Search Results (1,935)

Circuit carriers perform various functions within electrical systems and products. This includes being the assembly platform for various components. To mount these components, soldering processes are predominantly used because of economic and technical benefits compared to other assembly technologies. Therefore, novel circuit carrier technologies should be compatible with soldering processes to compete with the state of the art. One of these innovative circuit carrier technologies is based on anodized aluminum substrates, which are characterized by their low cost and low thermal resistance. In this article, circuit carriers made of anodized aluminum with two different oxide morphologies being investigated. In addition, three different metallization processes were compared with regard to their suitability for a reflow soldering process for the assembly of surface mount devices (SMDs). In order to evaluate the assemblies, the force required to shear off the SMDs was measured before and after a cyclic thermal shock test (TST). One of the three investigated metallization processes yielded circuit carriers based on anodic aluminum oxide that enabled reflow soldering of the given SMD components. It was determined that both, the layer morphology and the metallization process, had an influence on the measured shear forces before and after TST. Full article

Frictional energy piles are a more desirable form of shallow geothermal energy utilization. A pure friction pile condition cannot be achieved in field tests. In this study, foam was placed beneath the model pile tip to weaken the end-bearing resistance. The effects of different cyclic temperature patterns (including cyclic path, external load, and variable temperature duration) on the bearing characteristics of pure friction energy piles are investigated by conducting model tests in a self-designed model box, and the variation patterns of pile stress–strain and pile-top displacement are measured. The results show the following: (1) Under no load, the displacement of the pile top changes with temperature; each round of temperature change produces a partial irrecoverable displacement, and the pile maintains a raised state at the end of both rounds with no stress accumulation. (2) Under the combined action of working load and cyclic temperature, the pile strain reaches its peak and then partially rebounds. Thermal stress accumulates progressively with increasing cycle numbers, and after the cycling ends, an irrecoverable settlement displacement (0.52% D) remains at the pile top and continues to increase. (3) The temperature cycle caused the soil volume to shrink and decreased the shear strength of the pile–soil interface, resulting in a decrease in the ultimate bearing capacity of the test pile compared to the initial state. Full article

In this work, a formaldehyde-free bio-based wood adhesive was successfully fabricated using epoxidized soybean oil (ESO) cross-linked with maleic anhydride (MA) and carboxylated lignin sulfonate (CLS). The effect of CLS substitution dosage on the bonding performance was systematically investigated. The results indicated that the dry shear strength and wet shear strength of the adhesive exhibited a typical non-monotonic variation with increasing CLS content, reaching the maximum values of 1.79 MPa and 1.38 MPa, respectively, at a CLS substitution ratio of 40 mol% relative to MA. These mechanical properties fully meet and exceed the requirements of the Chinese national standard for wood adhesives. Orthogonal experiments were further conducted to optimize the hot-pressing process parameters and the optimal conditions were determined as follows: hot-pressing temperature of 130 °C, pressing time of 10 min, glue spread of 280 g/m², and pre-mixing time of 70 min. FTIR, DSC, and TGA characterizations confirmed the complete curing reaction of the adhesive system. The introduced CLS served as both a reactive curing agent and an efficient catalytic component, which effectively reduced the curing temperature, while the incorporation of MA significantly improved the thermal stability of the cured adhesive. This study provides a feasible strategy for the preparation of high-performance, low-cost, and environmentally friendly bio-based wood adhesives. Full article

To overcome the limitations of conventional biopolymer films and reduce reliance on petroleum-based plastics, a nacre-inspired film was developed via 3D printing. During printing process, shear-induced alignment of mica flakes was achieved within a sodium alginate/xanthan gum matrix. Additionally, zinc oxide nanoparticles (ZnO NPs) were incorporated to achieve a synergistic reinforcement effect. Structural analysis revealed that the mica flakes within the film exhibited an oriented distribution, with ZnO NPs uniformly embedded in the interlayer voids, and hydrogen bonding assisted in forming a dense network of the components. Performance testing showed that the tensile strength rose from 13.8 MPa to 62.9 MPa. Improvements in water resistance and thermal stability were also observed. Furthermore, the material exhibited outstanding comprehensive protective properties, including a low water vapor permeability value of 7.587 × 10⁻¹¹ g·m/m²·Pa·s, an ultraviolet blocking rate of 99.37% at a wavelength of 280 nm, and the ability to completely inhibit target bacterial strains, while also possessing good biodegradability and recyclability. Shelf-life tests indicated that the film fabricated in this work could notably prolong the shelf life of strawberries. Biocompatibility test results indicated that the film was safe and non-toxic, and showed no significant cytotoxicity. Full article

The aim of this study was to investigate the effects of surface treatments and thermocycling on the shear bond strength of a 3D-printed permanent crown resin. A total of 120 disc-shaped specimens (10 × 3 mm) were fabricated using a 3D printer and randomly assigned to four groups according to surface repair protocols: airborne-particle abrasion with Al₂O₃, bur roughening, 37% orthophosphoric acid etching, and a control group with no surface treatment. All specimens received a silane coupling agent followed by an adhesive resin application, and repair was performed using a highly filled flowable composite. Each group was divided into three subgroups and subjected to 1000, 5000, or 15,000 thermal cycles. Shear bond strength was measured, failure modes were analyzed, and data were evaluated using two-way ANOVA and Tukey’s post hoc test (p < 0.05). The sandblasting group exhibited the highest bond strength (18.7 ± 5.0 MPa), which was significantly higher than the control (12.6 ± 3.7 MPa) and acid-etching (14.2 ± 3.8 MPa) groups (p < 0.05). Aging periods had no significant effect on bond strength (p > 0.05). Additionally, the interaction between surface treatment and thermocycling had no significant effect (p = 0.823). Under the tested conditions, airborne-particle abrasion resulted in the highest shear bond strength of 3D-printed permanent crown resin. Full article

A simply supported rectangular isotropic ferromagnetic plate with magnetocaloric properties subjected to convective heating on its upper surface is considered. The governing equations comprise a system of two-dimensional transient equations for the thickness-averaged temperature characteristics of the plate and the two-dimensional bending equations for isotropic plates expressed in terms of generalized displacements within the framework of first-order shear deformation theory. Closed-form solutions to the governing equations are obtained by expanding all thermal and mechanical field quantities in double Fourier sine series satisfying the prescribed boundary conditions, combined with the Laplace transform in time applied to the thermal quantities. A comparative numerical analysis is carried out for the magnetocaloric ferromagnetic plate and a carbon steel plate under ambient temperature rising at a finite rate to a prescribed value. The dependences of all quantities under investigation on the ambient temperature rise rate, time, convective heat transfer coefficient, thermal conductivity of the ferromagnetic material, and geometric parameters of the plate are analyzed and presented graphically. The results obtained provide a quantitative basis for assessing the thermoelastic state and for optimizing the geometry and operating conditions of active magnetic regenerator plate stacks with a view to enhancing their structural reliability. Full article

To gain a deeper understanding of the lower-atmospheric dynamic characteristics in the transition zone on the northeastern margin of the Tibetan Plateau, high-resolution wind profile data collected by a Doppler wind lidar (DWL) at Yinchuan Hedong International Airport from 2021 to 2023 were used to analyze the vertical structure, seasonal variations, and diurnal characteristics of the low-height wind field and wind shear in this region. The results indicate that (1) the data acquisition rate (DAR) below 1.5 km is generally high, exceeding 90% during most periods, and decreases monotonically with height; the 90% DAR contour height exhibits clear seasonal and diurnal variations, with the largest diurnal amplitude in summer and the smallest in winter. (2) The middle- and low-height wind fields are jointly modulated by topographic forcing and local circulations. Below 0.4–0.7 km, north–northeast and south–southwest winds prevail across all seasons, which is consistent with the blocking and splitting effects of the Helan Mountains. At 42 m, the wind direction shows a marked diurnal transition that may reflect the combined influence of the Helan Mountains’ bypass flow, mountain–plain circulation, and thermal contrasts between the Yellow River and surrounding desert/plain surfaces. (3) Horizontal wind speeds are predominantly concentrated below 6 m s⁻¹, and the development height of this low-wind-speed zone varies seasonally. The vertical velocity statistics show weak positive values in parts of the observed layer, but these signals are interpreted cautiously because vertical-velocity retrieval is subject to additional uncertainty. (4) The low-level wind shear intensity reaches its peak below 100 m and generally exhibits a U-shaped vertical distribution; severe wind shear below 100 m occurs most frequently from nighttime to early morning during May–October, whereas its occurrence frequency is lowest in winter. These findings provide observational evidence for aviation meteorological support and boundary-layer studies in semi-arid regions of Northwest China. Full article

This study aimed to systematically evaluate the effects of the Zein/poly(vinylidene fluoride) (PVDF) blend ratio on the formation, structure, and performance of electrospun nanofiber membranes and to further assess the feasibility of incorporating bromothymol blue (BTB) into the optimized matrix as a pH-responsive functional component for intelligent food-packaging applications. Increasing PVDF content reduced the conductivity but increased the viscosity of the spinning solutions, and all formulations exhibited shear-thinning behavior. Pure Zein failed to form continuous fibers, whereas PVDF incorporation promoted uniform fibrous networks, with average fiber diameters increasing from 113.02 ± 27.06 nm to 530.68 ± 113.33 nm. FTIR and TGA/DTG analyses confirmed the coexistence of Zein and PVDF and the improved thermal stability associated with increasing PVDF content. Surface hydrophobicity and water resistance increased with PVDF content, whereas water vapor permeability (WVP) and water solubility (WS) increased with the Zein proportion. Considering spinnability, morphology, mechanical behavior, barrier performance, and water stability, the Zein/PVDF = 5:5 formulation provided a comparatively balanced performance and was selected as the functional carrier matrix. Incorporation of BTB into this matrix produced a distinct pH-responsive color change, and the color difference (ΔE) showed a strong correlation with shrimp pH during storage (R² = 0.997), demonstrating the feasibility of the optimized membrane as a freshness-responsive functional carrier. Full article

Due to system interactions, the formation and maintenance of dual squall lines are more complex than for single squall lines. In this study, we use upper-air soundings, ERA5 reanalysis data, high-density surface automatic weather station observations, and Doppler radar data to analyze a dual squall-line system that occurred over North China on 13 June 2022 under the Northeast China Cold Vortex. We focus on the differences between the two squall lines in mesoscale environments, convective triggering mechanisms, and maintenance processes. The main results are as follows: (1) The dual squall-line event occurred in different sectors of the Northeast China Cold Vortex, with both lines exhibiting a “dry-cold aloft, warm-moist below” stratification. However, significant spatiotemporal differences in mesoscale thermodynamic and dynamic conditions across Hebei and Shandong provinces led to distinct evolutionary pathways between the two squall lines. (2) Squall Line 1 (SL1) was triggered by the superposition of cold-pool outflow from convective cells over the Bohai Bay and convergence lines associated with surface cyclonic circulations. Squall Line 2 (SL2) was triggered by the thermal instability in the overlapping region of the temperature and dew-point fronts on the eastern slope of the Taihang Mountains, in conjunction with topographic uplift driven by the easterly flow. (3) This case study shows that squall-line maintenance depends not only on environmental CAPE and vertical wind shear but may also be closely related to the coordinated interplay between local thermal conditions and low-level shear. SL1, situated in a high-CAPE, low-LCL warm-moist environment, experienced relatively weak low-level shear; however, the ratio of cold-pool propagation speed to low-level shear remained near the RKW optimum, favoring persistence. Additionally, cold-pool spreading on the southern flank triggered new convection that merged into the southern end of the squall line, enhancing the cold pool via evaporative cooling and further promoting longevity. By contrast, SL2 displayed a pronounced north–south disparity: the northern segment failed to satisfy RKW balance due to insufficient cold-pool propagation relative to shear, leading to rapid echo dissipation; the southern segment, featuring an overly strong cold pool and low-CAPE, high-LCL conditions, inhibited deep convection. As a result, SL2 gradually split due to the spatial mismatch of thermodynamic and dynamic conditions along its north–south extent. Full article

Laser beam welding (LBW) offers low thermal distortion for thin austenitic stainless steel sheets but is sensitive to butt-joint fit-up and edge quality. This study compared machined and sheared joint edges under selected autogenous and ER308L filler-wire LBW conditions. Bead geometry, defects, microstructure, microhardness, tensile properties, and fracture behavior were characterized using conventional microscopy, EBSD-KAM, and three-dimensional digital image correlation (3D-DIC). The machined-edge autogenous condition (LBW-A-M) produced a stable bead with 0.04 mm top underfill and only a small number of internal discontinuities, while its tensile properties remained close to those of the base metal and fracture occurred in the base metal. In contrast, the sheared-edge autogenous condition (LBW-A-S) exhibited 0.24 mm top underfill, 0.18 mm misalignment, multiple pores, and localized strain near the weld, with tensile strength and elongation of 682.31 MPa and 44.04%, respectively. Under the selected filler-wire conditions, no measurable top underfill was observed, although pores remained. Because the autogenous and filler-wire modes used different process parameters and heat inputs, cross-mode differences are condition-specific rather than isolated filler-wire effects. Overall, joint-edge preparation and fit-up control remained important for thin-sheet LBW. Full article

High-temperature graphitization inevitably compromises the surface polarity and resin wettability of polyacrylonitrile (PAN)-based high-modulus carbon fibers (HMCFs), creating a long-standing trade-off between fiber modulus and interfacial adhesion that restricts its applications. Here we report a tension–temperature synergy to overcome this limitation. HMCFs were fabricated at 1700–2100 K under axial tensions of 0–70 N, and the resulting microstructures and surface activity were characterized by X-ray diffraction, Raman spectroscopy, dynamic contact angle testing, and microdroplet debond measurements. Temperature dominates crystallite coarsening and surface-active carbon (Sac) concentration, whereas tension enhances axial lamellar orientation without inducing appreciable grain growth. At constant temperature, two competing effects, both slight crystallite growth and radial lamella rearrangement, keep Sac stable under varying tension. Fibers processed at 1900 K with 60 N tension achieve a modulus of ~350 GPa, equivalent to that of the 2100 K/10 N sample, while delivering a 13.5% higher Sac, elevated surface energy (26.3 mN·m⁻¹), and 37.9% stronger interfacial shear strength (IFSS). The Sac parameter exhibits strong correlations with surface energy and IFSS. This one-step in situ thermal strategy eliminates post-treatment and offers an industrially viable route to HMCFs with balanced modulus and intrinsic interfacial bonding. Full article

This article presents an experimental investigation into the mechanical properties of new laminated bamboo and bamboo–timber hybrid composite materials for construction. A total of thirty-six bamboo and bamboo–timber hybrid composite specimens were manufactured, which include a new configuration that integrates bamboo and pine strips in hybrid bamboo–timber composite members. An interleaved configuration of the hybrid bamboo–timber composites is proposed to enhance stress transfer and interfacial bonding. Such a design can mitigate global hygroscopic and thermal mismatch effects, including composites panel warping and continuous interfacial shear, through redistributing differential strains into small, localized scales. To minimize manufacturing energy demand, cold hydraulic pressing was used to prepare the specimens with bio-epoxy and polyvinyl acetate adhesives (PVAs). The list of experimental tests includes compression parallel to the grain, compression perpendicular to the grain, and flexure. The experimental results revealed that the developed bamboo and bamboo–timber composites outperform the reference materials consisting of commercial engineered bamboo and natural softwood. In particular, the average modulus of elasticity of the hybrid specimens bonded with bio-epoxy adhesive reaches 11.6 GPa (CoV = 13.8%), which is 40 percent greater than that of the tested commercial engineered bamboo specimens (CoV = 15.7%), emphasizing a stiffer and more reliable engineered bamboo. In the case of flexural testing, the hybrid bamboo–timber specimens reach the highest modulus of elasticity, while the engineered bamboo bio-epoxy test series exhibited a modulus of rupture that was 36% higher than that of the commercial engineered bamboo material with a CoV equal to 8%. Full article

The development of indoor photovoltaic devices for powering Internet of Things (IoT) sensors requires low-cost and sustainable components, making dye-sensitized solar cells (DSSCs) an ideal candidate for artificial light harvesting. The counter electrode plays a critical role in transferring electrons and catalyzing the reduction in the redox electrolyte. However, the traditional use of expensive and scarce platinum (Pt) limits the cost-effective, large-scale commercialization of these devices. While carbon-based materials offer a highly porous, conductive, and abundant alternative, commercial carbon pastes frequently require energy-intensive high-temperature sintering. In this study, we propose a sustainable, low-temperature, and screen-printable carbon composite counter electrode (LoT-HPC) using bio-derived hydroxypropyl cellulose (HPC) as a highly effective binder. Rheological characterizations confirm that the formulated LoT-HPC ink possesses an ideal shear-thinning profile and rapid structural recovery, ensuring excellent printability and film homogeneity. By comparing the custom LoT-HPC composite against a commercial high-temperature screen-printed graphite paste (HT-Elco) and a standard sputtered Pt-FTO electrode, we demonstrate the structural and electrocatalytic advantages of this material. When integrated into full DSSC devices and evaluated under low indoor illumination (1000 lux), the LoT-HPC cell delivers a power conversion efficiency (PCE) of 14.8% and a high short-circuit current density of 103.9 µA cm⁻². Furthermore, the custom device demonstrated exceptional operational stability, retaining 98.6% of its initial efficiency (from 14.8% to 14.6%) after 200 h of continuous light-soaking and J-V cycling under 1000 lux. Ultimately, the successful implementation of the HPC binder enables the low-temperature fabrication of sustainable carbon counter electrodes without the need for energy-intensive thermal treatments, presenting a highly scalable pathway for indoor DSSC manufacturing. Full article

The growing demand for sustainable materials has renewed interest in replacing conventional petroleum-based wood adhesives with natural, environmentally friendly alternatives. This study evaluated the bonding performance of a conventional polyvinyl acetate (PVAc) adhesive and three natural adhesives—bone glue, fish glue and casein—for bonding European beech (Fagus sylvatica L.) wood of Greek origin. Bond quality was assessed according to ISO 6238:2018 by measuring shear strength and wood failure under ambient laboratory conditions (23 ± 2 °C) and after exposure to 50 °C for 15 days, simulating elevated temperatures that may occur in indoor environments. PVAc exhibited the most consistent bonding performance, whereas casein achieved shear strength comparable to that of PVAc, demonstrating its potential as a sustainable alternative for interior wood bonding. In contrast, bone glue and fish glue exhibited lower shear strength, greater variability in bond performance, and practical limitations associated with their shorter working and setting times. The percentage of wood failure generally followed the same trend as shear strength, confirming the relationship between bond quality and adhesive performance. Moderate thermal exposure did not significantly affect shear strength but resulted in lower wood failure percentages for the natural adhesives, whereas PVAc maintained, and slightly improved, its bond strength after thermal exposure. These findings demonstrate the promising performance of casein as a natural wood adhesive while highlighting the influence of moderate thermal exposure on the durability of natural adhesive systems intended for indoor applications. Full article

Pectin is a naturally occurring biopolymer extensively used for applications in the pharmaceutical, biotechnology, and food industries, and is abundantly present in lemon by-products. Although lemon peels represent a highly promising raw material, the structure of pectin is strongly influenced by extraction and drying processes, and the resulting attributes remain insufficiently understood. The present study systematically investigates the impact of conventional hot acid extraction using three different acidifying agents (citric, sulphuric, and hydrochloric) in combination with two drying techniques (oven-drying and freeze-drying) on the physicochemical, structural, thermal, and viscosity–shear rate properties of pectin obtained from lemon by-products (Citrus limon, Portuguese Eureka variety) following the prior recovery of bioactive compounds (essential oils and phenolic compounds). The results demonstrated that citric acid extraction followed by freeze-drying yielded the highest pectin recovery, at approximately 26.7%, highlighting the suitability of this approach for efficient by-product valorisation. Oven-dried pectins exhibited higher moisture contents (8.5–10%) and lower lightness values (L* = 57.02–65.67), indicating darker colouration compared to freeze-dried pectins (L* = 78.82–83.75). All extracted pectins presented a degree of esterification (DE ≥ 50%), classifying them as high-methoxyl pectins. The galacturonic acid (GalA) content ranged from 37.6 to 48.9% for oven-dried samples and increased to 44.1–58.6% for freeze-dried samples. Furthermore, pectin obtained from lemon by-products exhibited a well-defined structural organisation and enhanced thermal stability, especially for freeze-dried pectin samples, and suitable rheological properties, with no statistically significant variations observed between different acids or drying conditions, supporting its technological suitability for applications in the food, cosmetic, and pharmaceutical industries. Full article