Degree Of Inhomogeneity Research Articles

Measurement Techniques for Identifying Polarity Dependence of Ion Injection in Transformer Oil

Charge injection from metallic surfaces into mineral oil is investigated utilizing transient currents recorded in coaxial cylindrical electrode systems with different degrees of inhomogeneity of electric fields. The currents obtained with single polarity and reverse polarity methods demonstrate differences in their behavior depending on the geometry and type of the test voltage. The data show clear relation between the sign of the current and the polarity of the applied voltage, which is attributed to the polarity dependence of the ion injection from oil-metal interfaces. The results of the experiments are discussed in terms of relaxation time of the system and time of flight (drift time) of ions in the oil gap.

CONFIGURATIONAL FORCE EXERTED ON AN INHOMOGENEITY BY A PILEUP OF SCREW DISLOCATIONS

Configurational forces exerted by a screw dislocation pileup on a circular inhomogeneity or a bimaterial interface are determined for a given number of dislocations, the level of remotely applied stress, and a specified degree of material inhomogeneity. The interface shear stress is also evaluated and discussed.

Development, modeling and research of the system of automatic control and equalization of the charge state of a battery pack of a hybrid engine of a vehicle

The article is devoted to the topical problem of developing effective means of monitoring and leveling the charge state of batteries in a power unit of hybrid and electric cars. A system for automatic control and equalization of the charge state of a battery pack of a combined power plant, the originality of which is protected by the Russian Federation patent, is developed and described. A distinctive feature of the device is the possibility of using it both in conditions of charging (power consumption) and in operating conditions (energy recovery). The device is characterized by high reliability, simplicity of the circuit-making solution, low self-consumption and low cost. To test the efficiency of the proposed device, its computer simulation and experimental research were carried out. As a result of multi factorial experiment, a regression equation has been obtained which makes it possible to judge the high efficiency of detecting the degree of inhomogeneity of controlled batteries with respect to the parameters of an equivalent replacement circuit: voltage, internal resistance and capacitance in the magnitude of the obtained coefficients of influence of each of these factors, and also take into account the effects of their pair interactions.

Highly stabilized partially premixed flames of propane in a concentric flow conical nozzle burner with coflow

Partially premixed turbulent flames with non-homogeneous jet of propane were generated in a concentric flow conical nozzle burner in order to investigate the effect of the coflow on the stability and flame structure. The flame stability is first mapped and then high-speed stereoscopic particle image velocimetry, SPIV, plus OH planar laser-induced fluorescence, OH-PLIF, measurements were conducted on a subset of four flames. The jet equivalence ratio Φ = 2, Jet exit Reynolds number Re = 10,000, and degree of premixing are kept constant for the selected flames, while the coflow velocity, Uc, is progressively changed from 0 to 15 m/s. The results showed that the flame is stable between two extinction limits of mixture inhomogeneity, and the optimum stability is obtained at certain degree of mixture inhomogeneity. Increasing Φ, increases the span between these two extinction limits, while these limits converge to a single point (corresponding to optimum mixture inhomogeneity) with increasing Re. Regardless the value of Φ, increasing the coflow velocity improves the flame stability. The correlation between recessed distance of the burner tubes and the fluctuation of the mixture fraction, Δξ, shows that at Δξ around 40% of the flammability limits leads to optimum flame stability. The time averaged SPIV results show that the coflow induces a big annular recirculation zone surrounds the jet flames. The size and the location of this zone is seen to be sensitive to Uc. However, the instantaneous images show the existence of a small vortical structure close to the shear layer, where the flame resides there in the case of no-coflow. These small vertical structures are seen playing a vital role in the flame structure, and increasing the flame corrugation close to the nozzle exit. Increasing the coflow velocity expands the central jet at the expense of the jet velocity, and drags the flame in the early flame regions towards the recirculation zone, where the flame tracks and matches the spatial locations of low axial velocity fluctuations. At downstream, the flame is seen to conform to the passage of large scale structure. At Uc = 10 and 15 m/s, part of the primary reaction zone is rolled up towards upstream burner nozzle, anchoring the flame to the nozzle tip. This indicates that the stabilization of these flames in the presence of the coflow is controlled by the mutual interactions between the central jet and the coflow through the recirculation zone from one side, and the degree of the inhomogeneity of the central jet mixture from the other side.

Local and Global Active Contour Model for Image Segmentation With Intensity Inhomogeneity

The active contour model (ACM) is a popular approach for image segmentation. Many existing ACMs perform poorly in severe inhomogeneous images. To address this issue, a novel local and global ACM (LaG_ACM) is proposed in this paper. First, we define a global fitting image formulation that encodes the global property of an image and a global energy term using the relative entropy between the original image and the proposed global fitting image formulation. Then, a local image bias field formulation is defined to extract the local image information and to estimate the bias field. By integrating the proposed local image bias field formulation with the ACM, we specify a local energy term using the mean squared error to accommodate severe inhomogeneous images. More importantly, we define an adaptive weighting function using image entropy, which can automatically adjust the weight between the local and global energy terms according to the degree of intensity inhomogeneity. Finally, the experimental results on images with different degrees of intensity inhomogeneity validate the favorable performance of the LaG_ACM.

ВЛИЯНИЕ ХАРАКТЕРА И СТЕПЕНИ ЛЕГИРОВАНИЯ НА СКЛОННОСТЬ К ПРОЯВЛЕНИЮ ЛИКВАЦИИ ЛИТЫХ ЗАГОТОВОК ДЕФОРМИРУЕМЫХ АЛЮМИНИЕВЫХ СПЛАВОВ

Production of high-quality semi-finished product from aluminum wrought alloys for subsequent deformation (rolling, stamping or pressing) is provides by obtaining the initial defect-free cast billet. The level of mechanical properties of alloys in the cast and heat-treated state is determined mainly by the internal structure of the grains, therefore one of the main parameters affecting the quality of the cast billet for subsequent plastic deformation is the manifestation of chemical heterogeneity of grains in the content of alloying elements or segregation. In this work, the alloys Al–Mn, Al–Mg and duralumin are investigated according to the method previously proposed by the same authors. These alloys can be conventionally chosen as model ones, to study the influence of the alloying character on the tendency of wrought aluminum alloys to manifest segregation effects in the cast state. Comparing the local content of alloying elements on the axes of dendrites with the brand composition of the alloys, a significant discrepancy was noted. This discrepancy is a measure of the inhomogeneity of the alloy. Taking the degree of deviation of the local composition from the brand as the value characterizing the degree of inhomogeneity of cast alloys Al–Mn, Al–Mg and duralumin, the values of the average homogeneity coefficient of these alloys are calculated. The homogeneity criterion, determined for the aluminum base of alloys, shows the dependence of the degree of homogeneity on the change in the nature of alloying and the content of alloying elements. Significant differences between the local content of alloying elements in the axes of the dendrites and the grade composition of the alloys were revealed.

Necking and drawing of rubber-plastic bilayer laminates.

We examine the stretching behavior of rubber-plastic composites composed of a layer of styrene-ethylene/propylene-styrene (SEPS) rubber, bonded to a layer of linear low density polyethylene (LLDPE) plastic. Dog-bone shaped samples of rubber, plastic, and rubber-plastic bilayers with rubber : plastic thickness ratio in the range of 1.2-9 were subjected to uniaxial tension tests. The degree of inhomogeneity of deformation was quantified by digital image correlation analysis of video recordings of these tests. In tension, the SEPS layer showed homogeneous deformation, whereas the LLDPE layer showed necking followed by stable drawing owing to its elastoplastic deformation behavior and post-yield strain hardening. Bilayer laminates showed behavior intermediate between the plastic and the rubber, with the degree of necking and drawing reducing as the rubber : plastic ratio increased. A simple model was developed in which the force in the bilayer was taken as the sum of forces in the plastic and the rubber layers measured independently. By applying a mechanical energy balance to this model, the changes in bilayer necking behavior with rubber thickness could be predicted qualitatively.

АНАЛИТИЧЕСКИЕ ВОЗМОЖНОСТИ ОЦЕНКИ СТЕПЕНИ ГОМОГЕННОСТИ ЛИТЫХ АЛЮМИНИЕВЫХ СПЛАВОВ

Homogenization of castings from cast aluminum alloys is a priority for improving their technological parameters. The mode of homogenizing annealing is regulated by two parameters – temperature and holding time. Traditionally, one or two-stage annealing modes are used. To assess the degree of homogeneity of the alloy after such heat treatments at the enterprises, as a rule, various methods of mechanical testing are used. The paper proposes a new method for calculating the criterion for estimating the homogeneity of the structure of cast alloys using the aluminum alloy B95 as an example. The criterion of homogeneity (γ) can be the degree of approximation of compositions of local volumes of cast alloys to branded composition. Experience shows that it is more convenient to measure the content of alloying elements along the axes of dendrites. Dendrites, as a rule, contain a smaller number of basic alloying elements, which are usually localized in interdendritic volumes. Taking the value characterizing the degree of inhomogeneity of the cast alloy, the deviation of the composition from the branded (Δ), the homogeneity criterion can be represented as: γi = 1 – Δ. For a perfect homogeneous alloy, the value of the homogeneity criterion should approach 1. The average homogeneity coefficient for the cast alloy B95 calculated according to this formula is equal to γΣ = 0.503. Comparing the content of alloying elements in the center of grains and along the boundaries of homogenized grains, it should be noted that the local composition of grains, both in the center and at the boundaries, became close to the brand composition of alloy B95. This is indicated by the conditional homogeneity coefficient γ that is close to 1, introduced earlier. Indeed, the average homogeneity coefficient became equal to γΣ = 0.94. The proposed method is recommended as an analytical method for evaluating the degree of homogeneity of aluminum cast alloys, and as a criterion of homogeneity (γ), a generalized calculated index based on the analysis of local compositions along the dendrites and interdendritic regions can be proposed. Homogenization of castings from cast aluminum alloys is a priority for improving their technological parameters. The mode of homogenizing annealing is regulated by two parameters – temperature and holding time. Traditionally, one or two-stage annealing modes are used. To assess the degree of homogeneity of the melt after such heat treatments at the enterprises, as a rule, various methods of mechanical testing are used. The paper proposes a new method for calculating the criterion for estimating the homogeneity of a structure using the aluminum alloy B95 as an example. The proposed method consists in comparing the chemical composition in the dendritic and interdendritic areas and calculating on the basis of the obtained values of the homogeneity criterion (γ).

Dependence of the Energy Resolution of a Hemispherical Semiconductor Detector on the Bias Voltage

It is shown that the series expansion of the amplitude and variance of the hemispherical semiconductor detector signal in inverse bias voltage allows finding the Fano factor, the product of electron lifetime and mobility, the degree of inhomogeneity of the trap density in the semiconductor material, and the relative variance of the electronic channel gain. An important advantage of the proposed method is that it is independent of the electronic channel gain and noise.

Bulk superconducting tube subjected to the stray magnetic field of a solenoid

Hard type-II hollow superconductors are well suited for low frequency magnetic shielding. The properties and performances of superconducting magnetic shields subjected to homogeneous magnetic fields have been extensively discussed in the literature. In the present work, we investigate the magnetic shielding and the penetration of magnetic flux in a bulk high temperature superconducting tube subjected to the inhomogeneous fringe field of a solenoidal coil. Thanks to a bespoke microdisplacement measurement system, we measure the magnetic field distribution around the tube. We develop a full 3D finite element model based on an H formulation to understand the flux penetration mechanisms and predict the shape of the current loops. Using constitutive law parameters obtained from previous independent experiments, our model is found to be in excellent agreement with the measurements. We discuss how to assess the degree of inhomogeneity of the magnetic field and show that, in our case study, the field can be treated as the magnetic field of an equivalent magnetic dipole. We also show that some features of the flux penetration in inhomogeneous field can be also observed when the tube is subjected to an oblique homogeneous magnetic field, which offers a better understanding of the shielding current density distribution inside the shield. Finally, we discuss the magnetic field concentration occurring around the shield for different magnetic field configurations. In particular, we show that the extremities of the tube on the side not facing the magnetic field source experience the highest flux concentration.

Synthesis and Structural NMR Characterization of Novel PPG/PCL Conetworks Based upon Heterocomplementary Coupling Reactions

AbstractA new approach to hybrid model network formation based upon heterocomplementary end‐linking of four‐arm star poly‐ε‐caprolactone (PCL) and linear polypropylene glycol (PPG) precursors is demonstrated. Specifically, hydroxy‐terminated PCL(OH)4 and an amino‐terminated linear PPG(NH2)2 are reacted with a bifunctional coupling agent containing one carboxylic acid chloride group and one oxazinone group. PCL(OH)4 is first reacted with the former in a solution, and the so‐obtained oxazinone‐terminated intermediate is then reacted with PPG(NH2)2 to form a network both in the solution and in the melt. A strong effect of electron‐withdrawing groups on the reactivity of the oxazinone group, and thus on the network formation, is evidenced. Network structure and properties are studied by swelling experiments and low‐field multiple‐quantum (MQ) NMR, which confirm the successful formation of hybrid networks and provide information on the significant network inhomogeneities. On the methodological side, a reliable approach to MQ NMR data analysis for networks of variable degree of inhomogeneity is discussed.

An innovative lung model for multiple breath washout testing in health and disease

BackgroundMultiple breath washout (MBW) is a lung function test that identifies the degree of ventilation inhomogeneity (VI) in the lungs. In vitro validation of MBW devices is recommended. So far, plastic lung models for MBW validation ignored variable degrees of VI. Our primary aim was to create a plastic lung model applicable for physiological lung volumes and variable VI. MethodsA plastic box divided in two chambers was filled with water and ventilated in various lung volumes and respiratory rates. A ventilator was used for efficient gas distribution (model with low VI). An additional divider was inserted to create a model with high VI. The model was connected to commercial MBW devices and measurements were performed using different tracer gases and conditions. Primary outcome was the precision of generated functional residual capacity (FRC) and the ability to generate variable VI. The latter was estimated by lung clearance index (LCI) and expiratory phase III slopes (SIII). LCI was also compared to a mathematical model. FindingsThe intra-test variability for FRC was minimal, mean(SD) coefficient of variation 0.96(0.63)%, using different tracer gases under different conditions. Compared to the model with low VI, in the model with high VI LCI and washout SIII were significantly increased. LCI compared well to the mathematical model. InterpretationThis novel lung model shows excellent precision in lung volumes and VI estimates independent of tracer gases and conditions. The model can mimic the lungs of patients with uneven gas distribution.

Experimental and Finite Element Analysis of Flow Behavior of 2A14 Aluminum Alloy during Multi-directional Forging

The deformation flow behavior of 2A14 aluminum alloys during multi-directional forging (MDF) under various cumulative strains (∑Δɛ) has been investigated by combining experiment with finite element method (FEM). The forging process has been performed at 450oC with a deformation speed of 0.15 mms-1 and a pass strain (Δɛ) of 0.4. Numerical simulations of MDF using a commercial software (DEFORM-3D), have shown that the vortex, cross-flow and fold defect of flow lines of the forgings do not occur during deformation, and the degree of bent and inhomogeneity of flow lines also increase steadily with ∑Δɛ increases. The FEM analysis coincides well with experimental results. The effective strain in various areas of the forgings has been significantly enhanced during MDF. The dynamic recovery is dominant during deformation. The proportion of recrystallized grains and the degree of fragmentation of second phases in various areas of the annealed forgings increase with the increase of effective strain.

Disentangling the complex broad-band X-ray spectrum of IRAS 13197−1627 with NuSTAR, XMM–Newton and Suzaku

We present results from a coordinated $XMM$-$Newton$+$NuSTAR$ observation of the type 1.8 Seyfert galaxy IRAS 13197-1627. This is a highly complex source, with strong contributions from relativistic reflection from the inner accretion disk, neutral absorption and further reprocessing by more distant material, and ionised absorption from an outflow. We undertake a detailed spectral analysis combining the broadband coverage provided by $XMM$-$Newton$+$NuSTAR$ with a multi-epoch approach incorporating archival observations performed by $XMM$-$Newton$ and $Suzaku$. Our focus is on characterising the reflection from the inner accretion disk, which previous works have suggested may dominate the AGN emission, and constraining the black hole spin. Using lamppost disk reflection models, we find that the results for the inner disk are largely insensitive to assumptions regarding the geometry of the distant reprocessor and the precise form of the illuminating X-ray continuum. However, these results do depend on the treatment of the iron abundance of the distant absorber/reprocessor. The multi-epoch data favour a scenario in which the AGN is chemically homogeneous, and we find that a rapidly rotating black hole is preferred, with $a^* \geq 0.7$, but a slowly-rotating black hole is not strongly excluded. In addition to the results for the inner disk, we also find that both the neutral and ionised absorbers vary from epoch to epoch, implying that both have some degree of inhomogeneity in their structure.

Towards filtered drag force model for non-cohesive and cohesive particle-gas flows

Euler-Lagrange simulations of gas-solid flows in unbounded domains have been performed to study sub-grid modeling of the filtered drag force for non-cohesive and cohesive particles. The filtered drag forces under various microstructures and flow conditions were analyzed in terms of various sub-grid quantities: the sub-grid drift velocity, which stems from the sub-grid correlation between the local fluid velocity and the local particle volume fraction, and the scalar variance of solid volume fraction, which is a measure to identify the degree of local inhomogeneity of volume fraction within a filter volume. The results show that the drift velocity and the scalar variance exert systematic effects on the filtered drag force. Effects of particle and domain sizes, gravitational accelerations, and mass loadings on the filtered drag are also studied, and it is shown that these effects can be captured by both sub-grid quantities. Additionally, the effect of cohesion force through the van der Waals interaction on the filtered drag force is investigated, and it is found that there is no significant difference on the dependence of the filtered drag coefficient of cohesive and non-cohesive particles on the sub-grid drift velocity or the scalar variance of solid volume fraction. The assessment of predictabilities of sub-grid quantities was performed by correlation coefficient analyses in a priori manner, and it is found that the drift velocity is superior. However, the drift velocity is not available in “coarse-grid” simulations and a specific closure is needed. A dynamic scale-similarity approach was used to model drift velocity but the predictability of that model is not entirely satisfactory. It is concluded that one must develop a more elaborate model for estimating the drift velocity in “coarse-grid” simulations.

The Effect of a Spiral Gradient Magnetic Field on the Ionic Conductivity of Water

We discuss the experimental verification of changes in the structure of a liquid water sample inserted in a special spiral “gradient” magnetic field. The magnetic flux components are characterized by a high degree of inhomogeneity; thus, a gradient is found in the monitored section of space. The relevant measurement of the modified, rearranged water sample pointed to a specific ion conductivity lower than that of the untreated water. The results of the experiment, where a sample of demineralized water was exposed to a spiral “gradient“ magnetic field for the period of 5 min, show decreased ion conductivity in the examined samples.

Suppression of the superconducting gap near d-wave nodes caused by the structural disorder in fine-crystalline YBa2Cu3Oy high-Tc superconductors

The low-temperature (2 K ≤ T ≤ 10 K) specific heat of the series of fine-crystalline samples of YBa2Cu3O y high-Tc superconductor optimally doped with oxygen and having different degrees of nanoscale structural inhomogeneity has been studied at the applied magnetic field H = 8 T. The result are compared to those obtained for the equilibrium polycrystalline samples with different oxygen contents y. Information on the quasiparticle excitations in the magnetic field near d-wave nodes of the gap function is obtained. The changes introduced by the structural inhomogeneity to the nodal gap slope (νΔ) in the k-space, which is a key parameter of high-Tc superconductors, have also been studied. It is found that νΔ increases with the degree of structural disorder, but the superconducting transition temperature remains nearly the same (Tc = (91.5 ± 0.5) K). It is shown that this is possible if superconductivity is suppressed not only at the nodal point but also near it (owing to the structural disorder). In this case, the density of states in such parts of the Fermi surface is nonzero even at zero temperature, promoting the existence of the linear in temperature contribution to the specific heat (~γ(0)T), which is characteristic of metals.

Inert gas washout: background and application in various lung diseases.

Multiple breath inert gas washout (MBW) is a lung function technique to measure ventilation inhomogeneity. The technique was developed more than 60 years ago, but not much used for many decades. Technical improvements, easy protocols and higher sensitivity compared with standard lung function tests in some disease groups have led to a recent renaissance of MBW. The lung clearance index (LCI) is a common measure derived from MBW tests, and offers information on lung pathology complementary to that from conventional lung function tests such as spirometry. The LCI measures the overall degree of pulmonary ventilation inhomogeneity. There are other MBW-derived parameters, which describe more regional airway ventilation and enable specific information on conductive or acinar ventilation inhomogeneity. How this specific ventilation distribution is exactly related to different disease processes has not entirely been examined yet. MBW measurements are performed during tidal breathing, making this technique attractive for children, even young children and infants. These benefits and the additional physiological information on ventilation inhomogeneity early in the course of lung diseases have led to increasing research activities and clinical application of MBW, especially in paediatric lung diseases such as cystic fibrosis (CF). In these patients, LCI detects early airway damage and enables monitoring of disease progression and treatment response. Guidelines for the standardisation of the MBW technique were recently published. These guidelines will, hopefully, increase comparability of LCI data obtained in different centres or intervention trials in children and adults. In this non-systematic review article, we provide an overview of recent developments in MBW, with a special focus on children. We first explain the physiological and technical background to this technique with a short explanation of several methodological aspects that are important for understanding the principle behind the technique and enable high quality measurements. We then provide examples of MBW application in different lung diseases of children and adults, with regards to both clinical application and research activities. Lastly, we report on ongoing clinical trials using MBW as outcome and give an outlook on possible future developments.

Velocity Spectrum Estimation in Shock-Wave/Turbulent Boundary-Layer Interaction

The present paper presents the application of a technique to estimate velocity spectra on the complex supersonic flowfield of a shock-wave/turbulent boundary-layer interaction. A combined numerical–experimental approach relying on dual particle image velocimetry measurements and large-eddy simulations is used to optimize and validate a method allowing the reconstruction of spectral quantities from cross-correlations sampled at an arbitrary low sampling frequency from a Taylor-like hypothesis. The method, previously applied to a slowly streamwise developing boundary-layer flow, is refined so as to be able to better cope with flows having a higher degree of inhomogeneity. The accuracy and robustness of the resulting spectral estimates are evaluated in various characteristic regions distributed over the whole shock-wave/turbulent boundary-layer interaction flowfield thanks to the long-time large-eddy simulation database. Metrics allowing an a priori evaluation of the accuracy are also derived. Velocity spectra are then obtained from the experiments for the same locations. Comparisons with their large-eddy simulation counterparts make it possible to gain some insights into the origin of differences found between the experiments and the numerical simulation.

Multiscale structures of Zr-based binary metallic glasses and the correlation with glass forming ability

Thermal behaviors and structures of three Zr-based binary glass formers, Zr50Cu50, Zr64Cu36 and Zr64Ni36, were investigated and compared using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), high energy X-ray diffraction (XRD) and small angle X-ray scattering (SAXS). The high energy XRD results show that the bulk glass former Zr50Cu50 has a denser atomic packing efficiency and reduced medium-range order than those of marginal glass formers Zr64Cu36 and Zr64Ni36. Based on TEM observations for the samples after heat treatment at 10K above their crystallization onset temperatures, the number density of crystals for Zr50Cu50 was estimated to be 1023–1024m−3, which was four-orders higher than that in Zr64Cu36 and Zr64Ni36 metallic glasses. SAXS results indicate that Zr50Cu50 has higher degree of nanoscale inhomogeneities than those in Zr64Cu36 and Zr64Ni36 at as-cast state. The observed multiscale structures are discussed in terms of the phase stability and glass-forming ability of Zr-based binary glass formers.