Non-uniform Growth Research Articles

Modifications of the wetting characteristics of electrodeposited porous copper by controlling the plating parameters and storage conditions

The wetting behavior of copper is important for many engineering applications. The present study demonstrates a method to modify the wetting characteristics of copper surfaces by developing porous structures via the promotion of hydrogen bubbles and rapid and nonuniform growth of the deposits. The porous copper deposits are fabricated with various controlled plating parameters, and subsequently stored in different conditions, including air, water, and saline solution, to assess the possible influence of the storage conditions on the wetting behavior. The study shows that the wetting angles can be tailored by electrodeposition parameters, namely, plating bath formulation and applied current density, which influence the morphology of the porous structure. The storage conditions are found to largely affect the wetting behavior, owing to their influence on surface morphology and surface chemistry. Hydrophobic and hydrophilic surface characteristics are developed in the copper deposits stored in air and in the saline solution, respectively.

Fracturing and production analysis of the efficacy of hydraulic fracture stage reduction in the improvement of cost‐effectiveness in shale oil development: A case study of Jimsar shale oil, China

AbstractThe effective production of shale oil is important for the cost‐effectiveness in the oil and gas industry. Oil price volatility and uncertainty require suitable hydraulic fracturing schemes to maximize production and to minimize fracturing costs. Since the reduction of fracture stage saves bridge plugs and fracturing costs, it is considered as a possible method to improve the cost‐effectiveness. To maintain the stimulated reservoir volume, cluster numbers per stage are consequently increased, which may induce nonuniform fracture propagation and interference which affects the stimulation efficiency. This study conducts a comparative study for single‐stage (reduced) and two‐stage (not reduced) fracturing schemes with the same fracturing fluid volume. Reservoir geomechanics and rock mechanics analyses are conducted for Jimsar shale oil in north‐western China with a single‐stage multicluster fracturing model established. Fracture geometries and key factors are investigated followed by the evaluation of the fractured well production. The relationship between multicluster parameters and production is quantified. Meanwhile, two‐stage fracturing modeling is also set up to compare with single‐stage fracturing modeling. Fracturing results show that although single‐stage fracturing results in nonuniform fracture propagation, the overall stimulation is satisfactory. Production results show that the nonuniform growth of fracture clusters leads to different contributions to the production from individual clusters and the production from inner fractures is significantly inhibited. Compared with two‐stage fracturing with the same pumping volume, it is found out that single‐stage fracturing can lead to cost‐effective horizontal well production in Jimsar shale oil given certain values of hydraulic fracturing costs, and the reduced stage scheme is preferable in low oil price and high uncertainty scenarios.

Real-time control of dendritic propagation in rechargeable batteries using adaptive pulse relaxation.

The non-uniform growth of microstructures in dendritic form inside the battery during prolonged charge-discharge cycles causes short-circuit as well as capacity fade. We develop a feedback control framework for the real-time minimization of such microstructures. Due to the accelerating nature of the branched evolution, we focus on the early stages of growth, identify the critical ramified peaks, and compute the effective time for the dissipation of ions from the vicinity of those branching fingers. The control parameter is a function of the maximum interface curvature (i.e., minimum radius) where the rate of runaway is the highest. The minimization of the total charging time is performed for generating the most packed microstructures, which correlate closely with those of considerably higher charging periods, consisting of constant and uniform square waves. The developed framework could be utilized as a smart charging protocol for safe and sustainable operation of rechargeable batteries, where the branching of the microstructures could be correlated with the sudden variation in the current/voltage.

Modelling uniaxial non-uniform yeast colony growth: Comparing an agent-based model and continuum approximations

Biological experiments have shown that yeast can be restricted to grow in a uniaxial direction, vertically upwards from an agar plate to form a colony. The growth occurs as a consequence of cell proliferation driven by a nutrient supply at the base of the colony, and the height of the colony has been observed to increase linearly with time. Within the colony the nutrient concentration is non-constant and yeast cells throughout the colony will therefore not have equal access to nutrient, resulting in non-uniform growth. In this work, an agent based model is developed to predict the microscopic spatial distribution of labelled cells within the colony when the probability of cell proliferation can vary in space and time. We also describe a method for determining the average trajectories or pathlines of labelled cells within a colony growing in a uniaxial direction, enabling us to connect the microscopic and macroscopic behaviours of the system. We present results for six cases, which involve different assumptions for the presence or absence of a quiescent region (where no cell proliferation occurs), the size of the proliferative region, and the spatial variation of proliferation rates within the proliferative region. These six cases are designed to provide qualitative insight into likely growth scenarios whilst remaining amenable to analysis. We compare our macroscopic results to experimental observations of uniaxial colony growth for two cases where only a fixed number of cells at the base of the colony can proliferate. The model predicts that the height of the colony will increase linearly with time in both these cases, which is consistent with experimental observations. However, our model shows how different functional forms for the spatial dependence of the proliferation rate can be distinguished by tracking the pathlines of cells at different positions in the colony. More generally, our methodology can be applied to other biological systems exhibiting uniaxial growth, providing a framework for classifying or determining regions of uniform and non-uniform growth.

Quantitatively unravel the effect of chain length heterogeneity on polymer crystallization using discrete oligo l-lactide

As one of the most fundamental features of synthetic polymer, molecular weight distribution profoundly influences the structures and properties. In this work, chain length heterogeneity was precisely regulated by a reconstruction approach using a library of discrete oligol-lactide (oLLA). Crystallization of a series of binary blends were systemically investigated. At a specific crystallization temperature, each fraction experiences varied degrees of supercooling, leading to non-uniform nucleation and growth kinetics. Both oLLA fractions co-crystallize homogeneously when chain length heterogeneity is not significant, while partial segregation occurs when the difference is sufficiently large. The co-crystals consisting of non-uniform chains are metastable, which rearrange into a homo-crystal of longer chains by excluding the shorter components upon heating. This work highlights the profound contribution of chain length heterogeneity on crystallization, which not only provides insights into the importance of molecular weight distribution, but also bridges the intrinsic gap between discrete and disperse polymers.

A CFD model of frost formation based on dynamic meshes technique via secondary development of ANSYS fluent

To simulate the non-uniform frost growth in flow direction for humid air flowing through a freezing channel, a 2D numerical frosting model based on dynamic meshes technique is developed in the current work via the secondary development of commercial ANSYS Fluent. The computation domain consists of both frost layer and humid air regions, and the local heat and vapor fluxes at the surface of frost layer are determined by numerical temperature and vapor fraction fields in the humid air region rather than by empirical correlations. The frost layer is treated as a growing packed bed with heat and mass transfer dominated by molecular diffusion, where local absorption coefficient of vapor desublimation and local vapor fraction are both determined by solving the pseudo steady vapor diffusion equation with a source term theoretically. The interface of frost layer and humid air regions is treated as two walls for the iteration of its temperature, of which the humid air side is specified with the temperature equal to the frost-side counterpart and the frost side takes the heat flux including the extra latent heat caused by vapor deposit. User-defined functions are compiled to implement the above treatments to ANSYS Fluent. Frosting experiments in the literature are simulated with the current model for validation. How the profile of frost layer evolves with time in the frosting process is explored. The contours and profiles of velocity, temperature and vapor fraction are presented to discuss the effects of heat and mass transfer on frost formation. Numerical results demonstrate that the proposed CFD model can predict the frost growth and densification with a relative deviation less than 5% compared with experiments. Besides, the computation load of current model is small due to no solution of complex multiphase flow. In addition, dynamic meshes help current model to capture the interface of frost layer and humid air regions accurately.

Phenotyping the Preterm Brain: Characterizing Individual Deviations From Normative Volumetric Development in Two Large Infant Cohorts.

The diverse cerebral consequences of preterm birth create significant challenges for understanding pathogenesis or predicting later outcome. Instead of focusing on describing effects common to the group, comparing individual infants against robust normative data offers a powerful alternative to study brain maturation. Here we used Gaussian process regression to create normative curves characterizing brain volumetric development in 274 term-born infants, modeling for age at scan and sex. We then compared 89 preterm infants scanned at term-equivalent age with these normative charts, relating individual deviations from typical volumetric development to perinatal risk factors and later neurocognitive scores. To test generalizability, we used a second independent dataset comprising of 253 preterm infants scanned using different acquisition parameters and scanner. We describe rapid, nonuniform brain growth during the neonatal period. In both preterm cohorts, cerebral atypicalities were widespread, often multiple, and varied highly between individuals. Deviations from normative development were associated with respiratory support, nutrition, birth weight, and later neurocognition, demonstrating their clinical relevance. Group-level understanding of the preterm brain disguises a large degree of individual differences. We provide a method and normative dataset that offer a more precise characterization of the cerebral consequences of preterm birth by profiling the individual neonatal brain.

On colors of stainless-steel surfaces polished with magnetic abrasives

Multiple colors visible to the naked eye across the internal surfaces of stainless-steel 304 tubes polished with a magnetic abrasive finishing (MAF) process were investigated at varying levels of magnification. The colors were found to result from microscopic colored features of four different hues — green, blue, red, and yellow — having irregular sizes and shapes. Spectral analysis of their dispersion indicates that these colored features appear along the lay marks generated during MAF. Surface characterization employing energy dispersive spectroscopy and instrumented indentation testing indicates the presence of films of non-stochiometric chromium oxide and nickel oxide in the colored regions. Variations in the momentum and the density of the abrasive particles interacting with the surface during the MAF process, together with the chemical composition and morphology of the surface, provide thermodynamic conditions favorable for a non-uniform growth of the oxides film. Local color is dependent on the local composition and thickness of the oxides film.

Separate weighing of male and female broiler breeders by electronic platform weigher using camera technologies

The body weight of breeding broiler chickens (broiler breeders) is an important control variable used to optimize the amount, quality and fertility of the eggs being laid. In modern breeding barns, the population of animals generally supports a female:male ratio of 10:1, wherein males and females each receive their own food supply. To control this supply the broiler breeders are weighed using automatic electronic platform weighers and the weights are then classified into cockerel and hen categories using theoretical growth curves. However, due to the non-uniform growth of the animals and replacement (called spiking) of cockerals this classification is not always correct, causing a risk of under/over feeding of the population. To overcome this challenge, in this study we have developed a system that integrates the electronic platform weigher with the low-cost 3D Kinect camera was employed to separate weigh male and female broiler breeders under commercial conditions. A novel image processing algorithm is proposed. The algorithm first constructed the Height Accumulating Image (HAI) using depth image to locate the region of interest (ROI) where a broiler breeder jumps onto the weigher, then the comb size was calculated on RGB image as the gender classifying feature, and finally, an adaptive classification threshold was determined by the kernel density estimation using the recent days comb size measurements. The results showed that enough measurements can be obtained for estimating overall weight expectation with the average acceptance rate of 77.32%. Based on these accepted measurements, the accuracy, sensitivity, precision, and specificity were 99.7%, 98.82%, 100% and 100% respectively.

Excellent magnetic and mechanical properties of the Sm2Co17-based magnets fabricated via microwave processing

The development of high performance Sm2Co17-based permanent magnets (SCPMs) by employing efficient fabrication methods can be beneficial for many applications. In this study, we prove that Sm(CobalFe0.25Cu0.06Zr0.02)7.5 PMs with an improved energy product (BH)max (27.1–30.0 MGOe) and bending strength (168.2–177.5 MPa) can be achieved by using microwave (MW) ageing. During short-time MW-ageing at 840 °C for 1 h, phase separation was performed in the hexagonal Sm2Co17 (2:17H) supersaturated solid solution characterized with small wavelength of composition modulations (λ = 1–2 nm) and high density of pure-edge dislocations. This contributes to large gradient energy ΔGγ and high separation rate, thus results in the formation of 20-nm uniform nanoparticles. The nanoparticles grow into a homogeneous 50-nm cellular structure composed of rhombohedral Sm2Co17 (2:17R) cells and hexagonal SmCo5 (1:5H) cell boundaries after being MW-aged for 3 h, then the non-uniform grain growth to 80 nm takes place by further increasing the time to 5 h. Moreover, prolonging the ageing time from 3 to 5 h can increase the Cu enrichment in the 1:5H cell boundary phase and enhance the coercivity Hci from 17.4 to 23.1 kOe. As compared with conventional ageing, the MW ageing considerably reduces the ageing time and the MW-aged PMs exhibit finer and more homogeneous cellular structures.

Computational modeling of vascular growth in patient-specific pulmonary arterial patch reconstructions

Recent progress in vascular growth mechanics has involved the use of computational algorithms to address clinical problems with the use of three-dimensional patient specific geometries. The objective of this study is to establish a predictive computational model for the volumetric growth of pulmonary arterial (PA) tissue following complex cardiovascular patch reconstructive surgeries for congenital heart disease patients. For the first time in the literature, the growth mechanics and performance of artificial cardiovascular patches in contact with the growing PA tissue domain is established. An elastic-growing material model was developed in the open source FEBio software suite to first examine the surgical patch reconstruction process for an idealized main PA anatomy as a benchmark model and then for the patient-specific PA of a newborn. Following patch reconstruction, high levels of stress and strain are compensated by growth on the arterial tissue. As this growth progresses, the arterial tissue is predicted to stiffen to limit elastic deformations. We simulated this arterial growth up to the age of 18 years, when somatic growth plateaus. Our research findings show that the non-growing patch material remains in a low strain state throughout the simulation timeline, while experiencing high stress hot-spots. Arterial tissue growth along the surgical stitch lines is triggered mainly due to PA geometry and blood pressure, rather than due to material property differences in the artificial and native tissue. Thus, non-uniform growth patterns are observed along the arterial tissue proximal to the sutured boundaries. This computational approach is effective for the pre-surgical planning of complex patch surgeries to quantify the unbalanced growth of native arteries and artificial non-growing materials to develop optimal patch biomechanics for improved postoperative outcomes.

Multistage heat treatment and the development of a protective oxide-scale layer on the surface of FeCrAl sintered-metal-fibers

This study investigates the effects of Multistage Heat Treatment (MSHT) on the development of an oxide-scale layer on the surface of FeCrAl sintered-metal-fibers. The oxide-scale layer was developed using an MSHT cycle at 930 °C for 1 h, followed by 960 °C for 1 h, and finally at 990 °C for 2 h. In this study, three samples were considered: Sample 1 was kept without thermal oxidation, while Samples 2 and 3 were exposed to one and eighteen MSHT cycles. Thermo-gravimetric analyses show that the weight gain of the heat-treated sample slows with time, confirming the growth of the protective oxide-scale layer. Scanning electron microscope images, after one MSHT cycle, reveal nonuniform oxide-scale growth with platelet-like on the surface. After eighteen MSHT cycles, however, clumped particles formed on the surface of the fibers. Atomic force microscopy was utilized to study the surface topography of the fibers. The results show that MSHT increases the surface roughness, where the surface roughness of one and eighteen MSHT cycles are the same. The x-ray diffraction analyses of the baseline sample and the sample with one MSHT cycle show pattern peaks of crystalline Fe2CrAl. In contrast, the results of eighteen MSHT cycles displayed diffraction pattern peaks of crystalline Cr and stable α-Al2O3. In summary, the results of this study reveal the changing nature of the oxide-scale layer. The findings of this study form the foundation for new techniques to protect and prepare the FeCrAl fibers as a support for catalysts.

Lithographically patterned polypyrrole multilayer microstructures via sidewall-controlled electropolymerization

Composite materials comprising multilayers of metal and conductive polymer can have applications in sensing, biomedical, and energy storage/conversion scenarios. One attribute of such metal/polymer composites is that they typically display highly anisotropic electrical properties, which makes them useful as materials for microelectronic or magnetic devices. However, incorporating the deposition of conductive polymers into scalable and manufacturable fabrication processes can be challenging, as the mechanisms for electropolymerization are complex. We previously demonstrated an additive approach to fabricate metal/polymer multilayer structures, using soft magnetic alloys as the metal component and polypyrrole (PPy) as the polymer component. To extend the utility of these composites, the deposition of many multiples of alternating metal/polymer pairs within specifically defined lithographic molds is highly desirable. However, since the lateral growth of electrodeposited PPy is typically faster than vertical growth, non-uniform layer geometry and growth of the polymer on and above the patterned molds are often observed. In this work, we achieve suppression of lateral PPy growth by control of electropolymerization bath counter-anions and passivation of underlying metal layers during deposition. The lateral-to-vertical growth rate uniformity ratio is reduced by a factor of six (to approximately unity) through polymerization parameter optimization and exploiting a continuous five-bath electrodeposition approach. The reduction in lateral growth rate enhances the scalability of multilayer structures that are fabricated using this additive electrodeposition-based approach and provides a manufacturable route to additive, lithographically patterned metal/polymer composites with tunable volume and geometry, without sacrificing the microstructure and properties of the composite.

First radiative shock experiments on the SG-II laser

Abstract We report on the design and first results from experiments looking at the formation of radiative shocks on the Shenguang-II (SG-II) laser at the Shanghai Institute of Optics and Fine Mechanics in China. Laser-heating of a two-layer CH/CH–Br foil drives a $\sim 40$ km/s shock inside a gas cell filled with argon at an initial pressure of 1 bar. The use of gas-cell targets with large (several millimetres) lateral and axial extent allows the shock to propagate freely without any wall interactions, and permits a large field of view to image single and colliding counter-propagating shocks with time-resolved, point-projection X-ray backlighting ( $\sim 20$ μm source size, 4.3 keV photon energy). Single shocks were imaged up to 100 ns after the onset of the laser drive, allowing to probe the growth of spatial nonuniformities in the shock apex. These results are compared with experiments looking at counter-propagating shocks, showing a symmetric drive that leads to a collision and stagnation from $\sim 40$ ns onward. We present a preliminary comparison with numerical simulations with the radiation hydrodynamics code ARWEN, which provides expected plasma parameters for the design of future experiments in this facility.

Self-Improving inequalities for bounded weak solutions to nonlocal double phase equations

<p style='text-indent:20px;'>We prove higher Sobolev regularity for bounded weak solutions to a class of nonlinear nonlocal integro-differential equations. The leading operator exhibits nonuniform growth, switching between two different fractional elliptic "phases" that are determined by the zero set of a modulating coefficient. Solutions are shown to improve both in integrability and differentiability. These results apply to operators with rough kernels and modulating coefficients. To obtain these results we adapt a particular fractional version of the Gehring lemma developed by Kuusi, Mingione, and Sire in their work "Nonlocal self-improving properties" <i>Analysis & PDE</i>, 8(1):57–114 for the specific nonlinear setting under investigation in this manuscript.</p>

An Atomistic Modelling Study of the Properties of Dislocation Loops in Zirconium

Neutron irradiation progressively changes the properties of zirconium alloys: they harden and their average c/a lattice parameter ratio decreases with fluence [1, 2, 3, 4]. The bombardment by neutrons produces point defects, which evolve into dislocation loops that contribute to a non-uniform growth phenomenon called irradiation-induced growth (IIG). To gain insights into these dislocation loops in Zr we studied them using atomistic simulation. We constructed and relaxed dislocation loops of various types. We find that the energies of 〈a〉 loops on different habit planes are similar, but our results indicate that they are most likely to form on the 1st prismatic plane and then reduce their energy by rotating onto the 2nd prismatic plane. By simulating loops of different aspect ratios, we find that, based on energetics alone, the shape of 〈a〉 loops does not depend on character, and that these loops become increasingly elliptical as their size increases. Additionally, we find that interstitial 〈c/2+p〉 loops and vacancy 〈c〉 loops are both energetically feasible and so the possibility of these should be considered in future work. Our findings offer important insights into loop formation and evolution, which are difficult to probe experimentally.

Image-based modelling for Adolescent Idiopathic Scoliosis: Mechanistic machine learning analysis and prediction

Scoliosis, an abnormal curvature of the human spinal column, is characterized by a lateral deviation of the spine, accompanied by axial rotation of the vertebrae. Adolescent Idiopathic Scoliosis (AIS) is the most common type, affecting children between ages 8 to 18 when bone growth is at its maximum rate. We propose a mechanistic machine learning algorithm in order to study patient-specific AIS curve progression, which is associated with the bone growth and other genetic and environmental factors. Two different frameworks are used to analyse and predict curve progression, one with implementing clinical data extracted from 2D X-ray images and the other one with incorporating both clinical data and physical equations governing the non-uniform bone growth. The physical equations governing bone growth are affiliated with calculating all stress components at each region. The stress values are evaluated through a surrogate finite element simulation and a bone growth model on a detailed patient-specific geometry of the human spine. We also propose a patient-specific framework to generate the volumetric model of human spine which is partitioned into different tissues for both vertebra and intervertebral disc. It is shown that implementing physical equations governing bone growth into the prediction framework will notably improve the prediction results as compared to only using clinical data for prediction. In addition, we can predict curve progression at ages outside the range of training samples.

Nonlinear Destructive Interaction between Wind and Wave Loads Acting on the Substructure of the Offshore Wind Energy Converter: A Numerical Study

Even though the offshore wind industry’s growth potential is immense, the offshore wind industry is still suffering from problems, such as the large initial capital requirements. Many factors are involved, and among these, the extra costs incurred by the conservative design of offshore wind energy converters can be quickly addressed at the design stage by accounting for the nonlinear destructive interaction between wind and wave loads. Even when waves approach offshore wind energy converters collinearly with the wind, waves and wind do not always make the offshore wind energy converter’s substructure deformed. These environmental loads can intermittently exert a force of resistance against deformation due to the nonlinear destructive interaction between wind and wave loads. Hence, the nonlinear destructive interaction between wave and wind loads deserves much more attention. Otherwise, a very conservative design of offshore wind energy converters will hamper the offshore wind energy industry’s development, which is already suffering from enormous initial capital expenditures. In this rationale, this study numerically simulates a 5 MW offshore wind energy converter’s structural behavior subject to wind and random waves using the dynamic structural model developed to examine the nonlinear destructive interaction between wind and wave loads. Numerical results show that the randomly fluctuating water surface as the wind blows would restrict the offshore wind energy converter’s substructure’s deflection. Nonuniform growth of the atmospheric boundary layer due to the wavy motions at the water surface as the wind blows results in a series of hairpin vortices, which lead to the development of a large eddy out of hairpin vortices swirling in the direction opposite to the incoming wind near the atmospheric boundary layer. As a result, the vertical profile of the longitudinal wind velocity is modified; the subsequent energy loss drastically weakens the wind velocity, which consequently leads to the smaller deflection of the substructure of the offshore wind energy converter by 50% when compared with that in the case of wind with gusts over a calm sea.

Imaging the Surface of a Polycrystalline Electrodeposited Cu Film in Real Time Using In Situ High-Speed AFM

We studied the surface evolution of polycrystalline Cu films electrodeposited from an organic additive-free acid sulphate electrolyte on to a gold microelectrode using a high-speed Atomic Force Microscope (HS-AFM) which images an area of 2 × 2 μm at 2 frames per second and a resolution of 1000 × 1000 pixels. The ability to acquire data at this rate opens even fast growth processes to in situ investigation. Real-time images from a film deposited at ∼0.5 nm s−1 revealed many interesting phenomena, most significantly highly non-uniform grain growth rates with several examples of grains showing accelerated growth compared to their neighbours. Grain overgrowth was also observed in different regions of the sample. Surface roughness scaling and slope analysis provided evidence for structural coarsening of the film and an increase in the mean slope θ with increasing film thickness t. We show how both grain overgrowth and an increase in θ can contribute to the coarsening of the surface structure as deposition proceeds.

Simulation of Copper Electrodeposition in Millimeter Size Through-Silicon Vias

Computational predictions of copper deposition in millimeter size through-silicon vias (mm-TSV) are presented based on localized breakdown of a co-adsorbed polyether-chloride suppressor layer. The model builds upon previous work on localized Cu deposition in microscale TSV and through-holes by incorporating 3D fluid flow calculations to more effectively evaluate chemical transport of cupric ion and additives, both of which are critical to adlayer formation and disruption within the via. Simulations using potentiostatic and potentiodynamic waveforms are compared to previously reported filling experiments. Alternatively, the utility of galvanostatic control and variations in fluid flow are explored computationally. For appropriate applied potential(s) or current, deposition is localized to the via bottom, with subsequent growth proceeding in a bottom-up fashion. Selection of inappropriate current or potential waveforms, or forced convection conditions that supply insufficient cupric ion to the bottom of the via, results in prediction of voids. Simulations of deposition in via arrays (4 × 1) predict non-uniform growth across the arrays, with the passivation of individual vias associated with minor variations in convective flow and/or numerical perturbations in the simulation, that reflects the critical nature of the bifurcation process.