Journal articles on the topic 'Localized and distributed loading'
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1
Fazzolari, Fiorenzo A., and Puxue Tan. "A Linearised Hybrid FE-SEA Method for Nonlinear Dynamic Systems Excited by Random and Harmonic Loadings." Vibration 3, no. 3 (September 17, 2020): 304–19. http://dx.doi.org/10.3390/vibration3030021.
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The present paper proposes a linearised hybrid finite element-statistical energy analysis (FE-SEA) formulation for built-up systems with nonlinear joints and excited by random, as well as harmonic, loadings. The new formulation was validated via an ad-hoc developed stochastic benchmark model. The latter was derived through the combination of the Lagrange-Rayleigh-Ritz method (LRRM) and the Monte Carlo simulation (MCS). Within the build-up plate systems, each plate component was modelled by using the classical Kirchhoff’s thin-plate theory. The linearisation processes were carried out according to the loading-type. In the case of random loading, the statistical linearisation (SL) was employed, while, in the case of harmonic loading, the method of harmonic balance (MHB) was used. To demonstrate the effectiveness of the proposed hybrid FE-SEA formulation, three different case studies, made-up of built-up systems with localized cubic nonlinearities, were considered. Both translational and torsional springs, as joint components, were employed. Four different types of loadings were taken into account: harmonic/random point and distributed loadings. The response of the dynamic systems was investigated in terms of ensemble average of the time-averaged energy.
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Talone, Candida, Radoslav Sovják, Michal Mára, and Jindřich Fornůsek. "Post-impact flexural capacity of UHPFRC plates." MATEC Web of Conferences 352 (2021): 00006. http://dx.doi.org/10.1051/matecconf/202135200006.
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This work aims to demonstrate the effective use of fibre reinforcement in thin plate elements made of UHPFRC under projectile impact loading. The use of fibre reinforcement is very efficient in case of ballistic loading, as fibres are evenly distributed over the entire volume of the material body and possible damage to the plate is thus suppressed in all points of the plate element equally. The aim of this study is therefore to provide data on the residual flexural capacity of plates that have been significantly damaged by the impact of the projectile and to demonstrate the benefits of using fibre reinforcement for localized impact loading.
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Liu, Sufan, and Bo Li. "Design of 3D-printed metal micro-truss porous configurations with geometric inhomogeneity." Journal of Physics: Conference Series 2383, no. 1 (December 1, 2022): 012026. http://dx.doi.org/10.1088/1742-6596/2383/1/012026.
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The metal micro-truss porous structures demonstrate industrial application values in lightweight, high specific strength, impact resistance and energy absorption. 3D printing brings a feasible path to design and directly fabricate metal micro-truss parts. Spatially geometrically uniformly distributed and unit-symmetrically arrayed porous structures still need to further improve the structural performance. This work studies the design principles and several design cases of geometrically non-uniform micro-truss porous structures via metal 3D printing method. The high-stress localized micro-regions are filled with denser and more reinforced micro-truss cell arrays that conform to the main loading direction of localized stress.
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Chiu, Yi-Jui, Sheng-Rui Jian, Ti-Ju Liu, Phuoc Le, and Jenh-Yih Juang. "Localized Deformation and Fracture Behaviors in InP Single Crystals by Indentation." Micromachines 9, no. 12 (November 22, 2018): 611. http://dx.doi.org/10.3390/mi9120611.
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The indentation-induced deformation mechanisms in InP(100) single crystals were investigated by using nanoindentation and cross-sectional transmission electron microscopy (XTEM) techniques. The results indicated that there were multiple “pop-in” events randomly distributed in the loading curves, which were conceived to arise primarily from the dislocation nucleation and propagation activities. An energetic estimation on the number of nanoindentation-induced dislocations associated with pop-in effects is discussed. Furthermore, the fracture patterns were performed by Vickers indentation. The fracture toughness and the fracture energy of InP(100) single crystals were calculated to be around 1.2 MPa·m1/2 and 14.1 J/m2, respectively.
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Ma, Shao Peng, Lai Gui Wang, and Guan Chang Jin. "Damage Evolution Inspection of Rock Using Digital Speckle Correlation Method (DSCM)." Key Engineering Materials 326-328 (December 2006): 1117–20. http://dx.doi.org/10.4028/www.scientific.net/kem.326-328.1117.
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In order to evaluate the damage evolution of rock under external loading, the surface deformation field of a rectangle marble specimen is inspected and analyzed using digital speckle correlation method (DSCM). Experimental results show that the damage evolution of rock undergoes 3 stages: they are uniformly distributed damage, localized damage and catastrophic failure stage. A statistic indicator, standard deviation of the strain field, can be used to quantitatively express the damage localization level.
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ZHAO, GUIPING, SANG-KYO LEE, and CHONGDU CHO. "EFFECT OF COMPRESSIVE RESIDUAL STRESS INDUCED DURING FABRICATING PROCESS IN THE CORE OF CLAMPED SANDWICH PLATE UNDER SHOCK LOADING." International Journal of Modern Physics B 22, no. 09n11 (April 30, 2008): 1195–200. http://dx.doi.org/10.1142/s0217979208046530.
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Sandwich panels can be manufactured in many ways like lamination press, closed mold fabrication, and vacuum bag compaction. During manufacturing, the core and the sheets are attached under certain applied pressure and temperature, associated with a deformation and stress remaining in the sandwich core. This study presents an evaluation of the compressive residual stress effect of the core which occurs during the localized shock loading at the mid-span of a clamped sandwich plate. We simulate such a square lattice core sandwich plate by commercial finite element code, ABAQUS/Explicit. We apply uniform distributed loading on upper face sheet and temperature difference occurred during the manufacturing process is taken here before the impact simulation step. These loadings induce certain amount of residual stresses in core structure of sandwich panel. The computational result from non-residual stress case is verified by comparing with the results of published experimental data on similar investigation. In addition, the effect of existing residual stress at core is analyzed. We also compare the dynamic responses of two clamped sandwich plates with and without pre-stressed core. And impact resistance of sandwich panel is explained in the view of energy capacity. Results show that the shock loading behavior of sandwich panel depends on its manufacturing process and panels with compressive residual stresses have less deformation and high impact energy absorption characteristics.
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Xu, Y. G., W. Tiu, and Y. Z. Xu. "Numerical Simulation of Crack Tip Behavior under Fatigue Loading." Key Engineering Materials 525-526 (November 2012): 517–20. http://dx.doi.org/10.4028/www.scientific.net/kem.525-526.517.
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Fatigue damage is a localized phenomenon controlled by the near-tip crack behavior. This paper presents an application of a dislocation distribution technique to the simulation of crack tip behavior under fatigue loading. A centre-cracked tension specimen under uni-axial fatigue loading is used in the study. Crack opening and plastic deformation around the crack tip are simulated by distributions of dislocation dipoles in crack plane and four inclined planes ahead of the crack tip. Climb dislocation dipole is used to model the opening and closing of the crack while glide dislocation dipole is used to simulate the backward and forward slip in the inclined planes during loading and unloading of the fatigue cycle. Stress field around the crack tip is obtained by the superposition of the contributions of the applied external load and the distributed dislocation dipoles. Correct boundary conditions of the model are achieved by employing a quadratic programming technique to minimize a properly constructed non-negative object function. It is found that the simulated crack closure variations under the constant amplitude fatigue load agree well with the result of a previously developed modified strip yield model with an appropriate constraint factor.
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Carrera, Erasmo, and Gaetano Giunta. "Hierarchical models for failure analysis of plates bent by distributed and localized transverse loadings." Journal of Zhejiang University-SCIENCE A 9, no. 5 (May 2008): 600–613. http://dx.doi.org/10.1631/jzus.a072110.
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Bailey, R. T., M. Ahmadi, T. K. Gates, and M. Arabi. "Spatially-distributed influence of agro-environmental factors governing nitrate fate and transport in an irrigated stream-aquifer system." Hydrology and Earth System Sciences Discussions 12, no. 2 (February 4, 2015): 1653–96. http://dx.doi.org/10.5194/hessd-12-1653-2015.
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Abstract. Elevated levels of nitrate (NO3) in groundwater systems pose a serious risk to human populations and natural ecosystems. As part of an effort to remediate NO3 contamination in irrigated stream-aquifer systems, this study elucidates agricultural and environmental parameters and processes that govern NO3 fate and transport at the regional (500 km2), local (50 km2), and field scales (< 1 km2). Specifically, the revised Morris sensitivity analysis method was applied to a finite-difference nitrogen cycling and reactive transport model of a regional-scale study site in the Lower Arkansas River Valley in southeastern Colorado. The method was used to rank the influence of anthropogenic activities and natural chemical processes on NO3 groundwater concentration, NO3 mass leaching, and NO3 mass loading to the Arkansas River from the aquifer. Sensitivity indices were computed for the entire study area in aggregate as well as each canal command area, crop type, and individual grid cells. Results suggest that fertilizer loading, crop uptake, and heterotrophic denitrification govern NO3 fate and transport for the majority of the study area, while canal NO3 concentration and rates of autotrophic denitrification, nitrification, and humus decomposition dominate or partially dominate in several canal command areas. Also, NO3 leaching and groundwater concentration in adjacent cultivated fields often are governed by different processes and mass inputs/outputs. Results can be used to determine critical processes and key management actions for future data collection and remediation strategies, with efforts able to be focused on localized areas.
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Toribio, Jesús, Miguel Lorenzo, and Leticia Aguado. "Innovative Design of Residual Stress and Strain Distributions for Analyzing the Hydrogen Embrittlement Phenomenon in Metallic Materials." Materials 15, no. 24 (December 19, 2022): 9063. http://dx.doi.org/10.3390/ma15249063.
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Round-notched samples are commonly used for testing the susceptibility to hydrogen embrittlement (HE) of metallic materials. Hydrogen diffusion is influenced by the stress and strain states generated during testing. This state causes hydrogen-assisted micro-damage leading to failure that is due to HE. In this study, it is assumed that hydrogen diffusion can be controlled by modifying such residual stress and strain fields. Thus, the selection of the notch geometry to be used in the experiments becomes a key task. In this paper, different HE behaviors are analyzed in terms of the stress and strain fields obtained under diverse loading conditions (un-preloaded and preloaded causing residual stress and strains) in different notch geometries (shallow notches and deep notches). To achieve this goal, two uncoupled finite element (FE) simulations were carried out: (i) a simulation by FE of the loading sequences applied in the notched geometries for revealing the stress and strain states and (ii) a simulation of hydrogen diffusion assisted by stress and strain, for estimating the hydrogen distributions. According to results, hydrogen accumulation in shallow notches is heavily localized close to the wire surface, whereas for deep notches, hydrogen is more uniformly distributed. The residual stress and plastic strains generated by the applied preload localize maximum hydrogen concentration at deeper points than un-preloaded cases. As results, four different scenarios are established for estimating “a la carte” the HE susceptibility of pearlitic steels just combining two notch depths and the residual stress and strain caused by a preload.
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Alqwasmi, Nouman, Faris Tarlochan, and Sami E. Alkhatib. "Study of Mild Steel Sandwich Structure Energy Absorption Performance Subjected to Localized Impulsive Loading." Materials 13, no. 3 (February 3, 2020): 670. http://dx.doi.org/10.3390/ma13030670.
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Extensive research focus had been given to sacrificial sandwich panels to mitigate the effects of blast loads. This is due to their ability to distribute the load and absorb a significant portion of the blast energy. This paper studies the behavior of sacrificial sandwich mild steel panels of axially oriented octagonal tapered tubular cores subjected to near-field impulsive blast. The deformation behavior and several assessment parameters consisting of the peak force, stroke efficiency, energy absorption and core efficiency were investigated using validated finite element analysis. The developed deformation modes were mainly influenced by the top plate and tube thickness. Tubes of a 5° taper performed unfavorably, exhibiting increased peak force and lower energy absorption. Panels of top plate thickness of 4 mm exhibited higher stroke efficiency as compared to panels of lower thickness. The top plate and tube thickness significantly affected energy absorption. An increase of 73.5% in core efficiency was observed in thick-plate panels as compared to thin-plate ones.
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Bailey, R. T., M. Ahmadi, T. K. Gates, and M. Arabi. "Spatially distributed influence of agro-environmental factors governing nitrate fate and transport in an irrigated stream–aquifer system." Hydrology and Earth System Sciences 19, no. 12 (December 18, 2015): 4859–76. http://dx.doi.org/10.5194/hess-19-4859-2015.
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Abstract. Elevated levels of nitrate (NO3) in groundwater systems pose a serious risk to human populations and natural ecosystems. As part of an effort to remediate NO3 contamination in irrigated stream–aquifer systems, this study elucidates agricultural and environmental parameters and processes that govern NO3 fate and transport at the regional (500 km2), local (50 km2), and field scales (< 1 km2). Specifically, the revised Morris sensitivity analysis method was applied to a finite-difference nitrogen cycling and reactive transport model of a regional-scale study site in the lower Arkansas River valley in southeastern Colorado. The method was used to rank the influence of anthropogenic activities and natural chemical processes on NO3 groundwater concentration, NO3 mass leaching, and NO3 mass loading to the Arkansas River from the aquifer. Sensitivity indices were computed for the entire study area in aggregate as well as each canal command area, crop type, and individual grid cells. Results suggest that fertilizer loading, crop uptake, and heterotrophic denitrification govern NO3 fate and transport for the majority of the study area, although their order of influence on NO3 groundwater concentration and mass leaching varies according to crop type and command area. Canal NO3 concentration and rates of autotrophic denitrification, nitrification, and humus decomposition also dominate or partially dominate in other locations. Each factor, with the exception of O2 reduction rate, is the dominating influence on NO3 groundwater concentration at one or more locations within the study area. Results can be used to determine critical processes and key management actions for future data collection and remediation strategies, with efforts able to be focused on localized areas.
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Elveli, Benjamin S., Tore Børvik, and Vegard Aune. "Influence of material properties on the performance of blast-loaded steel plates with pre-cut defects." EPJ Web of Conferences 250 (2021): 02028. http://dx.doi.org/10.1051/epjconf/202125002028.
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Experimental and numerical investigations are carried out to determine how thin steel plates with pre-cut defects behave under blast loading. The defects considered in this study are represented by four square holes, symmetrically distributed around the centre of the target plates. The target plates were manufactured from two types of steel, i.e., a dual-phase medium strength steel and a high-strength martensitic steel. A shock tube facility was used to expose the plates to blast-like loading conditions. The experiments showed that both the blast resistance and the corresponding fracture mode changed with material properties. Numerical simulations were performed using the finite element code LS-DYNA, where the numerical results were found to be in good agreement with the experimental data in predicting the ductile fracture during the blast-structure interaction. The numerical simulations confirmed that significant work hardening will distribute the plasticity throughout the plate material during deformation, while limited work hardening will tend to localize the plasticity that results in earlier fracture.
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Duchen, Michael R., Anne Leyssens, and Martin Crompton. "Transient Mitochondrial Depolarizations Reflect Focal Sarcoplasmic Reticular Calcium Release in Single Rat Cardiomyocytes." Journal of Cell Biology 142, no. 4 (August 24, 1998): 975–88. http://dx.doi.org/10.1083/jcb.142.4.975.
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Digital imaging of mitochondrial potential in single rat cardiomyocytes revealed transient depolarizations of mitochondria discretely localized within the cell, a phenomenon that we shall call “flicker.” These events were usually highly localized and could be restricted to single mitochondria, but they could also be more widely distributed within the cell. Contractile waves, either spontaneous or in response to depolarization with 50 mM K+, were associated with propagating waves of mitochondrial depolarization, suggesting that propagating calcium waves are associated with mitochondrial calcium uptake and consequent depolarization. Here we demonstrate that the mitochondrial flicker was directly related to the focal release of calcium from sarcoplasmic reticular (SR) calcium stores and consequent uptake of calcium by local mitochondria. Thus, the events were dramatically reduced by (a) depletion of SR calcium stores after long-term incubation in EGTA or thapsigargin (500 nM); (b) buffering intracellular calcium using BAPTA-AM loading; (c) blockade of SR calcium release with ryanodine (30 μM); and (d) blockade of mitochondrial calcium uptake by microinjection of diaminopentane pentammine cobalt (DAPPAC), a novel inhibitor of the mitochondrial calcium uniporter. These observations demonstrate that focal SR calcium release results in calcium microdomains sufficient to promote local mitochondrial calcium uptake, suggesting a tight coupling of calcium signaling between SR release sites and nearby mitochondria.
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Gamez, Angeli, and Imad L. Al-Qadi. "Turning Maneuver Effect on Near-Surface Airfield Pavement Responses." Transportation Research Record: Journal of the Transportation Research Board 2673, no. 8 (April 22, 2019): 275–83. http://dx.doi.org/10.1177/0361198119841861.
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Airport pavement structures experience heavy aircraft tire loading through a localized contact area. Distributed three-dimensionally and non-uniformly, tire-pavement contact stresses directly influence the near-surface behavior of flexible airfield pavements. The resulting high shear stress levels induced by aircraft tire loading may lead to instability through shoving or slippage cracking. As the tire turns during taxiing, the risk of near-surface damage is exacerbated. In this study, numerical modeling of an inverted pavement system and a conventional flexible pavement structure loaded with a single tire from the A-380 landing gear was developed. The analysis matrix included two tire-inflation pressures, two speeds, and rolling conditions that varied from free-rolling to two turning maneuvers. Two analysis approaches were performed: 1) use of traditional critical point strains, and 2) domain analysis, which characterizes bulk pavement behavior using multiaxial stresses and strains. The critical strains, which are used as inputs for airfield pavement design, changed negligibly under varying tire turning conditions despite the asymmetric contact stress distribution. On the other hand, domain analysis not only captured the asymmetric pavement behavior, but also identified that altering the tire movement from a free-rolling condition to turning could induce a significant increase in the potential damage.
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Gajst, Hannah, Eyal Shalev, Ram Weinberger, Shmuel Marco, Wenlu Zh, and Vladimir Lyakhovsky. "Relating strain localization and Kaiser effect to yield surface evolution in brittle rocks." Geophysical Journal International 221, no. 3 (April 17, 2020): 2091–103. http://dx.doi.org/10.1093/gji/ggaa130.
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SUMMARY The yield surfaces of rocks keep evolving beyond the initial yield stress owing to the damage accumulation and porosity change during brittle deformation. Using a poroelastic damage rheology model, we demonstrate that the measure of coupling between the yield surface change and accumulated damage is correlated with strain localization and the Kaiser effect. Constant or minor yield surface change is associated with strong strain localization, as seen in low-porosity crystalline rocks. In contrast, strong coupling between damage growth and the yield surface leads to distributed deformation, as seen in high-porosity rocks. Assuming that during brittle deformation damage occurs primarily in the form of microcracks, we propose that the measured acoustic emission (AE) in rock samples correlates with the damage accumulation. This allows quantifying the Kaiser effect under cyclic loading by matching between the onset of AE and the onset of damage growth. The ratio of the stress at the onset of AE to the peak stress of the previous loading cycle, or Felicity Ratio (FR), is calculated for different model parameters. The results of the simulation show that FR gradually decreases in the case of weak coupling between yield surface and damage growth. For a strong damage-related coupling promoting significant yield surface change, the FR remains close to one and decreases only towards the failure. The model predicts that a steep decrease in FR is associated with a transition between distributed and localized modes of failure. By linking the evolving yield surface to strain localization patterns and the Kaiser effect, the poroelastic damage rheology model provides a new quantitative tool to study failure modes of brittle rocks.
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Preuss, Simon, Jean Paul Ampuero, Taras Gerya, and Ylona van Dinther. "Characteristics of earthquake ruptures and dynamic off-fault deformation on propagating faults." Solid Earth 11, no. 4 (July 22, 2020): 1333–60. http://dx.doi.org/10.5194/se-11-1333-2020.
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Abstract. Natural fault networks are geometrically complex systems that evolve through time. The evolution of faults and their off-fault damage patterns are influenced by both dynamic earthquake ruptures and aseismic deformation in the interseismic period. To better understand each of their contributions to faulting we simulate both earthquake rupture dynamics and long-term deformation in a visco-elasto-plastic crust subjected to rate- and state-dependent friction. The continuum mechanics-based numerical model presented here includes three new features. First, a 2.5-D approximation is created to incorporate the effects of a viscoelastic lower crustal substrate below a finite depth. Second, we introduce a dynamically adaptive (slip-velocity-dependent) measure of fault width to ensure grid size convergence of fault angles for evolving faults. Third, fault localization is facilitated by plastic strain weakening of bulk rate and state friction parameters as inspired by laboratory experiments. This allows us to simulate sequences of episodic fault growth due to earthquakes and aseismic creep for the first time. Localized fault growth is simulated for four bulk rheologies ranging from persistent velocity weakening to velocity strengthening. Interestingly, in each of these bulk rheologies, faults predominantly localize and grow due to aseismic deformation. Yet, cyclic fault growth at more realistic growth rates is obtained for a bulk rheology that transitions from velocity-strengthening friction to velocity-weakening friction. Fault growth occurs under Riedel and conjugate angles and transitions towards wing cracks. Off-fault deformation, both distributed and localized, is typically formed during dynamic earthquake ruptures. Simulated off-fault deformation structures range from fan-shaped distributed deformation to localized splay faults. We observe that the fault-normal width of the outer damage zone saturates with increasing fault length due to the finite depth of the seismogenic zone. We also observe that dynamically and statically evolving stress fields from neighboring fault strands affect primary and secondary fault growth and thus that normal stress variations affect earthquake sequences. Finally, we find that the amount of off-fault deformation distinctly depends on the degree of optimality of a fault with respect to the prevailing but dynamically changing stress field. Typically, we simulate off-fault deformation on faults parallel to the loading direction. This produces a 6.5-fold higher off-fault energy dissipation than on an optimally oriented fault, which in turn has a 1.5-fold larger stress drop. The misalignment of the fault with respect to the static stress field thus facilitates off-fault deformation. These results imply that fault geometries bend, individual fault strands interact, and optimal orientations and off-fault deformation vary through space and time. With our work we establish the basis for simulations and analyses of complex evolving fault networks subject to both long-term and short-term dynamics.
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Branford, O. A., D. A. Lee, D. L. Bader, and A. O. Grobbelaar. "The mechanics of flexor tendon adhesions." Journal of Hand Surgery (European Volume) 37, no. 6 (December 14, 2011): 555–63. http://dx.doi.org/10.1177/1753193411432675.
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The mechanics of adhesions at a local tissue level have not been extensively studied. This study compared microstrains and macrostrains in adhesions of immobilized and mobilized partially lacerated flexor digitorum profundus tendons in a New Zealand White rabbit model. At 2 weeks, 50 digits were randomized to either gross tensile testing or micromechanical assessment, in which the movement of fluorescently labelled cell nuclei, acting as dynamic markers, was visualized using real-time confocal microscopy. The structural stiffness and load at failure of immobilized adhesions were 140% and 160% of that of mobilized adhesions, respectively, and both differences were statistically significant. Micromechanically, different patterns of loading and failure were observed. Mobilized adhesions exhibited over a three-fold higher local strain, which was less uniformly distributed. Confocal microscopy provided an accurate measure of local strain. For the first time, it has been possible to visualize, define, and quantify local adhesion tissue mechanics. Mobilization appears to favour the formation of sites expressing increased local strain responses or those predisposed to heterogeneity and localized failure.
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Hahn, Eric N., Vincent R. Sherman, Andrei Pissarenko, Samuel D. Rohrbach, Daniel J. Fernandes, and Marc A. Meyers. "Nature's technical ceramic: the avian eggshell." Journal of The Royal Society Interface 14, no. 126 (January 2017): 20160804. http://dx.doi.org/10.1098/rsif.2016.0804.
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Avian eggshells may break easily when impacted at a localized point; however, they exhibit impressive resistance when subjected to a well-distributed compressive load. For example, a common demonstration of material strength is firmly squeezing a chicken egg along its major axis between one's hands without breaking it. This research provides insight into the underlying mechanics by evaluating both macroscopic and microstructural features. Eggs of different size, varying from quail (30 mm) to ostrich (150 mm), are investigated. Compression experiments were conducted along the major axis of the egg using force-distributing rubber cushions between steel plates and the egg. The force at failure increases with egg size, reaching loads upwards of 5000 N for ostrich eggs. The corresponding strength, however, decreases with increasing shell thickness (intimately related to egg size); this is rationalized by a micro-defects model. Failure occurs by axial splitting parallel to the loading direction—the result of hoop tensile stresses due to the applied compressive load. Finite-element analysis is successfully employed to correlate the applied compressive force to tensile breaking strength for the eggs, and the influence of geometric ratio and microstructural heterogeneities on the shell's strength and fracture toughness is established.
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Halama, Jonathan, Bradley Barnhart, Robert Kennedy, Robert McKane, James Graham, Paul Pettus, Allen Brookes, Kevin Djang, and Ronald Waschmann. "Improved Soil Temperature Modeling Using Spatially Explicit Solar Energy Drivers." Water 10, no. 10 (October 9, 2018): 1398. http://dx.doi.org/10.3390/w10101398.
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Modeling the spatial and temporal dynamics of soil temperature is deterministically complex due to the wide variability of several influential environmental variables, including soil column composition, soil moisture, air temperature, and solar energy. Landscape incident solar radiation is a significant environmental driver that affects both air temperature and ground-level soil energy loading; therefore, inclusion of solar energy is important for generating accurate representations of soil temperature. We used the U.S. Environmental Protection Agency’s Oregon Crest-to-Coast (O’CCMoN) Environmental Monitoring Transect dataset to develop and test the inclusion of ground-level solar energy driver data within an existing soil temperature model currently utilized within an ecohydrology model called Visualizing Ecosystem Land Management Assessments (VELMA). The O’CCMoN site data elucidate how localized ground-level solar energy between open and forested landscapes greatly influence the resulting soil temperature. We demonstrate how the inclusion of local ground-level solar energy significantly improves the ability to deterministically model soil temperature at two depths. These results suggest that landscape and watershed-scale models should incorporate spatially distributed solar energy to improve spatial and temporal simulations of soil temperature.
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Mitchell, R. M., S. K. Campbell, and Y. Qin. "Recent increase in aerosol loading over the Australian arid zone." Atmospheric Chemistry and Physics 10, no. 4 (February 15, 2010): 1689–99. http://dx.doi.org/10.5194/acp-10-1689-2010.
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Abstract. Collocated sun photometer and nephelometer measurements at Tinga Tingana in the Australian Outback over the decade 1997–2007 show a significant increase in aerosol loading following the onset of severe drought conditions in 2002. This increase is confined to the season of dust activity, particularly September to March. In contrast, background aerosol levels during May, June and July remained stable. The enhanced aerosol loadings during the latter 5 years of the study period can be understood as a combination of dune destabilisation through loss of ephemeral vegetation and surface crust, and the changing supply of fluvial sediments to ephemeral lakes and floodplains within the Lake Eyre Basin. Major dust outbreaks are generally highly localised, although significant dust activity was observed at Tinga Tingana on 50% of days when a major event occurred elsewhere in the Lake Eyre Basin, suggesting frequent basin-wide dust mobilisation. Combined analysis of aerosol optical depth and scattering coefficient shows weak correlation between the surface and column aerosol (R2=0.24). The aerosol scale height is broadly distributed with a mode typically between 2–3 km, with clearly defined seasonal variation. Climatological analysis reveals bimodal structure in the annual cycle of aerosol optical depth, with a summer peak related to maximal dust activity, and a spring peak related to lofted fine-mode aerosol. There is evidence for an increase in near-surface aerosol during the period 2003–2007 relative to 1997–2002, consistent with an increase in dust activity. This accords with an independent finding of increasing aerosol loading over the Australian region as a whole, suggesting that rising dust activity over the Lake Eyre Basin may be a significant contributor to changes in the aerosol budget of the continent.
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Ishikawa, Raga, Shosuke Yoshida, Shin-ichi Sawada, Yoshihiro Sasaki, and Kazunari Akiyoshi. "Fusogenic Hybrid Extracellular Vesicles with PD-1 Membrane Proteins for the Cytosolic Delivery of Cargos." Cancers 14, no. 11 (May 26, 2022): 2635. http://dx.doi.org/10.3390/cancers14112635.
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Extracellular vesicles (EVs) are cell-derived lipid membrane capsules that can deliver functional molecules, such as nucleic acids, to target cells. Currently, the application of EVs is limited because of the difficulty of loading cargo into EVs. We constructed hybrid EVs by the fusion of liposomes and insect cell-derived EVs expressing recombinant programmed cell death 1 (PD-1) protein and baculoviral fusogenic glycoprotein gp64, and evaluated delivery of the model cargo molecule, Texas Red-labeled dextran (TR-Dex), into the cytosol. When PD-1 hybrid EVs were added to HeLa cells, the intracellular uptake of the hybrid EVs was increased compared with hybrid EVs without PD-1. After cellular uptake, the PD-1 hybrid EVs were shown to be localized to late endosomes or lysosomes. The results of fluorescence resonance energy transfer (FRET) indicated that membrane fusion between the hybrid EVs and organelles had occurred in the acidic environment of the organelles. When TR-Dex-loaded liposomes were fused with the PD-1 EVs, confocal laser scanning microscopy indicated that TR-Dex was distributed throughout the cells, which suggested that endosomal escape of TR-Dex, through membrane fusion between the hybrid EVs and acidic organelles, had occurred. These engineered PD-1 hybrid EVs have potential as delivery carriers for biopharmaceuticals.
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Mitchell, R. M., S. K. Campbell, and Y. Qin. "Recent increase in aerosol loading over the Australian arid zone." Atmospheric Chemistry and Physics Discussions 9, no. 5 (October 14, 2009): 21619–45. http://dx.doi.org/10.5194/acpd-9-21619-2009.
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Abstract. Collocated sun photometer and nephelometer measurements at Tinga Tingana in the Australian Outback over the decade 1997–2007 show a significant increase in aerosol loading following the onset of severe drought conditions in 2002. The mean mid-visible scattering coefficient obtained from nephelometer measurements over the period 2003–2007 is approximately double that recorded over the preceding 5 yr, with consistent trends in the column aerosol optical depth derived from the sun photometer. This increase is confined to the season of dust activity, particularly September to March. In contrast, background aerosol levels during May, June and July remained stable. The enhanced aerosol loadings during the latter 5 yr of the study period can be understood as a combination of dune destabilisation through loss of ephemeral vegetation and surface crust, and the changing supply of fluvial sediments to ephemeral lakes and floodplains within the Lake Eyre Basin. Major dust outbreaks are generally highly localised, although significant dust activity was observed at Tinga Tingana on 50% of days when a major event occurred elsewhere in the Lake Eyre Basin, suggesting frequent basin-wide dust mobilisation. Combined analysis of aerosol optical depth and scattering coefficient shows weak correlation between the surface and column aerosol (R2=0.24). The aerosol scale height is broadly distributed with a mode typically between 2–3 km, with clearly defined seasonal variation. Climatological analysis reveals bimodal structure in the annual cycle of aerosol optical depth, with a summer peak related to maximal dust activity, and a spring peak related to lofted fine-mode aerosol. There is evidence for an increase in near-surface aerosol during the period 2003–2007 relative to 1997–2002, consistent with an increase in dust activity. This accords with an independent finding of increasing aerosol loading over the Australian region as a whole, suggesting that rising dust activity over the Lake Eyre Basin may be a significant contributor to changes in the aerosol budget of the continent.
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PERRONE, Lorena, Simona PALADINO, Marialuisa MAZZONE, Lucio NITSCH, Massimo GULISANO, and Chiara ZURZOLO. "Functional interaction between p75NTR and TrkA: the endocytic trafficking of p75NTR is driven by TrkA and regulates TrkA-mediated signalling." Biochemical Journal 385, no. 1 (December 14, 2004): 233–41. http://dx.doi.org/10.1042/bj20041155.
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The topology and trafficking of receptors play a key role in their signalling capability. Indeed, receptor function is related to the microenvironment inside the cell, where specific signalling molecules are compartmentalized. The response to NGF (nerve growth factor) is strongly dependent on the trafficking of its receptor, TrkA. However, information is still scarce about the role of the cellular localization of the TrkA co-receptor, p75NTR (where NTR is neurotrophin receptor), following stimulation by NGF. It has been shown that these two receptors play a key role in epithelial tissue and in epithelial-derived tumours, where the microenvironment at the plasma membrane is defined by the presence of tight junctions. Indeed, in thyroid carcinomas, rearrangements of TrkA are frequently found, which produce TrkA mutants that are localized exclusively in the cytoplasm. We used a thyroid cellular model in which it was possible to dissect the trafficking of the two NGF receptors upon neurotrophin stimulation. In FRT (Fischer rat thyroid) cells, endogenous TrkA is localized exclusively on the basolateral surface, while transfected p75NTR is selectively distributed on the apical membrane. This cellular system enabled us to selectively stimulate either p75NTR or TrkA and to analyse the role of receptor trafficking in their signalling capability. We found that, after binding to NGF, p75NTR was co-immunoprecipitated with TrkA and was transcytosed at the basolateral membrane. We showed that the TrkA–p75NTR interaction is necessary for this relocation of p75NTR to the basolateral side. Interestingly, TrkA-specific stimulation by basolateral NGF loading also induced the TrkA–p75NTR interaction and subsequent p75NTR transcytosis at the basolateral surface. Moreover, specific stimulation of p75NTR by NGF activated TrkA and the MAPK (mitogen-activated protein kinase) pathway. Our data indicate that TrkA regulates the subcellular localization of p75NTR upon stimulation with neurotrophins, thus affecting the topology of the signal transduction molecules, driving the activation of a specific signal transduction pathway.
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Carpinteri, Alberto, Giuseppe Lacidogna, and Gianni Niccolini. "Critical Behaviour in Concrete Structures and Damage Localization by Acoustic Emission." Key Engineering Materials 312 (June 2006): 305–10. http://dx.doi.org/10.4028/www.scientific.net/kem.312.305.
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Extensive research and studies on concrete fracture and failure have shown that concrete should be viewed as a quasi-brittle material having a size-dependent behaviour. Numerous experimental techniques have been employed to evaluate fracture processes, and a number of modelling approaches have been developed to predict fracture behaviour. The non-destructive method based on the Acoustic Emission (AE) technique has proved highly effective, especially to check and measure the damage phenomena that take place inside a structure subjected to mechanical loading. In this paper an experimental investigation conducted on concrete and RC structures by means of the AE technique is described. The AE signals reflecting the release of energy taking place during the damage process were recorded and micro-cracking sources were localised by measuring time delays by means of spatially distributed AE sensors.
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O'Donoughue, Patrick, Olivier Robin, and Alain Berry. "Time-space identification of mechanical impacts and distributed random excitations on plates and membranes." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 233, no. 18 (March 31, 2019): 6436–47. http://dx.doi.org/10.1177/0954406219839094.
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The identification of dynamic loads acting on structures is a key aspect of several engineering domains involving structure-borne sound and vibration problems, stress analysis, or even the study of fatigue-induced structural damages. This work is concerned with the reconstruction of localized transient and distributed random excitations on plates and membranes from their measured vibration response. In previous investigations by the authors, the virtual fields method, an identification approach based on the principle of virtual work, was employed to identify mechanical and acoustic loadings applied to a bending panel. However, vibration data were obtained using scanning laser Doppler vibrometry, which limits the application of the virtual fields method to stationary excitations in both space and frequency. In contrast, the deflectometry technique used here is an optical method that directly provides a full-field measurement of local slopes. With the addition of a high-speed camera, the measurements are resolved in both space and time, enabling the study of nonstationary excitations. Moreover, since the acquisition time is independent of the number of measurement points, high spatial density measurements can be performed in seconds. This paper reviews the principles of the virtual fields method for nonstationary excitations on plates and membranes. The deflectometry technique is then demonstrated and experimental reconstruction results on an aluminum panel are presented for two different load cases: impacting metal marbles (multiple unknown transient excitations) and a diffuse acoustic field excitation. Finally, the identification of acoustic and aerodynamic (turbulent boundary layer) excitations is considered using a membrane as the receiving structure.
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Pourfalah, Saeed, and Demetrios M. Cotsovos. "Enhancing the out-of-plane behaviour of unreinforced masonry walls under impact loading through the use of partially bonded layers of engineered cementitious composite." International Journal of Protective Structures 11, no. 2 (August 4, 2019): 209–34. http://dx.doi.org/10.1177/2041419619866457.
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Published experimental work reveals that the out-of-plane behaviour of unreinforced masonry walls under impact loading can be significantly enhanced through the use of engineered cementitious composite layers fully bonded to the surface of the masonry. The disadvantage of this method is associated with the localised cracking exhibited by the engineered cementitious composite layer close to the joints forming between bricks. This cracking is associated with the bond developing between the masonry and the engineered cementitious composite layer and does not allow the latter layer to achieve its full potential, thus resulting in its premature failure. In an attempt to address this problem, a series of drop-weight tests were carried on masonry prismatic specimens strengthened with a layer of engineered cementitious composite partially bonded to the surface of the masonry acting in tension. The latter prismatic specimens consist of a stack of bricks connected with mortar joints. The specimens are considered to provide a simplistic representation of a vertical strip of a masonry wall subjected to out-of-plane actions associated with impact or blast loading. Analysis of the test data reveals that under impact loading, the specimens retrofitted with partially bonded engineered cementitious composite layers can exhibit a more ductile performance compared to that exhibited by the same specimens when strengthened with fully bonded layers of engineered cementitious composite. This is attributed to the fact that along its unbonded length, the engineered cementitious composite layer is subjected to purely uniaxial tension (free from any interaction with the surface of the masonry), allowing for the development of multiple uniformly distributed fine cracks.
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Langdon, Genevieve S., CJ von Klemperer, GF Volschenk, T. van Tonder, and RA Govender. "The influence of interfacial bonding on the response of lightweight aluminium and glass fibre metal laminate panels subjected to air-blast loading." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 232, no. 8 (October 16, 2017): 1402–17. http://dx.doi.org/10.1177/0954406217718859.
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This paper examines the effects of glass fibre configuration and epoxy resin type on the response of glass fibre epoxy-based fibre metal laminate panels. These lightweight materials are excellent candidates for use in transportation applications, where mass is a major factor in design and materials selection. Interfacial bond strength was characterised through single leg bend testing and revealed varying failure characteristics for different epoxy configurations and surface treatments. A combination of bead blasting and silane treatment provided the best surface treatment for the aluminium, while SE84 epoxy resin gave superior adhesion properties compared to Prime 20ULV. Blast tests were performed to investigate the effect of bond strength on panel response under localised and more uniformly distributed air-blast loading conditions. Dimensionless analysis and failure mode identification were used to show that both fibre configuration and bond strength played a role in blast response but the bond strength (and particularly resin type) was more prominent.
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Yoon, Dong-Jin, W. Jason Weiss, and Surendra P. Shah. "Detecting the Extent of Corrosion with Acoustic Emission." Transportation Research Record: Journal of the Transportation Research Board 1698, no. 1 (January 2000): 54–60. http://dx.doi.org/10.3141/1698-08.
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Reinforced concrete beams were tested in flexure, and their acoustic emission (AE) response was recorded. This research was performed to investigate the characteristic AE response that is associated with microcrack development, localized crack propagation, corrosion, and debonding of the reinforcing steel in an attempt to use AE to characterize the source of damage. Concrete beams were prepared to isolate these damage mechanisms by using unreinforced, notched-unreinforced, reinforced, and corroded-reinforced specimens. The AE response was analyzed to obtain key parameters such as the total number and rate of AE events, the amplitude and duration of the events, and the characteristic features of the waveform. Initial analysis of the AE signal has shown that a difference in the AE response can be observed depending on the source of the damage. By plotting the AE signal amplitude versus duration (cross-plot), it can be seen that distributed microcracking is typically characterized by a relatively low amplitude and short duration, whereas debonding cracks have a higher amplitude and longer duration. The Felicity ratio (ratio of the load level at which AE activity begins to occur and the previous loading level) exhibits a favorable correlation with the overall damage level, and the total number of AE events that occur during unloading may provide an effective criterion for estimating the level of corrosion distress in reinforced concrete structures. Based on these results, AE parameter analysis may provide a promising approach for estimating the level of damage and corrosion distress in reinforced concrete structures.
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Mathur, Anirudh K., Vinaya S. Pai, S. Nandini, and Anirban Sarmah. "Finite Element Analysis of Dental Implant as Orthodontic Anchorage." Journal of Contemporary Dental Practice 12, no. 4 (2011): 259–64. http://dx.doi.org/10.5005/jp-journals-10024-1044.
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ABSTRACT Aim The purpose of this three-dimensional (3D) finite element study was to investigate orthodontic loading simulation on a single endosseous implant and its surrounding osseous structure, to analyze the resultant stresses and to identify the changes in the bone adjacent to the implant following orthodontic loading. Materials and methods Two models were constructed using finite element method consisting of endosseous dental implant and the surrounding bone. In the first model, the contact between the implant and the bone was simulated showing no osseointegration, while the second model showed 100% osseointegration. Simulated horizontal loads of 20 N, at 90° from the long axis, were applied to the top of the implant. The study simulated loads in a horizontal direction, similar to a distalmesial orthodontic movement. Results In the first model, the stress was mainly concentrated at the neck of the implant and at the closest surrounding bone. In the second model, the stress was chiefly concentrated at the neck of the implant at the level of the cortical superficial bone. The stresses decreased in the cancellous bone area. On the implant, the highest stress concentration was at the first cervical thread decreasing uniformly to the apex. The stress distribution on the mesial and distal sides showed that the maximum compressive stress was localized mesially and the maximum tensile stress distally. If both models are compared, it can be observed that the stresses were less and more evenly distributed in model 1 (initial stability) than in model 2 when osseointegration was assumed. Conclusion A lack of bony support for the implant represents an unfavorable situation from biomechanical point of view that should be considered and solved. As clinical problems mostly occur at the marginal bone region (bacterial plaque accumulation, overcontoured abutments, infections, osseous defects), attention should be focused on this region. Clinical significance When osseointegrated implants are primarily used as anchorage for orthodontic purposes and then as fixed prosthesis, the functional and structural union of titanium to bone should be preserved. How to cite this article Sarmah A, Mathur AK, Gupta V, Pai VS, Nandini S. Finite Element Analysis of Dental Implant as Orthodontic Anchorage. J Contemp Dent Pract 2011;12(4):259-264.
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Nagulapally, Prashanth, Md Shamsuddoha, Ginu Rajan, Luke Djukic, and Gangadhara B. Prusty. "Distributed Fibre Optic Sensor-Based Continuous Strain Measurement along Semicircular Paths Using Strain Transformation Approach." Sensors 21, no. 3 (January 25, 2021): 782. http://dx.doi.org/10.3390/s21030782.
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Distributed fibre optic sensors (DFOS) are popular for structural health monitoring applications in large engineering infrastructure because of their ability to provide spatial strain measurements continuously along their lengths. Curved paths, particularly semicircular paths, are quite common for optical fibre placement in large structures in addition to straight paths. Optical fibre sensors embedded in a curved path configuration typically measure a component of strain, which often cannot be validated using traditional approaches. Thus, for most applications, strain measured along curved paths is ignored as there is no proper validation tool to ensure the accuracy of the measured strains. To overcome this, an analytical strain transformation equation has been developed and is presented here. This equation transforms the horizontal and vertical strain components obtained along a curved semicircular path into a strain component, which acts tangentially as it travels along the curved fibre path. This approach is validated numerically and experimentally for a DFOS installed on a steel specimen with straight and curved paths. Under tensile and flexural loading scenarios, the horizontal and vertical strain components were obtained numerically using finite element analysis and experimentally using strain rosettes and then, substituted into the proposed strain transformation equation for deriving the transformed strain values. Subsequently, the derived strain values obtained from the proposed transformation equation were validated by comparing them with the experimentally measured DFOS strains in the curved region. Additionally, this study has also shown that a localised damage to the DFOS coating will not impact the functionality of the sensor at the remaining locations along its length. In summary, this paper presents a valid strain transformation equation, which can be used for transforming the numerical simulation results into the DFOS measurements along a semicircular path. This would allow for a larger scope of spatial strains measurements, which would otherwise be ignored in practice.
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Gurtovyi, O., and S. Tynchuk. "INVESTIGATION DEFORMATION OF A MULTILAYERED TRANSVERSAL-ISOTROPIC PLATE ON A RIGID FOUNDATION BY UNFLEXURAL REFINED CONTINUAL MODEL." Mechanics And Mathematical Methods 4, no. 1 (June 2022): 64–74. http://dx.doi.org/10.31650/2618-0650-2022-4-1-64-74.
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The high-precision estimation of the stress-strain state (SSS) of multilayered plates on a rigid foundation under the action of stationary transverse loading is an urgent task. As its includes the calculations of strength and deformability of various homogeneous and multilayer coatings. This is the calculation of road surface on relatively rigid bridge structures, or on a non-deformable underlying layer or calculation protective multilayer coatings of flat structural elements of greater rigidity than coatings, etc. The combining of materials with isotropic and transversal-isotropic physical characteristics into a multilayer package allows creating of the multifunctional designs. The SSS of such structures due to their structural heterogeneity and the relatively low transverse stiffness of the individual layers is significantly associated with the effect of transverse shear deformations and transverse compression deformations. Therefore, the problem of refined modelling of SSS of plates, which takes into account these types of deformations, is an urgent one. Based on the decomposition the SSS of plate into the flexural and unflexural components, it is proposed to optimize the design diagram of deformation a rectangular multilayer plate on a rigid foundation. The essence of optimization is to consider such a design diagram of the plate, in which the SSS of plate would be fully described by only one component, namely the unflexural component of SSS. To do this, instead of the actual design of the multilayer plate, which is deformed without separation from the foundation, it is suggested to consider the design diagram of the plate, which is formed by supplementing it with a symmetric one about the contact surface of the foundation. In this case, the plate will be symmetrically loaded with respect to the middle surface of the plate, and the thickness of the plate will double. The SSS of plate will be unflexural, which greatly simplifies its modeling. For unflexural SSS, a twodimensional and high-degree iterative approximation but three-dimensional by the nature reflection of SSS, model of deformation of multilayer rectangular plates on a rigid foundation with isotropic and transverse-isotropic layers is constructed in an elastic formulation. This model takes full account deformations of transverse shear and of transverse compression at transverse loading of a plate. Calculations of homogeneous and two-layer transverse-isotropic plates on a rigid foundation under the action evenly distributed and localized transverse loads on the surface of a plate are performed by the finite difference method.
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Hamed, Gary R. "Molecular Aspects of the Fatigue and Fracture of Rubber." Rubber Chemistry and Technology 67, no. 3 (July 1, 1994): 529–36. http://dx.doi.org/10.5254/1.3538689.
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Abstract This short review highlights molecular mechanisms controlling the fracture of rubber and rubber reinforcement, with emphasis on the importance of mechano-chemistry. The manuscript is an extension and update of a previous short review published in Rubber Chemistry and Technology in 1991. All solids, including vulcanizates, contain inevitable ubiquitous flaws of various shapes and sizes. When a solid is subjected to a global stress, the local stresses at the tips of these flaws are magnified and can be many times larger than the average applied stress. Generally, there will be a single flaw at which the stress is magnified to the greatest degree and where fracture begins. Macroscopic fracture of vulcanized rubber is a process in which network chains are broken and new free surface area is created as a result of mechanical loading. Loading may be continuously increasing up to fracture (monotonic fracture) or it may be applied periodically, typically at much lower levels, until fracture ensues (fatigue fracture). For example, a specimen which breaks at, say, 20 MPa when loaded monotonically in tension may fracture, nonetheless, at only 5 MPa, if this load is repeatedly applied. In many rubber articles, two important types of fatigue fracture are fatigue crack growth and abrasion. With the former a (bulk) crack initiates (perhaps at an included impurity or microvoid) and grows as a result of “far-field” loading, whereas, with abrasion, fracture is caused by the direct action of frictional, sliding forces. The events occurring at the tip of a crack are quite important in controlling its growth. In particular, if a crack tip becomes blunted during deformation, or if there are other processes occurring which reduce the load borne by the molecular chains at the crack tip, then stress concentration will be reduced and fracture inhibited. If an elastomeric network is capable of dissipating input energy into heat through irreversible molecular motions, less elastic nergy will be available to break network bonds apart, and fracture energy is increased. More on the role of energy dissipation in fracture is given later. Both fatigue crack growth and abrasion are the culmination of accumulated damage due to mechano-chemical processes. Consider a rubbery article which contains a distribution of chain lengths between crosslink points, and which is subject to fatigue. When deformed, chains align, and the load is inequitably carried by the network strands. The network strives to distribute the stress among the chains, but it is limited from completely doing so because of the complex topology. At sufficiently low elongation, no chains are broken, but as deformation progresses, one network chain eventually ruptures. The force that the chain was carrying prior to breakage is quickly distributed among neighboring chains. This results in the overloading and rupture of some of these chains. (Electron spin resonance spectroscopy has been used to detect free radicals resulting from homolytic cleavage of network chains.) At this point, there has been molecular chain breakage (network damage), but no macroscopic fracture (creation of new free surface area). Chain breakage is not random, but rather is more prevalent in those “elements” where chains broke in the first place. If deformation were monotonously continued to a high level, there would be a particular element which experienced more chain rupture than any other, and a macroscopic crack would open there (far-field loading) or a portion of the material would be removed (frictional loading). However, in (mild) fatigue the article is unloaded well before sufficient damage has occurred in the first cycle to cause crack growth or abrasive loss. After the first cycle, the article contains elements with varying degrees of damage. In subsequent cycles there is more chain rupture (damage accumulation) and eventually macroscopic fracture ensues. It is interesting to calculate the number of chains which must break at one location in order to create 1 µm2 of fracture surface. Assuming a chain cross-sectional area of 0.5 nm2, this would require the rupture of 2(106) chains. Nonetheless, the number of localized molecular chain ruptures necessary to constitute the onset of macroscopic fracture is unclear.
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Nickel, J. C., L. R. Iwasaki, Y. M. Gonzalez, L. M. Gallo, and H. Yao. "Mechanobehavior and Ontogenesis of the Temporomandibular Joint." Journal of Dental Research 97, no. 11 (July 13, 2018): 1185–92. http://dx.doi.org/10.1177/0022034518786469.
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Craniofacial secondary cartilages of the mandibular condyle and temporomandibular joint (TMJ) eminence grow in response to the local mechanical environment. The intervening TMJ disc distributes normal loads over the cartilage surfaces and provides lubrication. A better understanding of the mechanical environment and its effects on growth, development, and degeneration of the TMJ may improve treatments aimed at modifying jaw growth and preventing or reversing degenerative joint disease (DJD). This review highlights data recorded in human subjects and from computer modeling that elucidate the role of mechanics in TMJ ontogeny. Presented data provide an approximation of the age-related changes in jaw-loading behaviors and TMJ contact mechanics. The cells of the mandibular condyle, eminence, and disc respond to the mechanical environment associated with behaviors and ultimately determine the TMJ components’ mature morphologies and susceptibility to precocious development of DJD compared to postcranial joints. The TMJ disc may be especially prone to degenerative change due to its avascularity and steep oxygen and glucose gradients consequent to high cell density and rate of nutrient consumption, as well as low solute diffusivities. The combined effects of strain-related hypoxia and limited glucose concentrations dramatically affect synthesis of the extracellular matrix (ECM), which limit repair capabilities. Magnitude and frequency of jaw loading influence this localized in situ environment, including stem and fibrocartilage cell chemistry, as well as the rate of ECM mechanical fatigue. Key in vivo measurements to characterize the mechanical environment include the concentration of work input to articulating tissues, known as energy density, and the percentage of time that muscles are used to load the jaws out of a total recording time, known as duty factor. Combining these measurements into a mechanobehavioral score and linking these to results of computer models of strain-regulated biochemical events may elucidate the mechanisms responsible for growth, maintenance, and deterioration of TMJ tissues.
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LEDOUX, P., D. LAMBLIN, A. WUILBAUT, and F. SCHUIND. "A Finite-Element Analysis of Kienböck’s Disease." Journal of Hand Surgery (European Volume) 33, no. 3 (June 2008): 286–91. http://dx.doi.org/10.1177/1753193408090757.
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A finite-element analysis model of the lunate was established using geometrical data obtained from cadaveric bones. The lunate cortex was modelled with triangular and quadrilateral elements and its intraosseous structure was represented either as a homogenous elastic structure or as an anisotropic network of cortical bone beams (trabeculae) with different orientations and thicknesses. Compressive loads applied to the metacarpus were distributed in the carpus against the fixed radius and ulna. The ulnar variance had a strong influence on the ratios radiolunate/ulnolunate total load and peak pressures. The distribution of internal stresses was markedly affected by the lunate uncovering index. The evolution of a simulated incomplete fracture was dramatically influenced by morphological parameters: with positive ulnar variance, the fracture did not progress, but in the presence of three associated conditions, negative ulnar variance, a high lunate uncovering index and angulated trabeculae, the fracture progressed and the proximal part of the lunate collapsed. This study supports the concept that some lunates are predisposed to Kienböck’s disease because their anatomy induces abnormal internal stresses, which allow an incomplete fracture to progress, under heavy loading conditions, and cause progressive collapse and localised trabecular osteonecrosis.
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Lashkari, Mohammad Javad, and Omid Rahmani. "Bending analysis of sandwich plates with composite face sheets and compliance functionally graded syntactic foam core." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 230, no. 20 (November 14, 2016): 3606–30. http://dx.doi.org/10.1177/0954406215616417.
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In this paper, the problem of a rectangular plate with functionally graded soft core and composite face sheets is considered using high order sandwich plate theory. This theory applies no assumptions on the displacement and stress fields in the core. Face sheets were treated using classical theory and core was exposed to the theory of elasticity. Governing equations and boundary conditions are derived using principle of virtual displacement and the governing equations are based on eight primary variables including six displacements and two shear stresses. This solution is able to present localized displacements and stresses in places where concentrated loads are exerted to the structure since the displacements in the core can take a nonlinear form which could not be seen in the previous theories such as classical and higher order shear theories. This theory is suitable for rectangular plates under all types of loadings distributed or concentrated which can be different on upper and lower face sheets at the same point. The results were compared with the published literature using theory of elasticity and showed good agreement confirming the accuracy of the present theory. Subsequently, the solution for the core with functionally graded material is presented and effectively indicates positive role of functionally graded core.
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Плотников, К. В., В. Н. Тряскин, and В. В. Чижевский. "Recommendations for deck primary supporting members design as applied to pillarless construction of ro-ro ships." MORSKIE INTELLEKTUAL`NYE TEHNOLOGII)</msg>, no. 4(54) (December 2, 2021): 79–88. http://dx.doi.org/10.37220/mit.2021.54.4.071.
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Статья посвящена вопросам определения размеров набора грузовых стационарных палуб морских стальных судов типа Ro-Ro на ранних стадиях проектирования. В силу большого расстояния между поперечными переборками в случае отсутствия пиллерсов карлингсы палуб не являются опорами для рамных бимсов. Однако, как показывает практика, они всегда включаются в конструктивную схему палубы, так как позволяют разнести локальную нагрузку между соседними рамными бимсами, обеспечивают устойчивость их стенок, а также вовлекаются в работу в составе перекрытия при некоторых сценариях нагружения. В литературе отсутствуют рекомендации по выбору расчётной ширины их присоединенного пояска, расчётных значений изгибающих моментов и перерезывающих сил при восприятии нагрузки от разного типа груза. Исследование выполнялось на примере перекрытия грузовой палубы длиной 64,4 м на основе МКЭ. Были разработаны КЭ-модели палубы в балочной и оболочечно-балочной идеализациях. Вторая модель использовалась для оценки адекватности результата, получаемого на более простой модели. Рассмотрены 8 сценариев нагрузки. При определении ширины присоединенного пояска за величину условного пролёта принималось расстояние между точками, в которых величина изгибающего момента принимает нулевое значение. Показано, что карлингсы активно вовлекаются в работу при частичной загрузке трюма контейнерами в несколько ярусов, а также при работе погрузчика. Расчётная ширина их присоединенного пояска составила 0,60…0,75 расстояния между карлингсами при действии нагрузки от колёсной техники и оказалась близка к этому расстоянию при восприятии нагрузки от контейнеров при их поперечной укладке. Авторами предложено в качестве первого приближения значение расчётного изгибающего момента для карлингсов определять в долях от соответствующего значения для рамных бимсов. The paper deals with a design of deck primary structures of Ro-Ro vessels at early design stages. Due to the large distance between transverse bulkheads, in the case of no pillar construction, deck girders cannot be considered as supports for deck transverses. The common practice however, is to provide deck structures with deck girders anyway. It helps to distribute the local loads between transverses and to ensure the stability of deck transverses web plates. In addition, for a localized loads on deck structures girders to some extent contribute to local strength of the deck. Practically, deck girder scantlings are usually larger than those based on the minimum thickness, web depth and slenderness requirements of classification society rules. There are no publications proposing recommendations for deck girders design in pillarless structures of ro-ro ships at the early stages. Prescriptive recommendations should primarily include design bending moment value and effective breadth of the attached plate in different loading scenarios. The results presented in this paper are based on the linear finite element (FE) analysis of Ro-Ro deck having a length of 64.4 meters. Since the goal of the study was to develop recommendations for structural design aligned with prescriptive requirements of RS rules the research is provided with beam analysis carried out for 8 different loading scenarios. All of the reference calculations were made in FESTA-2020 software developed in SMTU as a part of CAD/СAE software ALMAZ-K. Verification is made with more sophisticated shell model analysis carried out in ANSYS with similar assumptions. The effective breadth of deck girders attached plate is calculated considering a distance between zero bending moment points as a nominal span. It is shown that the deck girders are highly stressed in loading cases with stacked containers and working fork lift. The calculated width of their attached plate which is in range from 0.60 to 0.75 of the distance between girders S under the load from the wheeled vehicles turns out to be close to Sin case of loading of transversely stacked containers. The authors propose to determine value of the design bending moment for deck girders at the early stages depending on span and loading of deck transverses.
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Taheri, Ramezan Ali, Reza Razaghi, Ali Bahramifar, Mahdi Morshedi, Majid Mafi, and Alireza Karimi. "Interaction of the Blood Components with Ascending Thoracic Aortic Aneurysm Wall: Biomechanical and Fluid Analyses." Life 12, no. 9 (August 24, 2022): 1296. http://dx.doi.org/10.3390/life12091296.
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Background: Ascending thoracic aortic aneurysm (ATAA) is an asymptomatic localized dilation of the aorta that is prone to rupture with a high rate of mortality. While diameter is the main risk factor for rupture assessment, it has been shown that the peak wall stress from finite element (FE) simulations may contribute to refinement of clinical decisions. In FE simulations, the intraluminal boundary condition is a single-phase blood flow that interacts with the thoracic aorta (TA). However, the blood is consisted of red blood cells (RBCs), white blood cells (WBCs), and plasma that interacts with the TA wall, so it may affect the resultant stresses and strains in the TA, as well as hemodynamics of the blood. Methods: In this study, discrete elements were distributed in the TA lumen to represent the blood components and mechanically coupled using fluid–structure interaction (FSI). Healthy and aneurysmal human TA tissues were subjected to axial and circumferential tensile loadings, and the hyperelastic mechanical properties were assigned to the TA and ATAA FE models. Results: The ATAA showed larger tensile and shear stresses but smaller fluid velocity compared to the ATA. The blood components experienced smaller shear stress in interaction with the ATAA wall compared to TA. The computational fluid dynamics showed smaller blood velocity and wall shear stress compared to the FSI. Conclusions: This study is a first proof of concept, and future investigations will aim at validating the novel methodology to derive a more reliable ATAA rupture risk assessment considering the interaction of the blood components with the TA wall.
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Sjostedt, S. J., J. G. Slowik, J. R. Brook, R. Y. W. Chang, C. Mihele, C. A. Stroud, A. Vlasenko, and J. P. D. Abbatt. "Diurnally resolved particulate and VOC measurements at a rural site: indication of significant biogenic secondary organic aerosol formation." Atmospheric Chemistry and Physics 11, no. 12 (June 21, 2011): 5745–60. http://dx.doi.org/10.5194/acp-11-5745-2011.
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Abstract. We report simultaneous measurements of volatile organic compound (VOC) mixing ratios including C6 to C8 aromatics, isoprene, monoterpenes, acetone and organic aerosol mass loadings at a rural location in southwestern Ontario, Canada by Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) and Aerosol Mass Spectrometry (AMS), respectively. During the three-week-long Border Air Quality and Meteorology Study in June–July 2007, air was sampled from a range of sources, including aged air from the polluted US Midwest, direct outflow from Detroit 50 km away, and clean air with higher biogenic input. After normalization to the diurnal profile of CO, a long-lived tracer, diurnal analyses show clear photochemical loss of reactive aromatics and production of oxygenated VOCs and secondary organic aerosol (SOA) during the daytime. Biogenic VOC mixing ratios increase during the daytime in accord with their light- and temperature-dependent sources. Long-lived species, such as hydrocarbon-like organic aerosol and benzene show little to no photochemical reactivity on this timescale. From the normalized diurnal profiles of VOCs, an estimate of OH concentrations during the daytime, measured O3 concentrations, and laboratory SOA yields, we calculate integrated local organic aerosol production amounts associated with each measured SOA precursor. Under the assumption that biogenic precursors are uniformly distributed across the southwestern Ontario location, we conclude that such precursors contribute significantly to the total amount of SOA formation, even during the period of Detroit outflow. The importance of aromatic precursors is more difficult to assess given that their sources are likely to be localized and thus of variable impact at the sampling location.
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Giunta, G., F. Biscani, S. Belouettar, and E. Carrera. "Hierarchical modelling of doubly curved laminated composite shells under distributed and localised loadings." Composites Part B: Engineering 42, no. 4 (June 2011): 682–91. http://dx.doi.org/10.1016/j.compositesb.2011.02.002.
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Halperin, Ana V., José Luis Cortés Cuevas, Juan Antonio Del Castillo Polo, Miriam Cuesta, Sergio Talens, Robert Birch, Ana María Sánchez Díaz, and Rafael Cantón. "11. Evaluation of the Bact/alert® VIRTUO™ in Terms of Time to Detection, Performance, Workflow Efficiency and Impact on Patient Management, Compared to the BACTEC™ FX Automated Blood Culture System." Open Forum Infectious Diseases 7, Supplement_1 (October 1, 2020): S7. http://dx.doi.org/10.1093/ofid/ofaa417.010.
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Abstract Background Bloodstream infections are associated with high rates of morbidity and mortality, therefore prompt identification and antimicrobial susceptibility testing of the causative organism(s) are critical. We compared the microbiological/clinical performance of BacT/ALERT®-VIRTUO™-(BioMerieux) to that of the BACTEC™FX-(BD) instrument, with time-to-detection (TTD, from loading into system until positivity) as the primary outcome. Secondary microbiological outcomes were positivity and contamination rates, hands-on-time, turn-around-time (TAT) and time-to-identification. Methods We performed a prospective cross-over study using blood cultures from patients (>18 years) suspected of bacteremia/fungemia, localized in different wards into two strata (Stratum-1: Emergency Department-ED-; Stratum-2: in-hospital patients). Testing was performed in BACTEC™-PlusAerobic/F and BACTEC-Lytic/10-Anaerobic/F bottles and incubated in BACTEC™FX, or BacT/ALERT®FA-Plus and FN-Plus bottles and incubated in VIRTUO™. Initially, each strata was randomly assigned to one of the incubators and then alternated every 2-weeks for 6 months (October-16th-2018 to April-16th-2019). All samples were processed in parallel with the same work-flow from the moment they were flagged positive. Maximum incubation time was 5 days. Results We included a total of 4782 extractions (9510 bottles) in VIRTUO and 5139 (10193 bottles) in BACTEC. The median age was 67 years for both groups and the samples were equally distributed for each ward (ED: VIRTUO 80.9%, BD 76.4%). The number of blood cultures with at least one positive extraction was 873(18.3%) for VIRTUO and 802(15.6%) for BACTEC (p=0.0003). TTD and proportion of aerobic/anaerobic bottles is shown in Table. Hands-on-time was reduced by 15 minutes/day when using VIRTUO. Table Conclusion We have compared on a large scale and in a “real world” setting the performance of two automatic blood culture incubators. TTD was significantly lower for the VIRTUO incubated samples, with differences in both systems depending on the type of bottle (aerobic vs. anaerobic). The number of positive results was significantly higher for the VIRTUO incubated samples, which might impact antimicrobial prescription and clinical outcomes. Disclosures Ana V. Halperin, MD, Biomérieux (Grant/Research Support) José Luis Cortés Cuevas, MD, biomerieux (Research Grant or Support)biomerieux (Research Grant or Support) Juan Antonio Del Castillo Polo, MD, Biomérieux (Research Grant or Support) Sergio Talens, n/a, Biomerieux (Research Grant or Support) Robert Birch, n/a, bioMerieux Inc. (Employee) Rafael Cantón, PharmD PhD, Biomérieux (Grant/Research Support)
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Baer, S. M., and J. Rinzel. "Propagation of dendritic spikes mediated by excitable spines: a continuum theory." Journal of Neurophysiology 65, no. 4 (April 1, 1991): 874–90. http://dx.doi.org/10.1152/jn.1991.65.4.874.
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1. Neuroscientists are currently hypothesizing on how voltage-dependent channels, in dendrites with spines, may be spatially distributed or how their numbers may divide between spine heads and the dendritic base. A new cable theory is formulated to investigate electrical interactions between many excitable and/or passive dendritic spines. The theory involves a continuum formulation in which the spine density, the membrane potential in spine heads, and the spine stem current vary continuously in space and time. The spines, however, interact only indirectly by voltage spread along the dendritic shaft. Active membrane in the spine heads is modeled with Hodgkin-Huxley (HH) kinetics. Synaptic currents are generated by transient conductance increases. For most simulations the membrane of spine stems and dendritic shaft is assumed passive. 2. Action-potential generation and propagation occur as localized excitatory synaptic input into spine heads causes a few excitable spines to fire, which then initiates a chain reaction of spine firings along a branch. This sustained wavelike response is possible for a certain range of spine densities and electrical parameters. Propagation is precluded for spine stem resistance (Rss) either too large or too small. Moreover, even if Rss lies in a suitable range for the local generation of an action potential (resulting from local synaptic excitatory input), this range may not be suitable to initiate a chain reaction of spine firings along the dendrite; success or failure of impulse propagation depends on an even narrower range of Rss values. 3. The success or failure of local excitation to spread as a chain reaction depends on the spatial distribution of spines. Impulse propagation is unlikely if the excitable spines are spaced too far apart. However, propagation may be recovered by redistributing the same number of equally spaced spines into clusters. 4. The spread of excitation in a distal dendritic arbor is also influenced by the branching geometry. Input to one branch can initiate a chain reaction that accelerates into the sister branch but rapidly attenuates as it enters the parent branch. In branched dendrites with many excitable and passive spines, regions of decreased conductance load (e.g., near sealed ends) can facilitate attenuating waves and enhance waves that are successfully propagating. Regions of increased conductance load (e.g., near common branch points) promote attenuation and tend to block propagation. Non-uniform loading and/or nonuniform spine densities can lead to complex propagation characteristics. 5. Some analytic results of classical cable theory are generalized for the case of a passive spiny dendritic cable.(ABSTRACT TRUNCATED AT 400 WORDS)
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Derbel, Bilel, Jérémie Humeau, Arnaud Liefooghe, and Sébastien Verel. "Distributed localized bi-objective search." European Journal of Operational Research 239, no. 3 (December 2014): 731–43. http://dx.doi.org/10.1016/j.ejor.2014.05.040.
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Stepanov, G. V., and V. A. Fedorchuk. "Localized shear in metals under impact loading." Le Journal de Physique IV 10, PR9 (September 2000): Pr9–707—Pr9–712. http://dx.doi.org/10.1051/jp4:20009118.
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Stepanov, G. V., and V. A. Fedorchuk. "Localized shear in metals under impact loading." Strength of Materials 32, no. 2 (March 2000): 125–35. http://dx.doi.org/10.1007/bf02511670.
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Snyder, G. Jeffrey, Saniya LeBlanc, Doug Crane, Herschel Pangborn, Chris E. Forest, Alex Rattner, Leah Borgsmiller, and Shashank Priya. "Distributed and localized cooling with thermoelectrics." Joule 5, no. 4 (April 2021): 748–51. http://dx.doi.org/10.1016/j.joule.2021.02.011.
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Gavoille, Cyril, and David Peleg. "Compact and localized distributed data structures." Distributed Computing 16, no. 2-3 (September 1, 2003): 111–20. http://dx.doi.org/10.1007/s00446-002-0073-5.
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Thompson, Richard F. "Are memory traces localized or distributed?" Neuropsychologia 29, no. 6 (January 1991): 571–82. http://dx.doi.org/10.1016/0028-3932(91)90011-v.
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Hoo Fatt, Michelle S., and Tomasz Wierzbicki. "Damage of plastic cylinders under localized pressure loading." International Journal of Mechanical Sciences 33, no. 12 (January 1991): 999–1016. http://dx.doi.org/10.1016/0020-7403(91)90055-8.
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Erofeev, Vladimir I., Sergey I. Gerasimov, and Alexey O. Malkhanov. "Nonlinear Spatial Localized Strain Waves." EPJ Web of Conferences 183 (2018): 02030. http://dx.doi.org/10.1051/epjconf/201818302030.
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A possible way of study of single waves in solids is discussed. The soliton is one of these waves without shape and parameters varying. Soliton deformation parameters are connected with the elastic moduli of the third order that allows defining values of these moduli by means of the measured solitondeformation parameters in various type waveguides made of the same material. The conditions under which a soliton can exist in a rod are analytically determined. For simultaneous excitation of loading in several wave guides two new energetic photosensitive structures (the mixtures are given) initiated by means of short light impulses of noncoherent light sources are proposed. Conditions of excitation of the waves on the basis of multipoint optical initiation loading impulses are described. As a technique for registration the shadowgraph visualization is proposed. It is discussed, how the problem connected to the use of energetic initiation structures consisting in the power background illumination can be solved. The shadow scheme with the use of a tiny dot explosive light source (Tbr ~41 kK) allows to carry out modelling experiments on research of slabbing actions, jet formations, fluffings, hydrodynamic instability during shock-wave loading of investigated samples, which makes it attractive for determination of parameters in equations-of-state for investigated materials, creation of numerical models and their validation. Some examples showing basic possibility of application of the declared techniques are included.