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We study the motion of an elastic rigid rod which is radially free-falling towards a Schwarzschild black hole. This is accomplished by reducing the corresponding free-boundary partial differential equation problem to a sequence of ODEs, which we integrate numerically. Starting with a rod at rest, we show that it is possible to choose its initial compression profile so that its midpoint falls substantially faster, or slower, than a free-falling particle with the same initial conditions. This seems to be a purely kinematic effect, since on average there is no net transfer of elastic energy to mechanical energy. [ABSTRACT FROM AUTHOR]

Introduction: The throwing motion in the javelin throw applies high loads to the musculoskeletal system of the shoulder, both in the acceleration and deceleration phases. While the loads occurring during the acceleration phase and their relationship to kinematics and energy flow have been relatively well investigated, there is a lack of studies focusing the deceleration phase. Therefore, the aim of this study is to investigate how the throwing arm is brought to rest, which resultant joint torques are placed on the shoulder and how they are influenced by the kinematics of the acceleration phase. Methods: The throwing movement of 10 javelin throwers were recorded using a 12-infrared camera system recording at 300 Hz and 16 markers placed on the body. Joint kinematics, kinetics and energy flow were calculated between the touchdown of the rear leg and the timepoint of maximum internal rotation after release +0.1 s. Elastic net regularization regression was used to predict the joint loads in the deceleration phase using the kinematics and energy flow of the acceleration phase. Results: The results show that a significant amount of energy is transferred back to the proximal segments, while a smaller amount of energy is absorbed. Furthermore, relationships between the kinematics and the energy flow in the acceleration phase and the loads placed on the shoulder joint in the deceleration phase, based on the elastic net regularized regression, could be established. Discussion: The results indicate that the loads of the deceleration phase placed on the shoulder can be influenced by the kinematics of the acceleration phase. For example, an additional upper body forward tilt can help to increase the braking distance of the arm and thus contribute to a reduced joint load. Furthermore, the energy flow of the acceleration phase can be linked to joint stress. However, as previously demonstrated the generation of mechanical energy at the shoulder seems to have a negative effect on shoulder loading while the transfer can help optimize the stress. The results therefore show initial potential for optimizing movement, to reduce strain and improve injury prevention in the deceleration phase. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) offers a novel approach for converting high‐entropy mechanical energy into electrical energy, yet achieving high charge density remains critical. Optimizations using dielectrics with high specific capacitance have mitigated air breakdown, but charge loss within dielectrics persists as a limiting factor. Here, based on poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) (P(VDF‐TrFE‐CFE)) with high specific capacitance, (P(VDF‐TrFE‐CFE)) composites’ trap density and energy are engineered using high‐polarity interfaces from barium titanate (BTO) nanoparticles and dense chain segment stacking induced by electrostatic interaction with polyetherimide (PEI) to enhance charge retention capability. With modified high interfacial traps, an ultrahigh charge density of 9.23 mC m−2 is achieved in external charge excitation (ECE) TENG using 0.2 vol% PEI/P(VDF‐TrFE‐CFE) film, marking the highest charge density reported for single‐unit TENGs. This work provides novel material strategies for high‐performance TENGs, paving the way for their large‐scale practical applications. [ABSTRACT FROM AUTHOR]

Ionic diode‐based generators show great superiority in harvesting low‐frequency mechanical energy from human motions for various wearable applications. The major challenge is to improve their extremely limited output voltage for the miniaturization/simplicity of ionic diode‐based self‐powered devices as well as further improvement of mechanoelectric conversion performance. Herein, the construction of gradient polycation/polyanion heterojunction is demonstrated to vastly boost the output voltage, energy‐harvesting efficiency, and sensing performance of ionic diode. Besides an inherent potential at the polyanion/polycation heterojunction interface, the additional transmembrane potentials can be generated across gradient polyanion and polycation conductors of ionic diodes due to their gradient charge distribution. Consequently, the gradient ionic diode‐based generators produce much higher output voltage (306.53 mV) than previously reported homogeneous ones (4.1–135 mV). Meanwhile, the high output voltage imparts gradient ionic diode‐based generator with ultrahigh power density (50.16 µW cm−2 or 250.8 µW cm−3) and pressure‐perception sensitivity (43582 mV/MPa), which are dramatically increased by 162.76% and 128.71%, respectively, compare to those of homogeneous one. Impressively, the resulting diode‐based generators can generate ultralarge current density (≈0.52 mA cm−2) with ultralong discharge time (>400 s), thus enabling the continuous power generation under the low‐frequency pressure for various wearable and implantable applications. [ABSTRACT FROM AUTHOR]

A novel approach is proposed for combining phosphor materials with triboelectric nanogenerators (TENGs) for mechanical energy harvesting and illumination applications. For this purpose, strongly reddish‐orange‐emitting Ba0.5Sr0.5Nb2O6:0.25 mol Eu3+ (BSNb:0.25Eu) phosphor materials are synthesized. The photoluminescence properties of the synthesized BSNb:0.25Eu are analyzed. The synthesized BSNb:0.25Eu is utilized as a dielectric filler inside a polydimethylsiloxane polymeric film due to its high dielectric properties to improve the overall dielectric properties of the composite film (CF). TENG devices are fabricated using phosphor‐loaded CFs as the tribonegative layer, transparent polyvinyl alcohol as the tribopositive layer, and aluminum as the conductive electrode. All the TENGs operate in a contact‐separation mode, and the highest electrical output is attained by optimizing the phosphor filler concentration in the CF. The optimized TENG exhibits excellent stability in long‐term operational tests, under varying harsh ambient temperatures. Indium tin oxide sputtered on both triboelectric films as an electrode and combined with a transparent hard substrate to obtain a fully transparent TENG. A self‐illuminating TENG (SI‐TENG) is fabricated by integrating near‐ultraviolet light‐emitting diodes between two identical TENGs. The SI‐TENG can harvest the mechanical energy available in the surrounding environment and illuminate it as a light source. Additionally, the proposed phosphor‐loaded polymer films can be employed for optical thermometry and mechanical energy harvesting via SI‐TENG on a large scale. [ABSTRACT FROM AUTHOR]

A triboelectric nanogenerator (TENG) is an emerging energy harvesting technology that utilizes the combination of triboelectrification and electrostatic induction to collect wasted mechanical energy and convert it into electricity. In this work, an aluminosilicate (AS)-based composite, considered as a potential alternative to cement material, has been developed for the fabrication of TENGs. Herein, the AS material is synthesized through the alkali activation of fly ash using a mixture of sodium hydroxide (NaOH) and sodium silicate (Na 2 SiO 3) solutions as activating agents. The electrical output of AS TENGs can be optimized by tuning the liquid-to-solid powder (L/S) ratio during the fabrication of AS composites. The AS composites fabricated at different L/S ratios exhibit the variations in dielectric properties, surface morphology and microstructure. It is found that a high dielectric constant is not the only requirement for achieving optimal TENG output performance. The contribution of dielectric properties and microstructures of the AS composites on TENG performance is discussed. The AS composite with an optimal L/S ratio of 0.5 results in the highest TENG power output density of 2.78 W/m2. Additionally, the versatility of AS TENG to harvest mechanical energy and its application as a power source for portable electronic device are demonstrated. This research has proposed the promising aspect of AS composites as alternative construction materials capable of harvesting mechanical energy, which is essential for the development of green and sustainable power sources. [ABSTRACT FROM AUTHOR]

To investigate the dynamic mechanical behavior and energy dissipation characteristics of low-temperature rock samples under cyclic impact loading, a temperature-controlled impact system that combines Hopkins bars with a low-temperature compensation device was used. Five temperature gradients were confirmed via a trial impact test, and impact tests were conducted under two kinds of impact air pressures. The macroscopic damage characteristics of rock samples under cyclic impact at different temperatures, dynamic stress-strain curves, changes in peak stress and strain, energy dissipation, and cumulative damage at different temperatures, and the macroscopic and microscopic structural characteristics of low-temperature rock samples after cyclic impact were analyzed in combination with damage. The findings indicated that low-temperature saturated granite primarily experienced tensile damage under cyclic impact loading, with the required number of impacts increasing with decreasing temperature, and rock samples exhibited freeze-induced brittleness and significantly increased fragmentation. The dynamic stress-strain curve generally exhibited rebound characteristics in the post-peak stage. With an increasing number of cycles, an overall decrease in peak stress was observed, whereas the peak strain and cumulative specific dissipated energy exhibited opposite trends. This trend was more pronounced at lower temperatures, with a significant increase in peak strain and specific energy amplitude. In addition, the cumulative damage factor of the rock samples increased at lower temperatures, consistent with macroscopic damage characteristics, and exhibited a negative correlation with peak stress. The degree of crack extension in the macroscopic samples corresponded with the observed fracture changes. Microanalysis (SEM) indicated that decreasing temperature resulted in freeze brittleness of the fracture surfaces, characterized by reduced flatness and an expansion of brittle cracks across the damage surface. The slip separation phenomenon became increasingly pronounced, and these observations were positively correlated with the cumulative damage value. [ABSTRACT FROM AUTHOR]

Direct current (DC) motors are crucial in drones, robotics, and electrical devices. Conventionally, the DC motor is driven by a switching electricity converter, which utilizes electrical energy to drive mechanical motion. However, the rapid on-off switching actions in the switching electricity converter would cause electromagnetic interference (EMI), impairing the functionality of drive systems. Here, we propose a photon-driven DC motor system based on photonic converter, which utilizes optical energy to drive mechanical motion, and therefore avoids EMI derived from electrical switching and immunizes against EMI during electrical energy transmission in conventional switching electricity-driven DC motor system. The operation principle and power modulation-based speed control are also presented for the proposed photon-driven DC motor system. The experiments demonstrate that the motor accurately follows the speed reference and withstands load disturbances. This innovation opens new potential for DC motor applications by improving electromagnetic compatibility. The researchers showcase a photon-driven DC motor system, that utilizes optical energy to drive mechanical motion, avoids EMI derived from electrical switching action and immunizes against EMI in conventional electricity-driven DC motor systems [ABSTRACT FROM AUTHOR]

Organometal halide perovskite (OHP) composites are flexible and easy to synthesize, making them ideal for ambient mechanical energy harvesting. Yet, the output current density from the piezoelectric nanogenerators (PENGs) remains orders of magnitude lower than their ceramic counterparts. In prior composites, high permittivity nanoparticles enhance the dielectric constant (ϵr) but reduce the dielectric strength (Eb). This guides our design: increase the dielectric constant by the high ϵr nanoparticle while enhancing the Eb by optimizing the perovskite structure. Therefore, we chemically functionalize the nanoparticles to suppress their electrically triggered ion migration for an improved piezoelectric response. The polystyrene functionalizes with FAPbBr2I enlarges the grains, homogenizes the halide ions, and maintains their structural integrity inside a polymer. Consequently, the PENG produces a current density of 2.6 µAcm−2N−1. The intercalated electrodes boost the current density to 25 µAcm−2N−1, an order of magnitude enhancement for OHP composites, and higher than ceramic composites. By functionalizing polystyrene with perovskite FAPbBr2I, both the dielectric constant and dielectric strength are controlled, leading to energy-dense composite films for piezoelectric nanogenerators with normalized current density of 25 µA.cm−2 N−1 [ABSTRACT FROM AUTHOR]

Piezoelectric nanostructures have attracted significant attention owing to their capacity for converting mechanical energy into electrical energy, enabling applications in biomedical fields, actuators, and energy harvesting devices. Boron nitride nanotubes (BNNTs) exhibit unique properties that make them attractive candidates for piezoelectric applications. However, the influence of BNNT chiralities on their piezoelectric behavior has not been thoroughly explored. In this study, we investigated the piezoelectric effect of zigzag and armchair chiralities of BNNT structures, aiming to elucidate the relationship between chirality and piezoelectric response by discovering a novel protocol for simulating the electrical behavior of BNNTs at the nanoscale level. We employed a computational method to examine the piezoelectric potential of BNNT structures. First, we established an equivalent-sized three-dimensional (3D) model of zigzag and armchair BNNT structures using nanotube modeler software. The obtained models were then subjected to mesh analysis to generate finite element method simulations. The simulations were finally performed to analyze the electrical response of the BNNT structures under external mechanical forces. We observed that the electrical responses of zigzag BNNT were 1.6 times greater than armchair one. In conclusion, our study sheds light on the piezoelectric potential of zigzag and armchair chiralities of BNNT structures. Furthermore, our findings contribute to the understanding of the electrical properties of BNNTs and their potential for various medical and industrial applications. The knowledge gained from this study provides a foundation for further research and development in the field of piezoelectric nanostructures, paving the way for innovative advancements in nanotechnology. [ABSTRACT FROM AUTHOR]

Aim: A 15-s all-out sprint cycle test (i.e., νLamax-test) and the post-exercise change in capillary blood lactate concentration is an emerging diagnostic tool that is used to quantify the maximal glycolytic rate. The goal of this study was to determine the relation between 15 s-work, change in capillary blood lactate concentration (∆La) and body composition in a νLamax-test. Method: Fifty cyclists performed a 15 s all-out sprint test on a Cyclus2 ergometer twice after a previous familiarization trial. Capillary blood was sampled before and every minute (for 8 min) after the sprint to determine ∆La. Body composition was determined employing InBody720 eight-electrode impedance analysis. Result: Simple regression models of fat-free mass (FFM) and also the product of FFM and ∆La showed similar ability to predict 15 s-work (R2 = 0.79; 0.82). Multiple regression combining both predictors explains 93% of variance between individuals. No differences between males and females were found regarding 15 s-work relative to the product of fat-free mass and ∆La. Considering pairs of similar FFM, a change 1 mmol/l of ∆La is estimated to be equal to 12 J/kg in 15 s-work (R2 = 0.85). Discussion: Fifteen s-work is both closely related to FFM and also the product of ∆La and lactate-distribution space approximated by FFM. Differences in 15 s-work between males and females disappear when total lactate production is considered. Considering interindividual differences, the mechanical energy equivalent of blood lactate accumulation seems a robust parameter displaying a clear relationship between ∆La and 15 s-work relative to FFM. [ABSTRACT FROM AUTHOR]

[Display omitted] • The catalytic mechanism and material preparation based on the piezoelectric effect. • The application of the piezoelectric effect in wastewater purification is expounded. • The development of the piezoelectric effect-assisted water purification technology. • The challenges and prospects of the piezoelectric effect in wastewater purification. The demands of human life and industrial activities result in a significant influx of toxic contaminants into aquatic ecosystems. In particular, organic pollutants such as antibiotics and dye molecules, bacteria, and heavy metal ions are represented, posing a severe risk to the health and continued existence of living organisms. The method of removing pollutants from water bodies by utilizing the principle of the piezoelectric effect in combination with chemical catalytic processes is superior to other wastewater purification technologies because it can collect water energy, mechanical energy, etc. to achieve cleanliness and high removal efficiency. Herein, we briefly introduced the piezoelectric mechanisms and then reviewed the latest advances in the design and synthesis of piezoelectric materials, followed by a summary of applications based on the principle of piezoelectric effect to degrade pollutants in water for wastewater purification. Moreover, water purification technologies incorporating the piezoelectric effect, including piezoelectric effect-assisted membrane filtration, activation of persulfate, and battery electrocatalysis are elaborated. Finally, future challenges and research directions for the piezoelectric effect are proposed. [ABSTRACT FROM AUTHOR]

Recently, significant interest has been shown in using ferroelectric or piezoelectric energy harvesting to collect mechanical energy from the surrounding atmosphere to power next-generation wearable electronic sensors and devices. Due to their pyroelectric and piezoelectric capabilities and high permittivity for energy storage, ferroelectrics are a significant class of electroactive materials. As a result of its low price and high usability, piezoelectric energy harvesters have seen rapid development over the last decade. When used as part of a larger energy harvesting strategy, ferroelectric/ferroelastic switching may significantly boost energy density. Hence, this study suggests the Stable Diffusion Model-based Composite Layered Ferroelectric Ceramic Materials (SDM-CLFCM) for effective energy harvesting under the background of Meta-Universe. The highest output current and peak power density shown by the composite layered porous piezoelectric composite energy harvester are much greater than those reported for existing porous piezoelectric materials. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) technology based on the coupling of triboelectric effect and electrostatic induction has shown great potential in the energy‐integration field. In recent years, the emerging of textile triboelectric nanogenerators (t‐TENGs) has enabled the rapid development of wearable energy‐integration technologies. The efficient mechanical energy harvesting and self‐powered sensing capabilities of TENGs and the advantages of textiles can be combined to create t‐TENGs for the construction of smart fabrics. Herein, a comprehensive review of t‐TENGs is presented. This review begins from the working mechanism of conventional TENGs, after which the construction of triboelectric layers with fibers, yarns, and fabrics is discussed. Then, the different working modes of t‐TENGs derived from TENGs, the critical features of t‐TENGs and power management strategies are discussed. Finally, this review ends with a description of the recent progress in typical wearable applications based on t‐TENGs. The light weight, low cost, flexibility, stretchability, washability, diverse material options, and excellent electrical performance of t‐TENGs will make this technology a great choice for smart energy‐integrated wearable devices in the future. [ABSTRACT FROM AUTHOR]

By producing micro-textures with different geometric parameters on the tool surface, the cutting performance of the tool can be effectively improved. Scientists have carried out the design and development of microstructures on the surface of tools based on the study of the performance of microstructured tools. Based on this, this theory first summarizes the production methods of surface microstructures, which are divided into photothermal energy composite processing, electrothermal energy composite processing, and mechanical energy processing according to the different energies. The effects of microtexturing on tool wear, tool strength, and tool life are then examined. Then, the geometric design of surface microtexturing tools from simple texturing to heterogeneous texturing is reviewed, and the mechanism of microtexturing tools is analyzed. Finally, the development direction of tools with surface micro-texture is given to provide guidance for the optimized design of the micro-texture of tool surfaces. [ABSTRACT FROM AUTHOR]

In the present study, a series of lattice structures with Gyroid minimal surfaces were meticulously designed to incorporate linear density gradients and two distinct trigonometric function-based density gradients. These advanced architectures were subsequently compared and contrasted with a uniform lattice sandwich structure. The mechanical behavior and energy absorption characteristics of the four lattice sandwich structures were rigorously investigated through a combination of experimental testing and finite element analysis (FEA). The results of this comprehensive analysis revealed that during compression, all four gradient lattice structures exhibited varying degrees of shear slip, which manifested as discernible discrepancies in their respective stress–strain curves. Relative to the uniform lattice structure, the linear gradient lattice sandwich structure exhibited an enhancement in elastic modulus by 1.69%, while the square sine function gradient lattice sandwich structure showed a significant increase of 14.45% in elastic modulus. Conversely, the square cosine function gradient lattice sandwich structure experienced a reduction in elastic modulus by 9.61%. Employing either a linear gradient or a square sine function density gradient design was found to augment the load-bearing capacity of the uniform lattice structure. Notably, when the strain in the uniform structure reached densification strain, it absorbed energy exceeding 5.842 MJ/m3, indicating superior energy absorption capabilities among the four structures examined, thus rendering it particularly suitable for applications where high energy absorption is imperative. Furthermore, finite element simulations were conducted to validate the experimental findings, and the simulation results demonstrated a high degree of correlation with the experimental data, with discrepancies less than 6%, thereby confirming the reliability of the FEA model in predicting the performance of these intricate lattice structures. [ABSTRACT FROM AUTHOR]

Rock fragmentation efficiency can be increased by microwave heating. The mechanical properties and energy evolution characteristics of coarse sandstone specimens under different microwave heating conditions are compared in this paper. The effects of microwave heating time and power on coarse sandstone specimens of peak stress, elastic modulus, brittleness index, damage variable, and impact energy index are analyzed. The results indicate that the microwave heating power and microwave heating time are inversely proportional to peak stress and elastic modulus and directly proportional to peak strain. With the increase of microwave heating power and microwave heating time, the brittleness index and damage variable of rock specimens increase, the impact energy index decreases. The microwave heating power and microwave heating time increase the rock brittleness index. The energy absorption rate of rock specimens decreases with the increase of microwave heating time. The impact energy index is inversely proportional to microwave heating power and microwave heating time. High-power and long-time microwave heating can reduce the possibility of rockbursts and the intensity of potential dynamic disasters. The research conclusion can provide the theoretical and technical basis for breaking rock by microwave heating. [ABSTRACT FROM AUTHOR]

The established research hotspots of shales, which play a significant roles in the stability of slopes, mainly focuses on its bedding plane effect under conventional stress paths, although landslides frequently suffer from complex stress disturbances. This study aims to investigate the effects of cyclic loading paths and interbed structure on the mechanical properties and energy evolution characteristics of shale. In the experiments, shale specimens with five types bedded angles (0°, 30°, 45°, 60°, and 90°) were prepared, and multilevel constant-amplitude cyclic loading (stress path Ⅰ) and multilevel increasing-amplitude cyclic loading (stress path Ⅱ) were performed. The results indicated that the mechanical behaviors including strength, deformation and failure modes, energy dissipation, and internal damping of shale samples were all highly affected by the bedding plane angles and the cyclic loading paths. Specifically, with the increasing of bedding angle, the peak strength, total dissipated energy, and total input energy of the shale specimens showed a "U" trend, the ultimate macro-failure mode changed from mixed tension-shear failure to failure along the bedding planes, and the damping ratio firstly increased and then decreased. In addition, test schemes of stepwise increase of the lower stress limit or keeping it constant were the differences between stress path Ⅰ and stress path Ⅱ, which significantly influenced the evolution of irreversible deformation of shale specimens. Peak strength of shale samples under stress path Ⅰ ranged from 4.3% to 23.9% lower than under stress path Ⅱ. Compared with stress path Ⅱ, elastic modulus and damping ratios of shales had the greater variations, under stress path Ⅰ, and dissipated energy and elastic strain energy were relatively low by an order of magnitude. [ABSTRACT FROM AUTHOR]

Light‐responsive shape‐changing polymers are photonastic materials: they can convert light into mechanical energy through macroscopic transformations. Indeed, photochromic molecules embedded in these polymer films present light‐induced structural modifications that can trigger a significant macroscopic deformation. In this theoretical study based on molecular dynamics simulations, analysis tools ranging from atomic to supramolecular scales are developed to investigate this photonastic phenomenon. To this purpose, a model system built upon an azobenzene photochrome embedded in different environments (tetrahydrofuran, cis‐1,4‐polybutadiene and hydroxyl‐terminated polybutadiene) is considered. First, the impact of the environment on the photochrome properties is discussed through the analysis of the structural properties, ultra‐violet visible (UV–vis) absorption spectra and dynamical properties of the photoswitch. Then, the impact of the presence of the photochrome on the polymer is studied. At the atomic scale, the radial distribution functions show some differences between the cis and trans isomers due to geometrical effects. At the molecular scale, the analysis of the size and shape of the polymer chains reveals that the photochrome has no impact on the chain properties. Finally, at the macroscopic scale, the cohesive energy density shows that the polymer is stabilized by the presence of photochrome molecules. [ABSTRACT FROM AUTHOR]

Emulsification is a feared and common complication of the use of silicone oil (SO) as tamponade fluid after vitrectomy as it potentially associated with significant risks to ocular health, including elevated intraocular pressure (IOP), glaucoma, corneal and retinal changes. The aim of this study was to investigate the role and interplay of physical factors on the formation of SO emulsion. Experiments were performed in a model of the vitreous chamber with a realistic shape, filled with SO and an aqueous solution containing different concentrations of albumin, an endogenous protein known to modify the interfacial properties between SO and aqueous solutions. The model was subjected to harmonic and saccadic rotations and kept at body temperature. Results indicated that no emulsions were detected in the absence of albumin in the aqueous solution, while the presence of the protein facilitated emulsion formation, acting as a surfactant. Mechanical energy from eye movements was also found to be a key mechanism to produce emulsification, with higher mechanical energy provided to the system leading to smaller droplet sizes. The emulsions formed were stable over extended times. This study highlights the complex interplay of factors influencing SO emulsification in the vitreous chamber. A better understanding of the mechanisms underlying SO emulsification is crucial for developing strategies to mitigate SO emulsion and the related complications. [ABSTRACT FROM AUTHOR]

In response to the frequent occurrence of impact events in isolated coal pillars between the upper (lower) mountain areas of mining areas under conditions without obvious mining disturbance, this study takes multiple isolated coal pillar impact events that occurred in Zhaolou Coal Mine and Gengcun Coal Mine as examples. It conducts a mechanism study on the creep-induced impact ground pressure of isolated coal pillars considering the time effect. The occurrence of such impact ground pressure accidents often exhibits significant "lag" and "spontaneity". Due to the unclear mechanism of occurrence and the difficulty in grasping the unloading timing, this type of impact ground pressure has become a typical hidden disaster, posing a serious threat to the deep mining of coal mines. Based on the analysis of the creep mechanical properties of coal and rock mass, the uniaxial compression acoustic emission creep test of coal body, and the FLAC3D numerical simulation, a creep instability impact mechanical model of coal and rock mass is established. This model reveals the mechanism of creep instability impact and the stress evolution law of coal and rock mass during creep. The mechanical and energy criteria for the occurrence of impact ground pressure in isolated coal pillars under the action of unstable creep are proposed. The study shows that the action of high ground stress is a necessary condition for the occurrence of "lag-type" impact ground pressure in isolated coal pillars. Long-term unstable creep will weaken the support strength of the entry. When the elastic energy accumulated in the isolated coal pillar exceeds its ultimate bearing capacity, impact instability will occur. Based on the mechanism of occurrence of such impact accidents, targeted deep hole blasting unloading measures are proposed, providing a good reference value for the prevention and control of "lag-type" impact ground pressure accidents in isolated coal pillars. [ABSTRACT FROM AUTHOR]

Summary: The aim of the present study was to texturise protein from sunflower press cake (SPC) for being consumed as dry snack or, in its hydrated state, as a meat analogue. In preliminary experiments, feed moisture (15–25 g 100 g−1) and extrusion temperature (180 °C–200 °C) were varied when processing commercial sunflower protein flour with a protein content of 51.8 g per 100 g dry matter using low moisture single‐screw extrusion. The extrudates were analysed with regard to specific mechanical energy needs, texture properties in dry and hydrated state, colour, expansion ratio and water binding capacity. Extrusion parameters for achieving maximum expansion, textural force and minimal product moisture were found to be 180 °C and 15 g 100 g−1. Consequently, texturised protein was derived from deoiled SPC using these extrusion parameters. Initial deoiling of the press cake was necessary as it improved texturisation; a higher SME input reached led to increased cross‐linking of the protein matrix. The light coloured and significantly expanded extrudates with high water binding capacity and could serve as basis for further development of snack products or meat analogues. [ABSTRACT FROM AUTHOR]

This study investigates lignocellulosic biocomposites' physicochemical properties and strength parameters with varying thermoplastic content. Biocomposites were prepared using wood (Pinus sylvestris) or hemp shives (Cannabis sativa L.) combined with 25% and 50% ABS regranulate. The research focused on evaluating the mechanical energy consumption during the compaction of wood-ABS biocomposites with different pine fractions pretreated with hot water extraction (HWE) and analyzing the relationship between strength and thermoplastic content. Results indicate that the composition of the mixture and the size of the hemp shives fraction did not significantly influence energy consumption during densification. Energy values ranged from 1.234 × 10⁻8 J to 8.296 × 10⁻8 J. While the densification of pine after HWE was unsuccessful without ABS, preheating the mixtures with ABS facilitated the production of a uniform composite. The work required for densification ranged from 1.404 × 10⁻5 J to 2.711 × 10⁻5 J for fractions without ABS. For mixtures with ABS, the work required was 1.954 × 10⁻5 J for fraction 0 ÷ 0.4 (f1) and 0.042 × 10⁻5 J for fraction 0.4 ÷ 0.8. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) made from biocompatible materials serve as promising integrated power sources for portable wearable electronics due to many advantages such as lightweight, high flexibility, simple technique, and excellent breathability. In this work, we report the fabrication of electrospun polycaprolactone micro-nanofiber films (s-PCL) and convex-microdome-patterned polydimethylsiloxane (c-PDMS) utilizing electrospinning and micromolding techniques. These materials, s-PCL and c-PDMS, are utilized as positively and negatively charged tribosurfaces, respectively, in the development of a bioTENG device. The developed TENG device can generate a superior power output of 2 mW with an open-circuit voltage (VOC) of 188 V and short-circuit current (ISC) of 18.5 µA, even under a low triggering frequency of 5 Hz. In addition, TENG possesses outstanding durability and output performance stability over a continuous operation of nearly 16,000 cycles. Furthermore, the TENG demonstrates its capacity to harvest mechanical energy and convert it into electricity, capable of directly illuminating more than 100 LEDs. The electrospun s-PCL- and c-PDMS-based TENG can be considered for self-powdered wearable devices attached to fingers, wrists, feet, and other human body parts. [ABSTRACT FROM AUTHOR]

Extensive research has focused on green and renewable energies to address the increasing demand for flexible, reliable, and self-sustaining advanced technology and electrical supplies. Piezoelectric nanogenerators (PENGs) have garnered significant interest as a pioneering energy-harvesting technology, due to their notable advancements and capacity to effectively capture and convert mechanical energy from the environment into electrical power. This review article seeks to cover the latest developments and innovations in piezoelectric materials for PENG applications. It explores key topics, such as the strategic selection of piezoelectric materials to optimize energy-harvesting efficiency, advancements in fabrication techniques, and the evaluation of PENGs performance. Throughout this manuscript, critical points are highlighted that require further investigation in the field of high-performance piezoelectric material fabrication. Ongoing research is crucial for improving the flexibility and durability of functional materials, thus advancing the development of superior electronic devices with enhanced piezoelectric properties. Furthermore, addressing enhancements in the electromechanical properties of current piezoelectric materials is imperative. This review article aims to support researchers in their quest for a comprehensive understanding of piezoelectric mechanisms and offers valuable insights for the progression and refinement of PENGs, which have broad potential applications. An overview of the PENGs applications, piezoelectric materials selection, fabrication methods and PENGs performance discussed in this review paper. [ABSTRACT FROM AUTHOR]

Mathematics is considered the language of physics. Starting from idealizations and kinematics, geometric-mathematical physics with paradigms such as flexible spacetime and dark energy has emerged whose physical reality has not been clarified. By analyzing processes regarding their causes and the functional dependencies of energies, this work identifies shortcomings in the basic energy concepts of physics, which cannot be remedied with mathematics. While formal transformations of process equations such as integration are mathematically correct, they do conceal vital physical information, suggesting that mathematics should be used with caution. We propose a physically justified approach that reconciles the mechanical and thermodynamic energy concepts and provides a revised interpretation of E = mc2. Our results suggest that geometric approaches were built too early on a shaky physical foundation, leading to undesirable developments in recent centuries. The language of physics should be physics, not just mathematics. [ABSTRACT FROM AUTHOR]

With the advancement of intelligent wearable sports monitoring devices, self-powered, flexible, and lightweight sensors have garnered significant attention. In this study, we propose a flat-structured triboelectric nanogenerator (PM-TENG) with multiple voids based on a PDMS/MXene film. The triboelectric layers consist of a PDMS/MXene film and a nylon film. When subjected to boxing impacts, the PM-TENG (size: 2 × 2 cm2) demonstrates remarkable performance, generating higher output. Our results show that the maximum open-circuit voltage (Voc) and short-circuit current density (Isc) of the PM-TENG reach 278 V and 8.46 µA/cm2, respectively. Additionally, when connected to a 40 MΩ load, the maximum output power of the PM-TENG can reach 4.44 mW/cm2. The PM-TENG effectively monitors various fundamental boxing techniques, including jabs, straight punches, and hook punches, thereby offering new opportunities for the development of smart sports technologies. This research underscores the potential of TENG applications in intelligent sports equipment, paving the way for future innovations in the field. [ABSTRACT FROM AUTHOR]

Over the past few decades, wind energy has expanded to become a widespread, clean, and sustainable energy source. However, integrating offshore wind energy with the onshore AC grids presents many stability and control challenges that hinder the reliability and resilience of AC grids, particularly during faults. To address this issue, current grid codes require offshore wind farms (OWFs) to remain connected during and after faults. This requirement is challenging because, depending on the fault location and power flow direction, DC link over- or under-voltage can occur, potentially leading to the shutdown of converter stations. Therefore, this necessitates the proper understanding of key technical concepts associated with the integration of OWFs. To help fill the gap, this article performs an in-depth investigation of existing alternating current fault ride through (ACFRT) techniques of modular multilevel converter-based high-voltage direct current (MMC-HVDC) for OWFs. These techniques include the use of AC/DC choppers, flywheel energy storage devices (FESDs), power reduction strategies for OWFs, and energy optimization of the MMC. This article covers both scenarios of onshore and offshore AC faults. Given the importance of wind turbines (WTs) in transforming wind energy into mechanical energy, this article also presents an overview of four WT topologies. In addition, this article explores the advanced converter topologies employed in HVDC systems to transform three-phase AC voltages to DC voltages and vice versa at each terminal of the DC link. Finally, this article explores the key stability and control concepts, such as small signal stability and large disturbance stability, followed by future research trends in the development of converter topologies for HVDC transmission such as hybrid HVDC systems, which combine current source converters (CSCs) and voltage source converters (VSCs) and diode rectifier-based HVDC (DR-HVDC) systems. [ABSTRACT FROM AUTHOR]

The mechanical energy balance over a bulk of fluid that oscillates between prolate and oblate shapes in another immiscible fluid is solved using a general spheroidal coordinate system. The drop shape is described by a unique parameter that may continuously vary over the time, making the implementation of the model rather simple. Potential flow is assumed, and inertial and viscous effects are accounted for in both the inner and outer flow fields. The characteristics of drop oscillation for small and large amplitudes are studied, and the results are compared with theoretical, experimental, and numerical data from the open literature. The rather satisfactory validation of the model over a large variety of operating conditions allows its extension to include other physical phenomenon, like evaporation and its effect on drop oscillation. [ABSTRACT FROM AUTHOR]

Buoyancy-driven ventilation is a zero-energy measure for removing residual heat and gaseous contaminant from building interior space, and buoyancy-driven natural smoke venting is prevalent in smoke control for guaranteeing human evacuation. This paper establishes a mechanical energy conservation equation, describing the non-isothermal fluid delivery and the associated mechanical energy transport along with natural convection. A field synergy principle regarding buoyancy and velocity fields is proposed based on the conservation equation. The multi-field synergetic relations among pressure gradient, velocity, and buoyancy are derived. The mechanical energy input resulted from the work done by thermal buoyancy in the buoyancy-driven non-isothermal flow is correlated with both Ra and the field synergy degree between buoyancy and velocity, which is characterized by a field synergy number, F s U , g . The proposed new field synergy principle has been verified with natural convection occurred in vertical channels bounded with parallel plates, and it is applied in typical buoyancy-driven ventilation or smoke venting scenarios. The buoyancy-driven ventilation or smoke venting capability can be enhanced through improving the degree of synergy between buoyancy and velocity in the flow domain, even though the indoor air or smoke temperature is decreased. This principle helps to further understand the physical essence and role of thermal force in buoyancy-driven ventilation and smoke flows, and it provides a new route for enhancing natural ventilation and smoke control effectiveness in buildings. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms behind the cavitation erosion resistance of elastic materials is the basis for the development of new cavitation erosion resistance materials. This paper employs underwater low-voltage discharge to induce cavitation bubble, combined with high-speed photography, shadowgraph methods, and transient pressure measurement systems to experimentally investigate the evolution and intensity of shockwave from bubble collapse near elastic-rigid composite boundary. Under the condition of constant elastic material thickness, with the bubble–wall distance increasing, shockwave shape evolves from multi-layers to single-layer. The peak pressure of the shockwave shows a trend of decreasing, then increasing, and finally stabilizing with increase in the bubble–wall distance. Furthermore, it was found that the elastic-rigid composite boundary causes the shockwave to reflect twice. As the material thickness increases, the intensity of the first reflected shockwave from the elastic surface decreases initially, then increases, and eventually stabilizes. However, that of the second reflected shockwave decreases. The total energy of the two reflections at the elastic interface is less than 4% of the mechanical energy of the bubble at its maximum volume. Finally, after the energy dissipation by the two reflections and material deformation, the elastic layer substrate withstands over 70% of the total mechanical energy of the cavitation bubble. There is an optimal elastic material thickness to minimize the shockwave load on the elastic layer substrate under the condition that the elastic-rigid composite boundary does not affect the evolution of cavitation bubble shape. These findings are significant for understanding bubble dynamics near elastic-rigid composite boundaries and provide theoretical support for developing cavitation erosion-resistant materials in engineering. [ABSTRACT FROM AUTHOR]

This study experimentally investigates the effects of viscoelastic dilute aqueous polyethylene oxide solutions on the water entry of spheres. The solutions are modified to manipulate viscoelastic properties which influence cavity dynamics and the behavior of the Worthington jet. The effects of viscoelasticity and impact velocity are quantified using dimensionless numbers, including the Deborah number (De), the Reynolds number (Re), and the Froude number (Fr). Three distinct cavity patterns are identified, and transitions between these patterns occur as De and Re change. As Re increases, the cavity patterns emerge sequentially in a specific order, with the critical transition points between patterns dependent on De. The combined influence of De and Fr determines the dimensionless pinch-off time and depth of the deep seal cavity. Higher De or Fr values result in increased dimensionless pinch-off time and depth. Furthermore, energy analysis of the Worthington jet reveals that kinetic energy transforms into potential, surface tension, and elastic energy, with the Deborah number (De) influencing this conversion. In viscoelastic solutions, unlike in filtered water, elastic energy constitutes a significant portion of the total mechanical energy, leading to a much more complex energy conversion process. [ABSTRACT FROM AUTHOR]

Modern medicine heavily relies on drug delivery systems to ensure targeted and effective administration of therapeutic agents. One such promising innovation is the development of self-propelled particles, inspired by motile cells like bacteria, for drug delivery purposes. These nano- and micro-motors have shown great potential in enhancing drug delivery effectiveness. Active fluids, containing self-propelled agents, have been shown to significantly improve transport properties by converting environmental or external energy into mechanical energy. Due to the aerotaxis and chemotaxis properties of bacteria, they are particularly useful in targeted drug delivery. In the present study, the impact of the band formation phenomenon on the probability of finding a particle with a specific orientation at a given time was investigated. This was achieved by coupling the equations describing bacterial density, Fokker–Planck, and Navier–Stokes. Furthermore, the comparison of drug distribution and penetration depth in porous tissue for bacterial suspensions containing pusher and puller bacteria was conducted by solving the mass transfer equation. The findings revealed that the presence of bacteria increases the penetration depth by a factor of 1.7 for the suspension containing puller bacteria, and 1.4 for the suspension containing pusher bacteria. The drug distribution in suspensions containing puller particles is more efficient due to the favorable flow direction. This study potentially has significant implications for targeted drug delivery and improving drug efficacy in porous tissues. The use of coupled complex equations provides a comprehensive approach to modeling the behavior of bacterial suspensions and their impact on drug distribution. [ABSTRACT FROM AUTHOR]

A triboelectric nanogenerator (TENG) working on a contact electrification and electrostatic induction principle is a promising energy source for fulfilling the energy demand of low power electronic devices by converting the ambient mechanical energy to useful electrical energy. Here, a polymer nanocomposite film-based triboelectric nanogenerator has been designed by embedding reduced graphene oxide (rGO) nanosheets in a polyvinylidene fluoride (PVDF) matrix as one of the friction layers. The PVDF nanocomposite film-based TENG was constructed and examined for structural, electrical, and surface properties with varied weight percentages of rGO nanofillers (0.0 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, and 2.0 wt%). The experimental results demonstrate that the addition of rGO in a PVDF matrix considerably increased the output performance of the TENG device. The TENG device with 1.5 wt% of rGO can deliver the maximum output voltage and current of 95.9 V, and 16.8 μA, respectively, which are ~ 3 and ~ 7 times the voltage and current produced by pristine PVDF film-based TENG. The enhanced performance of the nanogenerator is attributed to the addition of conductive nanofillers in the polymer matrix which improves the surface charge density of polymer nanocomposite films by forming a conduction network, resulting in more effective charge transfer. Moreover, the output of the nanogenerator is stored in the capacitor and used to drive commercial LEDs, revealing the TENGs' potential applications for designing self-powered electronic devices. [ABSTRACT FROM AUTHOR]

The ocean harbors an abundance of resources, encompassing not only wave energy but also considerable wind energy. Triboelectric nanogenerator (TENG), as a technology for harvesting low‐frequency, high‐entropy mechanical energy, has shown distinct advantages in the collection and application of marine and wind energy. This study introduces a triboelectric Wind and wave energy harvester (TWWEH), an energy collector based on TENG, which can be used to harness wind and wave energy. The TWWEHs comprise a wind‐driven TENG (W‐TENG) for wind energy collection and a ring‐shaped TENG (R‐TENG) for wave energy collection. The proposed vertically integrated TENG architecture enhances spatial utilization rate. Under oscillatory conditions of 0.8 Hz and ±30°, the R‐TENG generates a peak power of 0.20 mW. While at a wind speed of 10 m s−1, a peak power of the W‐TENG can reach 0.11 mW. This research provides a promising solution to harvest wave and wind energy from the ocean, offering significant potential applications in establishing self‐powered oceanic assessment and meteorological systems. [ABSTRACT FROM AUTHOR]

The development of high-performance composites for mechanical energy dissipation during impact or explosive events is of vital importance for the safety of personnel and infrastructures. Solid–liquid composites are an emerging class of energy absorbers where a liquid-phase filler is seamlessly integrated into a solid matrix to enhance the impact resistance of the protection target. This innovative approach leverages the distinct properties of both phases and the unique interactions between them to achieve superior performance under high-impact conditions. This paper aims to review the liquid-phase materials used in solid–liquid composites, ranging from neat liquids to complex fluids, including liquid nanofoam and shear-thickening fluids, to provide an in-depth analysis of the fundamental physics underpinning the resulting solid–liquid composites, and to explore how their unique properties contribute to enhanced impact resistance and energy absorption. Furthermore, this paper evaluates the advantages and limitations of these solid–liquid composites and offers insights into future directions for the development of solid–liquid composites in various fields, including personal protective equipment, automotive safety systems, and structural protection. [ABSTRACT FROM AUTHOR]

Due to excavation disturbances and the coupled hydro-mechanical effects, deep rock masses experience nonlinear large deformations in the surrounding rock, necessitating an urgent exploration of the rock damage and failure mechanisms from the perspectives of hydro-mechanical coupling and mechanical properties. Therefore, this study conducted uniaxial cyclic loading-unloading tests on sandstone samples with different water contents (0%, 0.26%, 0.52%, 0.78%, and 1.04%) to investigate the microstructural evolution, energy evolution laws, and failure characteristics under varying water contents and cyclic loading conditions. The main conclusions are as follows:(1) Concerning micro-pore structures, as the water content increases, the porosity and maximum pore size of the sandstone first decrease and then increase. At 0% water content, the porosity is 4.82% and the maximum pore size is 31.94 µm. At 0.26% water content, both porosity and maximum pore size decrease to 3.03% and 16.15 µm, respectively. When the water content reaches 1.04%, the porosity and maximum pore size increase to 14.34% and 45.99 µm, respectively. (2) Regarding energy evolution laws, the energy evolution of the specimens during cyclic loading-unloading mainly converts to elastic energy, showing a step-wise increase in energy. Further analysis reveals that the water content has a significant impact on the dissipation energy coefficient of the sandstone. At lower stress levels (<0.4σmax), the water content has a negligible effect, while at higher stress levels (>0.85σmax), an increase in water content leads to increased fluctuations in the dissipation energy coefficient. (3) In terms of failure characteristics, with increasing water content, the failure mode of the specimens shifts from primary crack failure to microcrack failure, corresponding to the energy evolution during cyclic loading-unloading processes. [ABSTRACT FROM AUTHOR]

To investigate the mechanical and energy dissipation characteristics of gray sandstone at critical failure, dynamic impact compression tests were conducted under different axial pressure and confining pressure levels. The critical energy dissipation density of gray sandstone under different dynamic-static combination loading conditions was determined, and an empirical model for predicting the critical energy dissipation density was established. The conclusions of the current research are: (1) the dynamic peak stress increases and then decreases with increasing axial pressure and increases with increasing confining pressure. The axial pressure turning points of dynamic peak stress from strong to poor under 4 MPa, 8 MPa, and 12 MPa confining pressure conditions were 22.54 MPa, 22.05 MPa, and 23.64 MPa, respectively. (2) The second type of cut line modulus increases and then decreases with the increase of axial pressure, showing a quadratic law of change. (3) When there is no axial pressure, the critical energy dissipation density increases and then decreases with the increase of confining pressure, showing an exponential function change rule. Under the condition of axial pressure, the critical energy dissipation density increases with the increase of confining pressure, showing the change rule of logarithmic function, and increases with the increase of axial pressure and then decreases, showing the change rule of quadratic function. (4) Under the conditions of confining pressure of 4 MPa, 8 MPa, 12 MPa, and axial pressure of 25.00 MPa, 28.33 MPa, and 20.00 MPa, the critical dissipation densities reached the maximum values of 7.01 J cm−3, 7.38 J cm−3, and 8.40 J cm−3, respectively. The empirical model can better predict the critical absorbed energy density of gray sandstone under different dynamic and static combinations loading conditions. [ABSTRACT FROM AUTHOR]

This study emphasized the need for postharvest technology in Nigeria's vegetable production to reduce postharvest losses ranging from 5% to 50%, focusing on enhancing processes of automated packaging unit of vegetable processing plant through the use of artificial neural networks (ANN). The experiment was conducted on a vegetable leaf processing plant with the objective of improving the reliability and performance of the automated packaging unit. Operating parameters such as moisture contents, leave particle size, time taken, throughput capacity, and specific mechanical energy consumption were varied to determine the optimum condition for each parameter. Statistical analysis was performed using R software. The appropriate model was chosen based on selection of the highest coefficient of prediction where the additional terms are significant and the model was not aliased, insignificant lack of fit and the maximization of the "Adjusted R2 value" and the "Predicted R2 value." An optimum packaging condition was obtained at 15% moisture content, and 104.4 particle sizes which gave an optimum packaging time of 0.02 h, optimum packaging capacity of 57.31 kg/h, optimum SMEC value of 0.008 kw/h/kg, optimum repeatability value of 0.128 kg, optimum linearity value of 4.713 cm, optimum accuracy value of 5.2 cm (±0.45). The performance of the ANN model was evaluated using various measures such as mean squared error (MSE), the coefficient of determination (R2), mean absolute error (MAE), and the adjusted R‐squared (Adj. R2) for packaging machine. The results of this study suggest that ANN can be used to effectively optimize packaging units of the vegetable leaf processing plant. [ABSTRACT FROM AUTHOR]

In metal cutting, a large amount of mechanical energy converts into heat, leading to a rapid temperature rise. Excessive heat accelerates tool wear, shortens tool life, and hinders chip breakage. Most existing thermal studies have focused on dry machining, with limited research on the effects of cutting fluids. This study addresses that gap by investigating the thermal behavior of cutting tools during continuous and interrupted turning with cutting fluid. Tool temperatures were first measured experimentally by embedding a thermocouple in a defined position within the tool. These experimental results were then combined with simulations to evaluate temperature changes, heat partition, and cooling efficiency under various cutting conditions. This work presents novel analytical and numerical models. Both models accurately predicted the temperature distribution, with the analytical model offering a computationally more efficient solution for industrial use. Experimental results showed that tool temperature increased with cutting speed, feed, and cutting depth, but the heat partition into the tool decreased. In continuous cutting, cooling efficiency was mainly influenced by feed rate and cutting depth, while cutting speed had minimal impact. Interrupted cutting improved cooling efficiency, as the absence of chips and workpieces during non-cutting phases allowed the cutting fluid to flow over the tool surface at higher speeds. The convective cooling coefficient was determined through inverse calibration. A comparative analysis of the analytical and numerical simulations revealed that the analytical model can underestimate the temperature distribution for complex tool structures, particularly non-orthogonal hexahedral geometries. However, the relative error remained consistent across different cutting conditions, with less error observed in interrupted cutting compared to continuous cutting. These findings highlight the potential of analytical models for optimizing thermal management in metal turning processes. [ABSTRACT FROM AUTHOR]

Modern methods of designing and constructing hydraulic pumps can no longer be imagined without the use of appropriate mathematical models, phenomena and processes that take place in concrete constructions. A mathematical model of a process represents an analytical interpretation with certain assumptions. Obtaining a mathematical model requires detailed theoretical research, based on knowledge of the laws of fundamental sciences and scientific disciplines, in order to fully understand and interpret the process, upon which assumptions are adopted and model equations are defined. As mobile machines continue to evolve, so do the demands on their hydraulic systems. Efficiency, automation and other major industry trends present ongoing development opportunities for the hydraulic systems used in mobile applications. Hydraulic systems remain an important component in a range of mobile applications, from construction and agricultural equipment to heavy trucks, because of the power density they can provide for a range of work functions. The power density of hydraulics remains unmatched in many applications. The pump, as an essential hydraulic component, converts mechanical energy into hydraulic energy with a relatively small amount and speed of fluid. [ABSTRACT FROM AUTHOR]

Environmental pollution and global warming caused by fossil fuels have become increasingly serious issues. Therefore, it is urgent to explore novel strategies to obtain sustainable, renewable and clean energy. Fortunately, ambient energy harvesting technologies, which are receiving increasing attention, provide an optimal solution. Additionally, the investigation of two-dimensional (2D) materials represented by transition metal dichalcogenides (TMDs) significantly facilitates the advancement of ambient energy harvesting technologies due to their unique properties, enabling the application of ambient energy harvesting. Herein, we summarized recent advances in the application of TMDs in thermal energy harvesting, osmotic energy harvesting, mechanical energy harvesting, water energy harvesting and radiofrequency energy harvesting respectively. In the meanwhile, we listed some representative structure and device optimization strategies for enhancing the energy conversion performance of these ambient energy harvesters, aiming to provide valuable insights for future investigations towards further optimization. Finally, we highlight the pressing issues currently faced in the application of the TMDs ambient energy harvesting technologies and propose some potential solutions to these challenges. We aimed to provide a comprehensive review in the applications of the energy harvesting technologies, in order to provide innovative insights for optimizing existing TMDs-based technologies. [ABSTRACT FROM AUTHOR]

The triboelectric nanogenerator (TENG) has demonstrated exceptional efficiency in harvesting diverse forms of mechanical energy and converting it into electrical energy. This technology is particularly valuable for powering low-energy electronic devices and self-powered sensors. Most traditional TENGs use single-sided patterned friction pairs, which restrict their effective contact area and overall performance. Here, we propose a novel TENG that incorporates microwave patterned aluminum (MC-Al) foil and microcone structured polydimethylsiloxane (MC-PDMS). This innovative design utilizes two PMMA molds featuring identical micro-hole arrays ablated by a CO2 laser, making it both cost-effective and easy to fabricate. A novel room imprinting technique has been employed to create the micromorphology of aluminum (Al) foil using the PMMA mold with shallower micro-hole arrays. Compared to TENGs with flat friction layers and single-side-patterned friction layers, the double-side-patterned MW-MC-TENG demonstrates superior output performance due to increased cone deformation and contact area. The open-circuit voltage of the MW-MC-TENG can reach 141 V, while the short-circuit current can attain 71.5 μA, corresponding to a current density of 2.86 µA/cm2. The power density reaches 1.4 mW/cm2 when the resistance is 15 MΩ, and it can charge a 0.1 μF capacitor to 2.01 V in 2.28 s. In addition, the MW-MC-TENG can function as an insole device to harvest walking energy, power 11 LED bulbs, monitor step speed, and power a timer device. Therefore, the MW-MC-TENG has significant application potential in micro-wearable devices. [ABSTRACT FROM AUTHOR]

A forward run-up and stepping are used to accelerate hitting tools or throwing objects in sports. This study aimed to investigate the effect of a forward cross-over step on the speed of a hitting tool by analyzing the joint work and mechanical energy of the whole body and the hitting tool using inverse dynamics. Thirteen advanced tennis players performed forehand groundstrokes at maximum effort with and without a forward cross-over step. From the whole body plus racket perspective, the body-weight-normalized mechanical energy at the start of the hitting motion increased by 1.74 ± 0.42 J·kg-1 due to the cross-over step. However, the increase in the magnitude of total negative joint work, primarily attributed to the lower limbs, was 1.38 ± 0.31 J·kg-1 due to the cross-over step, conventionally regarded as energy absorption. Consequently, the mechanical energy of the whole body plus the racket at ball impact was comparable between the conditions. Nevertheless, from the segmental perspective, the mechanical work performed by the net shoulder joint force of the playing upper limb with the cross-over step during the hitting motion was greater than that without the crossover step. Subsequently, the slight increase in the mechanical energy of the playing upper limb plus racket (0.25 ± 0.21 J·kg-1) resulted in increased racket speed (4.3%). Considering the comparable total mechanical energy and a resultant increase in racket speed, players and coaches should not overestimate the effect of the forward step on racket speed. [ABSTRACT FROM AUTHOR]

A new design of a flexible and compact electrostatic generator with dielectric fluid is presented in this work. The generator utilizes the flow of dielectric fluid between two dielectric films to change the capacitance and converts mechanical energy into electrical energy. We fabricate a dielectric fluid generator (DFG) and build up an experimental setup to investigate the performance of energy harvesting. We use an optimal triangular electromechanical cycle and achieve a maximum energy harvesting power of 1.83 mW with a device that the length of the longest side is 15 cm. The power density is 35.2 μW g−1, and the conversion efficiency is 17.8%. The parameters of the DFG, including the initial voltage, the applied force, and the mechanical loading time, are studied. As a demonstration, we use the DFG to harvest electrical energy from hand tapping to power LEDs. The DFG is flexible and compact, which is promising for harvesting energy from human movements. [ABSTRACT FROM AUTHOR]

[Display omitted] • A strategy to improve the performance of bio-based carbon aerogel was proposed. • Bio-based carbon aerogel with thermostable high elasticity and fatigue resistance. • Bio-based carbon aerogels have excellent electrochemical properties. • A reference for the development of novel thermostatic sensing materials. The poor mechanical properties of biomass-based carbon aerogels after carbonization severely limit their application in pressure sensing and energy storage for wearable devices and electronic skin. In this work, a supramolecular assembly structure was designed inspired by the unique microstructure of natural wood for the preparation of biomass-based carbon aerogels with supercompressibility, elasticity, stable strain electrical signal response, and wide sensitive detection. Bacterial cellulose and lignin were selected as the main components of the biomass-based composite aerogel 'cell wall'. The graphene oxide with an aromatic structure was introduced to induce the assembly of firmly attached lignin and bacterial cellulose. The prepared biomass-based carbon aerogels exhibit supercompressibility (at least 100 cycles at 90 % strain), high elasticity (88.88 % height retention after 1000 cycles at a strain of 50 %), surprising temperature-constant superelasticity and fatigue resistance (shape retention rate greater than 85 %) at −196 ℃. In particular, it exhibits temperature-invariant high linear sensitivity over an extremely wide operating pressure range (0–43 kPa), allowing accurate detection of human signals. In addition, the prepared carbon aerogels exhibit excellent performance in supercapacitors. It has a specific capacitance of 158F/g at a current density of 1 A/g and an energy density of 18.75 Wh/kg at a high power density of 2500 W/g. This strategy also demonstrates its promise as a wearable device in hostile environments. [ABSTRACT FROM AUTHOR]