Regional Strain Rate Research Articles

Myocardial Structural, Perfusion, and Metabolic Correlates of Left Bundle Branch Block Mechanical Derangement in Patients With Dilated Cardiomyopathy

Background— Left bundle branch block (LBBB) influences on regional left ventricular (LV) structure, perfusion, and metabolism have not yet been thoroughly investigated in dilated cardiomyopathy patients. Methods and Results— Eleven dilated cardiomyopathy patients with LBBB (mean±SD age, 62±11 years; LV ejection fraction, 35±8%) and 7 dilated cardiomyopathy patients without LBBB (mean±SD age, 58±9 years; LV ejection fraction, 37±10%) were studied by cardiac magnetic resonance and positron emission tomography. The left ventricle was divided in 3 regions: septum, adjacent (anterior-inferior walls), and lateral. Regional midwall circumferential strain, maximum shortening, and strain rate were obtained from tagged cardiac magnetic resonance. The systolic stretch index was calculated as positive strain rate (stretching) divided by total strain rate. Myocardial metabolic rate of glucose and resting and hyperemic myocardial blood flow were quantified by 2-[ 18 F]fluoro-2-deoxyglucose and [ 13 N]ammonia positron emission tomography, respectively. Compared with non-LBBB patients, LBBB patients showed a highly inhomogeneous systolic deformation pattern that changed gradually, moving from a discoordinate [(systolic stretch index, 0.485 (0.284)] and poorly contracting (maximum shortening, −1.14±0.96%) septum to a coordinate [systolic stretch index, 0.002 (0.168)] and strongly contracting (maximum shortening, −13.63±2.58%) lateral region (both P <0.0001). This pattern was closely matched to the myocardial metabolic rate of glucose, disclosing lowest, intermediate, and highest values in the septum, adjacent, and lateral regions, respectively ( P <0.0001). Septal-to-lateral thickness ratio was lower in LBBB than in non-LBBB patients ( P =0.03). In both groups, the LV distribution of resting and hyperemic myocardial blood flow and myocardial blood flow reserve did not differ significantly. Conclusions— In dilated cardiomyopathy patients, the extensive LV contraction abnormalities induced by LBBB cause regional myocardial metabolic and structural remodeling, without consistent changes in blood flow.

Structure of the present-day velocity field of the crust in the area of the Central-Asian GPS network

The structure of the vector field of present-day horizontal velocities on the Earth’s surface is investigated with the use of the territory covered by the Central-Asian GPS network as an example. A method of identification of groups of GPS points (statistically rigid clusters), for which the rate of change in distances between them is virtually zero, is proposed and realized. Sites of the Earth’s surface (regions) containing such groups of GPS points, within the required measurement accuracy, move in the horizontal plane as two-dimensional rigid bodies. The clustering algorithm, which is based on the Student t statistics in determining the so-called statistical “sample cost,” is developed and carefully tested. The results of identification of regions take into account possible random errors in velocity measurements and do not depend on the chosen frame of reference. The method of identification of regions is sufficiently stable with respect to variations in the number of GPS sites used for clustering. Of all the sites of the Central-Asian GPS network, 323 points were selected for clustering. These sites were measured from 3 to 11 times over an 11-year interval of observations (1995–2005). The estimates of errors of velocity measurement for these sites must not exceed 1.0 mm/yr. As a result, 29 statistically rigid clusters, containing from 3 to 17 GPS sites, were identified, and the kinematic regimes of motion of regions corresponding to these clusters were determined with respect to the stable part of Eurasia. With the general direction of the translatory motion of regions toward the north, the majority of them rotate counterclockwise. Nearly one third of GPS sites do not participate in the formation of clusters; these points fall into the interregional space (IRS), which is characterized by increased strain rates. The IRS structure is partitioned into zones with four directions, of which two directions virtually coincide with directions of the principal axes of the regional strain rate tensor, and the two other directions are oriented diagonally to the principal axes. The axis of the maximum rate of the regional shortening has a north-northwestern orientation. It is in this direction (mainly along the IRS) that the crust’s contraction takes place. There is no spatial correlation between IRS zones and geological faults; however, their angular distributions and the directions of strike-slips on them are interrelated. The resulting patterns of regional motions and IRS deformations consistently reflect the dynamic action of the Indian plate on the territory under investigation.

Acute Radiation Effects on Cardiac Function Detected by Strain Rate Imaging in Breast Cancer Patients

To investigate the occurrence of early radiation-induced changes in regional cardiac function using strain rate imaging (SRI) by tissue Doppler echocardiography. We included 20 left-sided and 10 right-sided breast cancer patients receiving radiotherapy (RT) to the breast or chest wall. Standard echocardiography and SRI were performed before RT (baseline), immediately after RT (post-RT), and at 2 months follow-up (FUP) after RT. Regional strain (S) and strain rate (SR) values were obtained from all 18 left ventricular (LV) segments. Data were compared to the regional radiation dose. A reduction in S was observed post-RT and at FUP in left-sided patients (S(post-RT): -17.6 ± 1.5%, and S(FUP): -17.4 ± 2.3%, vs. S(baseline): -19.5 ± 2.1%, p < 0.001) but not in right-sided patients. Within the left-sided patient group, S and SR were significantly reduced after RT in apical LV segments (S(post-RT): -15.3 ± 2.5%, and S(FUP): -14.3 ± 3.7%, vs. S(baseline): -19.3 ± 3.0%, p < 0.01; and SR(post-RT): -1.06 ± 0.15 s(-1), and SR(FUP): -1.16 ± 0.28 s(-1), vs. SR(baseline): -1.29 ± 0.27 s(-1), p = 0.01), but not in mid- or basal segments. Furthermore, we observed that segments exposed to more than 3 Gy showed a significant decrease in S after RT (S(post-RT): -16.1 ± 1.6%, and S(FUP): -15.8 ± 3.4%, vs. S(baseline): -18.9 ± 2.6%, p < 0.001). This could not be observed in segments receiving less than 3 Gy. SRI shows a dose-related regional decrease in myocardial function after RT. It might be a useful tool in the evaluation of modern RT techniques, with respect to cardiac toxicity.

Eruptive versus non-eruptive behaviour of large calderas: the example of Campi Flegrei caldera (southern Italy)

Caldera eruptions are among the most hazardous of natural phenomena. Many calderas around the world are active and are characterised by recurrent uplift and subsidence periods due to the dynamics of their magma reservoirs. These periods of unrest are, in some cases, accompanied by eruptions. At Campi Flegrei caldera (CFc), which is an area characterised by very high volcanic risk, the recurrence of this behaviour has stimulated the study of the rock rheology around the magma chamber, in order to estimate the likelihood of an eruption. This study considers different scenarios of shallow crustal behaviour, taking into account the earlier models of CFc ground deformation and caldera eruptions, and including recent geophysical investigations of the area. A semi-quantitative evaluation of the different factors that lead to magma storage or to its eruption (such as magma chamber size, wall-rock viscosity, temperature, and regional tectonic strain rate) is reported here for elastic and viscoelastic conditions. Considering the large magmatic sources of the CFc ignimbrite eruptions (400–2,000 km3) and a wall-rock viscosity between 1018 and 1020 Pa s, the conditions for eruptive failure are difficult to attain. Smaller source dimensions (a few cubic kilometres) promote the condition for fracture (eruption) rather than for the flow of wall rock. We also analyse the influence of the regional extensional stress regime on magma storage and eruptions, and the thermal stress as a possible source of caldera uplift. The present study also emphasises the difficulty of distinguishing eruption and non-eruption scenarios at CFc, since an unambiguous model that accounts for the rock rheology, magma-source dimensions and locations and regional stress field influences is still lacking.

Reconciling surface plate motions with rapid three-dimensional mantle flow around a slab edge

The direction of tectonic plate motion at the Earth's surface and the flow field of the mantle inferred from seismic anisotropy are well correlated globally, suggesting large-scale coupling between the mantle and the surface plates. The fit is typically poor at subduction zones, however, where regional observations of seismic anisotropy suggest that the direction of mantle flow is not parallel to and may be several times faster than plate motions. Here we present three-dimensional numerical models of buoyancy-driven deformation with realistic slab geometry for the Alaska subduction-transform system and use them to determine the origin of this regional decoupling of flow. We find that near a subduction zone edge, mantle flow velocities can have magnitudes of more than ten times the surface plate motions, whereas surface plate velocities are consistent with plate motions and the complex mantle flow field is consistent with observations from seismic anisotropy. The seismic anisotropy observations constrain the shape of the eastern slab edge and require non-Newtonian mantle rheology. The incorporation of the non-Newtonian viscosity results in mantle viscosities of 10(17) to 10(18) Pa s in regions of high strain rate (10(-12) s(-1)), and this low viscosity enables the mantle flow field to decouple partially from the motion of the surface plates. These results imply local rapid transport of geochemical signatures through subduction zones and that the internal deformation of slabs decreases the slab-pull force available to drive subducting plates.

High temperature tensile behavior of a PH stainless steel

High temperature tensile deformation of 15-5 PH stainless steel in peak age and overaged conditions has been studied over the temperature range of 300 to 600°C and different strain rates. Dynamic recrystallization was the main softening mechanism when the alloy deformed at imposed temperature and strain rate region. The apparent activation energy was calculated as 284.8 and 323.1kJ/mol for peak age and overaged conditions, respectively.

Ultrasonographic strain imaging is superior to conventional non-invasive measures of vascular stiffness in the detection of age-dependent differences in the mechanical properties of the common carotid artery

Elastic properties of large arteries have been shown to deteriorate with age and in the presence of atherosclerotic vascular disease. In this study, the performance of ultrasonographic strain measurements was compared with conventional measures of vascular stiffness in the detection of age-dependent differences in the elastic properties of the common carotid artery (CCA). In 10 younger (25-28 years, four women) and 10 older (50-59 years, four women) healthy individuals, global and regional circumferential, and radial strain variables were measured in the short-axis view of the right CCA using ultrasonographic two-dimensional (2D) strain imaging with recently introduced speckle tracking technique. Conventional elasticity variables, elastic modulus (E(p)), and beta stiffness index, were calculated using M-mode sonography and non-invasive blood pressure measurements. Global and regional circumferential systolic strain and strain rate values were significantly higher (P < 0.01 for regional late systolic strain rate, P < 0.001 otherwise) in the younger individuals, whereas the values of conventional stiffness variables in the same group were lower (P < 0.05). Among all strain and conventional stiffness variables, principal component analysis and its regression extension identified only circumferential systolic strain variables as contributing significantly to the observed discrimination between the younger and older age groups. Ultrasonographic 2D-strain imaging is a sensitive method for the assessment of elastic properties in the CCA, being in this respect superior to the conventional measures of vascular stiffness. The method has potential to become a valuable non-invasive tool in the detection of early atherosclerotic vascular changes.

High strain rate response of Zr-based bulk metallic glass in supercooled liquid region

The stress–strain curves of Zr-based bulk metallic glass (BMG) were measured at very high strain rates in the supercooled liquid region (SLR) using a uniaxial compression test. For this purpose, the composite samples consisting of Zr-based metallic glass particles embedded in the crystalline nickel matrix were prepared in order to avoid rapid failure of the BMG alloy. The stress–strain curves of the BMG alloy were calculated using the data of composite samples. The strain rate sensitivity m = ∼0.1 of the present BMG alloy was determined at strain rates ranging from 10 0 to 10 1 s −1.

Discrete Element Modeling of Constant Strain Rate Compression Tests on Idealized Asphalt Mixture

Discrete element modeling has been used to simulate constant strain rate compressive tests for an idealized asphalt mixture comprising approximately single-sized sand particles. A range of constant strain-rate compressive tests to failure have been undertaken in the laboratory and the axial stress-strain response has been carefully measured. The peak stress (compressive strength) of the material was found to be as a power-law function of the equivalent (temperature compensated) strain rate in the viscoelastic region of behavior. The internal geometry of the idealized asphalt mixture has been reproduced in PFC-3D and internal damage (cracking) in the material was modeled by allowing bond breakage between adjacent particles. Elastic contact properties have been used to investigate the effect of random variations in internal sample geometry, the distribution of bond strengths between adjacent particles and the coefficient of friction between particles where the bond has broken. A simple viscoelastic Burger's model was used to introduce time dependent shear and normal (tensile) contact stiffnesses and an elastic contact has been assumed for the compressive normal contact stiffness. To reduce the computation time, both viscosities in the Burger's model were scaled which has been shown to have the same effect as scaling the loading velocity (strain rate) by the same factor. A strain rate dependent bond breakage criterion has been developed and model results were found to compare well with the experimental data.

Energy Absorption Capability of Zn-22Al Superplastic Alloy Foam Manufactured through Melt Foaming Process

Superplastic Zn-22Al alloy foams were manufactured through the melt foaming process using titanium hydride powder as a foaming agent. The compressive properties of the Zn-22Al foams were investigated under quasi-static and dynamic loading conditions. Experimental results show that the flow stress and the energy absorption of the Zn-22Al foam significantly increased with increasing the strain rate. At high strain rate region, the energy absorption of the Zn-22Al foams is also larger than that of conventional aluminum foams. These behaviors are due to superplastic deformation of cell walls.

Mechanical Dyssynchrony After Myocardial Infarction in Patients With Left Ventricular Dysfunction, Heart Failure, or Both

Mechanical dyssynchrony is considered an independent predictor for adverse cardiovascular outcomes in patients with heart failure. However, its importance as a risk factor after myocardial infarction is not well defined. We examined the influence of mechanical dyssynchrony on outcome in patients with left ventricular dysfunction, heart failure, or both after myocardial infarction who were enrolled in the Valsartan in Acute Myocardial Infarction (VALIANT) echocardiography study. B-mode speckle tracking with velocity vector imaging was used to assess ventricular synchrony in 381 patients who had image quality sufficient for analysis. Time to regional peak velocity and time to strain rate were measured among 12 left ventricular segments from the apical 4- and 2- chamber views, and the SDs between all 12 segments were used as a measure of dyssynchrony. The relationships between the SD of time to regional peak velocity and strain rate and clinical outcome of death or heart failure were assessed. In a multivariate Cox model adjusted for clinical and echocardiographic variables, the SD of time to peak velocity (hazard ratio per 10 ms, 1.10; 95% confidence interval, 1.02 to 1.18; P=0.010) and the SD of time to strain rate (hazard ratio per 10 ms, 1.16; 95% confidence interval, 1.06 to 1.27; P=0.001) were independent predictors of death or heart failure. Left ventricular dyssynchrony is independently associated with increased risk of death or heart failure after myocardial infarction, suggesting that contractile pattern may play a role in post-myocardial infarction prognosis.

Mechanical Behavior and Microstructural Change of a High Nitrogen CrMn Austenitic Stainless Steel during Hot Deformation

The hot deformation behavior of a high nitrogen CrMn austenitic stainless steel in the temperature range 1173 to 1473 K (900 to 1200 °C) and strain rate range 0.01 to 10 s−1 was investigated using optical microscopy, stress-strain curve analysis, processing maps, etc. The results showed that the work hardening rate and flow stress decreased with increasing deformation temperature and decreasing strain rate in 18Mn18Cr0.5N steel. The dynamic recrystallization (DRX) grain size decreased with increasing Z value; however, deformation heating has an effect on the DRX grain size under high strain rate conditions. In the processing maps, flow instability was observed at higher strain rate regions (1 to 10 s−1) and manifested as flow localization near the grain boundary. Early in the deformation, the flow instability region was at higher temperatures, and then the extent of this unstable region decreased with increasing strain and was restricted to lower temperatures. The hot deformation equation as well as the quantitative dependence of the critical stress for DRX and DRX grain size on Z value was obtained.

電解チャージにより水素吸蔵した純アルミニウムにおける水素存在状態と引張特性に与える水素の影響

Hydrogen is introduced in commercial (99% pure) aluminum by electrochemical charging to study the existing state of hydrogen and its effect on the mechanical properties of aluminum. Electrochemical charging is conducted in an aqueous solution of H2SO4 with 0.1 mass% NH4SCN as a hydrogen recombination poison. The potential and pH during the charging are chosen from the immune, passive, and corrosive regions on Pourbaix diagram to determine the optimum conditions for the charging. The maximum amount of hydrogen absorbed is obtained in the immune region. The amount of hydrogen and its existing state are examined using hydrogen desorption curves, which are obtained by thermal desorption spectroscopy. The curves show distinctive peaks that correspond to trapping sites of hydrogen in the material. One of the peaks is observed at approximately 100°C and it corresponds to vacancies and dislocations in the material; another peak is observed at approximately 400°C and it corresponds to molecular hydrogen in blisters. It is presumed that charged hydrogen diffuses into the bulk of the material to form hydrogen-vacancy pairs, and then these pairs cluster to form blisters. The fracture strain of charged aluminum in the immune region decreased with a slower strain rate, showing an inverse dependence on the fracture strain of the uncharged material. This phenomenon is considered to be caused by the transport of hydrogen by dislocations through the interaction between hydrogen and the dislocations. The phenomenon is further confirmed by the observation of hydrogen release during tensile deformation, where the amount of hydrogen is higher in the strain rate region where the interaction between the dislocations and hydrogen is more prominent.

Role of time scale in the deformation patterns and hysteresis of NiTi SMA

In this paper we present our recent modelling and experiment on the roles of loading time scale and thermo-mechanical two-field coupling in the deformation domain patterns and stress hysteresis in NiTi SMA. We first report the effects of loading time or stretching rate on the domain patterns and stress hysteresis observed in NiTi strips in the strain rate range of 10-5/s ~ 10-1/s. It was found that the nominal stress-strain curve of the specimen changed from near-isothermal plateau-type with distinct stress-drops in the low strain rate region to the near-adiabatic smooth hardening-type in the high strain rate region. The pseudoelastic hysteresis varies non-monotonically with the external loading rate and the maximum hysteresis occurs at certain intermediate loading rate. The corresponding deformation mode changed from the localized-propagation mode with a few parallelepiped martensite domain patterns to the near-homogeneous multiple nucleation mode with fine alternating austenite-martensite stripes. The analysis shows that the number of the macroscopic domains (domain spacing) of the specimen increased (decreased) with the applied stretching rate in a power-law form, i.e., the higher the loading rate, the finer the deformation pattern. Such observed power-law dependency is originated from the coupling between the material’s nonlinear property (formation and growth of domains) and the transfer of heat in the phase transition process. The important roles of heat transfer dynamics and loading time in imposing the emerging length scale in the deformation pattern of the material is demonstrated. For the hysteresis, a simple two-scale thermo-mechanical coupling model is developed to explain the observed rate-dependent hysteresis phenomenon. We incorporate the effects of the released/absorbed heat of the phase transition and the heat transfer on the pseudoelastic hysteresis. An analytical expression for the rate-dependent hysteresis is derived and the theoretical predictions agree quantitatively well with the experiments.

Evaluation of the AZ31 Formability According to Temperature Using a Constant Strain Rate Test

The present paper is focused on the Finite Element modeling of the Marciniak stretch-forming test in warm condition. Such a test was proposed by the authors for evaluating the warm formability of the Mg alloy AZ31 according to the most important parameters: the temperature and the strain rate. Tensile tests confirmed the large influence of the strain rate on the deformation of the AZ31, especially when the test temperature is over 200°C. Three dimensional FE simulations were thus carried out in order to analyze the strain and strain rate evolutions during the formability test at the temperature of 200°C. In particular, simulations were aimed at investigating the effect of the specimen’s geometry on the strain rate evolution in the central region, where failure occurs during the Marciniak stretch-forming test. An equation for calculating the punch speed profile able to keep a constant equivalent strain rate in the central region of the specimen has been furnished according to the geometry of the specimen. Its efficiency was validated by means of additional simulations implementing the punch speed profile calculated using the proposed approach.

Microstructures and Mechanical Properties of Electro-deposited Nanocrystalline Ni with Broad Grain Size Distribution

Abstract The flawless nanocrystalline (nc) Ni with a broad grain size distribution ranging from 5 to 120 nm and an average grain size of 20-30 nm were prepared by direct current and pulse electrodeposition, respectively. In the region of room-temperature static tensile strain rates, for the nc Ni prepared by direct current electrodeposition, the average ultimate tensile strength and the average elongation to failure are 1176 MPa and 10.6%, respectively. While for the nc Ni prepared by pulse electrodeposition, the ultimate tensile strength exceeds 1500 MPa and the max elongation to failure reaches 13.3%. In contrast to the typical electrodeposited nc Ni with a narrow grain size distribution below 50 nm, the ductility is increased by more than 100% for the present nc Ni samples. This enhancement can be interpreted by the reason that dislocations can exist and multiply in the large grains by the mechanism of Frank-Read source in the plastic deformation process revealed by theoretical calculation.

Evaluation of regional left ventricular longitudinal function in 151 normal fetuses using velocity vector imaging

The purpose of this study was to investigate the clinical value of velocity vector imaging (VVI) in the assessment of normal fetal regional myocardial performance and to establish a normative data set for normal Chinese fetuses. One hundred and fifty-one healthy Chinese fetuses were divided into five groups according to their gestational age. Digital dynamic four-chamber views were collected and analyzed offline. The regional tissue velocity, strain, and strain rate of the interventricular septum and left lateral wall were measured in systole and diastole. Normal systolic and diastolic values for tissue velocity, strain, and strain rate were established. Tissue velocity decreased gradually from the basal segment to the apical segment (P < 0.01), whereas the strain and strain rate were stable among all segments in every group (P > 0.05). Tissue velocity was dependent on gestational age (P < 0.05), whereas strain and strain rate were stable throughout gestation (P > 0.05). VVI is a novel noninvasive tool for quantitative assessment of regional systolic and diastolic function of the fetal heart. Fetal myocardial velocity, strain, and strain rate measurements can be measured easily and reproducibly. This technique is useful for evaluating cardiac function.

Earthquake histories and Holocene acceleration of fault displacement rates

Displacement rates for normal and reverse faults (n = 57) are generally higher when averaged for the Holocene (~10 ka) than for the late Quaternary (~300 ka) and longer time scales. Holocene acceleration of displacement rates could be attributed to geological processes that produce increases of tectonic tempo. We propose an alternative model in which the observed rate changes arise from variability in earthquake slip and/or recurrence coupled with a sampling bias toward those faults that are best represented at the Earth’s surface and that accrued displacement fastest during the Holocene. This model is consistent with displacement rates measured over time intervals of as long as ~300 ka for 129 faults from the Taupo Rift, New Zealand. Departures of earthquake parameters and associated displacement rates from their long-term (>300 ka) averages are attributed to fault interactions and occur on time intervals inversely related to these long-term displacement rates and to regional strain rates.

Hot deformation of 15-5 PH stainless steel

The hot deformation behavior of 15-5 PH stainless steel has been studied using hot compression tests over the temperature range of 900–1150°C and strain rates varying between 0.001 and 0.5s−1. The results showed that dynamic recrystallization is the main softening mechanism when the alloy deformed at imposed temperature and strain rate region. Strain rate sensitivity of the material was evaluated in all the deformation conditions and the obtained values were used to calculate the apparent activation energy. Based on the flow stress data obtained as a function of temperature and strain rate, power dissipation map and instability map for hot working have been developed.

Gravitational potential energy and regional stress and strain rate fields for continental plateaus: Examples from the central Andes and Colorado Plateau

The commonly observed extension in areas of elevated and thickened crust is an expected consequence of having excess gravitational potential energy (GPE) compared to the low GPE of the surrounding crust. While this conceptual model is well founded, it is less clear how well GPE-related stress orientations compare quantitatively to observed stress and strain rate orientations and what any inconsistency tells us about the presence of other competing forces. We estimate the GPE distribution for the central Andes and the greater Colorado Plateau area using topography and crustal thickness variations, respectively, and compare the related stress fields with the World Stress Map as well as with a geodetic strain rate field (for the Colorado Plateau only). In both areas, deviatoric stresses associated with GPE variations alone cannot fully account for the observed deformation rate field. For the central Andes only a combination of deviatoric stresses associated with GPE and relative plate motions can account for the near N–S tensional stress observed in the Peruvian Andes and the margin–normal compressional stress along the eastern Cordillera and sub-Andean fold-and-thrust belt. The observed deformation field around the Colorado Plateau shows E–W extension, largely inconsistent with the deviatoric stresses associated with GPE variations except for the area east of the Rio Grande Rift. The NE–SW oriented stress observed on the southwestern Colorado Plateau is consistent with the orientations of tensional deviatoric stresses associated with GPE variations. We argue that this consistency could be haphazard; stress observations may not reflect the current state of stress due to inherited structure, or could result from the relative high strength of Colorado Plateau that allows for regional GPE variations (and possibly basal shear) to be more significant forces than far-field plate interactions. For the central Andes and Colorado Plateau, stresses associated with GPE variations have a strong influence on the total stress field, and can thus be used to calibrate the overall level of deviatoric stress acting within the lithosphere.