Evolution of the upper critical field and superconducting vortex phase with thickness in PLD-grown Ta fllms

High quality superconducting thin films are the basis for the application of superconducting devices. Here we report the fllm growth and superconducting properties of the Ta films. The films were grown by the pulsed laser deposition technique on the α-Al2O3 substrates. It is found that, with the increase of the fllm thickness from 20 nm to 61 nm, both the superconducting transition temperature Tc and residual resistance ratio RRR display an upward trend, while the upper critical field decreases monotonously in a wide temperature region. A clear anisotropic behavior is revealed by comparing the upper critical fields with two difierent orientations (H ⊥ film and H // film). The anisotropy parameter Γ is found to be as high as 20 for the sample with the thickness of 20 nm. The systematical evolution from two- to three-dimensional features for the superconductivity with the increase of fllm thickness is observed in the temperature dependent upper critical fleld data. Moreover, the vortex liquid region tends to expand with the increase of the fllm thickness.

Interaction of surfactants with poloxamers 338 and its effect on some properties of cream base

The aim. Study of the interaction of surfactants with poloxamer 338 (P338) and the effect of P338 on the properties of cream bases. Materials and methods. Solutions of the surfactants and P338 as well as cream bases were under study. The average hydrodynamic diameter (Dh) and zeta potential (ζ‑potential) were determined by the light scattering intensity and electrophoretic mobility of micelles. The electron paramagnetic resonance (EPR) spectra of spin probes in micelles, solvents and bases were obtained; the type of spectrum, isotropic constant (AN), rotational correlation times (τ) and anisotropy parameter (ε) were determined. Liquids and cream bases were studied by capillary and rotational viscometry; the flow behaviour and yield stress (t0), dynamic and apparent viscosity (η) as well as the hysteresis (thixotropic) area (AH) were determined. The microstructure of the bases was examined by optical microscopy. The strength of adhesion (Sm) was assessed by the pull-off test, and the absorption of water was studied by dialysis. Results. Under the impact of P338 the hydrodynamic diameters of micelles formed by cationic, anionic and nonionic surfactants decreased as well as the absolute values of their ζ‑potential became lower, but the microviscosity of the micelle nuclei increased. There was also a change in the structure of the aggregates of surfactant with fatty alcohols; EPR spectra, which were superpositions characteristic for the lateral phase separation, converted into triplets that indicated the uniform distribution of lipophilic probes in the surfactant phase. When the content of P338 increased to 17 %, the rheological parameters of the bases increased drastically, the flow behaviour and the microstructure changed. The bases had the consistency of cream within temperature range from 25 °C to 70 °C and completely restored their apparent viscosity, which had decreased under shear stress. P338 enhances the adhesive properties of the bases. Due to their microstructure, cream bases have a lower ability to absorb water compared to a solution and gel containing 17 % and 20 % P338, respectively. Conclusions. The structure of surfactant micelles and aggregates of surfactants with fatty alcohols changed under impact of P338 due to the interaction of surfactants with P338. As a result of this interaction, at a sufficiently high concentration of P338, the microstructure and flow behaviour of bases changed, their rheological parameters, which remain high at temperatures from 25 °C to 70 °C, increased significantly, and water absorption parameters decreased. The bases with P338 were more adhesive

Two-Dimensional Soil Geometric Tortuosity Model Based on Porosity and Particle Arrangement

Porosity and particle arrangement are important parameters affecting soil tortuosity, so it is of great significance to determine the intrinsic relationship between them when studying soil permeability characteristics. Theoretical derivation and geometric analysis methods are used to derive a two-dimensional geometric tortuosity model. The model is a function of particle arrangement parameters (m and θ) and porosity. An analysis of the model and its parameters shows that: (1) The arrangement of particles is one of the reasons for the different functional relationship between tortuosity and porosity, which proved that the tortuosity is not only related to the porosity but also affected by the particle arrangement. (2) The greater the anisotropy parameter m is, the greater the tortuosity is, indicating m varies when fluid passes through the soil from different sides resulting in different values of permeability. (3) The tortuosity increases with the increase in the blocking parameters θ. (4) With increasing porosity, the influence of the parameters m and θ on the tortuosity gradually decreases, suggesting that the influence of particle arrangement on tortuosity gradually decreases. The results presented here increase the understanding of the physical mechanisms controlling tortuosity and, hence, the process of fluid seepage through soil.

Localized forming limit analysis of substrate-supported metals: Influence of yield-dependent necking bound angle

In this paper, the influence of functional elastomeric substrate-supported layers for enhancing potential resistance capability against localized plastic failure of advanced high strength steels is considered based on a localized necking model of vertex theory. Application of this structure leads to postponing the plastic instability of the metallic part. By defining diffuse and localized modes of deformation in a general framework, the theoretical models are developed to predict necking limits at several stress states. In addition, the results of the Hookean and neo-Hookean elastomers are compared in terms of strain hardening with the anisotropy parameter of Hill’s yield criteria. Since necking band angle (NBA) is a principal factor for the necking prediction, its effect on bifurcation events is evaluated specifically for different ratios of stress rate, and quadratic and non-quadratic yield criteria. This analysis is performed by proposing a supported and yield-dependent necking bound angle (YD-NBA). All considerations are done by providing equilibrium conditions governed over the NBA. Finally, obtained results indicate good agreements between several theoretical considerations and experimental data.

A Novel Discontinuity Roughness Parameter and Its Correlation with Joint Roughness Coefficients

Joint roughness determination is a fundamental issue in many areas of rock engineering, because joint roughness has significant influences on mechanical properties and deformation behavior of rock masses. Available models suggested in the literature neglected combined effects of shear direction, scale of rock discontinuities, inclination angle, and amplitude of asperities during the roughness calculations. The main goals of this paper are to establish a comprehensive parameter that considers the characteristics of the size effect, anisotropy, and point spacing effect of the discontinuity roughness, and to investigate the correlation between the proposed comprehensive parameter and joint roughness coefficients. In this work, the Barton ten standard profiles are digitally represented, then the morphological characteristics of the discontinuity profiles are extracted. A comprehensive parameter that considers the characteristics of the size effect, anisotropy, and point spacing effect of the discontinuity roughness is established, and its correlation with joint roughness coefficients (JRC) is investigated. The correlation between the proposed discontinuity roughness parameter and the joint roughness coefficients can predict the JRC value of the natural discontinuities with high accuracy, which provides tools for comprehensively characterizing the roughness characteristics of rock discontinuities. The roughness index Rvh[−30°,0] reflects the gentle slope characteristics of the rock discontinuity profiles in the shear direction, which ignores the segments with steep slopes greater than 30° on the discontinuity profiles. The influence of steep slope segments greater than 30° should be considered for the roughness anisotropy parameter in the future.

Rayleigh-Benard Convection in Nanofluids Layer saturated in a Rotating Anisotropic Porous Medium with Feedback Control and Internal Heat Source

Control strategy on Rayleigh-Benard convection in rotating nanofluids saturated in anisotropic porous layer heated from below is studied in the presence of uniformly internal heat source for rigid-rigid, free-free, and lower-rigid and upper-free boundaries. Feedback control strategy with an array of sensors situated at the top plate and actuators located at the bottom plate of the nanofluids layer are considered in this study. Linear stability analysis based on normal mode technique has been performed, the eigenvalue problem is obtained numerically by implementing the Galerkin method and computed by using Maple software. Model employed for the nanofluids includes the mechanisms of Brownian motion and thermophoresis. The problem of the onset of convective rolls instabilities in a horizontal porous layer with isothermal boundaries at unequal temperatures known as Horton-Roger-Lapwood model based on the Darcy model for the fluids flow is used. The influences of internal heat source’s strength, modified diffusivity ratio, nanoparticles concentration Darcy-Rayleigh number and nanofluids Lewis number are found to advance the onset of convection, meanwhile the mechanical anisotropy parameter, thermal anisotropy parameter, porosity, rotation, and controller effects are to slow down the process of convective instability. No visible observation on the modified particle density increment and rigid-rigid boundaries are the most stable system compared to free-free and rigid-free boundaries.

Core-Derived Velocity Systematics, Mississippian Meramec Formation, Oklahoma

Summary Elastic wave velocities are commonly used to predict porosity, mineralogy, and lithology from formation properties. When only P-wave sonics are available in historical wells, systematics for predicting shear velocities are useful for developing elastic models. Although much research has been done on conventional reservoir velocity systematics, the equivalency for unconventional formations is still a work in progress. There has also been a limited number of research studies with laboratory measures published. Using laboratory pulse transmission ultrasonic data, we created a Vp-Vs systematic for the Meramec Formation in this study. The effects of porosity and mineralogy on velocities are explored, as well as a comparison of Meramec velocity systematics with well-established literature systematics. Vp and Vs measurements were taken on 385 dodecane-saturated core samples from seven Meramec wells (106 vertical and 279 horizontal plugs). S-wave and P-wave anisotropy in Meramec Formation samples used in this study are typically less than 10%. Each sample was also tested for porosity and mineralogy. We find that velocities are more sensitive to porosity than mineralogy by a factor of 10. Below are our equations for predicting Vp and Vs (in km/s), when only clay content and porosity are known. In these equations, φ is the volume fraction pores, and Clays is the weight fraction of clay. These equations are for those samples in which there is low P-wave and S-wave anisotropies:(1)Vp=6.4−1.2*Clays−15.4*φ(R2=0.5),(2)Vs=3.6−0.5*Clays−5.2*φ(R2=0.4). We suggest two methods for calculating Vs from Vp: Ignoring anisotropy, we combined both Vp and Vs measurements from all vertical plugs and low anisotropy horizontal plugs to create a single shear wave predictor; and considering anisotropy, Vp measurements from horizontal plugs were corrected using Thomsen’s compressional wave anisotropy parameter, after which a shear velocity predictor was generated. The shear wave predictors for dodecane-saturated measurements are as follows (all velocities are km/s):(3)Method 1: Vs= 0.90 + 0.42*Vp (R2=0.7),(4)Method 2: Vs= 0.80 + 0.45*Vp (R2=0.6). The residual and estimated error in Eq. 3 is slightly less than in Eq. 4. Even though there is a significant variance in measurement frequency, the Meramec velocity systematic shows good agreement with dipole wireline measurements using the first equation. The Meramec velocity systematics differ significantly from previously published systematics, such as the trend line by Greenberg and Castagna (1992) and the shale trend line by Vernik et al. (2018). Using the correlations by Greenberg and Castagna (1992) for limestone or dolomite, the shear velocities of the samples in this study cannot be predicted. These data have yielded shear wave systematics, which can be used in wireline and seismic investigations. The results suggest that the method of ignoring anisotropy yields a better Vs estimate than the one that takes anisotropy into account. Using well-established shear wave velocity systematics from the published literature can result in an estimated inaccuracy of greater than 16%. It is important to calibrate velocity systematics to the target formation.

Change in the acoustic anisotropy parameter of structural steel during fatigue failure

Material damages affect its microstructure, physical and acoustic properties. The article considers microstructural and ultrasonic studies of the St3sp5 steel carried out under cyclic uniaxial tension-compression in the low-cycle fatigue area. The fatigue tests were performed in stages. At each stage of cyclic deforming, the structure of steel samples was studied by the ultrasonic method and the change in the acoustic anisotropy parameter was determined. The relationship between the acoustic characteristics of the material and the degree of its damage is found. Based on the relationship the residual life can be predicted. The advantage of this method for determining the residual resource using the acoustic anisotropy parameter is that it is not required to determine the length of the acoustic path, for example, the wall thickness of the object under study. The influence of the deformation range of the cycle on the rate of the acoustic anisotropy parameter change is investigated. A direct linear relationship was established between the relative number of cycles and acoustic anisotropy parameter. An algorithm for determining the residual life of a material based on studies of microstructural changes and ultrasonic data is proposed.

The Use of Core & Log Anisotropy Parameters into Seismic Data Processing: A Case Study of Deep-Water Reservoir

The seismic far-offset data plays important role in seismic subsurface imaging and reservoir parameters derivation, however, it is often distorted by the hockey stick effect due to improper correction of the Vertical Transverse Isotropy (VTI) during the seismic velocity analysis. The anisotropy parameter η is needed to properly correct the VTI effect. The anisotropy parameters of ε and δ obtained from log and core measurements, can be used to estimate the η values, however, the upscaling effects due to the different frequencies of the wave sources used in the measurements must be carefully taken into account. The objective is to get better understanding on the proper uses of anisotropy parameters in the the velocity analysis of deepwater seismic gather data. To achieve the objective, the anisotropy parameters from ultrasonic core measurements and dipole sonic log were used to model the seismic CDP gathers. The upscaling effects is reflected by the big difference of measured anisotropy values, in which the core measurement value is about 40 times higher than the log measurement value. The CDP gathers modelling results show that, due to the upscaling effect, the log and core-based models show significant differences of far-offset amplitude and hockey sticks responses. The differences can be minimized by scaling-down the log anisotropy values to core anisotropy values by using equations established from core – log anisotropy values cross-plot. The study emphasizes the importances of integrating anisotropy parameters from core and log data to minimize the upscaling effect to get the best η for the VTI correction in seismic velocity analysis.