Slope Transition Research Articles

Effects of the post-perovskite phase transition properties on the stability and structure of primordial reservoirs in the lower mantle of the Earth

Two key features of the lowermost Earth's mantle are the presence of Large Low Shear Velocity Provinces (LLSVPs), which may be reservoirs of primordial, chemically distinct material, and the phase change from perovskite (pv) to post-perovskite (pPv), which may occur at lowermost mantle conditions. However, the influence of this phase change on the shape, dynamics, and stability of chemically distinct reservoirs is not well constrained. Here, we performed numerical experiments of thermo-chemical convection in 2-D spherical annulus geometry to investigate the effects on thermo-chemical structure in the lower mantle of three parameters affecting the pPv phase change: the core–mantle boundary (CMB) temperature (TCMB), the viscosity ratio between pv and pPv (ΔηpPv), and the Clapeyron slope of the pPv phase transition (ΓpPv). Our results indicate that increasing CMB temperature increases the wavelength of the primordial reservoirs. Furthermore, a high CMB temperature promotes the development of plumes outside the reservoir of primordial material. High CMB temperature and large Clapeyron slope both favour the formation of pPv patches and of a double-crossing of the phase boundary, thus preventing the formation of continuous layer of pPv above the CMB. Combined with a low CMB temperature and/or a low Clapeyron slope of the pPv phase transition, a full layer of weak pPv above the CMB strongly enhances the mixing efficiency of primordial material with ambient regular mantle material, which may not allow the generation of large reservoirs. Based on our experiments, we conclude that the models of convection best describing the Earth's mantle dynamics include a large pPv Clapeyron slope (typically in the range of 13–16 MPa/K), and a moderate CMB temperature (around 3750 K). Our models do not provide further constraints on the value of the pPv viscosity, both regular and low values giving similar results on stability and structure of large primordial reservoirs for models with a moderate CMB temperature and large Clapeyron slope, but more plumes can be observed outside these large reservoirs in the cases with regular pPv than those in the cases with weak pPv.

Relations Between Baseline and Nonlinear Longitudinal Changes in Children's Body Mass Index and Internalizing Symptoms.

To determine whether initial body mass index for age (zBMI) and internalizing symptoms predict longitudinal changes in zBMI and internalizing symptoms-and the extent to which sex and race moderate these relations. Participants included 12,674 (51% male) youth from the Early Childhood Longitudinal Study, Kindergarten Class 1998-1999. Data were collected in kindergarten, 1st, 3rd, 5th, and 8th grades. Teacher-reported internalizing symptoms were measured with the Social Rating Scale. Internalizing symptoms followed a quadratic growth trajectory, with initial low levels of symptoms that gradually increased over time and eventually leveled. zBMI followed a piecewise growth trajectory, with a transition in slope at 1st grade. Interactions emerged between zBMI and internalizing symptoms for White males. Associations between internalizing symptoms and BMI begin in early childhood for White males, and changes in zBMI are a function of the interactive effect of initial levels of internalizing difficulties and adiposity status.

Influence of cellulose nanocrystals concentration and ionic strength on the elaboration of cellulose nanocrystals–xyloglucan multilayered thin films

The effect of the variation of CNC concentration on the growth pattern of CNC–XG films is investigated. We found that a transition in the growth slope occurs at a CNC concentration of roughly 3–4gL−1. A close effect can be obtained by the increase of the ionic strength of the CNC suspensions, suggesting that electrostatic interactions are involved. Static light scattering investigation of CNC dispersions at increasing concentrations demonstrated that the particle–particle interactions change as the CNC concentration increases. Neutron Reflectivity (NR) was used to probe the internal structure of the films. The increase of the CNC concentration as well as the increase of the ionic strength in the CNC suspension were found to induce a densification of the adsorbed CNC layers, even though the mechanisms are not strictly identical in both cases. Small changes in these parameters provide a straightforward way of controlling the architecture of CNC-based multilayered thin films and, as a result, their functional properties.

Abrasive slurry jet micro-machining of edges, planar areas and transitional slopes in a talc-filled co-polymer

The abrasive slurry-jet erosion of a talc-filled thermoplastic olefin (TPO) (60% PP, 25% EP rubber and 15% talc) was measured as a function of the impact angle and the talc filler content. A ductile erosion response was observed, showing a maximum erosion rate at 45°. A superposition model was then developed to predict the cross-sectional shapes of small-scale flat-bottomed pockets and curved edges machined in TPO using abrasive slurry-jet micro-machining (ASJM). The model was based on the spatial distribution of the erosion across the jet footprint measured during a shallow “first pass” channel at a specific angle. The model predictions of planar depth and waviness were in close agreement with experimental measurements. The measured dependence of the erosion rate on the impact angle was used to develop novel machining configurations to increase the slope of bounding sidewalls.

On the instability of a buoyancy-driven downflow

Gravity currents flowing downslope, namely downflows, were observed to have a larger scale instability on high slope angles and such violent instability was absent for downflows on low slope angles. By linear theory, it is found that two branches of instability occur for slope angle in the range of 0°<θ<90°. The ensuing instability is on the upper branch for low slope angles and on the lower branch for high slope angles. There also exists a transitional slope angle, θE≈0.04°, at which the onset instability switches from one branch to the other. The scale of instability is found to increase and tend to skew towards the upper edge of the downflow as the ensuing instability switches from the upper branch to the lower one. Our findings surprisingly resonate with previously reported observations. Critical Reynolds number, below which the flow is stable to infinitesimal disturbances, is found to increase as the slope angle decreases. The role played by the bottom slope is essentially twofold. On one hand, the downslope component of gravity acts as the driving force for downflows. On the other hand, the wall-normal component of gravity acts for the stratification effect. Therefore, as the slope angle decreases, the driving force diminishes and the stratification intensifies, which can explain that the critical Reynolds number increases as the slope angle decreases. When a downflow propagates onto a sufficiently low slope angle, the low driving force and intensified stratification effect would make the downflow less prone to sustain a turbulent state of flow, which ultimately leads to the final stage of a gravity current event.

Characterization and Physical Modeling of Turn-On Voltage, Saturation Voltage and Transition Slope in Graphene Barristors

In this paper, we present theoretical definitions and physical backgrounds of turn-on voltage, saturation voltage and transition slope in graphene-based variable-barrier transistors (barristors). We show that they are three main characteristics parameters of the device and are of the key factors in determining whether barristor is applicable for the future nanoelectronics. Furthermore, because of the importance of physical modeling of semiconductor devices, we address this issue and develop physical expressions, in closed form, for these characteristics. We also investigate the conformity of the functional dependence of our models and their results variations regarding to the device parameters with the reports of the previous works. Finally, we physically discuss how the variation of the device parameters, such as bias condition and doping density, can influence the aforesaid main characteristics of barristor.

Shear Current Effects on Monochromatic Water Waves Crossing Trenches

The reflection coefficients of monochromatic water waves over trenches with shear current are estimated analytically. The diffraction of waves by an abrupt depth change and shear current is formulated by the matched eigenfunction expansion method. The proper number of steps and evanescent modes are proposed by a series of convergence tests. The accuracy of the predicted reflection coefficients is checked by estimating the wave energy. Reflection and transmission characteristics are studied for various shear current conditions. The different combinations of strength, width of shear current, and incident wave angle with constant water depth topography are examined. The optimal figure of the trench with shear current is obtained by estimating the reflection coefficients for various sloped transitions. The resonant reflection of the water waves is found by multiarrayed optimal trenches and the interaction of sinusoidally varying topography with shear current.

Vowels of four-year-old children with cerebral palsy in Mandarin-learning environment

Characteristics of vowel productions of children with cerebral palsy (CP) were investigated with data from two 4-year-old children with CP and two typically-developing (TD) children in Mandarin-learning environment. Clear vowel productions from picture naming and natural conversation in three 50-minute audio recordings of each child were transcribed and analyzed. Seven parameters were examined: vowel duration of /a/, F2 slope in transition of CV sequence, cumulative change of F2 for vowel /a/, degree of nasalization in oral vowel (A1-P1), percent of jitter, percent of shimmer, and the signal to noise ratio (SNR). Major findings are: (1) The CP group showed shorter vowel duration of /a/; (2) TD group has larger F2 slope in CV transition; (3) No obvious differences were found between TD and CP groups in cumulative change of F2 for vowel /a/, degree of nasalization (A1-P1), and voice perturbation (percent of jitter, percent of shimmer, and SNR). Further study with more participants and with careful data selection can verify findings of this study in search for valid parameters to characterize vowel production of children with CP.

The stability and structure of primordial reservoirs in the lower mantle: insights from models of thermochemical convection in three-dimensional spherical geometry

Large-scale chemical lateral heterogeneities are inferred in the Earth's lowermost mantle by seismological studies. We explore the model space of thermochemical convection that can maintain reservoirs of dense material for a long period of time, by using similar analysis in 3-D spherical geometry. In this study, we focus on the parameters thought to be important in controlling the stability and structure of primordial dense reservoirs in the lower mantle, including the chemical density contrast between the primordial dense material and the regular mantle material (buoyancy ratio), thermal and chemical viscosity contrasts, volume fraction of primordial dense material and the Clapeyron slope of the phase transition at 660 km depth. We find that most of the findings from the 3-D Cartesian study still apply to 3-D spherical cases after slight modifications. Varying buoyancy ratio leads to different flow patterns, from rapid upwelling to stable layering; and large thermal viscosity contrasts are required to generate long wavelength chemical structures in the lower mantle. Chemical viscosity contrasts in a reasonable range have a second-order role in modifying the stability of the dense anomalies. The volume fraction of the initial primordial dense material does not effect the results with large thermal viscosity contrasts, but has significant effects on calculations with intermediate and small thermal viscosity contrasts. The volume fraction of dense material at which the flow pattern changes from unstable to stable depends on buoyancy ratio and thermal viscosity contrast. An endothermic phase transition at 660 km depth acts as a 'filter' allowing cold slabs to penetrate while blocking most of the dense material from penetrating to the upper mantle.

Depositional facies and platform architecture of microbialite-dominated carbonate reservoirs, Ediacaran–Cambrian Ara Group, Sultante of Om

Intrasalt carbonates of the Ediacaran–Cambrian Ara Group constitute a significant reservoir element of the intrasalt “stringer” play in Oman, in which dolomitic carbonates are encased in salt at depths of 3 to 7 km (1.9 to 4.3 mi). These reservoir carbonates have significant microbial influences. Although Ara Group reservoirs are mostly latest Precambrian, the models developed here may be applicable to younger microbially dominated carbonate reservoirs in basins of higher salinity when higher organisms are excluded, in lacustrine settings where calcified invertebrates are not a significant source of carbonate, or after periods of mass extinction before faunal recovery. A broad range of carbonate facies provides the context in which to understand the origin of the microbialite-dominated reservoirs developed across both ramp and rimmed shelf profiles. Major facies associations include carbonate-evaporite transition zone, deep ramp and slope, subtidal microbialites, clastic-textured carbonates, and restricted peritidal carbonates. Microbialites are subdivisible into a number of facies that all have significance in terms of understanding environmental history as well as reservoir properties, and that help in predicting the location of reservoir fairways. Microbially influenced facies include shallow subtidal thrombolites with massive clotted textures and very high initial porosities (>50%), shallow subtidal pustular laminites with cm-scale variability of lamina morphology, deeper subtidal crinkly laminites that show mm-scale variability of lamina morphology, and intertidal tufted laminates that show mm- to cm-scale tufted textures. Other reservoir facies are more conventional grainy carbonates including ripple cross-stratified grainstone–packstone, hummocky cross-stratified grainstone–packstone, flat pebble conglomerate, ooid and intraclast grainstone–packstone, and Cloudina grainstone–packstone. These facies are almost invariably dolomitized and all have moderate to excellent reservoir quality. These facies comprise carbonate platforms, broken up during salt tectonics, that range up to 160 m (525 ft) in thickness and extended laterally, prior to halokinesis, for tens to over 50 km (31 mi). The distribution of reservoir facies follows sequence stratigraphic predictions, with microbialites occurring in every accommodation profile. Late highstand and early transgressive systems tracts favor greater lateral extent of thrombolite build-ups, whereas later transgressive to early highstand system tracts favor greater lateral discontinuity and compartmentalization of buildup reservoir facies. Pustular laminites occur in close association with thrombolite buildups but form laterally extensive sheets in late transgressive to late highstand periods. Crinkly laminites form during late transgressive to early highstand systems tracts and may represent maximum flooding intervals when the flux of carbonate sediment was greatly reduced allowing pelagically derived organics to accumulate.

Superconducting properties of (Ba-K)Fe2As2 single crystals disordered with fast neutron irradiation

Resistivity ρ(T), Hall coefficient RH(T), superconducting transition temperature Tc and slopes of the upper critical field dHc2/dT were studied in (Ba1−xKx)Fe2As2 (x = 0.218, 0.356, 0.531) single crystals irradiated with fast neutrons. It is found that dTc/dρSC—the rate of decreasing Tc as a function of the ρSC (ρSC is the resistivity at T = Tc)—linearly increases with concentration x. Slow changes in the Hall coefficient RH, as well as the quadratic electronic contribution to the resistivity, show that there are no substantial changes in the topology of the Fermi surface caused by irradiation. The slopes of the upper critical field dHc2/dT in ab and c directions as a function of ρSC determined by Hall measurements show a reasonable agreement with a model that suggests constancy of the band parameters.

The postspinel boundary in pyrolitic compositions determined in the laser‐heated diamond anvil cell

In situ multianvil press (MAP) studies have reported that the depth and the Clapeyron slope of the postspinel boundary are significantly less than those of the 660 km discontinuity inferred from seismic studies. These results have raised questions about whether the postspinel transition is associated with the discontinuity. We determined the postspinel transition in pyrolitic compositions in the laser-heated diamond anvil cell (LHDAC) combined with in situ synchrotron X-ray diffraction. The Clapeyron slope was determined to be −2.5 ± 0.4MPa/K and did not vary significantly with compositions and used pressure scales. Using Pt scales, our data indicate that the postspinel transition occurs in pyrolitic compositions at 23.6–24.5GPa (1850K). The transition pressure and slope are consistent with the depth and topography of the 660 km discontinuity. Our data reveal that inaccuracy in pressure scales alone cannot explain the discrepancy and technical differences between MAP and LHDAC contribute significantly to the discrepancy.

Structural, electrical and piezoelectric properties of V-, Nb- and W-substituted CaBi4Ti4O15 ceramics

The equimolar substitution of V5+, Nb5+ and W6+ ions in the B-site of CaBi4Ti4O15 (CBT) ceramics was performed, and their sintering characteristics and microstructures were investigated. The results indicated that V2O5 has a substantial effect on the structure and properties of CaBi4Ti4O15 ceramics compared to Nb2O5 and WO3. The V-substituted sample exhibited the lowest sintering temperature, the best sinterability and the lowest conductivity among all of these samples. The comparative Raman study of the V5+, Nb5+ and W6+ doping indicated that the Bi ions in the [Bi2O2]2+ layers are more stable than those at the A sites in the pseudo-perovskite blocks, and the volatilisation of Bi during sintering preferentially occurs at A sites in the pseudo-perovskite blocks. The decrease in the volatilisation of Bi in the V-doped sample helps to maintain the amount of Bi atoms in the pseudo-perovskite blocks and the stoichiometric composition of the ceramics resulting in excellent properties. In addition, the increase in Bi ions in the pseudo-perovskite structure and the dense microstructure with a closed-packed arrangement of small grains, which result from sintering of the ceramics at a low temperature, also contributed to the notable reduction in the electrical conductivity. In comparison to the Nb- and W-doped CBT ceramics, the V-doped samples exhibited a dual slope transition in the conductivity-temperature curves, a minimum conductivity over the measured temperature range and optimum piezoelectric properties.

An empirical model for landslide travel distance prediction in Wenchuan earthquake area

Sliding mass of landslides highly endangered the area along travel path, especially landslides with long travel distance. It is necessary to develop an effective prediction model for preliminarily evaluating landslide travel distance so as to improve disaster prevention and relocation. This paper collected 54 landslides with 347–4,170 m travel distance triggered by the 2008 Wenchuan earthquake to discuss the effectiveness of various influential factors on landslide travel distance and obtained an empirical model for its prediction. The results revealed that rock type, sliding source volume, and slope transition angle were the predominant factors on landslide travel distance. The validity of proposed model was verified by the satisfactory agreement between observations and predictions. Therefore, this model might be practically applicable in Wenchuan earthquake area and other similar geomorphological and geological regions.

Fault Diagnosis of Broken Rotor Bars in Squirrel-Cage Induction Motor of Hoister Based on Duffing Oscillator and Multifractal Dimension

This paper is to propose a novel fault diagnosis method for broken rotor bars in squirrel-cage induction motor of hoister, which is based on duffing oscillator and multifractal dimension. Firstly, based on the analysis of the structure and performance of modified duffing oscillator, the end of transitional slope from chaotic area to large-scale cycle area is selected as the optimal critical threshold of duffing oscillator by bifurcation diagrams and Lyapunov exponent. Secondly, the phase transformation duffing oscillator from chaos to intermittent chaos is sensitive to the signals, whose frequency difference is quite weak from the reference signal. The spectrums of the largest Lyapunov exponents and bifurcation diagrams of the duffing oscillator are utilized to analyze the variance in different parameters of frequency. Finally, this paper is to analyze the characteristics of both single fractal (box-counting dimension) and multifractal and make a comparison between them. Multifractal detrended fluctuation analysis is applied to detect extra frequency component of current signal. Experimental results reveal that the method is effective for early detection of broken rotor bars in squirrel-cage induction motor of hoister.

Formant Transitions in Varied Utterance Positions

Aim: Acoustic characteristics associated with varied utterance positions were examined to understand the acoustic consequences of potential articulatory changes near utterance boundaries. Methods: Second formant transition characteristics, including transition duration (ms), transition extent (Hz), and derived slope of transition (Hz/ms), of 12 healthy speakers of American English were examined for two diphthong transitions in sew and sigh and one consonant-vowel transition in bee in utterance-initial, utterance-final, and utterance-end positions. Speakers performed a task of contrastive stress variation that served to demonstrate the changeability of acoustic characteristics as an index of articulatory change in shaping the vocal tract. Results: Contrastive stress, as compared to words spoken without increased stress, was associated with longer transition duration, greater transition extent, and a decreased slope. Although some utterance position effects were present, no systematic differences consistent with boundary strengthening or declination were found. Conclusion: Findings suggest that varied utterance positions may be associated with stimulus-dependent variation in articulatory changes that is reflected in the acoustic output. These results indicate the need to further understand the construct of utterance-level speech materials, such as carrier phrases, in clinical practice and research.

Loads and propulsive efficiency of a flexible airfoil performing sinusoidal deformations

This paper presents the application of state-space airloads theory to a flexible airfoil performing sinusoidal deformations at high Reynolds numbers. Given the two-dimensional motion of a flexible airfoil, we derived the closed forms for the propulsive force, lift force, generalized forces of pitching and bending as functions of reduced frequency k, dimensionless wavelength z, and dimensionless amplitude A/(2b). We also calculate the power required to perform this sinusoidal deformation and the propulsive efficiency. Our results show a positive, time-averaged propulsive force for all k>k0=π/z, which is when the wave speed is greater than the moving speed. At k=k0, which is when the moving speed reaches the wave speed, the motion reaches a steady-state with all forces being zero. When k<k0, the system is the case of energy extraction in which the drag force (negative propulsive force) and wake are causing the airfoil to vibrate. For the propulsive case, the propulsive efficiency decreases from 1.0 to 0.5 as k goes to ∞, or k0 goes to 0. If there were no wake, the propulsive force would be zero at wavelengths of z=0.569 and z=1.3 for all k, and local optimum at z=0.82. Though these extrema of propulsive force with wavelength are smoothed out by the wake effect, one can still see around z=1.3 (k=2.4) the slope transitions of all three powers in Fig. 9. When k<2.4, the cost for high propulsion become more expensive as more power input is used by wake, thus less efficiency.

Hearing tongue loops: Perceptual sensitivity to acoustic signatures of articulatory dynamics

Previous work has shown that velar stops are produced with a forward movement during closure, forming a forward (anterior) loop for a VCV sequence, when the preceding vowels are back or mid. Are listeners aware of this aspect of articulatory dynamics? The current study used articulatory synthesis to examine how such kinematic patterns are reflected in the acoustics, and whether those acoustic patterns elicit different goodness ratings. In Experiment I, the size and direction of loops was modulated in articulatory synthesis. The resulting stimuli were presented to listeners for a naturalness judgment. Results show that listeners rate forward loops as more natural than backward loops, in agreement with typical productions. Acoustic analysis of the synthetic stimuli shows that forward loops exhibit shorter and shallower VC transitions than CV transitions. In Experiment II, three acoustic parameters were employed incorporating F3-F2 distance, transition slope, and transition length to systematically modulate the magnitude of VC and CV transitions. Listeners rated the naturalness in accord with those of Experiment I. This study reveals that there is sufficient information in the acoustic signature of "velar loops" to affect perceptual preference. Similarity to typical productions seemed to determine preferences, not acoustic distinctiveness.

Testing and modeling of Nomex™ honeycomb sandwich Panels with bolt insert

Nomex™ honeycomb core sandwich panels with a bolt insert were load tested and modeled. The objective was to predict the honeycomb local buckling load and to identify a Nomex™ honeycomb constituent material model. Sandwich specimens were subjected to bolt pull-out load tests. The same sandwich structure was also tested in flat-wise tension with strain gages installed on the honeycomb walls. Finite element models of the flat-wise tension and bolt pull-out tests were built. The honeycomb geometry and strain gages were modeled with shell elements. An orthotropic honeycomb material model was identified by comparing the two test models to the experimental data. The material parameters identified are in the mid-range of previously published values. The pull-out test model was used to predict honeycomb wall buckling with a nodal rotation vector sum criterion. The buckling loads predictions closely corresponded to the start of the experimental load/displacement slope transition zone.

Arc-induced long-period fiber gratings inscribed in asymmetric transition tapers

Long-period fiber gratings (LPFGs) and tapered fibers are spectrally selective devices with important applications in sensing, especially for monitoring chemical and physical parameters. When combined, they can give rise to devices with enhanced characteristics that can be tailored by varying their fabrication parameters. We analyze the characteristics of arc-induced LPFGs written on the longer transition of asymmetric tapers, which provide a variable diameter section whose slope can be adjusted in order to tailor the device performance. In comparison with LPFGs fabricated in nontapered fibers, the grating inscription in the linear taper transition produces deeper notches (>20 dB ), whose bandwidth and separation increase with the transition slope. The simplicity of the electric arc technique to fabricate LPFGs, and the degrees of freedom added by the tapered fiber open up the possibility to realize thorough studies on the many possible combinations, to develop devices with characteristics designed on purpose.