Degree Of Inhomogeneity Research Articles

Etched surface morphology analysis experiments under different reaction rates

Etched surface morphology is the main cause of etched fracture conductivity. It would be helpful to optimize acidification fracturing design and improve the reservoir reconstruction effect by analyzing the rock etched surface during the acid-rock reaction process. The chemical mechanism involved in forming the etched carbonate surface and reasons for non-uniform morphogenesis are thoroughly analyzed in this paper. By applying different viscous acid-rock reaction kinetic parameters, a measuring device, and a 3D laser scanner, the acid-rock reaction rate and etched surface morphology are tested under different acid concentrations, reaction temperatures, and flow rates. The regularity of the surface morphology is also obtained under different acid-rock reaction rates. The results demonstrate that, with an increase in the acid concentration, reaction temperature, and acid flow, the acid reaction rate can be accelerated and the etched masses are positively related to the etched volume and acid-rock reaction rate. The main controlling factors of the acid-etched surface morphology in the parallel and vertical acid flow directions are the acid-rock reaction rate and mineral composition distribution, respectively. The increase in the acid-rock reaction rate contributes to drastic changes in the rock wavy surface, as well as the differences in and degree of inhomogeneity. In the acid flow direction, it is more conducive to form acid-etched holes and grooves by increasing the acid-rock reaction rate.

Estimating Effects of Individual PV Panel Failures on PV Array Output

Photovoltaic (PV) plants are becoming an ever more popular source of energy. While individual PV panels are quite resilient, failures do happen. Due to the arrangement of interconnections between multiple PV panels in an array and the maximum power point tracking mechanism, the failure of a single panel can influence the output of the whole ensemble. This paper estimates the impact of a single panel short-circuit failure on the output of a series–parallel array. Generally, the array power loss is larger than the contribution of the failed panel. The dependence of this increase on various factors such as the number of panels/strings, the shape of the current–voltage ( I–V ) curve of the panels, and the degree of panel inhomogeneities is investigated. This increase is found to depend most significantly on the shape of the I–V curve of the panel, and only weakly on a range of other parameters. It is, therefore, useful in estimating the impact of panel failures without the need to know many details about the system.

Comprehensive Laboratory Core Analysis at CPGR IPE RAS

The article presents a complex of laboratory core analyses conducted at the Center for Petrophysical and Geomechanical Research, Schmidt Institute of Physics of the Earth, Russian Academy of Sciences (CPGR IPE RAS). The complex provides for multiscale studies of the elastic properties, microstructure, composition, and porosity and permeability properties of rocks. The laboratory studies determine the dynamic and static elastic moduli, rock strength and creep parameters, and acoustic emission characteristics; 2D and 3D microstructure analysis is also performed. Dynamic elastic moduli are determined both under normal and reservoir-simulating conditions. Under normal conditions, multilevel ultrasound examination of samples is carried out; its results, together with those of microstructure analysis, are then used to determine the degree of inhomogeneity of the elastic properties of a sample, to reveal the anisotropy of these properties, and to compare the elastic properties of rocks at different scales. The results of geomechanical rock tests are necessary for constructing geomechanical models of reservoirs. The elastic parameters determined under normal and reservoir conditions are the basis for constructing correlation dependences that allow the geomechanical properties and principal stresses under reservoir conditions to be forecasted from well log data. Data on the elastic properties and microstructure of samples are used to construct different-scale models of the elastic properties of rocks under normal and reservoir conditions using petrophysical methods; these models further serve as a basis for petroelastic modeling of hydrocarbon fields and for predicting the viscoelastic behavior of rocks.

Effective medium theory for anisotropic media with plasmonic core-shell nanoparticle inclusions

.Core-shell building blocks have been found useful in recent years as inclusions, in the search for metamaterials with tailored properties. Either the core or the shell of these composite inclusions may be metallic, and the dielectric component may be both radially anisotropic and radially inhomogeneous. In tunable anisotropic metamaterials, the tuning may then be achieved through the host, the core, or some combination thereof. However a theoretical picture is harder to build. Here we propose an approach to an effective medium theory for such materials, valid in the quasi-static limit. The method proceeds first by homogenising the interior of complex particle, and then uses standard anisotropic effective medium methods to provide bulk effective homogenized parameters. By varying the degree of inhomogeneity in the core, shell and dielectric-metal material volume fractions, the technique can be used as a tool for the design of metamaterials with specifically engineered properties. We find that metamaterial properties can be readily tuned by reorienting the optical axis of the host (e.g., liquid crystal). In particular, there is a possibility of switching between hyperbolic and conventional anisotropic metamaterial properties by changing inclusion shell properties.

Investigation of static/dynamic moduli and plastic response of shale specimens

High clay and organic content, irregular voids, presence of micro-cracks, and obvious bedding planes are among features of shale gas rocks that affect their mechanical response. These sedimentary rocks exhibit substantial degree of anisotropy and inhomogeneity, with non-linear response when subjected to axial loading. The laboratory characterization of these rocks is necessary to design an optimized hydraulic fracturing programme, and for reliable constitutive and numerical modeling of these formations. In this study, a series of triaxial multi-stage elastic and cyclic tests were performed on Marcellus Shale specimens, retrieved from a deep well (~2270 m deep) located in West Virginia, to characterize their elastic-plastic and hysteresis response subjected to loading/unloading cycles. The experimental results indicated a nonlinear response, particularly at low differential stress levels. In addition, the specimens with higher clay content exhibited a softer response with lower estimated static and dynamic moduli at different stress levels compared to those of specimens with higher calcite/quartz content. The ultrasonic P- and S-wave velocity measurements were found to be sensitive to the changes in the micro-structure of the rock caused by variation in stress condition. In general, the estimated Young's modulus during unloading was found to be higher than loading. The plastic deformations were pronounced in the first cycle of loading, followed by a decreasing trend in the subsequent cycles.

Characterization of nanocrystallised multilayered metallic materials produced by the SMAT followed by constrained compression

Nanocrystallised multilayered metallic material was obtained via duplex technique combining the surface mechanical attrition treatment (SMAT) with a novel constrained compression (CC) process. At the initial stage the 1 mm thick sheets of 316L austenitic stainless steel were processed by the SMAT in order to form a nanocrystalline structure. At the final stage disc-shaped plates excised from SMATed sheets, were assembled in a package and compressed in order to produce metallurgical bonding between individual plates. The characterization of such a multilayered structure was studied both experimentally and numerically. The microscopic examination revealed that the bonding occurred in the central portions of the package where the oxide scale covering each plate was fragmented by high shear strains. The numerical analysis confirmed that the strains at the interior interfaces are significantly higher than at the external ones. A high degree of structural inhomogeneity was observed via TEM studies in the regions where the successful bonding was achieved. Regions characterised by fine band structure with the presence of α′-martensite phase as well as coarse cellular structure within a single γ-austenite phase were identified.

Analysis of the inhomogeneous barrier and phase composition of W/4H-SiC Schottky contacts formed at different annealing temperatures**Project supported by the Opening Project of Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences and the National Key Research and Development Program of China (Grant No. 2016YFB0100601).

The electrical characteristics of W/4H-SiC Schottky contacts formed at different annealing temperatures have been measured by using current–voltage–temperatures (I–V–T) and capacitance–voltage–temperatures (C–V–T) techniques in the temperature range of 25 °C–175 °C. The testing temperature dependence of the barrier height (BH) and ideality factor (n) indicates the presence of inhomogeneous barrier. Tung’s model has been applied to evaluate the degree of inhomogeneity, and it is found that the 400 °C annealed sample has the lowest T0 of 44.6 K among all the Schottky contacts. The barrier height obtained from C–V–T measurement is independent of the testing temperature, which suggests a uniform BH. The x-ray diffraction (XRD) analysis shows that there are two kinds of space groups of W when it is deposited or annealed at lower temperature (≤ 500 °C). The phase of W2C appears in the sample annealed at 600 °C, which results in the low BH and the high T0. The 500 °C annealed sample has the highest BH at all testing temperatures, indicating an optimal annealing temperature for the W/4H-SiC Schottky rectifier for high-temperature application.

Renormalization group properties in the conformal sector: towards perturbatively renormalizable quantum gravity

The Wilsonian renormalization group (RG) requires Euclidean signature. The conformal factor of the metric then has a wrong-sign kinetic term, which has a profound effect on its RG properties. Generically for the conformal sector, complete flows exist only in the reverse direction (i.e. from the infrared to the ultraviolet). The Gaussian fixed point supports infinite sequences of composite eigenoperators of increasing infrared relevancy (increasingly negative mass dimension), which are orthonormal and complete for bare interactions that are square integrable under the appropriate measure. These eigenoperators are non-perturbative in ℏ and evanescent. For ℝ4 spacetime, each renormalized physical operator exists but only has support at vanishing field amplitude. In the generic case of infinitely many non-vanishing couplings, if a complete RG flow exists, it is characterised in the infrared by a scale Λp > 0, beyond which the field amplitude is exponentially suppressed. On other spacetimes, of length scale L, the flow ceases to exist once a certain universal measure of inhomogeneity exceeds O(1) + 2πL2Λp2. Importantly for cosmology, the minimum size of the universe is thus tied to the degree of inhomogeneity, with space-times of vanishing size being required to be almost homogeneous. We initiate a study of this exotic quantum field theory at the interacting level, and discuss what the full theory of quantum gravity should look like, one which must thus be perturbatively renormalizable in Newton’s constant but non-perturbative in ℏ.

Preparation of Fibrillated Cellulose Nanofiber from Lyocell Fiber and Its Application in Air Filtration.

Ambient particulate matter less than 2.5 μm (PM2.5) can substantially degrade the performance of cars by clogging the air intake filters. The application of nanofibers in air filter paper can achieve dramatic improvement of filtration efficiency with low resistance to air flow. Cellulose nanofibers have gained increasing attention because of their biodegradability and renewability. In this work, the cellulose nanofiber was prepared by Lyocell fiber nanofibrillation via a PFI-type refiner, and the influence of applying a cellulose nanofiber on filter paper was investigated. It was found that the cellulose nanofibers obtained under 1.00 N/mm and 40,000 revolutions were mainly macrofibrils of Lyocell fiber with average fiber diameter of 0.8 µm. For the filter papers with a different nanofiber fraction, both the pressure drop and fractional efficiency increased with the higher fraction of nanofibers. The results of the figure of merit demonstrated that for particles larger than 0.05 µm, the figure of merit increased substantially with a 5% nanofiber, but decreased when the nanofiber fraction reached 10% and higher. It was concluded that the optimal fraction of the cellulose nanofiber against PM2.5 was 5%. The results of the figure of merit were related to the inhomogeneous distribution of nanofibers in the fibrous structure. The discrepancy of the theoretical and measured pressure drop showed that a higher nanofiber fraction led to a higher degree of fiber inhomogeneity.

Feasibility study for the development of a certified reference material of nitrofuran metabolites in chicken breast muscle from incurred samples

Certified reference materials (CRM) provide measurements of quality and metrological traceability relative to the International System of Units (SI). The results of a feasibility study for the development of an incurred CRM for the mass fraction of nitrofuran metabolites in chicken muscles are presented in this work. A small-scale batch of material was produced from freeze-dried chicken breast muscles containing residues of 3-amino-2-oxazolidinone (AOZ) and 3-amino-5-morpholinomethyl-2-oxazolidinone (AMOZ) metabolites after the controlled in vivo administration of furazolidone and furaltadone antibiotics. A small-scale batch from a blank matrix, without the metabolites, was also produced. The granulometry, stability of residual moisture content, effect of the treatment by irradiation at 3 kGy, 5 kGy and 7 kGy, and degree of inhomogeneity of the property values and residual moisture were evaluated. All statistical approaches for homogeneity and stability assessments were performed based on the principles of ISO Guide 35:2006.

Giant magnetoresistance switching in multilayer graphene grown on cobalt

Magnetic multilayer devices, showing large magnetoresistance (MR) effects, have revolutionized magnetic sensing and data storage sectors over the last few decades. Two-dimensional van der Waals layered materials are relatively new entrants in this area, and these materials can give rise to large MR effects with diverse physical origins. Here we report observation of giant MR switching (∼10 orders of magnitude) in multilayered graphene grown on cobalt (Co) substrates, which persists even at room temperature. The origin of this effect is linked with weak interlayer coupling of the graphene stacks, which gives rise to an ‘interlayer MR’ effect. This effect is found to be robust against some degree of inhomogeneity in the graphene stack, making it an attractive platform for the emerging area of flexible magnetic sensorics.

Influence of transversely inhomogeneous pseudo-thermal light source on lensless ghost imaging

The influence of a transversely inhomogeneous pseudo-thermal light source on lensless ghost imaging is investigated theoretically and experimentally. Based on classical optical theory, a model of lensless ghost imaging with an inside inclined light source is analyzed. We use the optical path difference between different transverse positions of the light beam to estimate the degree of inhomogeneity. The results indicate that the transversely inhomogeneous light source decreases the visibility and signal-to-noise ratio of the reconstructed image. Finally, we implement experiments to verify our results using inclined ground glass.

Stabilization of nonvolatile memory operations using GaN/AlN resonant tunneling diodes by reducing structural inhomogeneity

A new nonvolatile memory based on intersubband transitions and electron accumulation in GaN/AlN resonant tunneling diodes (RTDs) was investigated toward the realization of a high-speed nonvolatile random-access memory (RAM) operating on picosecond time scales. It was shown that the endurance of write/erase memory operations can be enhanced by reducing the structural inhomogeneity of GaN/AlN RTDs. Neither mechanical damage nor significant degradation of current–voltage characteristics was observed after repeated write/erase memory operations using GaN/AlN RTDs with small degrees of inhomogeneity. High-endurance nonvolatile RAMs for computing systems are expected to be realized by further improvement in the crystal quality of GaN/AlN RTDs.

Statistics of scalar dissipation and reaction progress in turbulent flames with compositional inhomogeneities

This paper presents detailed measurements of three-dimensional (3D) scalar dissipation rates collected in turbulent, piloted flames with varying degree of compositional inhomogeneity. Joints statistics of mixture fraction and reaction progress variable are also shown for a range of conditions. These measurements complement the already existing substantial data set for mixed-mode flames stabilized on the Sydney piloted burner with compositionally inhomogeneous inlets. It is found that the difference between 2D (χr) and 3D (χ) scalar dissipation increases with axial distance along the flame such that the ratio χ/χr may be as high as 2.6. The effects of spatial resolution become more significant as compositional inhomogeneity increases. Mixture fraction, ξ is well-correlated with reaction progress variable, c, in turbulent homogenous flames but the correlations deteriorates significantly as the compositional inhomogeneity increases. This transition should clearly be accounted for in modeling mixed-mode combustion. A new mode of conditioning the scalar dissipation data with respect to burnt and unburnt fluid samples reveal separate trends: while the levels of χ remain similar for burnt samples, unburnt fluid experiences increasing levels of χ as the flames approach blow-off.

High Temperature Behavior Prediction Techniques for Non-Uniform Ni/SiC Schottky Diodes

Two characterization methods are compared in terms of their suitability for predicting the electrical behavior of non-uniform Ni/4H-SiC Schottky contacts up to 450°C, using data measured at lower temperatures. These techniques are based on the established Gaussian distribution of barrier heights model and a recently proposed discrete barrier distribution model, respectively. Two samples with different degrees of contact inhomogeneity are measured and their forward characteristics are fitted using both techniques. The Gaussian distribution approach is shown to accurately fit experimental data only for the nearly-uniform sample, while requiring the extraction of two separate barrier height values from measurements in the room-250°C range, only. When attempting to use this method to characterize the sample with strong non-uniformity, fitting accuracy (given by R2) drops under 90%. In contrast, the discrete barrier distribution technique is proven able to forecast the electrical behavior of both samples (with R2 > 99% in most cases), over the entire room-450°C range, using a single Schottky barrier for each device (1.61V, corresponding to a Ni2Si Schottky contact and 0.9V, afferent to a Ni metallization).

Multi-Variable and Bi-Objective Optimization of Electric Upsetting Process for Grain Refinement and Its Uniform Distribution

It is significant to adjust the microstructures of preforms in pursuit of high-quality exhaust valves. This work is a novel attempt to identify the optimum process parameters in electric upsetting of 3Cr20Ni10W2 high-alloy to achieve grain refinement and uniform distribution by multi-objective genetic algorithm (MOGA) optimization. A finite element (FE) model on basis of electric-thermal-mechanical and macro-micro sequential multi-physics analysis methods was developed in software MSC. Mar. And different schedules of four independent process variables (heating current (I), clamping length (L), upsetting pressure (Pset) and velocity of the anvil cylinder (v)) were performed aiming to achieve two objective indicators (average grain size (dav) and inhomogeneous degree of grain distribution (σd)). Then, two objective response surfaces were constructed as the functions between the two indicators and the four independent process variables. As per the criterion that simultaneously minimize dav and σd, the processing parameters (Pset, L, v, I) were optimized by MOGA, and corresponding numerical simulation were performed. The results show that both dav and σd are improved significantly at the optimal process condition as verified by the trial-manufacture experiments, which validated the optimal design and corresponding simulation based on grain refinement and uniform distribution by MOGA was credible and effective.

An adaptive-scale active contour model for inhomogeneous image segmentation and bias field estimation

The active contour model is a widely used method for image segmentation. Most existing active contour models yield poor performance when applied to images with severe intensity inhomogeneity. To address this issue, we propose an adaptive-scale active contour model (ASACM) based on image entropy and semi-naive Bayesian classifier, which achieves simultaneous segmentation and bias field estimation for images with severe intensity inhomogeneity. Firstly, an adaptive scale operator is constructed to adaptively adjust the scale of the ASACM according to the degree of the intensity inhomogeneity. Secondly, we define an improved bias field estimation term via distributing a dependent-membership function for each pixel to estimate the bias field in severe inhomogeneous images. Thirdly, a new penalty term is proposed using piecewise polynomial, which helps to avoid time-consuming re-initialization process and instability in conventional penalty term. The experimental results demonstrate that the proposed ASACM consistently outperforms many state-of-the-art models in segmentation accuracy, segmentation efficiency and robustness w.r.t initialization and noise.

Explicit size distributions of failure cascades redefine systemic risk on finite networks

How big is the risk that a few initial failures of nodes in a network amplify to large cascades that span a substantial share of all nodes? Predicting the final cascade size is critical to ensure the functioning of a system as a whole. Yet, this task is hampered by uncertain and missing information. In infinitely large networks, the average cascade size can often be estimated by approaches building on local tree and mean field approximations. Yet, as we demonstrate, in finite networks, this average does not need to be a likely outcome. Instead, we find broad and even bimodal cascade size distributions. This phenomenon persists for system sizes up to 107 and different cascade models, i.e. it is relevant for most real systems. To show this, we derive explicit closed-form solutions for the full probability distribution of the final cascade size. We focus on two topological limit cases, the complete network representing a dense network with a very narrow degree distribution, and the star network representing a sparse network with a inhomogeneous degree distribution. Those topologies are of great interest, as they either minimize or maximize the average cascade size and are common motifs in many real world networks.

Permissible Electrical-Field Intensities in the Cast Epoxy Insulation of a 6- to 110-kV Switchgear

The method of choice of the working intensity of the electrical field in the cast epoxy insulation of a 6- to 110-kV switchgear taking into account its dimensions, structure, and basic operational factors is studied. The volt–time characteristics of the electrical strength of the cast epoxy insulation corresponding to a low probability of the breakdown at the different intensity of the partial discharges are analyzed. It is shown that the distribution of the electrical strength of the cast insulation under the short-term and long-term action of the commercial-frequency voltage is well described by the Weibull law and the influence of the dimensions on the electrical strength is specified by the “active” volume of the dielectric—the area where the electricalfield intensity makes up no less than 85% of the maximum in the clearance. The estimation of the permissible field intensities in the cast insulation of a 10- to 35-kV switchgear with various degrees of the field inhomogeneity and intensities of the partial discharges is given.

Assessment of gasoline direct injector fouling effects on fuel injection, engine performance and emissions

The current optical and thermal experimental tests were mainly focused on obtaining a comprehensive understanding of the effects of gasoline direct injector fouling on mass flow rates, spray characteristics, engine emissions and engine performance. A robust injector fouling cycle was employed to produce coked injectors in a multi-cylinder thermal engine. Deposit build-up in the coked injectors and fouling cycle repeatability was first examined by measurements of fuel flow rate. Macroscopic spray characteristics of the clean and the coked injectors were carried out using high-speed imaging and Planar Laser Induced Fluorescence (PLIF) of sprays foot-print. Fuel droplets size and velocity were characterised with a two-dimensional Phase Doppler Particle Analyser (PDPA). It was observed that the deposit build-up inside injector nozzles and on injector tips reduced the plume cone angle while increased plume penetration length, plume separation angles, mean droplet velocity and size for the coked injector. Impact of injector fouling was further investigated by PLIF measurements of in-cylinder charge inhomogeneity and repeatability in mixture preparation. The coked injectors showed higher degree of inhomogeneity and poorer repeatability in mixture preparation. These were in agreement with combustion analysis results where the coked injectors showed lower load and lower combustion stability compared with the clean injector under same operating conditions. Significantly higher unburned hydrocarbon emissions and particulate number concentration were also observed for the coked injectors. This work was carried out to obtain a broad picture of injector cooking effects in GDI engines.