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Digital photography of cavitation in narrow gap flows, e.g., lubrication films in journal bearings or squeeze film dampers, demands a high time-resolution and a solution to approaching the particular spatial restrictions. Typically, the lubrication film thickness is in the range of a few microns and the characteristic time for vapor bubble generation and collapse is about one millisecond, respectively. The authors have developed a Journal Bearing Model Experiment, which is designed according to similarity laws providing fully similar flow conditions to real journal flows while offering ideal access to the flow by means of optical measurement equipment. Compared with other methods, e.g., pulsed laser, electrical discharge, tube arrest, applied to produce vapor bubbles, the work on hand applies a dynamic variation of the minimum film thickness to produce suction cavitation, which proves the applicability of this novel approach to study vapor cavitation in fluid films similar to lubricant flows. The results are obtained by means of digital high-speed photography of vapor bubbles from inception to implosion triggered by the dynamic variation of the minimum film thickness of a narrow gap flow. Moreover, the results are set in relation to a general overview of cavitation processes.

In this paper, an experiment is carried out to acquire the dynamic mechanical properties of a simulated sandstone tunnel by a dual DIC system. The sandstone tunnel is simulated by large sandstone with a prefabricated hole in the center. The speckle size required by DIC system was evaluated, and the results showed that for large specimens a marker pen could be used to spot speckles and make sure that the diameters of speckle points in an image should be ranged from three to five pixels. The dual DIC system is composed of a low-speed camera and a high-speed camera. The low-speed camera is used to record the speckle patterns of the sandstone in one side during the whole process of compression load, and the high-speed camera is placed in the other side to record speckle patterns for 11.5 seconds before and after failure. It is realized that monitoring whole process of deformation and instantaneous failure in two directions is required. Measurement results are effectively analyzed. The results are shown as follows: At the initial stage of loading the sandstone is in an elastic stage without macroscopic cracks. With the increase in compression load the sandstone has several small stress releases and several obvious macroscopic cracks. In the final stage of loading, the distribution of normal stress and shear stress are almost the same, and cracks are subjected to the coupling effect of normal stress and shear stress. The two ends of the prefabricated hole perpendicular to the applied load direction are prone to cracks parallel to the applied load direction.

Engineered cardiac tissues (ECTs) derived from human induced pluripotentstem cells (hiPSCs) are viable alternatives for cardiac repair, patient-specificdisease modeling, and drug discovery. However, the immature state of ECTslimits their clinical utility. The microenvironment fabricated using 3D scaffoldscan affect cell fate, and is crucial for the maturation of ECTs. Herein, theauthors demonstrate an electric-field-driven (EFD) printed 3D highly orderedmicrostructure with cell feature size to promote the maturation of ECTs. Thesimulation and experimental results demonstrate that the EFD jet microscale3D printing overcomes the jet repulsion without any prior requirements forboth conductive and insulating substrates. Furthermore, the 3D highlyordered microstructures with a fiber diameter of 10–20μmandspacingof60–80μm have been fabricated by maintaining a vertical jet, achieving thelargest ratio of fiber diameter/spacing of 0.29. The hiPSCs-derivedcardiomyocytes formed ordered ECTs with their sarcomere growth along thefiber and developed synchronous functional ECTs inside the 3D-printedscaffold with matured calcium handling compared to the 2D coverslip.Therefore, the EFD jet 3D microscale printing process facilitates thefabrication of scaffolds providing a suitable microenvironment to promote thematuration of ECTs, thereby showing great potential for cardiac tissueengineering.

Nanoscale aluminium (nAl)-based composites find important applications in propellant, explosives and pyrotechnics, and the improved combustion efficiency is always desirable but challenging. A core-shell nAl@CuO composite with improved combustion performance was prepared by means of a biological interfacial layer, which is inspired by the fast polymerization and strong adhesion of juglone and tannic acid in walnut peel juice. It is found that interfacial layer contains phenolic hydroxyl and amino groups, which could interact with nAl and introduce the growth of CuO crystal, respectively. Obtained nAl@CuO shows higher stability but 1.2 times more heat release than that of the mechanically mixed nAl/CuO. In addition, nAl@CuO also has 5 times faster burning rate than the mechanically mixed one. It is believed that interfacial layer hindered the direct contact of reactants but improved mass transport/diffusion efficiency in nAl@CuO. Thus, Al based composites with higher stability and superior combustion efficiency could be obtained by this interfacial layer.

The rotating detonation combustor (RDC) has received remarkable attention in the aerospace community. In this work, an experimental RDC model supplied by liquid kerosene and oxygen-enriched air is established. A parametric survey is performed with different injection throats, outlet restrictions, and equivalence ratios to analyze the rotating detonation wave propagation modes comprehensively. Dynamic pressure transducers and a high-speed camera are both employed to identify wave modes synchronously. Overall, the propagation modes are found to be highly dependent on the injection throat and combustor outlet restriction. With a large injection to annulus area ratio of 0.3, a single-wave mode is characterized when no restriction is added at the combustor outlet. Reducing the outlet area leads to a decrease in the wave frequency and a narrower steady rotating detonation propagation regime. The propagation stability of the rotating detonation is strengthened when the injection to annulus area ratio decreases to 0.2. A dual-wave collision mode and a four-wave collision mode are observed, depending on the outlet restriction. A preliminary stable RDC operation range correlated with outlet to injection throat area ratio and equivalence ratio is achieved. Furthermore, an interval value of the outlet to injection throat area ratio is proposed to reach the potential positive total pressure gain. These findings should serve as the reference for RDC configuration design in air-breathing and gas-turbine propulsion systems.

The understanding and experimentation of abrasive wear mechanisms at high speeds is still poorly investigated in literature. This is mainly due to a lack of suitable, well-instrumented test rigs for fundamental, single abrasive wear events. Standard scratch tests, which are often utilized for studies of abrasion phenomena, operate in the low-speed range up to some mm/s, while applications suffering from abrasive wear often operate at speeds exceeding 1 m/s (e.g., rolling, grinding, machining). Numerical approaches, especially particle-based methods, allow the simulation of such fast deformation processes, but rely on hardening models that require a precise knowledge of material parameters. Thus, the Johnson-Cook material model was parametrized using data from high-speed compression tests of pure aluminum. A series of scratch tests with increasing depths were then simulated using the particle- based Material Point Method (MPM). Experimentation was done on a pendulum scratch test rig equipped with a Rockwell C diamond cone. By adjusting the balance point of the swing arm of ~1 m length, a velocity of 6.8 m/s was achieved at its tip as measured with a high-speed camera. Scratches of several depths were performed, and their force signals acquired. Post-test analyses comprised topography measurements and EBSD on cross-sections of the scratches to investigate the microstructural changes due to the high-speed wear event. Scratch topographies and abrasive mechanisms compared favorably between experiment and simulation for the aluminum. The extent of strain hardening was significantly reduced compared to low-speed experiments. The calibration of the high-speed force sensor was successful and now allows the investigation of new alloys and determination of material parameters under high-speed abrasive conditions.

In the present effort, impact of bullets fired at high speeds on a stationary target was used as a high strain-rate plastic deformation method to generate Functionally Graded Materials (FGMs). The bullet-shaped Aluminum alloy Al5052 specimens impacted the UHMWPE target at different projectile velocities ranging from 100 m/s to 750 m/s, to study the effect of the impact speed. Moreover, few of the projectiles impacted along the longitudinal axis whereas the remaining projectiles impacted with an obliquity to investigate the effect of leading-edge shape. The metallography of the projectile specimens fired at 750 m/s shows grain refinement from 70 ± 3μm at the rear/ un-deformed point to 10 ± 1μm at the front/ severely deformed point which is in the impact zone. Similar but of less magnitude variations were observed at other impact speeds also. The hardness variation was 45% (70 ± 3 HV at the rear surface to 102 ± 2 HV at the front face) at 750 m/s. Moreover, least variation in hardness and grain size was observed for projectile impacted at lowest velocity tested (100 m/s). Further, functionality in hardness and grain refinement was seen in graded direction due to shape of the projectile specimens, impact velocity, and target material. Depending upon the impact angles, axisymmetric (impacted normal to the longitudinal axis) or unsymmetrical (impacted at an angle) variation of grain refinement and hardness was observed.

The presence of metal vapor influences arc stability in both arc and hybrid welding. It is assumed that the composition of the metal vapor, and therefore the substrate material composition, plays an important role due to the different ionization energies of the material elements. In this study, a special setup is used to investigate the influence of metal vapor on the behavior of a vertically oriented arc generated between two equal electrodes by a separate laser-induced vapor generation using a transversally oriented laser beam welding process with additional support materials beside the process zone of the arc. Several aluminum alloys, steel materials, and titanium alloys are used as vapor-producing support materials.

The experiments show that the arc voltage increased under the presence of metal vapor, which implies a decrease in arc stability, leading partially to an extinction of the arc. The influence of the ionization energy is evaluated by calculating the average ionization energy for each material composition. In the case of inducing metal vapor into the arc zone, a smaller ionization energy and a lower amount of alloying elements of the support material result in a lower arc voltage increase and, therefore, higher arc stability. A higher effect on the arc stability when using elements with a smaller ionization energy for the second electron than the first argon electron is not measurable.

Hardwood species are becoming increasingly important with the growing need for a diversity of forests that have recently been facing global temperature changes or conifer pests. This further leads to the growth of its potential as a building material that may originate from sustainable production. As hardwoods need to be properly processed, the article deals with the disintegration of European beech. The influence of wood grain direction, uncut chip thickness and cutting speed on the cutting force magnitudes was experimentally investigated using the device with a rotating arm of approximately 4 m in diameter. Then, the disintegration process was modelled using the finite element method in Abaqus/Explicit. The developed material model consisting of orthotropic elasticity and plasticity with rate-independent and rate-dependent tensile–compressive failure asymmetry was implemented through the user subroutine, while the crack initiation and propagation were realized using the element deletion technique. The computationally predicted average values of cutting forces and chip shapes were, except for a few tests, in good agreement with the experiments. It means that the model may be used for further investigation, such as the influence of tool wear.

Introduction of nanophases into the interface between fibers and matrix in fiber-reinforced polymer composites can form multiscale composites with significantly improved interfacial bonding. The nanophases of various geometric shapes (e.g., nanotubes, nanoparticles, or nanosheets) show quite different reinforcing efficiency. To elucidate the underlying mechanisms of this discrepancy, a multiscale mechanical model is proposed to establish the relation between the geometric shape of nanophases at nano-/micro-scale and the transverse tensile strength of composites at macro-scale. Three typical carbon-based nanophases are chosen for comparison, i.e., fibrous carbon nanotubes (CNTs), granular buckminsterfullerene (BF) nanoparticles, and lamellar graphene oxide (GO) nanosheets. The study indicates that high aspect ratio nanotubes have the superior enhancing effect as individual, but the advantage could be counteracted by the relatively low distribution density in the interfacial region due to their geometric features. The two factors need to be carefully balanced to achieve the desired ultimate performance of multiscale composites.

Depositing drops on a solid surface without entrapping bubbles is desirable for many spray coating and printing applications. Tian et al. [J. Fluid Mech. 946, A21 (2022)] reported that an electric field can be applied to eliminate air bubble entrapments for neutral drops. Herein we provide a complete physical picture of the entire process of a drop impacting onto the solid surface under an external electric field. The electrohydrodynamic behavior during the drop impact is divided into three stages: the deformation of the drop in the electric field prior to contact, the initial contact of the drop with the substrate, and the rich postcontact phenomena including spreading, receding, jetting, and fragmentation. The results show that under the increasingly stronger electric fields, the modest drop oscillation transforms into a vertically stretched spindle. As the drop approaches the substrate, the electric stress at the south pole increases rapidly, which sharpens the bottom surface into a conical shape. The cone angle is determined by both the impact velocity and the electric field strength. After the contact, the surface electric stress tends to pull the drop upward, breaking up the drop, forming several jetting modes, and reducing the maximum spreading radius. The various drop deposition modes are summarized in a phase diagram, which sheds light on identifying appropriate electric fields for high-quality drop depositions without air bubble entrapments or jettings.

A single-winged maple seed (samara) is dispersed laterally by a crosswind in contrast to simply descending straight down (zero dispersion) in quiescent air. This article presents the general kinematic response of a particular type of samaras (Acer buergerianum) in stable autorotation to the disturbance of a concentrated crosswind (simulated via slot jet) with the crosswind strength varied distinctively from weak to strong. A relatively weak crosswind slower than the tip velocity of the stably autorotating samara causes only damped undulations of its descent trajectory. In contrast, we demonstrate that the samara exhibits a bi-modal response when disturbed by a relatively strong crosswind (velocity greater than samara tip velocity). The strong crosswind enables the samara either to float laterally with the crosswind or drop-out through the crosswind with the switching of its rotational direction. Regardless of crosswind strength, stable autorotation is re-established after the samara leaves the crosswind zone, albeit accompanied by large-scale undulations in its descent trajectory. More importantly, before landing, the samara regains its original terminal descent velocity achieved in quiescent air.

Injectable granular gels consisting of densely packed microgels serving as scaffolding biomaterial have recently shown great potential for applications in tissue regeneration, which allow administration via minimally invasive surgery, on-target cargo delivery, and high efficiency in nutrient/waste exchange. However, limitations such as insufficient mechanical strength, structural integrity, and uncontrollable differentiation of the encapsulated cells in the scaffolds hamper their further applications in the biomedical field. Herein, we developed a new class of granular gels via bottom-up assembly of cell-laden microgels via photo-triggered imine-crosslinking (PIC) chemistry based on the microfluidic technique. The particulate nature of the granular gels rendered them with shear-thinning and self-healing behavior, thereby functioning as an injectable and adaptable cellularized scaffold for bone tissue regeneration. Specifically, single cell-laden, monodisperse microgels composed of methacrylate- and o-nitrobenzene-functionalized hyaluronic acid and gelatin were prepared using a high-throughput microfluidic technique with a production rate up to 3.7 × 108 microgels/hr, wherein the PIC chemistry alleviated the oxygen inhibition on free-radical polymerization and facilitated enhanced fabrication accuracy, accelerated gelation rate, and improved network strength. Further in vitro and in vivo studies demonstrated that the microgels can serve as carriers to support the activity of the encapsulated mesenchymal stem cells; these cell-laden microgels can also be used as cellularized bone fillers to induce the regeneration of bone tissues as evidenced by the in vivo experiment using the rat femoral condyle defect model. In general, these results represent a significant step toward the precise fabrication of engineered tissue mimics with single-cell resolution and high cell-density and can potentially offer a powerful tool for the design and applications of a next generation of tissue engineering strategy.

The emergence of tetrahydroborate (BH4–)/cyanoborohydride (BH3CN–) anion-based ionic liquid fuels in combination with high test peroxide (>90%H2O2, HTP) oxidizers has accelerated the greening of bipropellants. However, most BH4– and BH3CN– anion-based ionic liquids are sensitive to water, making it difficult to store them. Here, novel difunctional promoters are designed for hypergolic ignition of BH4–/BH3CN– anion-free ionic liquids with 90%H2O2. The transition metal in anions of promoters is expected to catalyze the exothermic decomposition of H2O2, and the substituted borohydride in cations of promoters acts as the ignition source. These novel difunctional promoters show good solubility in commercially available 1-allyl-3-methylimidazolium dicyanamide and 1-butyl-3-methylimidazolium dicyanamide ionic liquid fuels, and the composite fuels exhibit high density, acceptable viscosity, and high thermostability. The addition of difunctional promoters ensures the smooth hypergolic ignition of BH4–/BH3CN– anion-free ionic liquid fuels with a minimum ignition delay time of 34.0 ms, and no apparent microexplosion and secondary combustion are observed during the ignition process. With the increase in the amount of the promoter, density specific impulses of the composite fuels improve gradually. This work provides a platform strategy for designing promoters by synergy of cations and anions and makes efforts to seek green bipropellants.

We carried out experimental and numerical investigations on the axisymmetric spreading evolution of dynamic spin coating with a single drop of ethanol. The results show that the dynamic spreading process consists of two stages: inertial spreading stage and centrifugal thinning stage. These two stages are connected by a transient state in between characterized by the minimum contact line moving velocity. The Weber number determines the spreading in the first stage, similar to the case of the impact of a drop on a static substrate. The rotational Bond number has a marginal effect on the inertia spreading and the radius at the transient state. In the centrifugal thinning stage, the rotational Bond number dominates the flow while the effect of the Weber number is negligible.

3-D braided composite three-way circular tubes are integrated seamless connected tubes used for high strength connecting joints. We developed a novel braiding method of ‘yarn-added, yarn realigned’ to prepare three-way tubular preforms. Low-velocity impact compressions (LVIC) along axial direction were conducted to find effects of branch length and braiding layers on impact damage with drop-weight tester, high-speed camera, Micro-CT and digital image correlation (DIC). It was found that the three-way braided tubes have uniform structure both at the branches and joint regions. There is shear band induced by the weakened interface appeared after the peak load and formed within 60 μs under impact. The ultimate strength was positively correlated with the impact energy and braiding layers, while negatively correlated with the branch tube length. The test results showed that the branch length affected the position of stress concentration, and the influence of braiding layers on the LVIC behaviors is more significant than that of the branch length.

Revealing mechanical behaviors of three-dimensional five-directional (3D5d) braided composites at different strain rates is a key point to its durability design and structural optimization. Here we report compressive responses, surface deformations and failure behaviors of aged 3D5d braided composites under different strain rates with digital image correlation (DIC) technique, X-ray micro-computed (micro-CT) tomography and finite element analysis (FEA). The compressive rigidity, peak stress, maximum strain, energy absorption, surface strain and damages exhibit strain rate strengthening effects and ageing weakening behaviors. The strain concentration zone transfers from X-shaped to transverse V-shaped at the square cross-section with the increasing of strain rate. Moreover, ageing effect does not change the internal shear mode, while it changes the near-surface crack distribution along axial direction and crack propagation path under impact loading. The failure modes show strain rate correlation. The FEA results reveal the failure mechanisms of the aged 3D5d braided composites under different strain rates.

Anisotropic mechanical behaviors are the most prominent feature of 3D braided composites compared with homogeneous materials. This study reports anisotropic low-velocity impact behaviors of 3D braided carbon fiber/epoxy composites along in-plane (IP) and out-of-plane (OP) directions after thermo-oxidative ageing. The stress–strain responses, local strain and damage evolution were obtained. The stress distribution of each yarn and the interface damage propagation were analyzed with numerical analysis method. The retention rate of peak stress of 94.4% and elastic modulus of 91.45% along OP direction are greater than those along IP direction, which are 76.21% and 71.27% respectively. It reveals that the OP direction loading has a better performance on resistance ageing degradation than that in IP loading, and the stiffness degradation is more sensitive. There are X-shape shear damages along OP direction, and interior damages in surrounding area and yarn path along IP direction. Furthermore, the tight braided structure contributed to resisting degradation of mechanical properties along IP direction.

Achieving accurate and efficient target deposition of pesticide droplets is the principal factor in minimizing environmental risk. For hydrophobic surfaces, adding tank-mix adjuvants containing surfactants to modulate interfacial behavior is warranted, which lacks common laws to guide practical applications directly. Machine learning is developing rapidly and makes many data-based decisions in various industrial processes. Hence, according to machine learning-based analysis of fundamental physical quantities, proposing quantitative sustainability metrics to improve interface behavior is essential. Comparing the interfacial behavior of five adjuvants, the common denominator is that droplets in the Wenzel state with higher adhesion tension and lower contact angles can generate the pinning force that causes energy dissipation, reduces pesticide losses, and weakens environmental pollution. Simultaneously, the interfacial behavior of pesticide droplets including adjuvants on citrus leaves is verified, while the phytotoxicity experiment under high temperature and the laboratory bioassay are carried out. The results show that the eco-friendly alkyl polyglycoside (APG) as the glycosidic surfactant has nontarget biosafety and better mite control, which can be exploited as a commercial tank-mix adjuvant for promotion. This study provides a new insight into guiding adjuvants added to pesticides on account of quantitative sustainability metrics, which has important implications for food safety and agricultural green development.

Following a previously published paper in studying stone-skipping processes, detailed experimental figures are revealed in this paper. A mathematical model is also provided to explain the observed phenomena and measured data. The model separates the skipping process into several stages. It emphasizes, in particular, a hitting stage and a sliding stage, and also includes capillary-gravity wave resistance in its formulation. During these two stages, scale analysis is applied first to evaluate the relative importance among various forces acting on the stone. After reasonable simplification, a numerical algorithm is established to depict motion of the stone starting from its first hit of water to final sink. The total number of skips under specified initial throwing conditions can be predicted accordingly. The agreement between the analytical and experimental results indicates the applicability of the proposed model.

Functional textiles with superhydrophobicity and high adhesion to water, called parahydrophobic, are attracting increasing attention from industry and academia. The hierarchical (micronanoscale) surface patterns in nature provide an excellent reference for the manufacture of parahydrophobic functional textiles. However, the replication of the complex parahydrophobic micronanostructures in nature exceeds the ability of traditional manufacturing strategies, which makes it difficult to accurately manufacture controllable nanostructures on yarn and textiles. Herein, a two-photon femtosecond laser direct writing strategy with nanoscale process capability was utilized to accurately construct the functional parahydrophobic yarn with a diameter of 900 μm. Inspired by rose petals, the parahydrophobic yarn is composed of a hollow round tube, regularly arranged micropapillae (the diameter is 109 μm), and nanofolds (the distance is 800 nm) on papillae. The bionic yarn exhibited a superior parahydrophobic behavior, where the liquid droplet not only was firmly adhered to the bionic yarn at an inverted angle (180°) but also presented as spherical on the yarn (the maximum water contact angle is 159°). The fabric woven by the bionic yarn also exhibited liquid droplet-catching ability even when tilted vertically or turned upside down. Based on the excellent parahydrophobic function of bionic yarn, we demonstrated a glove that has very wide application potential in the fields of water droplet-based transportation, manipulation, microreactors, microextractors, etc.

In this paper, the puncture resistance of carbon fiber reinforced polymer (CFRP) with different thicknesses under various puncture energy was studied by in-situ observation. The puncture failure process of CFRP was analyzed using a high-speed camera and thin-film pressure sensor in terms of damage image and local pressure change. The experimental results show that the puncture threshold load (PTL) representing material penetration is usually located at the initial loss position of material stiffness. The penetration load can be divided into linear growth and delamination failure zones. Image localization was used to mark the puncture feature points on the puncture force–displacement curve to help characterize the puncture failure process. The theoretical equations of puncture force and displacement before material penetration are proposed and verified by introducing yield stress and friction force, and the correlation between the material thickness and the puncture resistance was proved. In addition, the failure modes and fracture morphology of CFRP after puncture are analyzed and summarized. After puncture impact, fiber fracture, pull out and slip deformation under the action of tensile force and cutting force, and matrix fracture and peel damage. The increase of impact energy leads to a broader range of impact damage but does not change the failure modes.

The stability of droplet transfer plays an important role in the weld formation and spatters suppression during the laser-MIG hybrid welding. However, a debate exists on whether increased laser power improves or suppresses the droplet transfer. In this study, the role of laser heat source was investigated in a wide range of laser power. The transfer frequency was firstly improved by increasing laser power, and then it was decreased once the laser power proceeded a critical value. The variation of droplet transfer frequency was determined by the competition between electromagnetic force and metal vapor reaction force. With increasing laser power, the arc conductivity was better and the arc current was improved, leading to increase of the electromagnetic force. As a result, the droplet transfer was promoted and the deposition rate of wire metal was increased. However, rapid increase of metal vapor reaction force was obtained when the laser power exceeded the critical value, producing a greater resistance on droplet transfer. Furthermore, the critical value of laser power was mainly determined by the characteristics of laser source, materials, laser focusing distance and laser-arc distance. This work will provide more guidance on matching processing parameters of the laser-MIG hybrid welding to improve weld formation and suppress spatters by stabilizing the droplet transfer.

Spinal cord injury (SCI) frequently results in motor, sensory and autonomic dysfunction for which there is currently no cure. Recent preclinical and clinical research has led to promising advances in treatment; however, therapeutics indicating promise in rodents have not translated successfully in human trials, likely due, in part, to gross anatomical and physiological differences between the species. Therefore, large animal models of SCI may facilitate the study of secondary injury processes that are influenced by scale, and assist the translation of potential therapeutic interventions. The aim of this study was to characterize two severities of thoracic contusion SCI in female domestic pigs, measuring motor function and spinal cord lesion characteristics, over two weeks post-SCI. A custom instrumented weight drop injury device was used to release a 50 g impactor from 10 cm (n=3) or 20 cm (n=7) onto the exposed dura, to induce a contusion at the T10 thoracic spinal level. Hind limb motor function was assessed at 8 and 13 days post-SCI using a 10-point scale. Volume and extent of lesion-associated signal hyperintensity in T2-weighted magnetic resonance (MR) images was assessed at 3, 7 and 14 days post-injury. Animals were transcardially perfused at 14 days post-SCI and spinal cord tissue was harvested for histological analysis. Bowel function was retained in all animals and transient urinary retention occurred in two animals after catheter removal. All animals displayed hind limb motor deficits. Animals in the 10 cm group demonstrated some stepping and weight bearing and scored a median 2-3 points higher on the 10-point motor function scale at 8 and 13 days post-SCI, than the 20 cm group. Histological lesion volume was 20 % greater, and 30 % less white matter was spared, in the 20 cm group than in the 10 cm group. The MR signal hyperintensity in the 20 cm injury group had a median cranial-caudal extent approximately 1.5 times greater than the 10 cm injury group at all three time points, and median volumes 1.8, 2.5 and 4.5 times greater at day 3, 7 and 14 post-injury, respectively. Regional differences in axonal injury were observed between groups, with amyloid precursor protein immunoreactivity greatest in the 20 cm group in spinal cord sections adjacent the injury epicenter. This study demonstrated graded injuries in a domestic pig strain, with outcome measures comparable to miniature pig models of contusion SCI. The model provides a vehicle for the study of SCI and potential treatments, particularly where miniature pig strains are not available and/or where small animal models are not appropriate for the research question.

Memristor-based in- memory computing paradigm is a promising path for edge detection in image preprocessing on end devices that reduces the computational pressure on data centers. However, the implementation of the well-performing Canny operator for edge detection faces challenges in terms of computational time and area overhead when mapped to memristor arrays. In this work, we proposed an efficient memristive one-step implementation of a fast-Canny operator. Exploiting the associative property of multiplication, the conventional Canny operator consisting of Gaussian and Sobel operators is converted into a fast-Canny operator and mapped to an array of nine parallel memristors. Then, the output currents are the final pixels of the edge image. To verify the feasibility of the method, successful edge detection with high accuracy (OIS = 0.73) is achieved in device-aware simulation under device variation (<50%) and image noise ( σ = 6%). Additionally, the implementation of the fast-Canny operator on memristor arrays can reduce the processing time by half and save the area of buffer compared to the prior two-convolution Canny operation. Our work suggests that the memristive fast-Canny operator could be a promising and efficient hardware solution for edge detection at the network edge.

Background
The wettability of the target surfaces affects the wetting and deposition of pesticides on them. The properties of leaf surfaces change after infestation by Tetranychus urticae Koch. Studying the surface wettability of T. urticae and the changes in leaf wettability after infestation is important to guide the use of acaricides.

Results
The body surface of T. urticae is an ellipsoidal crown covered with dense cuticle striations and hairs arranged in different directions, which makes the surface of T. urticae rough and hydrophobic. The abaxial surfaces of the leaves are rougher and more hydrophobic than the adaxial surfaces. After infestation by T. urticae, the faded spots were sunken on the adaxial surface and raised on the abaxial surface, where they had formed new wide peaks and valleys. The adaxial surface became obviously rougher and more hydrophobic, while the roughness of the abaxial surface became slightly larger, and the change in hydrophobicity was not obvious. The contact angles of the studied commercial acaricide on these surfaces were greater than 65° and were affected by the infestation. Reducing the surface tension can allow for better wetting of these surfaces and eliminate changes in leaf wettability.

Wire and arc additive manufacturing (WAAM) is a novel technique for fabricating large and complex components applied in the manufacturing industry. In this study, a low-carbon high-strength steel component deposited by WAAM for use in ship building was obtained. Its microstructure and mechanical properties as well as fracture mechanisms were investigated. The results showed that the microstructure consisted of an equiaxed zone, columnar zone, and inter-layer zone, while the phases formed in different parts of the deposited component were different due to various thermal cycles and cooling rates. The microhardness of the bottom and top varied from 290 HV to 260 HV, caused by temperature gradients and an inhomogeneous microstructure. Additionally, the tensile properties in transversal and longitudinal orientations show anisotropy characteristics, which was further investigated using a digital image correlation (DIC) method. This experimental fact indicated that the longitudinal tensile property has an inferior performance and tends to cause stress concentrations in the inter-layer areas due to the inclusion of more inter-layer zones. Furthermore, electron backscattered diffraction (EBSD) was applied to analyze the difference in Taylor factor between the inter-layer area and deposited area. The standard deviation of the Taylor factor in the inter-layer area was determined to be 0.907, which was larger than that in the deposited area (0.865), indicating nonuniform deformation and local stress concentration occurred in inter-layer area. Finally, as observed from the fracture morphology on the fractured surface of the sample, anisotropy was also approved by the comparison of the transversal and longitudinal tensile specimens

There is a scarcity of available data on boiling process in vertically oriented tube bundles in accessible sources. Lack of systematic studies is limiting further expansion of this highly efficient process of heat transfer into heat recovery field. In this paper boiling process of three triangular pitched and vertically oriented tubes has been studied in ethanol at 78 °C. The main focus of this work was to study the effect of tube spacings on heat transfer coefficient (HTC) and bubbles behavior (bubble departure diameter in particular) that were visualised with the help of a high speed camera. Experiments were performed in a wide range of tube spacings (from 10.75 to 0.25 mm) and heat flux densities (from 3 to 70 kW/m2).

By developing a thermo-mechanical coupled model, we quantitatively analyzed the effect of thermo-oxidative ageing on the temperature, thermal strain and thermal stress histories of braided composites during high-speed impact. We also considered temperature dependence of elastic modulus during impact in this model. The proposed model was first applied to the unaged composites, then the results were compared to the impact responses captured by the split Hopkinson bar and the high-speed camera. The comparisons of the experimental and numerical results show that the proposed model could capture the adiabatic temperature rise, stress-strain responses and failure process of braided composites during high-speed impact. The validated model was subsequently employed to thermo-oxidative aged composites. Results show that the temperature rise, thermal strain and thermal stress all depend on the mechanical properties of resin, and they decreased with the increase of ageing temperature since the performance of resin is compromised by thermo-oxidation ageing. The change of resin performance after ageing leads to the change in the temperature rise during impact, so the stiffness of composites will decrease in varying degrees after ageing.

Debris flows are common geological hazards in mountainous regions worldwide. The scale of debris flows can be significantly enhanced by basal erosion and bank collapse in the transportation process, resulting in an increase in casualties and property losses. However, the mechanisms of this growth are largely unclear. Here, we conduct a series of experiments to investigate the erosion of two different bed sediments (coarse-grained and widely graded) by released flows with three different densities and two different volumes. The erosion mechanisms of bed sediments are revealed by comparing detailed sensor data for flow level, pore pressure and total normal stress. A flow nose develops on the coarse-grained bed sediment, resulting in a high flow depth and low velocity, while a tabular flow develops on the widely graded bed sediment, leading to a low flow depth and high velocity. The mean erosion rates of the coarse-grained bed sediment are generally higher than those of the widely graded bed sediment due to significant pore pressure developed in coarse-grained bed sediment. The feedback effect of bed sediment on the erosion process strongly influences the flow depth and velocity, which in turn affects the mean erosion rate of bed sediment. The interaction between the overlying flow and sediment bed controls the erosion pattern: coarse-grained bed sediment is eroded by a layer of mass movement whereas widely graded bed sediment is progressively scoured. The interaction between debris flow and bed sediment during erosion is principally attributed to pore-pressure transmission.

The metal transfer behaviour of slant feature of thin-walls fabricated by cold metal transfer (CMT) process in step-over deposition mode was observed by high speed camera. A slanted short circuiting transfer (SSCT) was generated during deposition and then analysed by asymmetrical magnetic and force model, complicating metal transfer behaviour in comparison with conventional deposition process. The SSCT allowed the droplet to transfer obliquely into the molten pool on previous layer, owing to the pushing force generated by unevenly distributed electromagnetic field in asymmetrical deposition model. The surface tension between wire and liquid metal is the most important force that retarded droplet transfer. The retraction force and electromagnetic force are the main forces to promote droplet transition. The positive forces that promote droplet transfer process can be arranged as Fem > Fr > Fg. The wall width was mainly affected by wire feed speed and the inclined angle can be significantly increased with increasing step-over distance.

The macroscopic mechanical behaviors generally correlate with nanomechanical properties, especially elastic modulus. This paper presents the thermo-oxidative ageing effects on nanoscale elastic modulus and impact failure mechanism of 3D braided composites at micro and macro levels using PeakForce Quantitative Nano-Mechanics (PF-QNM) and digital image correlation (DIC) technologies. The values of nanoscale elastic modulus of near-fiber resin pocket were about three times than that of global modulus in neat resin under low-velocity impact compression (LVIC) loading. However, the modulus retention rates were consistent which was ∼88% after ageing for 16 days at 180 °C. The decline of them has provided a direct evidence for resin degradation after ageing. In addition, the in-plane impact failure mechanism of braided composites mainly contained five modes, i.e., matrix cracking, interface cracking, matrix fracture and peeling off, fiber buckling and slipping, and fiber breakage. Thermo-oxidative ageing only changed the crack propagation path but not the damage modes.

The stability of droplet transfer plays an important role in the weld formation and spatters suppression during the laser-MIG hybrid welding. However, a debate exists on whether increased laser power improves or suppresses the droplet transfer. In this study, the role of laser heat source was investigated in a wide range of laser power. The droplet transfer was firstly improved by increasing laser power, and then it was suppressed once the laser power proceeded a critical value. The variation of droplet transfer frequency was determined by the competition between electromagnetic force and metal vapor reaction force. With increasing laser power, the arc conductivity was better and the arc current was improved, leading to increase of the electromagnetic force. As a result, the droplet transfer was promoted and the deposition rate of wire metal was increased. However, rapid increase of metal vapor reaction force was obtained when the laser power exceeded the critical value, producing a greater resistance on droplet transfer. Furthermore, the critical value of laser power was mainly determined by the characteristics of laser source, materials and laser-arc distance. This work will provide more guidance on matching processing parameters of the laser-MIG hybrid welding to improve weld formation and suppress spatters by stabilizing the droplet transfer.

This work presents experimental studies with numerical modeling, aiming at the development of guidelines for shaping aluminum alloy AA6111-T4, t = 1.5 mm thick, with the use of a shear-slitting operation. During the experimental tests, parametric analyses were conducted for the selected material thickness. For the purposes of the material deformation’s analysis, a vision system based on the digital image correlation (DiC) method was used. Numerical models were developed with the use of finite element analysis (FEA) and the mesh-free method: smoothed particle hydrodynamics (SPH), which were used to analyze the residual stress and strain in the cutting zone at different process conditions. The results indicate a significant effect of the horizontal clearance between knives on the width of the deformation zone on sheet cut edge. Together with the clearance value increase, the deformation zone increases. The highest burrs on the cut edge were obtained, when the slitting speed was set to v = 17 m/min, and clearance to hc = 6%t. A strong influence was observed of the horizontal clearance value at high slitting speeds on burr unshapeliness. The most favorable conditions were obtained for v = 32 m/min, hc = 0.062 mm, and rake angle of upper knife for α = 30°. For this configuration, a smooth sheared edge with minimal burr height was obtained.

Previous methods for the investigation of high-speed cutting processes for bio-based materials failed since essential principles for the investigation of dynamic processes have not been taken into account. The novel self-developed device, based on the principle of a rotor arm, enables a detailed analysis of cutting processes. The rotor arm has a diameter of 4 m, enabling precise analysis of cutting processes. The device enables analysis of speeds up to 100 m/s of the more or less linear cutting process. Stiffness of the set-up, the natural frequency of the system, and a series of cuts per test may cause a convoluted signal demanding dynamic calibration of the measurement chain. The newly developed device enables the conduction of single cuts per examination at relatively high speed. Thus, the influence of the previous cut is eliminated. Previous research has not provided a possibility to study linear cutting processes at the mentioned velocity. The accuracy of the device was proven within various examinations. A correction based on real chip thickness measurement was applied. Finally cutting of beech, using a wide set of parameters, was examined. The cutting forces of the beech sample increased linearly with chip thickness. Nevertheless, the influence of velocity showed non-linear progression. The smallest force was observed at 20 m/s. From this cutting speed, force always increased when velocity was changed.

In this work, a design concept of bioinspired functional surfaces is proposed for lubricant control at surfaces and interfaces subjected to external thermal gradients. Inspired by the conical structures of cactus and the motion configuration of Centipedes, a bioinspired surface of wedged-groove with an oriented capillary pattern is constructed. The effect of geometrical parameters on the directional lubricant manipulation capacity and sliding anisotropy is discussed. It is found that by regulating the orientation of the capillary pattern, a controllable lubricant self-transport capacity can be achieved for varying conditions from surfaces to interfaces, with or without thermal gradients. The lubricant self-transport process is captured, and the mechanism is revealed. The design philosophy of the proposed bioinspired functional surface is believed to have potential applications for lubricant control in modern machinery and complex liquid control in lab-on-a-chip and microfluidics devices.

The collisional interaction process between bubbles and particles is considered to play an important role in flotation. This paper aims to investigate the effect of particle hydrophobicity on the bubble-particle collision and subsequent interaction process. Four types of bubble-particle interaction behaviors were observed, namely the non-collision, the collision but without attachment, the attachment with jump-in after collision, and the attachment without jump-in after collision. The ‘jump-in’ event was interpreted as the rupture of the water film, providing the formation and growth of a ‘three-phase contact line’ (TPCL). The mildly hydrophobic particle could attach to the bubble surface without the rupture of the water film, whereas the highly hydrophobic particle had the higher collision and attachment probability. The significant effect of particle hydrophobicity was found in the observed particle trajectories and velocities. The distance between the bubble and the particle of weakly hydrophobicity and mildly hydrophobicity remained almost constant in the particle sliding process on the bubble surface. However, the highly hydrophobic particle was observed to jump in instantaneously after a short interaction time. Influenced by hydrodynamic drag, the maximum sliding velocity of any particles near the bubble’s equatorial plane was higher than the particle terminal velocity, and highly hydrophobic particle had a higher difference. The analysis of the individual force components of particle provides valuable insights into the kinematic properties of particle as it slides. The hydrodynamic drag coefficient decreased with an increase in the particle contact angle, implying the highly hydrophobic particle had a smaller hydrodynamic drag. Additionally, the reaction force was introduced for the first time to satisfy the radial force balance relationship, and explanations were proposed in terms of its source.

Droplet rebound from hydrophobic leaves is a major factor influencing pesticide utilization. The use of a surfactant is a major strategy to reduce droplet rebound, promoting pesticide deposition on hydrophobic agricultural plant leaves. However, most surfactants known to regulate droplet rebound are either anionic or cationic. In this study, ethoxylated propoxylated 2-ethyl-1-haxanol (EH 6) was identified as a nonionic surfactant that inhibits droplet rebound while promoting the complete spreading of the droplet on hydrophobic leaves. Compared with the widely reported nonionic surfactant Tween 20, EH 6 performs better at concentrations above 0.3%. This phenomenon can be attributed to the rapid migration of EH 6 from the bulk to the newly generated interface, significantly reducing the surface tension. We introduce a simple and effective strategy that can be used to enhance droplet deposition on hydrophobic plant surfaces, which may offer future economic and environmental benefits.

This study used a nickel-based filler metal to fabricate a surfacing layer on a low-carbon steel substrate by a hybrid welding process with a rotating laser and arc. The surfacing layer's weld formation was studied using optical microscopic observation (OM). The microstructure of the layers was studied by using the scanning electron microscope (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD). The arc, metal transfer, molten pool flow behaviors, and U–I characteristics during hybrid laser arc welding (HLAW) were analyzed using the arc analyzer and high-speed camera. The results show that a rotating laser improves the weld formation of gas metal arc welding (GMAW). The microstructure of the two surfacing layers consists of dendritic γ phase and a small amount of Laves and NbC phases. The high dilution rate of the HLAW surfacing layer results in relatively more Laves and fewer NbC phases. The arc length of HLAW is dynamically deflected with the rotation of the laser, which expands the arc action and heating area of the molten pool. The droplet transfer mode changed from globular transfer dominant in GMAW to the projected transfer dominant in HLAW. The location where the droplet transfer into the molten pool is dynamic changed, forming a multi-point impact on the molten pool. Combined with the deflected arc with the laser rotating laser, the HLAW has a broad and deep molten pool. Understanding the metal transfer behavior of Ni-based alloys in rotating laser-induced arc hybrid surfacing is of great significance for improving surfacing forming.

The unsteady powder mass flowrate of the available feeding systems and the bad control of the areas being eroded have been often noticed in the abrasive air jet machining process. In addition to the delivery of dry powder, the powder can be evenly mixed with liquid to form a slurry, and then sent to the mixing chamber of an air jet machine; i.e., multiphase jet machining (MJM) was proposed in this paper. The method whereby using the viscous water to suspend the abrasives was found to enhance the stability of powder mass flowrate, thereby decreasing the fluctuation in the machining depth. Whereafter, five types of liquid-based slurries were prepared and their effects on the jet erosion zone were investigated. It was found that the control of the erosion zone was improved to varying degrees when the abrasives were transported into the air jet by viscous liquid as the carrier fluid due to the two roles: reducing the occurrence of third and/or second particle impacts; inducing a viscous boundary layer that could reduce the negative effect of the divergence of jet beam and particle rebounding. In particular, the use of an oil-based slurry could completely eliminate the unwanted frosted zone around the machined features. CFD simulations were used to understand the mechanisms causing these effects. Overall, it is shown that the abrasive air jets can be designed to have a good resolution, so it is feasible to mill or polish surface without the need for a mask to define the edges.

Direct writing technology is a promising approach for the preparation of reactive materials. The polymer binder provides a mechanically stable, processable and shapeable energetic structure for composites. Herein, Direct-writing energetic inks consisting of nitrocellulose (NC) and VitonF2311 as well as nanothermite were developed. Firstly, Fourier transform infrared spectroscopy (FT-IR) was used to analyze the intermolecular hydrogen bonds in the hybrid polymers, and the stability of the network structure was characterized by rheometer, and the mechanical properties of binders were also tested. The results show the best binder formulation is 20 wt% NC and 80 wt% F2311. The elongation at break of the binder is 600.94%, and the elastic modulus is 8.29 MPa. NC provides high tensile strength for the hybrid binder; F2311 provides high fracture tensile rate for the hybrid binder, and as a high-energy initiator, pre-ignition reaction occurs when the temperature reaches 350 °C. Then the as-prepared inks not only has excellent rheological properties so that it can be loaded with 90 wt% nanothermite, but also possess a homodisperse for components and good combustion performance. The average flame temperature is about 2400 K at atmospheric pressure.

Current techniques for the generation of cell-laden microgels are limited by numerous challenges, including poorly uncontrolled batch-to-batch variations, processes that are both labor- and time-consuming, the high expense of devices and reagents, and low production rates; this hampers the translation of laboratory findings to clinical applications. To address these challenges, we develop a droplet-based microfluidic strategy based on metastable droplet-templating and microchannel integration for the substantial large-scale production of single cell-laden alginate microgels. Specifically, we present a continuous processing method for microgel generation by introducing amphiphilic perfluoronated alcohols to obtain metastable emulsion droplets as sacrificial templates. In addition, to adapt to the metastable emulsion system, integrated microfluidic chips containing 80 drop-maker units are designed and optimized based on the computational fluid dynamics simulation. This strategy allows single cell encapsulation in microgels at a maximum production rate of 10 ml hr-1 of cell suspension while retaining cell viability and functionality. These results represent a significant advance toward using cell-laden microgels for clinical-relevant applications, including cell therapy, tissue regeneration and 3D bioprinting.

Surfaces designed to reduce the contact time of impacting droplets are potentially of great importance for fundamental science and technological applications, for example, anti-icing, self-cleaning and heating transfer applications. Previous studies have shown that the contact time can be reduced via introducing one or several crossing macroscale wires on superhydrophobic surfaces (SHSs). However, the impacts that strike far from the wires (off-center impacts) have contact times that are equal to those obtained on SHSs. Here we demonstrate that this problem can be largely solved by using macro anisotropic SHSs (macro-aniso-SHSs)—in which the wires are parallel and macroscaled. The droplet contact time depends on the spacing between the macrostripes and is remarkably reduced by 40–50% when the spacing is comparable to the droplet size. Obvious differences in the contact time are not observed for impacts that are centered on the stripe and in the groove. The impacts centered in the groove produce new hydrodynamics that are characterized by extended spreading, easy break up and bouncing in a flying-eagle configuration. The study discusses the underlying mechanisms of the impact processes. Moreover, the effect of parallel wires on the contact time is discussed by comparing the droplet impact data for grooved rice leaves and non-grooved cabbage leaves. The enhanced drop mobility associated with the macro-aniso-SHSs should be very useful in many industrial applications.

Interface debonding between fiber reinforced polymers (FPR) and substrates is the principal failure mode for FRP-reinforced structure. To understand the bond–slip relationship at FRP-to-brick interfaces under dynamic loading, the influences of the dynamic enhancement of material performance on the bond–slip curve were studied. Single-lap shear tests under two different loading rates were performed, and the slip distribution curves at different loading stages were fitted to derive the bond–slip relationship. Then a numerical model considering the strain rate effects on materials was built and verified with test results. Further, the influences of brick strength, FRP stiffness and slip rate on the bond–slip relationship were investigated numerically. The research results show that FRP stiffness mainly influences the shape of the bond–slip curve, while brick strength mainly influences the amplitude of the bond–slip curve. The variations of the bond–slip relationship under dynamic loading, i.e., under different slip rates, are mainly caused by the dynamic enhancement of brick strength, and also by the dynamic enhancement of FRP stiffness, especially within a specific slip rate range. The proposed empirical formula considering dynamic FRP stiffness and dynamic brick strength can be used to predict the bond–slip relationship at the FRP-to-brick interface under dynamic loading

This paper reports the damage mechanisms of 3-D carbon fiber/epoxy braided composite under multiple impact compressions along out-plane direction. The multiple compression tests were conducted on a split Hopkinson pressure bar (SHPB) apparatus. The compressive deformations and damages were photographed with high speed camera and compared with those from finite element analyses (FEA). We found that the initial compressive damages are fiber/resin interface damage and resin fragmentation. Then the braided preform was in a severe shear damage which accompanied with further damages of interface and resin under the followed impact compressions. The energy absorptions by the reinforcement and epoxy resin at the multiple impacts were decomposed. The braided composite has the highest energy absorption capability at the first impact. The yarn orientation in braided preform leads to non-uniform stress and strain distribution. This non-uniformity easily induced the local damage and furthermore the catastrophic failure under the multiple compressions.