Stress Pulse Research Articles

Marking Stress ExPLICitly in Written English Fosters Rhythm in the Reader's Inner Voice

AbstractSpoken English has a stress‐alternating rhythm that is not marked in its orthography. In two experiments, the authors evaluated whether stylistic alterations to print that marked stress pulses fostered the rendering of rhythm (experiment 1) and stress (experiment 2) during silent reading. In experiment 1, silent readers rated the helpfulness of the stylistic alterations appearing in the last line of poems. In experiment 2, silent readers rated the helpfulness of the stylistic alterations appearing in heteronyms embedded in prose. As predicted by linguistic theories, when the stylistic alterations mapped onto the rhythmic pulses of the poems, and the lexically stressed syllables of the heteronyms, silent readers rated these alterations as more helpful compared with the incongruous conditions. In experiment 2, readers’ inner voices were more tuned to the prosodic nuances of the first syllable than the second in the bisyllabic heteronyms. This prosodic tuning for the first syllable in a word was likely afforded by the strong tendency for stress to appear word‐initially. In addition, the stylistically marked stress was viewed as more helpful in the early half of the sentence, when readers likely recruited more bottom‐up processes. In both experiments, prior exposure to poetry was related to a refined prosodic awareness. In experiment 2, exposure to poetry predicted participants’ prosody sensitivity, after controlling for the other predictors of academic achievement. The authors’ ongoing studies are evaluating whether marking stress explicitly in written English might aid struggling readers and late speakers of English.

Meso-scale mechanism of compaction shock propagation in cellular materials

The meso-scale mechanism of a compaction shock in a cellular material is investigated numerically using a 2D Voronoi cellular model. The compaction shock is initiated by the compression of a 2D Voronoi cellular model at constant velocities sufficiently higher than the critical shock velocity. The compaction shock is featured by the propagation of a nearly planar (1D) shock front, across which, macroscopic physical quantities (i.e. stress, strain, particle velocity and density) show strong discontinuity. The 1D cross-sectional stress in the Voronoi model is decomposed into deformation-induced stress and contact-induced stress. It shows that the contact-induced stress plays a dominant role in the shock stress enhancement in dynamic compression. It is shown that the velocity-dependent inertia term in the 1D shock stress equation derived from conservation laws in continuum mechanics is the contact-induced stress produced by the internal collisions of cell walls in meso-scale at the compaction shock front. The internal collisions accelerate the adjacent layer of cell walls to the compression velocity rapidly, and a velocity discontinuity at the shock front is formed for the next internal collision. Meanwhile, the local cell-wall acceleration leads to an inertial pulse of the deformation-induced stress, which is generally smaller than the contact-induced stress. It is found that the stress distribution in the region ahead of shock-front is non-uniform. These findings reveal the meso-scale mechanisms of the compaction shock propagation in cellular materials subjected to intensive dynamic loads.

Reduction of interface traps between poly-Si and SiO2 layers through the dielectric recovery effect during delayed pulse bias stress

We investigate the interface trap behavior between tunneling oxide and poly-Si channel layer post erase/write cycling with a delayed pulse by using deep level transient spectroscopy. For comparison of the defect states depending on the stress pulses, a Schottky and a metal–oxide semiconductor device were fabricated. A defect state at about Ec −0.51 eV in the Schottky device was measured before the annealing process. Three-hole trap states with activation energies of Ev +0.28 eV, Ev +0.53 eV, and Ev +0.76 eV appeared after the post-annealing process. The electron trap was about Ec −0.15 eV after erase/write 3000 cycling was applied at ±10 V for 100 ms at 25 °C and 85 °C. These defect states may have an effect on the charge loss behavior of the electrons localized in the charge trap layer at the retention mode of three-dimensional non-volatile memory devices. Dramatically, after the endurance stress was applied with a delayed pulse of 300 cycling at 85 °C for 50.4 h, no interface traps of the deep level transient spectroscopy spectra appeared. Dielectric recovery can decrease the density of the interface trap and improve the retention properties. This may have been caused by the passivation effect on the dangling bond of the interface traps.

Impact of AlN layer sandwiched between the GaN and the Al2O3 layers on the performance and reliability of recessed AlGaN/GaN MOS-HEMTs

This work compares the performance and the reliability of recessed-gate AlGaN/GaN MOS-HEMTs with two different gate dielectrics: a single layer of Al2O3 and a bilayer of AlN/Al2O3. Although the normally-OFF operation is well observed in the AlN/Al2O3 device, the other characteristics are remarkable poor and directly prejudice the performance of the device. PBTI phenomenon was studied by using a pulse characterization technique in order to capture the fast charge trapping when a single stress pulse is applied to the gate contact. The physical origin of PBTI is ascribed to electron trapping and de-trapping in defect sites located in the gate dielectrics. The results during the stress phase show that the positive threshold voltage shift (ΔVth) in both devices follows a saturating log-time dependence model. From this analysis, the double stack exhibits a higher saturation threshold voltage and a faster trap time constant compared with the single layer device. The universal relaxation function fits well the experimental data during the relaxation phase at different stress pulse widths and clearly shows a faster defect discharge in the Al2O3 device.

Press-pulse: a novel therapeutic strategy for the metabolic management of cancer

BackgroundA shift from respiration to fermentation is a common metabolic hallmark of cancer cells. As a result, glucose and glutamine become the prime fuels for driving the dysregulated growth of tumors. The simultaneous occurrence of “Press-Pulse” disturbances was considered the mechanism responsible for reduction of organic populations during prior evolutionary epochs. Press disturbances produce chronic stress, while pulse disturbances produce acute stress on populations. It was only when both disturbances coincide that population reduction occurred.MethodsThis general concept can be applied to the management of cancer by creating chronic metabolic stresses on tumor cell energy metabolism (press disturbance) that are coupled to a series of acute metabolic stressors that restrict glucose and glutamine availability while also stimulating cancer-specific oxidative stress (pulse disturbances). The elevation of non-fermentable ketone bodies protect normal cells from energy stress while further enhancing energy stress in tumor cells that lack the metabolic flexibility to use ketones as an efficient energy source. Mitochondrial abnormalities and genetic mutations make tumor cells vulnerable metabolic stress.ResultsThe press-pulse therapeutic strategy for cancer management is illustrated with calorie restricted ketogenic diets (KD-R) used together with drugs and procedures that create both chronic and intermittent acute stress on tumor cell energy metabolism, while protecting and enhancing the energy metabolism of normal cells.ConclusionsOptimization of dosing, timing, and scheduling of the press-pulse therapeutic strategy will facilitate the eradication of tumor cells with minimal patient toxicity. This therapeutic strategy can be used as a framework for the design of clinical trials for the non-toxic management of most cancers.

Shear Stress Stimulated MSC Activities: Direct Changes of Membrane Tension or Cytoskeletal Stress?

Fluid shear stress induced membrane transport such as Ca2+ influx and the activation of ion channels has been widely reported. The shear stress can be mediated by a direct change in bilipid membrane tension and/or by a change in cytoskeletal stress via binding proteins that link channels to actin, but how the shear stress is coupled to ion channels is unclear. Using narrow shear pulse stimuli generated by a pressure servo in a microfluidic chamber, we measured the changes of membrane tension and cytoskeletal protein stress simultaneously in astrocytes. The membrane tension was reported using molecular motor probes (2-carboxy-2-cyanovinyl)-julolidine farnesyl ester (FCVJ) and cytoskeletal tension reported by genetically encoded force probe actinin-cpst-FRET. Our results show that the changes of membrane tension are highly localized and the gradient is relevant to the flow directions. A shear stress pulse (23 dyn/cm2, 400 ms duration) caused a rapid increase in membrane tension at the front edge of the cell with respect to the flow and a decrease in tension (compression) at the distal edge. The rise time was less than 30 ms, and the tension dropped to the initial state within ∼30 ms post stimulus, showing a typical elastic behavior. In contrast, the same shear pulse generated profound and long-lasting tension in cytoskeletal cross-linking proteins α-actinin at the front edge of the cell, and the tension persisted for the entire experimental duration of 60 s. In situ Ca2+ imaging showed that the initial Ca2+ influx was strongly correlated with the region having high cytoskeletal tension, but weakly linked to the bilayer tension. The results suggest the cytoskeletal tension plays primary role in shear stress activated Ca2+ influx. This work was funded by NINDS.

On some principal features of data processing of spall fracture tests

A method for processing the results of dynamic spall fracture tests, based on the exact solution of the wave equation, and its commonly used simplified version based on the assumed unique relation between the free surface velocity drop and the ultimate medium fracture stress, are analyzed. Using the considered exact solutions of the wave technique, tensile stress pulses during spalling are determined. The obtained stress levels at the fracture point are compared with the spall strength calculated by the velocity drop technique. The cases of agreement and disagreement of the results obtained using both techniques are shown. By the example of differently shaped loading pulses, possible scenarios of sample fracture are presented, in particular, the probability of the fracture delay effect is shown, which can be lost in the simplified processing method.

Effect of Strain Rate on Tension Response of Filled Silicone Rubber

Uniaxial tension tests for filled silicone rubber were performed at high strain rates using a split Hopkinson tension bar system. Quasi-static tension tests were carried out using an Instron-E3000 material test system. The grip fixture was designed to reliably connect the tensile specimen with the incident/transmitted bars. The method to increase the signal-noise ratio of the stress pulse in the transmitted bar was proposed. The effect of specimen gage length-to-width ratio on the stress-strain responses was experimentally studied. The suitable specimen geometry was determined by means of experimental investigation and finite element analysis. The automated grid method was used to capture the deformation information of the tensile specimen. Experiments indicate that the tension responses of silicone rubber exhibit the apparent hyper-elastic and rate-dependent characteristics. The values of tensile modulus increase with the increase of strain rate. The stress at a given elongation increases with the increase of strain rate.

Stress Propagation through Biological Lipid-Bilayers Revealed by Atomistic and Coarse-Grained Simulations

Membrane tension has been shown to play various critical roles in cell signaling. We here asked if and how pulses of local stress dynamically propagate through membranes, and propose this mechanism as a novel way of quickly propagating signals along the membrane.In both atomistic and coarse-grained MARTINI molecular dynamics simulations of biological lipid-bilayers, we observed short stress pulses to very efficiently propagate laterally at a velocity of the order of km/s, in close agreement with the expected speed of sound. The temperature dependence of pulse propagation shows tendencies very comparable to analogous experiments [1,2,3], with insightful differences between the atomistic and coarse-grained simulations. Remarkably, the propagation of the lateral stress was damped at length scales in the ∼100 nm range. Our data supports the notion of lateral stress propagation through membranes as a potential ultrafast way of short-range signal propagation in biology [4].[1] W. Schrader, et al. J. Phys. Chem. B. 106:6581-6586 (2002)[2] S. Shrivastava S and MF Schneider. J. R. Soc. Interface 11:20140098 (2014).[3] J. Kappler and R. Netz. EPL. 112: 19002 (2015)[4] C. Aponte-Santamaria and F. Grater. In preparation

Probabilistic Modeling of Tracked Vehicle Mover And Ground Interaction

The article is devoted to ensuring the strength reliability of the tracked vehicle running gear. The method of estimation of track link fatigue life is proposed. The technique is based on the method of resource modeling at the design stage of the machine. The technique involves computer modeling of movement of the machine on the road, the calculation of loads acting on the track, stresses in the most loaded areas of tracks and forecasting of durability based on the fatigue failure criterion. The simulation accounts for the dynamic properties of the machine and the typical working conditions in a variety of natural and climatic conditions.The laws of track link loading are determined based on the results of field tests. The maximum stress in track link arises in the moments when the wheels pass on the track. The stress value and pulses signs depend on the dynamic loads from the road wheels and ground reactions, randomly distributed over the surface of the track.To calculate the loads acting on the track in the supporting part of a caterpillar, a ground model is proposed. The ground is regarded as a Winkler half-space with randomly distributed elastic elements, which interact with caterpillar track. The results of the ground model identification and the method of calculating the loads acting on the track are presented. The load change processes are then used to calculate the stresses in the most loaded areas of a track and to predict the fatigue life.

The Effect of Acute Stress on Esophageal Motility and Gastroesophageal Reflux in Healthy Humans.

Background/AimsLittle research has been done to evaluate the effect of stress in exacerbating the symptoms associated with gastroesophageal reflux (GER). We aimed to investigate the effect of acute stress on esophageal motility and GER parameters in healthy volunteers.MethodsA total of 10 (M:F = 8:2, median age 34 years-old) healthy volunteers without any recurrent gastrointestinal symptoms participated in this study. They underwent esophageal high-resolution manometry with 10 wet swallows (Experiment I) and esophageal impedance-pH monitoring (Experiment II) in the basal period and in the stress period. In the stress period, either real stress or sham stress was given in a randomized cross-over design. The stress scores, symptom severity, and pulse rates were measured.ResultsThe stress scores and the severity of nausea were significantly greater under real stress, compared with sham stress. The percentages of weak, failed, rapid, premature, and hyper-contractile contractions were not significantly altered during real stress and during sham stress, compared with the basal period. The median resting pressure of the lower esophageal sphincter and distal contractile integral of esophageal contractions did not differ in the stress period, compared with the basal period. Contractile front velocity and distal latency of esophageal peristaltic contractions were significantly changed during real stress, which was not observed during sham stress. GER parameters were not significantly altered during real stress and during sham stress.ConclusionAlthough acute auditory and visual stress seems to affect esophageal body motility, it does not induce significant motor abnormalities or increase GER in healthy humans.

Reflection and Transmission of Longitudinal Elastic Stress Pulses at a Discontinuity of Two Dissimilar Cylindrical Bars

Reflection and Transmission of Longitudinal Elastic Stress Pulses at a Discontinuity of Two Dissimilar Cylindrical Bars

The structural temporal approach to dynamic and quasi-static strength of rocks and concrete

This work presents results of an experimental and theoretical study on dynamic and quasi-static failure of rocks and concrete. The results of dynamic compression and splitting of rocks (gabbro, granite, marble), as well as dry, water-saturated and frozen limestone and concrete are discussed. The tests were conducted using the Split-Hopkinson pressure bar with the diameter of 20 mm. It is shown that one material (or its condition) can have a lower dynamic strength for a higher static strength compared to the other material (or its condition). Also, it is shown a dependence of the threshold limit stress on the stress pulse duration. An unified interpretation of the experimental results, based on the structural–temporal approach is presented.

Mathematical Modeling of the Concentrated Energy Flow Effect on Metallic Materials

Numerous processes take place in materials under the action of concentrated energy flows. The most important ones include heating together with the temperature misdistribution throughout the depth, probable vaporization on the surface layer, melting to a definite depth, and hydrodynamic flotation; generation of thermo-elastic waves; dissolution of heterogeneous matrix particles; and formation of nanolayers. The heat-based model is presented in an enthalpy statement involving changes in the boundary conditions, which makes it possible to consider melting and vaporization on the material surface. As a result, a linear dependence of penetration depth vs. energy density has been derived. The model of thermo-elastic wave generation is based on the system of equations on the uncoupled one-dimensional problem of dynamic thermo-elasticity for a layer with the finite thickness. This problem was solved analytically by the symbolic method. It has been revealed for the first time that the generated stress pulse comprises tension and compression zones, which are caused by increases and decreases in temperature on the boundary. The dissolution of alloying elements is modeled on the example of a titanium-carbon system in the process of electron beam action. The mathematical model is proposed to describe it, and a procedure is suggested to solve the problem of carbon distribution in titanium carbide and liquid titanium-carbide solution in terms of the state diagram and temperature changes caused by phase transitions. Carbon concentration vs. spatial values were calculated for various points of time at diverse initial temperatures of the cell. The dependence of carbon particle dissolution on initial temperature and radius of the particle were derived. A hydrodynamic model based on the evolution of Kelvin-Helmholtz instability in shear viscous flows has been proposed to specify the formation of nanostructures in materials subjected to the action of concentrated energy flows. It has been pointed out for the first time that, for certain parameters of the problem, that there are two micro- and nanoscale peaks in the relation of the decrement to the wavelength of the interface disturbance.

A Parametric Study for the Design of an Optimized Ultrasonic Percussive Planetary Drill Tool.

Traditional rotary drilling for planetary rock sampling, in situ analysis, and sample return are challenging because the axial force and holding torque requirements are not necessarily compatible with lightweight spacecraft architectures in low-gravity environments. This paper seeks to optimize an ultrasonic percussive drill tool to achieve rock penetration with lower reacted force requirements, with a strategic view toward building an ultrasonic planetary core drill (UPCD) device. The UPCD is a descendant of the ultrasonic/sonic driller/corer technique. In these concepts, a transducer and horn (typically resonant at around 20 kHz) are used to excite a toroidal free mass that oscillates chaotically between the horn tip and drill base at lower frequencies (generally between 10 Hz and 1 kHz). This creates a series of stress pulses that is transferred through the drill bit to the rock surface, and while the stress at the drill-bit tip/rock interface exceeds the compressive strength of the rock, it causes fractures that result in fragmentation of the rock. This facilitates augering and downward progress. In order to ensure that the drill-bit tip delivers the greatest effective impulse (the time integral of the drill-bit tip/rock pressure curve exceeding the strength of the rock), parameters such as the spring rates and the mass of the free mass, the drill bit and transducer have been varied and compared in both computer simulation and practical experiment. The most interesting findings and those of particular relevance to deep drilling indicate that increasing the mass of the drill bit has a limited (or even positive) influence on the rate of effective impulse delivered.

Propagating Behavior of Stress Pulses in Large Diameter Hopkinson Tube

A large diameter Hopkinson tube has been developed to measure the dynamic fracture toughness of materials. The stress wave propagation behavior in the Hopkinson tube under different impact conditions were studied both experimentally and numerically. Both the experimental and simulated results indicated that the characteristics of the incident stress pulse critically depended on the impact alignment conditions. When the striker tube impacts the incident tube in an axial, normal alignment condition, the incident pulse shows an obvious dispersive effect. While under an oblique impact condition, a smooth incident pulse with a long rise time is achieved. Therefore, an oblique impact pulse shaping technique is proposed in this study.

Coupling of shear-circumferential stress pulses investigation through stress phase angle in FSI models of stenotic artery using experimental data.

Many cardiovascular diseases are closely associated with hemodynamic parameters. The main purpose of this study is mimicking a physiological blood flow in stenotic arteries to provide an understanding of hemodynamic parameters. An experimental setup was designed to produce original pulsatile flow and measure pressure pulse waves through a compliant tube. Moreover, a numerical model considering fluid-solid interaction was developed to investigate wall shear stress and circumferential stress waves, based on the results of the experiments. Results described elevated mean pressure by increasing stenosis severity especially at the critical obstacle of 50%, which the pressure rose significantly and raised up by 10mm Hg that may cause damage in endothelial cells. Increasing in stenosis severity led to: more negative wall shear stress and more oscillation of shear stress at the post-stenotic region and also more absolute value of angular phase difference between wall shear stress and circumferential stress waves at the stenotic throat. All of the aforementioned parameters determinant the endothelial cell pathology in predication of potential sites of progression of atherosclerotic plaques. Therefore, results can be applied in study of plaque growth and mechanisms of arterial remodeling in atherosclerosis.

Rate independence of material properties and remnant state variables during domain switching by electric field or stress in ferroelectric ceramics at room and high temperatures

Various numbers of electric field or compressive stress pulses with increasing magnitude are applied to a poled lead titanate zirconate rectangular parallelepiped specimen. Changes in linear material properties are estimated from measured responses and plotted versus remnant polarization. The dependence of linear material properties on remnant polarization is shown to be the same independent of the overall rate of domain switching by electric field or stress at room and high temperatures. The evolution path of remnant polarization and strains in the plane of remnant state variables is also found to be equal independent of switching rate at room and high temperatures. Finally, when the values of remnant state variables at high temperature are transformed to those of reference remnant state variables, the evolution path of the reference remnant state variables is compared to be coincident with that of remnant state variables at room temperature, implying the same switching process at different temperatures.

A prediction model for the dynamic mechanical degradation of sedimentary rock after a long-term freeze-thaw weathering: Considering the strain-rate effect

Rock engineering and stone construction in cold region are always suffering the recurrent freeze-thaw (F-T), and rock mechanical behaviors in projects usually involve responses to stress pulses or impact loads due to the widely existed blasting operation, mechanized construction and seismic oscillation. In this work, physical tests as well as static and impact mechanical experiments were carried out on red-sandstone free from and after F-T weathering. Totally five specimen groups were prepared for static and dynamic compressive tests respectively, of which one group was water-saturated and free from F-T, and four groups were water-saturated and then respectively suffered by 5, 10, 15, 25 cycles of artificial F-T. Changes of physico-mechanical properties of red-sandstone after F-T cycles, including density, porosity, P-wave velocity, uniaxial compressive strength (UCS) and deformation modulus (Ed), illustrated the F-T induced damages of sedimentary rock. For a better predicting of the dynamic mechanical degradation of sedimentary rock after a long-term F-T weathering, decay models of mechanical properties reflecting the strain rate effects were built. The UCS and Ed were adopted as the integrity indexes of rock in the decay model, and the model parameters, decay constant (λ) and half-life (N1/2) were expressed as functions of strain rate.

Effects of accelerator type on stress relaxation behavior and network structure of aged natural rubber/chloroprene rubber vulcanizates

Natural rubber/chloroprene rubber (NR/CR) blends are among the commonly used rubber blends in industry and continuously are exposed to severe weather changes. To investigate the effects of accelerator type on the network structure and stress relaxation of unaged and aged NR/CE vulcanizates, tetramethyl thiuram disulfide, 2-mercaptobenzothiazole, and diphenyl guanidine accelerators have been chosen to represent fast, moderate, and slow accelerator groups, respectively. Three batches have been prepared with exactly the same components and mixing conditions differing only in accelerator type. Temperatures scanning stress relaxation and pulse nuclear magnetic resonance techniques have been used to reveal the structural changes of differently accelerated rubber blends before and after weathering. Nonoxidative thermal decomposition analyses have been carried out using a thermogravimetric analyzer. Results indicate that there is a strong interdependence between accelerator type and stress relaxation behavior, network structure, cross-linking density, and aging behavior of the blends. Accelerator type also affects decomposition energy of the blends.