Slope Transition Research Articles

Radio-frequency biasing of ion acceleration grids with different propellants

In order to ensure the space charge compensation of the plume, conventional ion thrusters need an additional neutralizer to release electrons. When a radio-frequency (RF) voltage is applied across the grid system instead of a direct-current voltage, the simultaneous extraction of ions and electrons is achieved, thereby a neutralizer is not required. In this paper, based on the non-uniform distribution of neutral gas density calculated using the angular coefficient method, the particle-in-cell Monte Carlo collision method is used to thoroughly investigate the spatial and temporal dynamics of particles and the grid system performance for different propellants (argon, krypton and xenon) in such an RF grid system. RPA and E × B probe are employed to measure the ion flux distribution functions (IFDFs) of RF ion thruster with RF biasing, which are used to compare with the simulations. The simulated linear relationship between the self-bias voltage and the RF voltage amplitude and the multi-peak behavior of IFDF under low RF frequency conditions are comparable with the experimental data. The simulated IFDFs compare well with the experiments with the deviation of energy peak position less than 7% and 10% from those by RPA and E × B probe respectively, indicating the effectiveness of the used model. Simulations show the RF grid system is able to realize the extraction of electrons for all three propellants, so as to achieve the plume neutralization without an external neutralizer through the spatial and temporal oscillations of the beams. Electrons pass through the grid twice (extracted from the upstream, and backflow from the downstream), bringing two peaks of electron current to the accelerator grid in one period. The thrust-RF voltage curves for all three propellants show obvious slope transition, when the perveance limit is reached. The low-energy ions in the plume are mainly generated by the electron impact ionization processes for Xe while by CEX collisions for Ar. A larger ion current density of Xe on the downstream surface of the accelerator grid, which may lead to possibly more serious erosions of grids, is found compared with those of Kr and Ar. This is mainly contributed by the larger density of electron impact ionization generated ions of Xe in the downstream because Xe propellant has a larger electron density and ionization cross-section.

Investigation of the effects of whole-body vibration exposure on vehicle drivers when travelling over covered manholes embedded in public roadways

The study investigated the whole-body vibration (WBV) levels that people riding in the vehicle are exposed to while passing through the manhole covers subsidence of passenger cars. In this context, vibration measurements were made with a passenger car at different speeds on two separate road sections with a bump with a known geometry in the middle. With the help of these data obtained, a vehicle dynamic model was calibrated, and vehicle responses were digitized. WBVs were dynamically simulated at 2.5, 5.0, 7.5, and 10 cm manhole depths at one-to-one and five-to-one transition slopes on before and after manhole passes. The simulated vibrations were produced by increasing ten units at speeds between 10 and 50 km/h in these criteria and evaluated the effects of ride speed on WBV. Within the scope of the study, vertical vibration data were characterized and evaluated with the help of frequency weighted root-mean-square acceleration (aw), vibration dose value (VDV), and equivalent static compressive stress (Se) parameters defined in ISO 2631. The analysis found that many passes through the manhole at ride speeds of 40 km/h and above at depths of 7.5 cm and above, potential health risk occurs in the human body.

Inka Hydraulic Engineering at the Tipon Royal Compound (Peru)

The Inka site of Tipon had many unique hydraulic engineering features that have modern hydraulic theory counterparts. For example, the Tipon channel system providing water to the Principal Fountain had a channel contraction inducing critical flow as determined by CFD analysis- this feature designed to induce flow stability and preserve the aesthetic display of the downstream Waterfall. The Main Aqueduct channel sourced by the Pukara River had a given flow rate to limit channel overbank spillage induced by a hydraulic jump at the steep-mild slope transition channel location as determined by use of modern CFD methods- this flow rate corresponds to the duplication of the actual flow rate used in the modern restoration using flow blockage plates placed in the channel to limit over-bank spillage. Additional hydraulic features governing the water supply to agricultural terraces for specialty crops constitute further sophisticated water management control systems discussed in detail in the text.

The Noise Behavior of Gap-Type Amorphous Silicon TFT Under Illumination

Gap-type amorphous silicon (a-Si) thin-film transistor (TFT) used as photo sensor has been reported in previous literature. However, the noise behavior of gap-type a-Si TFT is not inspected yet. Therefore, we investigate the noise response of the gap-type a-Si TFT under illumination in this paper. We compare the difference between the results of the gap-type and the conventional-type TFTs. In addition, we analyze it including the perspectives of power spectrum, integral power spectrum, Hooge parameter, fluctuate slope. Finally, we explain the reason for its fluctuate slope transition and review the correlation between noise behavior and photo effect mechanism.

Numerical study of the robustness of steel moment connections under catenary effect

The local fracture will directly result in the consequent decrease in the vertical resistance of the beam-to-column assembly in the steel frame structure, which emphasizes the necessity of the ductile fracture prediction in the numerical study. In this paper, a monotonic plasticity and ductile fracture model is used to characterize the stress state and loading path dependency of the yield surface, as well as the combined effects of the shear stress and hydrostatic pressure on the damage evolution. On the basis of the validated material model, five push-down tests of the beam-to-column assemblies with different moment connections are chosen for the validation of this modeling method in terms of overall vertical force–displacement curves and the local crack initiation and propagation. Thereafter, the numerical studies of the weld access hole reveal that the gentle slope of transition cutting and larger distance between toe of weld access hole and flange weld will raise the connection ductility. The relationship between ultimate chord rotation and these two variables can be formulated by the empirical formulas. As for the bolted web-to-column connection, the deformation capacity can be improved by using compact bolt arrangement and larger bolt size. The implementation of the shear tab with long-slotted holes will also enhance the connection ductility under catenary mechanism. In general, these findings will be benefit to improve the robustness of the steel frame structure, along with the quantitative estimation of connection ductility for checking the structural safety.

Dynamics of a single bubble rising in a quiescent medium

In the present work, an experimental analysis was performed to characterise the flow field around a single bubble of different diameters ∼ 2.77–3.53 mm) rising in a quiescent medium aiming to determine the effect of bubble size on kinetic energy distribution. The velocity field was measured using a non-intrusive particle image velocimetry (PIV) technique and kinetic energy spectrum was determined in both transverse and longitudinal directions applying a Fast Fourier Transformation (FFT). Both small- and large-scale motions of the flow field were identified and separated using a discreate wavelet transformation (DWT) method. It was found that the energy spectrum of the large-scale motions depended on the bubble size while the small-scale energy spectrum was nearly independent of it. The slopes of the energy spectrum were found to be close to -5/3 and -3 for the large- and small-scale regimes, respectively and the transition of slope was observed to occur at the wavenumber corresponding to the bubble diameter. Using the measured velocity field data, a turbulence kinetic energy (TKE) budget analysis was performed involving five components namely kinetic energy production, turbulent transport, pressure diffusion, viscous diffusion, and energy dissipation. Overall, it was observed that in the vicinity of bubble surface, turbulence production term was not entirely balanced by the dissipation term; and turbulent transport and pressure diffusion term also had significant contributions.

Validation of an Acoustic-Based Framework of Speech Motor Control: Assessing Criterion and Construct Validity Using Kinematic and Perceptual Measures.

This study investigated the criterion (analytical and clinical) and construct (divergent) validity of a novel, acoustic-based framework composed of five key components of motor control: Coordination, Consistency, Speed, Precision, and Rate. Acoustic and kinematic analyses were performed on audio recordings from 22 subjects with amyotrophic lateral sclerosis during a sequential motion rate task. Perceptual analyses were completed by two licensed speech-language pathologists, who rated each subject's speech on the five framework components and their overall severity. Analytical and clinical validity were assessed by comparing performance on the acoustic features to their kinematic correlates and to clinician ratings of the five components, respectively. Divergent validity of the acoustic-based framework was then assessed by comparing performance on each pair of acoustic features to determine whether the features represent distinct articulatory constructs. Bivariate correlations and partial correlations with severity as a covariate were conducted for each comparison. Results revealed moderate-to-strong analytical validity for every acoustic feature, both with and without controlling for severity, and moderate-to-strong clinical validity for all acoustic features except Coordination, without controlling for severity. When severity was included as a covariate, the strong associations for Speed and Precision became weak. Divergent validity was supported by weak-to-moderate pairwise associations between all acoustic features except Speed (second-formant [F2] slope of consonant transition) and Precision (between-consonant variability in F2 slope). This study demonstrated that the acoustic-based framework has potential as an objective, valid, and clinically useful tool for profiling articulatory deficits in individuals with speech motor disorders. The findings also suggest that compared to clinician ratings, instrumental measures are more sensitive to subtle differences in articulatory function. With further research, this framework could provide more accurate and reliable characterizations of articulatory impairment, which may eventually increase clinical confidence in the diagnosis and treatment of patients with different articulatory phenotypes.

Neogene variations in slab geometry drive topographic change and drainage reorganization in the Northern Andes of Colombia

The tropical Northern Andes of Colombia are one the world's most biodiverse places, offering an ideal location for unraveling the linkages between the geodynamic forces that build topography and the evolution of the biota that inhabit it. In this study, we utilize geomorphic analysis to characterize the topography of the Western and Central Cordilleras of the Northern Andes to identify what drives landscape evolution in the region. We supplement our topographic analysis with erosion rate estimates based on gauged suspended sediment loads and river incision rates from volcanic sequences. In the northern Central Cordillera, an elevated low-relief surface (2500 m in elevation, ~40 × 110 km in size) with quasi-uniform lithology and surrounded by knickpoints, indicates a recent increase in rock and surface uplift rate. Whereas the southern segment of the Central Cordillera shows substantially higher local relief and mostly well graded river profiles consistent with longer term uplift-rate stability. We also identify several areas of major drainage reorganization, including captures and divide migrations. These changes in the topography coincide with the proposed location of a slab tear and flat slab subduction under the northern Central Cordillera, as well as with a major transition in the channel slope of the Cauca River. We identify slab flattening as the most likely cause of strong and recent uplift in the Northern Andes leading to ~2 km of surface uplift since 8–4 Ma. Large scale drainage reorganization of major rivers is likely driven by changes in upper plate deformation in relation to development of the flat slab subduction geometry; however, south of the slab tear other factors, such as emplacement of volcanic rocks, also play an important role. Several biologic observations above the area of slab flattening suggest that surface uplift isolated former lowland species on the high elevation plateaus, and drainage reorganization may have influenced the distribution of aquatic species.

Multivariate Modeling of Some Metals Concentrations in Agrarian Soils: Distribution and Soil Fertility Implications in the Tropics

Predicting metals concentration in agricultural soils is a sine qua non in establishing environmental policies and evaluating the soils’ agricultural potentials in an area. The relevance of metals to ecological health, agriculture and pollution has sprung a lot of related studies. This study was setup to determine the concentration and profile distribution of aqua regia (AR) extractable Fe, Al, Mn, Mg and K in agricultural soils, and to predict AR extracted elements via Al2O3 (Alx), K2O (Kx), physical and chemical properties for soil fertility interpretations. One soil pit was randomly sited in each slope transition obtained via digital elevation models (DEM), resulting in 27 composite soil samples. Soil samples meant for AR and X-ray florescence were analyzed in triplicate. The soils were dominated by AR extractable Fe with mean concentrations showing the trend; Fea > Ala > Mga > Mna ≈ Ka and ranges of 639.09–125,719.46, 1252.63–14,895.13, 67.61–2408.36, 4.51–2162.91 and 161.84–1356.23 mg/kg, respectively. The distribution of AR metals in the entire soils was quite similar, however, higher values of soluble Fe occurred in the 0–37 cm depth of IH1P1. Multiple linear regression functions were within acceptable and best prediction criteria (R2 = 0.55–0.77). The best performing models were Ka and Mna, with lower errors. The models selected Kx, Mg and CEC which contributed 89.9, 79.9 and 73.4%, respectively to the 44.2% contribution of PC1 to data variation. The dominance of Kx and Alx with ranges of 2381.0–50,401.0 and 57,766.67–119,433.35 mg/kg, respectively, over Ka and Ala is due to limitations associated with AR extraction of elements in silicate minerals, hence the necessity for extracting soil mineral elements by more than one method.

Evidence for melt leakage from the Hawaiian plume above the mantle transition zone

Dehydration reactions at the top of the mantle transition zone (MTZ) can stabilize partial melt in a seismic low-velocity layer (LVL), but the seismic effects of temperature, melt and volatile content are difficult to distinguish. We invert P-to-S receiver function phases converted at the top and bottom of a LVL above the MTZ beneath Hawaii. To separate the thermal and melting related seismic anomalies, we carry out over 10 million rock physics inversions. These inversions account for variations arising from the Clapeyron slope of phase transition, bulk solid composition, dihedral angle, and mantle potential temperature. We use two independent seismic constraints to evaluate the temperature and shear wave speed within the LVL. The thermal anomalies reveal the presence of a hot and seismically slow plume stem surrounded by a “halo” of cold and fast mantle material. In contrast to this temperature distribution, the plume stem contains less than 0.5vol% melt, while the surrounding LVL—within the coverage area—contains up to 1.7vol% melt, indicating possible lateral transport of the melt. When compared to the melting temperatures of mantle rocks, the temperature within the LVL, calculated from seismic observations of MTZ thickness, suggests that the observed small degrees of melting are sustained by the presence of volatiles such as CO2 and H2O. We estimate the Hawaiian plume loses up to 1.9Mt/yr H2O and 10.7Mt/yr CO2 to the LVL, providing a crucial missing flux for global volatile cycles.

Controlling factors of high-quality hydrocarbon source rocks developed in lacustrine shallow-water zone of the Junggar Basin, northwestern China

Deposits in the lake center, transitional steep slope, and marginal slope of the early Permian alkaline lacustrine system of the Mahu sag, Junggar Basin, have been studied via organic petrology and organic geochemistry to identify high-quality source rocks and investigate potential controlling factors. Organic geochemical data demonstrate that source rocks deposited on the steep slope and on the gentle slope show higher total organic carbon, higher Rock-Eval S2 and hydrogen index values, and lighter carbon isotopes of kerogen than those deposited in the lake center. Organic petrology results show: 1) enrichment of lamalginite in dolomitic laminae of the steep slope, 2) abundant alginite and sporinite in tuffaceous laminae of the gentle slope and, 3) only minor alginite relics and bituminite in evaporite-rich sediments of the lake center. Therefore, the lake slope sediments of the Fengcheng Formation have better source rock quality than the central sediments, which differs from the predicted lacustrine source rock models that place the organic-richest sediments in lake centers. The Mahu sag lake center deposits show strong microbial reworking and contain a high proportion of evaporite minerals, which dilute the organic matter. On its two slopes, shrinkage cracks and erosive surfaces indicate a shallow water setting for the deposition of alginite-rich sediments. These shallow-water organic-rich sediments could be formed and preserved through: 1) local hydrothermal input linked to normal faults, 2) a strong stratified water column related to lateral salinity variations, 3) early silicification of microbial mats induced by evaporation, and 4) high water alkalinity.

Imaging paleoslabs and inferring the Clapeyron slope in D″ beneath the northern Pacific based on high-resolution inversion of seismic waveforms for 3-D transversely isotropic structure

We use waveform inversion to infer high-resolution 3-D models of the S-velocity perturbation δVS and the anisotropy parameter δξ in the lowermost 400 km of the mantle beneath the northern Pacific. Our inferred models show three prominent features: (i) a widespread positive δVS layer with ~100 km thickness that exists ~250 km above the core-mantle boundary (CMB), which could be due to a bridgmanite to post-perovskite phase transition related to the D″ discontinuity; (ii) distinct positive -δVS anomalies with positive δξ resolved from 100 km to more than 400 km above the CMB, which could be the subducted Izanagi, Farallon, and Telkhinia slabs; (iii) a vertically continuous low-δVS anomaly with negative δξ at the edge of the subducted slab, which we interpret as an upwelling plume induced by slab sinking. We infer the Clapeyron slope of the post-perovskite phase transition in the lowermost mantle beneath the northern Pacific to be 10.2 ± 1.3 MPa/K, based on the δVS gradient as a function of depth for the inferred 3-D VS structure. Our estimated large positive Clapeyron slope at the CMB suggests vigorous convection in the lowermost mantle.

Simultaneous estimation of multiple thermal properties using single-sided step heating thermography

Thermal characterization of material based on a single thermal property is unreliable, as many materials have nearly the same thermal property. In order to completely characterize the thermal behaviour of a material, knowledge of more than one thermal property is necessary. In this paper, an approach of estimation of multiple thermal properties using step heating thermography technique is proposed. The characteristic features of the thermal response of material under step heating (like thermal transit time and slope) have been used to derive analytical expressions of thermal properties. A three-phase optimization technique has also been proposed for optimizing the parameters to be used in the analytical expressions. The proposed approach is simple, noncontact, single-sided and can simultaneously estimate more than one thermal property of a material. The approach has been verified by simulations and experiments on materials of different conductivity range. The approach would be helpful in the application requiring in situ thermal property estimation and can also be exploited in the field of material identification or handling.

Shared Control With Efficient Subgoal Identification and Adjustment for Human–Robot Collaborative Tasks

In this article, we describe a novel method to facilitate the process of subgoal identification from a robotics task demonstrated by a human operator. The method defines a unified metric to quantify the human operator's commands, which can be employed to effectively extract subgoal distributions and identify subgoals. We then address the problem of online subgoal adjustment for shared control (SC) applications, which is initiated by the human operator and is necessary to sustain performance in a dynamically changing environment. The adjustment is facilitated by designing a hyperrectangle around the subgoal whose volume is obtained via a hyperbolic slope transition function (HSTF) based on the distance between subgoals. The adjustment actions within the hyperrectangle are encoded by a skill-weighted action integral. A practical implementation of the automatic control input is also provided where proper scaling for input-blending is considered. The developed SC method is corroborated on a scaled hydraulic excavator platform with human operators. Experimental results are presented and discussed.

Emulating Artificial Synaptic Plasticity Characteristics from SiO2-Based Conductive Bridge Memories with Pt Nanoparticles.

The quick growth of information technology has necessitated the need for developing novel electronic devices capable of performing novel neuromorphic computations with low power consumption and a high degree of accuracy. In order to achieve this goal, it is of vital importance to devise artificial neural networks with inherent capabilities of emulating various synaptic properties that play a key role in the learning procedures. Along these lines, we report here the direct impact of a dense layer of Pt nanoparticles that plays the role of the bottom electrode, on the manifestation of the bipolar switching effect within SiO2-based conductive bridge memories. Valuable insights regarding the influence of the thermal conductivity value of the bottom electrode on the conducting filament growth mechanism are provided through the application of a numerical model. The implementation of an intermediate switching transition slope during the SET transition permits the emulation of various artificial synaptic functionalities, such as short-term plasticity, including paired-pulsed facilitation and paired-pulse depression, long-term plasticity and four different types of spike-dependent plasticity. Our approach provides valuable insights toward the development of multifunctional synaptic elements that operate with low power consumption and exhibit biological-like behavior.

The Alaska Convergent Margin Backstop Splay Fault Zone, a Potential Large Tsunami Generator Between the Frontal Prism and Continental Framework

AbstractThe giant tsunami that swept the Pacific from Alaska to Antarctica in 1946 was generated along one of three Alaska Trench instrumentally recorded aftershock areas following great and giant earthquakes. Aftershock areas were investigated during the past decade with multibeam bathymetry, ocean bottom seismograph wide‐angle seismic, reprocessed legacy, and new seismic reflection images. Summarized and updated here are previous papers and additional data. Tectonic structures collocated with aftershock area boundaries indicate possible lengths of rupture in future great earthquakes. NE aftershock area boundaries relate to subducted lower plate structures whereas the SW zone upper plate retains Beringian structural relicts. The lower to middle slope transition separating a stronger continental framework rock from a weaker accreted prism occurs along splay fault zones previously interpreted as backstops in seismic images. Damage zones along splay faults are generally 1‐km‐wide dipping typically 21°. Splays form slip paths from the plate interface to the seafloor much shorter than the 3–4° dipping plate interface beneath the frontal prism. Associated seafloor vent structures indicate overpressured fluids at depth. Splay fault dip and its rigid hanging wall impart greater seafloor uplift than the accreted prism per unit of slip making them effective tsunami generators. Backstop splay fault zones (BSFZs) run along the entire Alaska Trench. Beneath the frontal prism, active bend faults add rugosity to the plate interface and km high relief is commonly imaged in reprocessed legacy and new seismic data. The 1946 Unimak great (M8.6) earthquake epicenter is located near the BSFZ.

Dissipation processes in superconducting NbN nanostructures

In this paper, we present a comprehensive study of electrical transport measurements on a superconducting film of NbN (thickness, d ∼ 50 nm) and its nanostructures fabricated using Focused Ion Beam (FIB) in the form of one bridge (width, w ∼ 50 µm) and three meanders (w ∼ 500 nm, 250 nm, and 100 nm). The resistance (R) and current–voltage [V(I)] characteristics are measured as a function of temperature (2 K–16 K) and magnetic field (0 T–7 T). The photoresponse is measured under quasi-monochromatic light irradiation (wavelength of ∼800 nm). All our samples with w ≫ ξ and d > ξ are dimensionally on the borderline of the three-dimensional limit. However, the film and bridge samples show quasi-2D signatures of Brzezinski–Kosterlitz–Thouless transition in the R(T) and V(I) characteristics. On the other hand, our meander samples show two slope transitions in R(T) that seem to fit well with the thermally activated phase slip (TAPS) near the superconducting onset and quantum phase slip (QPS) at lower temperatures, expected in quasi-1D superconductors. The presence of TAPS and QPS in all the meander samples is further supported by several other observations at B = 0: (i) linear V(I) at lower excitation currents in the entire transition region; (ii) nonlinear and non-hysteretic V(I) at higher currents in the TAPS region; (iii) in the QPS region, at higher currents, the V(I) curves show a quadratic V ∝ I2 dependence before hysteretic and stepped jumps; and (iv) the switching current (IC*) reduces significantly to 5 μA–25 μA (T = 2 K) when compared to nearly ∼875 μA (T = 10.5 K) in the bridge sample. With the application and increase in the magnetic field, at fixed temperatures in the QPS region of the meander samples, the V(I) characteristics show a crossover to TAPS. This seems to be correlated with a drastic reduction in the activation barrier (Ub) extracted from the R(T,B) data. Typically, for B = 0 T–7 T, Ub varies from ∼3000 K–1200 K (film sample) to ∼1100 K–220 K (bridge sample) and ∼250 K–50 K, ∼150 K–20 K, and ∼50 K–6 K for the 500 nm, 250 nm, and 100 nm meander samples, respectively. Using the Langer, Ambegaokar, McCumber, and Halperin theory [J. S. Langer and V. Ambegaokar, Phys. Rev. 164(2), 498 (1967); D. E. McCumberand B. I. Halperin, Phys. Rev. B 1, 1054 (1970)] and considering the normal state transport properties reported earlier [Joshi et al., AIP Adv. 8, 055305 (2018)], these results are shown to be consistent with disorder induced nano-paths of ∼50 nm, ∼12 nm, ∼10 nm, and ∼7 nm width developed in the FIB fabricated bridge and 500 nm, 250 nm, and 100 nm meander samples, respectively.

Landslide response to vegetation by example of July 25–26, 2013, extreme rainstorm, Tianshui, Gansu Province, China

Loss Plateau of China is an area with long-term vegetation restoration while serious mass movements. Local vegetation does act as sediment reducing role while quantification of their effect on landslides is lacking. This work presents a first research work about the connection between landslides and vegetation by the example of July 25–26, 2013, extreme rainstorm. High-resolution sensing orthoimages, landside width, and simplified infinite slope theory were used to examine landslide distribution and the lateral apparent cohesion of roots. The results reveal that shallow landslides have a higher probability at the transitional slope area. The majority of them have a gradient of 20–25°, locate on south-facing slopes, and areas with sparse vegetation. Vegetation cover, represented by the Green-Red Vegetation Index (GRVI), is the controlling factor of landslide distribution and size. The estimated lateral apparent cohesion of plant roots is not positively related to GRVI, and increase when GRVI > 0.2. The relationship between landslide width and slope gradient indicates that strong root strength may result in larger landslide volume. This result of this work is a pioneering trial in correlating the lateral apparent cohesion from roots and forest crown, which is helpful for understanding the effect of vegetation on landslides.

Global variations of Earth's 520- and 560-km discontinuities

We investigate seismic discontinuities in the mantle transition zone (MTZ) by analyzing SS precursors recorded at global seismic stations. Our observations confirm the global existence of the 520-km discontinuity. Although substantial regional depth variations in the 520-km discontinuity are generally correlated with temperature in the mid-MTZ, they cannot be fully explained by the Clapeyron slope of the wadsleyite-ringwoodite phase transition, suggesting both thermal and compositional heterogeneities in the MTZ. A second discontinuity at ∼560-km depth, previously interpreted as splitting of the 520-km discontinuity, is most commonly detected in cold subduction zones and hot mantle regions. The depth separation between the 520- and 560-km discontinuities varies from ∼80 km in cold regions to ∼40 km in hot areas. The exsolution of calcium-perovskite (Ca-pv) from majorite garnet has been proposed to explain the velocity and density changes across the 560-km discontinuity. However, the gradual exsolution of perovskite and partitioning of Ca and Al between perovskite and garnet appear inconsistent with the relatively “sharp” discontinuity in seismic observations and thus need to be revisited in the future. Nevertheless, because the only known transition in major minerals at this depth in the MTZ is the formation of Ca-pv, the existence of the 560-km discontinuity may imply localized high calcium concentrations in the mid-MTZ possibly related to the recycling of oceanic crust.

Numerical Analysis of the Effect of External Circumferential Cracks in Transition Thickness Zone of Pressurized Pipes Using XFEM – Elastic-Plastic Behavior

The elastic-plastic behavior of the material is considered to analyze the effect of an external circumferential crack on a pipe with thickness transition and double slopes. Using the extended finite element method (XFEM), the J-integral of 3D cracks were investigated and compared between straight pipes and pipes with thickness transition and different slopes. Considering internal pressure, this work highlighted the investigation of a 3D crack problem in a thickness transition pipe with a double slope, In the extended finite element method (XFEM), the level sets and the enrichment zone were defined. A crack is easily modeled by enrichment functions. The comparison between the values of the J-integral showed that the pipe containing thickness transition with double slopes is more sensitive to the considered cracks, more precisely, the parameters of the first thickness transition have more influence on the variation of J-integral than the parameters of the second thickness transition. The decreasing of the angle of the slopes and the increase of the ratio of the thicknesses is one effective method of reducing the J-integral.