transformation Events in Metallic Glasses

Science.gov (United States)

Xu, Bin; Falk, Michael L.; Li, J. F.; Kong, L. T.

2018-03-01

Shear transformation is the elementary process for plastic deformation of metallic glasses, the prediction of the occurrence of the shear transformation events is therefore of vital importance to understand the mechanical behavior of metallic glasses. In this Letter, from the view of the potential energy landscape, we find that the protocol-dependent behavior of shear transformation is governed by the stress gradient along its minimum energy path and we propose a framework as well as an atomistic approach to predict the triggering strains, locations, and structural transformations of the shear transformation events under different shear protocols in metallic glasses. Verification with a model Cu64 Zr36 metallic glass reveals that the prediction agrees well with athermal quasistatic shear simulations. The proposed framework is believed to provide an important tool for developing a quantitative understanding of the deformation processes that control mechanical behavior of metallic glasses.

Stroop interference and reverse Stroop interference as potential measures of cognitive ability during exposure to stress

OpenAIRE

景山, 望; 箱田, 裕司; Kageyama, Nozomu; Hakoda, Yuji

2011-01-01

Stroop interference and reverse-Stroop interference are one of the easiest and most powerful effects to demonstrate in a classroom. Therefore, they have been studied not only through basic research in the laboratory but also through applied research in extreme environments. First, we reviewed studies tha investigated Stroop interference and reverse-Stroop interference as hallmark measures of selective at attention and conflict resolution. Second, we reviewed studies that examined the effects ...

Thrombus Formation at High Shear Rates.

Science.gov (United States)

Casa, Lauren D C; Ku, David N

2017-06-21

The final common pathway in myocardial infarction and ischemic stroke is occlusion of blood flow from a thrombus forming under high shear rates in arteries. A high-shear thrombus forms rapidly and is distinct from the slow formation of coagulation that occurs in stagnant blood. Thrombosis at high shear rates depends primarily on the long protein von Willebrand factor (vWF) and platelets, with hemodynamics playing an important role in each stage of thrombus formation, including vWF binding, platelet adhesion, platelet activation, and rapid thrombus growth. The prediction of high-shear thrombosis is a major area of biofluid mechanics in which point-of-care testing and computational modeling are promising future directions for clinically relevant research. Further research in this area will enable identification of patients at high risk for arterial thrombosis, improve prevention and treatment based on shear-dependent biological mechanisms, and improve blood-contacting device design to reduce thrombosis risk.

Modeling of shear wall buildings

Energy Technology Data Exchange (ETDEWEB)

Gupta, A K [North Carolina State Univ., Raleigh (USA). Dept. of Civil Engineering

1984-05-01

Many nuclear power plant buildings, for example, the auxiliary building, have reinforced concrete shear walls as the primary lateral load resisting system. Typically, these walls have low height to length ratio, often less than unity. Such walls exhibit marked shear lag phenomenon which would affect their bending stiffness and the overall stress distribution in the building. The deformation and the stress distribution in walls have been studied which is applicable to both the short and the tall buildings. The behavior of the wall is divided into two parts: the symmetric flange action and the antisymmetry web action. The latter has two parts: the web shear and the web bending. Appropriate stiffness equations have been derived for all the three actions. These actions can be synthesized to solve any nonlinear cross-section. Two specific problems, that of lateral and torsional loadings of a rectangular box, have been studied. It is found that in short buildings shear lag plays a very important role. Any beam type formulation which either ignores shear lag or includes it in an idealized form is likely to lead to erroneous results. On the other hand a rigidity type approach with some modifications to the standard procedures would yield nearly accurate answers.

Shear instability of a gyroid diblock copolymer

DEFF Research Database (Denmark)

Eskimergen, Rüya; Mortensen, Kell; Vigild, Martin Etchells

2005-01-01

-induced destabilization is discussed in relation to analogous observations on shear-induced order-to-order and disorder-to-order transitions observed in related block copolymer systems and in microemulsions. It is discussed whether these phenomena originate in shear-reduced fluctuations or shear-induced dislocations....

Focus detection by shearing interference of vortex beams for non-imaging systems.

Science.gov (United States)

Li, Xiongfeng; Zhan, Shichao; Liang, Yiyong

2018-02-10

In focus detection of non-imaging systems, the common image-based methods are not available. Also, interference techniques are seldom used because only the degree with hardly any direction of defocus can be derived from the fringe spacing. In this paper, we propose a vortex-beam-based shearing interference system to do focus detection for a focused laser direct-writing system, where a vortex beam is already involved. Both simulated and experimental results show that fork-like features are added in the interference patterns due to the existence of an optical vortex, which makes it possible to distinguish the degree and direction of defocus simultaneously. The theoretical fringe spacing and resolution of this method are derived. A resolution of 0.79 μm can be achieved under the experimental combination of parameters, and it can be further improved with the help of the image processing algorithm and closed-loop controlling in the future. Finally, the influence of incomplete collimation and the wedge angle of the shear plate is discussed. This focus detection approach is extremely appropriate for those non-imaging systems containing one or more focused vortex beams.

Accurate shear measurement with faint sources

International Nuclear Information System (INIS)

Zhang, Jun; Foucaud, Sebastien; Luo, Wentao

2015-01-01

For cosmic shear to become an accurate cosmological probe, systematic errors in the shear measurement method must be unambiguously identified and corrected for. Previous work of this series has demonstrated that cosmic shears can be measured accurately in Fourier space in the presence of background noise and finite pixel size, without assumptions on the morphologies of galaxy and PSF. The remaining major source of error is source Poisson noise, due to the finiteness of source photon number. This problem is particularly important for faint galaxies in space-based weak lensing measurements, and for ground-based images of short exposure times. In this work, we propose a simple and rigorous way of removing the shear bias from the source Poisson noise. Our noise treatment can be generalized for images made of multiple exposures through MultiDrizzle. This is demonstrated with the SDSS and COSMOS/ACS data. With a large ensemble of mock galaxy images of unrestricted morphologies, we show that our shear measurement method can achieve sub-percent level accuracy even for images of signal-to-noise ratio less than 5 in general, making it the most promising technique for cosmic shear measurement in the ongoing and upcoming large scale galaxy surveys

Shear and loading in channels: Oscillatory shearing and edge currents of superconducting vortices

Science.gov (United States)

Wambaugh, J. F.; Marchesoni, F.; Nori, Franco

2003-04-01

Via computer simulations we study the motion of quantized magnetic flux-lines, or vortices, confined to a straight pin-free channel in a strong-pinning superconducting sample. We find that, when a constant current is applied across this system, a very unusual oscillatory shearing appears, in which the vortices moving at the edges of the channel periodically trail behind and then suddenly leapfrog past the vortices moving in the inner rows. For small enough driving forces, this oscillatory shearing dynamic phase is replaced by a continuous shearing phase in which the distance between initially-nearby vortices grows in time, quickly destroying the order of the lattice. An animation of this novel “oscillatory leapfrogging shear” effect of the vortex edge currents appears in http://www-personal.engin.umich.edu/˜nori/channel/

Vesicle dynamics in shear and capillary flows

International Nuclear Information System (INIS)

Noguchi, Hiroshi; Gompper, Gerhard

2005-01-01

The deformation of vesicles in flow is studied by a mesoscopic simulation technique, which combines multi-particle collision dynamics for the solvent with a dynamically triangulated surface model for the membrane. Shape transitions are investigated both in simple shear flows and in cylindrical capillary flows. We focus on reduced volumes, where the discocyte shape of fluid vesicles is stable, and the prolate shape is metastable. In simple shear flow at low membrane viscosity, the shear induces a transformation from discocyte to prolate with increasing shear rate, while at high membrane viscosity, the shear induces a transformation from prolate to discocyte, or tumbling motion accompanied by oscillations between these two morphologies. In capillary flow, at small flow velocities the symmetry axis of the discocyte is found not to be oriented perpendicular to the cylinder axis. With increasing flow velocity, a transition to a prolate shape occurs for fluid vesicles, while vesicles with shear-elastic membranes (like red blood cells) transform into a coaxial parachute-like shape

An underwater shear compactor

International Nuclear Information System (INIS)

Biver, E.; Sims, J.

1997-01-01

This paper, originally presented at the WM'96 Conference in Tucson Arizona, describes a concept of a specialised decommissioning tool designed to operate underwater and to reduce the volume of radioactive components by shearing and compacting. The shear compactor was originally conceived to manage the size reduction of a variety of decommissioned stainless steel tubes stored within a reactor fuel cooling pond and which were consuming a substantial volume of the pond. The main objective of this tool was to cut the long tubes into shorter lengths and to compact them into a flat rectangular form which could be stacked on the pond floor, thus saving valuable space. The development programme, undertaken on this project, investigated a wide range of factors which could contribute to an extended cutting blade performance, ie: materials of construction, cutting blade shape and cutting loads required, shock effects, etc. The second phase was to review other aspects of the design, such as radiological protection, cutting blade replacement, maintenance, pond installation and resultant wall loads, water hydraulics, collection of products of shearing/compacting operations, corrosion of the equipment, control system, operational safety and the ability of the equipment to operate in dry environments. The paper summarises the extended work programme involved with this shear compactor tool. (author)

Evolution of allowable stresses in shear for lumber

Science.gov (United States)

Robert L. Ethington; William L. Galligan; Henry M. Montrey; Alan D. Freas

1979-01-01

This paper surveys research leading to allowable shear stress parallel to grain for lumber. In early flexure tests of lumber, some pieces failed in shear. The estimated shear stress at time of failure was generally lower than shear strength measured on small, clear, straight-grained specimens. This and other engineering observations gave rise to adjustments that...

Toroidal fusion reactor design based on the reversed-field pinch

International Nuclear Information System (INIS)

Hagenson, R.L.

1978-07-01

The toroidal reversed-field pinch (RFP) achieves gross equilibrium and stability with a combination of high shear and wall stabilization, rather than the imposition of tokamak-like q-constraints. Consequently, confinement is provided primarily by poloidal magnetic fields, poloidal betas as large as approximately 0.58 are obtainable, the high ohmic-heating (toroidal) current densities promise a sole means of heating a D-T plasma to ignition, and the plasma aspect ratio is not limited by stability/equilibrium constraints. A reactor-like plasma model has been developed in order to quantify and to assess the general features of a power system based upon RFP confinement. An ''operating point'' has been generated on the basis of this plasma model and a relatively detailed engineering energy balance. These results are used to generate a conceptual engineering model of the reversed-field pinch reactor (RFPR) which includes a general description of a 750 MWe power plant and the preliminary consideration of vacuum/fueling, first wall, blanket, magnet coils, iron core, and the energy storage/transfer system

Effect of shear span-to-depth ratio on the shear behavior of BFRP-RC deep beams

Directory of Open Access Journals (Sweden)

Alhamad Siyam

2017-01-01

Full Text Available This study investigates the shear behavior of deep concrete beams reinforced with basalt fiber reinforced polymer (BFRP bars for flexure without web reinforcements. The experimental testing performed herein consisted of a total of 4 short beams, three of which were reinforced with BFRP and one beam was reinforced with steel bars. The primary test variable was the shear-span-to-effective-depth ratio (a/d and its influence on the beams’ mid-span deflections, shear capacity, load-deformation relationships and the failure modes.

Evaluation of composite shear walls behavior (parametric study

Directory of Open Access Journals (Sweden)

Ali Nikkhoo

2017-11-01

Full Text Available Composite shear walls which are made of a layer of steel plate with a concrete cover in one or both sides of the steel plate, are counted as the third generation of the shear walls. Nowadays, composite shear walls are widely utilized in building new resisting structures as well as rehabilitating of the existing structures in earthquake-prone countries. Despite of its advantages, use of the composite shear walls is not yet prevalent as it demands more detailed appropriate investigation. Serving higher strength, flexibility and better energy absorption, while being more economical are the main advantages of this system which has paved its path to be used in high-rise buildings, structural retrofit and reservoir tanks. In this research, channel shear connectors are utilized to connect the concrete cover to the steel plate. As a key parameter, variation in the distance of shear connectors and their arrangement on the behavior of composite shear walls has been scrutinized. In addition, the shear stiffness, flexibility, out of plane displacement and the energy absorption of the structural system has been explored. For this purpose, several structural models with different shear distances and arrangements have been investigated. The obtained results reveal that with increase in shear connectors’ distance, the wall stiffness would reduce while its lateral displacement increases up to eighty percent While the out of plane displacement of the steel plate will reduce up to three times.

Acoustic waves in unbounded shear flows

International Nuclear Information System (INIS)

Chagelishvili, G.D.; Khujadze, G.R.; Lominadze, J.G.; Rogava, A.D.

1996-05-01

The linear evolution of acoustic waves in fluid flow with constant density and uniform shear of velocity is investigated. The process of the mean flow energy extraction by the three-dimensional acoustic waves which is due to the non-normality of linear dynamics in shear flows is analyzed. The thorough examination of the dynamics of different physical quantities, specifying the wave evolution, is outlined. The revealing of the behaviour becomes possible owing to the nonmodal approach that has been extensively used in the study of the perturbations evolution in shear flows since the beginning of the nineties. In addition, a detailed analyses of the physics of shear energy gain by vortex and acoustic perturbations is presented. (author). 28 refs, 7 figs

Torsional shear flow of granular materials: shear localization and minimum energy principle

Science.gov (United States)

Artoni, Riccardo; Richard, Patrick

2018-01-01

The rheological properties of granular matter submitted to torsional shear are investigated numerically by means of discrete element method. The shear cell is made of a cylinder filled by grains which are sheared by a bumpy bottom and submitted to a vertical pressure which is applied at the top. Regimes differing by their strain localization features are observed. They originate from the competition between dissipation at the sidewalls and dissipation in the bulk of the system. The effects of the (i) the applied pressure, (ii) sidewall friction, and (iii) angular velocity are investigated. A model, based on the purely local μ (I)-rheology and a minimum energy principle is able to capture the effect of the two former quantities but unable to account the effect of the latter. Although, an ad hoc modification of the model allows to reproduce all the numerical results, our results point out the need for an alternative rheology.

[Research on lateral shearing interferometer for field monitoring of natural gas pipeline leak].

Science.gov (United States)

Zhang, Xue-Feng; Gao, Yu-Bin

2012-09-01

Aimed at the mechanical scanning spectroscopy equipment with poor anti-interference and anti-jamming ability, which affects the accuracy of its natural gas pipeline leak detection in the wild, a new type of lateral shearing interferometer system was designed. The system uses a beam splitter to get optical path difference by a mechanical scanning part, and it cancel the introduction of external vibration interference through the linkage between the two beam splitterw. The interference intensity of interference fringes produced was calculated, and analysis of a rotating beam splitter corresponds to the angle of the optical path difference function, solving for the maximum angle of the forward rotation and reverse rotation, which is the maximum optical path range. Experiments using the gas tank deflated simulated natural gas pipeline leak process, in the interference conditions, and the test data of the type WQF530 spectrometer and the new type of lateral shearing interferometer system were comparedt. The experimental results show that the relative error of both systems is about 1% in indoor conditions without interference. However, in interference environment, the error of WQF530 type spectrometer becomes larger, more than 10%, but the error of the new type of lateral shearing interferometer system is still below 5%. The detection accuracy of the type WQF530 spectrometer decreased significantly due to the environment. Therefore, the seismic design of the system can effectively offset power deviation and half-width increases of center wavelength caused by external interference, and compared to conventional mechanical scanning interferometer devices the new system is more suitable for field detection.

Failure modes of low-rise shear walls

International Nuclear Information System (INIS)

Farrar, C.R.; Reed, J.W.; Salmon, M.W.

1993-01-01

A summary of available data concerning the structural response of low-rise shear walls is presented. These data will be used to address two failure modes associated with shear wall structures. First, the data concerning the seismic capacity of the shear walls are examined, with emphasis on excessive deformations that can cause equipment failure. Second, the data concerning the dynamic properties of shear walls (stiffness and damping) that are necessary for computing the seismic inputs to attached equipment are summarized. This case addresses the failure of equipment when the structure remains functional

Fully-reversible optical sensor for hydrogen peroxide with fast response.

Science.gov (United States)

Ding, Longjiang; Chen, Siyu; Zhang, Wei; Zhang, Yinglu; Wang, Xu-Dong

2018-05-09

A fully reversible optical sensor for hydrogen peroxide with fast response is presented. The sensor was fabricated by in-situ growing ultra-small platinum nanoparticles (PtNPs) inside the pores of fibrous silica particles (KCC-1). The nanocomposite was then embedded into a hydrogel matrix and form a sensor layer, the immobilized PtNPs can catalytically convert hydrogen peroxide into molecular oxygen, which is measured via luminescent quenching based oxygen sensor underneath. Owing to the high porosity and permeability of KCC-1 and high local concentration of PtNPs, the sensor exhibits fast response (less than 1 min) and full reversibility. The measurement range of the sensor covers 1.0 μM to 10.0 mM, and very small amount of sample is required during measurement (200 μL). Because of its high stability, excellent reversibility and selectivity, and extremely fast response, the sensor could fulfill all industry requirements for real-time measurement, and fill market vacancy.

Determination of wall shear stress from mean velocity and Reynolds shear stress profiles

Science.gov (United States)

Volino, Ralph J.; Schultz, Michael P.

2018-03-01

An analytical method is presented for determining the Reynolds shear stress profile in steady, two-dimensional wall-bounded flows using the mean streamwise velocity. The method is then utilized with experimental data to determine the local wall shear stress. The procedure is applicable to flows on smooth and rough surfaces with arbitrary pressure gradients. It is based on the streamwise component of the boundary layer momentum equation, which is transformed into inner coordinates. The method requires velocity profiles from at least two streamwise locations, but the formulation of the momentum equation reduces the dependence on streamwise gradients. The method is verified through application to laminar flow solutions and turbulent DNS results from both zero and nonzero pressure gradient boundary layers. With strong favorable pressure gradients, the method is shown to be accurate for finding the wall shear stress in cases where the Clauser fit technique loses accuracy. The method is then applied to experimental data from the literature from zero pressure gradient studies on smooth and rough walls, and favorable and adverse pressure gradient cases on smooth walls. Data from very near the wall are not required for determination of the wall shear stress. Wall friction velocities obtained using the present method agree with those determined in the original studies, typically to within 2%.

Temperature dependence of the shear modulus of soft tissues assessed by ultrasound

International Nuclear Information System (INIS)

Sapin-de Brosses, E; Gennisson, J-L; Pernot, M; Fink, M; Tanter, M

2010-01-01

Soft tissue stiffness was shown to significantly change after thermal ablation. To better understand this phenomenon, the study aims (1) to quantify and explain the temperature dependence of soft tissue stiffness for different organs, (2) to investigate the potential relationship between stiffness changes and thermal dose and (3) to study the reversibility or irreversibility of stiffness changes. Ex vivo bovine liver and muscle samples (N = 3 and N = 20, respectively) were slowly heated and cooled down into a thermally controlled saline bath. Temperatures were assessed by thermocouples. Sample stiffness (shear modulus) was provided by the quantitative supersonic shear imaging technique. Changes in liver stiffness are observed only after 45 deg. C. In contrast, between 25 deg. C and 65 deg. C, muscle stiffness varies in four successive steps that are consistent with the thermally induced proteins denaturation reported in the literature. After a 6 h long heating and cooling process, the final muscle stiffness can be either smaller or bigger than the initial one, depending on the stiffness at the end of the heating. Another important result is that stiffness changes are linked to thermal dose. Given the high sensitivity of ultrasound to protein denaturation, this study gives promising prospects for the development of ultrasound-guided HIFU systems.

Temperature dependence of the shear modulus of soft tissues assessed by ultrasound

Energy Technology Data Exchange (ETDEWEB)

Sapin-de Brosses, E; Gennisson, J-L; Pernot, M; Fink, M; Tanter, M [Langevin Institute (CNRS UMR 7587), INSERM ERL U979, ESPCI ParisTech, 10 rue Vauquelin, 75 005 Paris (France)], E-mail: emilie.sapin@espci.fr

2010-03-21

Soft tissue stiffness was shown to significantly change after thermal ablation. To better understand this phenomenon, the study aims (1) to quantify and explain the temperature dependence of soft tissue stiffness for different organs, (2) to investigate the potential relationship between stiffness changes and thermal dose and (3) to study the reversibility or irreversibility of stiffness changes. Ex vivo bovine liver and muscle samples (N = 3 and N = 20, respectively) were slowly heated and cooled down into a thermally controlled saline bath. Temperatures were assessed by thermocouples. Sample stiffness (shear modulus) was provided by the quantitative supersonic shear imaging technique. Changes in liver stiffness are observed only after 45 deg. C. In contrast, between 25 deg. C and 65 deg. C, muscle stiffness varies in four successive steps that are consistent with the thermally induced proteins denaturation reported in the literature. After a 6 h long heating and cooling process, the final muscle stiffness can be either smaller or bigger than the initial one, depending on the stiffness at the end of the heating. Another important result is that stiffness changes are linked to thermal dose. Given the high sensitivity of ultrasound to protein denaturation, this study gives promising prospects for the development of ultrasound-guided HIFU systems.

Adiabatic shear localization in ultrafine grained 6061 aluminum alloy

Energy Technology Data Exchange (ETDEWEB)

Wang, Bingfeng, E-mail: biw009@ucsd.edu [School of Materials Science and Engineering, Central South University, Changsha 410083 (China); Department of Mechanical and Aerospace Engineering, University of California, San Diego (United States); State Key Laboratory for Powder Metallurgy, Central South University, Changsha, Hunan (China); Key Lab of Nonferrous Materials, Ministry of Education, Central South University, Changsha 410083 (China); Ma, Rui; Zhou, Jindian [School of Materials Science and Engineering, Central South University, Changsha 410083 (China); Li, Zezhou; Zhao, Shiteng [Department of Mechanical and Aerospace Engineering, University of California, San Diego (United States); Huang, Xiaoxia [School of Materials Science and Engineering, Central South University, Changsha 410083 (China)

2016-10-15

Localized shear is an important mode of deformation; it leads to catastrophic failure with low ductility, and occurs frequently during high strain-rate deformation. The hat-shaped specimen has been successfully used to generate shear bands under controlled shock-loading tests. The microstructure in the forced shear band was characterized by optical microscopy, microhardness, and transmission electron microscopy. The true flow stress in the shear region can reach 800 MPa where the strain is about 2.2. The whole shear localization process lasts for about 100 μs. The shear band is a long and straight band distinguished from the matrix by boundaries. It can be seen that the grains in the boundary of the shear band are highly elongated along the shear direction and form the elongated cell structures (0.2 µm in width), and the core of the shear band consists of a number of recrystallized equiaxed grains with 0.2−0.3 µm in diameters, and the second phase particles distribute in the boundary of the ultrafine equiaxed new grains. The calculated temperature in the shear band can reach about 667 K. Finally, the formation of the shear band in the ultrafine grained 6061 aluminum alloy and its microstructural evolution are proposed.

Wind simulation for extreme and fatigue loads

Energy Technology Data Exchange (ETDEWEB)

Nielsen, M.; Larsen, G.C.; Mann, J.; Ott, S.; Hansen, K.S.; Pedersen, B.J.

2004-01-01

Measurements of atmospheric turbulence have been studied and found to deviate from a Gaussian process, in particular regarding the velocity increments over small time steps, where the tails of the pdf are exponential rather than Gaussian. Principles for extreme event counting and the occurrence of cascading events are presented. Empirical extreme statistics agree with Rices exceedence theory, when it is assumed that the velocity and its time derivative are independent. Prediction based on the assumption that the velocity is a Gaussian process underpredicts the rate of occurrence of extreme events by many orders of magnitude, mainly because the measured pdf is non-Gaussian. Methods for simulation of turbulent signals have been developed and their computational efficiency are considered. The methods are applicable for multiple processes with individual spectra and probability distributions. Non-Gaussian processes are simulated by the correlation-distortion method. Non-stationary processes are obtained by Bezier interpolation between a set of stationary simulations with identical random seeds. Simulation of systems with some signals available is enabled by conditional statistics. A versatile method for simulation of extreme events has been developed. This will generate gusts, velocity jumps, extreme velocity shears, and sudden changes of wind direction. Gusts may be prescribed with a specified ensemble average shape, and it is possible to detect the critical gust shape for a given construction. The problem is formulated as the variational problem of finding the most probable adjustment of a standard simulation of a stationary Gaussian process subject to relevant event conditions, which are formulated as linear combination of points in the realization. The method is generalized for multiple correlated series, multiple simultaneous conditions, and 3D fields of all velocity components. Generalization are presented for a single non-Gaussian process subject to relatively

NONLINEAR FINITE ELEMENT ANALYSIS OF NONSEISMICALLY DETAILED INTERIOR RC BEAM-COLUMN CONNECTION UNDER REVERSED CYCLIC LOAD

Directory of Open Access Journals (Sweden)

Teeraphot Supaviriyakit

2017-11-01

Full Text Available This paper presents a nonlinear finite element analysis of non-seismically detailed RC beam column connections under reversed cyclic load. The test of half-scale nonductile reinforced concrete beam-column joints was conducted. The tested specimens represented those of the actual mid-rise reinforced concrete frame buildings designed according to the non-seismic provisions of the ACI building code.  The test results show that specimens representing small and medium column tributary area failed in brittle joint shear while specimen representing large column tributary area failed by ductile flexure though no ductile reinforcement details were provided. The nonlinear finite element analysis was applied to simulate the behavior of the specimens. The finite element analysis employs the smeared crack approach for modeling beam, column and joint, and employs the discrete crack approach for modeling the interface between beam and joint face. The nonlinear constitutive models of reinforced concrete elements consist of coupled tension-compression model to model normal force orthogonal and parallel to the crack and shear transfer model to capture the shear sliding mechanism. The FEM shows good comparison with test results in terms of load-displacement relations, hysteretic loops, cracking process and the failure mode of the tested specimens. The finite element analysis clarifies that the joint shear failure was caused by the collapse of principal diagonal concrete strut.

Resolution of axial shear strain elastography

International Nuclear Information System (INIS)

Thitaikumar, Arun; Righetti, Raffaella; Krouskop, Thomas A; Ophir, Jonathan

2006-01-01

The technique of mapping the local axial component of the shear strain due to quasi-static axial compression is defined as axial shear strain elastography. In this paper, the spatial resolution of axial shear strain elastography is investigated through simulations, using an elastically stiff cylindrical lesion embedded in a homogeneously softer background. Resolution was defined as the smallest size of the inclusion for which the strain value at the inclusion/background interface was greater than the average of the axial shear strain values at the interface and inside the inclusion. The resolution was measured from the axial shear strain profile oriented at 45 0 to the axis of beam propagation, due to the absence of axial shear strain along the normal directions. The effects of the ultrasound system parameters such as bandwidth, beamwidth and transducer element pitch along with signal processing parameters such as correlation window length (W) and axial shift (ΔW) on the estimated resolution were investigated. The results show that the resolution (at 45 0 orientation) is determined by the bandwidth and the beamwidth. However, the upper bound on the resolution is limited by the larger of the beamwidth and the window length, which is scaled inversely to the bandwidth. The results also show that the resolution is proportional to the pitch and not significantly affected by the axial window shift

Interfacial shear behavior of composite flanged concrete beams

Directory of Open Access Journals (Sweden)

Moataz Awry Mahmoud

2014-08-01

Full Text Available Composite concrete decks are commonly used in the construction of highway bridges due to their rapid constructability. The interfacial shear transfer between the top slab and the supporting beams is of great significance to the overall deck load carrying capacity and performance. Interfacial shear capacity is directly influenced by the distribution and the percentage of shear connectors. Research and design guidelines suggest the use of two different approaches to quantify the required interfacial shear strength, namely based on the maximum compressive forces in the flange at mid span or the maximum shear flow at the supports. This paper investigates the performance of flanged reinforced concrete composite beams with different shear connector’s distribution and reinforcing ratios. The study incorporated both experimental and analytical programs for beams. Key experimental findings suggest that concentrating the connectors at the vicinity of the supports enhances the ductility of the beam. The paper proposes a simple and straight forward approach to estimate the interfacial shear capacity that was proven to give good correlation with the experimental results and selected code provisions. The paper presents a method to predict the horizontal shear force between precast beams and cast in-situ slabs.

Material Models to Study the Bauschinger Effect on an Aluminum Shear Test Specimen

International Nuclear Information System (INIS)

Cardoso, Rui P. R.; Gracio, Jose J.; Yoon, Jeong-Whan

2007-01-01

Sheet metal forming processes generally involve complex loadings and nonlinear material models. Combinations of drawing, re-drawing and/or reverse drawing operations commonly induce cyclic loads with non-proportional strain paths, leading to Bauschinger effects that can not be predicted by conventional isotropic hardening laws. In order to properly represent this effect, it is also required to accommodate an appropriate kinematic hardening model along with an anisotropic yield function. In this work, two different approaches will be used to predict the Bauschinger effect for an Aluminum shear test specimen: the rate dependent crystal plasticity model and a new combined isotropic/kinematic hardening model based on the two yield surfaces approach (loading and boundary yield surfaces), as recently proposed

Shear wave elastography with a new reliability indicator

Directory of Open Access Journals (Sweden)

Christoph F. Dietrich

2016-09-01

Full Text Available Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s. The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed. The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France, point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France. More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

Shear wave elastography with a new reliability indicator.

Science.gov (United States)

Dietrich, Christoph F; Dong, Yi

2016-09-01

Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral) to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s). The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed). The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France), point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany) and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France). More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

Continuous AFM observation of martensitic transformation and its reversion in training cycles of Fe-Mn-Si based shape memory alloys

International Nuclear Information System (INIS)

Liu, D.Z.; Kikuchi, T.; Kajiwara, S.; Shinya, N.

2000-01-01

The effect of thermomechanical treatment (so-called ''training'') cycles on stress-induced martensitic transformation and its reversion has been studied by atomic force microscopy (AFM) to make clear the origin of improvement of shape memory effect (SME) due to training in Fe-Mn-Si based shape memory alloys (SMAs). It was found that training cycles make martensite plates tend to grow on the primary shear system, i.e., on the most favorable shear system for the fcc to hcp martensitic transformation. In addition, training cycles lead to a more uniform distribution of thin martensite plates in a grain. Martensitic plates with the above characteristics are easier to be reverted back to parent phase when heated, and then nearly perfect SME is obtained. AFM observation shows that the key factor to realize perfect SME in Fe-Mn-Si based SMAs is to produce the uniform distribution of thin martensite plates on the primary shear system when deformed by external stress. (orig.)

Hydrodynamical fluctuations in smooth shear flows

International Nuclear Information System (INIS)

Chagelishvili, G.D.; Khujadze, G.R.; Lominadze, J.G.

1999-11-01

Background of hydrodynamical fluctuations in a intrinsically/stochastically forced, laminar, uniform shear flow is studied. The employment of so-called nonmodal mathematical analysis makes it possible to represent the background of fluctuations in a new light and to get more insight into the physics of its formation. The basic physical processes responsible for the formation of vortex and acoustic wave fluctuation backgrounds are analyzed. Interplay of the processes at low and moderate shear rates is described. Three-dimensional vortex fluctuations around a given macroscopic state are numerically calculated. The correlation functions of the fluctuations of physical quantities are analyzed. It is shown that there exists subspace D k in the wave-number space (k-space) that is limited externally by spherical surface with radius k ν ≡ A/ν (where A is the velocity shear parameter, ν - the kinematic viscosity) in the nonequilibrium open system under study. The spatial Fourier harmonics of vortex as well as acoustic wave fluctuations are strongly subjected by flow shear (by the open character of the system) at wave-numbers satisfying the condition k ν . Specifically it is shown that in D k : The fluctuations are non-Markovian; the spatial spectral density of energy of the vortex fluctuations by far exceeds the white-noise; the term of a new type associated to the hydrodynamical fluctuation of velocity appears in the correlation function of pressure; the fluctuation background of the acoustic waves is completely different at low and moderate shear rates (at low shear rates it is reduced in D k in comparison to the uniform (non-shear) flow; at moderate shear rates it it comparable to the background of the vortex fluctuations). The fluctuation background of both the vortex and the acoustic wave modes is anisotropic. The possible significance of the fluctuation background of vortices for the subcritical transition to turbulence and Brownian motion of small macroscopic

Simulation of shear thickening in attractive colloidal suspensions.

Science.gov (United States)

Pednekar, Sidhant; Chun, Jaehun; Morris, Jeffrey F

2017-03-01

The influence of attractive forces between particles under conditions of large particle volume fraction, ϕ, is addressed using numerical simulations which account for hydrodynamic, Brownian, conservative and frictional contact forces. The focus is on conditions for which a significant increase in the apparent viscosity at small shear rates, and possibly the development of a yield stress, is observed. The high shear rate behavior for Brownian suspensions has been shown in recent work [R. Mari, R. Seto, J. F. Morris and M. M. Denn PNAS, 2015, 112, 15326-15330] to be captured by the inclusion of pairwise forces of two forms, one a contact frictional interaction and the second a repulsive force often found in stabilized colloidal dispersions. Under such conditions, shear thickening is observed when shear stress is comparable to the sum of the Brownian stress, kT/a 3 , and a characteristic stress based on the combination of interparticle force, i.e. σ ∼ F 0 /a 2 with kT the thermal energy, F 0 the repulsive force scale and a the particle radius. At sufficiently large ϕ, this shear thickening can be very abrupt. Here it is shown that when attractive interactions are present with the noted forces, the shear thickening is obscured, as the viscosity shear thins with increasing shear rate, eventually descending from an infinite value (yield stress conditions) to a plateau at large stress; this plateau is at the same level as the large-shear rate viscosity found in the shear thickened state without attractive forces. It is shown that this behavior is consistent with prior observations in shear thickening suspensions modified to be attractive through depletion flocculation [V. Gopalakrishnan and C. F. Zukoski J. Rheol., 2004, 48, 1321-1344]. The contributions of the contact, attractive, and hydrodynamics forces to the bulk stress are presented, as are the contact networks found at different attractive strengths.

Two-dimensional Shear Wave Elastography on Conventional Ultrasound Scanners with Time Aligned Sequential Tracking (TAST) and Comb-push Ultrasound Shear Elastography (CUSE)

Science.gov (United States)

Song, Pengfei; Macdonald, Michael C.; Behler, Russell H.; Lanning, Justin D.; Wang, Michael H.; Urban, Matthew W.; Manduca, Armando; Zhao, Heng; Callstrom, Matthew R.; Alizad, Azra; Greenleaf, James F.; Chen, Shigao

2014-01-01

Two-dimensional (2D) shear wave elastography presents 2D quantitative shear elasticity maps of tissue, which are clinically useful for both focal lesion detection and diffuse disease diagnosis. Realization of 2D shear wave elastography on conventional ultrasound scanners, however, is challenging due to the low tracking pulse-repetition-frequency (PRF) of these systems. While some clinical and research platforms support software beamforming and plane wave imaging with high PRF, the majority of current clinical ultrasound systems do not have the software beamforming capability, which presents a critical challenge for translating the 2D shear wave elastography technique from laboratory to clinical scanners. To address this challenge, this paper presents a Time Aligned Sequential Tracking (TAST) method for shear wave tracking on conventional ultrasound scanners. TAST takes advantage of the parallel beamforming capability of conventional systems and realizes high PRF shear wave tracking by sequentially firing tracking vectors and aligning shear wave data in the temporal direction. The Comb-push Ultrasound Shear Elastography (CUSE) technique was used to simultaneously produce multiple shear wave sources within the field-of-view (FOV) to enhance shear wave signal-to-noise-ratio (SNR) and facilitate robust reconstructions of 2D elasticity maps. TAST and CUSE were realized on a conventional ultrasound scanner (the General Electric LOGIQ E9). A phantom study showed that the shear wave speed measurements from the LOGIQ E9 were in good agreement to the values measured from other 2D shear wave imaging technologies. An inclusion phantom study showed that the LOGIQ E9 had comparable performance to the Aixplorer (Supersonic Imagine) in terms of bias and precision in measuring different sized inclusions. Finally, in vivo case analysis of a breast with a malignant mass, and a liver from a healthy subject demonstrated the feasibility of using the LOGIQ E9 for in vivo 2D shear wave

Shear-induced phase changes in mixtures

International Nuclear Information System (INIS)

Romig, K.D.; Hanley, H.J.M.

1986-01-01

A thermodynamic theory to account for the behavior of liquid mixtures exposed to a shear is developed. One consequence of the theory is that shear-induced phase changes are predicted. The theory is based on a thermodynamics that includes specifically the shear rate in the formalism and is applied to mixtures by a straightforward modification of the corresponding states, conformalsolution approach. The approach is general but is used here for a mixture of Lennard-Jones particles with a Lennard-Jones equation of state as a reference fluid. The results are discussed in the context of the Scott and Van Konynenberg phase classification. It is shown that the influence of a shear does affect substantially the type of the phase behavior. Results from the model mixture are equated loosely with those from real polymeric liquids

Physics of Transitional Shear Flows Instability and Laminar–Turbulent Transition in Incompressible Near-Wall Shear Layers

CERN Document Server

Boiko, Andrey V; Grek, Genrih R; Kozlov, Victor V

2012-01-01

Starting from fundamentals of classical stability theory, an overview is given of the transition phenomena in subsonic, wall-bounded shear flows. At first, the consideration focuses on elementary small-amplitude velocity perturbations of laminar shear layers, i.e. instability waves, in the simplest canonical configurations of a plane channel flow and a flat-plate boundary layer. Then the linear stability problem is expanded to include the effects of pressure gradients, flow curvature, boundary-layer separation, wall compliance, etc. related to applications. Beyond the amplification of instability waves is the non-modal growth of local stationary and non-stationary shear flow perturbations which are discussed as well. The volume continues with the key aspect of the transition process, that is, receptivity of convectively unstable shear layers to external perturbations, summarizing main paths of the excitation of laminar flow disturbances. The remainder of the book addresses the instability phenomena found at l...

Results of shear studies with 241-AY-101 sludge

International Nuclear Information System (INIS)

WARRANT, R.W.

2001-01-01

The Department of Energy's Tanks Focus Area (TFA) authorized a project to study the effect of shear on the settling properties of high-level waste sludge to support retrieval programs. A series of settling studies was conducted on a composite sample of tank 241-AY-101 (AY-101) material. Comparisons were made with duplicate samples that were sheared with a tissue homogenizer and allowed to settle. Aliquots of sheared and unsheared settled solids were submitted for chemical and radiological analyses. There are five major conclusions from the study that apply to AY-101 sludge: (1) Sludge settling rates are detectably decreased after shearing of particles by means of a tissue homogenizer. A significant decrease in the settling rates was measured after 2 minutes of shearing. A smaller additional decrease in the settling rates was observed after an additional 10 minutes of shearing. (2) Sodium and Cesium appear to be present in both the liquid and solid phases of the composite sample. (3) The shearing of the solids does not appear to significantly change the distribution of the radionuclides, ( 241 Am, 90 Sr, Total Alpha, or other radionuclides), within the solids. (4) The mean particle diameter decreases after shearing with the tissue homogenizer and affects the settling rate in proportion to the square of the particle diameter. (5) The sonication of the unsheared particles produces a similar particle size reduction to that of shearing with a tissue homogenizer. It is difficult to quantitatively compare the shear produced by a mixer pump installed in a double-shell tank with that produced by the tissue homogenizer in the laboratory. On a qualitative basis, the mixing pump would be expected to have less mechanical and more hydraulic shearing effect than the tissue homogenizer. Since the particle size distribution studies indicate that (for the AY-101 solids) the breaking up of particle aggregates is the main means of particle size reduction, then the hydraulic shearing

Reversible flowchart languages and the structured reversible program theorem

DEFF Research Database (Denmark)

Yokoyama, Tetsuo; Axelsen, Holger Bock; Glück, Robert

2008-01-01

Many irreversible computation models have reversible counterparts, but these are poorly understood at present. We introduce reversible flowcharts with an assertion operator and show that any reversible flowchart can be simulated by a structured reversible flowchart using only three control flow...... operators. Reversible flowcharts are r- Turing-complete, meaning that they can simuluate reversible Turing machines without garbage data. We also demonstrate the injectivization of classical flowcharts into reversible flowcharts. The reversible flowchart computation model provides a theoretical...

Strain gradient drives shear banding in metallic glasses

Science.gov (United States)

Tian, Zhi-Li; Wang, Yun-Jiang; Chen, Yan; Dai, Lan-Hong

2017-09-01

Shear banding is a nucleation-controlled process in metallic glasses (MGs) involving multiple temporal-spatial scales, which hinders a concrete understanding of its structural origin down to the atomic scale. Here, inspired by the morphology of composite materials, we propose a different perspective of MGs as a hard particle-reinforced material based on atomic-scale structural heterogeneity. The local stable structures indicated by a high level of local fivefold symmetry (L5FS) act as hard "particles" which are embedded in the relatively soft matrix. We demonstrate this concept by performing atomistic simulations of shear banding in CuZr MG. A shear band is prone to form in a sample with a high degree of L5FS which is slowly quenched from the liquid. An atomic-scale analysis on strain and the structural evolution reveals that it is the strain gradient effect that has originated from structural heterogeneity that facilitates shear transformation zones (STZs) to mature shear bands. An artificial composite model with a high degree of strain gradient, generated by inserting hard MG strips into a soft MG matrix, demonstrates a great propensity for shear banding. It therefore confirms the critical role strain gradient plays in shear banding. The strain gradient effect on shear banding is further quantified with a continuum model and a mechanical instability analysis. These physical insights might highlight the strain gradient as the hidden driving force in transforming STZs into shear bands in MGs.

Understanding the fluid mechanics behind transverse wall shear stress.

Science.gov (United States)

Mohamied, Yumnah; Sherwin, Spencer J; Weinberg, Peter D

2017-01-04

The patchy distribution of atherosclerosis within arteries is widely attributed to local variation in haemodynamic wall shear stress (WSS). A recently-introduced metric, the transverse wall shear stress (transWSS), which is the average over the cardiac cycle of WSS components perpendicular to the temporal mean WSS vector, correlates particularly well with the pattern of lesions around aortic branch ostia. Here we use numerical methods to investigate the nature of the arterial flows captured by transWSS and the sensitivity of transWSS to inflow waveform and aortic geometry. TransWSS developed chiefly in the acceleration, peak systolic and deceleration phases of the cardiac cycle; the reverse flow phase was too short, and WSS in diastole was too low, for these periods to have a significant influence. Most of the spatial variation in transWSS arose from variation in the angle by which instantaneous WSS vectors deviated from the mean WSS vector rather than from variation in the magnitude of the vectors. The pattern of transWSS was insensitive to inflow waveform; only unphysiologically high Womersley numbers produced substantial changes. However, transWSS was sensitive to changes in geometry. The curvature of the arch and proximal descending aorta were responsible for the principal features, the non-planar nature of the aorta produced asymmetries in the location and position of streaks of high transWSS, and taper determined the persistence of the streaks down the aorta. These results reflect the importance of the fluctuating strength of Dean vortices in generating transWSS. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nonlinear interaction of Rayleigh--Taylor and shear instabilities

International Nuclear Information System (INIS)

Finn, J.M.

1993-01-01

Results on the nonlinear behavior of the Rayleigh--Taylor instability and consequent development of shear flow by the shear instability [Phys. Fluids B 4, 488 (1992)] are presented. It is found that the shear flow is generated at sufficient amplitude to reduce greatly the convective transport. For high viscosity, the time-asymptotic state consists of an equilibrium with shear flow and vortex flow (with islands, or ''cat's eyes''), or a relaxation oscillation involving an interplay between the shear instability and the Rayleigh--Taylor instability in the presence of shear. For low viscosity, the dominant feature is a high-frequency nonlinear standing wave consisting of convective vortices localized near the top and bottom boundaries. The localization of these vortices is due to the smaller shear near the boundary regions. The convective transport is largest around these convective vortices near the boundary and there is a region of good confinement near the center. The possible relevance of this behavior to the H mode and edge-localized modes (ELM's) in the tokamak edge region is discussed

Edge Sheared Flows and Blob Dynamics

Energy Technology Data Exchange (ETDEWEB)

Myra, J.; D' Ippolito, D.; Russell, D., E-mail: jrmyra@lodestar.com [Lodestar Research Corporation, Boulder (United States); Davis, W. M.; Zweben, S. [Princeton Plasma Physics Laboratory, Princeton (United States); Terry, J.; LaBombard, B. [Massachusetts Institute of Technology, Cambridge (United States)

2012-09-15

Full text: A study of sheared flows in the edge and scrape-off layer (SOL) and their interaction with blob-filaments is presented. Edge sheared flows are believed to be important for the L-H, and H-L transitions. Blob generation and dynamics impacts both the (near-separatrix) scrape-off-layer (SOL) width critical for power handling in the divertor, and the interaction of plasma in the far SOL with plasma-facing components. These topics are critical for ITER and future devices. A fluid-based 2D curvature-interchange model embedded in the SOLT code is employed to study these issues. Sheared binormal flows both regulate the power flux crossing the separatrix and control the character of emitted turbulence structures such as blob-filaments. At a critical power level (depending on parameters) the laminar flows containing intermittent, but bound, structures give way to full-blown blob emissions signifying a transition from quasi-diffusive to convective transport. In order to diagnose sheared flows in experiments and assess their interaction with blobs, a blob-tracking algorithm has been developed and applied to both NSTX and Alcator C-Mod data. Blob motion and ellipticity can be affected by sheared flows, and are diagnosed and compared with seeded blob simulations. A picture of the interaction of blobs and sheared flows is emerging from advances in the theory and simulation of edge turbulence, combined with ever-improving capabilities for edge diagnostics and their analysis. (author)

Evaluation of shear mounted elastomeric damper

Science.gov (United States)

Zorzi, E.; Walton, J.

1982-01-01

Viton-70 elastomeric shear mounted damper was built and tested on a T-55 power turbine spool in the rotor's high speed balancing rig. This application of a shear mounted elastomeric damper demonstrated for the first time, the feasibility of using elastomers as the primary rotor damping source in production turbine engine hardware. The shear damper design was selected because it was compatible with actual gas turbine engine radial space constraints, could accommodate both the radial and axial thrust loads present in gas turbine engines, and was capable of controlled axial preload. The shear damper was interchangeable with the production T-55 power turbine roller bearing support so that a direct comparison between the shear damper and the production support structure could be made. Test results show that the Viton-70 elastomer damper operated successfully and provided excellent control of both synchronous and nonsynchronous vibrations through all phases of testing up to the maximum rotor speed of 16,000 rpm. Excellent correlation between the predicted and experienced critical speeds, mode shapes and log decrements for the power turbine rotor and elastomer damper assembly was also achieved.

Shear Melting of a Colloidal Glass

Science.gov (United States)

Eisenmann, Christoph; Kim, Chanjoong; Mattsson, Johan; Weitz, David A.

2010-01-01

We use confocal microscopy to explore shear melting of colloidal glasses, which occurs at strains of ˜0.08, coinciding with a strongly non-Gaussian step size distribution. For larger strains, the particle mean square displacement increases linearly with strain and the step size distribution becomes Gaussian. The effective diffusion coefficient varies approximately linearly with shear rate, consistent with a modified Stokes-Einstein relationship in which thermal energy is replaced by shear energy and the length scale is set by the size of cooperatively moving regions consisting of ˜3 particles.

Shear induced structures in crystallizing cocoa butter

Science.gov (United States)

Mazzanti, Gianfranco; Guthrie, Sarah E.; Sirota, Eric B.; Marangoni, Alejandro G.; Idziak, Stefan H. J.

2004-03-01

Cocoa butter is the main structural component of chocolate and many cosmetics. It crystallizes in several polymorphs, called phases I to VI. We used Synchrotron X-ray diffraction to study the effect of shear on its crystallization. A previously unreported phase (phase X) was found and a crystallization path through phase IV under shear was observed. Samples were crystallized under shear from the melt in temperature controlled Couette cells, at final crystallization temperatures of 17.5^oC, 20^oC and 22.5^oC in Beamline X10A of NSLS. The formation of phase X was observed at low shear rates (90 s-1) and low crystallization temperature (17.5^oC), but was absent at high shear (720 s-1) and high temperature (20^oC). The d-spacing and melting point suggest that this new phase is a mixture rich on two of the three major components of cocoa butter. We also found that, contrary to previous reports, the transition from phase II to phase V can happen through the intermediate phase IV, at high shear rates and temperature.

Experimental study on the adiabatic shear bands

International Nuclear Information System (INIS)

Affouard, J.

1984-07-01

Four martensitic steels (Z50CDV5 steel, 28CND8 steel, 35NCDV16 steel and 4340 steel) with different hardness between 190 and 600 Hsub(B) (Brinell hardness), have been studied by means of dynamic compressive tests on split Hopkinson pressure bar. Microscopic observations show that the fracture are associated to the development of adiabatic shear bands (except 4340 steel with 190 Hsub(B) hardness). By means of tests for which the deformation is stopped at predetermined levels, the measurement of shear and hardness inside the band and the matrix indicates the chronology of this phenomenon: first the localization of shear, followed by the formation of adiabatic shear band and ultimatly crack initiation and propagation. These results correlated with few simulations by finite elements have permitted to suggest two mecanisms of deformation leading to the formation of adiabatic shear bands in this specific test [fr

Shear-induced inflation of coronal magnetic fields

International Nuclear Information System (INIS)

Klimchuk, J.A.

1990-01-01

Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z) squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes. 38 refs

A micro-kinematic framework for vorticity analysis in polyphase shear zones using integrated field, microstructural and crystallographic orientation-dispersion methods

Science.gov (United States)

Kruckenberg, S. C.; Michels, Z. D.; Parsons, M. M.

2017-12-01

We present results from integrated field, microstructural and textural analysis in the Burlington mylonite zone (BMZ) of eastern Massachusetts to establish a unified micro-kinematic framework for vorticity analysis in polyphase shear zones. Specifically, we define the vorticity-normal surface based on lattice-scale rotation axes calculated from electron backscatter diffraction data using orientation statistics. In doing so, we objectively identify a suitable reference frame for rigid grain methods of vorticity analysis that can be used in concert with textural studies to constrain field- to plate-scale deformation geometries without assumptions that may bias tectonic interpretations, such as relationships between kinematic axes and fabric forming elements or the nature of the deforming zone (e.g., monoclinic vs. triclinic shear zones). Rocks within the BMZ comprise a heterogeneous mix of quartzofeldspathic ± hornblende-bearing mylonitic gneisses and quartzites. Vorticity axes inferred from lattice rotations lie within the plane of mylonitic foliation perpendicular to lineation - a pattern consistent with monoclinic deformation geometries involving simple shear and/or wrench-dominated transpression. The kinematic vorticity number (Wk) is calculated using Rigid Grain Net analysis and ranges from 0.25-0.55, indicating dominant general shear. Using the calculated Wk values and the dominant geographic fabric orientation, we constrain the angle of paleotectonic convergence between the Nashoba and Avalon terranes to 56-75º with the convergence vector trending 142-160° and plunging 3-10°. Application of the quartz recrystallized grain size piezometer suggests differential stresses in the BMZ mylonites ranging from 44 to 92 MPa; quartz CPO patterns are consistent with deformation at greenschist- to amphibolite-facies conditions. We conclude that crustal strain localization in the BMZ involved a combination of pure and simple shear in a sinistral reverse transpressional

Utilizing stretch-tunable thermochromic elastomeric opal films as novel reversible switchable photonic materials.

Science.gov (United States)

Schäfer, Christian G; Lederle, Christina; Zentel, Kristina; Stühn, Bernd; Gallei, Markus

2014-11-01

In this work, the preparation of highly thermoresponsive and fully reversible stretch-tunable elastomeric opal films featuring switchable structural colors is reported. Novel particle architectures based on poly(diethylene glycol methylether methacrylate-co-ethyl acrylate) (PDEGMEMA-co-PEA) as shell polymer are synthesized via seeded and stepwise emulsion polymerization protocols. The use of DEGMEMA as comonomer and herein established synthetic strategies leads to monodisperse soft shell particles, which can be directly processed to opal films by using the feasible melt-shear organization technique. Subsequent UV crosslinking strategies open access to mechanically stable and homogeneous elastomeric opal films. The structural colors of the opal films feature mechano- and thermoresponsiveness, which is found to be fully reversible. Optical characterization shows that the combination of both stimuli provokes a photonic bandgap shift of more than 50 nm from 560 nm in the stretched state to 611 nm in the fully swollen state. In addition, versatile colorful patterns onto the colloidal crystal structure are produced by spatial UV-induced crosslinking by using a photomask. This facile approach enables the generation of spatially cross-linked switchable opal films with fascinating optical properties. Herein described strategies for the preparation of PDEGMEMA-containing colloidal architectures, application of the melt-shear ordering technique, and patterned crosslinking of the final opal films open access to novel stimuli-responsive colloidal crystal films, which are expected to be promising materials in the field of security and sensing applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Practical Weak-lensing Shear Measurement with Metacalibration

Energy Technology Data Exchange (ETDEWEB)

Sheldon, Erin S. [Brookhaven National Laboratory, Bldg. 510, Upton, NY 11973 (United States); Huff, Eric M. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109 (United States)

2017-05-20

Metacalibration is a recently introduced method to accurately measure weak gravitational lensing shear using only the available imaging data, without need for prior information about galaxy properties or calibration from simulations. The method involves distorting the image with a small known shear, and calculating the response of a shear estimator to that applied shear. The method was shown to be accurate in moderate-sized simulations with galaxy images that had relatively high signal-to-noise ratios, and without significant selection effects. In this work we introduce a formalism to correct for both shear response and selection biases. We also observe that for images with relatively low signal-to-noise ratios, the correlated noise that arises during the metacalibration process results in significant bias, for which we develop a simple empirical correction. To test this formalism, we created large image simulations based on both parametric models and real galaxy images, including tests with realistic point-spread functions. We varied the point-spread function ellipticity at the five-percent level. In each simulation we applied a small few-percent shear to the galaxy images. We introduced additional challenges that arise in real data, such as detection thresholds, stellar contamination, and missing data. We applied cuts on the measured galaxy properties to induce significant selection effects. Using our formalism, we recovered the input shear with an accuracy better than a part in a thousand in all cases.

Platelet-free shear flow assay facilitates analysis of shear-dependent functions of VWF and ADAMTS13.

Science.gov (United States)

Kraus, Emma; Kraus, Kristina; Obser, Tobias; Oyen, Florian; Klemm, Ulrike; Schneppenheim, Reinhard; Brehm, Maria A

2014-12-01

The multimeric form of von Willebrand factor (VWF), is the largest soluble protein in mammals and exhibits a multidomain structure resulting in multiple functions. Upon agonist stimulation endothelial cells secrete VWF multimers from Weibel-Palade bodies into the blood stream where VWF plays an essential role in platelet-dependent primary hemostasis. Elongation of VWF strings on the cells' surface leads to accessibility of VWF binding sites for proteins, such as platelet membrane glycoprotein Ib. The prothrombotic strings are size-regulated by the metalloprotease ADAMTS13 by shear force-activated proteolytic cleavage. VWF string formation was induced by histamine stimulation of HUVEC cells under unidirectional shear flow and VWF strings were detected employing the VWF binding peptide of platelet glycoprotein Ib coupled to latex beads. VWF strings were then used as substrate for kinetic studies of recombinant and plasma ADAMTS13. To investigate specific aspects of the shear-dependent functions of VWF and ADAMTS13, we developed a shear flow assay that allows observation of VWF string formation and their degradation by ADAMTS13 without the need for isolated platelets. Our assay specifically detects VWF strings, can be coupled with fluorescent applications and allows semi-automated, quantitative assessment of recombinant and plasma ADAMTS13 activity. Our assay may serve as a valuable research tool to investigate the biochemical characteristics of VWF and ADAMTS13 under shear flow and could complement diagnostics of von Willebrand Disease and Thrombotic Thrombocytopenic Purpura as it allows detection of shear flow-dependent dysfunction of VWD-associated VWF mutants as well as TTP-associated ADAMTS13 mutants. Copyright © 2014 Elsevier Ltd. All rights reserved.

An in silico framework to analyze the anisotropic shear wave mechanics in cardiac shear wave elastography

Science.gov (United States)

Caenen, Annette; Pernot, Mathieu; Peirlinck, Mathias; Mertens, Luc; Swillens, Abigail; Segers, Patrick

2018-04-01

Shear wave elastography (SWE) is a potential tool to non-invasively assess cardiac muscle stiffness. This study focused on the effect of the orthotropic material properties and mechanical loading on the performance of cardiac SWE, as it is known that these factors contribute to complex 3D anisotropic shear wave propagation. To investigate the specific impact of these complexities, we constructed a finite element model with an orthotropic material law subjected to different uniaxial stretches to simulate SWE in the stressed cardiac wall. Group and phase speed were analyzed in function of tissue thickness and virtual probe rotation angle. Tissue stretching increased the group and phase speed of the simulated shear wave, especially in the direction of the muscle fiber. As the model provided access to the true fiber orientation and material properties, we assessed the accuracy of two fiber orientation extraction methods based on SWE. We found a higher accuracy (but lower robustness) when extracting fiber orientations based on the location of maximal shear wave speed instead of the angle of the major axis of the ellipsoidal group speed surface. Both methods had a comparable performance for the center region of the cardiac wall, and performed less well towards the edges. Lastly, we also assessed the (theoretical) impact of pathology on shear wave physics and characterization in the model. It was found that SWE was able to detect changes in fiber orientation and material characteristics, potentially associated with cardiac pathologies such as myocardial fibrosis. Furthermore, the model showed clearly altered shear wave patterns for the fibrotic myocardium compared to the healthy myocardium, which forms an initial but promising outcome of this modeling study.

Nongeometrically converted shear waves in marine streamer data

NARCIS (Netherlands)

Drijkoningen, G.G.; El Allouche, N.; Thorbecke, J.W.; Bada, G.

2012-01-01

Under certain circumstances, marine streamer data contain nongeometrical shear body wave arrivals that can be used for imaging. These shear waves are generated via an evanescent compressional wave in the water and convert to propagating shear waves at the water bottom. They are called

Recent progress in shear punch testing

International Nuclear Information System (INIS)

Hamilton, M.L.; Toloczko, M.B.; Lucas, G.E.

1994-09-01

The shear punch test was developed in response to the needs of the materials development community for small-scale mechanical properties tests. Such tests will be of great importance when a fusion neutron simulation device is built, since such a device is expected to have a limited irradiation volume. The shear punch test blanks a circular disk from a fixed sheet metal specimen, specifically a TEM disk. Load-displacement data generated during the test can be related to uniaxial tensile properties such as yield and ultimate strength. Shear punch and tensile tests were performed at room temperature on a number of unirradiated aluminum, copper, vanadium, and stainless steel alloys and on several irradiated aluminum alloys. Recent results discussed here suggest that the relationship between shear punch strength and tensile strength varies with alloy class, although the relationship determined for the unirradiated condition remains valid for the irradiated aluminum alloys

Stress analysis of shear/compression test

International Nuclear Information System (INIS)

Nishijima, S.; Okada, T.; Ueno, S.

1997-01-01

Stress analysis has been made on the glass fiber reinforced plastics (GFRP) subjected to the combined shear and compression stresses by means of finite element method. The two types of experimental set up were analyzed, that is parallel and series method where the specimen were compressed by tilted jigs which enable to apply the combined stresses, to the specimen. Modified Tsai-Hill criterion was employed to judge the failure under the combined stresses that is the shear strength under the compressive stress. The different failure envelopes were obtained between the two set ups. In the parallel system the shear strength once increased with compressive stress then decreased. On the contrary in the series system the shear strength decreased monotonicly with compressive stress. The difference is caused by the different stress distribution due to the different constraint conditions. The basic parameters which control the failure under the combined stresses will be discussed

Shear-Induced Membrane Fusion in Viscous Solutions

KAUST Repository

Kogan, Maxim

2014-05-06

Large unilamellar lipid vesicles do not normally fuse under fluid shear stress. They might deform and open pores to relax the tension to which they are exposed, but membrane fusion occurring solely due to shear stress has not yet been reported. We present evidence that shear forces in a viscous solution can induce lipid bilayer fusion. The fusion of 1,2-dioleoyl-sn-glycero-3- phosphocholine (DOPC) liposomes is observed in Couette flow with shear rates above 3000 s-1 provided that the medium is viscous enough. Liposome samples, prepared at different viscosities using a 0-50 wt % range of sucrose concentration, were studied by dynamic light scattering, lipid fusion assays using Förster resonance energy transfer (FRET), and linear dichroism (LD) spectroscopy. Liposomes in solutions with 40 wt % (or more) sucrose showed lipid fusion under shear forces. These results support the hypothesis that under suitable conditions lipid membranes may fuse in response to mechanical-force- induced stress. © 2014 American Chemical Society.

Direct evidence of hydration into mantle during shearing below a trasform fault: Prince Edward transform fault, Southwest Indian Ridge

Science.gov (United States)

Michibayashi, K.; Kakihata, Y.; Dick, H. J.

2017-12-01

Southwest Indian Ridge (SWIR) is located to the southwest of Rodriguez Triple Junction, where three Indian ocean ridges meet (Zhou & Dick, 2013, Nature). SWIR is one of the slowest spreading ocean ridges in the world. In this study, we studied microstructural development of 21 peridotite samples obtained from Prince Edward transform fault of SWIR by PROTEA5 cruise in 1983. The peridotites consist dominantly of olivine, orthopyroxene and clinopyroxene with minor amounts of amphibole and plagioclase as well as secondary minerals such as serpentine and magnetite. The peridotites were classified into four groups based on their microstructures: 3 ultramylonites mostly consisting of extremely fine crystals (3-5µm), 13 heterogeneous tectonites consisting of coarse-grained crystals and fine-grained matrix, 1 cataclasite and 4 intensely serpentinized peridotites. Olivine Mg# is 0.90-0.91 and spinel Cr# is 0.1-0.35. Amphibole crystals have chemical compositions of tremolite and magnesio-hornblende and they were intensely deformed within the ultramylonites and the heterogeneous tectonites, indicating that they have occurred before or during intense shearing in mantle. Moreover, extremely fine grain sizes of olivine and microboudin textures in both pyroxene and spinel crystals suggest that these peridotites have been sheared under high stress conditions. Furthermore, olivine crystal-fabrics within the amphibole bearing peridotites have B and E types that could be developed under hydrous conditions, whereas olivine fabrics within the other peridotites have A and D types that could be developed under anhydrous conditions (Karato et al., 2008, Annu. Rev. Earth Planet. Sci.). Consequently, the petrophysical characteristics of peridotites in this study indicate that the uppermost mantle below the Prince Edward transform fault has been locally but intensely hydrated during shearing due to transform movement.

Reverse Algols

Science.gov (United States)

Leung, K. C.

1989-01-01

Reverse Algols, binary systems with a semidetached configuration in which the more massive component is in contact with the critical equipotential surface, are examined. Observational evidence for reverse Algols is presented and the parameters of seven reverse Algols are listed. The evolution of Algols and reverse Algols is discussed. It is suggested that, because reverse Algols represent the premass-reversal semidetached phase of close binary evolution, the evolutionary time scale between regular and reverse Algols is the ratio of the number of confirmed systems of these two Algol types.

Edge-Induced Shear Banding in Entangled Polymeric Fluids.

Science.gov (United States)

Hemingway, Ewan J; Fielding, Suzanne M

2018-03-30

Despite decades of research, the question of whether solutions and melts of highly entangled polymers exhibit shear banding as their steady state response to a steadily imposed shear flow remains controversial. From a theoretical viewpoint, an important unanswered question is whether the underlying constitutive curve of shear stress σ as a function of shear rate γ[over ˙] (for states of homogeneous shear) is monotonic, or has a region of negative slope, dσ/dγ[over ˙]<0, which would trigger banding. Attempts to settle the question experimentally via velocimetry of the flow field inside the fluid are often confounded by an instability of the free surface where the sample meets the outside air, known as "edge fracture." Here we show by numerical simulation that in fact even only very modest edge disturbances-which are the precursor of full edge fracture but might well, in themselves, go unnoticed experimentally-can cause strong secondary flows in the form of shear bands that invade deep into the fluid bulk. Crucially, this is true even when the underlying constitutive curve is monotonically increasing, precluding true bulk shear banding in the absence of edge effects.

Shear localization and microstructure in coarse grained beta titanium alloy

Energy Technology Data Exchange (ETDEWEB)

Wang, Bingfeng, E-mail: biw009@ucsd.edu [State Key Laboratory for Powder Metallurgy, Central South University, Changsha, Hunan (China); School of Materials Science and Engineering, Central South University, Changsha, Hunan (China); Department of Mechanical and Aerospace Engineering, University of California, San Diego, United States of America (United States); Key Lab of Nonferrous Materials, Ministry of Education, Central South University, Changsha, Hunan (China); Wang, Xiaoyan [State Key Laboratory for Powder Metallurgy, Central South University, Changsha, Hunan (China); School of Materials Science and Engineering, Central South University, Changsha, Hunan (China); Li, Zezhou [Department of Mechanical and Aerospace Engineering, University of California, San Diego, United States of America (United States); Ma, Rui [School of Materials Science and Engineering, Central South University, Changsha, Hunan (China); Zhao, Shiteng [Department of Mechanical and Aerospace Engineering, University of California, San Diego, United States of America (United States); Xie, Fangyu [State Key Laboratory for Powder Metallurgy, Central South University, Changsha, Hunan (China); School of Materials Science and Engineering, Central South University, Changsha, Hunan (China); Zhang, Xiaoyong [State Key Laboratory for Powder Metallurgy, Central South University, Changsha, Hunan (China)

2016-01-15

Adiabatic shear localization plays an important role in the deformation and failure of the coarse grained beta titanium alloy Ti-5 Al-5 Mo-5 V-1 Cr-1 Fe with grain size about 1 mm at high strain rate deformation. Hat shaped specimens with different nominal shear strains are used to induce the formation of shear bands under the controlled shock-loading experiments. The true stress in the specimens can reach about 1040 MPa where the strain is about 1.83. The whole shear localization process lasts about 35 μs. The microstructures within the shear band are investigated by optical microscopy, scanning electron microscopy / electron backscatter diffraction, and transmission electron microscopy. The results show that the width of the shear bands decreases with increasing nominal shear strain, and the grains in the transition region near the shear band are elongated along the shear band, and the core of the shear band consists of the ultrafine deformed grains with width of 0.1 μm and heavy dislocations. With the aims of accommodating the imposed shear strain and maintaining neighboring grain compatibility, the grain subdivision continues to take place within the band. A fiber texture is formed in the core of the shear band. The calculated temperature rise in the shear band can reach about 722 K. Dynamic recovery is responsible for the formation of the microstructure in coarse grained beta titanium alloy.

Neural mechanisms underlying sensitivity to reverse-phi motion in the fly.

Science.gov (United States)

Leonhardt, Aljoscha; Meier, Matthias; Serbe, Etienne; Eichner, Hubert; Borst, Alexander

2017-01-01

Optical illusions provide powerful tools for mapping the algorithms and circuits that underlie visual processing, revealing structure through atypical function. Of particular note in the study of motion detection has been the reverse-phi illusion. When contrast reversals accompany discrete movement, detected direction tends to invert. This occurs across a wide range of organisms, spanning humans and invertebrates. Here, we map an algorithmic account of the phenomenon onto neural circuitry in the fruit fly Drosophila melanogaster. Through targeted silencing experiments in tethered walking flies as well as electrophysiology and calcium imaging, we demonstrate that ON- or OFF-selective local motion detector cells T4 and T5 are sensitive to certain interactions between ON and OFF. A biologically plausible detector model accounts for subtle features of this particular form of illusory motion reversal, like the re-inversion of turning responses occurring at extreme stimulus velocities. In light of comparable circuit architecture in the mammalian retina, we suggest that similar mechanisms may apply even to human psychophysics.

Small-scale multi-axial hybrid simulation of a shear-critical reinforced concrete frame

Science.gov (United States)

Sadeghian, Vahid; Kwon, Oh-Sung; Vecchio, Frank

2017-10-01

This study presents a numerical multi-scale simulation framework which is extended to accommodate hybrid simulation (numerical-experimental integration). The framework is enhanced with a standardized data exchange format and connected to a generalized controller interface program which facilitates communication with various types of laboratory equipment and testing configurations. A small-scale experimental program was conducted using a six degree-of-freedom hydraulic testing equipment to verify the proposed framework and provide additional data for small-scale testing of shearcritical reinforced concrete structures. The specimens were tested in a multi-axial hybrid simulation manner under a reversed cyclic loading condition simulating earthquake forces. The physical models were 1/3.23-scale representations of a beam and two columns. A mixed-type modelling technique was employed to analyze the remainder of the structures. The hybrid simulation results were compared against those obtained from a large-scale test and finite element analyses. The study found that if precautions are taken in preparing model materials and if the shear-related mechanisms are accurately considered in the numerical model, small-scale hybrid simulations can adequately simulate the behaviour of shear-critical structures. Although the findings of the study are promising, to draw general conclusions additional test data are required.

Problems pilots face involving wind shear

Science.gov (United States)

Melvin, W. W.

1977-01-01

Educating pilots and the aviation industry about wind shears presents a major problem associated with this meteorological phenomenon. The pilot's second most pressing problem is the need for a language to discuss wind shear encounters with other pilots so that the reaction of the aircraft to the wind shear encounter can be accurately described. Another problem is the flight director which gives a centered pitch command for a given angular displacement from the glide slope. It was suggested that they should instead be called flight path command and should not center unless the aircraft is actually correcting to the flight path.

Cosmology with cosmic shear observations: a review.

Science.gov (United States)

Kilbinger, Martin

2015-07-01

Cosmic shear is the distortion of images of distant galaxies due to weak gravitational lensing by the large-scale structure in the Universe. Such images are coherently deformed by the tidal field of matter inhomogeneities along the line of sight. By measuring galaxy shape correlations, we can study the properties and evolution of structure on large scales as well as the geometry of the Universe. Thus, cosmic shear has become a powerful probe into the nature of dark matter and the origin of the current accelerated expansion of the Universe. Over the last years, cosmic shear has evolved into a reliable and robust cosmological probe, providing measurements of the expansion history of the Universe and the growth of its structure. We review here the principles of weak gravitational lensing and show how cosmic shear is interpreted in a cosmological context. Then we give an overview of weak-lensing measurements, and present the main observational cosmic-shear results since it was discovered 15 years ago, as well as the implications for cosmology. We then conclude with an outlook on the various future surveys and missions, for which cosmic shear is one of the main science drivers, and discuss promising new weak cosmological lensing techniques for future observations.

Kubo formulas for the shear and bulk viscosity relaxation times and the scalar field theory shear τπ calculation

Science.gov (United States)

Czajka, Alina; Jeon, Sangyong

2017-06-01

In this paper we provide a quantum field theoretical study on the shear and bulk relaxation times. First, we find Kubo formulas for the shear and the bulk relaxation times, respectively. They are found by examining response functions of the stress-energy tensor. We use general properties of correlation functions and the gravitational Ward identity to parametrize analytical structures of the Green functions describing both sound and diffusion mode. We find that the hydrodynamic limits of the real parts of the respective energy-momentum tensor correlation functions provide us with the method of computing both the shear and bulk viscosity relaxation times. Next, we calculate the shear viscosity relaxation time using the diagrammatic approach in the Keldysh basis for the massless λ ϕ4 theory. We derive a respective integral equation which enables us to compute η τπ and then we extract the shear relaxation time. The relaxation time is shown to be inversely related to the thermal width as it should be.

Extreme concentration fluctuations due to local reversibility of mixing in turbulent flows

Science.gov (United States)

Xia, Hua; Francois, Nicolas; Punzmann, Horst; Szewc, Kamil; Shats, Michael

2018-05-01

Mixing of a passive scalar in a fluid (e.g. a radioactive spill in the ocean) is the irreversible process towards homogeneous distribution of a substance. In a moving fluid, due to the chaotic advection [H. Aref, J. Fluid Mech. 143 (1984) 1; J. M. Ottino, The Kinematics of Mixing: Stretching,Chaos and Transport (Cambridge University Press, Cambridge, 1989)] mixing is much faster than if driven by molecular diffusion only. Turbulence is known as the most efficient mixing flow [B. I. Shraiman and E. D. Siggia, Nature 405 (2000) 639]. We show that in contrast to spatially periodic flows, two-dimensional turbulence exhibits local reversibility in mixing, which leads to the generation of unpredictable strong fluctuations in the scalar concentration. These fluctuations can also be detected from the analysis of the fluid particle trajectories of the underlying flow.

Sheared Rotation Effects on Kinetic Stability in Enhanced Confinement Tokamak Plasmas, and Nonlinear Dynamics of Fluctuations and Flows in Axisymmetric Plasmas

International Nuclear Information System (INIS)

Beer, M.A.; Chance, M.S.; Hahm, T.S.; Lin, Z.; Rewoldt, G.; Tang, W.M.

1997-01-01

Sheared rotation dynamics are widely believed to have signficant influence on experimentally observed confinement transitions in advanced operating modes in major tokamak experiments, such as the Tokamak Fusion Test Reactor (TFTR) [D.J. Grove and D.M. Meade, Nuclear Fusion 25, 1167 (1985)], with reversed magnetic shear regions in the plasma interior. The high-n toroidal drift modes destabilized by the combined effects of ion temperature gradients and trapped particles in toroidal geometry can be strongly affected by radially sheared toroidal and poloidal plasma rotation. In previous work with the FULL linear microinstability code, a simplified rotation model including only toroidal rotation was employed, and results were obtained. Here, a more complete rotation model, that includes contributions from toroidal and poloidal rotation and the ion pressure gradient to the total radial electric field, is used for a proper self-consistent treatment of this key problem. Relevant advanced operating mode cases for TFTR are presented. In addition, the complementary problem of the dynamics of fluctuation-driven E x B flow is investigated by an integrated program of gyrokinetic simulation in annulus geometry and gyrofluid simulation in flux tube geometry

Hydrogen ion induced ultralow wear of PEEK under extreme load

Science.gov (United States)

Yan, Shuai; Wang, Anying; Fei, Jixiong; Wang, Zhenyang; Zhang, Xiaofeng; Lin, Bin

2018-03-01

As a high-performance engineering polymer, poly(ether ether ketone) (PEEK) is a perfect candidate material for applications under extreme working conditions. However, its high wear rate greatly shortens its service life. In this study, ultralow friction and wear between PEEK and silicon nitride (Si3N4) under extreme-load conditions (with a mean contact pressure above 100 MPa) are found in acid lubricating solutions. Both friction and wear decrease sharply with decreasing pH. At pH = 1, the friction coefficient decreases by an order of magnitude and the wear rate of the PEEK decreases by two orders of magnitude compared to the results with water lubrication. These reductions in friction and wear occur for different speed, load, and surface roughness conditions. The underlying mechanism can be attributed to the formation of hydrogen-ion-induced electrical double layers on the surfaces of PEEK and Si3N4. The combined effect of the resulting repulsive force, electro-viscosity, and low shear strength of the water layer dramatically reduces both friction and wear.

Naesliden Project: direct shear tests of filled and unfilled joints

Energy Technology Data Exchange (ETDEWEB)

Ludvig, B.

1980-05-15

Joints from the Naesliden mine have been tested in a small field shear box and in a large shear rig. The large shear rig is described in detail, and its ability to test joints with an area of 600 mc/sup 2/ at a maximum normal stress of up to 20 MPa is emphasized. The stiffness and shear strength of the discontinuities in the Naesliden mine is presented. The values estimated at direct shear tests are compared with results from in situ measurements and tests on drillcores. The results show that the in situ measurements give lower values for the shear resistance than the direct shear tests. Estimation of the normal stiffness for joints in drill cores gave much higher stiffness than the estimations in the shear rig.

Simulations of biopolymer networks under shear

NARCIS (Netherlands)

Huisman, Elisabeth Margaretha

2011-01-01

In this thesis we present a new method to simulate realistic three-dimensional networks of biopolymers under shear. These biopolymer networks are important for the structural functions of cells and tissues. We use the method to analyze these networks under shear, and consider the elastic modulus,

Shear induced orientation of edible fat and chocolate crystals

Science.gov (United States)

Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.

2003-03-01

Shear-induced orientation of fat crystallites was observed during crystallization of cocoa butter, milk fat, stripped milk fat and palm oil. This universal effect was observed in systems crystallized under high shear. The minor polar components naturally present in milk fat were found to decrease the shear-induced orientation effect in this system. The competition between Brownian and shear forces, described by the Peclet number, determines the crystallite orientation. The critical radius size, from the Gibbs-Thomson equation, provides a tool to understand the effect of shear at the onset stages of crystallization.

Poor outcome of bilateral lower extremity morel-lavallee lesions: a case report.

Science.gov (United States)

Stanley, Sharon S; Molmenti, Ernesto P; Siskind, Eric; Kasabian, Armen K; Huang, Su-I D

2014-03-01

The Morel-Lavallee lesion is a closed, internal degloving injury that results when a strong, shearing force is applied parallel to the plane of injury, as is common in vehicular trauma. It is an underdiagnosed entity that is often missed during the initial trauma workup as symptoms can be subtle. There are few reports of lesions occurring below the knee. Most cases affect the proximal thigh and trochanter, as these tend to be dependent areas in high velocity trauma. To the best of our knowledge, this is the first literature report of bilateral lower extremity Morel-Lavallee lesions.

The microstructure and rheology of a model, thixotropic nanoparticle gel under steady shear and large amplitude oscillatory shear (LAOS)

International Nuclear Information System (INIS)

Min Kim, Jung; Kate Gurnon, A.; Wagner, Norman J.; Eberle, Aaron P. R.; Porcar, Lionel

2014-01-01

The microstructure-rheology relationship for a model, thermoreversible nanoparticle gel is investigated using a new technique of time-resolved neutron scattering under steady and time-resolved large amplitude oscillatory shear (LAOS) flows. A 21 vol. % gel is tested with varying strength of interparticle attraction. Shear-induced structural anisotropy is observed as butterfly scattering patterns and quantified through an alignment factor. Measurements in the plane of flow show significant, local anisotropy develops with alignment along the compressional axis of flow, providing new insights into how gels flow. The microstructure-rheology relationship is analyzed through a new type of structure-Lissajous plot that shows how the anisotropic microstructure is responsible for the observed LAOS response, which is beyond a response expected for a purely viscous gel with constant structure. The LAOS shear viscosities are observed to follow the “Delaware-Rutgers” rule. Rheological and microstructural data are successfully compared across a broad range of conditions by scaling the shear rate by the strength of attraction, providing a method to compare behavior between steady shear and LAOS experiments. However, important differences remain between the microstructures measured at comparatively high frequency in LAOS experiments and comparable steady shear experiments that illustrate the importance of measuring the microstructure to properly interpret the nonlinear, dynamic rheological response

The microstructure and rheology of a model, thixotropic nanoparticle gel under steady shear and large amplitude oscillatory shear (LAOS)

Energy Technology Data Exchange (ETDEWEB)

Min Kim, Jung; Kate Gurnon, A.; Wagner, Norman J., E-mail: wagnernj@udel.edu [Department of Chemical and Biomolecular Engineering and Center for Neutron Science, University of Delaware, Newark, Delaware 19716 (United States); Eberle, Aaron P. R. [NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Porcar, Lionel [NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 and Institut Laue-Langevin, BP 156, F-38042 Grenoble Cedex 9 (France)

2014-09-01

The microstructure-rheology relationship for a model, thermoreversible nanoparticle gel is investigated using a new technique of time-resolved neutron scattering under steady and time-resolved large amplitude oscillatory shear (LAOS) flows. A 21 vol. % gel is tested with varying strength of interparticle attraction. Shear-induced structural anisotropy is observed as butterfly scattering patterns and quantified through an alignment factor. Measurements in the plane of flow show significant, local anisotropy develops with alignment along the compressional axis of flow, providing new insights into how gels flow. The microstructure-rheology relationship is analyzed through a new type of structure-Lissajous plot that shows how the anisotropic microstructure is responsible for the observed LAOS response, which is beyond a response expected for a purely viscous gel with constant structure. The LAOS shear viscosities are observed to follow the “Delaware-Rutgers” rule. Rheological and microstructural data are successfully compared across a broad range of conditions by scaling the shear rate by the strength of attraction, providing a method to compare behavior between steady shear and LAOS experiments. However, important differences remain between the microstructures measured at comparatively high frequency in LAOS experiments and comparable steady shear experiments that illustrate the importance of measuring the microstructure to properly interpret the nonlinear, dynamic rheological response.

Value of shear wave arrival time contour display in shear wave elastography for breast masses diagnosis.

Science.gov (United States)

Zhou, Bang-Guo; Wang, Dan; Ren, Wei-Wei; Li, Xiao-Long; He, Ya-Ping; Liu, Bo-Ji; Wang, Qiao; Chen, Shi-Gao; Alizad, Azra; Xu, Hui-Xiong

2017-08-01

To evaluate the diagnostic performance of shear wave arrival time contour (SWATC) display for the diagnosis of breast lesions and to identify factors associated with the quality of shear wave propagation (QSWP) in breast lesions. This study included 277 pathologically confirmed breast lesions. Conventional B-mode ultrasound characteristics and shear wave elastography parameters were computed. Using the SWATC display, the QSWP of each lesion was assigned to a two-point scale: score 1 (low quality) and score 2 (high quality). Binary logistic regression analysis was performed to identify factors associated with QSWP. The area under the receiver operating characteristic curve (AUROC) for QSWP to differentiate benign from malignant lesions was 0.913, with a sensitivity of 91.9%, a specificity of 90.7%, a positive predictive value (PPV) of 74.0%, and a negative predictive value (NPV) of 97.5%. Compared with using the standard deviation of shear wave speed (SWS SD ) alone, SWS SD combined with QSWP increased the sensitivity from 75.8% to 93.5%, but decreased the specificity from 95.8% to 89.3% (P breast lesions.

Managing Reverse Logistics or Reversing Logistics Management?

OpenAIRE

Brito, Marisa

2004-01-01

textabstractIn the past, supply chains were busy fine-tuning the logistics from raw material to the end customer. Today an increasing flow of products is going back in the chain. Thus, companies have to manage reverse logistics as well.This thesis contributes to a better understanding of reverse logistics. The thesis brings insights on reverse logistics decision-making and it lays down theoretical principles for reverse logistics as a research field.In particular it puts together a framework ...

Multifractal spectra in shear flows

Science.gov (United States)

Keefe, L. R.; Deane, Anil E.

1989-01-01

Numerical simulations of three-dimensional homogeneous shear flow and fully developed channel flow, are used to calculate the associated multifractal spectra of the energy dissipation field. Only weak parameterization of the results with the nondimensional shear is found, and this only if the flow has reached its asymptotic development state. Multifractal spectra of these flows coincide with those from experiments only at the range alpha less than 1.

CFD simulation of estimating critical shear stress for cleaning flat ...

Indian Academy of Sciences (India)

Sumit Kawale

2017-11-22

Nov 22, 2017 ... Jet impingement; wall shear stress; cleaning of flat plate; turbulence model; critical shear stress; ... On comparing the theoretical predictions with wall shear ... distance and Reynolds number on peak value of local shear stress ...

Development of Shear Connections in Steelconcrete Composite Structures

Science.gov (United States)

Biegus, Antoni; Lorenc, Wojciech

2015-03-01

Different types of shear connectors and modelling techniques are presented. Basic research conducted or presented after year 2000 is taken into consideration, following the idea of concrete dowel implemented in the form of perfobond strip at the beginning of the 1980s by F. Leonhardt. The latest research in the field of continuous shear connectors applied in bridges is highlited with special focus at the composite dowel shear connection, as it seems to be the most modern solution being strongly introduced to the industry. Final shape of composite dowel shear connection is presented.

Time-dependent behavior of rough discontinuities under shearing conditions

Science.gov (United States)

Wang, Zhen; Shen, Mingrong; Ding, Wenqi; Jang, Boan; Zhang, Qingzhao

2018-02-01

The mechanical properties of rocks are generally controlled by their discontinuities. In this study, the time-dependent behavior of rough artificial joints under shearing conditions was investigated. Based on Barton’s standard profile lines, samples with artificial joint surfaces were prepared and used to conduct the shear and creep tests. The test results showed that the shear strength of discontinuity was linearly related to roughness, and subsequently an empirical equation was established. The long-term strength of discontinuity can be identified using the inflection point of the isocreep-rate curve, and it was linearly related to roughness. Furthermore, the ratio of long-term and instantaneous strength decreased with the increase of roughness. The shear-stiffness coefficient increased with the increase of shear rate, and the influence of shear rate on the shear stiffness coefficient decreased with the decrease of roughness. Further study of the mechanism revealed that these results could be attributed to the different time-dependent behavior of intact and joint rocks.

Small-scale wind shear definition for aerospace vehicle design.

Science.gov (United States)

Fichtl, G. H.

1972-01-01

Rawinsonde wind profile data provide adequate wind shear information for vertical height intervals greater than 1 km. To specify wind shears for intervals below 1 km for space vehicle design, detailed wind-profile information like that provided by the FPS-16 Radar/Jimsphere system or an extrapolation procedure is required. This paper is concerned with the latter alternative. It is assumed that any realization from an ensemble of wind profiles can be represented in terms of a Fourier integral. This permits the calculation of the ensemble standard deviation and mean of the corresponding shear ensemble for any altitude and shear interval in terms of the power spectrum of the ensemble of wind profiles. The results of these calculations show that the mean and standard deviation of the wind shear ensemble, as well as the wind shear for any percentile, asymptotically behave like the vertical interval to the 0.7 power. This result is in excellent agreement with shear data from Cape Kennedy, Fla.

Fluid Effects on Shear Waves in Finely Layered Porous Media

International Nuclear Information System (INIS)

Berryman, J G

2004-01-01

Although there are five effective shear moduli for any layered VTI medium, one and only one effective shear modulus for the layered system contains all the dependence of pore fluids on the elastic or poroelastic constants that can be observed in vertically polarized shear waves. Pore fluids can increase the magnitude the shear energy stored by this modulus by a term that ranges from the smallest to the largest shear moduli of the VTI system. But, since there are five shear moduli in play, the increase in shear energy overall is reduced by a factor of about 5 in general. We can therefore give definite bounds on the maximum increase of shear modulus, being about 20% of the permitted range, when gas is fully replaced by liquid. An attendant increase of density (depending on porosity and fluid density) by approximately 5 to 10% partially offsets the effect of this shear modulus increase. Thus, an increase of shear wave speed on the order of 5 to 10% is shown to be possible when circumstances are favorable - i.e., when the shear modulus fluctuations are large (resulting in strong anisotropy), and the medium behaves in an undrained fashion due to fluid trapping. At frequencies higher than seismic (such as sonic and ultrasonic waves for well-logging or laboratory experiments), short response times also produce the requisite undrained behavior and, therefore, fluids also affect shear waves at high frequencies by increasing rigidity

Localization in inelastic rate dependent shearing deformations

KAUST Repository

Katsaounis, Theodoros

2016-09-18

Metals deformed at high strain rates can exhibit failure through formation of shear bands, a phenomenon often attributed to Hadamard instability and localization of the strain into an emerging coherent structure. We verify formation of shear bands for a nonlinear model exhibiting strain softening and strain rate sensitivity. The effects of strain softening and strain rate sensitivity are first assessed by linearized analysis, indicating that the combined effect leads to Turing instability. For the nonlinear model a class of self-similar solutions is constructed, that depicts a coherent localizing structure and the formation of a shear band. This solution is associated to a heteroclinic orbit of a dynamical system. The orbit is constructed numerically and yields explicit shear localizing solutions. © 2016 Elsevier Ltd

Localization in inelastic rate dependent shearing deformations

KAUST Repository

Katsaounis, Theodoros; Lee, Min-Gi; Tzavaras, Athanasios

2016-01-01

Metals deformed at high strain rates can exhibit failure through formation of shear bands, a phenomenon often attributed to Hadamard instability and localization of the strain into an emerging coherent structure. We verify formation of shear bands for a nonlinear model exhibiting strain softening and strain rate sensitivity. The effects of strain softening and strain rate sensitivity are first assessed by linearized analysis, indicating that the combined effect leads to Turing instability. For the nonlinear model a class of self-similar solutions is constructed, that depicts a coherent localizing structure and the formation of a shear band. This solution is associated to a heteroclinic orbit of a dynamical system. The orbit is constructed numerically and yields explicit shear localizing solutions. © 2016 Elsevier Ltd

On the self-organizing process of large scale shear flows

Energy Technology Data Exchange (ETDEWEB)

Newton, Andrew P. L. [Department of Applied Maths, University of Sheffield, Sheffield, Yorkshire S3 7RH (United Kingdom); Kim, Eun-jin [School of Mathematics and Statistics, University of Sheffield, Sheffield, Yorkshire S3 7RH (United Kingdom); Liu, Han-Li [High Altitude Observatory, National Centre for Atmospheric Research, P. O. BOX 3000, Boulder, Colorado 80303-3000 (United States)

2013-09-15

Self organization is invoked as a paradigm to explore the processes governing the evolution of shear flows. By examining the probability density function (PDF) of the local flow gradient (shear), we show that shear flows reach a quasi-equilibrium state as its growth of shear is balanced by shear relaxation. Specifically, the PDFs of the local shear are calculated numerically and analytically in reduced 1D and 0D models, where the PDFs are shown to converge to a bimodal distribution in the case of finite correlated temporal forcing. This bimodal PDF is then shown to be reproduced in nonlinear simulation of 2D hydrodynamic turbulence. Furthermore, the bimodal PDF is demonstrated to result from a self-organizing shear flow with linear profile. Similar bimodal structure and linear profile of the shear flow are observed in gulf stream, suggesting self-organization.

Research Concerning the Shearing Strength of Black Locust Wood

Directory of Open Access Journals (Sweden)

Mihaela POROJAN

2011-06-01

Full Text Available The paper presents the experimental resultsobtained for the shearing strength of black locustwood (Robinia pseudacacia L. harvested from twogeographical areas (North and South of Romania.Wood is subjected to shearing stress when usedwithin different fields, and especially inconstructions. Tangential stresses are produced inthe shearing sections and they are influenced by thestructure of wood through the position of theshearing plane and of the force direction towards thegrain. Accordingly, several shearing types arepossible. The shearing strengths for the three mainshearing types, both on radial and tangentialdirection were determined within the present study.The evaluation of data was achieved by using theANOVA analysis, in order to test the level ofsignificance depending on the shearing planeorientation and the harvesting area. The obtainedresults were compared to the values mentionedwithin reference literature for this wood species andtwo other hardwood species with similar density. It isworth to be mentioned that the shearing strengths ofblack locust wood from Romania (both from Northand South are generally higher than those indicatedby reference literature for oak and beech. Thisrecommends black locust wood as constructionwood and for other applications where wood issubjected to shearing stress.

Seismic cycle feedbacks in a mid-crustal shear zone

Science.gov (United States)

Melosh, Benjamin L.; Rowe, Christie D.; Gerbi, Christopher; Smit, Louis; Macey, Paul

2018-07-01

Mid-crustal fault rheology is controlled by alternating brittle and plastic deformation mechanisms, which cause feedback cycles that influence earthquake behavior. Detailed mapping and microstructural observations in the Pofadder Shear Zone (Namibia and South Africa) reveal a lithologically heterogeneous shear zone core with quartz-rich mylonites and ultramylonites, plastically overprinted pseudotachylyte and active shear folds. We present evidence for a positive feedback cycle in which coseismic grain size reduction facilitates active shear folding by enhancing competency contrasts and promoting crystal plastic flow. Shear folding strengthens a portion of a shear zone by limb rotation, focusing deformation and promoting plastic flow or brittle slip in resulting areas of localized high stress. Using quartz paleopiezometry, we estimate strain and slip rates consistent with other studies of exhumed shear zones and modern plate boundary faults, helping establish the Pofadder Shear Zone as an ancient analogue to modern, continental-scale, strike-slip faults. This feedback cycle influences seismicity patterns at the scale of study (10s of meters) and possibly larger scales as well, and contributes to bulk strengthening of the brittle-plastic transition on modern plate boundary faults.

Earth's magnetic field is probably not reversing.

Science.gov (United States)

Brown, Maxwell; Korte, Monika; Holme, Richard; Wardinski, Ingo; Gunnarson, Sydney

2018-04-30

The geomagnetic field has been decaying at a rate of [Formula: see text]5% per century from at least 1840, with indirect observations suggesting a decay since 1600 or even earlier. This has led to the assertion that the geomagnetic field may be undergoing a reversal or an excursion. We have derived a model of the geomagnetic field spanning 30-50 ka, constructed to study the behavior of the two most recent excursions: the Laschamp and Mono Lake, centered at 41 and 34 ka, respectively. Here, we show that neither excursion demonstrates field evolution similar to current changes in the geomagnetic field. At earlier times, centered at 49 and 46 ka, the field is comparable to today's field, with an intensity structure similar to today's South Atlantic Anomaly (SAA); however, neither of these SAA-like fields develop into an excursion or reversal. This suggests that the current weakened field will also recover without an extreme event such as an excursion or reversal. The SAA-like field structure at 46 ka appears to be coeval with published increases in geomagnetically modulated beryllium and chlorine nuclide production, despite the global dipole field not weakening significantly in our model during this time. This agreement suggests a greater complexity in the relationship between cosmogenic nuclide production and the geomagnetic field than is commonly assumed.

Hydraulic Shearing and Hydraulic Jacking Observed during Hydraulic Stimulations in Fractured Geothermal Reservoir in Pohang, Korea

Science.gov (United States)

Min, K. B.; Park, S.; Xie, L.; Kim, K. I.; Yoo, H.; Kim, K. Y.; Choi, J.; Yoon, K. S.; Yoon, W. S.; Lee, T. J.; Song, Y.

2017-12-01

Enhanced Geothermal System (EGS) relies on sufficient and irreversible enhancement of reservoir permeability through hydraulic stimulation and possibility of such desirable change of permeability is an open question that can undermine the universality of EGS concept. We report results of first hydraulic stimulation campaign conducted in two deep boreholes in fractured granodiorite geothermal reservoir in Pohang, Korea. Borehole PX-1, located at 4.22 km, was subjected to the injection of 3,907 m3 with flow rate of up to 18 kg/s followed by bleeding off of 1,207 m3. The borehole PX-2, located at 4.35 km, was subjected to the injection of 1,970 m3 with flow rate of up to 46 kg/sIn PX-1, a sharp distinct decline of wellhead pressure was observed at around 16 MPa of wellhead pressure which was similar to the predicted injection pressure to induce hydraulic shearing. Injectivity interpretation before and after the hydraulic shearing indicates that permanent increase of permeability was achieved by a factor of a few. In PX-2, however, injectivity was very small and hydraulic shearing was not observed due possibly to the near wellbore damage made by the remedying process of lost circulation such as using lost circulation material during drilling. Flow rate of larger than 40 kg/s was achieved at very high well head pressure of nearly 90 MPa. Hydraulic jacking, that is reversible opening and closure of fracture with change of injection pressure, was clearly observed. Although sharp increase of permeability due to fracture opening was achieved with elevated injection pressure, the increased permeability was reversed with decreased injection pressure.Two contrasting response observed in the same reservoir at two different boreholes which is apart only 600 m apart provide important implication that can be used for the stimulation strategy for EGS.This work was supported by the New and Renewable Energy Technology Development Program of the Korea Institute of Energy Technology

Tunable reverse-biased graphene/silicon heterojunction Schottky diode sensor.

Science.gov (United States)

Singh, Amol; Uddin, Ahsan; Sudarshan, Tangali; Koley, Goutam

2014-04-24

A new chemical sensor based on reverse-biased graphene/Si heterojunction diode has been developed that exhibits extremely high bias-dependent molecular detection sensitivity and low operating power. The device takes advantage of graphene's atomically thin nature, which enables molecular adsorption on its surface to directly alter graphene/Si interface barrier height, thus affecting the junction current exponentially when operated in reverse bias and resulting in ultrahigh sensitivity. By operating the device in reverse bias, the work function of graphene, and hence the barrier height at the graphene/Si heterointerface, can be controlled by the bias magnitude, leading to a wide tunability of the molecular detection sensitivity. Such sensitivity control is also possible by carefully selecting the graphene/Si heterojunction Schottky barrier height. Compared to a conventional graphene amperometric sensor fabricated on the same chip, the proposed sensor demonstrated 13 times higher sensitivity for NO₂ and 3 times higher for NH₃ in ambient conditions, while consuming ∼500 times less power for same magnitude of applied voltage bias. The sensing mechanism based on heterojunction Schottky barrier height change has been confirmed using capacitance-voltage measurements. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Shear stresses around circular cylindrical openings

NARCIS (Netherlands)

Hoogenboom, P.C.J.; Van Weelden, C.; Blom, C.M.B.

2010-01-01

In this paper stress concentrations are studied around circular cylindrical openings or voids in a linear elastic continuum. The loading is such that a uniform shear stress occurs in the continuum, which is disturbed by the opening. The shear stress is in the direction of the centre axis of the

Reverse (posterior) cloaca with congenital rectal stenosis and pseudohermaphrodism: a rare entity with rare association

Science.gov (United States)

Ahmed, Intezar; Kureel, Shiv Narain; Chandra, Naveen

2010-01-01

Reverse (posterior) cloaca is itself a rare entity and association of this defect with other congenital syndromes or defects is extremely rare to find. To diagnose this unique anomaly one should be aware about this very infrequently encountered clinical entity. Reverse cloaca is a very rare variant of anorectal malformation in which urethra and vagina fused to form a urogenital sinus that diverts posteriorly and opens in the anterior rectal wall at the anus or immediately anterior to it. We report a neonate with the rare clinical entity of reverse cloaca type C, pseudophallus with rudimentary urethra as a component of female pseudohermaphrodism and congenital rectal stenosis. Surprisingly, there was no associated urological abnormality on ultrasonography and laparotomy. PMID:22797480

Swimming efficiency in a shear-thinning fluid

Science.gov (United States)

Nganguia, Herve; Pietrzyk, Kyle; Pak, On Shun

2017-12-01

Micro-organisms expend energy moving through complex media. While propulsion speed is an important property of locomotion, efficiency is another factor that may determine the swimming gait adopted by a micro-organism in order to locomote in an energetically favorable manner. The efficiency of swimming in a Newtonian fluid is well characterized for different biological and artificial swimmers. However, these swimmers often encounter biological fluids displaying shear-thinning viscosities. Little is known about how this nonlinear rheology influences the efficiency of locomotion. Does the shear-thinning rheology render swimming more efficient or less? How does the swimming efficiency depend on the propulsion mechanism of a swimmer and rheological properties of the surrounding shear-thinning fluid? In this work, we address these fundamental questions on the efficiency of locomotion in a shear-thinning fluid by considering the squirmer model as a general locomotion model to represent different types of swimmers. Our analysis reveals how the choice of surface velocity distribution on a squirmer may reduce or enhance the swimming efficiency. We determine optimal shear rates at which the swimming efficiency can be substantially enhanced compared with the Newtonian case. The nontrivial variations of swimming efficiency prompt questions on how micro-organisms may tune their swimming gaits to exploit the shear-thinning rheology. The findings also provide insights into how artificial swimmers should be designed to move through complex media efficiently.

Forflytning: shear og friktion

DEFF Research Database (Denmark)

2005-01-01

friktion). Formålet med filmprojektet er: At give personalet i Apopleksiafsnittet viden om shear og friktion, så det motiveres til forebyggelse. Mål At udarbejde et enkelt undervisningsmateriale til bed-side-brug Projektbeskrivelse (resume) Patienter med apopleksi er særligt udsatte for tryksår, fordi de...... ofte er immobile, har svært ved at opretholde en god siddestilling eller ligger tungt i sengen som følger efter apopleksien Hvis personalet bruger forkert lejrings-og forflytningsteknik, udsættes patienterne for shear og friktion. Målgruppen i projektet er de personer, der omgås patienterne, dvs...

Computerized lateral-shear interferometer

Science.gov (United States)

Hasegan, Sorin A.; Jianu, Angela; Vlad, Valentin I.

1998-07-01

A lateral-shear interferometer, coupled with a computer for laser wavefront analysis, is described. A CCD camera is used to transfer the fringe images through a frame-grabber into a PC. 3D phase maps are obtained by fringe pattern processing using a new algorithm for direct spatial reconstruction of the optical phase. The program describes phase maps by Zernike polynomials yielding an analytical description of the wavefront aberration. A compact lateral-shear interferometer has been built using a laser diode as light source, a CCD camera and a rechargeable battery supply, which allows measurements in-situ, if necessary.

Comparisons of physical experiment and discrete element simulations of sheared granular materials in an annular shear cell

Science.gov (United States)

Ji, S.; Hanes, D.M.; Shen, H.H.

2009-01-01

In this study, we report a direct comparison between a physical test and a computer simulation of rapidly sheared granular materials. An annular shear cell experiment was conducted. All parameters were kept the same between the physical and the computational systems to the extent possible. Artificially softened particles were used in the simulation to reduce the computational time to a manageable level. Sensitivity study on the particle stiffness ensured such artificial modification was acceptable. In the experiment, a range of normal stress was applied to a given amount of particles sheared in an annular trough with a range of controlled shear speed. Two types of particles, glass and Delrin, were used in the experiment. Qualitatively, the required torque to shear the materials under different rotational speed compared well with those in the physical experiments for both the glass and the Delrin particles. However, the quantitative discrepancies between the measured and simulated shear stresses were nearly a factor of two. Boundary conditions, particle size distribution, particle damping and friction, including a sliding and rolling, contact force model, were examined to determine their effects on the computational results. It was found that of the above, the rolling friction between particles had the most significant effect on the macro stress level. This study shows that discrete element simulation is a viable method for engineering design for granular material systems. Particle level information is needed to properly conduct these simulations. However, not all particle level information is equally important in the study regime. Rolling friction, which is not commonly considered in many discrete element models, appears to play an important role. ?? 2009 Elsevier Ltd.

Experimental study of a shear wall with numerous small openings

International Nuclear Information System (INIS)

Sotomura, K.; Murazumi, Y.; Yoshizaki, S.; Ezaki, T.

1981-01-01

Many small openings for piping and ducts are usually required in the shear walls for PWR nuclear power plant. It is generally believed that such openings oadversely affect the strength and stiffness of shear walls. However, little information is available concerning the behavior of walls with numerous small openings. Therefore, tests using wall specimens and an analysis using an FEM program were carried out to investigate this behavior. Main findings are as follows: 1) The ultimate strength of a shear wall with numerous small openings may be obtained by using the effective area at the critical cross section of the shear wall. 2) Shear walls with openings can be restored to the same shear strength and stiffness as shear walls without openings by diagonal reinforcement. (orig./HP)

Joint model to simulate inelastic shear behavior of poorly detailed exterior and interior beam-column connections reinforced with deformed bars under seismic excitations

International Nuclear Information System (INIS)

Sharma, Akanshu; Reddy, G.R.; Vaze, K.K.; Ghosh, A.K.; Kushwaha, H.S.; Eligehausen, Rolf

2009-12-01

A model for predicting the nonlinear shear behaviour of reinforced concrete beam column joints based on principal stresses reaching limits is proposed. The joint model proposes shear springs for the column region and rotational spring for the beam region of the joint. This is based on the actual displacement behaviour of the shear buildings. The spring characteristics are calculated based on well-known principal of mechanics using the principal stresses as the failure criteria. The model reasonably accurately predicts the shear behaviour of the joint and also can consider the effect of axial loads on the column. The model does not need any special element or special program for implementation and can be used for nonlinear static pushover analysis of RC framed structures giving due consideration to joint deformations. The model is therefore extremely useful for practical displacement based analysis of old RC buildings where the joints were not designed and detailed as per current codal requirements, invariably making them the weakest link in the structure. The background theory, assumptions followed and the complete formulations for generating the joint characteristics are given in this report. The model is validated with experimental results of tests on exterior and interior beam-column connections given in the published literature having substandard detailing using deformed bars. (author)

A new omnidirectional shear horizontal wave transducer using face-shear (d24) piezoelectric ring array.

Science.gov (United States)

Miao, Hongchen; Huan, Qiang; Wang, Qiangzhong; Li, Faxin

2017-02-01

The non-dispersive fundamental shear horizontal (SH 0 ) wave in plate-like structures is of practical importance in non-destructive testing (NDT) and structural health monitoring (SHM). Theoretically, an omnidirectional SH 0 transducer phased array system can be used to inspect defects in a large plate in the similar manner to the phased array transducers used in medical B-scan ultrasonics. However, very few omnidirectional SH 0 transducers have been proposed so far. In this work, an omnidirectional SH 0 wave piezoelectric transducer (OSH-PT) was proposed, which consists of a ring array of twelve face-shear (d 24 ) trapezoidal PZT elements. Each PZT element can produce face-shear deformation under applied voltage, resulting in circumferential shear deformation in the OSH-PT and omnidirectional SH 0 waves in the hosting plate. Both finite element simulations and experiments were conducted to examine the performance of the proposed OSH-PT. Experimental testing shows that the OSH-PT exhibits good omnidirectional properties, no matter it is used as a SH 0 wave transmitter or a SH 0 wave receiver. This work may greatly promote the applications of SH 0 waves in NDT and SHM. Copyright © 2016 Elsevier B.V. All rights reserved.

Shear induced phase transitions induced in edible fats

Science.gov (United States)

Mazzanti, Gianfranco; Welch, Sarah E.; Marangoni, Alejandro G.; Sirota, Eric B.; Idziak, Stefan H. J.

2003-03-01

The food industry crystallizes fats under different conditions of temperature and shear to obtain products with desired crystalline phases. Milk fat, palm oil, cocoa butter and chocolate were crystallized from the melt in a temperature controlled Couette cell. Synchrotron x-ray diffraction studies were conducted to examine the role of shear on the phase transitions seen in edible fats. The shear forces on the crystals induced acceleration of the alpha to beta-prime phase transition with increasing shear rate in milk fat and palm oil. The increase was slow at low shear rates and became very strong above 360 s-1. In cocoa butter the acceleration between beta-prime-III and beta-V phase transition increased until a maximum of at 360 s-1, and then decreased, showing competition between enhanced heat transfer and viscous heat generation.

Sense of shear and displacement estimates in the Abeibara-Rarhous late Pan-African shear zone, Adrar des Iforas, Mali

Science.gov (United States)

Boullier, Anne-Marie

The late Pan-African Abeibara-Rarhous shear zone in the Adrar des Iforas (Mali) is described and studied with the aim of defining the direction, sense of movement and amount of displacement along the zone. It is a strike-slip shear zone, the dextral sense of which is demonstrated at the scale of the map by the rotation of the related mylonitic foliation and at the scale of the thin section with characteristic microstructures. Preferred orientation of quartz c-axes is tentatively used; three quartz-rich samples of 35% or more quartz indicate dextral strike-slip movement, but other samples do not show preferred orientation of quartz c-axes. Strain measurements have been performed on one half of the shear zone using established techniques and a new technique using the thickness of mylonitic layering. The results vary along the length of the shear zone when using the same method and for the same cross-section when using the three methods together. A mean value of 4 km is obtained for total displacement which is low when considering the apparent width of the shear zone. This result is discussed in view of the assumptions involved in the strain estimation. The tectonic history of the Abeibara-Rarhous shear zone and its significance in the Trans-Saharan Pan-African collisional belt are discussed.

Membrane morphology and topology for fouling control in Reverse Osmosis filtration systems

Science.gov (United States)

Ling, Bowen; Battiato, Ilenia

2017-11-01

Reverse Osmosis Membrane (ROM) filtration systems are widely utilized in waste-water recovery, seawater desalination, landfill water treatment, etc. During filtration, the system performance is dramatically affected by membrane fouling which causes a significant decrease in permeate flux as well as an increase in the energy input required to operate the system. Design and optimization of ROM filtration systems aim at reducing membrane fouling by studying the coupling between membrane structure, local flow field and foulant adsorption patterns. Yet, current studies focus exclusively on oversimplified steady-state models that ignore any dynamic coupling between fluid flow and transport through the membrane. In this work, we develop a customized solver (SUMembraneFoam) under OpenFOAM to solve the transient equations. The simulation results not only predict macroscopic quantities (e.g. permeate flux, pressure drop, etc.) but also show an excellent agreement with the fouling patterns observed in experiments. It is observed that foulant deposition is strongly controlled by the local shear stress on the membrane, and channel morphology or membrane topology can be modified to control the shear stress distribution and reduce fouling. Finally, we identify optimal regimes for design.

The reversal of the Sun’s magnetic field in cycle 24

Directory of Open Access Journals (Sweden)

Mordvinov A.V.

2016-03-01

Full Text Available Analysis of synoptic data from the Vector Spectromagnetograph (VSM of the Synoptic Optical Long-term Investigations of the Sun (SOLIS and the NASA/NSO Spectromagnetograph (SPM at the NSO/Kitt Peak Vacuum Telescope facility shows that the reversals of solar polar magnetic fields exhibit elements of a stochastic process, which may include the development of specific patterns of emerging magnetic flux, and the asymmetry in activity between Northern and Southern hemispheres. The presence of such irregularities makes the modeling and prediction of polar field reversals extremely hard if possible. In a classical model of solar activity cycle, the unipolar magnetic regions (UMRs of predominantly following polarity fields are transported polewards due to meridional flows and diffusion. The UMRs gradually cancel out the polar magnetic field of the previous cycle, and rebuild the polar field of opposite polarity setting the stage for the next cycle. We show, however, that this deterministic picture can be easily altered by the developing of a strong center of activity, or by the emergence of an extremely large active region, or by a ‘strategically placed’ coronal hole. We demonstrate that the activity occurring during the current cycle 24 may be the result of this randomness in the evolution of the solar surface magnetic field.

Microalga propels along vorticity direction in a shear flow

Science.gov (United States)

Chengala, Anwar; Hondzo, Miki; Sheng, Jian

2013-05-01

Using high-speed digital holographic microscopy and microfluidics, we discover that, when encountering fluid flow shear above a threshold, unicellular green alga Dunaliella primolecta migrates unambiguously in the cross-stream direction that is normal to the plane of shear and coincides with the local fluid flow vorticity. The flow shear drives motile microalgae to collectively migrate in a thin two-dimensional horizontal plane and consequently alters the spatial distribution of microalgal cells within a given suspension. This shear-induced algal migration differs substantially from periodic rotational motion of passive ellipsoids, known as Jeffery orbits, as well as gyrotaxis by bottom-heavy swimming microalgae in a shear flow due to the subtle interplay between torques generated by gravity and viscous shear. Our findings could facilitate mechanistic solutions for modeling planktonic thin layers and sustainable cultivation of microalgae for human nutrition and bioenergy feedstock.

Critical wall shear stress for the EHEDG test method

DEFF Research Database (Denmark)

Jensen, Bo Boye Busk; Friis, Alan

2004-01-01

In order to simulate the results of practical cleaning tests on closed processing equipment, based on wall shear stress predicted by computational fluid dynamics, a critical wall shear stress is required for that particular cleaning method. This work presents investigations that provide a critical...... wall shear stress of 3 Pa for the standardised EHEDG cleaning test method. The cleaning tests were performed on a test disc placed in a radial flowcell assay. Turbulent flow conditions were generated and the corresponding wall shear stresses were predicted from CFD simulations. Combining wall shear...... stress predictions from a simulation using the low Re k-epsilon and one using the two-layer model of Norris and Reynolds were found to produce reliable predictions compared to empirical solutions for the ideal flow case. The comparison of wall shear stress curves predicted for the real RFC...

Effect of rock joint roughness on its cyclic shear behavior

Directory of Open Access Journals (Sweden)

S.M. Mahdi Niktabar

2017-12-01

Full Text Available Rock joints are often subjected to dynamic loads induced by earthquake and blasting during mining and rock cutting. Hence, cyclic shear load can be induced along the joints and it is important to evaluate the shear behavior of rock joint under this condition. In the present study, synthetic rock joints were prepared with plaster of Paris (PoP. Regular joints were simulated by keeping regular asperity with asperity angles of 15°–15° and 30°–30°, and irregular rock joints which are closer to natural joints were replicated by keeping the asperity angles of 15°–30° and 15°–45°. The sample size and amplitude of roughness were kept the same for both regular and irregular joints which were 298 mm × 298 mm × 125 mm and 5 mm, respectively. Shear test was performed on these joints using a large-scale direct shear testing machine by keeping the frequency and amplitude of shear load under constant cyclic condition with different normal stress values. As expected, the shear strength of rock joints increased with the increases in the asperity angle and normal load during the first cycle of shearing or static load. With the increase of the number of shear cycles, the shear strength decreased for all the asperity angles but the rate of reduction was more in case of high asperity angles. Test results indicated that shear strength of irregular joints was higher than that of regular joints at different cycles of shearing at low normal stress. Shearing and degradation of joint asperities on regular joints were the same between loading and unloading, but different for irregular joints. Shear strength and joint degradation were more significant on the slope of asperity with higher angles on the irregular joint until two angles of asperities became equal during the cycle of shearing and it started behaving like regular joints for subsequent cycles.

Tensile and shear strength of adhesives

Science.gov (United States)

Stibolt, Kenneth A.

1990-01-01

This experiment is conducted in a freshman-level course: Introduction to Engineering Materials. There are no prerequisites for the course although students should have some knowledge of basic algebra. The objectives are to tension and shear test adhesives and to determine the tensile and shear properties of adhesives. Details of equipment of procedure are given.

Thermal convection of viscoelastic shear-thinning fluids

International Nuclear Information System (INIS)

Albaalbaki, Bashar; Khayat, Roger E; Ahmed, Zahir U

2016-01-01

The Rayleigh–Bénard convection for non-Newtonian fluids possessing both viscoelastic and shear-thinning behaviours is examined. The Phan-Thien–Tanner (PTT) constitutive equation is implemented to model the non-Newtonian character of the fluid. It is found that while the shear-thinning and viscoelastic effects could annihilate one another for the steady roll flow, presence of both behaviours restricts the roll stability limit significantly compared to the cases when the fluid is either inelastic shear-thinning or purely viscoelastic with constant viscosity. (paper)

Size effects in shear interfaces

OpenAIRE

GARNIER, J

2001-01-01

In physical modelling (centrifuge tests, calibration chambers, laboratory tests), the size of the soil particles may not be negligible when compared to the dimensions of the models. Size effects may so disturb the response of the models and the experimental data obtained on these cannot be extended to true scale conditions. Different tests have been performed to study and quantify the size effects that may happen in shear interfaces between soils and structures : modified shear box tests, pul...

Shear Alfven waves in tokamaks

International Nuclear Information System (INIS)

Kieras, C.E.

1982-12-01

Shear Alfven waves in an axisymmetric tokamak are examined within the framework of the linearized ideal MHD equations. Properties of the shear Alfven continuous spectrum are studied both analytically and numerically. Implications of these results in regards to low frequency rf heating of toroidally confined plasmas are discussed. The structure of the spatial singularities associated with these waves is determined. A reduced set of ideal MHD equations is derived to describe these waves in a very low beta plasma

Reverse micelles in organic solvents: a medium for the biotechnological use of extreme halophilic enzymes at low salt concentration

Directory of Open Access Journals (Sweden)

Frutos C. Marhuenda-Egea

2002-01-01

Full Text Available Alkaline p-nitrophenylphosphate phosphatase (pNPPase from the halophilic archaeobacterium Halobacterium salinarum (previously halobium was solubilized at low salt concentration in reverse micelles of hexadecyltrimethylammoniumbromide in cyclohexane with 1-butanol as cosurfactant. The enzyme maintained its catalytic properties under these conditions. The thermodynamic “solvation–stabilization hypothesis” has been used to explain the bell-shaped dependence of pNPPase activity on the water content of reverse micelles, in terms of protein–solvent interactions. According to this model, the stability of the folded protein depends on a network of hydrated ions associated with acidic residues at the protein surface. At low salt concentration and low water content (the ratio of water concentration to surfactant concentration; w0, the network of hydrated ions within the reverse micelles may involve the cationic heads of the surfactant. The bell-shaped profile of the relationship between enzyme activity and w0 varied depending on the concentrations of NaCl and Mn2+.

Shear Tests and Calculation of Shear Resistance with the PC Program RFEM from Thin Partition Walls of Brick in Old Buildings

Directory of Open Access Journals (Sweden)

Korjenic Sinan

2015-11-01

Full Text Available This paper is about the shear capacity of partition walls in old buildings based on shear tests which were carried out under real conditions in an existing building. There were experiments conducted on different floors and in each case, the maximum recordable horizontal force and the horizontal displacement of the respective mortar were measured. At the same time material studies and material investigations were carried out in the laboratory. The material parameters were used for the calculation of the precise shear capacity of each joint. In the shear tests, the maximum displacement of a mortar joint was determined at a maximum of two to four millimetres. Furthermore, no direct linear relationship between the theoretical load (wall above it and the shear stress occurred could be detected in the analysis of the experiment, as it was previously assumed.

Shear Tests and Calculation of Shear Resistance with the PC Program RFEM from Thin Partition Walls of Brick in Old Buildings

Science.gov (United States)

Korjenic, Sinan; Nowak, Bernhard; Löffler, Philipp; Vašková, Anna

2015-11-01

This paper is about the shear capacity of partition walls in old buildings based on shear tests which were carried out under real conditions in an existing building. There were experiments conducted on different floors and in each case, the maximum recordable horizontal force and the horizontal displacement of the respective mortar were measured. At the same time material studies and material investigations were carried out in the laboratory. The material parameters were used for the calculation of the precise shear capacity of each joint. In the shear tests, the maximum displacement of a mortar joint was determined at a maximum of two to four millimetres. Furthermore, no direct linear relationship between the theoretical load (wall above it) and the shear stress occurred could be detected in the analysis of the experiment, as it was previously assumed.

FEM Simulation of Incremental Shear

International Nuclear Information System (INIS)

Rosochowski, Andrzej; Olejnik, Lech

2007-01-01

A popular way of producing ultrafine grained metals on a laboratory scale is severe plastic deformation. This paper introduces a new severe plastic deformation process of incremental shear. A finite element method simulation is carried out for various tool geometries and process kinematics. It has been established that for the successful realisation of the process the inner radius of the channel as well as the feeding increment should be approximately 30% of the billet thickness. The angle at which the reciprocating die works the material can be 30 deg. . When compared to equal channel angular pressing, incremental shear shows basic similarities in the mode of material flow and a few technological advantages which make it an attractive alternative to the known severe plastic deformation processes. The most promising characteristic of incremental shear is the possibility of processing very long billets in a continuous way which makes the process more industrially relevant

Reverse Logistics

OpenAIRE

Kulikova, Olga

2016-01-01

This thesis was focused on the analysis of the concept of reverse logistics and actual reverse processes which are implemented in mining industry and finding solutions for the optimization of reverse logistics in this sphere. The objective of this paper was the assessment of the development of reverse logistics in mining industry on the example of potash production. The theoretical part was based on reverse logistics and mining waste related literature and provided foundations for further...

Nocturnal Reversed Flows Above Parallel Ridges in Perdigão, Portugal

Science.gov (United States)

Krishnamurthy, R.; Fernando, H. J.; Leo, L. S.; Vassallo, D.; Hocut, C. M.; Creegan, E.; Rodriguez, C. V.; Palma, J. L.

2017-12-01

Prediction of topographically forced or induced wind events is extremely important for dispersion modeling and wind energy studies in complex terrain. To improve the current understanding of micro-scale processes over complex terrain, a large-scale field experiment was conducted in Perdigão, Portugal from May 1st, 2017 to June 15th, 2017. Measurements over a periodic valley were performed using 52 meteorological met-masts, 30 Doppler Lidars (scanning & vertical profilers), 2 tethered lifting systems and other remote sensing instruments (Sodar-rass, wind profilers & radiometer), and radiosondes were released every 6 hours over the period of study. The observations showed several cases of flow reversals confined to a thin layer of 70 - 100 m above the ridge under stably stratified conditions. These flow reversals were mostly observed during the lee wave formation over the periodic valley. It was observed that the flow reversal occurs predominantly under two atmospheric conditions: a) presence of large recirculation zones on the lee side of the hill causing a pressure gradient between the lee-side floor and the mountain ridge, and b) local change in the horizontal pressure gradient due to differential heating rates of the neighboring valley atmospheres. Microscale flow simulations could capture these observed flow reversals. Based on the network of tower instruments and remote sensing devices, the development, structure and occurrences of the flow reversals are being analyzed and quantified. Since these flow reversals are observed within the rotor swept area of modern wind turbines, they would drastically increase the fatigue loads on wind turbine blades. This presentation will include reversed flow observations from several synchronized scanning Doppler Lidars and meteorological towers and a theoretical framework for reverse flow over parallel valleys.

How shear increments affect the flow production branching ratio in CSDX

Science.gov (United States)

Li, J. C.; Diamond, P. H.

2018-06-01

The coupling of turbulence-driven azimuthal and axial flows in a linear device absent magnetic shear (Controlled Shear Decorrelation Experiment) is investigated. In particular, we examine the apportionment of Reynolds power between azimuthal and axial flows, and how the azimuthal flow shear affects axial flow generation and saturation by drift wave turbulence. We study the response of the energy branching ratio, i.e., ratio of axial and azimuthal Reynolds powers, PzR/PyR , to incremental changes of azimuthal and axial flow shears. We show that increasing azimuthal flow shear decreases the energy branching ratio. When axial flow shear increases, this ratio first increases but then decreases to zero. The axial flow shear saturates below the threshold for parallel shear flow instability. The effects of azimuthal flow shear on the generation and saturation of intrinsic axial flows are analyzed. Azimuthal flow shear slows down the modulational growth of the seed axial flow shear, and thus reduces intrinsic axial flow production. Azimuthal flow shear reduces both the residual Reynolds stress (of axial flow, i.e., ΠxzR e s ) and turbulent viscosity ( χzDW ) by the same factor |⟨vy⟩'|-2Δx-2Ln-2ρs2cs2 , where Δx is the distance relative to the reference point where ⟨vy⟩=0 in the plasma frame. Therefore, the stationary state axial flow shear is not affected by azimuthal flow shear to leading order since ⟨vz⟩'˜ΠxzR e s/χzDW .

Shear Stress-Relative Slip Relationship at Concrete Interfaces

Directory of Open Access Journals (Sweden)

Keun-Hyeok Yang

2016-01-01

Full Text Available This study develops a simple and rational shear stress-relative slip model of concrete interfaces with monolithic castings or smooth construction joints. In developing the model, the initial shear cracking stress and relative slip amount at peak stress were formulated from a nonlinear regression analysis using test data for push-off specimens. The shear friction strength was determined from the generalized equations on the basis of the upper-bound theorem of concrete plasticity. Then, a parametric fitting analysis was performed to derive equations for the key parameters determining the shapes of the ascending and descending branches of the shear stress-relative slip curve. The comparisons of predictions and measurements obtained from push-off tests confirmed that the proposed model provides superior accuracy in predicting the shear stress-relative slip relationship of interfacial shear planes. This was evidenced by the lower normalized root mean square error than those in Xu et al.’s model and the CEB-FIB model, which have many limitations in terms of the roughness of the substrate surface along an interface and the magnitude of equivalent normal stress.

Probabilistic Cosmological Mass Mapping from Weak Lensing Shear

Energy Technology Data Exchange (ETDEWEB)

Schneider, M. D.; Dawson, W. A. [Lawrence Livermore National Laboratory, Livermore, CA 94551 (United States); Ng, K. Y. [University of California, Davis, Davis, CA 95616 (United States); Marshall, P. J. [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94035 (United States); Meyers, J. E. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Bard, D. J., E-mail: schneider42@llnl.gov, E-mail: dstn@cmu.edu, E-mail: boutigny@in2p3.fr, E-mail: djbard@slac.stanford.edu, E-mail: jmeyers314@stanford.edu [National Energy Research Scientific Computing Center, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720-8150 (United States)

2017-04-10

We infer gravitational lensing shear and convergence fields from galaxy ellipticity catalogs under a spatial process prior for the lensing potential. We demonstrate the performance of our algorithm with simulated Gaussian-distributed cosmological lensing shear maps and a reconstruction of the mass distribution of the merging galaxy cluster Abell 781 using galaxy ellipticities measured with the Deep Lens Survey. Given interim posterior samples of lensing shear or convergence fields on the sky, we describe an algorithm to infer cosmological parameters via lens field marginalization. In the most general formulation of our algorithm we make no assumptions about weak shear or Gaussian-distributed shape noise or shears. Because we require solutions and matrix determinants of a linear system of dimension that scales with the number of galaxies, we expect our algorithm to require parallel high-performance computing resources for application to ongoing wide field lensing surveys.

Stabilization of ballooning modes with sheared toroidal rotation

International Nuclear Information System (INIS)

Miller, R.L.; Waelbroeck, F.L.; Hassam, A.B.; Waltz, R.E.

1995-01-01

Stabilization of magnetohydrodynamic ballooning modes by sheared toroidal rotation is demonstrated using a shifted circle equilibrium model. A generalized ballooning mode representation is used to eliminate the fast Alfven wave, and an initial value code solves the resulting equations. The s-α diagram (magnetic shear versus pressure gradient) of ballooning mode theory is extended to include rotational shear. In the ballooning representation, the modes shift periodically along the field line to the next point of unfavorable curvature. The shift frequency (dΩ/dq, where Ω is the angular toroidal velocity and q is the safety factor) is proportional to the rotation shear and inversely proportional to the magnetic shear. Stability improves with increasing shift frequency and direct stable access to the second stability regime occurs when this frequency is approximately one-quarter to one-half the Alfven frequency, ω A =V A /qR. copyright 1995 American Institute of Physics

Delayed shear enhancement in mesoscale atmospheric dispersion

Energy Technology Data Exchange (ETDEWEB)

Moran, M.D. [Atmospheric Environment Service, Ontario (Canada); Pielke, R.A. [Colorado State Univ., Fort Collins, CO (United States)

1994-12-31

Mesoscale atmospheric dispersion (MAD) is more complicated than smaller-scale dispersion because the mean wind field can no longer be considered steady or horizontally homogeneous over mesoscale time and space scales. Wind shear also plays a much more important role on the mesoscale: horizontal dispersion can be enhanced and often dominated by vertical wind shear on these scales through the interaction of horizontal differential advection and vertical mixing. Just over 30 years ago, Pasquill suggested that this interaction need not be simultaneous and that the combination of differential horizontal advection with delayed or subsequent vertical mixing could maintain effective horizontal diffusion in spite of temporal or spatial reductions in boundary-layer turbulence intensity. This two-step mechanism has not received much attention since then, but a recent analysis of observations from and numerical simulations of two mesoscale tracer experiments suggests that delayed shear enhancement can play an important role in MAD. This paper presents an overview of this analysis, with particular emphasis on the influence of resolvable vertical shear on MAD in these two case studies and the contributions made by delayed shear enhancement.

Shear strength behavior of geotextile/geomembrane interfaces

Directory of Open Access Journals (Sweden)

Belén M. Bacas

2015-12-01

Full Text Available This paper aims to study the shear interaction mechanism of one of the critical geosynthetic interfaces, the geotextile/geomembrane, typically used for lined containment facilities such as landfills. A large direct shear machine is used to carry out 90 geosynthetic interface tests. The test results show a strain softening behavior with a very small dilatancy (<0.5 mm and nonlinear failure envelopes at a normal stress range of 25–450 kPa. The influences of the micro-level structure of these geosynthetics on the macro-level interface shear behavior are discussed in detail. This study has generated several practical recommendations to help professionals to choose what materials are more adequate. From the three geotextiles tested, the thermally bonded monofilament exhibits the best interface shear strength under high normal stress. For low normal stress, however, needle-punched monofilaments are recommended. For the regular textured geomembranes tested, the space between the asperities is an important factor. The closer these asperities are, the better the result achieves. For the irregular textured geomembranes tested, the nonwoven geotextiles made of monofilaments produce the largest interface shear strength.

Significance of Shear Wall in Multi-Storey Structure With Seismic Analysis

Science.gov (United States)

Bongilwar, Rajat; Harne, V. R.; Chopade, Aditya

2018-03-01

In past decades, shear walls are one of the most appropriate and important structural component in multi-storied building. Therefore, it would be very interesting to study the structural response and their systems in multi-storied structure. Shear walls contribute the stiffness and strength during earthquakes which are often neglected during design of structure and construction. This study shows the effect of shear walls which significantly affect the vulnerability of structures. In order to test this hypothesis, G+8 storey building was considered with and without shear walls and analyzed for various parameters like base shear, storey drift ratio, lateral displacement, bending moment and shear force. Significance of shear wall has been studied with the help of two models. First model is without shear wall i.e. bare frame and other another model is with shear wall considering opening also in it. For modeling and analysis of both the models, FEM based software ETABS 2016 were used. The analysis of all models was done using Equivalent static method. The comparison of results has been done based on same parameters like base shear, storey drift ratio, lateral displacement, bending moment and shear force.

Models and Inference for Multivariate Spatial Extremes

KAUST Repository

Vettori, Sabrina

2017-12-07

The development of flexible and interpretable statistical methods is necessary in order to provide appropriate risk assessment measures for extreme events and natural disasters. In this thesis, we address this challenge by contributing to the developing research field of Extreme-Value Theory. We initially study the performance of existing parametric and non-parametric estimators of extremal dependence for multivariate maxima. As the dimensionality increases, non-parametric estimators are more flexible than parametric methods but present some loss in efficiency that we quantify under various scenarios. We introduce a statistical tool which imposes the required shape constraints on non-parametric estimators in high dimensions, significantly improving their performance. Furthermore, by embedding the tree-based max-stable nested logistic distribution in the Bayesian framework, we develop a statistical algorithm that identifies the most likely tree structures representing the data\\'s extremal dependence using the reversible jump Monte Carlo Markov Chain method. A mixture of these trees is then used for uncertainty assessment in prediction through Bayesian model averaging. The computational complexity of full likelihood inference is significantly decreased by deriving a recursive formula for the nested logistic model likelihood. The algorithm performance is verified through simulation experiments which also compare different likelihood procedures. Finally, we extend the nested logistic representation to the spatial framework in order to jointly model multivariate variables collected across a spatial region. This situation emerges often in environmental applications but is not often considered in the current literature. Simulation experiments show that the new class of multivariate max-stable processes is able to detect both the cross and inner spatial dependence of a number of extreme variables at a relatively low computational cost, thanks to its Bayesian hierarchical

Meniscal shear stress for punching.

Science.gov (United States)

Tuijthof, Gabrielle J M; Meulman, Hubert N; Herder, Just L; van Dijk, C Niek

2009-01-01

Experimental determination of the shear stress for punching meniscal tissue. Meniscectomy (surgical treatment of a lesion of one of the menisci) is the most frequently performed arthroscopic procedure. The performance of a meniscectomy is not optimal with the currently available instruments. To design new instruments, the punching force of meniscal tissue is an important parameter. Quantitative data are unavailable. The meniscal punching process was simulated by pushing a rod through meniscal tissue at constant speed. Three punching rods were tested: a solid rod of Oslash; 3.00 mm, and two hollow tubes (Oslash; 3.00-2.60 mm) with sharpened cutting edges of 0.15 mm and 0.125 mm thick, respectively. Nineteen menisci acquired from 10 human cadaveric knee joints were punched (30 tests). The force and displacement were recorded from which the maximum shear stress was determined (average added with three times the standard deviation). The maximum shear stress for the solid rod was determined at 10.2 N/mm2. This rod required a significantly lower punch force in comparison with the hollow tube having a 0.15 mm cutting edge (plt;0.01). The maximum shear stress for punching can be applied to design instruments, and virtual reality training environments. This type of experiment is suitable to form a database with material properties of human tissue similar to databases for the manufacturing industry.

Examining shear processes during magma ascent

Science.gov (United States)

Kendrick, J. E.; Wallace, P. A.; Coats, R.; Lamur, A.; Lavallée, Y.

2017-12-01

Lava dome eruptions are prone to rapid shifts from effusive to explosive behaviour which reflects the rheology of magma. Magma rheology is governed by composition, porosity and crystal content, which during ascent evolves to yield a rock-like, viscous suspension in the upper conduit. Geophysical monitoring, laboratory experiments and detailed field studies offer the opportunity to explore the complexities associated with the ascent and eruption of such magmas, which rest at a pivotal position with regard to the glass transition, allowing them to either flow or fracture. Crystal interaction during flow results in strain-partitioning and shear-thinning behaviour of the suspension. In a conduit, such characteristics favour the formation of localised shear zones as strain is concentrated along conduit margins, where magma can rupture and heal in repetitive cycles. Sheared magmas often record a history of deformation in the form of: grain size reduction; anisotropic permeable fluid pathways; mineral reactions; injection features; recrystallisation; and magnetic anomalies, providing a signature of the repetitive earthquakes often observed during lava dome eruptions. The repetitive fracture of magma at ( fixed) depth in the conduit and the fault-like products exhumed at spine surfaces indicate that the last hundreds of meters of ascent may be controlled by frictional slip. Experiments on a low-to-high velocity rotary shear apparatus indicate that shear stress on a slip plane is highly velocity dependent, and here we examine how this influences magma ascent and its characteristic geophysical signals.

Residual shear strength of a severely ASR-damaged flat slab bridge

DEFF Research Database (Denmark)

Barbosa, Ricardo Antonio; Gustenhoff Hansen, Søren; Hoang, Linh Cao

2018-01-01

moment carried by the beams. For the beams tested in asymmetric four-point bending, an increase in the shear span-to-effective depth ratio resulted in a decrease in the measured shear strength. The measured shear strengths were compared with calculated shear strengths using the Eurocode 2. Calculations...... based on the compressive strength of drilled cores were rather conservative at low shear span-to-effective depth ratios. However, the conservatism of the Eurocode 2 decreased with increasing shear span-to-effective depth ratios. With the inclusion of ASR-induced pre-stress effect, the calculated shear...... strengths correlated better with the measured shear strengths. The test results indicated that the ASR-induced pre-stress effect can, to some extent, compensate for the significant loss in material properties....

Rating precast prestressed concrete bridges for shear

Science.gov (United States)

2008-12-01

Shear capacity of real-world prestressed concrete girders designed in the 1960s and 1970s is a concern because : AASHTO Standard Specifications (AASHTO-STD) employed the quarter-point rule for shear design, which is less : conservative for shea...

High shear microfluidics and its application in rheological measurement

Science.gov (United States)

Kang, Kai; Lee, L. James; Koelling, Kurt W.

2005-02-01

High shear rheology was explored experimentally in microchannels (150×150 μm). Two aqueous polymer solutions, polyethylene oxide (viscoelastic fluid) and hydroxyethyl cellulose (viscous fluid) were tested. Bagley correction was applied to remove the end effect. Wall slip was investigated with Mooney’s analysis. Shear rates as high as 106 s-1 were obtained in the pressure-driven microchannel flow, allowing a smooth extension of the low shear rheological data obtained from the conventional rheometers. At high shear rates, polymer degradation was observed for PEO solutions at a critical microchannel wall shear stress of 4.1×103 Pa. Stresses at the ends of the microchannel also contributed to PEO degradation significantly.

Micromechanics of soil responses in cyclic simple shear tests

Directory of Open Access Journals (Sweden)

Cui Liang

2017-01-01

Full Text Available Offshore wind turbine (OWT foundations are subjected to a combination of cyclic and dynamic loading arising from wind, wave, rotor and blade shadowing. Under cyclic loading, most soils change their characteristics including stiffness, which may cause the system natural frequency to approach the loading frequency and lead to unplanned resonance and system damage or even collapse. To investigate such changes and the underlying micromechanics, a series of cyclic simple shear tests were performed on the RedHill 110 sand with different shear strain amplitudes, vertical stresses and initial relative densities of soil. The test results showed that: (a Vertical accumulated strain is proportional to the shear strain amplitude but inversely proportional to relative density of soil; (b Shear modulus increases rapidly in the initial loading cycles and then the rate of increase diminishes and the shear modulus remains below an asymptote; (c Shear modulus increases with increasing vertical stress and relative density, but decreasing with increasing strain amplitude. Coupled DEM simulations were performed using PFC2D to analyse the micromechanics underlying the cyclic behaviour of soils. Micromechanical parameters (e.g. fabric tensor, coordination number were examined to explore the reasons for the various cyclic responses to different shear strain amplitudes or vertical stresses. Both coordination number and magnitude of fabric anisotropy contribute to the increasing shear modulus.

Estimated strength of shear keys in concrete dams

Energy Technology Data Exchange (ETDEWEB)

Curtis, D.D. [Hatch Energy, Niagara Falls, ON (Canada); Lum, K.K.Y. [BC Hydro, Burnaby, BC (Canada)

2008-07-01

BC Hydro requested that Hatch Energy review the seismic stability of Ruskin Dam which was constructed in 1930 at Hayward Lake in British Columbia. The concrete gravity dam is founded nearly entirely on rock in a narrow valley. The vertical joints between blocks are keyed and grouted. The strength of the shear keys was assessed when a non-linear finite element model found that significant forces were being transferred laterally to the abutments during an earthquake. The lateral transfer of loads to the abutment relies on the strength of the shear keys. The dynamic finite element analysis was used to determine the stability of the dam. A review of the shear strength measurements reported in literature showed that the measurements compared well to those obtained by BC Hydro from cores taken from Ruskin Dam. The cohesive strength obtained using the Griffith failure criteria was also in good agreement with both sets of measurements. A simple ultimate shear strength equation was developed using the Mohr-Coulomb failure criteria to determine combined cohesive and frictional strength of shear keys. Safety factors of 2.0 for static loads and 1.5 for seismic loads were proposed to reduce the ultimate strength to allowable values. It was concluded that given the relatively high shear strength established for the shear keys, the abutment rock or dam/abutment contact will control the amount of load which can arch to the abutments. 8 refs., 4 tabs., 5 figs.

Experimental study of the vortex-induced vibration of drilling risers under the shear flow with the same shear parameter at the different Reynolds numbers.

Science.gov (United States)

Liangjie, Mao; Qingyou, Liu; Shouwei, Zhou

2014-01-01

A considerable number of studies for VIV under the uniform flow have been performed. However, research on VIV under shear flow is scarce. An experiment for VIV under the shear flow with the same shear parameter at the two different Reynolds numbers was conducted in a deep-water offshore basin. Various measurements were obtained by the fiber bragg grating strain sensors. Experimental data were analyzed by modal analysis method. Results show several valuable features. First, the corresponding maximum order mode of the natural frequency for shedding frequency is the maximum dominant vibration mode and multi-modal phenomenon is appeared in VIV under the shear flow, and multi-modal phenomenon is more apparent at the same shear parameter with an increasing Reynolds number under the shear flow effect. Secondly, the riser vibrates at the natural frequency and the dominant vibration frequency increases for the effect of the real-time tension amplitude under the shear flow and the IL vibration frequency is the similar with the CF vibration frequency at the Reynolds number of 1105 in our experimental condition and the IL dominant frequency is twice the CF dominant frequency with an increasing Reynolds number. In addition, the displacement trajectories at the different locations of the riser appear the same shape and the shape is changed at the same shear parameter with an increasing Reynolds number under the shear flow. The diagonal displacement trajectories are observed at the low Reynolds number and the crescent-shaped displacement trajectories appear with an increasing Reynolds number under shear flow in the experiment.

Experimental study of the vortex-induced vibration of drilling risers under the shear flow with the same shear parameter at the different Reynolds numbers.

Directory of Open Access Journals (Sweden)

Mao Liangjie

Full Text Available A considerable number of studies for VIV under the uniform flow have been performed. However, research on VIV under shear flow is scarce. An experiment for VIV under the shear flow with the same shear parameter at the two different Reynolds numbers was conducted in a deep-water offshore basin. Various measurements were obtained by the fiber bragg grating strain sensors. Experimental data were analyzed by modal analysis method. Results show several valuable features. First, the corresponding maximum order mode of the natural frequency for shedding frequency is the maximum dominant vibration mode and multi-modal phenomenon is appeared in VIV under the shear flow, and multi-modal phenomenon is more apparent at the same shear parameter with an increasing Reynolds number under the shear flow effect. Secondly, the riser vibrates at the natural frequency and the dominant vibration frequency increases for the effect of the real-time tension amplitude under the shear flow and the IL vibration frequency is the similar with the CF vibration frequency at the Reynolds number of 1105 in our experimental condition and the IL dominant frequency is twice the CF dominant frequency with an increasing Reynolds number. In addition, the displacement trajectories at the different locations of the riser appear the same shape and the shape is changed at the same shear parameter with an increasing Reynolds number under the shear flow. The diagonal displacement trajectories are observed at the low Reynolds number and the crescent-shaped displacement trajectories appear with an increasing Reynolds number under shear flow in the experiment.

Velocity shear generated Alfven waves in electron-positron plasmas

International Nuclear Information System (INIS)

Rogava, A.D.; Berezhiani, V.I.; Mahajan, S.M.

1996-01-01

Linear MHD modes in cold, nonrelativistic electron-positron plasma shear flow are considered. The general set of differential equations, describing the evolution of perturbations in the framework of the nonmodal approach is derived. It is found, that under certain circumstances, the compressional and shear Alfven perturbations may exhibit large transient growth fuelled by the mean kinetic energy of the shear flow. The velocity shear also induces mode coupling allowing the exchange of energy as well as the possibility of a strong mutual transformation of these modes into each other. The compressional Alfven mode may extract the energy of the mean flow and transfer it to the shear Alfven mode via this coupling. The relevance of these new physical effects to provide a better understanding of the laboratory e + e - plasma is emphasized. It is speculated that the shear-induced effects in the electron-positron plasmas could also help solve some astrophysical puzzles (e.g., the generation of pulsar radio emission). Since most astrophysical plasma are relativistic, it is shown that the major results of the study remain valid for weakly sheared relativistic plasmas. (author). 21 refs, 4 figs

Triglyceride glucose index and common carotid wall shear stress.

Science.gov (United States)

Tripolino, Cesare; Irace, Concetta; Scavelli, Faustina B; de Franceschi, Maria S; Esposito, Teresa; Carallo, Claudio; Gnasso, Agostino

2014-02-01

Alterations in wall shear stress contribute to both clinical and subclinical atherosclerosis. Several conditions such as hypertension, diabetes, and obesity can impair shear stress, but the role of insulin resistance has never been investigated. The present study was designed to investigate whether insulin resistance assessed by TyG Index associates with wall shear stress in the common carotid artery. One hundred six individuals were enrolled. Blood pressure, lipids, glucose, and cigarette smoking were evaluated. TyG Index was calculated as log[fasting triglycerides × fasting glucose / 2]. Subjects underwent blood viscosity measurement and echo-Doppler evaluation of carotid arteries to calculate wall shear stress. The association between TyG Index and carotid wall shear stress was assessed by simple and multiple regression analyses. TyG Index was significantly and inversely associated with carotid wall shear stress both in simple (r = -0.44, P glucose greater than 100 mg/dL, and triglycerides greater than 150 mg/dL. The present findings suggest that increasing insulin resistance, as assessed by TyG Index, associates with atherosclerosis-prone shear stress reduction in the common carotid artery.

Degree of coupling in high-rise mixed shear walls structures

Indian Academy of Sciences (India)

A simple method of analysis is presented to determine the influence of single shear walls (SSW) on the degree of coupling DoC and on the peak shear demand PSD for beams of coupled shear walls (CSW) in mixed shear wall structures (MSW). Non-coupled lateral load resisting structures such as singular planar walls and ...

Shear weakening for different lithologies observed at different saturation stages

Science.gov (United States)

Diethart-Jauk, Elisabeth; Gegenhuber, Nina

2018-01-01

For this study, samples from different lithologies ("Leitha"-limestone, "Dachstein"-limestone, "Haupt"-dolomite, "Bunt"-sandstone, Grey Berea sandstone, granite, quartzite and basalt) were selected. Samples were dried at 70 °C, respectively 105 °C and were saturated with brine. Mass, porosity, permeability, compressional and shear wave velocity were determined from dry and brine saturated samples at laboratory conditions, based on an individual measurement program. Shear modulus was calculated to find out, if shear weakening exists for the dataset. Shear weakening means that shear modulus of dry samples is higher than of saturated samples, but it is assumed that shear modulus is unaffected by saturation. "Dachstein"-limestone and basalt show shear weakening, quartzite samples show both weakening and hardening. Granite samples are affected by temperature, after drying with 105 °C no change can be observed anymore. "Bunt"-sandstone samples show a change in the shear modulus in a small extent, although they may contain clay minerals. The other lithologies show no effect. Explanations for carbonate samples can be the complicated pore structure, for basalt it could be that weathering creates clay minerals which are known as causes for a change of the shear modulus. Fluid viscosity can also be an important factor.

Focus: Nucleation kinetics of shear bands in metallic glass.

Science.gov (United States)

Wang, J Q; Perepezko, J H

2016-12-07

The development of shear bands is recognized as the primary mechanism in controlling the plastic deformability of metallic glasses. However, the kinetics of the nucleation of shear bands has received limited attention. The nucleation of shear bands in metallic glasses (MG) can be investigated using a nanoindentation method to monitor the development of the first pop-in event that is a signature of shear band nucleation. The analysis of a statistically significant number of first pop-in events demonstrates the stochastic behavior that is characteristic of nucleation and reveals a multimodal behavior associated with local spatial heterogeneities. The shear band nucleation rate of the two nucleation modes and the associated activation energy, activation volume, and site density were determined by loading rate experiments. The nucleation activation energy is very close to the value that is characteristic of the β relaxation in metallic glass. The identification of the rate controlling kinetics for shear band nucleation offers guidance for promoting plastic flow in metallic glass.

Investigation of sheared liquids by neutron backscattering and reflectivity

CERN Document Server

Wolff, M; Hock, R; Frick, B; Zabel, H

2002-01-01

We have investigated by neutron scattering structural and dynamical properties of water solutions of the triblock copolymer P85 under shear. To this end a shear cell that suits the requirements for neutron backscattering and another for reflectivity experiments have been built. In reflectivity measurements we find the polymer concentration (nominal concentration of 33% by weight) to vary right at the surface between 12% and 52% for hydrophilic or hydrophobic coated silicon wavers, for temperatures between 18 C and 73 C and for shear rates up to 2500 s sup - sup 1. Additional structural changes deeper in the bulk are also observed. On the backscattering instrument (IN10 at ILL) we find that the liquid appears to stick to the plates of the shear cell, implying an unusual macroscopic velocity distribution that differs from that found earlier for lubrication oils. We report further on changes of the quasielastic line width in the direction of the shear gradient for different temperatures and shear rates. (orig.)

Shear transfer capacity of reinforced concrete exposed to fire

Science.gov (United States)

Ahmad, Subhan; Bhargava, Pradeep; Chourasia, Ajay

2018-04-01

Shear transfer capacity of reinforced concrete elements is a function of concrete compressive strength and reinforcement yield strength. Exposure of concrete and steel to elevated temperature reduces their mechanical properties resulting in reduced shear transfer capacity of RC elements. The objective of present study is to find the effect of elevated temperature on shear transfer capacity of reinforced concrete. For this purpose pushoff specimens were casted using normal strength concrete. After curing, specimens were heated to 250°C and 500°C in an electric furnace. Cooled specimens were tested for shear transfer capacity in a universal testing machine. It was found that shear transfer capacity and stiffness (slope of load-slip curve) were reduced when the specimens were heated to 250°C and 500°C. Load level for the initiation of crack slip was found to be decreased as the temperature was increased. A simple analytical approach is also proposed to predict the shear transfer capacity of reinforced concrete after elevated temperature.

Determining the effect of turbulent shear on containment aerosol dynamics using microgravity experiments

International Nuclear Information System (INIS)

Scott, C.K.; Abdelbaky, M.

1997-01-01

Determining the characteristics of large aerosol aggregates 'clusters' under turbulent conditions is fundamental for predicting the behaviour of radioactive aerosols inside the reactor containment following a severe accident. Studying such rapidly settling clusters is extremely difficult in ground-based experiments due to the effect of the earth's gravity. In this study, the microgravity environment is exploited to investigate the effect of turbulent shear on the aggregation and breakage of clusters by examining their structure and measuring their strength parameters while suspended under weightlessness conditions. A parametric model is introduced to correlate the experimental results over into nuclear aerosol models. It was demonstrated that the cluster parameters depend mainly on the turbulent field intensity as well as initial powder conditions. (author)

Neural mechanisms underlying sensitivity to reverse-phi motion in the fly

Science.gov (United States)

Meier, Matthias; Serbe, Etienne; Eichner, Hubert; Borst, Alexander

2017-01-01

Optical illusions provide powerful tools for mapping the algorithms and circuits that underlie visual processing, revealing structure through atypical function. Of particular note in the study of motion detection has been the reverse-phi illusion. When contrast reversals accompany discrete movement, detected direction tends to invert. This occurs across a wide range of organisms, spanning humans and invertebrates. Here, we map an algorithmic account of the phenomenon onto neural circuitry in the fruit fly Drosophila melanogaster. Through targeted silencing experiments in tethered walking flies as well as electrophysiology and calcium imaging, we demonstrate that ON- or OFF-selective local motion detector cells T4 and T5 are sensitive to certain interactions between ON and OFF. A biologically plausible detector model accounts for subtle features of this particular form of illusory motion reversal, like the re-inversion of turning responses occurring at extreme stimulus velocities. In light of comparable circuit architecture in the mammalian retina, we suggest that similar mechanisms may apply even to human psychophysics. PMID:29261684

Shear-Induced Membrane Fusion in Viscous Solutions

KAUST Repository

Kogan, Maxim; Feng, Bobo; Nordé n, Bengt; Rocha, Sandra; Beke-Somfai, Tamá s

2014-01-01

Large unilamellar lipid vesicles do not normally fuse under fluid shear stress. They might deform and open pores to relax the tension to which they are exposed, but membrane fusion occurring solely due to shear stress has not yet been reported. We

Evaluating interfacial shear stresses in composite hollo

Directory of Open Access Journals (Sweden)

Aiham Adawi

2016-09-01

Full Text Available Analytical evaluation of the interfacial shear stresses for composite hollowcore slabs with concrete topping is rare in the literature. Adawi et al. (2014 estimated the interfacial shear stiffness coefficient (ks that governs the behavior of the interface between hollowcore slabs and the concrete topping using push-off tests. This parameter is utilized in this paper to provide closed form solutions for the differential equations governing the behavior of simply supported composite hollowcore slabs. An analytical solution based on the deformation compatibility of the composite section and elastic beam theory, is developed to evaluate the shear stresses along the interface. Linear finite element modeling of the full-scale tests presented in Adawi et al. (2015 is also conducted to validate the developed analytical solution. The proposed analytical solution was found to be adequate in estimating the magnitude of horizontal shear stress in the studied composite hollowcore slabs.

Shear crack formation and propagation in fiber reinforced cementitious composites (FRCC)

DEFF Research Database (Denmark)

Paegle, Ieva; Fischer, Gregor

2011-01-01

Knowledge of the mechanisms controlling crack formation, propagation and failure of FRCC under shear loading is currently limited. This paper presents a study that utilized photogrammetry to monitor the shear deformations of two FRCC materials and ordinary concrete (OC). Multiple shear cracks...... and strain hardening of both FRCC materials was observed under shear loading. The influence of fibers, fiber type, including polyvinyl alcohol (PVA) and polypropylene (PP) fibers, and shear crack angle were investigated. Based upon photogrammetric results, fundamental descriptions of shear crack opening...

Shear crack formation and propagation in fiber reinforced cementitious composites (FRCC)

DEFF Research Database (Denmark)

Paegle, Ieva; Fischer, Gregor

2012-01-01

Knowledge of the mechanisms controlling crack formation, propagation and failure of FRCC under shear loading is currently limited. This paper presents a study that utilized photogrammetry to monitor the shear deformations of two FRCC materials and ordinary concrete (OC). Multiple shear cracks...... and strain hardening of both FRCC materials was observed under shear loading. The influence of fibers, fiber type, including polyvinyl alcohol (PVA) and polypropylene (PP) fibers, and shear crack angle were investigated. Based upon photogrammetric results, fundamental descriptions of shear crack opening...

Undrained shear strength determination and correlations on Søvind Marl

DEFF Research Database (Denmark)

Grønbech, Gitte Lyng; Nielsen, Benjaminn Nordahl

2016-01-01

on both the preconsolidation and the undrained shear strength. Two apparent values of the preconsolidation stresses can be determined due to the fissured structure (Grønbech et al. 2015) which also considerably decreases the undrained shear strength. Determination of shear strength of fissured clay...... is done through field testing or triaxial testing. Christensen and Hansen (1959) tested fissured Danish Oligocene clay and found the undrained shear strength, Su, be approximately 1/3 of the measured field vane shear strength, cfv. This correlation has since been used in Danish geotechnical practice...

Diagonal Cracking and Shear Strength of Reinforced Concrete Beams

DEFF Research Database (Denmark)

Zhang, Jin-Ping

1997-01-01

The shear failure of non-shear-reinforced concrete beams with normal shear span ratios is observed to be governed in general by the formation of a critical diagonal crack. Under the hypothesis that the cracking of concrete introduces potential yield lines which may be more dangerous than the ones...

High shear microfluidics and its application in rheological measurement

Energy Technology Data Exchange (ETDEWEB)

Kang, Kai; Lee, L.James; Koelling, Kurt W. [The Ohio State University, Department of Chemical Engineering, Columbus, OH (United States)

2005-02-01

High shear rheology was explored experimentally in microchannels (150 x 150 {mu}m). Two aqueous polymer solutions, polyethylene oxide (viscoelastic fluid) and hydroxyethyl cellulose (viscous fluid) were tested. Bagley correction was applied to remove the end effect. Wall slip was investigated with Mooney's analysis. Shear rates as high as 10{sup 6} s {sup -1} were obtained in the pressure-driven microchannel flow, allowing a smooth extension of the low shear rheological data obtained from the conventional rheometers. At high shear rates, polymer degradation was observed for PEO solutions at a critical microchannel wall shear stress of 4.1 x 10 {sup 3} Pa. Stresses at the ends of the microchannel also contributed to PEO degradation significantly. (orig.)

Does the planetary dynamo go cycling on? Re-examining the evidence for cycles in magnetic reversal rate

Science.gov (United States)

Melott, Adrian L.; Pivarunas, Anthony; Meert, Joseph G.; Lieberman, Bruce S.

2018-01-01

The record of reversals of the geomagnetic field has played an integral role in the development of plate tectonic theory. Statistical analyses of the reversal record are aimed at detailing patterns and linking those patterns to core-mantle processes. The geomagnetic polarity timescale is a dynamic record and new paleomagnetic and geochronologic data provide additional detail. In this paper, we examine the periodicity revealed in the reversal record back to 375 million years ago (Ma) using Fourier analysis. Four significant peaks were found in the reversal power spectra within the 16-40-million-year range (Myr). Plotting the function constructed from the sum of the frequencies of the proximal peaks yield a transient 26 Myr periodicity, suggesting chaotic motion with a periodic attractor. The possible 16 Myr periodicity, a previously recognized result, may be correlated with `pulsation' of mantle plumes and perhaps; more tentatively, with core-mantle dynamics originating near the large low shear velocity layers in the Pacific and Africa. Planetary magnetic fields shield against charged particles, which can give rise to radiation at the surface and ionize the atmosphere, which is a loss mechanism particularly relevant to M stars. Understanding the origin and development of planetary magnetic fields can shed light on the habitable zone.

Starch-zein beldns formed by shear flow

NARCIS (Netherlands)

Habeych Narvaez, E.A.; Dekkers, B.; Goot, van der A.J.; Boom, R.M.

2008-01-01

A newly in-house developed shearing device was used to explore the formation of new types of microstructures in concentrated starch¿zein blends. The device allowed processing of the biopolymer blends under homogeneous, simple shear flow conditions. Water and glycerol were added as plasticizers.

The theoretical shear strength of fcc crystals under superimposed triaxial stress

Energy Technology Data Exchange (ETDEWEB)

Cerny, M., E-mail: cerny.m@fme.vutbr.cz [Institute of Engineering Physics, Faculty of Mechanical Engineering, Brno University of Technology, Technicka 2, CZ-616 69 Brno (Czech Republic); Pokluda, J. [Institute of Engineering Physics, Faculty of Mechanical Engineering, Brno University of Technology, Technicka 2, CZ-616 69 Brno (Czech Republic)

2010-05-15

The influence of a triaxial stress applied normally to shear planes and shear direction during affine shear deformation of face-centered cubic crystals on the theoretical shear strength is studied for the <112-bar >{l_brace}111{r_brace} shear system using first-principles methods. The applied relaxation procedure guarantees that the modeled system is subjected to a superposition of shear, normal and in-plane stresses with individually adjustable in-plane and normal stress values. The theoretical shear strengths of individual elements prove to be qualitatively different functions of the superimposed stresses. In the special case of hydrostatic loading, however, these functions are qualitatively uniform. This behavior is discussed in terms of the electronic structure.

Ballooning mode stabilization by moderate sheared rotation

International Nuclear Information System (INIS)

Hameiri, E.

1996-01-01

Sheared toroidal plasma rotation has been known for some time to have a stabilizing effect on the ballooning modes. A recent calculation showed that a large flow shear, with dΩ/dq of the order of the Alfven toroidal frequency, can stabilize the ballooning modes. This latest result is, in fact, not so optimistic. For observed flows with Mach number of order unity one gets dΩ/dq smaller by a factor O(√β) from the required level (if the flow shear length is of the same order as the magnetic shear length). Moreover, the calculation does not take into account a possibly large transient growth of the mode amplitude due to its Floquet structures We show here that, in fact, there is a general tendency of the ballooning mode to stabilize as soon as the flow shear dΩ/dq exceeds the (O√β smaller) open-quotes slowclose quotes magnetosonic wave frequency. Our analysis is perturbative, where the small parameter is related to the small coupling between the slow and Alfven waves-as is the case in a high aspect-ratio tokamak. (In the perturbation it is important to take the Hamiltonian nature of the governing equations into account.) Moreover, our results apply to the relevant transient growth of the mode amplitude

Shear behavior of concrete beams externally prestressed with Parafil ropes

Directory of Open Access Journals (Sweden)

A.H. Ghallab

2013-03-01

Full Text Available Although extensive work has been carried out investigating the use of external prestressing system for flexural strengthening, a few studies regarding the shear behavior of externally prestressed beams can be found. Five beams, four of them were externally strengthened using Parafil rope, were loaded up to failure to investigate the effect of shear span/depth ratio, external prestressing force and concrete strength on their shear behavior. Test results showed that the shear span to depth ratio has a significant effect on both the shear strength and failure mode of the strengthened beams and the presence of external prestressing force increased the ultimate load of the tested beams by about 75%. Equations proposed by different codes for both the conventional reinforced concrete beams and for ordinary prestressed beams were used to evaluate the obtained experimental results. In general, codes equations showed a high level of conservatism in predicting the shear strength of the beams. Also, using the full strength rather than half of the concrete shear strength in the Egyptian code PC-method improves the accuracy of the calculated ultimate shear strength.

Shear strength of palm oil clinker concrete beams

International Nuclear Information System (INIS)

Mohammed, Bashar S.; Foo, W.L.; Hossain, K.M.A.; Abdullahi, M.

2013-01-01

Highlights: ► Palm oil clinker can be used as lightweight aggregate for the production of structural concrete. ► The palm oil clinker concrete can be classified as lightweight concrete. ► Full scale reinforced palm oil clinker concrete beams without shear reinforcement were tested. ► The CSA based design equation can be used for the prediction of shear capacity with a limit. - Abstract: This paper presents experimental results on the shear behavior of reinforced concrete beams made of palm oil clinker concrete (POCC). Palm oil clinker (POC) is a by-product of palm oil industry and its utilization in concrete production not only solves the problem of disposing this solid waste but also helps to conserve natural resources. Seven reinforced POCC beams without shear reinforcement were fabricated and their shear behavior was tested. POCC has been classified as a lightweight structural concrete with air dry density less than 1850 kg/m 3 and a 28-day compressive strength more than 20 MPa. The experimental variables which have been considered in this study were the POCC compressive strength, shear span–depth ratio (a/d) and the ratio of tensile reinforcement (ρ). The results show that the failure mode of the reinforced POCC beam is similar to that of conventional reinforced concrete beam. In addition, the shear equation of the Canadian Standard Association (CSA) can be used in designing reinforced POCC beam with ρ ⩾ 1. However, a 0.5 safety factor should be included in the formula for ρ < 1

Introduction to the viewpoint set on shear bands

International Nuclear Information System (INIS)

Hutchinson, J.W.

1984-01-01

Recent work aimed at improving our understanding of shear banding and flow localization as modes of deformation and failure is summarized in the six viewpoint articles which follow. For the most part, the emphasis here is on the observation and analysis of shear banding in metals, but active efforts are also underway to understand the role of shear bands in the deformation and failure of soils and rocks. There is a tendency to regard shear bands as a failure mode, as indeed they often are. But extensive straining under highly constrained conditions such as rolling can give rise to profuse flow localization into shear bands which can be regarded as microscopic in the sense that their extent is on the scale of the grains rather than the overall dimensions of the block of material being deformed. Hatherly and Malin describe in detail the observation of such bands and emphasize that they should be considered as a mode of deformation under these circumstances. They relate the formation of the bands to microstructural aspects and discuss their role in the development of recrystallization textures. It will be clear from reading the articles in this viewpoint set that the beginnings of a quantitative theory of shear banding is in place. Continued progress will require parallel developments in constitutive theory and experimental observation. Moreover, basic questions remain to be explored related to the spatial development of the shear bands, their mutual interaction, their development into a failure mode, and how these are influenced by factors such as overall deformational constraint, rate of straining, and temperature

Shear behavior of reinforced Engineered Cementitious Composites (ECC) beams

DEFF Research Database (Denmark)

Paegle, Ieva; Fischer, Gregor

2010-01-01

This paper describes an experimental investigation of the shear behavior of beams consisting of steel reinforced Engineered Cementitious Composites (ECC). Based on the strain hardening and multiple cracking behavior of ECC, this study investigates the extent to which ECC can improve the shear...... capacity of beams loaded primarily in shear and if ECC can partially or fully replace the conventional transverse steel reinforcement in beams. However, there is a lack of understanding of how the fibers affect the shear carrying capacity and deformation behavior of structural members if used either...

Improvement of shearing machine in the Tokai Reprocessing Plant

International Nuclear Information System (INIS)

Takae, Akiyoshi; Otani, Yoshikuni

1994-01-01

The shearing machine in the Tokai Reprocessing Plant has been improved and refurbished through its operational experience for about 20 years. Every component except the shear housing and magazine is changed for improved things by PNC, while the shearing machine had been designed and fabricated originally by a French Company. The improvement of the shearing machine was carried out for the purpose of settling the problems which were experienced in the past operation, and improving durability, remote maintainability, and operability. The details of their improvement work are described. (author)

Reynolds and Maxwell stress measurements in the reversed field pinch experiment Extrap-T2R

Science.gov (United States)

Vianello, N.; Antoni, V.; Spada, E.; Spolaore, M.; Serianni, G.; Cavazzana, R.; Bergsåker, H.; Cecconello, M.; Drake, J. R.

2005-08-01

The complete Reynolds stress (RS) has been measured in the edge region of the Extrap-T2R reversed field pinch experiment. The RS exhibits a strong gradient in the region where a high E × B shear takes place. Experimental results show this gradient to be almost entirely due to the electrostatic contribution. This has been interpreted as experimental evidence of flow generation via turbulence mechanism. The scales involved in flow generation are deduced from the frequency decomposition of RS tensor. They are found related to magnetohydrodynamic activity but are different with respect to the scales responsible for turbulent transport.

Reynolds and Maxwell stress measurements in the reversed field pinch experiment Extrap-T2R

International Nuclear Information System (INIS)

Vianello, N.; Antoni, V.; Spada, E.; Spolaore, M.; Serianni, G.; Cavazzana, R.; Bergsaaker, H.; Cecconello, M.; Drake, J.R.

2005-01-01

The complete Reynolds stress (RS) has been measured in the edge region of the Extrap-T2R reversed field pinch experiment. The RS exhibits a strong gradient in the region where a high E x B shear takes place. Experimental results show this gradient to be almost entirely due to the electrostatic contribution. This has been interpreted as experimental evidence of flow generation via turbulence mechanism. The scales involved in flow generation are deduced from the frequency decomposition of RS tensor. They are found related to magnetohydrodynamic activity but are different with respect to the scales responsible for turbulent transport

Gelation under shear

Energy Technology Data Exchange (ETDEWEB)

Butler, B.D.; Hanley, H.J.M.; Straty, G.C. [National Institute of Standards and Technology, Boulder, CO (United States); Muzny, C.D. [Univ. of Colorado, Boulder, CO (United States)

1995-12-31

An experimental small angle neutron scattering (SANS) study of dense silica gels, prepared from suspensions of 24 nm colloidal silica particles at several volume fractions {theta} is discussed. Provided that {theta}{approx_lt}0.18, the scattered intensity at small wave vectors q increases as the gelation proceeds, and the structure factor S(q, t {yields} {infinity}) of the gel exhibits apparent power law behavior. Power law behavior is also observed, even for samples with {theta}>0.18, when the gel is formed under an applied shear. Shear also enhances the diffraction maximum corresponding to the inter-particle contact distance of the gel. Difficulties encountered when trying to interpret SANS data from these dense systems are outlined. Results of computer simulations intended to mimic gel formation, including computations of S(q, t), are discussed. Comments on a method to extract a fractal dimension characterizing the gel are included.

Freezing of a colloidal liquid subject to shear flow

International Nuclear Information System (INIS)

Bagchi, B.; Thirumalai, D.

1988-01-01

A nonequilibrium generalization of the density-functional theory of freezing is proposed to investigate the shear-induced first-order phase transition in colloidal suspensions. It is assumed that the main effect of a steady shear is to break the symmetry of the structure factor of the liquid and that for small shear rate, the phenomenon of a shear-induced order-disorder transition may be viewed as an equilibrium phase transition. The theory predicts that the effective density at which freezing takes place increases with shear rate. The solid (which is assumed to be a bcc lattice) formed upon freezing is distorted and specifically there is less order in one plane compared with the order in the other two perpendicular planes. It is shown that there exists a critical shear rate above which the colloidal liquid does not undergo a transition to an ordered (or partially ordered) state no matter how large the density is. Conversely, above the critical shear rate an initially formed bcc solid always melts into an amorphous or liquidlike state. Several of these predictions are in qualitative agreement with the light-scattering experiments of Ackerson and Clark. The limitations as well as possible extensions of the theory are also discussed

Evaluation of size dependent design shear strength of reinforced ...

Indian Academy of Sciences (India)

to the development of the size dependent models on the shear strength in ... predict the diagonal cracking strength and the ultimate shear strength of RC ... ing strength of normal beams was by Zsutty (1968) based on the data base available without .... The comparison of the calculated shear strength of the beams is shown.

Shear capacity of ASR damaged structures – in-depth analysis of some in-situ shear tests on bridge slabs

DEFF Research Database (Denmark)

Hansen, Søren Gustenhoff; Barbosa, Ricardo Antonio; Hoang, Linh Cao

2016-01-01

This paper deals with the influence of alkali-silica reaction (ASR) on the shear capacity for concrete slabs without shear reinforcement. An experimental full-scale in-situ program consisting of four slabs from a bridge (Vosnæsvej) has been carried out and the results have been published in ref. [1......] with the principal author of this paper as co-author. After the experiments, a detailed measurement of the test specimens was conducted. Based on these measurements a thorough analysis of the experimental results was carried out and evaluated by a plastic model for shear capacity, Crack Sliding Model (CSM...

Shear-wave dynamic behavior using two different orientations

International Nuclear Information System (INIS)

Ghassem Alaskari, M. K.; Hashemi, S. J.

2007-01-01

For laterally complex media, it may be more suitable to take a different orientation of the displacement vector of Shear-waves. This may change the sign of several imaginary reflections and conversion coefficients to be used in reservoir characterization and Amplitude Versus Offset analysis or modeling. In this new convention the positive direction of the displacement vector of reflected Shear-waves is chosen to the left of ray tangent (in the direction of wave propagation). Therefore, the definition of the displacement vector of shear-waves can be used properly even for very complicated media. Finally the shear-wave dynamic behavior of a reservoir zone can be illustrated for laterally varying structures in terms of the amplitude variation and phase behavior using this new orientation

Mean E×B shear effect on geodesic acoustic modes in Tokamaks

International Nuclear Information System (INIS)

Singh, Rameswar; Gurcan, Ozgur D.

2015-01-01

E × B shearing effect on geodesic acoustic mode (GAM) is investigated for the first time both as an initial value problem in the shearing frame and as an eigenvalue value problem in the lab frame. The nontrivial effects are that E × B shearing couples the standard GAM perturbations to their complimentary poloidal parities. The resulting GAM acquires an effective inertia increasing in time leading to GAM damping. Eigenmode analysis shows that GAMs are radially localized by E × B shearing with the mode width being inversely proportional and radial wave number directly proportional to the shearing rate for weak shear. (author)

Dilatancy induced ductile-brittle transition of shear band in metallic glasses

Science.gov (United States)

Zeng, F.; Jiang, M. Q.; Dai, L. H.

2018-04-01

Dilatancy-generated structural disordering, an inherent feature of metallic glasses (MGs), has been widely accepted as the physical mechanism for the primary origin and structural evolution of shear banding, as well as the resultant shear failure. However, it remains a great challenge to determine, to what degree of dilatation, a shear banding will evolve into a runaway shear failure. In this work, using in situ acoustic emission monitoring, we probe the dilatancy evolution at the different stages of individual shear band in MGs that underwent severely plastic deformation by the controlled cutting technology. A scaling law is revealed that the dilatancy in a shear band is linearly related to its evolution degree. A transition from ductile-to-brittle shear bands is observed, where the formers dominate stable serrated flow, and the latter lead to a runaway instability (catastrophe failure) of serrated flow. To uncover the underlying mechanics, we develop a theoretical model of shear-band evolution dynamics taking into account an atomic-scale deformation process. Our theoretical results agree with the experimental observations, and demonstrate that the atomic-scale volume expansion arises from an intrinsic shear-band evolution dynamics. Importantly, the onset of the ductile-brittle transition of shear banding is controlled by a critical dilatation.

Shear-stress fluctuations and relaxation in polymer glasses

Science.gov (United States)

Kriuchevskyi, I.; Wittmer, J. P.; Meyer, H.; Benzerara, O.; Baschnagel, J.

2018-01-01

We investigate by means of molecular dynamics simulation a coarse-grained polymer glass model focusing on (quasistatic and dynamical) shear-stress fluctuations as a function of temperature T and sampling time Δ t . The linear response is characterized using (ensemble-averaged) expectation values of the contributions (time averaged for each shear plane) to the stress-fluctuation relation μsf for the shear modulus and the shear-stress relaxation modulus G (t ) . Using 100 independent configurations, we pay attention to the respective standard deviations. While the ensemble-averaged modulus μsf(T ) decreases continuously with increasing T for all Δ t sampled, its standard deviation δ μsf(T ) is nonmonotonic with a striking peak at the glass transition. The question of whether the shear modulus is continuous or has a jump singularity at the glass transition is thus ill posed. Confirming the effective time-translational invariance of our systems, the Δ t dependence of μsf and related quantities can be understood using a weighted integral over G (t ) .

Line Crack Subject to Antiplane Shear.

Science.gov (United States)

1978-07-01

shear is obtained for the initiation of fracture. If the concept of the surface tension is usedone is able to calculate the cohesive stress for brittle ...Expression of the Griffith -racture criterion for brittle fracture. We have arrived at this result via the maximum shear-stress hypothesis, rather than...Crescent Beach Road, Glen Cove Prof. G.S. Heller Long Island, New York 11542 Division of Engineering Brown University Prof. Daniel

Supersonic shear imaging provides a reliable measurement of resting muscle shear elastic modulus

International Nuclear Information System (INIS)

Lacourpaille, Lilian; Hug, François; Bouillard, Killian; Nordez, Antoine; Hogrel, Jean-Yves

2012-01-01

The aim of the present study was to assess the reliability of shear elastic modulus measurements performed using supersonic shear imaging (SSI) in nine resting muscles (i.e. gastrocnemius medialis, tibialis anterior, vastus lateralis, rectus femoris, triceps brachii, biceps brachii, brachioradialis, adductor pollicis obliquus and abductor digiti minimi) of different architectures and typologies. Thirty healthy subjects were randomly assigned to the intra-session reliability (n = 20), inter-day reliability (n = 21) and the inter-observer reliability (n = 16) experiments. Muscle shear elastic modulus ranged from 2.99 (gastrocnemius medialis) to 4.50 kPa (adductor digiti minimi and tibialis anterior). On the whole, very good reliability was observed, with a coefficient of variation (CV) ranging from 4.6% to 8%, except for the inter-operator reliability of adductor pollicis obliquus (CV = 11.5%). The intraclass correlation coefficients were good (0.871 ± 0.045 for the intra-session reliability, 0.815 ± 0.065 for the inter-day reliability and 0.709 ± 0.141 for the inter-observer reliability). Both the reliability and the ease of use of SSI make it a potentially interesting technique that would be of benefit to fundamental, applied and clinical research projects that need an accurate assessment of muscle mechanical properties. (note)

Constitutive Behavior of Reinforced Concrete Membrane Elements under Tri-directional Shear

Science.gov (United States)

Labib, Moheb

The two-dimensional behavior of typical reinforced concrete (RC) structures has been extensively studied in the past several decades by investigating the constitutive behavior of full-scale reinforced concrete elements subjected to a bi-axial state of stress. In order to understand the true behavior of many large complex structures, the goal of this investigation is to develop new constitutive relationships for RC elements subjected to tri-directional shear stresses. Recently, additional out-of-plane jacks were installed on the panel tester at University of Houston so that concrete elements could be subjected to tri-directional shear stresses. This upgrade makes the panel tester the only one of its kind in the US that is capable of applying such combinations of stresses on full-scale reinforced concrete elements. This dissertation presents the details of the mounting and installation of the additional hydraulic jacks on the universal panel tester. The experimental program includes a series of seven reinforced concrete elements subjected to different combinations of in-plane and out-of-plane shear stresses. Increasing the applied out-of-plane shear stresses reduced the membrane shear strength of the elements. The effect of applying out-of-plane shear stresses on the in-plane shear strength was represented by modifying the softening coefficient in the compression stress strain curve of concrete struts. The modified model was able to capture the behavior and the ultimate capacity of the tested elements. The effect of the in-plane shear reinforcement ratio on the interaction between in-plane and out-of-plane shear stresses was evaluated. The model was implemented in the Finite Element package FEAP and was used to predict the ultimate capacity of many structures subjected to a combination of in-plane and out-of-plane shear stresses. The results of the analytical model were used to develop simplified design equations for members subjected to bi-directional shear loads

Shear viscosity of liquid mixtures: Mass dependence

International Nuclear Information System (INIS)

Kaushal, Rohan; Tankeshwar, K.

2002-06-01

Expressions for zeroth, second, and fourth sum rules of transverse stress autocorrelation function of two component fluid have been derived. These sum rules and Mori's memory function formalism have been used to study shear viscosity of Ar-Kr and isotopic mixtures. It has been found that theoretical result is in good agreement with the computer simulation result for the Ar-Kr mixture. The mass dependence of shear viscosity for different mole fraction shows that deviation from ideal linear model comes even from mass difference in two species of fluid mixture. At higher mass ratio shear viscosity of mixture is not explained by any of the emperical model. (author)

Shear viscosity of liquid mixtures Mass dependence

CERN Document Server

Kaushal, R

2002-01-01

Expressions for zeroth, second, and fourth sum rules of transverse stress autocorrelation function of two component fluid have been derived. These sum rules and Mori's memory function formalism have been used to study shear viscosity of Ar-Kr and isotopic mixtures. It has been found that theoretical result is in good agreement with the computer simulation result for the Ar-Kr mixture. The mass dependence of shear viscosity for different mole fraction shows that deviation from ideal linear model comes even from mass difference in two species of fluid mixture. At higher mass ratio shear viscosity of mixture is not explained by any of the emperical model.

Transport reduction via shear flow modification of the cross phase

International Nuclear Information System (INIS)

Ware, A.S.; Terry, P.W.; Diamond, P.H.; Carreras, B.A.

1996-01-01

As a model example of the effect of E x B shear flow on the cross phase between electrostatic potential and pressure fluctuations, a nonlinear theory of resistive pressure gradient driven turbulence (RPGDT) in a shear flow is presented. This work builds on numerical studies of RPGDT, which have shown that both flow shear and curvature can affect the cross phase as well as the fluctuation levels. In this work, we show that the effect of shear flow on transport can be expressed through the temporal response of pressure to potential. It is shown heuristically that even in the case where the fluctuation levels are not modified, the flow shear still acts to reduce the phase angle between potential and pressure fluctuations, thereby suppressing transport. The scaling of the cross phase with flow shear and flow curvature is presented. (author)

Haptic Edge Detection Through Shear

Science.gov (United States)

Platkiewicz, Jonathan; Lipson, Hod; Hayward, Vincent

2016-03-01

Most tactile sensors are based on the assumption that touch depends on measuring pressure. However, the pressure distribution at the surface of a tactile sensor cannot be acquired directly and must be inferred from the deformation field induced by the touched object in the sensor medium. Currently, there is no consensus as to which components of strain are most informative for tactile sensing. Here, we propose that shape-related tactile information is more suitably recovered from shear strain than normal strain. Based on a contact mechanics analysis, we demonstrate that the elastic behavior of a haptic probe provides a robust edge detection mechanism when shear strain is sensed. We used a jamming-based robot gripper as a tactile sensor to empirically validate that shear strain processing gives accurate edge information that is invariant to changes in pressure, as predicted by the contact mechanics study. This result has implications for the design of effective tactile sensors as well as for the understanding of the early somatosensory processing in mammals.

Piezoelectric energy harvesting through shear mode operation

International Nuclear Information System (INIS)

Malakooti, Mohammad H; Sodano, Henry A

2015-01-01

Piezoelectric materials are excellent candidates for use in energy harvesting applications due to their high electromechanical coupling properties that enable them to convert input mechanical energy into useful electric power. The electromechanical coupling coefficient of the piezoelectric material is one of the most significant parameters affecting energy conversion and is dependent on the piezoelectric mode of operation. In most piezoceramics, the d 15 piezoelectric shear coefficient is the highest coefficient compared to the commonly used axial and transverse modes that utilize the d 33 and the d 31 piezoelectric strain coefficients. However, complicated electroding methods and challenges in evaluating the performance of energy harvesting devices operating in the shear mode have slowed research in this area. The shear deformation of a piezoelectric layer can be induced in a vibrating sandwich beam with a piezoelectric core. Here, a model based on Timoshenko beam theory is developed to predict the electric power output from a cantilever piezoelectric sandwich beam under base excitations. It is shown that the energy harvester operating in the shear mode is able to generate ∼50% more power compared to the transverse mode for a numerical case study. Reduced models of both shear and transverse energy harvesters are obtained to determine the optimal load resistance in the system and perform an efficiency comparison between two models with fixed and adaptive resistances. (paper)

Impedance method for measuring shear elasticity of liquids

Science.gov (United States)

Badmaev, B. B.; Dembelova, T. S.; Damdinov, B. B.; Gulgenov, Ch. Zh.

2017-11-01

Experimental results of studying low-frequency (74 kHz) shear elasticity of polymer liquids by the impedance method (analogous to the Mason method) are presented. A free-volume thick liquid layer is placed on the horizontal surface of a piezoelectric quartz crystal with dimensions 34.7 × 12 × 5.5 cm. The latter performs tangential vibrations at resonance frequency. The liquid layer experiences shear strain, and shear waves should propagate in it. From the theory of the method, it follows that, with an increase in the layer thickness, both real and imaginary resonance frequency shifts should exhibit damped oscillations and tend to limiting values. For the liquids under study, the imaginary frequency shift far exceeds the real one, which testifies to the presence of bulk shear elasticity.

A simultaneous description of fast wave e-TTMP and ion current drive effects on shear in a tokamak: theory and experiments in JET

International Nuclear Information System (INIS)

Bhatnagar, V.P.; Bosia, G.; Jacquinot, J.; Porcelli, F.

1993-01-01

A controlled local modification of the plasma-current profile, the safety factor q or shear (dq/dr) in a tokamak can lead to an improvement in its performance. For example, enhanced confinement in JET discharges with deep pellet injection is found to be associated with a reversal of the shear. Also, a significant control over the sawteeth behaviour in the JET tokamak has been found to occur when the shear at the q = 1 surface is modified by a dipolar-current driven by ICRF in the minority-ion heating regime. This could give a handle on the ejection of fast particles and hence on burn control in a reactor. The above sawtooth control may also be used to ease the ash removal in a reactor. When an ICRH antenna array is phased (Δφ ≠ 0 or π), the excited asymmetric k // -spectrum can drive non inductive currents by interaction of waves both with electrons (TTMP and e-Landau damping) and ions at minority (fundamental) or harmonic cyclotron resonances depending upon the scenario. Therefore, in any modeling of ICRF current drive, both (electron and ion) current drive mechanisms must be included simultaneously to correctly represent the non inductive current drive profile. To devise scenarios of shear control by minority current drive, that take advantage of the inherent electron current drive as well, we have developed a model based on earlier theories to calculate, for the first time, the two effects simultaneously. (author) 11 refs., 5 figs

A novel reversible logic gate and its systematic approach to implement cost-efficient arithmetic logic circuits using QCA.

Science.gov (United States)

Ahmad, Peer Zahoor; Quadri, S M K; Ahmad, Firdous; Bahar, Ali Newaz; Wani, Ghulam Mohammad; Tantary, Shafiq Maqbool

2017-12-01

Quantum-dot cellular automata, is an extremely small size and a powerless nanotechnology. It is the possible alternative to current CMOS technology. Reversible QCA logic is the most important issue at present time to reduce power losses. This paper presents a novel reversible logic gate called the F-Gate. It is simplest in design and a powerful technique to implement reversible logic. A systematic approach has been used to implement a novel single layer reversible Full-Adder, Full-Subtractor and a Full Adder-Subtractor using the F-Gate. The proposed Full Adder-Subtractor has achieved significant improvements in terms of overall circuit parameters among the most previously cost-efficient designs that exploit the inevitable nano-level issues to perform arithmetic computing. The proposed designs have been authenticated and simulated using QCADesigner tool ver. 2.0.3.

Fusing Simulation Results From Multifidelity Aero-servo-elastic Simulators - Application To Extreme Loads On Wind Turbine

DEFF Research Database (Denmark)

Abdallah, Imad; Sudret, Bruno; Lataniotis, Christos

2015-01-01

Fusing predictions from multiple simulators in the early stages of the conceptual design of a wind turbine results in reduction in model uncertainty and risk mitigation. Aero-servo-elastic is a term that refers to the coupling of wind inflow, aerodynamics, structural dynamics and controls. Fusing...... the response data from multiple aero-servo-elastic simulators could provide better predictive ability than using any single simulator. The co-Kriging approach to fuse information from multifidelity aero-servo-elastic simulators is presented. We illustrate the co-Kriging approach to fuse the extreme flapwise...... bending moment at the blade root of a large wind turbine as a function of wind speed, turbulence and shear exponent in the presence of model uncertainty and non-stationary noise in the output. The extreme responses are obtained by two widely accepted numerical aero-servo-elastic simulators, FAST...

Flexible Micropost Arrays for Shear Stress Measurement

Science.gov (United States)

Wohl, Christopher J.; Palmieri, Frank L.; Hopkins, John W.; Jackson, Allen M.; Connell, John W.; Lin, Yi; Cisotto, Alexxandra A.

2015-01-01

Increased fuel costs, heightened environmental protection requirements, and noise abatement continue to place drag reduction at the forefront of aerospace research priorities. Unfortunately, shortfalls still exist in the fundamental understanding of boundary-layer airflow over aerodynamic surfaces, especially regarding drag arising from skin friction. For example, there is insufficient availability of instrumentation to adequately characterize complex flows with strong pressure gradients, heat transfer, wall mass flux, three-dimensionality, separation, shock waves, and transient phenomena. One example is the acoustic liner efficacy on aircraft engine nacelle walls. Active measurement of shear stress in boundary layer airflow would enable a better understanding of how aircraft structure and flight dynamics affect skin friction. Current shear stress measurement techniques suffer from reliability, complexity, and airflow disruption, thereby compromising resultant shear stress data. The state-of-the-art for shear stress sensing uses indirect or direct measurement techniques. Indirect measurements (e.g., hot-wire, heat flux gages, oil interferometry, laser Doppler anemometry, small scale pressure drag surfaces, i.e., fences) require intricate knowledge of the studied flow, restrictive instrument arrangements, large surface areas, flow disruption, or seeding material; with smaller, higher bandwidth probes under development. Direct measurements involve strain displacement of a sensor element and require no prior knowledge of the flow. Unfortunately, conventional "floating" recessed components for direct measurements are mm to cm in size. Whispering gallery mode devices and Fiber Bragg Gratings are examples of recent additions to this type of sensor with much smaller (?m) sensor components. Direct detection techniques are often single point measurements and difficult to calibrate and implement in wind tunnel experiments. In addition, the wiring, packaging, and installation

Detailed Jaramillo field reversals recorded in lake sediments from Armenia - Lower mantle influence on the magnetic field revisited

Science.gov (United States)

Kirscher, U.; Winklhofer, M.; Hackl, M.; Bachtadse, V.

2018-02-01

While it is well established that the Earth's magnetic field is generated by a self sustaining dynamo that reversed its polarity at irregular intervals in the geological past, the very mechanisms causing field reversals remain obscure. Paleomagnetic reconstructions of polarity transitions have been essential for physically constraining the underlying mechanisms in terms of time scale, but thus far remain ambiguous with regard to the transitional field geometry. Here we present new paleomagnetic records from a rapidly deposited lacustrine sediment sequence with extraordinarily stable paleomagnetic signals, which has captured in unprecedented detail the bottom (reverse to normal: R-N) and top (normal to reverse: N-R) transitions of the Jaramillo subchron (at 1.072 Ma and at 0.988 Ma). The obtained virtual geomagnetic pole (VGP) path indicates an oscillatory transitional field behavior with four abrupt transequatorial precursory jumps across the Pacific. The distribution of VGP positions indicates regions of preferred occurrence. Our results are in agreement with previously proposed bands of transitional VGP occurrence over the Americas and Australia/northwest Pacific. Additionally, our VGP positions seem to avoid large low shear velocity provinces (LLSVPs) above the core mantle boundary (CMB). Thus, our data supports the idea that the transitional field geometry is controlled by heat flux heterogeneities at the CMB linked to LLSVPs.